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Published on: July 30, 2020
Changes in mitochondrial function in porcine vitrified MII-stage oocytes and their impacts on apoptosis and
Jianjun Dai1, Caifeng Wu2, Caroline W Muneri3
1College of Veterinary Medicine, Nanjing Agricultural University, Jiangsu 210095, China; Institute of Animal Science and Veterinary Medicine, Shanghai Academy of Agricultural Sciences, Shanghai 201106, China; Division of Animal Genetic Engineering, Shanghai Municipal Key Laboratory of Agri-Genetics and Breeding, Shanghai 201106, China.
Abstract:
The purpose of this study was to investigate the changes in mitochondria in porcine MII-stage oocytes after open pulled straw (OPS) vitrification and to determine their roles in apoptosis and in vitro developmental ability. The mitochondrial membrane potential (ΔΨm), reactive oxygen species (ROS) level, adenosine-5'-triphosphate (ATP) concentration, mitochondrial distribution, mitochondrial ultrastructure, early-stage apoptosis with Annexin V-FITC staining, survival rate, parthenogenetic developmental ability and related gene expression were measured in the present experiments. The results showed that: (1) the mitochondrial ΔΨm of vitrified-thawed oocytes (1.05) was lower than that of fresh oocytes 1.24 (P<0.05). (2) ROS level in the OPS vitrification group was much higher than that of the fresh group, while the ATP concentration was much lower than that of fresh group (P<0.05). (3) Early-stage apoptosis rate from the OPS vitrification group (57.6%) was much higher than that of fresh group (8.53%) (P<0.05), and the survival rate and parthenogenetic cleavage rate of OPS vitrified oocytes were much lower than those from fresh ones (P<0.05). (4) Vitrification not only disrupted the mitochondrial distribution of porcine MII-stage oocytes, but also damaged the mitochondrial ultrastructure. (5) After vitrification, the gene expression level of Dnm1 was up-regulated, and other four genes (SOD1, Mfn2, BAX and Bcl2) were down-regulated. The present study suggested that not only the morphology and function of mitochondria were damaged greatly during the vitrification process, but also early-stage apoptosis was observed after vitrification. Intrinsic mitochondrial pathway could be in involved in the occurrence of apoptosis in vitrified-thawed porcine oocytes.
Insights
Open pulled straw (OPS) vitrification significantly damages porcine oocyte mitochondria, increasing apoptosis and reducing developmental potential. This study highlights mitochondrial dysfunction as a key factor in oocyte cryopreservation outcomes.
Area of Science:
- Reproductive Biology
- Cell Biology
- Cryobiology
Background:
- Mitochondria are crucial for oocyte function and development.
- Oocyte vitrification is a common cryopreservation technique.
- Understanding the impact of vitrification on mitochondrial health is vital for improving assisted reproductive technologies.
Purpose of the Study:
- To investigate mitochondrial changes in porcine MII-stage oocytes post-OPS vitrification.
- To determine the role of these mitochondrial alterations in apoptosis and developmental competence.
Main Methods:
- Assessed mitochondrial membrane potential (ΔΨm), reactive oxygen species (ROS), and ATP levels.
- Analyzed mitochondrial distribution and ultrastructure via microscopy.
- Quantified early-stage apoptosis using Annexin V-FITC staining.
- Evaluated oocyte survival and parthenogenetic developmental rates.
- Measured expression levels of key mitochondrial and apoptosis-related genes.
Main Results:
- Vitrified oocytes exhibited lower ΔΨm, higher ROS, and reduced ATP compared to fresh oocytes.
- OPS vitrification led to increased early-stage apoptosis (57.6% vs. 8.53%) and decreased survival and cleavage rates.
- Mitochondrial distribution and ultrastructure were disrupted, with altered expression of genes like Dnm1, SOD1, Mfn2, BAX, and Bcl2.
Conclusions:
- OPS vitrification severely impairs mitochondrial morphology and function in porcine oocytes.
- Mitochondrial damage contributes to increased apoptosis via the intrinsic pathway.
- These findings underscore the need for improved vitrification protocols to preserve oocyte quality for in vitro development.
