Thioredoxin reductase 1 suppresses adipocyte differentiation and insulin responsiveness

Water-soluble intracellular extract of Desmodesmus sp. YT enhanced the antioxidant capacity of human skin fibroblast to protect the skin from UV damage

BACKGROUND

The oxidative stress induced by ultraviolet (UV) radiation is a pivotal factor in skin aging and can even contribute to the development of skin cancer.

AIM

This study explored the antioxidant effect and mechanism of water-soluble intracellular extract (WIE) of Desmodesmus sp.YT (YT), aiming to develop a natural antioxidant suitable for incorporation into cosmetics.

METHODS

The study evaluated the scavenging capacity of YT-WIE against free radicals and assessed its impact on human skin fibroblasts (HSF) cell viability and UV resistance using Cell Counting Kit-8 (CCK-8). Transcriptome sequencing was employed to elucidate the mechanism of action, while RT-qPCR and western blot were used to validate the expression of key genes.

RESULTS

YT-WIE displayed robust antioxidant activity, demonstrating potent scavenging abilities against 2,2-diphenyl-1-picrylhydrazyl (DPPH; IC50 = 0.55 mg mL-1), 2,2'-Azino-bis (3 ethylbenzothiazoline-6-sulfonic acid; ABTS; IC50 = 3.11 mg mL-1), Hydroxyl (·OH; IC50 = 2.21 mg mL-1), and Superoxide anion (O2 •-; IC50 = 0.98 mg mL-1). Furthermore, compared to the control group, the YT-WIE group exhibited an 89.30% enhancement in HSF viability and a 44.63% increase in survival rate post-UV irradiation. Significant upregulation of antioxidant genes (GCLC, GCLM, TXNRD1, HMOX1, NQO1) was observed with YT-WIE treatment at 400 μg mL-1, with fold increases ranging from 1.13 to 5.85 times.

CONCLUSION

YT-WIE demonstrated considerable potential as an antioxidant, shielding human cells from undue oxidative stress triggered by external stimuli such as UV radiation. This suggests its promising application in cosmetics antioxidants.

Fluorescent Probes for Mammalian Thioredoxin Reductase: Mechanistic Analysis, Construction Strategies, and Future Perspectives

The modulation of numerous signaling pathways is orchestrated by redox regulation of cellular environments. Maintaining dynamic redox homeostasis is of utmost importance for human health, given the common occurrence of altered redox status in various pathological conditions. The cardinal component of the thioredoxin system, mammalian thioredoxin reductase (TrxR) plays a vital role in supporting various physiological functions; however, its malfunction, disrupting redox balance, is intimately associated with the pathogenesis of multiple diseases. Accordingly, the dynamic monitoring of TrxR of live organisms represents a powerful direction to facilitate the comprehensive understanding and exploration of the profound significance of redox biology in cellular processes. A number of classic assays have been developed for the determination of TrxR activity in biological samples, yet their application is constrained when exploring the real-time dynamics of TrxR activity in live organisms. Fluorescent probes offer several advantages for in situ imaging and the quantification of biological targets, such as non-destructiveness, real-time analysis, and high spatiotemporal resolution. These benefits facilitate the transition from a poise to a flux understanding of cellular targets, further advancing scientific studies in related fields. This review aims to introduce the progress in the development and application of TrxR fluorescent probes in the past years, and it mainly focuses on analyzing their reaction mechanisms, construction strategies, and potential drawbacks. Finally, this study discusses the critical challenges and issues encountered during the development of selective TrxR probes and proposes future directions for their advancement. We anticipate the comprehensive analysis of the present TrxR probes will offer some glitters of enlightenment, and we also expect that this review may shed light on the design and development of novel TrxR probes.

Biological and Catalytic Properties of Selenoproteins

Selenocysteine is a catalytic residue at the active site of all selenoenzymes in bacteria and mammals, and it is incorporated into the polypeptide backbone by a co-translational process that relies on the recoding of a UGA termination codon into a serine/selenocysteine codon. The best-characterized selenoproteins from mammalian species and bacteria are discussed with emphasis on their biological function and catalytic mechanisms. A total of 25 genes coding for selenoproteins have been identified in the genome of mammals. Unlike the selenoenzymes of anaerobic bacteria, most mammalian selenoenzymes work as antioxidants and as redox regulators of cell metabolism and functions. Selenoprotein P contains several selenocysteine residues and serves as a selenocysteine reservoir for other selenoproteins in mammals. Although extensively studied, glutathione peroxidases are incompletely understood in terms of local and time-dependent distribution, and regulatory functions. Selenoenzymes take advantage of the nucleophilic reactivity of the selenolate form of selenocysteine. It is used with peroxides and their by-products such as disulfides and sulfoxides, but also with iodine in iodinated phenolic substrates. This results in the formation of Se-X bonds (X = O, S, N, or I) from which a selenenylsulfide intermediate is invariably produced. The initial selenolate group is then recycled by thiol addition. In bacterial glycine reductase and D-proline reductase, an unusual catalytic rupture of selenium-carbon bonds is observed. The exchange of selenium for sulfur in selenoproteins, and information obtained from model reactions, suggest that a generic advantage of selenium compared with sulfur relies on faster kinetics and better reversibility of its oxidation reactions.

