Pathological calcium overload impairs skeletal muscle regeneration through sustained NFAT-dependent proliferative signaling.

Abstract

Skeletal muscle regeneration requires coordinated myoblast proliferation and differentiation. Calcium dysregulation is commonly observed in aging and disease-associated muscle weakness; however, its impact on myogenic progression remains unclear. In this study, we investigated the mechanism by which intracellular calcium overload impairs myogenic differentiation and muscle regeneration. Transcriptomic analysis of aged human muscle revealed coordinated activation of calcium signaling and proliferation pathways. In vitro calcium exposure increased myoblast proliferation under differentiation conditions while suppressing myogenic markers. RNA sequencing identified upregulation of proliferative programs with concurrent suppression of myogenic genes and enrichment of calcium-NFAT signaling. Mechanistically, calcium promoted NFATc1 nuclear translocation and upregulated Ccnd1 expression. Consistent with these in vitro findings, both ovariectomized mice (systemic calcium dysregulation) and human calcific tendinitis tissues (localized calcium overload) exhibited NFAT-associated proliferative signatures with suppressed myogenic markers. The selective NFAT inhibitor VIVIT prevented calcium-induced NFATc1 nuclear accumulation and restored myotube formation in vitro, while promoting myofiber maturation in an in vivo injury model. These findings implicate chronic calcium-NFAT signaling as a mechanism linking calcium dysregulation to impaired muscle regeneration.