ACE2 expression is elevated in airway epithelial cells from older and male healthy individuals but reduced in asthma

Abstract

Background and objective: COVID-19 is complicated by acute lung injury, and death in some individuals. It is caused by SARS-CoV-2 that requires the ACE2 receptor and serine proteases to enter AEC. We determined what factors are associated with ACE2 expression particularly in patients with asthma and COPD.

Methods: We obtained lower AEC from 145 people from two independent cohorts, aged 2-89 years, Newcastle (n = 115) and Perth (n = 30), Australia. The Newcastle cohort was enriched with people with asthma (n = 37) and COPD (n = 38). Gene expression for ACE2 and other genes potentially associated with SARS-CoV-2 cell entry was assessed by qPCR, and protein expression was confirmed with immunohistochemistry on endobronchial biopsies and cultured AEC.

Results: Increased gene expression of ACE2 was associated with older age (P = 0.03) and male sex (P = 0.03), but not with pack-years smoked. When we compared gene expression between adults with asthma, COPD and healthy controls, mean ACE2 expression was lower in asthma patients (P = 0.01). Gene expression of furin, a protease that facilitates viral endocytosis, was also lower in patients with asthma (P = 0.02), while ADAM-17, a disintegrin that cleaves ACE2 from the surface, was increased (P = 0.02). ACE2 protein expression was also reduced in endobronchial biopsies from asthma patients.

Conclusion: Increased ACE2 expression occurs in older people and males. Asthma patients have reduced expression. Altered ACE2 expression in the lower airway may be an important factor in virus tropism and may in part explain susceptibility factors and why asthma patients are not over-represented in those with COVID-19 complications.

Keywords: COVID-19; SARS-CoV-2; bronchial asthma; chronic obstructive pulmonary disease; coronavirus disease; pandemic; viral infections.

Figure 1

All values are represented individually. The mean and SD are also presented. Differences between the groups were assessed using one‐way analysis of variance (ANOVA), with Dunnett's multiple comparison test. If the ANOVA was significant (P < 0.05), the P‐values are labelled for the group that is different from the healthy controls.

Figure 2

(A) Data from the Newcastle cohort (n = 116), a two‐way comparison between angiotensin‐converting enzyme 2 (ACE2) expression and age. The univariate correlation was measured using Pearson's correlation coefficient with a two‐sided test for significance. (B) Same data with subjects divided by age group. The mean and SD are represented. Differences between the two groups were analysed using an unpaired t‐test.

Figure 3

Data represent angiotensin‐converting enzyme 2 (ACE2) gene expression seen in airway epithelial cells (AEC) from Perth adults (n = 16), Perth children (n = 14), Newcastle adult healthy controls (n = 40) and Newcastle asthma (n = 37). Differences between the groups were assessed using one‐way analysis of variance (ANOVA), with Dunnett's multiple comparison test.

Figure 4

(A–C) Representative immunofluorescent images of formalin‐fixed paraffin‐embedded endobronchial sections showing protein expression of CADHERIN1 (green) and angiotensin‐converting enzyme 2 (ACE2) (red) in healthy controls (HC) (A) under 40 years compared to (B) a HC over 40 years and (C) a participant with asthma (aged 49 years). (D–F) Representative images of endobronchial biopsies stained for ACE2. The images (D) show HC compared to patients with (E) asthma and (F) chronic obstructive pulmonary disease (COPD) (magnification, ×40). (G) The percentage (%) of ACE2 expression measured in the epithelium of HC compared to patients with asthma and COPD. Patients with asthma had significantly lower ACE2 expression compared to HC and COPD patients. There appeared to be a trend for COPD airway cells to have a higher expression compared to HC, this just failed to be significant.