ORCID Profile
0000-0002-8482-6031
Current Organisation
The University of Texas Health Science Center at Houston
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In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Biochemistry and Cell Biology | Cell Metabolism | Medical Biochemistry: Lipids | Cell Metabolism | Medical Biochemistry: Lipids | Oncology and Carcinogenesis | Environmental Technologies | Non-automotive Combustion and Fuel Engineering (incl. Alternative/Renewable Fuels) | Cancer Cell Biology | Cellular Interactions (incl. Adhesion, Matrix, Cell Wall) | Proteomics and Intermolecular Interactions (excl. Medical Proteomics) | Animal Neurobiology | Medical Biochemistry and Metabolomics | Gene Expression | Combustion And Fuel Engineering | Membrane Biology | Cell Development (Incl. Cell Division And Apoptosis) | Cellular Immunology | Medical Biochemistry: Proteins and Peptides (incl. Medical Proteomics) | Cell Neurochemistry
Expanding Knowledge in the Biological Sciences | Biofuel (Biomass) Energy | Oilseeds | Endocrine organs and diseases (incl. diabetes) | Health related to ageing | Neurodegenerative Disorders Related to Ageing | Cardiovascular system and diseases | Biological sciences | Expanding Knowledge in the Medical and Health Sciences | Renewable energy not elsewhere classified (e.g. geothermal) | Expanding Knowledge in the Chemical Sciences | Cancer and Related Disorders | Infectious Diseases |
Publisher: Proceedings of the National Academy of Sciences
Date: 28-04-2014
Abstract: The relationship between body fat and male reproduction is clearly seen when excess fat compromises fertility however, potential consequences of adipose tissue paucity on fertility are unclear. We report that lack of seipin, a transmembrane protein localizing to the endoplasmic reticulum, causes both paucity of adipose tissue and male sterility. Human patients and mouse models lacking seipin in germ cells produce severely abnormal sperm because of impaired lipid distribution during sperm maturation. These defects are testis-intrinsic scarcity of adipose tissue per se does not affect male fertility. Our work shows that two distinct organs—adipose tissue and the male germ line—depend on seipin function and that appropriate lipid distribution is essential for production of mature, functional sperm.
Publisher: Rockefeller University Press
Date: 04-02-2008
Abstract: Lipid droplets (LDs) are emerging cellular organelles that are of crucial importance in cell biology and human diseases. In this study, we present our screen of ∼4,700 Saccharomyces cerevisiae mutants for abnormalities in the number and morphology of LDs we identify 17 fld (few LDs) and 116 mld (many LDs) mutants. One of the fld mutants (fld1) is caused by the deletion of YLR404W, a previously uncharacterized open reading frame. Cells lacking FLD1 contain strikingly enlarged (supersized) LDs, and LDs from fld1Δ cells demonstrate significantly enhanced fusion activities both in vivo and in vitro. Interestingly, the expression of human seipin, whose mutant forms are associated with Berardinelli-Seip congenital lipodystrophy and motoneuron disorders, rescues LD-associated defects in fld1Δ cells. Lipid profiling reveals alterations in acyl chain compositions of major phospholipids in fld1Δ cells. These results suggest that an evolutionally conserved function of seipin in phospholipid metabolism and LD formation may be functionally important in human adipogenesis.
Publisher: Cold Spring Harbor Laboratory
Date: 08-02-2022
DOI: 10.1101/2022.02.08.479601
Abstract: Neuronal growth regulator 1 (NEGR1) is a glycosylphosphatidylinositol-anchored cell adhesion molecule encoded by an obesity susceptibility gene. We demonstrate that NEGR1 accumulates in GABAergic inhibitory synapses in hypothalamic neurons, a GABA-synthesizing enzyme GAD65 attaches to the plasma membrane, and NEGR1 promotes clustering of GAD65 at the synaptic plasma membrane. GAD65 is removed from the plasma membrane with newly formed vesicles. The association of GAD65 with vesicles results in increased GABA synthesis. In NEGR1 deficient mice, the synaptic targeting of GAD65 is decreased, the GABAergic synapse densities are reduced, and the reinforcing effects of food rewards are blunted. In mice fed a high fat diet, levels of NEGR1 are increased and GAD65 abnormally accumulates at the synaptic plasma membrane. Our results indicate that NEGR1 regulates a previously unknown step required for synaptic targeting and functioning of GAD65, which can be affected by bidirectional changes in NEGR1 levels causing disruptions in the GABAergic signaling controlling feeding behavior.
Publisher: Springer Science and Business Media LLC
Date: 07-01-2015
DOI: 10.1038/NCOMMS6949
Abstract: Fsp27 is a lipid droplet-associated protein almost exclusively expressed in adipocytes where it facilitates unilocular lipid droplet formation. In mice, Fsp27 deficiency is associated with increased basal lipolysis, ‘browning’ of white fat and a healthy metabolic profile, whereas a patient with congenital CIDEC deficiency manifested an adverse lipodystrophic phenotype. Here we reconcile these data by showing that exposing Fsp27 -null mice to a substantial energetic stress by crossing them with ob/ob mice or BATless mice, or feeding them a high-fat diet, results in hepatic steatosis and insulin resistance. We also observe a striking reduction in adipose inflammation and increase in adiponectin levels in all three models. This appears to reflect reduced activation of the inflammasome and less adipocyte death. These findings highlight the importance of Fsp27 in facilitating optimal energy storage in adipocytes and represent a rare ex le where adipose inflammation and hepatic insulin resistance are disassociated.
Publisher: Springer Science and Business Media LLC
Date: 12-03-2013
DOI: 10.1038/NCOMMS2581
Publisher: Elsevier BV
Date: 06-2003
DOI: 10.1016/S0006-291X(03)00833-7
Abstract: Sulphite oxidase (EC 1.8.3.1) is a molybdopterin-containing enzyme that catalyses the oxidation of sulphite to sulphate. Lack of active enzyme produces severe neurodegeneration and early death in humans, showing its essential role. Despite this, the expression of the sulphite oxidase gene in human and rat tissues (especially the brain) has not been elucidated. We therefore examined these tissues and found that the human liver, kidney, skeletal muscle, heart, placenta, and brain showed substantial expression while thymus, spleen, peripheral blood leucocytes, colon, small intestine, and lung showed little expression in humans. In rat, the liver, kidney, heart, brain, and lung (but not skeletal muscle) revealed a hybridization signal with the strongest signal in the liver. The spleen and testis also showed little expression. The differential expression of sulphite oxidase gene in various human brain regions was studied. Expression was seen in all brain regions examined (cerebellum, cerebral cortex, medulla, spinal cord, occipital pole, frontal lobe, amygdala, caudate nucleus, corpus callosum, hippoc us, thalamus, temporal lobe, and putamen). The cerebral cortex showed the highest level of expression.
Publisher: Elsevier BV
Date: 02-2019
DOI: 10.1016/J.BBALIP.2018.11.001
Abstract: Lipid droplets (LDs) are important organelles involved in energy storage and expenditure. LD dynamics has been investigated using genome-wide image screening methods in yeast and other model organisms. For most studies, genes were identified using two-dimensional images with LD enlargement as readout. Due to imaging limitation, reduction of LD size is seldom explored. Here, we aim to set up a screen that specifically utilizes reduced LD size as the readout. To achieve this, a novel yeast screen is set up to quantitatively and systematically identify genes that regulate LD size through a three-dimensional imaging-based approach. Cidea which promotes LD fusion and growth in mammalian cells was overexpressed in a yeast knockout library to induce large LD formation. Next, an automated, high-throughput image analysis method that monitors LD size was utilized. With this screen, we identified twelve genes that reduced LD size when deleted. The effects of eight of these genes on LD size were further validated in fld1 null strain background. In addition, six genes were previously identified as LD-regulating genes. To conclude, this methodology represents a promising strategy to screen for players in LD size control in both yeast and mammalian cells to aid in the investigation of LD-associated metabolic diseases.
Publisher: Elsevier BV
Date: 03-2019
DOI: 10.1016/J.TIBS.2018.10.001
Abstract: Cholesterol is dynamically transported among membrane-bound organelles primarily by nonvesicular mechanisms. Sterol transfer proteins (STPs) bind cholesterol in their hydrophobic pockets and facilitate its transfer across the aqueous cytosol. However, STPs alone may not account for the specific and efficient movement of cholesterol between intracellular membranes. Accumulating evidence has shown that membrane contact sites (MCSs), regions where two distinct organelles are in close apposition to one another, can facilitate STP-mediated cholesterol trafficking in a cell. At some MCSs, cholesterol can move against its concentration by using phosphatidylinositol 4-phosphate (PI4P) metabolism as the driving force. Finally, the emergence of more MCSs and the discovery of a new STP family further highlight the crucial roles of MCSs and STPs in intracellular cholesterol transport.
Publisher: Portland Press Ltd.
Date: 02-10-2015
DOI: 10.1042/BJ20150602
Abstract: Null mutations of the Niemann–Pick type C1 (NPC1) gene cause NPC disease, a lysosomal storage disorder characterized by cholesterol accumulation in late endosomes (LE) and lysosomes (Ly). Nascent or mutated NPC1 is degraded through the ubiquitin–proteasome pathway, but how NPC1 degradation is regulated remains currently unknown. In the present study, we demonstrated a link between NPC1 degradation and the Akt (protein kinase B)/mTOR [mammalian (or mechanistic) target of rapamycin] signalling pathway in cervical cancer cell lines. We provided evidence that activated Akt/mTOR pathway increased NPC1 degradation by ∼50% in C33A cells when compared with SiHa or HeLa cells. NPC1 degradation in C33A cells was reversed when Akt/mTOR activation was blocked by specific inhibitors or when mTORC1 (mTOR complex 1) was disrupted by regulatory associated protein of mTOR (Raptor) knockdown. Importantly, inhibition of the Akt/mTOR pathway led to decreased NPC1 ubiquitination in C33A cells, pointing to a role of Akt/mTOR in the proteasomal degradation of NPC1. Moreover, we found that NPC1 depletion in several cancer cell lines inhibited cell proliferation and migration. Our results uncover Akt as a key regulator of NPC1 degradation and link NPC1 to cancer cell proliferation and migration.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 11-2004
DOI: 10.1167/IOVS.04-0570
Abstract: Glutathione (GSH) plays a key role in protection against oxidative stress. L-cysteine is thought to be rate-limiting for the synthesis of glutathione (GSH) and therefore may be a critical component in protection against oxidative stress. The purpose of this study was to investigate the role of L-cysteine in GSH metabolism and oxidative stress in human retinal pigment epithelial (hRPE) cells. To identify the role of cysteine in GSH metabolism in hRPE cells, a strategy of cysteine starvation was used to determine (1) GSH levels and oxidative stress by measuring reactive oxygen species (ROS) production, (2) mitochondrial membrane potential (Deltapsim) and mitochondrial ultrastructure by using conventional electron microscopy (EM), and (3) indices of cell viability and apoptosis including analysis of cells containing hypodiploid amounts of DNA. Cysteine starvation resulted in approximately a 95% decrease in GSH concentrations over 24 hours. The GSH Nernst redox potential (Eh) increased approximately 70 mV (Eh=-248 +/- 2.9 mV in control cells compared with Eh=-179 +/- 2.0 mV in cysteine-starved cells) indicating significant intracellular oxidation. Cysteine starvation increased the production of ROS by mitochondrial respiratory complex III (cytochrome bc1), determined using a pharmacological strategy that resulted in the loss of Deltapsim and cell death. The loss of Deltapsim and cell death was prevented with bongkrekic acid, an inhibitor of the adenine nucleotide translocator inhibitor, suggesting activation of the mitochondrial permeability transition (MPT). This conclusion was further supported by electron microscopic studies that showed significant mitochondrial swelling, a hallmark of MPT activation. Cell death was not prevented with either the broad-spectrum caspase inhibitor zVADfmk or the caspase 3-specific inhibitor DEVD-CHO, indicating that cytochrome bc1-mediated ROS production results in the MPT and necrosis. These results show that cysteine is a required component for normal GSH metabolism and protection against oxidative stress in hRPE cells.
