Obesity Suppresses the GUCY2C endocrine Gut-Brain Axis Disrupting Satiety

 描述（由申请人提供）：肥胖是一种全球性流行病，发病率、死亡率和医疗费用呈加速趋势。治疗的疗效有限，或有安全性问题。在这种对更有效和安全的抗肥胖疗法的未满足的临床需求的背景下，最近发现了一种新的调节食欲和代谢的肠-脑内分泌轴，为推进这种疾病的治疗和预防提供了独特的机会。跨膜受体鸟苷酸环化酶C（GUCY 2C）被其同源旁分泌激素尿鸟苷素（小肠）和鸟苷素（结肠直肠）激活后充分表征为肠上皮稳态的关键调节剂。最近发现下丘脑中的GUCY 2C表达和功能，沿着循环尿鸟苷素水平在热量摄入后增加，将GUCY 2C信号传导扩展到介导饱腹感的内分泌调节回路中的中枢神经系统。事实上，这些观察结果表明了一种生理模型，其中食物的摄入刺激来自肠的尿鸟苷素的内分泌，尿鸟苷素循环到下丘脑以诱导促肾上腺素信号传导。此外，肥胖小鼠餐后尿鸟苷素分泌受抑制提示了导致肥胖的病理生理学机制，但在治疗上是可靶向的。该项目的最终长期目标是阐明下丘脑中GUCY 2C信号传导调节饱腹感的机制，以告知GUCY 2C配体治疗在治疗和预防肥胖中的效用。为实现这一长期目标，提出了三个具体目标。在目的1中，我们将绘制下丘脑中调节食欲的GUCY 2C表达。利用独特的β-半乳糖苷酶GUCY 2C报告小鼠，我们将确定表达GUCY 2C的下丘脑核、细胞类型和神经元亚型。这些结果将通过原位RNA杂交、免疫印迹、免疫染色和GUCY 2C信号传导分析来证实。在目标2中，我们将确定下丘脑和肠道GUCY 2C在调节食欲中的相对作用。使用我们实验室开发的组织特异性条件性小鼠模型，我们将消除肠道或大脑中的GUCY 2C表达，并确定这些治疗对GUCY 2C配体诱导的饱腹感的影响，以及对食物消耗和体重的慢性影响。在目标3中，我们将定义将GUCY 2C激活与饱腹感信号传导联系起来的机制。初步数据表明，GUYC 2C配体诱导的饱腹感与下丘脑POMC表达的增加有关，但与其他促食欲或促食欲转录物无关。在这里，我们将展示POMC在连接GUCY 2C下丘脑信号与饱腹感和食欲调节中的作用。总之，这些研究将确定一种新的内分泌机制，有助于正常的生理控制的食物摄入。它们代表了必要的证据基础，最终将这种以前未被认识到的肠-脑轴转化为靶向GUCY 2C的新治疗方法，以预防和治疗肥胖和代谢疾病。

 DESCRIPTION (provided by applicant): Obesity is a global pandemic with accelerating trends in morbidity, mortality, and medical expenditures. Treatments have been limited in efficacy, or burdened with safety concerns. In the context of this unmet clinical need for more effective and safe anti-obesity therapies, the recent discovery of a new gut-brain endocrine axis regulating appetite and metabolism offers a unique opportunity to advance treatment and prevention for this disease. The transmembrane receptor guanylyl cyclase C (GUCY2C) is well characterized as a key regulator of intestinal epithelial homeostasis upon activation by its cognate paracrine hormones uroguanylin (small intestine) and guanylin (colorectum). The recent discovery of GUCY2C expression and function in hypothalamus, along with circulating uroguanylin levels that increase following caloric intake, extends GUCY2C signaling to the central nervous system in an endocrine regulatory circuit mediating satiety. Indeed, these observations suggest a physiological model in which ingestion of food stimulates the endocrine secretion of uroguanylin from intestine, which circulates to hypothalamus to induce anorexigenic signaling. Further, suppressed postprandial uroguanylin secretion in obese mice suggests a pathophysiologic, but therapeutically targetable, mechanism driving obesity. The ultimate, long-term goal of this project is to elucidate mechanisms by which GUCY2C signaling in hypothalamus regulates satiety, to inform the utility of GUCY2C ligand therapy in the treatment and prevention of obesity. To achieve this long-term objective, three specific aims are proposed. In Aim 1, we will map GUCY2C expression regulating appetite in hypothalamus. Leveraging unique ß-galactosidase GUCY2C reporter mice, we will determine the hypothalamic nuclei, cell types, and neuronal subtypes expressing GUCY2C. These results will be confirmed by in situ RNA hybridization, immunoblot, immunostaining and GUCY2C signaling analyses. In Aim 2, we will determine the relative roles of hypothalamic and intestinal GUCY2C in regulating appetite. Using tissue-specific conditional mouse models developed in our laboratory, we will eliminate GUCY2C expression in either intestine or brain and determine the effects of these treatments on GUCY2C ligand-induced satiety, as well as chronic effects on food consumption and body weight. In Aim 3, we will define the mechanisms linking GUCY2C activation to satiety signaling. Preliminary data suggests that GUYC2C ligand-induced satiety is associated with increases in expression of hypothalamic POMC, but not other anorexigenic or orexigenic, transcripts. Here, we will demonstrate the role of POMC in linking GUCY2C hypothalamic signaling with regulation of satiety and appetite. Together, these studies will define a novel endocrine mechanism contributing to the normal physiologic control of food intake. They represent the requisite evidence base to ultimately translate this previously unrecognized gut-brain axis into new therapeutic approaches targeting GUCY2C to prevent and treat obesity and metabolic diseases.