PPARgamma and PPARdelta negatively regulate specific subsets of lipopolysaccharide and IFN-gamma target genes in macrophages

The PPAR-RXR Transcriptional Complex in the Vasculature

The peroxisome proliferator-activated receptors (PPARs) and the retinoid X receptors (RXRs) are ligand-activated transcription factors that coordinately regulate gene expression. This PPAR-RXR transcriptional complex plays a critical role in energy balance, including triglyceride metabolism, fatty acid handling and storage, and glucose homeostasis: processes whose dysregulation characterize obesity, diabetes, and atherosclerosis. PPARs and RXRs are also involved directly in inflammatory and vascular responses in endothelial and vascular smooth muscle cells. New insights into fundamental aspects of PPAR and RXR biology, and their actions in the vasculature, continue to appear. Although RXRs are obligate heterodimeric partners for PPAR action, the part that RXRs, and their endogenous retinoid mediators, exert in the vessel wall is less well understood. Biological insights into PPAR-RXRs may help inform interpretation of clinical trials with synthetic PPAR agonists and prospects for future PPAR therapeutics. Importantly, the extensive data establishing a key role for PPARs and RXRs in energy balance, inflammation, and vascular biology stands separately from the clinical experience with any given synthetic PPAR agonist. Both the basic science data and the clinical experience with PPAR agonists identify the need to better understand these important transcriptional regulators.

The macrophage-mediated effects of the peroxisome proliferator-activated receptor-gamma agonist rosiglitazone attenuate tactile allodynia in the early phase of neuropathic pain development

BACKGROUND

Neuroinflammation triggered by macrophage infiltration into sites of peripheral nerve injury may result in neuropathic pain. Peroxisome proliferator-activated receptor (PPAR)γ signaling regulates the properties of macrophages. However, the macrophage-mediated effects of PPARγ signaling on neuropathic pain triggered by peripheral inflammation have not been investigated.

METHODS

To evaluate the peripheral effects of PPARγ signaling on tactile allodynia, we administered the blood-brain barrier-impermeant PPARγ agonist, rosiglitazone, after partial sciatic nerve ligation (PSNL) as (1) systemic treatment during different phases of neuropathic pain development, (2) local injection to the PSNL site in the early phase, or (3) peritoneal macrophages pretreated with rosiglitazone transplanted into the PSNL site. In addition, the direct effect of rosiglitazone was evaluated in peritoneal macrophages activated with interferon-γ.

RESULTS

Systemic rosiglitazone treatment early in the course of progressive inflammation ameliorated tactile allodynia, macrophage infiltration, and production of proinflammatory mediators including cyclooxygenase-2, inducible nitric oxide synthase, and matrix metalloprotease 9 at the PSNL site. Local injection of rosiglitazone and transplantation of rosiglitazone-treated peritoneal macrophages at the ligation site significantly improved tactile allodynia. In peritoneal macrophages, rosiglitazone down-regulated interferon-γ-induced gene expression of cyclooxygenase-2 and inducible nitric oxide synthase and attenuated the chemotactic response to monocyte chemotactic protein-1.

DISCUSSION

Rosiglitazone treatment in the early phase of neuropathic pain significantly alleviated the development of tactile allodynia by regulating macrophage infiltration and production of proinflammatory molecules at the inflamed site. Our results indicate that the activation of PPARγ signaling in macrophages during the early phase may suppress neuropathic pain development.

Macrophage Mal1 deficiency suppresses atherosclerosis in low-density lipoprotein receptor-null mice by activating peroxisome proliferator-activated receptor-γ-regulated genes

OBJECTIVE

The adipocyte/macrophage fatty acid-binding proteins aP2 (FABP4) and Mal1 (FABP5) are intracellular lipid chaperones that modulate systemic glucose metabolism, insulin sensitivity, and atherosclerosis. Combined deficiency of aP2 and Mal1 has been shown to reduce the development of atherosclerosis, but the independent role of macrophage Mal1 expression in atherogenesis remains unclear.

METHODS AND RESULTS

We transplanted wild-type (WT), Mal1(-/-), or aP2(-/-) bone marrow into low-density lipoprotein receptor-null (LDLR(-/-)) mice and fed them a Western diet for 8 weeks. Mal1(-/-)→LDLR(-/-) mice had significantly reduced (36%) atherosclerosis in the proximal aorta compared with control WT→LDLR(-/-) mice. Interestingly, peritoneal macrophages isolated from Mal1-deficient mice displayed increased peroxisome proliferator-activated receptor-γ (PPARγ) activity and upregulation of a PPARγ-related cholesterol trafficking gene, CD36. Mal1(-/-) macrophages showed suppression of inflammatory genes, such as COX2 and interleukin 6. Mal1(-/-)→LDLR(-/-) mice had significantly decreased macrophage numbers in the aortic atherosclerotic lesions compared with WT→LDLR(-/-) mice, suggesting that monocyte recruitment may be impaired. Indeed, blood monocytes isolated from Mal1(-/-)→LDLR(-/-) mice on a high-fat diet had decreased CC chemokine receptor 2 gene and protein expression levels compared with WT monocytes.

CONCLUSION

Taken together, our results demonstrate that Mal1 plays a proatherogenic role by suppressing PPARγ activity, which increases expression of CC chemokine receptor 2 by monocytes, promoting their recruitment to atherosclerotic lesions.

Activated and inactivated PPARs-γ modulate experimentally induced colitis in rats

BACKGROUND

This study sought to define the mechanism by which PPAR-γ ligands affect the course of experimentally induced colitis in rats.

MATERIAL/METHODS

Inflammation was induced in Wistar rats by a single rectal administration of 2,4,6,-trinitrobenzene sulfonic acid (TNBS). The antagonist of PPARγ antagonist, bisphenol A diglycidyl ether (BADGE), was administrated intraperitoneally 120 mg/kg 4 times every other day. Rosiglitazone 8 mg/kg was administrated by gastric tube 4 times. Body weight was measured daily. After killing, the large intestinal tissue was weighed and collected for histopathologic and immunoenzymatic tests. Levels of IL-6, IL-10, and myeloperoxidase (MPO) were determined in serum and in intestinal homogenates.

RESULTS

Rats receiving rosiglitazone had higher body weight, whereas large intestine weight/length ratio was lower; histology showed fewer inflammatory markers. Rats receiving TNBS and TNBS along with BADGE had more intensive inflammatory changes. Rosiglitazone alone decreased expression of IL-6; used with TNBS it decreased expression of MPO in intestinal tissue, yet did not increase the expression of IL-10. Decreased levels of MPO indicate reduced neutrophil-dependent immune response. The antagonist of PPAR-γ increased IL-6 in serum and decreased IL-10 in intestinal homogenates. Bisphenol A diglycidyl ether administrated to healthy animals increases serum IL-6 levels.

CONCLUSIONS

Rosiglitazone inhibits experimental inflammation; administration of its selective antagonist abolishes this protective influence. Rosiglitazone inhibits expression of proinflammatory IL-6 and does not affect IL-10. Agonists of PPARs-γ are possibilities for inflammatory bowel disease prevention. Exogenous substances blocking PPARs-γ may contribute to development or relapse of nonspecific inflammatory bowel diseases.

