Mitochondrial Biomarkers Reflect Semen Quality: Results from the MARCHS Study in Chongqing, China

Mitochondrial content and mtDNA copy number in spermatozoa and penetrability into oocytes

The current narrative review aims to summarize the relation of mitochondrial content (MC) and mitochondrial DNA copy number (MDCN) in spermatozoa with sperm penetrability, and to discuss the various determining factors during the process of spermatogenesis in mammals. There are many potential factors associated with the quantitative alteration of MC and MDCN in male gametes from spermatogenesis to ejaculation. Particularly, spermatogenesis may be the first step to jointly contribute to an incomplete reduction of MC and MDCN in spermatozoon. It appears to be now quite clear that some abnormalities during spermatogenesis and oxidative stress are the main factors highly associated with the quantitative change of MC and MDCN in spermatozoa, consequently affecting sperm quality and their penetrability into oocytes. Currently, a series of proteins contributing to form sperm midpiece during spermatogenesis and cytoplasmic elimination during spermiation have been currently identified. The present review provides insight into how these factors interact with sperm MC and MDCN, and handholds to gain a better understanding of their roles. This review also highlights the uniqueness of normal fertile spermatozoa which have relatively lower MC and MDCN, but have mitochondria that function completely in multiple pivotal physiological pathways.

Inhaled toxins: A threat to male reproductive health

Exposure to air pollutants is known to be an important risk factor in reducing semen quality in men across the world. Poor semen quality results in decline in the global fertility rate and significant personal stress, dysfunctional sexual relationships, and psychosocial problems. Continuous monitoring and effective efforts to reduce air pollution in industries and the environment and making positive changes in daily lifestyle can prevent adverse effects on semen quality and reduce the high prevalence of men infertility. This review aims to summarize studies associating pollutant concentrations of polycyclic aromatic hydrocarbons (PAHs), formaldehyde (FA), and BTEX (benzene, toluene, ethyl-benzene, and xylene) on semen quality. In this systematic review, Scopus, PubMed and Web of Science databases were searched until November 13, 2022. The PECO statement was formulated to clarify the research question, and articles that did not satisfy the criteria outlined in this statement were excluded. Generally, 497 articles were obtained through searching databases, and after the investigations, 26 articles that met the entry criteria were extracted and finally considered in the systematic review. The results showed that occupational and environmental exposures to PAHs, formaldehyde, and BTEX were associated with increased metabolite concentration of toxic pollutants in body fluids. These toxin-associated pollutants directly or indirectly cause detrimental effects on sperm motility, vitality, DNA fragmentation, and morphology. There is evidence on the impact of PAHs, formaldehyde, and BTEX pollutants on the reduction of semen quality. Therefore, proving the relationship between air pollutants and testicular function in semen quality can play an effective role in macro policies and adopting stricter laws to reduce the emission of air pollutants and promote a healthy lifestyle to improve reproductive health in young men.

Human sperm mitochondrial DNA copy numbers and deletion rates: Comparing persons living in two urban industrial agglomerations differing in sources of air pollution

Persons living in industrial environments are exposed to levels of air pollution that can affect their health and fertility. The Czech capital city, Prague, and the Ostrava industrial agglomeration differ in their major sources of air pollution. In Prague, heavy traffic produces high levels of nitrogen oxides throughout the year. In the Ostrava region, an iron industry and local heating are sources of particulate matter (PM) and benzo[a]pyrene (B[a]P), especially in the winter. We evaluated the effects of air pollution on human sperm mitochondrial DNA (mtDNA). Using real-time PCR, we analysed sperm mtDNA copy number and deletion rate in Prague city policemen in two seasons (spring and autumn) and compared the results with those from Ostrava. In Prague, the sperm mtDNA deletion rate was significantly higher in autumn than in spring, which is the opposite of the results from Ostrava. The sperm mtDNA copy number did not show any seasonal differences in either of the cities; it was correlated negatively with sperm concentration, motility, and viability, and with sperm chromatin integrity (assessed with the Sperm Chromatin Structure Assay). The comparison between the two cities showed that the sperm mtDNA deletion rate in spring and the sperm mtDNA copy number in autumn were significantly lower in Prague vs. Ostrava. Our study supports the hypothesis that sperm mtDNA deletion rate is affected by the composition of air pollution. Sperm mtDNA abundance is closely associated with chromatin damage and standard semen characteristics.

Mechanistic target of rapamycin (mTOR) pathway in Sertoli cells regulates age-dependent changes in sperm DNA methylation

Over the past several decades, a trend toward delayed childbirth has led to increases in parental age at the time of conception. Sperm epigenome undergoes age-dependent changes increasing risks of adverse conditions in offspring conceived by fathers of advanced age. The mechanism(s) linking paternal age with epigenetic changes in sperm remain unknown. The sperm epigenome is shaped in a compartment protected by the blood-testes barrier (BTB) known to deteriorate with age. Permeability of the BTB is regulated by the balance of two mTOR complexes in Sertoli cells where mTOR complex 1 (mTORC1) promotes the opening of the BTB and mTOR complex 2 (mTORC2) promotes its integrity. We hypothesized that this balance is also responsible for age-dependent changes in the sperm epigenome. To test this hypothesis, we analyzed reproductive outcomes, including sperm DNA methylation in transgenic mice with Sertoli cell-specific suppression of mTORC1 (Rptor KO) or mTORC2 (Rictor KO). mTORC2 suppression accelerated aging of the sperm DNA methylome and resulted in a reproductive phenotype concordant with older age, including decreased testes weight and sperm counts, and increased percent of morphologically abnormal spermatozoa and mitochondrial DNA copy number. Suppression of mTORC1 resulted in the shift of DNA methylome in sperm opposite to the shift associated with physiological aging - sperm DNA methylome rejuvenation and mild changes in sperm parameters. These results demonstrate for the first time that the balance of mTOR complexes in Sertoli cells regulates the rate of sperm epigenetic aging. Thus, mTOR pathway in Sertoli cells may be used as a novel target of therapeutic interventions to rejuvenate the sperm epigenome in advanced-age fathers.

The impact of mitochondrial impairments on sperm function and male fertility: a systematic review

BACKGROUND

Besides adenine triphosphate (ATP) production for sustaining motility, the mitochondria of sperm also host other critical cellular functions during germ cell development and fertilization including calcium homeostasis, generation of reactive oxygen species (ROS), apoptosis, and in some cases steroid hormone biosynthesis. Normal mitochondrial membrane potential with optimal mitochondrial performance is essential for sperm motility, capacitation, acrosome reaction, and DNA integrity.

RESULTS

Defects in the sperm mitochondrial function can severely harm the fertility potential of males. The role of sperm mitochondria in fertilization and its final fate after fertilization is still controversial. Here, we review the current knowledge on human sperm mitochondria characteristics and their physiological and pathological conditions, paying special attention to improvements in assistant reproductive technology and available treatments to ameliorate male infertility.

CONCLUSION

Although mitochondrial variants associated with male infertility have potential clinical use, research is limited. Further understanding is needed to determine how these characteristics lead to adverse pregnancy outcomes and affect male fertility potential.

Addendum to: The relationship between sperm nuclear DNA fragmentation, mitochondrial DNA fragmentation and copy number in normal and abnormal human ejaculates

BACKGROUND

While the kinetics of human sperm nuclear DNA fragmentation (SDF-nDNA) following ejaculation have been described, the dynamics and relationships of mitochondrial DNA copy number per spermatozoon (mtDNAcn) and fragmentation (SDF-mtDNA) remain unexplored.

OBJECTIVES

To compare post-ejaculatory kinetics of mtDNAcn, SDF-mtDNA and SDF-nDNA, global, single-strand DNA breaks (SDF-SSBs) and double-strand DNA breaks (SDF-DSBs) in normozoospermic and non-normozoospermic samples.

MATERIALS AND METHODS

28 normozoospermic and 43 non-normozoospermic ejaculates were evaluated at 0, 6, 24 and 48 h of incubation in vitro. SDF-nDNA was determined by sperm chromatin dispersion (SCD) assays. mtDNAcn and SDF-mtDNA were analysed by dPCR.

RESULTS

SDF-nDNA-global values increased as a consequence of quadratic SDF-SSBs and linear SDF-DSBs kinetics. Non-normozoospermic samples showed a slower SDF-global rate between 6-24 h, due to lesser SSBs production. Regarding SDF-DSBs, non-normozoospermic samples exhibited a faster initial increase rate, followed by a slower final increment. The mtDNAcn median value decreased linearly, being 3.2× higher in non-normozoospermics at all time points; mtDNAcn in both cohorts reduced to half of the baseline by 48 h. mtDNAcn was identified as a risk factor for discriminating non-normozoospermia, a finding that was further strengthen when combined with SDF-Global or SDF-DSBs values. SDF-mtDNA frequencies were identical, increasing over time correspondingly in both cohorts. The mtDNA fragmentation rate was initially fast, decreasing progressively with time for both cohorts; half of the initially unfragmented copies were fragmented after 48 h. Rates of mtDNAcn loss and SDF-mtDNA increase were only marginally correlated with the rates of nuclear fragmentation.

