Regulation of macrophage gene expression by the peroxisome proliferator-activated receptor-gamma

Excessive dietary linoleic acid promotes plasma accumulation of pronociceptive fatty acyl lipid mediators

Various fatty acyl lipid mediators are derived from dietary polyunsaturated fatty acids (PUFAs) and modulate nociception. The modern diet is rich in linoleic acid, which is associated with nociceptive hypersensitivities and may present a risk factor for developing pain conditions. Although recommendations about fatty acid intake exist for some diseases (e.g. cardiovascular disease), the role of dietary fatty acids in promoting pain disorders is not completely understood. To determine how dietary linoleic acid content influences the accumulation of pro- and anti-nociceptive fatty acyl lipid mediators, we created novel rodent diets using custom triglyceride blends rich in either linoleic acid or oleic acid. We quantified the fatty acyl lipidome in plasma of male and female rats fed these custom diets from the time of weaning through nine weeks of age. Dietary fatty acid composition determined circulating plasma fatty acyl lipidome content. Exposure to a diet rich in linoleic acid was associated with accumulation of linoleic and arachidonic acid-derived pro-nociceptive lipid mediators and reduction of anti-nociceptive lipid mediators derived from the omega-3 PUFAs. Our findings provide mechanistic insights into exaggerated nociceptive hypersensitivity associated with excessive dietary linoleic acid intake and highlight potential biomarkers for pain risk stratification.

Oxidized Lipids in Persistent Pain States

Chemotherapy, nerve injuries, or diseases like multiple sclerosis can cause pathophysiological processes of persistent and neuropathic pain. Thereby, the activation threshold of ion channels is reduced in peripheral sensory neurons to normally noxious stimuli like heat, cold, acid, or mechanical due to sensitization processes. This leads to enhanced neuronal activity, which can result in mechanical allodynia, cold allodynia, thermal hyperalgesia, spontaneous pain, and may initiate persistent and neuropathic pain. The treatment options for persistent and neuropathic pain patients are limited; for about 50% of them, current medication is not efficient due to severe side effects or low response to the treatment. Therefore, it is of special interest to find additional treatment strategies. One approach is the control of neuronal sensitization processes. Herein, signaling lipids are crucial mediators and play an important role during the onset and maintenance of pain. As preclinical studies demonstrate, lipids may act as endogenous ligands or may sensitize transient receptor potential (TRP)-channels. Likewise, they can cause enhanced activity of sensory neurons by mechanisms involving G-protein coupled receptors and activation of intracellular protein kinases. In this regard, oxidized metabolites of the essential fatty acid linoleic acid, 9- and 13-hydroxyoctadecadienoic acid (HODE), their dihydroxy-metabolites (DiHOMEs), as well as epoxides of linoleic acid (EpOMEs) and of arachidonic acid (EETs), as well as lysophospholipids, sphingolipids, and specialized pro-resolving mediators (SPMs) have been reported to play distinct roles in pain transmission or inhibition. Here, we discuss the underlying molecular mechanisms of the oxidized linoleic acid metabolites and eicosanoids. Furthermore, we critically evaluate their role as potential targets for the development of novel analgesics and for the treatment of persistent or neuropathic pain.

Exploiting the Therapeutic Potential of Endogenous Immunomodulatory Systems in Multiple Sclerosis-Special Focus on the Peroxisome Proliferator-Activated Receptors (PPARs) and the Kynurenines

Multiple sclerosis (MS) is a progressive neurodegenerative disease, characterized by autoimmune central nervous system (CNS) demyelination attributable to a disturbed balance between encephalitic T helper 1 (Th1) and T helper 17 (Th17) and immunomodulatory regulatory T cell (Treg) and T helper 2 (Th2) cells, and an alternatively activated macrophage (M2) excess. Endogenous molecular systems regulating these inflammatory processes have recently been investigated to identify molecules that can potentially influence the course of the disease. These include the peroxisome proliferator-activated receptors (PPARs), PPARγ coactivator-1alpha (PGC-1α), and kynurenine pathway metabolites. Although all PPARs ameliorate experimental autoimmune encephalomyelitis (EAE), recent evidence suggests that PPARα, PPARβ/δ agonists have less pronounced immunomodulatory effects and, along with PGC-1α, are not biomarkers of neuroinflammation in contrast to PPARγ. Small clinical trials with PPARγ agonists have been published with positive results. Proposed as immunomodulatory and neuroprotective, the therapeutic use of PGC-1α activation needs to be assessed in EAE/MS. The activation of indolamine 2,3-dioxygenase (IDO), the rate-limiting step of the kynurenine pathway of tryptophan (Trp) metabolism, plays crucial immunomodulatory roles. Indeed, Trp metabolites have therapeutic relevance in EAE and drugs with structural analogy to kynurenines, such as teriflunomide, are already approved for MS. Further studies are required to gain deeper knowledge of such endogenous immunomodulatory pathways with potential therapeutic implications in MS.

PPAR-gamma pathways attenuate pulmonary granuloma formation in a carbon nanotube induced murine model of sarcoidosis

Peroxisome proliferator activated receptor gamma (PPARγ), a ligand activated nuclear transcription factor, is constitutively expressed in alveolar macrophages of healthy individuals. PPARγ deficiencies have been noted in several lung diseases including the alveolar macrophages of pulmonary sarcoidosis patients. We have previously described a murine model of multiwall carbon nanotubes (MWCNT) induced pulmonary granulomatous inflammation which bears striking similarities to pulmonary sarcoidosis, including the deficiency of alveolar macrophage PPARγ. Further studies demonstrate alveolar macrophage PPARγ deficiency exacerbates MWCNT-induced pulmonary granulomas. Based on these observations we hypothesized that activation of PPARγ via administration of the PPARγ-specific ligand rosiglitazone would limit MWCNT-induced granuloma formation and promote PPARγ-dependent pathways. Results presented here show that rosiglitazone significantly limits the frequency and severity of MWCNT-induced pulmonary granulomas. Furthermore, rosiglitazone attenuates alveolar macrophage NF-κB activity and downregulates the expression of the pro-inflammatory mediators, CCL2 and osteopontin. PPARγ activation via rosiglitazone also prevents the MWCNT-induced deficiency of PPARγ-regulated ATP-binding cassette lipid transporter-G1 (ABCG1) expression. ABCG1 is crucial to pulmonary lipid homeostasis. ABCG1 deficiency results in lipid accumulation which promotes pro-inflammatory macrophage activation. Our results indicate that restoration of homeostatic ABCG1 levels by rosiglitazone correlates with both reduced pulmonary lipid accumulation, and decreased alveolar macrophage activation. These data confirm and further support our previous observations that PPARγ pathways are critical in regulating MWCNT-induced pulmonary granulomatous inflammation.

Mechanisms of peroxisome proliferator activated receptor γ regulation by non-steroidal anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs (NSAIDs) display anti-inflammatory, antipyretic and analgesic properties by inhibiting cyclooxygenases and blocking prostaglandin production. Previous studies, however, suggested that some NSAIDs also modulate peroxisome proliferator activated receptors (PPARs), raising the possibility that such off target effects contribute to the spectrum of clinically relevant NSAID actions. In this study, we set out to understand how peroxisome proliferator activated receptor-γ (PPARγ/PPARG) interacts with NSAIDs using X-ray crystallography and to relate ligand binding modes to effects on receptor activity. We find that several NSAIDs (sulindac sulfide, diclofenac, indomethacin and ibuprofen) bind PPARγ and modulate PPARγ activity at pharmacologically relevant concentrations. Diclofenac acts as a partial agonist and binds to the PPARγ ligand binding pocket (LBP) in typical partial agonist mode, near the β-sheets and helix 3. By contrast, two copies of indomethacin and sulindac sulfide bind the LBP and, in aggregate, these ligands engage in LBP contacts that resemble agonists. Accordingly, both compounds, and ibuprofen, act as strong partial agonists. Assessment of NSAID activities in PPARγ-dependent 3T3-L1 cells reveals that NSAIDs display adipogenic activities and exclusively regulate PPARγ-dependent target genes in a manner that is consistent with their observed binding modes. Further, PPARγ knockdown eliminates indomethacin activities at selected endogenous genes, confirming receptor-dependence of observed effects. We propose that it is important to consider how individual NSAIDs interact with PPARγ to understand their activities, and that it will be interesting to determine whether high dose NSAID therapies result in PPAR activation.

