Mitochondrial oxygen consumption is a unique indicator of stallion spermatozoal health and varies with cryopreservation media

Change in the swimming pattern of Salmo salar spermatozoa caused by the high temperature of the sperm motility activation medium

Fish are ectotherms and many have an external reproductive mode. An environmental factor which triggers fish reproductive activity in fish is water temperature. However, climate change is causing increasingly frequent events in which the water temperature varies rapidly; as a result, both in hatchery and in natural conditions, fish sperm are exposed to varying environmental temperatures during their journey toward the egg. This study was based on two experiments: The first experiment was designed to determine how storage at 4 °C for four days affected the sperm functions of Atlantic salmon (Salmo salar) sperm collected by either abdominal massage (stripping/Pure) or testicular dissection (testicular macerate/Macerated). Further, computer-assisted semen analysis (CASA) was used to compare sperm velocity parameters (VCL, VSL, and VAP) and progressivity (STR, LIN, and WOB) after motility activation at different temperatures (8 and 16 °C) of sperm collected by both methods (Pure vs Macerated). The results show that spermatozoa from Macerated samples maintained a higher sperm function when stored at 4 °C for 4 days compared to Pure sperm samples. In the second experiment, CASA determined that all parameters for sperm velocity (VCL, VSL, and VAP) and progressivity (STR (50%/55%), LIN (25%-32%), and WOB (51%-57%) were affected by activation temperature (P < 0.05) and that the motility patterns after activation at 16 °C (P < 0.05), specifically the LIN or STR swimming trajectories of the sperm differed between the two groups. In conclusion, the sperm quality of testicular Macerate was superior to that of Pure sperm abdominal mass, based on the higher quality of various sperm functions during short-term storage. Moreover, there was a significant effect of the temperature of the activation medium on sperm speed and progressivity (motility pattern) in the collected samples of testicular macerate. The sensitivity of Salmo salar spermatozoa to elevated temperature varies markedly between collection methods (Pure and Macerated).

Pyruvate enhances stallion sperm function in high glucose media improving overall metabolic efficiency

If a mechanism of more efficient glycolysis depending on pyruvate is present in stallion spermatozoa, detrimental effects of higher glucose concentrations that are common in current commercial extenders could be counteracted. To test this hypothesis, spermatozoa were incubated in a 67 mM Glucose modified Tyrode's media in the presence of 1- or 10-mM pyruvate and in the Tyrode's basal media which contains 5 mM glucose. Spermatozoa incubated for 3 h at 37 °C in 67 mM Tyrode's media with 10 mM pyruvate showed increased motility in comparison with aliquots incubated in Tyrode's 5 mM glucose and Tyrode's 67 mM glucose (57.1 ± 3.5 and 58.1 ± 1.9 to 73.0 ± 1.1 %; P < 0.01). Spermatozoa incubated in Tyrode's with 67 mM glucose 10 mM pyruvate maintained the viability along the incubation (64.03 ± 15.4 vs 61.3 ± 10.2), while spermatozoa incubated in 67 mM Glucose-Tyrode's showed a decrease in viability (38.01 ± 11.2, P < 0.01). 40 mM oxamate, an inhibitor of the lactate dehydrogenase LDH, reduced sperm viability (P < 0.05, from 76 ± 5 in 67 mM Glucose/10 mM pyruvate to 68.0 ± 4.3 %, P < 0.05). Apoptotic markers increased in the presence of oxamate. (P < 0.01). UHPLC/MS/MS showed that 10 mM pyruvate increased pyruvate, lactate, ATP and NAD+ while phosphoenolpyruvate decreased. The mechanisms that explain the improvement of in presence of 10 mM pyruvate involve the conversion of lactate to pyruvate and increased NAD+ enhancing the efficiency of the glycolysis.

Arresting calcium-regulated sperm metabolic dynamics enables prolonged fertility in poultry liquid semen storage

The preservation of liquid semen is pivotal for both industrial livestock production and genetic management/conservation of species with sperm that are not highly cryo-tolerant. Nevertheless, with regard to poultry semen, even brief in vitro storage periods can lead to a notable decline in fertility, despite the in vivo capacity to maintain fertility for several weeks when within the hen's sperm storage tubules. For fertility in sperm, intracellular calcium ions ([Ca2+]i) play a key role in signaling towards modifying energy metabolism. While reducing [Ca2+]i has been found to enhance the preservation of sperm fertility in some mammals, the connection between semen fertility and calcium availability in avian sperm has received limited attention. In this study, we demonstrate that the use of extracellular and intracellular calcium chelators in liquid semen extenders, specifically EGTA and EGTA-AM, has distinct effects on prolonging the fertility of chicken sperm. These results were validated through in vivo fertility tests. Mechanistically, the effects observed were linked to coordination of mitochondrial metabolism and ATP catabolism. Despite both calcium chelators inducing hypoxia, they differentially regulated mitochondrial respiration and ATP accumulation. This regulation was closely linked to a bimodal control of dynein ATPase activity; a direct initial activation with reduction in [Ca2+]i, and subsequent suppression by cytoplasmic acidification caused by lactic acid. These findings not only contribute to advancing poultry liquid semen preservation techniques, but also elucidates biologically relevant mechanisms that may underlie storage within the female reproductive tract in birds.

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.

The sperm mitochondria: clues and challenges

Sperm cells rely on different substrates to fulfil thei energy demand for different functions and diverse moments of their life. Species specific mechanism involve both energy substrate transport and their utilization: hexose transporters, a protein family of facilitative passive transporters of glucose and other hexose, have been identified in spermatozoa of different species and, within the species, their localization has been identified and, in some cases, linked to specific glycilitic enzyme presence. The catabolism of hexose sources for energy purposes has been studied in various species, and recent advances has been made in the knowledge of metabolic strategies of sperm cells. In particular, the importance of aerobic metabolism has been defined and described in horse, boar and even mouse spermatozoa; bull sperm cells demonstrate to have a good adaptability and capacity to switch between glycolysis and oxidative phosphorylation; finally, dog sperm cells have been demonstrated to have a great plasticity in energy metabolism management, being also able to activate the anabolic pathway of glycogen syntesis. In conclusion, the study of energy management and mitochondrial function in spermatozoa of different specie furnishes important base knowledge to define new media for preservation as well as newbases for reproductive biotechnologies.

