The role of PPAR-gamma in macrophage differentiation and cholesterol uptake

High density lipoprotein metabolism in low density lipoprotein receptor-deficient mice

The LDL receptor (LDLR) and scavenger receptor class B type I (SR-BI) play physiological roles in LDL and HDL metabolism in vivo. In this study, we explored HDL metabolism in LDLR-deficient mice in comparison with WT littermates. Murine HDL was radiolabeled in the protein ((125)I) and in the cholesteryl ester (CE) moiety ([(3)H]). The metabolism of (125)I-/[(3)H]HDL was investigated in plasma and in tissues of mice and in murine hepatocytes. In WT mice, liver and adrenals selectively take up HDL-associated CE ([(3)H]). In contrast, in LDLR(-/-) mice, selective HDL CE uptake is significantly reduced in liver and adrenals. In hepatocytes isolated from LDLR(-/-) mice, selective HDL CE uptake is substantially diminished compared with WT liver cells. Hepatic and adrenal protein expression of lipoprotein receptors SR-BI, cluster of differentiation 36 (CD36), and LDL receptor-related protein 1 (LRP1) was analyzed by immunoblots. The respective protein levels were identical both in hepatic and adrenal membranes prepared from WT or from LDLR(-/-) mice. In summary, an LDLR deficiency substantially decreases selective HDL CE uptake by liver and adrenals. This decrease is independent from regulation of receptor proteins like SR-BI, CD36, and LRP1. Thus, LDLR expression has a substantial impact on both HDL and LDL metabolism in mice.

PPARγ and the global map of adipogenesis and beyond

Peroxisome proliferator-activated receptor γ (PPARγ) is a member of the nuclear receptor (NR) superfamily of ligand-dependent transcription factors (TFs) and function as a master regulator of adipocyte differentiation and metabolism. We review recent breakthroughs in the understanding of PPARγ gene regulation and function in the chromatin context. It is now clear that multiple TFs team up to induce PPARγ during adipogenesis, and that other TFs cooperate with PPARγ to ensure adipocyte-specific genomic binding and function. We discuss how this differs in other PPARγ-expressing cells such as macrophages and how these genome-wide mechanisms are preserved across species despite modest conservation of specific binding sites. These emerging considerations inform our understanding of PPARγ function as well as of adipocyte development and physiology.

Differential roles of PPARγ vs TR4 in prostate cancer and metabolic diseases

Peroxisome proliferator-activated receptor γ (PPARγ, NR1C3) and testicular receptor 4 nuclear receptor (TR4, NR2C2) are two members of the nuclear receptor (NR) superfamily that can be activated by several similar ligands/activators including polyunsaturated fatty acid metabolites, such as 13-hydroxyoctadecadienoic acid and 15-hydroxyeicosatetraenoic acid, as well as some anti-diabetic drugs such as thiazolidinediones (TZDs). However, the consequences of the transactivation of these ligands/activators via these two NRs are different, with at least three distinct phenotypes. First, activation of PPARγ increases insulin sensitivity yet activation of TR4 decreases insulin sensitivity. Second, PPARγ attenuates atherosclerosis but TR4 might increase the risk of atherosclerosis. Third, PPARγ suppresses prostate cancer (PCa) development and TR4 suppresses prostate carcinogenesis yet promotes PCa metastasis. Importantly, the deregulation of either PPARγ or TR4 in PCa alone might then alter the other receptor's influences on PCa progression. Knocking out PPARγ altered the ability of TR4 to promote prostate carcinogenesis and knocking down TR4 also resulted in TZD treatment promoting PCa development, indicating that both PPARγ and TR4 might coordinate with each other to regulate PCa initiation, and the loss of either one of them might switch the other one from a tumor suppressor to a tumor promoter. These results indicate that further and detailed studies of both receptors at the same time in the same cells/organs may help us to better dissect their distinct physiological roles and develop better drug(s) with fewer side effects to battle PPARγ- and TR4-related diseases including tumor and cardiovascular diseases as well as metabolic disorders.

Compare the effect of eicosapentaenoic acid and oxidized low-density lipoprotein on the expression of CD36 and peroxisome proliferator-activated receptor gamma

BACKGROUND

There is evidence that CD36 promotes foam cell formation through internalizing oxidized LDL (ox-LDL) into macrophages; therefore, it plays a key role in pathogenesis of atherosclerosis. In addition, CD36 expression seems to be mediated by nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR-γ). The aim of the present study was to evaluate and compare the effect of PPAR-γ ligands, eicosapentaenoic acid (EPA) as an anti-atherogenic factor and ox-LDL as an atherogenic factor on CD36 expression. Mechanism of PPAR- γ action and its ligands in CD36 expression were also investigated.

METHODS

Raw 264.7 macrophage cell line was treated with ox-LDL (100 and 150 μg protein/LDL) and EPA (100 and 200 μM) for 24 and 48 hours in absence or presence of PPAR-γ inhibitor, T0070907. Quantitative real-time PCR and Western-blotting were used for analysis of gene and protein expression, respectively.

RESULTS

Raw 264.7 exposures to ox-LDL and EPA resulted in increased expression of CD36 mRNA and protein; however, mRNA and PPAR-γ protein were not up-regulated significantly. Pre-incubation of cells with T0070907 led to decreased expression of CD36 when treated with ox-LDL and EPA.

CONCLUSION

It was confirmed that both EPA and ox-LDL increased CD36 expression but not PPAR-γ, and also co-treatment with PPAR-γ inhibitor decreased CD36 expression. We concluded that up-regulation of CD36 depends on PPAR-γ activation and is not related to increased expression of PPAR-γ. Induction of CD36 by EPA showed that CD36 suppression is not the means by which ω-3 fatty acids (EPA) provide protection against formation of atherosclerotic plaque.

Effect of cinnamon water extract on monocyte-to-macrophage differentiation and scavenger receptor activity

Background

Water soluble cinnamon extract has been shown to increase insulin sensitivity and modulate macrophage activation, a desirable trait for the management of obesity or atherosclerosis. Our present study investigated whether cinnamon water extract (CWE) may influence the differentiation of monocytes into macrophages and the activity of macrophage scavenger receptors, commonly observed in atherosclerotic lesions.

Methods

We investigated the effect of CWE on the expression of various surface markers and the uptake of acetylated low density lipoprotein (LDL) in phorbol-12-myristate-13-acetate (PMA)-stimulated THP-1 cells. The protein levels of PMA or macrophage-colony stimulating factor (M-CSF)-stimulated type 1 macrophage scavenger receptor (SRA) were analyzed. Finally, the role of extracellar signal-related kinase (ERK) 1/2 in SRA synthesis and the effect of CWE on PMA-stimulated ERK1/2 were determined.

Results

CWE inhibited the differentiation of monocyte by decreasing the expression of CD11b, CD36 and SRA and the uptake of acetyl LDL. CWE suppressed the upregulation of SRA by M-CSF and modulated ERK1/2 activity, which was required for PMA-induced SRA synthesis.

