Characterization and regulation of the urokinase receptor of human endothelial cells

Mechanism by which Alcohol and Wine Polyphenols Affect Coronary Heart Disease Risk

The reduction in coronary heart disease (CHD) from moderate alcohol intake may be mediated, in part, by increased fibrinolysis; endothelial cell (EC)-mediated fibrinolysis should decrease acute atherothrombotic consequences (eg, plaque rupture) of myocardial infarction (MI). We have shown that alcohol and individual polyphenols modulate EC fibrinolytic protein (t-PA, u-PA, PAI-1, u-PAR and Annexin-II) expression at the cellular, molecular, and gene levels to sustain increased fibrinolytic activity. Herein we describe the sequence of molecular events by which EC t-PA expression is increased through common activation of p38 MAPK signaling. Up-regulation of t-PA gene transcription, through specific alcohol and polyphenol transcription factor binding sites in the t-PA promoter, results in increased in vitro fibrinolysis and in vivo clot lytic activity (using real-time fluorescence [Fl] imaging of Cy5.5-labeled fibrin clot lysis in a mouse model). Fl-labeled fibrin clots injected into untreated C56Bl/6 wild-type control mice are lysed in approximately 2 hours and clot lytic rates significantly increased in mice treated with either alcohol, catechins, or quercetin (4-6 weeks). Fl-labeled clot lysis in ApoE knock-out mice (atherosclerosis model) showed impaired in vivo clot lysis that was "normalized" to wild-type control levels by treatment with alcohol, catechin, or quercetin for 6 to 8 weeks.

Role of fibrin and plasminogen activators in repair-associated angiogenesis: in vitro studies with human endothelial cells

Angiogenesis, the formation of new blood vessels from existing ones, plays a central role in development and in a number of pathological conditions. Tissue repair-associated angiogenesis usually involves cell invasion into a fibrin structure and the presence of inflammatory cells. In this chapter the role of plasminogen activators in the dissolution of fibrin and the invasion of endothelial cells into a fibrin matrix is described. Tissue-type plasminogen activator is stored in endothelial cells and can be released acutely into the vessel lumen upon stimulation of the endothelium to activate fibrinolysis and to prevent fibrin deposition. At the basolateral side of the cell, urokinase-type plasminogen activator (uPA) bound to a specific cellular receptor is involved in the proteolytic modulation of matrix proteins and cell-matrix interaction. The cytokine tumor necrosis factor-alpha (TNF-alpha) cooperates with the angiogenic factors basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) in inducing human microvascular endothelial cells in vitro to invade a three dimensional fibrin matrix and to form capillary-like tubular structures. The formation of these capillary-like tubules requires cell-bound uPA activity.

Plasminogen activators augment endothelial cell organization in vitro by two distinct pathways

Endothelial cell differentiation into capillary structures is a complex process that requires the concerted effects of several extracellular matrix proteases, including plasminogen activators. Here, the role of tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) was evaluated in an in vitro model of endothelial morphogenesis involving organization of human umbilical vein endothelial cells into tubular structures when they are cultured on the basement membrane preparation, Matrigel. Both uPA and tPA were detected in HUVEC cultures on Matrigel, and inhibitors of plasminogen activators or of serine proteases decreased the extent of the tube network formed by the cells. The decrease resulting from serine protease inhibitors was additive to that from matrix metalloproteinase inhibitors which have previously been shown to decrease tube formation in this model, suggesting that the two classes of proteases modulate tube formation by distinct mechanisms. Plasminogen activator inhibitor (PAI)-1 decreased tube formation by 50% when added up to 4.5 h after the initiation of an 18 h assay and caused 25% inhibition when added 9.5 h after culture initiation, indicating that the effects of plasminogen activators are not limited to an early event in the differentiation process. Steady-state expression of mRNA for uPA increased during the first several hours of culture on Matrigel, further supporting a role for PA activity throughout the process of tube formation. These findings suggested that PAs may affect multiple events during tube-forming activity. A fucosylated peptide comprising the amino-terminal domain of uPA that binds to the uPA receptor (uPAR) but lacking proteolytic activity enhanced tube formation. In contrast, a defucosylated form of the same peptide had no effect. Since fucosylation of this fragment has been shown to be essential in other models of cell stimulation by uPA-uPAR interaction, these data support the hypothesis that uPA enhances endothelial morphogenesis both through proteolytic activity and via uPAR occupancy. Plasminogen activators could facilitate angiogenesis in vivo.

