Publications by authors named "Einav Yehuda-Shnaidman"

21 Publications

  • Page 1 of 1

Breast cancer colonization by Fusobacterium nucleatum accelerates tumor growth and metastatic progression.

Nat Commun 2020 06 26;11(1):3259. Epub 2020 Jun 26.

The Institute of Dental Sciences, The Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Israel.

Fusobacterium nucleatum is an oral anaerobe recently found to be prevalent in human colorectal cancer (CRC) where it is associated with poor treatment outcome. In mice, hematogenous F. nucleatum can colonize CRC tissue using its lectin Fap2, which attaches to tumor-displayed Gal-GalNAc. Here, we show that Gal-GalNAc levels increase as human breast cancer progresses, and that occurrence of F. nucleatum gDNA in breast cancer samples correlates with high Gal-GalNAc levels. We demonstrate Fap2-dependent binding of the bacterium to breast cancer samples, which is inhibited by GalNAc. Intravascularly inoculated Fap2-expressing F. nucleatum ATCC 23726 specifically colonize mice mammary tumors, whereas Fap2-deficient bacteria are impaired in tumor colonization. Inoculation with F. nucleatum suppresses accumulation of tumor infiltrating T cells and promotes tumor growth and metastatic progression, the latter two of which can be counteracted by antibiotic treatment. Thus, targeting F. nucleatum or Fap2 might be beneficial during treatment of breast cancer.
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http://dx.doi.org/10.1038/s41467-020-16967-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7320135PMC
June 2020

The human tumor microbiome is composed of tumor type-specific intracellular bacteria.

Science 2020 05;368(6494):973-980

Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel.

Bacteria were first detected in human tumors more than 100 years ago, but the characterization of the tumor microbiome has remained challenging because of its low biomass. We undertook a comprehensive analysis of the tumor microbiome, studying 1526 tumors and their adjacent normal tissues across seven cancer types, including breast, lung, ovary, pancreas, melanoma, bone, and brain tumors. We found that each tumor type has a distinct microbiome composition and that breast cancer has a particularly rich and diverse microbiome. The intratumor bacteria are mostly intracellular and are present in both cancer and immune cells. We also noted correlations between intratumor bacteria or their predicted functions with tumor types and subtypes, patients' smoking status, and the response to immunotherapy.
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http://dx.doi.org/10.1126/science.aay9189DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7757858PMC
May 2020

Adipocytes Isolated from Visceral and Subcutaneous Depots of Donors Differing in BMI Crosstalk with Colon Cancer Cells and Modulate their Invasive Phenotype.

Transl Oncol 2019 Nov 7;12(11):1404-1415. Epub 2019 Aug 7.

The Robert H. Smith Faculty of Agriculture, Food and Environment, Institute of Biochemistry, Food Science and Nutrition, The Hebrew University of Jerusalem, Rehovot 76100, Israel. Electronic address:

Purpose: Mechanisms related the crosstalk between adipocytes and colon cancer cells are still not clear. We hypothesize that molecules and adipocytokines generated from the adipose tissue of obese individuals accentuate the effect on the metabolic reprogramming in colon cancer cells, i.e. induce disarray in energy metabolism networks of the targeted affected colonic epithelial cells, prompting their malignant phenotype.

Methods: To explore the mechanistic behind this crosstalk we conducted a co-culture model system using human colon cancer cells having different malignant abilities and adipocytes from different depots and subjects.

Results: The results demonstrate that co-culturing aggressive colon cancer cells such as HM-7 cells, with Visceral or Subcutaneous adipocytes (VA or SA respectively) from lean/obese subjects significantly up-regulate the secretion of the adipokines IL-8, MCP1, and IL-6 from the adipocytes. Surprisingly, the response of co-culturing HM-7 cells with obese SA was substantially more significant. In addition, these effects were significantly more pronounced when using HM-7 cells as compared to the less malignant HCT116 colon cancer cells. Moreover, the results showed that HM-7 cells, co-cultured with VA or SA from obese subjects, expressed higher levels of fatty acid binding protein 4; thus, the conditioned media obtained from the wells contained HM-7 cells and adipocytes from obese subjects was significantly more efficient in promoting invasion of HM-7 cells.

