Brain interleukin-18 control of food intake and energy expenditure

描述（由申请人提供）：数据表明白细胞介素-18（IL-18）是一种因其免疫系统调节特性而发现的细胞因子，可控制食物摄入和能量代谢。我们和其他人发现，IL-18调节小鼠成年期的能量稳态。缺乏IL-18（IL-18-/-）或其结合受体亚基（IL-18 Ra）的小鼠发展成熟型肥胖和胰岛素抵抗。作为年轻的成年人，在它们变得显著超重之前，IL-18-/-小鼠比野生型小鼠更胖，显示出减少的能量消耗，并且与野生型小鼠相比，低脂肪和高脂肪饮食都过量。由于杂合子IL-18+/-突变小鼠显示出中等吞噬表型，因此这些发现似乎是调节性的，而不是非特异性发育“病变”效应的假象。与这些功能丧失研究匡威，IL- 18的中枢给药与脂肪细胞激素瘦素一样有效地抑制饥饿小鼠的食物摄入和体重恢复，并且这样做不会产生与促炎性瘦素驱动的“疾病”厌食症典型相关的不良不适、发热或HPA轴激活。人类遗传学研究最近发现IL-18或其受体基因中的单核苷酸多态性（SNP）与肥胖和代谢综合征疾病的风险增加有关。IL-18及其受体在下丘脑中组成性表达，其水平通过外周免疫攻击而增加。因此，本申请中测试的指导假设是中枢IL-18系统可以控制食物摄入和能量消耗。翻译上，该功能将使IL-18成为疾病综合征/恶病质的临床相关靶标。此外，由于IL-18给药不具有促炎系统的“疾病综合征”效应，因此外源性IL-18作为抗肥胖治疗可能具有翻译相关性。为了检验这一假设，本跨学科的建议结合互补的，但不同的，专业知识的两个PI的，以确定机械如何中央IL-18响应系统调节食物摄入量，能量消耗，并最终，肥胖。两个特定目标的实验结合了联合收割机的整体和Cre/lox靶向的IL-18或IL-18 R缺陷的遗传功能丧失小鼠模型;经典的分子、药理学和生理学方法;以及创新的行为分析。目的1旨在确定中枢IL-18控制食物摄入和能量消耗的生理和受体机制。将确定中枢IL-18减少食物摄入和增加能量消耗的效力和IL-18 R依赖性。配对喂养用于确定过量食物摄入在IL-18无效突变体的肥胖中的功能作用。喂食微结构分析用于探索IL-18是否调节膳食大小或餐后饱腹感以控制食物摄入。最后，确定饮食诱导的肥胖对中枢IL-18系统的分子表达和功能敏感性的影响。目的2旨在确定IL-18作用于能量稳态的中心位点和分子机制。实验2.1将产生关于在基础条件下和在外周免疫攻击（脂多糖）后下丘脑内表达IL-18及其同源受体的细胞类型、组织化学区分神经元与神经胶质群体、快速突触传递模式以及与细胞因子厌食症相关的厌食途径的神经解剖学相互作用的关键信息。在实验2.2-2.3中，Cre/lox靶向将用于产生在下丘脑室旁核（PVN）和下丘脑腹内侧核（VMH）中选择性缺乏IL-18 R亚基的小鼠。研究将涉及对后代的能量平衡参数进行表型分析，以允许与全局敲除中获得的结果进行比较，并确定位点特异性缺失是否改变对中央IL-18给药的摄食或代谢反应。这些研究为PVN和VMH中IL-18/IL-18 R系统控制食物摄入和能量消耗的功能意义提供了强有力的测试。总的来说，这些结果将提供有关IL-18系统调节食物摄入和能量消耗的位点和作用机制的开创性数据。这些信息将是开始理解中枢IL-18信号传导与能量稳态紊乱（如肥胖或恶病质）的病理生理学和潜在治疗相关性的关键。 公共卫生相关性：更好地理解与负能量平衡的病理性“疾病”障碍（例如，恶病质消瘦，恶心厌食）或正能量平衡（例如，肥胖症、代谢综合症）的治疗。白细胞介素-18（IL- 18）是一种因其免疫系统调节特性而被发现的细胞因子，其在控制食物摄入和能量代谢中的作用已得到越来越多的研究。为了阐明中枢IL- 18信号传导与能量稳态紊乱的病理生理学和潜在治疗相关性，本多学科建议结合了两个PI互补但不同的专业知识，以确定中枢IL-18应答系统如何机械地调节食物摄入、能量消耗以及最终肥胖。

DESCRIPTION (provided by applicant): Data have accrued implicating interleukin-18 (IL-18), a cytokine discovered for its immune system-modulating properties, in the control of food intake and energy metabolism. We and others found that the IL-18 modulates energy homeostasis during adulthood in mice. Mice deficient in IL-18 (IL-18-/-) or its binding receptor subunit (IL-18Ra) develop maturity-onset obesity and insulin resistance. As young adults, before they become substantially overweight, IL-18-/- mice are fattier, show reduced energy expenditure, and overeat both low-fat and high-fat diets as compared to wildtype mice. Because heterozygote IL-18+/- mutant mice show an intermediate hyperphagic phenotype, the findings appear to be regulatory, rather than an artifact of non- specific developmental "lesion" effects. Converse to these loss-of-function studies, central administration of IL- 18 suppresses food intake and weight regain in hungry mice as potently as does the adipocyte hormone leptin and does so without producing the adverse malaise, fever or HPA-axis activation classically associated with proinflammatory cytokine-driven "sickness" anorexia. Human genetic studies have recently identified single nucleotide polymorphisms (SNPs) in the gene for IL-18 or its receptor associated with increased risk for obesity and metabolic syndrome disorders. IL-18 and its receptors are constitutively expressed in the hypothalamus, with levels increased by peripheral immune challenge. Therefore, the guiding hypothesis tested in the present application is that central IL-18 systems can control food intake and energy expenditure. Translationally, this function would make IL-18 a clinically relevant target for sickness syndrome/cachexia. Moreover, because IL-18 administration does not share "sickness syndrome" effects of the pro-inflammatory system, exogenous IL-18 may have