Publisher: Elsevier BV
Date: 04-2015
DOI: 10.1016/J.CELL.2015.02.019
Abstract: Cholesterol is dynamically transported among organelles, which is essential for multiple cellular functions. However, the mechanism underlying intracellular cholesterol transport has remained largely unknown. We established an hotericin B-based assay enabling a genome-wide shRNA screen for delayed LDL-cholesterol transport and identified 341 hits with particular enrichment of peroxisome genes, suggesting a previously unappreciated pathway for cholesterol transport. We show dynamic membrane contacts between peroxisome and lysosome, which are mediated by lysosomal Synaptotagmin VII binding to the lipid PI(4,5)P2 on peroxisomal membrane. LDL-cholesterol enhances such contacts, and cholesterol is transported from lysosome to peroxisome. Disruption of critical peroxisome genes leads to cholesterol accumulation in lysosome. Together, these findings reveal an unexpected role of peroxisome in intracellular cholesterol transport. We further demonstrate massive cholesterol accumulation in human patient cells and mouse model of peroxisomal disorders, suggesting a contribution of abnormal cholesterol accumulation to these diseases.
Publisher: Wiley
Date: 14-03-2021
Publisher: Wiley
Date: 11-08-2005
Publisher: Wiley
Date: 24-08-2005
DOI: 10.1111/J.1742-4658.2005.04886.X
Abstract: Oxysterol binding protein (OSBP) and its homologs have been shown to regulate lipid metabolism and vesicular transport. However, the exact molecular function of in idual OSBP homologs remains uncharacterized. Here we demonstrate that the yeast OSBP homolog, Osh6p, bound phosphatidic acid and phosphoinositides via its N-terminal half containing the conserved OSBP-related domain (ORD). Using a green fluorescent protein fusion chimera, Osh6p was found to localize to the cytosol and patch-like or punctate structures in the vicinity of the plasma membrane. Further examination by domain mapping demonstrated that the N-terminal half was associated with FM4-64 positive membrane compartments however, the C-terminal half containing a putative coiled-coil was localized to the nucleoplasm. Functional analysis showed that the deletion of OSH6 led to a significant increase in total cellular ergosterols, whereas OSH6 overexpression caused both a significant decrease in ergosterol levels and resistance to nystatin. Oleate incorporation into sterol esters was affected in OSH6 overexpressing cells. However, Lucifer yellow internalization, and FM4-64 uptake and transport were unaffected in both OSH6 deletion and overexpressing cells. Furthermore, osh6Delta exhibited no defect in carboxypeptidase Y transport and maturation. Lastly, we demonstrated that both the conserved ORD and the putative coiled-coil motif were indispensable for the in vivo function of Osh6p. These data suggest that Osh6p plays a role primarily in regulating cellular sterol metabolism, possibly stero transport.
Publisher: Public Library of Science (PLoS)
Date: 28-07-2011
Publisher: Elsevier BV
Date: 09-2006
DOI: 10.1016/J.TCB.2006.07.002
Abstract: Sterols, essential components of eukaryotic membranes, are actively transported between cellular membranes. Although it is known that both vesicular and non-vesicular means are used to move sterols, the molecules and molecular mechanisms involved have yet to be identified. Recent studies point to a key role for oxysterol binding protein (OSBP) and its related proteins (ORPs) in nonvesicular sterol transport. Here, evidence that OSBP and ORPs are bona fide sterol carriers is discussed. In addition, I hypothesize that ATPases associated with various cellular activities regulate the recycling of soluble lipid carriers and that the Niemann Pick C1 protein facilitates the delivery of sterols from endosomal membranes to ORPs and/or the ensuing membrane dissociation of ORPs.
Publisher: Elsevier BV
Date: 09-2005
DOI: 10.1016/J.CELLSIG.2004.12.003
Abstract: PRK1/PKN is a member of the protein kinase C (PKC) superfamily of serine/threonine protein kinases. Despite its important role as a RhoA effector, limited information is available regarding how this kinase is regulated. We show here that the last seven amino acid residues at the C-terminus is dispensable for the catalytic activity of PRK1 but is critical for the in vivo stability of this kinase. Surprisingly, the intact hydrophobic motif in PRK1 is dispensable for 3-phosphoinositide-dependent kinase-1 (PDK-1) binding and phosphorylation of the activation loop, as the PRK1-Delta940 mutant lacking the last two residues of the hydrophobic motif and the last 5 residues at the C-terminus interacts with PDK-1 in vivo and has a similar specific activity as the wild-type protein. We also found that the last four amino acid residues at the C-terminus of PRK1 is critical for the full lipid responsiveness as the PRK1-Delta942 deletion mutant is no longer activated by arachidonic acid. Our data suggest that the very C-terminus in PRK1 is critically involved in the control of the catalytic activity and activation by lipids. Since this very C-terminal segment is the least conserved among members of the PKC superfamily, it would be a promising target for isozyme-specific pharmaceutical interventions.
Publisher: Public Library of Science (PLoS)
Date: 06-08-2008
Publisher: American Physiological Society
Date: 15-03-2012
DOI: 10.1152/AJPENDO.00237.2011
Abstract: Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2) is a recessive disorder characterized by an almost complete loss of adipose tissue, insulin resistance, and fatty liver. BSCL2 is caused by loss-of-function mutations in the BSCL2/seipin gene, which encodes seipin. The essential role for seipin in adipogenesis has recently been established both in vitro and in vivo. However, seipin is highly upregulated at later stages of adipocyte development, and its role in mature adipocytes remains to be elucidated. We therefore generated transgenic mice overexpressing a short isoform of human BSCL2 gene (encoding 398 amino acids) using the adipocyte-specific aP2 promoter. The transgenic mice produced ∼150% more seipin than littermate controls in white adipose tissue. Surprisingly, the increased expression of seipin markedly reduced the mass of white adipose tissue and the size of adipocytes and lipid droplets. This may be due in part to elevated lipolysis rates in the transgenic mice. Moreover, there was a nearly 50% increase in the triacylglycerol content of transgenic liver. These results suggest that seipin promotes the differentiation of preadipocytes but may inhibit lipid storage in mature adipocytes.
Publisher: Springer Science and Business Media LLC
Date: 17-09-2014
DOI: 10.1038/NCOMMS5985
Publisher: Rockefeller University Press
Date: 30-04-2021
Abstract: TMEM41B and VMP1 are integral membrane proteins of the endoplasmic reticulum (ER) and regulate the formation of autophagosomes, lipid droplets (LDs), and lipoproteins. Recently, TMEM41B was identified as a crucial host factor for infection by all coronaviruses and flaviviruses. The molecular function of TMEM41B and VMP1, which belong to a large evolutionarily conserved family, remains elusive. Here, we show that TMEM41B and VMP1 are phospholipid scramblases whose deficiency impairs the normal cellular distribution of cholesterol and phosphatidylserine. Their mechanism of action on LD formation is likely to be different from that of seipin. Their role in maintaining cellular phosphatidylserine and cholesterol homeostasis may partially explain their requirement for viral infection. Our results suggest that the proper sorting and distribution of cellular lipids are essential for organelle biogenesis and viral infection.
Publisher: Wiley
Date: 04-2005
Publisher: Elsevier BV
Date: 05-2016
DOI: 10.1194/JLR.M060574
Publisher: American Society for Microbiology
Date: 02-2008
DOI: 10.1128/EC.00386-07
Abstract: The pandemic of lipid-related disease necessitates a determination of how cholesterol and other lipids are transported and stored within cells. The first step in this determination is the identification of the genes involved in these transport and storage processes. Using genome-wide screens, we identified 56 yeast ( Saccharomyces cerevisiae ) genes involved in sterol-lipid biosynthesis, intracellular trafficking, and/or neutral-lipid storage. Direct biochemical and cytological examination of mutant cells revealed an unanticipated link between secretory protein glycosylation and triacylglycerol (TAG)/steryl ester (SE) synthesis for the storage of lipids. Together with the analysis of other deletion mutants, these results suggested at least two distinct events for the biogenesis of lipid storage particles: a step affecting neutral-lipid synthesis, generating the lipid core of storage particles, and another step for particle assembly. In addition to the lipid storage mutants, we identified mutations that affect the localization of unesterified sterols, which are normally concentrated in the plasma membrane. These findings implicated phospholipase C and the protein phosphatase Ptc1p in the regulation of sterol distribution within cells. This study identified novel sterol-related genes that define several distinct processes maintaining sterol homeostasis.
Publisher: Elsevier BV
Date: 05-2000
Abstract: We have identified a 26S proteasome-associated ubiquitin carboxyl-terminal hydrolase (UCH) in Schizosaccharomyces pombe. The gene (designated uch2+) encodes a protein containing a UCH catalytic domain at its N-terminus and a short extension at its C-terminus. uch2+ is nonessential as the uch2 null mutant strain showed no significant difference from the wild-type strain. The GFP-tagged Uch2p is localized predominantly to the nuclear periphery, which is similar to the 26S proteasome localization. Deletion of the C-terminal extension of Uch2p resulted in a drastic change of its subcellular localization: it showed a generally diffused distribution instead of a perinuclear pattern. Glycerol gradient centrifugation analysis and coimmunoprecipitation studies of fission yeast extracts using anti-Mts4p antiserum suggest that Uch2p is associated with the 26S proteasome and the association of Uch2p with the 26S proteasome is mediated by its C-terminal extension.
Publisher: Elsevier BV
Date: 08-2012
DOI: 10.1016/J.CEB.2012.05.012
Abstract: Recent advances have transformed our understanding of lipid droplets (LDs). Once regarded as inert lipid storage granules, LDs are now recognized as multi-functional organelles that affect many aspects of cell biology and metabolism. However, fundamental questions concerning the biogenesis and growth of LDs remain unanswered. Recent studies have uncovered novel modes of LD growth (including rapid/homotypic as well as slow/atypical LD fusion), and identified key proteins (e.g. Fsp27, seipin, FITM2 and perilipin 1) and lipids (e.g. phosphatidylcholine and phosphatidic acid) that regulate the size of LDs. Phospholipids appear to have an evolutionarily conserved role in LD growth. Protein factors may regulate LD expansion directly and/or indirectly through modulating the level and composition of phospholipids on LD surface.
Publisher: Elsevier
Date: 2012
Publisher: Wiley
Date: 26-08-1996
DOI: 10.1016/0014-5793(96)00807-1
Abstract: Regulation of sterol biosynthesis in the terminal portion of the pathway represents an efficient mechanism by which the cell can control the production of sterol without disturbing the production of other essential mevalonate pathway products. We demonstrate that mutations affecting early and late steps in sterol homeostasis modulate the expression of the ERG3 gene: a late step in sterol biosynthesis in yeast. Expression of ERG3 is increased in response to a mutation in the major isoform of HMG CoA reductase which catalyzes the rate-limiting step of sterol biosynthesis. Likewise, mutations in non-auxotrophic ergosterol biosynthetic genes downstream of squalene production (erg2, erg3, erg4, erg5, and erg6) result in an up-regulation of ERG3 expression. Deletion analysis of the ERG3 promoter identified two upstream activation sequences: UAS1 which when deleted reduces ERG3 gene expression 3-4-fold but maintains sterol regulation and UAS2, which when deleted further reduces ERG3 expression and abolishes sterol regulation. The recent isolation of two yeast genes responsible for the esterification of intracellular sterol (ARE1 and ARE2) has enabled us to directly analyze the relationship between sterol esterification and de novo biosynthesis. Our results demonstrate that the absence of sterol esterification leads to a decrease in total intracellular sterol and ERG3 is a target of this negative regulation.
