Peroxisome proliferator activated receptor ligands as regulators of airway inflammation and remodelling in chronic lung disease

Integration of metabolomics and transcriptomics to reveal the mechanism of Gerberae piloselloidis herba in alleviating bronchial asthma

ETHNOPHARMACOLOGICAL RELEVANCE

Gerberae Piloselloides Herba (GPH) is derived from Gerbera piloselloides (Linn.) Cass. It is a commonly used traditional medicine in China, featured by its special bioactivities as antitussive, expectorant, anti-asthma, anti-bacterial and anti-tumor. It is often used as an effective treatment for cough and sore throat as well as bronchial asthma (BA) in China. It was demonstrated in our previous studies that GPH exerted significant effects on the treatment of BA, but its underlying mechanism remains unclear.

AIM OF THE STUDY

This study was aimed at revealing the mechanism through which GPH protects against BA.

MATERIALS AND METHODS

The protective effect of GPH against BA was evaluated in a mouse model of BA induced by ovalbumin. Through integrated metabolomics and transcriptomics analysis, the most critical pathways were discovered. The effects of GPH in regulating these pathways was verified through molecular biology experiments and molecular docking.

RESULTS

GPH have anti-BA effects. In plasma and lung tissue, 5 and 17 differentially expressed metabolites (DEMs), respectively, showed a reversed tendency in the GPH group compared with the model group; apart from gamma-aminobutyric acid and butyrylcarnitine, these DEMs might aid in BA diagnosis. The DEMs were involved primarily in the regulation of lipid metabolism, followed by glucose metabolism and amino acid metabolism. Transcriptomic analysis indicated that GPH modulated 268 differentially expressed genes (DEGs). Integration analysis of metabolomics and transcriptomics revealed that GPH might regulate the PPAR signaling pathway, thus affecting the expression of key gene targets such as Cyp4a12a, Cyp4a12b, Adh7, Acaa1b and Gpat2; controlling fatty acid degradation, unsaturated fatty acid biosynthesis, glycerophospholipid metabolism and other lipid metabolic pathways; and ameliorating BA. This possibility was confirmed through reverse-transcription quantitative polymerase chain reaction, western blotting, immunofluorescence and molecular docking.

CONCLUSION

GPH was found to activate the PPAR signaling pathway, decrease the levels of Cyp4a12a and Cyp4a12b, and increase the levels of Adh7, Acaa1b and Gpat2, thereby regulating lipid metabolism disorder, decreasing the generation of inflammatory mediators and limiting lung injury.

Circadian clock and lipid metabolism disorders: a potential therapeutic strategy for cancer

Recent research has emphasized the interaction between the circadian clock and lipid metabolism, particularly in relation to tumors. This review aims to explore how the circadian clock regulates lipid metabolism and its impact on carcinogenesis. Specifically, targeting key enzymes involved in fatty acid synthesis (SREBP, ACLY, ACC, FASN, and SCD) has been identified as a potential strategy for cancer therapy. By disrupting these enzymes, it may be possible to inhibit tumor growth by interfering with lipid metabolism. Transcription factors, like SREBP play a significant role in regulating fatty acid synthesis which is influenced by circadian clock genes such as BMAL1, REV-ERB and DEC. This suggests a strong connection between fatty acid synthesis and the circadian clock. Therefore, successful combination therapy should target fatty acid synthesis in addition to considering the timing and duration of drug use. Ultimately, personalized chronotherapy can enhance drug efficacy in cancer treatment and achieve treatment goals.

Bronchial Asthma, Airway Remodeling and Lung Fibrosis as Successive Steps of One Process

Bronchial asthma is a heterogeneous disease characterized by persistent respiratory system inflammation, airway hyperreactivity, and airflow obstruction. Airway remodeling, defined as changes in airway wall structure such as extensive epithelial damage, airway smooth muscle hypertrophy, collagen deposition, and subepithelial fibrosis, is a key feature of asthma. Lung fibrosis is a common occurrence in the pathogenesis of fatal and long-term asthma, and it is associated with disease severity and resistance to therapy. It can thus be regarded as an irreversible consequence of asthma-induced airway inflammation and remodeling. Asthma heterogeneity presents several diagnostic challenges, particularly in distinguishing between chronic asthma and other pulmonary diseases characterized by disruption of normal lung architecture and functions, such as chronic obstructive pulmonary disease. The search for instruments that can predict the development of irreversible structural changes in the lungs, such as chronic components of airway remodeling and fibrosis, is particularly difficult. To overcome these challenges, significant efforts are being directed toward the discovery and investigation of molecular characteristics and biomarkers capable of distinguishing between different types of asthma as well as between asthma and other pulmonary disorders with similar structural characteristics. The main features of bronchial asthma etiology, pathogenesis, and morphological characteristics as well as asthma-associated airway remodeling and lung fibrosis as successive stages of one process will be discussed in this review. The most common murine models and biomarkers of asthma progression and post-asthmatic fibrosis will also be covered. The molecular mechanisms and key cellular players of the asthmatic process described and systematized in this review are intended to help in the search for new molecular markers and promising therapeutic targets for asthma prediction and therapy.

Morin inhibits the transformation of fibroblasts towards myofibroblasts through regulating "PPAR-γ-glutaminolysis-DEPTOR" pathway in pulmonary fibrosis

Morin, a natural flavonoid exists in many foods and dietary plants, owns good bioactivities. Herein, we investigated its effect on pulmonary fibrosis (PF), and further explored the mechanisms. Results showed that morin remarkably improved the pathologic alterations, and inhibited the transformation of fibroblasts towards myofibroblasts in lungs of mice with bleomycin-induced PF as well as TGF-β1 or hypoxia-stimulated NIH-3T3 cells. Mechanistic studies revealed that morin activated peroxisome proliferator activated receptor-gamma (PPAR-γ), and GW9662 or siPPAR-γ significantly weakened the inhibition of morin on the transformation of NIH-3T3 cells. Furthermore, morin restricted glutaminolysis by down-regulating the level of glutaminase 1 (GLS1), which was confirmed by glutamine deprivation, and GLS1 overexpression. Replenishment of metabolite α-ketoglutarate (α-KG) and 2-hydroxyglutarate (2-HG) inhibited morin-prevented transformation of fibroblasts, but neither TGF-β1 nor hypoxia could induce the transformation of IDH2-knockdown fibroblasts, suggesting 2-HG was directly involved in the action of morin. Then, ubiquitination of DEPTOR was demonstrated to be prevented by morin, which was attributed to KDM4A, an enzyme inactivated by 2-HG, and leucine as well as KDM4A inhibitor obstructed the effect of morin. Finally, the mechanisms of morin were further confirmed in vivo. Collectively, morin inhibited PF through intervening in "PPAR-γ-glutaminolysis-DEPTOR" signals, and subsequent restriction on the transformation of fibroblasts towards myofibroblasts.

