Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) activation suppresses ischemic induction of Egr-1 and its inflammatory gene targets

The role of sRAGE in cardiovascular diseases

Advanced glycation end products (AGEs), by-products of glucose metabolism, have been linked to the emergence of cardiovascular disorders (CVD). AGEs can cause tissue damage in four different ways: (1) by altering protein function, (2) by crosslinking proteins, which makes tissue stiffer, (3) by causing the generation of free radicals, and (4) by activating an inflammatory response after binding particular AGE receptors, such as the receptor for advanced glycation end products (RAGE). It is suggested that the soluble form of RAGE (sRAGE) blocks ligand-mediated pro-inflammatory and oxidant activities by serving as a decoy. Therefore, several studies have investigated the possible anti-inflammatory and anti-oxidant characteristics of sRAGE, which may help lower the risk of CVD. According to the results of various studies, the relationship between circulating sRAGE, cRAGE, and esRAGE and CVD is inconsistent. To establish the potential function of sRAGE as a therapeutic target in the treatment of cardiovascular illnesses, additional studies are required to better understand the relationship between sRAGE and CVD. In this review, we explored the potential function of sRAGE in different CVD, highlighting unanswered concerns and outlining the possibilities for further investigation.

PPARγ inhibits small airway remodeling through mediating the polarization homeostasis of alveolar macrophages in COPD

The role of Peroxisome Proliferator-Activated Receptor-γ (PPARγ) in alveolar macrophages(AMs) polarization homeostasis is closely associated with airway remodeling in COPD, but the definite mechanism remains unclear. In this study, elevated percentage of M1-type AMs and the expression of functionally cytokines were found in COPD patients and mice, which closely related to the disease severity. PPARγ was markedly up-regulated in M2-type AMs and down-regulated in M1-type AMs, and was associated with disease severity in COPD. Co-cultured with M1- or M2-type AMs promoted the epithelial-mesenchymal transition (EMT) of airway epithelial cells and the proliferation of airway smooth muscle cells. Moreover, airway remodeling and functional damage were observed in both IL4R-/- COPD mice with runaway M1-type AMs polarization and TLR4-/- COPD mice with runaway M2-type AMs polarization. Cigarette extract (CS) or lipopolysaccharide (LPS) stimulated PPARγ-/- AMs showed more serious polarization disorder towards M1, as well as CS induced PPARγ-/- COPD mice, which led to more severe airway inflammation, lung function damage, and airway remodeling. Treatment with PPARγ agonist significantly improved the polarization disorder and function activity in CS/LPS stimulated-AMs by inhibiting the JAK-STAT, MAPK and NF-κB pathways, and alleviated the airway inflammation, restored the lung function and suppressed airway remodeling in CS induced-COPD mice. Our research demonstrates that polarization homeostasis of AMs mediated by PPARγ has the protective effect in airway remodeling, and may be a novel therapeutic target for the intervention and treatment of airway remodeling in COPD.

Tumor Progression Locus 2 Protects against Acute Respiratory Distress Syndrome in Influenza A Virus-Infected Mice

Excessive inflammation in patients with severe influenza disease may lead to acute lung injury that results in acute respiratory distress syndrome (ARDS). ARDS is associated with alveolar damage and pulmonary edema that severely impair gas exchange, leading to hypoxia. With no existing FDA-approved treatment for ARDS, it is important to understand the factors that lead to virus-induced ARDS development to improve prevention, diagnosis, and treatment. We have previously shown that mice deficient in the serine-threonine mitogen-activated protein kinase, Tpl2 (MAP3K8 or COT), succumb to infection with a typically low-pathogenicity strain of influenza A virus (IAV; HKX31, H3N2 [x31]). The goal of the current study was to evaluate influenza A virus-infected Tpl2-/- mice clinically and histopathologically to gain insight into the disease mechanism. We hypothesized that Tpl2-/- mice succumb to IAV infection due to development of ARDS-like disease and pulmonary dysfunction. We observed prominent signs of alveolar septal necrosis, hyaline membranes, pleuritis, edema, and higher lactate dehydrogenase (LDH) levels in the lungs of IAV-infected Tpl2-/- mice compared to wild-type (WT) mice from 7 to 9 days postinfection (dpi). Notably, WT mice showed signs of regenerating epithelium, indicative of repair and recovery, that were reduced in Tpl2-/- mice. Furthermore, biomarkers associated with human ARDS cases were upregulated in Tpl2-/- mice at 7 dpi, demonstrating an ARDS-like phenotype in Tpl2-/- mice in response to IAV infection. IMPORTANCE This study demonstrates the protective role of the serine-threonine mitogen-activated protein kinase, Tpl2, in influenza virus pathogenesis and reveals that host Tpl2 deficiency is sufficient to convert a low-pathogenicity influenza A virus infection into severe influenza disease that resembles ARDS, both histopathologically and transcriptionally. The IAV-infected Tpl2-/- mouse thereby represents a novel murine model for studying ARDS-like disease that could improve our understanding of this aggressive disease and assist in the design of better diagnostics and treatments.

hsa-miR-518-5p/hsa-miR-3135b Regulates the REL/SOD2 Pathway in Ischemic Cerebral Infarction

Objectives

Ischemic cerebral infarction (ICI) is a fatal neurovascular disorder. A bioinformatics approach based on single-cell and bulk RNA-seq analyses was applied to investigate the pathways and genes involved in ICI and study the expression profile of these genes.

Methods

First, the aberrantly regulated “small-molecule ribonucleic acids” [microRNA (miRNAs)] and messenger RNAs (mRNAs) were analyzed using transcriptome data from the ischemic brain infarction dataset of the Gene Expression Omnibus (GEO) database. In mouse cerebrovascular monocytes, the single-cell regulatory network inference and clustering (SCENIC) workflow was used to identify key transcription factors (TFs). Then, the two miRNA-TF-mRNA interaction networks were constructed. Moreover, the molecular complex detection (MCODE) extracted the core sub-networks and identified the important TFs within these sub-networks. Finally, whole blood samples were collected for validation of the expression of critical molecules in ICI.

Results

We identified four cell types and 266 regulons in mouse cerebrovascular monocytes using SCENIC analysis. Moreover, 112 differently expressed miRNAs and 3,780 differentially expressed mRNAs were identified. We discovered potential biomarkers in ICI by building a miRNA-TF-mRNA interaction network. The hsa-miR-518-5p/hsa-miR-3135b/REL/SOD2 was found to play a potential role in ICI progression. The expression of REL and superoxide dismutase 2 (SOD2) was significantly elevated in the ICI group in the clinical cohort (P < 0.05). Furthermore, a REL expression was elevated in endothelial cells and fibroblasts at the single-cell level, indicating that REL is a cell-specific regulon. Functional enrichment analyses revealed that REL is primarily engaged in neurotransmitter activity and oxidative phosphorylation.

Conclusions

Our research uncovered novel biomarkers for ICI of neurovascular disease. The hsa-miR-518-5p/hsa-miR-3135b may regulate the REL/SOD2 pathway in ICI progression.

PPARγ/LXRα axis mediated phenotypic plasticity of lung fibroblasts in silica-induced experimental silicosis

Silicosis is a disease mainly caused by pulmonary interstitial fibrosis caused by long-term inhalation of dust with excessively high content of free SiO₂. Transdifferentiation of lung fibroblasts into myofibroblasts is an important cellular basis for silicosis, but the key transcription factors (TFs) involved in this process are still unclear. In order to explore the biological regulation of transcription factor PPARγ/LXRα in silica-induced pulmonary fibrosis, this study explored the molecular mechanism of PPARγ/LXRα involved in regulating transcription factors related to SiO₂-induced lung injury at the cellular level and in animal models. ChIP-qPCR detected that PPARγ directly regulated the transcriptional activity of the LXRα gene promoter, while the PPARγ agonist RSG increased the expression of LXRα. In addition, we demonstrated in the cell model that upregulation of LXRα can inhibit silica-mediated fibroblast transdifferentiation, accompanied by an increase in the expression of SREBF1, PLTP and ABCA1. The results of LXRα silencing experiment matched those of overexpression experiment. These studies explored the role of LXRα in plasticity and phenotypic transformation between lung fibroblasts and myofibroblasts. Therefore, inhibiting or reversing the transdifferentiation of lung fibroblasts to myofibroblasts by intervening PPARγ/LXRα may provide a new therapeutic target for the treatment of silicosis.

