Cancer cells exhibit an altered metabolism which is characterized by a preference for aerobic glycolysis more than mitochondrial oxidation of pyruvate. This provides anabolic support and selective ...growth advantage for cancer cells. Recently, a new concept has arisen suggesting that these metabolic changes may be due, in part, to an attenuated mitochondrial function which results from the inhibition of the pyruvate dehydrogenase complex (PDC). This mitochondrial complex links glycolysis to the Krebs cycle and the current understanding of its regulation involves the cyclic phosphorylation and dephosphorylation by specific pyruvate dehydrogenase kinases (PDKs) and pyruvate dehydrogenase phosphatases (PDPs).
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Resveratrol (RES), a polyphenol found in natural foods, displays anti-oxidant, anti-inflammatory and anti-proliferative properties potentially beneficial in cancers, in particular in the prevention ...of tumor growth. However, the rapid metabolism of resveratrol strongly limits its bioavailability. The molecular mechanisms sustaining the potential biological activity of low doses of resveratrol has not been extensively studied and, thus, needs better characterization. Here, we show that resveratrol (10 µM, 48 hr) induces both a cell growth arrest and a metabolic reprogramming in colon cancer cells. Resveratrol modifies the lipidomic profile, increases oxidative capacities and decreases glycolysis, in association with a decreased pentose phosphate activity and an increased ATP production. Resveratrol targets the pyruvate dehydrogenase (PDH) complex, a key mitochondrial gatekeeper of energy metabolism, leading to an enhanced PDH activity. Calcium chelation, as well as the blockade of the mitochondrial calcium uniport, prevents the resveratrol-induced augmentation in oxidative capacities and the increased PDH activity suggesting that calcium might play a role in the metabolic shift. We further demonstrate that the inhibition of the CamKKB or the downstream AMPK pathway partly abolished the resveratrol-induced increase of glucose oxidation. This suggests that resveratrol might improve the oxidative capacities of cancer cells through the CamKKB/AMPK pathway.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Background: Epidemiological studies emphasize the possible role of persistent organic pollutants (POPs) in obesity and the metabolic syndrome. These pollutants are stored in adipose tissue (AT). ...Objectives: Our aim was to study the effects of POPs on human adipose cells and rodent AT. Methods: Using human multipotent adipose-derived stem cells, we carried out large-scale gene expression analysis to identify the major pathways modified by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), polychlorinated biphenyl (PCB) congener 126 (PCB-126), and PCB-153 and to evaluate their toxic effects. The effects of TCDD on gene expression and AT histology were also assessed in mice. Results: The most significantly regulated genes in both precursor cells and adipocytes were those involved in the inflammatory/immune response, cancer, and metabolism pathways. Interestingly, the fold induction and the number of modulated genes were higher in precursors than in adipocytes, suggesting that the former could be more sensitive to the effect of pollutants. When cells were treated with combinations of pollutants, the effects of the AhR ligands TCDD and PCB-126 were dominant compared with those of the non-dioxin-like PCB-153. The effects of AhR ligands were reduced by the AhR antagonist α-naphthoflavone. The regulation of inflammatory pathway was observed in wild-type AT but not in AhR-knockout mice. Conclusions: Both in vitro and in vivo studies showed that adipose cells were targets of AhR ligands and suggest that inflammation is one of the main regulated pathways. These observations suggest a possible contribution of pollutants to low-grade AT inflammation that accompanies the pathogenesis of metabolic diseases.