Cross-Linking Cellular Prion Protein Induces Neuronal Type 2-Like Hypersensitivity

Background

Previous reports identified proteins associated with ‘apoptosis’ following cross-linking PrP^C with motif-specific anti-PrP antibodies in vivo and in vitro. The molecular mechanisms underlying this IgG-mediated neurotoxicity and the role of the activated proteins in the apoptotic pathways leading to neuronal death has not been properly defined. Previous reports implicated a number of proteins, including apolipoprotein E, cytoplasmic phospholipase A2, prostaglandin and calpain with anti-PrP antibody-mediated ‘apoptosis’, however, these proteins are also known to play an important role in allergy. In this study, we investigated whether cross-linking PrP^C with anti-PrP antibodies stimulates a neuronal allergenic response.

Methods

Initially, we predicted the allergenicity of the epitope sequences associated with ‘neurotoxic’ anti-PrP antibodies using allergenicity prediction servers. We then investigated whether anti-PrP antibody treatment of mouse primary neurons (MPN), neuroblastoma cells (N2a) and microglia (N11) cell lines lead to a neuronal allergenic response.

Results

In-Silico studies showed that both tail- and globular-epitopes were allergenic. Specifically, binding regions that contain epitopes for previously reported ‘neurotoxic’ antibodies such as ICSM18 (146-159), ICSM35 (91-110), POM 1 (138-147) and POM 3 (95-100) lead to activation of allergenic related proteins. Following direct application of anti-PrP^C antibodies on N2a cells, we identified 4 neuronal allergenic-related proteins when compared with untreated cells. Furthermore, we identified 8 neuronal allergenic-related proteins following treatment of N11 cells with anti-PrP^C antibodies prior to co-culture with N2a cells when compared with untreated cells. Antibody treatment of MPN or MPN co-cultured with antibody-treated N11 led to identifying 10 and 7 allergenic-related proteins when compared with untreated cells. However, comparison with 3F4 antibody treatment revealed 5 and 4 allergenic-related proteins respectively. Of importance, we showed that the allergenic effects triggered by the anti-PrP antibodies were more potent when antibody-treated microglia were co-cultured with the neuroblastoma cell line. Finally, co-culture of N2a or MPN with N11-treated with anti-PrP antibodies resulted in significant accumulation of NO and IL6 but not TNF-α in the cell culture media supernatant.

Conclusions

This study showed for the first time that anti-PrP antibody binding to PrP^C triggers a neuronal hypersensitivity response and highlights the important role of microglia in triggering an IgG-mediated neuronal hypersensitivity response. Moreover, this study provides an important impetus for including allergenic assessment of therapeutic antibodies for neurodegenerative disorders to derive safe and targeted biotherapeutics.

Thiazolidine Derivatives Attenuate Carrageenan-Induced Inflammatory Pain in Mice

BACKGROUND

Peripheral inflammation leads to the development of persistent thermal hyperalgesia and mechanical allodynia associated with increased expression of interleukin-1β (IL-1β) in the spinal cord. The aim of the present study was to investigate the effects of thiazolidine derivatives, 1b ([2-(2-hydroxyphenyl)-1,3-thiazolidin-4-yl](morpholin-4-yl)methanone) and 1d (2-hydroxy-4-{[2-(2-hydroxyphenyl)-1,3-thiazolidine-4-carbonyl]amino}benzoic acid), on thermal hyperalgesia, mechanical allodynia and on IL-1β expression during carrageenan-induced inflammation in the spinal cord in mice. Inflammatory pain was induced by injecting 1% carrageenan into the right hind paw of the mice.

METHODS

The animals were administered thiazolidine derivatives, 1b and 1d (1 mg/kg, 3 mg/kg, or 10 mg/kg), intraperitoneally 30 minutes before carrageenan administration. The animals' behavior was evaluated by measuring thermal hyperalgesia, mechanical allodynia, and motor coordination. The IL-1β expression was measured by enzyme-linked immunosorbent assay. Acute and sub-acute toxicity studies were conducted to evaluate the toxicity profile of compounds.

RESULTS

Treatment with the thiazolidine derivative, 1b and 1d, attenuated carrageenan-induced thermal hyperalgesia and mechanical allodynia at doses of 1 mg/kg, 3 mg/kg, and 10 mg/kg. No motor coordination deficits were observed in animals. The compounds also reduced IL-1β expression in the spinal cord of mice. Acute and sub-acute toxicity studies revealed that both compounds were safe.

CONCLUSION

The compounds exhibit promising activity against inflammatory pain due to their ability to produce anti-hyperalgesic and anti-allodynic effects and to inhibit IL-1β expression in the spinal cord.

Influence of wood species on toxicity of log-wood stove combustion aerosols: a parallel animal and air-liquid interface cell exposure study on spruce and pine smoke

Background

Wood combustion emissions have been studied previously either by in vitro or in vivo models using collected particles, yet most studies have neglected gaseous compounds. Furthermore, a more accurate and holistic view of the toxicity of aerosols can be gained with parallel in vitro and in vivo studies using direct exposure methods. Moreover, modern exposure techniques such as air-liquid interface (ALI) exposures enable better assessment of the toxicity of the applied aerosols than, for example, the previous state-of-the-art submerged cell exposure techniques.

Methods

We used three different ALI exposure systems in parallel to study the toxicological effects of spruce and pine combustion emissions in human alveolar epithelial (A549) and murine macrophage (RAW264.7) cell lines. A whole-body mouse inhalation system was also used to expose C57BL/6 J mice to aerosol emissions. Moreover, gaseous and particulate fractions were studied separately in one of the cell exposure systems. After exposure, the cells and animals were measured for various parameters of cytotoxicity, inflammation, genotoxicity, transcriptome and proteome.

Results

We found that diluted (1:15) exposure pine combustion emissions (PM₁ mass 7.7 ± 6.5 mg m^− 3, 41 mg MJ^− 1) contained, on average, more PM and polycyclic aromatic hydrocarbons (PAHs) than spruce (PM₁ mass 4.3 ± 5.1 mg m^− 3, 26 mg MJ^− 1) emissions, which instead showed a higher concentration of inorganic metals in the emission aerosol. Both A549 cells and mice exposed to these emissions showed low levels of inflammation but significantly increased genotoxicity. Gaseous emission compounds produced similar genotoxicity and a higher inflammatory response than the corresponding complete combustion emission in A549 cells. Systems biology approaches supported the findings, but we detected differing responses between in vivo and in vitro experiments.

