Depletion of selenoprotein GPx4 in spermatocytes causes male infertility in mice

Sperm RNA elements as markers of health

Idiopathic infertility, an etiology not identified as part of standard clinical assessment, represents approximately 20% of all infertility cases. Current male infertility diagnosis focuses on the concentration, motility, and morphology of spermatozoa. This is of limited value when predicting birth success and of limited utility when selecting the optimum treatment. At fertilization, spermatozoa provide their genomic contribution, as well as a set of RNAs and proteins that have distinct roles in development. The potential of spermatozoal RNAs to be used as a prognostic of live birth has been shown [Jodar et al. (2015) Science Translational Medicine 7(295):295re6]. This relied on a set of 648 sperm RNA elements derived from 285 genes that are perhaps indicative of future health status. To address this tenet, the present study correlated the levels of each transcript among all samples to assess linkage between transcript absence, birth success, and possible disease association. Correlations between transcript levels of the 285 genes were analyzed amongst themselves, and within the context of the entire transcript population for these samples. The transcripts ACE, GIGYF2, and ODF2 had many negative correlations and form the majority of correlations, suggesting an important function for these transcripts. Eleven of the 285 queried genes had disease-associated variants within a sperm RNA element. Three genes, GPX4, NDRG1, and RPS24 had SREs were absent in at least one individual from the test cohort. GPX4 and RPS24 are associated with developmental defects and/or neonatal lethality. This leaves the intriguing possibility that, while sperm RNAs delivered to the oocyte inform the success of live birth, they may also be predictors of human health.

ABBREVIATIONS

GO: Gene Ontology; ART: assisted reproductive technology; IVF: in vitro fertilization; ICSI: intra-cytoplasmic sperm injection; RNA-seq: RNA-sequencing; TIC: timed intercourse; IUI: intrauterine insemination; SRE: sperm RNA elements; HPA: Human Protein Atlas; SMDS: sedaghatian-type spondylometaphyseal dysplasia; DBA: Diamond-Blackfan anemia; RPKM: reads per kilobase per million; TPM: transcripts per million; IPA: Ingenuity Pathway Analysis; OMIM: Online Mendelian Inheritance in Man.

Determination of Highly Sensitive Biological Cell Model Systems to Screen BPA-Related Health Hazards Using Pathway Studio

Bisphenol-A (BPA) is a ubiquitous endocrine-disrupting chemical. Recently, many issues have arisen surrounding the disease pathogenesis of BPA. Therefore, several studies have been conducted to investigate the proteomic biomarkers of BPA that are associated with disease processes. However, studies on identifying highly sensitive biological cell model systems in determining BPA health risk are lacking. Here, we determined suitable cell model systems and potential biomarkers for predicting BPA-mediated disease using the bioinformatics tool Pathway Studio. We compiled known BPA-mediated diseases in humans, which were categorized into five major types. Subsequently, we investigated the differentially expressed proteins following BPA exposure in several cell types, and analyzed the efficacy of altered proteins to investigate their associations with BPA-mediated diseases. Our results demonstrated that colon cancer cells (SW480), mammary gland, and Sertoli cells were highly sensitive biological model systems, because of the efficacy of predicting the majority of BPA-mediated diseases. We selected glucose-6-phosphate dehydrogenase (G6PD), cytochrome b-c1 complex subunit 1 (UQCRC1), and voltage-dependent anion-selective channel protein 2 (VDAC2) as highly sensitive biomarkers to predict BPA-mediated diseases. Furthermore, we summarized proteomic studies in spermatozoa following BPA exposure, which have recently been considered as another suitable cell type for predicting BPA-mediated diseases.

Glycerol kinase-like proteins cooperate with Pld6 in regulating sperm mitochondrial sheath formation and male fertility

Spermatids undergo the final steps of maturation during spermiogenesis, a process that necessitates extensive rearrangement of organelles such as the mitochondria. Male infertility has been linked to mitochondrial disorder, for example, hypospermatogenesis and asthenozoospermia. However, the mechanisms that regulate mitochondrial dynamics during spermiogenesis remain largely unknown. We found the glycerol kinase (Gyk)-like proteins glycerol kinase-like 1 (Gykl1) and glycerol kinase 2 (Gk2) were specifically localized to the mitochondria in spermatids. Male mice deficient in either Gykl1 or Gk2 were infertile due to dysfunctional spermatozoa, which exhibited unregulated ATP production, disordered mitochondrial sheath formation, abnormal mitochondrial morphology, and defective sperm tail. We demonstrated that the unique C-terminal sequences found in Gykl1 and Gk2 mediated their targeting to the mitochondrial outer membrane. Furthermore, both Gykl1 and Gk2 could interact with Pld6 (MitoPLD) and induce Pld6 and phosphatidic acid (PA)-dependent mitochondrial clustering in cells. Taken together, our study has revealed previously unsuspected functions of Gyk-like proteins in spermiogenesis, providing new insight into the potential mechanisms that lead to spermatozoa dysfunction and male infertility.

Lipid Peroxidation-Dependent Cell Death Regulated by GPx4 and Ferroptosis

Glutathione peroxidase 4 (Phospholipid hydroperoxide glutathione peroxidase, PHGPx) can directly reduce phospholipid hydroperoxide. Depletion of GPx4 induces lipid peroxidation-dependent cell death in embryo, testis, brain, liver, heart, and photoreceptor cells of mice. Administration of vitamin E in tissue specific GPx4 KO mice restored tissue damage in testis, liver, and heart. These results indicate that suppression of phospholipid peroxidation is essential for cell survival in normal tissues in mice. Ferroptosis is an iron-dependent non-apoptotic cell death that can elicited by pharmacological inhibiting the cystine/glutamate antiporter, system Xc^- (type I) or directly binding and loss of activity of GPx4 (Type II) in cancer cells with high level RAS-RAF-MEK pathway activity or p53 expression, but not in normal cells. Ferroptosis by Erastin (Type I) and RSL3 (RAS-selective lethal 3, Type II) treatment was suppressed by an iron chelator, vitamin E and Ferrostatin-1, antioxidant compound. GPx4 can regulate ferroptosis by suppression of phospholipid peroxidation in erastin and RSL3-induced ferroptosis. Recent works have identified several regulatory factors of erastin and RSL3-induced ferroptosis. In our established GPx4-deficient MEF cells, depletion of GPx4 induce iron and 15LOX-independent lipid peroxidation at 26 h and caspase-independent cell death at 72 h, whereas erastin and RSL3 treatment resulted in iron-dependent ferroptosis by 12 h. These results indicated the possibility that the mechanism of GPx4-depleted cell death might be different from that of ferroptosis induced by erastin and RSL3.

