Peroxisome proliferator-activated receptor-gamma agonists increase vascular endothelial growth factor expression in human vascular smooth muscle cells

Vascular endothelial growth factor (VEGF), expressed in a variety of mesenchymal cells including vascular smooth muscle cells (VSMC), is a potent mitogen for endothelial cells, and is used clinically applied for ischemic disease of peripheral vessels. To determine whether peroxisome proliferator-activated receptor gamma (PPARgamma) regulates VEGF production in VSMC, we examined VEGF secretion from VSMC treated with PPAR agonists. Troglitazone increased VEGF secretion in a time- and dose-dependent manner (261 +/- 35% with 25 mM of troglitazone for 24 h), and also increased levels of VEGF mRNA. VEGF secretion was also increased by other PPARgamma agonists, pioglitazone, LY171883, and 15d-PGJ2 (224 +/- 17.1%, 247 +/- 36.8% and 171 +/- 7.8%, respectively), but not the PPARgamma agonists bezafibrate and Wy14643 (85.2 +/- 1.5%, 94.6 +/- 3.2, respectively). Our findings suggest that thiazolidinediones might be useful for the therapeutic angiogenesis for ischemic artery disease.     

Peroxisome proliferator-activated receptor-gamma in cystic fibrosis lung epithelium

The pathophysiology of cystic fibrosis (CF) inflammatory lung disease is not well understood. CF airway epithelial cells respond to inflammatory stimuli with increased production of proinflammatory cytokines as a result of increased NF-kappaB activation. Peroxisome proliferator-activated receptor-gamma (PPARgamma) inhibits NF-kappaB activity and is reported to be reduced in CF. If PPARgamma participates in regulatory dysfunction in the CF lung, perhaps PPARgamma ligands might be useful therapeutically. Cell models of CF airway epithelium were used to evaluate PPARgamma expression and binding to NF-kappaB at basal and under conditions of inflammatory stimulation by Pseudomonas aeruginosa or TNFalpha/IL-1beta. An animal model of CF was used to evaluate the potential of PPARgamma agonists as therapeutic agents in vivo. In vitro, PPARgamma agonists reduced IL-8 and MMP-9 release from airway epithelial cells in response to PAO1 or TNFalpha/IL-1beta stimulation. Less NF-kappaB bound to PPARgamma in CF than normal cells, in two different assays; PPARgamma agonists abrogated this reduction. PPARgamma bound less to its target DNA sequence in CF cells. To test the importance of the reported PPARgamma inactivation by phosphorylation, we observed that inhibitors of ERK, but not JNK, were synergistic with PPARgamma agonists in reducing IL-8 secretion. In vivo, administration of PPARgamma agonists reduced airway inflammation in response to acute infection with P. aeruginosa in CF, but not wild-type, mice. In summary, PPARgamma inhibits the inflammatory response in CF, at least in part by interaction with NF-kappaB in airway epithelial cells. PPARgamma agonists may be therapeutic in CF.     

Peroxisome proliferator-activated receptor-gamma ligands regulate endothelial membrane superoxide production

Recently, we demonstrated that the peroxisome proliferator-activated receptor- (PPAR-) ligands, either 15-deoxy-^12,14-prostaglandin J₂ (15d-PGJ₂) or ciglitazone, increased endothelial nitric oxide (·NO) release without altering endothelial nitric oxide synthase (eNOS) expression (4). However, the precise molecular mechanisms of PPAR--stimulated endothelial·NO release remain to be defined. Superoxide anion radical (O₂^–·) combines with ·NO to decrease·NO bioavailability. NADPH oxidase, which produces O₂^–·, and Cu/Zn-superoxide dismutase (Cu/Zn-SOD), which degrades O₂^–·, thereby contribute to regulation of endothelial cell·NO metabolism. Therefore, we examined the ability of PPAR- ligands to modulate endothelial O₂^–· metabolism through alterations in the expression and activity of NADPH oxidase or Cu/Zn-SOD. Treatment with 10 µM 15d-PGJ₂ or ciglitazone for 24 h decreased human umbilical vein endothelial cell (HUVEC) membrane NADPH-dependent O₂^–· production detected with electron spin resonance spectroscopy. Treatment with 15d-PGJ₂ or ciglitazone also reduced relative mRNA levels of the NADPH oxidase subunits, nox-1, gp91^phox (nox-2), and nox-4, as measured using real-time PCR analysis. Concordantly, Western blot analysis demonstrated that 15d-PGJ₂ or ciglitazone decreased nox-2 and nox-4 protein expression. PPAR- ligands also stimulated both activity and expression of Cu/Zn-SOD in HUVEC. These data suggest that in addition to any direct effects on endothelial·NO production, PPAR- ligands enhance endothelial·NO bioavailability, in part by altering endothelial O₂^–· metabolism through suppression of NADPH oxidase and induction of Cu/Zn-SOD. These findings further elucidate the molecular mechanisms by which PPAR- ligands directly alter vascular endothelial function. reduced nicotinamide adenine dinucleotide phosphate oxidase; copper/zinc superoxide dismutase; nitric oxide; endothelial cells     

