肝脏GABA能系统调控肝枯否细胞功能在慢性HBV感染小鼠肝内HBV特异性CD8+ T细胞耗竭中的作用及其机制

Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the central nervous system and it is produced from gultamic acid by decarboxylation through the catalytic activity of glutamic acid decarboxylation (GAD). GABA generates biological signaling throuth activation of its ionotropic type A or metabotropic type B receptors (GABAARs or GABABRs). Our studies show that an auto- and/or para-crine GAD-GABA-GABAAR signaling system (GABAergic system) occurs in rodent liver, protecting the liver against toxic injuries. Further study showed that chronic hepatitis B virus (HBV) infection interfers with hepatic GABAergic system, and treating the HBV-infected mice with GABA decreased the percentage of intrahepatic IFN-γ+CD8+ T cells and increased the level of serum HBsAg. More interestingly, GABA treatment increased the release of IL-10 in primary cultured Kupffer cells from chronic HBV-infected mice. We thus hypothesized that hepatic GABA may serve as an auto- and/or para-crine cytokine, that through binding to GABAARs on Kupffer cells, may regulate the function of Kupffer cells by increasing the release of IL-10, which mediates the exhaustion of intrahepatic CD8+ T cells in chronic HBV-infected mice. This study may be useful for the design of immunotherapeutic strategies to complement and optimize available antiviral therapies.

γ-氨基丁酸（γ-aminobutyric acid, GABA）是一种主要的抑制性神经递质。由谷氨酸脱羧酶（glutamic acid decarboxylase，GAD）合成后通过A型（GABAAR）或B型受体（GABABR）发挥作用。我们发现肝内存在一个自分泌/旁分泌的GAD-GABA-GABAAR系统（即GABAergic system）且发挥肝保护作用。最近我们发现乙型肝炎病毒（hepatitis B virus，HBV）感染可干扰该系统表达，腹腔给予GABA可减少HBV慢性感染小鼠肝内HBV特异性IFN-γ+CD8+ T细胞的比例，增加HBsAg水平，并使枯否细胞释放IL-10增多。由此我们推测GABA在肝脏免疫微环境中可能做为一个自分泌/旁分泌细胞因子通过调控枯否细胞释放IL-10介导肝内HBV特异性CD8+T细胞耗竭。本研究将为完善和优化HBV免疫治疗的策略提供新的思路。

巨噬细胞不同表型在疾病中具有重要意义。HBV感染可使库普弗细胞既能向M1极化也能向M2极化。本课题证明肝巨噬细胞表达功能性的GABA系统，激活该系统可通过促使钙离子内流使巨噬细胞M2极化。利用尾静脉高压注射pAAV/HBV1.2建立HBV感染模型，腹膜腔注射GABA或GABAAR选择性激动剂muscimol可促进HBV小鼠体内HBV复制。利用氯磷酸盐脂质体清除小鼠体内库普弗细胞后，GABA促进HBV复制的作用被抑制。过继转输实验进一步证明库普弗细胞上的GABA信号系统在促进HBV复制中的关键作用。进一步利用HepG2.2.15 cells, HBV1.3-transfected Huh7 cells, 和 HBV-infected Huh7-NTCP cells细胞模型发现，GABA促进HBV复制的作用与肝实质细胞中的GABA系统并不相关。本课题研究结果提示库普弗细胞中的GABA系统可通过促进其M2极化促进HBV复制。抑制库普弗细胞上的GABA系统有望为临床HBV的预防和治疗提供新的思路。