DNA methylation analysis in immature testicular sperm cells at different developmental stages

Evaluation of DNA methylation at imprinted DMRs in the spermatozoa of oligozoospermic men in association with MTHFR C677T genotype

Altered DNA methylation has been previously identified in the spermatozoa of infertile men; however, the origins of these errors are poorly understood. DNA methylation is an epigenetic modification which is thought to play a fundamental role in male germline development. DNA methylation reactions rely on the cellular availability of methyl donors, which are primarily products of folate metabolism, where a key enzyme is methylenetetrahydrofolate reductase (MTHFR). The MTHFR C677T single nucleotide polymorphism (SNP) reduces enzyme activity and may potentially alter DNA methylation processes during germline development. The objective of this study was to determine whether altered DNA methylation in spermatozoa is associated with the MTHFR C677T SNP. DNA methylation was evaluated at the H19, IG-GTL2, and MEST imprinted differentially methylated regions in the spermatozoa of 53 men - 44 oligozoospermic men and nine fertile men with normal sperm parameters via bisulfite sequencing of sperm clones. The 44 infertile men were stratified by severity of oligozoospermia - three normal (>15 million spermatozoa/mL), eight moderate (5-15 million spermatozoa/mL), 23 severe (1-5 million spermatozoa/mL), and 10 very severe (<1 million spermatozoa/mL). MTHFR C677T SNP genotyping was conducted in a subset of 44 peripheral blood samples via restriction fragment length polymorphism. A total of three men - severe oligozoospermic and CT genotype - were found to be altered, which is defined as having ≥50% of their clones altered, where an altered clone was in turn defined as ≥50% of CpGs with incorrect DNA methylation patterns. The incidence of three altered men within the CT subgroup, however, was not significantly higher than the incidence in the CC subgroup. Taken together, altered DNA methylation in spermatozoa was not significantly associated with the MTHFR C677T SNP; however, there was a trend for higher incidence of alterations among severe oligozoospermic infertile men with CT genotypes.

Analysis of TET expression/activity and 5mC oxidation during normal and malignant germ cell development

During mammalian development the fertilized zygote and primordial germ cells lose their DNA methylation within one cell cycle leading to the concept of active DNA demethylation. Recent studies identified the TET hydroxylases as key enzymes responsible for active DNA demethylation, catalyzing the oxidation of 5-methylcytosine to 5-hydroxymethylcytosine. Further oxidation and activation of the base excision repair mechanism leads to replacement of a modified cytosine by an unmodified one. In this study, we analyzed the expression/activity of TET1-3 and screened for the presence of 5 mC oxidation products in adult human testis and in germ cell cancers. By analyzing human testis sections, we show that levels of 5-hydroxymethylcytosine, 5-formylcytosine and 5-carboxylcytosine are decreasing as spermatogenesis proceeds, while 5-methylcytosine levels remain constant. These data indicate that during spermatogenesis active DNA demethylation becomes downregulated leading to a conservation of the methylation marks in mature sperm. We demonstrate that all carcinoma in situ and the majority of seminomas are hypomethylated and hypohydroxymethylated compared to non-seminomas. Interestingly, 5-formylcytosine and 5-carboxylcytosine were detectable in all germ cell cancer entities analyzed, but levels did not correlate to the 5-methylcytosine or 5-hydroxymethylcytosine status. A meta-analysis of gene expression data of germ cell cancer tissues and corresponding cell lines demonstrates high expression of TET1 and the DNA glycosylase TDG, suggesting that germ cell cancers utilize the oxidation pathway for active DNA demethylation. During xenograft experiments, where seminoma-like TCam-2 cells transit to an embryonal carcinoma-like state DNMT3B and DNMT3L where strongly upregulated, which correlated to increasing 5-methylcytosine levels. Additionally, 5-hydroxymethylcytosine levels were elevated, demonstrating that de novo methylation and active demethylation accompanies this transition process. Finally, mutations of IDH1 (IDH1 (R132)) and IDH2 (IDH2 (R172)) leading to production of the TET inhibiting oncometabolite 2-hydroxyglutarate in germ cell cancer cell lines were not detected.

