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The carbohydrate response element‐binding protein (ChREBP), a glucose‐responsive transcription factor that plays a critical role in the glucose‐mediated induction of genes involved in hepatic glycolysis and lipogenesis, exists as two isoforms: ChREBPα and ChREBPβ. However, the mechanism responsible for regulating the expression of both ChREBPα and β, as well as the mechanism that determines which specific isoform is more responsive to different stimuli, remains unclear. To address this issue, we compared the effects of several stimuli, including oxidative stress, on the mRNA and protein expression levels of ChREBPα and β in the hepatocyte cell line, HepG2. We found that H2O2 stimulation suppressed the expression of both mRNA and protein in HepG2 cells, but the mRNA expression level of ChREBPβ was, The carbohydrate response element binding protein (ChREBP) is a glucose‐responsive transcription factor that strongly regulates glycolysis and lipogenesis. In this study, we showed that oxidative stress, including STS and TPA treatment, suppressed the expression of both ChREBPα and β through activation of ERK signaling in HepG2 cells.

Caffeine intake is associated with a reduced risk developing non-alcoholic fatty liver disease (NAFLD), but the underlying molecular mechanisms remain to be fully elucidated. We report here that caffeine markedly improved high fat diet-induced NAFLD in mice resulting in a 10-fold increase in circulating IL-6 levels, leading to STAT3 activation in the liver. Interestingly, the expression of IL-6 mRNA was not increased in the liver, but increased substantially in the muscles of caffeine-treated mice. Caffeine was found to stimulate IL-6 production in cultured myotubes but not in hepatocytes, adipocytes, or macrophages. The inhibition of p38/MAPK abrogated caffeine-induced IL-6 production in muscle cells. Caffeine failed to improve NAFLD in IL-6 and hepatocyte-specific STAT3 knockout mice, indicating that the IL-6/STAT3 pathway is vital for the hepatoprotective effects of caffeine in NAFLD. The possibility that IL-6/STAT3-mediated hepatic autophagosome induction and hepatocytic oxygen consumption are involved in the anti-NAFLD effects of caffeine cannot be excluded, based on the findings presented here. Our results reveal that caffeine ameliorates NAFLD via crosstalk between muscle IL-6 production and liver STAT3 activation.

The carbohydrate response element binding protein (ChREBP) is a glucose-responsive transcription factor that increases the transcription of multiple genes. ChREBP is highly localized in the liver, where it upregulates the expression of genes that code for glycolytic and lipogenic enzymes, resulting in the conversion of excess carbohydrate into storage fat. ChREBP knockout (KO) mice display an anti-obese phenotype. However, at this time, role of ChREBP in adipose tissue remains unclear. Therefore, the energy metabolism and morphology of mitochondrial brown adipose tissue (BAT) in ChREBP KO mice was examined. We found increased expression levels of electron transport system proteins including the mitochondrial uncoupling protein (UCP1), and mitochondrial structural alterations such as dysplasia of the cristae and the presence of small mitochondria in BAT of ChREBP KO mice. Mass spectrometry analyses revealed that fatty acid synthase was absent in the BAT of ChREBP KO mice, which probably led to a reduction in fatty acids and cardiolipin, a regulator of various mitochondrial events. Our study clarified the new role of ChREBP in adipose tissue and its involvement in mitochondrial function. A clearer understanding of ChREBP in mitochondria could pave the way for improvements in obesity management.

