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A series of biochemical and biophysical changes during sperm capacitation initiates various signaling pathways related to protein phosphorylation leading to sperm hyperactivation, simultaneously with the regulation of proteasomal activity responsible for protein degradation and turnover. Our study aimed to unveil the role of the proteasome in the regulation of boar sperm motility, hyperactivated status, tyrosine phosphorylation, and total protein ubiquitination. The proteolytic activity of the 20S proteasomal core was inhibited by MG-132 in concentrations of 10, 25, 50, and 100 μM; and monitored parameters were analyzed every hour during 3 h of in vitro capacitation (IVC). Sperm motility and kinematic parameters were analyzed by Computer Assisted Sperm Analysis (CASA) during IVC, showing a significant, negative, dose-dependent effect of MG-132 on total and progressive sperm motility (TMOT, PMOT, respectively). Furthermore, proteasomal inhibition by 50 and 100 μM MG-132 had a negative impact on velocity-based kinematic sperm parameters (VSL, VAP, and VCL). Parameters related to the progressivity of sperm movement (LIN, STR) and ALH were the most affected by the highest inhibitor concentration (100 μM). Cluster analysis revealed that the strongest proteasome-inhibiting treatment had a significant effect (p ≤ 0.05) on the hyperactivated sperm subpopulation. The flow cytometric viability results proved that reduced TMOT and PMOT were not caused by disruption of the integrity of the plasma membrane. Neither the protein tyrosine phosphorylation profile changes nor the accumulation of protein ubiquitination was observed during the course of capacitation under proteasome inhibition. In conclusion, inhibition of the proteasome reduced the ability of spermatozoa to undergo hyperactivation; however, there was no significant effect on the level of protein tyrosine phosphorylation and accumulation of ubiquitinated proteins. These effects might be due to the presence of compensatory mechanisms or the alteration of various ubiquitin-proteasome system-regulated pathways.

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

Estrogens are steroid hormones that affect a wide range of physiological functions. The effect of estrogens on male reproductive tissues and sperm cells through specific receptors is essential for sperm development, maturation, and function. Although estrogen receptors (ERs) have been studied in several mammalian species, including humans, they have not yet been described in bull spermatozoa and reproductive tissues. In this study, we analyzed the presence of all types of ERs (ESR1, ESR2, and GPER1) in bull testicular and epididymal tissues and epididymal and ejaculated spermatozoa, and we characterize them here for the first time. We observed different localizations of each type of ER in the sperm head by immunofluorescent microscopy. Additionally, using a selected polyclonal antibody, we found that each type of ER in bull sperm extracts had two isoforms with different molecular masses. The detailed detection of ERs is a prerequisite not only for understanding the effect of estrogen on all reproductive events but also for further studying the negative effect of environmental estrogens (endocrine disruptors) on processes that lead to fertilization.

The aim of this study was to evaluate differences in the presence of sperm subpopulations in frozen-thawed semen in stallions with different freezability. The motility of individual spermatozoa of 24 stallions from 15 breeds was evaluated using computer-assisted sperm analysis (CASA) immediately after thawing (T0) and after 30 min of incubation (T30). In accordance with our previous studies, samples were initially divided based on their total motility into categories of good (GF) and poor (PF) freezers. K-means cluster analysis of kinematic parameters of spermatozoa was used to divide motile sperm (n = 57 630) into three subpopulations. Analysis of variance was used to evaluate differences in the subpopulations between GF and PF stallions at the times of incubation T0 and T30. Statistically significant differences were found in most kinematic parameters between PF and GF stallions as well as between the times of incubation T0 and T30 (P < 0.05). Spermatozoa of good freezers are represented more frequently in the fast and medium fast subpopulations and are faster and more linear than those of poor freezers (P < 0.05). Sperm from PF stallions were more strongly affected by longer incubation. The percentage of sperm in the fast and medium fast subpopulations was lower in samples from PF stallions, but assessment of the motility parameters in particular sperm subpopulations revealed that these sperm had good velocity. Poor freezer samples had lower sperm quality due to a reduced total proportion of motile sperm, and these samples were more sensitive to prolonged time after thawing. Thus, an efficient sperm selection method or a special insemination technique should be used for obtaining doses from stallions with poor freezability. Our study showed that the CASA system and cluster analysis are promising tools for better understanding the significant differences in the individual stallion freezability, and further research should be focused on their application in the field.

The aim of the study was to evaluate the effect of two different extenders on sperm characteristic before equilibration and post-thaw in the endangered Old Kladruber stallions. Also, the response of individual stallions to the extenders used was tested. Semen was collected from six stallions every other day within one week. After centrifugation of the collected sperm-rich fraction, the supernatant was removed and sperm pellets were divided to two aliquots; these were diluted either with Gent (Minitube, Germany) or privately manufactured lactose-EDTA-egg yolk extender (Lact). Three cryopreserved insemination doses (IDs) from each extender (Gent and Lact) were prepared for each stallion from one collection (108 samples from six stallions in total). As a parameter of quality, the motility (computer assisted sperm analysis), viability (fluorescence staining), and morphology (eosin/nigrosine staining) were evaluated after dilution with freezing extenders (fresh) and after thawing (frozen-thawed). The different effects of chosen extenders on the quality of fresh semen were only manifested in higher kinematic parameters of sperm when the Lact extender was used. However, in frozen-thawed samples, the Gent extender yielded significantly better results in all of the evaluated parameters. The representation of sperm subpopulation was significantly influenced by extender in fresh as well as frozen-thawed samples; moreover, we found a significant effect of freezing on the distribution of these subpopulations. The response of individual stallions to chosen extenders was evident in the different quality of fresh as well as frozen-thawed IDs; Gent extender yielded better frozen-thawed IDs. Based on our results, among others describing quality parameters of ejaculate in endangered Old Kladruber stallions, we can recommend using Gent extender for the production of frozen-thawed IDs.

The aim of this study was to evaluate the effect of clarified egg yolk addition to semen extender, and the semen collection sequence on the quality of frozen-thawed semen in dogs. Semen was collected from 6 dogs in a time interval of 24 hours. As parameter of the quality of frozen-thawed (F-T) semen, the motility by computer assisted sperm analysis (CASA) and plasma membrane integrity by hypo-osmotic swelling test (HOS) were evaluated. All kinematic parameters of sperm motility were higher in F-T samples containing the whole in comparison to the clarified egg yolk. The sequence of semen collection affected sperm movement characteristics of native as well as F-T semen, but it was not possible to determine whether the fresh semen from the 1st or 2nd collection is of higher quality. All motility parameters of sperms frozen with extender containing the whole egg yolk were significantly higher in the case of the 2nd collection. The situation was not so clear in the case of clarified egg yolk addition, but the velocity values were higher in F-T samples from the 2nd collection. In contrast to proven differences in motility, the effect of the addition of clarified egg yolk and the sequence of semen collection were not projected at all on the quality of plasma membrane of canine sperms evaluated by HOS test.