Thioredoxin Activates MKK4-NFκB Pathway in a Redox-dependent Manner to Control Manganese Superoxide Dismutase Gene Expression in Endothelial Cells

Thioredoxin h2 inhibits the MPKK5-MPK3 cascade to regulate the CBF-COR signaling pathway in Citrullus lanatus suffering chilling stress

Thioredoxins (TRXs) are ubiquitous oxidoreductases and present as a multigenic family. TRXs determine the thiol redox balance, which is crucial for plants in the response to cold stress. However, limited knowledge is available about the role of TRXs in watermelon (Citrullus lanatus), which is highly sensitive to chilling stress in agricultural practice. Here, we identified 18 genes encoding 14 typical and 4 atypical TRXs from the watermelon genome, and found that ClTRX h2 localized at the plasma membrane was largely induced by chilling. Virus-induced gene silencing of ClTRX h2 resulted in watermelon plants that were more sensitive to chilling stress. We further found that ClTRX h2 physically interacted with mitogen-activated protein kinase kinase 5 (ClMPKK5), which was confirmed to phosphorylate and activate ClMPK3 in vitro, and the activation of ClMPK3 by ClMPKK5 was blocked by a point mutation of the Cys-229 residue to Ser in ClMPKK5. Additionally, ClTRX h2 inhibited the chilling-induced activation of ClMPK3, suggesting that the ClMPKK5-ClMPK3 cascade is regulated in a redox-dependent manner. We showed that ClMPK3-silenced plants had increased tolerance to chilling, as well as enhanced transcript abundances of the C-repeat/DREB binding factor (ClCBF) and cold-responsive (ClCOR) genes. Taken together, our results indicate that redox status mediated by ClTRX h2 inhibits ClMPK3 phosphorylation through the interaction between ClTRX h2 and ClMPKK5, which subsequently regulates the CBF-COR signaling pathway when submitted to chilling stress. Hence, our results provide a link between thiol redox balance and MAPK cascade signaling, revealing a conceptual framework to understand how TRX regulates chilling stress tolerance in watermelon.

Emerging Evidence of the Significance of Thioredoxin-1 in Hematopoietic Stem Cell Aging

The United States is undergoing a demographic shift towards an older population with profound economic, social, and healthcare implications. The number of Americans aged 65 and older will reach 80 million by 2040. The shift will be even more dramatic in the extremes of age, with a projected 400% increase in the population over 85 years old in the next two decades. Understanding the molecular and cellular mechanisms of ageing is crucial to reduce ageing-associated disease and to improve the quality of life for the elderly. In this review, we summarized the changes associated with the ageing of hematopoietic stem cells (HSCs) and what is known about some of the key underlying cellular and molecular pathways. We focus here on the effects of reactive oxygen species and the thioredoxin redox homeostasis system on ageing biology in HSCs and the HSC microenvironment. We present additional data from our lab demonstrating the key role of thioredoxin-1 in regulating HSC ageing.

Thioredoxin Prevents Loss of UCP2 in Hyperoxia via MKK4-p38 MAPK-PGC1α Signaling and Limits Oxygen Toxicity

Administration of high concentrations of oxygen (hyperoxia) is one of few available options to treat acute hypoxemia-related respiratory failure, as seen in the current coronavirus disease (COVID-19) pandemic. Although hyperoxia can cause acute lung injury through increased production of superoxide anion (O2•-), the choice of high-concentration oxygen administration has become a necessity in critical care. The objective of this study was to test the hypothesis that UCP2 (uncoupling protein 2) has a major function of reducing O2•- generation in the lung in ambient air or in hyperoxia. Lung epithelial cells and wild-type; UCP2-/-; or transgenic, hTrx overexpression-bearing mice (Trx-Tg) were exposed to hyperoxia and O2•- generation was measured by using electron paramagnetic resonance, and lung injury was measured by using histopathologic analysis. UCP2 expression was analyzed by using RT-PCR analysis, Western blotting analysis, and RNA interference. The signal transduction pathways leading to loss of UCP2 expression were analyzed by using IP, phosphoprotein analysis, and specific inhibitors. UCP2 mRNA and protein expression were acutely decreased in hyperoxia, and these decreases were associated with a significant increase in O2•- production in the lung. Treatment of cells with rhTrx (recombinant human thioredoxin) or exposure of Trx-Tg mice prevented the loss of UCP2 protein and decreased O2•- generation in the lung. Trx is also required to maintain UCP2 expression in normoxia. Loss of UCP2 in UCP2-/- mice accentuated lung injury in hyperoxia. Trx activates the MKK4-p38MAPK (p38 mitogen-activated protein kinase)-PGC1α (PPARγ [peroxisome proliferator-activated receptor γ] coactivator 1α) pathway, leading to rescue of UCP2 and decreased O2•- generation in hyperoxia. Loss of UCP2 in hyperoxia is a major mechanism of O2•- production in the lung in hyperoxia. rhTrx can protect against lung injury in hyperoxia due to rescue of the loss of UCP2.

