During embryogenesis, airway epithelial cells possess primary cilia, and HH signaling guides lung development. As epithelial cells mature, they produce hundreds of motile cilia and continue to produce the sonic hedgehog (SHH) ligand, which is found apically in the thin layer of liquid covering airways. However, whether ciliated airway cells express apical HH signaling components and what their function might be have remained unknown. Here we show that motile cilia are enriched for HH signaling proteins, including patched 1 and smoothened. These cilia are also enriched for proteins affecting cAMP-dependent signaling, including Gαi and adenylyl cyclase 5/6. Surprisingly, SHH in differentiated airway epithelia did not elicit the canonical SHH signaling pathway that regulates transcription during development. But instead, activating HH signaling decreases intracellular levels of cAMP, which reduces ciliary beat frequency and airway surface liquid pH, similar to changes that have been observed in the airway of people with chronic obstructive pulmonary disease (COPD). Furthermore, we observed that significant increase of SHH ligand expression in differentiated airway epithelia with COPD, suggesting a potential role of SHH signaling in the pathogenesis of airway disease. Collectively, our study indicates that airway cilia detect apical SHH to mediate airway physiology through noncanonical HH signaling. SHH may dampen defenses at the contact point between the environment and the lung, perhaps counterbalancing processes that stimulate airway defenses. This may suggest a potential role of SHH signaling in the pathogenesis of airway disease, such as COPD.

Medulloblastoma (MB), a cancer of the cerebellum, is the most common solid tumor affecting children. In the cerebellum, Sonic Hedgehog (Shh) drives the proliferative expansion of granule neuron progenitors (GNP). These cells are located in the external granule layer (EGL) and are the cells of origin of Shh-MB. We recently identified Norrie Disease Pseudoglioma (Ndp) as a novel downstream target of Hh signaling in the developing retina. Ndp encodes an X-linked cysteine-rich secreted protein called Norrin, which is best known for its role in angiogenesis and blood brain barrier (BBB) maintenance in the developing retina and cerebellum, respectively. Norrin mediates this effect by binding to its receptor Frizzled4 (Fzd4) and co-receptors LRP5/6 and Tpsan12 to activate the canonical, β-catenin-dependent Wnt signaling pathway in endothelial cells (ECs). We detected the expression of Ndp and all required receptors in mouse GNPs and MB samples. To investigate a potential role for Ndp in Hh-driven MB, we genetically and pharmacologically inactivated Ndp/Fzd4 signaling in Ptch+/- mice (a mouse model for human Gorlin syndrome), which dramatically increased the incidence and reduced the latency of MB. This accelerated rate of tumorigenesis was caused by an increase in the number of preneoplastic lesions (PNLs), the precursor lesions to MB, and a faster conversion of these lesions to MB. We showed that Ndp mediates this increase in tumorigenesis by signaling through endothelial cell receptor Fzd4 to alter the GNP stroma, which is characterised by 5 major alterations: 1) activated angiogenic program, 2) open BBB, 3) aberrant deposition of extracellular matrix, 4) aberrant lymphocyte recruitment and 5) reduction in meningeal lymphatic vasculature. We propose that these stromal alterations are associated with a pro-tumor microenvironment that promotes DNA damage in GNPs and leads to enhanced lesion formation and progression towards MB. This research highlights 1) an unanticipated role for Ndp/Fzd4 signaling in Shh-MB initiation and progression, 2) a role for stromal signaling in the regulation of MB development and 3) a previously undescribed role for Ndp signaling in maintaining meningeal cerebellum lymphatic vessels.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21257号 / 医博第4375号 / 新制||医||1029(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 増永 慎一郎, 教授 妹尾 浩, 教授 松田 道行 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM