Oxidative Phosphorylation-linked Respiration in Individual Bovine Oocytes

Abstract

Abstract. Mitochondrial bioenergetics in mammalian oocytes has not been sufficiently characterized. In this study, the function of oxidative phosphorylation (OXPHOS), a major pathway in mitochondria, was investigated in individual bovine oocytes by monitoring oxygen consumption using modified scanning electrochemical microscopy (SECM). At the germinal vesicle (GV) stage, 65% of basal respiration was used for mitochondrial respiration, which was inhibited by complex IV inhibitor. Around 63% of mitochondrial respiration was coupled to ATP synthesis, as determined by sensitivity to an ATP synthase inhibitor, and the remaining 37% was attributed to proton leak. In contrast, 50% and 43% of mitochondrial respiration were used for ATP synthesis in in vivo-and in vitro-derived metaphase II (MII)-stage oocytes, respectively. ATP-linked respiration, in both in vivo-and in vitro-derived MII-stage oocytes, was significantly lower than in GV-stage oocytes, suggesting that OXPHOS in bovine oocytes is more active at the GV stage compared with the MII stage. Interestingly, basal respiration in in vitro-derived MII oocytes was significantly higher than for in vivo-derived oocytes, reflecting an increase in proton leak. Next, we assessed respiration in MII oocytes cultured for 8 h. The aged oocytes had a significantly reduced maximum respiratory capacity, which was stimulated by a mitochondrial uncoupler, and reduced ATP-linked respiration compared with non-aged oocytes. However, the aging-related phenomenon could be prevented by caffeine treatment. We conclude that OXPHOS in bovine oocytes varies in the transition from GV to MII stage, in vitro maturation and the aging process. This approach will be particularly useful for analyzing mitochondrial bioenergetics in individual mammalian oocytes. Key words: Bovine, Mitochondrial function, Oocyte, Oxidative phosphorylation, Oxygen consumption (J. Reprod. Dev. 58: [636][637][638][639][640][641] 2012) M itochondria play fundamental roles in the cell, and mitochondrial dysfunction has been linked with several pathologies, including infertility and developmental failure. Although they share general characteristics, mitochondria can have distinct features based on inner membrane invaginations and matrix structures. Depending on their cell type and functional status, mitochondria present an extensive range of morphologies, are functionally heterogeneous [1], and vary in number [2]. Oxidative phosphorylation (OXPHOS), the process that couples substrate oxidation to ATP synthesis, is the major and best-known metabolic function of mitochondria. During OXPHOS, electrons are transferred from nutrients to reducing equivalents (e.g., NADH), then to electron carriers, and finally to oxygen. Such electron transfer is mediated by oxido-reductive reactions of the tricarboxylic acid cycle in the mitochondrial matrix and by electron transport in the inner mitochondrial membrane. The energy harvested during these oxido-reductive reactions is stored in a proton gradient across the inner mitochondrial ...

Does the maternal age affect the mesenchymal stem cell markers and gene expression in the human placenta? What is the evidence?

“…This finding is supported by earlier studies on the ATP content (Van Blerkom et al, 1995) and ultrastructure of human oocytes (de Bruin et al, 2004) as well as mice (Kushnir et al, 2012) bovine (Sugimura et al, 2012) and hamsters (Simsek-Duran et al, 2013) oocytes. It was reported that the level of telomerase activity is not sufficient to maintain telomere length of stem cells during aging with increased sensitivity toward senescence or apoptosis induced by telomere shortening (Ju and Rudolph, 2006;Mimeault and Batra, 2009).…”

Effects of maternal age on the expression of mesenchymal stem cell markers in the components of human umbilical cord

“…The results of some ultrastructural and biochemical studies make it clear that the structure and function of the cytoplasmic organelles, particularly mitochondria, of both the oocytes and the granulosa cells, which are critical for fertilization and normal embryonic development, are markedly compromised in the oocytes of older women [34]. This finding is supported by earlier studies on the ATP content [35] and ultrastructure of human oocytes [36] as well as murine [37], bovine [38] and hamster [39] oocytes. Ju and Rudolph reported that the level of telomerase www.fhc.viamedica.pl activity is not sufficient to maintain telomere length of stem cells during aging with increased sensitivity towards senescence or apoptosis induced by telomere shortening [40].…”

Oocyte environment: follicular fluid and cumulus cells are critical for oocyte health

“…Oxygen consumption increases during oocyte fertilization and embryo development (105,(159)(160)(161)(162). Oxygen consumption by the oocyte, however, is difficult to measure, hampering its application as a clinical assay.…”