A Role for Peroxisome Proliferator-Activated Receptor Gamma Agonists in Counteracting the Degeneration of Cardiovascular Grafts

ABSTRACT

Aortic valve replacement for severe stenosis is a standard procedure in cardiovascular medicine. However, the use of biological prostheses has limitations especially in young patients because of calcifying degeneration, resulting in implant failure. Pioglitazone, a peroxisome proliferator-activated receptor gamma (PPAR-gamma) agonist, was shown to decrease the degeneration of native aortic valves. In this study, we aim to examine the impact of pioglitazone on inflammation and calcification of aortic valve conduits (AoC) in a rat model. Cryopreserved AoC (n = 40) were infrarenally implanted into Wistar rats treated with pioglitazone (75 mg/kg chow; n = 20, PIO) or untreated (n = 20, controls). After 4 or 12 weeks, AoC were explanted and analyzed by histology, immunohistology, and polymerase chain reaction. Pioglitazone significantly decreased the expression of inflammatory markers and reduced the macrophage-mediated inflammation in PIO compared with controls after 4 (P = 0.03) and 12 weeks (P = 0.012). Chondrogenic transformation was significantly decreased in PIO after 12 weeks (P = 0.001). Calcification of the intima and media was significantly reduced after 12 weeks in PIO versus controls (intima: P = 0.008; media: P = 0.025). Moreover, echocardiography revealed significantly better functional outcome of the AoC in PIO after 12 weeks compared with control. Interestingly, significantly increased intima hyperplasia could be observed in PIO compared with controls after 12 weeks (P = 0.017). Systemic PPAR-gamma activation prevents inflammation as well as intima and media calcification in AoC and seems to inhibit functional impairment of the implanted aortic valve. To further elucidate the therapeutic role of PPAR-gamma regulation for graft durability, translational studies and long-term follow-up data should be striven for.

Chinese Herbs and Repurposing Old Drugs as Therapeutic Agents in the Regulation of Oxidative Stress and Inflammation in Pulmonary Diseases

Several pro-inflammatory factors and proteins have been characterized that are involved in the pathogenesis of inflammatory diseases, including acute respiratory distress syndrome, chronic obstructive pulmonary disease, and asthma, induced by oxidative stress, cytokines, bacterial toxins, and viruses. Reactive oxygen species (ROS) act as secondary messengers and are products of normal cellular metabolism. Under physiological conditions, ROS protect cells against oxidative stress through the maintenance of cellular redox homeostasis, which is important for proliferation, viability, cell activation, and organ function. However, overproduction of ROS is most frequently due to excessive stimulation of either the mitochondrial electron transport chain and xanthine oxidase or reduced nicotinamide adenine dinucleotide phosphate (NADPH) by pro-inflammatory cytokines, such as interleukin-1β and tumor necrosis factor α. NADPH oxidase activation and ROS overproduction could further induce numerous inflammatory target proteins that are potentially mediated via Nox/ROS-related transcription factors triggered by various intracellular signaling pathways. Thus, oxidative stress is considered important in pulmonary inflammatory processes. Previous studies have demonstrated that redox signals can induce pulmonary inflammatory diseases. Thus, therapeutic strategies directly targeting oxidative stress may be effective for pulmonary inflammatory diseases. Therefore, drugs with anti-inflammatory and anti-oxidative properties may be beneficial to these diseases. Recent studies have suggested that traditional Chinese medicines, statins, and peroxisome proliferation-activated receptor agonists could modulate inflammation-related signaling processes and may be beneficial for pulmonary inflammatory diseases. In particular, several herbal medicines have attracted attention for the management of pulmonary inflammatory diseases. Therefore, we reviewed the pharmacological effects of these drugs to dissect how they induce host defense mechanisms against oxidative injury to combat pulmonary inflammation. Moreover, the cytotoxicity of oxidative stress and apoptotic cell death can be protected via the induction of HO-1 by these drugs. The main objective of this review is to focus on Chinese herbs and old drugs to develop anti-inflammatory drugs able to induce HO-1 expression for the management of pulmonary inflammatory diseases.

Systematical Identification of the Protective Effect of Danhong Injection and BuChang NaoXinTong Capsules on Transcription Factors in Cerebral Ischemia Mice Brain

Cerebral ischemia has led to a high rate of both disability and mortality with massive healthcare costs. Although transcriptional regulation is typically mediated by different combinations of TFs, a combined regulatory unit to synergistically activate transcription has remained unclear in cerebral ischemia, especially in different drug treatments. In this study, TFs alterations after 6 h cerebral ischemic injury and repair were performed by a concatenated tandem array of consensus transcription factor response elements (catTFREs), and vital TFs were obtained by TFs-target imbalanced network. Drug intervention used Danhong injection (DHI) and BNC (BuChang NaoXinTong Capsules), which has been widely prescribed in Chinese herb medicine for the treatment of cerebrovascular and cardiovascular diseases. There were 198 TFs identified after 6 h MCAO operation, and six TFs (Sox2, Smad3, FoxO1, Creb1, Egr,1 and Smad4) were considered as critical TFs in response to cerebral ischemia. Moreover, Smad3 was identified as a hub TF among six vital TFs, and the transcription activity of Smad3 was further verified. These 6 TFs were all reversed by DHI or BNC, indicating different medications may regulate different transcription factors through TF synergy. Moreover, validation results indicated that Smad3 was a putative target TF for DHI and BNC-mediated protection against cerebral ischemia. The observations of the present study provide a fresh understanding of biomolecules and possible new avenues for therapeutic interventions, in addition to the new intervention pattern for different treatments for ischemia stroke.

Peroxisome Proliferator-Activated Receptors as Molecular Links between Caloric Restriction and Circadian Rhythm

The circadian rhythm plays a chief role in the adaptation of all bodily processes to internal and environmental changes on the daily basis. Next to light/dark phases, feeding patterns constitute the most essential element entraining daily oscillations, and therefore, timely and appropriate restrictive diets have a great capacity to restore the circadian rhythm. One of the restrictive nutritional approaches, caloric restriction (CR) achieves stunning results in extending health span and life span via coordinated changes in multiple biological functions from the molecular, cellular, to the whole-body levels. The main molecular pathways affected by CR include mTOR, insulin signaling, AMPK, and sirtuins. Members of the family of nuclear receptors, the three peroxisome proliferator-activated receptors (PPARs), PPARα, PPARβ/δ, and PPARγ take part in the modulation of these pathways. In this non-systematic review, we describe the molecular interconnection between circadian rhythm, CR-associated pathways, and PPARs. Further, we identify a link between circadian rhythm and the outcomes of CR on the whole-body level including oxidative stress, inflammation, and aging. Since PPARs contribute to many changes triggered by CR, we discuss the potential involvement of PPARs in bridging CR and circadian rhythm.

PPARγ Activation-Mediated Egr-1 Inhibition Benefits Against Brain Injury in an Experimental Ischaemic Stroke Model

BACKGROUND

Inflammatory response is a critical contributor to cerebral ischaemia injuries and blood-brain barrier (BBB) dysfunction. Early growth response-1 (Egr-1), an oxygen-sensing transcription factor which is rapidly and markedly triggered in ischaemic events, acts as a master switch coordinating the upregulation of multiple target proinflammatory genes. Here, we explored whether peroxisome proliferator-activated receptor-gamma (PPARγ) activation by telmisartan can modulate Egr-1 expression and the subsequent inflammatory responses in a rat model of cerebral ischaemia.

METHODS

Cerebral ischaemia was induced in rats by middle cerebral artery occlusion (MCAO). Brain injury was evaluated by brain water content, infarct volume, and Evans blue dye extravasation. Egr-1 and claudin-5 levels were assessed by western blot and real-time polymerase chain reaction.

