Low level of hydrogen peroxide induces lipid synthesis in BRL-3A cells through a CAP-independent SREBP-1a activation

Assessing the therapeutic potential of KK14 peptide derived from Cyprinus Carpio in reducing intercellular ROS levels in oxidative Stress-Induced In vivo zebrafish larvae model: An integrated bioinformatics, antioxidant, and neuroprotective analysis

H2O2 is a significant reactive oxygen species (ROS) that hinders redox-mediated processes and contributes to oxidative stress and neurodegenerative disorders. Oxidative stress causes impairment of cell macromolecules, which results in cell dysfunction and neurodegeneration. Alzheimer's disease and other neurodegenerative diseases are serious conditions linked to oxidative stress. Antioxidant treatment approaches are a novel and successful strategy for decreasing neurodegeneration and reducing oxidative stress. This study explored the antioxidant and neuroprotective characteristics of KK14 peptide synthesized from LEAP 2B (liver-expressed antimicrobial peptide-2B) derived from Cyprinus carpio L. Molecular docking studies were used to assess the antioxidant properties of KK14. The peptide at concentrations 5-45 μM was examined by using in vitro and in vivo assessment. Analysis was done on the developmental and neuroprotective potential of KK14 peptide treatment in H2O2-exposed zebrafish larvae which showed Nonlethal deformities. KK14 improves antioxidant enzyme activity like catalase and superoxide dismutase. Furthermore, it reduces neuronal damage by lowering lipid peroxidation and nitric oxide generation while increasing acetylcholinesterase activity. It improved the changes in swimming behavior and the cognitive damage produced by exposure to H2O2. To further substantiate the neuroprotective potential of KK14, intracellular ROS levels in zebrafish larvae were assessed. This led to a reduction in ROS levels and diminished lipid peroxidation. The KK14 has upregulated the antioxidant genes against oxidative stress. Overall, this study proved the strong antioxidant activity of KK14, suggesting its potential as a strong therapeutic option for neurological disorders caused by oxidative stress.

A paREDOX in the control of cholesterol biosynthesis: Does the NADPH sensor and E3 ubiquitin ligase MARCHF6 protect mammalian cells during oxidative stress by controlling sterol biosynthesis?

Sterols and the reductant nicotinamide adenine dinucleotide phosphate (NADPH), essential for eukaryotic life, arose because of, and as an adaptation to, rising levels of molecular oxygen (O2). Hence, the NADPH and O2-intensive process of sterol biosynthesis is inextricably linked to redox status. In mammals, cholesterol biosynthesis is exquisitely regulated post-translationally by multiple E3 ubiquitin ligases, with membrane associated Really Interesting New Gene (RING) C3HC4 finger 6 (MARCHF6) degrading at least six enzymes in the pathway. Intriguingly, all these MARCHF6-dependent enzymes require NADPH. Moreover, MARCHF6 is activated by NADPH, although what this means for control of cholesterol synthesis is unclear. Indeed, this presents a paradox for how NADPH regulates this vital pathway, since NADPH is a cofactor in cholesterol biosynthesis and yet, low levels of NADPH should spare cholesterol biosynthesis enzymes targeted by MARCHF6 by reducing its activity. We speculate MARCHF6 helps mammalian cells adapt to oxidative stress (signified by low NADPH levels) by reducing degradation of cholesterogenic enzymes, thereby maintaining synthesis of protective cholesterol.

Novel role of xanthine oxidase-dependent H2O2 production in 12/15-lipoxygenase-mediated de novo lipogenesis, triglyceride biosynthesis and weight gain

12/15-lipoxygenase (12/15-LOX) plays an essential role in oxidative conversion of polyunsaturated fatty acids into various bioactive lipid molecules. Although 12/15-LOX's role in the pathophysiology of various human diseases has been well studied, its role in weight gain is controversial and poorly clarified. Here, we demonstrated the role of 12/15-LOX in high-fat diet (HFD)-induced weight gain in a mouse model. We found that 12/15-LOX mediates HFD-induced de novo lipogenesis (DNL), triglyceride (TG) biosynthesis and the transport of TGs from the liver to adipose tissue leading to white adipose tissue (WAT) expansion and weight gain via xanthine oxidase (XO)-dependent production of H₂O₂. 12/15-LOX deficiency leads to cullin2-mediated ubiquitination and degradation of XO, thereby suppressing H₂O₂ production, DNL and TG biosynthesis resulting in reduced WAT expansion and weight gain. These findings infer that manipulation of 12/15-LOX metabolism may manifest a potential therapeutic target for weight gain and obesity.