Selective cellular probes for mammalian thioredoxin reductase TrxR1: Rational design of RX1, a modular 1,2-thiaselenane redox probe

Quantifying the activity of key cellular redox players is crucial for understanding physiological homeostasis, and for targeting their perturbed states in pathologies including cancer and inflammatory diseases. However, cellularly-selective probes for oxidoreductase turnover are sorely lacking. We rationally developed the first probes that selectively target the mammalian selenoprotein thioredoxin reductase (TrxR), using a cyclic selenenylsulfide oriented to harness TrxR's unique selenolthiol chemistry while resisting the cellular monothiol background. Lead probe RX1 had excellent TrxR1-selective performance in cells, cross-validated by knockout, selenium starvation, knock-in, and chemical inhibitors. Its background-free fluorogenicity enabled us to perform the first quantitative high-throughput live cell screen for TrxR1 inhibitors, which indicated that tempered S_NAr electrophiles may be more selective TrxR drugs than the classical electrophiles used hitherto. The RX1 design thus sets the stage for in vivo imaging of the activity of this key oxidoreductase in health and disease, and can also drive TrxR1-inhibitor drug design.

The role of selenium in type-2 diabetes mellitus and its metabolic comorbidities

This review addresses the role of the essential trace element, selenium, in type-2 diabetes mellitus (T2DM) and its metabolic co-morbidities, i.e., metabolic syndrome, obesity and non-alcoholic fatty liver disease. We refer to the dietary requirements of selenium and the key physiological roles of selenoproteins. We explore the dysregulated fuel metabolism in T2DM and its co-morbidities, emphasizing the relevance of inflammation and oxidative stress. We describe the epidemiology of observational and experimental studies of selenium in diabetes and related conditions, explaining that the interaction between selenium status and glucose control is not limited to hyperglycemia but extends to hypoglycemia. We propose that the association between high plasma/serum selenium and T2DM/fasting plasma glucose observed in many cross-sectional studies may rely on the upregulation of hepatic selenoprotein-P biosynthesis in conditions of hyperglycemia and insulin resistance. While animal studies have revealed potential molecular mechanisms underlying adverse effects of severe selenium/selenoprotein excess and deficiency in the pathogenesis of insulin resistance and β-cell dysfunction, their translational significance is rather limited. Importantly, dietary selenium supplementation does not appear to be a major causal factor for the development of T2DM in humans though we cannot currently exclude a small contribution of selenium on top of other risk factors, in particular if it is ingested at high (supranutritional) doses. Elevated selenium biomarkers that are often measured in T2DM patients are more likely to be a consequence, rather than a cause, of diabetes.

The Trace Element Selenium Is Important for Redox Signaling in Phorbol Ester-Differentiated THP-1 Macrophages

Physiological selenium (Se) levels counteract excessive inflammation, with selenoproteins shaping the immunoregulatory cytokine and lipid mediator profile. How exactly differentiation of monocytes into macrophages influences the expression of the selenoproteome in concert with the Se supply remains obscure. THP-1 monocytes were differentiated with phorbol 12-myristate 13-acetate (PMA) into macrophages and (i) the expression of selenoproteins, (ii) differentiation markers, (iii) the activity of NF-κB and NRF2, as well as (iv) lipid mediator profiles were analyzed. Se and differentiation affected the expression of selenoproteins in a heterogeneous manner. GPX4 expression was substantially decreased during differentiation, whereas GPX1 was not affected. Moreover, Se increased the expression of selenoproteins H and F, which was further enhanced by differentiation for selenoprotein F and diminished for selenoprotein H. Notably, LPS-induced expression of NF-κB target genes was facilitated by Se, as was the release of COX- and LOX-derived lipid mediators and substrates required for lipid mediator biosynthesis. This included TXB2, TXB3, 15-HETE, and 12-HEPE, as well as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Our results indicate that Se enables macrophages to accurately adjust redox-dependent signaling and thereby modulate downstream lipid mediator profiles.

