Expression of peroxisome proliferator-activated receptor gamma (PPARgamma) in rat aortic smooth muscle cells

Lessons from the Trials for the Desirable Effects of Sodium Glucose Co-Transporter 2 Inhibitors on Diabetic Cardiovascular Events and Renal Dysfunction

Recent large placebo-controlled trials of sodium glucose co-transporter 2 (SGLT2) inhibitors revealed desirable effects on heart failure (HF) and renal dysfunction; however, the mechanisms underlying these effects are unknown. The characteristic changes in the early stage of diabetic cardiomyopathy (DCM) are myocardial and interstitial fibrosis, resulting in diastolic and subsequent systolic dysfunction, which leads to clinical HF. Pericytes are considered to play crucial roles in myocardial and interstitial fibrosis. In both DCM and diabetic retinopathy (DR), microaneurysm formation and a decrease in capillaries occur, triggered by pericyte loss. Furthermore, tubulointerstitial fibrosis develops in early diabetic nephropathy (DN), in which pericytes and mesangial cells are thought to play important roles. Previous reports indicate that pericytes and mesangial cells play key roles in the pathogenesis of DCM, DR and DN. SGLT2 is reported to be functionally expressed in pericytes and mesangial cells, and excessive glucose and Na+ entry through SGLT2 causes cellular dysfunction in a diabetic state. Since SGLT2 inhibitors can attenuate the high glucose-induced dysfunction of pericytes and mesangial cells, the desirable effects of SGLT2 inhibitors on HF and renal dysfunction might be explained by their direct actions on these cells in the heart and kidney microvasculature.

The endocannabinoid system in cardiovascular function: novel insights and clinical implications

RATIONALE

Cardiovascular disease is now recognized as the number one cause of death in the world, and the size of the population at risk continues to increase rapidly. The dysregulation of the endocannabinoid (eCB) system plays a central role in a wide variety of conditions including cardiovascular disorders. Cannabinoid receptors, their endogenous ligands, as well as enzymes conferring their synthesis and degradation, exhibit overlapping distributions in the cardiovascular system. Furthermore, the pharmacological manipulation of the eCB system has effects on blood pressure, cardiac contractility, and endothelial vasomotor control. Growing evidence from animal studies supports the significance of the eCB system in cardiovascular disorders.

OBJECTIVE

To summarize the literature surrounding the eCB system in cardiovascular function and disease and the new compounds that may potentially extend the range of available interventions.

RESULTS

Drugs targeting CB1R, CB2R, TRPV1 and PPARs are proven effective in animal models mimicking cardiovascular disorders such as hypertension, atherosclerosis and myocardial infarction. Despite the setback of two clinical trials that exhibited unexpected harmful side-effects, preclinical studies are accelerating the development of more selective drugs with promising results devoid of adverse effects.

CONCLUSION

Over the last years, increasing evidence from basic and clinical research supports the role of the eCB system in cardiovascular function. Whereas new discoveries are paving the way for the identification of novel drugs and therapeutic targets, the close cooperation of researchers, clinicians and pharmaceutical companies is needed to achieve successful outcomes.

Grain feeding coordinately alters expression patterns of transcription factor and metabolic genes in subcutaneous adipose tissue of crossbred heifers

The ability to improve meat quality and production efficiency in cattle is limited by an inability to enhance marbling and simultaneously limit undesirable adipose tissue accretion. The objective of this study was to examine expression of regulatory genes in subcutaneous (SCF) adipose tissue of heifers in response to increasing days on feed (DOF) and finishing strategy. Crossbred heifers (n = 24) were allotted as follows: Group 1 = 0 d, Group 2 = 99 d on winter annual ryegrass (grass; Lolium multiflorum Lam.), Group 3 = 218 g on grass, Group 4 = 99 d on grass followed by 119 d on grain. Adipose tissue samples were collected at time of harvest and frozen. Carcass characteristics were measured 24 h postharvest. As expected, HCW (P < 0.0001), ribeye area (REA; P < 0.0002), backfat (BF; P < 0.0001), KPH (P < 0.0001), and marbling score (P < 0.0009) increased with DOF though frame score was not different (P < 0.95). Average daily gain decreased with DOF (P < 0.0001). Yield grade increased (P < 0.0014) but cook loss percentage decreased (P < 0.001) with DOF without changes in 24-h pH (P < 0.31). Interestingly, Warner-Bratzler shear force (WBS) was decreased with DOF (P < 0.0089). Meanwhile, BF (P < 0.01) and KPH (P < 0.05) were greater, whereas marbling values trended greater in grain versus grass-finished heifers. Neither ADG (P < 0.89), HCW (P < 0.26), frame score (P < 0.85), nor REA (P < 0.38) were different between these groups. Grain finishing increased yield grade (P < 0.001) but did not affect 24-h pH (P < 0.88), cook loss percentage (P < 0.98), or WBS (P < 0.44) compared with grass-finished heifers. The expression of PPARγ, bone morphogenic protein 2 (BMP2), and SMAD family member 1 (SMAD1) mRNA was upregulated in response to DOF and grain finishing, whereas sterol regulatory element binding protein 1c (SREBP-1c), sonic hedgehog (SHH), chicken ovalbumin protein transcription factor 1 (COUP-TF1), chicken ovalbumin protein transcription factor 2 (COUP-TF2), and preadipocyte factor-1 (PREF-1) mRNA was decreased in response to DOF and grain finishing. These changes were associated with increased expression of lipoprotein lipase (LPL), stearoyl-coenzyme A desaturase (SCD), and fatty acid synthase (FAS) mRNA. In summary, increasing DOF was associated with improved meat quality whereas gene expression studies suggest several novel genes are associated with subcutaneous adipose tissue development in growing and finishing cattle.

Effects of fenofibrate, a PPAR-α ligand, on the haemodynamics of glycerol-induced renal failure in rats

The modulating effect of peroxisome proliferator-activated receptor α ligand on haemodynamic effects of phenylepherine (PE), angiotensin II (AII), endothelin 1 (ET1), acetylcholine (Ach), sodium nitroprusside (SNP) and isoproterenol (ISO) were evaluated in glycerol-induced acute kidney injury in rats. The effect of PE on fenofibrate-treated animals was a dose-dependent increase in mean arterial blood pressure (MAP). For AII and ET1, MAP was also increased for the fenofibrate group but not in a dose-dependent fashion. On the medullary blood flow (MBF), while the lower doses of PE and AII increased the perfusion unit on the fenofibrate-treated group, the higher doses decreased the perfusion unit. The ET1 increased the perfusion unit on this group but not in dose-dependent fashion. The effects of PE and AII on the cortical blood flow (CBF) of fenofibrate-treated group is similar to that of MBF for the same group but not for ET1. The effect of Ach, SNP and ISO in all the groups was the decrease in MAP. ISO caused dose-dependent increase in MBF of fenofibrate-treated group. The effect of Ach, SNP and ISO on the CBF perfusion unit was that of the increase for the fenofibrate-treated group. The study showed that fenofibrate did not attenuate increased blood pressure induced by PE, AII and ET1 but caused enhanced vasodilation by Ach, SNP and ISO.

The PPAR-Platelet Connection: Modulators of Inflammation and Potential Cardiovascular Effects

Historically, platelets were viewed as simple anucleate cells responsible for initiating thrombosis and maintaining hemostasis, but clearly they are also key mediators of inflammation and immune cell activation. An emerging body of evidence links platelet function and thrombosis to vascular inflammation. peroxisome proliferator-activated receptors (PPARs) play a major role in modulating inflammation and, interestingly, PPARs (PPARβ/δ and PPARγ) were recently identified in platelets. Additionally, PPAR agonists attenuate platelet activation; an important discovery for two reasons. First, activated platelets are formidable antagonists that initiate and prolong a cascade of events that contribute to cardiovascular disease (CVD) progression. Dampening platelet release of proinflammatory mediators, including CD40 ligand (CD40L, CD154), is essential to hinder this cascade. Second, understanding the biologic importance of platelet PPARs and the mechanism(s) by which PPARs regulate platelet activation will be imperative in designing therapeutic strategies lacking the deleterious or unwanted side effects of current treatment options.

