Myotubularin controls desmin intermediate filament architecture and mitochondrial dynamics in human and mouse skeletal muscle
Karim Hnia, … , Jean Louis Mandel, Jocelyn Laporte
Karim Hnia, … , Jean Louis Mandel, Jocelyn Laporte
Published December 6, 2010
Citation Information: J Clin Invest. 2011;121(1):70-85. https://doi.org/10.1172/JCI44021.
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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 5

Effect of MTM1 on desmin filament polymerization.

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Effect of MTM1 on desmin filament polymerization. (A) Effect of MTM1 on ...
(A) Effect of MTM1 on in vitro assembly of desmin filaments. Assembly of recombinant desmin alone (scale bars: 200 nm) or in the presence of MTM1 WT (scale bars: 100 nm) or the control protein Sumo (scale bars: 200 nm) was monitored by electron microscopy at the indicated times. Addition of WT MTM1 led to irregular and ribbon-like filaments. (B) Filament parameters (width and length at 5 minutes of assembly) in the presence or absence of MTM1. Scale bar: 200 nm. (C) MTM1 cosedimented with desmin and interfered with polymerization. SDS-PAGE stained with Coomassie blue showed desmin exclusively in the pellet fraction (P; polymerized) in the presence of GST or GST-MTM1S209A, while it was also present in the soluble fraction (S; unpolymerized) in the presence of GST-MTM1. (D) Increasing amounts of recombinant GST-MTM1 caused a decrease in desmin polymerization. Lanes were run on the same gel but were noncontiguous (white line). Quantification of desmin assembly (calculated as the ratio of band intensities in pellet/supernatant) in the presence of increasing amounts (4, 8, and 16 μM) of GST-MTM1, GST-MTM1S209A, or GST. Data were correlated from 2 independent experiments. *P ≤ 0.05. (E) Model of MTM1’s effect on desmin assembly in vitro. In phase 1 of desmin assembly, 8 tetrameric subunits, made from 2 antiparallel, half-staggered coiled-coil dimers, associate laterally to form ULFs after initiation of assembly. In phase 2, ULFs and short filaments longitudinally anneal to other ULFs. In phase 3, filaments evolve to radial compacted structures. MTM1 addition (yellow) interferes with filament assembly in vitro, leading to a branched-like phenotype at the squiggles step and a ribbon-like structure.