Effect of cholesterol loaded cyclodextrin supplementation on tyrosine phosphorylation and apoptosis like changes in frozen thawed Hariana bull spermatozoa

Addition of low concentration of cholesterol-loaded cyclodextrin (CLC) has a positive effect on cryopreserved canine spermatozoa evaluated by andrological and biophysical methods

BACKGROUND

This study was conducted to find the best concentration of cholesterol-loaded cyclodextrin (CLC) which has a positive impact on canine post thaw semen quality. Three different concentrations of CLC (0.83 mg/ml; 1.66 mg/ml; 3.32 mg/ml) and 2-hydroxylpropyl-beta-cyclodextrin (HBCD) (1.66 mg/ml) were used in addition to cryopreservation extender and compared with the control after thawing. Samples were assessed using computer-assisted semen analyzer (CASA), flow cytometry, fluorimeter by measuring the fluorescence anisotropy (ANISO) and determining the generalized membrane polarization (GP).

RESULTS

An addition of 0.83 mg/ml CLC significantly increased the percentage of progressive motile (PROG) and rapid spermatozoa (RAP) (P < 0.05). 1.66 mg/ml HBCD decreased progressive motility of spermatozoa and population with rapid movement relative to the control (P < 0.05). Furthermore, the groups with an addition of 1.66 mg/ml and 3.32 mg/ml of CLC, as well as the group with only cyclodextrin, increased percentage of dead spermatozoa without lipid peroxidation and decreased percentage of viable spermatozoa without LPO which was lower in these groups than in the control (P < 0.05). Other sperm parameters assessed on flow cytometer were not significantly different. The addition of CLC at 0.83 mg/ml and 3.32 mg/ml concentrations and 1.66 mg/ml of HBCD caused an increase in ANISO measured at 23 ºC (P < 0.05).

CONCLUSIONS

In conclusion, the results suggest that increasing cholesterol in the plasma membrane of canine spermatozoa can improve their freezability. However, only low concentrations of CLC may improve semen quality after thawing without adversely affecting other parameters.

Treatment with cholesterol just after thawing maintains the fertility of bull sperm

Freezing and thawing diminish sperm motility and fertility by disrupting the cholesterol balance in sperm plasma and organelle membranes. The aim of this study was to elucidate the mechanisms through which exogeneous cholesterol treatment enhances the quality of frozen-thawed bull sperm. The incorporation of cholesterol was investigated using boron-dipyrromethene (BODIPY)-cholesterol, and BODIPY signals were detected not only in the plasma membrane but also in the midpiece region immediately after thawing. The positive signal of cholesterol in the midpiece region was inhibited by a scavenger receptor class B Type I (SR-BI) inhibitor, block lipid transport 1 (BLT-1). To comprehend the role of exogenous cholesterol in the functions of the plasma membrane, propidium iodide (PI)/Annexin V and peanut agglutinin lectin (PNA) staining were performed. The results showed that treatment with exogenous cholesterol increased the number of acrosome-intact sperm and decreased the number of sperm with damage to the plasma membrane. Moreover, since BODIPY signals were also observed in the midpiece region, mitochondrial function was evaluated using a flux analyzer and a flow cytometer with 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl carbocyanine iodide (JC-1) staining, revealing an increase in the number of sperm with high-mitochondrial activity and oxygen consumption. Finally, to assess sperm fertility, computer-assisted sperm analysis (CASA) and IVF were carried out. Sperm velocities and fertilization rates in IVF were significantly enhanced by the addition of cholesterol just after thawing. Thus, the treatment with cholesterol after thawing protected the plasma membrane from the stress of thawing and maintained mitochondrial function, thereby preserving the fertilization ability of frozen-thawed bull sperm for conventional IVF and artificial insemination (AI). Therefore, the application of cholesterol just after thawing is a promising option for improving the fertility of frozen-thawed sperm.

Does Better Post-Thaw Motility of Dog Sperm Frozen with CLC Mean Better Zona Pellucida Binding Ability?

Even though the search for methods improving cryopreservation of canine spermatozoa led to an improvement of post-thaw quality, fertilizing results after insemination with frozen-thawed semen are still not satisfying. In this study, we focused on modification of spermatozoa membrane fluidity and investigated whether kinematic parameters as assessed by computer-assisted semen analyzer (CASA) can be improved. The primary aim of our study was to investigate whether the use of cholesterol-loaded cyclodextrins (CLC; 0.5 mg, 1 mg, 2 mg) and 2-Hydroxypropyl-ß-cyclodextrin (HBCD; 1 mg) positively influence capacitation status as examined by tyrosinphosphorylation, cholesterol efflux and zona binding assay (ZBA) of spermatozoa. The use of 0.5 mg of CLC increased the percentage of motile, progressive and rapid spermatozoa compared to the control. Addition of HBCD decreased motility and progressive motility of spermatozoa and the population with rapid movement in comparison to the control. The percentage of live spermatozoa without efflux of cholesterol compared to the control was increased when extender with 0.5 mg of CLC was used. There was no change in capacitation status. The zona binding ability of spermatozoa was significantly lower in the group with 0.5 mg of CLC than in the control. In conclusion, these results suggest that improvement of kinematic parameters does not necessarily coincide with better zona pellucida binding ability of spermatozoa.