Conclusions

Our results demonstrate that CWE was able to interfere with monocyte differentiation and macrophage scavenger activity, indicating its potential in preventing the development of atherosclerotic lesions.

Proatherogenic conditions promote autoimmune T helper 17 cell responses in vivo

Patients with systemic autoimmune diseases show increased incidence of atherosclerosis. However, the contribution of proatherogenic factors to autoimmunity remains unclear. We found that atherogenic mice (herein referred to as LDb mice) exhibited increased serum interleukin-17, which was associated with increased numbers of T helper 17 (Th17) cells in secondary lymphoid organs. The environment within LDb mice was substantially favorable for Th17 cell polarization of autoreactive T cells during homeostatic proliferation, which was considerably inhibited by antibodies directed against oxidized low-density lipoprotein (oxLDL). Moreover, the uptake of oxLDL induced dendritic-cell-mediated Th17 cell polarization by triggering IL-6 production in a process dependent on TLR4, CD36, and MyD88. Furthermore, self-reactive CD4(+) T cells that expanded in the presence of oxLDL induced more profound experimental autoimmune encephalomyelitis. These findings demonstrate that proatherogenic factors promote the polarization and inflammatory function of autoimmune Th17 cells, which could be critical for the pathogenesis of atherosclerosis and other related autoimmune diseases.

Can an oral antidiabetic (rosiglitazone) be of benefit in leukemia treatment?

PPARs are ligand-regulated transcription factors and regulate expression of several gene products. Therefore, PPARs are being studied for their possible contribution to the treatment of cancer, atherosclerosis, inflammation, infertility and demyelinating diseases. Primary AML patients were observed to have significantly elevated PPARγ mRNA expression compared to normal peripheral blood or bone marrow mononuclear cells. This study investigated the cytotoxic effects of rosiglitazone maleate, a pure PPARγ agonist, in vitro in HL-60 cell line. This study obtained results which can provide guidance for future studies. Whether the PPARy agonist rosiglitazone maleate may provide additive effects in refractory or relapsing cases of acute leukemia may be set as an objective for the future studies.

The role of lipid-activated nuclear receptors in shaping macrophage and dendritic cell function: From physiology to pathology

Nuclear receptors are ligand-activated transcription factors linking lipid signaling to the expression of the genome. There is increasing appreciation of the involvement of this receptor network in the metabolic programming of macrophages and dendritic cells (DCs), essential members of the innate immune system. In this review we focus on the role of retinoid X receptor, retinoic acid receptor, peroxisome proliferator-associated receptor γ, liver X receptor, and vitamin D receptor in shaping the immune and metabolic functions of macrophages and DCs. We also provide an overview of the contribution of macrophage- and DC-expressed nuclear receptors to various immunopathologic conditions, such as rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus, asthma, and some others. We suggest that systematic analyses of the roles of these receptors and their activating lipid ligands in immunopathologies combined with complementary and focused translational and clinical research will be crucial for the development of new therapies using the many molecules available to target nuclear receptors.

Pleiotropic effects of peroxisome proliferator-activated receptor γ and δ in vascular diseases

Peroxisome proliferator-activated receptors gamma (PPARγ) and delta (PPARδ) are nuclear receptors that have significant physiological effects on glucose and lipid metabolism. Experimental studies in animal models of metabolic disease have demonstrated their effects on improving lipid profile, insulin sensitivity, and reducing inflammatory responses. PPARγ and -δ are also expressed in the vasculature and their beneficial effects have been examined in various cardiovascular disease models such as atherosclerosis, hypertension, diabetic vascular complications, etc. using pharmacological ligands or genetic tools including viral vectors and transgenic mice. These studies suggest that PPARγ and δ are antiinflammatory, antiatherogenic, antioxidant, and antifibrotic against vascular diseases. Several signaling pathways, effector molecules, as well as coactivators/repressors have been identified as responsible for the protective effects of PPARγ and -δ in the vasculature. We discuss the pleiotropic effect of PPARγ and δ in vascular dysfunction, including atherosclerosis, hypertension, vascular remodeling, vascular injury, and diabetic vasculopathy, in various animal models, and the major underlying mechanisms. We also compare the phenotypes of several endothelial cell/vascular smooth muscle-specific PPARγ and -δ knockout and overexpressing transgenic mice in various disease models, and the implications underlying the functional importance of vascular PPARγ and δ in regulating whole-body homeostasis.

Peroxisome-proliferator-activated receptors regulate redox signaling in the cardiovascular system

Peroxisome-proliferator-activated receptors (PPARs) comprise three subtypes (PPARα, δ and γ) to form a nuclear receptor superfamily. PPARs act as key transcriptional regulators of lipid metabolism, mitochondrial biogenesis, and anti-oxidant defense. While their roles in regulating lipid metabolism have been well established, the role of PPARs in regulating redox activity remains incompletely understood. Since redox activity is an integral part of oxidative metabolism, it is not surprising that changes in PPAR signaling in a specific cell or tissue will lead to alteration of redox state. The effects of PPAR signaling are directly related to PPAR expression, protein activities and PPAR interactions with their coregulators. The three subtypes of PPARs regulate cellular lipid and energy metabolism in most tissues in the body with overlapping and preferential effects on different metabolic steps depending on a specific tissue. Adding to the complexity, specific ligands of each PPAR subtype may also display different potencies and specificities of their role on regulating the redox pathways. Moreover, the intensity and extension of redox regulation by each PPAR subtype are varied depending on different tissues and cell types. Both beneficial and adverse effects of PPAR ligands against cardiovascular disorders have been extensively studied by many groups. The purpose of the review is to summarize the effects of each PPAR on regulating redox and the underlying mechanisms, as well as to discuss the implications in the cardiovascular system.

Nuclear receptor mediated mechanisms of macrophage cholesterol metabolism

Macrophages comprise a family of multi-faceted phagocytic effector cells that differentiate "in situ" from circulating monocytes to exert various functions including clearance of foreign pathogens as well as debris derived from host cells. Macrophages also possess the ability to engulf and metabolize lipids and this way connect lipid metabolism and inflammation. The molecular link between these processes is provided by certain members of the nuclear receptor family. For instance, peroxisome proliferator activated receptors (PPAR) and liver X receptors (LXR) are able to sense the dynamically changing lipid environment and translate it to gene expression changes in order to modulate the cellular phenotype. Atherosclerosis embodies both sides of this coin: it is a disease in which macrophages with altered cholesterol metabolism keep the arteries in a chronically inflamed state. A large body of publications has accumulated during the past few decades describing the role of nuclear receptors in the regulation of macrophage cholesterol homeostasis, their contribution to the formation of atherosclerotic plaques and their crosstalk with inflammatory pathways. This review will summarize the most recent findings from this field narrowly focusing on the contribution of various nuclear receptors to macrophage cholesterol metabolism.