RESULTS

MCAO-provoked Egr-1 expression was time dependent, peaking at 24 h and continuing to 72 h. The elevation in Egr-1 was coupled with a reduction in claudin-5. Telmisartan treatment significantly corrected the alterations of Egr-1 and claudin-5, alleviated the neurological deficits, and reduced brain water content, infarct volume, and Evans blue dye extravasation 24 h after MCAO. However, all the benefits of telmisartan were reversed by antagonising PPARγ with GW9662.

CONCLUSION

Egr-1, a proinflammatory factor, is positively associated with post-ischaemic inflammation and the associated BBB dysfunction. PPARγ serves as an upstream transcription factor of the Egr-1 cascade. Targeting Egr-1 may emerge as a potential strategy to suppress inflammatory responses following ischaemic stroke.

Peroxisome Proliferator-Activated Receptors and Caloric Restriction-Common Pathways Affecting Metabolism, Health, and Longevity

Caloric restriction (CR) is a traditional but scientifically verified approach to promoting health and increasing lifespan. CR exerts its effects through multiple molecular pathways that trigger major metabolic adaptations. It influences key nutrient and energy-sensing pathways including mammalian target of rapamycin, Sirtuin 1, AMP-activated protein kinase, and insulin signaling, ultimately resulting in reductions in basic metabolic rate, inflammation, and oxidative stress, as well as increased autophagy and mitochondrial efficiency. CR shares multiple overlapping pathways with peroxisome proliferator-activated receptors (PPARs), particularly in energy metabolism and inflammation. Consequently, several lines of evidence suggest that PPARs might be indispensable for beneficial outcomes related to CR. In this review, we present the available evidence for the interconnection between CR and PPARs, highlighting their shared pathways and analyzing their interaction. We also discuss the possible contributions of PPARs to the effects of CR on whole organism outcomes.

Oridonin inhibits LPS-induced inflammation in human gingival fibroblasts by activating PPARγ

Oridonin, the major terpene isolated from Rabdosia rubescens, has been used as dietary supplement. Recently, it has been known to exhibit anti-inflammatory effect. This study we employed an in vitro model of LPS-stimulated human gingival fibroblasts to investigate the anti-inflammatory effects and mechanism of oridonin. Oridonin (10-30 μg/mL) was administrated 1 h before LPS treatment. The results showed that oridonin significantly inhibited inflammatory mediators PGE₂, NO, IL-6, and IL-8 production. Immunoblotting experiments revealed that oridonin reduced the expression of phosphorylation levels of NF-κB p65 and IκBα. Furthermore, the expression of PPARγ was up-regulated by the treatment of oridonin. Further studies showed that PPARγ inhibitor GW9662 could reverse the inhibition of oridonin on PGE₂, NO, IL-6, and IL-8 production. In conclusion, oridonin inhibited LPS-induced microglia activation through activating PPARγ.

MiR-27-3p regulates TLR2/4-dependent mouse alveolar macrophage activation by targetting PPARγ

Activation of alveolar macrophages (AMs) and the release of cytokines play critical roles in the pathogenesis of chronic obstructive pulmonary disease (COPD). However, little is known about the mechanisms of AM activation. miRNAs have recently emerged as key regulators of inflammation and as mediators of macrophage activation and polarization. We identified potential miRNAs related to AM activation using miRNA microarray analysis, which showed that miR-27-3p expression was up-regulated in AMs and the lung tissues of mice exposed to cigarette smoke (CS)/lipopolysaccharide (LPS), and found that miR-27-3p regulated proinflammatory cytokine production and AM polarization depending on TLR2/4 intracellular signaling in AMs. We also found that miR-27-3p controlled TLR2/4 signaling in AMs via targetting the 3′-UTR sequences of peroxisome proliferator-activated receptor γ (PPARγ) and inhibiting PPARγ activation. Moreover, we found that PPARγ activation not only inhibited CS/LPS-induced TLR2/4 expression and miR-27-3p-mediated TLR2/4 signaling cascades involving the nuclear factor-κB (NF-κB), c-Jun NH2-terminal kinase (JNK)/p38, and Janus kinase-signal transducer and activator of transcription (JAK/STAT) pathways in AMs but also ameliorated CS/LPS-induced AM activation and pulmonary inflammation. Our study revealed that miR-27-3p mediated AM activation by the inhibition of PPARγ activation and sensitization of TLR signaling.

Peroxisome Proliferator-Activated Receptor γ Regulates the V-Ets Avian Erythroblastosis Virus E26 Oncogene Homolog 1/microRNA-27a Axis to Reduce Endothelin-1 and Endothelial Dysfunction in the Sickle Cell Mouse Lung

Pulmonary hypertension (PH), a serious complication of sickle cell disease (SCD), causes significant morbidity and mortality. Although a recent study determined that hemin release during hemolysis triggers endothelial dysfunction in SCD, the pathogenesis of SCD-PH remains incompletely defined. This study examines peroxisome proliferator-activated receptor γ (PPARγ) regulation in SCD-PH and endothelial dysfunction. PH and right ventricular hypertrophy were studied in Townes humanized sickle cell (SS) and littermate control (AA) mice. In parallel studies, SS or AA mice were gavaged with the PPARγ agonist, rosiglitazone (RSG), 10 mg/kg/day, or vehicle for 10 days. In vitro, human pulmonary artery endothelial cells (HPAECs) were treated with vehicle or hemin for 72 hours, and selected HPAECs were treated with RSG. SS mice developed PH and right ventricular hypertrophy associated with reduced lung levels of PPARγ and increased levels of microRNA-27a (miR-27a), v-ets avian erythroblastosis virus E26 oncogene homolog 1 (ETS1), endothelin-1 (ET-1), and markers of endothelial dysfunction (platelet/endothelial cell adhesion molecule 1 and E selectin). HPAECs treated with hemin had increased ETS1, miR-27a, ET-1, and endothelial dysfunction and decreased PPARγ levels. These derangements were attenuated by ETS1 knockdown, inhibition of miR-27a, or PPARγ overexpression. In SS mouse lung or in hemin-treated HPAECs, activation of PPARγ with RSG attenuated reductions in PPARγ and increases in miR-27a, ET-1, and markers of endothelial dysfunction. In SCD-PH pathogenesis, ETS1 stimulates increases in miR-27a levels that reduce PPARγ and increase ET-1 and endothelial dysfunction. PPARγ activation attenuated SCD-associated signaling derangements, suggesting a novel therapeutic approach to attenuate SCD-PH pathogenesis.

Protective Effect of PPARγ Agonists on Cerebellar Tissues Oxidative Damage in Hypothyroid Rats

The aim of the current study was to investigate the effects of peroxisome proliferator-activated receptor gamma (PPARγ) agonists on cerebellar tissues oxidative damage in hypothyroid rats. The animals included seven groups: group I (control), the animals received drinking water; group II, the animals received 0.05% propylthiouracil (PTU) in drinking water; besides PTU, the animals in groups III, IV, V, VI, and VII, were injected with 20 mg/kg vitamin E (Vit E), 10 or 20 mg/kg pioglitazone, and 2 or 4 mg/kg rosiglitazone, respectively. The animals were deeply anesthetized and the cerebellar tissues were removed for biochemical measurements. PTU administration reduced thiol content, superoxide dismutase (SOD), and catalase (CAT) activities in the cerebellar tissues while increasing malondialdehyde (MDA) and nitric oxide (NO) metabolites. Vit E, pioglitazone, and rosiglitazone increased thiol, SOD, and CAT in the cerebellar tissues while reducing MDA and NO metabolites. The results of present study showed that, similar to Vit E, both rosiglitazone and pioglitazone as PPARγ agonists exerted protective effects against cerebellar tissues oxidative damage in hypothyroid rats.

Egr-1 identifies neointimal remodeling and relates to progression in human pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is hallmarked by the development of neointimal lesions. The transcription factor Egr-1 seems to play a critical role in neointimal formation in experimental PAH and was identified as a putative target for intervention. In this study we investigated whether Egr-1 is also associated with neointimal-type vascular remodeling in different forms of human PAH or pulmonary hypertension.

