Julien Boris, Grenard Pascale, Teixeira-Clerc Fatima, Van Nhieu Jeanne Tran, Li Liying, Karsak Meliha, Zimmer Andreas, Mallat Ariane, Lotersztajn Sophie
INSERM, U581, Créteil, F-94010 France.
Gastroenterology. 2005 Mar;128(3):742-55. doi: 10.1053/j.gastro.2004.12.050.
BACKGROUND & AIMS: Hepatic myofibroblasts are central for the development of liver fibrosis associated with chronic liver diseases, and blocking their accumulation may prevent fibrogenesis. Cannabinoids are the active components of marijuana and act via 2 G-protein-coupled receptors, CB1 and CB2. Here, we investigated whether liver fibrogenic cells are a target of cannabinoids.
CB2 receptors were characterized in biopsy specimens of normal human liver and active cirrhosis by immunohistochemistry, and in cultures of hepatic stellate cells and hepatic myofibroblasts by reverse-transcription polymerase chain reaction (RT-PCR), immunocytochemistry, and GTPgammaS assays. Functional studies were performed in cultured hepatic myofibroblasts and activated hepatic stellate cells. Carbon tetrachloride-induced liver fibrosis was studied in mice invalidated for CB2 receptors.
In liver biopsy specimens from patients with active cirrhosis of various etiologies, CB2 receptors were expressed in nonparenchymal cells located within and at the edge of fibrous septa in smooth muscle alpha-actin-positive cells. In contrast, CB2 receptors were not detected in normal human liver. CB2 receptors were also detected in cultured hepatic myofibroblasts and in activated hepatic stellate cells. Their activation triggered potent antifibrogenic effects, namely, growth inhibition and apoptosis. Growth inhibition involved cyclooxygenase-2, and apoptosis resulted from oxidative stress. Finally, mice invalidated for CB2 receptors developed enhanced liver fibrosis following chronic carbon tetrachloride treatment as compared with wild-type mice.
These data constitute the first demonstration that CB2 receptors are highly up-regulated in the cirrhotic liver, predominantly in hepatic fibrogenic cells. Moreover, this study also highlights the antifibrogenic role of CB2 receptors during chronic liver injury.
肝肌成纤维细胞在与慢性肝病相关的肝纤维化发展过程中起核心作用，阻断其积聚可能预防纤维化形成。大麻素是大麻的活性成分，通过两种G蛋白偶联受体CB1和CB2发挥作用。在此，我们研究了肝纤维化细胞是否是大麻素的作用靶点。
通过免疫组织化学在正常人肝脏和活动性肝硬化的活检标本中对CB2受体进行表征，并通过逆转录聚合酶链反应（RT-PCR）、免疫细胞化学和GTPγS分析在肝星状细胞和肝肌成纤维细胞培养物中进行表征。在培养的肝肌成纤维细胞和活化的肝星状细胞中进行功能研究。在CB2受体缺失的小鼠中研究四氯化碳诱导的肝纤维化。
在各种病因的活动性肝硬化患者的肝活检标本中，CB2受体在位于纤维间隔内和边缘的非实质细胞中表达，这些细胞为平滑肌α-肌动蛋白阳性细胞。相比之下，在正常人肝脏中未检测到CB2受体。在培养的肝肌成纤维细胞和活化的肝星状细胞中也检测到了CB2受体。它们的激活引发了强大的抗纤维化作用，即生长抑制和凋亡。生长抑制涉及环氧化酶-2，凋亡由氧化应激导致。最后，与野生型小鼠相比，CB2受体缺失的小鼠在慢性四氯化碳处理后肝纤维化加重。
这些数据首次证明CB2受体在肝硬化肝脏中高度上调，主要在肝纤维化细胞中。此外，本研究还突出了CB2受体在慢性肝损伤期间的抗纤维化作用。