AICAR inhibits PPARγ during monocyte differentiation to attenuate inflammatory responses to atherogenic lipids

AIMS

Transcriptional regulation through peroxisome proliferator-activated receptor γ (PPARγ) is critical for an altered lipid metabolism during monocyte to macrophage differentiation. Here, we investigated how 5-aminoimidazole-4-carboxamide riboside (AICAR), an activator of AMP-dependent protein kinase (AMPK), affects PPARγ during monocyte differentiation.

METHODS AND RESULTS

During the differentiation of THP-1 monocytic cells or primary human monocytes to macrophages, we observed that AICAR inhibited the expression of PPARγ target genes, such as fatty acid-binding protein 4 or CD36. This effect was independent of AICAR conversion to AICAR ribotide and AMPK activation. While AICAR increased PPARγ mRNA expression that paralleled differentiation, it inhibited PPARγ protein synthesis without affecting PPARγ protein stability. Monocytes differentiated to macrophages in the presence of AICAR revealed an attenuated uptake of oxidized low-density lipoprotein (oxLDL) and reduced oxLDL-triggered c-Jun N-terminal kinase (JNK) activation. JNK and endoplasmic reticulum stress responses to the saturated fatty acid palmitate were attenuated as well, an effect mimicked by the knockdown of PPARγ. Although PPARγ has been reported to support alternative macrophage activation, AICAR did not inhibit interleukin-4-induced gene expression in differentiating monocytes.

CONCLUSION

Inhibition of PPARγ-dependent gene expression during monocyte differentiation may contribute to an AICAR-elicited macrophage phenotype characterized by reduced inflammatory responses to modified lipoproteins and saturated fatty acids.

Characterization of human adipose tissue-resident hematopoietic cell populations reveals a novel macrophage subpopulation with CD34 expression and mesenchymal multipotency

Adipose tissue (AT) is composed of mature adipocytes and stromal vascular fraction (SVF) cells, including adipose stem/stromal cells (ASCs). We characterized hematopoietic cells residing in human nonobese AT by analyzing the SVF isolated from human lipoaspirates and peripheral blood (PB). Flow cytometry revealed that AT-resident hematopoietic cells consisted of AT-resident macrophages (ATMs) or lymphocytes with a negligible number of granulocytes. AT-resident lymphocytes were composed of helper T cells and natural killer cells. Almost no B cells and few cytotoxic T cells were observed in nonobese AT. More than 90% of ATMs were M2 state CD206(+) macrophages (CD45(+)/CD14(+)) that were located in the periendothelium or interstitial spaces between adipocytes. We also discovered a novel subpopulation of CD34(+)/CD206(+) ATMs (11.1% of CD206(+)ATMs) that localized in the perivascular region. Microarray of noncultured CD34(+)/CD206(+) ATMs, CD34(-)/CD206(+) ATMs, CD45(-)/CD31(-)/CD34(+) ASCs, and PB-derived circulating monocytes revealed that CD34(+)/CD206(+) ATMs shared characteristics with ASCs and circulating monocytes. Unlike CD34(-)/CD206(+) ATMs, CD34(+)/CD206(+) ATMs could grow in adherent culture and were capable of differentiating into multiple mesenchymal (adipogenic, osteogenic, and chondrogenic) lineages, similar to ASCs. CD34(+)/CD206(+) ATMs grew rapidly and lost expression of CD45, CD14, and CD206 by passage 3, which resulted in a similar expression profile to ASCs. Thus, this novel ATM subpopulation (CD45(+)/CD14(+)/CD34(+)/CD206(+)) showed distinct biological properties from other ATMs and circulating monocytes/macrophages. The CD34(+)/CD206(+) ATMs possessed characteristics similar to ASCs, including adherence, localization, morphology, and mesenchymal multipotency. This AT-resident subpopulation may have migrated from the bone marrow and may be important to tissue maintenance and remolding.

An investigation of the resolution of inflammation (catabasis) in COPD

BACKGROUND

Chronic Obstructive Pulmonary Disease (COPD) is characterized by an enhanced inflammatory response to smoking that persists despite quitting. The resolution of inflammation (catabasis) is a complex and highly regulated process where tissue resident macrophages play a key role since they phagocytose apoptotic cells (efferocytosis), preventing their secondary necrosis and the spill-over of their pro-inflammatory cytoplasmic content, and release pro-resolution and tissue repair molecules, such as TGFβ, VEGF and HGF. Because inflammation does not resolve in COPD, we hypothesized that catabasis may be abnormal in these patients.

METHODS

To explore this hypothesis, we studied lung tissue samples obtained at surgery from 21 COPD patients, 22 smokers with normal spirometry and 13 non-smokers controls. In these samples we used: (1) immunohistochemistry to assess the expression of CD44, CD36, VEGF and TGFβ in lung macrophages; (2) real time PCR to determine HGF, PPARγ, TGFβ, VEGF and MMP-9 gene expression; and, (3) ELISA to quantify lipoxin A4, a lipid mediator of catabasis.

RESULTS

We found that current and former smokers with COPD showed: (1) more inflammation (higher MMP-9 expression); (2) reduced macrophage surface expression of CD44, a key efferocytosis receptor; and, (3) similar levels of TGFβ, VEGF, HGF, PPARγ, and lipoxin A4 than smokers with normal spirometry, despite the presence of inflammation and disease.

CONCLUSIONS

These results identify several potential abnormalities of catabasis in patients with COPD.

Transcription of liver X receptor is down-regulated by 15-deoxy-Δ(12,14)-prostaglandin J(2) through oxidative stress in human neutrophils

Liver X receptors (LXRs) are ligand-activated transcription factors of the nuclear receptor superfamily. They play important roles in controlling cholesterol homeostasis and as regulators of inflammatory gene expression and innate immunity, by blunting the induction of classical pro-inflammatory genes. However, opposite data have also been reported on the consequences of LXR activation by oxysterols, resulting in the specific production of potent pro-inflammatory cytokines and reactive oxygen species (ROS). The effect of the inflammatory state on the expression of LXRs has not been studied in human cells, and constitutes the main aim of the present work. Our data show that when human neutrophils are triggered with synthetic ligands, the synthesis of LXRα mRNA became activated together with transcription of the LXR target genes ABCA1, ABCG1 and SREBP1c. An inflammatory mediator, 15-deoxy-Δ^12,14-prostaglandin J₂ (15dPGJ₂), hindered T0901317-promoted induction of LXRα mRNA expression together with transcription of its target genes in both neutrophils and human macrophages. This down-regulatory effect was dependent on the release of reactive oxygen species elicited by 15dPGJ₂, since it was enhanced by pro-oxidant treatment and reversed by antioxidants, and was also mediated by ERK1/2 activation. Present data also support that the 15dPGJ₂-induced serine phosphorylation of the LXRα molecule is mediated by ERK1/2. These results allow to postulate that down-regulation of LXR cellular levels by pro-inflammatory stimuli might be involved in the development of different vascular diseases, such as atherosclerosis.

