Elevated ACE2 expression in the olfactory neuroepithelium: implications for anosmia and upper respiratory SARS-CoV-2 entry and replication

Abstract

The site of SARS-CoV-2 entry and replication critically impacts strategies for COVID-19 diagnosis, transmission mitigation, and treatment. We determined the cellular location of the SARS-CoV-2 target receptor protein, ACE2, in the human upper airway, finding striking enrichment (200-700 folds) in the olfactory neuroepithelium relative to nasal respiratory or tracheal epithelial cells. This cellular tropism of SARS-CoV-2 may underlie its high transmissibility and association with olfactory dysfunction, while suggesting a viral reservoir potentially amenable to intranasal therapy.

Figure 1.. Cellular location of ACE2 in human olfactory epithelium.

(A and B) Confocal image of ACE2 (red) and Krt18 (green) immunostaining in the healthy control olfactory neuroepithelium. ACE2 is localized to the apical surface of Krt18 positive sustentacular cells in the olfactory epithelium. (C and D) Representative image of ACE2 and Krt18 immunostaining in the olfactory neuroepithelium of a CRS patient. The Boxed area in Panel A and C was highlighted in B and D, respectively. (E and F) The location of ACE2 and DCX positive immature olfactory sensory neurons in control (E) and CRS biopsy (F). (G) The location of ACE2 and PGP9.5 positive mature olfactory sensory neurons in control. (H) Quantification of ACE2 positive cells in olfactory epithelium. Data are represented as mean ± SEM. p value was calculated by unpaired two-tailed Student’s t test (H). Scale bars, 20 μm.

Figure 2.. Elevated ACE2 in olfactory relative to respiratory epithelium.

(A-C) Expression of ACE2 in glands (A) and nasal respiratory epithelium (B and C). The Boxed area in Panel B was highlighted in C. (D) Quantification of the ACE2⁺ cell per mm epithelium. The positive cells in each nasal specimen that contained both respiratory and olfactory epithelium were counted. Dots in graph represent independent specimens. Data are represented as mean ± SEM. p value was calculated by unpaired two-tailed Student’s t test. (E) Representative image of respiratory-olfactory mucosa adjacent area. PGP9.5 and ACE2 co-staining image was obtained using confocal microscope under the tile scan mode. (F) Quantification of the ACE2 fluorescence intensity per μm epithelium using Image J. (G) Co-staining of ACE2 and secretory cell marker Muc5ac in tracheal airway epithelium. The inset represents magnification of the selected area. Scale bars, 20 μm.