ORCID Profile
0000-0002-0061-2168
Current Organisation
The University of Manitoba
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Publisher: Cold Spring Harbor Laboratory
Date: 04-11-2019
DOI: 10.1101/825828
Abstract: Lipotoxicity is a form of cellular stress caused by the accumulation of lipids resulting in mitochondrial dysfunction and insulin resistance in muscle. Previously, we demonstrated that the mitophagy receptor Nix is responsive to lipotoxicity and accumulates in response to diacylglycerols induced by high-fat (HF) feeding. In addition, previous studies have implicated autophagy and mitophagy in muscle insulin sensitivity. To provide a better understanding of these observations, we undertook gene expression array and shot-gun metabolomics studies in soleus muscle from rodents on an HF diet. Interestingly, we observed a modest reduction in several autophagy-related genes including Beclin-1, ATG3, and -5. Moreover, we observed alterations in the fatty acyl composition of cardiolipins and phosphatidic acids. Given the previously reported roles of these phospholipids and Nix in mitochondrial dynamics, we investigated aberrant mitochondrial fission and turn-over as a mechanism of myocyte insulin resistance. In a series of gain-of-function and loss-of-function experiments in rodent and human myotubes, we demonstrate that Nix accumulation triggers mitochondrial depolarization, fragmentation, calcium-dependent activation of DRP1, and mitophagy. In addition, Nix-induced mitochondrial fission leads to myotube insulin resistance through activation of mTOR-p70S6 kinase inhibition of IRS1, which is contingent on phosphatidic acids and Rheb. Finally, we demonstrate that Nix-induced mitophagy and insulin resistance can be reversed by direct phosphorylation of Nix by PKA, leading to the translocation of Nix from the mitochondria and sarcoplasmic reticulum to the cytosol. These findings provide insight into the role of Nix-induced mitophagy and myocyte insulin resistance during an overfed state when overall autophagy-related gene expression is reduced. Furthermore, our data suggests a mechanism by which exercise or pharmacological activation of PKA may overcome myocyte insulin resistance.
Publisher: Cold Spring Harbor Laboratory
Date: 18-03-2023
DOI: 10.1101/2023.03.18.532760
Abstract: Mitochondrial quality control is critical in muscle to ensure both contractile and metabolic function. Nix is a BCL-2 family member, mitophagy receptor, and has recently been implicated in muscle atrophy. Human GWAS suggests altered Nix expression could predispose in iduals to manifestations of mitochondrial disease. To interrogate the role of Nix in skeletal muscle, we generated a muscle-specific knockout model. Nix knockout mice displayed a ragged-red fibre phenotype, along with accumulation of senescent mitochondria and sarcoplasmic reticulum. Intriguingly, Nix knockout mice were more insulin sensitive with a corresponding increase in glycogen-rich muscle fibres. Kinome- and gene expression analyses revealed that Nix knockout impairs NFAT and canonical myostatin signaling, with alterations in muscle fibre-type composition and evidence of regeneration. Experiments in myotubes demonstrated that Nix modulates mitophagy, and also ER-phagy through a distinct mechanism leading to nuclear calcium signaling. Collectively, these observations indicate that Nix maintains muscle integrity and an oxidative phenotype. Removal of Nix in muscle results in a compensated mitochondrial myopathy Nix knockout alters cell signaling and oxidative muscle gene expression Nix also modulates myostatin expression and Smad signaling Nix knockout alters muscle fibre-type distribution and muscle function How mitochondria respond to cell stress to activate cell signaling pathways remains poorly understood. We show that genetic removal of the mitophagy receptor Nix from muscle leads to alterations in cell signaling and the muscle phenotype. These observations help explain how selective autophagy pathways can modulate tissue homeostasis during metabolic stress.