Publisher: American Diabetes Association
Date: 14-06-2014
DOI: 10.2337/DB13-0729
Abstract: Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2) is the most severe form of human lipodystrophy, characterized by an almost complete loss of adipose tissue and severe insulin resistance. BSCL2 is caused by loss-of-function mutations in the BSCL2/SEIPIN gene, which is upregulated during adipogenesis and abundantly expressed in the adipose tissue. The physiological function of SEIPIN in mature adipocytes, however, remains to be elucidated. Here, we generated adipose-specific Seipin knockout (ASKO) mice, which exhibit adipocyte hypertrophy with enlarged lipid droplets, reduced lipolysis, adipose tissue inflammation, progressive loss of white and brown adipose tissue, insulin resistance, and hepatic steatosis. Lipidomic and microarray analyses revealed accumulation/imbalance of lipid species, including ceramides, in ASKO adipose tissue as well as increased endoplasmic reticulum stress. Interestingly, the ASKO mice almost completely phenocopy the fat-specific peroxisome proliferator–activated receptor-γ (Pparγ) knockout (FKO-γ) mice. Rosiglitazone treatment significantly improved a number of metabolic parameters of the ASKO mice, including insulin sensitivity. Our results therefore demonstrate a critical role of SEIPIN in maintaining lipid homeostasis and function of adipocytes and reveal an intimate relationship between SEIPIN and PPAR-γ.
Publisher: Rockefeller University Press
Date: 29-07-2021
Abstract: Lipid droplets store neutral lipids, primarily triacylglycerol and steryl esters. Seipin plays a role in lipid droplet biogenesis and is thought to determine the site of lipid droplet biogenesis and the size of newly formed lipid droplets. Here we show a seipin-independent pathway of lipid droplet biogenesis. In silico and in vitro experiments reveal that retinyl esters have the intrinsic propensity to sequester and nucleate in lipid bilayers. Production of retinyl esters in mammalian and yeast cells that do not normally produce retinyl esters causes the formation of lipid droplets, even in a yeast strain that produces only retinyl esters and no other neutral lipids. Seipin does not determine the size or biogenesis site of lipid droplets composed of only retinyl esters or steryl esters. These findings indicate that the role of seipin in lipid droplet biogenesis depends on the type of neutral lipid stored in forming droplets.
Publisher: Springer Science and Business Media LLC
Date: 13-05-2020
Publisher: Elsevier BV
Date: 06-2011
DOI: 10.1016/J.TEM.2011.02.004
Abstract: Seipin, the human Berardinelli-Seip congenital lipodystrophy 2 gene product, regulates adipocyte differentiation and lipid droplet (LD) formation. The molecular function of seipin, however, remains to be elucidated. Here we summarize recent advances in the investigation of congenital generalized lipodystrophies (CGLs) and the cellular dynamics of LDs. Increasing evidence suggests that phospholipids play a crucial role in some key forms of CGL and also in determining the size and distribution of LDs. We explore the hypothesis that seipin functions in the metabolism of phospholipids, and that seipin deficiency causes accumulation of lipid intermediates and/or alters membrane phospholipid profiles. These changes could lead to tissue-specific abnormalities upon seipin dysfunction, such as defective adipocyte development and clustered LDs in fibroblasts.
Publisher: Wiley
Date: 2004
DOI: 10.1002/BIES.20071
Abstract: In this article, we discuss a hypothesis to explain the preferential synthesis of the superoxide sensitive form of aconitase in mitochondria and the phenotype observed in manganese superoxide dismutase mutant mice, which show a gross over accumulation of stored fat in liver. The model proposes that intermediary metabolism is redox regulated by mitochondrial superoxide generated during mitochondrial respiration. This regulates the level of reducing equivalents (NADH) entering the electron transport chain (ETC) through the reversible inactivation of mitochondrial aconitase. This control mechanism has a dual function firstly, it regulates levels of superoxide generated by the ETC and, secondly, it fine-tunes metabolism by channeling citrate either for the production of NADH for energy metabolism or erting it for the synthesis of fats. In this setting, the mitochondrial redox state influences metabolic decisions via a superoxide-aconitase rheostat.
Publisher: Elsevier BV
Date: 08-2015
DOI: 10.1016/J.CEB.2015.04.002
Abstract: Cholesterol is an essential membrane constituent, and also plays a key role in cell signalling. Within a cell, how cholesterol is transported and how its heterogeneous distribution is maintained are poorly understood. Recent advances have identified novel pathways and regulators of cholesterol trafficking. Sterol transfer by lipid-binding proteins, such as OSBP (oxysterol-binding protein), coupled with phosphatidylinositol 4-phosphate exchange at membrane contact sites (MCSs) has emerged as a new theme of cholesterol transport between organellar membranes. Moreover, a previously unappreciated role of peroxisomes in cholesterol trafficking has been revealed recently. These discoveries highlight the crucial role of MCSs, or junctions, in facilitating lipid movement, and provide mechanistic insights into how cholesterol is sorted in cells.
Publisher: Elsevier BV
Date: 03-2006
DOI: 10.1016/J.INTIMP.2005.08.026
Abstract: Many herbal medicines are widely used as immuno-modulators in Asian countries. Ganoderma lucidum (Lingzhi) is one of the most commonly used herbs in Asia and preclinical studies have established that the polysaccharide fractions of G. lucidum have potent immuno-modulating effects. However, clinical evidence for this is scanty. The present open-labeled study aimed to evaluate the effects of G. lucidum polysaccharides on selected immune functions in patients with advanced colorectal cancer. Forty-seven patients were enrolled and treated with oral G. lucidum at 5.4 g/day for 12 weeks. Selected immune parameters were monitored using various immunological methods throughout the study. In 41 assessable cancer patients, treatment with G. lucidum tended to increase mitogenic reactivity to phytohemagglutinin, counts of CD3, CD4, CD8 and CD56 lymphocytes, plasma concentrations of interleukin (IL)-2, IL-6 and interferon (IFN)-gamma, and NK activity, whereas plasma concentrations of IL-1 and tumor necrosis factor (TNF)-alpha were decreased. For all of these parameters, no statistical significance was observed when a comparison was conducted between baseline and those values after a 12-week treatment with G. lucidum. The changes of IL-1 were correlated with those for IL-6, IFN-gamma, CD3, CD4, CD8 and NK activity (p<0.05) and IL-2 changes were correlated with those for IL-6, CD8 and NK activity. The results indicate that G. lucidum may have potential immuno-modulating effect in patients with advanced colorectal cancer. Further studies are needed to explore the benefits and safety of G. lucidum in cancer patients.
Publisher: Elsevier BV
Date: 04-2011
DOI: 10.1016/J.FREERADBIOMED.2011.01.013
Abstract: Increased reactive oxygen species (ROS) are a feature of aging cells, but little is known about when ROS generation begins as cells age. Here we show how ROS change in Saccharomyces cerevisiae cells throughout their early replicative life span using the fluorescent ROS indicator dihydroethidium (DHE), which has some specificity for the superoxide anion. Cells in a particular age range were heterogeneous with respect to their ROS burden. Surprisingly, some cells as young as 5-7 generations acquired a greatly increased level of ROS detected by DHE relative to virgin cells. By 12 generations 50% of cells had a substantial ROS burden despite being only halfway through their life span. In contrast to the wild type, cells of a sir2 mutant had lower levels of ROS reacting with DHE. Daughters from older mothers had low ROS levels, and this asymmetric distribution of ROS was SIR2-independent. Mitochondrial fragmentation also began to occur in cells after 4 generations and increased markedly as cells aged. Daughter cells regenerated normal tubular mitochondria despite the fragmentation of mitochondria in the mother cells, whereas daughters of the sir2 mutant had fragmented mitochondria at all ages.
Publisher: Elsevier BV
Date: 02-1997
Publisher: Elsevier BV
Date: 07-2013
DOI: 10.1016/J.STR.2013.05.007
Abstract: The oxysterol-binding protein (OSBP)-related proteins (ORPs) are conserved from yeast to humans, and implicated in the regulation of lipid homeostasis and in signaling pathways. Saccharomyces cerevisiae has seven ORPs (Osh1-Osh7) that share one unknown essential function. Here, we report the 1.5-2.3 Å structures of the PH domain and ORD (OSBP-related domain) of yeast Osh3 in apo-form or in complex with phosphatidylinositol 4-phosphate (PI[4]P). Osh3 recognizes PI(4)P by the highly conserved residues in the tunnel of ORD whereas it lacks sterol binding due to the narrow hydrophobic tunnel. Yeast complementation tests suggest that PI(4)P binding to PH and ORD is essential for function. This study suggests that the unifying feature in all ORP homologs is the binding of PI(4)P to ORD and sterol binding is additional to certain homologs. Structural modeling of full-length Osh3 is consistent with the concept that Osh3 is a lipid transfer protein or regulator in membrane contact sites.
Publisher: eLife Sciences Publications, Ltd
Date: 19-01-2023
DOI: 10.7554/ELIFE.82843
Abstract: Cholesterol synthesis is both energy- and oxygen-intensive, yet relatively little is known of the regulatory effects of hypoxia on pathway enzymes. We previously showed that the rate-limiting and first oxygen-dependent enzyme of the committed cholesterol synthesis pathway, squalene monooxygenase (SM), can undergo partial proteasomal degradation that renders it constitutively active. Here, we show hypoxia is a physiological trigger for this truncation, which occurs through a two-part mechanism: (1) increased targeting of SM to the proteasome via stabilization of the E3 ubiquitin ligase MARCHF6 and (2) accumulation of the SM substrate, squalene, which impedes the complete degradation of SM and liberates its truncated form. This preserves SM activity and downstream pathway flux during hypoxia. These results uncover a feedforward mechanism that allows SM to accommodate fluctuating substrate levels and may contribute to its widely reported oncogenic properties.
Publisher: Springer Science and Business Media LLC
Date: 04-02-2020
DOI: 10.1038/S41598-020-58201-5
Abstract: An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Publisher: Elsevier BV
Date: 11-2019
Publisher: Springer Science and Business Media LLC
Date: 02-10-2017
DOI: 10.1038/S41467-017-00861-5
Abstract: ORP5 and ORP8, members of the oxysterol-binding protein (OSBP)-related proteins (ORP) family, are endoplasmic reticulum membrane proteins implicated in lipid trafficking. ORP5 and ORP8 are reported to localize to endoplasmic reticulum–plasma membrane junctions via binding to phosphatidylinositol-4-phosphate (PtdIns(4) P ), and act as a PtdIns(4) P hosphatidylserine counter exchanger between the endoplasmic reticulum and plasma membrane. Here we provide evidence that the pleckstrin homology domain of ORP5/8 via PtdIns(4,5) P 2 , and not PtdIns(4) P binding mediates the recruitment of ORP5/8 to endoplasmic reticulum–plasma membrane contact sites. The OSBP-related domain of ORP8 can extract and transport multiple phosphoinositides in vitro, and knocking down both ORP5 and ORP8 in cells increases the plasma membrane level of PtdIns(4,5) P 2 with little effect on PtdIns(4) P . Overall, our data show, for the first time, that phosphoinositides other than PtdIns(4) P can also serve as co-exchangers for the transport of cargo lipids by ORPs.
Publisher: Springer New York
Date: 2017
DOI: 10.1007/978-1-4939-6875-6_7
Abstract: Generating a cholesterol storage phenotype of Niemann-Pick Type C (NPC) disease is important for investigating the mechanisms of intracellular cholesterol trafficking, as well as screening drugs for potential treatment of NPC disease. The use of the CRISPR/Cas9 technology to knockout specific genes within the genome of mammals has become routine in the past few years. Here, we describe a protocol for producing a cellular NPC cholesterol storage phenotype in HeLa cells using the CRISPR-Cas9 system to disrupt the NPC1 gene. The protocol details the steps for single guide RNA oligo cloning, cell colony selection, and cell line verification by filipin staining and immunoblotting.
Publisher: Public Library of Science (PLoS)
Date: 08-2017
Publisher: Springer Science and Business Media LLC
Date: 17-12-2019
DOI: 10.1038/S41580-019-0190-7
Abstract: Cholesterol homeostasis is vital for proper cellular and systemic functions. Disturbed cholesterol balance underlies not only cardiovascular disease but also an increasing number of other diseases such as neurodegenerative diseases and cancers. The cellular cholesterol level reflects the dynamic balance between biosynthesis, uptake, export and esterification - a process in which cholesterol is converted to neutral cholesteryl esters either for storage in lipid droplets or for secretion as constituents of lipoproteins. In this Review, we discuss the latest advances regarding how each of the four parts of cholesterol metabolism is executed and regulated. The key factors governing these pathways and the major mechanisms by which they respond to varying sterol levels are described. Finally, we discuss how these pathways function in a concerted manner to maintain cholesterol homeostasis.
