ALBERT

Description: Plasma high molecular weight kininogen (HK) is cleaved in inflammatory diseases by kallikrein to cleaved HK (HKa). We have reported that HKa releases cytokines (TNFα , IL-1β , IL-6) and chemokines (IL-8 and MCP-1) from isolated human peripheral blood monocytes. At a concentration of 600nM, Glutathione -S- transferase (GST) fusion proteins of kininogen domain 3 (D3), E7P - an active fragment of domain 3 (aaG255-Q292), HK domain 5 (D5), and D5 recombinant peptide HG (aa K420-D474) each stimulated secretion of IL-1β from monocytes. Receptors on monocytes including Mac-1, LFA-1, uPAR and gC1qR are required for IL-1β secretion from monocytes. We now report the signaling pathways and evidence for synthesis of IL-1 β in monocytes stimulated by HKa. Inhibitors of signaling pathways initiated by NFkB, JNK and p38, but not ERK, decreased IL-1b release from monocytes. A specific inhibitor of NFkB, MG-132 (1, 10 and 100 μM) significantly reduced IL-1β release from monocytes by 69.7, 67.3, 88.5% respectively, when stimulated by GST-E7P. The release of IL-1β by LPS (10 μg/ml), was blocked 83.4% by MG-132 (100 μM). A specific inhibitor of JNK, SP 600125 (1, 10 and 100 μM) significantly reduced IL-1β release from monocytes by 55.7, 76.3, 78.9% respectively, when stimulated by GST-E7P. The release of IL-1β by LPS (10 μg/ml), was blocked 90.23% by SP 600125 (100 μM). A specific inhibitor of p38, SB202190 (1,10 and 100 μM) significantly reduced IL-1β release from monocytes by 27.8, 14.2, 91.0% respectively, when stimulated by E7P. The release of IL-1β by LPS (10 μg/ml), was blocked 76.8 % by SB202190 (100 μM). In contrast, the ERK activation inhibitor U0126 (1, 10 and 100 μM) failed to inhibit GST-E7P-induced release of IL-1β from monocytes but the release of IL-1β with LPS (10 μg/ml), was blocked by 77.4% at 100 μM. After monocytes (4 X 106/ml) were treated with HKa (600 nM) or LPS (10 ng/ml), total RNA was extracted and RT-PCR reactions for expression of IL-1β and gC1qR mRNA using specific primers were carried out. PCR products was separated in 4% ethidium bromide-stained agarose gels and photographed. No IL-1b mRNA was detected prior to exposure to HKa or LPS but both were detected at 1 hour. In contrast, gC1qR mRNA was present without stimulation by HKa. HKa domains 3 and 5 may contribute to the pathogenesis of inflammatory diseases by stimulating the synthesis and release of IL-1β from human monocytes using intracellular signaling pathways initiated by uPAR, β 2 integrins and gC1qR receptors.

Description: Proteolytic cleavage of single-chain high molecular weight kininogen (HK) by kallikrein releases the short-lived vasodilator bradykinin and leaves behind 2-chain high molecular weight kininogen (HKa) that has been previously reported to exert antiadhesive properties as well as to bind to the urokinase receptor (uPAR) on endothelial cells. In this study we defined the molecular mechanisms for the antiadhesive effects of HKa related to disruption of integrin- and uPAR-mediated cellular interactions. Vitronectin (VN) but not fibrinogen or fibronectin-dependent vβ3 integrin–mediated adhesion of endothelial cells was blocked by HKa or its isolated domain 5. In a purified system, HKa but not HK competed for the interaction of VN with vβ3 integrin, because HKa and the isolated domain 5 but not HK bound to both multimeric and native VN in a Zn2+-dependent manner. The interaction between HKa or domain 5 with VN was prevented by heparin, plasminogen activator inhibitor-1, and a recombinant glutathione-S-transferase (GST)-fusion peptide GST-VN (1-77) consisting of the amino terminal portion of VN (amino acids 1-77), but not by a cyclic arginyl-glycyl-aspartyl peptide, indicating that HKa interacts with the amino terminal portion of VN (“somatomedin B region”). Furthermore, we have confirmed that HKa but not HK bound to uPAR and to the truncated 2-domain form of uPAR lacking domain 1 in a Zn2+-dependent manner. Through these interactions, HKa or its recombinant His-Gly-Lys–rich domain 5 completely inhibited the uPAR-dependent adhesion of myelomonocytic U937 cells and uPAR-transfected BAF-3 cells to VN and thereby promoted cell detachment. By immunogold electron microscopy, both VN and HK/HKa were found to be colocalized in sections from human atherosclerotic coronary artery, indicating that the described interactions are likely to take place in vivo. Taken together, HK and HKa inhibit different VN-responsive adhesion receptor systems and may thereby influence endothelial cell- or leukocyte-related interactions in the vasculature, particularly under inflammatory conditions.

