Molecular impact of exercise training on regulation of hepatic fat and hepatic cholesterol metabolism with estrogens withdrawal

目的：我们未来5年研究计划的总体目标是继续努力了解运动训练如何在机制上促进肝脏脂质代谢的适当调节。在我们提出的研究计划中，我们将特别利用肝脏和肠道中脂肪和胆固醇代谢之间已知的相互作用来确定体育锻炼的作用。为了做到这一点，动物将被提交给富含脂质和/或胆固醇的不同饮食。这些方法将在卵巢切除（Ovx）和非Ovx大鼠中进行。众所周知，雌激素对肝脏脂肪代谢有重要影响。该模型的使用对我们理解脂肪代谢与胆固醇代谢是如何由肝脏调节的有重要贡献。将调查四个研究途径。1)在我们的下一个研究项目中，肝脏ldl受体通路包括关键相关分子（Pcsk9, SREBP-2, Lrp1）将在喂食高脂肪（HF; 42% kcal）和/或高胆固醇（HChol; 0.25%）饮食的运动训练Ovx动物中进行研究。这种方法的重要性是基于70%的ldl受体位于肝脏的事实。这种方法对于理解胆固醇如何在目前的操作下返回肝脏，从而影响脂肪代谢是必不可少的。这种方法将通过胆道代谢的测量加以补充，胆道代谢是肝脏胆固醇代谢的重要组成部分，已被证明与肝脏脂肪积累有关；2)在我们的第二种方法中，肝脏产生的VLDL是有针对性的。基本上，我们假设在HF/HChol饮食下，Ovx大鼠肝脏中脂肪和胆固醇的积累是由于VLDL产生的减少。为了证明这一点，我们将直接测量VLDL的产生以及VLDL合成的关键分子标记（即MTP， DGAT2 CideB）。3) Ovx与新生HDL的增加和循环HDL的胆固醇肝内流增加有矛盾的关系。在我们的下一个研究项目中，我们打算以参与高密度脂蛋白代谢的关键肝脏标志物（SR-B1, ABCA1）为目标，并利用我们的饮食方法更好地了解肝脏如何在雌激素戒断和运动训练中促进高密度脂蛋白代谢的适应。我们假设，在目前的情况下，HDL代谢可以适应甚至补偿肝脏中胆固醇可用性变化引起的LDL代谢紊乱。大约40%到达肝脏的胆固醇来自肠道对胆汁酸的再吸收。在我们的下一个研究项目中，我们打算通过观察核受体（如FXR）和下游基因（即ASBT和OSTa/ß）控制胆汁酸肠运输，对肠道部分（十二指肠、空肠和回肠）进行取样，以补充我们的实验方案。新颖性和预期意义：我们提出的研究项目的新颖性首先是将我们对肝脏脂肪代谢的知识扩展到与两种现实生活情况相关的肝脏胆固醇和胆酸代谢：绝经后妇女占人口的很大一部分，运动训练是替代药物治疗的一种重要的社会经济负担。

OBJECTIVES: The overall goal of our research program for the next 5 years is to pursue our effort in understanding how exercise training mechanistically contributes to the proper regulation of liver lipid metabolism. In our proposed research program we will especially use the interactions known to occur between fat and cholesterol metabolism in liver and intestine to determine the action of physical training. To do that, animals will be submitted to different diets rich in lipids and/or cholesterol. These approaches will be carry on in ovariectomized (Ovx) and non-Ovx rats. Estrogens are known to have an important impact on liver fat metabolism. The use of this model is an important contribution to our understanding on how fat metabolism in link with cholesterol metabolism is regulated by the liver. Four research avenues will be investigated. 1) Under this arm of our next research program the hepatic LDL-receptor pathway including key related molecules (Pcsk9, SREBP-2, Lrp1) will be investigated in exercise trained Ovx animals fed with high fat (HF; 42% kcal) and/or high cholesterol (HChol; 0.25%) diets. The importance of this approach is based on the fact that 70% of all LDL-receptors are located in the liver.This approach is essential to understand how cholesterol under the present manipulations returns to liver and thus influence fat metabolism. This approach will be complemented by measurements of biliary metabolism, an important component of cholesterol metabolism in liver that has been shown to be associated with liver fat accumulation; 2) In our second approach, VLDL production by the liver will be targeted. Basically we postulate that fat and cholesterol accumulation in liver of Ovx rats under HF/HChol diets is due to a decrease in VLDL production. To show that, we will directly measure VLDL production along with key molecular markers of VLDL synthesis (i.e. MTP, DGAT2 CideB). 3) Ovx is paradoxically associated with an increase in nascent HDL and an increased hepatic influx of cholesterol from circulating HDL. In our next research program we intend to target key hepatic markers involved in HDL metabolism (SR-B1, ABCA1) and use our dietary approaches to better understand how the liver contributes to adaptations of HDL metabolism in link to estrogens withdrawal and exercise training. We postulate that HDL metabolism under the present situations adapts and even compensates for perturbations in LDL metabolism induced by changes in cholesterol availability in liver. 4) Approximately 40% of cholesterol reaching the liver comes from biliary acid re-absorption from intestine. In our next research program we intend to sample parts of intestine (duodenum, jejunum and ileum) to complement our experimental protocols by looking at nuclear receptors such as FXR and downstream genes (i.e. ASBT and OSTa/ß) that control biliary acids intestinal transport. Novelty and expected significance: the novelty of our proposed research program is first to extend our knowledge of liver fat metabolism to liver cholesterol and biliary acid metabolism in link to two real life situations: postmenopausal women that constitute a large segment of the population, and exercise training an alternative to drugs therapies that represent an important socio-economic burden.