The Stimulated Glycolytic Pathway Is Able to Maintain ATP Levels and Kinetic Patterns of Bovine Epididymal Sperm Subjected to Mitochondrial Uncoupling

Transgenerational Inheritance Effects of Copper Oxide Nanoparticles (CuONPs) Induced Asthenospermia and Infertility via Gamete H3K9me3 Insufficiency Pathway in Mice

The widespread use of colloidal copper oxide nanoparticles (CuONPs) poses substantial health risks to humans. CuONPs can penetrate the blood-testis barrier and induce spermatocide, and the understanding of the adverse effects of asthenospermia on spermatogenesis, embryonic development, and transgenerational inheritance is limited. In this study, male mice were orally administered different doses of CuONPs via continuous exposure for one spermatozoon development period (35 days) and then exposed without CuONPs for another 35 days. The CuONPs that accumulated in the testes induced oxidative stress (OS), affected the progress of spermatogenesis and sperm capacitation, and compromised epigenetic modifications, resulting in asthenospermia and embryonic development anomalies in male offspring. In a mechanism, CuONP exposure impaired the self-renewal and differentiation of spermatogonial stem cells (SSCs) via the GDNF/PI3K/AKT signaling pathway under OS. Importantly, CuONP exposure was found to potentially lower H3K9me3 levels in paternal sperm, which would further transgenerational transmission and interfere with sperm mitochondrial energy metabolism and motility, leading to asthenospermia and subfertility in the offspring. Collectively, these data reveal a molecular mechanism by which CuONP exposure disturbs H3K9me3 levels via the OS pathway, which further mediates the asthenospermic effects of reproductive failure by interfering with mitochondrial arrangement and formation in the next generation.

Exogenous Oxidative Stress in Human Spermatozoa Induces Opening of the Mitochondrial Permeability Transition Pore: Effect on Mitochondrial Function, Sperm Motility and Induction of Cell Death

Oxidative stress (OS) and disrupted antioxidant defense mechanisms play a pivotal role in the etiology of male infertility. The alterations in reactive oxygen species (ROS) production and calcium (Ca2+) homeostasis are the main activators for the mitochondrial permeability transition pore (mPTP) opening. The mPTP opening is one of the main mechanisms involved in mitochondrial dysfunction in spermatozoa. This alteration in mitochondrial function adversely affects energy supply, sperm motility, and fertilizing capacity and contributes to the development of male infertility. In human spermatozoa, the mPTP opening has been associated with ionomycin-induced endogenous oxidative stress and peroxynitrite-induced nitrosative stress; however, the effect of exogenous oxidative stress on mPTP opening in sperm has not been evaluated. The aim of this study was to determine the effect of exogenous oxidative stress induced by hydrogen peroxide (H2O2) on mPTP opening, mitochondrial function, motility, and cell death markers in human spermatozoa. Human spermatozoa were incubated with 3 mmol/L of H2O2 for 60 min, and intracellular Ca2+ concentration, mPTP opening, mitochondrial membrane potential (ΔΨm), ATP levels, mitochondrial reactive oxygen species (mROS) production, phosphatidylserine (PS) externalization, DNA fragmentation, viability, and sperm motility were evaluated. H2O2-induced exogenous oxidative stress caused increased intracellular Ca2+, leading to subsequent mPTP opening and alteration of mitochondrial function, characterized by ΔΨm dissipation, decreased ATP levels, increased mROS production, and the subsequent alteration of sperm motility. Furthermore, H2O2-induced opening of mPTP was associated with the expression of apoptotic cell death markers including PS externalization and DNA fragmentation. These results highlight the role of exogenous oxidative stress in causing mitochondrial dysfunction, deterioration of sperm motility, and an increase in apoptotic cell death markers, including PS externalization and DNA fragmentation, through the mPTP opening. This study yielded new knowledge regarding the effects of this type of stress on mitochondrial function and specifically on mPTP opening, factors that can contribute to the development of male infertility, considering that the role of mPTP in mitochondrial dysfunction in human sperm is not completely elucidated. Therefore, these findings are relevant to understanding male infertility and may provide an in vitro model for further research aimed at improving human sperm quality.

