Teratozoospermia and asthenozoospermia are associated with specific epigenetic signatures

Novel bioinformatic analyses of somatic cell contamination in sperm samples

The assessment of epigenetic profiles in sperm is sensitive to somatic cell contamination, which can influence methylation signals at gene promoters. This contamination is particularly problematic in the assessment of DNA methylation in samples with low sperm counts, where fractional amounts of somatic cell DNA can lead to significant shifts in measured methylation state. In this study, a new method of detecting possible somatic cell contamination is proposed through two multi-region bioinformatic models: a traditional differential methylation analysis and a machine learning logistic regression model. These models were trained on publicly available sperm (n = 489) and blood (n = 1029) DNA methylation array data and tested on a contamination set, wherein the sperm of four donors with normal sperm counts were run on a 450k methylation array with four permutations each, including pure blood, half blood and half sperm by DNA concentration, half blood and half sperm by cell count, and pure sperm (n = 16). The DMR and logistic regression model classified the contamination testing set with 100% and 94% accuracy, respectively. These new methods of detecting the effects of somatic cell contamination allow for more accurate differentiation between epigenetic profiles that contain a biological somatic-like shift and those that have somatic-like signatures because of contamination.

Differential sperm histone retention in normozoospermic ejaculates of infertile men negatively affects sperm functional competence and embryo quality

BACKGROUND

The unique epigenetic architecture that sperm cells acquire during spermiogenesis by retaining <15% of either canonical or variant histone proteins in their genome is essential for normal embryogenesis. Whilst heterogeneous levels of retained histones are found in morphologically normal spermatozoa, their effect on reproductive outcomes is not fully understood.

METHODS

Processed spermatozoa (n = 62) were tested for DNA integrity by sperm chromatin dispersion assay, and retained histones were extracted and subjected to dot-blot analysis. The impact of retained histone modifications in normozoospermic patients on sperm functional characteristics, embryo quality, metabolic signature in embryo spent culture medium and pregnancy outcome was studied.

RESULTS

Dot-blot analysis showed heterogeneous levels of retained histones in the genome of normozoospermic ejaculates. Post-wash sperm yield was affected by an increase in H3K27Me3 and H4K20Me3 levels in the sperm chromatin (p < 0.05). Also, spermatozoa with higher histone H3 retention had increased DNA damage (p < 0.05). Spermatozoa from these cohorts, when injected into donor oocytes, correlated to a significant decrease in the fertilisation rate with an increase in sperm histone H3 (p < 0.05) and H3K27Me3 (p < 0.01). An increase in histone H3 negatively affected embryo quality (p < 0.01) and clinical pregnancy outcome post-embryo transfer (p < 0.05). On the other hand, spent culture medium metabolites assessed by high-resolution (800 MHz) nuclear magnetic resonance showed an increased intensity of the amino acid methionine in the non-pregnant group than in the pregnant group (p < 0.05) and a negative correlation with sperm histone H3 in the pregnant group (p < 0.05).

DISCUSSION AND CONCLUSION

Histone retention in spermatozoa can be one of the factors behind the development of idiopathic male infertility. Such spermatozoa may influence embryonic behaviour and thereby affect the success rate of assisted reproductive technology procedures. These results, although descriptive in nature, warrant further research to address the underlying mechanisms behind these clinically important observations.

Could the sperm epigenome become a diagnostic tool for evaluation of the infertile man?

Although male infertility is currently diagnosed when abnormal sperm parameters are found, the poor predictive ability of sperm parameters on natural fecundity and medically assisted reproduction outcome poses the need for improved diagnostic techniques for male infertility. The accumulating evidence about the role played by the sperm epigenome in modulation of the early phases of embryonic development has led researchers to focus on the epigenetic mechanisms within the sperm epigenome to find new molecular markers of male infertility. Indeed, sperm epigenome abnormalities could explain some cases of unexplained male infertility in men showing normal sperm parameters and were found to be associated with poor embryo development in IVF cycles. The present mini-review summarizes the current knowledge about this interesting topic, starting from a description of the epigenetic mechanisms of gene expression regulation (i.e. DNA methylation, histone modifications, and non-coding RNAs' activity). We also discuss possible mechanisms by which environmental factors might cause epigenetic changes in the human germline and affect embryonic development, as well as subsequent generations' phenotypes. Studies demonstrating sperm epigenome abnormalities in men with male infertility are reviewed, with particular emphasis on those with the more severe form of spermatogenic dysfunction. Observations demonstrate that the diagnostic and prognostic efficacy of sperm epigenome evaluation will help facilitate the management of men with male factor infertility.

An assessment of alterations to human sperm methylation patterns in coronavirus disease 2019 infected and healthy control males

OBJECTIVE

To determine whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection affects male reproductive health, considering the many potential factors that contribute to declines in male fertility on a semiglobal scale.

DESIGN

In total, 64 human semen samples-32 treatment and 32 control-were laboratory processed and bioinformatically analyzed to assess differences in DNA methylation patterns. Implementing multiple bioinformatic tools, the analyses conducted will elicit between-group differences with respect to epigenetic age, epigenetic instability, semiglobal, and regional methylation, in addition to methylation patterns as a function of time since infection.

SETTING

University hospital.

PATIENTS

The study cohort of 64 individuals was drawn from a larger population of 94 volunteer participants recruited at the Human Reproduction Center at the Clinical Hospital of the Ribeirao Preto Medical School-University of São Paulo between June 2021 and January 2022 as well as in accordance with the ethical guidelines established by the Declaration of Helsinki.

INTERVENTION

Exposure to SARS-CoV-2.

MAIN OUTCOME MEASURE(S)

Effects on male reproductive health were reported as differences in DNA methylation measured using an array. Mean β values at key regulatory loci for human spermatocytes were analyzed and compared between groups. Further analysis of β values using epigenetic age, instability, semiglobal, and regional methylation tools provided an analysis with substantial breadth and depth.

RESULTS

In all analyses, there were no differences between groups. Considering these results, it can be inferred that infection with SARS-CoV-2 does not alter the epigenome of human spermatocytes in significant and/or persistent ways. Tangentially, these data also suggest that human male reproductive health is minimally altered by the virus, or that it is altered in a way that is independent of epigenetic programming.

CONCLUSION

Infection with SARS-CoV-2 has been reportedly associated with alterations in male fertility. This study asserts that such alterations do not have an epigenetic basis but are likely a result of concomitant symptomatology, i.e., fever and inflammation. Across the multiple bioinformatic analyses conducted, the results of this test did not detect any differences in DNA methylation patterns between coronavirus disease 2019 and noncoronavirus disease semen donor groups.