Peroxisome proliferator-activated receptor-gamma ligands inhibit adipocyte 11beta -hydroxysteroid dehydrogenase type 1 expression and activity

Peroxisome proliferator-activated receptor-gamma (PPARgamma) has been shown to play an important role in the regulation of expression of a subclass of adipocyte genes and to serve as the molecular target of the thiazolidinedione (TZD) and certain non-TZD antidiabetic agents. Hypercorticosteroidism leads to insulin resistance, a variety of metabolic dysfunctions typically seen in diabetes, and hypertrophy of visceral adipose tissue. In adipocytes, the enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD-1) converts inactive cortisone into the active glucocorticoid cortisol and thereby plays an important role in regulating the actions of corticosteroids in adipose tissue. Here, we show that both TZD and non-TZD PPARgamma agonists markedly reduced 11beta-HSD-1 gene expression in 3T3-L1 adipocytes. This diminution correlated with a significant decrease in the ability of the adipocytes to convert cortisone to cortisol. The half-maximal inhibition of 11beta-HSD-1 mRNA expression by the TZD, rosiglitazone, occurred at a concentration that was similar to its K(d) for binding PPARgamma and EC(50) for inducing adipocyte differentiation thereby indicating that this action was PPARgamma-dependent. The time required for the inhibitory action of the TZD was markedly greater for 11beta-HSD-1 gene expression than for leptin, suggesting that these genes may be down-regulated by different molecular mechanisms. Furthermore, whereas regulation of PPARgamma-inducible genes such as phosphoenolpyruvate carboxykinase was maintained when cellular protein synthesis was abrogated, PPARgamma agonist inhibition of 11beta-HSD-1 and leptin gene expression was ablated, thereby supporting the conclusion that PPARgamma affects the down-regulation of 11beta-HSD-1 indirectly. Finally, treatment of diabetic db/db mice with rosiglitazone inhibited expression of 11beta-HSD-1 in adipose tissue. This decrease in enzyme expression correlated with a significant decline in plasma corticosterone levels. In sum, these data indicate that some of the beneficial effects of PPARgamma antidiabetic agents may result, at least in part, from the down-regulation of 11beta-HSD-1 expression in adipose tissue.     

Role of granulocyte/macrophage colony-stimulating factor in the regulation of murine alveolar macrophage proliferation and differentiation

Granulocyte/macrophage (GM)-CSF is one of the hemopoietic growth factors that stimulates neutrophilic granulocyte and macrophage production by bone marrow progenitor cells. In this study, the effect of GM-CSF on the growth and differentiation of murine pulmonary alveolar macrophages (PAM) was investigated. In the presence of GM-CSF, normal murine PAM were induced to proliferate and develop into macrophage colonies with a dose-response curve similar to that of bone marrow GM colony-forming cells. PAM also responded to CSF-1, a lineage-restricted growth factor, but required much higher doses of CSF-1 and a longer incubation time for optimal colony formation. The proliferative response of PAM to CSF-1, however, was greatly enhanced by the concurrent addition of low doses of GM-CSF. In contrast, low doses of CSF-1 failed to potentiate the proliferative response of PAM to GM-CSF. Macrophages derived from GM-CSF cultures were rounder and less stretched and possessed less FcR-mediated phagocytic activity than cells produced in CSF-1 cultures. A study with hydrocortisone-induced monocytopenia showed that nearly one half of lung macrophages may be sustained by local proliferation of PAM without the continuous migration of blood monocytes. This study suggests that GM-CSF may play a major role in the production of PAM by two modes of action, 1) direct stimulation of cell proliferation and 2) enhancement of their responsiveness to CSF-1, thereby producing more mature and functionally competent macrophages.     

