Dynamic distribution of muscle-specific calpain in mice has a key role in physical-stress adaptation and is impaired in muscular dystrophy
Koichi Ojima, … , Atsu Aiba, Hiroyuki Sorimachi
Koichi Ojima, … , Atsu Aiba, Hiroyuki Sorimachi
Published July 1, 2010
Citation Information: J Clin Invest. 2010;120(8):2672-2683. https://doi.org/10.1172/JCI40658.
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Research Article Muscle biology

Dynamic distribution of muscle-specific calpain in mice has a key role in physical-stress adaptation and is impaired in muscular dystrophy

Abstract

Limb-girdle muscular dystrophy type 2A (LGMD2A) is a genetic disease that is caused by mutations in the calpain 3 gene (CAPN3), which encodes the skeletal muscle–specific calpain, calpain 3 (also known as p94). However, the precise mechanism by which p94 functions in the pathogenesis of this disease remains unclear. Here, using p94 knockin mice (termed herein p94KI mice) in which endogenous p94 was replaced with a proteolytically inactive but structurally intact p94:C129S mutant protein, we have demonstrated that stretch-dependent p94 distribution in sarcomeres plays a crucial role in the pathogenesis of LGMD2A. The p94KI mice developed a progressive muscular dystrophy, which was exacerbated by exercise. The exercise-induced muscle degeneration in p94KI mice was associated with an inefficient redistribution of p94:C129S in stretched sarcomeres. Furthermore, the p94KI mice showed impaired adaptation to physical stress, which was accompanied by compromised upregulation of muscle ankyrin-repeat protein-2 and hsp upon exercise. These findings indicate that the stretch-induced dynamic redistribution of p94 is dependent on its protease activity and essential to protect muscle from degeneration, particularly under conditions of physical stress. Furthermore, our data provide direct evidence that loss of p94 protease activity can result in LGMD2A and molecular insight into how this could occur.

Authors

Koichi Ojima, Yukiko Kawabata, Harumi Nakao, Kazuki Nakao, Naoko Doi, Fujiko Kitamura, Yasuko Ono, Shoji Hata, Hidenori Suzuki, Hiroyuki Kawahara, Julius Bogomolovas, Christian Witt, Coen Ottenheijm, Siegfried Labeit, Henk Granzier, Noriko Toyama-Sorimachi, Michiko Sorimachi, Koichi Suzuki, Tatsuya Maeda, Keiko Abe, Atsu Aiba, Hiroyuki Sorimachi

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Figure 1

MD phenotypes in p94KI mice.

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MD phenotypes in p94KI mice. (A–J) H&E-stained TA muscle sections fr...
(A–J) H&E-stained TA muscle sections from WT (A, C, E, G, and I) and p94KI (B, D, F, H, and J) mice of the ages indicated. p94KI showed typical dystrophic phenotypes, such as cell invasion (dotted circles), central nuclei (black arrowheads), and the splitting of myofibers (white arrowheads). Scale bars: 100 μm. (K and L) Increased CNM during aging in p94KI mice. The number of CNM in the TA (K) and soleus (L) was compared with the number of total myofibers. (M) Frequency distribution of myofiber CSArs in the soleus of mice over 90 weeks old. A total of 302 fiber profiles was traced in each section from 3 mice of each type. The average myofiber CSAr was 1,542 μm2 in WT mice and 1,342 μm2 in p94KI mice. The fiber size in p94KI mice was significantly smaller than in WT mice (P < 0.01). White bars, WT; black bars, p94KI. (N) The mean serum CK level (IU/l) in p94KI mice appeared higher than in WT, but this difference was not statistically significant. *P < 0.05 versus WT. (O and P) Ultrastructural analysis showed a typical striated pattern with properly assembled sarcomeres in a 91-week-old p94KI mouse (P) with no apparent difference from the pattern of a 26-week-old WT mouse (O). Scale bars: 1 μm.