Genome-wide sperm deoxyribonucleic acid methylation is altered in some men with abnormal chromatin packaging or poor in vitro fertilization embryogenesis

Methylation Status of cAMP-responsive Element Modulator (CREM) Gene in Infertile Men and Its Association with Sperm Parameters

The methylation pattern of non-imprinting genes was little studied, although it is widely known that the abnormal methylation levels of imprinting genes are associated with different forms of male infertility. The purpose of this research was to assess the CREM gene's methylation status and seminal characteristics in infertile individuals who were potential intracytoplasmic sperm injection (ICSI) candidates. A total of 45 semen samples (15 normospermia, 15 asthenospermia, and 15 oligoasthenoteratospermia) were examined. Using aniline blue (AB) staining, we carried out conventional semen analysis, chromatin quality, and sperm maturity testing. DNA was taken from semen samples, and all isolated DNA was assessed using Nanodrop and gel electrophoresis. A quantitative methylation-specific polymerase chain reaction (Q-MSP) approach was used to quantify the methylation at the DMRs of the CREM gene. According to our findings, sperm count (P=0.012), concentration (P= 0.019), motility (P=0.006), progression (P=0.006), and normal morphology (P=0.004) were all inversely correlated with abnormal sperm chromatin condensation. Additionally, we noted that the methylation level of the CREM gene was considerably more significant in the oligoasthenoteratospermia group compared to the asthenospermia and normospermia groups (P<0.05). Additionally, sperm count (P=0.043), progression (P=0.026), and normal morphology (P=0.024) were all inversely linked with CREM methylation. Overall, the abnormal CREM methylation patterns have a negative impact on sperm parameters. Additionally, the CREM gene's DNA methylation status may serve as an epigenetic indicator of male infertility.

The Expression and Epigenetic Characteristics of the HSF2 Gene in Cattle-Yak and the Correlation with Its Male Sterility

Aberrant expression of the heat shock proteins and factors was revealed to be closely associated with male reproduction. Heat shock factor 2 (HSF2) is a transcription factor that is involved in the regulation of diverse developmental pathways. However, the role and the corresponding molecular mechanism of HSF2 in male cattle-yak sterility are still poorly understood. Therefore, the aim of this study was to obtain the sequence and the biological information of the cattle-yak HSF2 gene and to investigate the spatiotemporal expression profiles of the locus during the development of cattle-yak testes. Additionally, the differential expression was analyzed between the cattle-yak and the yak, and the methylation of corresponding promoter regions was compared. Our results showed an additional 54 bp fragment and a missense mutation (lysine to glutamic acid) were presented in the cattle-yak HSF2 gene, which correlated with enriched expression in testicular tissue. In addition, the expression of the HSF2 gene showed dynamic changes during the growth of the testes, reaching a peak in adulthood. The IHC indicated that HSF2 protein was primarily located in spermatocytes (PS), spermatogonia (SP), and Sertoli cells (SC) in cattle-yak testes, compared with the corresponding cells of cattle and the yak. Furthermore, bisulfite-sequencing PCR (BSP) revealed that the methylated CpG sites in the promoter region of the cattle-yak HSF2 were more numerous than in the yak counterpart, which suggests hypermethylation of this region in the cattle-yak. Taken together, the low expression abundance and hypermethylation of HSF2 may underpin the obstruction of spermatogenesis, which leads to male cattle-yak infertility. Our study provided a basic guideline for the HSF2 gene in male reproduction and a new insight into the mechanisms of male cattle-yak sterility.

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.

Effect of smoking on methylation and semen parameters

One type of epigenetic modification is genomic DNA methylation, which is induced by smoking, and both are associated with male infertility. In this study, the relationship between smoking and CHD5 gene methylation and semen parameters in infertile men was determined. After the MS-PCR of blood in 224 samples, 103 infertile patients (62 smokers and 41 non-smokers) and 121 fertile men, methylation level changes between groups and the effect of methylation and smoking on infertility and semen parameters in infertile men were determined. The results showed that there is a significant difference in the methylation status (MM, MU, UU) of the CHD5 gene between the patient and the control group, and this correlation also exists for the semen parameters (p < .001). The average semen parameters in smokers decreased significantly compared to non-smokers and sperm concentration was (32.21 ± 5.27 vs. 55.27 ± 3.38), respectively. MM methylation status was higher in smokers (22.5%) compared to non-smokers (14.6%). Smoking components affect the methylation pattern of CHD5 gene, and smokers had higher methylation levels and lower semen parameters than non-smokers, which can be biomarkers for evaluating semen quality and infertility risk factors. Understanding the epigenetic effects of smoking on male infertility can be very useful for predicting negative consequences of smoking and providing therapeutic solutions.

Harnessing male germline epigenomics for the genetic improvement in cattle

Sperm is essential for successful artificial insemination in dairy cattle, and its quality can be influenced by both epigenetic modification and epigenetic inheritance. The bovine germline differentiation is characterized by epigenetic reprogramming, while intergenerational and transgenerational epigenetic inheritance can influence the offspring's development through the transmission of epigenetic features to the offspring via the germline. Therefore, the selection of bulls with superior sperm quality for the production and fertility traits requires a better understanding of the epigenetic mechanism and more accurate identifications of epigenetic biomarkers. We have comprehensively reviewed the current progress in the studies of bovine sperm epigenome in terms of both resources and biological discovery in order to provide perspectives on how to harness this valuable information for genetic improvement in the cattle breeding industry.

Sperm deoxyribonucleic acid fragmentation index at the time of intracytoplasmic sperm injection and standard in vitro fertilization is correlated with lower fertilization but not with blastocyst genetic diagnosis

Objective

To determine the effects of sperm deoxyribonucleic acid (DNA) fragmentation at the time of fertilization on in vitro fertilization (IVF) outcomes and genetic diagnosis using next generation sequencing.

Design

Prospective double-blinded study.

Setting

Private Clinic.

Patients

Couples (n = 150).

Intervention

In vitro fertilization with preimplantation genetic testing for aneuploidy and sperm DNA fragmentation assay, as in sperm chromatin structure assay the day of retrieval.

Main Outcome Measures

Laboratory outcomes are listed in the results section. Statistical analysis was performed using JMP, XYLSTAT, and STATA version 15.

