Targeted Deletion of Thioredoxin-Interacting Protein Regulates Cardiac Dysfunction in Response to Pressure Overload

The role of TXNIP in cancer: a fine balance between redox, metabolic, and immunological tumor control

Thioredoxin-interacting protein (TXNIP) is commonly considered a master regulator of cellular oxidation, regulating the expression and function of Thioredoxin (Trx). Recent work has identified that TXNIP has a far wider range of additional roles: from regulating glucose and lipid metabolism, to cell cycle arrest and inflammation. Its expression is increased by stressors commonly found in neoplastic cells and the wider tumor microenvironment (TME), and, as such, TXNIP has been extensively studied in cancers. In this review, we evaluate the current literature regarding the regulation and the function of TXNIP, highlighting its emerging role in modulating signaling between different cell types within the TME. We then assess current and future translational opportunities and the associated challenges in this area. An improved understanding of the functions and mechanisms of TXNIP in cancers may enhance its suitability as a therapeutic target.

Myocardial ischemia-reperfusion injury; Molecular mechanisms and prevention

Cardiovascular diseases are one of the leading causes of mortality in developed countries. Among cardiovascular disorders, myocardial infarction remains a life-threatening problem predisposing to the development and progression of ischemic heart failure. Ischemia/reperfusion (I/R) injury is a critical cause of myocardial injury. In recent decades, many efforts have been made to find the molecular and cellular mechanisms underlying the development of myocardial I/R injury and post-ischemic remodeling. Some of these mechanisms are mitochondrial dysfunction, metabolic alterations, inflammation, high production of ROS, and autophagy deregulation. Despite continuous efforts, myocardial I/R injury remains a major challenge in medical treatments of thrombolytic therapy, heart disease, primary percutaneous coronary intervention, and coronary arterial bypass grafting. The development of effective therapeutic strategies to reduce or prevent myocardial I/R injury is of great clinical significance.

Txnip Gene Knockout Ameliorated High-Fat Diet-Induced Cardiomyopathy Via Regulating Mitochondria Dynamics and Fatty Acid Oxidation

ABSTRACT

Epidemic of obesity accelerates the increase in the number of patients with obesity cardiomyopathy. Thioredoxin interacting protein (TXNIP) has been implicated in the pathogenesis of multiple cardiovascular diseases. However, its specific role in obesity cardiomyopathy is still not well understood. Here, we evaluated the role of TXNIP in obesity-induced cardiomyopathy by feeding wild-type and txnip gene knockout mice with either normal diet or high-fat diet (HFD) for 24 weeks. Our results suggested that TXNIP deficiency improved mitochondrial dysfunction via reversing the shift from mitochondrial fusion to fission in the context of chronic HFD feeding, thus promoting cardiac fatty acid oxidation to alleviate chronic HFD-induced lipid accumulation in the heart, and thereby ameliorating the cardiac function in obese mice. Our work provides a theoretical basis for TXNIP exerting as a potential therapeutic target for the interventions of obesity cardiomyopathy.

The Function of MondoA and ChREBP Nutrient-Sensing Factors in Metabolic Disease

Obesity is a major global public health concern associated with an increased risk of many health problems, including type 2 diabetes, heart disease, stroke, and some types of cancer. Obesity is also a critical factor in the development of insulin resistance and type 2 diabetes. Insulin resistance is associated with metabolic inflexibility, which interferes with the body's ability to switch from free fatty acids to carbohydrate substrates, as well as with the ectopic accumulation of triglycerides in non-adipose tissue, such as that of skeletal muscle, the liver, heart, and pancreas. Recent studies have demonstrated that MondoA (MLX-interacting protein or MLXIP) and the carbohydrate response element-binding protein (ChREBP, also known as MLXIPL and MondoB) play crucial roles in the regulation of nutrient metabolism and energy homeostasis in the body. This review summarizes recent advances in elucidating the function of MondoA and ChREBP in insulin resistance and related pathological conditions. This review provides an overview of the mechanisms by which MondoA and ChREBP transcription factors regulate glucose and lipid metabolism in metabolically active organs. Understanding the underlying mechanism of MondoA and ChREBP in insulin resistance and obesity can foster the development of new therapeutic strategies for treating metabolic diseases.

Comparison of the efficacy of the mouse hepatic and renal antioxidant systems against inflammation-induced oxidative stress

This study was conducted to compare the efficacy of the mouse hepatic and renal antioxidant systems against inflammation-induced oxidative stress. Increased Il-1 and Il-6 expressions, markers of inflammation, were represented by inflammation models in mouse liver and kidney tissues injected intraperitoneally with LPS. After establishing the model, the GSH level and the GSH/GSSG ratio, which are oxidative stress markers, were investigated in both tissues treated with LPS and the control group. The expression of Trx1, TrxR, and Txnip genes increased in the liver tissues of LPS-treated mice. In the kidney tissue, while Trx1 expression decreased, no change was observed in TrxR1 expression, and Txnip expression increased. In the kidneys, TRXR1 and GR activities decreased, whereas GPx activity increased. In both tissues, the TRXR1 protein expression decreased significantly, while TXNIP expression increased. In conclusion, different behaviors of antioxidant system members were observed during acute inflammation in both tissues. Additionally, it can be said that the kidney tissue is more sensitive and takes earlier measures than the liver tissue against cellular damage caused by inflammation and inflammation-induced oxidative stress.

TXNIP DNA methylation is associated with glycemic control over 28 years in type 1 diabetes: findings from the Pittsburgh Epidemiology of Diabetes Complications (EDC) study

INTRODUCTION

DNA methylation (DNAme) has been cross-sectionally associated with type 2 diabetes and hemoglobin A1c (HbA1c) in the general population. However, longitudinal data and data in type 1 diabetes are currently very limited. Thus, we performed an epigenome-wide association study (EWAS) in an observational type 1 diabetes cohort to identify loci with DNAme associated with concurrent and future HbA1cs, as well as other clinical risk factors, over 28 years.

RESEARCH DESIGN AND METHODS

Whole blood DNAme in 683 597 CpGs was analyzed in the Pittsburgh Epidemiology of Diabetes Complications study of childhood onset (<17 years) type 1 diabetes (n=411). An EWAS of DNAme beta values and concurrent HbA1c was performed using linear models adjusted for diabetes duration, sex, pack years of smoking, estimated cell type composition variables, and technical/batch covariates. A longitudinal EWAS of subsequent repeated HbA1c measures was performed using mixed models. We further identified methylation quantitative trait loci (meQTLs) for significant CpGs and conducted a Mendelian randomization.

RESULTS

DNAme at cg19693031 (Chr 1, Thioredoxin-Interacting Protein (TXNIP)) and cg21534330 (Chr 17, Casein Kinase 1 Isoform Delta) was significantly inversely associated with concurrent HbA1c. In longitudinal analyses, hypomethylation of cg19693031 was associated with consistently higher HbA1c over 28 years, and with higher triglycerides, pulse rate, and albumin:creatinine ratio (ACR) independently of HbA1c. We further identified 34 meQTLs in SLC2A1/SLC2A1-AS1 significantly associated with cg19693031 DNAme.

CONCLUSIONS

Our results extend prior findings that TXNIP hypomethylation relates to worse glycemic control in type 1 diabetes by demonstrating the association persists over the long term. Additionally, the associations with triglycerides, pulse rate, and ACR suggest TXNIP DNAme could play a role in vascular damage independent of HbA1c. These findings strengthen potential for interventions targeting TXNIP to improve glycemic control in type 1 diabetes through its role in SLC2A1/glucose transporter 1-mediated glucose regulation.

Slow flow induces endothelial dysfunction by regulating thioredoxin-interacting protein-mediated oxidative metabolism and vascular inflammation

Endothelial cells are highly sensitive to hemodynamic shear stresses, which act in the blood flow's direction on the blood vessel's luminal surface. Thus, endothelial cells on that surface are exposed to various physiological and pathological stimuli, such as disturbed flow-induced shear stress, which may exert effects on adaptive vascular diameter or structural wall remodeling. Here we showed that plasma thioredoxin-interactive protein (TXNIP) and malondialdehyde levels were significantly increased in patients with slow coronary flow. In addition, human endothelial cells exposed to disturbed flow exhibited increased levels of TXNIP in vitro. On the other hand, deletion of human endothelial TXNIP increased capillary formation, nitric oxide production and mitochondrial function, as well as lessened oxidative stress response and endothelial cell inflammation. Additional beneficial impacts from TXNIP deletion were also seen in a glucose utilization study, as reflected by augmented glucose uptake, lactate secretion and extracellular acidification rate. Taken together, our results suggested that TXNIP is a key component involved in mediating shear stress-induced inflammation, energy homeostasis, and glucose utilization, and that TXNIP may serve as a potentially novel endothelial dysfunction regulator.

