Cryopreservation of cynomolgus macaque (Macaca fascicularis) sperm with glycerol and ethylene glycol, and its effect on sperm-specific ion channels - CatSper and Hv1

Sperm plasma membrane ion transporters and male fertility potential: A perspective under the prism of cryopreservation

Intracellular calcium homeostasis plays a crucial role in spermatozoa by regulating physiological functions associated with sperm quality and male fertility potential. Intracellular calcium fine balance in the sperm cytoplasm is strictly dependent on sperm surface channels including the CatSper channel. CatSpers' role is to ensure the influx of extracellular calcium, while intracellular pH alkalinization serves as a stimulus for the activation of several channels, including CatSper. Overall, the generation of intracellular calcium spikes through CatSper is essential for fertilization-related processes, such as sperm hyperactivation, acrosome reaction, egg chemotaxis, and zona pellucida penetration. Multiple lines of evidence suggest that disruption in the close interaction among ions, pH, and CatSper could impair male fertility potential. In contemporary times, the growing reliance on Medically Assisted Reproduction procedures underscores the impact of cryopreservation on gametes. In fact, a large body of literature raises concerns about the cryo-damages provoked by the freeze-thawing processes, that can affect the plasma membrane integrity, thus the structure of pivotal ion channels, and the fine regulation of both intracellular calcium and pH. This review aims to provide an overview of the importance of the CatSper channel in sperm quality and further fertilization potential. Additionally, it addresses the emerging issue of cryopreservation's impact on the functionality of this sperm channel.

Reduction of cryopreservation-induced structural, functional and molecular damages in ram sperm by hydrated C60 fullerene

This study aimed to investigate the morphological, functional and molecular changes in frozen-thawed ram sperm using an extender containing different concentrations of hydrated carbon 60 fullerene (C60 HyFn), a nanotechnological product. Semen taken from each of the seven Akkaraman rams were pooled. Semen collection was done twice a week and it continued for 3 weeks. Each pooled semen sample was divided into six equal groups and diluted with tris + egg yolk extender including 0 (control), 200, 400, 800 nM, 1 and 5 μM concentrations of C60 HyFn at 37°C. They were then frozen in liquid nitrogen vapour at -140°C, stored in liquid nitrogen container (-196°C) and thawed at 37°C for 25 s before analysis. In comparison with control, C60 HyFn addition prior to freezing procedure provided significant increases in total and progressive motility rates, glutathione peroxidase, catalase activities and percentage of highly active mitochondria, and significant decreases in dead and abnormal sperm rates, lipid peroxidation, caspase-3 and DNA fragmentation levels in frozen-thawed ram semen. When compared to control, C60 HyFn supplementation significantly down-regulated the expression levels of miR-200a and KCNJ11, and significantly up-regulated the expression levels of miR-3958-3p (at the concentrations of 200, 400, 800 nM and 1 μM), CatSper1 (at the concentrations of 200, 400 nM and 5 μM), CatSper2 (at the concentrations of 1 and 5 μM), CatSper3 (at the concentrations of 200, 400 nM, 1 and 5 μM), CatSper4 (at all concentrations), ANO1 (at the concentrations of 800 nM, 1 and 5 μM) and TRPV5 (at the concentrations of 200, 400 and 800 nM). The addition of C60 HyFn had no effect on global DNA methylation rates. As a result, C60 HyFn supplementation to ram semen extenders may be beneficial in reducing some of the functional, structural and molecular damages in sperm induced by the freeze-thawing procedure.

Signaling Roleplay between Ion Channels during Mammalian Sperm Capacitation

In order to accomplish their primary goal, mammalian spermatozoa must undergo a series of physiological, biochemical, and functional changes crucial for the acquisition of fertilization ability. Spermatozoa are highly polarized cells, which must swiftly respond to ionic changes on their passage through the female reproductive tract, and which are necessary for male gametes to acquire their functional competence. This review summarizes the current knowledge about specific ion channels and transporters located in the mammalian sperm plasma membrane, which are intricately involved in the initiation of changes within the ionic milieu of the sperm cell, leading to variations in the sperm membrane potential, membrane depolarization and hyperpolarization, changes in sperm motility and capacitation to further lead to the acrosome reaction and sperm-egg fusion. We also discuss the functionality of selected ion channels in male reproductive health and/or disease since these may become promising targets for clinical management of infertility in the future.

Generation of Transgenic Sperm Expressing GFP by Lentivirus Transduction of Spermatogonial Stem Cells In Vivo in Cynomolgus Monkeys

Nonhuman primates (NHPs) have been considered as the best models for biomedical research due to their high similarities in genomic, metabolomic, physiological and pathological features to humans. However, generation of genetically modified NHPs through traditional methods, such as microinjection into the pronuclei of one-cell embryos, is prohibitive due to the targeting efficiency and the number of NHPs needed as oocyte/zygote donors. Using spermatogonial stem cells (SSCs) as the target of gene editing, producing gene-edited sperm for fertilization, is proven to be an effective way to establish gene editing animal disease models. In this experiment, we used ultrasound to guide the echo dense injection needle into the rete testis space, allowing the EGFP lentivirus to be slowly injected at positive pressure from the rete testis into seminiferous tubules. We found Thy1 can be used as a surface marker of cynomolgus monkey SSCs, confirming that SSCs carry the GFP gene. Finally, we successfully obtained transgenic sperm, with a similar freezing and recovery rate to that of WT animals.

