Knockout of the transcription factor NRF2 disrupts spermatogenesis in an age-dependent manner

A Key regulatory protein QRICH2 governing sperm function with profound antioxidant properties, enhancing sperm viability

Infertility poses a global health and social challenge, affecting approximately 15% of couples at childbearing age, with half of the cases attributed to male factors, wherein genetic factors exert a substantial role. In our prior investigation, we identified loss-of-function variants within the gene encoding glutamine-rich protein 2 (QRICH2) in two consanguineous families, leading to various morphological abnormalities in sperm flagella and male infertility. Moreover, our observations in Qrich2 knockout mice revealed a pronounced reduction in spermatozoa count. However, the underlying mechanism remains elusive, prompting further investigation in the current study. By conducting experiments such as Hematoxylin-eosin (HE) staining, immunofluorescence staining, flow cytometry, and single sperm metabolism analysis on the testes and spermatozoa of Qrich2 knockout mice, we found a strong antioxidant capacity mediated by QRICH2 both in vivo and in vitro. Qrich2 knockout led to elevated levels of ROS, consequently inducing DNA damage in spermatids, which in turn triggered increased autophagy and apoptosis, ultimately causing a significant decrease in spermatozoa count. Incubation with the N-terminal purified protein of QRICH2 exhibited potent strong antioxidant activity at the cell and spermatozoa levels in vitro, thereby enhancing spermatozoa viability and motility. Therefore, QRICH2 plays a crucial role in safeguarding spermatids from excessive ROS-induced damage by augmenting antioxidant capacity, thereby promoting spermatozoa survival and improving motility. Furthermore, the N-terminal purified protein of QRICH2 shows promise as an additive for protecting spermatozoa during preservation and cryopreservation.

Role of nuclear factor erythroid 2-related factor 2 (Nrf2) in female and male fertility

Oxidative stress refers to a condition where there is an imbalance between the production of reactive oxygen species and their removal by antioxidants. While the function of reactive oxygen species as specific second messengers under physiological conditions is necessary, their overproduction can lead to numerous instances of cell and tissue damage. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master regulator of many cytoprotective genes that respond to redox stresses. Nrf2 is regularly degraded by kelch-like ECH-associated protein 1 through the ubiquitin-proteasome pathway. The kelch-like ECH-associated protein 1 and Nrf2 complex have attracted attention in both basic and clinical infertility research fields. Oxidative stress is implicated in the pathogenesis of female infertility, including primary ovarian insufficiency, polycystic ovarian syndrome, and endometriosis, as well as male infertility, namely varicocele, cryptorchidism, spermatic cord torsion, and orchitis. Most scientists believe that Nrf2 is a potential therapeutic method in female and male infertility disorders due to its antioxidant effect. Here, the potential roles of oxidative stress and Nrf2 in female and male infertility disorders are reviewed. Moreover, the key role of Nrf2 in the inhibition or induction of these diseases is discussed.

Benefits of heat-killed Lactobacillus acidophilus on growth performance, nutrient digestibility, antioxidant status, immunity, and cecal microbiota of rabbits

Introduction

Heat-killed probiotics, as a type of inactivated beneficial microorganisms, possess an extended shelf life and broader adaptability compared to their live counterparts. This study aimed to investigate the impact of heat-killed Lactobacillus acidophilus (L. acidophilus, LA) - a deactivated probiotic on the growth performance, digestibility, antioxidant status, immunity and cecal microbiota of rabbits.

Methods

Two hundred weaned Hyla rabbits were randomly allocated into five equal groups (CON, L200, L400, L600, and L800). Over a 28-day period, the rabbits were fed basal diets supplemented with 0, 200, 400, 600, and 800 mg/kg of heat-killed LA, respectively.

Results

Results revealed a significant reduction in the feed-to-gain ratio (F/G) in the L600 and L800 groups (p < 0.05). Additionally, the L800 group exhibited significantly higher apparent digestibility of crude fiber (CF) and crude protein (CP) (p < 0.05). Regarding digestive enzyme activities, enhanced trypsin and fibrinase activities were observed in the L600 and L800 groups (p < 0.05). Concerning the regulation of the body's antioxidant status, the L800 group demonstrated elevated levels of superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) in both serum and ileal tissue (p < 0.05). In terms of immune capacity modulation, serum tumor necrosis factor-α (TNF-α) levels were significantly lower in the L600 and L800 groups (p < 0.05), while immunoglobulin A (IgA) and immunoglobulin M (IgM) levels were higher (p < 0.05). Additionally, the L800 group exhibited a substantial increase in secretory immunoglobulin A (SIgA) levels in the intestinal mucosa (p < 0.05). In comparison to the CON group, the L800 group exhibited a significant increase in the relative abundance of Phascolarctobacterium and Alistipes in the cecum (p < 0.05). Phascolarctobacterium demonstrated a positive correlation with SIgA (p < 0.05), IgM (p < 0.01), and Glutathione peroxidase (GSH-Px) (p < 0.05), while displaying a negative correlation with TNF-α levels (p < 0.05). Concurrently, Alistipes exhibited positive correlations with IgA (p < 0.05), IgM (p < 0.05), SIgA (p < 0.01), GSH-Px (p < 0.05), SOD (p < 0.05), and T-AOC (p < 0.01), and a negative correlation with TNF-α (p < 0.05).

Discussion

In conclusion, the dietary incorporation of 600 mg/kg and 800 mg/kg of heat-killed LA positively influenced the growth performance, nutrient digestibility, antioxidant status, immune capacity and cecal microbiota of rabbits. This highlights the potential benefits of utilizing heat-killed probiotics in animal nutrition.

Possible mechanisms involved in the protective effect of lutein against cyclosporine-induced testicular damage in rats

Oxidative stress and aberrant inflammatory response have important implications in cyclosporin-induced reproductive functions. Previous studies have shown that agents with antioxidant and anti-inflammatory activities might be beneficial in reversing cyclosporin-induced reproductive impairment. Lutein is a naturally occurring compound with antioxidant and anti-inflammatory properties. However, the effect of lutein against cyclosporin-induced reproductive impairment remains in complete. Hence, we investigated the protective effect of lutein, specifically focusing on the role of nuclear factor erythroid 2 related factor-2 (Nrf2)/heme-oxygenase-1 (HO-1)/connexin-43 (Cx-43) upregulation system against cyclosporine-induced reproductive impairment. Six male Wistar rats were allotted into 5 groups and given daily gavage of cyclosporine (40 mg/kg) and/or lutein (30 mg/kg) for four (4) weeks or in combination, respectively. The testicular antioxidant scaffolds: superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH), add to sulfhydryl (T-SH), non-protein sulfhydryl (NP-SH), glutathione reductase (GR), glutathione-S -transferase (GST), glutathione peroxidase (GSH-Px), thiobarbituric acid reactive substances (TBARS), myeloperoxidase (MPO), testicular proinflammatory cytokines, apoptotic related protein, nucleic acids, sialic acid, testicular proton pump ATPase, stress responsive protein, BTB-related protein and total protein levels in the testes were assayed thereafter. Cyclosporin significantly increased NOX-1, TNF-α, IL-1β, MPO, caspase-3 and -9 levels, which were reversed by lutein. Lutein reversed cyclosporin-induced decreases in Nrf2, HO-1, BCL-2, cytochrome C, with corresponding increase in CAT, SOD, GSH, T-SH, NP-SH, GST, GR, GSH-Px, and Cx-43 levels compared to cyclosporin groups. Lutein also abates cyclosporin-induced alterations Na + -K + -ATPase activities. Our findings showed that lutein's protective effect against cyclosporin-induced reproductive impairment might be associated with mechanisms linked to its antioxidant, anti-apoptotic, and anti-inflammatory properties, notably through up-regulation of Nrf2/HO-1/Cx-43 signaling and down-regulation of NOX-1 signaling.

Redox Homeostasis and Nrf2-Regulated Mechanisms Are Relevant to Male Infertility

Infertility represents a significant global health challenge, affecting more than 12% of couples worldwide, and most cases of infertility are caused by male factors. Several pathological pathways are implicated in male infertility. The main mechanisms involved are driven by the loss of reduction-oxidation (redox) homeostasis and the resulting oxidative damage as well as the chronic inflammatory process. Increased or severe oxidative stress leads to sperm plasma membrane and DNA oxidative damage, dysregulated RNA processing, and telomere destruction. The signaling pathways of these molecular events are also regulated by Nuclear factor-E2-related factor 2 (Nrf2). The causes of male infertility, the role of oxidative stress in male infertility and the Keap1-Nrf2 antioxidant pathway are reviewed. This review highlights the regulatory role of Nrf2 in the balance between oxidants and antioxidants as relevant mechanisms to male fertility. Nrf2 is involved in the regulation of spermatogenesis and sperm quality. Establishing a link between Nrf2 signaling pathways and the regulation of male fertility provides the basis for molecular modulation of inflammatory processes, reactive oxygen species generation, and the antioxidant molecular network, including the Nrf2-regulated antioxidant response, to improve male reproductive outcomes.

KEAP1-NRF2 system regulates age-related spermatogenesis dysfunction

Purpose

The average fatherhood age has been consistently increasing in developed countries. Aging has been identified as a risk factor for male infertility. However, its impact on various mechanisms remains unclear. This study focused on the KEAP1-NRF2 oxidative stress response system, by investigating the relationship between the KEAP1-NRF2 system and age-related changes in spermatogenesis.

