Early stimulation and late inhibition of peroxisome proliferator-activated receptor gamma (PPAR gamma) gene expression by transforming growth factor beta in human aortic smooth muscle cells: role of early growth-response factor-1 (Egr-1), activator protein 1 (AP1) and Smads

The MEK-ERK-Egr-1 axis and its regulation in cardiovascular disease

Cardiovascular disease (CVD) is the primary cause of morbidity and mortality in the Western world. Multiple molecular and cellular processes underpinning the pathogenesis of CVD are regulated by the zinc finger transcription factor and product of an immediate-early gene, early growth response-1 (Egr-1). Egr-1 regulates multiple pro-inflammatory processes that underpin the manifestation of CVD. The activity of Egr-1 itself is influenced by a range of post-translational modifications including sumoylation, ubiquitination and acetylation. Egr-1 also undergoes phosphorylation by protein kinases, such as extracellular-signal regulated kinase (ERK) which is itself phosphorylated by MEK. This article reviews recent progress on the MEK-ERK-Egr-1 cascade, notably regulation in conjunction with factors and agents such as TET2, TRIB2, MIAT, SphK1, cAMP, teneligliptin, cholinergic drugs, red wine and flavonoids, wogonin, febuxostat, docosahexaenoic acid and AT1R blockade. Such insights should provide new opportunity for therapeutic intervention in CVD.

Modulation of inflammatory M1-macrophages phenotype by valvular interstitial cells

BACKGROUND

Aortic valve stenosis involves inflammation, excess deposition of a collagen-rich extracellular matrix, and calcification. Recent studies have shown that M1 or inflammatory macrophages derived from infiltrating monocytes promote calcification of valvular interstitial cells, the most prevalent cell type of the aortic valve. We hypothesized that valvular interstitial cells could modulate inflammatory macrophages phenotype.

METHODS

We first assessed macrophage phenotype in human aortic valve stenosis and control aortic valves from donors. Then, we examined profibrotic and inflammatory-related gene expression in valves and valvular interstitial cells. Finally, we investigated whether valvular interstitial cells can modify the phenotype of inflammatory macrophages.

RESULTS

Circulating monocytes and plasma transforming growth factor beta-1 levels of patients with aortic valve stenosis were significantly higher compared with patients without aortic valve stenosis. Histologic analysis of thickened spongiosa of the aortic valve from patients with aortic valve stenosis showed a high macrophage infiltration but a low matrix metalloproteinase-9 expression compared with control aortic valves. On the other hand, valvular interstitial cell culture of aortic valve stenosis exhibited a profibrotic phenotype with a high expression of transforming growth factor beta-1 and transforming growth factor beta-1/transforming growth factor beta-3 ratio but a decreased expression of the peroxisome proliferator-activated receptor gamma nuclear receptor. Valvular interstitial cell-conditioned media of aortic valve stenosis led to a decrease in enzymatic activity of matrix metalloproteinase-9 and an increase in production of collagen in inflammatory macrophages compared with valvular interstitial cell-conditioned media from control aortic valve donors.

CONCLUSIONS

These findings indicate that profibrotic valvular interstitial cells promote the imbalance of extracellular matrix remodeling by reducing matrix metalloproteinase-9 production on inflammatory macrophages that lead to excessive collagen deposition observed in aortic valve stenosis. Further investigation is needed to clarify the role of transforming growth factor beta-1/proliferator-activated receptor gamma nuclear receptor/matrix metalloproteinase-9 in aortic valve stenosis.

The role of tribbles homolog 2 in vascular smooth muscle cell proliferation

Tribbles homolog 2 (TRIB2) functions as an adapter protein that regulates signal transductions involved in a variety of cellular functions, including tumorigenesis. However, the role of TRIB2 in the proliferation of vascular smooth muscle cells (VSMCs) and the underlying expression mechanisms remain unclear. The present study investigated the role of TRIB2 in VSMC proliferation and revealed that TRIB2 expression increases following vascular injury and platelet-derived growth factor (PDGF)-BB-stimulated VSMCs. We found that pretreatment with diphenyleneiodonium (a nicotinamide adenine dinucleotide phosphate oxidase inhibitor), U0126 (an inhibitor of mitogen-activated protein kinase kinase 1 [MEK1]), or siRNA targeting the gene encoding early growth response 1 (EGR-1) significantly inhibits PDGF-BB-induced TRIB2 expression in VSMCs. Furthermore, TRIB2 knockdown significantly inhibits PDGF-BB-induced proliferation of VSMCs but does not affect the phosphorylation of AKT. However, phosphorylation of ERK1 and expression of proliferating cell nuclear antibody are significantly suppressed in VSMCs by PDGF-BB stimulation. Thus, PDGF-BB-induced TRIB2 expression is mediated by ROS/ERK/EGR-1 pathways and plays a critical role in VSMC proliferation via modulation of ERK activity. We propose TRIB2 as a promising therapeutic target for the prevention of neointima formation and vascular disease.

Early fish domestication affects methylation of key genes involved in the rapid onset of the farmed phenotype

Animal domestication is a process of environmental modulation and artificial selection leading to permanent phenotypic modifications. Recent studies showed that phenotypic changes occur very early in domestication, i.e., within the first generation in captivity, which raises the hypothesis that epigenetic mechanisms may play a critical role on the early onset of the domestic phenotype. In this context, we applied reduced representation bisulphite sequencing to compare methylation profiles between wild Nile tilapia females and their offspring reared under farmed conditions. Approximately 700 differentially methylated CpG sites were found, many of them associated not only with genes involved in muscle growth, immunity, autophagy and diet response but also related to epigenetic mechanisms, such as RNA methylation and histone modifications. This bottom-up approach showed that the phenotypic traits often related to domestic animals (e.g., higher growth rate and different immune status) may be regulated epigenetically and prior to artificial selection on gene sequences. Moreover, it revealed the importance of diet in this process, as reflected by differential methylation patterns in genes critical to fat metabolism. Finally, our study highlighted that the TGF-β1 signalling pathway may regulate and be regulated by several differentially methylated CpG-associated genes. This could be an important and multifunctional component in promoting adaptation of fish to a domestic environment while modulating growth and immunity-related traits.

A Modular Mathematical Model of Exercise-Induced Changes in Metabolism, Signaling, and Gene Expression in Human Skeletal Muscle

Skeletal muscle is the principal contributor to exercise-induced changes in human metabolism. Strikingly, although it has been demonstrated that a lot of metabolites accumulating in blood and human skeletal muscle during an exercise activate different signaling pathways and induce the expression of many genes in working muscle fibres, the systematic understanding of signaling-metabolic pathway interrelations with downstream genetic regulation in the skeletal muscle is still elusive. Herein, a physiologically based computational model of skeletal muscle comprising energy metabolism, Ca2+, and AMPK (AMP-dependent protein kinase) signaling pathways and the expression regulation of genes with early and delayed responses was developed based on a modular modeling approach and included 171 differential equations and more than 640 parameters. The integrated modular model validated on diverse including original experimental data and different exercise modes provides a comprehensive in silico platform in order to decipher and track cause-effect relationships between metabolic, signaling, and gene expression levels in skeletal muscle.

The Glitazars Paradox: Cardiotoxicity of the Metabolically Beneficial Dual PPARα and PPARγ Activation

The most common complications in patients with type-2 diabetes are hyperglycemia and hyperlipidemia that can lead to cardiovascular disease. Alleviation of these complications constitutes the major therapeutic approach for the treatment of diabetes mellitus. Agonists of peroxisome proliferator-activated receptor (PPAR) alpha and PPARγ are used for the treatment of hyperlipidemia and hyperglycemia, respectively. PPARs belong to the nuclear receptors superfamily and regulate fatty acid metabolism. PPARα ligands, such as fibrates, reduce circulating triglyceride levels, and PPARγ agonists, such as thiazolidinediones, improve insulin sensitivity. Dual-PPARα/γ agonists (glitazars) were developed to combine the beneficial effects of PPARα and PPARγ agonism. Although they improved metabolic parameters, they paradoxically aggravated congestive heart failure in patients with type-2 diabetes via mechanisms that remain elusive. Many of the glitazars, such as muraglitazar, tesaglitazar, and aleglitazar, were abandoned in phase-III clinical trials. The objective of this review article pertains to the understanding of how combined PPARα and PPARγ activation, which successfully targets the major complications of diabetes, causes cardiac dysfunction. Furthermore, it aims to suggest interventions that will maintain the beneficial effects of dual PPARα/γ agonism and alleviate adverse cardiac outcomes in diabetes.