Antioxidant additive melatonin in tris-based egg yolk extender improves post-thaw sperm attributes in Hariana bull

In the study, melatonin, a known antioxidant pineal peptide was used as an additive in the tris-egg yolk glycerol-based semen extender in Hariana bull semen and post-thaw sperm characters were evaluated. In the study, Group I was a control without melatonin; and Group II, III, and IV were having 0.5 mM, 1 mM, and 2 mM melatonin/80 × 10⁶ spermatozoa, respectively were treatment groups. Thirty-two semen ejaculates from 4 Hariana bulls were processed for freezing and post-thaw sperm characteristics were evaluated. Sperm motility, velocity, the viability with intact membrane, and total antioxidant capacity were markedly (P < 0.05) improved in Group IV compared to all other groups. The lipid peroxidation and total protein carbonylation were substantially (P < 0.05) decreased in Group IV compared to all other groups. The population of cryocapacitated, acrosome-reacted, and apoptotic-like spermatozoa were significantly (P < 0.05) decreased in Group IV. Further, the relative band intensity of 74 kDa protein and percent of spermatozoa showing positive immune reactivity to tyrosine-phosphorylated proteins was decreased in Group IV. The progesterone-receptor ligand binding, in vitro capacitation response, and Vanguard distance were markedly (P < 0.05) improved in Group IV. In summary- Group IV having 2 mM melatonin was found to be optimal in providing cryoprotective effects to Hariana bull spermatozoa after freezing-thawing and can be suitably used as a semen additive during semen cryopreservation.

Ameliorative effect of silymarin on the quality of frozen-thawed boar spermatozoa

Although Silymarin (SMN) has powerful antioxidant properties, little is known about its effects on the quality of frozen-thawed boar sperm. The present study aimed to evaluate the influences of SMN added to the thawing extender on boar sperm parameters essential for fertilization. The frozen-thawed semen was diluted in a Modena thawing extender supplemented with different concentrations of SMN (0, 5, 10, 20 and 50 μM respectively), and then the changes in quality parameters, antioxidant capacity, mitochondrial function and in vitro fertilization (IVF) capability of frozen-thawed sperm were assessed. Here we demonstrated that the motility, plasma membrane integrity and acrosomal integrity of frozen-thawed sperm improved efficiently by SMN (p < .05). In antioxidant parameters evaluation, the tROS level and MDA content of frozen-thawed spermatozoa were reduced in the 20 μM SMN group, while the T-AOC activity significantly increased (p < .05), indicating that the supplementation with SMN can promote the antioxidant capacity of frozen-thawed boar sperm. Besides, we also discovered that the addition of SMN significantly upregulated ATP content and enhanced the mitochondrial activity of sperm. More interestingly, SMN promoted the activities of mitochondrial respiratory chain complexes (MRCC) I, II, III and IV in frozen-thawed sperm significantly. Functionally, the higher penetration rate and increased total efficiency of fertilization were observed in the 20 μM SMN group. In summary, supplementation with SMN in the thawing medium ameliorates the quality of frozen-thawed boar sperm by enhancing mitochondrial respiratory capacity, producing large amounts of ATP and regulating ROS formation.

Improvement of Fertilization Capacity and Developmental Ability of Vitrified Bovine Oocytes by JUNO mRNA Microinjection and Cholesterol-Loaded Methyl-β-Cyclodextrin Treatment

Vitrification of oocytes is crucial for embryo biotechnologies, germplasm cryopreservation of endangered and excellent female animals, and the fertility of humans. However, vitrification significantly impairs the fertilization ability of oocytes, which significantly limits its widely used application. JUNO protein, a receptor for Izumo1, is involved in sperm-oocyte fusion and is an indispensable protein for mammalian fertilization, and its abundance is susceptible to vitrification. However, it is still unclear how vitrification reduces the fertilization capacity of bovine oocytes by affecting JUNO protein. This study was designed to investigate the effect of vitrification on the abundance and post-translational modifications of JUNO protein in bovine oocytes. Our results showed that vitrification did not alter the amino acid sequence of JUNO protein in bovine oocytes. Furthermore, the liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis results showed that vitrification significantly reduced the number and changed the location of disulfide bonds, and increased the number of both phosphorylation and glycosylation sites of JUNO protein in bovine oocytes. Finally, the fertilization capacity and development ability of vitrified oocytes treated with 200 pg JUNO mRNA microinjection and cholesterol-loaded methyl-β-cyclodextrin (CLC/MβCD) were similar to those of fresh oocytes. In conclusion, our results showed that vitrification of bovine oocytes did not alter the protein sequence of JUNO, but induced post-translational modifications and changed protein abundance. Moreover, the fertilization and development ability of vitrified bovine oocytes were improved by the combination treatment of JUNO mRNA microinjection and CLC/MβCD.

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.