Sperm parameters in the Great Dane: Influence of age on semen quality

Not all sires have sperm suitable for chilled or frozen storage, and success in artificial insemination (AI) varies highly among individual dogs and breeds. Fertilizing potential is further complicated as sperm quality declines with the aging process. Due to the rapidity of aging and senescence in large breed dogs, associated health and fertility changes may be observed over a shorter period, though this period remains undefined for any breed. Working with a population of purebred Great Danes (GD), our aims were (1) to characterize the distribution of a series of sperm parameters, (2) to distinguish sources of variation in sperm quality within this rapidly aging breed, and (3) to identify changes in sperm quality that may accompany aging. Ejaculates collected from young, middle-aged, and senior Great Dane dogs (n = 50) were evaluated for semen volume, total sperm number and viability, and reactive oxygen species (ROS), in addition to sperm morphology and kinematic parameters. Total testicular volume was also determined using ultrasonography. Testicular volume was not a predictor of sperm production in the GD, however, significant differences between coat colors were identified. Age was negatively associated with total motility, progressive motility, and amplitude of lateral head displacement (ALH) (p < .05). We identified significant relationships between GD male age and TM, PM, and immotility with -9.9%, -9.0%, and +8.3% change per year of age, respectively, which support the anecdotal reports of decline of the fertility with the advance of age in this breed. Sperm of younger GD dogs aged 12 ≤ x < 24 months had significantly higher TM, PM, ALH, and nonlinear motility (p < .05) than older dogs (x ≥ 48 months). High ROS levels were positively associated with TM and PM, average pathway distance (DAP) and straight line distance (DSL), average pathway velocity (VAP), straight line velocity (VSL), and the presence of hairpin tails (p < .05). While age and ROS have significant influences on sperm parameters in the GD, the influence of selection for breed specific phenotypes could help explain the functional significance of the diversity among GD males.

Imaging flow cytometry to characterize the relationship between abnormal sperm morphologies and reactive oxygen species in stallion sperm

Low levels of intracellular reactive oxygen species (ROS) are essential for normal sperm function and are produced by sperm mitochondria as a byproduct of metabolism, but in excess, ROS can cause catastrophic cellular damage and has been correlated with infertility, poor sperm motility and abnormal morphology in humans. Stallion sperm motility is fueled predominantly by oxidative phosphorylation-produced ATP, requiring high basal rates of mitochondrial function. Consequently, whether elevated ROS production by stallion sperm is an indicator of dysfunctional or highly motile cells has been debated by researchers over the last decade. The objective of this study was to evaluate the relationship between various sperm morphologies and ROS production in fresh and cooled stallion semen by employing the novel method of imaging flow cytometry for stallion semen assessment. For evaluation of fresh semen, single ejaculates (n = 5) were collected from four resident stallions at the University of California, Davis. For the evaluation of 24-h cool-stored semen, single ejaculates were collected from stallions at Texas A&M University (n = 5) and shipped to the University of California, Davis overnight for evaluation. Ejaculate volume, sperm concentration and motility parameters were recorded. Samples were co-stained for viability and ROS detection with SytoxGreen™ and dihydroethidium (DHE), respectively, and evaluated with the Amnis® ImageStream® system (Luminex Corporation). Antimycin, an electron transport chain inhibitor that triggers ROS production (1 μM), was used as a positive control for DHE, while dead cells (2× snap frozen in liquid nitrogen) served as a positive control for SytoxGreen™. Unstained samples were also evaluated as controls. Imaging flow cytometric analysis was performed with the ideas® software (Luminex Corporation). Evaluated morphologies included abnormal head (AH), abnormal midpiece (AM), abnormal tail (AT), proximal cytoplasmic droplet (PD), or distal cytoplasmic droplet (DD), and morphologically normal (MN) cells. For fresh semen, an additional abnormality, coiled tail and midpiece (CTM) was assessed; 24-h cool-stored semen did not contain enough viable CTM cells for analysis. Only cells with obvious, single abnormalities were selected for the first portion of analysis to minimize subjectivity. Mixed effects modelling was used to evaluate the relationship between each morphologic classification and the corresponding DHE fluorescence intensity. Compared to the MN population, ROS production was significantly higher in viable cells with AH, PD and AM (p < .0001) in both fresh and cooled semen. CTM cells had significantly higher levels of ROS production compared to MN cells in fresh semen (p < .0001). There was no significant difference in ROS levels between MN cells and AT and DD cells in either fresh or cooled semen (p > .05). These results suggest that ROS generation is indicative of abnormal cell morphology and function and confirm that imaging flow cytometry is a valuable tool for the assessment of stallion semen.

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.

Effects of egg yolk level, penetrating cryoprotectant, and pre-freeze cooling rate, on the post-thaw quality of stallion sperm

The current study determined the effect of the egg-yolk (phospholipid source) level (egg yolk [20% EY] vs. skim-milk + egg yolk [SM + 2% EY]), cryoprotectant (glycerol [Gly] vs. glycerol + methylformamide [Gly + MF]), and pre-freeze cooling rate (-0.1 vs. -1 vs. -5 °C/min) on post-thaw stallion sperm quality. In Experiment 1, ejaculates (n = 27) from 9 stallions (3 ejaculates each) with varied sperm quality (High, Average, or Low) were frozen in EY-Gly, SMEY-Gly, EY-Gly + MF, or SMEY-Gly + MF extenders. Sperm in each group were cooled from 22° to 5°C using either -0.1 °C/min or -1 °C/min linear cooling rates prior to freezing. In Experiment 2, ejaculates (n = 24) from 12 stallions (2 ejaculates each) with High or Average sperm quality were frozen in EY-Gly, EY-Gly + MF, or in BotuCrio (BC) extenders. Sperm in each group were cooled from 22° to 5°C using either -1 or -5 °C/min linear cooling rates prior to freezing. In Experiment 1, for stallions with High or Average sperm quality, either cooling rate generally resulted in lower sperm quality for the SMEY-based extenders than for the EY-based extenders (P < 0.05). Stallions with Low sperm quality were unaffected by any experimental treatment (P > 0.05). In Experiment 2, a -5 °C/min cooling rate yielded lower sperm quality in BC than in EY-Gly or EY-Gly + MF groups (P < 0.05); however, a -1 °C/min cooling rate yielded similar sperm quality among these treatments (P > 0.05). In summary, the phospholipid level in the freezing extender and the pre-freeze cooling rate, but not the penetrating cryoprotectant, affected the post-thaw quality of stallion sperm.

