Translating Cardiac and Cardiometabolic GWAS Using Zebrafish

Abstract: Genome-wide association studies (GWAS) have identified thousands of loci associated with cardiac and cardiometabolic traits. However, the trait-associated variants usually do not clearly point to causal gene(s), mechanism(s) or tissue(s). Model systems that allow for a comprehensive and quick candidate gene screening are necessary, ideally in vivo. The overall objective of my thesis is to establish large-scale, imaged-based screens in zebrafish embryos and larvae to examine candidate genes for their effects on heart rate and rhythm, as well as on early-onset atherosclerosis and dyslipidemia.In Study 1, I prioritized 18 candidate genes in eight loci identified in a meta-analysis of GWAS for heart rate variability. Some of these genes were already known to be involved in cardiac pacemaking, whereas others require functional characterization.In Study 2, I established an experimental pipeline to examine genetic effects on cardiac rate and rhythm and used it to characterize orthologues of six human candidate genes for heart rate and rhythm. I confirmed known effects of rgs6 and hcn4, and established a role for KIAA1755 in HRV.In Study 3, I contributed to large-scale experiments to establish the zebrafish as a model system for early-onset atherosclerosis and dyslipidemia. Overfeeding and cholesterol-supplementation of the diet were shown to propel independent pro-atherogenic effects. Atherosclerotic burden was alleviated using commonly prescribed drugs in humans. Lastly, the effects of proof-of-concept genes known to be involved in lipid metabolism were examined and showed higher LDLc (apoea) and early-onset atherosclerosis (apobb1).In Study 4, I characterized genes in GWAS-identified loci for triglyceride levels for a role in lipid metabolism and early-stage atherosclerosis. I identified three previously unanticipated genes that influence triglyceride levels in zebrafish larvae. Several additional genes influence other cardiometabolic risk factors. Interestingly, two genes showed trends towards lower triglycerides levels (dock7 and lpar2a), with directionally opposite effects on vascular inflammation. This emphasizes that candidate genes need to be examined comprehensively to guide further mechanistic studies.