METHODS

Using immunohistochemistry, we studied Egr-1 expression specifically in a wide morphologic spectrum of pulmonary arteries in the lung tissue of 72 patients with different forms and stages of PAH, specifically idiopathic PAH (n = 18), advanced-stage congenital heart disease‒associated PAH (PAH-CHD) (n = 21), early-stage PAH-CHD (n = 19) and non-neointimal hypoxic pulmonary hypertension (PH) (n = 4), and controls (n = 10).

RESULTS

In PAH patients, pulmonary vascular expression of Egr-1 protein was abundant, whereas it was sporadic in non-neointimal (hypoxic) PH patients and controls. In PAH-CHD, protein expression was more pronounced in patients with advanced vascular lesions compared to those with less advanced lesions, such as medial hypertrophy.

CONCLUSIONS

Pulmonary vascular Egr-1 expression is significantly increased in patients with PAH, appears specifically associated with neointimal-type vascular remodeling, and correlates with disease progression. These data translate the critical role of Egr-1 in the development of experimental PAH to human pulmonary vascular disease forms.

Ameliorative potential of pioglitazone and ceftriaxone alone and in combination in rat model of neuropathic pain: Targeting PPARγ and GLT-1 pathways

BACKGROUND

The relation between glutamate homeostasis and PPAR gamma has got tremendous importance in nerve trauma and pain. Present study has been designed to elucidate the interaction between the GLT-1 activator (ceftriaxone) and PPAR gamma agonist (pioglitazone) in the spinal nerve ligation induced neuropathic pain.

METHODS

Male SD rats were subjected to spinal nerve ligation to induce neuropathic pain. Pioglitazone, ceftriaxone and their combination treatments were given for 28 days. Various behavioral, biochemical, neuroinflammatory and apoptotic mediators were assessed subsequently.

RESULTS

In the present study, ligation of L5 and L6 spinal nerves resulted in marked hyperalgesia and allodynia to different mechanical and thermal stimuli. In addition there is marked increase in oxidative-nitrosative stress parameters, inflammatory and apoptotic markers in spinal cord of spinal nerve ligated rats. Treatment with pioglitazone and ceftriaxone significantly prevented these behavioral, biochemical, mitochondrial and cellular alterations in rats. Further, combination of pioglitazone (10mg/kg, ip) with ceftriaxone (100mg/kg, ip) significantly potentiated the protective effects as compared to their effects per se.

CONCLUSION

Based on these results we propose that possible interplay between the neuroprotective effects of pioglitazone and ceftriaxone exists in suppressing the behavioral, biochemical, mitochondrial, neuroinflammatory and apoptotic cascades in spinal nerve ligation induced neuropathic pain in rats.

Pioglitazone restores IGFBP-3 levels through DNA PK in retinal endothelial cells cultured in hyperglycemic conditions

PURPOSE

Previously, we reported that pioglitazone prevented insulin resistance and cell death in type 2 diabetic retina by reducing TNFα and suppressor of cytokine signaling 3 (SOCS3) levels. Numerous reports suggest prominent vasoprotective effects of insulin growth factor binding protein-3 (IGFBP-3) in diabetic retinopathy. We hypothesized that pioglitazone protects against retinal cell apoptosis by regulating IGFBP-3 levels, in addition to reducing TNFα. The current study explored potential IGFBP-3 regulatory pathways by pioglitazone in retinal endothelial cells cultured in high glucose.

METHODS

Primary human retinal endothelial cells (REC) were grown in normal (5 mM) and high glucose (25 mM) and treated with pioglitazone for 24 hours. Cell lysates were processed for Western blotting and ELISA analysis to evaluate IGFBP-3, TNFα, and cleaved caspase 3 protein levels.

RESULTS

Our results show that treatment with pioglitazone restored the high glucose-induced decrease in IGFBP-3 levels. This regulation was independent of TNFα actions, as reducing TNFα levels with siRNA did not prevent pioglitazone from increasing IGFBP-3 levels. Pioglitazone required protein kinase A (PKA) and DNA-dependent protein kinase (DNA PK) activity to regulate IGFBP-3, as specific inhibitors for each protein prevented pioglitazone-mediated normalization of IGFBP-3 in high glucose. Insulin growth factor binding protein-3 activity was increased and apoptosis decreased by pioglitazone, which was eliminated when serine site 156 of IGFBP-3 was mutated suggesting a key role of this phosphorylation site in pioglitazone actions.

CONCLUSIONS

Our findings suggest that pioglitazone mediates regulation of IGFBP-3 via activation of PKA/DNA PK pathway in hyperglycemic retinal endothelial cells.

Minireview: Challenges and opportunities in development of PPAR agonists

The clinical impact of the fibrate and thiazolidinedione drugs on dyslipidemia and diabetes is driven mainly through activation of two transcription factors, peroxisome proliferator-activated receptors (PPAR)-α and PPAR-γ. However, substantial differences exist in the therapeutic and side-effect profiles of specific drugs. This has been attributed primarily to the complexity of drug-target complexes that involve many coregulatory proteins in the context of specific target gene promoters. Recent data have revealed that some PPAR ligands interact with other non-PPAR targets. Here we review concepts used to develop new agents that preferentially modulate transcriptional complex assembly, target more than one PPAR receptor simultaneously, or act as partial agonists. We highlight newly described on-target mechanisms of PPAR regulation including phosphorylation and nongenomic regulation. We briefly describe the recently discovered non-PPAR protein targets of thiazolidinediones, mitoNEET, and mTOT. Finally, we summarize the contributions of on- and off-target actions to select therapeutic and side effects of PPAR ligands including insulin sensitivity, cardiovascular actions, inflammation, and carcinogenicity.

A critical role for Egr-1 during vascular remodelling in pulmonary arterial hypertension

AIMS

Pulmonary arterial hypertension (PAH) is characterized by the development of unique neointimal lesions in the small pulmonary arteries, leading to increased right ventricular (RV) afterload and failure. Novel therapeutic strategies are needed that target these neointimal lesions. Recently, the transcription factor Egr-1 (early growth response protein 1) was demonstrated to be up-regulated early in experimental neointimal PAH. Its effect on disease development, however, is unknown. We aimed to uncover a novel role for Egr-1 as a molecular inductor for disease development in PAH.

METHODS AND RESULTS

In experimental flow-associated PAH in rats, we investigated the effects of Egr-1 down-regulation on pulmonary vascular remodelling, including neointimal development, and disease progression. Intravenous administration of catalytic oligodeoxynucleotides (DNA enzymes, DNAzymes) resulted in down-regulation of pulmonary vascular Egr-1 expression. Compared with vehicle or scrambled DNAzymes, DNAzymes attenuated pulmonary vascular remodelling, including the development of occlusive neointimal lesions. Selective down-regulation of Egr-1 in vivo led to reduced expression of vascular PDGF-B, TGF-β, IL-6, and p53, resulting in a reduction of vascular proliferation and increased apoptosis. DNAzyme treatment further attenuated pulmonary vascular resistance, RV systolic pressure, and RV hypertrophy. In contrast, in non-neointimal PH rodents, DNAzyme treatment had no effect on pulmonary vascular and RV remodelling. Finally, pharmacological inhibition of Egr-1 with pioglitazone, a peroxisome proliferator activated receptor-γ ligand, attenuated vascular remodelling including the development of neointimal lesions.

CONCLUSIONS

These results indicate that Egr-1 governs pulmonary vascular remodelling and the development of characteristic vascular neointimal lesions in flow-associated PAH. Egr-1 is therefore a potential target for future PAH treatment.

Regulation of cigarette smoke-induced toll-like receptor 4 expression by peroxisome proliferator-activated receptor-gamma agonists in bronchial epithelial cells

BACKGROUND AND OBJECTIVE

This study was designed to determine the effects of peroxisome proliferator-activated receptor-gamma (PPARγ) on airway inflammatory response to cigarette smoke (CS) exposure.

