15-deoxy-delta(12,14)-PGJ(2) induces synoviocyte apoptosis and suppresses adjuvant-induced arthritis in rats

Induction of apoptosis in rheumatoid synovial fibroblasts by celecoxib, but not by other selective cyclooxygenase 2 inhibitors

OBJECTIVE

Selective cyclooxygenase 2 (COX-2) inhibitors are now being used as antiinflammatory agents that cause fewer gastrointestinal complications, compared with other antiinflammatory drugs, in patients with rheumatoid arthritis (RA). This study was undertaken to investigate whether selective COX-2 inhibitors could induce apoptosis of RA synovial fibroblasts (RASFs).

METHODS

RASFs were exposed to selective COX-2 inhibitors, i.e., celecoxib, etodolac, meloxicam, nimesulide, N-[2-(cyclohexyloxyl)-4-nitrophenyl]-methanesulfonamide, and rofecoxib, under various conditions. Cell proliferation and cell viability were assessed by incorporation of 5-bromo-2'-deoxyuridine and by the 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium monosodium salt assay, respectively. Apoptosis was detected by identifying DNA fragmentation. Activation of peroxisome proliferator-activated receptor gamma (PPARgamma) was measured by the luciferase reporter gene assay with a PPAR response element-driven luciferase reporter plasmid and a PPARgamma expression plasmid.

RESULTS

Celecoxib strongly inhibited the proliferation of RASFs, whereas other selective COX-2 inhibitors had little or no effect. In addition, celecoxib reduced the viability of RASFs by induction of apoptosis, in a concentration-dependent manner. This action was abolished by addition of caspase inhibitors. Interleukin-1beta had a weak enhancing effect on celecoxib-induced apoptosis in RASFs. In contrast, other selective COX-2 inhibitors at concentrations up to 100 microM did not induce apoptosis of RASFs. Indomethacin, a nonselective COX inhibitor, activated PPARgamma transcription, while celecoxib did not.

CONCLUSION

Celecoxib suppressed the proliferation of RASFs by COX-2-independent and PPARgamma-independent induction of apoptosis. Although the mechanism involved remains unclear, celecoxib may have not only antiinflammatory activity, but also a disease-modifying effect on rheumatoid synovial proliferation.

Role of peroxisome proliferator-activated receptor gamma and retinoid X receptor heterodimer in hepatogastroenterological diseases

The peroxisome proliferator-activated receptor gamma (PPARgamma) and its partner the retinoid X receptor (RXR) are two nuclear receptors that are expressed mainly in adipose tissue and which have a role in lipid metabolism and insulin sensitisation. New sites of PPARgamma/RXR expression have been described, especially in the intestinal tract, pancreas, and liver. Concomitantly, new functions have been attributed to this heterodimer in regulation of inflammation, by its inhibition of nuclear factor (NF)-kappaB and via stress-kinase pathways. These new sites and functions of PPARgamma/RXR have led to novel ideas about pathophysiology of different inflammatory digestive diseases and to development of innovative treatment strategies with PPARgamma activators.

Apoptosis induced by activation of peroxisome-proliferator activated receptor-gamma is associated with Bcl-2 and NF-kappaB in human colon cancer

Peroxisome-proliferator activated receptor-gamma (PPARgamma) has been demonstrated to exert an inhibitory effect on cell growth in most cell types studied, but its role in colon cancer is still uncertain. The molecular mechanism between the activation of PPARgamma and its consequence is unknown. In the present report, we show that the expression of PPARgamma was significantly increased in tumor tissues from human colon cancer compared with non-tumor tissues and that PPARgamma ligands, 15-Deoxy-delta(12,14)prostaglandin J2 or ciglitizone, induced apoptosis in HT-29 cells, a human colon cancer cell line. The occurrence of apoptosis induced by PPARgamma ligands was sequentially accompanied by reduced levels of NF-kappaB and Bcl-2. Over-expression of Bcl-2 significantly protected the cells from apoptosis. This study suggested that a PPARgamma-Bcl-2 feedback loop may function to control the life-death continuum in colonic cells and that a deficiency in generation of PPARgamma ligands may precede the development of human colon cancer.

Anti-inflammatory lipid mediators and insights into the resolution of inflammation

The pro-inflammatory signalling pathways and cellular mechanisms that initiate the inflammatory response have become increasingly well characterized. However, little is known about the mediators and mechanisms that switch off inflammation. Recent data indicate that the resolution of inflammation is an active process controlled by endogenous mediators that suppress pro-inflammatory gene expression and cell trafficking, as well as induce inflammatory-cell apoptosis and phagocytosis, which are crucial determinants of successful resolution. This review focuses on this emerging area of inflammation research and describes the mediators and mechanisms that are currently stealing the headlines.

Constitutive activation of peroxisome proliferator-activated receptor-gamma suppresses pro-inflammatory adhesion molecules in human vascular endothelial cells

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a ligand-activated nuclear receptor that has an essential role in adipogenesis and glucose homeostasis. PPAR-gamma is expressed in vascular tissues including endothelial cells (ECs). PPAR-gamma activity can be regulated by many pathophysiological and pharmacological agonists. However, the role of PPAR-gamma activation in ECs remains unclear. In this study, we examined the effect of the constitutive activation of PPAR-gamma on the phenotypic modulation of ECs. Adenovirus-mediated expression of a constitutively active mutant of PPAR-gamma resulted in significant ligand-independent activation of PPAR-gamma and specific induction of the PPAR-gamma target genes. However, PPAR-gamma activation significantly suppressed the expression of vascular adhesion molecules in ECs and the ensuing leukocyte recruitment. Furthermore, constitutive activation of PPAR-gamma resulted in simultaneous repression of AP-1 and NF-kappaB activity, which suggests that PPAR-gamma may reduce pro-inflammatory phenotypes via, at least in part, suppression of the AP-1 and NF-kappaB pathways. Therefore, using a gain-of-function approach, our study provides novel evidence showing that constitutive activation of PPAR-gamma is sufficient to prevent ECs from converting into a pro-inflammatory phenotype. These results also suggest that, in addition to pharmacological agonists, the genetic modification of the PPAR-gamma activity in ECs may be a potential approach for therapeutic intervention in various inflammatory disorders.

Effects of agonists of peroxisome proliferator-activated receptor gamma on proteoglycan degradation and matrix metalloproteinase production in rat cartilage in vitro

OBJECTIVE

To examine the effects of agonists of peroxisome proliferator-activated receptor (PPAR) gamma on proteoglycan degradation induced by interleukin (IL)-1beta or tumor necrosis factor (TNF)alpha in cartilage in vitro.

DESIGN

Proteoglycan degradation was measured as release of radioactivity from rat cartilage explants previously labeled with (35)SO2-4. Western blots were used to examine tissue levels of aggrecan neoepitopes NITEGE and VDIPEN, generated by aggrecanases and matrix metalloproteinases (MMP), respectively. Production of MMP-2, -3 and -9 by cultured rat chondrocytes was measured by zymography and by fluorimetric assay.

RESULTS

IL-1beta-induced proteoglycan degradation was likely due to aggrecanase, since it was associated with a strong increase of NITEGE signal. MMP-dependent VDIPEN signal increased only after further incubation with pro-MMP activator APMA. PPAR agonists 15d-PGJ(2) and GI262570 (10 microM) inhibited IL-1beta- and TNFalpha-induced proteoglycan degradation measured both before and after addition of APMA. The agonists also inhibited cytokine-induced MMP production by isolated chondrocytes.

CONCLUSION

This study shows that PPARgamma agonists inhibit cytokine-induced proteoglycan degradation mediated by both aggrecanase and MMP. This effect is associated with inhibition of production of MMP-3 and -9. These results support the interest for PPARgamma agonists as candidate inhibitors of pathological cartilage degradation.

Thiazolidinedione activation of peroxisome proliferator-activated receptor gamma can enhance mitochondrial potential and promote cell survival

Thiazolidinediones (TZDs) are widely used for treatment of type 2 diabetes mellitus. Peroxisome proliferator-activated receptor gamma (PPAR gamma) is the molecular target of TZDs and is believed to mediate the apoptotic effects of this class of drugs in a variety of cell types, including B and T lymphocytes. The finding that TZDs induce lymphocyte death has raised concerns regarding whether TZDs might further impair immune functions in diabetics. To address this issue, we investigated the roles of PPAR gamma and TZDs in lymphocyte survival. PPAR gamma was up-regulated upon T cell activation. As previously reported, PPAR gamma agonists induced T cell death in a dose-dependent manner. However, the concentrations of TZD needed to cause T cell death were above those needed to induce PPAR gamma-dependent transcription. Surprisingly, at concentrations that induce optimal transcriptional activation, TZD activation of PPAR gamma protected cells from apoptosis following growth factor withdrawal. The survival-enhancing effects depended on both the presence and activation of PPAR gamma. Measurements of mitochondrial potential revealed that PPAR gamma activation enhanced the ability of cells to maintain their mitochondrial potential. These data indicate that activation of PPAR gamma with TZDs can promote cell survival and suggest that PPAR gamma activation may potentially augment the immune responses of diabetic patients.