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BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK, VSZLJ
Butyrate, a short‐chain fatty acid produced by the colonic bacterial fermentation is able to induce cell growth inhibition and differentiation in colon cancer cells at least partially through its ...capacity to inhibit histone deacetylases. Since butyrate is expected to impact cellular metabolic pathways in colon cancer cells, we hypothesize that it could exert its antiproliferative properties by altering cellular metabolism. We show that although Caco2 colon cancer cells oxidized both butyrate and glucose into CO2, they displayed a higher oxidation rate with butyrate as substrate than with glucose. Furthermore, butyrate pretreatment led to an increase cell capacity to oxidize butyrate and a decreased capacity to oxidize glucose, suggesting that colon cancer cells, which are initially highly glycolytic, can switch to a butyrate utilizing phenotype, and preferentially oxidize butyrate instead of glucose as energy source to produce acetyl coA. Butyrate pretreated cells displayed a modulation of glutamine metabolism characterized by an increased incorporation of carbons derived from glutamine into lipids and a reduced lactate production. The butyrate‐stimulated glutamine utilization is linked to pyruvate dehydrogenase complex since dichloroacetate reverses this effect. Furthermore, butyrate positively regulates gene expression of pyruvate dehydrogenase kinases and this effect involves a hyperacetylation of histones at PDK4 gene promoter level. Our data suggest that butyrate exerts two distinct effects to ensure the regulation of glutamine metabolism: it provides acetyl coA needed for fatty acid synthesis, and it also plays a role in the control of the expression of genes involved in glucose utilization leading to the inactivation of PDC.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
CD14, CD68 and/or mouse F4/80 or human epidermal growth factor module-containing mucin-like receptor 1 (EMR1) are widely used as macrophage-specific markers. Since macrophages infiltrate several ...tissues during inflammatory processes, CD14, CD68 and EMR1-F4/80 have been employed to discriminate between tissue-containing macrophages, like adipose tissue (AT), and other cells. Using real-time PCR experiments, we show that isolated adipocytes from humans and mice AT express high levels of CD14 and CD68 mRNA, whereas EMR1-F4/80 is mainly present in the macrophage-containing stroma-vascular fraction. Furthermore, fibroblasts-like cells (adipoblasts), preadipocytes and adipocytes from the murine cell lines, 3T3-F442A and BFC-1, express CD14 and CD68 mRNA and protein as determined by fluorescence-activated cell sorter, but not F4/80 which, as expected, is strongly expressed in the macrophage cell line RAW264.7. These results reinforce the view that EMR1-F4/80 is the best macrophage marker to date and show that CD14 and CD68 are not macrophage-specific proteins.
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BFBNIB, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Leptin is secreted by white adipose tissue (WAT) and induces lipolysis and nonesterified fatty acid (NEFA) oxidation. During lipolysis, NEFA efflux is the result of triglyceride breakdown, NEFA ...oxidation, and re-esterification via glyceroneogenesis. Leptin's effects on glyceroneogenesis remain unexplored. We investigated the effect of a long-term treatment with leptin at a physiological concentration (10 μg/L) on lipolysis and glyceroneogenesis in WAT explants and analyzed the underlying mechanisms. Exposure of rat WAT explants to leptin for 2 h resulted in increased NEFA and glycerol efflux. However, a longer treatment with leptin (18 h) did not affect NEFA release and reduced glycerol output. RT-qPCR showed that leptin significantly downregulated the hormone-sensitive lipase (HSL), cytosolic phosphoenolpyruvate carboxykinase (Pck1), and PPARγ genes. In agreement with its effect on mRNA, leptin also decreased the levels of PEPCK-C and HSL proteins. Glyceroneogenesis, monitored by 1-¹⁴ C pyruvate incorporation into lipids, was reduced. Because leptin increases nitric oxide (NO) production in adipocytes, we explored the role of NO in the leptin signaling pathway. Pretreatment of explants with the NO synthase inhibitor Nω-nitro-L-arginine methyl ester eliminated the effect of leptin on lipolysis, glyceroneogenesis, and expression of the HSL, Pck1, and PPARγ genes. The NO donor S-nitroso-N-acetyl-DL penicillamine mimicked leptin effects, thus demonstrating the role of NO in these pathways. The inverse time-dependent action of leptin on WAT is consistent with a process that limits NEFA re-esterification and energy storage while reducing glycerol release, thus preventing hypertriglyceridemia.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Objective
The infrapatellar fat pad (IFP) of the knee joint has an inflammatory phenotype in osteoarthritis (OA). Its close proximity to the synovial membrane suggests that the IFP could be involved ...in the induction of OA synovitis. This study was undertaken to investigate the response of fibroblast‐like synoviocytes (FLS) to autologous IFP and subcutaneous adipose tissue (SCAT) from patients with severe knee OA.
