Thioredoxin-independent regulation of metabolism by the alpha-arrestin proteins

DPEP Inhibits Cancer Cell Glucose Uptake, Glycolysis and Survival by Upregulating Tumor Suppressor TXNIP

We have designed cell-penetrating peptides that target the leucine zipper transcription factors ATF5, CEBPB and CEBPD and that promote apoptotic death of a wide range of cancer cell types, but not normal cells, in vitro and in vivo. Though such peptides have the potential for clinical application, their mechanisms of action are not fully understood. Here, we show that one such peptide, Dpep, compromises glucose uptake and glycolysis in a cell context-dependent manner (in about two-thirds of cancer lines assessed). These actions are dependent on induction of tumor suppressor TXNIP (thioredoxin-interacting protein) mRNA and protein. Knockdown studies show that TXNIP significantly contributes to apoptotic death in those cancer cells in which it is induced by Dpep. The metabolic actions of Dpep on glycolysis led us to explore combinations of Dpep with clinically approved drugs metformin and atovaquone that inhibit oxidative phosphorylation and that are in trials for cancer treatment. Dpep showed additive to synergistic activities in all lines tested. In summary, we find that Dpep induces TXNIP in a cell context-dependent manner that in turn suppresses glucose uptake and glycolysis and contributes to apoptotic death of a range of cancer cells.

Txnip deletions and missense alleles prolong the survival of cones in a retinitis pigmentosa mouse model

Retinitis pigmentosa (RP) is an inherited retinal disease in which there is a loss of cone-mediated daylight vision. As there are >100 disease genes, our goal is to preserve cone vision in a disease gene-agnostic manner. Previously we showed that overexpressing TXNIP, an α-arrestin protein, prolonged cone vision in RP mouse models, using an AAV to express it only in cones. Here, we expressed different alleles of Txnip in the retinal pigmented epithelium (RPE), a support layer for cones. Our goal was to learn more of TXNIP's structure-function relationships for cone survival, as well as determine the optimal cell type expression pattern for cone survival. The C-terminal half of TXNIP was found to be sufficient to remove GLUT1 from the cell surface, and improved RP cone survival, when expressed in the RPE, but not in cones. Knock-down of HSP90AB1, a TXNIP-interactor which regulates metabolism, improved the survival of cones alone and was additive for cone survival when combined with TXNIP. From these and other results, it is likely that TXNIP interacts with several proteins in the RPE to indirectly support cone survival, with some of these interactions different from those that lead to cone survival when expressed only in cones.

Exosome-based WTAP siRNA delivery ameliorates myocardial ischemia-reperfusion injury

Myocardial ischemia/reperfusion (MI/R) injury is the primary cause of postischemicheartfailure. The increased expression of Thioredoxin-interacting protein (TXNIP) has been implicated in MI/R injury, although the detailed mechanism remains incompletely understood. In the present study, we observed the up-regulation of the m6A mRNA methylation complex component Wilms' tumor 1-associating protein (WTAP) in MI/R mice, which led to the m6A modification of TXNIP mRNA and an increase in mRNA abundance. Knock-down of WTAP resulted in a significant reduction in the m6A level of TXNIP mRNA and down-regulated TXNIP expression. Moreover, exosomes engineered with ischemic myocardium-targeting peptide (IMTP) were able to deliver WTAP siRNA into ischemic myocardial tissues, resulting in a specific gene knockdown and myocardial protection. In summary, our findings demonstrate that the WTAP-TXNIP regulatory axis plays a significant role in postischemicheartfailure, and the use of engineered exosomes targeting the ischemic heart shows promise as a strategy for siRNA therapy to protect the heart from injury.

Txnip deletions and missense alleles prolong the survival of cones in a retinitis pigmentosa mouse model

Retinitis pigmentosa (RP) is a prevalent inherited retinal degenerative disease worldwide, affecting 1 in 4,000 people. The disease is characterized by an initial loss of night vision followed by a loss of daylight and color vision. Many of the RP disease genes are expressed in the rod photoreceptors, the cell type that initiates dim light vision. Following loss of rods, the cone photoreceptors, which initiate daylight vision, also are affected and can die leading to total loss of vision. The reasons for loss of cone vision are not entirely clear, but appear to be due to loss of the rods. Previously we showed that overexpressing Txnip, an α-arrestin protein, in mouse models of RP using AAV gene therapy prolonged the survival of RP cones (Xue et al., 2021). At least part of the mechanism for cone survival was a switch in the fuel source, from glucose to lactate. In addition, the mitochondria of cones were both morphologically and functionally improved by delivery of Txnip. We have gone on to test several alleles of Txnip for the ability to prolong cone survival in rd1, a mouse model of RP. In addition, proteins that bind to Txnip and/or have homology to Txnip were tested. Five different deletion alleles of Txnip were expressed in cones or the retinal pigmented epithelium (RPE). Here we show that the C-terminal half of Txnip (149-397aa) is sufficient to remove GLUT1 from the RPE cell surface, and improved rd1 cone survival when expressed specifically in the RPE. Overexpressing Arrdc4, an α-arrestin that shares 60% similar protein sequence to Txnip, reduced rd1 cone survival. Reduction of the expression of HSP90AB1, a protein that interacts with Txnip and regulates metabolism, improved the survival of rd1 cones alone and was additive for cone survival when combined with Txnip. However, full length Txnip with a single amino acid change, C247S, as we tested in our original study, remains the most highly efficacious form of the gene for cone rescue. The above observations suggest that only a subset of the hypothesized and known activities of Txnip play a role in promoting RP cone survival, and that the activities of Txnip in the RPE differ from those in cone photoreceptors.

Single cell transcriptomics shows that malaria promotes unique regulatory responses across multiple immune cell subsets

Plasmodium falciparum malaria drives immunoregulatory responses across multiple cell subsets, which protects from immunopathogenesis, but also hampers the development of effective anti-parasitic immunity. Understanding malaria induced tolerogenic responses in specific cell subsets may inform development of strategies to boost protective immunity during drug treatment and vaccination. Here, we analyse the immune landscape with single cell RNA sequencing during P. falciparum malaria. We identify cell type specific responses in sub-clustered major immune cell types. Malaria is associated with an increase in immunosuppressive monocytes, alongside NK and γδ T cells which up-regulate tolerogenic markers. IL-10-producing Tr1 CD4 T cells and IL-10-producing regulatory B cells are also induced. Type I interferon responses are identified across all cell types, suggesting Type I interferon signalling may be linked to induction of immunoregulatory networks during malaria. These findings provide insights into cell-specific and shared immunoregulatory changes during malaria and provide a data resource for further analysis.

Circ_0001806 relieves LPS-induced HK2 cell injury by regulating the expression of miR-942-5p and TXNIP

Sepsis is a systemic inflammatory disease that can cause a variety of diseases, including septic acute kidney injury (AKI). Circular RNAs (circRNAs) are believed to be involved in the development of this disease. This study aims to clarify the function of circ_0001806 in lipopolysaccharide (LPS)-induced HK2 cell model and its related mechanisms. Circ_0001806 was up-regulated in septic AKI serum specimens and LPS-induced HK2 cells. Circ_0001806 knockdown promoted cell proliferation and restrained apoptosis, inflammation and oxidative stress in LPS-induced HK2 cells. In mechanism, circ_0001806 can be used as a sponge for miR-942-5p, and miR-942-5p can directly target TXNIP. Functional experiments revealed that the miR-942-5p inhibitor could reverse the alleviating effect of circ_0001806 knockdown on LPS-induced HK2 cell injury, and TXNIP addition can also reverse the inhibitory effect of miR-942-5p overexpression on LPS-induced HK2 cell injury. In addition, circ_0001806 regulated TXNIP expression through sponging miR-942-5p. Besides, exosome-derived circ_0001806 was upregulated in LPS-induced HK2 cells, while was downregulated by GW4869. The results showed that circ_0001806 knockdown could reduce LPS-induced HK2 cell injury by regulating TXNIP expression via targeting miR-942-5p, indicating that circ_0001806 might be an important biomarker for alleviating sepsis-related AKI. This might provide therapeutic strategy for the treatment of sepsis.