Publisher: Elsevier BV
Date: 12-1998
Publisher: Elsevier BV
Date: 03-2018
Publisher: Springer Science and Business Media LLC
Date: 18-07-2017
DOI: 10.1038/S41598-017-06077-3
Abstract: The epidemic of obesity and diabetes has markedly spurred the research interest in adipocyte biology. Brown adipocytes are specialized for energy expenditure and of therapeutic interest for treatment of metabolic diseases, but how brown adipocytes are distinguished from white adipocytes at the level of translational regulation remains poorly understood. To systemically determine the translational control of gene expression in adipose tissue, we performed ribosome profiling and RNA-seq in parallel to depict the translatome and transcriptome changes during primary brown and white adipogenesis, and between brown and white adipose tissue. The most prominent layer of translational regulation was the increased translation efficiency of genes encoding mitochondria components in brown adipocytes relative to white. Systemic analysis of the regulatory interactions between microRNAs and their targets revealed that microRNAs were more active in repressing targets’ mRNA abundance and translation in brown fat. Together, our data comprehensively delineated a landscape integrating transcriptome and translatome in adipose tissue.
Publisher: The Company of Biologists
Date: 15-08-2008
DOI: 10.1242/JCS.028977
Abstract: Understanding the mechanisms underlying lipid-induced cell death has significant implications in both cell biology and human diseases. Previously, we showed that fission-yeast Schizosaccharomyces pombe cells deficient in triacylglycerol synthesis display apoptotic markers upon entry into stationary phase. Here, we characterize the sequential molecular events that take place at the onset of cell death in S. pombe, including a surge of diacylglycerol, post-mitotic arrest, alterations in mitochondrial activities and in intracellular redox balance, chromatin condensation, nuclear-envelope fragmentation, and eventually plasma-membrane permeabilization. Our results demonstrated active roles of mitochondria and reactive oxygen species in cell death, and identified novel cell-death regulators – including metacaspase Pca1, BH3-domain protein Rad9, and diacylglycerol-binding proteins Pck1 and Bzz1. Most importantly, we show that, under different conditions and stimuli, failure to maintain intracellular-lipid homeostasis can lead to cell death with different phenotypic manifestations, genetic criteria and cellular mechanisms, pointing to the existence of multiple lipotoxic pathways in this organism. Our study represents the first in-depth analysis of cell-death pathways in S. pombe.
Publisher: Oxford University Press (OUP)
Date: 12-2005
DOI: 10.1016/J.FEMSYR.2005.07.004
Abstract: Yeasts being simple eukaryotes are established genetic systems that are often employed to solve important biological questions. Recently, it has become evident that certain cell death programs exist in these unicellular organisms. For ex le, it has been shown recently that strains of the fission yeast Schizosaccharomyces pombe deficient in triacylglycerol synthesis undergo cell death with prominent apoptotic markers. This minireview is intended to discuss key developments that have rendered fission yeast useful both as a tool and as a model for apoptosis and lipoapoptosis research. It is attempted to delineate a putative signaling pathway leading to the execution of lipoapoptosis in the fission yeast. Although in its infancy, apoptosis research in the fission yeast promises exciting breakthroughs in the near future.
Publisher: Cold Spring Harbor Laboratory
Date: 19-08-2022
DOI: 10.1101/2022.08.18.504470
Abstract: Cholesterol synthesis is both energy- and oxygen-intensive, yet relatively little is known of the regulatory effects of hypoxia on pathway enzymes. We previously showed that the rate-limiting and first oxygen-requiring enzyme of the committed cholesterol synthesis pathway, squalene monooxygenase (SM), can undergo partial proteasomal degradation that renders it constitutively active. Here, we show that hypoxia is the physiological trigger for this truncation, which occurs through a two-part mechanism: (1) increased targeting of SM to the proteasome via stabilization of the E3 ubiquitin ligase MARCHF6, and (2) accumulation of the SM substrate, squalene, which impedes the complete degradation of SM and liberates its truncated form. Truncation of SM is also increased in endometrial cancer tissues, where it correlates with levels of hypoxia-inducible factor−1α. These results uncover a feedforward mechanism that enables SM to accommodate fluctuations in substrate levels yet is also a likely contributor to its widely reported oncogenic properties.
Publisher: Elsevier BV
Date: 07-2015
DOI: 10.1016/J.GENE.2015.04.061
Abstract: Acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) plays a critical role in the formation of cholesteryl esters from cholesterol and fatty acids, and is a potential target for treating hypercholesterolemia. We recently reported the significant effects of two human ACAT2 gene polymorphisms, 41A>G (Glu(14)Gly, rs9658625) and 734C>T (Thr(254)Ile, rs2272296), on plasma lipid levels and coronary artery disease susceptibility in a case-control association study. In the present study, we evaluated the possible biological influence of the two polymorphism using two approaches. In the first approach, the functional impact of the two polymorphisms was predicted in-silico using available web-based software, and in the second approach, the varying functions of the two polymorphisms were characterized in in vitro experiments, using ACAT2-deficient AC-29 cells. Our results show that the enzymatic activity of mutant Glu(14)Gly is approximately two times higher than wildtype, and that this increase is primarily due to the increased expression and/or stability of the mutant ACAT2 protein. These results suggest that the genetic variation at Glu(14)Gly is functionally important and may contribute to ACAT2 protein expression and stability.
Publisher: Rockefeller University Press
Date: 05-12-2011
Abstract: Lipid droplets (LDs) are dynamic cellular organelles that control many biological processes. However, molecular components determining LD growth are poorly understood. Genetic analysis has indicated that Fsp27, an LD-associated protein, is important in controlling LD size and lipid storage in adipocytes. In this paper, we demonstrate that Fsp27 is focally enriched at the LD–LD contacting site (LDCS). Photobleaching revealed the occurrence of lipid exchange between contacted LDs in wild-type adipocytes and Fsp27-overexpressing cells but not Fsp27-deficient adipocytes. Furthermore, live-cell imaging revealed a unique Fsp27-mediated LD growth process involving a directional net lipid transfer from the smaller to larger LDs at LDCSs, which is in accordance with the biophysical analysis of the internal pressure difference between the contacting LD pair. Thus, we have uncovered a novel molecular mechanism of LD growth mediated by Fsp27.
Publisher: Elsevier BV
Date: 11-2011
DOI: 10.1016/J.BBRC.2011.10.091
Abstract: The proteomic makeup of lipid droplets (LDs) is believed to regulate the function of LDs, which are now recognized as important cellular organelles that are associated with many human metabolic disorders. However, factors that help determine LD proteome remain to be identified and characterized. Here we analyzed the phospholipid and protein composition of LDs isolated from wild type (WT) yeast cells, and also from fld1Δ, cds1, and ino2Δ mutant cells which produce 'supersized' LDs. LDs of fld1Δ and WT cells exhibited similar phospholipid profiles, whereas LDs of cds1 and ino2Δ strains had a higher (cds1) or lower (ino2Δ) percentage of phosphatidylcholine than those of WT, respectively. Unexpectedly, the presence of most known LD resident proteins was greatly reduced in the LD fraction isolated from cds1 and ino2Δ, including neutral lipid hydrolases. Consistent with this result, mobilization of neutral lipids was seriously impaired in these two strains. Contrary to the reduction of LD resident proteins, the Hsp90 family molecular chaperones, Hsc82 and Hsp82, were greatly increased in the LD fractions of cds1 and ino2Δ strains without changes at the level of expression. These data demonstrate the impact of LD phopholipids and size on the makeup of LD proteome.
Publisher: Elsevier BV
Date: 07-2008
DOI: 10.1016/J.BBAMCR.2008.02.002
Abstract: Yeasts have proven to be invaluable, genetically tractable systems to study various fundamental biological processes including programmed cell death. Recent advances in the elucidation of the molecular pathways underlying apoptotic cell death in yeasts have revealed remarkable similarities to mammalian apoptosis at cellular, organelle and macromolecular levels, thus making a strong case for the relevance of yeast models of regulated cell death. Programmed cell death has been reported in fission yeast Schizosaccharomyces pombe, primarily in the contexts of perturbed intracellular lipid metabolism, defective DNA replication, improper mitotic entry, chronological and replicative aging. Here we review the current understanding of the programmed cell death in fission yeast, paying particular attention to lipid-induced cell death. We discuss our recent findings that fission yeast exhibits plasticity of apoptotic and non-apoptotic modes of cell death in response to different lipid stimuli and growth conditions, and that mitochondria, reactive oxygen species and novel cell death mediators including metacaspase Pca1, SpRad9 and Pck1 are involved in the lipotoxic cell death. We also present perspectives on how various aspects of the cell and molecular biology of this organism can be explored to shed light on the governing principles underlying lipid-mediated signaling and cell demise.
Publisher: eLife Sciences Publications, Ltd
Date: 30-11-2022
Publisher: Springer Science and Business Media LLC
Date: 23-05-2023
Publisher: Wiley
Date: 14-10-2013
DOI: 10.1111/TRA.12015
Abstract: The exit of low-density lipoprotein derived cholesterol (LDL-C) from late endosomes (LE)/lysosomes (Ly) is mediated by Niemann-Pick C1 (NPC1), a multipass integral membrane protein on the limiting membranes of LE/Ly, and by NPC2, a cholesterol-binding protein in the lumen of LE/Ly. NPC2 delivers cholesterol to the N-terminal domain of NPC1, which is believed to insert cholesterol into the limiting membrane for subsequent transport to other subcellular organelles. Few cytoplasmic factors have been identified to govern cholesterol efflux from LE/Ly, and much less is known about the underlying molecular mechanisms. Here we establish VPS4, an AAA ATPase that has a well-established role in disassembling the ESCRT (endosomal sorting complex required for transport)-III polymer, as an important regulator of endosomal cholesterol transport. Knocking down VPS4 in HeLa cells resulted in prominent accumulation of LDL-C in LE/Ly, and disrupted cholesterol homeostatic responses at the endoplasmic reticulum. The level and localization of NPC1 and NPC2 appeared to be normal in VPS4 knockdown cells. Importantly, depleting any of the ESCRT-III components did not exert a significant effect on endosomal cholesterol transport. Our results thus identify an important cytoplasmic regulator of endosomal cholesterol trafficking and represent the first functional separation of VPS4 from ESCRT-III.
Publisher: Springer Science and Business Media LLC
Date: 06-2005
DOI: 10.1007/S11095-005-4585-0
Abstract: CPT-11 is a DNA topoisomerase I inhibitor for the therapy of colorectal cancer, whereas St. John's Wort (Hypericum perforatum, SJW) is a widely used herbal anti-depressant. This study aimed to investigate the effects of co-administered SJW on the toxicities and pharmacokinetics of CPT-11 and the underlying mechanisms. The body weight loss, gastrointestinal and hematological toxicities induced by CPT-11, and the pharmacokinetic parameters of CPT-11 were evaluated in rats pretreated with SJW or vehicle. Rats treated with CPT-11 alone experienced rapid decrease in body weight, whereas co-administration of SJW with CPT-11 resulted in lesser body weight loss. The gastrointestinal and hematological toxicities following CPT-11 injection were both alleviated in the presence of SJW. The rat pharmacokinetics of both CPT-11 and its metabolite SN-38 were significantly altered in presence of SJW. In conclusion, co-administered SJW significantly ameliorated the toxicities induced by CPT-11. The protective effect of SJW may be partially due to pharmacokinetic interaction between CPT-11 and SJW.