DNA polymerase β variant Ile260Met generates global gene expression changes related to cellular transformation

Maintenance of genomic stability is essential for cellular survival. The base excision repair (BER) pathway is critical for resolution of abasic sites and damaged bases, estimated to occur 20,000 times in cells daily. DNA polymerase β (Pol β) participates in BER by filling DNA gaps that result from excision of damaged bases. Approximately 30% of human tumours express Pol β variants, many of which have altered fidelity and activity in vitro and when expressed, induce cellular transformation. The prostate tumour variant Ile260Met transforms cells and is a sequence-context-dependent mutator. To test the hypothesis that mutations induced in vivo by Ile260Met lead to cellular transformation, we characterized the genome-wide expression profile of a clone expressing Ile260Met as compared with its non-induced counterpart. Using a 1.5-fold minimum cut-off with a false discovery rate (FDR) of <0.05, 912 genes exhibit altered expression. Microarray results were confirmed by quantitative real-time polymerase chain reaction (qRT-PCR) and revealed unique expression profiles in other clones. Gene Ontology (GO) clusters were analyzed using Ingenuity Pathways Analysis to identify altered gene networks and associated nodes. We determined three nodes of interest that exhibited dysfunctional regulation of downstream gene products without themselves having altered expression. One node, peroxisome proliferator-activated protein γ (PPARG), was sequenced and found to contain a coding region mutation in PPARG2 only in transformed cells. Further analysis suggests that this mutation leads to dominant negative activity of PPARG2. PPARG is a transcription factor implicated to have tumour suppressor function. This suggests that the PPARG2 mutant may have played a role in driving cellular transformation. We conclude that PPARG induces cellular transformation by a mutational mechanism.

Systemic analysis of PPARγ in mouse macrophage populations reveals marked diversity in expression with critical roles in resolution of inflammation and airway immunity

Although peroxisome proliferator-activated receptor γ (PPARγ) has anti-inflammatory actions in macrophages, which macrophage populations express PPARγ in vivo and how it regulates tissue homeostasis in the steady state and during inflammation remains unclear. We now show that lung and spleen macrophages selectively expressed PPARγ among resting tissue macrophages. In addition, Ly-6C(hi) monocytes recruited to an inflammatory site induced PPARγ as they differentiated to macrophages. When PPARγ was absent in Ly-6C(hi)-derived inflammatory macrophages, initiation of the inflammatory response was unaffected, but full resolution of inflammation failed, leading to chronic leukocyte recruitment. Conversely, PPARγ activation favored resolution of inflammation in a macrophage PPARγ-dependent manner. In the steady state, PPARγ deficiency in red pulp macrophages did not induce overt inflammation in the spleen. By contrast, PPARγ deletion in lung macrophages induced mild pulmonary inflammation at the steady state and surprisingly precipitated mortality upon infection with Streptococcus pneumoniae. This accelerated mortality was associated with impaired bacterial clearance and inability to sustain macrophages locally. Overall, we uncovered critical roles for macrophage PPARγ in promoting resolution of inflammation and maintaining functionality in lung macrophages where it plays a pivotal role in supporting pulmonary host defense. In addition, this work identifies specific macrophage populations as potential targets for the anti-inflammatory actions of PPARγ agonists.

Peroxisome proliferator-activated receptor-gamma expression in monocytes/macrophages from rheumatoid arthritis patients: relation to disease activity and therapy efficacy--a pilot study

OBJECTIVES

Peroxisome proliferator-activated receptor-gamma (PPARγ) is expressed by different cell types in the joints and plays a relevant anti-inflammatory role in various diseases. This pilot study aimed to evaluate PPARγ expression in monocytes/macrophages isolated from RA patients as compared with healthy subjects, the relationships between PPARγ expression, MMP-9 activity and disease, and the influence of therapy with anti-rheumatic drugs on these parameters.

METHODS

Thirty RA patients of both sexes (treated with CSs and MTX, mainly) and 15 healthy volunteers were enrolled in this study. Disease severity was evaluated by the 28-joint disease activity score (DAS-28). Monocytes and monocyte-derived macrophages (MDMs) were isolated by standard procedures. PPARγ protein and mRNA expression were assessed by immunoblotting and real-time PCR, respectively; MMP-9 activity was determined by gelatin zymography. Moreover, we checked the ability of 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ, a PPARγ agonist), MTX and methylprednisolone (MP) to affect PPARγ expression and lipopolysaccharide (LPS)-induced MMP-9 activity.

RESULTS

Monocytes/MDMs from RA patients have significantly enhanced PPARγ expression (both protein and mRNA) and MMP-9 activity as compared with healthy donors. Interestingly, cells from patients with less active disease (DAS-28 <3.2) present higher PPARγ protein expression and lower MMP-9 activity than RA patients with DAS-28 >3.2. At therapeutic concentrations, MTX and MP increase in vitro PPARγ protein expression and inhibit LPS-induced MMP-9 activity.

CONCLUSION

PPARγ expression in human monocytes/MDMs could represent an indicator of disease activity and therapy efficacy in RA because patients with a DAS-28 score <3.2 show the highest expression.

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

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

Effects of PPARγ Ligands on Leukemia

Peroxisome proliferator-activated receptors (PPARs) and retinoic acid receptors (RARs), members of the nuclear receptor superfamily, are transcription factors that regulate a variety of important cellular functions. PPARs form heterodimers retinoid X receptor (RXR), an obligate heterodimeric partner for other nuclear receptors. Several novel links between retinoid metabolism and PPAR responses have been identified, and activation of PPAR/RXR expression has been shown to increase response to retinoids. PPARγ has emerged as a key regulator of cell growth and survival, whose activity is modulated by a number of synthetic and natural ligands. While clinical trials in cancer patients with thiazolidinediones (TZD) have been disappointing, novel structurally different PPARγ ligands, including triterpenoids, have entered clinical arena as therapeutic agents for epithelial and hematopoietic malignancies. Here we shall review the antitumor advances of PPARγ, alone and in combination with RARα ligands in control of cell proliferation, differentiation, and apoptosis and their potential therapeutic applications in hematological malignancies.