Carrot Consumption Frequency Associated with Reduced BMI and Obesity through the SNP Intermediary rs4445711

It is unclear whether genetic interactions are involved in the association between vegetable intake and reduced body mass index (BMI) or obesity. We conducted a comprehensive search for single nucleotide polymorphisms (SNPs) which are associated with the interaction between vegetable intake frequency and BMI or obesity. We performed a genome-wide association analysis to evaluate the genetic interactions between self-reported intake of vegetables such as carrot, broccoli, spinach, other green vegetables (green pepper and green beans), pumpkin, and cabbage with BMI and obesity, which is defined as a BMI ≥ 25.0 kg/m2 in the Japanese population (n = 12,225). The mean BMI and prevalence of obesity was 23.9 ± 3.4 kg/m2 and 32.3% in men and 22.1 ± 3.8 kg/m2 and 17.3% in in women, respectively. A significant interaction was observed between rs4445711 and frequency of carrot intake on BMI (p = 4.5 × 10-8). This interaction was slightly attenuated after adjustment for age, sex, alcohol intake, smoking, physical activity and the frequency of total vegetable intake (p = 2.1 × 10-7). A significant interaction was also observed between rs4445711 and frequency of carrot intake on obesity (p = 2.5 × 10-8). No significant interactions that were the same as the interaction between frequency of carrot intake and rs4445711 were observed between the intake frequency of broccoli, spinach, other green vegetables, pumpkin or cabbage and BMI or obesity. The frequency of carrot consumption is implicated in reducing BMI by the intermediary of rs4445711. This novel genetic association may provide new clues to clarify the association between vegetable intake and BMI or obesity.

Thioredoxin reductase is a major regulator of metabolism in leukemia cells

Despite the fact that AML is the most common acute leukemia in adults, patient outcomes are poor necessitating the development of novel therapies. We identified that inhibition of Thioredoxin Reductase (TrxR) is a promising strategy for AML and report a highly potent and specific inhibitor of TrxR, S-250. Both pharmacologic and genetic inhibition of TrxR impairs the growth of human AML in mouse models. We found that TrxR inhibition leads to a rapid and marked impairment of metabolism in leukemic cells subsequently leading to cell death. TrxR was found to be a major and direct regulator of metabolism in AML cells through impacts on both glycolysis and the TCA cycle. Studies revealed that TrxR directly regulates GAPDH leading to a disruption of glycolysis and an increase in flux through the pentose phosphate pathway (PPP). The combined inhibition of TrxR and the PPP led to enhanced leukemia growth inhibition. Overall, TrxR abrogation, particularly with S-250, was identified as a promising strategy to disrupt AML metabolism.

Chemopreventive and Anticancer Property of Selenoproteins in Obese Breast Cancer

Obesity is a significant risk factor for various cancers including breast cancer resulting in an increased risk of recurrence as well as morbidity and mortality. Extensive studies on various pathways have been successful in establishing a biological relationship between obesity and breast cancer. The molecular classification of breast cancer includes five groups each having different responses to treatment. Increased levels of inflammatory cytokines seen in obese conditions drive the pro-proliferative pathways, such as the influx of macrophages, angiogenesis, and antiapoptotic pathways. Increased peripheral aromatization of androgens by aromatase increases the circulating estrogen levels which are also responsible for the association of obesity with breast cancer. Also, increased oxidative stress due to chronic low-grade inflammation in obese women plays an important role in carcinogenesis. Despite the availability of safe and effective treatment options for breast cancer, obese women are at increased risk of adverse outcomes including treatment-related toxicities. In the recent decade, selenium compounds have gained substantial interest as chemopreventive and anticancer agents. The chemical derivatives of selenium include inorganic and organic compounds that exhibit pro-oxidant properties and alter cellular redox homeostasis. They target more than one metabolic pathway by thiol modifications, induction of reactive oxygen species, and chromatin modifications to exert their chemopreventive and anticancer activities. The primary functional effectors of selenium that play a significant role in human homeostasis are selenoproteins like glutathione peroxidase, thioredoxin reductase, iodothyronine deiodinases, and selenoprotein P. Selenoproteins play a significant role in adipose tissue physiology by modulating preadipocyte proliferation and adipogenic differentiation. They correlate negatively with body mass index resulting in increased oxidative stress that may lead to carcinogenesis in obese individuals. Methylseleninic acid effectively suppresses aromatase activation thus reducing the estrogen levels and acting as a breast cancer chemopreventive agent. Adipose-derived inflammatory mediators influence the selenium metabolites and affect the proliferation and metastatic properties of cancer cells. Recently selenium nanoparticles have shown potent anticancer activity which may lead to a major breakthrough in the management of cancers caused due to multiple pathways. In this review, we discuss the possible role of selenoproteins as chemopreventive and an anticancer agent in obese breast cancer.

The skeletal muscles of mice infected with Plasmodium berghei and Plasmodium chabaudi reveal a crosstalk between lipid mediators and gene expression

Background

Malaria is one of the most prevalent infectious disease in the world with 3.2 billion humans at risk. Malaria causes splenomegaly and damage in other organs including skeletal muscles. Skeletal muscles comprise nearly 50% of the human body and are largely responsible for the regulation and modulation of overall metabolism. It is essential to understand how malaria damages muscles in order to develop effective preventive measures and/or treatments. Using a pre-clinical animal model, the potential molecular mechanisms of Plasmodium infection affecting skeletal muscles of mice were investigated.

