Abstract
Bradykinin (BK), generated from high-molecular-weight kininogen (HK) is the major mediator of swelling attacks in hereditary angioedema (HAE), a disease associated with C1-inhibitor deficiency. Plasma kallikrein, activated by factor XIIa, is responsible for most of HK cleavage. However other proteases, which activate during episodes of angioedema, might also contribute to BK production. The lectin pathway of the complement system activates after infection and oxidative stress on endothelial cells generating active serine proteases: MASP-1 and MASP-2. Our aim was to study whether activated MASPs are able to digest HK to release BK. Initially we were trying to find potential new substrates of MASP-1 in human plasma by differential gel electrophoresis, and we identified kininogen cleavage products by this proteomic approach. As a control, MASP-2 was included in the study in addition to MASP-1 and kallikrein. The proteolytic cleavage of HK by MASPs was followed by SDS-PAGE, and BK release was detected by HPLC. We showed that MASP-1 was able to cleave HK resulting in BK production. MASP-2 could also cleave HK but could not release BK. The cleavage pattern of MASPs is similar but not strictly identical to that of kallikrein. The catalytic efficiency of HK cleavage by a recombinant version of MASP-1 and MASP-2 was about 4.0×102 and 2.7×102 M−1s−1, respectively. C1-inhibitor, the major inhibitor of factor XIIa and kallikrein, also prevented the cleavage of HK by MASPs. In all, a new factor XII- and kallikrein-independent mechanism of bradykinin production by MASP-1 was demonstrated, which may contribute to the pro-inflammatory effect of the lectin pathway of complement and to the elevated bradykinin levels in HAE patients.
Highlights
Bradykinin (BK) is a potent proinflammatory peptide that is released from its precursors high-molecular-weight kininogen (HK) and low-molecular-weight kininogen (LK) by means of limited proteolysis
In the present work we demonstrate that Mannose-Binding Lectin-Associated Serine Protease (MASP)-1 is capable of digesting HK to release BK
We found that recombinant MASP-1 catalytic fragment (rMASP-1) is able to cleave HK, slower than kallikrein
Summary
Bradykinin (BK) is a potent proinflammatory peptide that is released from its precursors high-molecular-weight kininogen (HK) and low-molecular-weight kininogen (LK) by means of limited proteolysis. The contact activation system is the major source of BK production in plasma. It is a proteolytic cascade system in the blood that can be activated by incubation of plasma with negatively charged artificial surfaces (e.g. glass, kaolin) or with certain biological macromolecules (e.g. LPS, amyloid b protein) bound to the surface of different cell types, including endothelial cells, platelets, and polymorphonuclear neutrophils [7]. Most of the prekallikrein (about 85%) can be found in equimolar complex with HK which can bind to cell surfaces [1,2,8] In this way contact system activation results in immediate BK release on the cells, to which its components are bound
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