法尼醇X受体(FXR)通过诱导肝脏抗凝血酶Ⅲ的表达抑制小鼠凝血过程

Farnesoid X receptor (FXR) inhibits coagulation process via inducing hepatic antithrombin Ⅲ expression in mice

法尼醇X受体(farnesoid X receptor, FXR)已被发现可在凝血系统中发挥重要作用,包括抑制血小板功能、促进纤维蛋白原表达等。然而至今,FXR在凝血系统中的调节机制尚未完全阐明。本研究旨在探讨FXR对抗凝血酶Ⅲ (antithrombin Ⅲ,AT Ⅲ)的调节作用。用FXR特异性激动剂GW4064 (每天30 mg/kg)处理野生型(WT)和FXR基因敲除(FXR KO) C57BL/6小鼠1和3天,结果显示,在WT小鼠上,FXR激动可显著延长凝血酶原时间和活化部分凝血活酶时间,降低活化凝血因子X (activated factor X, FXa)活性,降低活化凝血因子Ⅱ (activated factor Ⅱ, FⅡa)和凝血酶-抗凝血酶复合物(thrombin-antithrombin complex,TAT)浓度,升高血浆AT Ⅲ浓度,使血液处于低凝状态;当FXR敲除时,以上指标全部逆转,血液处于高凝状态。激动FXR后,WT小鼠肝脏AT Ⅲ表达增加;而FXR KO小鼠肝脏中AT Ⅲ表达较WT小鼠明显降低。体外研究结果显示,GW4064和FXR过表达腺病毒均可显著上调小鼠原代肝细胞中AT Ⅲ的表达,相反,siRNA敲减FXR可明显抑制AT Ⅲ表达。AT Ⅲ启动子区含有FXR结合位点,GW4064可显著上调Luc-AT Ⅲ荧光素酶活性并增加FXR与AT Ⅲ启动子区的结合。以上结果提示,FXR可通过直接转录调控AT Ⅲ的表达而抑制凝血过程。本研究揭示了FXR在凝血平衡中的新作用,提示FXR可能成为血液高凝状态相关疾病的潜在治疗靶点。

Farnesoid X receptor(FXR) has been identified as an inhibitor of platelet function and an inducer of fibrinogen protein complex. However, the regulatory mechanism of FXR in hemostatic system remains incompletely understood. In this study, we aimed to investigate the functions of FXR in regulating antithrombin Ⅲ(AT Ⅲ). C57 BL/6 mice and FXR knockout(FXR KO) mice were treated with or without GW4064(30 mg/kg per day). FXR activation significantly prolonged prothrombin time(PT) and activated partial thromboplastin time(APTT), lowered activity of activated factor X(FXa) and concentrations of thrombin-antithrombin complex(TAT) and activated factor Ⅱ(FⅡa), and increased level of AT Ⅲ, whereas all of these effects were markedly reversed in FXR KO mice. In vivo, hepatic AT Ⅲ mRNA and protein expression levels were up-regulated in wild-type mice after FXR activation,but down-regulated in FXR KO mice. In vitro study showed that FXR activation induced, while FXR knockdown inhibited, AT Ⅲ expression in mouse primary hepatocytes. The luciferase assay and ChIP assay revealed that FXR can bind to the promoter region of AT Ⅲ gene where FXR activation increased AT Ⅲ transcription. These results suggest FXR activation inhibits coagulation process via inducing hepatic AT Ⅲ expression in mice. The present study reveals a new role of FXR in hemostatic homeostasis and indicates that FXR might act as a potential therapeutic target for diseases related to hypercoagulation.