Stable overexpression of p8 increases survival of INS-1E beta cells in response to streptozotocin (STZ)-induced beta cell damage in vitro

Within the pancreas, p8 expression is induced by pancreatitis and protects exocrine tissue from inflammatory damage. In previous work, we investigated the role of p8 within the endocrine pancreas and characterised p8 as a glucose-dependent mediator of beta cell proliferation. Here we investigate the cell protective properties of p8 in response to STZ treatment in INS-1E beta cells. Exposure of native INS-1E to STZ displays a dose-dependent upregulation of p8 gene expression and a 24h LD 50 of about 0.7 mM STZ. Initial data from transiently transfected INS-1E beta cells overexpressing p8 demonstrate increased survival upon STZ exposure. Hence, we generated INS-1E beta cells with stable p8 overexpression under the control of a CMV promoter (p8-INS1) and empty plasmid controls (mock-INS1). Compared to mock controls p8-INS1 cells demonstrate higher proliferation rate resulting in 1.3 fold increase in cell numbers after 48h. Furthermore, p8-INS-1 cells are about 30% more resistant to STZ-induced beta-cell damage than mock controls. In contrast to transient transfections stable p8 overexpression protects beta cells also in high STZ dosages above LD50 of native INS-1 (1 and 3,3 mM). This is accompanied by a corresponding reduction in apoptosis as measured by annexin V staining and FACS analysis. Whether the anti-apoptotic effect of stable ectopic p8 expression is mediated by inhibition of NFkB, caspases or other pro-apoptotic processes is under current research. In conclusion, these results demonstrate that, in beta cells, p8 is a stress-induced factor, which exerts cellular proliferation and protection against STZ-induced cell death.