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author:("stapels, Bart")
1.  miR-206 controls LXRα expression and promotes LXR-mediated cholesterol efflux in macrophages 
Biochimica et biophysica acta  2014;1841(6):827-835.
Liver X receptors (LXRα and LXRβ) are key transcription factors in cholesterol metabolism that regulate cholesterol biosynthesis/efflux and bile acid metabolism/excretion in the liver and numerous organs. In macrophages, LXR signaling modulates cholesterol handling and the inflammatory response, pathways involved in atherosclerosis. Since regulatory pathways of LXR transcription control are well understood, in the present study we aimed at identifying post-transcriptional regulators of LXR activity. MicroRNAs (miRs) are such post-transcriptional regulators of genes that in the canonical pathway mediate mRNA inactivation. In silico analysis identified miR-206 as a putative regulator of LXRα but not LXRβ. Indeed, as recently shown, we found that miR-206 represses LXRα activity and expression of LXRα and its target genes in hepatic cells. Interestingly, miR-206 regulates LXRα differently in macrophages. Stably overexpressing miR-206 in THP-1 human macrophages revealed an up-regulation and miR-206 knockdown led to a down-regulation of LXRα and its target genes. In support of these results, bone marrow-derived macrophages (BMDMs) from miR-206 KO mice also exhibited lower expression of LXRα target genes. The physiological relevance of these findings was proven by gain- and loss-of-function of miR-206; overexpression of miR-206 enhanced cholesterol efflux in human macrophages and knocking out miR-206 decreased cholesterol efflux from MPMs. Moreover, we show that miR-206 expression in macrophages is repressed by LXRα activation, while oxidized LDL and inflammatory stimuli profoundly induced miR-206 expression. We therefore propose a feed-back loop between miR-206 and LXRα that might be part of an LXR auto-regulatory mechanism to fine tune LXR activity.
doi:10.1016/j.bbalip.2014.02.006
PMCID: PMC3996726  PMID: 24603323
Micro-RNA; ox-LDL; LXR target gene; ABC; ApoA-I; HDL
2.  miR-206 controls LXRα expression and promotes LXR-mediated cholesterol efflux in macrophages 
Biochimica et Biophysica Acta  2014;1841(6):827-835.
Liver X receptors (LXRα and LXRβ) are key transcription factors in cholesterol metabolism that regulate cholesterol biosynthesis/efflux and bile acid metabolism/excretion in the liver and numerous organs. In macrophages, LXR signaling modulates cholesterol handling and the inflammatory response, pathways involved in atherosclerosis. Since regulatory pathways of LXR transcription control are well understood, in the present study we aimed at identifying post-transcriptional regulators of LXR activity. MicroRNAs (miRs) are such post-transcriptional regulators of genes that in the canonical pathway mediate mRNA inactivation. In silico analysis identified miR-206 as a putative regulator of LXRα but not LXRβ. Indeed, as recently shown, we found that miR-206 represses LXRα activity and expression of LXRα and its target genes in hepatic cells. Interestingly, miR-206 regulates LXRα differently in macrophages. Stably overexpressing miR-206 in THP-1 human macrophages revealed an up-regulation and miR-206 knockdown led to a down-regulation of LXRα and its target genes. In support of these results, bone marrow-derived macrophages (BMDMs) from miR-206 KO mice also exhibited lower expression of LXRα target genes. The physiological relevance of these findings was proven by gain- and loss-of-function of miR-206; overexpression of miR-206 enhanced cholesterol efflux in human macrophages and knocking out miR-206 decreased cholesterol efflux from MPMs. Moreover, we show that miR-206 expression in macrophages is repressed by LXRα activation, while oxidized LDL and inflammatory stimuli profoundly induced miR-206 expression. We therefore propose a feed-back loop between miR-206 and LXRα that might be part of an LXR auto-regulatory mechanism to fine tune LXR activity.
Graphical abstract
Highlights
•Functional differences of miR-206 in the liver and macrophages•In the liver, miR-206 suppresses LXRα expression and signaling.•In macrophages, miR-206 increases LXRα abundance and promotes cholesterol efflux.•In macrophages, LXRα activation represses miR-206 expression.•In macrophages, pro-inflammatory stimuli increase miR-206 expression.
doi:10.1016/j.bbalip.2014.02.006
PMCID: PMC3996726  PMID: 24603323
miR, Micro-RNA; LXRs, liver X receptors; ApoE, apolipoprotein E; ABCs, ATP-binding cassette transporters; KO, knockout; SREBP, sterol regulatory element-binding protein; Micro-RNA; ox-LDL; LXR target gene; ABC; ApoA-I; HDL
3.  Downregulation of the tumour suppressor p16INK4A contributes to the polarisation of human macrophages toward an adipose tissue macrophage (ATM)-like phenotype 
Diabetologia  2011;54(12):3150-3156.
Aims/hypothesis
Human adipose tissue macrophages (ATMs) display an alternatively activated (M2) phenotype, but are still able to produce excessive inflammatory mediators. However, the processes driving this particular ATM phenotype are not understood. Genome-wide association studies associated the CDKN2A locus, encoding the tumour suppressor p16INK4A, with the development of type 2 diabetes. In the present study, p16INK4A levels in human ATMs and the role of p16INK4A in acquiring the ATM phenotype were assessed.
Methods
Gene expression of p16INK4A in ATMs was analysed and compared with that in monocyte-derived macrophages (MDMs) from obese patients or with macrophages from human atherosclerotic plaques (AMs). Additionally, p16INK4A levels were studied during macrophage differentiation and polarisation of monocytes isolated from healthy donors. The role of p16INK4A in MDMs from healthy donors was investigated by small interfering (si)RNA-mediated silencing or adenovirus-mediated overproduction of p16INK4A.