Conclusions

Comprehensive in vitro and in vivo exposure studies with emission characterization and systems biology approaches revealed further information on the effects of combustion aerosol toxicity than could be achieved with either method alone. Interestingly, in vitro and in vivo exposures showed the opposite order of the highest DNA damage. In vitro measurements also indicated that the gaseous fraction of emission aerosols may be more important in causing adverse toxicological effects. Combustion aerosols of different wood species result in mild but aerosol specific in vitro and in vivo effects.

Epoxy-Oxylipins and Soluble Epoxide Hydrolase Metabolic Pathway as Targets for NSAID-Induced Gastroenteropathy and Inflammation-Associated Carcinogenesis

Polyunsaturated fatty acids (PUFAs) including epoxide-modified ω-3 and ω-6 fatty acids are made via oxidation to create highly polarized carbon-oxygen bonds crucial to their function as signaling molecules. A critical PUFA, arachidonic acid (ARA), is metabolized to a diverse set of lipids signaling molecules through cyclooxygenase (COX), lipoxygenase (LOX), cytochrome P450 epoxygenase, or cytochrome P450 hydroxylase; however, the majority of ARA is metabolized into anti-inflammatory epoxides via cytochrome P450 enzymes. These short-lived epoxide lipids are rapidly metabolized or inactivated by the soluble epoxide hydrolase (sEH) into diol-containing products. sEH inhibition or knockout has been a practical approach to study the biology of the epoxide lipids, and has been shown to effectively treat inflammatory conditions in the preclinical models including gastrointestinal ulcers and colitis by shifting oxylipins to epoxide profiles, inhibiting inflammatory cell infiltration and activation, and enhancing epithelial cell defense via increased mucin production, thus providing further evidence for the role of sEH as a pro-inflammatory protein. Non-steroidal anti-inflammatory drugs (NSAIDs) with COX-inhibitor activity are among the most commonly used analgesics and have demonstrated applications in the management of cardiovascular disease and intriguingly cancer. Major side effects of NSAIDs however are gastrointestinal ulcers which frequently precludes their long-term application. In this review, we hope to bridge the gap between NSAID toxicity and sEH-mediated metabolic pathways to focus on the role of epoxy fatty acid metabolic pathway of PUFAs in NSAIDS-ulcer formation and healing as well as inflammation-related carcinogenesis. Specifically we address the potential application of sEH inhibition to enhance ulcer healing at the site of inflammation via their activity on altered lipid signaling, mitochondrial function, and diminished reactive oxygen species, and further discuss the significance of dual COX and sEH inhibitor in anti-inflammation and carcinogenesis.

Rosiglitazone attenuates paraquat-induced lung fibrosis in rats in a PPAR gamma-dependent manner

Rosiglitazone, a PPAR-γ agonist, possesses anti-fibritic effect; however, its inhibitory effect on paraquat (PQ)-induced pulmonary fibrosis is not completely understood. Here, we investigated the inhibitory effect of rosiglitazone on PQ-induced acute pulmonary fibrosis in rats and its underlying mechanism. Male Sprague-Dawly rats were administered a single intraperitoneal injection of 30 mg/kg PQ and euthanised 7, 14, 21, and 28 days after PQ poisoning. PQ-induced pulmonary fibrosis was most obvious on day 28. Male Sprague-Dawly rats were exposed either against distilled water as control groups or PQ (30 mg/kg, i.p.) as test groups. The control groups were nominated as NC group (without treatment), RSG group (only treatment with rosiglitazone, 10 mg/kg/d), and GW group (only treatment with GW9662, a PPAR-γ antagonist, 1 mg/kg/d). The test groups were nominated as PQ group (PQ exposed without treatment), PQ + RSG group (treatment with rosiglitazone), and PQ + RSG + GW group (treatment with rosiglitazone and GW9662). Rosiglitazone was able to recover the PQ-induced decrease in arterial oxygen partial pressure (PaO₂), increase in the wet-to-dry (W/D) lung tissue weight ratio and lung fibrosis score. Rosiglitazone inhibited the PQ-induced reduction in protein and mRNA levels of PPAR-γ and PTEN and elevation in protein and mRNA levels of TGF-β1 and α-SMA. GW9662 administration antagonized the effect of rosiglitazone. These data suggest that rosiglitazone attenuated PQ-induced pulmonary fibrosis by upregulateing PTEN and downregulating TGF-β1 expression in a PPAR-γ dependent manner.

Airway Epithelial Cell Peroxisome Proliferator-Activated Receptor γ Regulates Inflammation and Mucin Expression in Allergic Airway Disease

Airway epithelial cells (AECs) orchestrate inflammatory responses to airborne irritants that enter the respiratory system. A viscous mucus layer produced by goblet cells in the airway epithelium also contributes to a physiological defense mechanism through the physical and chemical barriers it provides. Dysregulation or impairment in these functions has been implicated as a cause of the chronic inflammation and tissue remodeling that constitute major pathological features of asthma. In particular, mucus hypersecretion leading to airway obstruction and impaired pulmonary function is associated with morbidity and mortality in asthma patients. Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated transcription factor involved in a variety of cellular processes. Accumulating evidence indicates that PPARγ agonists antagonize exaggerated inflammatory responses, yet PPARγ's precise role in airway remodeling/mucus hypersecretion has yet to be defined. In this study, we created an AEC-specific PPARγ (AEC-PPARγ) deletion to investigate PPARγ's functions in a murine model of allergic airway disease. AEC-PPARγ deficiency exaggerated airway hyperresponsiveness, inflammation, cytokine expression, and tissue remodeling. We also found that PPARγ directly bound to a PPAR response element found in MUC5AC and repressed gene expression. Likewise, PPARγ regulated mucin and inflammatory factors in primary human bronchial epithelial cells. In light of the current standard therapies' limited and inadequate direct effect on airway mucus hypersecretion, our study showing AEC-PPARγ's role as a transcriptional repressor of MUC5AC highlights this receptor's potential as a pharmacological target for asthma.

