Membrane Lipids of the Stallion Spermatozoon in Relation to Sperm Quality and Susceptibility to Lipid Peroxidation

Molecular Biomarkers of Canine Reproductive Functions

The aim of the current study is to review potential molecular biomarker substances selected so far as useful for assessing the quality of dog semen. Proteins, lipids, carbohydrates, and ions can serve as molecular biomarkers of reproductive functions (BRFs) for evaluating male reproductive health and identifying potential risk factors for infertility or reproductive disorders. Evaluation of BRF levels in semen samples or reproductive tissues may provide insights into the underlying causes of infertility, such as impaired sperm function, abnormal sperm-egg interaction, or dysfunction of the male reproductive tract. Molecular biomarker proteins may be divided into two groups: proteins that are well-studied, such as A-kinase anchoring proteins (AKAPs), albumins (ALBs), alkaline phosphatase (ALPL), clusterin (CLU), canine prostate-specific esterase (CPSE), cysteine-rich secretory protein 2 (CRISP2), lactotransferrin (LTF), metalloproteinases (MMPs), and osteopontin (OPN) and proteins that are not well-studied. Non-protein markers include lipid-based substances (fatty acids, phosphatidylcholine), carbohydrates (glycosaminoglycans), and ions (zinc, calcium). Assessing the levels of BRFs in semen samples may provide valuable information for breeding management and reproductive assessments in dogs. This review systematizes current knowledge that could serve as a starting point for developing practical tests with the use of biomarkers of canine reproductive functions and their predictive value for assisted reproductive technique outcomes and semen preservation.

Advancements in Understanding and Enhancing Antioxidant-Mediated Sperm Cryopreservation in Small Ruminants: Challenges and Perspectives

Cryopreservation poses significant challenges to the preservation of sperm integrity and function, particularly in small ruminants where cryodamage is pronounced. This review explores the molecular mechanisms underlying sperm cryodamage and strategies for improving cryopreservation outcomes, with a focus on the role of antioxidants. Cryopreservation-induced alterations in proteins and RNA transcripts critical for sperm function, including motility, capacitation, fertilization, and embryo development, are discussed. Proteomic, transcriptomic, and epigenomic advancements have provided valuable insights into these mechanisms, offering potential biomarkers for predicting sperm freezability and enhancing cryopreservation strategies. Combining technologies such as mass spectrometry and flow cytometry allows for a comprehensive understanding of molecular and cellular changes induced by the freezing-thawing process. However, challenges remain in optimizing cryoprotectant formulations and antioxidant supplementation to improve post-thaw sperm fertility. Further research is needed to explore a wider range of novel cryoprotectants, antioxidants, and proteins for cryopreservation media, as well as to validate their efficacy in enhancing sperm viability and function. Additionally, investigations into the effects of cryopreservation on RNA transcripts and epigenetic factors in small ruminant species are warranted to advance our understanding of sperm preservation. Overall, this review highlights the importance of antioxidants in mitigating cryodamage and underscores the need for continued research to refine cryopreservation protocols and improve reproductive outcomes in small ruminants.

Fatty acid composition and biophysical characteristics of the cell membrane of feline spermatozoa

Sperm membrane composition and biophysical characteristics play a pivotal role in many physiological processes (i.e. sperm motility, capacitation, acrosome reaction and fusion with the oocyte) as well as in semen processing (e.g. cryopreservation). The aim of this study was to characterize the fatty acid content and biophysical characteristics (anisotropy, generalized polarization) of the cell membrane of domestic cat spermatozoa. Semen was collected from 34 adult male cats by urethral catheterization. After a basic semen evaluation, the fatty acid content of some of the samples (n = 11) was evaluated by gas chromatography. Samples from other individuals (n = 23) were subjected to biophysical analysis: membrane anisotropy (which is inversely proportional to membrane fluidity) and generalized polarization (describing lipid order); both measured by fluorimetry at three temperature points: 38 °C, 25 °C and 5 °C. Spermatozoa from some samples (n = 10) were cryopreserved in TRIS egg yolk-glycerol extender and underwent the same biophysical analysis after thawing. Most fatty acids in feline spermatozoa were saturated (69.76 ± 24.45%), whereas the polyunsaturated fatty acid (PUFA) content was relatively low (6.12 ± 5.80%). Lowering the temperature caused a significant decrease in membrane fluidity and an increase in generalized polarization in fresh spermatozoa, and these effects were even more pronounced following cryopreservation. Anisotropy at 38 °C in fresh samples showed strong positive correlations with viability and motility parameters after thawing. In summary, feline spermatozoa are characterized by a very low PUFA content and a low ratio of unsaturated:saturated fatty acids, which may contribute to low oxidative stress. Cryopreservation alters the structure of the sperm membrane, increasing the fluidity of the hydrophobic portion of the bilayer and the lipid order in the hydrophilic portion. Because lower membrane fluidity in fresh semen was linked with better viability and motility after cryopreservation, this parameter may be considered an important factor in determination of sperm cryoresistance.

The future of equine semen analysis

We are currently experiencing a period of rapid advancement in various areas of science and technology. The integration of high throughput 'omics' techniques with advanced biostatistics, and the help of artificial intelligence, is significantly impacting our understanding of sperm biology. These advances will have an appreciable impact on the practice of reproductive medicine in horses. This article provides a brief overview of recent advances in the field of spermatology and how they are changing assessment of sperm quality. This article is written from the authors' perspective, using the stallion as a model. We aim to portray a brief overview of the changes occurring in the assessment of sperm motility and kinematics, advances in flow cytometry, implementation of 'omics' technologies, and the use of artificial intelligence/self-learning in data analysis. We also briefly discuss how some of the advances can be readily available to the practitioner, through the implementation of 'on-farm' devices and telemedicine.

Lipidomic Profile of Human Sperm Membrane Identifies a Clustering of Lipids Associated with Semen Quality and Function

Reduced sperm motility and/or count are among the major causes of reduced fertility in men, and sperm membranes play an important role in the spermatogenesis and fertilization processes. However, the impact of sperm lipid composition on male fertility remains under-investigated. The aim of the present study was to perform a lipidomic analysis of human sperm membranes: we performed an untargeted analysis of membrane lipid composition in fertile (N = 33) and infertile subjects (N = 29). In parallel, we evaluated their serum lipid levels. Twenty-one lipids were identified by their mass/charge ratio and post-source decay spectra. Sulfogalactosylglycerolipid (SGG, seminolipid) was the most abundant lipid component in the membranes. In addition, we observed a significant proportion of PUFAs. Important differences have emerged between the fertile and infertile groups, leading to the identification of a lipid cluster that was associated with semen parameters. Among these, cholesterol sulfate, SGG, and PUFAs represented the most important predictors of semen quality. No association was found between the serum and sperm lipids. Dietary PUFAs and SGG have acknowledged antioxidant functions and could, therefore, represent sensitive markers of sperm quality and testicular function. Altogether, these results underline the important role of sperm membrane lipids, which act independently of serum lipids levels and may rather represent an independent marker of reproductive function.