Results

The sperm DNA fragmentation index (DFI) in the neat ejaculate did not predict fertilization rate, quality, blastulation, or genetic diagnosis. No statistically significant results were obtained comparing <15% with >15%, <20% with >20%, <30% with >30% except for DFI. No statistically significant differences in oocyte source age or male age were observed. No statistically significant differences comparing <15% with >15%, <20% with >20%, <30% with >30% DFI at the time of standard IVF or intracytoplasmic sperm injection (ICSI) were observed for % euploid, aneuploid, mosaic, blastulation, biopsied, or D5/total biopsied. The DFI of >15% had more good quality D3 embryos than the <15% group, as did the >20% group compared with the <20% group. The ICSI fertilization was significantly higher in all 3 lower percentage groups compared with the higher counterpart. Standard IVF had significantly more blastocysts/fertilized suitable for biopsy and more D5/total number biopsied than ICSI embryos despite no difference in DFI.

Conclusions

The DFI at fertilization is correlated with decreased fertilization for ICSI and IVF.

Smoking and Its Consequences on Male and Female Reproductive Health

Smoking contributes to the death of around one in 10 adults worldwide. Specifically, cigarettes are known to contain around 4000 toxins and chemicals that are hazardous in nature. The negative effects of smoking on human health and interest in smoking-related diseases have a long history. Among these concerns are the harmful effects of smoking on reproductive health. Thirteen percent of female infertility is due to smoking. Female smoking can lead to gamete mutagenesis, early loss of reproductive function, and thus advance the time to menopause. It has been also associated with ectopic pregnancy and spontaneous abortion. Even when it comes to assisted reproductive technologies cycles, smokers require more cycles, almost double the number of cycles needed to conceive as non-smokers. Male smoking is shown to be correlated with poorer semen parameters and sperm DNA fragmentation. Not only active smokers but also passive smokers, when excessively exposed to smoking, can have reproductive problems comparable to those seen in smokers. In this book chapter, we will approach the effect of tobacco, especially tobacco smoking, on male and female reproductive health. This aims to take a preventive approach to infertility by discouraging smoking and helping to eliminate exposure to tobacco smoke in both women and men.

Advanced molecular approaches in male infertility diagnosis

In the recent years a special attention has been given to a major health concern namely to male infertility, defined as the inability to conceive after 12 months of regular unprotected sexual intercourse, taken into account the statistics that highlight that sperm counts have dropped by 50-60% in recent decades. According to the WHO, infertility affects approximately 9% of couples globally, and the male factor is believed to be present in roughly 50% of cases, with exclusive responsibility in 30%. The aim of this manuscript is to present an evidence-based approach for diagnosing male infertility that includes finding new solutions for diagnosis and critical outcomes, retrieving up-to-date studies and existing guidelines. The diverse factors that induce male infertility generated in a vast amount of data that needed to be analysed by a clinician before a decision could be made for each individual. Modern medicine faces numerous obstacles as a result of the massive amount of data generated by the molecular biology discipline. To address complex clinical problems, vast data must be collected, analysed, and used, which can be very challenging. The use of artificial intelligence (AI) methods to create a decision support system can help predict the diagnosis and guide treatment for infertile men, based on analysis of different data as environmental and lifestyle, clinical (sperm count, morphology, hormone testing, karyotype, etc.) and "omics" bigdata. Ultimately, the development of AI algorithms will assist clinicians in formulating diagnosis, making treatment decisions, and predicting outcomes for assisted reproduction techniques.

Global 5mC and 5hmC DNA Levels in Human Sperm Subpopulations with Differentially Protaminated Chromatin in Normo- and Oligoasthenozoospermic Males

Epigenetic modifications play a special role in the male infertility aetiology. Published data indicate the link between sperm quality and sperm chromatin protamination. This study aimed to determine the relationship between methylation (5mC) and hydroxymethylation (5hmC) in sperm DNA, with respect to sperm chromatin protamination in three subpopulations of fertile normozoospermic controls and infertile patients with oligo-/oligoasthenozoospermia. For the first time, a sequential staining protocol was applied, which allowed researchers to analyse 5mC/5hmC levels by immunofluorescence staining, with a previously determined chromatin protamination status (aniline blue staining), using the same spermatozoa. TUNEL assay determined the sperm DNA fragmentation level. The 5mC/5hmC levels were diversified with respect to chromatin protamination status in both studied groups of males, with the highest values observed in protaminated spermatozoa. The linkage between chromatin protamination and 5mC/5hmC levels in control males disappeared in patients with deteriorated semen parameters. A relationship between 5mC/5hmC and sperm motility/morphology was identified in the patient group. Measuring the 5mC/5hmC status of sperm DNA according to sperm chromatin integrity provides evidence of correct spermatogenesis, and its disruption may represent a prognostic marker for reproductive failure.

Association of methyltetrahydrofolate reductase gene mutation, homocysteine level with semen quality of Iraqi infertile males

Background

Infertility is very common condition and almost 50% of cases are due to male factors. Several genetic and environmental factors are responsible for the poor quality and reduced number of sperms in several cases of infertility. The present study was designed to investigate the association between semen parameters, homocysteine, and the risk of C677T polymorphism of MTHFR gene in infertile males of Iraqi population.

Methods

This Case–control study has been conducted from February 2019 to July 2021 at a molecular laboratory in the Anatomy and Histology Department/college of Medicine/University of Kufa/Najaf/Iraq. It was composed of 353 infertile male patients. They were divided into five groups: 90 azoospermic, 84 oligospermia, 64 asthenospermic, 50 oligoasthenospermic, and 65 teratospermic with an age range 20–46 years compared with 100 fertile males as control with age range 21–49 years. In order to detect homocysteine levels, we used Hcy ELISA Kit. C677T mutation of MTHFR gene was employed by PCR–RFLP technique.