Vitamin B6 regulates mRNA expression of peroxisome proliferator-activated receptor-γ target genes

We previously demonstrated that vitamin B6 suppresses tumorigenesis in the colon of mice and exerts an anti-inflammatory effect through the inhibition of NF-κB activation. As these effects resemble the pharmacological properties of thiazolidinedione (TZD), a synthetic peroxisome proliferator-activated receptor-γ (PPARγ) ligand, this study was designed to examine the effect of vitamin B6 on the activation of PPARγ and adipogenesis in 3T3-L1 adipocyte cells. Pyridoxal 5'-phosphate (PLP), one of the vitamin B6 derivatives, was shown to promote adipogenesis in the 3T3-L1 adipocytes. In addition, PLP specifically induced mRNA expression of PPARγ target genes in the 3T3-L1 adipocytes and enhanced the lipid accumulation and adipocyte fatty acid-binding protein (aP2) mRNA expression in NIH3T3 cells stably expressing PPARγ. Furthermore, the administration of vitamin B6 increased the expression of aP2 mRNA in mouse adipose tissues. Collectively, these observations suggest a novel function of vitamin B6 as an activator for PPARγ, which may contribute to the anti-tumor and anti-inflammatory effects of vitamin B6.

PPARs are a unique set of fatty acid regulated transcription factors controlling both lipid metabolism and inflammation

Cells are constantly exposed to a large variety of lipids. Traditionally, these molecules were thought to serve as simple energy storing molecules. More recently it has been realized that they can also initiate and regulate signaling events that will decisively influence development, cellular differentiation, metabolism and related functions through the regulation of gene expression. Multicellular organisms dedicate a large family of nuclear receptors to these tasks. These proteins combine the defining features of both transcription factors and receptor molecules, and therefore have the unique ability of being able to bind lipid signaling molecules and transduce the appropriate signals derived from lipid environment to the level of gene expression. Intriguingly, the members of a subfamily of the nuclear receptors, the peroxisome proliferator-activated receptors (PPARs) are able to sense and interpret fatty acid signals derived from dietary lipids, pathogenic lipoproteins or essential fatty acid metabolites. Not surprisingly, Peroxisome proliferator-activated receptors were found to be key regulators of lipid and carbohydrate metabolism. Unexpectedly, later studies revealed that Peroxisome proliferator-activated receptors are also able to modulate inflammatory responses. Here we summarize our understanding on how these transcription factors/receptors connect lipid metabolism to inflammation and some of the novel regulatory mechanisms by which they contribute to homeostasis and certain pathological conditions. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.

Xenobiotic metabolism, disposition, and regulation by receptors: from biochemical phenomenon to predictors of major toxicities

To commemorate the 50th anniversary of the Society of Toxicology, this special edition article reviews the history and current scope of xenobiotic metabolism and transport, with special emphasis on the discoveries and impact of selected "xenobiotic receptors." This overall research realm has witnessed dynamic development in the past 50 years, and several of the key milestone events that mark the impressive progress in these areas of toxicological sciences are highlighted. From the initial observations regarding aspects of drug metabolism dating from the mid- to late 1800's, the area of biotransformation research witnessed seminal discoveries in the mid-1900's and onward that are remarkable in retrospect, including the discovery and characterization of the phase I monooxygenases, the cytochrome P450s. Further research uncovered many aspects of the biochemistry of xenobiotic metabolism, expanding to phase II conjugation and phase III xenobiotic transport. This led to hallmark developments involving integration of genomic technologies to elucidate the basis for interindividual differences in response to xenobiotic exposures and discovery of nuclear and soluble receptor families that selectively "sense" the chemical milieu of the mammalian cell and orchestrate compensatory changes in gene expression programming to accommodate complex xenobiotic exposures. This review will briefly summarize these developments and investigate the expanding roles of xenobiotic receptor biology in the underlying basis of toxicological response to chemical agents.

Cytokines (interferon-γ and tumor necrosis factor-α)-induced nuclear factor-κB activation and chemokine (C-X-C motif) ligand 10 release in Graves disease and ophthalmopathy are modulated by pioglitazone

Until now, the following are not known: (1) the mechanisms underlying the induction of chemokine (C-X-C motif) ligand 10 (CXCL10) secretion by cytokines in thyrocytes; (2) if pioglitazone is able, like rosiglitazone, to inhibit the interferon (IFN)-γ-induced chemokine expression in Graves disease (GD) or ophthalmopathy (GO); and (3) the mechanisms underlying the inhibition by thiazolidinediones of the cytokines-induced CXCL10 release in thyrocytes. The aims of this study were (1) to study the mechanisms underlying the induction of CXCL10 secretion by cytokines in GD thyrocytes; (2) to test the effect of pioglitazone on IFNγ-inducible CXCL10 secretion in primary thyrocytes, orbital fibroblasts, and preadipocytes from GD and GO patients; and (3) to evaluate the mechanism of action of thiazolidinediones on nuclear factor (NF)-κB activation. The results of the study (1) demonstrate that IFNγ + TNFα enhanced the DNA binding activity of NF-κB in GD thyrocytes, in association with the release of CXCL10; (2) show that pioglitazone exerts a dose-dependent inhibition on IFNγ + TNFα-induced CXCL10 secretion in thyrocytes, orbital fibroblasts, and preadipocytes, similar to the effect observed with rosiglitazone; and (3) demonstrate that thiazolidinediones (pioglitazone and rosiglitazone) act by reducing the IFNγ + TNFα activation of NF-κB in Graves thyrocytes. To the best of our knowledge, this is the first study showing that cytokines are able to activate NF-κB in Graves thyrocytes and a parallel inhibitory effect of pioglitazone both on CXCL10 chemokine secretion and NF-κB activation. Future studies will be needed to verify if new targeted peroxisome proliferator-activated receptor-γ activators may be able to exert the anti-inflammatory effects without the risk of expanding retrobulbar fat mass.

Abscisic acid regulates inflammation via ligand-binding domain-independent activation of peroxisome proliferator-activated receptor gamma

Abscisic acid (ABA) has shown efficacy in the treatment of diabetes and inflammation; however, its molecular targets and the mechanisms of action underlying its immunomodulatory effects remain unclear. This study investigates the role of peroxisome proliferator-activated receptor γ (PPAR γ) and lanthionine synthetase C-like 2 (LANCL2) as molecular targets for ABA. We demonstrate that ABA increases PPAR γ reporter activity in RAW 264.7 macrophages and increases ppar γ expression in vivo, although it does not bind to the ligand-binding domain of PPAR γ. LANCL2 knockdown studies provide evidence that ABA-mediated activation of macrophage PPAR γ is dependent on lancl2 expression. Consistent with the association of LANCL2 with G proteins, we provide evidence that ABA increases cAMP accumulation in immune cells. ABA suppresses LPS-induced prostaglandin E(2) and MCP-1 production via a PPAR γ-dependent mechanism possibly involving activation of PPAR γ and suppression of NF-κB and nuclear factor of activated T cells. LPS challenge studies in PPAR γ-expressing and immune cell-specific PPAR γ null mice demonstrate that ABA down-regulates toll-like receptor 4 expression in macrophages and T cells in vivo through a PPAR γ-dependent mechanism. Global transcriptomic profiling and confirmatory quantitative RT-PCR suggest novel candidate targets and demonstrate that ABA treatment mitigates the effect of LPS on the expression of genes involved in inflammation, metabolism, and cell signaling, in part, through PPAR γ. In conclusion, ABA decreases LPS-mediated inflammation and regulates innate immune responses through a bifurcating pathway involving LANCL2 and an alternative, ligand-binding domain-independent mechanism of PPAR γ activation.

