Regulation of redox metabolism in the mouse oocyte and embryo

Abstract

Energy homeostasis of the oocyte is a crucial determinant of fertility. Following ovulation, the oocyte is exposed to the unique environment of the Fallopian tube, and this is reflected in a highly specialised biochemistry. The minute amounts of tissue available have made the physiological analysis of oocyte intermediary metabolism almost impossible. We have therefore used confocal imaging of mitochondrial and cytosolic redox state under a range of conditions to explore the oxidative metabolism of intermediary substrates. It has been known for some time that the early mouse embryo metabolises external pyruvate and lactate but not glucose to produce ATP. We now show at the level of single oocytes, that supplied glucose has no effect on the redox potential of the oocyte. Pyruvate is a cytosolic oxidant but a mitochondrial reductant, while lactate is a strong cytosolic reductant via the activity of lactate dehydrogenase. Unexpectedly, lactate-derived pyruvate appears to be diverted from mitochondrial oxidation. Our approach also reveals that the level of reduced glutathione (GSH) in the oocyte is maintained by glutathione reductase, which oxidises intracellular NADPH to reduce oxidised glutathione. Surprisingly, NADPH does not seem to be supplied by the pentose phosphate pathway in the unfertilised oocyte but rather by cytosolic NADP-dependent isocitrate dehydrogenase. Remarkably, we also found that the oxidant action of pyruvate impairs development, demonstrating the fundamental importance of redox state on early development.

Lost in the zygote: the dilution of paternal mtDNA upon fertilization

“…Mammalian embryos are exposed to an environment with high levels of nutrients within the female reproductive tract (Gardner et al, 2002;Dumollard et al, 2007a). These nutrients are directly utilized by the developing embryo to satisfy its metabolic requirements, allowing for limited oxidative activity of mitochondria (Leese, 2002;Houghton and Leese, 2004;Dumollard et al, 2007b). Teleosts instead develop externally, depending fully on nutrients present in the lipid and protein-rich yolk.…”

Oxidative stress and ageing of the post-ovulatory oocyte

“…Operational mitochondria are crucial to normal oocyte function, with these organelles representing the primary source of ATP production within both oocytes and early embryos (Dumollard et al 2007). The functionality of the mitochondria does, however, become compromised with extended periods of time following ovulation, a factor that is thought to heavily influence oocyte quality.…”

Effect of inhibitors of NADPH oxidase complex and mitochondrial ATP‐sensitive potassium channels on generation of dopaminergic neurons from neurospheres of mesencephalic precursors

“…ROS take part in the signal transduction pathways of several growth and trophic factors, cytokines and G-proteincoupled receptors (Bartosz, 2009) and regulate proliferation, differentiation, migration and apoptosis in a wide variety of cells (Sauer et al, 2001;Bedard and Krause, 2007;Dumollard et al, 2007). ROS can signal to the nucleus and control gene expression to regulate cell metabolism appropriately (Finley and Haigis, 2009).…”

“…Modulation of intracellular ROS and oxidative stress is especially important in the nervous system because of the associated high energy requirements (Kann and Kovacs, 2007;Nicholls, 2008); dual effects of ROS on cell metabolism (as harmful species and as signal mediators) have also been observed in neural cells. Furthermore, changes in the redox state of cells have been observed throughout the neural lineage, suggesting that ROS have important functions during development and neural differentiation (Cho et al, 2006;Dumollard et al, 2007;Kim and Wong, 2009).…”