Background:Selective platelet release of pro- or anti-angiogenic factors distinctly regulated angiogenesis. We hypothesised that selective release of platelet angiogenic factors could differently regulate tumour growth.Methods:Breast cancer cell proliferation, cancer cell-induced endothelial tube formation in vitro, and tumour growth in vivo were studied in the presence of protease-activated receptor 1-stimulated platelet releasate (PAR1-PR; rich in pro-angiogenic factors) or PAR4-PR (rich in anti-angiogenic factors).Results:The PAR1-PR and PAR4-PR supplementation (10%) similarly enhanced cell proliferation of MCF-7 and MDA-MB-231 breast cancer cells. The cancer cells triggered capillary-like tube formation of endothelial cells that was further enhanced by pro-angiogenic factor-rich PAR1-PR. The VEGF, but not SDF-1α, receptor blockade abolished PAR1-PR/PAR4-PR-enhanced cancer cell proliferation. Integrin blockade by RGDS had identical effects as VEGF inhibition. The Src and ERK inhibition diminished, whereas PI3K and PKC blockade abolished platelet releasate-enhanced cancer cell proliferation. Using a model of subcutaneous implantation of MDA-MB-231 cells in nude mice, PAR1-PR enhanced tumour growth more markedly than PAR4-PR, and seemed to achieve the exaggeration by promoting more profound tumour angiogenesis.Conclusions:Platelet releasate increases breast cancer cell proliferation through VEGF–integrin cooperative signalling. Pro-angiogenic factor-rich platelet releasate enhances cancer cell-induced angiogenesis more markedly, and thus exaggerates tumour growth in vivo.

) or PAR4-AP (100 lmol L -1 ) to prepare PAR1-PR and PAR4-PR, respectively. PAR1-PR or PAR4-PR had little influence on EPC proliferation. EPC migration experiments using a modified Boyden chamber showed that both platelet releasates facilitated EPC migration. As for in vitro tube formation on Matrigel, PAR1-PR and PAR4-PR similarly enhanced capillary-like network formation of EPCs in the complete EPC medium containing 10% FBS and a cocktail of growth factors, while PAR1-PR more profoundly increased EPC tube formation in basal culture medium supplemented with only 0.5% FBS than did PAR4-PR. The latter was confirmed in the murine angiogenesis model of subcutaneous Matrigel implantation. Moreover, blockade of vascular endothelial growth factor, stromal cell-derived factor 1a, or matrix metalloproteinases attenuated EPC migration and tube formation, suggesting a cooperation of these factors in the enhancements. Conclusions: PAR1-PR enhances vasculogenesis more potently than PAR4-PR, and the enhancements require a cooperation of multiple platelet-derived angiogenic regulators.

Super-resolution imaging of P-selectin in platelets together with dictionary learning allow specifically activated platelets to be identified in an automatic objective manner.