Toll-Like Receptor 3 Activation Is Involved in Venous Thrombosis Development,

Abstract 3277

Venous thromboembolism (VTE) afflicts 117 people per 100,000 each year and is an important cause of morbidity and mortality. Inflammation may have a role in both the genesis and resolution of venous thrombi. Although septic thrombophlebitis occurs, most DVT are sterile. Recently, the role of toll-like receptor (TLR) signaling in modulating sterile inflammation has become better defined in experimental injury models. TLR3, for example, is activated by viral long double stranded RNA and endogenous RNA released by cellular apoptosis and necrosis, and induce a proinflammatory cellular response. Short single-stranded RNA, such as those used in RNA inhibition, stimulate TLR3 in endothelial cells and inhibit neoangiogenesis. Thus, we hypothesize that TLR3 might be involved in the inflammatory development of venous thrombosis. We first investigated whether stimulation of TLR3 influences venous thrombosis in mice. Intravenous injection of polyinosine polycytidylic acid (polyI:C), a synthetic double-stranded RNA analog and TLR3 ligand, increase the size and the cellular density of thrombi after FeCl₃-induced inferior vena cava injury. TLR3 stimulation with polyI:C is also associated with an increased reactive oxygen species production, as well as increased neutrophil and macrophage content. Using a specific fluorescent probe for RNA, we found that FeCl₃ induces RNA release and thus increases the RNA content in the thrombus. We next investigated the effect of RNase on thrombus development. Intravenous injection of RNase decreased thrombus size, as well as reactive oxygen species production and neutrophil and macrophage content in the thrombus. In vitro incubation of endothelial cells with polyI:C induces production of pro-inflammatory cytokines GM-CSF, G-CSF, IL-6, IL-8 and interferon-γ-induced protein 10 involved in the recruitment of neutrophils and macrophages. Taken together, these results strongly suggest that RNA release and TLR3 stimulation after endothelial cell injury participate in thrombus formation by inducing a pro-inflammatory response leading to the recruitment of neutrophils and macrophages.