Functional changes in rheumatoid fibroblast-like synovial cells through activation of peroxisome proliferator-activated receptor gamma-mediated signalling pathway

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand dependent transcriptional factor known to be a regulator of adipogenesis. Recent studies have also shown that stimulation of PPARgamma inhibits the transcriptional activities of other nuclear factors and down-regulates proinflammatory cytokine synthesis in T cells and monocytes. We examined, in the present study, the functional significance of PPARgamma expressed in fibroblast-like synovial cells (FLS) isolated from patients with rheumatoid arthritis (RA). Incubation of FLS with a synthetic PPARgamma ligand, troglitazone, inhibited endogenous production of TNF-alpha, IL-6 and IL-8, as well as matrix metalloprotease-3 (MMP-3), without inducing apoptosis of the cells. The gelatinase activity of FLS culture media was also inhibited by troglitazone. Electrophoretic mobility shift assay (EMSA) showed a significant reduction in the DNA binding activity of NF-kappaB in troglitazone-treated FLS in response to TNF-alpha or IL-1beta. Moreover, long-term cultivation of FLS with troglitazone resulted in morphological changes with marked lipid accumulation in these cells. Our results show a negative regulatory function for PPARgamma on cytokine and MMP production together with inhibition of cytokine-mediated inflammatory responses in rheumatoid synovial cells. Our results also suggest that FLS could differentiate into adipocyte-like cells in the presence of proper stimulatory signals including PPARgamma.

PPAR gamma ligands inhibit nitrotyrosine formation and inflammatory mediator expressions in adjuvant-induced rheumatoid arthritis mice

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor, whose activation has been linked to several physiologic pathways including those related to the regulation of insulin sensitivity. Here, we investigate effects of PPARgamma specific ligands, rosiglitazone and pioglitazone, on formation of nitrotyrosine and increased expression of inflammatory mediators such as inducible nitric oxide synthase (iNOS), cyclooxygenase-2 and intercellular adhesion molecule-1 (ICAM-1) in adjuvant-induced murine arthritis. Administration of rosiglitazone or pioglitazone (30 mg/kg, p.o.) significantly inhibited the adjuvant-induced increase in formation of nitrotyrosine and expression of iNOS on both ankle and temporomandibular joints. Rosiglitazone also inhibited the adjuvant-induced expression of M30 positive cells, as a marker of apoptosis, in the joint tissues. In addition, treatment with rosiglitazone or pioglitazone (30 microM) inhibited lipopolysaccharide plus tumor necrosis factor (TNF)-alpha-induced protein expression of iNOS, cyclooxygenase-2, ICAM-1 and nitrotyrosine formation in RAW 264 cells, a murine macrophage-like cell line. Rosiglitazone or pioglitazone inhibited increase in phosphorylated I-kappaB (pI-kappaB) expression, as an index of activation of nuclear factor (NF)-kappaB, in both joint tissues and RAW264 cells. Furthermore, in PPARgamma-transfected HEK293 cells, rosiglitazone inhibited the TNF-alpha-stimulated response using NF-kappaB-mediated transcription reporter assay. These results indicate that PPARgamma ligands may possess anti-inflammatory activity against adjuvant-induced arthritis via the inhibition of NF-kappaB pathway.

Perineuronal oligodendrocytes protect against neuronal apoptosis through the production of lipocalin-type prostaglandin D synthase in a genetic demyelinating model

The genetic demyelinating mouse "twitcher" is a model of the human globoid cell leukodystrophy, caused by galactosylceramidase (GALC) deficiency. Demyelination in the twitcher brain is secondary to apoptotic death of oligodendrocytes (OLs). Lipocalin-type prostaglandin (PG) D synthase (L-PGDS), a protein expressed in mature OLs, was progressively upregulated in twitcher OLs; whereas expression of OL-associated proteins such as carbonic anhydrase II, myelin basic protein, and myelin-associated glycoprotein was downregulated during demyelination in twitcher brains. The upregulation of L-PGDS was more remarkable in perineuronal OLs than in interfascicular OLs. A larger number of L-PGDS-positive OLs was found in selected fiber tracts of twitcher brains where fewer apoptotic cells were detected. The distribution of L-PGDS-positive OLs was inversely related to the severity of demyelination, as assessed by accumulation of scavenger macrophages. Mice doubly deficient for L-PGDS and GALC disclosed a large number of apoptotic neurons, which were never seen in twitcher brains, in addition to an increased number of apoptotic OLs. A linear positive correlation was observed between the population of L-PGDS-positive OLs in the twitcher brain and the ratio of apoptotic nuclei in the double mutant versus those in the twitcher, suggesting a dose-dependent effect of L-PGDS against apoptosis. These lines of evidence suggest that L-PGDS is an anti-apoptotic molecule protecting neurons and OLs from apoptosis in the twitcher mouse. This is a novel example of OL-neuronal interaction.

Nonsteroidal anti-inflammatory drugs induce apoptosis in association with activation of peroxisome proliferator-activated receptor gamma in rheumatoid synovial cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been reported to induce apoptosis in a variety of cell lines. In this study, we examined the effect of NSAIDs on the growth and apoptosis of synovial cells from patients with rheumatoid arthritis and analyzed the activation of peroxisome proliferator-activated receptor gamma (PPARgamma) as a possible mechanism of action of NSAIDs. Cell proliferation and viability were assessed from 5-bromo-2'-deoxyuridine incorporation and by 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1) assay, respectively. The apoptosis of synovial cells was identified by DNA fragmentation assay and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. Indometacin, diclofenac, oxaprozin, and zaltoprofen reduced cell proliferation and induced apoptotic cell death in synovial cells, whereas ketoprofen and acetaminophen did not. N-[2-(cyclohexyloxyl)-4-nitrophenyl]-methanesulfonamide (NS-398), a selective cyclooxygenase-2 inhibitor, also inhibited cell proliferation, whereas it did not cause apoptosis. Rheumatoid synovial cells expressed PPARgamma mRNA, and the PPARgamma ligands 15-deoxy-Delta(12,14)-prostaglandin J(2) and troglitazone reduced the proliferation and induced apoptosis in synovial cells. Luciferase reporter assay demonstrated that not only PPARgamma ligands but also NSAIDs, which could induce apoptosis, increased the activation of PPARgamma in synovial cells. Furthermore, the ability of NSAIDs and PPARgamma ligands to stimulate the activation of PPARgamma correlated with their ability to decrease cell viability(r = 0.92, p < 0.01) and ability to induce DNA fragmentation (r = 0.97, p < 0.001) in synovial cells. These results suggest that PPARgamma is an attractive target for induction of apoptosis in rheumatoid synovial cells and that the activation of the PPARgamma pathway is associated with the apoptotic action of NSAIDs.

Natural ligands of PPARgamma: are prostaglandin J(2) derivatives really playing the part?

The peroxisome proliferator-activated receptor (PPAR) family was discovered from an orphan nuclear receptor approach, and thereafter, three subtypes were identified, namely PPARalpha, PPARbeta or PPARgamma and PPARgamma. The two former seem to regulate lipid homeostasis, whereas the latter is involved, among others, in glucose homeostasis and adipocyte differentiation. PPARs were pharmacologically characterised first using peroxisome proliferators such as clofibrates, which demonstrate moderate affinity (efficiency at micromolar concentrations) and low PPARalpha/delta versus PPARgamma specificity. Hence, several laboratories have started the search for potent and subtype-specific natural PPAR activators. In this respect, prostaglandin (PG)-related compounds were identified as good PPARgamma agonists with varying specificity, the most notable PPAR ligand being 15-deoxy-Delta12-14-PGJ2 (15d-PGJ2). Recently, an oxidized phosphatidylcholine was identified as a potent alternative (patho)physiological natural ligand of PPARgamma. In the present review, we discuss the different PPARgamma-dependent and -independent biological effects of the PG PPARgamma ligands and the concern about their low potency in molecular models as compared with thiazolidinediones (TZDs), a family of potent (nanomolar) synthetic PPARgamma ligands. Finally, the oxidized lipids are presented as a novel and interesting alternative for discovering potent PPARgamma activators in order to understand more in details the implications of PPARgamma in various pathophysiological conditions.

