Accumulation of Electrophilic Aldehydes During Postovulatory Aging of Mouse Oocytes Causes Reduced Fertility, Oxidative Stress, and Apoptosis1

Abstract

With increasing periods of time following ovulation, the metaphase II (MII)-stage oocyte experiences overproduction of reactive oxygen species and elevated levels of lipid peroxidation that are implicitly linked with functional deficiencies acquired during postovulatory oocyte aging. We have demonstrated that the electrophilic aldehydes 4-hydroxynonenal (4HNE), malondialdehyde, and acrolein are by-products of nonenzymatic lipid peroxidation in the murine MII-stage oocyte, adducting to multiple proteins within the cell. The covalent modification of oocyte proteins by these aldehydes increased with extended periods of time postovulation; the mitochondrial protein succinate dehydrogenase (SDHA) was identified as a primary target for 4HNE adduction. Time- and dose-dependent studies revealed that exposure to elevated levels of electrophilic aldehydes causes mitochondrial reactive oxygen species production, lipid peroxidation, loss of mitochondrial membrane potential, and eventual apoptosis within the MII oocyte, presumably as a consequence of electron transport chain collapse following SDHA adduction. Additionally, we have determined that short-term exposure to low doses of 4HNE dramatically impairs the oocyte's ability to participate in fertilization and support embryonic development; however, this loss of functionality can be prevented by supplementation with the antioxidant penicillamine. In conclusion, this study has revealed that the accumulation of electrophilic aldehydes is linked to postovulatory oocyte aging, causing reduced fertility, oxidative stress, and apoptosis of this highly specialized cell. These data highlight the importance of timely fertilization of the mammalian oocyte postovulation and emphasize the potential advantages associated with antioxidant supplementation of oocyte culture medium in circumstances where reinsemination of oocytes may be desirable (i.e., rescue intracytoplasmic sperm injection), or where in vitro fertilization may be delayed.

The lipid peroxidation product 4-hydroxynonenal contributes to oxidative stress-mediated deterioration of the ageing oocyte

“…Penicillamine was selected as the nucleophile of choice owing to its capacity to covalently bind 4-HNE and thus limit its bio-availability 76 . Furthermore, penicillamine has been shown to reduce the negative effects of 4-HNE on embryo development 29 and human sperm zona-pellucida binding 59 by reducing 4-HNE adduction to vulnerable proteins. Thus, the impact of penicillamine supplementation was assessed via PBE rates, aneuploidy rates and PLA detection of 4-HNE adducted tubulin in oocytes that have experience OS.…”

“…Among the numerous consequences of mitochondrial dysfunction is an increase in ROS generation as a by-product of electron leakage from the electron transport chain (ETC). Unfortunately, elevated concentrations of ROS also have the potential to damage mtDNA and proteins, leading to a state of auto-oxidation 29 . Concomitantly, the repair and defensive capacity of the oocyte has been reported to decrease with increasing maternal age.…”

“…The resulting dysregulation of these proteins is known to compromise sperm-oocyte recognition and promote electron leakage from the electron transport chain, thus exacerbating the level of OS experienced by the spermatozoa 60 . Importantly, SDHA has also proven to be a conserved target for 4-HNE adduction in postovulatory aged metaphase II (MII) mouse oocytes, thus implicating the aldehyde in deterioration of oocyte quality 29 . Such findings take on added significance in view of the increase in 4-HNE generation observed within the ovarian interstitial tissue of ageing mice 62 .…”

Quercetin delays postovulatory aging of mouse oocytes by regulating SIRT expression and MPF activity

“…Oxidative stress acts as a ‘trigger’ for a cascade of other factors that orchestrate postovulatory aging, as well as directly affecting multiple aspects of oocyte biochemistry and functionality [5, 7, 24]. Increased oxidative stress in postovulatory aged oocytes is due to a progressive increase in ROS production and the concomitant depletion of antioxidant protection, as well as environmental factors [7].…”

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“…Immediately following fertilization, either in vivo or in vitro, the sperm initiates a series of irreversible biochemical and physiological oocyte modifications, which rescue it from predestined apoptosis [14]. The earliest detected fertilization signal is a distinctive series of cytosolic Ca 2+ oscillations, a prerequisite step for embryo development [15].…”