Results
Compared with MDMs and AMs, ATMs from obese patients expressed lower levels of p16INK4A. In vitro, IL-4-induced M2 polarisation resulted in lower p16INK4A protein levels after differentiation of monocytes from healthy donors in macrophages. Silencing of p16INK4A in MDMs mediated by siRNA increased the expression of M2 marker genes and enhanced the response to lipopolysaccharide (LPS), to give a phenotype resembling that of ATM. By contrast, adenovirus-mediated overproduction of p16INK4A in MDMs diminished M2 marker gene expression and the response to LPS. Western blot analysis revealed that p16INK4A overproduction inhibits LPS- and palmitate-induced Toll-like receptor 4 (TLR4)–nuclear factor of κ light polypeptide gene enhancer in B cells (NF-κB) signalling.
Conclusions/interpretation
These results show that p16INK4A inhibits the acquisition of the ATM phenotype. The age-related increase in p16INK4A level may thus influence normal ATM function and contribute to type 2 diabetes risk.
doi:10.1007/s00125-011-2324-0
PMCID: PMC4020795  PMID: 21968977
Adipose Tissue; metabolism; Cell Polarity; Cyclin-Dependent Kinase Inhibitor p16; biosynthesis; genetics; Diabetes Mellitus, Type 2; metabolism; Down-Regulation; Female; Gene Silencing; Humans; Macrophages; metabolism; Male; NF-kappa B; metabolism; Obesity; metabolism; Plaque, Atherosclerotic; metabolism; RNA, Small Interfering; metabolism; Toll-Like Receptor 4; metabolism; Adipose tissue macrophages; CDKN2A; Inflammation; Macrophage polarisation; Senescence; Type 2 diabetes
4.  Detrimental Effects of Diet-Induced Obesity on τ Pathology Are Independent of Insulin Resistance in τ Transgenic Mice 
Diabetes  2013;62(5):1681-1688.
The τ pathology found in Alzheimer disease (AD) is crucial in cognitive decline. Midlife development of obesity, a major risk factor of insulin resistance and type 2 diabetes, increases the risk of dementia and AD later in life. The impact of obesity on AD risk has been suggested to be related to central insulin resistance, secondary to peripheral insulin resistance. The effects of diet-induced obesity (DIO) on τ pathology remain unknown. In this study, we evaluated effects of a high-fat diet, given at an early pathological stage, in the THY-Tau22 transgenic mouse model of progressive AD-like τ pathology. We found that early and progressive obesity potentiated spatial learning deficits as well as hippocampal τ pathology at a later stage. Surprisingly, THY-Tau22 mice did not exhibit peripheral insulin resistance. Further, pathological worsening occurred while hippocampal insulin signaling was upregulated. Together, our data demonstrate that DIO worsens τ phosphorylation and learning abilities in τ transgenic mice independently from peripheral/central insulin resistance.
doi:10.2337/db12-0866
PMCID: PMC3636620  PMID: 23250356
5.  Activation of intestinal peroxisome proliferator-activated receptor-α increases high-density lipoprotein production 
European Heart Journal  2012;34(32):2566-2574.
Aims
Peroxisome Proliferator-Activated Receptor (PPAR) α is a transcription factor controlling lipid metabolism in liver, heart, muscle and macrophages. PPARα-activation increases plasma HDL-cholesterol and exerts hypotriglyceridemic actions via the liver. However, the intestine expresses PPARα, produces HDL and chylomicrons and is exposed to diet-derived PPARα ligands. Therefore, we examined the effects of PPARα-activation on intestinal lipid and lipoprotein metabolism.
Methods and Results
The impact of PPARα-activation was evaluated in term of HDL-related gene expression in mice, ex-vivo in human jejunal biopsies and in Caco-2/TC7 cells. ApoAI/HDL secretion, cholesterol esterification and trafficking were also studied in-vitro.
In parallel to improving plasma lipid profiles and increasing liver and intestinal expression of fatty-acid-oxidation genes, treatment with the dual PPARα/δ-ligand GFT505 resulted in a more pronounced increase of plasma HDL compared to fenofibrate in mice. GFT505, but not fenofibrate, increased the expression of HDL-production genes such as apolipoprotein-AI and ATP-Binding-Cassette-A1 transporter in murine intestines. A similar increase was observed upon PPARα-activation of human biopsies and Caco-2/TC7 cells. Additionally, HDL secretion by Caco-2/TC7 cells increased. Moreover, PPARα-activation decreased the cholesterol-esterification capacity of Caco-2/TC7 cells, modified cholesterol trafficking and reduced apolipoprotein-B secretion.
Conclusions
PPARα-activation reduces cholesterol esterification, suppresses chylomicron- and increases HDL-secretion by enterocytes. These results identify the intestine as a target organ of PPARα-ligands with entero-hepatic tropism to reduce atherogenic dyslipidemia.
doi:10.1093/eurheartj/ehs227
PMCID: PMC3984589  PMID: 22843443
Animals; Apolipoproteins B; metabolism; Butyrates; pharmacology; Caco-2 Cells; Cells, Cultured; Chalcones; pharmacology; Enterocytes; metabolism; Esterification; physiology; Fatty Acids; metabolism; Female; Humans; Jejunum; metabolism; Lipoproteins, HDL; metabolism; Mice; Mice, Knockout; PPAR alpha; antagonists & inhibitors; physiology; Phenylurea Compounds; pharmacology; Propionates; pharmacology; PPARα; intestine; HDL; dyslipidemia
6.  Beneficial Metabolic Effects of Rapamycin Are Associated with Enhanced Regulatory Cells in Diet-Induced Obese Mice 
PLoS ONE  2014;9(4):e92684.
