Beta cell markers of aging have heterogeneous distribution in islets and are induced by insulin resistance

Our hypothesis was that at any given point in time, islets will contain differing populations of beta cells at different stages of their lifecycle, with further changes occurring with metabolic stress and aging. We examined subpopulations of beta cells isolated from MIP-GFP mice on the basis of their insulin transcriptional activity and in their expression of p16Ink4a. In addition, using aging C57Bl/6 mice as a model, markers of beta cell aging were identified and validated: Igf1r and Cd99 expression increased with age, whereas Kcnq5 was decreased with age. These markers were correlated with an age-related decline in function. The functional aging of beta cells was accelerated by S961, an antagonist to the insulin receptor, which induced insulin resistance. Particularly surprising was the finding of marked islet heterogeneity as demonstrated with the marked staining differences of the markers: Igf1r, Cd99 and Kcnq5. These novel findings about beta cell and islet heterogeneity, and how they change with age, open up an entirely new set of questions that must be addressed about the pathogenesis of type 2 diabetes. The present study has identified new markers of aging in beta cells and found that the expression of these and other markers can be increased by insulin resistance. This provides insight into how insulin resistance might accelerate the death of beta cells. In addition, striking heterogeneity among islets was found, which opens up new ways to think about islet biology and the pathogenesis of T2D. We performed Affymetrix microarrays (n=3 or 4 per group) on RNA from FACS-purified MIP:GFP beta cells from different aged mice: 1) 3.5-9 w Young; 2) 1 y-old; 3) 2 y-old.