Improved age estimation from semen using sperm-specific age-related CpG markers

Accurate age estimation from semen has the potential to greatly narrow the pool of unidentified suspects in sexual assault investigations. However, previous efforts utilizing semen age-related CpG (AR-CpG) markers have shown lower accuracy compared to blood AR-CpG-based methods. This discrepancy may be attributed to DNA methylation (DNAm) interferences from "round cells" such as leukocytes and immature sperm cells in semen. This study aimed to develop age calculators based on sperm-specific AR-CpG markers and to achieve performance-improved age estimates from sperm DNA. Through an analysis of publicly available MethylationEPIC microarray data from 90 sperm samples of healthy males aged 22-51 years, we identified 31 sperm-specific AR-CpG markers with absolute Pearson's R values > 0.5 and Benjamini-Hochberg adjusted p values < 0.013. The top 19 AR-CpG markers with the largest absolute R values and beta ranges > 0.10, along with 3 reported semen AR-CpG markers (cg06304190, cg06979108, and cg12837463), were integrated into two methylation SNaPshot panels (Ⅰ and Ⅱ), each containing 11 markers. The 21 qualified AR-CpG markers showed absolute R values ≥ 0.427 in an independent validation cohort of 253 sperm DNA samples (22-67 years), with cg21843517 exhibiting the strongest age correlation (R = 0.853). The optimal models, constructed using sperm DNAm data of the training set (n = 214, 22-67 years) and markers from panel Ⅰ (n = 11), panel Ⅱ (n = 10), or both panels, achieved mean absolute errors (MAEs) of 2.526-4.746, 3.890-5.715, and > 9.800 years on the test sets of sperm (n = 39, 23-64 years), semen (same donors as the sperm test set), and whole blood (n = 40, 22-65 years), respectively. The simplified models incorporating 3, 5, 9, or 14 AR-CpG markers (MAE = 2.918-4.139 years for sperm) still outperformed the Lee et al. original model (MAE = 6.444 years for semen) and the reconstructed panel Lee model (MAE = 6.011 years for sperm). The final models, utilizing all sperm DNAm data (n = 253) and markers from panel Ⅰ, panel Ⅱ, or both panels, yielded mean MAEs of 2.587, 2.766, and 2.200 years, respectively, on the 50 test sets generated by 5 repeats of 10-fold cross-validations. Additionally, multiple markers in both panels demonstrated the ability to discern sperm or semen from blood with 100% accuracy. In summary, our study substantiates the potential of sperm-specific AR-CpG markers for precise age estimation from sperm DNA, providing an improved toolset for forensic investigations.

Epigenetic markers in the embryonal germ cell development and spermatogenesis

Spermatogenesis is the process of generation of male reproductive cells from spermatogonial stem cells in the seminiferous epithelium of the testis. During spermatogenesis, key spermatogenic events such as stem cell self-renewal and commitment to meiosis, meiotic recombination, meiotic sex chromosome inactivation, followed by cellular and chromatin remodeling of elongating spermatids occur, leading to sperm cell production. All the mentioned events are at least partially controlled by the epigenetic modifications of DNA and histones. Additionally, during embryonal development in primordial germ cells, global epigenetic reprogramming of DNA occurs. In this review, we summarized the most important epigenetic modifications in the particular stages of germ cell development, in DNA and histone proteins, starting from primordial germ cells, during embryonal development, and ending with histone-to-protamine transition during spermiogenesis.

Genome-wide DNA methylation profiles and small noncoding RNA signatures in sperm with a high DNA fragmentation index

BACKGROUND

A growing number of studies have reported that sperm DNA fragmentation (SDF) is associated with male infertility. However, no studies have compared genome-wide DNA methylation profiles and sncRNA signatures between sperm with high and low sperm DNA fragmentation indices (DFIs).

METHODS

Whole-genome bisulfite sequencing (WGBS) was performed on sperm samples from a weak group (DFI ≥ 30%, n = 6) and normal group (DFI ≤ 15%, n = 7). Small noncoding RNA (sncRNA) deep sequencing was conducted for sperm samples from the weak (DFI ≥ 30%, n = 13) and normal (DFI ≤ 15%, n = 17) groups.

RESULTS

A total of 4939 differentially methylated regions (DMRs) were identified in the weak group sperm samples relative to normal group sperm samples, with 2072 (41.95%) of them located in promoter regions. The percentages of hypermethylated DMRs were higher than those of hypomethylated DMRs in all seven examined gene annotation groups. Hypermethylated DMRs were significantly enriched in terms associated with neurons and microtubules. Compared with the normal group, the global DNA methylation level of the weak group sperm showed a downward trend, with lower correlation for methylation in the weak group sperm; therefore, the chromosomes of high-DFI sperm may be loose. On average, 40.5% of sncRNAs were annotated as rsRNAs, 19.3% as tsRNAs, 10.4% as yRNAs, and 7.1% as miRNAs. A total of 27 miRNAs, 151 tsRNAs, and 70 rsRNAs were differentially expressed between the two groups of sperm samples. Finally, 7 sncRNAs were identified as candidate sperm quality biomarkers, and the target genes of the differentially expressed miRNAs are involved in nervous system development.

CONCLUSION

Our findings suggest that genome-wide DNA methylation profiles and sncRNA signatures are significantly altered in high-DFI sperm. Our study provides potential biomarkers for sperm quality.

Genome-wide methylation analyses of human sperm unravel novel differentially methylated regions in asthenozoospermia

Aims & objectives: To investigate DNA methylation patterns in asthenozoospermic and normozoospermic sperm and to explore the potential roles of differential methylations in the etiology of the disease. Materials & methods: The authors performed whole-genome bisulfite sequencing analysis between normozoospermic controls and asthenozoospermic individuals. Results: The authors identified 238 significant differentially methylated regions. These differentially methylated regions were annotated to 114 protein-coding genes, with many genes showing associations with spermatogenesis, sperm motility etc. Conclusion: There are plenty of genomic regions exhibiting altered DNA methylation in asthenozoospermia, a number of which are located within or adjacent to sperm-related genes, suggesting novel methylation markers of asthenozoospermia and potential epigenetic regulation mechanisms through DNA methylation in the disease.

Prenatal exposure to phthalates and peripheral blood and buccal epithelial DNA methylation in infants: An epigenome-wide association study

BACKGROUND

Prenatal exposure to phthalates has been associated with adverse health and neurodevelopmental outcomes. DNA methylation (DNAm) alterations may be a mechanism underlying these effects, but prior investigations of prenatal exposure to phthalates and neonatal DNAm profiles are limited to placental tissue and umbilical cord blood.