An Overview on Assay Methods to Quantify ROS and Enzymatic Antioxidants in Erythrocytes and Spermatozoa of Small Domestic Ruminants

The present review aims to provide an overview of the assay methods for the quantification of ROS and principal enzymatic antioxidants as biomarkers of oxidative stress in erythrocytes and spermatozoa of small domestic ruminants. A complete literature search was carried out in PubMed, Scopus and the World Wide Web using relevant keywords and focusing on the last five years (2018-2023). Among spectrophotometry, fluorometry and chemiluminescence, the most widely used method for ROS assay is fluorometry, probably because it allows to simultaneously assay several ROS, using different probes, with greater economic advantages. Regarding intracellular antioxidant enzymes, recent literature reports only spectrophotometric methods, many of which use commercial kits. The use of a less sensitive but cheapest method is suitable because both erythrocytes and spermatozoa samples are highly concentrated in domestic ruminant species. All methods considered in this review have been found to be appropriate; in general, the differences are related to their costs and sensitivity. Quantification of ROS and enzymatic antioxidant activity in erythrocytes and spermatozoa may find application in the study of the welfare and health status of small domestic ruminants for monitoring livestock production.

Equine Spermatozoa Selection by Magnetic Activation for Use in Assisted Reproduction

This study aimed to select high-quality spermatozoa by sperm separation by magnetic activation of the fresh equine semen, compared to density gradient centrifugation and evaluating cell quality after selection. The semen of 10 stallions was collected by the artificial vagina technique. The samples analyzed were: (1) fresh semen; (2) density gradient centrifugation (DGC); (3) separation by magnetic activation (MASS) (nonapoptotic portion NAP); (4) separation by MASS (apoptotic portion-APT). Was analyzed: motility (light microscopy), concentration (Neubauer chamber), semen morphology (humid chamber in phase contrast), and supravital test (eosin/nigrosine). In DGC, 20 × 10⁶ spermatozoa were used in the gradient of Percoll at 90% and 45% (400 μL each), centrifugation at 900 G/5 min, the pellet was diluted in HEPES. In MASS, 10 × 10⁶ spermatozoa were diluted in 1.5 mL of HEPES, centrifugation at 300 G/10 min, pellet was resuspended in 150 μL of HEPES with 20 μL of nanoparticles bound to annexin V, incubation for 15 minutes and filtered in the magnetic separation column. The nonapoptotic fraction was collected directly and the apoptotic fraction after removal the column from the magnet and adding 300 μL of HEPES. The total abnormalities were 43.2% ± 2.78%, with the DGC and MASS being effective in reducing sperm abnormality by 15.6% ± 2.10% and 24.30% ± 1.63%, respectively, like the observed for the number of cells with intact membranes (50% lower in the APT portion). This nanotechnological method is efficient in producing high-quality semen samples for assisted reproduction procedures.

The Lipidomics of Spermatozoa and Red Blood Cells Membrane Profile of Martina Franca Donkey: Preliminary Evaluation

Fatty acid-based lipidomic analysis has been widely used to evaluate health status in human medicine as well as in the veterinary field. In equine species, there has been a developing interest in fertility and sperm quality. Fatty acids, being the principal components of the membranes, play an active role in the regulation of the metabolic activities, and their role on spermiogenesis seems to be of great importance for the resulting quality of the sperm and, thus, fertility. With the application of widely used lipidomic techniques, the aim of this study was to evaluate: (a) the fatty acid content of the spermatozoa's membranes of 26 healthy male Martina Franca donkeys and its possible correlation with sperm parameters, and (b) the evaluation of the composition of the red blood cells' membrane. PUFA omega-6 are the principal components (40.38%) of the total PUFA content (47.79%) in both types of cells; however, DPA is the predominant one on the spermatozoa's membrane (27.57%) but is not present in the erythrocyte's membrane. Spermatozoa's motility (%) is positively correlated with stearic acid and EPA, and progressive motility (%), with oleic acid. These findings offer information on the composition of both types of cells' membranes in healthy male MF donkeys and reflect the metabolic transformations of the spermatozoa's membrane during the maturation period, providing a better perception of the role of fatty acids in sperm parameters and fertility.

Implementation of a method for sperm cryopreservation in sceloporine lizards

Actual loss of lizard biodiversity continues, even with the implementation of conventional conservation programs. An approach including assisted reproductive techniques such as sperm cryopreservation may contribute to the management of endangered species. We developed a method for sperm cryopreservation in sceloporine lizards and compared the response among the studied species. Prior to the mating season, we obtained semen from adult males of Sceloporus aeneus (n = 21), Sceloporus grammicus (n = 20) and Sceloporus torquatus (n = 21) via pressure of the genital papilla. Volume and sperm concentration were measured before semen dilution in a Tris-egg yolk (TEY) medium to evaluate progressive motility, sperm viability, morphology, plasma membrane and acrosome integrity. Then, we cooled the remaining volumes to 5°C at a rate of 0.1°C per minute to incorporate glycerol (8% v/v) in two fractions. Immediately afterwards, we placed 40 μl of the mix on solid CO2 to form pellets and immersed them in liquid nitrogen for storage. We thawed the pellets at 29°C for 3 minutes and diluted them 1:1 (v/v) in TEY medium to assess sperm quality. We found a positive relationship between body weight and seminal volume in S. grammicus and S. torquatus and a negative correlation with sperm concentration in S. grammicus (P < 0.05). Moreover, we observed that the freezing-thawing process decreased sperm quality in the three species, mostly affecting motility and viability. However, S. torquatus and S. aeneus showed a higher sperm tolerance than S. grammicus.

A stallion spermatozoon's journey through the mare's genital tract: In vivo and in vitro aspects of sperm capacitation

Conventional in vitro fertilization is not efficacious when working with equine gametes. Although stallion spermatozoa bind to the zona pellucida in vitro, these gametes fail to initiate the acrosome reaction in the vicinity of the oocyte and cannot, therefore, penetrate into the perivitelline space. Failure of sperm penetration most likely relates to the absence of optimized in vitro fertilization media containing molecules essential to support stallion sperm capacitation. In vivo, the female reproductive tract, especially the oviductal lumen, provides an environmental milieu that appropriately regulates interactions between the gametes and promotes fertilization. Identifying these 'fertilization supporting factors' would be a great contribution for development of equine in vitro fertilization media. In this review, a description of the current understanding of the interactions stallion spermatozoa undergo during passage through the female genital tract, and related specific molecular changes that occur at the sperm plasma membrane is provided. Understanding these molecular changes may hold essential clues to achieving successful in vitro fertilization with equine gametes.

