Trophic Effects of Platelets on Cultured Endothelial Cells are Mediated by Platelet-associated Fibroblast Growth Factor-2 (FGF-2) and Vascular Endothelial Growth Factor (VEGF)

Abstract

SummaryIn addition to their role in primary hemostasis, platelets serve to support and maintain the vascular endothelium. Platelets contain numerous growth factors including the potent angiogenic inducers VEGF and FGF-2. To characterize the function of these two plateletassociated growth factors, the effects of the addition of purified platelets to cultured endothelial cells were examined. The survival and proliferation of endothelial cells were markedly stimulated (2-3-fold and 5-15-fold respectively) by the addition of gel-filtered platelets. Acetylsalicylic acid-treated or lyophilized fixed-platelets were ineffective in supporting endothelial cell proliferation. In Transwell assays, the stimulatory effect of platelets on endothelial cells was preserved, consistent with an effect mediated by secreted factors. The combined inhibition of VEGF and FGF-2 by neutralizing antibodies, in contrast to inhibition of either alone, abrogated both platelet-induced endothelial cell survival and proliferation. FGF-2 isoforms were detected in platelet lysates, as well as in the releasates of agonist-stimulated platelets. Megakaryocytes generated by ex vivo expansion of hematopoietic progenitor cells with kit ligand and thrombopoietin were analyzed for expression of FGF-2. Punctate cytoplasmic staining but no nuclear staining was observed by immunocytochemistry consistent with possible localization of the growth factor to cytoplasmic granules. The addition of platelets to cultured endothelial cells activated extracellular signal-regulated kinase (ERK) in a dose and time-dependent manner. This effect was abrogated by both anti-FGF-2 and anti-VEGF antibody. Since FGF-2 and VEGF are potent angiogenic factors and known endothelial cell survival factors, their release by platelets provides a plausible mechanism for the platelet support of vascular endothelium.

Resident Endothelial Cells Surrounding Damaged Arterial Endothelium Reendothelialize the Lesion

“…34 Platelet-derived vascular endothelial growth factors were reported to exert trophic effects on cultured ECs. 35 Thus, the previously mentioned angiogenic activators stored in platelets may locally promote the EC elongation, migration, and proliferation observed in this study.…”

Phagocytosis of platelets enhances endothelial cell survival under serum deprivation

“…For example, vascular endothelial growth factor, fibroblast growth factor, and platelet-derived growth factor can induce endothelial cell proliferation and cell migration, stimulate chemotaxis, and increase tubule formation. [5][6][7][8] In chronic wounds, platelet releasate can enhance endothelial cell proliferation and promote angiogenesis. 9,10 Furthermore, platelet-derived microparticles have also been reported to play an essential role in neovascularization and angiogenesis.…”

Platelet rich plasma treatment of superficial digital flexor tendon lesions in racing Thoroughbreds

“…The following thrombocyte factors are, transforming growth factor beta (TGF-β1, TGF-β2), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF) and fibroblastic growth factor (FGF) (Pintucci et al 2002;Anitua et al 2004;Blair and Flaumenhaft 2009). Insulin-like growth factor (IGF I) is an important plasma factor for musculoskeletal healing (Boswell et.…”