Integrating metabolomics into reproduction: Sperm metabolism and fertility enhancement in pigs

The last decades of research have revealed that many other factors besides gamete genomes are able to determine the reproductive outcomes. Indeed, paternal factors have been observed to be capable of modulating multiple crucial features of the reproductive process, such as sperm physiology, the maternal environment and, even, the offspring health. These recent advances have been encompassed with the emergence of OMICS technologies, as they comprehensively characterise the molecular composition of biological systems. The present narrative review aimed to take a closer look at the potential of these technologies in the field of reproductive biology. This literature revision shows that most studies up to date have followed a non-targeted approach to screen mammalian seminal plasma (SP) and sperm metabolite composition through different metabolome platforms. These studies have proposed metabolites of multiple natures as potential in vivo fertility biomarkers. Yet, targeted approaches can be used to answer specific biological question, and their power is exemplified herein. For instance, metabolomic studies have uncovered not only that glycolysis is the main ATP energy source of pig sperm, but also that sperm metabolism can trigger DNA damage, hence compromise embryo development. In conclusion, this review shows the potential of both non-targeted and targeted metabolomics for the discovery of cell pathways that govern the reproductive process. Understanding these systems could help make progress in different areas, including livestock efficient breeding, the improvement of artificial reproductive technologies, and the development of biomarkers for infertility detection.

mitoBKCa is functionally expressed in murine and human breast cancer cells and potentially contributes to metabolic reprogramming

Alterations in the function of K+ channels such as the voltage- and Ca2+-activated K+ channel of large conductance (BKCa) reportedly promote breast cancer (BC) development and progression. Underlying molecular mechanisms remain, however, elusive. Here, we provide electrophysiological evidence for a BKCa splice variant localized to the inner mitochondrial membrane of murine and human BC cells (mitoBKCa). Through a combination of genetic knockdown and knockout along with a cell permeable BKCa channel blocker, we show that mitoBKCa modulates overall cellular and mitochondrial energy production, and mediates the metabolic rewiring referred to as the 'Warburg effect', thereby promoting BC cell proliferation in the presence and absence of oxygen. Additionally, we detect mitoBKCa and BKCa transcripts in low or high abundance, respectively, in clinical BC specimens. Together, our results emphasize, that targeting mitoBKCa could represent a treatment strategy for selected BC patients in future.

Negative correlations of mitochondrial DNA copy number in commercial frozen bull spermatozoa with the motility parameters after thawing

The purpose of the current study was to investigate the relationship between mitochondrial content of commercial frozen-thawed bull spermatozoa and motility. Firstly, mitochondrial DNA copy number per spermatozoon (MDCN), mitochondrial content (MC), the percentage of spermatozoa with high mitochondrial membrane potential (HMMP), intracellular reactive oxygen species (ROS) and motility parameters of frozen-thawed spermatozoa derived from five bulls were determined by using qPCR, flow cytometry and CASA, respectively, and analyzed the relationships. Results showed that all parameters examined, including MDCN, MC, HMMP, ROS and motility indicators, significantly differed among frozen spermatozoa from different bulls. Both MDCN and MC were negatively correlated with HMMP and motility indicators, but positively with ROS, of course, whereas there was a highly positive relationship between MDCN and MC. Secondly, when MDCN and MC were examined in frozen spermatozoa prepared at different points in the lives of four bulls, those did not correlate overall throughout their lives (1.3-14.3 years old), but did correlate significantly in two sires. From these results, we conclude that MDCN and MC of frozen spermatozoa differ among sires, and are negatively correlated with HMMP and sperm motility parameters, probably due to mitochondrial oxidative stress resulted in the presence of ROS, demonstrating that these appear to be useful markers to assess sires' spermatozoa. It should be noted that the MDCN and MC of bull spermatozoa may not vary overall with the age of the sire, whereas those changes with age in some individuals and may affect sperm motility.

Expression of miR-138 in cryopreserved bovine sperm is related to their fertility potential

BACKGROUND

MicroRNAs (miRNAs) are small, single-stranded, non-coding RNA molecules of 22-24 nucleotides that regulate gene expression. In the last decade, miRNAs have been described in sperm of several mammals, including cattle. It is known that miRNAs can act as key gene regulators of early embryogenesis in mice and humans; however, little is known about the content, expression, and function of sperm-borne miRNAs in early bovine embryo. In this study, total sperm RNA was isolated from 29 cryopreserved sperm samples (each coming from a separate bull) using a RNeasy kit and treatment with DNase I. RNA concentration and purity were determined through an Epoch spectrophotometer and an Agilent Bioanalyzer. The expression of 10 candidate miRNAs in bovine sperm (bta-miR-10a, bta-miR-10b, bta-miR-138, bta-miR-146b, bta-miR-19b, bta-miR-26a, bta-miR-34a, bta-miR-449a, bta-miR-495 and bta-miR-7), previously identified in testis and/or epididymis, was evaluated with RT-qPCR. The cel-miR-39-3p was used as a spike-in exogenous control. Nonparametric Mann-Whitney tests were run to evaluate which miRNAs were differentially expressed between bulls with high fertility [HF; non-return rates (NRR) ranging from 39.5 to 43.5] and those with subfertility (SF; NRR ranging from 33.3 to 39.3). Several sperm functionality parameters (e.g., viability, membrane stability or oxygen consumption, among others) were measured by multiplexing flow cytometry and oxygen sensing technologies.

