Fetal hypothalamic-pituitary-adrenal responses to long term hypoxia

胎儿下丘脑-垂体-肾上腺对长期缺氧的反应

• 批准号: 7755432
• 负责人: Charles A Ducsay
• 金额: $ 3.91万
• 依托单位: LOMA LINDA UNIVERSITY
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/7755432
• 关键词: Acclimatization; Acute; Adrenal Cortex; Adrenal Glands; Adult; Animals; Anterior Pituitary Gland; Argipressin; Automobile Driving; Biochemical; Blood flow; CYP11A1 gene; CYP17A1 gene; Cholesterol; Chronic; Chronic stress; Clinical; Corticotropin; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Cytochrome P450; Enzymes; Extracellular Signal Regulated Kinases; Fetal Growth; Fetus; Genes; Glucocorticoids; Growth and Development function; Hydrocortisone; Hypothalamic structure; Hypoxia; Mediating; Mitogen-Activated Protein Kinases; Mixed Function Oxygenases; Molecular; Nitric Oxide; Output; Pathway interactions; Phosphorylation; Physiological; Pituitary Gland; Plasma; Pregnancy; Principal Investigator; Pro-Opiomelanocortin; Process; Production; Regulation; Research; Research Design; SF1; Secondary to; Sheep; Side; Signal Transduction; Stress; Testing; acute stress; fetal; inhibitor/antagonist; paraventricular nucleus; programs; release factor; response; steroidogenic acute regulatory protein; stressor

The fetus has the remarkable ability to adapt to conditions of chronic hypoxia over the course of gestation. One of the key factors mediating this adaptation is cortisol. Regulation of fetal cortisol is necessary for normal fetal growth and development and response to subsequent stressors. Understanding the mechanisms of fetal adaptation to chronic stress is also important in regard to effective use of antenatal glucocorticoid therapy. Our studies have shown that in late gestation, basal plasma cortisol levels are normal in the long-term hypoxic (LTH) sheep fetus, while expression of key adrenal steroidogenic enzymes (P450 cholesterol side chain cleavage [CYP11A] and P450 17alpha-hydroxylase [CYP17])is suppressed. Paradoxically, basal plasma adrenocorticotropin (ACTH) concentrations are elevated and, in response to a secondary stressor, cortisol production is enhanced compared to normoxic controls. Basal plasma concentrations of the ACTH precursors proopiomelanocortin (POMC) and 22 kDa proACTH (the major intermediate in processing of POMC to ACTH) are also elevated. We have further evidence that processing of POMC to ACTH in the anterior pituitary is enhanced during acute stress, leading to elevated plasma ACTH in LTH fetuses. Physiological concentrations of ACTH precursors have been demonstrated to be potent inhibitors of fetal cortisol production. Thus, it is apparent that the fetal hypothalamic-pituitary-adrenocortical (HPA) axis has acclimatized to LTH at all levels. However, the mechanisms driving this adaptation remain to be elucidated. The proposed studies will extend our previous observations on HPA function in the LTH fetus and examine specific mechanisms involved not only in maintaining basal glucocorticoid secretion but also in responding to secondary stressors. The proposed studies will test the general hypothesis that adaptive changes in the fetal HPA axis allow the fetus to acclimatize to the stress of long-term hypoxia while augmenting the ability to respond to a secondary, acute stressor. Specific Aim 1. To elucidate the mechanisms of enhanced hypothalamic drive (i.e., augmented corticotrope function) in LTH fetuses. These studies are designed to test the hypothesis that: LTH results in enhanced hypothalamic paraventricular nuclei (PVN) expression of cortiocotropin releasing factor (CRF) and/or arginine vasopressin (AVP) and/or increased pituitary responsiveness to these ACTH secretagogues resulting in the increased anterior pituitary corticotrope function observed in response to LTH. Specific Aim 2. To determine the molecular and cellular mechanisms by which the adrenal cortex has acclimatized to LTH that results in the observed suppressed adrenal expression of key rate limiting enzymes in glucocorticoid synthesis under basal conditions. Research to date supports that expression of CYP11A and CYP17 is regulated via interplay between the stimulatory ACTH-cAMP and inhibitory ERK pathways. Thus, these studies will test the hypothesis that LTH adrenals are more sensitive to inhibitory effects of the ACTH precursors POMC and 22kD pro ACTH, interfering with ACTH signaling, resulting in suppressed basal CYP expression. We also hypothesize that the extracellular signal-regulated kinase (ERK) pathway is enhanced in the adrenal cortex of the LTH fetus, leading to enhanced phosphorylation of steroidogenic factor-1 (SF-1) which, in turn, suppresses the expression of the key rate limiting genes regulating glucocorticoid production. Specific Aim 3. To elucidate the intracellular and molecular mechanisms for enhanced glucocorticoid secretion in response to an acute secondary stressor following LTH despite decreased CYP11A and CYP17 expression. These studies are designed to test the hypothesis that the enhanced cortisol output following a secondary stressor in LTH fetuses as compared to controls, is the result of enhanced ACTH stimulation of cAMP and protein kinase A, increasing activation of the steroidogenic acute regulatory protein (STAR). Specific Aim 4. To determine the mechanisms of potential changes in adrenal blood flow during a secondary stressor in LTH animals. These studies will test the hypothesis that: the enhanced cortisol output in LTH fetuses compared to controls following a secondary stressor is the result of enhanced adrenal blood flow and that such changes are mediated, at least in part, by nitric oxide.

