Exposing Mouse Oocytes to MitoQ During In Vitro Maturation Improves Maturation and Developmental Competence

Mitoquinone shifts energy metabolism to reduce ROS-induced oxeiptosis in female granulosa cells and mouse oocytes

The female reproductive system is quite sensitive to regulation, and external environmental stimuli may cause oxidative stress which in turn may lead to accelerated aging and programmed cell death in female reproductive cells. The aim of this study was to investigate whether or not mitoquinone (MitoQ) could resist ROS-induced apoptosis in human granulosa cells and mouse oocytes. We found that the MitoQ treatment significantly reduced production of reactive oxygen species (ROS) and imbalance in mitochondrial membrane potential. The MitoQ treatment prevented an excessive mitochondrial fragmentation by upregulating Drp1 S637 and decreasing Drp1 S637 phosphorylation. More importantly, MitoQ maintained aerobic respiration and reduced anaerobic respiration by regulating reprogramming of intracellular energy metabolism, which enhanced cellular ATP production. MitoQ effectively reduced the expressions of AIFM1 and PGAM5, key molecules whose expressions were reversed not only in granulosa cells but also in mouse oocytes. Our findings suggest that MitoQ can ameliorate the mitochondrial deterioration caused by ROS and reprogram cellular energy metabolism, providing protection to cells against apoptosis. The presence of MitoQ may help in protecting human germ cells under in vitro culture conditions.

Effects of Yu Linzhu on ovarian function and oocyte mitochondria in natural aging mice

Objective: To study the effect of Yu Linzhu on ovarian function and mitochondria in natural aging mice.

Methods: Female BALB/c mice were selected as normal group at 7–8 weeks and natural aging group at 9 months. The natural aging group was divided into Yu Linzhu intervention group and non-intervention group by intragastric administration once a day for 6 weeks. The morphology and blood flow of ovary were observed by ultrasound. Ovarian morphology and follicle were observed by HE staining. Hormone levels were analyzed by ELISA. Serum oxidative stress were detected by radioimmunoassay. The distribution of mitochondria in oocytes was observed by fluorescence staining. The ultrastructure of oocytes and the morphology of mitochondria were observed under electron microscope. The mitochondrial membrane potential was detected by JC-1.

Results: Two groups of aging mice had serious disturbance of estrus cycle. The ovarian area of the mice in the aging non-intervention group was smaller than that in the normal group, and the ovarian area of the mice in the aging intervention group recovered. The ovarian blood flow was weak or even disappear in the aging non-intervention group, and the blood flow in the intervention group was improved. The ovarian volume of mice in the non-intervention group was smaller than that in the normal group. Some ovarian tissues were adhered to the surrounding tissues. While in the intervention group, the ovarian volume increased, the degree of adhesion decreased, the infiltration of ovarian interstitial lymphocytes decreased, and the zona pellucida recovered. Granular cell arrangement returned neatly, egg cell shape recover regular and the number also increased. In the non-intervention group, E2 (Estrogen), AMH (Anti-Mullerian hormone) decreased (P = 0.0092 and P = 0.0334, respectively), FSH (Follicle stimulating hormone) increased (P < 0.0001). In the intervention group, FSH decreased (P = 0.0002), LH (luteinizing hormone) decreased and E2, AMH increased. In the non-intervention group, GSH-Px (Glutathione peroxidase) decreased (P = 0.0129), SOD (Superoxide dismutase) decreased, ROS (reactive oxidative species), MDA (Malondialdehyde) increased. In the aging intervention group, ROS, MDA decreased and GSH-Px increased. In the non-intervention group, mitochondrial expression was scattered at the concentrated distribution point, the length of mitochondria was mostly long and the average volume increased, the density decreased, the number decreased and some mitochondria fused, and lesions such as swelling, vacuolar degeneration and inclusion body formation, membrane potential decreased (P = 0.0002). In the aging intervention group, mitochondria were evenly distributed, the mitochondria were basically round, the distribution density was moderate, the inner ridge was clear, and the membrane potential of the aging intervention group increased.

Conclusion: Yu Linzhu can improve the ovarian function of natural aging mice by improving the mitochondrial function of oocytes.

The Role of Mitochondria in Oocyte Maturation

With the nucleus as an exception, mitochondria are the only animal cell organelles containing their own genetic information, called mitochondrial DNA (mtDNA). During oocyte maturation, the mtDNA copy number dramatically increases and the distribution of mitochondria changes significantly. As oocyte maturation requires a large amount of ATP for continuous transcription and translation, the availability of the right number of functional mitochondria is crucial. There is a correlation between the quality of oocytes and both the amount of mtDNA and the amount of ATP. Suboptimal conditions of in vitro maturation (IVM) might lead to changes in the mitochondrial morphology as well as alternations in the expression of genes encoding proteins associated with mitochondrial function. Dysfunctional mitochondria have a lower ability to counteract reactive oxygen species (ROS) production which leads to oxidative stress. The mitochondrial function might be improved with the application of antioxidants and significant expectations are laid on the development of new IVM systems supplemented with mitochondria-targeted reagents. Different types of antioxidants have been tested already on animal models and human rescue IVM oocytes, showing promising results. This review focuses on the recent observations on oocytes’ intracellular mitochondrial distribution and on mitochondrial genomes during their maturation, both in vivo and in vitro. Recent mitochondrial supplementation studies, aiming to improve oocyte developmental potential, are summarized.