Characterization of proteins regulated by interleukin-4 in 3T3-L1 adipocytes

Obesity is closely associated with metabolic syndrome, type 2 diabetes mellitus (T2DM) and cardiovascular diseases. Our previous reports uncover the significant associations between interleukin-4 (IL-4)/IL-4 receptor genotypes and T2DM, as well as IL-4 genotypes and high density lipoprotein-cholesterol. Theses observations suggest that IL-4 harbors the capacity to regulate lipid metabolism. The present study is aimed at further elucidating regulatory roles of IL-4 to lipid metabolism by identifying putative proteins in 3T3-L1 adipocytes which are differentially expressed under IL-4 treatment. Proteins in mature 3T3-L1 adipocytes with altered expression levels under IL-4 treatment were identified by proteomic strategy. Our results revealed that IL-4 up-regulated levels of ATP synthase δ chain, Cytochrome c reductase, Pyrophsphatase and Vimentin, whereas, Alpha-enolase, Gelsolin, Vinculin and Valosin were down-regulated. These observations suggest that IL-4 promotes energy metabolism and inhibit lipid deposits in adipocytes by up-regulating proteins accelerating ATP synthesis. Our results suggest that IL-4 facilitates adipocytes metabolism to catabolism with a favorable condition for lipolysis. These catabolized lipids in adipocytes triggered by IL-4 might either be released into periphery or metabolized intracellularlly, and modulate systemic energy metabolism.

PPARγ Agonists in Adaptive Immunity: What Do Immune Disorders and Their Models Have to Tell Us?

Adaptive immunity has evolved as a very powerful and highly specialized tool of host defense. Its classical protagonists are lymphocytes of the T- and B-cell lineage. Cytokines and chemokines play a key role as effector mechanisms of the adaptive immunity. Some autoimmune and inflammatory diseases are caused by disturbance of the adaptive immune system. Recent advances in understanding the pathogenesis of autoimmune diseases have led to research on new molecular and therapeutic targets. PPARγ are members of the nuclear receptor superfamily and are transcription factors involved in lipid metabolism as well as innate and adaptive immunity. PPARγ is activated by synthetic and endogenous ligands. Previous studies have shown that PPAR agonists regulate T-cell survival, activation and T helper cell differentiation into effector subsets: Th1, Th2, Th17, and Tregs. PPARγ has also been associated with B cells. The present review addresses these issues by placing PPARγ agonists in the context of adaptive immune responses and the relation of the activation of these receptors with the expression of cytokines involved in adaptive immunity.

The Role of PPARs in Placental Immunology: A Systematic Review of the Literature

Pregnancy is a state of immunotolerance, and pregnancy outcome is strongly linked to the correct activation and balancing of the maternal immune system. Besides abortion as possible result of improper early pregnancy development, other pregnancy associated conditions like preeclampsia (PE), intrauterine growth retardation (IUGR), preterm labour, or gestational diabetes mellitus (GDM) are linked to immunologic overactivation and dysregulation. Both the innate and the adaptive immune system, and therefore B and T lymphocytes, natural killer cells (NK), macrophages and dendritic cells (DCs) are all involved in trophoblast invasion, pregnancy maintenance, and development of pregnancy disorders. Peroxisome proliferator activated receptors (PPARs) are nuclear transcription factors with three known isotypes: PPARα, PPARβ/δ, and PPARγ. They are expressed in most human organs and their function extends from regulating metabolism, homeostasis, and carcinogenesis to immune response. In the recent years, PPARs have been identified in most reproductive tissues and in all lines of immune cells. Only in few cases, the role of PPARs in reproductive immunology has been elucidated though the role of PPARs in immune answer and immunotolerance is evident. Within this paper we would like to give an update on today's knowledge about PPARs and immune cells in reproduction and highlight interesting interferences in regard of future therapeutic targets.

Macrophage lipoprotein lipase modulates the development of atherosclerosis but not adiposity

The role of macrophage lipoprotein lipase (LpL) in the development of atherosclerosis and adiposity was examined in macrophage LpL knockout (MLpLKO) mice. MLpLKO mice were generated using cre-loxP gene targeting. Loss of LpL in macrophages did not alter plasma LpL activity or lipoprotein levels. Incubation of apolipoprotein E (ApoE)-deficient β-VLDL with peritoneal macrophages from ApoE knockout mice lacking macrophage LpL (MLpLKO/ApoEKO) led to less cholesteryl ester formation than that found with ApoEKO macrophages. MLpLKO/ApoEKO macrophages had reduced intracellular triglyceride levels, with decreased CD36 and carnitine palmitoyltransferase-1 mRNA levels compared with ApoEKO macrophages, when incubated with VLDL. Although both MLpLKO/ApoEKO and ApoEKO mice developed comparable hypercholesterolemia in response to feeding with a Western-type diet for 12 weeks, atherosclerosis was less in MLpLKO/ApoEKO mice. Epididymal fat mass and gene expression levels associated with inflammation did not differ between the two groups. In conclusion, macrophage LpL plays an important role in the development of atherosclerosis but not adiposity.

Effects of gut-targeted 15-LOX-1 transgene expression on colonic tumorigenesis in mice

Expression of 15-lipoxygenase-1 (15-LOX-1) is decreased in many human cancers; however, the mechanistic significance of its decreased expression has been difficult to determine because its mouse homolog 12/15-LOX has opposing functions. We generated a mouse model in which expression of a human 15-LOX-1 transgene was targeted to the intestinal epithelium via the villin promoter. Targeted expression was confirmed by real-time reverse transcription-polymerase chain reaction and immunoblotting. When the 15-LOX-1 transgene was expressed in colonic epithelial cells of two independent mouse lines (B6 and FVB), azoxymethane-inducible colonic tumorigenesis was suppressed (mean number of tumors: wild type [WT] = 8.2, 15-LOX-1(+/-) = 4.91, 15-LOX-1(+/+) = 3.57; WT vs 15-LOX-1(+/-) two-sided P = .003, WT vs 15-LOX-1(+/+) two-sided P < .001; n = 10-14 mice per group). 15-LOX-1 transgene expression was always decreased in the tumors that did develop. In the presence of expression of the 15-LOX-1 transgene, expression of tumor necrosis factor alpha and its target inducible nitric oxide synthase were decreased and activation of nuclear factor-kappa B in colonic epithelial cells was inhibited.

Peroxisome Proliferator-Activated Receptor-γ-Mediated Polarization of Macrophages in Leishmania Infection

Infection is the outcome of a contest between a pathogen and its host. In the disease leishmaniasis, the causative protozoan parasites are harbored inside the macrophages. Leishmania species adapt strategies to make the infection chronic, keeping a balance between their own and the host's defense so as to establish an environment that is favorable for survival and propagation. Activation of peroxisome proliferator-activated receptor (PPAR) is one of the tactics used. This ligand-activated nuclear factor curbs inflammation to protect the host from excessive injuries by setting a limit to its destructive force. In this paper, we report the interaction of host PPARs and the pathogen for visceral leishmaniasis, Leishmania donovani, in vivo and in vitro. PPAR expression is induced by parasitic infection. Leishmanial activation of PPARγ promotes survival, whereas blockade of PPARγ facilitates removal of the parasite. Thus, Leishmania parasites harness PPARγ to increase infectivity.