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12/15-LOX-12(S)-HETE axis via activation of CREB-Egr1 enhances TG biosynthesis.

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12/15-LOX-12(S)-HETE axis via activation of SREBP1c triggers DNL.

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H₂O₂ mediates 12/15-LOX-12(S)-HETE axis-induced DNL and TG biosynthesis.

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12/15-LOX via TG biosynthesis leads to WAT expansion and body weight gain.

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Downstream to 12/15-LOX, H₂O₂-mediates WAT expansion and body weight gain.

Further evidence for the involvement of mitochondrial aquaporin-8 in hepatocyte lipid synthesis

We recently provided evidence suggesting that mitochondrial aquaporin-8 (mtAQP8), a channel protein able to conduct H₂O₂, is involved in the modulation of hepatocyte cholesterogenesis. To expand that study, we cultured human hepatocyte-derived Huh-7 cells in medium with lipoprotein-deficient serum (LPDS) to induce the de novo synthesis of cholesterol and fatty acids. We found that LPDS induced mtAQP8 expression and that AQP8 gene silencing significantly down-regulated the LPDS-induced synthesis of cholesterol and fatty acids as well as the expression of the corresponding key biosynthetic enzymes, 3-hydroxy-3-methylglutaryl-CoA reductase and fatty acid synthase. Our data further support a regulatory role of mtAQP8 in hepatocyte lipid homeostasis.

Investigation of the Lipid-Lowering Mechanisms and Active Ingredients of Danhe Granule on Hyperlipidemia Based on Systems Pharmacology

Objective

Investigate the active ingredients and underlying hypolipidemic mechanisms of Danhe granule (DHG).

Methods

The lipid-lowering effect of DHG was evaluated in hyperlipidemic hamsters induced by a high-fat diet. The ingredients absorbed into the blood after oral administration of DHG in hamsters were identified by ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS). A systems pharmacology approach incorporating target prediction and network construction, gene ontology (GO) enrichment and pathway analysis was performed to predict the active compounds and map the compounds-targets-disease network. Real-time polymerase chain reaction (RT-PCR) and Western blot were utilized to analyze the mRNA and protein expression levels of predicted targets.

Results

DHG remarkably lowered the levels of serum total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-c), and arteriosclerosis index (AI), at the same time, elevated the levels of serum high-density lipoprotein cholesterol (HDL-c) and HDL-c/TC ratio in hyperlipidemic hamsters. Sixteen ingredients absorbed into blood after oral administration of DHG were identified as the possible components interacted with targets. Moreover, 65 potential targets were predicted after targets intersection and compounds–targets–disease network mapping. Then, compounds–targets–pathways network mapping revealed that six active compounds (emodin, naringenin, etc.) compounds could interact with 10 targets such as sterol regulatory element binding protein (SREBP) 1c, SREBP-2 and peroxisome proliferation-activated receptor (PPAR) α, regulate three lipid metabolism-related pathways including SREBP control of lipid synthesis pathway, PPAR signaling pathway and nuclear receptors in lipid metabolism and toxicity pathway, and further affect lipid metabolic processes including fatty acid biosynthesis, low-density lipoprotein receptor (LDLR)-mediated cholesterol uptake, bile acid biosynthesis, and cholesterol efflux. Experimental results indicated that DHG significantly increased SREBP-2, LDLR, PPARα, liver X receptor alpha (LXRα), cholesterol 7α-hydroxylase (CYP7A1), and ATP binding cassette subfamily A member 1 (ABCA1) mRNA and protein expressions while decreased SREBP-1c and fatty acid synthase (FAS) mRNA, and protein expressions.