Conclusions: We conclude that interaction between adipocytes and colon cancer cells, especially the highly malignant cells, results in metabolic alterations in colon cancer cells and in highly hypertrophy phenotype which characterized by increasing adipokines secretion from the adipocytes.
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http://dx.doi.org/10.1016/j.tranon.2019.07.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6700440PMC
November 2019

Ostreolysin induces browning of adipocytes and ameliorates hepatic steatosis.

J Gastroenterol Hepatol 2018 Dec 15;33(12):1990-2000. Epub 2018 May 15.

Institute of Biochemistry, Food Science and Nutrition, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.

Background And Aim: Non-alcoholic fatty liver disease (NAFLD) is associated with all features of the metabolic syndrome. Deposition of excess triglycerides in liver cells, a hallmark of NAFLD, is associated with loss of insulin sensitivity. Ostreolysin (Oly) is a 15-kDa fungal protein known to interact with cholesterol-enriched raft-like membrane domains. We aim to test whether a recombinant version of Oly (rOly) can induce functional changes in vitro in adipocytes or in vivo in mice fed a high-fat diet (HFD).

Methods: White preadipocyte 3T3-L1 cells or mouse primary adipocytes treated with rOly. Male C57BL/6 mice were fed a control or HFD and treated with saline or with rOly (1 mg/kg BW) every other day for 4 weeks.

Results: White preadipocyte 3T3-L1 cells or mouse primary adipocytes treated with rOly acquire a browning phenotype through activation of 5' adenosine monophosphate-activated protein kinase and downregulation of tumor necrosis factor α-mediated activation of IκB kinase ε and TANK-binding kinase 1. HFD-fed mice treated with rOly showed a 10% reduction in BW and improved glucose tolerance, which paralleled improved expression of liver and adipose functionality, metabolism, and inflammation status, mimicking the in vitro findings.

Conclusion: This study provides first evidence of rOly's prevention of HFD-induced NAFLD by stimulating liver and adipose muscle tissue functionality and oxidative potential, improving glucose tolerance, and ameliorating the metabolic profile of diet-induced obese mice.
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http://dx.doi.org/10.1111/jgh.14259DOI Listing
December 2018

Recombinant ostreolysin induces brown fat-like phenotype in HIB-1B cells.

Mol Nutr Food Res 2017 09 9;61(9). Epub 2017 Jun 9.

School of Nutritional Sciences, Institute of Biochemistry, Food Science and Nutrition, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.

Scope: Brown adipose tissue (BAT) is the main regulator of thermogenesis by increasing energy expenditure through the uncoupling of oxidative metabolism from ATP synthesis. There is a growing body of evidence for BAT being the key responsible organ in combating obesity and its related disorders. Herein we propose the fungal protein ostreolysin (Oly), which has been previously shown to bind to cholesterol-enriched raft-like membrane domains (lipid rafts) of mammalian cells, as a suitable candidate for interaction with brown preadipocytes. The aim of the present study was therefore to characterize the mechanism by which a recombinant version of ostreolysin (rOly) induces brown adipocyte differentiation.

Methods And Results: Primary isolated brown preadipocytes or HIB-1B brown preadipocyte cells were treated with rOly and the effects on morphology, lipid accumulation, respiration rate, and associated gene and protein expression were measured. rOly upregulated mRNA and protein levels of factors related to brown adipocyte differentiation, induced lipid droplet formation, and increased cellular respiration rate due to expression of uncoupling protein 1. rOly also upregulated β-tubulin expression, and therefore microtubules might be involved in its mechanism of action.

Conclusion: rOly promotes brown adipocyte differentiation, suggesting a new mechanism for rOly's contribution to the battle against obesity.
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http://dx.doi.org/10.1002/mnfr.201700057DOI Listing
September 2017

Mechanisms linking obesity to altered metabolism in mice colon carcinogenesis.

Oncotarget 2015 Nov;6(35):38195-209

Institute of Biochemistry, Food Science and Nutrition, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Jerusalem, Israel.