Publisher: Wiley
Date: 20-10-2004
DOI: 10.1111/J.1600-0854.2004.00241.X
Abstract: The Niemann Pick C1 protein localizes to late endosomes and plays a key role in the intracellular transport of cholesterol in mammalian cells. Cholesterol and other lipids accumulate in a lysosomal or late endosomal compartment in cells lacking normal NPC1 function. Other than accumulation of lipids, defects in lysosomal retroendocytosis, sorting of a multifunctional receptor and endosomal movement have also been detected in NPC1 mutant cells. Ncr1p is an ortholog of NPC1 in the budding yeast Saccharomyces cerevisiae. In this study, we show that Ncr1p is a vacuolar membrane protein that transits through the biosynthetic vacuolar protein sorting pathway, and that it can be solubilized by Triton X-100 at 4 degrees C. Using well-established assays, we demonstrate that the absence of Ncr1p had no effect on fluid phase and receptor- mediated endocytosis, biosynthetic delivery to the vacuole, retrograde transport from endosome to Golgi and ubiquitin- and nonubiquitin-dependent multivesicular body sorting. We conclude that Ncr1p does not have an essential role in known endocytic transport pathways in yeast.
Publisher: Elsevier BV
Date: 12-2019
Publisher: Elsevier BV
Date: 11-2003
Publisher: Springer Science and Business Media LLC
Date: 23-04-2003
DOI: 10.1007/S00439-003-0943-3
Abstract: Mutations in the ATP-binding cassette transporter ABCA1 underlie Tangier disease and familial hypoalphaliproteinemia (FHA), disorders that are characterised by reduced high-density lipoprotein-cholesterol (HDL-C) concentration and cholesterol efflux, and increased coronary artery disease (CAD). We explored if polymorphisms in the ABCA1 gene are associated with CAD and variations in plasma lipid levels, especially HDL-C, and whether the associations may depend on ethnicity. Male cases and controls from the Singapore Chinese, Malay and Indian populations were genotyped for five ABCA1 single nucleotide polymorphisms. Various single-locus frequency distribution differences between cases and controls were detected in different ethnic groups: the promoter -14C>T in Indians, exon 18 M883I in Malays, and 3'-untranslated (UTR) region 8994A>G in Chinese. For the Malay population, certain haplotypes carrying the I825- A (exon 17) and M883- G alleles were more frequent among cases than controls, whereas the converse was true for the alternative configuration of V825- G and I883- A, and this association was reinforced in multi-locus disequilibrium analysis that utilized genotypic data. In the healthy controls, associations were found for -14C>T genotypes with HDL-C in Chinese 237indelG (5'UTR) with apolipoprotein A1 (apoA1) in Malays and total cholesterol (TC) in Indians M883I with lipoprotein(a) [Lp(a)] in Malays and apolipoprotein B (apoB) in Chinese and 8994A>G with Lp(a) in Malays, and TC, low-density lipoprotein-cholesterol (LDL-C) as well as apoB in Indians. While genotype-phenotype associations were not reproduced across populations and loci, V825I and M883I were clearly associated with CAD status in Malays with no effects on HDL-C or apoA1.
Publisher: Public Library of Science (PLoS)
Date: 14-04-2011
Publisher: The Company of Biologists
Date: 10-2003
DOI: 10.1242/JCS.00751
Abstract: Vps4p (End13p) is an AAA-family ATPase that functions in membrane transport through endosomes, sorting of soluble vacuolar proteins to the vacuole, and multivesicular body (MVB) sorting of membrane proteins to the vacuole lumen. In a yeast two-hybrid screen with Vps4p as bait we isolated VPS20 (YMR077c) and the novel open reading frame YLR181c, for which the name VTA1 has recently been assigned (Saccharomyces Genome Database). Vps4p directly binds Vps20p and Vta1p in vitro and binding is not dependent on ATP - conversely, Vps4p binding to Vps20p is partially sensitive to ATP hydrolysis. Both ATP binding [Vps4p-(K179A)] and ATP hydrolysis [Vps4p-(E233Q)] mutant proteins exhibit enhanced binding to Vps20p and Vta1p in vitro. The Vps4p-Vps20p interaction involves the coiled-coil domain of each protein, whereas the Vps4p-Vta1p interaction involves the (non-coiled-coil) C-terminus of each protein. Deletion of either VPS20 (vps20Δ) or VTA1 (vta1Δ) leads to similar class E Vps- phenotypes resembling those of vps4Δ, including carboxypeptidase Y (CPY) secretion, a block in ubiquitin-dependent MVB sorting, and a delay in both post-internalisation endocytic transport and biosynthetic transport to the vacuole. The vacuole resident membrane protein Sna3p (whose MVB sorting is ubiquitin-independent) does not appear to exit the class E compartment or reach the vacuole in cells lacking Vps20p, Vta1p or Vps4p, in contrast to other proteins whose delivery to the vacuole is only delayed. We propose that Vps20p and Vta1p regulate Vps4p function in vivo.
Publisher: Ivyspring International Publisher
Date: 2020
DOI: 10.7150/THNO.39320
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/B913353D
Abstract: Recent rapid growth of lipidomics is mainly attributed to technological advances in mass spectrometry. Development of soft ionization techniques, in combination with computational tools, has spurred subsequent development of various methods for lipid analysis. However, none of these existing approaches can cover major cellular lipids in a single run. Here we demonstrate that a single method of liquid chromatography coupled with mass spectrometry (LCMS) can be used for simultaneous profiling of major cellular lipids including glycerophospholipids (PLs), sphingolipids (SPLs), waxes, sterols (ST) and mono-, di- as well as triacylglycerides (MAG, DAG, TAG). We applied this approach to analyze these lipids in various organisms including Saccharomyces cerevisiae and Schizosaccharomyces pombe. While phospholipids and triacylglycerides of S. pombe mainly contain 18 : 1 fatty acyls, those of S. cerevisiae contain 16 : 1, 16 : 0 and 18 : 1 fatty acyls. S. cerevisiae and S. pombe contain distinct sphingolipid profiles. S. cerevisiae has abundant inositol phytoceramides (IPC), while S. pombe contains high levels of free phytoceramides as well as short chain phytoceramides (t18:1/20 : 0-B) and IPC (t18:1/20 : 0-B). In S. cerevisiae, our results demonstrated accumulation of ergosterol esters in tgl1Delta cells and accumulation of various TAG species in tgl3Delta cells, which are consistent with the function of the respective enzymes. Furthermore, we, for the first time, systematically characterized lipids in S. pombe and measured their dynamic changes in Deltaplh1Deltadga1 cells at different growth phases. We further discussed dynamic changes of phospholipids, sphingolipids and neutral lipids in the progress of programmed cell death in Deltaplh1Deltadga1 cells of S. pombe.
Publisher: Elsevier BV
Date: 07-2019
DOI: 10.1016/J.PLIPRES.2019.100989
Abstract: Lipid droplets (LDs) are multi-functional cellular organelles that store energy, and regulate many aspects of cell physiology. However, our understanding of the biogenesis of LDs remains very limited. Originating from the endoplasmic reticulum (ER), LDs are highly unique organelles in that each LD is bounded by a monolayer of hipathic lipids. Recent progress has unveiled critical roles of non-bilayer lipids in LD formation. For instance, non-bilayer lipids such as lysophospholipids, diacylglycerol and phosphatidic acid (PA) can impact the curvature, surface and line tension of the ER, thereby impacting LD biogenesis. Two well-known regulators of LD formation, FIT2/FITM2 and seipin, have both been implicated in controlling the metabolism and/or distribution of non-bilayer lipids. We summarize and integrate these recent advances and propose that non-bilayer lipids may play a critical role in each step of LD biogenesis.
Publisher: Bentham Science Publishers Ltd.
Date: 2006
DOI: 10.2174/138920006774832550
Abstract: Topotecan (TPT) is a semisynthetic water-soluble derivative of c tothecin (CPT) used as second-line therapy in patients with metastatic ovarian carcinoma, small cell lung cancer, and other malignancies. However, both dose-limiting toxicity and tumor resistance hinder the clinical use of TPT. The mechanisms for resistance to TPT are not fully defined, but increased efflux of the drug by multiple drug transporters including P-glycoprotein (PgP), multidrug resistance associated protein 1 (MRP1) and breast cancer resistance protein (BCRP) from tumor cells has been highly implicated. This study aimed to investigate whether overexpression of human MRP4 rendered resistance to TPT by examining the cytotoxicity profiles using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazonium bromide (MTT) assay and cellular accumulation of TPT in HepG2 cells stably overexpressing MRP4. Two kinds of cell lines, HepG2 with insertion of an empty vector plasmid (V/HepG2), HepG2 cells stably expressing MRP4 (MRP4/HepG2), were exposed to TPT for 4 or 48 hr in the absence or presence of various MRP4 inhibitors including DL-buthionine-(S,R)-sulphoximine (BSO), diclofenac, celecoxib, or MK-571. The intracellular accumulation of TPT and paclitaxel (a PgP substrate) by V/HepG2 and MRP4/HepG2 cells was determined by incubation of TPT with the cells and the amounts of the drug in cells were determined by validated HPLC methods. The study demonstrated that MRP4 conferred a 12.03- and 6.86-fold resistance to TPT in the 4- and 48-hr drug-exposure MTT assay, respectively. BSO, MK-571, celecoxib, or diclofenac sensitised MRP4/HepG2 cells to TPT cytotoxicity and partially reversed MRP4-mediated resistance to TPT. In addition, the accumulation of TPT was significantly reduced in MRP4/HepG2 cells compared to V/HepG2 cells, and one-binding site model was found the best fit for the MRP4-mediated efflux of TPT, with an estimated K(m) of 1.66 microM and V(max) of 0.341 ng/min/106 cells. Preincubation of MRP4/HepG2 cells with BSO (200 microM) for 24 hr, celecoxib (50 microM), or MK-571 (100 microM) for 2 hr significantly increased the accumulation of TPT over 10 min in MRP4/HepG2 cells by 28.0%, 37.3% and 32.5% (P < 0.05), respectively. By contrast, there was no significant difference in intracellular accumulation of paclitaxel in V/HepG2 and MRP4/HepG2 cells over 120 min. MRP4 also rendered resistance to adefovir dipivoxil (bis-POM-PMEA) and methotrexate, two reported MRP4 substrates. MRP4 did not exhibit any significant resistance to other model drugs including vinblastine, vincristine, etoposide, carboplatin, cyclosporine and paclitaxel in both long (48 hr) and short (4 hr) drug-exposure MTT assays. These findings indicate that MRP4 confers resistance to TPT and TPT is the substrate for MRP4. Further studies are needed to explore the role of MRP4 in resistance to, toxicity and pharmacokinetics of TPT in cancer patients.
Publisher: Springer Science and Business Media LLC
Date: 11-06-2019
Publisher: Springer Science and Business Media LLC
Date: 08-06-2013
Abstract: Hyperlipidaemia is a major risk factor for coronary artery disease (CAD) and cholesteryl ester transfer protein (CETP) gene polymorphisms are known to be associated with lipid profiles. In this study, we investigated the association of two polymorphisms in the CETP, Taq1B (rs708272) and - 629C A (rs1800775), with CAD and lipid levels HDL-C in 662 CAD + cases and 927 controls from the Singapore population comprising Chinese, Malays and Indians. TaqB2 frequency was significantly lowest in the Malays (0.43) followed by Chinese (0.47) and highest in the Indians (0.56) in the controls. The B2 allele frequency was significantly lower in the Chinese CAD + cases compared to the controls (p = 0.002). The absence of the B2 allele was associated with CAD with an OR 2.0 (95% CI 1.2 to 3.4) after adjustment for the confounding effects of age, smoking, BMI, gender, hypertension, dyslipidemia and diabetes mellitus. The B2 allele was significantly associated with higher plasma HDL-C levels in the Chinese men after adjusting for confounders. Associations with plasma apoA1 levels were significant only in the Chinese men for Taq1B and - 629C A . In addition, the Taq1B polymorphism was only associated with plasma Apo B and Lp(a) in the Malay men. Significant associations were only found in non-smoking subjects with BMI th percentile. In this study, the LD coefficients between the Taq1B and - 629C A polymorphisms seemed to be weak. The absence the Taq1B2 allele was associated with CAD in the Chinese population only and the minor allele of the Taq1B polymorphism of the CETP gene was significantly associated with higher plasma HDL-C levels in Chinese men.
