Regulation of bile canalicular barrier by a novel tight junction protein claudin-2 during cholestasis

肝脏紧密连接(TJ)在阻止胆小管中的胆汁进入血液循环的屏障中起着至关重要的作用，我们称之为d-胆汁屏障。肝内胆汁淤积或胆汁流动障碍是遗传性和获得性肝病的重要表现。在啮齿动物肝脏中，检测到完整的TJ蛋白claudin-1、-2、-3、-5和-14。Claudin-2表现为从门静脉周围到中心周围肝细胞的小叶梯度递增，而Claudin-1和-3在整个肝小叶中表达。虽然Claudin-2的表达可诱导上皮细胞紧密连接的阳离子选择性通道，但Claudin-2在肝细胞中的生理功能和调控仍不清楚。OSM是一种参与肝细胞分化的多功能细胞因子，可诱导胎肝细胞形成基于E-钙粘附素的黏附连接。在这项研究中，我们检测了OSM是否可以诱导Roden…中claudin-2的表达和功能T肝细胞、永生化小鼠和原代培养的增殖性大鼠肝细胞较多。在永生化小鼠和原代培养的增殖期大鼠肝细胞中，OSM处理显著增加Claudin-2的mRNA和蛋白，并形成发达的TJ链网络。Claudin-2的增加增强了细胞旁屏障功能，这种增强作用依赖于分子大小。OSM诱导的啮齿动物肝细胞Claudin-2表达增加是通过包括PKC在内的不同信号通路来调节的。此外，我们利用具有肝细胞极性的WIF-B9肝细胞检测了Claudin-2对胆小管形成的影响。苯巴比妥可诱导和扩张胆小管，并增加Claudin-2的表达。在Claudin-2的siRNA处理中，Claudin-2的下调抑制了胆小管的形成。这些结果提示，肝细胞中Claudin-2的表达可能在控制细胞旁通透性屏障的大小以保持胆小管内的胆汁和胆小管的形成方面起着特殊的作用。较少

Hepatic tight junctions (TJs) play crucial roles in the barrier to keep bile in bile canaliculi away from the blood circulation, which we call the bloc d-billiary-barrier. Intrahepatic cholestasis or impairment of bile flow is an important manifestation of inherited and acquired liver disease. In rodent livers, integral TJ proteins claudin-1,-2,-3,-5 and-14 are detected. CLaudin-2 shows a lobular gradient increasing from periportal to pericentral hepatocytes, whereas claudin-1 and-3 are expressed in the whole liver lobule. Although claudin-2 expression induces cation-selective channels in tight junctions of epithelial cells, the physiological functions and regulation of claudin-2 in hepatocytes remain unclear. Oncostatin M (OSM) is a multifunctional cytokine implicated in the differentiation c f hepatocytes that induces formation of E-cadherin-based adherens junctions in fetal hepatocytes. In this study, we examined whether OSM could induce expression and function of claudin-2 in roden … More t hepatocytes, immortalized mouse and primary cultured proliferative rat hepatocytes. In the immortalized mouse and primary cultured proliferative rat hepatocytes, treatment with OSM markedly increased mRNA and protein of claudin-2 together with formation of developed networks of TJ strands. The increase of claudin-2 enhanced the paracellular barrier function which depended on molecular size. The increase of claudin-2 expression induced by OSM in rodent hepatocytes was regulated through distinct signaling pathways including PKC. Furthermore, we examined effects of claudin-2 on bile canaliculi formation using WIF-B9 hepatic cells which has hepatic cell polarity. In treatment with phenobarbital, bile canaliculi formation was induced and dilated together with an increase of claudin-2 expression. In treatment with siRNA of claudin-2, the bile canaliculi formation was inhibited by downregulation of claudin-2. These results suggest that expression of claudin-2 in hepatocytes may play a specific role as controlling the size of paracellular permeability in the barrier to keep bile in bile canaliculi and bile canaliculi formation. Less