Testosterone mediates expression of the selenoprotein PHGPx by induction of spermatogenesis and not by direct transcriptional gene activation

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.

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.

The Role of Selenium in Pathologies: An Updated Review

Selenium is an essential microelement required for a number of biological functions. Selenium—and more specifically the amino acid selenocysteine—is present in at least 25 human selenoproteins involved in a wide variety of essential biological functions, ranging from the regulation of reactive oxygen species (ROS) concentration to the biosynthesis of hormones. These processes also play a central role in preventing and modulating the clinical outcome of several diseases, including cancer, diabetes, Alzheimer’s disease, mental disorders, cardiovascular disorders, fertility impairments, inflammation, and infections (including SARS-CoV-2). Over the past years, a number of studies focusing on the relationship between selenium and such pathologies have been reported. Generally, an adequate selenium nutritional state—and in some cases selenium supplementation—have been related to improved prognostic outcome and reduced risk of developing several diseases. On the other hand, supra-nutritional levels might have adverse effects. The results of recent studies focusing on these topics are summarized and discussed in this review, with particular emphasis on advances achieved in the last decade.

Effect of feeding linseed diet on testis development, antioxidant capacity, and epididymal cauda sperm concentration in Chinese Hu lamb

Polyunsaturated fatty acids (PUFAs) are essential for mammalian testis development and sperm function. However, PUFAs that are contained in linseed oil are easily oxidized in the diet and biohydrogenated in the rumen. In this study, we investigated the effect of linseed as a source of PUFAs on the antioxidant capacity and testis development in Hu lamb. Seventy-five 3-month-old lambs were randomly assigned to three groups. Within each treatment group, 25 lambs were allocated to five pens (five lambs per pen). The lambs in the control group were fed a control diet without linseed for 42 days from D22 to D63. Group I (BS28) was fed a control diet from D22 to D35 and 8% linseed diet from D36 to D63. Group II (BS42) was fed an 8% linseed diet for 42 days from D22 to D63. After 63-day feeding trial, all lambs except the heaviest and lightest in each pen were humanely slaughtered and investigated. Results revealed that feeding linseed did not affect the body weight, scrotal circumference, and testis weight, whereas feeding linseed for 42 days increased the epididymis weight (37.85 ± 1.61 g vs. 32.09 ± 1.06 g, P < 0.05) compared with the control group. Feeding lambs with linseed for 42 days also significantly upregulated the expression of antioxidative (glutathione peroxidase 4 and copper-zinc superoxide dismutase), steroidogenesis (3β-hydroxysteroid dehydrogenase and steroid acute regulatory protein), and PUFA metabolism-related genes (fatty acid desaturase 2 and elongation of very long-chain fatty acid protein 2) and proliferating cell nuclear antigen mRNA (P < 0.05). It also increased the relative expression of mitochondrial DNA (P < 0.05), total antioxidant capacity (0.230 ± 0.019 mmol/mgprot vs. 0.175 ± 0.011 mmol/mgprot, P < 0.05), and superoxide dismutase (1661.467 ± 147.117 U/mgprot vs. 1158.891 ± 98.850 U/mgprot, P < 0.05) in testicular tissue but decreased the cholesterol concentration (0.331 ± 0.073 mmol/mgprot vs. 0.671 ± 0.092 mmol/mgprot, P < 0.05) compared with the control group. Therefore, feeding lambs with linseed for 42 days stimulated seminiferous tubule development and increased the number of Sertoli cells (20.71 ± 0.89 vs. 17.6 ± 0.73, P < 0.05), epididymal cauda lumina diameter (638.26 ± 22.32 μm vs. 444.41 ± 34.80 μm, P < 0.05), and the number of sperm in the epididymal cauda (68.91 ± 7.06 × 10⁸/g vs. 36.61 ± 7.50 × 10⁸/g). All these results suggested that feeding linseed in the early reproductive development stage of lambs upregulated the expression of antioxidative, steroidogenesis, and PUFA metabolism-related genes; increased the antioxidant capacity in lamb's testis; and contributed to testis development and spermatogenesis.

Regulatory Phenomena in the Glutathione Peroxidase Superfamily

Significance: The selenium-containing Glutathione peroxidases (GPxs)1-4 protect against oxidative challenge, inhibit inflammation and oxidant-induced regulated cell death. Recent Advances: GPx1 and GPx4 dampen phosphorylation cascades predominantly via prevention of inactivation of phosphatases by H₂O₂ or lipid hydroperoxides. GPx2 regulates the balance between regeneration and apoptotic cell shedding in the intestine. It inhibits inflammation-induced carcinogenesis in the gut but promotes growth of established cancers. GPx3 deficiency facilitates platelet aggregation likely via disinhibition of thromboxane biosynthesis. It is also considered a tumor suppressor. GPx4 is expressed in three different forms. The cytosolic form proved to inhibit interleukin-1-driven nuclear factor κB activation and leukotriene biosynthesis. Moreover, it is a key regulator of ferroptosis, because it reduces hydroperoxy groups of complex lipids and silences lipoxygenases. By alternate substrate use, the nuclear form contributes to chromatin compaction. Mitochondrial GPx4 forms the mitochondrial sheath of spermatozoa and, thus, guarantees male fertility. Out of the less characterized GPxs, the cysteine-containing GPx7 and GPx8 are unique in contributing to oxidative protein folding in the endoplasmic reticulum by reacting with protein isomerase as an alternate substrate. A yeast 2-Cysteine glutathione peroxidase equipped with CP and CR was reported to sense H₂O₂ for inducing an adaptive response. Critical Issues: Most of the findings compiled are derived from tissue culture and/or animal studies only. Their impact on human physiology is sometimes questionable. Future Directions: The expression of individual GPxs and GPx-dependent regulatory phenomena are to be further investigated, in particular in respect to human health.

Antioxidative Defense and Fertility Rate in the Assessment of Reprotoxicity Risk Posed by Global Warming

The objective of this review is to briefly summarize the recent progress in studies done on the assessment of reprotoxicity risk posed by global warming for the foundation of strategic tool in ecosystem-based adaptation. The selected animal data analysis that was used in this paper focuses on antioxidative markers and fertility rate estimated over the period 2000-2019. We followed a phylogenetic methodology in order to report data on a panel of selected organisms that show dangerous effects. The oxidative damage studies related to temperature fluctuation occurring in biosentinels of different invertebrate and vertebrate classes show a consistently maintained physiological defense. Furthermore, the results from homeothermic and poikilothermic species in our study highlight the influence of temperature rise on reprotoxicity.

