Truncated thioredoxin is a mitogenic cytokine for resting human peripheral blood mononuclear cells and is present in human plasma

Thiol Modifications in the Extracellular Space-Key Proteins in Inflammation and Viral Infection

Posttranslational modifications (PTMs) allow to control molecular and cellular functions in response to specific signals and changes in the microenvironment of cells. They regulate structure, localization, stability, and function of proteins in a spatial and temporal manner. Among them, specific thiol modifications of cysteine (Cys) residues facilitate rapid signal transduction. In fact, Cys is unique because it contains the highly reactive thiol group that can undergo different reversible and irreversible modifications. Upon inflammation and changes in the cellular microenvironment, many extracellular soluble and membrane proteins undergo thiol modifications, particularly dithiol-disulfide exchange, S-glutathionylation, and S-nitrosylation. Among others, these thiol switches are essential for inflammatory signaling, regulation of gene expression, cytokine release, immunoglobulin function and isoform variation, and antigen presentation. Interestingly, also the redox state of bacterial and viral proteins depends on host cell-mediated redox reactions that are critical for invasion and infection. Here, we highlight mechanistic thiol switches in inflammatory pathways and infections including cholera, diphtheria, hepatitis, human immunodeficiency virus (HIV), influenza, and coronavirus disease 2019 (COVID-19).

Serum Thioredoxin-80 is associated with age, ApoE4, and neuropathological biomarkers in Alzheimer's disease: a potential early sign of AD

Background

Thioredoxin-80 (Trx80) is a cleavage product from the redox-active protein Thioredoxin-1 and has been previously described as a pro-inflammatory cytokine secreted by immune cells. Previous studies in our group reported that Trx80 levels are depleted in Alzheimer’s disease (AD) brains. However, no studies so far have investigated peripheral Trx80 levels in the context of AD pathology and whether could be associated with the main known AD risk factors and biomarkers.

Methods

Trx80 was measured in serum samples from participants from two different cohorts: the observational memory clinic biobank (GEDOC) (N = 99) with AD CSF biomarker data was available and the population-based lifestyle multidomain intervention trial Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) (N = 47), with neuroimaging data and blood markers of inflammation available. The GEDOC cohort consists of participants diagnosed with subjective cognitive impairment (SCI), mild cognitive impairment (MCI), and AD, whereas the FINGER participants are older adults at-risk of dementia, but without substantial cognitive impairment. One-way ANOVA and multiple comparison tests were used to assess the levels of Trx80 between groups. Linear regression models were used to explore associations of Trx80 with cognition, AD CSF biomarkers (Aβ42, t-tau, p-tau and p-tau/t-tau ratio), inflammatory cytokines, and neuroimaging markers.

Results

In the GEDOC cohort, Trx80 was associated to p-tau/t-tau ratio in the MCI group. In the FINGER cohort, serum Trx80 levels correlated with lower hippocampal volume and higher pro-inflammatory cytokine levels. In both GEDOC and FINGER cohorts, ApoE4 carriers had significantly higher serum Trx80 levels compared to non-ApoE4 carriers. However, Trx80 levels in the brain were further decreased in AD patients with ApoE4 genotype.

Conclusion

We report that serum Trx80 levels are associated to AD disease stage as well as to several risk factors for AD such as age and ApoE4 genotype, which suggests that Trx80 could have potential as serum AD biomarker. Increased serum Trx80 and decreased brain Trx80 levels was particularly seen in ApoE4 carriers. Whether this could contribute to the mechanism by which ApoE4 show increased vulnerability to develop AD would need to be further investigated.

Trial registration

ClinicalTrials.govNCT01041989. Registered on 4 January 2010—retrospectively registered

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-00979-9.

Inflammation, Oxidative Stress, Senescence in Atherosclerosis: Thioredoxine-1 as an Emerging Therapeutic Target

Atherosclerosis is a leading cause of cardiovascular diseases (CVD) worldwide and intimately linked to aging. This pathology is characterized by chronic inflammation, oxidative stress, gradual accumulation of low-density lipoproteins (LDL) particles and fibrous elements in focal areas of large and medium arteries. These fibrofatty lesions in the artery wall become progressively unstable and thrombogenic leading to heart attack, stroke or other severe heart ischemic syndromes. Elevated blood levels of LDL are major triggering events for atherosclerosis. A cascade of molecular and cellular events results in the atherosclerotic plaque formation, evolution, and rupture. Moreover, the senescence of multiple cell types present in the vasculature were reported to contribute to atherosclerotic plaque progression and destabilization. Classical therapeutic interventions consist of lipid-lowering drugs, anti-inflammatory and life style dispositions. Moreover, targeting oxidative stress by developing innovative antioxidant agents or boosting antioxidant systems is also a well-established strategy. Accumulation of senescent cells (SC) is also another important feature of atherosclerosis and was detected in various models. Hence, targeting SCs appears as an emerging therapeutic option, since senolytic agents favorably disturb atherosclerotic plaques. In this review, we propose a survey of the impact of inflammation, oxidative stress, and senescence in atherosclerosis; and the emerging therapeutic options, including thioredoxin-based approaches such as anti-oxidant, anti-inflammatory, and anti-atherogenic strategy with promising potential of senomodulation.

Thioredoxin-80 protects against amyloid-beta pathology through autophagic-lysosomal pathway regulation

Aggregation and accumulation of amyloid beta (Aβ) are believed to play a key role in the pathogenesis of Alzheimer's disease (AD). We previously reported that Thioredoxin-80 (Trx80), a truncated form of Thioredoxin-1, prevents the toxic effects of Aβ and inhibits its aggregation in vitro. Trx80 levels were found to be dramatically reduced both in the human brain and cerebrospinal fluid of AD patients. In this study, we investigated the effect of Trx80 expression using in vivo and in vitro models of Aβ pathology. We developed Drosophila melanogaster models overexpressing either human Trx80, human Aβ₄₂, or both Aβ₄₂/Trx80 in the central nervous system. We found that Trx80 expression prevents Aβ₄₂ accumulation in the brain and rescues the reduction in life span and locomotor impairments seen in Aβ₄₂ expressing flies. Also, we show that Trx80 induces autophagosome formation and reverses the inhibition of Atg4b-Atg8a/b autophagosome formation pathway caused by Aβ₄₂. These effects were also confirmed in human neuroblastoma cells. These results give insight into Trx80 function in vivo, suggesting its role in the autophagosome biogenesis and thus in Aβ₄₂ degradation. Our findings put Trx80 on the spotlight as an endogenous agent against Aβ₄₂-induced toxicity in the brain suggesting that strategies to enhance Trx80 levels in neurons could potentially be beneficial against AD pathology in humans.

Thiol switches in membrane proteins - Extracellular redox regulation in cell biology

Redox-mediated signal transduction depends on the enzymatic production of second messengers such as hydrogen peroxide, nitric oxide and hydrogen sulfite, as well as specific, reversible redox modifications of cysteine-residues in proteins. So-called thiol switches induce for instance conformational changes in specific proteins that regulate cellular pathways e.g., cell metabolism, proliferation, migration, gene expression and inflammation. Reduction, oxidation and disulfide isomerization are controlled by oxidoreductases of the thioredoxin family, including thioredoxins, glutaredoxins, peroxiredoxins and protein dsisulfide isomerases. These proteins are located in different cellular compartments, interact with substrates and catalyze specific reactions. Interestingly, some of these proteins are released by cells. Their extracellular functions and generally extracellular redox control have been widely underestimated. Here, we give an insight into extracellular redox signaling, extracellular thiol switches and their regulation by secreted oxidoreductases and thiol-isomerases, a topic whose importance has been scarcely studied so far, likely due to methodological limitations. We focus on the secreted redox proteins and characterized thiol switches in the ectodomains of membrane proteins, such as integrins and the metalloprotease ADAM17, which are among the best-characterized proteins and discuss their underlying mechanisms and biological implications.

