Leptin function & resistance in midbrain VTA & SN in reward eating & obesity

描述(由申请人提供)： 肥胖症在美国很普遍。饮食诱导肥胖(DIO)是最常见的肥胖类型，也是一种威胁健康的主要慢性病。过度摄入能量密集、美味的食物，超出了基本的卡路里需求，会促进DIO。最近的数据支持了瘦素在中脑奖励回路腹侧被盖区(VTA)的直接作用，以缓和高脂肪(HF)喂养。我们最新的初步研究表明：(1)与下丘脑的前脑弓状核(ARC)相比，激活VTA的瘦素对HF摄取和相关的体重增加具有更大的反调节功能；(2)瘦素在黑质(SN)具有一种新的生理功能，以减少体重增加，黑质是中脑奖赏回路中的另一个区域。这项建议将研究瘦素和瘦素抵抗在VTA和/或SN在调节HF消耗和饮食体重增加中的作用，并探讨这些功能除了在下丘脑ARC中的功能外是否特别重要。我们假设瘦素在中脑VTA中的功能，特别是对抗HF的摄入，并与前脑ARC中的瘦素共同作用于能量平衡的总体控制。我们进一步推测，HF喂养诱导了瘦素抵抗，其特征是VTA内对瘦素的食物和体重反应减弱，这种抵抗是加剧饮食性肥胖的主要罪魁祸首。最后，我们提出了瘦素在SN能量平衡中的新作用，并假设瘦素直接调节SN中的摄食和体重，SN中的瘦素作用与VTA中的瘦素作用分别有助于抑制饮食体重增加。将在雄性SD大鼠身上实现三个特定的目标。目标1将阐述瘦素在VTA和ARC中的作用是否协同作用，以减少HF摄入量和阻止饮食体重增加。目的1还将评估瘦素在VTA中的作用，以减少对HF食物的偏好，使用饮食选择范例，与ARC中的瘦素效应进行比较。瘦素将通过定点定向的重组腺相关病毒介导的(RAAV)基因特异性地传递到VTA或ARC或这两个位置而长期过度表达。目的2试图确定慢性HF暴露的VTA中可能存在瘦素抵抗，并确定VTA中瘦素抵抗的因果作用，以促进更大的DIO。慢性HF暴露于VTA的瘦素抵抗的开始将通过评估大脑微针中的急性最大瘦素信号和中枢瘦素反应来检验。后者将根据24小时的食物摄入量和体重对单剂量瘦素的反应来确定，瘦素是通过植入VTA或ARC的脑管注入的。此外，瘦素抵抗将通过rAAV介导的瘦素拮抗剂在VTA或ARC特异地过度表达而被阻断瘦素受体来模拟，并比较这一阻断在这两个部位对HF消耗和饮食体重增加的影响。AIM 3旨在验证新提出的瘦素在SN中关于能量平衡和/或奖励进食的生理功能。瘦素在SN和VTA中的潜在作用将进行比较。瘦素将在SN或VTA中过度表达，或通过rAAV-Leptin基因在继续饮食或引入HF饮食的饲养大鼠的两个部位同时过度表达。食物消耗、体重增加和包括运动活动在内的能量消耗将与JAK2-STAT3和/或ERK瘦素信号一起被检测。特别令人感兴趣的是探索瘦素在VTA和SN中的过度表达是否会与单独在这两个部位的过度表达相比，对HF食物摄入和相关肥胖显示出相加或协同的抑制作用。这一应用的结果将为控制奖励进食和饮食诱导肥胖的新大脑机制提供有价值的见解。这些新信息可能会带来更好的战略，以应对迫在眉睫的肥胖症流行。 公共卫生相关性： 拟议工作与退伍军人病患护理任务的相关性：这项研究与全球公共卫生问题--肥胖症流行--高度相关。拟议中的实验结果将促进我们对大脑对过度食用美味、肥胖食物和饮食诱导肥胖(DIO)的控制的理解。肥胖及其相关疾病，包括II型糖尿病、高血压、高脂血症和残疾，在普通公众中正在增加，但对退伍军人群体构成更大的威胁。这项拨款是根据国会研究肥胖症的授权制定的。它将阐明新的中枢神经系统站点&管理奖励进食和DIO的机制。迫切需要这些新的见解来帮助更好地设计肥胖症治疗方案，并促进患有直接或间接受肥胖症影响的各种疾病的退伍军人的有效康复。我们的研究的长期好处将是减少退伍军人管理局患者护理系统中不断上升的长期医疗成本负担。

DESCRIPTION (provided by applicant): Obesity is prevalent in the United States. Diet-induced obesity (DIO) is the most common type of obesity and a major health-threatening chronic disease. Over-consumption of energy-dense, palatable food beyond basic caloric need promotes DIO. Recent data underpin a direct leptin function in the ventral tegmental area (VTA) of the midbrain reward circuitry to temper high-fat (HF) feeding. Our latest preliminary studies demonstrate (1) leptin activation of the VTA has a greater counter-regulatory function against HF intake and associated weight gain than that of the forebrain arcuate nucleus (ARC) of the hypothalamus; (2) a new physiological function of leptin to curtail weight gain in the substantia nigra (SN), another area within the midbrain reward circuitry. This proposal will investigate the role of leptin and leptin resistance specifically in the VTA and/or SN in modulating HF consumption and dietary weight gain and also address if these functions are especially important besides those in the hypothalamic ARC. We hypothesize that leptin function in the midbrain VTA, in particular, counters HF intake and contributes jointly with that in the forebrain ARC to the overall control of energy balance. We further postulate that HF feeding induces leptin resistance characterized by diminished food and body weight responses to leptin within the VTA, and that this resistance is a major culprit for exacerbating dietary obesity. Lastly, we propose a new role of leptin in energy homeostasis in the SN, and hypothesize that leptin directly regulates feeding and body weight in the SN and that leptin action in the SN contributes separately from that of the VTA to curb dietary weight gain. Three Specific Aims will be carried out in male