METTL3-mediated m ⁶ A modification alleviates skeletal muscle atrophy in ALS by regulating ACSL1-dependent triglyceride metabolism

Skeletal muscle-intrinsic defects are increasingly recognized as critical contributors to the pathogenesis of amyotrophic lateral sclerosis (ALS), yet the underlying molecular mechanisms remain poorly understood. N ⁶ -methyladenosine (m ⁶ A) is the most abundant post-transcriptional RNA modification in mammalian mRNAs that plays important regulatory roles in diverse physiological and pathological processes, however its role in ALS-associated skeletal muscle atrophy remains unknown. Here we found that global m ⁶ A methylation and the expression of its methyltransferase METTL3 are reduced in the skeletal muscle of hSOD1 ^G93A transgenic ALS mice. Multi-omics analyses reveal that m ⁶ A dysregulation is closely associated with impaired triglyceride metabolism. Functionally, METTL3 promotes triglyceride accumulation in ALS skeletal muscle in an m ⁶ A-dependent manner; overexpression of METTL3 in ALS myotubes improves energy supply and alleviates muscle atrophy by promoting triglyceride accumulation. In vivo overexpression of Mettl3 in skeletal muscle attenuates muscle atrophy, improves motor performance, and prolongs survival of ALS mice. Mechanistically, we identify the fatty acid activation enzyme ACSL1 as a key downstream effector of METTL3-mediated regulation of triglyceride metabolism. METTL3-mediated m ⁶ A modification promotes the expression of Acsl1 by enhancing its mRNA stability. Further investigation revealed that the regulatory effect of m ⁶ A on Acsl1 expression depends on the m ⁶ A reader protein IGF2BP2. Collectively, our findings establish m ⁶ A modification as a critical regulator of skeletal muscle atrophy in ALS by maintaining triglyceride metabolic homeostasis, highlighting a promising therapeutic target for ALS.