Description: The activity of phosphodiesterase (PDE)3A requires divalent cations. Putative metal-binding sites are expected at 2 highly conserved metal-binding motifs, HXXXH(X)25E. A functional truncated recombinant PDE3A containing the catalytic domain (PDE3A▵1) and mutant proteins were expressed in a baculovirus/Sf9 cell system. All the mutant proteins had decreased catalytic efficiency (kcat/Km). Mutants H752A, H756A, and E825A had kcat of less than 0.0008 s−1 to 0.0475 s−1 compared to PDE3A▵1, with 1.86 second−1, with unchanged Km. Although E866A had a kcat of 0.235 s−1, the Kmfor cyclic adenosine monophosphate (cAMP) was increased 11-fold and the Ki for cyclic guanosine monophosphate (cGMP) was 27-fold higher than PDE3A▵1. The Ki of H836A for cGMP was 177-fold higher than that of PDE3A▵1. The Km for E971A was 5-fold higher than PDE3A▵1. These results suggest that the cAMP and cGMP binding sites are overlapping, but not identical, involving both common and different amino acids. Mutants E825A, H836A, and E866A showed low activity in a metal ion-free assay; however, their enzymatic activities were increased 4- to 10-fold in buffers containing Mn2+, Mg2+, or Co2+. This observation indicates that conserved amino acids in the second metal-binding motif might not be involved in binding divalent cations but may serve other functions such as substrate or inhibitor binding in PDE3A.

Description: The plasma kallikrein–kinin system (KKS) plays an important role in inflammation, thrombosis and vascular pathology. Activation of the KKS results in bradykinin release, which increases vascular permeability and modulates inflammatory responses. Circulating endothelial progenitor cells (EPCs) home to ischemic and inflamed tissues and participate in the vasculogenesis. However, the homing mechanism remains poorly understood. We now report that activation of the KKS regulates the homing property of EPCs using in vivo and in vitro approaches. We have previously shown that the Lewis rat, which displays a mutant kininogen (Ser511Ala), is susceptible to peptidoglycan-polysaccharide (PG-PS)- induced systemic inflammation including arthritis and displays activation of the KKS and increased bradykinin levels. CD34-positive EPCs were isolated from bone marrow of disease-free Lewis rats by Ficoll gradient centrifugation. After culture in EGM2 on collagen surfaces for 7 days, a single colony with cobblestone-like morphology appeared and was subjected to large-scale expansion. Compared with differentiated rat lung microvessel endothelial cells (rLMECs), rat EPCs expressed similar levels of endothelial cell lineage marker mRNA such as VE-cadherin, CD31, vWF and uPAR. EPCs exclusively expressed hematopoietic progenitor cell markers, Sca-1 and CD34. Both of EPCs and rLMECs expressed bradykinin type 2 receptor (B2R) but not B1R. To observe the in vivo mobilization of EPCs, EPCs were labeled with carboxyfluorescein diacetate, succinimidyl ester (CFDA-SE) and injected into Lewis rats in which inflammation/arthritis was induced by PG-PS. Two weeks after PG-PS injection, pannus formed in the synovial tissues, representing the entry into the chronic phase of arthritis. The fluorescently-labeled EPCs were selectively detected in the inflamed synovium of PG-PS-treated rats, but not that of disease-free rats. As detected by confocal microscopy, implanted EPCs formed new blood vessels in the inflamed synovial tissues. To further investigate the mechanism by which the KKS regulates EPC mobilization, we observed that bradykinin (a B2R agonist), but not des-Arg9-bradykinin (a B1R agonist), stimulated EPC transmigration through confluent rLMEC layer at 100 and 1000 nM (P