Publisher: Cold Spring Harbor Laboratory
Date: 26-02-2022
DOI: 10.1101/2022.02.25.481852
Abstract: Extracellular vesicles (EVs) are small lipid membrane-bound structures that are secreted by all cells, and play a central role in cellular communication. EVs are released from skeletal muscle during exercise, but the effects of contractile activity on skeletal muscle-derived EVs (Skm-EVs) are poorly understood due to the challenges in distinguishing Skm-EVs derived from exercising muscle in vivo . To specifically characterize Skm-EVs, C2C12 myoblasts were differentiated into myotubes, and electrically paced (3h/day x 4days @14V, C-PACE EM, IonOptix) to mimic chronic exercise in vitro . EVs were isolated from conditioned media from control and stimulated myotubes using differential ultracentrifugation. Isolated EVs were characterized biophysically (size, zeta potential, yield, protein markers and by transmission electron microscopy TEM). Chronic stimulation increased markers of mitochondrial biogenesis such as MitoTracker Red staining, cytochrome c oxidase activity and expression of cytochrome c (p .05, N=7-8) in stimulated vs . non-stimulated myotubes. The average size of EVs from chronically stimulated myotubes (CS-EVs, 132 nm) was 26% smaller than control (CON-EVs, 178 nm) (p .05, N=8). Size distribution analysis revealed that CS-EVs were enriched with 100-150 nm sized small EVs, while CON-EVs were largely composed of 200-250 nm sized vesicles (p .05, main interaction effect, N=8). TEM confirmed the presence of round-shaped vesicles of about 30-100 nm with an intact lipid bilayer in CON-EVs and CS-EVs. Zeta potential was 27% lower in CS-EVs vs . CON-EVs (p .05, N=8), and total EV protein yield remained unchanged between groups. Protein-based EV characterization showed that both CON-EVs/CS-EVs were CD81+ but CD63-, and expressed hallmark cytosolic proteins recovered in EVs: Tsg101, Flotillin-1, HSP70, and Alix. CD81 and HSP70 expression increased in CS-EVs vs . CON-EVs (p .05, N=9). We evaluated if chronic stimulation affected whole cell expression of transmembrane and cytosolic proteins used in EV origin urity analysis. CD63 and ApoA1 were reduced with chronic stimulation in myotube lysates (p .05, N=7), whereas Tsg101, CD81, Flotillin-1 and HSP70 levels remained constant. Taken together, our study revealed that chronic stimulation triggers the release of more stable, smaller sized EVs, enriched with transmembrane and cytosolic protein markers of small EVs, and are CD81+/CD63-indicating the origin of these EVs might be ectosomal rather than endosomal. The upstream signaling cascades that regulate biogenesis of EVs with chronic stimulation, and whether skeletal muscle-EVs are released through endosomal or ectosomal pathways remains to be elucidated. Our findings support the role of chronic contractile activity in the modulation of EV biophysical characteristics. Whether this affects biological cargo recruitment into CS-EVs, and their subsequent biological activity remains to be established.
Publisher: Cold Spring Harbor Laboratory
Date: 10-10-2020
DOI: 10.1101/2020.10.09.333666
Abstract: Systemic hypoxia is a common element in most perinatal emergencies and is a known driver of Bnip3 expression in the neonatal heart. Bnip3 plays a prominent role in the evolution of necrotic cell death, disrupting ER calcium homeostasis and initiating mitochondrial permeability transition (MPT). Emerging evidence suggests a cardioprotective role for the prostaglandin E1 analogue misoprostol during periods of hypoxia, but the mechanisms for this protection are not completely understood. Using a combination of mouse and cell models, we tested if misoprostol is cardioprotective during neonatal hypoxic injury by altering Bnip3 function. Here we report that hypoxia elicits mitochondrial-fragmentation, MPT, reduced ejection fraction, and evidence of necroinflammation, which were abrogated with misoprostol treatment or Bnip3 knockout. Through molecular studies we show that misoprostol leads to PKA-dependent Bnip3 phosphorylation at threonine-181, and subsequent redistribution of Bnip3 from mitochondrial Opa1 and the ER through an interaction with 14-3-3 proteins. Taken together, our results demonstrate a role for Bnip3 phosphorylation in the regulation of cardiomyocyte contractile/metabolic dysfunction, and necroinflammation. Furthermore, we identify a potential pharmacological mechanism to prevent neonatal hypoxic injury.
Publisher: Springer Science and Business Media LLC
Date: 26-11-2021
DOI: 10.1038/S41419-021-04402-3
Abstract: Systemic hypoxia is a common element in most perinatal emergencies and is a known driver of Bnip3 expression in the neonatal heart. Bnip3 plays a prominent role in the evolution of necrotic cell death, disrupting ER calcium homeostasis and initiating mitochondrial permeability transition (MPT). Emerging evidence suggests a cardioprotective role for the prostaglandin E1 analog misoprostol during periods of hypoxia, but the mechanisms for this protection are not completely understood. Using a combination of mouse and cell models, we tested if misoprostol is cardioprotective during neonatal hypoxic injury by altering Bnip3 function. Here we report that hypoxia elicits mitochondrial-fragmentation, MPT, reduced ejection fraction, and evidence of necroinflammation, which were abrogated with misoprostol treatment or Bnip3 knockout. Through molecular studies we show that misoprostol leads to PKA-dependent Bnip3 phosphorylation at threonine-181, and subsequent redistribution of Bnip3 from mitochondrial Opa1 and the ER through an interaction with 14-3-3 proteins. Taken together, our results demonstrate a role for Bnip3 phosphorylation in the regulation of cardiomyocyte contractile/metabolic dysfunction, and necroinflammation. Furthermore, we identify a potential pharmacological mechanism to prevent neonatal hypoxic injury.
Publisher: EMBO
Date: 03-03-2021
Publisher: Springer Science and Business Media LLC
Date: 06-03-2018
Publisher: Informa UK Limited
Date: 12-10-2020
No related grants have been discovered for Joseph Gordon.