Therapeutic Implications of PPARgamma in Cardiovascular Diseases

Peroxisome proliferator-activated receptor-γ (PPARγ) is the members of the nuclear receptor superfamily as a master transcriptional factor that promotes differentiation of preadipocytes by activating adipose-specific gene expression. Although PPARγ is expressed predominantly in adipose tissue and associated with adipocyte differentiation and glucose homeostasis, PPARγ is also present in a variety of cell types including vascular cells and cardiomyocytes. Activation of PPARγ suppresses production of inflammatory cytokines, and there is accumulating data that PPARγ ligands exert antihypertrophy of cardiomyocytes and anti-inflammatory, antioxidative, and antiproliferative effects on vascular wall cells and cardiomyocytes. In addition, activation of PPARγ is implicated in the regulation of endothelial function, proliferation and migration of vascular smooth muscle cells, and activation of macrophages. Many studies suggest that PPARγ ligands not only ameliorate insulin sensitivity, but also have pleiotropic effects on the pathophysiology of atherosclerosis, cardiac hypertrophy, ischemic heart, and myocarditis.

Interaction of oxidative stress, nitric oxide and peroxisome proliferator activated receptor gamma in acute renal failure

Oxidative stress has been reported to play a critical role in the pathology of acute renal failure (ARF). An interaction between different reactive species and/or their sources have been the focus of extensive studies. The exact sources of reactive species generated in biological systems under different disease states are always elusive because they are also a part of physiological processes. Exaggerated involvement of different oxidation pathways including NAD(P)H oxidase has been proposed in different models of ARF. An interaction between oxygen species and nitrogen species has drawn extensive attention because of the deleterious effects of peroxynitrite and their possible effects on antioxidant systems. Recent advances in molecular biology have allowed us to understand glomerular function more precisely, especially the organization and importance of the slit diaphragm. Identification of slit diaphragm proteins came as a breakthrough and a possibility of therapeutic manipulation in ARF is encouraging. Transcriptional regulation of the expression of slit diaphragm protein is of particular importance because their presence is crucial in the maintenance of glomerular function. This review highlights the involvement of oxidative stress in ARF, sources of these reactive species, a possible interaction between different reactive species, and involvement of PPARgamma, a nuclear transcription factor in this process.

Controle da adipogênese por ácidos graxos

A obesidade é um dos principais problemas de saúde pública. Indivíduos obesos são mais suscetíveis a desenvolver doenças cardiovasculares e diabetes melito tipo 2. A obesidade resulta do aumento no tamanho e no número de adipócitos. O balanço entre adipogênese e adiposidade determina o grau de obesidade do indivíduo. Adipócitos maduros secretam adipocinas, tais como TNFα, IL-6, leptina e adiponectina, e lipocina, o ácido palmitoleico ω-7. A produção de adipocinas é maior na obesidade, o que contribui para o estabelecimento de resistência periférica à insulina. O conhecimento dos eventos moleculares que regulam a diferenciação dos pré-adipócitos e de células-tronco mesenquimais em adipócitos (adipogênese) é importante para o entendimento da gênese da obesidade. A ativação do fator de transcrição PPARγ é essencial na adipogênese. Certos ácidos graxos são ligantes de PPARγ e podem, assim, controlar a adipogênese. Além disso, alguns ácidos graxos atuam como moléculas sinalizadoras em adipócitos, regulando sua diferenciação ou morte. Dessa forma, a composição lipídica da dieta e os agonistas de PPARγ podem regular o balanço entre adipogênese e morte de adipócitos e, portanto, a obesidade.

Role of rosiglitazone in lipopolysaccharide-induced peritonitis: a rat peritoneal dialysis model

AIM

The aim of this study was to demonstrate the efficacy of the peroxisome proliferator-activated receptor (PPAR)-gamma agonist, rosiglitazone, in the amelioration or prevention of inflammation including peritoneal fibrosis secondary to the peritonitis in a peritoneal dialysis (PD) model of non-uraemic rats.

METHODS

Thirty male Sprague-Dawley rats were assigned to six groups according to treatment. A 90 min peritoneal equilibrium test, dialysate cellular components, peritoneal thickness and cellularity were assessed on day 21. Additionally, immunohistochemical stains of peritoneal membrane, such as PPAR-gamma, vascular endothelial growth factor (VEGF), transforming growth factor (TGF)-beta1, collagen-1 and monocyte chemoattractant protein-1 were performed.

RESULTS

The dialysate neutrophil count and peritoneal thickness in the high-dose rosiglitazone group was significantly decreased compared to the lipopolysaccharide (LPS)-only group. The peritoneal membrane from the LPS-only group showed marked cellular proliferation in the area of the submesothelial compact zone compared with the PD-only group, the rosiglitazone-only group, and the high-dose rosiglitazone group. The 90 min peritoneal equilibrium test (PET) results showed no statistical difference among the six groups excluding dialysate-to-plasma urea ratio. The number of PPAR-gamma expressing cells and the expression of TGF-beta1 were decreased in the high-dose rosiglitazone group compared to the LPS-only group. There were no differences in the expression of VEGF and collagen-1 among the six groups. Interestingly, the number of PPAR-gamma-positive cells was correlated with expression of VEGF, TGF-beta1, collagen-1 and monocyte chemoattractant protein-1 irrespective of the study group.

CONCLUSION

The results of this study showed that rosiglitazone ameliorated peritoneal inflammation induced by LPS and reduced the TGF-beta1 expression in the peritoneal membranes.

PPARs and the cardiovascular system

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

Role of G protein-coupled receptor kinase-2 in peroxisome proliferator-activated receptor gamma-mediated modulation of blood pressure and renal vascular reactivity in SHR

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPARgamma), a nuclear transcription factor, modulates the expression/activity of G protein-coupled receptors (GPCRs), but its role in GPCR signaling is not clear. Increased GPCR kinase-2 (GRK-2) activity and receptor desensitization have been reported in hypertension.

METHOD

In this study we investigated the role of GRK-2 in PPARgamma-mediated blood pressure regulation in hypertension. SHR or WKY rats were treated with GW1929, a selective PPARgamma ligand (0.5 mg/kg/day), or vehicle for 2 months. Systolic blood pressure (tail cuff plethysmography), whole kidney perfusion (laser scanner) and renal vascular reactivity (isolated perfused kidney) was determined.

RESULTS

GW1929 significantly reduced blood pressure (20 +/- 1%) and increased renal perfusion (61 +/- 3%) in SHR compared to WKY rats. Vasoconstriction to phenylephrine (100 microg) in the isolated perfused kidney was greater in SHRs (29 +/- 1%) compared to WKY rats and this was abolished by GW1929. GW1929 enhanced acetylcholine-induced (30-300 microg) and sodium nitroprusside-induced vasodilatation in SHR by 46 +/- 2% (p < 0.05) and 33 +/- 2% (p < 0.05), respectively. Isoprenalin-induced (5-30 microg) vasodilatation was 43 +/- 2% lower in SHR compared to WKY and GW1929 enhanced this vasodilatation by 55 +/- 2%. In SHR kidney, GW1929 enhanced expression of PPARgamma mRNA (34 +/- 1%) but reduced that of GRK-2 (31 +/- 3%).

CONCLUSION

We suggest that downregulation of PPARgamma but upregulation of GRK-2 increases blood pressure and impaired renal vascular reactivity in SHR and that PPARgamma-mediated improvement in hypertension may involve transcriptional regulation of GRK-2 function.

Peroxisome proliferator-activated receptors in diabetic nephropathy

Diabetic nephropathy is a leading cause of end-stage renal disease, which is increasing in incidence worldwide, despite intensive treatment approaches such as glycemic and blood pressure control in patients with diabetes mellitus. New therapeutic strategies are needed to prevent the onset of diabetic nephropathy. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated nuclear transcription factors that play important roles in lipid and glucose homeostases. These agents might prevent the progression of diabetic nephropathy, since PPAR agonists improve dyslipidemia and insulin resistance. Furthermore, data from murine models suggest that PPAR agonists also have independent renoprotective effects by suppressing inflammation, oxidative stress, lipotoxicity, and activation of the renin-angiotensin system. This review summarizes data from clinical and experimental studies regarding the relationship between PPARs and diabetic nephropathy. The therapeutic potential of PPAR agonists in the treatment of diabetic nephropathy is also discussed.

Peroxisome proliferator-activated receptor gamma and cardiovascular diseases

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily and form heterodimers with retinoid X receptor. Three PPAR isoforms have been isolated and termed alpha, beta (or delta) and gamma. Although PPARgamma is expressed predominantly in adipose tissue and associated with adipocyte differentiation and glucose homeostasis, PPARgamma is also present in a variety of cell types. Synthetic antidiabetic thiazolidinediones (TZDs) are well known as ligands and activators for PPARgamma. After it was reported that activation of PPARgamma suppressed production of pro-inflammatory cytokines in activated macrophages, medical interest in PPARgamma has grown and there has been a huge research effort. PPARgamma is currently known to be implicated in various human chronic diseases such as diabetes mellitus, atherosclerosis, rheumatoid arthritis, inflammatory bowel disease, and Alzheimer's disease. Many studies suggest that TZDs not only ameliorate insulin sensitivity, but also have pleiotropic effects on many tissues and cell types. Although activation of PPARgamma seems to have beneficial effects on cardiovascular diseases, the mechanisms by which PPARgamma ligands prevent their development are not fully understood. Recent data about the actions and its mechanisms of PPARgamma-dependent pathway in cardiovascular diseases are discussed here.

