Role of Protease Activated Receptor 1 and 2 Signaling in Hypoxia-Induced Angiogenesis

Abstract

Objective-Tissue factor (TF) initiates coagulation and indirectly triggers thrombin-dependent protease activated receptor (PAR) signaling. The TF-VIIa complex also directly cleaves PAR2 and promotes angiogenesis in vitro in TF cytoplasmic domain-deleted (TF ␦CT ) mice. Here we address the effect of PAR1 and PAR2 deficiency on angiogenesis in vivo. Methods and Results-In hypoxia-driven angiogenesis of oxygen induced retinopathy (OIR), wild-type, PAR1Ϫ/Ϫ , PAR2 Ϫ/Ϫ , and TF ␦CT mice showed a comparable regression of the superficial vascular plexus during the initial exposure of mice to hyperoxia. However, TF ␦CT mice revascularized areas of central vaso-obliteration significantly faster than wild-type animals. Pharmacological inhibition of the TF-VIIa complex, but not of Xa, and blockade of tyrosine kinase receptor pathways with Gleevec reversed accelerated angiogenesis of TF ␦CT mice to revascularization rates observed in wild-type mice. Genetic deletion of PAR2, but not of PAR1, abolished enhanced revascularization of TF ␦CT mice. PAR1 knock-out animals were indistinguishable from wild-type mice in the model of retinal neoangiogenesis and angiogenesis-dependent subcutaneous tumor growth was unaltered in PAR1-and PAR2-deficient animals. Key Words: tissue factor Ⅲ protease activated receptors Ⅲ angiogenesis Ⅲ coagulation Ⅲ thrombin T issue factor (TF), a transmembrane glycoprotein expressed by vascular and myeloid cells, is the primary cellular initiator of blood coagulation. TF exerts its biological activities by forming a catalytic enzyme complex with coagulation factor VIIa. The TF-VIIa complex then triggers coagulation by binding and activating factor X, leading to thrombin-dependent fibrin deposition and platelet activation. Thrombin can exhibit pleiotrophic effects which are typically mediated through G protein-coupled protease activated receptor (PAR) 1 signaling. 1 The TF-VIIa complex also signals directly by cleaving PAR2, but not PAR1. 2,3 However, the relative contributions of direct TF signaling, downstream coagulation activation, and indirect protease signaling to the underlying pathogenesis of cancer progression and angiogenesis, 3 are incompletely defined in vivo. Conclusion-LossTF deficiency results in vascular failure during development 4 and the proangiogenic phenotype of TF cytoplasmic domain deleted (TF ␦CT ) mice provided direct evidence that TF is involved in angiogenesis. 5 Whether direct TF-VIIa signaling is the only relevant pathway to drive angiogenesis in vivo has not been established. Indeed, thrombin-dependent PAR1 signaling stimulates angiogenesis in certain angiogenesis models in vivo, 6 -8 and the partial embryonic lethality of PAR1 knock-out mice attributable to vascular failure resembles the lethal phenotype of TF deficient animals. 9,10 However, the role of PAR1 in postnatal angiogenesis has not been directly addressed in PAR1 knock-out animals.Thrombin and/or TF-signaling pathways are also involved in tumor angiogenesis, 5,11 but production of proangiogenic factors by tumor cell...

Roles of Coagulation Pathway and Factor Xa in the Progression of Diabetic Nephropathy in db/db Mice

“…21) Recently, Uusitalo-Jarvinen et al have shown using genetically deficient mice that PAR1 and PAR2 play roles in hypoxia-driven angiogenesis and that PAR2 signaling is sufficient for this proangiogenic effect. 39) In the present study, the factor Xa inhibitor fondaparinux suppressed both glomerular hypertrophy and hypervascularity in db/db mice. Taken together, it is tempting to speculate that fondaparinux inhibits glomerular hypertrophy by the suppressing angiogenesis through PAR2 regulation.…”

Effects of the Factor Xa Inhibitor, Fondaparinux, on the Stability of Atherosclerotic Lesions in Apolipoprotein E-Deficient Mice

“…34 Both PAR-1 and PAR-2 play roles in hypoxia-driven angiogenesis, and PAR-2 signaling is sufficient for the pro-angiogenic effect. 35 In the present study, fondaparinux suppressed angiogenesis; meanwhile, the expression and signaling of PAR-1 and PAR-2 were reduced in the fondaparinux group. Taken together, it is tempting to speculate that fondaparinux might contribute to the stability of the plaque by inhibiting angiogenesis through PAR-1/2 regulation.…”

Neutrophil activation by the tissue factor/Factor VIIa/PAR2 axis mediates fetal death in a mouse model of antiphospholipid syndrome

“…The absence of the cytoplasmic domain of TF was previously associated with a diminished inflammatory response in a murine arthritis model (38). However, studies performed in a mouse model of oxygen-induced retinopathy showed that loss of the TF cytoplasmic domain resulted in increased angiogenesis mediated by TF/FVIIa signaling through PAR2 (39).…”