Evolution of the thioredoxin system as a step enabling adaptation to oxidative stress

Molecular characterization and functional analysis of Trx and Trp14 in roughskin sculpin (Trachidermus fasciatus)

Thioredoxins (Trxs) are a family of small and highly conserved proteins which play crucial roles in the maintenance and regulation of the cellular redox homeostasis. In this study, the full-length cDNAs of thioredoxin 1 (TfTrx1) and thioredoxin-related protein of 14 kDa (TfTrp14) were isolated from roughskin sculpin (Trachidermus fasciatus). TfTrx1 is 662 bp in length with a 336-bp open reading frame (ORF) that encodes for a peptide with 111 amino acids, and TfTrp14 consists of 1066 bp with a 372-bp ORF that is translated to 123 amino acids. TfTrx1 and TfTrp14 contain highly conserved catalytic site motif CGPC and CPDC, respectively. Tissue distribution analysis indicated that both genes were broadly expressed in all examined tissues with the highest expression of TfTrx1 in the blood and TfTrp14 in the brain. In post-LPS and heavy metal challenge, the mRNA of both genes was significantly increased in the skin, liver, spleen, and brain at various times. The results of western blot detection displayed that the time of the induced maximum protein expression was 6-h post-LPS injection in the skin and liver, which were slightly delayed compared with that of 2 h at mRNA level. The recombinant TfTrp14 and TfTrx1 proteins were expressed in E. coli BL21 (DE3). The increase of the fluorescence intensity in rTfTrx1 and rTfTrp14 suggested the redox state changes in the microenvironment around tryptophan residues. Both of the recombinant proteins exhibited concentration-dependent disulfide reductase activity towards insulin, and the catalytic activity of rTfTrx1 was much higher than that of rTfTrp14.

Effects of L-carnitine combined with pancreatic kininogenase on thioredoxin 2, thioredoxin reductase 1, and sperm quality in patients with oligoasthenospermia

Background

To study the effects of L-carnitine (LC) combined with pancreatic kininogenase on thioredoxin 2 (Trx 2), thioredoxin reductase 1 (TrxR 1), and sperm quality in patients with oligoasthenospermia.

Methods

A total of 300 male infertility patients with oligoasthenospermia who were treated in the andrology clinic of our hospital from December 2019 to December 2020 were randomly divided into an LC group and combined treatment group, and 50 males with normal semen were selected as a control group. The computer-assisted semen analysis system (CASA) was used to detect the total number, vitality, and forward motility of the sperm before and after treatment, and sperm morphology was detected by the Diff-Quik method of the sperm staining kit. Sperm chromatin dispersion (SCD) method was used to detect sperm DNA fragments, and Western-blot was used to detect the protein expression of Trx 2 and TrxR 1.

Results

There were no significant differences in sperm density, motility rate, forward motile sperm rate, and DNA fragmentation rate in oligoasthenospermia patients before treatment (P>0.05). However, after 1 month of treatment, the sperm density, motility rate, and forward motile sperm rate were all higher than before treatment (P<0.05), while the DNA fragmentation rate was lower than before treatment. At the same time, each index of semen in the combination group was higher than that in the LC group (P<0.05), and the total effective rate in the combination group was significantly higher than in the LC group (P<0.01). The expression of Trx2 protein in oligoasthenospermia patients was significantly increased (P<0.05), while the expression of TrxR1 protein was significantly decreased (P<0.05). After 3 months of treatment, the expression of Trx2 protein was significantly decreased (P<0.05), while the expression of TrxR1 protein was significantly increased (P<0.05).

Conclusions

The results suggest Trx 2 and TrxR 1 may be candidate protein markers for oligoasthenospermia. LC combined with pancreatic kininogenase in the treatment of male oligoasthenospermia can effectively promote sperm maturation, enhance sperm motility, and improve semen quality, which has high application value.