Conclusion

DHG possessed a good hypolipidemic effect that may be through affecting the mRNA and protein expressions of SREBP-1c, FAS, SREBP-2, LDLR, PPARα, LXRα, CYP7A1, and ABCA1, involving in fatty acid synthesis, LDLR-mediated cholesterol uptake, bile acid biosynthesis, and cholesterol efflux. This study further provided experimental evidence about its practical application for treating hyperlipidemia and its complications.

Mitochondrial aquaporin-8 is involved in SREBP-controlled hepatocyte cholesterol biosynthesis

Cholesterol, via sterol regulatory element-binding protein (SREBP) transcription factors, activates or represses genes involved in its hepatic biosynthetic pathway, and also modulates the expression of hepatocyte mitochondrial aquaporin-8 (mtAQP8), a channel that can function as peroxiporin by facilitating the transmembrane diffusion of H₂O₂. Here we tested the hypothesis that mtAQP8 is involved in the SREBP-mediated regulation of hepatocyte cholesterol biosynthesis. Using human hepatocyte-derived Huh-7 cells and primary rat hepatocytes, we found that mtAQP8 knockdown significantly downregulated de novo cholesterol synthesis as well as protein expressions of SREBP-2 and its target gene, a rate-limiting enzyme in cholesterol synthesis 3-Hydroxy-3-Methylglutaryl-CoA Reductase (HMGCR). In contrast, adenovirus-mediated human AQP8 mitochondrial expression significantly increased de novo cholesterol synthesis and protein expressions of SREBP-2 and HMGCR. In mtAQP8-overexpressed hepatocytes, mitochondrial H₂O₂ release was found to be increased; and a mitochondria-targeted antioxidant prevented the upregulation of mitochondrial H₂O₂ release and that of cholesterol synthesis. Our results suggest that peroxiporin mtAQP8 plays a role in the SREBP-controlled hepatocyte cholesterogenesis, a finding that might be relevant to cholesterol-related metabolic disorders.

Aquaporin Membrane Channels in Oxidative Stress, Cell Signaling, and Aging: Recent Advances and Research Trends

Reactive oxygen species (ROS) are produced as a result of aerobic metabolism and as by-products through numerous physiological and biochemical processes. While ROS-dependent modifications are fundamental in transducing intracellular signals controlling pleiotropic functions, imbalanced ROS can cause oxidative damage, eventually leading to many chronic diseases. Moreover, increased ROS and reduced nitric oxide (NO) bioavailability are main key factors in dysfunctions underlying aging, frailty, hypertension, and atherosclerosis. Extensive investigation aims to elucidate the beneficial effects of ROS and NO, providing novel insights into the current medical treatment of oxidative stress-related diseases of high epidemiological impact. This review focuses on emerging topics encompassing the functional involvement of aquaporin channel proteins (AQPs) and membrane transport systems, also allowing permeation of NO and hydrogen peroxide, a major ROS, in oxidative stress physiology and pathophysiology. The most recent advances regarding the modulation exerted by food phytocompounds with antioxidant action on AQPs are also reviewed.

Oleic Acid and Hydroxytyrosol Inhibit Cholesterol and Fatty Acid Synthesis in C6 Glioma Cells

Recently, the discovery of natural compounds capable of modulating nervous system function has revealed new perspectives for a healthier brain. Here, we investigated the effects of oleic acid (OA) and hydroxytyrosol (HTyr), two important extra virgin olive oil compounds, on lipid synthesis in C6 glioma cells. OA and HTyr inhibited both de novo fatty acid and cholesterol syntheses without affecting cell viability. The inhibitory effect of the individual compounds was more pronounced if OA and HTyr were administered in combination. A reduction of polar lipid biosynthesis was also detected, while triglyceride synthesis was marginally affected. To clarify the lipid-lowering mechanism of these compounds, their effects on the activity of key enzymes of fatty acid biosynthesis (acetyl-CoA carboxylase-ACC and fatty acid synthase-FAS) and cholesterologenesis (3-hydroxy-3-methylglutaryl-CoA reductase-HMGCR) were investigated in situ by using digitonin-permeabilized C6 cells. ACC and HMGCR activities were especially reduced after 4 h of 25 μM OA and HTyr treatment. No change in FAS activity was observed. Inhibition of ACC and HMGCR activities is corroborated by the decrease of their mRNA abundance and protein level. Our results indicate a direct and rapid downregulatory effect of the two olive oil compounds on lipid synthesis in C6 cells.

