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

Signaling transduction: target in osteoarthritis

PURPOSE OF REVIEW

The pathophysiology of osteoarthritis is the result of an imbalance between anabolic and catabolic pathways. This imbalance is the result of the activation of joint cells by inflammatory mediators, matrix components, and mechanical stress. All these mediators act through specific receptors that transmit the signals to the nucleus to activate the transcription of matrix metalloproteinases and inflammatory genes. Targeting these signaling pathways in osteoarthritis is considered a novel approach to modulate this imbalance.

RECENT FINDINGS

Although many signaling pathways are necessary for physiologic cell life, it is now well established that a few are more specifically induced in an inflammatory environment. In osteoarthritis, the nuclear factor-kappaB and mitogen-activated protein kinase pathways have been shown to play a predominant role in the expression of metalloproteinases and inflammatory genes and proteins. Also involved in the activation of osteoarthritic cells are other molecules interacting with one or several signaling pathways, such as nitric oxide, peroxisome proliferator-activated receptor-gamma ligands, or C/EBP transcriptional factors. Based on this knowledge, specific inhibitors for some of these signaling pathways have been designed and include p38 mitogen-activated protein kinase or nuclear factor-kappaB inhibitors. Experimental studies evaluating cartilage degradation in arthritis models are promising, although fewer have been done specifically in osteoarthritis models.

SUMMARY

Targeting signaling pathways in osteoarthritis did not seem feasible a few years ago because of the complexity of the multiple intracellular pathways, mainly physiologic, defined by a high degree of redundancy and cross-talk. However, important advances in the knowledge of chondrocyte and synoviocyte signaling in osteoarthritis have been achieved in recent years and suggest that inhibitors of specific signaling pathways could shortly provide effective treatments for this disease.

Cyclooxygenase isozymes: the biology of prostaglandin synthesis and inhibition

Nonsteroidal anti-inflammatory drugs (NSAIDs) represent one of the most highly utilized classes of pharmaceutical agents in medicine. All NSAIDs act through inhibiting prostaglandin synthesis, a catalytic activity possessed by two distinct cyclooxygenase (COX) isozymes encoded by separate genes. The discovery of COX-2 launched a new era in NSAID pharmacology, resulting in the synthesis, marketing, and widespread use of COX-2 selective drugs. These pharmaceutical agents have quickly become established as important therapeutic medications with potentially fewer side effects than traditional NSAIDs. Additionally, characterization of the two COX isozymes is allowing the discrimination of the roles each play in physiological processes such as homeostatic maintenance of the gastrointestinal tract, renal function, blood clotting, embryonic implantation, parturition, pain, and fever. Of particular importance has been the investigation of COX-1 and -2 isozymic functions in cancer, dysregulation of inflammation, and Alzheimer's disease. More recently, additional heterogeneity in COX-related proteins has been described, with the finding of variants of COX-1 and COX-2 enzymes. These variants may function in tissue-specific physiological and pathophysiological processes and may represent important new targets for drug therapy.

Fas ligand-dependent suppression of autoimmunity via recruitment and subsequent termination of activated T cells

Signals transmitted by binding of Fas ligand (FasL) to the Fas receptor (CD95/Apo-1) have pleiotropic effects on cellular function that present opportunities for therapeutic applications. For example, depending on the circumstances, overexpression of FasL can enhance, prevent, or reverse growth of spontaneous or transplantable tumors. Furthermore, local administration of FasL into a single paw in susceptible mice protects from or reduces the severity of collagen-induced arthritis (CIA) in all paws. Here, we define mechanisms that mediate systemic protection induced by locally delivered FasL. Protection is not solely dependent on local interactions between Fas and FasL, but rather requires induction of a paradoxical inflammatory response that not only destroys Fas-resistant tumors, but also recruits motile, activated, Fas-bearing T cells that are Fas sensitive. We demonstrate by following the antigen-specific recruitment and subsequent termination of transgenic T cells that activated T cells, including autoreactive cells responsible for CIA, are eliminated within this inflammatory environment through the overexpressed FasL. The nature of the inflammatory response, which depends on the Fas ligand being cell bound and not soluble, and the magnitude of FasL expression within the inflammatory milieu are essential for this effect, as arthritogenic inflammation alone resulting from CIA induction is insufficient to ameliorate the disease or eliminate antigen-specific T cells, even upon systemic delivery of soluble FasL. These data show that gene delivery of membrane-bound FasL can effectively recruit and eliminate autoreactive T cells.

Peroxisome proliferator-activated receptor alpha agonists as therapy for autoimmune disease

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily. PPAR gamma ligands, which include the naturally occurring PG metabolite 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)), as well as thiazolidinediones, have been shown to have anti-inflammatory activity. The PPAR alpha agonists, gemfibrozil, ciprofibrate, and fenofibrate, have an excellent track history as oral agents used to treat hypertriglyceridemia. In the present study, we demonstrate that these PPAR alpha agonists can increase the production of the Th2 cytokine, IL-4, and suppress proliferation by TCR transgenic T cells specific for the myelin basic protein Ac1-11, as well as reduce NO production by microglia. Oral administration of gemfibrozil and fenofibrate inhibited clinical signs of experimental autoimmune encephalomyelitis. More importantly, gemfibrozil was shown to shift the cytokine secretion of human T cell lines by inhibiting IFN-gamma and promoting IL-4 secretion. These results suggest that PPAR alpha agonists such as gemfibrozil and fenofibrate, may be attractive candidates for use in human inflammatory conditions such as multiple sclerosis.

Effect of 15-deoxy-delta 12,14-prostaglandin J2 on acute lung injury induced by lipopolysaccharide in mice

15-Deoxy-delta(12,14)-prostaglandin J(2) (15d-prostaglandin J(2)) has received attention for its anti-inflammatory properties. The present study investigated the efficacy of 15d-prostaglandin J(2) on acute lung injury induced by lipopolysaccharide in mice. ICR mice were administered with 15d-prostaglandin J(2) (10 microg/kg, 100 microg/kg, or 1 mg/kg) before intratracheal challenge with lipopolysaccharide (125 microg/kg). Treatment with 15d-prostaglandin J(2) did not ameliorate rather enhanced at a dose of 1 mg/kg the neutrophilic lung inflammation and pulmonary edema by lipopolysaccharide. The enhancement was concomitant with the increased lung expression of interleukin-1 beta, macrophage inflammatory protein-1 alpha, and macrophage chemoattractant protein-1. 15d-prostaglandin J(2) increased the nuclear protein expression of peroxisome proliferator-activated receptor (PPAR)-gamma and inhibited the nuclear localization of nuclear factor-kappa B related to lipopolysaccharide. 15d-prostaglandin J(2) increased the phosphorylation of c-Jun in the presence or absence of lipopolysaccharide. Our data suggest that 15d-prostaglandin J(2) may not be useful but potentially harmful for the therapeutic option of acute lung injury.

Peroxisome Proliferator-activated Receptor-γ Down-regulates Chondrocyte Matrix Metalloproteinase-1 via a Novel Composite Element

Interleukin-1beta (IL-1beta) induces degradation via hyperexpression of an array of genes, including metalloproteinases (MMP), in cartilage cells during articular degenerative diseases. In contrast, natural ligands for peroxisome proliferator-activated receptors (PPARs) display protective anti-cytokine effects in these cells. We used the PPAR agonist rosiglitazone (Rtz) to investigate PPAR-gamma isotype on IL-1beta-target genes. Immunocytochemistry, electrophoretic mobility shift, and transient transfection assays revealed a functional PPAR-gamma in chondrocytes in vitro. Rtz displayed significant inhibition of IL-1beta effects in chondrocytes. Low Rtz concentrations (close to K(d) values for PPAR-gamma, 0.1 to 1 microm) inhibited the effects of IL-1beta on (35)S-sulfated proteoglycan production and gelatinolytic activities and downregulated MMP1 expression at mRNA and protein levels. We have investigated the mechanism of action of Rtz against IL-1beta-mediated MMP1 gene hyperexpression. Rtz effect occurs at the transcriptional level of the MMP1 promoter, as observed in transiently transfected cells with pMMP1-luciferase vector. Transient expression of wild type PPAR-gamma enhanced Rtz inhibitory effect in chondrocytes, whereas a mutated dominant negative PPAR-gamma abolished it, supporting the role of PPAR-gamma in this effect. MMP1 gene promoter analysis revealed the involvement of a cis-acting element located at -83 to -77, shown to be a composite PPRE/AP1 site. Gel mobility and supershift assays demonstrated that PPAR-gamma and c-Fos/c-Jun proteins bind this cis-acting element in a mutually exclusive way. Our data highlight a new PPAR-gamma-dependent inhibitory mechanism on IL-1beta-mediated cartilage degradation occurring through DNA binding competition on the composite PPRE/AP1 site in the MMP1 promoter.

