Expression of genes involved in lipid metabolism correlate with peroxisome proliferator-activated receptor gamma expression in human skeletal muscle

Peroxisome proliferator-activated receptor gamma (PPAR-gamma) activation in adipose tissue is known to regulate genes involved in adipocyte differentiation and lipid metabolism. However, the role of PPAR-gamma in muscle remains unclear. To examine the potential regulation of genes by PPAR-gamma in human skeletal muscle, we used semiquantitative RT-PCR to determine the expression of PPAR-gamma, lipoprotein lipase (LPL), muscle carnitine palmitoyl transferase-1 (mCPT1), fatty acid-binding protein (FABP), carnitine acylcarnitine transferase (CACT), and glucose transporter-4 (GLUT4) in freeze-dried muscle samples from 14 male subjects. These samples were dissected free of adipose and other tissue contamination, as confirmed by minimal or absent adipsin expression. Between individuals, the messenger ribonucleic acid concentration of PPAR-gamma varied up to 3-fold, whereas LPL varied up to 6.5-fold, mCPT1 13-fold, FABP 4-fold, CACT 4-fold, and GLUT4 up to 3-fold. The expression of LPL (r2 = 0.54; P = 0.003), mCPT1 (r2 = 0.42; P = 0.012), and FABP (r2 = 0.324; P = 0.034) all correlated significantly with PPAR-gamma expression in the same samples. No significant correlation was observed between the expression of CACT and PPAR-gamma or between GLUT4 and PPAR-gamma. These findings demonstrate a relationship between PPAR-gamma expression and the expression of other genes of lipid metabolism in muscle and support the hypothesis that PPAR-gamma activators such as the antidiabetic thiazolidinediones may regulate fatty acid metabolism in skeletal muscle as well as in adipose tissue.     

衰老对大鼠过氧化体增殖物激活受体α表达的影响与脂质代谢的关系

目的　观察衰老对过氧化体增殖物激活受体α和目标基因脂蛋白脂酶、载脂蛋白CⅢ组织表达的影响 ,从而探讨衰老过程中出现脂质代谢异常的可能机制。方法　雄性SD年轻大鼠 (4～ 6周龄 ) 16只和老年大鼠 (2 4月龄 )16只 ,随机分为对照组和给药组 (非诺贝特喂养 2周 ) ,测定血清中甘油三酯 (TG)和总胆固醇 (TC)水平 ,采用半定量逆转录 聚合酶链反应法检测过氧化体增殖物激活受体α及脂蛋白脂酶、载脂蛋白CⅢmRNA水平 ,用Western印记法检测过氧化体增殖物激活受体α蛋白表达情况。结果　与年轻对照组比较 ,老年对照组的血脂中TG和TC水平升高 ,过氧化体增殖物激活受体αmRNA及过氧化体增殖物激活受体α蛋白表达随年龄增长而减少 ,同时脂蛋白脂酶、载脂蛋白CⅢ也受年龄的影响。给药组与对照组比较 ,给药后老年对照组TG下降。非诺贝特对不同年龄组过氧化体增殖物激活受体α的表达均无影响 ,但可影响脂蛋白脂酶、载脂蛋白CⅢ的表达。结论　衰老过程中过氧化体增殖物激活受体α表达减少可能与老年脂质代谢异常有关。     

低密度脂蛋白免疫复合物对单核细胞来源的巨噬细胞脂质代谢的影响

目的:研究动脉粥样硬化过程中低密度脂蛋白免疫复合物(LDL-IC)对单核细胞来源的巨噬细胞内脂质含量的影响。方法:以佛波酯刺激分化的THP-1细胞作为单核细胞来源巨噬细胞模型。固定后的细胞以苏丹Ⅳ染色,观察细胞内脂质含量变化。通过胆固醇酶联法测定细胞内胆固醇含量。结果:与LDL-IC孵育能使单核细胞来源巨噬细胞内胆固醇堆积,呈现泡沫细胞的外观。细胞内胆固醇水平随着LDL-IC的浓度增加与作用时间的延长而升高。在4组平行对照实验中,LDL-IC组细胞内胆固醇水平明显高于阴性对照组、LDL组和IgG-IC组(P<0.01)。结论:LDL-IC能通过增加细胞内脂质而在动脉粥样硬化过程中发挥作用。     