RESULTS

RNA concentration and purity (260/280 nm ratio) (mean ± SD) from the 29 samples were 99.3 ± 84.6 ng/µL and 1.97 ± 0.72, respectively. Bioanalyzer results confirmed the lack of RNA from somatic cells. In terms of the presence or absence of miRNAs, and after applying the Livak method, 8 out of 10 miRNAs (bta-miR-10b, -138, -146b, -19b, -26a, -449a, -495, -7) were consistently detected in bovine sperm, whereas the other two (bta-miR-10a, and -34a) were absent. Interestingly, the relative expression of one miRNA (bta-miR-138) in sperm was significantly lower in the SF than in the HF group (P = 0.038). In addition to being associated to fertility potential, the presence of this miRNA was found to be negatively correlated with sperm oxygen consumption. The expression of three other miRNAs (bta-miR-19b, bta-miR-26a and bta-miR-7) was also correlated with sperm function variables.

CONCLUSIONS

In conclusion, although functional validation studies are required to confirm these results, this study suggests that sperm bta-miR-138 is involved in fertilization events and beyond, and supports its use as a fertility biomarker in cattle.

Post-Thaw Parameters of Buck Semen Quality after Soy Lecithin Extender Supplementation with Fumaric Acid

The supplementation of cryopreservation media with antioxidants improves the post-thaw quality and fertilizing ability of spermatozoa. To maximize the fertility of frozen-thawed buck spermatozoa, further research is required to overcome obstacles that have yielded controversial results and standardize protocols. In the present work, the effect of adding fumaric acid (a well-described antioxidant) to a soy lecithin semen extender on certain quality parameters of spermatozoa following freezing and thawing was examined for the first time. Five sexually mature Skopelos bucks were used, and ejaculates were collected with an artificial vagina. The semen samples (98 samples, five replicates) were diluted (400 × 106 spermatozoa/mL) with OviXcell®, supplemented with fumaric acid (0 mM, 2.15 mM, 10 mM or 30 mM), equilibrated (5 °C; 3 h), packed (0.5 mL straws), frozen and stored (-196 °C) until further processing. After thawing, the spermatozoa total and progressive motility (CASA), viability (eosin-nigrosin), membrane functional integrity (HOST), acrosome integrity (SpermBlue®) and mitochondrial function (Rhodamine-123/SYBR-14/PI) were evaluated. Statistical analysis was performed with one-way ANOVA, followed by Duncan's test; significance was set at 0.05. The addition of 2.15 mM fumaric acid improved (p < 0.05) spermatozoa viability, membrane functional integrity, acrosome integrity and mitochondrial function compared to all other concentrations. The addition of 30 mM fumaric acid decreased (p < 0.05) spermatozoa viability and mitochondrial function compared to all other concentrations. These results indicate a beneficial effect of a 2.15 mM fumaric acid addition to a soy lecithin extender on post-thaw buck spermatozoa quality. Further research is required to evaluate the in vivo fertility of frozen-thawed buck spermatozoa treated with fumaric acid, as well as to elucidate the mechanism of action of fumaric acid in spermatozoa.

Sperm physiology and in vitro fertilising ability rely on basal metabolic activity: insights from the pig model

Whether basal metabolic activity in sperm has any influence on their fertilising capacity has not been explored. Using the pig as a model, the present study investigated the relationship of energetic metabolism with sperm quality and function (assessed through computer-assisted sperm analysis and flow cytometry), and fertility (in vitro fertilisation (IVF) outcomes). In semen samples from 16 boars, levels of metabolites related to glycolysis, ketogenesis and Krebs cycle were determined through a targeted metabolomics approach using liquid chromatography-tandem mass spectrometry. High-quality sperm are associated to greater levels of glycolysis-derived metabolites, and oocyte fertilisation and embryo development are conditioned by the sperm metabolic status. Interestingly, glycolysis appears to be the preferred catabolic pathway of the sperm giving rise to greater percentages of embryos at day 6. In conclusion, this study shows that the basal metabolic activity of sperm influences their function, even beyond fertilisation.

Pharmacological perturbation of peroxisome-proliferator-activated receptor gamma alters motility and mitochondrial function of bovine sperm

BACKGROUND

Sperm transit through the female reproductive relies upon maintenance of sperm motility. Peroxisome-proliferator-activated receptor gamma (PPARγ) is a ligand-activated nuclear transcription factor with roles in glucose metabolism and reproductive processes including placental function. PPARγ roles in the mammalian postejaculatory sperm function are incompletely defined.