Necrotizing Enterocolitis: LPS/TLR4-Induced Crosstalk Between Canonical TGF-β/Wnt/β-Catenin Pathways and PPARγ

Necrotizing enterocolitis (NEC) represents one of the major causes of morbidity and mortality in premature infants. Several recent studies, however, have contributed to a better understanding of the pathophysiology of this dreadful disease. Numerous intracellular pathways play a key role in NEC, namely: bacterial lipopolysaccharide (LPS), LPS toll-like receptor 4 (TLR4), canonical Wnt/β-catenin signaling and PPARγ. In a large number of pathologies, canonical Wnt/β-catenin signaling and PPARγ operate in opposition to one another, so that when one of the two pathways is overexpressed the other is downregulated and vice-versa. In NEC, activation of TLR4 by LPS leads to downregulation of the canonical Wnt/β-catenin signaling and upregulation of PPARγ. This review aims to shed light on the complex intracellular mechanisms involved in this pathophysiological profile by examining additional pathways such as the GSK-3β, NF-κB, TGF-β/Smads, and PI3K-Akt pathways.

Dual role of TGF-β in early pregnancy: clues from tumor progression

TGF-β signaling in the endometrium is active during the implantation period and has a pivotal role in regulating endometrial receptivity and embryo implantation. During embryo implantation, both apoptosis and proliferation of endometrial cells happen at the same time and it seems TGF-β is the factor that controls both of these processes. As shown in cancer cells, in special conditions this cytokine can have a dual effect and switch the action from apoptosis to proliferation. Owing to the similarity between embryo implantation and cancer development and also unusual pattern of proliferation and remodeling in the uterus, in this review we suggest the existence of such a switching in endometrium during the early pregnancy. Moreover, we address some potential mechanisms that could regulate the switching. A better understanding of the molecular mechanisms regulating TGF-β action and signaling during the implantation period could pave the way for introducing novel therapeutic strategies in order to solve implantation-associated issues such as repeated implantation failure.

The role of circadian clock gene BMAL1 in vascular proliferation

Brain and muscle Arnt-like protein-1 (BMAL1), a component of the molecular clock, is implicated in the development of cardiovascular diseases, including atherosclerosis and abdominal aortic aneurysms. However, the role of BMAL1 in vascular proliferation associated with vascular remodeling is unknown. In the present study, we investigated the mechanisms underlying BMAL1 expression in vascular smooth muscle cells (VSMCs) and the role of BMAL1 in VSMC proliferation. BMAL1 expression significantly increased in injured carotid arteries in C57BL/6J mice and platelet-derived growth factor (PDGF)-BB-stimulated VSMC cultures. Pretreatment with diphenyleneiodonium (an NADPH oxidase inhibitor) and U0126 or PD98059 (MEK Inhibitors) inhibited PDGF-BB-induced BMAL1 expression in a dose-dependent manner in VSMCs. In addition, the knockdown of early growth factor protein-1 (Egr-1) significantly inhibited PDGF-BB-induced BMAL1 mRNA or protein expression in VSMCs, and the knockdown of BMAL1 significantly decreased PDGF-BB-induced cell proliferation and extracellular signal-regulated kinase (ERK) phosphorylation but not Akt phosphorylation in VSMCs. The results demonstrate that PDGF-BB up-regulates BMAL1 expression through reactive oxygen species/ERK/Egr-1 pathways and that BMAL1 is involved in PDGF-BB-induced cell proliferation partially through ERK in VSMCs. Thus, BMAL1 may be a novel therapeutic target for the treatment of atherosclerosis including vascular remodeling.

Multiple Targets of the Canonical WNT/β-Catenin Signaling in Cancers

Canonical WNT/β-catenin signaling is involved in most of the mechanisms that lead to the formation and development of cancer cells. It plays a central role in three cyclic processes, which are the cell division cycle, the immune cycle, and circadian rhythms. When the canonical WNT pathway is upregulated as in cancers, the increase in β-catenin in the nucleus leads to activation of the expression of numerous genes, in particular CYCLIN D1 and cMYC, where the former influences the G1 phase of the cell division cycle, and the latter, the S phase. Every stage of the immune cycle is disrupted by the canonical WNT signaling. In numerous cancers, the dysfunction of the canonical WNT pathway is accompanied by alterations of the circadian genes (CLOCK, BMAL1, PER). Induction of these cyclic phenomena leads to the genesis of thermodynamic mechanisms that operate far from equilibrium, and that have been called “dissipative structures.” Moreover, upregulation of the canonical WNT/β-catenin signaling is important in the myofibroblasts of the cancer stroma. Their differentiation is controlled by the canonical WNT /TGF-β1 signaling. Myofibroblasts present ultraslow contractile properties due to the presence of the non-muscle myosin IIA. Myofibroblats also play a role in the inflammatory processes, often found in cancers and fibrosis processes. Finally, upregulated canonical WNT deviates mitochondrial oxidative phosphorylation toward the Warburg glycolysis metabolism, which is characteristic of cancers. Among all these cancer-generating mechanisms, the upregulated canonical WNT pathway would appear to offer the best hope as a therapeutic target, particularly in the field of immunotherapy.

GDF10 blocks hepatic PPARγ activation to protect against diet-induced liver injury

OBJECTIVE

Growth differentiation factors (GDFs) and bone-morphogenic proteins (BMPs) are members of the transforming growth factor β (TGFβ) superfamily and are known to play a central role in the growth and differentiation of developing tissues. Accumulating evidence, however, demonstrates that many of these factors, such as BMP-2 and -4, as well as GDF15, also regulate lipid metabolism. GDF10 is a divergent member of the TGFβ superfamily with a unique structure and is abundantly expressed in brain and adipose tissue; it is also secreted by the latter into the circulation. Although previous studies have demonstrated that overexpression of GDF10 reduces adiposity in mice, the role of circulating GDF10 on other tissues known to regulate lipid, like the liver, has not yet been examined.

METHODS

Accordingly, GDF10^-/- mice and age-matched GDF10^+/+ control mice were fed either normal control diet (NCD) or high-fat diet (HFD) for 12 weeks and examined for changes in liver lipid homeostasis. Additional studies were also carried out in primary and immortalized human hepatocytes treated with recombinant human (rh)GDF10.

RESULTS

Here, we show that circulating GDF10 levels are increased in conditions of diet-induced hepatic steatosis and, in turn, that secreted GDF10 can prevent excessive lipid accumulation in hepatocytes. We also report that GDF10^-/- mice develop an obese phenotype as well as increased liver triglyceride accumulation when fed a NCD. Furthermore, HFD-fed GDF10^-/- mice develop increased steatosis, endoplasmic reticulum (ER) stress, fibrosis, and injury of the liver compared to HFD-fed GDF10^+/+ mice. To explain these observations, studies in cultured hepatocytes led to the observation that GDF10 attenuates nuclear peroxisome proliferator-activated receptor γ (PPARγ) activity; a transcription factor known to induce de novo lipogenesis.

CONCLUSION

Our work delineates a hepatoprotective role of GDF10 as an adipokine capable of regulating hepatic lipid levels by blocking de novo lipogenesis to protect against ER stress and liver injury.

Bronchopulmonary Dysplasia: Crosstalk Between PPARγ, WNT/β-Catenin and TGF-β Pathways; The Potential Therapeutic Role of PPARγ Agonists

Bronchopulmonary dysplasia (BPD) is a serious pulmonary disease which occurs in preterm infants. Mortality remains high due to a lack of effective treatment, despite significant progress in neonatal resuscitation. In BPD, a persistently high level of canonical WNT/β-catenin pathway activity at the canalicular stage disturbs the pulmonary maturation at the saccular and alveolar stages. The excessive thickness of the alveolar wall impairs the normal diffusion of oxygen and carbon dioxide, leading to hypoxia. Transforming growth factor (TGF-β) up-regulates canonical WNT signaling and inhibits the peroxysome proliferator activated receptor gamma (PPARγ). This profile is observed in BPD, especially in animal models. Following a premature birth, hypoxia activates the canonical WNT/TGF-β axis at the expense of PPARγ. This gives rise to the differentiation of fibroblasts into myofibroblasts, which can lead to pulmonary fibrosis that impairs the respiratory function after birth, during childhood and even adulthood. Potential therapeutic treatment could target the inhibition of the canonical WNT/TGF-β pathway and the stimulation of PPARγ activity, in particular by the administration of nebulized PPARγ agonists.

