NUCLEUS TRACTUS SOLITARIUS MELANOCORTIN SIGNALING IN THE CONTROL OF FOOD INTAKE

描述（由申请人提供）：在西方文化中，肥胖的流行率正在急剧上升，造成了毁灭性的、代价高昂的健康问题。黑素皮质素4受体（MC4-R）基因突变是人类严重肥胖最常见的单基因原因。由于MC4-R激动剂在动物模型中能有效抑制食物摄入和体重，中枢黑素皮质素系统是治疗肥胖和相关代谢紊乱的临床药物开发的一个有希望的靶点。这一建议与临床药物开发和公共卫生相关，因为实验有可能深入了解MC4-R信号传导促进食物摄入抑制的机制。最近的数据表明，尾侧脑干的孤立束核（NTS）是与MC4-R配体控制食物摄入相关的关键部位，并且尾侧脑干MC4-R信号是外源性胆囊收缩素（CCK）（肠源性饱足激素）抑制食物摄入所必需的。Specific Aim 1中提出的实验将产生必要的数据，以更充分地评估尾侧脑干MC4-R信号介导各种GI饱足信号触发的摄入抑制的假设。尾侧脑干MC4-R拮抗剂治疗将用于评估这些受体的激活是否需要在胃肠道满足信号的内源性方法下抑制摄入，包括肠内营养输送和胃膨胀。未来的研究还将通过考察实质NTS MC4-R拮抗剂治疗对CCK摄入抑制的影响，更深入地探讨后脑MC4-R介导GI信号的功能部位。在NTS中，腺相关病毒介导的MC4-Rs的敲低将被用作拮抗剂治疗的补充方法，以评估NTS MC4-Rs在通过GI饱足信号介导摄入抑制中的内源性作用。重要的是，MC4-R敲低技术也将用于更广泛地评估内源性NTS MC4-R信号在能量调节中的作用。在Specific Aim 2中提出的实验将扩大对NTS细胞内信号通路的考虑，这些信号通路有助于MC4-R激动剂、GI饱和信号及其可能的组合后的摄入抑制。拟议的研究将建立在我们的初步发现和其他近期数据的基础上，针对p44/42丝裂原活化蛋白激酶（MAPK）信号通路和潜在的上游激酶（蛋白激酶A [PKA]和磷脂酰肌醇3-激酶[PI3K]）作为MC4-R配体和GI信号摄入抑制的NTS细胞内介质。实验将结合体内药物抑制p44/42 MAPK、PKA和PI3K的方法，以及体外使用活性测定和免疫印迹的方法，来评估这些细胞内信号通路在抑制MC4-R配体、GI饱和信号及其潜在组合后摄入中的生理作用。本提案中提出的研究有可能深化与食物摄入抑制的神经化学介质相关的基础科学。

DESCRIPTION (provided by applicant): Obesity prevalence is dramatically rising in Western cultures creating devastating and costly health problems. Mutations in the melanocortin 4-receptor (MC4-R) gene are the most common monogenetic cause of severe human obesity. The central melanocortin system is a promising target for clinical drug development for the treatment of obesity and related metabolic disorders, as MC4-R agonists potently suppress food intake and body weight in animal models. This proposal is relevant to clinical drug development and public health, as experiments have potential to yield insights into the mechanisms through which MC4-R signaling contributes to food intake suppression. The aims of this proposal are shaped by recent data showing that the nucleus tractus solitarius (NTS) of the caudal brainstem is a critical site of relevance to food intake control by MC4-R ligands, and that caudal brainstem MC4-R signaling is required for food intake suppression by exogenous cholecystokinin (CCK), the intestinally-derived satiation hormone. Experiments proposed in Specific Aim 1 will generate data that are necessary to more fully evaluate the hypothesis that caudal brainstem MC4-R signaling mediates the intake suppression triggered by various GI satiation signals. Caudal brainstem MC4-R antagonist treatment will be used to assess whether or not activation of these receptors is required for intake suppression following endogenous methods of GI satiation signaling, including intraintestinal nutrient delivery and gastric distention. Proposed research will also probe more deeply into the functional site of hindbrain MC4-R mediation of GI signals by examining the effects of parenchymal NTS MC4-R antagonist treatment on intake suppression by CCK. Adeno-associated virally-mediated knockdown of MC4-Rs in the NTS will be used as a complementary approach to antagonist treatment to assess the endogenous role of NTS MC4-Rs in mediating intake suppression by GI satiation signals. Importantly, MC4-R knockdown technology will also be used to assess the role of endogenous NTS MC4-R signaling in energy regulation more generally. Experiments proposed in Specific Aim 2 will expand consideration to the intracellular signaling pathways in the NTS contributing to intake suppression following MC4-R agonists, GI satiation signaling, and their putative combination. Proposed research will build upon our preliminary findings and other recent data by targeting the p44/42 mitogen-activated protein kinase (MAPK) signaling pathway and potential upstream kinases (protein kinase A [PKA] and phosphatidylinositol 3-kinase [PI3K]) as NTS intracellular mediators of intake suppression by MC4-R ligands and GI signals. Experiments will combine in vivo approaches using pharmacological inhibition of p44/42 MAPK, PKA, and PI3K, with in vitro approaches using activity assays and immunoblots, to assess the physiological role of these intracellular signaling pathways in the suppression of intake that follows MC4-R ligands, GI satiation signals, and potentially their combination. Research laid out in this proposal has the potential to deepen the basic science related to neurochemical mediators of food intake suppression. PUBLIC HEALTH RELEVANCE: The prevalence of obese and overweight humans in Western cultures has increased dramatically, leading to devastating and costly health problems. Effective drug treatments for obesity treatment are likely to come from basic science investigating the neuronal controls of food intake behavior. Research proposed here is relevant to clinical drug development for obesity by exploring neurohormonal mediators of food intake suppression following gastrointestinal contact with ingested nutrients and the processing of these signals by the human obesity-linked melanocortin receptors in the caudal brainstem.