Methylation levels of IGF2 and KCNQ1 in spermatozoa from infertile men are associated with sperm DNA damage

Etiology of Male Infertility: an Update

Spermatogenesis is a complex process of germ cell division and differentiation that involves extensive cross-talk between the developing germ cells and the somatic testicular cells. Defective endocrine signaling and/or intrinsic defects within the testes can adversely affect spermatogenic progression, leading to subfertility/infertility. In recent years, male infertility has been recognized as a global public health concern, and research over the last few decades has elucidated the complex etiology of male infertility. Congenital reproductive abnormalities, genetic mutations, and endocrine/metabolic dysfunction have been demonstrated to be involved in infertility/subfertility in males. Furthermore, acquired factors like exposure to environmental toxicants and lifestyle-related disorders such as illicit use of psychoactive drugs have been shown to adversely affect spermatogenesis. Despite the large body of available scientific literature on the etiology of male infertility, a substantial proportion of infertility cases are idiopathic in nature, with no known cause. The inability to treat such idiopathic cases stems from poor knowledge about the complex regulation of spermatogenesis. Emerging scientific evidence indicates that defective functioning of testicular Sertoli cells (Sc) may be an underlying cause of infertility/subfertility in males. Sc plays an indispensable role in regulating spermatogenesis, and impaired functional maturation of Sc has been shown to affect fertility in animal models as well as humans, suggesting abnormal Sc as a potential underlying cause of reproductive insufficiency/failure in such cases of unexplained infertility. This review summarizes the major causes of infertility/subfertility in males, with an emphasis on infertility due to dysregulated Sc function.

The methylation status of GATA3 potentially predicts the outcomes of assisted reproductive technologies

Evaluation of methylation status of genes in sperm samples has been suggested for diagnosis of male infertility as well as prognosis of assisted reproductive technologies (ART) outcomes. In this study, we compared the methylation pattern of the GATA3 gene in infertile and fertile men as well as in infertile men with positive and negative ART outcome based on clinical pregnancy. Ejaculates were obtained from 42 infertile men with a negative ART outcome (group 1), 30 infertile men with a positive ART outcome (group 2), and 21 fertile men (control). Then, samples were subjected to genomic DNA isolation and subsequent TUNEL assay and methylation-specific PCR. The number of infertile men with at least one methylated allele of GATA3 was significantly higher compared to the control group (p = 0.022). Also, the number of patients with at least one methylated allele was significantly higher in group 1 compared to group 2 (p = 0.013). Moreover, the TUNEL assay revealed that the amount of sperm DNA fragmentation is higher in group 1 compared to group 2 (p = 0.008). The findings of our study demonstrated that the degree of GATA3 methylation can potentially differentiate between infertile and fertile men and more importantly can potentially predict the outcome of ART.

Association of male factors with recurrent pregnancy loss

The role of male factors in recurrent pregnancy loss (RPL) is receiving increased attention since sperm quantity and quality, male genetic mutations, as well as epigenetic modifications, have all been associated with RPL. A growing number of studies have been published on the relationship between male factors and RPL; however, these reports are limited due to small sample sizes, inconsistent inclusion criteria, and detection methods. Herein, we investigate the effects of several male factors on RPL from a genetic and non-genetic perspective to aid clinicians in determining the etiology and optimal treatment strategy for patients with RPL.

Poor semen parameters are associated with abnormal methylation of imprinted genes in sperm DNA

BACKGROUND

Altered sperm DNA methylation patterns of imprinted genes as well as certain spermatogenesis-related genes has been proposed as a possible mechanism of male subfertility. Some reports suggest that there is an elevated risk of congenital diseases, associated with imprinted genes, in children conceived via intra-cytoplasmic sperm injection, due to the involvement of spermatozoa with aberrant imprinted genes obtained from infertile men.