Differential effects of sugar and fat on adipose tissue inflammation

Obese individuals experience low grade inflammation initiated within their adipose tissue. However, the early events that lead to the release of these inflammatory factors from adipose tissue are poorly characterized. To separate glucose effects from lipid effects on adipose tissue, we used an adipose-specific TXNIP knockout model where excess basal glucose influx into adipocytes led to modest increase in adiposity without using high fat diet. We found an uncoupling of two events that are generally presumed to be coregulated: (1) an increase of adipose tissue macrophage (ATM) number; and (2) pro-inflammatory activation of ATMs. These two events are associated with different triggering signals: elevated free fatty acids output and extracellular matrix remodeling with increased ATM number, whereas decreased adiponectin level with activated ATM. This separation reflects non-overlapping pathways regulated by glucose and lipids in adipocytes, and neither group alone is sufficient to elicit the full inflammatory response in adipose tissue.

What the BTBR/J mouse has taught us about diabetes and diabetic complications

Human and mouse genetics have delivered numerous diabetogenic loci, but it is mainly through the use of animal models that the pathophysiological basis for their contribution to diabetes has been investigated. More than 20 years ago, we serendipidously identified a mouse strain that could serve as a model of obesity-prone type 2 diabetes, the BTBR (Black and Tan Brachyury) mouse (BTBR T+ Itpr3tf/J, 2018) carrying the Lepob mutation. We went on to discover that the BTBR-Lepob mouse is an excellent model of diabetic nephropathy and is now widely used by nephrologists in academia and the pharmaceutical industry. In this review, we describe the motivation for developing this animal model, the many genes identified and the insights about diabetes and diabetes complications derived from >100 studies conducted in this remarkable animal model.

Cross-ancestry genome-wide association meta-analyses of hippocampal and subfield volumes

The hippocampus is critical for memory and cognition and neuropsychiatric disorders, and its subfields differ in architecture and function. Genome-wide association studies on hippocampal and subfield volumes are mainly conducted in European populations; however, other ancestral populations are under-represented. Here we conduct cross-ancestry genome-wide association meta-analyses in 65,791 individuals for hippocampal volume and 38,977 for subfield volumes, including 7,009 individuals of East Asian ancestry. We identify 339 variant-trait associations at P < 1.13 × 10^-9 for 44 hippocampal traits, including 23 new associations. Common genetic variants have similar effects on hippocampal traits across ancestries, although ancestry-specific associations exist. Cross-ancestry analysis improves the fine-mapping precision and the prediction performance of polygenic scores in under-represented populations. These genetic variants are enriched for Wnt signaling and neuron differentiation and affect cognition, emotion and neuropsychiatric disorders. These findings may provide insight into the genetic architectures of hippocampal and subfield volumes.

Optimal HSF1 activation in response to acute cold stress in BAT requires nuclear TXNIP

While TXNIP (thioredoxin interacting protein) in the plasma membrane and vesicular location is known to negatively regulate cellular glucose uptake by facilitating glucose transporter endocytosis, the function of TXNIP in the nucleus is far less understood. Herein, we sought to determine the function of nuclear TXNIP in vivo, using a new HA-tagged TXNIP knock-in mouse model. We observed that TXNIP can be found in the nucleus of a variety of cells from different tissues including hepatocytes (liver), enterocytes (small intestine), exocrine cells (pancreas), and brown adipocytes (BAT). Further investigations into the role of nuclear TXNIP in BAT revealed that cold stress rapidly and transiently activated HSF1 (heat shock factor 1). HSF1 interaction with TXNIP during its activation is required for optimal HSF1 directed cold shock response in BAT.

Physiological and Pathophysiological Roles of Thioredoxin Interacting Protein: A Perspective on Redox Inflammation and Metabolism

Significance: Thioredoxin interacting protein (TXNIP) is a member of the arrestin fold superfamily with important cellular functions, including cellular transport, mitochondrial energy generation, and protein cycling. It is the only arrestin-domain protein known to covalently bind to thioredoxin and plays roles in glucose metabolism, inflammation, apoptosis, and cancer. Recent Advances: The crystal structure of the TXNIP-thioredoxin complex provided details about this fascinating interaction. Recent studies showed that TXNIP is induced by endoplasmic reticulum (ER) stress, activates NLR family pyrin domain containing 3 (NLRP3) inflammasomes, and can regulate glucose transport into cells. The tumor suppressor role of TXNIP in various cancer types and the role of TXNIP in fructose absorption are now described. Critical Issues: The influence of TXNIP on redox state is more complex than its interaction with thioredoxin. Future Directions: It is incompletely understood which functions of TXNIP are thioredoxin-dependent. It is also unclear whether TXNIP binding can inhibit glucose transporters without endocytosis. TXNIP-regulated control of ER stress should also be investigated further. Antioxid. Redox Signal. 38, 442-460.

Txnip Gene Therapy of Retinitis Pigmentosa Improves Cone Health

Retinitis pigmentosa (RP) is a hereditary retinal degenerative disease that can lead to blindness. In RP, rod photoreceptors die first, followed by cone photoreceptors death due to unknown mechanisms. However, one clue for cone death concerns their metabolism. Early changes suggest that they do not have enough glucose, which normally fuels their metabolism. We sought to design adeno-associated virus (AAV)-based gene therapy to address their metabolic challenges and found that overexpressing Txnip is an effective gene therapy that extends cone survival and vision in three strains of RP mice. The Txnip-mediated rescue was found to be dependent upon lactate dehydrogenase b (Ldhb), which is required for lactate catabolism. Txnip also was found to improve mitochondrial health. Herein, we propose a model in which Txnip shifts cones from their normal reliance on glucose to enhanced utilization of lactate to benefit cones in a condition where the glucose supply is limiting.

T3 and glucose increase expression of phosphoenolpyruvate carboxykinase (PCK1) leading to increased β-cell proliferation

OBJECTIVES

Thyroid hormone (T3) and high glucose concentrations are critical components of β-cell maturation and function. In the present study, we asked whether T3 and glucose signaling pathways coordinately regulate transcription of genes important for β-cell function and proliferation.

METHODS

RNA-seq analysis was performed on cadaveric human islets from five different donors in response to low and high glucose concentrations and in the presence or absence of T3. Gene expression was also studies in sorted human β-cells, mouse islets and Ins-1 cells by RT-qPCR. Silencing of the thyroid hormone receptors (THR) was conducted using lentiviruses. Proliferation was assessed by ki67 immunostaining in primary human/mouse islets. Chromatin immunoprecipitation and proximity ligation assay were preformed to validate interactions of ChREBP and THR.

RESULTS

We found glucose-mediated expression of carbohydrate response element binding protein alpha and beta (ChREBPα and ChREBPβ) mRNAs and their target genes are highly dependent on T3 concentrations in rodent and human β-cells. In β-cells, T3 and glucose coordinately regulate the expression of ChREBPβ and PCK1 (phosphoenolpyruvate carboxykinase-1) among other important genes for β-cell maturation. Additionally, we show the thyroid hormone receptor (THR) and ChREBP interact, and their relative response elements are located near to each other on mutually responsive genes. In FACS-sorted adult human β-cells, we found that high concentrations of glucose and T3 induced the expression of PCK1. Next, we show that overexpression of Pck1 together with dimethyl malate (DMM), a substrate precursor, significantly increased β-cell proliferation in human islets. Finally, using a Cre-Lox approach, we demonstrated that ChREBPβ contributes to Pck1-dependent β-cell proliferation in mouse β-cells.

CONCLUSIONS

We conclude that T3 and glucose act together to regulate ChREBPβ, leading to increased expression and activity of Pck1, and ultimately increased β-cell proliferation.

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.

Interaction of ARRDC4 With GLUT1 Mediates Metabolic Stress in the Ischemic Heart

BACKGROUND

An ancient family of arrestin-fold proteins, termed alpha-arrestins, may have conserved roles in regulating nutrient transporter trafficking and cellular metabolism as adaptor proteins. One alpha-arrestin, TXNIP (thioredoxin-interacting protein), is known to regulate myocardial glucose uptake. However, the in vivo role of the related alpha-arrestin, ARRDC4 (arrestin domain-containing protein 4), is unknown.

