Expression Of PPARγ Target Genes Research Articles

Relaxin activation of PPAR[gamma] is ligand independent

Peroxisome proliferator‐activated receptor gamma (PPARγ) has many antifibrotic effects similar to those of relaxin (Rlx), raising the possibility that Rlx's antifibrotic effects may involve activation of the PPARγ pathway. To test this possibility, the Rlx effect on PPAR activity was assessed using a luciferase reporter vector fused to the PPAR response element (PPRE). Rlx increased the PPRE activity in a dose dependent manner. The PPARγ agonists increased the PPRE activity. The combined effect of Rlx and PPARγ agonists on PPRE activity was more than additive. Rlx increased the expression of PPARγ target genes, and when Rlx was combined with PPARγ agonists the effect was synergistic. PPARγ knockdown reduced the Rlx effect on PPRE activity, suggesting that part of Rlx effect is mediated through PPARγ. A PPARγ ligand blocker reduced PPRE activation and PPARγ target genes expression in response to PPARγ agonists but not Rlx, suggesting that Rlx stimulates ligand‐independent PPAR activation. Moreover, Rlx further increased the PPRE activity in cells overexpressing PPARγ without exogenous PPARγ ligands. PPARγ has diverse biological implications in broad range of diseases and the synergistic effects of PPARγ agonist with Rlx and better understanding of the signaling pathway will help to develop new therapies targeting PPARγ.Funding: NIAAADepartment of Veterans Affairs

FoxO1 Haploinsufficiency Protects Against High-Fat Diet–Induced Insulin Resistance With Enhanced Peroxisome Proliferator–Activated Receptor γ Activation in Adipose Tissue

OBJECTIVEForkhead box O (FoxO) transcription factors represent evolutionarily conserved targets of insulin signaling, regulating metabolism and cellular differentiation in response to changes in nutrient availability. Although the FoxO1 isoform is known to play a key role in adipogenesis, its physiological role in differentiated adipose tissue remains unclear.RESEARCH DESIGN AND METHODSIn this study, we analyzed the phenotype of FoxO1 haploinsufficient mice to investigate the role of FoxO1 in high-fat diet–induced obesity and adipose tissue metabolism.RESULTSWe showed that reduced FoxO1 expression protects mice against obesity-related insulin resistance with marked improvement not only in hepatic insulin sensitivity but also in skeletal muscle insulin action. FoxO1 haploinsufficiency also resulted in increased peroxisome proliferator–activated receptor (PPAR)γ gene expression in adipose tissue, with enhanced expression of PPARγ target genes known to influence metabolism. Moreover, treatment of mice with the PPARγ agonist rosiglitazone caused a greater improvement in in vivo insulin sensitivity in FoxO1 haploinsufficient animals, including reductions in circulating proinflammatory cytokines.CONCLUSIONSThese findings indicate that FoxO1 proteins negatively regulate insulin action and that their effect may be explained, at least in part, by inhibition of PPARγ function.

Anti-inflammatory effect of rosiglitazone is not reflected in expression of NFκB-related genes in peripheral blood mononuclear cells of patients with type 2 diabetes mellitus

BackgroundRosiglitazone not only improves insulin-sensitivity, but also exerts anti-inflammatory effects. We have now examined in type 2 diabetic patients if these effects are reflected by changes in mRNA expression in peripheral blood mononuclear cells (PBMCs) to see if these cells can be used to study these anti-inflammatory effects at the molecular level in vivo.MethodEleven obese type 2 diabetic patients received rosiglitazone (2 × 4 mg/d) for 8 weeks. Fasting blood samples were obtained before and after treatment. Ten obese control subjects served as reference group. The expression of NFκB-related genes and PPARγ target genes in PBMCs, plasma TNFα, IL6, MCP1 and hsCRP concentrations were measured. In addition, blood samples were obtained after a hyperinsulinemic-euglycemic clamp.ResultsRosiglitazone reduced plasma MCP1 and hsCRP concentrations in diabetic patients (-9.5 ± 5.3 pg/mL, p = 0.043 and -1.1 ± 0.3 mg/L p = 0.003), respectively). For hsCRP, the concentration became comparable with the non-diabetic reference group. However, of the 84 NFκB-related genes that were measured in PBMCs from type 2 diabetic subjects, only RELA, SLC20A1, INFγ and IL1R1 changed significantly (p < 0.05). In addition, PPARγ and its target genes (CD36 and LPL) did not change. During the clamp, insulin reduced plasma MCP1 concentration in the diabetic and reference groups (-9.1 ± 1.8%, p = 0.001 and -11.1 ± 4.1%, p = 0.023, respectively) and increased IL6 concentration in the reference group only (23.5 ± 9.0%, p = 0.028).ConclusionIn type 2 diabetic patients, the anti-inflammatory effect of rosiglitazone is not reflected by changes in NFκB and PPARγ target genes in PBMCs in vivo. Furthermore, our results do not support that high insulin concentrations contribute to the pro-inflammatory profile in type 2 diabetic patients.

