Hypothalamic SIRT1 and Energy Balance

描述（由申请人提供）：在美国，肥胖及其相关的医学并发症（包括II型糖尿病、心血管疾病、血脂异常和癌症）每年导致30多万人死亡。肥胖症治疗策略通常不会导致足够的持续体重减轻，并且在美国和许多其他国家，肥胖症的患病率和严重程度正在逐渐增加。最近的调查将大约三分之一的美国人归类为肥胖。肥胖症的复杂性是由环境因素和易患遗传因素之间的相互作用造成的。更深入地了解肥胖发病机制和能量代谢调控的分子机制对于开发有效的治疗方法至关重要。能量平衡是由感觉和响应身体营养状况的组织和器官维持的。在中枢水平，下丘脑是神经系统解释肥胖或营养相关输入的主要组成部分;它提供激素和行为反应，最终目的是调节能量摄入和消耗。在分子水平上，被称为营养或能量传感器的酶模拟了参与能量平衡的组织的作用。两个关键的能量/营养传感器，mTOR（哺乳动物雷帕霉素靶蛋白）和AMPK（AMP激活的激酶）-除了它们在外周组织中广泛的代谢作用-参与下丘脑中食物摄入的控制。 酶Sirt 1是一种进化上保守的NAD+依赖性脱乙酰酶，参与许多生物学过程，包括细胞分化、凋亡、代谢和衰老。由于其对NAD+的依赖性，Sirt 1也可以作为营养/氧化还原传感器。因此，我们假设Sirt 1可能在下丘脑水平上通过影响mTOR或AMPK通路在控制能量平衡中发挥作用。我们的初步结果表明，药理学抑制下丘脑Sirt 1或siRNA介导的敲低下丘脑弓状核（ARC）中的Sirt 1，减少食物摄入量和体重增加。因此，这一建议提供了一个新的观点分配给Sirt 1作为细胞能量传感器调节能量平衡在下丘脑水平。Sirt 1在下丘脑水平将营养物质的可利用性与能量稳态联系起来，这种作用至少部分取决于禁食诱导和Sirt 1介导的FoxO 1去乙酰化和mTOR信号转导的调节。基于这些发现，我们将：目的1：确定下丘脑Sirt 1信号调节能量平衡的作用靶点和机制。为此，我们将确定是否：1。Sirt 1通过FoxO 1以营养依赖的方式调节促食欲POMC以及促食欲Agouti相关肽（AgRP）和神经肽Y（NPY）。2. Sirt 1以营养敏感的方式去乙酰化并抑制Stat 3 3. Sirt 1在下丘脑水平抑制mTOR信号传导。目的2：确定下丘脑Sirt 1在调节激素原转化酶1和2中的作用。为此，我们将测试以下假设：1。Sirt 1在N43下丘脑细胞中调节PC 1和PC 2 2. Sirt 1调节弓状核中POMC和AgRP神经元中的PC。3. PC 2的调节导致1-MSH水平降低并加重DIO状况。目的3：确定下丘脑Sirt 1在饮食诱导肥胖（DIO）中的作用。为此，我们将研究以下假设：1。DIO大鼠摄食对抑制下丘脑Sirt 1表达敏感。2.暴露于高脂肪饮食（HFD）改变下丘脑Sirt 1表达、信号传导和Sirt 1共底物/激活剂NAD+水平。 3.在DIO条件下，Sirt 1对mTOR信号传导的抑制作用是肥胖的原因之一。 公共卫生相关性：根据世界卫生组织的数据，发达国家的肥胖症已达到流行病的程度。全球有超过10亿成年人超重，其中约3亿人临床肥胖。因此，肥胖的研究已成为医学研究的优先事项。尽管如此，寻找有效的抗肥胖药物一直不成功。最初，激素瘦素的发现提高了很多期望，因为它能够降低肥胖瘦素缺乏小鼠的食欲和体重。然而，很快就发现大多数肥胖的人类和啮齿动物具有高水平的血浆瘦素，其不能降低食欲和体重。这种瘦素抵抗状态的许多方面仍然是未知的。更好地了解瘦素影响神经回路的分子机制对于开发治疗肥胖的新策略至关重要。最近，营养传感器的发现在肥胖研究中占据了重要地位。除了mTOR（mammalian target of rapamycin）和AMPK（AMP activated kinase），已知是重要的能量/营养传感器之外，已知参与许多生物过程（包括细胞分化、凋亡、代谢和衰老）的酶Sirt 1现在具有作为能量传感器的另一种潜在作用。因此，这一建议提供了一个新的观点分配给Sirt 1作为细胞能量传感器调节能量平衡在下丘脑水平。

DESCRIPTION (provided by applicant): Obesity and its associated medical complications including type II diabetes, cardiovascular disease, dyslipidemia, and cancer account for more than 300,000 deaths per year in the United States. Obesity treatment strategies often do not result in adequate sustained weight loss, and the prevalence and severity of obesity in the U.S. and many other countries is progressively increasing. Recent surveys classify roughly 1/3 of all Americans as obese. The complexity of the obesity condition results from the interaction between environmental and predisposed genetic factors. A more thorough understanding of the molecular mechanisms underlying the pathogenesis of obesity and regulation of energy metabolism is essential for the development of effective therapies. Energy homeostasis is maintained by tissues and organs that sense and respond to the nutritional status of the body. At the central level, the hypothalamus is the primary component of the nervous system in interpreting adiposity or nutrient related inputs; it delivers hormonal and behavioral responses with the ultimate purpose of regulating energy intake and consumption. At the molecular level, enzymes called nutrient or energy sensors mimic the role of the tissues involved in energy balance. Two key energy/nutrient sensors, mTOR (mammalian target of rapamycin) and AMPK (AMP activated kinase) - in addition to their extensive metabolic roles in the peripheral tissues - are involved in the control of food intake in the hypothalamus. The enzyme Sirt1 is an evolutionarily conserved NAD+-dependent deacetylase involved in many biological processes including cellular differentiation, apoptosis, metabolism, and aging. Because of its dependence on NAD+, Sirt1 also functions as a nutrient/redox sensor. Thus, we hypothesized