METHODS

We first tested whether interaction with GLUTs (glucose transporters) is a conserved function of the mammalian alpha-arrestins. To define the in vivo function of ARRDC4, we generated and characterized a novel Arrdc4 knockout (KO) mouse model. We then analyzed the molecular interaction between arrestin domains and the basal GLUT1.

RESULTS

ARRDC4 binds to GLUT1, induces its endocytosis, and blocks cellular glucose uptake in cardiomyocytes. Despite the closely shared protein structure, ARRDC4 and its homologue TXNIP operate by distinct molecular pathways. Unlike TXNIP, ARRDC4 does not increase oxidative stress. Instead, ARRDC4 uniquely mediates cardiomyocyte death through its effects on glucose deprivation and endoplasmic reticulum stress. At baseline, Arrdc4-KO mice have mild fasting hypoglycemia. Arrdc4-KO hearts exhibit a robust increase in myocardial glucose uptake and glycogen storage. Accordingly, deletion of Arrdc4 improves energy homeostasis during ischemia and protects cardiomyocytes against myocardial infarction. Furthermore, structure-function analyses of the interaction of ARRDC4 with GLUT1 using both scanning mutagenesis and deep-learning Artificial Intelligence identify specific residues in the C-terminal arrestin-fold domain as the interaction interface that regulates GLUT1 function, revealing a new molecular target for potential therapeutic intervention against myocardial ischemia.

CONCLUSIONS

These results uncover a new mechanism of ischemic injury in which ARRDC4 drives glucose deprivation-induced endoplasmic reticulum stress leading to cardiomyocyte death. Our findings establish ARRDC4 as a new scaffold protein for GLUT1 that regulates cardiac metabolism in response to ischemia and provide insight into the therapeutic strategy for ischemic heart disease.

Thioredoxin-interacting protein: A new therapeutic target in bone metabolism disorders?

Target identification is essential for developing novel therapeutic strategies in diseases. Thioredoxin-interacting protein (TXNIP), also known as thioredoxin-binding protein-2, is a member of the α-arrestin protein family and is regulated by several cellular stress factors. TXNIP overexpression coupled with thioredoxin inhibits its antioxidant functions, thereby increasing oxidative stress. TXNIP is directly involved in inflammatory activation by interacting with Nod-like receptor protein 3 inflammasome. Bone metabolic disorders are associated with aging, oxidative stress, and inflammation. They are characterized by an imbalance between bone formation involving osteoblasts and bone resorption by osteoclasts, and by chondrocyte destruction. The role of TXNIP in bone metabolic diseases has been extensively investigated. Here, we discuss the roles of TXNIP in the regulatory mechanisms of transcription and protein levels and summarize its involvement in bone metabolic disorders such as osteoporosis, osteoarthritis, and rheumatoid arthritis. TXNIP is expressed in osteoblasts, osteoclasts, and chondrocytes and affects the differentiation and functioning of skeletal cells through both redox-dependent and -independent regulatory mechanisms. Therefore, TXNIP is a potential regulatory and functional factor in bone metabolism and a possible new target for the treatment of bone metabolism-related diseases.

Thioredoxin-interacting protein in diabetic retinal neurodegeneration: A novel potential therapeutic target for diabetic retinopathy

Diabetic retinopathy (DR) is a common complication of diabetes mellitus and has been considered a microvascular disease for a long time. However, recent evidence suggests that diabetic retinal neurodegeneration (DRN), which manifests as neuronal apoptosis, a decrease in optic nerve axons, and reactive gliosis, occurs prior to retinal microvascular alterations. Thioredoxin-interacting protein (TXNIP) is an endogenous inhibitor of thioredoxin (Trx), and it acts by inhibiting its reducing capacity, thereby promoting cellular oxidative stress. In addition, it participates in regulating multiple signaling pathways as a member of the α-arrestin family of proteins. Accumulating evidence suggests that TXNIP is upregulated in diabetes and plays a pivotal role in the pathophysiological process of DR. In this review, we summarized the role of TXNIP in DRN, aiming to provide evidence for DR treatment in the future.

TXNIP knockout improves cardiac function after myocardial infarction by promoting angiogenesis and reducing cardiomyocyte apoptosis

BACKGROUND

Myocardial infarction (MI) is a common cause of death. Thioredoxin-interacting protein (TXNIP) expression increases after MI, and it exerts a negative regulatory effect on cardiac function after MI. Our study aimed to investigate the specific regulatory mechanism of TXNIP on angiogenesis and cardiomyocyte apoptosis after MI.

METHODS

The TXNIP gene knock-in (TXNIP-KI) and knock-out (TXNIP-KO) mice were generated, respectively. Eight-week-old male TXNIP-KO, TXNIP-KI, and wild type (WT) mice were subjected to MI by permanent ligation of the left anterior descending artery. Cardiomyocyte apoptosis was detected by TUNEL assay on the 4th post-surgery day. The expressions of TXNIP, hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), phosphorylated protein kinase B (p-AKT), p-AMP-activated protein kinase (p-AMPK), cleaved caspase-3, and caspase-3 were detected by Western blot. Quantitative real-time PCR was performed to detect the expression of TXNIP, HIF-1α, VEGF, prolyl hydroxylase (PHD) 1, and factor inhibiting HIF (FIH). In addition, the superoxide dismutase (SOD) activity and malondialdehyde (MDA) level in each group were also measured. On day 7 after MI, the hearts of sacrificed animals were analyzed by immunohistochemistry to assess CD31 expression and determine the density of angiogenesis. One month after treatment, the cardiac functional and structural changes were determined by echocardiography and the level of myocardial fibrosis was observed by Masson staining.

RESULTS

Compared with WT mice, TXNIP-KO mice had a significantly improved cardiac functional recovery after MI, and the proportion of myocardial fibrosis area was dramatically reduced, cardiomyocyte apoptosis was decreased, and angiogenesis was significantly increased; TXNIP-KI mice reversed in these changes. The expression of HIF-1α, p-AKT, and p-AMPK increased after MI in TXNIP-KO mice, and the mRNA expression of PHD 1 and FIH decreased. TXNIP-KI mice reversed in these changes.

CONCLUSIONS

After MI, TXNIP down-regulated the level of HIF-1α and VEGF, reduced the number of angiogenesis, increased cardiomyocyte apoptosis, and ultimately led to a poor prognosis of ischemic myocardium. TXNIP was a protein with negative effects after MI and was expected to be a target for the prevention and treatment of MI.

Thioredoxin-Interacting Protein in Cancer and Diabetes

Significance: Thioredoxin-interacting protein (Txnip) is an α-arrestin protein that acts as a cancer suppressor. Txnip is simultaneously a critical regulator of energy metabolism. Other alpha-arrestin proteins also play key roles in cell biology and cancer. Recent Advances: Txnip expression is regulated by multilayered mechanisms, including transcriptional regulation, microRNA, messenger RNA (mRNA) stabilization, and protein degradation. The Txnip-based connection between cancer and metabolism has been widely recognized. Meanwhile, new aspects are proposed for the mechanism of action of Txnip, including the regulation of RNA expression and autophagy. Arrestin domain containing 3 (ARRDC3), another α-arrestin protein, regulates endocytosis and signaling, whereas ARRDC1 and ARRDC4 regulate extracellular vesicle formation. Critical Issues: The mechanism of action of Txnip is yet to be elucidated. The regulation of intracellular protein trafficking by arrestin family proteins has opened an emerging field of biology and medical research, which needs to be examined further. Future Directions: A fundamental understanding of the mechanism of action of Txnip and other arrestin family members needs to be explored in the future to combat diseases such as cancer and diabetes. Antioxid. Redox Signal. 36, 1001-1022.