Lysophospholipid-Related Diseases and PPARγ Signaling Pathway

The nuclear receptor superfamily includes ligand-inducible transcription factors that play diverse roles in cell metabolism and are associated with pathologies such as cardiovascular diseases. Lysophosphatidic acid (LPA) belongs to a family of lipid mediators. LPA and its naturally occurring analogues interact with G protein-coupled receptors on the cell surface and an intracellular nuclear hormone receptor. In addition, several enzymes that utilize LPA as a substrate or generate it as a product are under its regulatory control. Recent studies have demonstrated that the endogenously produced peroxisome proliferator-activated receptor gamma (PPARγ) antagonist cyclic phosphatidic acid (cPA), which is structurally similar to LPA, inhibits cancer cell invasion and metastasis in vitro and in vivo. We recently observed that cPA negatively regulates PPARγ function by stabilizing the binding of the co-repressor protein, a silencing mediator of retinoic acid, and the thyroid hormone receptor. We also showed that cPA prevents neointima formation, adipocyte differentiation, lipid accumulation, and upregulation of PPARγ target gene transcription. The present review discusses the arbitrary aspects of the physiological and pathophysiological actions of lysophospholipids in vascular and nervous system biology.

Transforming growth factor β suppresses peroxisome proliferator-activated receptor γ expression via both SMAD binding and novel TGF-β inhibitory elements

Transforming growth factor β (TGF-β) contributes to wound healing and, when dysregulated, to pathological fibrosis. TGF-β and the anti-fibrotic nuclear hormone receptor peroxisome proliferator-activated receptor γ (PPARγ) repress each other's expression, and such PPARγ down-regulation is prominent in fibrosis and mediated, via previously unknown SMAD-signaling mechanisms. Here, we show that TGF-β induces the association of SMAD3 with both SMAD4, needed for translocation of the complex into the nucleus, and the essential context-sensitive co-repressors E2F4 and p107. The complex mediates TGF-β-induced repression by binding to regulatory elements in the target promoter. In the PPARG promoter, we found that the SMAD3-SMAD4 complex binds both to a previously unknown consensus TGF-β inhibitory element (TIE) and also to canonical SMAD-binding elements (SBEs). Furthermore, the TIE and SBEs independently mediated the partial repression of PPARG transcription, the first demonstration of a TIE and SBEs functioning within the same promoter. Also, TGF-β-treated fibroblasts contained SMAD complexes that activated a SMAD target gene in addition to those repressing PPARG transcription, the first finding of such dual activity within the same cell. These findings describe in detail novel mechanisms by which TGF-β represses PPARG transcription, thereby facilitating its own pro-fibrotic activity.

Early Growth Response Protein-1 Involves in Transforming Growth factor-β1 Induced Epithelial-Mesenchymal Transition and Inhibits Migration of Non-Small-Cell Lung Cancer Cells

The zinc finger transcription factor EGR1 has a role in controlling synaptic plasticity, wound repair, female reproductive capacity, inflammation, growth control, apoptosis and tumor progression. Recent studies mainly focused on its role in growth control and apoptosis, however, little is known about its role in epithelial-mesenchymal transition (EMT). Here, we aim to explore whether EGR 1 is involved in TGF-β1-induced EMT in non-small- cell lung cancer cells. Transforming growth factor (TGF)-β1 was utilized to induce EMT in this study. Western blotting, RT-PCR, and transwell chambers were used to identify phenotype changes. Western blotting was also used to observe changes of the expression of EGR 1. The lentivirus-mediated EGR 1 vector was used to increase EGR1 expression. We investigated the change of migration to evaluate the effect of EGR 1 on non-small-cell lung cancer cells migration by transwell chambers. After stimulating with TGF-β1, almost all A549 cells and Luca 1 cells (Non-small-cell lung cancer primary cells) changed to mesenchymal phenotype and acquired more migration capabilities. These cells also had lower EGR 1 protein expression. Overexpression of EGR 1 gene with EGR 1 vector could decrease tumor cell migration capabilities significantly after adding TGF-β1. These data showed an important role of EGR 1 in the EMT of non-small-cell lung cancer cells, as well as migration.

PPARs: Protectors or Opponents of Myocardial Function?

Over 5 million people in the United States suffer from the complications of heart failure (HF), which is a rapidly expanding health complication. Disorders that contribute to HF include ischemic cardiac disease, cardiomyopathies, and hypertension. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor family. There are three PPAR isoforms: PPARα, PPARγ, and PPARδ. They can be activated by endogenous ligands, such as fatty acids, as well as by pharmacologic agents. Activators of PPARs are used for treating several metabolic complications, such as diabetes and hyperlipidemia that are directly or indirectly associated with HF. However, some of these drugs have adverse effects that compromise cardiac function. This review article aims to summarize the current basic and clinical research findings of the beneficial or detrimental effects of PPAR biology on myocardial function.

MuRF2 regulates PPARγ1 activity to protect against diabetic cardiomyopathy and enhance weight gain induced by a high fat diet

BACKGROUND

In diabetes mellitus the morbidity and mortality of cardiovascular disease is increased and represents an important independent mechanism by which heart disease is exacerbated. The pathogenesis of diabetic cardiomyopathy involves the enhanced activation of PPAR transcription factors, including PPARα, and to a lesser degree PPARβ and PPARγ1. How these transcription factors are regulated in the heart is largely unknown. Recent studies have described post-translational ubiquitination of PPARs as ways in which PPAR activity is inhibited in cancer. However, specific mechanisms in the heart have not previously been described. Recent studies have implicated the muscle-specific ubiquitin ligase muscle ring finger-2 (MuRF2) in inhibiting the nuclear transcription factor SRF. Initial studies of MuRF2-/- hearts revealed enhanced PPAR activity, leading to the hypothesis that MuRF2 regulates PPAR activity by post-translational ubiquitination.

METHODS

MuRF2-/- mice were challenged with a 26-week 60% fat diet designed to simulate obesity-mediated insulin resistance and diabetic cardiomyopathy. Mice were followed by conscious echocardiography, blood glucose, tissue triglyceride, glycogen levels, immunoblot analysis of intracellular signaling, heart and skeletal muscle morphometrics, and PPARα, PPARβ, and PPARγ1-regulated mRNA expression.

RESULTS

MuRF2 protein levels increase ~20% during the development of diabetic cardiomyopathy induced by high fat diet. Compared to littermate wildtype hearts, MuRF2-/- hearts exhibit an exaggerated diabetic cardiomyopathy, characterized by an early onset systolic dysfunction, larger left ventricular mass, and higher heart weight. MuRF2-/- hearts had significantly increased PPARα- and PPARγ1-regulated gene expression by RT-qPCR, consistent with MuRF2's regulation of these transcription factors in vivo. Mechanistically, MuRF2 mono-ubiquitinated PPARα and PPARγ1 in vitro, consistent with its non-degradatory role in diabetic cardiomyopathy. However, increasing MuRF2:PPARγ1 (>5:1) beyond physiological levels drove poly-ubiquitin-mediated degradation of PPARγ1 in vitro, indicating large MuRF2 increases may lead to PPAR degradation if found in other disease states.

CONCLUSIONS

Mutations in MuRF2 have been described to contribute to the severity of familial hypertrophic cardiomyopathy. The present study suggests that the lack of MuRF2, as found in these patients, can result in an exaggerated diabetic cardiomyopathy. These studies also identify MuRF2 as the first ubiquitin ligase to regulate cardiac PPARα and PPARγ1 activities in vivo via post-translational modification without degradation.

WIN induces apoptotic cell death in human colon cancer cells through a block of autophagic flux dependent on PPARγ down-regulation

Cannabinoids have been reported to possess anti-tumorigenic activity in cancer models although their mechanism of action is not well understood. Here, we show that the synthetic cannabinoid WIN55,212-2 (WIN)-induced apoptosis in colon cancer cell lines is accompanied by endoplasmic reticulum stress induction. The formation of acidic vacuoles and the increase in LC3-II protein indicated the involvement of autophagic process which seemed to play a pro-survival role against the cytotoxic effects of the drug. However, the enhanced lysosomal membrane permeabilization (LMP) blocked the autophagic flux after the formation of autophagosomes as demonstrated by the accumulation of p62 and LC3, two markers of autophagic degradation. Data also provided evidence for a role for nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) in cannabinoid signalling. PPARγ expression, at both protein and mRNA levels, was significantly down-regulated after WIN treatment and its inhibition, either by specific antagonists or by down-regulation via gene silencing, induced effects on cell viability as well as on ER stress and autophagic markers similar to those obtained in the presence of WIN. Moreover, the observation that the increase in p62 level and the induction of LMP were also modified by PPARγ antagonists seemed to indicate that PPARγ down-regulation was crucial to determinate the block of autophagic flux, thus confirming the critical role of PPARγ in WIN action. In conclusion, at our knowledge, our results are the first to show that the reduction of PPARγ levels contributes to WIN-induced colon carcinoma cell death by blocking the pro-survival autophagic response of cells.

