Sperm cryopreservation update: Cryodamage, markers, and factors affecting the sperm freezability in pigs

Advances in sperm cryopreservation in farm animals: Cattle, horse, pig and sheep

Sperm cryopreservation is one of the most important procedures in the development of biotechnologies for assisted reproduction. In some farm animals, the use of cryopreserved sperm has so many benefits for which relevance has become more evident in recent decades. Values for post-thaw sperm quality, however, are variable among species and within individuals of the same species. There is no standardized methodology for each of the stages of the cryopreservation procedure (andrological examination, semen collection, dilution, centrifugation, resuspension of the pellet with the freezing medium, packaging, freezing and post-thaw sperm evaluation), which also contributes to differences among studies. Cryotolerance markers of sperm and seminal plasma (SP) have been evaluated for prediction of ejaculate freezability. In addition, in previous research, there has been a focus on supplementing cryopreservation media with different substances, such as enzymatic and non-enzymatic antioxidants. In most studies, inclusion of these substances have led to improved post-thaw sperm quality and fertilizing capacity as a result of minimizing the adverse effects on sperm structure and function. Another approach is the use of different cryoprotectants. The aim with this review article is to provide an update on sperm cryopreservation in farm animals. The main detrimental effects of cryopreservation are described, including the negative repercussion on reproductive performance. Furthermore, the potential use of molecular biomarkers to predict sperm cryotolerance is discussed, as well as the addition of substances that can mitigate the harmful impact of freezing and thawing on sperm.

Extracellular vesicles in seminal fluid and effects on male reproduction. An overview in farm animals and pets

Extracellular vesicles (EVs) are lipid bilayer nanovesicles released by most functional cells to body fluids, containing bioactive molecules, mainly proteins, lipids, and nucleic acids having actions at target cells. The EVs have essential functions in cell-to-cell communication by regulating different biological processes in target cells. Fluids from the male reproductive tract, including seminal plasma, contain many extracellular vesicles (sEVs), which have been evaluated to a lesser extent than those of other body fluids, particularly in farm animals and pets. Results from the few studies that have been conducted indicated epithelial cells of the testis, epididymis, ampulla of ductus deferens and many accessory sex glands release sEVs mainly via apocrine mechanisms. The sEVs are morphologically heterogeneous and bind to functional cells of the male reproductive tract, spermatozoa, and cells of the functional tissues of the female reproductive tract after mating or insemination. The sEVs encapsulate proteins and miRNAs that modulate sperm functions and male fertility. The sEVs, therefore, could be important as reproductive biomarkers in breeding sires. Many of the current findings regarding sEV functions, however, need experimental confirmation. Further studies are particularly needed to characterize both membranes and contents of sEVs, as well as the interaction between sEVs and target cells (spermatozoa and functional cells of the internal female reproductive tract). A priority for conducting these studies is development of methods that can be standardized and that are scalable, cost-effective and time-saving for isolation of different subtypes of EVs present in the entire population of sEVs.

Cryopreservation process alters the expression of genes involved in pathways associated with the fertility of bull spermatozoa

In bovines, cryopreserved semen is used for artificial insemination; however, the fertility of cryopreserved semen is far lower than that of fresh semen. Although cryopreservation alters sperm phenotypic characteristics, its effect on sperm molecular health is not thoroughly understood. The present study applied next-generation sequencing to investigate the effect of cryopreservation on the sperm transcriptomic composition of bull spermatozoa. While freshly ejaculated bull spermatozoa showed 14,280 transcripts, cryopreserved spermatozoa showed only 12,375 transcripts. Comparative analysis revealed that 241 genes were upregulated, 662 genes were downregulated, and 215 genes showed neutral expression in cryopreserved spermatozoa compared to fresh spermatozoa. Gene ontology analysis indicated that the dysregulated transcripts were involved in nucleic acid binding, transcription-specific activity, and protein kinase binding involving protein autophosphorylation, ventricular septum morphogenesis, and organ development. Moreover, the dysregulated genes in cryopreserved spermatozoa were involved in pathways associated with glycogen metabolism, MAPK signalling, embryonic organ morphogenesis, ectodermal placode formation, and regulation of protein auto-phosphorylation. These findings suggest that the cryopreservation process induced alterations in the abundance of sperm transcripts related to potential fertility-associated functions and pathways, which might partly explain the reduced fertility observed with cryopreserved bull spermatozoa.

Evaluation of lipidomic change in goat sperm after cryopreservation

The current study aimed to detect the relationship between the spermatozoa cryotolerance and the post-thawed sperm lipidome. Ejaculates from 20 goats, and performed a uniform frozen-thawed procedure in this study. According to the total motility of thawed sperm of goats, semen samples were classified into HF group (High Freezers, n = 8) with >60% total motility and LF group (Low Freezers, n = 8) with < 45% total motility. The lipidomic analysis based on UHPLC-MS/MS was utilized to investigate the relationship between sperm cryotolerance and their lipid metabolites expression. The results showed that the cryotolerance of sperm from different individual goats were in great variation. The total motility of post-thawed sperm in HF group (60.93 ± 2.43%) is significantly higher than that in LF group (34.04 ± 3.41%, P < 0.01). And the post-thawed sperm in HF group exhibited significantly higher plasma membrane (59.06 ± 2.34%) and acrosome integrity (62.93 ± 1.15%) than that in LF group (34.06 ± 4.85%, 44.92 ± 2.19% respectively, P < 0.01). The total of 29 lipid subclasses and 1,133 lipid molecules in the post-thawed goat sperm were identified by lipidomics analysis. The lipid content of thawed sperm in HF group was higher than that in LF group, the lipid profile in HF group was significantly separated from LF group, which indicated that the difference in lipid composition and lipid metabolism mode of sperm between the two groups was existed, especially the expression of phosphatidylcholine and triglyceride molecules. In conclusion, the cryotolerance of sperm from different individual goats were in great variation. Sperm with high cryotolerance may be able to uptake more lipids during cryopreservation. The increase in phosphatidylcholine and triglyceride content of thawed. Sperm may relate to more active lipid anabolic processes.

Optimization of the Thawing Protocol for Iberian Boar Sperm

Simple Summary

Limited attention is paid to sperm thawing protocols, and their study could be relevant to endangered species or breeds, especially for cryopreserved material present in the existing gene banks. The aim of this study was to determine the most optimal thawing protocol for Iberian boar sperm through testing different thawing rates and different modifications of the thawing extender. Based on the findings, the most optimal results were obtained thawing at 70 °C for 8 s with the inclusion of cyclodextrins loaded with cholesterol (CLC) in the extender, revealing the importance of adapting the thawing protocols.

Abstract

Thawing protocols have been barely studied, and their modifications may lead to a substantial improvement in post-thawing sperm quality, which could be of great relevance to existing sperm banks, such as those for Iberian pig breeds with varieties in danger of extinction. For that, the study aimed to evaluate different thawing rates and to evaluate modifications in the composition of the thawing extender (basic pH to 8–8.2, incorporation of cyclodextrins loaded with cholesterol [CLC] and the incorporation of ion chelators [EDTA and EGTA]). After thawing, overall sperm motility and kinematic parameters, acrosome status and sperm membrane integrity were evaluated. The most optimal results were obtained with the thawing rate reaching 70 °C for 8 s with the inclusion of 12.5 mg of CLC/500 × 10⁶ spermatozoa in the thawing extender, which showed an improvement compared to the control at 70 °C. In conclusion, to adapt the thawing conditions may be relevant, especially for endangered species or breeds such as some varieties of Iberian pig, since this process could also be used in samples cryopreserved in gene banks.

Boar semen cryopreserved with trehalose-containing liposomes: disaccharide determination and rheological behaviour

This study aimed to detect intracellular trehalose in boar sperm that were cryopreserved with liposomes and conduct an analysis of its effects on some characteristics of thawed sperm, including rheological properties. First, soybean lecithin cholesterol-based liposomes were produced and characterized in the presence of 300 mM trehalose. Next, semen samples were frozen in two freezing media: a control medium with 300 mM trehalose and an experimental medium supplemented with 300 mM trehalose and 10% liposomes, both of which were thawed and then studied to ascertain their integrity, motility, rheological response, and trehalose quantities by testing two methods of spermatic lysis via high-performance liquid chromatography with an evaporative light-scattering detector (HPLC-ELSD). The results found spherical liposomes measuring 357 nm that were relatively stable in an aqueous medium and had an entrapment efficiency of 73%. An analysis of the cryopreserved ejaculates showed that their viability and motility did not significantly differ between groups (P > 0.05). The viscous response of the samples was influenced by the extracellular medium rather than by the freezing–thawing process, which resulted in a loss of interaction between the cells and cryoprotectants. Finally, intracellular trehalose levels were determined using HPLC-ELSD, with no differences observed (P > 0.05) when comparing both sperm lysis methods. The use of liposomes with trehalose appears to be a promising option for boar semen cryopreservation, with a marked effect on rheological properties. The proposed HPLC-ELSD method was effective for measuring trehalose in cryopreserved cell samples.