Prostaglandin D2 and its metabolites induce caspase-dependent granulocyte apoptosis that is mediated via inhibition of I kappa B alpha degradation using a peroxisome proliferator-activated receptor-gamma-independent mechanism

Many inflammatory mediators retard granulocyte apoptosis. Most natural PGs studied herein (e.g., PGE(2), PGA(2), PGA(1), PGF(2 alpha)) either delayed apoptosis or had no effect, whereas PGD(2) and its metabolite PGJ(2) selectively induced eosinophil, but not neutrophil apoptosis. This novel proapoptotic effect does not appear to be mediated via classical PG receptor ligation or by elevation of intracellular cAMP or Ca(2+). Intriguingly, the sequential metabolites Delta(12)PGJ(2) and 15-deoxy-Delta(12,) Delta(14)-PGJ(2) (15dPGJ(2)) induced caspase-dependent apoptosis in both granulocytes, an effect that did not involve de novo protein synthesis. Despite the fact that Delta(12)PGJ(2) and 15dPGJ(2) are peroxisome proliferator-activated receptor-gamma (PPAR-gamma) activators, apoptosis was not mimicked by synthetic PPAR-gamma and PPAR-alpha ligands or blocked by an irreversible PPAR-gamma antagonist. Furthermore, Delta(12)PGJ(2) and 15dPGJ(2) inhibited LPS-induced I kappa B alpha degradation and subsequent inhibition of neutrophil apoptosis, suggesting that apoptosis is mediated via PPAR-gamma-independent inhibition of NF-kappa B activation. In addition, we show that TNF-alpha-mediated loss of cytoplasmic I kappa B alpha in eosinophils is inhibited by 15dPGJ(2) in a concentration-dependent manner. The selective induction of eosinophil apoptosis by PGD(2) and PGJ(2) may help define novel therapeutic pathways in diseases in which it would be desirable to specifically remove eosinophils but retain neutrophils for antibacterial host defense. The powerful proapoptotic effects of Delta(12)PGJ(2) and 15dPGJ(2) in both granulocyte types suggest that these natural products control the longevity of key inflammatory cells and may be relevant to understanding the control and resolution of inflammation.

Perineuronal oligodendrocytes protect against neuronal apoptosis through the production of lipocalin-type prostaglandin D synthase in a genetic demyelinating model

The genetic demyelinating mouse "twitcher" is a model of the human globoid cell leukodystrophy, caused by galactosylceramidase (GALC) deficiency. Demyelination in the twitcher brain is secondary to apoptotic death of oligodendrocytes (OLs). Lipocalin-type prostaglandin (PG) D synthase (L-PGDS), a protein expressed in mature OLs, was progressively upregulated in twitcher OLs; whereas expression of OL-associated proteins such as carbonic anhydrase II, myelin basic protein, and myelin-associated glycoprotein was downregulated during demyelination in twitcher brains. The upregulation of L-PGDS was more remarkable in perineuronal OLs than in interfascicular OLs. A larger number of L-PGDS-positive OLs was found in selected fiber tracts of twitcher brains where fewer apoptotic cells were detected. The distribution of L-PGDS-positive OLs was inversely related to the severity of demyelination, as assessed by accumulation of scavenger macrophages. Mice doubly deficient for L-PGDS and GALC disclosed a large number of apoptotic neurons, which were never seen in twitcher brains, in addition to an increased number of apoptotic OLs. A linear positive correlation was observed between the population of L-PGDS-positive OLs in the twitcher brain and the ratio of apoptotic nuclei in the double mutant versus those in the twitcher, suggesting a dose-dependent effect of L-PGDS against apoptosis. These lines of evidence suggest that L-PGDS is an anti-apoptotic molecule protecting neurons and OLs from apoptosis in the twitcher mouse. This is a novel example of OL-neuronal interaction.

Possible participation of intracellular platelet-activating factor in NF-kappaB activation in rat peritoneal macrophages

As we had found previously that thapsigargin, an endomembrane Ca2+-ATPase inhibitor, induces production of intracellular platelet-activating factor (PAF) [Br. J. Pharmacol. 116 (1995) 2141], we decided to investigate the possible roles of intracellular PAF in nuclear factor (NF)-kappaB activation of thapsigargin-stimulated rat peritoneal macrophages. When rat peritoneal macrophages were stimulated with thapsigargin, the level of inhibitory protein of NF-kappaB-alpha (IkappaB-alpha) was decreased and the nuclear translocation of NF-kappaB was increased. The thapsigargin-induced activation of NF-kappaB was inhibited by the PAF synthesis inhibitor SK&F 98625 and the PAF antagonist E6123. Structurally unrelated PAF antagonists such as E5880 and L-652,731 also inhibited the thapsigargin-induced activation of NF-kappaB. Lipopolysaccharide (LPS)-induced activation of NF-kappaB was also suppressed by these drugs. In a culture of rat peritoneal macrophages, exogenously added PAF did not induce degradation of IkappaB-alpha. These findings suggest that the intracellular PAF produced by the stimulation with thapsigargin or LPS is involved in activation of the NF-kappaB pathway.

PPARgamma ligands suppress proliferation of human urothelial basal cells in vitro

Expression of peroxisome proliferator-activated receptor (PPAR) gamma in the human urinary tract through embryonic development suggests its possible roles in the development, proliferation, and differentiation of uroepithelium. Little is known, however, about physiological roles of PPARgamma in the urinary tract. We investigated effects of PPARgamma ligands on the proliferation of normal human urothelial cells and stromal cells cultivated from surgical specimens. Active proliferation in vitro as well as high molecular weight cytokeratin expression indicated that cultured urothelial cells possess basal cell phenotype. PPARgamma protein, expressed predominantly in the epithelial layer of the normal human urinary tract in vivo, was abundantly expressed in urothelial cells but barely detectable in stromal cells in vitro. Natural ligand for PPARgamma, 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)), as well as synthetic ones, troglitazone and pioglitazone, suppressed proliferation of the urothelial cells dose-dependently. These effects were PPARgamma specific because clofibrate or PGF(2alpha) did not affect proliferation of urothelial cells. Neither 9-cis retinoic acid or all-trans retinoic acid (ATRA) at 1 microM showed any synergism on the antiproliferative effects of PPARgamma ligands. Urothelial cells treated with PPARgamma ligands showed drastic morphologic changes and cell cycle arrest at G0/G1 phase accompanied with increased mRNA level of a cyclin-dependent kinase inhibitor p21(WAF1/CIP1). Since 15d-PGJ(2) is present in vivo during the resolution phase of inflammation, these results indicated that PPARgamma might be involved in the terminal phase of urothelial re-epithelialization processes.

Role of nuclear factor kappaB in synovial inflammation

The evaluation of molecular pathways has revealed novel insights into the pathophysiology of rheumatoid arthritis in the last several years. Gene transcription factors such as nuclear factor kB (NFkB) are activated by extracellular signals or cell-to-cell interactions that are converted into intracellular activation signals through receptor molecules located in the cell membrane. The number of known genes being translated after NFkB activation is increasing steadily. These genes includes cytokines, chemokines, growth factors, cellular ligands, and adhesion molecules. Because many of these genes are part of the pathogenesis of RA, there is considerable interest in the evaluation of the synovium-specific effects of NFkB to unveil its potential for future therapeutic strategies. The goal is to evolve these strategies from the therapies that have a wide spectrum of effects and side effects into rheumatoid arthritis-specific therapies designed to inhibit distinct molecular pathways within the synovium.

A proinflammatory role for the cyclopentenone prostaglandins at low micromolar concentrations: oxidative stress-induced extracellular signal-regulated kinase activation without NF-kappa B inhibition

An anti-inflammatory role and therapeutic potential for cyclopentenone PGs (cyPGs) has been suggested, based on observations that levels of cyPGs in exudates increase during the resolution phase of inflammation, and that exogenous cyPGs may attenuate the inflammatory response in vivo and in vitro mainly through inhibition of NF-kappaB, a critical activator of inflammatory gene expression. However, exogenous cyPGs inhibit NF-kappaB only at concentrations substantially higher than those of endogenous cyPGs present in inflammatory fluids, thus challenging the hypothesis that cyPGs are naturally occurring inhibitors of inflammation and suggesting that cyPGs at low concentrations might have previously unappreciated effects. In this study, using various cell types, we report that cyPGs, when used at concentrations substantially lower than required for NF-kappaB inhibition (viz, low micromolar concentrations), significantly potentiate the inflammatory response to TNF-alpha. At these concentrations, cyPGs induce production of reactive oxygen species, thereby synergizing with TNF-alpha to activate the extracellular signal-regulated kinase 1/2, an activation which in turn potentiates proinflammatory cytokine expression at both transcriptional and posttranscriptional levels. Our study establishes a proinflammatory role for cyPGs at low micromolar concentrations, raises the possibility that cyPGs do not act as physiologic anti-inflammatory mediators, and questions the therapeutic potential of these compounds.