OBJECTIVES

Determine expression, localization, and functions of PPARγ in postejaculatory bovine sperm.

MATERIALS AND METHODS

Frozen-thawed bovine sperm from three to four different bulls were pooled and subjected to immunofluorescence and western blot for detection and localization of PPARγ. Functions in sperm energetics were explored through the addition of pharmacological inhibition (GW; GW9662) and activation (Ros; Rosiglitazone) in the culture medium at 0 and 24 h under non-capacitating conditions. Samples were analyzed for sperm kinematics (CASA) and mitochondrial membrane potential (MMP; JC-1 fluorophore).

RESULTS

PPARγ was detected in bovine sperm and co-localized to the acrosome with re-localization to the equatorial region in acrosome-compromised sperm. The addition of Ros 50 µM for 24 h maintained superior total and progressive motility of sperm compared to vehicle control (VC-DMSO 0.01%). The PPARγ antagonist GW 1 µM was detrimental to both total and progressive motility. A challenge experiment (Ros + GW) partially rescued total and progressive motility phenotypes observed with GW incubation. GW-treated samples had a lower number of sperm with high MMP at 24 h compared to Ros or VC. The negative GW MMP phenotype was reversed with the addition of Ros + GW. Likewise, GW-treated samples had more sperm with low MMP compared to VC and Ros, and this phenotype was partially restored with Ros + GW.

CONCLUSION

PPARγ is expressed in post-ejaculatory bovine sperm with regulatory roles in sperm motility and MMP. These findings implicate PPARγ as a novel regulator of postejaculatory mammalian sperm energetics through non-canonical signaling mechanisms.

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.

Natural Astaxanthin Improves Testosterone Synthesis and Sperm Mitochondrial Function in Aging Roosters

Spermatogenesis, sperm motility, and apoptosis are dependent on the regulation of glandular hormones and mitochondria. Natural astaxanthin (ASTA) has antioxidant, anti-inflammatory, and anti-apoptotic properties. The present study evaluates the effects of ASTA on testosterone synthesis and mitochondrial function in aging roosters. Jinghong No. 1 layer breeder roosters (n = 96, 53-week old) were fed a corn−soybean meal basal diet containing 0, 25, 50, or 100 mg/kg ASTA for 6 weeks. The levels of plasma reproductive hormones and the mRNA and protein levels of molecules related to testosterone synthesis were significantly improved (p < 0.05) in the testes of the ASTA group roosters. In addition, antioxidant activities and free radical scavenging abilities in roosters of the ASTA groups were higher than those of the control group (p < 0.05). Mitochondrial electron transport chain complexes activities and mitochondrial membrane potential in sperm increased linearly with dietary ASTA supplementation (p < 0.05). The levels of reactive oxygen species and apoptosis factors decreased in roosters of the ASTA groups (p < 0.05). Collectively, these results suggest that dietary ASTA may improve testosterone levels and reduce sperm apoptosis, which may be related to the upregulation of the testosterone synthesis pathway and the enhancement of mitochondrial function in aging roosters.

Mitoquinone does not improve sperm cryo-resistance in bulls

Oxidative stress is associated with impaired post‐thaw sperm quality. As mitochondria are the main source of reactive oxygen species (ROS) in sperm, the goal of this study was to evaluate effects of the mitochondria‐targeting antioxidant Mitoquinone (MitoQ) during cryopreservation of bull sperm. Semen was collected from 11 Simmental bulls (two ejaculates per bull) and diluted in Triladyl^® supplemented with various concentrations of MitoQ (0, 0.2, 2, and 20 nM) to a final concentration of 65 × 10⁶ sperm/ml. After thawing (0 and 3 hr), we assessed the following sperm traits: sperm motility by computer‐assisted sperm analysis (CASA), DNA fragmentation index by SCSA^® and plasma and acrosome membrane integrity, intracellular calcium concentration, esterase activity, mitochondrial membrane potential and synthesis of ROS using two multicolour flow cytometric assays. After 3 hr of incubation, 20 nM MitoQ increased (p < .05) sperm ROS synthesis compared to Control, whereas none of the other quality parameters were altered (p > .05). Therefore, we concluded that addition of MitoQ to semen extender before cryopreservation of bull sperm was unable to improve post‐thaw sperm quality. Furthermore, 20 nM of MitoQ increased frozen‐thawed sperm ROS synthesis, without apparent negative effects on the evaluated sperm traits.

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.

Is addition or removal of seminal plasma able to compensate for the dilution effect of buffalo semen?

