Peroxisome proliferator-activated receptor gamma-mediated transcriptional up-regulation of the hepatocyte growth factor gene promoter via a novel composite cis-acting element

The rich pharmacological activities of Magnolia officinalis and secondary effects based on significant intestinal contributions

ETHNOPHARMACOLOGICAL RELEVANCE

Magnolia officinalis Cortex (M. officinalis) is a traditional herbal drug widely used in Asian countries. Depending on its multiple biological activities, M. officinalis is used to regulate gastrointestinal (GI) motility, relieve cough and asthma, prevent cardiovascular and cerebrovascular diseases, and treat depression and anxiety.

AIM OF THE REVIEW

We aimed to review the abundant form of pharmacodynamics activity and potential mechanisms of action of M. officinalis and the characteristics of the internal processes of the main components. The potential mechanisms of local and distance actions of M. officinalis based on GI tract was provided, and it was used to reveal the interconnections between traditional use, phytochemistry, and pharmacology.

MATERIALS AND METHODS

Published literatures about M. officinalis and its main components were collected from several scientific databases, including PubMed, Elsevier, ScienceDirect, Google Scholar and Web of Science etc. RESULTS: M. officinalis was shown multiple effects including effects on digestive system, respiratory system, central system, which is consistent with traditional applications, as well as some other activities such as cardiovascular system, anticancer, anti-inflammatory and antioxidant effects and so on. The mechanisms of these activities are abundant. Its chief ingredients such as magnolol and honokiol can be metabolized into active metabolites in vivo, which can increase water solubility and bioavailability and exert pharmacological activity in the whole body. In the GI tract, M. officinalis and its main ingredient can regulate GI hormones and substance metabolism, protect the intestinal barrier and affect the gut microbiota (GM). These actions are effective to improve local discomfort and some distal symptoms such as depression, asthma, or metabolic disorders.

CONCLUSIONS

Although M. officinalis has rich pharmacological effects, the GI tract makes great contributions to it. The GI tract is not only an important place for absorption and metabolism but also a key site to help M. officinalis exert local and distal efficacy. Pharmacodynamical studies on the efficacies of distal tissues based on the contributions of the GI tract hold great potential for understanding the benefits of M. officinalis and providing new ideas for the treatment of important diseases.

Development of mode of action networks related to the potential role of PPARγ in respiratory diseases

The peroxisome proliferator-activated receptor γ (PPARγ) is a key transcription factor, operating at the intercept of metabolic control and immunomodulation. It is ubiquitously expressed in multiple tissues and organs, including lungs. There is a growing body of information supporting the role of PPARγ signalling in respiratory diseases. The aim of the present study was to develop mode of action (MoA) networks reflecting the relationships between PPARγ signalling and the progression/alleviation of a spectrum of lung pathologies. Data mining was performed using the resources of the NIH PubMed and PubChem information systems. By linking available data on pathological/therapeutic effects of PPARγ modulation, knowledge-based MoA networking at different levels of biological organization (molecular, cellular, tissue, organ, and system) was performed. Multiple MoA networks were developed to relate PPARγ modulation to the progress or the alleviation of pulmonary disorders, triggered by diverse pathogenic, genetic, chemical, or mechanical factors. Pharmacological targeting of PPARγ signalling was discussed with regard to ligand- and cell type-specific effects in the context of distinct disease inductor- and disease stage-dependent patterns. The proposed MoA networking analysis allows for a better understanding of the potential role of PPARγ modulation in lung pathologies. It presents a mechanistically justified basis for further computational, experimental, and clinical monitoring studies on the dynamic control of PPARγ signalling in respiratory diseases.

Oral administration of curcumin ameliorates pulmonary fibrosis in mice through 15d-PGJ2-mediated induction of hepatocyte growth factor in the colon

Oral administration of curcumin has been shown to inhibit pulmonary fibrosis (PF) despite its extremely low bioavailability. In this study, we investigated the mechanisms underlying the anti-PF effect of curcumin in focus on intestinal endocrine. In bleomycin- and SiO₂-treated mice, curcumin (75, 150 mg· kg^-1 per day) exerted dose-dependent anti-PF effect when administered orally or rectally but not intravenously, implying an intestinal route was involved in the action of curcumin. We speculated that curcumin might promote the generation of gut-derived factors and the latter acted as a mediator subsequently entering the lungs to ameliorate fibrosis. We showed that oral administration of curcumin indeed significantly increased the expression of gut-derived hepatocyte growth factor (HGF) in colon tissues. Furthermore, in bleomycin-treated mice, the upregulated protein level of HGF in lungs by oral curcumin was highly correlated with its anti-PF effect, which was further confirmed by coadministration of c-Met inhibitor SU11274. Curcumin (5-40 μM) dose-dependently increased HGF expression in primary mouse fibroblasts, macrophages, CCD-18Co cells (fibroblast cell line), and RAW264.7 cells (monocyte-macrophage cell line), but not in primary colonic epithelial cells. In CCD-18Co cells and RAW264.7 cells, curcumin dose-dependently activated PPARγ and CREB, whereas PPARγ antagonist GW9662 (1 μM) or cAMP response element (CREB) inhibitor KG-501 (10 μM) significantly decreased the boosting effect of curcumin on HGF expression. Finally, we revealed that curcumin dose-dependently increased the production of 15-deoxy-Δ^{12, 14}-prostaglandin J2 (15d-PGJ2) in CCD-18Co cells and RAW264.7 cells, which was a common upstream of the two transcription factors. Moreover, both the in vitro and in vivo effects of curcumin were diminished by coadministration of HPGDS-inhibitor-1, an inhibitor of 15d-PGJ2 generation. Together, curcumin promotes the expression of HGF in colonic fibroblasts and macrophages by activating PPARγ and CREB via an induction of 15d-PGJ2, and the HGF enters the lungs giving rise to an anti-PF effect.