The α-Arrestin ARRDC3 Is an Emerging Multifunctional Adaptor Protein in Cancer

Significance: Adaptor proteins control the spatiotemporal dynamics of cellular signaling. Dysregulation of adaptor protein function can cause aberrant cell signaling and promote cancer. The arrestin family of adaptor proteins are known to regulate signaling by the superfamily of G protein-coupled receptors (GPCRs). The GPCRs are highly druggable and implicated in cancer progression. However, the molecular mechanisms responsible for arrestin dysregulation and the impact on GPCR function in cancer have yet to be fully elucidated. Recent Advances: A new family of mammalian arrestins, termed the α-arrestins, was recently discovered. The α-arrestin, arrestin domain-containing protein 3 (ARRDC3), in particular, has been identified as a tumor suppressor and is reported to control cellular signaling of GPCRs in cancer. Critical Issues: Compared with the extensively studied mammalian β-arrestins, there is limited information regarding the regulatory mechanisms that control α-arrestin activation and function. Here, we discuss the molecular mechanisms that regulate ARRDC3, which include post-translational modifications such as phosphorylation and ubiquitination. We also provide evidence that ARRDC3 can interact with a wide array of proteins that control diverse biological functions. Future Directions: ARRDC3 interacts with numerous proteins and is likely to display diverse functions in cancer, metabolic disease, and other syndromes. Thus, understanding the regulatory mechanisms of ARRDC3 activity in various cellular contexts is critically important. Recent studies suggest that α-arrestins may be regulated through post-translational modification, which is known to impact adaptor protein function. However, additional studies are needed to determine how these regulatory mechanisms affect ARRDC3 tumor suppressor function. Antioxid. Redox Signal. 36, 1066-1079.

α-Arrestins and Their Functions: From Yeast to Human Health

α-Arrestins, also called arrestin-related trafficking adaptors (ARTs), constitute a large family of proteins conserved from yeast to humans. Despite their evolutionary precedence over their extensively studied relatives of the β-arrestin family, α-arrestins have been discovered relatively recently, and thus their properties are mostly unexplored. The predominant function of α-arrestins is the selective identification of membrane proteins for ubiquitination and degradation, which is an important element in maintaining membrane protein homeostasis as well as global cellular metabolisms. Among members of the arrestin clan, only α-arrestins possess PY motifs that allow canonical binding to WW domains of Rsp5/NEDD4 ubiquitin ligases and the subsequent ubiquitination of membrane proteins leading to their vacuolar/lysosomal degradation. The molecular mechanisms of the selective substrate’s targeting, function, and regulation of α-arrestins in response to different stimuli remain incompletely understood. Several functions of α-arrestins in animal models have been recently characterized, including redox homeostasis regulation, innate immune response regulation, and tumor suppression. However, the molecular mechanisms of α-arrestin regulation and substrate interactions are mainly based on observations from the yeast Saccharomyces cerevisiae model. Nonetheless, α-arrestins have been implicated in health disorders such as diabetes, cardiovascular diseases, neurodegenerative disorders, and tumor progression, placing them in the group of potential therapeutic targets.

N-WASP Attenuates Cell Proliferation and Migration through ERK2-Dependent Enhanced Expression of TXNIP

Simple Summary

Neural Wiskott–Aldrich Syndrome Protein (N-WASP) regulates actin cytoskeleton remodeling and can, it has been suggested, suppress several cancers. In this study, HSC-5 cells, a mammalian cell line with reduced N-WASP expression, were used to generate control cells and HSC-5 cells with increased N-WASP expression that is comparable to that of normal keratinocytes. The two cell lines were used to elucidate the regulation of cell proliferation and migration by N-WASP. Our findings suggest that N-WASP increases ERK2-dependent phosphorylation of FOXO1 and increases TXNIP expression, which reduces cell proliferation and migration. This study is the first to propose an antiproliferative role of N-WASP, which is mediated via ERK2, and it suggests new avenues for cancer therapeutic research and treatment.

Abstract

Neural Wiskott–Aldrich Syndrome Protein (N-WASP) regulates actin cytoskeleton remodeling. It has been known that reduced N-WASP expression in breast and colorectal cancers is associated with poor prognosis. Here, we found reduced N-WASP expression in squamous cell carcinoma (SCC) patient samples. The SCC cell line HSC-5 with reduced N-WASP expression was used to generate HSC-5^CN (control) and HSC-5^NW (N-WASP overexpression) cells. HSC-5^NW cells had reduced cell proliferation and migration compared to HSC-5^CN cells. HSC-5^NW cells had increased phospho-ERK2 (extracellular signal-regulated kinase 2), phosphorylated Forkhead box protein class O1 (FOXO1) and reduced nuclear FOXO1 staining compared to HSC-5^CN cells. Proteasome inhibition stabilized total FOXO1, however, not nuclear staining, suggesting that FOXO1 could be degraded in the cytoplasm. Inhibition of ERK2 enhanced nuclear FOXO1 levels and restored cell proliferation and migration of HSC-5^NW to those of HSC-5^CN cells, suggesting that ERK2 regulates FOXO1 activity. The expression of thioredoxin-interacting protein (TXNIP), a FOXO1 target that inhibits thioredoxin and glucose uptake, was higher in HSC-5^NW cells than in HSC-5^CN cells. Knockdown of TXNIP in HSC-5^NW cells restored cell proliferation and migration to those of HSC-5^CN cells. Thus, we propose that N-WASP regulates cell proliferation and migration via an N-WASP-ERK2-FOXO1-TXNIP pathway.

Differentially Expressed Hepatic Genes Revealed by Transcriptomics in Pigs with Different Liver Lipid Contents

The liver is the center for uptake, synthesis, packaging, and secretion of lipids and lipoproteins. The research on lipid metabolism in pigs is limited. The objective of the present study is to identify the genes related to lipid metabolism and oxidative stress in pigs by using transcriptomic analysis. Liver segments were collected from 60 Jinhua pigs for the determination of liver lipid content. The 7 pigs with the highest and lowest liver lipid content were set as group H and group L, respectively. Liver segments and serum samples were collected from each pig of the H and L groups for RNA sequencing and the determination of triglycerides (TG) content and high-density lipoprotein cholesterol (HDL) content, respectively. The HDL content in the serum of pigs in the H group was significantly higher than the L group ( $P<0.05$ ). From transcriptomic sequencing, 6162 differentially expressed genes (DEGs) were identified, among which 2962 were upregulated and 3200 downregulated genes with the increase in the liver content of Jinhua pigs. After GO enrichment and KEGG analyses, lipid modification, cellular lipid metabolic process, cholesterol biosynthetic process, fatty acid metabolic process, oxidoreduction coenzyme metabolic process, oxidoreductase activity, acting on CH-OH group of donors, response to oxidative stress, nonalcoholic fatty liver disease (NAFLD), sphingolipid metabolism, and oxidative phosphorylation pathways were involved in lipid metabolism and oxidative stress in Jinhua pigs. For further validation, we selected 10 DEGs including 7 upregulated genes (APOE, APOA1, APOC3, LCAT, CYP2E1, GPX1, and ROMO1) and 4 downregulated genes (PPARA, PPARGC1A, and TXNIP) for RT-qPCR verification. To validate these results in other pig species, we analyzed these 10 DEGs in the liver of Duroc×Landrace×Yorkshire pigs. Similar expression patterns of these 10 DEGs were observed. These data would provide an insight to understand the gene functions regulating lipid metabolism and oxidative stress and would potentially provide theoretical basis for the development of strategies to modulate lipid metabolism and even control human diabetes and obesity by gene regulations.

Genistein alleviates H2O2-induced senescence of human umbilical vein endothelial cells via regulating the TXNIP/NLRP3 axis

CONTEXT

Genistein (Gen) has shown protective effects against ageing process.

OBJECTIVE

To explore the role of Gen on the senescence of H₂O₂-induced human umbilical vein endothelial cells (HUVECs) and investigate the possible mechanism.