There are an increasing number of reports on obesity being a key risk factor for the development of colon cancer. Our goal in this study was to explore the metabolic networks and molecular signaling pathways linking obesity, adipose tissue and colon cancer. Using in-vivo experiments, we found that mice fed a high-fat diet (HFD) and injected with MC38 colon cancer cells develop significantly larger tumors than their counterparts fed a control diet. In ex-vivo experiments, MC38 and CT26 colon cancer cells exposed to conditioned media (CM) from the adipose tissue of HFD-fed mice demonstrated significantly lower oxygen consumption rate as well as lower maximal oxygen consumption rate after carbonyl cyanide-4-trifluoromethoxy-phenylhydrazone treatment. In addition, in-vitro assays showed downregulated expression of mitochondrial genes in colon cancer cells exposed to CM prepared from the visceral fat of HFD-fed mice or to leptin. Interestingly, leptin levels detected in the media of adipose tissue explants co-cultured with MC38 cancer cells were higher than in adipose tissue explants cultures, indicating cross talk between the adipose tissue and the cancer cells. Salient findings of the present study demonstrate that this crosstalk is mediated at least partially by the JNK/STAT3-signaling pathway.
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http://dx.doi.org/10.18632/oncotarget.5561DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4741993PMC
November 2015

Prevention of diabetes-promoted colorectal cancer by (n-3) polyunsaturated fatty acids and (n-3) PUFA mimetic.

Oncotarget 2014 Oct;5(20):9851-63

Institute of Biochemistry, Food Science and Nutrition, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Israel.

The global obesity / diabetes epidemic has resulted in robust increase in the incidence of colorectal cancer (CRC). Epidemiological, animal and human studies have indicated efficacy of (n-3) PUFA in chemoprevention of sporadic and genetic-driven CRC. However, diabetes-promoted CRC presents a treatment challenge that surpasses that of sporadic CRC. This report analyzes the efficacy of (n-3) PUFA generated by the fat-1 transgene that encodes an (n-6) to (n-3) PUFA desaturase, and of synthetic (n-3) PUFA mimetic (MEDICA analog), to suppress CRC development in carcinogen-induced diabetes-promoted animal model. Carcinogen-induced CRC is shown here to be promoted by the diabetes context, in terms of increased aberrant crypt foci (ACF) load, cell proliferation and epithelial dedifferentiation, being accompanied by increase in the expression of HNF4α, β-catenin, and β-catenin-responsive genes. Incorporating the fat-1 transgene in the diabetes context, or oral MEDICA treatment, resulted in ameliorating the diabetic phenotype and in abrogating CRC, with decrease in ACF load, cell proliferation and the expression of HNF-4α, β-catenin, and β-catenin-responsive genes. The specificity of (n-3) PUFA in abrogating CRC development, as contrasted with enhancing CRC by (n-6) PUFA, was similarly verified in CRC cell lines. These findings may indicate prospective therapeutic potential of (n-3) PUFA or MEDICA in the management of CRC, in particular diabetes-promoted CRC.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4259442PMC
http://dx.doi.org/10.18632/oncotarget.2453DOI Listing
October 2014

Putative role of adipose tissue in growth and metabolism of colon cancer cells.

Front Oncol 2014 26;4:164. Epub 2014 Jun 26.

Institute of Biochemistry, Food Science and Nutrition, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem , Rehovot , Israel.

Newly emerging data highlight obesity as an important risk factor for developing certain types of cancer, including colorectal cancer. Although evidence supports a link between the two, the mechanisms responsible for this relationship have not yet been fully elucidated. Hypertrophied and dysfunctional adipose tissue of the obese state is characterized by low-grade inflammation. Adipokines and cytokines secreted from adipocytes, together with the abundant availability of lipids from adipocytes in the tumor microenvironment, promote adhesion, migration, and invasion of tumor cells and support tumor progression and uncontrolled growth. One of the predisposed targets of the deleterious effects exerted by secretions from adipose tissue in obesity is the activities associated with the cellular mitochondria. Mitochondrial oxidative metabolism plays a key role in meeting cells' energetic demands by oxidative phosphorylation (OxPhos). Here we discuss: (a) the dynamic relationship between glycolysis, the tricarboxylic acid cycle, and OxPhos; (b) the evidence for impaired OxPhos (i.e., mitochondrial dysfunction) in colon cancer; (c) the mechanisms by which mitochondrial dysfunction can predispose to cancer. We propose that impaired OxPhos increases susceptibility to colon cancer since OxPhos is sensitive to a large number of factors that are intrinsic to the host (e.g., inflammation). Given that adipocytes are a major source of adipokines and energy for the cancer cell, understanding the mechanisms of metabolic symbiosis between cancer cells and adipocytes should reveal new therapeutic possibilities.
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http://dx.doi.org/10.3389/fonc.2014.00164DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4071563PMC
July 2014

Secreted human adipose leptin decreases mitochondrial respiration in HCT116 colon cancer cells.

PLoS One 2013 20;8(9):e74843. Epub 2013 Sep 20.

Institute of Biochemistry, Food Science and Nutrition, The Robert H. Smith Faculty of Agriculture, Food and Environment, the Hebrew University of Jerusalem, Rehovot, Israel.

Obesity is a key risk factor for the development of colon cancer; however, the endocrine/paracrine/metabolic networks mediating this connection are poorly understood. Here we hypothesize that obesity results in secreted products from adipose tissue that induce malignancy-related metabolic alterations in colon cancer cells. Human HCT116 colon cancer cells, were exposed to conditioned media from cultured human adipose tissue fragments of obese vs. non-obese subjects. Oxygen consumption rate (OCR, mostly mitochondrial respiration) and extracellular acidification rate (ECAR, mostly lactate production via glycolysis) were examined vis-à-vis cell viability and expression of related genes and proteins. Our results show that conditioned media from obese (vs. non-obese) subjects decreased basal (40%, p<0.05) and maximal (50%, p<0.05) OCR and gene expression of mitochondrial proteins and Bax without affecting cell viability or expression of glycolytic enzymes. Similar changes could be recapitulated by incubating cells with leptin, whereas, leptin-receptor specific antagonist inhibited the reduced OCR induced by conditioned media from obese subjects. We conclude that secreted products from the adipose tissue of obese subjects inhibit mitochondrial respiration and function in HCT116 colon cancer cells, an effect that is at least partly mediated by leptin. These results highlight a putative novel mechanism for obesity-associated risk of gastrointestinal malignancies, and suggest potential new therapeutic avenues.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0074843PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3779244PMC
May 2014

Thyroid hormone, thyromimetics, and metabolic efficiency.

Endocr Rev 2014 Feb 4;35(1):35-58. Epub 2013 Dec 4.

Human Nutrition and Metabolism, Hebrew University Medical School, Jerusalem, Israel 91120.

Thyroid hormone (TH) has long been recognized as a major modulator of metabolic efficiency, energy expenditure, and thermogenesis. TH effects in regulating metabolic efficiency are transduced by controlling the coupling of mitochondrial oxidative phosphorylation and the cycling of extramitochondrial substrate/futile cycles. However, despite our present understanding of the genomic and nongenomic modes of action of TH, its control of mitochondrial coupling still remains elusive. This review summarizes historical and up-to-date findings concerned with TH regulation of metabolic energetics, while integrating its genomic and mitochondrial activities. It underscores the role played by TH-induced gating of the mitochondrial permeability transition pore (PTP) in controlling metabolic efficiency. PTP gating may offer a unified target for some TH pleiotropic activities and may serve as a novel target for synthetic functional thyromimetics designed to modulate metabolic efficiency. PTP gating by long-chain fatty acid analogs may serve as a model for such strategy.
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http://dx.doi.org/10.1210/er.2013-1006DOI Listing
February 2014

Epigenetic control of HNF-4α in colon carcinoma cells affects MUC4 expression and malignancy.

Cell Oncol (Dordr) 2013 Apr 11;36(2):155-67. Epub 2013 Jan 11.

Institute of Biochemistry, Food Science and Nutrition, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 76100, Israel.

Background: We previously found that enhanced expression of hepatocyte nuclear factor 4α (HNF-4α) is associated with hyper-proliferation of colon carcinoma cells. Here, the effect of histone deacetylase (HDAC) inhibitors on proliferation and the expression of HNF-4α and its downstream target genes were assessed in HM7, LS174T, HT29 and Caco-2 colon carcinoma cell lines.