Effect of Sperm Cryopreservation in Farm Animals Using Nanotechnology

Sperm cryopreservation is one of the sublime biotechnologies for assisted reproduction. In recent decades, there has been an increasing trend in the use of preserved semen. Post-thaw semen quality and values vary among animals of the same species. Similarly, there are species-specific variations in sperm morphology, i.e., sperm head, kinetic properties, plasma membrane integrity, and freezability. Similarly, the viability of sperm varies in the female reproductive tract, i.e., from a few hours (in cattle) to several days (in chicken). Various steps of sperm cryopreservation, i.e., male health examination, semen collection, dilution, semen centrifugation, pre- and post-thaw semen quality evaluation, lack standardized methodology, that result in differences in opinions. Assisted reproductive technologies (ART), including sperm preservation, are not applied to the same extent in commercial poultry species as in mammalian species for management and economic reasons. Sperm preservation requires a reduction in physiological metabolism by extending the viable duration of the gametes. Physiologically and morphologically, spermatozoa are unique in structure and function to deliver paternal DNA and activate oocytes after fertilization. Variations in semen and sperm composition account for better handling of semen, which can aid in improved fertility. This review aims to provide an update on sperm cryopreservation in farm animals.

Expression of TXNRD1, HSPA4L and ATP1B1 Genes Associated with the Freezability of Boar Sperm

Cryopreservation is associated with increased oxidative stress, which is responsible for sperm damage. We analyzed the effect of cryopreservation on mRNA and protein expression of thioredoxin reductase 1 (TXNRD1), heat shock protein family A (HSP 70) member 4 like (HSPA4L) and sodium/potassium-transporting ATPase subunit beta-1 (ATP1B1) genes in boar sperm with different freezability. Boars were classified as having good and poor semen freezability (GSF and PSF, respectively), according to the assessment of post-thaw sperm motility. Total RNA was isolated from fresh pre-freeze (PF) and frozen-thawed (FT) sperm from five boars of the GSF and PSF groups, respectively. Quantification of TXNRD1, HSPA4L and ATP1B1 gene expression was performed by RT-qPCR analysis. Proteins extracted from sperm were subjected to Western blotting and SDS-PAGE analyses. Poor freezability ejaculates were characterized by significantly higher relative mRNA expression levels of TXNRD1 and HSPA4L in FT sperm compared with the fresh PF sperm. Furthermore, the relative mRNA expression level of ATP1B1 was significantly higher in the fresh PF sperm of the GSF group. Western blotting analysis revealed significantly higher relative expression of TXNRD1 protein in the fresh PF sperm of the GSF group, while HSPA4L protein expression was markedly increased in FT sperm of the PSF group. Electrophoretic and densitometric analyses revealed a higher number of proteins in the fresh PF and FT sperm of the PSF and GSF groups, respectively. The results of this study indicate that ATP1B1 mRNA expression in the fresh PF sperm is a promising cryotolerance marker, while the variations of TXNRD1 and HSPA4L protein expression in the fresh PF or FT sperm provide useful information that may help to elucidate their biological significance in cryo-damage.

Cryopreservation of Pig Semen Using a Quercetin-Supplemented Freezing Extender

Reactive oxygen species (ROS) produced during freeze−thaw procedures cause oxidative damage to the sperm, reducing fertility. We aimed to improve the post-thaw quality of pig sperm by quercetin (QRN) supplementation to reduce the cryodamage associated with the freeze−thaw procedure. Four equal aliquots of pooled boar semen were diluted with a freezing extender supplemented with different concentrations of QRN (0, 25, 50, and 100 µM) and then were subjected to cryopreservation in liquid nitrogen. Semen analysis was performed following 7 days of cryopreservation. Results demonstrated that the semen samples supplemented with 50 µM QRN significantly improved the post-thaw sperm quality than those subjected to other supplementations (p < 0.05). Semen samples supplemented with 50 µM QRN showed significantly improved plasma membrane functional integrity (47.5 ± 1.4 vs. 43.1 ± 4.1, 45.3 ± 1.7, and 44.1 ± 1.4) and acrosome integrity (73.6 ± 3.4 vs. 66.3 ± 2.4, 66.7 ± 3.6, and 68.3 ± 32.9) as compared to the control, 25 µM, and 100 µM QRN groups, respectively. The mitochondrial activity of the 50 µM QRN group was greater than control and 25 µM QRN groups (43.0 ± 1.0 vs. 39.1 ± 0.9 and 41.9 ± 1.0) but showed no difference with the 100 µM QRN group. Moreover, the 50 µM QRN group showed a higher sperm number displaced to 1 cm and 3 cm points in the artificial mucus than other groups. Therefore, supplementing the freezing extender with QRN can serve as an effective tool to reduce the magnitude of oxidative damage associated with sperm freezing.

The effect of Caulerpa sertularioides extract on bull sperm freezablity and subsequent embryo development

Artificial insemination is a valuable and essential tool in genetic improvement programs, and its success requires proper semen collection, freezing, and thawing procedures. Nowadays, despite applying of advanced protocols for semen cryopreservation, post-thawing sperm quantitative and qualitative parameters are not satisfactorily comparable to fresh sperm. The present study was designed to evaluate the effects of the supplementation of an alcoholic extract of Caulerpa sertolarioides alga into the tris-egg yolk-based Simmental bull sperm freezing media. The pooled semen samples were divided into five groups, of which four were supplemented with 500, 1000, 1500, and 2000 ppm alga extract and one allocated as a control. Total motility, progressive motility, plasma membrane integrity, DNA integrity, apoptosis, superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities, and total antioxidant capacity (TAC) of sperm were measured. The frozen sperm from each group were used for IVF on the slaughterhouse-derived oocytes. Fertilization, cleavage, and blastocyst rates were assessed for all groups. Total motility, progressive motility, and velocity curvilinear (VCL) parameters were higher (p ≤ 0.05) in group 1000 ppm than the control group. Velocity in a straight path (VSL) was higher (p ≤ 0.05) in all treatment groups except in 500 ppm compared to the control group. Average path velocity (VAP) was higher (p ≤ 0.05) in 1000 and 1500 ppm groups than in the control group. Straightness (STR) showed a higher value (p ≤ 0.05) in 1000 and 2000 ppm than the control group. Groups 500 and 1000 ppm showed more viable sperm than the control group (p ≤ 0.05). DNA damage was lower (p ≤ 0.05) in group 1000 ppm than in the control group. HOST was higher (p ≤ 0.05) in all groups than in the control group. SOD, GPx, and TAC were higher (p ≤ 0.05) in 1000 ppm than the control and all other groups. Apoptosis was not significantly different among the treatment and control groups. In conclusion, supplementation of alcoholic extract of Caulerpa sertularioides into the Simmental bull freezing extender ameliorated the sperm parameters after the freeze-thawing process. Moreover, the results of this study indicated that the best dose to achieve the antioxidant properties of the alga extract in Simmental bull sperm freezing media was 1000 ppm. It was also evident that 1000 ppm alga extract supplementation into the bull sperm improved fertilization, cleavage, and blastocyst rates.

Frequency of Semen Collection Affects Ram Sperm Cryoresistance

The improvement of frozen-thawed sperm quality has been mostly approached from the view of cryopreservation protocol optimization in terms of cryoprotectant solutions, freezing-thawing rates and antioxidant supplementation, while the impact of sperm collection frequency remains unknown in rams. In this work, a multiparametric study was carried out in cooled and frozen-thawed semen to evaluate sperm quality after different semen collection frequencies during a month: zero sperm collection (0 CW), four sperm collections per week (4 CW), and ten sperm collections per week (10 CW). Traditional analyses have been applied, in combination with novel technologies related to redox balance. Frozen-thawed semen quality showed a significant decrease (p < 0.05) in 0 CW and 10 CW in comparison to 4 CW, concerning motility and kinetics parameters. However, apoptosis showed a significant increase (p < 0.05) in 10 CW in comparison to 0 CW and 4 CW. The employment methods related to redox balance provided us with the definitive probe to ensure the influence of collection frequency on balance redox after thawing. Specifically, glutathione peroxidase (GPX) and superoxide dismutase (SOD) activity showed a significant decrease (p < 0.05) in 10 CW compared to 0 CW and 4 CW. The characterization of alternative strategies to sperm cryopreservation based on consideration of male sexual regimes, could improve the quality of frozen-thawed sperm.