The “mechanistic target of rapamycin” (mTOR) is a central controller of growth, proliferation and/or motility of various cell-types ranging from adipocytes to immune cells, thereby linking metabolism and immunity. mTOR signaling is overactivated in obesity, promoting inflammation and insulin resistance. Therefore, great interest exists in the development of mTOR inhibitors as therapeutic drugs for obesity or diabetes. However, despite a plethora of studies characterizing the metabolic consequences of mTOR inhibition in rodent models, its impact on immune changes associated with the obese condition has never been questioned so far. To address this, we used a mouse model of high-fat diet (HFD)-fed mice with and without pharmacologic mTOR inhibition by rapamycin. Rapamycin was weekly administrated to HFD-fed C57BL/6 mice for 22 weeks. Metabolic effects were determined by glucose and insulin tolerance tests and by indirect calorimetry measures of energy expenditure. Inflammatory response and immune cell populations were characterized in blood, adipose tissue and liver. In parallel, the activities of both mTOR complexes (e. g. mTORC1 and mTORC2) were determined in adipose tissue, muscle and liver. We show that rapamycin-treated mice are leaner, have enhanced energy expenditure and are protected against insulin resistance. These beneficial metabolic effects of rapamycin were associated to significant changes of the inflammatory profiles of both adipose tissue and liver. Importantly, immune cells with regulatory functions such as regulatory T-cells (Tregs) and myeloid-derived suppressor cells (MDSCs) were increased in adipose tissue. These rapamycin-triggered metabolic and immune effects resulted from mTORC1 inhibition whilst mTORC2 activity was intact. Taken together, our results reinforce the notion that controlling immune regulatory cells in metabolic tissues is crucial to maintain a proper metabolic status and, more generally, comfort the need to search for novel pharmacological inhibitors of the mTOR signaling pathway to prevent and/or treat metabolic diseases.
doi:10.1371/journal.pone.0092684
PMCID: PMC3977858  PMID: 24710396
7.  Metformin interferes with bile acid homeostasis through AMPK-FXR crosstalk 
The Journal of Clinical Investigation  2014;124(3):1037-1051.
The nuclear bile acid receptor farnesoid X receptor (FXR) is an important transcriptional regulator of bile acid, lipid, and glucose metabolism. FXR is highly expressed in the liver and intestine and controls the synthesis and enterohepatic circulation of bile acids. However, little is known about FXR-associated proteins that contribute to metabolic regulation. Here, we performed a mass spectrometry–based search for FXR-interacting proteins in human hepatoma cells and identified AMPK as a coregulator of FXR. FXR interacted with the nutrient-sensitive kinase AMPK in the cytoplasm of target cells and was phosphorylated in its hinge domain. In cultured human and murine hepatocytes and enterocytes, pharmacological activation of AMPK inhibited FXR transcriptional activity and prevented FXR coactivator recruitment to promoters of FXR-regulated genes. Furthermore, treatment with AMPK activators, including the antidiabetic biguanide metformin, inhibited FXR agonist induction of FXR target genes in mouse liver and intestine. In a mouse model of intrahepatic cholestasis, metformin treatment induced FXR phosphorylation, perturbed bile acid homeostasis, and worsened liver injury. Together, our data indicate that AMPK directly phosphorylates and regulates FXR transcriptional activity to precipitate liver injury under conditions favoring cholestasis.
doi:10.1172/JCI68815
PMCID: PMC3938262  PMID: 24531544
8.  Rev-erb-α modulates skeletal muscle oxidative capacity by regulating mitochondrial biogenesis and autophagy 
Nature medicine  2013;19(8):1039-1046.
The nuclear receptor Rev-erb-α modulates hepatic lipid and glucose metabolism, adipogenesis and the inflammatory response in macrophages. We show here that Rev-erb-α is highly expressed in oxidative skeletal muscle and plays a role in mitochondrial biogenesis and oxidative function, in gain- and loss-of function studies. Rev-erb-α-deficiency in skeletal muscle leads to reduced mitochondrial content and oxidative function, resulting in compromised exercise capacity. This phenotype was recapitulated in isolated fibers and in muscle cells upon Rev-erbα knock-down, while Rev-erb-α over-expression increased the number of mitochondria with improved respiratory capacity. Rev-erb-α-deficiency resulted in deactivation of the Stk11–Ampk–Sirt1–Ppargc1-α signaling pathway, whereas autophagy was up-regulated, resulting in both impaired mitochondrial biogenesis and increased clearance. Muscle over-expression or pharmacological activation of Rev-erb-α increased respiration and exercise capacity. This study identifies Rev-erb-α as a pharmacological target which improves muscle oxidative function by modulating gene networks controlling mitochondrial number and function.
doi:10.1038/nm.3213
PMCID: PMC3737409  PMID: 23852339
Rev-erb-α; skeletal muscle; oxidative capacity; mitochondrial biogenesis; autophagy
9.  Farnesoid X Receptor Inhibits the Transcriptional Activity of Carbohydrate Response Element Binding Protein in Human Hepatocytes 
Molecular and Cellular Biology  2013;33(11):2202-2211.
The glucose-activated transcription factor carbohydrate response element binding protein (ChREBP) induces the expression of hepatic glycolytic and lipogenic genes. The farnesoid X receptor (FXR) is a nuclear bile acid receptor controlling bile acid, lipid, and glucose homeostasis. FXR negatively regulates hepatic glycolysis and lipogenesis in mouse liver. The aim of this study was to determine whether FXR regulates the transcriptional activity of ChREBP in human hepatocytes and to unravel the underlying molecular mechanisms. Agonist-activated FXR inhibits glucose-induced transcription of several glycolytic genes, including the liver-type pyruvate kinase gene (L-PK), in the immortalized human hepatocyte (IHH) and HepaRG cell lines. This inhibition requires the L4L3 region of the L-PK promoter, known to bind the transcription factors ChREBP and hepatocyte nuclear factor 4α (HNF4α). FXR interacts directly with ChREBP and HNF4α proteins. Analysis of the protein complex bound to the L4L3 region reveals the presence of ChREBP, HNF4α, FXR, and the transcriptional coactivators p300 and CBP at high glucose concentrations. FXR activation does not affect either FXR or HNF4α binding to the L4L3 region but does result in the concomitant release of ChREBP, p300, and CBP and in the recruitment of the transcriptional corepressor SMRT. Thus, FXR transrepresses the expression of genes involved in glycolysis in human hepatocytes.
doi:10.1128/MCB.01004-12
PMCID: PMC3648076  PMID: 23530060
10.  Human adipose tissue macrophages display activation of cancer-related pathways 
The Journal of Biological Chemistry  2012;287(26):21904-21913.
