Estradiol-17β Attenuates Directed Migration of Vascular Smooth Muscle Cells

Intimal proliferation and migration of smooth muscle cells are important components of atherosclerotic progression. Experimental studies suggest an antiatherogenic property of 17β-estradiol (βE2) independent of its effects on serum lipids and lipoproteins. Although the beneficial effect afforded by βE2 is thought to be mediated in part by its antiproliferative properties, its action on smooth muscle cell migration is unknown. To explore this relationship, female rat aortic smooth muscle cells (RASMC) were grown in hormone-free medium and the effect of various concentrations of βE2 on directed cellular migration was measured in-vitro using microwell Boyden chamber apparatus. Immunocytochemistry demonstrated positive staining for estrogen receptors on RASMC. Migration of RASMC to the known chemoattractants platelet-derived growth factor (PDGF-BB), insulin-like growth factor-1, and fibronectin (all at maximal doses for migratory activity) was attenuated by βE2 (0.1 to 10 ng/ml) in concentration-dependent manner relative to control cells treated with vehicle (0.01% ethanol). This effect was insensitive to pretreatment with indomethacin and stereospecific because the enantiomer 17α-estradiol had no response. Like βE2, the synthetic estrogen diethylstilbesterol attenuated directed RASMC chemotaxis whereas testosterone was ineffective. Further studies showed that βE2-mediated suppression of migration was inhibited by both the antiestrogen ICI 164,384 and the gene transcription inhibitor actinomycin D. Similarly, both staurosporine and the more selective protein kinase C inhibitor GF 109203X neutralized the inhibitory effects of βE2. [3H]Thymidine uptake in PDGF-BB stimulated RASMC was not significantly affected by βE2 in concentrations up to 100 ng/ml thus, providing further in vitro evidence of the importance of the effects of βE2 on smooth muscle cell migration. These are the first results demonstrating reduction in directed smooth muscle cell chemotaxis by βE2. The mechanism of this βE2-mediated response appears to involve gene transcription and is sensitive to modulation by protein kinase C.