Myotubularin controls desmin intermediate filament architecture and mitochondrial dynamics in human and mouse skeletal muscle
Karim Hnia, Helene Tronchère, Kinga K. Tomczak, Leonela Amoasii, Patrick Schultz, Alan H. Beggs, Bernard Payrastre, Jean Louis Mandel, Jocelyn Laporte
Karim Hnia, Helene Tronchère, Kinga K. Tomczak, Leonela Amoasii, Patrick Schultz, Alan H. Beggs, Bernard Payrastre, Jean Louis Mandel, Jocelyn Laporte
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Research Article Muscle biology

Myotubularin controls desmin intermediate filament architecture and mitochondrial dynamics in human and mouse skeletal muscle

Abstract

Muscle contraction relies on a highly organized intracellular network of membrane organelles and cytoskeleton proteins. Among the latter are the intermediate filaments (IFs), a large family of proteins mutated in more than 30 human diseases. For example, mutations in the DES gene, which encodes the IF desmin, lead to desmin-related myopathy and cardiomyopathy. Here, we demonstrate that myotubularin (MTM1), which is mutated in individuals with X-linked centronuclear myopathy (XLCNM; also known as myotubular myopathy), is a desmin-binding protein and provide evidence for direct regulation of desmin by MTM1 in vitro and in vivo. XLCNM-causing mutations in MTM1 disrupted the MTM1-desmin complex, resulting in abnormal IF assembly and architecture in muscle cells and both mouse and human skeletal muscles. Adeno-associated virus–mediated ectopic expression of WT MTM1 in Mtm1-KO muscle reestablished normal desmin expression and localization. In addition, decreased MTM1 expression and XLCNM-causing mutations induced abnormal mitochondrial positioning, shape, dynamics, and function. We therefore conclude that MTM1 is a major regulator of both the desmin cytoskeleton and mitochondria homeostasis, specifically in skeletal muscle. Defects in IF stabilization and mitochondrial dynamics appear as common physiopathological features of centronuclear myopathies and desmin-related myopathies.

Authors

Karim Hnia, Helene Tronchère, Kinga K. Tomczak, Leonela Amoasii, Patrick Schultz, Alan H. Beggs, Bernard Payrastre, Jean Louis Mandel, Jocelyn Laporte

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Figure 6

Effect of desmin on MTM1 PI phosphatase activity.

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Effect of desmin on MTM1 PI phosphatase activity. (A) GST-MTM1 recombina...
(A) GST-MTM1 recombinant proteins were incubated with PtdIns(3,5)P2 alone or in the presence of full-length desmin or specified desmin peptides (versus Sumo as a control protein and control peptide, respectively). No significant variation in the PtdIns5P/PtdIns(3,5)P2 ratio per mg protein was observed after quantification. Coomassie blue gel of purified GST-MTM1 and desmin are also shown. (B) Immunoprecipitated MTM1-containing complexes from cells cotransfected with MTM1-B10 and desmin-myc or with MTM1-B10 and NFL-myc (neurofilament light chain) were incubated with PtdIns(3,5)P2. Immunoprecipitated complexes were confirmed by Western blot analysis with anti-B10 and anti-myc antibodies. No significant changes in MTM1 phosphatase activity were found by quantification of the PtdIns5P/PtdIns(3,5)P2 ratio. (C) Immunolabeling of MTM1 substrate in Mtm1-KO and -KD cells showed accumulation of PtdIns(3,5)P2 compared with control cells. Single cells are outlined (original magnification, ×63). (D) MTM1 mutations within the desmin-binding domain (e.g., MTM1K255A and MTM1S209A) did not interfere with MTM1 PI phosphatase activity in cells, but XLCNM mutations (e.g., MTM1R241C and MTM1R421Q) or the catalytic inactive mutation (MTM1C375S) significantly impaired this activity. Single cells are outlined (original magnification, ×63). Histograms represent fluorescent intensities of PtdIns(3,5)P2 over 2 independent experiments. *P ≤ 0.05.