Paracrine regulation and improvement of β-cell function by thioredoxin

The failure of insulin-producing β-cells is the underlying cause of hyperglycemia in diabetes mellitus. β-cell decay has been linked to hypoxia, chronic inflammation, and oxidative stress. Thioredoxin (Trx) proteins are major actors in redox signaling and essential for signal transduction and the cellular stress response. We have analyzed the cytosolic, mitochondrial, and extracellular Trx system proteins in hypoxic and cytokine-induced stress using β-cell culture, isolated pancreatic islets, and pancreatic islet transplantation modelling low oxygen supply. Protein levels of cytosolic Trx1 and Trx reductase (TrxR) 1 significantly decreased, while mitochondrial Trx2 and TrxR2 increased upon hypoxia and reoxygenation. Interestingly, Trx1 was secreted by β-cells during hypoxia. Moreover, murine and human pancreatic islet grafts released Trx1 upon glucose stimulation. Survival of transplanted islets was substantially impaired by the TrxR inhibitor auranofin. Since a release was prominent upon hypoxia, putative paracrine effects of Trx1 on β-cells were examined. In fact, exogenously added recombinant hTrx1 mitigated apoptosis and preserved glucose sensitivity in pancreatic islets subjected to hypoxia and inflammatory stimuli, dependent on its redox activity. Human subjects were studied, demonstrating a transient increase in extracellular Trx1 in serum after glucose challenge. This increase correlated with better pancreatic islet function. Moreover, hTrx1 inhibited the migration of primary murine macrophages. In conclusion, our study offers evidence for paracrine functions of extracellular Trx1 that improve the survival and function of pancreatic β-cells.

The role of the thioredoxin/thioredoxin reductase system in the metabolic syndrome: towards a possible prognostic marker?

Mammalian thioredoxin reductase (TrxR) is a selenoprotein with three existing isoenzymes (TrxR1, TrxR2, and TrxR3), which is found primarily intracellularly but also in extracellular fluids. The main substrate thioredoxin (Trx) is similarly found (as Trx1 and Trx2) in various intracellular compartments, in blood plasma, and is the cell's major disulfide reductase. Thioredoxin reductase is necessary as a NADPH-dependent reducing agent in biochemical reactions involving Trx. Genetic and environmental factors like selenium status influence the activity of TrxR. Research shows that the Trx/TrxR system plays a significant role in the physiology of the adipose tissue, in carbohydrate metabolism, insulin production and sensitivity, blood pressure regulation, inflammation, chemotactic activity of macrophages, and atherogenesis. Based on recent research, it has been reported that the modulation of the Trx/TrxR system may be considered as a new target in the management of the metabolic syndrome, insulin resistance, and type 2 diabetes, as well as in the treatment of hypertension and atherosclerosis. In this review evidence about a possible role of this system as a marker of the metabolic syndrome is reported.

Thioredoxin 2 Offers Protection against Mitochondrial Oxidative Stress in H9c2 Cells and against Myocardial Hypertrophy Induced by Hyperglycemia

Mitochondrial oxidative stress is thought to be a key contributor towards the development of diabetic cardiomyopathy. Thioredoxin 2 (Trx2) is a mitochondrial antioxidant that, along with Trx reductase 2 (TrxR2) and peroxiredoxin 3 (Prx3), scavenges H₂O₂ and offers protection against oxidative stress. Our previous study showed that TrxR inhibitors resulted in Trx2 oxidation and increased ROS emission from mitochondria. In the present study, we observed that TrxR inhibition also impaired the contractile function of isolated heart. Our studies showed a decrease in the expression of Trx2 in the high glucose-treated H9c2 cardiac cells and myocardium of streptozotocin (STZ)-induced diabetic rats. Overexpression of Trx2 could significantly diminish high glucose-induced mitochondrial oxidative damage and improved ATP production in cultured H9c2 cells. Notably, Trx2 overexpression could suppress high glucose-induced atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) gene expression. Our studies suggest that high glucose-induced mitochondrial oxidative damage can be prevented by elevating Trx2 levels, thereby providing extensive protection to the diabetic heart.

Cell Signaling with Extracellular Thioredoxin and Thioredoxin-Like Proteins: Insight into Their Mechanisms of Action

Thioredoxins are small thiol-oxidoreductase enzymes that control cellular redox homeostasis. Paradoxically, human thioredoxin (TXN1) was first identified as the adult T cell leukemia-derived factor (ADF), a secreted protein. ADF has been implicated in a wide variety of cell-to-cell communication systems acting as a cytokine or a chemokine. TRX80 is a truncated TXN1 protein with cytokine activity. The unconventional secretion mechanism of these extracellular thioredoxins is unknown. The thioredoxin system is relying on glucose metabolism through the pentose phosphate pathway that provides reducing power in the form of NADPH, the cofactor of thioredoxin reductase (TXNRD). While a complete extracellular TXN system is present in the blood in the form of circulating TXN1 and TXNDR1, the source of extracellular NADPH remains a mystery. In the absence of redox regenerating capacity, extracellular thioredoxins may rather be prooxidant agents. Rod-derived cone viability factor (RdCVF) is the product of intron retention of the nucleoredoxin-like 1 (NXNL1) gene, a secreted truncated thioredoxin-like protein. The other product encoded by the gene, RdCVFL, is an enzymatically active thioredoxin. This is a very singular example of positive feedback of a superthioredoxin system encoded by a single gene likely emerging during evolution from metabolic constraints on redox signaling.

Human Plasma Thioredoxin-80 Increases With Age and in ApoE-/- Mice Induces Inflammation, Angiogenesis, and Atherosclerosis

BACKGROUND

Thioredoxin (TRX)-1, a ubiquitous 12-kDa protein, exerts antioxidant and anti-inflammatory effects. In contrast, the truncated form, called TRX80, produced by macrophages induces upregulation of proinflammatory cytokines. TRX80 also promotes the differentiation of mouse peritoneal and human macrophages toward a proinflammatory M1 phenotype.

METHODS

TRX1 and TRX80 plasma levels were determined with a specific ELISA. A disintegrin and metalloproteinase domain-containing protein (ADAM)-10, ADAM-17, and ADAM-10 activities were measured with SensoLyte 520 ADAM10 Activity Assay Kit, Fluorimetric, and InnoZyme TACE Activity Kit, respectively. Western immunoblots were performed with specific antibodies to ADAM-10 or ADAM-17. Angiogenesis study was evaluated in vitro with human microvascular endothelial cells-1 and in vivo with the Matrigel plug angiogenesis assay in mice. The expression of macrophage phenotype markers was investigated with real-time polymerase chain reaction. Phosphorylation of Akt, mechanistic target of rapamycin, and 70S6K was determined with specific antibodies. The effect of TRX80 on NLRP3 inflammasome activity was evaluated by measuring the level of interleukin-1β and -18 in the supernatants of activated macrophages with ELISA. Hearts were used for lesion surface evaluation and immunohistochemical studies, and whole descending aorta were stained with Oil Red O. For transgenic mice generation, the human scavenger receptor (SR-A) promoter/enhancer was used to drive macrophage-specific expression of human TRX80 in mice.

RESULTS

In this study, we observed a significant increase of plasma levels of TRX80 in old subjects compared with healthy young subjects. In parallel, an increase in expression and activity of ADAM-10 and ADAM-17 in old peripheral blood mononuclear cells compared with those of young subjects was observed. Furthermore, TRX80 was found to colocalize with tumor necrosis factor-α, a macrophage M1 marker, in human atherosclerotic plaque. In addition, TRX80 induced the expression of murine M1 macrophage markers through Akt2/mechanistic target of rapamycin-C1/70S6K pathway and activated the inflammasome NLRP3, leading to the release of interleukin-1β and -18, potent atherogenic cytokines. Moreover, TRX80 exerts a powerful angiogenic effect in both in vitro and in vivo mouse studies. Finally, transgenic mice that overexpress human TRX80 specifically in macrophages of apoE^-/- mice have a significant increase of aortic atherosclerotic lesions.