Cryopreservation Methods and Frontiers in the Art of Freezing Life in Animal Models

The development in cryobiology in animal breeding had revolutionized the field of reproductive medicine. The main objective to preserve animal germplasm stems from variety of reasons such as conservation of endangered animal species, animal diversity, and an increased demand of animal models and/or genetically modified animals for research involving animal and human diseases. Cryopreservation has emerged as promising technique for fertility preservation and assisted reproduction techniques (ART) for production of animal breeds and genetically engineered animal species for research. Slow rate freezing and rapid freezing/vitrification are the two main methods of cryopreservation. Slow freezing is characterized by the phase transition (liquid turning into solid) when reducing the temperature below freezing point. Vitrification, on the other hand, is a phenomenon in which liquid solidifies without the formation of ice crystals, thus the process is referred to as a glass transition or ice-free cryopreservation. The vitrification protocol applies high concentrations of cryoprotective agents (CPA) used to avoid cryoinjury. This chapter provides a brief overview of fundamentals of cryopreservation and established methods adopted in cryopreservation. Strategies involved in cryopreserving germ cells (sperm and egg freezing) are included in this chapter. Last section describes the frontiers and advancement of cryopreservation in some of the important animal models like rodents (mouse and rats) and in few large animals (sheep, cow etc).

Effects of riboflavin on boar sperm motility, sperm quality, enzyme activity and antioxidant status during cryopreservation

Objectives

This study was conducted to evaluate the effect of adding riboflavin to boar sperm freezing extender on the challenge of cryopreservation.

Methods

Different concentrations (0, 5, 10, 15, 20 or 25 μM) of riboflavin were added to the freezing extender. Spermatozoa motility, membrane integrity, acrosomal integrity, mitochondrial membrane potential and enzyme activities were analysed once 10 min after thawing. Q‐PCR was used to detect the mRNA expression of Caspase3, Bcl‐2 and Bax.

Results

The results showed that the addition of 10 μM riboflavin to boar sperm freezing extender significantly increased the frozen‐thawed sperm progressive motility compared with the control group (p < 0.05). Activities of superoxide dismutase, glutathione peroxidase and catalase improved after adding riboflavin to the extender (p < 0.05). During freezing‐thawing, the boar sperm mitochondrial membrane potential, acrosomal integrity, plasma membrane and DNA at 10 μM in the riboflavin group increased by 6.6%, 9.6%, 5.49% and 5.62% (p < 0.05), respectively, compared with the control group. The addition of 10 μM riboflavin to the extender significantly decreased the malondialdehyde (p < 0.05) content, whereas it increased the ATP content (p < 0.05) of boar sperm during freezing‐thawing. Furthermore, the expression of Caspase‐3 and Bax (p < 0.05) were significantly lower, whereas the expression of BCL‐2 (p < 0.05) was greater than the control group when adding 10 μM riboflavin to the extender.

Conclusions

Riboflavin showed cryoprotective capacity to the freezing extender used for boar sperm during the process of freezing‐thawing, and the optimal concentration of riboflavin for the frozen extender was 10 μM.

Potential Use of Tannin Extracts as Additives in Semen Destined for Cryopreservation: A Review

Cryopreservation and storage of semen for artificial insemination (AI) result in excessive accumulation of reactive oxygen species (ROS). This leads to a shortened life span and reduced motility of spermatozoa post-thawing, with consequent impairment of their function. However, certain levels of ROS are essential to facilitate the capacitation of spermatozoa required for successful fertilisation. Tannins, as well-known antioxidant compounds, may act as ROS binders/acceptors/scavengers to inhibit the damaging effects of ROS. This review comprises an analysis of the semen cryopreservation protocol and health functions of tannins, as well as the effects of ROS on fresh and cryopreserved semen's longevity and fertilisation. Additionally, we surveyed available evidence of the effects of tannin extract feed supplementation on male fertility. We furthermore interrogated existing theories on tannin use as a potential additive to semen extenders, its relationship with semen quality, and to what degree existing theories have been investigated to develop testable new hypotheses. Emphasis was placed on the effects of tannins on ROS, their involvement in regulating sperm structure and function during cryopreservation, and on post-thaw sperm motility, capacitation, and fertilising ability. The diverse effects of tannins on the reproductive system as a result of their potential metal ion chelation, protein precipitation, and biological antioxidant abilities have been identified. The current data are the first to support the further investigation of the incorporation of tannin-rich plant extracts into semen extenders to enhance the post-thaw survival, motility, and fertilising ability of cryopreserved spermatozoa.

Boar Sperm Cryopreservation Improvement Using Semen Extender Modification by Dextran and Pentaisomaltose

The long-term storage of boar sperm presents an ongoing challenge, and the modification of the cryoprotective compounds in semen extenders is crucial for improving cryopreservation’s success rate. The aim of our study was to reduce the percentage of glycerol in the extender by elimination or substitution with biocompatible, non-toxic polysaccharides. For boar semen extender improvement, we tested a novel modification with the polysaccharides dextran and pentaisomaltose in combination with unique in silico predictive modeling. We targeted the analysis of in vitro qualitative sperm parameters such as motility, viability, mitochondrial activity, acrosome integrity, and DNA integrity. Non-penetrating polysaccharide-based cryoprotective agents interact with sperm surface proteins such as spermadhesins, which are recognized as fertility markers of boar sperm quality. The in silico docking study showed a moderate binding affinity of dextran and pentaisomaltose toward one specific spermadhesin known as AWN, which is located in the sperm plasma membrane. Pentaisomaltose formed a hydrophobic pocket for the AWN protein, and the higher energy of this protein–ligand complex compared with dextran was calculated. In addition, the root mean square deviation (RMSD) analysis for the molecular dynamics (MD) of both polysaccharides and AWN simulation suggests their interaction was highly stable. The in silico results were supported by in vitro experiments. In the experimental groups where glycerol was partially or entirely substituted, the use of pentaisomaltose resulted in improved sperm mitochondrial activity and DNA integrity after thawing when compared with dextran. In this paper, we demonstrate that pentaisomaltose, previously used for cryopreservation in hematopoietic stem cells, represents a promising compound for the elimination or reduction of glycerol in extenders for boar semen cryopreservation. This novel approach, using in silico computer prediction and in vitro testing, represents a promising technique to help identify new cryoprotectants for use in animal breeding or genetic resource programs.

Canine Spermatozoa—Predictability of Cryotolerance

Simple Summary

Semen freezing in dogs is a field of growing interest. The international shipment of cryoconserved semen contributes to the avoidance of long travels and long-term storage of valuable gametes. However, the collection of one semen portion on average results in one to three doses for artificial insemination, which is a poor result in comparison to the outcome in large animals. The costs for the owners are therefore rather high. In individual dogs, the semen quality of raw semen is good; however, it could be suboptimal after thawing. To avoid costly freezing of these low-quality ejaculates, markers of freezability are useful. An abundance of markers are available for large animals, but not for dogs. This review provides an overview on markers for freezability of canine semen.

Abstract

Markers of freezability allow the selection of ejaculates of good freezability. So far, most investigations were conducted in boars, bulls, rams and horses, with high economic interests triggering the efforts. The progress in dogs is comparably slow. A critical evaluation of the methods requires consideration of practicability, with most labs not even possessing a computer assisted sperm analyser (CASA); furthermore, small canine ejaculates mostly do not allow the use of large semen volumes. In dogs, modern markers of freezability no longer assess single membrane constituents or seminal plasma components but comprise tests of cell functionality and adaptability, energy metabolism, cluster analyses of kinetic and morphometric parameters, as well as DNA intactness. Identification of the most efficient combination of tests seems useful. At present, examination by CASA combined with cluster analysis of kinetic subgroups, JC-1 staining and COMET assay or staining with toluidine blue seem most appropriate; however, cell volumetry and other functional tests deserve better attention. A better understanding of spermatozoa energy metabolism might reveal new markers. This review focuses on the requirements and markers of freezability of canine semen, highlighting potential future candidates.

Relevance of Aquaporins for Gamete Function and Cryopreservation

Simple Summary

The interaction between cells and the extracellular medium is of great importance; changes in medium composition can drive water movement across plasma membranes. Aquaporins (AQPs) are membrane channels involved in the transport of water and some solutes across membranes. When sperm enter the female reproductive tract after ejaculation, they encounter a drastic change in extracellular composition, which leads to water flowing across the plasma membrane. This triggers a series of events that are crucial to allowing fertilization to take place, such as regulation of sperm motility. In the context of assisted reproduction techniques (ART), long-term storage of gametes is sometimes required, and, during cryopreservation, these cells undergo drastic changes in extracellular medium composition. As a result, AQPs are crucial in both sperm and oocytes during this process. Cryopreservation is of considerable importance for fertility preservation in livestock, endangered species and for individuals undergoing certain medical treatments that compromise their fertility. Further research to fully elucidate the roles and underlying mechanisms of AQPs in mammalian sperm is therefore warranted.