Sprague Dawley (SD) rats. Aim 1 will address if leptin action in the VTA and in the ARC works in concert to curtail HF consumption and deter dietary weight gain. Aim 1 will also evaluate leptin function in the VTA to decrease the preference for HF food using a diet-selection paradigm compared to leptin effect in the ARC. Leptin will be chronically over-expressed via site-directed, recombinant adeno-associated virus-mediated (rAAV) gene delivery specifically to either the VTA, or ARC or both sites. Aim 2 seeks to identify a presumed leptin resistance in the VTA with chronic HF exposure and to establish a causal role of leptin resistance in the VTA to promote greater DIO. The onset of leptin resistance with chronic HF exposure in the VTA will be examined by assessing acute maximal leptin signaling in brain micro-punches and central leptin responsiveness. The latter will be determined from 24-hour food intake and body weight responses to a single dose of leptin introduced via implanted brain cannula in the VTA or ARC. Moreover, leptin resistance will be simulated by leptin receptor blockade achieved via rAAV-mediated leptin antagonist over-expression specifically in either the VTA or ARC, and the effect of this blockade in either site on HF consumption and dietary weight gain compared. Aim 3 is designed to validate the newly proposed leptin physiological function in the SN on energy homeostasis and/or reward eating. Potential effects of leptin in the SN will be compared to those in the VTA. Leptin will be over-expressed in the SN or VTA, or in both sites simultaneously via rAAV-leptin gene delivery in chow-raised rats remaining on chow or introduced to a HF diet. Food consumption, body weight gain, and energy expenditure including locomotor activity will be examined along with JAK2-STAT3 and/or ERK leptin signaling. It is of particular interest to explore if leptin over- expression in both the VTA and SN, simultaneously, will display an additive or synergistic inhibition of HF food intake and associated obesity compared to overexpression in either site alone. The outcomes of this application will provide valuable insights into new brain mechanisms governing reward eating and diet-induced obesity. The new information may lead to better strategies to address the looming obesity epidemic. PUBLIC HEALTH RELEVANCE: Relevance of Proposed Work to the VA Patient Care Mission: This study bares high relevance to a global public health issue, the obesity epidemic. The results emanating from the proposed experiments will advance our understanding of brain control of over-consumption of palatable, fattening food and diet-induced obesity (DIO). Obesity and associated disorders including type II diabetes, hypertension, hyperlipidemia, and disability, are increasing in the general public, but pose even a greater threat to the veteran population. This grant is developed in line with the congressional mandate to study obesity. It will elucidate new CNS sites & mechanisms governing reward eating and DIO. These new insights are critically needed to aid in better designs of obesity treatment and facilitate effective rehabilitation for veterans suffering from diverse forms of illnesses directly or indirectly affected by obesity. The long-range benefit from our study would be to reduce the ever-rising burden of long-term health care costs within the VA patient care system.