METHODS

In this study, the DNA methylation status of the promoter regions of six imprinted genes, namely potassium voltage-gated channel subfamily Q member 1 (KCNQ1), maternally expressed gene 3 (MEG3), insulin-like growth factor 2 (IGF-2), KCNQ1 overlapping transcript 1 (KCNQ1OT1), mesoderm specific transcript (MEST), and paternally expressed gene 3 (PEG3), were detected by a next generation sequencing-based multiple methylation-specific polymerase chain reaction analysis of sperm samples obtained from 166 men who sought fertility evaluation in our Reproductive Medicine Center. Thereafter, the semen samples were classified into subgroups according to sperm motility and DNA integrity status.

RESULTS

As compared to the normozoospermic group, the samples of the asthenospermic group exhibited significant hypermethylation in two CpG sites of IGF-2 and significant hypomethylation in one CpG site of KCNQ1 as well as three CpG sites of MEST (P < 0.05). However, we did not observe any significant differences in the overall methylation levels of these six imprinted genes (P > 0.05). Additionally, we found that 111 of 323 CpG sites were hypomethylated in the group with DNA fragmentation index (DFI) ≥ 30% as compared to the group with DFI < 30% (P < 0.05). In this case, there were significant differences in the overall methylation levels of MEG3, IGF-2, MEST, and PEG3 (P < 0.05), but not in that of KCNQ1OT1 and KCNQ1 (P > 0.05). Hence, aberrant methylation patterns of imprinted genes were more prevalent in males with poor sperm quality, especially in those with severe sperm DNA damage.

CONCLUSION

In conclusion, abnormal DNA methylation of some CpG sites of imprinted genes are associated with poor sperm quality, including asthenospermia and severe sperm DNA impairment.

DNA comethylation analysis reveals a functional association between BRCA1 and sperm DNA fragmentation

OBJECTIVES

To identify the DNA comethylation patterns associated with sperm DNA fragmentation (SDF) and to explore the potential associations of hub genes with SDF.

DESIGN

Prospective study.

SETTING

University-affiliated reproductive medicine center.

PATIENT(S)

A total of 300 male patients consulting for couple infertility were recruited from the First Affiliated Hospital of Wenzhou Medical University.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Comethylation network analysis based on the genome-wide methylation profile of spermatozoal DNA from 20 men was performed to identify hub modules and genes involved in SDF. Human spermatozoa were used for targeted bisulfite amplicon sequencing (267 men) or droplet digital polymerase chain reaction (45 men). The potential role of Brca1 in DNA damage was explored in mouse GC2 spermatocyte cells. Oxidative damage to spermatocytes was modeled by incubating GC2 cells with H₂O₂ (25 mM) for 90 minutes.

RESULT(S)

BRCA1 was identified as a hub gene in SDF. Promoter hypermethylation of BRCA1 was observed in those samples with a high DNA fragmentation index (DFI) compared to those with a low DFI. Concomitantly, BRCA1 mRNA expression was lower in samples with a high DFI than with a low DFI. In the GC2 cell model, Brca1 knockdown reduced cell proliferation and increased sensitivity to oxidative stress. Moreover, it increased double-strand breaks and decreased the protein levels of the DNA repair genes MRE11 and RAD51.

CONCLUSION(S)

A prominent cluster of comethylated patterns associated with SDF was identified. BRCA1 may be the hub gene involved in sperm DNA damage.

Epigenetics of Male Infertility: The Role of DNA Methylation

In recent years, a number of studies focused on the role of epigenetics, including DNA methylation, in spermatogenesis and male infertility. We aimed to provide an overview of the knowledge concerning the gene and genome methylation and its regulation during spermatogenesis, specifically in the context of male infertility etiopathogenesis. Overall, the findings support the hypothesis that sperm DNA methylation is associated with sperm alterations and infertility. Several genes have been found to be differentially methylated in relation to impaired spermatogenesis and/or reproductive dysfunction. Particularly, DNA methylation defects of MEST and H19 within imprinted genes and MTHFR within non-imprinted genes have been repeatedly linked with male infertility. A deep knowledge of sperm DNA methylation status in association with reduced reproductive potential could improve the development of novel diagnostic tools for this disease. Further studies are needed to better elucidate the mechanisms affecting methylation in sperm and their impact on male infertility.

