Thioredoxin is a metabolic rheostat controlling regulatory B cells.

Metabolic programming is important for B cell fate, but the bioenergetic requirement for regulatory B (Breg) cell differentiation and function is unknown. Here we show that Breg cell differentiation, unlike non-Breg cells, relies on mitochondrial electron transport and homeostatic levels of reactive oxygen species (ROS). Single-cell RNA sequencing analysis revealed that TXN, encoding the metabolic redox protein thioredoxin (Trx), is highly expressed by Breg cells, unlike Trx inhibitor TXNIP which was downregulated. Pharmacological inhibition or gene silencing of TXN resulted in mitochondrial membrane depolarization and increased ROS levels, selectively suppressing Breg cell differentiation and function while favoring pro-inflammatory B cell differentiation. Patients with systemic lupus erythematosus (SLE), characterized by Breg cell deficiencies, present with B cell mitochondrial membrane depolarization, elevated ROS and fewer Trx+ B cells. Exogenous Trx stimulation restored Breg cells and mitochondrial membrane polarization in SLE B cells to healthy B cell levels, indicating Trx insufficiency underlies Breg cell impairment in patients with SLE.

Oxidative Stress.

Oxidative stress is two sided: Whereas excessive oxidant challenge causes damage to biomolecules, maintenance of a physiological level of oxidant challenge, termed oxidative eustress, is essential for governing life processes through redox signaling. Recent interest has focused on the intricate ways by which redox signaling integrates these converse properties. Redox balance is maintained by prevention, interception, and repair, and concomitantly the regulatory potential of molecular thiol-driven master switches such as Nrf2/Keap1 or NF-κB/IκB is used for system-wide oxidative stress response. Nonradical species such as hydrogen peroxide (H2O2) or singlet molecular oxygen, rather than free-radical species, perform major second messenger functions. Chemokine-controlled NADPH oxidases and metabolically controlled mitochondrial sources of H2O2 as well as glutathione- and thioredoxin-related pathways, with powerful enzymatic back-up systems, are responsible for fine-tuning physiological redox signaling. This makes for a rich research field spanning from biochemistry and cell biology into nutritional sciences, environmental medicine, and molecular knowledge-based redox medicine.

Rod-derived cone viability factor promotes cone survival by stimulating aerobic glycolysis.

Rod-derived cone viability factor (RdCVF) is an inactive thioredoxin secreted by rod photoreceptors that protects cones from degeneration. Because the secondary loss of cones in retinitis pigmentosa (RP) leads to blindness, the administration of RdCVF is a promising therapy for this untreatable neurodegenerative disease. Here, we investigated the mechanism underlying the protective role of RdCVF in RP. We show that RdCVF acts through binding to Basigin-1 (BSG1), a transmembrane protein expressed specifically by photoreceptors. BSG1 binds to the glucose transporter GLUT1, resulting in increased glucose entry into cones. Increased glucose promotes cone survival by stimulation of aerobic glycolysis. Moreover, a missense mutation of RdCVF results in its inability to bind to BSG1, stimulate glucose uptake, and prevent secondary cone death in a model of RP. Our data uncover an entirely novel mechanism of neuroprotection through the stimulation of glucose metabolism.

TRP14 is the rate-limiting enzyme for intracellular cystine reduction and regulates proteome cysteinylation.

It has remained unknown how cells reduce cystine taken up from the extracellular space, which is a required step for further utilization of cysteine in key processes such as protein or glutathione synthesis. Here, we show that the thioredoxin-related protein of 14 kDa (TRP14, encoded by TXNDC17) is the rate-limiting enzyme for intracellular cystine reduction. When TRP14 is genetically knocked out, cysteine synthesis through the transsulfuration pathway becomes the major source of cysteine in human cells, and knockout of both pathways becomes lethal in C. elegans subjected to proteotoxic stress. TRP14 can also reduce cysteinyl moieties on proteins, rescuing their activities as here shown with cysteinylated peroxiredoxin 2. Txndc17 knockout mice were, surprisingly, protected in an acute pancreatitis model, concomitant with activation of Nrf2-driven antioxidant pathways and upregulation of transsulfuration. We conclude that TRP14 is the evolutionarily conserved enzyme principally responsible for intracellular cystine reduction in C. elegans, mice, and humans.