OXIDATIVE STRESS AND REPRODUCTIVE FUNCTION: Oxidative stress and the long-term storage of horse spermatozoa

In brief

The growing understanding of the mechanisms regulating redox homeostasis in the stallion spermatozoa, together with its interactions with energetic metabolism, is providing new clues applicable to the improvement of sperm conservation in horses. Based on this knowledge, new extenders, adapted to the biology of the stallion spermatozoa, are expected to be developed in the near future.

Abstract

The preservation of semen either by refrigeration or cryopreservation is a principal component of most animal breeding industries. Although this procedure has been successful in many species, in others, substantial limitations persist. In the last decade, mechanistic studies have shed light on the molecular changes behind the damage that spermatozoa experience during preservation. Most of this damage is oxidative, and thus in this review, we aim to provide an updated overview of recent discoveries about how stallion spermatozoa maintain redox homeostasis, and how the current procedures of sperm preservation disrupt redox regulation and cause sperm damage which affects viability, functionality, fertility and potentially the health of the offspring. We are optimistic that this review will promote new ideas for further research to improve sperm preservation technologies, promoting translational research with a wide scope for applicability not only in horses but also in other animal species and humans.

An integrated overview on the regulation of sperm metabolism (glycolysis-Krebs cycle-oxidative phosphorylation)

An overview of the sperm metabolism is presented; using the stallion as a model we review glycolysis, Krebs Cycle and oxidative phosphorylation, paying special attention to the interactions among them. In addition, metabolism implies a series of coordinated oxidation-reduction reactions and in the course of these reactions reactive oxygen species (ROS) and reactive oxoaldehydes are produced ; the electron transport chain (ETC) in the mitochondria is the main source of the anion superoxide and hydrogen peroxide, while glycolysis produces 2-oxoaldehydes such as methylglyoxal as byproducts; due to the adjacent carbonyl groups are strong electrophiles (steal electrons oxidizing other compounds). Sophisticated mechanisms exist to maintain redox homeostasis, because ROS under controlled production also have important regulatory functions in the spermatozoa. The interactions between metabolism and production of reactive oxygen species are essential for proper sperm function, and deregulation of these processes rapidly leads to sperm malfunction and finally death. Lastly, we briefly describe two techniques that will expand our knowledge on sperm metabolism in the coming decades, metabolic flow cytometry and the use of the "omics" technologies, proteomics and metabolomics, specifically the micro and nano proteomics/metabolomics. A better understanding of the metabolism of the spermatozoa will lead to big improvements in sperm technologies and the diagnosis and treatment of male factor infertility.

Use of specific mitochondrial complex inhibitors to investigate mitochondrial involvement on horse sperm motility and ROS production

Equine spermatozoa highly rely on oxidative phosphorylation for their energy management. The present work aimed to characterize the role of mitochondria on horse sperm motility and ROS production by incubating spermatozoa with specific inhibitors of the different mitochondrial complexes. Equine spermatozoa were incubated 1 h and 3 h at 37 °C with: complex I inhibitor rotenone (5 μM, ROT), complex II inhibitor dimethyl-malonate (10 mM, DMM), complex III inhibitor antimycin A (1.8 μM, ANTI), the uncoupling agent carbonyl cyanide m-chlorophenyl hydrazine (5 μM, CCCP), ATP synthase inhibitor oligomycin (5 μM, OLIGO), and 2 μL vehicle DMSO (control, CTL). Samples were analyzed for sperm motility and for mitochondrial membrane potential (MMP), mitochondrial integrity, mitochondrial O₂^•- production, and cytoplasmic H₂O₂. A multivariate analysis was performed on the data. CCCP caused a pronounced MMP reduction at both time points while ROT and ANTI showed the same effect at 3 h. All treatments at 3 h incubation significantly reduced the percentage of sperm with early changes in membrane permeability with active mitochondria. The H₂O₂ production of live cells was low at 1 h incubation in all treatments; after 3 h a slight decrease in the percentage of low-H₂O₂ producing cells was recorded. All treatments, except DMM, induced a significant decline in sperm motility and kinematics and modified the pattern of sperm subpopulations. The effect of DMM was evident only after 3 h, increasing the percentage of slow sperm subpopulation. In conclusion, the disruption of mitochondrial integrity induces an increase of mitochondrial ROS production that could be detrimental for cell function and survivior.

The Stallion Spermatozoa: A Valuable Model to Help Understand the Interplay Between Metabolism and Redox (De)regulation in Sperm Cells

Significance: Proper functionality of the spermatozoa depends on the tight regulation of their redox status; at the same time these cells are highly energy demanding and in the energetic metabolism, principally in the electron transport chain in the mitochondria, reactive oxygen species are continuously produced, in addition to that observed in the Krebs cycle and during the β-oxidation of fatty acids. Recent Advances: In addition, in glycolysis, elimination of phosphate groups from glyceraldehyde 3-phosphate and dihydroxyacetone phosphate results in the byproducts glyoxal (G) and methylglyoxal (MG); these products are 2-oxoaldehydes. The presence of adjacent carbonyl groups makes them strong electrophiles that react with nucleophiles in proteins, lipids, and DNA, forming advanced glycation end products. Critical Issues: This mechanism is behind subfertility in diabetic patients; in the animal breeding industry, commercial extenders for stallion semen contain a supraphysiological concentration of glucose that promotes MG production, constituting a potential model of interest. Future Directions: Increasing our knowledge of sperm metabolism and its interactions with redox regulation may improve current sperm technologies in use, and shall provide new clues to understanding infertility in males. Moreover, stallion spermatozoa due to its accessibility, intense metabolism, and suitability for proteomics/metabolomic studies may constitute a suitable model for studying regulation of metabolism and interactions between metabolism and redox homeostasis. Antioxid. Redox Signal. 37, 521-537.

Effect of a Novel Hydroxybenzoic Acid Based Mitochondria Directed Antioxidant Molecule on Bovine Sperm Function and Embryo Production

Sperm cells are particularly vulnerable to reactive oxygen species (ROS), impairing their fertilizing ability. Our objective was to study the effect of a novel mitochondrial-directed antioxidant, AntiOxBEN2, on bovine sperm function. This antioxidant was added to the semen capacitation medium (CAP), during the swim-up process, and to the fertilization medium (FERT) during the co-incubation of matured oocytes and capacitated spermatozoa, in concentrations of 0 (control), 1, and 10 µM. After the swim-up, sperm motility (CASA and visual analysis), vitality (eosin-nigrosin), mitochondrial membrane potential (JC1), intracellular ROS, adenosine triphosphate (ATP) levels, and basal metabolism (Seahorse Xfe96) were evaluated. Embryo development and quality were also assessed. Higher cleavage rates were obtained when 1 µM AntiOxBEN2 were added to CAP and FERT media (compared to control, p < 0.04). A positive effect of AntiOxBEN2 on intracellular ROS reduction (p = 0.01), on the increment of mitochondrial membrane potential (p ≤ 0.003) and, consequently, on the sperm quality was identified. However, the highest dose impaired progressive motility, ATP production, and the number of produced embryos. The results demonstrate a beneficial effect of AntiOxBEN2 (1 µM) on sperm capacitation and fertilization processes, thus improving embryonic development. This may constitute a putative novel therapeutic strategy to improve the outcomes of assisted reproductive techniques (ART).