The carbohydrate-response element-binding protein (ChREBP) is a glucose-responsive transcription factor that plays an essential role in converting excess carbohydrate to fat storage in the liver. In response to glucose levels, ChREBP is regulated by nuclear/cytosol trafficking via interaction with 14-3-3 proteins, CRM-1 (exportin-1 or XPO-1), or importins. Nuclear localization of ChREBP was rapidly inhibited when incubated in branched-chain α-ketoacids, saturated and unsaturated fatty acids, or 5-aminoimidazole-4-carboxamide ribonucleotide. Here, we discovered that protein-free extracts of high fat-fed livers contained, in addition to ketone bodies, a new metabolite, identified as AMP, which specifically activates the interaction between ChREBP and 14-3-3. The crystal structure showed that AMP binds directly to the N terminus of ChREBP-α2 helix. Our results suggest that AMP inhibits the nuclear localization of ChREBP through an allosteric activation of ChREBP/14-3-3 interactions and not by activation of AMPK. AMP and ketone bodies together can therefore inhibit lipogenesis by restricting localization of ChREBP to the cytoplasm during periods of ketosis.

Copper/zinc superoxide dismutase (SOD1), a primary anti-oxidative enzyme, protects cells against oxidative stress. We report herein on a comparison of behavioral and neurobiological changes between SOD1 knockout (KO) and wild-type mice, in an attempt to assess the role of SOD1 in brain functions. SOD1 KO mice exhibited impaired motivational behavior in both shuttle-box learning and three-chamber social interaction tests. High levels of dopamine transporter protein and an acceleration of serotonin turnover were also detected in the cerebrums of the SOD1 KO mice. These findings suggest that SOD1 deficiency disturbs monoaminergic neurotransmission leading to a decrease in motivational behavior.

Nonalcoholic fatty liver disease (NAFLD) is one of the most prevalent chronic diseases, and results in the development of fibrosis. Oxidative stress is thought to be one of the underlying causes of NAFLD. Copper/zinc superoxide dismutase (SOD1) is a primary antioxidative enzyme that scavenges superoxide anion radicals. Although SOD1 knockout (KO) mice have been reported to develop fatty livers, it is not known whether this lack of SOD1 leads to the development of fibrosis. Since the accumulation of collagen typically precedes liver fibrosis, we assessed the balance between the synthesis and degradation of collagen in liver tissue from SOD1 KO mice. We found a higher accumulation of collagen in the livers of SOD1 KO mice compared to wild type mice. The level of expression of HSP47, a chaperone of collagen, and a tissue inhibitor (TIMP1) of matrix metalloproteinases (a collagen degradating enzyme) was also increased in SOD1 KO mice livers. These results indicate that collagen synthesis is increased but that its degradation is inhibited in SOD1 KO mice livers. Moreover, SOD1 KO mice liver sections were extensively modified by advanced glycation end products (AGEs), which suggest that collagen in SOD1 KO mice liver might be also modified with AGEs and then would be more resistant to the action of collagen degrading enzymes. These findings clearly show that oxidative stress plays an important role in the progression of liver fibrosis.

Copper/zinc-superoxide dismutase (SOD1) plays a protective role in cells by catalyzing the conversion of the superoxide anion into molecular oxygen and hydrogen peroxide. Although SOD1 knockout (KO) mice exhibit a reduced life span and an elevated incidence of dysfunctions in old age, young SOD1 KO mice grow normally and exhibit no abnormalities. This fact leads to the hypothesis that other antioxidative proteins prevent oxidative stress, compensating for SOD1. Differently expressed genes in 3-week-old SOD1 KO and littermate wild-type mice were explored. A gene remarkably elevated in SOD1 KO mouse kidneys was identified as the glutathione S-transferase Alpha 4 gene (Gsta4), which encodes the GSTA4 subunit. The GSTA4 protein level and activity were also significantly increased in SOD1 KO mouse kidneys. The administration of an iron complex, a free radical generator, induced GSTA4 expression in wild-type mouse kidneys. Iron deposition detected in SOD1 KO mouse kidney is thought to be an inducer of GSTA4. In addition, overexpression of mouse GSTA4 cDNA in human embryonic kidney cells decreased cell death caused by both 4-hydroxynonenal and hydrogen peroxide. These findings suggest that compensatory induced GSTA4 plays a protective role against oxidative stress in young SOD1 KO mouse kidneys.

