Developing advanced cell culture models to study COVID19-associated pulmonary fibrosis

Patients with severe COVID-19-associated pneumonia are at risk to develop pulmonary fibrosis. To study the underlying mechanisms, we aim to develop advanced cell culture models that reliably reflect COVID-19-related profibrotic microenvironment. To identify key cellular players, we performed pilot immunohistochemistry analysis on lung tissue from COVID-19 patients with fibrosis collected during autopsy. Results revealed diffuse alveolar damage with macrophage infiltration, and myofibroblast accumulation with enriched collagen deposition surrounding the damaged alveoli. To mimic SARS-CoV-2 infection in alveoli, we infected human primary type II alveolar epithelial cells (AEC2) and found enhanced signaling of profibrotic cytokine transforming growth factor beta (TGFbeta) in some donors. To recreate the early fibrotic niche, an alveolar-macrophage-fibroblast (AMF) tri-culture model was established. After infecting AEC2 with SARS-CoV-2 in this AMF model, gene expression analysis provided evidence for fibroblast-to-myofibroblast transition. Furthermore, we found that overexpression of SARS-CoV-2 papain-like protease (PLpro) can promote TGFbeta signaling in HEK293T and A549 cells. After infecting AEC2 with SARS-CoV-2 PLpro lentivirus in the AMF model, we found signs of epithelial-to-mesenchymal transition and fibroblast-to myofibroblast transition. In future studies, we will use a detailed analysis of COVID-19-associated lung fibrosis with other types of lung fibrosis, to further refine COVID-19-related fibrosis models, including lung-on-chip models.

RNA sequencing unravels unique host transcriptional responses to infection with SARS-CoV-2 in well differentiated primary human bronchial epithelial cells compared to other coronaviruses

As the causative agent of COVID-19, SARS-CoV-2 remains a global cause for concern. Compared to other highly pathogenic coronaviruses (SARS-CoV and MERS-CoV), SARS-CoV-2 exhibits stronger transmissibility but less lethality, indicating that SARS-CoV-2 displays unique characteristics, despite the partial genomic proximity. Thus, we aim to employ RNA sequencing to define transcriptional differences in epithelial responses following infection with SARS-CoV-2 compared to pathogenic SARS-CoV and MERS-CoV, and low pathogenic HCoV-229E. Primary human bronchial epithelial cells (PBEC) were differentiated for 6 weeks at the air-liquid interface (ALI) before parallel infection by the 4 different coronaviruses. After infection following apical application of coronaviruses at low dose, cells were harvested for bulk RNA sequencing. Results demonstrated that all tested coronaviruses efficiently infected ALI-PBEC. RNA sequencing analysis revealed that infection with SARS-CoV, MERS-CoV and HCoV-229E resulted in largely similar transcriptional responses by the epithelial cells. However, whereas infection with these viruses was accompanied by an increased expression of genes associated with JNK/AP-1 signalling, including FOS, FOSB and NR4A1, no such increase was observed following SARS-CoV-2 infection. Further, preliminary experiments indicated that an NR4A1 antagonist reduced viral replication in Calu-3 cells. In conclusion, these data suggest that SARS-CoV2-infected ALI-PBEC exhibit a unique transcriptional response compared to other coronaviruses, which might relate to the pathogenicity of the virus.