Neutral lipid storage disease with ichthyosis: Serum apolipoprotein levels and cholesterol metabolism in monocyte-derived macrophages

Summary Neutral lipid storage disease with ichthyosis (NLSDI) is an inherited metabolic disorder characterized by accumulation of neutral lipids, in a wide variety of cells, by a still unknown mechanism. Previous studies have shown normal cholesterol content in NLSDI granulocytes, fibroblasts and skin cells. Monocyte-derived macrophages possess an additional pathway of cholesterol uptake, which is not shared by these cells and which is not regulated by intracellular cholesterol levels. This pathway is thought to play a rôle in the process of atherosclerosis. Three NLSDI patients were studied. The serum levels of triglycerides, cholesterol, high-density lipoprotein cholesterol, and apolipoproteins A-I and B were within normal limits in all three patients. The intracellular levels of free and esterified cholesterol were measured in the monocyte-derived macrophages of one patient and found to be normal, while the triglyceride concentrations were twice as high as normal. The cholesterol esterification rates, which serve as a sensitive indicator of intracellular changes in cholesteryl ester levels, were normal in the monocyte-derived macrophages of all three patients. These findings provide further evidence that cholesterol metabolism is not disturbed in NLSDI, and it may be inferred that in this respect these patients are not at increased risk for atherosclerosis.Correspondence     

A novel peroxisome proliferator-activated receptor alpha/gamma dual agonist demonstrates favorable effects on lipid homeostasis

Patients with type 2 diabetes mellitus exhibit hyperglycemia and dyslipidemia as well as a markedly increased incidence of atherosclerotic cardiovascular disease. Here we report the characterization of a novel arylthiazolidinedione capable of lowering both glucose and lipid levels in animal models. This compound, designated TZD18, is a potent agonist with dual human peroxisome proliferator-activated receptor (PPAR)-alpha/gamma activities. In keeping with its PPARgamma activity, TZD18 caused complete normalization of the elevated glucose in db/db mice and Zucker diabetic fatty rats. TZD18 lowered both cholesterol and triglycerides in hamsters and dogs. TZD18 inhibited cholesterol biosynthesis at steps before mevalonate and reduced hepatic levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity. Moreover, TZD18 significantly suppressed gene expression of fatty acid synthesis and induced expression of genes for fatty acid degradation and triglyceride clearance. Studies on 17 additional PPARalpha or PPARalpha/gamma agonists showed that lipid lowering in hamsters correlated with the magnitude of hepatic gene expression changes. Importantly, the presence of PPARgamma agonism did not affect the relationship between hepatic gene expression and lipid lowering. Taken together, these data suggest that PPARalpha/gamma agonists, such as TZD18, affect lipid homeostasis, leading to an antiatherogenic plasma lipid profile. Agents with these properties may provide favorable means for treatment of type 2 diabetes and dyslipidemia and the prevention of atherosclerotic cardiovascular disease.     

Fatty acids and retinoids control lipid metabolism through activation of peroxisome proliferator-activated receptor-retinoid X receptor heterodimers.

The nuclear hormone receptors called PPARs (peroxisome proliferator-activated receptors alpha, beta, and gamma) regulate the peroxisomal beta-oxidation of fatty acids by induction of the acyl-CoA oxidase gene that encodes the rate-limiting enzyme of the pathway. Gel retardation and cotransfection assays revealed that PPAR alpha heterodimerizes with retinoid X receptor beta (RXR beta; RXR is the receptor for 9-cis-retinoic acid) and that the two receptors cooperate for the activation of the acyl-CoA oxidase gene promoter. The strongest stimulation of this promoter was obtained when both receptors were exposed simultaneously to their cognate activators. Furthermore, we show that natural fatty acids, and especially polyunsaturated fatty acids, activate PPARs as potently as does the hypolipidemic drug Wy 14,643, the most effective activator known so far. Moreover, we discovered that the synthetic arachidonic acid analogue 5,8,11,14-eicosatetraynoic acid is 100 times more effective than Wy 14,643 in the activation of PPAR alpha. In conclusion, our data demonstrate a convergence of the PPAR and RXR signaling pathways in the regulation of the peroxisomal beta-oxidation of fatty acids by fatty acids and retinoids.     

