Epigenetics and genetics of ageing

We have investigated the change in methylation status of three regulatory regions at the human IGF 2 gene. These regions were the biallelically-expressed promoter P1, imprinted promoter P3 and the downstream differentially methylated region (DMR) 2. The two cohorts were “Young” <30 years and “Elderly” >80 years. In order to increase sensitivity and throughput of the methylation detection, a methylation-sensitive/bisulphite sequencing protocol was applied to human peripheral blood lymphocyte derived, bisulphite modified genomic DNA. Promoter 1 (p=0.13) and the downstream DMR2 (p=0.38) show neither hyper- nor hypo-methylation during ageing in peripheral blood lymphocytes. However, the distal region of the imprinted promoter 3 shows significant hypermethylation, in peripheral blood lymphocyte derived genomic DNA, with increasing age, p=0.004. The P3 result is in concordance with the report of Issa et al 1996 in which age-related hypermethylation of the IGF2 P3 region was demonstrated in colon tissue. As methylation is promoter, gene and tissue specific, the previous demonstration of age-related methylation in colon was insufficient to prove that age-related hypermethylation occurs in other tissues. This validates the use of peripheral blood lymphocyte derived DNA as a proxy for the methylation status of less easily available tissue and removes one of the barriers to high throughput studies of population methylation. A high throughput assay was designed, based upon the basic strategy of using a methylation sensitive enzyme to quantify methylation, and then aiming to achieve the necessary additional sensitivity by linking this analysis to quantitative PCR. One CpG site in the promoter 3 region (base 1130, sequence accession number X03562) was chosen for the initial target of this quantitation strategy. The bisulphite sequencing described above demonstrated age-related hypermethylation at this CpG site. This CpG site lies within an Hpall restriction site.