ASSOCIATION FOR ACADEMIC SURGERY The Role of Estrogen Receptor a and b in Regulating Vascular Smooth Muscle Cell Proliferation is Based on Sex 1

Background. We previously demonstrated that vascularsmoothmusclecells(VSMC)proliferationanddevelopment of neointimal hyperplasia as well as the ability of nitric oxide (NO) to inhibit these processes is dependent on sex and hormone status. The aim of this study was to evaluate the role of estrogen receptor (ER) in mediating proliferation in male and female VSMC. Materials and Methods. Proliferation was assessed in primary rat aortic male and female VSMC using 3 H-thymidine incorporation in the presence or absence of ER alpha (a) inhibitor methyl-piperidinopyrazole, the ER beta (b) inhibitor (R,R)-5,11-Diethyl5,6,11,12-tetrahydro-2,8-chrysenediol, the combined ERab inhibitor ICI 182,780, and/or the NO donor DETA/NO. Proliferation was also assessed in primary aortic mouse VSMC harvested from wildtype (WT), ERa knockout (ERa KO), and ERb knockout (ERb KO) mice in the presence or absence of DETA/NO and the ERa ,E Rb, and ERab inhibitors. Protein levels were assessed using Western blot analysis. Results. Protein expression of ERa and ERb was present and equal in male and female VSMC, and did not change after exposure to NO. Inhibition of either ERa or ERb had no effect on VSMC proliferation in the presence or absence of NO in either sex. However, inhibition of ERab in rat VSMC mitigated NOmediated inhibition in female but not male VSMC (P < 0.05). Evaluation of proliferation in the knockout mice revealed distinct patterns. Male ERaKO and ERbKO VSMC proliferated faster than male WT VSMC (P < 0.05). Female ERbKO proliferated faster than female WT VSMC (P < 0.05), but female ERaKO VSMC proliferated slower than female WT VSMC (P<0.05).Last,weevaluated theeffectofcombinedinhibition of ERa and ERb in these knockout strains. Combined ERab inhibition abrogated NO-mediated inhibition of VSMC proliferation in female WT and knockout VSMC (P < 0.05), but not in male VSMC. Conclusions. These data clearly demonstrate a role for the ER in mediating VSMC proliferation in both sexes. However, these data suggest that the antiproliferative effects of NO may be regulated by the ER in females but not males. Published by Elsevier Inc.