Abstract

The interaction between cells and the extracellular medium is of great importance, and drastic changes in extracellular solute concentrations drive water movement across the plasma membrane. Aquaporins (AQPs) are a family of transmembrane channels that allow the transport of water and small solutes across cell membranes. Different members of this family have been identified in gametes. In sperm, they are relevant to osmoadaptation after entering the female reproductive tract, which is crucial for sperm motility activation and capacitation and, thus, for their fertilizing ability. In addition, they are relevant during the cryopreservation process, since some members of this family are also permeable to glycerol, one of the most frequently used cryoprotective agents in livestock. Regarding oocytes, AQPs are very important in their maturation but also during cryopreservation. Further research to define the exact sets of AQPs that are present in oocytes from different species is needed, since the available literature envisages certain AQPs and their roles but does not provide complete information on the whole set of AQPs. This is of considerable importance because, in sperm, specific AQPs are known to compensate the role of non-functional members.

Impact of Seminal Plasma Antioxidants on Donkey Sperm Cryotolerance

This study investigated whether the activities of the antioxidant components of donkey seminal plasma (SP)—both enzymatic (superoxide dismutase (SOD), catalase-like (CAT), glutathione peroxidase-like (GPX), and paraoxonase type 1 (PON1)) and non-enzymatic (measured in terms of total thiol, copper-reducing antioxidant capacity (CUPRAC), ferric-reducing ability of plasma (FRAP), and Trolox equivalent antioxidant capacity (TEAC))—and oxidative stress index (OSI) are related to sperm cryotolerance. For this purpose, 15 ejaculates from jackasses (one per individual) were collected and split into two aliquots. The first one was used for measuring the activities levels of enzymatic and non-enzymatic antioxidants and OSI in SP, whereas the other aliquot was cryopreserved. Before cryopreservation, sperm quality parameters (concentration, motility, and viability) were evaluated. After thawing, sperm motility, plasma membrane integrity, lipid disorder, mitochondrial membrane potential, reactive oxygen species (ROS), and calcium intracellular levels were also determined. Based on the percentages of total motility (TM) and of sperm with an intact plasma membrane (SYBR14⁺/PI⁻) after thawing, samples were classified as good-freezability (GFE) or poor-freezability (PFE) ejaculates through cluster analyses. The SP activity levels of enzymatic (SOD and PON1) and non-enzymatic antioxidants (CUPRAC, FRAP, and TEAC) were higher (p < 0.05) in GFE than in PFE, whereas SP-OSI was higher (p < 0.05) in PFE than in GFE. In addition, the activity levels of SOD, PON1, GPX, CUPRAC, FRAP, and TEAC were positively (p < 0.05) related to post-thaw sperm motility and plasma membrane integrity and negatively to intracellular ROS levels. The SP-OSI was negatively correlated (p < 0.05) to post-thaw sperm quality parameters and positively to intracellular ROS levels. It can thus be concluded that donkey SP antioxidants are related to sperm cryotolerance and that measurements of antioxidants PON1, SOD, CUPRAC, FRAP, and TEAC, as well as SP-OSI, could be used as markers of sperm cryotolerance. Further research addressing the relationship of these antioxidants and SP-OSI with sperm cryotolerance and their potential use as freezing markers is warranted.

piR-121380 Is Involved in Cryo-Capacitation and Regulates Post-Thawed Boar Sperm Quality Through Phosphorylation of ERK2 via Targeting PTPN7

Cryopreservation induces capacitation-like (cryo-capacitation) changes, similar to natural capacitation, and affects the fertility potential of post-thawed sperm. The molecular mechanism of sperm cryo-capacitation during cryopreservation remains unknown. PIWI-interacting RNAs (piRNAs) have been reported to be involved in cryo-capacitation of post-thawed sperm and regulation of sperm motility, capacitation, and chemotaxis. In this study, protein tyrosine phosphatase nonreceptor type 7 (PTPN7) was positively targeted by piR-121380 after a dual luciferase assay. The mRNA expression of PTPN7 and piR-121380 was significantly decreased (p < 0.01); however, PTPN7 protein was significantly increased (p < 0.01) in post-thawed boar sperm. Furthermore, E1RK1/2 phosphorylation was reduced during cryopreservation. Six hours after transfection with piR-121380 mimic and inhibitor, the phosphorylation of ERK2 was significantly increased and decreased (p < 0.01), respectively. Furthermore, the highest and lowest total sperm motility, forward motility, and capacitation rate were observed after piR-121380 mimic and inhibitor treatments, respectively. The concentration of intracellular calcium ([Ca2+]i) showed no significant difference after transfection with either piR-121380 mimic or inhibitor at 1, 3, and 6 h. In conclusion, we demonstrated that piR-121380 modulates ERK2 phosphorylation by targeting PTPN7, which induces sperm cryo-capacitation, and eventually affects the motility and fertility potential of post-thawed sperm.

Polyvinyl alcohol, but not bovine serum albumin, promotes the induction of full‐type hyperactivation in boar cyclic AMP analog‐treated spermatozoa

This study aimed to verify the effects of polyvinyl alcohol (PVA) and bovine serum albumin (BSA) on the induction of full-type hyperactivation in boar spermatozoa treated with a cyclic AMP analog (cBiMPS). Washed spermatozoa were treated with cBiMPS (100 μM) for 180 min. As shown in the assessment of sperm motility, PVA (0.05%-0.4%) significantly promoted the induction of full-type hyperactivation, whereas BSA (0.025%-0.4%) did not affect the induction. In comparative experiments, BSA (0.4%) effectively promoted the induction of full-type hyperactivation in bovine spermatozoa treated with cBiMPS, calyculin A (a protein phosphatase inhibitor), and digoxin (a Na⁺ /K⁺ -ATPase inhibitor), while PVA (0.1%) did not affect the induction. Western blotting showed that protein tyrosine phosphorylation states of >50 kDa sperm proteins were effectively enhanced by treatment with cBiMPS in the PVA/BSA-free medium and not affected by the addition of PVA (0.1%). The assessment of plasma membrane integrity indicated that BSA (0.4%) significantly decreased spermatozoa with intact plasma membranes. These results indicate that PVA (0.1%) promotes the induction of full-type hyperactivation and does not influence the protein tyrosine phosphorylation states in boar cBiMPS-treated spermatozoa. They also suggest that BSA should not be added to medium containing cBiMPS for boar spermatozoa.

Effects of partially replacing glycerol with cholesterol-loaded cyclodextrin on protamine deficiency, in vitro capacitation and fertilization ability of frozen-thawed Yanbian Yellow cattle sperm

Glycerol is widely used as a cryoprotectant to protect the sperm from freezing damage during cryopreservation. However, glycerol at a high concentration has toxic effects on the sperm. Therefore, we explored the effects of partially replacing glycerol with cholesterol-loaded cyclodextrin (CLC) in a cryoprotectant on protamine deficiency, in vitro capacitation, and fertilization ability of freeze-thawed Yanbian Yellow cattle sperm. We used fresh semen, control (6% glycerol), and four treatment-I, II, III, and IV (3% glycerol + 0, 0.75, 1.5, and 3 mg/mL CLC, respectively)-groups. Computer-assisted semen analysis; JC-1, CMA3, and FluoZin-3-AM staining; flow cytometry; and IVF were conducted. Replacing a portion of glycerol with 1.5 mg/mL CLC significantly improved sperm motility, viability, plasma membrane integrity, acrosome integrity, and membrane lipid disorders, mitochondrial membrane potential (MMP), capacitation, and fertilization ability (P < 0.05) compared with the control. Additionally, in group I and III, the protamine deficiency were significantly lower (P < 0.05) than in the control group. It was found that 6% glycerol has a higher degree of damage to sperm DNA integrity than 3% glycerol. Overall, this study revealed that partial replacement of glycerol with CLC can be used as a novel cryoprotection method to reduce the toxicity of glycerol and improve the quality of thawed Yanbian Yellow cattle sperm.

An Exploration of Current and Perspective Semen Analysis and Sperm Selection for Livestock Artificial Insemination

Artificial insemination of livestock has been a staple technology for producers worldwide for over sixty years. This reproductive technology has allowed for the rapid improvement of livestock genetics, most notably in dairy cattle and pigs. This field has experienced continuous improvements over the last six decades. Though much work has been carried out to improve the efficiency of AI, there are still many areas which continue to experience improvement, including semen analysis procedures, sperm selection techniques, sperm sexing technologies, and semen storage methods. Additionally, the use of AI continues to grow in beef cattle, horses, and small ruminants as the technology continues to become more efficient and yield higher pregnancy rates. In this review, AI trends in the various livestock species as well as cutting edge improvements in the aforementioned areas will be discussed at length. Future work will continue to refine the protocols which are used for AI and continue to increase pregnancy rates within all livestock species.