Pioglitazone reduces secondary brain damage after experimental brain trauma by PPAR-γ-independent mechanisms

Inflammatory and ischemic processes contribute to the development of secondary brain damage after mechanical brain injury. Recent data suggest that thiazolidinediones (TZDs), a class of drugs approved for the treatment of non-insulin-dependent diabetes mellitus, effectively reduces inflammation and brain lesion by stimulation of the peroxisome proliferator-activated receptor-γ (PPAR-γ). The present study investigates the influence of the TZD pioglitazone and rosiglitazone on inflammation and secondary brain damage after experimental traumatic brain injury (TBI). A controlled cortical impact (CCI) injury was induced in male C57BL/6 mice to investigate following endpoints: (1) mRNA expression of PPAR-γ and PPAR-γ target genes (LPL, GLT1, and IRAP/Lnpep), and inflammatory markers (TNF-α, IL-1β, IL-6, and iNOS), at 15 min, 3 h, 6 h, 12 h, and 24 h post-trauma; (2) contusion volume, neurological function, and gene expression after 24 h in mice treated with pioglitazone (0.5 and 1 mg/kg) or rosiglitazone (5 and 10 mg/kg IP at 30 min post-trauma); and (3) the role of PPAR-γ to mediate protection was determined in animals treated with pioglitazone, the PPAR-γ inhibitor T0070907, and a combination of both. Inflammatory marker genes, but not PPAR-γ gene expression, was upregulated after trauma. Pioglitazone reduced the histological damage and inflammation in a dose-dependent fashion. In contrast, rosiglitazone failed to suppress inflammation and histological damage. PPAR-γ and PPAR-γ target gene expression was not induced by pioglitazone and rosiglitazone. In line with these results, pioglitazone-mediated protection was not reversed by T0070907. The results indicate that the neuroprotective effects of pioglitazone are not solely related to PPAR-γ-dependent mechanisms.

Galectin-12: A protein associated with lipid droplets that regulates lipid metabolism and energy balance

Galectin-12, a member of the galectin family of animal lectins, is preferentially expressed in adipocytes. We recently reported that this galectin is localized on lipid droplets, specialized organelles for fat storage. Galectin-12 regulates lipid degradation (lipolysis) by modulating lipolytic protein kinase A (PKA) signaling. Mice deficient in galectin-12 exhibit enhanced adipocyte lipolysis, increased mitochondria respiration, reduced adiposity and ameliorated insulin resistance associated with weight gain. The results suggest that galectin-12 may be a useful target for treatment of obesity-related metabolic conditions, such as insulin resistance, metabolic syndrome, and type 2 diabetes. Most previously described galectins largely reside in the cytosol, although they can also be induced to become associated with membrane-containing structures. Along with an in-depth characterization of galectin-12, this mini-review comments on this first report of a galectin normally localized specifically in an organelle that performs an important intracellular function. Further studies will help shed light on how this protein regulates cellular homeostasis, especially energy homeostasis, and provide additional insight into the intracellular functions of galectins.

Peroxisome Proliferator-Activator Receptor γ: A Link between Macrophage CD36 and Inflammation in Malaria Infection

Severe malaria infection caused by Plasmodium falciparum is a global life-threatening disease and a leading cause of death worldwide. Intensive investigations have demonstrated that macrophages play crucial roles in control of inflammatory and immune responses and clearance of Plasmodium-falciparum-parasitized erythrocytes (PE). This paper focuses on how macrophage CD36 recognizes and internalizes PE and participates the inflammatory signaling in response to Plasmodium falciparum. In addition, recent advances in our current understanding of the biological actions of PPARγ on CD36 and malaria clearance from the hosts are highlighted.

Extended release niacin-laropiprant in patients with hypercholesterolemia or mixed dyslipidemias improves clinical parameters

The progression of atherosclerosis remains a major cause of morbidity and mortality. Plaque formation is an immunological response driven by a number of risk factors, and reduction of risk is the primary goal of treatment. The role of LDL-C is well established and statins have proved effective drugs, although the relative risk reduction is only around 30%. The importance of other factors-notably low HDL-C and high TGs-has become increasingly clear and the search for alternative strategies continues. Niacin is particularly effective in achieving normalization of HDL-C but is clinically underutilized due to the side effect of cutaneous flushing. The discovery that flushing is mediated by mechanisms distinct from the lipid-lowering effects has led to the development of combination drugs with reduced side effects. This review considers the evidence regarding the clinical efficacy of extended-release niacin and the DP1 antagonist laropiprant in the treatment of hypercholesterolemia and mixed dyslipidemias.

Unique mode of lipogenic activation in rat preputial sebocytes

Lipoprotein delivery of fatty acids and cholesterol is linked with peroxisome proliferator-activated receptor (PPAR) activation in adipocytes and macrophages. We postulated that similar interactions exist in sebaceous epithelial cells (sebocytes) in which PPAR activation induces differentiation. High-density lipoprotein (HDL) and very low-density lipoprotein (VLDL) markedly enhanced sebocyte differentiation above that found with PPAR agonists and were more potent than explicable by their lipid content. The PPARγ antagonist GW5393 reduced sebocyte differentiation to all PPAR isoform agonists, HDL and VLDL, suggesting that the lipoprotein effect on differentiation occurs partially through activation of PPARγ. Furthermore, we found that sebocytes expressed a unique pattern of lipogenic genes. Our results demonstrate that HDL and VLDL are the most potent inducers of sebocyte differentiation tested to date, and these actions are partially inhibited by PPAR antagonists. This suggests that substrates provided by lipoproteins are targeted to sebocytes and affect their own disposition via PPAR activation.

'Striking the Right Balance' in Targeting PPARgamma in the Metabolic Syndrome: Novel Insights from Human Genetic Studies

At a time when the twin epidemics of obesity and type 2 diabetes threaten to engulf even the most well-resourced Western healthcare systems, the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) has emerged as a bona fide therapeutic target for treating human metabolic disease. The novel insulin-sensitizing antidiabetic thiazolidinediones (TZDs, e.g., rosiglitazone, pioglitazone), which are licensed for use in the treatment of type 2 diabetes, are high-affinity PPARγ ligands, whose beneficial effects extend beyond improvement in glycaemic control to include amelioration of dyslipidaemia, lowering of blood pressure, and favourable modulation of macrophage lipid handling and inflammatory responses. However, a major drawback to the clinical use of exisiting TZDs is weight gain, reflecting both enhanced adipogenesis and fluid retention, neither of which is desirable in a population that is already overweight and prone to cardiovascular disease. Accordingly, the “search is on” to identify the next generation of PPARγ modulators that will promote maximal clinical benefit by targeting specific facets of the metabolic syndrome (glucose intolerance/diabetes, dyslipidaemia, and hypertension), while simultaneously avoiding undesirable side effects of PPARγ activation (e.g., weight gain). This paper outlines the important clinical and laboratory observations made in human subjects harboring genetic variations in PPARγ that support such a therapeutic strategy.

PPARs in alveolar macrophage biology

PPARs, most notably PPAR-gamma, play a crucial role in regulating the activation of alveolar macrophages, which in turn occupy a pivotal place in the immune response to pathogens and particulates drawn in with inspired air. In this review, we describe the dual role of the alveolar macrophage as both a first-line defender through its phagocytotic activity and a regulator of the immune response. Depending on its state of activation, the alveolar macrophage may either enhance or suppress different aspects of immune function in the lung. We then review the role of PPAR-gamma and its ligands in deactivating alveolar macrophages-thus limiting the inflammatory response that, if unchecked, could threaten the essential respiratory function of the alveolus-while upregulating the cell's phagocytotic activity. Finally, we examine the role that inadequate or inappropriate PPAR-gamma responses play in specific lung diseases.