Thioredoxin-interacting protein is essential for memory T cell formation via the regulation of the redox metabolism.

CD4+ memory T cells are central to long-lasting protective immunity and are involved in shaping the pathophysiology of chronic inflammation. While metabolic reprogramming is critical for the generation of memory T cells, the mechanisms controlling the redox metabolism in memory T cell formation remain unclear. We found that reactive oxygen species (ROS) metabolism changed dramatically in T helper-2 (Th2) cells during the contraction phase in the process of memory T cell formation. Thioredoxin-interacting protein (Txnip), a regulator of oxidoreductase, regulated apoptosis by scavenging ROS via the nuclear factor erythroid 2-related factor 2 (Nrf2)-biliverdin reductase B (Blvrb) pathway. Txnip regulated the pathology of chronic airway inflammation in the lung by controlling the generation of allergen-specific pathogenic memory Th2 cells in vivo. Thus, the Txnip-Nrf2-Blvrb axis directs ROS metabolic reprogramming in Th2 cells and is a potential therapeutic target for intractable chronic inflammatory diseases.

Thioredoxin regulates the redox state and the activity of the human tRNA ligase complex.

The mammalian tRNA ligase complex (tRNA-LC) catalyzes the splicing of intron-containing pre-tRNAs in the nucleus and the splicing of XBP1 mRNA during the unfolded protein response (UPR) in the cytoplasm. We recently reported that the tRNA-LC coevolved with PYROXD1, an essential oxidoreductase that protects the catalytic cysteine of RTCB, the catalytic subunit of the tRNA-LC, against aerobic oxidation. In this study, we show that the oxidoreductase Thioredoxin (TRX) preserves the enzymatic activity of RTCB under otherwise inhibiting concentrations of oxidants. TRX physically interacts with oxidized RTCB, and reduces and reactivates RTCB through the action of its redox-active cysteine pair. We further show that TRX interacts with RTCB at late stages of UPR. Since the interaction requires oxidative conditions, our findings suggest that prolonged UPR generates reactive oxygen species. Thus, our results support a functional role for TRX in securing and repairing the active site of the tRNA-LC, thereby allowing pre-tRNA splicing and UPR to occur when cells encounter mild, but still inhibitory levels of reactive oxygen species.

Hepatitis E virus ORF3 protein hijacking thioredoxin domain-containing protein 5 (TXNDC5) for its stability to promote viral particle release.

Hepatitis E virus (HEV) is the most common cause of acute viral hepatitis worldwide, responsible for approximately 20 million infections annually. Among the three open reading frames (ORFs) of the HEV genome, the ORF3 protein is involved in virus release. However, the host proteins involved in HEV release need to be clarified. In this study, a host protein, thioredoxin domain-containing protein 5 (TXNDC5), interacted with the non-palmitoylated ORF3 protein by co-immunoprecipitation analysis. We determined that the overexpression or knockdown of TXNDC5 positively regulated HEV release from the host cells. The 17FCL19 mutation of the ORF3 protein lost the ability to interact with TXNDC5. The releasing amounts of HEV with the ORF3 mutation (FCL17-19SSP) were decreased compared with wild-type HEV. The overexpression of TXNDC5 can stabilize and increase ORF3 protein amounts, but not the TXNDC5 mutant with amino acids 1-88 deletion. Meanwhile, we determined that the function of TXNDC5 on the stabilization of ORF3 protein is independent of the Trx-like domains. Knockdown of TXNDC5 could lead to the degradation of ORF3 protein by the endoplasmic reticulum (ER)-associated protein degradation-proteasome system. However, the ORF3 protein cannot be degraded in the knockout-TXNDC5 stable cells, suggesting that it may hijack other proteins for its stabilization. Subsequently, we found that the other members of protein disulfide isomerase (PDI), including PDIA1, PDIA3, PDIA4, and PDIA6, can increase ORF3 protein amounts, and PDIA3 and PDIA6 interact with ORF3 protein. Collectively, our study suggested that HEV ORF3 protein can utilize TXNDC5 for its stability in ER to facilitate viral release. IMPORTANCE: Hepatitis E virus (HEV) infection is the leading cause of acute viral hepatitis worldwide. After the synthesis and modification in the cells, the mature ORF3 protein is essential for HEV release. However, the host protein involved in this process has yet to be determined. Here, we reported a novel host protein, thioredoxin domain-containing protein 5 (TXNDC5), as a chaperone, contributing to HEV release by facilitating ORF3 protein stability in the endoplasmic reticulum through interacting with non-palmitoylated ORF3 protein. However, we also found that in the knockout-TXNDC5 stable cell lines, the HEV ORF3 protein may hijack other proteins for its stabilization. For the first time, our study demonstrated the involvement of TXNDC5 in viral particle release. These findings provide some new insights into the process of the HEV life cycle, the interaction between HEV and host factors, and a new direction for antiviral design.