Regulation of Lymphocyte Function by PPARgamma: Relevance to Thyroid Eye Disease-Related Inflammation

Thyroid eye disease (TED) is an autoimmune condition in which intense inflammation leads to orbital tissue remodeling, including the accumulation of extracellular macromolecules and fat. Disease progression depends upon interactions between lymphocytes and orbital fibroblasts. These cells engage in a cycle of reciprocal activation which produces the tissue characteristics of TED. Peroxisome proliferator-activated receptor-gamma (PPARgamma) may play divergent roles in this process, both attenuating and promoting disease progression. PPARgamma has anti-inflammatory activity, suggesting that it could interrupt intercellular communication. However, PPARgamma activation is also critical to adipogenesis, making it a potential culprit in the pathological fat accumulation associated with TED. This review explores the role of PPARgamma in TED, as it pertains to crosstalk between lymphocytes and fibroblasts and the development of therapeutics targeting cell-cell interactions mediated through this signaling pathway.

Pathophysiological Roles of PPARgamma in Gastrointestinal Epithelial Cells

Although the highest levels of PPARγ expression in the body have been reported in the gastrointestinal epithelium, little is known about the physiological functions of that receptor in the gut. Moreover, there is considerable controversy concerning the effects of thiazolidinedione PPARγ agonists on the two major diseases of the gastrointestinal track: colorectal cancer and inflammatory bowel disease. We will undertake to review both historical and recently published data with a view toward summarizing what is presently known about the roles of PPARγ in both physiological and pathological processes in the gastrointestinal epithelium.

Role of peroxisome proliferator-activated receptor gamma and its ligands in the treatment of hematological malignancies

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a multifunctional transcription factor with important regulatory roles in inflammation, cellular growth, differentiation, and apoptosis. PPARgamma is expressed in a variety of immune cells as well as in numerous leukemias and lymphomas. Here, we review recent studies that provide new insights into the mechanisms by which PPARgamma ligands influence hematological malignant cell growth, differentiation, and survival. Understanding the diverse properties of PPARgamma ligands is crucial for the development of new therapeutic approaches for hematological malignancies.

Nitroalkylation--a redox sensitive signaling pathway

Redox-sensitive posttranslational modification emerged as important signaling mechanisms. Besides other posttranslational modifications nitroalkylation by nitrated fatty acids mediate favorable anti-inflammatory effects. This review gives an overview of the generation and the reactivity of nitrated fatty acids. Additionally, it provides insights into the so far described pathways regulated by nitrated fatty acids. This article is part of a Special Issue entitled Regulation of Cellular Processes by S-nitrosylation.

Do PPAR-Gamma Agonists Have a Future in Parkinson's Disease Therapy?

Thiazolidinediones (TZDs) are peroxisome proliferator-activated receptor (PPAR)-γ agonists commonly used as insulin-sensitizing drugs for the treatment of type 2 diabetes. In the last decade, PPAR-γ agonists have received increasing attention for their neuroprotective properties displayed in a variety of neurodegenerative diseases, including Parkinson's disease (PD), likely related to the anti-infammatory activity of these compounds. Recent studies indicate that neuroinflammation, specifically reactive microglia, plays important roles in PD pathogenesis. Moreover, after the discovery of infiltrating activated Limphocytes in the substantia nigra (SN) of PD patients, most recent research supports a role of immune-mediated mechanisms in the pathological process leading to chronic neuroinflammation and dopaminergic degeneration. PPAR-γ are highly expressed in cells of both central and peripheral immune systems, playing a pivotal role in microglial activation as well as in monocytes and T cells differentiation, in which they act as key regulators of immune responses. Here, we review preclinical evidences of PPAR-γ-induced neuroprotection in experimental PD models and highlight relative anti-inflammatory mechanisms involving either central or peripheral immunomodulatory activity. Specific targeting of immune functions contributing to neuroinflammation either directly (central) or indirectly (peripheral) may represent a novel therapeutic approach for disease modifying therapies in PD.

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.

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.

The anti-inflammatory effects of interleukin-4 are not mediated by suppressor of cytokine signalling-1 (SOCS1)

While it is known that the anti-inflammatory effects of interleukin (IL)-4 require new protein synthesis, the exact mechanisms by which IL-4 suppresses the production of pro-inflammatory cytokines by human monocytes and macrophages is unclear. IL-4 rapidly induced suppressor of cytokine signalling-1 (SOCS1) mRNA and protein, which peaked at 60 min, much earlier than lipopolysaccharide (LPS)-induced SOCS1 mRNA and protein which were consistently maximal 4 hr post-exposure. SOCS1 is a molecule generally considered to be induced for negative feedback of inflammatory processes. We investigated whether the early induction of SOCS1 by IL-4 was responsible for the suppression of LPS-induced tumour necrosis factor (TNF)-alpha production by IL-4. IL-4 suppressed LPS-induced TNF-alpha in freshly isolated monocytes at the level of transcription but acted by a different, possibly translational, mechanism in monocytes cultured overnight in macrophage colony-stimulating factor (M-CSF). Despite different modes of regulation by IL-4, the kinetics and magnitude of induction of SOCS1 mRNA and protein by IL-4 in the two cell types were identical. There was no significant difference in the suppression by IL-4 of LPS-induced TNF-alpha production by bone-marrow derived macrophages from wild-type mice, Ifngamma(-/-) mice and mice lacking SOCS1 (Socs1(-/-)Ifngamma(-/-)). These data suggest that SOCS1 is not involved in the suppression of LPS-induced TNF-alpha production by IL-4.

PPARs in Irradiation-Induced Gastrointestinal Toxicity

The use of radiation therapy to treat cancer inevitably involves exposure of normal tissues. Although the benefits of this treatment are well established, many patients experience distressing complications due to injury to normal tissue. These side effects are related to inflammatory processes, and they decrease therapeutic benefit by increasing the overall treatment time. Emerging evidence indicates that PPARs and their ligands are important in the modulation of immune and inflammatory reactions. This paper discusses the effects of abdominal irradiation on PPARs, their role and functions in irradiation toxicity, and the possibility of using their ligands for radioprotection.

Human articular chondrocytes express 15-lipoxygenase-1 and -2: potential role in osteoarthritis

Introduction

15-Lipoxygenases and their metabolites have been shown to exhibit anti-inflammatory and immunomodulatory properties, but little is known regarding their expression and function in chondrocytes. The objective of this study was to evaluate the expression of 15-lipoxygenase-1 and -2 in human articular chondrocytes, and to investigate the effects of their metabolites 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids on IL-1β-induced matrix metalloproteinase (MMP)-1 and MMP-13 expression.

Methods

The expression levels of 15-lipoxygenase-1 and -2 were analyzed by reverse transcription PCR and Western blotting in chondrocytes, and by immunohistochemistry in cartilage. Chondrocytes or cartilage explants were stimulated with IL-1β in the absence or presence of 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids, and the levels of MMP-1 and MMP-13 protein production and type II collagen cleavage were evaluated using immunoassays. The role of peroxisome proliferator-activated receptor (PPAR)γ was evaluated using transient transfection experiments and the PPARγ antagonist GW9662.

Results

Articular chondrocytes express 15-lipoxygenase-1 and -2 at the mRNA and protein levels. 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids dose dependently decreased IL-1β-induced MMP-1 and MMP-13 protein and mRNA expression as well as type II collagen cleavage. The effect on MMP-1 and MMP-13 expression does not require de novo protein synthesis. 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids activated endogenous PPARγ, and GW9662 prevented their suppressive effect on MMP-1 and MMP-13 production, suggesting the involvement of PPARγ in these effects.

Conclusions

This study is the first to demonstrate the expression of 15-lipoxygenase-1 and -2 in articular chondrocytes. Their respective metabolites, namely 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids, suppressed IL-1β-induced MMP-1 and MMP-13 expression in a PPARγ-dependent pathway. These data suggest that 15-lipoxygenases may have chondroprotective properties by reducing MMP-1 and MMP-13 expression.