PPARs: Key Regulators of Airway Inflammation and Potential Therapeutic Targets in Asthma

Asthma affects approximately 300 million people worldwide, significantly impacting quality of life and healthcare costs. While current therapies are effective in controlling many patients' symptoms, a large number continue to experience exacerbations or treatment-related adverse effects. Alternative therapies are thus urgently needed. Accumulating evidence has shown that the peroxisome proliferator-activated receptor (PPAR) family of nuclear hormone receptors, comprising PPARα, PPARβ/δ, and PPARγ, is involved in asthma pathogenesis and that ligand-induced activation of these receptors suppresses asthma pathology. PPAR agonists exert their anti-inflammatory effects primarily by suppressing pro-inflammatory mediators and antagonizing the pro-inflammatory functions of various cell types relevant to asthma pathophysiology. Experimental findings strongly support the potential clinical benefits of PPAR agonists in the treatment of asthma. We review current literature, highlighting PPARs' key role in asthma pathogenesis and their agonists' therapeutic potential. With additional research and rigorous clinical studies, PPARs may become attractive therapeutic targets in this disease.

Prostanoid EP4 agonist L-902,688 activates PPARγ and attenuates pulmonary arterial hypertension

Prostacyclin agonists that bind the prostacyclin receptor (IP) to stimulate cAMP synthesis are effective vasodilators for the treatment of idiopathic pulmonary arterial hypertension (IPAH), but this signaling may occur through nuclear peroxisome proliferator-activated receptor-γ (PPARγ). There is evidence of scant IP and PPARγ expression but stable prostanoid EP₄ receptor (EP₄) expression in IPAH patients. Both IP and EP₄ functionally couple with stimulatory G protein (G_s), which activates signal transduction. We investigated the effect of an EP₄-specific agonist on pulmonary arterial remodeling and its regulatory mechanisms in pulmonary arterial smooth muscle cells (PASMCs). Immunoblotting evealed IP, EP₄, and PPARγ expression in human pulmonary arterial hypertension (PAH) and monocrotaline (MCT)-induced PAH rat lung tissue. Isolated PASMCs from MCT-induced PAH rats (MCT-PASMCs) were treated with L-902,688, a selective EP₄ agonist, to investigate the anti-vascular remodeling effect. Scant expression of IP and PPARγ but stable expression of EP₄ was observed in IPAH patient lung tissues and MCT-PASMCs. L-902,688 inhibited IP-insufficient MCT-PASMC proliferation and migration by activating PPARγ in a time- and dose-dependent manner, but these effects were reversed by AH-23848 (an EP₄ antagonist) and H-89 [a protein kinase A (PKA) inhibitor], highlighting the crucial role of PPARγ in the activity of this EP₄ agonist. L-902,688 attenuated pulmonary arterial remodeling in hypoxic PAH mice and MCT-induced PAH rats; therefore, we conclude that the selective EP₄ agonist L-902,688 reverses vascular remodeling by activating PPARγ. This study identified a novel EP₄-PKA-PPARγ pathway, and we propose EP₄ as a potential therapeutic target for PAH.

15-Deoxy-Delta-12,14-Prostaglandin J2 Inhibits Lung Inflammation and Remodeling in Distinct Murine Models of Asthma

15-deoxy-Δ-12,14-prostaglandin J₂ (15d-PGJ₂) has been described as an anti-inflammatory lipid mediator in several in vitro and in vivo studies, but its effect on allergic pulmonary inflammation remains elusive. The aim of this study was to investigate the therapeutic potential of 15d-PGJ₂ based on distinct murine models of allergic asthma triggered by either ovalbumin (OVA) or house dust mite extract (HDM). Characteristics of lung inflammation, airway hyper-reactivity (AHR), mucus exacerbation, and lung remodeling in sensitized A/J mice treated or not with 15d-PGJ₂ were assessed. 15d-PGJ₂ treatments were carried out systemically or topically given via subcutaneous injection or intranasal instillation, respectively. Analyses were carried out 24 h after the last allergen provocation. Irrespective of the route of administration, 15d-PGJ₂ significantly inhibited the peribronchial accumulation of eosinophils and neutrophils, subepithelial fibrosis and also mucus exacerbation caused by either OVA or HDM challenge. The protective effect of 15d-PGJ₂ occurred in parallel with inhibition of allergen-induced AHR and lung tissue production of pro-inflammatory cytokines, such as interleukin (IL)-5, IL-13, IL-17, and TNF-α. Finally, 15d-PGJ₂ was found effective in inhibiting NF-κB phosphorylation upon HDM challenge as measured by Western blotting. In conclusion, our findings suggest that 15d-PGJ₂ can reduce crucial features of asthma, including AHR, lung inflammation, and remodeling in distinct murine models of the disease. These effects are associated with a decrease in lung tissue generation of pro-inflammatory cytokines by a mechanism related to downregulation of NF-κB phosphorylation.

PPAR Agonists for the Prevention and Treatment of Lung Cancer

Lung cancer is the most common and most fatal of all malignancies worldwide. Furthermore, with more than half of all lung cancer patients presenting with distant metastases at the time of initial diagnosis, the overall prognosis for the disease is poor. There is thus a desperate need for new prevention and treatment strategies. Recently, a family of nuclear hormone receptors, the peroxisome proliferator-activated receptors (PPARs), has attracted significant attention for its role in various malignancies including lung cancer. Three PPARs, PPARα, PPARβ/δ, and PPARγ, display distinct biological activities and varied influences on lung cancer biology. PPARα activation generally inhibits tumorigenesis through its antiangiogenic and anti-inflammatory effects. Activated PPARγ is also antitumorigenic and antimetastatic, regulating several functions of cancer cells and controlling the tumor microenvironment. Unlike PPARα and PPARγ, whether PPARβ/δ activation is anti- or protumorigenic or even inconsequential currently remains an open question that requires additional investigation. This review of current literature emphasizes the multifaceted effects of PPAR agonists in lung cancer and discusses how they may be applied as novel therapeutic strategies for the disease.

Differential effects of dexamethasone and rosiglitazone in a sephadex-induced model of lung inflammation in rats: possible role of tissue inhibitor of metalloproteinase-3

Objectives:

To study the effects of two different classes of drugs in sephadex-induced lung inflammation using rats and explore the potential mechanism (s).

Materials and Methods:

Effects of dexamethasone (0.3 mg/kg, p.o.) and rosiglitazone (10 mg/kg, p.o.) treatments were evaluated up to 3 days in sephadex challenged rats. 72 h postsephadex administration, broncho-alveolar lavage fluid (BALF) was collected for cell count and cytokine estimation. Lung tissues were harvested for gene expression and histopathology.

