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) oxygen tension, as well as a combination of the two, on oocyte metabolism and quality during maturation. Cumulus cell-oocyte complexes collected from gilt ovaries were used for in vitro maturation. In addition, RNA-seq was conducted on the cumulus cells. Low oxygen tension throughout oocyte maturation did not alter the developmental rate to the blastocyst stage; however, it increased oocyte ATP and lipid content while reducing mitochondrial reactive oxygen species and mitochondrial membrane potential. Low-oxygen conditions increased glucose consumption but reduced mitochondrial DNA copy number and mitochondrial protein in cumulus cells. RNA-seq of cumulus cells revealed that low oxygen tension reduced mitochondrial activity and increased glycolysis, with the upregulation of glycolytic genes and downregulation of oxidative phosphorylation and steroidogenesis-related genes. In addition, a two-step oxygen protocol with low (5%) for the first period (0-21 h) and high (20%) for the last half period (21-44 h) increased the ATP and lipid content in oocytes and improved the embryonic developmental ability of the oocytes compared to the high-oxygen group. In conclusion, low oxygen tension during the first part of the maturation period is beneficial for oocyte quality, considering the observed metabolic changes.
Inoue et al. (Fri,) studied this question.