Methods
Samples of IFP, SCAT, and autologous synovial membrane tissue close to the IFP were harvested during surgery from 28 patients with end‐stage knee OA. FLS from 14 patients were stimulated with autologous IFP‐ or SCAT‐conditioned medium, and levels of messenger RNA (mRNA) expression and protein release of interleukin‐6 (IL‐6), IL‐8, secretory phospholipase A2 (sPLA2), cytosolic PLA2, cyclooxygenase 2 (COX‐2), microsomal prostaglandin E synthase, prostaglandin E2 (PGE2), and matrix metalloproteinases (MMPs) 1, 3, 9, and 13 were evaluated. Both IFP‐ and SCAT‐conditioned medium were evaluated by enzyme‐linked immunosorbent assay for secretion of IL‐6, soluble IL‐6 receptor (sIL‐6R), IL‐8, tumor necrosis factor α (TNFα), PGE2, IL‐1β, and interferon‐γ. In addition, OA FLS were treated with PGE2 receptor antagonists to evaluate the contribution of IFP‐derived PGE2 to the inflammatory response of FLS to the IFP.
Results
Stimulation of OA FLS with IFP‐conditioned medium induced the mRNA expression and protein release of IL‐6, IL‐8, sPLA2, COX‐2, PGE2, and MMPs 1, 3, 9, and 13. The extent of stimulation was consistently stronger with IFP‐conditioned medium than with SCAT‐conditioned medium. Moreover, secretion of IL‐6, sIL‐6R, IL‐8, TNFα, and PGE2 was greater in IFP‐conditioned medium than in SCAT‐conditioned medium, especially PGE2, whose secretion was 75‐fold stronger in IFP‐conditioned medium (P < 0.0001). PGE2 receptor antagonists dose‐dependently inhibited the release of IL‐6, IL‐8, and PGE2 by IFP‐stimulated FLS.
Conclusion
This study showed that the IFP has a potential role in the induction of synovial inflammation in patients with severe knee OA. Furthermore, secretion of PGE2 by the IFP may be involved in the OA inflammatory process.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Pyruvate Dehydrogenase Kinase 4
Regulation by Thiazolidinediones and Implication in Glyceroneogenesis in Adipose Tissue
Thomas Cadoudal ,
Emilie Distel ,
Sylvie Durant ,
Françoise Fouque ,
Jean-Marc ...Blouin ,
Martine Collinet ,
Sylvie Bortoli ,
Claude Forest and
Chantal Benelli
From the Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche-S 747, Université Paris Descartes,
Centre Universitaire des Saints-Pères, Paris, France
Corresponding author: Dr. Claude Forest, claude.forest{at}univ-paris5.fr
Abstract
OBJECTIVE— Pyruvate dehydrogenase complex (PDC) serves as the metabolic switch between glucose and fatty acid utilization. PDC activity
is inhibited by PDC kinase (PDK). PDC shares the same substrate, i.e., pyruvate, as glyceroneogenesis, a pathway controlling
fatty acid release from white adipose tissue (WAT). Thiazolidinediones activate glyceroneogenesis. We studied the regulation
by rosiglitazone of PDK2 and PDK4 isoforms and tested the hypothesis that glyceroneogenesis could be controlled by PDK.
RESEARCH DESIGN AND METHODS— Rosiglitazone was administered to Zucker fa/fa rats, and then PDK4 and PDK2 mRNAs were examined in subcutaneous, periepididymal, and retroperitoneal WAT, liver, and muscle
by real-time RT-PCR. Cultured WAT explants from humans and rats and 3T3-F442A adipocytes were rosiglitazone-treated before
analyses of PDK2 and PDK4 mRNA and protein. Small interfering RNA (siRNA) was transfected by electroporation. Glyceroneogenesis
was determined using 1- 14 Cpyruvate incorporation into lipids.
RESULTS— Rosiglitazone increased PDK4 mRNA in all WAT depots but not in liver and muscle. PDK2 transcript was not affected. This isoform
selectivity was also found in ex vivo–treated explants. In 3T3-F442A adipocytes, Pdk4 expression was strongly and selectively induced by rosiglitazone in a direct and transcriptional manner, with a concentration
required for half-maximal effect at 1 nmol/l. The use of dichloroacetic acid or leelamine, two PDK inhibitors, or a specific
PDK4 siRNA demonstrated that PDK4 participated in glyceroneogenesis, therefore altering nonesterified fatty acid release in
both basal and rosiglitazone-activated conditions.
