Reactive Oxygen Species Evoked by Potassium Deprivation and Staurosporine Inactivate Akt and Induce the Expression of TXNIP in Cerebellar Granule Neurons

ROS produced by NOX promote the neurite growth in a PI3K/Akt independent manner

Reactive oxygen species (ROS) function as signaling molecules in several physiologic and pathologic processes. In central nervous system, ROS are critical for differentiation, migration, polarization, and neurite growth. These actions are mediated by reversible oxidation of target proteins. On the other hand, PI3K/Akt signaling pathway is susceptible to be modulated by ROS and it has been implicated in neurite growth. In this study, we evaluated the participation of ROS in the neurite growth of cultured rat cerebellar granule neurons (CGN), as well as the possible regulation of the PI3K/Akt pathway by ROS during neurite outgrowth. For this purpose, CGN were treated with cellular or mitochondrial antioxidants, or an NOX inhibitor and neurite growth was evaluated. Moreover, to assess the participation Akt in this process, the p-Akt levels were measured in CGN treated with antioxidants or a NOX inhibitor. The effect of antioxidants on the neurite growth in the presence of a PI3K inhibitor was also measured. We found that cellular antioxidants and the NOX inhibitor decreased the neurite growth, but not the mitochondrial antioxidant. Interestingly, the antioxidants increased the p-Akt levels; however, the effect of antioxidants on neurite growth was no dependent on the Akt activity since the inhibitor of PI3K did not modify the antioxidant action on neurite growth. Our results show that the PI3K/Akt pathway participates in neurite growth and that ROS produced by NOX could function as signals in this process; however, this action is not mediated by a redox regulation of Akt activity.

Thioredoxin-interacting protein-activated intracellular potassium deprivation mediates the anti-tumour effect of a novel histone acetylation inhibitor HL23, a fangchinoline derivative, in human hepatocellular carcinoma

INTRODUCTION

Hyperactivated histone deacetylases (HDACs) act as epigenetic repressors on gene transcription and are frequently observed in human hepatocellular carcinoma (HCC). Although multiple pharmacological HDAC inhibitors (HDACis) have been developed, none is available in human HCC.

OBJECTIVES

To investigate the pharmacological effects of a fangchinoline derivative HL23, as a novel HDACi and its molecular mechanisms through TXNIP-mediated potassium deprivation in HCC.

METHODS

Both in vitro assays and orthotopic HCC mouse models were used to investigate the effects of HL23 in this study. The inhibitory activity of HL23 on HDACs was evaluated by in silico studies and cellular assays. Chromatin immunoprecipitation (ChIP) was conducted to confirm the regulation of HL23 on acetylation mark at TXNIP promoter. Genome-wide transcriptome analysis together with bioinformatic analysis were conducted to identify the regulatory mechanisms of HL23. The clinical significance of TXNIP and HDACs was evaluated by analysing publicly available database.

RESULTS

HL23 exerted compatible HDACs inhibition potency as Vorinostat (SAHA) while had superior anti-HCC effects than SAHA and sorafenib. Both in vitro and in vivo studies showed HL23 significantly suppressed HCC progression and metastasis. HL23 significantly upregulated TXNIP expression via regulating acetylation mark (H3K9ac) at TXNIP promoter. TXNIP was responsible for anti-HCC activity of HL23 through mediating potassium channel activity. HDAC1 was predicted to be the target of HL23 and HDAC1lowTXNIPhigh could jointly predict promising survival outcome of patients with HCC. Combination treatment with HL23 and sorafenib could significantly enhance sorafenib efficacy.

CONCLUSION

Our study identified HL23 as a novel HDACi through enhancing acetylation at TXNIP promoter to trigger TXNIP-dependent potassium deprivation and enhance sorafenib efficacy in HCC treatment.