Iron and thiol redox signaling in cancer: An exquisite balance to escape ferroptosis

Epidemiological data indicate a constant worldwide increase in cancer mortality, although the age of onset is increasing. Recent accumulation of genomic data on human cancer via next-generation sequencing confirmed that cancer is a disease of genome alteration. In many cancers, the Nrf2 transcription system is activated via mutations either in Nrf2 or Keap1 ubiquitin ligase, leading to persistent activation of the genes with antioxidative functions. Furthermore, deep sequencing of passenger mutations is clarifying responsible cancer causative agent(s) in each case, including aging, APOBEC activation, smoking and UV. Therefore, it is most likely that oxidative stress is the principal initiating factor in carcinogenesis, with the involvement of two essential molecules for life, iron and oxygen. There is evidence based on epidemiological and animal studies that excess iron is a major risk for carcinogenesis, suggesting the importance of ferroptosis-resistance. Microscopic visualization of catalytic Fe(II) has recently become available. Although catalytic Fe(II) is largely present in lysosomes, proliferating cells harbor catalytic Fe(II) also in the cytosol and mitochondria. Oxidative stress catalyzed by Fe(II) is counteracted by thiol systems at different functional levels. Nitric oxide, carbon monoxide and hydrogen (per)sulfide modulate these reactions. Mitochondria generate not only energy but also heme/iron sulfur cluster cofactors and remain mostly dysfunctional in cancer cells, leading to Warburg effects. Cancer cells are under persistent oxidative stress with a delicate balance between catalytic iron and thiols, thereby escaping ferroptosis. Thus, high-dose L-ascorbate and non-thermal plasma as well as glucose/glutamine deprivation may provide additional benefits as cancer therapies over preexisting therapeutics.

Male Subfertility Induced by Heterozygous Expression of Catalytically Inactive Glutathione Peroxidase 4 Is Rescued in Vivo by Systemic Inactivation of the Alox15 Gene

Glutathione peroxidase 4 (GPX4) and arachidonic acid 15-lipoxygenase (ALOX15) are antagonizing enzymes in the metabolism of hydroperoxy lipids. In spermatoid cells and/or in the male reproductive system both enzymes are apparently expressed, and GPX4 serves as anti-oxidative enzyme but also as a structural protein. In this study we explored whether germ line inactivation of the Alox15 gene might rescue male subfertility induced by heterozygous expression of catalytically silent Gpx4. To address this question we employed Gpx4 knock-in mice expressing the Sec46Ala-Gpx4 mutant, in which the catalytic selenocysteine was replaced by a redox inactive alanine. Because homozygous Gpx4 knock-in mice (Sec46Ala-Gpx4^+/+) are not viable we created heterozygous animals (Sec46Ala-Gpx4^+/-) and crossed them with Alox15 knock-out mice (Alox15^-/-). Male Sec46Ala-Gpx4^+/- mice, but not their female littermates, were subfertile. Sperm extracted from the epididymal cauda showed strongly impaired motility characteristics and severe structural midpiece alterations (swollen mitochondria, intramitochondrial vacuoles, disordered mitochondrial capsule). Despite these structural alterations, they exhibited similar respiration characteristics than wild-type sperm. When Sec46Ala-Gpx4^+/- mice were crossed with Alox15-deficient animals, the resulting males (Sec46Ala-Gpx4^+/-+Alox15^-/-) showed normalized fertility, and sperm motility was reimproved to wild-type levels. Taken together these data suggest that systemic inactivation of the Alox15 gene normalizes the reduced fertility of male Sec46Ala-Gpx4^+/- mice by improving the motility of their sperm. If these data can be confirmed in humans, ALOX15 inhibitors might counteract male infertility related to GPX4 deficiency.

Paradoxical Roles of Antioxidant Enzymes: Basic Mechanisms and Health Implications

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.

Selenium Nanoparticles for Stress-Resilient Fish and Livestock

The fisheries and livestock sectors capture the highest share of protein-rich animal food and demonstrate accelerated growth as an agriculture subsidiary. Environmental pollution, climate change, as well as pathogenic invasions exert increasing stress impacts that lead the productivity momentum at a crossroads. Oxidative stress is the most common form of stress phenomenon responsible for the retardation of productivity in fisheries and livestock. Essential micronutrients play a determinant role in combating oxidative stress. Selenium, one of the essential micronutrients, appears as a potent antioxidant with reduced toxicity in its nanoscale form. In the present review, different methods of synthesis and characterization of nanoscale selenium have been discussed. The functional characterization of nano-selenium in terms of its effect on growth patterns, feed digestibility, and reproductive system has been discussed to elucidate the mechanism of action. Moreover, its anti-carcinogenic and antioxidant potentiality, antimicrobial and immunomodulatory efficacy, and fatty acid reduction in liver have been deciphered as the new phenomena of nano-selenium application. Biologically synthesized nano-selenium raises hope for pharmacologically enriched, naturally stable nanoscale selenium with high ecological viability. Hence, nano-selenium can be administered with commercial feeds for improvising stress resilience and productivity of fish and livestock.

Nuclear selenoproteins and genome maintenance

Selenium is an essential metalloid required for the expression of selenoproteins. While cells are constantly challenged by clastogens of endogenous and exogenous origins, genome integrity is maintained by direct repair of DNA damage, redox balance, and epigenetic regulation. To date, only five selenoproteins are experimentally demonstrated to reside in nucleus, exclusively or partially, including selenoprotein H, methionine-R-sulfoxide reductase 1, glutathione peroxidase-4, thioredoxin reductase-1, and thioredoxin glutathione reductase. All these five selenoproteins have demonstrated or potential roles in redox regulation and genome maintenance. Selenoprotein H is known to transactivate the expression of a couple of genes against oxidative stress. The thioredoxin reductase-1b isoform delivers estrogen receptor-α and -β to the nucleus. Nuclear glutathione peroxidase-4 epigenetically and globally inhibits gene expression through the maintenance of chromatin compactness in testes. Continued studies on how these and additional nuclear selenoproteins regulate genome stability will have profound impact on advancing our understanding in selenium regulation of optimal health. © 2015 IUBMB Life, 68(1):5-12, 2016.

Variations in Antioxidant Genes and Male Infertility

Oxidative stress and reactive oxygen species (ROS) are generated from both endogenous and environmental resources, which in turn may cause defective spermatogenesis and male infertility. Antioxidant genes, which include catalase (CAT), glutathione peroxidase (GPX), glutathione S-transferase (GST), nitric oxide synthase (NOS), nuclear factor erythroid 2-related factor 2 (NRF2), and superoxide dismutase (SOD), play important roles in spermatogenesis and normal sperm function. In this review, we discuss the association between variations in major antioxidant genes and male infertility. Numerous studies have suggested that genetic disruption or functional polymorphisms in these antioxidant genes are associated with a higher risk for male infertility, which include low sperm quality, oligoasthenoteratozoospermia, oligozoospermia, and subfertility. The synergistic effects of environmental ROS and functional polymorphisms on antioxidant genes that result in male infertility have also been reported. Therefore, variants in antioxidant genes, which independently or synergistically occur with environmental ROS, affect spermatogenesis and contribute to the occurrence of male infertility. Large cohort and multiple center-based population studies to identify new antioxidant genetic variants that increase susceptibility to male infertility as well as validate its potential as genetic markers for diagnosis and risk assessment for male infertility for precise clinical approaches are warranted.

