Specific epigenetic alterations of IGF2-H19 locus in spermatozoa from infertile men

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Abstract
DNA methylation marks, a key modification of imprinting, are erased in primordial germ cells and sex specifically re-established during gametogenesis. Abnormal epigenetic programming has been proposed as a possible mechanism compromising male fertility. We analysed by pyrosequencing the DNA methylation status of 47 CpGs located in differentially methylated regions (DMRs), the DMR0 and DMR2 of the IGF2 gene and in the 3rd and 6th CTCF-binding sites of the H19 DMR in human sperm from men with normal semen and patients with teratozoospermia (T) and/or oligo-astheno-teratozoospermia (OAT). All normal semen samples presented the expected high global methylation level for all CpGs analysed. In the teratozoospermia group, 11 of 19 patients presented a loss of methylation at variable CpG positions either in the IGF2 DMR2 or in both the IGF2 DMR2 and the 6th CTCF of the H19 DMR. In the OAT group, 16 of 22 patients presented a severe loss of methylation of the 6th CTCF, closely correlated with sperm concentration. The methylation state of DMR0 and of the 3rd CTCF was never affected by the pathological status of sperm samples. This study demonstrates that epigenetic perturbations of the 6th CTCF site of the H19 DMR might be a relevant biomarker for quantitative defects of spermatogenesis in humans. Moreover, we defined a methylation threshold sustaining the classification of patients in two groups, unmethylated and methylated. Using this new classification of patients, the observed intrinsic imprinting defects of spermatozoa appear not to impair significantly the outcome of assisted reproductive technologies.