Expression of Pro- and Antiapoptotic Molecules of the Bcl-2 Family in Human Islets Postisolation

Abstract

Human islets are subjected to a number of stresses before and during their isolation that may influence their survival and engraftment after transplantation. Apoptosis is likely to be activated in response to these stresses. Apoptosis due to intrinsic stresses is regulated by pro- and antiapoptotic members of the Bcl-2 family. While the role of the Bcl-2 family in apoptosis of rodent islets is becoming increasingly understood, little is known about which of these molecules are expressed or required for apoptosis of human islets. This study investigated the expression of the Bcl-2 family of molecules in isolated human islets. RNA and protein lysates were extracted from human islets immediately postisolation. At the same time, standard quality control assays including viability staining and β-cell content were performed on each islet preparation. Microarrays, RT-PCR, and Western blotting were performed on islet RNA and protein. The prosurvival molecules Bcl-xl and Mcl-1, but not Bcl-2, were highly expressed. The multidomain proapoptotic effector molecule Bax was expressed at higher levels than Bak. Proapoptotic BH3-only molecules were expressed at low levels, with Bid being the most abundant. The proapoptotic molecules BNIP3, BNIP3L, and Beclin-1 were all highly expressed, indicating exposure of islets to oxygen and nutrient deprivation during isolation. Our data provide a comprehensive analysis of expression levels of pro- and antiapoptotic Bcl-2 family members in isolated human islets. Knowledge of which molecules are expressed will guide future research to understand the apoptotic pathways activated during isolation or after transplantation. This is crucial for the design of methods to achieve improved transplantation outcomes.