Alteration of sperm protein profile induced by cigarette smoking

Cigarette smoking is associated with lower semen quality, but how cigarette smoking changes the semen quality remains unclear. The aim of this study was to screen the differentially expressed proteins in the sperm of mice with daily exposure to cigarette smoke. The 2D gel electrophoresis (2DE) and mass spectrometry (MS) analyses results showed that the mouse sperm protein profile was altered by cigarette smoking. And 22 of the most abundant proteins that correspond to differentially expressed spots in 2DE gels of the sperm samples were identified. These proteins were classified into different groups based on their functions, such as energy metabolism, reproduction, and structural molecules. Furthermore, the 2DE and MS results of five proteins (Aldoa, ATP5a1, Gpx4, Cs, and Spatc1) were validated by western blot analysis and reverse transcriptase-polymerase chain reaction. Results showed that except Spatc1 the other four proteins showed statistically significant different protein levels between the smoking group and the control group (P < 0.05). The expressions of three genes (Aldoa, Gpx4, and Spatc1) were significantly different (P < 0.05) at transcription level between the smoking group and the control group. In addition, five proteins (Aldoa, ATP5a1, Spatc1, Cs, and Gpx4) in human sperm samples from 30 male smokers and 30 non-smokers were detected by western blot analysis. Two proteins (Aldoa and Cs) that are associated with energy production were found to be significantly altered, suggesting that these proteins may be potential diagnostic markers for evaluation of smoking risk in sperm. Further study of these proteins may provide insight into the pathogenic mechanisms underlying infertility in smoking persons.

Role of Glutathione Peroxidase 4 in Glutamate-Induced Oxytosis in the Retina

Purpose

The purpose of the present study was to investigate the role of glutathione peroxidase 4 (GPx4) in glutamate-induced oxytosis in the retina.

Methods

For in vitro studies, an immortalized rat retinal precursor cell line R28 was used. Cells were transfected with siRNA specifically silencing GPx4 or with scrambled control siRNA. Lipid peroxidation was evaluated by 4-hydroxy-2-nonenal (4-HNE) immunostaining. Cytotoxicity and cell death were evaluated using an LDH activity assay and annexin V staining, respectively. Cells transfected with GPx4 siRNA or control siRNA were treated with glutamate (1 or 2 mM), and the cytotoxicity was evaluated using the LDH activity assay. For in vivo studies, retinal ganglion cell damage was induced by intravitreal injection of 25-mM N-methyl-D-aspartate (NMDA, 2 μL/eye) in GPx4^+/+ and GPx4^+/− mice. The evaluation of lipid peroxidation (4-HNE immunostaining), apoptosis (TUNEL staining), and cell density in the ganglion cell layer (GCL) were performed at 12 h, 1 day, and 7 days after the NMDA injection.

Results

GPx4 knockdown significantly increased LDH activity by 13.9-fold (P < 0.01) and increased peroxidized lipid levels by 3.2-fold in R28 cells (P < 0.01). In cells transfected with scrambled control siRNA, treatment with glutamate at 1 or 2 mM did not increase LDH activity; whereas, in cells transfected with GPx4 siRNA, glutamate treatment significantly increased LDH activity (1.52-fold, P < 0.01). GPx4^+/− mice exhibited higher levels of lipid peroxidation in retinas treated with NMDA than GPx4^+/+ mice (1.26-fold, P < 0.05). GPx4^+/− mice had more TUNEL-positive cells induced by NMDA in GCL (1.45-fold, P < 0.05). In addition, the cell density in GCL of GPx4^+/− mice was 19% lower than that in GPx4^+/+ mice after treatment with NMDA (P < 0.05).

Conclusion

These results suggest that defective GPx4 expression is associated with enhanced cytotoxicity by glutamate-induced oxytosis in the retina.

Physiological and pathological views of peroxiredoxin 4

Peroxiredoxins (PRDXs) form an enzyme family that exhibits peroxidase activity using electrons from thioredoxin and other donor molecules. As the signaling roles of hydrogen peroxide in response to extracellular stimuli have emerged, the involvement of PRDX in the hydrogen peroxide-mediated signaling has become evident. Among six PRDX members in mammalian cells, PRDX4 uniquely possesses a hydrophobic signal peptide at the amino terminus, and, hence, it undergoes either secretion or retention by the endoplasmic reticulum (ER) lumen. The role of PRDX4 as a sulfoxidase in ER is now attracting much attention regarding the oxidative protein folding of nascent proteins. Contrary to this role in the ER, the functional significance of PRDX4 in the extracellular milieu is virtually unknown despite its implications as a biomarker under pathological conditions in some diseases. Other than its systemically expressed form, a variant form of PRDX4 is transcribed from the upstream promoter/exon 1 of the systemic promoter/exon 1 and is uniquely expressed in sexually matured testes. Circumstantial evidence, together with deduced functions from the systemic form, suggests that there are potential roles for testicular PRDX4 in the reproductive processes such as the regulation of hormonal signals and the oxidative packaging of sperm chromatin. Elucidation of these PRDX4 functions under in vivo situations is expected to show the whole picture of how PRDX4 has evolved in multicellular organisms.

The subcellular location of selenoproteins and the impact on their function

Most human selenium containing proteins contain selenium in the form of the amino acid selenocysteine, which is encoded in the corresponding mRNA as a UGA codon. Only a few non-selenocysteine containing selenoproteins are present and the nature of the association with selenium is not well understood. This review focuses on two selenocysteine-containing proteins that are members of the glutathione peroxidase family, GPx-1 and GPx-4, and the selenium-associated protein referred to as Selenium Binding Protein 1. Each of these proteins have been described to reside in two or more cellular compartments, and in the case of GPx-1 and SBP1, interact with each other. The enzymatic activity of GPx-1 and GPx-4 have been well described, but it is less clear how their cellular location impacts the health related phenotypes associated with activities, while no catalytic function is assigned to SBP1. The distribution of these proteins is presented as is the possible consequences of that compartmentalization.

