Identification of non-mitochondrial NADPH oxidase and the spatio-temporal organization of its components in mouse spermatozoa

Calpain Regulates Reactive Oxygen Species Production during Capacitation through the Activation of NOX2 and NOX4

Capacitation is a series of physiological, biochemical, and metabolic changes experienced by mammalian spermatozoa. These changes enable them to fertilize eggs. The capacitation prepares the spermatozoa to undergo the acrosomal reaction and hyperactivated motility. Several mechanisms that regulate capacitation are known, although they have not been fully disclosed; among them, reactive oxygen species (ROS) play an essential role in the normal development of capacitation. NADPH oxidases (NOXs) are a family of enzymes responsible for ROS production. Although their presence in mammalian sperm is known, little is known about their participation in sperm physiology. This work aimed to identify the NOXs related to the production of ROS in guinea pig and mouse spermatozoa and define their participation in capacitation, acrosomal reaction, and motility. Additionally, a mechanism for NOXs' activation during capacitation was established. The results show that guinea pig and mouse spermatozoa express NOX2 and NOX4, which initiate ROS production during capacitation. NOXs inhibition by VAS2870 led to an early increase in the capacitation and intracellular concentration of Ca²⁺ in such a way that the spermatozoa also presented an early acrosome reaction. In addition, the inhibition of NOX2 and NOX4 reduced progressive motility and hyperactive motility. NOX2 and NOX4 were found to interact with each other prior to capacitation. This interaction was interrupted during capacitation and correlated with the increase in ROS. Interestingly, the association between NOX2-NOX4 and their activation depends on calpain activation, since the inhibition of this Ca²⁺-dependent protease prevents NOX2-NOX4 from dissociating and ROS production. The results indicate that NOX2 and NOX4 could be the most important ROS producers during guinea pig and mouse sperm capacitation and that their activation depends on calpain.

OXIDATIVE STRESS AND REPRODUCTIVE FUNCTION: The impact of oxidative stress on reproduction: a focus on gametogenesis and fertilization

In brief

Many aspects of the reproductive process are impacted by oxidative stress. This article summarizes the chemical nature of reactive oxygen species and their role in both the physiological regulation of reproductive processes and the pathophysiology of infertility.

Abstract

This article lays out the fundamental principles of oxidative stress. It describes the nature of reactive oxygen species (ROS), the way in which these potentially toxic metabolites interact with cells and how they impact both cellular function and genetic integrity. The mechanisms by which ROS generation is enhanced to the point that the cells' antioxidant defence mechanisms are overwhelmed are also reviewed taking examples from both the male and female reproductive system, with a focus on gametogenesis and fertilization. The important role of external factors in exacerbating oxidative stress and impairing reproductive competence is also examined in terms of their ability to disrupt the physiological redox regulation of reproductive processes. Developing diagnostic and therapeutic strategies to cope with oxidative stress within the reproductive system will depend on the development of a deeper understanding of the nature, source, magnitude, and location of such stress in order to fashion personalized treatments that meet a given patient's clinical needs.

Relationship between sperm NAD + concentration and reproductive aging in normozoospermia men:A Cohort study

BACKGROUND

The mechanisms of age-dependent reproductive decline in men are largely overlooked. An age-dependent reduction in nicotinamide adenine dinucleotide (NAD+) levels has been reported in multiple somatic and female reproductive tissues, including oocytes and ovarian tissue. However, the relationship between NAD + levels and male reproduction has not yet been studied. In the current study, the association between sperm NAD + level and paternal age was investigated. In addition, we also investigated whether sperm NAD + levels were related to semen quality.

METHODS

In this pilot observational cohort study, semen samples from 51 male subjects who visited a university-affiliated reproductive medical center for preconception consultation (< 30 years: n = 13, 30-40 years: n = 19, > 40 years: n = 19) were recruited. Their anthropometric characteristics were recorded, and semen analysis was performed. Their sperm NAD + levels were evaluated spectrophotometrically.

RESULTS

There were significant differences among the three age groups in the major parameters of semen quality. The sperm NAD + level was, however, similar among the three groups (< 30 years: 91.61 ± 15.59 nmol/10⁶ sperm, 30-40 years: 125.60 ± 16.28 nmol/10⁶ sperm, > 40 years: 115.59 ± 16.55 nmol/10⁶ sperm). Additionally, linear regression also revealed no correlation between sperm NAD + concentration and the age of the participants (r² = 0.018, p = 0.35). Noticeably, a negative correlation was found between the sperm NAD + concentrations and the sperm quality parameters, including sperm concentration (r² = 0.78, p < 0.0001), sperm count (r² = 0.47, p < 0.0001), mobile sperm number (r² = 33, p < 0.0001), and DFI (r² = 0.35, p < 0.0001). The semen volume and mobility rate were not related to the sperm NAD + concentration.

