Omega-3 fatty acids and the control of fatty liver disease

肥胖和2型糖尿病（T2DM）患者是非酒精性脂肪性肝病（NAFLD）的高发人群。NAFLD是一种连续的慢性肝脏疾病，从良性脂肪变性到非酒精性脂肪性肝炎（NASH）、肝硬化和原发性肝细胞癌（HCC）。由于NAFLD与肥胖流行密切相关，NAFLD正迅速成为西方社会主要的公共卫生问题。令人惊讶的是，没有FDA批准的NAFLD疗法；目前的治疗方法是治疗与NAFLD相关的合并症，即肥胖、高血糖、血脂异常和高血压。我们的重点是预防NAFLD并阻止其发展为NASH。我们建立了西方饮食（WD）诱导的NASH的临床前Ldlr-/-小鼠模型。高脂高糖饮食，比如WD，被认为是促进肥胖流行的原因之一。我们的临床前模型概括了代谢综合征(MetS)-NASH患者的特征，即肥胖、高血糖、血脂异常、肝骨化症、全身和肝脏炎症及肝纤维化。该应用的关键前提是肝脏C20-22 ω3 PUFA含量与NASH的发病和进展之间存在因果关系。这一假设基于我们实验室的以下研究：1)WD诱导的NASH与C20-22 ω3 PUFA和生物活性ω3 PUFA衍生的氧化脂质（氧脂素）的肝脏消耗有关；与最近NASH患者报告相一致的发现；2)补充二十二碳六烯酸（DHA, 22:6,ω3）以补充肝脏C20-22 ω3 PUFA和氧脂素可预防NASH并阻止其进展；3)新的证据表明，DHA可减弱wd介导的NASH关键通路[SREBP1、NFκB、TGFβ-Smad3、Notch、Hedgehog （Hh）和骨桥蛋白（Opn）]的诱导；新的证据表明，ω6- pufa衍生的，而不是ω3- pufa衍生的，氧脂素增强了tgf - β对人肝星状细胞中关键纤维化标志物（smActin）的诱导作用。因此，DHA及其氧脂衍生物调节了多个nash相关途径。我们有能力利用临床前Ldlr -/-小鼠模型揭示dha介导的NASH抑制的代谢和分子基础。我们的目标是为在NASH治疗中使用DHA提供机制基础。我们假设饮食诱导的NASH和纤维化的DHA衰减涉及直接和间接机制，控制与NASH相关的主要调节通路（TGFβ、Notch、HH和Opn）。AIM 1将使用体内时间过程方法来验证DHA会诱导肝膜脂组成和pufa衍生的氧化脂质的变化的假设，这些变化先于与NASH和纤维化相关的信号通路的表达/活性变化。AIM 2将验证PUFA和氧化脂素直接作用于分离的肝细胞（肝细胞、巨噬细胞和星状细胞）以调节与NASH病理相关的信号通路（TGFβ、Notch、Hh和Opn）的假设。

Obese and type 2 diabetic (T2DM) patients have a high incidence of nonalcoholic fatty liver disease (NAFLD). NAFLD is a continuum of chronic liver diseases ranging from benign steatosis to nonalcoholic steatohepatitis (NASH), cirrhosis and primary hepatocellular cancer (HCC). Because of its strong association with the obesity epidemic, NAFLD is rapidly becoming a major public health concern in western societies. Surprisingly, there are no FDA approved NAFLD therapies; and current therapies treat the co-morbidities associated with NAFLD, viz., obesity, hyperglycemia, dyslipidemia, & hypertension. Our focus is on prevention of NAFLD and stopping its progression to NASH. We developed a preclinical Ldlr-/- mouse model of western diet (WD)-induced NASH. High fat-high sucrose diets, like the WD, have been implicated in promoting the obesity epidemic. Our preclinical model recapitulates the features seen in the metabolic syndrome (MetS)-NASH patient, i.e., obesity, hyperglycemia, dyslipidemia, hepatosteatosis, systemic and hepatic inflammation & hepatic fibrosis. The key premise of this application is that there is a causal link between hepatic C20-22 ω3 PUFA content and the onset and progression of NASH. This premise is based on the following research from our lab: 1) WD induced NASH is associated with hepatic depletion of C20-22 ω3 PUFA and bioactive ω3 PUFA-derived oxidized lipids (oxylipins); findings that parallel recent reports on NASH patients; 2) repletion of hepatic C20-22 ω3 PUFA and oxylipins with docosahexaenoic acid (DHA, 22:6,ω3) supplementation prevents NASH and stops its progression; 3) New evidence shows that DHA attenuates WD-mediated induction of key NASH pathways [SREBP1, NFκB, TGFβ-Smad3, Notch, Hedgehog (Hh) and osteopontin (Opn)]; and 4) more New evidence shows that ω6-PUFA-derived, but not ω3-PUFA-derived, oxylipins augment TGFβ induction of a key fibrosis marker (smActin) in human hepatic stellate cells. Thus, DHA and its oxylipin derivatives regulate multiple NASH-linked pathways. We are well-positioned to uncover the metabolic and molecular basis for DHA-mediated suppression of NASH using our preclinical Ldlr -/- mouse model. Our goal is to provide the mechanistic foundation for the use of DHA in NASH therapy. We hypothesize that DHA attenuation of diet-induced NASH and fibrosis involves both direct and indirect mechanisms controlling major regulatory pathways (TGFβ, Notch, HH & Opn) linked to NASH. AIM 1 will use an in vivo time course approach to test the hypothesis that DHA will induce changes in hepatic membrane lipid composition and PUFA-derived oxylipins that precede changes in the expression/activity of signaling pathways linked to NASH & fibrosis. AIM 2 will test the hypothesis that PUFA & oxylipins act directly on isolated liver cells (hepatocytes, macrophage & stellate cells) to regulate signaling pathways (TGFβ, Notch, Hh & Opn) linked to NASH pathology.