CCN2 requires TGF-β signalling to regulate CCAAT/enhancer binding proteins and inhibit fat cell differentiation

INTRODUCTION

Fat cell differentiation (FCD) potentiates adipose cell characteristics including lipid storage and insulin sensitivity. In vitro, we have demonstrated that CCN2, also known as connective tissue growth factor (CTGF), inhibits FCD in NIH3T3-L1 cells and in adipocytes isolated from mouse epididymal fat pads. The aim of this study was to determine if the CCN2 effect on FCD is dependent on TGF-β and TGF-β downstream pathway signalling.

METHODS

NIH3T3-L1 cells were differentiated using standard methods with IBMX/Dex/Insulin. FCD at day 10 was confirmed by induced gene markers resistin and adiponectin and by lipid accumulation. Cells were treated at d0 with single dose active rhTGF-β1 (2 ng/mL), rhCCN2 (500 ng/mL) and/or TGF-β type 1 receptor blocker (SB431542, 5 μM). Early induction of FCD transcription factors: CCAAT/enhancer binding proteins (C/EBPs) and peroxisome proliferator-activated receptor-γ (PPAR-γ), were also determined.

RESULTS

In an early time course from 2 h, single doses of rhTGF-β1 or rhCCN2 significantly inhibited by ~70 % the induction of C/EBP-β and -δ mRNA, and also nuclear protein levels otherwise seen during FCD, whereas only delayed effects on PPAR-γ, at 48 h, occurred. Furthermore, the CCN2 inhibition of FCD markers adiponectin and resistin and lipid accumulation by Oil red O stain were each prevented by TGF-β receptor blockade. Similar prevention was found using pan-specific anti-TGF-β neutralising antibody. CCN2 and TGF-β treatment each rapidly phosphorylated SMAD-3 signalling in early stages of FCD.

CONCLUSION

This work shows novel findings that CCN2 effects on FCD are both TGF-β and TGF-β pathway dependent and are related to early effects on C/EBPs.

Nitrated fatty acids reverse pulmonary fibrosis by dedifferentiating myofibroblasts and promoting collagen uptake by alveolar macrophages

Idiopathic pulmonary fibrosis (IPF) is a progressive, fatal disease, thought to be largely transforming growth factor β (TGFβ) driven, for which there is no effective therapy. We assessed the potential benefits in IPF of nitrated fatty acids (NFAs), which are unique endogenous agonists of peroxisome proliferator-activated receptor γ (PPARγ), a nuclear hormone receptor that exhibits wound-healing and antifibrotic properties potentially useful for IPF therapy. We found that pulmonary PPARγ is down-regulated in patients with IPF. In vitro, knockdown or knockout of PPARγ expression in isolated human and mouse lung fibroblasts induced a profibrotic phenotype, whereas treating human fibroblasts with NFAs up-regulated PPARγ and blocked TGFβ signaling and actions. NFAs also converted TGFβ to inactive monomers in cell-free solution, suggesting an additional mechanism through which they may inhibit TGFβ. In vivo, treating mice bearing experimental pulmonary fibrosis with NFAs reduced disease severity. Also, NFAs up-regulated the collagen-targeting factor milk fat globule-EGF factor 8 (MFG-E8), stimulated collagen uptake and degradation by alveolar macrophages, and promoted myofibroblast dedifferentiation. Moreover, treating mice with established pulmonary fibrosis using NFAs reversed their existing myofibroblast differentiation and collagen deposition. These findings raise the prospect of treating IPF with NFAs to halt and perhaps even reverse the progress of IPF.

Role of promoter DNA sequence variations on the binding of EGR1 transcription factor

In response to a wide variety of stimuli such as growth factors and hormones, EGR1 transcription factor is rapidly induced and immediately exerts downstream effects central to the maintenance of cellular homeostasis. Herein, our biophysical analysis reveals that DNA sequence variations within the target gene promoters tightly modulate the energetics of binding of EGR1 and that nucleotide substitutions at certain positions are much more detrimental to EGR1-DNA interaction than others. Importantly, the reduction in binding affinity poorly correlates with the loss of enthalpy and gain of entropy-a trend indicative of a complex interplay between underlying thermodynamic factors due to the differential role of water solvent upon nucleotide substitution. We also provide a rationale for the physical basis of the effect of nucleotide substitutions on the EGR1-DNA interaction at atomic level. Taken together, our study bears important implications on understanding the molecular determinants of a key protein-DNA interaction at the cross-roads of human health and disease.

Reduced expression of 11β-hydroxysteroid dehydrogenase type 2 in preeclamptic placentas is associated with decreased PPARγ but increased PPARα expression

Placental 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) is reduced in pregnancies complicated with preeclampsia (PE). Peroxisome proliferator-activated receptors β/δ (PPARβ/δ) have been shown to suppress 11β-HSD2 expression in human placental cells. Our objectives were to investigate whether the reduced 11β-HSD2 expression is associated with the changes in PPARs in PE placentas, and whether PPARα and PPARγ affect 11β-HSD2 expression in placental cells. PPARα and PPARβ/δ mRNA and protein expression was increased, whereas PPARγ mRNA and protein expression was decreased in PE placentas. 11β-HSD2 protein expression was inversely correlated with PPARβ/δ in normal placentas but correlated positively with PPARγ and inversely to PPARα in PE placentas. In cultured placental cells, PPARα agonist inhibited, whereas PPARγ agonist stimulated, 11β-HSD2 mRNA and protein expression and activity in a dose-dependent manner. Knockdown of retinoid X nuclear receptor α (RXRα) resulted in a loss of PPARγ effect but not PPARα effect on11β-HSD2. The PPARα effect remained, but the PPARγ effect was lost in the presence of the translational inhibitor cycloheximide. PPARγ agonist dose-dependently stimulated specificity protein 1 (Sp-1) protein expression. Inhibition or knockdown of Sp-1 resulted in a loss of the effects of PPARα and PPARγ. The Sp-1 protein level was not correlated with 11β-HSD2 and PPARs in normal placentas, whereas Sp-1 expression was correlated with 11β-HSD2, PPARγ, and PPARβ/δ in PE placentas. Our data indicate that 11β-HSD2 expression can be modulated by PPARα and PPARγ in placental trophoblasts through Sp-1. Decreased 11β-HSD2 expression in PE placenta might be associated with decreased PPARγ but increased PPARα expression.

Leishmania donovani prevents oxidative burst-mediated apoptosis of host macrophages through selective induction of suppressors of cytokine signaling (SOCS) proteins

One of the mechanisms for establishment of infection employed by intra-macrophage pathogen-like Leishmania is inhibition of oxidative burst-mediated macrophage apoptosis to protect their niche for survival and replication. We tried to elucidate the underlying mechanism for this by using H2O2 for induction of apoptosis. Leishmania donovani-infected macrophages were much more resistant to H2O2-mediated apoptosis compared with control. Although infected cells were capable of comparable reactive oxygen species production, there was less activation of the downstream cascade consisting of caspase-3 and -7 and cleaved poly(ADP)-ribose polymerase. Suppressors of cytokine signaling (SOCS) 1 and 3 proteins and reactive oxygen species scavenging enzyme thioredoxin, known to be involved in stabilization of protein-tyrosine phosphatases, were found to be induced during infection. Induction of SOCS proteins may be mediated by Egr1, and silencing of Socs1 and -3 either alone or in combination resulted in reduced thioredoxin levels, enhanced activation of caspases, and increased apoptosis of infected macrophages. The induction of protein-tyrosine phosphatases, thioredoxin, SOCS, and Egr1 in L. donovani-infected macrophages was found to be unaffected by H2O2 treatment. SOCS knocked down cells also displayed decreased parasite survival thus marking reduction in disease progression. Taken together, these results suggest that L. donovani may exploit SOCS for subverting macrophage apoptotic machinery toward establishing its replicative niche inside the host.