Results:

Dexamethasone treatment resulted in significant inhibition of lymphocytes, monocytes, eosinophils and neutrophils, whereas rosiglitazone inhibited eosinophils and neutrophils only. Further, dexamethasone reduced the elevated levels of prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) after sephadex challenge while rosiglitazone significantly reduced the PGE2 levels without altering LTB4 in the BALF. Hydroxyproline content in rat lung homogenate was significantly reduced with dexamethasone treatment but not with rosiglitazone. Both the drugs were found to suppress matrix metallo proteinase 9, whereas only dexamethasone showed inhibition of tumor necrosis factor-alpha and up-regulation of tissue inhibitor of metalloproteinase 3 (TIMP-3) expression and preserved the broncho-alveolar microstructure.

Conclusions:

Our results revealed that up-regulation of TIMP-3 corroborated well with dexamethasone mediated inhibition of collagen degradation and restoration of alveolar micro-architecture.

Airway epithelial cell PPARγ modulates cigarette smoke-induced chemokine expression and emphysema susceptibility in mice

Chronic obstructive pulmonary disease (COPD) is a highly prevalent, chronic inflammatory lung disease with limited existing therapeutic options. While modulation of peroxisome proliferator-activating receptor (PPAR)-γ activity can modify inflammatory responses in several models of lung injury, the relevance of the PPARG pathway in COPD pathogenesis has not been previously explored. Mice lacking Pparg specifically in airway epithelial cells displayed increased susceptibility to chronic cigarette smoke (CS)-induced emphysema, with excessive macrophage accumulation associated with increased expression of chemokines, Ccl5, Cxcl10, and Cxcl15. Conversely, treatment of mice with a pharmacological PPARγ activator attenuated Cxcl10 and Cxcl15 expression and macrophage accumulation in response to CS. In vitro, CS increased lung epithelial cell chemokine expression in a PPARγ activation-dependent fashion. The ability of PPARγ to regulate CS-induced chemokine expression in vitro was not specifically associated with peroxisome proliferator response element (PPRE)-mediated transactivation activity but was correlated with PPARγ-mediated transrepression of NF-κB activity. Pharmacological or genetic activation of PPARγ activity abrogated CS-dependent induction of NF-κB activity. Regulation of NF-κB activity involved direct PPARγ-NF-κB interaction and PPARγ-mediated effects on IKK activation, IκBα degradation, and nuclear translocation of p65. Our data indicate that PPARG represents a disease-relevant pathophysiological and pharmacological target in COPD. Its activation state likely contributes to NF-κB-dependent, CS-induced chemokine-mediated regulation of inflammatory cell accumulation.

Novel small airway bronchodilator responses to rosiglitazone in mouse lung slices

There is a need to identify novel agents that elicit small airway relaxation when β2-adrenoceptor agonists become ineffective in difficult-to-treat asthma. Because chronic treatment with the synthetic peroxisome proliferator activated receptor (PPAR)γ agonist rosiglitazone (RGZ) inhibits airway hyperresponsiveness in mouse models of allergic airways disease, we tested the hypothesis that RGZ causes acute airway relaxation by measuring changes in small airway size in mouse lung slices. Whereas the β-adrenoceptor agonists albuterol (ALB) and isoproterenol induced partial airway relaxation, RGZ reversed submaximal and maximal contraction to methacholine (MCh) and was similarly effective after precontraction with serotonin or endothelin-1. Concentration-dependent relaxation to RGZ was not altered by the β-adrenoceptor antagonist propranolol and was enhanced by ALB. RGZ-induced relaxation was mimicked by other synthetic PPARγ agonists but not by the putative endogenous agonist 15-deoxy-PGJ2 and was not prevented by the PPARγ antagonist GW9662. To induce airway relaxation, RGZ inhibited the amplitude and frequency of MCh-induced Ca(2+) oscillations of airway smooth muscle cells (ASMCs). In addition, RGZ reduced MCh-induced Ca(2+) sensitivity of the ASMCs. Collectively, these findings demonstrate that acute bronchodilator responses induced by RGZ are PPARγ independent, additive with ALB, and occur by the inhibition of ASMC Ca(2+) signaling and Ca(2+) sensitivity. Because RGZ continues to elicit relaxation when β-adrenoceptor agonists have a limited effect, RGZ or related compounds may have potential as bronchodilators for the treatment of difficult asthma.

Antifibrotic effect of atorvastatin on paraquat-induced pulmonary fibrosis: role of PPARγ receptors

This study was carried out to highlight the role of PPARγ in the paraquat (PQ)-induced pulmonary fibrosis. Forty-two male Wistar rats were exposed either against saline as a control group or PQ (3.5mg/kg, i.p.) as test groups. The test groups were nominated as PQ (PQ-exposed non-treated animals), pioglitazone (PGT, 10mg/kg, orally), atorvastatin (STN, 10mg/kg, orally), PGT+STN, PGT+GW9662 (1mg/kg, i.p.) and STN+GW9662 (1mg/kg). Atorvastatin but not PGT was able to reverse significantly (P<0.05) the PQ-increased ratio of lung to body weight. STN was successfully able to recover the PQ-reduced antioxidant potency and the GW9662 administration resulted in antagonizing the protective effect of both PGT and STN. Although both PGT and STN were able to reduce the hydrxoproline content of the lungs, GW9662, however, could reverse only STN-related effect. Histochemical studies revealed that PQ exposure resulted in a remarkable increase of fibroblasts and collagen fibers in the interstitial tissue and around vessels and bronchioles, which was improved by the STN administration. Only STN-received animals showed the down-regulation of the TGF-β1 expression and GW9662 was able to antagonize this down-regulation. Co-administration of PGT and STN could not exert any synergistic protective effect. These data suggest that the PQ-induced pulmonary fibrosis could be more effectively reversed by STN rather than PGT. Moreover, STN-induced protective effects might attribute to the regulation of TGF-β1 expression, which is antagonized by PPARγ antagonist, suggesting that STN may improve the PQ-induced damages via PPARγ.