胎儿在​​整个过程中都具有显着适应慢性缺氧状况的能力 妊娠。介导这种适应的关键因素之一是皮质醇。胎儿皮质醇的调节对于正常的胎儿生长，发育以及对随后的压力源的反应是必要的。了解胎儿适应慢性应激的机制对于有效使用产前糖皮质激素治疗也很重要。我们的研究表明，在妊娠晚期，长期缺氧（LTH）绵羊胎儿的基础等离子体皮质醇水平正常，而关键肾上腺类固醇激素生成酶的表达（P450胆固醇侧链裂解[CYP11A]和P450 17Alpha-Hydroxylase [Cyp11a]和p450。矛盾的是， 基础等离子体肾上腺皮质激素（ACTH）浓度升高，并且响应于二级应激源，与常氧对照相比，皮质醇的产生得到了增强。 ACTH前体的基底血浆浓度蛋白质素（POMC）和22 kDa ProACTH（POMC加工到ACTH的主要中间体）也升高。我们有进一步的证据表明，在急性应激期间，在垂体前体中POMC到ACTH的加工会增强，从而导致LTH胎儿的血浆ACTH升高。 ACTH前体的生理浓度已被证明是胎儿皮质醇产生的有效抑制剂。因此，很明显，胎儿下丘脑 - 垂体 - 肾上腺皮质（HPA）轴具有 适应各个级别的LTH。但是，推动这种适应的机制仍有待阐明。拟议的研究将扩展我们先前对LTH胎儿中HPA功能的观察结果，并检查不仅在维持基础糖皮质激素分泌方面涉及的特定机制，而且还涉及对次应力源的反应。拟议的研究将检验一个总体假设，即胎儿HPA轴的适应性变化使胎儿能够适应长期缺氧的压力，同时增强对二次急性应激源反应的能力。具体目的1。阐明LTH胎儿中增强的下丘脑驱动器（即增强皮质功能）的机制。 These studies are designed to test the hypothesis that: LTH results in enhanced hypothalamic paraventricular nuclei (PVN) expression of cortiocotropin releasing factor (CRF) and/or arginine vasopressin (AVP) and/or increased pituitary responsiveness to these ACTH secretagogues resulting in the increased anterior pituitary corticotrope function observed in response to LTH.具体目的2。确定肾上腺皮质已适应LTH的分子和细胞机制，从而导致观察到的抑制肾上腺表达受到关键率限制酶的肾上腺表达。 基础条件下的糖皮质激素合成。迄今为止的研究支持CYP11A和CYP17的表达通过刺激ACTH-cAMP和抑制性ERK途径之间的相互作用来调节。因此，这些研究将检验以下假设：LTH肾上腺对ACTH前体POMC和22KD Pro ACTH的抑制作用更为敏感，从而干扰ACTH信号，从而导致抑制基础CYP表达。我们还假设细胞外信号调节激酶（ERK）途径在 LTH胎儿的肾上腺皮质，导致类固醇生成因子-1（SF-1）的磷酸化增强，这反过来抑制了调节糖皮质激素产生的关键率限制基因的表达。具体目的3。为了阐明细胞内和分子机制，尽管CYP11A和CYP17表达降低，但在LTH之后急性二级应激源响应糖皮质激素分泌增强。这些研究旨在检验以下假设：与对照组相比，LTH胎儿二级应激源后的皮质醇输出增强是cAMP刺激和蛋白激酶A的增强的结果，从而增加了类固醇急性调节蛋白的激活。 具体目的4。确定LTH动物次应激源期间肾上腺血流潜在变化的机制。这些研究将检验以下假设：与次级应激源后对照组相比，LTH胎儿的皮质醇输出增强是肾上腺血流增强的结果，并且至少部分通过一氧化氮介导了这种变化。