Protein kinase C activity in boar sperm

Boar Sperm Motility Assessment Using Computer-Assisted Sperm Analysis: Current Practices, Limitations, and Methodological Challenges

Spermatozoa are highly specialized male cells that are characterized by a unique ability to move, which is a critical factor for successful fertilization. The relative simplicity of motility assessment, especially in livestock, has made it a widely used parameter for evaluating ejaculate quality or cryopreserved semen in the clinical field, and an advanced tool in reproductive physiology and toxicology research. Technological advances in image analysis and computational methods have substantially increased its accuracy through the use of computer-assisted sperm analysis (CASA) to minimize subjective bias in motility assessments. Nevertheless, this more objective method still presents some significant challenges, including variability in the sample preparation, imaging conditions, and analytical parameters. These issues contribute to inconsistency and impair the reproducibility and comparability of data between laboratories. The implementation of standardized protocols, combined with comprehensive training and rigorous evaluation, can serve to mitigate some of the emerging inconsistencies. In addition, the in vitro conditions under which CASA analyses are performed often differ significantly from the natural environment of the female reproductive tract in vivo. This review discusses the methodologies, critical issues, and limitations of sperm motility analyses using CASA, with a particular focus on the boar as an important agricultural and biomedical model species in which this system is widely used.

Effect of zinc on sperm recovered by swim-up

PURPOSE

Zinc is known to influence chromatin stability, motility and protection against oxidative stress. While swim-up remains the preferred method for selecting sperm in Assisted Reproductive Technologies (ART), concerns arise regarding sperm DNA fragmentation associated with this procedure. Given zinc's significant role in protecting sperm DNA integrity and motility, we aimed to investigate the impact of zinc supplementation during the swim-up process on sperm quality.

METHODS

Semen samples from 203 normozoospermic men were used. Samples were divided into fractions and swim-up procedure was applied using human tubal fluid (mHTF) supplemented with three different concentrations of zinc or medium without supplementation as control. DNA fragmentation, chromatin maturity, reactive oxygen species (ROS) levels, motility and protein phosphorylation levels analyses were addressed to each fraction.

RESULTS

The sperm DNA fragmentation was reduced in sperm recovered by swim-up in media with all concentrations of zinc assayed with respect to the control (p < 0.0001). Aniline blue staining showed better chromatin maturity in sperm recovered with 2.5- and 3.5-mM zinc (p = 0.045; p = 0.021). Kinematic parameters such as curvilinear velocity and beat-cross frequency showed improvement with 2.5 mM zinc (p = 0.0080 and p = 0.0400), whereas straightness, linearity, and hypermotility showed improvement with 5 mM zinc (p = 0.0075, p = 0.0069, and p = 0.0244). Protein phosphorylation patterns showed changes associated with treatment with zinc, and only 5 mM zinc treatment showed a decrease in ROS levels.

CONCLUSION

The addition of zinc to mHTF provided optimal physiological conditions for sperm recovered through swim-up. This supplementation should be considered for selecting sperm for use in ART.

In vitro versus cryo-induced capacitation of bovine spermatozoa, part 3: Compositional and molecular changes to the plasma membrane

The aim of this study was to assess the level of membrane cryodamage through the levels of selected capacitation and apoptosis-associated proteins, together with compositional membrane changes in capacitated (CAP), cryopreserved (CRYO) and non-capacitated bovine spermatozoa (CRTL). Sperm kinetic parameters were analyzed by the computer assisted sperm analysis (CASA) while the capacitation patterns were examined with the chlortetracycline (CTC) assay. In the case of DNA integrity, sperm chromatin structure assay and aniline blue staining were used. For the quantification of fatty acid content gas chromatography was performed. Using Western blotting the expression of capacitation (protein kinase C - PKC; phospholipases A2 and Cζ - PLA2, PLCζ; soluble adenylyl cyclase 10 - sAC10) and apoptosis-associated (apoptosis regulator Bax; B-cell lymphoma 2 - Bcl-2; caspase 3) proteins were evaluated. Data indicate a significant decline (p < 0.0001) of sperm kinetic parameters and higher occurrence (p < 0.0001) of DNA fragmentation in the CRYO group. CTC assay revealed a significant increase of acrosome-reacted spermatozoa in the CRYO group when compared to others. Compositional changes in the sperm membrane were visible as a notable decline of docosahexaenoic acid (p < 0.0001) associated with a significant decrease of membrane cholesterol (p < 0.05) and proteins (p < 0.0001) in the CRYO group while the amount of palmitic, stearic, oleic, and linoleic acid increased (p < 0.0001) significantly. Protein expression of all capacitation-associated proteins (PKC, PLA2, PLCζ, sAC10) was significantly down-regulated (p < 0.001; p < 0.0001) in the CRYO group. Relative quantification of apoptosis-associated proteins revealed increased Bax and decreased Bcl-2 levels in the CRYO group, except for caspase-3, which remained without significant changes.

