Impact of SARS-CoV-2 on the barrier function of the airway epithelium

临床试验显示，地塞米松等糖皮质激素可以降低Covid-19重症患者的死亡率，这可能是由于它们的免疫调节作用。气道上皮形成导电气道的表面，是SARS-CoV-2暴露的主要部位，并构成病毒入侵和传播到生物体的屏障。这种屏障阻止病毒入侵的能力取决于其细胞完整性和紧密连接，这些连接密封相邻上皮细胞之间的外侧细胞间隙，以防止溶质和水的泄漏。病毒感染导致的紧密连接损伤可能在上皮屏障的破坏和促进严重的肺损伤中起关键作用。我们证明了糖皮质激素通过促进claudin 8的结合来稳定蛋白质组装和紧密连接的收紧。后一种功能可能有助于糖皮质激素在Covid-19治疗中的有益作用。因此，本项目的目的如下：1)解决SARS-CoV-2对气道上皮紧密连接的影响；2)表征SARS-CoV-2感染期间上皮运输和气道表面液体稳态的变化；3)阐明糖皮质激素是否能预防SARS-CoV-2诱导的紧密连接损伤。研究将主要在气道上皮的体外模型中进行，该模型基于人原代肺上皮细胞，将在气液界面培养。该模型类似于气道上皮的细胞组成和功能特性，并允许研究其功能和生物物理特性。关于SARS-CoV-2对紧密连接和上皮运输特性影响的研究将为SARS-CoV-2诱导肺损伤的机制和糖皮质激素的作用方式提供新的见解。

Clinical trails revealed that glucocorticoids like dexamethasone reduce the mortality of severely diseased Covid-19 patients, presumably because of their immune modulatory effects. The airway epithelium forms the surface of the conductive airways, is a primary site of SARS-CoV-2 exposure and constitutes a barrier for viral invasion and dissemination into the organism. The ability of this barrier to prevent virus invasion depends on its cellular integrity and on tight junctions that seal the lateral intercellular space between adjacent epithelial cells in order to prevent leaking of solutes and water. Damage of tight junctions as a result of virus infection might play a key role in the breakdown of the epithelial barrier and promote severe lung damage.We demonstrated that glucocorticoids stabilize protein assembly and tightening of tight junctions by promoting incorporation of claudin 8. The latter function might contribute to the beneficial effect of glucocorticoids in Covid-19 treatment. Thus, the project has the following aims: i) to resolve the impact of SARS-CoV-2 on airway epithelial tight junctions, ii) to characterize the changes in epithelial transport and airway surface liquid homeostasis during SARS-CoV-2 infection and iii) to elucidate, whether glucocorticoids prevent SARS-CoV-2 induced tight junction damage.The investigations will be performed primarily in an in-vitro model of the airway epithelium that bases on human primary lung epithelial cells, which will be cultivated at an air-liquid interface. This model resembles the cellular composition as well as the functional properties of the airway epithelium and allows to study its functional and biophysical properties. The proposed studies on the impact of SARS-CoV-2 on tight junctions and epithelial transport properties will provide new insights into the mechanisms of SARS-CoV-2 induced lung damage and the mode of action of glucocorticoids.