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-NH2). The PAR4 agonist concentration dependently suppressed VEGF release. A selective PAR1 agonist (TFLLR-NH2) 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-NH2), 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.angiogenesis ͉ aggregation ͉ thrombin ͉ protease I n addition to its central roles in blood coagulation and hemostasis, thrombin participates in a variety of biological processes, including inflammation and wound healing (1). Activation of platelets by thrombin is mediated at least in part through cleavage of proteinase-activated receptors (PARs). Four distinct PARs have been identified, with PAR1, PAR3, and PAR4 acting as receptors for thrombin. Human platelets express PAR1 and PAR4, and activation of either is sufficient to trigger platelet aggregation and secretion (2-5). A variety of bioactive substances, including growth factors and chemokines (6-8), are stored in platelets and released during activation. We have reported (9) that endostatin, a potent inhibitor of angiogenesis, is contained within rat platelets and released in response to thrombin via PAR4 in an aggregation-independent manner (10). In studies in rats, we demonstrated that pharmacological manipulation of platelet and͞or serum levels of proangiogenic (VEGF) and antiangiogenic (endostatin) factors resulted in profound effects on healing of gastric ulcers (11,12).Whether human platelets contain endostatin is unknown. Moreover, the relative importance of PAR1 vs. PAR4 in regulating platelet endostatin release has not been reported. In the present study, we have demonstrated that human platelets contain endostatin, and that its release can be triggered by activation of PAR4 but not PAR1. Indeed, PAR1 activation leads to suppression of e...

Bleeding and delayed healing of ulcers are well recognized clinical problems associated with the use of aspirin and other nonsteroidal antiinflammatory drugs, which have been attributed to their antiaggregatory effects on platelets. We hypothesized that antiplatelet drugs might interfere with gastric ulcer healing by suppressing the release of growth factors, such as vascular endothelial growth factor (VEGF), from platelets. Gastric ulcers were induced in rats by serosal application of acetic acid. Daily oral treatment with vehicle, aspirin, or ticlopidine (an ADP receptor antagonist) was started 3 days later and continued for 1 week. Ulcer induction resulted in a significant increase in serum levels of VEGF and a significant decrease in serum levels of endostatin (an antiangiogenic factor). Although both aspirin and ticlopidine markedly suppressed platelet aggregation, only ticlopidine impaired gastric ulcer healing and angiogenesis as well as reversing the ulcerassociated changes in serum levels of VEGF and endostatin. The effects of ticlopidine on ulcer healing and angiogenesis were mimicked by immunodepletion of circulating platelets, and ticlopidine did not influence ulcer healing when given to thrombocytopenic rats. Incubation of human umbilical vein endothelial cells with serum from ticlopidine-treated rats significantly reduced proliferation and increased apoptosis, effects reversed by an antibody directed against endostatin. Ticlopidine treatment resulted in increased platelet endostatin content and release. These results demonstrate a previously unrecognized contribution of platelets to the regulation of gastric ulcer healing. Such effects likely are mediated through the release from platelets of endostatin and possibly VEGF. As shown with ticlopidine, drugs that influence gastric ulcer healing may do so in part through altering the ability of platelets to release growth factors.angiogenesis ͉ ticlopidine ͉ aspirin ͉ proliferation ͉ endothelium

SummaryClathrin-coated vesicles form by rapid assembly of discrete coat constituents into a cargo-sorting lattice. How the sequential phases of coat construction are choreographed is unclear, but transient protein-protein interactions mediated by short interaction motifs are pivotal. We show that arrayed Asp-Pro-Phe (DPF) motifs within the early-arriving endocytic pioneers Eps15/R are differentially decoded by other endocytic pioneers Fcho1/2 and AP-2. The structure of an Eps15/R⋅Fcho1 μ-homology domain complex reveals a spacing-dependent DPF triad, bound in a mechanistically distinct way from the mode of single DPF binding to AP-2. Using cells lacking FCHO1/2 and with Eps15 sequestered from the plasma membrane, we establish that without these two endocytic pioneers, AP-2 assemblies are fleeting and endocytosis stalls. Thus, distinct DPF-based codes within the unstructured Eps15/R C terminus direct the assembly of temporary Fcho1/2⋅Eps15/R⋅AP-2 ternary complexes to facilitate conformational activation of AP-2 by the Fcho1/2 interdomain linker to promote AP-2 cargo engagement.

Enhancing solar energy conversion is imperative and maximizing solar energy capture remains significant. Here, nanotechnology toward engineering hybrid photosystem involving biological photosynthetic chloroplasts and dualemissive carbon dots (CDs) is employed for improved photosynthesis by harnessing more effective light. Specifically, the as-prepared CDs show strong absorption in ultraviolet (UV) light region and exhibit intense blue and red light in water, which exactly match the absorption spectrum of chloroplasts. After coating the CDs on the surface of extracted chloroplasts, the hybrid photosystem produces 2.8 times more adenosine triphosphate (ATP) than chloroplasts themselves in vitro. Moreover, CD-induced enhancement of photosynthesis in living plant is proved as well, showing a maximum increase of 25% in electron transport rates over the leaves without CDs, demonstrating the effective nanobionics engineering of plant performance in vivo. This is the first report on employing the unique dual-emission trait of nanoparticles, especially the red emission, to augment photoabsorption of both extracted chloroplasts and intact leaves for enhanced photosynthetic properties. This work provides a promising strategy for engineering biological photosynthetic system with dual-emissive CDs to enhance solar energy conversion both in vivo and in vitro, and promotes the development in the field of nanobionic.