Platelet-released supernatant increases matrix metalloproteinase-2 production, migration, proliferation, and tube formation of human umbilical vascular endothelial cells.

Local application of platelets represents a promising tool to enhance bone regeneration. New bone formation strictly requires blood vessel formation, a sequential process involving matrix degradation, migration, proliferation, and tube formation of endothelial cells. Here we investigated the impact of secreted granula products from activated platelets on endothelial cells, and determined the involvement of extracellular signal-regulated kinase (ERK) signaling. The effects of platelet-released supernatant on endothelial cells were investigated using in vitro models. Matrix metalloproteinase-2 (MMP-2) release, migration, proliferation, and tube formation of human umbilical vascular endothelial cells (HUVEC) were determined in response to platelet-released supernatant by gelatine zymography, Boyden chamber assay, 3[H]thymidine incorporation, and basement membrane assay, respectively. All experiments were performed in the presence of the ERK signaling inhibitor PD98059. ERK phosphorylation was detected by Western blot analysis. Incubation with platelet-released supernatant increased the production of MMP-2, migration, proliferation, and tube formation of HUVEC. Platelet-released supernatant also stimulated ERK phosphorylation in HUVEC. Inhibition of ERK signaling decreased platelet-released supernatant-stimulated endothelial cell proliferation, but not MMP-2 activity, migration, and the formation of capillary tubes. Our data suggest that secreted granula products from platelets can enhance different stages of blood vessel formation, and that ERK signaling is required to mediate the mitogenic effects of the supernatant. These findings support the hypothesis of a potential link between platelet activation and blood vessel formation during bone regeneration.