NTRC and thioredoxins m1/m2 underpin the light acclimation of plants on proteome and metabolome levels.

During photosynthesis, plants must manage strong fluctuations in light availability on different time scales, leading to long-term acclimation and short-term responses. However, little is known about the regulation and coordination of these processes and the modulators involved. In this study, we used proteomics, metabolomics, and reverse genetics to investigate how different light environmental factors, such as intensity or variability, affect long-term and short-term acclimation responses of Arabidopsis (Arabidopsis thaliana) and the importance of the chloroplast redox network in their regulation. In the wild type, high light, but not fluctuating light, led to large quantitative changes in the proteome and metabolome, accompanied by increased photosynthetic dynamics and plant growth. This finding supports light intensity as a stronger driver for acclimation than variability. Deficiencies in NADPH-thioredoxin reductase C (NTRC) or thioredoxins m1/m2, but not thioredoxin f1, almost completely suppressed the re-engineering of the proteome and metabolome, with both the induction of proteins involved in stress and redox responses and the repression of those involved in cytosolic and plastid protein synthesis and translation being strongly attenuated. Moreover, the correlations of protein or metabolite levels with light intensity were severely disturbed, suggesting a general defect in the light-dependent acclimation response, resulting in impaired photosynthetic dynamics. These results indicate a previously unknown role of NTRC and thioredoxins m1/m2 in modulating light acclimation at proteome and metabolome levels to control dynamic light responses. NTRC, but not thioredoxins m1/m2 or f1, also improves short-term photosynthetic responses by balancing the Calvin-Benson cycle in fluctuating light.

Thioredoxin A regulates protein synthesis to maintain carbon and nitrogen partitioning in cyanobacteria.

Thioredoxins play an essential role in regulating enzyme activity in response to environmental changes, especially in photosynthetic organisms. They are crucial for metabolic regulation in cyanobacteria, but the key redox-regulated central processes remain to be determined. Physiological, metabolic, and transcriptomic characterization of a conditional mutant of the essential Synechocystis sp. PCC 6803 thioredoxin trxA gene (STXA2) revealed that decreased TrxA levels alter cell morphology and induce a dormant-like state. Furthermore, TrxA depletion in the STXA2 strain inhibited protein synthesis and led to changes in amino acid pools and nitrogen/carbon reserve polymers, accompanied by oxidation of the elongation factor-Tu. Transcriptomic analysis of TrxA depletion in STXA2 revealed a robust transcriptional response. Downregulated genes formed a large cluster directly related to photosynthesis, ATP synthesis, and CO2 fixation. In contrast, upregulated genes were grouped into different clusters related to respiratory electron transport, carotenoid biosynthesis, amino acid metabolism, and protein degradation, among others. These findings highlight the complex regulatory mechanisms that govern cyanobacterial metabolism, where TrxA acts as a critical regulator that orchestrates the transition from anabolic to maintenance metabolism and regulates carbon and nitrogen balance.

The impact of light and thioredoxins on the plant thiol-disulfide proteome.