Seasonal and pharmaceutical-induced changes in selenoprotein glutathione peroxidase 4 activity in the reproductive dynamics of the soil biosentinel Podarcis sicula (Chordata: Reptilia)

There is rising concern for the interaction of environmental contaminants with brain transcriptome and the potential effect on reproductive processes. The present study sought to determine selenoprotein glutathione peroxidase 4 (gpx4) transcriptional activity in the brain and testis of the soil biosentinel, Podarcis sicula, through the main phases of the reproductive cycle and whether pharmaceuticals exert an endocrine disruption. Based on gpx4 cloned amminoacids sequence (GenBank AEX09236.1.), we used a bioinformatic approach to assess the structural role. Specifically, we detected seasonally the reactive oxygen species (ROS) level using electron spin resonance spectroscopy and gpx4 transcriptional activity using quantitative real-time polymerase chain reaction. In addition, the impact of pharmaceuticals was assessed after 21-days of treatment with ICI 182,780 and human chorionic gonadotropin administration in mating and winter stasis, respectively. Bioinformatic data shows the gpx4 proteic activity and a phylogenetic profile. ROS contents in lizard brain are significantly less than in testis and display higher levels after treatments. Brain gpx4 expression gives statistically significant seasonal differences, opposite trends in testis and altered expression in both tissues, with evidence of testis morphological and DNA disruption. Taken together, these results provide direct evidence that gpx4 in P. sicula plays a seasonal regulatory role and may be a reliable biomarker for reproductive health toxicity screening.

Effects of Selenium Nanoparticles on Reproductive Performance of Male Sprague-Dawley Rats at Supranutritional and Nonlethal Levels

This research investigated the influence of selenium nanoparticles (SeNPs) on the reproductive performance of male Sprague-Dawley (SD) rats. A suspension of SeNPs was consecutively administered by oral gavage for 2 weeks at supranutritional (0.2, 0.4, or 0.8 mg Se/kg bw) and nonlethal (2.0, 4.0, or 8.0 mg Se/kg bw) levels to male SD rats. The normal control (NC) rats were exposed to physiological saline alone. Biochemical parameters, sperm motility, gene expression of GPx1 and GPx4, and histopathological evaluation of male spermary were measured in this work. The supranutritional doses could promote the sperm motility (P < 0.001) and movement parameters (P < 0.05). The nonlethal levels of 4.0 and 8.0 mg Se/kg bw reduced the testis weight (P < 0.001), sperm concentration, and motility (P < 0.05), and also caused histopathological injury of testis and epididymis tissues to various degrees. The content of testosterone in serum was increased in the 0.8 group (P < 0.05) and decreased in the 4.0 (P < 0.01) and 8.0 mg Se/kg bw groups (P < 0.001), respectively. No significant effects were observed on antioxidant enzyme activities and mRNA concentration of GPx in the supranutritional dose group, and nonlethal levels were also not observed. In conclusion, SeNPs in the supranutritional dose has a positive effect on the reproductive function of male SD rats and has damaging effect higher than 4.0 mg Se/kg bw.

Dietary Selenium Deficiency or Excess Reduces Sperm Quality and Testicular mRNA Abundance of Nuclear Glutathione Peroxidase 4 in Rats

Background: Glutathione peroxidase (GPX) 4 and selenoprotein P (SELENOP) are abundant, and several variants are expressed in the testis.Objective: We determined the effects of dietary selenium deficiency or excess on sperm quality and expressions of GPX4 and SELENOP variants in rat testis and liver.Methods: After weaning, male Sprague-Dawley rats were fed a Se-deficient basal diet (BD) for 5 wk until they were 9 wk old [mean ± SEM body weight (BW) = 256 ± 5 g]. They were then fed the BD diet alone (deficient) or with 0.25 (adequate), 3 (excess), or 5 (excess) mg Se/kg for 4 wk. Testis, liver, blood, and semen were collected to assay for selenoprotein mRNA and protein abundances, selenium concentration, GPX activity, 8-hydroxy-deoxyguanosine concentration, and sperm quality.Results: Dietary selenium supplementations elevated (P < 0.05) tissue selenium concentrations and GPX activities. Compared with those fed BD + 0.25 mg Se/kg, rats fed BD showed lower (P < 0.05) BW gain (86%) and sperm density (57%) but higher (P < 0.05) plasma 8-hydroxy-deoxyguanosine concentrations (189%), and nonprogressive sperm motility (4.4-fold). Likewise, rats fed BD + 5 mg Se/kg had (P = 0.06) lower BW gain and higher (1.9-fold) sperm deformity rates than those in the selenium-adequate group. Compared with the selenium-adequate group, dietary selenium deficiency (BD) or excess (BD + 3 or 5 mg Se/kg) resulted in 45-77% lower (P < 0.05) nuclear Gpx4 (nGpx4) mRNA abundance in the testis. Rats fed BD had lower (P < 0.05) mRNA levels of 2 Selenop variants in both testis and liver than those in the other groups. Testicular SELENOP was 155-170% higher (P < 0.05) in rats fed BD + 5 mg Se/kg and hepatic c/mGPX4 was 13-15% lower (P < 0.05) in rats fed BD than in the other groups.Conclusions: The mRNA abundance of rat testicular nGPX4 responded to dietary selenium concentrations in similar ways to sperm parameters and may be used as a sensitive marker to assess appropriate Se status for male function.

p,p'-DDE damages spermatogenesis via phospholipid hydroperoxide glutathione peroxidase depletion and mitochondria apoptosis pathway

One, 1-dichloro-2,2-bis(p-chlorophenyl) ethylene (p,p'-DDE), the major metabolite of 2,2-bis(4-chlorophenyl)-1,1,1-trichloroethane (DDT), is a known persistent organic pollutant (POPs) and male reproductive toxicant. However, the mechanism by which p,p'-DDE exposure causes male reproductive toxicity remains unknown. The objective of this study was to elucidate some mechanisms involved in this process, including the mitochondria apoptosis pathway and the role of phospholipid hydroperoxide glutathione peroxidase (PHGPx). Puberty male SD rats were given different doses of p,p'-DDE (0, 20, 60, 100 mg/kg body weight), after the treatment, the semen quality was evaluated. Western blotting was used to detect the PHGPx protein expression. Furthermore, real-time PCR was used to analyze the genetic expression of PHGPx, Bax, Cytochrom C (Cyt C), Apaf-1, and caspase-3 in the testis. Results indicated that after the exposure, sperm malformation rate showed a significant rise compared with the control group, and meanwhile, the sperm density and sperm motility parameters were reduced to some extent in different treated groups. The mitochondria apoptosis pathway was activated. And remarkably, the expression of PHGPx protein was greatly reduced by the exposure. We conclude that p,p'-DDE can damage spermatogenesis via PHGPx depletion and mitochondria apoptosis pathway.

