The SARS-CoV-2 receptor angiotensin-converting enzyme 2 (ACE2) in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: analysis of high-throughput epigenetic and gene expression studies.
Are people with ME/CFS at higher risk of complications from COVID infection? A recent publication by Malato et al. carried out using ME/CFS patients from Germany has shown that this could be the case.
Due to the complex nature of this paper, we have divided this research review into sections, where a basic understanding can be gained in the first section, and a deeper scientific understanding can be gained from reading on.
What are the basics in this study?
- The etiology (the cause) of ME/CFS remains largely unknown, but many patients report an infection which triggers the onsets.
- There is growing evidence of the overlap in symptoms of ME/CFS and long-COVID, such as persisting fatigue and post-exertional malaise (PEM) leading to more studies about the two conditions.
- Evolving technologies have allowed more detailed research into gene expressions in diseases, which produces large amounts of data.
- An unbalance in certain enzymes in the body can lead to different diseases and also increase the potential for “catching” viruses, such as COVID-19.
- This study looked at one particular enzyme, ACE2, which is the key receptor enzyme used by COVID-19 to enter human cells.
- The key finding of this study was a decreased gene expression of ACE2 in patients with ME/CFS compared to healthy controls, which could mean a could be at a higher risk of developing severe symptoms of COVID-19.
- It is hoped that this study could help to improve the understanding of the health risk imposed by the COVID-19 virus when infecting patients affected by ME/CFS.
What is the background?
Previous studies on ME/CFS have shown that patients have different gene expressions compared to healthy controls (Kerr, 2008; Almenar-Pérez et al., 2019; Dibble et al., 2020), however, it is not known whether these changes affect certain key enzymes in the body.
This paper looked at two enzymes called ACE and ACE2 (human angiotensin-converting enzymes). The enzyme ACE2 is of significant importance due to it being found to be the main receptor used by the virus COVID-19 (SARS-CoV2) to enter human cells.
There is a complex relationship between these two enzymes and COVID-19:
- The failure in the body to balance the ratio between the amount of these two enzymes ACE and ACE2 can lead to hypertension and cardiovascular diseases, which is also thought to play a key part in COVID-19.
- It has also been found that ACE2-deficient individuals also seem to be at a higher risk of COVID-19, because viral entry typically induces a downregulation of this enzyme, which ultimately affects its balance with ACE.
Patients with ME/CFS are often found to have an unbalanced immune system. Previous studies have suggested that the ACE enzyme could provide a potential biomarker with the ACE enzyme being elevated in 80% of patients (Lieberman and Bell, 1993). This study looked at increasing our knowledge of the role of the ACE2 enzyme as little is known about its role in ME/CFS to date.
What do some of the key scientific terms mean in this paper?
- Gene expression is the amount of transcription of a gene that can be found in a biological sample at the time of sample collection.
- Gene expression is affected by both genetic variation and epigenetic modifications.
- Genetic variation relates to changes in the nucleotide sequence of the gene.
- Epigenetic modifications refer to all the additional changes that occurs from the translation of the encoding nucleotide sequence into the respective encoded protein.
- DNA methylation is an epigenetic modification in which a chemical called methyl is added to pairs of cytosine/guanine nucleotides present along the human genome.
DNA methylation is of particular importance. The pairs of cytosine/guanine in the adjacent nucleotide sequence of a gene makes the opening of the respective chromosomes more difficult for the respective gene translation. Hence, low methylation levels (hypomethylation) of these pairs typically indicate an easiness to express a gene by a given cell, whilst high methylation levels (hypermethylation) pairs indicate the opposite.
Previous studies investigated the expression and DNA methylation of all the genes present in the human genome in patients with ME/CFS and healthy controls. They found that, when compared to healthy controls, patients have altered expression of different genes and methylation levels of these cytosine/guanine pairs located in specific positions of the genome (de Vega et al., 2014; Triveda et al., 2018; Helliwell et al., 2020).
However, we do not know whether these alterations could include the ACE2 enzyme, which is the receptor used by SARS-CoV2 to enter the human cells. In particular, low levels of ACE2 in patients could imply a higher risk of developing severe symptoms of COVID-19.
What was investigated?
The study used DNA methylation and gene expression data from published studies and focused their analysis on ACE2 and its related enzyme, ACE.
The study aimed to compare the gene expression and DNA methylation levels of these two enzymes between patients and healthy controls.
To complement the analysis, they collected samples from German women with ME/CFS and matched healthy controls and measured the levels of ACE and ACE2 in these samples.
What are the main findings of this study?
The study found increased DNA methylation levels of a pair of cytosine/guanine adjacent to the nucleotide sequence in ACE2 using published data from 4 DNA methylation studies. This suggested an increased expression of ACE2.
However, when the research group conducted a joint analysis of data from published gene expression studies, they found a decreased gene expression of ACE2 in patients with ME/CFS than in healthy controls. Along with similar evidence in data from the German cohort where many samples from patients had an ACE2 expression below the detection level.
What are the implications of this research?
If patients with ME/CFS have a decreased expression of ACE2, then they could be at a higher risk of developing severe symptoms of COVID-19. As a possible implication, patients with ME/CFS alongside patients of other diseases but with comorbidities affecting ACE2 levels could be considered a priority group for vaccination.
