The role of alveolar epithelial junctions in early lung injury and COVID-19-induced fibrosis

Pulmonary fibrosis is a chronic progressive disease, caused by numerous factors, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Damage to the alveolar epithelial barrier (formed by junctions between alveolar epithelial cells I) has been described as a key mechanism of early fibrosis and therefore could be crucial for COVID-19-associated sequelae. The integrity of adherens junctions is regulated by p120 catenin and is crucial for barrier regulation in epithelial-mesenchymal-transition-driven diseases such as fibrogenesis and cancer. Abundance and expression of p120 catenin and intercellular contact regulating proteins (caveolin-1, P2X7R) were investigated retrospectively in COVID-19 lungs (acute, chronic) compared with healthy controls and interstitial lung disease of different etiologies (n = 6). p120 Catenin was further investigated in early injury models using profibrotic agents in murine lung and human alveolar epithelial cell culture. p120 Catenin abundance was higher in chronic COVID-19 compared with acute COVID-19, suggesting a role in fibrotic development. The interacting proteins caveolin-1 and P2X7R were simultaneously decreased in COVID-19, indicating a role in early pathophysiology. Early epithelial damage showed no changes in p120 catenin and its phospho-Y228 site in cell culture whereas p120 catenin was reduced in murine lung culture. Thus, alterations in and interactions between p120 catenin and caveolae associated proteins may represent a potential mechanism underlying COVID-19-induced pulmonary fibrosis.