Peroxisome Proliferator-Activated Receptor gamma negatively regulates liver regeneration after partial hepatectomy via the HGF/c-Met/ERK1/2 pathways

Peroxisome Proliferator-Activated Receptor gamma (PPARγ) is a nuclear receptor demonstrated to play an important role in various biological processes. The aim of this study was to determine the effect of PPARγ on liver regeneration upon partial hepatectomy (PH) in mice. Mice were subjected to two-thirds PH. Before surgery, mice were either treated with the PPARγ agonist rosiglitazone, the PPARγ antagonist GW9662 alone, or with the c-met inhibitor SGX523. Liver-to-body-weight ratio, lab values, and proliferation markers were assessed. Components of the PPARγ-specific signaling pathway were identified by western blot and qRT-PCR. Our results show that liver regeneration is being inhibited by rosiglitazone and accelerated by GW9662. Inhibition of c-Met by SGX523 treatment abrogates GW9662-induced liver regeneration and hepatocyte proliferation. Hepatocyte growth factor (HGF) protein levels were significantly downregulated after rosiglitazone treatment. Activation of HGF/c-Met pathways by phosphorylation of c-Met and ERK1/2 were inhibited in rosiglitazone-treated mice. In turn, blocking phosphorylation of c-Met significantly abrogated the augmented effect of GW9662 on liver regeneration. Our data support the concept that PPARγ abrogates liver growth and hepatocellular proliferation by inhibition of the HGF/c-Met/ERK1/2 pathways. These pathways may represent potential targets in response to liver disease and could impact on the development of molecular therapies.

Species-specific control of hepatocyte growth factor expression and production in adipocytes in a differentiation-dependent manner

Hepatocyte growth factor (HGF) is a mesenchymal cell-derived factor that regulates cell growth, cell motility, and morphogenesis. Since there are conflicting reports on HGF-producing cells, we herein examined HGF activity in conditioned medium (CM) of bovine and mouse preadipocytes before and after adipogenic differentiation. CM of bovine adipocytes and mouse preadipocytes induced the morphogenesis of mammary epithelial cells that was inhibited by an NK4 HGF antagonist, whereas CM of bovine preadipocytes and mouse adipocytes did not. HGF mRNA expression was increased by a treatment with dexamethasone and isobutylmethylxanthine in bovine as well as human cells, whereas it was decreased in rodent cells. It was unfortunate that HGF gene promoter activity failed to reflect HGF mRNA expression in these cells. After actinomycin D treatment, expression of HGF mRNA remained stable in pre- and differentiated bovine adipocytes and mouse preadipocytes, whereas rapidly decreased in mouse-differentiated adipocytes. These results indicate that expression and production of HGF are regulated in a species-specific adipogenic differentiation-dependent manner and suggest that the decrease in HGF mRNA in mouse differentiated adipocytes is, at least in part, mediated by differentiation-dependent loss of its stability.

Progesterone dose-dependently modulates hepatocyte growth factor production in 3T3-L1 mouse preadipocytes

It is well documented that estrogen is predominant inducer of hepatocyte growth factor (HGF) in a variety of cell types. However, the effect of progesterone (P) remains to be elusive. Thus, in the present study, we examined the effect of P and combined effect of P and 17β-estradiol (E2) on HGF expression and production in 3T3-L1 fibroblastic preadipocytes and mature adipocytes, as a model of stromal cells. Northern blot analysis showed that hgf mRNA expressed in preadipocytes was notably higher than that of mature adipocytes, and increased by treatment of preadipocytes with E2 or 10 nM P, but not with 1,000 nM P. The E2-induced hgf mRNA expression was enhanced by 10 nM P, but suppressed by 1,000 nM P. Western blot analysis revealed that biological active forms of HGF protein was found in the preadipocyte culture medium, while the lesser amount of HGF precursor protein was detected in the mature adipocyte culture medium. The amounts of HGF were changed dependently on the hgf mRNA expression levels. These results indicate that HGF production is intricately regulated by E2 and P at the transcriptional levels in 3T3-L1 cells, and may explain the changes in the HGF production during the mammary gland development, especially decrease in HGF expression during pregnancy when P concentration is high.

Madecassoside ameliorates bleomycin-induced pulmonary fibrosis in mice through promoting the generation of hepatocyte growth factor via PPAR-γ in colon

BACKGROUND AND PURPOSE

Madecassoside has potent anti-pulmonary fibrosis (PF) effects when administered p.o., despite having extremely low oral bioavailability. Herein, we explored the mechanism of this anti-PF effect with regard to gut hormones.

EXPERIMENTAL APPROACH

A PF model was established in mice by intratracheal instillation of bleomycin. Haematoxylin and eosin stain and Masson's trichrome stain were used to assess histological changes in the lung. Quantitative-PCR and Western blot detected mRNA and protein levels, respectively, and cytokines were measured by ELISA. Small interfering RNA was used for gene-silencing. EMSA was applied to detect DNA-binding activity.

KEY RESULTS

Administration of madecassoside, p.o., but not its main metabolite madecassic acid, exhibited a direct anti-PF effect in mice. However, i.p. madecassoside had no anti-PF effect. Madecassoside increased the expression of hepatocyte growth factor (HGF) in colon tissues, and HGF receptor antagonists attenuated its anti-PF effect. Madecassoside facilitated the secretion of HGF from colonic epithelial cells by activating the PPAR-γ pathway, as shown by an up-regulation of PPAR-γ mRNA expression, nuclear translocation and DNA-binding activity both in vitro and in vivo. Also GW9662, a selective PPAR-γ antagonist, almost completely prevented the madecassoside-induced increased expression of HGF and amelioration of PF.

CONCLUSIONS AND IMPLICATIONS

The potent anti-PF effects induced by p.o. madecassoside in mice are not mediated by its metabolites or itself after absorption into blood. Instead, madecassoside increases the activity of PPAR-γ, which subsequently increases HGF expression in colonic epithelial cells. HGF then enters into the circulation and lung tissue to exert an anti-PF effect.

