Cathepsin L inactivates human trypsinogen, whereas cathepsin L-deletion reduces the severity of pancreatitis in mice.
OBJECTIVE
Acute pancreatitis is characterized by an activation cascade of digestive enzymes in the pancreas. The first of these, trypsinogen, can be converted to active trypsin by the peptidase cathepsin B (CTSB). We investigated whether cathepsin L (CTSL) can also process trypsinogen to active trypsin and has a role in pancreatitis.


METHODS
In CTSL-deficient (Ctsl(-/-)) mice, pancreatitis was induced by injection of cerulein or infusion of taurocholate into the pancreatic duct. Human tissue, pancreatic juice, mouse pancreatitis specimens, and recombinant enzymes were studied by enzyme assay, immunoblot, N-terminal sequencing, immunocytochemistry, and electron microscopy analyses. Isolated acini from Ctsl(-/-) and Ctsb(-/-) mice were studied.


RESULTS
CTSL was expressed in human and mouse pancreas, colocalized with trypsinogen in secretory vesicles and lysosomes, and secreted into pancreatic juice. Severity of pancreatitis was reduced in Ctsl(-/-) mice, whereas apoptosis and intrapancreatic trypsin activity were increased. CTSL-induced cleavage of trypsinogen occurred 3 amino acids toward the C-terminus from the CTSB activation site and resulted in a truncated, inactive form of trypsin and an elongated propeptide (trypsinogen activation peptide [TAP]). This elongated TAP was not detected by enzyme-linked immunosorbent assay (ELISA) but was effectively converted to an immunoreactive form by CTSB. Levels of TAP thus generated by CTSB were not associated with disease severity, although this is what the TAP-ELISA is used to determine in the clinic.


CONCLUSIONS
CTSL inactivates trypsinogen and counteracts the ability of CTSB to form active trypsin. In mouse models of pancreatitis, absence of CTSL induces apoptosis and reduces disease severity.
Wartmann
Thomas
T
Division of Experimental Surgery, Department of Surgery, Otto-von-Guericke-Universität Magdeburg, Magdeburg, Germany.
Mayerle
Julia
J
Kähne
Thilo
T
Sahin-Tóth
Miklós
M
Ruthenbürger
Manuel
M
Matthias
Rainer
R
Kruse
Anne
A
Reinheckel
Thomas
T
Peters
Christoph
C
Weiss
F Ulrich
FU
Sendler
Matthias
M
Lippert
Hans
H
Schulz
Hans-Ulrich
HU
Aghdassi
Ali
A
Dummer
Annegret
A
Teller
Steffen
S
Halangk
Walter
W
Lerch
Markus M
MM
D000681:Amylases / Q000378:metabolism; D000818:Animals; D017209:Apoptosis; D002401:Cathepsin B / Q000235:genetics / Q000378:metabolism; D056668:Cathepsin L / Q000235:genetics / Q000378:metabolism*; D002108:Ceruletide / Q000009:adverse effects; D004195:Disease Models, Animal; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008049:Lipase / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D010195:Pancreatitis / Q000139:chemically induced / Q000378:metabolism* / Q000473:pathology; D012720:Severity of Illness Index; D013656:Taurocholic Acid / Q000009:adverse effects; D014357:Trypsin / Q000378:metabolism; D014362:Trypsinogen / Q000378:metabolism*
D013656:Taurocholic Acid; D002108:Ceruletide; D014362:Trypsinogen; D008049:Lipase; D000681:Amylases; D014357:Trypsin; D002401:Cathepsin B; D056668:Cathepsin L