ACE2, TMPRSS2, and furin gene expression in the airways of people with asthma—implications for COVID-19
Authors: Peter Bradding, Matthew Richardson, Timothy S.C. Hinks, Peter H. Howarth, David F. Choy, Joseph R. Arron, Sally E. Wenzel, Salman Siddiqui
Journal: Journal of Allergy and Clinical Immunology (2020)

Coronavirus disease 2019 (COVID-19) is caused by a novel zoonotic coronavirus known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has been identified as a pandemic by the World Health Organization. Several risk factors have been identified for severe COVID-19–associated pneumonia including increased age and the presence of comorbidities, in particular diabetes, cardiovascular disease, and tobacco smoking.1Zhou F. Yu T. Du R. Fan G. Liu Y. Liu Z. et al.Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study.Lancet. 2020; 39: 1054-1062Abstract Full Text Full Text PDF Scopus (18962) Google Scholar However, a number of reports have failed to identify excess risk in patients with respiratory airway diseases such as asthma.2Zhang JJ, Dong X, Cao YY, Yuan YD, Yang YB, Yan YQ, et al. Clinical characteristics of 140 patients infected with SARS-CoV-2 in Wuhan, China [published online ahead of print February 19, 2020]. Allergy https://doi.org/10.1111/all.14238.Google Scholar SARS-CoV-2 infects people by binding to the angiotensin-converting enzyme 2 (ACE2) receptor, a transmembrane endopeptidase that cleaves both angiotensin 1 and 2, and which is expressed by epithelial cells in several organs including the airways. Cofactors facilitating SARS-CoV-2 infectivity are the transmembrane peptidase serine 2 (TMPRSS2), which cleaves the SARS-CoV-2 spike protein, and possibly the protease furin.3Lukassen S. Chua R.L. Trefzer T. Kahn N.C. Schneider M.A. Muley T. et al.SARS-CoV-2 receptor ACE2 and TMPRSS2 are primarily expressed in bronchial transient secretory cells.EMBO J. 2020; 39e105114Crossref PubMed Scopus (715) Google Scholar Understanding the expression of ACE2, TMPRSS2, and furin in the airways of people with asthma may help determine whether asthma itself or treatment with inhaled or oral corticosteroids may alter susceptibility to SARS-CoV-2 infection and potentially related disease severity. We have therefore explored the RNA expression of ACE2, TMPRSS2, and furin in human bronchial brushes and biopsies from previously described cohorts of people with asthma of varying corticosteroid treatment intensity (as an index of severity) and healthy controls. Airway brushes and biopsies were collected at bronchoscopy with written informed consent and ethical approvals. Airway brushes were placed into RNAprotect and airway biopsies from the second- to fifth-generation airways were placed into RNAlater. Bronchial brush ACE2 expression data were available from 356 patients (88 healthy volunteers and 268 patients with asthma [mild to moderate asthma, 125; severe asthma, 143]), across 5 asthma/healthy volunteer cohorts, Leicester, UK (n = 34),4Choy D.F. Hart K.M. Borthwick L.A. Shikotra A. Nagarkar D.R. Siddiqui S. et al.Th2 and Th17 inflammatory pathways are reciprocally regulated in asthma.Sci Transl Med. 2015; 7301ra129Crossref PubMed Scopus (388) Google Scholar the multicenter Bronchoscopic Exploratory Research Study of Biomarkers in Corticosteroid-refractory Asthma (n = 54),5Jia G. Erickson R.W. Choy D.F. Mosesova S. Wu L.C. Solberg O.D. et al.Periostin is a systemic biomarker of eosinophilic airway inflammation in asthmatic patients.J Allergy Clin Immunol. 2012; 130: 647-654Abstract Full Text Full Text PDF PubMed Scopus (514) Google Scholar the Severe Asthma Research Program cohort (n = 154),6Modena B.D. Bleecker E.R. Busse W.W. Erzurum S.C. Gaston B.M. Jarjour N.N. et al.Gene expression correlated with severe asthma characteristics reveals heterogeneous mechanisms of severe disease.Am J Respir Crit Care Med. 2017; 195: 1449-1463Crossref PubMed Scopus (116) Google Scholar and Southampton, UK (n = 114).7Singhania A. Wallington J.C. Smith C.G. Horowitz D. Staples K.J. Howarth P.H. et al.Multitissue transcriptomics delineates the diversity of airway T cell functions in asthma.Am J Respir Cell Mol Biol. 2018; 58: 261-270Crossref PubMed Scopus (79) Google Scholar,8Singhania A. Rupani H. Jayasekera N. Lumb S. Hales P. Gozzard N. et al.Altered epithelial gene expression in peripheral airways of severe asthma.PLoS One. 2017; 12e0168680Crossref PubMed Scopus (45) Google Scholar Bronchial biopsy ACE2 expression data (n = 94) were available in 17 healthy volunteers and 77 patients with asthma from the Leicester and Bronchoscopic Exploratory Research Study of Biomarkers in Corticosteroid-refractory Asthma cohorts. For bronchial brush data, the 5 data sets were combined into a single data set after first adjusting for batch