The cyclopentenone prostaglandin 15-deoxy-Delta(12,14)-prostaglandin J(2) attenuates the development of acute and chronic inflammation

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily of ligand-activated transcription factors that are related to retinoid, steroid, and thyroid hormone receptors. The PPAR-gamma receptor subtype seems to play a pivotal role in the regulation of cellular proliferation and inflammation. Recent evidence also suggests that the cyclopentenone prostaglandin (PG) 15-deoxyDelta(12,14)-PGJ(2) (15d-PGJ(2)), which is a metabolite of prostaglandin D(2), functions as an endogenous ligand for PPAR-gamma. We postulated that 15d-PGJ(2) would attenuate inflammation. In the present study, we have investigated the effects of 15d-PGJ(2) of acute and chronic inflammation (carrageenan-induced pleurisy and collagen-induced arthritis, respectively) in animal models. We report for the first time, to our knowledge, that 15d-PGJ(2) (given at 10, 30, or 100 microg/kg i.p. in the pleurisy model or at 30 microg/kg i.p every 48 h in the arthritis model) exerts potent anti-inflammatory effects (e.g., inhibition of pleural exudate formation, mononuclear cell infiltration, delayed development of clinical indicators, and histological injury) in vivo. Furthermore, 15d-PGJ(2) reduced the increase in the staining (immunohistochemistry) for nitrotyrosine and poly (ADP-ribose) polymerase and the expression of inducible nitric-oxide synthase and cyclooxygenase-2 in the lungs of carrageenan-treated mice and in the joints from collagen-treated mice. Thus, 15d-PGJ(2) reduces the development of acute and chronic inflammation. Therefore, the cyclopentenone prostaglandin 15d-PGJ(2) may be useful in the therapy of acute and chronic inflammation.

Peroxisome proliferator-activated receptor-gamma agonists inhibit experimental allergic encephalomyelitis by blocking IL-12 production, IL-12 signaling and Th1 differentiation

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a nuclear receptor transcription factor that regulates adipocyte differentiation and glucose homeostasis. PPARgamma agonists are potent therapeutic agents for the treatment of type 2 diabetes and obesity. PPARgamma agonists also prevent inflammation in animal models, suggesting their use for the treatment of human inflammatory diseases. Experimental allergic encephalomyelitis (EAE) is a Th1 cell-mediated inflammatory demyelinating disease model of multiple sclerosis (MS) and IL-12 plays a crucial role in the pathogenesis of EAE and MS. In this study we have examined the effect of PPARgamma agonists on the pathogenesis of EAE. In vivo treatment of SJL/J mice with PPARgamma agonists, 15-deoxydelta(12,14) prostaglandin J2 or Ciglitazone, decreased the duration and clinical severity of active immunization and adoptive transfer models of EAE. PPARgamma agonists inhibited EAE in association with a decrease in IL-12 production and differentiation of neural antigen-specific Th1 cells. In vitro treatment of activated T cells with PPARgamma agonists inhibited IL-12-induced activation of JAK-STAT signaling pathway and Th1 differentiation. These findings highlight the fact that PPARgamma agonists regulate central nervous system inflammation and demyelination by inhibiting IL-12 production, IL-12 signaling and Th1 differentiation in EAE.

Regulation of cytokine expression by ligands of peroxisome proliferator activated receptors

Peroxisome proliferator activated receptors (PPARs) are ligand-activated transcription factors with diverse actions including adipocyte differentiation and lipid metabolism. Recent studies have revealed anti-inflammatory activities, but the majority of these studies have been performed in monocyte/macrophages. In these studies, we investigate the effects of PPAR ligands in murine mitogen-activated splenocytes. Ciglitazone, a PPARgamma ligand, consistently decreased IFN-gamma and IL-2 production by mitogen-activated splenocytes and had modest effects on splenocyte proliferation. The effects of WY14,643, a representative of the fibrate class of PPARalpha ligands, on splenocyte proliferation and IL-2 levels are less marked than those observed with the PPARgamma ligand. In addition, treatment with WY14,643 and other fibrates led to marked increases in supernatant concentrations of IL-4. However, treatment with a potent and specific PPARalpha ligand (GW7,647) did not augment IL-4. Also, WY14,643 induced IL-4 expression in splenocytes from PPARalpha knockout mice, suggesting that the fibrate effect on IL-4 was largely through a PPARalpha-independent mechanism. This increase in IL-4 was associated with and causatively related to augmented expression of CD23 by CD45R/B220(+) cells. We also demonstrate that PPARgamma gene expression is up-regulated in T cells by mitogen activation, that it is positively regulated by IL-4 and WY14,643, and that it is blocked by anti-IL-4. Finally, we demonstrate that WY14,643 can modestly augment IL-4 promoter activity in a PPARalpha-independent manner. In concert, these findings support the roles of PPAR ligands in modulating inflammatory responses involving lymphocytes but also establish potent effects of the fibrate class of PPARalpha ligands on IL-4 expression that are receptor independent.

Inhibition of inducible prostaglandin E(2) synthase by 15-deoxy-Delta(12,14)-prostaglandin J(2) and polyunsaturated fatty acids

Prostaglandin E(2) synthase (PGE synthase) is one of the membrane-associated proteins in the eicosanoid and glutathione metabolism (MAPEG) family of microsomal enzymes and constitutes a novel inducible enzyme involved in inflammation and pyretic responses. We report, using a reversed-phase HPLC assay for the production of tritiated prostaglandin E(2) (PGE(2)) by membranes from cells overexpressing human microsomal PGE synthase, that PGE synthase activity is inhibited effectively by 15-deoxy-Delta(12,14)-prostaglandin J(2) and arachidonic acid. The anti-inflammatory compound 15-deoxy-PGJ(2) was considerably more potent at inhibiting PGE synthase (IC(50)=0.3 microM) than the closely related PGJ(2) or Delta(12)-PGJ(2), or the reaction product PGE(2). Arachidonic acid, docosahexaenoic acid, and eicosapentaenoic acid inhibited PGE synthase with a similar potency (IC(50)=0.3 microM) and were more potent inhibitors than various fatty acid analogues. The present results on the inducible PGE synthase extend observations on the ability to bind arachidonic acid to another member of the MAPEG family, and also suggest a novel mechanism of action for the anti-inflammatory effects of DHA, EPA, and 15-deoxy-PGJ(2).

Prostaglandins as modulators of immunity

Prostaglandins are potent lipid molecules that affect key aspects of immunity. The original view of prostaglandins was that they were simply immunoinhibitory. This review focuses on recent findings concerning prostaglandin E2 (PGE2) and the PGD2 metabolite 15-deoxy-Delta(12,14)-PGJ2, and their divergent roles in immune regulation. We will highlight how these two seminal prostaglandins regulate immunity and inflammation, and play an emerging role in cancer progression. Understanding the diverse activities of these prostaglandins is crucial for the development of new therapies aimed at immune modulation.

Ligands of peroxisome proliferator-activated receptor-gamma induce apoptosis in AR42J cells

INTRODUCTION

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a ligand-activated transcription factor that controls growth, differentiation, and inflammation in different tissues. Roles of PPAR-gamma activation in pancreatic acinar cells are poorly characterized.

AIMS

To examine the effects of PPAR-gamma activation on the induction of apoptosis in rat pancreatic AR42J cells.

METHODOLOGY

AR42J cells were treated with ligands of PPAR-gamma, and induction of apoptosis was evaluated by cell viability, DNA-fragmentation, and flow cytometry.

RESULTS

Treatment of the cells with ligands of PPAR-gamma (15-deoxy-open triangle12,14-prostaglandin J2 or troglitazone) induced apoptosis in a dose-dependent manner. Troglitazone-induced apoptosis was not blocked by inhibitors of caspases (acetyl-DEVD-aldehyde and benzoyloxycarbonyl-VAD-fluoromethylketone). Troglitazone induced the expression of pancreatitis-associated protein-1 and clusterin mRNAs. Troglitazone activated c-Jun NH2-terminal kinase/stress-activated protein kinase, but inhibited the activation of extracellular signal-regulated kinases 1/2. Troglitazone did not activate NF-kappaB, suggesting a role of NF-kappaB-independent pathways. In AR42J cells and isolated pancreatic acini, PPAR-gamma gene and protein were detected. In addition, troglitazone increased the PPAR-dependent transcriptional activity, suggesting that PPAR-gamma is functional in AR42J cells.

