Myt3 suppression sensitizes islet cells to high glucose-induced cell death via Bim induction.

B R Tennant,D Dai,B Vanderkruk,C B Verchere,J Dhillon,B G Hoffman

doi:10.1038/cddis.2016.141

Abstract

Diabetes is a chronic disease that results from the body's inability to properly control circulating blood glucose levels. The loss of glucose homoeostasis can arise from a loss of β-cell mass because of immune-cell-mediated attack, as in type 1 diabetes, and/or from dysfunction of individual β-cells (in conjunction with target organ insulin resistance), as in type 2 diabetes. A better understanding of the transcriptional pathways regulating islet-cell survival is of great importance for the development of therapeutic strategies that target β-cells for diabetes. To this end, we previously identified the transcription factor Myt3 as a pro-survival factor in islets following acute suppression of Myt3 in vitro. To determine the effects of Myt3 suppression on islet-cell survival in vivo, we used an adenovirus to express an shRNA targeting Myt3 in syngeneic optimal and marginal mass islet transplants, and demonstrate that suppression of Myt3 impairs the function of marginal mass grafts. Analysis of grafts 5 weeks post-transplant revealed that grafts transduced with the shMyt3 adenovirus contained ~20% the number of transduced cells as grafts transduced with a control adenovirus. In fact, increased apoptosis and significant cell loss in the shMyt3-transduced grafts was evident after only 5 days, suggesting that Myt3 suppression sensitizes islet cells to stresses present in the early post-transplant period. Specifically, we find that Myt3 suppression sensitizes islet cells to high glucose-induced cell death via upregulation of the pro-apoptotic Bcl2 family member Bim. Taken together these data suggest that Myt3 may be an important link between glucotoxic and immune signalling pathways.

Highlights

There was no difference in the ability of shScramble or shMyt[3] grafts to respond to a glucose challenge as determined by performing intraperitoneal glucose tolerance tests (IPGTT) 5 days or 5 weeks posttransplant (Supplementary Figures S2a–f)
During diabetes progression exposure of β-cells to cytokines produced by infiltrating immune cells activates pro-inflammatory signalling cascades that lead to amplification of inflammatory signals and initiation of apoptosis.[2,3,4,6,7,8,13,14,15,16,17]
We previously demonstrated that the transcription factor Myt[3] is one of the downstream targets of IL-1β, TNFα and IFNγ signalling in β-cells, and that its suppression is sufficient to induce a two-fold increase in apoptosis when islet cells are cultured in vitro, without affecting islet function.[12]

Summary

Introduction

Cell Death and Disease marginal (150) mass of islets transduced with adenoviruses expressing an shRNA targeting Myt[3] (shMyt3) or a scramble control (shScramble). At 5 weeks post-transplant, mice receiving shMyt3-transduced islets were moderately less able to respond to a glucose challenge, but neither shScramble and shMyt[3] grafts were able to re-stabilize blood glucose levels in the time frame of the IPGTT, and this difference was not significant (Supplementary Figures S2g–i).

Results

Conclusion