"Fine feathers make fine birds" - The mammalian sperm plasma membrane lipid composition and effects on assisted reproduction

The sperm plasma membrane is important in modulating many sperm functions. The sperm membrane is composed of a complex mixture of lipids including phospholipids, glycolipids and sterols. There are differences of sperm membrane composition among mammalian species with two groups differing in the most abundant polyunsaturated fatty acid (PUFA), either docosahexaenoic (ω-3 PUFA) or docosapentaenoic acid (ω-6 PUFA). During testicular and epididymal maturation, composition of the sperm plasma membrane evolves with spermatozoa gaining the capacity for fertilization. The importance of fatty acid metabolism for complete spermatogenesis has been elucidated using gene knockout mice. During epididymal transit cholesterol content decreases and PUFA content increases, conferring more fluidity properties to the sperm membrane. The relatively lesser content of antioxidant enzymes and the relatively larger content of PUFA make the spermatozoa particularly susceptible to lipid peroxidation during sperm preservation. In numerous studies, there was adding of PUFA and antioxidants to the diet of animals or to semen extenders with the aim to improve sperm membrane integrity. This review highlights the current knowledge on the sperm membrane composition and effects on sperm function in mammalian domestic animals.

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.

Seminal lipid profiling and antioxidant capacity: A species comparison

On their way to the oocyte, sperm cells are subjected to oxidative stress, which may trigger the oxidation of phospholipids (PL). Applying MALDI-TOF MS, HPTLC and ESI-IT MS, we comparatively analyzed the PL compositions of semen and blood of species differing in their reproductive systems and types of nutrition (bull, boar, stallion, lion and man) with regard to the sensitivity to oxidation as well as the accumulation of harmful lyso-PL (LPL), transient products of lipid oxidation. In addition, the protective capacity of seminal fluid (SF) was also examined. The PL composition of erythrocytes and blood plasma is similar across the species, while pronounced differences exist for sperm and SF. Since the blood function is largely conserved across mammalian species, but the reproductive systems may vary in many aspects, the obtained results suggest that the PL composition is not determined by the type of nutrition, but by the relatedness of species and by functional requirements of cell membranes such as fluidity. Sperm motion and fertilization of oocytes require a rather flexible membrane, which is accomplished by significant moieties of unsaturated fatty acyl residues in sperm lipids of most species, but implies a higher risk of oxidation. Due to a high content of plasmalogens (alkenyl ether lipids), bull sperm are most susceptible to oxidation. Our data indicate that bull sperm possess the most effective protective power in SF. Obviously, a co-evolution of PL composition and protective mechanisms has occurred in semen and is related to the reproductive characteristics. Although the protective capacity in human SF seems well developed, we recorded the most pronounced individual contaminations with LPL in human semen. Probably, massive oxidative challenges related to lifestyle factors interfere with natural conditions.

The seminal plasma proteins Peptidyl arginine deaminase 2, rRNA adenine N (6)-methyltransferase and KIAA0825 are linked to better motility post thaw in stallions

Seminal plasma plays an important role in sperm physiology. Seminal plasma proteins vehiculated in microvesicles, carry RNAs and proteins with a potential role in early embryo development. Additionally, proteins present in seminal plasma participate in redox regulation and energy metabolism. In view of these facts, we hypothesized that differences in protein composition of the seminal plasma among stallions may help to explain differences in freeze-ability seen among them. Three independent ejaculates from 10 different stallions of varying breeds were frozen using standard protocols in our laboratory. Aliquots of the ejaculate were separated and stored at -80 °C until further proteomic analysis. Semen analysis was performed using computer assisted sperm analysis and flow cytometry. Significant differences in proteome composition of seminal plasma were observed in the group of stallions showing better motility post thaw. 3116 proteins were identified, and of these, 34 were differentially expressed in stallions with better motility post thaw, 4 of them were also differentially expressed in stallions with different percentages of linearly motile sperm post thaw and 1 protein, Midasin, was expressed in stallions showing high circular velocity post thaw. Seminal plasma proteins may play a major role in sperm functionality; being vehiculated through extracellular vesicles and participating in sperm physiology. Bioinformatic analysis identifies discriminant proteins able to predict the outcome of cryopreservation, identifying potential new biomarkers to assess ejaculate quality.

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.

Cryotolerance of equine spermatozoa correlates with specific fatty acid pattern: A pilot study

Sperm cryopreservation represents a powerful tool for horse breeding. To improve the efficiency of artificial insemination in the horse using cryopreserved spermatozoa, an adequate understanding of the underlying biophysical properties that affect sperm cryosurvival needs to be reached yet. In this pilot study, we described isolation and analysis of the main fatty acids from sperms of stallions classified as good and poor freezers (7 GF and 5 PF, according to sperm motility and viability, before and after cryopreservation). Fatty acid profiles were only assessed in pre-thaw sperms. Eight main fatty acids were identified, using gas chromatography, and their contents were expressed as percentage of the total lipid content. We found that lauric, myristic and oleic acid (C12:0, C14:0 and C18:1n9c) turned out to be about 2-fold more abundant in the sperm cells of the GFs compared with PFs. Moreover, we described for the first time the presence of a very high amount of a trans geometrical isomer of linoleic acid, linolelaidic acid (C18:2n6t), in pre-thaw PF spermatozoa. Notably, we found in fresh sperms of PF stallions a ratio of unsaturated fatty acids to saturated fatty acids which was twice that of those of GF group, suggesting a positive effect of a high saturated-to-unsaturated fatty acid ratio for the "freezability" of equine spermatozoa. Finally, principal component analysis (PCA) confirmed the relationships between specific fatty acids and cryotolerance of equine spermatozoa, also providing a graphical classification and additional information about the dominant variables governing the classification process.

Seminal plasma components from fertile stallions involved in the epididymal sperm freezability

BACKGROUND

Seminal plasma (SP) plays a crucial role in sperm protection and functionality. However, the effect of SP on the sperm cryopreservation is dependent on the stallion and SP composition. The use of epididymal spermatozoa incubated in the presence of SP could help the identification of the components of SP that are able to confer protection upon the spermatozoa during freezing.

OBJECTIVE

The aims of this study were (i) to identify SP components involved in the potential protection of epididymal spermatozoa during the freeze-thawing process and (ii) to identify and evaluate the proteins likely related to sperm freezability, using two-dimensional difference gel electrophoresis (2D-DIGE).

