Characterization of mammalian thioredoxin reductase, thioredoxin and glutaredoxin by immunochemical methods

The significance of blood and salivary oxidative stress markers and chemerin in gestational diabetes mellitus

OBJECTIVE

Gestational diabetes mellitus (GDM) is a medical complication of pregnancy. The aim of this study was to evaluate the correlations between the salivary and blood levels of oxidative stress markers and an adipokine chemerin, which play a role in the pathogenesis of GDM.

MATERIALS AND METHODS

Study groups (Control (n = 29), GDM (n = 22)) had been assessed clinically healthy oral hygiene, according to the age range between 25 and 40 years, BMI<30 kg/m2, who were non-smokers and who were not having systemic diseases. GDM was diagnosed using a 100 g OGTT. Saliva samples were collected without stimulation between 08.30 and 10.00 a.m.. Chemerin and TrxR levels were measured by ELISA. Malondialdehyde, sulfhydryl and NO levels were determined by spectrophotometric analysis. Statistical analysis were performed by Shapiro Wilk, Mann Whitney U, Student's t test.

RESULTS

Blood pressure, BMI, and plasma chemerin, salivary chemerin, fasting glucose, LDL, triglyceride, CRP levels in GDM were not different when compared to Control. There were significant differences between Plasma TrxR and HDL levels. Also, significant differences between salivary TrxR and Malondialdehyde levels were observed in GDM.

CONCLUSION

It was concluded that the optimal cut-off points for oxidative stress parameters and chemerin level can be used to distinguish between healthy pregnant and GDM.

The Relationship Between Salivary Redox, Diet, and Food Flavor Perception

The mouth is the gateway for entrance of food and microorganisms into the organism. The oral cavity is bathed by saliva, which is thus the first fluid that food and microorganisms will face after their entrance. As a result, saliva plays different functions, including lubrication, predigestion, protection, detoxification, and even transport of taste compounds to chemoreceptors located in the taste buds. To ensure its function of protection, saliva contains reactive harmful compounds such as reactive oxygen species that are controlled and neutralized by the antioxidant activity of saliva. Several antioxidant molecules control the production of molecules such as reactive oxygen compounds, neutralize them and/or repair the damage they have caused. Therefore, a balance between reactive oxidant species and antioxidant compounds exists. At the same time, food can also contain antioxidant compounds, which can participate in the equilibrium of this balance. Numerous studies have investigated the effects of different food components on the antioxidant capacity of saliva that correspond to the ability of saliva to neutralize reactive oxygen species. Contradictory results have sometimes been obtained. Moreover, some antioxidant compounds are also cofactors of enzymatic reactions that affect flavor compounds. Recent studies have considered the salivary antioxidant capacity to explain the release of flavor compounds ex vivo or in vivo. This article aims to review the effect of food on the antioxidant capacity of saliva and the impact of salivary antioxidant capacity on flavor perception after a brief presentation of the different molecules involved.

Thioredoxin and thioredoxin target proteins: from molecular mechanisms to functional significance

The thioredoxin (Trx) system is one of the central antioxidant systems in mammalian cells, maintaining a reducing environment by catalyzing electron flux from nicotinamide adenine dinucleotide phosphate through Trx reductase to Trx, which reduces its target proteins using highly conserved thiol groups. While the importance of protecting cells from the detrimental effects of reactive oxygen species is clear, decades of research in this field revealed that there is a network of redox-sensitive proteins forming redox-dependent signaling pathways that are crucial for fundamental cellular processes, including metabolism, proliferation, differentiation, migration, and apoptosis. Trx participates in signaling pathways interacting with different proteins to control their dynamic regulation of structure and function. In this review, we focus on Trx target proteins that are involved in redox-dependent signaling pathways. Specifically, Trx-dependent reductive enzymes that participate in classical redox reactions and redox-sensitive signaling molecules are discussed in greater detail. The latter are extensively discussed, as ongoing research unveils more and more details about the complex signaling networks of Trx-sensitive signaling molecules such as apoptosis signal-regulating kinase 1, Trx interacting protein, and phosphatase and tensin homolog, thus highlighting the potential direct and indirect impact of their redox-dependent interaction with Trx. Overall, the findings that are described here illustrate the importance and complexity of Trx-dependent, redox-sensitive signaling in the cell. Our increasing understanding of the components and mechanisms of these signaling pathways could lead to the identification of new potential targets for the treatment of diseases, including cancer and diabetes.