Publisher: Springer Science and Business Media LLC
Date: 25-11-2021
DOI: 10.1038/S41467-021-27279-4
Abstract: AGPATs (1-acylglycerol-3-phosphate O -acyltransferases) catalyze the acylation of lysophosphatidic acid to form phosphatidic acid (PA), a key step in the glycerol-3-phosphate pathway for the synthesis of phospholipids and triacylglycerols. AGPAT2 is the only AGPAT isoform whose loss-of-function mutations cause a severe form of human congenital generalized lipodystrophy. Paradoxically, AGPAT2 deficiency is known to dramatically increase the level of its product, PA. Here, we find that AGPAT2 deficiency impairs the biogenesis and growth of lipid droplets. We show that AGPAT2 deficiency compromises the stability of C DP- d iacylglycerol (DAG) s ynthases (CDSs) and decreases CDS activity in both cell lines and mouse liver. Moreover, AGPAT2 and CDS1/2 can directly interact and form functional complexes, which promote the metabolism of PA along the CDP-DAG pathway of phospholipid synthesis. Our results provide key insights into the regulation of metabolic flux during lipid synthesis and suggest substrate channelling at a major branch point of the glycerol-3-phosphate pathway.
Publisher: Elsevier BV
Date: 07-2004
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-03-2021
Abstract: Cholesterol levels in cells are controlled by the sterol regulatory element–binding protein (SREBP) pathway. When the cell has sufficient cholesterol, the transcription factor that regulates cholesterol metabolism is sequestered at the endoplasmic reticulum membrane, but when cholesterol is depleted, the transcription factor is released to activate the expression of genes involved in cholesterol synthesis and uptake. Yan et al. determined the structure of a central complex in human SREBP containing the proteins Scap and Insig-2. These two membrane-embedded proteins undergo 25-hydroxycholesterol (25HC)–dependent association and must dissociate for the pathway to be activated. The structure shows that 25HC is sandwiched between Scap and Insig-2 to facilitate their association. A mutational analysis is consistent with the structural model. Science , this issue p. eabb2224
Publisher: Informa UK Limited
Date: 05-2005
Publisher: Elsevier BV
Date: 06-2020
Publisher: Wiley
Date: 19-01-2001
DOI: 10.1016/S0014-5793(00)02436-4
Abstract: By the use of the yeast two-hybrid screen we have identified two proteins that interacted with UCH37: S14, which is a subunit of PA700 and a novel protein, UIP1 (UCH37 interacting protein 1). The interaction of UCH37 with S14 or UIP1 was confirmed by in vitro binding assay and in vivo co-immunoprecipitation analysis. The C-terminal extension of UCH37 is essential for interaction with S14 or UIP1 as shown by the yeast two-hybrid assay and the in vitro binding assay. Furthermore, UIP1 blocked the interaction between UCH37 and S14 in vitro.
Publisher: Rockefeller University Press
Date: 25-10-2020
Abstract: Lipid droplets (LDs) are evolutionarily conserved organelles that play important roles in cellular metabolism. Each LD is enclosed by a monolayer of phospholipids, distinct from bilayer membranes. During LD biogenesis and growth, this monolayer of lipids expands by acquiring phospholipids from the endoplasmic reticulum (ER) through nonvesicular mechanisms. Here, in a mini-screen, we find that ORP5, an integral membrane protein of the ER, can localize to ER–LD contact sites upon oleate loading. ORP5 interacts with LDs through its ligand-binding domain, and ORP5 deficiency enhances neutral lipid synthesis and increases the size of LDs. Importantly, there is significantly more phosphatidylinositol-4-phosphate (PI(4)P) and less phosphatidylserine (PS) on LDs in ORP5-deficient cells than in normal cells. The increased presence of PI(4)P on LDs in ORP5-deficient cells requires phosphatidylinositol 4-kinase 2-α. Our results thus demonstrate the existence of PI(4)P on LDs and suggest that LD-associated PI(4)P may be primarily used by ORP5 to deliver PS to LDs.
Publisher: Rockefeller University Press
Date: 04-09-2018
Abstract: The evolutionarily conserved VPS13 proteins localize to multiple membrane contact sites though their function and regulation has been elusive. Bean et al. (2018. J. Cell Biol. 0.1083/jcb.201804111) found that competitive adaptors control the different localizations of yeast Vps13p, while Kumar et al. (2018. J. Cell Biol. 0.1083/jcb.201807019) provide biochemical and structural evidence for VPS13 proteins in the nonvesicular transport of phospholipids.
Publisher: Rockefeller University Press
Date: 24-01-2018
Abstract: Lipid incorporation from endoplasmic reticulum (ER) to lipid droplet (LD) is important in controlling LD growth and intracellular lipid homeostasis. However, the molecular link mediating ER and LD cross talk remains elusive. Here, we identified Rab18 as an important Rab guanosine triphosphatase in controlling LD growth and maturation. Rab18 deficiency resulted in a drastically reduced number of mature LDs and decreased lipid storage, and was accompanied by increased ER stress. Rab3GAP1/2, the GEF of Rab18, promoted LD growth by activating and targeting Rab18 to LDs. LD-associated Rab18 bound specifically to the ER-associated NAG-RINT1-ZW10 (NRZ) tethering complex and their associated SNAREs (Syntaxin18, Use1, BNIP1), resulting in the recruitment of ER to LD and the formation of direct ER–LD contact. Cells with defects in the NRZ/SNARE complex function showed reduced LD growth and lipid storage. Overall, our data reveal that the Rab18-NRZ-SNARE complex is critical protein machinery for tethering ER–LD and establishing ER–LD contact to promote LD growth.
Publisher: Wiley
Date: 21-03-2017
DOI: 10.1111/TRA.12471
Abstract: Mammalian cells acquire most exogenous cholesterol through receptor-mediated endocytosis of low-density lipoproteins (LDLs). After internalization, LDL cholesteryl esters are hydrolyzed to release free cholesterol, which then translocates to late endosomes (LEs)/lysosomes (LYs) and incorporates into the membranes by co-ordinated actions of Niemann-Pick type C (NPC) 1 and NPC2 proteins. However, how cholesterol exits LEs/LYs and moves to other organelles remain largely unclear. Growing evidence has suggested that nonvesicular transport is critically involved in the post-endosomal cholesterol trafficking. Numerous sterol-transfer proteins (STPs) have been identified to mediate directional cholesterol transfer at membrane contact sites (MCSs) formed between 2 closely apposed organelles. In addition, a recent study reveals that lysosome-peroxisome membrane contact (LPMC) established by a non-STP synaptotagmin VII and a specific phospholipid phosphatidylinositol 4,5-bisphosphate also serves as a novel and important path for LDL-cholesterol trafficking. These findings highlight an essential role of MCSs in intracellular cholesterol transport, and further work is needed to unveil how various routes are regulated and integrated to maintain proper cholesterol distribution and homeostasis in eukaryotic cells.
Publisher: American Society for Pharmacology & Experimental Therapeutics (ASPET)
Date: 23-02-2006
Abstract: The nature of intestinal absorption of most herbal medicine is unknown. Cryptotanshinone (CTS) is the principal active constituent of the widely used cardiovascular herb Salvia miltiorrhiza (Danshen). We investigated the oral bioavailability of CTS in rats and the mechanism for its intestinal absorption using several in vitro and in vivo models: 1) Caco-2 cell monolayers 2) monolayers of MDCKII cells overexpressing P-glycoprotein (PgP) and 3) single-pass rat intestinal perfusion with mesenteric vein cannulation. The systemic bioavailabilities of CTS after oral and intraperitoneal administration at 100 mg/kg were 2.05 and 10.60%, respectively. In the perfused rat intestinal model, permeability coefficients based on CTS disappearance from the luminal perfusate (Plumen) were 6.7- to 10.3-fold higher than permeability coefficients based on drug appearance in venous blood (Pblood). Pblood significantly increased in the presence of the P-gP inhibitor, verapamil. CTS transport across Caco-2 monolayers was pH-, temperature- and ATP-dependent. The transport from the apical (AP) to the basolateral (BL) side was 3- to 9-fold lower than that from the BL to the AP side. Inclusion of verapamil (50 microM) in both AP and BL sides abolished the polarized CTS transport across Caco-2 cells. Moreover, CTS was significantly more permeable in the BL to AP than in the AP to BL direction in MDCKII and MDR1-MDCKII cells. The permeability coefficients in the BL to AP direction were significantly higher in MDCKII cells overexpressing PgP. These findings indicate that CTS is a substrate for PgP that can pump CTS into the luminal side.
Publisher: Oxford University Press (OUP)
Date: 24-12-2019
DOI: 10.1093/HMG/DDZ300
Abstract: Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2) is the most severe form of human lipodystrophy and is caused by loss-of-function mutations in the BSCL2/seipin gene. Exactly how seipin may regulate adipogenesis remains unclear. A recent study in vitro suggested that seipin may function to inhibit the activity of glycerol-3-phosphate acyltransferases (GPATs), and increased GPAT activity may be responsible for the defective adipogenesis under seipin deficiency. Here we generated Seipin−/−Gpat3−/− mice, which had mild but significant recovery of white adipose tissue mass over Seipin−/− mice. The mass of brown adipose tissue (BAT) of the Seipin−/−Gpat3−/− mice was almost completely restored to normal level. Importantly, the Seipin−/−Gpat3−/− mice showed significant improvement in liver steatosis and insulin sensitivity over Seipin−/− mice, which is attributable to the increased BAT mass and to the enhanced browning of the subcutaneous fat of the Seipin−/−Gpat3−/− mice. Together, our results establish a functional link between seipin and GPAT3 in vivo and suggest that GPAT inhibitors may have beneficial effects on BSCL2 patients.
Publisher: Proceedings of the National Academy of Sciences
Date: 05-03-2021
Abstract: Metabolic disorders related to aberrant fat accumulation, including lipodystrophy and obesity, are a serious health concern. Inside cells, fat accumulates in organelles named lipid droplets (LDs). LDs form in the endoplasmic reticulum (ER), where triglycerides (TG), the most abundant form of fat, are produced. The Berardinelli–Seip congenital lipodystrophy type 2 protein, seipin, has been identified as a key regulator of LD formation, but its mechanism of action remains debated and its molecular details mostly obscure. Here, we use molecular dynamics simulations to investigate the mechanism of seipin action. We find that seipin clusters and traps both TG and its precursor, diacylglycerol. Our results suggest that seipin organizes the lipid composition of specific ER sites to prime them for LD biogenesis.
Publisher: Elsevier BV
Date: 02-2019
DOI: 10.1016/J.MOLCEL.2018.11.014
Abstract: Cholesterol is highly enriched at the plasma membrane (PM), and lipid transfer proteins may deliver cholesterol to the PM in a nonvesicular manner. Here, through a mini-screen, we identified the oxysterol binding protein (OSBP)-related protein 2 (ORP2) as a novel mediator of selective cholesterol delivery to the PM. Interestingly, ORP2-mediated enrichment of PM cholesterol was coupled with the removal of phosphatidylinositol 4, 5-bisphosphate (PI(4,5)P
Publisher: Portland Press Ltd.
Date: 23-10-2009
DOI: 10.1042/BJ20090785
Abstract: LDs (lipid droplets) are cellular organelles which can be found in nearly all eukaryotic cells. Despite their importance in cell biology, the mechanism underlying LD biogenesis remains largely unknown. In the present study we report that conditions of ER (endoplasmic reticulum) stress stimulate LD formation in Saccharomyces cerevisiae. We found that LDs accumulated in yeast mutants with compromised protein glycosylation or ER-associated protein degradation. Moreover, tunicamycin and Brefeldin A, agents which induce ER stress, were found to stimulate LD formation. In contrast, the restoration of protein glycosylation reduced LD accumulation. Interestingly, enhanced neutral lipids synthesis and LD formation under conditions of ER stress was not dependent on Ire1p. Lastly, we demonstrated that the absence of LDs did not compromise cell viability under ER stress. Our results suggest that although more LDs are produced, LDs are not essential to cell survival under ER stress.