The combined effect of clothianidin and environmental stress on the behavioral and reproductive function in male mice

Neonicotinoids, some of the most widely used pesticides in the world, act as agonists to the nicotinic acetylcholine receptors (nAChRs) of insects, resulting in death from abnormal excitability. Neonicotinoids unexpectedly became a major topic as a compelling cause of honeybee colony collapse disorder, which is damaging crop production that requires pollination worldwide. Mammal nAChRs appear to have a certain affinity for neonicotinoids with lower levels than those of insects; there is thus rising concern about unpredictable adverse effects of neonicotinoids on vertebrates. We hypothesized that the effects of neonicotinoids would be enhanced under a chronic stressed condition, which is known to alter the expression of targets of neonicotinoids, i.e., neuronal nAChRs. We performed immunohistochemical and behavioral analyses in male mice actively administered a neonicotinoid, clothianidin (CTD; 0, 10, 50 and 250 mg/kg/day), for 4 weeks under an unpredictable chronic stress procedure. Vacuolated seminiferous epithelia and a decrease in the immunoreactivity of the antioxidant enzyme glutathione peroxidase 4 were observed in the testes of the CTD+stress mice. In an open field test, although the locomotor activities were not affected, the anxiety-like behaviors of the mice were elevated by both CTD and stress. The present study demonstrates that the behavioral and reproductive effects of CTD become more serious in combination with environmental stress, which may reflect our actual situation of multiple exposure.

Expression of a Catalytically Inactive Mutant Form of Glutathione Peroxidase 4 (Gpx4) Confers a Dominant-negative Effect in Male Fertility

The selenoenzyme Gpx4 is essential for early embryogenesis and cell viability for its unique function to prevent phospholipid oxidation. Recently, the cytosolic form of Gpx4 was identified as an upstream regulator of a novel form of non-apoptotic cell death, called ferroptosis, whereas the mitochondrial isoform of Gpx4 was previously shown to be crucial for male fertility. Here, we generated and analyzed mice with a targeted mutation of the active site selenocysteine of Gpx4 (Gpx4_U46S). Mice homozygous for Gpx4_U46S died at the same embryonic stage (E7.5) as Gpx4(-/-) embryos as expected. Surprisingly, male mice heterozygous for Gpx4_U46S presented subfertility. Subfertility was manifested in a reduced number of litters from heterozygous breeding and an impairment of spermatozoa to fertilize oocytes in vitro. Morphologically, sperm isolated from heterozygous Gpx4_U46S mice revealed many structural abnormalities particularly in the spermatozoa midpiece due to improper oxidation and polymerization of sperm capsular proteins and malformation of the mitochondrial capsule surrounding and stabilizing sperm mitochondria. These findings are reminiscent of sperm isolated from selenium-deprived rodents or from mice specifically lacking mitochondrial Gpx4. Due to a strongly facilitated incorporation of Ser in the polypeptide chain as compared with selenocysteine at the UGA codon, expression of the catalytically inactive Gpx4_U46S was found to be strongly increased. Because the stability of the mitochondrial capsule of mature spermatozoa depends on the moonlighting function of Gpx4 both as an enzyme oxidizing capsular protein thiols and as a structural protein, tightly controlled expression of functional Gpx4 emerges as a key for full male fertility.

Expression of inactive glutathione peroxidase 4 leads to embryonic lethality, and inactivation of the Alox15 gene does not rescue such knock-in mice

AIMS

Glutathione peroxidases (Gpx) and lipoxygenases (Alox) are functional counterplayers in the metabolism of hydroperoxy lipids that regulate cellular redox homeostasis. Gpx4 is a moonlighting protein that has been implicated not only as an enzyme in anti-oxidative defense, gene expression regulation, and programmed cell death, but also as a structural protein in spermatogenesis. Homozygous Gpx4 knock-out mice are not viable, but molecular reasons for intrauterine lethality are not completely understood. This study was aimed at investigating whether the lack of catalytic activity or the impaired function as structural protein is the dominant reason for embryonic lethality. We further explored whether the pro-oxidative enzyme mouse 12/15 lipoxygenase (Alox15) plays a major role in embryonic lethality of Gpx4-deficient mice.

RESULTS

To achieve these goals, we first created knock-in mice, which express a catalytically inactive Gpx4 mutant (Sec46Ala). As homozygous Gpx4-knock-out mice Sec46Ala-Gpx4(+/+) knock-in animals are not viable but undergo intrauterine resorption between embryonic day 6 and 7 (E6-7). In contrast, heterozygous knock-in mice (Sec46Ala-Gpx4(-/+)) are viable, fertile and do not show major phenotypic alterations. Interestingly, homozygous Alox15 deficiency did not rescue the U46A-Gpx4(+/+) mice from embryonic lethality. In fact, when heterozygous U46A-Gpx4(-/+) mice were stepwise crossed into an Alox15-deficent background, no viable U46A-Gpx4(+/+)+Alox15(-/-) individuals were obtained. However, we were able to identify U46A-Gpx4(+/+)+Alox15(-/-) embryos in the state of resorption around E7.

INNOVATION AND CONCLUSION

These data suggest that the lack of catalytic activity is the major reason for the embryonic lethality of Gpx4(-/-) mice and that systemic inactivation of the Alox15 gene does not rescue homozygous knock-in mice expressing catalytically silent Gpx4.

Sensing a sensor: identifying the mechanosensory function of primary cilia

Over the past decade, primary cilia have emerged as the premier means by which cells sense and transduce mechanical stimuli. Primary cilia are sensory organelles that have been shown to be vitally involved in the mechanosensation of urine in the renal nephron, bile in the hepatic biliary system, digestive fluid in the pancreatic duct, dentin in dental pulp, lacunocanalicular fluid in bone and cartilage, and blood in vasculature. The prevalence of primary cilia among mammalian cell types is matched by the tremendously varied disease states caused by both structural and functional defects in cilia. In the process of delineating the mechanisms behind these disease states, calcium fluorimetry has been widely utilized as a means of quantifying ciliary function to both fluid flow and pharmacological agents. In this review, we will discuss the approaches used in associating calcium levels to cilia function.

Genotoxic effects of two-generational selenium deficiency in mouse somatic and testicular cells

Many studies have investigated genotoxic effects of high Se diets but very few have addressed the genotoxicity of Se deprivation and its consequences in germ cells and none in somatic cells. To address these data gaps, C57BL/6 male mice were subjected to Se deprivation starting in the parental generation, i.e. before conception. Mice were given a diet of either low (0.01mg Se/kg diet) or normal (0.23mg Se/kg diet) Se content. Ogg1-deficient (Ogg1 (-/-) ) mice were used as a sensitive model towards oxidative stress due to their reduced capacity to repair oxidised purines. Ogg1 (-/-) mice also mimic the repair characteristics of human post-meiotic male germ cells which have a reduced ability to repair such lesions. The genotoxicity of Se deficiency was addressed by measuring DNA lesions with the alkaline single cell gel electrophoresis (+ Fpg to detect oxidised DNA lesions) in somatic cells (nucleated blood cells and lung cells) and male germ cells (testicular cells). Total Se concentration in liver and GPx activity in plasma and testicular cells were measured. Gene mutation was evaluated by an erythrocyte-based Pig-a assay. We found that Se deprivation of F1 from their conception and until early adulthood led to the induction of DNA lesions in testicular and lung cells expressed as significantly increased levels of DNA lesions, irrespective of the mouse genotype. In blood cells, Se levels did not appear to affect DNA lesions or mutant cell frequencies. The results suggest that the testis was the most sensitive tissue. Thus, genotoxicity induced by the low Se diet in the spermatozoal genome has potential implications for the offspring.