Results: HNF-4α expression was found to vary in the different colon carcinoma cell lines tested, being highest in HM7. Additionally, a direct correlation with proliferation was observed. In HM7 cells, the weak HDAC inhibitor butyrate significantly inhibited the transcription of HNF-4α, its downstream target gene MUC4, and genes associated with proliferation, including the proliferating cell nuclear antigen gene PCNA. siRNA-mediated silencing of HNF-4α exerted an effect similar to butyrate on HM7 cell proliferation. The stronger HDAC inhibitor trichostatin A (TSA) exerted an effect similar to that of siRNA-mediated HNF-4α silencing and, concomitantly, inhibited the expression of the transcription factor gene SP1. Also, siRNA-mediated silencing of HDAC3 and HDAC4 reduced HNF-4α expression. Chromatin immunoprecipitation (ChIP) assays revealed that TSA induces hyperacetylation of histones H3 and H4 and, concomitantly, inhibits SP1 binding to the HNF-4α promoter. Subsequent electromobility shift assays supported these latter findings.

Conclusions: HNF-4α transcriptional expression and activity are tightly controlled by epigenetic mechanisms. HDAC inhibitor targeting of HNF-4α may serve as an effective treatment for advanced colon carcinomas, since downstream cancer-associated target genes such as MUC4 are significantly down-regulated by this treatment.
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http://dx.doi.org/10.1007/s13402-012-0123-3DOI Listing
April 2013

Uncoupling and reactive oxygen species (ROS)--a double-edged sword for β-cell function? "Moderation in all things".

Best Pract Res Clin Endocrinol Metab 2012 Dec 18;26(6):753-8. Epub 2012 Sep 18.

Diabetes and Obesity Research Center, Sanford-Burnham Medical Research Institute, SBMRI-Lake Nona, 6400 Sanger Road, Orlando, FL 32827, USA.

The ability of the mitochondrion to (a) manage fuel import to oxidize for adenosine tri-phosphate (ATP) generation while (b) protecting itself and the cellular environment from electron leak, which can generate highly reactive oxygen species (ROS) is a delicate balancing act. ATP is the currency of the cell and as such serves a signaling function as a substrate partner to many kinases and ion channels. While various ROS species have been viewed as a dangerous and toxic group of molecules, it also has a role as a signal derived from mitochondria, as well as other enzymatic sources: a double-edged sword. Current efforts to understand the biochemical mechanisms affected by ROS as a signal--usually noted to be hydrogen peroxide (H(2)O(2))--are exciting, but this duality of ROS effects also pose challenges in managing its levels to protect cells. The mitochondrial uncoupling protein-2 (UCP2), UCP3, and the permeability transition pore have been integral to efforts to try to understand what role mitochondrial-derived ROS have in cells. In this piece we reflect on mitochondrial ROS and uncoupling proteins as signaling regulators. It seems that when it comes to ROS and uncoupling the proverb "Moderation in all things" is apt.
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http://dx.doi.org/10.1016/j.beem.2012.08.002DOI Listing
December 2012

Acute stimulation of white adipocyte respiration by PKA-induced lipolysis.

Diabetes 2010 Oct 3;59(10):2474-83. Epub 2010 Aug 3.

Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina, USA.

Objective: We examined the effect of β-adrenergic receptor (βAR) activation and cAMP-elevating agents on respiration and mitochondrial uncoupling in human adipocytes and probed the underlying molecular mechanisms.

Research Design And Methods: Oxygen consumption rate (OCR, aerobic respiration) and extracellular acidification rate (ECAR, anaerobic respiration) were examined in response to isoproterenol (ISO), forskolin (FSK), and dibutyryl-cAMP (DB), coupled with measurements of mitochondrial depolarization, lipolysis, kinase activities, and gene targeting or knock-down approaches.

Results: ISO, FSK, or DB rapidly increased oxidative and glycolytic respiration together with mitochondrial depolarization in human and mouse white adipocytes. The increase in OCR was oligomycin-insensitive and contingent on cAMP-dependent protein kinase A (PKA)-induced lipolysis. This increased respiration and the uncoupling were blocked by inhibiting the mitochondrial permeability transition pore (PTP) and its regulator, BAX. Interestingly, compared with lean individuals, adipocytes from obese subjects exhibited reduced OCR and uncoupling capacity in response to ISO.

