Physiological Mechanisms Underlying Heightened Responsiveness of Gonadotropes to

促性腺激素反应增强的生理机制

• 批准号: 7947530
• 负责人: TORRANCE M NETT
• 金额: $ 30.25万
• 依托单位: COLORADO STATE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-08-01 至 2015-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7947530
• 关键词: Agonist; Anterior Pituitary Gland; Binding; Biological; Blood Circulation; Carcinoma; Cell Line; Cell membrane; Cells; Clinical; Competence; Contraceptive methods; Cues; Cyclic AMP Response Element; Cyclic AMP-Responsive DNA-Binding Protein; Development; Disease; Endocrine Glands; Estradiol; Estrogen Antagonists; Estrogen Receptors; Estrogens; Event; Fertility; Fibroid Tumor; Generations; Genes; Genetic Transcription; Gonadotropin Hormone Releasing Hormone; Gonadotropin-Releasing Hormone Receptor; Gonadotropins; Health; Hormones; Hypothalamic structure; Luteinizing Hormone; Mediating; Membrane; Mus; Neurons; Neuropeptides; Ovulation; Pathway interactions; Peripheral; Pharmacologic Substance; Phenotype; Physiological; Pituitary Gland; Receptor Gene; Regulation; Regulatory Element; Reproduction; Reproductive Endocrinology; Research; Sheep; Signal Transduction; Site; Testing; Tissues; Transgenic Mice; Uterine Fibroids; Vertebrates; Work; endometriosis; in vitro Model; in vitro testing; in vivo; mouse model; novel; promoter; public health relevance; receptor; receptor expression; reproductive; reproductive hormone; response

DESCRIPTION (provided by applicant): Ovulation is one of the most fundamental events in reproduction and requires a dramatic surge of luteinizing hormone (LH) released by the anterior pituitary gland into the peripheral circulation. The secretion of LH from the pituitary is cued by the hypothalamic neuropeptide, gonadotropin-releasing hormone (GnRH). Thus, the secretion of GnRH from hypothalamic neurons and its interpretation by gonadotropes in the pituitary constitute the essential central events for reproductive competence. Thus, understanding and, ultimately, controlling the mechanisms underlying the generation of the preovulatory LH surge remains a primary focus of research in reproductive endocrinology at both the basic and clinical levels. It has become almost axiomatic that estradiol- 172 (E2) secreted from the preovulatory follicle serves as the most proximate regulator of the LH surge via two sites of action. First, E2 enhances sensitivity of the pituitary by increasing GnRH receptor expression. Second and temporally delayed, it stimulates increased hypothalamic secretion of GnRH. As these 2 physiological sequelae to elevated E2 have been known for decades, it is troubling that our understanding of the underlying mechanisms at both the level of GnRH secretion (hypothalamic) and GnRH responsiveness (pituitary) remains quite undeveloped. In regard to the latter, the lack of progress reflects the inability of in vitro models (cell lines) and promoters (mouse GnRH receptor gene) to recapitulate the increase in pituitary responsiveness to GnRH induced by E2. In contrast, using transgenic mouse models we have demonstrated that the proximal promoter of the ovine GnRH receptor gene is highly E2 responsive. This E2 responsive phenotype does not; however, appear to involve direct binding of activated estrogen receptor (ER) to the sheep gene. Rather, we find that membrane impermeable conjugates of E2 regulate LH secretion in sheep and increase GnRH receptor expression. As such, heightened responsiveness of the pituitary preceding the preovulatory LH surge may reflect E2 signaling through a membrane site of action - this is the central biological issue that exists as the core of our proposed research. Accordingly, using both in vivo and in vitro tests of promoter function and parallel analyses of the endogenous ovine GnRH receptor gene we will determine the hierarchy of ER subtypes that underlie E2 responsiveness of GnRH receptor expression, the initial cellular site of action of E2 that elicits enhanced expression of GnRH receptors and the identity of the regulatory element(s) that mediate the transcriptional response of the GnRHR gene to E2. Understanding regulation of GnRH and its receptor is important for fertility control; however, GnRH agonists and antagonists are used to treat fibroid tumors, endometriosis, and reproductive tissue carcinomas thus underscoring the need for a full understanding of GnRH and the GnRH receptor in both health and disease. PUBLIC HEALTH RELEVANCE: These studies will refine our understanding of estrogen signaling in the anterior pituitary gland (the "master" endocrine gland) as well novel mechanisms underlying estrogen regulation of important physiological targets throughout the body. Understanding these mechanisms is critical to the development of new generations of both pro and anti-estrogen-like pharmaceuticals that are increasingly specific for the desired biological effect. Understanding physiological regulation of reproductive hormones like gonadotropin releasing hormone (GnRH) and the GnRH receptor is important to fertility regulation; however, the application of potent GnRH agonists and antagonists in the treatment of uterine fibroids, endometriosis and reproductive tissue carcinomas underscores the importance of this topic in both health and disease.

