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Pro-apoptotic BH3-only protein Bid is essential for death receptor-induced apoptosis of pancreatic β cells

¹ St. Vincent's Institute, 41 Victoria Parade, Fitzroy, 3065, Australia
² The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, 3050, Australia

Objective: Apoptosis of pancreatic β cells is critical in both diabetes development and failure of islet transplantation. The role in these processes of pro- and anti-apoptotic Bcl-2 family proteins, that regulate apoptosis by controlling mitochondrial integrity, remains poorly understood. We investigated the role of the BH3-only protein Bid and the multi-BH domain pro-apoptotic Bax, Bak as well as pro-survival Bcl-2 in β-cell apoptosis.

Research Design And Methods: We isolated islets from mice lacking, Bid, Bax or Bak and those over-expressing Bcl-2 and exposed them to Fas ligand, TNF, and pro-inflammatory cytokines or cytotoxic stimuli that activate the mitochondrial apoptotic pathway (staurosporine, etoposide, -radiation, tunicamycin, and thapsigargin). Nuclear fragmentation was measured by flow cytometry.

Results: Development and function of islets was not affected by loss of Bid, and Bid-deficient islets were as susceptible as wild-type islets to cytotoxic stimuli that cause apoptosis via the mitochondrial pathway. In contrast, Bid-deficient islets and those over-expressing anti-apoptotic Bcl-2 were protected from Fas ligand-induced apoptosis. Bid-deficient islets were also resistant to apoptosis induced by TNF plus cycloheximide and were partially resistant to pro-inflammatory cytokine-induced death. Loss of the multi-BH domain pro-apoptotic Bax or Bak protected islets partially from death receptor-induced apoptosis.

Conclusions: These results demonstrate that Bid is essential for death receptor-induced apoptosis of islets, similar to its demonstrated role in hepatocytes. This indicates that blocking Bid activity may be useful for protection of islets from immune-mediated attack and possibly also in other pathological states in which β cells are destroyed.

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