BCL-XL IS UPREGULATED IN DIFFERENT MODELS OF ACUTE PANCREATITIS AND PROTECTS PANCREAS FROM CELL DEATH

Abstract

Background and Aims: Very little is known about the mechanisms of parenchymal cell death in pancreatitis. Bcl-2 proteins are key regulators of cell death; however, their roles in pancreatitis are not known. The aim of this study was to determine the expression of key pro- and anti-apoptotic Bcl-2 proteins in pancreas and their role in different models of acute pancreatitis. Methods: Pancreatitis was induced in mice and rats by i.p. injections of 50 μg/kg cerulein (CR); by i.p. injections of L-arginine (2.5 g/kg) in rats; and by feeding a choline deficient, ethionine supplemented (CDE) diet to mice. Bcl-2 protein levels and cytochrome c release were measured by Western blot in both pancreatic tissue homogenates and mitochondrial fractions. Membrane potential of isolated pancreatic mitochondria (ΔΨm) was measured using TPP electrode and fluorescent probe TMRM. Results: Key anti-apoptotic protein Bcl-xL was greatly (up to 7-fold) upregulated in all 4 models of pancreatitis under study, both in tissue homogenates and mitochondrial fractions. Changes in pro-apoptotic Bax, Bak and Bim and the anti-apoptotic Bcl-2 were not pronounced and varied between the models. CR-induced Bcl-xL upregulation was prevented in p50−/−p65+/− mice deficient in key NF-κB proteins, indicating that Bcl-xL stimulation in pancreatitis is controlled by NF-κB. We next evaluated the role of Bcl-xL in death responses of pancreatic mitochondria by applying Bcl-xL inhibitors BH3I-2′ and HA14-1. In mitochondria isolated from normal pancreas, the inhibitors induced dose-dependent depolarization and cytochrome c release, indicating an important protective role for Bcl-xL. Mitochondria isolated from pancreas of rats and mice with CR pancreatitis were more sensitive to the deleterious effects of Bcl-xL inhibition, as compared with normal pancreas. Conclusions: Significant upregulation of Bcl-xL is a common event in models of acute pancreatitis. Bcl-xL is stimulated via NF-κB and protects the pancreas from mitochondrial damage in pancreatitis. The results suggest that increasing the level of Bcl-xL may have a therapeutic benefit in pancreatitis.