Methods

For examination of age-related changes, we used 10-, 30-, 60-, and 90-week-old mice to compare sperm count, sperm motility, and protein expression. For assessment of Keap1 inhibition, 85-week-old C57BL/6J mice were randomly assigned to the following groups: control and bardoxolone methyl (KEAP1 inhibitor). Whole-exome sequencing of a Japanese cohort of patients with non-obstructive azoospermia was performed for evaluating.

Results

Sperm count decreased significantly with aging. Oxidative stress and KEAP1 expression in the testes were elevated. Inhibition of KEAP1 in aging mice significantly increased sperm count compared with that in the control group. In the human study, the frequency of a missense-type SNP (rs181294188) causing changes in NFE2L2 (NRF2) activity was significantly higher in patients with non-obstructive azoospermia than in healthy control group.

Conclusions

The KEAP1-NRF2 system, an oxidative stress response system, is associated with age-related spermatogenesis dysfunction.

Therapeutic potential of virgin coconut oil in mitigating sodium benzoate- model of male infertility: Role of Nrf2/Hmox-1/NF-kB signaling pathway

Objectives

Male infertility is a major public health issue due to increased prevalence, so there is an urgent need for a therapeutic solution. The search for a natural dietary substance that could modulate redox balance and inflammation and protect testicular function is in demand. Virgin Coconut Oil (VCO) has found use in the treatment of diabetes, and cancer owing to the presence of polyphenols. However, there is a dearth of information on its effect on testicular toxicity. The present study investigated VCO as a possible treatment for testicular toxicity in the Sodium Benzoate (SB) model of male infertility by evaluating the oxidative and inflammatory status, circulating hormonal levels, and key sperm indices.

Materials and Methods

Twenty adult male rats were randomly assigned to four groups of 5 rats each and were treated with normal saline, sodium benzoate, sodium benzoate+5% VCO, and sodium benzoate+15% VCO for 30 days respectively. Biochemical analysis of reproductive hormones was assessed. Sperm parameters assessed include sperm function tests and sperm kinematics. One-way analysis of variance (ANOVA) followed by post hoc Tukey tests was performed.

Results

5% VCO reverts the deranged serum reproductive hormones caused by sodium benzoate. 5% VCO was more potent as an antioxidant and anti-inflammatory treatment than 15% VCO. However, both doses prevented SB's effect on the sperm function test and kinematics.

Conclusion

VCO-supplemented diet can ameliorate SB-induced testicular toxicity by inhibiting its mechanisms of toxicity that are related to oxidative stress, apoptosis, and inflammation.

PCB126 impairs human sperm functions by affecting post-translational modifications and mitochondrial functions

Over the past few decades, there has been a consistent decline in semen quality across the globe, with environmental pollution being identified as the primary cause. Among the various contaminants present in the environment, persistent organic pollutants (POPs) have garnered significant attention due to their high toxicity, slow degradation, bio-accumulation, and long-range migration. PCBs, which include 210 congeners, are a crucial type of POPs that are known to have harmful effects on the environment and human health. Among the various PCB congeners, 3,3',4,4',5-pentachlorobiphenyl (PCB126) is a typical environmental endocrine-disrupting chemical that is widely distributed and has been associated with several health hazards. However, the impact and mechanism of PCB126 on human sperm function has not been fully elucidated. We aimed to investigate the effects of different concentrations of PCB126 (0.01, 0.1, 1, 10 μg/mL) on sperm motility, viability, hyperactivation, and acrosome reaction after incubation for different periods (1 and 2 h), delving deeper into the molecular mechanism of human sperm dysfunction caused by PCB126. First, we investigated the link between PCB126 treatment and the occurrence of protein modifications that are critical to sperm function regulation, such as tyrosine phosphorylation and lysine glutarylation. Second, we examined the potential impact of PCB126 on different parameters related to mitochondrial function, including reactive oxygen species, malondialdehyde levels, mitochondrial membrane potential, mitochondria respiration and adenosine triphosphate generation. Our findings indicate that exposure to environmental pollutants such as PCB126 in vitro may have a negative impact on human sperm functions by interfering with post-translational modifications and mitochondrial functions.

Cantharidin-induced toxic injury, oxidative stress, and autophagy attenuated by Astragalus polysaccharides in mouse testis

Cantharidin (CTD) is a chemical constituent derived from Mylabris and has good antitumor effects, but its clinical use is restricted by its inherent toxicity. However, few researches have reported its reproductive toxicity and mechanisms. This study aims to assess CTD's toxicity on mouse testes and the protective effect of Astragalus polysaccharides (APS). Briefly, biochemical analysis, histopathology, transmission electron microscopy, immunohistochemistry, and Western blotting were used to evaluate the oxidative damage of mouse testicular tissue after exposure to CTD and treatment by APS. Our research suggests a dramatic decrease in testicular index and serum testosterone levels after CTD exposure. The testis showed obvious oxidative damage accompanied by an increase in mitochondrial autophagy, the Nfr2-Keap1 pathway was inhibited, and the blood-testis barrier was destroyed. Notably, these changes were significantly improved after APS treatment. The internal mechanisms of APS ameliorate CTD-induced testicular oxidative damage in mice may be closely connected to regulatory the Nrf2-Keap1 signaling pathway, restraining autophagy, and repairing the blood-testis barrier, providing theoretical support for further study on the reproductive toxicity mechanism of CTD and clinical treatments to ameliorate it.

Exogenous Nucleotides Ameliorate Age-Related Decline in Testosterone in Male Senescence-Accelerated Mouse Prone-8 (SAMP8) Mice by Modulating the Local Renin-Angiotensin System Antioxidant Pathway

In older men, an age-related decline in testosterone is closely associated with various adverse health outcomes. With the progression of aging, hyperactivation of the local renin-angiotensin system (RAS) and oxidative stress increase in the testis. The regulation of RAS antioxidants may be a target to delay testicular aging and maintain testosterone levels. Exogenous nucleotides (NTs) have anti-aging potential in several systems, but there are no studies of their effects on the reproductive system. In our study, we examined the effects of exogenous NTs on testosterone synthesis and explored possible mechanisms of action. Therefore, senescence-accelerated mouse prone-8 (SAMP8) mice and senescence-accelerated mouse resistant 1 (SAMR1) were used in the experiment, and they were randomly divided into an NTs free group (NTs-F), a normal control group (control), a low-dose NTs group (NTs-L), a middle-dose NTs (NTs-M), a high-dose NTs group (NTs-H) and SAMR1 groups, and the testis of the mice were collected for testing after 9 months of intervention. The results showed that exogenous NTs could increase the testicular organ index in mice during aging, and delayed the age-associated decline in testosterone levels in SAMP8 male mice, possibly by modulating the local RAS antioxidant pathway and reducing oxidative stress to protect the testis. The present study provides new research clues for the development of preventive and therapeutic strategies for related diseases.

AOP Report: Glutathione Conjugation Leading to Reproductive Dysfunction via Oxidative Stress

We propose an adverse outcome pathway (AOP) for reproductive dysfunction via oxidative stress (OS). The AOP was developed based on Organisation for Economic Co-operation and Development (OECD) Guidance Document 184 and on the specific considerations of the OECD users' handbook supplement to the guidance document for developing and assessing AOPs (no. 233). According to the qualitative and quantitative experimental data evaluation, glutathione (GSH) conjugation is the first upstream key event (KE) of this AOP to reproductive dysfunction triggering OS. This event causes depletion of GSH basal levels (KE2 ). Consequently, this drop of free GSH induces an increase of reactive oxygen species (KE3 ) generated by the natural cellular metabolic processes (cellular respiration) of the organism. Increased levels of these reactive species, in turn, induce an increase of lipid peroxidation (KE4 ). This KE consequently leads to a rise in the amount of toxic substances, such as malondialdehyde and hydroxynonenal, which are associated with decreased quality and competence of gamete cell division, consequently impairing fertility (KE5 and adverse outcome). The overall assessment of the general biological plausibility, the empirical support, and the essentiality of KE relationships was considered as high for this AOP. We conclude that GSH conjugation is able to lead to reproductive disorder in fishes and mammals, via OS, but that the amount of stressor needed to trigger the AOP differs between stressors. Environ Toxicol Chem 2023;42:2519-2528. © 2023 SETAC.

Guilu-Erxian-Glue alleviates Tripterygium wilfordii polyglycoside-induced oligoasthenospermia in rats by resisting ferroptosis via the Keap1/Nrf2/GPX4 signaling pathway

CONTEXT

Guilu-Erxian-Glue (GLEXG) is a traditional Chinese formula used to improve male reproductive dysfunction.

OBJECTIVE

To investigate the ferroptosis resistance of GLEXG in the improvement of semen quality in the oligoasthenospermia (OAS) rat model.

MATERIALS AND METHODS

Male Sprague-Dawley (SD) rats were administered Tripterygium wilfordii polyglycoside, a compound extracted from Tripterygium wilfordii Hook F. (Celastraceae), at a dose of 40 mg/kg/day, to establish an OAS model. Fifty-four SD rats were randomly divided into six groups: sham, model, low-dose GLEXG (GLEXGL, 0.25 g/kg/day), moderate-dose GLEXG (GLEXGM, 0.50 g/kg/day), high-dose GLEXG (GLEXGH, 1.00 g/kg/day) and vitamin E (0.01 g/kg/day) group. The semen quality, structure and function of sperm mitochondria, histopathology, levels of oxidative stress and iron, and mRNA levels and protein expression in the Keap1/Nrf2/GPX4 pathway, were analyzed.