TGFβ1 Controls PPARγ Expression, Transcriptional Potential, and Activity, in Part, through Smad3 Signaling in Murine Lung Fibroblasts

Transforming growth factor β1 (TGFβ1) promotes fibrosis by, among other mechanisms, activating quiescent fibroblasts into myofibroblasts and increasing the expression of extracellular matrices. Recent work suggests that peroxisome proliferator-activated receptor γ (PPARγ) is a negative regulator of TGFβ1-induced fibrotic events. We, however, hypothesized that antifibrotic pathways mediated by PPARγ are influenced by TGFβ1, causing an imbalance towards fibrogenesis. Consistent with this, primary murine primary lung fibroblasts responded to TGFβ1 with a sustained downregulation of PPARγ transcripts. This effect was dampened in lung fibroblasts deficient in Smad3, a transcription factor that mediates many of the effects of TGFβ1. Paradoxically, TGFβ1 stimulated the activation of the PPARγ gene promoter and induced the phosphorylation of PPARγ in primary lung fibroblasts. The ability of TGFβ1 to modulate the transcriptional activity of PPARγ was then tested in NIH/3T3 fibroblasts containing a PPARγ-responsive luciferase reporter. In these cells, stimulation of TGFβ1 signals with a constitutively active TGFβ1 receptor transgene blunted PPARγ-dependent reporter expression induced by troglitazone, a PPARγ activator. Overexpression of PPARγ prevented TGFβ1 repression of troglitazone-induced PPARγ-dependent gene transcription, whereas coexpression of PPARγ and Smad3 transgenes recapitulated the TGFβ1 effects. We conclude that modulation of PPARγ is controlled by TGFβ1, in part through Smad3 signals, involving regulation of PPARγ expression and transcriptional potential.

Peptidoglycan induced expression of peroxisome proliferator-activated receptor γ in mouse peritoneal macrophages: role of ERK and JNK MAP kinases

The peroxisome proliferator-activated receptor (PPAR) γ plays an important role in macrophage inflammatory homeostasis. Here we investigate the cross talk between PPARγ and TLR2 signaling pathway in mouse peritoneal macrophages. Real time RT-PCR and immunoblot analysis revealed that peptidoglycan (PGN) treatment of macrophages leads to biphasic effect on PPARγ expression i.e. an early upregulation and a late suppression. Inhibition of ERK MAP kinase by PD98059 abolished the early and rapid induction of PPARγ, while the inhibition of JNK MAP kinase by SP600125 nullifies the late inhibitory effect on the PPARγ expression in a dose-dependent manner. Furthermore, PPARγ knockdown macrophages showed enhanced NF-κB activity after PGN treatment. PGN treatment also enhances PPARγ interaction with p65 as observed by immunoprecipitation. This interaction may inhibit NF-κB (p65) activity as increased nuclear localization of p65 was observed in PPARγ knockdown macrophages after PGN treatment. PPARγ knockdown also increased the PGN-induced inflammatory cytokines (TNF-α, IL-1β, IL-12p40) production. Thus, our observations suggest that PGN induces PPARγ expression which is regulated by MAPKs activation and this enhanced PPARγ in turn attenuate NF-κB activity probably via enhancing p65 nuclear export. These results provide insight into how these pathways could be modulated in inflammatory diseases.

Ciprofibrate regulation of rat hepatic bilirubin glucuronidation and UDP-glucuronosyltransferases expression

Synthetic fibrates are hypolipidemic drugs known to stimulate hepatic peroxisome proliferation and bilirubin glucuronidation. This study was designed to estimate the effects of ciprofibrate simultaneously on rat hepatic bilirubin glucuronoconjugation and on hepatic expression of UGT1A1, UGT1A2 and UGT1A5, all of which belong to the bilirubin cluster. Hepatic bilirubin glucuronidation activity and UDP-glucuronosyltransferase expression (RT-PCR and Western blotting) were measured after a single-dose ciprofibrate treatment (5 mg/kg by gastric intubation) in 36-h time course experiments. Ciprofibrate regulation of PPARα and UGT1A5 mRNA expression was also investigated in rat hepatocytes. Bilirubin conjugation activity was induced by ciprofibrate, reaching a maximum level (2.4×) 24 h after the treatment. UGT1A1 and UGT1A5 mRNA expression was induced 1.5 times by ciprofibrate, with UGT1A5 reaching the basal level of UGT1A1. Although UGT1A2 mRNA was induced approximately threefold by ciprofibrate, its expression level remained low in comparison with basal or induced levels of UGT1A1 and UGT1A5 mRNA. In the 36-h time course experiment, bilirubin conjugation activity as well as UGT1A5 and PPARα mRNA expression presented a biphasic induction profile. Although a similar level of induction was observed in primary cultured hepatocyte experiments, such biphasic variation was not observed for both UGT1A5 and PPARα, and the induction of UGT1A5 mRNA expression by ciprofibrate required de novo protein synthesis. A single dose of ciprofibrate significantly induces rat liver bilirubin conjugation as well as UGT1A1, UGT1A5 and PPARα expression. The induction mechanism may involve PPARα, at least regarding UGT1A5 regulation.

A calcium-induced signaling cascade leading to osteogenic differentiation of human bone marrow-derived mesenchymal stromal cells

The response of osteoprogenitors to calcium (Ca(2+)) is of primary interest for both normal bone homeostasis and the clinical field of bone regeneration. The latter makes use of calcium phosphate-based bone void fillers to heal bone defects, but it is currently not known how Ca(2+) released from these ceramic materials influences cells in situ. Here, we have created an in vitro environment with high extracellular Ca(2+) concentration and investigated the response of human bone marrow-derived mesenchymal stromal cells (hMSCs) to it. Ca(2+) enhanced proliferation and morphological changes in hMSCs. Moreover, the expression of osteogenic genes is highly increased. A 3-fold up-regulation of BMP-2 is observed after only 6h and pharmaceutical interference with a number of proteins involved in Ca(2+) sensing showed that not the calcium sensing receptor, but rather type L voltage-gated calcium channels are involved in mediating the signaling pathway between extracellular Ca(2+) and BMP-2 expression. MEK1/2 activity is essential for the effect of Ca(2+) and using microarray analysis, we have identified c-Fos as an early Ca(2+) response gene. We have demonstrated that hMSC osteogenesis can be induced via extracellular Ca(2+), a simple and economic way of priming hMSCs for bone tissue engineering applications.

PPAR gamma, bioactive lipids, and cancer progression

In this article we review the evolution of cancer research involving PPARgamma, including mechanisms, target genes, and clinical applications. For the last thirteen years, the effects of PPARgamma activity on tumor biology have been studied intensely. Most of this research has focused upon the potential for employing agonists of this nuclear receptor in cancer treatment. As a monotherapy such agonists have shown little success in clinical trials, while they have shown promise as components of combination treatments both in culture and in animal models. Other investigations have explored a possible role for PPARgamma as a tumor suppressor, and as an inducer of differentiation of cancer stem cells. Whereas early studies have yielded variable conclusions regarding the prevalence of PPARgamma mutations in cancer, the protein level of this receptor has been more recently identified as a significant prognostic marker. We predict that indicators of PPARgamma activity may also serve as predictive markers for tailoring treatments.

Transforming growth factor-β inhibits myocardial PPARγ expression in pressure overload-induced cardiac fibrosis and remodeling in mice

OBJECTIVES

Pharmacological activation of peroxisome proliferator-activated receptor gamma (PPARγ) has been shown to attenuate pressure overload-induced cardiac fibrosis, suggesting that PPARγ has an antifibrotic effect. This study tested the hypothesis that there is a functional interaction between transforming growth factor-β (TGF-β) signaling and endogenous PPARγ expression in cardiac fibroblasts and pressure overloaded heart.

METHODS AND RESULTS

We observed that, in response to pressure overload induced by transverse aortic constriction, left-ventricular PPARγ protein levels were decreased in wild-type mice, but increased in mice with an inducible overexpression of dominant negative mutation of the human TGF-β type II receptor (DnTGFβRII), in which TGF-β signaling is blocked. In isolated mouse cardiac fibroblasts, we demonstrated that TGF-β1 treatment decreased steady state PPARγ mRNA (-34%) and protein (-52%) levels, as well as PPARγ transcriptional activity (-53%). Chromatin immunoprecipitation analysis showed that TGF-β1 treatment increased binding of Smad2/3, Smad4 and histone deacetylase 1, and decreased binding of acetylated histone 3 to the PPARγ promoter in cardiac fibroblasts. Both pharmacological activation and overexpression of PPARγ significantly inhibited TGF-β1-induced extracellular matrix molecule expression in isolated cardiac fibroblasts, whereas treatment with the PPARγ agonist rosiglitazone inhibited, and treatment with the PPARγ antagonist T0070907 exacerbated chronic pressure overload-induced cardiac fibrosis and remodeling in wild-type mice in vivo.

CONCLUSION

These data provide strong evidence that TGF-β1 directly suppresses PPARγ expression in cardiac fibroblasts via a transcriptional mechanism and suggest that the down-regulation of endogenous PPARγ expression by TGF-β may be involved in pressure overload-induced cardiac fibrosis.