Investigation of the lncRNA THOR in Mice Highlights the Importance of Noncoding RNAs in Mammalian Male Reproduction

THOR is a highly conserved testis-specific long noncoding RNA (lncRNA). The interaction between THOR and the development of the male reproductive system remains unclear. Herein, CRISPR/Cas9 technology was used to establish a stable THOR-deficient mouse model, and the relationship between THOR and the fertility of adult male mice was investigated. The male mice in which THOR was deleted were smaller than the WT male mice. Moreover, their survival rate was reduced by 60%, their fertility was reduced by 50%, their testicular size and sperm motility were reduced by 50%, their testicular cell apoptosis was increased by 7-fold, and their ratio of female-to-male offspring was imbalanced (approximately 1:3). Furthermore, to elucidate the mechanisms of male reproductive system development, the mRNA levels of THOR targets were measured by qRT-PCR. Compared with WT mice, the THOR-deficient mice exhibited significantly decreased mRNA levels of IGF2BP1, c-MYC, IGF1, and IGF2. MEK-ERK signaling pathway expression was downregulated as determined by Western blot. We found that THOR targeted the MER-ERK signaling pathway downstream of IGF2 by binding to IGF2BP1 and affected testicular and sperm development in male mice. These results may also provide perspectives for exploring the roles of lncRNAs in human reproductive development and the pathogenesis and potential therapeutic targets of infertility.

Deoxyribonucleic acid methylation signatures in sperm deoxyribonucleic acid fragmentation

OBJECTIVE

To evaluate Deoxyribonucleic acid (DNA) methylation patterns in sperm from men with differential levels of sperm DNA fragmentation index (DFI).

DESIGN

Prospective study.

SETTING

University-affiliated reproductive medicine center.

PATIENT(S)

A total of 278 male patients consulting for couple infertility were recruited from the First Affiliated Hospital of Wenzhou Medical University.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Genome-wide DNA methylation analysis was performed using Infinium MethylationEPIC BeadChip on spermatozoal DNA from 20 male patients. Differentially methylated regions (DMRs) were identified and validated using targeted bisulfite amplicon sequencing in spermatozoal DNA from 266 males.

RESULT(S)

Unsupervised hierarchical clustering analysis revealed three main clusters corresponding to sperm DFI levels (low, medium, or high). Between-cluster comparisons identified 959 (medium-low), 738 (high-medium), and 937 (high-low) DMRs. Sixty-six DMRs were validated in the 266-sample cohort, of which nine CpG fragments corresponding to nine genes (BLCAP, DIRAS3, FAM50B, GNAS, MEST, TSPAN32, PSMA8, SYCP1, and TEX12) exhibited significantly altered methylation in those with high DFI (≥25%) compared with those with low DFI (<25%).

CONCLUSION(S)

We identified and validated a distinct DNA methylation signature associated with sperm DNA damage in a large, unselected cohort. These results indicate that sperm DNA damage may affect DNA methylation patterns in human sperm.

Relevance of sperm imprinted gene methylation on assisted reproductive technique outcomes and pregnancy loss: a systematic review

Recent evidence suggests that gamete-imprinted genes play a role in embryo and placenta development and growth. This systematic review aimed to evaluate whether altered methylation of sperm-imprinted genes associates with sperm DNA fragmentation (SDF), pregnancy loss rate and assisted reproductive technique (ART) outcome. To accomplish this, Pubmed, MEDLINE, Cochrane, Academic One Files, Google Scholar, and Scopus databases were used for search strategy from each database inception until December 2020. Specific keywords were used. Studies satisfying the PECOS (Population, Exposure, Comparison/Comparator, Outcomes, Study design) model were retrieved. Ten studies could be included in the qualitative analysis. A significant association was reported between increased SDF rate and aberrant methylation of H19/IGF2 and KCNQ1 genes by two studies. A significantly lower H19 methylation was found in patients with idiopathic recurrent pregnancy loss (RPL) and in infertile patients compared to fertile men. Methylation of GLT2, PEG1/MEST, and ZAC/PLACL1 were similar in patients with RPL and controls. The ART outcome was similar in patients with aberrant and normal methylation of H19, SNRPN, KCNQ1OT1, PEG1/MEST, LIT1, PEG3, NESPAS, and GLT2. By contrast, a study showed an association between altered GLT2 methylation and more inferior ART results. If further confirmed by well-sized studies, these data might be helpful to identify possible epigenetic predictors of ART outcome. Particularly, aberrant methylation of H19/IGF2 and KCNQ1 genes might represent interesting targets that deserve further investigation.

