Dual function of the selenoprotein PHGPx during sperm maturation

Multigenerational effects of disperse blue 79 at environmentally relevant concentrations on zebrafish (Danio rerio) fecundity: An integrated approach

The brominated azo dye (BAD) Disperse Blue (DB79) is a widespread environmental pollutant. The long-term toxicological effects of DB79 and the mechanisms thereof must be understood to allow assessment of the risks of DB79 pollution. A dual-omics approach employing in silico analysis, bioinformatics, and in vitro bioassays was used to investigate the transgenerational (F0-F2) toxicity of DB79 in zebrafish at environmentally relevant concentrations and identify molecular initiating events and key events associated with DB79-induced fertility disorders. Exposure to 500 µg/L DB79 decreased fecundity in the F0 and F1 generations by > 30 % and increased the condition factor of the F1 generation 1.24-fold. PPARα/RXR and PXR ligand binding activation were found to be critical molecular initiating events associated with the decrease in fecundity. Several key events (changes in fatty acid oxidation and uptake, lipoprotein metabolism, and xenobiotic metabolism and transport) involved in lipid dysregulation and xenobiotic disposition were found to be induced by DB79 through bioinformatic annotation using dual-omics data. The biomolecular underpinnings of decreased transgenerational fertility in zebrafish attributable to BAD exposure were elucidated and novel biomolecular targets in the adverse outcome pathway framework were identified. These results will inform future studies and facilitate the development of mitigation strategies.

Association between blood heavy metal element and all-cause mortality in asthmatic adults: a cohort study

Asthma start, development, and exacerbation have all been linked in numerous studies to exposure to a variety of metal elements. However, there is still a dearth of epidemiological data linking heavy metal exposure to death in asthmatics. The investigation included 2432 eligible adults with asthma. The study examined the possible correlation between blood heavy metal levels and all-cause mortality. This was done by utilizing Cox proportional hazards models, restricted cubic spline (RCS), threshold effect models, and CoxBoost models. Subgroup analyses were conducted to investigate the associations between blood metal levels and all-cause mortality among distinct asthmatic populations. An inverse association was found between blood selenium and all-cause mortality in asthmatics, while blood manganese showed a positive association with all-cause mortality. However, there were no significant connections found between blood lead, cadmium, mercury, and all-cause mortality via multivariate Cox proportional hazard models. In model 3, after accounting for all factors, all-cause mortality dropped by 10% for every additional 10 units of blood selenium (μg/L) and increased by 6% for every additional unit of blood manganese (μg/L). The RCS and threshold effect model found a U-shaped correlation between blood selenium, blood manganese, and all-cause mortality. The lowest all-cause mortality among asthmatics was observed when blood selenium and manganese were 188.66 μg/L and 8.47 μg/L, respectively. Our investigation found a U-shaped correlation between blood selenium levels, blood manganese levels, and all-cause mortality in asthmatic populations. Optimizing dietary selenium intake and effectively managing manganese exposure could potentially improve the prognosis of asthma.

A comprehensive review on potential role of selenium, selenoproteins and selenium nanoparticles in male fertility

Selenium (Se), a component of selenoproteins and selenocompounds in the human body, is crucial for the development of male reproductive organs, DNA synthesis, thyroid hormone, metabolism, and defence against infections and oxidative damage. In the testis, it must exceed a desirable level since either a shortage or an overabundance causes aberrant growth. The antioxidant properties of selenium are essential for preserving human reproductive health. Selenoproteins, which have important structural and enzymatic properties, control the biological activities of Se primarily. These proteins specifically have a role in metabolism and a variety of cellular processes, such as the control of selenium transport, thyroid hormone metabolism, immunity, and redox balance. Selenium nanoparticles (SeNPs) are less hazardous than selenium-based inorganic and organic materials. Upon being functionalized with active targeting ligands, they are both biocompatible and capable of efficiently delivering combinations of payloads to particular cells. In this review, we discuss briefly the chemistry, structure and functions of selenium and milestones of selenium and selenoproteins. Next we discuss the various factors influences male infertility, biological functions of selenium and selenoproteins, and role of selenium and selenoproteins in spermatogenesis and male fertility. Furthermore, we discuss the molecular mechanism of selenium transport and protective effects of selenium on oxidative stress, apoptosis and inflammation. We also highlight critical contribution of selenium nanoparticles on male fertility and spermatogenesis. Finally ends with conclusion and future perspectives.

Rhizosphere enrichment and crop utilization of selenium and metals in typical permian soils of Enshi

Enshi, China, is renowned as "Selenium(Se) Capital" where widely distributed soils derived from Permian parent rocks are notably rich in Se, as well as metals, particularly cadmium(Cd). However, the soil enrichment and crop uptake of Se and metals in these high-Se and high-Cd areas are not well understood. To propose the optimal crop planting plan to ensure the safety of agricultural products, we investigated the soils and corresponding typical crops (rice, tea, and maize). The results showed significant soil enrichment of elements, with average contents (mg/kg) as follows: Cr (185), Zn (126), Cu (58.8), Pb (31.1), As (15.7), Se (6.85), Cd (5.41), and Hg (0.211). All soil Se contents were above 0.4 mg/kg, indicating Se-rich soils. Se primarily existed in an organic-bound form, accounting for an average proportion of 61.3%, while Cd was mainly exchangeable, with an average of 62.5%. Cd exhibited higher activity according to the Relative Index of Activity (RIA). Nemerow single-factor index analysis confirmed significant soil contamination, with Cd showing the highest level, followed by Cr and Cu, while Pb had the lowest level. Tea exhibited a high Se rich ratio (82.0%) without exceeding the Cd standard. In contrast, corn and rice had relatively lower Se-rich ratios (42.0% and 51.5% respectively) and high rates of Cd exceeding the standard, at 49.0% and 61.0% respectively. Canonical analysis revealed that rice was more influenced by soil factors related to Se and Cd compared to maize and tea crops. Therefore, tea cultivation in the Enshi Permian soil area is recommended for safe crop production. This study provides insights into the enrichment, fractionation, and bioavailability of soil Se, Cd, and other metals in the high-Se and high-Cd areas of permian stratas in Enshi, offering a scientific basis for selecting local food crops and producing safe Se-rich agricultural products in the region.

Integrative bioinformatics analysis to identify ferroptosis-related genes in non-obstructive azoospermia

PURPOSE

The objective of this study was to discern ferroptosis-related genes (FRGs) linked to non-obstructive azoospermia and investigate the associated molecular mechanisms.

METHOD

A dataset related to azoospermia was retrieved from the Gene Expression Omnibus database, and FRGs were sourced from GeneCards. Ferroptosis-related differentially expressed genes (FRDEGs) were discerned. Subsequently, these genes underwent analyses encompassing Gene Ontology and Kyoto Encyclopedia of Genes and Genomes, as well as protein-protein interaction (PPI) networks and assessments of functional similarity. Following the identification of hub genes, an exploration of immune infiltration, single-cell expression, diagnostic utility, and interactions involving hub genes, RNA-binding proteins (RBPs), transcription factors (TFs), microRNAs (miRNAs), and drugs was conducted.

RESULTS

A total of 35 differentially expressed FRGs were discerned. These genes demonstrated enrichment in functions and pathways associated with ferroptosis. From the PPI network, eight hub genes were selected. Functional similarity analysis highlighted the potential pivotal roles of HMOX1 and GPX4 in azoospermia. Analysis of immune cell infiltration indicated a significant decrease in activated dendritic cells in the azoospermia group, with notable correlations between hub genes, particularly SAT1 and HMGCR, and immune cell infiltration. Unique expression patterns of hub genes across various cell types in the human testis were observed, with GPX4 prominently enriched in spermatid/sperm. Eight hub genes exhibited robust diagnostic value (AUC > 0.75). Lastly, a comprehensive hub gene-miRNA-TF-RBP-drug network was constructed.