Abstract 2468: Chronic Treatment Of Hypertensive Patients With The At1 Receptor Blocker Losartan Results In Sufficient Serum Levels Of The Metabolite Exp3179 Exhibiting Pparγ-stimulating Properties

The losartan metabolite EXP3174 exhibits angiotensin II receptor 1 (AT1R)-blocking properties, whereas the metabolite EXP3179 potently induces the activity of the insulin-sensititzing peroxisome proliferator-activated receptor γ (PPARγ) as a partial agonist in vitro.. We investigated, whether hypertensive patients chronically treated with losartan exhibit sufficient plasma levels of EXP3179 to activate PPARγ in monocytes derived from losartan-treated patients. Hypertensive patients (n=9) treated with losartan (100mg/daily during at least the past two months), and control patients (n=7) with no chronic AT1R-blocking therapy were included. Blood was taken from all individuals and serum was prepared. Monocytes were extracted by negative isolation using a Dynal Monocyte Kit, followed by RNA-isolation and measurement of PPARγ target gene expression (CD36, ABC transporter G1 (ABCG1)) by quantitative real-time RT-PCR. Losartan-treated patients received 100mg orally, and serum was prepared 2, 4, and 6h after drug ingestion for HPLC-based determination of losartan and losartan metabolites (EXP3174/ EXP3179) in serum. Serum levels were standardized to measurements of purified compounds. Chronic treatment with losartan resulted in basal levels (24h after drug intake) of losartan, EXP3174 and EXP3179 of 382,5ng/ml, 97,0ng/ml and 164,2ng/ml, respectively. Levels of both, EXP3174 and EXP3179 were time-dependently enhanced in serum with a maximum 2h after drug intake (2619,6ng/ml, 980,9ng/ml, respectively). In order to evaluate the possible agonistic property of chronic EXP3179 serum levels on PPARγ, we determined the transcript levels of CD36 and ABCG1 as known PPARγ target genes. Gene expression was significantly upregulated in patients chronically treated with losartan by 5.26±1.55- and 188.54±56.92-fold for CD36 and ABCG1 (p=0.039, p=0.023 vs. control patients, respectively). This is the first clinical description of monocytic PPARγ-target gene regulation by chronic treatment with losartan, which likely is mediated by its metabolite EXP3179. Our data show that sufficient serum levels of EXP3179 are present under losartan treatment. PPARγ activation by AT1R-blockers may translate into synergistic beneficial actions in monocytes.

The orphan nuclear receptor DAX-1 acts as a novel transcriptional corepressor of PPARγ

DAX-1 is an atypical nuclear receptor (NR) which functions primarily as a transcriptional corepressor of other NRs via heterodimerization. Peroxisome proliferator-activated receptor (PPAR) γ is a ligand-dependent NR which performs a key function in adipogenesis. In this study, we evaluated a novel cross-talk mechanism between DAX-1 and PPARγ. Transient transfection assays demonstrated that DAX-1 inhibits the transactivity of PPARγ in a dose-dependent manner. DAX-1 directly competed with the PPARγ coactivator (PGC)-1α for binding to PPARγ. Endogenous levels of DAX-1 were significantly lower in differentiated 3T3-L1 adipocytes as compared to preadipocytes. Using a retroviral expression system, we demonstrated that DAX-1 overexpression downregulates the expression of PPARγ target genes, resulting in an attenuation of adipogenesis in 3T3-L1 cells. Our results suggest that DAX-1 acts as a corepressor of PPARγ and performs a potential function in the regulation of PPARγ-mediated cellular differentiation.