Atomic Force Microscopy to Elicit Conformational Transitions of Ferredoxin-Dependent Flavin Thioredoxin Reductases

Flavin and redox-active disulfide domains of ferredoxin-dependent flavin thioredoxin reductase (FFTR) homodimers should pivot between flavin-oxidizing (FO) and flavin-reducing (FR) conformations during catalysis, but only FR conformations have been detected by X-ray diffraction and scattering techniques. Atomic force microscopy (AFM) is a single-molecule technique that allows the observation of individual biomolecules with sub-nm resolution in near-native conditions in real-time, providing sampling of molecular properties distributions and identification of existing subpopulations. Here, we show that AFM is suitable to evaluate FR and FO conformations. In agreement with imaging under oxidizing condition, only FR conformations are observed for Gloeobacter violaceus FFTR (GvFFTR) and isoform 2 of Clostridium acetobutylicum FFTR (CaFFTR2). Nonetheless, different relative dispositions of the redox-active disulfide and FAD-binding domains are detected for FR homodimers, indicating a dynamic disposition of disulfide domains regarding the central protein core in solution. This study also shows that AFM can detect morphological changes upon the interaction of FFTRs with their protein partners. In conclusion, this study paves way for using AFM to provide complementary insight into the FFTR catalytic cycle at pseudo-physiological conditions. However, future approaches for imaging of FO conformations will require technical developments with the capability of maintaining the FAD-reduced state within the protein during AFM scanning.

A chloroplast redox relay adapts plastid metabolism to light and affects cytosolic protein quality control

In chloroplasts, thiol-dependent redox regulation is linked to light since the disulfide reductase activity of thioredoxins (Trxs) relies on photo-reduced ferredoxin (Fdx). Furthermore, chloroplasts harbor an NADPH-dependent Trx reductase (NTR) with a joint Trx domain, termed NTRC. The activity of these two redox systems is integrated by the redox balance of 2-Cys peroxiredoxin (Prx), which is controlled by NTRC. However, NTRC was proposed to participate in redox regulation of additional targets, prompting inquiry into whether the function of NTRC depends on its capacity to maintain the redox balance of 2-Cys Prxs or by direct redox interaction with chloroplast enzymes. To answer this, we studied the functional relationship of NTRC and 2-Cys Prxs by a comparative analysis of the triple Arabidopsis (Arabidopsis thaliana) mutant, ntrc-2cpab, which lacks NTRC and 2-Cys Prxs, and the double mutant 2cpab, which lacks 2-Cys Prxs. These mutants exhibit almost indistinguishable phenotypes: in growth rate, photosynthesis performance, and redox regulation of chloroplast enzymes in response to light and darkness. These results suggest that the most relevant function of NTRC is in controlling the redox balance of 2-Cys Prxs. A comparative transcriptomics analysis confirmed the phenotypic similarity of the two mutants and suggested that the NTRC-2-Cys Prxs system participates in cytosolic protein quality control. We propose that NTRC and 2-Cys Prxs constitute a redox relay, exclusive to photosynthetic organisms that fine-tunes the redox state of chloroplast enzymes in response to light and affects transduction pathways towards the cytosol.

Redox regulation of chloroplast metabolism

Regulation of enzyme activity based on thiol-disulfide exchange is a regulatory mechanism in which the protein disulfide reductase activity of thioredoxins (TRXs) plays a central role. Plant chloroplasts are equipped with a complex set of up to 20 TRXs and TRX-like proteins, the activity of which is supported by reducing power provided by photosynthetically reduced ferredoxin (FDX) with the participation of a FDX-dependent TRX reductase (FTR). Therefore, the FDX-FTR-TRXs pathway allows the regulation of redox-sensitive chloroplast enzymes in response to light. In addition, chloroplasts contain an NADPH-dependent redox system, termed NTRC, which allows the use of NADPH in the redox network of these organelles. Genetic approaches using mutants of Arabidopsis (Arabidopsis thaliana) in combination with biochemical and physiological studies have shown that both redox systems, NTRC and FDX-FTR-TRXs, participate in fine-tuning chloroplast performance in response to changes in light intensity. Moreover, these studies revealed the participation of 2-Cys peroxiredoxin (2-Cys PRX), a thiol-dependent peroxidase, in the control of the reducing activity of chloroplast TRXs as well as in the rapid oxidation of stromal enzymes upon darkness. In this review, we provide an update on recent findings regarding the redox regulatory network of plant chloroplasts, focusing on the functional relationship of 2-Cys PRXs with NTRC and the FDX-FTR-TRXs redox systems for fine-tuning chloroplast performance in response to changes in light intensity and darkness. Finally, we consider redox regulation as an additional layer of control of the signaling function of the chloroplast.

