Age-associated changes in methylation of the insulin-like growth factor II (IGF-II) gene

During normal human ageing, changes in DNA methylation are seen, with global hypomethylation occurring in tandem with gene and tissue specific hypermethylation. This epigenetic change is thought to be one of the mechanisms by which genes may become dysregulated during normal ageing, with affected tissues becoming increasingly susceptible to carcinogenesis.In 1996, Issa et al. demonstrated, using normal and tumour derived colonic tissue, age-associated hypermethylation in the human IGF II gene using a Southern blotting based methodology. We have investigated the change in methylation status of three regulatory regions of the human IGF II gene. These regions were the biallelically expressed promoter (P) 1, imprinted promoter (P) 3 and the downstream differentially methylated region (DMR) 2. The two cohorts were ‘Young’s’ 30 years and ‘Elderly’ 75 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 and the downstream DMR2 showed neither hyper- nor hypo-methylation during ageing in peripheral blood lymphocytes. However, the distal region of the imprinted promoter 3 showed significant hypermethylation with increasing age. The P3 result is in concordance with the report of Issa et al. 1996. 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