ORCID Profile
0000-0002-6358-2920
Current Organisations
IT University of Copenhagen
,
Københavns Universitet
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Publisher: Oxford University Press (OUP)
Date: 19-06-2013
DOI: 10.1093/HMG/DDT289
Abstract: Multiple congenital myopathies, including nemaline myopathy, can arise due to mutations in the ACTA1 gene encoding skeletal muscle α-actin. The main characteristics of ACTA1 null mutations (absence of skeletal muscle α-actin) are generalized skeletal muscle weakness and premature death. A mouse model (ACTC(Co)/KO) mimicking these conditions has successfully been rescued by transgenic over-expression of cardiac α-actin in skeletal muscles using the ACTC gene. Nevertheless, myofibres from ACTC(Co)/KO animals generate less force than normal myofibres (-20 to 25%). To understand the underlying mechanisms, here we have undertaken a detailed functional study of myofibres from ACTC(Co)/KO rodents. Mechanical and X-ray diffraction pattern analyses of single membrane-permeabilized myofibres showed, upon maximal Ca(2+) activation and under rigor conditions, lower stiffness and disrupted actin-layer line reflections in ACTC(Co)/KO when compared with age-matched wild-types. These results demonstrate that in ACTC(Co)/KO myofibres, the presence of cardiac α-actin instead of skeletal muscle α-actin alters actin conformational changes upon activation. This later finely modulates the strain of in idual actomyosin interactions and overall lowers myofibre force production. Taken together, the present findings provide novel primordial information about actin isoforms, their functional differences and have to be considered when designing gene therapies for ACTA1-based congenital myopathies.
Publisher: Public Library of Science (PLoS)
Date: 20-09-2202
Publisher: Springer Science and Business Media LLC
Date: 17-02-2020
DOI: 10.1186/S40478-020-0893-1
Abstract: Nemaline myopathy (NM) caused by mutations in the gene encoding nebulin ( NEB ) accounts for at least 50% of all NM cases worldwide, representing a significant disease burden. Most NEB -NM patients have autosomal recessive disease due to a compound heterozygous genotype. Of the few murine models developed for NEB -NM, most are Neb knockout models rather than harbouring Neb mutations. Additionally, some models have a very severe phenotype that limits their application for evaluating disease progression and potential therapies. No existing murine models possess compound heterozygous Neb mutations that reflect the genotype and resulting phenotype present in most patients. We aimed to develop a murine model that more closely matched the underlying genetics of NEB -NM, which could assist elucidation of the pathogenetic mechanisms underlying the disease. Here, we have characterised a mouse strain with compound heterozygous Neb mutations one missense (p.Tyr2303His), affecting a conserved actin-binding site and one nonsense mutation (p.Tyr935*), introducing a premature stop codon early in the protein. Our studies reveal that this compound heterozygous model, Neb Y2303H, Y935X , has striking skeletal muscle pathology including nemaline bodies. In vitro whole muscle and single myofibre physiology studies also demonstrate functional perturbations. However, no reduction in lifespan was noted. Therefore, Neb Y2303H,Y935X mice recapitulate human NEB -NM and are a much needed addition to the NEB -NM mouse model collection. The moderate phenotype also makes this an appropriate model for studying NEB -NM pathogenesis, and could potentially be suitable for testing therapeutic applications.
Publisher: Elsevier BV
Date: 09-2023
Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.JSB.2015.09.008
Abstract: In humans, mutant skeletal muscle α-actin proteins are associated with contractile dysfunction, skeletal muscle weakness and a wide range of primarily skeletal muscle diseases. Despite this knowledge, the exact molecular mechanisms triggering the contractile dysfunction remain unknown. Here, we aimed to unravel these. Hence, we used a transgenic mouse model expressing a well-described D286G mutant skeletal muscle α-actin protein and recapitulating the human condition of contractile deregulation and severe skeletal muscle weakness. We then recorded and analyzed the small-angle X-ray diffraction patterns of isolated membrane-permeabilized myofibers. Results showed that upon addition of Ca(2+), the intensity changes of the second (1/19 nm(-1)) and sixth (1/5.9 nm(-1)) actin layer lines and of the first myosin meridional reflection (1/14.3 nm(-1)) were disrupted when the thin-thick filament overlap was optimal (sarcomere length of 2.5-2.6 μm). However these reflections were normal when the thin and thick filaments were not interacting (sarcomere length>3.6 μm). These findings demonstrate, for the first time, that the replacement of just one amino acid in the skeletal muscle α-actin protein partly prevents actin conformational changes during activation, disrupting the strong binding of myosin molecules. This leads to a limited myosin-related tropomyosin movement over the thin filaments, further affecting the amount of cross-bridges, explaining the contractile dysfunction.
Publisher: Wiley
Date: 22-03-2016
DOI: 10.1002/ANA.24619
Publisher: Wiley
Date: 25-03-2018
DOI: 10.1002/JCP.26542
Abstract: Skeletal muscle fibers are giant multinucleated cells wherein in idual nuclei govern the protein synthesis in a finite volume of cytoplasm this is termed the myonuclear domain (MND). The factors that control MND size remain to be defined. In the present study, we studied the contribution of the NAD + ‐dependent deacetylase, sirtuin 1 (SIRT1), to the regulation of nuclear number and MND size. For this, we isolated myofibers from mice with tissue‐specific inactivation (mKO) or inducible overexpression (imOX) of SIRT1 and analyzed the 3D organisation of myonuclei. In imOX mice, the number of nuclei was increased whilst the average MND size was decreased as compared to littermate controls. Our findings were the opposite in mKO mice. Muscle stem cell (satellite cell) numbers were reduced in mKO muscles, a possible explanation for the lower density of myonuclei in these mice however, no change was observed in imOX mice, suggesting that other factors might also be involved, such as the functional regulation of stem cells/muscle precursors. Interestingly, however, the changes in the MND volume did not impact the force‐generating capacity of muscle fibers. Taken together, our results demonstrate that SIRT1 is a key regulator of MND sizes, although the underlying molecular mechanisms and the cause‐effect relationship between MND and muscle function remain to be fully defined.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Julien Ochala.