CONCLUSION

These results indicate that activation of PPAR-gamma induces apoptosis in AR42J cells and imply that PPAR-gamma may be a potential therapeutic target of pancreatic inflammation, because of its anti-inflammatory effects in addition to its proapoptotic effects.

Peroxisome proliferator-activated receptor-gamma agonist 15-deoxy-Delta(12,14)-prostaglandin J(2) ameliorates experimental autoimmune encephalomyelitis

Peroxisome proliferator-activated receptors (PPAR) are members of a nuclear hormone receptor superfamily that includes receptors for steroids, retinoids, and thyroid hormone, all of which are known to affect the immune response. Previous studies dealing with PPAR-gamma expression in the immune system have been limited. Recently, PPAR-gamma was identified in monocyte/macrophage cells. In this study we examined the role of PPAR-gamma in experimental autoimmune encephalomyelitis (EAE), an animal model for the human disease multiple sclerosis. The hypothesis we are testing is whether PPAR-gamma plays an important role in EAE pathogenesis and whether PPAR-gamma ligands can inhibit the clinical expression of EAE. Initial studies have shown that the presence of the PPAR-gamma ligand 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ2) inhibits the proliferation of Ag-specific T cells from the spleen of myelin basic protein Ac(1-11) TCR-transgenic mice. 15d-PGJ2 suppressed IFN-gamma, IL-10, and IL-4 production by both Con A- and myelin basic protein Ac(1-11) peptide-stimulated lymphocytes as determined by ELISA and ELISPOT assay. Culture of encephalitogenic T cells with 15d-PGJ2 in the presence of Ag reduced the ability of these cells to adoptively transfer EAE. Examination of the target organ, the CNS, during the course of EAE revealed expression of PPAR-gamma in the spinal cord inflammatory infiltrate. Administration of 15d-PGJ2 before and at the onset of clinical signs of EAE significantly reduced the severity of disease. These results suggest that PPAR-gamma ligands may be a novel therapeutic agent for diseases such as multiple sclerosis.

15-deoxy-Delta 12,14-PGJ2 induces IL-8 production in human T cells by a mitogen-activated protein kinase pathway

Mast cells, platelets, and some macrophages are abundant sources of PGD(2) and its active metabolite 15-deoxy-Delta(12,14)-PGJ(2) (15-d-PGJ(2)). The lipid mediator 15-d-PGJ(2) regulates numerous processes, including adipogenesis, apoptosis, and inflammation. The 15-d-PGJ(2) has been shown to both inhibit as well as induce the production of inflammatory mediators such as TNF-alpha, IL-1beta, and cyclooxygenase, mostly occurring via a nuclear receptor called peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Data concerning the effects of 15-d-PGJ(2) on human T cells and immune regulation are sparse. IL-8, a cytokine with both chemotactic and angiogenic effects, is produced by T lymphocytes following activation. Whether 15-d-PGJ(2) can regulate the production of IL-8 in T cells in unknown. Interestingly, 15-d-PGJ(2) treatment of unstimulated T cells induces cell death. In contrast, in activated human T lymphocytes, 15-d-PGJ(2) does not kill them, but induces the synthesis of IL-8. In this study, we report that 15-d-PGJ(2) induced a significant increase in both IL-8 mRNA and protein from activated human T lymphocytes. The induction of IL-8 by 15-d-PGJ(2) did not occur through the nuclear receptor PPAR-gamma, as synthetic PPAR-gamma agonists did not mimic the IL-8-inducing effects of 15-d-PGJ(2). The mechanism of IL-8 induction was through a mitogen-activated protein kinase and NF-kappaB pathway, as inhibitors of both systems abrogated IL-8 protein induction. Therefore, 15-d-PGJ(2) can act as a potent proinflammatory mediator in activated T cells by inducing the production of IL-8. These findings show the complexity with which 15-d-PGJ(2) regulates T cells by possessing both pro- and anti-inflammatory properties depending on the activation state of the cell. The implications of this research also include that caution is warranted in assigning a solely anti-inflammatory role for 15-d-PGJ(2).

Peroxisome proliferator-activated receptor gamma activators inhibit MMP-1 production in human synovial fibroblasts likely by reducing the binding of the activator protein 1

OBJECTIVE

To investigate the expression and activity of PPARgamma in human synovial fibroblasts and the effects of PPARgamma agonists on the expression of MMP-1. The molecular mechanisms by which PPARgamma agonists modulate MMP-1 expression were also examined.

METHODS

PPARgamma expression and activity were measured using reverse-transcription polymerase chain reaction (RT-PCR) and transient transfection assays. Human synovial fibroblasts were cultured with IL-1beta in the absence or presence of PPARgamma activators, and the expression and production of MMP-1 were evaluated by Northern blot and ELISA, respectively. The effect of 15d-PGJ(2) on MMP-1 promoter activation was analysed in transient transfection experiments, while electrophoretic mobility shift assays were performed to study the binding activity of the transcription factor AP-1.

RESULTS

PPARgamma was expressed and transcriptionally functional in human synovial fibroblasts. PPARgamma activators (15d-PGJ(2) and BRL 49653) inhibited IL-1beta-induced MMP-1 synthesis in a dose-dependent manner. Similarly, both activators inhibited IL-1-induced MMP-1 mRNA expression. Activation of the human MMP-1 promoter was also attenuated by 15d-PGJ(2), indicating that the inhibitory effect of 15d-PGJ(2) occurs at the transcriptional level. Interestingly, 15d-PGJ(2) reduced both basal and IL-1beta-induced AP-1 binding activity.

CONCLUSIONS

These data indicate that PPARgamma agonists inhibit MMP-1 gene expression by transcriptional mechanisms, and suggest that they may be useful in reducing joint tissue destruction.

Ligands of peroxisome proliferator-activated receptor-gamma block activation of pancreatic stellate cells

Activated pancreatic stellate cells (PSCs) have recently been implicated in the pathogenesis of pancreatic fibrosis and inflammation. Peroxisome proliferator-activated receptor gamma (PPAR-gamma) is a ligand-activated transcription factor which controls growth, differentiation, and inflammation in different tissues. Roles of PPAR-gamma activation in PSCs are poorly characterized. Here we examined the effects of PPAR-gamma ligands on the key parameters of PSC activation. PSCs were isolated from rat pancreas tissue, and used in their culture-activated, myofibroblast-like phenotype. Activation of PPAR-gamma was induced with 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) or with troglitazone. Expression of PPAR-gamma was predominantly localized in the nuclei, and PPAR-gamma was transcriptionally active after ligand stimulation. PPAR-gamma ligands inhibited platelet-derived growth factor-induced proliferation. This effect was associated with inhibition of cell cycle progression beyond the G1 phase. PPAR-gamma ligands decreased alpha-smooth muscle actin protein expression and alpha1(I) procollagen and prolyl 4-hydroxylase(alpha) mRNA levels. Activation of PPAR-gamma also resulted in the inhibition of inducible monocyte chemoattractant protein-1 expression. 15d-PGJ2, but not troglitazone, inhibited the degradation of IkappaB-alpha and consequent NF-kappaB activation. In conclusion, activation of PPAR-gamma inhibited profibrogenic and proinflammatory actions in activated PSCs, suggesting a potential application of PPAR-gamma ligands in the treatment of pancreatic fibrosis and inflammation.

Roles of peroxisome proliferator-activated receptor gamma in cardiovascular disease

Peroxisome proliferator-activated receptors (PPARs) are transcription factors belonging to a nuclear receptor superfamily. PPARs have three isoforms: alpha, beta (or delta), and gamma. It is known that PPARgamma is expressed predominantly in adipose tissue and promotes adipocyte differentiation and glucose homeostasis. Recently, synthetic antidiabetic thiazolidinediones (TZDs) and the natural prostaglandin D2 (PGD2) metabolite, 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2), have been identified as ligands for PPARgamma. Furthermore, it has become apparent that PPARs are present both in a variety of different cell types and in atherosclerotic lesions and the studies about PPARgamma have been extended. Although activation of PPARgamma appears to have protective effects on atherosclerosis, it is still largely uncertain whether PPARgamma ligands prevent the development of cardiovascular disease. Recent evidence suggests that some benefit from antidiabetic agents, TZDs, may occur independent of increased insulin sensitivity. In this article, we review the latest developments in the PPAR field and summarize the roles of PPARgamma and the actions of PPARgamma ligands in the cardiovascular system.

