The Role of Syndecans in Melanocortin Signaling and Energy Balance

描述(由申请人提供)：虽然中枢黑素皮质素系统被认为是能量平衡和食欲的关键调节因素，但关于这一途径的非黑素皮质素成分仍有许多需要了解。下丘脑黑素皮质素受体，MC4R，是一种G蛋白偶联受体，可被多肽配体刺鼠相关蛋白(AgRP)拮抗，从而导致摄食增加和体重增加。Syndecan-3是一种硫酸乙酰肝素蛋白多糖，先前已被认为与增强AgRP拮抗有关。这项提议旨在从分子水平和体内研究Syndecans的作用。我们假设AgRP与Syndecans的糖胺多聚糖(GAG)组分结合，这种相互作用增加了MC4R附近多肽的局部浓度。此外，我们先前已经证明，设计的针对AgRP的正电荷突变可以增加体内的疗效，这不依赖于MC4R的结合，我们假设这是由于增加了对受体近端带负电荷的GaG的亲和力。这一提议将用量热法和磁共振技术揭示AgRP多肽与GAG相互作用的分子细节。我们的初步量热数据显示，AgRP与肝素紧密结合，这种亲和力因额外的多肽正电荷而得到加强。我们还将使用Syndecan基因敲除小鼠系来研究Syndecan对AgRP的调制机制。我们的带电多肽将被用来测试这些小鼠在进食和体重增加方面的反应是否与它们的野生型小鼠不同。这条基因敲除线还将使我们能够通过免疫组织化学染色来探索Syndecans的局部浓度效应。最后，我们将继续设计增加正电荷的AgRP突变体，以开发出更有效的多肽，并使用头尾环化来提高多肽的稳定性。这将提供一种特定的、双功能配体的模型，以增加喂养。我们期望这项拟议的研究将对Syndecans在AgRP-MC4R途径中发挥明确的作用，该途径会导致过度吞噬、体重增加和刺激时长时间的进食。这一贡献将是重要的，因为GPCR系统的复杂性允许我们在结构水平上增加对这些途径的理解，从而有针对性地针对令人兴奋的新治疗途径

DESCRIPTION (provided by applicant): While the central melanocortin system is recognized as a key regulator of energy balance and appetite, there remains much to learn regarding non-melanocortin components of this pathway. The hypothalamic melanocortin receptor, MC4R, is a G-protein coupled receptor that is antagonized by the peptide ligand, agouti-related protein (AgRP), which leads to increased feeding and weight gain. Syndecan-3, a heparan sulfate proteoglycan, has previously been implicated in potentiating AgRP antagonism. This proposal aims to investigate the role of syndecans, both at a molecular level and in vivo. We hypothesize that AgRP binds the glycosaminoglycan (GAG) components of syndecans, and that this interaction increases the local concentration of the peptide near MC4R. Furthermore, we have previously shown that designed positive charge mutations to AgRP lead to increased in vivo efficacy that is independent of MC4R binding, and we hypothesize that this is due to an increased affinity for the negatively charged GAGs proximal to the receptor. This proposal will reveal the molecular details of the interaction between AgRP peptides and GAGs using calorimetry and magnetic resonance. Our preliminary calorimetry data show tight binding between AgRP and heparin, and this affinity is strengthened by additional peptide positive charge. We will also investigate the mechanism of syndecan modulation of AgRP using a syndecan knockout mouse line. Our charged peptides will be used to test whether these mice respond differently from their wild type littermates in terms of feeding and weight gain. This knockout line will also allow us to probe the local concentration effects of syndecans using immunohistochemical staining. Finally, we will continue to engineer AgRP mutants with increased positive charge in order to develop an even more potent peptide, and use head-to-tail cyclization to increase peptide stability. This will provide a model of a specific, bi-functional ligand that increases feeding. We expect the proposed research to contribute a definitive role for syndecans in the AgRP-MC4R pathway that leads to hyperphagia, weight gain, and prolonged feeding when stimulated. This contribution will be significant because the complexity of GPCR systems allows for exciting new therapeutic avenues to be specifically targeted as we increase our understanding of these pathways at a structural level