UC Irvine

Numerous studies have identified estrogens as a driving force that regulates uterine vasodilation during the estrous cycle and pregnancy and by estrogen replacement therapy (ERT). Estrogen-induced and pregnancy-associated increases in uterine blood flow (UBF) are mediated largely by nitric oxide (NO) production at the uterine artery (UA) endothelium. However, estrogen-induced uterine vasodilation is only inhibited by ~65% with local blockade of NO, suggesting other mechanisms play a crucial role in the estrogen-induced uterine vasodilation.

Hydrogen sulfide (H2S) is a novel vasodilator in mammalian organs and tissues. Endogenous H2S is biosynthesized primarily by two enzymes: cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). However, to date virtually nothing is known as to whether the H2S biosynthesis system exists in the UA and whether this system is regulated by estrogen or pregnancy.

In the present studies we sought out to determine if estradiol-17β (E2β) stimulates UA H2S biosynthesis in UA and systemic (mesenteric, MA; and carotid, CA) arteries of nonpregnant ovariectomized sheep subjected to ERT in vivo. We utilized the Methylene blue assay to determine H2S production in the lysates of arteries, and qPCR and Western blotting to assess CBS/CSE mRNA and protein. Immunofluorescence microscopy determined CBS/CSE cellular localization. We found ERT to stimulate H2S production and CBS expression in UA and MA, but not CA. CBS was expressed in UA endothelium and vascular smooth muscle. Additionally, CSE was expressed in all arteries examined but was not influenced by ERT.

Next, we used the well-established primary UA endothelial cell (UAEC) model, and established a novel primarily UA smooth muscle cell (UASMC) model to assess the molecular mechanisms by which E2β stimulates H2S production in UA in vitro. We found that E2β stimulated H2S production and upregulated CBS and CSE expression in UAEC and UASMC in culture. Additionally, the ER antagonist ICI 182, 780 inhibited E2β-stimulated H2S biosynthesis and CBS/CSE transcription in both cell types. By using specific antagonists and agonist to ERα/β, we also found that both ER isoforms play a role in E2β-stimulated H2S biosynthesis in UAEC and UASMC.

Collectively these data suggest that E2β stimulates UA H2S biosynthesis via ER-dependent transcription, serving as a novel mechanism in E2β-stimulated vasodilation.