A common CTRB misfolding variant associated with pancreatic cancer risk causes ER stress and inflammation in mice

Abstract

ObjectiveGenome wide association studies have identified an exon 6 CTRB2 deletion variant that associates with increased risk of pancreatic cancer. To acquire evidence on its causal role, we developed a new mouse strain carrying an equivalent variant in Ctrb1, the mouse orthologue of CTRB2. DesignWe used CRISPR/Cas9 to introduce a 707bp deletion in Ctrb1 encompassing exon 6 (Ctrb1{Delta}exon6). This mutation closely mimics the human deletion variant. Mice carrying the mutant allele were extensively profiled at 3 months to assess their phenotype. ResultsCtrb1{Delta}exon6 mutant mice express a truncated CTRB1 that accumulates in the ER. The pancreas of homozygous mutant mice displays reduced chymotrypsin activity and total protein synthesis. The histological aspect of the pancreas is inconspicuous but ultrastructural analysis shows evidence of dramatic ER stress and cytoplasmic and nuclear inclusions. Transcriptomic analyses of the pancreas of mutant mice reveals acinar program down-regulation and increased activity of ER stress-related and inflammatory pathways. Heterozygous mice have an intermediate phenotype. Agr2 is one of the most up-regulated genes in mutant pancreata. Ctrb1{Delta}exon6 mice exhibit impaired recovery from acute caerulein-induced pancreatitis. Administration of TUDCA or sulindac partially alleviates the phenotype. A transcriptomic signature derived from the mutant pancreata is significantly enriched in normal human pancreas of CTRB2 exon 6 deletion variant carriers from the GTEx cohort. ConclusionsThis mouse strain provides formal evidence that the Ctrb1{Delta}exon6 variant causes ER stress and inflammation in vivo, providing an excellent model to understand its contribution to pancreatic ductal adenocarcinoma development and to identify preventive strategies. SUMMARY BOX What is already known about this subject?- CTRB2 is one of the most abundant proteins produced by human pancreatic acinar cells. - A common exon 6 deletion variant in CTRB2 has been associated with an increased risk of pancreatic ductal adenocarcinoma. - Misfolding of digestive enzymes is associated with pancreatic pathology. What are the new findings?- We developed a novel genetic model that recapitulates the human CTRB2 deletion variant in the mouse orthologue, Ctrb1. - Truncated CTRB1 misfolds and accumulates in the ER; yet, mutant mice display a histologically normal pancreas at 3 months age. - CTRB1 and associated chaperones colocalize in the ER, the cytoplasm, and the nucleus of acinar cells. - Transcriptomics analysis reveals reduced activity of the acinar program and increased activity of pathways involved in ER stress, unfolded protein response, and inflammation. - Mutant mice are sensitized to pancreatic damage and do not recover properly from a mild caerulein-induced pancreatitis. - TUDCA administration partially relieves the ER stress in mutant mice. How might it impact on clinical practice in the foreseeable future?- The new mouse model provides a tool to identify the mechanisms leading to increased pancreatic cancer risk in CTRB2 exon 6 carriers. - The findings suggest that drugs that cause ER stress relief and/or reduce inflammation might provide preventive opportunities.