Role of FoxO Proteins in Pancreatic beta Cells.

Forkhead transcription factors of the FoxO family have important roles in cellular proliferation, apoptosis, differentiation and stress resistance. FoxO proteins also play important roles in metabolism of complex organisms. FoxO1 regulates glucose and lipid metabolism in liver, as well as preadipocyte, myoblast and vascular endothelial cell differentiation. In the hypothalamus, FoxO controls food intake. In this chapter, we review the role of FoxO in pancreatic beta cells. Pancreatic beta cells secrete insulin to maintain the plasma glucose levels in a strict physiological range. Defects of beta cell function cause diabetes. The expression pattern of FoxO1 during pancreatic organogenesis is similar to that of Pdx1, Nkx2.2 and Pax4, transcription factors known to be critical for beta cell development. FoxO1 is expressed in a subset of pancreatic duct cells, in which insulin and/or Pdx1 are occasionally expressed. FoxO1 inhibits beta cell proliferation through suppression of Pdx1 by competing with FoxA2 and protects against beta cell failure induced by oxidative stress through NeuroD and MafA induction. Thus, a series of FoxO1 studies in pancreas suggested that FoxO1 plays important roles in pancreatic beta cell differentiation, neogenesis, proliferation and stress resistance. Genetic or pharmacological manipulation of FoxO can be used to prevent beta cell failure or aid in the differentiation of uncommitted endocrine progenitors into beta cells for transplantation.