MATERIALS AND METHODS

HUVECs were treated with different concentrations of H₂O₂ (50, 100, 200 and 400 μmol/L) for 1 h or Gen administration (20, 40, 80 and 160 μg/mL) for 24 h. Functional experiments (cell counting kit-8, β-galactosidase staining and flow cytometry) were used to detect the effect of Gen on H₂O₂-induced HUVECs. After HUVECs were transfected with TXNIP overexpression plasmids, the expression of p16, p21, thioredoxin-interacting protein (TXNIP), nucleotide-binding and oligomerization domain-like receptor 3 (NLRP3), cleaved caspase-3 and cleaved caspase-1 in HUVECs were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot.

RESULTS

H₂O₂ (200 and 400 μmol/L) inhibited the proliferation of HUVECs. At concentrations of >50 μmol/L, H₂O₂ induced the cell cycle progression arrests in G1 phase and promoted cell senescence of HUVECs. Gen had no obvious cytotoxicity to HUVECs below 160 µg/mL. H₂O₂-induced HUVEC senescence and the expression of TXNIP and NLRP3 in HUVECs were down-regulated by Gen (40 and 80 µg/mL). Expressions of TXNIP and NLRP3 in HUVECs were up-regulated by H₂O₂ but down-regulated by Gen. Overexpressed TXNIP partially reversed the suppressive effect of Gen on H₂O₂-induced senescence and apoptosis of HUVECs. Expressions of p16, p21, TXNIP, NLRP3, cleaved caspase-3 and cleaved caspase-1 in H₂O₂-treated HUVECs were inhibited by Gen, while the inhibition as such was partially reversed by overexpressed TXNIP.

DISCUSSION AND CONCLUSIONS

H₂O₂-induced HUVEC senescence was alleviated by Gen via suppressing the TXNIP/NLRP3 axis, which may offer a potential therapeutic approach for improving HUVEC senescence and provide a new direction for the treatment of cardiovascular disease.

ARRDC4 and UBXN1: Novel Target Genes Correlated with Prostate Cancer Gleason Score

To investigate potential markers of the prostate cancer (PCa) Gleason score (GS), genetic arrays in 841 PCa patients were conducted followed by functional validation in PCa cell lines. A total of 841 PCa patients who received radical prostatectomy (RP) from November 2003 to July 2019 were enrolled. HumanExome BeadChip 12v1-1 (Illumina, Inc.; San Diego, CA, USA) exomic arrays were performed on RP tissue samples. Unconditional logistic regression was used to calculate odds ratios to generate estimates of the relative risk of pathologic GS (≥8); SNPs with the highest association were selected and validated using PCa cell lines (PC3, LNCaP, 22Rv1 and DU145). Following transfection with target-gene siRNA, assays for cell viability, wound healing, and transwell invasion were performed. Mean age of enrolled subjects was 66.34 years and median PSA was 8.43 ng/mL. After RP, 122 patients (14.5%) had pathological Gleason scores ≥8. The results from genotyping with 242,186 SNPs by exomic array revealed that 4 SNPs (rs200944490, rs117555780, rs34625170, and rs61754877) were significantly associated with high pathological GS (≥8) within cut-off level to p < 10^-5. The most highly associated rs200944490 in ARRDC4 (p = 1.39 × 10^-6) and rs117555780 in UBXN1 (p = 2.92 × 10^-5) were selected for further validation. The knockdown of UBXN1 and ARRDC4 led to significantly reduced cell proliferation and suppressed migration and invasiveness in PCa cell lines. Epithelial mesenchymal transition (EMT) markers were significantly down-regulated in si-ARRDC4 and si-UBXN1-transfected cells. The expression levels of PI3K-phosphorylation and Akt phosphorylation and NF-κB were also suppressed following knockdown of UBXN1 and ARRDC4. The rs200944490 (ARRDC4) and rs117555780 (UBXN1) were identified as candidate markers predictive of PCa Gleason score which is strongly associated with cancer aggressiveness. Additional validation in future studies is warranted.

The Effect of Verapamil on TXNIP Gene Expression, GLP1R mRNA, FBS, HbA1c, and Lipid Profile in T2DM Patients Receiving Metformin and Sitagliptin

INTRODUCTION

Type 2 diabetes mellitus (T2DM) is the most common type of diabetes. A decrease in the number of pancreatic beta cells is a pathological sign of diabetes, and to date there is no drug treatment that targets damage to these cells. Pancreatic beta cells have a weak antioxidant system and are highly sensitive to oxidative stress reactions that occur within cells. Thioredoxin interacting protein (TXNIP) inhibits thioredoxin, which is part of the intracellular antioxidant system, thereby accelerating oxidative stress and apoptosis of pancreatic beta cells. Verapamil is a non-dihydropyridine calcium channel blocker. The efficacy of this drug to improve beta cell survival and glucose homeostasis by inhibiting TXNIP expression has been demonstrated in in vitro studies. Although several retrospective studies have shown a lower incidence of T2DM with verapamil treatment, no prospective intervention studies have determined the efficacy of this drug in patients with T2DM.

METHODS

The aim of this randomized, double-blind, placebo-controlled study was to evaluate the efficacy and safety of oral verapamil administration in T2DM patients. In this 90-day study, the effects of verapamil on fasting blood sugar (FBS), hemoglobin A1C (HbA1c), and the lipid profile were evaluated and compared with those of the placebo.

RESULTS

There was a significant decrease in HbA1c (about 0.5%) in the verapamil group at the end of the intervention period. The effects of verapamil on TXNIP gene expression and glucagon-like peptide-1 receptor (GLP1R) mRNA were compared with those of the placebo (at baseline, after 15 and 30 days, and at the end of the study). During the first month of the study, decreased TXNIP gene expression and increased GLP1R mRNA were associated with the administration of verapamil when compared with the placebo, although the differences were not significant.

CONCLUSION

Verapamil can lead to better control of T2DM by reducing TXNIP gene expression and increasing beta cell survival and, possibly, by other mechanisms.

CLINICAL TRIAL REGISTRATION

IRCT registration no.: IRCT20180417039339N1 ( https://www.IRCT.ir ).

A Convergent Functional Genomics Analysis to Identify Biological Regulators Mediating Effects of Creatine Supplementation

Creatine (Cr) and phosphocreatine (PCr) are physiologically essential molecules for life, given they serve as rapid and localized support of energy- and mechanical-dependent processes. This evolutionary advantage is based on the action of creatine kinase (CK) isozymes that connect places of ATP synthesis with sites of ATP consumption (the CK/PCr system). Supplementation with creatine monohydrate (CrM) can enhance this system, resulting in well-known ergogenic effects and potential health or therapeutic benefits. In spite of our vast knowledge about these molecules, no integrative analysis of molecular mechanisms under a systems biology approach has been performed to date; thus, we aimed to perform for the first time a convergent functional genomics analysis to identify biological regulators mediating the effects of Cr supplementation in health and disease. A total of 35 differentially expressed genes were analyzed. We identified top-ranked pathways and biological processes mediating the effects of Cr supplementation. The impact of CrM on miRNAs merits more research. We also cautiously suggest two dose-response functional pathways (kinase- and ubiquitin-driven) for the regulation of the Cr uptake. Our functional enrichment analysis, the knowledge-based pathway reconstruction, and the identification of hub nodes provide meaningful information for future studies. This work contributes to a better understanding of the well-reported benefits of Cr in sports and its potential in health and disease conditions, although further clinical research is needed to validate the proposed mechanisms.

Redox-dependent and independent effects of thioredoxin interacting protein

Thioredoxin interacting protein (TXNIP) is an important physiological inhibitor of the thioredoxin (TXN) redox system in cells. Regulation of TXNIP expression and/or activity not only plays an important role in redox regulation but also exerts redox-independent physiological effects that exhibit direct pathophysiological consequences including elevated inflammatory response, aberrant glucose metabolism, cellular senescence and apoptosis, cellular immunity, and tumorigenesis. This review provides a brief overview of the current knowledge concerning the redox-dependent and independent roles of TXNIP and its relevance to various disease states. The implications for the therapeutic targeting of TXNIP will also be discussed.