Carbohydrate response element-binding protein (ChREBP) is a glucose-responsive transcription factor that plays a critical role in the glucose-mediated induction of gene products involved in hepatic glycolysis and lipogenesis. Glucose affects the activity of ChREBP largely through post-translational mechanisms involving phosphorylation-dependent cellular localization. In this work we show that the N-terminal region of ChREBP (residues 1-251) regulates its subcellular localization via an interaction with 14-3-3. 14-3-3 binds an α-helix in this region (residues 125-135) to retain ChREBP in the cytosol, and binding of 14-3-3 is facilitated by phosphorylation of nearby Ser-140 and Ser-196. Phosphorylation of ChREBP at these sites was essential for its interaction with CRM1 for export to the cytosol, whereas nuclear import of ChREBP requires dephosphorylated ChREBP to interact with importin α. Notably, 14-3-3 appears to compete with importin α for ChREBP binding. 14-3-3β bound to a synthetic peptide spanning residues 125-144 and bearing a phosphate at Ser-140 with a dissociation constant of 1.1 μm, as determined by isothermal calorimetry. The interaction caused a shift in the fluorescence maximum of the tryptophan residues of the peptide. The corresponding unphosphorylated peptide failed to bind 14-3-3β. These results suggest that interactions with importin α and 14-3-3 regulate movement of ChREBP into and out of the nucleus, respectively, and that these interactions are regulated by the ChREBP phosphorylation status.

alpha1,6-Fucosyltransferase (Fut8) catalyzes the transfer of a fucose residue from GDP-fucose to the innermost N-acetylglucosamine residue of N-glycans. Here we report that the loss of core fucosylation impairs the function of low-density lipoprotein (LDL) receptor-related protein-1 (LRP-1), a multifunctional scavenger and signaling receptor, resulting in a reduction in the endocytosis of insulin like growth factor (IGF)-binding protein-3 (IGFBP-3) in the cells derived from Fut8-null (Fut8-/-) mice. The reduced endocytosis was restored by the re-introduction of Fut8. Serum levels of IGFBP-3 were markedly upregulated in Fut8-/- mice. These data clearly indicate that core fucosylation is crucial for the scavenging activity of LRP-1 in vivo.

beta1-6 GlcNAc branching, a product of N-acetylglucosaminyltransferase V (GnT-V), is a key structure that is associated with malignant transformations and cancer metastasis. Although a number of reports concerning tumor metastasis-related glycoproteins that contain beta1-6 GlcNAc branching have appeared, the precise function of beta1-6 GlcNAc branching on glycoproteins remains to be elucidated. We previously reported on the importance of beta1-6 GlcNAc branching on matriptase in terms of proteolytic degradation in tumor metastasis. We report here that matriptase purified from GnT-V transfectant (beta1-6 GlcNAc matriptase) binds strongly to L4-PHA, which preferentially recognizes beta1-6 GlcNAc branches of tri- or tetraantennary sugar chains, indicating that the isolated matriptase contains beta1-6 GlcNAc branching. The beta1-6 GlcNAc matriptase was resistant to autodegradation, as well as trypsin digestion, compared with matriptase purified from mock-transfected cells. Furthermore, N-glycosidase-F treatment of beta1-6 GlcNAc matriptase greatly reduced its resistance to degradation. An analysis of matriptase mutants that do not contain potential N-glycosylation sites clearly shows that the beta1-6 GlcNAc branching on N-glycans attached to Asn 772 in the serine protease domain plays a major role in trypsin resistance. This is the first example of a demonstration of a direct relationship between beta1-6 GlcNAc branching and a biological function at the protein level.

Copper/zinc-superoxide dismutase knockout (SOD1 KO) mice have been extensively used as an experimental animal model of pathology associated with oxidative stress. The mice spontaneously develop mild chronic hemolytic anaemia (HA). We previously reported that the kidneys of these types of mice contain massive amounts of iron. In this study, to clarify the role of the kidney for iron metabolism under HA, changes in the levels of expression and functions of iron-related proteins were examined. In SOD1 KO mice kidneys, protein levels of iron transporters, the iron-responsive element (IRE)-binding activity of IRP1 and the levels of phosphorylation of IRP1 are all increased. These findings indicate that oxidative stress caused by a SOD1 deficiency probably enhances the phosphorylation of and the conversion of IRP1 to the IRE-binding form, which may accelerate the reabsorption of iron by renal tubular cells. Kidney could play an important role in iron homeostasis under conditions of HA.