that Sirt1 could play a role in the control of energy balance, perhaps by influencing the mTOR or AMPK pathways, at the level of the hypothalamus. Our preliminary results indicate that pharmacological inhibition of hypothalamic Sirt1 or siRNA mediated knock down of Sirt1 in the arcuate nucleus (ARC) of the hypothalamus decreases food intake and body weight gain. Therefore, this proposal provides a novel view assigned to Sirt1 as a cellular energy sensor regulating energy balance at the hypothalamic level. Sirt1 links nutrient availability to energy homeostasis at the hypothalamic level, and this effect depends -at least in part- on the fasting induced and Sirt1 mediated regulation of FoxO1 deacetylation and mTOR signaling. Based on these findings we will: Aim 1: Determine the targets and mechanism of action hypothalamic Sirt1 signaling regulating energy balance. To this purpose we will determine whether: 1. Sirt1 regulates the anorexigenic POMC as well as the orexigenic Agouti-related peptide (AgRP) and neuropeptide Y (NPY) through FoxO1 in a nutrient dependent manner. 2. Sirt1 deacetylates and inhibits Stat3 in a nutrient sensitive manner 3. Sirt1 represses mTOR signaling at the hypothalamic level. Aim 2: Determine the role of hypothalamic Sirt1 in the regulation of the Prohormone Convertases 1 and 2. To this purpose we will test the following hypotheses: 1. Sirt1 regulates PC1 and PC2 in N43 hypothalamic cells 2. Sirt1 regulates the PC's in POMC and AgRP neurons in the arcuate nucleus. 3. The regulation of PC2 causes a decrease in 1-MSH levels and aggravates the DIO condition. Aim 3: Determine the role of hypothalamic Sirt1 in the diet-induced obesity (DIO) condition. To this purpose we will investigate the following hypotheses: 1. Food intake of DIO rats is sensitive to inhibition of hypothalamic Sirt1. 2. Exposure to High Fat Diet (HFD) alters hypothalamic Sirt1 expression, signaling, and Sirt1 co- substrate/activator NAD+ levels. 3. The inhibitory effect of Sirt1 on mTOR signaling in the DIO condition is one of the causes of obesity. PUBLIC HEALTH RELEVANCE: According to the World Health Organization, obesity in developed countries has reached epidemic proportions. There are globally more than 1 billion adults overweight, with around 300 million of them clinically obese. As a consequence, the study of obesity has become a priority in medical research. Still, the search for effective anti-obesity drugs has been unsuccessful. Initially, the discovery of the hormone leptin raised a lot of expectations, given its capacity to decrease appetite and body weight of obese leptin deficient mice. However, it was soon established that most obese humans and rodents have high levels of plasma leptin, which fail to reduce appetite and body weight. Many aspects of this leptin-resistant state are still unknown. A better understanding of leptin molecular mechanisms affecting neural circuits is essential to develop new strategies for the treatment of obesity. Very recently, the discovery of nutrient sensors took a big stage in the obesity research. Aside from mTOR (mammalian target of rapamycin) and AMPK (AMP activated kinase), known to be important energy/nutrient sensors, the enzyme Sirt1, known to be involved in many biological processes including cellular differentiation, apoptosis, metabolism, and aging, now has another potential role as energy sensor. Therefore, this proposal provides a novel view assigned to Sirt1 as a cellular energy sensor regulating energy balance at the hypothalamic level.