Results

Our data revealed three genotypes of MTHFR C677T, 167 (47.3%) subjects had CC genotype, 116 (32.9%) subjects had CT genotype and 70 (21.1%) subjects had TT genotype. Furthermore, T allele was associated with higher risk of infertility in all patients groups for any genetic model. In total infertile subjects (codominant model: CT vs. CC, OR = 2.0, 95% C.I = 1.2–3.3, P = 0.011; TT vs. CC, OR = 4.8, 95% C.I = 3.3–8.2, P = 0.0003; dominant model: CT + TT vs. CC, OR = 2.8, 95% C.I = 1.7–4.5, P = 0.0001). Oligoasthenospermic patients associated with higher risk in CT heterozygous genotype (OR = 2.8, 95% C.I = 1.0–4.9, P = 0.03) and TT homozygous of mutant allele (OR = 6.3, 95% C.I = 1.9–9.2, P = 0.002). Homocystein level was elevated in all infertile groups when compared with control group (P < 0.01), but the elevation was marked in oligoasthenospermia group. As well as, the level of Serum Hcy exhibited the highest value in TT mutant genotype (39.7 µmol/ml) followed by CT genotype (28.5 µmol/ml) while the lowest level of Hcy recorded in CC genotype (14.6 µmol/ml) for oligoasthenospermia group.

Conclusions

By relating the MTHFR C677T gene mutation with a higher homocystein level, the results showed that Iraqi males with this mutation are more likely to suffer from infertility.

Sperm DNA integrity status is associated with DNA methylation signatures of imprinted genes and non-imprinted genes

PURPOSE

To evaluate the association between the DNA methylation of specific genes and sperm DNA integrity status in human sperm samples.

METHODS

A total of 166 semen samples were evaluated (86 controls and 80 cases with impaired sperm DNA integrity). We detected the methylation status of 257 CpG sites among two imprinted genes (H19 and SNRPN) and four non-imprinted genes related to male infertility (MTHFR, GSTM1, DAZL, and CREM) by using a targeted next-generation sequencing method.

RESULTS

Differential methylation was found in 43 CpG sites of the promoters of the six candidate genes. H19, SNRPN, MTHFR, DAZL, GSTM1, and CREM contained 22, 12, 1, 4, 0, and 4 differentially methylated CpG sites (P<0.05), respectively. The imprinting genes were associated with relatively higher rates of differentially methylated CpG sites (28.21% in H19 and 41.38% in SNRPN) than the non-imprinting genes. One CpG site in H19 remained significant after performing strict Bonferroni correction.

CONCLUSION

In this study, we found that different site-specific DNA methylation signatures were correlated with sperm DNA integrity status. Further studies are needed to investigate the specific mechanisms leading to the epigenetic modifications.

Advances in sperm analysis: techniques, discoveries and applications

Infertility affects one in six couples worldwide, and fertility continues to deteriorate globally, partly owing to a decline in semen quality. Sperm analysis has a central role in diagnosing and treating male factor infertility. Many emerging techniques, such as digital holography, super-resolution microscopy and next-generation sequencing, have been developed that enable improved analysis of sperm motility, morphology and genetics to help overcome limitations in accuracy and consistency, and improve sperm selection for infertility treatment. These techniques have also improved our understanding of fundamental sperm physiology by enabling discoveries in sperm behaviour and molecular structures. Further progress in sperm analysis and integrating these techniques into laboratories and clinics requires multidisciplinary collaboration, which will increase discovery and improve clinical outcomes.

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.

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.

The prolonged disease state of infertility is associated with embryonic epigenetic dysregulation

OBJECTIVE

To evaluate the epigenetic consequence of a prolonged disease state of infertility in euploid blastocysts.

DESIGN

Methylome analysis as well as targeted imprinted methylation and expression analysis on individual human euploid blastocysts examined in association with duration of patient infertility and time to live birth.

SETTING

Research study.

PATIENT(S)

One hundred four surplus cryopreserved euploid blastocysts of transferrable-quality were donated with informed patient consent and grouped based on time to pregnancy (TTP).

INTERVENTION(S)

None MAIN OUTCOME MEASURE(S): The Methyl Maxi-Seq platform (Zymo Research) was used to determine genome-wide methylation, while targeted methylation and expression analyses were performed by pyrosequencing and quantitative real-time polymerase chain reaction, respectively. Statistical analyses used Student's t test, 1-way ANOVA, Fisher's exact test, and pairwise-fixed reallocation randomization test, where appropriate.

RESULT(S)

The methylome analysis of individual blastocysts revealed significant alterations at 6,609 CpG sites associated with prolonged infertility (≥60 months) compared with those of fertile controls (0 months). Significant CpG alterations were localized to numerous imprinting control regions and imprinted genes, and several signaling pathways were highly represented among genes that were differentially methylated. Targeted imprinting methylation analysis uncovered significant hypomethylation at KvDMR and MEST imprinting control regions, with significant decreases in the gene expression levels upon extended TTP (≥36 months) compared to minimal TTP (≤24 months).

CONCLUSION(S)

The prolonged disease state of infertility correlates with an altered methylome in euploid blastocysts, with particular emphasis on genomic imprinting regulation, compared with assisted reproductive technologies alone.

Role of HP1β during spermatogenesis and DNA replication

Heterochromatin protein 1β (HP1β), encoded by the Cbx1 gene, has been functionally linked to chromatin condensation, transcriptional regulation, and DNA damage repair. Here we report that testis-specific Cbx1 conditional knockout (Cbx1 cKO) impairs male germ cell development in mice. Depletion of HP1β negatively affected sperm maturation and increased seminiferous tubule degeneration in Cbx1 cKO mice. In addition, the spermatogonia have elevated γ-H2AX foci levels as do Cbx1 deficient mouse embryonic fibroblasts (MEFs) as compared to wild-type (WT) control MEFs. The increase in γ-H2AX foci in proliferating Cbx1 cKO cells indicates defective replication-dependent DNA damage repair. Depletion or loss of HP1β from human cells and MEFs increased DNA replication fork stalling and firing of new origins of replication, indicating defective DNA synthesis. Taken together, these results suggest that loss of HP1β in proliferating cells leads to DNA replication defects with associated DNA damage that impact spermatogenesis.

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.

