Inhibition of deubiquitinases alters gamete ubiquitination states and sperm-oocyte binding ability in pigs

SUMO1 modification reduces oxidative stress and SUMO1ylated AKAP4 degradation affects frozen-thawed boar sperm quality

Low-temperature injury affects normal physiological function and viability of boar sperm during cryopreservation. Small ubiquitin-like modifier (SUMO) modification of proteins after translation is related to the cell stress response but the relationship between SUMO modification and oxidative stress in freeze-thawed sperm remains unclear. A-kinase ankyrin 4 (AKAP4) and its precursor proAKAP4 are two main proteins in mammalian sperm. Although AKAP4 expression has been studied in many species, its expression in porcine sperm has not been described in detail. In this study, liquid chromatography-mass spectrometry was used to determine the differentially expressed SUMO-modified proteins in porcine sperm after freezen and thawed. The results identified 26 down-regulated SUMO-modified proteins, with AKAP4 identified as one of the target proteins of SUMO1 under sperm stress. In addition, the level of SUMO1 protein increased significantly (P < 0.001) and the level of AKAP4 protein decreased (P < 0.05) after freezing and oxidative stress treatment. Inhibition of SUMO1 modification of AKAP4 protein did not affect its degradation (P > 0.05), indicating that SUMO1 is not involved in the degradation of AKAP4. The inhibition of SUMO1 modification by sperm protein decreased sperm motility (P < 0.05), ATP content, and DNA integrity (P < 0.05). In summary, cryopreservation and oxidative stress can induce SUMO modification of porcine sperm proteins and the modification of sperm protein SUMO1 can help sperm resist oxidative stress; and its role in protecting sperm quality is not via regulating the degradation of AKAP4. These findings provide new insights into the mechanisms underlying SUMO1 modifications during sperm cryopreservation and oxidative stress.

The Deubiquitinating Enzyme Inhibitor PR-619 is a Potent DNA Topoisomerase II Poison

2,6-Diaminopyridine-3,5-bis(thiocyanate) (PR-619) is a broad-spectrum deubiquitinating enzyme (DUB) inhibitor that has been employed in cell-based studies as a tool to investigate the role of ubiquitination in various cellular processes. Here, we demonstrate that in addition to its action as a DUB inhibitor, PR-619 is a potent DNA topoisomerase II (TOP2) poison, inducing both DNA topoisomerase IIα (TOP2A) and DNA topoisomerase IIβ (TOP2B) covalent DNA complexes with similar efficiency to the archetypal TOP2 poison etoposide. However, in contrast to etoposide, which induces TOP2-DNA complexes with a pan-nuclear distribution, PR-619 treatment results in nucleolar concentration of TOP2A and TOP2B. Notably, neither the induction of TOP2-DNA covalent complexes nor their nucleolar concentration are due to TOP2 hyperubiquitination since both occur even under conditions of depleted ubiquitin. Like etoposide, since PR-619 affected TOP2 enzyme activity in in vitro enzyme assays as well as in live cells, we conclude that PR-619 interacts directly with TOP2A and TOP2B. The concentration at which PR-619 exhibits robust cellular DUB inhibitor activity (5-20 μM) is similar to the lowest concentration at which TOP2 poison activity was detected (above 20 μM), which suggests that caution should be exercised when employing this DUB inhibitor in cell-based studies.

Evaluation of ε-polylysine as antimicrobial alternative for liquid-stored boar semen

ε-polylysine (ε-PL) has potent antibacterial effects and is often used in the food industry. However, no studies have clarified the antibacterial effects of ε-PL during storage of boar semen. In this study, boar semen samples were diluted with BTS buffer supplemented with different concentrations (0, 0.04, 0.08, 0.16, 0.32, 0.64, and 1.28 g/L) of ε-PL and different combinations of ε-PL plus gentamicin during liquid storage at 17 °C for 5 days. Bacterial concentrations, bacterial community compositions, sperm quality parameters, and in vitro fertilization (IVF) were evaluated in order to analyze the antibacterial effects of these parameters during boar semen preservation. The results indicated that the optimum concentration of ε-PL was 0.16 g/L, which significantly improved sperm quality parameters, including sperm motility, plasma membrane integrity, mitochondrial membrane potential, and acrosome integrity, and changed bacterial proliferation and composition (P < 0.05). Moreover, compared with the control group, IVF parameters in the treatment groups also significantly improved (P < 0.05), although there were no significant differences among treatment groups. Interestingly, the antibacterial effect of 0.16 g/L ε-PL in combination with 0.125 g/L gentamycin was similar to that of 0.25 g/L gentamicin alone. In conclusion, our results showed that 0.16 g/L ε-PL is promising for the replacement of gentamicin to improve sperm quality parameters, sperm capacitation, and IVF by reducing bacterial concentrations and disrupting bacterial community composition.