Sexual dimorphism, hepatic mitochondrial adaptations, and hepatic steatosis

项目摘要/摘要 肝脏脂肪变性(脂肪肝)是2型糖尿病、心血管疾病和进一步肝脏损伤的危险因素， 退伍军人的所有主要健康问题。目前有160万名女性退伍军人，预计这一数字将 稳步增长，使妇女健康问题成为未来的一个主要关切。在更年期之前，女性 防止脂肪变性，但在卵巢功能丧失和积聚后，风险会急剧增加 有证据表明，雌激素信号的差异是一个主要的调节因素。缺乏身体活动和低水平 健身还会增加患肝脏脂肪变性和相关病理疾病的风险。相比之下，增加了 体育活动和锻炼可以预防和治疗脂肪变性，甚至对肥胖患者也是如此。肝脏异常 线粒体功能对脂肪变性的病理有很大的贡献，很可能是 体力活动和锻炼对缓解这种情况的影响，但机制在很大程度上仍不清楚。 雌激素可能是预防雌性啮齿动物肝脏脂肪变性的原因，但雌激素的直接作用 雌激素对肝脏线粒体功能的信号转导作用尚未引起足够的重视。我们最近的发现表明 雌性小鼠表现出线粒体呼吸增加，活性氧(H_2O_2)释放减少，以及 与男性相比，久坐状态下防止脂肪变性的保护作用。雌性肝脏线粒体 呼吸能力对饮食和运动诱导的代谢压力也更敏感，但这些 线粒体翻转的遗传消融小鼠的适应性特征部分减弱(生物发生和 有丝分裂)。这些数据形成了我们的假设，即增强女性的线粒体功能对她们的 对脂肪变性的固有保护和对代谢应激的适应性反应。我们将检验这一假设 通过雌激素受体α(ERα)传递的雌激素信号对肝脏线粒体的升高是必需的 通过驱动增强的线粒体生物发生和有丝分裂来增强女性的功能和适应性。一秒钟 这项提案的目的是测试胆汁酸(BA)代谢的差异是否提供保护 女性的脂肪变性。雌性啮齿动物表现出长期较高的血清和粪便BA水平，并伴随着较高的 控制胆固醇/BA合成的肝脏基因的表达。增加BA合成和排泄物的速率 BA阻滞剂排泄和慢性CYP7a1过度表达也预防和治疗肝脏 脂肪变性，表明这种影响与我们在女性肝脏中看到的类似。我们的初步数据表明 雌激素和运动只有在女性中才能协同增加BA的合成和排泄量。我们将测试 假设过量的乙酰辅酶A运输远离新的脂肪生成(新脂肪酸的合成) 而在餐后条件下促进BA合成和粪便丢失是另一种机制， 保护女性免受肝脏脂肪变性。总体而言，该提案将检查肝脏ERα信号是否 肝脏线粒体功能和BA代谢的性别差异以及这些因素 对雌性小鼠肝脏脂肪变性的独立影响风险。我们将利用肝脏来测试这些问题- 特异性ERα基因敲除小鼠(LERKO)、运动、外科手术(卵巢切除)、药理(雌二醇)和 分子(shRNA CYP7a1的AAV)方法与新的体内代谢示踪技术相结合， 以及线粒体质量控制和功能的直接措施。这项提议的总体目标是 确定雌激素、运动和线粒体功能之间的机械性相互作用，从而增加患高血压的风险 肝脏脂肪变性，目标是确定女性退伍军人的治疗目标。

Project Summary/Abstract Hepatic steatosis (fatty liver) is a risk factor for type 2 diabetes, cardiovascular disease, and further liver injury, all major health issues for Veterans. Currently there are 1.6 million women Veterans, a number predicted to grow steadily making women's health issues a major concern going forward. Prior to menopause, women are protected against steatosis, but risk dramatically increases after loss of ovarian function and accumulating evidence shows that differences in estrogen signaling are a primary mediator. Physical inactivity and low fitness also drive increased risk for hepatic steatosis and associated pathologies. In contrast, increased physical activity and exercise protects and treats steatosis, even in obese patients. Abnormalities in hepatic mitochondrial function strongly contribute to the pathology of steatosis and are likely a primary target for the effects of physical activity and exercise to mitigate the condition, but mechanisms remain largely unknown. Estrogen is likely the cause of protection against hepatic steatosis in female rodents but the direct effects of estrogen signaling on hepatic mitochondria function have received little attention. Our recent findings show that female mice display increased mitochondrial respiration, lower reactive oxygen species (H2O2) emission and protection against steatosis in a sedentary condition compared to males. Female hepatic mitochondria respiratory capacity was also more responsive to diet- and exercise-induced metabolic stress, but these adaptive traits were partially diminished in mice with genetic ablation of mitochondrial turnover (biogenesis and mitophagy). These data form our hypothesis that enhanced mitochondrial function in females is critical for their inherent protection against steatosis and adaptive responses to metabolic stress. We will test the hypothesis that estrogen signaling through estrogen receptor α (ERα) is obligatory for elevated hepatic mitochondrial function and adaptability in females by driving enhanced mitochondrial biogenesis and mitophagy. A second objective of this proposal will test if differences in bile acid (BA) metabolism provide protection against steatosis in females. Female rodents display chronically higher serum and fecal BA levels, paired with higher expression of hepatic genes controlling cholesterol/BA synthesis. Increasing rates of BA synthesis and fecal excretion via BA sequestrant drugs and chronic CYP7a1 overexpression also prevent and treat hepatic steatosis, suggesting a similar affect to what we see in female livers. Our preliminary data suggest that estrogen and exercise synergize to increase BA synthesis and fecal excretion only in females. We will test the hypothesis that trafficking of excess acetyl CoA away from de novo lipogenesis (synthesis of new fatty acids) and towards BA synthesis and fecal loss during postprandial conditions is an additional mechanism that protects females against hepatic steatosis. Overall, this proposal will examine if hepatic ERα signaling is obligatory for sex differences in hepatic mitochondrial function and BA metabolism and if these factors independently impact risk for hepatic steatosis in female mice. We will test these questions by utilizing liver- specific ERα knockout mice (LERKO), exercise, surgical (ovariectomy), pharmacological (estradiol), and molecular (AAV for shRNA CYP7a1) approaches combined with novel in vivo metabolic tracing techniques, and direct measures of mitochondrial quality control and function. The overall objective of this proposal is to determine mechanistic interactions between estrogen, exercise, and mitochondrial function that drive risk for hepatic steatosis with a goal of determining therapeutic targets for female Veterans.