Peroxisome proliferator-activated receptor gamma overexpression suppresses growth and induces apoptosis in human multiple myeloma cells

PURPOSE

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a transcription factor that regulates immune and inflammatory responses. Our laboratory has shown that normal and malignant B cells, including multiple myeloma, express PPARgamma. Moreover, certain PPARgamma ligands can induce apoptosis in multiple myeloma cells. Because PPARgamma ligands can also have PPARgamma-independent effects, the role of PPARgamma in B-cell malignancies remains poorly understood. To further understand the role of PPARgamma, we examined the functional consequences of its overexpression in human multiple myeloma.

EXPERIMENTAL DESIGN

In the present work, we developed a lentiviral vector for PPARgamma gene delivery. We transduced multiple myeloma cells with a lentivirus-expressing PPARgamma and studied the involvement of this receptor on cell growth and viability.

RESULTS

PPARgamma overexpression decreased multiple myeloma cell proliferation and induced spontaneous apoptosis even in the absence of exogenous ligand. These PPARgamma-overexpressing cells were dramatically more sensitive to PPARgamma ligand-induced apoptosis compared with uninfected or LV-empty-infected cells. Apoptosis was associated with the down-regulation of antiapoptotic proteins X-linked inhibitor of apoptosis protein and myeloid cell leukemia-1 as well as induction of caspase-3 activity. Importantly, PPARgamma overexpression-induced cell death was not abrogated by coincubation with bone marrow stromal cells (BMSC), which are known to protect multiple myeloma cells from apoptosis. Additionally, PPARgamma overexpression in multiple myeloma or BMSC inhibited both basal and multiple myeloma-induced interleukin-6 production by BMSC.

CONCLUSIONS

Our results indicate that PPARgamma negatively controls multiple myeloma growth and viability in part through inhibition of interleukin-6 production by BMSC. As such, PPARgamma is a viable therapeutic target in multiple myeloma.

A phase i study of bolus 5-fluorouracil and leucovorin combined with weekly paclitaxel (FLTAX) as first-line therapy for advanced gastric cancer

OBJECTIVE

To determine the dose-limiting toxicity (DLT) and the maximum-tolerated dose (MTD) of combination chemotherapy with leucovorin-modulated weekly bolus 5-fluorouracil (5-FU) and weekly paclitaxel in patients with advanced gastric cancer (GC).

METHODS

Chemotherapy-naive patients with histologically proven metastatic or recurrent GC were enrolled. Paclitaxel was administered as a 1-h intravenous (i.v.) infusion followed by 5-FU as a bolus i.v. infusion on Days 1, 8 and 15. A 2-h i.v. infusion of l-leucovorin was started at the same time as the paclitaxel infusion on Days 1, 8 and 15. Treatment cycles were repeated every 28 days until disease progression or unacceptable toxicity occurred. Patients were scheduled to receive 5-FU, l-leucovorin and paclitaxel at four dose levels (mg/m(2)/week): 500/250/60 (level 1), 500/250/80 (level 2), 600/250/80 (level 3) and 600/250/100 (level 4), respectively.

RESULTS

Eighteen patients were enrolled. During the first cycle of the highest dose level (level 4), two of the six patients had DLT involving Grade 3 diarrhea and Grade 3 skin rash. Furthermore, three of the four patients who received the second consecutive cycle of treatment at dose level 4 had Grade 4 neutropenia. Dose level 3 was thus determined to be the MTD. Eleven (61%) of the 18 patients had partial responses, and the median progression-free survival time was 6.8 months.

CONCLUSIONS

The MTD and the recommended dose for phase II studies of this regimen were determined to be 5-FU 600 mg/m(2)/week, l-leucovorin 250 mg/m(2)/week and paclitaxel 80 mg/m(2)/week.

Effect of dopaminergic substances on sleep/wakefulness in saline- and MPTP-treated mice

Sleep/wakefulness (S/W) disorders are frequent in Parkinson's disease (PD). The underlying causes have yet to be elucidated but dopaminergic neurodegenerative lesions seem to contribute to appearance of the disorders and anti-Parkinsonian medication is known to accentuate S/W problems. Hence, we reasoned that studying the acute effect of dopaminergic compounds on S/W in an animal model of PD might improve our knowledge of S/W regulation in the context of partial dopaminergic depletion. To this end, we tested the effect of levodopa (l-dopa), pergolide (a mixed D(2)/D(1) agonist) and lisuride (a D(2) agonist) on S/W recordings in MPTP-treated mice, in comparison with controls. Our results showed that dopaminergic compounds modify S/W amounts in both control and MPTP mice. Wakefulness amounts are greater in MPTP mice after l-dopa (50 mg kg(-1)) and lisuride (1 mg kg(-1)) injections compared with control mice. Moreover, the paradoxical sleep latency was significantly longer in MPTP mice after high-dose l-dopa administration. Our observations suggest that the actions of both l-dopa and lisuride on S/W differ slightly in MPTP mice relative to controls. Hence, MPTP-induced partial DA depletion may modulate the effect of dopaminergic compounds on S/W regulation.

Cyclosporine A and Rapamycin induce in vitro cholesteryl ester transfer protein activity, and suppress lipoprotein lipase activity in human plasma

PURPOSE

Cyclosporine A (CsA), Rapamycin (RAPA), Tacrolimus (FK-506) and Mycophenolate mofetil (MMF) are immunosuppressants that are widely used in solid organ transplant patients. However, some of these drugs have been reported to cause dyslipidemia in patients. Our aim was to determine the effects of these drugs on in vitro cholesteryl ester transfer protein (CETP), hepatic lipase (HL) and lipoprotein lipase (LPL) activity within human plasma.

METHODS

We measured CETP activity in human normolipidemic plasma with and without drug treatment, by measuring the incorporation of labeled cholesteryl ester into lipoproteins. To further confirm the result, we also measured recombinant CETP (rCETP) activity with and without drug treatment. We measured HL and LPL activity in post-heparin normal human plasma in the presence and absence of the drugs by measuring the release of fatty acids from radiolabeled triolein.

RESULTS

We found an increase in CETP activity in human normolipidemic plasma and rCETP treated with CsA and RAPA. By contrast, CETP activity was not altered significantly in the presence of FK-506 and MMF. LPL activity in post-heparin normal human plasma was suppressed following the co-incubation with CsA, RAPA, FK-506 or MMF whereas HL activity remained unaffected.

CONCLUSIONS

The increase in CETP activity and suppression in LPL activity following CsA and RAPA treatment observed in the present study may be associated with elevated LDL cholesterol levels and hypertriglyceridemia seen in patients administered these drugs.

Lipoxygenase-derived metabolites are regulators of peroxisome proliferator-activated receptor gamma-2 expression in human vascular smooth muscle cells

BACKGROUND

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a member of the nuclear receptor family that has been implicated in cell differentiation and proliferation, glucose metabolism, macrophage development, and inflammatory responses. PPAR-gamma can be activated by a range of synthetic substances and also by products of lipid oxidation such as oxidized low-density lipoprotein, 13-hydroxyoctadecadienoic acid (13-HODE) and 15-hydroxyeicosatetraenoic acid (15-HETE). Since 12- and 15-lipoxygenase (12- and 15-LO) are expressed in human vascular smooth muscle cells (VSMCs), we set out to investigate the possible relation between PPAR-gamma and LO system in these cells.

METHODS

In vitro experiments in human VSMC using standard methods.

RESULTS

The LO products, 12-HETE (10(-7) mol/l), 15-HETE (10(-7) mol/l) and 13-HODE (10(-7) mol//l) increased the expression of PPAR-gamma-2 messenger RNA (mRNA) in VSMC (by 100, 50, and 100%, respectively. Rosiglitazone (1-10 micromol/l) was found to upregulate both the mRNA expression of two LO enzymes, platelet-type 12-lipoxygenase (12-LO; +70%) and 15-lipoxygenase type 2 (15-LO; +60%), and the secretion of their eicosanoid products 12- and 15-HETE. In addition, rosiglitazone-induced a threefold increase in PPAR-gamma-2 mRNA expressions and modest 50% rise in PPAR-gamma-1 mRNA expression. The effect of rosiglitazone on PPAR-gamma-2 could be entirely blocked by the LO inhibitor baicalein and restored by the addition of exogenous 12-HETE.