The present study aimed to compensate dilution effect using additional seminal plasma (SP) in conventional (80 million (M) spermatozoa/ml) dose and low spermatozoa/dose (8M spermatozoa/ml). We also attempted to confirm whether removal of SP before the extension of ejaculates affects post-thaw sperm quality of buffalo semen. For this, semen ejaculates (N = 15) were divided into four groups: control (CON), removal of SP by centrifugation (NSP), resuspension of the centrifuged semen pellet into SP (CEN) and extra supplementation of SP (ESP). All groups were diluted into two different semen doses to 20 and 2M spermatozoa/0.25 ml using tris egg yolk extender and subsequently cryopreserved. We found that neither addition nor removal of SP affected sperm motility, kinematics, longevity, mitochondrial superoxide production and high mitochondrial membrane potential (MMP). Further, the addition or removal of SP was not able to compensate dilution effect in 2M groups resulting in a significantly (p < .05) reduction in sperm motility, kinematics, sperm longevity, membrane integrity, MMP, and an increase production of mitochondrial superoxide. In conclusion, it appears that role of SP in the sperm cryopreservation process is insignificant.

Effect of glucose concentration and cryopreservation on mitochondrial functions of bull spermatozoa and relationship with sire conception rate

Mitochondrial function is essential for sperm viability, not only from a sperm metabolism perspective, but also for improvement of sperm storage in liquid and frozen states. Bull sperm have notable metabolic variability with energy production for motility and subsequently for fertilizing capacity resulting from both glycolysis and oxidative phosphorylation. The objective of this study was to determine mitochondrial function of sperm using high-throughput Seahorse Analyzer technology in fresh semen and subsequent to freezing-thawing when there was incubation in media commonly used for sperm storage (relatively large glucose concentration) and female tract (relatively small glucose concentration). Additionally, there were determinations whether there were differences in values for fertility variables by regressing sire conception rate on values for mitochondrial variables when there was evaluation of semen from bulls with varying fertility. Media with larger concentrations of glucose inhibited mitochondrial function in fresh sperm, as indicated by less maximal oxygen consumption, spare respiratory capacity and coupling efficiency when compared to sperm in the media containing less glucose. Furthermore, there was greater (P <  0.05) mitochondrial function in cryopreserved-thawed compared to fresh samples with there being no effect of incubation media. These results indicate that mitochondrial damage from cryopreservation cannot be simply overcome post-thawing with glucose supplementation of bull semen incubation media. The increase in mitochondrial function is likely due to "non-productive" oxygen consumption to maintain the mitochondrial proton gradient. Furthermore, there was a negative association of mitochondrial proton leakage with sire conception rate indicating this could be a potential biomarker of bull fertility.

Pathophysiology of Mitochondrial Dysfunction in Human Spermatozoa: Focus on Energetic Metabolism, Oxidative Stress and Apoptosis

The dogma of mitochondria as the major source of energy in supporting sperm motility should be critically reconsidered in the light of several experimental data pointing to a major role of glycolysis in mammalian spermatozoa. In this light, the reported positive correlation between the mitochondrial membrane potential (ΔΨm) and motility of ejaculated spermatozoa cannot be explained convincingly by an impaired mitochondrial ATP generation only. Evidence has been produced suggesting that, in human sperm, dysfunctional mitochondria represent the main site of generation of reactive oxygen species (ROS). Furthermore, in these organelles, a complex bidirectional relationship could exist between ROS generation and apoptosis-like events that synergize with oxidative stress in impairing sperm biological integrity and functions. Despite the activity of enzymatic and non-enzymatic antioxidant factors, human spermatozoa are particularly vulnerable to oxidative stress, which plays a major role in male factor infertility. The purpose of this article is to provide an overview of metabolic, oxidative and apoptosis-like inter-linkages of mitochondrial dysfunction and their reflections on human sperm biology.

Advancing Semen Evaluation Using Lipidomics

Developing a deeper understanding of biological components of sperm is essential to improving cryopreservation techniques and reproductive technologies. To fully ascertain the functional determinants of fertility, lipidomic methods have come to the forefront. Lipidomics is the study of the lipid profile (lipidome) within a cell, tissue, or organism and provides a quantitative analysis of the lipid content in that sample. Sperm cells are composed of various lipids, each with their unique contribution to the overall function of the cell. Lipidomics has already been used to find new and exciting information regarding the fatty acid content of sperm cells from different species. While the applications of lipidomics are rapidly evolving, gaps in the knowledge base remain unresolved. Current limitations of lipidomics studies include the number of available samples to analyze and the total amount of cells within those samples needed to detect changes in the lipid profiles across different subjects. The information obtained through lipidomics research is essential to systems and cellular biology. This review provides a concise analysis of the most recent developments in lipidomic research. This scientific resource is important because these developments can be used to not only combat the reproductive challenges faced when using cryopreserved semen and artificial reproductive technologies in livestock such as cattle, but also other mammals, such as humans or endangered species.

