EXERCISE INDUCES MYONUCLEAR UBIQUITINATION AND APOPTOSIS IN DYSTROPHIN-DEFICIENT MUSCLE OF MICE

Apoptosis plays a major role in several diseases, including viral infe ctions, autoimmune diseases, cancer, cardiac infarct, and neurological disorders. To investigate the role of apoptosis in muscular dystrophy , dystrophin-deficient (mdx) mice were subjected to spontaneous exerci se and skeletal muscles were analyzed for apoptosis and ubiquitin. The increase of apoptotic myonuclei after exercise was detected by TUNEL, by electron microscopy, and by DNA analyses for high molecular weight and for ladder fragments. Expression of ubiquitin correlated with exe rcise and with positive myonuclei for apoptosis. Biochemical analysis confirmed a high level of ubiquitination both in sarcoplasmic and myof ibrillar proteins. Muscles from sedentary congenit control mice (C57B) were negative for apoptosis, while after exercise some nuclei were po sitive. We also revealed that normal myoblasts committed to apoptosis in vitro showed an increased expression of ubiquitin. Western blot for bcl-2, FasL, and BAG1 showed a significant decrease of bcl-2 product only in mdx mice after exercise. Thus, spontaneous exercise results in the increase of ubiquitin expression and in the reduction of bcl-2 ti ghtly related to programmed cell death in mdx mice. These findings con firm that DNA fragmentation, absent in muscles of sedentary normal mic e but present in mdx mice at rest, dramatically increases after exerci se, shedding new Light on exercise-induced muscle damage and on its pr ogression in dystrophinopathies.