Embryonic Deletion of TXNIP in GABAergic Neurons Enhanced Oxidative Stress in PV+ Interneurons in Primary Somatosensory Cortex of Aging Mice: Relevance to Schizophrenia

The brain is susceptible to perturbations of redox balance, affecting neurogenesis and increasing the risks of psychiatric disorders. Thioredoxin-interacting protein (TXNIP) is an endogenous inhibitor of the thioredoxin antioxidant system. Its deletion or inhibition suggests protection for a brain with ischemic stroke or Alzheimer’s disease. Combined with conditional knockout mice and schizophrenia samples, we aimed to investigate the function of TXNIP in healthy brain and psychiatric disorders, which are under-studied. We found TXNIP was remarkedly expressed in the prefrontal cortex (PFC) during healthy mice’s prenatal and early postnatal periods, whereas it rapidly decreased throughout adulthood. During early life, TXNIP was primarily distributed in inhibitory and excitatory neurons. Contrary to the protective effect, the embryonic deletion of TXNIP in GABAergic (gamma-aminobutyric acid-ergic) neurons enhanced oxidative stress in PV⁺ interneurons of aging mice. The deleterious impact was brain region-specific. We also investigated the relationship between TXNIP and schizophrenia. TXNIP was significantly increased in the PFC of schizophrenia-like mice after MK801 administration, followed by oxidative stress. First episode and drug naïve schizophrenia patients with a higher level of plasma TXNIP displayed severer psychiatric symptoms than patients with a low level. We indicated a bidirectional function of TXNIP in the brain, whose high expression in the early stage is protective for development but might be harmful in a later period, associated with mental disorders.

Silencing TXNIP ameliorates high uric acid-induced insulin resistance via the IRS2/AKT and Nrf2/HO-1 pathways in macrophages

Insulin resistance (IR) promotes atherosclerosis and increases the risk of diabetes and cardiovascular diseases. Our previous studies have demonstrated that high uric acid (HUA) increased oxidative stress, leading to IR in cardiomyocytes and pancreatic β cells. However, whether HUA can induce IR in monocytes/macrophages, which play critical roles in all stages of atherosclerosis, is unclear. Recent findings revealed that thioredoxin-interacting protein (TXNIP) negatively regulates insulin signaling; however, the roles and mechanisms of TXNIP in HUA-induced IR remain unclear. Therefore, in this study, we investigated the function of TXNIP in macrophages treated with UA. Transcriptomic profiling revealed TXNIP as one of the most upregulated genes, and subsequent RT-PCR and Western blot analyses confirmed that TXNIP was upregulated by HUA. HUA treatment significantly increased mitochondrial reactive oxygen species (MtROS) levels and decreased insulin-stimulated glucose uptake. Silencing TXNIP by RNA interference significantly diminished HUA-induced oxidative stress and IR. Mechanistically, silencing TXNIP reversed the inhibition of the phosphorylation of insulin receptor substrate 2 (IRS2)/protein kinase B (AKT) pathway induced by HUA. Additional study revealed that HUA induced the activation of the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase 1 (HO-1) signaling pathway, but silencing TXNIP abolished it. Moreover, Nrf2 inhibitor (ML385) ameliorated HUA-induced IR independent of IRS2/AKT signaling. Probenecid, a well-known UA-lowering drug, significantly suppressed the activation of TXNIP and Nrf2/HO-1 signaling. Furthermore, RNA-seq revealed that activation of the TXNIP-related redox pathway may be a key regulator in patients with asymptomatic hyperuricemia. These data suggest that silencing TXNIP could ameliorate HUA-induced IR via the IRS2/AKT and Nrf2/HO-1 pathways in macrophages. Additionally, TXNIP might be a promising therapeutic target for preventing and treating oxidative stress and IR induced by HUA.

Antidiabetic effects of quercetin and liraglutide combination through modulation of TXNIP/IRS-1/PI3K pathway

The study was designed to assess the possible augmented antidiabetic effects of combining quercetin and liraglutide in a type 1 diabetes model, with emphasis on the contribution of hepatic thioredoxin interacting protein (TXNIP)/insulin receptor substrate 1 (IRS-1)/phosphatidyl inositol-3 kinase (PI3K) pathway. The wound-healing effects were also examined. Diabetes was induced by a single i.p STZ injection (55 mg/kg). Diabetic rats were treated with either quercetin (100 mg/kg/day, orally) or liraglutide (0.3 mg/kg/twice daily, S.C.) or their combination. Drugs were also applied topically on the wound. Blood glucose levels, serum albumin, total protein, total cholesterol and triglycerides were measured. Histopathological examination of the liver, pancreas and skin tissues was performed using haematoxylin and eosin staining. The hepatic malondialdehyde level was measured spectrophotometrically. Hepatic TXNIP and PI3K levels were measured by enzyme-linked immunsorbent assay (ELISA). Tissue expression of IRS-1 and phospho-IRS-1 (Ser 616) was assessed by immunohistochemistry. Quercetin, liraglutide and their combination effectively decreased blood glucose levels, improved lipid profile, upregulated albumin and total protein serum levels and reduced hepatic oxidative stress with the combination being most effective. Moreover, the combination group showed enhanced wound-healing effects and almost normalized hepatic and pancreatic histopathology. Quercetin and/or liraglutide significantly decreased TXNIP levels and serine phosphorylation of IRS-1 and increased PI3K levels compared to the diabetic untreated group. Interestingly, only the combination therapy normalized hepatic IRS-1 expression. The combination of quercetin and liraglutide showed enhanced antidiabetic effects, possibly through lowering hepatic TXNIP levels, with the resultant up-regulation of the IRS-1/PI3K pathway.

Cardiomyocyte-specific Txnip C247S mutation improves left ventricular functional reserve in streptozotocin-induced diabetic mice

Underlying molecular mechanisms for the development of diabetic cardiomyopathy remain to be determined. Long-term exposure to hyperglycemia causes oxidative stress, which leads to cardiomyocyte dysfunction. Previous studies established the importance of thioredoxin-interacting protein (Txnip) in cellular redox homeostasis and glucose metabolism. Txnip is a highly glucose-responsive molecule that interacts with the catalytic center of reduced thioredoxin and inhibits the antioxidant function of thioredoxin. Here, we show that the molecular interaction between Txnip and thioredoxin plays a pivotal role in the regulation of redox balance in the diabetic myocardium. High glucose increased Txnip expression, decreased thioredoxin activities, and caused oxidative stress in cells. The Txnip-thioredoxin complex was detected in cells with overexpressing wild-type Txnip but not Txnip cysteine 247 to serine (C247S) mutant that disrupts the intermolecular disulfide bridge. Then, diabetes was induced in cardiomyocyte-specific Txnip C247S knock-in mice and their littermate control animals by injections of streptozotocin (STZ). Prolonged hyperglycemia upregulated myocardial Txnip expression in both genotypes. The absence of Txnip's inhibition of thioredoxin in Txnip C247S mutant hearts promoted mitochondrial antioxidative capacities in cardiomyocytes, thereby protecting the heart from oxidative damage by diabetes. Stress hemodynamic analysis uncovered that Txnip C247S knock-in hearts have a greater left ventricular contractile reserve than wild-type hearts under STZ-induced diabetic conditions. These results provide novel evidence that Txnip serves as a regulator of hyperglycemia-induced cardiomyocyte toxicities through direct inhibition of thioredoxin and identify the single cysteine residue in Txnip as a therapeutic target for diabetic injuries.NEW & NORTEWORTHY Thioredoxin-interacting protein (Txnip) has been of great interest as a molecular mechanism to mediate diabetic organ damage. Here, we provide novel evidence that a single mutation of Txnip confers a defense mechanism against myocardial oxidative stress in streptozotocin-induced diabetic mice. The results demonstrate the importance of Txnip as a cysteine-containing redox protein that regulates antioxidant thioredoxin via disulfide bond-switching mechanism and identify the cysteine in Txnip as a therapeutic target for diabetic cardiomyopathy.