Methods

Mouse Signal Transduction Pathway Finder PCR Array was used to monitor gene expression changes of 10 essential signalling pathways in skeletal muscles from mice infected with Plasmodium berghei and Plasmodium chabaudi. Then, a new targeted-lipidomic approach using liquid chromatography with tandem mass spectrometry (LC–MS/MS) to profile 158 lipid signalling mediators (LMs), mostly eicosanoids derived from arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), was applied. Finally, 16 key LMs directly associated with inflammation, oxidative stress, and tissue healing in skeletal muscles, were quantified.

Results

The results showed that the expression of key genes altered by Plasmodium infection is associated with inflammation, oxidative stress, and atrophy. In support to gene profiling results, lipidomics revealed higher concentrations of LMs in skeletal muscles directly related to inflammatory responses, while on the levels of LMs crucial in resolving inflammation and tissue repair reduced significantly.

Conclusion

The results provide new insights into the molecular mechanisms of malaria-induced muscle damage and revealed a potential mechanism modulating inflammation in malarial muscles. These pre-clinical studies should help with future clinical studies in humans aimed at monitoring of disease progression and development of specific interventions for the prevention and mitigation of long-term chronic effects on skeletal muscle function.

Selenium and Selenoproteins in Adipose Tissue Physiology and Obesity

Selenium (Se) homeostasis is tightly related to carbohydrate and lipid metabolism, but its possible roles in obesity development and in adipocyte metabolism are unclear. The objective of the present study is to review the current data on Se status in obesity and to discuss the interference between Se and selenoprotein metabolism in adipocyte physiology and obesity pathogenesis. The overview and meta-analysis of the studies on blood Se and selenoprotein P (SELENOP) levels, as well as glutathione peroxidase (GPX) activity in obese subjects, have yielded heterogenous and even conflicting results. Laboratory studies demonstrate that Se may modulate preadipocyte proliferation and adipogenic differentiation, and also interfere with insulin signaling, and regulate lipolysis. Knockout models have demonstrated that the selenoprotein machinery, including endoplasmic reticulum-resident selenoproteins together with GPXs and thioredoxin reductases (TXNRDs), are tightly related to adipocyte development and functioning. In conclusion, Se and selenoproteins appear to play an essential role in adipose tissue physiology, although human data are inconsistent. Taken together, these findings do not support the utility of Se supplementation to prevent or alleviate obesity in humans. Further human and laboratory studies are required to elucidate associations between Se metabolism and obesity.

Comprehensive Transcriptome Analysis of lncRNAs Reveals the Role of lncAD in Chicken Intramuscular and Abdominal Adipogenesis

Adipose tissue-specific distribution and deposition speed are the main factors affecting the slaughter performance and meat quality in poultry. Previous studies suggested that different adipose tissues owned various biochemical characteristics and gene expression patterns. To investigate the functional role of long noncoding RNAs (lncRNAs) during chicken intramuscular and abdominal adipogenesis, we performed transcriptome analysis by Ribo-Zero RNA-Seq technology. A total of 11247 lncRNAs were observed in the adipocytes derived from IMF and AbF in chicken. Among them, we got 1624 differentiated expressed novel lncRNAs. A large amount of lncRNAs were involved in several lipid metabolism and adipogenesis-related signaling pathways. Of these, lncRNAs, lncAD is one of the most upregulated lncRNA and was coexpressed with several genes of the PPAR signaling pathway. Here, we report that knockdown of lncAD inhibited its upstream gene TXNRD1 expression in a cis-regulation manner, thus to decrease intramuscular preadipocytes adipogenic differentiation and promoted cell proliferation. Our present study revealed huge lncRNAs profile differences between IMF- and AbF-derived preadipocyte adipogenesis. Collectively, our findings not only provide valuable evidence for the identification of adipogenic lncRNAs but also contribute to further studies about the post-transcriptional regulation mechanism underlying tissue-specific fat deposition in poultry.

