Epigenetic signature of heterogeneity in aging: Findings from the Canadian Longitudinal Study on Aging

Human aging does not follow a single trajectory. Epigenetic changes offer insight into the heterogeneity in aging by reflecting the combined influence of genetic, environmental, and lifestyle factors on the timing and progression of age-related changes beyond what chronological age alone can explain. Emerging research in cancer and aging highlights the importance of methylation variability as a marker of biological disruption. It also shows little overlap between CpGs differing in means versus variability. We investigated the role of DNA methylation in aging heterogeneity by performing epigenome-wide differential methylation and variance association analysis in blood samples from 1,445 Canadians aged 45 to 85. We identified 448 differentially methylated (DMRs) and 488 differentially variable regions associated with health decline across health deficit accumulation (i.e. the Frailty Index), cognitive, and physical function. We observed minimal overlap between these types of regions, with distinct gene coverage, highlighting a unique and potentially additional contribution of variability to age-related epigenetic changes. Gene ontology analyses of DMRs revealed enrichment in immune and inflammation-related pathways pointing to immune function as a key driver of aging heterogeneity. By integrating significant positions from both analyses, we constructed a composite epigenetic biomarker. Our biomarker outperformed control models built on differential methylation alone as well as established epigenetic biomarkers (e.g. GrimAge, PhenoAge) in predicting mortality and the onset of chronic obstructive pulmonary disease.