Sci Rep. 2017;7(1):8727.
Multiple Sclerosis (MS) is an immune-mediated demyelinating disease of the human central nervous system (CNS). Memory impairments and hippocampal demyelination are common features in MS patients. Our previous data have shown that demyelination alters neuronal gene expression in the hippocampus. DNA methylation is a common epigenetic modifier of gene expression. In this study, we investigated whether DNA methylation is altered in MS hippocampus following demyelination. Our results show that mRNA levels of DNA methyltransferase were increased in demyelinated MS hippocampus, while de-methylation enzymes were decreased. Comparative methylation profiling identify hypo-methylation within upstream sequences of 6 genes and hyper-methylation of 10 genes in demyelinated MS hippocampus. Genes identified in the current study were also validated in an independent microarray dataset generated from MS hippocampus. Independent validation using RT-PCR revealed that DNA methylation inversely correlated with mRNA levels of the candidate genes. Queries across cell-specific databases revealed that a majority of the candidate genes are expressed by astrocytes and neurons in mouse and human CNS. Taken together, our results expands the list of genes previously identified in MS hippocampus and establish DNA methylation as a mechanism of altered gene expression in MS hippocampus.
In this study some genes are methylated others are not
Methylation is the addition of a methyl group which is one carbon atom and three hydrogen atoms
DNA contains combinations of four nucleotides which include cytosine, guanine, thymine and adenine. DNA methylation refers to the addition of a methyl (CH3) group to the DNA strand itself, often to the fifth carbon atom of a cytosine ring. This conversion of cytosine bases to 5-methylcytosine is catalysed by DNA methyltransferases (DNMTs). These modified cytosine residues usually lie next to a guanine base (CpG methylation) and the result is two methylated cytosines positioned diagonally to each other on opposite strands of DNA.
Different DNMTs work together either as nw DNMTs, establishing the methyl group pattern on a sequence of DNA or as maintenance DNMTs that copy the methylation pattern on an existing strand of DNA to its new partner following replication. Methylation is sparse but global in mammals, found in CpG sequences across the entire genome, aside from certain stretches (of around one kilobase) where the content of CpG is high (CpG islands). When those sequences are methylated, the result can be silencing of gene.