Role of selenium in spermatogenesis: differential expression of cjun and cfos in tubular cells of mice testis

Trace and essential elements as vital components to improve the performance of the male reproductive system: Implications in cell signaling pathways

Successful male fertilization requires the main processes such as normal spermatogenesis, sperm capacitation, hyperactivation, and acrosome reaction. The progress of these processes depends on some endogenous and exogenous factors. So, the optimal level of ions and essential and rare elements such as selenium, zinc, copper, iron, manganese, calcium, and so on in various types of cells of the reproductive system could affect conception and male fertility rates. The function of trace elements in the male reproductive system could be exerted through some cellular and molecular processes, such as the management of active oxygen species, involvement in the action of membrane channels, regulation of enzyme activity, regulation of gene expression and hormone levels, and modulation of signaling cascades. In this review, we aim to summarize the available evidence on the role of trace elements in improving male reproductive performance. Also, special attention is paid to the cellular aspects and the involved molecular signaling cascades.

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

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

Role for Selenium in Metabolic Homeostasis and Human Reproduction

Selenium (Se) is a micronutrient essential for life. Dietary intake of Se within the physiological range is critical for human health and reproductive functions. Selenium levels outside the recommended range have been implicated in infertility and variety of other human diseases. However, presently it is not clear how different dietary Se sources are processed in our bodies, and in which form or how much dietary Se is optimum to maintain metabolic homeostasis and boost reproductive health. This uncertainty leads to imprecision in published dietary guidelines and advice for human daily intake of Se and in some cases generating controversies and even adverse outcomes including mortality. The chief aim for this review is to describe the sources of organic and inorganic Se, the metabolic pathways of selenoproteins synthesis, and the critical role of selenprotenis in the thyroid gland homeostasis and reproductive/fertility functions. Controversies on the use of Se in clinical practice and future directions to address these challenges are also described and discussed herein.

The reproductive toxicity and potential mechanisms of combined exposure to dibutyl phthalate and diisobutyl phthalate in male zebrafish (Danio rerio)

Dibutyl phthalate (DBP) and diisobutyl phthalate (DiBP) are phthalate compounds frequently detected in the environment. Despite increasing awareness of their toxicity in human and animals, the male reproductive toxicity of their combined exposure remains elusive. The purposes of this study were to investigate whether combined exposure to DBP and DiBP could induce male reproductive toxicity, and to explore the potential toxicological mechanisms. Adult male zebrafish were exposed to DBP (11, 113 and 1133 μg L^-1), DiBP (10, 103 and 1038 μg L^-1) and their mixtures (Mix) (11 + 10, 113 + 103, 1133 + 1038 μg L^-1) for 30 days, and their effects on plasma hormone secretion, testis histology and transcriptomics were examined. Highest concentrations of Mix exposure caused greater imbalance ratio of T/E2 and more severe structural damage to testis than single exposure. These effects were consistent with the testis transcriptome analysis for which 4570 genes were differentially expressed in Mix exposure, while 2795 and 1613 genes were differentially expressed in DBP and DiBP, respectively. KEGG pathway analysis showed that both single and combined exposure of DBP and DiBP could affect cytokine-cytokine receptor interaction. The difference was that combined exposure could also affect steroid hormone synthesis, extracellular matrix receptor interaction, retinol metabolism, and PPAR signaling pathways. These results demonstrated that combined exposure to DBP and DiBP could disrupt spermatogenesis and elicit male reproductive toxicity in zebrafish.

Role of Selenium and Selenoproteins in Male Reproductive Function: A Review of Past and Present Evidences

Selenium (Se) is an important trace mineral having many essential roles at the cellular and organismal levels in animal and human health. The biological effects of Se are mainly carried out by selenoproteins (encoded by 25 genes in humans and 24 in mice). As an essential component of selenoproteins, Se performs structural and enzymic roles; in the latter context it is well known for its catalytic and antioxidative functions. Studies involving different animal models have added great value to our understanding regarding the potential implications of Se and selenoproteins in mammalian fertility and reproduction. In this review, we highlight the implications of selenoproteins in male fertility and reproduction followed by the characteristic biological functions of Se and selenoproteins associated with overall male reproductive function. It is evident from observations of past studies (both animal and human) that Se is essentially required for spermatogenesis and male fertility, presumably because of its vital role in modulation of antioxidant defense mechanisms and other essential biological pathways and redox sensitive transcription factors. However, bearing in mind the evidences from mainstream literature, it is also advisable to perform more studies focusing on the elucidation of additional roles played by the peculiar and canonical selenoproteins i.e., glutathione peroxidase 4 (GPX4) and selenoprotein P (SELENOP) in the male reproductive functions. Nevertheless, search for the elucidation of additional putative mechanisms potentially modulated by other biologically relevant selenoproteins should also be included in the scope of future studies. However, as for the implication of Se in fertility and reproduction in men, though a few clinical trials explore the effects of Se supplementation on male fertility, due to inconsistencies in the recruitment of subjects and heterogeneity of designs, the comparison of such studies is still complicated and less clear. Therefore, further research focused on the roles of Se and selenoproteins is awaited for validating the evidences at hand and outlining any therapeutic schemes intended for improving male fertility. As such, new dimensions could be added to the subject of male fertility and Se supplementation.