Description: Circulating endothelial progenitor cells (EPCs) are involved in repairing damaged vasculature and in tumor angiogenesis, thus promoting wide interest in their therapeutic potential in ischemic diseases and cancer. Cleaved high molecular weight kininogen (HKa) potently inhibits endothelial cell (EC) functions including in vivo angiogenesis. We have shown that HKa inhibits differentiation of ECs. We now test a new hypothesis that HKa can inhibit EPC differentiation by blocking matrix metalloprotease-2 (MMP-2) activation. EPCs were isolated from human blood and cultured on collagen type I-coated surface. As detected by flow cytometry and Western-blot, they expressed MMP-2 and membrane-type 1-MMP (MT1-MMP), avb3 integrin, uPAR and caveolin-1, but did not express monocyte markers such as HLA-DR and CD14. A clone-forming assay using retroviral infection indicated that an early single EPC exhibited colony forming property, but mature ECs such as human umbilical vein endothelial cells (HUVECs) did not. Upon stimulation by VEGF, EPCs, but not HUVECs, formed vacuoles and differentiated into capillary networks. Gene silencing of either MT1-MMP or MMP-2 by siRNA completely blocked the vacuole and tube formation by EPCs, suggesting that MT1-MMP and MMP-2 are both essential for differentiation of EPCs. HKa inhibited tube formation by EPCs, as well as the conversion of pro-MMP-2 to MMP-2 as a functioning concentration in the conditioned medium. CS-1 cells expressing endogenous av subunit were transfected with human b3 cDNA. We found that HKa inhibition of MMP-2 activation in these cells is dependent on avb3 heterodimer. The binding of avb3 integrin to MMP-2 was via RGD-dependent and RGD-independent mechanisms, both of which, however, were completely blocked by HKa. Further, we found that HKa inhibited the association of MMP-2 with immunoprecipitated avb3 integrin, and prevented MMP-2 localization in caveolae in EPCs. Since HKa inhibited VEGF-stimulated proliferation of EPCs but not HUVECs on collagen-coated surface, we postulate that EPCs are more sensitive than mature ECs to HKa inhibition. Thus, HKa targets EPCs and inhibits their differentiation via blocking avb3 integrin and MMP-2 interaction. These observations provide novel insight into understanding the interactions between the kallikrein-kinin system and biologic functions of EPCs.

Description: Soluble plasma tissue factor (TF) circulates in picomolar concentrations in healthy individuals and increases in a wide spectrum of diseases. This study tests the hypothesis that both truncated or long length TF antigens in low concentrations combine with monocytes or platelets to convert factor VII (fVII) to fVIIa. Both recombinant truncated TF (rsTF, kDa 33) and long length (47 kDa) plasma TF (pTF), obtained from pericardial wounds of patients having cardiac surgery using cardiopulmonary bypass, were studied in association with blood cells and TF bearing microparticles. Tissue factor was measured by ELISA. RsTF binds to erythrocytes, platelets, mononuclear cells and neutrophils. The rate of fVII conversion with rsTF (1.0 – 103nmoles/L) is fastest with mononuclear cells, less with platelets, minimal with neutrophils and undetectable with erythrocytes. Both unstimulated and stimulated mononuclear cells or platelets in the presence of 3.5 pmoles/L rsTF or pTF convert fVII (10 nmoles/L) to fVIIa, but the amounts of fVIIa produced is greater in mononuclear cells. When leukocytes or platelets are absent, microparticles associated with 3.5 pmoles/L TF antigen, derived from pericardial wound plasma, do not activate fVII. Stimulated mononuclear cells convert nearly all available fVII (10 nmoles/L) to fVIIa with 3.5 pmoles/L pTF. Unstimulated mononuclear cells convert small amounts of fVII with as little as 1 pmole/L rsTF but no VIIa is produced by platelets, neutrophils or erythrocytes under these conditions. At all concentrations (0.001 to 1m moles/L) mononuclear cells more efficiently convert fVII to fVIIa than platelets. This study shows that stimulated mononuclear cells provide the most efficient phospholipid platform for activation of truncated or long length molecules of soluble TF at low concentrations of TF antigen. The results suggest a new mechanism by which soluble TF, which is increased in clinical inflammatory diseases, may lead to a prothrombotic state.