CONCLUSIONS

TRX80 showed an age-dependent increase in human plasma. In mouse models, TRX80 was associated with a proinflammatory status and increased atherosclerosis.

Truncated Escherichia coli thioredoxin induces proliferation of human blood mononuclear cells and production of reactive oxygen species as well as proinflammatory cytokines

Thioredoxin (Trx) is a redox protein characterized by a Trx fold. A naturally occurring truncated human Trx, Trx 80, which lacks the C-terminal strand-helix of the Trx fold, stimulates proliferation of peripheral blood mononuclear cells (PBMCs). It has not been clear how Trx80 gains this function. This study investigates whether a peptide with substantial sequence difference from Trx80, but retaining an abridged Trx fold can elicit PBMC proliferation. We genetically truncated a carboxy-terminal β-α motif of Escherichia coli Trx to produce a peptide, Trx83, which shares low sequence identity with human Trx80. Addition of reduced-form Trx83 to resting human PBMCs promoted cell proliferation, while oxidized-form Trx83 lacked the function. By contrast, oxidized-form Trx80 exhibited a high activity in promoting PBMC proliferation, indicating the importance of sequence context of an abridged thioredoxin in influencing PBMC proliferation. Trx83 increases cellular reactive oxygen species and proinflammatory cytokines TNF-α and IL-1β, suggesting that Trx83 modulates inflammatory pathways. This notion is supported by the observation that cystine or cysteine abolishes the Trx83 induced PBMC proliferation. The PBMC stimulatory activity of Trx83 may have potential for pharmacological developments.

SIGNIFICANCE OF THE STUDY

Elicitation of primary proliferative responses of PBMCs by a protein is generally difficult. We show that Escherichia coli Trx83 with a truncated Trx fold induces PBMC proliferation, but only in the disulfide-reduced form. In contrast, oxidized-form human Trx80 is a potent stimulator. These results demonstrate that the sequence context of an abridged Trx fold is influential in inducing PBMC proliferation. The stimulatory effect of Trx83 is associated with an increase of inflammatory response. The possibility of eliciting PBMC proliferation and switching this activity on/off by redox control provides a perspective for developing Trx83 as a PBMC stimulatory agent. Copyright © 2016 John Wiley & Sons, Ltd.

Thioredoxin-1/peroxiredoxin-1 as sensors of oxidative stress mediated by NADPH oxidase activity in atherosclerosis

To assess the potential association between TRX-1/PRX-1 and NADPH oxidase (Nox) activity in vivo and in vitro, TRX-1/PRX-1 levels were assessed by ELISA in 84 asymptomatic subjects with known phagocytic NADPH oxidase activity and carotid intima-media thickness (IMT). We found a positive correlation between TRX-1/PRX-1 and NADPH oxidase-dependent superoxide production (r=0.48 and 0.47; p<0.001 for both) and IMT (r=0.31 and 0.36; p<0.01 for both) adjusted by age and sex. Moreover, asymptomatic subjects with plaques have higher PRX-1 and TRX plasma levels (p<0.01 for both). These data were confirmed in a second study in which patients with carotid atherosclerosis showed higher PRX-1 and TRX plasma levels than healthy subjects (p<0.001 for both). In human atherosclerotic plaques, the NADPH oxidase subunit p22phox colocalized with TRX-1/PRX-1 in macrophages (immunohistochemistry). In monocytes and macrophages, phorbol 12-myristate 13-acetate (PMA) induced NADPH activation and TRX-1/PRX-1 release to the extracellular medium, with a concomitant decrease in their intracellular levels, which was reversed by the NADPH inhibitor apocynin (Western blot). In loss-of-function experiments, genetic silencing of the NADPH oxidase subunit Nox2 blocked PMA-induced intracellular TRX-1/PRX-1 downregulation in macrophages. Furthermore, the PMA-induced release of TRX-1/PRX-1 involves the modulation of their redox status and exosome-like vesicles. TRX-1/PRX-1 levels are associated with NADPH oxidase-activity in vivo and in vitro. These data could suggest a coordinated antioxidant response to oxidative stress in atherothrombosis.

Thioredoxin and hematologic malignancies

Thioredoxin (Trx) is an inflammation-inducible small oxidoreductase protein ubiquitously expressed in all organisms. Trx acts both intracellularly and extracellularly and is involved in a wide range of physiological cellular responses. Inside the cell, Trx alleviates oxidative stress by scavenging reactive oxygen species (ROS), regulates a variety of redox-sensitive signaling pathways as well as ROS-independent genes, and exerts cytoprotective effects. Outside the cell, Trx acts as growth factors or cytokines and promotes cell growth and many other cellular responses. Trx is also implicated in tumorigenesis. Trx is a proto-oncogene and is overexpressed in many cancers and correlates with poor prognosis. Trx stimulates cancer cell survival, promotes tumor angiogenesis, and inhibits both spontaneous apoptosis and drug-induced apoptosis. Inhibitors targeting Trx pathway provide a promising therapeutic strategy for cancer prevention and intervention. More recently, data from our laboratory demonstrate an important role of Trx in expanding long-term repopulating hematopoietic stem cells. In this chapter, we first provide an overview of Trx including its isoforms, compartmentation, and functions. We then discuss the roles of Trx in hematologic malignancies. Finally, we summarize the most recent findings from our lab on the use of Trx to enhance hematopoietic reconstitution following hematopoietic stem cell transplantation.

Protective effects of the thioredoxin and glutaredoxin systems in dopamine-induced cell death

Although the etiology of sporadic Parkinson disease (PD) is unknown, it is well established that oxidative stress plays an important role in the pathogenic mechanism. The thioredoxin (Trx) and glutaredoxin (Grx) systems are two central systems upholding the sulfhydryl homeostasis by reducing disulfides and mixed disulfides within the cell and thereby protecting against oxidative stress. By examining the expression of redox proteins in human postmortem PD brains, we found the levels of Trx1 and thioredoxin reductase 1 (TrxR1) to be significantly decreased. The human neuroblastoma cell line SH-SY5Y and the nematode Caenorhabditis elegans were used as model systems to explore the potential protective effects of the redox proteins against 6-hydroxydopamine (6-OHDA)-induced cytotoxicity. 6-OHDA is highly prone to oxidation, resulting in the formation of the quinone of 6-OHDA, a highly reactive species and powerful neurotoxin. Treatment of human cells with 6-OHDA resulted in an increased expression of Trx1, TrxR1, Grx1, and Grx2, and small interfering RNA for these genes significantly increased the cytotoxic effects exerted by the 6-OHDA neurotoxin. Evaluation of the dopaminergic neurons in C. elegans revealed that nematodes lacking trxr-1 were significantly more sensitive to 6-OHDA, with significantly increased neuronal degradation. Importantly, both the Trx and the Grx systems were also found to directly mediate reduction of the 6-OHDA-quinone in vitro and thus render its cytotoxic effects. In conclusion, our results suggest that the two redox systems are important for neuronal survival in dopamine-induced cell death.