CONCLUSION

mtDNA fragmentation and loss occur post ejaculation. Their dynamics are likely to be associated with different and/or uncoupled mechanisms to that which cause nuclear DNA fragmentation. Our results indicate that while mtDNA fragmentation is not influenced by the sperm quality, the number of copies of sperm mtDNAcn can potentially serve as a risk factor for predicting non-normozoospermia.

Genetic Causes of Qualitative Sperm Defects: A Narrative Review of Clinical Evidence

Several genes are implicated in spermatogenesis and fertility regulation, and these genes are presently being analysed in clinical practice due to their involvement in male factor infertility (MFI). However, there are still few genetic analyses that are currently recommended for use in clinical practice. In this manuscript, we reviewed the genetic causes of qualitative sperm defects. We distinguished between alterations causing reduced sperm motility (asthenozoospermia) and alterations causing changes in the typical morphology of sperm (teratozoospermia). In detail, the genetic causes of reduced sperm motility may be found in the alteration of genes associated with sperm mitochondrial DNA, mitochondrial proteins, ion transport and channels, and flagellar proteins. On the other hand, the genetic causes of changes in typical sperm morphology are related to conditions with a strong genetic basis, such as macrozoospermia, globozoospermia, and acephalic spermatozoa syndrome. We tried to distinguish alterations approved for routine clinical application from those still unsupported by adequate clinical studies. The most important aspect of the study was related to the correct identification of subjects to be tested and the correct application of genetic tests based on clear clinical data. The correct application of available genetic tests in a scenario where reduced sperm motility and changes in sperm morphology have been observed enables the delivery of a defined diagnosis and plays an important role in clinical decision-making. Finally, clarifying the genetic causes of MFI might, in future, contribute to reducing the proportion of so-called idiopathic MFI, which might indeed be defined as a subtype of MFI whose cause has not yet been revealed.

The relationship between sperm nuclear DNA fragmentation, mitochondrial DNA fragmentation, and copy number in normal and abnormal human ejaculates

BACKGROUND

While it is common to clinically evaluate sperm nuclear DNA fragmentation, less attention has been given to sperm mitochondrial DNA. Recently, a digital PCR assay has allowed accurate estimation of the proportion of fragmented mtDNA molecules and relative copy number.

OBJECTIVES

To determine the correlation of classical sperm parameters, average mtDNA copies per spermatozoon and the level of mtDNA fragmentation (SDF-mtDNA) to that of nuclear DNA fragmentation (SDF-nDNA), measured as the proportion of global, single-strand DNA (SDF-SSBs) and double-strand DNA breaks (SDF-DSBs). To determine whether the level of nuclear and mitochondrial DNA fragmentation and/or copy number can differentiate normozoospermic from non-normozoospermic samples.

MATERIALS AND METHODS

Ejaculates from 29 normozoospermic and 43 non-normozoospermic were evaluated. SDF was determined using the sperm chromatin dispersion assay. mtDNA copy number and SDF-mtDNA were analyzed using digital PCR assays.

RESULTS

Relative mtDNA copy increased as sperm concentration or motility decreased, or abnormal morphology increased. Unlike SDF-mtDNA, mtDNA copy number was not correlated with SDF-nDNA. SDF-mtDNA increased as the concentration or proportion of non-vital sperm increased; the higher the mtDNA copy number, the lower the level of fragmentation. Non-normozoospermic samples showed double the level of SDF-nDNA compared to normozoospermic (median 25.00 vs. 13.67). mtDNA copy number per spermatozoon was 3× higher in non-normozoospermic ejaculates (median 16.06 vs. 4.99). Although logistic regression revealed SDF-Global and mtDNA copy number as independent risk factors for non-normozoospermia, when SDF-Global and mtDNA copy number were combined, ROC curve analysis resulted in an even stronger discriminatory ability for predicting the probability of non-normozoospermia (AUC = 0.85, 95% CI 0.76-0.94, p < 0.001).

CONCLUSION

High-quality ejaculates show lower nuclear SDF and retain less mtDNA copies, with approximately half of them fragmented, so that the absolute number of non-fragmented mtDNA molecules per spermatozoon is extremely low.

In vitro effects of pentoxifylline and coenzyme Q10 on the sperm of oligoasthenoteratozoospermia patients

The effect of in-vitro sperm incubation with Pentoxifylline (PTX) and Coenzyme Q10 (CoQ10) in Oligoasthenoteratozoospermia (OAT) patients was evaluated. Semen samples were obtained from men with Normozoospermia and men with OAT. Motile sperm from the two groups were subdivided into four subgroups: (i) without incubation with PTX + CoQ10; (ii) incubation with PTX; (iii) Incubation with CoQ10; and (iv) incubation with a combination of PTX + CoQ10. Then, sperm parameters, chromatin, DNA and membrane integrity, protamine deficiency, apoptosis, mitochondrial activity, sperm chromatin dispersion test (SCD), hypo-osmotic swelling test (HOS), chromomycin A3 (CMA3), Terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL), and diaminobenzidine (DAB) assays were evaluated, respectively. Sperm incubated with CoQ10 and a combination of CoQ10 and PTX resulted in a significant increase in the sperm parameters. Also, a significant decrease was noted with a combination of PTX and CoQ10 in normal men. There was a significant difference between CoQ10 treated and CoQ10 + PTX treated groups in comparison with the OAT group in the percentage of the DNA fragmentation, sperm apoptosis, AB+, HOS test + and sperm mitochondrial activity. Incubated sperm with CoQ10, PTX, and in combination with each other can improve sperm parameters in OAT patients.

Mitochondrial uncouplers impair human sperm motility without altering ATP content†

In human spermatozoa, the electrochemical potentials across the mitochondrial and plasma membranes are related to sperm functionality and fertility, but the exact role of each potential has yet to be clarified. Impairing sperm mitochondrial function has been considered as an approach to creating male or unisex contraceptives, but it has yet to be shown whether this approach would ultimately block the ability of sperm to reach or fertilize an egg. To investigate whether the mitochondrial and plasma membrane potentials are necessary for sperm fertility, human sperm were treated with two small-molecule mitochondrial uncouplers (niclosamide ethanolamine and BAM15) that depolarize membranes by inducing passive proton flow, and evaluated the effects on a variety of sperm physiological processes. BAM15 specifically uncoupled human sperm mitochondria while niclosamide ethanolamine induced proton current in the plasma membrane in addition to depolarizing the mitochondria. In addition, both compounds significantly decreased sperm progressive motility with niclosamide ethanolamine having a more robust effect. However, these uncouplers did not reduce sperm adenosine triphosphate (ATP) content or impair other physiological processes, suggesting that human sperm can rely on glycolysis for ATP production if mitochondria are impaired. Thus, systemically delivered contraceptives that target sperm mitochondria to reduce their ATP production would likely need to be paired with sperm-specific glycolysis inhibitors. However, since niclosamide ethanolamine impairs sperm motility through an ATP-independent mechanism, and niclosamide is FDA approved and not absorbed through mucosal membranes, it could be a useful ingredient in on-demand, vaginally applied contraceptives.

Sperm mitochondrial DNA copy number mediates the association between seminal plasma selenium concentrations and semen quality among healthy men

Selenium (Se) is essential for successful male reproduction. However, the association of Se status with human semen quality remains controversial and the underlying mechanisms are poorly understood. We measured seminal plasma Se concentrations, sperm mitochondrial DNA copy number (mtDNAcn), and sperm quality parameters among healthy Chinese men screened as potential sperm donors. Linear mixed-effects models were used to investigate the associations of within-subject pooled seminal plasma Se concentrations (n = 1159) with repeated sperm quality parameters (n = 5617); mediation analyses were applied to evaluate the mediating role of sperm mtDNAcn (n = 989). Seminal plasma Se concentrations were positively associated with sperm concentration and total count (both P for trend < 0.001). In adjusted models, men in the top vs. bottom quartiles of seminal plasma Se concentrations had 70.1 % (95 % CI: 53.3 %, 88.9 %) and 59.1 % (95 % CI: 40.5 %, 80.2 %) higher sperm concentration and total count, respectively. Meanwhile, we observed inverse associations between seminal plasma Se concentrations and sperm mtDNAcn, and between sperm mtDNAcn and sperm motility, concentration, and total count (all P for trend < 0.05). Mediation analyses suggested that sperm mtDNAcn mediated 19.7 % (95 % CI: 15.9 %, 25.3 %) and 23.1 % (95 % CI: 17.4 %, 33.4 %) of the associations between seminal plasma Se concentrations and sperm concentration and total count, respectively. Our findings suggest that Se is essential for male spermatogenesis, potentially by affecting sperm mtDNAcn.