A potential role of 15-deoxy-delta(12,14)-prostaglandin J2 for induction of human articular chondrocyte apoptosis in arthritis

The cyclopentenone prostaglandin (PG) J2 is formed within the cyclopentenone ring of the endogenous prostaglandin PG D2 by a nonenzymatic reaction. The PG J family is involved in mediating various biological effects including the regulation of cell cycle progression and inflammatory responses. Here we demonstrate the potential role of 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PG J2) in human articular chondrocyte apoptosis. 15d-PG J2 was released by human articular chondrocytes and found in joint synovial fluids taken from osteoarthritis or rheumatoid arthritis patients. Proinflammatory cytokines such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) up-regulated chondrocyte release of 15d-PG J2. PG D2 synthase mRNA expression was up-regulated by IL-1beta, TNF-alpha, or nitric oxide. 15d-PG J2 induced apoptosis of chondrocytes from osteoarthritis or rheumatoid arthritis patients as well as control nonarthritic subjects in a time- and dose-dependent manner and in a peroxisome proliferator-activated receptor gamma-dependent manner. Peroxisome proliferator-activated receptor gamma expression was up-regulated by IL-1beta and TNF-alpha. Inhibition of NF-kappaB, and the activation of p38 MAPK were also found to be involved in 15d-PG J2-induced chondrocyte apoptosis. Such signal pathways led to the activation of the downstream pro-apoptotic molecule p53 and caspase cascades. Together, these results suggest that 15d-PGJ2 may play an important role in the pathogenesis of arthritic joint destruction via a regulation of chondrocyte apoptosis.

Peroxisome Proliferator-Activated Receptor-γ Ligands Ameliorate Experimental Autoimmune Myocarditis Associated with Inhibition of Self-Sensitive T Cells

OBJECTIVE

Recent evidence has suggested that peroxisome proliferator-activated receptor-gamma (PPAR-gamma) serves as a negative regulator in the immune system. In the present study, we investigated the expression of PPAR-gamma and the effect of PPAR-gamma ligands on experimental autoimmune myocarditis (EAM).

METHODS AND RESULTS

Experimental autoimmune myocarditis was induced in Lewis rats by immunization with porcine cardiac myosin. PPAR-gamma ligands 15-deoxy-Delta-PGJ2 200 microg x kg(-1) x d(-1) by ip and pioglitazone 10 mg x kg(-1) x d(-1) by oral were administered for 3 weeks. PPAR-gamma expression was upregulated in myocarditis and the enhanced PPAR-gamma expression was prominently stained in the nuclear and perinuclear regions of the positive-stained cells in the inflammatory lesions. Administration of PPAR-gamma ligands markedly reduced the severity of myocarditis, as indicated by the heart weight/body weight ratio, pericardial effusion scores, macroscopic scores, and microscopic scores. The upregulated PPAR-gamma expression was also reduced by PPAR-gamma ligands treatment. In addition, PPAR-gamma ligands suppressed the proliferative response and interferon-gamma production of T cell-enriched splenocytes from rats with EAM. Furthermore, the cytotoxic activity and myocarditogenic potential of these T cells were inhibited by PPAR-gamma ligands treatment.

CONCLUSIONS

PPAR-gamma ligands ameliorate EAM associated with inhibition of expansion and activation of the self-sensitive T cells. These results suggest that PPAR-gamma ligands may have the potential to modulate human inflammatory heart diseases as myocarditis.

Disruption of transforming growth factor beta signaling and profibrotic responses in normal skin fibroblasts by peroxisome proliferator-activated receptor gamma

OBJECTIVE

In fibroblasts, transforming growth factor beta (TGF beta) stimulates collagen synthesis and myofibroblast transdifferentiation through the Smad intracellular signal transduction pathway. TGF beta-mediated fibroblast activation is the hallmark of scleroderma and related fibrotic conditions, and disrupting the intracellular TGF beta/Smad signaling may provide a novel approach to controlling fibrosis. Because of its potential role in modulating inflammatory and fibrotic responses, we examined the expression of the nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPAR gamma) in normal skin fibroblasts and its effect on TGF beta-induced cellular responses.

METHODS

The expression and activity of PPAR gamma in normal dermal fibroblasts were examined by Northern and Western blot analyses, immunocytochemistry, flow cytometry, and transient transfections with reporter constructs. The same approaches were used to evaluate the effects of PPAR gamma activation by naturally occurring and synthetic ligands on collagen synthesis and alpha-smooth muscle actin (alpha-SMA) expression. Modulation of Smad-mediated transcriptional responses was examined by transient transfection assays using wild-type and dominant-negative PPAR gamma expression constructs.

RESULTS

The PPAR gamma receptor was expressed and fully functional in quiescent normal skin fibroblasts. Whereas ligand activation of cellular PPAR gamma resulted in modest suppression of basal collagen gene expression, it abrogated TGF beta-induced stimulation in a concentration-dependent manner. This response was mimicked by overexpressing PPAR gamma in fibroblasts, and was blocked by a selective antagonist of PPAR gamma signaling or by transfection of fibroblasts with dominant-negative PPAR gamma constructs. Furthermore, PPAR gamma ligands abrogated TGF beta-induced expression of alpha-SMA, a marker of myofibroblasts. Stimulation of Smad-dependent transcriptional responses by TGF beta was suppressed by PPAR gamma despite the absence of a consensus PPAR gamma-response element in the targeted promoters. Ligand-induced activation of fibroblast PPAR gamma had no effect on protein expression of cellular Smad3 or Smad7.

CONCLUSION

By abrogating of TGF beta-induced stimulation of collagen gene expression, myofibroblast transdifferentiation, and Smad-dependent promoter activity in normal fibroblasts, PPAR gamma may play a physiologic role in the regulation of the profibrotic response. Furthermore, our results suggest that PPAR gamma activation by pharmacologic agonists may represent a novel approach to the control of fibrosis in scleroderma.

15-Deoxy-Δ12,14-prostaglandin J2 Inhibits Bay 11-7085-induced Sustained Extracellular Signal-regulated Kinase Phosphorylation and Apoptosis in Human Articular Chondrocytes and Synovial Fibroblasts

We have previously shown that nuclear factor-kappaB inhibition by adenovirus expressing mutated IkappaB-alpha or by proteasome inhibitor increases human articular chondrocytes sensibility to apoptosis. Moreover, the nuclear factor-kappaB inhibitor BAY11-7085, a potent anti-inflammatory drug in rat adjuvant arthritis, is itself a proapoptotic agent for chondrocytes. In this work, we show that BAY 11-7085 but not the proteasome inhibitor MG-132 induced a rapid and sustained phosphorylation of extracellular signal-regulated kinases (ERK1/2) in human articular chondrocytes. The level of ERK1/2 phosphorylation correlated with BAY 11-7085 concentration and chondrocyte apoptosis. 15-Deoxy-delta(12,14)-prostaglandin J2 (15d-PGJ2) and its precursor prostaglandin (PG) D2 but not PGE2 and PGF2alpha rescued chondrocytes from BAY 11-7085-induced apoptosis. 15d-PGJ2 markedly inhibited BAY 11-7085-induced phosphorylation of ERK1/2. BAY 11-7085 also induced ERK1/2 phosphorylation and apoptosis in human synovial fibroblasts, and these reactions were down-regulated by 15d-PGJ2. Further analysis in synovial fibroblasts showed that only molecules that suppressed BAY 11-7085-induced phosphorylation of ERK1/2 (i.e. 15d-PGJ2, PGD2, and to a lesser extent, MEK1/2 inhibitor UO126, but not prostaglandins E2 and F2alpha or peroxisome proliferator-activated receptor-gamma agonist ciglitazone) were able protect cells from apoptosis. These results suggested that the antiapoptotic effect of 15d-PGJ2 on chondrocytes and synovial fibroblasts might involve inhibition of ERK1/2 phosphorylation.