Microelements in seminal and serum plasma are associated with fresh semen quality in Yorkshire boars

This study aimed to explore associations between semen quality and trace element level in serum and seminal plasma in Yorkshire boars. Semen quality of 112 Yorkshire boars was assessed for 13 weeks to calculate semen utilization rate, which was then divided into three categories: low utilization rate group (LG, < 60% utilization rate), medium utilization rate group (MG, 60-80%), and high utilization rate group (HG, > 80%). After grouping, serum and seminal plasma samples of selected boars were collected to determine concentrations of 10 elements including Ca, Mg, Cu, Fe, Zn, Mn, Se, Cr, Pb and Cd using inductively coupled plasma mass spectrometry. Results showed the increase of semen utilization rate was accompanied by the increase of sperm motility and the decrease of abnormal sperm rate among three groups (P < 0.01). Serum Fe concentration in LG boars was lower than that in HG boars (P < 0.05). Regression analysis revealed serum Fe concentration was positively correlated with sperm motility (r = 0.251; P < 0.05), while negatively correlated with abnormal sperm rate (r = -0.207; P < 0.05). However, MG and HG boars had lower serum Se concentration than LG boars (P < 0.05), and serum Se concentration contribution to sperm motility varied in a quadratic manner (Sperm motility = -0.0004 Se_(serum)² +0.136 Se+74.06; r = 0.300; P < 0.01). Semen utilization rate tended to decrease with the increase of seminal plasma Pb concentration (P = 0.09). Regression analysis exhibited seminal plasma Pb negatively related to sperm motility (r = -0.237; P < 0.05), while positively correlated with abnormal sperm rate (r = 0.237; P < 0.05). Furthermore, seminal plasma Pb was the most influential factor among trace element in serum and seminal plasma on sperm motility basing on the generalized linear model analysis (P < 0.05). Sperm motility decreased by approximately 3.47% when seminal plasma Pb concentration increased from 0 μg/L to 11.16 μg/L. In conclusion, deficiency of serum Fe reduces semen utilization rate by impairing sperm motility and morphology, whereas excessive serum Se decreases sperm motility. More importantly, the mere existence of seminal plasma Pb has more impact on semen quality than other trace elements in serum and seminal plasma in Yorkshire boars.

Impotentia generandi in male dromedary camels: heavy metal and trace element profiles and their relations to clinical findings and semen quality

The aim of this study was to investigate the profiles of cadmium (Cd), lead (Pb), selenium (Se), zinc (Zn), copper (Cu), molybdenum (Mo), iron (Fe), and manganese (Mn) in serum of dromedary camels with impotentia generandi and their associations with the clinical findings and semen analysis data. Sixteen male dromedary camels with impotentia generandi (IG group) and 5 fertile camels (FERT group) were used. The external and internal genital organs were examined using visual inspection, palpation, and ultrasonography. Semen was collected by electroejaculation and examined for volume, count, motility, viability, and abnormality. Blood was collected from all camels and serum was harvested. All serum samples were digested by concentrated acids and analyzed for heavy metals and trace elements by flame emission atomic absorption spectrophotometer. Results showed that the mean heavy metal and trace element concentrations in serum were in the following descending order Fe > Zn > Cu > Cd > Mo > Se > Mn > Pb. Cd was higher in IG than in FERT males (P = 0.02). Se was greater in FERT than in IG groups (P = 0.003). Zn was higher in in FERT than in IG groups (P = 0.001). There were positive correlations between Zn and sperm count (r = 0.59, P = 0.005) and sperm motility (r = 0.57, P = 0.005) and a tendency for negative correlation between Zn and sperm abnormalities (r = - 0.44, P = 0.05). In conclusion, Cd might be implicated as a cause of infertility in male camels. Deficiencies of Se and Zn may also have adverse impacts on male camel reproduction.

