Epigenetic landscapes in human pancreatic islets reveal distinct drivers for adaptation to age and type 2 diabetes

Age is the strongest risk factor for type 2 diabetes, yet their independent contribution to pancreatic islet dysfunction remains unclear. We integrate DNA methylation, transcriptomic, and genotyping data from 144 islet donors. We identify 996 age- and 902 T2D-associated CpGs with minimal overlap, and 251 age- and 310 diabetes CpG target genes, usually distant from the CpG. Age-linked CpGs are enriched in promoters, form co-regulated gene modules, link to beta-cell function, including insulin secretion. Diabetes-associated CpGs are enriched in enhancer/non-regulatory regions, and modules suggest stress-induced epigenetic drift. CpG-gene associations are independent of genetic variation. Mendelian randomisation supports a causal role for age-associated CpGs regulating KLHL42, a T2D GWAS locus. A blood-based methylation risk score based on age-linked CpGs correlates with insulin secretion and improves diabetes classification when combined with genetic risk (AUC = 0.91). Altogether, age is associated with a coordinated epigenetic programme, whereas diabetes links to a heterogeneous, stress-related epigenetic signature.