Selenium: an element for life

This review aims to illustrate the importance of selenium (Se) for maintenance of overall health, especially for the thyroid, immunity, and homeostasis. Furthermore, it outlines the role of Se in reproduction and in virology and discusses the effects of Se supplementation in critical illness. The multifaceted aspects of this essential nutrient have attracted worldwide clinical and research interest in the last few decades. Se exerts its activity in the form of the aminoacid selenocysteine incorporated in selenoproteins. The impact of Se administration should be considered in relation to its apparent U shaped effects, i.e., exhibiting major advantages in Se-deficient individuals but specific health risks in those with Se excess. Addition of selenium to the administration of levothyroxine may be useful in patients with low Se intake and with mild-form or early-stage Hashimoto's thyroiditis (HT). Serum Se concentration (possibly also at tissue level) decreases in inflammatory conditions and may vary with the severity and duration of the inflammatory process. In such cases, the effect of Se supplementation seems to be useful and rational. Meanwhile, Se's ability to improve the activity of T cells and the cytotoxicity of natural killer cells could render it effective in viral disease. However, the evidence, and this should be stressed, is at present conflicting as to whether Se supplementation is of benefit in patients with HT, though there are indications that it is advantageous in cases of mild/moderate Graves' Orbitopathy. The role of Se in type 2 diabetes mellitus (T2DM) is ambiguous, driven by both Se intake and serum levels. The evidence that insulin and glycaemia influence the transport and activity of Se, via regulatory activity on selenoproteins, and that high serum Se may have a diabetogenic effect suggests a 'Janus-effect' of Se in T2DM. Though the evidence is not as yet clear-cut, the organic form (selenomethionine), due to its pharmacokinetics, is likely to be more advantageous in long-term prevention, and supplementation efforts, while the inorganic form (sodium selenite) has proven effective in an acute, e.g., sepsis, clinical setting. Recent data indicate that functional selenoprotein single-nucleotide polymorphisms (SNPs) may interfere with Se utilization and effectiveness.

Effects of di(2-ethylhexyl)phthalate on testicular oxidant/antioxidant status in selenium-deficient and selenium-supplemented rats

Di(ethylhexyl)phthalate (DEHP), the most widely used plasticizer, was investigated to determine whether an oxidative stress process was one of the underlying mechanisms for its testicular toxicity potential. To evaluate the effects of selenium (Se), status on the toxicity of DEHP was further objective of this study, as Se is known to play a critical role in testis and in the modulation of intracellular redox equilibrium. Se deficiency was produced in 3-weeks-old Sprague-Dawley rats feeding them ≤0.05 mg Se /kg diet for 5 weeks, and Se-supplementation group was on 1 mg Se/kg diet. DEHP-treated groups received 1000 mg/kg dose by gavage during the last 10 days of the feeding period. Activities of antioxidant selenoenzymes [glutathione peroxidase 1 (GPx1), glutathione peroxidase 4 (GPx4), thioredoxin reductase (TrxR)], catalase (CAT), superoxide dismutase (SOD), and glutathione S-transferase (GST); concentrations of reduced glutathione (GSH), oxidized glutathione (GSSG), and thus the GSH/GSSG redox ratio; and thiobarbituric acid reactive substance (TBARS) levels were measured. DEHP was found to induce oxidative stress in rat testis, as evidenced by significant decrease in GSH/GSSG redox ratio (>10-fold) and marked increase in TBARS levels, and its effects were more pronounced in Se-deficient rats with ∼18.5-fold decrease in GSH/GSSG redox ratio and a significant decrease in GPx4 activity, whereas Se supplementation was protective by providing substantial elevation of redox ratio and reducing the lipid peroxidation. These findings emphasized the critical role of Se as an effective redox regulator and the importance of Se status in protecting testicular tissue from the oxidant stressor activity of DEHP.

Roles of reactive oxygen species in the spermatogenesis regulation

Spermatogenesis is a complex process of male germ cells proliferation and maturation from diploid spermatogonia, through meiosis, to mature haploid spermatozoa. The process involves dynamic interactions between the developing germ cells and their supporting Sertoli cells. The gonadal tissue, with abundance of highly unsaturated fatty acids, high rates of cell division, and variety of testis enzymes results very vulnerable to the overexpression of reactive oxygen species (ROS). In order to address this risk, testis has developed a sophisticated array of antioxidant systems comprising both enzymes and free radical scavengers. This chapter sets out the major pathways of testis generation, the metabolism of ROS, and highlights the transcriptional regulation by steroid receptors of antioxidant stress enzymes and their functional implications. It also deals with of the advantages of the system biology for an antioxidant under steroid control, the major selenoprotein expressed by germ cells in the testis, the phospholipid hydroperoxide glutathione peroxidase (PHGPx/GPx4) having multiple functions and representing the pivotal link between selenium, sperm quality, and species preservation.

Identification and characterization of two phospholipid hydroperoxide glutathione peroxidase genes from Apis cerana cerana

Phospholipid hydroperoxide glutathione peroxidase (PHGPX) plays a crucial role in maintaining the integrity of membrane by reducing hydroperoxides of phospholipids. Here, we report the identification and characterization of two genes, designated AccGtpx-1 and AccGtpx-2, encoding PHGPX proteins from the Chinese honeybees, Apis cerana cerana. Alignment analysis showed that AccGtpx-1 and AccGtpx-2 shared high similarity with other known PHGPXs, which show similar structure to thioredoxin. These single copy genes showed complex exon-intron structures. The mRNA of AccGtpx-1 was detected in larvae, pupae and adults and that AccGtpx-2 was only found in adult worker bees. Furthermore, the expression of AccGtpx-1 could be induced by H(2)O(2), ultraviolet (UV) light, heat shock (37 degrees C), HgCl(2), imidacloprid, cyhalothrin, pyriproxyfen and methomyl. In contrast, AccGtpx-2 expression could only be induced by UV. These results indicated for the first time that the AccGtpx-1 and AccGtpx-2 genes encoding A. cerana cerana PHGPXs are regulated differently in response to environmental stressors.

Selenium bioavailability: current knowledge and future research requirements

Information on selenium bioavailability is required to derive dietary recommendations and to evaluate and improve the quality of food products. The need for robust data is particularly important in light of recent suggestions of potential health benefits associated with different intakes of selenium. The issue is not straightforward, however, because of large variations in the selenium content of foods (determined by a combination of geologic/environmental factors and selenium supplementation of fertilizers and animal feedstuffs) and the chemical forms of the element, which are absorbed and metabolized differently. Although most dietary selenium is absorbed efficiently, the retention of organic forms is higher than that of inorganic forms. There are also complications in the assessment and quantification of selenium species within foodstuffs. Often, extraction is only partial, and the process can alter the form or forms present in the food. Efforts to improve, standardize, and make more widely available techniques for species quantification are required. Similarly, reliable and sensitive functional biomarkers of selenium status are required, together with improvements in current biomarker methods. This requirement is particularly important for the assessment of bioavailability, because some functional biomarkers respond differently to the various selenium species. The effect of genotype adds a potential further dimension to the process of deriving bioavailability estimates and underlines the need for further research to facilitate the process of deriving dietary recommendations in the future.