Activation of Peroxisome Proliferator-activated Receptor γ Inhibits Interleukin-1β-induced Membrane-associated Prostaglandin E2 Synthase-1 Expression in Human Synovial Fibroblasts by Interfering with Egr-1

Membrane-associated prostaglandin (PG) E(2) synthase-1 (mPGES-1) catalyzes the conversion of PGH(2) to PGE(2), which contributes to many biological processes. Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-activated transcription factor and plays an important role in growth, differentiation, and inflammation in different tissues. Here, we examined the effect of PPARgamma ligands on interleukin-1beta (IL-1beta)-induced mPGES-1 expression in human synovial fibroblasts. PPARgamma ligands 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)) and the thiazolidinedione troglitazone (TRO), but not PPARalpha ligand Wy14643, dose-dependently suppressed IL-1beta-induced PGE(2) production, as well as mPGES-1 protein and mRNA expression. 15d-PGJ(2) and TRO suppressed IL-1beta-induced activation of the mPGES-1 promoter. Overexpression of wild-type PPARgamma further enhanced, whereas overexpression of a dominant negative PPARgamma alleviated, the suppressive effect of both PPARgamma ligands. Furthermore, pretreatment with an antagonist of PPARgamma, GW9662, relieves the suppressive effect of PPARgamma ligands on mPGES-1 protein expression, suggesting that the inhibition of mPGES-1 expression is mediated by PPARgamma. We demonstrated that PPARgamma ligands suppressed Egr-1-mediated induction of the activities of the mPGES-1 promoter and of a synthetic reporter construct containing three tandem repeats of an Egr-1 binding site. The suppressive effect of PPARgamma ligands was enhanced in the presence of a PPARgamma expression plasmid. Electrophoretic mobility shift and supershift assays for Egr-1 binding sites in the mPGES-1 promoter showed that both 15d-PGJ(2) and TRO suppressed IL-1beta-induced DNA-binding activity of Egr-1. These data define mPGES-1 and Egr-1 as novel targets of PPARgamma and suggest that inhibition of mPGES-1 gene transcription may be one of the mechanisms by which PPARgamma regulates inflammatory responses.

15-Deoxy-Δ12,14-prostaglandin J2 Induces Heme Oxygenase-1 Gene Expression in a Reactive Oxygen Species-dependent Manner in Human Lymphocytes

15-Deoxy-delta(12,14)-prostaglandin J(2) (15dPGJ(2) has been recently proposed as a potent anti-inflammatory agent. However, the mechanisms by which 15dPGJ(2) mediates its therapeutic effects in vivo are unclear. We demonstrate that 15dPGJ(2) at micromolar (2.5-10 microm) concentrations induces the expression of heme oxygenase-1 (HO-1), an anti-inflammatory enzyme, at both mRNA and protein levels in human lymphocytes. In contrast, troglitazone and ciglitazone, two thiazolidinediones that mimic several effects of 15dPGJ(2) through their binding to the peroxisome proliferator-activated receptor (PPAR)-gamma, did not affect HO-1 expression, and the positive effect of 15dPGJ(2) on this process was mimicked instead by other cyclopentenone prostaglandins (PG), such as PGD(2) (the precursor of 15dPGJ(2)) and PGA(1) and PGA(2) which do not interact with PPAR-gamma. Also, 15dPGJ(2) enhanced the intracellular production of reactive oxygen species (ROS) and increased xanthine oxidase activity in vitro. Inhibition of intracellular ROS production by N-acetylcysteine, TEMPO, Me(2)SO, 1,10-phenanthroline, or allopurinol resulted in a decreased 15dPGJ(2)-dependent HO-1 expression in the cells. Furthermore, buthionine sulfoximine, an inhibitor of reduced glutathione synthesis, or Fe(2+)/Cu(2+) ions enhanced the positive effect of 15dPGJ(2) on HO-1 expression. On the other hand, the inhibition of phosphatidylinositol 3-kinase or p38 mitogen-activated protein kinase, or the blockade of transcription factor NF-kappaB activation, hindered 15dPGJ(2)-elicited HO-1 expression. Collectively, the present data suggest that 15dPGJ(2) anti-inflammatory actions at pharmacological concentrations involve the induction of HO-1 gene expression through mechanisms independent of PPAR-gamma activation and dependent on ROS produced via the xanthine/xanthine oxidase system and/or through Fenton reactions. Both phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase signaling pathways also appear implicated in modulation of HO-1 expression by 15dPGJ(2).

The intricate interface between immune system and metabolism

Increasing experimental evidence indicates that several factors that influence metabolism also play a role in the regulation of immune responses. Dissection of the interface connecting the metabolic and immune systems has recently gained wide interest. Particular focus has been on certain cytokines [interleukin-1 (IL-1), IL-6, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma)], hormones (leptin and insulin), neuropeptides (corticotropin-releasing hormone and alpha-melanocyte-stimulating hormone), immune-related proteins (zinc-alpha2-glycoprotein and attractin and/or mahogany), transcription factors (peroxisome-proliferator-activated receptors) and glucose metabolism. A better knowledge of the intricate network of interactions among energy regulation, immune surveillance and vital organ functions could in the near future lead to valuable strategies for therapeutic intervention in several immune-mediated diseases.

PPARγ ligands attenuate mesangial contractile dysfunction in high glucose

BACKGROUND

To elucidate the regulation of peroxisome proliferator-activated receptor gamma (PPARgamma) and its roles in mesangial cells, we examined the expression of PPARgamma1 and effects of its ligands on cell phenotypes and angiotensin II-induced contractile response in cultured rat mesangial cells under a high (20 mmol/L) glucose condition.

METHODS

The effects of tumor necrosis factor alpha (TNFalpha), protein kinase C (PKC) activation, antisense DNA for PPARgamma1, PPARgamma ligands and PD98059 were examined in mesangial cells cultured in either 5 mmol/L or 20 mmol/L glucose. The expressions of PPARgamma1 protein and alpha-smooth muscle actin (alphaSMA) as a marker of phenotype of cells were determined by Western blot. The expression of PPARgamma1 mRNA was determined by a reverse transcription-polymerase chain reaction method. The reduction of cell surface area in response to angiotensin II was measured by microscope to determine cellular contraction.

RESULTS

PKC activation, TNFalpha, and 20 mmol/L glucose decreased PPARgamma1 at both protein and mRNA levels, which was inhibited by PD98059, a specific inhibitor of mitogen-activated protein kinase (MAPK). Decreases of PPARgamma1 protein and contractile response and an increase of alphaSMA occurred simultaneously in the cells treated with 20 mmol/L glucose after 5 days, which were attenuated to the normal levels by PPARgamma ligands. The antisense DNA also induced the decrease of PPARgamma1 protein, contractile dysfunction, and increase of alphaSMA.

CONCLUSION

MAPK suppresses PPARgamma1 at the transcriptional level, and the reduction of PPARgamma1 in cultured rat mesangial cells under the high glucose condition induces phenotypic change and loss of contractile function. PPARgamma ligands recover both reductions of PPARgamma 1 protein and contractile response.

Cyclopentenone prostaglandins induce lymphocyte apoptosis by activating the mitochondrial apoptosis pathway independent of external death receptor signaling

15-Deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) is a naturally occurring cyclopentenone metabolite of PGD(2) that possesses both peroxisome proliferator-activated receptor gamma (PPAR-gamma)-dependent and PPAR-gamma-independent anti-inflammatory properties. Recent studies suggest that cyclopentenone PGs may play a role in the down-regulation of inflammation-induced immune responses. In this study, we report that 15d-PGJ(2) as well as synthetic PPAR-gamma agonists inhibit lymphocyte proliferation. However, only 15d-PGJ(2), but not the specific PPAR-gamma activators, induce lymphocyte apoptosis. We found that blocking of the death receptor pathway in Fas-associated death domain(-/-) or caspase-8(-/-) Jurkat T cells has no effect on apoptosis induction by 15d-PGJ(2). Conversely, overexpression of Bcl-2 or Bcl-x(L) completely inhibits the initiation of apoptosis, indicating that 15d-PGJ(2)-mediated apoptosis involves activation of the mitochondrial pathway. In line with these results, 15d-PGJ(2) induces mitochondria disassemblage as demonstrated by dissipation of mitochondrial transmembrane potential (Deltapsi(m)) and cytochrome c release. Both of these events are partially inhibited by the broad spectrum caspase inhibitor benzyloxycarbonil-Val-Ala-Asp-fluoromethylketone, suggesting that caspase activation may amplify the mitochondrial alterations initiated by 15d-PGJ(2). We also demonstrate that 15d-PGJ(2) potently stimulates reactive oxygen species production in Jurkat T cells, and Deltapsi(m) loss induced by 15d-PGJ(2) is prevented by the reactive oxygen species scavenger N-acetyl-L-cysteine. In conclusion, our data indicate that cyclopentenone PGs like 15d-PGJ(2) may modulate immune responses even independent of PPAR-gamma by activating the mitochondrial apoptosis pathway in lymphocytes in the absence of external death receptor signaling.

