Serp-1, a Viral Anti-inflammatory Serpin, Regulates Cellular Serine Proteinase and Serpin Responses to Vascular Injury

Abstract

Complex DNA viruses have tapped into cellular serpin responses that act as key regulatory steps in coagulation and inflammatory cascades. Serp-1 is one such viral serpin that effectively protects virus-infected tissues from host inflammatory responses. When given as purified protein, Serp-1 markedly inhibits vascular monocyte invasion and plaque growth in animal models. We have investigated mechanisms of viral serpin inhibition of vascular inflammatory responses. In vascular injury models, Serp-1 altered early cellular plasminogen activator (tissue plasminogen activator), inhibitor (PAI-1), and receptor (urokinase-type plasminogen activator) expression (p < 0.01). Serp-1, but not a reactive center loop mutant, up-regulated PAI-1 serpin expression in human endothelial cells. Treatment of endothelial cells with antibody to urokinase-type plasminogen activator and vitronectin blocked Serp-1-induced changes. Significantly, Serp-1 blocked intimal hyperplasia (p < 0.0001) after aortic allograft transplant (p < 0.0001) in PAI-1-deficient mice. Serp-1 also blocked plaque growth after aortic isograft transplant and after wire-induced injury (p < 0.05) in PAI-1-deficient mice indicating that increase in PAI-1 expression is not required for Serp-1 to block vasculopathy development. Serp-1 did not inhibit plaque growth in uPAR-deficient mice after aortic allograft transplant. We conclude that the poxviral serpin, Serp-1, attenuates vascular inflammatory responses to injury through a pathway mediated by native uPA receptors and vitronectin.An integrated balance between the thrombotic and thrombolytic cascades, both of which are regulated by serine proteinases, activates arterial clot formation and also mediates inflammatory cell responses at sites of vascular injury (1-7). Serine proteinase inhibitors, termed serpins, in turn regulate these cascades (7). Larger DNA containing viruses have captured host serpins during millions of years of evolution, and adapted them into highly effective shields against host inflammatory responses (8). Serp-1, a secreted anti-inflammatory protein encoded by myxoma virus, is one such poxviral serpin that binds and inhibits, in vitro, the thrombolytic serine proteinases tissue-type and urokinase-type plasminogen activators (tPA 1 and uPA, respectively) and plasmin (9, 10). In vivo, Serp-1 reduces inflammatory leukocyte responses to myxoma viral infection (9, 10). Furthermore, infusion of picogram to nanogram doses of purified Serp-1 protein also profoundly inhibits monocytic cell invasion and subsequent atherosclerotic plaque growth following vascular injury induced by angioplasty (11) or allograft transplant (12,13) 2 in animal models, thus providing a new class of anti-inflammatory drugs.The precise targets and/or receptors, through which viral serpins, specifically Serp-1, inhibit inflammatory cell responses are not yet defined (10 -17). uPA, when bound to the uPA receptor (uPAR), enhances inflammatory cell migration (3, 4, 7, 17, 18), cell adhesion mediated by vitronectin (3, 19, 21), cell ...

Myxoma virus in the European rabbit: interactions between the virus and its susceptible host

“…Serp-1 interacts with and inhibits, among others, plasmin, urokinase, and tissue-type plasminogen activator [19,53]. However, many of these serine proteases were identified through human studies and little is know how Serp-1 interacts with similar proteins in the rabbit.…”

Serine Protease Inhibitor Serp-1 Strongly Impairs Atherosclerotic Lesion Formation and Induces a Stable Plaque Phenotype in ApoE −/− Mice

“…However, in uPA Ϫ/Ϫ mice, VSMC migration was found to be reduced, suggesting that additional effects are involved in the Serp-1 effect as well. Just recently, data by Dai et al 36 indicate that Serp-1 acts through an uPA receptor-dependent mechanism, as lesion formation after allograft transplantation of uPAR Ϫ/Ϫ aortas to uPAR ϩ/ϩ animals was not affected by Serp-1 treatment.…”

Comparative Analysis of Plaque Growth after Arterial Stent Implant with Anti-Inflammatory Chemokine and Serine Protease Inhibitors Treatment

“…Plaque area, was measured by morphometric analysis using an Olympus CCD color video camera attached to an Olympus microscope, and the ImagePro application program calibrated to the microscope objective [26][27][28][29][30][31]33]. Both the mean total cross-sectional intimal area and the mean intimal thickness after normalized to the medial thickness were calculated for each arterial section.…”

“…These inflammatory moderators function at femptomolar to picomolar concentrations when secreted by the originating viruses [23,24]. Two such proteins, Serp-1 that inhibits uPA/uPAR [23][24][25][26][27][28] and M-T7 [26,[29][30][31] that blocks the C terminal GAG binding domain of C, CC and CXC class chemokines [26,[29][30][31] have been purified individually and studied as anti-inflammatory reagents in a wide range of animal models with demonstrated reduction in inflammatory cell invasion and plaque growth. One protein, Serp-1 has been successfully tested in clinical trial for treatment of patients with unstable coronary syndromes (Unstable angina and NSTEMI) who have received stent implants [26,32].…”

“…Harvested arterial sections were processed and stained with hematoxylin and eosin (H & E) or Masson's trichrome stains as previously described [25][26][27][28][29][30][31]33]. Plaque area, was measured by morphometric analysis using an Olympus CCD color video camera attached to an Olympus microscope, and the ImagePro application program calibrated to the microscope objective [26][27][28][29][30][31]33].…”