Differential regulation of acute beta cell survival and glucose homeostasis by Tp53

Background:

The reduction of pancreatic beta cell mass due to apoptosis has been linked to type 2 diabetes etiology. The tumor suppressor Tp53 is a critical regulator of cell death and may regulate beta cell survival in the context of type 2 diabetes. We investigated the molecular pathways modulated by Tp53 in vitro and the impact of beta cell specific Tp53 ablation in diabetes models in vivo.

Methods:

Tp53 mRNA was knocked down in the rat insulinoma cell line INS-1E using RNA interference. The cells were further treated with the chemical streptozotocin (STZ) inducing beta cell DNA damage. We performed Western Blotting for detection of cleaved CASP3, CASP9 and PARP1, phosphorylated H2AX and PDX1. We analyzed beta cell specific Tp53 knockout mice exposed to a high fat diet (HFD), or treated with multiple low dose STZ injections to induce a diabetic phenotype.

Results:

Knockdown of Tp53 did not affect PDX1 expression. While the activation of the DNA damage response (phospho-H2AX) by STZ treatment was unaltered by Tp53 knockdown, downstream activation of CASP9 was blunted, and apoptosis was almost completely abolished as determined by cleavage of CASP3 and PARP1. In contrast, in vivo, beta cell specific ablation of Tp53 neither protected against a diabetic phenotype induced by STZ injections nor ameliorated HFD induced hyperglycemia.

Conclusion:

We demonstrate a differential regulation of acute beta cell survival and long term glucose homeostasis by Tp53 in pancreatic beta cells in vitro and in vivo.