Microbiota-associated metabolite pantothenic acid enhances skeletal muscle contusion repair via epigenetic regulation of macrophage M2 polarization.

backgroundThe quality of skeletal muscle contusion repair hinges on the timely resolution of inflammation and the initiation of regeneration, processes in which M2 macrophage polarization plays a critical role. Nevertheless, the upstream signals that regulate this polarization—particularly specific instructions mediated via the “gut-muscle axis”—remain poorly defined.

methodsThe study was conducted as follows. First, intestinal barrier integrity following skeletal muscle contusion was assessed using histochemical staining and molecular assays. To elucidate the role of the gut microbiota in skeletal muscle repair, dysbiosis models and fecal microbiota transplantation (FMT) were established. Key gut microbiota and metabolites were subsequently identified through 16S rDNA sequencing and untargeted metabolomics analysis of fecal and serum samples. Based on these findings, targeted metabolite intervention experiments were conducted to evaluate their effects on the repair process of skeletal muscle contusion. To delineate the role of macrophages in this context, macrophage depletion was achieved via administration of clodronate liposomes. The impact of the key metabolites on macrophage polarization was then tested both in vivo and in vitro and the subsequent effect of polarized macrophages on C2C12 myoblast differentiation was examined in co-culture system. Finally, we explored the underlying epigenetic mechanisms through which the important metabolites regulates macrophage polarization.

resultsHere, we identify a gut microbiota-dependent pathway that facilitates skeletal muscle injury repair. We observed that gut microbiota dysbiosis following skeletal muscle contusion was accompanied by a marked enrichment of the microbial metabolite pantothenic acid (vitamin B5). Functional assays demonstrated that depletion of the gut microbiota severely compromised muscle repair, whereas exogenous supplementation with pantothenic acid significantly enhanced regeneration and attenuated fibrosis. Mechanistically, pantothenic acid exerted its beneficial effects not by acting directly on myocytes, but through remodeling the immune microenvironment. In cultured macrophages, pantothenic acid elevated intracellular acetyl-CoA levels, promoted histone H3 lysine 27 acetylation (H3K27ac) at the promoter of the M2-associated gene Arg1, and acted synergistically with IL-4 to drive macrophage polarization toward the M2 phenotype. This epigenetic regulation was validated in vivo by ChIP-qPCR on macrophages sorted from contused muscles of pantothenic acid-treated mice, confirming that the modification occurs within the muscle microenvironment. This shift in macrophage polarization subsequently promoted myoblast differentiation and maturation.

conclusionCollectively, our findings delineate a comprehensive mechanism whereby a gut microbiota-associated metabolite, pantothenic acid, epigenetically programs macrophage M2 polarization via a “metabolism-epigenetics” axis to accelerate skeletal muscle repair. This work provides a novel conceptual framework for therapeutic interventions targeting the gut-muscle axis.