Sperm Mitochondria, the Driving Force Behind Human Spermatozoa Activities: Its Functions and Dysfunctions - A Narrative Review

Male infertility is a major issue, and numerous factors contribute to it. One of the important organelles involved in the functioning of human spermatozoa is mitochondria. There are 50-75 mitochondria helically arranged in mid-piece bearing one mitochondrial DNA each. Sperm mitochondria play a crucial role in sperm functions, including the energy production required for sperm motility and the production of reactive oxygen species, which in the physiological range helps in sperm maturation, capacitation, and acrosome reaction. It also plays a role in calcium signaling cascades, intrinsic apoptosis, and sperm hyperactivation. Any structural or functional dysfunction of sperm mitochondria results in increased production of reactive oxygen species and, a state of oxidative stress, decreased energy production, all leading to sperm DNA damage, impaired sperm motility and semen parameters, and reduced male fertility. Furthermore, human sperm mitochondrial DNA mutations can result in impaired sperm motility and parameters leading to male infertility. Numerous types of point mutations, deletions, and missense mutations have been identified in mtDNA that are linked with male infertility. Methods: Recent literature was searched from English language peer-reviewed journals from databases including PubMed, Scopus, EMBASE, Scholar, and Web of Science till September 2021. Search terms used were "Sperm mitochondria and male fertility", "Bioenergetics of sperm", "Sperm mitochondria and reactive oxygen species", "Sperm mitochondrial mutations and infertility". Conclusion: Sperm mitochondria is an important organelle involved in various functions of human spermatozoa and sperm mitochondrial DNA has emerged as one of the potent biomarkers of sperm quality and male fertility.

Sperm mitochondrial DNA copy number in relation to semen quality: A cross-sectional study of 1164 potential sperm donors

OBJECTIVE

To investigate the association between mitochondrial DNA copy number (mtDNAcn) and semen quality.

DESIGN

A cross-sectional study.

SETTING

Hubei Province Human Sperm Bank of China (from April 2017 to July 2018).

POPULATION

A total of 1164 healthy male sperm donors with 5739 specimens.

MAIN OUTCOME MEASURES

Real-time quantitative polymerase chain reaction (RT-PCR) was used to measure sperm mtDNAcn. We also determined semen volume, concentration and motility parameters (progressive motility, nonprogressive motility and immotility).

METHODS

Mixed-effect models and general linear models were uses.

RESULTS

After adjusting for relevant confounding factors, mixed-effect models revealed diminished sperm motility (progressive and total), concentration, and total count across the quartiles of mtDNAcn (all P < 0.05). Compared with men in the lowest quartile, men in the highest quartile of mtDNAcn had lower progressive sperm motility, total motility, concentration and total count of -8.9% (95% CI -12.7% to -5.0%), -8.0% (95% CI -11.6% to -4.4%), -42.8% (95% CI -47.7% to -37.4%), and - 44.3% (95% CI -50.1% to -37.7%), respectively. These inverse dose-response relationships were further confirmed in the cubic spline models, where mtDNAcn was modelled as a continuous variable.

CONCLUSIONS

We found that mtDNAcn was inversely associated with semen quality in a dose-dependent manner. Our results provide novel clues that sperm mtDNAcn may serve as a useful predictor of human semen characteristics.

TWEETABLE ABSTRACT

Sperm mitochondrial DNA copy number was markedly associated with diminished sperm motility (progressive and total), concentration and total count.

Spectrum of sperm mtDNA deletions in men exposed to industrial air pollution

Sperm mtDNA status can serve as a molecular marker of oxidative stress and environmental exposure. High levels of air pollution may be associated with increased mitochondrial DNA (mtDNA) deletion rates in sperm. We compared the length spectra of sperm mtDNA deletions in semen samples collected from city policemen exposed to traffic and industrial air pollution in two seasons with different levels of air pollution. We used long-range PCR to amplify a fragment of mtDNA (8066 bp) frequently affected by deletions, visualized the PCR products by gel electrophoresis, and analysed aberrant bands corresponding to deleted mtDNA, using gel documentation software. The predominance of undeleted sperm mtDNA was accompanied by a variety of shorter PCR product lengths in the vast majority of sperm samples, in both seasons. Sperm mtDNA molecules and bands corresponding to long deletions were more frequently detected than shorter deletions, in both seasons. We did not detect any difference in the total number of electrophoretic bands corresponding to deleted sperm mtDNA and in the number of deleted sperm mtDNA molecules between the two seasons. In our study, air pollution during sperm maturation did not induce formation of large mtDNA deletions detectable by long PCR and gel electrophoresis (>1 kb) in maturing sperm mtDNA.

Assessment of Semen Respiratory Activity of Domesticated Species before and after Cryopreservation: Boars, Bulls, Stallions, Reindeers and Roosters

Simple Summary

Artificial insemination is actively used in animal husbandry. It is important to know the quality of the sperm for artificial insemination. One of the indicators of sperm quality can be an assessment of energy metabolism, since energy is needed for sperm to move and fertilize the egg. We studied the respiration rate in spermatozoa of different animal species: bulls, stallions, boars, reindeer and roosters. To determine the production of energy (ATP), the substance 2.4-dinetrophenol (2.4-DNP) was used, which stopped the production of ATP. Semen was assessed before and after freezing. The evaluation showed the same response to the addition of 2.4-DNP to the semen of different species, as well as a sufficient relationship between the reaction of semen respiration to the addition of 2.4-DNP and the fertilizing ability of sperm. At the same time, no relationship was found between the respiratory rate and fertility. The 2.4-DNP test can be a suitable additional measure of sperm quality.

Abstract

To assess sperm quality, it is important to evaluate energy metabolism. The test substance 2.4-dinitrophenol (2.4-DNP) is an agent for destroying oxidative phosphorylation. 2.4-DNP shuts off the production of adenosine triphosphate (ATP) from oxidation and then, the respiration rate increases. If the respiratory chain is damaged, there is little or no response to adding 2.4-DNP. The aim of this study was to analyze the respiratory activity and oxidative phosphorylation in semen before and after freezing and compare the obtained data with the fertilizing ability of sperm. There was a reduction in sperm respiration rates in all species after thawing. The respiration of spermatozoa of boars, bulls, stallions, reindeers and chicken showed responses to 2.4-dinitrophenol. The only difference is in the strength of the response to the test substance. After freezing and thawing, respiratory stimulation by 2.4-DNP decreased. The results of our study show that respiration rate is not correlated with pregnancy rates and egg fertility. However, there was a high correlation between the stimulation of respiration by 2.4-dinitrophenol and pregnancy rates. The test for an increase in respiration rate after adding 2.4-dinitrophenol could be a suitable test of the fertilizing ability of sperm.

Associations between isoflavone exposure and reproductive damage in adult males: evidence from human and model system studies

It's controversial whether exposure to isoflavones, constituents of certain plants such as soy bean, exerts male reproductive toxicity. This study was designed to investigate whether isoflavone exposure during adulthood could have deleterious impacts on male reproductive health by the cross-sectional study, animal experiments, and in vitro tests. In the cross-sectional study, we observed that urinary isoflavones were not significantly associated with semen quality including sperm concentrations, sperm count, progressive motility, and total motility, respectively (All P-value for trend>0.05). However, negative associations were found between plasma testosterone and urinary Σisoflavones, genistein, glycitein, and dihydrodaidzein (all P-value for trend <0.05). In the animal experiments, serum and intratesticular testosterone levels were decreased in mice exposed to several dosages of genistein. Genistein administration caused up-regulation of estrogen receptor alpha (ERα) and down-regulation of cytochrome P45017A1 (CYP17A1) protein levels in testes of mice. However, genistein treatment during adulthood did not induce appreciable structural damages of reproductive system in mice. In vitro tests, we observed that genistein of different dosages (0.01, 2.5, 10 μM) caused a concentration dependent inhibition of testosterone production by TM3 Leydig cells (half-maximal inhibitory concentration = 3.796 nM, P < 0.05). Elevated protein expression of ERα and decreased mRNA/protein level of CYP17A1 were also observed in genistein-treated cells. Protein level of CYP17A1 and testosterone concentration were significantly restored in the ERα siRNA-transfected cells, compared to cells that treated with genistein alone (P < 0.05). The results demonstrate that exposure to isoflavones during adulthood may be associated with alterations of reproductive hormones. Particularly for genistein, which inhibits testosterone biosynthesis through up-regulation of ERα in Leydig cells of mice, might induce the disruption of testosterone production in human. The present study provides novel perspective into potential targets for male reproductive compromise induced by isoflavone exposure.