Triptolide, an active compound identified in a traditional Chinese herb, induces apoptosis of rheumatoid synovial fibroblasts

Background

Extracts of Tripterygium wilfordii Hook F (TWHF), a traditional Chinese herb, have been reported to show efficacy in patients with rheumatoid arthritis (RA). Since RA is not only characterized by inflammation but also by synovial proliferation in the joints, we examined whether triptolide (a constituent of TWHF) could influence the proliferation of rheumatoid synovial fibroblasts (RSF) by induction of apoptosis.

Results

RSF were obtained from RA patients during surgery and were treated with triptolide under various conditions. The viability and proliferation of RSF were measured by the 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1) assay and by 5-bromo-2'-deoxyuridine incorporation, respectively. Apoptosis was identified by detection of DNA fragmentation using an enzyme-linked immunosorbent assay and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL). The role of caspases in apoptosis of RSF was analyzed by measuring caspase-3 activity. Activation of the peroxisome proliferator-activated receptor (PPAR) γ was assessed by a luciferase reporter gene assay using RSF transfected with a plasmid containing the peroxisome proliferator response element. Triptolide decreased viability, inhibited proliferation, and induced apoptosis of RSF in a concentration-dependent manner at very low (nM) concentrations. Caspase-3 activity was increased by treatment with triptolide and was suppressed by caspase inhibitors. Although PPARγ activation was induced by 15-deoxy-Δ^12,14-prostaglandin J₂, triptolide did not induce it under the same experimental conditions. An extract of TWHF also induced DNA fragmentation in RSF.

Conclusion

The mechanism of action remains to be studied; however, triptolide may possibly have a disease-modifying effect in patients with RA.

NF-kappa B-binding activity in an animal diet-induced overweightness model and the impact of subsequent energy restriction

An impaired immune function linked to obesity has been shown in both human and animal studies. The purpose of this work was to analyse the hypothesis that PPAR gamma 1 participates in the inhibition of the immune response by affecting the DNA-binding ability of the NF-kappa B complex and whether the SREBP-1 expression can regulate PPAR gamma 1 expression in spleen. Diet-induced overweight rats showed higher PPAR gamma 1 (p<0.05) and lower SREBP-1 (p<0.01) mRNA expression levels with an inhibition of the DNA-binding ability of NF-kappa B compared to control rats as determined by gel-shift analysis. On the other hand, energy restriction decreased SREBP-1 (p<0.01) mRNA expression with no differences in PPAR gamma 1 mRNA expression compared to non-restricted rats, which was accompanied by a restoration in the DNA-binding ability of NF-kappa B as shown by gel-shift analysis. These results suggest that PPAR gamma 1 may be involved in the altered immune response through changes in the activity of NF-kappa B.

Peroxisome proliferator-activated receptor-gamma-independent repression of collagenase gene expression by 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid and prostaglandin 15-deoxy-delta(12,14) J2: a role for Smad signaling

Matrix metalloproteinases (MMPs) degrade extracellular matrix components, and overexpression of these enzymes contributes to tissue destruction in arthritis. Of particular importance are the collagenases, MMP-1 and MMP-13, which have high activity against the interstitial collagens in cartilage. In this study, we address the mechanisms of two inhibitors of collagenase gene expression, the synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) and 15-deoxy-delta(12,14)-prostaglandin J2 (15-dPGJ2). Although both inhibitors are ligands for the nuclear hormone receptor peroxisome proliferator-activated receptor-gamma (PPAR-gamma), a connection between PPAR-gamma and collagenase gene expression has yet to be established. Here, we test the hypothesis that CDDO and 15-dPGJ2 use PPAR-gamma to repress MMP gene expression. Our findings with the PPAR-gamma antagonist 2-[4-[2-[3-(2,4-difluorophenyl)-1-heptylureido]ethyl]rsqb]-phenylsulfanyl]-2-methylpropionic acid (GW9662) and mouse embryonic fibroblasts lacking PPAR-gamma demonstrate that CDDO and 15-dPGJ2 use PPAR-gamma-independent mechanisms to inhibit collagenase gene expression. To address a potential PPAR-gamma-independent mechanism leading to the repression of MMPs by CDDO, we tested the effect of CDDO on the transforming growth factor-beta (TGF-beta) signaling pathway. We found that CDDO requires Smads (transcription factors activated by TGF-beta) for the repression of MMP-1. Specifically, MMP-1 is inhibited neither by CDDO in the absence of TGF-beta receptor-activated Smad3 nor when a negative regulator, Smad7, attenuates TGF-beta signaling. We conclude that CDDO represses MMP gene expression through a novel PPAR-gamma-independent mechanism that requires Smad signaling.

Role of Peroxisome Proliferator-Activated Receptors in Inflammation Control

Peroxisome proliferator-activated receptors (PPARs) were discovered over a decade ago, and were classified as orphan members of the nuclear receptor superfamily. To date, three PPAR subtypes have been discovered and characterized (PPAR $\alpha$, $\beta/\delta$, $\gamma$ ). Different PPAR subtypes have been shown to play crucial roles in important diseases and conditions such as obesity, diabetes, atherosclerosis, cancer, and fertility. Among the most studied roles of PPARs is their involvement in inflammatory processes. Numerous studies have revealed that agonists of PPAR $\alpha$ and PPAR $\gamma$ exert anti-inflammatory effects both in vitro and in vivo. Using the carrageenan-induced paw edema model of inflammation, a recent study in our laboratories showed that these agonists hinder the initiation phase, but not the late phase of the inflammatory process. Furthermore, in the same experimental model, we recently also observed that activation of PPAR $\delta$ exerted an anti-inflammatory effect. Despite the fact that exclusive dependence of these effects on PPARs has been questioned, the bulk of evidence suggests that all three PPAR subtypes, PPAR $\alpha, \delta, \gamma$, play a significant role in controlling inflammatory responses. Whether these subtypes act via a common mechanism or are independent of each other remains to be elucidated. However, due to the intensity of research efforts in this area, it is anticipated that these efforts will result in the development of PPAR ligands as therapeutic agents for the treatment of inflammatory diseases.

Peroxisome proliferator-activated receptor gamma ligands attenuate immunological symptoms of experimental allergic asthma

Asthma is characterized by a predominant T(H)2 type immune response to airborne allergens. Controlling T(H)2 cell function has been proposed as therapy for this disease. We show here that ligands for the nuclear receptor peroxisome proliferator activated receptor (PPAR)gamma significantly reduced the immunological symptoms of allergic asthma in a murine model of this disease. A PPARgamma ligand, 15-deoxy-delta(12,14)-prostaglandin J(2), significantly inhibited production of the T(H)2 type cytokine IL-5 from T cells activated in vitro. More importantly, in a murine model of allergic asthma, mice treated orally with ciglitazone, a potent synthetic PPARgamma ligand, had significantly reduced lung inflammation and mucous production following induction of allergic asthma. T cells from these ciglitazone treated mice also produced less IFNgamma, IL-4, and IL-2 upon rechallenge in vitro with the model allergen. Our results suggest that ligands for PPARgamma may be effective treatments for asthmatic patients.

Lysosomal acid lipase deficiency causes respiratory inflammation and destruction in the lung

The functional roles of neutral lipids are poorly understood in the lung. Blocking cholesteryl ester and triglyceride metabolism in lysosomal acid lipase gene knockout mice (lal-/-) resulted in a high level of neutrophil influx in the lungs as early as 2 mo of age. Bronchoalveolar macrophages appeared foamy and gradually increased in number with age progression. Affymetrix GeneChip array analysis of lung mRNA showed increased levels of proinflammatory cytokine (including IL-1beta, IL-6, and TNF-alpha) and matrix metalloproteinase (including MMP-8, MMP-9, and MMP-12) expression in lal-/- mice. With age progression, some areas of lal-/- mice developed severe abnormal cell proliferation and alveolar remodeling. In other areas, alveolar destruction (i.e., emphysema) was observed. In addition, Clara cell hypertrophy and hyperplasia developed in conducting airways. The pathophysiological phenotypes in the lal-/- mouse lungs became more severe with increasing age. The studies support the concept that neutral lipid metabolites play essential roles in pulmonary homeostasis, inflammatory responses, remodeling, and injury repair.