DNA methylation in human sperm: a systematic review

BACKGROUND

Studies in non-human mammals suggest that environmental factors can influence spermatozoal DNA methylation, and some research suggests that spermatozoal DNA methylation is also implicated in conditions such as subfertility and imprinting disorders in the offspring. Together with an increased availability of cost-effective methods of interrogating DNA methylation, this premise has led to an increasing number of studies investigating the DNA methylation landscape of human spermatozoa. However, how the human spermatozoal DNA methylome is influenced by environmental factors is still unclear, as is the role of human spermatozoal DNA methylation in subfertility and in influencing offspring health.

OBJECTIVE AND RATIONALE

The aim of this systematic review was to critically appraise the quality of the current body of literature on DNA methylation in human spermatozoa, summarize current knowledge and generate recommendations for future research.

SEARCH METHODS

A comprehensive literature search of the PubMed, Web of Science and Cochrane Library databases was conducted using the search terms 'semen' OR 'sperm' AND 'DNA methylation'. Publications from 1 January 2003 to 2 March 2020 that studied human sperm and were written in English were included. Studies that used sperm DNA methylation to develop methodologies or forensically identify semen were excluded, as were reviews, commentaries, meta-analyses or editorial texts. The Grading of Recommendations, Assessment, Development and Evaluations (GRADE) criteria were used to objectively evaluate quality of evidence in each included publication.

OUTCOMES

The search identified 446 records, of which 135 were included in the systematic review. These 135 studies were divided into three groups according to area of research; 56 studies investigated the influence of spermatozoal DNA methylation on male fertility and abnormal semen parameters, 20 studies investigated spermatozoal DNA methylation in pregnancy outcomes including offspring health and 59 studies assessed the influence of environmental factors on spermatozoal DNA methylation. Findings from studies that scored as 'high' and 'moderate' quality of evidence according to GRADE criteria were summarized. We found that male subfertility and abnormal semen parameters, in particular oligozoospermia, appear to be associated with abnormal spermatozoal DNA methylation of imprinted regions. However, no specific DNA methylation signature of either subfertility or abnormal semen parameters has been convincingly replicated in genome-scale, unbiased analyses. Furthermore, although findings require independent replication, current evidence suggests that the spermatozoal DNA methylome is influenced by cigarette smoking, advanced age and environmental pollutants. Importantly however, from a clinical point of view, there is no convincing evidence that changes in spermatozoal DNA methylation influence pregnancy outcomes or offspring health.

WIDER IMPLICATIONS

Although it appears that the human sperm DNA methylome can be influenced by certain environmental and physiological traits, no findings have been robustly replicated between studies. We have generated a set of recommendations that would enhance the reliability and robustness of findings of future analyses of the human sperm methylome. Such studies will likely require multicentre collaborations to reach appropriate sample sizes, and should incorporate phenotype data in more complex statistical models.

RNA-sequencing and bioinformatics analysis of long noncoding RNAs and mRNAs in the asthenozoospermia