The compound YK 3-237 promotes pig sperm capacitation-related events

Before fertilization of the oocyte, the spermatozoa must undergo through a series of biochemical changes in the female reproductive tract named sperm capacitation. Spermatozoa regulates its functions by post-translational modifications, being historically the most studied protein phosphorylation. In addition to phosphorylation, recently, protein acetylation has been described as an important molecular mechanism with regulatory roles in several reproductive processes. However, its role on the mammal's sperm capacitation process remains unraveled. Sirtuins are a deacetylase protein family with 7 members that regulate protein acetylation. Here, we investigated the possible role of SIRT1 on pig sperm capacitation-related events by using YK 3-237, a commercial SIRT1 activator drug. SIRT1 is localized in the midpiece of pig spermatozoa. Protein tyrosine phosphorylation (focused at p32) is an event associated to pig sperm capacitation that increases when spermatozoa are in vitro capacitated in presence of YK 3-237. Eventually, YK 3-237 induces acrosome reaction in capacitated spermatozoa: YK 3-237 treatment tripled (3.40 ± 0.40 fold increase) the percentage of acrosome-reacted spermatozoa compared to the control. In addition, YK 3-237 induces sperm intracellular pH alkalinization and raises the intracellular calcium levels through a CatSper independent mechanism. YK 3-237 was not able to bypass sAC inhibition by LRE1. In summary, YK 3-237 promotes pig sperm capacitation by a mechanism upstream of sAC activation and independent of CatSper calcium channel.

Sperm traits and seminal plasma proteome of locally adapted hairy rams subjected to intermittent scrotal insulation

The present study evaluated the effects of heat stress on reproductive parameters of hairy rams. Six animals were subjected to scrotal insulation during four consecutive nights (6 PM - 6 AM). Day (D) 0 was the first day of insulation. Scrotal circumference increased from 30.5 ± 0.3 cm (at pre-insulation) to 31.8 ± 0.4 cm on D4, decreased 3.9 cm on D28, returning to 30.6 ± 0.6 cm on D57. Sperm concentration decreased from 3.7 ± 0.12 ×109 sperm/mL before insulation to 2.6 ± 0.1 ×109 on D23, returning to normal on D57. Sperm motility averaged 75 ± 2.9% before insulation, was undetectable on D23, and became normal on D77. Sperm with normal morphology reached 5.9 ± 2.6% on D35 but recovered (86.8 ± 2.1%) on D91. Sperm DNA integrity decreased from 86.5 ± 4.7% before insulation to 11.1 ± 3.7% on D63, returning to pre-insulation values on D120. Sperm BSP immunostaining was reduced after scrotal insulation. Variations in seminal protein abundances coincided with changes in sperm parameters. Seminal plasma superoxide dismutase, carboxypeptidase Q-precursor and NPC intracellular cholesterol transporter 2 decreased on D18, returning to normal after D28. Albumin, inhibitor of carbonic anhydrase precursor, EGF-like repeat and discoid I-like domain-containing protein 3 and polymeric immunoglobulin receptor increased after insulation. In summary, intermittent scrotal insulation drastically altered ram sperm attributes and seminal proteins, especially those associated with oxidative stress. Knowledge of animal´s response to thermal stress is vital in the scenario of climate changes.

Effect of glucose and reactive oxygen species on boar sperm induced-acrosome exocytosis

Ejaculated boar spermatozoa can be liquid preserved for several days and be easily activated to produce physiological changes. One of the major changes is acrosome exocytosis that is physiologically related to capacitation. Glycolysis and reactive oxygen species (ROS) were studied regarding several boar sperm functions, but data available about their effect on boar sperm acrosome exocytosis are scarce. The objective of this work was to evaluate the effect of glucose and ROS on boar sperm acrosome exocytosis. We evaluated acrosome exocytosis by progesterone induction of capacitated sperm and assess viability, kinematics parameters, ROS levels, ATP content and Protein Kinase A activity in media with or without glucose and hydrogen peroxide or potassium chromate, as source of ROS. Our results show that glucose has no effect on acrosome exocytosis and also, it is not necessary for boar sperm capacitation, although it has a positive effect in the presence of ROS. On the other hand, ROS effects are related to spontaneous acrosome reaction. We conclude that glycolysis may function as a metabolic pathway that provides sustain but is not directly involved in boar sperm acrosome exocytosis and capacitation. Also, ROS do not promote capacitation in boar sperm, but affect spontaneous acrosome exocytosis.

Aquaporins Are Essential to Maintain Motility and Membrane Lipid Architecture During Mammalian Sperm Capacitation

Aquaporins are a family of ubiquitous transmembrane proteins that allow the transport of water and small molecules across the cell plasma membrane. The different members of this family present a characteristic distribution across different cell types, which is species-specific. In mammalian sperm, different AQPs, including AQP3, AQP7, and AQP11, have been identified; their main roles are related to osmoadaptation and sperm motility activation after ejaculation. Capacitation, which is a post-ejaculatory process that sperm must undergo to achieve fertilizing ability, is triggered by pH changes and different extracellular ions that are present in the female reproductive tract. Considering the function of AQPs and their influence on pH through the regulation of water flow, this study aimed to elucidate the potential role of different AQPs during in vitro sperm capacitation using three different transition metal compounds as AQP inhibitors. Cooper sulfate, a specific inhibitor of AQP3, caused a drastic increase in peroxide intracellular levels compared to the control. Mercury chloride, an unspecific inhibitor of all AQPs except AQP7 produced an increase in membrane lipid disorder and led to a decrease in sperm motility and kinetics parameters. Finally, the addition of silver sulfadiazine, an unspecific inhibitor of all AQPs, generated the same effects than mercury chloride, decreased the intracellular pH and altered tyrosine phosphorylation levels after the induction of the acrosome reaction. In the light of the aforementioned, (a) the permeability of AQP3 to peroxides does not seem to be crucial for sperm capacitation and acrosome reaction; (b) AQPs have a key role in preserving sperm motility during that process; and (c) AQPs as a whole seem to contribute to the maintenance of lipid membrane architecture during capacitation and may be related to the intracellular signaling pathways involved in the acrosome reaction. Hence, further research aimed to elucidate the mechanisms underlying the involvement of AQPs in mammalian sperm capacitation and acrosome reaction is warranted.