RESULTS

Compared with the model group, GLEXGH significantly improved sperm concentration (35.73 ± 15.42 vs. 17.40 ± 4.12, p < 0.05) and motility (58.59 ± 11.06 vs. 28.59 ± 9.42, p < 0.001), and mitigated testicular histopathology. Moreover, GLEXGH markedly reduced the ROS level (5684.28 ± 1345.47 vs. 15500.44 ± 2307.39, p < 0.001) and increased the GPX4 level (48.53 ± 10.78 vs. 23.14 ± 11.04, p < 0.01), decreased the ferrous iron level (36.31 ± 3.66 vs. 48.64 ± 7.74, p < 0.05), and rescued sperm mitochondrial morphology and potential via activating the Keap1/Nrf2/GPX4 pathway.

DISCUSSION AND CONCLUSIONS

Ferroptosis resistance from GLEXG might be driven by activation of the Keap1/Nrf2/GPX4 pathway. Targeting ferroptosis is a novel approach for OAS therapy.

Sericin and melatonin mitigate diethylnitrosamine-instigated testicular impairment in mice: Implications of oxidative stress, spermatogenesis, steroidogenesis, and modulation of Nrf2/WT1/SF-1 signaling pathways

AIMS

This study aimed to investigate the therapeutic influence of combination therapy with sericin and melatonin on attenuating diethylnitrosamine (DEN)-instigated testicular dysfunction in mice and defining the molecular mechanisms involved in orchestrating redox signaling pathways and restoring spermatogenesis and steroidogenesis.

MATERIALS AND METHODS

Different groups of male Swiss albino mice were established and injected with respective drugs intraperitoneally. Semen analysis, hormonal assays, and oxidative stress biomarkers were evaluated. Additionally, melatonin and its receptors, WT1, SF-1, vimentin, Nrf2, and ANXA1 expressions were assessed. Histopathological and ultrastructural features of the testes were investigated by semithin, SEM, and TEM analyses.

KEY FINDINGS

Exposure to DEN exhibited pathophysiological consequences, including a remarkable increase in lipid peroxidation associated with substantial diminutions in SOD, CAT, GPx, GSH, GSH:GSSG, and GST. Furthermore, it disrupted spermatozoa integrity, testosterone, FSH, LH, melatonin, and its receptors (MT1 and MT2) levels, implying spermatogenesis dysfunction. By contrast, treatment with sericin and melatonin significantly restored these disturbances. Interestingly, the combination therapy of sericin and melatonin noticeably augmented the Nrf2, WT1, and SF-1 expressions compared to DEN-treated mice, deciphering the amelioration perceived in antioxidant defense and spermatogenesis inside cells. Furthermore, immunohistochemical detection of ANXA1 alongside histopathological and ultrastructural analyses revealed evident maintenance of testicular structures without discernible inflammation or anomalies in mice administered with sericin and melatonin compared to the DEN-treated group.

SIGNIFICANCE

Our findings highlighted that treatment with sericin and melatonin alleviated the testicular tissues in mice from oxidative stress and dysregulated spermatogenesis and steroidogenesis engendered by DEN.

A comprehensive review on the decabromodiphenyl ether (BDE-209)-induced male reproductive toxicity: Evidences from rodent studies

Polybrominated diphenyl ethers (PBDEs), a class of brominated flame retardants (BFRs), are employed in various manufactured products to prevent fires, slow down their spread and reduce the resulting damages. Decabromodiphenyl ether (BDE-209), an example of PBDEs, accounts for approximately 82 % of the total production of PBDEs. BDE-209 is a thyroid hormone (TH)-disrupting chemical owing to its structural similarity with TH. Currently, increase in the level of BDE-209 in biological samples has become a major issue because of its widespread use. BDE-209 causes male reproductive toxicity mainly via impairment of steroidogenesis, generation of oxidative stress (OS) and interference with germ cell dynamics. Further, exposure to this chemical can affect metabolic status, sperm concentration, epigenetic regulation of various developmental genes and integrity of blood-testis barrier in murine testis. However, the possible adverse effects of BDE-209 and its mechanism of action on the male reproductive health have not yet been critically evaluated. Hence, the present review article, with the help of available literature, aims to elucidate the reproductive toxicity of BDE-209 in relation to thyroid dysfunction in rodents. Further, several crucial pathways have been also highlighted in order to strengthen our knowledge on BDE-209-induced male reproductive toxicity. Data were extracted from scientific articles available in PubMed, Web of Science, and other databases. A thorough understanding of the risk assessment of BDE-209 exposure and mechanisms of its action is crucial for greater awareness of the potential threat of this BFR to preserve male fertility.

Male reproductive ageing: a radical road to ruin

In modern post-transition societies, we are reproducing later and living longer. While the impact of age on female reproductive function has been well studied, much less is known about the intersection of age and male reproduction. Our current understanding is that advancing age brings forth a progressive decline in male fertility accompanied by a reduction in circulating testosterone levels and the appearance of age-dependent reproductive pathologies including benign prostatic hypertrophy and erectile dysfunction. Paternal ageing is also associated with a profound increase in sperm DNA damage, the appearance of multiple epigenetic changes in the germ line and an elevated mutational load in the offspring. The net result of such changes is an increase in the disease burden carried by the progeny of ageing males, including dominant genetic diseases such as Apert syndrome and achondroplasia, as well as neuropsychiatric conditions including autism and spontaneous schizophrenia. The genetic basis of these age-related effects appears to involve two fundamental mechanisms. The first is a positive selection mechanism whereby stem cells containing mutations in a mitogen-activated protein kinase pathway gain a selective advantage over their non-mutant counterparts and exhibit significant clonal expansion with the passage of time. The second is dependent on an age-dependent increase in oxidative stress which impairs the steroidogenic capacity of the Leydig cells, disrupts the ability of Sertoli cells to support the normal differentiation of germ cells, and disrupts the functional and genetic integrity of spermatozoa. Given the central importance of oxidative stress in defining the impact of chronological age on male reproduction, there may be a role for antioxidants in the clinical management of this process. While animal studies are supportive of this strategy, carefully designed clinical trials are now needed if we are to realize the therapeutic potential of this approach in a clinical context.

The Regulatory Effects of JAK2/STAT3 on Spermatogenesis and the Redox Keap1/Nrf2 Axis in an Animal Model of Testicular Ischemia Reperfusion Injury

The male reproductive system requires the pleiotropic activity of JAK/STAT to maintain its function, especially spermatogenesis. The study aims to investigate the effect of JAK2 signaling on the expression of the Keap1/Nrf2 axis, spermatogenesis, and the Sertoli cells (Sc) junctions in an animal model of testicular ischemia reperfusion injury (tIRI). Testes subjected to tIRI exhibited increased JAK2/STAT3 activity associated with spermatogenic arrest and reduced expression of the Sc junctions. In addition, there was an increased protein expression of Keap1 and decreased Nrf2., which was coupled with the downregulation of gene expression of antioxidant enzymes. Reduced SOD and CAT activities were accompanied by increased lipid peroxidation and protein carbonylation during tIRI. Increased caspase 9 activity and Bax/Bcl2 ratio indicated initiation of apoptosis. Inhibition of JAK2 activity by AG490 maintained the integrity of spermatogenesis and SC junctions, normalized the expression of the Keap1/Nrf2 axis and its downstream antioxidant enzymes, and prevented germ cell apoptosis. The results further emphasized the regulatory role of JAK2/STAT3 on spermatogenesis, Keap1/Nrf2 signaling, and maintenance of the testicular redox balance to combat testicular dysfunction and male infertility.

Post-Thaw Parameters of Buck Semen Quality after Soy Lecithin Extender Supplementation with Fumaric Acid

The supplementation of cryopreservation media with antioxidants improves the post-thaw quality and fertilizing ability of spermatozoa. To maximize the fertility of frozen-thawed buck spermatozoa, further research is required to overcome obstacles that have yielded controversial results and standardize protocols. In the present work, the effect of adding fumaric acid (a well-described antioxidant) to a soy lecithin semen extender on certain quality parameters of spermatozoa following freezing and thawing was examined for the first time. Five sexually mature Skopelos bucks were used, and ejaculates were collected with an artificial vagina. The semen samples (98 samples, five replicates) were diluted (400 × 106 spermatozoa/mL) with OviXcell®, supplemented with fumaric acid (0 mM, 2.15 mM, 10 mM or 30 mM), equilibrated (5 °C; 3 h), packed (0.5 mL straws), frozen and stored (-196 °C) until further processing. After thawing, the spermatozoa total and progressive motility (CASA), viability (eosin-nigrosin), membrane functional integrity (HOST), acrosome integrity (SpermBlue®) and mitochondrial function (Rhodamine-123/SYBR-14/PI) were evaluated. Statistical analysis was performed with one-way ANOVA, followed by Duncan's test; significance was set at 0.05. The addition of 2.15 mM fumaric acid improved (p < 0.05) spermatozoa viability, membrane functional integrity, acrosome integrity and mitochondrial function compared to all other concentrations. The addition of 30 mM fumaric acid decreased (p < 0.05) spermatozoa viability and mitochondrial function compared to all other concentrations. These results indicate a beneficial effect of a 2.15 mM fumaric acid addition to a soy lecithin extender on post-thaw buck spermatozoa quality. Further research is required to evaluate the in vivo fertility of frozen-thawed buck spermatozoa treated with fumaric acid, as well as to elucidate the mechanism of action of fumaric acid in spermatozoa.

