The neuronal nitric oxide synthase expression increases during satellite cell-derived primary myoblasts differentiation.

Abstract

Theneuronal nitric oxide synthase (nNOS; encoded byNOS1)-derivednitric oxide (NO) plays an important role in maintaining skeletal muscle mass. In adult skeletal muscle, nNOS localizes to the cell membrane, cytosol, and nucleus, and regulates muscle hypertrophy and atrophy in various subcellular fractions.However, its role in muscle stem cells (also known as muscle satellite cells), which provide myonuclei for postnatal muscle growth, maintenance, and regeneration, remains unclear. The present study aimed to determinenNOS expression in muscle satellite cell-derived primary myoblasts during differentiation and its DNA methylation levels, an epigenetic modification that controls gene expression. Undifferentiated and differentiated satellite cell-derived primary myoblasts were found to express nNOS. Immunohistochemical analysis revealed that nNOS colocalized with Pax7 (satellite cell marker) only in the undifferentiated myoblasts. Furthermore, nNOS immunoreactivity spread to the cytosol of Pax7-negative differentiated myotube-like cells. Thelevel of Nos1µmRNA, the main isoform of skeletal muscle nNOS, was increased in differentiated satellite cell-derived primary myoblasts compared to that in the undifferentiated cells. However,Nos1methylation levelsremained unchangedduring differentiation.These findings suggest that nNOS induction and the appropriate transition of its subcellular localization may contribute to muscle differentiation.