Enhanced venous thrombus resolution in plasminogen activator inhibitor type‐2 deficient mice

Abstract

Background The resolution of deep vein thrombosis (DVT) requires an inflammatory response and mobilization of proteases, such as urokinase-type plasminogen activator (uPA) and matrix metalloproteinases (MMPs), to degrade the thrombus and remodel the injured vein wall. PAI-2 is a serine protease inhibitor (serpin) with unique immunosuppressive and cell survival properties that was originally identified as an inhibitor of uPA. Objective To investigate the role of PAI-2 in venous thrombus formation and resolution. Methods Venous thrombus resolution was compared in wild type C57BL/6, PAI-2 -/- and PAI-1 -/- mice using the stasis model of DVT. Formed thrombi were harvested, thrombus weights were recorded, and tissue was analyzed for uPA, and MMP activities, PAI-1 expression, and the nature of inflammatory cell infiltration. Results We found that absence of PAI-2 enhanced venous thrombus resolution, while thrombus formation was unaffected. Enhanced venous thrombus resolution in PAI-2 -/- mice was associated with increased uPA activity and reduced levels of PAI-1, with no significant effect on MMP-2 and -9 activities. PAI-1 deficiency resulted in an increase in thrombus resolution similar to PAI-2 deficiency, but additionally reduced venous thrombus formation and altered MMP activity. PAI-2 deficient thrombi had increased levels of the neutrophil chemoattractant, CXCL2, which was associated with early enhanced neutrophil recruitment. Conclusions These data identify PAI-2 as a novel regulator of venous thrombus resolution, which modulates several pathways involving both inflammatory and uPA activity mechanisms, distinct from PAI-1. Further examination of these pathways may lead to potential therapeutic prospects in accelerating thrombus resolution.

Serpins in Venous Thrombosis and Venous Thrombus Resolution

“…Increased levels of PAI-1 activity are correlated with impaired fibrinolytic responses in patients with DVT, however reports on the role of elevated levels of PAI-1 in venous thrombosis have been contradictory (20;21). PAI-1 deficiency in mice has been shown to enhance both venous thrombus formation and resolution (22;23). Enhanced thrombus resolution in PAI-1 deficient mice occurs via altered MMP and uPA activities (22-24).…”

“…PAI-1 deficiency in mice has been shown to enhance both venous thrombus formation and resolution (22;23). Enhanced thrombus resolution in PAI-1 deficient mice occurs via altered MMP and uPA activities (22-24). Additionally the endothelial cell marker, CD31 and vein wall smooth muscle cell (VSMC) gene expression were enhanced in PAI-1 deficient models, suggesting a role for PAI-1 in endothelial integrity and vein wall remodeling (24).…”

“…Mice with PAI-2 deficiency also demonstrate enhanced venous thrombus resolution, although, unlike PAI-1 deficiency, thrombus formation is unaffected (22). In addition, the enhanced venous thrombus resolution observed in PAI-2 deficient mice is associated with increased uPA activity and reduced levels of PAI-1, with no significant effect on MMP-2 and −9 activities (22;26).…”

“…Murine experimental models of venous thrombosis accurately mimic many of the clinical and pathophysiological features observed in human DVT, and have yielded important insights into the molecular and cellular processes that drive venous thrombosis and its resolution (22;28-30). Venous thrombosis models mimic different aspects of DVT and its resolution, each having unique advantages and limitations (31;32).…”

“…Importantly they offer the advantage of genetic manipulation to dissect molecular mechanisms. We find the stasis inferior vena cava (IVC) ligation model (22;28-30;33), to be a robust, reproducible murine model that accurately mimics many of the clinical and pathophysiological features observed in human DVT (32). This well established model involves laparotomy, division of the lumbar veins from the renal veins to the caval bifurcation, and complete ligation of the IVC immediately below the renal veins.…”