MATERIALS AND METHODS

Epididymal spermatozoa from 4 stallions were incubated with SP (80%, v/v) or without SP (control) before freezing. Sperm parameters were evaluated after thawing (viability, chromatin condensation, acrosomal integrity, reactive oxygen species [ROS]) and SP composition: total antioxidant capacity (TAC), fatty acid composition, total protein concentration, and protein components by 2D-DIGE.

RESULTS

After thawing, the proportions of viable and acrosome-intact spermatozoa were higher than control when SP from two stallions was used (F and O). The SP of all stallions reduced ROS production in comparison with the control. After analyzing the SP components, it was found that total protein concentration, TAC, polyunsaturated fatty acids (PUFA), and eight specific proteins identified by 2D-DIGE were different between stallions.

DISCUSSION

These studies allow the identification of SP components that could be involved in sperm protection or cryotolerance. Use of this information could help in the selection of stallions according to their semen freezing capacity.

CONCLUSION

The composition of the SP probably contributes to semen cryotolerance capacity. Total protein, TAC, PUFA, and some proteins such as cysteine-rich secreted protein 3 could be used as biomarkers for the selection for sperm cryotolerance.

Lipidomic markers of sperm cryotolerance in cattle

The objective of the current study was to determine the fatty acid composition of sperm from Holstein bulls with different freezability (Good and Poor; n = 12). Fatty acids were extracted from frozen sperm in 1:2 (v/v) chloroform-methanol solvent, fractionated into neutral and polar fractions, and composition determined by gas chromatography-mass spectrometry. Thirty-four fatty acids were quantified and their concentrations and percentages within each lipid fraction were calculated. Overall, saturated fatty acids (SFA) were predominant, accounting for 71 to 80% of fatty acids in neutral and polar lipid factions. There were marked differences in fatty acid composition between the lipid fractions (P < 0.001). The branched chain fatty acid (BCFA) concentration (15 to 18 µg) was almost twice as much as polyunsaturated fatty acids (PUFA) concentration found in the polar lipid fraction (8 to 9 µg; P < 0.001). Sperm with different freezability phenotypes only had a few differences in 22:0, 18:1 cis 9, and 14:0 13-methyl fatty acids (P ≤ 0.011). These results are significant because they reveal key understandings of fatty acid composition of sperm membrane and lay a foundation for the manipulation of membrane integrity, fluidity, and stability to advance the assisted reproductive technologies.

Metabolomic signature of the seminal plasma in men with severe oligoasthenospermia

BACKGROUND

Male factor is incriminated in approximately 50% of cases of infertility. The metabolomic approach has recently been used in the assessment of sperm quality and male fertility.

MATERIALS AND METHODS

We analyzed the metabolomic signatures of the seminal plasma in 20 men with severe oligoasthenospermia (prewash total motile sperm count < 5.10⁶ ) (SOA) and compared it to 20 men with normal semen parameters, with a standardized approach of targeted and quantitative metabolomics using high-performance liquid chromatography, coupled with tandem mass spectrometry, and the Biocrates Absolute IDQ p180 kit.

RESULTS

Among the 188 metabolites analyzed, 110 were accurately measured in the seminal plasma. A robust model discriminating the two populations (Q_2(cum) = 55.2%) was obtained by OPLS-DA (orthogonal partial least-squares discriminant analysis), based on the drop in concentrations of 37 metabolites with a VIP (variable important for projection) greater than 1. Overall, in men with SOA, there was a significant decrease in: 17 phosphatidylcholines and four sphingomyelins; acylcarnitines, with free L-carnitine being the most discriminating metabolite; polyunsaturated fatty acids; six amino acids (glutamate, aspartate, methionine, tryptophan, proline, and alanine); and four biogenic amines (spermine, spermidine, serotonin, and alpha-aminoadipate).

DISCUSSION

Our signature includes several metabolic changes with different impacts on the sperm quality: a change in phospholipid composition and the saturation of their fatty acids that is potentially linked to the deterioration of sperm membranes; a carnitine deficiency that can negatively impact the energy production via fatty acid oxidation and oxidative phosphorylation; and a decreased level of amino acids and biogenic amines that can lead to dysregulated metabolic and signaling pathways.

CONCLUSION

We provide a global overview of the metabolic defects contributing to the structural and functional alteration of spermatozoa in severe oligoasthenospermia. These findings offer new insights into the pathophysiology of male factor infertility that could help to develop future specific treatments.

Fatty Acid Profile and Metabolism Are Related to Human Sperm Parameters and Are Relevant in Idiopathic Infertility and Varicocele

Objectives

Fatty acids (FA) modulate oxidative stress, reactive oxygen species (ROS) production, and inflammatory processes in spermatogenesis.

Methods

The amount of 17 different FAs and the level of F₂-isoprostanes (F₂-IsoPs) and cytoplasmic phospholipase A₂ (cPLA₂) were compared and correlated to sperm characteristics; these last ones were evaluated by light and electronic microscopy in varicocele and idiopathic infertile patients.

Results

Total n-3 polyunsaturated acids (PUFAs) and docosahexaenoic acid (DHA), one of the n-3 PUFAs, were significantly reduced in idiopathic infertile men compared to controls (P < 0.05). In the whole studied population, oleic acid and total monounsaturated acids (MUFAs) correlated negatively with sperm concentration, progressive motility, normal morphology, vitality, and fertility index and positively with sperm necrosis. Eicosapentaenoic acid (EPA) amount was positively correlated with the percentage of sperm necrosis and cPLA₂ level and negatively with sperm concentration. Sperm vitality was negatively correlated with the saturated fatty acids (SFAs). In infertile groups, cPLA₂ was negatively correlated with DHA and n-3 PUFAs (both P < 0.05) and positively with EPA (P < 0.05). In the varicocele group, sperm vitality was negatively correlated with palmitoleic acid and total n-6 PUFAs (P < 0.05); sperm apoptosis was positively correlated with the total SFA percentage (P < 0.05).

Conclusions

FA composition in sperm membrane and the metabolism of sperm FAs are interrelated parameters, both relevant in sperm maturation processes and fertility.

Redox Regulation and Oxidative Stress: The Particular Case of the Stallion Spermatozoa

Redox regulation and oxidative stress have become areas of major interest in spermatology. Alteration of redox homeostasis is recognized as a significant cause of male factor infertility and is behind the damage that spermatozoa experience after freezing and thawing or conservation in a liquid state. While for a long time, oxidative stress was just considered an overproduction of reactive oxygen species, nowadays it is considered as a consequence of redox deregulation. Many essential aspects of spermatozoa functionality are redox regulated, with reversible oxidation of thiols in cysteine residues of key proteins acting as an “on–off” switch controlling sperm function. However, if deregulation occurs, these residues may experience irreversible oxidation and oxidative stress, leading to malfunction and ultimately death of the spermatozoa. Stallion spermatozoa are “professional producers” of reactive oxygen species due to their intense mitochondrial activity, and thus sophisticated systems to control redox homeostasis are also characteristic of the spermatozoa in the horse. As a result, and combined with the fact that embryos can easily be collected in this species, horses are a good model for the study of redox biology in the spermatozoa and its impact on the embryo.