CONCLUSIONS

These results suggest a novel amplification cycle in which PPAR-gamma activation induces production of 12- and 15-LO-derived metabolites which in turn feed back to upregulate PPAR-gamma-2's own expression. The implications of this link in VSMC pathophysiology remain to be elucidated.

Peroxisome proliferator-activated receptors: new players in the field of reproduction

Peroxisome proliferator-activated receptors (PPAR) are members of the nuclear hormone receptor superfamily. Synthetic ligands to one family member, PPARgamma, are currently widely used as treatment for chronic diseases such as diabetes type II and other insulin resistances, e.g. as seen in polycystic ovary syndrome (PCOS). Moreover, novel approaches employing knock-out mice demonstrated that PPARgamma seems to play a key role in placental and fetal development. This review describes recent insights into the role of PPARs in human reproduction with specific reference to infertility, placental maturation and fetal development as well as disturbed pregnancy. Further, we highlight the current knowledge on synthetic ligands to PPARgamma used as a treatment in women with PCOS.

Biliary innate immunity and cholangiopathy

The intrahepatic biliary tree is a conduit of bile which contains pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharide (LPS) originated from intestinal flora. Human biliary epithelial cells (BEC) express toll-like receptors (TLR) and intracellular adaptor molecules and secrete antibiotic peptides and (pro)inflammatory cytokines via the activation of nuclear transcription factors. However, although human bile contains several PAMPs in normal as well as diseased livers, PAMPs physiologically do not elicit an inflammatory response in the biliary tree, suggesting that tolerance against commensal PAMPs including LPS (endotoxin tolerance) is important in maintaining the homeostasis of biliary innate immunity. Negative regulators of intracellular TLR signalings, peroxisome proliferator activating receptor-gamma (PPAR-gamma) and IRAK-M, are associated with the endotoxin tolerance in BEC. In vivo, PPAR-gamma and IRAK-M are ubiquitously expressed in intrahepatic biliary epithelium, while the expression of PPAR-gamma is reduced in damaged bile ducts of primary biliary cirrhosis (PBC). In addition to antibiotic peptides, several cytokines andchemokines are also secreted from BEC as an innate immune response and these humoral components participate in attracting immunocytes and modulating peribiliary cytokine milieu. BEC have receptors for several cytokines and the expression of TLR in BEC is affected by cytokines, suggesting that biliary innate immunity is regulated by an acquired immunity. A T-helper (Th)1-type cytokine, interferon-gamma, downregulates PPAR-gamma and upregulates TLR, and consequently increases the susceptibility of biliary innate immunity. Because periductal cytokine milieu in PBC is Th1-dominant, the increased susceptibility to PAMPs may be associated with the development of cholangiopathy in PBC. Biliary innate immunity is speculated to be associated with the pathogenesis of biliary diseases as well as the defense against biliary microbial infection.

PPARgamma expression profile and its cytokine driven regulation in atopic dermatitis

BACKGROUND

Recent studies point to the pathophysiological role of the peroxisome proliferators-activated receptor gamma (PPARgamma) in the inflammatory immune response. We have showed that activation of PPARgamma by specific ligands attenuates the allergic immune response via monocytes and lymphocytes. The objective of this study was to analyse the PPARgamma expression and its regulation via inflammatory cytokines.

METHODS

We examined the PPARgamma expression in the lesional and nonlesional skin of atopic patients by immunohistochemistry. The expression patterns of PPARgamma mRNA and its isoforms were investigated in peripheral mononuclear blood cells of atopic and nonatopic donors and in cytokine-stimulated populations by quantitative real-time RT-PCR.

RESULTS

Our data show an increased PPARgamma expression in lesional skin from atopic dermatitis patients. The analysis of PPARgamma mRNA reveals a significantly up-regulated expression of PPARgamma1 but not of PPARgamma2 in monocytes and CD4(+) T-cells from atopic dermatitis patients. Furthermore, we demonstrate that Th-cytokines, like IL-4, IL-13 and IFNgamma, which regulate the biphasic atopic immune response, directly regulate the expression of PPARgamma1.

CONCLUSION

Taken together, these data demonstrate that PPARgamma isoforms are differently expressed and regulated by the local cytokine-milieu. Whether the increased expression of the PPARgamma1 receptor may be beneficial or not for a PPARgamma ligand-based treatment of atopic dermatitis, is currently under investigation.

Adipose tissue macrophages

It is now broadly accepted that low-grade chronic inflammation associated with obesity leads to the onset of insulin resistance and type 2 diabetes mellitus. Obesity-associated inflammation is characterized by an increased abundance of macrophages in adipose tissue along with production of inflammatory cytokines. Adipose tissue macrophages (ATMs) are suspected to be the major source of inflammatory mediators such as TNF-alpha and IL-6 that interfere with adipocyte function by inhibiting insulin action. However, ATMs phenotypically resemble alternatively activated (M2) macrophages and are capable of anti-inflammatory mediator production challenging the concept that ATMs are simply the "bad guys" in obese adipose tissue. Triggers promoting ATM recruitment, ATM functions and dysfunctions, and stimuli and molecular mechanisms that drive them into becoming detrimental to their environment are subject to current research. Strategies to interfere with ATM recruitment and adverse activation could give rise to novel options for treatment and prevention of insulin resistance and type 2 diabetes mellitus.

Differential ability of a thiazolidinedione PPARgamma agonist to attenuate cytokine secretion in primary microglia and macrophage-like cells

Peroxisome proliferator-activated receptor gamma (PPARgamma) agonists are known to inhibit select pro-inflammatory changes in models of CNS and systemic inflammation. Recent reports suggest that these anti-inflammatory effects are due to mechanisms other than canonical nuclear receptor-mediated transcriptional alteration. Using primary microglia and the monocytic cell line, THP-1, we demonstrate that rosiglitazone, a PPARgamma-activating thiazolidinedione, decreases pro-inflammatory cytokine secretion as measured by ELISA. Cells were pre-treated with various thiazolidinediones, including rosiglitazone, prior to stimulation with lipopolysaccharide or phorbol 12-myristate 13-acetate (PMA) to stimulate cytokine production. Tumor necrosis factor alpha (TNFalpha) secretion was significantly inhibited in both primary microglia and THP-1 cells differentiated for 72 h in the presence of PMA to induce a macrophage-like phenotype. No reduction in TNFalpha secretion was observed in undifferentiated THP-1 cells with rosiglitazone pre-treatment. Electrophoretic mobility shift assay revealed no significant difference in PPARgamma activation between PMA-differentiated and undifferentiated THP-1 cells. When PMA-differentiated and undifferentiated THP-1 cells were treated with the irreversible PPARgamma antagonist, GW 9662, a significant, dose-dependent decrease in TNFalpha secretion was observed. These results suggest that the anti-inflammatory benefit of PPARgamma ligands occur independently of classical PPARgamma activation.

Interleukin-4 inhibition of interleukin-1-induced expression of matrix metalloproteinase-3 (MMP-3) is independent of lipoxygenase and PPARgamma activation in human gingival fibroblasts

Background

Interleukin 4 (IL-4) has been shown to suppress interleukin-1 (IL-1) induced expression of matrix metalloproteinase-3 (MMP-3) in human synovial and gingival fibroblasts, but the mechanism of suppression has not been determined. Activators of peroxisome proliferator-activated receptor-γ (PPARγ) have been shown to inhibit cytokine induced expression of MMPs in other cell types, and IL-4 has been shown to activate PPARγ by stimulating production of ligands through the lipoxygenase pathway. It has been suggested that PPARγ may inhibit expression of MMPs by competing with transcription factor AP-1 for binding to a putative composite binding element in the promoters. The objective of this study was to determine whether the suppressive effects of IL-4 on the IL-1 induced expression of MMP-3 involve activation of lipoxygenase and/or PPARγ.

