Defining the Role of FHL5, a Novel Hypertension Associated Gene in Smooth Muscle Cells

摘要

ABSTRACT Hypertension, a condition defined by a chronic elevation in blood pressure is one of the most significant heritable risk factors for cardiovascular disease. Genome wide association studies (GWAS) in hypertension have provided an unbiased survey of loci relevant to blood pressure regulation, many of which harbor genes that cluster into functional pathways that regulate smooth muscle cell (SMC) phenotypes. As the most abundant cell type in the healthy vessel wall, SMCs regulate vascular tone through coordinated contraction and relaxation. In response to environmental stress, SMCs dedifferentiate and contribute to the pathogenic remodeling of the vessel that increases vascular tone. Functional characterization of these loci, may reveal new insights into SMC dysregulation and inform novel drug candidates. One such hypertension locus with a predicted role in the vessel wall, UFL1-FHL5 is also associated with multiple vascular disorders, including coronary artery disease, myocardial infarction, and migraines. Statistical fine-mapping approaches implicate FHL5 as the top candidate gene at the UFL1-FHL5 locus. FHL5 expression is enriched in artery tissues, specifically in contractile SMC and pericytes in the vessel wall. FHL5 is a member of Four and Half LIM domain family, which include proteins FHL1, FHL2, and FHL3 that function as transcriptional regulators for the transcription factors, SRF and CREB1 in skeletal and cardiac muscle tissue. FHL5, the most understudied member of this family, was implicated in vein intimal hyperplasia by activating CREB1 target genes. Thus, I hypothesize that vascular disease associated genetic variation reduces FHL5 expression and that FHL5 functions as a critical cofactor to activate contractile SMC pathways in the vessel wall. Studies in aim 1 will provide insights into the upstream regulatory mechanisms of FHL5 by identifying critical FHL5 regulatory elements. I will epigenetically activate putative enhancers harboring top candidate hypertension variants in primary SMCs and assess changes in FHL5 gene expression, SMC contractility, actin cytoskeletal organization and intracellular calcium levels. In aim 2, I will elucidate the downstream functional role of FHL5 protein by mapping its binding sites in human coronary artery tissues using the high resolution, low input Cleavage Under Target and Release Upon Nuclease (CUT&RUN) method. I will intersect FHL5 binding sites with SRF and CREB1 binding sites in matched tissue samples to determine the pathways regulated by different FHL5 transcriptional complexes. I will also determine the impact of deleting top FHL5 regulatory elements residing in hypertension loci on SMC functions. Overall, in this study I will characterize a novel hypertension associated locus and define the role of this cofactor in SMC biology. These studies may also inform the development of anti-hypertensive therapies targeting vessel wall related pathways to circumvent multiple vascular diseases and address significant gaps in the clinic.