PPARγ activation following apoptotic cell instillation promotes resolution of lung inflammation and fibrosis via regulation of efferocytosis and proresolving cytokines

Changes in macrophage phenotype have been implicated in apoptotic cell-mediated immune modulation via induction of peroxisome proliferator-activated receptor-γ (PPARγ). In this study, we characterized PPARγ induction by apoptotic cell instillation over the course of bleomycin-induced lung injury in C57BL/6 mice. Next, the role of PPARγ activation in resolving lung inflammation and fibrosis was investigated. Our data demonstrate that apoptotic cell instillation after bleomycin results in immediate and prolonged enhancement of PPARγ mRNA and protein in alveolar macrophages and lung. Moreover, PPARγ activity and expression of its target molecules, including CD36, macrophage mannose receptor, and arginase 1, were persistently enhanced following apoptotic cell instillation. Coadministration of the PPARγ antagonist, GW9662, reversed the enhanced efferocytosis, and the reduced proinflammatory cytokine expression, neutrophil recruitment, myeloperoxidase activity, hydroxyproline contents, and fibrosis markers, including type 1 collagen α2, fibronectin and α-smooth muscle actin (α-SMA), in the lung by apoptotic cell instillation. In addition, inhibition of PPARγ activity reversed the expression of transforming growth factor-β (TGF-β), interleukin (IL)-10, and hepatocyte growth factor (HGF). These findings indicate that one-time apoptotic cell instillation contributes to anti-inflammatory and antifibrotic responses via upregulation of PPARγ expression and subsequent activation, leading to regulation of efferocytosis and production of proresolving cytokines.

Hepatocyte Growth Factor Isoforms in Tissue Repair, Cancer, and Fibrotic Remodeling

Hepatocyte growth factor (HGF), also known as scatter factor (SF), is a pleotropic factor required for normal organ development during embryogenesis. In the adult, basal expression of HGF maintains tissue homeostasis and is up-regulated in response to tissue injury. HGF expression is necessary for the proliferation, migration, and survival of epithelial and endothelial cells involved in tissue repair in a variety of organs, including heart, lung, kidney, liver, brain, and skin. The administration of full length HGF, either as a protein or using exogenous expression methodologies, increases tissue repair in animal models of tissue injury and increases angiogenesis. Full length HGF is comprised of an N-terminal hairpin turn, four kringle domains, and a serine protease-like domain. Several naturally occurring alternatively spliced isoforms of HGF were also identified. The NK1 variant contains the N-terminal hairpin and the first kringle domain, and the NK2 variant extends through the second kringle domain. These alternatively spliced forms of HGF activate the same receptor, MET, but they differ from the full length protein in their cellular activities and their biological functions. Here, we review the species-specific expression of the HGF isoforms, their regulation, the signal transduction pathways they activate, and their biological activities.

Regulation of hepatocyte growth factor expression by NF-κB and PPARγ in adipose tissue

Hepatocyte growth factor (HGF) is expressed as an angiogenic factor in adipose tissue. However, the molecular mechanism of Hgf expression remains largely unknown in the tissue. We addressed the issue by studying Hgf expression in adipocytes and macrophages. Hgf was expressed more in the stromal-vascular fraction than the adipocyte fraction. The expression was fivefold more in macrophages than the stromal-vascular faction and was reduced by 50% after macrophage deletion in adipose tissue. The expression was reduced by differentiation in adipocytes and by tumor necrosis factor-α or lipopolysaccharide treatment in macrophages. The expression was suppressed by nuclear factor (NF)-κB in C57BL/6 mice with NF-κB p65 overexpression under the aP2 gene promoter (aP2-p65 mice) but enhanced by inactivation of NF-κB p65 in mouse embryonic fibroblasts. The Hgf gene promoter was suppressed by p65 overexpression, which blocked peroxisome proliferator-activated receptor-γ (PPARγ) interaction with RNA polymerase II. The p65 activity was abolished by knockdown of histone deacetylase 3. Hgf expression was upregulated by hypoxia in vitro and in vivo. Compared with vascular endothelial growth factor (Vegf), which was predominately expressed in mature adipocytes, Hgf was mainly expressed in nonadipocytes, suggesting that Hgf and Vegf may have different cell sources in adipose tissue. In mechanism, Hgf expression is inhibited by NF-κB through suppression of PPARγ function in the Hgf gene promoter. Both Hgf and Vegf are induced by hypoxia. The study provides a molecular mechanism for the difference of inflammation and hypoxia in the regulation of angiogenic factors.

CDK5-induced p-PPARγ(Ser 112) downregulates GFAP via PPREs in developing rat brain: effect of metal mixture and troglitazone in astrocytes

The peroxisome proliferator-activated receptor gamma (PPARγ), a group of ligand-activated transcriptional factors, is expressed in glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes. Here, we investigated the role of PPARγ in regulating GFAP using a mixture of As, Cd and Pb (metal mixture, MM) that induces apoptosis and aberrant morphology in rat brain astrocytes. We observed a phospho PPARγ (serine 112 (S112)) (p-PPARγ (S112))-mediated downregulation of GFAP in the MM-exposed astrocytes. We validated this using pure PPARγ agonist, troglitazone (TZ). As reported with MM, TZ induced astrocyte damage owing to reduced GFAP. In silico analysis in the non-coding region of GFAP gene revealed two PPARγ response elements (PPREs); inverted repeat 10 and direct repeat 1 sequences. Gel shift and chromatin immunoprecipitation assays demonstrated enhancement in binding of p-PPARγ (S112) to the sequences, and luciferase reporter assay revealed strong repression of GFAP via PPREs, in response to both MM and TZ. This indicated that suppression in GFAP indeed occurs through direct regulation of these elements by p-PPARγ (S112). Signaling studies proved that MM, as well as TZ, activated the cyclin-dependent kinase 5 (CDK5) and enhanced its interaction with PPARγ resulting into increased p-PPARγ (S112). The p-CDK5 levels were dependent on proximal activation of extracellular signal-regulated protein kinase 1/2 and downstream Jun N-terminal kinase. Taken together, these results are the first to delineate downregulation of GFAP through genomic and non-genomic signaling of PPARγ. It also brings forth a resemblance of TZ with MM in terms of astrocyte disarray in developing brain.

Enhancement of head and neck squamous cell carcinoma proliferation, invasion, and metastasis by tumor-associated fibroblasts in preclinical models

BACKGROUND

Head and neck squamous cell carcinoma (HNSCC) has had little improvement in mortality rates in decades. A clearer understanding of the HNSCC tumor microenvironment will aid in finding more effective targeted therapies for this disease. Tumor-associated fibroblasts (TAFs) are the largest stromal cellular components of the tumor microenvironment in HNSCC.

METHODS

We isolated TAFs from clinical HNSCC cases and propagated in vitro. The effects of TAF-secreted paracrine factors on in vitro HNSCC migration, invasion, and proliferation was assessed. The effect of TAFs on HNSCC growth and metastases was determined in an orthotopic floor-of-the-mouth tumor model.

