Background Mitochondria are multitasking organelles involved in ATP synthesis, reactive oxygen species (ROS) production, calcium signalling and apoptosis; and mitochondrial defects are known to cause physiological dysfunction, including infertility. The goal of this review was to identify and discuss common themes in mitochondrial function related to mammalian reproduction. Methods The scientific literature was searched for studies reporting on the several aspects of mitochondrial activity in mammalian testis, sperm, oocytes, early embryos and embryonic stem cells. Results ATP synthesis and ROS production are the most discussed aspects of mitochondrial function. Metabolic shifts from mitochondria-produced ATP to glycolysis occur at several stages, notably during gametogenesis and early embryo development, either reflecting developmental switches or substrate availability. The exact role of sperm mitochondria is especially controversial. Mitochondria-generated ROS function in signalling but are mostly described when produced under pathological conditions. Mitochondria-based calcium signalling is primarily important in embryo activation and embryonic stem cell differentiation. Besides pathologically triggered apoptosis, mitochondria participate in apoptotic events related to the regulation of spermatogonial cell number, as well as gamete, embryo and embryonic stem cell quality. Interestingly, data from knock-out (KO) mice is not always straightforward in terms of expected phenotypes. Finally, recent data suggests that mitochondrial activity can modulate embryonic stem cell pluripotency as well as differentiation into distinct cellular fates. Conclusions Mitochondria-based events regulate different aspects of reproductive function, but these are not uniform throughout the several systems reviewed. Low mitochondrial activity seems a feature of 'stemness', being described in spermatogonia, early embryo, inner cell mass cells and embryonic stem cells.

/pdf/mitochondrial-functionality-in-reproduction-from-gonads-and-3sa7b019k2.pdf

Mitochondrial functionality in reproduction: from gonads and gametes to embryos and embryonic stem cells

The use of frozen semen in the swine industry is limited by problems with viability and fertility compared with liquid semen. Part of the reduction in sperm motility and fertility associated with cryopreservation may be due to oxidative damage from excessive or inappropriate formation of reactive oxygen species (ROS). Chemiluminescence measurements of ROS are not possible in live cells and are problematic because of poor specificity. An alternative approach, flow cytometry, was developed to identify viable boar sperm containing ROS utilizing the dyes hydroethidine and 2', 7'-dichlorodihydrofluorescein diacetate as oxidizable substrates and impermeant DNA dyes to exclude dead sperm. The percentage of sperm with high mitochondrial transmembrane potential was determined by flow cytometry using the mitochondrial probe 5, 5', 6, 6'-tetrachloro-1, 1', 3, 3'-tetraethylbenzimidazolylcarbocyanine iodide with propidium iodide staining to exclude nonviable cells. Sperm were incubated with and without ROS generators and free radical scavengers. Basal ROS formation was low (less than 4%) and did not differ (P = 0.26) between viable fresh and frozen-thawed boar sperm. In addition, fresh and frozen-thawed viable sperm were equally susceptible (P = 0.20) to intracellular formation of ROS produced by xanthine/xanthine oxidase (94.4 and 87.9% of sperm, respectively). Menadione increased (P < 0.05) ROS formation, decreased (P < 0.05) JC-1-aggregate fluorescence intensity, and decreased (P < 0.05) motion variables by 25 to 60%. The mechanism of inhibition of motility by ROS formation may be related to a decrease in mitochondrial charge potential below a critical threshold. Catalase and superoxide dismutase treatment in the presence of xanthine/xanthine oxidase indicated that hydrogen peroxide was the primary intracellular ROS measured. Further, catalase, but not superoxide dismutase, was capable of attenuating ROS-induced inhibition of motility. Whereas basal intracellular hydrogen peroxide formation was low in viable fresh and frozen-thawed boar sperm, both were quite susceptible to external sources of hydrogen peroxide.

Determination of intracellular reactive oxygen species and high mitochondrial membrane potential in Percoll-treated viable boar sperm using fluorescence-activated flow cytometry.

Concentration, motility and morphology are parameters commonly used to determine the fertilization potential of an ejaculate. These parameters give a general view on the quality of sperm but do not provide information about one of the most important components of the reproductive outcome: DNA. Either single or double DNA strand breaks can set the difference between fertile and infertile males. Sperm DNA fragmentation can be caused by intrinsic factors like abortive apoptosis, deficiencies in recombination, protamine imbalances or oxidative stress. Damage can also occur due to extrinsic factors such as storage temperatures, extenders, handling conditions, time after ejaculation, infections and reaction to medicines or post-testicular oxidative stress, among others. Two singular characteristics differentiate sperm from somatic cells: Protamination and absence of DNA repair. DNA repair in sperm is terminated as transcription and translation stops post-spermiogenesis, so these cells have no mechanism to repair the damage occurred during their transit through the epididymis and post-ejaculation. Oocytes and early embryos have been shown to repair sperm DNA damage, so the effect of sperm DNA fragmentation depends on the combined effects of sperm chromatin damage and the capacity of the oocyte to repair it. In this contribution we review some of these issues.

https://www.mdpi.com/1422-0067/13/11/14026/pdf

Types, Causes, Detection and Repair of DNA Fragmentation in Animal and Human Sperm Cells

Effects of reactive oxygen species on sperm function

Farm animals are exposed to zearalenone through the feed because of the widespread occurrence of this mycotoxin in cereals and clinical reproductive disorders due to mycotoxin effects are often reported in farm animal species. This review describes the metabolism, the mechanistic aspects, the clinical reproductive symptoms and the in vitro effects on functional parameters of oocytes and sperm cells induced by zearalenone and its derivatives in farm animals. The studies on in vitro effects allow to understand the action mechanisms of mycotoxins and, sometime, to explain the in vivo symptoms. The impairment of semen quality and female reproductive function induced by zearalenone could be a factor responsible for the reproductive failure in farm animals.

Zearalenone and reproductive function in farm animals.

Effect of storage time and temperature on stallion sperm DNA and fertility

Relationship between stallion sperm motility and viability as detected by two fluorescence staining techniques using flow cytometry.

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Effect of storage time and temperature on stallion sperm DNA and fertility

Relationship between stallion sperm motility and viability as detected by two fluorescence staining techniques using flow cytometry.