Hypoxia induces downregulation of PPAR-γ in isolated pulmonary arterial smooth muscle cells and in rat lung via transforming growth factor-β signaling

Chronic hypoxia activates transforming growth factor-β (TGF-β) signaling and leads to pulmonary vascular remodeling. Pharmacological activation of peroxisome proliferator-activated receptor-γ (PPAR-γ) has been shown to prevent hypoxia-induced pulmonary hypertension and vascular remodeling in rodent models, suggesting a vasoprotective effect of PPAR-γ under chronic hypoxic stress. This study tested the hypothesis that there is a functional interaction between TGF-β/Smad signaling pathway and PPAR-γ in isolated pulmonary artery small muscle cells (PASMCs) under hypoxic stress. We observed that chronic hypoxia led to a dramatic decrease of PPAR-γ protein expression in whole lung homogenates (rat and mouse) and hypertrophied pulmonary arteries and isolated PASMCs. Using a transgenic model of mouse with inducible overexpression of a dominant-negative mutant of TGF-β receptor type II, we demonstrated that disruption of TGF-β pathway significantly attenuated chronic hypoxia-induced downregulation of PPAR-γ in lung. Similarly, in isolated rat PASMCs, antagonism of TGF-β signaling with either a neutralizing antibody to TGF-β or the selective TGF-β receptor type I inhibitor SB431542 effectively attenuated hypoxia-induced PPAR-γ downregulation. Furthermore, we have demonstrated that TGF-β1 treatment suppressed PPAR-γ expression in PASMCs under normoxia condition. Chromatin immunoprecipitation analysis showed that TGF-β1 treatment significantly increased binding of Smad2/3, Smad4, and the transcriptional corepressor histone deacetylase 1 to the PPAR-γ promoter in PASMCs. Conversely, treatment with the PPAR-γ agonist rosiglitazone attenuated TGF-β1-induced extracellular matrix molecule expression and growth factor in PASMCs. These data provide strong evidence that activation of TGF-β/Smad signaling, via transcriptional suppression of PPAR-γ expression, mediates chronic hypoxia-induced downregulation of PPAR-γ expression in lung.

Regulation of peroxisome proliferator-activated receptor-γ by angiotensin II via transforming growth factor-β1-activated p38 mitogen-activated protein kinase in aortic smooth muscle cells

OBJECTIVE

Peroxisome proliferator-activated receptor-γ (PPARγ) ligands attenuate angiotensin II (Ang II)-induced atherosclerosis through interactions with vascular smooth muscle cell (VSMC)-specific PPARγ in hypercholesterolemic mice. Therefore, the purpose of this study was to determine the mechanism of Ang II-mediated intracellular regulation of PPARγ in VSMCs.

METHODS AND RESULTS

Incubation of cultured mouse aortic VSMCs with Ang II for 24 hours reduced abundance of PPARγ protein, mRNA, and transcriptional activity (P<0.001). This effect was attenuated by an angiotensin type 1 receptor antagonist, losartan. Ang II-induced PPARγ reduction was dependent on stimulation of transforming growth factor (TGF)-β1 as demonstrated using either a neutralizing antibody or small interfering RNA (siRNA). Ang II-induced TGF-β1 secretion was dependent on epidermal growth factor receptor kinase activation through reactive oxygen species production. Inhibition of p38 mitogen-activated protein kinase by SB203580 or siRNA inhibited both Ang II- and TGF-β1-induced PPARγ reduction. Blockade of TGF-β1 decreased p38 phosphorylation induced by Ang II. siRNA-mediated inhibition of histone deacetylase 3 attenuated p38-mediated reductions in PPARγ abundance.

CONCLUSIONS

These findings suggest that Ang II decreases PPARγ abundance in cultured VSMCs via an angiotensin type 1 receptor-dependent secretion of TGF-β1 via phosphorylation of p38 mitogen-activated protein kinase and histone deacetylase 3.

Peroxisome proliferator-activated receptor-γ cross-regulation of signaling events implicated in liver fibrogenesis

Peroxisome proliferator-activated receptor-γ (PPARγ) is a nuclear receptor with transcriptional activity controlling multiple physical and pathological processes. Recently, PPARγ has been implicated in the pathogenesis of liver fibrosis. Its depleted expression has strong associations with the activation and transdifferentiation of hepatic stellate cells, the central event in liver fibrogenesis. Studies over the past decade demonstrate that PPARγ cross-regulates a number of signaling pathways mediated by growth factors and adipokines, and cellular events including apoptosis and senescence. These signaling and cellular events and their molecular interactions with PPARγ system are profoundly involved in liver fibrogenesis. We critically summarize these mechanistic insights into the PPARγ regulation in liver fibrogenesis based on the updated findings in this area. We conclude with a discussion of the impacts of these discoveries on the interpretation of liver fibrogenesis and their potential therapeutic implications. PPARγ activation could be a promising strategy for antifibrotic therapy.

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.

Arginine decreases peroxisome proliferator-activated receptor-γ activity via c-Jun

We have previously shown in the post ischemic gut that enteral arginine enhanced injury and inflammation via c-Jun/AP-1 and abrogated peroxisome proliferator-activated receptor (PPAR) γ activity. In the current study, we investigated the mechanism by which arginine inhibited PPARγ in vitro in rat small bowel epithelial IEC-6 cells. Arginine repressed PPARγ transcriptional activity in a time and dose-dependent fashion. Furthermore, downregulation of PPARγ by arginine involved phosphorylation of c-Jun that occurred before to changes in PPARγ transcriptional activity. Silencing of c-Jun increased PPARγ beyond that of nonsilenced cells and was not mitigated by arginine. Using a series of blocking studies, we found no relationship between arginine and the ligand-dependent binding site of PPARγ. In conclusion, arginine decreased PPARγ transcriptional activity in small bowel intestinal epithelial cells. These changes are due, in part, to phosphorylation of c-Jun and may explain the deleterious effects of enteral arginine in the post ischemic gut.

Hypoxia-induced inhibition of lung development is attenuated by the peroxisome proliferator-activated receptor-γ agonist rosiglitazone

Hypoxia enhances transforming growth factor-β (TGF-β) signaling, inhibiting alveolar development and causing abnormal pulmonary arterial remodeling in the newborn lung. We hypothesized that, during chronic hypoxia, reduced peroxisome proliferator-activated receptor-γ (PPAR-γ) signaling may contribute to, or be caused by, excessive TGF-β signaling. To determine whether PPAR-γ was reduced during hypoxia, C57BL/6 mice were exposed to hypoxia from birth to 2 wk and evaluated for PPAR-γ mRNA and protein. To determine whether rosiglitazone (RGZ, a PPAR-γ agonist) supplementation attenuated the effects of hypoxia, mice were exposed to air or hypoxia from birth to 2 wk in combination with either RGZ or vehicle, and measurements of lung histology, function, parameters related to TGF-β signaling, and collagen content were made. To determine whether excessive TGF-β signaling reduced PPAR-γ, mice were exposed to air or hypoxia from birth to 2 wk in combination with either TGF-β-neutralizing antibody or vehicle, and PPAR-γ signaling was evaluated. We observed that hypoxia reduced PPAR-γ mRNA and protein, in association with impaired alveolarization, increased TGF-β signaling, reduced lung compliance, and increased collagen. RGZ increased PPAR-γ signaling, with improved lung development and compliance in association with reduced collagen and TGF-β signaling. However, no reduction was noted in hypoxia-induced pulmonary vascular remodeling. Inhibition of hypoxia-enhanced TGF-β signaling increased PPAR-γ signaling. These results suggest that hypoxia-induced inhibition of lung development is associated with a mutually antagonistic relationship between reduced PPAR-γ and increased TGF-β signaling. PPAR-γ agonists may be of potential therapeutic significance in attenuating TGF-β signaling and improving alveolar development.