Low doses of carbendazim and chlorothalonil synergized to impair mouse spermatogenesis through epigenetic pathways

Pesticides have been extensively produced and used to help the agricultural production which leads to the contamination of the environment, soil, groundwater sources, and even foodstuffs. Fungicides carbendazim (CBZ) and chlorothalonil (Chl) are widely applied in agriculture and other aspects. CBZ or Chl have been reported to disrupt spermatogenesis and decrease semen quality. However, it is not understood the effects of pubertal exposure to low doses of CBZ and Chl together, and the underlying mechanisms. Therefore, the aim of current investigation was to explore the negative impacts of pubertal exposure to low doses of CBZ and Chl together on spermatogenesis and the role of epigenetic modifications in the process. We demonstrated that CBZ and Chl together synergize to decrease sperm motility in vitro (CBZ 1.0 + Chl 0.1, CBZ 10.0 + CHl 1.0, CBZ 100.0 + Chl 10 μM in incubation medium for 24 h) and sperm concentration and motility in vivo with ICR mice (CBZ 0.1 + Chl 0.1, CBZ 1.0 + CHl 1.0, CBZ 10.0 + Chl 10 mg/kg body weight; oral gavage for five weeks). CBZ + Chl significantly increase reactive oxygen species (ROS) and apoptosis by the increase in the protein level of caspase 8 in vitro. Moreover, CBZ + Chl synergized to disrupt mouse spermatogenesis with the disturbance in sperm production proteins and sperm proteins (VASA, A-Myb, STK31, AR, Acrosin). CBZ + Chl synergized to decrease the protein level of estrogen receptor alpha and the protein level of DNA methylation marker 5 mC in Leydig cells, and to increase the protein levels of histone methylation marker H3K9 and the methylation enzyme G9a in germ cells. Therefore, greater attention should be paid to the use of CBZ and Chl as pesticides to minimise their adverse impacts on spermatogenesis.

Influence of variation in global sperm DNA methylation level on the expression level of protamine genes and human semen parameters

An infertility problem is a complex issue that affects 15% approximately of couples worldwide. The current study was designed to evaluate if there is a variation in the status of global DNA methylation among the study groups and to assess their impact on the protamine expression level and human semen parameters. Totalling 200 semen samples were collected from men (50 proved fertile, 60 normospermia and 90 oligospermia) with an average age of 34.9 ± 4.3 years. The DNA and RNA were isolated from purified spermatozoa; then, ELISA and qPCR were applied to estimate the status of global sperm DNA methylation and protamine expression level respectively. Besides that, the sperm chromatin decondensation and sperm DNA fragmentation were assessed. A significant variation was found in the global sperm DNA methylation and the protamine 1 and protamine 2 expression level among the study groups (p ≤ .001). Down-regulation has been found in the protamine 1 and protamine 2 expression levels in the oligospermia group compared to the proved fertile group with fold change (0.001 and 0.0002 respectively). In conclusion, this study proposes that the alteration in global DNA methylation may influence the protamine expression level and may be lead to abnormalities in human semen parameters.

Estrogen Receptor-Related DNA and Histone Methylation May Be Involved in the Transgenerational Disruption in Spermatogenesis by Selective Toxic Chemicals

Air pollution is a global threat to human health especially spermatogenesis. Animal and epidemiological studies suggest that epigenetic factors can transmit the pathologies transgenerationally. Paternal epigenetic effects can greatly impact offspring health. In this study and together with our previous report, we found that H₂S donor Na₂S and/or NH₃ donor NH₄Cl diminished mouse fertility, decreased spermatozoa concentration and motility, and impaired spermatogenesis in three consequent generations (F0, F1, and F2). In the current study, we found that DNA methylation, histone methylation, and estrogen receptor alpha (ERα) were impaired by NH₄Cl and/or Na₂S in F0, F1, and F2 mouse testes. Moreover, NH₄Cl and/or Na₂S might act as environmental endocrine-disrupting chemicals to decrease estrogen and testosterone in mouse blood. It has been reported that ERα signaling is intertwined together with DNA methylation and histone methylation, which plays very important roles in spermatogenesis. These data together indicate that the transgenerational disruption in spermatogenesis by NH₄Cl and/or Na₂S may be through ERα-related DNA methylation and histone methylation pathways. Therefore, we strongly recommend that greater attention should be paid to NH₃ and/or H₂S contamination to minimize their impact on human health especially spermatogenesis.

Low dose chlorothalonil impairs mouse spermatogenesis through the intertwining of Estrogen Receptor Pathways with histone and DNA methylation

Recently, environment contaminants including pesticides, fungicides, mycotoxin and others chemicals have been suggested to be responsible for the decline in the human spermatozoa quality especially motility and the increase in infertility rate. Chlorothalonil is used widely for protection of vegetables and crops because it is a broad spectrum fungicide. It has been reported that chronic occupational exposure to fungicides was associated with poor spermatozoa morphology in young men. The pubertal period is very important for the male reproductive system development due to spermatogonial cell proliferation, the expansion of meiotic and haploid germ cells. Although some investigations have studied the male reproductive toxicity of chlorothalonil, almost no studies focused on spermatogenesis. The aim of our current investigation was to explore the impacts of chlorothalonil on spermatogenesis and the underlying mechanisms. It demonstrates: i) chlorothalonil decreased boar spermatozoa motility in vitro and increased the cell apoptosis; ii) chlorothalonil inhibited mouse spermatogenesis in vivo; iii) chlorothalonil disturbed spermatogenesis through the disruption of estrogen receptor signalling; iv) chlorothalonil disrupted histone methylation and DNA methylation which might be through estrogen signalling pathways. Due to the over use or incorrect use, chlorothalonil might cause serious problems to human health, especially spermatogenesis. Therefore we strongly recommend that greater attention should be paid to this fungicide to minimise its impact on human health especially spermatogenesis.

Low dose carbendazim disrupts mouse spermatogenesis might Be through estrogen receptor related histone and DNA methylation

Pesticides, fungicides are reportedly involved in a decline in spermatozoa quality, especially motility, and a consequent increase in the rate of infertility. Fungicide carbendazim (CBZ) is widely used in agriculture and other aspects. Although CBZ is known to disrupt spermatogenesis, causing a decrease in spermatozoa concentration and motility, the mechanisms are not fully understood. We aimed to further explore the underlying mechanisms of CBZ disruption of spermatogenesis. Pubertal mice were exposed to low doses (0.1, 1 and 10 mg/kg body weight) of CBZ for 5 weeks, then many factors related to spermatogenesis have been explored. It was found that 0.1-10 mg/kg body weight of CBZ exposure decreased mouse sperm motility and concentration, diminished the important protein factors (VASA, PGK2, B-Amy and CREM) for spermatogenesis, reduced sperm protein acrosin level, disrupted very vital epigenetic factors H3K27, 5 mC and 5 hmC. Furthermore, CBZ exposure damaged estrogen receptor alpha (ERα) pathway by decreased the protein levels of ERα and its targets PI3K and AKT. In summary low doses of CBZ exposure disrupted mouse spermatogenesis through estrogen receptor signaling; and that histone methylation and DNA methylation might play vital roles in CBZ disturbance of spermatogenesis through intertwining with estrogen signaling pathways. CBZ from the contamination in environment or food chain poses a serious threat to the normal development of spermatozoa. Therefore we strongly recommend to minimise the use of CBZ since it causes the severe issues on spermatogenesis.