Green Tea Extract in the Extender Improved the Post-Thawed Semen Quality and Decreased Amino Acid Mutation of Kacang Buck Sperm

This study was the first to combine the addition of antioxidants to a skim milk–egg yolk (SM–EY) extender and different equilibration periods to obtain higher quality post-thawed Kacang buck semen. This study aimed to determine the effects of green tea extract (GTE) on the quality of frozen Kacang goat sperm equilibrated for one and two hours. The pool of Kacang buck ejaculate was equally divided into four portions and was diluted in an SM–EY extender that contained four doses of 0, 0.05, 0.10, and 0.15 mg of GTE/100 mL for T0, T1, T2, and T3 groups, respectively. The aliquots were treated for an equilibration period of 1–2 h before further processing as frozen semen. Post-thawed semen quality was evaluated for sperm quality. The Sanger method was used for DNA sequencing, and the amino acid sequence was read using MEGA v.7.0. The post-thawed semen of the T2 group that was equilibrated for one hour had the highest semen quality. Pre-freezing motility had the highest determination coefficient compared to post-thawed sperm motility. This study is the first to report amino acid mutation due to freeze–thawing. The frequency of amino acid mutations revealed that T2 was the least mutated amino acid. Glycine, valine, leucine, serine, and asparagine strongly correlated to post-thawed sperm motility. It can be concluded that a combination of 0.1 mg GTE/100 mL extender as an antioxidant and one-hour equilibration period resulted in the best post-thawed Kacang buck semen quality.

Altered methyltransferase gene expression, mitochondrial copy number and 4977-bp common deletion in subfertile men with variable sperm parameters

Semen parameters have been found to predict reproductive success poorly and are the most prevalent diagnostic tool for male infertility. There are few conflicting reports regarding the correlation of DNMT genes expression, mitochondrial DNA copy number (mtDNAcn) and deletion (mtDNAdel) with different sperm parameters. To investigate DNMT mRNA level, mtDNAcn and deletion in infertile men, with different sperm parameters, compared with fertile men, semen samples from 30 men with unknown male infertility and normal sperm parameters (experimental group I), 30 infertile patients with at least two abnormal sperm parameters (experimental group II) and 30 fertile normozoospermic men (control group) were collected. After semen analysis, total RNA and DNA were extracted. The isolated DNA was used for assessing the respective mtDNAcn and the presence of common 4977 bp deletion in mtDNA by applying real-time quantitative PCR and multiplex PCR, respectively. Synthesized cDNA from total RNAs was used to quantify DNMT1, DNMT3A and DNMT3B transcripts in study groups by using real-time quantitative reverse-transcription PCR. Significantly higher proportions of mtDNAcn were found in experimental group II. DNMT1 was significantly downregulated in both experimental groups and 4977 bp deletion was not detected. Progressive motility and normal morphology were significantly and negatively correlated with mtDNAcn. A significant positive correlation was detected between sperm parameters and DNMT1 mRNA levels. In conclusion, infertile men with different sperm parameter qualities showed elevated mtDNA content. Abnormal sperm parameters associated with DNMT1 gene expression indicate the possibility of changes in some epigenetic aspects of spermatogenesis in subfertile men with different sperm parameters.

The semenogelin I-derived peptide SgI-52 in seminal plasma participates in sperm selection and clearance by macrophages

BACKGROUND

Macrophages can phagocytose sperm, especially damaged spermatozoa, in the female genital tract. The semenogelin I-derived peptide SgI-52 in seminal plasma exhibits seminal plasma motility inhibitor (SPMI) activity and can inhibit sperm motility. This raises the question of the role played by SPMIs in macrophage-mediated phagocytosis of sperm. We speculated that SgI-52 promotes sperm clearance by macrophages. Therefore, we investigated the phagocytosis of sperm in different states using this peptide.

METHODS

SgI-52 was fluorescently labeled, and its binding site for sperm was observed. The ability of macrophages to phagocytose sperm was observed using fluorescence confocal microscopy. Spermatozoa from different sources were co-cultured with SgI-52 in BWW medium for 4 and 22 h to compare the differences in their phagocytosis by macrophages. Sperm motility, induced acrosome reaction, mitochondrial membrane potential, and ATP content were examined after incubation with SgI-52.

RESULTS

SgI-52 could bind to spermatozoa in different states, mainly to the tail, and then spread to the acrosome. This effect was more pronounced in demembranated spermatozoa. SgI-52 promoted phagocytosis of spermatozoa by macrophages, decreased the mitochondrial membrane potential, and increased the average ATP content of spermatozoa (P < 0.05).

CONCLUSIONS

We found for the first time that SgI-52 can bind to spermatozoa in different states and promote their phagocytosis by macrophages. Therefore, we speculate that SgI-52 is involved in the screening of sperm in the female reproductive tract and has potential value in improving assisted reproductive technology.

Effects of The Mitochondrial Genome on Germ Cell Fertility: A Review of The Literature

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters cells through angiotensin converting enzyme 2 (ACE2), which expression of its gene increases during pregnancy that is resulted in an enhanced level of the ACE2 enzyme. It might enhance the risk of SARS-CoV-2 infection and its complications in the pregnant women. Although, pregnancy hypertensive disorders and severe infection with SARS-CoV-2 are correlated with high comorbidity, these two entities should be discriminated from each other. Also, there is a concern about the risk of preeclampsia and consequently severe coronavirus disease 2019 (COVID-19) development in the pregnant women. So, to answer these questions, in the present review the literature was surveyed. It seems there is higher severity of COVID-19 among pregnant women than non-pregnant women and more adverse pregnancy outcomes among pregnant women infected with SARS-CoV-2. In addition, an association between COVID-19 with preeclampsia and the role of preeclampsia and gestational hypertension as risk factors for SARS-CoV-2 infection and its complications is suggested. However, infection of the placenta and the SARS-CoV-2 vertical transmission is rare. Various mechanisms could explain the role of COVID-19 in the risk of preeclampsia and association between preeclampsia and COVID-19. Suggested mechanisms are included decreased ACE2 activity and imbalance between Ang II and Ang-(1-7) in preeclampsia, association of both of severe forms of COVID-19 and pregnancy hypertensive disorders with comorbidity, and interaction between immune system, inflammatory cytokines and the renin angiotensin aldosterone system and its contribution to the hypertension pathogenesis. It is concluded that preeclampsia and gestational hypertension might be risk factors for SARS-CoV-2 infection and its complications.Infertility is one of the major problems faced in medicine. There are numerous factors that play a role in infertility. For example, numerous studies mention the impact of the quantity and quality of mitochondria in sexual gametes. This is a narrative review of the effects of the mitochondrial genome on fertility. We searched the PubMed, Science Direct, SID, Google Scholar, and Scopus databases for articles related to "Fertility, Infertility, Miscarriage, Mitochondria, Sperm, mtDNA, Oocytes" and other synonymous keywords from 2000 to 2020. The mitochondrial genome affects infertility in both male and female gametes; in sperm, it mainly releases free radicals. In the oocyte, a mutation in this genome can affect the amount of energy required after fertilisation, leading to gestation failure. In both cases, infertile cells have substantially less mitochondrial DNA (mtDNA) copies. The effects of mtDNA on gamete fertility occur via changes in oxidative phosphorylation and cellular energy production. Also, a reduction in the number of mtDNA copies is directly associated with sex cell infertility. Therefore, evaluation of the mitochondrial genome can be an excellent diagnostic option for couples who have children with neonatal disorders, infertile couples who seek assisted reproductive treatment, and those in whom assisted reproductive techniques have failed.

Sperm mitochondrial DNA copy numbers in normal and abnormal semen analysis: a systematic review and meta-analysis

BACKGROUND

Normal mature sperm have a considerably reduced number of mitochondria which provide the energy required for progressive sperm motility. Literature suggests that disorders of sperm motility may be linked to abnormal sperm mitochondrial number and function.

OBJECTIVES

To summarize the evidence from literature regarding the association of mitochondrial DNA copy numbers and semen quality with a particular emphasis on the spermatozoa motility.

SEARCH STRATEGY

Standard methodology recommended by Cochrane.

SELECTION CRITERIA

All published primary research reporting on the association between mitochondrial DNA copy numbers and semen quality.

DATA COLLECTION AND ANALYSIS

Using standard methodology recommended by Cochrane we pooled results using a random effects model and the findings were reported as a standardised mean difference.

MAIN RESULTS

We included 10 studies. The primary outcome was sperm mitochondrial DNA copy numbers. A meta-analysis including five studies showed significantly higher mitochondrial DNA copy numbers in abnormal semen analysis as compared to normal semen analysis(SMD 1.08, 95% CI 0.74-1.43). Seven studies included in the meta-analysis showed a significant negative correlation between mitochondrial DNA copy numbers and semen parameters. The quality of evidence was assessed as good to very good in 60% of studies.

CONCLUSIONS

Our review demonstrates significantly higher mitochondrial DNA in human sperm cells of men with abnormal semen analysis in comparison to men with normal semen analysis.

