The Mechanism of Cetp-Mediated Protection from High-Fat Diet-Induced Insulin Resistance

描述(申请人提供)：肥胖导致胰岛素抵抗，从而增加患2型糖尿病(T2D)和冠心病(CHD)的风险。虽然减肥是肥胖症临床治疗的主要目标，但长期的减肥很少持续。因此，了解可能改善肥胖对T2D和CHD影响的途径是非常必要的。我们发现，转基因表达胆固醇酯转移蛋白(CETP)对肥胖背景下高脂饮食(HFD)诱导的雌性小鼠胰岛素抵抗具有保护作用。CETP在血浆脂蛋白之间运输甘油三酯和胆固醇酯(CE)，最终将CE输送到肝脏进行分泌，称为胆汁反向胆固醇转运(RCT)。CETP抑制剂可升高高密度脂蛋白，但不能降低冠心病的发病风险，这可能表明CETP具有非高密度脂蛋白的功能。小鼠缺乏CETP，因此我们使用表达CETP的转基因小鼠来确定CETP如何影响胰岛素抵抗。使用高胰岛素-正常血糖钳夹技术，我们发现CETP在服药4周后对女性的胰岛素抵抗有保护作用，但对男性没有保护作用。尽管肥胖程度相似，但这种保护作用仍然存在。这项建议的目的是了解CETP如何预防饮食诱导的肥胖小鼠的胰岛素抵抗。我们的发现代表了CETP在肥胖病理生理学方面的一种新的有益功能。尽管高脂饮食，CETP的表达保留了肝脏和肌肉中的胰岛素信号通路，并在胰岛素介导下下调了糖异生基因磷酸烯丙酮酸羧激酶(Pck 1)和葡萄糖-6-磷酸酶(G6PC)的mRNA表达。我们发现CETP增加了胆汁酸信号分子小异二聚体伙伴(SHP)的mRNA，并增加了肝脏中的雌激素信号。我们假设CETP促进肝脏中的胆汁酸和雌激素信号，以保护饮食诱导的胰岛素抵抗。了解CETP如何预防饮食诱导的胰岛素抵抗可能会产生新的治疗目标，以减轻肥胖对CHD和T2D的影响。在目标1中，我们将确定女性特异性在CETP介导的高脂诱导的胰岛素抵抗保护中的作用机制。我们预计，肝脏雌激素受体α的缺失将削弱CETP对高脂诱导的胰岛素抵抗的保护作用。在目标2中，我们将确定参与CETP介导的保护高脂蛋白诱导的胰岛素抵抗的肝脏胆汁酸信号转导通路。我们预计，SHP的肝脏敲除将消除CETP介导的对HFD诱导的胰岛素抵抗的保护作用。完成这项拟议的工作将1)确定导致性别差异的机制，以预防代谢性疾病；2)确定CETP下游的肝胆汁酸信号通路，以防止饮食诱导的胰岛素抵抗。此外，这项申请中提出的工作将支持我作为一名内科科学家的培训的关键一步，他的职业生涯旨在建立肥胖症和糖尿病之间的治疗联系。

DESCRIPTION (provided by applicant): Obesity causes insulin resistance, which increases the risk of Type 2 Diabetes (T2D) and Coronary Heart Disease (CHD). Although weight loss is a primary goal in clinical management of obesity, long-term weight loss is rarely sustained. Therefore, it is imperative to understand pathways that might ameliorate the impact of obesity on T2D and CHD. We discovered that transgenic expression of Cholesteryl Ester Transfer Protein (Cetp) protects against high-fat diet (HFD)-induced insulin resistance in female mice in the setting of obesity. Cetp traffics triglyceride and cholesteryl ester (CE) between plasma lipoproteins, culminating in delivery of CE to the liver for secretion as bile - termed reverse cholesterol transport (RCT). Cetp inhibitors raise high- density lipoprotein (HDL) but fail to reduce risk for CHD, which may indicate that Cetp has non-HDL functions. Mice lack Cetp, so we used transgenic mice expressing Cetp to define how Cetp impacts insulin resistance. Using the hyperinsulinemic-euglycemic clamp technique, we found that Cetp protects against insulin resistance in females, but not males following 4 weeks of HFD. This protection was despite a similar degree of obesity. The objective of this proposal is to understand how Cetp protects against insulin resistance in diet-induced obese mice. Our discovery represents a novel and beneficial function of Cetp with regard to obesity pathophysiology. Despite high-fat feeding, Cetp expression preserved insulin signaling pathways in liver and muscle and insulin-mediated downregulation of mRNA for gluconeogenic genes Phosphoenopyruvate Carboxykinase (Pck1) and Glucose-6-Phosphatase (G6pc). We found that Cetp increased mRNA of the bile acid signaling molecule Small Heterodimer Partner (Shp) and increased estrogen signaling in liver. We hypothesize that Cetp promotes bile acid and estrogen signaling in liver to protect against diet-induced insulin resistance. Understanding how Cetp protects against diet-induced insulin resistance may yield novel therapeutic targets that lessen obesity's impact on CHD and T2D. In Aim 1, we will determine the mechanism of female-specificity in Cetp-mediated protection from HFD-induced insulin resistance. We expect that liver deletion of estrogen receptor alpha will diminish Cetp-mediated protection from HFD-induced insulin resistance. In Aim 2, we will determine the hepatic bile acid signaling pathways contributing to Cetp-mediated protection from HFD-induced insulin resistance. We expect that liver knockdown of Shp will abrogate Cetp- mediated protection from HFD-induced insulin resistance. Accomplishing the proposed work will 1) identify mechanisms responsible for sex differences that prevent metabolic disease and 2) identify liver bile acid signaling pathways downstream of Cetp that protect against diet-induced insulin resistance. Additionally, the work proposed in this application will support a critical nex step in my training as a physician-scientist whose career aims to make therapeutic connections between obesity and diabetes.