Pdx1 Expression in Irs2-deficient Mouse β-Cells Is Regulated in a Strain-dependent Manner

We previously demonstrated that Irs2^-/- mice develop diabetes due to β-cell growth failure and insulin resistance; however, glucose-induced insulin secretion was increased in islets isolated from Irs2^-/- mice. Pdx-1, a transcription factor important for maintenance of the β-cell function, was recently reported to be severely reduced in Irs2^-/- murine β-cells. We report herein that Pdx-1 expression, including the amount of Pdx-1 localized in the nucleus, is not down-regulated in our Irs2^-/- murine β-cells with a C57BL/6 background. We have also demonstrated the expression of upstream genes of Pdx-1, such as HNF3β and HNF1α, as well as its downstream genes, including insulin, Glut2, and Nkx6.1, to be well preserved. We have further demonstrated Pdx-1 expression to also be preserved in β-cells of 30-week-old diabetic Irs2^-/- mice. In addition, surprisingly, even in Irs2^-/- mice on a high fat diet with markedly elevated blood glucose, exceeding 400 mg/dl, Pdx-1 expression was not reduced. Furthermore, we found Pdx-1 to be markedly decreased in certain severely diabetic Irs2^-/- mice with a mixed C57BL/6J x 129Sv background. We conclude that 1) Pdx-1 expression in Irs2^-/- mice is regulated in a strain-dependent manner, 2) Irs2 ^-/- mice develop diabetes associated with β-cell growth failure even when Pdx1 expression is preserved, and 3) Pdx-1 expression is preserved in severely hyperglycemic Irs2^-/- mice with a C57BL/6 background on a high fat diet.