m6A-Mediated epitranscriptional reprogramming drives cardiac fibrosis by suppressing PGC-1α and boosting mitochondrial fission.

BACKGROUND: Dysregulated mitochondrial fission drives pathological cell states in cardiac fibrosis, but its upstream regulatory mechanisms remain poorly understood. The role of epitranscriptomic regulation, particularly N6-methyladenosine (m6A) modification, in this process has not been defined. METHODS: We employed integrated approaches including in vitro models of TGF-β1-stimulated cardiac fibroblasts, in vivo mouse models of isoproterenol-induced cardiac fibrosis, and analysis of human atrial fibrillation tissues. Techniques encompassed molecular profiling, m6A-specific assays (MeRIP-qPCR, RIP-qPCR), functional studies, high-resolution imaging, and fibroblast-targeted AAV9-mediated gene manipulation. RESULTS: METTL3 and YTHDF2 were significantly upregulated in experimental and human fibrotic hearts. METTL3 mediated m6A modification of PGC-1α mRNA, enhancing its recognition and degradation by YTHDF2. This suppression of PGC-1α led to excessive Drp1-dependent mitochondrial fission, which in turn promoted cardiac fibroblast proliferation, migration, and extracellular matrix production. Inhibition of METTL3 or YTHDF2 restored PGC-1α expression, normalized mitochondrial dynamics, and attenuated fibrotic responses in vitro. Fibroblast-specific knockdown of METTL3 or YTHDF2 in vivo robustly ameliorated fibrosis, improved mitochondrial ultrastructure, and restored systolic function. In human atrial fibrillation, activation of this axis correlated with suppressed PGC-1α, enhanced mitochondrial fission, and disease severity. CONCLUSION: Our findings introduce a novel epitranscriptomic pathway involving METTL3 and YTHDF2, which regulates PGC-1α through m6A modification. Targeting this axis presents a promising strategy for therapeutic intervention in cardiac fibrosis, offering new insights into both the molecular mechanisms driving fibrosis and potential treatment avenues.