CONCLUSION

In summary, our investigation unveiled eight FRDEGs associated with azoospermia, which hold potential as biomarkers for the diagnosis and treatment of azoospermia.

Unresolved questions regarding cellular cysteine sources and their possible relationships to ferroptosis

Cysteine is required for synthesis of glutathione (GSH), coenzyme A, other sulfur-containing metabolites, and most proteins. In most cells, cysteine comes from extracellular disulfide sources including cystine, glutathione-disulfide, and peptides. The thioredoxin reductase-1 (TrxR1)- or glutathione-disulfide reductase (GSR)-driven enzymatic systems can fuel cystine reduction via thioredoxins, glutaredoxins, or other thioredoxin-fold proteins. Free cystine enters cells thorough the cystine-glutamate antiporter, xCT, but systemically, plasma glutathione-disulfide might predominate as a cystine source. Erastin, inhibiting both xCT and voltage-dependent anion channels, induces ferroptotic cell death, so named because this type of cell death is antagonized by iron-chelators. Many cancer cells seem to be predisposed to ferroptosis, which has been proposed as a targetable cancer liability. Ferroptosis is associated with lipid peroxidation and loss of either glutathione peroxidase-4 (GPX4) or ferroptosis suppressor protein-1 (FSP1), which each prevent accumulation of lipid peroxides. It has been suggested that an xCT inhibition-induced cellular cysteine-deficiency lowers GSH levels, starving GPX4 for reducing power and allowing membrane lipid peroxides to accumulate, thereby causing ferroptosis. Aspects of ferroptosis are however not fully understood and need to be further scrutinized, for example that neither disruption of GSH synthesis, loss of GSH, nor disruption of glutathione disulfide reductase (GSR), triggers ferroptosis in animal models. Here we reevaluate the relationships between Erastin, xCT, GPX4, cellular cysteine and GSH, RSL3 or ML162, and ferroptosis. We conclude that, whereas both Cys and ferroptosis are potential liabilities in cancer, their relationship to each other remains insufficiently understood.

The influence of oral antioxidants on men with infertility: a systemic review

OBJECTIVE

This study aims to investigate the current evidence regarding the impact of oral antioxidant supplementation on semen parameters of infertile men.

MATERIALS AND METHODS

We conducted a systematic search of PubMed, and Cochrane electronic databases, adhering to modified Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The focus was on studies exploring the effects of antioxidant therapy on infertile men, with an examination of antioxidants in terms of types, doses, rationale for use, and their impact on semen parameters measures.

RESULTS

A total of 18 studies that met the inclusion criteria were included in this study. Out of these, 14 studies reported a significantly positive influence of antioxidant therapy on basic semen parameters and advanced sperm function. These comprised 11 randomized clinical trials and 7 prospective studies. Commonly utilized antioxidants included Vitamin E, Vitamin C, carnitines, co-enzyme Q10, N-acetyl cysteine, zinc, selenium, folic acid, and lycopene.

CONCLUSIONS

Overall, antioxidants generally demonstrate a favorable effect on semen parameters of infertile men. However, further research is necessary to pinpoint the optimal antioxidant regimen that can be applied safely and effectively in clinical practice.

Insights Into Antioxidant Strategies to Counteract Radiation-Induced Male Infertility

Significance: Radiotherapy, which employs ionizing radiation to destroy or prevent the multiplication of tumor cells, has been increasingly used in the treatment of neoplastic diseases, especially cancers. However, radiation collaterally leads to prolonged periods of sperm count suppression, presumably due to impaired spermatogenesis by depleting the germ cell pool, which has long-term side effects for male reproduction. Recent Advances: Studies of antioxidant compounds as a potential strategy for male fertility preservation have been performed mainly from animal models, aiming to prevent and restore the male germinal tissue and its function, particularly against the oxidative stress effects of radiation. Evidence in preclinical and clinical trials has shown that inhibitors of the renin-angiotensin system and other drugs, such as statins and metformin, are candidates for ameliorating radiation-induced damage to several tissues, including the testis and prostate. Critical Issues: Research for developing an ideal radioprotective agent is challenging due to toxicity in the normal tissue, tumor radioresistance, cellular response to radiation, costs, regulation, and timeline development. Moreover, male radioprotection experiments in humans, mainly clinical trials, are scarce and use few individuals. This scenario is reflected in the slow progress of innovation in the radioprotection field. Future Directions: Expanding human studies to provide clues on the efficacy and safety of radioprotective compounds in the human reproductive system is necessary. Drug repurposing, frequently used in clinical practice, can be a way to shorten the development pipeline for innovative approaches for radioprotection or radiomitigation of the repercussions of radiotherapy in the male reproductive system.

GPX4, ferroptosis, and diseases

GPX4 (Glutathione peroxidase 4) serves as a crucial intracellular regulatory factor, participating in various physiological processes and playing a significant role in maintaining the redox homeostasis within the body. Ferroptosis, a form of iron-dependent non-apoptotic cell death, has gained considerable attention in recent years due to its involvement in multiple pathological processes. GPX4 is closely associated with ferroptosis and functions as the primary inhibitor of this process. Together, GPX4 and ferroptosis contribute to the pathophysiology of several diseases, including sepsis, nervous system diseases, ischemia reperfusion injury, cardiovascular diseases, and cancer. This review comprehensively explores the regulatory roles and impacts of GPX4 and ferroptosis in the development and progression of these diseases, with the aim of providing insights for identifying potential therapeutic strategies in the future.

LanCL2 Implicates in Testicular Redox Homeostasis and Acrosomal Maturation

Redox balance plays an important role in testicular homeostasis. While lots of antioxidant molecules have been identified as widely expressed, the understanding of the critical mechanisms for redox management in male germ cells is inadequate. This study identified LanCL2 as a major male germ cell-specific antioxidant gene that is important for testicular homeostasis. Highly expressed in the brain and testis, LanCL2 expression correlates with testicular maturation and brain development. LanCL2 is enriched in spermatocytes and round spermatids of the testis. By examining LanCL2 knockout mice, we found that LanCL2 deletion did not affect postnatal brain development but injured the sperm parameters of adult mice. With histopathological analysis, we noticed that LanCL2 KO caused a pre-maturation and accelerated the self-renewal of spermatogonial stem cells in the early stage of spermatogenesis. In contrast, at the adult stage, LanCL2 KO damaged the acrosomal maturation in spermiogenesis, resulting in spermatogenic defects with a reduced number and motility of spermatozoa. Furthermore, we show that this disruption of testicular homeostasis in the LanCL2 KO testis was due to dysbalanced testicular redox homeostasis. This study demonstrates the critical role of LanCL2 in testicular homeostasis and redox balance.

Oxytosis/Ferroptosis in Neurodegeneration: the Underlying Role of Master Regulator Glutathione Peroxidase 4 (GPX4)

Oxytosis/ferroptosis is an iron-dependent oxidative form of cell death triggered by lethal accumulation of phospholipid hydroperoxides (PLOOHs) in membranes. Failure of the intricate PLOOH repair system is a principle cause of ferroptotic cell death. Glutathione peroxidase 4 (GPX4) is distinctly vital for converting PLOOHs in membranes to non-toxic alcohols. As such, GPX4 is known as the master regulator of oxytosis/ferroptosis. Ferroptosis has been implicated in a number of disorders such as neurodegenerative diseases (amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), etc.), ischemia/reperfusion injury, and kidney degeneration. Reduced function of GPX4 is frequently observed in degenerative disorders. In this study, we examine how diminished GPX4 function may be a critical event in triggering oxytosis/ferroptosis to perpetuate or initiate the neurodegenerative diseases and assess the possible therapeutic importance of oxytosis/ferroptosis in neurodegenerative disorders. These discoveries are important for advancing our understanding of neurodegenerative diseases because oxytosis/ferroptosis may provide a new target to slow the course of the disease.

