Effects of cryopreservation on cAMP-dependent protein kinase and AMP-activated protein kinase in Atlantic salmon (Salmo salar) spermatozoa: Relation with post-thaw motility

Selenium nanoparticles improve fish sperm quality by enhancing glucose uptake capacity via AMPK activation

Appropriate additives can provide a suitable physiological environment for storage of fish sperm and facilitate the large-scale breeding of endangered species and commercial fish. Suitable additives for fish sperm storage in vitro are required for artificial insemination. This study evaluate the effects of 0.1, 0.5, 1.5, and 4.5 mg/L selenium nanoparticles (SeNPs) on the quality of Schizothorax prenanti and Onychostoma macrolepis sperm storage in vitro at 4 °C for 72 h. We found that 0.5 mg/L SeNPs was a suitable concentration for maintaining the normal physiological state of O. macrolepis sperm during storage at 4 °C (p < 0.05). Higher adenosine triphosphate (ATP) content of O. macrolepis sperm before and after activation was present at that concentration. To further explore the potential mechanism of action of SeNPs on O. macrolepis sperm, western blotting and glucose uptake analyses were performed. The results implied that after 24 h of in vitro preservation, 0.5 mg/L SeNPs significantly improved p-AMPK levels and glucose uptake capacity of O. macrolepis sperm, while compound C (CC), the inhibitor of activated AMP-activated protein kinase (p-AMPK), significantly restricted the function of SeNPs on stored sperm. Similar effects of 0.5 mg/L SeNPs were found on Schizothorax prenanti sperm. Our study demonstrates that SeNPs maintained ATP content and O. macrolepis and Schizothorax prenanti sperm function during storage in vitro for 72 h, possibly because SeNPs enhanced the glucose uptake capacity of sperm by maintaining the level of p-AMPK.

Sperm quality parameters, fertilizing potential, metabolites, and DNA methylation in cold-stored and cryopreserved milt from Atlantic salmon (Salmo salar L.)

Cold storage and freezing/thawing of milt may affect sperm functionality and the subsequent fertilization ability of milt. This study aimed to investigate sperm quality parameters and fertilization potential of Atlantic salmon milt, stored cold and subsequently cryopreserved, using different storage conditions. The objective was also to assess if analysis of milt metabolites and sperm DNA methylation signatures could be applicable to further elucidate sperm quality and fertilization following preservation. Milt samples were collected from eight mature Atlantic salmon males and stored for 4 days at 2°C and 8°C. Samples were taken on day one of storage at 2°C and on day four of storage at 2°C and 8°C. Storage for 4 days at 8°C is expected to be detrimental to sperm quality, and was included to create contrasts. Correspondingly, aliquots of cold-stored milt were prepared for cryopreservation, resulting in a total of six experimental conditions. Samples from all six experimental conditions were used in fertilization trials and analyzed for sperm viability, motility, ATP content, DNA fragmentation index, and High DNA stainability. In addition, milt samples from four of the males were analyzed for targeted metabolites and DNA methylation signatures by reduced representation bisulfite sequencing. The fertilization trials were performed using sperm:egg ratios of 75 × 103 and 500 × 103, respectively. Storage duration, temperature, and cryopreservation of cold-stored milt influenced several sperm quality parameters, metabolites, and DNA methylation signatures. The total motility, progressive motility, ATP, and velocity parameters were the sperm parameters with the strongest correlation to fertilization rates (p < 0.01). Several metabolites were correlated with fertility rates in both cold-stored and cryopreserved samples (p < 0.05). The fertilizing capacity of cold-stored milt was significantly reduced after 4 days of storage at 8°C, while corresponding cryopreserved milt showed reduced fertilization at both storage temperatures (2°C and 8°C) (p < 0.05). The results indicate that cryopreservation of milt stored for 1 day does not compromise either fertilization ability or DNA methylation signatures.

