RasGAP-Derived Fragment N Increases the Resistance of Beta Cells towards Apoptosis in NOD Mice and Delays the Progression from Mild to Overt Diabetes

Natasa Bulat,Hadi Khalil,Nieves Peltzer,Christian Widmann,Jiang-Yan Yang,Gilles Dubuis,Evrim Jaccard

doi:10.1371/journal.pone.0022609

Abstract

The caspase-3-generated RasGAP N-terminal fragment (fragment N) inhibits apoptosis in a Ras-PI3K-Akt-dependent manner. Fragment N protects various cell types, including insulin-secreting cells, against different types of stresses. Whether fragment N exerts a protective role during the development of type 1 diabetes is however not known. Non-obese diabetic (NOD) mice represent a well-known model for spontaneous development of type 1 diabetes that shares similarities with the diseases encountered in humans. To assess the role of fragment N in type 1 diabetes development, a transgene encoding fragment N under the control of the rat insulin promoter (RIP) was back-crossed into the NOD background creating the NOD-RIPN strain. Despite a mosaic expression of fragment N in the beta cell population of NOD-RIPN mice, islets isolated from these mice were more resistant to apoptosis than control NOD islets. Islet lymphocytic infiltration and occurrence of a mild increase in glycemia developed with the same kinetics in both strains. However, the period of time separating the mild increase in glycemia and overt diabetes was significantly longer in NOD-RIPN mice compared to the control NOD mice. There was also a significant decrease in the number of apoptotic beta cells in situ at 16 weeks of age in the NOD-RIPN mice. Fragment N exerts therefore a protective effect on beta cells within the pro-diabetogenic NOD background and this prevents a fast progression from mild to overt diabetes.

Highlights

Apoptosis of pancreatic beta cells leads to type 1 diabetes [1,2] and may contribute to the development of type 2 diabetes [3]
Shows that fragment N is expressed in islets isolated from NODRIPN albeit to lower levels compared to mice expressing the transgene in the FVBN background (FVBN-RIPN mice)
We provide evidence that fragment N expressed in,40% of the pancreatic beta cells of Non-obese diabetic (NOD) mice significantly increases the time these mice can remain free of overt diabetes (.20 mM) once they have started to lose their ability to maintain a normo-glycaemia (i.e. ,10 mM)

Summary

Introduction

Apoptosis of pancreatic beta cells leads to type 1 diabetes [1,2] and may contribute to the development of type 2 diabetes [3]. Finding ways of increasing the resistance of beta cells towards apoptotic stimuli would be beneficial in the context of diabetes therapy. Despite the fact that Akt can activate the NFkB transcription factor [11,12,13], NFkB stimulation does not occur when Akt is activated by fragment N [10,14]. This could be beneficial for beta cells because in contrast to what is found in many cell types, sustained activation of NFkB in beta cells induces apoptosis [15,16,17,18]

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Conclusion