Cryopreservation did not affect sperm DNA methylation levels of genes related to fertilization and embryonic development of cynomolgus macaque (Macaca fascicularis)

DNA methylation alters gene expression in numerous biological processes, including embryonic development. It is little known about the effect of cryopreservation on sperm DNA methylation. The present study has investigated whether cryopreservation causes abnormal DNA methylation in cynomolgus macaque sperm for five critical genes that includes the maternally imprinted gene (SNRPN), genes associated with male infertility (HSPA1L, MTHFR) and genes involved in embryonic development (TET3, LZTR1). Our results showed that sperm motility, the percentage of acrosomal integrity, DNA integrity and mitochondrial membrane potential were decreased after cryopreservation either being frozen with penetrating cryoprotectant, glycerol (Gly) or ethylene glycol (EG), compared to fresh sperm (p = 0.000), but the methylation patterns of the five target genes from cynomolgus macaque sperm samples were not affected after cryopreservation as evaluated by the Bisulfite Sequencing PCR (BSP) method. The data indicates that the current protocol for sperm cryopreservation of cynomolgus macaque is safe in terms of DNA methylation levels in these genes related to critical sperm functions.

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.

Semen extenders: An evaluative overview of preservative mechanisms of semen and semen extenders

Reproduction is fundamental for all living things as it ensures the continued existence of a species and an improved economy in animal husbandry. Reproduction has developed since history, and diverse processes, such as artificial insemination and in vitro fertilization, have been developed. Semen extenders were discovered and developed to protect sperm from harmful factors, such as freeze and osmotic shock, oxidative stress, and cell injury by ice crystals. Semen extenders preserve sperm by stabilizing its properties, including sperm morphology, motility, and viability and membrane, acrosomal, and DNA integrity. Therefore, semen extenders must provide a favorable pH, adenosine triphosphate, anti-cooling and anti-freeze shock, and antioxidant activity to improve semen quality for fertilization. Hence, this review provides precise data on different semen extenders, preservative mechanisms, and essential additives for semen extenders in different animals.

Structure and Function of Ion Channels Regulating Sperm Motility-An Overview

Sperm motility is linked to the activation of signaling pathways that trigger movement. These pathways are mainly dependent on Ca²⁺, which acts as a secondary messenger. The maintenance of adequate Ca²⁺ concentrations is possible thanks to proper concentrations of other ions, such as K⁺ and Na⁺, among others, that modulate plasma membrane potential and the intracellular pH. Like in every cell, ion homeostasis in spermatozoa is ensured by a vast spectrum of ion channels supported by the work of ion pumps and transporters. To achieve success in fertilization, sperm ion channels have to be sensitive to various external and internal factors. This sensitivity is provided by specific channel structures. In addition, novel sperm-specific channels or isoforms have been found with compositions that increase the chance of fertilization. Notably, the most significant sperm ion channel is the cation channel of sperm (CatSper), which is a sperm-specific Ca²⁺ channel required for the hyperactivation of sperm motility. The role of other ion channels in the spermatozoa, such as voltage-gated Ca²⁺ channels (VGCCs), Ca²⁺-activated Cl-channels (CaCCs), SLO K⁺ channels or voltage-gated H⁺ channels (VGHCs), is to ensure the activation and modulation of CatSper. As the activation of sperm motility differs among metazoa, different ion channels may participate; however, knowledge regarding these channels is still scarce. In the present review, the roles and structures of the most important known ion channels are described in regard to regulation of sperm motility in animals.

HVCN1 but Not Potassium Channels Are Related to Mammalian Sperm Cryotolerance

Little data exist about the physiological role of ion channels during the freeze–thaw process in mammalian sperm. Herein, we determined the relevance of potassium channels, including SLO1, and of voltage-gated proton channels (HVCN1) during mammalian sperm cryopreservation, using the pig as a model and through the addition of specific blockers (TEA: tetraethyl ammonium chloride, PAX: paxilline or 2-GBI: 2-guanidino benzimidazole) to the cryoprotective media at either 15 °C or 5 °C. Sperm quality of the control and blocked samples was performed at 30- and 240-min post-thaw, by assessing sperm motility and kinematics, plasma and acrosome membrane integrity, membrane lipid disorder, intracellular calcium levels, mitochondrial membrane potential, and intracellular O₂⁻⁻ and H₂O₂ levels. General blockade of K⁺ channels by TEA and specific blockade of SLO1 channels by PAX did not result in alterations in sperm quality after thawing as compared to control samples. In contrast, HVCN1-blocking with 2-GBI led to a significant decrease in post-thaw sperm quality as compared to the control, despite intracellular O₂⁻⁻ and H₂O₂ levels in 2-GBI blocked samples being lower than in the control and in TEA- and PAX-blocked samples. We can thus conclude that HVCN1 channels are related to mammalian sperm cryotolerance and have an essential role during cryopreservation. In contrast, potassium channels do not seem to play such an instrumental role.