The risk of occupational exposure to mercury vapor in some public dental clinics of Baghdad city, Iraq

BACKGROUND

Dental workers are exposed to elevated levels of elemental mercury vapor substantially above the occupational exposure standards when placing or removing mercury/silver tooth restorations and disposing of mercury waste. This results in a significant increase in occupational exposure and risk of mercury intoxication.

METHODS

To evaluate the occupational exposure of dental workers to amalgam in four dental clinics in Baghdad city, the concentrations of mercury vapor were measured seasonally from February to November 2016. Samples of blood and urine were collected from 30 dental workers (exposed individuals) and five non-occupationally exposed individuals. Biochemical parameters such as cholesterol, liver enzymes (alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase), renal enzymes (urea and creatinine), total protein and reduced glutathione (GSH) were observed.

RESULTS

The results indicated that mercury vapor levels varied from 84.7 ± 18.67 to 609.3 ± 238.90 µg/m³ and most concentrations were above the occupational exposure standards. The results of the biochemical parameters showed a significant increase in levels of cholesterol, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and no significant increase in blood urea and creatinine in dental workers in comparison with unexposed persons (control). Although the results showed a significant reduction in the levels of glutathione and total protein, there was no significant decrease in the levels of alkaline phosphatase (ALP) in exposed dental workers when compared with non-occupationally exposed individuals.

CONCLUSIONS

It is concluded that mercury vapor concentrations in the indoor air of some dental clinics in Baghdad city are high and exceed the OSHA STEL(Occupational Safety and Health Administration Short Term Exposure Limit). The present data showed that altered biochemical parameters can be used as efficient bioindicators for mercury toxicity.

β-Catenin Knockdown Affects Mitochondrial Biogenesis and Lipid Metabolism in Breast Cancer Cells

β-catenin plays an important role as regulatory hub in several cellular processes including cell adhesion, metabolism, and epithelial mesenchymal transition. This is mainly achieved by its dual role as structural component of cadherin-based adherens junctions, and as a key nuclear effector of the Wnt pathway. For this dual role, different classes of proteins are differentially regulated via β-catenin dependent mechanisms. Here, we applied a liquid chromatography-mass spectrometry (LC-MS/MS) approach to identify proteins modulated after β-catenin knockdown in the breast cancer cell line MCF-7. We used a label free analysis to compare trypsin-digested proteins from CTR (shCTR) and β-catenin knockout cells (shβcat). This led to the identification of 98 differentially expressed proteins, 53 of them were up-regulated and 45 down-regulated. Loss of β-catenin induced morphological changes and a significant modulation of the expression levels of proteins associated with primary metabolic processes. In detail, proteins involved in carbohydrate metabolism and tricarboxylic acid cycle were found to be down-regulated, whereas proteins associated to lipid metabolism were found up-regulated in shβcat compared to shCTR. A loss of mitochondrial mass and membrane potential was also assessed by fluorescent probes in shβcat cells with respect to the controls. These data are consistent with the reduced expression of transcriptional factors regulating mitochondrial biogenesis detected in shβcat cells. β-catenin driven metabolic reprogramming resulted also in a significant modulation of lipogenic enzyme expression and activity. Compared to controls, β-catenin knockout cells showed increased incorporation of [1-¹⁴C]acetate and decreased utilization of [U-¹⁴C]glucose for fatty acid synthesis. Our data highlight a role of β-catenin in the regulation of metabolism and energy homeostasis in breast cancer cells.

