Mitochondrial dysfunction reshapes methyl-group allocation inskeletal muscle

Mitochondria are central metabolic organelles with functions extending beyond energy production to anabolic and folate-mediated one-carbon (1C) metabolism. One-carbon metabolism supports methylation reactions that modify diverse targets including metabolites, nucleic acids, and chromatin, and has emerged as a contributor to mitochondrial disease-related stress responses. Here, we report tissue-specific remodeling of methylation events in response to mtDNA replication defect, using the deletor mice carrying a dominant mutation in Twinkle, the replicative helicase of mtDNA, causing adult-onset mitochondrial myopathy (MM) in humans and mice. In affected skeletal muscle, deletors show a distinct methylation signature, with increased creatine synthesis and reduced phosphatidylcholine production, two major consumers of S-adenosylmethionine-derived methyl groups. We further observed tissue-specific upregulation of selected RNA methylation marks and redistribution of the repressive histone mark H3K9me3, indicating coordinated remodeling of metabolic and epigenetic methylation pathways. Our evidence shows that a mtDNA replication defect remodels muscle-specific methylation signature of phospholipids, histones and RNA, identifying methylation remodeling as a key component of MM pathogenesis.