METHODS

For the in vivo experiments, 50 male Wistar rats were randomly assigned to one of four groups and were exposed to CS and pretreatment with a PPARγ agonist, rosiglitazone or a vehicle (saline). PPARγ antagonist bisphenol A diglycidyl ether (BADGE) or saline was administered before rosiglitazone treatment. Leukotriene B4 (LTB4) and interleukin-8 (IL-8) were measured by enzyme-linked immunosorbent assay. PPARγ and toll-like receptor 4 (TLR4) expression levels were assessed by immunohistochemistry and real-time polymerase chain reaction. For the in vitro experiments, human bronchial epithelial cells were stimulated with CS or phosphate buffer saline, pretreated with PPARγ agonist rosiglitazone or 15-deoxy-(Δ12,14)-PG J2 before CS exposure. BADGE was administered prior to the agonist treatment. PPARγ, TLR4 and inhibitor of κB (IκBα) expression levels were assessed by Western bot.

RESULTS

CS exposure decreased PPARγ expression, as well as increased IL-8, LTB4 and TLR4 expression levels in bronchial epithelial cells in vivo and in vitro. Moreover, PPARγ ligands counteracted CS-induced airway inflammation by reducing IL-8 and LTB4 expression levels that are associated with TLR4 and nuclear factor-kappa B (NF-κB).

CONCLUSION

CS exposure increased the pro-inflammatory activity of bronchial epithelial cells by affecting PPARγ expression. Moreover, PPARγ may play a significant role as a modulator of the TLR4-dependent inflammatory pathway through NF-κB in bronchial epithelial cells.

Effect of salidroside on lung injury by upregulating peroxisome proliferator-activated receptor γ expression in septic rats

Successful drug treatment for sepsis-related acute lung injury (ALI) remains a major clinical problem. Thus, the aim of the present study was to investigate the beneficial effects of salidroside on ameliorating cecal ligation and puncture (CLP)-induced lung inflammation. Rats underwent CLP surgery to induce ALI and 800 mg/kg salidroside (i.v.) was administered 24 h after the CLP challenge. Subsequently, biochemical changes in the blood and lung tissues, as well as morphological and histological alterations in the lungs, that were associated with inflammation and injury were analysed. CLP was shown to significantly increase the serum levels of plasma tumour necrosis factor-α and interleukin-6, -1β and-10. In addition, CLP increased pulmonary oedema, thickened the alveolar septa and caused inflammation in the lung cells. These changes were ameliorated by the administration of 800 mg/kg salidroside (i.v.) 24 h after the CLP challenge. This post-treatment drug administration also significantly attenuated the lipopolysaccharide-induced activation of nuclear factor-κβ and increased the release of peroxisome proliferator-activated receptor γ in the lung tissue. Therefore, salidroside administered following the induction of ALI by CLP significantly prevented and reversed lung tissue injuries. The positive post-treatment effects of salidroside administration indicated that salidroside may be a potential candidate for the management of lung inflammation in CLP-induced endotoxemia and septic shock.

PPARγ agonists regulate tobacco smoke-induced Toll like receptor 4 expression in alveolar macrophages

Background

Peroxisome proliferator-activated receptor-gamma (PPARγ) is a ligand-activated transcription factor that exerts multiple biological effects. Growing evidence suggests that PPARγ plays an important role in inflammation; however, the effects of this transcription factor on the inflammation caused by smoking are unclear.

Methods

We measured the expression of inflammatory cytokines (leukotriene B4, LTB4 and interleukin 8, IL-8), PPARγ and toll-like receptors (TLR2 and TLR4) in alveolar macrophages (AMs) harvested from rats exposed to cigarette smoke (CS) for 3 months in vivo. Some of the rats were pre-treated with rosiglitazone (PPARγ agonist, 3 mg/kg/day, ip), rosiglitazone (3 mg/kg/day, ip) + BADGE (bisphenol A diglycidyl ether, a PPARγ antagonist, 30 mg/kg/day, ig), or BADGE alone (30 mg/kg/day, ig). We also measured the expression of PPARγ, TLR2, TLR4 and nuclear factor-kappaB (NF-κB) in AMs gained from normal rats, which exposed to 5% CSE (cigarette smoke extract) for 12hrs, respectively pretreated with PBS, rosiglitazone (30 uM), rosiglitazone (30 uM) + BADGE (100 uM), 15d-PGJ2 (PPARγ agonist, 5 uM), 15d-PGJ2 (5 uM) + BADGE (100 uM), or BADGE (100 uM) alone for 30 min in vitro.

Results

In vivo, rosiglitazone counteracted CS-induced LTB4 and IL-8 release and PPARγ downregulation, markedly lowering the expression of TLR4 and TLR2. In vitro, both rosiglitazone and 15d-PGJ2 inhibited CS-induced inflammation through the TLR4 signaling pathway.

Conclusions

These results suggest that PPARγ agonists regulate inflammation in alveolar macrophages and may play a role in inflammatory diseases such as COPD.

Ribosomal alteration-derived signals for cytokine induction in mucosal and systemic inflammation: noncanonical pathways by ribosomal inactivation

Ribosomal inactivation damages 28S ribosomal RNA by interfering with its functioning during gene translation, leading to stress responses linked to a variety of inflammatory disease processes. Although the primary effect of ribosomal inactivation in cells is the functional inhibition of global protein synthesis, early responsive gene products including proinflammatory cytokines are exclusively induced by toxic stress in highly dividing tissues such as lymphoid tissue and epithelia. In the present study, ribosomal inactivation-related modulation of cytokine production was reviewed in leukocyte and epithelial pathogenesis models to characterize mechanistic evidence of ribosome-derived cytokine induction and its implications for potent therapeutic targets of mucosal and systemic inflammatory illness, particularly those triggered by organellar dysfunctions.

Hypoxia mediates mutual repression between microRNA-27a and PPARγ in the pulmonary vasculature

Pulmonary hypertension (PH) is a serious disorder that causes significant morbidity and mortality. The pathogenesis of PH involves complex derangements in multiple pathways including reductions in peroxisome proliferator-activated receptor gamma (PPARγ). Hypoxia, a common PH stimulus, reduces PPARγ in experimental models. In contrast, activating PPARγ attenuates hypoxia-induced PH and endothelin 1 (ET-1) expression. To further explore mechanisms of hypoxia-induced PH and reductions in PPARγ, we examined the effects of hypoxia on selected microRNA (miRNA or miR) levels that might reduce PPARγ expression leading to increased ET-1 expression and PH. Our results demonstrate that exposure to hypoxia (10% O₂) for 3-weeks increased levels of miR-27a and ET-1 in the lungs of C57BL/6 mice and reduced PPARγ levels. Hypoxia-induced increases in miR-27a were attenuated in mice treated with the PPARγ ligand, rosiglitazone (RSG, 10 mg/kg/d) by gavage for the final 10 d of exposure. In parallel studies, human pulmonary artery endothelial cells (HPAECs) were exposed to control (21% O₂) or hypoxic (1% O₂) conditions for 72 h. Hypoxia increased HPAEC proliferation, miR-27a and ET-1 expression, and reduced PPARγ expression. These alterations were attenuated by treatment with RSG (10 µM) during the last 24 h of hypoxia exposure. Overexpression of miR-27a or PPARγ knockdown increased HPAEC proliferation and ET-1 expression and decreased PPARγ levels, whereas these effects were reversed by miR-27a inhibition. Further, compared to lungs from littermate control mice, miR-27a levels were upregulated in lungs from endothelial-targeted PPARγ knockout (ePPARγ KO) mice. Knockdown of either SP1 or EGR1 was sufficient to significantly attenuate miR-27a expression in HPAECs. Collectively, these studies provide novel evidence that miR-27a and PPARγ mediate mutually repressive actions in hypoxic pulmonary vasculature and that targeting PPARγ may represent a novel therapeutic approach in PH to attenuate proliferative mediators that stimulate proliferation of pulmonary vascular cells.