CsTrx80, a truncated form of thioredoxin, possesses chemokine-like property and enhances the immune defense of Cynoglossus semilaevis against bacterial infection

Thioredoxin (Trx) is a redox protein that plays an important role in anti-oxidative stress and redox signaling. In a recent report, we observed that the Trx of tongue sole (Cynoglossus semilaevis), CsTrx1, is a reductase and an antioxidant with immunostimulatory property. In the current work, we studied the biological effect of a truncated CsTrx1, CsTrx80, which is composed of the N-terminal 80 residues of CsTrx1. We found that recombinant CsTrx80 (rCsTrx80) purified from Escherichia coli exhibited no insulin disulfide reductase activity; however, unlike rCsTrx1, which showed no apparent chemotactic activity, rCsTrx80 was able to bind to the head kidney monocytes of tongue sole and caused cellular migration in a dose-dependent manner. Mutation of the two cysteine residues in the highly conserved CXXC motif had no effect on the chemotactic activity of rCsTrx80. Like rCsTrx1, rCsTrx80 induced the expression of immune relevant genes in the target cells, but the induction patterns differed from that induced by rCsTrx1. In vivo study showed that when tongue sole were administered with rCsTrx80 before being infected with a bacterial pathogen, bacterial dissemination and colonization in fish tissues were significantly reduced compared to control fish. Taken together, these results indicate for the first time that a Trx80 derived from fish Trx possesses chemotactic and immunoregulatory properties which promote host resistance against bacterial infection.

Truncated thioredoxin (Trx-80) promotes pro-inflammatory macrophages of the M1 phenotype and enhances atherosclerosis

Vascular cells are particularly susceptible to oxidative stress that is believed to play a key role in the pathogenesis of cardiovascular disorders. Thioredoxin-1 (Trx-1) is an oxidative stress-limiting protein with anti-inflammatory and anti-apoptotic properties. In contrast, its truncated form (Trx-80) exerts pro-inflammatory effects. Here we analyzed whether Trx-80 might exert atherogenic effects by promoting macrophage differentiation into the M1 pro-inflammatory phenotype. Trx-80 at 1 µg/ml significantly attenuated the polarization of anti-inflammatory M2 macrophages induced by exposure to either IL-4 at 15 ng/ml or IL-4/IL-13 (10 ng/ml each) in vitro, as evidenced by the expression of the characteristic markers, CD206 and IL-10. By contrast, in LPS-challenged macrophages, Trx-80 significantly potentiated the differentiation into inflammatory M1 macrophages as indicated by the expression of the M1 cytokines, TNF-α and MCP-1. When Trx-80 was administered to hyperlipoproteinemic ApoE2.Ki mice at 30 µg/g body weight (b.w.) challenged either with LPS at 30 µg/30 g (b.w.) or IL-4 at 500 ng/30 g (b.w.), it significantly induced the M1 phenotype but inhibited differentiation of M2 macrophages in thymus and liver. When ApoE2.Ki mice were challenged once weekly with LPS for 5 weeks, they showed severe atherosclerotic lesions enriched with macrophages expressing predominantly M1 over M2 markers. Such effect was potentiated when mice received daily, in addition to LPS, the Trx-80. Moreover, the Trx-80 treatment led to a significantly increased aortic lesion area. The ability of Trx-80 to promote differentiation of macrophages into the classical proinflammatory phenotype may explain its atherogenic effects in cardiovascular diseases.

Thioredoxins, glutaredoxins, and peroxiredoxins--molecular mechanisms and health significance: from cofactors to antioxidants to redox signaling

Thioredoxins (Trxs), glutaredoxins (Grxs), and peroxiredoxins (Prxs) have been characterized as electron donors, guards of the intracellular redox state, and "antioxidants". Today, these redox catalysts are increasingly recognized for their specific role in redox signaling. The number of publications published on the functions of these proteins continues to increase exponentially. The field is experiencing an exciting transformation, from looking at a general redox homeostasis and the pathological oxidative stress model to realizing redox changes as a part of localized, rapid, specific, and reversible redox-regulated signaling events. This review summarizes the almost 50 years of research on these proteins, focusing primarily on data from vertebrates and mammals. The role of Trx fold proteins in redox signaling is discussed by looking at reaction mechanisms, reversible oxidative post-translational modifications of proteins, and characterized interaction partners. On the basis of this analysis, the specific regulatory functions are exemplified for the cellular processes of apoptosis, proliferation, and iron metabolism. The importance of Trxs, Grxs, and Prxs for human health is addressed in the second part of this review, that is, their potential impact and functions in different cell types, tissues, and various pathological conditions.

The thioredoxin system as a therapeutic target in human health and disease

The thioredoxin (Trx) system comprises Trx, truncated Trx (Trx-80), Trx reductase, and NADPH, besides a natural Trx inhibitor, the thioredoxin-interacting protein (TXNIP). This system is essential for maintaining the balance of the cellular redox status, and it is involved in the regulation of redox signaling. It is also pivotal for growth promotion, neuroprotection, inflammatory modulation, antiapoptosis, immune function, and atherosclerosis. As an ubiquitous and multifunctional protein, Trx is expressed in all forms of life, executing its function through its antioxidative, protein-reducing, and signal-transducing activities. In this review, the biological properties of the Trx system are highlighted, and its implications in several human diseases are discussed, including cardiovascular diseases, heart failure, stroke, inflammation, metabolic syndrome, neurodegenerative diseases, arthritis, and cancer. The last chapter addresses the emerging therapeutic approaches targeting the Trx system in human diseases.

Thioredoxin-80 is a product of alpha-secretase cleavage that inhibits amyloid-beta aggregation and is decreased in Alzheimer's disease brain

Thioredoxin-1 (Trx1) is an endogenous dithiol reductant and antioxidant that was shown to be decreased in Alzheimer's disease (AD) neurons. A truncated form of Trx1, thioredoxin 80 (Trx80), was reported to be secreted from monocytes having cytokine activity. Here, we show that Trx80 is present in human brain in an aggregated form. Trx80 localizes mainly to neurons and is dramatically decreased in AD brains. Trx80 levels in cerebrospinal fluid (CSF) correlate with those of the classical AD biomarkers amyloid-β (Aβ) 1-42 and total tau. Moreover, Trx80 measurements in CSF discriminate between patients with stable mild cognitive impairment, prodomal AD and mild AD. We report that ADAM10 and 17, two α-secretases processing the Aβ precursor protein, are responsible for Trx80 generation. In contrast to the periphery, Trx80 has no pro-inflammatory effects in glia, either by itself or in combination with Aβ or apolipoprotein E. Instead, Trx80 inhibits Aβ(1-42) aggregation and protects against its toxicity. Thus, a reduction in Trx80 production would result in increased Aβ polymerization and enhanced neuronal vulnerability. Our data suggest that a deficit in Trx80 could participate in AD pathogenesis.

Cell stress proteins in atherothrombosis

Cell stress proteins (CSPs) are a large and heterogenous family of proteins, sharing two main characteristics: their levels and/or location are modified under stress and most of them can exert a chaperon function inside the cells. Nonetheless, they are also involved in the modulation of several mechanisms, both at the intracellular and the extracellular compartments. There are more than 100 proteins belonging to the CSPs family, among them the thioredoxin (TRX) system, which is the focus of the present paper. TRX system is composed of several proteins such as TRX and peroxiredoxin (PRDX), two thiol-containing enzymes that are key players in redox homeostasis due to their ability to scavenge potential harmful reactive oxygen species. In addition to their main role as antioxidants, recent data highlights their function in several processes such as cell signalling, immune inflammatory responses, or apoptosis, all of them key mechanisms involved in atherothrombosis. Moreover, since TRX and PRDX are present in the pathological vascular wall and can be secreted under prooxidative conditions to the circulation, several studies have addressed their role as diagnostic, prognostic, and therapeutic biomarkers of cardiovascular diseases (CVDs).

