Bile Acids and Sphingosine 1-Phosphate in Non-Alcoholic Steatohepatitis (NASH)

非酒精性脂肪性肝病（NAFLD）正在成为一种全球性的流行病，尤其是在美国， 老兵NAFLD和非酒精性脂肪性肝炎（NASH）被认为是肝硬化的肝脏表现。 代谢综合征疾病从单纯性脂肪变性进展为NASH、纤维化、肝硬化和肝硬化。 肝细胞癌（HCC）是通过多次打击而不是两次打击来促进的，包括肝内 胆汁酸（BA）稳态、先天免疫应答的异常激活、胰岛素抵抗、血脂异常， 和生态失调尽管在NAFLD/NASH的发病机制方面已经获得了许多新的信息， 在过去的十年里，由于对肿瘤的不完全理解，没有开发出有效的治疗方法。 这一复杂疾病的发病机制。考虑到世界范围内的发病率和流行率迅速增加， 由于脂肪肝疾病的严重性，开发新的NAFLD治疗干预措施尤为迫切， 这个应用程序的长期目标。BA是参与调节脂质的重要信号分子， 通过激活核受体和G蛋白偶联受体（GPCR），如 如法尼醇X受体（FXR）、TGR 5和鞘氨醇-1磷酸受体2（S1 PR 2）。我们已经报道了 结合的初级BA通过Gαi蛋白偶联的S1 PR 2激活AKT和ERK 1/2途径。它也有 据报道，神经鞘氨醇激酶2（SphK 2）被ERK 1/2磷酸化， 1磷酸盐（S1 P）水平。核S1 P是特异性组蛋白去乙酰化酶1和2的有效内源性抑制剂 （HDAC 1和2）。据报道，HDAC 1的抑制可减少肝脏脂质蓄积。BA也 先天免疫的重要调节剂。我们以前的研究报道，S1 PR 2或SphK 2的缺失在人乳腺癌的发生中起重要作用。 肝细胞显著增加脂质积聚。S1 PR 2-/-和SphK 2-/-小鼠都更倾向于 西方饮食（WD）诱导的肝脏脂肪变性和炎症。在肝脏中，S1 PR 2和SphK 2都高度表达。 在肝细胞、巨噬细胞和胆管细胞中表达。最近的一项研究报告说，SphK 2产生的 S1 P通过抑制1型干扰素基因（STING）的刺激因子激活抗炎反应 巨噬细胞中的信号传导。还报道了NASH中肝STING表达上调， 患者和巨噬细胞中STING的活化有助于NASH疾病进展。我们的初步 数据进一步表明，在饮食诱导的小鼠中， NASH模型，这与人类NASH患者中的发现相似。此外，SphK 2的表达 显著下调，但STING的表达在人NASH的肝脏中上调 患者和NASH小鼠模型。因此，我们假设BA介导的激活 S1 PR 2/SphK 2在维持肝脏脂质稳态和调节先天性高脂血症中起关键作用。 代谢应激下的免疫反应。提出了两个具体目标来检验这一假设。目标1： 探讨BA介导的S1 PR 2/SphK 2活化在调节肝脏脂质中的作用及其机制 NASH疾病进展期间的代谢。目的2：确定BA介导的激活 S1 PR 2/SphK 2在调节代谢应激下的先天免疫应答中的作用，并进一步鉴定 潜在的细胞/分子机制。S1 PR 2和SphK 2肝细胞特异性基因敲除小鼠和a 将使用充分表征的西方饮食加糖水（WDSW）诱导的NASH小鼠模型。 这项研究的完成不仅将确定潜在的新的细胞/分子机制，在启动 和NAFLD/NASH的进展，但也将在概念上取得重大进展， 这将为开发新的治疗方法奠定基础， 非酒精性脂肪肝/NASH。因此，该提案的主题是及时的，临床意义重大的，直接适合于 美国退伍军人管理局的使命

Non-alcoholic fatty liver disease (NAFLD) is becoming a globally prevalent disease, especially among US veterans. NAFLD and non-alcoholic steatohepatitis (NASH) are recognized as hepatic manifestations of metabolic syndrome. The disease progression from simple steatosis to NASH, fibrosis, cirrhosis, and hepatocellular carcinoma (HCC) is promoted by multiple-hit instead of two-hit, including disruption of intrahepatic bile acid (BA) homeostasis, aberrant activation of the innate immune response, insulin resistance, dyslipidemia, and dysbiosis. Although much new information on the pathogenesis of NAFLD/NASH has been gained during the last decade, no effective therapy has been developed due to the incomplete understanding of the pathogenesis of this complex disease. Considering the rapid increase in the incidence and prevalence worldwide of fatty liver diseases, the development of new therapeutic interventions for NAFLD is especially urgent and is the long-term objective of this application. BAs are important signaling molecules involved in regulating lipid, glucose, and energy metabolism by activating nuclear receptors and G protein-coupled receptors (GPCRs), such as farnesoid X receptor (FXR), TGR5, and sphingosine-1 phosphate receptor 2 (S1PR2). We have reported that conjugated primary BAs activate the AKT and ERK1/2 pathways via Gαi protein-coupled S1PR2. It also has been reported that phosphorylation of sphingosine kinase 2 (SphK2) by ERK1/2 increases nuclear sphingosine- 1 phosphate (S1P) levels. Nuclear S1P is a potent endogenous inhibitor of specific histone deacetylase 1 &2 (HDAC1 and 2). Inhibition of HDAC1 has been reported to reduce hepatic lipid accumulation. BAs are also important modulators of innate immunity. Our previous studies reported that deletion of S1PR2 or SphK2 in hepatocytes significantly increased lipid accumulation. Both S1PR2-/- and SphK2-/- mice are more prone to western diet (WD)-induced hepatic steatosis and inflammation. In the liver, both S1PR2 and SphK2 are highly expressed in hepatocytes, macrophages, and cholangiocytes. A recent study reported that SphK2-generated S1P activated an anti-inflammatory response by suppressing the stimulator of type 1 interferon gene (STING) signaling in macrophages. It has also been reported that hepatic STING expression is upregulated in NASH patients and activation of STING in macrophages contributes to NASH disease progression. Our preliminary data further indicate that serum BA composition and levels were significantly changed in a diet-induced mouse NASH model, which was similar to the finding in human NASH patients. Furthermore, the expression of SphK2 was significantly down-regulated, but the expression of STING was upregulated in the livers of human NASH patients and the NASH mouse model. Therefore we HYPOTHESIZE that BA-mediated activation of S1PR2/SphK2 is pivotal in the maintenance of hepatic lipid homeostasis and modulation of innate immune response under metabolic stress. Two specific aims are proposed to test this hypothesis. Aim 1: To investigate the role and mechanisms of BA-mediated activation of S1PR2/SphK2 in regulating hepatic lipid metabolism during NASH disease progression. Aim 2: To define the role of BA-mediated activation of S1PR2/SphK2 in modulating the innate immune response under metabolic stress and further identify the underlying cellular/molecular mechanisms. The hepatic cell-specific knockout mice of S1PR2 and SphK2 and a well-characterized western diet plus sugar water (WDSW)-induced NASH mouse model will be used. Completion of this study will not only identify the potential novel cellular/molecular mechanisms in the initiation and progression of NAFLD/NASH but will also make a significant conceptual advance linking BAs and sphingolipids with metabolic diseases which will create a fundamental base for developing novel therapies for NAFLD/NASH. Therefore, the subject matter of this proposal is timely, clinically significant, and directly fits into the mission of the US Veteran's Administration.