Cryopreservation of Mauritian Cynomolgus Macaque (Macaca fascicularis) Sperm in Chemically Defined Medium

The objective of this study was to optimize cryopreservation of sperm from Mauritian cynomolgus macaques (MCM) in defined conditions. Sperm viability and motility were compared between sperm cryopreserved in chemically-defined freezing media with variable osmolarity and the presence of either ethylene glycol or glycerol. The highest percentage viability (after freeze-thaw) was seen in sperm samples that were cryopreserved in medium with an osmolarity of 310 mOsm, while higher osmolarities markedly decreased sperm viability. Ethylene glycol and glycerol at concentrations of 4.6% and 5%, respectively, preserved sperm viability to an equivalent degree. Although higher motility rates and higher straight-line velocities were observed in sperm samples frozen in glycerol compared with ethylene glycol, these differences were not statistically significant. Thawed sperm frozen in defined conditions with glycerol were capable of fertilizing MCM oocytes in vitro, with development to the blastocyst stage. The protocol described here provides an effective method for cryopreservation of sperm to facilitate subsequent in vitro fertilization and genome editing of embryos in MCM species.

Differential motility parameters and identification of proteomic profiles of human sperm cryopreserved with cryostraw and cryovial

Background

Although sperm cryopreservation has been widely used in human reproductive medicine as an integral infertility management in infertility clinics and for banking sperm in sperm banks, the freezing/thawing protocols are not optimal. The freezing and thawing processes result in changes at both structural and molecular levels, some even detrimental, in human sperm when compared with fresh sperm. The change of sperm proteins after cryopreservation may play negative roles for fertilization and early embryo development. Conventionally, cryostraws (CS) and cryovials (CV) are the most widely used cryopreservation carriers (CPCs) for human sperm cryopreservation accompanied with the use of egg yolk free commercial media. However, the influence of cryopreservation on the proteomic profile of human sperm preserved with the two CPCs is unknown. Therefore the purpose of the present study was to compare the frozen-thawed motility, investigate the proteomic profile of human sperm cryopreserved with the two types of CPCs, and identify the susceptible proteins that play key roles for sperm function and fertility.

Methods

The present study compared the cryosurvival of human sperm frozen with the two different CPCs and identified the sperm proteomic changes by using the isobaric tags for relative and absolute quantification labeling technique coupled with 2D LC–MS/MS analysis after freezing and thawing.

Results

Our results indicated that sperm cryopreserved with CV showed higher values for percentage of motile sperm and forward activity rate than those with CS. Compared to fresh sperm, 434 and 432 proteins were differentially identified in human sperm cryopreserved with CS and CV, respectively.

Conclusion

The proteomic profiles of human sperm are greatly affected by cryopreservation with either type of CPC. GO analysis revealed that most of the differentially identified sperm proteins enriched in the extracellular membrane-bounded organelles, cytoplasm and cytosol. In addition, 106 susceptible proteins having known identities related to sperm functions were identified. In general, cryovial seems to be the preferred CPC for human sperm cryopreservation based on the post-thaw motility parameters and the effect on sperm proteomic profiles. These results are beneficial for the insight into the understanding of the cryoinjury mechanism of sperm and the development of human sperm cryopreservation strategies.

Electronic supplementary material

The online version of this article (10.1186/s12014-019-9244-2) contains supplementary material, which is available to authorized users.

A new role for RU486 (mifepristone): it protects sperm from premature capacitation during cryopreservation in buffalo

The objective of this study was to determine the mechanism by which RU 486 (mifepristone) protects sperm to undergo premature capacitation during cryopreservation. For this, semen ejaculate (n = 20) was divided into four equal fractions and diluted using egg yolk-based extender supplemented with different concentrations of RU 486 (0, 5, 10 and 20 µM) and cryopreserved. We found that RU 486 did not impair the post-thaw sperm kinetics and motility but prevented cholesterol efflux, calcium influx, and protected CatSper channels during cryopreservation. The RU 486 protected sperm from premature capacitation which was confirmed by intracellular calcium level, expression of tyrosine phosphorylated proteins (75 and 80 kDa) and CTC (chlortetracycline) assay. Furthermore, antioxidant ability of RU 486 was reflected by the ferric reducing ability, lower production of sperm malondialdehyde and intracellular reactive oxygen species. Also, we demonstrated that RU 486 treated sperm underwent normal capacitation, zona pellucida binding and zygote cleavage indicating normal fertilizing ability of sperm. In conclusion, we report a new role of RU 486 in protecting buffalo sperm from premature capacitation during cryopreservation.