The Emerging Role of TXNIP in Ischemic and Cardiovascular Diseases; A Novel Marker and Therapeutic Target

Thioredoxin interacting protein (TXNIP) is a metabolism- oxidative- and inflammation-related marker induced in cardiovascular diseases and is believed to represent a possible link between metabolism and cellular redox status. TXNIP is a potential biomarker in cardiovascular and ischemic diseases but also a novel identified target for preventive and curative medicine. The goal of this review is to focus on the novelties concerning TXNIP. After an overview in TXNIP involvement in oxidative stress, inflammation and metabolism, the remainder of this review presents the clues used to define TXNIP as a new marker at the genetic, blood, or ischemic site level in the context of cardiovascular and ischemic diseases.

TXNIP/Redd1 signalling and excessive autophagy: a novel mechanism of myocardial ischaemia/reperfusion injury in mice

AIMS

Either insufficient or excessive autophagy causes cellular death and contributes to myocardial ischaemia/reperfusion (I/R) injury. However, mechanisms controlling the 'right-level' of autophagy in the heart remains unidentified. Thioredoxin-interacting protein (TXNIP) is a pro-oxidative molecule knowing to contribute to I/R injury. However, whether and how TXNIP may further inhibit suppressed autophagy or promote excessive cardiac autophagy in I/R heart has not been previously investigated.

METHODS AND RESULTS

Wild type or gene-manipulated adult male mice were subjected to myocardial I/R. TXNIP was increased in myocardium during I/R. Cardiac-specific TXNIP overexpression increased cardiomyocytes apoptosis and cardiac dysfunction, whereas cardiac-specific TXNIP knock-out significantly mitigated I/R-induced apoptosis and improved cardiac function. Importantly, TXNIP overexpression significantly promoted cardiac autophagy and TXNIP knock-out significantly inhibited cardiac autophagy. In vitro studies demonstrated that TXNIP increased autophagosome formation but inhibited autophagosome clearance during myocardial reperfusion. Atg5 siRNA significantly decreased hypoxia/reoxygenation induced apoptosis in cardiomyocytes with TXNIP overexpression. Mechanistically, TXNIP suppressed autophagosome clearance via increasing reactive oxygen species (ROS) level. However, TXNIP-increased autophagosome formation was not mediated by ROS as a ROS scavenger failed to block increased autophagosome formation in TXNIP overexpression heart. Finally, TXNIP directly interacted and stabilized Redd1 (an autophagy regulator), resulting in mTOR inhibition and autophagy activation. Redd1 knock-down significantly reduced autophagy formation and ameliorated I/R injury in TXNIP overexpression hearts.

CONCLUSIONS

Our results demonstrated that increased TXNIP-Redd1 expression is a novel signalling pathway that contributes to I/R injury by exaggerating excessive autophagy during reperfusion. These observations advance our understanding of the mechanisms of myocardial I/R injury.

Thioredoxin Interacting Protein (TXNIP) Is Differentially Expressed in Human Tumor Samples but Is Absent in Human Tumor Cell Line Xenografts: Implications for Its Use as an Immunosurveillance Marker

Simple Summary

The metabolic protein TXNIP plays a crucial role in various cellular processes. Abnormal TXNIP levels are notable, e.g., in type II diabetes, cardiovascular diseases, and tumors. Using immunohistochemical staining for TXNIP in different tumor entities, we give new insights of TXNIP expression on the protein level. In human tumors, staining intensity inversely correlated with aggressiveness of the tumor entity. In contrast, human tumor cell lines grown in mice (xenografts), consistently revealed no staining. Hence, loss of TXNIP suggests a critical role for the development of tumors in xenografts. Furthermore, we investigated TXNIP staining of immunocompetent cells in the proximity of the xenograft tumor tissue. Our findings demonstrate that TXNIP downregulation is a common feature in human tumor xenograft models. Subsequently, TXNIP expression might be used to monitor the functional state of tumor-infiltrating leukocytes in tissue sections and may help to predict response to modern immune therapy.

Abstract

Thioredoxin interacting protein (TXNIP) is a metabolic protein critically involved in redox homeostasis and has been proposed as a tumor suppressor gene in a variety of malignancies. Accordingly, TXNIP is downregulated in breast, bladder, and gastric cancer and in tumor transplant models TXNIP overexpression inhibits growth and metastasis. As TXNIP protein expression has only been investigated in few malignancies, we employed immunohistochemical detection in a large multi-tumor tissue microarray consisting of 2,824 samples from 94 different tumor entities. In general, TXNIP protein was present only in a small proportion of primary tumor samples and in these cases was differently expressed depending on tumor stage and subtype (e.g., renal cell carcinoma, thyroid cancer, breast cancer, and ductal pancreatic cancer). Further, TXNIP protein expression was determined in primary mouse xenograft tumors derived from human cancer cell lines and was immunohistochemically absent in all xenograft tumors investigated. Intriguingly, TXNIP expression became gradually lower in the proximity of the primary tumor tissue and was absent in leukocytes directly adjacent to tumor tissue. In conclusion, these findings suggest that TXNIP downregulation is as a common feature in human tumor xenograft models and that intra-tumoral leukocytes down-regulate TXNIP. Hence TXNIP expression might be used to monitor the functional state of tumor-infiltrating leukocytes in tissue sections.

The thioredoxin-1 inhibitor Txnip restrains effector T-cell and germinal center B-cell expansion

Thioredoxin-1 (Trx1) is a vital component for cellular redox homeostasis. In T cells, Trx1 donates electrons for the de novo synthesis of deoxyribonucleotides to allow rapid cell proliferation. The Trx-interacting protein (Txnip) binds to the reduced Trx1 and inhibits its activity. However, the role of Txnip in adaptive immunity in vivo is unknown. Here, we show that absence of Txnip increased proliferation of effector T cells and GC B-cell responses in response to lymphocytic choriomeningitis virus and Qβ virus-like particles, respectively, but did not affect development and homeostasis of T and B cells. While downregulation of Txnip and concomitant upregulation of Trx1 is critical for rapid T-cell expansion upon viral infection, re-expression of Txnip and consequently inhibition of Trx1 is important to restrain late T-cell expansion. Importantly, we demonstrated that T-cell receptor (TCR) engagement but not CD28 costimulation is critically required for Txnip downregulation. Thus, this study further uncovers positive and negative control of lymphocyte proliferation by the Trx1 system.

TXNIP/TBP-2: A Master Regulator for Glucose Homeostasis

Identification of thioredoxin binding protein-2 (TBP-2), which is currently known as thioredoxin interacting protein (TXNIP), as an important binding partner for thioredoxin (TRX) revealed that an evolutionarily conserved reduction-oxidation (redox) signal complex plays an important role for pathophysiology. Due to the reducing activity of TRX, the TRX/TXNIP signal complex has been shown to be an important regulator for redox-related signal transduction in many types of cells in various species. In addition to its role in redox-dependent regulation, TXNIP has cellular functions that are performed in a redox-independent manner, which largely rely on their scaffolding function as an ancestral α-Arrestin family. Both the redox-dependent and -independent TXNIP functions serve as regulatory pathways in glucose metabolism. This review highlights the key advances in understanding TXNIP function as a master regulator for whole-body glucose homeostasis. The potential for therapeutic advantages of targeting TXNIP in diabetes and the future direction of the study are also discussed.

Thioredoxin-1 distinctly promotes NF-κB target DNA binding and NLRP3 inflammasome activation independently of Txnip

Antioxidant systems, such as the thioredoxin-1 (Trx1) pathway, ensure cellular redox homeostasis. However, how such systems regulate development and function of myeloid cells is barely understood. Here we show that in contrast to its critical role in T cells, the murine Trx1 system is dispensable for steady-state myeloid-cell hematopoiesis due to their capacity to tap the glutathione/glutaredoxin pathway for DNA biosynthesis. However, the Trx1 pathway instrumentally enables nuclear NF-κB DNA-binding and thereby pro-inflammatory responses in monocytes and dendritic cells. Moreover, independent of this activity, Trx1 is critical for NLRP3 inflammasome activation and IL-1β production in macrophages by detoxifying excessive ROS levels. Notably, we exclude the involvement of the Trx1 inhibitor Txnip as a redox-sensitive ligand of NLRP3 as previously proposed. Together, this study suggests that targeting Trx1 may be exploited to treat inflammatory diseases.