CONCLUSION

Unlike the age-related decrease of NAD + levels in oocytes and ovarian tissue, the sperm NAD + concentration is not age dependent. Sperm NAD + levels are negatively correlated with sperm quality, suggesting a unique role of NAD + in spermatogenesis, which warrants further study and opens opportunities for pharmaceutical interventions for oligozoospermia.

Roles of Oxidative Stress in the Male Reproductive System: Potential of Antioxidant Supplementation for Infertility Treatment

The decline of fertility in modern society is a serious worldwide concern, and the reasons behind it are complex and difficult to unveil. The fact that a big percentage of infertility cases remain diagnosed as idiopathic, turn the strategies to treat such conditions very limited. Nevertheless, one must agree that keeping the oxidative balance of the reproductive tissues should be one of the first lines of treatment for infertile patients. As reported, 30-80% of male infertile individuals present high levels of prooxidant species in the seminal fluid. Thus, antioxidant therapies, which consist of dietary supplementation therapy with one or more antioxidant compound, remain the first step in the treatment of male infertility. Nevertheless, the efficacy of such therapies is variable between individuals. The most common prescribed antioxidants are carnitines and vitamins C and E, but recently phytochemical quercetin has emerged as a potential compound for the treatment of oxidative stress in the male reproductive system. Although there are several animals' evidence about the great potential of quercetin for the treatment of infertility, clinical trials on this subject remain scarce.

Impacts of obesity, maternal obesity and nicotinamide mononucleotide supplementation on sperm quality in mice

Male fertility and sperm quality are negatively impacted by obesity. Furthermore, recent evidence has shown that male offspring from obese rat mothers also have reduced sperm quality and fertility. Here, we extend work in this area by comparing the effects of both maternal obesity and offspring post-weaning diet-induced obesity, as well as their combination, on sperm quality in mice. We additionally tested whether administration of the NAD⁺-booster nicotinamide mononucleotide (NMN) can ameliorate the negative effects of obesity and maternal obesity on sperm quality. We previously showed that intraperitoneal (i.p.) injection of NMN can reduce the metabolic deficits induced by maternal obesity or post-weaning dietary obesity in mice. In this study, female mice were fed a high-fat diet (HFD) for 6 weeks until they were 18% heavier than a control diet group. Thereafter, HFD and control female mice were mated with control diet males, and male offspring were weaned into groups receiving control or HFD. At 30 weeks of age, mice received 500 mg/kg body weight NMN or vehicle PBS i.p. for 21 days. As expected, adiposity was increased by both maternal and post-weaning HFD but reduced by NMN supplementation. Post-weaning HFD reduced sperm count and motility, while maternal HFD increased offspring sperm DNA fragmentation and levels of aberrant sperm chromatin. There was no evidence that the combination of post-weaning and maternal HFD exacerbated the impacts in sperm quality suggesting that they impact spermatogenesis through different mechanisms. Surprisingly NMN reduced sperm count, vitality and increased sperm oxidative DNA damage, which was associated with increased NAD⁺ in testes. A subsequent experiment using oral NMN at 400 mg/kg body weight was not associated with reduced sperm viability, oxidative stress, mitochondrial dysfunction or increased NAD⁺ in testes, suggesting that the negative impacts on sperm could be dependent on dose or mode of administration.

Trans-plasma membrane electron transport in mammals: functional significance in health and disease

Trans-plasma membrane electron transport (t-PMET) has been established since the 1960s, but it has only been subject to more intensive research in the last decade. The discovery and characterization at the molecular level of its novel components has increased our understanding of how t-PMET regulates distinct cellular functions. This review will give an update on t-PMET, with particular emphasis on how its malfunction relates to some diseases, such as cancer, abnormal cell death, cardiovascular diseases, aging, obesity, neurodegenerative diseases, pulmonary fibrosis, asthma, and genetically linked pathologies. Understanding these relationships may provide novel therapeutic approaches for pathologies associated with unbalanced redox state.

Redox regulation of human sperm function: from the physiological control of sperm capacitation to the etiology of infertility and DNA damage in the germ line

Defective sperm function is the largest single defined cause of human infertility and one of the major reasons we are witnessing an exponential increase in the uptake of assisted conception therapy in the developed world. A major characteristic of defective human spermatozoa is the presence of large amounts of DNA damage, which is, in turn, associated with reduced fertility, increased rates of miscarriage, and an enhanced risk of disease in the offspring. This DNA damage is largely oxidative and is closely associated with defects in spermiogenesis. To explain the origins of this DNA damage, we postulate that spermiogenesis is disrupted by oxidative stress, leading to the creation of defective gametes with poorly remodeled chromatin that are particularly susceptible to free radical attack. To compound the problem, these defective cells have a tendency to undergo an unusual truncated form of apoptosis associated with high amounts of superoxide generation by the sperm mitochondria. This leads to significant oxidative DNA damage that eventually culminates in the DNA fragmentation we see in infertile patients. In light of the significance of oxidative stress in the etiology of defective sperm function, a variety of antioxidant therapies are now being assessed for their therapeutic potential.

