Angiogenesis is a physiological process for endometrial regeneration in the menstrual cycle and remodeling during pregnancy. Endogenous hydrogen sulfide (H₂S), produced by cystathionine-β synthase (CBS) and cystathionine-γ lyase (CSE), is a potent proangiogenic factor; yet, whether the H₂S system is expressed in the endometrium and whether H₂S plays a role in endometrial angiogenesis are unknown.  This study was to test whether estrogens stimulate endometrial H₂S biosynthesis to promote endometrial microvascular endothelial cell (EMEC) angiogenesis.  CBS mRNA/protein and H₂S production significantly differed among endometria from postmenopausal (POM), premenopausal secretory (sPRM) and proliferative (pPRM) nonpregnant (NP) and pregnant (Preg) women (p<0.05) in a rank order of POM ≈ sPRM < pPRM <<< Preg, positively correlating with angiogenesis indices and endogenous estrogens and with no difference in CSE expression.  CBS and CSE proteins were localized to stroma, glands, and vessels in endometrium, and greater stromal CBS protein was observed in the pPRM and Preg states.  Estradiol (but not progesterone) stimulated CBS (but not CSE) expression and H₂S production in endometrial stromal cells (ESCs) in vitro, which were attenuated by ICI 182,780.  The H₂S donor sodium hydrosulfide promoted in vitro endometrial microvascular endothelial cell (EMEC) angiogenesis.  Co-culture with sPRM, pPRM, and Preg ESCs all stimulated EMEC migration with a rank order of sPRM < pPRM ≈ Preg.  CBS (but not CSE) inhibition attenuated ESC-stimulated EMEC migration.  Estradiol did not affect EMEC migration but potentiated ESC-stimulated EMEC migration.  Altogether, estradiol-stimulated specific receptor-dependent stromal CBS-H₂S production to promote endometrial EMEC angiogenesis in women.

Supplemental table S1-S3, and supplemental figure S1