OBJECTIVE

Conduct an epigenome-wide association study (EWAS) of the associations between prenatal exposure to phthalates and DNAm in two accessible infant tissues, venous buffy coat blood and buccal epithelial cells (BECs).

METHODS

Participants included 152 maternal-infant pairs from the Alberta Pregnancy Outcomes and Nutrition (APrON) study. Maternal second trimester urine samples were analyzed for nine phthalate metabolites. Blood (n = 74) or BECs (n = 78) were collected from 3-month-old infants and profiled for DNAm using the Infinium HumanMethylation450 (450K) BeadChip. Robust linear regressions were used to investigate the associations between high (HMWPs) and low molecular weight phthalates (LMWPs) and change in methylation levels at variable Cytosine-phosphate-Guanine (CpG) sites in infant tissues, as well as the sensitivity of associations to potential confounders.

RESULTS

One candidate CpG in gene RNF39 reported by a previous study examining prenatal exposure to phthalates and cord blood DNAm was replicated. The EWAS identified 12 high-confidence CpGs in blood and another 12 in BECs associated with HMWPs and/or LMWPs. Prenatal exposure to bisphenol A (BPA) associated with two of the CpGs associated with HMWPs in BECs.

DISCUSSION

Prenatal exposure to phthalates was associated with DNAm variation at CpGs annotated to genes associated with endocrine hormone activity (i.e., SLCO4A1, TPO), immune pathways and DNA damage (i.e., RASGEF1B, KAZN, HLA-A, MYO18A, DIP2C, C1or109), and neurodevelopment (i.e., AMPH, NOTCH3, DNAJC5). Future studies that characterize the stability of these associations in larger samples, multiple cohorts, across tissues, and investigate the potential associations between these biomarkers and relevant health and neurodevelopmental outcomes are needed.

Semen quality and sperm DNA methylation in relation to long-term exposure to air pollution in fertile men: A cross-sectional study

Some studies have examined the association between air pollution and semen quality. While it is less of evidence on the sperm quality after long-term air pollution exposure, especially the co-exposure of different air pollution components. Additionally, the role of DNA methylation in it hasn't been confirmed. This study aimed to investigate whether long-term exposure to air pollution was associated with semen quality, as well as to explore the effect of sperm DNA methylation in such association. From 2014 to 2016, 1607 fertile men were enrolled to evaluate 14 parameters of semen quality. Exposure window was defined as one-year before semen sampling. Multivariable linear regression and weighted quantile sum (WQS) regression model were used to investigate the association between six air pollutants co-exposure and semen quality. Sensitivity analysis regarding at the normal semen quality group was also conducted. Semen samples were randomly selected from 200 participants to detect the genomic 5-methylcytosine (5 mC) and 5-hydroxymethylcytosine (5-hmC) levels in sperm. In the total population, PM₁₀, PM_2.5, SO₂, and NO₂ were negatively associated with sperm total motility (PM₁₀: β = -2.67, P = 0.009; PM_2.5: β = -2.86, P = 0.004; SO₂: β = -2.32, P = 0.011; NO₂: β = -2.21, P = 0.012). Results of the normal semen quality group were consistent with those from the whole population. WQS regression results indicated significant decreasing sperm total motility after the co-exposure of the six air pollutants (β = -1.64, P = 0.003) in whole participants. Wherein, PM₁₀ accounted for largest proportion (43.4%). The 5-hmC level was positively associated with PM₁₀ exposure (β = 0.002, P < 0.001). Long-term exposure to PM₁₀, PM_2.5, SO₂, and NO₂, as well as co-exposure to six air pollutants, reduced semen quality in fertile men. As the most significant contributor of air pollutant, PM₁₀ exposure decreased sperm DNA methylation.

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.

Assessment of seminal cell-free DNA as a potential contaminate in studies of human sperm DNA methylation

BACKGROUND

Human seminal cell-free DNA (cfDNA) methylation patterns have not yet been thoroughly explored, however, recent work in mouse has suggested that some cfDNA encountered in the epididymis may contaminate DNA methylation studies assessing the mature sperm. Such contamination could clearly prove to be a significant confounder, for many reasons, in epigenetic studies of male factor infertility.

OBJECTIVES

To explore the nature of seminal cfDNA methylation and the likelihood that it would be retained following standard semen sample processing for epigenetic analysis.

MATERIALS AND METHODS

We assessed 12 semen samples collected at Utah Fertility Center. For each sample, seminal cfDNA was isolated from the sperm pellet. The sperm was split into three aliquots including one exposed to DNase to remove any additional cfDNA (termed "pure sperm"), one not exposed to DNase, and one exposed to DNase but reintroduced to seminal cfDNA. We additionally assessed blood DNA as our benchmark for somatic cell DNA methylation patterns. DNA methylation was measured via Illumina's 850k array and assessed for differential regional methylation.

RESULTS

46,352 differentially methylated regions (FDR > 40) were identified between pure sperm and seminal cfDNA. We found at these sites that the average DNA methylation in cfDNA always fell somewhere between the average methylation in sperm and in blood. We also assessed each sperm treatment groups at all 46,352 regions of interest and found no significant differences at any of these sites.

DISCUSSION AND CONCLUSION

Our data suggest that seminal cfDNA is a clear mixture of both somatic and germline DNA and that cfDNA is not a contaminating feature in sperm DNA methylation studies following standard protocols in human sperm DNA extraction. This article is protected by copyright. All rights reserved.

Metabolic syndrome and male fertility disorders: Is there a causal link?

Infertility is a global health problem affecting 10-15% of couples in reproductive age. Recent studies have provided growing evidence supporting that lifestyle factors can affect male fertility through alterations in endocrine profiles, spermatogenesis and/or sperm function. One of these critical factors could be the change in the food intake behavior in modern societies that produces metabolic alterations. Regarding this, metabolic syndrome (MetS) prevalence has increased in epidemic in the last 40-50 years. Although MetS is associated with advanced age, changes in lifestyles have accelerated the appearance of symptoms in the reproductive age. We review herein the current understanding of the relationship between MetS and the male reproductive status. For this purpose, in this narrative review a comprehensive literature search was made in both animal models and men, allowing us to evaluate such relationship. This analysis showed a high variability in the reproductive phenotypes observed in patients and mice suffering MetS, including sperm parameters, fertility and offspring health. In view of this, we proposed that the reproductive effects, which are diverse and not robust, observed among MetS-affected males, might depend on additional factors not associated with the metabolic condition and contributed not only by the affected male but also by his partner. With this perspective, this review provides a more accurate insight of this syndrome critical for the identification of specific diagnostic indicators and treatment of MetS-induced fertility disorders.