Chasing high and stable wheat grain mineral content: Mining diverse spring genotypes under induced drought stress

Climate change-induced drought has an effect on the nutritional quality of wheat. Here, the impact of drought at different plant stages on mineral content in mature wheat was evaluated in 30 spring-wheat lines of diverse backgrounds (modern, old and wheat-rye-introgressions). Genotypes with rye chromosome 3R introgression showed a high accumulation of several important minerals, including Zn and Fe, and these also showed stability across drought conditions. High Se content was found in genotypes with chromosome 1R. Old cultivars (K, Mg, Na, P and S) and 2R introgression lines (Fe, Ca, Mn, Mg and Na) demonstrated high mineral yield at early and late drought, respectively. Based on the low nutritional value often reported for modern wheat and negative climate effects on the stability of mineral content and yield, genes conferring high Zn/Fe, Se, and stable mineral yield under drought at various plant stages should be explicitly explored among 3R, 1R, old and 2R genotypes, respectively.

Selenium mitigates methotrexate-induced testicular injury: Insights from male NMRI mice model

BACKGROUND AND AIM

Chemotherapy, particularly with methotrexate (MTX), often elicits testicular toxicity, leading to impaired spermatogenesis and hormone imbalances. This study aimed to investigate the potential protective effects of selenium (Se) against MTX-induced testicular injury.

MATERIALS AND METHODS

Male mice were divided into control, MTX, Se, and MTX + Se groups. Histopathological examination involved the preparation of testicular tissue sections using the Johnsen's tubular biopsy score (JTBS) for spermatogenesis evaluation. Biochemical tests included the assessment of testosterone, malondialdehyde (MDA), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) levels. Real-time quantitative polymerase chain reaction (RT-qPCR) was employed to analyze the expression of caspase 3 (casp3), tumor protein 53 (p53), B-cell lymphoma 2 (Bcl2), and Bcl2-associated X protein (Bax) genes. Statistical analysis was performed using ANOVA and Tukey's tests (p < .05).

RESULTS

Histopathological analysis revealed significant testicular damage in the MTX group, with decreased spermatogenesis and Leydig cell count, while Se administration mitigated these effects, preserving the structural integrity of the reproductive epithelium. Biochemical analysis demonstrated that MTX led to elevated malondialdehyde (MDA) levels and reduced testosterone, LH, and FSH levels, suggesting oxidative stress and Leydig cell dysfunction. Gene expression analysis indicated that MTX upregulated proapoptotic genes (casp3, p53, and bax) while downregulating the antiapoptotic Bcl2 gene. In contrast, Se treatment reversed these trends, highlighting its potential antiapoptotic properties.

CONCLUSION

Our findings underscore the potential of Se as a therapeutic agent to mitigate the reproductive toxicity associated with MTX-induced testicular injury. Se exerts protective effects by regulating oxidative stress, preserving hormone balance, and modulating apoptotic pathways. These results suggest that Se supplementation could be a promising strategy to alleviate chemotherapy-induced testicular damage and preserve male fertility.

Preservation of rooster post-thawed sperm epigenetic modifications, fertility potential and other quality parameters in different extenders using reduced glutathione

Although rooster semen cryopreservation is an efficient procedure to spread qualified semen samples for reproductive goals, some post-thawed qualified semen samples resulted in poor fertility rate that could be related to epigenetic modifications during the cryopreservation process. This research was conducted to investigate the effect of reduced glutathione (GSH) in different cryopreservation extenders (Lake and Beltsville) on preservation of epigenetic modifications, fertility potential and other quality parameters of rooster sperm after thawing. Semen samples were collected and diluted in Lake and Beltsville extenders as follows: L-0: Lake without GSH, L-G: Lake with GSH, B-0: Beltsville without GSH, and B-G: Beltsville with GSH. After freeze-thawing process, sperm motility, membrane functionality, mitochondrial activity, acrosome integrity, viability, apoptosis status, lipid peroxidation, DNA fragmentation, ROS concentration, epigenetic modifications and fertility potential were evaluated. In results, the type of extender had no effect (P > 0.05) of post-thawed sperm quality. The treatments containing GSH presented higher (P ≤ 0.05) total motility, progressive motility, membrane functionality, mitochondrial activity, acrosome integrity, viability, DNA methylation, fertility as well as lower (P ≤ 0.05) lipid peroxidation, apoptosis, DNA fragmentation and ROS concentration than other treatments. Extender supplementation with GSH had no effect (P > 0.05) on histone methylation, histone acetylation and hatching rate. In conclusion, supplementation of rooster sperm cryopreservation extender with GSH could be an effective strategy to preserve post-thawed sperm DNA methylation, fertility and other quality parameters during reproductive programs.

Current Understanding of Human Polymorphism in Selenoprotein Genes: A Review of Its Significance as a Risk Biomarker

Selenium has been proven to influence several biological functions, showing to be an essential micronutrient. The functional studies demonstrated the benefits of a balanced selenium diet and how its deficiency is associated with diverse diseases, especially cancer and viral diseases. Selenium is an antioxidant, protecting the cells from damage, enhancing the immune system response, preventing cardiovascular diseases, and decreasing inflammation. Selenium can be found in its inorganic and organic forms, and its main form in the cells is the selenocysteine incorporated into selenoproteins. Twenty-five selenoproteins are currently known in the human genome: glutathione peroxidases, iodothyronine deiodinases, thioredoxin reductases, selenophosphate synthetase, and other selenoproteins. These proteins lead to the transport of selenium in the tissues, protect against oxidative damage, contribute to the stress of the endoplasmic reticulum, and control inflammation. Due to these functions, there has been growing interest in the influence of polymorphisms in selenoproteins in the last two decades. Selenoproteins' gene polymorphisms may influence protein structure and selenium concentration in plasma and its absorption and even impact the development and progression of certain diseases. This review aims to elucidate the role of selenoproteins and understand how their gene polymorphisms can influence the balance of physiological conditions. In this polymorphism review, we focused on the PubMed database, with only articles published in English between 2003 and 2023. The keywords used were "selenoprotein" and "polymorphism". Articles that did not approach the theme subject were excluded. Selenium and selenoproteins still have a long way to go in molecular studies, and several works demonstrated the importance of their polymorphisms as a risk biomarker for some diseases, especially cardiovascular and thyroid diseases, diabetes, and cancer.

Effects of sodium selenite, cysteamine, bacterially synthesized Se-NPs, and cysteamine loaded on Se-NPs on ram sperm cryopreservation

During the cryopreservation of sperm, the production of highly reactive oxygen species (ROS) can reduce their viability and fertility. However, the addition of antioxidants can help reduce the harmful effects of ROS. One such antioxidant is selenium, which is a co-factor of the glutathione peroxidase enzyme that is effective in scavenging ROS. Cysteamine can also take part in the structure of this enzyme. The use of nanoparticles can be less toxic to cells than their salt form. To this end, researchers synthesized Se-NPs using the streptococcus bacteria and loaded cysteamine onto the synthesized Se-NPs. The biosynthesis of Se-NPs and cysteamine loaded on Se-NPs was confirmed by UV-visible spectroscopy, X-ray diffraction (EDX), Fourier transforms infrared (FTIR) spectroscopy, and Field Emission Scanning Electron Microscope (FE-SEM). For cryopreservation, ram semen samples were diluted, and different concentrations (0, 1, 5, 25, and 125 µg/mL) of cysteamine, Se-NPs, cysteamine loaded on Se-NPs, and sodium selenite were added. An extender containing no supplement was considered as control group. After cooling the semen samples, they were frozen and stored in liquid nitrogen for evaluation. The samples were thawed and analyzed for mobility, viability, membrane and DNA integrity, and sperm abnormalities, as well as malondialdehyde level (MDA) and superoxide dismutase (SOD). The data was processed using SPSS, and a significance level of p < 0.05 was considered. The results of this experiment showed that adding 1 μg/mL of cysteamine loaded on Se-NPs to the diluent significantly increased the motility, viability, and membrane integrity and SOD of spermatozoa compared to the other treatment groups and control group, and reduced the abnormality, apoptosis, and MDA level of spermatozoa in comparison with the other treatment groups and control group (p < 0.05). In conclusion, the addition of cysteamine loaded on Se-NPs was found to improve the quality of ram sperm after cryopreservation.