Genome-wide differential methylation analyses identifies methylation signatures of male infertility

STUDY QUESTION

Do methylation changes in sperm DNA correlate with infertility?

STUDY ANSWER

Loss of spermatogenesis and fertility was correlated with 1680 differentially-methylated CpGs (DMCs) across 1052 genes.

WHAT IS KNOWN ALREADY

Methylation changes in a number of genes have been correlated with reduced sperm count and motility.

STUDY DESIGN, SIZE, DURATION

This case-control study used spermatozoal DNA from 38 oligo-/oligoastheno-zoospermic infertile patients and 26 normozoospermic fertile men.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

Genome-wide methylation analysis was undertaken using 450 K BeadChip on spermatozoal DNA from six infertile and six fertile men to identify DMCs. This was followed by deep sequencing of spermatozoal DNA from 32 infertile patients and 20 fertile controls.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 1680 DMCs were identified, out of which 1436 were hypermethylated and 244 were hypomethylated. Classification of DMCs according to the genes identified BCAN, CTNNA3, DLGAP2, GATA3, MAGI2 and TP73 among imprinted genes, SPATA5, SPATA7, SPATA16 and SPATA22 among spermatogenesis-associated genes, KDM4C and JMJD1C, EZH2 and HDAC4 among genes which regulate methylation and gene expression, HLA-C, HLA-DRB6 and HLA-DQA1 among complementation and immune response genes, and CRISPLD1, LPHN3 and CPEB2 among other genes. Genes showing significant differential methylation in deep sequencing, i.e. HOXB1, GATA3, EBF3, BCAN and TCERG1L, are strong candidates for further investigations. The role of chance was ruled out by deep sequencing of select genes.

LARGE-SCALE DATA

N/A.

LIMITATIONS, REASON FOR CAUTION

Genome-wide analyses are fairly accurate, but may not be exactly validated in replication studies across all DMCs. We used the 't' test in the genome-wide methylation analysis, whereas other tests could provide a more robust and powerful analysis.

WIDER IMPLICATIONS OF THE FINDINGS

DMCs can serve as markers for inclusion in infertility screening panels, particularly those in the genes showing differential methylation consistent with previous studies. The genes validated by deep sequencing are strong candidates for investigations of their roles in spermatogenesis.

STUDY FUNDING/COMPETING INTEREST(S)

The study was funded by the Council of Scientific and Industrial Research (CSIR), Govt. of India with grant number BSC0101 awarded to Rajender Singh. None of the authors has any competing interest to declare.

Gestational exposure to low-dose zearalenone disrupting offspring spermatogenesis might be through epigenetic modifications

Zearalenone (ZEA), a F-2 mycotoxin produced by Fusarium, has been found to be an endocrine disruptor through oestrogen receptor signalling pathway to impair spermatogenesis. The disruption on reproductive systems by ZEA exposure might be transgenerational. In our previous report, we have found that low dose (lower than no-observed effect level, NOEL) of ZEA impaired mouse spermatogenesis and decreased mouse semen quality. The purpose of the current investigation was to explore the impacts of low-dose ZEA on spermatogenesis in the offspring after prenatal exposure and the underlying mechanisms. And it demonstrated that prenatal low-dose ZEA exposure disrupted the meiosis process to inhibit the spermatogenesis in offspring and even to diminish the semen quality by the decrease in spermatozoa motility and concentration. The DNA methylation marker 5hmC was decreased, the histone methylation markers H3K9 and H3K27 were elevated, and oestrogen receptor alpha was reduced in the offspring testis after prenatal low-dose ZEA exposure. The data suggest that the disruption in spermatogenesis by prenatal low-dose ZEA exposure may be through the modifications on epigenetic pathways (DNA methylation and histone methylation) and the interactions with oestrogen receptor signalling pathway. Moreover, in the current study, the male offspring were indirectly exposed to low-dose ZEA through placenta and the spermatogenesis in offspring was disrupted which suggested that the toxicity of ZEA on reproductive systems was very severe. Therefore, we strongly recommend that greater attention should be paid to this mycotoxin to minimize its adverse impact on human spermatogenesis.

Epigenetics, infertility, and cancer: future directions

Although direct correlates between cancer and infertile epigenetic profiles are rare, the general similarities between the two disease processes offer insights into the study of both abnormalities. Foremost among them is the nature of these pathologies, where one disease (cancer) is categorized by an inability to control or inhibit cellular proliferation, and the other (male infertility) is caused by an inability to maintain the normally efficient extreme proliferation of the male germ cell. Based on this similarity alone, the study of epigenetics in both male fertility and cancer has the potential to offer intriguing insights in both fields. The creative application of harmonious studies of both infertility and cancer is likely to yield useful and informative data that may aid in both the understanding and treatment of both pathologies.

Aberrant DNA Methylation of IGF2-H19 Locus in Human Fetus and in Spermatozoa From Assisted Reproductive Technologies

Given the higher risk of developing imprinting disorders in assisted reproductive technology (ART)-conceived children, we hypothesized that ART may affect DNA methylation of the insulin-like growth factor 2 (IGF2), H19, small nuclear ribonucleoprotein polypeptide N (SNRPN) differentially methylated regions (DMRs) at the fetal stage, which in turn may be associated with sperm abnormalities. A total of 4 patient groups were recruited, namely, multifetal reduction following in vitro fertilization (IVF)/ intracytoplasmic sperm injection (ICSI; n = 56), multifetal reduction following controlled ovarian hyperstimulation (COH; n = 42), male patients with normal semen parameters denoted as normozoospermia group (NZ) for IVF (n = 36), and male patients presenting with asthenozoospermia (OAZ) for ICSI (n = 38). The expression levels and the DNA methylation status of IGF2-H19 and SNRPN DMRs in the fetuses and the semen samples were evaluated by real-time quantitative polymerase chain reaction and pyrosequencing. In our results, the expression levels of H19 were significantly higher, whereas the methylation rates were lower in IVF-conceived fetuses compared to the control group (P < .05). Furthermore, higher methylation rates of IGF2 DMR2 and SNRPN DMR were detected both in IVF- and ICSI-conceived fetuses (P < .05). The data further indicated that the patients who presented with the majority of the CpG sites in the H19 DMR region that were lower methylated were those in the OAZ group. The results demonstrated that the epigenetic dysregulations of IGF2-H19 and SNRPN DMRs that were caused by ART were noted in the fetuses. Moreover, the present study suggested that epigenetic perturbations of the H19 DMR might be a key biomarker for spermatogenesis defects in humans.