The expression of a disintegrin and metalloproteinase with thrombospondin motifs 4 in human macrophages is inhibited by the anti-atherogenic cytokine transforming growth factor-β and requires Smads, p38 mitogen-activated protein kinase and c-Jun

Atherosclerosis is an inflammatory disorder of the vasculature that is orchestrated by the action of cytokines. Macrophages play a prominent role in all stages of this disease, including foam cell formation, production of reactive oxygen species, modulation of the inflammatory response and the regulation of the stability of atherosclerotic plaques. The role of the matrix metalloproteinase family in the control of plaque stability is well established. A disintegrin and metalloproteinase with thrombospondin motif (ADAMTS) family has been implicated in several diseases and the expression of ADAMTS-4 in macrophages of atherosclerotic lesions has suggested a potential role for this protease in atherosclerosis. However, the action of cytokines on the expression of ADAMTS-4 in macrophages is poorly understood. We have investigated here the effect of transforming growth factor-β (TGF-β) on ADAMTS-4 expression in macrophages along with the regulatory mechanisms underlying its actions. Consistent with the anti-atherogenic role of TGF-β, this cytokine decreased the expression of ADAMTS-4 mRNA and protein in human macrophages. Transient transfection assays showed that the −100 to +10 promoter region contained the minimal TGF-β response elements. Small-interfering RNA-mediated knockdown revealed a critical role for Smads, p38 mitogen-activated protein kinase and c-Jun in the action of TGF-β on ADAMTS-4 mRNA expression. These studies show for the first time that TGF-β inhibits the expression of ADAMTS-4 in human macrophages and identifies the signalling pathways underlying this response. The inhibition of macrophage ADAMTS-4 expression is likely to contribute to the anti-atherogenic, plaque stabilisation action of TGF-β.

Oxidative stress modulates PPAR gamma in vascular endothelial cells

The peroxisome proliferator-activated receptor gamma (PPAR gamma) plays an important role in vascular regulation. However, the impact of oxidative stress on PPAR gamma expression and activity has not been clearly defined. Human umbilical vein endothelial cells (HUVECs) were exposed to graded concentrations of H(2)O(2) for 0.5-72h, or bovine aortic endothelial cells (BAECs) were exposed to alterations in extracellular thiol/disulfide redox potential (E(h)) of the cysteine/cystine couple. Within 2h, H(2)O(2) reduced HUVEC PPAR gamma mRNA and activity and reduced the expression of two PPAR gamma-regulated genes without altering PPAR gamma protein levels. After 4h H(2)O(2) exposure, mRNA levels remained reduced, whereas PPAR gamma activity returned to control levels. PPAR gamma mRNA levels remained depressed for up to 72 h after exposure to H(2)O(2), without any change in PPAR gamma activity. Catalase prevented H(2)O(2)-induced reductions in PPAR gamma mRNA and activity. H(2)O(2) (1) reduced luciferase expression in HUVECs transiently transfected with a human PPAR gamma promoter reporter, (2) failed to alter PPAR gamma mRNA half-life, and (3) transiently increased expression and activity of c-Fos and phospho-c-Jun. Treatment with the AP1 inhibitor curcumin prevented H(2)O(2)-mediated reductions in PPAR gamma expression. In addition, medium having an oxidized E(h) reduced BAEC PPAR gamma mRNA and activity. These findings demonstrate that oxidative stress, potentially through activation of inhibitory redox-regulated transcription factors, attenuates PPAR gamma expression and activity in vascular endothelial cells through suppression of PPAR gamma transcription.

Genetic variations in peroxisome proliferator-activated receptor gamma expression affect blood pressure

Metabolic syndrome, a clustering of conditions including obesity, insulin resistance, and hypertension, is a risk factor for cardiovascular morbidity and mortality. Because peroxisome proliferator-activated receptor gamma (PPARgamma) regulates adipocyte differentiation and lipid metabolism and is the molecular target of a class of insulin sensitizers, genetic variants that alter Pparg gene expression are potential contributors to the metabolic syndrome. To test this possibility, we generated mice having 182% of the normal steady-state level of PPARgamma mRNA by replacing the 3'-UTR of the natural Pparg gene with that of the beta-globin gene, thereby stabilizing the Pparg transcripts. This increase in PPARgamma mRNA level had no apparent consequences in various physiological parameters, except that the mice repeatedly showed a trend toward lower blood pressures (by about 3 mm Hg) than their WT littermates. In contrast, the opposite trend, toward increased blood pressure, was observed in mice with genetically reduced levels of PPARgamma mRNA as a consequence of insertion of an allele with an mRNA-destabilizing sequence into the endogenous 3'-UTR of the Pparg gene. By combining 12 sets of blood pressure measurements in more than 350 mutant mice having PPARgamma expression levels varying from 28% to 182% and more than 280 WT littermates, we show that a 2-fold genetic increase (or decrease) in PPARgamma expression levels decreases (or increases) blood pressure by about 2.8 mm Hg. Thus, our experiments demonstrate that quantitative variants causing decreased Pparg expression are a potential causative risk factor for essential hypertension.

Rosiglitazone prevents high glucose-induced vascular endothelial growth factor and collagen IV expression in cultured mesangial cells

Peroxisome proliferator-activated receptor (PPARγ), a ligand-dependent transcription factor, negatively modulates high glucose effects. We postulated that rosiglitazone (RSG), an activator of PPARγ prevents the upregulation of vascular endothelial growth factor (VEGF) and collagen IV by mesangial cells exposed to high glucose. Primary cultured rat mesangial cells were growth-arrested in 5.6 mM (NG) or 25 mM D-glucose (HG) for up to 48 hours. In HG, PPARγ mRNA and protein were reduced within 3 h, and enhanced ROS generation, expression of p22^phox, VEGF and collagen IV, and PKC-ζ membrane association were prevented by RSG. In NG, inhibition of PPARγ caused ROS generation and VEGF expression that were unchanged by RSG. Reduced AMP-activated protein kinase (AMPK) phosphorylation in HG was unchanged with RSG, and VEGF expression was unaffected by AMPK inhibition. Hence, PPARγ is a negative modulator of HG-induced signaling that acts through PKC-ζ but not AMPK and regulates VEGF and collagen IV expression by mesangial cells.

PPARs and the cardiovascular system

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear hormone-receptor superfamily. Originally cloned in 1990, PPARs were found to be mediators of pharmacologic agents that induce hepatocyte peroxisome proliferation. PPARs also are expressed in cells of the cardiovascular system. PPAR gamma appears to be highly expressed during atherosclerotic lesion formation, suggesting that increased PPAR gamma expression may be a vascular compensatory response. Also, ligand-activated PPAR gamma decreases the inflammatory response in cardiovascular cells, particularly in endothelial cells. PPAR alpha, similar to PPAR gamma, also has pleiotropic effects in the cardiovascular system, including antiinflammatory and antiatherosclerotic properties. PPAR alpha activation inhibits vascular smooth muscle proinflammatory responses, attenuating the development of atherosclerosis. However, PPAR delta overexpression may lead to elevated macrophage inflammation and atherosclerosis. Conversely, PPAR delta ligands are shown to attenuate the pathogenesis of atherosclerosis by improving endothelial cell proliferation and survival while decreasing endothelial cell inflammation and vascular smooth muscle cell proliferation. Furthermore, the administration of PPAR ligands in the form of TZDs and fibrates has been disappointing in terms of markedly reducing cardiovascular events in the clinical setting. Therefore, a better understanding of PPAR-dependent and -independent signaling will provide the foundation for future research on the role of PPARs in human cardiovascular biology.

Troglitazone suppresses transforming growth factor-beta1-induced collagen type I expression in keloid fibroblasts

BACKGROUND

Peroxisome proliferator-activated receptor (PPAR)-gamma agonists are increasingly used in patients with diabetes and some studies have suggested a beneficial effect on organ fibrosis. However their effects on dermal fibrosis in keloids are unknown.

OBJECTIVE

To investigate the effect of the PPAR-gamma agonist troglitazone on transforming growth factor (TGF)-beta1-induced collagen type I expression in keloid fibroblasts.

METHODS

Keloid fibroblasts were cultured and exposed to different concentrations of troglitazone in the presence of TGF-beta1. The mRNA expression of PPAR-gamma was determined by semiquantitative reverse transcriptase-polymerase chain reaction. The protein of PPAR-gamma, Smad2, Smad3, phoshpo-Smad2/3 and collagen type I was determined by Western blotting and collagen synthesis was evaluated by measuring (3)H-proline incorporation. The effect of troglitazone on cell viability was evaluated by the colorimetric conversion of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide.

RESULTS

PPAR-gamma was expressed at a moderate level in keloid fibroblasts. Troglitazone depressed TGF-beta1-stimulated collagen type I expression and collagen synthesis in keloid fibroblasts in a concentration-dependent manner. Moreover, troglitazone inhibited expression and phosphorylation of TGF-beta1-induced Smad2/3. Cell viability was unaffected. These inhibitory effects of troglitazone were reversed by the PPAR-gamma-specific antagonist GW9662.

CONCLUSIONS

Our data suggest that PPAR-gamma is present in keloid fibroblasts and PPAR-gamma activation inhibits TGF-beta1-induced collagen type I expression at least in part by decreasing collagen synthesis. PPAR-gamma may be a promising therapeutic target for keloids.

