Regulation of lung alveolar epithelial protein transport

描述（由申请人提供）：我们的长期目标是 阐明与大分子相关的调节机制和途径 通过肺泡上皮的运输。蛋白质转运的初步研究 在原代培养的细胞单层中，其表现出表型和 体内肺泡上皮I型（AT 1）细胞的形态特征， 揭示了肺泡上皮蛋白转运的重要信息， 某些血清蛋白（例如，白蛋白（Alb）和免疫球蛋白G（IgG））， 通过饱和过程吸收的速率大于 被动扩散机制，而二聚免疫球蛋白A（dIgA）是 通过多聚免疫球蛋白受体分泌到肺泡液中 （pIgR）介导的过程。我们最近还发现一种糖皮质激素 类似物地塞米松可减少IgG在肺泡中的净吸收 上皮细胞，暗示可能调节肺泡上皮细胞转运 血清蛋白通过可溶性（例如，体液）因素。作为一种逻辑延伸， 对这三种关键蛋白质的这些功能性转运研究（即，白蛋白，IgG， dIgA）穿过肺泡上皮时，转运机制的调节将被调节。 研究了我们的核心假设包括i）这三种关键蛋白质 穿过肺泡上皮屏障主要利用可调节的 囊泡转运，ii）Alb和dIgA内吞作用主要 由聚集在小窝蛋白包被结构中的同源受体介导 (i.e.,小窝）和网格蛋白包被的小窝，而IgG是 通过液相内吞作用内化（即，不结合受体， 细胞表面由于非最佳流体pH），和iii）这些蛋白质的转运 在肺泡上皮细胞中受到不同的调节。为了测试这些 假设，我们将研究以下四个具体目标：i）差异 特定蛋白质的跨肺泡上皮转运的性质，ii） 特定蛋白质的结合/内化的表征，iii） 调节特定蛋白质穿过肺泡上皮的运输，以及 iv）调节穿过受损肺泡上皮的蛋白质转运。我们将 利用原代培养的肺泡上皮细胞单层作为体外 模型，提供有关差异调节的机制信息 这三种关键蛋白质的肺泡上皮转运。调控 这些关键蛋白质的同源受体的肺泡上皮表达将 在适当的时候进行调查。从这些研究中获得的结果将 有助于阐明易位的特定机制（和相关途径） 蛋白质在肺泡上皮细胞中的作用及相关受体的作用 对于健康肺泡上皮细胞蛋白质转运中的关键蛋白质， 疾病

DESCRIPTION (provided by applicant): Our long-term goal has been the elucidation of regulatory mechanisms and pathways associated with macromolecule transport across alveolar epithelium. Preliminary studies on protein transport across primary cultured cell monolayers, which exhibit phenotypic and morphological traits of in vivo alveolar epithelial Type I (ATl) cells, uncovered important information on alveolar epithelial protein transport, in that some serum proteins (e.g., albumin (Alb) and immunoglobulins G (IgG)) are absorbed via saturable processes at rates greater than those predicted by passive diffusional mechanisms, whereas dimeric immunoglobulin A (dIgA) is secreted into alveolar fluid via a polymeric immunoglobulin receptor (pIgR)-mediated process. We also found very recently that a glucocorticoid analog, dexamethasone, decreases net absorption of IgG across alveolar epithelium, implicating possible regulation of alveolar epithelial transport of serum proteins by soluble (e.g., humoral) factors. As a logical extension of these functional transport studies on these three key proteins (i.e., Alb, IgG, dIgA) across alveolar epithelium, regulation of transport mechanisms will be investigated. Our central hypotheses include i) that these three key proteins traverse the alveolar epithelial barrier predominantly utilizing regulable vesicular transport, ii) that endocytosis of Alb and dIgA is predominantly mediated by their cognate receptors clustered in caveolin-coated structures (i.e., caveolae) and clathrincoated pits, respectively, while IgG is internalized by fluid-phase endocytosis (i.e., without binding receptors at the cell surface due to non-optimal fluid pH), and iii) transport of these proteins is regulated differentially in alveolar epithelium. In order to test these hypotheses, we will study the following four Specific Aims: i) differential properties of transalveolar epithelial transport of specific proteins, ii) characterization of binding / internalization of specific proteins, iii) regulation of trafficking of specific proteins across alveolar epithelium, and iv) regulation of protein transport across injured alveolar epithelium. We will utilize primary cultured alveolar epithelial cell monolayers as an in vitro model to provide pertinent mechanistic information on differential regulation of alveolar epithelial transport of these three key proteins. Regulation of alveolar epithelial expression of cognate receptors for these key proteins will be investigated where appropriate. Results obtained from these studies will help elucidate specific mechanisms (and associated pathways) for translocation of proteins across lung alveolar epithelium and roles of the cognate receptors for the key proteins in alveolar epithelial protein transport in health and disease.