Epigenetics in Abdominal Aortic Aneurysm: Mechanisms and Risk Prediction.

Background: Epigenetic mechanism 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 would 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 mediation. Finally, we developed a risk predictor using methylation data using a penalized regression model, evaluating its performance against a comprehensive clinical model. Results: EWAS identified 1,253 CpGs associated with incident AAA, and MR supported a putative causal role for 151 of these associations. Functional annotation pointed to predominantly distal, enhancer-centered regulation and enrichment of inflammatory transcription factor programs (e.g., AP-1). This distal architecture was consistent with eQTM results, which showed a larger number of trans associations. Network MR identified 231 putative mediation pathways linking CpGs to AAA, including 179 via cardiometabolic traits and 52 via immune/inflammation-related traits. Among cardiometabolic mediators, blood lipids accounted for >40% of mediation effect linking LDLR-associated CpGs to AAA risk. Among immune/inflammation-related mediators, platelet count and circulating proteins including NEXN, IL1RN, ADH1B, and MMP12 emerged as key intermediates. Genetic colocalization highlighted an aorta-specific cg17511968-WNT6-AAA axis, and network MR implicated IL1RN and MMP12 as downstream protein mediators of association between WNT6-proximal CpGs and AAA. Finally, a methylation risk score improved discrimination when added to a clinical model (AUC 0.775; 95% CI, 0.749-0.801) for incident AAA prediction. Conclusions: This study identified putative causal DNA methylation markers for AAA, and multi-omics analyses implicate AP-1-linked inflammatory transcriptional programs, blood lipids, platelet count, and multiple immune/inflammation-related proteins as key pathways underlying methylation-associated AAA risk.