Independent evolution of the thioredoxin system in photosynthetic Paulinella species

Redox regulation allows phytoplankton to monitor and stabilize metabolic pathways under changing conditions¹. In plastids, the thioredoxin (TRX) system is linked to photosynthetic electron transport and fine tuning of metabolic pathways to fluctuating light levels. Expansion of the number of redox signal transmitters and their protein targets, as seen in plants, is believed to increase cell robustness². In this study, we searched for genes related to redox regulation in the photosynthetic amoeba Paulinella micropora KR01 (hereafter, KR01). The genus Paulinella includes testate filose amoebae, in which a single clade acquired a photosynthetic organelle, the chromatophore, from an alpha-cyanobacterial donor³. This independent primary endosymbiosis occurred relatively recently (∼124 million years ago) when compared to Archaeplastida (>1 billion years ago), making photosynthetic Paulinella a valuable model for studying the early stages of primary endosymbiosis⁴. Our comparative analysis demonstrates that this lineage has evolved a TRX system similar to other algae, relying, however, on genes with diverse phylogenetic origins (including the endosymbiont, host, bacteria, and red algae). One TRX of eukaryotic provenance is targeted to the chromatophore, implicating host-endosymbiont coordination of redox regulation. A chromatophore-targeted glucose-6-phosphate dehydrogenase (G6PDH) of red algal origin suggests that Paulinella exploited the existing redox regulation system in Archaeplastida to foster integration. Our study elucidates the independent evolution of the TRX system in photosynthetic Paulinella, whose parts derive from the existing genetic toolkit in diverse organisms.

Oxygen conditions oscillating between hypoxia and hyperoxia induce different effects in the pulmonary endothelium compared to constant oxygen conditions

The pulmonary endothelium is an immediate recipient of high oxygen concentrations upon oxygen therapy and mediates down-stream responses. Cyclic collapse and reopening of atelectatic lung areas during mechanical ventilation with high fractions of inspired oxygen result in the propagation of oxygen oscillations in the hypoxic/hyperoxic range. We used primary murine lung endothelial cell cultures to investigate cell responses to constant and oscillating oxygen conditions in the hypoxic to hyperoxic range. Severe constant hyperoxia had pro-inflammatory and cytotoxic effects including an increase in expression of ICAM1, E-selectin, and RAGE at 24 hr exposure. The coagulative/fibrinolytic system responded by upregulation of uPA, tPA, and vWF and PAI1 under constant severe hyperoxia. Among antioxidant enzymes, the upregulation of SOD2, TXN1, TXNRD3, GPX1, and Gstp1 at 24 hr, but downregulation of SOD3 at 72 hr constant hyperoxia was evident. Hypoxic/hyperoxic oscillating oxygen conditions induced pro-inflammatory cytokine release to a lesser extent and later than constant hyperoxia. Gene expression analyses showed upregulation of NFKB p65 mRNA at 72 hr. More evident was a biphasic response of NOS3 and ACE1 gene expression (downregulation until 24 hr and upregulation at 72 hr). ACE2 mRNA was upregulated until 72 hr, but shedding of the mature protein from the cell surface favored ACE1. Oscillations resulted in severe production of peroxynitrite, but apart from upregulation of Gstp1 at 24 hr responses of antioxidative proteins were less pronounced than under constant hyperoxia. Oscillating oxygen in the hypoxic/hyperoxic range has a characteristical impact on vasoactive mediators like NOS3 and on the activation of the renin-angiotensin system in the lung endothelium.

