Thromboxane A2 induces blood flow recovery via platelet adhesion to ischaemic regions

Aims Thromboxane A2 (TXA2) induces platelet adhesion through thromboxane prostanoid (TP) receptor. Platelets contain many pro-angiogenic factors and are recruited to the site of vascular injury. However, the cellular and molecular mechanisms of platelet-dependent angiogenesis, especially the involvement of TP signalling, have not been fully elucidated. The present study hypothesized that TP-dependent platelet adhesion would contribute to angiogenesis in a mouse hindlimb ischaemic model. Methods and results Blood flow recovery was suppressed by the TXA2 receptor antagonist (S-1452) and the TXA2 synthase inhibitor (OKY-046) compared with control mice. TP knockout mice (TP−/−) showed delayed blood flow recovery from ischaemia and impaired angiogenesis compared with wild-type (WT) mice and prostacyclin receptor knockout mice (IP−/−). Selective platelet adhesion to ischaemic endothelial cells (ECs) via P-selectin was identified in WT and IP−/−, but not in TP−/−, via in vivo microscopy. IF analysis showed that P-selectin glycoprotein ligand-1 (PSGL-1) co-localized with endothelial CD31 in ischaemic muscle in WT and IP−/− but not diminished in TP−/−. Platelet-rich plasma levels of stromal cell-derived factor-1 and VEGF were increased after ischaemia in WT, and suppressed by antibody against P-selectin in WT but not in TP−/−. Furthermore, the blood flow recovery was suppressed by neutralizing antibodies against VEGF or C-X-C chemokine receptor type 4 in WT and IP−/− but not in TP−/−. Conclusion These results indicated that TP signalling facilitates ischaemia-induced angiogenesis via P-selectin-mediated platelet adhesion to PSGL-1 on the ECs at ischaemic sites and the supply of pro-angiogenic factors by the adherent platelets.