Divergent effects of selective peroxisome proliferator-activated receptor-gamma 2 ligands on adipocyte versus osteoblast differentiation

PPAR gamma is activated by diverse ligands and regulates the differentiation of many cell types. Based on evidence that activation of PPAR gamma 2 by rosiglitazone stimulates adipogenesis and inhibits osteoblastogenesis in U-33/gamma 2 cells, a model mesenchymal progenitor of adipocytes and osteoblasts, we postulated that the increase in marrow fat and the decrease in osteoblast number that occur during aging are due to increased PPAR gamma 2 activation. Here, we show that the naturally occurring PPAR gamma ligands 9,10-dihydroxyoctadecenoic acid, and 15-deoxy-Delta(12,14)-PGJ(2), also stimulate adipocytes and inhibit osteoblast differentiation of U-33/gamma 2 cells. Strikingly, 9,10-epoxyoctadecenoic acid and the thiazolidine acetamide ligand GW0072 [(+/-)-(2S,5S)-4-(4-(4-carboxyphenyl)butyl)-2-heptyl-4-oxo-5-thaizolidineN,N-dibenzyl-acetamide] prevent osteoblast differentiation, but do not stimulate adipogenesis, whereas 9-hydroxyoctadecadienoic acid stimulates adipogenesis but does not affect osteoblast differentiation. The divergent effects of PPAR gamma 2 ligands on osteoblast and adipocyte differentiation were confirmed in primary murine bone marrow cultures using rosiglitazone and GW0072. These findings indicate that the proadipogenic and antiosteoblastogenic effects of PPAR gamma 2 are mediated by distinct regulatory pathways that can be differentially modulated depending on the nature of the ligand, and they support the idea that increased fatty acid oxidation during aging may inhibit osteoblast differentiation. Moreover, there may be selective PPAR gamma 2 modulators that block the adverse effects of fatty acid oxidation products while retaining beneficial activities such as insulin sensitization.     

Angiotensin type 1 receptor antagonists induce human in-vitro adipogenesis through peroxisome proliferator-activated receptor-gamma activation

OBJECTIVE: In clonal animal cells, certain angiotensin receptor blockers (ARB) activate the peroxisome proliferator-activated receptor-gamma (PPARgamma). The aim of this work was to validate that observation in human cells and humans. METHODS: We investigated the induction of in-vitro adipogenesis and the activation of PPARgamma-target genes, adiponectin and lipoprotein lipase, by ARB in human preadipocytes. We also studied PPARgamma response-element-driven luciferase reporter gene activation in human adipocytes. Finally, we treated 14 obese men for 10 days with placebo crossed over with 150 mg/day irbesartan. Subcutaneous fat was analyzed for mRNA expression of adiponectin and lipoprotein lipase. RESULTS: Telmisartan and irbesartan, and to a lesser degree losartan, induced adipogenesis and activated PPARgamma-target genes. This stimulation of PPARgamma-target genes was prevented by the PPARgamma antagonist GW9662. Eprosartan had no effect. Paradoxically, all ARB activated the luciferase reporter gene. PPARgamma activity increased approximately two-fold with pioglitazone and 1.5-fold with the ARB in all assays. In the cross-over clinical study, irbesartan lowered blood pressure but had no effect on adiponectin or lipoprotein lipase mRNA expression. CONCLUSIONS: Our data are the first to show that ARB induce adipogenesis and PPARgamma-target gene expression in human adipocytes. Pharmacokinetic differences may contribute to the heterogeneous effects on metabolism and preadipocyte differentiation. In humans, larger doses of ARB, longer treatments, or both may be required to activate PPARgamma in adipose cells.     

Telmisartan inhibits CD4-positive lymphocyte migration independent of the angiotensin type 1 receptor via peroxisome proliferator-activated receptor-gamma

