Heterozygous Spink1 Deficiency Promotes Trypsin-dependent Chronic Pancreatitis in Mice.

BACKGROUND & AIMS: Heterozygous SPINK1 mutations are strong risk factors for chronic pancreatitis in humans, yet heterozygous disruption of mouse Spink1 yielded no pancreatic phenotype. To resolve this contradiction, we used CRISPR/Cas9-mediated genome editing to generate heterozygous Spink1-deleted mice (Spink1-KOhet) in the C57BL/6N strain and studied the effect of this allele in trypsin-independent and trypsin-dependent pancreatitis models. METHODS: We investigated severity of acute pancreatitis and progression to chronic pancreatitis in Spink1-KOhet mice after transient (10 injections) and prolonged (2 × 8 injections) cerulein hyperstimulation. We crossed Spink1-KOhet mice with T7D23A and T7D22N,K24R mice that carry strongly autoactivating trypsinogen mutants and exhibit spontaneous chronic pancreatitis. RESULTS: Prolonged but not transient cerulein stimulation resulted in increased intrapancreatic trypsin activity and more severe acute pancreatitis in Spink1-KOhet mice relative to the C57BL/6N control strain. After the acute episode, Spink1-KOhet mice developed progressive disease with chronic pancreatitis-like features, whereas C57BL/6N mice recovered rapidly. Trypsinogen mutant mice carrying the Spink1-KOhet allele exhibited strikingly more severe chronic pancreatitis than the respective parent strains. CONCLUSIONS: Heterozygous Spink1 deficiency caused more severe acute pancreatitis after prolonged cerulein stimulation and promoted chronic pancreatitis after the cerulein-induced acute episode, and in two strains of trypsinogen mutant mice with spontaneous disease. In contrast, acute pancreatitis induced with limited cerulein hyperstimulation was unaffected by heterozygous Spink1 deletion, in agreement with recent observations that trypsin activity does not mediate pathologic responses in this model. Taken together, the findings strongly support the notion that loss-of-function SPINK1 mutations in humans increase chronic pancreatitis risk in a trypsin-dependent manner

Mesotrypsin Signature Mutation in a Chymotrypsin C (CTRC) Variant Associated with Chronic Pancreatitis

Human chymotrypsin C (CTRC) protects against pancreatitis by degrading trypsinogen and thereby curtailing harmful intra-pancreatic trypsinogen activation. Loss-of-function mutations in CTRC increase the risk for chronic pancreatitis. Here we describe functional analysis of eight previously uncharacterized natural CTRC variants tested for potential defects in secretion, proteolytic stability, and catalytic activity. We found that all variants were secreted from transfected cells normally, and none suffered proteolytic degradation by trypsin. Five variants had normal enzymatic activity, whereas variant p.R29Q was catalytically inactive due to loss of activation by trypsin and variant p.S239C exhibited impaired activity possibly caused by disulfide mispairing. Surprisingly, variant p.G214R had increased activity on a small chromogenic peptide substrate but was markedly defective in cleaving bovine β-casein or the natural CTRC substrates human cationic trypsinogen and procarboxypeptidase A1. Mutation p.G214R is analogous to the evolutionary mutation in human mesotrypsin, which rendered this trypsin isoform resistant to proteinaceous inhibitors and conferred its ability to cleave these inhibitors. Similarly to the mesotrypsin phenotype, CTRC variant p.G214R was inhibited poorly by eglin C, ecotin, or a CTRC-specific variant of SGPI-2, and it readily cleaved the reactive-site peptide bonds in eglin C and ecotin. We conclude that CTRC variants p.R29Q, p.G214R, and p.S239C are risk factors for chronic pancreatitis. Furthermore, the mesotrypsin-like CTRC variant highlights how the same natural mutation in homologous pancreatic serine proteases can evolve a new physiological role or lead to pathology, determined by the biological context of protease function

Overlapping Specificity of Duplicated Human Pancreatic Elastase 3 Isoforms and Archetypal Porcine Elastase 1 Provides Clues to Evolution of Digestive Enzymes

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