DNA damage in preimplantation embryos and gametes: specification, clinical relevance and repair strategies

BACKGROUND

DNA damage is a hazard that affects all cells of the body. DNA-damage repair (DDR) mechanisms are in place to repair damage and restore cellular function, as are other damage-induced processes such as apoptosis, autophagy and senescence. The resilience of germ cells and embryos in response to DNA damage is less well studied compared with other cell types. Given that recent studies have described links between embryonic handling techniques and an increased likelihood of disease in post-natal life, an update is needed to summarize the sources of DNA damage in embryos and their capacity to repair it. In addition, numerous recent publications have detailed novel techniques for detecting and repairing DNA damage in embryos. This information is of interest to medical or scientific personnel who wish to obtain undamaged embryos for use in offspring generation by ART.

OBJECTIVE AND RATIONALE

This review aims to thoroughly discuss sources of DNA damage in male and female gametes and preimplantation embryos. Special consideration is given to current knowledge and limits in DNA damage detection and screening strategies. Finally, obstacles and future perspectives in clinical diagnosis and treatment (repair) of DNA damaged embryos are discussed.

SEARCH METHODS

Using PubMed and Google Scholar until May 2021, a comprehensive search for peer-reviewed original English-language articles was carried out using keywords relevant to the topic with no limits placed on time. Keywords included ‘DNA damage repair’, ‘gametes’, ‘sperm’, ‘oocyte’, ‘zygote’, ‘blastocyst’ and ‘embryo’. References from retrieved articles were also used to obtain additional articles. Literature on the sources and consequences of DNA damage on germ cells and embryos was also searched. Additional papers cited by primary references were included. Results from our own studies were included where relevant.

OUTCOMES

DNA damage in gametes and embryos can differ greatly based on the source and severity. This damage affects the development of the embryo and can lead to long-term health effects on offspring. DDR mechanisms can repair damage to a certain extent, but the factors that play a role in this process are numerous and altogether not well characterized. In this review, we describe the multifactorial origin of DNA damage in male and female gametes and in the embryo, and suggest screening strategies for the selection of healthy gametes and embryos. Furthermore, possible therapeutic solutions to decrease the frequency of DNA damaged gametes and embryos and eventually to repair DNA and increase mitochondrial quality in embryos before their implantation is discussed.

WIDER IMPLICATIONS

Understanding DNA damage in gametes and embryos is essential for the improvement of techniques that could enhance embryo implantation and pregnancy success. While our knowledge about DNA damage factors and regulatory mechanisms in cells has advanced greatly, the number of feasible practical techniques to avoid or repair damaged embryos remains scarce. Our intention is therefore to focus on strategies to obtain embryos with as little DNA damage as possible, which will impact reproductive biology research with particular significance for reproductive clinicians and embryologists.

An Update on Semen Physiology, Technologies, and Selection Techniques for the Advancement of In Vitro Equine Embryo Production: Section I

Simple Summary

Male fertility is often estimated by simple sperm assessment, and therefore, it is crucial to establish species-specific baselines for normal sperm parameters. In this paper, sperm physiology, function, and common abnormalities in stallions will be reviewed.

Abstract

As the use of assisted reproductive technologies (ART) and in vitro embryo production (IVP) expand in the equine industry, it has become necessary to further our understanding of semen physiology as it applies to overall fertility. This segment of our two-section review will focus on normal sperm parameters, beginning with development and extending through the basic morphology of mature spermatozoa, as well as common issues with male factor infertility in IVP. Ultimately, the relevance of sperm parameters to overall male factor fertility in equine IVP will be assessed.

Increased mitochondrial activity upon CatSper channel activation is required for mouse sperm capacitation

To fertilize an oocyte, sperm must undergo several biochemical and functional changes known as capacitation. A key event in capacitation is calcium influx through the cation channel of sperm (CatSper). However, the molecular mechanisms of capacitation downstream of this calcium influx are not completely understood. Capacitation is also associated with an increase in mitochondrial oxygen consumption, and several lines of evidence indicate that regulated calcium entry into mitochondria increases the efficiency of oxidative respiration. Thus, we hypothesized that calcium influx through CatSper during capacitation increases mitochondrial calcium concentration and mitochondrial efficiency and thereby contributes to sperm hyperactivation and fertilization capacity. To test this hypothesis, we used high-resolution respirometry to measure mouse sperm mitochondrial activity. We also measured mitochondrial membrane potential, ATP/ADP exchange during capacitation, and mitochondrial calcium concentration in sperm from wild-type and CatSper knockout mice. We show that the increase in mitochondrial activity in capacitated wild-type sperm parallels the increase in mitochondrial calcium concentration. This effect is blunted in sperm from CatSper knockout mice. Importantly, these mechanisms are needed for optimal hyperactivation and fertilization in wild-type mice, as confirmed by using mitochondrial inhibitors. Thus, we describe a novel mechanism of sperm capacitation. This work contributes to our understanding of the role of mitochondria in sperm physiology and opens the possibility of new molecular targets for fertility treatments and male contraception.

Dysregulation of mitochondrial sirtuin genes is associated with human male infertility

Mitochondrial sirtuins (SIRT3, SIRT4, SIRT5) are post-translational modifiers that regulate energy production, body homeostasis and mitochondrial activities via different substrates in response to environmental stressors. The present study aimed at assessing the expression of SIRT3, SIRT4, and SIRT5 in the semen of infertile men. Expression analysis was performed using q-RT PCR. All mitochondrial sirtuin genes were significantly down-regulated in the semen of infertile men compared to fertile men. Mitochondrial sirtuin genes expression levels were correlated with mitochondrial HSP90 expression. HSP90 expression was positively correlated with SIRT3, SIRT4 and SIRT5 expression in the semen of fertile men, while a negative correlation was observed between HSP90 in the semen of infertile men and mitochondrial sirtuin genes in the semen of fertile men. These data suggest that dysregulation of mitochondrial sirtuin genes causes mitochondrial dysfunction due to stress, which appears to be associated with human male infertility by compromising functional and structural sperm integrity.

