Lactate as a metabolic-epigenetic signal linking high-intensity interval training (HIIT) to miRNA-Centered remodeling of the skeletal muscle methylome and transcriptome

Lactate and HIIT each induced broad, site-specific remodeling of the methylome and transcriptome with substantial overlap at promoter CpGs and among DEGs. Promoter methylation changes showed weak coupling to steady-state mRNA, whereas integrative analyses revealed robust anti-directional miRNA–mRNA networks and enriched for chromatin/epigenetic regulators, identifying a lactate-driven miRNA axis as a proximate regulator of transcriptional output. At the protein level, lactate selectively increased TET2 and DNMT3A and activated PAX7, VEGF, and AKT–S6 signaling, consistent with integrative miRNA–mRNA findings. HIIT increased TET1/2 and DNMT3A with DNMT3B reduction and uniquely enhanced mitochondrial/antioxidant signaling. Blocking MCT1/2 abrogated HIIT-induced methylome and miRNA remodeling and blunted transcriptomic and protein adaptation, demonstrating that intact lactate flux is required for exercise-evoked epigenetic and transcriptomic reprogramming. Despite molecular convergence, chronic lactate did not improve running performance, indicating that lactate is necessary but not sufficient for the full physiological adaptation of training. These findings position a lactate–miRNA axis linking metabolic perturbation to epigenetic and transcriptional remodeling in skeletal muscle.