A key role of toll-like receptor 3 in tissue factor activation through extracellular signal regulated kinase 1/2 pathway in a murine hypoxia model

Hypoxemia in the circulation can lead to venous thrombosis (VT) through tissue factor (TF) activation, but the mechanism of TF activation in hypoxia remains obscure. Ligands released from damaged tissues or cells due to hypoxia are identified by various pattern-recognition receptors (PRR), including Toll-like receptor3 (TLR3). In the present study, we investigated the mechanism of TF activation during acute hypoxia in a rat model. The expression of TLR3 and TF was analyzed by immunoblotting and RT-PCR. The TF activity was evaluated by two-stage chromogenic assay and fibrin deposition was detected by immunohistochemistry.The expression of TLR3, TF, and TF activity was increased significantly 6 h post acute hypoxia and then decreased gradually. The contribution of TLR3 in TF activation was investigated by poly I:C and TLR3 neutralizing antibody. We also found increased ERK phosphorylation both in acute hypoxia and poly I:C treatment. We further showed that the pre-treatment of TLR3 neutralizing antibody or ERK inhibitor (PD98059) 2 h prior to acute hypoxia or poly I:C treatment completely abrogated ERK phosphorylation and TF activation. The pre-treatment of TLR3 neutralizing antibody also inhibited fibrin deposition in lung vasculature.These data indicate that acute hypoxia induced TF activation is mediated through TLR3-ERK1/2 pathway.