Apoptosis and DNA damage in human spermatozoa

DNA damage is frequently encountered in spermatozoa of subfertile males and is correlated with a range of adverse clinical outcomes including impaired fertilization, disrupted preimplantation embryonic development, increased rates of miscarriage and an enhanced risk of disease in the progeny. The etiology of DNA fragmentation in human spermatozoa is closely correlated with the appearance of oxidative base adducts and evidence of impaired spermiogenesis. We hypothesize that oxidative stress impedes spermiogenesis, resulting in the generation of spermatozoa with poorly remodelled chromatin. These defective cells have a tendency to default to an apoptotic pathway associated with motility loss, caspase activation, phosphatidylserine exteriorization and the activation of free radical generation by the mitochondria. The latter induces lipid peroxidation and oxidative DNA damage, which then leads to DNA fragmentation and cell death. The physical architecture of spermatozoa prevents any nucleases activated as a result of this apoptotic process from gaining access to the nuclear DNA and inducing its fragmentation. It is for this reason that a majority of the DNA damage encountered in human spermatozoa seems to be oxidative. Given the important role that oxidative stress seems to have in the etiology of DNA damage, there should be an important role for antioxidants in the treatment of this condition. If oxidative DNA damage in spermatozoa is providing a sensitive readout of systemic oxidative stress, the implications of these findings could stretch beyond our immediate goal of trying to minimize DNA damage in spermatozoa as a prelude to assisted conception therapy.

Role of glycerol-3-phosphate dehydrogenase 2 in mouse sperm capacitation

A tyrosine phosphoproteome study of hamster spermatozoa indicated that glycerol-3-phosphate dehydrogenase 2 (GPD2), is one of the proteins that enables tyrosine phosphorylation during sperm capacitation. Further, enzymatic activity of GPD2 correlated positively with sperm capacitation [Kota et al., 2009; Proteomics 9:1809-1826]. Therefore, understanding the function of GPD2 would help to unravel the molecular mechanism of sperm capacitation. In this study, involving the use of spermatozoa from Gpd2(+/+) and Gpd2(-/-) mice, it has been demonstrated that in the absence of Gpd2, hyperactivation and acrosome reaction were significantly altered, and a few changes in protein tyrosine phosphorylation were also observed during capacitation. Evidence is provided to demonstrate that GPD2 activity is required for ROS generation in mouse spermatozoa during capacitation, failing which, capacitation is impaired. These results imply that GPD2 is involved in sperm capacitation.

Control of superoxide and nitric oxide formation during human sperm capacitation

We studied the modulation of superoxide anion (O(2).(-)) and nitric oxide (NO.) generation during human sperm capacitation (changes needed for the acquisition of fertility). The production of NO. (diaminofluorescein-2 fluorescence assay), but not that of O(2).(-) (luminescence assay), related to sperm capacitation was blocked by inhibitors of protein kinase C, Akt, protein tyrosine kinase, etc., but not by those of protein kinase A. Extracellular calcium (Ca(2+)) controlled O(2).(-) synthesis but extra- and intracellular Ca(2+) regulated NO. formation. Zinc inhibited capacitation and formation of O(2).(-) and NO.. Zinc chelators (TPEN and EDTA) and sulfhydryl-targeted compounds (diamide and N-ethylmaleimide) stimulated capacitation and formation of O(2).(-) and NO.; superoxide dismutase (SOD) and nitric oxide synthase inhibitor (L-NMMA) prevented these events. Diphenyliodonium (flavoenzyme inhibitor) blocked capacitation and related O(2).(-) synthesis but promoted NO. formation, an effect canceled by SOD and L-NMMA. NADPH induced capacitation and NO. (but not O(2).(-)) synthesis and these events were blocked by L-NMMA and not by SOD. Integration of these data on O(2).(-) and NO. production during capacitation reinforces the concept that a complex, but flexible, network of factors is involved and probably is associated with rescue mechanisms, so that spermatozoa can achieve successful fertilization.