Decreased Klotho Expression Causes Accelerated Decline of Male Fecundity through Oxidative Injury in Murine Testis

Oxidative stress is the etiology for 30-80% of male patients affected by infertility, which is a major health problem worldwide. Klotho protein is an aging suppressor that functions as a humoral factor modulating various cellular processes including antioxidation and anti-inflammation, and its dysregulation leads to human pathologies. Male mice lacking Klotho are sterile, and decreased Klotho levels in the serum are observed in men suffering from infertility with lower sperm counts. However, the mechanism by which Klotho maintains healthy male fertility remains unclear. Klotho haplodeficiency (Kl+/-) accelerates fertility reduction by impairing sperm quality and spermatogenesis in Kl+/- mice. Testicular proteomic analysis revealed that loss of Klotho predominantly disturbed oxidation and the glutathione-related pathway. We further focused on the glutathione-S-transferase (GST) family which counteracts oxidative stress in most cell types and closely relates with fertility. Several GST proteins, including GSTP1, GSTO2, and GSTK1, were significantly downregulated, which subsequently resulted in increased levels of the lipid peroxidation product 4-hydroxynonenal and apoptosis in murine testis with low or no expression of Klotho. Taken together, the loss of one Kl allele accelerates male fecundity loss because diminished antioxidant capability induces oxidative injury in mice. This is the first study that highlights a connection between Klotho and GST proteins.

Quercetin Protects against Levetiracetam induced gonadotoxicity in rats

The purpose of this study was to determine whether quercetin may counteract the negative effects of levetiracetam on rat reproductive capabilities by examining its influence on a few reproductive parameters following levetiracetam administration. Twenty (20) experimental rats were employed, with five (n = 5) animals per treatment group. Rats in group 1 received saline (10mL/kg, p.o.) which served as control. Quercetin (20mg/kg, p.o./day) was given to groups 2 and 4 for 28 days starting from 29 to 56 days, respectively. However, animals in groups 3-4 received LEV (300mg/kg) once daily for 56 days with a 30-minute break in between treatments. All rats had their serum sex hormone levels, sperm characteristics, testicular antioxidant capability, and levels of oxido-inflammatory/apoptotic mediators evaluated. Additionally, the expression of proteins associated to BTB, autophagy, stress response was examined in rat testes. LEV increased sperm morphological defects and decreased sperm motility, sperm viability, sperm count body weight and testes weight, MDA and 8OHdG levels in the testis of LEV-treated rats were elevated, while antioxidant enzyme expression was concurrently decreased. Additionally, it reduced the levels of serum gonadotropins, testosterone, mitochondrial membrane potential, and cytochrome C liberation into the cytosol from the mitochondria. Caspase-3 and Caspase-9 activity increased. While Bcl-2, Cx-43, Nrf2, HO-1, mTOR, and Atg-7 levels were lowered, NOX-1, TNF-α, NF-kß, IL-1ß, and tDFI levels increased. Histopathological scoring provided further support for the decreased spermatogenesis. In contrast to all of these gonadotoxic effects of LEV, improvements in LEV-induced gonadal damage were seen through upregulation of Nrf2/ HO-1, Cx-43/NOX-1, mTOR/Atg-7 expression and attenuation of hypogonadism, poor sperm quality, mitochondria-mediated apoptosis, and oxidative inflammation due to quercetin post-treatment. The modulation of Nrf2/HO-1, /mTOR/Atg-7 and Cx-43/NOX-1 levels and the inhibition of mitochondria-mediated apoptosis and oxido-inflammation in LEV-induced gonadotoxicity in rats suggest that quercetin may hold promise as a possible therapeutic treatment.

2,3',4,4',5-Pentachlorobiphenyl induces mitochondria-dependent apoptosis mediated by AhR/Cyp1a1 in mouse germ cells

Polychlorinated biphenyls (PCBs) are environmental organic pollutants widely used in industry that can bioaccumulate and affect the reproductive systems of male animals of different species. 2,3',4,4',5-Pentachlorobiphenyl (PCB118) is a representative of the 209 toxic PCB congeners. In this study, male mice were exposed to PCB118 at 0, 50, and 500 μg/kg/day for 35 days beginning 3-4 weeks after birth. The results of the study showed that PCB118 exposure during puberty reduced testicular quality, caused tissue damage, decreased sperm motility and sperm count, and increased malformation and testicular cell apoptosis in mice. Moreover, PCB118 increased the oxidative stress levels in sperm and testicular tissue and the expression of aryl hydrocarbon receptor (AhR) and Cyp1a1 and siginificantly decreased the level of nuclear factor-erythroid 2-related factor 2 (Nrf2). The results indicate that PCB118 can activate the AhR/Cyp1a1 pathway and inhibit Nrf2 expression to aggravate testicular oxidative stress and induce cell apoptosis, resulting in testicular and sperm quality damage.

Chronic oral exposure to short chain chlorinated paraffins induced testicular toxicity by promoting NRF2-mediated oxidative stress

As a widespread environmental contaminant, short chain chlorinated paraffins (SCCPs) has attracted great attention. However, the toxicity of SCCPs on male reproductive system remains ambiguous. In this study, we treated mice with SCCPs by gavage and investigated the toxic effects of SCCPs on testis. According to the results, the sperm parameters of mice were significantly reduced after exposure to 1, 10, 100 mg/kg body mass per day SCCPs for 35 days. SCCPs resulted in disorderly arranged seminiferous epithelium and increased apoptotic cells in testes. Both in vivo and in vitro experiments indicated that the oxidative stress was induced after SCCPs exposure, and dysfunction of nuclear factor erythroid-related factor (NRF2) signaling pathway played a role in this process. Moreover, resveratrol, an NRF2 activator, could alleviate the damage of SCCPs onmale reproductive system. Our study indicated that oxidative stress is the key point for explaining the testicular toxicity caused by SCCPs, and NRF2 could be used as a potential target for clinical treatment to alleviate the reproductive toxicity induced by SCCPs.

NRF2 and the Moirai: Life and Death Decisions on Cell Fates

Significance: The transcription factor NRF2 (NF-E2-related factor 2) plays an important role as a master regulator of the cellular defense system by activating transcriptional programs of NRF2 target genes encoding multiple enzymes related to cellular redox balance and xenobiotic detoxication. Comprehensive transcriptional analyses continue to reveal an ever-broadening range of NRF2 target genes, demonstrating the sophistication and diversification of NRF2 biological signatures beyond its canonical cytoprotective roles. Recent Advances: Accumulating evidence indicates that NRF2 has a strong association with the regulation of cell fates by influencing key processes of cellular transitions in the three major phases of the life cycle of the cell (i.e., cell birth, cell differentiation, and cell death). The molecular integration of NRF2 signaling into this regulatory program occurs through a wide range of NRF2 target genes encompassing canonical functions and those manipulating cell fate pathways. Critical Issues: A singular focus on NRF2 signaling for dissecting its actions limits in-depth understanding of its intersection with the molecular machinery of cell fate determinations. Compensatory responses of downstream pathways governed by NRF2 executed by a variety of transcription factors and multifactorial signaling crosstalk require further exploration. Future Directions: Further investigations using optimized in vivo models and active engagement of overarching approaches to probe the interplay of widespread pathways are needed to study the properties and capabilities of NRF2 signaling as a part of a large network within the cell fate regulatory domain. Antioxid. Redox Signal. 38, 684-708.

A systematic review on anti-diabetic plant essential oil compounds: Dietary sources, effects, molecular mechanisms, and safety

Type 2 diabetes mellitus (T2DM) is a multifaceted metabolic syndrome defined through the dysfunction of pancreatic β-cells driven by a confluence of genetic and environmental elements. Insulin resistance, mediated by interleukins and other inflammatory elements, is one of the key factors contributing to the progression of T2DM. Many essential oils derived from dietary plants are beneficial against various chronic diseases. We reviewed the anti-diabetic properties of dietary plant-derived essential oil compounds, with a focus on their molecular mechanisms by modulating specific signaling pathways and other critical inflammatory mediators involved in insulin resistance. High-quality literature published in the last 12 years, from 2010 to 2022, was collected from the Scopus, Web of Science, PubMed, and Embase databases using the search terms "dietary plants," "essential oils," "anti-diabetic," "insulin resistance," "antihyperglycemic," "T2DM," "anti-diabetic essential oils," and anti-diabetic mechanism." According to the results, the essential oil compounds, including cinnamaldehyde, carvacrol, zingerone, sclareol, zerumbone, myrtenol, thujone, geraniol, citral, eugenol, thymoquinone, thymol, citronellol, α-terpineol, and linalool have been demonstrated to contain strong anti-diabetic effects via modulating various signal transduction pathways linked to glucose metabolism. Additionally, in diabetes-related animal models, they can also considerably reduce the expression of TNF-α, IL-1β, IL-4, IL-6, iNOS, and COX-2. The main signaling molecules regulated by these compounds include AMPK, GLUT4, Caspase-3, PPARγ, PPARα, NF-κB, p-IκBα, MyD88, MCP-1, SREBP-1c, AGEs, RAGE, VEGF, Nrf2/HO-1, and SIRT-1. They can also significantly inhibit the generation of TBARS and MDA, reduce oxidative stress, increase insulin levels, adiponectin, and glycoprotein enzymes, boost antioxidant enzymes like SOD, CAT, and GPx, as well as reduce glutathione and vital glycolytic enzymes. Besides, they can significantly lower the levels of liver enzymes and lipid profile markers. Moreover, most essential oil compounds are generally safe based on animal studies. In conclusion, dietary plant-derived essential oil compounds have potential anti-diabetic effects by influencing different signaling pathways and molecular targets linked to glucose metabolism, and should be safe and beneficial against diabetes and related complications.