Asthenozoospermia is one of the major causes of human male infertility. Long noncoding RNAs (lncRNAs) play critical roles in the spermatogenesis processes. The present study aims to investigate the intricate regulatory network associated with asthenozoospermia. The lncRNAs expression profile was analyzed in the asthenozoospermia seminal plasma exosomes by RNA-sequencing, and the functions of differentially expressed genes (DEGs) were analyzed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and DO (Disease Ontology) enrichment analyses. Pearson’s correlation test was utilized to calculate the correlation coefficients between lncRNA and mRNAs. Moreover, the lncRNA–miRNA–mRNA co-expression network was constructed with bioinformatics. From the co-expression analyses, we identified the cis regulated correlation pairs lncRNA–mRNA. To confirm sequencing results with five of the identified DElncRNAs were verified with quantitative reverse-transcription polymerase chain reaction (qRT-PCR). We identified 4228 significantly DEGs, 995 known DElncRNAs, 2338 DEmRNAs and 11,706 novel DElncRNAs between asthenozoospermia and normal group. GO and KEGG analyses showed that the DEGs were mainly associated with metabolism, transcription, ribosome and channel activity. We found 254,981 positive correlations lncRNA–mRNA pairs through correlation analysis. The detailed lncRNA–miRNA–mRNA regulatory network included 11 lncRNAs, 35 miRNAs and 59 mRNAs. From the co-expression analyses, we identified 7 cis-regulated correlation pairs lncRNA–mRNA. Additionally, the qRT-PCR analysis confirmed our sequencing results. Our study constructed the lncRNA–mRNA–miRNA regulation networks in asthenozoospermia. Therefore, the study findings provide a set of pivotal lncRNAs for future investigation into the molecular mechanisms of asthenozoospermia.

The marker of alkyl DNA base damage, N7-methylguanine, is associated with semen quality in men

Sperm DNA contains a range of DNA base damage that can arise, in part, from exposure to methylating agents. However, the effects are not fully characterized and so the aim of this study was to investigate associations between semen quality and the levels of N7-methyldeoxyguanosine (N7-MedG), a marker of exposure to methylating agents, and other markers of DNA damage and DNA methylation. Sperm samples were collected from 105 men attending an assisted reproduction clinic as part of a couple undergoing treatment for infertility and semen quality assessed manually according to WHO guidelines. Semen levels of N7-MedG, quantified by immunoslotblot, were significantly higher in men with sperm concentration < 15 × 10⁶/ml (p ≤ 0.01), semen volume < 1.5 ml (p ≤ 0.05) and also in men with any aspect of semen quality below WHO reference levels (p ≤ 0.001). Measures of neutral Comet DNA damage were correlated with semen quality in a univariate analysis but not after adjustment for N7-MedG levels. Sperm concentration was negatively associated with % methylation at the gene for DAZL but no other marker of global or gene-specific DNA methylation. Results support the hypothesis that the known toxic and DNA damaging properties of alkylating agent exposure may have direct deleterious consequences on semen quality.

Momordica cymbalaria improves reproductive parameters in alloxan-induced male diabetic rats

Male reproductive dysfunction is one of the common complications of diabetes mellitus that causes infertility. This study was designed to investigate the protective effect of Momordica cymbalaria (M. cymbalaria) extracts on diabetes mediated reproductive toxicity in male Wistar rats. The induction of diabetes was performed using a single intraperitoneal injection of alloxan (120 mg/kg). Skin and seed extracts (250 and 500 mg/kg) of M. cymbalaria were orally administered to alloxan-induced diabetic male rats for 28 days. Postprandial blood glucose (PBG) levels were recorded at 7-day interval for four weeks. The effects of the treatment on blood glucose, weight of reproductive organs, sperm count, testosterone levels, antioxidant capacity, and histomorphology were evaluated. Treatment with the above extracts of M. cymbalaria significantly (p < 0.05) improved the reproductive parameters as well as the antioxidant levels superoxide dismutase (SOD) and glutathione-s-transferase (GST) in the diabetic rats. Also, oral treatment with M. cymbalaria extracts significantly reduced the PBG and malondialdehyde (MDA) levels. Further, it revived the histomorphology of reproductive organs in diabetic rats. Interestingly, skin extract at a dose of 500 mg/kg was found to be more efficient in elevating the level of testosterone and sperm count in the diabetic rats. Based on the results, it is clear that M. cymbalaria not only regulates the postprandial blood glucose levels but also improves the reproductive health in the diabetic state.

