Abstract MP39: FHL5 , A Novel Cofactor Associated With Coronary Artery Disease, Regulates Smooth Muscle Cell Function Through A Transcriptional Network Linking Multiple Risk Loci

Introduction: Coronary artery disease (CAD) is the leading cause of death worldwide with an estimated heritability of ~50%. The most recent genome wide association study (GWAS) for CAD and myocardial infarction (MI) identified over 200 loci. One such novel CAD/MI locus, UFL1-FHL5 (P = 1.1E-8), is associated with additional vascular pathologies, including hypertension, migraines, and coronary calcification. We previously showed through statistical fine-mapping that FHL5 is the top candidate causal gene underlying each of these vascular trait associations and highly enriched in the contractile mural cell populations in the artery. These preliminary studies motivate our hypothesis that FHL5 functions as a transcriptional regulator of SMC contractility to affect vascular disease risk. Methods and Results: Given the reported role of FHL5 as a cofactor, we mapped 17,201 candidate FHL5 binding sites in coronary artery SMCs using the Cleavage Under Targets and Release Using Nuclease (CUT&RUN) method. Binding sites were enriched for AP-1 family motifs and strongly overlapped CREB binding sites and H3K27ac enhancer marks. FHL5 target genes were functionally enriched in well characterized CAD pathways, such as extracellular matrix organization (P=5.2E-15, OR=2.1) and TGF-beta signaling (P=8.0E-5, OR=2.0). Interestingly, FHL5 binding sites were also enriched for CAD (P=1.8E-7, OR=2.3) and blood pressure (BP) risk variants (P=0.04, OR=1.2), thereby linking FHL5 with the regulation of multiple downstream CAD/BP loci. Weighted gene co-expression network and key driver analyses of human coronary artery transcriptomic data further support this regulatory role. Lastly, we validated these findings by performing confocal based calcium imaging and collagen gel contraction assays. Consistent with our functional genomic analyses, overexpression of FHL5 elevated intracellular calcium levels 2.5X and increased SMC contractility by ~45%. Conclusion: Taken together, our results provide evidence that FHL5 may impact CAD risk by regulating a network of disease-associated genes mediating SMC functions. These findings further contribute to our understanding of the heritable risk for multiple vascular diseases.