SARS-CoV-2 induced damage of the alveolar epithelium in the lung and its inhibition by α1-antitrypsin.

最近的2019冠状病毒病（COVID-19）大流行引起的卫生紧急情况突出表明，需要找到针对传染性严重呼吸综合征冠状病毒2 （SARS - CoV-2）的有效治疗方法。SARS-CoV-2感染主要针对呼吸道。最近的研究表明，鼻表面可能是SARS-CoV-2呼吸道感染的主要初始部位。随后将病毒接种物吸入远端肺并感染肺泡II型肺细胞（ATII细胞）。最严重的SARS-CoV-2感染会导致急性呼吸窘迫综合征（ARDS），这是由肺泡空气-血液屏障的结构和/或功能损伤引起的。这些患者中约有25%需要机械通气，这与高死亡率（50%至80%）相关。这种临床表型被认为是随着病毒逐渐靶向远端肺上皮，特别是ATII细胞而出现的。然而，引起病毒诱导的肺泡和肺泡上皮病理改变的机制尚不清楚。因此，研究SARS-CoV-2感染对肺泡上皮细胞功能和肺泡屏障完整性的影响是本研究的主要目的。COVID-19诱导的ARDS严重程度与肺泡SARS-CoV-2病毒载量密切相关。因此，减少肺泡间室的感染性病毒载量将降低COVID-19 - ARDS的严重程度。我们最近从bonchio肺泡灌洗液中发现急性期蛋白α1-抗胰蛋白酶（α1-AT）是SARS-CoV-2的特异性抑制剂。内源性α1-AT是一种广谱丝氨酸蛋白酶抑制剂（serpin），在SARS-CoV-2感染期间上调。我们发现α1-AT在生理浓度下抑制SARS-CoV-2感染人气道上皮。研究结果表明，α1-AT可能是SARS-CoV-2感染的天然抑制剂，特别是在α1-AT浓度升高的急性感染期间。此外，这可能为重新利用已经批准的基于α1- at的药物用于COVID-19治疗提供了机会。事实上，已经开展了几项临床试验来评估α1-AT对住院COVID-19患者的治疗效果。因此，我们的第二个目的是研究α1-AT是否能减少SARS-CoV-2在肺泡上皮，特别是ATII细胞中的感染，并保护肺泡屏障免受损伤。为了实现这两个目标，我们将使用人类原代分离的ATII细胞和最近建立的肺泡-毛细血管屏障体外模型，并用从不同地理区域获得的SARS-CoV-2分离株感染这些模型。我们将分析SARS-CoV-2感染对肺泡屏障完整性和功能的影响，并阐明α1-AT是否可能抑制病毒感染和损伤。

The health emergency caused by the recent coronavirus disease 2019 (COVID-19) pandemic highlights the need to identify effective treatments against the causative severe respiratory syndrome coronavirus 2 (SARS CoV-2). SARS-CoV-2 infection primarily targets the respiratory tract. Recent studies suggest that nasal surfaces might be the dominant initial site for SARS-CoV-2 respiratory tract infection. This is followed by aspiration of the viral inoculum into the distal lung and infection of alveolar type II pneumocytes (ATII cells). The most severe infections with SARS-CoV-2 result in acute respiratory distress syndrome (ARDS) caused by structural and/or functional damage of the alveolar air-blood barrier. About 25% of these patients will require mechanical ventilation, which is associated with high mortality (50 to 80%). This clinical phenotype is thought to arise as the virus progressively targets the epithelium of the distal lung, particularly ATII cells. The mechanisms, however, that cause virus-induced pathological changes in the alveolus and the alveolar epithelium are still poorly understood. Thus, it is a main aim of this proposal is to investigate the effect of SARS-CoV-2 infection on alveolar epithelial cell function and alveolar barrier integrity. The severity in COVID-19 induced ARDS is tightly correlated with alveolar SARS-CoV-2 viral load. Reducing infectious virus load in the alveolar compartment will therefore reduce COVID-19 ARDS severity. We recently identified the acute phase protein α1-antitrypsin (α1-AT) from bonchioalveolar lavages as specific inhibitor of SARS-CoV-2. Endogenous α1-AT is a broad-spectrum serine protease inhibitor (serpin) that is upregulated during SARS-CoV-2 infection. We found that α1-AT inhibits SARS-CoV-2 infection of human airway epithelia at physiological concentrations. Our findings showed that α1-AT may serve as natural inhibitor of SARS-CoV-2 infection, in particular during acute infection when α1-AT concentrations increase. Moreover, this potentially offers an opportunity for repurposing of already approved α1-AT-based drugs for COVID-19 therapy. In fact, several clinical trials have been initiated to evaluate the therapeutic efficacy of α1-AT in hospitalized COVID-19 patients. Thus, the second aim of our proposal is to investigate whether α1-AT reduces SARS-CoV-2 infection in alveolar epithelia, in particular ATII cells, and protects from alveolar barrier damage. To address these two aims we will use human primary isolated ATII cells and recently established in vitro models of the alveolar-capillary barrier and infect these with SARS-CoV-2 isolates obtained from different geographical regions. We will analyze the effects of SARS-CoV-2 infection on alveolar barrier integrity and function, and clarify whether α1-AT may suppress viral infection and damage.