Spinal cord injury and male infertility-a review of current literature, knowledge gaps, and future research

Spinal cord injury (SCI) affects nearly half a million new patients worldwide, with 17,700 in the US each year, and disproportionately impacts young males of reproductive age. Almost every aspect of male reproduction is affected by SCI, resulting in: erectile, endocrine and sexual dysfunction, decreased sperm motility despite an often-normal count, and abnormal semen emission and ejaculation. The aim of this review is to focus on how SCI impacts testicular spermatogenesis, sperm function, semen quality, and overall fecundity while discussing what is not known, and future avenues for research.

Impact of cigarette-smoking on sperm DNA methylation and its effect on sperm parameters

DNA methylation is an epigenetic modification of the genome. The purpose of this study was to determine the influence of cigarette-smoking on sperm DNA methylation from a genomewide survey of sperm samples and to ascertain its effect on sperm parameters. Twenty-eight sperm DNA samples (from 14 fertile smokers as a case study and 14 proven fertile nonsmokers as controls) were subjected to Infinium 450K BeadChip arrays to identify the changes in the DNA methylation level between the two groups. Then, deep bisulphite sequencing was used to validate five CpGs on 78 samples. The results from the Infinium 450K found that only 11 CpGs showed a significant difference in DNA methylation between the case and the control groups. Five CpGs of the eleven (cg00648582, cg0932376, cg19169023, cg23841288 and cg27391564) underwent deep bisulphite sequencing where cg00648582, related to the PGAM5 gene, and the cg23841288 CpGs, related to the PTPRN2 gene amplicons, showed a significant increase in their DNA methylation level in more than one CpG in the case group. In contrast, a significant decrease was found at cg19169023 and at its various neighbouring CpGs in the TYRO3 gene-related amplicons. Furthermore, this study demonstrated a significant correlation between the variation in sperm DNA methylation level and standard sperm parameters in the case group.

The environment and male reproduction: The effect of cadmium exposure on reproductive function and its implication in fertility

Cadmium is an environmental pollutant known as endocrine disruptor. Testis is particularly susceptible to cadmium, and testis injury occurs at high but even low levels of exposure. Cadmium reproductive toxicity is mediated by multiple mechanisms, including structural damage to testis vasculature and blood-testis barrier, inflammation, cytotoxicity on Sertoli and Leydig cells, oxidative stress mainly by means of mimicry and interference with essential ions, apoptosis, interference with selected signaling pathways and epigenetic regulation of genes involved in the regulation of reproductive function, and disturbance of the hypothalamus-pituitary-gonadal axis. The current review outlines epidemiological observational findings from environmental and occupational exposure in humans, and reports experimental studies in humans and animals. Lastly, a focus on the pathogenetic mechanisms of cadmium toxicity and on the specific mechanisms of cadmium sensitivity and resistance, particularly assessed in animal models, is included. Despite convincing experimental findings in animals and supporting evidences in humans identifying cadmium as reproductive toxicant, observational findings are controversial, suffering from heterogeneity of study design and pattern of exposure, and from co-exposure to multiple pollutants.

Epigenetic dynamics and interplay during spermatogenesis and embryogenesis: implications for male fertility and offspring health

Mapping epigenetic modifications and identifying their roles in the regulation of spermatogenesis and embryogenesis are essential for gaining fundamental medical understandings and for clinical applications. More and more evidence has shown that specific epigenetic modifications are established during spermatogenesis, which will be transferred into oocyte via fertilisation, and play an important role in the early embryo development. Defects in epigenetic patterns may increase the risk of abnormal spermatogenesis, fertilisation failure, early embryogenesis abnormality and several other complications during pregnancy. This review mainly discusses the relationship between altered epigenetic profiles and reproductive diseases, highlighting how epigenetic defects affect the quality of sperm and embryo.

Global methylation status of sperm DNA in carriers of chromosome structural aberrations

Male infertility might be clearly associated with aberrant DNA methylation patterns in human spermatozoa. An association between oxidative stress and the global methylation status of the sperm genome has also been suggested. The aim of the present study was to determine whether the global sperm DNA methylation status was affected in the spermatozoa of carriers of chromosome structural aberrations. The relationships between the 5-methylcytosine (m⁵C) levels in spermatozoa and chromatin integrity status were evaluated. The study patients comprised male carriers of chromosome structural aberrations with reproductive failure (n = 24), and the controls comprised normozoospermic sperm volunteers (n = 23). The global m⁵C level was measured using thin-layer chromatography (TLC) and immunofluorescence (IF) techniques. The sperm chromatin integrity was assessed using aniline blue (AB) staining and TUNEL assay. The mean m⁵C levels were similar between the investigated chromosome structural aberrations carriers (P) and controls (K). However, sperm chromatin integrity tests revealed significantly higher values in chromosomal rearrangement carriers than in controls (P < 0.05). Although the potential relationship between sperm chromatin integrity status and sperm DNA fragmentation and the m⁵C level juxtaposed in both analyzed groups (P vs K) was represented in a clearly opposite manner, the low chromatin integrity might be associated with the high hypomethylation status of the sperm DNA observed in carriers of chromosome structural aberrations.