Truncated and full-length thioredoxin-1 have opposing activating and inhibitory properties for human complement with relevance to endothelial surfaces

Thioredoxin (Trx)-1 is a small, ubiquitously expressed redox-active protein with known important cytosolic functions. However, Trx1 is also upregulated in response to various stress stimuli, is found both at the cell surface and secreted into plasma, and has known anti-inflammatory and antiapoptotic properties. Previous animal studies have demonstrated that exogenous Trx1 delivery can have therapeutic effects in a number of disease models and have implicated an interaction of Trx1 with the complement system. We found that Trx1 is expressed in a redox-active form at the surface of HUVEC and acts as an inhibitor of complement deposition in a manner dependent on its Cys-Gly-Pro-Cys active site. Inhibition occurred at the point of the C5 convertase of complement, regulating production of C5a and the membrane attack complex. A truncated form of Trx1 also exists in vivo, Trx80, which has separate nonoverlapping functions compared with the full-length Trx1. We found that Trx80 activates the classical and alternative pathways of complement activation, leading to C5a production, but the inflammatory potential of this was also limited by the binding of inhibitors C4b-binding protein and factor H. This study adds a further role to the known anti-inflammatory properties of Trx1 and highlights the difference in function between the full-length and truncated forms.

Role of thioredoxin in lung disease

Thioredoxin system is a ubiquitous thiol oxidoreductase system that regulates cellular reduction/oxidation (redox) status. It includes thioredoxin (Trx), thioredoxin reductase (TrxR), and NADPH. Trx plays an essential role in cell function by limiting oxidative stress directly via antioxidant effects and indirectly by proteins interaction with key signal transduction molecules. A variety of signaling molecules have been implicated in the cytoprotection conferred by Trx, such as autophagic proteins, p38 mitogen-activated protein kinase, nuclear factor-κB, phosphatidylinositol 3-kinase. Recent studies indicated that Trx may contribute to the pathogenesis of COPD, asthma and lung injury. Enhanced Trx expression or application of recombinant Trx afforded protection in preclinical models of pulmonary tissue injury, which suggested Trx may be used in future therapeutic applications. The focus of this review is on the significance of Trx in various pulmonary diseases, which as a potential therapeutic strategy to protect against oxidative stress and inflammation.

Alleviation of oxidative stress by potent and selective thioredoxin-mimetic peptides

One of the major enzymatic cell defenses providing protection from oxidative injury is the TrxR-Trx system. It consists of NADPH and thioredoxin reductase (TrxR), which maintain thioredoxin (Trx) in a reduced state. Perturbing the TrxR-Trx system with the selective TrxR inhibitor auranofin (AuF; 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranosato-S-(triethylphosphine) gold) induces oxidative stress by keeping Trx in its oxidized state. We have prepared a family of tri- and tetra-oligopeptides derived from the canonical CxxC motif of the Trx active site and a modified CxC motif. These Trx-mimetic compounds are N- and C-terminal-blocked peptides that consist of two cysteine residues that flank the two-amino-acid CxxC motif (CB4 and CB6) or the single-amino-acid CxC motif (CB3). Catecholamine (CA) secretion in bovine chromaffin cells, which is a highly redox sensitive process, is abolished by AuF. The Trx-mimetic peptides effectively restore CA secretion, as monitored by amperometry in single cells. They also prevent the AuF-induced phosphorylation of p38 mitogen-activated protein kinase (MAPK) and c-Jun NH2-terminal kinase. In PC12 cells, the alleviation of AuF-induced ERK1/2-MAPK phosphorylation by Trx-like peptides parallels their effect of restoring CA secretion. CB3, CB4, and CB6 act intracellularly and are significantly more potent than the traditional antioxidants NAC, GSH, DTT, AD4 (NAC-amide), and ascorbic acid. Taken together, the CxxC and CxC peptides represent a new family of potent and selective redox compounds that could serve as potential candidates for prevention and treatment of oxidative-stress-related disorders.

Thioredoxin 80-activated-monocytes (TAMs) inhibit the replication of intracellular pathogens

Background

Thioredoxin 80 (Trx80) is an 80 amino acid natural cleavage product of Trx, produced primarily by monocytes. Trx80 induces differentiation of human monocytes into a novel cell type, named Trx80-activated-monocytes (TAMs).

Principal Findings

In this investigation we present evidence for a role of TAMs in the control of intracellular bacterial infections. As model pathogens we have chosen Listeria monocytogenes and Brucella abortus which replicate in the cytosol and the endoplasmic reticulum respectively. Our data indicate that TAMs efficiently inhibit intracellular growth of both L. monocytogenes and B. abortus. Further analysis shows that Trx80 activation prevents the escape of GFP-tagged L. monocytogenes into the cytosol, and induces accumulation of the bacteria within the lysosomes. Inhibition of the lysosomal activity by chloroquine treatment resulted in higher replication of bacteria in TAMs compared to that observed in control cells 24 h post-infection, indicating that TAMs kill bacteria by preventing their escape from the endosomal compartments, which progress into a highly degradative phagolysosome.

Significance

Our results show that Trx80 potentiates the bactericidal activities of professional phagocytes, and contributes to the first line of defense against intracellular bacteria.

Extracellular/microenvironmental redox state

Extracellular redox (reduction-oxidation) state is a factor that serves as an important regulator of cell-microenvironmental interactions and is determined by several known variables; including redox-modulating proteins that are located on the plasma membrane or outside of cells, extracellular thiol/disulfide couples, and reactive oxygen species (ROS)/reactive nitrogen species (RNS) that are capable of traveling across plasma membranes into the extracellular space. The extracellular redox state works in concert with the intracellular redox state to control both the influx and efflux of ROS/RNS that may serve to modulate redox signaling or to perturb normal cellular processes or both. Under physiologic conditions, the extracellular space is known to have a relatively more-oxidized redox state than the interior of the cell. During pathologic conditions, such as cancer, the extracellular redox state may be altered, causing specific proteins such as proteases, soluble factors, or the extracellular matrix to have altered functions or activities. Recent studies have strongly supported an important relation between the extracellular redox state and cancer cell aggressiveness. The purpose of this review is to identify redox buffer networks in extracellular spaces and to emphasize the possible roles of the extracellular redox state in cancer, knowledge that may contribute to potential therapeutic interventions.

Redox atlas of the mouse. Immunohistochemical detection of glutaredoxin-, peroxiredoxin-, and thioredoxin-family proteins in various tissues of the laboratory mouse

BACKGROUND

Oxidoreductases of the thioredoxin family of proteins have been thoroughly studied in numerous cellular and animal models mimicking human diseases. Despite of their well documented role in various disease conditions, no systematic information on the presence of these proteins is available.

METHODS

Here, we have systematically analyzed the presence of some of the major constituents of the glutaredoxin (Grx)-, peroxiredoxin (Prx)-, and thioredoxin (Trx)-systems, i.e. Grx1, Grx2, Grx3 (TXNL-2/PICOT), Grx5, nucleoredoxin (Nrx), Prx1, Prx2, Prx3, Prx4, Prx5, Prx6, Trx1, thioredoxin reductase 1 (TrxR1), Trx2, TrxR2, and γ-glutamyl cysteine synthetase (γ-GCS) in various tissues of the mouse using immunohistochemistry.

RESULTS

The identification of the Trx family proteins in the central nervous system, sensory organs, digestive system, lymphatic system, reproductive system, urinary system, respiratory system, endocrine system, skin, heart, and muscle revealed a number of significant differences between these proteins with respect to their distribution in these tissues.

CONCLUSION

Our results imply more specific functions and interactions between the proteins of this family than previously assumed.

GENERAL SIGNIFICANCE

Crucial functions of Trx family proteins have been demonstrated in various disease conditions. A detailed overview on their distribution in various tissues will be helpful to fully comprehend their potential role and the interactions of these proteins in the most thoroughly studied model for human diseases-the laboratory mouse. This article is part of a Special Issue entitled Human and Murine Redox Protein Atlases.