New Strategy of Functional Analysis of PHGPx Knockout Mice Model Using Transgenic Rescue Method and Cre-LoxP System

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is an intracellular antioxidant enzyme that directly reduces peroxidized phospholipids. PHGPx is transcribed from one gene into three types of mRNA, mitochondrial, non-mitochondrial and nucleolar PHGPx by alternative transcription. In this review, we focus on our recent experiments on the regulation of promoter activity of the types of PHGPx and on the novel strategy of functional analysis of a PHGPx knockout mice model using the transgenic rescue method and Cre-LoxP system. PHGPx is especially high in testis and spermatozoa. A deficiency is implicated in human infertility. We established spermatocyte-specific PHGPx knockout (KO) mice using a Cre-loxP system. Targeted disruption of all exons of the PHGPx gene in mice by homologous recombination caused embryonic lethality at 7.5 days post coitum. The PHGPx-loxP transgene rescued PHGPx KO mice from embryonic lethality. These rescued floxed PHGPx mice were mated with spermatocyte specific Cre expressing mice. All the spermatocyte-specific PHGPx KO male mice were infertile and displayed a significant decrease in the number of spermatozoa and significant reductions in forward motility by mitochondrial dysfunction of spermatozoa. These results demonstrate that depletion of PHGPx in spermatozoa may be one of the causes of male infertility in mice and humans.

Aluminum accumulation induced testicular oxidative stress and altered selenium metabolism in mice

Present work was carried out to investigate how testicular selenium (Se) metabolisms respond to oxidative stress induced by aluminum (Al). Mice were intraperitoneally exposed to 0, 7, or 35mg Al/kg/d for 14 days (CNL, LAL and HAL groups). Al administration significantly increased Al, reactive oxygen radical and malondialdehyde (MDA) levels, as well as decreased glutathione peroxidase (GPx) and glutathione reductase (GR) activities in serum and testes. The serum concentrations of Se were remarkably lower at LAL and HAL groups compared to the controls, whereas the testicular Se levels significantly reduced only in the HAL group. In addition, RT-PCR analysis revealed an increased testicular selenoprotein P (SelP) expression by Al treatment. Western blot analysis showed increased levels of SelP protein expression in the LAL group, but the expression levels were significantly reduced in HAL group. It was suggested that altered metabolism of Se, further stimulated testicular SelP transcription that may compensate for the loss of SelP protein resulted from Al-induced oxidative damage.

Selenium requirements are higher for glutathione peroxidase-1 mRNA than gpx1 activity in rat testis

Selenium (Se) plays a critical role in testis, sperm, and reproduction, and testis Se levels are remarkably maintained in Se deficiency. In most other tissues, Se levels decrease dramatically as do levels of most selenoproteins and levels of a subset of Se-regulated selenoprotein mRNAs. Because of the recent identification of key molecules in the targeted trafficking of Se to the testis, we examined the hierarchy of Se regulation in testis by determining the dietary Se regulation of the full testis selenoproteome in rats fed graded levels of Se (0 to 0.8 microg Se/g) as Na2SeO3 for 28 d. Se status did not significantly affect testis weight or glutathione peroxidase 4 (Gpx4) activity (P>0.05). qRT-PCR analysis of selenoprotein mRNA expression revealed that 21 of the 24 selenoprotein mRNAs and ApoER2 mRNA (the selenoprotein P [Sepp1] receptor) were also not regulated significantly by dietary Se status. In contrast, Gpx1 activity decreased to 28% of Se-adequate levels, and mRNA levels for Gpx1, Sepp1, and Sepw1 (selenoprotein W) decreased significantly in Se-deficient rats to 45, 46, and 55%, respectively, of Se-adequate plateau levels. Overlap of hyperbolic Gpx4 activity and Sepw1 mRNA response curves with testis Se concentration, all with minimum dietary Se requirements<0.016 microg Se/g, showed the priority for synthesis of Gpx4. Higher minimum dietary Se requirements of 0.04 microg Se/g for Gpx1 activity and Sepp1 mRNA, and the even higher minimum dietary Se requirement of 0.08 microg Se/g for Gpx1 mRNA, suggest that the hierarchy of these biomarkers reflects distinct, lower priority pools, cell types, and roles for Se within the testis.

Evolutionary and structural insights into the multifaceted glutathione peroxidase (Gpx) superfamily

Glutathione peroxidase (GPx) is a widespread protein superfamily found in many organisms throughout all kingdoms of life. Although it was initially thought to use only glutathione as reductant, recent evidence suggests that the majority of GPxs have specificity for thioredoxin. We present a thorough in silico analysis performed on 724 sequences and 12 structures aimed to clarify the evolutionary, structural, and sequence determinants of GPx specificity. Structural variability was found to be limited to only two regions, termed oligomerization loop and functional helix, which modulate both reduced substrate specificity and oligomerization state. We show that mammalian GPx-1, the canonic selenocysteine-based tetrameric glutathione peroxidase, is a recent "invention" during evolution. Contrary to common belief, cysteine-based thioredoxin-specific GPx, which we propose the TGPx, are both more common and more ancient. This raises interesting evolutionary considerations regarding oligomerization and the use of active-site selenocysteine residue. In addition, phylogenetic analysis has revealed the presence of a novel member belonging to the GPx superfamily in Mammalia and Amphibia, for which we propose the name GPx-8, following the present numeric order of the mammalian GPxs.