RESULTS

TAF-conditioned media increased HNSCC cell migration, invasion, and proliferation. TAFs increased HNSCC tumor growth and metastases in vivo.

CONCLUSION

TAFs play a major role in increasing tumor growth and metastasis in HNSCC. Targeting the tumor stroma may be important to reduce the rate of HNSCC metastasis.

Regulation of signal transduction by glutathione transferases

Glutathione transferases (GST) are essentially known as enzymes that catalyse the conjugation of glutathione to various electrophilic compounds such as chemical carcinogens, environmental pollutants, and antitumor agents. However, this protein family is also involved in the metabolism of endogenous compounds which play critical roles in the regulation of signaling pathways. For example, the lipid peroxidation product 4-hydroxynonenal (4-HNE) and the prostaglandin 15-deoxy-Δ12,14-prostaglandin J(2) (15d-PGJ(2)) are metabolized by GSTs and these compounds are known to influence the activity of transcription factors and protein kinases involved in stress response, proliferation, differentiation, or apoptosis. Furthermore, several studies have demonstrated that GSTs are able to interact with different protein partners such as mitogen activated protein kinases (i.e., c-jun N-terminal kinase (JNK) and apoptosis signal-regulating kinase 1 (ASK1)) which are also involved in cell signaling. New functions of GSTs, including S-glutathionylation of proteins by GSTs and ability to be a nitric oxide (NO) carrier have also been described. Taken together, these observations strongly suggest that GST might play a crucial role during normal or cancer cells proliferation or apoptosis.

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.

A hepatocyte growth factor receptor (Met)-insulin receptor hybrid governs hepatic glucose metabolism

Met is the transmembrane tyrosine kinase cell surface receptor for hepatocyte growth factor (HGF) and is structurally related to the insulin receptor (INSR) tyrosine kinase. Here we report that the HGF-Met axis regulates metabolism by stimulating hepatic glucose uptake and suppressing hepatic glucose output. We show that Met is essential for an optimal hepatic insulin response by directly engaging INSR to form a Met-INSR hybrid complex, which culminates in a robust signal output. We also found that the HGF-Met system restores insulin responsiveness in a mouse model of insulin refractoriness. These results provide new insights into the molecular basis of hepatic insulin resistance and suggest that HGF may have therapeutic potential for type 2 diabetes in the clinical setting.

To Live or to Die: Prosurvival Activity of PPARgamma in Cancers

The role of PPARγ in tumorigenesis is controversial. In this article, we review and analyze literature from the past decade that highlights the potential proneoplastic activity of PPARγ. We discuss the following five aspects of the nuclear hormone receptor and its agonists: (1) relative expression of PPARγ in human tumor versus normal tissues; (2) receptor-dependent proneoplastic effects; (3) impact of PPARγ and its agonists on tumors in animal models; (4) clinical trials of thiazolidinediones (TZDs) in human malignancies; (5) TZDs as chemopreventive agents in epidemiology studies. The focus is placed on the most relevant in vivo animal models and human data. In vitro cell line studies are included only when the effects are shown to be dependent on the PPARγ receptor.

AMPK-Dependent Metabolic Regulation by PPAR Agonists

Comprehensive studies support the notion that the peroxisome proliferator-activated receptors, (PPARs), PPARα, PPARβ/δ, and PPARγ, regulate cell growth, morphogenesis, differentiation, and homeostasis. Agonists of each PPAR subtype exert their effects similarly or distinctly in different tissues such as liver, muscle, fat, and vessels. It is noteworthy that PPARα or PPARγ agonists have pharmacological effects by modulating the activity of AMPK, which is a key cellular energy sensor. However, the role of AMPK in the metabolic effects of PPAR agonists has not been thoroughly focused. Moreover, AMPK activation by PPAR agonists seems to be independent of the receptor activation. This intriguing action of PPAR agonists may account in part for the mechanistic basis of the therapeutics in the treatment of metabolic disease. In this paper, the effects of PPAR agonists on metabolic functions were summarized with particular reference to their AMPK activity regulation.

Thiazolidinediones inhibit hepatocarcinogenesis in hepatitis B virus-transgenic mice by peroxisome proliferator-activated receptor gamma-independent regulation of nucleophosmin

Antidiabetic thiazolidinediones (TZD) have in vitro antiproliferative effect in epithelial cancers, including hepatocellular carcinoma (HCC). The effective anticancer properties and the underlying molecular mechanisms of these drugs in vivo remain unclear. In addition, the primary biological target of TZD, the ligand-dependent transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma), is up-regulated in HCC and seems to provide tumor-promoting responses. The aim of our study was to evaluate whether chronic administration of TZD may affect hepatic carcinogenesis in vivo in relation to PPARgamma expression and activity. The effect of TZD oral administration for 26 weeks was tested on tumor formation in PPARgamma-expressing and PPARgamma-deficient mouse models of hepatic carcinogenesis. Proteomic analysis was performed in freshly isolated hepatocytes by differential in gel electrophoresis and mass spectrometry analysis. Identified TZD targets were confirmed in cultured PPARgamma-deficient hepatocytes. TZD administration in hepatitis B virus (HBV)-transgenic mice (TgN[Alb1HBV]44Bri) reduced tumor incidence in the liver, inhibiting hepatocyte proliferation and increasing apoptosis. PPARgamma deletion in hepatocytes of HBV-transgenic mice (Tg[HBV]CreKOgamma) did not modify hepatic carcinogenesis but increased the TZD antitumorigenic effect. Proteomic analysis identified nucleophosmin (NPM) as a TZD target in PPARgamma-deficient hepatocytes. TZD inhibited NPM expression at protein and messenger RNA levels and decreased NPM promoter activity. TZD inhibition of NPM was associated with the induction of p53 phosphorylation and p21 expression.

CONCLUSION

These findings suggest that chronic administration of TZD has anticancer activity in the liver via inhibition of NPM expression and indicate that these drugs might be useful for HCC chemoprevention and treatment.