Interference with PPARgamma signaling causes cerebral vascular dysfunction, hypertrophy, and remodeling

The transcription factor PPARgamma is expressed in endothelium and vascular muscle where it may exert antiinflammatory and antioxidant effects. We tested the hypothesis that PPARgamma plays a protective role in the vasculature by examining vascular structure and function in heterozygous knockin mice expressing the P465L dominant negative mutation in PPARgamma (L/+). In L/+ aorta, responses to the endothelium-dependent agonist acetylcholine (ACh) were not affected, but there was an increase in contraction to serotonin, PGF(2alpha), and endothelin-1. In cerebral blood vessels both in vitro and in vivo, ACh produced dilation that was markedly impaired in L/+ mice. Superoxide levels were elevated in cerebral arterioles from L/+ mice and responses to ACh were restored to normal with a scavenger of superoxide. Diameter of maximally dilated cerebral arterioles was less, whereas wall thickness and cross-sectional area was greater in L/+ mice, indicating cerebral arterioles underwent hypertrophy and remodeling. Thus, interference with PPARgamma signaling produces endothelial dysfunction via a mechanism involving oxidative stress and causes vascular hypertrophy and inward remodeling. These findings indicate that PPARgamma has vascular effects which are particularly profound in the cerebral circulation and provide genetic evidence that PPARgamma plays a critical role in protecting blood vessels.

PPARs and the kidney in metabolic syndrome

The metabolic syndrome (MetS) is defined by a set of metabolic risk factors, including insulin resistance, central obesity, dyslipidemia, hyperglycemia, and hypertension for type 2 diabetes and cardiovascular disease. Although both retrospective and prospective clinical studies have revealed that MetS is associated with chronic renal disease, even with a nondiabetic cause, the cellular and molecular mechanisms in this association remain largely uncharacterized. Recently, increasing evidence suggests that peroxisome proliferator-activated receptors (PPARs), a subgroup of the nuclear hormone receptor superfamily of ligand-activated transcription factors, may play an important role in the pathogenesis of MetS. All three members of the PPAR nuclear receptor subfamily, PPARalpha, -beta/delta, and -gamma, are critical in regulating insulin sensitivity, adipogenesis, lipid metabolism, inflammation, and blood pressure. PPARs have also been implicated in many renal pathophysiological conditions, including diabetic nephropathy and glomerulosclerosis. Ligands for PPARs such as hypolipidemic PPARalpha activators, and antidiabetic thiazolidinedione PPARgamma agonists affect not only diverse aspects of MetS but also renal disease progression. Emerging data suggest that PPARs may be potential therapeutic targets for MetS and its related renal complications. This review focuses on current knowledge of the role of PPARs in MetS and discusses the potential therapeutic utility of PPAR modulators in the treatment of kidney diseases associated with MetS.

Physiology, Genetics, and Cardiovascular Disease: Focus on African Americans

The disproportionate impact of cardiovascular disease in African Americans is well recognized. Not only do risk factors such as obesity occur at a higher rate in the African-American community, but this population experiences a greater mortality from cardiovascular disease than their white counterparts. The cardiovascular system is regulated in part by two opposing mediators linking the risk factors of obesity, vascular dysfunction, and diabetes. One of these mediators--angiotensin II--increases blood pressure, impairs endothelial function, decreases peroxisome proliferator activated-receptor gamma, and is proinflammatory, growth stimulating, profibrotic, and proatherogenic. The other mediator, peroxisome proliferator activated-receptor gamma, lowers blood pressure, improves endothelial function, decreases angiotensin II type 1 receptor function, and is anti-inflammatory, growth-inhibiting, antifibrotic, and antiatherogenic. Genotypic variants have been discovered that affect the functioning of both of these important systems. Some of these variants--like some genotypic variants discovered in the adrenergic system--occur with different frequencies in African Americans than in Americans of European descent and may help to explain racial/ethnic differences in susceptibility to cardiovascular disease and aspects of the response to treatment. Recognition of these genotypic differences may permit the development of therapies tailored to individual patients.

Lack of association between the Pro12Ala polymorphism in PPAR-gamma2 gene and body weight changes, insulin resistance and chronic diabetic complications in obese patients with type 2 diabetes

BACKGROUND

It is generally accepted that the Pro12Ala polymorphism in peroxisome proliferator-activated receptor-gamma2 (PPAR-gamma2) is associated with an increased risk of type 2 diabetes. However, studies on an association between the polymorphism and obesity have yielded inconsistent findings. Also, a role of PPAR-gamma receptors in development of chronic diabetic complications cannot be excluded. The aim of this study was to investigate an association between Pro12Ala polymorphism and body weight changes, insulin resistance, insulin secretion and incidence of diabetic complications in obese patients with long-lasting type 2 diabetes.

METHODS

In 216 obese patients with at least a 10-year history of type 2 diabetes, a detailed medical history was taken and a physical examination with assessment of diabetic complications was performed as well as evaluation of insulin resistance (homeostatic model assessment-HOMA), insulin secretion and other biochemical parameters. PCR-RFLP was used to assess Pro12Ala polymorphism. Two subgroups of patients were compared: homozygotic Pro/Pro and Ala allele carriers (Ala/Ala + Ala/Pro).

RESULTS

No differences between the analyzed groups in body weight changes, insulin resistance and insulin secretion were found, but Ala allele was significantly more frequent in males than in females. There was no difference in incidence and progression of diabetic complications with only a trend towards higher incidence of diabetic retinopathy in patients with Ala allele.

CONCLUSIONS

There is no association between Pro12Ala PPAR-gamma2 polymorphism and body mass changes observed during a course of type 2 diabetes, differences in peripheral insulin resistance and incidence and progression of diabetic complications in obese patients with long-lasting type 2 diabetes.

The effect of rosiglitazone in the prevention of intra-abdominal adhesion formation in a rat uterine horn model

BACKGROUND

Effects of rosiglitazone in the prevention of adhesion formation were evaluated.

METHODS

Eighty Wistar albino rats were randomly grouped into eight equally sized groups. A 2-cm segment of the antimesenteric surface of the right uterine horn was traumatized to form a standardized lesion, using bipolar cautery. A dose-response study was performed with 0.1, 0.3, 1 and 3 mg/kg/day rosiglitazone. Fifteen days later, adhesions were evaluated clinically and histopathologically. A time-response study was performed with 1 mg/kg/day rosiglitazone (the minimum dose found to significantly affect adhesion formation). Rosiglitazone was given for 7 days post-operatively and results were compared with those of control and the 15-day group (time-response). In all these studies, rosiglitazone was orally administered 3 days before the operation and continued post-operatively. In two further experimental groups, rosiglitazone was only administered pre-operatively or post-operatively.

RESULTS

Approximately 1 mg/kg/day rosiglitazone was found to reduce adhesion scores both clinically and histopathologically. Duration of treatment was also found to affect the extent of adhesion formation. However, giving rosiglitazone either just pre-operatively or post-operatively did not significantly reduce adhesion formation.

CONCLUSION

Rosiglitazone with peroxisome proliferator-activated receptor (PPAR)-gamma agonist activity reduced the formation of i.p. adhesion possibly by reducing the initial inflammatory response and the subsequent exudation in this study.

Effects of astragaloside IV on pathogenesis of metabolic syndrome in vitro

AIM

To investigate the diverse pharmacological actions of astragaloside IV from the perspective of metabolic syndrome, and to investigate the effect of the drug on the pathogenesis of metabolic syndrome.

METHODS

Adipogenesis was used as an indicator of the effect of astragaloside IV on preadipocyte differentiation, and was measured by using an oil red O assay. Glucose uptake was determined by measuring the transport of [2-(3)H]-deoxyglucose into the cells. The concentrations of peroxisome proliferator-activated receptor-gamma (PPARgamma) and aP2 mRNA were determined by using reverse transcription-polymerase chain reaction. Apoptosis and viability loss of endothelial cells were detected by using flow cytometry and the WST-1 assay, respectively. Intracellular free Ca2+ was labeled with Fluo-3 AM and measured by using a laser scanning confocal microscope.