Uncovering sperm metabolome to discover biomarkers for bull fertility

Background

Subfertility decreases the efficiency of the cattle industry because artificial insemination employs spermatozoa from a single bull to inseminate thousands of cows. Variation in bull fertility has been demonstrated even among those animals exhibiting normal sperm numbers, motility, and morphology. Despite advances in research, molecular and cellular mechanisms underlying the causes of low fertility in some bulls have not been fully elucidated. In this study, we investigated the metabolic profile of bull spermatozoa using non-targeted metabolomics. Statistical analysis and bioinformatic tools were employed to evaluate the metabolic profiles high and low fertility groups. Metabolic pathways associated with the sperm metabolome were also reported.

Results

A total of 22 distinct metabolites were detected in spermatozoa from bulls with high fertility (HF) or low fertility (LF) phenotype. The major metabolite classes of bovine sperm were organic acids/derivatives and fatty acids/conjugates. We demonstrated that the abundance ratios of five sperm metabolites were statistically different between HF and LF groups including gamma-aminobutyric acid (GABA), carbamate, benzoic acid, lactic acid, and palmitic acid. Metabolites with different abundances in HF and LF bulls had also VIP scores of greater than 1.5 and AUC- ROC curves of more than 80%. In addition, four metabolic pathways associated with differential metabolites namely alanine, aspartate and glutamate metabolism, β-alanine metabolism, glycolysis or gluconeogenesis, and pyruvate metabolism were also explored.

Conclusions

This is the first study aimed at ascertaining the metabolome of spermatozoa from bulls with different fertility phenotype using gas chromatography-mass spectrometry. We identified five metabolites in the two groups of sires and such molecules can be used, in the future, as key indicators of bull fertility.

Does lipid peroxidation and oxidative DNA damage differ in cryopreserved semen samples from young, adult and aged Nellore bulls?

The aims of this study were to evaluate cryopreserved semen of Nellore bulls of different ages and verify whether sperm quality declines with advancing age and whether lipid peroxidation and DNA damage are involved in this process. For this purpose, 40 Nellore bulls were divided into three age groups: Young, aged 1.8-2 years (n = 9); Adult, aged 3.5-7.0 years (n = 19); and Seniors, aged 8.0-14.3 years (n = 12). Three ejaculates were collected from each bull, cryopreserved and evaluated for various parameters including membrane integrity, mitochondrial potential (FITC-PSA and JC1), lipid peroxidation (C-11BODIPY 581 / 591) and oxidative DNA damage (8OHdG) using flow cytometry. The thawed semen of senior bulls was characterized by a low percentage of motile sperm (33.7 ± 6.1%), higher damage to the plasma and acrosomal membrane (37.5 ± 9.8%), and low mitochondrial potential (29.1 ± 13.8%), as well as higher percentages of peroxidated cells (53.6 ± 12.2%) and DNA damage (44.1 ± 11.0%; P < 0.05). Lipid peroxidation was negatively correlated with motility (r = -0.35, P < 0.0002), average mitochondrial potential (r = -0.42; P < 0.0001) and showed a positive correlation with membrane injury and oxidative DNA damage (r = 039; P = 0.0003). Young bulls presented superior thawed sperm quality, possibly due to greater resistance to oxidative stress and, consequently, to cryopreservation. In conclusion, the sperm quality of bull semen declines with advancing age and is strongly associated with increased oxidative damage to both the plasma membrane and DNA.

Epigallocatechin-3-gallate (EGCG) and green tea polyphenols do not improve stallion semen parameters during cooling at 4°C

Stallion semen storage for artificial insemination is mainly based on liquid cooled storage. In many stallions this technique maintains sperm quality for an extended period of time (24-72 hr) at 7°C. While this technique is commonly used in the horse industry, there can be a decline in fertility in some stallions, due to an inability of their sperm to tolerate the cool storage process. The aim of the present work was to evaluate the effect of two natural antioxidants (epigallocatechin-3-gallate (EGCG) at 20, 60 and 120 μm and green tea polyphenols, and p at .001, .01 and .1 mg/ml) on some sperm parameters (sperm motility, viability/acrosome integrity and DNA quality) in extended semen immediately after its collection (T0) and after 2, 6, 24 and 48 hr of cool storage. Two ejaculates from three trotter stallions were analysed after 48 hr of storage at 4°C. No beneficial effect on the analysed parameters was observed: the two antioxidants were not able to improve sperm quality after 48 hr of storage. These results are in agreement with previous findings on the effect of different antioxidants reported by other researches, who have demonstrated that stallion semen keeps good antioxidant capacity after dilution for 24 hr. In conclusion, the positive effect exerted by antioxidant molecules in other species is not confirmed in the equine one.

Computational flow cytometry reveals that cryopreservation induces spermptosis but subpopulations of spermatozoa may experience capacitation-like changes

The reduced lifespan of cryopreserved spermatozoa in the mare reproductive tract has been attributed to both capacitative and apoptotic changes. However, there is a lack of studies investigating both phenomena simultaneously. In order to improve our knowledge in this particular point, we studied in raw and frozen-thawed samples apoptotic and capacitative markers using a wide battery of test based in flow cytometry. Apoptotic markers evaluated were caspase 3 activity, externalization of phosphatidylserine (PS), and mitochondrial membrane potential. Markers of changes resembling capacitation were membrane fluidity, tyrosine phosphorylation, and intracellular sodium. Conventional and computational flow cytometry using nonlinear dimensionally reduction techniques (t-distributed stochastic neighbor embedding (t-SNE)) and automatic classification of cellular expression by nonlinear stochastic embedding (ACCENSE) were used. Most of the changes induced by cryopreservation were apoptotic, with increase in caspase 3 activation (P < 0.01), PS translocation to the outer membrane (P < 0.001), loss of mitochondrial membrane potential (P < 0.05), and increase in intracellular Na+ (P < 0.01). Average values of markers of capacitative changes were not affected by cryopreservation; however, the analysis of the phenotype of individual spermatozoa using computational flow cytometry revealed the presence of subpopulations of spermatozoa experiencing capacitative changes. For the first time advanced computational techniques were applied to the analysis of spermatozoa, and these techniques were able to disclose relevant information of the ejaculate that remained hidden using conventional flow cytometry.