Effects of Mammalian Thioredoxin Reductase Inhibitors

The mammalian thioredoxin system is driven by NADPH through the activities of isoforms of the selenoprotein thioredoxin reductase (TXNRD, TrxR), which in turn help to keep thioredoxins (TXN, Trx) and further downstream targets reduced. Due to a wide range of functions in antioxidant defense, cell proliferation, and redox signaling, strong cellular aberrations are seen upon the targeting of TrxR enzymes by inhibitors. However, such inhibition can nonetheless have rather unexpected consequences. Accumulating data suggest that inhibition of TrxR in normal cells typically yields a paradoxical effect of increased antioxidant defense, with metabolic pathway reprogramming, increased cellular proliferation, and altered cellular differentiation patterns. Conversely, inhibition of TrxR in cancer cells can yield excessive levels of reactive oxygen species (ROS) resulting in cell death and thus anticancer efficacy. The observed increases in antioxidant capacity upon inhibition of TrxR in normal cells are in part dependent upon activation of the Nrf2 transcription factor, while exaggerated ROS levels in cancer cells can be explained by a non-oncogene addiction of cancer cells to TrxR1 due to their increased endogenous production of ROS. These separate consequences of TrxR inhibition can be utilized therapeutically. Importantly, however, a thorough knowledge of the molecular mechanisms underlying effects triggered by TrxR inhibition is crucial for the understanding of therapy outcomes after use of such inhibitors. The mammalian thioredoxin system is driven by thioredoxin reductases (TXNRD, TrxR), which keeps thioredoxins (TXN, Trx) and further downstream targets reduced. In normal cells, inhibition of TrxR yields a paradoxical effect of increased antioxidant defense upon activation of the Nrf2 transcription factor. In cancer cells, however, inhibition of TrxR yields excessive reactive oxygen species (ROS) levels resulting in cell death and thus anticancer efficacy, which can be explained by a non-oncogene addiction of cancer cells to TrxR1 due to their increased endogenous production of ROS. These separate consequences of TrxR inhibition can be utilized therapeutically.

miR-125b-5p inhibits cell proliferation, migration, and invasion in hepatocellular carcinoma via targeting TXNRD1

Background

Thioredoxin reductase 1 (TXNRD1) is an antioxidant enzyme reportedly overexpressed in hepatocellular carcinoma (HCC); however, the detailed function and mechanisms of TXNRD1 in HCC remain obscure. In this study, we investigated the miR-125b-5p-specific regulation of TXNRD1 levels and its effect on HCC cells.

Methods

We detected miR-125b-5p levels in human HCC tissue samples through quantitative reverse transcription polymerase chain reaction (qRT-PCR), and in vitro experiments were employed to investigate the effect of miR-125b-5p on HCC cell proliferation, migration, and invasion. Additionally, we examined miR-125b-5p-mediated changes in TXNRD1 levels by qRT-PCR and western blotting, and a dual luciferase-reporter assay was conducted to confirm direct targeting of the 3' untranslated region of TXNRD1 mRNA by miR-125b-5p.

Results

miR-125b-5p expression was reduced in HCC tissues relative to that in matched para-carcinoma tissues; this finding was verified in HCC cohorts from the Gene Expression Omnibus and The Cancer Genome Atlas. Additionally, low miR-125b-5p expression was associated with poor prognosis in HCC patients, and gene-set enrichment analysis indicated that miR-125b-5p levels were associated with HCC proliferation and metastasis. As predicted, overexpressing miR-125b-5p restrained the proliferation, migration, and invasion of Huh7 and SK-Hep-1 cells and forced expression of the miR-125b-5p-downregulated TXNRD1 mRNA and protein levels in HCC cells. Moreover, dual luciferase-reporter assays revealed that miR-125b-5p targets TXNRD1 to directly regulate its expression, whereas TXNRD1 overexpression abolishes the inhibitory effect of miR-125b-5p on HCC cell proliferation, migration, and invasion.

Conclusions

These results demonstrated miR-125b-5p as a tumor suppressor in HCC through its inhibition of TXNRD1, thereby suggesting it as a potential target for the clinical treatment of HCC.

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.

Adipocytokines, inflammatory, epigenetic instability & angiogenesis biomarkers in type 2 diabetic Egyptian women with breast cancer

Obesity is the main determinant of type 2 diabetes. Some adipocytokines play important roles in diabetic complications. Lipid transport is an important aspect of lipid metabolism in cancer. Present study aimed to evaluate the effect of some adipocytokines, inflammatory, epigenetic instability & angiogenesis biomarkers in type 2 diabetic Egyptian women with breast cancer. Study Design was performed on eighty females divided into 20 healthy subjects (Group I), 20 patients with type 2 diabetes (Group II), 20 patients with breast cancer (Group III) & 20 patients with diabetes and breast cancer (Group IV). Demographic data & body mass index have been collected. Biochemical analysis included fasting & postprandial blood glucose, lipid profile, fatty acid-binding proteins-4 (FABP-4), tumor necrosis factor-α (TNF-α), vascular endothelial growth factor (VEGF), 8-hydroxy-2'-deoxyguanosine (8-OHdG) & thioredoxin reductase (TrxR) activity. Results revealed significant increase in FABP-4, TNF-α, VEGF, 8-OHdG and significant decreased TrxR activity in diabetic patients with breast cancer in comparison with other groups. These changes were evident in breast cancer subjects than diabetic and healthy cases and in diabetic than healthy cases. Conclusion: This study confirmed the role of FABP-4 in pathogenesis of type 2 diabetes & breast cancer via enhancing angiogenesis, inflammatory and epigenetic instability biomarkers.