Absence of MerTK disrupts spermatogenesis in an age-dependent manner

Spermatogenesis is a highly specialized cell differentiation process regulated by the testicular microenvironment. During the process of spermatogenesis, phagocytosis performs an essential role in male germ cell development, and its dysfunction in the testis can cause reproduction defects. MerTK, as a critical protein of phagocytosis, facilitates the removal of apoptotic substrates from the retina and ovaries through cooperation with several phagocytosis receptors. However, its role in mammalian spermatogenesis remains undefined. Here, we found that 30-week-old MerTK^-/- male mice developed oligoasthenospermia due to abnormal spermatogenesis. These mice showed damaged seminiferous tubule structure, as well as altered spermatogonia proliferation and differentiation. We also found that Sertoli cells from MerTK^-/- mice had decreased phagocytic activity on apoptotic germ cells in vitro. Moreover, a transcriptomic analysis demonstrated that the pivotal genes involved in spermatid differentiation and development changed expression. These results indicate that MerTK is crucial for spermatogenesis, as it regulates the crosstalk between germ cells and Sertoli cells. This provides us insight into the molecular mechanism of MerTK on spermatogenesis and its implications for the diagnosis and treatment of human male infertility.

Effect of Administration of an Equal Dose of Selected Dietary Chemicals on Nrf2 Nuclear Translocation in the Mouse Liver

Certain dietary chemicals influenced the expression of chemopreventive genes through the Nrf2-Keap1 pathway. However, the difference in Nrf2 activation potency of these chemicals is not well studied. This study is aimed at determining the difference in the potency of liver Nrf2 nuclear translocation induced by the administration of equal doses of selected dietary chemicals in mice. Male ICR white mice were administered 50 mg/kg of sulforaphane, quercetin, curcumin, butylated hydroxyanisole, and indole-3-carbinol for 14 days. On day 15, the animals were sacrificed, and their livers were isolated. Liver nuclear extracts were prepared, and Nrf2 nuclear translocation was detected through Western blotting. To determine the implication of the Nrf2 nuclear translocation on the expression levels of several Nrf2-regulated genes, liver RNA was extracted for qPCR assay. Equal doses of sulforaphane, quercetin, curcumin, butylated hydroxyanisole, and indole-3-carbinol significantly induced the nuclear translocation of Nrf2 with different intensities and subsequently increased the expression of Nrf2-regulated genes with an almost similar pattern as the Nrf2 nuclear translocation intensities (sulforaphane > butylated hydroxyanisole = indole-3-carbinol > curcumin > quercetin). In conclusion, sulforaphane is the most potent dietary chemical that induces the Nrf2 translocation into the nuclear fraction in the mouse liver.

Potential Mechanism of Platelet-rich Plasma Treatment on Testicular Problems Related to Diabetes Mellitus

Diabetes mellitus is a condition of continuously increased blood glucose levels that causes hyperglycemia. This condition can result in disorders of various organs including testicular problems. The use of platelet-rich plasma (PRP) which is contained in several growth factors shows its potential in overcoming testicular problems. This literature review study was conducted to identify the potential of PRP in overcoming various testicular problems due to diabetic conditions.

Apoptosis, inflammation, and oxidative stress in infertility: A mini review

Infertility has been a major issue in our society for many years, and millions of couples all over the world are still experiencing it. There are several reasons for and causes of infertility in both men and women. Recent studies have shown that apoptosis, inflammation, and oxidative stress contribute immensely to infertility. The data regarding this report were obtained through a thorough review of scientific articles published in various databases, including Elsevier, Web of Science, PubMed, Scopus, and Google Scholar. Furthermore, PhD and MSc theses were also reviewed when compiling the data. Apoptosis, also known as "programmed cell death," is a natural and harmless process that occurs in human beings. Although it can become harmful if altered, Inflammation, on the other hand, is the body's reaction to detrimental stimuli caused by toxic substances or compounds, while oxidative stress is a phenomenon that results in an imbalance between the generation and aggregation of reactive oxygen species (ROS) in the cells against antioxidants. These three factors interchangeably bring about several reproductive disorders in the body, resulting in infertility. This review aims at discussing how apoptosis, inflammation, and oxidative stress play a role in human infertility.

Availability of data and material

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Reduction of SLC7A11 and GPX4 Contributing to Ferroptosis in Sperm from Asthenozoospermia Individuals

Ferroptosis is a newly defined form of regulated cell death, which is involved in various pathophysiological conditions. However, the role of ferroptosis in male infertility remains unclear. In this study, 42 asthenozoospermic and 45 normozoospermic individuals participated. To investigate the ferroptosis level in the two groups, the levels of reactive oxygen species (ROS), malondialdehyde (MDA), and iron were measured, and mitochondrial membrane potential (MMP) was detected as an indicator of mitochondrial injuries. Compared with the normozoospermic group, ROS (p < 0.05), MDA (p < 0.001), and iron (p < 0.001) of the asthenozoospermic group were significantly increased. However, the asthenozoospermia group had a decreased MMP level (p < 0.05). In addition, the expression levels of GSH-dependent peroxidase 4 (GPX4) (p < 0.001) and solute carrier family 7 member 11 (SLC7A11) (p < 0.05) were also reduced in asthenozoospermic individuals. In asthenozoospermic samples, a significantly high positive correlation was observed between GPX4 mRNA levels and progressive motility (r = 0.397, p = 0.009) and total motility (r = 0.389, p = 0.011), while a negative correlation was observed between GPX4 and iron concentration (r =  - 0.276, p = 0.077). The function of ferroptosis in asthenozoospermic males has never been studied before. In our study, we concluded that GPX4 and SLC7A11 expression levels in asthenozoospermia patients were related to increased ferroptosis and impaired sperm function, revealing novel molecular insights into the complex systems involved in male infertility.

OXIDATIVE STRESS AND REPRODUCTIVE FUNCTION: The protection of mammalian spermatozoa against oxidative stress

In brief

This review focuses on the enzymatic antioxidant mechanisms to fight oxidative stress by spermatozoa, highlighting the differences among mammalian species. We discuss recent evidence about players that promote and fight oxidative stress and the need for novel strategies to diagnose and treat cases of male infertility associated with oxidative damage of the spermatozoon.

Abstract

The spermatozoon is very sensitive to high reactive oxygen species (ROS) levels due to its limited antioxidant system. A consortium of antioxidant enzymes, including superoxide dismutase (SOD), glutathione peroxidases (GPXs), peroxiredoxins (PRDXs), thioredoxins, and glutathione-S-transferases, is necessary to produce healthy spermatozoa and to maintain sperm quality to ensure motility, capacitation, and DNA integrity. A delicate balance between ROS production and antioxidant enzymes is needed to ensure ROS-dependent sperm capacitation. GPX4 is an essential component of the mitochondrial sheath in mammalian spermatozoa, and GPX5 is a crucial antioxidant defence in the mouse epididymis to protect the sperm genome during the maturation of the spermatozoon. The mitochondrial superoxide (O2·–) production is controlled by SOD2, and the hydrogen peroxide (H2O2) generated by SOD2 activity and peroxynitrite (ONOO–) are scavenged mainly by PRDXs in human spermatozoa. PRDXs regulate the redox signalling necessary for sperm motility and capacitation, particularly by PRDX6. This enzyme is the first line of defence against oxidative stress to prevent lipid peroxidation and DNA oxidation by scavenging H2O2 and ONOO– through its peroxidase activity and repairing oxidized membranes by its calcium-independent phospholipase A2 activity. The success of antioxidant therapy in treating infertility resides in the proper diagnosis of the presence of oxidative stress and which type of ROS are produced. Thus, more research on the molecular mechanisms affected by oxidative stress, the development of novel diagnostic tools to identify infertile patients with oxidative stress, and randomized controlled trials are of paramount importance to generate personalized antioxidant therapy to restore male fertility.

Animal models of male reproductive ageing to study testosterone production and spermatogenesis

Ageing is the time-dependent gradual decline of the functional characteristics in an organism. It has been shown that it results in the loss of reproductive health and fertility. The age-dependent decline of fertility is a potential issue as the parenthood age is increasing in Western countries, mostly due to socioeconomic factors. In comparison to women, for whom the consequences of ageing are well documented and general awareness of the population is extensively raised, the effects of ageing for male fertility and the consequences of advanced paternal age for the offspring have not been widely studied. Studies with humans are welcome but it is hard to implement relevant experimental approaches to unveil the molecular mechanisms by which ageing affects male reproductive potential. Animal models have thus been extensively used. These models are advantageous due to their reduced costs, general easy maintenance in laboratory facilities, rigorous manipulation tools, short lifespan, known genetic backgrounds, and reduced ethical constraints. Herein, we discuss animal models for the study of male reproductive ageing. The most well-known and studied reproductive ageing models are rodents and non-human primates. The data collected from these models, particularly studies on testicular ageing, steroidogenesis, and genetic and epigenetic changes in spermatogenesis are detailed. Notably, some species challenge the currently accepted ageing theories and the concept of senescence itself, which renders them interesting animal models for the study of male reproductive ageing.