Conclusions: Lipolysis stimulated by βAR activation or other maneuvers that increase cAMP levels in white adipocytes acutely induces mitochondrial uncoupling and cellular energetics, which are amplified in the absence of scavenging BSA. The increase in OCR is dependent on PKA-induced lipolysis and is mediated by the PTP and BAX. Because this effect is reduced with obesity, further exploration of this uncoupling mechanism will be needed to determine its cause and consequences.
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http://dx.doi.org/10.2337/db10-0245DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3279548PMC
October 2010

Low-level arsenic impairs glucose-stimulated insulin secretion in pancreatic beta cells: involvement of cellular adaptive response to oxidative stress.

Environ Health Perspect 2010 Jun 25;118(6):864-70. Epub 2010 Jan 25.

Division of Translational Biology, The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina 27709 , USA.

Background: Chronic exposure of humans to inorganic arsenic, a potent environmental oxidative stressor, is associated with incidence of type 2 diabetes (T2D). A key driver in the pathogenesis of T2D is impairment of pancreatic beta-cell function, with the hallmark of beta-cell function being glucose-stimulated insulin secretion (GSIS). Reactive oxygen species (ROS) derived from glucose metabolism serve as one of the metabolic signals for GSIS. Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a central transcription factor regulating cellular adaptive response to oxidative stress.

Objectives: We tested the hypothesis that activation of Nrf2 and induction of antioxidant enzymes in response to arsenic exposure impedes glucose-triggered ROS signaling and thus GSIS.

Methods And Results: Exposure of INS-1(832/13) cells to low levels of arsenite led to decreased GSIS in a dose- and time-dependent fashion. Consistent with our hypothesis, a significantly enhanced Nrf2 activity, determined by its nuclear accumulation and induction of its target genes, was observed in arsenite-exposed cells. In keeping with the activation of Nrf2-mediated antioxidant response, intracellular glutathione and intracellular hydrogen peroxide-scavenging activity was dose dependently increased by arsenite exposure. Although the basal cellular peroxide level was significantly enhanced, the net percentage increase in glucose-stimulated intracellular peroxide production was markedly inhibited in arsenite-exposed cells. In contrast, insulin synthesis and the consensus GSIS pathway, including glucose transport and metabolism, were not significantly reduced by arsenite exposure.

Conclusions: Our studies suggest that low levels of arsenic provoke a cellular adaptive oxidative stress response that increases antioxidant levels, dampens ROS signaling involved in GSIS, and thus disturbs beta-cell function.
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http://dx.doi.org/10.1289/ehp.0901608DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2898865PMC
June 2010

Deficiency in the nuclear factor E2-related factor-2 transcription factor results in impaired adipogenesis and protects against diet-induced obesity.

J Biol Chem 2010 Mar 20;285(12):9292-300. Epub 2010 Jan 20.

Department of Laboratory Medicine and Pathology, University of California, Irvine, California 92697, USA.

Nuclear factor E2-related factor 2 (Nrf2) is a cap-n-collar basic leucine zipper (CNC-bZIP) transcription factor that is well established as a master regulator of phase II detoxification and antioxidant gene expression and is strongly expressed in tissues involved in xenobiotic metabolism including liver and kidney. Nrf2 is also abundantly expressed in adipose tissue; however, the exact function of Nrf2 in adipocyte biology is unclear. In the current study we show that targeted knock-out of Nrf2 in mice decreases adipose tissue mass, promotes formation of small adipocytes, and protects against weight gain and obesity otherwise induced by a high fat diet. In mouse embryonic fibroblasts, 3T3-L1 cells, and human subcutaneous preadipocytes, selective deficiency of Nrf2 impairs adipocyte differentiation. Deficiency of Nrf2 also leads to decreased expression of peroxisome proliferator-activated receptor gamma (PPARgamma), CCAAT enhancer-binding protein alpha (C/EBPalpha), and their downstream targets during adipocyte differentiation. Conversely, activation of Nrf2 in 3T3-L1 cells by stable knockdown of its negative regulator Keap1 enhances and accelerates hormone-induced adipocyte differentiation. Transfection of Nrf2 stimulates Ppargamma promoter activity, and stable knockdown of Keap1 enhances PPARgamma expression in 3T3-L1 cells. In addition, chromatin immunoprecipitation studies show that Nrf2 associates with consensus binding sites for Nrf2 in the Ppargamma promoter. These findings demonstrate a novel biologic role for Nrf2 beyond its participation in detoxification and antioxidant pathways and place Nrf2 within the limited network of transcription factors that control adipocyte differentiation by regulating expression of PPARgamma.
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http://dx.doi.org/10.1074/jbc.M109.093955DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2838347PMC
March 2010

Gating of the mitochondrial permeability transition pore by long chain fatty acyl analogs in vivo.

