Abstract

Objective: High concentrations of circulating glucose are believed to contribute to defective insulin secretion and beta-cell function in diabetes and at least some of this effect appears to be caused by glucose-induced beta-cell apoptosis. In mammalian cells, apoptotic cell death is controlled by the interplay of pro-and anti-apoptotic members of the Bcl-2 family. We investigated the apoptotic pathway induced in mouse pancreatic islet cells after exposure to high concentrations of the reducing sugars ribose and glucose as a model of beta cell death due to long-term metabolic stress.

Research design and methods: Islets isolated from mice lacking molecules implicated in cell death pathways were exposed to high concentrations of glucose or ribose. Apoptosis was measured by analysis of DNA fragmentation and release of mitochondrial cytochrome c.

Results: Deficiency of IL-1 receptors or Fas did not diminish apoptosis, making involvement of inflammatory cytokine receptor or death receptor signalling in glucose-induced apoptosis unlikely. In contrast, overexpression of the pro-survival protein Bcl-2 or deficiency of the apoptosis initiating BH3-only proteins Bim or Puma or the downstream apoptosis effector Bax, markedly reduced glucose or ribose-induced killing of islets. Loss of other BH3-only proteins Bid or Noxa, or the Bax-related effector Bak had no impact on glucose-induced apoptosis.

Conclusions: These results implicate the Bcl-2 regulated apoptotic pathway in glucose-induced islet cell killing and indicate points in the pathway at which interventional strategies can be designed.