Spermatic profile of captive giant anteaters (Myrmecophaga tridactyla): Knowing more to preserve better

The giant anteater (Myrmecophaga tridactyla) is being threatened by natural habitat destruction and fragmentation, illegal hunting and road kills. In this context, the generation of basic information on the reproductive parameters of this species is vital, aiming to improve reproductive management via, amongst others, assisted reproductive technologies. This study aimed to describe the morphological and functional features of semen collected from captive giant anteaters. Electroejaculation was performed in 13 animals housed in zoos located in São Paulo state, Brazil. Semen samples were collected from 13 animals in 16 procedures. Samples were evaluated for volume, motility, vigor, pH, concentration, sperm morphology, and functional tests. The following mean values were obtained: volume 1.28 ± 0.27 mL; motility 28.3 ± 6.2%; vigor 2.4 ± 0.25; concentration 129.4 ± 36.1 × 10⁶ sperm/mL; pH 7.4 ± 0.2. Total acrosome, head, midpiece, and tail sperm abnormalities were 3.2 ± 0.8%, 25.4 ± 3.6%, 20.7 ± 3.2%, and 14.7 ± 2.6%, respectively. Intact acrosome was found in 83.7 ± 3.1% and intact membrane in 81.1 ± 4.0% of all samples collected. Mitochondrial activity was 66.4 ± 6.0% (Class I), 18.7 ± 2.9% (Class II), 8.0 ± 2.0% (Class III), 3.9 ± 1.0% (Class IV), and 3.0 ± 0.9% (Class V). Sperm DNA fragmentation rate was 13.2 ± 3.7%. These results indicated that electroejaculation is a feasible method for semen collection in giant anteaters, allowing a more detailed description of the semen in this species.

Mitochondrial Dysfunction and Oxidative Stress Caused by Cryopreservation in Reproductive Cells

Mitochondria, fundamental organelles in cell metabolism, and ATP synthesis are responsible for generating reactive oxygen species (ROS), calcium homeostasis, and cell death. Mitochondria produce most ROS, and when levels exceed the antioxidant defenses, oxidative stress (OS) is generated. These changes may eventually impair the electron transport chain, resulting in decreased ATP synthesis, increased ROS production, altered mitochondrial membrane permeability, and disruption of calcium homeostasis. Mitochondria play a key role in the gamete competence to facilitate normal embryo development. However, iatrogenic factors in assisted reproductive technologies (ART) may affect their functional competence, leading to an abnormal reproductive outcome. Cryopreservation, a fundamental technology in ART, may compromise mitochondrial function leading to elevated intracellular OS that decreases sperm and oocytes' competence and the dynamics of fertilization and embryo development. This article aims to review the role played by mitochondria and ROS in sperm and oocyte function and the close, biunivocal relationships between mitochondrial damage and ROS generation during cryopreservation of gametes and gonadal tissues in different species. Based on current literature, we propose tentative hypothesis of mechanisms involved in cryopreservation-associated mitochondrial dysfunction in gametes, and discuss the role played by antioxidants and other agents to retain the competence of cryopreserved reproductive cells and tissues.

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.

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 motility-based swim-up technique separates bull sperm based on differences in metabolic rates and tail length

Swim-up is a sperm purification method that is being used daily in andrology labs around the world as a simple step for in vitro sperm selection. This method accumulates the most motile sperm in the upper fraction and leaves sperm with low or no motility in the lower fraction. However, the underlying reasons are not fully understood. In this article, we compare metabolic rate, motility and sperm tail length of bovine sperm cells of the upper and lower fraction. The metabolic assay platform reveals oxygen consumption rates and extracellular acidification rates simultaneously and thereby delivers the metabolic rates in real time. Our study confirms that the upper fraction of bull sperm has not only improved motility compared to the cells in the lower fraction but also shows higher metabolic rates and longer flagella. This pattern was consistent across media of two different levels of viscosity. We conclude that the motility-based separation of the swim-up technique is also reflected in underlying metabolic differences. Metabolic assays could serve as additional or alternative, label-free method to evaluate sperm quality.