Migration of CD4-positive lymphocytes into the vessel wall represents an important step in early atherogenesis. Telmisartan is an angiotensin type 1 receptor (AT1R) blocker with peroxisome proliferator-activated receptor (PPAR)-gamma-activating properties. The present study examined the effect of telmisartan on CD4-positive cell migration and the role of PPARgamma in this context. CD4-positive lymphocytes express both the AT1R and PPARgamma. Stimulation of CD4-positive lymphocytes with stromal cell-derived factor (SDF)-1 leads to a 4.1+/-3.1-fold increase in cell migration. Pretreatment of cells with telmisartan reduces this effect in a concentration-dependent manner to a maximal 1.6+/-0.7-fold induction at 10 mumol/L of telmisartan (P<0.01 compared with SDF-1-treated cells; n=22). Three different PPARgamma activators, rosiglitazone, pioglitazone, and GW1929, had similar effects, whereas eprosartan, a non-PPARgamma-activating AT1R blocker, did not affect chemokine-induced lymphocyte migration. Telmisartan's effect on CD4-positive lymphocyte migration was mediated through an early inhibition of chemokine-induced phosphatidylinositol 3-kinase activity. Downstream, telmisartan inhibited F-actin formation, as well as intercellular adhesion molecule-3 translocation. Transfection of CD4-positive lymphocytes with PPARgamma small interfering RNA abolished telmisartan's effect on migration, whereas blockade of the AT1R had no such effect. Telmisartan inhibits chemokine-induced CD4-positive cell migration independent of the AT1R via PPARgamma. These data provide a novel mechanism to explain how telmisartan modulates lymphocyte activation by its PPARgamma-activating properties.     

The developmental regulation of peroxisome proliferator-activated receptor-gamma coactivator-1alpha expression in the liver is partially dissociated from the control of gluconeogenesis and lipid catabolism

The developmental regulation of peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) gene expression was studied in mice and compared with that of marker genes of liver energy metabolism. The PGC-1alpha gene was highly expressed in fetal liver compared with that in adults and remained high in neonatal liver. The regulation of PGC-1alpha gene expression during the fetal and early neonatal periods was dissociated from that of gluconeogenic genes, i.e. the phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) genes. Only under the effects of starvation was PGC-1alpha gene expression induced in parallel to phosphoenolpyruvate carboxykinase and G6Pase mRNAs during the perinatal period. Furthermore, the PGC-1alpha gene was not regulated as part of the developmental program of gene expression associated with the maturation of hepatic gluconeogenesis, as revealed by the impaired PEPCK and G6Pase gene expression but unaltered PGC-1alpha mRNA levels in CCAAT/enhancer-binding protein-alpha-null fetus and neonates. Regulation of the PGC-1alpha gene and that of mitochondrial 3-hydroxy-3-methyl-glutaryl-coenzyme A synthase, acyl-coenzyme A oxidase, and long-chain acyl-coenzyme dehydrogenase, marker genes of lipid catabolism, were dissociated in fetuses and neonates. The expression of lipid catabolism genes was down-regulated in fasted neonates, whereas PGC-1alpha was oppositely regulated. The independent regulation of PGC-1alpha and lipid catabolism genes was also found in peroxisome proliferator-activated receptor-alpha-null neonates, in which PGC-1alpha mRNA levels were unaffected whereas gene expression for 3-hydroxy-3-methyl-glutaryl-coenzyme A synthase and acyl-coenzyme A oxidase was impaired. Thus, regulation of the PGC-1alpha gene is partially dissociated from the patterns of regulation of hepatic genes encoding enzymes involved in gluconeogenesis and lipid catabolism during fetal ontogeny and in response to the initiation of lactation.     

Effect of peroxisome proliferator-activated receptor-gamma ligand on inflammation of human gallbladder epithelial cells

AIM: To investigate the effect of peroxisome proliferatoractivated receptor gamma (PPAR-γ) and its ligand, ciglitazone, on inflammatory regulation of human gallbladder epithelial cells (HGBECs) and to assess the effect of human epithelial growth factor (hEGF) on growth of HGBECs. METHODS: HGBECs were cultured in media containing hEGF or in hEGF-free media. HGBECs were divided into normal control group, inflammatory control group and ciglitazone group (test group). Inflammatory control group and ciglitazone group were treated with 5 μg/L of human interleukin-1β (hIL-1β) to make inflammatory model of HGBECs. The ciglitazone group was treated with various concentrations of ciglitazone, a potent ligand of PPAR-γ. Subsequently, interleukin-8 (IL-8), IL-6, and tumor necrosis factor-α (TNF-α) concentrations in all groups were measured. The data were analyzed statistically. RESULTS: HGBECs were cultured in medium successfully. The longevity of HGBECs in groups containing hEGF was longer than that in hEGF-free groups. So was the number of HGBECs. The longest survival time of HGBEC was 25 d. The inflammatory model of HGBECs was obtained by treating with hIL-lp. The concentrations of IL-6 and IL-8 in ciglitazone group were lower than those in inflammatory control group (P<0.05). The secretion of IL-6 in inflammatory control group was higher (350.31±37.05 μg/L) than that in normal control group (50.0±0.00 μg/L, P<0.001). Compared to normal control group, IL-8 concentration in inflammatory control was higher (P<0.05). CONCLUSION: hEGF improves the growth of HGBECs in vitro. Ciglitazone inhibits the inflammation of HGBECs in vitro and has potential therapeutic effect on cholecystitis in vivo.     