PPARs and Adipose Cell Plasticity

Due to the importance of fat tissues in both energy balance and in the associated disorders arising when such balance is not maintained, adipocyte differentiation has been extensively investigated in order to control and inhibit the enlargement of white adipose tissue. The ability of a cell to undergo adipocyte differentiation is one particular feature of all mesenchymal cells. Up until now, the peroxysome proliferator-activated receptor (PPAR) subtypes appear to be the keys and essential players capable of inducing and controlling adipocyte differentiation. In addition, it is now accepted that adipose cells present a broad plasticity that allows them to differentiate towards various mesodermal phenotypes. The role of PPARs in such plasticity is reviewed here, although no definite conclusion can yet be drawn. Many questions thus remain open concerning the definition of preadipocytes and the relative importance of PPARs in comparison to other master factors involved in the other mesodermal phenotypes.

Adipose triglyceride lipase expression in human adipose tissue and muscle. Role in insulin resistance and response to training and pioglitazone

Adipose triglyceride lipase (ATGL) catalyzes the first step in adipocyte and muscle triglyceride hydrolysis, and comparative gene identification-58 (CGI-58) is an essential cofactor. We studied the expression of ATGL and CGI-58 in human adipose and muscle and examined correlations with markers of muscle fatty acid oxidation. Nondiabetic volunteers were studied. Subjects with impaired glucose tolerance were treated with pioglitazone or metformin for 10 weeks. Subjects with normal glucose tolerance underwent a 12-week training program. We examined changes in ATGL and CGI-58 with obesity and insulin resistance, and effects of exercise and pioglitazone. Adipose triglyceride lipase messenger RNA (mRNA) expression showed no correlation with either body mass index or insulin sensitivity index in either adipose or muscle. However, adipose ATGL protein levels were inversely correlated with body mass index (r = -0.64, P < .02) and positively correlated with insulin sensitivity index (r = 0.67, P < .02). In muscle, ATGL mRNA demonstrated a strong positive relationship with carnitine palmitoyltransferase I mRNA (r = 0.82, P < .0001) and the adiponectin receptors AdipoR1 mRNA (r = 0.71, P < .0001) and AdipoR2 mRNA (r = 0.74, P < .0001). Muscle CGI-58 mRNA was inversely correlated with intramyocellular triglyceride in both type 1 (r = -0.35, P < .05) and type 2 (r = -0.40, P < .05) fibers. Exercise training resulted in increased muscle ATGL, and pioglitazone increased adipose ATGL by 31% (P < .05). Pioglitazone also increased ATGL in adipocytes. Adipose ATGL protein is decreased with insulin resistance and obesity; and muscle ATGL mRNA is associated with markers of fatty acid oxidation in muscle, as is CGI-58. The regulation of ATGL and CGI-58 has important implications for the control of lipotoxicity.

Deficiency of PXR decreases atherosclerosis in apoE-deficient mice

The pregnane X receptor (PXR, also known as SXR) is a nuclear hormone receptor activated by xenobiotics as well as diverse sterols and their metabolites. PXR functions as a xenobiotic sensor to coordinately regulate xenobiotic metabolism via transcriptional regulation of xenobiotic-detoxifying enzymes and transporters. Recent evidence indicates that PXR may also play an important role in lipid homeostasis and atherosclerosis. To define the role of PXR in atherosclerosis, we generated PXR and apoE double knockout (PXR(-/-)apoE(-/-)) mice. Here we show that deficiency of PXR did not alter plasma triglyceride and cholesterol levels in apoE(-/-) mice. However, PXR(-/-)apoE(-/-) mice had significantly decreased atherosclerotic cross-sectional lesion area in both the aortic root and brachiocephalic artery by 40% (P < 0.01) and 60% (P < 0.001), respectively. Interestingly, deficiency of PXR reduced the expression levels of CD36, lipid accumulation, and CD36-mediated oxidized LDL uptake in peritoneal macrophages of PXR(-/-)apoE(-/-) mice. Furthermore, immunofluorescence staining showed that PXR and CD36 were expressed in the atherosclerotic lesions of apoE(-/-) mice, and the expression levels of PXR and CD36 were diminished in the lesions of PXR(-/-)apoE(-/-) mice. Our findings indicate that deficiency of PXR attenuates atherosclerosis development, which may result from decreased CD36 expression and reduced lipid uptake in macrophages.

Dyslipidemic diabetic serum increases lipid accumulation and expression of stearoyl-CoA desaturase in human macrophages

Type 2 diabetes and dyslipidemia are risk factors for cardiovascular disease. However, mechanisms by which hypertriglyceridemia influences atherogenesis remain unclear. We examined effects of dyslipidemic diabetic serum on macrophage lipid accumulation as a model of foam cell formation. Normal human macrophages were cultured in media supplemented with 10% serum from non-diabetic normolipidemic or non-diabetic hypercholesterolemic adults versus adults with Type 2 diabetes; diabetes and hypertriglyceridemia; or diabetes and hypercholesterolemia. Exposure to diabetic sera resulted in increased macrophage fatty acids (2-3 fold higher, both saturated and unsaturated). Macrophage expression of CD36, scavenger receptor A (SR-A) and stearoyl-CoA desaturase (SCD) was increased, most prominently in macrophages exposed to hypertriglyceridemic diabetic serum (twofold increase in CD36 and fourfold increase in SCD, p < 0.05). In these conditions, RNA inhibition of CD36 reduced macrophage free cholesterol (163.9 ± 10.5 vs. 221.9 ± 26.2 mmol free cholesterol/g protein, p = 0.04). RNA inhibition of SCD decreased macrophage fatty acid content, increased ABCA1 level and enhanced cholesterol efflux (18.0 ± 3.9 vs. 8.0 ± 0.8% at 48 h, p = 0.03). Diabetic dyslipidemia may contribute to accelerated atherosclerosis via alterations in macrophage lipid metabolism favoring foam cell formation. Increased expression of CD36 and SR-A would facilitate macrophage lipid uptake, while increased expression of SCD could block compensatory upregulation of ABCA1 and cholesterol efflux. Further studies are needed to clarify whether modulation of macrophage lipid metabolism might reduce progression of diabetic atherosclerosis.