The effects of neutrophil-generated hypochlorous acid and other hypohalous acids on host and pathogens

Neutrophils are predominant immune cells that protect the human body against infections by deploying sophisticated antimicrobial strategies including phagocytosis of bacteria and neutrophil extracellular trap (NET) formation. Here, we provide an overview of the mechanisms by which neutrophils kill exogenous pathogens before we focus on one particular weapon in their arsenal: the generation of the oxidizing hypohalous acids HOCl, HOBr and HOSCN during the so-called oxidative burst by the enzyme myeloperoxidase. We look at the effects of these hypohalous acids on biological systems in general and proteins in particular and turn our attention to bacterial strategies to survive HOCl stress. HOCl is a strong inducer of protein aggregation, which bacteria can counteract by chaperone-like holdases that bind unfolding proteins without the need for energy in the form of ATP. These chaperones are activated by HOCl through thiol oxidation (Hsp33) or N-chlorination of basic amino acid side-chains (RidA and CnoX) and contribute to bacterial survival during HOCl stress. However, neutrophil-generated hypohalous acids also affect the host system. Recent studies have shown that plasma proteins act not only as sinks for HOCl, but get actively transformed into modulators of the cellular immune response through N-chlorination. N-chlorinated serum albumin can prevent aggregation of proteins, stimulate immune cells, and act as a pro-survival factor for immune cells in the presence of cytotoxic antigens. Finally, we take a look at the emerging role of HOCl as a potential signaling molecule, particularly its role in neutrophil extracellular trap formation.

Comprehensive genomic and proteomic profiling reveal Acinetobacter johnsonii JH7 responses to Sb(III) toxicity

Antimony (Sb) pollution poses a severe health threat to ecosystems. However, the toxic effects of Sb on biota are far from being elucidated. One of the unresolved questions is the molecular signal pathways underlying microbial adaptation to excess antimonite or Sb(III) exposure. The response of a Sb(III)-resistant bacterium Acinetobacter. johnsonii JH7 to Sb(III) stress was investigated using genomic and proteomic profiling. Sb(III) induced the formation of reactive oxygen species thereby leading to oxidative stress and the up-regulation of antioxidant enzyme activities. In addition, two important operons (ars and pst) playing critical roles in this cellular response were identified. The ars proteins functioned cooperatively to expel Sb(III) thereby decreasing antimonite toxicity. Downregulation of the phosphate-specific transporter might reduce the uptake of Sb(V) while hindering phosphorus assimilation. Interaction of Sb(III) with JH7 strain cells also affected peptide syntheses and folding, energy conversion, and stability of the cellular envelope. The present study provides for the first time a global map of cellular adaptation to excess Sb(III). Such information is potentially useful to future Sb pollution remediation strategies.

Calsequestrin: a well-known but curious protein in skeletal muscle

Calsequestrin (CASQ) was discovered in rabbit skeletal muscle tissues in 1971 and has been considered simply a passive Ca²⁺-buffering protein in the sarcoplasmic reticulum (SR) that provides Ca²⁺ ions for various Ca²⁺ signals. For the past three decades, physiologists, biochemists, and structural biologists have examined the roles of the skeletal muscle type of CASQ (CASQ1) in skeletal muscle and revealed that CASQ1 has various important functions as (1) a major Ca²⁺-buffering protein to maintain the SR with a suitable amount of Ca²⁺ at each moment, (2) a dynamic Ca²⁺ sensor in the SR that regulates Ca²⁺ release from the SR to the cytosol, (3) a structural regulator for the proper formation of terminal cisternae, (4) a reverse-directional regulator of extracellular Ca²⁺ entries, and (5) a cause of human skeletal muscle diseases. This review is focused on understanding these functions of CASQ1 in the physiological or pathophysiological status of skeletal muscle.