J Biol Chem 2010 Mar 26;285(10):6879-90. Epub 2009 Dec 26.

Department of Human Nutrition and Metabolism, Hebrew University Medical School, Jerusalem 91120, Israel.

The role played by long chain fatty acids (LCFA) in promoting energy expenditure is confounded by their dual function as substrates for oxidation and as putative classic uncouplers of mitochondrial oxidative phosphorylation. LCFA analogs of the MEDICA (MEthyl-substituted DICarboxylic Acids) series are neither esterified into lipids nor beta-oxidized and may thus simulate the uncoupling activity of natural LCFA in vivo, independently of their substrate role. Treatment of rats or cell lines with MEDICA analogs results in low conductance gating of the mitochondrial permeability transition pore (PTP), with 10-40% decrease in the inner mitochondrial membrane potential. PTP gating by MEDICA analogs is accounted for by inhibition of Raf1 expression and kinase activity, resulting in suppression of the MAPK/RSK1 and the adenylate cyclase/PKA transduction pathways. Suppression of RSK1 and PKA results in a decrease in phosphorylation of their respective downstream targets, Bad(Ser-112) and Bad(Ser-155). Decrease in Bad(Ser-112, Ser-155) phosphorylation results in increased binding of Bad to mitochondrial Bcl2 with concomitant displacement of Bax, followed by PTP gating induced by free mitochondrial Bax. Low conductance PTP gating by LCFA/MEDICA may account for their thyromimetic calorigenic activity in vivo.
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http://dx.doi.org/10.1074/jbc.M109.080416DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2844138PMC
March 2010

Gating of the mitochondrial permeability transition pore by thyroid hormone.

FASEB J 2010 Jan 1;24(1):93-104. Epub 2009 Sep 1.

Department of Human Nutrition and Metabolism, Hebrew University Medical School, Jerusalem, Israel.

The calorigenic-thermogenic activity of thyroid hormone (T3) has long been ascribed to uncoupling of mitochondrial oxidative phosphorylation. However, the mode of action of T3 in promoting mitochondrial proton leak is still unresolved. Mitochondrial uncoupling by T3 is reported here to be transduced in vivo in rats and in cultured Jurkat cells by gating of the mitochondrial permeability transition pore (PTP). T3-induced PTP gating is shown here to be abrogated in inositol 1,4,5-trisphosphate (IP(3)) receptor 1 (IP(3)R1)(-/-) cells, indicating that the endoplasmic reticulum IP(3)R1 may serve as upstream target for the mitochondrial activity of T3. IP(3)R1 gating by T3 is due to its increased expression and truncation into channel-only peptides, resulting in IP(3)-independent Ca(2+) efflux. Increased cytosolic Ca(2+) results in activation of protein phosphatase 2B, dephosphorylation and depletion of mitochondrial Bcl2 (S70), and increase in mitochondrial free Bax leading to low-conductance PTP gating. The T3 transduction pathway integrates genomic and nongenomic activities of T3 in regulating mitochondrial energetics and may offer novel targets for thyromimetics designed to modulate energy expenditure.
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http://dx.doi.org/10.1096/fj.09-133538DOI Listing
January 2010

Prolonged exposure to insulin suppresses mitochondrial production in primary hepatocytes.

J Biol Chem 2009 May 31;284(21):14087-95. Epub 2009 Mar 31.

Translational Biology, The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina 27709, USA.