RESULTS

Astragaloside IV can significantly potentiate insulin-induced preadipocyte differentiation at concentrations of 3, 10, and 30 microg/mL, improve high glucose-induced insulin resistance in adipocytes at a concentration of 30 microg/mL, and prevent tumor necrosis factor (TNF)-alpha-induced apoptosis and viability loss at concentrations of 10 and 30 microg/mL, and 30 microg/mL, respectively, in endothelial cells. Furthermore, we found that these effects were partly due to the promotion of PPARgamma expression and to the inhibition of abnormal TNF-alpha-induced intracellular free Ca(2+) accumulation in endothelial cells.

CONCLUSION

The diverse pharmacological actions of astragaloside IV can all be linked to metabolic syndrome pathogenesis. Our study provides a new insight into the mechanism by which astragaloside IV exerts its effect.

Platelets as a Novel Target for PPAR?? Ligands

Peroxisome proliferator-activated receptor gamma (PPARgamma) is an important transcription factor for lipid and glucose metabolism. Currently, the PPARgamma ligands rosiglitazone and pioglitazone are used for the treatment of type 2 diabetes mellitus because they are potent insulin sensitizers. Recently, PPARgamma has emerged as an important anti-inflammatory factor. Platelets, anucleate cells involved in hemostasis, have also been implicated as key contributors to inflammation, because they produce many pro-inflammatory and pro-atherogenic mediators when activated. Surprisingly, it was discovered recently that platelets contain PPARgamma and that PPARgamma ligands, both natural and synthetic, inhibit platelet activation and release of bioactive mediators. In particular, release of soluble CD40 ligand (sCD40L) and thromboxane (TXA(2)) was inhibited by PPARgamma ligands in thrombin-activated platelets. CD40L signaling induces pro-inflammatory processes in many cell types, and increased blood levels of sCD40L are closely associated with inflammation, diabetes, and cardiovascular disease. Targeting platelet PPARgamma will, therefore, be an important treatment strategy for the attenuation of chronic inflammatory processes and prevention of thrombus formation.

PPAR-gamma agonists and diabetic nephropathy

Diabetic nephropathy is a clinical syndrome of albuminuria, declining glomerular filtration rate, and increased risk of cardiovascular disease. Multiple mechanisms have been implicated in its pathogenesis. Although current therapies appear to be effective, treatment of diabetic nephropathy remains suboptimal. This review summarizes the recently emerging evidence suggesting that peroxisome proliferator-activated receptor-gamma agonists may prove to be effective therapeutic agents in the treatment of diabetic renal complications.

The study of anti-metabolic syndrome effect of puerarin in vitro

Puerarin is an isoflavone extracted from Chinese plant, Pueraria lobata (Wild.) Ohwi. It has been reported to have comprehensive pharmacological action in treatment of diabetes and cardiovascular diseases. The purpose of this study was to link the scattered effects of puerarin and to find the common mechanisms underlying. We investigated the effect of puerarin on the pivotal common pathogenic factors of metabolic syndrome, which includes obesity, Type II diabetes and cardiovascular diseases. Recently, a large body of evidence indicates that there is a complicated interplay among insulin resistance, adipocytes and endothelial dysfunction that links the abnormalities of metabolic syndrome. Results of present study showed that puerarin could potentiate insulin-induced preadipocyte differentiation, promote glucose-uptake of adipocytes that have been induced insulin resistance by high glucose, and prevent TNF-a-induced apoptosis and viability loss of endothelial cells. Furthermore, we found that these effects are probably due to promote PPARgamma expression and partly through inhibiting abnormal TNF-a-induced intracellular-free Ca(2+) accumulation of endothelial cells. Overall, our synthetical study links the comprehensive pharmacological actions of puerarin to the recognized common pathogenesis of metabolic syndrome, and provides a new insight into the mechanism of puerarin effect.

Role of fibric acid derivatives in the management of risk factors for coronary heart disease

Although elevated low-density lipoprotein (LDL)-cholesterol is a well established coronary heart disease (CHD) risk factor, the ability to adequately discriminate high-risk individuals by this risk factor alone is limited and other metabolic risk variables are known to modulate CHD risk. For instance, it has been reported that the cluster of metabolic disturbances observed among individuals with abdominal obesity, the so-called metabolic syndrome, is associated with a substantially increased risk of CHD. Among the features of the dyslipidaemic profile observed in these individuals, the high triglyceride-low high-density lipoprotein (HDL)-cholesterol dyslipidaemia is predictive of an elevated risk of CHD. Fibric acid derivatives (fibrates) have been used in clinical practice for more than 2 decades as a class of agents known to decrease triglyceride levels while substantially increasing HDL-cholesterol levels, with a limited but significant additional lowering effect on LDL-cholesterol levels. Although the clinical benefits of HMG-CoA reductase inhibitors (statins) have been well documented by primary and secondary prevention trials that justify their widespread use, it was not until the publication of the VA-HIT (Veterans Affairs High-Density Lipoprotein Intervention Trial) that the relevance of identifying HDL-cholesterol as a therapeutic target to reduce the risk of recurrent CHD events was finally confirmed. The clinical benefits of fibrate therapy are especially important in the subpopulation of patients with low HDL-cholesterol levels with the metabolic syndrome, particularly in patients with type 2 diabetes mellitus or in abdominally obese, hyperinsulinaemic patients. Evidence also suggests that there is a 'fibrate effect' that mediates the reduction in CHD risk beyond the favourable impact of these agents on HDL-cholesterol levels. This last notion is consistent with the pleiotropic effects of fibrates which are known to be related to their mechanisms of action. Through peroxisome proliferator-activated alpha-receptors, fibrates have a significant impact on the synthesis of several apolipoproteins (apo) and enzymes of lipoprotein metabolism as well as on the expression of several genes involved in fibrinolysis and inflammation. Fibrate therapy has been reported to decrease apo CIII levels (a powerful inhibitor of lipoprotein lipase) and increase apo AI levels, as well as to increase lipoprotein lipase activity. Such changes contribute to improve the catabolism of triglyceride-rich lipoproteins, leading to a substantial increase in HDL-cholesterol levels accompanied by a shift in the size and density of LDL particles (from small, dense LDL particles to larger, more buoyant cholesteryl ester-rich LDL). It is proposed that some of these pleiotropic effects could explain some of the clinical benefits of fibrate therapy beyond its HDL-raising properties, particularly among patients with abdominal obesity, hyperinsulinaemia or type 2 diabetes with both low HDL- and low/normal LDL-cholesterol levels.

Insulin alters nuclear factor-κB and peroxisome proliferator-activated receptor-γ protein expression induced by glycated bovine serum albumin in vascular smooth-muscle cells

In both type 2 diabetes and insulin-resistance syndromes, hyperglycemia and advanced glycation end products (AGEs) activate the transcription factor nuclear factor-kappaB (NF-kappaB) through a mechanism that partly involves the generation of reactive oxygen species (ROS). The contribution of hyperinsulinemia in this sequence has not been completely elucidated. In this work we investigated the actions of insulin and PPAR-gamma on the stimulation by AGEs of NF-kappaB protein expression in cultured aortic vascular smooth-muscle cells (VSMCs) from non-insulin-dependent diabetic rats and nondiabetic rats. The expression of proteins was evaluated with the use of Western immunoblotting. Incubations (24 hours) of VSMCs with 10 to 100 microg/mL glycated bovine serum albumin (AGE- BSA) increased NF-kappaB protein expression in both models. PPAR-gamma protein expression was only enhanced at concentrations of 500 to 1000 microg/mL (AGE-BSA). In the presence of insulin (10-100 nmol/L), the stimulation of NF-kappaB protein expression by AGE-BSA (100 microg/mL) was decreased, whereas the expression of PPAR-gamma, protein was enhanced. 15-Deoxyprostaglandin J2, a direct activator of PPAR-gamma, decreased AGE-BSA-stimulated NF-kappaB expression. These findings suggest that insulin decreases the incidence of alterations in VSMCs induced by AGEs through the reduction of NF-kappaB and an increase in PPAR-gamma protein expression (as far as the model could be extrapolated to in vivo situations). These data may help justify current therapeutic approaches involving the use of insulin and PPAR-gamma agonists.