Qiangjing Tablets Regulate Apoptosis and Oxidative Stress via Keap/Nrf2 Pathway to Improve the Reproductive Function in Asthenospermia Rats

Asthenozoospermia (AZS), is a common cause of male infertility. Currently, most drugs for azoospermia lack desirable therapeutic efficiency, therefore developing new drug therapy is important. Qiangjing tablets could enhance renal function and improve sperm quality. The purpose of this study was to examine whether Qiangjing tablets could improve the reproductive function in azoospermia rats through activating the Nrf2/ARE pathway, and how to regulate energy metabolism and oxidative stress in this process. Sperm motility, sperm concentration and sperm viability were detected by WLJY-9000 Weili Digital Color Sperm Quality Detection System. HE staining was used to observe the pathological condition of testis in AZS rats. Cell apoptosis was analyzed by Tunnel staining and flow cytometry. The changes of mitochondrial membrane potential were detected by JC-1. The levels of Estradiol, testosterone and luteinizing hormone, activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and content of malondialdehyde (MDA) and glutathione (GSH) were detected by ELISA. The effects of Qiangjing Tablets on GC-1 spgs and Nrf2 protein were investigated through CCK-8 assay and western blot. The expression levels of HO-1, Keap1, and P-Nrf2 were detected by western blot. The results demonstrated that Qiangjing tablets upregulated levels of sperm motility, sperm concentration and sperm viability, which was shown to significantly increase levels of HO-1, Keap1, P-Nrf2, Estradiol and testosterone, along with increasing the activity of SOD, GSH-Px and GSH and suppressing the MDA content, luteinizing hormone and Vimentin level. Qiangjing tablets could significantly inhibit spermatogenic cells apoptosis and promote GC-1 spgs viability, increase PE/FITC ratio, mitochondrial membrane potential and reduc oxidative stress. Qiangjing tablets protected spermatogenic cell to upregulate male sex hormoneto, improved the sperm quality and reproductive function in AZS rats via activating the Keap/Nrf2 signaling pathway.

A sex chromosome inversion is associated with copy number variation of mitochondrial DNA in zebra finch sperm

The propulsion of sperm cells via movement of the flagellum is of vital importance for successful fertilization. While the exact mechanism of energy production for this movement varies between species, in avian species energy is thought to come predominantly from the mitochondria located in the sperm midpiece. Larger midpieces may contain more mitochondria, which should enhance the energetic capacity and possibly promote mobility. Due to an inversion polymorphism on their sex chromosome TguZ, zebra finches (Taeniopygia guttata castanotis) exhibit large within-species variation in sperm midpiece length, and those sperm with the longest midpieces swim the fastest. Here, we test through quantitative real-time PCR in zebra finch ejaculates whether the inversion genotype has an effect on the copy number of mitochondrial DNA (mtDNA). We find that zebra finches carrying the derived allele (correlated with longer sperm midpieces) have more copies of the mtDNA in their ejaculates than those homozygous for the ancestral allele (shorter midpieces). We suggest downstream effects of mtDNA copy number variation on the rate of adenosine triphosphate production, which in turn may influence sperm swimming speed and fertilization success. Central components of gamete energy metabolism may thus be the proximate cause for a fitness-relevant genetic polymorphism, stabilizing a megabase-scale inversion at an intermediate allele frequency in the wild.

Mitochondria Content and Activity Are Crucial Parameters for Bull Sperm Quality Evaluation

Standard sperm evaluation parameters do not enable predicting their ability to survive cryopreservation. Mitochondria are highly prone to suffer injuries during freezing, and any abnormalities in their morphology or function are reflected by a decline of sperm quality. Our work focused on describing a link between the number and the activity of mitochondria, with an aim to validate its applicability as a biomarker of bovine sperm quality. Cryopreserved sperm collected from bulls with high (group 1) and low (group 2) semen quality was separated by swim up. The spermatozoa of group 1 overall retained more mitochondria (MitoTrackerGreen) and mtDNA copies, irrespective of the fraction. Regardless of the initial ejaculate quality, the motile sperm contained significantly more mitochondria and mtDNA copies. The same trend was observed for mitochondrial membrane potential (ΔΨm, JC-1), where motile sperm displayed high ΔΨm. These results stay in agreement with transcript-level evaluation (real-time polymerase chain reaction, PCR) of antioxidant enzymes (PRDX1, SOD1, GSS), which protect cells from the reactive oxygen species. An overall higher level of glutathione synthetase (GSS) mRNA was noted in group 1 bulls, suggesting higher ability to counteract free radicals. No differences were noted between basal oxygen consumption rate (OCR) (Seahorse XF Agilent) and ATP-linked respiration for group 1 and 2 bulls. In conclusion, mitochondrial content and activity may be used as reliable markers for bovine sperm quality evaluation.

Protective effects of selenium on Bisphenol A-induced oxidative stress in mouse testicular mitochondria and sperm motility

OBJECTIVE

This study aimed to explore the impact of selenium (SE) on Bisphenol-A (BPA)-exposed sperm and isolated testicular mitochondria of mice.

METHODS

Mouse sperm and isolated mitochondria were exposed to BPA (0.8 mM) and different concentrations of SE (50, 100, and 200 μM) for four hours. The viability of sperm and isolated mitochondria as well as the mitochondrial membrane potential (MMP) were evaluated. SOD (superoxide dismutase), GSH (glutathione), MDA (malondialdehyde), and ROS (reactive oxygen species) levels in testicular mitochondria were also examined.

RESULTS

BPA concentration-dependently enhanced ROS and MDA levels in isolated mitochondria, while MMP and acclivity of GSH and SOD significantly reduced. BPA also considerably impaired spermatozoa survival and motility. SE concentration-dependently reduced mitochondrial oxidative stress, MMP, sperm survival, and total sperm motility.

CONCLUSIONS

Our findings collectively suggested that SE concentration-dependently reversed BPA-caused mitochondrial toxicity and reduced sperm motility by suppressing oxidative stress.

Sperm mitochondrial DNA biomarkers and couple fecundity

STUDY QUESTION

Do sperm mitochondrial DNA measures predict probability of pregnancy among couples in the general population?

SUMMARY ANSWER

Those with high sperm mitochondrial DNA copy number (mtDNAcn) had as much as 50% lower odds of cycle-specific pregnancy, and 18% lower probability of pregnancy within 12 months.

WHAT IS KNOWN ALREADY

Semen parameters have been found to poorly predict reproductive success yet are the most prevalent diagnostic tool for male infertility. Increased sperm mtDNAcn and mitochondrial DNA deletions (mtDNAdel) have been associated with decreased semen quality and lower odds of fertilization in men seeking fertility treatment.

STUDY DESIGN, SIZE, DURATION

A population-based prospective cohort study of couples discontinuing contraception to become pregnant recruited from 16 US counties from 2005 to 2009 followed for up to 16 months.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Sperm mtDNAcn and mtDNAdel from 384 semen samples were assessed via triplex probe-based quantitative PCR. Probability of pregnancy within 1 year was compared by mitochondrial DNA, and discrete-time proportional hazards models were used to evaluate the relations with time-to-pregnancy (TTP) with adjustment for covariates.

MAIN RESULTS AND THE ROLE OF CHANCE

Higher sperm mtDNAcn was associated with lower pregnancy probability within 12 months and longer TTP. In unadjusted comparisons by quartile (Q), those in Q4 had a pregnancy probability of 63.5% (95% CI: 53.1% to 73.1%) compared to 82.3% (95% CI: 73.2% to 89.9%) for Q1 (P = 0.002). Similar results were observed in survival analyses adjusting for covariates to estimate fecundability odds ratios (FORs) comparing mtDNAcn in quartiles. Relative to those in Q1 of mtDNAcn, FORs (95% CI) were for Q2 of 0.78 (0.52 to 1.16), Q3 of 0.65 (0.44 to 0.96) and Q4 of 0.55 (0.37 to 0.81), and this trend of decreasing fecundability with increasing mtDNAcn quartile was statistically significant (FOR per log mtDNAcn = 0.37; P < 0.001). Sperm mtDNAdel was not associated with TTP.

LIMITATIONS, REASONS FOR CAUTION

This prospective cohort study consisted primarily of Caucasian men and women and thus large diverse cohorts are necessary to confirm the associations between sperm mtDNAcn and couple pregnancy success in other races/ethnicities.

