Histone methyltransferase G9a drives vascular smooth muscle cell proliferation and intimal hyperplasia in mice

Abnormal proliferation of vascular smooth muscle cells (VSMCs) plays a critical role in vascular remodeling associated with various cardiovascular disorders. G9a, also known as euchromatic histone methyltransferase 2 (EHMT2), is a lysine methyltransferase that influences histone modifications, particularly H3K9me1 and H3K9me2. In this study we investigated the role of G9a in promoting VSMC proliferation and vascular intimal hyperplasia and the underlying mechanisms. To induce VSMC proliferation, primary aortic VSMCs were treated with platelet-derived growth factor-BB (PDGF-BB) and 10% fetal bovine serum (FBS) in vitro. An in vivo model of carotid intimal hyperplasia was established in mice by ligating the left common carotid artery just below the bifurcation. We showed that the expression levels of G9a were significantly elevated in both in vitro and in vivo models of VSMC proliferation. In the primary aortic VSMCs, co-treatment with G9a inhibitor UNC0642 (1 μM) effectively reduced cell viability, cyclin D1 expression, and EdU incorporation induced by PDGF-BB or 10% FBS. In mouse carotid intimal hyperplasia model, administration of UNC0642 (50 mg·kg^-1·d^-1, i.p.) for 14 days significantly decreased the intimal area and cyclin D1 levels, whereas intravenous administration of G9a adenovirus worsened neointimal hyperplasia. RNA-seq analysis identified CCAAT/enhancer binding protein delta (CEBPδ) as the downstream target gene that was upregulated following G9a modulation. ChIP assays revealed that G9a mediated VSMC proliferation primarily by regulating H3K9me1 at the promoter of CEBPδ. Knockdown of CEBPδ counteracted the pro-proliferative effects of G9a. In conclusion, G9a serves as a positive regulator of VSMC proliferation and presents a potential therapeutic target for cardiovascular diseases concomitant with vascular remodeling.