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机械地促进肝脏脂质代谢的适当调节。在我们提出的研究计划中，我们将特别使用已知发生在肝脏和肠道中的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。已知雌激素对肝脏脂肪代谢有重要影响。该模型的使用对于我们理解脂肪代谢与胆固醇代谢如何由肝脏调节是一个重要贡献。将研究四种研究途径。1)在我们下一个研究计划的这一分支下，将在喂食高脂肪（HF; 42% kcal）和/或高胆固醇（HChol; 0.25%）饲料的运动训练Ovx动物中研究肝脏LDL受体途径，包括关键相关分子（Pcsk 9、SREBP-2、Lrp 1）。这种方法的重要性是基于70%的LDL受体位于肝脏这一事实。这种方法对于了解胆固醇在目前的操作下如何返回肝脏并从而影响脂肪代谢至关重要。这种方法将通过测量胆汁代谢来补充，胆汁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相关; 2）在我们的第二种方法中，肝脏产生的VLDL将被靶向。基本上，我们假设HF/HChol饮食下Ovx大鼠肝脏中的脂肪和胆固醇积累是由于VLDL产生减少。为了证明这一点，我们将直接测量VLDL产生沿着VLDL合成的关键分子标志物（即MTP、DGAT 2 CideB）。3)卵巢切除与新生HDL增加和循环HDL胆固醇肝内流增加矛盾相关。在我们的下一个研究项目中，我们打算针对HDL代谢中涉及的关键肝脏标志物（SR-B1，ABCA 1），并使用我们的饮食方法更好地了解肝脏如何促进HDL代谢与雌激素戒断和运动训练的适应。我们假设，在目前的情况下，HDL代谢适应，甚至补偿LDL代谢的扰动引起的胆固醇在肝脏中的可用性的变化。4)大约40%到达肝脏的胆固醇来自肠的胆汁酸重吸收。在我们的下一个研究计划中，我们打算对部分肠道（十二指肠，空肠和回肠）进行采样，以通过观察控制胆汁酸肠道转运的核受体如FXR和下游基因（即ASBT和OSTa/ESTs）来补充我们的实验方案。新奇和预期意义：我们所提出的研究计划的新奇首先是将我们对肝脏脂肪代谢的认识扩展到与两种真实的生活情况相关的肝脏胆固醇和胆汁酸代谢：构成人口中很大一部分的绝经后妇女，以及代表重要社会经济负担的药物疗法的替代方案运动训练。

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.