Chaperone-Mediated Autophagy of eNOS in Myocardial Ischemia-Reperfusion Injury

[Figure: see text].

YTHDF2 mediates LPS-induced osteoclastogenesis and inflammatory response via the NF-κB and MAPK signaling pathways

Aberrant elevation of osteoclast differentiation and function is responsible for disrupting bone homeostasis in various inflammatory bone diseases. YTH domain family 2 (YTHDF2) is a well-known m⁶A-binding protein that plays an essential role in regulating cell differentiation and inflammatory processes by mediating mRNA degradation. However, the regulatory role of YTHDF2 in inflammatory osteoclast differentiation remains unelucidated. Here, we detected the expression of m⁶A-related genes and found that YTHDF2 was upregulated in RANKL-primed osteoclast precursors stimulated with lipopolysaccharide (LPS). Ythdf2 knockdown in RAW264.7 cells and primary bone marrow-derived macrophages (BMMs) enhanced osteoclast formation and bone resorption, which was assessed by TRAP staining assay and pit formation assay. Ythdf2 depletion upregulated osteoclast-related gene expression and proinflammatory cytokine secretion. In contrast, overexpression of Ythdf2 produced the reverse effect. Furthermore, Ythdf2 knockdown enhanced the phosphorylation of IKKα/β, IκBα, ERK, P38 and JNK. NF-κB and MAPK signaling pathway inhibitors effectively abrogated the enhanced expression of Nfact1, c-Fos, IL-1β and TNF-α caused by Ythdf2 knockdown. Mechanistically, the mRNA stability assay revealed that Ythdf2 depletion led to stabilization of Tnfrsf11a, Traf6, Map4k4, Map2k3, Map2k4 and Nfatc1 mRNA. In summary, our findings demonstrated that YTHDF2 has a negative regulatory role in LPS-induced osteoclast differentiation and the inflammatory response via the NF-κB and MAPK signaling pathways.

Thioredoxin protects mitochondrial structure, function and biogenesis in myocardial ischemia-reperfusion via redox-dependent activation of AKT-CREB- PGC1α pathway in aged mice

Aging is an independent risk factor for cardiovascular diseases, such as myocardial infarction due to ischemia-reperfusion injury (I/R) of the heart. Cytosolic thioredoxin (Trx) is a multifunctional redox protein which has antioxidant and protein disulfide reducing properties. We hypothesized that high levels of Trx will protect against multifactorial disease such as myocardial infarction due to I/R injury in aged mice. Aged mice overexpressing human Trx (Trx-Tg), mice expressing redox-inactive mutant of human Trx (dnTrx-Tg) and non-transgenic litter-mates (NT) were subjected to I/R (60/30 min), and cardiac function, mitochondrial structure and function, and biogenesis involving PGC1α pathway were evaluated in these mice. While aged Trx-Tg mice were protected from I/R-induced reduction in ejection fraction (EF) and fractional shortening (FS), had smaller infarct with decreased apoptosis and preserved mitochondrial function, aged dnTrx-Tg mice showed enhanced myocardial injury and mitochondrial dysfunction. Further, Trx-Tg mice were protected from I/R induced loss of PGC1α, ACO2, MFN1 and MFN2 in the myocardium. The dnTrx-Tg mice were highly sensitive to I/R induced apoptosis. Overall, our study demonstrated that the loss of Trx redox balance in I/R in aged NT or dnTrx-Tg mice resulted in decreased PGC1α expression that decreased mitochondrial gene expression with increased myocardial apoptosis. High levels of Trx, but not mitochondrial thioredoxin (Trx-2) maintained Trx redox balance in I/R resulting in increased PGC1α expression via AKT/CREB activation upregulating mitochondrial gene expression and protection against I/R injury.

Thioredoxin Decreases Anthracycline Cardiotoxicity, But Sensitizes Cancer Cell Apoptosis

Cardiotoxicity is a major limitation for anthracycline chemotherapy although anthracyclines are potent antitumor agents. The precise mechanism underlying clinical heart failure due to anthracycline treatment is not fully understood, but is believed to be due, in part, to lipid peroxidation and the generation of free radicals by anthracycline-iron complexes. Thioredoxin (Trx) is a small redox-active antioxidant protein with potent disulfide reductase properties. Here, we present evidence that cancer cells overexpressing Trx undergo enhanced apoptosis in response to daunomycin. In contrast, cells overexpressing redox-inactive mutant Trx were not effectively killed. However, rat embryonic cardiomyocytes (H9c2 cells) overexpressing Trx were protected against daunomycin-mediated apoptosis, but H9c2 cells with decreased levels of active Trx showed enhanced apoptosis in response to daunomycin. We further demonstrate that increased level of Trx is specifically effective in anthracycline toxicity, but not with other topoisomerase II inhibitors such as etoposide. Collectively these data demonstrate that whereas high levels of Trx protect cardiomyocytes against anthracycline toxicity, it potentiates toxicity of anthracyclines in cancer cells.