Opposite action of peroxisome proliferator-activated receptor-gamma in regulating renal inflammation: functional switch by its ligand

Peroxisome proliferator-activated receptor-γ (PPARγ) agonists, a new class of antidiabetic agents, have been shown to possess antiinflammatory activity. In this study, we investigated the molecular mechanism by which PPARγ agonists inhibit proinflammatory cytokine expression in rat glomerular mesangial cells. Both natural and synthetic PPARγ agonists potently inhibited RANTES (regulated upon activation, normal T cell expressed and secreted) and monocyte chemoattractant protein-1 expression induced by TNF-α in mesangial cells, which was dependent on NF-κB signaling. However, PPARγ agonists had little effect on TNF-α-triggered IκBα phosphorylation and its subsequent degradation, p65 phosphorylation, and nuclear translocation. In the absence of PPARγ ligand, TNF-α induced a physical interaction between nuclear p65 and PPARγ, as demonstrated by co-immunoprecipitation. Such an interaction was mediated by the C-terminal region of p65. Activation of PPARγ by its agonist prevented PPARγ·p65 complex formation. Chromatin immunoprecipitation assay revealed that TNF-α induced p65 binding to the cis-acting κB elements in rat RANTES promoter, whereas disruption of PPARγ·p65 by its agonist blocked p65 interaction with its cognate κB sites. Knockdown of PPARγ via siRNA strategy completely abolished TNF-α-mediated p65 binding to κB sites and negated RANTES induction, suggesting that unliganded PPARγ is obligatory for NF-κB signaling. Consistently, overexpression of PPARγ in the absence of its ligand sensitized mesangial cells to TNF-α stimulation. These results uncover a paradoxical action of the unliganded and ligand-activated PPARγ in regulating NF-κB signaling and demonstrate PPARγ ligand as a molecular switch that controls its ability to modulate inflammatory responses in opposite directions.

Chemical genomics of cancer chemopreventive dithiolethiones

3H-1,2-dithiole-3-thione (D3T) and its analogues 4-methyl-5-pyrazinyl-3H-1,2-dithiole-3-thione (OLT) and 5-tert-butyl-3H-1,2-dithiole-3-thione (TBD) are chemopreventive agents that block or diminish early stages of carcinogenesis by inducing activities of detoxication enzymes. While OLT has been used in clinical trials, TBD has been shown to be more efficacious and possibly less toxic than OLT in animals. Here, we utilize a robust and high-resolution chemical genomics procedure to examine the pharmacological structure-activity relationships of these compounds in livers of male rats by microarray analyses. We identified 226 differentially expressed genes that were common to all treatments. Functional analysis identified the relation of these genes to glutathione metabolism and the nuclear factor, erythroid derived 2-related factor 2 pathway (Nrf2) that is known to regulate many of the protective actions of dithiolethiones. OLT and TBD were shown to have similar efficacies and both were weaker than D3T. In addition, we identified 40 genes whose responses were common to OLT and TBD, yet distinct from D3T. As inhibition of cytochrome P450 (CYP) has been associated with the effects of OLT on CYP expression, we determined the half maximal inhibitory concentration (IC(50)) values for inhibition of CYP1A2. The rank order of inhibitor potency was OLT >> TBD >> D3T, with IC(50) values estimated as 0.2, 12.8 and >100 microM, respectively. Functional analysis revealed that OLT and TBD, in addition to their effects on CYP, modulate liver lipid metabolism, especially fatty acids. Together, these findings provide new insight into the actions of clinically relevant and lead dithiolethione analogues.

Somatic mutation and functional polymorphism of a novel regulatory element in the HGF gene promoter causes its aberrant expression in human breast cancer

The HGF gene is transcriptionally silenced in normal differentiated breast epithelial cells, but its repression fails to occur in mammary carcinoma tissues and cell lines. The molecular mechanisms underpinning aberrant HGF expression in breast cancer cells are unknown. Here we report the discovery of a DNA element located 750 bp upstream from the transcription start site in the human HGF promoter that acts as a transcriptional repressor and is a target of deletion mutagenesis in human breast cancer cells and tissues. This HGF promoter element consists of a mononucleotide repeat of 30 deoxyadenosines (30As), which we have termed "deoxyadenosine tract element" (DATE). Functional studies revealed that truncation mutations within DATE have profound local and global effects on the HGF promoter region by modulating chromatin structure and DNA-protein interactions, leading to constitutive activation of the HGF promoter in human breast carcinoma cell lines. We found that 51% of African Americans and 15% of individuals of mixed European descent with breast cancer harbor a truncated DATE variant (25As or fewer) in their breast tumors and that the truncated allele is associated with cancer incidence and aberrant HGF expression. Notably, breast cancer patients with the truncated DATE variant are substantially younger than those with a wild-type genotype. We also suggest that DATE may be used as a potential genetic marker to identify individuals with a higher risk of developing breast cancer.

Protective effects of peroxisome proliferator-activated receptor gamma ligand on apoptosis and hepatocyte growth factor induction in renal ischemia-reperfusion injury

BACKGROUND

Renal ischemia-reperfusion injury affects the long-term outcome of renal graft survival. Thiazolidinediones (TZDs), synthetic peroxisome proliferator-activated receptor (PPAR)-gamma ligands, have been shown to exert therapeutic effects upon renal ischemia-reperfusion injury far beyond their use as insulin sensitizers. It has also been reported that hepatocyte growth factor (HGF) has a beneficial effect on renal ischemia-reperfusion injury and that TZDs induce increased HGF mRNA expression and protein secretion. We investigated the effect of troglitazone, one of the TZDs, in a rat model of renal ischemia-reperfusion injury.

METHODS

A 45-minute period of warm renal ischemia was induced by bilateral clamping at 37 degrees C with rats being sacrificed before the onset of ischemia and at 2, 4, 6, and 12 hr after reperfusion. The expression of PPAR-gamma was measured by reverse-transcriptase polymerase chain reaction (RT-PCR) and western blotting while the production of HGF was investigated by RT-PCR and immunohistochemistry. The effect of troglitazone treatment on the level of apoptosis was determined by staining for cleaved caspase-3 and single-stranded DNA (ssDNA).

RESULTS

The numbers of cleaved caspase-3 and ssDNA positive cells were decreased in rats treated with troglitazone. The production of HGF mRNA and protein was most intense at 4 hr. The expression of PPAR-gamma and HGF was increased in the group treated with troglitazone compared with the control group. CONCLUSIONS.: Pretreatment of rats with the PPAR-gamma ligand troglitazone decreased apoptotic cell death in renal ischemia-reperfusion injury as a result of the induction of HGF.

