Regulation of mRNA transcripts, protein isoforms, glycosylation and spatial localization of ACE2 and other SARS-CoV-2-associated molecules in human airway epithelium upon viral infection and type 2 inflammation

SARS-CoV-2 infection continues to pose a significant life threat, especially in patients with comorbidities. It remains unknown, if asthma or allergen- and virus-induced airway inflammation are risk factors or can constitute some forms of protection against COVID-19. ACE2 and other SARS-CoV-2-related host proteins are limiting factors of an infection, expression of which is regulated in a more complex way than previously anticipated. Hence, we studied the expression of ACE2 mRNA and protein isoforms, together with its glycosylation and spatial localization in house dust mite (HDM)-, interleukin-13 (IL-13)- and human rhinovirus (RV)-induced inflammation in the primary human bronchial airway epithelium of healthy subjects and patients with asthma. IL-13 decreased the expression of long ACE2 mRNA and glycosylation of full-length ACE2 protein via alteration of the N-linked glycosylation process, limiting its availability on the apical side of ciliated cells. RV infection increased short ACE2 mRNA, but it did not influence its protein expression. HDM exposure did not affect ACE2 mRNA or protein. IL-13 and RV significantly regulated mRNA, but not protein expression of TMPRSS2 and NRP1. Regulation of ACE2 and other host proteins was similar in healthy and asthmatic epithelium, underlining the lack of intrinsic differences, but rather the dependence on the inflammatory milieu in the airways.

Epithelial RIG-I inflammasome activation suppresses antiviral immunity and promotes inflammatory responses in virus-induced asthma exacerbations and COVID-19

Rhinoviruses (RV) and inhaled allergens, such as house dust mite (HDM) are the major agents responsible for asthma onset, exacerbations and progression to the severe disease, but the mechanisms of these pathogenic reciprocal virus-allergen interactions are not well understood. To address this, we analyzed mechanisms of airway epithelial sensing and response to RV infection using controlled experimental in vivo RV infection in healthy controls and patients with asthma and in vitro models of HDM exposure and RV infection in primary airway epithelial cells. We found that intranasal RV infection in patients with asthma led to the highly augmented inflammasome-mediated lower airway inflammation detected in bronchial brushes, biopsies and bronchoalveolar lavage fluid. Mechanistically, RV infection in bronchial airway epithelium led to retinoic acid-inducible gene I (RIG-I), but not via NLR family pyrin domain containing 3 (NLRP3) inflammasome activation, which was highly augmented in patients with asthma, especially upon pre-exposure to HDM. This excessive activation of RIG-I inflammasomes was responsible for the impairment of antiviral type I/III interferons (IFN), prolonged viral clearance and unresolved inflammation in asthma in vivo and in vitro. Pre-exposure to HDM amplifies RV-induced epithelial injury in patients with asthma via enhancement of pro-IL1{beta} expression and release, additional inhibition of type I/III IFNs and activation of auxiliary proinflammatory and pro-remodeling proteins. Finally, in order to determine whether RV-induced activation of RIG-I inflammasome may play a role in the susceptibility to severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection in asthma, we analyzed the effects of HDM exposure and RV/SARS-CoV-2 coinfection. We found that prior infection with RV restricted SARS-CoV-2 replication, but co-infection augmented RIG-I inflammasome activation and epithelial inflammation in patients with asthma, especially in the presence of HDM. Timely inhibition of epithelial RIG-I inflammasome activation may lead to more efficient viral clearance and lower the burden of RV and SARS-CoV-2 infections.