Abstract MP11: Histone Methyl Transferase (suv39h1): Function In Smooth Muscle Cell Phenotypic Plasticity

Abstract

Introduction: The phenotypic plasticity of vascular smooth muscle cells (VSMCs) is central to growth and remodeling processes, but also contributes to cardiovascular disease. This unique ability of VSMCs to reversibly differentiate and de-differentiate is incompletely understood. SUV39H1 is a histone methyltransferase that specifically trimethylates Lysine-9 of histone H3 (H3K9me3), resulting in transcriptional repression through epigenetic gene silencing. Hypothesis: We hypothesized that SUV39H1 may play a role in SMC phenotypic switch. Methods: Using in vitro and in vivo approaches including knockdown, qPCR, western, and chromatin immunoprecipitation (ChIP) assays to determine role of SUV39H1 in SMC plasticity. Results: A qPCR array screen of epigenetic regulators in VSMCs identified SUV39H1 mRNA as upregulated with PDGF induced dedifferentiation and downregulated with rapamycin induced differentiation. This was confirmed at the protein level. SUV39H1 knockdown significantly increased VSMC contractile protein mRNA, protein levels and decreased dedifferentiation associated gene expression, and also decreased PDGF-induced VSMC migration (n=4). Interestingly, we found that expression of KLF4, the master transcriptional regulator of dedifferentiation in SMCs, was dramatically decreased after SUV39H1 knockdown (n=5). We further noted that SUV39H1 knockdown decreased KLF4 mRNA stability (n=3). Mechanistically, SUV39H1 knockdown increased miRNA143, a well-known repressor of KLF4. ChIP assays at contractile gene promoters showed a significant decrease in H3K9me3 mark and an increase in H3K27 acetylation, an activation mark (n=4). Carotid artery ligation induced intimal hyperplastic lesions in wild type C57BL/6 mice, showed a significant increase in SUV39H1 and H3K9me3 expression compared to uninjured vessels. Conclusion: We identify SUV39H1 an epigenetic regulator of VSMC phenotype whose expression and activity increase with dedifferentiation in vitro and in vivo . Mechanistically, SUV39H1 influences VSMC chromatin marks and KLF4 expression to repress contractile phenotype. Understanding the role of SUV39H1 and its targets may have implications for developing new therapeutic strategies for treating vascular diseases.