STAT6 transcription factor is a facilitator of the nuclear receptor PPARγ-regulated gene expression in macrophages and dendritic cells

Peroxisome proliferator-activated receptor γ (PPARγ) is a lipid-activated transcription factor regulating lipid metabolism and inflammatory response in macrophages and dendritic cells (DCs). These immune cells exposed to distinct inflammatory milieu show cell type specification as a result of altered gene expression. We demonstrate here a mechanism how inflammatory molecules modulate PPARγ signaling in distinct subsets of cells. Proinflammatory molecules inhibited whereas interleukin-4 (IL-4) stimulated PPARγ activity in macrophages and DCs. Furthermore, IL-4 signaling augmented PPARγ activity through an interaction between PPARγ and signal transducer and activators of transcription 6 (STAT6) on promoters of PPARγ target genes, including FABP4. Thus, STAT6 acts as a facilitating factor for PPARγ by promoting DNA binding and consequently increasing the number of regulated genes and the magnitude of responses. This interaction, underpinning cell type-specific responses, represents a unique way of controlling nuclear receptor signaling by inflammatory molecules in immune cells.

Peroxisome proliferator-activated receptor gamma negatively regulates IFN-beta production in Toll-like receptor (TLR) 3- and TLR4-stimulated macrophages by preventing interferon regulatory factor 3 binding to the IFN-beta promoter

Toll-like receptors 3 and 4 utilize adaptor TRIF to activate interferon regulatory factor 3 (IRF3), resulting in IFN-β production to mediate anti-viral and bacterial infection. Peroxisome proliferator-activated receptor (PPAR)-γ is a ligand-activated transcription factor expressed in various immune cells and acts as a transcriptional repressor to inhibit the transcription of many proinflammatory cytokines. But, the function of PPAR-γ in TLR3- and -4-mediated IFN-β production is not well elucidated. Here, we have analyzed the effect of the PPAR-γ agonists on IFN-β production in peritoneal primary macrophages in response to LPS and poly(I:C). PPAR-γ agonists inhibited LPS and poly(I:C)-induced IFN-β transcription and secretion. siRNA knockdown of PPAR-γ expression and transfection of PPAR-γ expression plasmid demonstrated that PPAR-γ agonist inhibits IFN-β production in a PPAR-γ-dependent manner. The ability of the PPAR-γ agonist to inhibit IFN-β production was confirmed in vivo as mice treated with troglitazone exhibited decreased levels of IFN-β upon LPS and poly(I:C) challenge. Chromatin immunoprecipitation (CHIP) assay and electrophoretic mobility shift assay (EMSA) demonstrated that troglitazone treatment impaired IRF3 binding to the IFN-β promoter. Furthermore, troglitazone could inhibit LPS and poly(I:C)-induced STAT1 phosphorylation and subsequent ISRE activation. These results demonstrate that PPAR-γ negatively regulates IFN-β production in TLR3- and 4-stimulated macrophages by preventing IRF3 binding to the IFN-β promoter.

Autoimmune kidney disease and impaired engulfment of apoptotic cells in mice with macrophage peroxisome proliferator-activated receptor gamma or retinoid X receptor alpha deficiency

Autoimmune glomerulonephritis is a common manifestation of systemic lupus erythematosus (SLE). In this study, we show that mice lacking macrophage expression of the heterodimeric nuclear receptors PPARγ or RXRα develop glomerulonephritis and autoantibodies to nuclear Ags, resembling the nephritis seen in SLE. These mice show deficiencies in phagocytosis and clearance of apoptotic cells, and they are unable to acquire an anti-inflammatory phenotype upon feeding of apoptotic cells, which is critical for the maintenance of self-tolerance. These results demonstrate that stimulation of PPARγ and RXRα in macrophages facilitates apoptotic cell engulfment, and they provide a potential strategy to avoid autoimmunity against dying cells and to attenuate SLE.

New treatments for chronic hepatitis C

Treatments for chronic hepatitis C has evolved significantly in the past 15 years. The standard of care (SOC) is peginterferon alfa-2a/-2b with ribavirin for 48 weeks or 24 weeks in patients infected with HCV genotype 1 or 2/3, respectively. The treatment duration can be individualized based on the baseline viral load and the speed of the virologic response during treatment. However, current therapies are associated with side effects, complications, and poor patient tolerability. Therefore, there is an urgent need to identify better strategies for treating this disease. An improved sustained virologic response (SVR) can be achieved with new HCV-specific inhibitors against NS3/4A and NS5B polymerases. Recent trials have found SVR rates in patients with HCV genotype 1 infection of 61~68% and 67~75% for combining the SOC with the protease inhibitors telaprevir and boceprevir, respectively. Several new HCV-specific inhibitors such as protease inhibitors and nucleoside and non-nucleoside polymerase inhibitors as well as non-HCV-specific compounds with anti-HCV activity are currently in clinical evaluation. In this review we discuss these new treatments for chronic hepatitis C.

Peroxisome proliferator-activated receptor {delta} regulates inflammation via NF-{kappa}B signaling in polymicrobial sepsis

The nuclear peroxisome proliferator-activated receptor δ (PPARδ) is an important regulator of lipid metabolism. In contrast to its known effects on energy homeostasis, its biological role on inflammation is not well understood. We investigated the role of PPARδ in the modulation of the nuclear factor-κB (NF-κB)-driven inflammatory response to polymicrobial sepsis in vivo and in macrophages in vitro. We demonstrated that administration of GW0742, a specific PPARδ ligand, provided beneficial effects to rats subjected to cecal ligation and puncture, as shown by reduced systemic release of pro-inflammatory cytokines and neutrophil infiltration in lung, liver, and cecum, when compared with vehicle treatment. Molecular analysis revealed that treatment with GW0742 reduced NF-κB binding to DNA in lung and liver. In parallel experiments, heterozygous PPARδ-deficient mice suffered exaggerated lethality when subjected to cecal ligation and puncture and exhibited severe lung injury and higher levels of circulating tumor necrosis factor-α (TNFα) and keratinocyte-derived chemokine than wild-type mice. Furthermore, in lipopolysaccharide-stimulated J774.A1 macrophages, GW0742 reduced TNFα production by inhibiting NF-κB activation. RNA silencing of PPARδ abrogated the inhibitory effects of GW0742 on TNFα production. Chromatin immunoprecipitation assays revealed that PPARδ displaced the NF-κB p65 subunit from the κB elements of the TNFα promoter, while recruiting the co-repressor BCL6. These data suggest that PPARδ is a crucial anti-inflammatory regulator, providing a basis for novel sepsis therapies.

Activation of PPAR-gamma by carbon monoxide from CORM-2 leads to the inhibition of iNOS but not COX-2 expression in LPS-stimulated macrophages

The effect of CO on the expression of iNOS and COX-2 was investigated by using a CO-releasing molecule (CORM)-2 in LPS-activated RAW 264.7 cells in vitro. Interestingly, CORM-2 significantly inhibited iNOS (NO) but not COX-2 (PGE(2)) expression. PPAR-gamma activators such as troglitazone, GW1929, and 15-deoxy-Delta12, 14- prostaglandin J(2) showed preferential inhibitory effect on iNOS over COX-2 expression in LPS-activated macrophages. The same effect was shown in lung tissues (iNOS, COX-2) and serum (NO, PGE(2)) when administered of CORM-2 in LPS-induced septic mice, indicating that CO derived from CORM-2 differentially regulates iNOS and COX-2 through PPAR-gamma activation under inflammation state.

