The Fosl1-Kdm6b Axis Controls Skeletal Muscle Fibrosis by Regulating  Histone H3K27me3 [bulk RNA-seq]
Skeletal muscle fibrosis, characterized by the replacement of functional muscle tissue with fibrotic scarring, leads to muscle function loss and potentially fatal respiratory failure, particularly in muscular dystrophy. The mechanisms driving muscle fibrosis is not yet fully understood. Our study utilized single-cell RNA-seq and single-nuclei ATAC-seq to analyze the transcriptome and chromatin accessibility of regenerating and dystrophic skeletal muscle, identifying a specific subset of fibro-adipogenic precursors (FAPs) enriched in dystrophic muscles, termed fibrotic FAPs. We further demonstrated that chronic inflammation upregulates Fosl1, an early response gene, which activates the expression of Kdm6b in fibrotic FAPs. Kdm6b, a histone demethylase, specifically removes the repressive histone H3K27me3 mark. Notably, targeting Kdm6b genetically and pharmacologically inhibits fibrotic di^erentiation in human and mouse FAPs in vitro and ameliorated muscle fibrosis in mouse models in vivo. Furthermore, constitutive activation of the Fosl1-Kdm6b pathway reduced H3K27me3 modification at critical fibrotic gene loci, leading to their transcriptional activation. Taken together, our findings reveal that chronic inflammation perpetuates the Fosl1-Kdm6b axis in FAPs, causing epigenomic reprogramming and altering the H3K27me3 landscape, which is essential for preventing fibrotic di^erentiation of FAPs and skeletal muscle fibrosis. Overall design: mRNA measurements from fibro-adipogenic progenitors in wildtype, Mdx, and Utrophin-dystrophin double knockout mice. Other comparisons include conditional knockout of Kdm6b in FAPs (using Pdgfra-Cre and Kdm6b-flox mice) versus genetically matched control (without Cre)).