Interplay mechanisms between progesterone and endocannabinoid receptors in regulating bull sperm capacitation and acrosome reaction

After ejaculation, sperm show a limited capacity for transcription and translation. In the oviduct, most of the signalling in sperm is nongenomic and is mediated through membrane receptors. Studies have shown that the cation channel of sperm (CatSper), cAMP, cGMP, protein kinases, and tyrosine phosphorylation are involved in the nongenomic signalling of progesterone (P4) in sperm. However, it is not known whether there is an interplay between P4 and cannabinoid receptors 1 and 2 (CB1 and CB2), transient receptor potential vanilloid 1 (TRPV1), CatSper channels, cAMP, inositol trisphosphate receptor (IP3R), and mitogen-activated protein kinase (MAPK); these potential regulators are involved in the regulation of capacitation and the acrosome reaction. In the present study, selective blockers of CB1, CB2, TRPV1, CatSper channels, cAMP, protein kinase A (PKA), IP3R, and MAPK were used to identify their involvement in P4-mediated bull sperm capacitation and the acrosome reaction. Selective blocking of any one of the molecules caused a significant reduction in P4 signalling (p < 0.05). Interestingly, blocking these molecules in combination followed by treatment with P4 resulted in the complete absence of capacitation and the acrosome reaction. Blocking a single receptor was not able to eliminate the P4-induced capacitation and the acrosome reaction. In addition to the CB1 and CB2 receptors, there may be other signalling pathways that mediate P4 signalling. In conclusion, P4 signalling exhibited interplay with the cannabinoid receptors. The regulation of sperm capacitation and the acrosome reaction also involved cAMP, PKA, l-type and T-type calcium channels, TRPV1, inositol trisphosphate, and MAPK.

Effect of Synthetic Cholesterol (Synthechol®) Supplementation in an Egg Yolk-free Extender on Dog Sperm Cryopreservation

BACKGROUND: SyntheChol® is a new synthetic, non-animal-derived cholesterol that is easily dissolved in ethanol, ready to use, and behaves in a similar way as natural cholesterol. Therefore, it could be used as a substitute of natural cholesterol in dog sperm freezing extender. OBJECTIVE: To evaluate the effect of supplementing an egg yolk-free (EY-free) extender with synthetic cholesterol (SyntheChol®) on cryopreserved dog sperm. MATERIALS AND METHODS: Spermatozoa (1 × 108 sperm/mL) were suspended in EY-free extender supplemented with 0% (control), 0.25, 0.5, 1, 2, 4, or 6% SyntheChol® (Extender 1), cooled at 4 °C for 1 h, and diluted (1:1, v/v) with Extender 1 containing 1 M glycerol. The spermatozoa were then cooled to 4 °C for 30 min. Sperm-containing straws were frozen using LN2 vapor. Sperm motility (computer-assisted sperm analysis, CASA), sperm membrane integrity (SYBR-14 and PI staining), and acrosome integrity (FITC-PSA) were evaluated after thawing. Thereafter, optimal concentrations were determined (0.25, 0.5, 1, or 2%) and used to evaluate reactive oxygen species (ROS) generation, apoptosis, and the gene expression of motility-related sperm mitochondria-associated cysteine-rich protein, apoptosis-related B-cell lymphoma 2 (BCL2), and BCL2-associated X protein ( BAX) in cryopreserved sperm. RESULTS: Sperm progressive motility, membrane integrity, and acrosome integrity were markedly greater in the SyntheChol®-supplemented groups (0.25, 0.5, 1, or 2%) than in the control group. Only BAX expression was significantly reduced in the SyntheChol® groups (0.25, 1, or 2%) compared with the control group. However, there were no significant effects on the ROS generation or apoptosis index. CONCLUSION: SyntheChol® (0.25, 1, or 2%) proved to be effective in reducing the BAX gene expression level and improving sperm progressive motility, and membrane and acrosome integrity.

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.

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.

Evaluation of Microscopic, Flow Cytometric, and Oxidative Parameters of the Frozen-Thawed Bull Sperm in a Freezing Extender Containing Myo-Inositol

Introduction: This research was conducted to assess the effect of myo-inositol (MYO) in the freezing extender on the semen quality and oxidative stress parameters of frozen-thawed bull sperm. Materials and Methods: Semen samples were obtained from four bulls (n = 24, six ejaculates per bull), twice a week, and diluted into four equal aliquots in freezing extenders containing different concentrations of MYO (0, 2, 3, and 4 mg/mL). After a freezing/thawing process, velocity parameters, plasma membrane integrity, apoptosis status, malondialdehyde level, and oxidative stress parameters were assessed. Results: Supplementation of freezing extender with 3 mg/mL MYO resulted in higher rapid motility (62.22% ± 2.63%), progressive motility (77.45% ± 2.65%), viability (78% ± 0.91%), plasma membrane integrity (86 ± 0.85), catalase (20.03 ± 0.39 U/mL) activity, and lower significance of lipid peroxidation (3.60 ± 0.15 nmol/dL) than those of the control group (p < 0.05). A significantly lower percentage of normal morphology and intact acrosomes were observed for frozen-thawed semen in the extender supplemented with 4 mg/mL MYO than those of the control group (p < 0.05). Freezing of the sperm in the extender containing 3 mg/mL of MYO leads to a higher percentage of live cells (38.3 ± 2.76). Beat-cross-frequency, amplitude of lateral head displacement, linearity, total antioxidant capacity, total peroxidase activity, early apoptotic status, and superoxide dismutase activities were not affected by MYO levels in the extenders (p > 0.05). Conclusion: The findings of this study suggest that the supplementation of the freezing extender with 3 mg/mL MYO resulted in a higher quality of frozen-thawed bull sperm.

