Epigenetic mechanisms play a crucial role in the regulation of gene expression. The underlying mechanisms include DNA methylation and covalent modification of histones by methylation, acetylation, phosphorylation, or ubiquitination. The complex interplay of various epigenetic mechanisms is mediated by enzymes operating in the cell nucleus. Modifications in DNA methylation are carried out primarily by DNA methyltransferases (DNMTs) and ten-eleven translocation proteins (TETs), while a variety of enzymes such as histone acetyltransferases (HATs), histone deacetylases (HDACs), histone methyltransferases (HMTs), and histone demethylases (HDMs)) regulate histone covalent modifications. In many pathological conditions such as cancer, autoimmune, microbial inflammatory, metabolic, allergic diseases and/or low vitamin D availability, the epigenetic regulatory system is often disrupted. Vitamin D interacts with the epigenome at several levels. First, critical genes in the vitamin D signaling system that encode for the vitamin D receptor (VDR) and the enzymes 25-hydroxylase (CYP2R1), 1α-hydroxylase (CYP27B1), and 24-hydroxylase (CYP24A1) have large CpG islands in their promoters. areas and therefore can be suppressed by DNA methylation. Second, the VDR protein physically interacts with coactivator and corepressor proteins, which in turn are in contact with chromatin modifiers such as HATs, HDACs, HMTS, and chromatin remodelers. Third, a number of genes encoding chromatin modifiers and remodelers, such as HDM from the Jumonji C (JmjC) domain containing proteins and lysine-specific demethylase (LSD) families, are primary targets for VDR and its ligands. Finally, there is evidence that certain VDR ligands have DNA demethylating effects. In this review, the authors discuss the regulation of the vitamin D system by epigenetic modifications and how vitamin D contributes to the maintenance of the epigenome and assess its impact on health and disease.