Description: When blood (plasma) contacts certain foreign surfaces, factor XII can activate and trigger a series of reactions leading to cleavage of kininogens with subsequent release of bradykinin. In this study, we investigated two different widely used leukocyte removal filters, Pall PXL8K (A) and Asahi PLS-5A (B), to test whether clinically significant contact activation occurred during leukodepletion of platelet-rich plasma (PRP). Kininogens were measured by particle concentration fluorescence immunoassay (PCFIA), which can detect cleavage of high and low molecular weight kininogens (HK and LK), the parent molecules of bradykinin, to determine if contact activation had occurred. A slight, nonsignificant decrease in HK and LK was observed with filter A after the first 5 mL was filtered that returned to prefiltration levels by the end of the filtration. Specific TotK (the combined measurement of HK and LK heavy chains divided by plasma protein concentration) showed a small, significant decrease with filter A after the first 5 mL of platelet concentrates was filtered that returned to prefiltration levels by the end of the filtration. There were no significant increases or decreases in the cleaved kininogen index (CKI), an index of HK proteolytic activation or HK and LK destruction (with release of bradykinin). These data suggest that small amounts of both HK and LK initially adsorb to filter A and then desorb, primarily intact. These data also indicate that no significant contact activation, as measured by PCFIA, occurs during leukodepletion of platelet concentrates with either filter A or B.

Description: We have shown that HKa inhibits angiogenesis by inducing detachment and apoptosis of human umbilical vein endothelial cells (HUVECs) from specific extracellular matrix proteins, such as vitronectin and fibrinogen, but not collagen. To investigate which intracellular signaling pathway led to cell detachment, several specific inhibitors were selected and utilized. SP600125, a JNK inhibitor, and PP2, a Src kinase inhibitor, both produced HUVECs detachment from surfaces coated with fibrinogen while MG-132, a NF-κB inhibitor, induced apoptosis. Neither U0126, an ERK inhibitor, nor SB202190, a p38 inhibitor, detached HUVECs from fibrinogen surfaces. By Western blot analysis, we found that HKa inhibited JNK, but not Src kinase activity. Previous investigators have demonstrated Rho-associated protein kinase (ROCK) regulates the JNK pathway. We demonstrated that Y27632, a ROCK inhibitor, not only inhibited JNK activity, but also caused detachment of HUVECs. Using phospho-antibodies, we found that HKa decreased the phosphorylation of paxillin at Ser178 site, but not Tyr 118 site indicating a serine kinase. Paxillin is a multi-domain adaptor found at the interface between the plasma membrane and the actin cytoskeleton. Paxillin phosphorylation is known to be associated with the coordinate formation of focal adhesions and stress fibres. Since the Ser178 of paxillin is a substrate for JNK, while Tyr 118 is a substrate for FAK and Src, it appears that JNK is responsible. Our studies have uncovered the novel finding that HKa detached HUVECs from fibrinogen through the ROCK-JNK-paxillin (Ser178) pathway, but not Src-paxillin (Tyr118) signaling.

Description: Bradykinin is a potent activator of endothelial cells and is known to induce vasodilation, vascular permeability, and nitric oxide production. Bradykinin signaling is initiated by binding to G protein-coupled bradykinin receptors 1 and 2 (B1R and B2R). In this study we investigated whether these two receptors are involved in regulation of endothelial progenitor cell (EPC) biology. First we isolated CD34+ cells from wild-type (WT) and double B1R and B2R knockout (B1RB2R-/-) mice, and compared their capacities of proliferation, migration, as well as tube formation in a 3D cell culture system. Bone marrow-derived B1RB2R-/- EPCs displayed a reduction in proliferation and migration through collagen-coated transwell, compared with EPCs from WT mice. Moreover, implanted B1RB2R-/- EPCs into immunocompromised NOD-SCID mice showed significantly less vasculogenesis in matrigel plug. Human EPCs were isolated from peripheral blood of healthy donors using CD34+ selection. In a concentration-dependent manner, bardykinin stimulated proliferation, migration and tube formation of human EPCs. In contrast to human EPCs, human umbilicial vein endothelial cells (HUVECs) did not display a significant increase in proliferation, migration, and tube formation upon bradykinin stimulation, suggesting that bradykinin selectively enhances the function of EPCs, but not mature endothelial cells. Pre-incubation with a B2R selective antagonist (Icatibant) reduced these functions of human EPCs. When human EPCs were stimulated with [des-Arg9]-BK, a selective B1R agonist, their proliferation and tube formation remained unchanged. Moreover, preincubation of human EPCs with [des-Arg10]-Icatibant, a B1R selective antagonist, did not affect their proliferation, migration and tube formation. As detected by Western blot and real time RT-PCR, B2R was constitutively expressed in EPCs, while the expression of B1R was only induced when stimulated by inflammatory stimuli, such as TNFα and IL-1β. Take together, bradykinin regulates proliferation, migration and tube formation of EPCs through constitutively expressed B2R, whereas B1R is probably involved in inflammatory settings. Disclosures No relevant conflicts of interest to declare.