Plasticity of Alveolar Epithelial Phenotypic Expression

描述(申请人提供)：肺泡上皮由两个形态不同的分化上皮细胞组成，I型(TI)和II型(TII)细胞，这两种细胞被认为是正常肺功能的关键。虽然正常肺泡上皮的建立、维持和修复对哺乳动物的生命是必不可少的，但我们对调节这些事件的重要过程的了解有限。这项研究的广泛目标是了解肺泡上皮的维持和修复是如何调节的。在此背景下，本项目的总体目标是阐明肺损伤后TI和TLL细胞的命运以及导致这两种细胞转分化的细胞机制。30年前使用放射自显影和电子显微镜技术进行的研究产生了目前的范式，即肺损伤后TII细胞增殖和转分化为TI细胞。根据对进展报告和初步数据中提出的文献和工作的研究，目前的范例现在看来是不完整的。已发表的文献中有报道称TI细胞可能具有修复能力，最近有推测肺内可能发生上皮-间充质转化，与肾纤维化的发病机制相似。本申请中提供的免疫组织化学数据提供了在间充质和上皮室之间发生转分化的额外证据。最近，我们发现了TI细胞在体外的增殖，支持了TI细胞也可能参与体内修复过程的观点。这些观察结果促使我们提出了一个工作假说，即肺损伤后的修复比从成熟的TII细胞到TI细胞的简单线性过程更复杂，涉及其他细胞过程，如TI细胞、TII细胞和间充质细胞之间的转分化，以及TI细胞的增殖。建议的研究包括三个特定的目标，以确定TI和TII细胞表现出表达可塑性的程度，并阐明转分化的机制。1)通过转基因小鼠的命运图谱研究确定肺损伤后TI和TII细胞的命运；2)在肺损伤的不同时间点确定不同肺泡上皮细胞群的分子表型和增殖特性，包括表达TI和TII细胞表型标记的中间细胞和过渡细胞；以及3)通过Q-PCR、原位杂交和体内外功能研究来评估候选调控基因。

DESCRIPTION (provided by applicant): The alveolar epithelium is comprised of 2 morphologically distinct differentiated epithelial cells, type I (TI) and type II (TII) cells, both of which are thought to be critical for normal lung function. Although the establishment, maintenance, and repair of a normal alveolar epithelium are essential for mammalian life, we have a limited understanding of the important processes that regulate these events. The broad objectives of the research are to understand how alveolar epithelial maintenance and repair are regulated. Within this context, the overall goals of this project are to elucidate the fates of TI and Tll cells and the cellular mechanisms responsible for the transdifferentiation of both cell types following lung injury. Studies performed 30 years ago using techniques of autoradiography and electron microscopy generated the current paradigm that after lung injury TII cells proliferate and transdifferentiate into TI cells. Based on studies in the literature and work presented in the Progress Report and Preliminary Data, the current paradigm appears now to be incomplete. There are reports in the published literature that TI cells may have reparative potential, and there has been recent speculation that epithelial-mesenchymal transformation may occur in the lung, in a similar fashion to the pathogenesis of renal fibrosis. Immunohistochemical data presented in this application provide additional evidence that transdifferentiation occurs between the mesenchymal and epithelial compartments. Recently, we found that TI cells proliferate in vitro, supporting the concept that TI cells may also participate in the repair process in vivo. These observations have prompted us to generate the working hypothesis that repair following lung injury is more complex than a simple linear progression from mature TII to TI cells, involving other cellular processes such as transdifferentiation among TI cells, TII cells, and mesenchymal cells, and the proliferation of TI cells. The proposed studies comprise 3 specific aims to determine the extent to which TI and TII cells exhibit plasticity of expression and to elucidate the mechanisms for transdifferentiation. 1) To determine the fates of TI and TII cells following injury by fate-mapping studies in transgenic mice; 2) To ascertain at various time points in lung injury the molecular phenotypes and proliferative properties of various populations of alveolar epithelial cells, including "intermediate cells," transitional cells expressing markers of both TI and TII cell phenotypes; and 3) To evaluate candidate regulatory genes by Q-PCR, by in situ hybridization, and by functional studies in vitro and in vivo.