Decreased proliferation of aged rat beta cells corresponds with enhanced expression of the cell cycle inhibitor p27(KIP1).

BACKGROUND: Over 400 million people are diabetic. Type 1 and type 2 diabetes are characterized by decreased functional β-cell mass and, consequently, decreased glucose-stimulated insulin secretion. A potential intervention is transplantation of β-cell containing islets from cadaveric donors. A major impediment to greater application of this treatment is the scarcity of transplant-ready β-cells. Therefore, inducing β-cell proliferation ex vivo could be used to expand functional β-cell mass prior to transplantation. Various molecular pathways are sufficient to induce proliferation of young β-cells; however, aged β-cells are refractory to these proliferative signals. Given that the majority of cadaveric donors fit an aged demographic, defining the mechanisms that impede aged β-cell proliferation is imperative. RESULTS: We demonstrate that aged rat (5-month-old) β-cells are refractory to mitogenic stimuli that otherwise induce young rat (5-week-old) β-cell proliferation. We hypothesized that this change in proliferative capacity could be due to differences in cyclin-dependent kinase inhibitor expression. We measured levels of p16(INK4a) , p15(INK4b) , p18(INK4c) , p19(INK4d) , p21(CIP1) , p27(KIP1) and p57(KIP2) by immunofluorescence analysis. Our data demonstrates an age-dependent increase of p27(KIP1) in rat β-cells by immunofluorescence and was validated by increased p27(KIP1) protein levels by western blot analysis. Interestingly, HDAC1, which modulates the p27(KIP1) promoter acetylation state, is downregulated in aged rat islets. These data demonstrate increased p27(KIP1) protein levels at 5 months of age, which may be due to decreased HDAC1 mediated repression of p27(KIP1) expression. SIGNIFICANCE: As the majority of transplant-ready β-cells come from aged donors, it is imperative that we understand why aged β-cells are refractory to mitogenic stimuli. Our findings demonstrate that increased p27(KIP1) expression occurs early in β-cell aging, which corresponds with impaired β-cell proliferation. Furthermore, the correlation between HDAC1 and p27 levels suggests that pathways that activate HDAC1 in aged β-cells could be leveraged to decrease p27(KIP1) levels and enhance β-cell proliferation.