Inhibition of monosodium urate monohydrate crystal-induced acute inflammation by retrovirally transfected prostaglandin D synthase

OBJECTIVE

Hematopoietic prostaglandin D synthase (H-PGDS) is a key enzyme in the production of prostaglandin D and its J series metabolites. We evaluated the antiinflammatory effect of retrovirally transfected H-PGDS in order to investigate the role of H-PGDS in monosodium urate monohydrate (MSU) crystal-induced acute inflammation.

METHODS

Expression of endogenous PGDS in a murine air-pouch model of MSU crystal-induced acute inflammation was determined by real-time polymerase chain reaction. H-PGDS complementary DNA (cDNA) was retrovirally transfected into C57BL/6J fibroblasts, and the cells were designated as C57-PGDS cells. Production of prostaglandins by C57-PGDS cells was measured by enzyme immunoassay. The effect of C57-PGDS cells on crystal-induced inflammation was investigated.

RESULTS

Injection of the crystals caused a rapid decrease in H-PGDS expression by infiltrating cells and by the soft tissues around the air pouches. In contrast, expression of interleukin-1beta (IL-1beta) and macrophage inflammatory protein 2 (MIP-2) as well as cellular infiltration were significantly increased during the early stage of inflammation. C57-PGDS cells, but not control cells, produced an increased amount of PGD(2) in vitro, but suppressed production of PGE(2). Injection of C57-PGDS cells into air pouches inhibited cellular infiltration and MIP-2 and IL-1beta expression.

CONCLUSION

In this murine air-pouch model of MSU crystal-induced inflammation, retrovirally transfected H-PGDS cDNA could reduce cellular infiltration, at least partly by inhibiting MIP-2 and IL-1beta. These findings suggest that gene therapy with H-PGDS may be useful for treating inflammatory diseases.

Peroxisome Proliferator-Activated Receptor-γ-Deficient Heterozygous Mice Develop an Exacerbated Neural Antigen-Induced Th1 Response and Experimental Allergic Encephalomyelitis

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a nuclear receptor transcription factor that regulates cell growth, differentiation, and homeostasis. PPARgamma agonists are potent therapeutic agents for type 2 diabetes, obesity, and inflammation. Experimental allergic encephalomyelitis (EAE) is a Th1 cell-mediated inflammatory demyelinating autoimmune disease model of multiple sclerosis. We have shown recently that PPARgamma agonists inhibit EAE by blocking IL-12 production, IL-12 signaling, and neural Ag-induced Th1 differentiation. In this study, we show that the PPARgamma-deficient heterozygous mice develop an exacerbated EAE with prolonged clinical symptoms than the wild-type littermates, following immunization with myelin oligodendrocyte glycoprotein (MOG) p35-55 peptide. The exacerbation of EAE in PPARgamma(+/-) mice associates with an increased expansion of CD4(+) and CD8(+) T cells and expression of CD40 and MHC class II molecules in response to MOGp35-55 Ag. The PPARgamma(+/-) mice also showed an increase in T cell proliferation and Th1 response to MOGp35-55 Ag than the wild-type littermates. These findings suggest that PPARgamma be a critical physiological regulator of CNS inflammation and demyelination in EAE and perhaps multiple sclerosis and other Th1 cell-mediated autoimmune diseases.

Antiinflammatory roles of peroxisome proliferator-activated receptor gamma in human alveolar macrophages

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-activated transcriptional factor belonging to the nuclear receptor superfamily. PPARgamma, which is predominantly expressed in adipose tissue, plays a major regulatory role in glucose metabolism and adipogenesis. Interestingly, recent studies have demonstrated PPARgamma expression in monocytes/macrophages and its antiinflammatory activities. However, it is unclear whether alveolar macrophages (AMs) express functional PPARgamma. The present study was conducted to investigate the expression of PPARgamma by AMs and to elucidate its functional role. Using reverse transcription-polymerase chain reaction and Western blotting, we demonstrated the strong expression of PPARs messenger RNA and protein in freshly isolated human AMs. Ligands of PPARgamma, 15-deoxy-delta(12,14)prostaglandin J2, and troglitazone significantly decreased LPS-induced tumor necrosis factor-alpha production by AMs. These ligands markedly upregulated the expression of CD36, a scavenger receptor that mediates the phagocytosis of apoptotic neutrophils. Indeed, ligand-treated AMs ingested a significantly higher number of apoptotic neutrophils than untreated AMs. These data indicate that PPARgamma expressed by AMs play an antiinflammatory role through inhibiting cytokine production and increasing their CD36 expression together with the enhanced phagocytosis of apoptotic neutrophils, which is an essential process for the resolution of inflammation. This suggests the potential therapeutic application of PPARgamma ligands in inflammatory disorders of the lung.

PPARgamma ligands induce prostaglandin production in vascular smooth muscle cells: indomethacin acts as a peroxisome proliferator-activated receptor-gamma antagonist

Peroxisome proliferator-activated receptor (PPAR)gamma and inducible cyclooxygenase-2 (COX-2) are expressed in atherosclerotic lesions, particularly in the intimal monocytic and vascular smooth muscle cells. We have therefore studied the interaction between PPARgamma and inducible cyclo-oxygenase (COX-2) in rat aortic vascular smooth muscle cells (RASMC)s. The synthetic PPARgamma ligand rosiglitazone induced prostaglandin (PG) release from RASMCs, including that of PGD2, the precursor of the putative endogenous PPARgamma ligand 15-deoxy-Delta12,14-prostaglandin J2. Moreover, rosiglitazone both synergized with IL-1beta to further induce prostaglandin release and affected the expression of phospholipase A2 and COX-2. Rosiglitazone-induced prostaglandin release was inhibited by the PPARgamma partial agonist GW0072 and the PPARgamma antagonist GW9662. Rosiglitazone also induced RASMC apoptosis, an effect not explained as an autocrine effect of the induced-prostanoids, but on arachidonic acid release, as cell death was unaffected by either the nonselective COX inhibitor piroxicam or the selective COX-2 inhibitor DFP, but by inhibitors of either secretory or cytosolic phospholipase A2. In contrast, indomethacin, an alternative inhibitor of cyclooxygenase activity, inhibited both rosiglitazone-induced cell death, and rosiglitazone-induced PPAR reporter gene activation.

Peroxisome proliferator-activated receptor gamma and ligands inhibit surfactant protein B gene expression in the lung

Pulmonary nonciliated bronchiolar epithelial cells (Clara cells) and alveolar type II (AT II) epithelial cells are responsible for surfactant synthesis and secretion. These cells are highly lipogenic with a high lipid turnover rate. Although only 10% of surfactant lipids are neutral lipids, they play very important roles in maintaining pulmonary surfactant homeostasis. Many metabolic intermediate products of neutral lipids serve as ligands for various nuclear receptors that bind to target genes to influence gene transcription. In this report, the functional role of the neutral lipid metabolites, 15-deoxy-Delta12,14-prostaglandin J2 and 9-hydroxyoctadecanoic acids, and peroxisome proliferator-activated receptor gamma was evaluated in surfactant protein B gene regulation. These reagents down-regulated surfactant protein B gene expression in respiratory epithelial cells at the transcriptional level in both cell line and whole lung explant systems. The studies support the concept that surfactant protein B homeostasis is influenced by neutral lipid metabolites in the lung.

Suppression of intestinal ischemia-reperfusion injury by a specific peroxisome proliferator-activated receptor-gamma ligand, pioglitazone, in rats

Neutrophil activation and tumor necrosis factor-alpha (TNF-alpha) induction play a critical role in ischemia-reperfusion-induced intestinal inflammation. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma), a member of the nuclear hormone receptor superfamily, has recently been implicated as a regulator of inflammatory responses. The aim of the present study was to determine whether pioglitazone, a specific PPAR-gamma ligand, can ameliorate reperfusion-induced intestinal injury in rats, and whether the agent can inhibit the increase in neutrophil accumulation associated with TNF-alpha expression. Intestinal damage was induced in male Sprague-Dawley rats by clamping the superior mesenteric artery for 30 min followed by reperfusion. Reperfusion after 30 min ischemia resulted in an increase in luminal protein concentrations with levels reaching a maximum after 60 min of reperfusion. In contrast, pretreatment with pioglitazone 2 h before ischemia inhibited the increase in luminal protein concentrations after 60 min reperfusion in a dose-dependent manner (1-30 mg/kg). The increase in tissue-associated myeloperoxidase activity, an index of neutrophil infiltration, after reperfusion was significantly inhibited by pretreatment with pioglitazone. Pioglitazone also inhibited increases in intestinal TNF-alpha protein and mRNA expression determined by ELISA and RT-PCR, respectively. In conclusion, activation of PPAR-gamma may represent a novel approach to the treatment of intestinal inflammation induced by ischemia-reperfusion.