Extension of the neuroprotective time window for thiazolidinediones in ischemic stroke is dependent on time of reperfusion

Stroke is a leading cause of death and disability but has limited therapeutic options. Thiazolidinediones (TZDs), agonists for the nuclear receptor, peroxisome proliferator-activated receptor (PPAR)γ, reduce infarct volume and improve neurologic function following transient middle cerebral artery occlusion (MCAO) in rats. Translation of these findings into clinical therapy will require careful assessment of dosing paradigms and effective time windows for treatment. Understanding the mechanisms by which TZDs protect the brain provides insight into how time windows for neuroprotection might be extended. We find that two TZDs, pioglitazone and rosiglitazone, significantly reduce infarct volume at doses similar to those used clinically (1 mg/kg for pioglitazone and 0.1 mg/kg for rosiglitazone). We also find that pioglitazone reduces infarction volume in a transient, but not a permanent MCAO model suggesting that reperfusion plays an important role in TZD mediated neuroprotection. Since PPARγ agonists reduce inflammation and oxidative stress, both of which are exacerbated by reperfusion, we hypothesized that TZDs would be most effective if administered prior to reperfusion. We administered TZDs 3 h after MCAO and found that infarction volume and neurologic function are significantly improved in animals reperfused at 3 h and 15 min (after TZD treatment), but not in animals reperfused at 2 h (before TZD treatment) when assessed either 24 h or 3 weeks after MCAO. While TZDs reduce intercellular adhesion molecule (ICAM) expression to a similar extent regardless of the time of reperfusion, leukocyte entry into brain parenchyma is more dramatically reduced when reperfusion is delayed until after drug treatment. The finding that delaying reperfusion until after TZD treatment is beneficial despite a longer period of ischemia, is dramatic given the widely held view that duration of ischemia is the most important determinate of injury.

C-reactive protein triggers inflammatory responses partly via TLR4/IRF3/NF-κB signaling pathway in rat vascular smooth muscle cells

AIMS

C-reactive protein (CRP) plays an important role in the inflammatory process of atherosclerosis. Toll-like receptor 4 (TLR4) participates in atherogenesis by mediating the inflammatory responses. The aim of this experiment was to investigate the pro-inflammatory effects and mechanisms of CRP in rat vascular smooth muscle cells (VSMCs), especially focusing on the effects of CRP on IL-6 and peroxisome proliferator-activated receptor γ (PPARγ), and TLR4-dependent signal pathway.

MAIN METHODS

rat VSMCs were cultured, and CRP was used as a stimulant for IL-6 and peroxisome proliferator-activated receptor γ (PPARγ). IL-6 level in the culture supernatant was measured by ELISA, and mRNA and protein expressions were assayed by quantitative real-time PCR and western blot, respectively. RNA interference was used to assess the roles of TLR4 and interferon regulatory factor 3 (IRF3) in the pro-inflammatory signal pathway of CRP.

KEY FINDINGS

CRP stimulated IL-6 secretion, and inhibited mRNA and protein expression of PPARγ in VSMCs in a concentration-dependent manner. Additionally, CRP induced TLR4 expression, promoted nuclear translocation of NF-κB (p65), and augmented IκBα phosphorylation in VSMCs. Taken together, CRP induces the inflammatory responses through increasing IL-6 generation and reducing PPARγ expression in VSMCs, which is mediated by TLR4/IRF3/NF-κB signal pathway.

SIGNIFICANCE

CRP is able to stimulate IL-6 production and to inhibit PPARγ expression in VSMCs via MyD88-independent TLR4 signaling pathway (TLR4/IRF3/NF-κB). These provide the novel evidence for the pro-inflammatory action of CRP involved in atherogenesis.

The Role of Peroxisome Proliferator-Activated Receptor beta/delta on the Inflammatory Basis of Metabolic Disease

The pathophysiology underlying several metabolic diseases, such as obesity, type 2 diabetes mellitus, and atherosclerosis, involves a state of chronic low-level inflammation. Evidence is now emerging that the nuclear receptor Peroxisome Proliferator-Activated Receptor (PPAR)β/δ ameliorates these pathologies partly through its anti-inflammatory effects. PPARβ/δ activation prevents the production of inflammatory cytokines by adipocytes, and it is involved in the acquisition of the anti-inflammatory phenotype of macrophages infiltrated in adipose tissue. Furthermore, PPARβ/δ ligands prevent fatty acid-induced inflammation in skeletal muscle cells, avoid the development of cardiac hypertrophy, and suppress macrophage-derived inflammation in atherosclerosis. These data are promising and suggest that PPARβ/δ ligands may become a therapeutic option for preventing the inflammatory basis of metabolic diseases.

+294T/C polymorphism in the PPAR-delta gene is associated with risk of coronary artery disease in normolipidemic Tunisians

Peroxisome proliferator-activated receptor delta (PPAR-delta) is a transcription factor implicated in metabolism and inflammation. The +294T/C polymorphism in the PPAR-delta gene is associated with risk of coronary artery disease (CAD) in dyslipidemic women and hypercholesterolemic men. Whether this polymorphism influences the risk of CAD in the absence of dyslipidemia was not known, so we investigated a possible association of this polymorphism with plasma lipid and lipoprotein levels and with risk and outcome of CAD in a normolipidemic Tunisian population. Genotyping was performed by PCR-RFLP in 112 CAD patients and 113 healthy volunteers. The C-allele was significantly more frequent in patients than in controls (0.320 vs 0.189, P = 0.001). This association remained significant after adjustment for age, gender, body mass index, smoking, hypertension, and high-density lipoprotein cholesterol. Subjects carrying either one or two copies of the C-allele had a 2.7-fold higher risk of CAD than subjects homozygous for the T-allele. PPAR-delta genotypes were not associated with lipoprotein concentrations or outcome of CAD. We conclude that PPAR-delta +294T/C polymorphism is an independent risk factor of CAD in normolipidemic Tunisian subjects. The lack of association with lipoprotein concentrations suggests that the effect of the polymorphism on CAD is not mediated through lipoprotein levels in this population and that it may influence the atherosclerotic process through mechanisms involving inflammation.

Topical rosiglitazone treatment improves ulcerative colitis by restoring peroxisome proliferator-activated receptor-gamma activity

OBJECTIVES

Impaired epithelial expression of peroxisome proliferator-activated receptor-gamma (PPARgamma) has been described in animal colitis models and briefly in patients with ulcerative colitis, but the functional significance in humans is not well defined. We examined PPARgamma expression and functional activity in human colonic epithelium and explored the potential of topical treatment with rosiglitazone (a PPARgamma ligand) in patients with ulcerative colitis.

METHODS

Spontaneous and rosiglitazone-mediated PPARgamma and adipophillin expression (a gene transcriptionally activated by PPARgamma) were measured by reverse transcriptase PCR in colonic biopsies and isolated epithelial cells from patients with ulcerative colitis and controls. Fourteen patients with active distal ulcerative colitis were randomized to either rosiglitazone (4 mg) or mesalazine (1 g) enema treatment once daily for 14 days.

RESULTS

PPARgamma expression was fourfold reduced in epithelial cells from inflamed compared with uninflamed mucosa and controls. Adipophillin levels were decreased in parallel. Rosiglitazone induced a concentration-dependent increase in adipophillin levels and restored PPARgamma activity in epithelial cells from inflamed mucosa in vitro. Rosiglitazone enema treatment was well tolerated and reduced the Mayo ulcerative colitis score from 8.9 to 4.3 (P<0.01), similar to the effect of mesalazine. Rosiglitazone increased adipophillin levels in the epithelial cells of the patients, indicating PPARgamma activation in vivo.

CONCLUSIONS

Roziglitasone enemas improve impaired PPARgamma activity in inflamed colonic epithelium and have beneficial clinical effect in patients with active distal ulcerative colitis. These findings raise interest in further studies of PPARgamma ligands that exhibit their anti-inflammatory effect locally in the gut to avoid possible systemic side effects.