Antioxidant Effect of a Polyphenol-Rich Murtilla (Ugni molinae Turcz.) Extract and Its Effect on the Regulation of Metabolism in Refrigerated Boar Sperm

The production of reactive oxygen species (ROS) in boar spermatozoa increases in refrigeration; this can have an impact on sperm quality and fertilization capacity. We evaluated the effect of polyphenol-rich aqueous extract of murtilla (Ugni molinae Turcz) on boar sperm stored at 17°C in order to reduce oxidative stress and improve sperm quality in the long term. Five experiments were performed: first, characterization of the polyphenol content from five genotypes of murtilla; second, determination of the genotype with the best antioxidant effect (MT-Ex); third, the antioxidant capacity on O₂⁻ and lipid peroxidation; fourth, the influence of MT-Ex on motility, calcium movement, cAMP, and metabolic parameters; and fifth, analysis of long-term refrigeration. The average phenolic content was 344 ppm; gallic acid, catechin, quercetin, myricetin, and kaempferol were detected. All extracts evaluated presented a concentration-dependent antioxidant effect. MT-Ex reduces intracellular O₂⁻/peroxides but low lipid peroxidation. MT-Ex in nonstimulated ROS conditions reduces sperm motility, mitochondrial membrane potential, cAMP, and ATP, but the succinate dehydrogenase activity remained normal; also, we observed a reduction in calcium movement in in vitro sperm capacitation. The long-term analyses showed that MT-Ex improved sperm motility decay and reduced membrane damage and ROS at 168 h. Based on this study, we propose MT-Ex as a supplement in semen extenders.

Insights into soy lecithin and egg yolk-based extenders for chilling canine spermatozoa

SummaryThe aim of this study was to compare different concentrations of soy lecithin (LEC0.01%, LEC0.05% and LEC0.1%) with egg yolk (Control) in cooling extenders during the storage of semen at 5ºC for 5 days. Twelve dogs (n = 12) were selected, and semen was cooled and assessed after 2, 24, 48, 72, 96 or 120 h. At each time point, sperm were analyzed for kinetic patterns (using computer-assisted sperm analysis), mitochondrial activity (3'3- diaminobenzidine assay), lipid peroxidation (TBARS assay), DNA fragmentation (SCSA®) and plasma and acrosome membrane integrity (eosin/nigrosin and fast green/rose Bengal stains, respectively). The Control group (1814.4 ± 197.2) presented the highest rates of lipid peroxidation at 120 h. Conversely, progressive motility (42.8 ± 4%), linearity (45.4 ± 1%), and VAP (88 ± 3%) were higher in the Control group. In addition, there was lower mitochondrial activity in the Control group at 72 h. Therefore, our data show that lecithin used at these concentrations was not able to maintain sperm viability at as high qualities as would egg yolk. Moreover, the decrease in high mitochondrial activity and the persistence of sperm motility may indicate a compensatory mechanism in canine spermatozoa (i.e., glycolytic pathway). Furthermore, these higher lipid peroxidation indexes could indicate the necessity for future therapy using extenders and antioxidants over a long cooling time for dog sperm.

Spermatic mitochondria: role in oxidative homeostasis, sperm function and possible tools for their assessment

SummaryDespite sperm mitochondrial relevance to the fertilization capacity, the processes involved in the production of ATP and functional dynamics of sperm mitochondria are not fully understood. One of these processes is the paradox involved between function and formation of reactive oxygen species performed by the organelle. Therefore, this review aimed to provide data on the role of sperm mitochondria in oxidative homeostasis and functionality as well the tools to assess sperm mitochondrial function.

Relationship between post-thaw adenosine triphosphate content, motility and viability in cryopreserved bovine semen applying two different preservation methods

Motility and energy level in sperm cells are tightly linked, but not totally understood. The aim of this study was to examine whether adenosine triphosphate (ATP) content as a sperm quality parameter for bull semen could give additional information together with viability and motility. The objective was therefore to examine the relationships between alterations in sperm ATP content, motility and viability in bovine semen samples immediately after thawing and following post-thaw incubation at physiological temperature. Two different cryopreservation methods were compared. Ejaculates from ten young bulls were split into two and cryopreserved using conventional procedure with Biladyl^® (B) extender and with SpermVital^® (SV) immobilization technology. From each sample, simultaneous analysis of ATP content, motility and viability was performed post-thaw (T0) and after incubation at physiological temperature for three hours (T3). Multivariate correlation analysis showed high correlation at T0 between ATP content and viability (p < 0.05), ATP and total motility (p < 0.05), as well as progressive motility and viability (p < 0.05). However, there was no significant correlation between progressive motility and ATP content at T3, neither for B nor SV semen. We conclude that both preservation method and post-thaw incubation at physiological temperature affect ATP level in bull sperm cells partly independent of motility and viability. The ATP level of bovine spermatozoa post-thaw is therefore implicated to give supplementary information of sperm quality.

