Apoptosis of skeletal muscles during development and disease.

Cells from multicellular organisms self-destroy when no longer needed or when damaged. They do this by activating genetically controlled machineries that lead to apoptosis. Skeletal muscles in adult animals are fully differentiated syncytial cells. Apoptosis has been described in developing and, recently, in adult skeletal muscle. The cellular and molecular aspects of myoblast and myofibre apoptosis and their role in disease are analysed in this review. Alterations in the pathways that regulate myoblasts proliferation/differentiation lead to induction of apoptosis during myogenesis both in vivo and in vitro. In adult muscle myofibres apoptosis seems to start from segmental areas of myofibres often producing loss of a single myonucleus. The bcl2/bax system is active in muscle when apoptosis occurs. On the other hand conflicting results are reported on the role played by FasL/Fas system. These findings are confirmed by in vitro results on myotubes and on their susceptibility to apoptosis. Though apoptosis has been shown to occur in the skeletal muscle, the role played in diseases and the pattern followed in myogenic cells are far from being clear.