The impact of zinc and folic acid supplementation on sperm DNA methylation: results from the folic acid and zinc supplementation randomized clinical trial (FAZST)

OBJECTIVE

To determine if 6-month folic acid (5 mg) and zinc (30 mg) supplementation impacts sperm DNA methylation patterns.

DESIGN

A multicenter, double-blind, block randomized, placebo-controlled trial titled "The Folic Acid and Zinc Supplementation Trial (FAZST)."

SETTING

Infertility care centers.

PATIENT(S)

Male partners (18 years and older) from heterosexual couples (female partners aged 18-45 years) seeking fertility treatment were recruited.

INTERVENTION(S)

Men were randomized 1:1 to receive folic acid (5 mg) and elemental zinc (30 mg) (n = 713) or a matching placebo (n = 757) daily for 6 months.

MAIN OUTCOME MEASURE(S)

Sperm DNA methylation was analyzed using the EPIC methylation array (Illumina) at 6 months. Differential sperm DNA methylation was assessed at multiple levels (regional, single cytosine phosphate guanine, etc.). We additionally assessed the impact of supplementation on epigenetic age.

RESULT(S)

No significant differences were identified between the treatment and placebo groups although some trends appeared to be present. To determine if these trends were noteworthy, we implemented various permutations and found that the patterns we identified were no more than would be expected by random chance.

CONCLUSION(S)

The data presented here strongly suggest that this supplementation regimen is not effective at altering sperm DNA methylation. These data comport well with previous findings from the FAZST study that found no impact of supplementation on basic semen analysis parameters or live birth.

CLINICAL TRIAL REGISTRATION NUMBER

ClinicalTrials.gov Identifier: NCT01857310.

Epigenetic age prediction in semen - marker selection and model development

DNA methylation analysis is becoming increasingly useful in biomedical research and forensic practice. The discovery of differentially methylated sites (DMSs) that continuously change over an individual's lifetime has led to breakthroughs in molecular age estimation. Although semen samples are often used in forensic DNA analysis, previous epigenetic age prediction studies mainly focused on somatic cell types. Here, Infinium MethylationEPIC BeadChip arrays were applied to semen-derived DNA samples, which identified numerous novel DMSs moderately correlated with age. Validation of the ten most age-correlated novel DMSs and three previously known sites in an independent set of semen-derived DNA samples using targeted bisulfite massively parallel sequencing, confirmed age-correlation for nine new and three previously known markers. Prediction modelling revealed the best model for semen, based on 6 CpGs from newly identified genes SH2B2, EXOC3, IFITM2, and GALR2 as well as the previously known FOLH1B gene, which predict age with a mean absolute error of 5.1 years in an independent test set. Further increases in the accuracy of age prediction from semen DNA will require technological progress to allow sensitive, simultaneous analysis of a much larger number of age correlated DMSs from the compromised DNA typical of forensic semen stains.

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.

Lack of association between single polymorphic variants of the mitochondrial nicotinamide adenine dinucleotide dehydrogenase 3, and 4L (MT-ND3 and MT-ND4L) and male infertility

Male infertility is a multifactorial condition associated with different genetic abnormalities in at least 15%-30% of cases. The purpose of this study was to identify suspected correlations between infertility and polymorphisms in mitochondrial NADH dehydrogenase subunits 3 and 4L (MT-ND3 and MT-ND4L) in subfertile male spermatozoa. Sanger sequencing of the mitochondrial DNA target genes was performed on 68 subfertile and 44 fertile males. Eight single nucleotide polymorphisms (SNPs) in MT-ND3 (rs2853826, rs28435660, rs193302927, rs28358278, rs41467651, rs3899188, rs28358277 and rs28673954) and seven SNPs in MT-ND4L (rs28358280, rs28358281, rs28358279, rs2853487, rs2853488, rs193302933 and rs28532881) were detected and genotyped. The genotypes and allele frequencies of the study population have shown a lack of statistically significant association between MT-ND3 and MT-ND4L SNPs and male infertility. However, no statistically significant association was found between the asthenozoospermia, oligozoospermia, teratozoospermia, asthenoteratozoospermia, oligoasthenoteratozoospermia and oligoteratozoospermia subgroups of subfertile males. However, rs28358278 genotype of the MT-ND3 gene was reported in the subfertile group but not in the fertile group, which implies a possible role of this SNP in male infertility. In conclusion, the investigated polymorphic variants in the MT-ND3 and MT-ND4L genes did not show any significant association with the occurrence of male infertility. Further studies are required to evaluate these findings. Moreover, the subfertile individuals who exhibit a polymorphism at rs28358278 require further monitoring and evaluation.

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.

Sperm DNA methylation changes after short-term nut supplementation in healthy men consuming a Western-style diet

BACKGROUND

Many environmental and lifestyle factors have been implicated in the decline of sperm quality, with diet being one of the most plausible factors identified in recent years. Moreover, several studies have reported a close association between the alteration of specific sperm DNA methylation signatures and semen quality.

OBJECTIVES

To evaluate the effect of tree nut consumption on sperm DNA methylation patterns in healthy individuals reporting eating a Western-style diet.

MATERIAL AND METHODS

This is a post hoc analysis conducted in a subset of participants (healthy, non-smoking, and young) from the FERTINUTS 14-wk randomized-controlled, parallel trial, recruited between December 2015 and February 2017. The participants included in the current study (n = 72) were randomly selected in a proportion 2:1 from the original FERTINUTS trial between the 98 participants that completed the entire dietary intervention (nut group, n = 48; control group, n = 24). Sperm DNA methylation patterns were examined at baseline and after 14 weeks in 48 individuals consuming 60 g/d of mixed nuts (nut group) and in 24 individuals following the usual Western-style diet avoiding consumption of nuts (control group).

RESULTS

Over the course of the trial, no significant changes in global methylation were observed between groups. However, in the nut group, we identified 36 genomic regions that were significantly differentially methylated between the baseline and the end of the trial and 97.2% of the regions displayed hypermethylation. We identified no such change in the control group over the same period of time. We also utilized the recently developed germ line age calculator to determine if nut consumption resulted in alterations to the epigenetic age of cells and no significant differences were found.

DISCUSSION AND CONCLUSION

Adding nuts to a regular Western-style diet subtly impacts sperm DNA methylation in specific regions, demonstrating that there are some sperm epigenome regions that could respond to diet.

