Early Loss of Thrombomodulin Expression Impairs Vein Graft Thromboresistance

Abstract

Abstract-Thrombosis is the major cause of early vein graft failure. Our aim was to determine whether alterations in the expression of the anticoagulant proteins, thrombomodulin (TM) and the endothelial cell protein C receptor (EPCR), impair endothelial thromboresistance that may contribute to vein graft failure. Immunohistochemical staining of autologous rabbit vein graft sections revealed that the expression of TM, but not EPCR, was reduced significantly early after graft implantation. Western blot analysis revealed that TM expression was reduced by Ͼ95% during the first 2 weeks after implantation, with gradual but incomplete recovery by 42 days. This resulted in up to a 95% reduction in the capacity of the grafts to activate protein C and was associated with an increase in bound thrombin activity, which peaked on day 7 at 28.7Ϯ3.8 mU/cm 2 and remained elevated for more than 14 days. Restoration of TM expression using adenovirus vector-mediated gene transfer significantly enhanced the capacity of grafts to activate protein C and reduced bound thrombin activity on day 7 to levels comparable to that of normal veins (5.7Ϯ0.4 versus 5.2Ϯ1.1 mU/cm 2 , respectively, Pϭ0.74). Surprisingly, neointima formation was not affected by this inhibition of local thrombin activity. These data suggest that the early loss of TM expression significantly impairs vein graft thromboresistance and results in enhanced local thrombin generation. Although enhanced local thrombin generation may predispose to early vein graft failure due to thrombosis, it does not seem to contribute significantly to late vein graft failure due to neointimal hyperplasia.

Matrix metalloproteinase expression in vein grafts: role of inflammatory mediators and extracellular signal-regulated kinases-1 and -2

“…Thrombin activates MT1-MMP-bound MMP-2 in cultured vascular cells (16,23), and tissue factor-generated thrombin has been implicated in the development of intimal hyperplasia (12). In a rabbit vein graft model, vessel-bound thrombin activity increases on day 7 and remains elevated for more than 14 days, indicating that vein grafts are subjected to a chronic form of injury (15). Our finding of a very rapid increase in vein graft-associated thrombin activity coincident with MMP-2 activation indicates that, besides chronic inflammation, vein grafts are also subjected to a significant acute form of injury.…”

Thrombomodulin Deficiency in Human Diabetic Nerve Microvasculature

“…In experimental arterial occlusion models, the TM-protein C mechanism plays a crucial role in protecting the coronary and cerebral artery microcirculation (9,10,14,25). Augmenting TM-protein C antithrombotic function prevents thrombosis formation in arterialvenous graft models (26,27) and protects against organ failure and the lethal effects of disseminated coagulation in both animals (28) and humans (11). Studies in transgenic mice specifically establish the fundamental importance of TM deficiency.…”

Anchoring Fusion Thrombomodulin to the Endothelial Lumen Protects against Injury-induced Lung Thrombosis and Inflammation

“…Pulmonary and vascular pathologies, including oxidative stress, inflammation, and ischemia-reperfusion (I/R) (e.g., vascular bypass and organ transplantation) suppress TM expression or activity (see Video E1) (9)(10)(11)(12)(13)(14)(15), which correlates with increased thrombotic and inflammatory injury to underlying tissue (11,16). In animal studies, a deficit in TM expression or function results in a greater propensity to develop thrombosis and inflammation (2,7).…”