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

目标：我们未来5年的研究计划的总体目标是继续我们的努力，了解运动训练如何机械地有助于适当调节肝脏脂肪代谢。在我们提出的研究计划中，我们将特别利用已知的肝脏和肠道中脂肪和胆固醇代谢之间的相互作用来确定体育锻炼的作用。为了做到这一点，动物将接受不同的富含脂质和/或胆固醇的饮食。这些方法将在去卵巢(OVX)大鼠和非去卵巢大鼠身上进行。众所周知，雌激素对肝脏脂肪代谢有重要影响。这个模型的使用对我们理解脂肪代谢与胆固醇代谢是如何被肝脏调节的做出了重要贡献。将调查四个研究途径。1)在我们下一项研究计划的这一部分中，将在运动训练的OVX动物中研究肝脏低密度脂蛋白受体途径，包括关键相关分子(PCSK9、SREBP-2、LRP1)，这些动物喂食高脂肪(HF；42%千卡)和/或高胆固醇(HChol；0.25%)饲料。这种方法的重要性是基于这样一个事实，即70%的低密度脂蛋白受体位于肝脏。这种方法对于了解在目前的操作下胆固醇是如何返回到肝脏从而影响脂肪代谢是至关重要的。这一方法将得到胆汁代谢测量的补充，胆汁代谢是肝脏中胆固醇代谢的重要组成部分，已被证明与肝脏脂肪堆积有关；2)在我们的第二种方法中，将针对肝脏产生极低密度脂蛋白。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极低密度脂蛋白产生的减少。为了证明这一点，我们将直接测量VLDL的产生以及VLDL合成的关键分子标志物(即MTP、DGAT2 CideB)。3)OVX与新生高密度脂蛋白的增加和循环高密度脂蛋白对肝脏的胆固醇流入增加有矛盾的关系。在我们的下一个研究计划中，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，并使用我们的饮食方法来更好地了解肝脏如何在雌激素停用和运动训练的联系中对高密度脂蛋白代谢的适应做出贡献。我们推测，在目前的情况下，高密度脂蛋白代谢适应甚至补偿了由肝脏中胆固醇供应变化引起的低密度脂蛋白代谢的扰动。4)进入肝脏的胆固醇约有40%来自肠道胆汁酸的再吸收。在我们的下一个研究计划中，我们打算采样部分肠道(十二指肠、空肠和回肠)，以通过观察FXR等核受体和控制胆汁酸肠道运输的下游基因(即ASBT和OSTA/？)来补充我们的实验方案。新颖性和预期意义：我们提议的研究计划的新颖性是首先将我们关于肝脏脂肪代谢的知识扩展到肝脏胆固醇和胆汁酸代谢，并与两种现实情况相联系：绝经后女性构成人口的一大部分，运动训练是代表重要社会经济负担的药物疗法的替代方案。

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.