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Xingji You, Zixi Chen, Huina Zhao, Chen Xu, Weina Liu, Qianqian Sun, Ping He, Hang Gu, and Xin Ni

Recent evidence suggests that uterine activation for labor is associated with inflammation within uterine tissues. Hydrogen sulfide (H2S) plays a critical role in inflammatory responses in various tissues. Our previous study has shown that human myometrium produces H2S via its generating enzymes cystathionine-γ-lyase (CSE) and cystathionine-β-synthetase (CBS) during pregnancy. We therefore explored whether H2S plays a role in the maintenance of uterine quiescence during pregnancy. Human myometrial biopsies were obtained from pregnant women at term. Uterine smooth muscle cells (UMSCs) isolated from myometrial tissues were treated with various reagents including H2S. The protein expression of CSE, CBS and contraction-associated proteins (CAPs) including connexin 43, oxytocin receptor and prostaglandin F receptor determined by Western blot. The levels of cytokines were measured by ELISA. The results showed that CSE and CBS expression inversely correlated to the levels of CAPs and activated NF-κB in pregnant myometrial tissues. H2S inhibited the expression of CAPs, NF-κB activation and the production of interleukin (IL)-1β, IL-6 and tumor necrosis factor α (TNFα) in cultured USMCs. IL-1β treatment reversed H2S inhibition of CAPs. Knockdown of CSE and CBS prevented H2S suppression of inflammation. H2S modulation of inflammation is through KATP channels and phosphoinositide 3-kinase (PI3K) and extracellular signal-regulated kinase (ERK) signaling pathways. H2S activation of PI3K and ERK signaling is dependent on KATP channels. Our data suggest that H2S suppresses the expression of CAPs via inhibition of inflammation in myometrium. Endogenous H2S is one of the key factors in maintenance of uterine quiescence during pregnancy.

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Zixi Chen, Yali Shan, Xingji You, Hang Gu, Chen Xu, Jing Long, and Xin Ni

The nucleotide binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome plays a critical role in various inflammatory diseases. We sought to investigate the role of NLRP3 inflammasome in uterine activation for labor at term and preterm. We found that NLRP3 inflammasome was activated in the myometrium tissues obtained from the pregnant women undergoing labor at term (TL) compared with those not undergoing labor (TNL) at term. NLRP3 inflammasome was also activated in amnion and chorion-deciduas in TL and preterm labor (PTL) groups. In the mouse model, uterine NLRP3 inflammasome and nuclear factor kappaB (NF-κB) were activated toward term and during labor. Treatment of pregnant mice with lipopolysaccharide (LPS) and RU38486 induced preterm birth (PTB) and also promoted uterine NLRP3 inflammasome and NF-κB activation. Treatment of pregnant mice with NLRP3 inflammasome inhibitor BAY11-7082 and MCC950 delayed the onset of labor and suppressed NLRP3 inflammasome and NF-κB activation in uterus. MCC950 postponed labor onset of the mice with LPS and RU38486 treatment and inhibited NLRP3 inflammasome activation in uterus. Our data provide the evidence that NLRP3 inflammasome is involved in uterine activation for labor onset in term and PTB in humans and mouse model.

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Xingji You, Zixi Chen, Qianqian Sun, Ruojin Yao, Hang Gu, and Xin Ni

Urocortins (UCNs), belonging to corticotropin-releasing hormone (CRH) family, exert their function via CRH receptor type 1 (CRHR1) and 2 (CRHR2). Our previous studies have demonstrated that CRH acts on CRHR1 to potentiate prostaglandins (PGs) output induced by inflammatory stimuli in myometrial cells. In the present study, we sought to investigate the effects of UCNs on prostaglandin (PG) output via CRHR2 in cultured human uterine smooth muscle cells (HUSMCs) from pregnant women at term. We found that UCN and UCN 3 treatment promoted PGE2 and PGF2α secretion in a dose-dependent manner. In contrast, UCN2 dose-dependently inhibited PGE2 and PGF2α secretion. Their effects were reversed by CRHR2 antagonist and CRHR2 siRNA. Mechanically, we showed that UCN and UCN3 suppressed cAMP production and led to Gi activation while UCN2 stimulated cAMP production and activated Gs signaling. Further, UCN and UCN3 but not UCN2 activated NF-κB and MAPK signaling pathways through Gi signaling. UCN and UCN3 stimulation of PGs secretion were dependent on Gi/adenylyl cyclase (AC)/cAMP, NF-κB and MAPK signaling pathways. UCN2 suppression of PGs output was through Gs/AC/cAMP signaling pathways. Our data suggest that UCN, UCN2 and UCN3 can finely regulate PGs secretion via CRHR2, which facilitates the functional status of the uterus during pregnancy.