Apoptosis of pancreatic β-cells in type 1 diabetes: The role of Caspase-3 in β-cell apoptosis

Abstract

Type 1 diabetes (T1D) results from autoimmune destruction of pancreatic β-cells after asymptomatic period over years. Insulitis activates antigen presenting cells, which trigger activating DC4+ helper-T cells, releasing cytokines. Cytokines activate CD8+ cytotoxic –T cells and lead to β-cell destruction. Apoptosis pathway consists of extrinsic and intrinsic pathway. Extrinsic pathway includes Fas pathway to CD4+-CD8+ interaction whereas intrinsic pathway includes mitochondria-driven pathway at balance between anti-apoptotic Bcl-2 and Bcl-xL and pro-apoptotic proteins. Activated cleaved caspase-3 (ACC) is the converging point between extrinsic and intrinsic pathway. ACC may be used as a marker for β-cell apoptosis: inT1DM islets weakly insulin-positive β-cells are present with increased ACC positive β-cells whereas β-cell absent islets, which exclusively consist of α-cells and PP-cells with decreased ACC-cells, represent the end-stage of regenerating β-cells. Weakly insulin-positive β-cells could be rejuvenated to supply endogenous insulin. Apoptosis takes place only when pro-apoptotic protein exceeds anti-apoptotic proteins. Since concordance rate of T1D in the identical twins is about 50%, environmental factors are involved in development of T1D, opening a door to means to prevent autoimmune β-cell destruction for therapeutic application by transfecting β-cells with Casp3-/- genes or pan-caspase inhibitor therapy. Prudent glucose control prevents ongoing hyperglycemia-induced β-cell apoptosis.