In vitro effects of two different commercial freezing and thawing extenders on boar sperm quality

This study was conducted to evaluate whether there were differences in viability of cryopreserved semen when using two different freezing (Minitube Cryoguard - F1 or Androstar® CryoPlus - F2) and thawing (Minitube Cryoguard Thawing solution - T1 or Androstar® Plus - T2) extenders. Ejaculates were collected, diluted (1:1), and cooled before shipping at 17 °C overnight. Samples were aliquoted in cryopreservation extender F1 or F2. Four straws from each treatment sample were thawed and diluted in T1 or T2, resulting in four treatments (F1-T1, F1-T2, F2-T1, and F2-T2). The sperm in diluted semen were evaluated for motility kinetics at 30, 180, and 360 min after thawing. The integrity assessments of the plasma and acrosomal membranes were performed at 30 and 360 min after thawing. There was no interaction between F × T × Time (P > 0.05), and no interaction between F × T (P > 0.05). The sperm progressive motility (PMOT) as time post-thawing increased was greater (P = 0.015) when dilutions occurred using F1 compared with F2 extender. Sperm thawed in T1 had a greater TMOT (P = 0.008) and PMOT (P = 0.033) at all times evaluated. The sperm plasma and acrosomal membrane integrity (AIMI) were greater (P = 0.009) when samples were preserved in F1 compared to F2 extender. The use of T2, as compared with T1 thawing extender, resulted in an enhanced integrity of the plasma and acrosomal membranes (P = 0.008). It is concluded different combinations of commercial freezing extenders and thawing solutions have effects on the quality of cryopreserved boar semen in vitro.

Addition of Reduced Glutathione (GSH) to Freezing Medium Reduces Intracellular ROS Levels in Donkey Sperm

In donkeys, the use of frozen-thawed sperm for artificial insemination (AI) leads to low fertility rates. Furthermore, donkey sperm produce a large amount of reactive oxygen species (ROS), and post-AI inflammation induces the formation of neutrophil extracellular traps (NETosis), which further generates many more ROS. These high ROS levels may induce lipid peroxidation in the sperm plasma membrane, thus affecting its integrity. Enzymatic and non-enzymatic antioxidants, mainly found in the seminal plasma (SP), are responsible for maintaining the redox balance. However, this fluid is removed prior to cryopreservation, thereby exposing sperm cells to further oxidative stress. The exogenous addition of antioxidants to the freezing medium can reduce the detrimental effects caused by ROS generation. Therefore, the aim of this study was to evaluate how the addition of different reduced glutathione (GSH) concentrations (control, 2 mM, 4 mM, 6 mM, 8 mM, and 10 mM) to fresh sperm affect their cryotolerance. Total and progressive motility, kinematic parameters and motile sperm subpopulations were significantly (p < 0.05) different from the control in treatments containing 8 mM and 10 mM GSH, but not at lower concentrations. Plasma and acrosome membrane integrity, mitochondrial membrane potential (MMP) and intracellular superoxide levels (O₂⁻) were not affected (p > 0.05) by any GSH concentration. Interestingly, however, the addition of 8 mM or 10 mM GSH reduced (p < 0.05) the percentages of viable sperm with high overall ROS levels compared to the control. In conclusion, frozen-thawed donkey sperm are able to tolerate high GSH concentrations, which differs from what has been observed in other species. This antioxidant capacity suggests that ROS could be important during post-AI and that the impact of using exogenous antioxidants like GSH to improve the sperm resilience to freeze-thawing is limited in this species.

Direct but Not Indirect Methods Correlate the Percentages of Sperm With Altered Chromatin to the Intensity of Chromatin Damage

Although sperm chromatin damage, understood as damage to DNA or affectations in sperm protamination, has been proposed as a biomarker for sperm quality in both humans and livestock, the low incidence found in some animals raises concerns about its potential value. In this context, as separate methods measure different facets of chromatin damage, their comparison is of vital importance. This work aims at analyzing eight techniques assessing chromatin damage in pig sperm. With this purpose, cryopreserved sperm samples from 16 boars were evaluated through the following assays: TUNEL, TUNEL with decondensation, SCSA, alkaline and neutral sperm chromatin dispersion (SCD) tests, alkaline and neutral Comet assays, and chromomycin A3 test (CMA3). In all cases, the extent of chromatin damage and the percentage of sperm with fragmented DNA were determined. The degree of chromatin damage and the percentage of sperm with fragmented DNA were significantly correlated (p < 0.05) in direct methods (TUNEL, TUNEL with decondensation, and alkaline and neutral Comet) and CMA3, but not in the indirect ones (SCD and SCSA). Percentages of sperm with fragmented DNA determined by alkaline Comet were significantly (p < 0.05) correlated with TUNEL following decondensation and CMA3; those determined by neutral Comet were correlated with the percentage of High DNA Stainability (SCSA); those determined by SCSA were correlated with neutral and alkaline SCD; and those determined by neutral SCD were correlated with alkaline SCD. While, in pigs, percentages of sperm with fragmented DNA are directly related to the extent of chromatin damage when direct methods are used, this is not the case for indirect techniques. Thus, the results obtained herein differ from those reported for humans in which TUNEL, SCSA, alkaline SCD, and alkaline Comet were found to be correlated. These findings may shed some light on the interpretation of these tests and provide some clues for the standardization of chromatin damage methods.

Sperm chromatin condensation as an in vivo fertility biomarker in bulls: a flow cytometry approach

Background

Genetic selection in cattle has been directed to increase milk production. This, coupled to the fact that the vast majority of bovine artificial inseminations (AI) are performed using cryopreserved sperm, have led to a reduction of fertility rates over the years. Thus, seeking sensitive and specific sperm biomarkers able to predict fertility rates is of vital importance to improve cattle reproductive efficiency. In humans, sperm chromatin condensation evaluated through chromomycin A3 (CMA3) has recently been purported to be a powerful biomarker for sperm functional status and male infertility. The objectives of the present study were: a) to set up a flow cytometry method for simultaneously evaluating chromatin condensation and sperm viability, and b) to test whether this parameter could be used as a predictor of in vivo fertility in bulls. The study included pools of three independent cryopreserved ejaculates per bull from 25 Holstein males. Reproductive outcomes of each sire were determined by non-return rates, which were used to classify bulls into two groups (highly fertile and subfertile).

Results

Chromatin condensation status of bovine sperm was evaluated through the combination of CMA3 and Yo-Pro-1 staining and flow cytometry. Sperm quality parameters (morphology, viability, total and progressive motility) were also assessed. Pearson correlation coefficients and ROC curves were calculated to assess their capacity to predict in vivo fertility. Sperm morphology, viability and total motility presented an area under the ROC curve (AUC) of 0.54, 0.64 and 0.68, respectively (P > 0.05), and thus were not able to discriminate between fertile and subfertile individuals. Alternatively, while the percentage of progressively motile sperm showed a significant predictive value, with an AUC of 0.73 (P = 0.05), CMA3/Yo-Pro-1 staining even depicted superior results for the prediction of in vivo fertility in bulls. Specifically, the percentage of viable sperm with poor chromatin condensation showed better accuracy and precision to predict in vivo fertility, with an AUC of 0.78 (P = 0.02).

Conclusions

Chromatin condensation evaluated through CMA3/Yo-Pro-1 and flow cytometry is defined here as a more powerful tool than conventional sperm parameters to predict bull in vivo fertility, with a potential ability to maximising the efficiency of dairy breeding industry.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00634-7.

Antioxidant effect of Moringa olifera leaves extract in extender improves post-thaw quality, kinematics, lipid peroxidation, total antioxidant capacity and fertility of water buffalo bull semen

Our objectives were to determine the antioxidant effect of Moringa olifera leave extract (MLE) in tris extender on post-thaw quality, kinematics, lipid peroxidation, total antioxidant capacity and field fertility of water buffalo bull semen. Semen was collected on a weekly basis for 5 weeks (n = 5 bulls & n = 25). After collection, every sample was diluted individually with extender (tris egg yolk) containing MLE concentrations (0%, 5%, 10%, 15% and 20%) at 37°C. After dilution, semen was filled in 0.54 mL straws and frozen in automatic freezer. After thawing, sperm motility (%) (progressive & total), path velocity (µm/s), straight velocity (µm/s), curvilinear velocity (%), beat cross frequency (Hz), linearity (%), straightness (%), length of average path (µm), length of straight-line path (µm), length of curvilinear path (µm), plasma membrane integrity (%), acrosome membrane integrity (%), DNA integrity (%) and morphology (%) were higher (p < 0.05) in spermatozoa preserved in extender containing 15% MLE as compared to control. The fertility rate (60%, vs. 45%) was higher (p < 0.05) with semen doses frozen with 15% MLE in extender than the control. In conclusion, 15% MLE improves semen quality, kinematics and field fertility in water buffaloes.

