The impact of histones linked to sperm chromatin on embryo development and ART outcome

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.

ICSI using testicular spermatozoa after failure of ICSI with ejaculated spermatozoa could be a good choice: A propensity score-matched cohort study

BACKGROUND

Ejaculated spermatozoa are considered to possess a higher fertilisation potential than testicular spermatozoa. In selected cases, the use of testicular spermatozoa from non-azoospermic infertile men resulted in a higher implantation and pregnancy rate than the use of ejaculated spermatozoa.

OBJECTIVE

The primary objective was to compare the live birth rate and cumulative live birth rate between couples with failed intracytoplasmic sperm injection procedure using ejaculated spermatozoa who subsequently had an intracytoplasmic sperm injection cycle with testicular spermatozoa and those who subsequently had an intracytoplasmic sperm injection cycle with ejaculated spermatozoa. The secondary objective was to determine the indications for the use of testicular spermatozoa after intracytoplasmic sperm injection failure with ejaculated spermatozoa.

MATERIALS AND METHODS

A retrospective study of matched couples using propensity score matching analysis was performed. After an intracytoplasmic sperm injection failure (cycle_1), intracytoplasmic sperm injection with either ejaculated spermatozoa (ejaculated sperm group), or testicular spermatozoa (testicular sperm group), was performed (cycle_2). The matching was on intracytoplasmic sperm injection performed in cycle_1 according to spermatozoa used (testicular or ejaculated) in cycle_2. Logistic regression was used to evaluate the influence of sperm origin on cumulative live birth rate. Univariate analysis on parameters of cycle_1 was used to identify the prognostic factors to propose an intracytoplasmic sperm injection with testicular spermatozoa in case of cycle_1 failure. The study outcomes were live birth rate and cumulative live birth rate.

RESULTS

Among the 6034 couples available, 63 were selected to constitute the testicular sperm group and 63 were selected by propensity score matching to constitute the ejaculated sperm group. After matching, the DNA fragmentation index was higher in the testicular sperm group (13.43% ± 9.65% vs. 8.93% ± 4.47%, p = 0.013); no significant difference was observed for the fertilisation rate, the number of obtained embryos, blastulation rate and frozen embryo rate. In cycle_2, the live birth rate was higher in the testicular group (22.2% vs. 0.0%, p < 0.001), as was the cumulative live birth rate (25.4% vs. 6.3%, p = 0.065). The prognostic factors identified for the proposal of intracytoplasmic sperm injection procedure with testicular spermatozoa after intracytoplasmic sperm injection failure with ejaculated spermatozoa were: teratozoospermia, cryptozoospermia and high DNA fragmentation index.

DISCUSSION

According to the present study and current knowledge, the use of testicular spermatozoa after failed intracytoplasmic sperm injection procedure in non-azoospermic men could be proposed instead of sperm donation in case of high sperm DNA fragmentation index, cryptozoospermia and teratozoospermia. A good oocyte response to ovarian stimulation during the previous assisted reproductive technology attempt will increase the chance of success. Although the main limitation of the current study is its retrospective nature, the use of the propensity score matching to perform causal inference study increases its reliability.

CONCLUSION

The present study supports that the use of testicular spermatozoa outside the classical indication of azoospermia is a good option when the indication is well established. However, before proposing a testicular biopsy, an improvement in sperm characteristics should be considered by treating the causes of sperm alteration.

Sperm DNA methylation patterns at discrete CpGs and genes involved in embryonic development are related to bull fertility

Background

Despite a multifactorial approach being taken for the evaluation of bull semen quality in many animal breeding centres worldwide, reliable prediction of bull fertility is still a challenge. Recently, attention has turned to molecular mechanisms, which could uncover potential biomarkers of fertility. One of these mechanisms is DNA methylation, which together with other epigenetic mechanisms is essential for the fertilising sperm to drive normal embryo development and establish a viable pregnancy. In this study, we hypothesised that bull sperm DNA methylation patterns are related to bull fertility. We therefore investigated DNA methylation patterns from bulls used in artificial insemination with contrasting fertility scores.

