It is well recognized that the regenerative capacity of pancreatic insulin-producing beta cells declines with age, with the most dramatic reduction occurring shortly after birth. However, the mechanism that accounts for this decline remains poorly understood. We sought to determine the molecular changes that attribute to this decrease in beta cell proliferation. Here, we show that activation of the DNA damage response (DDR) coincides with the decline in beta cell proliferation occurring during early postnatal life. In addition, we discovered a postnatal increase in the expression levels of replication stress-related DNA damage markers such as replication protein A (RPA) and phosphorylated Chk1 (pChk1). Furthermore, inhibition of the downstream effector Wee1 increases beta cell proliferation in vitro and in vivo. The results of this study provide insight into age-dependent changes in beta cells that lead to the increased incidence of cell cycle arrest. We hope that these findings will not only contribute to uncovering mechanisms underlying the age-dependent decline in beta cell proliferation, but also assist in the identification of factors that could potentially be pharmacologically targeted to improve beta cell function and stimulate their expansion for the management and treatment of diabetes mellitus.

The replicative capacity of insulin-producing pancreatic beta cells is dynamically regulated during development, maturation, and aging. Early in life, beta cells proliferate rapidly to expand beta cell mass but quickly become quiescent with age. While this decline is well documented, the mechanisms that underlie this age-dependent beta cell replicative senescence are still poorly understood. Using mouse genetics and in vivo quantitative proteomics approaches, we found that nutrient sensing plays an important role in controlling the proliferation of beta cells. We show that the transcription factor Nkx6.1 is required for expanding beta cell mass during the early wave of rapid postnatal beta cell proliferation by regulating the expression of the nutrient sensing receptors Glut2 and Glp1r. Furthermore, by quantitatively comparing the proteome of islets from young and aged mice, we found dynamic regulation of not only cell cycle proteins, but also proteins critical for beta cell function. Proteins important for insulin secretion and metabolic regulation increased with age, while proteins involved in expanding cell number declined with age. From our proteomic screen, we identified a protein deacetylase upregulated during aging. Pharmacologic inhibition of this protein promoted both rodent and human beta cell proliferation ex vivo, indicating the deacetylation activity of this candidate represses beta cell proliferation. Beta cell-specific deletion of the protein deacetylase increased rodent beta cell proliferation and mass in diabetic mice in vivo. Importantly, inhibition of this protein in human islets ex vivo did not negatively affect beta cell function or survival. Finally, we show that the protein deacetylase specifically regulates beta cell proliferation in conditions of elevated blood glucose through modulating the glucose-dependent MAPK pathway. Overall, our studies have uncovered dynamic regulation of beta cell proliferation from birth to advanced age and identified a viable therapeutic target for enhancing beta cell mass for the treatment of diabetes.