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

注：您必须以Word格式提交，而不是PDF格式，ERA才能更新所有系统。 肝脏是我们最大的新陈代谢器官。它产生蛋白质、脂类、凝血因子和糖原，同时分配胆汁和解毒外源物质。为了运输这些不同的物质，一个由肝小静脉、毛细血管和间质管道组成的复杂网络已经进化。这一网络的一个基本特征是形成管腔的上皮细胞，它产生了两个主要的肝细胞群：(1)肝细胞--主要的实质细胞类型，(2)胆管细胞。两者都获得了完全不同的极性表型，以适应它们不同的功能(图1)：胆管细胞形成简单的胆汁管道，像其他管状上皮细胞一样围绕中央管腔组织。相比之下，肝细胞形成单细胞索，沿着两侧的血管排列，并在它们之间有一个毛细管状的管腔网络(胆小管)。这种组织有助于它们与血液进行广泛的双向分子交换，同时允许胆汁酸排泄到胆小管。肝细胞如何获得这种独特的形态表型目前还知之甚少。事实上，由于常规HE组织染色看不到胆小管，对肝细胞极性的研究在很大程度上被忽视了。由此导致的知识差距极大地阻碍了我们更好地了解常见肝病的分子基础的能力，这些疾病通常表现为肝细胞极性和形态的变化。这也严重限制了我们正在进行的努力，即设计可用于移植、毒理学和基因治疗研究的肝组织。 为了解决这些问题，我们开发了一种独特的组织培养模型，在该模型中，极性表型可以从导管转换为肝细胞，并利用该模型来识别区分肝细胞和导管极化程序的分子机制。同时，我们开发了在体外将极化的肝细胞与其前体细胞区分开来的方案，并评估了这些生理相关系统中对肝细胞极性转换至关重要的蛋白质。这导致发现了双重的PKA锚定和Rho激活蛋白AKAP13作为胆小管延长的调节因子。阐明其潜在的功能机制，将揭示肝细胞极化的一个关键的形态机制。

NOTE: You must submit in Word format, not PDF, for eRA to update all the systems. 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) hepatocytes - the main parenchymal cell type, and (2) bile duct cells. Both acquire radically different polarity phenotypes adapted to their different functions (Fig.1): Bile duct cells, which form simple conduits for bile, organize like other tubular epithelia around a central lumen. Hepatocytes, by contrast form single-cell cords, aligned along blood vessels on either side and with a capillary-like luminal network (bile canaliculi) running between them. This organization facilitates their extensive bi-directional molecular exchange with the blood, while allowing bile acid excretion into the bile canaliculi. How hepatocytes obtain this unique morphological phenotype is poorly understood. Indeed, because bile canaliculi are not visible by conventional H&E tissue stain, the study of hepatocyte polarity 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 hepatocyte polarity and morphology. 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 developed a unique tissue culture model in which the polarity phenotype can be switched from ductal to hepatocytic and utilized it to identify molecular mechanisms that distinguish the hepatocytic from the ductal polarization program. In parallel, we developed protocols to in vitro differentiate polarized hepatocytes from their precursors and evaluated proteins critical for the hepatocytic polarity switch in these physiological relevant systems. This led to the discovery of the dual PKA-anchoring and Rho-activating protein AKAP13 as regulator of bile canaliculi elongation. Elucidating the mechanisms underlying its function, as proposed here, will reveal a critical morphological mechanisms of hepatocyte polarization.