Involvement of metabolic pathway in the sperm spontaneous acrosome reaction

Comparative Proteomics Elucidates the Potential Mechanism of Sperm Capacitation of Chinese Mitten Crabs (Eriocheir sinensis)

Sperm capacitation is broadly defined as a suite of biochemical and biophysical changes resulting from the acquisition of fertilization ability. To gain insights into the regulation mechanism of crustacean sperm capacitation, 4D label-free quantitative proteomics was first applied to analyze the changes of sperm in Eriocheir sinensis under three sequential physiological conditions: seminal vesicles (X2), hatched with the seminal receptacle content (X3), and incubated with egg water (X5). In total, 1536 proteins were identified, among which 880 proteins were quantified, with 82 and 224 proteins significantly altered after incubation with the seminal receptacle contents and egg water. Most differentially expressed proteins were attributed to biological processes by Gene Ontology annotation analysis. As the fundamental bioenergetic metabolism of sperm, the oxidative phosphorylation, glycolysis, and the pentose phosphate pathway presented significant changes under the treatment of seminal receptacle contents, indicating intensive regulation for sperm in the seminal receptacle. Additionally, the seminal receptacle contents also significantly increased the oxidation level of sperm, whereas the enhancement of abundance in superoxide dismutase, peroxiredoxin 1, and glutathione S-transferase after incubation with egg water significantly improved the resistance against oxidation. These results provided a new perspective for reproduction studies in crustaceans.

Mechanisms That Protect Mammalian Sperm from the Spontaneous Acrosome Reaction

To acquire the capacity to fertilize the oocyte, mammalian spermatozoa must undergo a series of biochemical reactions in the female reproductive tract, which are collectively called capacitation. The capacitated spermatozoa subsequently interact with the oocyte zona-pellucida and undergo the acrosome reaction, which enables the penetration of the oocyte and subsequent fertilization. However, the spontaneous acrosome reaction (sAR) can occur prematurely in the sperm before reaching the oocyte cumulus oophorus, thereby jeopardizing fertilization. One of the main processes in capacitation involves actin polymerization, and the resulting F-actin is subsequently dispersed prior to the acrosome reaction. Several biochemical reactions that occur during sperm capacitation, including actin polymerization, protect sperm from sAR. In the present review, we describe the protective mechanisms that regulate sperm capacitation and prevent sAR.

Supplementation of Thymoquinone Nanoparticles to Semen Extender Boosts Cryotolerance and Fertilizing Ability of Buffalo Bull Spermatozoa

Thymoquinone nanoparticles (TQNPs) are broadly utilized in numerous pharmaceutical applications. In the present study, we tested the effects of TQNP supplementation on sperm quality and kinematics, acrosome exocytosis, oxidative biomarkers, apoptosis-like and morphological changes of frozen-thawed buffalo sperm, as well as the fertilizing capacity. Semen was collected from buffalo bulls, diluted (1:10; semen/extender), and divided into five aliquots comprising various concentrations of TQNP 0 (CON), 12.5 (TQNP12.5), 25 (TQNP25), 37.5 (TQNP37.5), and 50 (TQNP50) µg/mL, and then cryopreserved and stored in liquid nitrogen (-196 °C). The results revealed that TQNPs (25 to 50 µg/mL) provided the most optimal results in terms of membrane integrity (p < 0.001) and progressive motility (p < 0.01). In contrast, TQNP50 resulted in a greater post-thawed sperm viability (p = 0.02) compared with other groups. The addition of TQNPs to the extender had no discernible effects on sperm morphology measures. Sperm kinematic motion was significantly improved in the TQNP50 group compared to the control group (p < 0.01). TQNPs effectively reduced the content of H2O2 and MDA levels and improved the total antioxidant capacity of post-thawed extended semen (p < 0.01). The addition of TQNP significantly increased the number of intact acrosomes (p < 0.0001) and decreased the number of exocytosed acrosomes (p < 0.0001). A significant reduction in apoptosis-like changes was observed in TQNP groups. The non-return rates of buffalo cows inseminated with TQNP50-treated spermatozoa were higher than those in the control group (p < 0.05; 88% vs. 72%). These findings suggested that the freezing extender supplemented with TQNPs could effectively enhance the cryotolerance and fertility of buffalo sperm.

Mouse sperm energy restriction and recovery (SER) revealed novel metabolic pathways

Mammalian sperm must undergo capacitation to become fertilization-competent. While working on mice, we recently developed a new methodology for treating sperm in vitro, which results in higher rates of fertilization and embryo development after in vitro fertilization. Sperm incubated in media devoid of nutrients lose motility, although they remain viable. Upon re-adding energy substrates, sperm resume motility and become capacitated with improved functionality. Here, we explore how sperm energy restriction and recovery (SER) treatment affects sperm metabolism and capacitation-associated signaling. Using extracellular flux analysis and metabolite profiling and tracing via nuclear magnetic resonance (NMR) and mass spectrometry (MS), we found that the levels of many metabolites were altered during the starvation phase of SER. Of particular interest, two metabolites, AMP and L-carnitine, were significantly increased in energy-restricted sperm. Upon re-addition of glucose and initiation of capacitation, most metabolite levels recovered and closely mimic the levels observed in capacitating sperm that have not undergone starvation. In both control and SER-treated sperm, incubation under capacitating conditions upregulated glycolysis and oxidative phosphorylation. However, ATP levels were diminished, presumably reflecting the increased energy consumption during capacitation. Flux data following the fate of 13C glucose indicate that, similar to other cells with high glucose consumption rates, pyruvate is converted into 13C-lactate and, with lower efficiency, into 13C-acetate, which are then released into the incubation media. Furthermore, our metabolic flux data show that exogenously supplied glucose is converted into citrate, providing evidence that in sperm cells, as in somatic cells, glycolytic products can be converted into Krebs cycle metabolites.

