Background: The COVID-19 pandemic is an ongoing threat to public health. Since the identification of COVID-19, the disease caused by SARS-CoV-2, no drugs have been developed to specifically target SARS-CoV-2. To develop effective and safe treatment options, a better understanding of cellular mechanisms underlying SARS-CoV-2 infection is required. To fill this knowledge gap, researchers require reliable experimental systems that express the host proteins necessary for the cellular entry of SARS-CoV-2. These proteins include the viral receptor, ACE2 and the proteases TMPRSS2 and furin. A number of studies have reported cell-type specific expression of the genes encoding these molecules. However, less is known about the protein expression of these molecules. Methods: We assessed the suitability of primary human bronchial epithelial (HBE) cells maintained in air-liquid interface (ALI) as an experimental system for studying SARS-CoV-2 infection in vitro. During cellular differentiation, we measured the expression of ACE2, TMPRSS2, and furin over progressive ALI days by RT-qPCR, western blot and immunofluorescence staining. We also explored the effect of the fibrotic cytokine TGF-b on the expression of these proteins in well-differentiated HBE cells. Results/Discussion: Like ACE2, TMPRSS2 and furin proteins are localized in differentiated ciliated cells as confirmed by immunofluorescence staining. These data suggest that well-differentiated HBE cells maintained in air-liquid interface is a reliable in vitro system for investigating cellular mechanisms of SARS-CoV-2 infection. We further identified that profibrotic mediators, TGF-β1 and TGF-β2, increase the expression of furin, which is a protease required for the cellular entry of SARS-CoV-2.

中文翻译：

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在分化良好的原代人支气管上皮细胞中，TGF-β1 和 TGF-β2 诱导弗林蛋白酶的表达

背景：COVID-19 大流行是对公共卫生的持续威胁。自从发现由 SARS-CoV-2 引起的疾病 COVID-19 以来，还没有开发出专门针对 SARS-CoV-2 的药物。为了开发有效和安全的治疗方案，需要更好地了解 SARS-CoV-2 感染的细胞机制。为了填补这一知识空白，研究人员需要可靠的实验系统来表达 SARS-CoV-2 进入细胞所必需的宿主蛋白。这些蛋白质包括病毒受体、ACE2 和蛋白酶 TMPRSS2 和弗林蛋白酶。许多研究报告了编码这些分子的基因的细胞类型特异性表达。然而，对这些分子的蛋白质表达知之甚少。方法：我们评估了维持在气液界面 (ALI) 中的原代人支气管上皮 (HBE) 细胞作为体外研究 SARS-CoV-2 感染的实验系统的适用性。在细胞分化过程中，我们通过 RT-qPCR、蛋白质印迹和免疫荧光染色测量了进行性 ALI 天数内 ACE2、TMPRSS2 和弗林蛋白酶的表达。我们还探讨了纤维化细胞因子 TGF-b 对这些蛋白质在分化良好的 HBE 细胞中表达的影响。结果/讨论：免疫荧光染色证实，与 ACE2 一样，TMPRSS2 和弗林蛋白位于分化的纤毛细胞中。这些数据表明，维持在气液界面中的分化良好的 HBE 细胞是研究 SARS-CoV-2 感染细胞机制的可靠体外系统。