effects by separately mean centering each of the 5 data sets. The same method was applied to the biopsy data. The Wilcoxon rank-sum test and the Kruskal-Wallis test were used to test for between-group differences in ACE2 expression. The Spearman rank correlation was used when reporting correlations. All analyses were performed using R statistics, version 3.6.0, and figures were generated in GraphPad Prism 8.1.2 (GraphPad Software, San Diego, Calif). The clinical characteristics of the participants (median [Q1:3]) for healthy volunteers versus people with asthma were respectively as follows: age—25 (22-34) versus 40 (27-49) years, FEV1% predicted—101 (93-109) versus 71.5 (58-88), and FEV1/forced vital capacity—82 (78-85) versus 72 (62-79). Overall, there was no difference for ACE2, TMPRSS2, or furin mRNA expression between people with asthma compared with healthy controls (P = .96), no significant differences in ACE2 expression between males and females, and no correlation between ACE2 gene expression and age (data not shown). There were no differences in ACE2, TMPRSS2, or furin gene expression between healthy volunteers and people with mild to moderate and severe asthma (Fig 1, A-C). ACE2, TMPRSS2, or furin gene expressions were not correlated. There were weak but highly significant inverse and positive correlations between ACE2 expression and the expression of TH2-dependent and IL-17 (TH17)-dependent epithelial gene signatures, respectively, defined as previously4Choy D.F. Hart K.M. Borthwick L.A. Shikotra A. Nagarkar D.R. Siddiqui S. et al.Th2 and Th17 inflammatory pathways are reciprocally regulated in asthma.Sci Transl Med. 2015; 7301ra129Crossref PubMed Scopus (388) Google Scholar (Fig 1, D and E). Similar observations were noted in bronchial biopsies, with no differences in ACE2 gene expression between healthy volunteers and patients with mild to moderate asthma and patients with severe asthma (P = .43) (not shown). These data would suggest that differences in ACE2, TMPRSS2, and furin epithelial and airway gene expression are unlikely to confer enhanced COVID-19 pneumonia risk in patients with asthma across all treatment intensities and severity. It is therefore possible that the risk of severe COVID-19 pneumonia is no greater than the background population risk in patients with asthma in the absence of other known risk factors such as diabetes and cardiovascular disease. This would support current guidance on the use of inhaled steroids and rescue prednisolone in patients with asthma who experience exacerbations during the COVID-19 pandemic. A previous mouse model of infection demonstrated that ACE2 inhibits neutrophil infiltration and lung inflammation by limiting IL-17 signaling by reducing the activity of the signal transducer and activator of transcription 3 pathway.9Sodhi C.P. Nguyen J. Yamaguchi Y. Werts A.D. Lu P. Ladd M.R. et al.A dynamic variation of pulmonary ACE2 is required to modulate neutrophilic inflammation in response to Pseudomonas aeruginosa lung infection in mice.J Immunol. 2019; 203: 3000-3012Crossref PubMed Scopus (76) Google Scholar However, our observations in bronchial brush airway epithelial cells identified a positive correlation between ACE2 gene expression and a previously described IL-17–dependent gene expression signature, with an inverse association with TH2 gene expression. It is possible that ACE2 protein expression in the airways might not mirror the RNA expression, which is a limitation of our study. Furthermore, the precise relationship between other host immunoregulatory factors that may modify the risk of severe COVID-19 pneumonia and asthma, as well as corticosteroid exposure, which may induce TH17 immunity in asthma, have not been examined here directly. However, our data are in keeping with a recent report demonstrating that in nasal brushings from children, ACE2 expression was inversely correlated with markers of type 2 immunity, with no influence of sex or use of nasal corticosteroids.10Jackson D.J. Busse W.W. Bacharier L.B. Kattan M. O'Connor G.T. Wood R.A. et al.Association of respiratory allergy, asthma and expression of the SARS-CoV-2 receptor, ACE2.J Allergy Clin Immunol. 2020; 146: 203-206Abstract Full Text Full Text PDF PubMed Scopus (426) Google Scholar In the same article, it was shown that segmental bronchial allergen challenge in adults with mild asthma led to decreases in ACE2 expression, and that IL-13 reduces ACE2 expression on cultured bronchial epithelial cells. In summary, these data suggest that it will be important to understand further the effects of TH2 and IL-17–driven inflammation, and of inhaled corticosteroids on airway epithelial cell ACE2 expression, and the susceptibility of these cells to infection and replication by SARS-CoV-2.