Peroxisome proliferator-activated receptor γ B cell-specific-deficient mice have an impaired antibody response

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily. PPARγ, a ligand-activated transcription factor, has important anti-inflammatory and antiproliferative functions, and it has been associated with diseases including diabetes, scarring, and atherosclerosis, among others. PPARγ is expressed in most bone marrow-derived cells and influences their function. PPARγ ligands can stimulate human B cell differentiation and promote Ab production. A knowledge gap is that the role of PPARγ in B cells under physiological conditions is not known. We developed a new B cell-specific PPARγ (B-PPARγ) knockout mouse and explored the role of PPARγ during both the primary and secondary immune response. In this article, we show that PPARγ deficiency in B cells decreases germinal center B cells and plasma cell development, as well as the levels of circulating Ag-specific Abs during a primary challenge. Inability to generate germinal center B cells and plasma cells is correlated to decreased MHC class II expression and decreased Bcl-6 and Blimp-1 levels. Furthermore, B-PPARγ-deficient mice have an impaired memory response, characterized by low titers of Ag-specific Abs and low numbers of Ag-experienced, Ab-secreting cells. However, B-PPARγ-deficient mice have no differences in B cell population distribution within primary or secondary lymphoid organs during development. This is the first report, to our knowledge, to show that, under physiological conditions, PPARγ expression in B cells is required for an efficient B cell-mediated immune response as it regulates B cell differentiation and Ab production.

Suppression of IL-8 production in gastric epithelial cells by MUC1 mucin and peroxisome proliferator-associated receptor-γ

MUC1 is a membrane-tethered mucin expressed on the apical surface of epithelial cells. Our previous report (Guang W, Ding H, Czinn SJ, Kim KC, Blanchard TG, Lillehoj EP. J Biol Chem 285: 20547-20557, 2010) demonstrated that expression of MUC1 in AGS gastric epithelial cells limits Helicobacter pylori infection and reduces bacterial-driven IL-8 production. In this study, we identified the peroxisome proliferator-associated receptor-γ (PPARγ) upstream of MUC1 in the anti-inflammatory pathway suppressing H. pylori- and phorbol 12-myristate 13-acetate (PMA)-stimulated IL-8 production. Treatment of AGS cells with H. pylori or PMA increased IL-8 levels in cell culture supernatants compared with cells treated with the respective vehicle controls. Prior small interfering (si)RNA-induced MUC1 silencing further increased H. pylori- and PMA-stimulated IL-8 levels compared with a negative control siRNA. MUC1-expressing AGS cells pretreated with the PPARγ agonist troglitazone (TGN) had reduced H. pylori- and PMA-stimulated IL-8 levels compared with cells treated with H. pylori or PMA alone. However, following MUC1 siRNA knockdown, no differences in IL-8 levels were seen between TGN/H. pylori and H. pylori-only cells or between TGN/PMA and PMA-only cells. Finally, TGN-treated AGS cells had increased Muc1 promoter activity, as measured using a Muc1-luciferase reporter gene, and greater MUC1 protein levels by Western blot analysis, compared with vehicle controls. These results support the hypothesis that PPARγ stimulates MUC1 expression by AGS cells, thereby attenuating H. pylori- and PMA-induced IL-8 production.

PPARγ Ligands Regulate Noncontractile and Contractile Functions of Airway Smooth Muscle: Implications for Asthma Therapy

In asthma, the increase in airway smooth muscle (ASM) can contribute to inflammation, airway wall remodeling and airway hyperresponsiveness (AHR). Targetting peroxisome proliferator-activated receptor γ (PPARγ), a receptor upregulated in ASM in asthmatic airways, may provide a novel approach to regulate these contributions. This review summarises experimental evidence that PPARγ ligands, such as rosiglitazone (RGZ) and pioglitazone (PGZ), inhibit proliferation and inflammatory cytokine production from ASM in vitro. In addition, inhaled administration of these ligands reduces inflammatory cell infiltration and airway remodelling in mouse models of allergen-induced airways disease. PPARγ ligands can also regulate ASM contractility, with acute treatment eliciting relaxation of mouse trachea in vitro through a PPARγ-independent mechanism. Chronic treatment can protect against the loss of bronchodilator sensitivity to β₂-adrenoceptor agonists and inhibit the development of AHR associated with exposure to nicotine in utero or following allergen challenge. Of particular interest, a small clinical trial has shown that oral RGZ treatment improves lung function in smokers with asthma, a group that is generally unresponsive to conventional steroid treatment. These combined findings support further investigation of the potential for PPARγ agonists to target the noncontractile and contractile functions of ASM to improve outcomes for patients with poorly controlled asthma.

Nuclear hormone receptors enable macrophages and dendritic cells to sense their lipid environment and shape their immune response

A key issue in the immune system is to generate specific cell types, often with opposing activities. The mechanisms of differentiation and subtype specification of immune cells such as macrophages and dendritic cells are critical to understand the regulatory principles and logic of the immune system. In addition to cytokines and pathogens, it is increasingly appreciated that lipid signaling also has a key role in differentiation and subtype specification. In this review we explore how intracellular lipid signaling via a set of transcription factors regulates cellular differentiation, subtype specification, and immune as well as metabolic homeostasis. We introduce macrophages and dendritic cells and then we focus on a group of transcription factors, nuclear receptors, which regulate gene expression upon receiving lipid signals. The receptors we cover are the ones with a recognized physiological function in these cell types and ones which heterodimerize with the retinoid X receptor. These are as follows: the receptor for a metabolite of vitamin A, retinoic acid: retinoic acid receptor (RAR), the vitamin D receptor (VDR), the fatty acid receptor: peroxisome proliferator-activated receptor γ (PPARγ), the oxysterol receptor liver X receptor (LXR), and their obligate heterodimeric partner, the retinoid X receptor (RXR). We discuss how they can get activated and how ligand is generated and eliminated in these cell types. We also explore how activation of a particular target gene contributes to biological functions and how the regulation of individual target genes adds up to the coordination of gene networks. It appears that RXR heterodimeric nuclear receptors provide these cells with a coordinated and interrelated network of transcriptional regulators for interpreting the lipid milieu and the metabolic changes to bring about gene expression changes leading to subtype and functional specification. We also show that these networks are implicated in various immune diseases and are amenable to therapeutic exploitation.

PPARγ as a Potential Target to Treat Airway Mucus Hypersecretion in Chronic Airway Inflammatory Diseases

Airway mucus hypersecretion (AMH) is a key pathophysiological feature of chronic airway inflammatory diseases such as bronchial asthma, cystic fibrosis, and chronic obstructive pulmonary disease. AMH contributes to the pathogenesis of chronic airway inflammatory diseases, and it is associated with reduced lung function and high rates of hospitalization and mortality. It has been suggested that AMH should be a target in the treatment of chronic airway inflammatory diseases. Recent evidence suggests that a key regulator of airway inflammation, hyperresponsiveness, and remodeling is peroxisome proliferator-activated receptor gamma (PPARγ), a ligand-activated transcription factor that regulates adipocyte differentiation and lipid metabolism. PPARγ is expressed in structural, immune, and inflammatory cells in the lung. PPARγ is involved in mucin production, and PPARγ agonists can inhibit mucin synthesis both in vitro and in vivo. These findings suggest that PPARγ is a novel target in the treatment of AMH and that further work on this transcription factor may lead to new therapies for chronic airway inflammatory diseases.