Activated microglia produces inflammatory cytokines and nitric oxide (NO) that involved in neuronal injury and neurodegenerative diseases. We report herein, that H(2)O(2) intensifies the LPS-triggered expression of iNOS in the microglia cell line, BV-2, resulting in an enhancement in the production of NO. The NO production induced by a combination of LPS and H(2)O(2) was blocked by the addition of an anti-interferonβ (IFNβ) neutral antibody, suggesting that IFNβ levels are correlated with the LPS/H(2)O(2)-induced production of NO. However, although the expression of IFNβ was induced by H(2)O(2) treatment alone, neither the expression of iNOS mRNA nor the production of NO were induced. In addition, the expression of IFN receptor (IFNR) was induced by LPS but not by H(2)O(2). These data indicate that although H(2)O(2) alone cannot induce iNOS expression because of the insufficient expression of IFNR, in the presence of LPS, H(2)O(2) enhances iNOS expression via the expression of IFNβ. Our findings suggest that H(2)O(2) produced by activated microglia further enhances NO production in various inflammatory states.

The carbohydrate response element-binding protein (ChREBP) functions as a transcription factor in mediating the glucose-activated gene expression of multiple liver enzymes, which are responsible for converting excess carbohydrate to storage fat. ChREBP is translocated into the nucleus in response to high glucose levels, and then up-regulates transcriptional activity. Although this glucose activation of ChREBP is generally observed only in liver cells, overexpression of wild type max-like protein X (Mlx), but not an inactive mutant Mlx, resulted in the exhibition of the ChREBP functions also in a human kidney cell line. Because high glucose conditions induce the glycosylation of cellular proteins, the effect of O-linked GlcNAc modification on ChREBP functions was examined. Treatment with an O-GlcNAcase inhibitor (PUGNAc), which increases the O-linked GlcNAc modification of cellular proteins, caused an increase in the glucose response of ChREBP. In contrast, treatment with a glutamine fructose amidotransferase inhibitor (DON), which decreases O-GlcNAcylation by inhibiting the hexosamine biosynthetic pathway, completely blocked the glucose response of ChREBP. These results suggest that the O-linked glycosylation of ChREBP itself or other proteins that regulate ChREBP is essential for the production of functional ChREBP.

3-Deoxyglucosone (3-DG), a dicarbonyl compound produced by glycation, plays a role in the modification and cross-linking of long-lived proteins. We synthesized [ 3 H]3-DG from [ 3 H]glucose and developed an intemalization assay system using HPLC to examine its cellular metabolism. When smooth muscle cells or human umbilical vein endothelial cells were incubated with [ 3 H]3-DG, it was found that [ 3 H]3-DG was internalized by cells in a time dependent manner. The rate of internalization was reduced when the cells were incubated at 4°C or treated with phenylarsine oxide (PAO). By monitoring [ 3 H]3-DG taken up by cells, it was confirmed that 3-DG is reduced to 3-deoxyfructose (3-DF) and that this reaction was inhibited by an aldo-keto reductase inhibitor (ARI). The presence of 3-DG led to an increase in reactive oxygen species levels in the cells and subsequent apoptosis, and the effect was enhanced by pretreatment with ARI. These results suggest that 3-DG is internalized by cells and reduced to 3-DF by aldo-keto reductases, and that the internalized 3-DG is responsible for the production of intracellular oxidative stress.