Trans-10, Cis-12 Conjugated Linoleic Acid Antagonizes Ligand-Dependent PPARγ Activity in Primary Cultures of Human Adipocytes

We previously demonstrated that trans-10, cis-12 (10,12) conjugated linoleic acid (CLA) causes human adipocyte delipidation, insulin resistance, and inflammation in part by attenuating PPARγ target gene expression. We hypothesized that CLA antagonizes the activity of PPARγ in an isomer-specific manner. 10,12 CLA, but not cis-9, trans-11 (9,11) CLA, suppressed ligand-stimulated activation of a peroxisome proliferator response element-luciferase reporter. This decreased activation of PPARγ by 10,12 CLA was accompanied by an increase in PPARγ and extracellular signal-related kinase (ERK)1/2 phosphorylation, followed by decreased PPARγ protein levels. To investigate if 10,12 CLA-mediated delipidation was preventable with a PPARγ ligand (BRL), cultures were treated for 1 wk with 10,12 CLA or 10,12 CLA + BRL and adipogenic gene and protein expression, glucose uptake, and triglyceride (TG) were measured. BRL cosupplementation completely prevented 10,12 CLA suppression of adipocyte fatty acid-binding protein, lipoprotein lipase, and perilipin mRNA levels without preventing reductions in PPARγ or insulin-dependent glucose transporter 4 (GLUT4) expression, glucose uptake, or TG. Lastly, we investigated the impact of CLA withdrawal in the absence or presence of BRL for 2 wk. CLA withdrawal did not rescue CLA-mediated reductions in adipogenic gene and protein expression. In contrast, BRL supplementation for 2 wk following CLA withdrawal rescued mRNA levels of PPARγ target genes. However, the levels of PPARγ and GLUT4 protein and TG were only partially rescued by BRL. Collectively, we demonstrate for the first time, to our knowledge, that 10,12 CLA antagonizes ligand-dependent PPARγ activity, possibly via PPARγ phosphorylation by ERK.

Alternative Mechanisms by Which Mediator Subunit MED1/TRAP220 Regulates Peroxisome Proliferator-Activated Receptor γ-Stimulated Adipogenesis and Target Gene Expression

Mediator is a general coactivator complex connecting transcription activators and RNA polymerase II. Recent work has shown that the nuclear receptor-interacting MED1/TRAP220 subunit of Mediator is required for peroxisome proliferator-activated receptor gamma (PPARgamma)-stimulated adipogenesis of mouse embryonic fibroblasts (MEFs). However, the molecular mechanisms remain undefined. Here, we show an intracellular PPARgamma-Mediator interaction that requires the two LXXLL nuclear receptor recognition motifs on MED1/TRAP220 and, furthermore, we show that the intact LXXLL motifs are essential for optimal PPARgamma function in a reconstituted cell-free transcription system. Surprisingly, a conserved N-terminal region of MED1/TRAP220 that lacks the LXXLL motifs but gets incorporated into Mediator fully supports PPARgamma-stimulated adipogenesis. Moreover, in undifferentiated MEFs, MED1/TRAP220 is dispensable both for PPARgamma-mediated target gene activation and for recruitment of Mediator to a PPAR response element on the aP2 target gene promoter. However, PPARgamma shows significantly reduced transcriptional activity in cells deficient for a subunit (MED24/TRAP100) important for the integrity of the Mediator complex, indicating a general Mediator requirement for PPARgamma function. These results indicate that there is a conditional requirement for MED1/TRAP220 and that a direct interaction between PPARgamma and Mediator through MED1/TRAP220 is not essential either for PPARgamma-stimulated adipogenesis or for PPARgamma target gene expression in cultured fibroblasts. As Mediator is apparently essential for PPARgamma transcriptional activity, our data indicate the presence of alternative mechanisms for Mediator recruitment, possibly through intermediate cofactors or other cofactors that are functionally redundant with MED1/TRAP220.

Identification of a Domain within Peroxisome Proliferator-Activated Receptor γ Regulating Expression of a Group of Genes Containing Fibroblast Growth Factor 21 That Are Selectively Repressed by SIRT1 in Adipocytes