A novel PGD(2) receptor expressed in eosinophils

PGD(2) is a major product of arachidonic acid metabolism by mast cells and is released in the lungs following allergen challenge. Activation of the classic PGD(2) receptor (DP receptor) results in stimulation of adenylyl cyclase, resulting in inhibition of platelet aggregation and smooth muscle relaxation. A second PGD(2) receptor has recently been identified and designated as the DP(2) receptor, or chemoattractant receptor-homologous molecule expressed on Th2 cells. PGD(2) acts through the DP(2) receptor to induce eosinophil chemotaxis, actin polymerization, calcium mobilization, and adhesion molecule expression. The most potent DP(2) receptor agonist yet identified is 15R-methyl-PGD(2), which has the unnatural R configuration at C(15). 15-Deoxy-Delta(12,14)-PGJ(2) is also a potent DP(2) receptor agonist that activates eosinophils at concentrations much lower than those required for its anti-inflammatory effects. Because of its critical location in the lung and its potent effects on eosinophils, PGD(2) may be an important proinflammatory mediator in asthma.

Activation of peroxisome proliferator-activated receptor-gamma inhibits differentiation of preosteoblasts

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is critical for phenotype determination at early differentiation stages of mesenchymal cells. Activation of this nuclear receptor inhibits gene expression in part by antagonizing the activities of several transcription factors. In this study we examined inhibitory mechanisms of osteoblast differentiation markers by activating PPAR-gamma. Our data indicate that the PPAR-gamma natural ligand 15d-PGJ2 dose-dependently inhibits expression of alkaline phosphatase and mineral deposition by primary stromal cells and by cell lines such as ST2 and MC3T3-E1. We next show that PPAR-gamma nuclear translocation coincides with duration and doses of ligand addition, indicating that 15d-PGJ2-activated PPAR-gamma rapidly translocates to the nuclear component where it exerts its biological effects. Further examination of downstream osteogenic signaling pathways induced by beta-glycerophosphate and ascorbic acid reveals that induction of osteoblast differentiation by these agents involves activation of the transcription factors Cbfa1 and NF-kappaB. The former is critical for osteoblast differentiation. To test whether inhibition of alkaline phosphatase expression and mineral deposition by activated PPAR-gamma reflects attenuation of transcriptional activity, we performed DNA protein-binding assays for NF-kappaB and Cbfa1. Our findings indicate that 15d-PGJ2-induced PPAR-gamma abrogates beta-glycerophosphate-activated Cbfa1 and NF-kappaB. These findings were consistent in primary and stromal cell lines, ST2 and MC3T3-E1. Thus activation of PPAR-gamma by 15d-PGJ2 inhibits DNA-binding activity of the transcription factors Cbfa1 and NF-kappaB, leading to diminished expression of osteoblast/stromal differentiation markers.

The PPARgamma ligand, 15d-PGJ2, attenuates the severity of cerulein-induced acute pancreatitis

INTRODUCTION

The prostaglandin D2 metabolite, 15d-PGJ2, a potent natural ligand for peroxisome proliferator-activated receptor gamma (PPARgamma), exerts antiinflammatory effects by inhibiting the induction of inflammatory response genes and NF-kappaB-dependent transcription. AIM To determine whether 15d-PGJ2 decreases the severity of secretagogue-induced acute pancreatitis (AP) and to assess cellular mechanisms contributing to these effects. METHODOLOGY Swiss Webster mice were injected with either saline or cerulein (50 microg/kg) hourly for 8 hours and received either 15d-PGJ2 (2 mg/kg) or vehicle 1 hour before and 4 hours after induction of AP. RESULTS Treatment with 15d-PGJ2 significantly attenuated AP, as determined by histologic assessment of edema, vacuolization, inflammation, and necrosis. This attenuation was associated with decreased cyclooxygenase-2 (COX-2) and intercellular adhesion molecule-1 (ICAM-1) expression and decreased serum and pancreatic IL-6 levels. Treatment with 15d-PGJ2 markedly inhibited NF-kappaB DNA-binding activity, and, moreover, this decreased activity was associated with a concomitant inhibition of IkappaB protein degradation. CONCLUSION Our findings demonstrate that 15d-PGJ2 attenuates the severity of AP most likely through the inhibition of COX-2 expression, IL-6 production, and NF-kappaB activation. Ligands specific for PPARgamma may represent novel and effective means of clinical therapy for AP.

Anti-inflammatory activity of 15-deoxy-delta12,14-PGJ2 and 2-cyclopenten-1-one: role of the heat shock response

The transcription factor heat shock factor 1 (HSF1) plays a key role in the expression of several genes, such as heat shock protein (hsp) genes, which are cytoprotective against several pathological conditions, including inflammation. Cyclopentenone prostaglandins (cyPG) are able to activate HSF1 and induce the synthesis of the 70-kDa hsp (hsp70) in mammalian cells. These molecules are characterized by the presence of a reactive alpha,beta-unsatured carbonyl group in the cyclopentane ring (cyclopentenone) which is the key structure for triggering HSF1 activation. In the present study, we investigated, in carrageenin hind-paw edema, an acute model of inflammation, the effect of double-stranded oligodeoxynucleotides with consensus HSF1 sequence as transcription factor decoys to inhibit HSF1 binding to native DNA sites. We show that HSF1 activation and hsp72 expression occurs in inflamed tissue and that this effect is associated with the remission of the inflammatory reaction. Moreover, we studied the effect of prostaglandin 15-deoxy-delta12,14-prostaglandin (PG) J2, of its precursor, PGD2 and, for the first time in vivo, the effect of the cyclopentenone ring structure itself, 2-cyclopenten-1-one. Our results demonstrated that all agents used had anti-inflammatory properties and that this effect was associated with HSF1-induced hsp72 expression in vivo, suggesting that the use of cyclopentenone derivatives may represent a novel therapeutic approach to the treatment of inflammatory diseases.

Suppression of endothelial adhesion molecule up-regulation with cyclopentenone prostaglandins is dissociated from IkappaB-alpha kinase inhibition and cell death induction

The cyclopentenone prostaglandins (cPG) 15-deoxy-Delta12,14-prostaglandin J2 (dPGJ2) and PGA1 can inhibit multiple steps in nuclear factor (NF)-kappaB signaling and can induce cell death. Here we characterized the effects of dPGJ2 and PGA1 on the inflammatory induction of endothelial cell adhesion molecules (CAM). Pretreatment of endothelial cells with dPGJ2 or PGA1 at low concentrations dose dependently inhibited the up-regulation of CAM expression and monocyte arrest by tumor necrosis factor (TNF)-alpha but not expression of inhibitor of apoptosis proteins. Only at high concentrations, cPG enhanced TNF-alpha-induced cell death and inhibited TNF-alpha-induced IkappaB-alpha kinase (IKK) activation, IkappaB-alpha degradation, and NF-kappaB/p65 translocation, while promoting AP-1/c-jun phosphorylation. Expression of an IKK-beta mutant (C179A) resistant to interaction with cPG impaired cell death induction but not inhibition of CAM up-regulation by cPG. Gel shift and reporter gene analysis revealed that cPG at low concentrations directly impaired DNA binding of NF-kappaB and NF-kappaB-dependent transactivation. The synthetic analogs dPGA1 or dPGA2 were ineffective, indicating structural specificity of cPG. Thus, the suppression of endothelial CAM up-regulation with cPG is dissociated from cell death sensitization and IKK inhibition above threshold concentrations and related to interference with NF-kappaB binding. Our findings define distinct mechanisms for anti-inflammatory and proapoptotic effects of cPG in endothelial cells.

Peroxisome proliferator-activated receptor gamma (PPARgamma) expression is decreased in pulmonary hypertension and affects endothelial cell growth

PPARgamma is a member of a family of nuclear receptors/ligand-dependent transcription factors, which bind to hormone response elements on target gene promoters. An antiproliferative and proapoptotic action profile of PPARgamma has been described and PPARgamma may function as a tumor suppressor gene, but little is known about the role of PPARgamma in vascular remodeling. One group of human diseases that shows impressive vascular remodeling exclusively in the lungs is the group of severe pulmonary hypertensive disorders, which is characterized by complex, endothelial cell-proliferative lesions of lung precapillary arterioles composed of clusters of phenotypically altered endothelial cells that occlude the vessel lumen and contribute to the elevation of the pulmonary arterial pressure and reduce local lung tissue blood flow. In the present study, we report the ubiquitous PPARgamma expression in normal lungs, and in contrast, a reduced lung tissue PPARgamma gene and protein expression in the lungs from patients with severe PH and loss of PPARgamma expression in their complex vascular lesions. We show that fluid shear stress reduces PPARgamma expression in ECV304 endothelial cells, that ECV304 cells that stably express dominant-negative PPARgamma (DN-PPARgamma ECV304) form sprouts when placed in matrigel and that DN-PPARgamma ECV304 cells, after tail vein injection in nude mice, form lumen-obliterating lung vascular lesions. We conclude that fluid shear stress decreases the expression of PPARgamma in endothelial cells and that loss of PPARgamma expression characterizes an abnormal, proliferating, apoptosis-resistant endothelial cell phenotype.

