ENDOCRINE CASCADES AND PARTURITION: REGULATION OF THE HUMAN FETAL ADRENAL

虽然调控分娩的信号传递过程几乎肯定是多因素的，但也有 相当多的目的论证据表明，胎儿肾上腺会影响分娩时机。人胎儿肾上腺近期开始产生皮质醇，并增加硫酸脱氢表雄酮(脱氢表雄酮-S)的产生，脱氢表雄酮是胎盘雌激素产生的底物。胎儿皮质醇增加胎盘促肾上腺皮质激素释放激素(CRH)，启动内分泌前馈级联反应，直到分娩和胎儿与胎盘分离时才结束。越来越多的证据支持这一观点，即雌激素和胎盘CRH作用于子宫肌层，启动从静止收缩状态到反应性收缩状态的转变，而皮质醇改变胎膜前列腺素的产生。拟议的研究将 明确CRH直接激活胎儿肾上腺的机制，从而启动这一前馈内分泌级联反应，最终导致分娩。为了实现这些目标，提出了三个目标：具体目标1将定义CRH受体和信号通路，这些受体和信号通路调节胎儿肾上腺皮质醇和DHEA-S的产生。本研究的目的是明确调节胎儿肾上腺的促肾上腺皮质激素释放激素受体亚型，确定促肾上腺皮质激素释放激素调节皮质醇和脱氢表雄酮-S生物合成的细胞内信号通路，确定促肾上腺皮质激素释放激素受体表达的机制，明确促肾上腺皮质激素释放激素受体的表达模式。具体目标2的目标是确定CRH对胎儿肾上腺细胞产生皮质醇和DHEA-S能力的慢性影响。在妊娠的大部分时间里，胎儿肾上腺几乎不表达3β-羟基类固醇脱氢酶(HSD3B2)，因此不可能产生皮质醇。妊娠后半程CRH水平升高与胎儿肾上腺皮质醇生物合成和HSD3B2表达的启动相一致。在目标2中，我们将确定CRH基因靶点，通过激活HSD3B2基因转录来促进胎儿肾上腺皮质醇的产生。具体目标3将确定CRH是否增加胎儿肾上腺对ACTH的反应，导致妊娠最后几周类固醇产生的戏剧性激活。CRH的这种效应将解释被认为是相互矛盾的观察，即在胎儿肾上腺类固醇合成最多的最后三个月，循环中的ACTH水平并没有增加。本申请中提出的目标的完成将决定CRH如何在妊娠后期激活胎儿肾上腺，并将提供 正常和早产的内分泌控制的重要细节。

While the signaling processes that regulate parturition are almost certainly multifactorial, there is considerable teleological evidence that the fetal adrenal glands act to influence the timing of labor. Near term the human fetal adrenals commence cortisol production and increase production of dehydroepiandrosterone-sulfate (DHEA-S), which acts as substrate for placental estrogen production. Fetal derived cortisol increases placental corticotropin releasing hormone (CRH) that initiates an endocrine feed-forward cascade that does not end until labor and separation of the fetus from the placenta. Increasing evidence supports the idea that estrogens and placental CRH act on the myometrium to initiate the transition from a quiescent to responsive contractile state, while cortisol alters fetal membrane prostaglandin production. The proposed research will define the mechanisms through which CRH directly activates the fetal adrenal gland thus initiating this feedforward endocrine cascade that ends in labor. To achieve these goals three aims are proposed: Specific Aim 1 will define the CRH receptors and signaling pathways that regulate fetal adrenal production of cortisol and DHEA-S. The goal of this aim is to define the CRH receptor isoform that regulates the fetal adrenal, determine the intracellular signaling pathways used by CRH to regulate cortisol and DHEA-S biosynthesis, determine the mechanism regulating adrenal expression of CRH receptors and define the pattern of CRH receptor expression. The goal of Specific Aim 2 is to define the chronic effects of CRH on the capacity of fetal adrenal cells to produce cortisol and DHEA-S. During most of gestation the fetal adrenal gland expresses little 3beta-hydroxysteroid dehydrogenase (HSD3B2) making cortisol production impossible. Elevated levels of CRH in the second half of gestation coincide with the initiation of fetal adrenal cortisol biosynthesis and expression of HSD3B2. In Aim 2 we will determine CRH gene targets that promote fetal adrenal production of cortisol via activation of HSD3B2 gene transcription. Specific Aim 3 will determine if CRH increases fetal adrenal responsiveness to ACTH leading to the dramatic activation of steroid production seen in the last weeks of gestation. This effect of CRH would explain what was thought to be the conflicting observation that circulating levels of ACTH do not increase during the last trimester when fetal adrenal steroidogenesis most increases. Completion of the goals set forth in this application will determine how CRH activates the fetal adrenal glands late in gestation and will provide important details into endocrine controls of normal and preterm labor.