Txnip expression promotes JNK-mediated neuronal death in response to reactive oxygen species

TXNIP is a protein sensitive to oxidant conditions whose expression is related to the progression of death in cancer, diabetes, ischemia, and neurodegenerative diseases, among others. Because of this, many studies propose TXNIP as a therapeutic target in several diseases. Exposure of cerebellar granule neurons to staurosporine or low potassium leads to apoptotic death. Both conditions generate an early production of reactive oxygen species (ROS) that induces the activation of the ASK1 pathway and the apoptotic machinery. In these models, it has been shown an increase in TXNIP protein mediated by ROS. Here, we evaluated the molecular mechanisms involved in the regulation of the Txnip expression during neuronal death, as well as the role of the protein in the progression of cell death induced by these two apoptotic conditions. In cultured cerebellar granule neurons, we observed that low potassium and staurosporine induced an early increase in ROS that correlated with an increase in Txnip mRNA. When we evaluated the promoter of the gene, we found that the JASPAR-reported FOXO1/3 transcription factor motifs are close to the transcription start site (TSS). We then verified through the Chromatin immunoprecipitation technique (ChIP) that FOXO3 interacts with the Txnip promoter after 1 h of low potassium treatment. We also detected FOXO3 nuclear translocation by low potassium and staurosporine treatments. Finally, by using shRNA in the neuroblastoma MSN cell line, we found that Txnip downregulation decreased neuronal death induced by staurosporine stimulus. Together, these results suggest that ROS promotes the expression of Txnip through the activation of the FOXO3 transcription factor mediated by Akt inhibition. We also demonstrated that TXNIP is necessary for neuronal death progression.

ChemR23 signaling ameliorates cognitive impairments in diabetic mice via dampening oxidative stress and NLRP3 inflammasome activation

Diabetes mellitus is associated with cognitive impairment characterized by memory loss and cognitive inflexibility. Recent studies have revealed that ChemR23 is implicated in both diabetes mellitus and Alzheimer's disease. However, the impact of ChemR23 on diabetes-associated cognitive impairment remains elusive. In this study, we explored the longitudinal changes of ChemR23 expression and cognitive function in STZ-induced type 1 diabetic mice and leptin receptor knockout type 2 diabetic mice at different ages. We also treated diabetic mice with ChemR23 agonists RvE1 or chemerin-9 to explore whether ChemR23 activation could alleviate diabetes-associated cognitive impairment. The underlying mechanism was further investigated in diabetic mice with genetic deletion of ChemR23. The results showed that ChemR23 expression was decreased along with aging and the progression of diabetes, suggesting that abnormal ChemR23 signaling may be involved in diabetes-associated cognitive impairment. Administration of RvE1 or chemerin-9 ameliorated oxidative stress and inhibited NLRP3 inflammasome activation through Nrf2/TXNIP pathway, and ultimately alleviated cognitive impairment in diabetic mice. Depletion of ChemR23 in diabetic mice abolished the beneficial effects of RvE1 and chemerin-9, and exacerbated cognitive impairment via increasing oxidative stress and activating NLRP3 inflammasome. Collectively, our data highlight the crucial role of ChemR23 signaling in diabetes-associated cognitive impairment via regulating oxidative stress and NLRP3 inflammasome, and targeting ChemR23 may serve as a promising novel strategy for the treatment of diabetes-associated cognitive impairment.

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.

Differential ROS-Mediated Phosphorylation of Drp1 in Mitochondrial Fragmentation Induced by Distinct Cell Death Conditions in Cerebellar Granule Neurons

