The Role of Syndecans in Melanocortin Signaling and Energy Balance

描述（由申请人提供）：虽然中央黑素皮质素系统被认为是能量平衡和食欲的关键调节器，但关于该途径的非黑素皮质素成分仍有很多需要了解。下丘脑黑素皮质素受体（MC4R）是一种g蛋白偶联受体，可被肽配体agouti相关蛋白（AgRP）拮抗，从而导致摄食增加和体重增加。Syndecan-3，一种硫酸肝素蛋白聚糖，先前被认为与增强AgRP的拮抗作用有关。本研究旨在探讨syndecans在分子水平和体内的作用。我们假设AgRP与syndecans的糖胺聚糖（GAG）成分结合，这种相互作用增加了MC4R附近肽的局部浓度。此外，我们之前已经证明，设计的AgRP正电荷突变会导致与MC4R结合无关的AgRP体内功效的增加，我们假设这是由于对靠近受体的带负电荷的GAGs的亲和力增加。本研究将利用量热法和磁共振技术揭示AgRP肽与GAGs相互作用的分子细节。我们的初步量热数据显示AgRP和肝素之间的紧密结合，并且这种亲和力被额外的肽正电荷加强。我们还将使用syndecan敲除小鼠系研究syndecan对AgRP的调节机制。我们的带电肽将用于测试这些小鼠在喂养和体重增加方面是否与野生型小鼠有不同的反应。这个基因敲除线也将允许我们使用免疫组织化学染色来探测晕厥的局部浓度效应。最后，我们将继续设计带更多正电荷的AgRP突变体，以开发更有效的肽，并使用头尾环化来增加肽的稳定性。这将提供一个特定的模型，双功能配体，增加喂养。我们希望这项研究能够为syndecans在AgRP-MC4R通路中的明确作用做出贡献，该通路在受到刺激时导致嗜食、体重增加和进食时间延长。这一贡献将是重要的，因为随着我们在结构水平上增加对这些途径的理解，GPCR系统的复杂性允许令人兴奋的新治疗途径成为专门针对的目标

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