Expression of Estrogen Receptors-(alpha) and -(beta)in the Pregnant Ovine Uterine Artery Endothelial Cells In Vivo and In Vitro

Estrogen is recognized to be one of the driving forces in increases in uterine blood flow through both rapid and delayed actions via binding to its receptors, ER(alpha) and ER(beta) at the uterine artery (UA) wall, and especially in UA endothelium (UAE). However, information regarding estrogen receptor (ER) expression in UAE is limited. This study was designed to test whether ERs are expressed in UAE in vivo, and if they are, whether these receptors are maintained in cultured UA endothelial cells (UAECs) in vitro. By using immunohistochemical and Western blot analyses, we clearly demonstrated ER(alpha) and ER(beta) protein expression in pregnant (Days 120–130) sheep UA and UAE in vivo and as well as cultured UAECs in vitro. Reverse transcription-polymerase chain reaction (RT-PCR) amplified both ER(alpha) and ER(beta) mRNAs in UA, UAE, and UAECs. Of interest, a truncated ER(beta) (ER(beta)2) variant due to a splicing deletion of exon 5 of the ER(beta) gene was detected in these cells. Quantitative RT-PCR analysis revealed that ER(alpha) mRNA levels are ~8-fold (P < 0.01) higher than that of ER(beta) in UAECs, indicating that ER(alpha) may play a more important role than ER(beta) in the UAEC responses to estrogen. Fluorescence immunolabeling analysis showed that ER(alpha) is present in both nuclei and plasma membranes in UAECs, and the latter is also colocalized with caveolin-1. The membrane and nuclear ER(alpha) presumably participate in rapid and delayed responses, respectively, to estrogen on UAE. Taken together, our data demonstrated that UAE is a direct target of estrogen actions and that the UAEC culture model we established is suitable for dissecting estrogen actions on UAE.