A feedback loop in PPARγ-adenosine A2A receptor signaling inhibits inflammation and attenuates lung damages in a mouse model of LPS-induced acute lung injury

Although peroxisome proliferator-activated receptor-γ (PPARγ) and adenosine A2A receptor (A2AR) are reported to be anti-inflammatory factors in acute lung injury (ALI), their internal link and synergic or antagonistic effect after activation are poorly understood. Here, we found that PPARγ and A2AR could upregulate the mRNA and protein expressions of each other in lung tissues of LPS-induced mouse ALI model and murine macrophages. Further investigation demonstrated that PPARγ upregulated A2AR expression by directly binding to a DR10 response element (-218 to -197) within A2AR gene promoter region. Instead of directly interacting with PPARγ, A2AR stimulated PPARγ expression via protein kinase A (PKA)-cAMP response element binding protein (CREB) signaling by provoking the binding of CREB to a cAMP responsive element (CRE)-like site in PPARγ gene promoter region. In addition, combination of PPARγ and A2AR agonists was found to exert obviously better effect on suppressing neutrophil infiltration and inflammatory cytokine expressions, attenuating lung edema, pathological changes and improving lung function of blood gas exchange than their single application. These findings reveal a novel functional positive feedback loop between PPARγ and A2AR signaling to potentialize their effect on inhibiting inflammation and attenuating lung damages in ALI. It suggests that targeting this PPARγ-A2AR signaling rather than PPARγ or A2AR alone may be a more attractive and efficient potential therapeutic strategy for ALI.

Egr-1: new conductor for the tissue repair orchestra directs harmony (regeneration) or cacophony (fibrosis)

Fibroblasts and myofibroblasts are the key effector cells executing physiological tissue repair leading to regeneration on the one hand, and pathological fibrogenesis leading to chronic fibrosing conditions on the other. Recent studies identify the multifunctional transcription factor early growth response-1(Egr-1) as an important mediator of fibroblast activation triggered by diverse stimuli. Egr-1 has potent stimulatory effects on fibrotic gene expression, and aberrant Egr-1 expression or function is associated with animal models of fibrosis and human fibrotic disorders, including emphysema, pulmonary fibrosis, pulmonary hypertension and systemic sclerosis. Pharmacological suppression or genetic targeting of Egr-1 blocks fibrotic responses in vitro and ameliorates experimental fibrosis in the skin and lung. In contrast, Egr-1 appears to act as a negative regulator of hepatic fibrosis in mouse models, suggesting a context-dependent role in fibrosis. The Egr-1-binding protein Nab2 is an endogenous inhibitor of Egr-1-mediated signalling and abrogates the stimulation of fibrotic responses induced by transforming growth factor-β (TGFβ). Moreover, mice deficient in Nab2 show excessive collagen accumulation in the skin. These observations highlight a previously unsuspected fundamental physiological function for the Egr-1-Nab2 signalling axis in regulating fibrogenesis, and suggest that Egr-1 may be a potential novel therapeutic target in human diseases complicated by fibrosis. This review summarizes recent advances in understanding the regulation and complex functional role of Egr-1 and its related proteins and inhibitors in pathological fibrosis.

Pioglitazone, a PPARγ agonist, suppresses CYP19 transcription: evidence for involvement of 15-hydroxyprostaglandin dehydrogenase and BRCA1

Estrogen synthesis is catalyzed by cytochrome P450 aromatase, which is encoded by the CYP19 gene. In obese postmenopausal women, increased aromatase activity in white adipose tissue is believed to contribute to hormone-dependent breast cancer. Prostaglandin E(2) (PGE(2)) stimulates the cAMP→protein kinase A (PKA) pathway leading to increased CYP19 transcription and elevated aromatase activity in inflamed white adipose tissue. 15-hydroxyprostaglandin dehydrogenase (15-PGDH) plays a major role in the catabolism of PGE(2). Here, we investigated the mechanism by which pioglitazone, a ligand of the nuclear receptor PPARγ suppressed aromatase expression. Treatment of human preadipocytes with pioglitazone suppressed Snail, a repressive transcription factor, resulting in elevated levels of 15-PGDH and reduced levels of PGE(2) in the culture medium. Pioglitazone also inhibited cAMP→PKA signaling leading to reduced interaction between phosphorylated cAMP responsive element-binding protein, p300, and CYP19 I.3/II promoter. BRCA1, a repressor of CYP19 transcription, was induced by pioglitazone. Consistent with these in vitro findings, treatment of mice with pioglitazone activated PPARγ, induced 15-PGDH and BRCA1 while suppressing aromatase levels in the mammary gland. Collectively, these results indicate that the activation of PPARγ induces BRCA1 and suppresses the PGE(2)→cAMP→PKA axis leading to reduced levels of aromatase. PPARγ agonists may have a role in reducing the risk of hormone-dependent breast cancer in obese postmenopausal women.

Regulation of ROS production and vascular function by carbon monoxide

Carbon monoxide (CO) is a gaseous molecule produced from heme by heme oxygenase (HO). CO interacts with reduced iron of heme-containing proteins, leading to its involvement in various cellular events via its production of mitochondrial reactive oxygen species (ROS). CO-mediated ROS production initiates intracellular signal events, which regulate the expression of adaptive genes implicated in oxidative stress and functions as signaling molecule for promoting vascular functions, including angiogenesis and mitochondrial biogenesis. Therefore, CO generated either by exogenous delivery or by HO activity can be fundamentally involved in regulating mitochondria-mediated redox cascades for adaptive gene expression and improving blood circulation (i.e., O₂ delivery) via neovascularization, leading to the regulation of mitochondrial energy metabolism. This paper will highlight the biological effects of CO on ROS generation and cellular redox changes involved in mitochondrial metabolism and angiogenesis. Moreover, cellular mechanisms by which CO is exploited for disease prevention and therapeutic applications will also be discussed.

Pioglitazone, a PPAR-γ activator, attenuates the severity of cerulein-induced acute pancreatitis by modulating early growth response-1 transcription factor

The purpose of this study was to test the hypothesis that activation of endogenous peroxisome proliferator-activated receptor (PPARγ) inhibits induction of early growth response factor-1 (Egr-1), which is rapidly induced in the pancreas following cerulein intraperitoneal injection. Acute pancreatitis was induced in mice by hourly intraperitoneal injection of cerulein. Pioglitazone was administered prophylactically and pancreatic inflammation was assessed. AR42J cells were stimulated with caerulein 10⁻⁸ M co-incubated in presence of different concentration of pioglitazone. The expression of PPARγ, Egr-1, and the target genes of Egr-1 were studied by real-time reverse transcriptase polymerase chain reaction (PCR), Western blot, and immunohistochemistry. In vitro, a PPAR-γ activator (pioglitazone) strikingly diminished Egr-1 mRNA and protein expression corresponding to Egr-1. In vivo, treatment with pioglitazone prior to the intraperitoneal injection of cerulein induction of Egr-1 and its target genes such as, monocyte chemotactic protein-1 (MCP-1) and macrophage inflammatory protein-1 (MIP-1). The inhibitory effect of pioglitazone on Egr-1 expression induced by cerulein was almost fully restored by GW9662. Activation of PPAR-γ suppressed the activation of Egr-1 and its inflammatory gene targets and provided potent protection against pancreas injury. These data suggest a new mechanism in which PPAR-γ activation may decrease tissue inflammation in response to a cerulein insult.

Early growth response-1 transcription factor promotes hepatic fibrosis and steatosis in long-term ethanol-fed Long-Evans rats

BACKGROUND

Previous studies demonstrated that the Long-Evans (LE) rats exhibited liver injury and lipid metabolic abnormalities after 8 weeks of ethanol feeding.

AIMS

The goal of this study was to investigate if the LE rats develop more advanced hepatic abnormalities (e.g., fibrosis) after long-term feeding with an ethanol-containing Lieber-DeCarli diet. In addition, the contribution of early growth response-1 (EGR1) transcription factor to these pathological changes was assessed.

METHODS

Long-Evans rats were fed an ethanol-containing or isocaloric control liquid diet for 18 months. Livers were processed for histological analyses, studies of fibrosis-related gene expression, cell fractionation and triglyceride measurement. Serum alanine aminotransferase (ALT) levels were assessed. DNA binding activities of p53 and the sterol regulatory element-binding protein-1c (SREBP1c) were analysed. The abundance of EGR1 and enzymes involved in fatty acid synthesis were determined. Chromatin immunoprecipitation was employed to study EGR1 binding to the SREBP1c promoter region.