The effectiveness of the use of selenium-containing top dressing in the cultivation of radish

Vegetable crops of the Brassicaceae family have the ability to include the necessary trace element selenium (Se) in the composition of organic compounds such as selenoproteins, in addition, they have important properties for human health based on the content of selenium. In our work, we investigated the effect of non-root processing of vegetating radish plants on the quality of finished products. The research results showed that the selenium content in the product part of plants significantly increased with an increase in the concentration of this element in the working solution. The dry matter content also increased, while its greatest amount was observed at lower concentrations of Se in the working solution. The use of non-root treatment with a selenium-containing solution on vegetative plants led to a significant decrease in the content of ascorbic acid and nitrates, and the decrease in the amount of nitrates in radish root crops was inversely dependent on the concentration of selenium in the working solution.

Responses and modulation of the white shrimp Litopenaeus vannamei glutathione peroxidases 2 and 4 during hypoxia, reoxygenation and GPx4 knock-down

Glutathione peroxidases (GPxs) are important antioxidant enzymes that act at distinct levels of the antioxidant defense. In vertebrates, there are several glutathione peroxidase (GPx) isoforms with different cellular and tissue distribution, but little is known about their interrelationships. The shrimp Litopenaeus vannamei is the main crustacean cultivated worldwide. It is affected by environmental stressors, including hypoxia and reoxygenation that cause reactive oxygen species accumulation. Thus, the antioxidant response modulation is key for shrimp resilience. Recently, several GPx isoforms genes were identified in the L. vannamei genome sequence, but their functions are just beginning to be studied. As in vertebrates, shrimp GPx isoforms can present differences in their antioxidant responses. Also, there could be interrelationships among the isoforms that may influence their responses. We evaluated shrimp GPx2 and GPx4 expressions during hypoxia, reoxygenation, and GPx4 knock-down using RNAi for silencing, as well as the enzymatic activity of total GPx and GPx4. Also, glutathione content in hepatopancreas was evaluated. GPx2 and GPx4 presented similar expression patterns during hypoxia and reoxygenation. Their expressions decreased during hypoxia and were reestablished in reoxygenation at 6 h in non-silenced shrimp. GPx2 expression was down-regulated by GPx4 knock-down, suggesting that GPx4 affects GPx2 expression. Total GPx activity changed in hypoxia and reoxygenation at 6 h but not at 12 h, while GPx4 activity was not affected by any stressor. The GSH/GSSG ratio in hepatopancreas indicated that at early hours, the redox status remains well-modulated but at 12 h it is impaired by hypoxia and reoxygenation.

"Alphabet" Selenoproteins: Implications in Pathology

Selenoproteins are a group of proteins containing selenium in the form of selenocysteine (Sec, U) as the 21st amino acid coded in the genetic code. Their synthesis depends on dietary selenium uptake and a common set of cofactors. Selenoproteins accomplish diverse roles in the body and cell processes by acting, for example, as antioxidants, modulators of the immune function, and detoxification agents for heavy metals, other xenobiotics, and key compounds in thyroid hormone metabolism. Although the functions of all this protein family are still unknown, several disorders in their structure, activity, or expression have been described by researchers. They concluded that selenium or cofactors deficiency, on the one hand, or the polymorphism in selenoproteins genes and synthesis, on the other hand, are involved in a large variety of pathological conditions, including type 2 diabetes, cardiovascular, muscular, oncological, hepatic, endocrine, immuno-inflammatory, and neurodegenerative diseases. This review focuses on the specific roles of selenoproteins named after letters of the alphabet in medicine, which are less known than the rest, regarding their implications in the pathological processes of several prevalent diseases and disease prevention.

The MAEL expression in mitochondria of human spermatozoa and the association with asthenozoospermia

PURPOSE

The maelstrom spermatogenic transposon silencer (MAEL) function in postmeiotic germ cells remains unclear, and its protein localization in human testis and spermatozoa awaits determination. This study aims to clarify the MAEL expression in human spermatogenesis and to explore its role in sperm function.

MATERIALS AND METHODS

Twenty-seven asthenozoospermic men, 40 normozoospermic controls, and three obstructive azoospermic men were enrolled. The transcripts of MAEL in the seminiferous epithelium and MAEL downstream targets were identified by bioinformatics analysis. MAEL protein expression in human testis and ejaculated sperms were examined by immunohistochemical and immunogold staining, respectively. The roles of MAEL in mitochondria function were investigated by siRNA knockdown in human H358 cells. The association between MAEL protein levels and clinical sperm features was evaluated.

RESULTS

Abundant MAEL was expressed in spermatid and spermatozoa of the human testis. Remarkably, MAEL was located in the mitochondria of ejaculated sperm, and bioinformatics analysis identified GPX4 and UBL4B as MAEL's downstream targets. Knockdown of MAEL sabotaged mitochondria function and reduced adenosine triphosphate (ATP) production in H358 cells. MAEL, GPX4, and UBL4B expression levels were significantly decreased in asthenozoospermic sperms than in controls. The MAEL protein levels were positively correlated with GPX4 and UBL4B in human sperm. Total motile sperm count (TMSC) was positively correlated with protein levels of MAEL, GPX4, and UBL4B in ejaculated sperms.

CONCLUSIONS

We highlight prominent MAEL expression in the intratesticular spermatid and the mitochondria of ejaculated spermatozoa. MAEL directly binds to GPX4 and UBL4B, and loss of MAEL induces mitochondrial dysfunction. MAEL-mitochondrial function-motility relationship might advance our understanding of the causes of asthenozoospermia.

The role of selenium and nano selenium on physiological responses in plant: a review

Selenium (Se), being an essential micronutrient, enhances plant growth and development in trace amounts. It also protects plants against different abiotic stresses by acting as an antioxidant or stimulator in a dose-dependent manner. Knowledge of Se uptake, translocation, and accumulation is crucial to achieving the inclusive benefits of Se in plants. Therefore, this review discusses the absorption, translocation, and signaling of Se in plants as well as proteomic and genomic investigations of Se shortage and toxicity. Furthermore, the physiological responses to Se in plants and its ability to mitigate abiotic stress have been included. In this golden age of nanotechnology, scientists are interested in nanostructured materials due to their advantages over bulk ones. Thus, the synthesis of nano-Se or Se nanoparticles (SeNP) and its impact on plants have been studied, highlighting the essential functions of Se NP in plant physiology. In this review, we survey the research literature from the perspective of the role of Se in plant metabolism. We also highlight the outstanding aspects of Se NP that enlighten the knowledge and importance of Se in the plant system.