PPAR-gamma ligands modulate effects of LPS in stimulated rat synovial fibroblasts

This work demonstrated the constitutive expression of peroxisome proliferator-activated receptor (PPAR)-gamma and PPAR-alpha in rat synovial fibroblasts at both mRNA and protein levels. A decrease in PPAR-gamma expression induced by 10 microg/ml lipopolysaccharide (LPS) was observed, whereas PPAR-alpha mRNA expression was not modified. 15-Deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) dose-dependently decreased LPS-induced cyclooxygenase (COX)-2 (-80%) and inducible nitric oxide synthase (iNOS) mRNA expression (-80%), whereas troglitazone (10 microM) only inhibited iNOS mRNA expression (-50%). 15d-PGJ(2) decreased LPS-induced interleukin (IL)-1 beta (-25%) and tumor necrosis factor (TNF)-alpha (-40%) expression. Interestingly, troglitazone strongly decreased TNF-alpha expression (-50%) but had no significant effect on IL-1 beta expression. 15d-PGJ(2) was able to inhibit DNA-binding activity of both nuclear factor (NF)-kappa B and AP-1. Troglitazone had no effect on NF-kappa B activation and was shown to increase LPS-induced AP-1 activation. 15d-PGJ(2) and troglitazone modulated the expression of LPS-induced iNOS, COX-2, and proinflammatory cytokines differently. Indeed, troglitazone seems to specifically target TNF-alpha and iNOS pathways. These results offer new insights in regard to the anti-inflammatory potential of the PPAR-gamma ligands and underline different mechanisms of action of 15d-PGJ(2) and troglitazone in synovial fibroblasts.

Prostaglandin D(2), its metabolite 15-d-PGJ(2), and peroxisome proliferator activated receptor-gamma agonists induce apoptosis in transformed, but not normal, human T lineage cells

Prostaglandin D(2) (PGD(2)) is abundantly produced by mast cells, platelets, and alveolar macrophages and has been proposed as a key immunoregulatory lipid mediator. 15-Deoxy-Delta(12,14)-PGJ(2) (15-d-PGJ(2)), a key PGD(2) metabolite, is under intense study as a potential anti-inflammatory mediator. Little is known about PGD(2) or the role of 15-d-PGJ(2), if any, in regulating the activities of human T lineage cells. In this report we demonstrate that both PGD(2) and 15-d-PGJ(2) have potent antiproliferative effects, and in fact kill human T lymphocyte lines derived from malignant cells by an apoptotic mechanism. Interestingly, normal human T cells were not similarly affected. Although the T lymphocyte lines express mRNA for the PGD(2) receptor (DP-R), a potent DP receptor agonist, BW245C, did not inhibit the proliferation or viability of the cells, suggesting an alternative mechanism of action. PGD(2) and 15-d-PGJ(2) can bind to the peroxisome proliferator activated receptor-gamma (PPAR-gamma) which is implicated in lipid metabolism and apoptosis. Exposure to synthetic PPAR-gamma ligands (e.g. ciglitazone, troglitazone) mimicked the inhibitory responses of PGD(2) and 15-d-PGJ(2), and induced apoptosis in the transformed T cells consistent with a PPAR-gamma-dependent mechanism. These observations suggest that PPAR-gamma ligands (which may include PGD2) provide strong apoptotic signals to transformed, but not normal T lymphocytes. Thus, the efficacy of utilizing PPAR-gamma and its ligands as therapeutics for human T cell cancers needs to be further evaluated.

Possible new role for NF-kappaB in the resolution of inflammation

Inflammation involves the sequential activation of signaling pathways leading to the production of both pro- and anti-inflammatory mediators. Although much attention has focused on pro-inflammatory pathways that initiate inflammation, relatively little is known about the mechanisms that switch off inflammation and resolve the inflammatory response. The transcription factor NF-kappaB is thought to have a central role in the induction of pro-inflammatory gene expression and has attracted interest as a new target for the treatment of inflammatory disease. We show here that NF-kappaB activation in leukocytes recruited during the onset of inflammation is associated with pro-inflammatory gene expression, whereas such activation during the resolution of inflammation is associated with the expression of anti-inflammatory genes and the induction of apoptosis. Inhibition of NF-kappaB during the resolution of inflammation protracts the inflammatory response and prevents apoptosis. This suggests that NF-kappaB has an anti-inflammatory role in vivo involving the regulation of inflammatory resolution.

Nitric oxide and inflammatory mediators in the perpetuation of osteoarthritis

Articular chondrocyte production of nitric oxide (NO) and other inflammatory mediators, such as eicosanoids and cytokines, are increased in human osteoarthritis. The excessive production of nitric oxide inhibits matrix synthesis and promotes its degradation. Furthermore, by reacting with oxidants such as superoxide anion, nitric oxide promotes cellular injury and renders the chondrocyte susceptible to cytokine-induced apoptosis. PGE(2) exerts anabolic and catabolic effects on chondrocytes, depending on the microenvironment and physiologic condition. The increased expression of inducible NOS (iNOS) and cyclo-oxygenase-2 (COX-2) in OA chondrocytes is largely due to the increased expression of pro-inflammatory cytokines, particularly IL-1, which act in an autocrine/paracrine fashion to perpetuate a catabolic state that leads to progressive destruction of articular cartilage. The initiating factors for the production of inflammatory mediators include altered biomechanical forces; their continued production may be augmented by an increase in extracellular matrix proteins acting through ligation of surface integrins.

Peroxisome proliferator-activated receptor-gamma haploinsufficiency enhances B cell proliferative responses and exacerbates experimentally induced arthritis

Peroxisome proliferator-activated receptor-gamma (PPAR gamma) controls adipogenesis and glucose metabolism. It was reported recently that PPAR gamma activation by its agonistic ligands modifies lymphocyte function. Since synthetic ligands are known to exert their effect via PPAR gamma-dependent and -independent pathways, we examined the physiological role of PPAR gamma in lymphocytes by using heterozygote mutant mice in which one allele of PPAR gamma is deleted (PPAR gamma(+/-)). In contrast to T cells, which did not exhibit a significant difference, B cells from PPAR gamma(+/-) showed an enhanced proliferative response to stimulation by either lipopolysaccharide or cross-linking of antigen receptors. Dysregulation of the NF-kappa B pathway in B cells from PPAR gamma(+/-) was indicated by spontaneous NF-kappa B activation, as well as increased I kappa B alpha phosphorylation and gel-shift activity following LPS stimulation. Mice primed with either ovalbumin or methylated BSA also showed enhanced antigen-specific immune response of both T and B cells, an immunological abnormality that exacerbated antigen-induced arthritis. These findings indicate that PPAR gamma plays a critical role in the control of B cell response and imply a role in diseases in which B cell hyperreactivity is involved, such as arthritis and autoimmunity.

15-deoxy-delta12,14-prostaglandin J2-induced apoptosis in amnion-like WISH cells

Apoptosis at the site of rupture has been proposed to play a role in premature rupture of the fetal membranes, a condition associated with increased risk of neonatal sepsis and preterm birth. We investigated the ability of peroxisome proliferator-activated receptor (PPAR)-gamma ligands 15-deoxy-delta12,14PGJ2 (15d-PGJ2), delta12PGJ2, ciglitizone and rosiglitazone to induce apoptosis in the amnion-like WISH cell line. 15d-PGJ2 (10 microM) induced morphological characteristics of apoptosis within 2 h, with biochemical indices (caspase activation and substrate cleavage) following shortly after; maximum cell death (approximately 60%) was observed by 16 h, with an EC50) of approximately 7 microM 15d-PGJ2. Delta12-PGJ2 also induced apoptosis but was less potent and acted at a much slower rate. While ciglitizone also induced apoptosis, rosiglitazone had no effect on cell viability. The mechanism of induction of apoptosis by 15d-PGJ2 and delta12PGJ2, which may be independent of PPAR-gamma activation, requires further elucidation.

Effects of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) on the expression of inflammatory cytokines and apoptosis induction in rheumatoid synovial fibroblasts and monocytes

This study was performed to investigate whether peroxisome proliterator-activated receptor-gamma (PPAR-gamma) exerted an anti-inflammatory effect on rheumatoid synovial cells and inhibited dysregulated proliferation. The expression of PPAR-gamma mRNA in cultured human synoviocytes and THP-1 cells was analysed by RT-PCR. PPAR-gamma was expressed in normal, osteoarthritis (OA), rheumatoid arthritis (RA) synovial cells as well as a human monocytic cell line, THP-1. In RA and OA synoviocytes, the induction of inflammatory cytokine mRNA expression such as TNF-alpha and IL-1beta was significantly inhibited by the natural PPAR-gamma agonist, 15 deoxy-Delta(12,14)prostaglandin J(2)(15d-PGJ(2)). The effect of PPAR-gamma on the nuclear factor (NF)-kappaB activity was tested by electrophoretic mobility shift assay (EMSA). Both troglitazone and 15d-PGJ(2)markedly inhibited TNF-alpha-induced NF-kappaB activation at 30 microM. However, PPAR-gamma agonist neither reduced proliferation nor induced apoptosis in RA synoviocytes when measured by XTT assay and fluorescence activated cell sorter (FACS) analysis. In contrast, it induced apoptosis in a dose-dependent manner in THP-1 cells and augmented TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis as well. In conclusion, these data demonstrate that PPAR-gamma is expressed in human synoviocytes and THP-1 cells, and the PPAR-gamma activation inhibits expression of inflammatory cytokines in RA synoviocytes. Furthermore, PPAR-gamma activation induces apoptosis by itself and augments TRAIL/Apo2L-induced apoptosis in THP-1 cells. These results suggest that PPAR-gamma agonists may provide a new therapeutic approach for RA.