Carnosine as malondialdehyde scavenger in stallion seminal plasma and its role in sperm function and oxidative status

Semen biotechniques may impair sperm quality due to excessive production of reactive oxygen species (ROS). Additionally, products of the oxidative reaction, especially involving lipids (e.g., malondialdehyde - MDA), may be even more harmful to sperm. Carnosine, previously reported to be present in seminal plasma of several species, may be a key factor on sperm tolerance to biotechniques by counterattacking the deleterious influence of MDA. Therefore, the aim of this study was to measure the levels of carnosine present in equine seminal plasma and relate these findings with sperm function and oxidative status during cooling and cryopreservation. Thus, semen samples were collected from 40 stallions in duplicate (N = 80) and then submitted to cooling and cryopreservation. Samples were then allocated into groups of high and low tolerance to refrigeration and cryopreservation (bad cooler and good cooler/bad freezer and good freezer, respectively), and in groups of different concentrations of carnosine (High, Medium-high, Medium-low and Low carnosine). Samples were evaluated for sperm kinetics patterns, function of sperm structures and oxidative status. In good cooler samples, it was observed higher concentrations of carnosine (Good cooler: 224.98 ± 19.16 ng/mL; Bad cooler: 159.72 ± 15.99 ng/mL; p = 0.0056), ROS production (Good cooler: 26.40 ± 18.33%; Bad cooler: 18.33 ± 1.84%; p = 0.001) and lipid peroxidation rates (Good cooler: 193.23 ± 18.22 ng/mL; Bad cooler: 131.92 ± 12.25; p = 0.0064). Groups of samples with higher carnosine concentrations had lower levels of malondialdehyde (High: 79.33 ± 6.72 ng/mL; Medium-high: 140.45 ± 11.70 ng/mL; Medium-low: 202.57 ± 16.30 ng/mL and Low: 231.02 ± 32.35 ng/mL; p < 0.05), demonstrating that carnosine was effective in removing lipid peroxidation products. Due to the removal of seminal plasma during the cryopreservation process, no differences occurred in carnosine levels between bad and good freezer groups. In this context, this study provides relevant data for future therapies using carnosine during cryopreservation, aiming to replace the levels lost due to the necessary removal of seminal plasma.

The addition of docosahexaenoic acid (DHA) and antioxidants (glutathione peroxidase and superoxide dismutase) in extenders to epididymal sperm cryopreservation in bulls

SummaryThe cryopreservation of epididymal sperm is an important technique that allows genetic material to be preserved, even post mortem. However, cryopreservation leads to increased oxidative stress and impaired sperm viability. Polyunsaturated fatty acid (PUFA) supplementation may improve certain sperm characteristics, but it also makes sperm more susceptible to oxidative stress, therefore adding antioxidants that counteract oxidative stress has become an option. In this context, this study aimed to evaluate the effect of the interaction between docosahexaenoic acid (DHA) and antioxidants on the quality after the cryopreservation of epididymal bull sperm. Twenty epididymides were collected after slaughter, and epididymal sperm was cryopreserved with bovine extender supplemented with docosahexaenoic acid (DHA), glutathione peroxidase (GPx) and superoxide dismutase (SOD). We verified an improvement in motility in the group that was treated only with DHA 5 µM and a concentration-dependent effect on susceptibility to lipid peroxidation that was associated with DHA concentration (1 µM, 5 µM or 10 µM). Moreover, treatment with DHA (5 µM) and SOD (20 IU/ml) resulted in higher sperm motility. Thus, the association between DHA (5 µM) and SOD (20 IU/ml) appears to be an option for increased epididymal sperm features in bulls.

A mechanism by which Astragalus polysaccharide protects against ROS toxicity through inhibiting the protein dephosphorylation of boar sperm preserved at 4 °C

Numerous studies have shown that Astragalus polysaccharide (APS) has strong antioxidant effects and high practical value for preserving semen at low temperatures in vitro. However, to date, little attention has been paid to the precise mechanism of APS in sperm preservation at 4 °C. Thus, to gain further insight into the protective effects of APS, the present study was performed to assess the changes in sperm quality parameters, antioxidant capacity, ATP content, and protein phosphorylation levels. Here, we demonstrated that supplementation with APS could effectively preserve boar sperm quality parameters such as sperm motility, acrosome integrity, and mitochondrial membrane potential. Moreover, we found that the positive effects of APS on boar sperm quality were mainly due to the elimination of excessive mitochondrial ROS, the improvement of antioxidant capacities and the enhancement of ATP levels. Interestingly, by conducting a series of studies on protein phosphorylation, we also discovered that APS could protect boar sperm from oxidative stress and energy deficiency through inhibiting the protein dephosphorylation caused by ROS via the cAMP-PKA signaling pathway. To our knowledge, this is the first exploration of the molecular mechanism underlying the protective roles of APS toward ROS toxicity from the perspective of energy metabolism and protein modification. This study comprehensively provides novel insights into the action mechanism of the protective effects of antioxidants on sperm stored at 4 °C and reveals the practical feasibility of using APS as a boar semen extender supplement for assisted reproductive technology.