Whole-Blood Methylation Analysis Reveals Respiratory Environmental Functional Pathways Involved in Severity Following SARS-CoV-2 Infection (preprint)

SARS-CoV-2 causes a severe inflammatory syndrome called COVID-19 that primarily affects the lungs leading, in many cases, to bilateral pneumonia, severe dyspnea and in ~5% of the cases, death. The mechanisms through which this occurs are still being elucidated. A strong relationship between COVID-19 progression and autoimmune disorder pathogenesis has been identified as an exacerbated interferon immune response or an inflammatory condition mediated by an increase of pro-inflammatory cytokine production, among other. DNA methylation is known to regulate immune response processes, thus COVID-19 progression might be also conditioned by DNA methylation changes not studied in depth, yet. Thus, here an epigenome-wide DNA methylation analysis combined with DNA genotyping for 101 and 473 SARS-CoV-2 negative and positive lab tested individuals, respectively, from two different clinical centers is presented in order to evaluate the implications of the epigenetic regulation in the course of COVID-19 disease. The results reveal the existence of an epigenome regulation of functional pathways associated with the COVID-19 progression, such as innate interferon responses, hyperactivation of B and T lymphocytes, phagocytosis and innate C-type lectin DC-SIGN. These DNA methylation changes were found to be regulated by genetic loci associated with COVID-19 susceptibility and autoimmune disease. In mild COVID-19 patients hypomethylation of CpGs regulating genes within the AKT signaling pathway, and the hypermethylation of a group of CpGs related to environmental traits regulating IL-6 expression via the transcription factor CEBP, discriminate these individuals from those who develop the most critical outcomes of the disease. Thus, the analysis points out to an environmental contribution that mediated by DNA methylation changes in SARS-CoV-2 positive patients, might be playing a role in triggering the cytokine storm described in the most severe cases. In addition, important differences were found in terms of epigenetic regulation between severe and mild cases when compared with systemic autoimmune diseases.

Cytotoxic lymphocytes are dysregulated in multisystem inflammatory syndrome in children (preprint)

Multisystem inflammatory syndrome in children (MIS-C) presents with fever, inflammation and multiple organ involvement in individuals under 21 years following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. To identify genes, pathways and cell types driving MIS-C, we sequenced the blood transcriptomes of MIS-C cases, pediatric cases of coronavirus disease 2019, and healthy controls. We define a MIS-C transcriptional signature partially shared with the transcriptional response to SARS-CoV-2 infection and with the signature of Kawasaki disease, a clinically similar condition. By projecting the MIS-C signature onto a co-expression network, we identified disease gene modules and found genes downregulated in MIS-C clustered in a module enriched for the transcriptional signatures of exhausted CD8+ T-cells and CD56dimCD57+ NK cells. Bayesian network analyses revealed nine key regulators of this module, including TBX21, a central coordinator of exhausted CD8+ T-cell differentiation. Together, these findings suggest dysregulated cytotoxic lymphocyte response to SARS-Cov-2 infection in MIS-C.

SARS-CoV-2 causes severe alveolar inflammation and barrier dysfunction (preprint)

Infections with SARS-CoV-2 lead to mild to severe coronavirus disease-19 (COVID-19) with systemic symptoms. Although the viral infection originates in the respiratory system, it is unclear how the virus can overcome the alveolar barrier, which is observed in severe COVID-19 disease courses. To elucidate the viral effects on the barrier integrity and immune reactions, we used mono-cell culture systems and a complex human alveolus-on-a-chip model composed of epithelial, endothelial, and mononuclear cells. Our data show that SARS-CoV-2 efficiently infected epithelial cells with high viral loads and inflammatory response, including the interferon expression. By contrast, the adjacent endothelial layer was no infected and did neither show productive virus replication or interferon release. With prolonged infection, both cell types are damaged, and the barrier function is deteriorated, allowing the viral particles to overbear. In our study, we demonstrate that although SARS-CoV-2 is dependent on the epithelium for efficient replication, the neighboring endothelial cells are affected, e.g., by the epithelial cytokine release, which results in the damage of the alveolar barrier function and viral dissemination.