PPARγ inhibits airway epithelial cell inflammatory response through a MUC1-dependent mechanism

This study was conducted to examine the relationship between the peroxisome proliferator-associated receptor-γ (PPARγ) and MUC1 mucin, two anti-inflammatory molecules expressed in the airways. Treatment of A549 lung epithelial cells or primary mouse tracheal surface epithelial (MTSE) cells with phorbol 12-myristate 13-acetate (PMA) increased the levels of tumor necrosis factor (TNF)-α in cell culture media compared with cells treated with vehicle alone. Overexpression of MUC1 in A549 cells decreased PMA-stimulated TNF-α levels, whereas deficiency of Muc1 expression in MTSE cells from Muc1 null mice increased PMA-induced TNF-α levels. Treatment of A549 or MTSE cells with the PPARγ agonist troglitazone (TGN) blocked the ability of PMA to stimulate TNF-α levels. However, the effect of TGN required the presence of MUC1/Muc1, since no differences in TNF-α levels were seen between PMA and PMA plus TGN in MUC1/Muc1-deficient cells. Similarly, whereas TGN decreased interleukin-8 (IL-8) levels in culture media of MUC1-expressing A549 cells treated with Pseudomonas aeruginosa strain K (PAK), no differences in IL-8 levels were seen between PAK and PAK plus TGN in MUC1-nonexpressing cells. EMSA confirmed the presence of a PPARγ-binding element in the MUC1 gene promoter. Finally, TGN treatment of A549 cells increased MUC1 promoter activity measured using a MUC1-luciferase reporter gene, augmented MUC1 mRNA levels by quantitative RT-PCR, and enhanced MUC1 protein expression by Western blot analysis. These combined data are consistent with the hypothesis that PPARγ stimulates MUC1/Muc1 expression, thereby blocking PMA/PAK-induced TNF-α/IL-8 production by airway epithelial cells.

Smooth muscle proliferation and role of the prostacyclin (IP) receptor in idiopathic pulmonary arterial hypertension

RATIONALE

Prostacyclin analogs, used to treat idiopathic pulmonary arterial hypertension (IPAH), are assumed to work through prostacyclin (IP) receptors linked to cyclic AMP (cAMP) generation, although the potential to signal through peroxisome proliferator-activated receptor-γ (PPARγ) exists.

OBJECTIVES

IP receptor and PPARγ expression may be depressed in IPAH. We wished to determine if pathways remain functional and if analogs continue to inhibit smooth muscle proliferation.

METHODS

We used Western blotting to determine IP receptor expression in peripheral pulmonary arterial smooth muscle cells (PASMCs) from normal and IPAH lungs and immunohistochemistry to evaluate IP receptor and PPARγ expression in distal arteries.

MEASUREMENTS AND MAIN RESULTS

Cell proliferation and cAMP assays assessed analog responses in human and mouse PASMCs and HEK-293 cells. Proliferative rates of IPAH cells were greater than normal human PASMCs. IP receptor protein levels were lower in PASMCs from patients with IPAH, but treprostinil reduced replication and treprostinil-induced cAMP elevation appeared normal. Responses to prostacyclin analogs were largely dependent on the IP receptor and cAMP in normal PASMCs, although in IP(-/-) receptor cells analogs inhibited growth in a cAMP-independent, PPARγ-dependent manner. In IPAH cells, antiproliferative responses to analogs were insensitive to IP receptor or adenylyl cyclase antagonists but were potentiated by a PPARγ agonist and inhibited (∼ 60%) by the PPARγ antagonist GW9662. This coincided with increased PPARγ expression in the medial layer of acinar arteries.

CONCLUSIONS

The antiproliferative effects of prostacyclin analogs are preserved in IPAH despite IP receptor down-regulation and abnormal coupling. PPARγ may represent a previously unrecognized pathway by which these agents inhibit smooth muscle proliferation.

Epoxyeicosatrienoic acids and soluble epoxide hydrolase: potential therapeutic targets for inflammation and its induced carcinogenesis

Chronic inflammation is an important factor contributing to human carcinoma, and non-steroidal anti-inflammatory drugs (NSAIDs) have been shown to have a preventive effect in the development of various types of carcinoma. However, NSAIDs also have adverse side effects including increased cardiovascular events, making them less than ideal for routine chemoprevention. Soluble epoxide hydrolase (sEH) is an enzyme that converts endogenous anti-inflammatory compounds, the epoxyeicosatrienoic acids (EETs), to the less anti-inflammatory dihydroxyeicosatrienoic acids (DHETs). Inhibition of sEH, by a highly selective and potent sEH inhibitor (sEHI), increases EETs leading to decreased inflammation. In our studies, administration of a sEHI in mouse colitis models led to decreased ulcer incidence and number of ulcers compared to controls, with no adverse side effects seen. In human tissue, sEH showed an increase in expression, as seen immunohistochemically, in ulcerative colitis (UC), UC-induced dysplasia, and UC-induced carcinoma. Thus, inhibition of sEH may be a novel biomarker and potential therapeutic target in inflammation and inflammation-induced carcinoma.

Effects of PPAR gamma ligands on TGF-beta1-induced epithelial-mesenchymal transition in alveolar epithelial cells

Background

Transforming growth factor β1 (TGF-β1)-mediated epithelial mesenchymal transition (EMT) of alveolar epithelial cells (AEC) may contribute to lung fibrosis. Since PPARγ ligands have been shown to inhibit fibroblast activation by TGF-β1, we assessed the ability of the thiazolidinediones rosiglitazone (RGZ) and ciglitazone (CGZ) to regulate TGF-β1-mediated EMT of A549 cells, assessing changes in cell morphology, and expression of cell adhesion molecules E-cadherin (epithelial cell marker) and N-cadherin (mesenchymal cell marker), and collagen 1α1 (COL1A1), CTGF and MMP-2 mRNA.

Methods

Serum-deprived A549 cells (human AEC cell line) were pre-incubated with RGZ and CGZ (1 - 30 μM) in the absence or presence of the PPARγ antagonist GW9662 (10 μM) before TGFβ-1 (0.075-7.5 ng/ml) treatment for up to 72 hrs. Changes in E-cadherin, N-cadherin and phosphorylated Smad2 and Smad3 levels were analysed by Western blot, and changes in mRNA levels including COL1A1 assessed by RT-PCR.

