GABA 对非酒精性脂肪性肝炎的防治作用及其机制研究

Non-alcoholic steatohepatitis (NASH) is the leading cause of hepatic failure and the main cause of death in people with chronic liver diseases. Because the pathogenesis of NASH is not fully identified, there is no effective and specific therapy available. Recent studies suggested that liver inflammation due to excessive hepatic lipids deposit can cause liver insulin resistance which contributes to the development of NASH. Therefore，an effective therapy for treating NASH should contain two actions: anti-insulin resistance and inflammation. Currently there is no such reagent available containing the two actions. Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter, this naturally occurring amino acid is produced by the β-cells in a large quantity. GABA exerts peripheral endocrine actions mainly through activation of the GABA receptors expressed mainly in the organs tissues such as pancreatic islets and liver cells. We reported recently that GABA stimulates insulin secretion in the islet β-cells and enhances peripheral insulin responsiveness. We further demonstrated that GABA exerted immunoregulatory effects through repressing cytotoxic T cells while enhancing regulatory T cells. This is exemplified by that GABA improved dyslipidemia in obese mice challenged with high fat diet feeding. We postulate that GABA can improve liver insulin resistance via suppressing inflammation and thus ameliorate NASH.The objective of this project thus is to test our hypothesis and to study the molecular mechanism by which GABA improves insulin resistance and clinical manifestations of NASH. This proposed project is aimed to use cell molecular biology in vitro techniques and in vivo animal model approaches to study the mechanism underlying GABA induced effects in the context of anti-inflammation and improving insulin resistance. Specifically, we will use gene knockout technique to generate inducible liver tissue specific GABA receptor knockout mice to validate whether the anti-inflammation effects of GABA in the liver is mediated by GABA-GABAAR receptor system. Furthermore, we will use in vitro cell and molecular biology approaches to delineate the GABA-GABAAR signal transduction in the liver cells. Our proposed work in identifying novel mechanisms of action will certainly advance the knowledge on understanding the molecular pathogenesis of NASH. These studies are highly likely to lead to the development of novel therapies for NASH and chronic liver diseases.

非酒精性脂肪性肝炎（NASH）是造成肝功能衰竭导致死亡的主要原因。由于NASH发病机理不清，迄今尚无有效的治疗手段。最新研究显示，肝脏炎症是引起肝脏胰岛素抵抗（IR）并导致NASH的主要因素。因此,一个有效的NASH治疗应同时具有对抗IR及炎症的功效。γ-氨基丁酸（GABA）是一种神经递质，通过激活胰腺、肝脏等多种外周组织细胞表面的受体发挥生物效应。我们前期报道了GABA能促进β细胞胰岛素的分泌，并抑制胰岛炎症；还发现GABA可以抑制免疫反应，改善小鼠体内脂代谢紊乱。因此，我们假设GABA可以通过抑制肝脏炎症反应减轻肝脏IR并改善NASH。我们的初步实验结果显示，GABA能够减轻高脂喂养小鼠的肝脏脂肪浸润，抑制肝脏巨噬细胞的激活和炎症因子的生成，改善IR。本课题将用分子生物学手段及基因敲除技术建立可诱导的肝脏组织特异性GABA受体敲除小鼠模型来探究GABA对NASH的防治作用及机制。

非酒精性脂肪性肝炎(NASH)是造成肝功能衰竭导致死亡的主要原因。由于NASH发病机理不清，迄今尚无有效的治疗手段。最新研究显示，肝脏炎症是引起肝脏胰岛素抵抗(IR)并导致NASH的主要因素。因此,一个有效的NASH治疗应同时具有对抗IR及炎症的功效。前期研究表明，γ-氨基丁酸（GABA）在调节胰岛细胞功能和葡萄糖稳态中具有重要作用。然而，GABA对肝脏脂质和葡萄糖代谢的影响还不清楚。本项目研究了GABA改善肝脏脂质代谢及胰岛素抵抗的作用和机制。.结果显示，口服GABA改善高脂饮食（HFD）诱导的肥胖小鼠肝脂肪变性，改善肝脂代谢，提高肝胰岛素敏感性。GABA增加肝脏SIRT1表达，从而导致肝脏脂肪酸β-氧化相关基因表达的增加和脂肪生成基因表达的降低。与这些研究结果相一致，GABA治疗HepG2细胞还增加SIRT1和脂肪酸β-氧化基因的表达，并降低脂肪生成基因的表达，从而减弱脂肪酸诱导的HepG2细胞脂质积累。值得注意的是，在缺乏Sirt1的HepG2细胞中，GABA的这些有益作用明显减弱。此外，GABA在改善HFD诱导的小鼠肝脂肪变性中的作用明显减弱，并具有抑制Sirt1信号的药理作用。我们的数据表明，GABA调节肝脏脂质代谢，并且靶向GABA信号通路可能被用来减轻肝脏脂肪变性。另一方面，我们的数据表明GABA抑制肝脏巨噬细胞活化从而改善肝脏胰岛素敏感性，其机制可能是GABA激活巨噬细胞的GABAA受体，减少巨噬细胞钙离子内流，抑制其活化。因此，我们得出初步结论：GABA能够减轻高脂喂养小鼠的肝脏脂肪浸润，抑制肝脏巨噬细胞的激活和炎症因子的生成，改善肝脏胰岛素抵抗。由于目前临床尚缺乏 NASH 的有 效治疗药物，本课题的研究结果有望为临床 NASH 的防治提供一种安全、有效、 经济的新型候选药物，具有十分重大的社会和经济意义。