Insulin is the central regulator of metabolism and is necessary for storing energy as fat efficiently. Mitochondria are primary sites of energy consumption of most cells. Increased plasma insulin level and mitochondrial dysfunction are features of insulin resistance. The exact role of insulin in regulation of mitochondrial production and function remains unestablished. In this study, we observed that mitochondrial production in liver and skeletal muscle gastrocnemius was increased in mice with insulin deficiency (streptozotocin-induced type 1 diabetes). In contrast, prolonged exposure (24 h) of isolated hepatocytes to insulin decreased mitochondrial mass, mitochondrial DNA (mtDNA), intracellular ATP content, and cellular O(2) consumption. Transcript levels of genes associated with mitochondrial production and beta oxidation were decreased, whereas those of lipogenic genes were increased by the prolonged exposure to insulin. Insulin-induced changes in mtDNA, mitochondrial mass, intracellular ATP content, and transcripts of mitochondrion-associated genes were prevented by blockade of Akt activation with the phosphatidylinositol 3-kinase inhibitor LY294002. Conversely, levels of mtDNA, intracellular ATP content, and expression of mitochondrion-associated genes were decreased by overexpression of the constitutively active Akt. Finally, insulin suppression of mtDNA, ATP production, and expression of mitochondrion-related genes was largely prevented by inhibition of cyclic nucleotide phosphodiesterase with isobutylmethylxanthine. Together, our results show prolonged exposure of isolated hepatocytes to insulin suppresses mitochondrial production and function through the classical Akt-dependent insulin signaling pathway.
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http://dx.doi.org/10.1074/jbc.M807992200DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2682857PMC
May 2009

Liver X receptor alpha is a transcriptional repressor of the uncoupling protein 1 gene and the brown fat phenotype.

Mol Cell Biol 2008 Apr 14;28(7):2187-200. Epub 2008 Jan 14.

The Hamner Institutes for Health Sciences, 6 Davis Drive, P.O. Box 12137, Research Triangle Park, NC 27709, USA.

The adipocyte integrates crucial information about metabolic needs in order to balance energy intake, storage, and expenditure. Whereas white adipose tissue stores energy, brown adipose tissue is a major site of energy dissipation through adaptive thermogenesis mediated by uncoupling protein 1 (UCP1) in mammals. In both white and brown adipose tissue, nuclear receptors and their coregulators, such as peroxisome proliferator-activated receptor gamma (PPARgamma) and PPARgamma coactivator 1alpha (PGC-1alpha), play key roles in regulating their development and metabolic functions. Here we show the unexpected role of liver X receptor alpha (LXRalpha) as a direct transcriptional inhibitor of beta-adrenergic receptor-mediated, cyclic AMP-dependent Ucp1 gene expression through its binding to the critical enhancer region of the Ucp1 promoter. The mechanism of inhibition involves the differential recruitment of the corepressor RIP140 to an LXRalpha binding site that overlaps with the PPARgamma/PGC-1alpha response element, resulting in the dismissal of PPARgamma. The ability of LXRalpha to dampen energy expenditure in this way provides another mechanism for maintaining a balance between energy storage and utilization.
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http://dx.doi.org/10.1128/MCB.01479-07DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2268430PMC
April 2008

Modulation of mitochondrial transition pore components by thyroid hormone.

Endocrinology 2005 May 3;146(5):2462-72. Epub 2005 Feb 3.

Department of Human Nutrition and Metabolism, Hebrew University Medical School, Jerusalem 91120, Israel.

Thyroid hormone (TH) modulates metabolic efficiency by controlling the coupling of mitochondrial oxidative phosphorylation. However, its uncoupling mode of action is still enigmatic. Treatment of Jurkat or GH3 cells with T3 is reported here to result in limited, Cyclosporin A-sensitive mitochondrial depolarization, conforming to low conductance gating of the mitochondrial transition pore (MTP). MTP protein components induced by T3 treatment were verified in T3-treated and hypothyroid rat liver as well as in Jurkat cells. T3 treatment resulted in increase in mitochondrial Bax and Bak together with decreased mitochondrial Bcl2. T3-induced mitochondrial depolarization was aborted by overexpression of Bcl2. In contrast to Bax-Bcl2 family proteins, some other MTP components were either not induced by T3 (e.g. voltage-dependent anion channel) or were induced, but were not involved in Cyclosporin A-sensitive MTP gating (e.g. Cyclophilin D and adenine nucleotide translocase-2) Hence, TH-induced mitochondrial uncoupling may be ascribed to low conductance MTP gating mediated by TH-induced increase in mitochondrial proapoptotic combined with a decrease in mitochondrial antiapoptotic proteins of the Bax-Bcl2 family.
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http://dx.doi.org/10.1210/en.2004-1161DOI Listing
May 2005