Arginine transport in human monocytic leukemia THP-1 cells during macrophage differentiation

L-arginine metabolism in myeloid cells plays a central role in the processes of macrophage activation and in the regulation of immune responses. In this study, we investigated arginine transport activity and the expression of the related transporter genes during the differentiation of monocytes to macrophages. We show here that the induction of THP-1 monocyte differentiation by PMA markedly increases the expression of SLC7A7 mRNA and of y(+)LAT1 protein and consequently, the activity of system y(+)L-mediated arginine transport. Conversely, the activity of system y(+) decreases during macrophage differentiation as a result of a reduction in CAT1 protein expression. The PMA-induced, macrophage-differentiated phenotype and the increased activity of system y(+)L through the induction of SLC7A7 gene are mediated by the specific activation of PKCβ. SLC7A7 gene silencing causes a significant reduction of system y(+)L activity and a subsequent, marked increase of arginine and lysine cell content, thus suggesting that in macrophagic cells, system y(+)L activity is mainly directed outwardly. Differentiating agents other than PMA, i.e., VD3 and ATRA, are equally effective in the stimulation of system y(+)L transport activity through the increased expression of SLC7A7 mRNA and y(+)LAT1 protein. Moreover, we found that also during differentiation of human monocytes from peripheral blood SLC7A7 mRNA and system y(+)L activity are increased. These findings point to SLC7A7 gene as a marker of macrophage differentiation.

miR-615-3p promotes the phagocytic capacity of splenic macrophages by targeting ligand-dependent nuclear receptor corepressor in cirrhosis-related portal hypertension

Hypersplenism is a condition in which the spleen is overactive. It is common in patients with cirrhosis-related portal hypertension. The over-activated hemophagocytic splenic macrophages are an important cause of hypersplenism. MicroRNAs (miRNAs) are 21-22 nt single-stranded RNAs expressed endogenously, which play important roles in many diseases. We have found by microarray, previously, that miR-615-3p is highly expressed in splenic macrophages of hypersplenism. In this study, we found that miR-615-3p enhanced the phagocytic capacity of splenic macrophages. Bioinformatics analysis indicated that ligand-dependent nuclear receptor corepressor (LCoR) was a potential phagocytosis-related target of miR-615-3p. This was proved by dual luciferase assay and Western blot in THP-1 cells and normal/hypersplenisum splenic macrophages. Our results showed that the presence of miR-615-3p repressed the expression of LCoR, a derepressor of peroxisome proliferator-activated receptor gamma (PPARγ), which has been confirmed to be able to promote the phagocytic capacity of macrophages. In conclusion, high expression of miR-615-3p in over-activated splenic macrophages depresses LCoR expression, low level of LCoR derepresses the expression of PPARγ and finally upregulated PPARγ enhances the phagocytic capacity of splenic macrophages. This finding might be useful in the study of hypersplenism and other macrophage-associated diseases.

Scavenger receptor CD36 mediates uptake of high density lipoproteins in mice and by cultured cells

The mechanisms of HDL-mediated cholesterol transport from peripheral tissues to the liver are incompletely defined. Here the function of scavenger receptor cluster of differentiation 36 (CD36) for HDL uptake by the liver was investigated. CD36 knockout (KO) mice, which were the model, have a 37% increase (P = 0.008) of plasma HDL cholesterol compared with wild-type (WT) littermates. To explore the mechanism of this increase, HDL metabolism was investigated with HDL radiolabeled in the apolipoprotein (¹²⁵I) and cholesteryl ester (CE, [³H]) moiety. Liver uptake of [³H] and ¹²⁵I from HDL decreased in CD36 KO mice and the difference, i. e. hepatic selective CE uptake ([³H]¹²⁵I), declined (-33%, P = 0.0003) in CD36 KO compared with WT mice. Hepatic HDL holo-particle uptake (¹²⁵I) decreased (-29%, P = 0.0038) in CD36 KO mice. In vitro, uptake of ¹²⁵I-/[³H]HDL by primary liver cells from WT or CD36 KO mice revealed a diminished HDL uptake in CD36-deficient hepatocytes. Adenovirus-mediated expression of CD36 in cells induced an increase in selective CE uptake from HDL and a stimulation of holo-particle internalization. In conclusion, CD36 plays a role in HDL uptake in mice and by cultured cells. A physiologic function of CD36 in HDL metabolism in vivo is suggested.

Pioglitazone abrogates cyclosporine-evoked hypertension via rectifying abnormalities in vascular endothelial function

In addition to insulin sensitization, the thiazolidenedione drug pioglitazone exhibits favorable circulatory effects. Here, we hypothesized that pioglitazone protects against the hypertension and related vascular derangements caused by the immunosuppressant drug cyclosporine (CSA). Compared with vehicle (olive oil)-treated rats, chronic treatment with CSA (20mg/kg/day s.c., for 14 days) increased blood pressure (BP), reduced the aortic protein expression of phosphorylated eNOS (p-eNOS), and impaired responsiveness of isolated aortas to endothelium-dependent vasorelaxations induced by carbachol. The effects of CSA on BP, aortic p-eNOS, and carbachol relaxations were abolished upon concurrent administration of pioglitazone (2.5mg/kg/day). Serum levels of adiponectin, an adipose tissue-derived adipokine, were not altered by CSA but showed significant elevations in rats treated with pioglitazone or pioglitazone plus CSA. The possibility that alterations in the antioxidant and/or lipid profile contributed to the CSA-pioglitazone BP interaction was investigated. Pioglitazone abrogated the oxidative (aortic superoxide dismutase), lipid peroxidation (aortic malondialdyde), and dyslipidemic (serum LDL levels and LDL/HDL ratio) effects of CSA. Histologically, CSA caused focal disruption in the endothelial lining of the aorta and this effect disappeared in rats co-treated with pioglitazone. Collectively, pioglitazone abrogates the hypertensive effect of CSA via ameliorating detrimental changes in vascular endothelial NOS/NO pathway and oxidative and lipid profiles caused by CSA.

Anti-inflammatory effects of thiazolidinediones in human airway smooth muscle cells

Airway smooth muscle (ASM) cells have been reported to contribute to the inflammation of asthma. Because the thiazolidinediones (TZDs) exert anti-inflammatory effects, we examined the effects of troglitazone and rosiglitazone on the release of inflammatory moieties from cultured human ASM cells. Troglitazone dose-dependently reduced the IL-1β-induced release of IL-6 and vascular endothelial growth factor, the TNF-α-induced release of eotaxin and regulated on activation, normal T expressed and secreted (RANTES), and the IL-4-induced release of eotaxin. Rosiglitazone also inhibited the TNF-α-stimulated release of RANTES. Although TZDs are known to activate peroxisome proliferator-activated receptor-γ (PPARγ), these anti-inflammatory effects were not affected by a specific PPARγ inhibitor (GW 9662) or by the knockdown of PPARγ using short hairpin RNA. Troglitazone and rosiglitazone each caused the activation of adenosine monophosphate-activated protein kinase (AMPK), as detected by Western blotting using a phospho-AMPK antibody. The anti-inflammatory effects of TZDs were largely mimicked by the AMPK activators, 5-amino-4-imidazolecarboxamide ribose (AICAR) and metformin. However, the AMPK inhibitors, Ara A and Compound C, were not effective in preventing the anti-inflammatory effects of troglitazone or rosiglitzone, suggesting that the effects of these TZDs are likely not mediated through the activation of AMPK. These data indicate that TZDs inhibit the release of a variety of inflammatory mediators from human ASM cells, suggesting that they may be useful in the treatment of asthma, and the data also indicate that the effects of TZDs are not mediated by PPARγ or AMPK.

