A Comprehensive Review of Mitochondrial Complex I During Mammalian Oocyte Maturation

This review provides a comprehensive overview of Complex I during mammalian oocyte maturation. Complex I (NADH:ubiquinone oxidoreductase) is a crucial member of the electron transport chain and serves two principal functions during oxidative phosphorylation: NADH oxidation and proton pumping. It is located at the inner mitochondrial membrane and consists of 14 core and 31 accessory subunits that are necessary for its function and assembly. Moreover, Complex I is the primary site of reactive oxygen species (ROS) production among the different tissues. In light of the literature, it has been demonstrated that ROS and oxidative stress are significantly important among the various factors that can affect oocyte maturation. Factors such as malnutrition, alcohol use, obesity, PCOS, aging, and smoking are some of the common causes of infertility. Each one of them causes disruption in the equilibrium of the body's redox system and related with oxidative stress. During oocyte maturation, excessive ROS levels are associated with chromosomal errors and developmental insufficiency. In addition, excess oxidative stress adversely affects embryo growth and development and may cause fetal embryopathies with damage to macromolecules in the cytoskeleton. At this particular juncture, Complex I plays a key role in determining ROS production and the success of the oocyte maturation. This review evaluates mitochondrial Complex I's function, structure, and its crucial role during oocyte maturation.