Reproductive medicine and inheritance of infertility by offspring: the role of fetal programming

OBJECTIVE

To summarize the molecular processes involved in fetal programming, to describe how assisted reproduction technologies (ART) may affect the epigenetic pattern of the embryo, and to highlight the current knowledge of the role of perinatal events in the subsequent development of reproductive pathology affecting infertile patients.

DESIGN

A literature review of fetal programming of adulthood gynecologic diseases and ART. A Medline search was performed with the following keywords: (fetal programming OR epigenetics OR methylation OR acetylation) AND (IVF OR ART) AND (gynecology). Articles up to October 2010 were selected. Articles and recent reviews were classified by human and animals studies and also according to their experimental or observational design.

SETTING

University hospital research center.

PATIENT(S)

None.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

None.

RESULT(S)

Data from experimental animal models and case-control studies support the potential effect of ART in changing methylation patterns in gametes and embryos. However, these findings are not supported by population studies or experimental studies performed in human gametes/embryos. Experimental and epidemiologic studies support the hypothesis that some adult gynecologic diseases causing infertility may have a fetal origin.

CONCLUSION(S)

Although it seems clear that some adult gynecologic diseases causing infertility may have a fetal origin, there is insufficient evidence to confirm that ART is the origin of later onset, adulthood diseases. Further research in this field must be conducted.

Aberrant DNA methylation at imprinted genes in testicular sperm retrieved from men with obstructive azoospermia and undergoing vasectomy reversal

Male factor infertility has been associated with abnormal DNA methylation at imprinted genes. Little information is available on the status of imprinting in the sperm of men with azoospermia, including the association between aberrant imprinting and obstructive azoospermia (OA) or non-OA (NOA). Analysis of DNA methylation at imprinted genes in the sperm of men undergoing vasectomy reversal would aid determination of whether aberrant imprinting is associated with obstruction. Testicular sperm was retrieved from testicular biopsies obtained from men with azoospermia (N=18), including OA (N=10), NOA (N=5), and unknown pathology (N=3), and from men undergoing vasectomy reversal (N=17). Sperm was also obtained from proven fertile men (N=9). DNA methylation was investigated at multiple CpG sites within the differentially methylated regions (DMRs) of three imprinted genes,H19,IG-GTL2andMEST, using bisulphite sequencing. Unique clones representative of single cells were analyzed. We found a significant decrease in DNA methylation at theH19DMR in testicular sperm of azoospermic men compared with proven fertile men. The decrease was also significant between OA and proven fertile men, and between men undergoing vasectomy reversal and proven fertile men, suggesting that aberrant DNA methylation may be associated with obstruction. Changes in DNA methylation atIG-GTL2andMESTDMRs among groups were not significant. Our data suggest that imprinting abnormalities may be associated with obstruction and may occur in response to changes in testicular environment and not only spermatogenesis failure, as previously reported. Methylation at theH19DMR was particularly prone to modification in testicular sperm.

Aberrant DNA methylation of imprinted loci in sperm from oligospermic patients

Recent studies suggest that assisted reproductive technologies (ART), which involve the isolation, handling and culture of gametes and early embryos, are associated with an increased incidence of rare imprinting disorders. Major epigenetic events take place during this time and the process of ART may expose the epigenome to external influences, preventing the proper establishment and maintenance of genomic imprints. However, the risks of ART cannot be simply evaluated because the patients who receive ART may differ both demographically and genetically from the general population at reproductive age. In this study, we examined the DNA methylation status of seven imprinted genes using a combined bisulphite-PCR restriction analysis and sequencing technique on sperm DNA obtained from 97 infertile men. We found an abnormal paternal methylation imprint in 14 patients (14.4%) and abnormal maternal imprint in 20 patients (20.6%). The majority of these doubly defective samples were in men with moderate or severe oligospermia. These abnormalities were specific to imprinted loci as we found that global DNA methylation was normal in these samples. The outcome of ART with sperm shown to have an abnormal DNA methylation pattern was generally poor. However, one sample of sperm with both paternal and maternal methylation errors used in ICSI produced a child of normal appearance without any abnormalities in their imprinted methylation pattern. Our data suggest that sperm from infertile patients, especially those with oligospermia, may carry a higher risk of transmitting incorrect primary imprints to their offspring, highlighting the need for more research into ART.

