The Role of Mitochondria in the Aging Ovary

This chapter discusses the role of mitochondria in aging ovary. Human mitochondrial deoxyribonucleic acid (mtDNA) is a maternally inherited double-stranded circular DNA molecule, which is involved in respiratory and oxidative phosphorylation. The human metaphase II oocyte is estimated to have 100,000 mitochondria; however, there is only one mitochondrial genome per organelle. The mtDNA is not protected by histones and is exposed in high concentrations of reactive oxygen species (ROS) and free radicals in the matrix of mitochondria. Thus, the aged oocytes are very vulnerable to oxidative damage and mtDNA mutation. The current study demonstrates that mtDNA 4977bp deletions in compromised human oocytes may range from 56.3% when maternal age is younger than 32 up to 73% when maternal age is older than 37. Most nondisjunction and aneuplodies take place during meiosis, which are highly energy-intensive, and increase exponentially with maternal age. Mitochondria in oocyte and early embryos are structurally immature. They are round or ovoid, with few cristae. They become more elongated with numerous transverse cristae at the blastocyst stage. Nevertheless, after ovulation the multiplication of mitochondria and the replication of mtDNA are not resumed until the gastrulation stage.