However, caution should be taken with these results as vaccination could trigger ME/CFS and it could also aggravate the ME/CFS-related symptoms in a natural infection by SARS-CoV-2.
More about the ME Association communities experience on vaccination can be found here.
Furthermore, as the authors comments, that the findings of this study could be improve with making data more publicly available along investigations such as this study.
“It could also promote collaboration among researchers, and to make science open to everyone, specifically, when it is funded by taxpayers and charities. Data sharing is also essential to cut down the costs of research by sharing resources among the research community. Reducing the costs of research by sharing limited resources is particularly important for the underfunded ME/CFS research field, as alluded above.”
What are the next steps from the findings in this research?
The next step is to perform similar analysis on other receptors used by SARS-CoV-2 to invade human cells.
Examples of these alternative receptors are: (i) the human transmembrane protease serine 2 (TMPRSS2); (ii) the A disintegrin and metallopeptidase domain 17 protein (ADAM17) recognized by the immune system as a stress-response signal, and (iii) Dipeptidyl peptidase-4 (DPP4 known to be the main receptor for the Middle East respiratory syndrome–related coronavirus.
The first author of this paper and PhD student João Malato might perform this follow-up analysis. Given that the study was based on analysis on data from peripheral blood mononuclear cells, it would be also interesting to study different cell types, namely, those mainly targeted by the virus (e.g., pulmonary epithelial and endothelial cells).
What are the limitations of the findings in this research?
The authors from the study say:
“This was an opportunistic study and, as such, we could only analyse data derived from peripheral blood mononuclear cells (e.g., T and B cells, monocytes, macrophages, and dendritic cells) – because they are easily collected. We should emphasize these cells are not the primary targets of SARS-CoV-2 and therefore, our findings may not reflect what is happening in cells of the lungs and other organs affecting by a SARS-CoV2 infection. Another limitation is that most of published gene expression studies did not deposit their data in any public database. Therefore, we could not analyse data from many different studies that could strengthen our findings.”
What are the authors connections to ME/CFS?
“I was the Portuguese representative and a member of the managing committee in the EUROMENE network. I was also working as an Assistant Professor at the London School of Hygiene & Tropical when I started a close collaboration with the CureME group led by Dr Eliana Lacerda and Luis Nacul and the United Kingdom ME/CFS biobank. I am actively collaborating with Prof Carmen Scheibenbogen and Dr Eliana Lacerda in a project about EBV immune responses funded by ME Research UK. I am also collaborating with Dr Francisco Westermeier in endothelial function in ME/CFS. I also started a ME/CFS-related project on the impact of viral infections on genes related to circadian rhythm. More information about this is available on the research group’s webpage.”Professor Nuno Sepúlveda
“I am post-doctorate researcher in the working group of Prof. Carmen Scheibenbogen at the Charité Universitätsmedizin Berlin (Germany). I am currently working on several research projects on autoimmunity/autoantibodies and endothelial function in ME/CFS. Among others, I also support the collaboration project about EBV immune responses funded by ME Research UK.”Dr Franziska Sotzny
Almenar-Pérez E, Ovejero T, Sánchez-Fito T, Espejo JA, Nathanson L, Oltra E. (2019) Epigenetic Components of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Uncover Potential Transposable Element Activation. Clinical Therapeutics 41 (4): 675-698. Link: https://pubmed.ncbi.nlm.nih.gov/30910331/
Dibble JJ, McGrath SJ, Ponting CP. (2020) Genetic risk factors of ME/CFS: a critical review. Human Molecular Genetics 29 (R1): R117-R124. Link: https://pubmed.ncbi.nlm.nih.gov/32744306/
Helliwell AM, Sweetman EC, Stockwell PA, Edgar CD, Chatterjee A, Tate WP. (2020) Changes in DNA methylation profiles of myalgic encephalomyelitis/chronic fatigue syndrome patients reflect systemic dysfunctions. Clinical Epigenetics 12 (1): 167. Link: https://pubmed.ncbi.nlm.nih.gov/33148325/
Kerr JR. (2008) Gene profiling of patients with chronic fatigue syndrome/myalgic encephalomyelitis. Current Rheumatology Reports 10 (6): 482-91. Link: https://pubmed.ncbi.nlm.nih.gov/19007540/
Lieberman J and Bell DS (1993) Serum angiotensin-converting enzyme as a marker for the chronic fatigue-immune dysfunction syndrome: a comparison to serum angiotensin-converting enzyme in sarcoidosis. The American Journal of Medicine 95 (4): 407-12. Link: https://pubmed.ncbi.nlm.nih.gov/8213873/
Trivedi MS, Oltra E, Sarria L, Rose N, Beljanski V, Fletcher MA, Klimas NG, Nathanson L. (2018) Identification of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome-associated DNA methylation patterns. PLoS One 13 (7): e0201066. Link: https://pubmed.ncbi.nlm.nih.gov/30036399/
de Vega WC, Vernon SD, McGowan PO. (2014) DNA methylation modifications associated with chronic fatigue syndrome. PLoS One 9 (8): e104757. Link: https://pubmed.ncbi.nlm.nih.gov/25111603/