Inflammatory pathways in atherosclerosis and acute coronary syndromes

Evidence from a broad range of studies demonstrates that atherosclerosis is a chronic disease that, from its origins to its ultimate complications, involves inflammatory cells (T cells, monocytes, macrophages), inflammatory proteins (cytokines, chemokines), and inflammatory responses from vascular cells (endothelial cell expression of adhesion molecules). Investigators have identified a variety of proteins whose levels might predict cardiovascular risk. Of these candidates, C-reactive protein, tumor necrosis factor-alpha, and interleukin-6 have been most widely studied. There is also the prospect of inflammation as a therapeutic target, with investigators currently debating to what extent the decrease in cardiovascular risk seen with statins, angiotensin-converting enzyme inhibitors, and peroxisome proliferator-activated receptor ligands derives from changes in inflammatory parameters. These advances in basic and clinical science have placed us on a threshold of a new era in cardiovascular medicine.

Regulation of peroxisome proliferator-activated receptor gamma expression in human asthmatic airways: relationship with proliferation, apoptosis, and airway remodeling

Airway inflammation and alterations in cellular turnover are histopathologic features of asthma. We show that the expression of peroxisome proliferator-activated receptor gamma (PPAR gamma), a nuclear hormone receptor involved in cell activation, differentiation, proliferation, and/or apoptosis, is augmented in the bronchial submucosa, the airway epithelium, and the smooth muscle of steroid-untreated asthmatics, as compared with control subjects. This is associated with enhanced proliferation and apoptosis of airway epithelial and submucosal cells, as assessed by the immunodetection of the nuclear antigen Ki67, and of the cleaved form of caspase-3, respectively, and with signs of airway remodeling, including thickness of the subepithelial membrane (SBM) and collagen deposition. PPAR gamma expression in the epithelium correlates positively with SBM thickening and collagen deposition, whereas PPAR gamma expressing cells in the submucosa relate both to SBM thickening and to the number of proliferating cells. The intensity of PPAR gamma expression in the bronchial submucosa, the airway epithelium, and the smooth muscle is negatively related to FEV(1) values. Inhaled steroids alone, or associated with oral steroids, downregulate PPAR gamma expression in all the compartments, cell proliferation, SBM thickness, and collagen deposition, whereas they increase apoptotic cell numbers in the epithelium and the submucosa. Our findings have demonstrated that PPAR gamma (1) is a new indicator of airway inflammation and remodeling in asthma; (2) may be involved in extracellular matrix remodeling and submucosal cell proliferation; (3) is a target for steroid therapy.

Peroxisome proliferator-activated receptors in macrophage biology: friend or foe?

Peroxisome proliferator-activated receptor (PPAR)-gamma is a nuclear hormone receptor, with a well-established role in adipogenesis and glucose metabolism. Over the past 3 years several laboratories have reported that this protein can influence macrophage responses to a variety of inflammatory stimuli. The effect of PPAR-gamma activation on macrophage lipid uptake, cholesterol efflux, and cytokine production have all recently been examined in several in-vitro culture systems. In addition, PPAR-gamma ligands have been shown to influence atherosclerotic lesion formation in murine models of that disease. This review attempts to summarize and critically evaluate that work and its implications for the use of PPAR-gamma activators in understanding and treating the pathogenetic processes that contribute to atherosclerotic plaque formation.

Prostaglandin-J2 induces synthesis of interleukin-8 by endothelial cells in a PPAR-gamma-independent manner

PPARgamma is a transcription factor of nuclear receptor superfamily, involved in the regulation of inflammation. We investigated the influence of PPARgamma-ligands, 15-deoxy-delta12,14 prostaglandin-J2 (15d-PGJ2), and ciglitazone, on the generation of interleukin-8 (IL-8) by the human microvascular endothelial cell line (HMEC- 1). Expression of PPARgamma in HMEC-1 was confirmed by RT-PCR. Both PPARgamma-ligands tested induced the activation of PPAR, but the potency of ciglitazone was higher, as evidenced by luciferase assay. Resting HMEC-1 released about 150 pg/ml of IL-8 protein. Treatment with LPS increased the IL-8 secretion up to 1 ng/ml. 15d-PGJ2 potently and dose-dependently increased both the steady-state and LPS-induced generation of IL-8 mRNA and IL-8 protein. In contrast, neither basal nor LPS-elicited expression of IL-8 was influenced by ciglitazone. We conclude, that 15d-PGJ2 is a potent inducer of IL-8 production and can be a mediator of inflammatory response, but this effect is independent of PPARgamma activation.

Cyclooxygenase-independent actions of cyclooxygenase inhibitors

Several studies have demonstrated unequivocally that certain nonsteroidal anti-inflammatory drugs (NSAIDs) such as sodium salicylate, sulindac, ibuprofen, and flurbiprofen cause anti-inflammatory and antiproliferative effects independent of cyclooxygenase activity and prostaglandin synthesis inhibition. These effects are mediated through inhibition of certain transcription factors such as NF-kappaB and AP-1. The respective NSAIDs might interfere directly with the transcription factors, but their effects are probably mediated predominantly through alterations of the activity of cellular kinases such as IKKbeta, Erk, p38 MAPK, or Cdks. These effects apparently are not shared by all NSAIDs, since indomethacin failed to inhibit NF-kappaB and AP-1 activation as well as Erk and Cdk activity. In contrast, indomethacin was able to activate PPARgamma, which was not affected by sodium salicylate or aspirin. The differences in cyclooxygenase-independent mechanisms may have consequences for the specific use of these drugs in individual patients because additional effects may either enhance the efficacy or reduce the toxicity of the respective compounds.

Expression of peroxisome proliferator-activated receptor gamma in renal cell carcinoma and growth inhibition by its agonists

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a ligand-activated transcriptional factor belonging to the steroid receptor superfamily. It plays a role in both adipocyte differentiation and tumorgenesis. Up-date, the up-regulation of PPAR-gamma expression is a frequent occurrence in a variety of different malignant tumors. In this study, we investigated the expression of PPAR-gamma in human renal cell carcinoma (RCC) tissues, and the role of PPAR-gamma in cell growth in human RCC-derived cell lines. Immunohistochemistry showed a strong immunoreactive expression of PPAR-gamma in all slides from cancer specimens. RT-PCR and Western blot analysis showed 3 RCC cell lines expressed PPAR-gamma mRNA and its protein. MTT assay in 3 RCC cells showed that the synthetic PPAR-gamma agonists thiazolidinedione compounds (pioglitazone and troglitazone) and the endogeneous PPAR-gamma ligand, 15-deoxy-Delta12,14-prostaglandin J(2) (15dPGJ(2)) inhibited the growth of the RCC cells. These results suggest that PPAR-gamma may become a new target in the treatment of RCC.

Nitric oxide synthase 2 and cyclooxygenase 2 interactions in inflammation

Nitric oxide (NO) and prostaglandin (PG) E2 produced by NO synthase type 2 (NOS2) and cyclooxygenase type 2 (COX2), respectively, are important mediators in inflammation. There is much information regarding their roles in models of inflammation in mice and in humans with diseases such as rheumatoid arthritis (RA). A variety of stimuli including cytokines, microbial components, immune complexes, and mechanical stress can induce both NOS2 and COX2 mRNA transcription and protein synthesis and enhance inflammation. This has been demonstrated in both mice and humans. NOS2-specific inhibitors reduce inflammation in mice, and COX2-specific inhibitors reduce inflammation in mice and in humans. There is significant cross-talk between PGE2/NO and COX2/NOS2. Treatments that inhibit both NOS2 and COX2 should provide the most potent antiinflammatory effects.

