The complex role of kininogens in hereditary angioedema

Abstract

Human high molecular weight kininogen (HK) is the substrate from which bradykinin is released as a result of activation of the plasma "contact" system, a cascade that includes the intrinsic coagulation pathway, and a fibrinolytic pathway leading to the conversion of plasminogen to plasmin. Its distinction from low molecular weight kininogen (LK) was first made clear in studies of bovine plasma. While early studies did suggest two kininogens in human plasma also, their distinction became clear when plasma deficient in HK or both HK and LK were discovered. The light chain of HK is distinct and has the site of interaction with negatively charged surfaces (domain 5) plus a 6th domain that binds either prekallikrein or factor XI. HK is a cofactor for multiple enzymatic reactions that relate to the light chain binding properties. It augments the rate of conversion of prekallikrein to kallikrein and is essential for the activation of factor XI. It indirectly augments the "feedback" activation of factor XII by plasma kallikrein. Thus, HK deficiency has abnormalities of intrinsic coagulation and fibrinolysis akin to that of factor XII deficiency in addition to the inability to produce bradykinin by factor XII-dependent reactions. The contact cascade binds to vascular endothelial cells and HK is a critical binding factor with binding sites within domains 3 and 5. Prekallikrein (or factor XI) is attached to HK and is brought to the surface. The endothelial cell also secretes proteins that interact with the HK-prekallikrein complex resulting in kallikrein formation. These have been identified to be heat shock protein 90 (HSP 90) and prolylcarboxypeptidase. Cell release of urokinase plasminogen activator stimulates fibrinolysis. There are now 6 types of HAE with normal C1 inhibitors. One of them has a mutated kininogen but the mechanism for overproduction (presumed) of bradykinin has not yet been determined. A second has a mutation involving sulfation of proteoglycans which may lead to augmented bradykinin formation employing the cell surface reactions noted above.

Keywords: angioedema; bradykinin; kallikrein; kininogen; vascular permeability.

Figure 1

(A) Sephadex G-200 gel filtration of reduced kinin-free HMW kininogen. The absorbance at 280 nm is shown (black line) in addition to the ability of fractions to correct the partial thromboplastin time of HK kininogen-deficient plasma (white line). Above (inset) is shown the SDS-PAGE pattern obtained after electrophoresis of 100 μl of tubes 60, 65, 70, and 75 (heavy chain), and electrophoresis of 100 μl of a 10-fold concentration of tubes 80, 85, and 90 (light chain). (B) Urea disc gel electrophoresis of samples taken from the Sephadex G-200 gel filtration of reduced kinin-free HWM kininogen [in this figure (A)]. A 100 μl of tubes 60, 65, 70, and 75 followed by 100 μl of a 20-fold concentration of tubes 80, 85, and 90 were applied. A replicate gel was sliced, each slice was eluted with 0.2 ml phosphate-buffered saline, and the eluates were assayed for their ability to correct the partial thromboplastin time of HMW kininogen-deficient plasma. The peaks of coagulant activity seen at slices 36–38 and 40–44 correspond to the two fainter light chain bands seen on the right side of the gel.

Figure 2

Gel filtration of human plasma on Sephadex G-200. The OD 280 indicates 3 protein peaks. The location of factor XI, prekallikrein, factor XII (Hageman factor) and plasminogen was identified immunologically. The molecular sizes of factor XI and prekallikrein reflect the binding of each to HK.

Figure 3

Depiction of the structure of human HWM kininogen and the consequences of cleavages at the sites indicated. The amino-terminal portion (heavy chain of cleaved kininogen) has the cysteine protease inhibitor activation. The light chain of cleaved HWM kininogen serves as the cofactor function in coagulation, fibrinolysis, and initiation of bradykinin formation.

Figure 4

Addition of ¹²⁵I—factor XI (solid lines) or ¹²⁵I—prekallikrein (dotted line) to surface-bound light chain or heavy chain purified from HK. The counts bound (vertical) per moles added (horizontal) are plotted.

Figure 5

The gene structure for HK and LK. The boxes labeled 1–9 represent the exon coding for the heavy chain of HK and LK. Exon 10 codes for the bradykinin sequence and the light chain of HK. The respective mRNA's are assembled by alternative spicing events in which the light chain sequences are attached to the 3′ end of the 10 amino acid sequence C-terminal to bradykinin. Attachment of exon 10 in its entirety produces HK. Splicing of exon 10 (blackened portion) to exon 11 produces LK. Reproduced from Kitamura et al. (27).

Figure 6

Localization of gC1qR on HUVEC's by immunochemical staining. Monolayer cultures of HUVECs on slides are fixed using 4% formaldehyde. The cells were first probed with rabbit anti gC1qR antibody and subsequently with horse radish -labeled goat anti-rabbit IgG. The gC1qR was visualized by 3,3-diaminobenzidine. Preimmune rabbit IgG staining showed no signal (A) and the anti-gC1qR antibody stained at the cell surface in non-permobilized cells (B) while in permimobilized cells (C), the perinuclear and nuclear regions were prominently stained. In D, the cells were treated as in (B) but the antibody was pretreated with excess recombinant gC1qR.

Figure 7

A diagrammatic representation of the zinc-dependent binding of HK-prekallikrein and factor XII to the surface, employing primarily complexes of gC1qR-cytokeratin-1 and cytokeratin 1—uPAR, respectively. Activation of factor XII, or activation of HK-prekallikrein by HSP 90, results in the formation of both factor XIIa and kallikrein. The latter digests HK to release bradykinin which binds to the B-2 receptor to increase vascular permeability.

Figure 8

Schematic of the suggested involvement of 3-OST-6 in HK docking on the endothelial cell surface. The upper panel shows the normal (wild type) situation with HK being taken up via endocytosis due to interaction with heparan sulfate (HS)-containing proteoglycans. This prevents cleavage and bradykinin production. The lower panel shows the mutant situation: Because of incomplete HS modification, HK interacts with alternative interaction partners on the cell surface. This does not result in endocytosis and allows for HK cleavage and increased bradykinin production. The bar at the right indicates a shift in the balance of bradykinin production. Reproduced with permission: Bork et al. (60).