The combined effect of obesity and aging on human sperm DNA methylation signatures: inclusion of BMI in the paternal germ line age prediction model

Male aging and obesity have both been shown to contribute to declines in fertility in men. Recent work in aging has shown consistent epigenetic changes to sperm as a man ages. In fact, our lab has built a tool that utilizes DNA methylation signatures from sperm to effectively predict an individual’s age. Herein, we performed this preliminary cohort study to determine if increased BMI accelerates the epigenetic aging in sperm. A total of 96 participants were divided into four age groups (22–24, 30, 40–41, and > 48 years of age) and additionally parsed into two BMI sub-categories (normal and high/obese). We found no statistically significant epigenetic age acceleration. However, it is important to note that within each age category, high BMI individuals were predicted to be older on average than their actual age (~ 1.4 years), which was not observed in the normal BMI group. To further investigate this, we re-trained a model using only the present data with and without BMI as a feature. We found a modest but non-significant improvement in prediction with BMI [r² = 0.8814, mean absolute error (MAE) = 3.2913] compared to prediction without BMI (r² = 0.8739, MAE = 3.3567). Future studies with higher numbers of age-matched individuals are needed to definitively understand the impact of BMI on epigenetic aging in sperm.

Differential DNA methylation pattern and sperm quality in men with varicocele

OBJECTIVE

To study the global DNA methylation pattern in spermatozoa of patients with varicocele as well as investigate their semen quality.

DESIGN

Prospective observational case-control study.

SETTING

University-affiliated hospital.

PATIENT(S)

A total of 26 men with varicocele and 26 fertile men without the disorder.

INTERVENTIONS

Analysis of semen quality and sperm DNA methylation patterns.

MAIN OUTCOME MEASURE(S)

Semen quality evaluated by semen analysis, and sperm DNA methylation patterns investigated using the Infinium MethylationEPIC BeadChip platform.

RESULT(S)

Men with varicocele displayed decreased semen quality. The sperm DNA methylation analysis showed that men with varicocele exhibit global hypomethylation in comparison with the control group. A total of 59 differentially methylated CpG sites were identified, most of them hypomethylated in the varicocele group. In regional analyses, 1,695 DNA regions were differentially methylated in men with varicocele. These regions show associations with gamete generation, meiotic and meiosis cell cycle, and semen quality based on gene ontology analysis.

CONCLUSION(S)

Gene ontology results suggest that changes in methylation may be associated with the low semen quality phenotype observed in some varicocele patients because the observed differentially methylated regions in varicocele patients are related to male reproductive pathways. Additionally, the varicocele grade may influence the magnitude of global sperm DNA methylation change. To our knowledge, this is the first report analyzing changes at a regional or CpG-specific level in men with varicocele.

Genetic aspects of idiopathic asthenozoospermia as a cause of male infertility

Infertility is a worldwide problem affecting about 15% of couples trying to conceive. Asthenozoospermia (AZS) is one of the major causes of male infertility, diagnosed by reduced sperm motility, and has no effective therapeutic treatment. To date, a few genes have been found to be associated with AZS in humans and mice, but in most of cases its molecular aetiology remains unknown. Genetic causes of AZS may include chromosomal abnormalities, specific mutations of nuclear and mitochondrial genes. However recently, epigenetic factors, altered microRNAs expression signature, and proteomics have shed light on the pathophysiological basis of AZS. This review article summarises the reported genetic causes of AZS.

Harnessing the full potential of reproductive genetics and epigenetics for male infertility in the era of "big data"

The complexity of male reproductive impairment has hampered characterization of the underlying genetic causes of male infertility. However, in the last 20 years, more powerful and affordable tools to interrogate the genetic and epigenetic determinants of male infertility have accelerated the number of new discoveries in the characterization of male infertility. With this explosion of new data, integration in a systems-based approach-including complete phenotypic information-to male infertility is imperative. We briefly review the current understanding of genetic and epigenetic causes of male infertility and how findings may be translated into a practical component for the diagnosis and treatment of male infertility.

The preconception environment and sperm epigenetics

BACKGROUND

Infertility is a common reproductive disorder, with male factor infertility accounting for approximately half of all cases. Taking a paternal perceptive, recent research has shown that sperm epigenetics, such as changes in DNA methylation, histone modification, chromatin structure, and noncoding RNA expression, can impact reproductive and offspring health. Importantly, environmental conditions during the preconception period has been demonstrated to shape sperm epigenetics.

OBJECTIVES

To provide an overview on epigenetic modifications that regulate normal gene expression and epigenetic remodeling that occurs during spermatogenesis, and to discuss the epigenetic alterations that may occur to the paternal germline as a consequence of preconception environmental conditions and exposures.

MATERIALS AND METHODS

We examined published literature available on databases (PubMed, Google Scholar, ScienceDirect) focusing on adult male preconception environmental exposures and sperm epigenetics in epidemiologic studies and animal models.

RESULTS

The preconception period is a sensitive developmental window in which a variety of exposures such as toxicants, nutrition, drugs, stress, and exercise, affects sperm epigenetics.

DISCUSSION AND CONCLUSION

Understanding the environmental legacy of the sperm epigenome during spermatogenesis will enhance our understanding of reproductive health and improve reproductive success and offspring well-being.

Increased DNA methylation in the spermatogenesis-associated (SPATA) genes correlates with infertility

BACKGROUND

Spermatogenesis-associated (SPATA) family of genes plays important roles in spermatogenesis, sperm maturation or fertilization. The knockout studies in mice have demonstrated that SPATA genes are crucial for fertility. Gene expression and genetic polymorphism studies have further suggested their correlation with infertility; however, methylation analysis of SPATA genes in human male infertility has not yet been undertaken.

OBJECTIVES

To analyze the methylation status of SPATA4, SPATA5 and SPATA6 genes in oligozoospermic male infertility.

MATERIALS AND METHODS

In the present study, we have analyzed DNA methylation pattern in the promoter regions of SPATA4, SPATA5 and SPATA6 genes in oligozoospermic patients and compared it with normozoospermic fertile controls. Semen samples were obtained from 30 oligozoospermic infertile and 19 normozoospermic fertile controls, and DNA methylation levels of the target gene promoters were analyzed by amplicon based deep sequencing methylation analysis using MiSeq.

RESULTS

SPATA4 (P < 0.0008), SPATA5 (P = 0.009) and SPATA6 (Promoter, P < 0.0005; Exon 1, P = 0.0128) genes were significantly hypermethylated in oligozoospermic patients in comparison to controls. This is the first study reporting a higher methylation in the promoters of SPATA4, SPATA5 and SPATA6 in oligozoospermic infertile individuals in comparison to the normozoospermic fertile controls.

DISCUSSION

Altered methylation of SPATA genes would affect pathways involved in sperm production or affect various processes linked to sperm fertility.