Transient expression of interferon-inducible p204 in the early stage is required for adipogenesis in 3T3-L1 cells

A member of the interferon-inducible p200 family of proteins, p204, has recently been reported to function in the development of many mesoderm-derived tissues, such as bone, muscle, and cartilage. However, no published study has yet investigated the role of p204 in adipogenesis. Our preliminary experiments showed that p204 can be found in 3T3-L1 preadipocytes, and its expression was up-regulated in a differentiation-dependent manner. As such, we hypothesized that p204 is associated with adipogenesis and focused on the influence of p204 on adipogenesis. In the present study, we investigated the transient elevated expression and cytoplasm-to-nucleus translocation of p204 in the early stage of adipogenesis. To determine the effect of p204 on adipogenesis, p204-siRNA and expression vector were produced for p204 suppression and overexpression, respectively. The knockdown of p204 resulted in a significantly depressed adipocyte differentiation, whereas p204 overexpression promoted adipocyte differentiation. The mRNA expression of adipogenic markers, such as peroxisome-proliferator-activated receptor (PPAR)gamma, CCAAT/enhancer-binding-protein (C/EBP)alpha, lipoprotein lipase, and adipsin, was decreased by p204 suppression and increased by p204 overexpression. A coimmunoprecipitation assay coupled with an indirect immunofluorescence assay also indicated that p204 interacted and colocalized with C/EBPdelta in the nucleus. Furthermore, the knockdown of p204 disrupted the interaction between p204 and C/EBPdelta and partially suppressed the PPARgamma transcriptional activity by dissociating C/EBPdelta with the PPARgamma promoter element. Collectively, our data indicate that the transient expression of p204 in the early stage is indispensable for adipocyte differentiation. Disruption of p204 expression patterns at this stage leads to irreversible damage in fat formation.

Is there a biological basis for treatment of fibrodysplasia ossificans progressiva with rosiglitazone? Potential benefits and undesired effects

Thiazolidinediones (TZDs), among which Rosiglitazone, are known agonists of the peroxisome-proliferator-activated receptor γ (PPARγ) commonly used for treatment of hyperglycemia. A recently published article describing a case report on a patient affected by Fibrodysplasia Ossificans Progressiva (FOP) treated with Rosiglitazone has prompted interest for careful analysis of the rational basis of such treatment. This article reviews the effects of PPARγ agonists in relationship with various pathogenic steps that occur during the course of FOP by reviewing the particularly rich literature on the effects of Rosiglitazone, to underscore their relevance to FOP and to consider possible adverse effects.

Evidence for the role of peroxisome proliferator-activated receptor-beta/delta in the development of spinal cord injury

Several lines of evidence suggest a biological role for peroxisome proliferator-activated receptor (PPAR)-beta/delta in the pathogenesis many diseases. The aim of the present study was to evaluate the contribution of PPAR-beta/delta in the secondary damage in experimental spinal cord injury (SCI) in mice. To this purpose, we used 4-[[[2-[3-fluoro-4-(trifluoromethyl)phenyl]-4-methyl-5-thiazolyl]methyl]thio]-2-methylphenoxy]acetic acid (GW0742), a high-affinity PPAR-beta/delta agonist. Spinal cord trauma was induced by the application of vascular clips (force of 24 g) to the dura via a four-level T5 to T8 laminectomy. SCI in mice resulted in severe trauma characterized by edema, neutrophil infiltration, production of inflammatory mediators, tissue damage, and apoptosis. GW0742 treatment (0.3 mg kg(-1) i.p.) 1 and 6 h after the SCI significantly reduced 1) the degree of spinal cord inflammation and tissue injury (histological score), 2) neutrophil infiltration (myeloperoxidase activity), 3) nitrotyrosine formation, 4) proinflammatory cytokines expression, 5) nuclear factor-kappaB activation, 6) inducible nitric-oxide synthase expression, and 6) apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling staining, FasL, Bax, and Bcl-2 expression). Moreover, GW0742 significantly ameliorated the recovery of limb function (evaluated by motor recovery score). To elucidate whether the protective effects of GW0742 are related to activation of the PPAR-beta/delta receptor, we also investigated the effect of PPAR-beta/delta antagonist methyl 3-({[2-(methoxy)-4 phenyl]amino}sulfonyl)-2-thiophenecarboxylate (GSK0660) on the protective effects of GW0742. GSK0660 (1 mg/kg i.p. 30 min before treatment with GW0742) significantly blocked the effect of the PPAR-beta/delta agonist and thus abolished the protective effect. Our results clearly demonstrate that GW0742 treatment reduces the development of inflammation and tissue injury associated with spinal cord trauma.

PPARgamma1 and LXRalpha face a new regulator of macrophage cholesterol homeostasis and inflammatory responsiveness, AEBP1

Peroxisome proliferator-activated receptor γ1 (PPARγ1) and liver X receptor α (LXRα) are nuclear receptors that play pivotal roles in macrophage cholesterol homeostasis and inflammation; key biological processes in atherogenesis. The activation of PPARγ1 and LXRα by natural or synthetic ligands results in the transactivation of ABCA1, ABCG1, and ApoE; integral players in cholesterol efflux and reverse cholesterol transport. In this review, we describe the structure, isoforms, expression pattern, and functional specificity of PPARs and LXRs. Control of PPARs and LXRs transcriptional activity by coactivators and corepressors is also highlighted. The specific roles that PPARγ1 and LXRα play in inducing macrophage cholesterol efflux mediators and antagonizing macrophage inflammatory responsiveness are summarized. Finally, this review focuses on the recently reported regulatory functions that adipocyte enhancer-binding protein 1 (AEBP1) exerts on PPARγ1 and LXRα transcriptional activity in the context of macrophage cholesterol homeostasis and inflammation.

Systemic hyperthermia masks the neuroprotective effects of MK-801, but not rosiglitazone in brain ischaemia

The use of neuroprotective agents has been under investigation for the treatment of ischaemic brain stroke. In this study, we examined the effects of rosiglitazone and MK-801, two potential neuroprotectants, on thromboembloic focal stroke in hyperthermic rats. The animals were assigned into groups of rosiglitazone, MK-801 and control, all under both normothermic and hyperthermic conditions. A focal ischaemia was induced by injection of preformed clot into the origin of the middle cerebral artery. The animals were assessed by measuring infarct size and brain oedema and also evaluating neurological deficit and seizure activity. Rosiglitazone improved infarct volume and neurological deficit in both normo- (36%) and hyperthermic (63%) animals; but MK-801 only improved normothermic animals. Our results do not support the use of MK-801 in hyperthermic conditions of brain stroke but suggest that rosiglitazone may preserve its efficiency even in hyperthermia.

Regulation of IkappaBalpha function and NF-kappaB signaling: AEBP1 is a novel proinflammatory mediator in macrophages

NF-κB comprises a family of transcription factors that are critically involved in various inflammatory processes. In this paper, the role of NF-κB in inflammation and atherosclerosis and the regulation of the NF-κB signaling pathway are summarized. The structure, function, and regulation of the NF-κB inhibitors, IκBα and IκBβ, are reviewed. The regulation of NF-κB activity by glucocorticoid receptor (GR) signaling and IκBα sumoylation is also discussed. This paper focuses on the recently reported regulatory function that adipocyte enhancer-binding protein 1 (AEBP1) exerts on NF-κB transcriptional activity in macrophages, in which AEBP1 manifests itself as a potent modulator of NF-κB via physical interaction with IκBα and a critical mediator of inflammation. Finally, we summarize the regulatory roles that recently identified IκBα-interacting proteins play in NF-κB signaling. Based on its proinflammatory roles in macrophages, AEBP1 is anticipated to serve as a therapeutic target towards the treatment of various inflammatory conditions and disorders.