Mineral profiling of ostrich (Struthio camelus) seminal plasma and its relationship with semen traits and collection day

Successful assisted reproduction techniques, with specific focus on in vitro semen storage for artificial insemination, are dependent on certain key elements which includes the biochemical profiling of semen. The objective of this study was to complete an ostrich seminal plasma (SP) evaluation by inductively coupled plasma mass spectrometry (ICP-MS) among seven males at different daily intervals (day 1, 3, 7, 11, 15, 19, 21, 23, 25, 26, 27, 28) for a period of 28 days during spring (August to September) for mineral profiling. The effect of collection day and male on sperm concentration, semen volume and seminal plasma volume, was explored as well as the relationships amongst these specific sperm traits and SP minerals. Variation amongst SP mineral concentrations, accounted for by the fixed effects of sperm concentration, semen volume, seminal plasma volume, collection day and male, ranged from 18% to 77%. Male had the largest effect on variation in SP minerals, namely: phosphorus (P), potassium (K), calcium (Ca), sodium (Na), boron (B), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), barium (Ba), arsenic (As) and selenium (Se). Sperm concentration instigated fluctuations of P, magnesium (Mg), B, zinc (Zn), Fe, aluminium (Al), Se, manganese (Mn) and lead (Pb). Semen volume had an effect on Na, K, B, Pb and Ba while seminal plasma volume only influenced variation in Na. There were fluctuations among collection days of specific micro minerals, Ni and Mo, with initial Ni concentrations being relatively greater and Mo at lesser concentrations. Semen volume, seminal plasma volume and sperm concentration varied amongst males. Sperm concentrations during the initial collection days, 1 and 3, were less than that for days 7 to 28. Significant variation of SP minerals and sperm characteristics among ejaculates and males suggest an association of these specific elements with sperm function and are, therefore, considered to be of potential importance to success of assisted reproduction technology for the ostrich. The relationship amongst sperm concentration and collection day confirms the need to conduct an initial period of collection to stabilise a greater sperm concentration to optimise sperm numbers for artificial insemination purposes.

Mouse dead end 1-β interacts with c-Jun and stimulates activator protein 1 transactivation

Dead end 1 (DND1), important for maintaining the viability of primordial germ cells, is the first protein containing an RNA recognition motif that has been directly implicated as a heritable cause of spontaneous tumorigenesis. In the present study, c-Jun was identified through yeast two-hybrid screening of a 10.5-day old mouse embryo cDNA library as one of the proteins which interact with DND1-β. The interaction between DND1-β and c-Jun was demonstrated to occur by glutathione S‑transferase pull‑down and co-immunoprecipitation. Using confocal microscopy, DND1-β was found to be specifically expressed in GC-1 spermatogonia cells, mainly in the nuclei. When transfected into GC-1 cells, DND1-β and c-Jun were demonstrated to be co-localized principally in the nuclei. Furthermore, in a dual luciferase reporter assay, the transcriptional activity of activator protein 1 was demonstrated to be significantly increased by co-transfection with DND1-β and c-Jun plasmids in GC-1 cells. The identification and confirmation of an additional protein interacting with DND1-β facilitates the investigation of the functions and molecular mechanisms of DND1.

ALKBH5 is a mammalian RNA demethylase that impacts RNA metabolism and mouse fertility

N(6)-methyladenosine (m(6)A) is the most prevalent internal modification of messenger RNA (mRNA) in higher eukaryotes. Here we report ALKBH5 as another mammalian demethylase that oxidatively reverses m(6)A in mRNA in vitro and in vivo. This demethylation activity of ALKBH5 significantly affects mRNA export and RNA metabolism as well as the assembly of mRNA processing factors in nuclear speckles. Alkbh5-deficient male mice have increased m(6)A in mRNA and are characterized by impaired fertility resulting from apoptosis that affects meiotic metaphase-stage spermatocytes. In accordance with this defect, we have identified in mouse testes 1,551 differentially expressed genes that cover broad functional categories and include spermatogenesis-related mRNAs involved in the p53 functional interaction network. The discovery of this RNA demethylase strongly suggests that the reversible m(6)A modification has fundamental and broad functions in mammalian cells.