Reactive oxygen species (ROS) production has been associated with neuronal death. ROS are also involved in mitochondrial fission, which is mediated by Dynamin-related protein 1 (Drp1). The regulation of mitochondrial fragmentation mediated by Drp1 and its relationship to mitochondrial ROS (mtROS) in neuronal death have not been completely clarified. The aim of this study is to evaluate the role of mtROS in cell death and their involvement in the activation of Drp1 and mitochondrial fission in a model of cell death of cultured cerebellar granule neurons (CGN). Neuronal death of CGN induced by potassium deprivation (K5) and staurosporine (ST) triggers mitochondrial ROS production and mitochondrial fragmentation. K5 condition evoked an increase of Drp1 phosphorylation at Ser616, but ST treatment led to a decrease of Drp1 phosphorylation. Moreover, the death of CGN induced by both K5 and ST was markedly reduced in the presence of MitoTEMPO; however, mitochondrial morphology was not recovered. Here, we show that the mitochondria are the initial source of ROS involved in the neuronal death of CGN and that mitochondrial fragmentation is a common event in cell death; however, this process is not mediated by Drp1 phosphorylation at Ser616.

Radiotherapy programs neutrophils to an antitumor phenotype by inducing mesenchymal-epithelial transition

Background

Neutrophils can play a pro-tumor or anti-tumor role depending on the tumor microenvironment. The effects of concurrent treatment with granulocyte colony-stimulating factor (G-CSF) and radiotherapy (RT) on neutrophils have not yet to be described.

Methods

Hypofractionated radiation of 8 Gy ×3 fractions was administered with or without recombinant G-CSF to Lewis lung carcinoma tumor-bearing C57BL/6 model mice. The activation status of cytotoxic T cells in the mice was measured, along with the levels of tumor-associated neutrophils, cytotoxic T cells, and Treg cells. Tumor growth, survival, cytokine expression, and signaling pathways underlying anti-tumor effects of tumor-associated neutrophils after treatment were also studied. To ascertain the effects of concurrent RT and G-CSF on tumor-associated neutrophils, neutrophil depletion was performed.

Results

RT affected early neutrophil infiltration, which is the first-line immune response. Subsequently, enhanced accumulation of lymphocytes, particularly CD8 cytotoxic T cells, was observed. Notably, lymphocytic infiltration was inhibited by neutrophil depletion but enhanced by G-CSF treatment. RT generated persistent DNA damage, as evidenced by an accumulation of phosphorylation of histone H2AX (γH2AX), and subsequently triggered inflammatory chemokine secretion. The chemokines CXCL1, CXCL2, and CCL5 were upregulated in both radiation-treated cells and the corresponding supernatants. Neutrophils that were newly recruited after RT improved radiosensitivity by inhibiting epithelial-mesenchymal transition via the reactive oxygen species-mediated PI3K/Akt/Snail signaling pathway, and G-CSF treatment enhanced this effect.

Conclusions

The results of this study suggest that RT activates neutrophil recruitment and polarizes newly recruited neutrophils toward an antitumor phenotype, which is enhanced by the concurrent administration of G-CSF. Mesenchymal-epithelial transition induced by reactive oxygen species accumulation plays a major role in this process. Thus, the polarization of tumor-associated neutrophils might play a role in future cancer immunotherapies.

Peroxisomal Dysfunction Contributes to White Matter Injury Following Subarachnoid Hemorrhage in Rats via Thioredoxin-Interacting Protein-Dependent Manner

Background and Purpose

White matter injury (WMI) exists in the early stage of subarachnoid hemorrhage (SAH) and has not been well addressed so far.

Methods

We utilized short hairpin RNA (shRNA) and clustered regularly interspaced short palindromic repeats (CRISPR) to verify the role of peroxisomes in WMI following SAH. We evaluated short- and long-term neurobehavior after SAH. Western blotting, immunofluorescence, and Golgi staining techniques were performed to assess the changes in protein levels.

Results

Catalase (CAT) CRISPR treatment significantly attenuated neurological deficits and reduced long-term spatial learning and memory impairments after SAH by increasing the level of myelin basic protein (MBP) while decreasing the levels of amyloid precursor protein (APP), interleukin 6 (IL-6), and tumor necrosis factor (TNF)-α. The use of thioredoxin-interacting protein (TXNIP) shRNA significantly offset the effects of CAT shRNA, and the use of glycerone phosphate acyl transferase (GNPAT) shRNA significantly reversed the effects of CAT CRISPR by decreasing the levels of plasmalogens and reactive oxidative species (ROS).