Publisher: Elsevier BV
Date: 05-2016
DOI: 10.1016/J.BBALIP.2016.02.018
Abstract: Adipose tissue can store over 50% of whole-body cholesterol however, the physiological role of adipose tissue in cholesterol metabolism and atherogenesis has not been directly assessed. Here, we examined lipoprotein metabolism and atherogenesis in a unique mouse model of severe lipodystrophy: the Seipin(-/-) mice, and also in mice deficient in both low-density lipoprotein receptor (Ldlr) and Seipin: the Ldlr(-/-)Seipin(-/-) mice. Plasma cholesterol was moderately increased in the Seipin(-/-) mice when fed an atherogenic diet. Strikingly, plasma cholesterol reached ~6000 mg/dl in the Seipin(-/-)Ldlr(-/-) mice on an atherogenic diet, as compared to ~1000 mg/dl in the Ldlr(-/-) mice on the same diet. The Seipin(-/-)Ldlr(-/-) mice also developed spontaneous atherosclerosis on chow diet and severe atherosclerosis on an atherogenic diet. Rosiglitazone treatment significantly reduced the hypercholesterolemia of the Seipin(-/-)Ldlr(-/-) mice, and also alleviated the severity of atherosclerosis. Our results provide direct evidence, for the first time, that the adipose tissue plays a critical role in the clearance of plasma cholesterol. Our results also reveal a previously unappreciated strong link between adipose tissue and LDLR in plasma cholesterol metabolism.
Publisher: Elsevier BV
Date: 10-2018
DOI: 10.1016/J.DEVCEL.2018.09.010
Abstract: The biogenesis of lipid droplets (LDs) and the development of adipocytes are two key aspects of mammalian fat storage. SEIPIN, an integral membrane protein of the endoplasmic reticulum (ER), plays a critical role in both LD formation and adipogenesis. The molecular function of SEIPIN, however, has yet to be elucidated. Here, we report the cryogenic electron microscopy structure of human SEIPIN at 3.8 Å resolution. SEIPIN exists as an undecamer, and this oligomerization state is critical for its physiological function. The evolutionarily conserved lumenal domain of SEIPIN forms an eight-stranded β sandwich fold. Both full-length SEIPIN and its lumenal domain can bind anionic phospholipids including phosphatidic acid. Our results suggest that SEIPIN forms a scaffold that helps maintain phospholipid homeostasis and surface tension of the ER.
Publisher: Elsevier BV
Date: 10-2017
DOI: 10.1016/J.BBALIP.2017.06.016
Abstract: The differentiation of preadipocytes into mature adipocytes is accompanied by the growth and formation of a giant, unilocular lipid droplet (LD). Mechanistically however, LD growth and adipogenesis are two different processes. Recent studies have uncovered a number of proteins that are able to regulate both LD dynamics and adipogenesis, such as SEIPIN, LIPIN and CDP-Diacylglycerol Synthases. It appears that phospholipids, phosphatidic acid in particular, play a critical role in both LD budding/growth and adipocyte development. This review summarizes recent advances, and aims to provide a better understanding of LD growth as well as adipogenesis, two critical aspects in mammalian fat storage. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.
Publisher: American Society for Cell Biology (ASCB)
Date: 12-2022
Abstract: PI(3)P and DFCP1, both known for their association with autophagy initiation, regulate the biogenesis of lipid droplets.
Publisher: Springer Science and Business Media LLC
Date: 28-11-2019
DOI: 10.1038/S41598-019-54392-8
Abstract: Lipodystrophy is a severe adipose dysfunction that can be classified as congenital or acquired lipodystrophy, in term of the etiology. Previous knowledge about the metabolic disorders and cardiovascular consequences were mostly obtained from lipodystrophic mice with genetic defects. To completely rule out the genetic influence, we established a mouse model of acquired generalized lipodystrophy by surgical removal of multiple fat depots, including subcutaneous fat in the inguinal, visceral fat in the epididymis and brown fat in the scapula, in atherosclerosis-prone LDLR −/− mice which were fed with a high-fat diet (HFD). It was observed that fat removal increased diet-induced hyperlipidemia, especially hypercholesteremia, as early as 2 weeks after HFD and till the end of HFD feeding. After 12 weeks on the HFD, the residual fats of fat-removed mice were found expanded. Although fat removal aggravated diet-induced lipid deposition in the liver and systemic insulin resistance, there was no significant difference in atherogenesis in fat-removed mice compared with sham-operated control mice. Acquired generalized lipodystrophy by surgical fat removal promoted metabolic disorders but not atherogenesis in LDLR −/− mice fed on HFD.
Publisher: Elsevier BV
Date: 09-2018
DOI: 10.1016/J.SEMCDB.2017.07.017
Abstract: Oxysterol-binding protein (OSBP) and its related proteins (ORPs) constitute a large, evolutionarily conserved family of lipid-binding proteins that are associated with a wide range of cellular activities. The core function of OSBP/ORPs appears to be moving lipids between cellular membranes in a non-vesicular manner. Recent studies have unveiled a novel, counter-transport mechanism of cellular lipid transfer mediated by OSBP/ORPs at the membrane contact sites that involves phosphatidylinositol 4-phosphate. Importantly, the OSBP/ORPs family has also been implicated in cell signalling pathways and cancer development. Here, we summarize recent progress in understanding the role of OSBP/ORPs in cancer development, and discuss how the lipid transfer function of OSBP/ORPs may underpin their role in tumorigenesis.
Publisher: Public Library of Science (PLoS)
Date: 04-08-2010
Publisher: Elsevier BV
Date: 11-2008
DOI: 10.1016/J.BBALIP.2008.08.006
Abstract: Previously, using an oxysterol to induce cholesterol trafficking to the Endoplasmic Reticulum (ER), we reported a dissociation between cholesterol transport to two important cholesterol regulatory components in the ER: the cholesterol esterifying enzyme ACAT (Acyl CoA:Cholesterol Acyltransferase) and the membrane-bound transcription factor SREBP (Sterol Regulatory Element Binding Protein) (X. Du, Y.H. Pham and A.J. Brown, Effects of 25-hydroxycholesterol on cholesterol esterification and SREBP processing are dissociable: implications for cholesterol movement to the regulatory pool in the endoplasmic reticulum, J. Biol Chem. 279 (2004) 47010-47016). Here, we employed low-density lipoprotein (LDL) as a more physiologically-relevant mode of cholesterol delivery, and compared cholesterol transport to ACAT (determined by esterification) and SREBP (assessed by processing) in mutant Chinese Hamster Ovary cells that have cholesterol-trafficking defects (including Niemann-Pick type C). We showed clear differences in kinetics between the two, with impaired cholesterol trafficking to SREBP being resolved more rapidly than to ACAT. This is unlikely to be due to a reduced threshold of cholesterol sensed by the SREBP system relative to ACAT, since both responded to LDL-derived cholesterol within 2 h whereas the ergence observed between the two was prolonged (>20 h). Furthermore, ACAT inhibition did not expand the ER regulatory pool of cholesterol as judged by unaltered sensitivity of SREBP processing to LDL. Collectively, our data favor the contention that there are different cholesterol pools and/or transport pathways which feed ACAT and SREBP within the ER.
Publisher: Oxford University Press (OUP)
Date: 18-01-2023
Publisher: China Science Publishing & Media Ltd.
Date: 2013
DOI: 10.1093/ABBS/GMS095
Abstract: The delivery of low-density lipoprotein-derived cholesterol (LDL-C) from endosomal compartments to the plasma membrane and the endoplasmic reticulum (ER) is an important yet poorly understood cellular process. Niemann-Pick C1 (NPC1), a multi-pass integral membrane protein on the limiting membranes of late endosomes (LE)/lysosomes (Ly), is known to insert lumenal LDL-C to the limiting membrane of LE/Ly. Recent progress has identified novel cytoplasmic proteins that regulate the exit of LDL-C from LE/Ly, such as ORP5, a member of the oxysterol-binding protein-related protein (ORPs) family, and Hrs/VPS27, a well-established regulator of the endosomal sorting complex required for transport pathway. Whereas ORP5/ORPs may serve as cytosolic cholesterol carriers and deliver cholesterol in a non-vesicular manner, how Hrs/VPS27 regulate endosomal cholesterol sorting remains enigmatic. We discuss the functional relationship between NPC1, Hrs, and ORP5, and formulate possible schemes on how LDL-C may be moved from endosomal compartments to other cellular organelles.
Publisher: Wiley
Date: 06-2005
DOI: 10.1002/PTR.1559
Abstract: In vitro and in vivo studies have indicated that the induction or inhibition of cytochrome P450 (CYP) is one of the major mechanisms for some clinically important pharmacokinetic herb-drug interactions. An attempt was made to simulate the effects of herbal preparation with single or multiple CYP-inhibiting constituents on the area of the plasma concentration-time curve (AUC) of coadministered drug that was either a low clearance drug by intravenous (i.v.) injection or a high clearance drug by oral route. Our simulation studies indicated that the expected increase (Rc) in the AUC of the coadministered drug by inhibiting herbal constituent(s) was dependent on the route of administration. For low clearance drug by i.v. injection, Rc was generally determined by inhibition constant (Ki), unbound inhibitor concentration ([I]), hepatic fraction (fh), number of inhibitory herbal constituents (n) and metabolic pathway fraction in hepatic metabolism (fm), while Rc for a high clearance drug by oral route, Rc was determined by Ki, [I], n and fm. By varying these parameters, Rc changed accordingly. It appeared likely to predict a herb-drug metabolic interaction, if the inhibiting herbal constituents could be quantitatively determined. However, many herb- and drug-related factors may cause difficulties with the prediction, and thus in vivo animal and human studies are always necessary.
Publisher: Rockefeller University Press
Date: 10-01-2011
Abstract: Oxysterol-binding protein (OSBP) and its related proteins (ORPs) constitute a large and evolutionarily conserved family of lipid-binding proteins that target organelle membranes to mediate sterol signaling and/or transport. Here we characterize ORP5, a tail-anchored ORP protein that localizes to the endoplasmic reticulum. Knocking down ORP5 causes cholesterol accumulation in late endosomes and lysosomes, which is reminiscent of the cholesterol trafficking defect in Niemann Pick C (NPC) fibroblasts. Cholesterol appears to accumulate in the limiting membranes of endosomal compartments in ORP5-depleted cells, whereas depletion of NPC1 or both ORP5 and NPC1 results in luminal accumulation of cholesterol. Moreover, trans-Golgi resident proteins mislocalize to endosomal compartments upon ORP5 depletion, which depends on a functional NPC1. Our results establish the first link between NPC1 and a cytoplasmic sterol carrier, and suggest that ORP5 may cooperate with NPC1 to mediate the exit of cholesterol from endosomes/lysosomes.
Publisher: Springer Science and Business Media LLC
Date: 30-09-2005
DOI: 10.1007/S00439-005-0055-3
Abstract: Acyl-CoA: cholesterol acyltransferase-2 (ACAT2), an intracellular cholesterol esterification enzyme found only in the intestine and liver, has been demonstrated to be associated with hypercholesterolemia and atherosclerosis in mice. To explore the possible impact of ACAT2 gene variants on CAD susceptibility and plasma lipid levels, three polymorphisms, 41A>G (Glu>Gly), 734C>T (Thr>Ile), and IVS4-57_58 ins48 bp (D/I), were genotyped in 809 CAD patients (CAD+) and 1,304 controls (CAD-) from three distinct Singaporean ethnic groups (1,228 Chinese, 367 Malays and 518 Indians). The 734T allele frequency was significantly lower in CAD+ (0.20) than CAD- (0.26) in Chinese (P=0.003) and I allele of D/I was significantly higher in CAD+ (0.17) than CAD- (0.10) in Indians (P=0.011). The 41G allele was significantly more frequent among normolipidemic (0.19) than dyslipidemic (0.13) in iduals in Chinese (P=0.008). In normolipidemic females, 734C>T was associated with apoA1, apoB and lipoprotein (a) in Indians, and with apoA1 in Malays, whereas 41A>G is associated with total cholesterol in Indians. The 734C>T polymorphism was in almost complete linkage disequilibrium (LD) with the IVS4-57_58 ins48 bp and in very strong LD with 41A>G in all the three ethnic groups. In the normolipidemic females, the AG/CT had much higher apoB than AA/CC in Indians. We found that the three ACAT2 polymorphisms studied are associated with CAD risk and plasma lipid levels but their effects are not consistent across genders and ethnic groups.