Identification and Analysis of Long Non-coding RNAs in Leuciscus waleckii Adapted to Highly Alkaline Conditions

Leuciscus waleckii is a freshwater fish that is known to inhabit the Dali Nor Lake, Inner Mongolia, China. The water in this lake has an HCO3 -/CO3 2- concentration of 54 mM (pH 9.6) and a salinity of 0.6‰. The physiological mechanisms that allow this fish to tolerate these saline/alkaline conditions have yet to be elucidated. Transcriptional component analysis has shown that the expression levels of a large number of genes involved in the pathways responsible for osmo-ionoregulation and arachidonic acid metabolism pathway expression change significantly (p < 0.05) during the regulation of acid-base balance under high alkaline stress. In this study, we investigated the role of long non-coding RNAs (lncRNAs) during adaptation to high alkaline conditions. Fish were challenged to an NaHCO3-adjusted alkalinity of 0 mM, 30 mM (pH 9.44 ± 0.08), and 50 mM (pH 9.55 ± 0.06) for 20 days in the laboratory. Gill and kidney tissues were then collected for high-throughput sequencing assays. A total of 159 million clean reads were obtained by high-throughput sequencing, and 41,248 lncRNA transcripts were identified. Of these, the mean number of exons and the mean length of the lncRNA transcripts were 4.8 and 2,079 bp, respectively. Based on the analysis of differential lncRNA transcript expression, a total of 5,244 and 6,571 lncRNA transcripts were found to be differentially expressed in the gills and kidneys, respectively. Results derived from Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of the coding genes were correlated with the lncRNA expression profiles. GO analysis showed that many lncRNAs were enriched in the following processes: "transporter activity," "response to stimulus," and "binding." KEGG analysis further revealed that metabolic pathways were significantly enriched. A random selection of 16 lncRNA transcripts was tested by RT-qPCR; these results were consistent with our sequencing results. We found that a large number of genes, with the same expression profiles as those with differentially expressed lncRNAs, were associated with the regulation of acid-base balance, ion transport, and the excretion of ammonia and nitrogen. Collectively, our data indicate that lncRNA-regulated gene expression plays an important role in the process of adaptation to high alkaline conditions in L. waleckii.

Identification and profiles of microRNAs in different development stages of miniature pig secondary palate

Cleft palate is one of the most frequent craniofacial malformation birth defects. Miniature pigs (Sus scrofa) are a valuable alternative large animal model to explore human palate development. Presently, the microRNA (miRNA) expression profiles in miniature pigs during palatogenesis from embryonic day (E) 30 to 50 were identified. A total of 2044 known miRNAs and 192 novel miRNAs were identified. The functional characteristics of their potential target genes were identified using Gene Ontology function and Kyoto Encyclopedia of Genes and Genomes pathway analysis. MiRNAs displayed diverse expression levels among the different stages. Using Short Time-series Expression Miner software to investigate the expression patterns of miRNAs from E30-50, all miRNAs were clustered into 20 profiles. The profiles showing miRNAs expression decreased (profile 0)/increased (profile 19) from E30-50 were the main patterns during palatogenesis. Hub genes of four significant modules were identified by weighted correlation network analysis, including ssc-miR-98, ssc-miR-27a_R + 1, and ssc-miR-150, etc. which might be novel potential targets for regulating palate development. The data are expected to improve the understanding of palate development and the etiology of cleft palate in further studies.

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.

Arrdc4-dependent extracellular vesicle biogenesis is required for sperm maturation

Extracellular vesicles (EVs) are important players in cell to cell communication in reproductive systems. Notably, EVs have been found and characterized in the male reproductive tract, however, direct functional evidence for their importance in mediating sperm function is lacking. We have previously demonstrated that Arrdc4, a member of the α-arrestin protein family, is involved in extracellular vesicle biogenesis and release. Here we show that Arrdc4-mediated extracellular vesicle biogenesis is required for proper sperm function. Sperm from Arrdc4-/- mice develop normally through the testis but fail to acquire adequate motility and fertilization capabilities through the epididymis, as observed by reduced motility, premature acrosome reaction, reduction in zona pellucida binding and two-cell embryo production. We found a significant reduction in extracellular vesicle production by Arrdc4-/- epididymal epithelial cells, and further, supplementation of Arrdc4-/- sperm with additional vesicles dampened the acrosome reaction defect and restored zona pellucida binding. These results indicate that Arrdc4 is important for proper sperm maturation through the control of extracellular vesicle biogenesis.

AAV-Txnip prolongs cone survival and vision in mouse models of retinitis pigmentosa

Retinitis pigmentosa (RP) is an inherited retinal disease affecting >20 million people worldwide. Loss of daylight vision typically occurs due to the dysfunction/loss of cone photoreceptors, the cell type that initiates our color and high-acuity vision. Currently, there is no effective treatment for RP, other than gene therapy for a limited number of specific disease genes. To develop a disease gene-agnostic therapy, we screened 20 genes for their ability to prolong cone photoreceptor survival in vivo. Here, we report an adeno-associated virus vector expressing Txnip, which prolongs the survival of cone photoreceptors and improves visual acuity in RP mouse models. A Txnip allele, C247S, which blocks the association of Txnip with thioredoxin, provides an even greater benefit. Additionally, the rescue effect of Txnip depends on lactate dehydrogenase b (Ldhb) and correlates with the presence of healthier mitochondria, suggesting that Txnip saves RP cones by enhancing their lactate catabolism.

Dual regulation of TxNIP by ChREBP and FoxO1 in liver

TxNIP (Thioredoxin-interacting protein) is considered as a potential drug target for type 2 diabetes. Although TxNIP expression is correlated with hyperglycemia and glucotoxicity in pancreatic β cells, its regulation in liver cells has been less investigated. In the current study, we aim at providing a better understanding of Txnip regulation in hepatocytes in response to physiological stimuli and in the context of hyperglycemia in db/db mice. We focused on regulatory pathways governed by ChREBP (Carbohydrate Responsive Element Binding Protein) and FoxO1 (Forkhead box protein O1), transcription factors that play central roles in mediating the effects of glucose and fasting on gene expression, respectively. Studies using genetically modified mice reveal that hepatic TxNIP is up-regulated by both ChREBP and FoxO1 in liver cells and that its expression strongly correlates with fasting, suggesting a major role for this protein in the physiological adaptation to nutrient restriction.

Txnip C247S mutation protects the heart against acute myocardial infarction

RATIONALE

Thioredoxin-interacting protein (Txnip) is a novel molecular target with translational potential in diverse human diseases. Txnip has several established cellular actions including binding to thioredoxin, a scavenger of reactive oxygen species (ROS). It has been long recognized from in vitro evidence that Txnip forms a disulfide bridge through cysteine 247 (C247) with reduced thioredoxin to inhibit the anti-oxidative properties of thioredoxin. However, the physiological significance of the Txnip-thioredoxin interaction remains largely undefined in vivo.

OBJECTIVE

A single mutation of Txnip, C247S, abolishes the binding of Txnip with thioredoxin. Using a conditional and inducible approach with a mouse model of a mutant Txnip that does not bind thioredoxin, we tested whether the interaction of thioredoxin with Txnip is required for Txnip's pro-oxidative or cytotoxic effects in the heart.

METHODS AND RESULTS

Overexpression of Txnip C247S in cells resulted in a reduction in ROS, due to an inability to inhibit thioredoxin. Hypoxia (1% O₂, 24 h)-induced killing effects of Txnip were decreased by lower levels of cellular ROS in Txnip C247S-expressing cells compared with wild-type Txnip-expressing cells. Then, myocardial ischemic injuries were assessed in the animal model. Cardiomyocyte-specific Txnip C247S knock-in mice had better survival with smaller infarct size following myocardial infarction (MI) compared to control animals. The absence of Txnip's inhibition of thioredoxin promoted mitochondrial anti-oxidative capacities in cardiomyocytes, thereby protecting the heart from oxidative damage induced by MI. Furthermore, an unbiased RNA sequencing screen identified that hypoxia-inducible factor 1 signaling pathway was involved in Txnip C247S-mediated cardioprotective mechanisms.

CONCLUSION

Txnip is a cysteine-containing redox protein that robustly regulates the thioredoxin system via a disulfide bond-switching mechanism in adult cardiomyocytes. Our results provide the direct in vivo evidence that regulation of redox state by Txnip is a crucial component for myocardial homeostasis under ischemic stress.

