The Role of Estrogen Receptor α and β in Regulating Vascular Smooth Muscle Cell Proliferation is Based on Sex

Abstract

We previously demonstrated that vascular smooth muscle cells (VSMC) proliferation and development 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. Proliferation was assessed in primary rat aortic male and female VSMC using (3)H-thymidine incorporation in the presence or absence of ER alpha (α) inhibitor methyl-piperidino-pyrazole, the ER beta (β) inhibitor (R,R)-5,11-Diethyl-5,6,11,12-tetrahydro-2,8-chrysenediol, the combined ERαβ inhibitor ICI 182,780, and/or the NO donor DETA/NO. Proliferation was also assessed in primary aortic mouse VSMC harvested from wildtype (WT), ERα knockout (ERα KO), and ERβ knockout (ERβ KO) mice in the presence or absence of DETA/NO and the ERα, ERβ, and ERαβ inhibitors. Protein levels were assessed using Western blot analysis. Protein expression of ERα and ERβ was present and equal in male and female VSMC, and did not change after exposure to NO. Inhibition of either ERα or ERβ had no effect on VSMC proliferation in the presence or absence of NO in either sex. However, inhibition of ERαβ in rat VSMC mitigated NO-mediated inhibition in female but not male VSMC (P < 0.05). Evaluation of proliferation in the knockout mice revealed distinct patterns. Male ERαKO and ERβKO VSMC proliferated faster than male WT VSMC (P < 0.05). Female ERβKO proliferated faster than female WT VSMC (P < 0.05), but female ERαKO VSMC proliferated slower than female WT VSMC (P < 0.05). Last, we evaluated the effect of combined inhibition of ERα and ERβ in these knockout strains. Combined ERαβ inhibition abrogated NO-mediated inhibition of VSMC proliferation in female WT and knockout VSMC (P < 0.05), but not in male VSMC. 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.