PCK1 Downregulation Promotes TXNRD1 Expression and Hepatoma Cell Growth via the Nrf2/Keap1 Pathway

Gluconeogenesis, generates glucose from small carbohydrate substrates, and drives the metabolic flux in parallel but opposite to glycolysis. The cytoplasmic isoform of phosphoenolpyruvate carboxykinase (PCK1 or PEPCK-C), a rate-limiting enzyme in gluconeogenesis, initiates the gluconeogenesis process and is reportedly dysregulated in multiple types of cancer. Gluconeogenesis mainly occurs in the liver during fasting, and previous studies have demonstrated that PCK1 acts as a tumor suppressor in hepatocellular carcinoma (HCC); however, the role of PCK1 in cancer progression remains incompletely understood. In the current study, we found that PCK1 expression was decreased in HCC as compared to adjacent normal liver tissues, and low PCK1 expression correlated with poor patient prognosis. Furthermore, overexpression of PCK1 suppressed reactive oxygen species (ROS) production and nuclear translocation of Nrf2 in hepatoma cells. In addition, thioredoxin reductase 1 (TXNRD1), an antioxidant enzyme regulated by the Nrf2/Keap1 pathway, was downregulated upon overexpression of PCK1 in HCC cell lines. Furthermore, we verified this axis using nude mouse xenograft model. Finally, we found that auranofin, a TXNRD1 inhibitor, enhanced the sensitivity of PCK1-knockout hepatoma cells to sorafenib-induced apoptosis. Taken together, our findings suggest that PCK1 deficiency promotes hepatoma cell proliferation via the induction of oxidative stress and the activation of transcription factor Nrf2, and that targeting the TXNRD1 antioxidant pathway sensitizes PCK1-knockout hepatoma cells to sorafenib treatment in vitro.

Essential role of Ahnak in adipocyte differentiation leading to the transcriptional regulation of Bmpr1α expression

The role of Ahnak in obesity has been reported previously. Loss of Ahnak leads to decreased Bmp4/Smad1 signaling, resulting in the downregulation of adipocyte differentiation. However, the biological significance of Ahnak remains largely unknown. In this study, we demonstrate that Ahnak-mediated impaired adipogenesis results in decreased Bmpr1α transcriptional expression. To confirm this, Ahnak siRNA was used to knock-down Ahnak in C3H10T1/2 and primary stromal vascular fraction cells. Ahnak siRNA transfected cells showed suppression of Bmpr1α expression and decreased BMP4/ Bmpr1α signaling. The differential adipogenesis was further confirmed by knock-down of Bmpr1α in C3H10T1/2 cells, which resulted in reduced adipogenesis. Moreover, stable Ahnak knock-out C3H10T1/2 cells stably transfected with Ahnak CRISPR/Cas9 plasmid suppressed expression of Bmpr1α and prevented differentiation into adipocytes. Furthermore, we developed immortalized pre-adipocytes from wild-type or Ahnak Knock-out mice's stromal vascular fraction (SVF) to confirm the function of Ahnak in pre-adipocyte transition. Immortalized Ahnak knock-out SVF cells showed lower level of Bmpr1α expression, evidence by their impaired BMP4/Bmpr1α signaling. Upon adipogenic induction, immortalized Ahnak knock-out SVF cells exhibited a marked decrease in adipocyte differentiation compared with immortalized wild-type pre-adipocytes. Furthermore, over-expression of Bmpr1α restored the adipogenic activity of Ahnak knock-out C3H10T1/2 cells and immortalized Ahnak knock-out SVF cells. Our data reveal the missing link in Ahnak-mediated adipose tissue remodeling and suggest that precise regulation of Ahnak in adipose tissue might have a therapeutic advantage for metabolic disease treatment.

The thioredoxin-1 system is essential for fueling DNA synthesis during T-cell metabolic reprogramming and proliferation

The thioredoxin-1 (Trx1) system is an important contributor to cellular redox balance and is a sensor of energy and glucose metabolism. Here we show critical c-Myc-dependent activation of the Trx1 system during thymocyte and peripheral T-cell proliferation, but repression during T-cell quiescence. Deletion of thioredoxin reductase-1 (Txnrd1) prevents expansion the CD4⁻CD8⁻ thymocyte population, whereas Txnrd1 deletion in CD4⁺CD8⁺ thymocytes does not affect further maturation and peripheral homeostasis of αβT cells. However, Txnrd1 is critical for expansion of the activated T-cell population during viral and parasite infection. Metabolomics show that TrxR1 is essential for the last step of nucleotide biosynthesis by donating reducing equivalents to ribonucleotide reductase. Impaired availability of 2′-deoxyribonucleotides induces the DNA damage response and cell cycle arrest of Txnrd1-deficient T cells. These results uncover a pivotal function of the Trx1 system in metabolic reprogramming of thymic and peripheral T cells and provide a rationale for targeting Txnrd1 in T-cell leukemia.

Thioredoxin (Trx), Trx reductase, Txnip and NADPH together comprise the Trx system. Here the authors make a T cell-specific thioredoxin reductase-1 knockout mouse to show how this system reprograms cellular metabolism to enable T cell development, proliferation and responses.