m6A Reader YTHDF2 Regulates LPS-Induced Inflammatory Response

N6-methyladenosine (m6A) is an abundant mRNA modification that affects multiple biological processes, including those involved in the cell stress response and viral infection. YTH domain family 2 (YTHDF2) is an m6A-binding protein that affects the localization and stability of targeted mRNA. RNA-binding proteins (RBPs) can regulate the stability of inflammatory gene mRNA transcripts, thus participating in the regulation of inflammatory processes. As an RBP, the role of YTHDF2 in the LPS-induced inflammatory reaction has not been reported. To elucidate the function of YTHDF2 in the inflammatory response of macrophages, we first detected the expression level of YTHDF2 in RAW 264.7 cells, and found that it was upregulated after LPS stimulation. YTHDF2 knockdown significantly increased the LPS-induced IL-6, TNF-α, IL-1β, and IL-12 expression and the phosphorylation of p65, p38, and ERK1/2 in NF-κB and MAPK signaling. Moreover, the upregulated expression of TNF-α and IL-6 in cells with silenced YTHDF2 expression was downregulated by the NF-κB, p38, and ERK inhibitors. YTHDF2 depletion increased the expression and stability of MAP2K4 and MAP4K4 mRNAs. All of these results suggest that YTHDF2 knockdown increases mRNA expression levels of MAP2K4 and MAP4K4 via stabilizing the mRNA transcripts, which activate MAPK and NF-κB signaling pathways, which promote the expression of proinflammatory cytokines and aggravate the inflammatory response in LPS-stimulated RAW 264.7 cells.

Short-duration hyperoxia causes genotoxicity in mouse lungs: protection by volatile anesthetic isoflurane

High concentrations of oxygen (hyperoxia) are routinely used during anesthesia, and supplemental oxygen is also administered in connection with several other clinical conditions. Although prolonged hyperoxia is known to cause acute lung injury (ALI), whether short-duration hyperoxia causes lung toxicity remains unknown. We exposed mice to room air (RA or 21% O₂) or 60% oxygen alone or in combination with 2% isoflurane for 2 h and determined the expression of oxidative stress marker genes, DNA damage and DNA repair genes, and expression of cell cycle regulatory proteins using quantitative PCR and Western analyses. Furthermore, we determined cellular apoptosis using TUNEL assay and assessed the DNA damage product 8-hydroxy-2'-deoxyguanosine (8-Oxo-dG) in the urine of 60% hyperoxia-exposed mice. Our study demonstrates that short-duration hyperoxia causes mitochondrial and nuclear DNA damage and that isoflurane abrogates this DNA damage and decreases apoptosis when used in conjunction with hyperoxia. In contrast, isoflurane mixed with RA caused significant 8-Oxo-dG accumulations in the mitochondria and nucleus. We further show that whereas NADPH oxidase is a major source of superoxide anion generated by isoflurane in normoxia, isoflurane inhibits superoxide generation in hyperoxia. Additionally, isoflurane also protected the mouse lungs against ALI (95% O₂ for 36-h exposure). Our study established that short-duration hyperoxia causes genotoxicity in the lungs, which is abrogated when hyperoxia is used in conjunction with isoflurane, but isoflurane alone causes genotoxicity in the lung when delivered with ambient air.

Role of Thioredoxin in Age-Related Hypertension

PURPOSE OF REVIEW

Although the roles of oxidant stress and redox perturbations in hypertension have been the subject of several reviews, role of thioredoxin (Trx), a major cellular redox protein in age-related hypertension remains inadequately reviewed. The purpose of this review is to bring readers up-to-date with current understanding of the role of thioredoxin in age-related hypertension.

RECENT FINDINGS

Age-related hypertension is a major underlying cause of several cardiovascular disorders, and therefore, intensive management of blood pressure is indicated in most patients with cardiovascular complications. Recent studies have shown that age-related hypertension was reversed and remained lowered for a prolonged period in mice with higher levels of human Trx (Trx-Tg). Additionally, injection of human recombinant Trx (rhTrx) decreased hypertension in aged wild-type mice that lasted for several days. Both Trx-Tg and aged wild-type mice injected with rhTrx were normotensive, showed increased NO production, decreased arterial stiffness, and increased vascular relaxation. These studies suggest that rhTrx could potentially be a therapeutic molecule to reverse age-related hypertension in humans. The reversal of age-related hypertension by restoring proteins that have undergone age-related modification is conceptually novel in the treatment of hypertension. Trx reverses age-related hypertension via maintaining vascular redox homeostasis, regenerating critical vasoregulatory proteins oxidized due to advancing age, and restoring native function of proteins that have undergone age-related modifications with loss-of function. Recent studies demonstrate that Trx is a promising molecule that may ameliorate or reverse age-related hypertension in older adults.