Effect of Taurine on Cell Function via TXNIP Induction in Caco-2 Cells

Taurine (2-aminoethanesulfonic acid), a sulfur-containing β-amino acid, is a free amino acid present in high concentrations in mammalian tissues. Taurine has pivotal roles in anti-oxidation, membrane stabilization, osmoregulation, anti-inflammation, and other process. In a DNA microarray analysis, we previously found that taurine markedly increases the mRNA expression of thioredoxin interacting protein (TXNIP) in Caco-2 cells. In this study, we investigated the effect of these taurine-induced changes in TXNIP on the function of Caco-2 cells. We found that taurine decreases glucose uptake in a dose-dependent manner. The taurine-induced decrease in glucose uptake was completely abolished by transfection with siRNA against TXNIP, suggesting that TXNIP is involved in the taurine-induced down-regulation of glucose uptake. We also revealed that taurine induces AMPK activation and further increases the intracellular ATP content in Caco-2 cells. These results suggest that taurine could regulate the function of Caco-2 cells via TXNIP induction, leading to extend our understanding of the functions of taurine.

MicroRNAs Associated With Reverse Left Ventricular Remodeling in Humans Identify Pathways of Heart Failure Progression

BACKGROUND

Plasma extracellular RNAs have recently garnered interest as biomarkers in heart failure (HF). Most studies in HF focus on single extracellular RNAs related to phenotypes and outcomes, and few describe their functional roles. We hypothesized that clusters of plasma microRNAs (miRNAs) associated with left ventricular (LV) remodeling in human HF would identify novel subsets of genes involved in HF in animal models.

METHODS AND RESULTS

We prospectively measured circulating miRNAs in 64 patients with systolic HF (mean age, 64.8 years; 91% men; median LV ejection fraction, 26%) with serial echocardiography (10 months apart) during medical therapy. We defined LV reverse remodeling as a 15% reduction in LV end-systolic volume index. Using principal components analysis, we identified a component associated with LV reverse remodeling (odds ratio=3.99; P=0.01) that provided risk discrimination for LV reverse remodeling superior to a clinical model (C statistic, 0.58 for a clinical model versus 0.71 for RNA-based model). Using network bioinformatics, we uncovered genes not previously widely described in HF regulated simultaneously by >2 miRNAs. We observed increased myocardial expression of these miRNAs during HF development in animals, with downregulation of target gene expression, suggesting coordinate miRNA-mRNA regulation. Target mRNAs were involved in autophagy, metabolism, and inflammation.

CONCLUSIONS

Plasma miRNAs associated with LV reverse remodeling in humans are dysregulated in animal HF and target clusters of genes involved in mechanisms implicated in HF. A translational approach integrating human HF, bioinformatics, and model systems may uncover novel pathways involved in HF.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT00351390.

Absence of TXNIP in Humans Leads to Lactic Acidosis and Low Serum Methionine Linked to Deficient Respiration on Pyruvate

Thioredoxin-interacting protein (TXNIP) is an α-arrestin that can bind to and inhibit the antioxidant protein thioredoxin (TXN). TXNIP expression is induced by glucose and promotes β-cell apoptosis in the pancreas, and deletion of its gene in mouse models protects against diabetes. TXNIP is currently studied as a potential new target for antidiabetic drug therapy. In this study, we describe a family with a mutation in the TXNIP gene leading to nondetectable expression of TXNIP protein. Symptoms of affected family members include lactic acidosis and low serum methionine levels. Using patient-derived TXNIP-deficient fibroblasts and myoblasts, we show that oxidative phosphorylation is impaired in these cells when given glucose and pyruvate but normalized with malate. Isolated mitochondria from these cells appear to have normal respiratory function. The cells also display a transcriptional pattern suggestive of a high basal activation of the Nrf2 transcription factor. We conclude that a complete lack of TXNIP in human is nonlethal and leads to specific metabolic distortions that are, at least in part, linked to a deficient respiration on pyruvate. The results give important insights into the impact of TXNIP in humans and thus help to further advance the development of antidiabetic drugs targeting this protein.

Genetic polymorphisms associated with reactive oxygen species and blood pressure regulation

Hypertension is the most prevalent cause of cardiovascular disease and kidney failure, but only about 50% of patients achieve adequate blood pressure control, in part, due to inter-individual genetic variations in the response to antihypertensive medication. Significant strides have been made toward the understanding of the role of reactive oxygen species (ROS) in the regulation of the cardiovascular system. However, the role of ROS in human hypertension is still unclear. Polymorphisms of some genes involved in the regulation of ROS production are associated with hypertension, suggesting their potential influence on blood pressure control and response to antihypertensive medication. This review provides an update on the genes associated with the regulation of ROS production in hypertension and discusses the controversies on the use of antioxidants in the treatment of hypertension, including the antioxidant effects of antihypertensive drugs.

TXNIP in Metabolic Regulation: Physiological Role and Therapeutic Outlook

Background & Objective:

Thioredoxin-interacting protein (TXNIP) also known as thioredoxin binding protein-2 is a ubiquitously expressed protein that interacts and negatively regulates expression and function of Thioredoxin (TXN). Over the last few years, TXNIP has attracted considerable attention due to its wide-ranging functions impacting several aspects of energy metabolism. TXNIP acts as an important regulator of glucose and lipid metabolism through pleiotropic actions including regulation of β-cell function, hepatic glucose production, peripheral glucose uptake, adipogenesis, and substrate utilization. Overexpression of TXNIP in animal models has been shown to induce apoptosis of pancreatic β-cells, reduce insulin sensitivity in peripheral tissues like skeletal muscle and adipose, and decrease energy expenditure. On the contrary, TXNIP deficient animals are protected from diet induced insulin resistance and type 2 diabetes.

Summary:

Consequently, targeting TXNIP is thought to offer novel therapeutic opportunity and TXNIP inhibitors have the potential to become a powerful therapeutic tool for the treatment of diabetes mellitus. Here we summarize the current state of our understanding of TXNIP biology, highlight its role in metabolic regulation and raise critical questions that could help future research to exploit TXNIP as a therapeutic target.

Diabetes pathogenic mechanisms and potential new therapies based upon a novel target called TXNIP

PURPOSE OF REVIEW

Thioredoxin-interacting protein has emerged as a major factor regulating pancreatic β-cell dysfunction and death, key processes in the pathogenesis of type 1 and type 2 diabetes. Accumulating evidence based on basic, preclinical, and retrospective epidemiological research suggests that TXNIP represents a promising therapeutic target for diabetes. The present review is aimed at providing an update regarding these developments.

RECENT FINDINGS

TXNIP has been shown to be induced by glucose and increased in diabetes and to promote β-cell apoptosis, whereas TXNIP deletion protected against diabetes. More recently, TXNIP inhibition has also been found to promote insulin production and glucagon-like peptide 1 signaling via regulation of a microRNA. β-Cell TXNIP expression itself was found to be regulated by hypoglycemic agents, carbohydrate-response-element-binding protein, and cytosolic calcium or the calcium channel blocker, verapamil. Retrospective studies now further suggest that verapamil use might be associated with a lower incidence of type 2 diabetes in humans.

SUMMARY

TXNIP has emerged as a key factor in the regulation of functional β-cell mass and TXNIP inhibition has shown beneficial effects in a variety of studies. Thus, the inhibition of TXNIP may provide a novel approach to the treatment of diabetes.