The Long-Term Effects of the Periconceptional Period on Embryo Epigenetic Profile and Phenotype; The Paternal Role and His Contribution, and How Males Can Affect Offspring's Phenotype/Epigenetic Profile

The number of adults afflicted with heart disease, obesity and diabetes, central components of metabolic disorder, has grown rapidly in recent decades, affecting up to one quarter of the world's population. Typically, these diseases are attributed to lifestyle factors such as poor diet, lack of exercise and smoking. However, studies have now identified strong associations between patterns of growth during foetal and neonatal life and an increase predisposition towards developing heart disease, obesity and diabetes in adult life. While the connection between a mother's diet and the long-term health of her offspring has been studied in great detail, our understanding of whether offspring health might be affected by a father's diet remains limited. Greater insight into the impact that paternal nutrition has on sperm quality, epigenetic status and potential offspring programming mechanisms is needed to redress this parental-programming knowledge imbalance. Disturbances in paternal reproductive epigenetic status represents one key mechanism linking paternal diet with the programing of offspring development and adult health, as many enzymatic processes involved in epigenetic regulation use metabolic intermediates to modify DNA and histones. Here, poor paternal nutrition could result in perturbed sperm and testicular epigenetic status, impacting on post-fertilisation gene transcriptional regulation and protein expression in offspring tissues, resulting in increased incidences of metabolic disorder in adult life.

Obesity-induced sperm DNA methylation changes at satellite repeats are reprogrammed in rat offspring

There is now strong evidence that the paternal contribution to offspring phenotype at fertilisation is more than just DNA. However, the identity and mechanisms of this nongenetic inheritance are poorly understood. One of the more important questions in this research area is: do changes in sperm DNA methylation have phenotypic consequences for offspring? We have previously reported that offspring of obese male rats have altered glucose metabolism compared with controls and that this effect was inherited through nongenetic means. Here, we describe investigations into sperm DNA methylation in a new cohort using the same protocol. Male rats on a high-fat diet were 30% heavier than control-fed males at the time of mating (16-19 weeks old, n = 14/14). A small (0.25%) increase in total 5-methyl-2Ͳ-deoxycytidine was detected in obese rat spermatozoa by liquid chromatography tandem mass spectrometry. Examination of the repetitive fraction of the genome with methyl-CpG binding domain protein-enriched genome sequencing (MBD-Seq) and pyrosequencing revealed that retrotransposon DNA methylation states in spermatozoa were not affected by obesity, but methylation at satellite repeats throughout the genome was increased. However, examination of muscle, liver, and spermatozoa from male 27-week-old offspring from obese and control fathers (both groups from n = 8 fathers) revealed that normal DNA methylation levels were restored during offspring development. Furthermore, no changes were found in three genomic imprints in obese rat spermatozoa. Our findings have implications for transgenerational epigenetic reprogramming. They suggest that postfertilization mechanisms exist for normalising some environmentally-induced DNA methylation changes in sperm cells.

From the Cover: Sperm Molecular Biomarkers Are Sensitive Indicators of Testicular Injury following Subchronic Model Toxicant Exposure

Traditional testis histopathology endpoints remain the gold standard for evaluating testicular insult and injury in a non-clinical setting, but are invasive and unfeasible for monitoring these effects clinically in humans. Assessing testicular injury in humans relies on semen and serum hormone analyses, both of which are insensitive and poor indicators of effect. Therefore, we hypothesized that sperm messenger RNA (mRNA) transcripts and DNA methylation marks can be used as translatable and sensitive indicators or testicular injury. Dose-response studies using adult male Fischer 344 rats subchronically exposed to model Sertoli cell toxicants (0.14, 0.21, and 0.33% 2,5-hexanedione, and 30, 50, and 70 mg/kg/day carbendazim), and a model germ cell toxicant (1.4, 3.4, and 5.1 mg/kg/day cyclophosphamide) for 3 months were evaluated for testicular injury by traditional histopathological endpoints, changes in sperm mRNA transcript levels using custom PCR arrays, and alterations in sperm DNA methylation via reduced representation bisulfite sequencing. Testis histopathological evaluation and PCR array analysis of the sperm transcriptome identified dose-dependent changes elicited by toxicant exposure (P < 0.05). Global sperm DNA methylation analysis of subchronic 0.33% 2,5-hexandione and 5.1 mg/kg/day cyclophosphamide exposure using a Monte Carlo approach did not identify differentially methylated regions (methylation difference > 10% and q < 0.05) with robust signatures. Overall, these results suggest that sperm mRNA transcripts are sensitive indicators of low dose toxicant-induced testicular injury in the rat, while sperm DNA methylation changes are not. Additionally, the Monte Carlo analysis is a powerful approach that can be used to assess the robustness of signals resulting from -omic studies.

Increased N6-methyladenosine in Human Sperm RNA as a Risk Factor for Asthenozoospermia

Male infertility is a worldwide medical problem. Asthenozoospermia is a common cause of infertility. Epigenetic modifications of DNA and histones have been shown to influence human infertility, but no research has explored whether N(6)-methyladenosine (m(6)A) level in RNA is associated with asthenozoospermia. Here, we collected a total of 52 semen samples, including 20 asthenozoospermia patients and 32 healthy controls. An LC-ESI-MS/MS method was used to detect m(6)A contents in sperm RNA, and real-time PCR was performed to determine the mRNA expression of demethylase (FTO, ALKBH5), methyltransferase (METTL3, METTL14, WTAP) and an m(6)A-selective-binding protein (YTHDF2). We found that m(6)A content (p = 0.033) and the mRNA expression of METTL3 (p = 0.016) and METTL14 (p = 0.025) in asthenozoospermia patients were significantly higher than those of controls. Increased m(6)A content was a risk factor for asthenozoospermia (odds ratio (OR) 3.229, 95% confidence interval (CI) 1.178 - 8.853, p = 0.023). Moreover, m(6)A content was correlated with the expression of METTL3 (r = 0.303, p = 0.032) and with sperm motility (progressive motility: r = -0.288, p = 0.038; non-progressive motility: r = -0.293, p = 0.037; immotility: r = 0.387, p = 0.005). Our data suggest that increased m(6)A content is a risk factor for asthenozoospermia and affects sperm motility. Methyltransferases, particularly METTL3, play key roles in increasing m(6)A contents in sperm RNA.

