Aging-related Changes in <i>In Vitro</i>-matured Bovine Oocytes: Oxidative Stress, Mitochondrial Activity and ATP Content After Nuclear Maturation

Abstract

The objective of this research was to clarify the aging-related changes in in vitro-matured bovine oocytes. Firstly, we examined the fertilization and embryonic development of bovine oocytes after 22 and 30–34 h of in vitro maturation (IVM). The oocytes after 30–34 h of IVM (penetrated by sperm at around 40 h after starting IVM) showed a lower developmental rate to blastocysts (P<0.01), although normal fertilization rates were similar regardless of IVM duration. In the next experiment, reactive oxygen species (ROS), mitochondrial activity and ATP content in oocytes after 20, 30 and 40 h of IVM were examined. The lowest level of ROS was found in the group subjected to 30 h of IVM. The mitochondrial activity and ATP content in the group subjected to 40 h of IVM were higher than in the group subjected to 20 h of IVM (P<0.01), and those in the group subjected to 30 h of IVM showed intermediate values. Thereafter, the mitochondrial activities at 3 days after in vitro fertilization in embryos derived from the oocytes subjected to 22 and 34 h of IVM were evaluated. In the group subjected to 34 h of IVM, high-polarized mitochondria were frequently observed at the periphery of blastomeres. The present results suggest that high mitochondrial activity observed in oocytes after prolonged IVM culture and localization of high-polarized mitochondria at the periphery of blastomeres during early embryonic development may be associated with the low developmental competence in aged bovine oocytes.

Cytoskeletal and mitochondrial properties of bovine oocytes obtained by Ovum Pick‐Up: the effects of follicle stimulation and in vitro maturation

“…) – and the increased ATP levels (Koyama et al . ) in this group. Besides aging, other factors such as stress or abnormal expression or regulatory proteins might possibly affect the morphology of the meiotic spindle and cytoskeleton.…”

“…The actual ATP levels in matured oocytes may reflect their aging status since aging has been found to increase ATP levels in bovine oocytes (Koyama et al . ). In this respect, higher ATP levels in non‐stimulated IVM oocytes may refer to their increased aging status as suggested above.…”

Comparison of different fertilisation media for an in vitro maturation–fertilisation–culture system using flow-cytometrically sorted X chromosome-bearing spermatozoa for bovine embryo production

“…There is an optimal window for fertilisation after maturation, and if fertilisation does not occur within that time, unfertilised oocytes will undergo time-dependent deterioration in quality (oocyte aging; Ottolenghi et al 2004;Miao et al 2009;Koyama et al 2014). The effect of oocyte quality on embryonic developmental potential after fertilisation is significant (Krisher 2004;Wang and Sun 2007).…”

Oocyte mitochondrial function and reproduction

“…This could be due to mitochondrial dysfunction observed in vitrified oocytes [63]. Prolonged in-vitro maturation (IVM) reduces developmental rate of bovine oocytes to blastocysts, despite increasing their mitochondrial activity [64]. Epidermal growth factor-like peptides improve IVM outcomes in mouse cumulus oocyte complexes by inducing mitochondrial activity [65].…”