CONCLUSION

In conclusion, hypermethylation in the SPATA4, SPATA5 and SPATA6 genes correlates with oligozoospermic infertility.

CircRNA Role and circRNA-Dependent Network (ceRNET) in Asthenozoospermia

The role of circRNA in reproduction is under investigation. CircRNAs are expressed in human testis, spermatozoa (SPZ), and seminal plasma. Their involvement in embryo development has also been suggested. Asthenozoospermia, a common cause of male infertility, is characterized by reduced or absent sperm motility in fresh ejaculate. While abnormal mitochondrial function, altered sperm tail, and genomic causes have been deeply investigated, the epigenetic signature of asthenozoospermic derived SPZ still remains unexplored. CircRNAs may take part in the repertoire of differentially expressed molecules in infertile men. Considering this background, we carried out a circRNA microarray, identifying a total of 9,138 transcripts, 22% of them novel based and 83.5% with an exonic structure. Using KEGG analysis, we evaluated the circRNA contribution in pathways related to mitochondrial function and sperm motility. In order to discriminate circRNAs with a differential expression in SPZ with differential morphological parameters, we separated sperm cells by Percoll gradient and analyzed their differential circRNA payload. A bioinformatic approach was then utilized to build a circRNA/miRNA/mRNA network. With the aim to demonstrate a dynamic contribution of circRNAs to the sperm epigenetic signature, we verified their modulation as a consequence of an oral amino acid supplementation, efficacious in improving SPZ motility.

Treatment of idiopathic oligozoospermia with combined human chorionic gonadotropin/human menopausal gonadotrophin: A randomised, double-blinded, placebo-controlled clinical study

To evaluate whether hCG/hMG therapy has beneficial effects on idiopathic oligozoospermia in Chinese infertility population. The patients were randomly divided into the treatment group receiving hCG/hMG for 3 months and the placebo group receiving placebo for 3 months. Semen and biochemical analysis was performed, and DNA fragmentation as well as spermatid concentration was evaluated. Administration of hCG/hMG for 3 months could significantly improve sperm concentration, rate of forward motile spermatozoa, total motile sperm count, the percentage of sperm with normal morphology and the rate of spontaneous pregnancy in medium- and higher-level inhibin B group respectively. Moreover, in medium- and higher-level inhibin B group, sperm DNA fragmentation index and spermatid concentration were significantly declined respectively at the end of treatment. However, there were no significant differences in lower-level inhibin B group before and after treatment in term of seminal parameters, DNA fragmentation and spermatid concentration. HCG/hMG therapy for 3 months has a beneficial effect on a part of male with idiopathic oligozoospermia, and the efficacy of hCG/hMG therapy is associated with the inhibin B level.

The clinical usefulness of a novel grading system for varicocoeles using duplex Doppler ultrasound examination based on postsurgical modifications of seminal parameters

BACKGROUND

The existing classifications of varicocoeles have poor predictive value regarding the effects of surgery on sperm count.

OBJECTIVE

To develop a new grading system for varicocoeles, useful as an indication for surgery.

MATERIALS AND METHODS

This is a three-center prospective study which examined 173 men having clinically detectable left varicocoeles and oligo ± astheno ± terato-spermia. The patients underwent medical history collection, objective examination, duplex Doppler ultrasound scrotal examination, hormonal profiles, two semen analyses before surgery, and two semen analyses after surgery. Sperm concentration, motility, and morphology (standard semen parameters) were evaluated 6 months after surgery in function of the following preoperative variables: patient age, follicle-stimulating hormone, clinical grade of varicocoele, right and left testicular volume, extension of venous reflux, and semen parameters. The venous reflux was graded in two centers using duplex Doppler ultrasound: reflux visible only with Valsalva and continuous reflux. Spearman's rank semiquantitative analysis was used. All patients had their varicocoeles corrected according to the Colpi technique.

RESULTS

The variables capable of determining an improvement in semen parameters after varicocoele correction were in order of decreasing importance: venous reflux extent assessed by scrotal duplex Doppler ultrasound examination, varicocoele clinical grade, basal semen parameters, and follicle-stimulating hormone. Male age did not influence postoperative semen quality. Only patients with continuous reflux had their standard semen parameters improved after surgery.

DISCUSSION

Venous reflux extent is the most critical variable capable of predicting semen improvement after varicocoelectomy.

CONCLUSIONS

A correct duplex Doppler assessment of venous reflux is mandatory for predicting postoperative improvement of the sperm count.

Alterations in the sperm histone-retained epigenome are associated with unexplained male factor infertility and poor blastocyst development in donor oocyte IVF cycles

STUDY QUESTION

Is there a distinct sperm histone-retained epigenetic signature in unexplained male factor infertility patients resulting in compromised blastocyst development?

SUMMARY ANSWER

Using only donor oocyte IVF cycles, sperm DNA methylation patterns and miRNA profiles were significantly altered in normozoospermic patients resulting in poor blastocyst development, reflecting a subset of unexplained male factor infertility.

WHAT IS KNOWN ALREADY

Aberrant sperm DNA methylation has been associated with known male factor infertility, particularly noted in oligozoospermic patients. Unexplained male factor infertility remains a significant proportion of in vitro fertilization failures having unknown underlying physiology.

STUDY DESIGN, SIZE, DURATION

Sperm samples (n = 40) and blastocysts (n = 48) were obtained during fertile donor oocyte IVF cycles with normozoospermic parameters, thereby excluding known female and male infertility factors. Samples were divided into two groups based on blastocyst development (Good Group = ≥20% embryos with D5 grade 'AA' blastocysts, and ≥60% embryos of transferable quality on D5 and D6; Poor Group = ≤10% embryos with D5 grade 'AA' blastocysts, and ≤40% embryos of transferable quality on D5 and D6).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Samples were obtained from patients undergoing IVF treatments with informed consent and institutional review board approval. The Infinium HumanMethylation450 BeadChip microarray was used to identify histone-retained CpG island genes and genomic regions showing differences in sperm DNA methylation between the Good Group and the Poor Group. Pathway and gene network analysis for the significantly altered genes was performed, and targeted DNA methylation validation was completed for 23 genes and two imprinting control regions. Sperm miRNA profiles were assessed using the TaqMan® Human MicroRNA Array Card, with corresponding blastocyst mRNA gene expression examined by qRT-PCR.

