TRANSFORMED RAT ARTERIAL SMOOTH-MUSCLE CELLS INDUCE PLATELET-AGGREGATION

Atherogenesis is characterized by a proliferation of arterial smooth m uscle cells that may be of transformed nature. Platelets are implicate d in the progression of atherosclerotic lesions through thrombotic com plications. The present study was designed to investigate whether tran sformed arterial smooth muscle cells (SMC) could specifically aggregat e platelets. We used rat transformed arterial SMC lines, V6- and V8-li nes, that we bad previously established. Experiments were performed wi th an in vitro homologous rat system. Suspensions of SMC were added wi thout any other aggregating agent to rat heparinized platelet-rich pla sma (PRP) in a coagulo-aggregometer. The effect of transformed V6-line and V8-line SMC was compared to that of their normal parental counter parts, V6- and Vs-parent cells. Suspensions of transformed SMC induced , in a dose-dependent manner, an immediate and reversible ADP-like pla telet aggregation. The amplitude of platelet aggregation was much high er with addition of transformed cells than of the corresponding contro l SMC (7.39 +/- 0.75 cm vs. 0.85 +/- 0.62 cm with 2 x 10(6) SMC, V6-li ne vs. V6-parent cells, respectively). ADP-like aggregation did not si gnificantly differ between the two transformed V6- and Vs-lines. ADP-l ike platelet aggregation was also obtained with supernatants of transf ormed SMC suspensions, the amplitude being higher with supernatants th an with cell suspensions (21.0 +/- 3.64 cm vs. 6.8 +/- 1.22 cm with 1. 0 x 10(6) V8-line cells, supernatant vs, cell suspension, respectively ). The transformed SMC-induced aggregation of platelets was inhibited by apyrase (125 mu M) and iodoacetate (25mM) and thus was ascribable t o ADP released by the SMC. In addition, all suspensions of SMC, normal or transformed, but not their supernatants, induced plasma clotting a fter variable coagulation times. Coagulation was inhibited by hirudin (25 to 100 U/ml) and phospholipase A2 (10 U/ml) indicating thrombin ge neration through activity of the SMC membrane tissue factor. The prese nt results show that transformed arterial smooth muscle cells may dire ctly aggregate platelets via a release of ADP and this could be of pat hophysiological relevance for thrombosis associated with atheroscleros is.