Effects from disruption of mitochondrial electron transport chain function on bull sperm motility

Sperm mitochondrial function is essential for normal physiology and fertility, but the importance of mitochondrial activity to support specific sperm functions, such as motility, varies between species. It was previously believed that mitochondrial function was not necessary for bull sperm motility [1]; however, this theory is contradicted by recently reported findings that the upper fraction of bull sperm swim-up preparations had both high motility and elevated mitochondrial oxygen consumption rates [2]. The objective of this study was to investigate the relationship between mitochondrial function and motility in bull sperm. We hypothesized that sperm motility would be positively correlated with mitochondrial oxygen consumption (MITOX) but unaffected by pharmacological inhibition of electron transport chain (ETC) activity. This was accomplished by monitoring both mitochondrial oxygen consumption and motility parameters in the presence of mitochondrial effector drug treatments. Duplicate ejaculates were collected by electroejaculation from Black Angus bulls (n = 4). Oxygen consumption, as % air saturation (pO_2; oxygen partial pressure), over time was monitored in the presence of 5 drug treatments: vehicle control, FCCP, Antimycin (ANTI), Oligomycin (Oligo), and FCCP + Oligomycin (FCCP + OLIGO). Duplicate aliquots were prepared for concurrent motility assessment by computer-assisted sperm analysis (CASA) at 6 and 30 min post-treatment (t6 and t30). The impact of treatments on pO₂ (in % air saturation) over time were assessed by generalized linear mixed effects modeling (GLMM) which was also used to test for differences in average motility across treatment conditions and time points (t6 and t30). Pearson product-moment correlation was used to investigate relationships between oxygen consumption and motility parameters. Overall, pO₂ differed over time between treatment conditions (p < 0.0001). When compared to the vehicle treatment, ANTI and OLIGO significantly inhibited oxygen consumption (p < 0.05, adjusted), and FCCP stimulated a marked increase in oxygen consumption. No significant differences in motility over time were observed between treatments, so comparison of motility parameters between treatment conditions was performed with pooled timepoints. Motility parameters were only observed to differ significantly from the vehicle with ANTI Treatment, for which significant decreases in numerous parameters, including total motility (p = 0.007), progressive motility (p = 0.01), DAP (p = 0.01), VAP (p = 0.01) and VSL (p = 0.02) were identified. For the vehicle treatment, correlational analysis did not reveal any significant correlations between pO₂ and any motility parameters at t6; however, several significant correlations were identified at t30. Mean pO₂ was negatively correlated with local motility (p < 0.01) and positively correlated with DCL, DAP, and VCL (p < 0.05). Results from this study suggest that bovine sperm motility is impacted by mitochondrial functionality, with ETC inhibition by ANTI causing significant reduction in motility parameters. This study also demonstrates the use of a new technology for the assessment of bovine sperm mitochondrial function. This modality for evaluation of bull sperm mitochondrial function will inform future efforts to understand bull sperm function and fertility and aid investigations into toxicological agents.

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.

Proteins involved in mitochondrial metabolic functions and fertilization predominate in stallions with better motility

Even in stallions with sperm quality within normal reference ranges at ejaculation, subtle differences in sperm quality exist that in many cases lead to reduced time frames for conservation of the ejaculate and/or reduced fertility. The spermatozoon is a cell highly suitable for proteomics studies, and the use of this technique is allowing rapid advances in the understanding of sperm biology. The aim of the present study was to investigate differences among stallions of variable sperm quality (based on motility and sperm velocities), although all horses had sperm characteristics within normal ranges. The proteome was studied using UHPLC/MS/MS and posterior bioinformatic and enrichment analysis; data are available via ProteomeXchange with identifier PXD025807. Sperm motility, linear motility and circular, straight line and average velocities (VCL, VSL, VAP) were measured using computer assisted sperm analysis (CASA). In stallions showing better percentages of motility, circular and average velocity predominated mitochondrial proteins with roles in the Citric acid cycle, pyruvate metabolism and oxidative phosphorylation. Interestingly, in stallions with better percentages of total motility, sperm proteins were also enriched in proteins within the gene ontology (G0) terms, single fertilization (G0: 0007338), fertilization (G0: 0009566), and zona pellucida receptor complex (GO:0002199). The enrichment of this proteins in samples with better percentages of total motility may offer a molecular explanation for the link between this parameter and fertility. SIGNIFICANCE: Proteomic analysis identified a high degree of specificity of stallion sperm proteins with discriminant power for motility, linear motility, and sperm velocities (VCL, VAP and VSL). These findings may represent an interesting outcome in relation to the molecular biology regulating the movement of the spermatozoa, and the biological meaning of the measurements that computer assisted sperm analysis (CASA) provide. Of a total of 903 proteins identified in stallion spermatozoa, 24 were related to the percentage of total motility in the sample; interestingly, gene ontology (G0) analysis revealed that these proteins were enriched in terms like single fertilization and fertilization, providing a molecular link between motility and fertility. Field studies indicate that the percentage of total motility is the CASA derived parameter with the best correlation with fertility in stallions.

Impact of Oxidative Stress on Male Reproduction in Domestic and Wild Animals

Oxidative stress occurs when the levels of reactive oxygen species (ROS) overcome the antioxidant defenses of the organism, jeopardizing several biological functions, including reproduction. In the male reproductive system, oxidative stress not only impairs sperm fertility but also compromises offspring health and survival, inducing oxidative damage to lipids, proteins and nucleic acids. Although a clear link between oxidative stress and male fertility disorders has been demonstrated in humans and laboratory rodents, little information is available about the implications of impaired redox homeostasis in the male fertility of domestic and wild animals. Therefore, this review aims to provide an update regarding the intrinsic and extrinsic factors that are associated with oxidative stress in the male reproductive system and their impact on the reproductive performance of domestic and wild animals. The most recent strategies for palliating the detrimental effects of oxidative stress on male fertility are reviewed together with their potential economic and ecological implications in the livestock industry and biodiversity conservation.

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.