描述（由申请人提供）：排卵是生殖过程中最基本的事件之一，需要垂体前叶释放大量促黄体激素（LH）进入外周循环。促性腺激素释放激素（GnRH）是下丘脑神经肽的一种。因此，下丘脑神经元分泌GnRH和垂体中促性腺激素的解释构成了生殖能力的基本中心事件。因此，了解并最终控制排卵前LH峰产生的机制仍然是生殖内分泌学基础和临床研究的主要焦点。从排卵前卵泡分泌的雌二醇-172（E2）通过两个作用位点作为LH峰的最接近调节剂，这几乎已成为公理。首先，E2通过增加GnRH受体表达增强垂体的敏感性。第二和暂时延迟，它刺激下丘脑GnRH分泌增加。由于E2升高的这两种生理学后遗症已被人们了解了几十年，令人不安的是，我们对GnRH分泌（下丘脑）和GnRH反应性（垂体）水平的潜在机制的理解仍然相当不成熟。关于后者，缺乏进展反映了体外模型（细胞系）和启动子（小鼠GnRH受体基因）无法重现E2诱导的垂体对GnRH反应性的增加。相反，使用转基因小鼠模型，我们已经证明，绵羊GnRH受体基因的近端启动子是高度E2响应。这种E2反应表型没有;然而，似乎涉及激活的雌激素受体（ER）与绵羊基因的直接结合。相反，我们发现E2的膜不透性缀合物调节绵羊LH分泌并增加GnRH受体表达。因此，在排卵前LH峰之前垂体的反应性增强可能反映了E2信号通过膜作用位点-这是作为我们拟议研究的核心而存在的中心生物学问题。因此，使用启动子功能的体内和体外试验以及内源性绵羊GnRH受体基因的平行分析，我们将确定GnRH受体表达的E2反应性基础的ER亚型的层次，E2的初始细胞作用位点，其增强GnRH受体的表达和调节元件的特性介导GnRHR基因对E2的转录反应。了解GnRH及其受体的调节对于生育控制很重要;然而，GnRH激动剂和拮抗剂用于治疗纤维瘤，子宫内膜异位症和生殖组织癌，因此强调需要充分了解GnRH和GnRH受体在健康和疾病中的作用。 公共卫生相关性：这些研究将完善我们对垂体前叶（“主”内分泌腺）雌激素信号传导的理解，以及雌激素调节全身重要生理靶点的新机制。了解这些机制对于开发新一代的促雌激素样药物和抗雌激素样药物至关重要，这些药物对所需的生物效应越来越具有特异性。了解生殖激素如促性腺激素释放激素（GnRH）和GnRH受体的生理调节对生育调节很重要;然而，有效的GnRH激动剂和拮抗剂在治疗子宫肌瘤，子宫内膜异位症和生殖组织癌中的应用强调了这一主题在健康和疾病中的重要性。