MAIN RESULTS AND THE ROLE OF CHANCE

Our study is the first to investigate unexplained male factor infertility while significantly eliminating confounding female factors from our sample population by using only young fertile donor oocytes. We identified 1634 CpG sites located at retained histone CpG island regions that had significant sperm DNA methylation differentials between the two embryogenesis groups (P < 0.05). A largely hypermethylated profile was evident in the Good Group, with a small but distinct and statistically significant shift (P < 0.05) observed in the Poor Group. Genes involved in embryonic development were highly represented among histone-retained CpG sites with decreased methylation in the Poor Group (P < 0.05). Ten significantly altered sperm miRNAs (P < 0.05), correlated with altered target gene mRNA expression in the blastocysts from the Poor Group (P < 0.05). Taken together, significantly impacted sperm miRNA and target transcript levels in blastocysts from the Poor Group may contribute alongside aberrant sperm DNA methylation to the compromised blastocyst development observed.

LIMITATIONS, REASONS FOR CAUTION

Our examination of CpG island regions restricted to retained histones represents only a small part of the sperm epigenome. The results observed are descriptive and further studies are needed to elucidate the functional effects of differential sperm DNA methylation on unexplained male factor infertility and blastocyst development.

WIDER IMPLICATIONS OF THE FINDINGS

Slight epigenetic changes in sperm may have a cumulative effect on fertility and embryonic developmental competence. Knowledge of sperm epigenetics and inheritance has important implications for future generations, while providing evidence for potential causes of unexplained male factor infertility.

STUDY FUNDING/COMPETING INTEREST(S)

No external funding was used for this study. None of the authors have any competing interest.

The status of global DNA methylation in the spermatozoa of smokers and non-smokers

RESEARCH QUESTION

Does regular smoking affect semen quality and the levels of DNA methylation in mature human spermatozoa?

DESIGN

Spermatozoa from 109 men were evaluated (55 smokers and 54 non-smokers). DNA was extracted from purified spermatozoa, and DNA methylation was quantified by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Global DNA methylation of non-smokers is significantly lower (P < 0.001) than that of smokers (4.85 ± 2.72 and 7.08 ± 1.77 ng/μl, respectively). Moreover, the mean global DNA methylation levels were significantly correlated (r = 0.22;P = 0.02) with non-condensed chromatin in the spermatozoa. Levels of non-condensed chromatin were significantly higher (P < 0.001) in smokers (29.75 ± 9.38%) compared with non-smokers (20.96 ± 11.31%). Furthermore, global sperm DNA methylation was negatively correlated with high significance (P < 0.010) with sperm: count (r = -0.27), motility (r = -0.30) and vitality (r = -0.26).

CONCLUSION

Smoking interferes with DNA methylation. Also, DNA methylation is significantly correlated with sperm parameters and sperm non-condensed chromatin. These data emphasize another detrimental effect of smoking on male fertility. DNA methylation may, therefore, be considered as a fertility marker in men.

Pre-screening method for somatic cell contamination in human sperm epigenetic studies

Sperm epigenetic profiles are frequently studied and are of great interest in many fields. One major technical concern when assessing these marks is the potential for somatic cell contamination. Because somatic cells have dramatically different epigenetic signatures, even small levels of contamination can result in significant problems in analysis and interpretation of data. In this study we evaluate an assay, which we designed to offer a reliable 'pre-screen' for somatic cell contamination that directly assesses the DNA being used in the study to determine tissue purity. In brief, we designed an inexpensive and simple assay that utilizes the strong differential methylation between sperm and somatic cells at four genomic loci to assess the general purity of samples prior to performing expensive and time intensive assays. The assay is able to reliably detect contamination qualitatively by running the sample on an agarose gel, or quantitatively with the use of a bioanalyzer. With this technique we have found that we can detect potentially contaminating signals in samples of many different types, including those from patients with poor sperm phenotypes (oligozoospermia, asthenozoospermia, and teratozoospermia). We also have found that the use of multiple sites to determine potential contamination is key, as some conditions (asthenozoospermia specifically) appear at one site to reflect a somatic-like profile, while at all other sites it appears to have very typical sperm DNA methylation signatures. Taken together, the use of the assay described herein was effective at identifying contamination and could be implemented in many labs to quickly and inexpensively pre-screen samples prior to performing far more expensive and labor intensive procedures. Additionally, the principles applied to the development of this assay could be easily adapted for the development of other assays to pre-screen different tissue/cell types or model organisms.

Inheritance of epigenetic dysregulation from male factor infertility has a direct impact on reproductive potential

OBJECTIVE

To evaluate the epigenetic consequence on the methylome and subsequent transcriptome in euploid blastocysts of male-factor (MF) infertility patients.

DESIGN

Methylome and transcriptome analysis on individual oligoasthenoteratozoospermia (OAT [MF]) blastocysts.

SETTING

Infertility clinic.

PATIENT(S)

Clinical data from 128 couples presenting with OAT (MF) and 118 maternal age-matched control (no MF) subjects undergoing infertility treatment from 2010 to 2014, along with 72 surplus cryopreserved blastocysts donated from 33 couples with their informed consents.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Methyl Maxi-Seq (Zymo Research) was used to determine genome-wide DNA methylation, and small cell number RNA-Seq was used to examine the global transcriptome. Validation experiments were performed with the use of pyrosequencing or quantitative real-time polymerase chain reaction. Statistical analysis used Student t test, analysis of variance in R, Fisher exact test, and pairwise fixed reallocation randomization test where appropriate, with significance at P<.05.

RESULT(S)

Clinical pregnancy rates were similar between OAT (MF) patients and control (no MF) subjects after euploid embryo transfer. However, the miscarriage rate for OAT (MF) patients was significantly higher (14.7% vs. 2.2%; P<.05). Methylome and transcriptome analyses of individual blastocysts revealed significant alterations in 1,111 CpG sites and 469 transcripts, respectively (P<.05). Pathway analysis elucidated genes involved in "regulation of cellular metabolic process" as universally affected. Validation of the genome-wide approaches was performed for SBF1 and SLC6A9 (P<.05).

CONCLUSION(S)

Methylation and transcription aberrations in individual OAT (MF) blastocysts illustrate an epigenetic consequence of MF infertility on embryogenesis, significantly altering key developmental genes and affecting embryonic competence. This epigenetic dysregulation provides an explanation for the reduced reproductive potential in OAT (MF) patients despite euploid blastocyst transfers.

Do paternal semen parameters influence the birth weight or BMI of the offspring? A study from the Utah Population Database

PURPOSE

To study the role of individual semen parameters on the offspring birth weight and body mass index (BMI) from a population of men evaluated in an assisted reproduction technology (ART) clinic compared to fertile controls.