Influence of Non-conventional Sperm Quality Parameters on Field Fertility in Ovine

The prediction of the fertilizing ability of a seminal dose continues to be a primary aim in the field of artificial insemination (AI). To achieve this goal, in this study we have included the evaluation of some non-conventional sperm quality markers. A total of 3,906 ewes from 52 different farms were inseminated with 357 refrigerated seminal doses obtained from 45 mature Rasa Aragonesa rams. The same samples were used for sperm quality analysis including membrane integrity, capacitation status, oxygen consumption and apoptotic-like markers such as phosphatidylserine translocation (PS), plasmalemma disorganization/mitochondrial membrane potential, caspase activation and DNA damage. Seminal doses from the breeding (B) season presented higher percentages of intact membrane (IM), non permeant (NP) membrane with high mitochondrial membrane potential (ΔΨm) and IM without PS translocation spermatozoa than those from the non-breeding (NB) season. Therefore, we can conclude that there were less spermatozoa showing apoptotic-like features in the seminal doses from the B than the NB season, although these differences did not affect field fertility. Only the percentage of intact membrane, non-capacitated (IM-NC) spermatozoa showed a significant correlation with in vivo fertility (P = 0.005) and fecundity (P = 0.007) values obtained after cervical AI when all data were evaluated. When the data were sorted by season and distance to the farms where AI was performed, the correlation between the percentage of IM-NC spermatozoa and reproductive parameters increased in the NB season and progressively with remoteness from the farms. Some other sperm parameters, like NP with high ΔΨm, IM sperm without active caspases and DNA-intact spermatozoa, also showed significant correlations with the reproductive parameters in the sorted data. Moreover, the increment in both the percentage of IM-NC and DNA-intact spermatozoa would increase the probability of obtaining a fertility higher than the mean (>52%), as revealed by a multiple logistic regression analysis. In conclusion, we have identified two seminal markers—the percentage of intact membrane, non-capacitated spermatozoa, and DNA intact spermatozoa—which could be used as a test to discard males in AI programs, which is highly important from an economic point of view and can contribute to achieving satisfactory fertility rates.

Low glucose and high pyruvate reduce the production of 2-oxoaldehydes, improving mitochondrial efficiency, redox regulation, and stallion sperm function†

Energy metabolism in spermatozoa is complex and involves the metabolism of carbohydrate fatty acids and amino acids. The ATP produced in the electron transport chain in the mitochondria appears to be crucial for both sperm motility and maintaining viability, whereas glycolytic enzymes in the flagella may contribute to ATP production to sustain motility and velocity. Stallion spermatozoa seemingly use diverse metabolic strategies, and in this regard, a study of the metabolic proteome showed that Gene Ontology terms and Reactome pathways related to pyruvate metabolism and the Krebs cycle were predominant. Following this, the hypothesis that low glucose concentrations can provide sufficient support for motility and velocity, and thus glucose concentration can be significantly reduced in the medium, was tested. Aliquots of stallion semen in four different media were stored for 48 h at 18°C; a commercial extender containing 67 mM glucose was used as a control. Stallion spermatozoa stored in media with low glucose (1 mM) and high pyruvate (10 mM) (LG-HP) sustained better motility and velocities than those stored in the commercial extender formulated with very high glucose (61.7 ± 1.2% in INRA 96 vs 76.2 ± 1.0% in LG-HP media after 48 h of incubation at 18°C; P < 0.0001). Moreover, mitochondrial activity was superior in LG-HP extenders (24.1 ± 1.8% in INRA 96 vs 51.1 ± 0.7% in LG-HP of spermatozoa with active mitochondria after 48 h of storage at 18°C; P < 0.0001). Low glucose concentrations may permit more efficient sperm metabolism and redox regulation when substrates for an efficient tricarboxylic acid cycle are provided. The improvement seen using low glucose extenders is due to reductions in the levels of glyoxal and methylglyoxal, 2-oxoaldehydes formed during glycolysis; these compounds are potent electrophiles able to react with proteins, lipids, and DNA, causing sperm damage.

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.

Dimethyl sulfoxide and glycerol as cryoprotectant agents of stallion semen: effects on blastocyst rates following intracytoplasmic sperm injection of IVM equine oocytes

Numerous variables affect invitro blastocyst development following intracytoplasmic sperm injection (ICSI). The paternal factor is affected by initial semen quality, processing techniques and final selection of individual spermatozoon for injection. This study investigated whether there was an effect of sperm cryoprotectant agent (CPA) on equine invitro blastocyst production, and reviews recent developments examining how processing equine semen affects ICSI outcomes. Single ejaculates from five stallions were collected and processed in a freezing extender containing either 1M dimethyl sulfoxide (DMSO) or 3.5% glycerol. Immature equine oocytes were obtained from ovarian follicles of mares during diestrus by transvaginal aspiration (n=128). After invitro maturation, MII oocytes (n=90) were fertilised by ICSI with thawed stallion spermatozoa (n=45 in both the DMSO and glycerol groups). The embryo cleavage rate was greater in the DMSO than glycerol group (73.3% vs 46.7% respectively; P=0.0098), but the blastocyst development rate per fertilised oocyte was similar between the two groups (28.9% vs 15.6% respectively; P=0.128), as was the blastocyst production rate per cleaved embryo (39.4% vs 33.3% respectively; P=0.653). In this study, cryopreservation of equine spermatozoa in 1M DMSO was correlated with significantly higher cleavage rates in IVM oocytes fertilised by ICSI compared with spermatozoa cryopreserved using 3.5% glycerol. Although not statistically significant in this small number of stallions, increased blastocyst production and individual stallion variability was observed among CPA treatments. This warrants further critical examination of cryoprotectants used in equine sperm subpopulations used for ICSI in a larger number of stallions.

