Reduced oxygen concentration improves the developmental competence of mouse oocytes following in vitro maturation

Abstract

Reduced atmospheric oxygen concentration is beneficial to embryo development; however, optimal oxygen concentration for oocyte maturation remains undetermined. Likewise, there is no consensus of appropriate medium supplementation during maturation. The objective of this study was to determine whether oxygen tension (20% or 5% O2) and epidermal growth factor (EGF) affect oocyte metabolism and subsequent embryo development. Cumulus-oocyte complexes (COCs) were collected from 28-day-old equine chorionic gonadotropin (eCG) primed or unprimed F1 (C57BL/6xCBA) mice. COCs were matured in defined medium in one of four groups: 20% O2, 20% O2 + EGF, 5% O2, 5% O2 + EGF. In vivo matured COCs were also collected for analysis. COCs from unprimed mice, matured in 5% O2 +/- EGF or 20% O2 + EGF had higher metabolic rates than COCs matured in 20% O2 (P < 0.05). COCs from primed mice had higher metabolic rates when matured in the presence of EGF, regardless of oxygen tension (P < 0.01). Oxygen uptake and mitochondrial membrane potential were higher for in vivo matured oocytes and oocytes matured under 5% O2 compared to oocytes matured under 20% O2 (P < 0.05). Blastocyst formation was not different between maturation groups (primed or unprimed); however, embryo cell numbers were 20-45% significantly higher when COCs were matured at 5% O2 (P < 0.05). Results suggest that oocytes matured in physiological concentrations of oxygen have improved development and metabolic activity, more closely resembling in vivo maturation. These findings have implications for oocyte maturation in both clinical and research laboratories.

Oxidative Phosphorylation-linked Respiration in Individual Bovine Oocytes

“…Stimulation of maximum respiratory capacity by CCCP may be due to substrate uptake, metabolism and electron transport activity [15]. The observed decrease in maximum respiratory capacity is in agreement with a previous study showing that oocytes matured in vitro under 20% oxygen tension have a lower membrane potential compared with those matured in vivo, as a result of increased reactive oxygen species (ROS) production during IVM [26]. Moreover, increased proton leak can also protect against mitochondrial damage induced by ROS such as superoxide [27].…”

Exogenous Adenosine Reduces the Mitochondrial Membrane Potential of Murine Oocytes During the Latter Half of In Vitro Maturation and Pronuclear Formation Following Chemical Activation

“…under 20% O2 [35], the current study using alpha-MEM without adenosine did not show any differences in MMP between oocytes matured in vivo and in vitro. The changes in the distribution of active mitochondria observed in the present study during oocyte maturation were similar in oocytes collected in vivo and those cultured in vitro, and the distributional changes were similar to those previously reported [8,9].…”

Lipids and oocyte developmental competence: the role of fatty acids and β-oxidation

“…Oocytes matured by IVM are however less likely to develop to the blastocyst stage (Rizos et al 2002 and result in higher rates of miscarriage compared with oocytes that mature in follicles in vivo (Buckett et al 2008). The causal mechanisms responsible for this poor oocyte quality following IVM are not clear; however, oocyte developmental competence is associated with the metabolism and metabolic rate of the oocyte and its surrounding cumulus cells (Biggers et al 1967, Downs 1995, Sugiura & Eppig 2005, Preis et al 2007. Adequate levels of intracellular ATP are also required for optimal oocyte developmental potential (Van Blerkom et al 1995) and therefore energy substrate supply to the COC via the follicular fluid or culture medium during in vivo maturation or IVM, respectively, is likely to affect oocyte quality.…”