SARS-CoV2 infectivity is potentially modulated by host redox status

The current coronavirus disease (COVID-19) outbreak caused by Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV2) has emerged as a threat to global social and economic systems. Disparity in the infection of SARS-CoV2 among host population and species is an established fact without any clear explanation. To initiate infection, viral S-protein binds to the Angiotensin-Converting Enzyme 2 (ACE2) receptor of the host cell. Our analysis of retrieved amino acid sequences deposited in data bases shows that S-proteins and ACE2 are rich in cysteine (Cys) residues, many of which are conserved in various SARS-related coronaviruses and participate in intra-molecular disulfide bonds. High-resolution protein structures of S-proteins and ACE2 receptors highlighted the probability that two of these disulfide bonds are potentially redox-active, facilitating the primal interaction between the receptor and the spike protein. Presence of redox-active disulfides in the interacting parts of S-protein, ACE2, and a ferredoxin-like fold domain in ACE2, strongly indicate the role of redox in COVID-19 pathogenesis and severity. Resistant animals lack a redox-active disulfide (Cys133-Cys141) in ACE2 sequences, further strengthening the redox hypothesis for infectivity. ACE2 is a known regulator of oxidative stress. Augmentation of cellular oxidation with aging and illness is the most likely explanation of increased vulnerability of the elderly and persons with underlying health conditions to COVID-19.

Hypoglycemia-Sensing Neurons of the Ventromedial Hypothalamus Require AMPK-Induced Txn2 Expression but Are Dispensable for Physiological Counterregulation

The ventromedial nucleus of the hypothalamus (VMN) is involved in the counterregulatory response to hypoglycemia. VMN neurons activated by hypoglycemia (glucose-inhibited [GI] neurons) have been assumed to play a critical although untested role in this response. Here, we show that expression of a dominant negative form of AMPK or inactivation of AMPK α1 and α2 subunit genes in Sf1 neurons of the VMN selectively suppressed GI neuron activity. We found that Txn2, encoding a mitochondrial redox enzyme, was strongly downregulated in the absence of AMPK activity and that reexpression of Txn2 in Sf1 neurons restored GI neuron activity. In cell lines, Txn2 was required to limit glucopenia-induced reactive oxygen species production. In physiological studies, absence of GI neuron activity after AMPK suppression in the VMN had no impact on the counterregulatory hormone response to hypoglycemia or on feeding. Thus, AMPK is required for GI neuron activity by controlling the expression of the antioxidant enzyme Txn2. However, the glucose-sensing capacity of VMN GI neurons is not required for the normal counterregulatory response to hypoglycemia. Instead, it may represent a fail-safe system in case of impaired hypoglycemia sensing by peripherally located glucose detection systems that are connected to the VMN.

Exploring the Functional Relationship between y-Type Thioredoxins and 2-Cys Peroxiredoxins in Arabidopsis Chloroplasts

Thioredoxins (Trxs) are small, ubiquitous enzymes that catalyze disulphide–dithiol interchange in target enzymes. The large set of chloroplast Trxs, including f, m, x and y subtypes, use reducing equivalents fueled by photoreduced ferredoxin (Fdx) for fine-tuning photosynthetic performance and metabolism through the control of the activity of redox-sensitive proteins. Although biochemical analyses suggested functional diversity of chloroplast Trxs, genetic studies have established that deficiency in a particular Trx subtype has subtle phenotypic effects, leading to the proposal that the Trx isoforms are functionally redundant. In addition, chloroplasts contain an NADPH-dependent Trx reductase with a joint Trx domain, termed NTRC. Interestingly, Arabidopsis mutants combining the deficiencies of x- or f-type Trxs and NTRC display very severe growth inhibition phenotypes, which are partially rescued by decreased levels of 2-Cys peroxiredoxins (Prxs). These findings indicate that the reducing capacity of Trxs f and x is modulated by the redox balance of 2-Cys Prxs, which is controlled by NTRC. In this study, we explored whether NTRC acts as a master regulator of the pool of chloroplast Trxs by analyzing its functional relationship with Trxs y. While Trx y interacts with 2-Cys Prxs in vitro and in planta, the analysis of Arabidopsis mutants devoid of NTRC and Trxs y suggests that Trxs y have only a minor effect, if any, on the redox state of 2-Cys Prxs.

