Chemokine CXCL12 Mediates Transcription Factor HSF1-Dependent Small Extracellular Vesicle Secretion Through Different Endosomal Stages

Extracellular vesicles (EVs) serve as key facilitators mediating intercellular communication in skeletal muscle, but the upstream mechanisms regulating their secretion remain incompletely understood. Using proteomic screening, we identified CXCL12 as a candidate HSF1-associated downstream factor. Functional assays showed that CXCL12 promoted C2C12 myoblast proliferation, restrained myogenic differentiation in a stage-dependent manner, and enhanced sEV secretion, accompanied by altered expression of early endosome- and MVB-associated markers. Functionally, CXCL12 knockdown attenuated the HSF1-induced increase in sEV secretion and the upregulation of EEA1 and CD63 protein levels, whereas exogenous recombinant CXCL12 partially restored EEA1 and CD63 expression in the skeletal muscle of muscle-specific HSF1 knockout mice. Collectively, these results are consistent with a model in which CXCL12 is associated with sEV secretion in coordination with changes in early endosome- and MVB-associated protein abundance, suggesting a previously underappreciated role for CXCL12 in vesicle trafficking in the skeletal muscle microenvironment.