Nrf2-and p53-inducible REDD2/DDiT4L/Rtp801L confers pancreatic β-cell dysfunction, leading to glucose intolerance in high-fat diet-fed mice

Abstract

Pancreatic β-cells play a critical role in glucose homeostasis by secreting insulin. Chronic oxidative stress causes β-cell dysfunction, including β-cell loss; however, the underlying mechanisms remain unclear. Here, we demonstrate the critical role of the regulated in development and DNA damage response 2 (REDD2/DDiT4L/Rtp801L) in β-cell dysfunction. In INS-1 β-cells, Redd2 was induced by high glucose/palmitate or streptozotocin (STZ) exposure. Knockdown of Redd2 attenuated STZ-induced loss of cell viability, while REDD2 overexpression reduced cell viability and p70S6K phosphorylation, suggesting the involvement of suppression of mTORC1 activation. STZ also activated the transcription factors nuclear factor erythroid 2-related factor 2 (Nrf2) and p53, and overexpression of these transcription factors synergistically induced Redd2 expression. Reporter assays using the Redd2 promoter (-2328/-1) and chromatin immunoprecipitation identified the functional binding sites for Nrf2 (EpRE2, -349/-340) and p53 (p53RE1, -90/-81) on the Redd2 promoter. Purified recombinant p53 and Nrf2 bound directly. There were no noticeable changes in male global Redd2-knockout mice (C57BL/6J background), except for inguinal adipose tissue decrease when the mice were fed a standard diet. In contrast, when the mice were fed a high-fat diet (HFD), Redd2-knockout mice exhibited improved glucose tolerance relative to littermate controls. Redd2-knockout in HFD-fed mice increased β-cell mass due to reduced β-cell apoptosis and elevated plasma insulin concentrations, whereas insulin sensitivity remained unaffected. In both STZ-induced male and female and HFD-fed male models, β-cell-specific Redd2-knockout improved glucose tolerance without affecting insulin sensitivity. Our results identify REDD2 as a novel regulator of β-cell dysfunction under oxidative stress.

Keywords: DNA damage-inducible transcript 4-like (DDiT4L); gene knockout; nuclear factor erythroid 2-related factor 2 (Nrf2); oxidative stress; p53; pancreatic β-cell; streptozotocin (STZ); stress response; the regulated in development and DNA damage response 2 (REDD2); type 2 diabetes.