PAR1 and PAR4 counter-regulated the release of endostatin and VEGF from human platelets, and PAR1 antagonism significantly retarded the healing of gastric ulcers in rats.
PAR1 and PAR4 counter-regulate the release of angiogenic factors (endostatin and VEGF) from platelets, suggesting a role in angiogenesis, wound healing, and tumor growth.
The roles of proteinase-activated receptors (PARs) in platelet functions other than aggregation are not well understood. Among these is the release of factors that regulate the process of angiogenesis, such as endostatin and VEGF, which, respectively, inhibit and promote angiogenesis. PAR1 and PAR4 are expressed on the surface of human platelets and can be activated by thrombin. In the present study, we have attempted to determine the roles of PAR1 and PAR4 in regulating release of endostatin and VEGF from human platelets. Aggregation and endostatin release could be elicited by a specific PAR4 agonist (AYPGKF-NH(2)). The PAR4 agonist concentration dependently suppressed VEGF release. A selective PAR1 agonist (TFLLR-NH(2)) induced platelet aggregation and VEGF release but suppressed endostatin release. Thrombin did not affect endostatin or VEGF release. However, in the presence of a selective PAR1 antagonist (SCH79797), thrombin stimulated endostatin release and suppressed VEGF release. Conversely, in the presence of a selective PAR4 antagonist (transcinnamoyl-YPGKF-NH(2)), thrombin stimulated VEGF release. In vivo, treatment of rats with established gastric ulcers with a PAR1 antagonist each day for 1 wk resulted in a significant retardation of healing. We conclude that PAR1 and PAR4 counter-regulate the release of endostatin and VEGF from platelets. These protease-activated receptors could therefore play a crucial role in regulating angiogenesis and in turn could regulate the processes of wound healing and tumor growth.
Ma et al. (Wed,) conducted a other in Gastric ulcers (in vivo) / Platelet function (in vitro). PAR1 and PAR4 agonists and antagonists was evaluated on Endostatin and VEGF release; gastric ulcer healing. PAR1 and PAR4 counter-regulated the release of endostatin and VEGF from human platelets, and PAR1 antagonism significantly retarded the healing of gastric ulcers in rats.