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Generation of biologically active, complement-(C5) derived peptides by cathepsin H
Abstract:
The thiol proteinase cathepsin H, isolated and purified from rat liver lysosomes, provokes acute inflammation characterized by the accumulation of polymorphonuclear leukocytes (PMN) when injected intracutaneously into newborn rats. We have examined the possibility that the accumulation of PMN at skin sites injected with cathepsin H is due, in part, to generation locally of C-derived chemotactic factors. We have found that cathepsin H acts in a concentration- and time-dependent fashion in whole human (and rat) EDTA-plasma to generate C5-derived peptides with chemotactic activity for PMN. Chemotactic activity was not generated in EDTA-plasma by either heat-inactivated cathepsin H or by a combination of active enzyme and a thiol proteinase inhibitor isolated from rat epidermis. Cathepsin H also acted in a concentration- and time-dependent fashion on isolated (functionally pure) human C5 to yield chemotactic activity for PMN as well as PMN lysosomal enzyme-releasing activity. Whereas 10 ng/ml cathepsin H generated significant chemotactic activity from isolated C5 (1000 CH50 U/ml), 7 to 10 micrograms/ml were required to generate chemotactic activity in whole EDTA-plasma. Cathepsin H not only was capable of generating biologically active, C5-derived peptides, but also was capable of degrading these peptides. Incubation of either whole EDTA-plasma or isolated C5 with high concentrations of cathepsin H (e.g., 25 micrograms/ml and 100 ng/ml, respectively) caused the rapid appearance of chemotactic activity followed by an equally rapid disappearance. PMN accumulated more rapidly in the skin of newborn rats injected with cathepsin H-treated C5 than in the skin of animals injected with cathepsin H alone. These data suggest that generation by cathepsin H of C-derived chemotactic activity contributes to the ability of this enzyme to induce dermal inflammation.
Insights
Cathepsin H, a thiol proteinase, triggers inflammation by generating complement-derived chemotactic factors. This enzyme activates complement component 5 (C5) in plasma, attracting polymorphonuclear leukocytes (PMN) to inflammatory sites.
Area of Science:
- Biochemistry
- Immunology
- Inflammation Research
Background:
- Cathepsin H is a thiol proteinase found in rat liver lysosomes.
- Intracutaneous injection of cathepsin H in newborn rats causes acute inflammation and polymorphonuclear leukocyte (PMN) accumulation.
Purpose of the Study:
- To investigate if cathepsin H generates complement (C)-derived chemotactic factors, contributing to PMN accumulation during inflammation.
- To determine the role of cathepsin H in activating complement component 5 (C5) and its subsequent effects.
Main Methods:
- Incubation of human and rat EDTA-plasma with purified rat liver cathepsin H.
- Treatment of isolated human C5 with cathepsin H.
- Assays for PMN chemotactic activity and lysosomal enzyme release.
- Intracutaneous injections in newborn rats to assess inflammatory responses.
Main Results:
- Cathepsin H generated C5-derived peptides with PMN chemotactic activity in a concentration- and time-dependent manner in EDTA-plasma.
- Active cathepsin H, but not heat-inactivated enzyme or enzyme with a thiol proteinase inhibitor, generated chemotactic activity.
- Cathepsin H also induced PMN lysosomal enzyme release from isolated C5.
- Higher concentrations of cathepsin H degraded the generated chemotactic peptides.
- PMN accumulation was more pronounced with cathepsin H-treated C5 compared to cathepsin H alone.
Conclusions:
- Cathepsin H generates C-derived chemotactic activity by activating C5, contributing to PMN recruitment in inflammatory responses.
- The enzyme's dual role in both generating and degrading chemotactic factors influences the inflammatory process.
- These findings highlight cathepsin H as a mediator of inflammation through complement system activation.