Brain interleukin-18 control of food intake and energy expenditure

描述(由申请人提供)：已有数据表明，白介素18(IL-18)是一种细胞因子，可调节免疫系统，控制食物摄入量和能量代谢。我们和其他人发现，IL-18调节小鼠成年后的能量平衡。缺乏IL-18(IL-18-/-)或其结合受体亚单位(IL-18Ra)的小鼠会出现成熟期肥胖和胰岛素抵抗。与野生型小鼠相比，IL-18-/-小鼠在成年后显著超重之前，会更胖，能量消耗更少，并且同时过量食用低脂肪和高脂肪饮食。由于杂合子IL-18/-突变小鼠表现出中等程度的巨噬表型，这些发现似乎是调节性的，而不是非特异性发育“损伤”效应的产物。与这些功能丧失研究相反，中央给药IL-18可以像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，并且不会产生不良的不适、发热或HPA轴激活，这些不良反应通常与促炎细胞因子驱动的厌食症有关。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(SNPs)与肥胖和代谢综合征障碍的风险增加有关。IL-18及其受体在下丘脑有结构性表达，外周免疫刺激可使IL-18水平升高。因此，在本应用中检验的指导性假说是中枢IL-18系统可以控制食物摄入量和能量消耗。从翻译上讲，这一功能将使IL-18成为疾病综合征/恶病质的临床相关靶点。此外，由于IL-18的应用不分享促炎系统的“疾病综合征”效应，外源性IL-18作为一种抗肥胖治疗可能具有翻译相关性。为了验证这一假设，目前的跨学科建议结合了两个PI的互补但不同的专业知识，以机械地确定中枢IL-18反应系统如何调节食物摄入、能量消耗，并最终调节肥胖。两个特定目标的实验结合了全局和针对Cre/lox的缺乏IL-18或IL-18R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试图确定中枢IL-18控制食物摄入量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对IL-18R的依赖。配对喂养用于确定过量食物摄入在IL-18缺失突变体肥胖中的功能作用。饲喂微结构分析被用来探索IL-18是否在控制食物摄入量方面调节膳食大小或餐后饱足感。最后，确定饮食诱导肥胖对中枢IL-18系统分子表达和功能敏感性的影响。目的2试图确定IL-18对能量稳态作用的中心部位和分子机制。示例：2.1将提供关于下丘脑在基础条件下和在外周免疫挑战(脂多糖)后表达IL-18及其同源受体的细胞类型的关键信息，组织化学区分神经元和神经胶质群体，快速突触传递的模式，以及与细胞因子厌食症有关的厌食途径的神经解剖相互作用。在执行部分2.2-2.3中，Cre/lox靶向将被用来产生选择性地在下丘脑室旁核(PVN)和下丘脑腹内侧核(VMH)缺乏IL-18R亚基的小鼠。研究将涉及对后代进行能量平衡参数的表型分析，以便与全球基因敲除中获得的结果进行比较，并确定特定位点的缺失是否改变了对中央给药IL-18的摄食或代谢反应。这些研究为IL-18/IL-18R系统在PVN和VMH中控制食物摄入量和能量消耗的功能意义提供了强有力的测试。总而言之，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部位和作用机制的开创性数据。这些信息将是开始了解中枢IL-18信号与能量平衡紊乱(如肥胖或恶病质)的病理生理学和潜在治疗相关性的关键。 与公共卫生的相关性：迫切需要更好地了解具有治疗相关性的新机制，以治疗负能量平衡(例如，恶病质消耗、病理性厌食症)或正能量平衡(例如，肥胖、代谢综合征障碍)的病理性“疾病”障碍。已有数据表明，白介素18(IL-18)是一种细胞因子，因其免疫系统调节特性而被发现，在控制食物摄入量和能量代谢中发挥作用。为了阐明中枢IL-18信号在能量稳态紊乱中的病理生理学和潜在的治疗意义，本多学科方案结合了两个PI的互补但不同的专业知识，以机械地确定中枢IL-18反应系统如何调节食物摄取、能量消耗，并最终调节肥胖。

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.