Phospholipase D2-dependent inhibition of the nuclear hormone receptor PPARgamma by cyclic phosphatidic acid

Cyclic phosphatidic acid (1-acyl-2,3-cyclic-glycerophosphate, CPA), one of nature's simplest phospholipids, is found in cells from slime mold to humans and has a largely unknown function. We find here that CPA is generated in mammalian cells in a stimulus-coupled manner by phospholipase D2 (PLD2) and binds to and inhibits the nuclear hormone receptor PPARgamma with nanomolar affinity and high specificity through stabilizing its interaction with the corepressor SMRT. CPA production inhibits the PPARgamma target-gene transcription that normally drives adipocytic differentiation of 3T3-L1 cells, lipid accumulation in RAW264.7 cells and primary mouse macrophages, and arterial wall remodeling in a rat model in vivo. Inhibition of PLD2 by shRNA, a dominant-negative mutant, or a small molecule inhibitor blocks CPA production and relieves PPARgamma inhibition. We conclude that CPA is a second messenger and a physiological inhibitor of PPARgamma, revealing that PPARgamma is regulated by endogenous agonists as well as by antagonists.

Oxidized low-density lipoprotein activates adipophilin through ERK1/2 signal pathway in RAW264.7 cells

It has been reported that oxidized low-density lipoprotein (Ox-LDL) can increase the expression of adipophilin. However, the detailed mechanisms are not fully understood. The aim of this study was to investigate the mechanism of Ox-LDL on adipophilin expression and the intracellular lipid droplet accumulation. A mouse macrophage-like cell line, RAW264.7, was used throughout, and it was found that Ox-LDL induced adipophilin expression in a dose-dependent manner. Moreover, Ox-LDL induced peroxisome proliferator-activated receptor-gamma (PPARgamma) expression and PPARgamma-specific inhibitor T0070907 abrogated Ox-LDL-induced adipophilin expression, but specific agonist GW1929 not. Furthermore, Ox-LDL induced phosphorylation of ERK1/2, and ERK1/2-specific inhibition by PD98059 suppressed the Ox-LDL-induced PPARgamma and adipophilin expression. The results showed that ERK1/2 or PPARgamma-specific inhibition decreased the amounts of intracellular lipid droplets. Meanwhile, the PPARgamma-specific agonist increased intracellular lipid droplets. These results suggested that Ox-LDL-induced increase in adipophilin level via ERK1/2 activation is one of the mechanisms of inducing greater amounts of intracellular lipid droplets in RAW264.7 cells, which indicated that adipophilin is involved in atherosclerotic progression.

Troglitazone suppresses telomerase activity independently of PPARgamma in estrogen-receptor negative breast cancer cells

Background

Breast cancer is one the highest causes of female cancer death worldwide. Many standard chemotherapeutic agents currently used to treat breast cancer are relatively non-specific and act on all rapidly dividing cells. In recent years, more specific targeted therapies have been introduced. It is known that telomerase is active in over 90% of breast cancer tumors but inactive in adjacent normal tissues. The prevalence of active telomerase in breast cancer patients makes telomerase an attractive therapeutic target. Recent evidence suggests that telomerase activity can be suppressed by peroxisome proliferator activated receptor gamma (PPARγ). However, its effect on telomerase regulation in breast cancer has not been investigated.

Methods

In this study, we investigated the effect of the PPARγ ligand, troglitazone, on telomerase activity in the MDA-MB-231 breast cancer cell line. Real time RT-PCR and telomerase activity assays were used to evaluate the effect of troglitazone. MDA-MB-231 cells had PPARγ expression silenced using shRNA interference.

Results

We demonstrated that troglitazone reduced the mRNA expression of hTERT and telomerase activity in the MDA-MB-231 breast cancer cell line. Troglitazone reduced telomerase activity even in the absence of PPARγ. In agreement with this result, we found no correlation between PPARγ and hTERT mRNA transcript levels in breast cancer patients. Statistical significance was determined using Pearson correlation and the paired Student's t test.

Conclusions

To our knowledge, this is the first time that the effect of troglitazone on telomerase activity in breast cancer cells has been investigated. Our data suggest that troglitazone may be used as an anti-telomerase agent; however, the mechanism underlying this inhibitory effect remains to be determined.

Aged garlic extract inhibits CD36 expression in human macrophages via modulation of the PPARgamma pathway

Expression of CD36 scavenger receptors on macrophages is involved in oxidized low-density lipoprotein uptake and foam cell formation during atherosclerotic lesion development. We examined the effects of aged garlic extract (AGE), a garlic preparation enriched in water-soluble cysteinyl moieties that increases cellular total thiols and glutathione concentrations, on CD36 expression in human monocytes/macrophages (THP-1 cells and primary human monocytes). Compared to control, AGE (1-5 mg/mL) dose-dependently and significantly suppressed CD36 expression up to by 61.8 +/- 7.4% in THP-1-derived macrophages and up to 50.5 +/- 7.1% in primary human macrophages, respectively. Furthermore, AGE prevented induction of CD36 expression by the peroxisome proliferator activator receptor (PPAR) gamma agonist troglitazone, and decreased binding of nuclear proteins to a PPARgamma response element. AGE showed a stronger inhibitory effect on CD36 expression in THP-1 cells during simultaneous incubation with phorbol 12-myristate 13-acetate (PMA) compared to cells that had been pre-incubated with PMA. Furthermore, AGE decreased CD11b expression in a dose-dependent manner. These data indicate that AGE inhibits CD36 expression by modulating the PPARgamma pathway in human macrophages and monocytes differentiation into macrophages, and suggests that the extract could be useful for the prevention of atherosclerotic lesions.

Agonism of Peroxisome Proliferator Receptor-Gamma may have Therapeutic Potential for Neuroinflammation and Parkinson's Disease

Evidence suggests inflammation, mitochondria dysfunction, and oxidative stress play major roles in Parkinson's disease (PD), where the primary pathology is the significant loss of dopaminergic neurons in the substantia nigra (SN). Current methods used to treat PD focus mainly on replacing dopamine in the nigrostriatal system. However, with time these methods fail and worsen the symptoms of the disease. This implies there is more to the treatment of PD than just restoring dopamine or the dopaminergic neurons, and that a broader spectrum of factors must be changed in order to restore environmental homeostasis. Pharmacological agents that can protect against progressive neuronal degeneration, increase the level of dopamine in the nigrostriatal system, or restore the dopaminergic system offer various avenues for the treatment of PD. Drugs that reduce inflammation, restore mitochondrial function, or scavenge free radicals have also been shown to offer neuroprotection in various animal models of PD. The activation of peroxisome proliferator receptor- gamma (PPAR-gamma ) has been associated with altering insulin sensitivity, increasing dopamine, inhibiting inflammation, altering mitochondrial bioenergetics, and reducing oxidative stress - a variety of factors that are altered in PD. Therefore, PPAR-gamma activation may offer a new clinically relevant treatment approach to neuroinflammation and PD related neurodegeneration. This review will summarize the current understanding of the role of PPAR-gamma agonists in neuroinflammation and discuss their potential for the treatment of PD.