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

非酒精性脂肪性肝病(NAFLD)正在成为一种全球流行的疾病，特别是在美国 退伍军人。NAFLD和非酒精性脂肪性肝炎(NASH)是公认的肝脏表现 代谢综合征。疾病从单纯性脂肪变性进展为NASH、纤维化、肝硬变和 肝细胞癌是由多次打击而不是二次打击促进的，包括肝内破裂 胆汁酸(BA)的动态平衡，先天性免疫反应的异常激活，胰岛素抵抗，血脂异常， 和生物失调。尽管在NAFLD/NASH的发病机制上已经获得了许多新的信息 在过去的十年里，由于对疾病的不完全认识，还没有开发出有效的治疗方法。 这种复杂疾病的发病机制。考虑到全球范围内发病率和流行率的快速增长 在脂肪肝疾病中，开发治疗NAFLD的新的治疗干预措施尤为迫切 这个应用程序的长期目标。BA是调节血脂的重要信号分子， 葡萄糖和能量代谢通过激活核受体和G蛋白偶联受体(GPCRs)，如 分别为法尼醇X受体(FXR)、TGR5和鞘氨醇-1磷酸受体2(S1PR2)。我们已经报道了 结合的初级BA通过GαI蛋白偶联的S1PR2激活AKT和ERK1/2通路。它还拥有 已有报道ERK1/2对鞘氨醇激酶2(SphK2)的磷酸化增加了核鞘氨醇-2。 1磷酸盐(S1P)水平。核S1P是特异组蛋白脱乙酰基酶1和2的内源性抑制物 (HDAC1和2)。据报道，抑制HDAC1可以减少肝脏脂肪堆积。BAS也是 先天免疫的重要调节剂。我们以前的研究报告S1PR2或SphK2的缺失在 肝细胞显著增加脂质蓄积。S1PR2-/-和SphK2-/-小鼠更容易患上 西方饮食(WD)诱导的肝脏脂肪变性和炎症。在肝脏中，S1PR2和SphK2都高度 表达于肝细胞、巨噬细胞和胆管细胞。最近的一项研究报告说，SphK2产生 S1P通过抑制1型干扰素基因刺激物(STING)激活抗炎反应 巨噬细胞中的信号。也有报道称，肝脏刺痛在NASH中表达上调 患者和巨噬细胞中刺痛的激活促进了NASH疾病的进展。我们的预赛 数据进一步表明，饮食诱导的小鼠血清BA的组成和水平发生了显著变化 Nash模型，这与在人类NASH患者中的发现相似。此外，SphK2的表达 在人NASH的肝脏中表达显著下调，但在肝脏中表达上调 患者和Nash小鼠模型。因此，我们假设BA介导的激活 S1PR2/SphK2在维持肝脏脂质平衡和调节先天代谢中起关键作用 代谢应激状态下的免疫反应。为了检验这一假说，本文提出了两个具体目标。目标1： BA介导的S1PR2/SphK2的激活在调节肝脏脂质中的作用及机制 NASH疾病进展过程中的代谢。目的2：明确BA介导的血管紧张素转换酶激活作用 S1PR2/SphK2在调节代谢应激下的先天免疫反应中的作用 潜在的细胞/分子机制。肝细胞特异性基因敲除小鼠S1PR2、SphK2和a 将采用西方饮食加糖水(WDSW)诱导的NASH小鼠模型。 这项研究的完成不仅将确定在启动过程中潜在的新的细胞/分子机制 和NAFLD/NASH的进展，但也将在概念上取得重大进展，将BAS和NASH 鞘磷脂与代谢性疾病的关系将为开发新的治疗方法奠定基础 NAFLD/NASH。因此，这项建议的主题是及时的，具有临床意义的，并直接适合 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.