Thiol-based redox regulation is a crucial posttranslational mechanism to acclimate plants to changing light availability. Here, we conducted a biotin switch-based redox proteomics study in Arabidopsis (Arabidopsis thaliana) to systematically investigate dynamics of thiol-redox networks in response to temporal changes in light availability and across genotypes lacking parts of the thioredoxin (Trx) or NADPH-Trx-reductase C (NTRC) systems in the chloroplast. Time-resolved dynamics revealed light led to marked decreases in the oxidation states of many chloroplast proteins with photosynthetic functions during the first 10 min, followed by their partial reoxidation after 2 to 6 h into the photoperiod. This involved f, m, and x-type Trx proteins showing similar light-induced reduction-oxidation dynamics, while NTRC, 2-Cys peroxiredoxins, and Trx y2 showed an opposing pattern, being more oxidized in light than dark. In Arabidopsis trxf1f2, trxm1m2, or ntrc mutants, most proteins showed increased oxidation states in the light compared to wild type, suggesting their light-dependent dynamics were related to NTRC/Trx networks. While NTRC deficiency had a strong influence in all light conditions, deficiencies in f- or m-type Trxs showed differential impacts on the thiol-redox proteome depending on the light environment, being higher in constant or fluctuating light, respectively. The results indicate plant redox proteomes are subject to dynamic changes in reductive and oxidative pathways to cooperatively fine-tune photosynthetic and metabolic processes in the light. The importance of the individual elements of the NTRC/Trx networks mediating these responses depend on the extent of light variability, with NTRC playing a crucial role to balance protein-redox states in rapidly fluctuating light.

Txnip regulates the Oct4-mediated pluripotency circuitry via metabolic changes upon differentiation.

Thioredoxin interacting protein (Txnip) is a stress-responsive factor regulating Trx1 for redox balance and involved in diverse cellular processes including proliferation, differentiation, apoptosis, inflammation, and metabolism. However, the biological role of Txnip function in stem cell pluripotency has yet to be investigated. Here, we reveal the novel functions of mouse Txnip in cellular reprogramming and differentiation onset by involving in glucose-mediated histone acetylation and the regulation of Oct4, which is a fundamental component of the molecular circuitry underlying pluripotency. During reprogramming or PSC differentiation process, cellular metabolic and chromatin remodeling occur in order to change its cellular fate. Txnip knockout promotes induced pluripotency but hinders initial differentiation by activating pluripotency factors and promoting glycolysis. This alteration affects the intracellular levels of acetyl-coA, a final product of enhanced glycolysis, resulting in sustained histone acetylation on active PSC gene regions. Moreover, Txnip directly interacts with Oct4, thereby repressing its activity and consequently deregulating Oct4 target gene transcriptions. Our work suggests that control of Txnip expression is crucial for cell fate transitions by modulating the entry and exit of pluripotency.

Zbtb16 increases susceptibility of atrial fibrillation in type 2 diabetic mice via Txnip-Trx2 signaling.

Atrial fibrillation (AF) is the most prevalent sustained cardiac arrhythmia, and recent epidemiological studies suggested type 2 diabetes mellitus (T2DM) is an independent risk factor for the development of AF. Zinc finger and BTB (broad-complex, tram-track and bric-a-brac) domain containing 16 (Zbtb16) serve as transcriptional factors to regulate many biological processes. However, the potential effects of Zbtb16 in AF under T2DM condition remain unclear. Here, we reported that db/db mice displayed higher AF vulnerability and Zbtb16 was identified as the most significantly enriched gene by RNA sequencing (RNA-seq) analysis in atrium. In addition, thioredoxin interacting protein (Txnip) was distinguished as the key downstream gene of Zbtb16 by Cleavage Under Targets and Tagmentation (CUT&Tag) assay. Mechanistically, increased Txnip combined with thioredoxin 2 (Trx2) in mitochondrion induced excess reactive oxygen species (ROS) release, calcium/calmodulin-dependent protein kinase II (CaMKII) overactivation, and spontaneous Ca2+ waves (SCWs) occurrence, which could be inhibited through atrial-specific knockdown (KD) of Zbtb16 or Txnip by adeno-associated virus 9 (AAV9) or Mito-TEMPO treatment. High glucose (HG)-treated HL-1 cells were used to mimic the setting of diabetic in vitro. Zbtb16-Txnip-Trx2 signaling-induced excess ROS release and CaMKII activation were also verified in HL-1 cells under HG condition. Furthermore, atrial-specific Zbtb16 or Txnip-KD reduced incidence and duration of AF in db/db mice. Altogether, we demonstrated that interrupting Zbtb16-Txnip-Trx2 signaling in atrium could decrease AF susceptibility via reducing ROS release and CaMKII activation in the setting of T2DM.