Cholesterol-loaded cyclodextrin attenuates dilution effect and improves quality of bovine low sperm insemination doses during cryopreservation

In the present study, the effect of cholesterol-loaded cyclodextrin (CLC) on the quality of low sperm doses at post-thaw was evaluated. Twenty four ejaculates (6 from each bull) were collected and split into eight aliquots. First four aliquots were diluted up to 20-, 15-, 10- and 5-million sperm/0.25 ml, and remaining four were treated with CLC at the rate of 1 mg/120 million spermatozoa, followed by dilution up to 20-, 15-, 10- and 5-million sperm/0.25 ml. The diluted semen was equilibrated, cryopreserved and evaluated post-thaw. The averages of total motility, progressive motility, average path velocity, straight linear velocity, membrane intact spermatozoa and noncapacitated spermatozoa were higher (p < .05) in CLC-treated sperm doses compared to control ones. However, the moribund spermatozoa, capacitated spermatozoa and acrosome-reacted spermatozoa were reduced (p < .05) in CLC-treated spermatozoa compared to control. The curvilinear velocity and linearity did not differ (p > .05) between control and CLC-treated sperm doses. In conclusion, treatment of spermatozoa with CLC at the rate of 1 mg/120 million spermatozoon attenuates the dilution effect and improves the quality of bovine low sperm insemination doses during cryopreservation; hence it could be a favourable cryoprotectant for preserving bovine semen at higher dilutions.

Implications of cryopreservation on structural and functional attributes of bovine spermatozoa: An overview

Sperm cryopreservation is an important adjunct to assisted reproduction techniques (ART) for improving the reproductive efficiency of dairy cattle and buffaloes. Improved understanding of mechanisms and challenges of bovine semen cryopreservation is vital for artificial insemination on a commercial basis. Although cryopreservation of bovine spermatozoa is widely practiced and advanced beyond that of other species, there are still major gaps in the knowledge and technology. Upon cryopreservation, disruption of spermatozoal plasma membrane configuration due to alterations in metabolic pathways, enzymes and antioxidants activity add to lower efficiency with loss of sperm longevity and fertilising ability. Therefore, the effective amalgamation of cryo-variables like ambient temperature, cooling and thawing rates, nucleation temperature, type and concentration of the cryoprotectant, seminal plasma composition, free radicals and antioxidant status are required to optimise cryopreservation. Novel strategies like supplementation of cholesterol-loaded cyclodextrins (CLC), nanovesicles, osteopontin, antioxidants, etc., in an extender and recent techniques like nano-purification and modified packaging have to be optimised to ameliorate the cryodamage. This article is intended to describe the basic facts about the sperm cryopreservation process in bovine and the associated biochemical, biophysical, ultra-structural, molecular and functional alterations.

Freezing-thawing induces deprotamination, cryocapacitation-associated changes; DNA fragmentation; and reduced progesterone sensitivity in buck spermatozoa

In the present study, there was evaluation of cryocapacitation-associated changes, apoptotic-like changes, deprotamination, total antioxidant capacity (TAC), and in vitro sperm functional attributes in Barbari bucks after freezing-thawing. The correlation between deprotamination and sperm functional characteristics was established. Using immunoblotting procedures, there was detection of the presence of a single 28-kDa protein band corresponding to protamine-1. The localization in the head region of the spermatozoa was further validated by an immunofluorescence test. Capacitated (B-) and acrosome-reacted (AR-) pattern spermatozoa, spermatozoa with the externalization of phosphatidylserine and a relatively lesser mitochondrial transmembrane potential, and deprotamination and DNA fragmentation was greater (P < 0.05) after freezing-thawing and indicated there were cryocapacitation- and apoptotic-like changes, respectively. Furthermore, the detection of phosphorylation of tyrosine-containing proteins with use of immunoblotting and immunofluorescence procedures confirmed there were cryocapacitation-like changes in the buck spermatozoa after freezing-thawing. Total antioxidant capacity (TAC), in vitro thermal resistance response, Vanguard distance, progesterone sensitivity, and in vitro capacitation response were less (P < 0.05) in the spermatozoa after freezing-thawing compared with spermatozoa after initial dilution and equilibration. Deprotamination (chromomycin A3-positive cells, CMA3+) and DNA fragmentation (TUNEL+ve) were positively correlated with B- and AR-pattern spermatozoa, while other values for other variables were negatively correlated. In conclusion, the results of this study indicated there was protamine-1 in buck spermatozoa and after freezing-thawing there was a loss of protamine-1 combined with cryocapacitation-associated changes and apoptotic-like changes in buck spermatozoa. Spermatozoa deprotamination might be attributed to increased DNA fragmentation, resulting in compromised fertilizing capacity of buck spermatozoa.