Exercise-induced oxidative stress: Friend or foe?

The first report demonstrating that prolonged endurance exercise promotes oxidative stress in humans was published more than 4 decades ago. Since this discovery, many ensuing investigations have corroborated the fact that muscular exercise increases the production of reactive oxygen species (ROS) and results in oxidative stress in numerous tissues including blood and skeletal muscles. Although several tissues may contribute to exercise-induced ROS production, it is predicted that muscular contractions stimulate ROS production in active muscle fibers and that skeletal muscle is a primary source of ROS production during exercise. This contraction-induced ROS generation is associated with (1) oxidant damage in several tissues (e.g., increased protein oxidation and lipid peroxidation), (2) accelerated muscle fatigue, and (3) activation of biochemical signaling pathways that contribute to exercise-induced adaptation in the contracting muscle fibers. While our understanding of exercise and oxidative stress has advanced rapidly during the last decades, questions remain about whether exercise-induced increases in ROS production are beneficial or harmful to health. This review addresses this issue by discussing the site(s) of oxidant production during exercise and detailing the health consequences of exercise-induced ROS production.

Subcellular compartmentalization of the plant antioxidant system: an integrated overview

The antioxidant system (AOS) maintains the optimal concentration of reactive oxygen species (ROS) in a cell and protects it against oxidative stress. In plants, the AOS consists of seven main classes of antioxidant enzymes, low-molecular antioxidants (e.g., ascorbate, glutathione, and their oxidized forms) and thioredoxin/glutaredoxin systems which can serve as reducing agents for antioxidant enzymes. The number of genes encoding AOS enzymes varies between classes, and same class enzymes encoded by different gene copies may have different subcellular localizations, functional loads and modes of evolution. These facts hereafter reinforce the complex nature of AOS regulation and functioning. Further studies can describe new trends in the behavior and functioning of systems components, and provide new fundamental knowledge about systems regulation. The system is revealed to have a lot of interactions and interplay pathways between its components at the subcellular level (antioxidants, enzymes, ROS level, and hormonal and transcriptional regulation). These facts should be taken into account in further studies during the AOS modeling by describing the main pathways of generating and utilizing ROS, as well as the associated signaling processes and regulation of the system on cellular and organelle levels, which is a complicated and ambitious task. Another objective for studying the phenomenon of the AOS is related to the influence of cell dynamics and circadian rhythms on it. Therefore, the AOS requires an integrated and multi-level approach to study. We focused this review on the existing scientific background and experimental data used for the systems biology research of the plant AOS.

Stress-responsive MTK1 SAPKKK serves as a redox sensor that mediates delayed and sustained activation of SAPKs by oxidative stress

Cells respond to oxidative stress by inducing intracellular signaling, including stress-activated p38 and JNK MAPK (SAPK) pathways, but the underlying mechanisms remain unclear. Here, we report that the MAP three kinase 1 (MTK1) SAPK kinase kinase (SAPKKK) functions as an oxidative-stress sensor that perceives the cellular redox state and transduces it into SAPK signaling. Following oxidative stress, MTK1 is rapidly oxidized and gradually reduced at evolutionarily conserved cysteine residues. These coupled oxidation-reduction modifications of MTK1 elicit its catalytic activity. Gene knockout experiments showed that oxidative stress-induced SAPK signaling is mediated by coordinated activation of the two SAPKKKs, MTK1 and apoptosis signal-regulating kinase 1 (ASK1), which have different time and dose-response characteristics. The MTK1-mediated redox sensing system is crucial for delayed and sustained SAPK activity and dictates cell fate decisions including cell death and interleukin-6 production. Our results delineate a molecular mechanism by which cells generate optimal biological responses under fluctuating redox environments.