Graphical abstract

Both selenium deficiency and excess impair male reproductive system via inducing oxidative stress-activated PI3K/AKT-mediated apoptosis and cell proliferation signaling in testis of mice

Selenium (Se) deficiency or excess impairs testicular development and spermatogenesis, while the underlying mechanisms in this regard remain unclear. This study was designed to explore the molecular biology of Se deficiency or excess in spermatogenesis in mice. Three-week-old male mice (n = 10 mice/diet) were fed with Se-deficient diet (SeD, 0.02 mg Se/kg), adequate-Se diet (SeA, 0.2 mg Se/kg), or excess-Se diet (SeE, 2.0 mg Se/kg) for 5 months. Compared with SeA, SeD reduced (P < 0.05) the body weight (10.4%) and sperm density (84.3%) but increased (P < 0.05) sperm deformity (32.8%); SeE decreased (P < 0.05) the sperm density (78.5%) and sperm motility (35.9%) of the mice. Meanwhile, both SeD and SeE increased (P < 0.05) serum FSH concentrations (10.4-25.6%) and induced testicular damage in mice in comparison with the SeA. Compared with SeA, SeD increased (P < 0.05) the 8-OHdG concentration by 25.5%; SeE increased (P < 0.05) both MDA and 8-OHdG concentrations by 118.8-180.3% in testis. Furthermore, transcriptome analysis showed that there 1325 and 858 transcripts were altered (P < 0.05) in the testis by SeD and SeE, respectively, compared with SeA. KEGG pathway analysis revealed that these differentially expressed genes were mainly enriched in the PI3K-AKT signaling pathway, which is regulated by oxidative stress. Moreover, western blotting analysis revealed that SeD and SeE dysregulated PI3K-AKT-mediated apoptosis and cell proliferation signaling, including upregulating (P < 0.05) caspase 3, cleaved-caspase 3, BCL-2 and (or) P53 and downregulating (P < 0.05) PI3K, p-AKT, p-mTOR, 4E-BP1, p-4E-BP1 and (or) p-p70S6K in the testis of mice compared with SeA. Additionally, compared with SeA, both SeD and SeE increased (P < 0.05) GPX3 and SELENOO; SeD decreased (P < 0.05) GPX1, TXRND3 and SELENOW, but SeE increased (P < 0.05) production of three selenoproteins in the testis. Conclusively, both Se deficiency and excess impairs male reproductive system in mice, potentially with the induction of oxidative stress and activation of PI3K/AKT-mediated apoptosis and cell proliferation signaling in the testis.

GPX4: The hub of lipid oxidation, ferroptosis, disease and treatment

Glutathione peroxidase 4 (GPx4) moonlights as structural protein and antioxidase that powerfully inhibits lipid oxidation. In the past years, it is considered as a key regulator of ferroptosis, which takes role in the lipid and amine acid metabolism and influences the cell aging, oncogenesis, and cell death. More and more evidences show that targeting GPX4-induced ferroptosis is a promising strategy for disease therapy, especially cancer treatment. In view of these, we generalize the function of GPX4 and regulatory mechanism between GPX4 and ferroptosis, discuss its roles in the disease pathology, and focus on the recent advances of disease therapeutic potential.

Sperm mitochondrial DNA copy number mediates the association between seminal plasma selenium concentrations and semen quality among healthy men

Selenium (Se) is essential for successful male reproduction. However, the association of Se status with human semen quality remains controversial and the underlying mechanisms are poorly understood. We measured seminal plasma Se concentrations, sperm mitochondrial DNA copy number (mtDNAcn), and sperm quality parameters among healthy Chinese men screened as potential sperm donors. Linear mixed-effects models were used to investigate the associations of within-subject pooled seminal plasma Se concentrations (n = 1159) with repeated sperm quality parameters (n = 5617); mediation analyses were applied to evaluate the mediating role of sperm mtDNAcn (n = 989). Seminal plasma Se concentrations were positively associated with sperm concentration and total count (both P for trend < 0.001). In adjusted models, men in the top vs. bottom quartiles of seminal plasma Se concentrations had 70.1 % (95 % CI: 53.3 %, 88.9 %) and 59.1 % (95 % CI: 40.5 %, 80.2 %) higher sperm concentration and total count, respectively. Meanwhile, we observed inverse associations between seminal plasma Se concentrations and sperm mtDNAcn, and between sperm mtDNAcn and sperm motility, concentration, and total count (all P for trend < 0.05). Mediation analyses suggested that sperm mtDNAcn mediated 19.7 % (95 % CI: 15.9 %, 25.3 %) and 23.1 % (95 % CI: 17.4 %, 33.4 %) of the associations between seminal plasma Se concentrations and sperm concentration and total count, respectively. Our findings suggest that Se is essential for male spermatogenesis, potentially by affecting sperm mtDNAcn.

Glutathione improves testicular spermatogenesis through inhibiting oxidative stress, mitochondrial damage, and apoptosis induced by copper deposition in mice with Wilson disease

BACKGROUND AND OBJECTIVE

There are considerable evidence of reproductive impairment in male organisms with Wilson disease (WD). The purpose of this study was to observe spermatogenesis, mitochondrial damage, apoptosis, and the level of oxidative stress in the testes of Wilson disease model TX mice, and to observe the effect and mechanism of glutathione on testicular spermatogenesis.

METHODS

Mice were divided into a normal control group (control group), Wilson disease model TX mice group (WD group), penicillamine-treated TX mice group (penicillamine group) and glutathione-treated TX mice group (glutathione group). Testicular coefficient, histomorphology of testis and epididymis, number of spermatozoa, apoptosis of spermatogenic cells and expression of apoptosis-related proteins were observed. Ultrastructural analysis of mitochondria and mitochondrial membrane potential (MMP) monitored using JC-1 dye were used to detect mitochondrial damage. The levels of malondialdehyde (MDA), glutathione (GSH), catalase (CAT), and reactive oxygen species (ROS) in testicular cells were measured to assess oxidative stress.

RESULTS

Testicular coefficient did not change in mice with Wilson disease. However, the tissue structure of the testicular seminiferous tubules was damaged, and the number of spermatozoa in the epididymal lumen was significantly reduced in WD group. The apoptosis rate in the testes was significantly increased. The protein expression of the pro-apoptotic proteins Bax and Caspase-3 significantly increased, and the expressions of the anti-apoptotic protein Bcl-2 significantly decreased. The levels of ROS and MDA significantly increased, and the levels of CAT and GSH significantly decreased. Mitochondria with abnormal ultrastructure and the rate of JC-1 positive cells were significantly increased in the WD group. After copper chelation by penicillamine, the structure of the testicular seminiferous tubules and the number of spermatozoa in the epididymal lumen were significantly improved. The number of apoptotic cells was significantly reduced. The levels of Bax and Caspase-3 decreased, and the expression of Bcl-2 increased. The contents of CAT and GSH increased, and the levels of ROS and MDA decreased significantly. The abnormal mitochondria and JC-1 positive cells was significantly decreased. The histomorphology of seminiferous tubules, spermatogenic function, apoptosis rate, apoptosis-related proteins, mitochondrial damage, and oxidative stress in Wilson disease TX mice significantly improved after glutathione treatment.

CONCLUSION

Copper deposition in Wilson disease can lead to oxidative stress injury, mitochondrial damage, and apoptosis in the testis, leading to the impairment of spermatogenesis. Glutathione may improve testicular spermatogenesis in male Wilson disease TX mice by inhibiting copper deposition-induced oxidative stress, mitochondrial damage, and apoptosis.

Comprehensive review on the positive and negative effects of various important regulators on male spermatogenesis and fertility

With the increasing global incidence of infertility, the influence of environmental factors, lifestyle habits, and nutrients on reproductive health has gradually attracted the attention of researchers. The quantity and quality of sperm play vital roles in male fertility, and both characteristics can be affected by external and internal factors. In this review, the potential role of genetic, environmental, and endocrine factors; nutrients and trace elements in male reproductive health, spermatozoa function, and fertility potency and the underlying mechanisms are considered to provide a theoretical basis for clinical treatment of infertility.

Gpx4, Selenov, and Txnrd3 Are Three Most Testis-Abundant Selenogenes Resistant to Dietary Selenium Concentrations and Actively Expressed During Reproductive Ages in Rats

Almost all selenogenes are expressed in the testis, and those have the highest and constant expressions will be the primary candidates for functional analysis of selenium (Se) in male reproduction. This study aimed to profile the mRNA expressions of the testis-abundant selenogenes of rat models in responses to growth and dietary Se concentrations. Forty-eight weaning SD male rats were fed Se deficient basal diet (BD) for 5 weeks and then randomly grouped (n = 12/group) for being fed BD or BD plus 0.25, 3, or 5 mg Se/kg for 4 more weeks before sacrifice. Abundances of selenogenomic mRNAs in the liver and testis were determined with relative qPCR and those of the testis-abundant selenogenes in 13 kinds of tissues were assayed with a molecular beacon-based qPCR. Spatiotemporal expressions of rat selenogenome were also analyzed with the RNA-Seq transcriptomic data published by NCBI. mRNA abundances of glutathione peroxidase 4 (Gpx4), nuclear Gpx4 (nGpx4), selenoprotein V (Selenov), and thioredoxin reductase 3 (Txnrd3) in the testis were significantly higher than that in any other tissues (P < 0.05). Moreover, testicular mRNA abundances of Gpx4, Selenov, and Txnrd3 were not affected by levels of dietary Se supplementation (P > 0.05), and much higher at 6-21 weeks old than at 2 and 104 weeks old (P < 0.05). The result showed that Gpx4, Selenov, and Txnrd3 were most highly expressed in the testis of rats especially at reproductive ages and resistant to the impact of dietary Se levels, which suggested their specific importance in male reproduction.

