SARS-CoV-2-encoded miR-nsp3-3p promotes pulmonary fibrosis by inhibiting expression of ALCAM.

microRNAs (miRNAs) derived from viruses, have been detected in body fluids and are known to regulate the expression of host genes. Recent evidence indicates that SARS-CoV-2-encoded miRNAs could contribute to pulmonary disease. Pulmonary fibrosis is an important complication in SARS-CoV-2 infected patients, either during hospitalization or after discharge, however, the underlying mechanisms are not fully elucidated. Here, we report a SARS-CoV-2-encoded miRNA, miR-nsp3-3p, facilitates host pulmonary fibrosis by inhibiting expression of activated leukocyte cell adhesion molecule (ALCAM) and promoting epithelial-mesenchymal transition (EMT). First, we detected miR-nsp3-3p in clinical specimens and found it was remarkably increased in throat swabs and alveolar lavage fluids from severe/critical COVID-19 patients compared to control groups or mild/moderate patients. We further revealed that adeno-associated virus (AAV)-nsp3 infection can induce pulmonary fibrosis in BALB/c mice while miR-nsp3-3p antagomirs can reverse that, and ALCAM was found to be as a target gene of miR-nsp3-3p. miR-nsp3-3p overexpression can inhibit the expression of ALCAM and promote EMT of pulmonary epithelial cells. Moreover, overexpression of ALCAM can reverse the miR-nsp3-3p-induced EMT and fibrosis. These findings highlight the essential role of SARS-CoV-2-encoded miRNAs in promoting the pathological progression of lung disease, and provide novel insights into the interactions between viral miRNAs and host pathology.