Results

TGFβ-1 (2.5 ng/ml)-induced reductions in E-cadherin expression were associated with a loss of epithelial morphology and cell-cell contact. Concomitant increases in N-cadherin, MMP-2, CTGF and COL1A1 were evident in predominantly elongated fibroblast-like cells. Neither RGZ nor CGZ prevented TGFβ1-induced changes in cell morphology, and PPARγ-dependent inhibitory effects of both ligands on changes in E-cadherin were only evident at submaximal TGF-β1 (0.25 ng/ml). However, both RGZ and CGZ inhibited the marked elevation of N-cadherin and COL1A1 induced by TGF-β1 (2.5 ng/ml), with effects on COL1A1 prevented by GW9662. Phosphorylation of Smad2 and Smad3 by TGF-β1 was not inhibited by RGZ or CGZ.

Conclusions

RGZ and CGZ inhibited profibrotic changes in TGF-β1-stimulated A549 cells independently of inhibition of Smad phosphorylation. Their inhibitory effects on changes in collagen I and E-cadherin, but not N-cadherin or CTGF, appeared to be PPARγ-dependent. Further studies are required to unravel additional mechanisms of inhibition of TGF-β1 signalling by thiazolidinediones and their implications for the contribution of EMT to lung fibrosis.

Treatment with a peroxisomal proliferator activated receptor gamma agonist has a modest effect in the allergen challenge model in asthma: a randomised controlled trial

PURPOSE

A considerable body of non clinical evidence has accumulated to support peroxisomal proliferator-activated receptor gamma agonists as candidate anti-inflammatory drugs in asthma. We utilized rosiglitazone as a tool compound in the inhaled allergen challenge model of asthma.

METHODS

A single centre, double-blind, randomised, placebo controlled, two period cross-over study. Subjects received rosiglitazone 4mg and placebo twice daily for 28 days in random order. On day 28, inhaled allergen challenge was performed 1 hour post-dose. A methacholine challenge was performed on day 29 and an adenosine monophosphate challenge on day 14. Exhaled nitric oxide was measured on days 1, 14, 28, 29. Blood was collected pre dose on days 1, 14 and 28 and analysed for markers associated with PPAR activity and systemic markers of inflammation.

RESULTS

The late asthmatic reaction (LAR) change from post saline FEV(1) from 4-10 hrs post allergen on day 28 was statistically significant for the weighted mean LAR. The difference in weighted mean was 0.06 L (95% CI 0.01 to 0.11) which equates to a 15% attenuation of the response during placebo treatment. This was accompanied by trends in other markers of efficacy and anti-inflammatory activity but none were considered major effects.

DISCUSSION

Treatment with a PPARgamma agonist (rosiglitazone) was associated with a modest (15%) reduction in the late asthmatic reaction in the allergen challenge model of asthma. Based on the results of this study, PPARgamma agonist monotherapy is unlikely to represent a clinically useful intervention in human asthma. Registered with www.clinicaltrials.gov (NCT00318630).

Protease-activated receptors and prostaglandins in inflammatory lung disease

Protease-activated receptors (PARs) are a novel family of G protein-coupled receptors. Signalling through PARs typically involves the cleavage of an extracellular region of the receptor by endogenous or exogenous proteases, which reveals a tethered ligand sequence capable of auto-activating the receptor. A considerable body of evidence has emerged over the past 20 years supporting a prominent role for PARs in a variety of human physiological and pathophysiological processes, and thus substantial attention has been directed towards developing drug-like molecules that activate or block PARs via non-proteolytic pathways. PARs are widely expressed within the respiratory tract, and their activation appears to exert significant modulatory influences on the level of bronchomotor tone, as well as on the inflammatory processes associated with a range of respiratory tract disorders. Nevertheless, there is debate as to whether the principal response to PAR activation is an augmentation or attenuation of airways inflammation. In this context, an important action of PAR activators may be to promote the generation and release of prostanoids, such as prostglandin E(2), which have well-established anti-inflammatory effects in the lung. In this review, we primarily focus on the relationship between PARs, prostaglandins and inflammatory processes in the lung, and highlight their potential role in selected respiratory tract disorders, including pulmonary fibrosis, asthma and chronic obstructive pulmonary disease.

PPARalpha/gamma-Independent Effects of PPARalpha/gamma Ligands on Cysteinyl Leukotriene Production in Mast Cells

Peroxisome proliferator-activated receptor (PPAR) α ligands (Wy-14,643, and fenofibrate) and PPARγ ligands (troglitazone and ciglitazone) inhibit antigen-induced cysteinyl leukotriene production in immunoglobulin E-treated mast cells. The inhibitory effect of these ligands on cysteinyl leukotriene production is quite strong and is almost equivalent to that of the anti-asthma compound zileuton. To develop new aspects for anti-asthma drugs the pharmacological target of these compounds should be clarified. Experiments with bone-marrow-derived mast cells from PPARα knockout mice and pharmacological inhibitors of PPARγ suggest that the inhibitory effects of these ligands are independent of PPARs α and γ. The mechanisms of the PPAR-independent inhibition by these agents on cysteinyl leukotriene production are discussed in this review.

The many faces of PPARgamma: anti-inflammatory by any means?

The peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear receptor superfamily, a group of transcription factors that regulate expression of their target genes upon ligand binding. As endogenous ligands, oxidized fatty acids and prostanoids can bind to and activate the receptor. Natural and synthetic PPARgamma activators have been studied extensively in many inflammatory settings and in most instances they have been shown to be anti-inflammatory. In this review we give an overview of the different molecular mechanisms how PPARgamma and its agonists exert their anti-inflammatory effects both at the cellular level and the level of the organism. The action of PPARgamma in acute and chronic inflammatory diseases and disease models will be presented.

Therapeutic approaches for control of transcription factors in allergic disease

The inflammatory response observed in allergic disease involves multiple cell types but is orchestrated in part by the T(H)2 cytokines IL-4, IL-5, and IL-13. In recent years, the transcription factors that control the expression and function of these cytokines have been elucidated, including signal transducer and activator of transcription 6, GATA3, nuclear factor of activated T cells, and nuclear factor kappaB. These molecules are attractive targets for therapeutic intervention because they regulate the expression of numerous effector molecules and functions simultaneously. For instance, the immunosuppressive agents glucocorticoids and cyclosporin A both function by repressing the activity of transcription factors through a variety of mechanisms. In this review we examine the role of each transcription factor in allergic disease and discuss approaches that have been taken to therapeutically interfere with transcription factor function in allergic disease.