Obesity is associated with a significantly increased risk for cancer suggesting that adipose tissue dysfunctions might play a crucial role therein. Macrophages play important roles in adipose tissue as well as in cancers. Here, we studied whether human adipose tissue macrophages (ATM) modulate cancer cell function.
Therefore, ATM were isolated and compared to monocyte-derived macrophages (MDM) from the same obese patients. ATM, but not MDM, were found to secrete factors inducing inflammation and lipid accumulation in human T47D and HT-29 cancer cells. Gene expression profile comparison of ATM and MDM revealed over-expression of functional clusters, such as cytokine-cytokine receptor interaction (especially CXC-chemokine) signalling as well as cancer-related pathways, in ATM. Comparison with gene expression profiles of human tumour-associated macrophages (TAM) showed that ATM, but not MDM resemble TAM. Indirect co-culture experiments demonstrated that factors secreted by pre-adipocytes, but not mature adipocytes, confer an ATM-like phenotype to MDM. Finally, the concentrations of ATM secreted factors related to cancer are elevated in serum of obese subjects. In conclusion, ATM may thus modulate the cancer cell phenotype.
doi:10.1074/jbc.M111.315200
PMCID: PMC3381151  PMID: 22511784
Adipocytes; cytology; Adipose Tissue; metabolism; Azo Compounds; pharmacology; Cell Line, Tumor; Chemokines; metabolism; Disease Progression; Gene Expression Regulation, Neoplastic; Humans; Immunohistochemistry; methods; Inflammation; Macrophages; cytology; metabolism; Neoplasms; metabolism; Obesity; metabolism; Oligonucleotide Array Sequence Analysis; Phenotype; macrophages; obesity; cancer; adipose tissue; chemokines
11.  Increased Atherosclerotic Lesions in LDL Receptor Deficient Mice With Hematopoietic Nuclear Receptor Rev‐erbα Knock‐ Down 
Background
Nuclear receptor Rev‐erbα plays important roles in circadian clock timing, lipid metabolism, adipogenesis, and vascular inflammation. However, the role of Rev‐erbα in atherosclerotic lesion development has not been assessed in vivo.
Methods and Results
The nuclear receptor Rev‐erbα was knocked down in mouse haematopoietic cells by means of shRNA‐lentiviral transduction, followed by bone marrow transplantation into LDL receptor knockout mice. The Rev‐erbα protein in peripheral macrophage was reduced by 70% as compared to control mice injected with nontargeting shRNA lentivirus‐transduced bone marrow. A significant increase in atherosclerotic lesions was observed around the aorta valves as well as upon en face aorta analysis of Rev‐erbα knock‐down bone marrow recipients (P<0.01) as compared to the control mice, while plasma cholesterol, phospholipid, and triacylglycerol levels were not affected. Overexpression of Rev‐erbα in bone marrow mononuclear cells decreased inflammatory M1 while increasing M2 macrophage markers, while Rev‐erbα knock down increased the macrophage inflammatory phenotype in vitro and in vivo. Furthermore, treatment of differentiating macrophages with the Rev‐erbα ligand heme promoted expression of antiinflammatory M2 markers.
Conclusions
These observations identify hematopoietic cell Rev‐erbα as a new modulator of atherogenesis in mice.
doi:10.1161/JAHA.113.000235
PMCID: PMC3828791  PMID: 23963755
atherosclerosis; macrophages; Rev‐erbα
12.  p16INK4a deficiency promotes IL-4-induced polarization and inhibits proinflammatory signaling in macrophages 
Blood  2011;118(9):2556-2566.
The CDKN2A locus, which contains the tumor suppressor gene p16INK4a, is associated with an increased risk of age-related inflammatory diseases, such as cardiovascular disease and type 2 diabetes, in which macrophages play a crucial role. Monocytes can polarize towards classically (CAMφ) or alternatively (AAMφ) activated macrophages. However, the molecular mechanisms underlying the acquisition of these phenotypes are not well defined.
Here, we show that p16INK4a-deficiency (p16−/−) modulates the macrophage phenotype. Transcriptome analysis revealed that p16−/− bone marrow-derived macrophages (BMDM) exhibit a phenotype resembling interleukin (IL)-4-induced macrophage polarization. In line with this observation, p16−/− BMDM displayed a decreased response to classically polarizing IFNγ and LPS and an increased sensitivity to alternative polarization by IL-4. Furthermore, mice transplanted with p16−/− bone marrow displayed higher hepatic AAMφ marker expression levels upon Schistosoma mansoni infection, an in vivo model of AAMφ phenotype-skewing. Surprisingly, p16−/− BMDM did not display increased IL-4-induced STAT6 signaling, but decreased IFNγ-induced STAT1 and LPS-induced IKKα,β phosphorylation. This decrease correlated with decreased JAK2 phosphorylation and with higher levels of inhibitory acetylation of STAT1 and IKKα,β. These findings identify p16INK4a as a modulator of macrophage activation and polarization via the JAK2-STAT1 pathway with possible roles in inflammatory diseases.
doi:10.1182/blood-2010-10-313106
PMCID: PMC3677739  PMID: 21636855
Animals; Bone Marrow Transplantation; Cyclin-Dependent Kinase Inhibitor p16; deficiency; physiology; Cytokines; biosynthesis; Genes, p16; I-kappa B Kinase; physiology; Inflammation; genetics; Interferon-gamma; pharmacology; Interleukin-4; pharmacology; Janus Kinase 2; physiology; Lipopolysaccharides; pharmacology; Liver; metabolism; pathology; Macrophage Activation; drug effects; Macrophages; drug effects; physiology; Mice; Mice, Inbred C57BL; Phosphorylation; Protein Processing, Post-Translational; Radiation Chimera; STAT1 Transcription Factor; physiology; STAT6 Transcription Factor; physiology; Schistosomiasis; immunology; Signal Transduction
13.  The Elongation Complex Components BRD4 and MLLT3/AF9 Are Transcriptional Coactivators of Nuclear Retinoid Receptors 
PLoS ONE  2013;8(6):e64880.