The proportion of tyrosine phosphorylated spermatozoa in cryopreserved semen is negatively related to crossbred bull fertility

Sub-fertility is a major problem in crossbred bulls. Identification of subtle differences in the quality of cryopreserved spermatozoa among bulls belonging to different fertility rankings would help determine the latent fertility of semen before their use at field conditions. In the present study, we assessed the status of tyrosine phosphorylation, membrane integrity and acrosome reaction of cryopreserved spermatozoa in crossbred bulls (n = 22) with different levels of field fertility and assessed their relationship with fertility. Bulls were categorized into above-average (n = 4), average (n = 14) and below-average (n = 4) based on their different field fertility rates. The progressive sperm motility was significantly (P < 0.05) higher in above-average fertile bulls compared to either average or below-average fertile bulls whereas sperm membrane integrity and acrosomal reaction status did not differ among the three groups. The proportion of live tyrosine-phosphorylated spermatozoa were significantly (P < 0.05) higher in below-average and average fertile bulls compared to above-average bulls. Immunolocalization of protein tyrosine phosphorylation in spermatozoa revealed that the proportion of spermatozoa showing tyrosine phosphorylation at acrosome and post-acrosomal area (APA) and at acrosome, post-acrosome and tail (APAT) were significantly (P < 0.05) higher in below-average fertile bulls than other groups. The APA pattern (r = -0.605; P < 0.01) and APAT (r = 0.507; P < 0.05) pattern were significantly and negatively correlated with bull fertility. It was concluded that the proportion of live tyrosine-phosphorylated spermatozoa in cryopreserved semen was negatively related to bull fertility.

Cholesterol-loaded cyclodextrin is efficient in preserving sperm quality of cryopreserved ram semen with low freezability

Semen freezability is positive correlated with the cholesterol content in the sperm cell. Freeze-thawing mainly cause temperature chock and change on media osmolarity, which can modify plasma membrane lipids content and sperm conformation, resulting in decreased fertility. Therefore, the aim of this study is to investigate the effect of adding cholesterol-loaded cyclodextrin (CLC) to the cryopreservation process of ram semen with low freezability. For that, two experiments were performed using 5 ejaculates of 6 rams, totalizing 30 samples. For experiment 1 the following treatments were tested: in natura (IN), Tris solution (CON), CLC + Tris solution (CLC), and pure methyl-β-cyclodextrin + Tris solution (MCD). For experiment 2 treatments CON and CLC were tested in samples subdivided into three freezability classes: high (n = 10), intermediate (n = 10) and low (n = 10). Freezability classes were based on the variation of sperm motility between IN and CON groups from the first experiment. Sample analyzes included sperm motility, sperm morphology, plasma and acrosome membrane integrity, mitochondrial membrane potential, reactive oxygen species content, lipid peroxidation, and fluidity of plasma membrane. Results showed that CLC treatment was more efficient in maintaining sperm motility, integrity of plasma membrane, integrity of acrosome, and mitochondria membrane potential. In addition, CLC treatment in the groups with low and intermediate freezability showed improvement on progressive motility and percentage of rapid cells. In contrast, no difference was noted between CLC and CON treatments in the high freezability group. Therefore, the addition of CLC to semen extender improved sperm cryopreservation, especially in rams with low freezability.

Melatonin supplementation improves the intactness of plasma membrane and acrosomal membrane of cryopreserved spermatozoa in Hariana bull

Supplementation of MT @ 2 mM was more beneficial in cryopreservation of Hariana bull spermatozoa as evidenced from post-thawed sperm membrane integrity and acrosomal intactness. Melatonin can be recommended to be used @ 2 mM concentration into the semen extender to increase the post thaw sperm functional attributes in Hariana bull.

