Adaptive unfolded protein response attenuates alcohol-induced pancreatic damage

Abstract

Background & Aims: Endoplasmic reticulum (ER) stress responses (collectively known the unfolded protein response [UPR]) have important roles in several human disorders, but their contribution to alcoholic pancreatitis is not known. We investigated the role of X-box binding protein 1 (XBP1), a UPR regulator, in prevention of alcohol-induced ER stress in the exocrine pancreas. Methods: Wild-type and Xbp1+/- mice were fed control or ethanol diets for 4 weeks. Pancreatic tissue samples were then examined by light and electron microscopy to determine pancreatic alterations; UPR regulators were analyzed biochemically. Results: In wild-type mice, ethanol activated a UPR, increasing pancreatic levels of XBP1 and XBP1 targets such as protein disulfide isomerase (PDI). In these mice, pancreatic damage was minor. In ethanol-fed Xbp1 +/- mice, XBP1 and PDI levels were significantly lower than in ethanol-fed wild-type mice. The combination of XBP1 deficiency and ethanol feeding reduced expression of regulators of ER function and the up-regulation of proapoptotic signals. Moreover, ethanol feeding induced oxidation of PDI, which might compromise PDI-mediated disulfide bond formation during ER protein folding. In ethanol-fed Xbp1+/- mice, ER stress was associated with disorganized and dilated ER, loss of zymogen granules, accumulation of autophagic vacuoles, and increased acinar cell death. Conclusions: Long-term ethanol feeding causes oxidative ER stress, which activates a UPR and increases XBP1 levels and activity. A defective UPR due to XBP1 deficiency results in ER dysfunction and acinar cell pathology. © 2011 AGA Institute.