Nuclear all-trans retinoic acid receptors (RARs) initiate early transcriptional events which engage pluripotent cells to differentiate into specific lineages. RAR-controlled transactivation depends mostly on agonist-induced structural transitions in RAR C-terminus (AF-2), thus bridging coactivators or corepressors to chromatin, hence controlling preinitiation complex assembly. However, the contribution of other domains of RAR to its overall transcriptional activity remains poorly defined. A proteomic characterization of nuclear proteins interacting with RAR regions distinct from the AF-2 revealed unsuspected functional properties of the RAR N-terminus. Indeed, mass spectrometry fingerprinting identified the Bromodomain-containing protein 4 (BRD4) and ALL1-fused gene from chromosome 9 (AF9/MLLT3), known to associate with and regulates the activity of Positive Transcription Elongation Factor b (P-TEFb), as novel RAR coactivators. In addition to promoter sequences, RAR binds to genomic, transcribed regions of retinoid-regulated genes, in association with RNA polymerase II and as a function of P-TEFb activity. Knockdown of either AF9 or BRD4 expression affected differentially the neural differentiation of stem cell-like P19 cells. Clusters of retinoid-regulated genes were selectively dependent on BRD4 and/or AF9 expression, which correlated with RAR association to transcribed regions. Thus RAR establishes physical and functional links with components of the elongation complex, enabling the rapid retinoid-induced induction of genes required for neuronal differentiation. Our data thereby extends the previously known RAR interactome from classical transcriptional modulators to components of the elongation machinery, and unravel a functional role of RAR in transcriptional elongation.
doi:10.1371/journal.pone.0064880
PMCID: PMC3677938  PMID: 23762261
14.  Impaired alternative macrophage differentiation of peripheral blood mononuclear cells from obese subjects 
Visceral obesity, a chronic, low-grade inflammatory disease, predisposes to the metabolic syndrome, type 2 diabetes and its cardiovascular complications. Adipose tissue is not a passive storehouse for fat, but an endocrine organ synthesizing and releasing a variety of bioactive molecules, some of which are produced by infiltrated immune-inflammatory cells including macrophages. Two different sub-populations of macrophages have been identified in adipose tissue: pro-inflammatory “classical” M1 and anti-inflammatory “alternative” M2 macrophages and their ratio is suggested to influence the metabolic complications of obesity. These macrophages derive primarily from peripheral blood mononuclear cells (PBMC). We hypothesized that obesity and the metabolic syndrome modulate PBMC functions. Therefore, alteration of the monocyte response, and more specifically their ability to differentiate toward alternative anti-inflammatory macrophages was assessed in PBMC isolated from lean and obese subjects with or without alterations in glucose homeostasis. Our results indicate that PBMC from obese subjects have an altered expression of M2 markers and that their monocytes are less susceptible to differentiate toward an alternative phenotype. Thus PBMC in obesity are programmed, which may contribute to the inflammatory dysregulation and increased susceptibility to inflammatory diseases in these patients.
doi:10.1177/1479164111430242
PMCID: PMC3655375  PMID: 22192929
Adipose Tissue; metabolism; Adult; Cell Differentiation; Diabetes Mellitus, Type 2; complications; metabolism; Female; Gene Expression Profiling; Humans; Inflammation; etiology; metabolism; Inflammation Mediators; metabolism; Leukocytes, Mononuclear; metabolism; Macrophages; cytology; metabolism; Middle Aged; Obesity; complications; metabolism; Phenotype; obesity; macrophages; polarization; inflammation; gene expression
15.  11β-hydroxysteroid dehydrogenase type 1 deficiency in bone marrow-derived cells reduces atherosclerosis 
The FASEB Journal  2013;27(4):1519-1531.
11β-Hydroxysteroid dehydrogenase type-1 (11β-HSD1) converts inert cortisone into active cortisol, amplifying intracellular glucocorticoid action. 11β-HSD1 deficiency improves cardiovascular risk factors in obesity but exacerbates acute inflammation. To determine the effects of 11β-HSD1 deficiency on atherosclerosis and its inflammation, atherosclerosis-prone apolipoprotein E-knockout (ApoE-KO) mice were treated with a selective 11β-HSD1 inhibitor or crossed with 11β-HSD1-KO mice to generate double knockouts (DKOs) and challenged with an atherogenic Western diet. 11β-HSD1 inhibition or deficiency attenuated atherosclerosis (74–76%) without deleterious effects on plaque structure. This occurred without affecting plasma lipids or glucose, suggesting independence from classical metabolic risk factors. KO plaques were not more inflamed and indeed had 36% less T-cell infiltration, associated with 38% reduced circulating monocyte chemoattractant protein-1 (MCP-1) and 36% lower lesional vascular cell adhesion molecule-1 (VCAM-1). Bone marrow (BM) cells are key to the atheroprotection, since transplantation of DKO BM to irradiated ApoE-KO mice reduced atherosclerosis by 51%. 11β-HSD1-null macrophages show 76% enhanced cholesterol ester export. Thus, 11β-HSD1 deficiency reduces atherosclerosis without exaggerated lesional inflammation independent of metabolic risk factors. Selective 11β-HSD1 inhibitors promise novel antiatherosclerosis effects over and above their benefits for metabolic risk factors via effects on BM cells, plausibly macrophages.—Kipari, T., Hadoke, P. W. F., Iqbal, J., Man, T. Y., Miller, E., Coutinho, A. E., Zhang, Z., Sullivan, K. M., Mitic, T., Livingstone, D. E. W., Schrecker, C., Samuel, K., White, C. I., Bouhlel, M. A., Chinetti-Gbaguidi, G., Staels, B., Andrew, R., Walker, B. R., Savill, J. S., Chapman, K. E., Seckl, J. R. 11β-hydroxysteroid dehydrogenase type 1 deficiency in bone marrow-derived cells reduces atherosclerosis.
doi:10.1096/fj.12-219105
PMCID: PMC3606528  PMID: 23303209
atherogenesis; glucocorticoids; inflammation
16.  Hepatic glucose sensing is required to preserve β cell glucose competence 
The Journal of Clinical Investigation  2013;123(4):1662-1676.
