Deficiency of cathepsin C ameliorates severity of acute pancreatitis by reduction of neutrophil elastase activation and cleavage of E-cadherin.

Acute pancreatitis is characterized by premature intracellular protease activation and infiltration of inflammatory cells, mainly neutrophil granulocytes and macrophages, into the organ. The lysosomal proteases cathepsin B, D, and L have been identified as regulators of early zymogen activation and thus modulators of the severity of pancreatitis. Cathepsin C (CTSC, syn. dipeptidly-peptidase I) is a widely expressed, exo-cystein-protease involved in the proteolytic processing of various other lysosomal enzymes. We have studied its role in pancreatitis. We used CTSC-deleted mice and their WT littermates in two experimental models of pancreatitis. The mild model involved eight hourly caerulein injections and the severe model partial duct ligation. Isolated pancreatic acini and spleen-derived leukocytes were used for ex vivo experiments. CTSC is expressed in the pancreas and in inflammatory cells. CTSC deletion reduced the severity of pancreatitis (more prominently in the milder model) without directly affecting intra-acinar cell trypsin activation in vitro The absence of CTSC reduced infiltration of neutrophil granulocytes impaired their capacity for cleaving E-cadherin in adherens junctions between acinar cells and reduced the activity of neutrophil serine proteases polymorphonuclear (neutrophil) elastase, cathepsin G, and proteinase 3, but not neutrophil motility. Macrophage invasion was not dependent on the presence of CTSC. CTSC is a regulator and activator of various lysosomal enzymes such as cathepsin B, D, and L. Its loss mitigates the severity of pancreatitis not by reducing intra-acinar cell zymogen activation but by reducing infiltration of neutrophil granulocytes into the pancreas. In this context one of its key roles is that of an activator of neutrophil elastase.

Cathepsin D regulates cathepsin B activation and disease severity predominantly in inflammatory cells during experimental pancreatitis.

Acute pancreatitis is a complex disorder involving both premature intracellular protease activation and inflammatory cell invasion. An initiating event is the intracellular activation of trypsinogen by cathepsin B (CTSB), which can be induced directly via G protein-coupled receptors on acinar cells or through inflammatory cells. Here, we studied CTSB regulation by another lysosomal hydrolase, cathepsin D (CTSD), using mice with a complete (CTSD-/-) or pancreas-specific conditional CTSD knockout (KO) (CTSDf/f/p48Cre/+). We induced acute pancreatitis by repeated caerulein injections and isolated acinar and bone marrow cells for ex vivo studies. Supramaximal caerulein stimulation induced subcellular redistribution of CTSD from the lysosomal to the zymogen-containing subcellular compartment of acinar cells and activation of CTSD, CTSB, and trypsinogen. Of note, the CTSD KO greatly reduced CTSB and trypsinogen activation in acinar cells, and CTSD directly activated CTSB but not trypsinogen in vitro During pancreatitis in pancreas-specific CTSDf/f/p48Cre/+ animals, markers of severity were reduced only at 1 h, whereas in the complete KO, this effect also included the late disease phase (8 h), indicating an important effect of extra-acinar CTSD on course of the disease. CTSD-/- leukocytes exhibited reduced cytokine release after lipopolysaccharide (LPS) stimulation, and CTSD KO also reduced caspase-3 activation and apoptosis in acinar cells stimulated with the intestinal hormone cholecystokinin. In summary, CTSD is expressed in pancreatic acinar and inflammatory cells, undergoes subcellular redistribution and activation during experimental pancreatitis, and regulates disease severity by potently activating CTSB. Its impact is only minimal and transient in the early, acinar cell-dependent phase of pancreatitis and much greater in the later, inflammatory cell-dependent phase of the disease.

Absence of the neutrophil serine protease cathepsin G decreases neutrophil granulocyte infiltration but does not change the severity of acute pancreatitis.

Acute pancreatitis is characterized by an early intracellular protease activation and invasion of leukocytes into the pancreas. Cathepsins constitute a large group of lysosomal enzymes, that have been shown to modulate trypsinogen activation and neutrophil infiltration. Cathepsin G (CTSG) is a neutrophil serine protease of the chymotrypsin C family known to degrade extracellular matrix components and to have regulatory functions in inflammatory disorders. The aim of this study was to investigate the role of CTSG in pancreatitis. Isolated acinar cells were exposed to recombinant CTSG and supramaximal cholezystokinin stimulation. In CTSG-/- mice and corresponding controls acute experimental pancreatitis was induced by serial caerulein injections. Severity was assessed by histology, serum enzyme levels and zymogen activation. Neutrophil infiltration was quantified by chloro-acetate ersterase staining and myeloperoxidase measurement. CTSG was expessed in inflammatory cells but not in pancreatic acinar cells. CTSG had no effect on intra-acinar-cell trypsinogen activation. In CTSG-/- mice a transient decrease of neutrophil infiltration into the pancreas and lungs was found during acute pancreatitis while the disease severity remained largely unchanged. CTSG is involved in pancreatic neutrophil infiltration during pancreatitis, albeit to a lesser degree than the related neutrophil (PMN) elastase. Its absence therefore leaves pancreatitis severity essentially unaffected.