ATOH8: a novel marker in human muscle fiber regeneration.

Regenerating muscle fibers emerge from quiescent satellite cells, which differentiate into mature multinuclear myofibers upon activation. It has recently been found that ATOH8, a bHLH transcription factor, is regulated during myogenic differentiation. In this study, expression and localization of ATOH8, the other well-described regeneration markers, vimentin, nestin and neonatal myosin, and the satellite cell marker Pax7 were analyzed on protein level in human myopathy samples by immunofluorescence studies. On mRNA level, expression levels of ATOH8 and vimentin were studied by quantitative real-time PCR. ATOH8 is expressed in activated satellite cells and proliferating myoblasts of human skeletal muscle tissue. Quantitative analyses of ATOH8+, Pax7+, vimentin+, nestin+ and neonatal myosin+ muscle fibers showed the highest amount of regenerating muscle fibers in inflammatory myopathies, followed by muscular dystrophy. The relative co-expression of ATOH8 with the above-mentioned markers did not vary among the disorders. These results show that the novel regeneration marker ATOH8 contributes to muscle cell differentiation in healthy and diseased human muscle tissue.