Expression of the calcium-activated potassium channel in upper and lower segment human myometrium during pregnancy and parturition.

BACKGROUND: Large conductance calcium-activated potassium channel (BKCa) plays an important role in the control of uterine contractility during pregnancy. The change from uterine quiescence to enhanced contractile activity may be associated with the spatial and temporal expression of BKCa within myometrium. The objectives of this study were to examine the expression of BKCa alpha- and beta-subunit in upper segment (US) and lower segment (LS) regions of uterus, and to investigate for the possibly differential expression of these proteins in US and LS myometrium obtained from three functional states: (1) non-pregnant (NP); (2) term pregnant not in labour (TNL) and (3) term pregnant in labour (TL). METHODS: Myometrial biopsies were collected from non-pregnant women at hysterectomy and pregnant women at either elective caesarean section or emergency caesarean section. Protein expression level and cellular localization of BKCa alpha- and beta-subunit in US and LS myometrium were determined by Western blot analysis and immunohistochemistry, respectively. RESULTS: BKCa alpha- and beta-subunit were predominantly localized to myometrial smooth muscle in both US and LS myometrium obtained from non-pregnant and pregnant patients. The level of BKCa alpha-subunit in US but not in LS was significantly higher in NP myometrium than those measured in myometrium obtained during pregnancy. Lower expression of BKCa alpha-subunit in both US and LS was found in TL than in TNL biopsies. Expression of beta-subunit in both US and LS myometrium was significantly reduced in TL group compared with those measured in TNL group. There was no significant difference in BKCa beta-subunit expression in either US or LS between NP and TNL group. CONCLUSION: Our results suggest that expression of BKCa alpha- and beta-subunit in pregnant myometrium is reduced during labour, which is consistent with the myometrial activity at the onset of parturition.

MiR-22/Sp-1 Links Estrogens With the Up-Regulation of Cystathionine γ-Lyase in Myocardium, Which Contributes to Estrogenic Cardioprotection Against Oxidative Stress.

Hydrogen sulfide, generated in the myocardium predominantly via cystathionine-γ-lyase (CSE), is cardioprotective. Our previous study has shown that estrogens enhance CSE expression in myocardium of female rats. The present study aims to explore the mechanisms by which estrogens regulate CSE expression, in particular to clarify the role of estrogen receptor subtypes and the transcriptional factor responsible for the estrogenic effects. We found that either the CSE inhibitor or the CSE small interfering RNA attenuated the protective effect of 17ß-estradiol (E2) against H2O2- and hypoxia/reoxygenation-induced injury in primary cultured neonatal cardiomyocytes. E2 stimulates CSE expression via estrogen receptor (ER)-α both in cultured cardiomyocytes in vitro and in the myocardium of female mice in vivo. A specificity protein-1 (Sp-1) consensus site was identified in the rat CSE promoter and was found to mediate the E2-induced CSE expression. E2 increases ERα and Sp-1 and inhibits microRNA (miR)-22 expression in myocardium of ovariectomized rats. In primary cardiomyocytes, E2 stimulates Sp-1 expression through the ERα-mediated down-regulation of miR-22. It was confirmed that both ERα and Sp-1 were targeted by miR-22. In the myocardium of ovariectomized rats, the level of miR-22 inversely correlated to CSE, ERα, Sp-1, and antioxidant biomarkers and positively correlated to oxidative biomarkers. In summary, this study demonstrates that estrogens stimulate Sp-1 through the ERα-mediated down-regulation of miR-22 in cardiomyocytes, leading to the up-regulation of CSE, which in turn results in an increase of antioxidative defense. Interaction of ERα, miR-22, and Sp-1 may play a critical role in the control of oxidative stress status in the myocardium of female rats.