Peroxisome proliferator-activated receptor gamma (PPARgamma) activity is regulated through association with ligands that include the thiazolidinedione class of antidiabetic drugs, as well as derivatives of polyunsaturated fatty acids. Induction of PPARgamma target gene expression involves ligand-dependent reconfiguration of the ligand-binding domain (LBD), followed by recruitment of specific transcriptional coactivators. In this study, we have identified an amino acid (F372) within helix 7 of the LBD that is required for the response of PPARgamma to endogenous ligands. Additionally, the data show that this amino acid is also required for expression of a novel subset of adipocyte genes (group 2), including fibroblast growth factor 21 (FGF21), and that the FGF21 gene is a direct target of PPARgamma. Expression of the group 2 genes is selectively repressed by the NAD-dependent deacetylase SIRT1 in mature 3T3-L1 adipocytes, since knockdown of SIRT1 through the constitutive expression of a corresponding RNA interference enhances their expression without affecting the expression of classic adipogenic genes, such as adiponectin and FABP4/aP2. It appears that many of the group 2 genes repressed by SIRT1 in mature adipocytes correspond to the same set of genes that are selectively activated by treatment of fat cells with the PPARgamma ligand, troglitazone. These data support a role for helix 7 of the LBD of PPARgamma in regulating adipocyte function and suggest that inhibition of SIRT1 in adipocytes induces the same insulin-sensitizing action as PPARgamma ligands.

Peroxisome Proliferator-activated Receptor (PPAR)-2 Controls Adipocyte Differentiation and Adipose Tissue Function through the Regulation of the Activity of the Retinoid X Receptor/PPARγ Heterodimer

Peroxisome Proliferator-activated Receptor (PPAR)-2 Controls Adipocyte Differentiation and Adipose Tissue Function through the Regulation of the Activity of the Retinoid X Receptor/PPARγ Heterodimer

Peroxisome Proliferator-Activated Receptor γ Is a Zac Target Gene Mediating Zac Antiproliferation

Zac is a C2H2 zinc finger protein, which regulates apoptosis and cell cycle arrest through DNA binding and transactivation. During tumorigenesis and in response to mitogenic activation, Zac gene expression is down-regulated in a methylation-sensitive manner. As yet, no target genes have been identified that could explain the potent antiproliferative function of Zac. Here, applying genome-wide expression analysis, we identify peroxisome proliferator-activated receptor gamma (PPARgamma) as a new bona fide Zac target gene, which is induced by direct Zac binding to the proximal PPARgamma1 promoter. We show that in human colon carcinoma cells, ZAC activates expression of PPARgamma target genes in a PPARgamma-dependent manner. Moreover, we show that treatment of pituitary tumor cells with octreotide, a somatostatin analogue, leads to Zac induction and subsequent Zac-dependent up-regulation of PPARgamma, which thereupon mediates part of the antiproliferative activity of Zac. Our work provides a first step toward elucidating a functional relationship between Zac and PPARgamma that could be relevant to the understanding of tumorigenesis and diabetes as well.

Non-DNA binding, dominant-negative, human PPARγ mutations cause lipodystrophic insulin resistance

SummaryPPARγ is essential for adipogenesis and metabolic homeostasis. We describe mutations in the DNA and ligand binding domains of human PPARγ in lipodystrophic, severe insulin resistance. These receptor mutants lack DNA binding and transcriptional activity but can translocate to the nucleus, interact with PPARγ coactivators and inhibit coexpressed wild-type receptor. Expression of PPARγ target genes is markedly attenuated in mutation-containing versus receptor haploinsufficent primary cells, indicating that such dominant-negative inhibition operates in vivo. Our observations suggest that these mutants restrict wild-type PPARγ action via a non-DNA binding, transcriptional interference mechanism, which may involve sequestration of functionally limiting coactivators.

Functional Interaction between Peroxisome Proliferator-Activated Receptor γ and β-Catenin

Studies have demonstrated cross talk between beta-catenin and peroxisome proliferator-activated receptor gamma (PPARgamma) signaling pathways. Specifically, activation of PPARgamma induces the proteasomal degradation of beta-catenin in cells that express an adenomatous polyposis coli-containing destruction complex. In contrast, oncogenic beta-catenin is resistant to such degradation and inhibits the expression of PPARgamma target genes. In the present studies, we demonstrate a functional interaction between beta-catenin and PPARgamma that involves the T-cell factor (TCF)/lymphocyte enhancer factor (LEF) binding domain of beta-catenin and a catenin binding domain (CBD) within PPARgamma. Mutation of K312 and K435 in the TCF/LEF binding domain of an oncogenic beta-catenin (S37A) significantly reduces its ability to interact with and inhibit the activity of PPARgamma. Furthermore, these mutations render S37A beta-catenin susceptible to proteasomal degradation in response to activation of PPARgamma. Mutation of F372 within the CBD (helices 7 and 8) of PPARgamma disrupts its binding to beta-catenin and significantly reduces the ability of PPARgamma to induce the proteasomal degradation of beta-catenin. We suggest that in normal cells, PPARgamma can function to suppress tumorigenesis and/or Wnt signaling by targeting phosphorylated beta-catenin to the proteasome through a process involving its CBD. In contrast, oncogenic beta-catenin resists proteasomal degradation by inhibiting PPARgamma activity, which requires its TCF/LEF binding domain.

