Role of sensory neuron ghrelin signaling in regulating metabolic homeostasis

项目摘要/摘要 肥胖是一个主要的健康和经济负担，大约35%的美国公民 被归类为超重或肥胖，以及用于治疗肥胖及其 合并症每年超过2000亿美元。胃源性促食欲激素Ghrelin是一种 由于它对食物摄入量的调节，它是人类能量平衡和肥胖的关键介质， 肠道动力、能量消耗、营养分配、血糖和体温。这个 Ghrelin受体是生长激素促分泌素受体1a(Ghsr)，在大脑中广泛表达。 而胃肠迷走感觉神经元和神经元的GHSR基因敲除导致了深刻的 有益的代谢特征和高脂饮食(HFD)诱导的肥胖抵抗。此外，GHSR 基因敲除小鼠在能量挑战和GHSR恢复期间代谢调节受损 并不能完全恢复Ghrelin的作用，这表明外周Ghrelin信号是 对新陈代谢控制至关重要。我们发现除了特征明确的迷走神经外 脊神经背根神经节(DRG)发出的胃肠感觉神经元 快递GHSR。此外，DRG GHSR的表达在能量挑战时显著上调 提示了一种新的机制来调节Ghrelin对能量动态平衡的影响。因为这是 首次在DRG上发现了这些受体，它们的功能和表型(即 他们还检测到胃拉伸或营养物质)是完全未知的。因此，总的目标是 该项目旨在鉴定含有GHSR的DRGs的表型和器官，并 阐明DRG和迷走感觉神经元Ghrelin信号的总体必要性。一个ghsrGFP 记者老鼠将与神经元逆行示踪剂一起用于识别器官 被含有GHSR的DRGs所支配。此外，免疫组织化学分析测量神经元 对旨在激活GHSR-GFP感觉神经元的外周操作的反应活动将 阐明这些神经元的表型。测试感觉神经元Ghrelin信号的必要性 为了调节代谢稳态，我们将产生一种新的、感觉神经元特异性的GHSR 通过与我们的ghsrloxP/loxP小鼠品系(允许依赖Cre重组酶)杂交来敲除小鼠 GHSR基因的缺失)与我们的感觉神经元特异性Cre驱动小鼠Advelin-Cre。与 由此产生的后代，我们将测试总体表型、维持代谢动态平衡的能力 在精力充沛的时候，容易发生饮食引起的肥胖。这些首要目标 符合国家糖尿病、消化和肾脏疾病研究所的使命 调查肥胖和包括糖尿病在内的其他代谢性疾病的根本原因。 此外，这项研究的发现将极大地扩展我们对神经内分泌的了解 调节能量动态平衡，并将为行为和/或 与肥胖作斗争的药物干预。

Project Summary/Abstract Obesity is a major health and economic burden with approximately 35% of United States citizens classified as either overweight or obese, and medical spending for treating obesity and its comorbidities exceeds $200 billion annually. The stomach-derived orexigenic hormone ghrelin is a key mediator of energy homeostasis and adiposity in humans due to its regulation of food intake, gut motility, energy expenditure, nutrient partitioning, glycemia, and body temperature. The ghrelin receptor, growth hormone secretagogue receptor 1a (GHSR), is widely expressed in the brain and on gastrointestinal vagal sensory neurons, and neuronal GHSR knockout results in a profoundly beneficial metabolic profile and high fat diet (HFD)-induced obesity resistance. Moreover, ghsr knockout mice have impaired metabolic regulation during energetic challenges, and ghsr restoration in the brain does not fully restore ghrelin’s effects suggesting peripheral ghrelin signaling is critical for metabolic control. We discovered that in addition to the well characterized vagal GHSRs, gastrointestinal sensory neurons emanating from spinal dorsal root ganglia (DRG) robustly express GHSRs. In addition, DRG GHSR expression is markedly upregulated by energetic challenges suggesting a novel mechanism mediating ghrelin’s effects on energy homeostasis. As this is the first time these receptors have been identified on DRGs, their function and phenotype (i.e. whether they also detect gastric stretch or nutrients) is completely unknown. Thus, the overall goal of this project is to identify the phenotype and organs innervated by GHSR-containing DRGs, and to elucidate the overall necessity of DRG and vagal sensory neuron ghrelin signaling. A ghsrGFP reporter mouse will be used in conjunction with neuronal retrograde tracers to identify the organs innervated by GHSR-containing DRGs. In addition, immunohistochemical analysis measuring neuronal activity in response to peripheral manipulations designed to activate GHSR-GFP sensory neurons will elucidate the phenotype of these neurons. To test the necessity of sensory neuron ghrelin signaling for regulating metabolic homeostasis, we will generate a novel, sensory neuron-specific GHSR knockout mouse by crossing our ghsrloxP/loxP mouse line (that allow for Cre-recombinase dependent deletion of the ghsr gene) with our sensory neuron-specific Cre driver mice Advillin- Cre. With the resulting offspring, we will test the overall phenotype, ability to maintain metabolic homeostasis when energetically challenged, and susceptibility to diet-induced obesity. These overarching goals are in line with the National Institute of Diabetes and Digestive and Kidney Diseases mission to investigate the fundamental causes of obesity and other metabolic diseases including diabetes. Moreover, the findings from this study will greatly expand our knowledge of the neuroendocrine regulation of energy homeostasis, and will provide another point of attack for behavioral and/or pharmacological interventions to combat obesity.