ROS, thiols and thiol-regulating systems in male gametogenesis

BACKGROUND

During maturation and storage, spermatozoa generate substantial amounts of reactive oxygen species (ROS) and are thus forced to cope with an increasingly oxidative environment that is both needed and detrimental to their biology. Such a janus-faceted intermediate needs to be tightly controlled and this is done by a wide array of redox enzymes. These enzymes not only have to prevent unspecific modifications of essential cellular biomolecules by quenching undesired ROS, but they are also required and often directly involved in critical protein modifications.

SCOPE OF REVIEW

The present review is conceived to present an update on what is known about critical roles of redox enzymes, whereby special emphasis is put on the family of glutathione peroxidases, which for the time being presents the best characterized tasks during gametogenesis.

MAJOR CONCLUSIONS

We therefore demonstrate that understanding the function of (seleno)thiol-based oxidases/reductases is not a trivial task and relevant knowledge will be mainly gained by using robust systems, as exemplified by several (conditional) knockout studies. We thus stress the importance of using such models for providing unequivocal evidence in the molecular understanding of redox regulatory mechanisms in sperm maturation.

GENERAL SIGNIFICANCE

ROS are not merely detrimental by-products of metabolism and their proper generation and usage by specific enzymes is essential for vital functions as beautifully exemplified during male gametogenesis. As such, lessons learnt from thiol-based oxidases/reductases in male gametogenesis could be used as a general principle for other organs as it is most likely not only restricted to this developmental phase. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

The Enzymatic Antioxidant System of Human Spermatozoa

The ejaculated spermatozoon, as an aerobic cell, must fight against toxic levels of reactive oxygen species (ROS) generated by its own metabolism but also by other sources such as abnormal spermatozoa, chemicals and toxicants, or the presence of leukocytes in semen. Mammalian spermatozoa are extremely sensitive to oxidative stress, a condition occurring when there is a net increase in ROS levels within the cell. Opportunely, this specialized cell has a battery of antioxidant enzymes (superoxide dismutase, peroxiredoxins, thioredoxins, thioredoxins reductases, and glutathione s-transferases) working in concert to assure normal sperm function. Any impairment of the antioxidant enzymatic activities will promote severe oxidative damage which is observed as plasma membrane lipid peroxidation, oxidation of structural proteins and enzymes, and oxidation of DNA bases that lead to abnormal sperm function. Altogether, these damages occurring in spermatozoa are associated with male infertility. The present review contains a description of the enzymatic antioxidant system of the human spermatozoon and a reevaluation of the role of its different components and highlights the necessity of sufficient supply of reducing agents (NADPH and reduced glutathione) to guarantee normal sperm function.

Protective role of glutathione peroxidase 4 in laser-induced choroidal neovascularization in mice

Purpose

To evaluate the influence of glutathione peroxidase 4 (GPx4) expression in retinal pigment epithelium (RPE)/choroid tissue using a mouse model of laser-induced choroidal neovascularization (CNV).

Methods

In this study, GPx4^+/−, GPx4^+/+, and GPx4-overexpressing transgenic mice were created for comparison. The mRNA and protein expression of vascular endothelial growth factor (VEGF)-A in RPE/choroid tissue were evaluated before and after CNV induction by laser. Moreover, we investigated the changes in the VEGF-A mRNA level in RPE/choroid tissue in the CNV model that have not been clearly shown previously. Lipid peroxidation in RPE/choroid tissue was evaluated by immunohistochemistry using antibody against 4-hydroxy-2-nonenal. To investigate the protective role of GPx4, the size of laser-induced CNV was compared on day 7 among the mice expressing different levels of GPx4.

Results

In the laser-induced CNV mouse model, laser treatment reduced the VEGF-A mRNA level in RPE/choroid tissue, while it increased the VEGF-A protein level. Evaluation of VEGF-A expression in RPE/choroid tissue of the GPx4^+/−, GPx4^+/+, and GPx4 transgenic mice revealed that GPx4 increased the VEGF-A protein level under physiological conditions (i.e., without laser treatment), while GPx4 suppressed the increase in the VEGF-A protein level under pathological conditions (i.e., after CNV induction by laser). In addition, GPx4 reduced the CNV size in a dose-dependent manner in vivo.

Conclusions

GPx4 suppresses the increase in the VEGF-A protein level, which occurs during the development of pathological CNV, thus partly explaining the protective effect of GPx4 against CNV.

Oxidative stress and adrenocortical insufficiency

Maintenance of redox balance is essential for normal cellular functions. Any perturbation in this balance due to increased reactive oxygen species (ROS) leads to oxidative stress and may lead to cell dysfunction/damage/death. Mitochondria are responsible for the majority of cellular ROS production secondary to electron leakage as a consequence of respiration. Furthermore, electron leakage by the cytochrome P450 enzymes may render steroidogenic tissues acutely vulnerable to redox imbalance. The adrenal cortex, in particular, is well supplied with both enzymatic (glutathione peroxidases and peroxiredoxins) and non-enzymatic (vitamins A, C and E) antioxidants to cope with this increased production of ROS due to steroidogenesis. Nonetheless oxidative stress is implicated in several potentially lethal adrenal disorders including X-linked adrenoleukodystrophy, triple A syndrome and most recently familial glucocorticoid deficiency. The finding of mutations in antioxidant defence genes in the latter two conditions highlights how disturbances in redox homeostasis may have an effect on adrenal steroidogenesis.

Redox reactions in mammalian spermatogenesis and the potential targets of reactive oxygen species under oxidative stress

Reduction-oxidation (Redox) reactions are ubiquitous mechanisms for vital activities in all organisms, and they play pivotal roles in the regulation of spermatogenesis as well. Here we focus on 3 redox-involved processes that have drawn much recent attention: the regulation of signal transduction by reactive oxygen species (ROS) such as hydrogen peroxide, oxidative protein folding in the endoplasmic reticulum (ER), and sulfoxidation of protamines during sperm chromatin condensation. The first 2 of these processes are emerging topics in cell biology and are applicable to most living cells, which includes spermatogenic cells. The roles of ROS in signal transduction have been elucidated in the last 2 decades and have received broad attention, most notably from the viewpoint of the proper control of mitotic signals. Redox processes in the ER are important because this is the organelle where secretory and membrane proteins are synthesized and proceed toward their functional structure, so that malfunction of the ER affects not only the involved cells but also the accepting cells of the secreted proteins in multicellular organisms. Sulfoxidation is the third of these processes, and the sulfoxidation of chromatin is a unique process in sperm maturation. During recent sulfoxidase research, GPX4 has emerged as a promising enzyme that plays essential roles in the production of fertile sperm, but the involvement of other redox proteins is also becoming evident. Because the molecules involved in the redox reactions are prone to oxidation, they can be sensitive to oxidative damage, which makes them potential targets for antioxidant therapy.