Small-molecule allosteric inhibitors of GPX4

Encouraged by the dependence of drug-resistant, metastatic cancers on GPX4, we examined biophysical mechanisms of GPX4 inhibition, which revealed an unexpected allosteric site. We found that this site was involved in native regeneration of GPX4 under low glutathione conditions. Covalent binding of inhibitors to this allosteric site caused a conformational change, inhibition of activity, and subsequent cellular GPX4 protein degradation. To verify this site in an unbiased manner, we screened a library of compounds and identified and validated that an additional compound can covalently bind in this allosteric site, inhibiting and degrading GPX4. We determined co-crystal structures of six different inhibitors bound in this site. We have thus identified an allosteric mechanism for small molecules targeting aggressive cancers dependent on GPX4.

Male guanine-rich RNA sequence binding factor 1 knockout mice (Grsf1-/-) gain less body weight during adolescence and adulthood

The guanine-rich RNA sequence binding factor 1 (GRSF1) is an RNA-binding protein of the heterogenous nuclear ribonucleoprotein H/F (hnRNP H/F) family that binds to guanine-rich RNA sequences forming G-quadruplex structures. In mice and humans there are single copy GRSF1 genes, but multiple transcripts have been reported. GRSF1 has been implicated in a number of physiological processes (e.g. embryogenesis, erythropoiesis, redox homeostasis, RNA metabolism) but also in the pathogenesis of viral infections and hyperproliferative diseases. These postulated biological functions of GRSF1 originate from in vitro studies rather than complex in vivo systems. To assess the in vivo relevance of these findings, we created systemic Grsf1^-/- knockout mice lacking exons 4 and 5 of the Grsf1 gene and compared the basic functional characteristics of these animals with those of wildtype controls. We found that Grsf1-deficient mice are viable, reproduce normally and have fully functional hematopoietic systems. Up to an age of 15 weeks they develop normally but when male individuals grow older, they gain significantly less body weight than wildtype controls in a gender-specific manner. Profiling Grsf1 mRNA expression in different mouse tissues we observed high concentrations in testis. Comparison of the testicular transcriptomes of Grsf1^-/- mice and wildtype controls confirmed near complete knock-out of Grsf1 but otherwise subtle differences in transcript regulations. Comparative testicular proteome analyses suggested perturbed mitochondrial respiration in Grsf1^-/- mice which may be related to compromised expression of complex I proteins. Here we present, for the first time, an in vivo complete Grsf1 knock-out mouse with comprehensive physiological, transcriptomic and proteomic characterization to improve our understanding of the GRSF1 beyond in vitro cell culture models.

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.

1H, 13C, and 15N resonance assignments of human glutathione peroxidase 4

Glutathione peroxidase 4 (GPx4) behaves as an antioxidant enzyme capable of directly reducing peroxidized phospholipids within cell membranes. Recently, GPx4 has attracted attention as a target molecule for cancer therapy because it induces the immortalization of cancer cells suppressing ferroptosis. In this study, to analyze the function and structure of GPx4 by solution NMR, we performed resonance assignments of GPx4 and assigned almost all backbone ¹H, ¹³C, and ¹⁵N resonances and most of the side chain ¹H and ¹³C resonances. Using these assignments, the secondary structure of GPx4 was analyzed by the TALOS + program. GPx4 has six helices and seven strands. Then, the backbone dynamics were examined by the {¹H}-¹⁵N heteronuclear NOE experiment. GPx4 was found to be rigid except for a short loop region. These results will provide basis for functional analysis and the first solution structure determination of GPx4.

Selenoprotein P - Selenium transport protein, enzyme and biomarker of selenium status

The habitual intake of selenium (Se) varies strongly around the world, and many people are at risk of inadequate supply and health risks from Se deficiency. Within the human organism, efficient transport mechanisms ensure that organs with a high demand and relevance for reproduction and survival are preferentially supplied. To this end, selenoprotein P (SELENOP) is synthesized in the liver and mediates Se transport to essential tissues such as the endocrine glands and the brain, where the "SELENOP cycle" maintains a privileged Se status. Mouse models indicate that SELENOP is not essential for life, as supplemental Se supply was capable of preventing the development of severe symptoms. However, knockout mice died under limiting supply, arguing for an essential role of SELENOP in Se deficiency. Many clinical studies support this notion, pointing to close links between health risks and low SELENOP levels. Accordingly, circulating SELENOP concentrations serve as a functional biomarker of Se supply, at least until a saturated status is achieved and SELENOP levels reach a plateau. Upon toxic intake, a further increase in SELENOP is observed, i.e., SELENOP provides information about possible selenosis. The SELENOP transcripts predict an insertion of ten selenocysteine residues. However, the decoding is imperfect, and not all these positions are ultimately occupied by selenocysteine. In addition to the selenocysteine residues near the C-terminus, one selenocysteine resides central within an enzyme-like environment. SELENOP proved capable of catalyzing peroxide degradation in vitro and protecting e.g. LDL particles from oxidation. An enzymatic activity in the intact organism is unclear, but an increasing number of clinical studies provides evidence for a direct involvement of SELENOP-dependent Se transport as an important and modifiable risk factor of disease. This interaction is particularly strong for cardiovascular and critical disease including COVID-19, cancer at various sites and autoimmune thyroiditis. This review briefly highlights the links between the growing knowledge of Se in health and disease over the last 50 years and the specific advances that have been made in our understanding of the physiological and clinical contribution of SELENOP to the current picture.

Progress of Selenium Deficiency in the Pathogenesis of Arthropathies and Selenium Supplement for Their Treatment

Selenium, an essential trace element for human health, exerts an indispensable effect in maintaining physiological homeostasis and functions in the body. Selenium deficiency is associated with arthropathies, such as Kashin-Beck disease, rheumatoid arthritis, osteoarthritis, and osteoporosis. Selenium deficiency mainly affects the normal physiological state of bone and cartilage through oxidative stress reaction and immune reaction. This review aims to explore the role of selenium deficiency and its mechanisms existed in the pathogenesis of arthropathies. Meanwhile, this review also summarized various experiments to highlight the crucial functions of selenium in maintaining the homeostasis of bone and cartilage.

Unbalanced Expression of Glutathione Peroxidase 4 and Arachidonate 15-Lipoxygenase Affects Acrosome Reaction and In Vitro Fertilization

Glutathione peroxidase 4 (Gpx4) and arachidonic acid 15 lipoxygenase (Alox15) are counterplayers in oxidative lipid metabolism and both enzymes have been implicated in spermatogenesis. However, the roles of the two proteins in acrosomal exocytosis have not been explored in detail. Here we characterized Gpx4 distribution in mouse sperm and detected the enzyme not only in the midpiece of the resting sperm but also at the anterior region of the head, where the acrosome is localized. During sperm capacitation, Gpx4 translocated to the post-acrosomal compartment. Sperm from Gpx4^+/Sec46Ala mice heterozygously expressing a catalytically silent enzyme displayed an increased expression of phosphotyrosyl proteins, impaired acrosomal exocytosis after in vitro capacitation and were not suitable for in vitro fertilization. Alox15-deficient sperm showed normal acrosome reactions but when crossed into a Gpx4-deficient background spontaneous acrosomal exocytosis was observed during capacitation and these cells were even less suitable for in vitro fertilization. Taken together, our data indicate that heterozygous expression of a catalytically silent Gpx4 variant impairs acrosomal exocytosis and in vitro fertilization. Alox15 deficiency hardly impacted the acrosome reaction but when crossed into the Gpx4-deficient background spontaneous acrosomal exocytosis was induced. The detailed molecular mechanisms for the observed effects may be related to the compromised redox homeostasis.