Fank1 interacts with Jab1 and regulates cell apoptosis via the AP-1 pathway

Regulation of apoptosis at various stages of differentiation plays an important role in spermatogenesis. Therefore, the identification and characterisation of highly expressed genes in the testis that are involved in apoptosis is of great value to delineate the mechanism of spermatogenesis. Here, we reported that Fank1, a novel gene highly expressed in testis, functioned as an anti-apoptotic protein that activated the activator protein 1 (AP-1) pathway. We found that Jab1 (Jun activation domain-binding protein 1), a co-activator of AP-1, specifically interacted with Fank1. Reporter analyses showed that Fank1 activated AP-1 pathway in a Jab1-dependent manner. Fank1 overexpression also increased the expression and activation of endogenous c-Jun. Further study showed that Fank1 inhibited cell apoptosis by upregulating and activating endogenous c-Jun and its downstream target, Bcl-3. This process was shown to be Jab1 dependent. Taken together, our results indicated that by interacting with Jab1, Fank1 could suppress cell apoptosis by activating the AP-1-induced anti-apoptotic pathway.

Effects of organic and inorganic dietary selenium supplementation on gene expression profiles in oviduct tissue from broiler-breeder hens

Selenium (Se) is an essential component of at least 25 selenoproteins involved in a multitude of physiological functions, including reproduction. However, relatively little is known about the mechanisms by which Se exerts its physiological effects in reproductive tissue. The objective of this study was to compare the effect of long-term inorganic Se (sodium selenite, SS) and organic yeast-derived Se (Sel-Plex(®), SP) supplementations on tissue Se content and gene expression patterns in the oviduct of broiler-breeder hens. Hens were randomly assigned at 6 weeks of age to one of the three treatments: basal semi-purified diet (control), basal diet+0.3 ppm Se as SP or basal diet+0.3 ppm Se as SS. At 49 weeks, oviduct tissue from hens randomly selected from each treatment (n=7) was analyzed for Se content and gene expression profiles using the Affymetrix Chicken genome array. Gene expression data were evaluated using GeneSpring GX 10.0 (Silicon Genetics, Redwood, CA) and Ingenuity Pathways Analysis software (Ingenuity Systems, Redwood City, CA). Oviduct Se concentration was greater with Se supplementation compared with the control (P≤0.05) but did not differ between SS- and SP-supplemented groups. Gene expression analysis revealed that the quantity of gene transcripts associated with energy production and protein translation were greater in the oviduct with SP but not SS supplementation. Targets up-regulated by SP, but not SS, included genes encoding several subunits of the mitochondrial respiratory complexes, ubiquinone production and ribosomal subunits. SS hens showed a decrease in transcripts of genes involved in respiratory complexes, ATP synthesis and protein translation and metabolism in oviduct relative to control hens. In this study, although tissue Se concentrations did not differ between hens fed SS- and SP-supplemented diets, expression patterns of genes involved in energy production and protein synthesis pathways differed between treatments. These variations may partially explain the differences in reproductive performance reported in hens fed different forms of Se.

DUSP13B/TMDP inhibits stress-activated MAPKs and suppresses AP-1-dependent gene expression

The dual-specificity phosphatase (DUSP) 13 gene encodes two atypical DUSPs, DUSP13B/TMDP and DUSP13A/MDSP using alternative exons. DUSP13B protein is most highly expressed in testis, particularly in spermatocytes and round spermatids of the seminiferous tubules, while that of DUSP13A is restricted to skeletal muscle. Here, we show that DUSP13B inactivated MAPK activation in the order of selectivity, JNK = p38>ERK in cells, while DUSP13A did not show MAPK phosphatase activity. Reporter gene analysis showed that DUSP13B had significant inhibitory effect on AP-1-dependent gene expression, but DUSP13A did not. To our knowledge, DUSP13B is the first identified testis-specific phosphatase that inhibits stress-activated MAPKs. These data suggest an important role for DUSP13B in protection from external stress during spermatogenesis.

