THROMBOSPONDIN-1 IS A POTENT MITOGEN AND CHEMOATTRACTANT FOR HUMAN VASCULAR SMOOTH-MUSCLE CELLS

Thrombospondin-1 (TSP-1) is a matricellular protein that is present in negligible amounts in normal human vasculature but occurs in signific ant amounts in diseased vessels. In this study, we examined the effect of TSP-1 on DNA synthesis, proliferation, and migration in human vasc ular smooth muscle cells grown from saphenous vein. TSP-1 (0.1 to 30 m u g/mL) elicited a concentration-dependent increase in DNA synthesis u nder serum-free conditions. In combination with platelet-derived growt h factor, TSP-1 induced a synergistic effect on DNA synthesis that was significantly higher than the additive effect of both agents. In prol iferation assays, TSP-1 increased cell numbers by 50% relative to the serum-free controls over 14 days. In migration assays, conducted using modified Boyden chambers, TSP-1 (greater than or equal to 10 mu g/mL) elicited marked chemotaxis to a degree equivalent to platelet-derived growth factor. The chemotactic response to TSP-1 (10 mu g/mL) was abo lished by the GRGDSP peptide but unaffected by the control GRGESP pept ide, whereas neither peptide inhibited DNA synthesis stimulated by TSP -1. Inhibition of tyrosine kinase activity with genistein or tyrphosti n A23 abolished DNA synthesis induced by TSP-1, and a neutralizing ant ibody to platelet-derived growth factor had no effect on DNA synthesis . Similarly, migration in response to TSP-1 was largely inhibited by t hese tyrosine kinase inhibitors. TSP-1 is a strong mitogen and chemoat tractant for human vascular smooth muscle cells under serum-free condi tions. The novel finding that TSP-1 is mitogenic for human cells contr asts with previous studies that have not shown any significant effect of TSP-1 itself on the growth of animal-derived smooth muscle cells. T SP-1 may play an important modulatory role in the local regulation of vascular smooth muscle function in vascular pathologies in humans.