Sperm interaction with bacteria induces the spontaneous acrosome reaction

Bacterial contamination in the semen deteriorates spermatozoa function. One mechanism through which this may occur is by inducing a premature form of the acrosome reaction (spontaneous acrosome reaction (sAR)) which has been shown to abrogate fertilization. To understand the mechanism by which bacteria affect sperm functions, we determined the effects of bacteria on sperm sAR and on other parameters involved in sperm capacitation. Sperm cells undergo biochemical changes in the female reproductive tract collectively called capacitation. Only capacitated sperm can undergo the physiological acrosomal exocytosis process near or on the oocyte, which allows the spermatozoon to penetrate and fertilize the egg. Bovine sperm incubated with the bacteria Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) or Pseudomonas aeruginosa (P. aeruginosa), revealed a sperm-bacteria interaction, however only E. coli and P. aeruginosa caused an increase in sperm sAR. This effect was seen only when the bacteria were present with the sperm during the full incubation under capacitation conditions but not when the bacteria were added to capacitated sperm. These results indicate that bacteria affect sperm during capacitation and not at the AR step. In addition, Ca²⁺ influx, protein kinase A, and protein tyrosine phosphorylation activities, three essential processes that promote capacitation, were inhibited by the bacteria. Moreover, increasing intracellular cAMP, which also occur during sperm capacitation, caused significant reverse of sAR induced by the bacteria.

Sperm physiology and in vitro fertilising ability rely on basal metabolic activity: insights from the pig model

Whether basal metabolic activity in sperm has any influence on their fertilising capacity has not been explored. Using the pig as a model, the present study investigated the relationship of energetic metabolism with sperm quality and function (assessed through computer-assisted sperm analysis and flow cytometry), and fertility (in vitro fertilisation (IVF) outcomes). In semen samples from 16 boars, levels of metabolites related to glycolysis, ketogenesis and Krebs cycle were determined through a targeted metabolomics approach using liquid chromatography-tandem mass spectrometry. High-quality sperm are associated to greater levels of glycolysis-derived metabolites, and oocyte fertilisation and embryo development are conditioned by the sperm metabolic status. Interestingly, glycolysis appears to be the preferred catabolic pathway of the sperm giving rise to greater percentages of embryos at day 6. In conclusion, this study shows that the basal metabolic activity of sperm influences their function, even beyond fertilisation.

Fer and FerT: A New Regulatory Link between Sperm and Cancer Cells

Fer and its sperm and cancer specific variant, FerT, are non-receptor tyrosine kinases which play roles in cancer progression and metastasis. Recent studies have shed light on the regulatory role of these kinases in ensuring proper sperm function. Comparison of the regulatory cascades in which Fer and FerT are engaged in sperm and cancer cells presents an interesting picture, in which similar regulatory interactions of these enzymes are integrated in a similar or different regulatory context in the two cell types. These diverse compositions extend from the involvement of Fer in modulation of actin cytoskeleton integrity and function, to the unique regulatory interactions of Fer with PARP-1 and the PP1 phosphatase. Furthermore, recent findings link the metabolic regulatory roles of Fer and FerT in sperm and cancer cells. In the current review, we discuss the above detailed aspects, which portray Fer and FerT as new regulatory links between sperm and malignant cells. This perspective view can endow us with new analytical and research tools that will deepen our understanding of the regulatory trajectories and networks that govern these two multi-layered systems.

Alkaline Dilution Alters Sperm Motility in Dairy Goat by Affecting sAC/cAMP/PKA Pathway Activity

In dairy goat farming, increasing the female kid rate is beneficial to milk production and is, therefore, economically beneficial to farms. Our previous study demonstrated that alkaline incubation enriched the concentration of X-chromosome-bearing sperm; however, the mechanism by which pH affects the motility of X-chromosome-bearing sperm remains unclear. In this study, we explored this mechanism by incubating dairy goat sperm in alkaline dilutions, examining the pattern of changes in sperm internal pH and Ca2+ concentrations and investigating the role of the sAC/cAMP/PKA pathway in influencing sperm motility. The results showed that adding a calcium channel inhibitor during incubation resulted in a concentration-dependent decrease in the proportion of spermatozoa with forward motility, and the sperm sAC protein activity was positively correlated with the calcium ion concentration (r = 0.9972). The total motility activity, proportion of forward motility, and proportion of X-chromosome-bearing sperm decreased (p < 0.05) when cAMP/PKA protease activity was inhibited. Meanwhile, the enrichment of X-chromosome-bearing sperm by pH did not affect the sperm capacitation state. These results indicate that alkaline dilution incubation reduces Ca2+ entry into X-sperm and the motility was slowed down through the sAC/cAMP/PKA signaling pathway, providing a theoretical foundation for further optimization of the sex control method.