Reactive oxygen species: impact on skeletal muscle

It is well established that contracting muscles produce both reactive oxygen and nitrogen species. Although the sources of oxidant production during exercise continue to be debated, growing evidence suggests that mitochondria are not the dominant source. Regardless of the sources of oxidants in contracting muscles, intense and prolonged exercise can result in oxidative damage to both proteins and lipids in the contracting myocytes. Further, oxidants regulate numerous cell signaling pathways and modulate the expression of many genes. This oxidant-mediated change in gene expression involves changes at transcriptional, mRNA stability, and signal transduction levels. Furthermore, numerous products associated with oxidant-modulated genes have been identified and include antioxidant enzymes, stress proteins, and mitochondrial electron transport proteins. Interestingly, low and physiological levels of reactive oxygen species are required for normal force production in skeletal muscle, but high levels of reactive oxygen species result in contractile dysfunction and fatigue. Ongoing research continues to explore the redox-sensitive targets in muscle that are responsible for both redox regulation of muscle adaptation and oxidant-mediated muscle fatigue.

Human Protein Atlas of redox systems - what can be learnt?

BACKGROUND

High-throughput screening projects are popular approaches to yield a vast amount of information amenable for database mining and "hypothesis generation". The keys to success for these approaches depend upon the quality of primary data, choice of algorithms for data analyses, solidity in data annotations and the general usefulness of the results. A large initiative aimed at mapping the expression of all human proteins is the Human Protein Atlas (www.proteinatlas.org), encompassing immunohistochemical analyses of human tissues utilizing antibodies raised against a large number of human proteins. Here, we wished to probe what could be learnt from this atlas using a manual in-depth analysis of the results regarding the expression of key proteins in the human glutathione and thioredoxin systems.

METHODS

The freely available on-line data of immunohistochemical analyses for selected human redox proteins within the Human Protein Atlas were here analyzed, provided that reasonably solid data existed for the antibodies that were employed. This included tissue expression data for thioredoxin 1 (Trx1), Trx2, thioredoxin reductase 1 (TrxR1), TrxR2, glutathione reductase (GR), glucose 6-phosphate dehydrogenase (G6PD), γ-glutamyl cysteinyl synthase (gGCS) and the six peroxiredoxins Prx1 to Prx6. The data were further complemented with a screen using a polyclonal peptide antibody raised against the unique glutaredoxin domain of TXNRD1_v3 ("v3"). The results from fifteen major tissues and organs are presented (lung, kidney, liver, lymph node, testis, prostate, ovary, breast, pancreas, cerebellum, hippocampus, cerebral cortex, skin, skeletal muscle and heart muscle) and discussed considering earlier findings described in the literature.

RESULTS

Staining patterns proved to be highly variable and often unexpected both in terms of tissues analyzed and the individual target proteins. Among the analyzed tissues, only macrophages of the lung, tubular cells of the kidney, lymphoid cells of lymph nodes, Leydig cells in the testis, glandular cells of the prostate and exocrine glandular cells of the pancreas, showed positive staining with all of the fourteen antibodies that were analyzed. Among these antibodies, those against Trx1, TrxR2 and G6PD showed the most restricted staining across different tissues, while others including the antibodies against Trx2, TrxR1, GR, Prx3, Prx4 and Prx6 gave strong staining in most tissues. Staining for v3 was strong in many cells and tissues, which was unexpected considering previous results mapping transcripts for this protein. No obvious co-variation in staining across tissues could be noted when comparing any two of the analyzed antibodies. Staining for G6PD was weak in most tissues, except for cells of the seminiferous ducts in testis and follicular cells of the ovary, where G6PD staining was strong.

