The Hillock: A Newly Discovered Airway Epithelial Structure and its Relationship with Squamous Metaplasia

摘要 四年前，Rajagopal实验室发现了气道小丘，一种新的小鼠气道上皮结构， 未知函数此后，在人类气道中发现了小山丘，这表明它们在进化过程中 保守的大部分气道被假复层上皮覆盖，主要由基底细胞组成， 分泌性棒状细胞和纤毛细胞。丘与上皮的区别主要有三个方面：（1） 位于小丘基部茎顶部的扁平KRT 13+（一种细胞角蛋白）细胞的分层出现 细胞（2）缺乏纤毛细胞，和（3）增强的丘基底干细胞的复制。我们有 初步数据表明，小丘对多种形式的气道损伤具有抵抗力， 烟草烟雾的主要成分萘和二氧化硫气体。我们有证据表明 小山丘是储备干细胞的来源。山丘的分层性质类似于病理性的 发现鳞状上皮化生，也是特征性分层，被认为是 鳞状细胞肺癌 维生素A缺乏是气管、子宫颈鳞状上皮化生的可重复模型， 和人的肾盂。在维生素A缺乏的情况下，气管发育为扁平的无纤毛细胞 表达经典小丘标记KRT13的簇。因此，我假设小丘是先前 鳞状上皮化生来源不明。我将使用不同细胞类型的遗传谱系追踪， 在维生素A缺乏症的设置岗确定维生素A缺乏症引起的细胞起源 鳞状上皮化生由于维甲酸（RA）是维生素A的活性代谢产物，我将定义RA的作用 对小丘扩展和分化的影响。为了研究RA缺乏是否会导致小山丘扩大，我 将使用丘特异性谱系驱动因子表达RA受体的显性负等位基因。我还将补充说 RA和RA受体抑制剂对再生试验的影响，以检查RA对小丘介导的损伤的影响 修复. 最后，我假设小山丘是损伤后气道上皮化的主要干细胞。的确， 先前的工作已经显示了多种细胞群能够扩增以使受损的气道表面重新形成。 因此，目前尚不清楚小山丘是否是有效的上皮修复所必需的，以及它们是否是主要的储备。 上皮干细胞。为了研究这个假设，我会先从基因上烧蚀小丘， 损伤，一种在香烟烟雾中发现的化学物质，以确定小丘是否是适当再生所必需的。

Abstract Four years ago, the Rajagopal lab identified the airway hillock, a novel murine airway epithelial structure of unknown function. Hillocks have since been reported in human airways, suggesting that they are evolutionarily conserved. Most of the airway is covered by pseudostratified epithelium, composed primarily of basal cells, secretory club cells, and ciliated cells. The hillock is distinguished from this epithelium in three major ways: (1) the presence of stratified-appearing layers of flat KRT13+ (a cytokeratin) cells which sit atop hillock basal stem cells (2) the lack of ciliated cells, and (3) the enhanced replication of the hillock basal stem cells. We have preliminary data demonstrating that the hillock is resistant to multiple forms of airway injury including naphthalene, a key component of tobacco smoke, and sulfur dioxide gas. We have evidence to suggest that hillocks serve as a source of reserve stem cells. The stratified nature of the hillock resembles the pathologic finding of squamous metaplasia that is also characteristically stratified, and which is thought to be a precursor of squamous lung cancer. Vitamin A deficiency represents a reproducible model of squamous metaplasia in the trachea, uterine cervix, and renal pelvis in mice and humans. In the setting of vitamin A deficiency, trachea develop flat non-ciliated cell clusters that express the classic hillock marker KRT13. I therefore hypothesize that hillocks are the previously unidentified source of squamous metaplasia. I will use genetic lineage tracing of different cell types including the hillock in the setting of vitamin A deficiency to determine the cell of origin of vitamin A deficiency-induced squamous metaplasia. Since retinoic acid (RA) is the active metabolite of vitamin A, I will define the role of RA on hillock expansion and differentiation. To investigate whether hillocks expand in response to RA deficiency, I will express a dominant negative allele of the RA receptor using a hillock specific lineage driver. I will also add RA and RA receptor inhibitor to regeneration assays to examine the effects of RA on hillock-mediated injury repair. Finally, I hypothesize that hillocks are the primary stem cell that re-epithelializes the airway post-injury. Indeed, previous work has shown a variety of cell populations capable of expanding to resurface the injured airway. Therefore, it is unclear if hillocks are required for efficient epithelial repair and if they are the primary reserve stem cell of the epithelium. To investigate this hypothesis, I will genetically ablate hillocks prior to naphthalene injury, a chemical found in cigarette smoke, to determine if hillocks are necessary for proper regeneration.