Role of calpains in promoting desmin filaments depolymerization and muscle atrophy.

Muscle atrophy is an inevitable sequel of fasting, denervation, aging, exposure to microgravity, and many human diseases including, cancer, type-2 diabetes, and renal failure. During atrophy the destruction of the muscle's fundamental contractile machinery, the myofibrils, is accelerated leading to a reduction in muscle mass, weakness, frailty, and physical disability. Recent findings indicate that atrophy can be a major cause of death in affected individuals, and inhibition of muscle wasting is likely to prolong survival. Major advances in our understanding of the mechanisms for myofibril breakdown in atrophy include the discovery of biological pathways and key components that play prominent roles. On fasting or denervation, degradation of myofibrillar proteins requires an initial dissociation of the desmin cytoskeleton, whose integrity is critical for myofibril stability. This loss of desmin filaments involves phosphorylation, ubiquitination, and subsequent depolymerization by calpain-1, and appears to reduce myofibrils integrity and facilitate their destruction. Consequently, depolymerization of desmin filament in atrophy seems to be an early key event for overall proteolysis. A focus of this review is to discuss these new insights and the specific role of calpain-1 in promoting desmin filaments loss, and to highlight important key questions that merit further study.