Global Methylation and Hydroxymethylation in DNA from Blood and Saliva in Healthy Volunteers

Variations in 5-methylcytosine and 5-hydroxymethylcytosine among human brain, blood, and saliva using oxBS and the Infinium MethylationEPIC array

Investigating 5-methylcytosine (5mC) has led to many hypotheses regarding molecular mechanism underlying human diseases and disorders. Many of these studies, however, utilize bisulfite conversion alone, which cannot distinguish 5mC from its recently discovered oxidative product, 5-hydroxymethylcytosine (5hmC). Furthermore, previous array-based technologies do not have the necessary probes to adequately investigate both modifications simultaneously. In this manuscript, we used technical replicates of DNA from human brain, human blood, and human saliva, in combination with oxidative bisulfite conversion and Illumina's Infinium MethylationEPIC array, to analyze 5mC and 5hmC at more than 650 000 and 450 000 relevant loci, respectively, in the human genome. We show the presence of loci with detectable 5mC and 5hmC to be equally distributed across chromosomes and genomic features, while also being present in genomic regions with transcriptional regulatory properties. We also describe 2528 5hmC sites common across tissue types that show a strong association with immune-related functions. Lastly, in human brain, we show that 5hmC accounts for one-third of the total signal from bisulfite-converted data. As such, not only do our results confirm the efficacy and sensitivity of pairing oxidative bisulfite conversion and the EPIC array to detect 5mC and 5hmC in all three tissue types, but they also highlight the importance of dissociating 5hmC from 5mC in future studies related to cytosine modifications.

Evaluation of DNA methylation markers and their potential to predict human aging

We present epigenetic methylation data for two genetic loci, GRIA2, and NPTX2, which were tested for prediction of age from different donors of biofluids. We analyzed 44 saliva samples and 23 blood samples from volunteers with ages ranging from 5 to 72 years. DNA was extracted and bisulfite modified using commercial kits. Specific primers were used for amplification and methylation profiles were determined by pyrosequencing. Methylation data from both markers and their relationship with age were determined using linear regression analysis, which indicates a positive correlation between methylation and age. Older individuals tend to have increased methylation in both markers compared to younger individuals and this trend was more pronounced in the GRIA2 locus when compared to NPTX2. The epigenetic predicted age, calculated using a GRIA2 regression analysis model, was strongly correlated to chronological age (R(2) = 0.801), with an average difference of 6.9 years between estimated and observed ages. When using a NPTX2 regression model, we observed a lower correlation between predicted and chronological age (R(2) = 0.654), with an average difference of 9.2 years. These data indicate these loci can be used as a novel tool for age prediction with potential applications in many areas, including clinical and forensic investigations.