A new role of H89: Reduces capacitation-like changes through inhibition of cholesterol efflux, calcium influx, and proteins tyrosine phosphorylation during sperm cryopreservation in buffalo

It is a known fact that cryopreservation initiates premature capacitation in spermatozoa during the cryopreservation process. Protein tyrosine phosphorylation is a landmark of cascade reaction accountable for capacitation or capacitation-like changes in spermatozoa. Therefore, our hypothesis was to test an inhibitor (H89) that reversibly inhibits the cascade reaction responsible for capacitation during the cryopreservation process but does not hamper normal capacitation and fertilizing ability of sperm. For this, sixteen ejaculates were collected from Murrah buffalo bulls (n = 4). Each ejaculate was divided into four equal aliquots and diluted in an egg yolk-based semen dilutor supplemented with 0, 2, 10, and 30 μM concentrations of H89 and cryopreserved. Interestingly, H89 reduces cholesterol efflux from spermatozoa and protects spermatozoa from membrane damage during the cryopreservation process. H89 did not prevent lipid peroxidation of the sperm membrane. H89 reduced intracellular calcium concentration in spermatozoa in a dose-dependent manner, but tyrosine phosphorylation reduction was observed in the 2 and 10 μM H89 groups. The CTC assay revealed that the percentage of uncapacitated spermatozoa in different treatment groups increases in a dose-dependent manner. In the in vitro capacitation medium, the effect of H89 is abolished and spermatozoa underwent normal capacitation, but H89-treated spermatozoa attached to zona pellucida in large numbers compared to untreated spermatozoa. In conclusion, H89 does not only inhibit tyrosine phosphorylation of spermatozoa but it reduces cholesterol efflux and calcium influx, and ultimately reduces capacitation-like changes during the cryopreservation process.

Epicatechin Prevents Cryocapacitation of Bovine Spermatozoa through Antioxidant Activity and Stabilization of Transmembrane Ion Channels

Epicatechin (EPC) is a flavonoid belonging to the family of catechins; it has been described as a powerful scavenger of a wide spectrum of reactive oxygen species (ROS) and a modulator of ex vivo sperm vitality. In this study, we assessed the potential protective abilities of EPC on cryopreserved bovine spermatozoa. We focused on conventional quality parameters, as well as the oxidative profile of spermatozoa alongside capacitation patterns, and expression profiles of proteins involved in the process of capacitation. Semen samples were cryopreserved in the presence of 25, 50 or 100 μmol/L EPC and compared to native semen (negative control) as well as ejaculates frozen in the absence of EPC (positive control). A dose-dependent improvement of conventional sperm quality parameters was observed following EPC administration, particularly in case of the sperm motility, membrane, acrosome and DNA integrity in comparison to the positive control. Experimental groups exposed to all EPC doses presented with a significantly lower proportion of capacitated spermatozoa as opposed to the positive control. While no significant effects of EPC were observed in cases of superoxide production, a significant decrease in the levels of hydrogen peroxide and hydroxyl radical were recorded particularly in the experimental groups supplemented with 50 and 100 μmol/L EPC. Western blot analysis revealed that supplementation of particularly 100 μmol/L EPC to the semen extender prevented the loss of the cation channel of sperm (CatSper) isoforms 1 and 2, sodium bicarbonate cotransporter (NBC) and protein kinase A (PKA), which play important roles in the process of sperm capacitation. In summary, we may hypothesize that EPC is particularly effective in the stabilization of the sperm membrane during the freeze-thaw process through its ability to quench ROS involved in damage to the membrane lipids and to prevent the loss of membrane channels crucial to initiate the process of sperm capacitation. These attributes of EPC provide an additional layer of protection to spermatozoa exposed to low temperatures, which may be translated into a higher post-thaw structural integrity and functional activity of male gametes.

Metformin improves fish sperm quality by regulating glucose uptake capacity during in vitro storage

A suitable additive for fish sperm storage in vitro is necessary for artificial reproduction. In this study, we evaluated the effects of different concentrations (100, 200, 400, and 800 µmol/L) of metformin (Met) on Schizothorax prenanti and Onychostoma macrolepis sperm under storage in vitro for 72 h. Compared with the control group, 400 µmol/L Met was more effective at improving the quality and fertilization capacity of S. prenanti sperm by increasing the adenosine triphosphate (ATP) content within the sperm. Further study found that Met stabilized the ATP level by enhancing the glucose uptake in S. prenanti sperm, and this effect might be associated with the activation of AMP-activated protein kinase (AMPK) in sperm. In this study, we also found that glucose could be absorbed by the sperm of S. prenanti, which was mainly accumulated in the midpiece of S. prenanti sperm, where mitochondria were located. In addition, Compound C significantly inhibited the beneficial effects of Met on the quality and glucose uptake capacity of S. prenanti sperm by inhibiting AMPK phosphorylation. These results revealed that AMPK played an important role in vitro sperm storage, and Met maintained ATP content and increased the storage time of S. prenanti sperm in vitro for 72 h, possibly due to Met enhanced glucose uptake capacity of sperm by activating AMPK. Similarly, the beneficial effects of Met on S. prenanti sperm were also found in O. macrolepis sperm, suggesting that Met may hold great promise for the practice of storing fish in vitro.