Functional insights into voltage gated proton channel (Hv1) in bull spermatozoa

Acid extrusion and intracellular alkalisation are the key events during sperm capacitation and these are mediated through proton gated channels (Hv1). Role of Hv1 in regulating sperm motility, capacitation and acrosome reaction has been documented in human spermatozoa; but no such data is available in bull spermatozoa; therefore, the present study was undertaken in Hariana bull spermatozoa. Sixty four ejaculates were collected from four Hariana bulls to investigate the functional involvement of Hv1 in regulation of sperm motility, capacitation and acrosome reaction in bull spermatozoa. Immunoblotting revealed the presence of a single band of 31.8 kDa corresponding to Hv1 in Hariana bull spermatozoa and immunoflourescence confirmed the positive immune-reactivity at principal piece of spermatozoa for Hv1. Functional study was carried out using 200 μM 2-Guanidinobenzimidazole (2-Guanidinobenzimidazole,selective Hv1 blocker) and 1 mM zinc chloride (potent Hv1 blocker), and 0.3 μM Anandamide (AEA), an activator of Hv1. Blocking of Hv1 resulted in significant (P < 0.05) reduction in progressive sperm motility (PSM). Activation of Hv1 with AEA also resulted in significant (P < 0.05) reduction in PSM till 1 h and thereafter, the PSM was restored and reduction was almost similar to that in control. However, during activation and inactivation of Hv1, per cent spermatozoa showing hyperactive motility were found to be markedly increased (20-30%) compared to 10-20% in control. 2-Guanidinobenzimidazole, zinc and AEA treated spermatozoa revealed significant (P < 0.05) increase in B-pattern of spermatozoa indicating induction of capacitation. Downstream signalling of Hv1 activation or inactivation seemed to be mediated through cAMP and PKA pathways. Catsper channels were found to be intimately associated with Hv1 function in regulating sperm motility. Blocking as well as activation of Hv1 resulted in significant (P < 0.05) reduction in sperm livability, spermatozoa having intact membrane, intact acrosome, and high mitochondrial transmembrane potential (MTP). Our findings evidently suggest that Hv1 channels are present in bull spermatozoa and these regulate sperm functions like hypermotility, capacitation and acrosome reaction through complex interplay between different pathways involving cAMP, PKC, and Catsper. Further studies are required to find out the possible relationship between Hv1 channels and other channels in regulating spermatozoa functions.

Exogenous cholesterol modulates oxidative stress and freezability of mithun spermatozoa

Effect of cholesterol loaded cyclodextrin (CLC) on improvement of semen quality parameters (SQPs) and deduction of oxidative stresses following cryopreservation in mithun was explored. Total 50 ejaculates were selected out of 105 collected based on preliminary SQPs. Sperm was treated with 1 mg (Gr II) and 2 mg (Gr III) of CLC/ 120×106 spermatozoa and without CLC served as control (Gr I). Diluted semen samples were cryopreserved at ultralow temperature. Frozen thawed samples were evaluated for motility (progressive forward [FPM]; in bovine cervical mucus penetration test [BCMPT] and in computer assisted sperm analyzer [CASA]), viability, total sperm and nuclear abnormality, intactness of plasma membrane and acrosome, intracellular enzymatic leakage and oxidative profile (Malondialdehyde; MDA). Result revealed a significant improvement in motility (FPM, BCMPT and CASA), viability, acrosomal integrity, cholesterol content and reduction of sperm and nuclear abnormalities, leakage of intracellular enzymes and oxidative stressors in 1 mg CLC treated group as compared to control. Moreover, intactness of acrosome and biochemical membrane was protected significantly in extender containing 1 mg CLC. Hence inclusion of mithun spermatozoa with CLC (1 mg/120×106) prior to freezing improved the survivability in cryopreservation. The results clearly indicated the beneficial effects of CLC supplementation on freezability by reducing cryodamage and protecting the spermatozoa integrity.

Molecular and functional insights into Transient Receptor Potential Vanilloid 1 (TRPV1) in bull spermatozoa

In view of the limited information available on functional significance of TRPV1 in regulating sperm functions, present study was undertaken on bull spermatozoa. Sixty four ejaculates were collected from four Hariana bulls and were used for molecular and functional characterisation of TRPV1. Immunoblotting using TRPV1 specific antibody revealed the presence of a single band of 104 kDa corresponding to TRPV1 in Hariana bull spermatozoa. Indirect immuno fluorescence revealed positive immune-reactivity to TRPV1 at acrosomal, pre-acrosomal, post acrosomal and flagellar regions of spermatozoa. Based on the results of pilot study dose-response analysis, doses of anandamide (AEA; 0.3 μM) and capsazepine (Cp; 10 μM) were selected for further studies. Three groups of semen samples (control 100 μL diluted semen having 1 × 10⁶ spermatozoa; anandamide (3 μL AEA+97 μL of diluted semen containing 1 × 10⁶ spermatozoa and Cp (1 μL Cp+99 μL of diluted semen containing 1 × 10⁶ spermatozoa) were used to study the functional involvement of TRPV1 in bull spermatozoa. Blocking of TRPV1 with Cp resulted in significant (P < 0.05) reduction in progressive sperm motility (PSM) as compared to control. With activation of TRPV1 using AEA also, PSM was significantly (P < 0.05) decreased till 1h and thereafter the PSM was sustained to the level as observed in control. However, both during blocking and activation of TRPV1, per cent spermatozoa showing hyperactive motility were significantly (P < 0.05) increased (20-30%) compared to the control. Treatment with both Cp and AEA revealed significant (P < 0.05) increase in B-pattern of spermatozoa in chlortetracycline hydrochloride (CTC) staining indicating induction of capacitation. Inhibition of soluble adenyl cyclase (sAC) with 99 nM KH7and protein kinase A (PKA) with 3 μM P9115 significantly (P < 0.05) decreased PSM both in the presence of Cp and AEA. Blocking as well as activation of TRPV1 showed significant (P < 0.05) reduction in sperm livability, intact membrane, intact acrosome, high mitochondrial transmembrane potential; hence indicating the involvement of TRPV1 in regulation of sperm functions in bulls. From the study-it was concluded that TRPV1 channels are found in bull spermatozoa and mediate number of sperm functions like motility, hypermotility, capacitation and acrosome reaction. Further studies are required to find out the possible relationship between TRPV1 channels and other channels in regulating spermatozoa function and possible mechanisms associated with TRPV1 activation as well as its role in sperm function regulation.

