Epigenome-Wide Association Study of Abdominal Aortic Aneurysm Identifies Central Role for Inflammatory Pathways

Abstract

Background Epigenetic mechanisms underlying susceptibility to abdominal aortic aneurysm (AAA) remain poorly understood. Identifying causal DNA methylation markers for AAA can elucidate the regulatory processes that drive aneurysm formation and accelerate translational applications. We leveraged the VA Million Veteran Program (MVP) to identify methylation biomarkers and delineate underlying pathways. Methods We first conducted an epigenome-wide association study (EWAS) of incident AAA (1,324 cases; 42,065 non-cases), performed stratified analyses by population group and smoking status, and conducted Mendelian randomization (MR) to facilitate casual inference of the CpG-AAA association. Chromatin state, island context, and TF binding were implicated through functional annotation of identified CpGs. To identify genes impacted by change in methylation state, we aligned associations with transcriptional data obtained in blood, aorta, and liver. We performed expression quantitative trait methylation (eQTM) to capture CpG–gene-expression links across the genome. Network MR was used to test cardiometabolic and inflammatory mediation. Finally, we developed a methylation risk score for AAA using penalized regression and evaluated its performance against a clinical model in MVP and two external studies. Results: EWAS identified 1,253 CpGs associated with incident AAA, and MR supported a putative causal role for 143 of these associations. Functional annotation pointed to predominantly distal, enhancer-centered regulation and enrichment of inflammatory transcription factor programs (e.g., AP-1, NF-κB). This distal architecture was consistent with eQTM results, which showed a larger number of trans associations. Among 143 CpGs associated with AAA in MR analyses, we identified 213 CpG–gene expression pairs with strong colocalization support, including AGER, C2, and DDR1. Multi-trait colocalization further prioritized 8 CpG–gene expression–AAA links with evidence of a shared genetic signal. Network MR identified 135 putative mediation pathways linking CpGs to AAA, including 58 via cardiometabolic traits and 77 via inflammation-related traits. Blood lipid traits mediated more than 40% of the associations between AAA risk and CpGs near LDLR (cg19305903) and TRIB1 (cg14128479). Among inflammation-related mediators, circulating DAG1, NEXN, MMP9, IL1RN, and MMP13 were prioritized as potential intermediates. Additionally, a CpG selection process was used to develop a methylation risk score for AAA, which strongly associated with disease in both the discovery cohort and two external validation cohorts, even after adjustment for a full suite of clinical covariates. Conclusions This study identified putative causal DNA methylation markers for AAA, and multi-omics analyses implicate AP-1–linked inflammatory transcriptional programs, blood lipids, and multiple inflammation-related proteins as key pathways underlying methylation-associated AAA risk.