The role of the thioredoxin/thioredoxin reductase system in the metabolic syndrome: towards a possible prognostic marker?

Mammalian thioredoxin reductase (TrxR) is a selenoprotein with three existing isoenzymes (TrxR1, TrxR2, and TrxR3), which is found primarily intracellularly but also in extracellular fluids. The main substrate thioredoxin (Trx) is similarly found (as Trx1 and Trx2) in various intracellular compartments, in blood plasma, and is the cell's major disulfide reductase. Thioredoxin reductase is necessary as a NADPH-dependent reducing agent in biochemical reactions involving Trx. Genetic and environmental factors like selenium status influence the activity of TrxR. Research shows that the Trx/TrxR system plays a significant role in the physiology of the adipose tissue, in carbohydrate metabolism, insulin production and sensitivity, blood pressure regulation, inflammation, chemotactic activity of macrophages, and atherogenesis. Based on recent research, it has been reported that the modulation of the Trx/TrxR system may be considered as a new target in the management of the metabolic syndrome, insulin resistance, and type 2 diabetes, as well as in the treatment of hypertension and atherosclerosis. In this review evidence about a possible role of this system as a marker of the metabolic syndrome is reported.

The A to Z of modulated cell patterning by mammalian thioredoxin reductases

Mammalian thioredoxin reductases (TrxRs) are selenocysteine-containing proteins (selenoproteins) that propel a large number of functions through reduction of several substrates including the active site disulfide of thioredoxins (Trxs). Well-known enzymatic systems that in turn are supported by Trxs and TrxRs include deoxyribonucleotide synthesis through ribonucleotide reductase, antioxidant defense through peroxiredoxins and methionine sulfoxide reductases, and redox modulation of a number of transcription factors. Although these functions may be essential for cells due to crucial roles in maintenance of cell viability and proliferation, findings during the last decade reveal that mammals have major redundancy in their cellular reductive systems. The synthesis of glutathione (GSH) and reductive functions of GSH-dependent pathways typically act in parallel with Trx-dependent pathways, with only one of these systems often being sufficient to support viability. Importantly, this does not imply that a modulation of the Trx system will remain without consequences, even when GSH-dependent pathways remain functional. As suggested by several recent findings, the Trx system in general and the TrxRs in particular, function as key regulators of signaling pathways. In this review article we will discuss findings that collectively suggest that modulation in mammalian systems of cytosolic TrxR1 (TXNRD1) or mitochondrial TrxR2 (TXNRD2) influence cell patterning and cellular stress responses. Effects of lower activities include increased adipogenesis, insulin responsiveness, glycogen accumulation, hyperproliferation, and distorted embryonic development, while increased activities correlate with decreased proliferation and extended lifespan, as well as worse cancer prognosis. The molecular mechanisms that underlie these diverse effects, involving regulation of protein phosphorylation cascades and of key transcription factors that guide cellular differentiation pathways, will be discussed. We conclude that the selenium-dependent oxidoreductases TrxR1 and TrxR2 should be considered as key components of signaling pathways that control cell differentiation and cellular stress responses.

The transcriptional response to oxidative stress is part of, but not sufficient for, insulin resistance in adipocytes

Insulin resistance is a major risk factor for metabolic diseases such as Type 2 diabetes. Although the underlying mechanisms of insulin resistance remain elusive, oxidative stress is a unifying driver by which numerous extrinsic signals and cellular stresses trigger insulin resistance. Consequently, we sought to understand the cellular response to oxidative stress and its role in insulin resistance. Using cultured 3T3-L1 adipocytes, we established a model of physiologically-derived oxidative stress by inhibiting the cycling of glutathione and thioredoxin, which induced insulin resistance as measured by impaired insulin-stimulated 2-deoxyglucose uptake. Using time-resolved transcriptomics, we found > 2000 genes differentially-expressed over 24 hours, with specific metabolic and signalling pathways enriched at different times. We explored this coordination using a knowledge-based hierarchical-clustering approach to generate a temporal transcriptional cascade and identify key transcription factors responding to oxidative stress. This response shared many similarities with changes observed in distinct insulin resistance models. However, an anti-oxidant reversed insulin resistance phenotypically but not transcriptionally, implying that the transcriptional response to oxidative stress is insufficient for insulin resistance. This suggests that the primary site by which oxidative stress impairs insulin action occurs post-transcriptionally, warranting a multi-level ‘trans-omic’ approach when studying time-resolved responses to cellular perturbations.