Dietary selenium deficiency as well as excess supplementation induces multiple defects in mouse epididymal spermatozoa: understanding the role of selenium in male fertility

Selenium (Se) is essential for male fertility. The present study was carried out to observe the defects associated with Se deficiency as well as excess Se supplementation by analyzing the sperm ultrastructure and chromatin organization. Different Se status mice were generated viz. Se deficient (group I), Se adequate (group II) and Se excess (group III) by feeding the respective diets for a period of 4 (group Ia, IIa and IIIa) and 8 weeks (group Ib, IIb and IIIb). Reduction in sperm concentration, motility and percentage fertility was observed in Se deficient and Se excess groups. Electron microscopy revealed mitochondrial swelling and gaps between adjacent mitochondria in mice fed Se-deficient diet for 4 weeks. At 8 weeks, several abnormalities such as loose contact of the mitochondrial helix with the plasma membrane, loss of mitochondria, retention of cytoplasmic droplet, fracturing of outer dense fibres and presence of both the midpiece and the principal piece cross-sections in a common plasma membrane were observed. In Se excess group, the predominant defect was the frequent presence of equidistant, cross-sectioned midpieces of the tail embedded in a common cytoplasm. These defects are indicative of loss of sperm motility. Spermatozoa from Se-deficient mice had incompletely condensed chromatin and indicated an increase in occurrence of DNA strand breaks. The animals fed Se excess diet also indicated increase in DNA breaks but this was significantly less than the deficient diet fed groups. Our study reveals the defects associated with Se deficiency that result in loss of reproductive ability and also reflects its possible harmful effects on spermatozoa after prolonged consumption at supranutritional level.

Sensitivity of mouse lung fibroblasts heterozygous for GPx4 to oxidative stress

Phospholipid hydroperoxide glutathione peroxidase (GPx4) is a member of the family of selenium-dependent enzymes that catalyze the reduction of cell membrane-bound phospholipid hydroperoxides in situ and thus protects against membrane damage. Overexpression of GPx4 protects cultured cells from phosphatidylcholine hydroperoxide (PCOOH)-induced loss of mitochondrial membrane potential and blocks cell death induced by treatment with various apoptotic agents. We have generated mice that are heterozygous for a GPx4 null allele (GPx4 +/-); the homozygous null genotype is embryonic lethal. We report that cultured lung fibroblasts (LFs) isolated from adult GPx4 +/- mice had approximately 50% of the GPx4 activity of LFs from GPx4 +/+ mice and were significantly more susceptible to H2O2, cadmium, and cumene hydroperoxide-induced cytotoxicity, as measured by neutral red assay. Both GPx4 +/+ and GPx4 +/- LFs were susceptible to PCOOH-induced cytotoxicity at a high PCOOH concentration. We also found that GPx4 +/- LFs have lower mitochondrial membrane potential, greater cardiolipin oxidation, and lower amounts of reduced thiols relative to GPx4 +/+ LFs, but are more resistant than GPx4 +/+ LFs to further decrements in these endpoints following PCOOH treatment. These results suggest that adult lung fibroblasts deficient in GPx4 may have upregulated compensatory mechanisms to deal with the highly oxidized environment in which they developed.

Effects of endocrine disrupting chemicals on expression of phospholipid hydroperoxide glutathione peroxidase mRNA in rat testes

Phospholipid hydroperoxide glutathione peroxidase (PHGPx), an antioxidative selenoprotein, is modulated by estrogen in the testis and oviduct. To examine whether potential endocrine disrupting chemicals (EDCs) affect the microenvironment of the testes, the expression patterns of PHGPxmRNA and histological changes were analyzed in 5-week-old Sprague-Dawley male rats exposed to several EDCs such as an androgenic compound [testosterone (50, 200, and 1,000 µg/kg)], anti-androgenic compounds [flutamide (1, 5, and 25 mg/kg), ketoconazole (0.2 and 1 mg/kg), and diethylhexyl phthalate (10, 50, and 250 mg/kg)], and estrogenic compounds [nonylphenol (10, 50, 100, and 250 mg/kg), octylphenol (10, 50, and 250 mg/kg), and diethylstilbestrol (10, 20, and 40 µg/kg)] daily for 3 weeks via oral administration. Mild proliferation of germ cells and hyperplasia of interstitial cells were observed in the testes of the flutamide-treated group and deletion of the germinal epithelium and sloughing of germ cells were observed in testes of the diethylstilbestrol-treated group. Treatment with testosterone was shown to slightly decrease PHGPxmRNA levels in testes by the reverse transcriptionpolymerase chain reaction. However, anti-androgenic compounds (flutamide, ketoconazole, and diethylhexyl phthalate) and estrogenic compounds (nonylphenol, octylphenol, and diethylstilbestrol) significantly upregulated PHGPxmRNA in the testes (p < 0.05). These findings indicate that the EDCs might have a detrimental effect on spermatogenesis via abnormal enhancement of PHGPx expression in testes and that PHGPx is useful as a biomarker for toxicity screening of estrogenic or antiandrogenic EDCs in testes.

Identification of a responsible promoter region and a key transcription factor, CCAAT/enhancer-binding protein epsilon, for up-regulation of PHGPx in HL60 cells stimulated with TNF alpha

In the present study we investigated promoter regions of the PHGPx [phospholipid hydroperoxide GPx (glutathione peroxidase)] gene and transcription factors involved in TNFalpha (tumour necrosis factor alpha)-induced up-regulation of PHGPx in non-differentiated HL60 cells. Non-differentiated HL60 cells displayed up-regulation of non-mitochondrial and mitochondrial PHGPx mRNA in response to TNFalpha stimulation. The promoter activity was up-regulated by TNFalpha stimulation in cells transfected with a luciferase reporter vector encoding the region from -282 to -123 of the human PHGPx gene compared with the non-stimulated control. The up-regulated promoter activity was effectively abrogated by a mutation in the C/EBP (CCAAT/enhancer-binding protein)-binding sequence in this region. ChIP (chromatin immunoprecipitation) assays demonstrated that C/EBPepsilon bound to the -247 to -34 region in HL60 cells, but C/EBPalpha, beta, gamma and delta did not. The binding of C/EBPepsilon to the promoter region was increased in HL60 cells stimulated with TNFalpha compared with that of the non-stimulated control. An increased binding of nuclear protein to the C/EBP-binding sequence was observed by EMSA (electrophoretic mobility-shift assay) in cells stimulated with TNFalpha, and it was inhibited by pre-treatment with an anti-C/EBPepsilon antibody, but not with other antibodies. The C/EBPepsilon mRNA was expressed in PMNs (polymorphonuclear cells), non-differentiated HL60 cells and neutrophil-like differentiated HL60 cells displaying TNFalpha-induced up-regulation of PHGPx mRNA, but not in macrophage-like differentiated HL60 cells, HEK-293 cells (human embryonic kidney-293 cells) and other cell lines exhibiting no up-regulation. The up-regulation of PHGPx mRNA, however, was detected in HEK-293 cells overexpressing C/EBPepsilon as a result of TNFalpha stimulation. These results indicate that C/EBPepsilon is a critical transcription factor in TNFalpha-induced up-regulation of PHGPx expression.

