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

非酒精性脂肪肝（NAFLD）正在成为全球流行的疾病，尤其是在美国 退伍军人。 NAFLD 和非酒精性脂肪性肝炎 (NASH) 被认为是以下疾病的肝脏表现： 代谢综合征。疾病进展从单纯性脂肪变性到 NASH、纤维化、肝硬化和 肝细胞癌 (HCC) 是通过多次打击而不是两次打击来促进的，包括肝内组织的破坏 胆汁酸 (BA) 稳态、先天免疫反应异常激活、胰岛素抵抗、血脂异常、 和生态失调。尽管在 NAFLD/NASH 发病机制方面获得了许多新的信息。 近十年来，由于对这一疾病的认识不完全，尚未开发出有效的治疗方法。 这种复杂疾病的发病机制。考虑到全球发病率和患病率的迅速增加 随着脂肪肝疾病的发展，开发针对 NAFLD 的新治疗干预措施尤为紧迫 此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) 来调节葡萄糖和能量代谢，例如 如法尼醇 X 受体 (FXR)、TGR5 和 1 磷酸鞘氨醇受体 2 (S1PR2)。我们曾报道过 缀合的初级 BA 通过 Gαi 蛋白偶联的 S1PR2 激活 AKT 和 ERK1/2 途径。它还具有 据报道，ERK1/2 磷酸化鞘氨醇激酶 2 (SphK2) 会增加核鞘氨醇 - 1 磷酸盐 (S1P) 水平。核 S1P 是特定组蛋白脱乙酰酶 1 和 2 的有效内源性抑制剂 （HDAC1 和 2）。据报道，抑制 HDAC1 可减少肝脏脂质积累。 BA 也 先天免疫的重要调节剂。我们之前的研究报道，S1PR2 或 SphK2 的缺失 肝细胞脂质积累显着增加。 S1PR2-/- 和 SphK2-/- 小鼠均更容易发生 西方饮食（WD）引起的肝脏脂肪变性和炎症。在肝脏中，S1PR2 和 SphK2 都高度 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称，SphK2 生成 S1P 通过抑制 1 型干扰素基因 (STING) 刺激物激活抗炎反应 巨噬细胞中的信号传导。另据报道，NASH 中肝脏 STING 表达上调 巨噬细胞中 STING 的激活有助于 NASH 疾病的进展。我们的初步 数据进一步表明，饮食诱导的小鼠血清 BA 组成和水平发生显着变化 NASH 模型，与人类 NASH 患者的发现相似。此外，SphK2 的表达 人 NASH 肝脏中 STING 表达显着下调，但表达上调 患者和 NASH 小鼠模型。因此我们假设 BA 介导的激活 S1PR2/SphK2 在维持肝脂质稳态和调节先天性 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S1PR2/SphK2激活在调节肝脂中的作用及机制 NASH 疾病进展期间的代谢。目标 2：确定 BA 介导的激活的作用 S1PR2/SphK2 在代谢应激下调节先天免疫反应并进一步鉴定 潜在的细胞/分子机制。 S1PR2和SphK2肝细胞特异性敲除小鼠 将使用特征良好的西方饮食加糖水（WDSW）诱导的 NASH 小鼠模型。 这项研究的完成不仅将确定启动过程中潜在的新型细胞/分子机制 和 NAFLD/NASH 的进展，但也将在连接 BA 和 鞘脂与代谢疾病的关系，这将为开发新疗法奠定基础 NAFLD/NASH。因此，本提案的主题是及时的、具有临床意义的，并且直接适合 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.