Epigenetic mechanisms and host factors impact ACE2 gene expression: Implications in COVID-19 susceptibility

Abstract

Background: The ACE2 protein acts as a gateway for SARS-CoV-2 in the host cell, playing an essential role in susceptibility to infection by this virus. Genetics and epigenetic mechanisms related to the ACE2 gene are associated with changes in its expression and, therefore, linked to increased susceptibility to infection. Although some variables such as sex, age, and obesity have been described as risk factors for COVID-19, the molecular causes involved in the disease susceptibility are still unknown.

Aim: To evaluate the ACE2 gene expression profiles and their association with epigenetic mechanisms and demographic or clinical variables.

Methods: In 500 adult volunteers, the mRNA expression levels of the ACE2 gene in nasopharyngeal swab samples and its methylation status in peripheral blood samples were quantified by RT-qPCR and qMSP, respectively. The existence of significant differences in the ACE2 gene expression and its determinants were evaluated in different study groups according to several demographic or clinical variables such as sex, age, body mass index (BMI), smoking, SARS-CoV-2 infection, and presence of underlying diseases such as type II diabetes mellitus (DM2), asthma and arterial hypertension (AHT).

Results: Our results show that ACE2 gene overexpression, directly involved in susceptibility to SARS-CoV-2 infection, depends on multiple host factors such as male sex, age over 30 years, smoking, the presence of obesity, and DM2. Likewise, it was determined that the ACE2 gene expression is regulated by changes in the DNA methylation patterns in its promoter region.

Conclusions: The ACE2 gene expression is highly variable, and this variability is related to habits such as smoking and demographic or clinical variables, which details the impact of environmental and host factors on our epigenome and, therefore, in susceptibility to SARS-CoV-2 infection.

Keywords: Angiotensin-converting enzyme 2; COVID-19; Disease susceptibility; Epigenetics; Host factors; SARS-CoV-2.

Fig. 1

ACE2 gene expression levels differ by sex (A.) ACE2 mRNA expression levels across the studied population (n = 500). (B.) Comparison of ACE2 mRNA expression levels by sex. Patients with comorbidities or smoking history were excluded from the analysis and were matched by age and BMI to avoid bias. Data is presented as median and 95% CI of each group, and significance p-values are showed as * = p < 0.05; ** = p < 0.01; *** = p < 0.001; **** = p < 0.0001.

Fig. 2

ACE2 gene expression levels differ by age. (A.) Comparison of ACE2 mRNA expression levels by age-groups consistent with those defined and used across CDC COVID-19 surveillance pages. (B.) Age distribution comparison in population with high and low ACE2 gene expression levels. (C.) Spearman correlation of ACE2 mRNA expression levels and age. Patients with comorbidities or smoking history were excluded from the analysis to avoid bias. Data is presented as median and 95% CI of each group, and significance p-values are showed as * = p < 0.05; ** = p < 0.01; *** = p < 0.001; **** = p < 0.0001.

Fig. 3

ACE2 gene is overexpressed in smokers. Comparison of ACE2 gene mRNA expression levels in smokers against non-smokers matched by age, sex, and BMI. Patients with comorbidities were excluded from the analysis and to avoid bias. Data is presented as median and 95% CI of each group, and significance p-values are showed as * = p < 0.05; ** = p < 0.01; *** = p < 0.001; **** = p < 0.0001.

Fig. 4

ACE2 gene is overexpressed in obese subjects. (A.) Comparison of the mRNA expression levels of ACE2 gene by BMI category in the entire population and (B.) matched analysis of obesity and normal weight BMI categories. (C.) BMI distribution comparison in population within the different ACE2 gene expression categories. (D.) Spearman correlation of ACE2 mRNA expression levels and BMI. Patients with comorbidities or smoking history were excluded from all analysis and were matched by age, sex, and BMI in (B.) to avoid bias. Data is presented as median and 95% CI of each group, and significance p-values are showed as * = p < 0.05; ** = p < 0.01; *** = p < 0.001; **** = p < 0.0001.

Fig. 5

ACE2 gene expression profiles associated with certain diseases. (A.) Comparison of ACE2 gene mRNA expression levels in patients with type II diabetes mellitus, (B.) asthma and (C.) arterial hypertension against matched subjects. (D.) Comparison of ACE2 gene mRNA expression levels in hypertensive patients by treatment type. Subjects were matched by age, sex, and BMI. Also, patients with comorbidities or smoking history were excluded from the analysis to avoid bias. Data is presented as median and 95% CI of each group, and significance p-values are showed as * = p < 0.05; ** = p < 0.01; *** = p < 0.001; **** = p < 0.0001.

Fig. 6

Differences of ACE2 gene expression profiles in COVID-19 patients. Comparison of ACE2 mRNA expression levels in patients infected by SARS-CoV-2 against closely exposed non-infected matched subjects. Patients with comorbidities, vaccinated, or smoking history were excluded from the analysis and were matched by age, sex, and BMI to avoid bias. Data is presented as median and 95% CI of each group, and significance p-values are showed as * = p < 0.05; ** = p < 0.01; *** = p < 0.001; **** = p < 0.0001.

Fig. 7

ACE2 gene expression is regulated by DNA methylation. (A.) Relative methylation percentages of the ACE2 gene promoter in subjects with high and low levels of ACE2 expression. (B.) Spearman's correlation between relative methylation levels of the ACE2 gene promoter and ACE2 mRNA expression. (C.) Comparison of relative methylation levels of the ACE2 gene promoter in female and male subjects. Significance p-values are shown as * = p < 0.05; ** = p < 0.01; *** = p < 0.001; **** = p < 0.0001.