Present concepts and future outlook: function of peroxisome proliferator-activated receptors (PPARs) for pathogenesis, progression, and therapy of cancer

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily of transcriptional regulators that regulate lipid, glucose, and amino acid metabolism. In recent studies it also has been shown that these receptors are implicated in tumor progression, cellular differentiation, and apoptosis and modulation of their function is therefore considered as a potential target for cancer prevention and treatment. PPAR ligands and other agents influencing PPAR signalling pathways have been shown to reveal chemopreventive potential by mediating tumor suppressive activities in a variety of human cancers and could represent a potential novel strategy to inhibit tumor carcinogenesis and progression. This review summarizes the currently available data on the roles of PPARs in relation to the processes of cell differentiation and carcinogenesis as well as their role as promising future therapeutic targets.

A novel activating function of c-Src and Stat3 on HGF transcription in mammary carcinoma cells

In the normal breast, hepatocyte growth factor (HGF) is primarily expressed by stromal cells, and stimulates in a paracrine manner epithelial cells expressing the HGF receptor (Met). In invasive human breast carcinomas, HGF and Met are frequently overexpressed, possibly establishing an autocrine HGF/Met loop that promotes tumour cell invasion. However, the mechanisms leading to autocrine HGF expression in carcinoma cells are not known. We previously demonstrated a cooperative effect between c-Src and Stat3 in the activation of HGF transcription in mammary carcinoma cells. The present report defines a novel Stat3 consensus site at nt -95 in the HGF promoter that is highly conserved in human and mouse, and is required for c-Src and Stat3 to activate HGF transcription in breast epithelial cells. DNA-protein binding studies demonstrated high affinity binding of a Stat3-containing complex to the nt -95 site. Endogenous Stat3 binding to this region of the HGF promoter in carcinoma cells expressing HGF was demonstrated using a chromatin immunoprecipitation assay. In addition, coexpression of Stat3 and activated c-Src caused increased expression of endogenous HGF mRNA and protein and marked cell scattering in breast epithelial cells. Our results delineate a novel c-Src/Stat3-dependent mechanism that regulates HGF promoter activity, and is linked to transformation of mammary epithelial cells.

hepatocyte growth factor is a downstream effector that mediates the antifibrotic action of peroxisome proliferator-activated receptor-gamma agonists

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a ligand-dependent transcription factor that plays an important role in the regulation of insulin sensitivity and lipid metabolism. Evidence shows that PPAR-gamma agonists also ameliorate renal fibrotic lesions in both diabetic nephropathy and nondiabetic chronic kidney disease. However, little is known about the mechanism underlying their antifibrotic action. This study demonstrated that PPAR-gamma agonists could exert their actions by inducing antifibrotic hepatocyte growth factor (HGF) expression. Incubation of mesangial cells with natural or synthetic PPAR-gamma agonists 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) or troglitazone and ciglitazone suppressed TGF-beta1-mediated alpha-smooth muscle actin, fibronectin, and plasminogen activator inhibitor-1 expression. PPAR-gamma agonists also induced HGF mRNA expression and protein secretion. Transfection studies revealed that 15d-PGJ2 stimulated HGF gene promoter activity, which was dependent on the presence of a novel peroxisome proliferator response element. Treatment of mesangial cells with 15d-PGJ2 induced the binding of PPAR-gamma to the peroxisome proliferator response element in the HGF promoter region. PPAR-gamma agonists also activated c-met receptor tyrosine phosphorylation, induced Smad transcriptional co-repressor TG-interacting factor expression, and blocked TGF-beta/Smad-mediated gene transcription in mesangial cells. Furthermore, ablation of c-met receptor through the LoxP-Cre system in mesangial cells abolished the antifibrotic effect of 15d-PGJ2. PPAR-gamma activation also induced HGF expression in renal interstitial fibroblasts and repressed TGF-beta1-mediated myofibroblast activation. Both HGF and 15d-PGJ2 attenuated Smad nuclear translocation in response to TGF-beta1 stimulation in renal fibroblasts. Together, these findings suggest that HGF may act as a downstream effector that mediates the antifibrotic action of PPAR-gamma agonists.

Hepatocyte growth factor, its receptor, and their potential value in cancer therapies

Hepatocyte growth factor plays multiple roles in cancer, by acting as a motility and invasion stimulating factor, promoting metastasis and tumour growth. Furthermore, it acts as a powerful angiogenic factor. The pivotal role of this factor in cancer has indicated HGF as being a potential target in cancer therapies. The past few years have seen rapid progress in developing tools in targeting HGF, in the context of cancer therapies, including development of antagonists, small compounds, antibodies and genetic approaches. The current article discusses the potential value of HGF and its receptor as targets in cancer therapies, the current development in anti-HGF research, and the clinical value of HGF in prognosis and treatment.

Modulation of hepatocyte growth factor induction in human skin fibroblasts by retinoic acid

Topical treatment of skin with all-trans-retinoic acid (ATRA), the major biologically active form of vitamin A, results in hyperproliferation of basal keratinocytes, leading to an accelerated turnover of epidermis cells and thickening of the epidermis, probably via induction of production of paracrine growth factors for keratinocytes in epidermal suprabasal keratinocytes and/or dermal fibroblasts. Since hepatocyte growth factor (HGF) is a factor mitogenic to epidermal keratinocytes secreted from dermal fibroblasts, the effect of ATRA on basal and induced HGF production in human dermal fibroblasts in culture was examined. ATRA alone did not induce HGF production, but it significantly enhanced HGF production induced by the cAMP-elevating agent cholera toxin or the membrane-permeable cAMP analog 8-bromo-cAMP. Cholera toxin-induced activation of cAMP responsive element (CRE)-binding protein (CREB) was enhanced by pretreating cells with ATRA for 24 h. In contrast, HGF production induced by epidermal growth factor (EGF) or phorbol 12-myristate 13-acetate (PMA) was potently inhibited by ATRA. These modulatory effects of ATRA were different from the effects of transforming growth factor-beta1 (TGF-beta) and dexamethasone, both of which inhibited HGF production induced by all of the four inducers. Up-regulation of HGF gene expression by cholera toxin and EGF was also enhanced and inhibited, respectively, by ATRA. Both 9-cis-retinoic acid (9-cis-RA) and 13-cis-retinoic acid (13-cis-RA), which are stereo-isomers of ATRA, showed a modulatory effect on HGF induction similar to that of ATRA. These results suggest that ATRA augments the induction of HGF production caused by increased intracellular cAMP.

