Mitochondria: participation to infertility as source of energy and cause of senescence.

Mitochondria is a powerhouse organelle involved in ATP synthesis, calcium signaling, reactive oxygen species (ROS) by oxidative stress production, cell cycle arrest via apoptosis and sex steroid hormones biosynthesis. Improvement of sperm parameters such as motility, capacitation, acrosome reaction, and oocyte interaction, involve regulation of ROS levels by the mitochondria. In human, the relation between the quantitative level of mitochondrial DNA (mtDNA), oocyte cytoplasm maturation and fertilization potential, is not clear. It has been hypothesized that oocytes without sufficient wild type mtDNA and therefore able to generate ATP, would not normally be ovulated. This is reflected in the low numbers of mtDNA observed in degenerate oocytes obtained through super ovulation protocols during assisted reproductive technology programs. Different theories place mitochondria in a central role of oxidative damage to cells and tissues related to infertility declining and aging. Mitochondria-dependent apoptosis seems to be responsible for the pre and post-natal decline in germ cells, embryo development, implantation failure, and miscarriages.