Superoxide dismutase, catalase, and glutathione peroxidase in the testis of the Mexican big-eared bat (Corynorhinus mexicanus) during its annual reproductive cycle

The reproductive physiology of Corynorhinus mexicanus includes a testes growth-involution cycle. Testis recrudescence begins in May-June, peaks in August and then undergoes a profound involution being totally regressed in November. Adult, male individuals were captured monthly during one year and ROS scavenging enzyme activities were measured in testes and expressed per total wet-weight and per mg protein. SOD total activity is very low from October to February; increases sharply one full month before testes recrudescence starts, and in August, when testis activity was at its peak, SOD is 3-4 times lower than in July. Catalase total activity is bimodal. The main peak of activity occurs during testicular recrudescence with an additional smaller peak, two months before the onset of recrudescence. Glutathione peroxidase total activity parallels almost exactly the testis growth cycle, increases in July, reaches a peak in August and decreases through September to almost disappear in October. SOD specific activity shows a pre-testicular increase of activity, maintains its activity from March to July and then descends drastically to almost nil in August, maintaining these low values until February. Catalase specific activity is particularly important during the period of testicular regression. GPX specific activity is low from March to July, months of testicular recrudescence; whereas its activity increases in August and peaks in November, when testes regression occurs. Our data show that ROS-scavenging enzymes may play a very important role during testes involution-recrudescence in C. mexicanus, and we believe their participation could be equally important in all seasonally breeding mammals.

Identification of the Positive Regulatory and Distinct Core Regions of Promoters, and Transcriptional Regulation in Three Types of Mouse Phospholipid Hydroperoxide Glutathione Peroxidase

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is transcribed into three types of mRNA, mitochondrial, non-mitochondrial and nucleolar types, from one gene by alternative transcription using different first exons, Ia and Ib. We investigated the regulatory mechanisms of the expressions of the three types of PHGPx using promoter analysis with luciferase as the reporter gene and electrophoretical mobility shift analysis. Here we report a draft of the positive regulatory region and the core promoter regions of PHGPx in several cell lines. From promoter deletion analysis we identified the three distinct core regions of mitochondrial PHGPx, non-mitochondrial PHGPx and nucleolar PHGPx. The core promoter activity of non-mitochondrial PHGPx was high in L929 cells, but relatively low for mitochondrial and nucleolar PHGPx. We also identified the positive regulatory region of mitochondrial PHGPx by deletion and mutation analysis of 5'-flanking regions of mitochondrial PHGPx. This region could regulate the promoter activity of non-mitochondrial PHGPx; however, up-regulation by this region was normally suppressed by the upstream region in somatic cells. Electrophoretical mobility shift analysis demonstrated that a specific transcription factor complex bound to this region in adult testis, but not in young testis and different sizes of complexes bound to this region between testis and brain.

Failure of phospholipid hydroperoxide glutathione peroxidase expression in oligoasthenozoospermia and mutations in the PHGPx gene

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is a selenoprotein belonging to the family of glutathione peroxidases. PHGPx has long been considered a major antioxidant that, in cooperation with vitamin E, protects biomembranes. To determine the expression pattern of PHGPx mRNA in human, quantitative RT-polymerase chain reaction (PCR) analyses using RNA from different embryonal and adult tissues were performed. A predominant expression was found in testes. In spermatozoa, PHGPx was found to be localized in the mid-piece of spermatozoa. We studied the relationship between spermatozoa PHGPx expression, mutations in PHGPx gene and human oligoasthenozoospermia, a defect in which both the number and the motility of spermatozoa are significantly below normal. Spermatozoa specimens from 45 infertile males were analysed for fertility-related parameters according to World Health Organisation and were classified as suffering from oligoasthenozoospermia. Two patients (4.44%) showed no expression of PHGPx and in nine patients (20.00%), a reduced expression of the enzyme was observed. DNA sequences of various regions of the PHGPx gene (coding, 5'flanking region and intron 1) from these patients and 58 fertile volunteers were analysed for mutations by PCR amplification and direct sequencing. Sequence data revealed no cause/effect relationship for any of the variants. From these data it can be concluded that oligoasthenozoospermia is associated with a decrease in the level of expression of PHGPx in the spermatozoa of some infertile men (24.44%), but is not linked to mutations in PHGPx gene.

Up-regulation of phospholipid hydroperoxide glutathione peroxidase in rat casein-induced polymorphonuclear neutrophils

Antioxidant enzymes play key roles in the protection of cells from oxidative damage. Little is known, however, about the expression of antioxidants and/or their roles in PMNs (polymorphonuclear leucocytes), which are thought to suffer from oxidative stress in an inflammation site. In the present paper, we report on the regulation of expression of PHGPx (phospholipid hydroperoxide glutathione peroxidase) and cGPx (cytosolic glutathione peroxidase) in rat PMNs in the inflammation site. PHGPx mRNA levels were much lower in casein-induced peritoneal and carrageenan-induced pleural PMNs just after their collection than in peripheral PMNs. cGPx mRNA was also reduced in the casein-induced PMNs, but not in carrageenan-induced PMNs. Both enzymes with decreased levels in the casein-induced PMNs were up-regulated during further 24 h cultivation in vitro and in vivo, with elevation of their protein levels and activities, and reduction of intracellular peroxides. Up-regulation of PHGPx mRNA was attenuated by cycloheximide, a protein synthesis inhibitor, and this effect was cancelled by culturing the cells in the conditioned medium of the cultured casein-induced PMNs. This latter effect was attenuated by pre-treatment with anti-GRO (growth-regulated oncogene) antibody. Recombinant rat GRO could also induce the up-regulation in the presence of cycloheximide, demonstrating that GRO may play an important role in the PHGPx up-regulation of casein-induced PMNs. Production of the lipid mediators leukotriene B4 and 5-HETE (5-hydroxyeicosatetraenoic acid) was decreased in the cultured casein-induced PMNs exhibiting PHGPx up-regulation. The evidence obtained indicates that PHGPx activity in the activated PMNs would be related to the appearance of the intrinsic function of PMNs in the inflammatory site.

Selenium, the thyroid, and the endocrine system

Recent identification of new selenocysteine-containing proteins has revealed relationships between the two trace elements selenium (Se) and iodine and the hormone network. Several selenoproteins participate in the protection of thyrocytes from damage by H(2)O(2) produced for thyroid hormone biosynthesis. Iodothyronine deiodinases are selenoproteins contributing to systemic or local thyroid hormone homeostasis. The Se content in endocrine tissues (thyroid, adrenals, pituitary, testes, ovary) is higher than in many other organs. Nutritional Se depletion results in retention, whereas Se repletion is followed by a rapid accumulation of Se in endocrine tissues, reproductive organs, and the brain. Selenoproteins such as thioredoxin reductases constitute the link between the Se metabolism and the regulation of transcription by redox sensitive ligand-modulated nuclear hormone receptors. Hormones and growth factors regulate the expression of selenoproteins and, conversely, Se supply modulates hormone actions. Selenoproteins are involved in bone metabolism as well as functions of the endocrine pancreas and adrenal glands. Furthermore, spermatogenesis depends on adequate Se supply, whereas Se excess may impair ovarian function. Comparative analysis of the genomes of several life forms reveals that higher mammals contain a limited number of identical genes encoding newly detected selenocysteine-containing proteins.