Regulation of Peroxisome Proliferator–Activated Receptor γ Activity by Losartan Metabolites

Two active metabolites of the angiotensin type 1 (AT 1 ) receptor blocker losartan have been described previously, EXP3174 and EXP3179. Whereas EXP3174 is the main antihypertensive AT 1 receptor–blocking metabolite, the role of EXP3179 is widely unknown. Recently, a subgroup of AT 1 receptor blockers has been identified as ligands for the peroxisome proliferator–activated receptor γ (PPAR-γ). Here we characterize the PPAR-γ–activating properties of the 2 active losartan metabolites. PPAR-γ activity was measured with a chimeric Gal4-DNA–binding domain–hPPARγ-ligand–binding domain (LBD) fusion protein on a Gal4-dependent luciferase reporter system. EXP3179 prominently induced the activation of the PPAR-γ–LBD reaching a maximum at 100 μmol/L with a 7.1±1-fold induction ( P &lt;0.05 versus vehicle-treated cells). Maximum PPAR-γ–LBD activation by EXP3179 reached 51% of the maximum response induced by the full PPAR-γ agonist pioglitazone, identifying EXP3179 as a partial PPAR-γ agonist. EXP3174 did not induce PPAR-γ–LBD activation. EC 50 values were calculated for PPAR-γ–LBD activity (pioglitazone EC 50 : 0.88 μmol/L; EXP3179 EC 50 : 17.1 μmol/L; losartan EC 50 : &gt;50 μmol/L). Consistent with the activation of PPAR-γ, EXP3179 potently induced 3T3-L1 adipocyte differentiation, a typical PPAR-γ–dependent cell function, and markedly stimulated PPAR-γ target gene expression. EXP3174 failed to regulate differentiation or PPAR-γ target gene expression. The present study characterizes the active losartan metabolite EXP3179 as a partial PPAR-γ agonist. PPAR-γ activation by EXP3179 may help us to understand the beneficial metabolic effects of losartan observed in clinical trials.

Anti-Inflammatory Effects of Laminar Flow

Atherosclerosis occurs most often in the arterial system at locations where blood flow is disturbed, at branches or curved parts of the vessels. This may be because the laminar blood flow stimulates an anti-inflammatory response in the endothelium. Liu et al. show that epoxyeicosatrienoic acids (EETs) are peroxisome proliferator-activated receptor γ (PPARγ) ligands that activate PPARγ transcriptional activity in a reporter assay in bovine aortic endothelial cells (BAECs) and stimulate expression of PPARγ target genes in human umbilical cord endothelial cells (HUVECs) and 3T3-L1 cells. These responses were seen only if soluble epoxide hydrolase (sEH) was inhibited, because this enzyme rapidly metabolizes EETs. Laminar flow also stimulated PPARγ activity in the mammalian two-hybrid assay using BAECs, and inhibition of sEH enhanced this response, whereas overexpression of sEH decreased the response. Laminar flow decreased the abundance and expression of sEH in BAECs and stimulated production of EETs. To confirm that EETs acted through PPARγ, BAECs were treated with an inhibitor of sEH and exogenous EETs in the presence and absence of a PPARγ inhibitor and then treated with tumor necrosis factor-α (TNF-α) to stimulate nuclear factor κβ (NF-κβ) through degradation of IκBα. The presence of EETs (and the sEH inhibitor) prevented TNF-α-mediated degradation of IκBα, and addition of an inhibitor of PPARγ attenuated this anti-inflammatory effect. Thus, production of EETs by endothelial cells and stimulation of an anti-inflammatory pathway through PPARγ may be one mechanism by which laminar flow protects blood vessels from becoming atherosclerotic. Y. Liu, Y. Zhang, K. Schmelzer, T.-S. Lee, X. Fang, Y. Zhu, A. A. Spector, S. Gill, C. Morisseau, B. D. Hammock, J. Y.-J. Shyy, The antiinflammatory effect of laminar flow: The role of PPARγ, epoxyeicosatrienoic acids, and soluble epoxide hydrolase. Proc. Natl. Acad. Sci. U.S.A. 102 , 16747-16752 (2005). [Abstract] [Full Text]