Characterization of thioredoxin-like PROTEIN-5 (TRXLP-5) and its differential response to grafting challenge in the black coloured selected line and control stocks of Pinctada fucata martensii

Thioredoxin-like protein 5 (Trxlp-5) is a thioredoxin isoform associated with cellular redox homeostasis through the activity of thiol-disulfide reductase. In our study, Trxlp-5 was identified and characterized in Pinctada fucata martensii. The expression of PmTrxlp-5 was detected in response to polyinosinic: polycytidylic acid (poly I:C) and lipopolysaccharides (LPS) stimulation. The differences in PmTrxlp-5 expression were evaluated between the black coloured selected line and the control stock after grafting operation. The open reading frame (ORF) consisted of 1167bp encoding a 388 amino acid, 5'-UTR of 41bp and a 3'-UTR of 846bp. PmTrxlp-5 exhibited a conserved WCXXC functional motif similar to thioredoxins from other species. Tissue analysis showcased the highest relative mRNA expressions of PmTrxlp-5 in the haemocytes. Interestingly, after the grafting operation, mRNA expression of PmTrxlp-5 in the haemocytes was differentially expressed post grafting with a peak 6 h after grafting suggesting the high involvement of the gene in immune response in the early stage after grafting. The black coloured selected line group (BS) had significantly higher expression than the control group (CG) at 24 h, 6 d and 30 d after grafting operation. PmTrxlp-5 also showed a wave-like pattern in mRNA expression after bacterial endotoxin LPS and viral mimic poly I:C. These results suggested that PmTrxlp-5 plays a vital function in cellular redox homeostasis and immune response against grafting operation and pathogenic infections and can be used as a gene marker for selective breeding programs.

Oxidative Stress in Rheumatoid Arthritis: What the Future Might Hold regarding Novel Biomarkers and Add-On Therapies

Numerous rheumatologic autoimmune diseases, among which rheumatoid arthritis, are chronic inflammatory diseases capable of inducing multiple cumulative articular and extra-articular damage, if not properly treated. Nevertheless, benign conditions may, similarly, exhibit arthritis as their major clinical finding, but with short-term duration instead, and evolve to spontaneous resolution in a few days to weeks, without permanent articular damage. Such distinction—self-limited arthritis with no need of immunosuppressive treatment or chronic arthritis at early stages?—represents one of the greatest challenges in clinical practice, once many metabolic, endocrine, neoplastic, granulomatous, infectious diseases and other autoimmune conditions may mimic rheumatoid arthritis. Indeed, the diagnosis of rheumatoid arthritis at early stages is a crucial step to a more effective mitigation of the disease-related damage. As a prototype of chronic inflammatory autoimmune disease, rheumatoid arthritis has been linked to oxidative stress, a condition in which the pool of reactive oxygen species increases over time, either by their augmented production, the reduction in antioxidant defenses, or the combination of both, ultimately implying compromise in the redox signaling. The exact mechanisms through which oxidative stress may contribute to the initiation and perpetuation of local (in the articular milieu) and systemic inflammation in rheumatoid arthritis, particularly at early stages, still remain to be determined. Furthermore, the role of antioxidants as therapeutic adjuvants in the control of disease activity seems to be overlooked, as a little number of short studies addressing this issue is currently found. Thus, the present review focuses on the binomial rheumatoid arthritis-oxidative stress, bringing insights into their pathophysiological relationships, as well as the implications of potential diagnostic oxidative stress biomarkers and therapeutic interventions directed to the oxidative status in patients with rheumatoid arthritis.