PPARgamma and Agonists against Cancer: Rational Design of Complementation Treatments

PPARγ is a member of the ligand-activated nuclear receptor superfamily: its ligands act as insulin sensitizers and some are approved for the treatment of metabolic disorders in humans. PPARγ has pleiotropic effects on survival and proliferation of multiple cell types, including cancer cells, and is now subject of intensive preclinical cancer research. Studies of the recent decade highlighted PPARγ role as a potential modulator of angiogenesis in vitro and in vivo. These observations provide an additional facet to the PPARγ image as potential anticancer drug. Currently PPARγ is regarded as an important target for the therapies against angiogenesis-dependent pathological states including cancer and vascular complications of diabetes. Some of the studies, however, identify pro-angiogenic and tumor-promoting effects of PPARγ and its ligands pointing out the need for further studies. Below, we summarize current knowledge of PPARγ regulatory mechanisms and molecular targets, and discuss ways to maximize the beneficial activity of the PPARγ agonists.

Pharmacological application of caffeine inhibits TGF-beta-stimulated connective tissue growth factor expression in hepatocytes via PPARgamma and SMAD2/3-dependent pathways

BACKGROUND/AIMS

Epidemiological studies suggest that coffee drinking is inversely correlated with the risk of development of liver fibrosis but the molecular basis is unknown.

METHODS

We investigated the pharmacological mechanisms involved in caffeine-dependent regulation of CTGF expression, an important modulator protein of fibrogenic TGF-beta, in rat hepatocytes using Western-blot, co-immunoprecipitations, reporter-gene-assays and ELISAs.

RESULTS

It is demonstrated that caffeine, similar to 8-Br-cAMP, suppresses CTGF expression, decreases SMAD2 protein levels and inhibits SMAD1/3-phosphorylation. The SMAD2 level can be restored by a proteasome inhibitor. Additionally, caffeine leads to an up-regulation of PPARgamma expression, that enhances the inhibitory effect of the natural PPARgamma agonist 15-PGJ(2) on CTGF expression by inducing a dissociation of the SMAD2/3-CBP/p300-transcriptional complex.

CONCLUSIONS

We show that caffeine strongly down-modulates TGF-beta-induced CTGF expression in hepatocytes by stimulation of degradation of the TGF-beta effector SMAD 2, inhibition of SMAD3 phosphorylation and up-regulation of the PPARgamma-receptor. Long-term caffeinization might be an option for anti-fibrotic trials in chronic liver diseases.

Divergent transforming growth factor-beta signaling in hepatic stellate cells after liver injury: functional effects on ECE-1 regulation

In liver wound healing, transforming growth factor-beta (TGF-beta) plays a critical role in stellate cell activation as well as signaling cascades in the fibrogenic response to injury. We postulate that the TGF-beta-dependent downstream signaling pathway may vary according to the mechanism of stellate cell activation; this study was undertaken to ascertain whether the downstream signaling pathways mediated by TGF-beta vary in different liver injury models. We measured Smad3 and MAP kinase activation after isolating stellate cells from rat livers injured by either bile duct ligation (BDL) or repeated carbon tetrachloride (CCl(4)) administration. Phospho-Smad3 was dramatically up-regulated in stellate cells after CCl(4) injury, but not after BDL-induced injury. TGF-beta signaling in stellate cells activated after BDL was mediated prominently through ERK activation, whereas activation induced by CCl(4) injury or culture led to a cross-signaling mechanism involving both Smad3 and p38. The divergent Smad signaling pathways observed appeared to be attributable to the differential regulation of the early growth response gene-1 (Egr-1), an apparent negative transcriptional factor for Smad3 in our system. In addition, inhibition of ERK activation in stellate cells from BDL-injured liver led to a decrease in expression of endothelin-converting enzyme-1, a critical regulator of endothelin-1. We speculate that TGF-beta signaling proceeds through differential signaling pathways depending on the mechanism of liver injury that leads to stellate cell activation.

Smad-independent transforming growth factor-beta regulation of early growth response-1 and sustained expression in fibrosis: implications for scleroderma

Transforming growth factor-beta (TGF-beta) plays a key role in scleroderma pathogenesis. The transcription factor early growth response-1 (Egr-1) mediates the stimulation of collagen transcription elicited by TGF-beta and is necessary for the development of pulmonary fibrosis in mice. Here, we report that TGF-beta causes a time- and dose-dependent increase in Egr-1 protein and mRNA levels and enhanced transcription of the Egr-1 gene via serum response elements in normal fibroblasts. The ability of TGF-beta to stimulate Egr-1 was preserved in Smad3-null mice and in explanted Smad3-null fibroblasts. The response was blocked by a specific mitogen-activated protein kinase kinase 1 (MEK1) inhibitor but not by an ALK5 kinase inhibitor. Furthermore, MEK1 was phosphorylated by TGF-beta, which was sufficient to drive Egr-1 transactivation. Stimulation by TGF-beta enhanced the transcriptional activity of Elk-1 via the MEK-extracellular signal-regulated kinase 1/2 pathway. Bleomycin-induced scleroderma in the mouse was accompanied by increased Egr-1 accumulation in lesional fibroblasts. Furthermore, biopsies of lesional skin and lung from patients with scleroderma showed increased Egr-1 levels, which were highest in early diffuse disease. Moreover, both Egr-1 mRNA and protein were elevated in explanted scleroderma skin fibroblasts in vitro. Together, these findings define a Smad-independent TGF-beta signal transduction mechanism that underlies the stimulation of Egr-1, demonstrate for the first time sustained Egr-1 up-regulation in fibrotic lesions and suggests that Egr-1 has a role in the induction and progression of fibrosis.

Pathobiology of pulmonary hypertension

A variety of conditions can lead to the development of pulmonary arterial hypertension (PAH). Current treatments can improve symptoms and reduce the severity of the hemodynamic abnormality, but most patients remain quite limited, and deterioration in their condition necessitates a lung transplant. This review discusses current experimental and clinical studies that investigate the pathobiology of PAH. An emerging theme is the consideration of ways in which one might reverse the advanced occlusive structural changes in the pulmonary circulation causing PAH. The current debate concerning the role of regeneration through stem cells is presented. This review also highlights investigations in a number of laboratories relating the pathobiology of PAH to mutations causing loss of function of bone morphogenetic protein receptor II in patients with familial PAH, as well as sporadic cases.

Transcriptional regulation of peroxisome proliferator-activated receptors and liver X receptors

Peroxisome proliferator-activated receptors (PPAR) and liver X receptors (LXR) regulate a plethora of biologic processes and key metabolic and physiologic events. Deregulation of their transcription and activity is commonly associated with dyslipidemic disorders, diabetes, cancer, and cardiovascular disease. This review addresses recent advances in our understanding of the molecular mechanisms regulating transcription of these nuclear receptors. The heterogeneity of factors regulating their transcription and activity suggests intricate regulatory networks that determine their tissue expression pattern and their responses to pharmacologic agents. Understanding such mechanisms will facilitate unraveling their protective effects in disease as well as the design of effective targeted therapies.

Differentiation of human circulating fibrocytes as mediated by transforming growth factor-beta and peroxisome proliferator-activated receptor gamma

Fibrocytes are a distinct population of fibroblast-like progenitor cells in peripheral blood that have recently been shown to possess plasticity to differentiate along mesenchymal lineages, including commitment to myofibroblast and adipocyte cells. Here, we demonstrated that transforming growth factor (TGF) beta1 drives fibrocyte-to-myofibroblast differentiation through activating Smad2/3 and SAPK/JNK MAPK pathways, which in turn stimulates alpha-smooth muscle actin expression. We determined that SAPK/JNK signaling acts in a positive feedback loop to modulate Smad2/3 nuclear availability and Smad2/3-dependent transcription. Conversely, fibrocyte-to-adipocyte differentiation is driven by the peroxisome proliferator-activated receptor (PPAR) gamma agonist troglitazone, which is associated with cytoplasmic lipid accumulation and induction of aP2. Treatment with troglitazone also disrupted TGF beta 1-activated SAPK/JNK signaling, leading to decreased Smad2/3 transactivation activity and alpha-smooth muscle actin expression. Interestingly, TGF beta 1 was demonstrated to have reciprocal inhibition on fibrocyte differentiation to adipocytes. By activating SAPK/JNK signaling, which is normally suppressed during adipogenesis, PPARgamma-dependent transactivation activity and induction of aP2 expression were disrupted. Taken together, within the context of the local microenvironmental niche, the delicate balance of PPARgamma and TGF beta 1 activation drives the selection of an adipocyte or myofibroblast differentiation pathway through SAPK/JNK signaling.