Evidence that platelets promote tube formation by endothelial cells on matrigel

1 The involvement of platelets in neovascularization was investigated in the matrigel tube formation assay, an in vitro model of angiogenesis. 2 Platelets promoted the formation of capillary-like structures (expressed as relative tube area) number- and time-dependently. Relative tube area increased from 0.98±0.02 (n = 8) in the presence of 6.25×104, to 3.21±0.12 (n = 8) in the presence of 106 platelets/well compared to 0.54±0.04 (n = 8) in their absence. This increase was unaffected by acetyl salicylic acid (ASA), apyrase, and hirudin. Photographs from representative experiments, showed that platelets adhered along the differentiating endothelium. 3 Addition of α-thrombin (0.1–1 i.u. ml−1), the nitric oxide (NO) donor sodium nitroprusside (SNP; 1–100 μm) or the NO synthase inhibitor, l-NG-arginine-methylester (l-NAME, 30–300 μm) to the assay, had no effect on tube formation compared to that seen with platelets alone. 4 Neuraminidase (0.01 i.u./107 platelets), which strips sialic acid residues from membrane glycoproteins, abolished the promoting effect of platelets on tube formation. The relative tube area in the presence of neuraminidase-treated platelets was 0.81±0.03 (n = 8), in the presence of untreated platelets 1.69±0.09, P < 0.001 (n = 8) and in the absence of platelets, 0.80±0.04 (n = 8). The tetrapeptide Arg-Gly-Asp-Ser (RGDS; 20–200 μm) which inhibits von Willebrand factor, fibrinogen and fibronectin-mediated adhesion, had no effect on the promoting effect of platelets on tube formation. 5 These results indicate that platelets promote angiogenesis in vitro. This effect is largely independent from activation by α-thrombin, is not modified by manipulating NO and prostaglandin metabolism and proceeds possibly through adhesion of the platelets to the differentiating endothelium. British Journal of Pharmacology (1998) 125, 1252–1257; doi:10.1038/sj.bjp.0702191