Attenuative Role of Idebenone on Deltamethrin Mediated Peroxidative Toxicity of Ram Semen Stored at 4°C

The current study was conducted to evaluate the different concentrations of deltamethrin (DEL; Exp. 1) and the protective role of idebenone (IDB) supplemented with toxic dose of deltamethrin (Exp. 2) during chilled storage of ram semen. Collected samples were pooled and diluted at 500×106 spermatozoa per mL. In Exp. 1, effect of DEL at 1, 2.5, 5, 10, 20, 40, 80 μM levels was evaluated on different variables of spermatozoa motion characteristics. In Exp. 2, different amounts of IDB (2, 4, and 8 μM) concurrent with constant doses of DEL (10 μM) were examined on semen quality upon chilled preservation up to 72 h. Indices of spermatozoa kinematics, functionality of plasma membrane and viability were recorded. Biochemical metabolites were measured in spermatozoa and its medium (extender) at different time points. In Exp. 1, different parameters of spermatozoa kinematics were affected by exposure to DEL in a dose dependent manner. In Exp. 2, combination of IDB with DEL resulted in a significant (P<0.05) increase in total motility, forward progressive motility and curvilinear path velocity compared to DEL group at 24, 48 and 72 h. Simultaneous administration of IDB with DEL increased the percentage of spermatozoa with functional membrane and viability compared to DEL group at 72 h (P<0.05). The amounts of lipid peroxidation index were lower in medium of combination groups compared to DEL group at 48 h and 72 h (P<0.05). Antioxidant capacity was higher in spermatozoa and medium of IDB treated groups compared to DEL group at 72 h (P<0.05). Amounts of total nitrate-nitrite and superoxide dismutase activity of spermatozoa and medium were not affected by treatment (P>0.05). In conclusion, IDB could ameliorate oxidative and peroxidative damages induced by DEL mild toxicity upon cold preservation of ram semen.

Ex Situ Conservation and Genetic Rescue of Endangered Polish Cattle and Pig Breeds with the Aid of Modern Reproductive Biotechnology – A Review

The development and optimization of reproductive biotechnology – specifically semen cryopreservation, spermatological diagnostics, and intraspecies cloning by somatic cell nuclear transfer (SCNT) – have become essential techniques to conserve the genetic resources and establish genetic reserves of endangered or vanishing native Polish livestock breeds. Moreover, this biotechnology is necessary for perpetuating biological diversity and enhancing genetic variability as well as for restoring and reintroducing breeds into anthropogenic agricultural ecosystems. On the one hand, the purpose of our paper is to interpret recent efforts aimed at the ex situ conservation of native cattle and pig breeds. On the other, it emphasizes the prominent role played by the National Research Institute of Animal Production (NRIAP) in maintaining biodiversity in agricultural environmental niches. Furthermore, our paper provides an overview of the conventional and modern strategies of the banking and cryopreservation of germplasm-carrier biological materials and somatic cell lines, spermatological diagnostics, and semen-based and SCNT-mediated assisted reproductive technologies (ART s). These are the most reliable and powerful tools for ex situ protection of the genetic resources of endangered breeds of livestock, especially cattle and pigs.

The TUNEL assay underestimates the incidence of DNA damage in pig sperm due to chromatin condensation

Inconsistencies in the relationship between sperm DNA fragmentation and reproductive outcomes as well as the low incidence in farm animals raise concerns on its actual value as a sperm quality parameter. Previous studies suggested that the different sensitivity of techniques evaluating DNA fragmentation could explain variations in the correlation with reproductive outcomes. While the TUNEL assay is one of the most standardized methods to detect DNA damage and cell death, the steric impediment for the terminal nucleotidyl transferase enzyme to access the highly condensed sperm nucleus may decrease the ability of this test to detect internal DNA breaks. In the present study, we sought to determine whether increasing chromatin decondensation makes the TUNEL assay more sensitive to detect DNA damage in pig sperm. We compared three chromatin decondensation treatments (2 mM DTT for 45 min; 5 mM DTT for 8 min and further 45 min; and 5 mM DTT+ 1 M NaCl for 8 min) through the Chromomycin A3 test (CMA3). While incubation with DTT increased the percentages of sperm with decondensed chromatin, regardless of concentration and time of incubation (P < 0.05), the extent of that decondensation was higher when 5 mM DTT was combined with 1 M NaCl. In addition, the TUNEL assay detected a higher number of DNA breaks in sperm with decondensed chromatin (1.89% ± 1.63% vs 8.74% ± 6.05%; P = 0.003). This study shows, for the first time, that previous chromatin decondensation increases the sensitivity of the TUNEL assay to detect DNA damage in pig sperm. These findings also support that larger chromatin decondensation is needed in order for DNA damage to be evaluated properly in species containing protamine P1 only.

Spermatozoa and seminal plasma small extracellular vesicles miRNAs as biomarkers of boar semen cryotolerance

Freeze boar semen is still the biggest challenge for the swine industry due to the high cold shock sensitivity of boar sperm cells and the variance of post-thaw results among individuals and ejaculates from the same boar. To solve this problem, we investigate if miRNAs present in sperm cells and small extracellular vesicles (EVs) from seminal plasma of raw boar ejaculates can predict high-quality ejaculates after underwent the freeze-thaw process. For this, we obtained miRNAs samples of sperm cells and EVs from raw seminal plasma from 27 ejaculates before the cryopreservation process. Two groups with different freezability considering the analysis post-thaw of structure and sperm functionality were formed: High freezability (HF; n = 04) and low freezability (LF; n = 04). That done, we investigated the miRNAs profile of sperm cells and EVs from seminal plasma in both groups. Three miRNAs were differently abundant in LF ejaculates, being the ssc-miR-503 found in higher levels in sperm cells (P < 0.10). The ssc-miR-130a and ssc-miR-9 most abundant in EVs from seminal plasma (P < 0.10), in LF ejaculates. Through enrichment analysis, it was possible to verify that these miRNAs could be performing modifications in the development of male germ cells and in the production of energy to spermatozoa to maintain their viability and functionality. Therefore, we can demonstrate that ssc-miR-503, ssc-miR-130a, and ssc-miR-9 are related to low sperm cryotolerance in boars semen. So those miRNAs can be used as a biomarker to predict their low ability to tolerate the cryopreservation process.

Parkinson Disease Protein 7 (PARK7) Is Related to the Ability of Mammalian Sperm to Undergo In Vitro Capacitation

Parkinson disease protein 7 (PARK7) is a multifunctional protein known to be involved in the regulation of sperm motility, mitochondrial function, and oxidative stress response in mammalian sperm. While ROS generation is needed to activate the downstream signaling pathways required for sperm to undergo capacitation, oxidative stress has detrimental effects for sperm cells and a precise balance between ROS levels and antioxidant activity is needed. Considering the putative antioxidant role of PARK7, the present work sought to determine whether this protein is related to the sperm ability to withstand in vitro capacitation. To this end, and using the pig as a model, semen samples were incubated in capacitation medium for 300 min; the acrosomal exocytosis was triggered by the addition of progesterone after 240 min of incubation. At each relevant time point (0, 120, 240, 250, and 300 min), sperm motility, acrosome and plasma membrane integrity, membrane lipid disorder, mitochondrial membrane potential, intracellular calcium and ROS were evaluated. In addition, localization and protein levels of PARK7 were also assessed through immunofluorescence and immunoblotting. Based on the relative content of PARK7, two groups of samples were set. As early as 120 min of incubation, sperm samples with larger PARK7 content showed higher percentages of viable and acrosome-intact sperm, lipid disorder and superoxide levels, and lower intracellular calcium levels when compared to sperm samples with lower PARK7. These data suggest that PARK7 could play a role in preventing sperm from undergoing premature capacitation, maintaining sperm viability and providing a better ability to keep ROS homeostasis, which is needed to elicit sperm capacitation. Further studies are required to elucidate the antioxidant properties of PARK7 during in vitro capacitation and acrosomal exocytosis of mammalian sperm, and the relationship between PARK7 and sperm motility.

Recombinant TrxAFNIIx4His6 improves post-thaw motility of ram sperm measured by a sperm motility tracker software

The aim of the present study was to evaluate a freezing extender supplemented with recombinant TrxAFNIIx4His_6, a reported decapacitating factor. Semen samples were diluted in tris-egg yolk medium with 0, 1.5 µM and 3.0 µM of TrxAFNIIx4His₆. Computer-assisted sperm motility tracking and subpopulations evaluation showed that addition of TrxAFNIIx4His₆ improved post-thaw total and progressive motility at both concentrations evaluated. TrxAFNIIx4His₆ increased the sperm subpopulation with the highest progressiveness and great velocity and decreased the subpopulation of poorly motile and almost non-progressive sperm. Incorporation of TrxAFNIIx4His₆ to freezing extender shows potential for the development of cryoprotection media which may lead to improved fertility after artificial insemination.