Induction of heme oxygenase-1 expression in murine macrophages is essential for the anti-inflammatory effect of low dose 15-deoxy-Delta 12,14-prostaglandin J2

15-Deoxy-Delta 12,14-prostaglandin J2 (15d-PGJ2), a cyclopentenone prostaglandin, displays a potent anti-inflammatory effect at micromolar concentrations (>2 microM) through direct inhibition of nuclear factor (NF)-kappa B activation. Here we show that at submicromolar concentrations (0.1-0.5 microM) 15d-PGJ2 retains the ability to suppress the production of tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) in lipopolysaccharide (LPS)-activated murine J774 macrophages under the conditions of a prolonged incubation (>12 h). Western blot analysis revealed that the expression of the cytoprotective enzyme, heme oxygenase-1 (HO-1), was induced and coincident with the anti-inflammatory action of 15d-PGJ2. Inhibition of HO-1 activity or scavenging carbon monoxide (CO), a byproduct derived from heme degradation, significantly attenuated the suppressive activity of 15d-PGJ2. Furthermore, LPS-induced NF-kappa B activation assessed by the inhibitory protein of NF-kappa B(I kappa B) degradation and p50 nuclear translocation was diminished in cells subjected to prolonged treatment with the low concentration of 15d-PGJ2. Treatment of cells with the protein synthesis inhibitor, cycloheximide, or the specific p38 MAP kinase inhibitor, SB203580, blocked the induction of HO-1 and suppression of LPS-induced I kappa B degradation mediated by 15d-PGJ2. Likewise, HO inhibitor and CO scavenger were effective in abolishing the inhibitory effects of 15d-PGJ2 on NF-kappa B activation induced by LPS. The functional role of CO was further demonstrated by the use of a CO releasing molecule, tricarbonyldichlororuthenium(II) dimer, which significantly suppressed LPS-induced nuclear translocation of p50 as assessed by confocal immunofluorescence. Collectively, these data suggest that even at submicromolar concentrations 15d-PGJ2 can exert an anti-inflammatory effect in macrophages through a mechanism that involves the action of HO/CO.

Retrovirally introduced prostaglandin D2 synthase suppresses lung injury induced by bleomycin

Hematopoietic prostaglandin D synthase (PGDS) is a key enzyme to produce prostaglandin (PG) D and J series. These PGs are involved in inflammation and immune system. The PGDS complementary DNA (cDNA)-expressing retrovirally transfected fibroblasts were introduced in vivo, and effect of the expression on lung injury induced by bleomycin was investigated in mice. Intravenous injection of PGDS cDNA-expressing fibroblasts significantly reduced lung edema, leukocyte infiltration in bronchoalveolar lavage (BAL) fluid, and pulmonary collagen content at 4 wk after instillation of bleomycin. Survival rate in mice instilled with the PGDS-expressing fibroblasts was higher than that in mice that received the mock transfection. Administration of 15-deoxy-Delta 12,14-PGJ2, which is a nonenzymatic metabolite of PGD2, also attenuated the lung injury, suggesting mediation of PGs produced by PGDS for the attenuation. Introduction of PGDS cDNA-expressing fibroblasts suppressed expression of basic fibroblast growth factor, connective tissue growth factor, and collagen messenger RNAs in the lungs, as well as the levels of total proteins and hemoglobin in BAL fluid. These data suggest that the suppressive effect of PGDS on the lung injury could be partly mediated by edema formation and inhibition of genes involved in the fibrotic change.

Diminished production of anti-inflammatory mediators during neutrophil apoptosis and macrophage phagocytosis in chronic granulomatous disease (CGD)

Genetic defects in the phagocyte nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase enzyme system result in chronic granulomatous disease (CGD). In addition to recurrent, life-threatening infections, patients with CGD frequently present with sterile inflammatory complications, suggesting that NADPH-oxidase deficiency predisposes to these responses in the absence of persistent microbial infection. The mechanisms involved in the aberrant, inflammatory process are unknown. In this study, we have shown that neutrophils isolated from CGD patients, which are more resistant to spontaneous apoptosis in vitro, also produce significantly less of the anti-inflammatory mediator cyclopentenone prostaglandin D(2) (PGD(2)). In addition, during phagocytosis of opsonized and nonopsonized apoptotic targets, CGD macrophages are severely compromised in their ability to produce PGD(2) and transforming growth factor-beta (TGF-beta). We suggest that delayed apoptosis of inflammatory cells, such as neutrophils and deficient production of the anti-inflammatory mediators PGD(2) and TGF-beta during macrophage clearance of apoptotic debris and invading pathogens, contributes to persistence of inflammation in CGD.

The cyclopentenone-type prostaglandin 15-deoxy-delta 12,14-prostaglandin J2 inhibits CD95 ligand gene expression in T lymphocytes: interference with promoter activation via peroxisome proliferator-activated receptor-gamma-independent mechanisms

15-Deoxy-delta(12,14)-PGJ(2) (15d-PGJ(2)) is a cyclopentenone-type PG endowed with anti-inflammatory properties and produced by different cells, including those of the immune system. 15d-PGJ(2) is a natural ligand of the peroxisome proliferator-activated receptor (PPAR)-gamma nuclear receptor, but relevant PPARgamma-independent actions mediated by this prostanoid have been described. Fas (APO-1/CD95) and its ligand (Fas-L) are cell surface proteins whose interaction activates apoptosis of Fas-expressing targets. In T cells, the Fas-Fas-L system regulates activation-induced cell death and has been implicated in diseases in which lymphocyte homeostasis is compromised. Moreover, several studies have described the pathogenic functions of Fas and Fas-L in vivo, particularly in the induction-progression of organ-specific autoimmune diseases. In this study we describe the effect of 15d-PGJ(2) on the activation of the fas-L gene in T lymphocytes. We show that 15d-PGJ(2) inhibits fas-L mRNA expression, activation-induced cell death, and fas-L promoter activity by mechanisms independent of PPARgamma and mediated by its chemically reactive cyclopentenone moiety. Our data indicate that 15d-PGJ(2) may repress fas-L activation by interfering with the expression and/or transcriptional activity of different transcription factors (early growth response types 3 and 1, NF-kappaB, AP-1, c-Myc, Nur77) whose altered balancing and transactivation may contribute for overall repression of this gene. In addition, the activation/expression of the heat shock response genes HSF-1 and HSP70 is not directly involved in the repression, and the electrophilic molecule cyclopentenone (2-cyclopenten-1-one) may reproduce the effects mediated by 15d-PGJ(2). These results suggest that modulation of Fas-L by 15d-PGJ(2) in T cells may represent an additional tool to consider for treatment of specific autoimmune and inflammatory disorders.

Activation and binding of peroxisome proliferator-activated receptor gamma by synthetic cannabinoid ajulemic acid

Ajulemic acid (AJA) is a synthetic analog of the tetrahydrocannabinol (THC) metabolite THC-11-oic acid; THC is a major active ingredient of the drug marijuana derived from the plant cannabis. AJA has potent analgesic and anti-inflammatory activity without the psychotropic action of THC. Unlike the nonsteroidal anti-inflammatory drugs, AJA is not ulcerogenic at therapeutic doses, making it a promising anti-inflammatory drug. However, the mechanism of AJA action remains unknown. Here we report that AJA binds directly and specifically to the peroxisome proliferator-activated receptor gamma (PPARgamma), a pharmacologically important member of the nuclear receptor superfamily. Functional assay indicates that AJA activates the transcriptional activity of both human and mouse PPARgamma at pharmacological concentrations. Activation of PPARgamma by AJA requires the AF-2 helix of the receptor, suggesting that AJA activates PPARgamma through the ligand-dependent AF-2 function. AJA binding consistently enables PPARgamma to recruit nuclear receptor coactivators. In addition, we show that AJA inhibits interleukin-8 promoter activity in a PPARgamma-dependent manner, suggesting a link between the anti-inflammatory action of AJA and the activation of PPARgamma. Finally, we find that AJA treatment induces differentiation of 3T3 L1 fibroblasts into adipocytes, a process mediated by PPARgamma. Together, these data indicate that PPARgamma may be a molecular target for AJA, providing a potential mechanism for the anti-inflammatory action of AJA, and possibly other cannabinoids. These studies also implicate other potential therapeutic actions of AJA through PPARgamma activation in multiple signaling pathways.