The effects of metabolic substrates glucose, pyruvate, and lactate added to a skim milk-based semen extender for cooled storage of stallion sperm

Under in vitro conditions, stallion sperm might preferentially use energy substrates that primarily undergo mitochondrial metabolism. The present study sought to determine the effects of glucose, pyruvate, lactate, or their combinations on the quality of stallion sperm subjected to cooled storage at different temperatures, when using a skim milk-based semen extender. In Experiment 1, no substrate (Control), glucose (40 mM; Glu-40), pyruvate (2 mM, 19.8 mM; Pyr-2, Pyr-19), lactate (2 mM, 19.8 mM; Lac-2, Lac-19, respectively), or their combinations (G/P/L-2 or G/P/L-19, respectively) were added to a milk-based extender and their effects were determined on motion characteristics, viability/acrosomal intactness (VAI), lipid peroxidation status (VLPP), and DNA integrity (COMP_α-t) of sperm incubated for 1 h at 37 °C, or sperm stored for 24 h at either 10 or 20 °C. At any period and temperature tested, Glu-40, G/P/L-2, and G/P-L-19 resulted in similar motion characteristics (P > 0.05) but were higher than that of other treatment groups (P < 0.05). Mean VAI was highest in Glu-40 (P < 0.05). Mean VLPP was highest in G/P/L-2 and G/P/L-19 groups (P < 0.05), and mean COMP_α-t was lowest in Control, Glu-40, G/P/L-2 and G/P/L-19 groups (P < 0.05). All measures of sperm quality were higher in semen stored at 10 °C than 20 °C (P < 0.05). In Experiment 2, increasing concentrations of either pyruvate or lactate (Pyr-40, Lac-40 or Pyr-80, Lac-80) were added to the extender as energy substrates and compared to glucose (40 mM), following storage for 72 h at either 10 or 20 °C. Groups Glu-40 and Pyr-40 yielded similar sperm motion characteristics and VAI, while VLPP and COMP_α-t were reduced in these treatment groups, as compared to Pyr-80, Lac-40, and Lac-80 (P < 0.05). All measures of sperm quality were higher in semen stored at 10 °C vs 20 °C (P < 0.05). This study demonstrates that at storage temperatures of 10 or 20 °C, stallion sperm quality is optimized by the presence of glucose in a skim milk-based semen extender. The addition of substrates that readily support oxidative phosphorylation (i.e., pyruvate or lactate) did not improve the quality of stallion sperm over that of glucose alone and resulted in deleterious effects on sperm quality over time. These effects appeared to be associated with oxidative stress. Use of pyruvate (40 mM) as an alternative energy substrate to glucose generally yielded similar results to that of glucose when sperm were stored at 10 °C only.

Lipid Peroxidation Assay Using BODIPY-Phenylbutadiene Probes: A Methodological Overview

The assessment of reactive oxygen species has increasing importance in biomedical sciences, due to their biological role in signaling pathways and induction of cell damage at low and high concentrations, respectively. Detection of lipid peroxidation with sensing probes such as some BODIPY dyes has now wide application in studies using fluorescent microplate readers, flow cytometry, and fluorescence microscopy. Two phenylbutadiene derivatives of BODIPY are commonly used as peroxidation probes, non-oxidized probes and oxidized products giving red and green fluorescence, respectively. Peculiar features of lipoperoxidation and BODIPY dye properties make this assessment a rather complex process, not exempt of doubts and troubles. Color changes and fluorescence fading that are not due to lipid peroxidation must be taken into account to avoid misleading results. As a characteristic feature of lipoperoxidation is the propagation of peroxyl radicals, pitfalls and advantages of a delayed detection by BODIPY probes should be considered.

Kinematic, bioenergetic and oxidative evaluations of donkey sperm preserved at +4°C

Information on donkey sperm bioenergetics, kinetics and oxidative status is scarce even though crucial for development of reproductive technologies and germplasm conservation. For these reasons, it is interesting to monitor sperm kinetics, bioenergetics, and oxidative status during sperm storage at +4°C and with several sperm extenders and concentrations. Donkey semen was collected from three jackasses, three times each. It was diluted with four extenders (Kenney, Equiplus, INRA96 or Hippex), set at three sperm concentrations (30, 50 or 70 × 106 spermatozoa/ml) and evaluated for its functionality after 0, 3, 24, 48 and 72 h storage at +4°C. Sperm kinetics was analyzed by Sperm Computer Analysis; sperm bioenergetics was assessed by mitochondrial membrane potential (MMP); sperm oxidative status was evaluated by lipid peroxidation (LPO), anti-LPO potential and nitroblue tetrazolium (NBT) assays. Incubation produced a progressive (P < 0.01) decline in sperm kinetics and MMP, whereas parameters related to oxidative status either increased (LPO, NBT) or decreased (anti-LPO). The anti-LPO potential was the index better related to sperm motility and kinetics. Extenders proved to be differently (P < 0.01) effective in preserving sperm kinetics, MMP, and oxidative status. The concentration of 30 × 106 spermatozoa/ml provided an optimum preservation of sperm functions. Significant correlations emerged between most parameters examined. This study identified reference criteria for storing donkey spermatozoa at +4°C. A low sperm concentration together with a proper extender are crucial requirements for optimum sperm cryopreservation efficiency. Field trials are, however, required to validate these findings, making them operational in practice.

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.

Centrifugation Force and Time Alter CASA Parameters and Oxidative Status of Cryopreserved Stallion Sperm

Conventional sperm selection techniques used in ARTs rely on centrifugation steps. To date, the different studies reported on the effects of centrifugation on stallion sperm motility provided contrasting results and do not include effects on mitochondrial functionality and different oxidative parameters. The effects of different centrifugation protocols (300 ×g for 5', 300 ×g for 10', 1500 ×g for 5' and 1500 ×g for 10' vs no centrifugation) on motility and oxidative status in cryopreserved stallion sperm, were analyzed. After centrifugation, almost all motility parameters were significantly altered, as observed by computer-assisted sperm analysis. A polarographic assay of oxygen consumption showed a progressive decrease in mitochondria respiration from the gentlest to the strongest protocol. By laser scanning confocal microscopy, significant reduction of mitochondrial membrane potential, at any tested protocol, and time-dependent effects, at the same centrifugal force, were found. Increased DNA fragmentation index at any tested protocol and time-dependent effects at the same centrifugal force were found, whereas increased protein carbonylation was observed only at the strongest centrifugal force. These results provide more comprehensive understandings on centrifugation-induced effects on cryopreserved stallion sperm and suggest that, even at a weak force for a short time, centrifugation impairs different aspects of equine sperm metabolism and functionality.