Hepatic rRNA transcription regulates high-fat-diet-induced obesity

Ribosome biosynthesis is a major intracellular energy-consuming process. We previously identified a nucleolar factor, nucleomethylin (NML), which regulates intracellular energy consumption by limiting rRNA transcription. Here, we show that, in livers of obese mice, the recruitment of NML to rRNA gene loci is increased to repress rRNA transcription. To clarify the relationship between obesity and rRNA transcription, we generated NML-null (NML-KO) mice. NML-KO mice show elevated rRNA level, reduced ATP concentration, and reduced lipid accumulation in the liver. Furthermore, in high-fat-diet (HFD)-fed NML-KO mice, hepatic rRNA levels are not decreased. Both weight gain and fat accumulation in HFD-fed NML-KO mice are significantly lower than those in HFD-fed wild-type mice. These findings indicate that rRNA transcriptional activation promotes hepatic energy consumption, which alters hepatic lipid metabolism. Namely, hepatic rRNA transcriptional repression by HFD feeding is essential for energy storage.

Phosphatidic acid (PA)-preferring phospholipase A1 regulates mitochondrial dynamics

Recent studies have suggested that phosphatidic acid (PA), a cone-shaped phospholipid that can generate negative curvature of lipid membranes, participates in mitochondrial fusion. However, precise mechanisms underling the production and consumption of PA on the mitochondrial surface are not fully understood. Phosphatidic acid-preferring phospholipase A1 (PA-PLA1)/DDHD1 is the first identified intracellular phospholipase A1 and preferentially hydrolyzes PA in vitro. Its cellular and physiological functions have not been elucidated. In this study, we show that PA-PLA1 regulates mitochondrial dynamics. PA-PLA1, when ectopically expressed in HeLa cells, induced mitochondrial fragmentation, whereas its depletion caused mitochondrial elongation. The effects of PA-PLA1 on mitochondrial morphology appear to counteract those of MitoPLD, a mitochondrion-localized phospholipase D that produces PA from cardiolipin. Consistent with high levels of expression of PA-PLA1 in testis, PA-PLA1 knock-out mice have a defect in sperm formation. In PA-PLA1-deficient sperm, the mitochondrial structure is disorganized, and an abnormal gap structure exists between the middle and principal pieces. A flagellum is bent at that position, leading to a loss of motility. Our results suggest a possible mechanism of PA regulation of the mitochondrial membrane and demonstrate an in vivo function of PA-PLA1 in the organization of mitochondria during spermiogenesis.

Role of selenium in male reproduction - a review

The role of Se and various selenoproteins in male reproductive performance is reviewed. Development of male reproductive tissue requires an optimal level of Se in testis, and a small deviation, either deficiency or excess, leads to abnormal development. Selenium is a constituent of selenoproteins including GPx1, GPx3, mGPx4, cGPx4, and GPx5 that protect against oxidative damage to spermatozoa throughout the process of sperm maturation, whereas selenoproteins, such as mGPx4 and snGPx4, serve as structural components of mature spermatozoa. Thus Se and selenoproteins ensure viability of spermatozoa as well as providing protection against reactive oxygen species. Gene knock-out studies of selenoproteins revealed that their absence during spermatogenesis results in abnormal spermatozoa, which in turn affects semen quality and fertility. Deviation from the optimal quantities of dietary Se, both above or below, may cause multiple abnormalities of spermatozoa and affect motility and fertility. Libido may also be increased by Se. Dietary Se should be in optimal quantity to maintain reproductive function in males and to avoid infertility.

Genetics of male fertility

Early in embryogenesis, cells that are destined to become germ cells take on a different destiny from other cells in the embryo. The germ cells are not programmed to perform "vital" functions but to perpetuate the species through the transfer of genetic materials to the next generation. To fulfill their destiny, male germ cells undergo meiosis and extensive morphogenesis that transforms the round-shaped cells into freely motile sperm propelled by a beating flagellum to seek out their missing half. Apparently, extra genes and additional regulatory mechanisms are required to achieve all these unique features, and an estimated 11 % of genes are involved in fertility in Drosophila (Hackstein et al., Trends Genet 16(12):565-572, 2000). If comparative numbers of male fertility genes are needed in mammals, extra risks of male fertility problems are associated with disruptive mutations in those genes. Among human male infertility cases, approximately 22 % were classified as "idiopathic," a term used to describe diseases of unknown causes, with idiopathic oligozoospermia being the most common semen abnormality (11.2 %) (Comhaire et al., Int J Androl (Suppl 7):1-53, 1987). "Idiopathic" is a widely used adjective that is used to reflect our lack of understanding of the genetics of male fertility. Fortunately, after more than two decades of phenotypic studies using knockout mice and identifying genes disrupted in spontaneous mutant mice, we have unveiled new and unexpected aspects of crucial gene functions for fertility. Other efforts to categorize genes involved in male fertility in mammals have suggested a total of 1,188 genes (Hermo et al., Microsc Res Tech 73(4):241-494, 2010). Although intracytoplasmic sperm injection (ICSI) can be used to bypass many fertilization obstacles to achieve fertilization with only a few extracted sperm, the widespread use of ICSI without proper knowledge for genetic testing and counseling could still potentially propagate pleiotropic gene mutations associated with male infertility and other genetic diseases (Alukal and Lamb, Urol Clin North Am 35(2):277-288, 2008). In this chapter, we give a brief account of major events during the development of male germ cells and focus on the functions of several crucial genes that have been studied in mutant mouse models and are potential causes of human male infertility.

Development of Cre-loxP technology in zebrafish to study the regulation of fish reproduction

One cannot seek permission to market transgenic fish mainly because there is no field test or any basic research on technological developments for evaluating their biosafety. Infertility is a necessary adjunct to exploiting transgenic fish unless completely secure land-locked facilities are available. In this study, we report the generation of a Cre transgenic zebrafish line using a cytomegalovirus promoter. We also produced fish carrying the Bax1 and Bax2 plasmids; these genes were separated by two loxP sites under a zona pellucida C promoter or were driven by an anti-Müllerian hormone promoter. We inserted a red fluorescent protein gene between the two loxP sites. After obtaining transgenic lines with the two transgenic fish crossed with each other (Cre transgenic zebrafish x loxP transgenic zebrafish), the floxed DNA was found to be specifically eliminated from the female or male zebrafish, and apoptosis gene expressions caused ovarian and testicular growth cessation and degeneration. Overexpression of the Bax1 and Bax2 genes caused various expression levels of apoptosis-related genes. Accordingly, this transgenic zebrafish model system provides a method to produce infertile fish and may be useful for application to genetically modified fish.