Human bone marrow megakaryocytes and platelets express PPARgamma, and PPARgamma agonists blunt platelet release of CD40 ligand and thromboxanes

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-activated transcription factor important in lipid metabolism, diabetes, and inflammation. We evaluated whether human platelets and megakaryocytes express PPARgamma and whether PPARgamma agonists influence platelet release of bioactive mediators. Although PPARgamma is mainly considered a nuclear receptor, we show that enucleate platelets highly express PPARgamma protein as shown by Western blotting, flow cytometry, and immunocytochemistry. Meg-01 megakaryocyte cells and human bone marrow megakaryocytes also express PPARgamma. Platelet and Meg-01 PPARgamma bound the PPARgamma DNA consensus sequence, and this was enhanced by PPARgamma agonists. Platelets are essential not only for clotting, but have an emerging role in inflammation in part due to their release or production of the proinflammatory and proatherogenic mediators CD40 ligand (CD40L) and thromboxanes (TXs). Platelet incubation with a natural PPARgamma agonist, 15d-PGJ(2), or with a potent synthetic PPARgamma ligand, rosiglitazone, prevented thrombin-induced CD40L surface expression and release of CD40L and thromboxane B(2) (TXB(2)). 15d-PGJ(2) also inhibited platelet aggregation and adenosine triphosphate (ATP) release. Our results show that human platelets express PPARgamma and that PPARgamma agonists such as the thiazolidinedione class of antidiabetic drugs have a new target cell, the platelet. This may represent a novel mechanism for treatment of inflammation, thrombosis, and vascular disease in high-risk patients.

Zinc Modulates PPARγ Signaling and Activation of Porcine Endothelial Cells

Dietary zinc has potent antioxidant and anti-inflammatory properties and is a critical component of peroxisome proliferator-activated receptor (PPAR) gene expression and regulation. To assess the protective mechanisms of PPARgamma in endothelial cell dysfunction and the role of zinc in the modulation of PPARgamma signaling, cultured porcine pulmonary artery endothelial cells were exposed to the membrane-permeable zinc chelator N,N,N'N'-tetrakis (2-pyridylmethyl)-ethylene diamine (TPEN), thiazolidinedione (TZD; PPARgamma agonist) or bisphenol A diglycidyl ether (BADGE; PPARgamma antagonist). Subsequently, endothelial cells were activated by treatment with linoleic acid (90 micro mol/L) for 6 h. Zinc chelation by TPEN increased the DNA binding activity of nuclear factor (NF)-kappaB and activator protein (AP)-1, decreased PPARgamma expression and activation as well as up-regulated interleukin (IL)-6 expression and production. These effects were fully reversed by zinc supplementation. In addition, exposure to TZD down-regulated linoleic acid-induced DNA binding activity of NF-kappaB and AP-1, whereas BADGE further induced activation of these oxidative stress-sensitive transcription factors. Most importantly, the TZD-mediated down-regulation of NF-kappaB and AP-1 and reduced inflammatory response were impaired during zinc chelation. These data suggest that zinc plays a critical role in PPARgamma signaling in linoleic acid-induced endothelial cell activation and indicate that PPARgamma signaling is impaired during zinc deficiency.

Nuclear receptors and the control of metabolism

The metabolic nuclear receptors act as metabolic and toxicological sensors, enabling the organism to quickly adapt to environmental changes by inducing the appropriate metabolic genes and pathways. Ligands for these metabolic receptors are compounds from dietary origin, intermediates in metabolic pathways, drugs, or other environmental factors that, unlike classical nuclear receptor ligands, are present in high concentrations. Metabolic receptors are master regulators integrating the homeostatic control of (a) energy and glucose metabolism through peroxisome proliferator-activated receptor gamma (PPARgamma); (b) fatty acid, triglyceride, and lipoprotein metabolism via PPARalpha, beta/delta, and gamma; (c) reverse cholesterol transport and cholesterol absorption through the liver X receptors (LXRs) and liver receptor homolog-1 (LRH-1); (d) bile acid metabolism through the farnesol X receptor (FXR), LXRs, LRH-1; and (e) the defense against xeno- and endobiotics by the pregnane X receptor/steroid and xenobiotic receptor (PXR/SXR). The transcriptional control of these metabolic circuits requires coordination between these metabolic receptors and other transcription factors and coregulators. Altered signaling by this subset of receptors, either through chronic ligand excess or genetic factors, may cause an imbalance in these homeostatic circuits and contribute to the pathogenesis of common metabolic diseases such as obesity, insulin resistance and type 2 diabetes, hyperlipidemia and atherosclerosis, and gallbladder disease. Further studies should exploit the fact that many of these nuclear receptors are designed to respond to small molecules and turn them into therapeutic targets for the treatment of these disorders.

PPAR(gamma) and glucose homeostasis

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor involved in the control of metabolism. Research on PPARgamma is oriented towards understanding its role in insulin sensitization, which was inspired by the discovery that antidiabetic agents, the thiazolidinediones, were agonists for PPARgamma. PPARgamma stimulation improves glucose tolerance and insulin sensitivity in type 2 diabetic patients and in animal models of insulin resistance through mechanisms that are incompletely understood. Upon activation, PPARgamma heterodimerizes with retinoid X receptor, recruits specific cofactors, and binds to responsive DNA elements, thereby stimulating the transcription of target genes. Because PPARgamma is highly enriched in adipose tissue and because of its major role in adipocyte differentiation, it is thought that the effects of PPARgamma in adipose tissue are crucial to explain its role in insulin sensitization, but recent studies have highlighted the contribution of other tissues as well. Although relatively potent for their insulin-sensitizing action, currently marketed PPARgamma activators have some important undesirable side effects. These concerns led to the discovery of new ligands with potent antidiabetic properties but devoid of certain of these side effects. Data from human genetic studies and from PPARgamma heterozygous knockout mice indicate that a reduction in PPARgamma activity could paradoxically improve insulin sensitivity. These findings suggest that modulation of PPARgamma activity by partial agonists or compounds that affect cofactor recruitment might hold promise for the treatment of insulin resistance.

Troglitazone inhibits growth and improves insulin signaling by suppression of angiotensin II action in vascular smooth muscle cells from spontaneously hypertensive rats

Troglitazone, a thiazolizidinedione, has recently been reported to possess anti-arteriosclerotic properties. To evaluate mechanisms underlying the anti-arteriosclerotic effects of troglitazone, we examined the effect of troglitazone on growth, expression of growth factors, and insulin signaling in vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) which produce angiotensin II (Ang II) in a homogeneous culture. Troglitazone inhibited basal and serum-stimulated DNA synthesis and inhibited increases in the number of VSMC from SHR and normotensive Wistar-Kyoto (WKY) rats. Its inhibition was greater in VSMC from SHR. Troglitazone abolished DNA synthesis in response to Ang II in VSMC from both rat strains and markedly inhibited DNA synthesis in response to epidermal growth factor (EGF) and platelet-derived growth factor (PDGF)-AA in VSMC from SHR. Troglitazone did not alter the expression of transforming growth factor (TGF)-beta1, PDGF A-chain, or basic fibroblast growth factor (bFGF) mRNAs in VSMC from WKY rats, but it markedly decreased expression of these growth factor mRNAs in VSMC from SHR. Troglitazone markedly decreased basal and Ang II-stimulated expression of extracellular signal-regulated kinase proteins in VSMC from both rat strains. Troglitazone abolished Ang II-induced suppression of phosphatidilinositol 3-kinase (PI3-kinase) activity, insulin receptor substrate-1 (IRS-1) associated tyrosine phosphorylation, and IRS-1 associated p85 levels in VSMC from WKY rats. Basal PI3-kinase activity, tyrosine phosphorylation of IRS-1, and IRS-1 associated p85 levels were lower in VSMC from SHR than in cells from WKY rats. Troglitazone significantly increased PI3-kinase activity, IRS-1 associated tyrosine phosphorylation, and IRS-1 associated p85 levels in VSMC from SHR. These results indicate that troglitazone produce its anti-arteriosclerotic effects through suppression of the action of growth-promoting factors including Ang II, and that troglitazone inhibits Ang II-induced suppression of insulin signaling in VSMC from SHR, suggesting that tissue Ang II may lead to insulin resistance and to arteriosclerosis in hypertension. Troglitazone may be useful in the treatment of insulin resistance as well as of hypertensive vascular diseases.

Effects of different PPARgamma-agonists on MCP-1 expression and monocyte recruitment in experimental glomerulonephritis

BACKGROUND

Activators of peroxisome proliferator activated receptor gamma (PPARgamma) have been shown to modulate chemokine expression in isolated monocytes/macrophages (M/M) and to exert anti-inflammatory effects in some models of experimental inflammatory diseases. We evaluated the effects of different forms of PPARgamma activators in a model of experimental glomerulonephritis (GN) in rats.