Reduced endothelial thioredoxin-interacting protein protects arteries from damage induced by metabolic stress in vivo

Although thioredoxin-interacting protein (TXNIP) is involved in a variety of biologic functions, the contribution of endothelial TXNIP has not been well defined. To investigate the endothelial function of TXNIP, we generated a TXNIP knockout mouse on the Cdh5-cre background (TXNIP^fl/fl cdh5^cre). Control (TXNIP^fl/fl) and TXNIP^fl/fl cdh5^cre mice were fed a high protein-low carbohydrate (HP-LC) diet for 3 mo to induce metabolic stress. We found that TXNIP^fl/fl and TXNIP^fl/fl cdh5^cre mice on an HP-LC diet displayed impaired glucose tolerance and dyslipidemia concretizing the metabolic stress induced. We evaluated the impact of this metabolic stress on mice with reduced endothelial TXNIP expression with regard to arterial structure and function. TXNIP^fl/fl cdh5^cre mice on an HP-LC diet exhibited less endothelial dysfunction than littermate mice on an HP-LC diet. These mice were protected from decreased aortic medial cell content, impaired aortic distensibility, and increased plasminogen activator inhibitor 1 secretion. This protective effect came with lower oxidative stress and lower inflammation, with a reduced NLRP3 inflammasome expression, leading to a decrease in cleaved IL-1β. We also show the major role of TXNIP in inflammation with a knockdown model, using a TXNIP-specific, small interfering RNA included in a lipoplex. These findings demonstrate a key role for endothelial TXNIP in arterial impairments induced by metabolic stress, making endothelial TXNIP a potential therapeutic target.-Bedarida, T., Domingues, A., Baron, S., Ferreira, C., Vibert, F., Cottart, C.-H., Paul, J.-L., Escriou, V., Bigey, P., Gaussem, P., Leguillier, T., Nivet-Antoine, V. Reduced endothelial thioredoxin-interacting protein protects arteries from damage induced by metabolic stress in vivo.

Mapping Txnip: Key connexions in progression of diabetic nephropathy

Studies demonstrates the major involvement of inflammatory and apoptotic pathway in the pathophysiology of diabetic nephropathy. The cross talk between inflammatory and apoptotic pathway suggests Txnip as a molecular connexion in progression of disease state. Txnip modulates inflammatory pathway (via ROS production and NLRP3 inflammasome activity) and apoptotic pathway (via mTOR pathway). The key contribution of Txnip in both the pathways, reflects, its crucial role in diabetic nephropathy. In the present review, we have first provided an overview of diabetic nephropathy and Txnip system, followed by the mechanistic insight of Txnip in the progression of diabetic nephropathy. This new mechanistic approach suggests to explore Txnip modulators as a promising therapeutic drug target in diabetic nephropathy.

Calcium Signaling and Transcriptional Regulation in Cardiomyocytes

Calcium (Ca 2+ ) is a universal regulator of various cellular functions. In cardiomyocytes, Ca 2+ is the central element of excitation–contraction coupling, but also impacts diverse signaling cascades and influences the regulation of gene expression, referred to as excitation–transcription coupling. Disturbances in cellular Ca 2+ -handling and alterations in Ca 2+ -dependent gene expression patterns are pivotal characteristics of failing cardiomyocytes, with several excitation–transcription coupling pathways shown to be critically involved in structural and functional remodeling processes. Thus, targeting Ca 2+ -dependent transcriptional pathways might offer broad therapeutic potential. In this article, we (1) review cytosolic and nuclear Ca 2+ dynamics in cardiomyocytes with respect to their impact on Ca 2+ -dependent signaling, (2) give an overview on Ca 2+ -dependent transcriptional pathways in cardiomyocytes, and (3) discuss implications of excitation–transcription coupling in the diseased heart.

B-cell identity as a metabolic barrier against malignant transformation

B-lineage and myeloid leukemia cells are often transformed by the same oncogenes, but have different biological and clinical characteristics. Although B-lineage acute lymphoblastic leukemia (B-ALL) cells are characterized by a state of chronic energy deficit, myeloid leukemia cells show abundant energy reserve. Interestingly, fasting has been demonstrated to inhibit selectively the development of B-ALL but not myeloid leukemia, further suggesting that lineage identity may be linked to divergent metabolic states in hematopoietic malignancies. The B-lymphoid transcription factors IKZF1, EBF1, and PAX5 are essential for early B-cell development and commitment to B-cell identity. However, in >80% of human pre-B-ALL cases, the leukemic clones harbor genetic lesions of these transcription factors. The significance of these defects has only recently been investigated. Here, we discuss the unexpected function of a B-lymphoid transcriptional program as a metabolic barrier against malignant transformation of B-cell precursor cells. The metabolic gatekeeper function of B-lymphoid transcription factors may force silent preleukemic clones carrying potentially oncogenic lesions to remain in a latent state. In addition, this program sets the threshold for responses to glucocorticoids in pre-B-ALL. Finally, the link between the tumor-suppressor and metabolic functions of B-lymphoid transcription factors is matched by observations in clinical trials: obesity and hyperglycemia are associated with poor clinical outcome in patients with pre-B-ALL.

The Role of NOX4 and TRX2 in Angiogenesis and Their Potential Cross-Talk

The nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) family is the major source of reactive oxygen species (ROS) in the vascular system. In this family, NOX4, a constitutive active form of NOXs, plays an important role in angiogenesis. Thioredoxin 2 (TRX2) is a key mitochondrial redox protein that maintains normal protein function and also provides electrons to peroxiredoxin 3 (PRX3) to scavenge H₂O₂ in mitochondria. Angiogenesis, a process of new blood vessel formation, is involved in a variety of physiological processes and pathological conditions. It seems to be paradoxical for ROS-producing NOX4 and ROS-scavenging TRX2 to have a similar role in promoting angiogenesis. In this review, we will focus on data supporting the role of NOX4 and TRX2 in angiogenesis and their cross-talks and discuss how ROS can positively or negatively regulate angiogenesis, depending on their species, levels and locations. NOX4 and TRX2-mediated ROS signaling could be promising targets for the treatment of angiogenesis-related diseases.

Metabolic Remodeling in Diabetic Cardiomyopathy

Diabetes is a risk factor for heart failure and cardiovascular mortality with specific changes to myocardial metabolism, energetics, structure, and function. The gradual impairment of insulin production and signalling in diabetes is associated with elevated plasma fatty acids and increased myocardial free fatty acid uptake and activation of the transcription factor PPARα. The increased free fatty acid uptake results in accumulation of toxic metabolites, such as ceramide and diacylglycerol, activation of protein kinase C, and elevation of uncoupling protein-3. Insulin signalling and glucose uptake/oxidation become further impaired, and mitochondrial function and ATP production become compromised. Increased oxidative stress also impairs mitochondrial function and disrupts metabolic pathways. The diabetic heart relies on free fatty acids (FFA) as the major substrate for oxidative phosphorylation and is unable to increase glucose oxidation during ischaemia or hypoxia, thereby increasing myocardial injury, especially in ageing female diabetic animals. Pharmacological activation of PPARγ in adipose tissue may lower plasma FFA and improve recovery from myocardial ischaemic injury in diabetes. Not only is the diabetic heart energetically-impaired, it also has early diastolic dysfunction and concentric remodelling. The contractile function of the diabetic myocardium negatively correlates with epicardial adipose tissue, which secretes proinflammatory cytokines, resulting in interstitial fibrosis. Novel pharmacological strategies targeting oxidative stress seem promising in preventing progression of diabetic cardiomyopathy, although clinical evidence is lacking. Metabolic agents that lower plasma FFA or glucose, including PPARγ agonism and SGLT2 inhibition, may therefore be promising options.

The Emerging Role of Thioredoxin-Interacting Protein in Myocardial Ischemia/Reperfusion Injury

Myocardial ischemia/reperfusion injury represents a major threat to human health and contributes to adverse cardiovascular outcomes worldwide. Despite the identification of numerous molecular mechanisms, understanding of the complex pathophysiology of this clinical syndrome remains incomplete. Thioredoxin-interacting protein (Txnip) has been of great interest in the past decade since it has been reported to be a critical regulator in human diseases with several important cellular functions. Thioredoxin-interacting protein binds to and inhibits thioredoxin, a redox protein that neutralizes reactive oxygen species (ROS), and through its interaction with thioredoxin, Txnip sensitizes cardiomyocytes to ROS-induced apoptosis. Interestingly, evidence from recent studies also suggests that some of the effects of Txnip may be unrelated to changes in thioredoxin activity. These pleiotropic effects of Txnip are mediated by interactions with other signaling molecules, such as nod-like receptor pyrin domain-containing 3 inflammasome and glucose transporter 1. Indeed, Txnip has been implicated in the regulation of inflammatory response and glucose homeostasis during myocardial ischemia/reperfusion injury. This review attempts to make the case that in addition to interacting with thioredoxin, Txnip contributes to some of the pathological consequences of myocardial ischemia and infarction through endogenous signals in multiple molecular mechanisms.

