Regulation of gene expression involves mechanisms that control the intensity and mode of gene activity under given conditions. In a complex multicellular organism, each stage in the development of the organism, as well as the type of tissue, is characterized by the presence of specific proteins in the cell. The diversity of cells of a multicellular organism is primarily a consequence of differences in the number and type of synthesized proteins - gene products. This means that the activity of genes in different cells and at different stages of development of the organism is different and strictly controlled. Every step in gene expression, from DNA molecules to the formation of a functional protein, is controlled by the mechanisms of gene expression regulation.
Epigenetic modifications are inheritable changes in gene expression that do not involve changes in the nucleotide sequence of DNA, but are based on changes in chromatin structure. One of the main mechanisms of epigenetic regulation in eukaryotes is DNA methylation, which represents the process leading to the addition of a methyl group onto the fifth carbon of a cytosine located in CpG motifs. Modifications at regulatory regions, particularly within gene promoters, correlate well with the transcriptional state of a gene: hyper-methylation represses transcription, while hypo-methylation can lead to increased transcription levels. About 80% of CpGs in the genome of mammals are methylated, and this epigenetic mark is generally associated to gene repression and heterochromatin condensation.
Many viruses have developed mechanisms that alter regulatory machinery of the host epigenome, resulting in regulated changes in host gene expression and the creation of favourable conditions for virus replication and spread. Coronaviruses target epigenetic molecular networks during virus-host interactions, providing further risk factors for virus shedding and inadequate host response. To investigate methylation status of genes of interest, and its potential COVID-19-related alterations, the extent of methylation will be determined in promoter regions using bisulfite conversion and subsequent high-resolution melting (HRM) analysis will be performed in DNA isolated from nasal swabs for ACE2, TMPRSS2, FUR, and CTSL genes, and DNA blood samples for TLR3, TLR7, RIG-1, CD14, IFNλ3, IFNλ4, OAS1, IFITM3, TNF, IL6, IL10, CCL2, CCL5, CCR5, FCGR2A, and MAP1LC3B genes. Global genome methylation status will be assessed using high performance liquid chromatography with ultraviolet detection (HPLC-UV) in DNA isolated from blood samples.
