Robust ACE2 protein expression localizes to the motile cilia of the respiratory tract epithelia and is not increased by ACE inhibitors or angiotensin receptor blockers

Abstract

We investigated the expression and subcellular localization of the SARS-CoV-2 receptor, angiotensin-converting enzyme 2 (ACE2), within the upper (nasal) and lower (pulmonary) respiratory tracts of healthy human donors. We detected ACE2 protein expression within the cilia organelle of ciliated airway epithelial cells, which likely represents the initial or early subcellular site of SARS-CoV-2 viral entry during respiratory transmission. We further determined whether ACE2 expression in the cilia of upper respiratory cells was influenced by patient demographics, clinical characteristics, co-morbidities, or medication use, and found no evidence that the use of angiotensin-converting enzyme inhibitors (ACEI) or angiotensin II receptor blockers (ARBs) increases ACE2 protein expression.Coronavirus disease 2019 is an ongoing pandemic infection caused by the positivesense RNA virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) 1 . The high transmissibility of the virus, along with case fatality estimates ranging from 1% to above 5%, has raised concerns worldwide. Patients with comorbid conditions including hypertension, diabetes, and pulmonary disease are highly represented among hospitalized patients with COVID-19 disease, suggesting the presence of risk factors that may determine susceptibility to SARS-CoV-2 infection [2][3][4][5] .A molecular connection between SARS-CoV-2 and hypertension, in particular, is suggested by the discovery that ACE2 is the major essential receptor for SARS-CoV-2 6,7 . ACE2 plays an important role in the renin-angiotensin-aldosterone system (RAAS), which consists of a cascade of vasoactive peptides that maintain blood pressure and electrolyte homeostasis. ACE2 converts vasoconstrictor peptides, angiotensin (Ang) II and Ang I, into the vasodilator peptides, Ang (1-7) and Ang (1-9), respectively 8 . These actions counterbalance the enzymatic effect of the related ACE, which generates angiotensin II from angiotensin I. ACEI and ARBs are commonly used antihypertensive drugs that target components of the RAAS. Several recent correspondences have raised concerns that ACEI and ARBs may increase expression of ACE2 and thereby elevate the risk of infection by SARS-CoV-2, thus potentially explaining why hypertension is a common comorbidity in patients with COVID-19 9-12 . This hypothesis is also rooted in human and rodent studies showing upregulation of ACE2 mRNA in the heart, kidney, and urine after ACEI/ARB administration [13][14][15] . Notably, however, the effects of ACEI and ARBs on the expression of ACE2 in the respiratory tract are currently unknown. Given SARS-CoV-2 causes respiratory infections, whether ACE2 expression is altered in the airway of patients taking ACEI or ARBs is a critical question that needs to be addressed to support continued clinical use of these antihypertensive drugs.We first determined the expression patterns of the ACE2 protein in the upper and lower respiratory tract. Gene expression analyses have identified ACE2 expression in the nasopharynx, oral muc...

SARS-CoV-2 receptor Angiotensin I-Converting Enzyme type 2 (ACE2) is expressed in human pancreatic β-cells and in the human pancreas microvasculature

“…As a positive control for our immunohistochemistry method and ACE2 antibodies adopted, we evaluated FFPE lung tissue sections. As previously shown (7,41,42), we observed scattered positive cells (putatively AT2 pneumocytes) in the alveolar epithelium both using MAB933 and Ab 15348 ( Figure S3A and S3B ). In contrast, we did not observe any signal using Ab108252 ( Figure S3C ).…”

“…On the contrary, by using two different antibodies (MAB933 and Ab15348) - which can recognize the C-terminal domain shared between short- and long-ACE2 - we obtained clear and concordant results, with identification of ACE2 in pancreatic islet endocrine cells in addition to the microvasculature. As a positive control for the antibodies and our IHC procedure, MAB933 and Ab15348 were also tested in FFPE lung tissue sections, showing overlapping results with previously published studies (7,41,42).…”

“…Such subcellular localization was observed both in-vitro in EndoC-βH1 and ex vivo in β-cells of primary human pancreatic tissues. Although ACE2 has been primarily observed on cell surfaces (42,79), some studies also described ACE2 granular localization in other cell types of epithelial origin (9,80). A similar intracellular localization and putative trafficking was observed for the viral receptor CAR-SIV (78), also expected to be mainly localized on the cell membrane.…”

ACE2 and SARS-CoV-2 Expression in the Normal and COVID-19 Pancreas

“…In our hands, all four antibodies demonstrated robust and essentially commensurate staining in human duodenum and kidney FFPE sections ( Fig. S2D), consistent with (Hikmet et al, 2020;Lee et al, 2020a).…”

“…In contrast, an analysis of tissue microarrays containing pancreatic FFPE sections from 10 donors (aged 30-79 years) utilizing two ACE2 antibodies (MAB933 and HPA000288) reported ACE2 expression restricted to endothelial cells/pericytes and interlobular ducts while ACE2 was not detectable in islets, acinar glandular cells, intercalated ducts, or intralobular ducts (Hikmet et al, 2020). This study, together with a preprint employing six ACE2 antibodies (Lee et al, 2020a), is noteworthy for the broad range of major human tissues and organs investigated as well as the delineation of mostly shared but also, some distinctive ACE2 antibody staining properties. In light of these diverging observations, it is imperative to utilize multiple ACE2 antibodies on larger donor cohorts to gather a comprehensive description of ACE2 expression in the pancreas.…”