CONCLUSIONS

Results from high-throughput screening projects such as the Human Protein Atlas must be taken with caution and need to be duly confirmed by thorough in-depth follow-up studies. The varying staining intensities comparing tissues as seen here for most of the analyzed antibodies nonetheless suggest that the overall profile of the human redox systems may vary significantly between different cell types and between different tissues.

GENERAL SIGNIFICANCE

The Human Protein Atlas data suggest that the individual proteins of the human thioredoxin and glutathione systems may be strikingly tissue- and cell type-specific in terms of expression levels, but we also conclude that these type of high-throughput results should be taken with significant caution and must be duly verified using subsequent focused and detailed hypothesis-guided follow-up studies. This article is part of a Special Issue entitled Human and Murine Redox Protein Atlases.

Exercise-induced oxidative stress: cellular mechanisms and impact on muscle force production

The first suggestion that physical exercise results in free radical-mediated damage to tissues appeared in 1978, and the past three decades have resulted in a large growth of knowledge regarding exercise and oxidative stress. Although the sources of oxidant production during exercise continue to be debated, it is now well established that both resting and contracting skeletal muscles produce reactive oxygen species and reactive nitrogen species. Importantly, intense and prolonged exercise can result in oxidative damage to both proteins and lipids in the contracting myocytes. Furthermore, oxidants can modulate a number of cell signaling pathways and regulate the expression of multiple genes in eukaryotic cells. This oxidant-mediated change in gene expression involves changes at transcriptional, mRNA stability, and signal transduction levels. Furthermore, numerous products associated with oxidant-modulated genes have been identified and include antioxidant enzymes, stress proteins, DNA repair proteins, and mitochondrial electron transport proteins. Interestingly, low and physiological levels of reactive oxygen species are required for normal force production in skeletal muscle, but high levels of reactive oxygen species promote contractile dysfunction resulting in muscle weakness and fatigue. Ongoing research continues to probe the mechanisms by which oxidants influence skeletal muscle contractile properties and to explore interventions capable of protecting muscle from oxidant-mediated dysfunction.

Muscle-derived ROS and thiol regulation in muscle fatigue

Muscles produce oxidants, including reactive oxygen species (ROS) and reactive nitrogen species (RNS), from a variety of intracellular sources. Oxidants are detectable in muscle at low levels during rest and at higher levels during contractions. RNS depress force production but do not appear to cause fatigue of healthy muscle. In contrast, muscle-derived ROS contribute to fatigue because loss of function can be delayed by ROS-specific antioxidants. Thiol regulation appears to be important in this biology. Fatigue causes oxidation of glutathione, a thiol antioxidant in muscle fibers, and is reversed by thiol-specific reducing agents. N-acetylcysteine (NAC), a drug that supports glutathione synthesis, has been shown to lessen oxidation of cellular constituents and delay muscle fatigue. In humans, NAC pretreatment improves performance of limb and respiratory muscles during fatigue protocols and extends time to task failure during volitional exercise. These findings highlight the importance of ROS and thiol chemistry in fatigue, show the feasibility of thiol-based countermeasures, and identify new directions for mechanistic and translational research.