Thioredoxin-1 Attenuates Ventricular and Mitochondrial Postischemic Dysfunction in the Stunned Myocardium of Transgenic Mice

AIM

We evaluated the effect of thioredoxin1 (Trx1) system on postischemic ventricular and mitochondrial dysfunction using transgenic mice overexpressing cardiac Trx1 and a dominant negative (DN-Trx1) mutant (C32S/C35S) of Trx1. Langendorff-perfused hearts were subjected to 15 min of ischemia followed by 30 min of reperfusion (R). We measured left ventricular developed pressure (LVDP, mmHg), left ventricular end diastolic pressure (LVEDP, mmHg), and t63 (relaxation index, msec). Mitochondrial respiration, SERCA2a, phospholamban (PLB), and phospholamban phosphorylation (p-PLB) Thr17 expression (Western blot) were also evaluated.

RESULTS

At 30 min of reperfusion, Trx1 improved contractile state (LVDP: Trx1: 57.4 ± 4.9 vs. Wt: 27.1 ± 6.3 and DN-Trx1: 29.2 ± 7.1, p < 0.05); decreased myocardial stiffness (LVEDP: Wt: 24.5 ± 4.8 vs. Trx1: 11.8 ± 2.9, p < 0.05); and improved the isovolumic relaxation (t63: Wt: 63.3 ± 3.2 vs. Trx1: 51.4 ± 1.9, p < 0.05). DN-Trx1 mice aggravated the myocardial stiffness and isovolumic relaxation. Only the expression of p-PLB Thr17 increased at 1.5 min R in Wt and DN-Trx1 groups. At 30 min of reperfusion, state 3 mitochondrial O2 consumption was impaired by 13% in Wt and by 33% in DN-Trx1. ADP/O ratios for Wt and DN-Trx1 decrease by 25% and 28%, respectively; whereas the Trx1 does not change after ischemia and reperfusion (I/R). Interestingly, baseline values of complex I activity were increased in Trx1 mice; they were 24% and 47% higher than in Wt and DN-Trx1 mice, respectively (p < 0.01).

INNOVATION AND CONCLUSION

These results strongly suggest that Trx1 ameliorates the myocardial effects of I/R by improving the free radical-mediated damage in cardiac and mitochondrial function, opening the possibility of new therapeutic strategies in coronary artery disease. Antioxid. Redox Signal. 25, 78-88.

Regulation of the Yeast Hxt6 Hexose Transporter by the Rod1 α-Arrestin, the Snf1 Protein Kinase, and the Bmh2 14-3-3 Protein

Cell viability requires adaptation to changing environmental conditions. Ubiquitin-mediated endocytosis plays a crucial role in this process, because it provides a mechanism to remove transport proteins from the membrane. Arrestin-related trafficking proteins are important regulators of the endocytic pathway in yeast, facilitating selective ubiquitylation of target proteins by the E3 ubiquitin ligase, Rsp5. Specifically, Rod1 (Art4) has been reported to regulate the endocytosis of both the Hxt1, Hxt3, and Hxt6 glucose transporters and the Jen1 lactate transporter. Also, the AMP kinase homologue, Snf1, and 14-3-3 proteins have been shown to regulate Jen1 via Rod1. Here, we further characterized the role of Rod1, Snf1, and 14-3-3 in the signal transduction route involved in the endocytic regulation of the Hxt6 high affinity glucose transporter by showing that Snf1 interacts specifically with Rod1 and Rog3 (Art7), that the interaction between the Bmh2 and several arrestin-related trafficking proteins may be modulated by carbon source, and that both the 14-3-3 protein Bmh2 and the Snf1 regulatory domain interact with the arrestin-like domain containing the N-terminal half of Rod1 (amino acids 1-395). Finally, using both co-immunoprecipitation and bimolecular fluorescence complementation, we demonstrated the interaction of Rod1 with Hxt6 and showed that the localization of the Rod1-Hxt6 complex at the plasma membrane is affected by carbon source and is reduced upon overexpression of SNF1 and BMH2.

TXNIP regulates myocardial fatty acid oxidation via miR-33a signaling

Myocardial fatty acid β-oxidation is critical for the maintenance of energy homeostasis and contractile function in the heart, but its regulation is still not fully understood. While thioredoxin-interacting protein (TXNIP) has recently been implicated in cardiac metabolism and mitochondrial function, its effects on β-oxidation have remained unexplored. Using a new cardiomyocyte-specific TXNIP knockout mouse and working heart perfusion studies, as well as loss- and gain-of-function experiments in rat H9C2 and human AC16 cardiomyocytes, we discovered that TXNIP deficiency promotes myocardial β-oxidation via signaling through a specific microRNA, miR-33a. TXNIP deficiency leads to increased binding of nuclear factor Y (NFYA) to the sterol regulatory element binding protein 2 (SREBP2) promoter, resulting in transcriptional inhibition of SREBP2 and its intronic miR-33a. This allows for increased translation of the miR-33a target genes and β-oxidation-promoting enzymes, carnitine octanoyl transferase (CROT), carnitine palmitoyl transferase 1 (CPT1), hydroxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase/enoyl-CoA hydratase-β (HADHB), and AMPKα and is associated with an increase in phospho-AMPKα and phosphorylation/inactivation of acetyl-CoA-carboxylase. Thus, we have identified a novel TXNIP-NFYA-SREBP2/miR-33a-AMPKα/CROT/CPT1/HADHB pathway that is conserved in mouse, rat, and human cardiomyocytes and regulates myocardial β-oxidation.

Deletion of thioredoxin-interacting protein improves cardiac inotropic reserve in the streptozotocin-induced diabetic heart

Although the precise pathogenesis of diabetic cardiac damage remains unclear, potential mechanisms include increased oxidative stress, autonomic nervous dysfunction, and altered cardiac metabolism. Thioredoxin-interacting protein (Txnip) was initially identified as an inhibitor of the antioxidant thioredoxin but is now recognized as a member of the arrestin superfamily of adaptor proteins that classically regulate G protein-coupled receptor signaling. Here we show that Txnip plays a key role in diabetic cardiomyopathy. High glucose levels induced Txnip expression in rat cardiomyocytes in vitro and in the myocardium of streptozotocin-induced diabetic mice in vivo. While hyperglycemia did not induce cardiac dysfunction at baseline, β-adrenergic challenge revealed a blunted myocardial inotropic response in diabetic animals (24-wk-old male and female C57BL/6;129Sv mice). Interestingly, diabetic mice with cardiomyocyte-specific deletion of Txnip retained a greater cardiac response to β-adrenergic stimulation than wild-type mice. This benefit in Txnip-knockout hearts was not related to the level of thioredoxin activity or oxidative stress. Unlike the β-arrestins, Txnip did not interact with β-adrenergic receptors to desensitize downstream signaling. However, our proteomic and functional analyses demonstrated that Txnip inhibits glucose transport through direct binding to glucose transporter 1 (GLUT1). An ex vivo analysis of perfused hearts further demonstrated that the enhanced functional reserve afforded by deletion of Txnip was associated with myocardial glucose utilization during β-adrenergic stimulation. These data provide novel evidence that hyperglycemia-induced Txnip is responsible for impaired cardiac inotropic reserve by direct regulation of insulin-independent glucose uptake through GLUT1 and plays a role in the development of diabetic cardiomyopathy.

Resveratrol Decreases TXNIP mRNA and Protein Nuclear Expressions With an Arterial Function Improvement in Old Mice

Aging leads to a high prevalence of glucose intolerance and cardiovascular diseases, with oxidative stress playing a potential role. Resveratrol has shown promising effects on glucose tolerance and tends to improve endothelial function in elderly patients. Thioredoxin-interacting protein (TXNIP) was recently proposed as a potential link connecting glucose metabolism to oxidative stress. Here, we investigated the resveratrol-induced improvement of arterial aging phenotype in old mice and the expression of aortic TXNIP. Using an in vivo model of old mice with or without 3-month resveratrol treatment, we investigated the effects of resveratrol on age-related impairments from a cardiovascular Doppler analysis, to a molecular level, by studying inflammation and oxidative stress factors. We found a dual effect of resveratrol, with a decrease of age-related glucose intolerance and oxidative stress imbalance leading to reduced matrix remodeling that forestalls arterial aging phenotype in terms of intima-media thickness and arterial distensibility. These results provide the first evidence that aortic TXNIP mRNA and protein nuclear expressions are increased in the arterial aging and decreased by resveratrol treatment. In conclusion, we demonstrated that resveratrol helped to restore several aging impaired processes in old mice, with a decrease of aortic TXNIP mRNA and protein nuclear expressions.