METHODS

We performed a retrospective study using a cohort with fertile, age-matched controls of men evaluated with semen analysis at the University of Utah Andrology Clinic from 1996 to 2011 and Intermountain Healthcare from 2002 to 2011. We use the offspring from both our sub-fertile cohort and controls using the Utah Population Database. The two main outcomes of interest were offspring birth weight and adolescent BMI.

RESULTS

The offspring of men with impaired sperm parameters had significantly lower birth weight compared to fertile control offspring. Low-concentration offspring weighed 158 g less (95% CI - 278~- 38; p = 0.01), low total count weighed 172 g less (95% CI - 294~- 51; p = 0.005), and low total motility weighed 155 g less (95% CI - 241~- 69; p < 0.001) compared to those of the controls. When we controlled for the use of ART within the sub-fertile group, we found that there was a significant trend of increasing birth weight across levels of total motile count and total sperm count compared to the azoospermic group. We did not find any consistent significant differences between the subject and control adolescence BMI based on semen parameters.

CONCLUSIONS

Despite limitations within our population-based dataset, we found that poor quality semen analysis parameters pointed towards an association with low birth weight in the offspring of sub-fertile men compared to the offspring of normal fertile controls. However, in contrast to studies of ART effects on offspring, we did not find evidence of long-term associations between semen quality and offspring BMI.

Impairment of sperm DNA methylation in male infertility: a meta-analytic study

Considering the widespread use of assisted reproductive techniques (ART), DNA methylation of specific genes involved in spermatogenesis achieves increasingly clinical relevance, representing a possible explanation of increased incidence of syndromes related to genomic imprinting in medically assisted pregnancies. Several trials suggested a relationship between male sub-fertility and sperm DNA methylation, although its weight on seminal parameters alteration is still a matter of debate. To evaluate whether aberrant sperm DNA methylation of imprinted genes is associated with impaired sperm parameters. Meta-analysis of controlled clinical trials evaluating imprinted genes sperm DNA methylation comparing men with idiopathic infertility to fertile controls. Twenty-four studies were included, allowing a meta-analytic evaluation for H19, MEST, SNRPN, and LINE-1. When a high heterogeneity of the results was demonstrated, the random effect model was used. H19 methylation levels resulted significantly lower in 879 infertile compared with 562 fertile men (7.53%, 95% CI: 5.14-9.93%, p < 0.001), suggesting a 9.91-fold higher risk ratio to show aberrant sperm DNA methylation (95% CI: 5.55-17.70, p < 0.001, I²  = 19%) in infertile men. The mean MEST methylation level was significantly higher in 846 infertile compared with 353 fertile men (3.35%, 95% CI: 1.41-5.29%, p < 0.001), as well as for SNRPN comparing 301 infertile men with 124 controls (3.23%, 95% CI: 0.75-5.72%, p < 0.001). LINE-1 methylation levels did not differ between 291 infertile men and 198 controls (0.44%, 95% CI: -2.04-1.16%, p = 0.63). The meta-analytic approach demonstrated that male infertility is associated with altered sperm methylation at H19, MEST, and SNRPN. Although its role in infertility remains unclear, sperm DNA methylation could be associated with the epigenetic risk in ART. In this setting, before proposing this analysis in clinical practice, an accurate identification of the most representative genes and a cost-effectiveness evaluation should be assessed in ad hoc prospective studies.

Aberrations in sperm DNA methylation patterns of males suffering from reduced fecundity

The purpose of this study was to evaluate the aberrations in sperm DNA methylation patterns of males suffering from reduced fecundity. A total of 108 males (65 males suffering from reduced fecundity as cases and 43 proven fertile males as a control) were included in the study. Thirty samples were subjected to 450K arrays as a screening phase, and then, three CpG sites located in the following genes: TYRO3, CGβ and FAM189A1 were selected to validate on 78 samples using deep bisulphite sequencing. A significant difference in the methylation level was found between cases and controls at all CpGs in TYRO3 gene-related amplicon (CpG1, p ≤ .003, CpG2, p ≤ .0001, CpG3, p ≤ .003 and CpG4, p ≤ .030) and CpG1 in CGβ gene-related amplicon (p ≤ .0001). Besides, a significant difference was found at two CpGs (CpG1, p ≤ .004 and CpG2, p ≤ .002) tested in the FAM189A1 gene-related amplicon. A significant correlation was found between the methylation level at CpG1 in the FAM189A1 gene and the different types of sperm motility. In conclusion, an alteration in the methylation levels of sperm DNA from males with reduced fecundity was showed. In addition, a relationship between variations in the methylation level of these CpGs and sperm motility has been observed.

What the human sperm methylome tells us

Aim: To characterize the sperm methylome in semen samples from 19 donors with proven fertility. Materials & methods: Bisulfite-converted sperm DNA was hybridized on the HumanMethylation450 Infinium BeadChip platform. CpG fluorescence intensities were extracted and converted to β-values. Results: The sperm methylome is highly homogeneous and hypomethylated. Genes with hypomethylated promoters are ontologically associated to biological functions related to spermatogenesis and embryogenesis. Sex chromosomes are the most hypomethylated chromosomes, supporting data that indicated their essential role in spermatogenesis. A total of 94 genes are resistant to demethylation, being strong candidates for transgenerational inheritance. Conclusion: Spermatozoa carry a homogeneous methylation profile that is a footprint of past events (spermatogenesis), is designed to facilitate future events (embryogenesis) and has a possible influence in the adult life (transgenerational effects).

Cigarette smoking significantly alters sperm DNA methylation patterns

Numerous health consequences of tobacco smoke exposure have been characterized, and the effects of smoking on traditional measures of male fertility are well described. However, a growing body of data indicates that pre-conception paternal smoking also confers increased risk for a number of morbidities on offspring. The mechanism for this increased risk has not been elucidated, but it is likely mediated, at least in part, through epigenetic modifications transmitted through spermatozoa. In this study, we investigated the impact of cigarette smoke exposure on sperm DNA methylation patterns in 78 men who smoke and 78 never-smokers using the Infinium Human Methylation 450 beadchip. We investigated two models of DNA methylation alterations: (i) consistently altered methylation at specific CpGs or within specific genomic regions and (ii) stochastic DNA methylation alterations manifest as increased variability in genome-wide methylation patterns in men who smoke. We identified 141 significantly differentially methylated CpGs associated with smoking. In addition, we identified a trend toward increased variance in methylation patterns genome-wide in sperm DNA from men who smoke compared with never-smokers. These findings of widespread DNA methylation alterations are consistent with the broad range of offspring heath disparities associated with pre-conception paternal smoke exposure and warrant further investigation to identify the specific mechanism by which sperm DNA methylation perturbation confers risk to offspring health and whether these changes can be transmitted to offspring and transgenerationally.