Plasminogen activator system in human coronary atherosclerosis

Altered coronary artery expression of plasminogen activator (PA) system components may predispose to thrombosis and modulate the vascular response to injury. By immunohistochemistry, we studied the expression of PAs (tPA and uPA), their major physiological inhibitor (PAI-1), and a receptor for uPA (uPAR) in human coronary arteries with either pure fibrointimal proliferation (n = 15) or developed atherosclerotic plaques (n = 10). Overall, the degree of staining showed the following rank order: PAI-1 > tPA > uPAR > uPA. A similar pattern was seen in two normal coronary arteries. There were no significant differences in the extent of staining in any vascular compartment between atherosclerotic arteries and those with only fibrointimal proliferation. However, the ratio of intimal to medial expression of tPA (P = .001) and uPAR (P = .004) was significantly increased in atherosclerotic arteries, with a similar trend for uPA (P = .069) but not for PAI-1 (P = .73). Four of 10 atherosclerotic arteries had higher uPAR expression in the intima than in the media, whereas none of the 15 arteries with only fibrointimal proliferation had this pattern (P < .01). Dual labeling studies demonstrated colocalization of all four PA system components in endothelial cells, smooth muscle cells, and macrophages, with a predominance of PAI-1. Thus, coronary arteries with a wide range of vascular pathology express an abundance of antifibrinolytic potential with enhanced local expression of profibrinolytic proteins, mainly within atherosclerotic plaques.

Balance between matrix synthesis and degradation: a determinant of glomerulosclerosis

In glomerular health and disease, the balance between extracellular matrix (ECM) protein synthesis and degradation determines the amount of matrix that accumulates locally. While cell and whole animal regulation of ECM synthesis has been the subject of ongoing study, attention has become focused on proteases that degrade matrix components only recently. Two major ECM protease systems have been defined. The plasminogen activators (PAs) are serine proteases that have matrix-degrading capability and also activate plasminogen to plasmin. Plasmin not only degrades ECM proteins, but also may activate members of the matrix metalloproteinase (MMP) family which comprise the second major matrix-degrading system. Specific biological antagonists of both the PAs and the MMPs tightly regulate proteolysis by these enzymes. All of these enzymes and inhibitors have been detected in the kidney, and their expression may be altered to facilitate ECM accumulation in conditions associated with matrix expansion, such as glomerulosclerosis. Work is in progress to determine how these systems are regulated in the kidney and to further define their contribution to the sclerotic process.

Cytokine regulation of endothelial cell extracellular proteolysis

The vascular endothelium plays a central role in the regulation of extrinsic fibrinolysis and thus maintains vascular patency through clot dissolution. Plasminogen activation provides an important source of localized proteolytic activity not only during fibrinolysis but also during a variety of other physiological and pathological processes. Numerous studies have indicated that human endothelial cells can directly synthesize and secrete plasminogen activators (PA) and inhibitors of these activators. PAs specifically hydrolyse a single arginine-valine bond in plasminogen, an abundant and widely distributed plasma zymogen, to form the broad spectrum serine protease, plasmin. Tissue type-PA (t-PA) and urokinase type PA (u-PA) forms of PA have been described in endothelial cells, although t-PA production and secretion is elevated most frequently. The tPA form of PA functions predominantly in endothelial cell mediated fibrinolysis, while uPA is involved in tissue remodeling. During inflammatory reactions activated mononuclear phagocytes produce a variety of cytokines which may influence the phenotype of the endothelium through a process termed "endothelial cell activation". Tumor necrosis factor alpha (TNF alpha), a mononuclear cytokine, is a distinct polypeptide of Mr 17,000 and has been implicated as a mediator of gram negative induced sepsis as well as angiogenesis. TNF alpha is known to interact with specific endothelial cell receptors and to alter endothelial coagulant and anticoagulant properties implying that cytokines may be potent modulators of hemostasis. Recent observations have indicated that TNF alpha and lymphotoxin (TNF beta) can promote the expression, synthesis and secretion of urokinase plasminogen activator (uPA) in human endothelial cells. The upregulation of uPA results in an alteration in the fibrinolytic capacity of endothelial cells and allows cells the selective ability to degrade and invade underlying subendothelial extracellular matrix (ECM). Endothelial cells treated with TNF alpha also display, in an in vitro angiogenic assay, the ability to invade Matrigel and reorganize into tube-like structures, unlike control cultures. The effects of TNF alpha on the PA proteolytic system of endothelial cells, the biological significance of this event and potential in vivo consequences will be discussed. In addition, the influence of cytokine regulatory control systems will be described, since it is becoming increasingly clear that cytokines do not act in isolation. The vascular endothelium serves as a widely distributed anatomical interface between the blood and tissue with diverse capabilities, performing distinctive biologic functions at different sites and within specific organs.(ABSTRACT TRUNCATED AT 400 WORDS)