Altering ß-Cell Proliferation In Vivo by Pharmacological Manipulation of the Nrf2 Pathway

Glucose is a natural mitogen that drives adaptive β-cell mass expansion by promoting proliferation. We previously demonstrated that induction of Nrf2 is required for glucose-stimulated and carbohydrate response element binding protein (ChREBPa)-augmented β-cell proliferation. Here we found that adenoviral delivery of Nrf2 increased human β-cell proliferation by 8.9 ± 0.2 fold (n=6), which exceeded the effect of 20 mM glucose (4.3 ± 0.4 fold). To test if activation of the Nrf2 pathway is necessary for adaptive β-cell expansion in vivo, we used pharmacological inhibitors and activators of Nrf2. Mice were placed on a high fat diet (HFD) or standard chow diet (SD) for 7 days and treated with vehicle or brusatol, which depletes Nrf2 by a post-translational mechanism. Treatment with brusatol effectively diminished Nrf2 abundance in β-cells as determined by immunofluorescence. Further, brusatol treatment ameliorated the increased β-cell proliferation normally seen with a one-week HFD (2.7±03% ki67 positive β-cells in control HFD mice, vs. 1.6±0.3% in HFD mice treated with brusatol, p < 0.05, n=5). Brusatol-treated mice also displayed significantly diminished glucose tolerance on a HFD by IPGTT, without altering the food intake or weight of the animals. Using an activator of Nrf2, bardoxolone methyl (CDDO-Me), for 7 days in the presence or absence of HFD. We found, consistent with previous reports, improved glycemic levels and decreased body weight in mice treated with CDDO-Me on a HFD. Remarkably, we also found increased β-cell proliferation in mice fed a SD and treated with CDDO-Me (1.7 ± 0.1% controls compared to 2.6±0.1% ki67 positive, insulin positive β-cells in mice treated with CDDO-Me). Crucially, in human β-cells, brusatol inhibited glucose-stimulated proliferation (1.9 fold vs. 12.7 fold, n=2) and CDDO-Me increased proliferation in 5 mM glucose (37.5 fold, n=2). Thus, we conclude that the Nrf2 pathway is an exciting novel target for manipulation of β-cell proliferation in vivo.