EHMT1/KMT1D drives neointima formation via epigenetic repression of the PPARγ–PDIA6 axis

Neointima formation underlies restenosis and other occlusive vascular diseases, yet the epigenetic regulators that drive this process remain poorly understood. We aimed to define the role of the histone methyltransferase EHMT1 in neointima formation and to delineate its downstream mechanisms. Here, we found that the EHMT1 expression and its histone marks H3K9me1/2 were markedly upregulated in proliferating VSMCs and in injured arteries exhibiting neointima formation. Deletion of EHMT1 in VSMCs suppressed phenotypic switching and significantly reduced neointimal hyperplasia in vivo. In vitro, EHMT1 knockdown inhibited, whereas EHMT1 overexpression promoted, VSMC proliferation, migration, and acquisition of a synthetic phenotype. Unbiased transcriptome sequencing revealed significant enrichment of peroxisome proliferator-activated receptor gamma (PPARγ) target genes following EHMT1 knockdown. Mechanistically, we demonstrated that EHMT1 directly repressed PPARγ expression via H3K9 dimethylation, and pharmacological activation of PPARγ with rosiglitazone reversed the proliferative, migratory, and synthetic effects induced by EHMT1 overexpression. Further analysis identified protein disulfide isomerase A6 (PDIA6) as a direct PPARγ target: PPARγ bound to the PDIA6 promoter (-567 to -385 bp) to suppress its expression. Overexpression of PDIA6 rescued the inhibitory effects of EHMT1 knockdown on VSMC proliferation and migration, whereas PDIA6 silencing abrogated the pro-proliferative and pro-migratory effects of EHMT1 overexpression. EHMT1 acts as a critical epigenetic regulator of neointima formation by controlling VSMC phenotypic switching through a novel EHMT1–PPARγ–PDIA6 axis. These findings provide mechanistic insight into epigenetic regulation of vascular remodeling and identify EHMT1–PPARγ–PDIA6 as a promising target for therapeutic intervention in restenosis.