Hamster sperm capacitation: role of pyruvate dehydrogenase A and dihydrolipoamide dehydrogenase

Recently, we demonstrated that pyruvate dehydrogenase A2 (PDHA2) is tyrosine phosphorylated in capacitated hamster spermatozoa. In this report, using bromopyruvate (BP), an inhibitor of PDHA, we demonstrated that hamster sperm hyperactivation was blocked regardless of whether PDHA was inhibited prior to or after the onset of hyperactivation, but the acrosome reaction was blocked only if PDHA was inhibited prior to the onset of the acrosome reaction. Further, inhibition of PDHA activity did not inhibit capacitation-associated protein tyrosine phosphorylation observed in hamster spermatozoa. It is demonstrated that the essentiality of PDHA for sperm capacitation is probably dependent on its ability to generate effectors of capacitation such as reactive oxygen species (ROS) and cAMP, which are significantly decreased in the presence of BP. MICA (5-methoxyindole-2-carboxylic acid, a specific inhibitor of dihydrolipoamide dehydrogenase [DLD]), another component of the pyruvate dehydrogenase complex (PDHc), also significantly inhibited ROS generation and cAMP levels thus implying that these enzymes of the PDHc are required for ROS and cAMP generation. Furthermore, dibutryl cyclic adenosine monophosphate could significantly reverse the inhibition of hyperactivation observed in the presence of BP and inhibition of acrosome reaction observed in the presence of BP or MICA. The calcium ionophore, A23187, could also significantly reverse the inhibitory effect of BP and MICA on sperm acrosome reaction. These results establish that PDHA is required for hamster sperm hyperactivation and acrosome reaction, and DLD is required for hamster acrosome reaction. This study also provides evidence that ROS, cAMP, and calcium are involved downstream to PDHA.

The NOX family of ROS-generating NADPH oxidases: physiology and pathophysiology

For a long time, superoxide generation by an NADPH oxidase was considered as an oddity only found in professional phagocytes. Over the last years, six homologs of the cytochrome subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the phagocyte NADPH oxidase itself (NOX2/gp91(phox)), the homologs are now referred to as the NOX family of NADPH oxidases. These enzymes share the capacity to transport electrons across the plasma membrane and to generate superoxide and other downstream reactive oxygen species (ROS). Activation mechanisms and tissue distribution of the different members of the family are markedly different. The physiological functions of NOX family enzymes include host defense, posttranlational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. NOX enzymes also contribute to a wide range of pathological processes. NOX deficiency may lead to immunosuppresion, lack of otoconogenesis, or hypothyroidism. Increased NOX activity also contributes to a large number or pathologies, in particular cardiovascular diseases and neurodegeneration. This review summarizes the current state of knowledge of the functions of NOX enzymes in physiology and pathology.

The antioxidant glutathione peroxidase family and spermatozoa: a complex story

Oxidative damage is one threat spermatozoa have to face during epididymal maturation and storage. However, it is clear that reactive oxygen species (ROS) are also central for sperm physiology in processes such as sperm maturation and capacitation. It is therefore essential that there exists around sperm cells a fine balance between ROS production and recycling. To do so, sperm cells and epididymal epithelial cells rely on common enzymatic ROS scavengers such as superoxide dismutase (SOD), glutathione peroxidases (GPX) and catalase (CAT) as well as more specific types such as indoleamine dioxygenase (IDO). Among the catalytic triad (SOD/GPX/CAT), the glutathione peroxidase protein family occupies a peculiar position, since several GPX have been found to be present on and around epididymal transiting sperm cells. Here, we will review our present knowledge regarding GPX expression, presence and putative role(s) within the epididymis and on spermatozoa. Taking into account our recent findings regarding the epididymal expression of indoleamine dioxygenase in mouse we will also discuss how we think this superoxide anion recycling enzyme completes the complex ROS generation/recycling balance in this organ.

Reactive oxygen species in spermatozoa: methods for monitoring and significance for the origins of genetic disease and infertility

Human spermatozoa generate low levels of reactive oxygen species in order to stimulate key events, such as tyrosine phosphorylation, associated with sperm capacitation. However, if the generation of these potentially pernicious oxygen metabolites becomes elevated for any reason, spermatozoa possess a limited capacity to protect themselves from oxidative stress. As a consequence, exposure of human spermatozoa to intrinsically- or extrinsically- generated reactive oxygen intermediates can result in a state of oxidative stress characterized by peroxidative damage to the sperm plasma membrane and DNA damage to the mitochondrial and nuclear genomes. Oxidative stress in the male germ line is associated with poor fertilization rates, impaired embryonic development, high levels of abortion and increased morbidity in the offspring, including childhood cancer. In this review, we consider the possible origins of oxidative damage to human spermatozoa and reflect on the important contribution such stress might make to the origins of genetic disease in our species.