78 Preeclampsia Diminishes Pregnancy-augmented Myometrial H2S Biosynthesis and Myometrial Artery Cystathionine ß-Synthase Expression in Women

Abstract

An inadequate rise in uterine blood flow in pregnancy can lead to preeclampsia. Endogenous hydrogen sulfide (H2S) is a potent vasodilator that is synthesized from L-cysteine by cystathionine-β synthase (CBS) and cystathionine-γ lyase (CSE). Enhanced H2S production by selective upregulation of CBS, but not CSE, has been recognized as a uterine artery vasodilator in pregnancy. This study using human myometrial biopsies tests a hypothesis that preeclampsia diminishes pregnancy-augmented uterine artery H2S biosynthesis. Human myometrial biopsies were collected from normal pregnant, severe preeclamptic women, and hysterectomies of nonpregnant women (n = 3-5/group) with IRB approval and written consent. Levels of CBS and CSE mRNAs were assessed by qRT-PCR and their proteins were assessed by immunoblotting and immunofluorescence microscopy. H2S production was determined by methylene blue assay with or without specific inhibitors of CBS (CHH, 1 mM) and CSE (BCA, 1 mM). Myometrial CBS mRNA and protein were greater (p < 0.01) in normal pregnant (P) compared to nonpregnant women (NP). Pregnancy did not change myometrial CSE mRNA and protein. Myometrial H2S production was greater (p<0.05) in P vs. NP women, which was blocked by incubation with CHH or its combination with BCA, but not BCA alone. Compared to normal pregnant subjects, preeclampsia reduced myometrial CBS mRNA, protein, and H2S production to levels comparable to that of nonpregnant women. Immunofluorescence microscopy identified CBS and CSE protein localization in the myocytes, endothelium, and smooth muscle of myometrial arteries. Quantitation of the immunoreactive CBS and CSE signals showed greater CBS, but not CSE protein in P vs. NP myocytes and myometrial artery endothelium and smooth muscle, while preeclampsia reduced CBS protein levels to that in nonpregnant controls, without changing CSE protein in these cells. Pregnancy augments myometrial myocyte and myometrial artery endothelial and smooth muscle CBS expression. CBS expression and H2S production are significantly downregulated in severe preeclampsia.