Human skeletal muscle cytosols are refractory to cytochrome c-dependent activation of type-II caspases and lack APAF-1

Apoptotic regulatory mechanisms in skeletal muscle have not been revealed, This is despite indications that remnant apoptotic events are detected foll owing exercise, muscle injury and the progression of dystrophinopathies. Th e recent elicitation of a cytochrome c-mediated induction of caspases has l ed to speculation regarding a cytochrome c mechanism in muscle, We demonstr ate that cytosols from skeletal muscle biopsies from healthy human voluntee rs lack the ability to activate type-it caspases by a cytochrome c-mediated pathway despite the confirmed presence of both procaspase-3 and -9, This w as not due to the presence of an endogenous inhibitor, as the muscle cytoso ls enhanced caspase activity when added to a control cytosol, subsequently activated by cytochrome c and dATP, In addition, we demonstrate that muscle cytosols lack the apoptosis protease activator protein-1 (APAF-1), both at the protein and mRNA levels. These data indicate that human skeletal muscl e cells will be refractory to mitochondrial-mediated events leading to apop tosis and thus can escape a major pro-apoptotic regulatory mechanism. This may reflect an evolutionary adaptation of cell survival in the presence of the profusion of mitochondria required for energy generation in motility.