Involvement of selenoprotein P and GPx4 gene expression in cadmium-induced testicular pathophysiology in rat

To investigate the effect of co-exposure to cadmium (Cd) and selenium (Se) on selenoprotein P (SelP) and phospholipid hydroperoxide glutathione peroxidase (GPx4) gene expression in testis and to evaluate their possible involvement in Cd-induced testicular pathophysiology, male rats received either tap water, Cd or Cd+Se in their drinking water for 5 weeks. Cd exposure caused a down-regulation of SelP and GPx4 gene expression and a significant decrease in plasma and testicular concentrations of Se. These changes were accompanied by decreased plasma testosterone level, sperm count and motility, GSH content, protein-bound sulfhydryl concentration (PSH), enzymatic activities of catalase (CAT) and glutathione peroxidase (GSH-Px) as well as by increased glutathione-S-transferase (GST) activity, lipid peroxidation (as malondialdehyde, MDA) and proteins carbonyls (PC). The decrease of testicular SelP and GPx4 gene expression under Cd influence was significantly restored in Cd+Se group. Co-treatment with Cd and Se also totally reversed the Cd-induced depletion of Se, decrease in plasma testosterone level and partially restored Cd-induced oxidative stress and decrease in sperm count and motility. Taken together, these data suggest that down-regulation of SelP and GPx4 gene expression induces plasma and testicular Se depletion leading, at least in part, to Cd-induced testicular pathophysiology.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 4: intercellular bridges, mitochondria, nuclear envelope, apoptosis, ubiquitination, membrane/voltage-gated channels, methylation/acetylation, and transcription factors

As germ cells divide and differentiate from spermatogonia to spermatozoa, they share a number of structural and functional features that are common to all generations of germ cells and these features are discussed herein. Germ cells are linked to one another by large intercellular bridges which serve to move molecules and even large organelles from the cytoplasm of one cell to another. Mitochondria take on different shapes and features and topographical arrangements to accommodate their specific needs during spermatogenesis. The nuclear envelope and pore complex also undergo extensive modifications concomitant with the development of germ cell generations. Apoptosis is an event that is normally triggered by germ cells and involves many proteins. It occurs to limit the germ cell pool and acts as a quality control mechanism. The ubiquitin pathway comprises enzymes that ubiquitinate as well as deubiquitinate target proteins and this pathway is present and functional in germ cells. Germ cells express many proteins involved in water balance and pH control as well as voltage-gated ion channel movement. In the nucleus, proteins undergo epigenetic modifications which include methylation, acetylation, and phosphorylation, with each of these modifications signaling changes in chromatin structure. Germ cells contain specialized transcription complexes that coordinate the differentiation program of spermatogenesis, and there are many male germ cell-specific differences in the components of this machinery. All of the above features of germ cells will be discussed along with the specific proteins/genes and abnormalities to fertility related to each topic.

Up-regulation of CatSper genes family by selenium

BACKGROUND

CatSper1-4 are a unique family of sperm cation channels, which are exclusively expressed in the testis and play an important role in sperm motility and male fertility. Despite their vital role in male fertility, almost nothing is known about the factors regulating their expression. Here, we investigated the effects of selenium (Se) on the expression of CatSper genes and sperm parameters in aging versus young male mice.

METHODS

Forty 11-13 months aging male mice and forty 2-3 months young adult male mice were used. The animals were divided in two experimental groups: first group including aging males and second group comprising of young adult males, both treated with Se. The experimental groups were injected intra-peritoneally with Se (0.2 mg/kg) daily, for up to 5 weeks. Two other groups, aging and young adult mice without Se treatment were used as controls. All the animals were rapidly sacrificed by cervical dislocation on the days 21, 28, 35 and 42 after Se treatment. Subsequently, the morphology of the collected sperms was analyzed, and one of the testes from each mouse used for semi-quantitative RT-PCR. The significancy of the data was analyzed using ANOVA.

RESULTS AND DISCUSSION

Our data revealed that there was a significant up-regulation of CatSper genes in the experimental groups compared to the control ones. Furthermore, the results of sperm analysis showed that the sperm parameters were improved in the aging as well as young adult male mice following Se treatment.

CONCLUSION

Se treatment in the aging subjects could up-regulate the expression of CatSper genes, and therefore results in elevation of sperm motility. Furthermore, Se treatment improved sperm parameters, especially morphology and viability rates.

Identification of proteins interacting with selenocysteine lyase

Yeast two-hybrid screening of mouse cDNA libraries was performed to identify proteins interacting with selenocysteine lyase (SCL), which decomposes L-selenocysteine. Several proteins related to spermatogenesis, protein synthesis, and cell viability/apoptosis were identified as potential interactors. Major urinary proteins 1 and 2 interacted with SCL and inhibited its activity. Coimmunoprecipitation revealed interactions between SCL and each of two selenophosphate synthetase isozymes.