Lipid profiles of canine spermatozoa as revealed via matrix-assisted laser desorption/ionization mass spectrometry

In this study, we investigated the ability of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to characterize the lipid contents of canine spermatozoa. For that, samples of pure semen were analysed. Indeed, quite comprehensive lipid coverage was observed, and the most abundant phospholipid ions detected were from four phosphatidylcholines, that is those of m/z 760.6; 782.6; 808.6; and 830.6 and one of m/z 725.6 from a sphingomyelin. In conclusion, MALDI-MS was found to offer an easy, fast, accurate, and sensitive analytical method for lipid profiling in canine spermatozoa and could be used as a tool to select sires by assessing the relationship between sperm lipid profiles and variables such as age and breeding history as well as to study the effects of cryopreservation on lipid contents.

Relationship between in vitro sperm functional assessments, seminal plasma composition, and field fertility after AI with either non-sorted or sex-sorted bull semen

The hypothesis of this study was that different in vitro parameters are required to predict the in vivo fertility of non-sorted (NS) and sex-sorted (SS) semen. Thus, the aim was to correlate in vitro bull sperm functional parameters (experiment 1) and seminal plasma composition (experiment 2) with pregnancy rates using 2 cohorts of bulls (NS and SS). Experiment 1: ejaculates from each bull (n = 3 ejaculates per bull; n = 6 bulls for both NS and SS) were assessed for motility, thermal stress tolerance and morphology using microscopy, and viability, osmotic resistance, mitochondrial membrane potential, and acrosome integrity using flow cytometry. Fertilizing ability was assessed using IVF. Experiment 2: ejaculates (n = 3 per bull; n = 8 and 6 bulls for NS and SS, respectively) were collected, seminal plasma harvested and frozen and later analyzed for amino acid and fatty acid composition using gas chromatography mass spectrometry. In the NS cohort of bulls, there was no correlation between pregnancy rate and any of the sperm functional parameters assessed. However, within the SS cohort, motility and viability were correlated with pregnancy rate (r = 0.84 and 0.80, respectively; P < 0.05). There was no correlation between IVF outcome and pregnancy rate in either the SS or NS cohort of bulls. In the NS cohort of bulls, concentrations of the amino acid isoleucine and the fatty acid tricosylic acid (C23:0) were correlated with pregnancy rate (r = 0.80 and 0.74, respectively; P < 0.05). Within the SS cohort of bulls, the amino acid glutamic acid and the fatty acid arachidic acid (C20:0) were correlated with pregnancy rate (r = 0.84 and 0.82, respectively; P < 0.05). In conclusion, this study suggests that different in vitro markers of fertility are required to predict the fertility of NS and SS sperm.

Perfluorooctanoic acid exposure alters polyunsaturated fatty acid composition, induces oxidative stress and activates the AKT/AMPK pathway in mouse epididymis

Perfluorooctanoic acid (PFOA) is a degradation-resistant compound with a carbon-fluorine bond. Although PFOA emissions have been reduced since 2000, it remains persistent in the environment. Several studies on laboratory animals indicate that PFOA exposure can impact male fertility. Here, adult male mice received either PFOA (1.25, 5 or 20 mg/kg/d) or an equal volume of water for 28 d consecutively. PFOA accumulated in the epididymis in a dose-dependent manner and resulted in reduced epididymis weight, lower levels of triglycerides (TG), cholesterol (CHO), and free fatty acids (FFA), and activated AKT/AMPK signaling in the epididymis. Altered polyunsaturated fatty acid (PUFA) compositions, such as a higher arachidonic acid:linoleic acid (AA:LA) ratio, concomitant with excessive oxidative stress, as demonstrated by increased malonaldehyde (MDA) and decreased glutathione peroxidase (GSH-Px) in the epididymis, were observed in epididymis tissue following treatment with PFOA. These results indicate that the epididymis is a potential target of PFOA. Oxidative stress and PUFA alteration might help explain the sperm injury and male reproductive dysfunction induced by PFOA exposure.

Depletion of Intracellular Thiols and Increased Production of 4-Hydroxynonenal that Occur During Cryopreservation of Stallion Spermatozoa Lead to Caspase Activation, Loss of Motility, and Cell Death

Oxidative stress has been linked to sperm death and the accelerated senescence of cryopreserved spermatozoa. However, the molecular mechanisms behind this phenomenon remain poorly understood. Reactive oxygen species (ROS) are considered relevant signaling molecules for sperm function, only becoming detrimental when ROS homeostasis is lost. We hereby hypothesize that a major component of the alteration of ROS homeostasis in cryopreserved spermatozoa is the exhaustion of intrinsic antioxidant defense mechanisms. To test this hypothesis, semen from seven stallions was frozen using a standard technique. The parameters of sperm quality (motility, velocity, and membrane integrity) and markers of sperm senescence (caspase 3, 4-hydroxynonenal, and mitochondrial membrane potential) were assessed before and after cryopreservation. Changes in the intracellular thiol content were also monitored. Cryopreservation caused significant increases in senescence markers as well as dramatic depletion of intracellular thiols to less than half of the initial values (P < 0.001) postthaw. Interestingly, very high and positive correlations were observed among thiol levels with sperm functionality postthaw: total motility (r = 0.931, P < 0.001), progressive motility (r = 0.904, P < 0.001), and percentage of live spermatozoa without active caspase 3 (r = 0.996, P < 0.001). In contrast, negative correlations were detected between active caspase 3 and thiol content both in living (r = -0.896) and dead (r = -0.940) spermatozoa; additionally, 4-hydroxynonenal levels were negatively correlated with thiol levels (r = -0.856). In conclusion, sperm functionality postthaw correlates with the maintenance of adequate levels of intracellular thiols. The accelerated senescence of thawed spermatozoa is related to oxidative and electrophilic stress induced by increased production of 4-hydroxynoneal in thawed samples once intracellular thiols are depleted.

