EBV transformation and cell culturing destabilizes DNA methylation in human lymphoblastoid cell lines

Recent research suggests that epigenetic alterations involving DNA methylation can be causative for neurodevelopmental, growth and metabolic disorders. Although lymphoblastoid cell lines have been an invaluable resource for the study of both genetic and epigenetic disorders, the impact of EBV transformation, cell culturing and freezing on epigenetic patterns is unknown. We compared genome-wide DNA methylation patterns of four white blood cell samples, four low-passage lymphoblastoid cell lines pre and post freezing and four high-passage lymphobastoid cell lines, using two microarray platforms: Illumina HumanMethylation27 platform containing 27,578 CpG sites and Agilent Human CpG island Array containing 27,800 CpG islands. Comparison of genome-wide methylation profiles between white blood cells and lymphoblastoid cell lines demonstrated methylation alterations in lymphoblastoid cell lines occurring at random genomic locations. These changes were more profound in high-passage cells. Freezing at low-passages did not have a significant effect on DNA methylation. Methylation changes were observed in several imprinted differentially methylated regions, including DIRAS3, NNAT, H19, MEG3, NDN and MKRN3, but not in known imprinting centers. Our results suggest that lymphoblastoid cell lines should be used with caution for the identification of disease-associated DNA methylation changes or for discovery of new imprinted genes, as the methylation patterns seen in these cell lines may not always be representative of DNA methylation present in the original B-lymphocytes of the patient.