Glycogen synthase kinase 3β suppresses myogenic differentiation through negative regulation of NFATc3

Skeletal muscle atrophy is a prominent and disabling feature in many chronic diseases. Prevention or reversal of muscle atrophy by stimulation of skeletal muscle growth could be an important therapeutic strategy. Glycogen synthase kinase 3 beta (GSK-3 beta) has been implicated in the negative regulation of skeletal muscle growth. Since myogenic differentiation is an essential part of muscle growth, we investigated if inhibition of GSK-3 beta is sufficient to stimulate myogenic differentiation and whether this depended on regulation of the transcription factor nuclear factor of activated T-cells (NFAT). In both myogenically converted mouse embryonic fibroblasts and C2C12 myoblasts, deficiency of GSK-3 beta protein ( activity) resulted in enhanced myotube formation and muscle-specific gene expression during differentiation, which was reversed by reintroduction of wild type but not kinase-inactive (K85R) GSK-3 beta. In addition, GSK-3 beta inhibition restored myogenic differentiation following calcineurin blockade, which suggested the involvement of NFAT. GSK-3 beta-deficient mouse embryonic fibroblasts or myoblasts displayed enhanced nuclear translocation of NFATc3 and elevated NFAT-sensitive promoter transactivation, which was reduced by reintroducing wild type, but not K85R GSK-3 beta. Overexpression of NFATc3 increased muscle gene promoter transactivation, which was abolished by co-expression of wild type GSK-3 beta. Finally, stimulation of muscle gene expression observed following GSK-3 beta inhibition was strongly attenuated in NFATc3- deficient myoblasts, indicating that this response requires NFATc3. Collectively, our data demonstrate negative regulation of myogenic differentiation by GSK-3 beta through a transcriptional mechanism that depends on NFATc3. Inhibition of GSK-3 beta may be a potential strategy in prevention or treatment of muscle atrophy.