Bcl-XL disrupts death-inducing signal complex formation in plasma membrane induced by hypoxia/reoxygenation

Hypoxia/reoxygenation (H/R) causes cellular injury and death. The cell death pathways induced by H/R remain incompletely understood. H/R can induce Bid and Bax mitochondrial translocation and cytochrome c release. Using mouse lung endothelial cells (MLEC), we examined the role of Bcl-X(L), an anti-apoptotic Bcl-2-related protein, in H/R-induced cell death. The expression of Bcl-X(L) protected MLEC against H/R-induced cell death by blocking Bax and Bid translocation and inhibiting mitochondrial cytochrome c release. Bcl-X(L) expression inhibited caspase-8 cleavage and death-inducing signal complex (DISC) formation in plasma membrane. By isolating mitochondrial, nuclear, and Golgi fractions, we found that H/R induced DISC formation in these organelles. Bcl-X(L) expression inhibited DISC formation in the nuclear and Golgi fractions relative to LacZ-infected controls. In contrast, DISC formation was elevated in the mitochondrial fraction of Bcl-X(L)-infected cells. GRASP65, a Golgi-associated protein, physically associated with Fas and caspase-8; Bcl-X(L) expression decreased these associations. Bcl-X(L) expression also up-regulated FLIP, a caspase-8 inhibitor. In conclusion, Bcl-X(L) may inactivate caspase-8 by decreasing DISC formation in the plasma membrane, nucleus, and Golgi complex while diverting DISC formation to the mitochondria. The inhibitory effects of Bcl-X(L) on DISC formation may play significant roles in protecting endothelial cells from H/R-induced cell death.

Peroxisome proliferator-activated receptor gamma inhibition prevents adhesion to the extracellular matrix and induces anoikis in hepatocellular carcinoma cells

Activation of the nuclear transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) inhibits growth and survival of hepatocellular carcinoma (HCC) cell lines. To further investigate the function of PPARgamma in HCC, PPARgamma expression patterns in primary tumors were examined, and the responses of two HCC cell lines to PPARgamma activation and inhibition were compared. PPARgamma expression was increased in HCC and benign-appearing peritumoral hepatocytes compared with remote benign hepatocytes. Both compound PPARgamma inhibitors and PPARgamma small interfering RNAs prevented HCC cell lines from adhering to the extracellular matrix. Loss of adhesion was followed by caspase-dependent apoptosis (anoikis). PPARgamma inhibitors had no effect on initial beta1 integrin-mediated adhesion, or on total focal adhesion kinase levels but did reduce focal adhesion kinase phosphorylation. The PPARgamma inhibitor T0070907 was significantly more efficient at causing cancer cell death than the activators troglitazone and rosiglitazone. T0070907 caused cell death by reducing adhesion and inducing anoikis, whereas the activators had no direct effect on adhesion and caused cell death at much higher concentrations. In conclusion, PPARgamma overexpression is present in HCC. Inhibition of PPARgamma function causes HCC cell death by preventing adhesion and inducing anoikis-mediated apoptosis. PPARgamma inhibitors represent a potential novel treatment approach to HCC.

Activity-dependent hepatocyte growth factor expression and its role in organogenesis and cancer growth suppression

Studies by Murphy et al. have shown that neuronal stimulation can activate immediate early genes that code for transcription factors. Recent data suggest that Ca(2+) elevation in both neuronal cytoplasmic and nuclear compartments is responsible for the coupling of synaptic excitation to gene expression. Deisseroth et al. suggest that Ca(2+) influx through L-type voltage-sensitive Ca(2+) channels (VSCCs) activates cytoplasmic Ca(2+) targets such as calmodulin (CaM). The Ca(2+)-CaM complex then translocates to the nucleus leading to Ca(2+) and cAMP response element-binding protein (CREB) phosphorylation and gene expression. Reports have shown that L-type VSCCs are found on the vagus nerve. Other studies have suggested that activation of L-type VSCCs leads to a Ca(2+) store-dependent elevation of nuclear [Ca(2+)] that triggers gene expression by more direct activation of nuclear Ca(2+)/CaM-dependent protein kinase (CaMK). Moreover, nuclear transcription factors such as DREAM are themselves Ca(2+)-dependent, further supporting the importance of both nuclear and cytoplasmic Ca(2+) elevation in regulating gene expression. Our simulation studies suggest that intense synaptic stimulation in combination with amplification by release from intracellular Ca(2+) stores can produce elevations in nuclear Ca(2+) concentration and CaMK phosphorylation leading to CREB phosphorylation and gene expression. One of the downstream events would be the production of hepatocyte growth factor (HGF). HGF has trophic, repair, therapeutic or mitotic effect on kidney, pancreas, spleen, liver, lung, heart and spinal cord. These organs and systems' regeneration can be achieved by either upregulation of HGF release from the vagus nerve or upregulation of HGF production within the system (spinal cord). Conversely, inhibition of HGF release from the vagus nerve can inhibit cancer growth. Vagus nerve seems to be the nerve that nature intends to regulate organ growth and regeneration, it is very possible that other than HGF and injurin, other growth factors could be found in the vagus nerve. Electrical depolarization and hyperpolarization of the vagus nerve would be the most natural and effective way to induce organ regeneration and suppress cancer growth, respectively. A similar pathway seems to exist for different organs as HGF has trophic, repair, therapeutic or mitotic effect on different vagally innervated organs.