过氧化物酶体增殖物激活受体对哮喘患者树突状细胞免疫调控的影响

支气管哮喘是以Th1/Th2细胞比例失衡和Th2细胞优势分化为免疫学发病基础的慢性气道炎症性疾病。树突状细胞(DC)在哮喘发病中起重要作用,髓系DC(DC1)能促使支气管哮喘原始Th细胞向Th2细胞分化增殖,肺脏淋巴系DC(肺脏DC2)能诱导免疫耐受;过氧化物酶体增殖物激活受体-γ(PPAR-γ)能减轻哮喘气道炎症。因此,我们综述了PPAR-γ对哮喘患者DC免疫调控功能的影响,为哮喘的研究防治探索新思路。     

Effect of the peroxisome proliferator-activated receptor-gamma C161T polymorphism on lipid profile in Brazilian patients with Type 2 diabetes mellitus

AIM: The aim of the present study was to examine the effects of the C161T polymorphism of the peroxisome proliferator-activated receptor gamma (PPARgamma) gene in Brazilian subjects with Type 2 diabetes mellitus (T2DM) and controls residing in Sao Paulo City, Brazil. METHODS: Genomic DNA was obtained from 207 patients with T2DM and 170 unrelated normoglycemic individuals (CG). Anthropometric data included: body mass index, waist, hip, waist-to-hip ratio; biochemical parameters: fasting plasma glucose, total cholesterol, HDL- and LDL-cholesterol, triglycerides, glycated hemoglobin and insulin. Systolic and diastolic blood pressure was also measured. Screening for mutations in the entire coding region of the PPARgamma gene was carried out by PCR, single strand conformational polymorphism analysis (SSCP) and sequencing. C161T polymorphism was analyzed by PCR-RFLP. RESULTS: The C161T polymorphism was the only variant found in exon 6 of the PPARgamma gene. The frequency of the 161T allele in T2DM (0.10) was similar to that found in CG (0.07, p=0.210). Serum triglycerides (p=0.040), VLDL-cholesterol (p=0.040) and Atherogenic Index of Plasma (AIP; p=0.003) were significantly lower in 161T allele carriers than non-carriers in women of the T2DM group. CONCLUSIONS: Our results show that the C161T polymorphism in the PPARgamma gene is not associated with variables related to T2DM or insulin resistance in the Brazilian population. However, a reduction of serum triglycerides and AIP was observed in women with 161T allele of the C161T polymorphism of the PPARgamma gene.     

Differential effects of peroxisome proliferator-activated receptor ligands and sulfonylurea plus statin treatment on plasma concentrations of adipokines in type 2 diabetes with dyslipidemia

OBJECTIVES: Peroxisome proliferator-activated receptor gamma is the master regulator of adipocyte differentiation and controls many adipocyte genes in response to anti-diabetic thiazolidinediones (TZDs) and lipid-lowering fibrates. We hypothesized that the combination of TZD+fibrate may be better than the sulfonylurea + statin approach regarding modifying the adipokine profile in diabetic patients with dyslipidemia. METHODS: We measured the lipid profiles and circulating levels of adiponectin, resistin, and inflammatory markers before and after treatment in 24 type 2 diabetic patients with dyslipidemia (aged 64+/-9 years; M/F=5/19). The study patients were randomly assigned to receive an 8-week treatment of either rosiglitazone 4 mg daily and fenofibrate 160 mg daily (PPAR group) or glibenclamide 5 mg daily and atorvastatin 10 mg daily (non-PPAR group). RESULTS: Even though the administration of sulfonylurea+statin can achieve a greater reduction of total cholesterol and LDL-cholesterol levels and a comparable glucose control compared to PPAR treatment, their administration did not change the plasma adipokine levels significantly. In contrast, a significant greater increase of the plasma concentrations of adiponectin (P<0.0001), a trend to a greater decrease of the plasma resistin levels (P=0.061), a significantly greater increase of HDL-cholesterol (P=0.002), and a significantly greater reduction of triglyceride levels (P=0.018) were seen in the PPAR group. CONCLUSIONS: Considering the clinical significance of the adipokine-endothelial interaction in the progression and long-term prognosis of atherosclerosis, the differential effects of PPAR ligands and sulfonylurea+statin on plasma adipokine concentrations demonstrated in this study are interesting foci of investigation in the future.     