Association of XRCC1 and ERCC2 promoters' methylation with chromatin condensation and sperm DNA fragmentation in idiopathic oligoasthenoteratozoospermic men

The aim of the study was to investigate whether the promoter methylation of XRCC1 and ERCC2 genes is associated with sperm DNA fragmentation and chromatin condensation in idiopathic oligoasthenoteratozoospermic men. This study involved 77 infertile men with idiopathic oligoasthenoteratozoospermia and 51 normozoospermic controls. The methylight method, TUNEL assay and aniline blue staining were used for the evaluation of XRCC1 and ERCC2 genes' methylation, SDF and sperm chromatin condensation, respectively. SDF (p = .004) and XRCC1 methylation (p = .0056) were found to be significantly higher in men with idiopathic OAT than in the controls, while mature spermatozoa frequency was higher in controls as compared to infertile men (p < .0001). No significant association was found between SDF and methylation of XRCC1 and ERCC2 genes (p = .9277 and p = .8257, respectively). However, compared to the cut-off point obtained by receiver operating characteristic analysis, a significant association was found between SDF and XRCC1 methylation, positive and negative methylation groups, generated according to the cut-off value for XRCC1. XRCC1 methylation was found to have a significant effect on chromatin condensation (p = .0017). No significant difference was detected among ERCC2 methylation, male infertility and SDF. In conclusion, XRCC1 methylation may have a role in sperm chromatin condensation and idiopathic OAT.

Minor DNA methylation changes are observed in spermatozoa prepared using different protocols

BACKGROUND

DNA methylation patterns can show transgenerational inheritance and are influenced by lifestyle and environmental factors. It is suggested that these patterns can be changed by assisted reproductive technology.

OBJECTIVES

To evaluate the impact of two different sperm preparation methods, conventional density gradient centrifugation (DGC) vs. density gradient centrifugation followed by magnetic-activated cell sorting (MACS) of non-apoptotic spermatozoa, on sperm DNA methylation profile.

MATERIALS AND METHODS

We analyzed semen of patients included in our IVF treatment program. Half of the semen from each included patient was prepared for ICSI using the DGC method and the other half with DGC followed by MACS. The remaining samples were processed for DNA methylation analysis with reduced representation bisulfite sequencing (RRBS). In addition to the DNA methylation profile, we assessed the morphology and DNA fragmentation of spermatozoa.

RESULTS

RRBS analysis revealed that the average genome-wide methylation level was similar between both groups (DGC vs. MACS group) and ranged from 0.53 to 0.56. Furthermore, RRBS analysis identified 99 differentially methylated regions (DMRs) and 800 differentially methylated positions (DMPs). In the DGC group, 43 DMRs and 392 DMPs were hypermethylated whereas 56 DMRs and 408 DMPs were hypomethylated compared with those in the MACS group. When DMRs and DMPs were annotated to genes, 3 genes associated with imprinting were found: IGF2, PRDM16, and CLF4/BRUNOL4. The percentage of morphologically normal spermatozoa (MACS vs. DGC; 14.0 ± 10.8 vs. 13.2 ± 10.0; P = .335) and of spermatozoa with fragmented DNA of patients with RRBS analysis (22.9 ± 21.1% vs. 34.4 ± 21.2; P = .529) were also similar between groups.

DISCUSSION AND CONCLUSION

Although the average genome-wide level of sperm DNA methylation was similar in both sample groups, a distinctive number of methylation changes were observed in DMR and DMP levels. A larger number of samples should be analyzed and additional sperm preparation methods should be tested to confirm our findings.

Molecular Biology of Spermatogenesis: Novel Targets of Apparently Idiopathic Male Infertility

Male infertility affects half of infertile couples and, currently, a relevant percentage of cases of male infertility is considered as idiopathic. Although the male contribution to human fertilization has traditionally been restricted to sperm DNA, current evidence suggest that a relevant number of sperm transcripts and proteins are involved in acrosome reactions, sperm‒oocyte fusion and, once released into the oocyte, embryo growth and development. The aim of this review is to provide updated and comprehensive insight into the molecular biology of spermatogenesis, including evidence on spermatogenetic failure and underlining the role of the sperm-carried molecular factors involved in oocyte fertilization and embryo growth. This represents the first step in the identification of new possible diagnostic and, possibly, therapeutic markers in the field of apparently idiopathic male infertility.