Peroxisome proliferator-activated receptor-gamma agonists in atherosclerosis: current evidence and future directions

PURPOSE OF REVIEW: The prevalence of type 2 diabetes globally is reaching epidemic proportions. Type 2 diabetes is strongly associated with increased risk of cardiovascular disease. Atherosclerosis is thought to arise as a result of a chronic inflammatory process within the arterial wall. Insulin resistance is central to the pathogenesis of type 2 diabetes and may contribute to atherogenesis, either directly or through associated risk factors. The peroxisome proliferator-activated receptor-gamma agonists, the thiazolidinediones, pioglitazone and rosiglitazone, are insulin sensitizing agents, that are licensed for the management of hyperglycaemia. Growing evidence supports an array of additional effects of thiazolidinedione therapy, both immunomodulatory and antiinflammatory, which may attenuate atherogenesis in type 2 diabetes. RECENT FINDINGS: Studies have shown that thiazolidinedione therapy may lead to risk factor modulation in type 2 diabetes. Thiazolidinediones treatment has been shown to reduce blood pressure, modify the atherogenic lipid profile associated with type 2 diabetes, reduce microalbuminuria and ameliorate the prothrombotic diathesis. Further evidence suggests that thiazolidinediones therapy inhibits the inflammatory processes which may be involved in atherosclerotic plaque initiation, propagation and destabilization. SUMMARY: Modification of insulin resistance by thiazolidinedione therapy in type 2 diabetes and the range of pleiotropic effects may not only impact on incident type 2 diabetes, but also on associated cardiovascular disease. Numerous large clinical endpoint studies are under way to investigate these issues.     

Peroxisome proliferator-activated receptor-gamma agonists suppress the production of IL-12 family cytokines by activated glia

The IL-12 family of cytokines, which include IL-12, IL-23, and IL-27, play critical roles in the differentiation of Th1 cells and are believed to contribute to the development of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Relatively little is known concerning the expression of IL-12 family cytokines by cells of the CNS, the affected tissue in MS. Previously, we and others demonstrated that peroxisome proliferator-activated receptor (PPAR)-gamma agonists suppress the development of EAE, alter T cell proliferation and phenotype, and suppress the activation of APCs. The present studies demonstrated that PPAR-gamma agonists, including the naturally occurring 15-deoxy-Delta(12,14)-PGJ(2) and the synthetic thiazoladinedione rosiglitazone, inhibited the induction of IL-12p40, IL-12p70 (p35/p40), IL-23 (p19/p40), and IL-27p28 proteins by LPS-stimulated primary microglia. In primary astrocytes, LPS induced the production of IL-12p40, IL-23, and IL-27p28 proteins. However, IL-12p70 production was not detected in these cells. The 15-deoxy-Delta(12,14)-PGJ(2) potently suppressed IL-12p40, IL-23, and IL-27p28 production by primary astrocytes, whereas rosiglitazone suppressed IL-23 and IL-27p28, but not IL-12p40 in these cells. These novel observations suggest that PPAR-gamma agonists modulate the development of EAE, at least in part, by inhibiting the production of IL-12 family cytokines by CNS glia. In addition, we demonstrate that PPAR-gamma agonists inhibit TLR2, MyD88, and CD14 expression in glia, suggesting a possible mechanism by which these agonists modulate IL-12 family cytokine expression. Collectively, these studies suggest that PPAR-gamma agonists may be beneficial in the treatment of MS.     

PU.1 regulation of human alveolar macrophage differentiation requires granulocyte-macrophage colony-stimulating factor

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is critically implicated in lung homeostasis in the GM-CSF knockout mouse model. These animals develop an isolated lung lesion reminiscent of pulmonary alveolar proteinosis (PAP) seen in humans. The development of the adult form of human alveolar proteinosis is not due to the absence of a GM-CSF gene or receptor defect but to the development of an anti-GM-CSF autoimmunity. The role of GM-CSF in the development of PAP is unknown. Studies in the GM-CSF knockout mouse have shown that lack of PU.1 protein expression in alveolar macrophages is correlated with decreased maturation, differentiation, and surfactant catabolism. This study investigates PU.1 expression in vitro and in vivo in human PAP alveolar macrophages as well as the regulation of PU.1 by GM-CSF. We show for the first time that PU.1 mRNA expression in PAP bronchoalveolar lavage cells is deficient compared with healthy controls. PU.1-dependent terminal differentiation markers CD32 (FCgammaII), mannose receptor, and macrophage colony-stimulating factor receptor (M-CSFR) are decreased in PAP alveolar macrophages. In vitro studies demonstrate that exogenous GMCSF treatment upregulated PU.1 and M-CSFR gene expression in PAP alveolar macrophages. Finally, in vivo studies showed that PAP patients treated with GM-CSF therapy have higher levels of PU.1 and M-CSFR expression in alveolar macrophages compared with healthy control and PAP patients before GM-CSF therapy. These observations suggest that PU.1 is critical in the terminal differentiation of human alveolar macrophages.