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.

The α-arrestin family of ubiquitin ligase adaptors links metabolism with selective endocytosis

The regulation of nutrient uptake into cells is important, as it allows to either increase biomass for cell growth or to preserve homoeostasis. A key strategy to adjust cellular nutrient uptake is the reconfiguration of the nutrient transporter repertoire at the plasma membrane by the addition of nutrient transporters through the secretory pathway and by their endocytic removal. In this review, we focus on the mechanisms that regulate selective nutrient transporter endocytosis, which is mediated by the α-arrestin protein family. In the budding yeast Saccharomyces cerevisiae, 14 different α-arrestins (also named arrestin-related trafficking adaptors, ARTs) function as adaptors for the ubiquitin ligase Rsp5. They instruct Rsp5 to ubiquitinate subsets of nutrient transporters to orchestrate their endocytosis. The ART proteins are under multilevel control of the major nutrient sensing systems, including amino acid sensing by the general amino acid control and target of rapamycin pathways, and energy sensing by 5'-adenosine-monophosphate-dependent kinase. The function of the six human α-arrestins is comparably under-characterised. Here, we summarise the current knowledge about the function, regulation and substrates of yeast ARTs and human α-arrestins, and highlight emerging communalities and general principles.

Redox regulation of immunometabolism

Metabolic pathways and redox reactions are at the core of life. In the past decade(s), numerous discoveries have shed light on how metabolic pathways determine the cellular fate and function of lymphoid and myeloid cells, giving rise to an area of research referred to as immunometabolism. Upon activation, however, immune cells not only engage specific metabolic pathways but also rearrange their oxidation-reduction (redox) system, which in turn supports metabolic reprogramming. In fact, studies addressing the redox metabolism of immune cells are an emerging field in immunology. Here, we summarize recent insights revealing the role of reactive oxygen species (ROS) and the differential requirement of the main cellular antioxidant pathways, including the components of the thioredoxin (TRX) and glutathione (GSH) pathways, as well as their transcriptional regulator NF-E2-related factor 2 (NRF2), for proliferation, survival and function of T cells, B cells and macrophages.

Thioredoxin-Interacting Protein (TXNIP) with Focus on Brain and Neurodegenerative Diseases

The development of new therapeutic approaches to diseases relies on the identification of key molecular targets involved in amplifying disease processes. One such molecule is thioredoxin-interacting protein (TXNIP), also designated thioredoxin-binding protein-2 (TBP-2), a member of the α-arrestin family of proteins and a central regulator of glucose and lipid metabolism, involved in diabetes-associated vascular endothelial dysfunction and inflammation. TXNIP sequesters reduced thioredoxin (TRX), inhibiting its function, resulting in increased oxidative stress. Many different cellular stress factors regulate TXNIP expression, including high glucose, endoplasmic reticulum stress, free radicals, hypoxia, nitric oxide, insulin, and adenosine-containing molecules. TXNIP is also directly involved in inflammatory activation through its interaction with the nucleotide-binding domain, leucine-rich-containing family, and pyrin domain-containing-3 (NLRP3) inflammasome complex. Neurodegenerative diseases such as Alzheimer’s disease have significant pathologies associated with increased oxidative stress, inflammation, and vascular dysfunctions. In addition, as dysfunctions in glucose and cellular metabolism have been associated with such brain diseases, a role for TXNIP in neurodegeneration has actively been investigated. In this review, we will focus on the current state of the understanding of possible normal and pathological functions of TXNIP in the central nervous system from studies of in vitro neural cells and the brains of humans and experimental animals with reference to other studies. As TXNIP can be expressed by neurons, microglia, astrocytes, and endothelial cells, a complex pattern of regulation and function in the brain is suggested. We will examine data suggesting TXNIP as a therapeutic target for neurodegenerative diseases where further research is needed.

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.

Regulation of Metabolic Homeostasis in Cell Culture Bioprocesses

Mammalian cells are the main tool for the production of therapeutic proteins, viruses for gene therapy, and cells for cell therapy. In production processes cell metabolism is the main driver that causes changes in the growth environment and affects productivity and product quality. Of all nutrients, glucose has the most prominent impact on bioprocesses. We summarize recent findings on the regulation of glucose and energy metabolism in cultured cells. Local allosteric regulations and post-translational modifications of enzymes in metabolic networks interplay with global signaling and transcriptional regulation. These regulatory networks sustain homeostasis across the cytosolic and mitochondrial compartments. Understanding the regulation of glucose metabolism and metabolic state is crucial for enhancing process productivity and product quality.

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.

The structure of importin α and the nuclear localization peptide of ChREBP, and small compound inhibitors of ChREBP-importin α interactions

The carbohydrate response element binding protein (ChREBP) is a glucose-responsive transcription factor that plays a critical role in glucose-mediated induction of genes involved in hepatic glycolysis and lipogenesis. In response to fluctuating blood glucose levels ChREBP activity is regulated mainly by nucleocytoplasmic shuttling of ChREBP. Under high glucose ChREBP binds to importin α and importin β and translocates into the nucleus to initiate transcription. We have previously shown that the nuclear localization signal site (NLS) for ChREBP is bipartite with the NLS extending from Arg158 to Lys190. Here, we report the 2.5 Å crystal structure of the ChREBP-NLS peptide bound to importin α. The structure revealed that the NLS binding is monopartite, with the amino acid residues K¹⁷¹RRI¹⁷⁴ from the ChREBP-NLS interacting with ARM2–ARM5 on importin α. We discovered that importin α also binds to the primary binding site of the 14-3-3 proteins with high affinity, which suggests that both importin α and 14-3-3 are each competing with the other for this broad-binding region (residues 117–196) on ChREBP. We screened a small compound library and identified two novel compounds that inhibit the ChREBP-NLS/importin α interaction, nuclear localization, and transcription activities of ChREBP. These candidate molecules support developing inhibitors of ChREBP that may be useful in treatment of obesity and the associated diseases.

The Small-Molecule Flunarizine in Spinal Muscular Atrophy Patient Fibroblasts Impacts on the Gemin Components of the SMN Complex and TDP43, an RNA-Binding Protein Relevant to Motor Neuron Diseases

The motor neurodegenerative disease spinal muscular atrophy (SMA) is caused by alterations of the survival motor neuron 1 (SMN1) gene involved in RNA metabolism. Although the disease mechanisms are not completely elucidated, SMN protein deficiency leads to abnormal small nuclear ribonucleoproteins (snRNPs) assembly responsible for widespread splicing defects. SMN protein localizes in nuclear bodies that are lost in SMA and adult onset amyotrophic lateral sclerosis (ALS) patient cells harboring TDP-43 or FUS/TLS mutations. We previously reported that flunarizine recruits SMN into nuclear bodies and improves the phenotype of an SMA mouse model. However, the precise mode of action remains elusive. Here, a marked reduction of the integral components of the SMN complex is observed in severe SMA patient fibroblast cells. We show that flunarizine increases the protein levels of a subset of components of the SMN-Gemins complex, Gemins2-4, and markedly reduces the RNA and protein levels of the pro-oxydant thioredoxin-interacting protein (TXNIP) encoded by an mRNA target of Gemin5. We further show that SMN deficiency causes a dissociation of the localization of the SMN complex components from the same nuclear bodies. The accumulation of TDP-43 in SMN-positive nuclear bodies is also perturbed in SMA cells. Notably, TDP-43 is found to co-localize with SMN in nuclear bodies of flunarizine-treated SMA cells. Our findings indicate that flunarizine reverses cellular changes caused by SMN deficiency in SMA cells and further support the view of a common pathway in RNA metabolism underlying infantile and adult motor neuron diseases.