A Molecular Perspective on Procedures and Outcomes with Assisted Reproductive Technologies

The emerging association of assisted reproductive technologies with adverse perinatal outcomes has prompted the in-depth examination of clinical and laboratory protocols and procedures and their possible effects on epigenetic regulatory mechanism(s). The application of various approaches to study epigenetic regulation to problems in reproductive medicine has the potential to identify relative risk indicators for particular conditions, diagnostic biomarkers of disease state, and prognostic indicators of outcome. Moreover, when applied genome-wide, these techniques are likely to find novel pathways of disease pathogenesis and identify new targets for intervention. The analysis of DNA methylation, histone modifications, transcription factors, enhancer binding and other chromatin proteins, DNase-hypersensitivity and, micro- and other noncoding RNAs all provide overlapping and often complementary snapshots of chromatin structure and resultant "gene activity." In terms of clinical application, the predictive power and utility of epigenetic information will depend on the power of individual techniques to discriminate normal levels of interindividual variation from variation linked to a disease state. At present, quantitative analysis of DNA methylation at multiple loci seems likely to hold the greatest promise for achieving the level of precision, reproducibility, and throughput demanded in a clinical setting.

Genetic evaluation of male infertility

Men with severe oligospermia (<5 million sperm/mL ejaculate fluid) or azoospermia should receive genetic testing to clarify etiology of male infertility prior to treatment. Categorization by obstructive azoospermia (OA) or non-obstructive azoospermia (NOA) is critical since genetic testing differs for the former with normal testicular function, testicular volume (~20 mL), and follicle-stimulating hormone (FSH) (1-8 IU/mL) when compared to the latter with small, soft testes and increased FSH. History and physician examination along with laboratory testing (following appropriate genetic counseling) is critical to accurate selection of genetic testing appropriate for azoospermia due to primary testicular failure as compared with congenital hypogonadotropic hypogonadism (HH). Genetic testing options include cystic fibrosis transmembrane conductance regulator (CFTR) testing for men with congenital absence of the vas, while karyotype, Y chromosome microdeletions (YCMD), and other specific genetic tests may be warranted depending on the clinical context of severe oligospermia or NOA. The results of genetic testing guide management options. The most recent techniques for genetic analysis, including sperm microRNA (miRNA) and epigenetics, are forming the foundation for future genetic diagnosis and therapeutic targets in male infertility.

Smoking and Male Infertility: An Evidence-Based Review

Many studies have reported that the contents of cigarette smoke negatively affect sperm parameters, seminal plasma, and various other fertility factors. Nevertheless, the actual effect of smoking on male fertility is not clear. The effect of smoking on semen parameters is based on the well-established biological finding that smoking increases the presence of reactive oxygen species, thereby resulting in oxidative stress (OS). OS has devastating effects on sperm parameters, such as viability and morphology, and impairs sperm function, hence reducing male fertility. However, not all studies have come to the same conclusions. This review sheds light upon the arguable association between smoking and male fertility and also assesses the impact of non-smoking routes of tobacco consumption on male infertility. It also highlights the evidence that links smoking with male infertility, including newly emerging genetic and epigenetic data, and discusses the clinical implications thereof.

The "omics" of human male infertility: integrating big data in a systems biology approach

Spermatogenesis is a complex process in which >2300 genes are temporally and spatially regulated to form a terminally differentiated sperm cell that must maintain the ability to contribute to a totipotent embryo which can successfully differentiate into a healthy individual. This process is dependent on fidelity of the genome, epigenome, transcriptome, and proteome of the spermatogonia, supporting cells, and the resulting sperm cell. Infertility and/or disease risk may increase in the offspring if abnormalities are present. This review highlights the recent advances in our understanding of these processes in light of the "omics revolution". We briefly review each of these areas, as well as highlight areas of future study and needs to advance further.

Promoter targeted bisulfite sequencing reveals DNA methylation profiles associated with low sperm motility in asthenozoospermia

STUDY QUESTION

Is there an association between sperm DNA methylation profiles and asthenozoospermia?

SUMMARY ANSWER

DNA methylation, at specific CpGs but not at the global level, was significantly different between low motile sperm cells of asthenozoospermic individuals and high motile sperm cells of normozoospermic controls.

WHAT IS KNOWN ALREADY

Aberrant DNA methylation, both globally and restricted to a specific gene locus, has been associated with male infertility and abnormal semen parameters.

STUDY DESIGN, SIZE, DURATION

This was a case-control study investigating the differences in DNA methylation at CpGs in promoter regions between high and low motile sperm cells from eight normozoospermic controls and seven asthenozoospermic patients.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The liquid hybridization capture-based bisulfite sequencing method was used to determine DNA methylation at CpGs in promoter regions. The global inter-individual and intra-individual methylation variability were estimated by evaluating the methylation variance between and within different motile sperm fractions from the same or different individuals. Asthenozoospermia-associated differentially methylated or variable CpGs and differentially methylated regions were identified by comparing the DNA methylation of high motile sperm cells from normozoospermic controls with that of low motile sperm cells from asthenozoospermic patients.

MAIN RESULTS AND THE ROLE OF CHANCE

In this study, we determined the global DNA methylation level (24.7%), inter-individual variance (14.4%) and intra-individual differences between high and low motile sperm fractions (3.9%). We demonstrated that there were no statistically significant differences in either the global DNA methylation level or global methylation variability between sperm from men with normozoospermia or asthenozoospermia. Between high motile sperm from men with normozoospermia and low motile sperm from men with asthenozoospermia, we identified 134 differentially methylated CpGs, 41 differentially methylated regions and 134 differentially variable CpGs. The genomic distribution patterns of the differential methylation spectrum suggested that gene expression may be affected in low motile sperm cells of asthenozoospermic patients. Finally, through a functional analysis, we detected 16 differentially methylated or variable genes that are required for spermatogenesis and sperm motility or dominantly expressed in testis.

LIMITATIONS, REASONS FOR CAUTION

The sample size in this study was limited, although the participants in the two groups were carefully selected and well matched. Our results must be verified in larger cohorts with the use of different techniques. Furthermore, our results were descriptive, and follow-up studies will be needed to elucidate the effect of differential methylation profiles on asthenozoospermia.

WIDER IMPLICATIONS OF THE FINDINGS

Our study identified asthenozoospermia-associated DNA methylation profiles and proposed a list of genes, which were suggested to be involved in the regulation of sperm motility through an alteration of DNA methylation. These results will provide promising clues for understanding the effect of DNA methylation on sperm motility and asthenozoospermia.

STUDY FUNDING/COMPETING INTERESTS

This study was funded primarily by the National Natural Science Foundation of China, Shenzhen Project of Science and Technology and the National Basic Research Program of China. The authors have no competing interests.