The Altered Anatomical Distribution of ACE2 in the Brain With Alzheimer's Disease Pathology

Abstract

The whole world is suffering from the coronavirus disease 2019 (COVID-19) pandemic, induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) through angiotensin-converting enzyme 2 (ACE2). Neurological manifestations in COVID-19 patients suggested the invasion of SARS-CoV-2 into the central nervous system. The present study mapped the expression level of ACE2 in 12 brain regions through immunohistochemistry and detected ACE2 in endothelial cells and non-vascular cells. The comparison among brain regions found that pons, visual cortex, and amygdala presented a relatively high level of ACE2. In addition, this study demonstrates that the protein level of ACE2 was downregulated in the basal nucleus, hippocampus and entorhinal cortex, middle frontal gyrus, visual cortex, and amygdala of the brain with Alzheimer's disease (AD) pathology. Collectively, our results suggested that ACE2 was expressed discriminatorily at different human brain regions, which was downregulated in the brain with AD pathology. This may contribute to a comprehensive understanding of the neurological symptoms caused by SARS-CoV-2 and provide clues for further research on the relationship between COVID-19 and AD.

Keywords: ACE2; Alzheimer’s disease; COVID-19; anatomical distribution; brain regions.

FIGURE 1

Representative images of Alzheimer’s disease (AD)-related pathology. (A) Immunohistochemical detection of β-amyloid plaques using 6F3D antibody in the hippocampus and entorhinal cortex (PTB297). (B) Immunohistochemical detection of neurofibrillary degeneration using a p-Tau antibody (Ser202 and Thr205) in the hippocampus and entorhinal cortex of (PTB 297). (C) Immunohistochemical detection of neuritic plaques in inferior parietal lobule (PTB297). Scale bar = 50 μm.

FIGURE 2

Representative images of ACE2 expression among brain regions. (A) Immunostaining of negative control for ACE2 in the anterior cingulate cortex (PTB270). Scale bar = 100 μm. (B) Immunostaining of ACE2 by Rabbit anti-ACE2 antibody in the anterior cingulate cortex (PTB270). Scale bar = 100 μm. The enlarged views were listed on the right. EC, endothelial cell; NC, non-vascular cell. (C–N) Representative images of ACE2 expression among brain regions in health control. Scale bar = 100 μm. (O) Heatmap showed the average of MOD in each brain region for the five control subjects. The legend scaled the average of MOD.

FIGURE 3

Comparison of ACE2 expression between Control and AD group by heatmap. (A) Heatmap showed the average of MOD in each brain region for the five AD subjects (left panel) and five control subjects (right panel), n = 5, Student’s t-test, *p < 0.05, **p < 0.01, AD vs. Control group. (B) Heatmap showed the number of ACE2 positive non-vascular cell in each brain region for the five AD subjects (left panel) and five control subjects (right panel), n = 5, Student’s t-test, *p < 0.05, **p < 0.01, AD vs. Control group. (C) Percentages of ACE2⁺ non-vascular cells among human brain regions of control and AD. *p < 0.05, AD vs. Control group, Student’s t-test.

FIGURE 4

Downregulated neural ACE2 in hippocampus CA1 and CA4 regions of AD subjects. (A–F) Immunofluorescence staining of ACE2 with neuronal marker NeuN, astrocytic marker GFAP, and microglial marker IBA1 within CA1 region of control and AD subjects. Scale bar = 100 μm. (G) Percentage s of ACE2⁺ cells among NeuN, GFAP, and IBA1 marked cells within CA1 region of control and AD subjects. *p < 0.05, AD vs. Control group, Student’s t-test. (H–M) Immunofluorescence staining of ACE2 with neuronal marker NeuN, astrocytic marker GFAP, and microglial marker IBA1 within CA4 region of control and AD subjects. Scale bar = 100 μm. (N) Percentages of ACE2⁺ cells among NeuN, GFAP, and IBA1 marked cells within CA4 region of control and AD subjects. **p < 0.01, AD vs. Control group, Student’s t-test.