Development of Leptin-Sensitive Hypothalamic Pathways

描述（由申请人提供）：导致肥胖的新生儿因素了解甚少。本研究的长期目标是阐明脂肪细胞衍生的激素瘦素如何影响调节哺乳动物能量稳态的神经内分泌通路的发育。这一目标的核心是确定瘦素如何影响来自下丘脑弓状核（ARH）的神经投射的发展，ARH是整合与外周能量储存相关的信息的关键部位。瘦素信号通过ARH传递到参与体重调节的其他脑区，如下丘脑室旁核（PVH），这是调节能量代谢的最终共同途径的重要组成部分。本提案正文中提出的证据支持瘦素在新生儿生命中作为一个发育因子的概念，通过指导参与控制摄食和能量平衡的神经回路的形成。本提案提出的总体假设是，瘦素在受限的新生儿关键期直接作用于ARH，促进PVH的神经投射形成，参与体重调节。我们认为，出生后的瘦素激增对ARH的预测具有持久的影响，并且在成熟动物中，瘦素信号的发育扰动导致传递瘦素信号的神经通路的永久性变化。生理和体外实验方法将通过解决以下具体目标来验证这一假设。具体目标我们建议使用轴突标记方法和组织化学技术来定义缺乏瘦素的肥胖小鼠（ob/ob小鼠）和缺乏功能性长形式受体的糖尿病小鼠（db/db小鼠）中ARH投射的组织和发展。具体目标2。我们还将通过检测外源性瘦素治疗的ob/ob和db/db小鼠ARH-PVH通路的发育来测试瘦素的发育活性，并确定这种发育活性是否仅限于新生儿关键期。具体目标3。为了确定瘦素在指导ARH- pvh通路发展中的作用位点，我们将利用一种新的外植体共培养试验，以及在体外检测瘦素对分离的ARH外植体轴突生长的直接影响。具体目标此外，我们将研究瘦素水平的营养调控如何影响ARH-PVH通路的发展。5.具体目标最后，我们将确定瘦素依赖性下丘脑内信号模式的改变是否伴随着观察到的ARH-PVH通路的发育变化。拟议的研究结果将扩大我们对瘦素的认识，包括促进瘦素反应性下丘脑神经通路形成的深刻发育活动。这些研究也可能为新生儿的营养环境如何在整个生命过程中对喂养和能量平衡的中枢调节施加持久的影响提供重要线索。

DESCRIPTION (provided by applicant): Neonatal factors that contribute to obesity are poorly understood. The long-range goal of this research is to clarify how the adipocyte-derived hormone leptin influences development of neuroendocrine pathways that regulate mammalian energy homeostasis. Central to this goal is determining how leptin affects development of neural projections from the arcuate nucleus of the hypothalamus (ARH), a key site for integration of information related to peripheral energy stores. Leptin signals are conveyed via the ARH to other brain regions involved in the regulation of body weight, such as the paraventricular nucleus of the hypothalamus (PVH), an important component of the final common pathway for regulation of energy metabolism. Evidence presented in the body of this proposal supports the concept that leptin functions as a developmental factor during neonatal life by directing formation of neural circuits involved in the control of feeding and energy balance. The overall hypothesis addressed in this proposal is that leptin acts directly on the ARH during a restricted neonatal critical period to promote formation of neural projections to the PVH involved in the regulation of body weight. We propose that the postnatal leptin surge has an enduring effect on ARH projections, and that developmental perturbations in leptin signaling cause permanent changes in neural pathways that transmit leptin signals in mature animals. Both physiological and in vitro experimental approaches will be used to test this hypothesis by addressing the following specific aims. Specific Aim 1. We propose to use axonal labeling methods and histochemical techniques to define the organization and development of ARH projections in obese mice that lack leptin (ob/ob mice) and in diabetic mice that lack a functional long form of its receptor (db/db mice). Specific Aim 2. We will also test the developmental activity of leptin by examining development of the ARH-PVH pathway in ob/ob and db/db mice treated with exogenous leptin, and determine if this developmental activity is restricted to a neonatal critical period. Specific Aim 3. To determine the site of action for leptin in directing development of the ARH-PVH pathway, we will utilize a new explant coculture assay, in addition to examining the direct effects of leptin on axon outgrowth from isolated ARH explants in vitro. Specific Aim 4. In addition, we will examine how nutritional manipulation of leptin levels impacts development of the ARH-PVH pathway. Specific Aim 5. Finally, we will determine if altered patterns of leptin dependent intrahypothalamic signaling accompany observed developmental changes in the ARH-PVH pathway. The results of the proposed research will expand our appreciation of leptin to include a profound developmental activity that promotes formation of leptin-responsive hypothalamic neural pathways. These studies may also provide essential clues about how the neonatal nutritional environment imposes enduring consequences on central regulation of feeding and energy balance throughout life.