Conclusion

Peroxisomal dysfunction induced by SAH reversely exacerbated cerebral WMI following SAH, which was at least partly mediated by TXNIP and GNPAT pathways.

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

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

GLP-1 Receptor Activation Abrogates β-Cell Dysfunction by PKA Cα-Mediated Degradation of Thioredoxin Interacting Protein

Glucagon-like peptide 1 receptor (GLP-1R) agonist (Exendin-4) is a well-known agent used to improve β-cell dysfunctions via protein kinase A (PKA), but the detailed downstream molecular mechanisms are still elusive. We have now found that PKA Cα mediated- TXNIP phosphorylation and degradation played a vital role in the β-cell protective role of exendin-4. After PKA activator (Exendin-4 or FSK) treatment, PKA Cα could directly interact with TXNIP by bimolecular fluorescence complementation and Co-IP assays in INS-1 cells. And PKA Cα overexpression decreased TXNIP level, whereas TXNIP level was largely increased in PKA Cα-KO β-cells by CRISPR-Cas9. Interestingly, TXNIP overexpression or PKA Cα-KO has impaired β-cell functions, including loss of insulin secretion and activation of inflammation. PKA Cα directly phosphorylated TXNIP at Ser307 and Ser308 positions, leading to its degradation via activation of cellular proteasome pathway. Consistent with this observation, TXNIP (S307/308A) mutant resisted the degradation effects of PKA Cα. However, exendin-4 neither affected TXNIP level in TXNIP (S307/308A) mutant overexpressed β-cells nor in PKA Cα-KO β-cells. Moreover, exendin-4 treatment reduced the inflammation gene expression in TXNIP overexpressed β-cells, but exendin-4 treatment has no effect on the inflammation gene expression in TXNIP (S307/308A) overexpressed β-cells. In conclusion, our study reveals the integral role of PKA Cα/TXNIP signaling in pancreatic β-cells and suggests that PKA Cα-mediated TXNIP degradation is vital in β-cell protective effects of exendin-4.

Notoginsenoside R1 ameliorates diabetic encephalopathy by activating the Nrf2 pathway and inhibiting NLRP3 inflammasome activation

Numerous researches supported that oxidative stress and inflammation play important roles in the development of diabetic encephalopathy (DEP). Notoginsenoside R1 (NGR1), one major component of Panax notoginseng, is believed to have anti-oxidative, anti-inflammatory and neuroprotective properties. However, its neuroprotective effects against DEP and underlying mechanisms are still unknown. In this study, db/db mice as well as high-glucose (HG)-treated HT22 hippocampal neurons were used as in vivo and in vitro models to estimate NGR1 neuroprotection. NGR1 administration for 10 weeks could ameliorate cognitive dysfunction, depression-like behaviors, insulin resistance, hyperinsulinemia, dyslipidemia, and inflammation in db/db mice. NGR1 markedly decreased the oxidative stress induced by hyperglycemia in hippocampal neurons. NGR1 significantly activated the protein kinase B (Akt)/nuclear factor-erythroid 2-related factor2 (Nrf2) pathway, and inhibited NLRP3 inflammasome activation in hippocampal neurons, which might be essential for the neuroprotective effects of NGR1. Further supporting these results, we observed that pretreatment with the phosphatidylinositol 3-kinase inhibitor LY294002 abolished NGR1-mediated neuroprotective effects against oxidative stress and NLRP3 inflammasome activation in HG-treated HT22 hippocampal neurons. In conclusion, the present study demonstrates the neuroprotective effects of NGR1 on DEP by activating the Akt/Nrf2 pathway and inhibiting NLRP3 inflammasome activation. This study also provides a novel strategy for the application of NGR1 as a therapeutic agent for patients with DEP.