SARS-CoV-2 infection aggravates cigarette smoke-exposed cell damage in primary human airway epithelia

The coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a worldwide pandemic with over 627 million cases and over 6.5 million deaths. It was reported that smoking-related chronic obstructive pulmonary disease (COPD) might be a crucial risk for COVID-19 patients to develop severe condition. As cigarette smoke (CS) is the major risk factor for COPD, we hypothesize that barrier dysfunction and an altered cytokine response in CS-exposed airway epithelial cells may contribute to increased SARS-CoV-2-induced immune response that may result in increased susceptibility to severe disease. The aim of this study was to evaluate the role of CS on SARS-CoV-2-induced immune and inflammatory responses, and epithelial barrier integrity leading to airway epithelial damage.

Primary human airway epithelial cells were differentiated under air-liquid interface culture. Cells were then exposed to cigarette smoke medium (CSM) before infection with SARS-CoV-2 isolated from a local patient. The infection susceptibility, morphology, and the expression of genes related to host immune response, airway inflammation and damages were evaluated.

Cells pre-treated with CSM significantly caused higher replication of SARS-CoV-2 and more severe SARS-CoV-2-induced cellular morphological alteration. CSM exposure caused significant upregulation of long form angiotensin converting enzyme (ACE)2, a functional receptor for SARS-CoV-2 viral entry, transmembrane serine protease (TMPRSS)2 and TMPRSS4, which cleave the spike protein of SARS-CoV-2 to allow viral entry, leading to an aggravated immune response via inhibition of type I interferon pathway. In addition, CSM worsened SARS-CoV-2-induced airway epithelial cell damage, resulting in severe motile ciliary disorder, junctional disruption and mucus hypersecretion.

Smoking led to dysregulation of host immune response and cell damage as seen in SARS-CoV-2-infected primary human airway epithelia. These findings may contribute to increased disease susceptibility with severe condition and provide a better understanding of the pathogenesis of SARS-CoV-2 infection in smokers.