Abietic acid activates peroxisome proliferator-activated receptor-γ (PPARγ) in RAW264.7 macrophages and 3T3-L1 adipocytes to regulate gene expression involved in inflammation and lipid metabolism

Abietic acid is one of the terpenoids, which are multifunctional natural compounds. It has been reported that abietic acid suppresses effects on inflammation. However, the mechanism underlying the anti-inflammatory effects remains unclear. The present work indicates that abietic acid suppresses the protein expression of tumor necrosis factor-α and cyclooxygenase 2, which are involved in inflammation, in lipopolysaccharide-stimulated macrophages. Moreover, this effect resembles that of thiazolidinedione, a synthetic peroxisome proliferator-activated receptor-γ (PPARγ) ligand. Indeed, abietic acid activates PPARγ in luciferase reporter assays. The activity of abietic acid induces PPARγ target gene expression in RAW264.7 macrophages and 3T3-L1 adipocytes. These data indicate that abietic acid is a PPARγ ligand and that its anti-inflammatory effect is partly due to the activation of PPARγ in stimulated macrophages. The present work suggests a novel possibility that abietic acid, a naturally occurring compound, can be used not only for anti-inflammation but also for regulating lipid metabolism and atherosclerosis.

Signal cross-talk between estrogen receptor alpha and beta and the peroxisome proliferator-activated receptor gamma1 in MDA-MB-231 and MCF-7 breast cancer cells

We have previously demonstrated that peroxisome proliferator-activated receptor gamma (PPARγ) is expressed and transcriptionally responsive to both synthetic and natural ligands in a variety of human breast cancer cells. We also observed significant differences in basal and ligand-mediated transactivation of PPARγ in cells with variable expression of the estrogen receptor. While previous reports indicate that PPARγ can mediate the expression of estrogen target genes, no data have suggested that estrogen receptor (ER) expression can alter the transcriptional regulation of PPARγ target gene expression. Here we have demonstrated that the expression of either ERα or β, but not the androgen or aryl hydrocarbon receptors, lowers both basal and stimulated PPARγ-mediated reporter activity. Interestingly, the presence of an ER antagonist does not inhibit this response while estradiol treatment further inhibits the ligand-stimulated transactivation of PPARγ in cells expressing ERα but not ERβ. Cells transfected with ERα deletion mutants demonstrate that the DNA binding domain of the ER is required to repress PPAR transactivation in these cells. Finally, using RNase protection assays we show that the inhibition of PPAR function is not due to a decrease in the expression of PPARγ. These data suggest that signal cross talk exists bidirectionally between PPARγ and ER in breast cancer cells.

Tetradecylthioacetic acid prevents high fat diet induced adiposity and insulin resistance

Tetradecylthioacetic acid (TTA) is a non-β-oxidizable fatty acid analog, which potently regulates lipid homeostasis. Here we evaluate the ability of TTA to prevent diet-induced and genetically determined adiposity and insulin resistance. In Wistar rats fed a high fat diet, TTA administration completely prevented diet-induced insulin resistance and adiposity. In genetically obese Zucker (fa/fa) rats TTA treatment reduced the epididymal adipose tissue mass and improved insulin sensitivity. All three rodent peroxisome proliferator-activated receptor (PPAR) subtypes were activated by TTA in the ranking order PPARα > PPARδ > PPARγ. Expression of PPARγ target genes in adipose tissue was unaffected by TTA treatment, whereas the hepatic expression of PPARα-responsive genes encoding enzymes involved in fatty acid uptake, transport, and oxidation was induced. This was accompanied by increased hepatic mitochondrial β-oxidation and a decreased fatty acid/ketone body ratio in plasma. These findings indicate that PPARα-dependent mechanisms play a pivotal role, but additionally, the involvement of PPARα-independent pathways is conceivable. Taken together, our results suggest that a TTA-induced increase in hepatic fatty acid oxidation and ketogenesis drains fatty acids from blood and extrahepatic tissues and that this contributes significantly to the beneficial effects of TTA on fat mass accumulation and peripheral insulin sensitivity.—Madsen, L., M. Guerre-Millo, E. N. Flindt, K. Berge, K. J. Tronstad, E. Bergene, E. Sebokova, A. C. Rustan, J. Jensen, S. Mandrup, K. Kristiansen, I. Klimes, B. Staels, and R. K. Berge. Tetradecylthioacetic acid prevents high fat diet induced adiposity and insulin resistance. J. Lipid Res. 2002. 43: 742–750.