A white paper on Phospholipid Hydroperoxide Glutathione Peroxidase (GPx4) forty years later

The purification of a protein inhibiting lipid peroxidation led to the discovery of the selenoperoxidase GPx4 forty years ago. Thus, the evidence of the enzymatic activity was reached after identifying the biological effect and unambiguously defined the relationship between the biological function and the enzymatic activity. In the syllogism where GPx4 inhibits lipid peroxidation and its inhibition is lethal, cell death is operated by lipid peroxidation. Based on this rationale, this form of cell death emerged as regulated iron-enforced oxygen toxicity and was named ferroptosis in 2012. In the last decades, we learned that reduction of lipid hydroperoxides is indispensable and, in cooperation with prooxidant systems, controls the critical steady state of lipid peroxidation. This concept defined the GPx4 reaction as both the target for possible anti-cancer therapy and if insufficient, as cause of degenerative diseases. We know the reaction mechanism, but the details of the interaction at the membrane cytosol interface are still poorly defined. We know the gene structure, but the knowledge about expression control is still limited. The same holds true for post-transcriptional modifications. Reverse genetics indicate that GPx4 has a role in inflammation, immunity, and differentiation, but the observations emerging from these studies need a more specifically addressed biochemical evidence. Finally, the role of GPx4 in spermatogenesis disclosed an area unconnected to lipid peroxidation. In its mitochondrial and nuclear form, the peroxidase catalyzes the oxidation of protein thiols in two specific aspects of sperm maturation: stabilization of the mid-piece and chromatin compaction. Thus, although available evidence converges to the notion that GPx4 activity is vital due to the inhibition of lipid peroxidation, it is reasonable to foresee other unknown aspects of the GPx4 reaction to be disclosed.

Selenocysteine Machinery Primarily Supports TXNRD1 and GPX4 Functions and Together They Are Functionally Linked with SCD and PRDX6

The human genome has 25 genes coding for selenocysteine (Sec)-containing proteins, whose synthesis is supported by specialized Sec machinery proteins. Here, we carried out an analysis of the co-essentiality network to identify functional partners of selenoproteins and Sec machinery. One outstanding cluster included all seven known Sec machinery proteins and two critical selenoproteins, GPX4 and TXNRD1. Additionally, these nine genes were further positively associated with PRDX6 and negatively with SCD, linking the latter two genes to the essential role of selenium. We analyzed the essentiality scores of gene knockouts in this cluster across one thousand cancer cell lines and found that Sec metabolism genes are strongly selective for a subset of primary tissues, suggesting that certain cancer cell lineages are particularly dependent on selenium. A separate outstanding cluster included selenophosphate synthetase SEPHS1, which was linked to a group of transcription factors, whereas the remaining selenoproteins were linked neither to these clusters nor among themselves. The data suggest that key components of Sec machinery have already been identified and that their primary role is to support the functions of GPX4 and TXNRD1, with further functional links to PRDX6 and SCD.

The glutathione peroxidase family: Discoveries and mechanism

The discoveries leading to our present understanding of the glutathione peroxidases (GPxs) are recalled. The cytosolic GPx, now GPx1, was first described by Mills in 1957 and claimed to depend on selenium by Rotruck et al., in 1972. With the determination of a stoichiometry of one selenium per subunit, GPx1 was established as the first selenoenzyme of vertebrates. In the meantime, the GPxs have grown up to a huge family of enzymes that prevent free radical formation from hydroperoxides and, thus, are antioxidant enzymes, but they are also involved in regulatory processes or synthetic functions. The kinetic mechanism of the selenium-containing GPxs is unusual in neither showing a defined K_M nor any substrate saturation. More recently, the reaction mechanism has been investigated by the density functional theory and nuclear magnetic resonance of model compounds mimicking the reaction cycle. The resulting concept sees a selenolate oxidized to a selenenic acid. This very fast reaction results from a concerted dual attack on the hydroperoxide bond, a nucleophilic one by the selenolate and an electrophilic one by a proton that is unstably bound in the reaction center. Postulated intermediates have been identified either in the native enzymes or in model compounds.

Redox regulation by TXNRD3 during epididymal maturation underlies capacitation-associated mitochondrial activity and sperm motility in mice

During epididymal transit, redox remodeling protects mammalian spermatozoa, preparing them for survival in the subsequent journey to fertilization. However, molecular mechanisms of redox regulation in sperm development and maturation remain largely elusive. In this study, we report that thioredoxin-glutathione reductase (TXNRD3), a thioredoxin reductase family member particularly abundant in elongating spermatids at the site of mitochondrial sheath formation, regulates redox homeostasis to support male fertility. Using Txnrd3-/- mice, our biochemical, ultrastructural, and live cell imaging analyses revealed impairments in sperm morphology and motility under conditions of TXNRD3 deficiency. We find that mitochondria develop more defined cristae during capacitation in wildtype sperm. Furthermore, we show that absence of TXNRD3 alters thiol redox status in both the head and tail during sperm maturation and capacitation, resulting in defective mitochondrial ultrastructure and activity under capacitating conditions. These findings provide insights into molecular mechanisms of redox homeostasis and bioenergetics during sperm maturation, capacitation, and fertilization.

GPX4: old lessons, new features

GPX4 is a selenocysteine-containing protein that plays an essential role in repairing peroxidised phospholipids. Its role in organismal homeostasis has been known for decades, and it has been reported to play a pivotal role in cell survival and mammalian embryonic development. In recent years, GPX4 has been associated with a cell death modality dubbed ferroptosis. The framing of this molecular pathway of cell death was essential for understanding the conditions that determine GPX4 dependency and ultimately to the process of lipid peroxidation. Since its discovery, ferroptosis has been gaining momentum as a promising target for yet-incurable diseases, including cancer and neurodegeneration. Given the current interest, in the present review, we provide newcomers in the field with an overview of the biology of GPX4 and cover some of its most recent discoveries.

Gamma-oryzanol supplemented in extender enhances the quality of semen cryopreservation and alters proteomic profile in Thai swamp buffalo

Reactive oxygen species (ROS) exert an adverse effect on sperm quality during the freezing process. Gamma-oryzanol is an effective antioxidant and has the ability to inhibit lipoperoxidation in various cells. Therefore, this study aims to investigate the effect of gamma-oryzanol supplementation in extender on post-thawed motility and proteomic profiles of swamp buffalo spermatozoa. Each ejaculate of an individual bull was divided into four equal aliquots. Gamma-oryzanol was supplemented at 0 (control), 0.1, 0.25, and 0.5 mM in tris-citrate egg yolk extender. The parameters of sperm motility were evaluated using computer assisted semen analyzer (CASA). The results showed that the progressive motility was significantly higher in 0.5 mM of gamma-oryzanol supplementation group when compared with the control group (p < 0.05), but no significant differences were observed among the treatments. In addition, a proteomic approach was applied to analyze the differentially expressed proteins in post-thawed sperm with or without gamma-oryzanol supplementation in extender. We confirmed that 2-phospho-d-glycerate hydro-lyase (ENO1), glutathione s-transferase mu 1 (GSTM1), phospholipid hydroperoxide glutathione peroxidase (GPX4), outer dense fiber protein 2 (ODF2), tektin-4 (TEKT4), tubulin beta-4B chain (TUBB4B), and ATP synthase subunit beta (ATP5B) were up-regulated in 0.5 mM of gamma-oryzanol supplementation group, which might be associated with the improved post-thawed motility observed in this treatment group. These results demonstrate the beneficial effect of gamma-oryzanol on post-thawed survival of swamp buffalo spermatozoa and help advance the understanding about molecular metabolism of sperm in this species.