Bisphenol A exposure induces testicular oxidative damage via FTO/m6A/Nrf2 axis during postnatal development in mice

Bisphenol A (BPA), a commonly used plasticizer in the production of polycarbonate plastics and epoxy resins, has been shown to induce male reproductive toxicity. However, the effects of BPA exposure on early testicular development have not been thoroughly studied, and the underlying mechanism is yet to be elucidated. In the current study, neonatal male mice were exposed to BPA at 0, 0.1, and 5 mg/kg, respectively, by daily subcutaneous injection during postnatal day (PND) 1-35 to explore its effects on testicular development at PND 36 (the end of the first round of spermatogenesis). Morphological analyses showed that BPA exposure significantly induced apoptosis of testicular cells (p < 0.01 and p < 0.001) and reduced the thickness of seminiferous epithelium (p < 0.01). In addition, BPA exposure significantly decreased the total antioxidant capacity of testes and levels of transcription factor Nrf2 as well as its downstream antioxidant molecules of NQO1 and GPx-1 (p < 0.05 and p < 0.01). Furthermore, global m6A modifications of mRNAs were upregulated accompanied by declined m6A demethylase (FTO) in the testes of BPA groups (p < 0.05 and p < 0.01). MeRIP-quantitative real-time polymerase chain reaction (qPCR) demonstrated that BPA exposure markedly increased the m6A modification of Nrf2 mRNA (p < 0.05 and p < 0.01). These findings suggest that upregulation of m6A induced by inhibited FTO may be involved in BPA-induced testicular oxidative stress and developmental injury during postnatal development, which provides a new idea to reveal the mechanism underlying BPA interfering with testicular development.

Inhibition of ferroptosis attenuates oligospermia in male Nrf2 knockout mice

Nuclear factor-E2-related factor 2 (Nrf2) expression in sperm decreases in some oligospermia patients. However, the mechanism of reduced Nrf2 expression in sperm of oligospermia men is not elucidated. In the present study, our clinical trial results showed that Nrf2 and glutathione peroxidase 4 (GPX4) protein expressions in sperm of oligospermia men significantly decreased than those of healthy men. In animal experiments, mice were randomly divided into 3 groups: wild type (WT), Nrf2 knockout (Nrf2^-/-) and Nrf2^-/- + ferroptosis inhibitor (Fer-1) groups. Fer-1 was intraperitoneally injected in Nrf2^-/- mice for 4 weeks. The results showed that male Nrf2^-/- mice displayed decreased sperm concentration and motility, and significantly lower fertility. Compared with WT mice, malondialdehyde (MDA) content and prostaglandin-endoperoxide synthase 2 (Ptgs2) mRNA expression increased, but nicotinamide adenine dinucleotide phosphate oxidase (NADPH) content decreased in the testes of Nrf2^-/- mice, which were biomarkers of ferroptosis. Furthermore, treatment with Fer-1 in Nrf2^-/- mice reversed the decreased sperm concentration and motility. Meanwhile, histology showed that spermatogenic cells obviously decreased, and vacuolization formed in the testes of Nrf2^-/- mice, which were reversed by Fer-1 treatment. Additionally, compared with WT mice, GPX4, solute carrier family 7 member 11 (SLC7A11), glutamate-cysteine ligase, catalytic subunit (Gclc), glutamate-cysteine ligase, modifier subunit (Gclm) and ferroportin 1 (FPN1) mRNA and protein expressions significantly decreased, but transferrin receptor 1 (TfR1) and divalent metal transporter 1 (DMT1) mRNA and protein expressions increased in testicular tissues in Nrf2^-/- mice. After treatment with Fer-1, only Gclc and Gclm mRNA and protein expressions increased. Taken together, our data suggested that deletion of Nrf2 leads to downregulation of GPX4 and regulation of other ferroptosis-related genes, resulting in ferroptosis occurrence in spermatogenic cells and ultimately oligospermia.

Testicular aging, male fertility and beyond

Normal spermatogenesis and sperm function are crucial for male fertility. The effects of healthy testicular aging and testicular premature aging on spermatogenesis, sperm function, and the spermatogenesis microenvironment cannot be ignored. Compared with younger men, the testis of older men tends to have disturbed spermatogenic processes, sperm abnormalities, sperm dysfunction, and impaired Sertoli and Leydig cells, which ultimately results in male infertility. Various exogenous and endogenous factors also contribute to pathological testicular premature aging, such as adverse environmental stressors and gene mutations. Mechanistically, Y-chromosomal microdeletions, increase in telomere length and oxidative stress, accumulation of DNA damage with decreased repair ability, alterations in epigenetic modifications, miRNA and lncRNA expression abnormalities, have been associated with impaired male fertility due to aging. In recent years, the key molecules and signaling pathways that regulate testicular aging and premature aging have been identified, thereby providing new strategies for diagnosis and treatment. This review provides a comprehensive overview of the underlying mechanisms of aging on spermatogenesis. Furthermore, potential rescue measures for reproductive aging have been discussed. Finally, the inadequacy of testicular aging research and future directions for research have been envisaged to aid in the diagnosis and treatment of testicular aging and premature aging.

Effects of Moderate-Intensity Continuous Training and High-Intensity Interval Training on Testicular Oxidative Stress, Apoptosis and m6A Methylation in Obese Male Mice

Exercise is an effective way to improve reproductive function in obese males. Oxidative stress and apoptosis are important pathological factors of obesity-related male infertility. Accumulating studies have demonstrated that N6-methyladenosine (m6A) methylation is associated with obesity and testicular reproductive function. Our study aimed to investigate and compare the effect of 8 weeks of moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) on testicular oxidative stress, apoptosis and m6A methylation in obese male mice. Male C57BL/6 mice were randomly allocated into the four groups: normal diet (ND) group, high-fat diet (HFD) group, high-fat diet with moderate-intensity continuous training (HFD-MICT) group and high-fat diet with high-intensity interval training (HFD-HIIT) group. Mice in the HFD-MICT and HFD-HIIT groups were subjected to 8 weeks of MICT or HIIT treadmill protocols after 12 weeks of HFD feeding. We found that MICT and HIIT increased the protein expression of Nrf2, HO-1 and NQO-1 in the testes of obese mice, and HIIT increased it more than MICT. The Bax/Bcl-2 ratio, Cleaved Caspase-3 protein expression and TUNEL-positive cells were consistently up-regulated in the testes of obese mice, but MICT and HIIT restrained these HFD-induced effects. In addition, HFDs increased m6A levels and the gene expression of METTL3, YTHDF2 and FTO in the testes, but these effects were reversed by MICT and HIIT. However, HIIT was more effective than MICT in reducing m6A methylation in the testes of obese mice. These results demonstrate that both MICT and HIIT protected against HFD-induced oxidative stress, apoptosis and m6A methylation in testicular tissues; as a result, testicular morphological and functional impairment improved. In particular, HIIT was more beneficial than MICT in increasing the mRNA expression of steroidogenic enzymes and testicular antioxidant capacity and decreasing m6A methylation in the testes of HFD-fed mice.

Fumonisin B1 promotes germ cells apoptosis associated with oxidative stress-related Nrf2 signaling in mice testes

Fumonisins (FBs) are widespread Fusarium toxins commonly found in corn. This study aimed to establish the mechanism of oxidative stress via the Nrf2 signaling pathway associated with FB₁-induced toxicity in mice testis. Male mice were fed with 5 mg/kg FB₁ diet for 21 or 42 days, the expression of inflammatory related genes, apoptosis related genes and Nrf2 pathway genes were detected by RT-qPCR, Western blot and immunohistochemical. Furthermore, Sertoli cell was treatment with FB₁. Cell viability was measured by CCK8 assay, ROS level and apoptosis related genes were detected by immunofluorescence staining. The results showed that FB₁ had toxic effects on testis, which could increase the ROS level of Sertoli cells, affect the Keap1-Nrf2 pathway related factors, destroy the oxidative balance of testis, lead to the occurrence of inflammation and the initiation of apoptosis, and finally destroy the testicular tissue structure and affect the formation of sperm.

Polymorphisms in the HSF2, LRRC6, MEIG1 and PTIP genes correlate with sperm motility in idiopathic infertility

The aim of this study was to investigate the association of 24 functionally important single nucleotide polymorphisms (SNPs) with male infertility. In this cross-sectional study, we genotyped 24 functionally important single nucleotide polymorphisms in 24 infertility candidate genes in 500 oligo-/astheno-/oligoastheno-/normo-zoospermic infertile men with idiopathic infertility. Sequenom iPlex gold assay was used for genotyping. Sperm count and motility were compared between prevalent genotypes at each test locus. We did not observe any significant difference in the average sperm count between the alternate genotypes for the loci in the KLK3, LRRC6, MEIG1, HSF2, ESR2 and PTIP genes. However, we observed a significant difference in sperm motility between the alternate genotypes for the loci in the LRRC6, MEIG1, HSF2 and PTIP genes. Polymorphisms in the LRRC6 (rs200321595), MEIG1 (rs150031795), HSF2 (rs143986686) and PTIP (rs61752013) genes show association with sperm motility.

