Abstract
The consensus that assisted reproduction technologies (ART), like in vitro fertilization, to induce oxidative stress (i.e., the known) belies how oocyte/zygote mitochondria—a major presumptive oxidative stressor—produce reactive oxygen species (ROS) with ART being unknown. Unravelling how oocyte/zygote mitochondria produce ROS is important for disambiguating the molecular basis of ART-induced oxidative stress and, therefore, to rationally target it (e.g., using site-specific mitochondria-targeted antioxidants). I review the known mechanisms of ROS production in somatic mitochondria to critique how oocyte/zygote mitochondria may produce ROS (i.e., the unknown). Several plausible site- and mode-defined mitochondrial ROS production mechanisms in ART are proposed. For example, complex I catalyzed reverse electron transfer-mediated ROS production is conceivable when oocytes are initially extracted due to at least a 10% increase in molecular dioxygen exposure (i.e., the intriguing). To address the term oxidative stress being used without recourse to the underlying chemistry, I use the species-specific spectrum of biologically feasible reactions to define plausible oxidative stress mechanisms in ART. Intriguingly, mitochondrial ROS-derived redox signals could regulate embryonic development (i.e., their production could be beneficial). Their potential beneficial role raises the clinical challenge of attenuating oxidative damage while simultaneously preserving redox signaling. This discourse sets the stage to unravel how mitochondria produce ROS in ART, and their biological roles from oxidative damage to redox signaling.
Highlights
The Major and Minor Mitochondiral Electron PathwaysThe major fate of substrate-derived electrons—free radicals—tunneling (a quantum mechanical property that enables electrons to penetrate a potential energy barrier without further input energy), according to the principles of quantum mechanics, through the redox centers nestled within the mitochondrial respiratory complexes is to reduce O2 —a diradical—to H2 O (reaction 1, see Figure 1) [21,25,37,38,39,40]
The consensus that assisted reproduction technologies (ART), like in vitro fertilization, to induce oxidative stress belies how oocyte/zygote mitochondria—a major presumptive oxidative stressor—produce reactive oxygen species (ROS) with ART being unknown
A fascinating finding arguing against a role for pyruvate dehydrogenase (PDH) is that it migrates to the nucleus, along with several other tricarboxylic acid cycle (TCA) enzymes, to support epigenetic wiring and genome activation in mouse and human zygotes [200,201]
Summary
The major fate of substrate-derived electrons—free radicals—tunneling (a quantum mechanical property that enables electrons to penetrate a potential energy barrier without further input energy), according to the principles of quantum mechanics, through the redox centers nestled within the mitochondrial respiratory complexes is to reduce O2 —a diradical—to H2 O (reaction 1, see Figure 1) [21,25,37,38,39,40]. A minor fate of substrate-derived electrons in the respiratory chain is to support the univalent reduction of O2 to superoxide at complex I, II and III (reaction 3, see Box 1 and Figure 1) [47]. Complex I oxidizes NADH to NAD to reduce ubiquinone (Q) to ubiquinol (QH2)
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