METHODS

GN was induced in rats by application of an anti-thymocyte antibody (ATS). Nephritic rats were treated with two synthetic PPARgamma ligands of the thiazolidinedione (TZD) group, troglitazone (200 mg/kg/day) and ciglitazone (100 mg/kg/day), and with a natural ligand 15d-PGJ2 (1.5 mg/day). Twenty-four hours after induction of the GN, the glomerular mRNA expression of the chemokine monocyte chemoattractant protein-1 (MCP-1) and the cognate chemokine receptor CCR-2 were examined by Northern blotting and RT-PCR. The glomerular M/M infiltration was determined by immunohistology. The activation of the transcription factors PPARgamma, nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) in glomeruli was analyzed by electrophoretic mobility shift assay.

RESULTS

Induction of GN up-regulated glomerular nuclear protein binding of NF-kappaB and AP-1. Treatment of nephritic rats with troglitazone and ciglitazone augmented nuclear PPARgamma and AP-1 DNA binding but did not affect NF-kappaB binding. TZD enhanced glomerular MCP-1 expression and increased glomerular M/M recruitment. In contrast, 15d-PGJ2 attenuated NF-kappaB activation and did not affect AP-1 activity or MCP-1 expression.

CONCLUSION

Our data show that PPARgamma activators of the TZD group, but not 15d-PGJ2, enhance MCP-1 expression and M/M infiltration in the induction phase of experimental GN. The results demonstrate that TZD and 15d-PGJ2 may exert different effects in the immune response in experimental GN. Our study underscores the need to critically evaluate whether PPARgamma ligands will have beneficial or possibly deleterious effects in GN.

15-Deoxy-Delta12,14-prostaglandin J2 inhibits IL-1beta-induced cyclooxygenase-2 expression in mesangial cells

BACKGROUND

Cyclooxygenase-2 (COX-2), a key enzyme in the synthesis of prostaglandins, is induced in mesangial cells in response to proinflammatory cytokines. Recently, 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2), one of the natural ligands of peroxisome proliferator-activated receptor gamma (PPARgamma), has been reported to have an anti-inflammatory effect. Therefore, we examined the effect of 15d-PGJ2 on COX-2 expression in cultured rat mesangial cells.

METHODS

Mesangial cells were incubated with 15d-PGJ2 for 30 minutes and then exposed to interleukin-1beta (IL-1beta). The expression of COX-2 mRNA and proteins was determined by Northern blot and immunoblot analyses, respectively. Accumulation of prostaglandin E2 (PGE2) was measured by an enzyme-linked immunosorbent assay (ELISA). Activities of mitogen-activated protein kinases (MAPKs) were evaluated by an immunoblot analysis. DNA binding activities of activator protein-1 (AP-1) or nuclear factor-kappaB (NF-kappaB) were examined by an electrophoretic mobility shift assay (EMSA). The activities of PPAR responsive elements (PPRE) and COX-2 promoter were measured by a luciferase reporter assay.

RESULTS

15D-PGJ2 significantly suppressed IL-1beta-induced COX-2 expression and PGE2 production, but thiazolidinediones, synthetic PPARgamma ligands, did not affect COX-2 expression. Moreover, the cells transfected with a PPRE luciferase reporter did not respond to 15d-PGJ2. IL-1beta rapidly activated extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK), which were involved in the up-regulation of COX-2 induction, but 15d-PGJ2 inhibited the activation of these kinases. 15d-PGJ2 inhibited the IL-1beta-induced increase in binding activities of nuclear proteins to consensus AP-1 site and AP-1-like site of COX-2 promoter but not of NF-kappaB. IL-1beta was unable to activate the COX-2 promoter when the AP-1-like site was mutated.

CONCLUSIONS

These data suggest that 15d-PGJ2 inhibits IL-1beta-induced COX-2 expression, independent of PPARgamma activation, by suppression of ERK and JNK pathways and AP-1 activation in mesangial cells. Thus, 15d-PGJ2 may play an important role in the negative feedback mechanism of COX-2 expression in renal inflammation and may be useful as an anti-inflammatory agent.

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.

15-Deoxy-delta 12,14-prostaglandin J2 and thiazolidinediones activate the MEK/ERK pathway through phosphatidylinositol 3-kinase in vascular smooth muscle cells

Peroxisome proliferator-activated receptor (PPAR) gamma belongs to the nuclear receptor superfamily of ligand-dependent transcription factors. Recent results have shown that the ligands for nuclear receptors have rapid effects so called "nongenomic" effects, which are observed within minutes after stimulation. We examined whether 15-deoxy-Delta(12,14)-prostaglandin J(2) (15-d-PGJ2) had rapid effects on cultured vascular smooth muscle cells. Phosphorylation of ERK and c-fos mRNA expression were determined by Western and Northern blot analyses, respectively. PPAR gamma agonists 15-d-PGJ2 and thiazolidinediones such as pioglitazone and troglitazone elicited rapid activation of ERK within 15 min and induced c-fos mRNA expression within 30 min, whereas the PPAR alpha agonist bezafibrate failed to activate ERK. 15-d-PGJ2-induced expression of c-fos mRNA was blocked by PD98059 or U0126, two ERK kinase inhibitors, suggesting that the MEK/ERK pathway mediates 15-d-PGJ2-induced c-fos gene expression. Furthermore, pretreatment with wortmannin, an inhibitor of phosphatidylinositol 3 (PI3)-kinase, inhibited 15-d-PGJ2-induced ERK activation and c-fos mRNA expression, suggesting that PI3-kinase is involved in the process. An electrophoretic mobility shift assay showed that 15-d-PGJ2 enhanced AP-1 binding activity to AP-1 consensus sequence in a time-dependent manner. 15-d-PGJ2 increased thymidine incorporation in a PI3-kinase-dependent manner. Taken together, our findings show that 15-d-PGJ2 and thiazolidinediones activate the MEK/ERK pathway through PI3-kinase and lead to c-fos mRNA expression and DNA synthesis. These findings indicate a novel regulatory mechanism of gene expression by 15-d-PGJ2 and thiazolidinediones.

Peroxisome proliferator-activated receptor-gamma ligands inhibit nuclear but not cytosolic extracellular signal-regulated kinase/mitogen-activated protein kinase-regulated steps in vascular smooth muscle cell migration

Vascular smooth muscle cell (VSMC) migration involves adhesion, locomotion, and invasion regulated by various signaling molecules, among which the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinases (MAPK) play a critical role. We have shown that the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligands troglitazone and rosiglitazone inhibit VSMC migration downstream of ERK MAPK. The purpose of the current study was to more specifically determine which step(s) in VSMC migration are targeted by inhibition of the ERK MAPK pathway or activation of PPAR-gamma. VSMC adhesion was not affected by the ERK MAPK pathway inhibitor PD98059 or PPAR-gamma ligands. Phosphorylation and activation of myosin light chain kinase (MLCK) play important roles in cell locomotion. Platelet-derived growth factor (PDGF)-induced MLCK phosphorylation (1.7-fold) was completely blocked by PD98059 at 30 microM (p < 0.05), but not by troglitazone or rosiglitazone. PDGF-directed migration (5.8-fold) was inhibited by PD98059 (-88% at 30 microM) and the MLCK inhibitor ML9 (0.1-1 microM, -84% at 1 microM) (all p < 0.05). The transcription factor Ets-1 mediates matrix metalloproteinase induction required for tissue invasion by VSMC. PDGF (20 ng/ml) stimulated an Ets-1 protein expression (14-fold at 60 min) in VSMC, which was inhibited by PD98059 (-72% at 30 microM), troglitazone (-69% at 20 microM), and rosiglitazone (-54% at 10 microM) (all p < 0.05). Immunohistochemistry of rat aortae 2 h after balloon injury showed a dramatic upregulation of Ets-1, which was markedly inhibited in animals that had received troglitazone treatment. In contrast, phosphorylated ERK MAPK was not affected by troglitazone. These data are consistent with PPAR-gamma ligands exerting their anti-migratory effects downstream of ERK MAPK activation by blocking nuclear events, such as Ets-1 expression, required for cell invasion in response to arterial injury.