The Paracrine Effect of Skeletal Myoblasts Is Cardioprotective Against Oxidative Stress and Involves EGFR-ErbB4 Signaling, Cystathionase, and the Unfolded Protein Response

Therapeutic effects of skeletal myoblast transplantation into the myocardium are mediated via paracrine factors. We investigated the ability of myoblast-derived soluble mediators to protect cardiomyocytes from oxidative stress. Fetal rat cardiac cells were treated with conditioned medium from cultures of myoblasts or cardiac fibroblasts, and oxidative stress was induced with H2O2. Myoblast-derived factors effectively prevented oxidative stress-induced cardiac cell death and loss of mitochondrial membrane potential. This protective effect was mediated via epidermal growth factor (EGF) receptor and c-Met signaling, and mimicked by neuregulin 1 but not EGF. Microarray analysis of cardiac cells treated with myoblast versus cardiac fibroblast-derived mediators revealed differential regulation of genes associated with antioxidative effects: cystathionine-γ-lyase (cst), xanthine oxidase, and thioredoxin-interacting protein as well as tribbles homolog 3 (trib3). Cardiac cell pretreatment with tunicamycin, an inducer of trib3, also protected them against H2O2-induced cell death. Epicardial transplantation of myoblast sheets in a rat model of acute myocardial infarction was used to evaluate the expression of CST and trib3 as markers of myoblasts' paracrine effect in vivo. Myoblast sheets induced expression of the CST as well as trib3 in infarcted myocardium. CST localized around blood vessels, suggesting smooth muscle cell localization. Our results provide a deeper molecular insight into the therapeutic mechanisms of myoblast-derived paracrine signaling in cardiac cells and suggest that myoblast transplantation therapy may prevent oxidative stress-induced cardiac deterioration and progression of heart failure.

Thioredoxin-interacting protein: pathophysiology and emerging pharmacotherapeutics in cardiovascular disease and diabetes

The thioredoxin system, which consists of thioredoxin (Trx), nicotinamide adenine dinucleotide phosphate (NADPH) and thioredoxin reductase (TrxR), has emerged as a major anti-oxidant involved in the maintenance of cellular physiology and survival. Dysregulation in this system has been associated with metabolic, cardiovascular, and malignant disorders. Thioredoxin-interacting protein (TXNIP), also known as vitamin D-upregulated protein or thioredoxin-binding-protein-2, functions as a physiological inhibitor of Trx, and pathological suppression of Trx by TXNIP has been demonstrated in diabetes and cardiovascular diseases. Furthermore, TXNIP effects are partially Trx-independent; these include direct activation of inflammation and inhibition of glucose uptake. Many of the effects of TXNIP are initiated by its dissociation from intra-nuclear binding with Trx or other SH-containing proteins: these effects include its migration to cytoplasm, modulating stress responses in mitochondria and endoplasmic reticulum, and also potentially activating apoptotic pathways. TXNIP also interacts with the nitric oxide (NO) signaling system, with apparent suppression of NO effect. TXNIP production is modulated by redox stress, glucose levels, hypoxia and several inflammatory activators. In recent studies, it has been shown that therapeutic agents including insulin, metformin, angiotensin converting enzyme inhibitors and calcium channel blockers reduce TXNIP expression, although it is uncertain to what extent TXNIP suppression contributes to their clinical efficacy. This review addresses the role of TXNIP in health and in cardiovascular and metabolic disorders. Finally, the potential advantages (and disadvantages) of pharmacological suppression of TXNIP in cardiovascular disease and diabetes are summarized.

Thioredoxin-Interacting Protein Deficiency Protects against Diabetic Nephropathy

Expression of thioredoxin-interacting protein (TxNIP), an endogenous inhibitor of the thiol oxidoreductase thioredoxin, is augmented by high glucose (HG) and promotes oxidative stress. We previously reported that TxNIP-deficient mesangial cells showed protection from HG-induced reactive oxygen species, mitogen-activated protein kinase phosphorylation, and collagen expression. Here, we investigated the potential role of TxNIP in the pathogenesis of diabetic nephropathy (DN) in vivo. Wild-type (WT) control, TxNIP(-/-), and TxNIP(+/-) mice were rendered equally diabetic with low-dose streptozotocin. In contrast to effects in WT mice, diabetes did not increase albuminuria, proteinuria, serum cystatin C, or serum creatinine levels in TxNIP(-/-) mice. Whereas morphometric studies of kidneys revealed a thickened glomerular basement membrane and effaced podocytes in the diabetic WT mice, these changes were absent in the diabetic TxNIP(-/-) mice. Immunohistochemical analysis revealed significant increases in the levels of glomerular TGF-β1, collagen IV, and fibrosis only in WT diabetic mice. Additionally, only WT diabetic mice showed significant increases in oxidative stress (nitrotyrosine, urinary 8-hydroxy-2-deoxy-guanosine) and inflammation (IL-1β mRNA, F4/80 immunohistochemistry). Expression levels of Nox4-encoded mRNA and protein increased only in the diabetic WT animals. A significant loss of podocytes, assessed by Wilms' tumor 1 and nephrin staining and urinary nephrin concentration, was found in diabetic WT but not TxNIP(-/-) mice. Furthermore, in cultured human podocytes exposed to HG, TxNIP knockdown with siRNA abolished the increased mitochondrial O2 (-) generation and apoptosis. These data indicate that TxNIP has a critical role in the progression of DN and may be a promising therapeutic target.

Necrostatin-1 inhibits Hmgb1-IL-23/IL-17 pathway and attenuates cardiac ischemia reperfusion injury

Ischemia reperfusion (IR) injury is a major issue in cardiac transplantation and inflammatory processes play a major role in myocardial IR injury. Necrostatin-1 (Nec-1) is a small molecule capable of inhibiting RIP1 kinase activity and attenuates inflammation-mediated tissue injury. In our study, hearts of C57Bl/6 mice were flushed and stored in cold Bretschneider solution for 8 h and then transplanted into syngeneic recipients. We found that Nec-1 decreased cardiomyocyte necrosis and recruitment of neutrophils and macrophages. Troponin T (TnT) production on 24 h after myocardial IR injury was reduced by Nec-1 administration. Cardiac output at 60 mmHg of afterload pressure was significantly increased in hearts with Nec-1 administration and the cardiac allograft survival in Nec-1-treated animals was significantly prolonged (MST = 90 days in IR + Nec-1 group, P < 0.05 as compared with IR group, MST = 83.5 days). Nec-1 treatment attenuated ROS generation and increased expression of NOS2 and COX-2. The expression of Hmgb1, IL-23, and IL-17A were also decreased with Nec-1 administration. Furthermore, the decreased TnT expression induced by Nec-1 was abrogated with exogenous Hmgb1 administration. In conclusion, Nec-1 played a protective role in cardiomyocyte IR injury, and this was associated with inhibited Hmgb1-IL-23/IL-17 pathway.

Mechanisms for the adverse effects of late gestational increases in maternal cortisol on the heart revealed by transcriptomic analyses of the fetal septum

We have previously shown in sheep that 10 days of modest chronic increase in maternal cortisol resulting from maternal infusion of cortisol (1 mg/kg/day) caused fetal heart enlargement and Purkinje cell apoptosis. In subsequent studies we extended the cortisol infusion to term, finding a dramatic incidence of stillbirth in the pregnancies with chronically increased cortisol. To investigate effects of maternal cortisol on the heart, we performed transcriptomic analyses on the septa using ovine microarrays and Webgestalt and Cytoscape programs for pathway inference. Analyses of the transcriptomic effects of maternal cortisol infusion for 10 days (130 day cortisol vs 130 day control), or ∼25 days (140 day cortisol vs 140 day control) and of normal maturation (140 day control vs 130 day control) were performed. Gene ontology terms related to immune function and cytokine actions were significantly overrepresented as genes altered by both cortisol and maturation in the septa. After 10 days of cortisol, growth factor and muscle cell apoptosis pathways were significantly overrepresented, consistent with our previous histologic findings. In the term fetuses (∼25 days of cortisol) nutrient pathways were significantly overrepresented, consistent with altered metabolism and reduced mitochondria. Analysis of mitochondrial number by mitochondrial DNA expression confirmed a significant decrease in mitochondria. The metabolic pathways modeled as altered by cortisol treatment to term were different from those modeled during maturation of the heart to term, and thus changes in gene expression in these metabolic pathways may be indicative of the fetal heart pathophysiologies seen in pregnancies complicated by stillbirth, including gestational diabetes, Cushing's disease and chronic stress.