WIDER IMPLICATIONS OF THE FINDINGS

Our results demonstrate that sperm mtDNAcn has utility as a biomarker of male reproductive health and probability of pregnancy success in the general population.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded in part by the National Institute of Environmental Health Sciences, National Institutes of Health (R01-ES028298; PI: J.R.P.) and the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland (Contracts N01-HD-3-3355, N01-HD-3-3356 and N01-HD-3-3358). The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Sperm mtDNA copy number, telomere length, and seminal spermatogenic cells in relation to ambient air pollution: Results of a cross-sectional study in Jing-Jin-Ji region of China

Evidences on the association of air pollutants and semen quality were limited and mechanism-based biomarkers were sparse. We enrolled 423 men at a fertility clinic in Shijiazhuang, China to evaluate associations between air pollutants and semen quality parameters including the conventional ones, sperm mitochondrial DNA copy number (mtDNAcn), sperm telomere length (STL) and seminal spermatogenic cells. PM_2.5, PM₁₀, CO, SO₂, NO₂ and O₃ exposure during lag0-90, lag0-9, lag10-14 and lag70-90 days were evaluated with ordinary Kringing model. The exposure-response correlations were analyzed with multiple linear regression models. CO, PM_2.5 and PM₁₀ were adversely associated with conventional semen parameters including sperm count, motility and morphology. Besides, CO was positively associated with seminal primary spermatocyte (lag70-90, 0.49; 0.14, 0.85) and mtDNAcn (lag0-90, 0.37; 0.12, 0.62, lag10-14, 0.31; 0.12, 0.49), negatively associated with STL (lag0-9, -0.30; -0.57, -0.03). PM_2.5 was positively associated with mtDNAcn (0.50; 0.24, 0.75 and 0.38; 0.02, 0.75 for lag0-90 and lag70-90) while negatively associated with STL (lag70-90, -0.49; -0.96, -0.01). PM₁₀ and NO₂ were positively associated with mtDNAcn. Our findings indicate CO and PM might impair semen quality testicularly and post-testicularly while seminal spermatogenic cell, STL and mtDNAcn change indicate necessity for more attention on these mechanisms.

Green tea extract increases the quality and reduced DNA mutation of post-thawed Kacang buck sperm

The study aimed to determine the addition of green tea extract (GTE) in extender on the quality and DNA mutation of post-thawed Kacang buck sperm. The sperm DNA mutation was observed on nicotinamide adenine dinucleotide hydride (NADH) dehydrogenase 1 (ND1) of mitochondrial Deoxyribonucleic Acid (mtDNA). A pool of 12 Kacang buck ejaculates was diluted in skim milk-egg yolk extender contained 0, 0.05, 0.10, and 0.15 mg of GTE/100 mL for T0, T1, T2, and T3 group, respectively. Each of the aliquot groups was packaged in 0.25 mL French mini straw contained 60 million alive sperm and froze according to the protocol. The ND1 mtDNA amplification of samples was carried out Polymerase Chain Reaction machine, followed by DNA sequencing using the Sanger method. Meanwhile, the phylogenetic tree was constructed using the neighbor-joining (NJ) method with MEGA 7.0 software. The results showed that the T2 group maintained the highest quality for Kacang buck post-thawed semen. There was the highest percentages of sperms viability, motility, intact plasma membrane (IPM), the lowest of malondialdehyde (MDA) concentration, sperm DNA fragmentation (SDF), the total and types of ND1 mtDNA mutation frequency. The phylogenetic tree analysis revealed that the clade of the T2 group was most closely related to the sequence reference. However, there was no correlation between the semen quality parameters (sperm viability, motility, IPM, MDA concentration, and SDF) with ND1 mtDNA mutation of post-thawed Kacang buck semen. It could be concluded that GTE was useful as an antioxidant for Kacang buck semen extender for frozen sperm.

Mitochondria: their role in spermatozoa and in male infertility

BACKGROUND

The best-known role of spermatozoa is to fertilize the oocyte and to transmit the paternal genome to offspring. These highly specialized cells have a unique structure consisting of all the elements absolutely necessary to each stage of fertilization and to embryonic development. Mature spermatozoa are made up of a head with the nucleus, a neck, and a flagellum that allows motility and that contains a midpiece with a mitochondrial helix. Mitochondria are central to cellular energy production but they also have various other functions. Although mitochondria are recognized as essential to spermatozoa, their exact pathophysiological role and their functioning are complex. Available literature relative to mitochondria in spermatozoa is dense and contradictory in some cases. Furthermore, mitochondria are only indirectly involved in cytoplasmic heredity as their DNA, the paternal mitochondrial DNA, is not transmitted to descendants.

OBJECTIVE AND RATIONAL

This review aims to summarize available literature on mitochondria in spermatozoa, and, in particular, that with respect to humans, with the perspective of better understanding the anomalies that could be implicated in male infertility.

SEARCH METHODS

PubMed was used to search the MEDLINE database for peer-reviewed original articles and reviews pertaining to human spermatozoa and mitochondria. Searches were performed using keywords belonging to three groups: 'mitochondria' or 'mitochondrial DNA', 'spermatozoa' or 'sperm' and 'reactive oxygen species' or 'calcium' or 'apoptosis' or signaling pathways'. These keywords were combined with other relevant search phrases. References from these articles were used to obtain additional articles.

OUTCOMES

Mitochondria are central to the metabolism of spermatozoa and they are implicated in energy production, redox equilibrium and calcium regulation, as well as apoptotic pathways, all of which are necessary for flagellar motility, capacitation, acrosome reaction and gametic fusion. In numerous cases, alterations in one of the aforementioned functions could be linked to a decline in sperm quality and/or infertility. The link between the mitochondrial genome and the quality of spermatozoa appears to be more complex. Although the quantity of mtDNA, and the existence of large-scale deletions therein, are inversely correlated to sperm quality, the effects of mutations seem to be heterogeneous and particularly related to their pathogenicity.

WIDER IMPLICATIONS

The importance of the role of mitochondria in reproduction, and particularly in gamete quality, has recently emerged following numerous publications. Better understanding of male infertility is of great interest in the current context where a significant decline in sperm quality has been observed.

Analysis by Metabolomics and Transcriptomics for the Energy Metabolism Disorder and the Aryl Hydrocarbon Receptor Activation in Male Reproduction of Mice and GC-2spd Cells Exposed to PM2.5

Fine particulate matter (PM_2.5)-induced male reproductive toxicity arouses global public health concerns. However, the mechanisms of toxicity remain unclear. This study aimed to further investigate toxicity pathways by exposure to PM_2.5in vitro and in vivo through the application of metabolomics and transcriptomics. In vitro, spermatocyte-derived GC-2spd cells were treated with 0, 25, 50, 100 μg/mL PM_2.5 for 48 h. In vivo, the real-world exposure of PM_2.5 for mouse was established. Forty-five male C57BL/6 mice were exposed to filtered air, unfiltered air, and concentrated ambient PM_2.5 in Tangshan of China for 8 weeks, respectively. The results in vitro and in vivo showed that PM_2.5 exposure inhibited GC-2spd cell proliferation and reduced sperm motility. Mitochondrial damage was observed after PM_2.5 treatment. Increased Humanin and MOTS-c levels and decreased mitochondrial respiratory indicated that mitochondrial function was disturbed. Furthermore, nontargeted metabolomics analysis revealed that PM_2.5 exposure could disturb the citrate cycle (TCA cycle) and reduce amino acids and nucleotide synthesis. Mechanically, the aryl hydrocarbon receptor (AhR) pathway was activated after exposure to PM_2.5, with a significant increase in CYP1A1 expression. Further studies showed that PM_2.5 exposure significantly increased both intracellular and mitochondrial reactive oxygen species (ROS) and activated NRF2 antioxidative pathway. With the RNA-sequencing technique, the differentially expressed genes induced by PM_2.5 exposure were mainly enriched in the metabolism of xenobiotics by the cytochrome P450 pathway, of which Cyp1a1 was the most significantly changed gene. Our findings demonstrated that PM_2.5 exposure could induce spermatocyte damage and energy metabolism disorder. The activation of the aryl hydrocarbon receptor might be involved in the mechanism of male reproductive toxicity.

DNA Methylation Differences Between Zona Pellucida-Bound and Manually Selected Spermatozoa Are Associated With Autism Susceptibility

Children conceived through intracytoplasmic sperm injection (ICSI) have been reported to have a higher risk of many abnormalities and disorders, including autism and intellectual disability, which may be due to bypassing of the natural sperm selection process during ICSI. Zona pellucida (ZP)-bound spermatozoa (ZPBS) have normal morphology and nuclear DNA. Using these spermatozoa for ICSI results in better outcomes compared with conventional ICSI. However, differences besides morphology that exist between sperm selected by ZP and by an embryologist and whether these differences affect the risk of autism in offspring after ICSI are unclear. To explore these questions, we compared genome-wide DNA methylation profiles between ZPBS and manually selected spermatozoa (MSS)using single-cell bisulfite sequencing. Global DNA methylation levels were significantly lower in ZPBS than in MSS. Using gene ontology (GO) analysis, genes overlapping differentially methylated regions (DMRs) were enriched in biological processes involving neurogenesis. Furthermore, we found that 47.8% of autism candidate genes were associated with DMRs, compared with 37.1% of matched background genes (P<0.001). This was mainly because of the high proportion of autism candidate genes with bivalent chromatin structure. In conclusion, bivalent chromatin structure results in large differences in the methylation of autism genes between MSS and ZPBS. ICSI using MSS, which increases the risk of methylation mutations compared with ZPBS, may lead to a higher risk of autism in offspring.