Cyclodextrins or cholesterol-loaded-cyclodextrins? A better choice for improved cryosurvival of chicken spermatozoa

This study was designed to test if treating chicken sperm with i) the cyclodextrins 2-hydroxypropyl-β-cyclodextrin (HBCD) and methyl-β-cyclodextrin (MBCD) alone improve fresh, liquid-stored and cryopreserved semen quality, or ii) cholesterol-loaded cyclodextrins (CLCs): 2-hydroxypropyl-β-cyclodextrin loaded with cholesterol (HCLC) and methyl-β-cyclodextrin loaded with cholesterol (MCLC) enhance chicken semen quality for application to assisted reproductive technologies. Three consecutive experiments were performed with different concentrations of additives: Exp. 1: 1, 2, 4 mg of HBCD and MBCD in fresh and liquid stored semen; Exp. 2: 1, 2, 4 mg of HCLC and MCLC in fresh and liquid stored semen; and Exp. 3: 1, 2 mg of HBCD, HCLC, 1 mg MBCD, MCLC in cryopreserved and post-thaw storage semen. Sperm motility parameters were assessed by CASA system and comprehensive sperm characteristics were evaluated by flow cytometry. Supplementation with 4 mg HBCD, MBCD, HCLC and MCLC resulted in the lowest motility and functional parameters of fresh and stored spermatozoa for 24 h at 5 °C. After cryopreservation, spermatozoa stored with CLCs showed significantly lower progressive motility and velocity of movement, and exhibited the lowest percentage of cells with intact plasma membranes and acrosomes, mitochondrial activity and cells without apoptosis. These results indicated that CLCs did not improve chicken sperm viability after cryopreservation. However, spermatozoa treated with 2 mg HBCD showed higher proportion of motile sperm (28%; P < 0.01) together with higher proportion of sperm cells with high mitochondrial potential (25%; P < 0.05) compared to the control (18%; 21%, respectively) after 3 h of post-thaw storage. CLC, especially with methyl-β-cyclodextrin, appeared to be detrimental to chicken spermatozoa, causing apoptosis, impairment of mitochondrial potential, and damaged acrosomes and sperm plasma membranes.

Molecular characterization of voltage-gated potassium channel (Kv) and its importance in functional dynamics in bull spermatozoa

Present study was undertaken to characterize the voltage gated potassium channel (K_v 1.1) in bull spermatozoa using sixty four ejaculates collected from four Hariana bulls. Functional characterization was undertaken using a selective blocker of Kv channel, 4-Aminopyridine (4-AP) while molecular presence of Kv on bull spermatozoa by immunoblotting and indirect immunofluorescence. Three sets of 100 μL diluted sperm samples namely-negative control (100 μL of sperm dilution medium (SDM) containing 10 × 10⁶ cells), vehicle control (99 μL of SDM containing 10 × 10⁶ cells, and DMSO- 1  μL) and 4-AP treatment group (99 μL of SDM containing 10 × 10⁶ cells, and drug 1 μL 4-AP) were used in the study. Immunoblotting identified a single band of 56 kDa corresponding to Kv1.1 in Hariana bull spermatozoa. Immunolocalization showed the positive immunoreactivity at head, middle piece and principal piece of the spermatozoa for Kv 1.1. Blocking of Kv using 4-AP resulted in significant (p < 0.05) reduction in sperm progressive motility, per cent capacitated spermatozoa (B-pattern) and acrosome reacted (AR-pattern) spermatozoa, while significant (P < 0.05) increase in per cent swollen spermatozoa. Blocking of Kv channels resulted in significantly (P < 0.05) increased percentage of spermatozoa with lower mitochondrial transmembrane potential. Computer assisted semen analysis (CASA) of motion and kinematic parameters in 4-AP treated spermatozoa indicated reduction in sperm motion parameters like LIN, STR, VSL and VAP and higher ALH, VCL, and BCF indicating hyperactivity of spermatozoa. Based on our findings, it may be concluded that voltage-gated potassium channel (Kv) are present on bull spermatozoa and these are associated with functional dynamics of spermatozoa. However, based on our limited study, it is not possible to deduce that how these channels are associated with induction of hyperactivity. Therefore, further studies are warranted to unravel the mechanistic signaling pathways involved in Kv-mediated alterations in functional dynamics of spermatozoa.

