Objectives: It has been suggested that estrogen may improve endothelial cell function to delay the onset of atherosclerosis in pre-menopausal females, though its mechanism of action is not fully understood. We examined the hypothesis that human estrogen receptor-alpha (ER alpha) gene transfection improves the endothelial cell function.
Methods: A replication deficient adenoviral vector was used to transfect the ER alpha gene into bovine aortic endothelial cells (BAEC) and a GFP gene containing vector was used as control. Expression of the eNOS gene was determined by Northern blot analysis and enzyme activity assay; cell migration was assayed using a Transwell apparatus; and tyrosine phosphorylation of FAK was estimated by Western blot analysis.
Results: ER alpha gene transfection of endothelial cells produced a 2-3-fold increase in eNOS mRNA and protein levels as well as a significant increase (P < 0.05) in NOS activity as measured by citrulline assay and nitrite accumulation in the media in response to bradykinin stimulation. Treatment of cells with estrogen blocking agent ICI 182780 inhibited eNOS induction in response to ER alpha transfection. ER alpha gene transfection significantly inhibited (P < 0.05) bFGF-induced chemotactic migration of endothelial cells but increased cell attachment to fibronectin, laminin, and type I and IV collagens. ER alpha gene transfer also inhibited bFGF-stimulated tyrosine phosphorylation of FAK.
Conclusion: Our results suggest that the atheroprotective effects of estrogen may in part be mediated by ER alpha-induced upregulation of eNOS gene expression and maintenance of endothelial cell function and integrity.