Association between sperm mitochondarial DNA copy number and nuclear DNA methylation

Aim: Accumulating evidence associates sperm mitochondria DNA copy number (mtDNAcn) with male infertility and reproductive success. However, the mechanism underlying mtDNAcn variation is largely unknown. Patients & methods: Sperm mtDNAcn and genome-wide DNA methylation were assessed using triplex probe-based quantitative PCR and Illumina's 450K array, respectively. Multivariable models assessed the association between sperm mtDNAcn and DNA methylation profiles of 47 men seeking infertility treatment. Results:  A priori candidate-gene approach showed sperm mtDNAcn was associated with 16 CpGs located at/near POLG and TWNK genes. Unbiased genome-wide analysis revealed that sperm mtDNAcn was associated with 218 sperm differentially methylated regions (q < 0.05), which displayed predominantly (94%) increases in methylation. Conclusion: Findings suggest that DNA methylation may play a role in regulating sperm mtDNAcn.

Taurine effects on Bisphenol A-induced oxidative stress in the mouse testicular mitochondria and sperm motility

Objectives:

This study was performed to investigate the protective effects of taurine (2-aminoethanesulfonic acid, TAU) on oxidative stress in the isolated mouse testicular mitochondria, mitochondrial membrane potential (MMP), viability and motility of the exposed sperms to the BPA.

Methods:

We treated epididymal spermatozoa obtained from mice and isolated mouse testicular mitochondria with BPA (0.8 mmol/mL) and various doses of TAU (5, 10, 30 and 50 µmol/L). We used the MTT assay and Rhodamine 123 uptake to assess sperm viability and MMP. We assessed the oxidative stress through measuring ROS (reactive oxygen species), MDA (malondialdehyde), GSH (glutathione), and SOD (super-oxide dismutase) levels in the testicular mitochondrial tissue.

Results:

BPA significantly elevated ROS, MDA and MMP levels, and markedly reduced SOD and GSH levels in the isolated mitochondria. BPA also considerably impaired spermatozoa viability and motility. Pretreatment with 30 and 50 µmol/L of TAU could considerably suppressed mitochondrial oxidative stress, enhanced MMP, and improved sperm motility and viability.

Conclusion:

TAU may attenuate the BPA-induced mitochondrial toxicity and impaired sperm motility via decreasing oxidative stress.

Inhibitory effect of Lycium barbarum polysaccharide on sperm damage during cryopreservation

With the development of cryopreservation technology, marked progress has been made regarding sperm cryopreservation. However, as conventional cryopreservation agents are not effective at freezing weak sperm, improved cryopreservation agents are in demand. In the present study, the addition of Lycium barbarum polysaccharides to glycerol-egg-yolk-citrate sperm cryopreservation agent was determined to improve sperm forward speed, reduce the DNA fragmentation index and improve the mitochondrial membrane potential. Furthermore, during the freezing and thawing of sperm, the improved cryopreservative increased the content of Bcl-2 while reducing the content of Bax, cytochrome C and caspase-3. These results indicated that polysaccharides added as a protective agent preserved the normal function of sperm mitochondria. Transmission electron microscopy also confirmed the protective effect of the polysaccharides on the structure of mitochondria. It was also indicated that improved cryopreservative lowered the levels of reactive oxygen species (ROS) during the freeze-thawing process. Therefore, it is hypothesized that improved cryopreservative agents may be beneficial for maintaining the structure and function of the mitochondria of weak sperm when cryopreserved, which may be facilitated via reducing the production of ROS in the freezing-thawing process, thus avoiding activation of the apoptotic pathway in sperm mitochondria and protecting mitochondrial structure and sperm function.

N, N-Dimethylacetamide, an FDA approved excipient, acts post-meiotically to impair spermatogenesis and cause infertility in rats

N, N-Dimethylacetamide is an FDA approved solvent widely used in pharmaceutical industry to facilitate the solubility of lipophilic, high molecular weight drugs with poor water solubility. However, the cytotoxic effects of DMA raises the concern about its use in clinical applications. In the present study, we address the effect of DMA on spermatogenesis. Male Sprague Dawley rats were injected intra-peritoneally for 8 weeks, once a week at a dose of 862 mg/kg. Analysis of reproductive parameters revealed that DMA treated animals exhibit spermatid formation defects within the testis describing the characteristics of oligozoospermia. A subsequent decrease in epididymal sperm concentration along with distortion of sperm morphology was observed. The mitochondrial and microtubule organization in the sperm is considerably modified by DMA. This disrupts the sperm kinetics thus decreasing the total and progressive sperm motility. Finally, DMA treatment resulted in loss of fertility. Our results indicate that exposure to DMA has a negative impact on spermatogenesis and leads to infertility in male rats by inhibiting the post meiotic stages of sperm development. Therefore, the use of DMA in humans must be closely monitored.

Causes and consequences of sperm mitochondrial dysfunction

Mitochondria have multiple functions, including synthesis of adenine triphosphate, production of reactive oxygen species, calcium signalling, thermogenesis and apoptosis. Mitochondria have a significant contribution in regulating the various physiological aspects of reproductive function, from spermatogenesis up to fertilisation. Mitochondrial functionality and intact mitochondrial membrane potential are a pre-requisite for sperm motility, hyperactivation, capacitation, acrosin activity, acrosome reaction and DNA integrity. Optimal mitochondrial activity is therefore crucial for human sperm function and semen quality. However, the precise role of mitochondria in spermatozoa remains to be fully explored. Defects in sperm mitochondrial function severely impair the maintenance of energy production required for sperm motility and may be an underlying cause of asthenozoospermia. Sperm mtDNA is susceptible to oxidative damage and mutations that could compromise sperm function leading to infertility. Males with abnormal semen parameters have increased mtDNA copy number and reduced mtDNA integrity. This review discusses the role of mitochondria in sperm function, along with the causes and impact of its dysfunction on male fertility. Greater understanding of sperm mitochondrial function and its correlation with sperm quality could provide further insights into their contribution in the assessment of the infertile male.

Sperm Mitochondrial DNA Copy Number Is Not a Predictor of Intracytoplasmic Sperm Injection (ICSI) Cycle Outcomes

This study is to determine if sperm mitochondrial DNA copy number (mtDNA CN) is associated with fertilization, blastulation, blastocyst euploidy, and live birth rates in in vitro fertilization (IVF) with ICSI cycles. This is a cohort study conducted on stored sperm samples which were collected prospectively and used to create blastocysts transferred in a couple's first ICSI transfer cycle between 2007 and 2013 at a single large infertility center. Samples from ICSI cycles utilizing surgical or cryopreserved sperm or day 3 embryo biopsy were excluded. The primary outcome was live birth rate. Secondary outcomes included fertilization, usable blastocyst development, and blastocyst euploidy rates. Unique sperm samples used to create transferred embryos were identified. Mitochondrial DNA CN was evaluated using TaqMan® quantitative real-time polymerase chain reaction (qPCR) assays normalized to a nuclear control for relative quantitation. Linear regression and mixed effects logistic regression used were appropriate. A total of 2062 unique sperm samples used to create transferred embryos were included. Lower relative sperm mtDNA content was associated with increased pre-wash sperm motility (p < 0.001). No significant association was identified between sperm mtDNA CN and fertilization (p = 0.40), usable blastocyst development (p = 0.36), blastocyst euploid (p = 0.10), and live birth rates (p = 0.42) while adjusting for sperm pre-wash motility and maternal age. Sperm mtDNA CN is not prognostic of fertilization, usable blastocyst development, euploidy and live birth rates in an infertile population undergoing IVF with ICSI.

Evaluation of Sperm Mitochondrial Function: A Key Organelle for Sperm Motility

Introduction: The role of nutraceuticals in the treatment of male infertility, especially in the “idiopathic form”, remains the subject of significant debate. Many antioxidants improve sperm motility but the exact mechanism by which they act is still unclear. Although several studies have shown a correlation between sperm motility and mitochondrial function, the effects of antioxidant therapy on mitochondrial membrane potential (MMP) are poorly studied. The first aim of this review was to evaluate the efficacy of antioxidants on mitochondrial function and, consequently, on sperm motility in male infertile patients. Material and Methods: we performed a systematic search of all randomized controlled and uncontrolled studies available in the literature that reported sperm motility and MMP at baseline and after antioxidant administration in-vivo and in-vitro in patients with idiopathic asthenozoospermia. Pubmed, MEDLINE, Cochrane, Academic One Files, Google Scholar and Scopus databases were used. Results: Unexpectedly, among 353 articles retrieved, only one study met our inclusion criteria and showed a significant effect of myoinositol on both MMP and sperm motility. We then summarized the main knowledge on anatomy and metabolism of sperm mitochondria, techniques allowing to assess sperm mitochondria function and its relationships with low sperm motility. Finally, we paid special attention to the effect of antioxidant/prokinetic molecules for the treatment of asthenozoospermia. Conclusions: This is the first systematic review that has attempted to evaluate the effects of antioxidants on MMP and sperm motility. Although results are not conclusive due to the dearth of studies, the close relationship between mitochondria and sperm motility is clear. The investigation of this correlation could provide valuable information to be exploited in clinical practice for the treatment of male infertility.

