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Novel regulation of pregnant human myometrial smooth muscle cell gap junctions by human chorionic gonadotropin
1Department of Obstetrics and Gynecology, University of Louisville School of Medicine, Kentucky 40292.
Human myometrium contains hCG/LH receptors. There are fewer of these receptors during labor compared to no labor at preterm or term deliveries. Exogenous hCG can directly inhibit oxytocin-stimulated human myometrial contractions. These findings suggest that hCG may directly maintain myometrial quiescence during pregnancy. As maintenance of uterine quiescence may involve down-regulation of myometrial gap junctions, we investigated the effect of hCG on connexin-43 (CX-43) gene expression from RNA to protein and morphological gap junctions. The addition of 5 or 10 nM highly purified hCG to subconfluent cultures of pregnant myometrial smooth muscle cells resulted in a significant decrease in CX-43 protein levels. Higher hCG concentrations (100 and 1000 nM), however, had no effect. The maximal effect of hCG was seen at 4-8 h of culture, followed by recovery after a longer duration of culture. hCG treatment also concomitantly decreased CX-43 messenger RNA and morphological gap junctions. The hCG effect on CX-43 protein levels is hormone specific and mediated by protein kinase-A signaling. Estradiol and oxytocin increased, whereas progesterone decreased, CX-43 protein levels and morphological gap junctions. The oxytocin-induced increase was reversed by cotreatment with hCG. Although RU 486 alone had no effect on CX-43 protein levels, it prevented the down-regulating action of hCG and progesterone. In summary, our results demonstrate that hCG can directly decrease CX-43 messenger RNA, protein, and morphological gap junctions in cultured pregnant human myometrial smooth muscle cells. The hCG action is concentration and time dependent, hormone specific, and mediated by protein kinase-A signaling and appears to involve progesterone receptors. These data lend support to the concept that hCG could be one of the hormones responsible for maintaining uterine quiescence by down-regulating myometrial gap junctions during pregnancy.
Human myometrium contains hCG/LH receptors. There are fewer of these receptors during labor compared to no labor at preterm or term deliveries. Exogenous hCG can directly inhibit oxytocin-stimulated human myometrial contractions. These findings suggest that hCG may directly maintain myometrial quiescence during pregnancy. As maintenance of uterine quiescence may involve down-regulation of myometrial gap junctions, we investigated the effect of hCG on connexin-43 (CX-43) gene expression from RNA to protein and morphological gap junctions. The addition of 5 or 10 nM highly purified hCG to subconfluent cultures of pregnant myometrial smooth muscle cells resulted in a significant decrease in CX-43 protein levels. Higher hCG concentrations (100 and 1000 nM), however, had no effect. The maximal effect of hCG was seen at 4-8 h of culture, followed by recovery after a longer duration of culture. hCG treatment also concomitantly decreased CX-43 messenger RNA and morphological gap junctions. The hCG effect on CX-43 protein levels is hormone specific and mediated by protein kinase-A signaling. Estradiol and oxytocin increased, whereas progesterone decreased, CX-43 protein levels and morphological gap junctions. The oxytocin-induced increase was reversed by cotreatment with hCG. Although RU 486 alone had no effect on CX-43 protein levels, it prevented the down-regulating action of hCG and progesterone. In summary, our results demonstrate that hCG can directly decrease CX-43 messenger RNA, protein, and morphological gap junctions in cultured pregnant human myometrial smooth muscle cells. The hCG action is concentration and time dependent, hormone specific, and mediated by protein kinase-A signaling and appears to involve progesterone receptors. These data lend support to the concept that hCG could be one of the hormones responsible for maintaining uterine quiescence by down-regulating myometrial gap junctions during pregnancy.