translational relevance as an anti-obesity treatment. To test this hypothesis, the present interdisciplinary proposal combines complementary but distinct, expertise of two PI's to determine mechanistically how central IL-18-responsive systems modulate food intake, energy expenditure, and, ultimately, adiposity. Experiments in two Specific Aims combine global and Cre/lox-targeted genetic loss- of-function mouse models deficient in IL-18 or the IL-18R; classic molecular, pharmacological, and physiologic approaches; and innovative behavioral analyses. AIM 1 seeks to identify physiologic and receptor mechanisms for central IL-18 control of food intake and energy expenditure. The potency and IL-18R- dependence of central IL-18 reductions in food intake and increases in energy expenditure will be determined. Pair-feeding is used to determine the functional role of excess food intake in the obesity of IL-18 null mutants. Feeding microstructure analysis is used to explore whether IL-18 modulates meal size or post-meal satiety in controlling food intake. Finally, the influence of diet-induced obesity on molecula expression and functional sensitivity of the central IL-18 system is determined. AIM 2 seeks to identify central sites and molecular mechanisms of IL-18 action on energy homeostasis. Expt. 2.1 will yield key information regarding the cell types the express IL-18 and its cognate receptors within the hypothalamus under basal conditions and following peripheral immune challenge (lipopolysaccharide), histochemically differentiating neuronal from glial populations, modes of fast synaptic transmission, and neuroanatomical interactions with anorectic pathways implicated in cytokine anorexia. In Expts 2.2-2.3, Cre/lox targeting will be used to generate mice that lack IL- 18R subunits selectively in the paraventricular nucleus of the hypothalamus (PVN) and the ventromedial hypothalamic nucleus (VMH). Studies will involve phenotyping the offspring for energy balance parameters to allow comparison with results obtained in the global knockout and also to determine whether the site-specific deletion alters feeding or metabolic responses to central IL-18 administration. The studies provide a powerful test of the functional significance of IL-18/IL-18R systems in the PVN and VMH for the control of food intake and energy expenditure. Collectively, the results will provide seminal data regarding the sites and mechanisms of action by which IL-18 systems modulate food intake and energy expenditure. Such information will be key for beginning to understand the pathophysiologic and potential therapeutic relevance of central IL-18 signaling for disorders of energy homeostasis, such as obesity or cachexia. PUBLIC HEALTH RELEVANCE: A better understanding of novel mechanisms with therapeutic relevance for pathological "sickness" disorders of negative energy balance (e.g., cachexia wasting, sickness anorexia) or of positive energy balance (e.g., obesity, metabolic syndrome disorders) is urgently needed. Data have accrued implicating interleukin-18 (IL- 18), a cytokine discovered for its immune system-modulating properties, in the control of food intake and energy metabolism. In order to elucidate the pathophysiologic and potential therapeutic relevance of central IL- 18 signaling for disorders of energy homeostasis., the present multidisciplinary proposal combines complementary but distinct, expertise of two PI's to determine mechanistically how central IL-18-responsive systems modulate food intake, energy expenditure, and, ultimately, adiposity.