Human <i>CPA1</i> mutation causes digestive enzyme misfolding and chronic pancreatitis in mice.

Abstract

Chronic pancreatitis is a progressive, relapsing inflammatory disorder of the pancreas, which often develops in the background of genetic susceptibility. Recently, loss-of-function mutations in <i>CPA1</i>, which encodes the digestive enzyme carboxypeptidase A1, were described in sporadic early onset cases and in hereditary pancreatitis. Mutation-induced misfolding of CPA1 and associated endoplasmic reticulum (ER) stress was suggested as potential disease mechanism; however, in vivo evidence has been lacking. The objective of the present study was to create a mouse model that recapitulates features of <i>CPA1</i>-associated chronic pancreatitis. We knocked-in the most frequently occurring p.N256K human <i>CPA1</i> mutation to the mouse <i>Cpa1</i> locus. Mutant mice were characterised with respect to pancreas pathology and ER stress and compared with C57BL/6N and <i>CPA1 null</i> control mice. In the <i>CPA1 N256K</i> mutant mice, we observed hallmarks of chronic pancreatitis that included progressive acinar cell atrophy, inflammatory cell infiltration, fibrosis and acinar-ductal metaplasia. In contrast, similarly to the C57BL/6N mice, the <i>CPA1 null</i> control strain exhibited no signs of pancreatic disease. Mutation p.N256K induced misfolding of mouse CPA1 and resulted in elevated expression of ER stress markers <i>Hspa5</i> (BiP) and <i>Ddit3</i> (CHOP) both in cell culture and mutant mice. The results offer categorical evidence that <i>CPA1</i> mutations elicit enzyme misfolding and cause chronic pancreatitis via an ER stress-related mechanism.