Induction of nuclear orphan receptor NGFI-B gene and apoptosis in rat vascular smooth muscle cells treated with pyrrolidinedithiocarbamate

NGFI-B is one of the orphan nuclear receptors, and its gene is implicated in the apoptosis of T cells. The aim of this study was to investigate the expression and the role of NGFI-B in vascular smooth muscle cells (VSMCs). Pyrrolidinedithiocarbamate (PDTC) is a modulator of an oxidative state and is reported to induce apoptosis only when the density of VSMCs is low. Under low VSMC density (10 000 cells/cm(2)), addition of PDTC (0.1 to 10 micromol/L) caused apoptosis of VSMCs, which was confirmed by Hoechst 33258 staining under fluorescence microscopy. At low VSMC density, expression of NGFI-B mRNA was induced 1 hour after the addition of PDTC, peaking at 6 hours, and persisted for up to 12 hours. The protein level of NGFI-B was increased 4 hours after PDTC addition and persisted for up to 12 hours. Under low VSMC density, PDTC-induced expression of NGFI-B mRNA was correlated with the magnitude of apoptosis, which was quantified by enzyme immunoassay for histone-associated DNA fragments. In contrast, when the density of VSMCs was high (50 000 cells/cm(2)), PDTC did not induce apoptosis, and the expression of NGFI-B was only transient. This transient expression pattern was also seen when VSMCs were treated with phorbol ester, calcium ionophore, hydrogen peroxide, or angiotensin II, even at low cell density. We next investigated whether the NGFI-B gene may act as a transcription factor under treatment with PDTC by measuring the promoter activity of luciferase reporter plasmids that contained typical NGFI-B-responsive elements. The PDTC-induced transcriptional activity of NGFI-B was 2-fold higher at low cell density than at high cell density. These data demonstrate that NGFI-B can be induced in VSMCs and suggest that NGFI-B may play a role in PDTC-induced VSMC apoptosis.

Increased expression of peroxisome proliferator-activated receptor-alpha and -gamma in blood vessels of spontaneously hypertensive rats

Peroxisome proliferator-activated receptors (PPARs) are a family of ligand-activated transcription factors that include PPAR-alpha, PPAR-gamma, and PPAR-delta. We hypothesized that PPAR expression in blood vessels could be reduced in hypertension to result in increased vascular growth and reduced apoptosis. We investigated the abundance of PPAR-alpha and PPAR-gamma in aorta and mesenteric arteries from young (6-week-old) and adult (16-week-old) spontaneously hypertensive rats (SHR) compared with age-matched control Wistar-Kyoto rats (WKY). mRNA levels of PPAR-alpha and PPAR-gamma were determined by reverse transcription-polymerase chain reaction. Protein expression was evaluated by Western blot and by immunohistochemistry. PPAR-gamma was expressed in aortic and mesenteric vascular smooth muscle cells (VSMCs) from intact tissue and cultured cells. PPAR-alpha was expressed in intact vascular tissue but was almost undetectable in cultured VSMCs. In mesenteric arteries from adult SHR, PPAR-alpha and PPAR-gamma mRNA levels were significantly greater than in WKY (P<0.05). In aorta, PPAR-alpha mRNA was significantly (P<0.05) more abundant in adult (but not in young) SHR than in WKY, whereas there was no difference in PPAR-gamma mRNA between WKY and SHR. PPAR-alpha and PPAR-gamma mRNA were greater in mesenteric arteries (P<0.05) in young and adult SHR than in WKY. Expression of PPAR-alpha and PPAR-gamma was similar in SHR and WKY in other tissues. In cultured mesenteric VSMCs, PPAR-gamma mRNA was 3-fold higher in SHR than in WKY. Immunohistochemistry demonstrated that PPAR-gamma resided constitutively in the cytoplasm in primary and low-passaged aortic and mesenteric VSMCs, whereas PPAR-alpha was almost undetectable. Thus, aorta and mesenteric resistance arteries from SHR in the prehypertensive and the established phase of hypertension exhibit increased expression of both PPAR isoforms, whereas other tissues do not. Changes (increases) in PPAR expression may play a compensatory role in the remodeling of blood vessels in SHR.

Pioglitazone enhances cytokine-induced apoptosis in vascular smooth muscle cells and reduces intimal hyperplasia

BACKGROUND

Cytokines induce apoptosis in vascular disease lesions through enhancement of inducible nitric oxide (NO) synthase (iNOS) activation. The thiazolidinediones, novel insulin-sensitizing agents, have been demonstrated to modulate cytokine-induced NO production. We have investigated the role of pioglitazone in the apoptosis of vascular smooth muscle cells (VSMCs) in vitro and developed intimal hyperplasia in vivo.

METHODS AND RESULTS

Pioglitazone (0.1 to 10 micromol/L) significantly enhanced cytokine-induced expression of iNOS and NO production in a dose-dependent manner in rat VSMCs, but 15-deoxy-Delta(12,14)-prostaglandin J2 (up to 10 micromol/L), a native peroxisome proliferator-activated receptor-gamma ligand, showed no effect. Pioglitazone also significantly enhanced reduction of cell viability, as evidenced by the increase in the number of TUNEL-positive cells. All of these effects of pioglitazone were blocked by treatment with N-monomethyl-L-arginine, an NO synthesis inhibitor. In an in vivo study with a balloon-injured rat carotid artery, neointimal thickness had reached maximum levels at 2 weeks after injury. Then, rats were fed with or without pioglitazone (3 mg. kg(-1). d(-1)) for an additional week. The ratio of intima to media area of carotid artery was significantly decreased by 30%, and the ratio of apoptotic cells in neointima was significantly increased in pioglitazone-treated rats compared with vehicle-treated control rats.

CONCLUSIONS

Pioglitazone enhanced apoptosis in an NO-dependent manner in cytokine-activated VSMCs and induced significant regression of intimal hyperplasia in balloon-injured rat carotid artery. It appears that pioglitazone is a potent apoptosis inducer in vascular lesions, providing a novel pharmacological strategy to prevent restenosis after vascular intervention.

Peroxisome proliferator-activated receptors (PPARs): novel therapeutic targets in renal disease

Peroxisome proliferator-activated receptors (PPARs): Novel therapeutic targets in renal disease. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily of ligand-dependent transcription factors. PPARs play an important role in the general transcriptional control of numerous cellular processes, including lipid metabolism, glucose homeostasis, cell cycle progression, cell differentiation, inflammation and extracellular matrix remodeling. Three PPAR isoforms, designated PPARalpha, PPARbeta and PPARgamma, have been cloned and are differentially expressed in several tissues including the kidney. PPARalpha primary regulates lipid metabolism and modulates inflammation. PPARalpha is the molecular target of the hypolipidemic fibrates including bezafibrate and clofibrate. PPARbeta participates in embryonic development, implantation and bone formation. PPARgamma is a key factor in adipogenesis and also plays an important role in insulin sensitivity, cell cycle regulation and cell differentiation. Antidiabetic thiazolidinediones (TZDs) such as troglitazone and rosiglitazone are specific ligands of PPARgamma, and this interaction is responsible for the insulin-sensitizing and hypoglycemic effect of these drugs. The kidney has been shown to differentially express all PPAR isoforms. PPARalpha is predominantly expressed in proximal tubules and medullary thick ascending limbs, while PPARgamma is expressed in medullary collecting ducts, pelvic urothelium and glomerular mesangial cells. PPARbeta is ubiquitously expressed at low levels in all segments of nephron. Accumulating data has begun to emerge suggesting physiological and pathophysiological roles of PPARs in several tissues including the kidney. The availability of PPAR-selective agonists and antagonists may provide a new approach to modulate the renal response to diseases including glomerulonephritis, glomerulosclerosis and diabetic nephropathy.

Transcriptional suppression of type 1 angiotensin II receptor gene expression by peroxisome proliferator-activated receptor-gamma in vascular smooth muscle cells

Angiotensin (A) II plays a critical role in vascular remodeling, and its action is mediated by type 1 AII receptor (AT1R). Recently, 15-deoxy-(Delta)(12,14)-prostaglandin J(2) and thiazolidinediones have been shown to be ligands for peroxisome proliferator-activated receptor (PPAR)-gamma and activate PPAR-gamma. In the present work, we have studied the effect of PPAR-gamma on AT1R expression in rat vascular smooth muscle cells (VSMCs). We observed that: 1) endogenous AT1R expression was significantly decreased by PPAR-gamma ligands both at messenger RNA and protein levels, whereas AT1R messenger RNA stability was not affected; 2) AII-induced increase of (3)H-thymidine incorporation into VSMCs was inhibited by PPAR-gamma ligands; 3) rat AT1R gene promoter activity was significantly suppressed by PPAR-gamma ligands, and PPAR-gamma overexpression further suppressed the promoter activity; 4) transcriptional analyses using AT1R gene promoter mutants revealed that a GC-box-related sequence within the -58/-34 region of the AT1R gene promoter was responsible for the suppression; 5) Sp1 overexpression stimulated AT1R gene transcription via the GC-box-related sequence, which was inhibited by additional PPAR-gamma overexpression; 6) electrophoretic mobility shift assay suggested that Sp1 could bind to the GC-box-related sequence whereas PPAR-gamma could not; 7) antibody supershift experiments using VSMC nuclear extracts revealed that protein-DNA complexes formed on the GC-box-related sequence, which were decreased by PPAR-gamma coincubation, were mostly composed of Sp1; and 8) glutathione S-transferase pull-down assay revealed a direct interaction between PPAR-gamma and Sp1. Taken together, it is suggested that activated PPAR-gamma suppresses AT1R gene at a transcriptional level by inhibiting Sp1 via a protein-protein interaction. PPAR-gamma ligands, thus, may inhibit AII-induced cell growth and hypertrophy in VSMCs by AT1R expression suppression and possibly be beneficial for treatment of diabetic patients with hypertension and atherosclerosis.

