MD/PhD Candidate University of British Columbia Vancouver, British Columbia, Canada
Background: Advancements in genome-wide association studies (GWAS) have revealed strong genetic underpinnings to atrial fibrillation (AF). Over 100 loci have been associated with AF, with most signals found in noncoding genomic regions. The clinical relevance of such noncoding signals and the mechanisms by which they contribute to AF remain unknown. A notable example is the common single nucleotide polymorphism, rs13376333, which is robustly associated with AF in various GWAS and across ancestries and is located in the first intron of the KCNN3 gene, encoding small-conductance calcium-activated potassium channel 3 (SK3). We aimed to characterize the clinical, functional, and molecular consequences of rs13376333.
METHODS AND RESULTS: We characterized the clinical outcomes of nearly 500,000 participants from the United Kingdom (UK) biobank, stratified by their rs13376333 genotype. Hazard and odds ratios were calculated using multivariate cox regression and logistic regression analyses, respectively. We generated human induced pluripotent stem cell-derived atrial cardiomyocytes (hiPSC-aCMs) heterozygous for rs13376333 and isogenic controls, which we phenotyped using various methods including patch clamp, optical mapping, and multielectrode array. We examined the transcriptomic impact of rs13376333 on human atrial tissue and hiPSC-CMs using publicly available expression quantitative trait locus (eQTL) datasets. To dissect the molecular mechanisms of rs13376333, we employed epigenomics analyses using hiPSC-CM datasets (e.g., ATAC-seq, H3K27Ac) and motif binding tools. Using the UKB, we confirmed the previously identified association between rs13376333 and AF incidence and found rs13376333 to be significantly associated with stroke and heart failure, known sequelae of AF, and with paroxysmal tachycardia. Functional studies in hiPSC-aCMs revealed that rs13376333 reduces apamin-sensitive SK current density, prolongs action potential duration, and increases spontaneous beat rate. Interestingly, rs13376333 was significantly associated with increased KCNN3 expression in human atrial tissue and hiPSC-CMs from 71 multiethnic individuals. Epigenomic analyses showed rs13376333 lies within a candidate enhancer that physically contacts the promoter of KCNN3, and rs13376333 is predicted to disrupt the binding of a transcription factor PU.1 which has been previously linked to AF
Conclusion: Using a multifaceted approach, we highlight the impact of rs13376333 on patient outcomes and the molecular mechanisms underlying this biological predisposition to AF.