Amelioration of glucose intolerance by the synthetic androstene HE3286: link to inflammatory pathways

Insulin resistance, the major metabolic abnormality underlying type 2 diabetes, is associated with chronic inflammation and heavy macrophage infiltration in white adipose tissue (WAT). The therapeutic properties of the synthetic adrenal steroid Delta(5)-androstene-17alpha-ethynyl-3beta,7beta,17beta-triol (HE3286) were characterized in metabolic disease models. Treatment of diabetic db/db mice with HE3286 suppressed progression to hyperglycemia and markedly improved glucose clearance. Similar effects were also observed in insulin-resistant, diet-induced obese C57BL/6J mice and genetically obese ob/ob mice. This effect appeared to be a consequence of reduced insulin resistance because HE3286 lowered blood insulin levels in db/db and ob/ob mice. Treatment with HE3286 was accompanied by suppressed expression of the prototype macrophage-attracting chemokine monocyte chemoattractant protein-1 in WAT, along with its cognate receptor C-C motif chemokine receptor-2. Exposure of mouse macrophages to HE3286 in vitro caused partial suppression of endotoxin (lipopolysaccharide)-induced nuclear factor kappa-B (NF-kappaB)-sensitive reporter gene expression, NF-kappaB nuclear translocation, and NF-kappaB/p65 serine phosphorylation. Proinflammatory kinases, including IkappaB kinase, c-Jun NH2-terminal kinase, and p38, were also inhibited by HE3286. In ligand competition experiments HE3286 did not bind to classical sex steroid or corticosteroid receptors, including androgen receptor (AR), progesterone receptor, estrogen receptor (ER) alpha or ERbeta, and glucocorticoid receptor (GR). Likewise, in cells expressing nuclear receptor-sensitive reporter genes HE3286 did not substantially stimulate transactivation of AR, ER, GR, or peroxisome proliferator-activated receptor (PPAR) alpha, PPARdelta, and PPARgamma. These findings indicate that HE3286 improves glucose homeostasis in diabetic and insulin-resistant mice and suggest that the observed therapeutic effects result from attenuation of proinflammatory pathways, independent of classic sex steroid receptors, corticosteroid receptors, or PPARs.

Repression of beta-catenin signaling by PPAR gamma ligands

Aberrant activation of the Wnt/beta-catenin signaling pathway plays a crucial role in oncogenesis of various human malignancies. It has been demonstrated that there is a direct interaction between beta-catenin and PPAR gamma. Here we examined the effects of fifteen reported PPAR ligands in a reporter gene assay that is dependent on beta-catenin activation of TCF/LEF transcription factors; only the thiazolidinedione PPAR gamma agonists troglitazone, rosiglitazone and pioglitazone, and a non-thiazolidinedione PPAR gamma activator GW1929 inhibited beta-catenin-induced transcription in a PPAR gamma dependent fashion. The results from mammalian one-hybrid experiments showed that functional PPAR gamma was necessary for ligand-dependent inhibition of beta-catenin transactivation. However, a PPAR gamma activator Fmoc-Leu could not repress beta-catenin-mediated signaling and its transactivation activity. These results indicate that activation of PPAR gamma is necessary, but not sufficient, for the beta-catenin antagonistic activity of a PPAR gamma agonist, and that the inhibitory compounds interfere directly with beta-catenin transactivation activity.

Lipotoxicity in macrophages: evidence from diseases associated with the metabolic syndrome

Accumulation of lipid metabolites within non-adipose tissues can induce chronic inflammation by promoting macrophage infiltration and activation. Oxidized and glycated lipoproteins, free fatty acids, free cholesterol, triacylglycerols, diacylglycerols and ceramides have long been known to induce cellular dysfunction through their pro-inflammatory and pro-apoptotic properties. Emerging evidence suggests that macrophage activation by lipid metabolites and further modulation by lipid signaling represents a common pathogenic mechanism underlying lipotoxicity in atherosclerosis, obesity-associated insulin resistance and inflammatory diseases related to metabolic syndrome such as liver steatosis and chronic kidney disease. In this review, we discuss the latest discoveries that support the role of lipids in modulating the macrophage phenotype in different metabolic diseases. We describe the common mechanisms by which lipid derivatives, through modulation of macrophage function, promote plaque instability in the arterial wall, impair insulin responsiveness and contribute to inflammatory liver, muscle and kidney disease. We discuss the molecular mechanism of lipid activation of pro-inflammatory pathways (JNK, NFkappaB) and the key roles played by the PPAR and LXR nuclear receptors-lipid sensors that link lipid metabolism and inflammation.

Targeting host factors: a novel rationale for the management of hepatitis C virus

Hepatitis C is recognized as a major threat to global public health. The current treatment of patients with chronic hepatitis C is the addition of ribavirin to interferon-based therapy which has limited efficacy, poor tolerability, and significant expense. New treatment options that are more potent and less toxic are much needed. Moreover, more effective treatment is an urgent priority for those who relapse or do not respond to current regimens. A major obstacle in combating hepatitis C virus (HCV) infection is that the fidelity of the viral replication machinery is notoriously low, thus enabling the virus to quickly develop mutations that resist compounds targeting viral enzymes. Therefore, an approach targeting the host cofactors, which are indispensable for the propagation of viruses, may be an ideal target for the development of antiviral agents because they have a lower rate of mutation than that of the viral genome, as long as they have no side effects to patients. Drugs targeting, for example, receptors of viral entry, host metabolism or nuclear receptors, which are factors required to complete the HCV life cycle, may be more effective in combating the viral infection. Targeting host cofactors of the HCV life cycle is an attractive concept because it imposes a higher genetic barrier for resistance than direct antiviral compounds. However the principle drawback of this strategy is the greater potential for cellular toxicity.

Influence of conjugated linoleic acids on functional properties of vascular cells

Conjugated linoleic acids (CLA) are biologically highly active lipid compounds that inhibit the development of atherosclerotic plaques in experimental animals. The underlying mechanisms of action, however, are only poorly understood. Since cell-culture experiments are appropriate to provide a detailed view into the mechanisms of action of a compound, the present review summarises results fromin vitrostudies dealing with the effects of CLA isomers and CLA mixtures on functional properties of cells of the vascular wall, such as endothelial cells, smooth muscle cells and monocyte-derived macrophages, which are amongst the major cells contributing to atherosclerotic lesion development. Based on these studies, it can be concluded that CLA exert several beneficial actions in cells of the vascular wall through the activation of nuclear PPAR. These actions of CLA, which may, at least partially, explain the inhibition of atherogenesis by dietary CLA, include modulation of vasoactive mediator release from endothelial cells, inhibition of inflammatory and fibrotic processes in activated smooth muscle cells, abrogation of inflammatory responses in activated macrophages, and reduction of cholesterol accumulation in macrophage-derived foam cells.

PPARs and the cardiovascular system

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear hormone-receptor superfamily. Originally cloned in 1990, PPARs were found to be mediators of pharmacologic agents that induce hepatocyte peroxisome proliferation. PPARs also are expressed in cells of the cardiovascular system. PPAR gamma appears to be highly expressed during atherosclerotic lesion formation, suggesting that increased PPAR gamma expression may be a vascular compensatory response. Also, ligand-activated PPAR gamma decreases the inflammatory response in cardiovascular cells, particularly in endothelial cells. PPAR alpha, similar to PPAR gamma, also has pleiotropic effects in the cardiovascular system, including antiinflammatory and antiatherosclerotic properties. PPAR alpha activation inhibits vascular smooth muscle proinflammatory responses, attenuating the development of atherosclerosis. However, PPAR delta overexpression may lead to elevated macrophage inflammation and atherosclerosis. Conversely, PPAR delta ligands are shown to attenuate the pathogenesis of atherosclerosis by improving endothelial cell proliferation and survival while decreasing endothelial cell inflammation and vascular smooth muscle cell proliferation. Furthermore, the administration of PPAR ligands in the form of TZDs and fibrates has been disappointing in terms of markedly reducing cardiovascular events in the clinical setting. Therefore, a better understanding of PPAR-dependent and -independent signaling will provide the foundation for future research on the role of PPARs in human cardiovascular biology.