RESULTS

Ethanol feeding generated steatosis, chicken wire fibrosis and ALT elevations in the LE rats. Fibrosis was associated with the upregulation of EGR1 and its downstream target genes. EGR1 upregulation was associated with enhanced p53 activity and an increase in the cellular p66(shc) abundance. Steatosis was linked to the activation of SREBP1c. Importantly, EGR1 upregulation paralleled the expression and transcriptional activity of SREBP1c. Finally, EGR1 was shown to bind to the SREBP1c promoter region.

CONCLUSIONS

Long-term ethanol feeding promoted steatosis and fibrosis in LE rats via EGR1 activation. The highly abundant EGR1 bound to the SREBP1c promoter and contributed to the steatosis observed in the LE rat model.

New insights into the role of peroxisome proliferator-activated receptors in regulating the inflammatory response after tissue injury

Major trauma results in a strong inflammatory response in injured tissue. This posttraumatic hyperinflammation has been implied in the adverse events leading to a breakdown of host defense mechanisms and ultimately to delayed organ failure. Ligands to peroxisome proliferator-activated receptors (PPARs) have recently been identified as potent modulators of inflammation in various acute and chronic inflammatory conditions. The main mechanism of action mediated by ligand binding to PPARs is the inhibition of the nuclear transcription factor NF-κB, leading to downregulation of downstream gene transcription, such as for genes encoding proinflammatory cytokines. Pharmacological PPAR agonists exert strong anti-inflammatory properties in various animal models of tissue injury, including central nervous system trauma, ischemia/reperfusion injury, sepsis, and shock. In addition, PPAR agonists have been shown to induce wound healing process after tissue trauma. The present review was designed to provide an up-to-date overview on the current understanding of the role of PPARs in the pathophysiology of the inflammatory response after major trauma. Therapeutic options for using recombinant PPAR agonists as pharmacological agents in the management of posttraumatic inflammation will be discussed.

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.

Atherogenic ω-6 Lipids Modulate PPAR- EGR-1 Crosstalk in Vascular Cells

Atherogenic ω-6 lipids are physiological ligands of peroxisome proliferator-activated receptors (PPARs) and elicit pro- and antiatherogenic responses in vascular cells. The objective of this study was to investigate if ω-6 lipids modulated the early growth response-1 (Egr-1)/PPAR crosstalk thereby altering vascular function. Rat aortic smooth muscle cells (RASMCs) were exposed to ω-6 lipids, linoleic acid (LA), or its oxidized form, 13-HPODE (OxLA) in the presence or absence of a PPARα antagonist (MK886) or PPARγ antagonist (GW9662) or PPAR-specific siRNA. Our results demonstrate that ω-6 lipids, induced Egr-1 and monocyte chemotactic protein-1 (MCP-1) mRNA and protein levels at the acute phase (1-4 hrs) when PPARα was downregulated and at subacute phase (4-12 hrs) by modulating PPARγ, thus resulting in altered monocyte adhesion to RASMCs. We provide novel insights into the mechanism of action of ω-6 lipids on Egr-1/PPAR interactions in vascular cells and their potential in altering vascular function.

Egr-1 induces a profibrotic injury/repair gene program associated with systemic sclerosis

Transforming growth factor-ß (TGF-ß) signaling is implicated in the pathogenesis of fibrosis in scleroderma or systemic sclerosis (SSc), but the precise mechanisms are poorly understood. The immediate-early gene Egr-1 is an inducible transcription factor with key roles in mediating fibrotic TGF-ß responses. To elucidate Egr-1 function in SSc-associated fibrosis, we examined change in gene expression induced by Egr-1 in human fibroblasts at the genome-wide level. Using microarray expression analysis, we derived a fibroblast "Egr-1-responsive gene signature" comprising over 600 genes involved in cell proliferation, TGF-ß signaling, wound healing, extracellular matrix synthesis and vascular development. The experimentally derived "Egr-1-responsive gene signature" was then evaluated in an expression microarray dataset comprising skin biopsies from 27 patients with localized and systemic forms of scleroderma and six healthy controls. We found that the "Egr-1 responsive gene signature" was substantially enriched in the "diffuse-proliferation" subset comprising exclusively of patients with diffuse cutaneous SSc (dcSSc) of skin biopsies. A number of Egr-1-regulated genes was also associated with the "inflammatory" intrinsic subset. Only a minority of Egr-1-regulated genes was concordantly regulated by TGF-ß. These results indicate that Egr-1 induces a distinct profibrotic/wound healing gene expression program in fibroblasts that is associated with skin biopsies from SSc patients with diffuse cutaneous disease. These observations suggest that targeting Egr-1 expression or activity might be a novel therapeutic strategy to control fibrosis in specific SSc subsets.

Role of Peoxisome Proliferator Activator Receptor gamma on Blood Retinal Barrier Breakdown

The retinal vessels have two barriers: the retinal pigment epithelium and the retinal vascular endothelium. Each barrier exhibits increased permeability under various pathological conditions. This condition is referred to as blood retinal barrier (BRB) breakdown. Clinically, the most frequently encountered condition causing BRB breakdown is diabetic retinopathy. In recent studies, inflammation has been linked to BRB breakdown and vascular leakage in diabetic retinopathy. Biological support for the role of inflammation in early diabetes is the adhesion of leukocytes to the retinal vasculature (leukostasis) observed in diabetic retinopathy. PPARγ is a member of a ligand-activated nuclear receptor superfamily and plays a critical role in a variety of biological processes, including adipogenesis, glucose metabolism, angiogenesis, and inflammation. There is now strong experimental evidence to support the theory that PPARγ inhibits diabetes-induced retinal leukostasis and leakage, playing an important role in the pathogenesis of diabetic retinopathy. Therapeutic targeting of PPARγ may be beneficial to diabetic retinopathy.

PPAR Gamma: Coordinating Metabolic and Immune Contributions to Female Fertility

Peroxisome proliferator-activated receptor gamma (PPARG) regulates cellular functions such as adipogenesis and immune cell activation. However, new information has indicated additional roles of PPARG directing the cyclic changes that occur within ovarian tissue of female mammals, including those that facilitate the release of oocytes each estrous cycle. In addition to ovarian PPARG expression and function, many PPARG actions within adipocytes and macrophages have additional direct and indirect implications for ovarian function and female fertility. This encompasses the regulation of lipid uptake and transport, insulin sensitivity, glucose metabolism, and the regulation of inflammatory mediator synthesis and release. This review discusses the developing links between PPARG activity and female reproductive function, and highlights several mechanisms that may facilitate such a relationship.

Peroxisome proliferator-activated receptors and acute lung injury

Peroxisome proliferator-activated receptors are ligand-activated transcription factors belonging to the nuclear hormone receptor superfamily. PPARs regulate several metabolic pathways by binding to sequence-specific PPAR response elements in the promoter region of target genes, including lipid biosynthesis and glucose metabolism. Recently, PPARs and their respective ligands have been implicated as regulators of cellular inflammatory and immune responses. These molecules are thought to exert anti-inflammatory effects by negatively regulating the expression of proinflammatory genes. Several studies have demonstrated that PPAR ligands possess anti-inflammatory properties and that these properties may prove helpful in the treatment of inflammatory diseases of the lung. This review will outline the anti-inflammatory effects of PPARs and PPAR ligands and discuss their potential therapeutic effects in animal models of inflammatory lung disease.

