Regulation of arterial remodeling and angiogenesis by urokinase-type plasminogen activator.

A wide variety of disorders are associated with an imbalance in the plasminogen activator system, including inflammatory diseases, atherosclerosis, intimal hyperplasia, the response mechanism to vascular injury, and restenosis. Urokinase-type plasminogen activator (uPA) is a multifunctional protein that in addition to its fibrinolytic and matrix degradation capabilities also affects growth factor bioavailability, cytokine modulation, receptor shedding, cell migration and proliferation, phenotypic modulation, protein expression, and cascade activation of proteases, inhibitors, receptors, and modulators. uPA is the crucial protein for neointimal growth and vascular remodeling. Moreover, it was recently shown to be implicated in the stimulation of angiogenesis, which makes it a promising multipurpose therapeutic target. This review is focused on the mechanisms by which uPA can regulate arterial remodeling, angiogenesis, and cell migration and proliferation after arterial injury and the means by which it modulates gene expression in vascular cells. The role of domain specificity of urokinase in these processes is also discussed.

Urokinase plasminogen activator in injured adventitia increases the number of myofibroblasts and augments early proliferation.

Myofibroblasts are involved in vessel remodeling during the development of hypertension as well as after angioplasty and aortocoronary grafting, but the mechanisms of myofibroblastic phenotypic modulation are not fully elucidated. We assessed the role of urokinase plasminogen activator (uPA) and its proteolytic activity in myofibroblast differentiation and the early proliferation following mechanical injury of the rat carotid adventitia. The effects of perivascular application of recombinant uPA (r-uPA), proteolytically inactive r-uPA(H/Q) and uPA neutralizing antibody were evaluated 4 days after surgical injury to the adventitia. The phenotype of adventitial cells was assessed using anti-alpha-smooth muscle actin (alpha-SM actin) antibody, anti-SM heavy chain myosin, anti-high-molecular-weight caldesmon, anti-smoothelin and anti-ED-1 antibodies, proliferation by the expression of proliferating cell nuclear antigen, and the size of the adventitia by quantitative morphometry. Four days after injury, the intensive immunostaining for urokinase appeared in the rat carotid artery adventitia. At the same time, the frequency of alpha-SM actin-positive adventitial cells was 1.8+/-1.1% in uninjured arteries and 25.2+/-5.4% in injured arteries (p<0.05), and the respective frequency of ED-1-positive cells 1.5+/-1.1 and 25.0+/-5.2%. The application of exogenous r-uPA doubled the numbers of alpha-SM actin-positive adventitial cells to 55.7+/-6.8% (p<0.05). ED-1-positive cells and proliferating cell nuclear antigen-positive cells as well as the size of the adventitia were also significantly increased after r-uPA compared with injury alone. In contrast, the proteolytically inactive r-uPA(H/Q) did not affect any parameters. The application of uPA neutralizing antibody attenuated the frequency of alpha-SM actin-positive cells to 12.6+/-3.5% (p<0.05), the frequency of ED-1-positive cells, and the numbers of adventitial cells. r-uPA stimulation of cultured human skin fibroblasts significantly increased the alpha-SM actin content in a concentration-dependent manner. In contrast, r-uPAH/Q did not induce changes in alpha-SM actin content. We conclude that uPA, which is upregulated in the injured adventitia, can augment adventitial cell accumulation, including myofibroblasts, and adventitia growth early after injury of the rat carotid artery adventitia by mechanisms involving proteolysis.

Plasminogen activator expression correlates with genetic differences in vascular remodeling.

Intima-media thickening (IMT) of the carotid artery, a form of vascular remodeling, correlates well with coronary artery disease risk in humans. Vascular remodeling in response to blood flow is a complex process that critically involves altered cell matrix interactions. To gain insight into these events, we performed partial carotid ligation (left carotid (LCA) = low flow and right carotid (RCA) = high flow) in 2 inbred mouse strains: C57Bl/6J (C57) and FVB/NJ (FVB). To evaluate the role of the 2 major matrix-degrading systems, plasminogen activators (PAs) and matrix metalloproteinases (MMPs), we compared the expression of u-PA, t-PA, MMP-2 and MMP-9 in ligated carotids of C57 and FVB mice. The extent of remodeling was greater in response to low LCA than high RCA flow. Despite a similar decrease in LCA flow in both strains, maximal IMT volume was greater in FVB (82 +/- 7 x 10(-6) microm(3)) than in C57 (38 +/- 4 x 10(-6) microm(3)) after ligation. Among PAs and MMPs, increased expression of t-PA and u-PA correlated with increased IMT (p < 0.0005 and p < 0.001, respectively). MMP-2, MMP-9 and tissue inhibitors of metalloproteinase-2 expression also increased, but did not differ between strains. In summary, flow-induced IMT of the carotid is genetically determined and correlates with t-PA and u-PA expression in 2 inbred mouse strains.