Effects of the PPAR-beta agonist GW501516 in an in vitro model of brain inflammation and antibody-induced demyelination

Background

Brain inflammation plays a central role in numerous brain pathologies, including multiple sclerosis (MS). Microglial cells and astrocytes are the effector cells of neuroinflammation. They can be activated also by agents such as interferon-γ (IFN-γ) and lipopolysaccharide (LPS). Peroxisome proliferator-associated receptor (PPAR) pathways are involved in the control of the inflammatory processes, and PPAR-β seems to play an important role in the regulation of central inflammation. In addition, PPAR-β agonists were shown to have trophic effects on oligodendrocytes in vitro, and to confer partial protection in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. In the present work, a three-dimensional brain cell culture system was used as in vitro model to study antibody-induced demyelination and inflammatory responses. GW 501516, a specific PPAR-β agonist, was examined for its capacity to protect from antibody-mediated demyelination and to prevent inflammatory responses induced by IFN-γ and LPS.

Methods

Aggregating brain cells cultures were prepared from embryonal rat brain, and used to study the inflammatory responses triggered by IFN-γ and LPS and by antibody-mediated demyelination induced by antibodies directed against myelin-oligodendrocyte glycoprotein (MOG). The effects of GW 501516 on cellular responses were characterized by the quantification of the mRNA expression of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), inducible NO synthase (i-NOS), PPAR-β, PPAR-γ, glial fibrillary acidic protein (GFAP), myelin basic protein (MBP), and high molecular weight neurofilament protein (NF-H). GFAP expression was also examined by immunocytochemistry, and microglial cells were visualized by isolectin B4 (IB4) and ED1 labeling.

Results

GW 501516 decreased the IFN-γ-induced up-regulation of TNF-α and iNOS in accord with the proposed anti-inflammatory effects of this PPAR-β agonist. However, it increased IL-6 m-RNA expression. In demyelinating cultures, reactivity of both microglial cells and astrocytes was observed, while the expression of the inflammatory cytokines and iNOS remained unaffected. Furthermore, GW 501516 did not protect against the demyelination-induced changes in gene expression.

Conclusion

Although GW 501516 showed anti-inflammatory activity, it did not protect against antibody-mediated demyelination. This suggests that the protective effects of PPAR-β agonists observed in vivo can be attributed to their anti-inflammatory properties rather than to a direct protective or trophic effect on oligodendrocytes.

Pioglitazone reduces inflammatory responses of human adipocytes to factors secreted by monocytes/macrophages

Infiltration of monocyte-derived macrophages into adipose tissue may contribute to tissue and systemic inflammation and insulin resistance. We hypothesized that pioglitazone (Pio) could specifically reduce the inflammatory response of adipocytes to factors released by monocytes/macrophages. We show that macrophage factors (Mphi-factors) greatly increase expression levels of proinflammatory adipokines, chemokines, and adhesion molecules in human subcutaneous and visceral adipose tissue (SAT and VAT) as well as in adipocytes (up to several hundredfold of control). Compared with SAT, VAT showed enhanced basal and Mphi-factor-induced inflammatory responses. Mphi-factors also induced greater lipolysis in adipocytes, as assessed by concentrations of glycerol released from the cells (196 +/- 13 vs. 56 +/- 7 microM in control, P < 0.05). Pretreatment of adipose tissue or adipocytes with Pio reduced these responses to Mphi-factors (by 13-86%, P < 0.05) and prevented Mphi-factor suppression of adiponectin expression. Furthermore, Pio pretreatment of adipocytes and macrophages tended to further reduce inflammatory responses of adipocytes to Mphi-factors and monocyte adhesion to Mphi-factor-activated adipocytes. In support of these in vitro data, media conditioned by monocytes isolated from impaired glucose-tolerant subjects treated with Pio (compared with placebo) induced release of lower concentrations of proinflammatory adipokines and glycerol (100 +/- 7 vs. 150 +/- 15 microM, P < 0.05) from adipocytes. In summary, Pio decreases inflammatory responses in adipose tissue/cells induced by monocytes/macrophages by acting on either or both cell types. These beneficial effects of Pio may attenuate proinflammatory responses resulting from monocyte/macrophage infiltration into adipose tissue and suppress tissue inflammation resulting from the interaction between both cell types.

MBX-102/JNJ39659100, a novel peroxisome proliferator-activated receptor-ligand with weak transactivation activity retains antidiabetic properties in the absence of weight gain and edema

MBX-102/JNJ39659100 (MBX-102) is in clinical development as an oral glucose-lowering agent for the treatment of type 2 diabetes. MBX-102 is a nonthiazolidinedione (TZD) selective partial agonist of peroxisome proliferator-activated receptor (PPAR)-gamma that is differentiated from the TZDs structurally, mechanistically, preclinically and clinically. In diabetic rodent models, MBX-102 has insulin-sensitizing and glucose-lowering properties comparable to TZDs without dose-dependent increases in body weight. In vitro, in contrast with full PPAR-gamma agonist treatment, MBX-102 fails to drive human and murine adipocyte differentiation and selectively modulates the expression of a subset of PPAR-gamma target genes in mature adipocytes. Moreover, MBX-102 does not inhibit osteoblastogenesis of murine mesenchymal cells. Compared with full PPAR-gamma agonists, MBX-102 displays differential interactions with the PPAR-gamma ligand binding domain and possesses reduced ability to recruit coactivators. Interestingly, in primary mouse macrophages, MBX-102 displays enhanced antiinflammatory properties compared with other PPAR-gamma or alpha/gamma agonists, suggesting that MBX-102 has more potent transrepression activity. In summary, MBX-102 is a selective PPAR-gamma modulator with weak transactivation but robust transrepression activity. MBX-102 exhibits full therapeutic activity without the classical PPAR-gamma side effects and may represent the next generation insulin sensitizer.

Transcriptional profiling of mycobacterial antigen-induced responses in infants vaccinated with BCG at birth

Background

Novel tuberculosis (TB) vaccines recently tested in humans have been designed to boost immunity induced by the current vaccine, Mycobacterium bovis Bacille Calmette-Guérin (BCG). Because BCG vaccination is used extensively in infants, this population group is likely to be the first in which efficacy trials of new vaccines will be conducted. However, our understanding of the complexity of immunity to BCG in infants is inadequate, making interpretation of vaccine-induced immune responses difficult.

Methods

To better understand BCG-induced immunity, we performed gene expression profiling in five 10-week old infants routinely vaccinated with BCG at birth. RNA was extracted from 12 hour BCG-stimulated or purified protein derivative of tuberculin (PPD)-stimulated PBMC, isolated from neonatal blood collected 10 weeks after vaccination. RNA was hybridised to the Sentrix^® HumanRef-8 Expression BeadChip (Illumina) to measure expression of >16,000 genes.

