Abstract Tu0055: YBX1 Regulates Vascular Fibroblast Activation and Is the Causal Gene Underlying Coronary Artery Disease Risk Loci at 1p34

Background: Genome-wide association studies (GWAS) of coronary artery disease (CAD) are an effective way to identify disease modifiers and therapeutic targets. However, translation of GWAS to therapies is limited by inability to assign non-coding GWAS loci to causal genes, causal cells, and specific mechanisms. A locus at 1p34 has been associated with increased risk of CAD, but the causal gene, cell, and function remain unknown. The nearest gene to 1p34 risk loci, CCDC30, is not expressed in adult somatic cells, though human coronary single cell epigenetic data revealed accessibility around the loci. Vascular adventitial fibroblasts (AdvFib) have recently been shown to undergo phenotypic modulation during atherosclerosis development and alter plaque formation through interaction with SMC and immune cells. Decreasing AdvFib activation attenuates atherosclerosis, though the regulators of AdvFib activation are unknown. Approach: Epigenetic profiling of the human coronary artery revealed several risk-associated SNPs at 1p34 located within open chromatin in AdvFib. Cut and Tag of human AdvFib linked 1p34 to H3K27acetylation, suggesting these regions function as active enhancers. CRISPRi mediated epigenetic modulation of CAD-risk loci in 1p34 suppresses expression of YBX1, 100kb away. This data in conjunction with human eQTL data confirms risk loci at 1p34 regulates YBX1 expression in AdvFib. Functionally, we knocked down and over-expressed YBX1 in AdvFib to determine its function. Loss of YBX1 impaired AdvFib activation of inflammatory signals, proliferation, and recruitment of inflammatory cells. Pathway analysis revealed YBX1 increases cytokine-cytokine receptor interactions and TNF signaling while it decreases hippo and TGF-beta signaling. Mechanistically, YBX1 regulates several key AdvFib regulators, including key GWAS risk gene TCF21. Co-IP and Mass-Spec revealed YBX1 physically binds to TCF21 and regulates its downstream effectors. Conclusion: Our study identifies YBX1 as a novel regulator of AdvFib proliferation and atherosclerotic phenotypic modulation. YBX1 is the causal gene associated with CAD risk at 1p34, which regulates human risk for CAD at least in part through its effect on alteration in TCF21 expression and its cell autonomous and non-cell-autonomous sequelae. These findings highlight YBX1 as a potential therapeutic target for vascular diseases and underscore the importance of noncoding genetic variants in atherosclerotic gene regulation.