In Vitro versus Cryo-Induced Capacitation of Bovine Spermatozoa, Part 2: Changes in the Expression Patterns of Selected Transmembrane Channels and Protein Kinase A

Since the molecular similarities and differences among physiological capacitation and cryocapacitation have not been studied in detail, this study was designed to assess the gene and protein expression levels of the Cation channel of sperm (CatSper) 1 and 2, sodium bicarbonate (Na+/HCO3−) cotransporter (NBC) and protein kinase A (PKA) in un-capacitated (control), in vitro capacitated (CAP) and cryopreserved (CRYO) bovine spermatozoa. All samples were subjected to motility evaluation using the computer assisted sperm analysis and chlortetracycline (CTC) assay for the assessment of the capacitation patterns. Furthermore, quantitative reverse transcription PCR (qRT-PCR) and Western blots were used to monitor the expression patterns of the selected capacitation markers. The results showed a significant reduction in the gene and protein expression levels of CatSper1 and 2 in the CRYO group when compared to the CAP group (p < 0.0001). In the case of NBC, the results were not significantly different or were inconclusive. While a non-significant down-regulation of PKA was found in the CRYO group, a significant reduction in the expression of the PKA protein was found in frozen-thawed spermatozoa in comparison to the CAP group (p < 0.05). In conclusion, we may hypothesize that while in vitro capacitated and cryopreserved spermatozoa exhibit CTC-patterns consistent with capacitation events, the molecular machinery underlying CTC-positivity may be different.

In vitro versus cryo-induced capacitation of bovine spermatozoa, part 1: Structural, functional, and oxidative similarities and differences

Low temperatures during cryopreservation activate a cascade of changes, which may lead into irreversible damage and reduction of the fertilization potential, including the process of premature capacitation. The aim of our study was to evaluate the range of cell damage following the cryopreservation process and possible activation of cryocapacitation in bovine spermatozoa. For the experiments semen samples were obtained from 30 sexually mature Holstein bulls. Within the analysed parameters, we focused on the functional activity, structural integrity, capacitation status and oxidative profile. The samples were divided into three experimental groups, control (CTRL), in vitro capacitated (CAP) and cryopreserved (CRYO). Based on the collected data, there was a significant decrease in the sperm motility, mitochondrial membrane potential and concentration of cyclic adenosine monophosphate in the CRYO group when compared to CAP and CTRL (P<0.0001). A significant decrease (P<0.01; P<0.0001) in the membrane and acrosome integrity as well as DNA fragmentation index and a significant increase (P<0.0001) of necrotic cells were observed in the CRYO group. Following capacitation, a significant increase (P<0.01; P<0.0001) was recorded in the number of cells which underwent the acrosome reaction in the CRYO group against CAP and CTRL. Changes in the oxidative profile of the CRYO group indicates an increase (P<0.0001) in the reactive oxygen species generation, except for the superoxide radical, which was significantly higher (P<0.0001; P<0.001) in the CAP group in comparison with CRYO and CTRL. In summary, premature capacitation may be considered a consequence of cryopreservation and the assessed parameters could serve as physical markers of cryogenic damage to bovine spermatozoa in the future.

Saccharides Influence Sperm Quality and Expressions of Motility and Fertilization-Associated Genes in Cryopreserved Sperm of Pacific Abalone, Haliotis discus hannai

