Biology of ACE2 activity in the airway epithelium

呼吸道上皮细胞是SARS和NL 63冠状病毒通过与其受体血管紧张素转换酶2（ACE 2）相互作用结合和进入的关键部位。ACE 2是一种末端羧肽酶，表达于气道上皮细胞的顶面，也表达于肺泡上皮细胞。ACE 2通过以下途径从上皮细胞表面释放到气道表面液体（ASL）中： 通过TACE（ADAM 17）和其他脱落酶切割。这种可溶性ACE 2（sACE 2）在ASL中具有催化活性，尽管其天然底物和生物学功能知之甚少。ACE 2似乎还具有其他功能，包括诱导上皮细胞信号传导和防御功能，并且SARS-CoV S蛋白或SARS病毒感染直接下调肺ACE 2表达。肺ACE 2功能的丧失被假设为与SARS、脓毒症和酸中毒相关的急性肺损伤的原因。 抱负该项目的总体目标是更好地了解如何表达和释放的ACE 2是支配在气道上皮细胞，使用分化良好的人气道上皮细胞模型和小鼠模型的SARS冠状病毒感染，并将其与SARS冠状病毒的发病机制。我们的总体假设是，肺ACE 2表达和活性的变化通过降低羧肽酶活性和上皮宿主防御信号的变化促成SARS-CoV肺病。有三个具体目标。 目标1.确定SARS-CoV感染如何影响气道上皮细胞ACE 2表达。在这个目标中，我们将调查的假设，即肺血管和上皮细胞表达ACE 2的细胞分化状态，年龄，炎症和感染的介质进行调节。 我们还将研究S蛋白参与和TACE如何影响sACE 2的释放。 目标2.描述SARS-CoV感染过程中气道上皮ACE 2的生理功能。 在这里，我们强调详细评估ACE 2的酶功能的背景下，当地的肺RAS和激肽系统，以及他们如何在SARS冠状病毒感染的干扰，并有助于肺部疾病。 目标3.确定调节宿主防御反应的酶活性独立的ACE 2功能。为了这个目的，我们专注于ACE 2在气道上皮细胞的功能，独立于其受体特性和羧肽酶活性。将研究直接调节上皮宿主防御的ACE 2作用。

The airway epithelium is a critical site for binding and entry of the SARS and NL63 coronaviruses throughinteractions with their receptor angiotensin converting enzyme 2 (ACE2). ACE2, a terminal carboxypeptidase, is expressed on the apical surface of the epithelial cells that line conducting airways, as well as alveolar epithelial cells. ACE2 is released from the surface of epithelia into airway surface liquid (ASL) via cleavage by TACE (ADAM17) and other sheddases. This soluble ACE2 (sACE2) is catalytically active in ASL, although its native substrates and biologic funcfions are poorly understood. ACE2 appears to have other functions that include induction of epithelial cell signaling and defense function, and SARS-CoV S protein or SARS virus infection directly downregulate pulmonary ACE2 expression. Loss of pulmonary ACE2 function has been hypothesized to contribute to acute lung injury associated with SARS, sepsis, and acid aspiration. The overall goal of this project is to better understand how the expression and release of ACE2 is governed in ainway epithelia, using models of well-differentiated human airway epithelia and mouse models of SARS-CoV infection, and relate this to SARS-CoV pathogenesis. Our overall hypothesis is that changes in pulmonary ACE2 expression and activity contribute to SARS-CoV lung disease through reduced carboxypeptidase activity and changes in epithelial host defense signaling. There are 3 specific aims. Aim 1. Determine how airway epithelial cell ACE2 expression is affected by SARS-CoV infection. In this aim we will investigate the hypothesis that pulmonary ACE2 expression in the vascular and epithelial compartments is regulated by cellular differentiation state, age, and mediators of infiammation and infection. We will also investigate how S-protein engagement and TACE affect sACE2 release. Aim 2. Characterize the physiologic function of airway epithelial ACE2 during SARS-CoV infection. Here we emphasize detailed assessment of the enzymatic functions of ACE2 in the context of a local pulmonary RAS and kinin system and how they are perturbed during SARS-CoV infection and contribute to lung disease. Aim 3. Identify enzyme activity-independent ACE2 functions that modulate host defense responses. For this aim, we focus on ACE2 function in airway epithelia independent of its receptor properties and carboxypeptidase activity. ACE2 effects that directly modulate epithelial host defenses will be studied.