Animal models of male subfertility targeted on LanCL1-regulated spermatogenic redox homeostasis

Oxidative stress in spermatozoa is a major contributor to male subfertility, which makes it an informed choice to generate animal models of male subfertility with targeted modifications of the antioxidant systems. However, the critical male germ cell-specific antioxidant mechanisms have not been well defined yet. Here we identify LanCL1 as a major male germ cell-specific antioxidant gene, reduced expression of which is related to human male infertility. Mice deficient in LanCL1 display spermatozoal oxidative damage and impaired male fertility. Histopathological studies reveal that LanCL1-mediated antioxidant response is required for mouse testicular homeostasis, from the initiation of spermatogenesis to the maintenance of viability and functionality of male germ cells. Conversely, a mouse model expressing LanCL1 transgene is protected against high-fat-diet/obesity-induced oxidative damage and subfertility. We further show that germ cell-expressed LanCL1, in response to spermatogenic reactive oxygen species, is regulated by transcription factor specific protein 1 (SP1) during spermatogenesis. This study demonstrates a critical role for the SP1-LanCL1 axis in regulating testicular homeostasis and male fertility mediated by redox balance, and provides evidence that LanCL1 genetically modified mice have attractive applications as animal models of male subfertility.

Silencing of Nrf2 in Litopenaeus vannamei, decreased the antioxidant capacity, and increased apoptosis and autophagy

Nuclear factor E2-related factor 2 (Nrf2) is a multifunctional transcription factor that plays an important role in antioxidant activities. However, its effect on antioxidant capacity in Litopenaeus vannamei, an economically important crustacean, remains unclear. In this study, the role of Nrf2 in response to oxidative stress in L. vannamei was determined by its effect on relevant gene expression and enzymatic activity. Nrf2 was cloned and analyzed. Results revealed that Nrf2 contains a 1575 bp open reading frame encoding 524 amino acids and a conserved bZIP Maf domain. The sequence similarity of Nrf2 between L. vannamei and Homarus americanus is 81%. Although the Nrf2 expression was detected in all tissues, the Nrf2 expression levels were the highest in the hepatopancreas, followed by the eyestalk and muscle. RNA interference significantly decreased the expression of antioxidant-related genes (SOD, GPX, CAT, Trx, and HO-1; p < 0.05), significantly upregulated the expression of autophagy genes (Atg3, Atg4, Atg5, Atg10, and Atg12; p < 0.05) and apoptosis genes (Caspase-3 and P53; p < 0.05). Moreover, SOD, CAT, and GPX enzyme activities decreased whereas the MDA activity increased. The histological results of the shrimp injected with dsRNA-Nrf2 showed that the hepatic tubules were irregularly arranged, the lumen was abnormal, and a few hepatic tubules were significantly enlarged compared with those of the dsRNA-EGFP group. The hepatocytes were also vacuolated. In conclusion, this study provided evidence that Nrf2 is involved in the regulation of antioxidant capacity, oxidative stress, apoptosis, and autophagy in shrimp.

Guilingji Protects Against Spermatogenesis Dysfunction From Oxidative Stress via Regulation of MAPK and Apoptotic Signaling Pathways in Immp2l Mutant Mice

Male infertility is a major health issue with an estimated prevalence of 4.2% of male infertility worldwide. Oxidative stress (OS) is one of the main causes of male infertility, which is characterized by excessive reactive oxygen species (ROS) or lack of antioxidants. Meanwhile, it is reported that oxidative stress plays an important role in the spermatogenic impairment in Inner mitochondrial membrane peptidase 2-like (Immp2l) mutant mice. In this study, we focused on the potential mechanism of Guilingji in protecting the spermatogenic functions in Immp2l mutant mice. The results revealed that Immp2l mutant mice exhibit impaired spermatogenesis and histology shows seminiferous tubules with reduced spermatogenic cells. After administration of Guilingji [150 mg/kg per day intragastric gavage], however, alleviated spermatogenesis impairment and reversed testis histopathological damage and reduced apoptosis. What’s more, western blotting and the levels of redox classic markers revealed that Guilingji can markedly reduce reactive oxygen species. Moreover, Guilingji treatment led to inhibition of the phosphorylation of mitogen-activated protein kinase (MAPK), regulated apoptosis in the cells. In summary, Guilingji can improve spermatogenesis in Immp2l mutant mice by regulating oxidation-antioxidant balance and MAPK pathway. Our data suggests that Guilingji may be a promising and effective antioxidant candidate for the treatment of male infertility.

Predictors of pregnancy and time to pregnancy in infertile men with idiopathic oligoasthenospermia pre- and post-coenzyme Q10 therapy

Different antioxidants including coenzyme Q10 (CoQ10) have been tried to treat idiopathic male infertility (IMI) with variable results. Therefore, this study aimed to determine the clinical and biochemical predictors of pregnancy outcome and time to pregnancy (TTP) in infertile men with idiopathic oligoasthenospermia (OA) pre‐ and post‐CoQ10 therapy. This prospective controlled clinical study included 178 male patients with idiopathic OA and 84 fertile men (controls). Patients received 200 mg of oral CoQ10 once daily for 6 months. Demographics, semen parameters, seminal CoQ10 levels, reactive oxygen species (ROS) levels, total antioxidant capacity (TAC), catalase (CAT), glutathione peroxidase (GPx), sperm DNA fragmentation (SDF) and body mass index were measured and compared at baseline and after 6 months. All participants were followed up for another 18 months for pregnancy outcome and TTP. CoQ10 therapy for 6 months significantly improved semen parameters, antioxidant measures and reduced SDF. The pregnancy rate was 24.2% and TTP was 20.52 ± 6.72 months in patients as compared to 95.2% and 5.73 ± 6.65 months in fertile controls. After CoQ10 therapy, CoQ10 level, sperm concentration, motility and ROS were independent predictors of pregnancy outcome and CoQ10 level, male age, sperm concentration, motility, ROS and GPx were independent predictors of TTP in patients. In conclusion, CoQ10 therapy of 6 months is a potential treatment for men with idiopathic OA. CoQ10 level, male age, semen parameters, ROS and GPx could potentially be used as diagnostic biomarkers for male fertility and predictors for pregnancy outcome and TTP in these patients.

Alternative splicing and MicroRNA: epigenetic mystique in male reproduction

Infertility is rarely life threatening, however, it poses a serious global health issue posing far-reaching socio-economic impacts affecting 12–15% of couples worldwide where male factor accounts for 70%. Functional spermatogenesis which is the result of several concerted coordinated events to produce sperms is at the core of male fertility, Alternative splicing and microRNA (miRNA) mediated RNA silencing (RNAi) constitute two conserved post-transcriptional gene (re)programming machinery across species. The former by diversifying transcriptome signature and the latter by repressing target mRNA activity orchestrate a spectrum of testicular events, and their dysfunctions has several implications in male infertility. This review recapitulates the knowledge of these mechanistic events in regulation of spermatogenesis and testicular homoeostasis. In addition, miRNA payload in sperm, vulnerable to paternal inputs, including unhealthy diet, infection and trauma, creates epigenetic memory to initiate intergenerational phenotype. Naive zygote injection of sperm miRNAs from stressed father recapitulates phenotypes of offspring of stressed father. The epigenetic inheritance of paternal pathologies through miRNA could be a tantalizing avenue to better appreciate ‘Paternal Origins of Health and Disease’ and the power of tiny sperm.

Transcription Factors in the Regulation of Leydig Cell Gene Expression and Function

Cell differentiation and acquisition of specialized functions are inherent steps in events that lead to normal tissue development and function. These processes require accurate temporal, tissue, and cell-specific activation or repression of gene transcription. This is achieved by complex interactions between transcription factors that form a unique combinatorial code in each specialized cell type and in response to different physiological signals. Transcription factors typically act by binding to short, nucleotide-specific DNA sequences located in the promoter region of target genes. In males, Leydig cells play a crucial role in sex differentiation, health, and reproductive function from embryonic life to adulthood. To better understand the molecular mechanisms regulating Leydig cell differentiation and function, several transcription factors important to Leydig cells have been identified, including some previously unknown to this specialized cell type. This mini review summarizes the current knowledge on transcription factors in fetal and adult Leydig cells, describing their roles and mechanisms of action.

Comparative transcriptomic analysis reveals reproductive impairments caused by PCBs and OH-PCBs through the dysregulation of ER and AR signaling

Reports have highlighted the presence of PCBs and their metabolites, OH-PCBs, in human serum as well as their endocrine-disrupting effects on reproductive function through direct interactions with the androgen receptor (AR) and estrogen receptor (ER). However, the molecular mechanisms directly linking the actions of PCBs and OH-PCBs on the AR and ER to induce reproductive impairment remain poorly understood. In this study, we characterized the cellular response to PCBs and OH-PCBs acting on AR and ER transactivation at the transcriptome level coupled with bioinformatics analysis to identify the downstream pathways of androgen and estrogen signaling that leads to reproductive dysfunction. We first confirmed the agonistic and antagonistic effects of several PCBs and OH-PCBs on AR- and ER-mediated reporter gene activity using the androgen-responsive LNCaP and estrogen-responsive MCF-7 cell lines, respectively. Anti-estrogenic activity was not detected among the tested compounds; however, we found that in addition to anti-androgenic and estrogenic activity, PCB 28 and PCB 138 exhibited androgenic activity, while most of the tested OH-PCBs showed a synergistic effect on DHT-mediated transactivation of the AR. Bioinformatics analysis of transcriptome profiles from selected PCBs and OH-PCBs revealed various pathways that were dysregulated depending on their agonistic, antagonistic, or synergistic effects. The OH-PCBs with estrogenic activity affected pathways including vitamin metabolism and calcium transport. Other notable dysregulated pathways include cholesterol transport in response to androgenic PCBs, thyroid hormone metabolism in response to anti-androgenic PCBs, and antioxidant pathways in response to androgen-synergistic OH-PCBs. Our results demonstrate that PCBs and OH-PCBs directly alter specific pathways through androgen- or estrogen-mediated signaling, thereby providing additional insights into the mechanisms by which these compounds cause reproductive dysfunction.

