下丘脑Esyt3在能量平衡调控与肥胖形成中作用的研究

Obesity is a major risk factor for a plethora of chronic diseases. The pathogenesis of obesity is not yet clear. Leptin is one of the most important hormones in maintaining animal’s energy homeostasis through action in the hypothalamus and promoting catabolism. Nonetheless, efforts trying to treat obesity with Leptin failed due to the fact that obese people often showed resistance to the action of this hormone. The underlying mechanism of Leptin resistance is not fully understood. Extended Synaptotagmin 3 (Esyt3) is a key protein mediating the contact of endoplasmic reticulum and plasma membrane. Our preliminary data show that Esyt3 is overexpressed in the hypothalamus of obese mouse. Knockdown the expression of Esyt3 in the mediobasal hypothalamus enhances the catabolism of mice fed a high-fat diet. These results encourage us to investigate the potential roles of Esyt3 in energy homeostasis and the pathogenesis of diet-induced obesity. By utilizing Esyt3 knockout mouse, lentivirus-mediated gene manipulation, pharmacological and metabolic phenotyping approaches, we will study three specific aims in the present proposal. In aim 1, we plan to study the loss-of-function metabolic phenotype of Esyt3 by characterizing two cohorts of mice: i) Esyt3 knockout and wildtype mice, ii) mice injected with Esyt3 knockdown lentivirus or control virus in the mediobasal hypothalamus. In aim 2, we will investigate the gain-of-function metabolic phenotype of hypothalamic Esyt3. We plan to establish two additional cohorts of mice. In the first cohort, we will deliver control lentivirus or lentivirus expressing Esyt3 to the mediobasal hypothalami of mice. In the second cohort, we plan to inject control virus or Esyt3 lentivirus to the mediobasal hypothalami of Esyt3 knockout mice and control wildtype mice. We will feed these mice high-fat diet or chow diet, and monitor an array of metabolic parameters. In aim 3, we will interrogate the mechanism of Esyt3 mediated obesogenesis under overnutrition condition. Since our preliminary data indicate that ectopic expression of Esyt3 activates the endoplasmic reticulum stress pathway and triggers leptin resistance, we hypothesize that Esyt3 plays a critical role in diet-induced obesity by the induction of endoplasmic reticulum stress and leptin resistance. Our proposed research will clearly establish a key role of Esyt3 in both energy homeostasis and diet-induced obesity. Targeting Esyt3 could represent a new avenue in countering obesity.

肥胖是多种疾病的高危因素，其形成机制还不完全清楚。瘦素是通过作用于下丘脑来促进分解代谢的重要激素，但因肥胖者常存在瘦素抵抗，因此无法用于减肥。瘦素抵抗形成的机制还不明确。Esyt3是介导内质网与细胞膜接触的重要分子。我们的预实验显示Esyt3在肥胖小鼠下丘脑过表达，抑制下丘脑Esyt3表达能够促进肥胖动物的分解代谢。这鼓舞我们计划利用Esyt3敲除小鼠、病毒介导的基因操作、药理学和代谢表型分析等方法来研究其在能量平衡和肥胖形成中的作用。首先，我们计划观察Esyt3敲除和中下部下丘脑Esyt3 Knockdown对于小鼠能量代谢的影响。然后，分析下丘脑过表达Esyt3，以及在敲除小鼠下丘脑重表达Esyt3对于代谢的影响。最后，研究Esyt3通过内质网应激和瘦素抵抗介导食源性肥胖形成的机制。本研究将阐明Esyt3在能量代谢调控和肥胖形成中的作用和机制，从而找到一个潜在的预防或治疗肥胖的新靶点。

肥胖人群在我国呈逐年增加的趋势。肥胖是能量平衡失调的结果，但其原因还不清楚。下丘脑是动物调控体重和食欲的关键部位。在本研究中，我们综合利用组织学和药理学方法，以及病毒介导的基因表达和基因工程小鼠模型，发现C2结构域蛋白E-Syt3在下丘脑神经元中表达。E-Syt3全身敲除小鼠能显著保护高脂食物引起的肥胖，并改善动物的糖耐量。反之，在小鼠下丘脑弓状核神经元中过表达E-Syt3，则引起动物体重的过度增加，并出现糖耐量异常。我们发现E-Syt3敲除小鼠下丘脑中抑制食欲的神经肽，即α-MSH的含量增加。进一步的分析显示，这些小鼠下丘脑中介导α-MSH加工的蛋白酶PC1/3和PC2表达增加，而这两种酶表达的增加是由于蛋白激酶C和AP-1的活化引起的。总之，我们的研究显示，下丘脑神经元中E-Syt3在营养性肥胖的形成过程中具有重要的作用，可能成为治疗的靶点。