Regulation of Il6 expression by single CpG methylation in downstream of Il6 transcription initiation site

The innate immune system is an immediate defense against infectious pathogens by the production of inflammatory cytokines and other mediators. Deficiencies of epigenetic regulatory enzymes, such as Tet1 and Dnmt1, cause dysregulation of cytokine expression. However, it is unclear if DNA methylation at a single CpG dinucleotide in a specific gene locus can regulate gene expression. In this study, we demonstrated that CpG+286 and CpG+348 in exon 2 of the Il6 gene are similar in various primary mouse cells. In lipopolysaccharide-stimulated condition, hypomethylated CpG+286 promoted Il6 expression whereas deletion of CpG+348 led to a reduction in Il6 expression associated with enhanced CTCF binding to the Il6 locus. Moreover, hypomethylation at CpG+286 in alveolar macrophages from aged mice led to higher Il6 expression in response to LPS compared with young mice. Thus, DNA methylation at specific CpG dinucleotides plays an important regulatory role in Il6 expression.