Conserved role of the linker alpha-helix of the bacterial disulfide isomerase DsbC in the avoidance of misoxidation by DsbB

In the bacterial periplasm the co-existence of a catalyst of disulfide bond formation (DsbA) that is maintained in an oxidized state and of a reduced enzyme that catalyzes the rearrangement of mispaired cysteine residues (DsbC) is important for the folding of proteins containing multiple disulfide bonds. The kinetic partitioning of the DsbA/DsbB and DsbC/DsbD pathways partly depends on the ability of DsbB to oxidize DsbA at rates >1000 times greater than DsbC. We show that the resistance of DsbC to oxidation by DsbB is abolished by deletions of one or more amino acids within the alpha-helix that connects the N-terminal dimerization domain with the C-terminal thioredoxin domain. As a result, mutant DsbC carrying alpha-helix deletions could catalyze disulfide bond formation and complemented the phenotypes of dsbA cells. Examination of DsbC homologues from Haemophilus influenzae, Pseudomonas aeruginosa, Erwinia chrysanthemi, Yersinia pseudotuberculosis, Vibrio cholerae (30-70% sequence identity with the Escherichia coli enzyme) revealed that the mechanism responsible for avoiding oxidation by DsbB is a general property of DsbC family enzymes. In addition we found that deletions in the linker region reduced, but did not abolish, the ability of DsbC to assist the formation of active vtPA and phytase in vivo, in a DsbD-dependent manner, revealing that interactions between DsbD and DsbC are also conserved.

New aspects of the location of neuronal nitric oxide synthase in the skeletal muscle: A light and electron microscopic study

The action of nitric oxide (NO) synthesized by NO synthases (NOS) is spatially restricted. Hence, the intracellular location of NOS might play an important role for the functional interactions of NO with its target molecules. In the skeletal muscle the neuronal NOS (nNOS) is considered to be the predominant isoform expressed as a muscle specific elongated splice variant. There are only a few and highly discrepant reports of the subcellular distribution of nNOS, which prompted us to re-examine the distribution of nNOS in the skeletal muscle of rat and mouse applying immunocytochemistry and NADPH-diaphorase (NADPH-d) histochemistry. Light microscopically, the sarcolemma, areas beneath the sarcolemma, areas around the nuclei, and the cross striation were labeled by antibodies and by the NADPH-d reaction as well. Ultrastructurally, nNOS visualized immunocytochemically or by the histochemical BSPT-reaction, was associated discretely with extrajunctional portions of the sarcolemma. Both reaction products were additionally observed in the vicinity of endoplasmic reticulum and mitochondria, or associated with their outer membranes. In the neuromuscular junction (NMJ)-region NOS was localized to the cytoplasm of nerve terminals and terminal Schwann cells. In contrast to the commonly accepted assumption, the enzyme was found in association with the presynaptic, and not with the postsynaptic membrane. Cytosolic NADPH-d was exhibited especially between mitochondria accumulated in the postsynaptic region of the NMJ. Surprisingly, in nNOS-/--mice the skeletal muscle showed patterns of significant nNOS-immunoreactivity and NADPH-d activity possibly due to alternative nNOS-splice isoforms, which might be up-regulated to compensate for decreased NO formation.

Engineered DsbC chimeras catalyze both protein oxidation and disulfide-bond isomerization in Escherichia coli: Reconciling two competing pathways

In the Escherichia coli periplasm, the formation of protein disulfide bonds is catalyzed by DsbA and DsbC. DsbA is a monomer that is maintained in a fully oxidized state by the membrane enzyme DsbB, whereas DsbC is a dimer that is kept reduced by a second membrane protein, DsbD. Although the catalytic regions of DsbA and DsbC are composed of structurally homologous thioredoxin motif domains, DsbA serves only as an oxidase in vivo, whereas DsbC catalyzes disulfide reduction and isomerization and also exhibits significant chaperone activity. To reconcile the distinct catalytic activities of DsbC and DsbA, we constructed a series of chimeras comprising of the dimerization domain of DsbC, with or without the adjacent alpha-helical linker region, fused either to the first, second, third, or fifth residue of intact DsbA or to thioredoxin. The chimeras fully substituted for DsbC in disulfide-bond rearrangement and also were able to restore protein oxidation in a dsbA background. Remarkably, the chimeras could serve as a single catalyst for both disulfide-bond formation and rearrangement, thus reconciling the kinetically competing DsbB-DsbA and DsbD-DsbC pathways. This property appeared to depend on the orientation of the DsbA active-site cysteines with respect to the DsbC dimerization domain. In vitro, the chimeras had high chaperone activity and significant reductase activity but only 15-22% of the disulfide-isomerization activity of DsbC, suggesting that rearrangement of nonnative disulfides may be mediated primarily by cycles of random reduction and reoxidation.

