Light-microscopic study of phosphoprotein B-50 in myopathies.

The growth-associated protein B-50, also termed GAP-43, is a membrane-bound phosphoprotein that is expressed in neurons. It is particularly abundant during periods of axonal outgrowth in development and regeneration of the central and peripheral nervous system. In this paper we study the expression of B-50 in inflammatory and dystrophic myopathies. To investigate the state of regeneration, N-CAM and vimentin serial sections were performed, because N-CAM and cytoskeletal protein vimentin are excellent markers for regenerating muscle. Light-microscopic evaluation showed that muscle fiber regeneration in myopathies corresponds closely to B-50 immunoreactivity in satellite cells, myoblasts, myotubes and small regenerating myocytes in cytoplasmatic distribution. In normal muscle and in biopsies of neurogenic muscular atrophy, however, no light-microscopically demonstrable B-50 staining was found. B-50 in muscles apparently plays a role in the growth morphology of regenerating myocytes, and the phosphoprotein B-50 can no longer be regarded as a neuron-specific molecule.