Functional Interaction of Phospholipid Hydroperoxide Glutathione Peroxidase with Sperm Mitochondrion-associated Cysteine-rich Protein Discloses the Adjacent Cysteine Motif as a New Substrate of the Selenoperoxidase

The mitochondrial capsule is a selenium- and disulfide-rich structure enchasing the outer mitochondrial membrane of mammalian spermatozoa. Among the proteins solubilized from the sperm mitochondrial capsule, we confirmed, by using a proteomic approach, the presence of phospholipid hydroperoxide glutathione peroxidase (PHGPx) as a major component, and we also identified the sperm mitochondrion-associated cysteine-rich protein (SMCP) and fragments/aggregates of specific keratins that previously escaped detection (Ursini, F., Heim, S., Kiess, M., Maiorino, M., Roveri, A., Wissing, J., and Flohé, L. (1999) Science 285, 1393-1396). The evidence for a functional association between PHGPx, SMCP, and keratins is further supported by the identification of a sequence motif of regularly spaced Cys-Cys doublets common to SMCP and high sulfur keratin-associated proteins, involved in bundling hair shaft keratin by disulfide cross-linking. Following the oxidative polymerization of mitochondrial capsule proteins, catalyzed by PHGPx, two-dimensional redox electrophoresis analysis showed homo- and heteropolymers of SMCP and PHGPx, together with other minor components. Adjacent cysteine residues in SMCP peptides are oxidized to cystine by PHGPx. This unusual disulfide is known to drive, by reshuffling oxidative protein folding. On this basis we propose that oxidative polymerization of the mitochondrial capsule is primed by the formation of cystine on SMCP, followed by reshuffling. Occurrence of reshuffling is further supported by the calculated thermodynamic gain of the process. This study suggests a new mechanism where selenium catalysis drives the cross-linking of structural elements of the cytoskeleton via the oxidation of a keratin-associated protein.

PHGPx in spermatogenesis: how many functions?

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is a unique intracellular enzyme that directly reduces lipid hydroperoxides in membranes and has the ability to use protein thiol groups as donor substrates. Three isoforms of PHGPx have so far been identified, namely, a mitochondrial, a cytosolic and a nuclear variant. This article is focused on recent evidence demonstrating that (1) mitochondrial and nuclear PHGPx isoforms display a different pattern of expression during male germ cell differentiation; (2) different PHGPx isoforms play specific and independent functions during sperm maturation. The data are discussed in light of the idea that PHGPx is a moonlighting protein, changing roles depending on the intracellular localization, expression in a specific cell type and different partners which it interacts with.

The nuclear form of phospholipid hydroperoxide glutathione peroxidase is a protein thiol peroxidase contributing to sperm chromatin stability

The selenoenzyme phospholipid hydroperoxide glutathione peroxidase (PHGPx) is regarded as the major molecular target of selenodeficiency in rodents, accounting for most of the histopathological and structural abnormalities of testicular tissue and male germ cells. PHGPx exists as a cytosolic form, mitochondrial form, and nuclear form (nPHGPx) predominantly expressed in late spermatids and spermatozoa. Here, we demonstrate that mice with a targeted deletion of the nPHGPx gene were, unlike mice with the full knockout (KO) of PHGPx, not only viable but also, surprisingly, fully fertile. While both morphological analysis of testis and epididymis and sperm parameter measurements did not show any apparent abnormality, toluidine blue and acridine orange stainings of spermatozoa indicated defective chromatin condensation in the KO sperm isolated from the caput epididymis. Furthermore, upon drying and hydrating, KO sperm exhibited a significant proportion of morphologically abnormal heads. Monobromobimane labeling and protein-free thiol titration revealed significantly less extensive oxidation in the cauda epididymis when compared to that in the wild type. We conclude that nPHGPx, by acting as a protein thiol peroxidase in vivo, contributes to the structural stability of sperm chromatin.

The GI-GPx gene is a target for Nrf2

The gastrointestinal glutathione peroxidase (GI-GPx, GPx2) is a selenoprotein that was suggested to act as barrier against hydroperoxide absorption but has also been implicated in the control of inflammation and malignant growth. In CaCo-2 cells, GI-GPx was induced by t-butyl hydroquinone (tBHQ) and sulforaphane (SFN), i.e., "antioxidants" known to activate the "antioxidant response element" (ARE) via electrophilic thiol modification of Keap1 in the Nrf2/Keap1 system. The functional significance of a putative ARE in the GI-GPx promoter was validated by transcriptional activation of reporter gene constructs upon exposure to electrophiles (tBHQ, SFN, and curcumin) or overexpression of Nrf2 and by reversal of these effects by mutation of the ARE in the promoter and by overexpressed Keap1. Binding of Nrf2 to the ARE sequence in authentic gpx2 was corroborated by chromatin immunoprecipitation. Thus, the presumed natural antioxidants sulforaphane and curcumin may exert their anti-inflammatory and anticarcinogenic effects not only by induction of phase 2 enzymes but also by the up-regulation of the selenoprotein GI-GPx.

Estrogen selectively up-regulates the phospholipid hydroperoxide glutathione peroxidase in the oviducts

The oviduct plays a crucial role in mammalian reproduction by providing an optimal environment for the final maturation and transport of gametes, fertilization, and early embryonic development. It is now recognized that these reproductive events in vitro can be either negatively or positively affected by reactive oxygen species such as hydrogen peroxide and lipid hydroperoxides. In the current study, we analyzed the expression of the phospholipid hydroperoxide glutathione peroxidase (PHGPx or GPx-4), a selenoenzyme that directly reduces membrane-bound lipid hydroperoxides in the bovine oviduct. Using in situ hybridization, we demonstrated that GPx-4 expression is almost restricted to the oviductal luminal epithelium in contrast to GPx-1, which is widely distributed, and GPx-2 and -3, which are mainly detected in the epithelial cells and lamina propria. Interestingly, real-time quantitative RT-PCR analysis showed that GPx-4 expression was highest during the follicular and postovulatory phases. In addition, GPx-4 expression was highest in the isthmus proximal to the dominant follicle during the follicular stage and remained high during the postovulatory period. This increased in expression of GPx-4 corresponded to increased GPx-4 enzymatic activity. Based on intrauterine infusion of estradiol, we determined that the increase in expression and activity of GPx-4 is estrogen mediated. This work clearly demonstrates that GPx-4 gene expression is influenced by the proximity of the dominant follicle in the oviduct in vivo. We propose that GPx-4 has an important role in the physiological control of peroxide tone in the bordering cells of the oviductal lumen.