Peroxisome proliferator-activated receptor-gamma-independent inhibition of macrophage activation by the non-thiazolidinedione agonist L-796,449. Comparison with the effects of 15-deoxy-delta(12,14)-prostaglandin J(2)

The effects of L-796,449 (3-chloro-4-(3-(3-phenyl-7-propylbenzofuran-6-yloxy)propylthio)phenylacetic acid; referred to henceforth as compound G), a thiazolidinedione-unrelated peroxisome proliferator activated-receptor-gamma (PPAR-gamma) agonist, on early signaling in lipopolysaccharide-activated RAW 264.7 macrophages were analyzed and compared with those elicited by 15-deoxy-Delta(12,14)-prostaglandin J(2) and the thiazolidinedione rosiglitazone. Compound G inhibited the activation of nuclear factor kappa B through the impairment of the targeting and degradation of I kappa B proteins and promoted a redistribution of I kappa B alpha and I kappa B beta in the nucleus of activated cells. Compound G inhibited I kappa B kinase (IKK) activity both in vivo and in vitro, suggesting a direct mechanism of interaction between this molecule and the IKK complex. The effect of compound G on IKK activity was independent of PPAR-gamma engagement because RAW 264.7 cells expressed negligible levels of this nuclear receptor, and rosiglitazone failed to mimic these actions. Moreover, treatment of activated macrophages with compound G enhanced the synthesis of superoxide anion, which, in combination with the NO produced under activation conditions, triggered apoptosis through the intracellular synthesis of peroxynitrite. These results suggest that compound G might contribute to the resolution of inflammation by favoring the induction of apoptosis through mechanisms independent of PPAR-gamma engagement.

15-Deoxy-delta12,14-PGJ2, but not troglitazone, modulates IL-1beta effects in human chondrocytes by inhibiting NF-kappaB and AP-1 activation pathways

The activation of peroxisome proliferator-activated receptor gamma (PPARgamma) has been shown to inhibit the production and the effects of proinflammatory cytokines. Since interleukin-1beta (IL-1beta) directly mediates cartilage degradation in osteoarthritis, we investigated the capability of PPARgamma ligands to modulate IL-1beta effects on human chondrocytes. RT-PCR and Western blot analysis revealed that PPARgamma expression was decreased by IL-1beta. 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2), in contrast to troglitazone, was highly potent to counteract IL-1beta-induced cyclooxygenase-2 and inductible nitric oxide synthase expression, NO production and the decrease in proteoglycan synthesis. Western blot and gel-shift analyses demonstrated that 15d-PGJ2 inhibited NF-kappaB activation, while troglitazone was ineffective. Although 15d-PGJ2 attenuated activator protein-1 binding on the DNA, it potentiated c-jun migration in the nucleus. The absence or the low effect of troglitazone suggests that 15d-PGJ2 action in human chondrocytes is mainly PPARgamma-independent.

Modulation of keratinocyte gene expression and differentiation by PPAR-selective ligands and tetradecylthioacetic acid

Peroxisome proliferator-activated receptors (PPARs) are pleiotropic regulators of growth and differentiation of many cell types. We have performed a comprehensive analysis of the expression of PPARs, transcriptional cofactors, and marker genes during differentiation of normal human keratinocytes using a combination of reverse transcriptase polymerase chain reaction, Northern and Western blotting, and immunohistochemistry. PPARdelta was the predominant PPAR subtype in human keratinocytes and highly expressed in basal cells and suprabasal cells. Induction of PPARalpha and PPARgamma expression was linked to differentiation, and accordingly, expression of PPARalpha and PPARgamma was in essence confined to suprabasal cells. Differentiation was not accompanied by significant changes in the expression of the coactivators CREB-binding protein, p300, steroid receptor coactivator 1, or the corepressors nuclear receptor corepressor and silence mediator for retinoid and thyroid hormone receptors. We critically evaluated the effects of selective PPAR ligands and a synthetic fatty acid analog, tetradecylthioacetic acid. Tetradecylthioacetic acid activated all human PPAR subtypes in the ranking order PPARdelta >> PPARalpha > PPARgamma. All selective PPAR ligands marginally induced transglutaminase-1 expression with the PPARdelta-selective ligand L165041 being the most potent. The PPARalpha- and PPARgamma-selective ligands Wy14643 and BRL49653 had negligible effect on involucrin expression, whereas a dose-dependent induction was observed with L165041. Simultaneous addition of L165041 and BRL49653 synergistically induced strong involucrin expression. Additionally, L165041 potently induced CD36 mRNA expression. Administration of tetradecylthioacetic acid resulted in a dramatic decrease in proliferation and a robust upregulation of the expression of involucrin and transglutaminase. Our results indicate that tetradecylthioacetic acid may affect keratinocyte gene expression and differentiation via PPAR-dependent and PPAR-independent pathways, and that the latter play an important role.

Feedback control of the arachidonate cascade in rheumatoid synoviocytes by 15-deoxy-Delta(12,14)-prostaglandin J2

Rheumatoid arthritis (RA) is a chronic polyarticular joint disease associated with massive synovial proliferation, inflammation, and angiogenesis. PPAR-gamma ligands, both 15-deoxy-Delta(12,14)-prostaglandin J2 (15d- PGJ2) and troglitazone (TRO), can inhibit the growth of RA synoviocytes in vitro, and suppress the chronic inflammation of adjuvant-induced arthritis in rats, but the potency of 15d-PGJ2 is higher than TRO. Prostaglandin (PG) E2 plays important roles in joint erosion and synovial inflammation. In the present study, 15d-PGJ2, but not TRO and other prostanoids, suppressed interleukin (IL)-1beta-induced PGE2 synthesis in rheumatoid synovial fibroblasts (RSFs) through the inhibition of cyclooxygenase (COX-2) and cytosolic phospholipase A2 (cPLA2) expression. Furthermore, the inhibition was not affected by pretreatment with anti-PPAR-gamma antibody. It means that this anti-inflammatory effect of 15d-PGJ2 for PG synthesis may be independent of PPAR-gamma and 15d-PGJ2 is a key regulator of negative feedback of the arachidonate cascade on the COX pathway. These findings provide new insight into the feedback mechanism of the arachidonate cascade.

Amelioration of experimental autoimmune encephalomyelitis in C57BL/6 mice by an agonist of peroxisome proliferator-activated receptor-gamma

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma), a member of the nuclear hormone receptor superfamily, plays a critical role in adipocyte differentiation and glucose homeostasis. It has been implicated that PPAR-gamma functions as a regulator of cellular proliferation and inflammatory responses. In the present study, we examined whether troglitazone, a selective PPAR-gamma agonists, ameliorated experimental autoimmune encephalomyelitis (EAE) induced by administration of myelin oligodendrocyte glycoprotein (MOG) peptide 35-55 in C57BL/6 mice. We found that troglitazone attenuated the inflammation and decreased the clinical symptoms. It was suggested that the amelioration was attributed to the attenuation of pro-inflammatory cytokine gene expressions.

Peroxisome proliferator-activated receptor gamma ligands suppress the transcriptional activation of cyclooxygenase-2. Evidence for involvement of activator protein-1 and CREB-binding protein/p300

We investigated whether peroxisome proliferator-activated receptor gamma (PPARgamma) ligands (ciglitazone, troglitazone, and 15-deoxy-Delta(12,14) prostaglandin J(2)) inhibited cyclooxygenase-2 (COX-2) induction in human epithelial cells. Ligands of PPARgamma inhibited phorbol ester (phorbol 12-myristate 13-acetate, PMA)-mediated induction of COX-2 and prostaglandin E(2) synthesis. Nuclear run-offs revealed increased rates of COX-2 transcription after treatment with PMA, an effect that was inhibited by PPARgamma ligands. PMA-mediated induction of COX-2 promoter activity was inhibited by PPARgamma ligands; this suppressive effect was prevented by overexpressing a dominant negative form of PPARgamma or a PPAR response element decoy oligonucleotide. The stimulatory effects of PMA were mediated by a cyclic AMP response element in the COX-2 promoter. Treatment with PMA increased activator protein-1 (AP-1) activity and the binding of c-Jun, c-Fos, and ATF-2 to the cyclic AMP response element, effects that were blocked by PPARgamma ligands. These findings raised questions about the mechanism underlying the anti-AP-1 effect of PPARgamma ligands. The induction of c-Jun by PMA was blocked by PPARgamma ligands. Overexpression of either c-Jun or CREB-binding protein/p300 partially relieved the suppressive effect of PPARgamma ligands. When CREB-binding protein and c-Jun were overexpressed together, the ability of PPARgamma ligands to suppress PMA-mediated induction of COX-2 promoter activity was essentially abrogated. Bisphenol A diglycidyl ether, a compound that binds to PPARgamma but lacks the ability to activate transcription, also inhibited PMA-mediated induction of AP-1 activity and COX-2. Taken together, these findings are likely to be important for understanding the anti-inflammatory and anti-cancer properties of PPARgamma ligands.