A large body of evidence suggests that carbonyl compounds induce intracellular signaling by increasing oxidative stress in the cell; however, the mechanisms involved have not been fully described. The focus of our research is on the pathway in which antioxidative enzymes are modified and inactivated by carbonyl compounds, resulting in the accumulation of active oxygen species in the cell. A common pathway appears to exist for cellular signaling evoked by nitroxidative stress. It could be concluded that some glycoxidative stress and nitroxidative stress cause intracellular signaling via similar mechanisms. The elucidation of the pathway for extracellular stress-induced reactive oxygen species (ROS) production would be important for our understanding of the role of ROS as signaling molecules.

Acrolein is a highly electrophilic alpha,beta-unsaturated aldehydes to which humans are exposed in a variety of environment situations and is also a product of lipid peroxidation. Increased levels of unsaturated aldehydes play an important role in the pathogenesis of a number of human diseases such as Alzheimer's disease, atherosclerosis and diabetes. A number of studies have reported that acrolein evokes downstream signaling via an elevation in cellular oxidative stress. Here, we report that low concentrations of acrolein induce Hsp72 in human umbilical vein endothelial cells (HUVEC) and that both the PKCdelta/JNK pathway and calcium pathway were involved in the induction. The findings confirm that the production of reactive oxygen species (ROS) is not directly involved in the pathway. The induction of Hsp72 was not observed in other cells such as smooth muscle cells (SMC) or COS-1 cells. The results suggest that HUVEC have a unique defense system against cell damage by acrolein in which Hsp72 is induced via activation of both the PKCd/JNK and the calcium pathway.

Reactive oxygen species (ROS) are generated as by-products of cellular metabolism, primarily in the mitochondria. When the cellular production of ROS exceeds the cell's antioxidant capacity, cellular macromolecules such as lipids, proteins and DNA can be damaged. Because of this, 'oxidative stress' is thought to contribute to aging and pathogenesis of a variety of human diseases. However, in the last 10-15 years, a considerable body of evidence has accumulated that ROS serve as subcellular messengers, and play a role in gene regulation and signal transduction pathways, which may be involved in defensive mechanisms against oxidative stress. This review focuses on oxidative stress caused by the inactivation of glutathione peroxidase (GPx), a major peroxide scavenging enzyme. GPx is inactivated by a variety of physiological substances, including nitric oxide and carbonyl compounds in vitro and in cell culture. Decreased GPx activity has also been reported in tissues where oxidative stress occurs in several pathological animal models. The accumulation of increased levels of peroxide resulting from inactivation of GPx may act as a second messenger and regulate expression of anti-apoptotic genes and the GPx itself to protect against cell damage. These findings suggest that GPx undergoes inactivation under various conditions such as nitroxidative stress and glycoxidative stress, and that these changes are a common feature of various types of oxidative stress which may be associated with the modification of redox regulation and cellular function.

Amyotrophic lateral sclerosis (ALS) involves the progressive degeneration of motor neurons in the spinal cord and motor cortex. It has been shown that 15-20% of patients with familial ALS (FALS) have defects in the Sod1 gene that encodes Cu, Zn-superoxide dismutase (SOD). To elucidate the pathological role of mutated Cu, Zn-SODs in FALS, the susceptibility of mutants to glycation was examined. Mutated Cu, Zn-SODs (G37R, G93A, and I113T) related to FALS and wild type were produced in a baculovirus/insect cell expression system. Glycated and nonglycated proteins were separated on a boronate column, and the nonglycated fraction was then incubated with glucose. The mutated Cu, Zn-SODs were found to be highly susceptible to glycation compared with the wild-type enzyme as estimated by Western blot analysis using an anti-hexitol lysine antibody. The mutated Cu, Zn-SOD incubated with glucose generated higher levels of hydrogen peroxide than the wild-type enzyme. Mutated Cu, Zn-SODs were also shown to be highly susceptible to fructation, and the fructated mutant also produced higher levels of hydrogen peroxide than the wild type. These results suggest that high susceptibility of mutated Cu, Zn-SODs to glycation could be the origin of the oxidative stress associated with neuronal dysfunction in FALS.