Liver glucose metabolism plays a central role in glucose homeostasis and may also regulate feeding and energy expenditure. Here we assessed the impact of glucose transporter 2 (Glut2) gene inactivation in adult mouse liver (LG2KO mice). Loss of Glut2 suppressed hepatic glucose uptake but not glucose output. In the fasted state, expression of carbohydrate-responsive element-binding protein (ChREBP) and its glycolytic and lipogenic target genes was abnormally elevated. Feeding, energy expenditure, and insulin sensitivity were identical in LG2KO and control mice. Glucose tolerance was initially normal after Glut2 inactivation, but LG2KO mice exhibited progressive impairment of glucose-stimulated insulin secretion even though β cell mass and insulin content remained normal. Liver transcript profiling revealed a coordinated downregulation of cholesterol biosynthesis genes in LG2KO mice that was associated with reduced hepatic cholesterol in fasted mice and reduced bile acids (BAs) in feces, with a similar trend in plasma. We showed that chronic BAs or farnesoid X receptor (FXR) agonist treatment of primary islets increases glucose-stimulated insulin secretion, an effect not seen in islets from Fxr–/– mice. Collectively, our data show that glucose sensing by the liver controls β cell glucose competence and suggest BAs as a potential mechanistic link.
doi:10.1172/JCI65538
PMCID: PMC3613916  PMID: 23549084
17.  Macrophage polarization in metabolic disorders: functions and regulation 
Current Opinion in Lipidology  2011;22(5):365-372.
Purpose of review
To discuss recent findings on the role and regulation of macrophage polarization in obesity and atherosclerosis.
Recent findings
Macrophages infiltrate the vascular wall during atherosclerosis and adipose tissue during obesity. At least two distinct sub-populations with different functions, the classically (M1) and the alternatively (M2) activated macrophages, have been found in these tissues. Reciprocal skewing of macrophage polarization between the M1 and M2 states is a process modulated by diet, humoral and transcription factors, such as the nuclear receptor Peroxisome Proliferator-Activated Receptor gamma (PPARγ).
Summary
Recent literature highlights the importance not only of the number of infiltrated macrophages, but also their activation in the maintenance of the inflammation state. Identifying mechanisms and molecules able to modify the balance between M1 and M2 represents a promising field of research.
doi:10.1097/MOL.0b013e32834a77b4
PMCID: PMC3565956  PMID: 21825981
Adipose Tissue; immunology; Animals; Humans; Inflammation; immunology; Macrophages; cytology; metabolism; Metabolic Diseases; immunology; macrophages; obesity; atherosclerosis; nuclear receptors
18.  Impaired Expression of the Inducible cAMP Early Repressor Accounts for Sustained Adipose CREB Activity in Obesity 
Diabetes  2011;60(12):3169-3174.
OBJECTIVE
Increase in adipose cAMP-responsive element\x{2013}binding protein (CREB) activity promotes adipocyte dysfunction and systemic insulin resistance in obese mice. This is achieved by increasing the expression of activating transcription factor 3 (ATF3). In this study, we investigated whether impaired expression of the inducible cAMP early repressor (ICER), a transcriptional antagonist of CREB, is responsible for the increased CREB activity in adipocytes of obese mice and humans.
RESEARCH DESIGN AND METHODS
Total RNA and nuclear proteins were prepared from visceral adipose tissue (VAT) of human nonobese or obese subjects and white adipose tissue (WAT) of C57Bl6-Rj mice that were fed with normal or high-fat diet for 16 weeks. The expression of genes was monitored by real-time PCR, Western blotting, and electromobility shift assays. RNA interference was used to silence the expression of Icer.
RESULTS
The expression of Icer/ICER was reduced in VAT and WAT of obese humans and mice, respectively. Diminution of Icer/ICER was restricted to adipocytes and was accompanied by a rise of Atf3/ATF3 and diminution of Adipoq/ADIPOQ and Glut4/GLUT4. Silencing the expression of Icer in 3T3-L1 adipocytes mimicked the results observed in human and mice cells and hampered glucose uptake, thus confirming the requirement of Icer for appropriate adipocyte function.
CONCLUSIONS
Impaired expression of ICER contributes to elevation in CREB target genes and, therefore, to the development of insulin resistance in obesity.
doi:10.2337/db10-1743
PMCID: PMC3219947  PMID: 21998402
19.  The novel antibacterial compound walrycin A induces human PXR transcriptional activity 
Toxicological Sciences  2012;127(1):225-235.