Cloning and expression of a novel human glutaredoxin (Grx2) with mitochondrial and nuclear isoforms

Glutaredoxin (Grx) is a glutathione-dependent hydrogen donor for ribonucleotide reductase. Today glutaredoxins are known as a multifunctional family of GSH-disulfide-oxidoreductases belonging to the thioredoxin fold superfamily. In contrast to Escherichia coli and yeast, a single human glutaredoxin is known. We have identified and cloned a novel 18-kDa human dithiol glutaredoxin, named glutaredoxin-2 (Grx2), which is 34% identical to the previously known cytosolic 12-kDa human Grx1. The human Grx2 sequence contains three characteristic regions of the glutaredoxin family: the dithiol/disulfide active site, CSYC, the GSH binding site, and a hydrophobic surface area. The human Grx2 gene, located at chromosome 1q31.2--31.3, consisted of five exons that were transcribed to a 0.9-kilobase human Grx2 mRNA ubiquitously expressed in several tissues. Two alternatively spliced Grx2 mRNA isoforms that differed in their 5' region were identified. These corresponded to alternative proteins with a common 125-residue C-terminal Grx domain but with different N-terminal extensions of 39 and 40 residues, respectively. The 125-residue Grx domain and the two full-length variants were expressed in E. coli and exhibited GSH-dependent hydroxyethyl disulfide and dehydroascorbate reducing activities. Western blot analysis of subcellular fractions from Jurkat cells with a specific anti-Grx2 antibody showed that human Grx2 was predominantly located in the nucleus but also present in the mitochondria. We further showed that one of the mRNA isoforms corresponding to Grx2a encoded a functional N-terminal mitochondrial translocation signal.

Relationship between NADP-specific isocitrate dehydrogenase and glutathione peroxidase in aging rat skeletal muscle

The glutathione peroxidase (GPX) system detoxifies hydroperoxides in cells and uses NADPH to regenerate reduced glutathione. Enzymatic sources of NADPH in skeletal muscle include NADP-specific isocitrate dehydrogenase (ICDP), glucose-6-phosphate dehydrogenase (G6PD), and malic enzyme (ME). Our purpose was to explore the relationship in skeletal muscle between GPX and ICDP along with other NADPH-generating enzymes as a function of progressive age and muscle fiber-type. Soleus (SOL), red gastrocnemius (RG), and white gastrocnemius (WG) muscles were extracted from Fischer-344 rats of three different ages: 4 months old (Y); 18 months old (M); and 24 months old (O). Assays were conducted to determine activities of GPX, ICDP, G6PD, and ME along with levels of lipid hydroperoxides. GPX activities were significantly greater in RG and WG of old rats than in younger. ICDP activities were higher in the WG of old and middle aged rats when compared to young adults. GPX and ICDP activities exhibited similar differences among the muscles tested (SOL>RG>WG). In contrast, G6PD and ME activities were not significantly different across muscles. G6PD activities increased in RG with age, but were well over an order of magnitude lower than ICDP in all muscles. ME activities were universally lower than ICDP in all muscles, and decreased with old age in the WG and RG. Lipid hydroperoxides were significantly higher with aging in RG. Significant correlations were found between GPX and ICDP in all muscles. Stepwise regression resulted in a model (R(2)=0.82) that included ICDP and ME in predicting GPX. In summary, these data are consistent with the hypotheses that ICDP is higher in more oxidative fibers, inducible with aging, and most closely associated with the glutathione peroxidase system in skeletal muscle.