Inhibition of Mitochondrial Complex I Leads to Decreased Motility and Membrane Integrity Related to Increased Hydrogen Peroxide and Reduced ATP Production, while the Inhibition of Glycolysis Has Less Impact on Sperm Motility

Mitochondria have been proposed as the major source of reactive oxygen species in somatic cells and human spermatozoa. However, no data regarding the role of mitochondrial ROS production in stallion spermatozoa are available. To shed light on the role of the mitochondrial electron transport chain in the origin of oxidative stress in stallion spermatozoa, specific inhibitors of complex I (rotenone) and III (antimycin-A) were used. Ejaculates from seven Andalusian stallions were collected and incubated in BWW media at 37 °C in the presence of rotenone, antimycin-A or control vehicle. Incubation in the presence of these inhibitors reduced sperm motility and velocity (CASA analysis) (p<0.01), but the effect was more evident in the presence of rotenone (a complex I inhibitor). These inhibitors also decreased ATP content. The inhibition of complexes I and III decreased the production of reactive oxygen species (p<0.01) as assessed by flow cytometry after staining with CellRox deep red. This observation suggests that the CellRox probe mainly identifies superoxide and that superoxide production may reflect intense mitochondrial activity rather than oxidative stress. The inhibition of complex I resulted in increased hydrogen peroxide production (p<0.01). The inhibition of glycolysis resulted in reduced sperm velocities (p<0.01) without an effect on the percentage of total motile sperm. Weak and moderate (but statistically significant) positive correlations were observed between sperm motility, velocity and membrane integrity and the production of reactive oxygen species. These results indicate that stallion sperm rely heavily on oxidative phosphorylation (OXPHOS) for the production of ATP for motility but also require glycolysis to maintain high velocities. These data also indicate that increased hydrogen peroxide originating in the mitochondria is a mechanism involved in stallion sperm senescence.

Sperm selection in natural conception: what can we learn from Mother Nature to improve assisted reproduction outcomes?

BACKGROUND

In natural conception only a few sperm cells reach the ampulla or the site of fertilization. This population is a selected group of cells since only motile cells can pass through cervical mucus and gain initial entry into the female reproductive tract. In animals, some studies indicate that the sperm selected by the reproductive tract and recovered from the uterus and the oviducts have higher fertilization rates but this is not a universal finding. Some species show less discrimination in sperm selection and abnormal sperm do arrive at the oviduct. In contrast, assisted reproductive technologies (ART) utilize a more random sperm population. In this review we contrast the journey of the spermatozoon in vivo and in vitro and discuss this in the context of developing new sperm preparation and selection techniques for ART.

METHODS

A review of the literature examining characteristics of the spermatozoa selected in vivo is compared with recent developments in in vitro selection and preparation methods. Contrasts and similarities are presented.

RESULTS AND CONCLUSIONS

New technologies are being developed to aid in the diagnosis, preparation and selection of spermatozoa in ART. To date progress has been frustrating and these methods have provided variable benefits in improving outcomes after ART. It is more likely that examining the mechanisms enforced by nature will provide valuable information in regard to sperm selection and preparation techniques in vitro. Identifying the properties of those spermatozoa which do reach the oviduct will also be important for the development of more effective tests of semen quality. In this review we examine the value of sperm selection to see how much guidance for ART can be gleaned from the natural selection processes in vivo.

The Impact of Reproductive Technologies on Stallion Mitochondrial Function

The traditional assessment of stallion sperm comprises evaluation of sperm motility and membrane integrity and identification of abnormal morphology of the spermatozoa. More recently, the progressive introduction of flow cytometry is increasing the number of tests available. However, compared with other sperm structures and functions, the evaluation of mitochondria has received less attention in stallion andrology. Recent research indicates that sperm mitochondria are key structures in sperm function suffering major changes during biotechnological procedures such as cryopreservation. In this paper, mitochondrial structure and function will be reviewed in the stallion, when possible specific stallion studies will be discussed, and general findings on mammalian mitochondrial function will be argued when relevant. Especial emphasis will be put on their role as source of reactive oxygen species and in their role regulating sperm lifespan, a possible target to investigate with the aim to improve the quality of frozen-thawed stallion sperm. Later on, the impact of current sperm technologies, principally cryopreservation, on mitochondrial function will be discussed pointing out novel areas of research interest with high potential to improve current sperm technologies.

Effect of Conjugated Linoleic Acid on Boar Semen Quality After Long-term Refrigeration at 17°C

In this study, the effect of conjugated linoleic acid (10 trans, 12 cis) (CLA) on refrigerated boar sperm quality parameters up to 14 days at 17°C was assessed. Semen was extended in Androhep and divided into four treatments supplemented with CLA (25, 50, 100 and 200 μm) and control group, then kept for 2 h at 22°C. Afterwards an aliquot of each treatment was removed, and mitochondrial activity, viability, lipid membrane peroxidation (LPO) and stability of the sperm plasma membrane were assessed by flow cytometry. The remaining extended semen was maintained at 17°C until 336 h, repeating the same analysis every 48 h. Regarding percentage of live spermatozoa, no statistical differences were observed among treatments up to 96 h. After this time, viability decreased significantly (p < 0.05) for CLA concentrations of 100 and 200 μm. Despite these results, there was an individual response to CLA. Although in the control group, the boar A presented better results when compared with the other boars, especially at concentrations of 50 and 100 μm boar B showed significantly higher results (p < 0.05). Supplementation with CLA improved (p < 0.05) LPO, but not the mitochondrial membrane potential of sperm. The highest two CLA concentrations showed to be toxic for sperm as all results were lower than the observed for the control. In conclusion, CLA at 50 μm seems to be an efficient concentration for reducing the oxidative stress, decreasing LPO, maintaining viability, membrane stability and mitochondrial potential on refrigerated boar spermatozoa.

Investigation of the stallion sperm proteome by mass spectrometry

Stallion spermatozoa continue to present scientific and clinical challenges with regard to the biological mechanisms responsible for their survival and function. In particular, deeper understanding of sperm energy metabolism, defence against oxidative damage and cell–cell interactions should improve fertility assessment and the application of advanced reproductive technologies in the equine species. In this study, we used highly sensitive LC–MS/MS technology and sequence database analysis to identify and characterise the proteome of Percoll-isolated ejaculated equine spermatozoa, with the aim of furthering our understanding of this cell's complex biological machinery. We were able to identify 9883 peptides comprising 1030 proteins, which were subsequently attributed to 975 gene products. Gene ontology analysis for molecular and cellular processes revealed new information about the metabolism, antioxidant defences and receptors of stallion spermatozoa. Mitochondrial proteins and those involved in catabolic processes constituted dominant categories. Several enzymes specific to β-oxidation of fatty acids were identified, and further experiments were carried out to ascertain their functional significance. Inhibition of carnitine palmitoyl transferase 1, a rate-limiting enzyme of β-oxidation, reduced motility parameters, indicating that β-oxidation contributes to maintenance of motility in stallion spermatozoa.

