Biomechanical regulation of Ca ²⁺ dynamics during muscle stem cell activation

Muscle satellite cells (MuSCs) are muscle-resident stem cells that are responsible for myofiber regeneration. Although the importance of calcium ions (Ca ²⁺ ) in muscle physiology has been well established, the mechanism by which Ca ²⁺ mobilization governs MuSC function remains poorly understood. In this study, we aimed to systematically characterize Ca ²⁺ dynamics in MuSCs and to define the mechanisms regulating these signals during muscle regeneration. By employing modified protocols for mouse MuSC isolation and Ca ²⁺ measurement, we observed spontaneous Ca ²⁺ fluctuations in MuSCs isolated from regenerating muscle after cardiotoxin-induced myofiber injury. Our detailed analysis using chemical Ca ²⁺ indicators and a genetically encoded Ca ²⁺ indicator revealed that the frequency and amplitude of Ca ²⁺ fluctuations increased significantly during the activated and proliferative stages of MuSCs in muscle regeneration. This effect was more pronounced in MuSCs isolated from dystrophic and aged mice. Mechanistically, these Ca ²⁺ fluctuations were at least partially mediated by mechanosensitive ion channels, including PIEZO1 and TRPM7, which promote MuSC migration. Collectively, our findings demonstrate that Ca ²⁺ fluctuations through mechanosensitive ion channels act as a key regulator of MuSC activation during muscle regeneration and may provide new insights into the role of Ca ²⁺ influx in muscle biology and the pathogenesis of muscle diseases.