The SARS-CoV-2 receptor angiotensin-converting enzyme 2 (ACE2) in myalgic encephalomyelitis/chronic fatigue syndrome: A meta-analysis of public DNA methylation and gene expression data

Abstract

People with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) often report a high frequency of viral infections and flu-like symptoms during their disease course. Given that this reporting agrees with different immunological abnormalities and altered gene expression profiles observed in the disease, we aimed at answering whether the expression of the human angiotensin-converting enzyme 2 (ACE2), the major cell entry receptor for SARS-CoV-2, is also altered in these patients. In particular, a low expression of ACE2 could be indicative of a high risk of developing COVID-19. We then performed a meta-analysis of public data on CpG DNA methylation and gene expression of this enzyme and its homologous ACE protein in peripheral blood mononuclear cells and related subsets. We found that patients with ME/CFS have decreased methylation levels of four CpG probes in the ACE locus (cg09920557, cg19802564, cg21094739, and cg10468385) and of another probe in the promoter region of the ACE2 gene (cg08559914). We also found a decreased expression of ACE2 but not of ACE in patients when compared to healthy controls. Accordingly, in newly collected data, there was evidence for a significant higher proportion of samples with an ACE2 expression below the limit of detection in patients than healthy controls. Altogether, patients with ME/CFS can be at a higher COVID-19 risk and, if so, they should be considered a priority group for vaccination by public health authorities. To further support this conclusion, similar research is recommended for other human cell entry receptors and cell types, namely, those cells targeted by the virus.

Keywords: ACE2; DNA methylation; Gene expression; Myalgic encephalomyelitis/chronic fatigue syndrome; SARS-CoV-2.

Figure 1

DNA methylation analysis of 19 and 8 CpG probes located in the ACE and ACE2 genes, respectively. (A) Minor allele frequency in European and North American populations of SNPs located in the probes under analysis (see the respective data in Supplementary Table 2). (B) Boxplot of all possible Pearson's correlation coefficients (y axis) between the M-values of the probes under analysis. Horizontal dashed line represents the situation of lack of correlation. (C) Adjusted p-values for the overall association between each probe and ME/CFS. Adjusted p-values were calculated according to the Benjamini-Hochberg procedure with a false discovery rate of 5% (dashed line). Grey areas in the plots represent the TSS of the genes. (D) and (E) The same analyses as shown in C but for women and men separately.

Figure 2

Boxplots per study, group and gender of the M-values referring to probes identified in Figures 1C and 1D. (A) Significant probes located in ACE. (B) Significant probe located in ACE2.

Figure 3

Analysis of ACE/ACE2-related data from eligible microarray-based gene expression studies. (A) Boxplots of the data from these studies (Saiki et al (2008), ref. [41]; Gow et al (2009); ref. [43]). (B) Forest plot for the study-specific and pooled estimate of the mean of the log₂(fold-change) between patients with ME/CFS and healthy controls using data shown in A.

Figure 4

Analysis of ACE and ACE2 expression levels from the German study. (A) Violin plots of ACE (left side) and ACE2 (right side) mRNA raw data (upper row) and transformed data using a Box-Cox transformation (lower row). (B) Scatterplot between the transformed ACE and ACE2 expression levels (Spearman's correlation coefficient = -0.120).