The effect of vitrification after warming on the expressions of p38, CDK1, and cyclin B in immature goat oocytes followed by in vitro maturation

Melatonin Promotes In Vitro Maturation of Vitrified-Warmed Mouse Germinal Vesicle Oocytes, Potentially by Reducing Oxidative Stress through the Nrf2 Pathway

Simple Summary

Cryopreservation of oocytes can cause high oxidative stress, reduce the quality of vitrified-warmed oocytes, and seriously hinder the application of oocyte cryopreservation technology in production and medicine. In this work, we found for the first time that melatonin can exert antioxidant effects through receptors and regulate the Nrf2 antioxidant pathway to respond to oxidative stress of vitrified-warmed oocytes, thereby improving both oocyte quality and the potential for subsequent development. The results illustrated the molecular mechanism of melatonin’s antioxidant effect in vitrified-warmed oocytes and provided a theoretical basis for the application of melatonin in the cryopreservation of oocytes. These findings are of great significance for the further application of oocyte cryopreservation technology to production and assisted reproduction in the future.

Abstract

Previously it was reported that melatonin could mitigate oxidative stress caused by oocyte cryopreservation; however, the underlying molecular mechanisms which cause this remain unclear. The objective was to explore whether melatonin could reduce oxidative stress during in vitro maturation of vitrified-warmed mouse germinal vesicle (GV) oocytes through the Nrf2 signaling pathway or its receptors. During in vitro maturation of vitrified-warmed mouse GV oocytes, there were decreases (p < 0.05) in the development rates of metaphase I (MI) oocytes and metaphase II (MII) and spindle morphology grades; increases (p < 0.05) in the reactive oxygen species (ROS) levels; and decreases (p < 0.05) in expressions of Nrf2 signaling pathway-related genes (Nrf2, SOD1) and proteins (Nrf2, HO-1). However, adding 10⁻⁷ mol/L melatonin to both the warming solution and maturation solutions improved (p < 0.05) these indicators. When the Nrf2 protein was specifically inhibited by Brusatol, melatonin did not increase development rates, spindle morphology grades, genes, or protein expressions, nor did it reduce vitrification-induced intracellular oxidative stress in GV oocytes during in vitro maturation. In addition, when melatonin receptors were inhibited by luzindole, the ability of melatonin to scavenge intracellular ROS was decreased, and the expressions of genes (Nrf2, SOD1) and proteins (Nrf2, HO-1) were not restored to control levels. Therefore, we concluded that 10⁻⁷ mol/L melatonin acted on the Nrf2 signaling pathway through its receptors to regulate the expression of genes (Nrf2, SOD1) and proteins (Nrf2, HO-1), and mitigate intracellular oxidative stress, thereby enhancing in vitro development of vitrified-warmed mouse GV oocytes.

The Assessment of Various Factors Affecting the Postwarming Viability and Developmental Capability of Goat Metaphase II Oocytes Vitrified by Cryotop

The effects of the equilibration time, the vitrification procedure, and the warming procedure on the quality of goat oocytes vitrified by Cryotop were assessed. In the first part of the study, oocytes were exposed to 10% dimethyl sulfoxide (DMSO) and 10% ethylene glycol (EG) for 1, 3, 5, or 10 minutes, respectively, followed by vitrification. In the second part, after equilibration in 7.5% DMSO +7.5% EG for 3 minutes, 10% DMSO +10% EG for 3 minutes, or 4% EG for 10 minutes, oocytes were equilibrated in 15% DMSO +15% EG, 20% DMSO +20% EG, or 35% EG for 30 seconds before vitrification. The vitrification procedures were designated as first vitrification procedure (VPI), second vitrification procedure (VPII), and third vitrification procedure (VPIII), respectively. In the third part, oocytes vitrified using VPIII were warmed by the three procedures (first warming procedure [TPI], second warming procedure [TPII], or third warming procedure [TPIII]) containing different concentrations of trehalose. The results showed that after equilibration for 1 or 3 minutes in 10% DMSO and 10% EG, the viability and developmental capability of vitrified oocytes were significantly superior to the groups after equilibration for over 5 minutes (p < 0.05). With the VPIII procedure, the frequencies with normal morphology, cleavage, and blastocyst formation of vitrified oocytes were 91.87% ± 4.14%, 76.51% ± 4.37%, and 39.84% ± 2.91%, respectively, demonstrating a significant increase compared to the VPI or VPII group (p < 0.05). The rates of vitrified oocytes with normal morphology and cleavage in the TPI group were higher than the TPII or TPIII group (p < 0.05). In conclusion, equilibration in 10% DMSO and 10% EG for <3 minutes benefits the viability of vitrified oocytes. EG may be more efficient for vitrification of goat oocytes compared to DMSO. Higher concentrations (more than 1 M) of trehalose enhance cryosurvival of goat oocytes when warming.