Unfolded Protein Response (UPR) Predicts and Exacerbates the Development of Alcohol-Induced Pancreatitis

Abstract

Introduction: Pancreatitis affects ˜0.04-5% of the U.S. population. The exact pathogenesis of pancreatitis, either acute or chronic, is not fully understood; to date, there are no pathogenesis-based treatment options for pancreatitis. The unfolded protein response (UPR) is a coordinated adaptive response to limit the accumulation of unfolded proteins in the endoplasmic reticulum (ER), which perturbs calcium homeostasis, energy balance, and redox state; all these components of cellular stress have been reported in pancreatitis, yet the role of UPR in pancreatitis is yet to be fully understood. We hypothesized that redox stressors, such as alcohol, will increase UPR; we further predicted that UPR exacerbation will lead to advanced pancreatic tissue damage and thus development of pancreatitis. Methods: We analyzed pancreas tissue from humans with alcoholic pancreatitis and C57Bl6 mice with alcohol+/-LPS-induced pancreatitis; tissue was analyzed by histology, enzyme biochemically, proteins by Western and RNA by PCR assays. Results: We report significant UPR activation in humans with pancreatitis, manifested as increased expression of PERK, eIF2α, Ire1α-Xbp-1, and XBP1 target protein disulfide isomerase (PDI) RNA levels. We identified similarly increased expression of PERK, eIF2α, Ire1α-Xbp-1, and PDI RNA in pancreas tissue of mice fed alcohol, yet the pancreas histology in these mice looked normal and there was no elevation of serum lipase. Challenges of alcohol-fed mice with LPS caused disorganized and dilated ER, loss of zymogen granules, accumulation of vacuoles, increased acinar cell death detected by microscopy, and lead to elevated serum lipase/activated zymogen suggestive of pancreatitis. More importantly, alcohol+LPS had additive effects on increased expression of PERK, eIF2α, Ire1α-Xbp-1, and PDI RNA levels, lead to increased production of several pro-inflammatory mediators (TNFa, IL-6), increased P-c-JUN, CHOP, and cleavage of caspase-3. These findings suggest that UPR occurs in stressed pancreatic tissue, in our case by exposure to alcohol, prior to biochemical signature (elevated pancreatic enzymes and altered histology) of pancreatitis. Further, multi-hit oxidative stressors, such as combination of alcohol and LPS, exacerbate alcohol-induced UPR and facilitate translation to florid pancreatitis with elevated serum levels of pancreatic enzymes, signs of inflammation, and tissue remodeling on histology. Conclusion: Our findings point to an early role of UPR in pancreatitis even prior to evident biochemical signature in the serum and tissue, and identify UPR-based therapeutic targets of potential translational importance.