Effect of diesel on chemokines and chemokine receptors involved in helper T cell type 1/type 2 recruitment in patients with asthma

The objective of this study was to evaluate if diesel exhausts could favor helper T cell type (Th) 2-associated allergic reactions either through an increased production of Th2-associated chemokines and of their associated receptors or through a decrease of Th1-attracting chemokines and chemokine receptors. Diesel but not allergen exposure of peripheral blood mononuclear cells from subjects with allergy induced a release of I-309, whereas both diesel and Der p 1 induced an early but transient release of monokine induced by IFN-gamma and a late release of pulmonary and activation-regulated chemokine. Although both Th1- and Th2-attracting chemokines were induced, the resulting effect was an increased chemotactic activity on Th2 but not Th1 cells. Surprisingly, diesel induced a late increase in the expression of the Th1-associated CXC receptor 3 and CC receptor 5. T cell CXC receptor 3 upregulation was not associated with an increased migration to its ligands. These two antagonistic effects have been previously reported as a scavenger mechanism to clear chemokines. Altogether, these results suggest that diesel, even without allergen, may amplify a type 2 immune response but that it can also increase late Th1-associated chemokine receptor expression, perhaps as a scavenger mechanism to clear pro-Th1 chemokines and promote the Th2 pathway.     

Effects of food restriction on peroxisome proliferator-activated receptor-gamma and glucocorticoid receptor signaling in adipose tissues of normal rats

In adipocytes, peroxisome proliferator-activated receptor (PPAR)-gamma activates adipocyte differentiation and glucocorticoid (GC) stimulates the expression of PPAR-gamma mRNA. The local tissue concentrations of GC, in turn, are modulated by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). To clarify the change of energy metabolism in condition of reduced energy intake, we investigated whether food restriction alters the adipocyte size and levels of PPAR-gamma, GC receptor (GR), and 11beta-HSD1 mRNA expression in the white adipose tissues of normal rats. Male Wistar rats weighing 340 g were housed under free feeding or 20% reduction of food intake for 2 or 14 days. We found that 2-day food restriction did not cause any change in the mean size or number of adipocytes in the omentum, while 14-day food restriction decreased the size and increased the number of adipocytes. In addition, the levels of PPAR-gamma2, GR, and 11beta-HSD1 mRNA expression in the omentum were lower in the food-restricted rats after 2 days, while they did not differ after 14 days. Also, after both 2 and 14 days, plasma concentrations of free fatty acid (FFA) were higher in the food-restricted rats than in control rats. Finally, plasma concentrations of adrenocorticotropin (ACTH) and corticosterone were the same in the both groups after 2 days, although they were higher in the food-restricted rats after 14 days. These results suggest that adipocyte differentiation in the omentum of food-restricted rats is attenuated after 2 days but recovers after 14 days, resulting in an increase in the number of small adipocytes. It is also likely that lipolysis induced during the 14-day period of food restriction decreased the size of adipocytes. Further, food restriction may affect the efficiency of local GC effects by altering GR and 11beta-HSD1 mRNA expression. Also, higher levels of plasma GC and recovery of GR and 11beta-HSD1 mRNA expression may contribute to the recovery of the levels of PPAR-gamma2 mRNA expression in the omentum and result in the recovery of adipocyte differentiation.     

过氧化物酶体增生因子激活受体α和γ配体对游离脂肪酸介导的β细胞损害的干预作用

目的：研究过氧化物酶体增生因子激活受体α和γ(PPARα和PPARγ)配体对游离脂肪酸(FFA)介导的胰岛β细胞损害的干预作用。方法：应用PPARα配体氯贝丁酯及PPARγ配体曲格列酮(troglitazone,TGZ)和噻唑烷二酮(thiazolidinedione,TZD)处理大鼠胰岛素瘤细胞系β细胞(INS-1细胞),采用细胞活力和DNA片段梯度分析评价PPARα和PPARγ配体对FFA诱导的INS-1细胞损害的影响。结果：INS-1细胞与0．25～1mmol／L的FFA孵育24h后细胞活力下降,1mmol／L的FFA可诱导INS-1细胞发生凋亡。比较是否使用氯贝丁酯(100μmol／L)、TGZ(10μmol／L)和TZD(100μmol/L)处理β细胞的结果,发现这些配体可保护INS-1细胞免于FFA的细胞毒性(包括脂性凋亡)作用。结论：FFA可介导β细胞发生明显的脂毒性和脂性凋亡,应用PPARα和PPARγ配体可能具有保护β细胞免于FFA的细胞毒性的作用。