The Thioredoxin System is Regulated by the ASK-1/JNK/p38/Survivin Pathway During Germ Cell Apoptosis

The aim is to explore the mechanism of the apoptosis signal-regulating kinase-1 (ASK-1) signaling pathway and the involvement of the thioredoxin (Trx) system during testicular ischemia reperfusion injury (tIRI) by using ASK-1 specific inhibitor, NQDI-1. Male Sprague-Dawley rats (n = 36, 250–300 g) were equally divided into 3 groups: sham, tIRI, and tIRI + NQDI-1 (10 mg/kg, i.p, pre-reperfusion). For tIRI induction, the testicular cord and artery were occluded for 1 h followed by 4 h of reperfusion. Histological analyses, protein immunoexpression, biochemical assays, and real-time PCR were used to evaluate spermatogenesis, ASK-1/Trx axis expression, enzyme activities, and relative mRNA expression, respectively. During tIRI, ipsilateral testes underwent oxidative stress indicated by low levels of superoxide dismutase (SOD) and Glutathione (GSH), increased oxidative damage to lipids and DNA, and spermatogenic damage. This was associated with induced mRNA expression of pro-apoptosis genes, downregulation of antiapoptosis genes, increased caspase 3 activity and activation of the ASK-1/JNK/p38/survivin apoptosis pathway. In parallel, the expression of Trx, Trx reductase were significantly reduced, while the expression of Trx interacting protein (TXNIP) and the NADP⁺/ nicotinamide Adenine Dinucleotide phosphate (NADPH) ratio were increased. These modulations were attenuated by NQDI-1 treatment. In conclusion, the Trx system is regulated by the ASK-1/Trx/TXNIP axis to maintain cellular redox homeostasis and is linked to tIRI-induced germ cell apoptosis via the ASK-1/JNK/p38/survivin apoptosis pathway.

The Redox Role of G6PD in Cell Growth, Cell Death, and Cancer

The generation of reducing equivalent NADPH via glucose-6-phosphate dehydrogenase (G6PD) is critical for the maintenance of redox homeostasis and reductive biosynthesis in cells. NADPH also plays key roles in cellular processes mediated by redox signaling. Insufficient G6PD activity predisposes cells to growth retardation and demise. Severely lacking G6PD impairs embryonic development and delays organismal growth. Altered G6PD activity is associated with pathophysiology, such as autophagy, insulin resistance, infection, inflammation, as well as diabetes and hypertension. Aberrant activation of G6PD leads to enhanced cell proliferation and adaptation in many types of cancers. The present review aims to update the existing knowledge concerning G6PD and emphasizes how G6PD modulates redox signaling and affects cell survival and demise, particularly in diseases such as cancer. Exploiting G6PD as a potential drug target against cancer is also discussed.

Functional analyses of ancestral thioredoxins provide insights into their evolutionary history

Thioredoxin (Trx) is a conserved, cytosolic reductase in all known organisms. The enzyme receives two electrons from NADPH via thioredoxin reductase (TrxR) and passes them on to multiple cellular reductases via disulfide exchange. Despite the ubiquity of thioredoxins in all taxa, little is known about the functions of resurrected ancestral thioredoxins in the context of a modern mesophilic organism. Here, we report on functional in vitro and in vivo analyses of seven resurrected Precambrian thioredoxins, dating back 1–4 billion years, in the Escherichia coli cytoplasm. Using synthetic gene constructs for recombinant expression of the ancestral enzymes, along with thermodynamic and kinetic assays, we show that all ancestral thioredoxins, as today's thioredoxins, exhibit strongly reducing redox potentials, suggesting that thioredoxins served as catalysts of cellular reduction reactions from the beginning of evolution, even before the oxygen catastrophe. A detailed, quantitative characterization of their interactions with the electron donor TrxR from Escherichia coli and the electron acceptor methionine sulfoxide reductase, also from E. coli, strongly hinted that thioredoxins and thioredoxin reductases co-evolved and that the promiscuity of thioredoxins toward downstream electron acceptors was maintained during evolution. In summary, our findings suggest that thioredoxins evolved high specificity for their sole electron donor TrxR while maintaining promiscuity to their multiple electron acceptors.