Comparative actions of insulin sensitizers on ion channels in vascular smooth muscle

Thiazolidinedione and isoxazolidinedione insulin sensitizers activate peroxisome proliferator-activated receptor gamma (PPAR gamma). Some thiazolidinediones modify ion channels in smooth muscles; however, the mechanism by which their actions occur has not been clarified. We, thus, examined the effects of three thiazolidinediones (troglitazone, pioglitazone, and rosiglitazone) and isoxazolidinedione (JTT-501), as well as an intrinsic ligand for PPAR gamma, 15-deoxy-Delta(12,14) prostaglandin J(2) (prostaglandin J(2)), on voltage-operated Ca(2+) currents (I(Ca)), voltage-dependent K(+) currents (I(Kv)), and Ca(2+)-activated K(+) currents (I(Kca)), to clarify whether a thiazolidinedione structure or PPAR gamma activation is related to their actions on ion channels. The whole-cell patch clamp method was used to record currents in smooth muscle cells from guinea-pig mesenteric arteries. Thiazolidinediones inhibited I(Ca) in a dose-dependent manner (troglitazone>pioglitazone=rosiglitazone). Troglitazone (> or =1 microM) and rosiglitazone (100 microM), but not pioglitazone, inhibited I(Kv). Rosiglitazone (> or =10 microM) enhanced, troglitazone (> or =1 microM) inhibited, and pioglitazone did not affect I(Kca). A high concentration of JTT-501 (100 microM) inhibited I(Ca), I(Kv), and I(Kca) to a similar extent. Prostaglandin J(2) enhanced I(Kca), but affected neither I(Ca) nor I(Kv). In summary, the three thiazolidinediones and isoxazolidinedione act differently on Ca(2+) and K(+) channels in vascular smooth muscle. The action of thiazolidinediones on I(Ca) could be attributed to specific regions of the molecules and not to activation of PPAR gamma. Involvement of PPAR gamma activation in the stimulation of I(Kca) is possible but should be tested further.

Troglitazone corrects metabolic changes but not vascular dysfunction in dietary-obese rats

Insulin resistance has been attributed to the defect in vascular function associated with obesity, type 2 diabetes and dyslipidaemia. We have investigated vascular effects of chronic (3-week) administration of troglitazone on female Wistar rats with moderate dietary obesity. Compared with lean controls, untreated obese rats had significantly higher body weights, fat pad masses, plasma triglycerides, free fatty acids and leptin levels (for all P < 0.01). These metabolic changes were corrected by troglitazone treatment. In mesenteric arteries, responses to noradrenaline or KCl were similar in all groups. However, in noradrenaline-preconstricted arteries, vasorelaxations to acetylcholine and insulin were significantly (50-60% less than in lean, P < 0.001) attenuated in both untreated and troglitazone-treated obese rats. Relaxations to sodium nitroprusside showed similar but lesser impairment in both untreated and troglitazone-treated obese animals. Our data show that although troglitazone markedly improved obesity-induced metabolic changes, it failed to correct vascular dysfunction associated with obesity in female Wistar rats.

Transcriptional control of adipogenesis

The major transcriptional factors involved in the adipogenic process include proteins belonging to the CCAAT/enhancer binding protein family, peroxisome proliferator-activated receptor gamma, and adipocyte determination and differentiation dependent factor 1, also known as sterol regulatory element-binding protein 1. This process has been characterized with the aid of cell lines that represent various stages in the path of adipocyte commitment, ranging from pluripotent mesodermal fibroblasts to preadipocytes. Molecular analyses have led to a cascade model for adipogenesis based on timed expression of CCAAT/enhancer-binding proteins and peroxisome proliferator-activated receptor gamma. Gene targeting and transgenic-mouse technologies, which allow the manipulation of endogenous genes for these transcription factors, have also contributed to the understanding of adipogenesis. This review aims to integrate this information to gain an understanding of the transcriptional regulation of fat cell formation.

Lessons from pregnancy and parturition: uterine leiomyomas result from discordant differentiation and dedifferentiation responses in smooth muscle cells

Leiomyomas, benign smooth muscle tumors of the uterus, are the most common gynecological neoplasm in women. Studies with human tissues and primary cultures have revealed little about the development of leiomyomas, although several genes have been shown to be differentially expressed in leiomyomas compared to matched normal myometrium. We propose that uterine smooth muscle tumor cells mimic a differentiated myometrial cell of pregnancy, and are associated with a hypersensitivity to sex steroid hormones, preventing the cells from responding to normal apoptotic or dedifferentiation signals which would return the cells to a nongravid phenotype. Support of this hypothesis is derived from experimental studies in female Eker rats which develop uterine leiomyoma with many similarities to the human disease. Members of the steroid receptor superfamily as well as the binding partners and co-regulators necessary for transactivation and gene transcription, may be involved in the altered pathway of cellular differentiation and regulation observed in uterine leiomyomas.

PPAR agonists as direct modulators of the vessel wall in cardiovascular disease

Successful management of cardiovascular (CV) disease and associated metabolic syndromes, such as diabetes, is a major challenge to the clinician. Reducing CV risk factors, such as abnormal lipid profiles, insulin resistance or hypertension is the foundation of such therapy. A relatively new class of therapeutic agent, activators of peroxisome proliferator-activated receptors (PPAR), is poised to make a major impact with regard to several areas of risk factor management. However, there is growing evidence that PPAR agonists may also influence the CV system directly by modulating vessel wall function. These observations suggest that additional benefit, in the treatment of CV disease, may derive not only from the ability of agents to modify risk factors but also to influence directly the cellular mechanisms of disease within the vessel wall. A precedent for this dual action comes from examination of the effects of inhibitors of HMG CoA reductase (statins), where risk factor modulation is accompanied by direct actions on the vessel wall. In this review, we summarize the evidence suggesting that PPAR agonists may directly modulate vessel wall function, and that these may parallel those effects reported recently for the statins.

PPAR signaling in the control of cardiac energy metabolism

Cardiac energy metabolic shifts occur as a normal response to diverse physiologic and dietary conditions and as a component of the pathophysiologic processes which accompany cardiac hypertrophy, heart failure, and myocardial ischemia. The capacity to produce energy via the utilization of fats by the mammalian postnatal heart is controlled in part at the level of expression of nuclear genes encoding enzymes involved in mitochondrial fatty acid beta-oxidation (FAO). The principal transcriptional regulator of FAO enzyme genes is the peroxisome proliferator-activated receptor alpha (PPARalpha), a member of the ligand-activated nuclear receptor superfamily. Among the ligand activators of PPARalpha are long-chain fatty acids; therefore, increased uptake of fatty acid substrate into the cardiac myocyte induces a transcriptional response leading to increased expression of FAO enzymes. PPARalpha-mediated control of cardiac metabolic gene expression is activated during postnatal development, short-term starvation, and in response to exercise training. In contrast, certain pathophysiologic states, such as pressure overload-induced hypertrophy, result in deactivation of PPARalpha and subsequent dysregulation of FAO enzyme gene expression, which sets the stage for abnormalities in cardiac lipid homeostasis and energy production, some of which are influenced by gender. Thus, PPARalpha not only serves a critical role in normal cardiac metabolic homeostasis, but alterations in PPARalpha signaling likely contribute to the pathogenesis of a variety of disease states. PPARalpha as a ligand-activated transcription factor is a potential target for the development of new therapeutic strategies aimed at the prevention of pathologic cardiac remodeling.

Peroxisome proliferator-activated receptors in vascular biology and atherosclerosis: emerging insights for evolving paradigms

Peroxisome Proliferator-Activated Receptors (PPARs), members of the steroid hormone nuclear receptor superfamily, act as ligand-activated transcription factors controlling the expression of specific target genes. Known PPAR isoforms include PPAR gamma, important in adipogenesis and lipid metabolism, PPAR alpha, implicated in fatty acid metabolism, and PPAR delta, about which the least is known. Recent work implicates PPAR alpha and gamma in vascular biology and atherosclerosis, and will be reviewed here. Such effects may have clinical implications given PPAR agonists in use as pharmacologic agents (eg, thiazolidinediones as insulin sensitizers [gamma] and fibric acids as lipid lowering agents [alpha]).