ABSTRACT
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.