Repression of Akt3 gene transcription by the tumor suppressor RIZ1

RIZ1 has been studied as a tumor suppressor and may play a role in metabolic diseases related to the Western style diet, such as cancer and obesity. The Akt pathway is known to play a role in both cancer and obesity, and a link between Akt and RIZ1 has also been found. To better understand the role of RIZ1 in obesity and cancer, we investigated how RIZ1 regulates the expression of Akt3. We found that overexpression of RIZ1 in HEK293 cells reduced the expression of Akt3 protein. Luciferase reporter activity of Akt3 gene promoter was significantly reduced in cells co-transfected with RIZ1. Recombinant proteins of RIZ1 was able to bind the Akt3 promoter in vitro, and chromatin immunoprecipitation assay also demonstrated the ability of RIZ1 binding to the Akt3 promoter in vivo. Overexpression of RIZ1 increased H3K9 methylation on the Akt3 promoter. These results identify Akt3 as a target of RIZ1 regulation and expand our understanding of the Akt pathway in cancer and obesity.

Effect of Mutant p53 Proteins on Glycolysis and Mitochondrial Metabolism

TP53 is one of the most commonly mutated genes in human cancers. Unlike other tumor suppressors that are frequently deleted or acquire loss-of-function mutations, the majority of TP53 mutations in tumors are missense substitutions, which lead to the expression of full-length mutant proteins that accumulate in cancer cells and may confer unique gain-of-function (GOF) activities to promote tumorigenic events. Recently, mutant p53 proteins have been shown to mediate metabolic changes as a novel GOF to promote tumor development. There is a strong rationale that the GOF activities, including alterations in cellular metabolism, might vary between the different p53 mutants. Accordingly, the effect of different mutant p53 proteins on cancer cell metabolism is largely unknown. In this study, we have metabolically profiled several individual frequently occurring p53 mutants in cancers, focusing on glycolytic and mitochondrial oxidative phosphorylation pathways. Our investigation highlights the diversity of different p53 mutants in terms of their effect on metabolism, which might provide a foundation for the development of more effective targeted pharmacological approaches toward variants of mutant p53.

Annual Wormwood Leaf Inhibits the Adipogenesis of 3T3-L1 and Obesity in High-Fat Diet-Induced Obese Rats

Annual wormwood (AW) (Artemisia annua L.) has anti-malarial, anti-bacterial, anti-oxidant, anti-tumour, and anti-inflammatory activities. In the present study, we evaluated the effects of annual wormwood leaves (AWL) on adipocyte differentiation in 3T3-L1 cells and high-fat diet (HFD)-induced obese rats. 3T3-L1 adipocytes and HFD-induced obese rats were treated with AWL, and its effect on gene expression was analyzed using RT-PCR and Western blotting experiments. Treatment with AWL effectively prevented triglyceride accumulation during adipogenesis in a dose-dependent manner. Consistently, AWL suppressed the differentiation of 3T3-L1 preadipocytes into adipocytes through the downregulation of dexamethasone, 3-isobutyl-1- methylxanthine, and insulin (DMI)-induced serine/threonine kinase protein kinase B (PKB/Akt) activation and the expression of adipogenic genes, including the CCAAT/enhancer binding protein-α (C/EBPα) and peroximal proliferator-activated receptor-γ (PPARγ). Moreover, the expression of adipocyte fatty acid-binding protein 4 (aP2), which is a known PPARγ-target gene, was downregulated by AWL treatment. Oral administration of AWL extracts significantly decreased the body weight gain, adipose tissue mass, adipocyte cell size, serum triglyceride (TG), and total cholesterol (TC) levels in HFD-induced obese rats. These results provide novel insight into the molecular mechanisms underlying the anti-obesity effects of AWL that are mediated by the downregulation of the expression of major adipogenic transcription factors, C/EBPα and PPARγ and Akt signalling.

Diet Modulates Adipose Tissue Oxidative Stress in a Murine Acute Chagas Model

Chagas disease, also known as American trypanosomiasis, is a tropical parasitic disease caused by the protozoan Trypanosoma cruzi. T. cruzi targets adipose tissue, which serves as a reservoir of this parasite. T. cruzi infection of adipose tissue is characterized by increased lipolysis, oxidative stress, and parasitemia. High fat diet (HFD) decreases lipolysis and increases the survival rate in the mice infected with T. cruzi during acute infection. However, the effect of HFD on oxidative stress in adipose tissue has not been examined in detail. In the present study we evaluated the effect of HFD on oxidative stress markers in both white and brown adipose tissues (WAT and BAT) during acute infection. We used qPCR to examine the mRNA expression levels of genes involved in several antioxidant defence systems, such as those acting in ROS metabolism, peroxidases, and relevant oxygen transporter genes. The result of our study showed that HFD regulates the expression levels of oxidative stress genes in adipose tissues and that these effects are often different in WAT and BAT. For instance, while HFD down-regulated the levels of most antioxidant genes in both WAT and BAT, it differentially affected the expression pattern of genes involved in ROS metabolism (e.g. peroxidases) in WAT and BAT tissues of infected mice. Together with our previous studies, these findings show that infection and diet both regulate antioxidant enzymes and other oxidative stress defenses in mouse adipose tissues during acute T. cruzi infection.