Transactivation of the PPAR-responsive enhancer module in chemopreventive glutathione S-transferase gene by the peroxisome proliferator-activated receptor-gamma and retinoid X receptor heterodimer

Cancer chemopreventive agents transcriptionally induce glutathione S-transferase (GST), which can protect cells from chemical-induced carcinogenesis. Activation of either NF-E2-related factor-2 (Nrf2) or the CCAAT/enhancer binding protein-beta (C/EBPbeta) contributes to GST induction. Peroxisome proliferator-activated receptor-gamma (PPARgamma) and the retinoic acid X receptor (RXR) play roles in regulating cell differentiation and chemoprevention. This study examined GSTA2 gene induction by the PPARgamma activator and 9-cis-retinoic acid (RA), a RXR ligand, and investigated the molecular basis of PPAR-RXR-mediated GSTA2 induction in the H4IIE hepatocytes. Either 15-deoxy-delta (12, 14)-prostaglandin J(2) (PGJ(2)) or RA induced GSTA2 with Nrf2 and C/EBPbeta activation. When compared with PGJ(2) or RA alone, PGJ(2) + RA enhanced GSTA2 induction, with increases in Nrf2 and C/EBPbeta activation. PGJ(2) + RA increased the luciferase reporter gene activity in the cells transfected with the -1.65-kb flanking region of the GSTA2 gene. Thiazolidinedione PPARgamma agonists, troglitazone, rosiglitazone, and pioglitazone, in combination with RA, potentiated GSTA2 induction, confirming that the activation of the PPARgamma and RXR heterodimer contributed to GSTA2 expression. Deletion of the antioxidant response element- or C/EBP-binding sites or the overexpression of dominant-negative mutant of C/EBP abolished the reporter gene expression. PGJ2 + RA increased the binding of the PPARgamma - RXR heterodimer to the putative PPAR-response elements (PPREs) in the GSTA2 promoter. Specific mutations of these multiple PPRE sites resulted in the complete loss of its responsiveness to PGJ2 + RA, which suggests that these binding sites function as a PPRE-responsive enhancer module (PPREM). Transactivation of PPREM by the PPARgamma - RXR heterodimer was verified by the effective GSTA2 induction in the cells treated with PGJ2 + RA after transfecting them with the plasmids encoding PPARgamma1 and RXRalpha. In conclusion, the PPARgamma - RXR heterodimer promotes GSTA2 induction by activating PPREM in the GSTA2 gene, as well as inducing Nrf2 and C/EBPbeta activation.

Transforming growth factor beta receptor family ligands inhibit hepatocyte growth factor synthesis and secretion from astrocytoma cells

Transforming growth factor beta (TGFbeta) and hepatocyte growth factor (HGF) promote glioma progression. Using U87human astrocytoma cells, which express TGFbeta receptors (TbetaRs), we show (1) mRNA expression of Smads (2, 3, 4), bone morphogenetic protein (BMP)- and activin-A receptors; (2) TGFbeta1 inhibits and HGF induces proliferation; (3) TGFbeta1 and activin-A equipotently inhibit HGF secretion more than BMP-2, but none alters c-Met expression. Because interfering with TbetaR signaling might nullify the beneficial inhibition of HGF secretion, activin-A should instead be considered for combination glioma therapy.

A critical function of USF in HGF gene regulation mediated by a multiconsensus region

Hepatocyte growth factor (HGF) is a multifunctional growth factor implicated in a variety of tissue restructuring processes. Since HGF acts as a highly potent mitogen, HGF expression is suggested to be under a well-defined transcriptional control. The 5' sequence of the HGF gene clusters a set of several binding sites for transcription factors in a so-called multiconsensus region (MCR) located between -230 and 260. Our studies demonstrate that a NF1-like element and the E(1)-box of the MCR form the main complexes with nuclear proteins and that both are involved in transcriptional silencing of the HGF gene in non-HGF expressing cell types. The E(1)-box of two tandemly arranged E-boxes was shown to be a binding site of high affinity interacting with the upstream stimulatory factor (USF). While recombinant expression of a wild-type USF did not affect gene expression, a USF variant lacking the DNA binding domain restored the MCR mediated transcriptional repression. In conclusion, our data provide evidence that USF is a central factor of cell-type specific HGF regulation, acting in cooperation with additional regulatory proteins as a bivalent mediator of transcriptional activation or repression.

Intimal smooth muscle cells as a target for peroxisome proliferator-activated receptor-gamma ligand therapy

Activation of the nuclear receptor/transcription factor, peroxisome proliferator-activated receptor gamma (PPARgamma), is a newly defined target for limiting vascular pathologies. PPARgamma is expressed in human and animal models of vascular disease, with particularly high levels being present in the cells of the neointimal microenvironment. In the present study, we show that intimal smooth muscle cells in vitro contain higher amounts of functional PPARgamma than medial smooth muscle cells. The PPARgamma ligand rosiglitazone more potently induced CD36 expression at low concentrations, and cell death by apoptosis at higher concentrations in intimal compared with medial smooth muscle cells. Intimal smooth muscle cells also contained high levels of cyclooxygenase-2 protein, and released a more diverse and larger amount of eicosanoids on arachidonic acid stimulation. Furthermore, when exogenous arachidonic acid was added, PPAR reporter gene activation was induced in a cyclooxygenase inhibitor-sensitive manner, an effect that correlated with an increase in CD36 expression. In summary, intimal smooth muscle cells contain functionally higher levels of PPARgamma, PPARgamma ligands have high- and low-potency targets in vascular smooth muscle cells, and cyclooxygenase can serve as a source of potential endogenous PPAR ligands. Intimal vascular smooth muscle cells therefore represent a potentially important target for the antiproliferative, and antiatherosclerotic actions of PPARgamma ligands.

Roles of peroxisome proliferator-activated receptor gamma in cardiovascular disease

Peroxisome proliferator-activated receptors (PPARs) are transcription factors belonging to a nuclear receptor superfamily. PPARs have three isoforms: alpha, beta (or delta), and gamma. It is known that PPARgamma is expressed predominantly in adipose tissue and promotes adipocyte differentiation and glucose homeostasis. Recently, synthetic antidiabetic thiazolidinediones (TZDs) and the natural prostaglandin D2 (PGD2) metabolite, 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2), have been identified as ligands for PPARgamma. Furthermore, it has become apparent that PPARs are present both in a variety of different cell types and in atherosclerotic lesions and the studies about PPARgamma have been extended. Although activation of PPARgamma appears to have protective effects on atherosclerosis, it is still largely uncertain whether PPARgamma ligands prevent the development of cardiovascular disease. Recent evidence suggests that some benefit from antidiabetic agents, TZDs, may occur independent of increased insulin sensitivity. In this article, we review the latest developments in the PPAR field and summarize the roles of PPARgamma and the actions of PPARgamma ligands in the cardiovascular system.