Infertility, and the zona pellucida (5) and abnormalities in

Infertility, there is approximately 10% of couples. The young
and healthy people, the possibility of pregnancy in each reproductive cycle is
usually 20-25% and during a year is about 90%. Indeed, a standard definition of
clinical infertility is one year of unprotected intercourse without pregnancy
(1). The effect of maternal age on reducing fertility and increasing the
pregnancy loss cannot be ignored (2). In spite of the causes of infertility,
in
vitro fertilization (IVF) is the treatment that results in
the highest fertility rate per cycle. Frequent failure in IVF is usually
defined as failure in pregnancy after 2-6 cycles of IVF (3). There are several
reasons for failure in fertilization after IVF. Sperm defect (4), the
interaction of defective sperm and the zona pellucida (5) and abnormalities in
the oocyte have all been reported as potential causes of failure in
fertilization (6, 7). The oocyte quality is always considered as a limiting
factor in fertility,
especially IVF, which is often influenced by age. The quality of the oocyte is
affected by two important factors: nuclear maturity and cytoplasmic maturity (8).
Nuclear maturity occurs when the first polar body is seen, but the cytoplasmic
maturation of the oocyte is not visible and is affected by several factors,
including mitochondria (9). Because mitochondria are the only autonomous
cytoplasmic organelles and have their own specific genome that has 13 genes
encoding the main units of the proteins involved in the respiratory chain (10),
therefore, mitochondria are the only ATP-supplied cellular organs that produce
energy during the process of fertilization and replacement of the fetus (11).
Also, mitochondria are a source of intracellular calcium stores and factors
involved in apoptosis (12). Cell aging is a degenerative process associated
with progressive accumulation of adverse changes during the time, reduced
physiological function, and increased risk of death. Studies in several species
showed a wide range of mitochondrial changes and mitochondrial DNA (mtDNA)
associated with cell aging, including: (1) mitochondrial dysfunction, (2)
decreased oxidative mitochondrial phosphorylation (OXPHOS), (3) accumulation of
mtDNA mutations, (4) increased mitochondrial production of reactive oxygen
species (ROS), and (5) increased oxidative damage to DNA, proteins and lipids
(13). 4977-bp deletion mutation of mtDNA (?mtDNA4977) occurs between 8469 and
13,447 nucleotides and in many diseases, its association with age has been
reported (14, 15). This segment contains genes that encode ATPase6, ATPase8,
cytochrome oxidase III, 3-NADH-dehydrogenase (ND3), ND4, ND4 subunit L (ND4L),
and ND5 (17). Therefore, cells that have ?mtDNA4977, lack the multiple
oxidative phosphorylation genes, which leads to a general decrease in energy.
In tissues that are not divided, these mutations can serve as a marker for the study
of the cell aging, including oocytes, which indicate the reduced quality of the
egg for fertilization. Oocytes, due to the fact that these are more likely to
have aging (16, 17), therefore, these
are suitable cells for the study of these deletions, but some studies have
proven that these can also be studied in blood cells.