Fractionated Seminal Plasma of Boar Ejaculates Analyzed by LC-MS/MS: Its Effects on Post-Thaw Semen Quality

This study aimed to characterize the protein composition of fractionated seminal plasma (SP) by liquid chromatography mass spectrometry (LC–MS/MS) analysis and investigate its effects on survival of frozen-thaw (FT) boar spermatozoa following storage. Seminal plasma (SP) was fractionated by gel filtration chromatography to give two fractions, SP1 with more than 40 kDa (>40 kDa) and SP2 with less than 40 kDa (<40 kDa). SP1 and SP2 were subjected to LC–MS/MS and bioinformatics analysis. Following cryopreservation, FT boar semen (n = 7) was thawed in Beltsville Thawing Solution (BTS), BTS + SP1 or BTS + SP2, stored at different periods and subjected to post-thaw (PT) quality assessment. A total of 52 and 22 abundant proteins were detected in SP1 and SP2, respectively. FN1, ANGPTL1, and KIF15 proteins were more abundance in SP1, whereas a high abundance of spermadhesins (PSP-I and PSP-II) was detected in SP2. Proteins of the fractionated SP were involved in various biological processes, such as cell motility and signal transduction. The dominant pathway of SP1 proteins was the apelin signaling pathway (GNA13, MEF2D, SPHK2, and MEF2C), whereas a pathway related to lysosome (CTSH, CTSB, and NPC2) was mainly represented by SP2 proteins. In most of the boars, significantly higher motility characteristics, membrane integrity, and viability were observed in FT spermatozoa exposed to SP1 or SP2 compared with BTS. The results of our study confirm that a combination of several proteins from the fractionated SP exerted beneficial effects on the sperm membrane, resulting in improved quality characteristics following PT storage.

Role of exogenous antioxidants on the performance and function of pig sperm after preservation in liquid and frozen states: A systematic review

In situations where an excessive generation of reactive oxygen species overwhelms antioxidant capacity, a harmful effect on sperm function is exerted. Antioxidants are molecules capable of minimizing this detrimental effect, which is important in pig sperm due to the high content of polyunsaturated fatty acids in their plasma membrane. The present systematic review aims at evaluating whether supplementing semen extenders (for liquid storage at 17 °C) or freezing and/or thawing media (for cryopreservation) with antioxidants influences sperm quality and functionality parameters, and in vitro/in vivo fertility outcomes. We defined inclusion and exclusion criteria in a PICOS table according to PRISMA guidelines, and conducted a literature search through MEDLINE-PubMed in November 2020. After systematic selection, 75 studies were included: 47 focused on cryopreservation and 28 on liquid storage at 17 °C. More than 70% of the studies included in this review showed that adding semen extenders for liquid storage and/or freezing/thawing media for cryopreservation with antioxidants enhances sperm quality and functionality parameters. In addition, this supplementation improves in vivo/in vitro fertility outcomes, supporting the hypothesis that the beneficial effect observed upon sperm quality has a positive impact on reproduction outcomes.

Effect of freeze-thawing process on lipid peroxidation, miRNAs, ion channels, apoptosis and global DNA methylation in ram spermatozoa

This study was carried out to investigate the effect of the semen freeze-thawing process on the functionality and molecular structure of ram spermatozoa. The temperature of pooled and diluted semen at 38°C (group 1, control) was lowered to 5°C (group 2), and it was subjected to glycerolisation-equilibration (group 3), frozen and thawed (group 4). Compared to the control, deterioration in spermatological parameters and significant increases in lipid peroxidation and global DNA methylation levels were observed in groups 3 and 4. When compared with the control, significant downregulation in the levels of miR-485 of group 2, miR-29a of group 3 and let-7a, miR-485 and miR-29a of group 4, and significant upregulation in the levels of miR-107 of group 3 and miR-127 of groups 3 and 4 were detected. In comparison to the control, significant upregulation in the levels of CatSper1, CatSper2, CatSper3, CatSper4, ANO1 and TRPM3 of group 2, CatSper4, ANO1 and TRPM3 of group 3 and KCNJ11 of group 4, and significant downregulation in the CatSper 3 level of group 4 were determined. As a result, the semen freeze-thawing process causes motility and morphological disorders in rams. This may be due to molecular changes associated with lipid peroxidation in spermatozoa.

Curcumin in a tris-based semen extender improves cryosurvival of Hariana bull spermatozoa

In this study, the cryoprotective potential of natural antioxidant curcumin in Hariana bull semen was evaluated as an additive in a tris-based extender with the assessment of motility and motion parameters of spermatozoa, membrane intactness, progesterone-receptor binding, protein carbonyl content, cervical mucus penetration, cryocapacitation-associated and apoptotic-like changes. The collected ejaculates were divided into five groups in the tris-based extender (control without curcumin-I, 10 µM-II, 25 µM-III, 50 µM-IV and 75µM-V) and were cryopreserved. Groups II and III containing 10 and 25 µM curcumin substantially (p < .05) improved the post-thaw sperm parameters like viability, motility, and velocity parameters; intact acrosome and membrane; lowered protein carbonyl content; DNA fragmentation and cryocapacitation-associated changes in comparison to control. It was interesting to note that early apoptotic-like changes in sperm cells were significantly (p < .05) decreased in Group II along with an increase in a higher population of sperm cells having high mitochondrial transmembrane potential. Higher progesterone-receptor binding, Vanguard distance and in vitro capacitation response were observed only in Group II (10µM) compared to other groups. In conclusion, curcumin in a semen extender manifests cryoprotective effects and may be incorporated at 10 µM concentration in a Hariana bull semen extender for better post-thaw sperm quality.

Identifying new sperm Western blot loading controls

The measurement of protein expression level plays a pivotal role in both biological and medical studies. Housekeeping proteins, generally encoded by housekeeping genes are used as loading control proteins to normalize protein expression. Obviously, proper reference standards are essential for adequate analysis of protein expression. However, our study showed that the widely used normalisation proteins, whose expression levels varied greatly among sperm samples, were unsuitable for data standardisation. To uncover the proteins steadily expressed in sperm, we analysed several published transcriptome data of sperm. Seven proteins whose expression levels were relatively stable (co-efficient variation values less than 0.35) were selected and further evaluated by quantitative real-time polymerase chain reaction, Western Blot (WB) and immunocytochemistry. Our results showed that among the classical housekeeping proteins, only β-tubulin remained constant in sperm samples from 85 individuals. Compared with other classical housekeeping proteins such as glyceraldehyde 3-phosphate dehydrogenase, actin and histone H3, Cullin-1 (CUL1) and F-box only protein 7 (FBXO7) seemed to be more suitable to be used as internal controls for WB in sperm protein studies. Combined with the locations of these proteins, CUL1 and FBXO7 were suggested to be used as a housekeeping protein for total proteins.

Nanocarried antioxidants in freezing extenders for boar spermatozoa

Post-thawing cryoinjuries in boar spermatozoa due to oxidative stress may be reduced by adding nanoencapsulated antioxidants to freezing extenders. This study evaluated post-thawing kinetics, structural and biochemical functions of boar spermatozoa frozen with extenders including resveratrol and vitamin E loaded into polymeric nanocapsules. Resveratrol was added at 0 (control), 5, 10, 20, 40 and 80 µg/ml, whereas Vitamin E was added at 0 (control), 50, 100, 200 and 400 µg/ml. Both antioxidants were tested in free and nanoencapsulated presentations. In contact with empty nanocapsules, some sperm kinetics parameters were impaired compared to the control (p < .05), whereas lipoperoxidation declined (p < .05). With inclusion of 40 µg/ml nanoencapsulated resveratrol, some sperm kinetics parameters were improved (p < .01), but sperm motility, structural and biochemical functions did not differ from the control (p > .05). No improvement in sperm quality occurred with inclusion of vitamin E, although sperm kinetics with 400 µg/ml nanoencapsulated vitamin E was reduced compared to the control (p < .01). Inclusion of 40 µg/ml nanoencapsulated resveratrol benefitted boar sperm kinetics after thawing, but no improvement resulted from inclusion of vitamin E.

Transcriptome-wide m6A profiling reveals mRNA post-transcriptional modification of boar sperm during cryopreservation

Background

Cryopreservation induces transcriptomic and epigenetic modifications that strongly impairs sperm quality and function, and thus decrease reproductive performance. N⁶-methyladenosine (m⁶A) RNA methylation varies in response to stress and has been implicated in multiple important biological processes, including post-transcriptional fate of mRNA, metabolism, and apoptosis. This study aimed to explore whether cryopreservation induces m⁶A modification of mRNAs associated with sperm energy metabolism, cryoinjuries, and freezability.