Arrestin domain-containing 3 (Arrdc3) modulates insulin action and glucose metabolism in liver

Insulin action in the liver is critical for glucose homeostasis through regulation of glycogen synthesis and glucose output. Arrestin domain-containing 3 (Arrdc3) is a member of the α-arrestin family previously linked to human obesity. Here, we show that Arrdc3 is differentially regulated by insulin in vivo in mice undergoing euglycemic-hyperinsulinemic clamps, being highly up-regulated in liver and down-regulated in muscle and fat. Mice with liver-specific knockout (KO) of the insulin receptor (IR) have a 50% reduction in Arrdc3 messenger RNA, while, conversely, mice with liver-specific KO of Arrdc3 (L-Arrdc3 KO) have increased IR protein in plasma membrane. This leads to increased hepatic insulin sensitivity with increased phosphorylation of FOXO1, reduced expression of PEPCK, and increased glucokinase expression resulting in reduced hepatic glucose production and increased hepatic glycogen accumulation. These effects are due to interaction of ARRDC3 with IR resulting in phosphorylation of ARRDC3 on a conserved tyrosine (Y382) in the carboxyl-terminal domain. Thus, Arrdc3 is an insulin target gene, and ARRDC3 protein directly interacts with IR to serve as a feedback regulator of insulin action in control of liver metabolism.

Thioredoxin-interacting protein regulates glucose metabolism and improves the intracellular redox state in bovine oocytes during in vitro maturation

The extent of glucose metabolism during oocyte maturation is closely related to oocyte developmental potential. Thioredoxin-interacting protein (TXNIP) is an α-arrestin family protein that negatively regulates glucose uptake into cells. However, little information is available regarding the function of TXNIP in bovine oocytes. Accordingly, the present study was performed to investigate the influence of TXNIP on glucose metabolism in bovine oocytes during in vitro maturation. Pharmacological inhibition of TXNIP by azaserine enhanced glucose uptake and imparted a specific metabolic effect on glycolysis and pentose phosphate pathway (PPP). RNA interference (RNAi) was adopted to further determine the biological significance of TXNIP in regulating glucose metabolism. The maturation rate and the developmental competence of TXNIP siRNA-treated oocytes were significantly improved. Knockdown of TXNIP in bovine oocytes significantly increased glycolysis by increasing the activities of phosphofructokinase (PFK), pyruvate kinase, and lactate dehydrogenase; pyruvate and lactate production; and intracellular ATP level, as well as mitochondrial activity. Furthermore, glucose metabolism through PPP was also enhanced by TXNIP depletion, as TXNIP siRNA treatment promoted glucose-6-phosphate dehydrogenase (G6PDH) activity and NADPH content, and helped maintain a high level of glutathione and a low level of reactive oxygen species within the oocytes. Further studies revealed that inhibition of TXNIP resulted increases in glucose transporter 1 (GLUT1) expression, as well as PFK1 platelet isoform (PFKP) and G6PDH mRNA levels. These results reveal that TXNIP depletion promotes oocyte maturation by enhancing both glycolysis and the PPP. During in vitro maturation of bovine oocytes, TXNIP serves as a key regulator of glucose uptake by controlling GLUT1 expression.

Metabolic Syndrome, Brain Insulin Resistance, and Alzheimer's Disease: Thioredoxin Interacting Protein (TXNIP) and Inflammasome as Core Amplifiers

Empirical evidence indicates a strong association between insulin resistance and pathological alterations related to Alzheimer's disease (AD) in different cerebral regions. While cerebral insulin resistance is not essentially parallel with systemic metabolic derangements, type 2 diabetes mellitus (T2DM) has been established as a risk factor for AD. The circulating "toxic metabolites" emerging in metabolic syndrome may engage several biochemical pathways to promote oxidative stress and neuroinflammation leading to impair insulin function in the brain or "type 3 diabetes". Thioredoxin-interacting protein (TXNIP) as an intracellular amplifier of oxidative stress and inflammasome activation may presumably mediate central insulin resistance. Emerging data including those from our recent studies has demonstrated a sharp TXNIP upregulation in stroke, aging and AD and well underlining the significance of this hypothesis. With the main interest to illustrate TXNIP place in type 3 diabetes, the present review primarily briefs the potential mechanisms contributing to cerebral insulin resistance in a metabolically deranged environment. Then with a particular focus on plausible TXNIP functions to drive and associate with AD pathology, we present the most recent evidence supporting TXNIP as a promising therapeutic target in AD as an age-associated dementia.

Tumor necrosis factor induces rapid down-regulation of TXNIP in human T cells

In addition to antigen-driven signals, T cells need co-stimulatory signals for robust activation. Several receptors, including members of the tumor necrosis factor receptor superfamily (TNFRSF), can deliver co-stimulatory signals to T cells. Thioredoxin interacting protein (TXNIP) is an important inhibitor of glucose uptake and cell proliferation, but it is unknown how TXNIP is regulated in T cells. The aim of this study was to determine expression levels and regulation of TXNIP in human T cells. We found that naïve T cells express high levels of TXNIP and that treatment of blood samples with TNF results in rapid down-regulation of TXNIP in the T cells. TNF-induced TXNIP down-regulation correlated with increased glucose uptake. Furthermore, we found that density gradient centrifugation (DGC) induced down-regulation of TXNIP. We demonstrate that DGC induced TNF production that paralleled the TXNIP down-regulation. Treatment of blood with toll-like receptor (TLR) ligands induced TNF production and TXNIP down-regulation, suggesting that damage-associated molecular patterns (DAMPs), such as endogenous TLR ligands, released during DGC play a role in DGC-induced TXNIP down-regulation. Finally, we demonstrate that TNF-induced TXNIP down-regulation is dependent on caspase activity and is caused by caspase-mediated cleavage of TXNIP.

Oxidative stress-mediated TXNIP loss causes RPE dysfunction

The disruption of the retinal pigment epithelium (RPE), for example, through oxidative damage, is a common factor underlying age-related macular degeneration (AMD). Aberrant autophagy also contributes to AMD pathology, as autophagy maintains RPE homeostasis to ensure blood–retinal barrier (BRB) integrity and protect photoreceptors. Thioredoxin-interacting protein (TXNIP) promotes cellular oxidative stress by inhibiting thioredoxin reducing capacity and is in turn inversely regulated by reactive oxygen species levels; however, its role in oxidative stress-induced RPE cell dysfunction and the mechanistic link between TXNIP and autophagy are largely unknown. Here, we observed that TXNIP expression was rapidly downregulated in RPE cells under oxidative stress and that RPE cell proliferation was decreased. TXNIP knockdown demonstrated that the suppression of proliferation resulted from TXNIP depletion-induced autophagic flux, causing increased p53 activation via nuclear localization, which in turn enhanced AMPK phosphorylation and activation. Moreover, TXNIP downregulation further negatively impacted BRB integrity by disrupting RPE cell tight junctions and enhancing cell motility by phosphorylating, and thereby activating, Src kinase. Finally, we also revealed that TXNIP knockdown upregulated HIF-1α, leading to the enhanced secretion of VEGF from RPE cells and the stimulation of angiogenesis in cocultured human retinal microvascular endothelial cells. This suggests that the exposure of RPE cells to sustained oxidative stress may promote choroidal neovascularization, another AMD pathology. Together, these findings reveal three distinct mechanisms by which TXNIP downregulation disrupts RPE cell function and thereby exacerbates AMD pathogenesis. Accordingly, reinforcing or restoring BRB integrity by targeting TXNIP may serve as an effective therapeutic strategy for preventing or attenuating photoreceptor damage in AMD.

A protein found in retinal cells promotes the development of age-related macular degeneration and may provide a therapeutic target. Sight loss through macular degeneration is triggered by disruption to the retinal pigment epithelium (RPE), a layer of cells that carries nutrients to the eye. RPE cells can be disrupted under oxidative stress conditions, but how this influences macular degeneration is unclear. Jeong-Ki Min and Sang-Hyun Lee at the Korea Research Institute of Bioscience and Biotechnology in Daejeon, South Korea, and co-workers found that oxidative stress reduces levels of the thioredoxin-interacting protein (TXNIP) in human RPE cell cultures. This interrupts cellular communication and disturbs the balance between cell proliferation and cell recycling. It also increases the levels of proteins that promote excess blood vessel formation, a key process contributing to macular degeneration.

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.