Mitochondria and redox balance in coeliac disease: A case-control study

BACKGROUND

Coeliac disease (CD) is a gluten-sensitive autoimmune disorder. Gluten toxicity encompasses a wide spectrum of target organ functions and pathologies, including the activation of the immune response and triggering of oxidative stress. The aim of this study was to investigate inflammation and the redox balance in patients with active CD, and to evaluate whether alteration of mitochondrial function is involved in the disease status.

DESIGN

In this prospective case-control study, blood samples from sixteen adult CD patients and sixteen healthy controls (HC) were investigated for IL-1β, IL-6 and IL-8 plasma concentrations, for serum PON1 arylesterase, total and MnSOD antioxidant enzyme activities, induced TBARs levels, and for lymphocyte mtDNA content.

RESULTS

Patients showed IL-8 and IL-1β concentrations significantly higher than HC counterparts. Patients had a significantly higher content of induced TBARS compared to HC value, indicating a shift in their serum redox balance towards pro-oxidant species. The assay of antioxidant enzyme activities showed a significant 25% increase in PON1, a higher total SOD, and a significant 21% higher MnSOD in patients compared to HC. Lymphocyte mtDNA content in patients was significantly twofold higher than in HC, supporting the induction of mitochondrial biogenesis. The patients' mitochondrial compensatory response may explain the correlation between MnSOD activity and mtDNA content. The patients' mitochondrial oxidative stress, cooperating to cytokines secretion, may justify the correlation between IL-1β concentration and mtDNA content.

CONCLUSIONS

These results highlight the mitochondrial involvement in CD and suggest the evaluation of the mtDNA content as a potential diagnostic and follow-up parameter.

Thioredoxin reverses age-related hypertension by chronically improving vascular redox and restoring eNOS function

The incidence of high blood pressure with advancing age is notably high, and it is an independent prognostic factor for the onset or progression of a variety of cardiovascular disorders. Although age-related hypertension is an established phenomenon, current treatments are only palliative but not curative. Thus, there is a critical need for a curative therapy against age-related hypertension, which could greatly decrease the incidence of cardiovascular disorders. We show that overexpression of human thioredoxin (TRX), a redox protein, in mice prevents age-related hypertension. Further, injection of recombinant human TRX (rhTRX) for three consecutive days reversed hypertension in aged wild-type mice, and this effect lasted for at least 20 days. Arteries of wild-type mice injected with rhTRX or mice with TRX overexpression exhibited decreased arterial stiffness, greater endothelium-dependent relaxation, increased nitric oxide production, and decreased superoxide anion (O₂^•-) generation compared to either saline-injected aged wild-type mice or mice with TRX deficiency. Our study demonstrates a potential translational role of rhTRX in reversing age-related hypertension with long-lasting efficacy.

Thioredoxin Uses a GSH-independent Route to Deglutathionylate Endothelial Nitric-oxide Synthase and Protect against Myocardial Infarction

Reversible glutathionylation plays a critical role in protecting protein function under conditions of oxidative stress generally and for endothelial nitric-oxide synthase (eNOS) specifically. Glutathione-dependent glutaredoxin-mediated deglutathionylation of eNOS has been shown to confer protection in a model of heart damage termed ischemia-reperfusion injury, motivating further study of eNOS deglutathionylation in general. In this report, we present evidence for an alternative mechanism of deglutathionylation. In this pathway thioredoxin (Trx), a small cellular redox protein, is shown to rescue eNOS from glutathionylation during ischemia-reperfusion in a GSH-independent manner. By comparing mice with global overexpression of Trx and mice with cardiomyocyte-specific overexpression of Trx, we demonstrate that vascular Trx-mediated deglutathionylation of eNOS protects against ischemia-reperfusion-mediated myocardial infarction. Trx deficiency in endothelial cells promoted eNOS glutathionylation and reduced its enzymatic activity, whereas increased levels of Trx led to deglutathionylated eNOS. Thioredoxin-mediated deglutathionylation of eNOS in the coronary artery in vivo protected against reperfusion injury, even in the presence of normal levels of GSH. We further show that Trx directly interacts with eNOS, and we confirmed that Cys-691 and Cys-910 are the glutathionylated sites, as mutation of these cysteines partially rescued the decrease in eNOS activity, whereas mutation of a distal site, Cys-384, did not. Collectively, this study shows for the first time that Trx is a potent deglutathionylating protein in vivo and in vitro that can deglutathionylate proteins in the presence of high levels of GSSG in conditions of oxidative stress.