Thioredoxin-interacting protein regulates protein disulfide isomerases and endoplasmic reticulum stress

The endoplasmic reticulum (ER) is responsible for protein folding, modification, and trafficking. Accumulation of unfolded or misfolded proteins represents the condition of ER stress and triggers the unfolded protein response (UPR), a key mechanism linking supply of excess nutrients to insulin resistance and type 2 diabetes in obesity. The ER harbors proteins that participate in protein folding including protein disulfide isomerases (PDIs). Changes in PDI activity are associated with protein misfolding and ER stress. Here, we show that thioredoxin-interacting protein (Txnip), a member of the arrestin protein superfamily and one of the most strongly induced proteins in diabetic patients, regulates PDI activity and UPR signaling. We found that Txnip binds to PDIs and increases their enzymatic activity. Genetic deletion of Txnip in cells and mice led to increased protein ubiquitination and splicing of the UPR regulated transcription factor X-box-binding protein 1 (Xbp1s) at baseline as well as under ER stress. Our results reveal Txnip as a novel direct regulator of PDI activity and a feedback mechanism of UPR signaling to decrease ER stress.

A critical role for thioredoxin-interacting protein in diabetes-related impairment of angiogenesis

Impaired angiogenesis in ischemic tissue is a hallmark of diabetes. Thioredoxin-interacting protein (TXNIP) is an exquisitely glucose-sensitive gene that is overexpressed in diabetes. As TXNIP modulates the activity of the key angiogenic cytokine vascular endothelial growth factor (VEGF), we hypothesized that hyperglycemia-induced dysregulation of TXNIP may play a role in the pathogenesis of impaired angiogenesis in diabetes. In the current study, we report that high glucose-mediated overexpression of TXNIP induces a widespread impairment in endothelial cell (EC) function and survival by reducing VEGF production and sensitivity to VEGF action, findings that are rescued by silencing TXNIP with small interfering RNA. High glucose-induced EC dysfunction was recapitulated in normal glucose conditions by overexpressing either TXNIP or a TXNIP C247S mutant unable to bind thioredoxin, suggesting that TXNIP effects are largely independent of thioredoxin activity. In streptozotocin-induced diabetic mice, TXNIP knockdown to nondiabetic levels rescued diabetes-related impairment of angiogenesis, arteriogenesis, blood flow, and functional recovery in an ischemic hindlimb. These findings were associated with in vivo restoration of VEGF production to nondiabetic levels. These data implicate a critical role for TXNIP in diabetes-related impairment of ischemia-mediated angiogenesis and identify TXNIP as a potential therapeutic target for the vascular complications of diabetes.

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.

Thioredoxin-interacting protein and myocardial mitochondrial function in ischemia-reperfusion injury

Cellular metabolism and reactive oxygen species (ROS) formation are interrelated processes in mitochondria and are implicated in a variety of human diseases including ischemic heart disease. During ischemia, mitochondrial respiration rates fall. Though seemingly paradoxical, reduced respiration has been observed to be cardioprotective due in part to reduced generation of ROS. Enhanced myocardial glucose uptake is considered beneficial for the myocardium under stress, as glucose is the primary substrate to support anaerobic metabolism. Thus, inhibition of mitochondrial respiration and uncoupling oxidative phosphorylation can protect the myocardium from irreversible ischemic damage. Growing evidence now positions the TXNIP/thioredoxin system at a nodal point linking pathways of antioxidant defense, cell survival, and energy metabolism. This emerging picture reveals TXNIP's function as a regulator of glucose homeostasis and may prove central to regulation of mitochondrial function during ischemia. In this review, we summarize how TXNIP and its binding partner thioredoxin act as regulators of mitochondrial metabolism. While the precise mechanism remains incompletely defined, the TXNIP-thioredoxin interaction has the potential to affect signaling that regulates mitochondrial bioenergetics and respiratory function with potential cardioprotection against ischemic injury.

Growth differentiation factor 11 is a circulating factor that reverses age-related cardiac hypertrophy

The most common form of heart failure occurs with normal systolic function and often involves cardiac hypertrophy in the elderly. To clarify the biological mechanisms that drive cardiac hypertrophy in aging, we tested the influence of circulating factors using heterochronic parabiosis, a surgical technique in which joining of animals of different ages leads to a shared circulation. After 4 weeks of exposure to the circulation of young mice, cardiac hypertrophy in old mice dramatically regressed, accompanied by reduced cardiomyocyte size and molecular remodeling. Reversal of age-related hypertrophy was not attributable to hemodynamic or behavioral effects of parabiosis, implicating a blood-borne factor. Using modified aptamer-based proteomics, we identified the TGF-β superfamily member GDF11 as a circulating factor in young mice that declines with age. Treatment of old mice to restore GDF11 to youthful levels recapitulated the effects of parabiosis and reversed age-related hypertrophy, revealing a therapeutic opportunity for cardiac aging.

A role for thioredoxin-interacting protein (Txnip) in cellular creatine homeostasis

Creatine is important for energy metabolism, yet excitable cells such as cardiomyocytes do not synthesize creatine and rely on uptake via a specific membrane creatine transporter (CrT; SLC6A8). This process is tightly controlled with downregulation of CrT upon continued exposure to high creatine via mechanisms that are poorly understood. Our aim was to identify candidate endogenous CrT inhibitors. In 3T3 cells overexpressing the CrT, creatine uptake plateaued at 3 h in response to 5 mM creatine but peaked 33% higher (P < 0.01) in the presence of cycloheximide, suggesting CrT regulation depends on new protein synthesis. Global gene expression analysis identified thioredoxin-interacting protein (Txnip) as the only significantly upregulated gene (by 46%) under these conditions (P = 0.036), subsequently verified independently at mRNA and protein levels. There was no change in Txnip expression with exposure to 5 mM taurine, confirming a specific response to creatine rather than osmotic stress. Small-interfering RNA against Txnip prevented Txnip upregulation in response to high creatine, maintained normal levels of creatine uptake, and prevented downregulation of CrT mRNA. These findings were relevant to the in vivo heart since creatine-deficient mice showed 39.71% lower levels of Txnip mRNA, whereas mice overexpressing the CrT had 57.6% higher Txnip mRNA levels and 28.7% higher protein expression compared with wild types (mean myocardial creatine concentration 124 and 74 nmol/mg protein, respectively). In conclusion, we have identified Txnip as a novel negative regulator of creatine levels in vitro and in vivo, responsible for mediating substrate feedback inhibition and a potential target for modulating creatine homeostasis.

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

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

Interacting with thioredoxin-1--disease or no disease?

SIGNIFICANCE

Many cardiovascular disorders are accompanied by a deregulated cellular redox balance resulting in elevated levels of intracellular reactive oxygen species (ROS). One major antioxidative cellular molecule is thioredoxin-1 (Trx-1). Its indispensability is demonstrated by the embryonic lethality of Trx-1 deficient mice. Trx-1 is ubiquitously expressed in cells and has numerous, diverse functions. It not only reduces oxidized proteins or, together with peroxiredoxins, detoxifies H(2)O(2), but also binds to several proteins and thereby regulates their functions. The interaction partners of Trx-1 differ depending on its localization in the cytosol or in the nucleus.

RECENT ADVANCES/CRITICAL ISSUES

Over the past decade it has become clear that Trx-1 is not only critical for tumor functions, which has resulted in therapeutic approaches targeting this protein, but also essential for proper functions of the vasculature and the heart. Changes in post-translational modifications of Trx-1 or in its interactions with other proteins can lead to a switch from a physiologic state of cells and organs to diverse pathologies. This review provides insights into the role of Trx-1 in different physiological situations and cardiac hypertrophy, ischemia reperfusion injury, heart failure, atherosclerosis, and diabetes mellitus type 2, underscoring the central role of Trx-1 in cardiovascular health and disease.

FUTURE DIRECTIONS

Thus, the manipulation of Trx-1 activity in the heart and/or vasculature, for example, by small molecules, seems to be a promising therapeutic option in cardiovascular diseases, as general anti-oxidant treatments would not take into account interactions of Trx-1 with other proteins and also eliminate vital ROS.