The current status and future of andrology: A consensus report from the Cairo workshop group

BACKGROUND

In attempting to formulate potential WHO guidelines for the diagnosis of male infertility, the Evidence Synthesis Group noted a paucity of high-quality data on which to base key recommendations. As a result, a number of authors suggested that key areas of research/evidence gaps should be identified, so that appropriate funding and policy actions could be undertaken to help address key questions.

OBJECTIVES

The overall objective of this Consensus workshop was to clarify current knowledge and deficits in clinical laboratory andrology, so that clear paths for future development could be navigated.

MATERIALS AND METHODS

Following a detailed literature review, each author, prior to the face-to-face meeting, prepared a summary of their topic and submitted a PowerPoint presentation. The topics covered were (a) Diagnostic testing in male fertility and infertility, (b) Male fertility/infertility in the modern world, (c) Clinical management of male infertility, and (d) The overuse of ICSI. At the meeting in Cairo on February 18, 2019, the evidence was presented and discussed and a series of consensus points agreed.

RESULTS

The paper presents a background and summary of the evidence relating to these four topics and addresses key points of significance. Following discussion of the evidence, a total of 36 consensus points were agreed.

DISCUSSION

The Discussion section presents areas where there was further debate and key areas that were highlighted during the day.

CONCLUSION

The consensus points provide clear statements of evidence gaps and/or potential future research areas/topics. Appropriate funding streams addressing these can be prioritized and consequently, in the short and medium term, answers provided. By using this strategic approach, andrology can make the rapid progress necessary to address key scientific, clinical, and societal challenges that face our discipline now and in the near future.

Advances in Cryopreservation of Bull Sperm

Cryopreservation of semen and artificial insemination have an important, positive impact on cattle production, and product quality. Through the use of cryopreserved semen and artificial insemination, sperm from the best breeding bulls can be used to inseminate thousands of cows around the world. Although cryopreservation of bull sperm has advanced beyond that of other species, there are still major gaps in the knowledge and technology bases. Post-thaw viability of sperm is still low and differs significantly among the breeding bulls. These weaknesses are important because they are preventing advances both in fundamental science of mammalian gametes and reproductive biotechnology. Various extenders have been developed and supplemented with chemicals to reduce cryodamage or oxidative stress with varying levels of success. More detailed insights on sperm morphology and function have been uncovered through application of advanced tools in modern molecular and cell biology. This article provides a concise review of progress in the cryopreservation of bull sperm, advances in extender development, and frontiers using diverse techniques of the study of sperm viability. This scientific resource is important in animal biotechnology because with the advances in discovery of sperm fertility markers, there is an urgent need to improve post-thaw viability and fertility of sperm through enhanced cryopreservation for precision agriculture to produce food animals to ensure food security on the global scale.

Associations of sperm mitochondrial DNA copy number and deletion rate with fertilization and embryo development in a clinical setting

STUDY QUESTION

Are sperm mitochondrial DNA copy number (mtDNAcn) and deletion rate (mtDNAdel) associated with odds of fertilization and high embryo quality at Days 3 and 5?

SUMMARY ANSWER

Higher sperm mtDNAcn and mtDNAdel were associated with lower odds of high quality Day 3 embryos and transfer quality Day 5 embryos, both of which were primarily driven by lowered odds of fertilization.

WHAT IS KNOWN ALREADY

Sperm mtDNAcn and mtDNAdel have been previously associated with poor semen parameters and clinical male infertility. One prior study has shown that mtDNAdel is associated with lower fertilization rates. However, it is unknown whether these characteristics are linked with ART outcomes.

STUDY DESIGN, SIZE, DURATION

This prospective observational study included 119 sperm samples collected from men undergoing ART in Western Massachusetts. ART outcomes were observed through to Day 5 post-insemination.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

As part of the Sperm Environmental Epigenetics and Development Study (SEEDS), 119 sperm samples were collected from men undergoing ART in Western Massachusetts. Sperm mtDNAcn and mtDNAdel were measured via triplex probe-based qPCR. Fertilization, Day 3 embryo quality and Day 5 embryo quality measures were fitted with mtDNAcn and mtDNAdel using generalized estimating equations.

MAIN RESULTS AND THE ROLE OF CHANCE

After adjusting for male age and measurement batches, higher sperm mtDNAcn and mtDNAdel were associated with lower odds of fertilization (P = 0.01 and P < 0.01), high quality Day 3 embryos (P = 0.02 for both) and transfer quality Day 5 embryos (P = 0.01 and P = 0.09). However, the associations of mtDNAcn and mtDNAdel with Day 3 high quality status and Day 5 transfer quality status were attenuated in models restricted to fertilized oocytes. Sperm mtDNAcn and mtDNAdel remained statistically significant in models adjusted for both male age and semen parameters, although models including both mtDNA markers generally favoured mtDNAdel.

LIMITATIONS, REASONS FOR CAUTION

Our sample only included oocytes and embryos from 119 couples and thus large diverse cohorts are necessary to confirm the association of sperm mtDNA biomarkers with embryo development.

WIDER IMPLICATIONS OF THE FINDINGS

To our knowledge, our study is the first to assess the associations of sperm mtDNAcn and mtDNAdel with fertilization and embryo quality. The biological mechanism(s) underlying these associations are unknown. Multivariable models suggest that sperm mtDNAcn and mtDNAdel provide discrimination independent of age and semen parameters; therefore, future investigation of the utility of sperm mtDNA as a biomarker for ART outcomes is warranted.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by Grant (K22-ES023085) from the National Institute of Environmental Health Sciences. The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Sperm mitochondrial DNA measures and semen parameters among men undergoing fertility treatment

RESEARCH QUESTION

To examine associations between sperm mitochondrial DNA copy number (mtDNAcn), sperm mitochondrial DNA deletions (mtDNAdel), semen parameters and clinical infertility in an IVF setting.

DESIGN

A total of 125 sperm samples were collected from men undergoing assisted reproductive procedures in an IVF clinic in Western Massachusetts, USA. Sperm mtDNAcn and mtDNAdel were measured by probe-based quantitative polymerase chain reaction. Semen parameters, clinical diagnoses of infertility, and infertility based on consecutive semen parameters, were fitted with mtDNAcn and mtDNAdel in linear models. The utility of sperm mtDNAcn and mtDNAdel to predict infertility was assessed by receiver operating characteristic curves.

RESULTS

Adjusting for relevant covariates, both sperm mtDNAcn and mtDNAdel were associated with lower sperm concentration, count, motility and morphology (P ≤ 0.03). Sperm mtDNAcn and mtDNAdel were also associated with increased risks of clinical infertility based on current and consecutive semen samples. Sperm mtDNAcn had high predictive accuracy for consecutive diagnoses of clinical infertility (C-statistic: 0.91), whereas sperm mtDNAdel had moderate predictive accuracy (C-statistic: 0.75).

CONCLUSIONS

Sperm mtDNAcn is a measure of consecutive abnormal semen parameters and has promise as a diagnostic test.

Associations of urinary phthalate metabolites and lipid peroxidation with sperm mitochondrial DNA copy number and deletions

BACKGROUND

Phthalates, a chemical class of plasticizers, are ubiquitous environmental contaminants that have been associated with oxidative stress. Mitochondria DNA copy number (mtDNAcn) and DNA deletions (mtDNAdel) are emerging biomarkers for cellular oxidative stress and environment exposures.

OBJECTIVES

To examine associations of urinary phthalate metabolite and isoprostane concentrations on sperm mtDNAcn and mtDNAdel in male partners undergoing assisted reproductive technologies (ART).

METHODS

Ninety-nine sperm samples were collected from male partners undergoing ART at Baystate Medical Center in Springfield, MA as part of the Sperm Environmental Epigenetics and Development Study (SEEDS). Seventeen urinary phthalate metabolite concentrations were analyzed by the Centers for Disease Control using tandem mass spectrometry. Urinary 15-F2t-isoprostane concentrations, a biomarker of lipid peroxidation, were measured using a competitive enzyme-linked immunosorbent assay. A triplex qPCR method was used to determine the relative quantification of mtDNAcn and mtDNAdel.

RESULTS

Sperm mtDNAcn and mtDNAdel were positively correlated (Spearman rho = 0.31; p = .002). Adjusting for age, BMI, current smoking, race, and measurement batch, urinary monocarboxy-isononyl phthalate (MCNP) concentrations were positively associated with mtDNAcn (β = 1.63, 95% CI: 0.14, 3.11). Other urinary phthalate metabolite and isoprostane concentrations were not associated with sperm mtDNAcn or mtDNAdel.

CONCLUSIONS

Among this cohort of male ART participants, those with higher MCNP had higher mtDNAcn; other phthalate metabolites and isoprostane were not associated with mtDNAcn and mtDNAdel. Given our relatively small sample size, our results should be interpreted with caution. Future research is needed to replicate the findings in larger studies and among sperm samples obtained from the general population.