Role of the ER acetyl CoA transporter in alcoholic pancreatitis

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ABSTRACT Chronic pancreatitis (CP), a painful, debilitating disorder of the exocrine pancreas, lacks treatments and strategies to prevent disease progression. Alcohol abuse and smoking are common causes of CP but the mechanisms underlying their toxic effects on the pancreas are unclear. Recently, adaptive mechanisms that prevent pancreatitis with stressors such as alcohol were identified in the pancreatic acinar cell. These adaptive mechanisms involve the endoplasmic reticulum (ER) Unfolded Protein Response (UPR) and the UPR transcription factor, X-box binding protein 1 (XBP1s) that upregulates ER chaperones, ER transporters, and quality control machinery to maintain ER function. Our previous work showed that alcohol administration induces oxidative stress but also upregulates XBP1s and a protective UPR that prevents pathology, while smoking inhibits alcohol induced XBP1s formation, and upregulates a pathologic UPR signal mediated by C/EBP homologous protein (CHOP) resulting in ER dysfunction and pancreatitis. This project investigates molecular determinants of pancreatitis associated with alcohol abuse, smoking and perturbed ER protein folding and trafficking. Reversible Nε-lysine acetylation regulates the efficiency of ER protein transit to Golgi and the secretory pathway. Acetylation of properly folded proteins enables ER-to-Golgi exit, while non- acetylated, misfolded proteins divert to protein degradation systems. Thus, disruption of ER protein acetylation perturbs ER function and protein trafficking. The acetyl CoA transporter, AT-1 mediates ER entry of acetyl CoA from cytoplasm to provide substrate for acetylation. In humans, the AT-1-S113R mutant reduces AT-1 transport capacity, and individuals with this mutant exhibit neurodegenerative disorders. We found that XBP1s regulates AT-1 levels in acinar cells. Moreover, AT-1S113r/+ or acinar-specific AT-1 deficient mice develop mild/ moderate CP and chronic ER stress with elevated XBP1s. Strikingly, AP induction in these mice decreases XBP1s levels and markedly exacerbates CP progression. Our results indicate AT-1 and XBP1s are interdependent and important for pancreas adaption in response to alcohol but when overwhelmed by environmental stressors these adaptive systems fail leading to pathology. Our overarching hypothesis is that chronic acinar cell stress and reduced XBP1s protective programs by drinking/smoking attenuate AT-1 expression, disrupting ER acetylation and ER function, and inducing severe CP. Using experimental models of alcoholic + smoking CP, we will pursue 3 aims. Aim 1 will test whether alcohol consumption/smoking converts mild/moderate CP into severe disease in acinar-specific AT-1 KO mice. Aim 2 will evaluate whether enhanced XBP1s expression or CHOP genetic deletion partially mitigates CP severity in AT-1 KO mice. Aim 3 will investigate ER acetylation pathway regulation of ER protein folding and trafficking as well as ER protein degradation. We expect this project to provide insights into the pathways driving CP development, and pinpoint molecular targets for strategies to halt CP progression.