The human pregnane X receptor (PXR) is a ligand-regulated transcription factor belonging to the nuclear receptor superfamily. PXR is activated by a large, structurally diverse, set of endogenous and xenobiotic compounds, and coordinates the expression of genes central to metabolism and excretion of potentially harmful chemicals and therapeutic drugs in humans. Walrycin A is a novel antibacterial compound targeting the WalK/WalR two-component signal transduction system of Gram (+) bacteria. Here we report that, in hepatoma cells, walrycin A potently activates a gene set known to be regulated by the xenobiotic sensor PXR. Walrycin A was as efficient as the reference PXR agonist rifampicin to activate PXR in a transactivation assay at non cytoxic concentrations. Using a limited proteolysis assay, we show that walrycin A induces conformational changes at a concentration which correlates with walrycin A ability to enhance the expression of prototypic target genes, suggesting that walrycin A interacts with PXR. The activation of the canonical human PXR target gene CYP3A4 by walrycin A is dose- and PXR-dependent. Finally, in silico docking experiments suggest that the walrycin A oxidation product Russig’s blue is the actual a ligand for PXR. Taken together, these results identify walrycin A as novel human PXR activator.
doi:10.1093/toxsci/kfs073
PMCID: PMC3435511  PMID: 22314385
Anti-Bacterial Agents; toxicity; Cell Line, Transformed; Cell Survival; drug effects; Computational Biology; Computer Simulation; Cytochrome P-450 CYP3A; biosynthesis; genetics; Gene Expression; drug effects; Hepatocytes; drug effects; metabolism; Humans; Naphthols; toxicity; Oligonucleotide Array Sequence Analysis; Protein Binding; Quantitative Structure-Activity Relationship; RNA, Small Interfering; administration & dosage; genetics; Real-Time Polymerase Chain Reaction; Receptors, Steroid; drug effects; genetics; Rifampin; pharmacology; Transfection; Walrycin A; Pregnane X Receptor; Nuclear Receptor; CYP3A4; Ligand Binding Domain; Xenobiotic
20.  Coordinated Regulation of PPARγ Expression and Activity through Control of Chromatin Structure in Adipogenesis and Obesity 
PPAR Research  2012;2012:164140.
The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) is required for differentiation and function of mature adipocytes. Its expression is induced during adipogenesis where it plays a key role in establishing the transcriptome of terminally differentiated white fat cells. Here, we review findings indicating that PPARγ expression and activity are intricately regulated through control of chromatin structure. Hierarchical and combinatorial activation of transcription factors, noncoding RNAs, and chromatin remodelers allows for temporally controlled expression of PPARγ and its target genes through sequential chromatin remodelling. In obesity, these regulatory pathways may be altered and lead to modified PPARγ activity.
doi:10.1155/2012/164140
PMCID: PMC3444001  PMID: 22991504
21.  Effects of the New Dual PPARα/δ Agonist GFT505 on Lipid and Glucose Homeostasis in Abdominally Obese Patients With Combined Dyslipidemia or Impaired Glucose Metabolism 
Diabetes Care  2011;34(9):2008-2014.
OBJECTIVE
We evaluated the metabolic effects and tolerability of GFT505, a novel dual peroxisome proliferator–activated receptor α/δ agonist, in abdominally obese patients with either combined dyslipidemia or prediabetes.
RESEARCH DESIGN AND METHODS
The S1 study was conducted in 94 patients with combined dyslipidemia while the S2 study was conducted in 47 patients with prediabetes. Participants were randomly assigned in a double-blind manner to GFT505 at 80 mg/day or placebo for 28 (S1) or 35 (S2) days. Primary efficacy end points were changes from baseline at week 4 in both fasting plasma triglycerides and HDL cholesterol in the S1 group and 2-h glucose upon oral glucose tolerance test in the S2 group.
RESULTS
In comparison with placebo, GFT505 significantly reduced fasting plasma triglycerides (S1: least squares means −16.7% [95% one-sided CI −∞ to −5.3], P = 0.005; S2: −24.8% [−∞ to −10.5], P = 0.0003) and increased HDL cholesterol (S1: 7.8% [3.0 to ∞], P = 0.004; S2: 9.3% [1.7 to ∞], P = 0.009) in both studies, whereas LDL cholesterol only decreased in S2 (−11.0% [ −∞ to −3.5], P = 0.002). In S2, GFT505 did not reduce 2-h glucose (−0.52 mmol/L [−∞ to 0.61], P = 0.18) but led to a significant decrease of homeostasis model assessment of insulin resistance (−31.4% [−∞ to 12.5], P = 0.001), fasting plasma glucose (−0.37 mmol/L [−∞ to −0.10], P = 0.01) and fructosamine (−3.6% [−∞ to −0.20], P = 0.02). GFT505 also reduced γ glutamyl transferase levels in both studies (S1: −19.9% [−∞ to −12.8], P < 0.0001; S2: −15.1% [−∞ to −1.1], P = 0.004). No specific adverse safety signals were reported during the studies.
CONCLUSIONS
GFT505 may be considered a new drug candidate for the treatment of lipid and glucose disorders associated with the metabolic syndrome.
doi:10.2337/dc11-0093
PMCID: PMC3161281  PMID: 21816979
22.  Peroxisome proliferator-activated receptor ɣ activation induces 11β-hydroxysteroid dehydrogenase type 1 activity in human alternative macrophages 
Objectives
11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) catalyses the intracellular reduction of inactive cortisone to active cortisol, the natural ligand activating the glucocorticoid receptor (GR). Peroxisome Proliferator-Activated Receptor gamma (PPARγ) is a nuclear receptor controlling inflammation, lipid metabolism and the macrophage polarization state. In this study, we investigated the impact of macrophage polarization on the expression and activity of 11β-HSD1 and the role of PPAR therein.
Methods and Results
11β-HSD1 gene expression is higher in pro-inflammatory M1 and anti-inflammatory M2 macrophages than in resting macrophages (RM), whereas its activity is highest in M2 macrophages. Interestingly, PPARγ activation induces 11β-HSD1 enzyme activity in M2 macrophages, but not in RM or M1 macrophages. Consequently, human M2 macrophages displayed enhanced responsiveness to the 11β-HSD1 substrate cortisone, an effect amplified by PPAR -induction of 11β-HSD1 activity, as illustrated by an increased expression of GR target genes.