Results

Western blotting revealed the presence of PPARγ in nuclear extract of HGF. IL-1 induced binding of nuclear extract to the putative composite PPRE/AP-1 site was diminished in the presence of pioglitazone, but there was no evidence of any change in the composition of the retarded complexes, and no evidence of PPARγ binding to this site. Nordihydroguaiaretic acid (NDGA), a non-selective lipoxygenase inhibitor, and MK886, a specific inhibitor of 5-lipoxygenase, induced MMP-3 expression synergistically with IL-1. However IL-4 was still able to inhibit MMP-3 expression in the presence of NDGA or MK886 and IL-1. Activation of PPARγ with pioglitazone not only failed to inhibit IL-1 induced expression of MMP-3 mRNA, but rather super-induced MMP-3 in the presence of IL-1. PPARγ antagonist GW9662 failed to abolish the suppressive effects of IL-4. Another PPARγ activator, 15-deoxy-Delta12,14prostaglandin J2 (15dPGJ2), also super-induced MMP-3 mRNA, and this was due at least in part to increased transcription.

Conclusion

IL-4 suppression of IL-1-induced MMP-3 expression in HGF is independent of lipoxygenase activity and activation of PPARγ. Super-induction of MMP-3 by pioglitazone may have important implications for patients using pioglitazone to treat type II diabetes in the presence of chronic inflammation.

The Pharmacodynamic Effects of Sirolimus andSirolimus-Calcineurin Inhibitor Combinations on Macrophage Scavenger and Nuclear Hormone Receptors

BACKGROUND

Sirolimus (SIR) alone or in combination with cyclosporine (CsA) or tacrolimus (TAC) are used in solid organ transplantation, but uncertainty remains regarding their respective atherogenic potentials.

METHODS

THP-1 cells were cultured as macrophages and then treated with plasma trough and peak concentration doses of SIR, SIR/CsA or SIR/TAC to assess the time- and dose-dependent mRNA or protein expression of selected atherogenic genes. The selected atherogenic genes included: the macrophage scavenger receptors (MSRs) CD36, CD68, scavenger receptor (SR)-A, SR-BII, and LOX-1; the nuclear hormone receptors peroxisome proliferator activated receptor gamma (PPARgamma) and liver-X-receptor alpha (LXRalpha); and the cholesterol efflux transporter (ABCA-1).

RESULTS

SIR-mediated changes in mRNA included the upregulation of ABCA1, downregulation of CD68, SR-A and SR-BII, and concentration- and/or time-dependent effects on CD36, LOX-1, PPARgamma, and LXRalpha that did not translate into significant protein changes. With SIR/CsA, the protein expressions of PPARgamma and ABCA-1 were downregulated at 8 h. In contrast, with SIR/TAC, PPARgamma, and ABCA-1 protein expressions were upregulated at 8 h.

CONCLUSIONS

Combination results differed from findings with SIR alone, supporting the observed clinical phenotype with calcineurin inhibitors. These findings may provide a rationale for the development of novel drug delivery strategies to mitigate adverse pharmacodynamic responses.

Activation of peroxisome proliferator-activated receptor-γ protects pancreatic β-cells from cytokine-induced cytotoxicity via NFκB pathway

Diabetes mellitus is characterized by cytokine-induced insulitis and a deficit in beta-cell mass. Ligands for peroxisome proliferator-activated receptor-gamma (PPAR-gamma) have been shown to have anti-inflammatory effects in various experimental models. We questioned whether activation of endogenous PPAR-gamma by either PPAR-gamma ligands or adenoviral-directed overexpression of PPAR-gamma (Ad-PPAR-gamma) could inhibit cytokine-induced beta-cell death in RINm5F (RIN) cells, a rat insulinoma cell line. Treatment of RIN cells with interleukin-1 beta (IL-1 beta) and interferon-gamma (IFN-gamma) induced beta-cell damage through NF kappaB-dependent signaling pathways. Activation of PPAR-gamma by PPAR-gamma ligands or Ad-PPAR-gamma inhibited IL-1 beta and IFN-gamma-stimulated nuclear translocation of the p65 subunit and DNA binding activity. NF kappaB target gene expression and their product formation, namely inducible nitric oxide synthase and cyclooxygenase-2 were decreased by PPAR-gamma activation, as established by real-time PCR, Western blots and measurements of NO and PGE(2). The mechanism by which PPAR-gamma activation inhibited NF kappaB-dependent cell death signals appeared to involve the inhibition of I kappa B alpha degradation, evidenced by inhibition of cytokine-induced NF kappaB-dependent signaling events by Ad-I kappaB alpha (S32A, S36A), non-degradable I kappaB alpha mutant. I kappaB beta mutant, Ad-I kappaB beta (S19A, S23A) was not effective in preventing cytokine toxicity. Furthermore, a protective effect of PPAR-gamma ligands was proved by assaying for normal insulin secreting capacity in response to glucose in isolated rat pancreatic islets. The beta-cell protective function of PPAR-gamma ligands might serve to counteract cytokine-induced beta-cell destruction.

Interleukin-4 induction of the CC chemokine TARC (CCL17) in murine macrophages is mediated by multiple STAT6 sites in the TARC gene promoter

Background

Macrophages (Mθ) play a central role in the innate immune response and in the pathology of chronic inflammatory diseases. Macrophages treated with Th2-type cytokines such as Interleukin-4 (IL-4) and Interleukin-13 (IL-13) exhibit an altered phenotype and such alternatively activated macrophages are important in the pathology of diseases characterised by allergic inflammation including asthma and atopic dermatitis. The CC chemokine Thymus and Activation-Regulated Chemokine (TARC/CCL17) and its murine homologue (mTARC/ABCD-2) bind to the chemokine receptor CCR4, and direct T-cell and macrophage recruitment into areas of allergic inflammation. Delineating the molecular mechanisms responsible for the IL-4 induction of TARC expression will be important for a better understanding of the role of Th2 cytokines in allergic disease.

Results

We demonstrate that mTARC mRNA and protein are potently induced by the Th2 cytokine, Interleukin-4 (IL-4), and inhibited by Interferon-γ (IFN-γ) in primary macrophages (Mθ). IL-4 induction of mTARC occurs in the presence of PI3 kinase pathway and translation inhibitors, but not in the absence of STAT6 transcription factor, suggesting a direct-acting STAT6-mediated pathway of mTARC transcriptional activation. We have functionally characterised eleven putative STAT6 sites identified in the mTARC proximal promoter and determined that five of these contribute to the IL-4 induction of mTARC. By in vitro binding assays and transient transfection of isolated sites into the RAW 264.7 Mθ cell-line, we demonstrate that these sites have widely different capacities for binding and activation by STAT6. Site-directed mutagenesis of these sites within the context of the mTARC proximal promoter revealed that the two most proximal sites, conserved between the human and mouse genes, are important mediators of the IL-4 response.

Conclusion

The induction of mTARC by IL-4 results from cooperative interactions between STAT6 sites within the mTARC gene promoter. Significantly, we have shown that transfer of the nine most proximal mTARC STAT6 sites in their endogenous conformation confers potent (up to 130-fold) IL-4 inducibility on heterologous promoters. These promoter elements constitute important and sensitive IL-4-responsive transcriptional units that could be used to drive transgene expression in sites of Th2 inflammation in vivo.

Classical and alternative activation of mononuclear phagocytes: Picking the best of both worlds for tumor promotion

Mononuclear phagocytes often function as control switches of the immune system, securing the balance between pro- and anti-inflammatory reactions. For this purpose and depending on the activating stimuli, these cells can develop into different subsets: classically (M1) or alternatively (M2) activated mononuclear phagocytes, the molecular and functional characterization of which is a current topic of investigation. Accumulating evidence suggests that cells of the monocyte/macrophage lineage can be hijacked by tumors for their own benefit. Either as immature cells in the periphery, or as mature macrophages at the tumor site, mononuclear phagocytes are able to influence the behavior of cancer cells, shape the tumor microenvironment and subvert anti-tumor immunity, thereby contributing to tumor growth and progression. This review focuses on the mechanisms behind monocyte/macrophage-mediated tumor promotion and interprets the available data within the M1/M2 conceptual frame.

