Significance of Pituitary Leptin to Gonadotropes

描述（由申请人提供）：垂体瘦素以循环的方式变化，表明它可能促进或允许促性腺激素的分泌。在食物剥夺和葡萄糖介导的平行恢复期间，垂体瘦素和LH平行减少。这一间接证据表明，如果营养状况良好，垂体瘦素可能是促性腺激素功能的代谢通道。本初步研究旨在建立细胞和动物模型，以验证来自促性腺激素的垂体瘦素对促性腺激素释放激素（GnRH）的正常发育和反应至关重要的假设。这些研究将在Aim 1中通过体外方法验证这一假设，其中瘦素mRNA的siRNA将用于敲除垂体瘦素。在Aim 2中，这一假设将通过体内研究进行验证，在体内研究中，通过Cre-loxP技术删除了瘦素在somatotrope中的表达。为了去除生长性状中的瘦素基因，将携带转基因rGHp-Cre的突变小鼠与携带瘦素基因两侧loxP的小鼠杂交。在这两组目的中，将测试促性腺激素对GnRH的反应，以确定体外或体内（在促生长激素中）切除垂体瘦素是否会影响促性腺激素功能。促性腺激素的发育和生育能力也将在突变小鼠身上进行测试，这些突变小鼠在促性腺激素中切除了瘦素。这项初步研究提供了一种集中的方法来回答垂体瘦素对促性腺激素功能的重要性的问题，从而避免了与影响促性腺激素的全球瘦素敲除所见的代谢问题和对瘦素功能的混淆解释。这项初步研究将为未来的研究奠定基础，这些研究将测试垂体瘦素对其他调节因子（类固醇、神经肽Y和激活素）对促性腺激素反应的影响。未来可以提出使用Cre-loxP技术进行体内研究，以检验其他垂体细胞类型（促皮质激素和促性腺激素）产生的瘦素的意义。这项研究的最终目的是确定瘦素如何支持生殖能力，以及关于营养不良的信息如何与不孕症联系起来。

DESCRIPTION (provided by applicant): Pituitary leptin changes in a cyclic manner that indicates it may facilitate or permit the secretion of gonadotropins. There are parallel reductions in pituitary leptin and LH during food deprivation and a parallel recovery mediated by glucose. This circumstantial evidence suggests that pituitary leptin may serve as a metabolic gateway to permit gonadotrope function, if the nutritional status is optimal. This proposed pilot study is designed to develop cellular and animal models that test the hypothesis that pituitary leptin from somatotropes is vital for the normal development and responses of gonadotropes to gonadotropin releasing hormone (GnRH). The studies will test the hypothesis with in vitro approaches in Aim 1 in which siRNA for leptin mRNA will be used to knock out pituitary leptin. In Aim 2, the hypothesis will be tested by in vivo studies, in which leptin expression is deleted in somatotropes by Cre-loxP technology. To ablate the leptin gene in somatotropes, mutant mice bearing the transgene rGHp-Cre will be crossed with mice that bear loxP flanking the leptin gene. In both sets of aims, gonadotrope responses to GnRH will be tested to determine if ablation of pituitary leptin in vitro or in vivo (in somatotropes) affects gonadotrope functions. Gonadotrope development and fertility will also be tested in the mutant mice that have leptin excised in somatotropes. This pilot study provides a focused approach to answer the question of the significance of pituitary leptin to gonadotrope functions, which avoids metabolic problems seen with global leptin knockouts that affect gonadotropes and confound interpretation of leptin functions. The pilot study will lay the foundation for the development of future studies that test the effect of pituitary leptin on gonadotrope responses to other regulators (steroids, neuropeptide Y and activin). Future in vivo studies with Cre-loxP technology can be proposed to test the significance of leptin produced by other pituitary cell types (corticotropes and gonadotropes). The ultimate aim of the study will be to determine how leptin supports reproductive competence and how information about malnutrition may be linked with infertility. PUBLIC HEALTH RELEVANCE: This proposed pilot study is focused on the significance of pituitary leptin to gonadotropes; testing the hypothesis that pituitary leptin is vital for gonadotrope development and/or functions. Aim 1 will develop an in vitro model; the studies will use siRNA for leptin mRNA to ablate pituitary leptin to determine its effects on gonadotrope function. Aim 2 will develop an in vivo transgenic mouse model in which leptin is ablated specifically in somatotropes by Cre-loxP technology. Transgenic mice, in which leptin is knocked out in somatotropes, will be tested for the time of onset of puberty, fertility, and responses by gonadotropes to stimuli. These studies focus on basic regulatory mechanisms that link nutritional status to fertility.