Estradiol regulates monocyte chemotactic protein-1 in human coronary artery smooth muscle cells: a mechanism for its antiatherogenic effect

Objective: The protective effect of estrogen against early atherosclerosis in animal models is well documented, but the mechanisms responsible for thi s effect are not well understood. The earliest recognizable event in the pa thogenesis of atherosclerosis is an increased recruitment of macrophages in to the arterial subendothelium. Macrophages first play a protective role by removing low-density lipoproteins, but when the cholesterol is in excess, macrophages are converted into foam cells and form atheromas. Recent human and animal data indicate that the recruitment of macrophages to the arteria l wall is mediated by monocyte chemotactic protein-1 (MCP-1). We hypothesiz ed that one of the mechanisms of estrogen's protective effect against ather osclerosis may be the down-regulation of MCP-1 expression in the arterial w all. Design: Human coronary artery smooth muscle cells were replicated to conflu ence in smooth muscle cell basal medium supplemented with growth factors an d 5% fetal bovine serum. Before each experiment, cells were incubated for 2 4 h with phenol red-free medium containing 5% charcoal-stripped calf serum, and then they were treated with various concentrations of 17 beta -estradi ol as well as selective estrogen receptor (ER) modulators, raloxifene and t amoxifen. MCP-1 messenger ribonucleic acid (mRNA) levels were quantified by Northern blots. MCP-1 protein was quantified using an enzyme-linked immuno sorbent assay. ER expression was evaluated by reverse transcriptase-polymer ase chain reaction. Results: Human coronary artery smooth muscle cells expressed MCP-1 mRNA and produced MCP-1 protein. Estradiol induced up to 40% inhibition in mRNA exp ression at concentrations 10(-9) M and higher. Raloxifene and tamoxifen als o resulted in an inhibition, but the inhibition was less than when induced by estradiol. Estradiol also inhibited the MCP-1 protein production in a co ncentration-dependent manner (p < 0.05). Coronary smooth muscle cells expre ssed both ER alpha and ERP. Conclusion: Our findings suggest that one of the mechanisms by which estrog en prevents atherosclerosis is by down-regulating MCP-1 expression, thus de creasing macrophage recruitment to the arterial wail.