Publisher: Springer Science and Business Media LLC
Date: 19-02-2019
DOI: 10.1038/S41467-019-08791-0
Abstract: Phosphatidylinositol phosphates (PIPs) and cholesterol are known to regulate the function of late endosomes and lysosomes (LELs), and ORP1L specifically localizes to LELs. Here, we show in vitro that ORP1 is a PI(4,5)P 2 - or PI(3,4)P 2 -dependent cholesterol transporter, but cannot transport any PIPs. In cells, both ORP1L and PI(3,4)P 2 are required for the efficient removal of cholesterol from LELs. Structures of the lipid-binding domain of ORP1 (ORP1-ORD) in complex with cholesterol or PI(4,5)P 2 display open conformations essential for ORP function. PI(4,5)P 2 /PI(3,4)P 2 can facilitate ORP1-mediated cholesterol transport by promoting membrane targeting and cholesterol extraction. Thus, our work unveils a distinct mechanism by which PIPs may allosterically enhance OSBP/ORPs-mediated transport of major lipid species such as cholesterol.
Publisher: Elsevier BV
Date: 08-2014
DOI: 10.1016/J.DEVCEL.2014.07.005
Abstract: Rab GTPases, by targeting to specific membrane compartments, play essential roles in membrane trafficking. Lipid droplets (LDs) are dynamic subcellular organelles whose growth is closely linked to obesity and hepatic steatosis. Fsp27 is shown to be required for LD fusion and growth by enriching at LD-LD contact sites. Here, we identify Rab8a as a direct interactor and regulator of Fsp27 in mediating LD fusion in adipocytes. Knockdown of Rab8a in the livers of ob/ob mice results in the accumulation of smaller LDs and lower hepatic lipid levels. Surprisingly, it is the GDP-bound form of Rab8a that exhibits fusion-promoting activity. We further discover AS160 as the GTPase activating protein (GAP) for Rab8a, which forms a ternary complex with Fsp27 and Rab8a to positively regulate LD fusion. MSS4 antagonizes Fsp27-mediated LD fusion activity through Rab8a. Our results have thus revealed a mechanistic signaling circuit controlling LD fusion and fatty liver formation.
Publisher: Rockefeller University Press
Date: 15-12-2021
Abstract: Nuclear lipid droplets (nLDs) are poorly characterized outside of the liver. In this issue, Sołtysik et al. (2020. J. Cell Biol.0.1083/jcb.202005026) show that seipin is absent from the nucleus but seipin deficiency promotes nLD formation by increasing nuclear phosphatidic acid.
Publisher: Wiley
Date: 22-10-2012
DOI: 10.1111/FEBS.12015
Abstract: The isoprenoid squalene is an important precursor for the biosynthesis of sterols. The cellular storage of squalene and its impact on membrane properties have been the subject of recent investigations. In a screen for abnormal lipid droplet morphology and distribution in the yeast Saccharomyces cerevisiae, we found significant lipid droplet clustering (arbitrarily defined as an aggregation of six or more lipid droplets) in a number of mutants (e.g. erg1) that are defective in sterol biosynthesis. Interestingly, these mutants are also characterized by accumulation of large amounts of squalene. Reducing the level of squalene in these mutants restored normal lipid droplet distribution. Moreover, inhibition of squalene monooxygenase in two mammalian cell lines (CHO-K1 and 3T3-L1) by terbinafine also resulted in lipid droplet clustering. These results indicate that the level of squalene may affect the growth and distribution of lipid droplets.
Publisher: Elsevier BV
Date: 03-2012
DOI: 10.1194/JLR.M021899
Publisher: Elsevier BV
Date: 2012
DOI: 10.1016/J.CELREP.2011.10.004
Abstract: The endosomal sorting complex required for transport (ESCRT) plays a crucial role in the degradation of ubiquitinated endosomal membrane proteins. Here, we report that Hrs, a key protein of the ESCRT-0 complex, is required for the transport of low-density lipoprotein-derived cholesterol from endosomes to the endoplasmic reticulum. This function of Hrs in cholesterol transport is distinct from its previously defined role in lysosomal sorting and downregulation of membrane receptors via the ESCRT pathway. In line with this, knocking down other ESCRT proteins does not cause prominent endosomal cholesterol accumulation. Importantly, the localization and biochemical properties of key cholesterol-sorting proteins, NPC1 and NPC2, appear to be unchanged upon Hrs knockdown. Our data identify Hrs as a regulator of endosomal cholesterol trafficking and provide additional insights into the budding of intralumenal vesicles.
Publisher: Elsevier BV
Date: 12-2011
DOI: 10.1194/JLR.M017566
Publisher: Hindawi Limited
Date: 2013
DOI: 10.1155/2013/636287
Abstract: In Saccharomyces cerevisiae , mitochondrial morphology changes when cells are shifted between nonfermentative and fermentative carbon sources. Here, we show that cells of S. cerevisiae grown in different glucose concentrations display different mitochondrial morphologies. The morphology of mitochondria in the cells growing in 0.5% glucose was similar to that of mitochondria in respiring cells. However, the mitochondria of cells growing in higher glucose concentrations (2% and 4%) became fragmented after growth in these media, due to the production of acetic acid however, the fragmentation was not due to intracellular acidification. From a screen of mutants involved in sensing and utilizing nutrients, cells lacking TOR1 had reduced mitochondrial fragmentation, and autophagy was found to be essential for this reduction. Mitochondrial fragmentation in cells grown in high glucose was reversible by transferring them into conditioned medium from a culture grown on 0.5% glucose. Similarly, the chronological lifespan of cells grown in high glucose medium was reduced, and this phenotype could be reversed when cells were transferred to low glucose conditioned medium. These data indicate that chronological lifespan seems correlated with mitochondrial morphology of yeast cells and that both phenotypes can be influenced by factors from conditioned medium of cultures grown in low glucose medium.
Publisher: Springer Science and Business Media LLC
Date: 30-11-2016
DOI: 10.1007/S00429-015-1151-3
Abstract: Immunohistochemical staining was used to investigate the expression pattern of SEIPIN in the mouse central nervous system. SEIPIN was found to be present in a large number of areas, including the motor and somatosensory cortex, the thalamic nuclei, the hypothalamic nuclei, the mesencephalic nuclei, some cranial motor nuclei, the reticular formation of the brainstem, and the vestibular complex. Double labeling with NeuN antibody confirmed that SEIPIN-positive cells in some nuclei were neurons. Retrograde tracer injections into the spinal cord revealed that SEIPIN-positive neurons in the motor and somatosensory cortex and other movement related nuclei project to the mouse spinal cord. The present study found more nuclei positive for SEIPIN than shown using in situ hybridization and confirmed the presence of SEIPIN in neurons projecting to the spinal cord. The results of this study help to explain the clinical manifestations of patients with Berardinelli-Seip congenital lipodystrophy (Bscl2) gene mutations.
Publisher: Elsevier BV
Date: 11-2004
Publisher: Oxford University Press (OUP)
Date: 06-05-2011
DOI: 10.1093/HMG/DDR205
Abstract: Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2) is an autosomal recessive disorder characterized by an almost complete loss of adipose tissue, insulin resistance and fatty liver. Here, we create the first murine model of BSCL2 by targeted disruption of seipin, the causative gene for BSCL2. Compared with their wild-type littermates, the seipin(-/-) mice are viable and of normal weight but display significantly reduced adipose tissue mass, hepatic steatosis, glucose intolerance and hyperinsulinemia. The levels of leptin and adiponectin were both significantly decreased in seipin(-/-) mice, so were non-esterified fatty acids upon fasting. Surprisingly, however, hypertriglyceridemia which is common in human BSCL, was not observed in seipin(-/-) mice. Our findings suggest a possible tissue-autonomous role of seipin in liver lipid storage. The availability of the seipin(-/-) mice should help elucidate the molecular function of seipin and lead to a better understanding of the many metabolic consequences of human BSCL2.
Publisher: Springer Science and Business Media LLC
Date: 09-2005
DOI: 10.1007/S11095-005-7595-Z
Abstract: The multidrug resistance associated protein (MRP) 4 is a member of the adenosine triphosphate (ATP)-binding cassette transporter family. C tothecins (CPTs) have shown substantial anticancer activity against a broad spectrum of tumors by inhibiting DNA topoisomerase I, but tumor resistance is one of the major reasons for therapeutic failure. P-glycoprotein, breast cancer resistance protein, MRP1, and MRP2 have been implicated in resistance to various CPTs including CPT-11 (irinotecan), SN-38 (the active metabolite of CPT-11), and topotecan. In this study, we explored the resistance profiles and intracellular accumulation of a panel of CPTs including CPT, CPT-11, SN-38, rubitecan, and 10-hydroxy-CPT (10-OH-CPT) in HepG2 cells with stably overexpressed human MRP4. Other anticancer agents such as paclitaxel, cyclophosphamide, and carboplatin were also included. HepG2 cells were transfected with an empty vehicle plasmid (V/HepG2) or human MRP4 (MRP4/HepG2). The resistance profiles of test drugs in exponentially growing V/HepG2 and MRP4/HepG2 cells were examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazonium bromide (MTT) assay with 4 or 48 h exposure time of the test drug in the absence or presence of various MRP4 inhibitors. The accumulation of CPT-11, SN-38, and paclitaxel by V/HepG2 and MRP4/HepG2 cells was determined by validated high-performance liquid chromatography methods. Based on the resistance folds from the MTT assay with 48 h exposure time of the test drug, MRP4 conferred resistance to CPTs tested in the order 10-OH-CPT (14.21) > SN-38 carboxylate (9.70) > rubitecan (9.06) > SN-38 lactone (8.91) > CPT lactone (7.33) > CPT-11 lactone (5.64) > CPT carboxylate (4.30) > CPT-11 carboxylate (2.68). Overall, overexpression of MRP4 increased the IC50 values 1.78- to 14.21-fold for various CPTs in lactone or carboxylate form. The resistance of MRP4 to various CPTs tested was significantly reversed in the presence of dl-buthionine-(S,R)-sulfoximine (BSO, a gamma-glutamylcysteine synthetase inhibitor), MK571, celecoxib, or diclofenac (all MRP4 inhibitors). In addition, the accumulation of CPT-11 and SN-38 over 120 min in MRP4/HepG2 cells was significantly reduced compared to V/HepG2 cells, whereas the addition of celecoxib, MK571, or BSO significantly increased their accumulation in MRP4/HepG2 cells. There was no significant difference in the intracellular accumulation of paclitaxel in V/HepG2 and MRP4/HepG2 cells, indicating that P-glycoprotein was not involved in the observed resistance to CPTs in this study. MRP4 also conferred resistance to cyclophosphamide and this was partially reversed by BSO. However, MRP4 did not increase resistance to paclitaxel, carboplatin, etoposide (VP-16), 5-fluorouracil, and cyclosporine. Human MRP4 rendered significant resistance to cyclophosphamide, CPT, CPT-11, SN-38, rubitecan, and 10-OH-CPT. CPT-11 and SN-38 are substrates for MRP4. Further studies are needed to explore the role of MRP4 in resistance, toxicity, and pharmacokinetics of CPTs and cyclophosphamide.
Publisher: Elsevier BV
Date: 11-2016
Location: No location found
Location: United States of America
Start Date: 2009
End Date: 06-2012
Amount: $170,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2021
End Date: 06-2024
Amount: $541,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2013
End Date: 01-2016
Amount: $285,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2021
End Date: 06-2024
Amount: $493,720.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2013
End Date: 01-2014
Amount: $235,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 01-2010
End Date: 01-2014
Amount: $788,800.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2012
End Date: 12-2014
Amount: $310,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2008
End Date: 12-2012
Amount: $564,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2014
End Date: 12-2014
Amount: $370,000.00
Funder: Australian Research Council
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