Modeling protease-sensitive human pancreatic lipase mutations in the mouse ortholog

Pancreatic lipase (PNLIP) is the major lipolytic enzyme secreted by the pancreas. A recent study identified human PNLIP variants P245A, I265R, F300L, S304F, and F314L in European cohorts with chronic pancreatitis. Functional analyses indicated that the variants were normally secreted but exhibited reduced stability when exposed to pancreatic proteases. Proteolysis of the PNLIP variants yielded an intact C-terminal domain, while the N-terminal domain was degraded. The protease-sensitive PNLIP phenotype was strongly correlated with chronic pancreatitis, suggesting a novel pathological pathway underlying the disease. To facilitate preclinical mouse modeling, here we investigated how the human mutations affected the secretion and proteolytic stability of mouse PNLIP. We found that variants I265R, F300L, S304F, and F314L were secreted at high levels, while P245A had a secretion defect and accumulated inside the cells. Proteolysis experiments indicated that wild-type mouse PNLIP was resistant to cleavage, while variant I265R was readily degraded by mouse trypsin and chymotrypsin C. Variants F300L, S304F, and F314L were unaffected by trypsin but were slowly proteolyzed by chymotrypsin C. The proteases degraded the N-terminal domain of variant I265R, leaving the C-terminal domain intact. Structural analyses suggested that changes in stabilizing interactions around the I265R mutation site contribute to the increased proteolytic susceptibility of this variant. The results demonstrate that variant I265R is the best candidate for modeling the protease-sensitive PNLIP phenotype in mice.