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 stretchinduced 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.

Expanding Members and Roles of the Calpain Superfamily and Their Genetically Modified Animals

“…A primary cause of LGMd2A is a defect in the protease activity, not the structural properties, of calpain-3/p94 [121]. This was confirmed by the demonstration that calpain-3/p94:C129S inactive mutant knock-in mice showed a muscular dystrophy phenotype [117].…”

The sarcomeric cytoskeleton: from molecules to motion

“…Whether these activities require titin kinase activity or solely its scaffolding role remains to be clarified (Bogomolovas et al, 2014;Lange et al, 2005b). Titin interacts additionally with the cysteine protease calpain-3 in the differentially spliced insertion between domains M9 and M10 (Kinbara et al, 1997); this interaction seems to be dynamically modulated by mechanical forces (Ojima et al, 2010). Interestingly, calpain-3 interacts in turn with myospryn, linking the activity of the two pathways in protein degradation (Sarparanta et al, 2010); the generation of C-terminal titin fragments by calpain might be the prelude to their ubiquitin-dependent degradation, a process that is disrupted in several hereditary titinopathies (Charton et al, 2015;Sarparanta et al, 2010).…”

Mechanisms of exercise-induced muscle damage and fatigue: Intracellular calcium accumulation

“…The physiological roles of these proteases are not well understood. Calpain-3 seems to be involved in muscle repair and maintenance 32,33) . Also it is demonstrated that calpain-3 shifts its location from the M-line to the N2A region when the sarcomere is extended, suggesting that calpain-3 functions as a sarcomere-length sensor, in cooperation with connectin/titin, to mediate signal transduction and mdx skeletal muscle 20,21) .…”

“…Recent studies indicate that calpain-3 protease activity is essential for the signaltransduction pathway by which muscles adapt to physical stress 33) . Thus, whereas in human vastus lateralis muscle, exhaustive sprint cycling does not acutely increase the amount of activated calpain-3 or μ-calpain 35) , nor does ECC knee extensor exercise elevate autolyzed calpain-3 within 3 hours post-exercise; calpain-3 levels increased markedly at 24 hours post-exercise 36) .…”