Three classes of epigenomic regulators converge to hyperactivate the essential maternal gene deadhead within a heterochromatin mini-domain.

The formation of a diploid zygote is a highly complex cellular process that is entirely controlled by maternal gene products stored in the egg cytoplasm. This highly specialized transcriptional program is tightly controlled at the chromatin level in the female germline. As an extreme case in point, the massive and specific ovarian expression of the essential thioredoxin Deadhead (DHD) is critically regulated in Drosophila by the histone demethylase Lid and its partner, the histone deacetylase complex Sin3A/Rpd3, via yet unknown mechanisms. Here, we identified Snr1 and Mod(mdg4) as essential for dhd expression and investigated how these epigenomic effectors act with Lid and Sin3A to hyperactivate dhd. Using Cut&Run chromatin profiling with a dedicated data analysis procedure, we found that dhd is intriguingly embedded in an H3K27me3/H3K9me3-enriched mini-domain flanked by DNA regulatory elements, including a dhd promoter-proximal element essential for its expression. Surprisingly, Lid, Sin3a, Snr1 and Mod(mdg4) impact H3K27me3 and this regulatory element in distinct manners. However, we show that these effectors activate dhd independently of H3K27me3/H3K9me3, and that dhd remains silent in the absence of these marks. Together, our study demonstrates an atypical and critical role for chromatin regulators Lid, Sin3A, Snr1 and Mod(mdg4) to trigger tissue-specific hyperactivation within a unique heterochromatin mini-domain.

FTO Deficiency Alleviates LPS-induced Acute Lung Injury by TXNIP/NLRP3-mediated Alveolar Epithelial Cell Pyroptosis.

N6-methyladenosine (m6A) plays a role in various diseases, but it has rarely been reported in acute lung injury (ALI). The FTO (fat mass and obesity-associated) protein can regulate mRNA metabolism by removing m6A residues. The aim of this study was to examine the role and mechanism of the m6A demethylase FTO in LPS-induced ALI. Lung epithelial FTO-knockout mice and FTO-knockdown/overexpression human alveolar epithelial (A549) cell lines were constructed to evaluate the effects of FTO on ALI. Bioinformatics analysis and a series of in vivo and in vitro assays were used to examine the mechanism of FTO regulation. Rescue assays were conducted to examine whether the impact of FTO on ALI depended on the TXNIP/NLRP3 pathway. In LPS-induced ALI, RNA m6A modification amounts were upregulated, and FTO expression was downregulated. In vivo, lung epithelial FTO knockout alleviated alveolar structure disorder, tissue edema, and pulmonary inflammation and improved the survival of ALI mice. In vitro, FTO knockdown reduced A549 cell damage and death induced by LPS, whereas FTO overexpression exacerbated cell damage and death. Mechanistically, bioinformatics analysis revealed that TXNIP was a downstream target of FTO. FTO deficiency mitigated pyroptosis in LPS-induced ALI via the TXNIP/NLRP3 pathway. Rescue assays confirmed that the impact of FTO on the TXNIP/NLRP3 pathway was significantly reversed by the TXNIP inhibitor SRI-37330. Deficiency of FTO alleviates LPS-induced ALI via TXNIP/NLRP3 pathway-mediated alveolar epithelial cell pyroptosis, which might be a novel therapeutic strategy for combating ALI.

Catalytic Activity of the Archetype from Group 4 of the FTR-like Ferredoxin:Thioredoxin Reductase Family Is Regulated by Unique S = 7/2 and S = 1/2 [4Fe-4S] Clusters.