Molecular chaperones and protein-folding catalysts as intercellular signaling regulators in immunity and inflammation

This review critically examines the hypothesis that molecular chaperones and protein-folding catalysts from prokaryotes and eukaryotes can be secreted by cells and function as intercellular signals, principally but not exclusively, for leukocytes. A growing number of molecular chaperones have been reported to function as ligands for selected receptors and/or receptors for specific ligands. Molecular chaperones initially appeared to act primarily as stimulatory signals for leukocytes and thus, were seen as proinflammatory mediators. However, evidence is now emerging that molecular chaperones can have anti-inflammatory actions or, depending on the protein and concentration, anti- and proinflammatory functions. Recasting the original hypothesis, we propose that molecular chaperones and protein-folding catalysts are "moonlighting" proteins that function as homeostatic immune regulators but may also under certain circumstances, contribute to tissue pathology. One of the key issues in the field of molecular chaperone biology relates to the role of microbial contaminants in their signaling activity; this too will be evaluated critically. The most fascinating aspect of molecular chaperones probably relates to evidence for their therapeutic potential in human disease, and ongoing studies are evaluating this potential in a range of clinical settings.

Thioredoxins and glutaredoxins: unifying elements in redox biology

Since their discovery as a substrate for ribonucleotide reductase (RNR), the role of thioredoxin (Trx) and glutaredoxin (Grx) has been largely extended through their regulatory function. Both proteins act by changing the structure and activity of a broad spectrum of target proteins, typically by modifying redox status. Trx and Grx are members of families with multiple and partially redundant genes. The number of genes clearly increased with the appearance of multicellular organisms, in part because of new types of Trx and Grx with orthologs throughout the animal and plant kingdoms. The function of Trx and Grx also broadened as cells achieved increased complexity, especially in the regulation arena. In view of these progressive changes, the ubiquitous distribution of Trx and the wide occurrence of Grx enable these proteins to serve as indicators of the evolutionary history of redox regulation. In so doing, they add a unifying element that links the diverse forms of life to one another in an uninterrupted continuum. It is anticipated that future research will embellish this continuum and further elucidate the properties of these proteins and their impact on biology. The new information will be important not only to our understanding of the role of Trx and Grx in fundamental cell processes but also to future societal benefits as the proteins find new applications in a range of fields.

Thioredoxin reduces C-C chemokine-induced chemotaxis of human eosinophils

BACKGROUND

Human thioredoxin (TRX) is one of redox-active proteins that regulate reactive oxidative metabolisms. In recent study, we found that serum levels of TRX were elevated in asthmatic patients with exacerbation; however, few details are known about the physiological role of TRX in allergic inflammation, involving eosinophil infiltration.

OBJECTIVE

In the present study, we examined whether TRX modulated C-C chemokine-induced chemotaxis of human eosinophils.

METHODS

Eosinophils were isolated from subjects with mild eosinophilia by modified CD16 negative selection. After incubation with or without recombinant TRX, chemotaxis of human eosinophils was measured using Boyden chamber.

RESULTS

Preincubation with TRX suppressed eotaxin- and regulated on activation, normal T-cell expressed and secreted (RANTES)-induced chemotaxis of eosinophils. Although, TRX had no effect on the expression of C-C chemokine receptor 3, which is a receptor of eotaxin and RANTES, we demonstrated that the activation of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinases, which play an important role in eosinophil migration, was attenuated by the treatment with TRX.

CONCLUSION

Our results suggest that the elicited TRX is beneficial to reduce allergic inflammation through negative regulation of eosinophil functions and has potential in the treatment of allergic diseases, such as asthma.

Thioredoxin-1 and endothelial cell aging: role in cardiovascular diseases

The thioredoxin-1 (Trx-1) system consists of two oxidoreductases, thioredoxin reductase and Trx-1. Trx-1 is a ubiquitously expressed oxidoreductase. The cellular functions of Trx-1 are wide range. They include protein disulfide reduction, DNA synthesis, protection from apoptosis, redox regulation of a variety of proteins, transcription factors and reduction of H(2)O(2), respectively. This review will first focus on the essential role for Trx-1 in different cardiovascular cells, namely smooth muscle cells, endothelial cells, and cardiomyocytes. Thereby, the review will demonstrate the predominant role of Trx-1 to limit oxidative stress directly due to reactive oxygen species scavenging and by protein-protein interaction with key signaling molecules. Second, this review will highlight the role of Trx-1 in cardiovascular aging, focusing on its importance on shear stress and the profound changes with age. Finally, the review will focus on important in vivo studies showing a protective role of Trx-1 in different cardiovascular diseases. Thus, the Trx system and Trx-1 could be important future targets to develop clinical therapies for cardiovascular disorders.

Phenotype-dependent apoptosis signalling in mesothelioma cells after selenite exposure

Background

Selenite is a promising anticancer agent which has been shown to induce apoptosis in malignant mesothelioma cells in a phenotype-dependent manner, where cells of the chemoresistant sarcomatoid phenotype are more sensitive.

Methods

In this paper, we investigate the apoptosis signalling mechanisms in sarcomatoid and epithelioid mesothelioma cells after selenite treatment. Apoptosis was measured with the Annexin-PI assay. The mitochondrial membrane potential, the expression of Bax, Bcl-XL, and the activation of caspase-3 were assayed with flow cytometry and a cytokeratin 18 cleavage assay. Signalling through JNK, p38, p53, and cathepsins B, D, and E was investigated with chemical inhibitors. Furthermore, the expression, nuclear translocation and DNA-binding activity of p53 was investigated using ICC, EMSA and the monitoring of p21 expression as a downstream event. Levels of thioredoxin (Trx) were measured by ELISA.

Results

In both cell lines, 10 μM selenite caused apoptosis and a marked loss of mitochondrial membrane potential. Bax was up-regulated only in the sarcomatoid cell line, while the epithelioid cell line down-regulated Bcl-XL and showed greater caspase-3 activation. Nuclear translocation of p53 was seen in both cell lines, but very little p21 expression was induced. Chemical inhibition of p53 did not protect the cells from apoptosis. p53 lost its DNA binding ability after selenite treatment and was enriched in an inactive form. Levels of thioredoxin decreased after selenite treatment. Chemical inhibition of MAP kinases and cathepsins showed that p38 and cathepsin B had some mediatory effect while JNK had an anti-apoptotic role.

Conclusion

We delineate pathways of apoptosis signalling in response to selenite, showing differences between epithelioid and sarcomatoid mesothelioma cells. These differences may partly explain why sarcomatoid cells are more sensitive to selenite.

Identification of human thioredoxin as a novel IFN-gamma-induced factor: mechanism of induction and its role in cytokine production

Background

IFN-γ is a multifunctional peptide with a potent immune defense function which is also known as a prototypic Th1 cytokine. While screening for genes differentially expressed by Th1 and Th2 cytokines, human thioredoxin was identified as a novel target gene induced by IFN-γ. The mechanism by which thioredoxin is induced by IFN-γ and the signaling pathways involved in its induction were analyzed. In addition, the effects of thioredoxin on immune cell survival and cytokine production were examined by thioredoxin over-expression and recombinant thioredoxin treatment.

Results

Human thioredoxin was selectively induced by IFN-γ in monocytic and T cell lines. In monocytic cells, the induction of thioredoxin gene expression by IFN-γ was dose-dependent, and both the mRNA and protein levels were increased by 2~3 fold within 4 to 24 h hours of IFN-γ treatment. The thioredoxin induction by IFN-γ was insensitive to cycloheximide treatment, suggesting that it is a primary response gene induced by IFN-γ. Subsequent analysis of the signaling pathways indicated that the Jak/Stat, Akt, and Erk pathways play a role in IFN-γ signaling that leads to thioredoxin gene expression. Thioredoxin was induced by oxidative or radiation stresses, and it protected the immune cells from apoptosis by reducing the levels of reactive oxygen species. Furthermore, thioredoxin modulated the oxidant-induced cytokine balance toward Th1 by counter-regulating the production of IL-4 and IFN-γ in T cells.

Conclusion

These data suggest that thioredoxin is an IFN-γ-induced factor that may play a role in developing Th1 immunity and in the maintenance of immune homeostasis upon infection, radiation, and oxidative stress.