Tolerance of spermatozoa to hypotonic stress: role of membrane fluidity and correlation with cryosurvival

The aim of this study was to evaluate inter-individual variability in osmotic properties of stallion spermatozoa and its correlation with cryosurvival. In addition, temperature dependency of hypo-osmotic tolerance and membrane fluidity were studied. Stallion sperm membranes exhibited good resistance towards hypotonic stress in the 15–30°C temperature range, whereas membrane stability was found to be decreased at 4 and 37°C. Bull spermatozoa showed greater hypo-osmotic tolerance compared with stallion spermatozoa, especially at temperatures above 30°C, which coincided with decreased membrane fluidity of bovine spermatozoa in this temperature range. The critical osmolality at 22°C, at which half of the sperm population survived exposure to hypotonic saline solution, was found to vary between 55 and 170 mOsm kg–1 among different stallions. Clear correlations were found for pre- versus post-freeze sperm motility and membrane integrity. Pre-freeze percentages of membrane-intact spermatozoa after exposure to hypotonic stress showed a weak correlation with sperm motility after cryopreservation. This correlation, however, was not found when data were corrected for initial numbers of membrane-intact spermatozoa in the sample. We thus conclude that studies on pre-freeze tolerance towards hypotonic stress cannot be used to predict sperm cryosurvival rates for individual stallions.

Effect of calcium, bicarbonate, and albumin on capacitation-related events in equine sperm

Repeatable methods for IVF have not been established in the horse, reflecting the failure of standard capacitating media to induce changes required for fertilization capacity in equine sperm. One important step in capacitation is membrane cholesterol efflux, which in other species is triggered by cholesterol oxidation and is typically enhanced using albumin as a sterol acceptor. We incubated equine sperm in the presence of calcium, BSA, and bicarbonate, alone or in combination. Bicarbonate induced an increase in reactive oxygen species (ROS) that was abolished by the addition of calcium or BSA. Bicarbonate induced protein tyrosine phosphorylation (PY), even in the presence of calcium or BSA. Incubation at high pH enhanced PY but did not increase ROS production. Notably, no combination of these factors was associated with significant cholesterol efflux, as assessed by fluorescent quantitative cholesterol assay and confirmed by filipin staining. By contrast, sperm treated with methyl-β-cyclodextrin showed a significant reduction in cholesterol levels, but no significant increase in PY or ROS. Presence of BSA increased sperm binding to bovine zonae pellucidae in all three stallions. These results show that presence of serum albumin is not associated with a reduction in membrane cholesterol levels in equine sperm, highlighting the failure of equine sperm to exhibit core capacitation-related changes in a standard capacitating medium. These data indicate an atypical relationship among cholesterol efflux, ROS production, and PY in equine sperm. Our findings may help to elucidate factors affecting failure of equine IVF under standard conditions.

Phosphorylated AKT preserves stallion sperm viability and motility by inhibiting caspases 3 and 7

AKT, also referred to as protein kinase B (PKB or RAC), plays a critical role in controlling cell survival and apoptosis. To gain insights into the mechanisms regulating sperm survival after ejaculation, the role of AKT was investigated in stallion spermatozoa using a specific inhibitor and a phosphoflow approach. Stallion spermatozoa were washed and incubated in Biggers–Whitten–Whittingham medium, supplemented with 1% polyvinyl alcohol (PVA) in the presence of 0 (vehicle), 10, 20 or 30 μM SH5, an AKT inhibitor. SH5 treatment reduced the percentage of sperm displaying AKT phosphorylation, with inhibition reaching a maximum after 1 h of incubation. This decrease in phosphorylation was attributable to either dephosphorylation or suppression of the active phosphorylation pathway. Stallion spermatozoa spontaneously dephosphorylated during in vitro incubation, resulting in a lack of a difference in AKT phosphorylation between the SH5-treated sperm and the control after 4 h of incubation. AKT inhibition decreased the proportion of motile spermatozoa (total and progressive) and the sperm velocity. Similarly, AKT inhibition reduced membrane integrity, leading to increased membrane permeability and reduced the mitochondrial membrane potential concomitantly with activation of caspases 3 and 7. However, the percentage of spermatozoa exhibiting oxidative stress, the production of mitochondrial superoxide radicals, DNA oxidation and DNA fragmentation were not affected by AKT inhibition. It is concluded that AKT maintains the membrane integrity of ejaculated stallion spermatozoa, presumably by inhibiting caspases 3 and 7, which prevents the progression of spermatozoa to an incomplete form of apoptosis.

Free Spanish abstract

A Spanish translation of this abstract is freely available at http://www.reproduction-online.org/content/148/2/221/suppl/DC1.

Influences of a diet supplemented with linseed oil and antioxidants on quality of equine semen after cooling and cryopreservation during winter

Seasonal changes in the reproductive physiology of stallions contribute to a decrease in the quality of frozen-thawed semen during late winter. Changes in the lipid composition of the sperm plasma membrane may contribute to this phenomenon. In the present study, we have, therefore, investigated the effects of adding linseed oil (LO) in combination with antioxidants to the diet of breeding stallions on the motility and membrane integrity of cooled-stored and cryopreserved semen. Starting in November, the diet of LO stallions (n = 6) but not control (C) stallions (n = 5) was supplemented with LO (100 mL once daily) plus an antioxidant (Myostem Protect; Audevard, Clichy, France) for a total of 84 days. Before (November) and at the end of this period (February), ejaculates were processed for cryopreservation (n = 3 ejaculates per stallion) and cooled shipping at 5 °C. Frozen-thawed and cooled-shipped semen was sent to the laboratory for computer-assisted semen analysis of total motility, progressive motility, and velocity parameters (average path velocity [VAP], curved line velocity [VCL], and straight-line velocity [VSL]) and evaluation of membrane integrity. The quality of frozen-thawed semen decreased (P < 0.05) from November (e.g., total motility LO 69 ± 3% and C 67 ± 3%) to February (total motility: LO 55 ± 4% and C 59 ± 3%) independent of treatment (P > 0.05). A decrease in the velocity parameters VAP, VCL, and VSL was more pronounced in LO stallions than in C stallions (e.g., VSL: November LO 67 ± 1 μm/s, C 64 ± 2 μm/s; February LO 59 ± 2 μm/s, C 63 ± 2 μm/s; interaction month by treatment, P < 0.05). In cooled-stored semen, total motility, progressive motility, and membrane integrity were lower in February than in November (P < 0.001 for all parameters). Supplementation of the diet with LO and antioxidants attenuated this decrease (e.g., Day 1 of cooled storage = 24 hours after semen collection: total motility in November LO 88 ± 1% and C 87 ± 3%; in February LO 83 ± 2% and C 73 ± 11%; interaction month by treatment: P < 0.05). Velocity parameters VAP, VCL, and VSL were significantly lower in February than in November (P < 0.001), but this decrease was not affected by treatment. In summary, dietary supplementation of stallions with LO plus antioxidants attenuated a decline in motility and membrane integrity of cooled-stored stallion semen during winter. This may improve the fertility of cooled-shipped semen. In contrast, the treatment did not counteract the decrease in quality of frozen-thawed semen that occurs in late winter.