TRPV1 manipulating polarization of M1/M2 macrophages to promote skeletal muscle regeneration

Skeletal muscle regeneration is a dynamically complex and multistage process in which balanced polarization of M1/M2 macrophages plays a crucial role. M1/M2 macrophages defend against microbial invasion, regulate tissue repair by engulfing pathogens and cellular debris, and secrete a variety of cytokines. However, the precise molecular mechanisms involved in M1/M2 macrophage polarization during skeletal muscle regeneration remain poorly understood. Transient receptor potential vanilloid 1 (TRPV1) is a cation channel implicated in pain perception and inflammation during tissue repair. This study aimed to investigate the role of TRPV1 in cardiotoxin (CTX)-induced skeletal muscle injury and regeneration, focusing on its impact on macrophage polarization and myogenesis. Using a CTX-induced muscle injury model in mice, we examined the effects of TRPV1 on skeletal muscle regeneration, macrophage infiltration, and M1/M2 polarization. Mice were pretreated with capsaicin (CAP, a TRPV1 agonist) and capsazepine (CPZ, a TRPV1 antagonist). In vitro, the impact of TRPV1 on RAW264.7 macrophage polarization and myoblast differentiation was evaluated using co-culture experiments. Histological analysis and expression of TRPV1, MyoD, myogenin, CD86, CD206, Arg1, and IL-6 were assessed by Hematoxylin and Eosin staining, Sirius Red staining, immunofluorescence, western blotting, RT-qPCR and enzyme-linked immunosorbent assay. RAW264.7 macrophages were stimulated with LPS /IFN-γ or IL-4/IL-10 before pretreatment with CAP and CPZ and co-cultured with C2C12 myoblasts. Cell Counting Kit-8, immunofluorescence, western blotting, and Giemsa staining were utilized to evaluate macrophage proliferation, polarization and its effects on C2C12 differentiation. The expression of TRPV1 was markedly upregulated following CTX-induced skeletal muscle injury. Activation of TRPV1 by CAP reversed the M1/M2 macrophage imbalance, significantly reduced M1 macrophage infiltration, slightly increased M2 macrophage infiltration, and markedly increased MyoD and myogenin expression, thereby enhancing myogenesis. Additionally, CAP administration dramatically decreased M1-associated marker CD86 while increasing M2-associated marker Arg1 compared with controls or CPZ-treated mice. In vitro, TRPV1 activation inhibited M1 polarization and promoted M2 polarization. Co-culture of C2C12 cells with CAP-pretreated macrophages further implies that enhanced M2 polarization and reduced M1 polarization could be a contributing factor to the facilitation of myoblast differentiation. Our findings indicate that TRPV1 promotes skeletal muscle regeneration at least in part by modulating M1/M2 macrophage polarization.