Discovery, identification, and characterization of candidate pharmacodynamic markers of methionine aminopeptidase-2 inhibition

The catalytic activity of methionine aminopeptidase-2 (MetAP2) has been pharmacologically linked to cell growth, angiogenesis, and tumor progression, making this an attractive target for cancer therapy. An assay for monitoring specific protein changes in response to MetAP2 inhibition, allowing pharmacokinetic (PK)/pharmacodynamic (PD) models to be established, could dramatically improve clinical decision-making. Candidate MetAP2-specific protein substrates were discovered from undigested cell culture-derived proteomes by MALDI-/SELDI-MS profiling and a biochemical method using (35)S-Met labeled protein lysates. Substrates were identified either as intact proteins by FT-ICR-MS or applying in-gel protease digestions followed by LC-MS/MS. The combination of these approaches led to the discovery of novel MetAP2-specific substrates including thioredoxin-1 (Trx-1), SH3 binding glutamic acid rich-like protein (SH3BGRL), and eukaryotic elongation factor-2 (eEF2). These studies also confirmed glyceraldehye 3-phosphate dehydrogenase (GAPDH) and cyclophillin A (CypA) as MetAP2 substrates. Additional data in support of these proteins as MetAP2-specific substrates were provided by in vitro MetAP1/MetAP2 enzyme assays with the corresponding N-terminal derived peptides and 1D/2D Western analyses of cellular and tissue lysates. FT-ICR-MS characterization of all intact species of the 18 kDa substrate, CypA, enabled a SELDI-MS cell-based assay to be developed for correlating N-terminal processing and inhibition of proliferation. The MetAP2-specific protein substrates discovered in this study have diverse properties that should facilitate the development of reagents for testing in preclinical and clinical environments.

Redox regulation in the extracellular environment

The oxidizing nature of the extracellular environment is vastly different from the highly reducing nature of the intracellular compartment. The redox potential of the cytosolic compartment of the intracellular environment limits disulfide bond formation, whereas the oxidizing extracellular environment contains proteins rich in disulfide bonds. If not for an extracellular antioxidant system to eliminate reactive oxygen and nitrogen species, lipid peroxidation and protein oxidation would become excessive, resulting in cellular damage. Many reviews have focused on the role of intracellular antioxidants in the elimination of oxidative stress, but this one will focus on the coordinated action of both intracellular and extracellular antioxidants in limiting cellular oxidant stress.

Leukotriene B4 activates T cells that inhibit B-cell proliferation in EBV-infected cord blood–derived mononuclear cell cultures

Epstein-Barr virus (EBV)–specific cellular memory is not transferred from mother to child. Therefore, EBV-induced B-cell proliferation in in vitro–infected cord blood mononuclear cell cultures is not inhibited. However, by addition of immunomodulators, polysaccharide K (PSK) or truncated thioredoxin (Trx80) that activate monocytes, EBV-specific T-cell response could be generated in such cultures. Presently, we demonstrate that leukotriene B4 (LTB4) is involved in the effect of the immunomodulators. LTB4 was detected in the medium, and T-cell activation was compromised by addition of leukotriene biosynthesis inhibitors. Moreover, we found that LTB4 added to infected cultures, which did not receive the immunomodulators, induced functional activation of the T cells. LTB4 activated the monocytes and acted directly on the T cells. In consequence, addition of LTB4 inhibited the EBV-induced proliferation of B lymphocytes. Specific cytotoxicity could be generated by restimulation of the T cells. The experiments showed successive stages of T-cell activation in acquisition of their immunologic effector function. This is orchestrated by complex cellular interactions, and autocrine loops mediated by soluble factors—here interferon (IFN)-γ, interleukin (IL)-15, IL-12, and LTB4. Importantly, the results indicate that endogenous LTB4 can induce T-cell activation that inhibits the EBV-induced proliferation of B lymphocytes.

Emerging potential of thioredoxin and thioredoxin interacting proteins in various disease conditions

Reactive oxygen species (ROS) are known to be mediators of intracellular signaling pathways. However the excessive production of ROS may be detrimental to the cell as a result of the increased oxidative stress and loss of cell function. Hence, well tuned, balanced and responsive antioxidant systems are vital for proper regulation of the redox status of the cell. The cells are normally able to defend themselves against the oxidative stress induced damage through the use of several antioxidant systems. Even though the free radical scavenging enzymes such as superoxide dismutase (SOD) and catalase can handle huge amounts of reactive oxygen species, should these systems fail some reactive molecules will evade the detoxification process and damage potential targets. In such a scenario, cells recruit certain small molecules and proteins as 'rescue specialists' in case the 'bodyguards' fail to protect potential targets from oxidative damage. The thioredoxin (Trx) system thus plays a vital role in the maintenance of a reduced intracellular redox state which is essential for the proper functioning of each individual cell. Trx alterations have been implicated in many diseases such as cataract formation, ischemic heart diseases, cancers, AIDS, complications of diabetes, hypertension etc. The interactions of Trx with many different proteins and different metabolic and signaling pathways as well as the significant species differences make it an attractive target for therapeutic intervention in many fields of medical science. In this review, we present, the critical roles that thioredoxins play in limiting oxidant stress through either its direct effect as an antioxidant or through its interactions with other key signaling proteins (thioredoxin interacting proteins) and its implications in various disease models.

Induction of IFN-gamma gene expression by thioredoxin: positive feed-back regulation of Th1 response by thioredoxin and IFN-gamma

T cell differentiation, which leads to the generation of Th cells with a characteristic cytokine expression pattern, is regulated by diverse factors. In addition to the cytokine environment, the cellular redox status often serves as an important factor in survival and differentiation of Th cells. Thioredoxin, an intracellular redox sensor protein, has been suggested in the induction of Th1 response through the production of IL-12 by monocytes. Here we report that thioredoxin expression is up-regulated by IFN-gamma and other Th1 type cytokines in human primary immune cells, and that the overexpression of thioredoxin resulted in a specific increase in the mRNA level and promoter activity of IFN-gamma in mitogen-stimulated Jurkat T cells. Using the active site mutant (C32S/C35S) of thioredoxin, we demonstrate that such IFN-gamma-inducing capacity of thioredoxin is dependent on the redox-sensing activity of thioredoxin and involves the activation of transcription factors such as NF-kappaB and Stat1. Together, the results of the present study suggest that thioredoxin is a direct stimulator of IFN-gamma gene expression in human T cells and that there is a positive feed-back circuit by IFN-gamma and thioredoxin in the regulation of Th1 immune response.

Rod-derived Cone Viability Factor-2 is a novel bifunctional-thioredoxin-like protein with therapeutic potential

Background

Cone degeneration is the hallmark of the inherited retinal disease retinitis pigmentosa. We have previously identified a trophic factor "Rod-derived Cone Viability Factor (RdCVF) that is secreted by rods and promote cone viability in a mouse model of the disease.

Results

Here we report the bioinformatic identification and the experimental analysis of RdCVF2, a second trophic factor belonging to the Rod-derived Cone Viability Factor family. The mouse RdCVF gene is known to be bifunctional, encoding both a long thioredoxin-like isoform (RdCVF-L) and a short isoform with trophic cone photoreceptor viability activity (RdCVF-S). RdCVF2 shares many similarities with RdCVF in terms of gene structure, expression in a rod-dependent manner and protein 3D structure. Furthermore, like RdCVF, the RdCVF2 short isoform exhibits cone rescue activity that is independent of its putative thiol-oxydoreductase activity.

Conclusion

Taken together, these findings define a new family of bifunctional genes which are: expressed in vertebrate retina, encode trophic cone viability factors, and have major therapeutic potential for human retinal neurodegenerative diseases such as retinitis pigmentosa.

