Glucose catabolism drives adaptive beta cell mass expansion by promoting proliferation under conditions of increased insulin demand. Previously, we showed that induction of the antioxidant regulator, Nrf2, is required for glucose-stimulated β-cell proliferation, and that overexpression of Nrf2 stimulates human beta cell proliferation. Here we manipulate the Nrf2 pathway using pharmacological and genetic approaches to explore the link between glucose metabolism, Nrf2 activation and beta cell proliferation. Treatment of isolated mouse islets with either a Nrf2 inhibitor (brusatol) or Cre-recombinase deleted Nrf2, resulted in complete inhibition of glucose-stimulated proliferation (both n=3, p < 0.01). Conversely, stimulation of Nrf2 by CDDO-me or genetic gain of function (Cre-mediated depletion of Nrf2 inhibitor, Keap1) increased beta cell proliferation of beta cells from isolated mouse islets cultured in 5 mM glucose (4.9 ± 0.2 fold and 6.9 ± 1.4 fold, respectively; n=3, p < 0.05). Inhibition or depletion of Nrf2 was associated with a remarkable decrease in insulin content, suggesting that beta cell identity requires basal levels of Nrf2 expression. Importantly, isolated human beta cells displayed similar responses to Nrf2 loss and gain of function. Activation and nuclear translocation of Nrf2 requires dissociation from its inhibitor, Keap1, and phosphorylation of Ser-40 on Nrf2. Five minutes of 20 mM glucose treatment profoundly increased Ser-40 phosphorylation and translocation of Nrf2, while the same effect by CDDO-Me treatment took 50 minutes in INS1 cells. The glucose-mediated activation and translocation of Nrf2 was blocked by the antioxidant N-acetylcysteine (NAC), which also attenuated glucose-stimulated proliferation of isolated mouse beta cells. In addition, the activation and phosphorylation of Nrf2 was prevented by the pan-PKC inhibitor, calphostin C. We conclude that manipulation of the Nrf2 pathway is an exciting novel target for regulation of beta cell proliferation.
S. Baumel-Alterzon: None. L.S. Katz: None. G. Brill: None. A. Garcia-Ocaña: None. D. Scott: None.
American Diabetes Association (1-17-IBS-116 to D.S.); National Institutes of Health