TGF-beta inhibition of CTL re-stimulation requires accessory cells and induces peroxisome-proliferator-activated receptor-gamma (PPAR-gamma)

Effective cellular immunity to Epstein-Barr virus (EBV), necessary to prevent or cure many post-transplant lymphoproliferative disorders (PTLD), can be inhibited by transforming growth factor-beta (TGF-beta). In vitro, TGF-beta inhibits memory CTL re-stimulation from whole PBMC. We show that the effect of TGF-beta on CTL re-stimulation is not directly on the T cell, but requires an accessory cell (AC) population. Further, pre-treatment of AC with TGF-beta significantly reduces memory CTL re-stimulation and suppresses delayed type hypersensitivity (DTH) responses. Addition of exogenous interferon-gamma to the AC overcomes the effects of TGF-beta. TGF-beta pre-treatment also up-regulates expression of peroxisome-proliferator-activated receptor-gamma (PPAR-gamma) in CD14(+) AC. Importantly, pre-treatment of AC with the PPAR-gamma ligand, ciglitazone, results in significantly reduced memory CTL re-stimulation. Thus, the effects of TGF-beta in this system may be mediated in part via PPAR-gamma, and PPAR-gamma activation could have significant inhibitory effects on memory T-cell responses by affecting AC function. These data have important implications in understanding how memory CTL are re-stimulated and function to prevent disease, especially PTLD.

IL-4-induced peroxisome proliferator-activated receptor gamma activation inhibits NF-kappaB trans activation in central nervous system (CNS) glial cells and protects oligodendrocyte progenitors under neuroinflammatory disease conditions: implication for CNS-demyelinating diseases

Th2 phenotype cytokine, IL-4, plays an important role in the regulation of Th1 cell responses and spontaneous remission of inflammatory CNS demyelinating diseases such as multiple sclerosis (MS). In this study we demonstrate IL-4-induced down-regulation of inducible NO synthase (iNOS) expression and survival of differentiating oligodendrocyte progenitors (OPs) in proinflammatory cytokine (Cyt-Mix)-treated CNS glial cells, which is a condition similar to that observed in the brain of a patient with MS. IL-4 treatment of Cyt-Mix-treated CNS glial cells significantly decreased iNOS expression/NO release with a parallel increase in survival of differentiating OPs. IL-4 effects were concentration-dependent and could be reversed by anti-IL-4R Abs. The use of inhibitors for Akt, p38 MAPK, and peroxisome proliferator-activated receptor gamma (PPAR-gamma) antagonist revealed that inhibition of Cyt-Mix-induced iNOS expression and survival of differentiating OPs by IL-4 is via PPAR-gamma activation. There was a coordinate increase in the expression of both PPAR-gamma and its natural ligand-producing enzyme 12/15-lipoxygenase (12/15-LOX) in IL-4-treated cells. Next, EMSA, immunoblots, and transient cotransfection studies with reporter plasmids (pNF-kappaB-Luc and pTK-PPREx3-Luc) and 12/15-LOX small interfering RNA revealed that IL-4-induced PPAR-gamma activation antagonizes NF-kappaB transactivation in Cyt-Mix-treated astrocytes. In support of this finding, similarly treated 12/15-LOX(-/-) CNS glial cells further corroborated the result. Furthermore, there was reversal of IL-4 inductive effects in the brain of LPS-challenged 12/15-LOX(-/-) mice when compared with LPS-challenged wild-type mice. Together, these data for the first time demonstrate the inhibition of Cyt-Mix-induced NF-kappaB transactivation in CNS glial cells by IL-4 via PPAR-gamma activation, hence its implication for the protection of differentiating OPs during MS and other CNS demyelinating diseases.

A selective retinoid X receptor agonist bexarotene (LGD1069, targretin) inhibits angiogenesis and metastasis in solid tumours

The present study determined the influence of a retinoid X receptor agonist bexarotene on angiogenesis and metastasis in solid tumours. In the experimental lung metastasis xenograft models, treatment with bexarotene inhibited the development of the lung tumour nodule formation compared to control. In vivo angiogenesis assay utilising gelfoam sponges, bexarotene reduced angiogenesis in sponges containing vascular endothelial growth factor, epidermal growth factor and basic fibroblast growth factor to various extent. To determine the basis of these observations, human breast and non-small-cell lung cancer cells were subjected to migration and invasion assays in the presence of bexarotene. Our data showed that bexarotene decrease migration and invasiveness of tumour cells in a dose-dependent manner. Furthermore, bexarotene inhibited angiogenesis by directly inhibiting human umbilical vein endothelial cell growth and indirectly inhibiting tumour cell-mediated migration of human umbilical vein endothelial cells through Matrigel matrix. Analysis of tumour-conditioned medium indicated that bexarotene decreased the secretion of angiogenic factors and matrix metalloproteinases and increased the tissue inhibitor of matrix metalloproteinases. The ability of bexarotene to inhibit angiogenesis and metastasis was dependent on activation of its heterodimerisation partner peroxisome proliferator-activated receptor gamma. Collectively, our results suggest a role of bexarotene in treatment of angiogenesis and metastasis in solid tumours.

Inverse relationship between 15-lipoxygenase-2 and PPAR-gamma gene expression in normal epithelia compared with tumor epithelia

15-Lipoxygenase-2 (15-LOX-2) synthesizes 15-S-hydroxyeicosatetraenoic acid (15-S-HETE), an endogenous ligand for the nuclear receptor, peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Several studies have described an inverse relationship between 15-LOX-2 and PPAR-gamma expression in normal versus tumor samples. To systematically determine if this is a ubiquitous phenomenon, we used a variety of epithelial and nonepithelial cells and some tissues to further evaluate the extent of this inverse relationship. The levels of mRNA or protein were measured by reverse transcriptase polymerase chain reaction or Western gray level intensity, whereas distribution was determined by in situ hybridization or immunofluorescence. 15-S-HETE was measured by liquid chromatography/tandem mass spectrometry. Normal epithelial cells/samples generally expressed high levels of 15-LOX-2 along with the enzyme product 15-S-HETE, but both levels were reduced in cancer cells/samples. In contrast, most cancer cells expressed high levels of PPAR-gamma mRNA and protein, which were absent from normal epithelial cells. Overall, the inverse relationship between these two genes was primarily restricted to epithelial samples. Forced expression of PPAR-gamma reduced 15-LOX-2 protein levels in normal cells, whereas forced expression of 15-LOX-2 in tumor cells suppressed PPAR-gamma protein levels. These results suggest that feedback mechanisms may contribute to the loss of 15-LOX-2 pathway components, which coincide with an increase in PPAR-gamma in many epithelial cancers.

PPARgamma ligands induce ER stress in pancreatic beta-cells: ER stress activation results in attenuation of cytokine signaling

Peroxisome proliferator-activated receptor (PPAR)gamma ligands are known to have anti-inflammatory properties that include the inhibition of cytokine signaling, transcription factor activation, and inflammatory gene expression. We have recently observed that increased expression of heat shock protein (HSP)70 correlates with, but is not required for, the anti-inflammatory actions of PPARgamma ligands on cytokine signaling. In this study, we provide evidence that the inhibitory actions of PPARgamma ligands on cytokine signaling are associated with endoplasmic reticulum (ER) stress or unfolded protein response (UPR) activation in pancreatic beta-cells. 15-Deoxy-Delta(12,14)-prostaglandin J(2), at concentrations that inhibit cytokine signaling, stimulates phosphorylation of eukaryotic initiation factor-2alpha, and this event is followed by a rapid inhibition of protein translation. Under conditions of impaired translation, PPARgamma ligands stimulate the expression of a number of ER stress-responsive genes, such as GADD 153, BiP, and HSP70. Importantly, ER stress activation in response to PPARgamma ligands or known UPR activators results in the attenuation of IL-1 and IFN-gamma signaling. These findings indicate that PPARgamma ligands induce ER stress, that ER stress activation is associated with an attenuation of cytokine signaling in beta-cells, and that the attenuation of responsiveness to extracellular stimuli appears to be a novel protective action of the UPR in cells undergoing ER stress.