Expression and extracellular release of Trx80, the truncated form of thioredoxin, by TNF-alpha- and IL-1beta-stimulated human synoviocytes from patients with rheumatoid arthritis

Thioredoxin (Trx) plays several important roles, through changes to sulfhydryl reactions and protein interactions, in controlling cellular signalling processes in RA (rheumatoid arthritis). Trx80, the 10 kDa C-terminal truncated form of Trx, is a potent mitogenic cytokine and is involved in the Th1 response. In the present study, we have investigated the ability of synoviocytes from five RA patients to induce Trx80 after ex vivo stimulation by the pro-inflammatory cytokines IL-1beta (interleukin-1beta) and TNF-alpha (tumour necrosis factor-alpha) or by H(2)O(2). Synoviocytes from five OA (osteoarthritis) patients were used as controls. Immunoprecipitation assays using two different antibodies showed that RA, but not OA, cells expressed intact Trx80 protein in culture even when not stimulated. Treatment with pro-inflammatory cytokines alone or in combination enhanced this basal production and induced the extracellular release of Trx80 by all of the RA cells tested. Under our experimental conditions, the rate of Trx80 release from RA cells was approx. 30% of the total Trx produced. In contrast, Trx80 was not detected in response to H(2)O(2) in RA or OA synoviocyte lysates and their respective culture supernatants, indicating that the oxidative process induced by H(2)O(2) in synoviocytes was unable to modify Trx80 release. Moreover, Trx80 induced synoviocyte proliferation as evaluated by [(3)H]thymidine incorporation. These results highlight the effect of the inflammatory process on the release of both Trx and Trx80 from RA synoviocytes, and suggest that the cytokine-induced increase in Trx80 cell release may constitute a link between inflammation and the immune system in RA.

Thioredoxin and related molecules--from biology to health and disease

Thioredoxin and glutaredoxin systems in mammalian cells utilize thiol and selenol groups to maintain a reducing intracellular redox state acting as antioxidants and reducing agents in redox signaling with oxidizing reactive oxygen species. During the last decade, the functional roles of thioredoxin in particular have continued to expand, also including novel functions such as a secreted growth factor or a chemokine for immune cells. The role of thioredoxin and glutaredoxin in antioxidant defense and the role of thioredoxin in controlling recruitment of inflammatory cells offer potential use in clinical therapy. The fundamental differences between bacterial and mammalian thioredoxin reductases offer new principles for treatment of infections. Clinical drugs already in use target the active site selenol in thioredoxin reductases, inducing cell death in tumor cells. Thioredoxin and binding proteins (ASK1 and TBP2) appear to control apoptosis or metabolic states such as carbohydrate and lipid metabolism related to diseases such as diabetes and atherosclerosis.

Extracellular thioredoxin and thioredoxin-binding protein 2 in control of cancer

Thioredoxin-1 (TRX) is a redox-active protein with multiple intracellular and extracellular functions. Intracellular redox balance is maintained by the TRX family and its related molecules. Extracellular TRX shows cytoprotective effects, while truncated Trx80 has more mitogenic activity. Exogenously administered TRX does not promote the growth of cancer in vivo and shows anti-chemotactic effect for neutrophils and anti-inflammatory functions. Thioredoxin is released from cells in response to oxidative stress and TRX levels in plasma or serum are good markers for oxidative stress associated with cancer. Thioredoxin-binding protein 2 (TBP-2) is an endogenous negative regulator of TRX and a tumor suppressor.

Redox regulation of human thioredoxin network

Oxidative stresses are largely mediated by intracellular protein oxidations by reactive oxygen species (ROS). Host cells are equipped with antioxidants that scavenge ROS. The cellular reduction/oxidation (redox) balance is maintained by ROS and antioxidants. Accumulating evidence suggests that the redox balance plays an important role in cellular signaling through the redox modification of cysteine residues in various important components of the signal transduction pathway. Thioredoxin (TRX) is a small protein playing important roles in cellular responses, including cell growth, cell cycle, gene expression, and apoptosis, to maintain the redox circumstance. Moreover, many recent papers have shown that the redox regulation by TRX is deeply involved in the pathogenesis of various oxidative stress-associated disorders. This review focuses on TRX and its related molecules, and discusses the role of TRX-dependent redox regulation in oxidative stress-induced signal transduction.

Nucleoprotein assemblies for cellular biomarker detection

In this report, we have used DNA Y-junctions as fluorescent scaffolds for EcoRII methyltransferase-thioredoxin (M.EcoRII-Trx) fusion proteins. Covalent links between the DNA scaffold and the methyltransferase were formed at preselected sites on the scaffold containing 5FdC. The resulting thioredoxin-targeted nanodevice was found to bind selectively to certain cell lines but not to others. The fusion protein was constructed so as to permit proteolytic cleavage of the thioredoxin peptide from the nanodevice. Proteolysis with thrombin or enterokinase effectively removed the thioredoxin peptide from the nanodevice and extinguished cell line specific binding measured by fluorescence. A number of potential applications for devices of this type can be envisioned. In particular, the ability of the fused protein to selectively target the nanodevice to certain tumor cell lines and not others suggests that this approach may serve as an adjunct to immunohistochemical methods in tumor classification as well as probe cell surface receptor architecture and function.

Thioredoxin induced antioxidant gene expressions in human lens epithelial cells

Thioredoxin (Trx) is one of the major redox-regulating proteins. It catalyzes dithiol/disulfide exchange reactions and displays many unique intracellular and extracellular activities thereby controlling multiple mammalian cell functions. In the present study we examine the effect of exogenous Trx on the expression of several antioxidant genes in human lens epithelial (HLE B3) cells. mRNA levels for gene expression were monitored by RT-PCR and real-time PCR while protein levels were measured by western blot analysis. We have found that recombinant human Trx (hTrx)-treated HLE B3 cells have a simultaneous increase in mRNA expressions of mitochondrial manganese superoxide dismutase (MnSOD), thioltranferase 1 (TTase 1) or glutaredoxin 1 (Grx1), mitochondrial thioltransferase (TTase 2) or glutaredoxin 2 (Grx2), and thioredoxin peroxidase IV (Prx IV). The increased MnSOD and TTase 1 mRNA expressions were accompanied with their respective increases in protein levels. Other antioxidant genes, including Cu/ZnSOD, catalase, glutathione peroxidase 1 (GPx1), thioredoxin reductase 1 (TrxR1), thioredoxin peroxidase III (Prx III), and gamma-glutamyl cysteine synthetase were not affected. The ability of Trx to induce selectively these antioxidant genes in the absence of oxidative stress suggest a cytokine/growth factor-like new physiological role of hTrx in HLE B3 cells. Our data also provide evidence of a strong antioxidant defense system in HLE B3 cells that can be activated by extracellular hTrx, as well as of a possible link between the thioredoxin (Trx) and glutathione (GSH) redox regulating systems in these cells.

Redox regulation of mast cell histamine release in thioredoxin-1 (TRX) transgenic mice

Thioredoxin-1 (TRX) is a stress-inducible redox-regulatory protein with antioxidative and anti-inflammatory effects. Here we show that the release of histamine from mast cells elicited by cross-linking of high-affinity receptor for IgE (FcepsilonRI) was significantly suppressed in TRX transgenic (TRX-tg) mice compared to wild type (WT) mice. Intracellular reactive oxygen species (ROS) of mast cells stimulated by IgE and antigen was also reduced in TRX-tg mice compared to WT mice. Whereas there was no difference in the production of cytokines (IL-6 and TNF-alpha) from mast cells in response to 2,4-dinitrophenylated bovine serum albumin (DNP-BSA) stimulation in TRX-tg and WT mice. Immunological status of TRX-tg mice inclined to T helper (Th) 2 dominant in primary immune response, although there was no difference in the population of dendritic cells (DCs) and regulatory T cells. We conclude that the histamine release from mast cells in TRX-tg mice is suppressed by inhibition of ROS generation. As ROS are involved in mast cell activation and facilitate mediator release, TRX may be a key signaling molecule regulating the early events in the IgE signaling in mast cells and the allergic inflammation.