Conclusions
Our data identify a positive cross-talk between PPARγ and GR in human M2 macrophages via the induction of 11β-HSD1 expression and activity.
doi:10.1161/ATVBAHA.111.241364
PMCID: PMC3428270  PMID: 22207732
11-beta-Hydroxysteroid Dehydrogenase Type 1; biosynthesis; genetics; Cells, Cultured; Cortisone; metabolism; Enzyme Induction; Genes, Reporter; Humans; Hydrocortisone; metabolism; Inflammation; enzymology; genetics; immunology; Interleukin-4; metabolism; Macrophages; drug effects; enzymology; immunology; PPAR gamma; agonists; genetics; metabolism; RNA Interference; Receptors, Glucocorticoid; metabolism; Thiazolidinediones; pharmacology; Time Factors; Transfection; 11beta-HSDI; PPARgamma; human alternative macrophages; inflammation; GR
23.  Genome-Wide Profiling of Liver X Receptor, Retinoid X Receptor, and Peroxisome Proliferator-Activated Receptor α in Mouse Liver Reveals Extensive Sharing of Binding Sites 
Molecular and Cellular Biology  2012;32(4):852-867.
The liver X receptors (LXRs) are nuclear receptors that form permissive heterodimers with retinoid X receptor (RXR) and are important regulators of lipid metabolism in the liver. We have recently shown that RXR agonist-induced hypertriglyceridemia and hepatic steatosis in mice are dependent on LXRs and correlate with an LXR-dependent hepatic induction of lipogenic genes. To further investigate the roles of RXR and LXR in the regulation of hepatic gene expression, we have mapped the ligand-regulated genome-wide binding of these factors in mouse liver. We find that the RXR agonist bexarotene primarily increases the genomic binding of RXR, whereas the LXR agonist T0901317 greatly increases both LXR and RXR binding. Functional annotation of putative direct LXR target genes revealed a significant association with classical LXR-regulated pathways as well as peroxisome proliferator-activated receptor (PPAR) signaling pathways, and subsequent chromatin immunoprecipitation-sequencing (ChIP-seq) mapping of PPARα binding demonstrated binding of PPARα to 71 to 88% of the identified LXR-RXR binding sites. The combination of sequence analysis of shared binding regions and sequential ChIP on selected sites indicate that LXR-RXR and PPARα-RXR bind to degenerate response elements in a mutually exclusive manner. Together, our findings suggest extensive and unexpected cross talk between hepatic LXR and PPARα at the level of binding to shared genomic sites.
doi:10.1128/MCB.06175-11
PMCID: PMC3272984  PMID: 22158963
24.  Farnesoid X Receptor Deficiency Improves Glucose Homeostasis in Mouse Models of Obesity 
Diabetes  2011;60(7):1861-1871.
OBJECTIVE
Bile acids (BA) participate in the maintenance of metabolic homeostasis acting through different signaling pathways. The nuclear BA receptor farnesoid X receptor (FXR) regulates pathways in BA, lipid, glucose, and energy metabolism, which become dysregulated in obesity. However, the role of FXR in obesity and associated complications, such as dyslipidemia and insulin resistance, has not been directly assessed.
RESEARCH DESIGN AND METHODS
Here, we evaluate the consequences of FXR deficiency on body weight development, lipid metabolism, and insulin resistance in murine models of genetic and diet-induced obesity.
RESULTS
FXR deficiency attenuated body weight gain and reduced adipose tissue mass in both models. Surprisingly, glucose homeostasis improved as a result of an enhanced glucose clearance and adipose tissue insulin sensitivity. In contrast, hepatic insulin sensitivity did not change, and liver steatosis aggravated as a result of the repression of β-oxidation genes. In agreement, liver-specific FXR deficiency did not protect from diet-induced obesity and insulin resistance, indicating a role for nonhepatic FXR in the control of glucose homeostasis in obesity. Decreasing elevated plasma BA concentrations in obese FXR-deficient mice by administration of the BA sequestrant colesevelam improved glucose homeostasis in a FXR-dependent manner, indicating that the observed improvements by FXR deficiency are not a result of indirect effects of altered BA metabolism.
CONCLUSIONS
Overall, FXR deficiency in obesity beneficially affects body weight development and glucose homeostasis.
doi:10.2337/db11-0030
PMCID: PMC3121443  PMID: 21593203
25.  Farnesoid x receptor deficiency improves glucose homeostasis in mouse models of obesity 
Diabetes  2011;60(7):1861-1871.
Objective
Bile acids (BA) participate in the maintenance of metabolic homeostasis acting through different signaling pathways. The nuclear BA receptor farnesoid X receptor (FXR) regulates pathways in BA, lipid, glucose and energy metabolism which become dysregulated in obesity. However, the role of FXR in obesity and associated complications, such as dyslipidemia and insulin resistance, has not been directly assessed.
Research Design and Methods
Here, we evaluate the consequences of FXR-deficiency on body weight development, lipid metabolism and insulin resistance in murine models of genetic and diet-induced obesity.
Results
FXR-deficiency attenuated body weight gain and reduced adipose tissue mass in both models. Surprisingly, glucose homeostasis improved due to an enhanced glucose clearance and adipose tissue insulin sensitivity. In contrast, hepatic insulin sensitivity did not change, and liver steatosis aggravated due to the repression of β-oxidation genes. In agreement, liver-specific FXR-deficiency did not protect from diet-induced obesity and insulin resistance indicating a role for non-hepatic FXR in the control of glucose homeostasis in obesity. Decreasing elevated plasma BA concentrations in obese FXR-deficient mice by administration of the BA sequestrant colesevelam improved glucose homeostasis in a FXR-dependent manner indicating that the observed improvements by FXR-deficiency are not due to indirect effects of altered BA metabolism.
Conclusions
Overall, FXR-deficiency in obesity beneficially affects body weight development and glucose homeostasis.
doi:10.2337/db11-0030
PMCID: PMC3121443  PMID: 21593203
FXR; bile acids; obesity; glucose homeostasis; insulin resistance; energy metabolism; triglyceride metabolism; bile acid sequestrants

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