Peroxisome proliferator-activated receptors: a critical review on endogenous pathways for ligand generation

Lipid mediators can exert their effects by interactions with well-characterised cell surface G-protein-linked receptors. Recently, a group of intracellular receptors have been identified that are activated by a large variety of lipid-derived mediators. Amongst these novel targets, the peroxisome proliferator-activated receptors (PPARs), a family of three (PPARalpha, beta/delta and gamma) nuclear receptor/transcription factors have become a major area for investigation. PPARs are found throughout the body, where they have diverse roles regulating lipid homeostasis, cellular differentiation, proliferation and the immune response. There is a great interest, therefore, in the roles of PPARs in a variety of pathological conditions, including diabetes, atherosclerosis, cancer and chronic inflammation. Although, a number of naturally occurring compounds can activate PPARs, it has been difficult, as yet, to characterise any of these mediators as truly endogenous ligands. These findings have lead to the suggestion that PPARs may act just as general lipid sensors. Acting as lipid sensors, PPARs may take changes in lipid/fatty acid balance in the diet or local metabolism and translate them to tissue-specific ligands, exerting tissue-specific effects. Using classical pharmacological criteria for endogenous mediator classification we will critically discuss the variety of pathways for putative ligand generation.

Induction of cyclooxygenase-2 in monocyte/macrophage by mucins secreted from colon cancer cells

Up-regulation of cyclooxygenase-2 (COX-2) and overproduction of prostaglandins have been implicated in the initiation and/or progression of colon cancer. However, it is uncertain in which cells and how COX-2 is induced initially in the tumor microenvironment. We found that a conditioned medium of the colon cancer cell line, LS 180, contained a factor to induce COX-2 in human peripheral blood mononuclear cells. This factor was purified biochemically and revealed to be mucins. A small amount of mucins (approximately 100 ng of protein per ml) could elevate prostaglandin E2 production by monocytes. The mucins induced COX-2 mRNA and protein levels of monocytes in a dose- and time-dependent manner, indicating a COX-2-mediated pathway. We also have examined immunohistochemically the localization of COX-2 protein and mucins in human colorectal cancer tissues. It is noteworthy that COX-2-expressing macrophages were located around the region in which mucins were detectable, suggesting that COX-2 also was induced by mucins in vivo. These results suggest that mucins produced by colon cancer cells play a critical role in the initial induction of COX-2 in the tumor microenvironment.

Activation of peroxisome proliferator-activated receptors in human airway smooth muscle cells has a superior anti-inflammatory profile to corticosteroids: relevance for chronic obstructive pulmonary disease therapy

Airway smooth muscle is actively involved in the inflammatory process in diseases such as chronic obstructive pulmonary disease and asthma by 1) contributing to airway narrowing through hyperplasia and hypertrophy and 2) the release of GM-CSF and G-CSF, which promotes the survival and activation of infiltrating leukocytes. Thus, the identification of novel anti-inflammatory pathways in airway smooth muscle will have important implications for the treatment of inflammatory airway disease. This study identifies such a pathway in the activation of peroxisome proliferator-activated receptors (PPARs). PPAR ligands are known therapeutic agents in the treatment of diabetes; however, their role in human airway disease is unknown. We demonstrate, for the first time, that human airway smooth muscle cells express PPAR alpha and -gamma subtypes. Activation of PPAR gamma by natural and synthetic ligands inhibits serum-induced cell growth more effectively than does the steroid dexamethasone, and induces apoptosis. Moreover, PPAR gamma activation, like dexamethasone, inhibits the release of GM-CSF. However, PPAR gamma ligands, but not dexamethasone, similarly inhibits G-CSF release. These results reveal a novel anti-inflammatory pathway in human airway smooth muscle, where PPAR gamma activation has additional anti-inflammatory effects to those of steroids. Hence, PPAR ligands might act as potential treatments in human respiratory diseases.

Potentiation of protein kinase C zeta activity by 15-deoxy-delta(12,14)-prostaglandin J(2) induces an imbalance between mitogen-activated protein kinases and NF-kappa B that promotes apoptosis in macrophages

Activation of the macrophage cell line RAW 264.7 with lipopolysaccharide (LPS) transiently activates protein kinase C zeta (PKC zeta) and Jun N-terminal kinase (JNK) through a phosphoinositide-3-kinase (PI3-kinase)-dependent pathway. Incubation of LPS-treated cells with the cyclopentenone 15-deoxy-Delta(12,14)-prostaglandin J(2) (15dPGJ(2)) promoted a sustained activation of PKC zeta and JNK and inhibited I kappa B kinase (IKK) and NF-kappa B activity. Accordingly, 15dPGJ(2) induced an imbalance between JNK and IKK activities by increasing the former signaling pathway and inhibiting the latter signaling pathway. Under these conditions, apoptosis was significantly enhanced; this response was very dependent on PKC zeta and JNK activation. The effect of 15dPGJ(2) on PKC zeta activity observed in LPS-activated macrophages was not dependent on a direct action of this prostaglandin on the enzyme but was due to the activation of a step upstream of PI3-kinase. Moreover, LPS promoted the redistribution of activated PKC zeta from the cytosol to the nucleus, a process that was enhanced by treatment of the cells with 15dPGJ(2) that favored a persistent and broader distribution of PKC zeta in the nucleus. These results indicate that 15dPGJ(2) and other cyclopentenone prostaglandins, through the sustained activation of PKC zeta, might contribute significantly to the process of resolution of inflammation by promoting apoptosis of activated macrophages.

Effects of peroxisome proliferator-activated receptor-gamma agonists on central nervous system inflammation

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) plays a critical role in glucose and lipid metabolism. More recently, PPAR-gamma ligands have been reported to inhibit the expression of proinflammatory molecules by monocytes/macrophages. Of relevance to CNS disease is that PPAR-gamma agonists have been demonstrated to have similar effects on microglia. PPAR-gamma agonists also ameliorate experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. This Mini-Review summarizes the effects of PPAR-gamma agonists in mediating immune responses and the potential of these agonists in the treatment of inflammatory disorders of the CNS.

Advances in understanding the regulation of apoptosis and mitosis by peroxisome-proliferator activated receptors in pre-clinical models: relevance for human health and disease

Peroxisome proliferator activated receptors (PPARs) are a family of related receptors implicated in a diverse array of biological processes. There are 3 main isotypes of PPARs known as PPARalpha, PPARbeta and PPARgamma and each is organized into domains associated with a function such as ligand binding, activation and DNA binding. PPARs are activated by ligands, which can be both endogenous such as fatty acids or their derivatives, or synthetic, such as peroxisome proliferators, hypolipidaemic drugs, anti-inflammatory or insulin-sensitizing drugs. Once activated, PPARs bind to DNA and regulate gene transcription. The different isotypes differ in their expression patterns, lending clues on their function. PPARalpha is expressed mainly in liver whereas PPARgamma is expressed in fat and in some macrophages. Activation of PPARalpha in rodent liver is associated with peroxisome proliferation and with suppression of apoptosis and induction of cell proliferation. The mechanism by which activation of PPARalpha regulates apoptosis and proliferation is unclear but is likely to involve target gene transcription. Similarly, PPARgamma is involved in the induction of cell growth arrest occurring during the differentiation process of fibroblasts to adipocytes. However, it has been implicated in the regulation of cell cycle and cell proliferation in colon cancer models. Less in known concerning PPARbeta but it was identified as a downstream target gene for APC/beta-catenin/T cell factor-4 tumor suppressor pathway, which is involved in the regulation of growth promoting genes such as c-myc and cyclin D1. Marked species and tissue differences in the expression of PPARs complicate the extrapolation of pre-clinical data to humans. For example, PPARalpha ligands such as the hypolipidaemic fibrates have been used extensively in the clinic over the past 20 years to treat cardiovascular disease and side effects of clinical fibrate use are rare, despite the observation that these compounds are rodent carcinogens. Similarly, adverse clinical responses have been seen with PPARgamma ligands that were not predicted by pre-clinical models. Here, we consider the response to PPAR ligands seen in pre-clinical models of efficacy and safety in the context of human health and disease.