Results

The mRNA and protein expression of m⁶A modification enzymes were significantly dysregulated in sperm after cryopreservation. Furthermore, m⁶A peaks were mainly enriched in coding regions and near stop codons with classical RRACH motifs. The mRNAs containing highly methylated m⁶A peaks (fts vs. fs) were significantly associated with metabolism and gene expression, while the genes with less methylated m⁶A peaks were primarily involved in processes regulating RNA metabolism and transcription. Furthermore, the joint analysis of DMMGs and differentially expressed genes indicated that both of these play a vital role in sperm energy metabolism and apoptosis.

Conclusions

Our study is the first to reveal the dynamic m⁶A modification of mRNAs in boar sperm during cryopreservation. These epigenetic modifications may affect mRNA expression and are closely related to sperm motility, apoptosis, and metabolism, which will provide novel insights into understanding of the cryoinjuries or freezability of boar sperm during cryopreservation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07904-8.

Metabolomic Analysis and Identification of Sperm Freezability-Related Metabolites in Boar Seminal Plasma

Simple Summary

In the freezing process of boar sperm, there are obvious differences in freezability between individuals. Studies suggest that specific freezability markers might be useful in good (GFE) and poor freezability ejaculate (PFE) selection prior to cryopreservation. Therefore, we performed UHPLC-qTOF-MS analysis to explore the difference in the metabolic level of seminal plasma between boars with differential freezability, and the results showed that the content of D-aspartic acid, N-acetyl-L-glutamate (NAG), and inosine were significantly different. These findings present new insights into the role of metabolism in sperm freezability and provide research directions for exploring potential biomarkers of freezability.

Abstract

Some potential markers of boar sperm freezability have been found in spermatozoa, but little attention has been paid to seminal plasma. The seminal plasma is composed of secretions from the testis, epididymis, and accessory sex glands. The exposure of spermatozoa to small molecules such as metabolites can affect sperm function. However, details and significance of the seminal plasma metabolome related to boar sperm freezability are unknown. Therefore, the main aim of this study was to explore the differences in the metabolic level of seminal plasma between boars with differential freezability and to explore the candidate biomarkers of semen freezability. A total of 953 metabolites were identified in boar semen plasma by UHPLC-qTOF-MS analysis, and 50 metabolites showed significant change between the GFE group and PFE group. Further, twelve metabolites were subjected to metabolic target analysis, and three metabolites (D-aspartic acid, N-acetyl-L-glutamate (NAG), and inosine) showed differences. In conclusion, there is significant difference in the metabolome of seminal plasma between GFE and PFE individuals. D-aspartic acid, NAG, and inosine in seminal plasma may be potential markers for assessing sperm cryopreservation resistance in boars.

Post-Thaw Sperm Quality and Functionality in the Autochthonous Pig Breed Gochu Asturcelta

Simple Summary

Genetic resource banks were created to preserve the genetic material of endangered, rare, valuable individuals or genetically relevant breeds. Sperm cryopreservation is a practical and widespread strategy to preserve these genetic materials. This study aimed to characterize the frozen-thawed sperm of the native pig breed Gochu Asturcelta, considering the effects of boar age and season of semen collection on post-thaw sperm quality. We found that the boar age did not have a significant effect on the sperm parameters assessed. However, the season significantly affected many of these parameters (motility, viability, acrosomal status, mitochondrial activity). In general, sperm samples collected in spring and summer showed higher quality post-thawing, the lowest in winter. Our findings demonstrated that the post-thawing sperm quality of Gochu Asturcelta was in the range of results for commercial breeds, bringing a good prospect for the use of assisted reproductive technologies in this local breed.

Abstract

Genetic resource banks (GRB) preserve the genetic material of endangered, valuable individuals or genetically relevant breeds. Semen cryopreservation is a crucial technique to reach these goals. Thus, we aimed to assess the sperm parameters of semen doses from the native pig breed Gochu Asturcelta stored at the GRB of Principado de Asturias (GRB-PA, Gijón, Spain), focusing on intrinsic and extrinsic (boar, season) factors. Two straws per boar (n = 18, 8–71 months of age) were thawed, pooled, and assessed after 30 and 150 min at 37 °C by CASA (computer-assisted sperm analysis system; motility and kinematic parameters) and flow cytometry (viability, acrosomal status, mitochondrial activity, apoptosis, reactive oxygen species, and chromatin status). The effects of age, incubation, and season on post-thawing quality were determined using linear mixed-effects models. Parameters were on the range for commercial boar breeds, with chromatin status (SCSA: fragmentation and immaturity) being excellent. Incubation decreased sperm quality and functionality. The boar age did not have a significant effect (p > 0.05), but the between-boar variability was significant (p < 0.001). The season significantly affected many parameters (motility, kinematics, viability, acrosomal status, mitochondrial activity), especially after 150 min of incubation. In general, samples collected in spring and summer showed higher quality post-thawing, the lowest in winter. In conclusion, the sperm doses from the Gochu Asturcelta breed stored at the GRB-PA showed excellent chromatin status and acceptable characteristics after thawing. Therefore, boar and seasonal variability in this autochthonous breed could be relevant for cryobank management.

Improvement of the in vitro fertilization and embryo development using frozen-thawed spermatozoa of microminipigs

This study aimed to compare the quality and the penetration ability of frozen–thawed spermatozoa from three microminipigs and Large White boars and to evaluate the effects of caffeine and heparin as well as the sperm–oocyte co-incubation length on the fertilization and embryonic development in vitro. Results showed that the fertilization rates of spermatozoa from three microminipig boars were significantly lower than those of a Large White boar. In the post-thaw spermatozoa from one of three microminipig boars, the sperm quality, penetration ability, and the oocyte development after in vitro fertilization were significantly lower than those of the spermatozoa from other boars. The caffeine supplementation in the fertilization media increased the rates of fertilization and blastocyst formation for the microminipig spermatozoa with low sperm quality. In addition to caffeine supplementation, the rates of fertilization and blastocyst formation after using microminipig spermatozoa were significantly higher with a 10 h sperm–oocyte co-incubation than with 3 h of co-incubation length. Our results indicate that the differences between the males and the breed influence the quality and fertility of frozen–thawed boar spermatozoa. In conclusion, the presence of caffeine in the in vitro fertilization (IVF) medium and adequate length of sperm–oocyte co-incubation may have beneficial effects for improving IVF results when using microminipig spermatozoa with low quality.

Ameliorative role of trans-ferulic acid on induced oxidative toxicity of rooster semen by β-cyfluthrin during low temperature liquid storage

Current study was designed to evaluate the effects of β-cyfluthrin, as a toxicant substance, and trans-ferulic acid (trans-FA), as a protective agent, on different parameters of rooster semen upon liquid storage. For this purpose, semen samples of roosters (Ross 308, n = 10, 32-wk-old) were collected twice a week. Good quality samples (≥70% progressive motion) were diluted, pooled and then divided for the purposes of the study. In the first experiment, motility of spermatozoa was evaluated following exposure to different concentrations of β-cyfluthrin (1, 2.5, 5, 10, 20, 40, and 80 µM) at 0, 24, and 48 h of storage. In the second experiment, constant doses of β-cyfluthrin (10 µM) alone or in combination with trans-FA (10, 25 mM) were assessed on motility and viability of spermatozoa at 0, 24, and 48 h time points. Moreover, amounts of malondialdehyde (MDA), total antioxidant capacity (TAC), total nitrate-nitrite, total hydroperoxide (HPO), and activity of superoxide dismutase (SOD) were evaluated in the homogenate of spermatozoa-diluent at studied time points. Results of the first experiment showed that amounts of β-cyfluthrin greater than 5 µM, significantly reduced the motility of spermatozoa at 24 and 48 h of storage (P < 0.05). The second experiment demonstrated that, trans-FA especially at 10, 25 mM doses restored the motility and viability of spermatozoa compared to β-cyfluthrin treated group (P < 0.05). Amounts of MDA (10, 25 mM), hydroperoxide (10, 25, and 50 mM), and nitrate-nitrite (10, 25, and 50 mM) were lower and TAC (10 and 25 mM) were greater in trans-FA + β-cyfluthrin treated groups compared to β-cyfluthrin alone treated samples (P < 0.05). However, activity of SOD did not show significant changes by the treatment (P > 0.05). It seems that trans-FA could ameliorate toxic effect of β-cyfluthrin via reduction of peroxidative (as evident by measurement of MDA) and nitrosative (as evident by measurement of nitrate-nitrite) reactions over cold preservation of rooster semen.