Results

The DNA methylation patterns were obtained by reduced representative bisulphite sequencing from 10 high-fertility bulls and 10 low-fertility bulls, having average fertility scores of − 6.6 and + 6.5%, respectively (mean of the population was zero). Hierarchical clustering analysis did not distinguish bulls based on fertility but did highlight individual differences. Despite this, using stringent criteria (DNA methylation difference ≥ 35% and a q-value < 0.001), we identified 661 differently methylated cytosines (DMCs). DMCs were preferentially located in intergenic regions, introns, gene downstream regions, repetitive elements, open sea, shores and shelves of CpG islands. We also identified 10 differently methylated regions, covered by 7 unique genes (SFRP1, STXBP4, BCR, PSMG4, ARSG, ATP11A, RXRA), which are involved in spermatogenesis and early embryonic development.

Conclusion

This study demonstrated that at specific CpG sites, sperm DNA methylation status is related to bull fertility, and identified seven differently methylated genes in sperm of subfertile bulls that may lead to altered gene expression and potentially influence embryo development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08614-5.

The Effects of Sperm and Seminal Fluid of Immunized Male Mice on In Vitro Fertilization and Surrogate Mother-Embryo Interaction

The latest vaccination campaign has actualized the potential impact of antigenic stimuli on reproductive functions. To address this, we mimicked vaccination’s effects by administering keyhole limpet hemocyanin (KLH ) to CD1 male mice and used their sperm for in vitro fertilization (IVF). Two-cell embryos after IVF with spermatozoa from control (C) or KLH-treated (Im) male mice were transferred to surrogate mothers mated with vasectomized control (C) or KLH-treated (Im) male mice, resulting in four experimental groups: C–C, Im–C, C–Im, and Im–Im. The pre-implantation losses were significantly lower in the Im–C group than in the C–Im group. At the same time, the resorption rates reduced markedly in the C–Im compared to the Im–C group. Embryo and placenta weights were significantly higher in the Im–Im group. Although the GM-CSF levels were lower in the amniotic fluid of the gestating surrogate mothers in the Im–Im group, they were strongly correlated with embryo mass. The number–size trade-off was only significant in the Im–Im group. This suggests a positive, cooperative effect of spermatozoa and seminal fluid from immune-primed males on embryo growth and the optimal distribution of surrogate mother maternal resources despite the negative impact of males’ antigenic challenge on the IVF success rate.

Epigenetics of Male Fertility: Effects on Assisted Reproductive Techniques

During the last decades the study of male infertility and the introduction of the assisted reproductive techniques (ARTs) has allowed to understand that normal sperm parameters do not always predict fertilization. Sperm genetic components could play an important role in the early stages of embryonic development. Based on these acquisitions, several epigenetic investigations have been developed on spermatozoa, with the aim of understanding the multifactorial etiology of male infertility and of showing whether embryonic development may be influenced by sperm epigenetic abnormalities. This article reviews the possible epigenetic modifications of spermatozoa and their effects on male fertility, embryonic development and ART outcome. It focuses mainly on sperm DNA methylation, chromatin remodeling, histone modifications and RNAs.

Paternal factors contributing to embryo quality

PURPOSE

Advancing maternal and paternal age leads to a decrease in fertility, and hence, many infertile couples opt for assisted reproductive technologies [ART] to achieve biological parenthood. One of the key determinants of achieving a live outcome of ART, embryo quality, depends on both the quality of the oocyte and sperm that have created the embryo. Several studies have explored the effect of oocyte parameters on embryo quality, but the effects of sperm quality on the embryo have not been comprehensively evaluated.

METHOD

In this review, we assess the effect of various genetic factors of paternal origin on the quality and development of the embryo.

RESULTS

The effects of sperm aneuploidy, sperm chromatin structure, deoxyribonucleic acid [DNA] fragmentation, role of protamines and histones, sperm epigenetic profile, and Y chromosome microdeletions were explored and found to negatively affect embryo quality.

CONCLUSION

We propose that careful assessment of spermatozoal parameters is essential to achieve embryo development and a healthy live birth. However, the heterogeneity in test results and the different approaches of assessing a single sperm parameter highlight the need for more research and the development of standardized protocols to assess the role of sperm factors affecting embryo quality.