Throughout most of pregnancy, uterine quiescence is maintained by increased progesterone receptor (PR) transcriptional activity, whereas spontaneous labor is initiated/facilitated by a concerted series of biochemical events that activate inflammatory pathways and have a negative impact on PR function. In this study, we uncovered a previously undescribed regulatory pathway whereby micro-RNAs (miRNAs) serve as hormonally modulated and conserved mediators of contraction-associated genes in the pregnant uterus in the mouse and human. Using miRNA and gene expression microarray analyses of uterine tissues, we identified a conserved family of miRNAs, the miR-200 family, that is highly induced at term in both mice and humans as well as two coordinately downregulated targets, zinc finger E-box binding homeobox proteins ZEB1 and ZEB2, which act as transcriptional repressors. We also observed up-regulation of the miR-200 family and down-regulation of ZEB1 and ZEB2 in two different mouse models of preterm labor. We further demonstrated that ZEB1 is directly up-regulated by the action of progesterone (P 4 )/PR at the ZEB1 promoter. Excitingly, we observed that ZEB1 and ZEB2 inhibit expression of the contractionassociated genes, oxytocin receptor and connexin-43, and block oxytocin-induced contractility in human myometrial cells. Together, these findings implicate the miR-200 family and their targets, ZEB1 and ZEB2, as unique P 4 /PR-mediated regulators of uterine quiescence and contractility during pregnancy and labor and shed light on the molecular mechanisms involved in preterm birth.A lthough premature labor is the leading cause of neonatal morbidity and mortality in developed countries, the signaling mechanisms that maintain uterine quiescence during pregnancy and promote increased uterine contractility leading to labor at term and preterm remain incompletely defined (1). In mammalian pregnancy, uterine quiescence is maintained by elevated circulating progesterone (P 4 ) acting via the progesterone receptor (PR). Conversely, parturition is associated with a decline in maternal circulating P 4 and/or a decrease in the function of the PR, termed "functional P 4 withdrawal," (2, 3) and an increased inflammatory response within the uterus and cervix (4). Studies from a number of laboratories, including our own, suggest that P 4 and PR maintain uterine quiescence until term by inhibiting expression of contraction-associated genes [e.g., connexin-43 (CXN-43), oxytocin receptor (OXTR), cyclooxygenase 2 (COX-2)] in the myometrium, in part, via anti-inflammatory actions. For example, P 4 and PR inhibit activation of COX-2 expression in myometrial cells through direct interaction of PR with NF-κB p65 (5) and by P 4 -induced expression of the NF-κB inhibitor, IκB-α (6).Recently, it has been shown that micro-RNAs (miRNAs) play especially powerful roles in vascular smooth muscle cells and in female reproduction, wherein they have been implicated in proliferation, differentiation, and hormone responsiveness (7-9). The identification o...
Chronic morphine administration (via subcutaneous pellet) decreases the size of dopamine neurons in the ventral tegmental area (VTA), a key reward region in the brain, yet the molecular basis and functional consequences of this effect are unknown. In this study, we used viral-mediated gene transfer in rat to show that chronic morphine-induced downregulation of the insulin receptor substrate 2 (IRS2)-thymoma viral proto-oncogene (Akt) signaling pathway in the VTA mediates the decrease in dopamine cell size seen after morphine exposure and that this downregulation diminishes morphine reward, as measured by conditioned place preference. We further show that the reduction in size of VTA dopamine neurons persists up to 2 weeks after morphine withdrawal, which parallels the tolerance to morphine's rewarding effects caused by previous chronic morphine exposure. These findings directly implicate the IRS2-Akt signaling pathway as a critical regulator of dopamine cell morphology and opiate reward.
During pregnancy, uterine quiescence is maintained by increased progesterone receptor (PR) activity, but labor is facilitated by a series of events that impair PR function. Previously, we discovered that miR-200 family members serve as progesterone (P 4 )-modulated activators of contraction-associated genes in the pregnant uterus. In this study, we identified a unique role for miR-200a to enhance the local metabolism of P 4 in myometrium and, thus, decrease PR function during the progression toward labor. miR-200a exerts this action by direct repression of STAT5b, a transcriptional repressor of the P 4 -metabolizing enzyme 20α-hydroxysteroid dehydrogenase (20α-HSD). We observed that miR-200a expression increased and STAT5b expression coordinately decreased in myometrium of mice as they progressed to labor and in laboring myometrium from pregnant women. These changes were associated with a dramatic increase in expression and activity of 20α-HSD in laboring myometrium from mouse and human. Notably, overexpression of miR-200a in cultured human myometrial cells (hTERT-HM) suppressed STAT5b and increased 20α-HSD mRNA levels. In uterine tissues of ovariectomized mice injected with P 4 , miR-200 expression was significantly decreased, STAT5b expression was up-regulated, and 20α-HSD mRNA was decreased, but in 15 d postcoitum pregnant mice injected with the PR antagonist RU486, preterm labor was associated with increased miR-200a, decreased STAT5b, and enhanced 20α-HSD expression. Taken together, these findings implicate miR-200a as an important regulator of increased local P 4 metabolism in the pregnant uterus near term and provide insight into the importance of miR-200s in the decline in PR function leading to labor.
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