Thioredoxin reductases (TrxR) activate thioredoxins (Trx) that regulate the activity of diverse target proteins essential to prokaryotic and eukaryotic life. However, very little is understood of TrxR/Trx systems and redox control in methanogenic microbes from the domain Archaea (methanogens), for which genomes are abundant with annotations for ferredoxin:thioredoxin reductases [Fdx/thioredoxin reductase (FTR)] from group 4 of the widespread FTR-like family. Only two from the FTR-like family are characterized: the plant-type FTR from group 1 and FDR from group 6. Herein, the group 4 archetype (AFTR) from Methanosarcina acetivorans was characterized to advance understanding of the family and TrxR/Trx systems in methanogens. The modeled structure of AFTR, together with EPR and Mössbauer spectroscopies, supports a catalytic mechanism similar to plant-type FTR and FDR, albeit with important exceptions. EPR spectroscopy of reduced AFTR identified a transient [4Fe-4S]1+ cluster exhibiting a mixture of S = 7/2 and typical S = 1/2 signals, although rare for proteins containing [4Fe-4S] clusters, it is most likely the on-pathway intermediate in the disulfide reduction. Furthermore, an active site histidine equivalent to residues essential for the activity of plant-type FTR and FDR was found dispensable for AFTR. Finally, a unique thioredoxin system was reconstituted from AFTR, ferredoxin, and Trx2 from M. acetivorans, for which specialized target proteins were identified that are essential for growth and other diverse metabolisms.

Unveiling success determinants for AMB-assisted phase expansion of fusion proteins in ARP/wARP.

Fusion proteins (FPs) are frequently utilized as a biotechnological tool in the determination of macromolecular structures using X-ray methods. Here, we explore the use of different protein tags in various FP, to obtain initial phases by using them in a partial molecular replacement (MR) and constructing the remaining FP structure with ARP/wARP. Usually, the tag is removed prior to crystallization, however leaving the tag on may facilitate crystal formation, and structural determination by expanding phases from known to unknown segments of the complex. In this study, the Protein Data Bank was mined for an up-to-date list of FPs with the most used protein tags, Maltose Binding Protein (MBP), Green Fluorescent Protein (GFP), Thioredoxin (TRX), Glutathione transferase (GST) and the Small Ubiquitin-like Modifier Protein (SUMO). Partial MR using the protein tag, followed by automatic model building, was tested on a subset of 116 FP. The efficiency of this method was analyzed and factors that influence the coordinate construction of a substantial portions of the fused protein were identified. Using MBP, GFP, and SUMO as phase generators it was possible to build at least 75 % of the protein of interest in 36 of the 116 cases tested. Our results reveal that tag selection has a significant impact; tags with greater structural stability, such as GFP, increase the success rate. Further statistical analysis identifies that resolution, Wilson B factor, solvent percentage, completeness, multiplicity, protein tag percentage in the FP (considering amino acids), and the linker length play pivotal roles using our approach. In cases where a structural homologous is absent, this method merits inclusion in the toolkit of protein crystallographers.

Biophysical and biochemical characterization of the thioredoxin system from Colwellia psychrerythraea.

The thioredoxin system is a ubiquitous oxidoreductase system consisting of the enzyme thioredoxin reductase, the protein thioredoxin, and the cofactor nicotinamide adenine dinucleotide phosphate. The system has been comprehensively studied from many organisms, such as Escherichia coli; however, structural and functional analysis of this system from psychrophilic bacteria has not been as extensive. In this study, the thioredoxin system proteins of a psychrophilic bacterium, Colwellia psychrerythraea, were characterized using biophysical and biochemical techniques. Analysis of the complete genome sequence of the C. psychrerythraea thioredoxin system suggested the presence of a putative thioredoxin reductase and at least three thioredoxin. In this study, these identified putative thioredoxin system components were cloned, overexpressed, purified, and characterized. Our studies have indicated that the thioredoxin system proteins from E. coli were more stable than those from C. psychrerythraea. Consistent with these results, kinetic assays indicated that the thioredoxin reductase from E. coli had a higher optimal temperature than that from C. psychrerythraea.

Fluorinated curcumin derivative (Shiga-Y6) modulates the level of thioredoxin-interacting protein (TXNIP) in a mouse model of diabetes.