Nrf2 activation mediates the protection of mouse Sertoli Cells damage under acute heat stress conditions

Heat stress is known to negatively impact the reproductive process of livestock, which inevitably leads to a decline in animal fertility. Nuclear factor E2-related factor 2 (Nrf2) is an inducible transcription factor, which is essential for maintaining redox signal transmission against oxidative stress. However, there is no reliable research on the response mechanism of Sertoli Cells (SCs) against heat stress and the activation of Nrf2 when SCs are exposed to heat stress. Here, we used primary mouse SCs and SCs line TM4, along with Nrf2 specific inhibitor to determine the reaction mechanism of SCs to maintain intracellular redox homeostasis and self-survival by activating Nrf2. We found that acute heat stress only affected the vitality of SCs and the expression of functional molecules (tight junction-associated proteins and lactate dehydrogenase A [LDHA]) but did not cause cell apoptosis. When Nrf2 was inhibited, more cell death occurred in TM4 cells post heat stress treatment, along with a greater decrease in cell viability and a significant increase in intracellular ROS levels. Our study clarified for the first time the protective effect of Nrf2 activation on heat stress-induced SCs damage. It explained the possible reasons or mechanisms involved in the survival of SCs, the critical protective cells in the testis, which were not affected by heat stress. This study further improved the response mechanism of SCs in the reproductive injury caused by a high-temperature environment.

Combination of trehalose and low boron in presence of decreased glycerol improves post-thawed ram sperm parameters: A model study in boron research

BACKGROUND

Sperm cryopreservation has been widely used in the field of reproductive biotechnology. It applies to certain males of economic and scientific values, including livestock breeds or endangered animal species. The development of a semen extender with a low cryoprotectant concentration and an appropriate amount of trehalose and boron can prevent the deterioration of sperm parameters.

OBJECTIVE

The main goal of this study is to establish a suitable ram extender model, by examining different combinations of high (5%) and low (3%) glycerol concentrations (to reduce its toxic effects on sperm freezing), a fixed amount of trehalose and an increased dose of boron to prevent the deterioration of sperm parameters, and investigate the levels of gene expressions.

MATERIALS AND METHODS

The Merino ram ejaculates were collected. The collected ejaculates providing the defined criteria were pooled. The pooled ejaculates were divided into eight aliquots and diluted with the Tris extender including different combinations of glycerol (5% and 3%) and boron (0.25, 0.5, and 1 mm) concentrations and a fixed amount of trehalose, then frozen. After freeze-thawing process, sperm motility, mitochondrial membrane activity, plasma membrane integrity, acrosomal membrane integrity, DNA damage (single cell gel electrophoresis (COMET) and TUNEL assays) as well as NAD(P)H quinone oxyreductase (NQO1), glutamate-cycteine ligase (GCLC), and glutathione S-transferase (GSTP1) for molecular mechanisms of sperm cell response to oxidative stress were assessed for different extender groups following freeze-thawing process: 5% glycerol + 0 mm boron (G5B0.00), 5% glycerol + 0.25 mm boron (G5B0.25), 5% glycerol + 0.5 mm boron (G5B0.50), 5% glycerol + 1 mm boron (G5B1.00), 3% glycerol + 0 mm boron (G3B.00), 3% glycerol + 0.25 mm boron (G3B0.25), 3% glycerol + 0.5 mm boron (G3B0.50), and 3% glycerol + 1 mm boron (G3B1.00).

RESULTS

G3B0.25 presented higher percentages of subjective motility, mitochondrial activity, and viability of spermatozoa comparing with G5B0.00 and groups with boron. Supplementation of 0.25 mm boron with and without trehalose (G3B0.25 and G5B0.25) showed higher acrosome integrity, compared with G5B0.00, G5B1.00, G3B0.50, and G3B1.00. For TUNEL analysis, G3B1.00 showed the highest DNA integrity among the experimental groups which was statistically significant only with G5B0.50 (p < 0.05). The mRNA levels of NQO1 were significantly decreased in G5B1.00, G3B0.50, and G3B1.00, when compared to G5B0.00. In comparison with G5B0.00, supplementation of 1 mm boron with and without trehalose had significantly lower expression of GCLC. The level of GSTP1 gene was significantly lower (approximately threefold) in G3B1.00, compared to G5B0.00 (p < 0.05).

DISCUSSION AND CONCLUSION

It can be assumed that the increase of the boron concentration in the extender may have important adverse effects on sperm parameters and antioxidant gene expression after thawing. The results obtained from this study will help to understand the toxicity limits of boron and eliminate the toxicity of glycerol in studies of gametes and tissue freezing. Therefore, it can be concluded that the use of sufficient boron can decrease cryodamages of cryopreservation of mammalian spermatozoa as well tissue engineering.

Qiangjing Tablets Regulate Apoptosis and Oxidative Stress via Keap/Nrf2 Pathway to Improve the Reproductive Function in Asthenospermia Rats

Asthenozoospermia (AZS), is a common cause of male infertility. Currently, most drugs for azoospermia lack desirable therapeutic efficiency, therefore developing new drug therapy is important. Qiangjing tablets could enhance renal function and improve sperm quality. The purpose of this study was to examine whether Qiangjing tablets could improve the reproductive function in azoospermia rats through activating the Nrf2/ARE pathway, and how to regulate energy metabolism and oxidative stress in this process. Sperm motility, sperm concentration and sperm viability were detected by WLJY-9000 Weili Digital Color Sperm Quality Detection System. HE staining was used to observe the pathological condition of testis in AZS rats. Cell apoptosis was analyzed by Tunnel staining and flow cytometry. The changes of mitochondrial membrane potential were detected by JC-1. The levels of Estradiol, testosterone and luteinizing hormone, activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and content of malondialdehyde (MDA) and glutathione (GSH) were detected by ELISA. The effects of Qiangjing Tablets on GC-1 spgs and Nrf2 protein were investigated through CCK-8 assay and western blot. The expression levels of HO-1, Keap1, and P-Nrf2 were detected by western blot. The results demonstrated that Qiangjing tablets upregulated levels of sperm motility, sperm concentration and sperm viability, which was shown to significantly increase levels of HO-1, Keap1, P-Nrf2, Estradiol and testosterone, along with increasing the activity of SOD, GSH-Px and GSH and suppressing the MDA content, luteinizing hormone and Vimentin level. Qiangjing tablets could significantly inhibit spermatogenic cells apoptosis and promote GC-1 spgs viability, increase PE/FITC ratio, mitochondrial membrane potential and reduc oxidative stress. Qiangjing tablets protected spermatogenic cell to upregulate male sex hormoneto, improved the sperm quality and reproductive function in AZS rats via activating the Keap/Nrf2 signaling pathway.

Relationship between functional Nrf2 gene promoter polymorphism and sperm DNA damage in male infertility

This study examines the association of the -617 C > A polymorphism in the Nrf2 gene (rs6721961) with male infertility in a Turkish population and determines its functional role in spermatogenesis in correlation with the impact of different levels of DNA damage on the genotypes. A total of 100 infertile men and 100 healthy fertile men were included in the study. Nrf2 genotyping was performed with the PCR-based restriction fragment length gene polymorphism (RFLP-PCR) analysis. According to our results, the Nrf2 CC, CA, and AA genotype distribution frequencies were 58.6%, 38.4%, and 3% in the control group, respectively, and 38%, 48%, and 14% in the infertile men, respectively. The AA genotype was significantly higher in the patient group. In smokers, a significant difference was found in progressive motility values between the genotypes (p = 0.001). Also, sperm progressive motility and concentration decreased significantly in those smokers with the AA genotype; smokers carrying this genotype were also 5.75 times more likely to have oligoasthenozoospermia than those with CC (p < 0.05). There was a significant relationship between the number of cases with high sperm-DNA damage when comparing the frequency of Nrf2 AA genotype carriers with the CC genotype 16.3% vs. 6.9%, respectively (p < 0.001). These results suggest the importance of the Nrf2 gene C > A (rs 6,721,961) polymorphism in the etiology of sperm DNA damage as a risk factor for male infertility. Smokers carrying the AA genotype are more likely to impair seminal parameters through antioxidant mechanisms.Abbreviations: Polymerase chain reaction (PCR)-based restriction fragment length gene polymorphism (RFLP-PCR); reactive oxygen species (ROS); deoxyribonucleic acid (DNA); catalases (CATs); superoxide dismutase (SOD); glutathione peroxidase (GPX); glutathione-S-transferase (GST); Nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2); basic leucine zipper (bZIP); antioxidant response element (ARE); World Health Organization (WHO);normospermia(NS);asthenozoospermia(AS);oligozoospermia(OS);oligoasthenozoospermia (OAS); follicle stimulating hormone (FSH); ultraviolet (UV); low-melting-point agarose (LMA); normal-melting-point agarose (NMA); arbitrary units (AU); total comet score (TCS); A one-way analysis of variance (ANOVA); standard deviation (SD); N-acetyltransferase (NAT2); small non-coding RNAs (ncRNAs); microRNAs (miRNA).