Oligo-astheno-teratozoospermia in mice lacking ORP4, a sterol-binding protein in the OSBP-related protein family

Oligo-astheno-teratozoospermia (OAT), a condition that includes low sperm number, low sperm motility and abnormal sperm morphology, is the commonest cause of male infertility. Because genetic analysis is frequently impeded by the infertility phenotype, the genetic basis of many of OAT conditions has been hard to verify. Here, we show that deficiency of ORP4, a sterol-binding protein in the oxysterol-binding protein (OSBP)-related protein family, causes male infertility due to severe OAT in mice. In ORP4-deficient mice, spermatogonia proliferation and subsequent meiosis occurred normally, but the morphology of elongating and elongated spermatids was severely distorted, with round-shaped head, curled back head or symplast. Spermatozoa derived from ORP4-deficient mice had little or no motility and no fertilizing ability in vitro. In ORP4-deficient testis, postmeiotic spermatids underwent extensive apoptosis, leading to a severely reduced number of spermatozoa. At the ultrastructural level, nascent acrosomes appeared to normally develop in round spermatids, but acrosomes were detached from the nucleus in elongating spermatids. These results suggest that ORP4 is essential for the postmeiotic differentiation of germ cells.

Loss of mitochondrial peptidase Clpp leads to infertility, hearing loss plus growth retardation via accumulation of CLPX, mtDNA and inflammatory factors

The caseinolytic peptidase P (CLPP) is conserved from bacteria to humans. In the mitochondrial matrix, it multimerizes and forms a macromolecular proteasome-like cylinder together with the chaperone CLPX. In spite of a known relevance for the mitochondrial unfolded protein response, its substrates and tissue-specific roles are unclear in mammals. Recessive CLPP mutations were recently observed in the human Perrault variant of ovarian failure and sensorineural hearing loss. Here, a first characterization of CLPP null mice demonstrated complete female and male infertility and auditory deficits. Disrupted spermatogenesis already at the spermatid stage and ovarian follicular differentiation failure were evident. Reduced pre-/post-natal survival and marked ubiquitous growth retardation contrasted with only light impairment of movement and respiratory activities. Interestingly, the mice showed resistance to ulcerative dermatitis. Systematic expression studies detected up-regulation of other mitochondrial chaperones, accumulation of CLPX and mtDNA as well as inflammatory factors throughout tissues. T-lymphocytes in the spleen were activated. Thus, murine Clpp deletion represents a faithful Perrault model. The disease mechanism probably involves deficient clearance of mitochondrial components and inflammatory tissue destruction.

Deficiency of NPGPx, an oxidative stress sensor, leads to obesity in mice and human

Elevated oxidative stress is closely associated with obesity. Emerging evidence shows that instead of being a consequence of obesity, oxidative stress may also contribute to fat formation. Nonselenocysteine-containing phospholipid hydroperoxide glutathione peroxidase (NPGPx) is a conserved oxidative stress sensor/transducer and deficiency of NPGPx causes accumulation of reactive oxygen species (ROS). In this communication, we show that NPGPx was highly expressed in preadipocytes of adipose tissue. Deficiency of NPGPx promoted preadipocytes to differentiate to adipocytes via ROS-dependent dimerization of protein kinase A regulatory subunits and activation of CCAAT/enhancer-binding protein beta (C/EBPβ). This enhanced adipogenesis was alleviated by antioxidant N-acetylcysteine (NAC). Consistently, NPGPx-deficient mice exhibited markedly increased fat mass and adipocyte hypertrophy, while treatment with NAC ablated these phenotypes. Furthermore, single nucleotide polymorphisms (SNPs) in human NPGPx gene, which correlated with lower NPGPx expression level in adipose tissue, were associated with higher body mass index (BMI) in several independent human populations. These results indicate that NPGPx protects against fat accumulation in mice and human via modulating ROS, and highlight the importance of targeting redox homeostasis in obesity management.

Deficiency of the glutathione peroxidase NPGPx increases ROS levels in preadipocytes and promotes adipocyte differentiation via increasing oxidative stress and consequent increased fat mass and adipocyte hypertrophy.

Selenium. Role of the essential metalloid in health

Selenium is an essential micronutrient in mammals, but is also recognized as toxic in excess. It is a non-metal with properties that are intermediate between the chalcogen elements sulfur and tellurium. Selenium exerts its biological functions through selenoproteins. Selenoproteins contain selenium in the form of the 21st amino acid, selenocysteine (Sec), which is an analog of cysteine with the sulfur-containing side chain replaced by a Se-containing side chain. Sec is encoded by the codon UGA, which is one of three termination codons for mRNA translation in non-selenoprotein genes. Recognition of the UGA codon as a Sec insertion site instead of stop requires a Sec insertion sequence (SECIS) element in selenoprotein mRNAs and a unique selenocysteyl-tRNA, both of which are recognized by specialized protein factors. Unlike the 20 standard amino acids, Sec is biosynthesized from serine on its tRNA. Twenty-five selenoproteins are encoded in the human genome. Most of the selenoprotein genes were discovered by bioinformatics approaches, searching for SECIS elements downstream of in-frame UGA codons. Sec has been described as having stronger nucleophilic and electrophilic properties than cysteine, and Sec is present in the catalytic site of all selenoenzymes. Most selenoproteins, whose functions are known, are involved in redox systems and signaling pathways. However, several selenoproteins are not well characterized in terms of their function. The selenium field has grown dramatically in the last few decades, and research on selenium biology is providing extensive new information regarding its importance for human health.

Molecular analysis of cell type-specific gene expression profile during mouse spermatogenesis by laser microdissection and qRT-PCR

Laser microdissection (LMD) is a selective cell isolation technique that enables the separation of desired homogenous cell subpopulations from complex tissues such as the testes under direct microscopic visualization. The LMD accompanied by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) represents an indispensable tool in quantifying messenger RNA (mRNA) expression among defined cell populations. Gene expression is temporally and spatially regulated at 3 sequential phases of mitotic, meiotic, and postmeiotic stages of spermatogenesis. The present study demonstrates a short modified LMD protocol based upon hematoxylin and eosin (H&E) staining. Stage-specific LMD success was validated by the use of mRNA profiling of "marker genes" which are conserved across species and are known to be differentially expressed during spermatogenesis. Magea4, Hspa2, Cox6b2, Tnp1, Prm1, and Prm2 are used to differentiate among the microdissected cell populations, namely spermatogonia (group I), spermatocytes (group II), round and condensing spermatids (group III), and elongated and condensed spermatids (group IV), respectively. The LMD combined with qRT-PCR is further extended to assess the cell stage-specific distribution of selected stress response genes such as Hsp90aa1, Gpx4, Ucp2, Sod1, and Sod2. The germ cell-specific mRNA profiles are suitably complemented by Western blot of the LMD samples, immunohistochemistry, and confocal localization of the corresponding proteins. The current study suggests that LMD can successfully isolate cell subpopulations from the complex tissues of the testes; and establish cell stage-specific basal expression patterns of selected stress response genes and proteins. It is our hypothesis that the baseline expression of stress response genes will differ by cell stage to create discrete stage-specific vulnerabilities to reproductive toxicants.

