T3 and Glucose Increase Expression of ChREBPß to Induce Expression of Phosphoenolpyruvate Carboxykinase (Pck1) Leading to Increased ß-Cell Proliferation

Thyroid hormone (T3) is required for islet development and function. Both T3 and high glucose concentrations are critical components of differentiation protocols of stem cells to β-cells. We previously demonstrated that in brown adipose tissue, T3 and glucose synergistically regulate carbohydrate response element binding protein (ChREBP), which in turn upregulates Ucp1, Glut4 and Fasn, resulting in increased thermogenesis, decreased body weight and improved glycemic levels. In the present study, we asked whether T3 and glucose signaling pathways can coordinately regulate transcription of genes important for β-cell function and mass. RNA-seq analysis was performed on cadaveric human islets from five different donors in response to low and high glucose concentrations (6 and 20 mM, respectively) and in the presence or absence of T3 (10 nM). We found that T3 and glucose coordinately regulate the expression of ChREBPβ and Pck1 (phosphoenolpyruvate carboxykinase-1). Typically, it is thought that Pck1 is not expressed in pancreatic β-cells, but it is a known target of T3 in hepatocytes. However, in FACS sorted adult human β-cells, we found that high concentrations of glucose (20 mM) and T3 (10 nM) induced the expression of Pck1 by 17.2±1.3 fold for mRNA levels. In addition, we found that overexpression of Pck1 together with its substrate dimethyl malate (DMM) increased β- cell proliferation in human islets (0.49±0.03% for human islets overexpressing Pck1, treated with DMM compared with 0.01±0.01% for control islets, n=4). Finally, using a sh-RNA knockdown approach, we demonstrated that in Ins-1 cells, ChREBPβ is necessary for Pck1 dependent β-cell proliferation. We conclude that T3 and glucose act together to regulate ChREBPβ which in turn upregulates expression of Pck1. In turn, Pck1 activity leads to increased β-cell mass. Disclosure L.S. Katz: None. D. Scott: None.