Muscle regeneration and mitochondrial calmitine increase in the dystrophic dy/dy mouse after intramuscular chlorpromazine injection

Absence of caspase-3 protects against denervation-induced skeletal muscle atrophy

The ubiquitin-proteasome system is a key proteolytic pathway activated during skeletal muscle atrophy. The proteasome, however, cannot degrade intact myofibrils or actinomyosin complexes. In rodent models of diabetes mellitus and uremia, caspase-3 is involved in actinomyosin cleavage, generating fragments that subsequently undergo ubiquitin-proteasome-mediated degradation. Here, we demonstrate that caspase-3 also mediates denervation-induced muscle atrophy. At 2 wk after tibial nerve transection, the denervated gastrocnemius of caspase-3-knockout mice weighed more and demonstrated larger fiber-type-specific cross-sectional area than the denervated gastrocnemius of wild-type mice. However, there was no difference between caspase-3-knockout and wild-type denervated muscles in the magnitude or pattern of actinomyosin degradation, as determined by Western blotting for actin and the 14-kDa actin fragment. Similarly, there was no difference between caspase-3-knockout and wild-type denervated muscles in the magnitude of increase in proteasome activity, total protein ubiquitination, or atrogin-1 and muscle-specific ring finger protein 1 transcript levels. In contrast, there was an increase in TdT-mediated dUTP nick end label-positive nuclei in the denervated muscle of wild-type compared with caspase-3-knockout mice. Apoptotic signaling upstream of caspase-3 remained intact, with equivalent mitochondrial Bax translocation and cytochrome c release and caspase-9 activation in the denervated gastrocnemius muscle of wild-type and caspase-3-knockout mice. In contrast, diminished poly(ADP-ribose) polymerase cleavage in the denervated muscle of caspase-3-knockout compared with wild-type mice revealed that apoptotic signaling downstream of caspase-3 was impaired, suggesting that the absence of caspase-3 protects against denervation-induced muscle atrophy by suppressing apoptosis as opposed to ubiquitin-proteasome-mediated protein degradation.

A drug inhibits the mitochondrial protease inducing calmitine deficiency in skeletal muscle of patients with Duchenne's muscular dystrophy and dy/dy dystrophic mice

This study demonstrates that the cause of calmitine deficiency in dy/dy dystrophic mice and patients with Duchenne's muscular dystrophy (DMD) is the same; i.e., the absence of an inhibitor of calmitine-specific mitochondrial protease. This inhibitor, which is present in control mice and control subjects, prevented degradation of the protein. It is also shown that a drug (IP96) was capable in vitro of inhibiting calmitine-specific mitochondrial protease from muscle of DMD patients and dy/dy mice. This drug was also active in vivo in an experimental model of myopathy created in the normal mouse by a single injection of chlorpromazine, a myotoxic drug, which induced temporary calmitine degradation. Thus, it seems quite likely that IP96 prevents calmitine degradation by inhibiting the specific protease.