Oxidative stress is involved in age-dependent spermatogenic damage of Immp2l mutant mice

Mitochondrial reactive oxygen species (ROS) have been implicated in spermatogenic damage, although direct in vivo evidence is lacking. We recently generated a mouse in which the inner mitochondrial membrane peptidase 2-like (Immp2l) gene is mutated. This Immp2l mutation impairs the processing of signal peptide sequences from mitochondrial cytochrome c₁ and glycerol phosphate dehydrogenase 2. The mitochondria from mutant mice generate elevated levels of superoxide ion, which causes age-dependent spermatogenic damage. Here we confirm age-dependent spermatogenic damage in a new cohort of mutants, which started at the age of 10.5 months. Compared with age-matched controls, protein carbonyl content was normal in testes of 2- to 5-month-old mutants, but significantly elevated in testes of 13-month-old mutants, indicating elevated oxidative stress in the testes at the time of impaired spermatogenesis. Testicular expression of superoxide dismutases was not different between control and mutant mice, whereas that of catalase was increased in young and old mutants. The expression of cytosolic glutathione peroxidase 4 (phospholipid hydroperoxidase) in testes was significantly reduced in 13-month-old mutants, concomitant with impaired spermatogenesis. Apoptosis of all testicular populations was increased in mutant mice with spermatogenic damage. The mitochondrial DNA (mtDNA) mutation rate in germ cells of mutant mice with impaired spermatogenesis was unchanged, excluding a major role of mtDNA mutation in ROS-mediated spermatogenic damage. Our data show that increased mitochondrial ROS are one of the driving forces for spermatogenic impairment.

Walking the oxidative stress tightrope: a perspective from the naked mole-rat, the longest-living rodent

Reactive oxygen species (ROS), by-products of aerobic metabolism, cause oxidative damage to cells and tissue and not surprisingly many theories have arisen to link ROS-induced oxidative stress to aging and health. While studies clearly link ROS to a plethora of divergent diseases, their role in aging is still debatable. Genetic knock-down manipulations of antioxidants alter the levels of accrued oxidative damage, however, the resultant effect of increased oxidative stress on lifespan are equivocal. Similarly the impact of elevating antioxidant levels through transgenic manipulations yield inconsistent effects on longevity. Furthermore, comparative data from a wide range of endotherms with disparate longevity remain inconclusive. Many long-living species such as birds, bats and mole-rats exhibit high-levels of oxidative damage, evident already at young ages. Clearly, neither the amount of ROS per se nor the sensitivity in neutralizing ROS are as important as whether or not the accrued oxidative stress leads to oxidative-damage-linked age-associated diseases. In this review we examine the literature on ROS, its relation to disease and the lessons gleaned from a comparative approach based upon species with widely divergent responses. We specifically focus on the longest lived rodent, the naked mole-rat, which maintains good health and provides novel insights into the paradox of maintaining both an extended healthspan and lifespan despite high oxidative stress from a young age.

Understanding selenoprotein function and regulation through the use of rodent models

Selenium (Se) is an essential micronutrient. Its biological functions are associated with selenoproteins, which contain this trace element in the form of the 21st amino acid, selenocysteine. Genetic defects in selenocysteine insertion into proteins are associated with severe health issues. The consequences of selenoprotein deficiency are more variable, with several selenoproteins being essential, and several showing no clear phenotypes. Much of these functional studies benefited from the use of rodent models and diets employing variable levels of Se. This review summarizes the data obtained with these models, focusing on mouse models with targeted expression of individual selenoproteins and removal of individual, subsets or all selenoproteins in a systemic or organ-specific manner. This article is part of a Special Issue entitled: Cell Biology of Metals.

Glutathione peroxidase 4 is required for maturation of photoreceptor cells

Oxidative stress is implicated in the pathologies of photoreceptor cells, and the protective role of antioxidant enzymes for photoreceptor cells have been well understood. However, their essentiality has remained unknown. In this study we generated photoreceptor-specific conditional knock-out (CKO) mice of glutathione peroxidase 4 (GPx4) and showed the critical role of GPx4 for photoreceptor cells. In the wild-type retina the dominant GPx4 expression was in the mitochondria, indicating the mitochondrial variant was the major GPx4 in the retina. In the GPx4-CKO mice, although photoreceptor cells developed and differentiated into rod and cone cells by P12, they rapidly underwent drastic degeneration and completely disappeared by P21. The photoreceptor cell death in the GPx4-CKO mice was associated with the nuclear translocation of apoptosis-inducing factor (AIF) and TUNEL-positive cells. Photoreceptor cells before undergoing apoptosis (P11) exhibited decreased mitochondrial biomass, decreased number of connecting cilia, as well as disorganized structure of outer segments. These findings indicate that GPx4 is a critical antioxidant enzyme for the maturation and survival of photoreceptor cells.

Source of selenium supplementation influences testis selenium content and gene expression profiles in Single Comb White Leghorn roosters

Spermatogenesis is a tightly regulated, selenium-dependent process. Nutritional deficiencies, including Se, have been associated with decreased fertility. During Se depletion, testes preferentially retain Se while other tissues are depleted. This study was aimed at evaluating the effect of Se source (inorganic or organic yeast derived) on testes weight, Se content, and gene expression. At 17 weeks of age, roosters were randomly assigned to one of three treatments: basal diet (control), basal diet + 0.3 mg organic Se/kg organic yeast-derived Se (YS; Sel-Plex®, Alltech Inc.), or basal diet + 0.3 mg inorganic Se /kg inorganic Se as sodium selenite (SS). At 40 weeks of age, seven roosters from each treatment were euthanized and testes removed. Testes weight did not differ between treatments, but Se content was greater (P ≤ 0.01) in YS than SS and control. Testicular differential gene expression profiling was accomplished using the Affymetrix Genechip® chicken genome array. Ingenuity® pathway analysis revealed that Se supplementation, regardless of source, results in the up-regulation of genes governing cell structure/morphology. The enrichment of such pathways was greater with YS than SS. These expression patterns suggest that aside from playing a role in antioxidant defense, Se, especially in the organic YS form, is useful for maintaining testicular cell structure.