Genome-wide DNA methylation analysis of hippocampal tissue in a murine model of Attention Deficit-Hyperactivity Disorder

Background. Attention Deficit-Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder with a prevalence around 5% in children and adolescents and 2.5% in adults. Recent reports using GWAS approaches have identified several genetic risk loci for this disorder. However, the epigenetic influence of extrinsic factors during pregnancy or the exposure to environmental factors during childhood, on the onset of the disorder remains unclear. This question has been addressed mainly by analyzing fluid samples such as blood and saliva taken from ADHD patients or by postmortem analysis. The aim of this study was to determine differential patterns in DNA methylation in hippocampal samples using a murine model of ADHD to identify putative epigenetic biomarkers. Methods. We analyzed the genome-wide pattern of differentially methylated CpG sites identified after bisulfite conversion using the Illumina Infinium Mouse Methylation BeadChip in fresh hippocampal tissue samples from the prenatal nicotine exposure (PNE) mouse model of ADHD and control animals. Results. Our analysis revealed 218 DMPs including genes with the highest difference between beta-values in PNE and control samples associated with growth factors signaling, such as adhesion G protein-coupled receptor B2 (ADGRB2), leukemia inhibitory factor receptor (LIFR) and erb-b2 receptor tyrosine kinase 3 (ERBB3) involved in synaptogenesis, proliferation, and differentiation of neural stem cells. The functional gene enrichment analysis of DMPs revealed the nervous system development as the biological process with highest enrichment factor. In addition, the analysis of 113 DMR revealed several loci associated with the positive regulation of Hippo signaling in PNE samples. Notably, the SPTBN2 gene emerged as DMR in our analysis has also been described as a DMP in blood samples of children with ADHD, and NGR3 (a ligand of the ERBB3 receptor) has been described as a DMR in postmortem analysis of human brain samples. Conclusions. Our results revealing a DMP previously associated with ADHD support the validation of the PNE murine model of ADHD allowing further in vivo and ex vivo experiments required to characterize the molecular mechanisms underlying the onset and persistence of the disorder. In addition, the identification of new DMPs and DMRs in the hippocampal samples of PNE animals will contribute to evaluate the epigenetic status in human samples and the identification of new putative epigenetic markers of the disorder.