CSRP3 promotes skeletal muscle remodeling toward aerobic metabolism and enhances exercise endurance through...

Exercise performance and skeletal muscle homeostasis are influenced by myofiber type composition. Cysteine and glycine-rich protein 3 (CSRP3) is highly expressed in the oxidative fiber-rich mammalian soleus muscle. However, the mechanistic basis of CSRP3's involvement in skeletal muscle development and myofiber type specification remains unclear. Here, we used various exercise training (aerobic/anaerobic) bioinformatics datasets and experimental model systems involving live mice and cell lines to determine the role of CSRP3 in driving mitochondrial metabolic reconfiguration, skeletal muscle fiber type remodeling, and improved exercise endurance. CSRP3 promotes the formation of oxidative myofibers while suppressing glycolytic myofiber differentiation. It enhances mitochondrial biogenesis, oxidative phosphorylation capacity, and elevates mitochondrial membrane potential. Conversely, AAV-mediated CSRP3 knockdown perturbs mitochondrial energy metabolism, compromises exercise performance, and reduces the proportion of oxidative myofibers. Mechanistically, CSRP3 binds to D-lactate dehydrogenase (LDHD) via a specific 33-amino acid region, promoting D-lactate metabolism in skeletal muscle. This interaction regulates mitochondrial morphology, biogenesis, oxidative phosphorylation efficiency, and TCA cycle activity, ultimately driving skeletal muscle mitochondrial energy metabolic rewiring and skeletal muscle fiber type remodeling.