Post-Translational Modification of GPX4 is a Promising Target for Treating Ferroptosis-Related Diseases

Glutathione peroxidase 4 (GPX4) is one of the most important antioxidant enzymes. As the key regulator of ferroptosis, GPX4 has attracted considerable attention in the fields of cancer, cardiovascular, and neuroscience research in the past 10 years. How to regulate GPX4 activity has become a hot topic nowadays. GPX4 protein level is regulated transcriptionally by transcription factor SP2 or Nrf2. GPX4 activity can be upregulated by supplementing intracellular selenium or glutathione, and also be inhibited by ferroptosis inducers such as ML162 and RSL3. These regulatory mechanisms of GPX4 level/activity have already shown a great potential for treating ferroptosis-related diseases in preclinical studies, especially in cancer cells. Until recently, research show that GPX4 can undergo post-translational modifications (PTMs), such as ubiquitination, succination, phosphorylation, and glycosylation. PTMs of GPX4 affect the protein level/activity of GPX4, indicating that modifying these processes can be a potential therapy for treating ferroptosis-related diseases. This article summarizes the protein characteristics, enzyme properties, and PTMs of GPX4. It also provides a hypothetical idea for treating ferroptosis-related diseases by targeting the PTMs of GPX4.

The Intestinal Redox System and Its Significance in Chemotherapy-Induced Intestinal Mucositis

Chemotherapy-induced intestinal mucositis (CIM) is a significant dose-limiting adverse reaction brought on by the cancer treatment. Multiple studies reported that reactive oxygen species (ROS) is rapidly produced during the initial stages of chemotherapy, when the drugs elicit direct damage to intestinal mucosal cells, which, in turn, results in necrosis, mitochondrial dysfunction, and ROS production. However, the mechanism behind the intestinal redox system-based induction of intestinal mucosal injury and necrosis of CIM is still undetermined. In this article, we summarized relevant information regarding the intestinal redox system, including the composition and regulation of redox enzymes, ROS generation, and its regulation in the intestine. We innovatively proposed the intestinal redox “Tai Chi” theory and revealed its significance in the pathogenesis of CIM. We also conducted an extensive review of the English language-based literatures involving oxidative stress (OS) and its involvement in the pathological mechanisms of CIM. From the date of inception till July 31, 2021, 51 related articles were selected. Based on our analysis of these articles, only five chemotherapeutic drugs, namely, MTX, 5-FU, cisplatin, CPT-11, and oxaliplatin were shown to trigger the ROS-based pathological mechanisms of CIM. We also discussed the redox system-mediated modulation of CIM pathogenesis via elaboration of the relationship between chemotherapeutic drugs and the redox system. It is our belief that this overview of the intestinal redox system and its role in CIM pathogenesis will greatly enhance research direction and improve CIM management in the future.

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.

Humoral immune response to COVID-19 mRNA vaccination in relation to selenium status

The essential trace element selenium (Se) is of central importance for human health and particularly for a regular functioning of the immune system. In the context of the current pandemic, Se deficiency in patients with COVID-19 correlated with disease severity and mortality risk. Selenium has been reported to be associated with the immune response following vaccination, but it is unknown whether this also applies to SARS-CoV-2 vaccines. In this observational study, adult health care workers (n = 126) who received two consecutive anti-SARS-CoV-2 vaccinations by BNT162b2 were followed for up to 24 weeks, with blood samples collected at the first and second dose and at three and 21 weeks after the second dose. Serum SARS-CoV-2 IgG titres, neutralising antibody potency, total Se and selenoprotein P concentrations, and glutathione peroxidase 3 activity were quantified. All three biomarkers of Se status were significantly correlated at all the time points, and participants who reported supplemental Se intake displayed higher Se concentrations. SARS-CoV-2 IgG titres and neutralising potency were highest three weeks after the second dose and decreased towards the last sampling point. The humoral immune response was not related to any of the three Se status biomarkers. Supplemental Se intake had no effect at any time point on the vaccination response as measured by serum SARS-CoV-2 IgG levels or neutralising potency. Overall, no association was found between Se status or supplemental Se intake and humoral immune response to COVID-19 mRNA vaccination.

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Humoral SARS-CoV-2 vaccination response in healthy adults was unrelated to baseline Se status or supplemental Se intake.

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Vaccine-induced neutralising activity correlated with SARS-CoV-2 IgG concentration, but not with Se status.

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Rise and decline of the vaccination-induced SARS-CoV-2 IgG was Se status-independent during 24 weeks after first dose.

Mitochondrial glutathione peroxidase 4 is indispensable for photoreceptor development and survival in mice

Glutathione peroxidase 4 (GPx4) is known for its unique function in the direct detoxification of lipid peroxides in the cell membrane and as a key regulator of ferroptosis, a form of lipid peroxidation–induced nonapoptotic cell death. However, the cytosolic isoform of GPx4 is considered to play a major role in inhibiting ferroptosis in somatic cells, whereas the roles of the mitochondrial isoform of GPx4 (mGPx4) in cell survival are not yet clear. In the present study, we found that mGPx4 KO mice exhibit a cone–rod dystrophy-like phenotype in which loss of cone photoreceptors precedes loss of rod photoreceptors. Specifically, in mGPx4 KO mice, cone photoreceptors disappeared prior to their maturation, whereas rod photoreceptors persisted through maturation but gradually degenerated afterward. Mechanistically, we demonstrated that vitamin E supplementation significantly ameliorated photoreceptor loss in these mice. Furthermore, LC–MS showed a significant increase in peroxidized phosphatidylethanolamine esterified with docosahexaenoic acid in the retina of mGPx4 KO mice. We also observed shrunken and uniformly condensed nuclei as well as caspase-3 activation in mGPx4 KO photoreceptors, suggesting that apoptosis was prevalent. Taken together, our findings indicate that mGPx4 is essential for the maturation of cone photoreceptors but not for the maturation of rod photoreceptors, although it is still critical for the survival of rod photoreceptors after maturation. In conclusion, we reveal novel functions of mGPx4 in supporting development and survival of photoreceptors in vivo.

Peroxiredoxin 6 Peroxidase and Ca2+-Independent Phospholipase A2 Activities Are Essential to Support Male-Mouse Fertility

Human infertility is an important health problem that affects one in six couples worldwide. Half of these cases are due to male infertility. Oxidative stress is a common culprit of male infertility, promoting lipid peroxidation and the oxidation of proteins and DNA in spermatozoa, thereby impairing motility, capacitation and fertilization. Peroxiredoxin 6 (PRDX6) possesses peroxidase and Ca²⁺-independent-phospholipase-A₂ (iPLA₂) activities that scavenge ROS and repair oxidized sperm membranes, respectively. PRDX6 protects spermatozoa against oxidative stress. Infertile men’s spermatozoa have impaired motility, elevated lipid peroxidation levels and DNA damage due to low PRDX6 levels. A lack of PRDX6 is associated with male-mouse infertility. Here, we determined the impact of the absence of PRDX6 peroxidase or iPLA₂ activities on male-mouse fertility. Two-month-old male C57Bl6/J (wild-type), Prdx6^−/−, C47S and D140A knock-in (peroxidase- and iPLA₂-deficient, respectively) male mice were challenged with an in vivo oxidative stress triggered by tert-butyl hydroperoxide (t-BHP). C47S and D140A males produced smaller litters compared to wild-type controls. The t-BHP treatment promoted a lower number of pups, high levels of lipid peroxidation, tyrosine nitration, and DNA oxidation in all mutant spermatozoa compared to wild-type controls. All mutant spermatozoa had impaired capacitation and motility. In summary, both PRDX6 peroxidase and iPLA₂ activities are essential to support male-mouse fertility.