cAMP-response element modulator-tau activates a distinct promoter element for the expression of the phospholipid hydroperoxide/sperm nucleus glutathione peroxidase gene

PHGPx (phospholipid hydroperoxide glutathione peroxidase) is a selenoprotein present in at least three isoforms in testis: cytosolic, mitochondrial and nuclear. All of these derive from the same gene and are structurally related with the exception of the snPHGPx (sperm nucleus-specific form), which differs from the others due to the presence of an arginine-rich N-terminus. It has been demonstrated recently that this N-terminus is encoded by an alternative exon located in the first intron of the PHGPx gene. The expression of snPHGPx has been attributed either to an alternative pre-mRNA splicing or to the presence of a distinct promoter region. Nevertheless, the exact molecular mechanism by which the expression of snPHGPx occurs has not been demonstrated so far. Preliminary sequence analysis of the region located upstream of the alternative exon revealed some potential DNA-binding sites, one of which is specific to the binding of CREM (cAMP-response element modulator) transcription factors. By using electrophoretic mobility-shift assays, we demonstrated that both nuclear protein extract from highly purified rat spermatid cells and recombinant CREM-tau protein can specifically bind to this element. Furthermore, we cloned a 1059 bp comprising the intron and the alternative exon for snPHGPx in the pCAT3 reporter vector. By transient transfection experiments, we demonstrated that the expression of the transcription factor CREM-tau can induce the activation of the reporter gene in NIH-3T3 cell line. These results were confirmed by chromatin immunoprecipitation experiments performed on highly purified rat spermatid cells. On the basis of these results, we demonstrate that snPHGPx expression is mediated by the transcription factor CREM-tau, which acts as a cis-acting element localized in the first intron of the PHGPx gene.

Oral carnitine supplementation increases sperm motility in asthenozoospermic men with normal sperm phospholipid hydroperoxide glutathione peroxidase levels

OBJECTIVE

To clarify the role of carnitine supplementation in idiopathic asthenozoospermia and to look for a rationale for its use in asthenozoospermic patients.

DESIGN

Blind clinical study.

SETTING

Academic.

PATIENT(S)

Thirty asthenozoospermic patients divided in two groups according to phospholipid hydroperoxide glutathione peroxidase (PHGPx) levels.

INTERVENTION(S)

Placebo for 3 months, then oral L-carnitine (2 g/day) for 3 months; semen samples were collected at baseline, after placebo, after carnitine administration, and again after 3 months with no drugs.

MAIN OUTCOME MEASURE(S)

Evaluation of seminal parameters and determination of seminal PHGPx levels, measured as rescued activity.

RESULT(S)

When asthenozoospermic subjects were divided in two groups on the basis of PHGPx levels, we observed an improvement of mean sperm motility only in the group of patients with normal PHGPx levels.

CONCLUSION(S)

Phospholipid hydroperoxide glutathione peroxidase has an important role in male infertility, and carnitine treatment might improve sperm motility in the presence of normal mitochondrial function.

Phospholipid hydroperoxide glutathione peroxidase: expression pattern during testicular development in mouse and evolutionary conservation in spermatozoa

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is a selenoprotein belonging to the family of glutathione peroxidases and has been implicated in antioxidative defense and spermatogenesis. PHGPx accounts for almost the entire selenium content of mammalian testis. In an attempt to verify the expression pattern of PHGPx, testes of mouse mutants with arrest at different stages of germ cell development and testes of mice at different ages were subjected to immunostaining with a monoclonal anti-PHGPx antibody. PHGPx was detected in Leydig cells of testes in all developmental stages. In the seminiferous tubuli, the PHGPx staining was first observed in testes of 21-day-old mice which is correlated with the appearance of the first spermatids. This result was confirmed when the testes of mutant mice with defined arrest of germ cell development were used. An immunostaining was observed in the seminiferous tubuli of olt/olt and qk/qk mice which show an arrest at spermatid differentiation. In Western blot analysis of proteins extracted from testes of mutant mice and from developing testes, two signals at 19- and 22-kDa were observed which confirm the existence of two PHGPx forms in testicular cells. In mouse spermatozoa, a subcellular localization of PHGPx and sperm mitochondria-associated cysteine-rich protein (SMCP) was demonstrated, indicating the localization of PHGPx in mitochondria of spermatozoa midpiece. For verifying the midpiece localization of PHGPx in other species, spermatozoa of Drosophila melanogaster, frog, fish, cock, mouse, rat, pig, bull, and human were used in immunostaining using anti-PHGPx antibody. A localization of PHGPx was found in the midpiece of spermatozoa in all species examined. In electronmicroscopical analysis, PHGPx signals were found in the mitochondria of midpiece. These results indicate a conserved crucial role of PHGPx during sperm function and male fertility.

Transgenic mice overexpressing glutathione peroxidase 4 are protected against oxidative stress-induced apoptosis

Glutathione peroxidase 4 (Gpx4) is uniquely involved in the detoxification of oxidative damage to membrane lipids. Our previous studies showed that Gpx4 is essential for mouse survival and that Gpx4 deficiency makes cells vulnerable to oxidative injury. In the present study, we generated two lines of transgenic mice overexpressing Gpx4 (Tg(GPX4) mice) using a genomic clone containing the human GPX4 gene. Both lines of Tg-(GPX4) mice, Tg5 and Tg6, had elevated levels of Gpx4 (mRNA and protein) in all tissues investigated, and overexpression of Gpx4 did not cause alterations in activities of glutathione peroxidase 1, catalase, Cu/Zn superoxide dismutase, and manganese superoxide dismutase. The human GPX4 transgene rescued the lethal phenotype of null mutation of the mouse Gpx4 gene, indicating that the transgene can replace the essential role of mouse Gpx4 in mouse development. Cell death induced by t-butylhydroperoxide and diquat was significantly less in murine embryonic fibroblasts from Tg(GPX4) mice compared with wild type mice. Liver damage and lipid peroxidation induced by diquat were reduced significantly in Tg(GPX4) mice. In addition, diquat-induced apoptosis was decreased in Tg(GPX4) mice, as evidenced by attenuated caspase-3 activation and reduced cytochrome c release from mitochondria. These data demonstrate that Gpx4 plays a role in vivo in the mechanism of apoptosis induced by oxidative stress that most likely occurs through oxidative damage to mitochondrial phospholipids such as cardiolipin.