Results

We found that ex vivo stimulation of PBMC with PPD and BCG induced largely similar gene expression profiles, except that BCG induced greater macrophage activation. The peroxisome proliferator-activated receptor (PPAR) signaling pathway, including PPAR-γ, involved in activation of the alternative, anti-inflammatory macrophage response was down-regulated following stimulation with both antigens. In contrast, up-regulation of genes associated with the classic, pro-inflammatory macrophage response was noted. Further analysis revealed a decrease in the expression of cell adhesion molecules (CAMs), including integrin alpha M (ITGAM), which is known to be important for entry of mycobacteria into the macrophage. Interestingly, more leukocyte genes were down-regulated than up-regulated.

Conclusion

Our results suggest that a combination of suppressed and up-regulated genes may be key in determining development of protective immunity to TB induced by vaccination with BCG.

Peroxisome proliferator activated receptor beta/delta activation prevents extracellular regulated kinase 1/2 phosphorylation and protects the testis from ischemia and reperfusion injury

PURPOSE

Testicular torsion is a medical emergency that requires immediate diagnosis and treatment to avoid subsequent testicular injury and infertility. PPARs are a family of nuclear hormone receptors belonging to the steroid receptor superfamily. Three PPAR isotypes (alpha, beta/delta and gamma) encoded by separate genes and showing different tissue distribution patterns have been identified. PPARbeta/delta is expressed in testis and its role is largely unknown. We tested whether pharmacological activation of PPARbeta/delta might protect the testis from ischemia and reperfusion injury.

MATERIALS AND METHODS

Adult male Sprague-Dawley rats were subjected to 1-hour testicular ischemia, followed by 24 hours of reperfusion. Sham testicular ischemia-reperfusion rats served as controls. The animals were randomized to receive immediately after detorsion 1) L-165,041 (4 mg/kg intraperitoneally), a potent agonist of PPARbeta/delta, 2) GW9662 (Calbiochem(R)) (4 mg/kg intraperitoneally), an antagonist of PPAR, 3) L-165,041 (4 mg/kg intraperitoneally) plus GW9662 (4 mg/kg intraperitoneally) concomitantly or 4) vehicle (1 ml/kg 10% dimethyl sulfoxide/NaCl solution). We evaluated testicular extracellular signal regulated kinase, tumor necrosis factor-alpha and interleukin-6 by Western blot. We also investigated PPARbeta/delta activation by Western blot, mRNA expression and organ damage.

RESULTS

Testicular ischemia-reperfusion injury caused a significant increase in extracellular signal regulated kinase, tumor necrosis factor-alpha and interleukin-6 expression in each testis. Furthermore, histological examination revealed marked damage. L-165,041 administration increased the PPARbeta/delta message and protein, inhibited extracellular signal regulated kinase, tumor necrosis factor-alpha and interleukin-6 expression, and decreased histological damage. Concomitant administration of GW9662 reversed the protection exerted by PPARbeta/delta agonist.

CONCLUSIONS

These findings indicate that PPARbeta/delta agonists might be an attractive therapeutic candidate for managing testicular torsion.

Ligand-activated peroxisome proliferator-activated receptor-gamma protects against ischemic cerebral infarction and neuronal apoptosis by 14-3-3 epsilon upregulation

BACKGROUND

Thiazolidinediones have been reported to protect against ischemia-reperfusion injury. Their protective actions are considered to be peroxisome proliferator-activated receptor-gamma (PPAR-gamma)-dependent; however, it is unclear how PPAR-gamma activation confers resistance to ischemia-reperfusion injury.

METHODS AND RESULTS

We evaluated the effects of rosiglitazone or PPAR-gamma overexpression on cerebral infarction in a rat model and investigated the antiapoptotic actions in the N2-A neuroblastoma cell model. Rosiglitazone or PPAR-gamma overexpression significantly reduced infarct volume. The protective effect was abrogated by PPAR-gamma small interfering RNA. In mice with knock-in of a PPAR-gamma dominant-negative mutant, infarct volume was enhanced. Proteomic analysis revealed that brain 14-3-3epsilon was highly upregulated in rats treated with rosiglitazone. Upregulation of 14-3-3epsilon was abrogated by PPAR-gamma small interfering RNA or antagonist. Promoter analysis and chromatin immunoprecipitation revealed that rosiglitazone induced PPAR-gamma binding to specific regulatory elements on the 14-3-3epsilon promoter and thereby increased 14-3-3epsilon transcription. 14-3-3epsilon Small interfering RNA abrogated the antiapoptotic actions of rosiglitazone or PPAR-gamma overexpression, whereas 14-3-3epsilon recombinant proteins rescued brain tissues and N2-A cells from ischemia-induced damage and apoptosis. Elevated 14-3-3epsilon enhanced binding of phosphorylated Bad and protected mitochondrial membrane potential.

CONCLUSIONS

Ligand-activated PPAR-gamma confers resistance to neuronal apoptosis and cerebral infarction by driving 14-3-3epsilon transcription. 14-3-3epsilon Upregulation enhances sequestration of phosphorylated Bad and thereby suppresses apoptosis.

LPS-induced suppression of macrophage cholesterol efflux is mediated by adipocyte enhancer-binding protein 1

Macrophages facilitate clearance of cholesterol from the body via reverse cholesterol transport (RCT). The first event in RCT is internalization of modified low density lipoprotein by macrophages, upon which PPARgamma1 and LXRalpha signaling pathways are turned on, leading to the transactivation of a cascade of genes (e.g. ABCA1 and ABCG1), whose products promote macrophage cholesterol efflux. Down-regulation of macrophage cholesterol efflux mediators leads to an imbalance in cholesterol homeostasis, promoting foam cell formation. Lipopolysaccharide (LPS) has been shown to suppress PPARgamma1 and its downstream target genes in macrophages, inducing foam cell formation; a key mechanism proposed to underlie bacterial infection-induced atherosclerosis. Herein, we show that adipocyte enhancer-binding protein 1 (AEBP1) is up-regulated during monocyte differentiation. Moreover, we provide experimental evidence suggesting that AEBP1 expression is induced by LPS, and that LPS-induced down-regulation of pivotal macrophage cholesterol efflux mediators, leading to foam cell formation, is largely mediated by AEBP1. Although AEBP1-independent pathways seem to contribute to these LPS effects, such pathways can only mediate lesser and delayed effects of LPS on macrophage cholesterol efflux and development of foam cells. We speculate that AEBP1 may serve as a potential therapeutic target for the prevention/treatment of bacterial infection-induced atherosclerosis.

Peroxisome proliferator-activated receptors and hepatitis C virus-induced insulin resistance

Insulin resistance and type 2 diabetes are associated with hepatitis C virus infection. A wealth of clinical and experimental data suggests that the virus is directly interfering with the insulin signalling in hepatocytes. In the case of at least one viral genotype (the type 3a), insulin resistance seems to be directly mediated by the downregulation of the peroxisome proliferator-activated receptor gamma. Whether and how this interaction may be manipulated pharmacologically, in order to improve the responsiveness to antivirals of insulin resistant chronic hepatitis C, patients remain to be fully explored.

PPAR-delta in Vascular Pathophysiology

Peroxisome proliferator-activated receptors belong to the superfamily of ligand-dependent nuclear receptor transcription factors, which include three subtypes: PPAR-α, β/δ, and γ. PPAR-δ, play important roles in the regulation of cell growth and differentiation as well as tissue wound and repair. Emerging evidence has also demonstrated that PPAR-δ is implicated in lipids and glucose metabolism. Most recently, the direct effects of PPAR-δ on cardiovascular processes such as endothelial function and angiogenesis have also been investigated. Therefore, it is suggested that PPAR-δ may have critical roles in cardiovascular pathophysiology and is a potential target for therapeutic intervention of cardiovascular disorders such as atherosclerosis.