Thioredoxin interacting protein (TXNIP) has emerged as a significant regulator of ß-cell mass and loss, rendering it an attractive target for treating diabetes. We previously showed that Shiga-Y6, a fluorinated curcumin derivative, inhibited TXNIP mRNA and protein expression in vitro, raising the question of whether the same effect could be translated in vivo. Herein, we examined the effect of Shiga-Y6 on TNXIP levels and explored its therapeutic potential in a mouse model of diabetes, Akita mice. We intraperitoneally injected Shiga-Y6 (SY6; 30 mg/kg of body weight) or vehicle into 8-week-old Akita mice for 28 consecutive days. On day 29, the mice were euthanized, following which the serum levels of glucose, insulin, and glucagon were measured using ELISA, the expression of TXNIP in pancreatic tissue lysates was determined using western blotting, and the level of ß-cell apoptosis was assessed using the TUNEL assay. TXNIP levels in the pancreatic tissue of Akita mice were significantly elevated compared with wild-type (WT) mice. Shiga-Y6 administration for 28 days significantly lowered those levels compared with Akita mice that received vehicle to a level comparable to WT mice. In immunohistochemical analysis, both α- to ß-cell ratio and the number of apoptotic ß-cells were significantly reduced in SY6-treated Akita mice, compared with vehicle-treated Akita mice. Findings from the present study suggest a potential of Shiga-Y6 as an antidiabetic agent through lowering TXNIP protein levels and ameliorating pancreatic ß-cells apoptosis.

x- and y-type thioredoxins maintain redox homeostasis on photosystem I acceptor side under fluctuating light.

Plants cope with sudden increases in light intensity through various photoprotective mechanisms. Redox regulation by thioredoxin (Trx) systems also contributes to this process. Whereas the functions of f- and m-type Trxs in response to such fluctuating light conditions have been extensively investigated, those of x- and y-type Trxs are largely unknown. Here, we analyzed the trx x single, trx y1 trx y2 double, and trx x trx y1 trx y2 triple mutants in Arabidopsis (Arabidopsis thaliana). A detailed analysis of photosynthesis revealed changes in photosystem I (PSI) parameters under low light in trx x and trx x trx y1 trx y2. The electron acceptor side of PSI was more reduced in these mutants than in the wild type. This mutant phenotype was more pronounced under fluctuating light conditions. During both low- and high-light phases, the PSI acceptor side was largely limited in trx x and trx x trx y1 trx y2. After fluctuating light treatment, we observed more severe PSI photoinhibition in trx x and trx x trx y1 trx y2 than in the wild type. Furthermore, when grown under fluctuating light conditions, trx x and trx x trx y1 trx y2 plants showed impaired growth and decreased level of PSI subunits. These results suggest that Trx x and Trx y prevent redox imbalance on the PSI acceptor side, which is required to protect PSI from photoinhibition, especially under fluctuating light. We also propose that Trx x and Trx y contribute to maintaining the redox balance even under constant low-light conditions to prepare for sudden increases in light intensity.

Calredoxin regulates the chloroplast NADPH-dependent thioredoxin reductase in Chlamydomonas reinhardtii.

Calredoxin (CRX) is a calcium (Ca2+)-dependent thioredoxin (TRX) in the chloroplast of Chlamydomonas (Chlamydomonas reinhardtii) with a largely unclear physiological role. We elucidated the CRX functionality by performing in-depth quantitative proteomics of wild-type cells compared with a crx insertional mutant (IMcrx), two CRISPR/Cas9 KO mutants, and CRX rescues. These analyses revealed that the chloroplast NADPH-dependent TRX reductase (NTRC) is co-regulated with CRX. Electron transfer measurements revealed that CRX inhibits NADPH-dependent reduction of oxidized chloroplast 2-Cys peroxiredoxin (PRX1) via NTRC and that the function of the NADPH-NTRC complex is under strict control of CRX. Via non-reducing SDS-PAGE assays and mass spectrometry, our data also demonstrated that PRX1 is more oxidized under high light (HL) conditions in the absence of CRX. The redox tuning of PRX1 and control of the NADPH-NTRC complex via CRX interconnect redox control with active photosynthetic electron transport and metabolism, as well as Ca2+ signaling. In this way, an economic use of NADPH for PRX1 reduction is ensured. The finding that the absence of CRX under HL conditions severely inhibited light-driven CO2 fixation underpins the importance of CRX for redox tuning, as well as for efficient photosynthesis.