Early growth response transcription factors: key mediators of fibrosis and novel targets for anti-fibrotic therapy

Fibrosis is a deregulated and ultimately defective form of tissue repair that underlies a large number of chronic human diseases, as well as obesity and aging. The pathogenesis of fibrosis involves multiple cell types and extracellular signals, of which transforming growth factor-ß (TGF-ß) is pre-eminent. The prevalence of fibrosis is rising worldwide, and to date no agents has shown clinical efficacy in the attenuating or reversing the process. Recent studies implicate the immediate-early response transcription factor Egr-1 in the pathogenesis of fibrosis. Egr-1 couples acute changes in the cellular environment to sustained alterations in gene expression, and mediates a broad spectrum of biological responses to injury and stress. In contrast to other ligand-activated transcription factors such as NF-κB, c-jun and Smad2/3 that undergo post-translational modification such as phosphorylation and nuclear translocation, Egr-1 activity is regulated via its biosynthesis. Aberrant Egr-1 expression or activity is implicated in cancer, inflammation, atherosclerosis, and ischemic injury and recent studies now indicate an important role for Egr-1 in TGF-ß-dependent profibrotic responses. Fibrosis in various animal models and human diseases such as scleroderma (SSc) and idiopathic pulmonary fibrosis (IPF) is accompanied by aberrant Egr-1 expression. Moreover Egr-1 appears to be required for physiologic and pathological connective tissue remodeling, and Egr-1-null mice are protected from fibrosis. As a novel profibrotic mediator, Egr-1 thus appears to be a promising potential target for the development of anti-fibrotic therapies.

Bardoxolone methyl (BARD) ameliorates ischemic AKI and increases expression of protective genes Nrf2, PPARγ, and HO-1

Ischemic acute kidney injury (AKI) triggers expression of adaptive (protective) and maladaptive genes. Agents that increase expression of protective genes should provide a therapeutic benefit. We now report that bardoxolone methyl (BARD) ameliorates ischemic murine AKI as assessed by both renal function and pathology. BARD may exert its beneficial effect by increasing expression of genes previously shown to protect against ischemic AKI, NF-E2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor-γ (PPARγ), and heme oxygenase 1 (HO-1). Although we found that BARD alone or ischemia-reperfusion alone increased expression of these genes, the greatest increase occurred after the combination of both ischemia-reperfusion and BARD. BARD had a different mode of action than other agents that regulate PPARγ and Nrf2. Thus we report that BARD regulates PPARγ, not by acting as a ligand but by increasing the amount of PPARγ mRNA and protein. This should increase ligand-independent effects of PPARγ. Similarly, BARD increased Nrf2 mRNA; this increased Nrf2 protein by mechanisms in addition to the prolongation of Nrf2 protein half-life previously reported. Finally, we localized expression of these protective genes after ischemia and BARD treatment. Using double-immunofluorescence staining for CD31 and Nrf2 or PPARγ, we found increased Nrf2 and PPARγ on glomerular endothelia in the cortex; Nrf2 was also present on cortical peritubular capillaries. In contrast, HO-1 was localized to different cells, i.e., tubules and interstitial leukocytes. Although Nrf2-dependent increases in HO-1 have been described, our data suggest that BARD's effects on tubular and leukocyte HO-1 during ischemic AKI may be Nrf2 independent. We also found that BARD ameliorated cisplatin nephrotoxicity.

Exacerbated brain damage, edema and inflammation in type-2 diabetic mice subjected to focal ischemia

One of the limiting factors in stroke therapeutic development is the use of animal models that do not well represent the underlying medical conditions of patients. In humans, diabetes increases the risk of stroke incidence as well as post-stroke mortality. To understand the mechanisms that render diabetics to increased brain damage, we evaluated the effect of transient middle cerebral artery occlusion in adult db/db mice. The db/db mouse is a model of type-2 diabetes with four times higher blood sugar than its normoglycemic genetic control(db/+ mouse). Following transient middle cerebral artery occlusion, the db/db mice showed significantly higher mortality, bigger infarcts, increased cerebral edema, worsened neurological status compared to db/+ mice. The db/db mice also showed significantly higher post-ischemic inflammatory markers (ICAM1(+) capillaries, extravasated macrophages/neutrophils and exacerbated proinflammatory gene expression) compared to db/+ mice. In addition, the post-ischemic neuroprotective heat-shock chaperone gene expression was curtailed in the db/db compared to db/+ mice.

Peroxisome proliferator-activated receptor α and γ agonists together with TGF-β convert human CD4+CD25- T cells into functional Foxp3+ regulatory T cells

Human peripheral CD4(+)CD25(-) T cells can be induced to express Foxp3 when activated in vitro by TCR stimulation with TGF-β and IL-2. However, these TGF-β-induced Foxp3(+) regulatory T cells (iTregs) lack a regulatory phenotype. From libraries of nuclear receptor ligands and bioactive lipids, we screened three peroxisome proliferator-activated receptor (PPAR)α (bezafibrate, GW7647, and 5,8,11,14-eicosatetraynoic acid) and two PPARγ agonists (ciglitazone and 15-deoxy-Δ-(12,14)-PG J(2)) as molecules that increased Foxp3 expression in human iTregs significantly compared with that in DMSO-treated iTregs (control). These PPARα and PPARγ agonist-treated iTregs maintained a high level of Foxp3 expression and had suppressive properties. There were no significant differences in the suppressive properties of iTregs treated with the three PPARα and two PPARγ agonists, and all of the treated iTregs increased demethylation levels of the Foxp3 promoter and intronic conserved noncoding sequence 3 regions. Furthermore, PPARα and PPARγ agonists, together with TGF-β, more strongly inhibited the expression of all three DNA methyltransferases (DNMTs) (DNMT1, DNMT3a, and DNMT3b) in activated CD4(+) T cells. These results demonstrate that PPARα and PPARγ agonists together with TGF-β elicit Foxp3 DNA demethylation through potent downregulation of DNMTs and induce potent and stable Foxp3 expression, resulting in the generation of functional iTregs. Moreover, trichostatin A and retinoic acid enhanced the generation of iTregs synergistically with PPARα and PPARγ agonists.

Modulation of nitrosative/oxidative stress in the lung of hyperglycemic rabbits by two antidiabetics, pioglitazone and repaglinide

The lungs are involved in diabetes in the cause of the complex phenomena diabetes generates. In the present study, hyperglycemia inhibited pulmonary antioxidants, including superoxide dismutase, catalase, glutathione peroxidase, and glutathione. These effects were accompanied by significant elevation of lipid peroxidation, total nitrites, and nitrotyrosine levels. The study investigated the effects of 2 oral antidiabetics, pioglitazone and repaglinide, on the mentioned parameters. It is concluded that pioglitazone exerts protective effect in the lung by inhibiting nitrosative stress and normalizing the nitrites and nitrotyrosine levels. Administration of repaglinide prevents oxidative and, to a smaller extent, nitrosative changes.

Peroxisome proliferator-activated receptor gamma activation alleviates postoperative ileus in mice by inhibition of Egr-1 expression and its downstream target genes

Postoperative ileus, a major cause of morbidity after abdominal surgery, is characterized by intestinal dysmotility and a complex inflammatory cascade within the intestinal muscularis. Treatment with carbon monoxide (CO)--inhaled or intraperitonea--has been shown to ameliorate bowel dysmotility caused by surgical manipulation of the gut in experimental animals. Recent evidence indicates that CO exerts its anti-inflammatory effects through the induction of peroxisome proliferator-activated receptor (PPAR)-gamma, a nuclear receptor whose activation has been linked to several physiological pathways, including those related to the regulation of intestinal inflammation. The purpose of this study was to evaluate pharmacological activation of PPARgamma in a murine model of postoperative ileus by use of the PPARgamma agonist rosiglitazone. Postoperative bowel dysmotility was induced by surgical manipulation of the colon. The functional severity of postoperative ileus was significantly ameliorated in mice pretreated with rosiglitazone (0.3 to 10 mg/kg i.p.); this was associated with a down-regulation of pro-inflammatory cytokines/chemokines, inducible nitric oxide synthase activity, cyclooxygenase-2 activity, as well as a decrease in leukocyte recruitment into the muscularis of both colon and jejunum. These anti-inflammatory effects were preceded by a PPARgamma-dependent down-regulation of early growth response (Egr)-1, a key regulator of inflammatory gene expression. In conclusion, these results indicate that rosiglitazone significantly attenuates postoperative ileus in mice by suppression of the muscularis inflammatory cascade through a PPARgamma-dependent down-regulation of Egr-1 and encourage the further clinical evaluation of synthetic PPARgamma agonists as pharmacological tool to prevent this postoperative event.