Effects of Different Freezing Protocols on Motility, Viability, Mitochondrial Membrane Potential, Intracellular Calcium Level, and DNA Integrity of Cryopreserved Equine Epididymal Sperm

The aim of the present study was to evaluate the effect of different freezing procedures on sperm motion, viability, the acrosome status, mitochondrial membrane potential (MMP), intracellular calcium content, and DNA integrity on epididymal stallion sperm. Therefore, the sperm of 10 healthy stallions was harvested by retrograde flushing after testectomy, diluted with a semen extender containing defined milk proteins and a freezing extender containing egg yolk and glycerol and frozen according to 4 different protocols, using a programmable freezer and a floating rack performing a slow (processes 1 and 2) or a fast cooling rate (processes 3 and 4, respectively). Post-thaw total motility and slow sperm values were lower when using process 4 compared with processes 1 and 2 (P < .05) after 1 hour of incubation. Progressive motility was lower in process 4 compared with process 1 immediately after thawing and after 1 hour of incubation (P < .05). The amount of rapid sperm was lower when using process 4 compared with process 1 immediately after thawing (P < .05). After 1 hour of incubation, the amount of rapid sperm was lower when using process 4 compared with processes 1 and 2 (P < .05). Higher values for viable sperm were seen in processes 1 and 2 compared with process 4 (P < .05) after 1 hour of incubation. Immediately after thawing, more viable sperm with high MMP (hMMP) were observed when using process 3 compared with process 2 (P < .05). After 1 hour of incubation, a significantly higher amount of viable hMMP sperm were detected when using processes 1 and 2 compared with process 4 (P < .05). Process 2 yielded a lower percentage of sperm containing low calcium (lCa) than process 3 immediately after thawing (P < .05). After 1 hour of incubation, the lowest amount of lCa sperm was observed using process 4 (P < .05). The subpopulation of viable/hMMP/lCa sperm was higher when using process 3 compared with process 2 immediately after thawing (P < .05). After 1 hour of incubation, the lowest amount of this subpopulation was detected in process 4 (P < .05). The DNA integrity was similar in all groups. In conclusion, a slow cooling rate with a controlled rate freezer resulted in best sperm quality after thawing. Using a floating rack in nitrogen vapor as an alternative to a programmable freezer, equilibration in a cooled environment is advantageous.

Rosiglitazone in the thawing medium improves mitochondrial function in stallion spermatozoa through regulating Akt phosphorylation and reduction of caspase 3

BACKGROUND

The population of stallion spermatozoa that survive thawing experience compromised mitochondrial functionality and accelerated senescence, among other changes. It is known that stallion spermatozoa show very active oxidative phosphorylation that may accelerate sperm senescence through increased production of reactive oxygen species. Rosiglitazone has been proven to enhance the glycolytic capability of stallion spermatozoa maintained at ambient temperature.

OBJECTIVES

Thus, we hypothesized that thawed sperm may also benefit from rosiglitazone supplementation.

MATERIALS AND METHODS

Thawed sperm were washed and resuspended in Tyrodes media, and the samples were divided and supplemented with 0 or 75 μM rosiglitazone. After one and two hours of incubation, mitochondrial functionality, Akt phosphorylation and caspase 3 activity were evaluated. Additional samples were incubated in the presence of an Akt1/2 inhibitor, compound C (an AMPK inhibitor) or GW9662 (an antagonist of the PPARγ receptor).

RESULTS

Rosiglitazone maintained Akt phosphorylation and reduced caspase 3 activation (p<0.01), both of which were prevented by incubation in the presence of the three inhibitors. Rosiglitazone also enhanced mitochondrial functionality (P<0.01).

CONCLUSION

We provide the first evidence that the functionality of frozen stallion spermatozoa can be potentially improved after thawing through the activation of pro survival pathways, providing new clues for improving current sperm biotechnology.

Comparison of the Effects of Five Semen Extenders on the Quality of Frozen-Thawed Equine Epididymal Sperm

Cryopreservation of epididymal sperm allows the saving of genetic material in case of unexpected death or emergency castration. The aim of the present study was the comparison of five different combinations of extenders commercially available for equine frozen semen processing for cryopreservation of epididymal sperm. Epididymal sperm were harvested from gonads of 10 healthy stallions after routine castration by retrograde flush technique. Then, samples were split and diluted with (1) INRA96 + INRA Freeze, (2) BotuSemen + BotuCRIO, (3) EquiPlus + Gent Freeze, (4) EquiPlus + EquiPlus Freeze, and (5) Gent + Gent Freeze. Extenders 1 and 2 showed higher values for total and progressive motility after thawing compared with extender 4 (P < .05). Extender 3 was in between 1 and 2 (P > .05), and extender 5 resulted in the lowest values (P < .05). The subpopulation of viable frozen-thawed sperm with high mitochondrial membrane potential and low intracellular calcium content was higher using extender 1 compared with extenders 3, 4, and 5 (P < .05) and higher in extender 2 compared with extenders 4 and 5 immediately after thawing (P < .05). After 1 hour of incubation, this subpopulation yielded the highest values in extender 2 (P < .05). Immediately after thawing, extender 1 yielded higher values for percentage of DFI and mean DFI than extenders 3, 4, and 5 (P < .05). Following 1 hour of incubation after thawing, sperm processed with extender 1 resulted in the highest values for percentage of DFI and mean DFI (P < .05). Using extender 2, mean DFI values were lower than those in extender 1 and higher than the extenders 3, 4, and 5 (P < .05). The study revealed that according to the examined sperm quality parameters, freezing extenders (extender 1, extender 2) using low concentrations of glycerol either combined with or without methylformamide were beneficial for cryopreservation of stallion epididymal sperm. For processing of stallion epididymal sperm, an extender containing milk proteins (extenders 1-4) for initial dilution after sperm harvesting is preferable to an extender including egg yolk (extender 5).

Changes in sperm function and structure after freezing in domestic cat spermatozoa

Sperm cryopreservation allows for a long-term storage of genetic. However, changes due to factors as cold shock, osmotic and oxidative stress cause reduction in viability and fertilising ability of frozen/thawed spermatozoa. Therefore, evaluation of cryoinjury of cat spermatozoa is a key factor in achieving better cryopreservation results. This study analysed the changes in structural and functional after freezing in ejaculated domestic cats spermatozoa. Semen samples (n = 60) were analysed before and after freezing, progressive motility was determined with computer-assisted sperm analysis and viability, and acrosome intact spermatozoa, mitochondrial function and superoxide anion ( O 2 - ) were assessed by flow cytometry. The results demonstrated that cryopreservation induced changes in all sperm parameters (p < 0.05). Total sperm motility, viability, acrosome integrity and mitochondrial function of fresh samples were near to 80% and decrease near to 40% in frozen/thawed spermatozoa (p < 0.05); nevertheless, in contrast to all other sperm parameters, the sperm positive with O 2 - increased post/thawing (p < 0.05). In conclusion, changes in frozen/thawed spermatozoa could be related to the effect of oxidative stress due to the increase in the synthesis of O 2 - and a concomitant loss of functional competence. Therefore, the evaluation of these sperm parameters could contribute to complement the analysis of fresh or frozen semen used ART.