EFFECT OF TACROLIMUS ON THE EXPRESSION OF MACROPHAGE SCAVENGER AND NUCLEAR HORMONE RECEPTORS IN THP-1–DERIVED HUMAN MACROPHAGES

BACKGROUND

Data indicate that tacrolimus and cyclosporine A (CsA) differentially affect the risk of atherosclerosis. The results of our recent in vitro studies of clinically relevant CsA concentrations demonstrated the modulation of macrophage scavenger receptors (MSRs) involved in atherogenesis. This work evaluated the effects of clinically relevant tacrolimus concentrations on the expression of the MSR genes CD36 and CD68, SR-A and SR-BII, lectin-like oxidized low-density lipoprotein receptor-1, the nuclear hormone receptors peroxisome proliferator-activated receptor (PPAR)gamma and liver-X-receptor-alpha, and the cholesterol efflux pump ABCA1 in the in vitro human THP-1 macrophage model.

METHODS

The cells were cultured and differentiated into macrophages. Macrophages were treated with the tacrolimus to assess gene expression in a time-dependent (1, 2, 4, 8, and 24 hr) and dose-dependent (concentrations [micrograms/liter] corresponding to the trough [15], peak [30], and 4 x peak [120]) manner using reverse-transcriptase polymerase chain reactions. The gene expression levels of interest were normalized to GAPDH expression in each sample to provide semiquantitative reverse-transcriptase polymerase chain reaction results. Additional immunoblotting studies demonstrated protein expression of CD36, PPARgamma, and ABCA1. RESULTS.: The gene expression of CD36, SR-BII, and lectin-like oxidized low-density lipoprotein receptor-1 were down-regulated, and ABCA1 was up-regulated. CD68, SR-AI, liver-X-receptor-alpha, and PPARgamma were regulated in a dose-dependent manner. Protein expression of CD36 was down-regulated, and PPARgamma and ABCA1 were relatively unchanged.

CONCLUSIONS

Tacrolimus seems to regulate MSRs, nuclear hormone receptors, and ABCA1 in THP-1 macrophages. These results differ from previous findings with CsA and may provide insight into the mechanisms of posttransplant atherosclerosis.

PPARgamma is not required for the inhibitory actions of PGJ2 on cytokine signaling in pancreatic beta-cells

Peroxisome proliferator-activated receptor (PPAR)gamma agonists, such as 15-deoxy-delta 12,14-prostaglandin J2 (PGJ2) and troglitazone, have been shown to elicit anti-inflammatory effects in pancreatic beta-cells that include inhibition of cytokine-stimulated inducible nitric oxide synthase (iNOS) gene expression and production of nitric oxide. In addition, these ligands impair IL-1-induced NF-kappaB and MAPK as well as IFN-gamma-stimulated signal transducer and activator of transcription (STAT)1 activation in beta-cells. The purpose of this study was to determine if PPARgamma activation participates in the anti-inflammatory actions of PGJ2 in beta-cells. Pretreatment of RINm5F cells for 6 h with PGJ2 results in inhibition of IL-1-stimulated IkappaB degradation and IFN-gamma-stimulated STAT1 phosphorylation. Overexpression of a dominant-negative (dn) PPARgamma mutant or treatment with the PPARgamma antagonist GW-9662 does not modulate the inhibitory actions of PGJ2 on cytokine signaling in RINm5F cells. Although these agents fail to attenuate the inhibitory actions of PGJ2 on cytokine signaling, they do inhibit PGJ2-stimulated PPARgamma response element reporter activity. Consistent with the inability to attenuate the inhibitory actions of PGJ2 on cytokine signaling, neither dnPPARgamma nor GW-9662 prevents the inhibitory actions of PGJ2 on IL-1-stimulated iNOS gene expression or nitric oxide production by RINm5F cells. These findings support a PPARgamma-independent mechanism by which PPARgamma ligands impair cytokine signaling and iNOS expression by islets.

Quantitative analysis of peroxisome proliferator-activated receptor gamma (PPARγ) expression in arteries and hearts of patients with ischaemic or dilated cardiomyopathy

PPARgamma, a nuclear transcription factor, is expressed in various cells within the vasculature and in cardiomyocytes. It has been suggested that PPARgamma is involved in atherogenesis and in cardiac hypertrophy. Therefore, we sought to quantify PPARgamma mRNA in coronary arteries, the aorta and left ventricular specimens from patients with ischaemic (CHD) and dilated cardiomyopathy (CMP). Using real-time PCR, we were able to demonstrate the expression of PPARgamma in all of the human specimens. The lowest expression of PPARgamma was detected in the aorta specimens of both groups (this was set to one). In comparison, the expression in coronary arteries was 2.32-fold in CHD- and 3.78-fold in CMP specimens and in the left ventricle specimens, 2.12-fold in CHD- and 3.51-fold in CMP. Samples from CHD patients showed a higher expression of PPARgamma in all of the samples compared to those from CMP patients (aorta: 1.99-fold; coronary arteries: 1.35; left ventricles: 1.23). PPARgamma levels were not significantly correlated to CD 36 expression values in any group, suggesting that higher levels of PPARgamma are not principally due to increased PPARgamma expression in macrophages. This was confirmed by immunohistochemical analysis, which showed that PPARgamma is also located in the smooth muscle layer and in cardiomyocytes. In conclusion, our observations of increased PPAR mRNA expression in the coronary arteries and left ventricles from CHD and CMP patients suggest an important function of this nuclear receptor in the pathogenesis of heart disease.

The aryl hydrocarbon receptor and its xenobiotic ligands: a fundamental trigger for cardiovascular diseases

This review reconsiders a major cause of cardiovascular diseases, tobacco smoking, as the activation of the Aryl hydrocarbon Receptor (AhR), also known as the dioxin receptor, by aryl hydrocarbons from the tar fraction of tobacco in various organs of the cardiovascular domain. This concept sheds new light on well-known albeit controversial epidemiological concepts such as the Mediterranean diet and the French paradox. We also review the discovery that resveratrol, a natural AhR antagonist, may be of interest in the prevention and treatment of cardiovascular diseases.

UVB light suppresses nitric oxide production by murine keratinocytes and macrophages

Nitric oxide is an important mediator of excessive cell growth and inflammation associated with many epidermal proliferative disorders. It is a highly reactive oxidant generated in keratinocytes and macrophages via the inducible form of the enzyme nitric oxide synthase (NOS2). In the present studies, we examined the effects of ultraviolet light (UVB, 2.5-25mJ/cm(2)) on interferon-gamma (IFN-gamma)-induced expression of NOS2 in these cells. Transient transfection assays using wild-type and mutant NOS2 promoter/luciferase reporter constructs showed that DNA binding of the transcription factors Stat1 and NF-kappaB was essential for optimal expression of the NOS2 gene. Whereas NF-kappaB was constitutively expressed in both cell types, Stat1 phosphorylation and nuclear binding activity were dependent upon IFN-gamma. UVB light, which is used therapeutically to treat inflammatory dermatosis, was found to suppress IFN-gamma-induced expression of NOS2 mRNA and protein, and nitric oxide production in both keratinocytes and macrophages. In macrophages, this was associated with complete inhibition of NF-kappaB nuclear binding activity and partial (approximately 20-25%) reduction of Stat1 activity. In keratinocytes, both responses were partially reduced at the highest doses of UVB light (15-25mJ/cm(2)). Whereas in macrophages UVB light suppressed NOS2 wild-type promoter-luciferase reporter activity, this activity was stimulated in keratinocytes. These data suggest that UVB light functions to suppress NOS2 gene expression in macrophages by inhibiting the activity of key regulatory transcription factors. In contrast, in keratinocytes, inhibition occurs downstream of NOS2 promoter activity.