Possible mechanisms of cholesterol-loaded cyclodextrin action on sperm during cryopreservation

Artificial insemination (AI) with cryopreserved semen has a pivotal role in wider dissemination of germplasm of elite livestock and also for conservation of various endangered species. Cryopreservation allows storage of semen for a prolonged period of time and facilitates greater exchange of genetic material among distant populations. Cryopreservation, however, leads to certain deleterious effects on sperm including premature induction of the acrosome reaction, reduced sperm motility and viability, and impaired sperm DNA integrity and fertility. During cooling procedures, membrane phase transitions take place, which result in micro-domain formation from aggregation of lipids, leading to impaired functions of the sperm membrane, and gap formation between gel and fluid domains. Cyclodextrins are produced by enzymatic degradation of starch and possess a unique feature, that when added alone to sperm cyclodextrins facilitate the removal of cholesterol from the membrane. When preloaded with cholesterol, however, cyclodextrins stimulate the insertion of cholesterol into the sperm membrane due to presence of a hydrophobic core in addition to an outer hydrophilic face. Treating sperm of various species with cholesterol-loaded cyclodextrin improves the quality of sperm during cryopreservation. It is still not clearly known how cholesterol-loaded cyclodextrin functions at sperm cells to enhance the survival during cryopreservation. The present review, therefore, highlights possible mechanisms of cholesterol-loaded cyclodextrin action on sperm during cryopreservation.

Modulation of voltage-gated sodium channels induces capacitation in bull spermatozoa through phosphorylation of tyrosine containing proteins

In our previous study, we have reported the molecular presence of Na_v 1.8 in bull spermatozoa and its potential involvement in regulation of sperm functions. With the selective blocking of Nav 1.8 using A-803467, alterations in sperm functions were observed, therefore, we envisaged of investigating the involvement of Na_v in regulating sperm function and the mechanism(s) involved in it using veratridine, a selective opener of Na_v channels. Forty ejaculates were collected from four Hariana bulls and semen samples were pooled in view of the non-significant variations between the different ejaculates. Treatment of sperm cells with veratridine (6, 8, and 10 μM) resulted in concentration- and time-dependent increase in forward progressive sperm motility and it persisted up to 6 h. However, hyperactive motility was induced by veratridine at higher concentrations (8 and 10 μM) and after 2 h of incubation, which was confirmed by subjective assessment followed by chlortetracycline staining showing the increased B-pattern spermatozoa, and thereby suggesting the involvement of Na_v in regulation of capacitation in spermatozoa. To substantiate the functional study observations especially veratridine-induced capacitation, immunoblotting and indirect immune fluorescence assays were performed for detection of the tyrosine-phosphorylated proteins. The immune blot study revealed the presence of five tyrosine phosphorylated proteins, namely-p17, p30, p54, p90 and p100. The p17 protein showed the highest band intensity compared to other protein bands indicating its potential involvement in the process of capacitation. Immunolocalization study revealed positive immunoreactivity for tyrosine phosphorylated proteins in the middle piece, post acrosomal region (high fluorescence) and tail of the spermatozoa (low fluorescence). From the results of present study, it is evident that activation of Na_V by veratridine, especially at higher concentrations, induced capacitation which is evidently mediated through phosphorylation of the tyrosine containing proteins localized in the post acrosomal regions, middle piece and tail of the spermatozoa. However, further studies will help in unraveling the involvement of Na_v and other ion channels regulating different physiological functions of sperm.

Effect of reduced glutathione supplementation in semen extender on tyrosine phosphorylation and apoptosis like changes in frozen thawed Hariana bull spermatozoa

To provide new insights into the mechanisms through which reduced glutathione (GSH) is able to protect spermatozoa, we tested the hypothesis that cryocapacitation and apoptosis like changes can contribute to the negative effect of freezing and thawing on bull spermatozoa, and that GSH prevent this damage. Having known protective effects of GSH in terms of a potent antioxidant, we evaluated capacitation, tyrosine phosphorylation and apoptosis like changes in bull spermatozoa after freezing and thawing in egg yolk tris glycerol extender containing (0.5m M-GSH-T1 & 1mM GSH-T2) and without GSH serving as the control (C). Forty ejaculates were collected from four Hariana bulls and were pooled due to non significant variations among the bull ejaculates for the evaluation of sperm attributes. Capacitation like changes, tyrosine phosphorylation, localization of tyrosine phosphorylated proteins, apoptosis like changes in terms of mitochondrial transmembrane potential and DNA fragmentation after final dilution, 4h of equilibration at 4°C and 24h after freezing and thawing were evaluated. GSH supplementation at 0.5mM showed significant reduction in B- and AR- pattern spermatozoa during all stages of semen freezing and thawing. Immunoblot revealed six proteins which were tyrosine phosphorylated and protein of 30 and 75kDa (p30, p75) were the major tyrosine phosphorylted proteins. On further analysis, the p30 showed differential variation in intensity in all the three groups after freezing and thawing. Positive immune reactivity for tyrosine phosphorylated proteins was found in neck, middle piece and post-acrosomal regions of spermatozoa. Addition of 0.5mM GSH decreased percentage of spermatozoa showing fragmented DNA and increased the percentage of spermatozoa having high transmembrane mitochondrial potential (P<0.05). This study demonstrates that GSH favours survival of bull spermatozoa by interfering with apoptotic and cryocapacitation pathways, and thereby protects the spermatozoa from deleterious effects of cryopreservation. The findings of the study indicated that GSH at 0.5mM can be effectively used as an additive in bull semen extender for freezing and thawing.