Activated platelets and leucocytes cooperatively stimulate smooth muscle cell proliferation and proto-oncogene expression via release of soluble growth factors

Background: Previous studies indicate that platelets and leucocytes might c ontribute to the development of neointimal hyperplasia following arterial i njury. The present study was aimed at further investigating the role of pla telets and leucocytes, alone or in combination, in promoting vascular smoot h muscle cell (SMC) proliferation in vitro, focusing on the relative contri bution of different soluble growth factors released by these cells, and on the ability to induce proto-oncogene expression. such as c-fos. Methods: SM Cs from rabbit aortas, made quiescent by serum deprivation, were stimulated with either activated platelets, leucocytes, or both, separated from SMCs by a membrane insert. SMC proliferation was evaluated by measuring the inco rporation of H-3-thymidine. The relative contribution of different platelet -derived mediators to SMC growth was evaluated by adding either ketanserin, a 5-HT2 receptor antagonist, R68070, a TxA(2) receptor antagonist, BN52021 , a platelet activating factor (PAF) receptor antagonist, and trapidil, a p latelet derived growth factor (PDGF) receptor antagonist. The role of diffe rent leucocyte sub-populations (neutrophils and monocytes+lymphocytes) was also determined in additional experiments. Results: SMC proliferation was s ignificantly increased by activated platelets to 360+/-9% of control values (P<0.05). This effect was reduced by ketanserin R68070, BN 52021 or trapid il. Whole leucocytes, neutrophils or lymphocytes + monocytes also increased SMC proliferation with respect to control experiments. simultaneous stimul ation of SMCs by platelets and whole leucocytes was associated with a signi ficant greater increase in SMC proliferation as compared to SMC stimulated with platelets or leucocytes alone. c-fos expression, almost undetectable i n unstimulated SMCs, was markedly increased by activated platelets or leuco cytes. Conclusions: Activated platelets promote SMC proliferation in vitro via release of soluble mediators, including serotonin, thromboxane A(2) PAF and PDGF; activated leucocytes also induce a significant SMC proliferation and exert an additive effect when activated together with platelets; SMCs stimulated with activated platelets and leucocytes show an early expression of the proto-oncogene c-fos. (C) 1999 Published by Elsevier Science B.V. A ll rights reserved.