Cell-cell adhesion-mediated signaling determines epithelial polarization in the liver

摘要 肝脏是我们最大的新陈代谢器官。它产生蛋白质、脂质、凝血因子和糖原，而 分发胆汁和解毒外源生物。为了运输这些不同的物质，一种复杂的 肝小静脉、毛细血管和间质管道的网络已经演变。该网络的一个基本功能 是形成管腔的上皮细胞，产生两种主要的肝细胞群：(1)成熟肝细胞-- 主要实质细胞类型；(2)胆管细胞。肝细胞形成具有毛细血管样结构的单细胞索 管腔网络(胆小管)贯穿其间。相反，胆管细胞形成小管，每个小管都有一个 中央管腔，接收在肝细胞旁边形成的胆小管内容物。在初始阶段 肝脏的发育和再生，无论是肝细胞还是胆管细胞都起源于共同的 上皮性前体。肝细胞和胆管上皮细胞如何获得其独特的形态和功能 这种常见前体的表型还知之甚少。的确，因为胆小管不容易 从常规HE组织染色可以看出，对肝脏上皮极性的研究在很大程度上被忽视了。 由此造成的知识鸿沟极大地阻碍了我们更好地理解 常见的肝病，通常表现为管腔组织的改变。它也严重限制了我们的 正在努力设计可用于移植、毒理学和基因治疗的肝组织 学习。 为了解决这些问题，我们开发了一种独特的组织培养模型来检查和解释如何 肝细胞和胆管管腔表型形成。它强烈地表明管腔的极性在两个 不同的脚步。首先，细胞-细胞黏附在细胞-细胞接触部位触发初始管腔形成。第二，卢米纳 稳定性随后通过E-钙粘素信号被改变。强大的E-钙粘素信号拮抗这些鲁米诺 细胞-细胞接触以确定具有单一顶端表面的胆管上皮。相比之下，弱E-钙粘附素 信号转导未能阻断这些细胞间的接触，因此默认途径确保了肝细胞的极性 现在多个胆小管之间可以形成管腔连接。 这一假说得到了我们通过开发细胞获得的已发表的初步数据的支持 可以切换极性表型的系统。我们还进一步建立了干细胞来源的 胆汁和肝细胞原代培养比较两种肝上皮细胞的信号机制 直接去吧。预计这些新的方法将使我们能够理解基本的核心 驱动肝脏细胞类型规格和极性表型的机制。

ABSTRACT The liver is our largest metabolic organ. It produces proteins, lipids, clotting factors and glycogen while dispensing bile and detoxifying xenobiotics. In order to transport these different substances, a sophisticated network of liver venules, capillaries and interstitial conduits has evolved. An essential feature of this network are the lumen-forming epithelia that give rise to two major liver cell populations: (1) mature hepatocytes - the main parenchymal cell type, and (2) bile duct cells. Hepatocytes form single-cell cords with a capillary-like luminal network (bile canaliculi) running between them. In contrast, bile duct cells form tubules, each with a central lumen that receives the content of the bile canaliculi that has formed next to hepatocytes. During initial liver development and bouts of regeneration, both hepatocytes and bile duct cells are derived from a common epithelial precursor. How hepatocytes and biliary epithelia obtain their unique morphological and functional phenotypes from this common precursor is poorly understood. Indeed, because bile canaliculi are not readily visible by conventional H&E tissue stain, the study of epithelial polarity in the liver has largely been neglected. The resulting gap in our knowledge has greatly hindered our ability to better understand the molecular basis of common liver diseases, which typically present with changes in lumen organization. It also severely limits our ongoing efforts to engineer hepatic tissue that can be used for transplantation, toxicology and gene therapy studies. To tackle these issues, we have developed a unique tissue culture model to examine and explain how hepatocyte and bile duct luminal phenotypes form. It strongly suggests lumen polarity is established in two distinct steps. First, cell-cell adhesion triggers initial lumen formation at cell-cell contact sites. Second, luminal stability is then modified through E-cadherin signaling. Strong E-cadherin signaling antagonizes these luminal cell-cell contacts to determine a bile duct epithelium with a single apical surface. In contrast, weak E-cadherin signaling fails to block these cell-cell contacts and as a result the default pathway ensures hepatocytic polarity proceeds where multiple bile canaliculi can now form luminal junctions running between them. This hypothesis is supported by published and preliminary data that we obtained by developing cell systems in which the polarity phenotype can be switched. We have furthermore established stem cell-derived biliary and hepatocyte primary cultures to compare signaling mechanisms in the two liver epithelial cell types directly. It is expected that these novel approaches will enable us to understand the fundamental core mechanisms that drive cell type-specification and polarity phenotypes in the liver.