Pacific abalone, Haliotis discus hannai, is a highly commercial seafood in Southeast Asia. The present study aimed to determine the influence of saccharides and vitamins on post-thaw sperm quality, ATP content, fertilization capacity, hatching capacity, and mRNA content of motility and fertilization-associated genes of Pacific abalone. Sperm cryopreserved using saccharides improved the post-thaw sperm quality including motility, acrosome integrity (AI), plasma membrane integrity (PMI), and mitochondrial membrane potential (MMP). However, vitamins (l-ascorbic acid) did not result in any significant improvement in sperm quality. Sperm cryopreserved using saccharides also improved ATP content, DNA integrity, and mRNA content of motility and fertilization-associated genes of post-thaw sperm than sperm cryopreserved without saccharides. Among sperm cryopreserved using different saccharides, post-thaw sperm quality indicators (except PMI) and mRNA content of motility and fertilization-associated genes did not show significant differences between sperm cryopreserved using 3% sucrose (S) combined with 8% dimethyl sulfoxide (DMSO) and sperm cryopreserved using 1% glucose (G) combined with 8% ethylene glycol (EG). However, sperm cryopreserved using 3% S + 8% DMSO showed higher post-thaw sperm quality (motility: 58.4 ± 2.9%, AI: 57.1 ± 3.2%, PMI: 65.3 ± 3.3%, and MMP: 59.1 ± 3.2%), ATP content (48.4 ± 1.8 nmol/ml), and % DNA in tail (2.09 ± 0.20%) than sperm cryopreserved using other saccharides. When sperms were cryopreserved using 3% S + 8% DMSO, the mRNA content of motility (heat shock protein 70, HSP70; heat shock protein 90, HSP90; protein kinase A, PKA-C; axonemal protein 66.0, Axpp66.0; and tektin-4) and fertilization-associated (sperm protein 18 kDa, SP18 kDa) genes were higher than in sperm cryopreserved using other saccharides. However, changes in the mRNA contents of these genes were insignificant between sperm cryopreserved using 3% S + 8% DMSO and 1% G + 8% EG. Taken together, these results indicate that cryopreservation using 3% S + 8% DMSO can improve post-thaw sperm quality and mRNA contents better than other examined cryoprotectants. The present study suggests that 3% S + 8% DMSO is a suitable cryoprotectant for sperm cryopreservation and molecular conservation of this valuable species.

Comparative Analysis of piRNA Profiles Helps to Elucidate Cryoinjury Between Giant Panda and Boar Sperm During Cryopreservation

Cryopreservation induces sperm cryoinjuries, including physiological and functional changes. However, the molecular mechanisms of sperm cryoinjury and cryoresistance are still unknown. Cryoresistance or the freeze tolerance of sperm varies across species, and boar sperm is more susceptible to cold stress. Contrary to boar sperm, giant panda sperm appears to be strongly freeze-tolerant and is capable of surviving repeated cycles of freeze-thawing. In this study, differentially expressed (DE) PIWI-interacting RNAs (piRNAs) of fresh and frozen-thawed sperm with different freeze tolerance capacity from giant panda and boar were evaluated. The results showed that 1,160 (22 downregulated and 1,138 upregulated) and 384 (110 upregulated and 274 downregulated) DE piRNAs were identified in giant panda and boar sperm, respectively. Gene ontology (GO) enrichment analysis revealed that the target DE messenger RNAs (mRNAs) of DE piRNAs were mainly enriched in biological regulation, cellular, and metabolic processes in giant panda and boar sperm. Moreover, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that the target DE mRNAs of DE piRNAs were only distributed in DNA replication and the cyclic adenosine monophosphate (cAMP) signaling pathway in giant panda, but the cAMP, cyclic guanosine monophosphate (cGMP), and mitogen-activated protein kinase (MAPK) signaling pathways in boar sperm were considered as part of the olfactory transduction pathway. In conclusion, we speculated that the difference in the piRNA profiles and the DE piRNAs involved in the cAMP signaling pathway in boar and giant panda may have contributed to the different freeze tolerance capacities between giant panda and boar sperm, which helps to elucidate the molecular mechanism behind sperm cryoinjury and cryoresistance.

Odorant and Taste Receptors in Sperm Chemotaxis and Cryopreservation: Roles and Implications in Sperm Capacitation, Motility and Fertility

Sperm chemotaxis, which guide sperm toward oocyte, is tightly associated with sperm capacitation, motility, and fertility. However, the molecular mechanism of sperm chemotaxis is not known. Reproductive odorant and taste receptors, belong to G-protein-coupled receptors (GPCR) super-family, cause an increase in intracellular Ca²⁺ concentration which is pre-requisite for sperm capacitation and acrosomal reaction, and result in sperm hyperpolarization and increase motility through activation of Ca²⁺-dependent Cl^¯ channels. Recently, odorant receptors (ORs) in olfactory transduction pathway were thought to be associated with post-thaw sperm motility, freeze tolerance or freezability and cryo-capacitation-like change during cryopreservation. Investigation of the roles of odorant and taste receptors (TRs) is important for our understanding of the freeze tolerance or freezability mechanism and improve the motility and fertility of post-thaw sperm. Here, we reviewed the roles, mode of action, impact of odorant and taste receptors on sperm chemotaxis and post-thaw sperm quality.