CONCLUSIONS— These data show that PDK4 upregulation in adipocytes participates in the hypolipidemic effect of thiazolidinediones through
modulation of glyceroneogenesis.
Footnotes
Published ahead of print at http://diabetes.diabetesjournals.org on 2 June 2008.
T.C. and E.D. contributed equally to this work.
Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work
is not altered. See http://creativecommons.org/licenses/by-nc-nd/3.0/ for details.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore
be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Accepted May 22, 2008.
Received April 8, 2008.
DIABETES
Objective
Obesity is a potent risk factor in knee osteoarthritis (OA). It has been suggested that adipokines, secreted by adipose tissue (AT) and largely found in the synovial fluid of OA patients, ...derive in part from the infrapatellar fat pad (IFP), also known as Hoffa's fat pad. The goal of this study was to characterize IFP tissue in obese OA patients and to compare its features with thigh subcutaneous AT to determine whether the IFP contributes to local inflammation in knee OA via production of specific cytokines.
Methods
IFP and subcutaneous AT samples were obtained from 11 obese women (body mass index ≥30 kg/m2) with knee femorotibial OA. Gene expression was measured by real‐time quantitative polymerase chain reaction. Cytokine concentrations in plasma and in conditioned media of cultured AT explants were determined by enzyme‐linked immunosorbent assay or by Luminex xMAP technology.
Results
In IFP tissue versus subcutaneous AT, there was a decrease in the expression of genes for key enzymes implicated in adipocyte lipid metabolism, whereas the expression levels of genes for AT markers remained similar. A 2‐fold increase in the expression of the gene for interleukin‐6 (IL‐6), a 2‐fold increase in the release of IL‐6, and a 3.6‐fold increase in the release of soluble IL‐6 receptor (sIL‐6R) were observed in IFP samples, compared with subcutaneous AT, but the rates of secretion of other cytokines in IFP samples were similar to the rates in subcutaneous AT. In addition, leptin secretion was decreased by 40%, whereas adiponectin secretion was increased by 70%, in IFP samples versus subcutaneous AT.
Conclusion
Our results indicate that the IFP cytokine profile typically found in OA patients could play a role in paracrine inflammation via the local production of IL‐6/sIL‐6R and that such a profile might contribute to damage in adjacent cartilage.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Scope
Vitamin A and its metabolites, such as retinoic acids (RA), are related to metabolic diseases, in particular insulin resistance and obesity. Here, we studied the roles of 9‐cis RA and all‐trans ...RA on the regulation of pyruvate dehydrogenase kinase 4 (PDK4), an enzyme involved in fatty acid reesterification, which is a crucial metabolic pathway in adipose tissue (AT) lipid homeostasis.
Methods and results
9‐cis RA and all‐trans RA treatment of human and murine AT explants, as well as adipocytes (3T3‐F442A cell line) induces PDK4 expression both at the mRNA and the protein level, via a transcriptional mechanism. Using site‐directed mutagenesis and chomatin immuno‐precipitation, we showed that this activation involves two new RA responsive elements in the Pdk4 promoter, RAREa (DR1: −125/−112) and RAREb (DR1: −86/−73), specific to AT. Furthermore, even though endogeneous Pdk4 gene was upregulated by RA in Fao cells, a rat hepatoma cell line, the induction did not occur through the newly found RAREs.
Conclusion
In this study, we showed that adipocyte PDK4 gene is a new target of the vitamin A derived RA and might participate to the reduced fatty acid efflux from the adipocyte, a step that plays an important role in the developement of metabolic diseases.
Adipocyte PDK4, by inhibiting PDH activity, is a key actor of fatty acid release via glyceroneogenesis. Here, we describe PDK4 as a new transcriptional target of RAs through two responsive elements (RAREa and RAREb). This regulation might participate to the reduced fatty acid release from the adipocyte and could play an important role in the development of metabolic diseases.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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