Localization of survival motor neuron protein in human apoptotic-like and regenerating muscle fibers, and neuromuscular junctions

MUTATIONS in the gene encoding survival motor neuron (SMN) protein are foun d in > 98% of patients with autosomal-recessive spinal muscular atrophy. We investigated the possible role of SMN in normal and abnormal human muscle by immunostaining biopsies of 20 patients with various neuromuscular diseas es using monoclonal antibodies against SMN. SMN was strongly expressed cyto plasmically in chronic peripheral neuropathies, in about 80% of chronically denervated, very atrophic muscle fibers containing clumps of TUNEL-positiv e pyknotic nuclei: about 60% of those fibers also had cytoplasmic Bcl-2 and Bar immunoreactivity. In regenerating muscle fibers of various myopathies SMN co-localized with desmin, Bcl-2 and Bar; it was also present at the pos tsynaptic domain of normal human neuromuscular junctions. Thus, SMN may pla y a role in normal and pathological processes of adult human muscle fibers. NeuroReport 10:1637-1641 (C) 1999 Lippincott Williams & Wilkins.