Methylation status of the SNRPN and HUMARA genes in testicular biopsy samples

OBJECTIVE

To analyze the methylation status of two differentially inherited and methylated loci (the human androgen receptor [HUMARA] and the small nuclear ribonucleoprotein-associated polypeptide N [SNRPN] gene) in testicular biopsy samples, and to compare the results with microscopic evaluation.

DESIGN

Retrospective study.

SETTING

Infertility clinics and genetics laboratories.

PATIENT(S)

Twelve obstructive and 74 nonobstructive azoospermic men.

INTERVENTION(S)

Deoxyribonucleic acid samples from testicular biopsies and peripheral blood were modified with sodium bisulfite and amplified by methylation-specific polymerase chain reaction assay. Polymerase chain reaction primers specific for the methylated regions of the HUMARA locus and for the methylated and unmethylated CpG islands of the SNRPN gene were used.

MAIN OUTCOME MEASURE

Polymerase chain reaction product bands specific for methylated and unmethylated alleles.

RESULT(S)

Obstructive azoospermia patients were positive for spermatozoa and germ cells by all approaches (microscopic, HUMARA, and SNRPN analysis) with absolute consistency. In contrast, for the nonobstructive men, microscopy was consistent with SNRPN analysis as regards the presence of germ cells in 82% of the testicular tissues tested. Nonobstructive patients with maturation arrest were positive for the presence of germ cells only by HUMARA analysis, with 84% sensitivity.

CONCLUSION(S)

Methylation analysis of testicular tissue is consistent with microscopic analysis, in terms of the prevalence of germ cells and the stage of spermatogenic arrest in biopsy samples.

Global sperm deoxyribonucleic acid methylation is unaffected in protamine-deficient infertile males

Sperm protamine-1 (P1) and protamine-2 (P2) concentrations were evaluated concomitantly with global DNA methylation patterns in a population of male infertility patients. Protamine quantification and immunofluorescence microscopy in conjunction with quantitative image analysis revealed no significant relationships between the P1/P2 ratio, P1 concentrations, or P2 concentrations and levels of global DNA methylation in mature spermatozoa.

Epigenetics and the germline

Epigenetic processes affect three stages of germline development, namely (1) specification and formation of primordial germ cells and their germline derivatives through lineage-specific epigenetic modifications, in the same manner as other embryonic lineages are formed, (2) a largely genome-wide erasure and re-establishment of germline-specific epigenetic modifications that only occurs in the embryonic primordial germ cell lineage, followed by re-establishment of sex-specific patterns during gametogenesis, and (3) differential epigenetic modifications to the mature male and female gamete genomes shortly after fertilisation. This review will detail current knowledge of these three processes both at the genome-wide level and at specific imprinted loci. The consequences of epigenetic perturbation are discussed and new in vitro models which may allow further understanding of a difficult developmental period to study, especially in the human, are highlighted.

Spermatozoal nuclear determinants of reproductive outcome: implications for ART

A male factor is implicated in more than 50% of couples treated with IVF. However, neither the routine testing of male fertility potential nor its treatment address the specific mechanisms by which spermatozoal factors may impact upon reproductive outcome. An important function of spermatozoa is to deliver the paternal genome to the oocyte. Recently, a number of acquired spermatozoal nuclear factors that may have implications on reproductive outcome have been described. These include non-specific DNA strand breaks, numerical abnormalities in spermatozoal chromosome content, Y chromosome microdeletions and alterations in the epigenetic regulation of paternal genome. The exact mechanisms by which these factors affect reproduction are unknown and their implications for assisted reproduction technology outcome need to be further investigated. These recent findings point to the need for novel and more personalized approaches to test and treat male factor infertility.