Hydrogen peroxide induces La cytoplasmic shuttling and increases hepatitis C virus internal ribosome entry site-dependent translation

We have previously shown that physio/pathological levels of hydrogen peroxide (H₂O₂) stimulate translation from the hepatitis C virus (HCV) internal ribosome entry site (IRES) element in tissue-cultured cells. Here, using in vitro translation, we further show that H₂O₂ upregulates HCV IRES-dependent mRNA translation and correlates with an increase in intracellular oxidant level. Using Western blotting, immunocytochemistry, microscopy and affinity pulldown, we show that H₂O₂ stimulates HCV IRES-dependent translation and correlates with nuclear–cytoplasmic shuttling of the La autoantigen, resulting in enhanced binding of cytoplasmic La to HCV IRES RNA. The role of the La protein in H₂O₂-stimulated IRES-dependent translation is further confirmed by the ability of an anti-La antibody to suppress H₂O₂-activated IRES-dependent translation in vitro. This is further supported by the ability of an ectopically expressed dominant, negative La mutant protein to suppress H₂O₂-inducible IRES-mediated translation in Huh7 cells, transiently transfected with a bicistronic reporter and in a sub-genomic replicon cell line resembling a persistent infection. On the other hand, translation from the encephalomyocarditis virus IRES is diminished in the presence of H₂O₂, suggesting that H₂O₂ translational responsiveness is a specific property of the HCV IRES and is not a general phenomenon for all viral IRESs. Altogether, these results suggest that HCV adapts to physio/pathological oxidative stress in the host cell by mediating La cytoplasmic shuttling to enhance its IRES-dependent translation.

Lipid accumulation stimulates the cap-independent translation of SREBP-1a mRNA by promoting hnRNP A1 binding to its 5'-UTR in a cellular model of hepatic steatosis

Non-alcoholic fatty liver disease (NAFLD) is a chronic disease characterized by accumulation of lipid droplets in hepatocytes. Enhanced release of non-esterified fatty acids from adipose tissue accounts for a remarkable fraction of accumulated lipids. However, the de novo lipogenesis (DNL) is also implicated in the etiology of the NAFLD. Sterol Regulatory Element-Binding Protein-1 (SREBP-1) is a transcription factor modulating the expression of several lipogenic enzymes. In the present study, in order to investigate the effect of lipid droplet accumulation on DNL, we used a cellular model of steatosis represented by HepG2 cells cultured in a medium supplemented with free oleic and palmitic fatty acids (FFAs). We report that FFA supplementation induces the expression of genes coding for enzymes involved in the DNL as well as for the transcription factor SREBP-1a. The SREBP-1a mRNA translation, dependent on an internal ribosome entry site (IRES), and the SREBP-1a proteolytic cleavage are activated by FFAs. Furthermore, FFA treatment enhances the expression and the nucleus-cytosolic shuttling of hnRNP A1, a trans-activating factor of SREBP-1a IRES. The binding of hnRNP A1 to the SREBP-1a IRES is also increased upon FFA supplementation. The relocation of hnRNP A1 and the consequent increase of SREBP-1a translation are dependent on the p38 MAPK signal pathway, which is activated by FFAs. By RNA interference approach, we demonstrate that hnRNP A1 is implicated in the FFA-induced expression of SREBP-1a and of its target genes as well as in the lipid accumulation in cells.

Stress-mediated translational control in cancer cells

Tumor cells are continually subjected to diverse stress conditions of the tumor microenvironment, including hypoxia, nutrient deprivation, and oxidative or genotoxic stress. Tumor cells must evolve adaptive mechanisms to survive these conditions to ultimately drive tumor progression. Tight control of mRNA translation is critical for this response and the adaptation of tumor cells to such stress forms. This proceeds though a translational reprogramming process which restrains overall translation activity to preserve energy and nutrients, but which also stimulates the selective synthesis of major stress adaptor proteins. Here we present the different regulatory signaling pathways which coordinate mRNA translation in the response to different stress forms, including those regulating eIF2α, mTORC1 and eEF2K, and we explain how tumor cells hijack these pathways for survival under stress. Finally, mechanisms for selective mRNA translation under stress, including the utilization of upstream open reading frames (uORFs) and internal ribosome entry sites (IRESes) are discussed in the context of cell stress. This article is part of a Special Issue entitled: Translation and Cancer.