Department of Cell and Developmental Biology and Center for Stem Cell Biology, Vanderbilt Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
Dis Model Mech. 2011 May;4(3):359-67. doi: 10.1242/dmm.005793. Epub 2011 Jan 31.
Abnormal Notch signaling in humans results in Alagille syndrome, a pleiotropic disease characterized by a paucity of intrahepatic bile ducts (IHBDs). It is not clear how IHBD paucity develops as a consequence of atypical Notch signaling, whether by a developmental lack of bile duct formation, a post-natal lack of branching and elongation or an inability to maintain formed ducts. Previous studies have focused on the role of Notch in IHBD development, and demonstrated a dosage requirement of Notch signaling for proper IHBD formation. In this study, we use resin casting and X-ray microtomography (microCT) analysis to address the role of Notch signaling in the maintenance of formed IHBDs upon chronic loss or gain of Notch function. Our data show that constitutive expression of the Notch1 intracellular domain in bi-potential hepatoblast progenitor cells (BHPCs) results in increased IHBD branches at post-natal day 60 (P60), which are maintained at P90 and P120. By contrast, loss of Notch signaling via BHPC-specific deletion of RBP-J (RBP KO), the DNA-binding partner for all Notch receptors, results in progressive loss of intact IHBD branches with age. Interestingly, in RBP KO mice, we observed a reduction in bile ducts per portal vein at P60; no further reduction had occurred at P120. Thus, bile duct structures are not lost with age; instead, we propose a model in which BHPC-specific loss of Notch signaling results in an initial developmental defect resulting in fewer bile ducts being formed, and in an acquired post-natal defect in the maintenance of intact IHBD architecture as a result of irresolvable cholestasis. Our studies reveal a previously unappreciated role for Notch signaling in the post-natal maintenance of an intact communicating IHBD structure, and suggest that liver defects observed in Alagille syndrome patients might be more complex than bile duct paucity.
人类异常的 Notch 信号导致 Alagille 综合征，这是一种多系统疾病，其特征为肝内胆管（IHBD）稀少。目前尚不清楚异常 Notch 信号如何导致 IHBD 稀少，是由于胆管形成的发育缺陷、出生后分支和伸长缺乏，还是由于无法维持已形成的胆管。以前的研究集中在 Notch 在 IHBD 发育中的作用，并证明 Notch 信号在适当的 IHBD 形成中需要剂量。在这项研究中，我们使用树脂铸造和 X 射线微断层扫描（microCT）分析来解决 Notch 信号在慢性丧失或获得 Notch 功能后维持已形成的 IHBD 的作用。我们的数据表明，在双潜能肝祖细胞（BHPC）中组成型表达 Notch1 细胞内结构域会导致出生后第 60 天（P60）IHBD 分支增加，这些分支在 P90 和 P120 时得以维持。相比之下，通过 BHPC 特异性删除 Notch 受体的 DNA 结合伙伴 RBP-J（RBP KO）来丧失 Notch 信号，会导致 IHBD 分支随着年龄的增长而逐渐丧失。有趣的是，在 RBP KO 小鼠中，我们在 P60 时观察到每门静脉的胆管减少；在 P120 时没有进一步减少。因此，胆管结构不会随年龄丢失；相反，我们提出了一个模型，即 BHPC 特异性 Notch 信号丧失导致最初的发育缺陷，导致形成的胆管较少，并且由于不可解决的胆汁淤积，出生后维持完整 IHBD 结构的获得性缺陷。我们的研究揭示了 Notch 信号在维持完整的 IHBD 结构的出生后维持中的以前未被认识的作用，并表明 Alagille 综合征患者中观察到的肝脏缺陷可能比胆管稀少更为复杂。