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.

Focus on mammalian thioredoxin reductases--important selenoproteins with versatile functions

Thioredoxin systems, involving redox active thioredoxins and thioredoxin reductases, sustain a number of important thioredoxin-dependent pathways. These redox active proteins support several processes crucial for cell function, cell proliferation, antioxidant defense and redox-regulated signaling cascades. Mammalian thioredoxin reductases are selenium-containing flavoprotein oxidoreductases, dependent upon a selenocysteine residue for reduction of the active site disulfide in thioredoxins. Their activity is required for normal thioredoxin function. The mammalian thioredoxin reductases also display surprisingly multifaceted properties and functions beyond thioredoxin reduction. Expressed from three separate genes (in human named TXNRD1, TXNRD2 and TXNRD3), the thioredoxin reductases can each reduce a number of different types of substrates in different cellular compartments. Their expression patterns involve intriguingly complex transcriptional mechanisms resulting in several splice variants, encoding a number of protein variants likely to have specialized functions in a cell- and tissue-type restricted manner. The thioredoxin reductases are also targeted by a number of drugs and compounds having an impact on cell function and promoting oxidative stress, some of which are used in treatment of rheumatoid arthritis, cancer or other diseases. However, potential specific or essential roles for different forms of human or mouse thioredoxin reductases in health or disease are still rather unclear, although it is known that at least the murine Txnrd1 and Txnrd2 genes are essential for normal development during embryogenesis. This review is a survey of current knowledge of mammalian thioredoxin reductase function and expression, with a focus on human and mouse and a discussion of the striking complexity of these proteins. Several yet open questions regarding their regulation and roles in different cells or tissues are emphasized. It is concluded that the intriguingly complex regulation and function of mammalian thioredoxin reductases within the cellular context and in intact mammals strongly suggests that their functions are highly fi ne-tuned with the many pathways involving thioredoxins and thioredoxin-related proteins. These selenoproteins furthermore propagate many functions beyond a reduction of thioredoxins. Aberrant regulation of thioredoxin reductases, or a particular dependence upon these enzymes in diseased cells, may underlie their presumed therapeutic importance as enzymatic targets using electrophilic drugs. These reductases are also likely to mediate several of the effects on health and disease that are linked to different levels of nutritional selenium intake. The thioredoxin reductases and their splice variants may be pivotal components of diverse cellular signaling pathways, having importance in several redox-related aspects of health and disease. Clearly, a detailed understanding of mammalian thioredoxin reductases is necessary for a full comprehension of the thioredoxin system and of selenium dependent processes in mammals.

Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study

PURPOSE

We explored the efficacy of selenium and/or or N-acetyl-cysteine for improving semen parameters in infertile men, and the associations among semen quality and the concentrations of selenium and N-acetyl-cysteine in seminal plasma.

MATERIALS AND METHODS

The study included 468 infertile men with idiopathic oligo-asthenoteratospermia who were randomized to receive 200 microg selenium orally daily (selenium group of 116), 600 mg N-acetyl-cysteine orally daily (N-acetyl-cysteine group of 118), 200 microg selenium plus 600 mg N-acetyl-cysteine orally daily (selenium plus N-acetyl-cysteine group of 116) or similar regimen of placebo (control group of 118) for 26 weeks, followed by a 30-week treatment-free period. These patients provided blood samples for the measurement of serum testosterone, estradiol, follicle-stimulating hormone, luteinizing hormone, prolactin, inhibin B, selenium and N-acetyl-cysteine. Semen samples were also obtained for routine semen analysis, and the measurement of seminal plasma selenium and N-acetyl-cysteine.

RESULTS

In response to selenium and N-acetyl-cysteine treatment serum follicle-stimulating hormone decreased but serum testosterone and inhibin B increased. All semen parameters significantly improved with selenium and N-acetyl-cysteine treatment. Administering selenium plus N-acetyl-cysteine resulted in additive beneficial effects. A significant positive correlation existed between the seminal plasma concentrations of selenium and N-acetyl-cysteine, and semen parameters. A strong correlation was observed between the sum of the selenium and N-acetyl-cysteine concentrations, and mean sperm concentration (r = 0.67, p = 0.01), sperm motility (r = 0.64, p = 0.01) and percent normal morphology (r = 0.66, p = 0.01).

CONCLUSIONS

These results indicate that supplemental selenium and N-acetyl-cysteine improve semen quality. We advocate their use for male infertility treatment.