Differential regulation of macrophage peroxisome proliferator-activated receptor expression by glucose : role of peroxisome proliferator-activated receptors in lipoprotein lipase gene expression

Peroxisome proliferator-activated receptors (PPARs) are implicated in several metabolic disorders with altered glucose and lipid metabolism, including atherosclerosis and diabetes. In the present study, we evaluated the in vitro and ex vivo effects of high glucose concentrations on macrophage PPAR mRNA expression. Exposition of monocyte-derived macrophages isolated from healthy donors to a high glucose environment led to an increase in PPARalpha and PPARbeta mRNA expression. In contrast, this treatment significantly decreased human macrophage PPARgamma mRNA expression. Overexpression of PPARalpha and PPARbeta mRNA and inhibition of PPARgamma mRNA expression were also observed in monocyte-derived macrophages isolated from patients with type 2 diabetes. Because high glucose and PPARalpha agonists increase lipoprotein lipase (LPL) gene expression, the role of PPARalpha in the glucose-mediated upregulation of macrophage LPL gene expression was next evaluated. Incubation of murine J774 macrophages with high glucose concentrations increased the expression of PPARalpha at the mRNA and protein levels and enhanced nuclear protein binding to the peroxisome proliferator responsive element of the LPL promoter. Incubation of nuclear extracts in the presence of anti-PPARalpha and anti-PPARbeta antibodies decreased glucose-stimulated nuclear protein binding to the peroxisome proliferator responsive element. These results demonstrate that glucose is an important regulator of macrophage PPAR expression and suggest a role of PPARalpha and PPARbeta in the upregulation of macrophage LPL by glucose. Dysregulation of macrophage PPAR expression in type 2 diabetes may contribute, by altering arterial lipid metabolism and inflammatory response, to the accelerated atherosclerosis associated with diabetes.     

过氧化物酶增殖物活化受体γ在胰腺癌生长中的调节作用

目的 探讨过氧化物酶增殖物活化受体γ(PPARγ)在人胰腺癌生长中的调节作用。方法 应用逆转录(RT)-PCR检测胰腺癌细胞系SWl990中PPARγ和维甲酸受体α(RXRα)的表达。培养细胞经PPARγ配体15-脱氧-前列腺素J2(15d-PGJ2)及RXRα配体9-顺式-维甲酸(9-cis-RA)作用后,用四唑氮蓝还原法测定细胞活力,并评价药物的抗增殖效果。建立裸鼠胰腺癌移植瘤模型,并予以PPARγ激动剂罗格列酮体内干预,75d后处死裸鼠,测量移植瘤的大小,计算抑瘤率。应用免疫组化观察移植瘤组织中增殖细胞核抗原(PCNA)的表达。结果 RT-PCR结果显示SW1990细胞系存在PPARγ和RXRα mRNA表达。15d-PGJ2和9-cis-RA及其联合应用对胰腺癌细胞的增殖具有抑制作用,且作用呈剂量依赖性。9-cis-RA对15d-PGJ2抑制胰腺癌细胞增殖具有协同效应。罗格列酮治疗组裸鼠移植瘤的平均体积和重量均显著低于对照组,抑瘤率达80．7％。免疫组化显示治疗组和对照组移植瘤组织中均表达PCNA,但治疗组的阳性表达强度和表达区域均呈下降趋势。结论 PPARγ的活化在体内外均对胰腺癌的生长呈负向调节作用,提示PPARγ可能是胰腺癌治疗的一个新分子靶点。RXRα的激活可协同增强PPARγ激动剂的抗增殖作用。     

Potential effects of peroxisome proliferator-activated receptor activator on LPS-induced lung injury in rats

Multiple factors contribute to the pathogenesis and prognosis of chronic obstructive pulmonary disease (COPD), still requiring new therapeutic strategies and medications for the disease. The aim of the present study is to investigate the model of lipopolysaccharide (LPS)-induced chronic lung injury and hyperinflation and test therapeutic effects of peroxisome proliferator-activated receptor (PPAR)-γ agonist. Wister rats were challenged with intra-tracheal instillation of LPS at concentrations of 0.006, 0.060, 0.600, and 6.000 mg/ml per kg, twice a week, for 1, 2, 4 and 6 weeks. PPAR activator, 15-deoxy-Δ^12,14-prostaglandin J2 (15D-PGJ2), or vehicle (PBS) was administered orally and daily at the dose of 1 and 10 mg/ml per kg in animals challenged with LPS or PBS at the dose of 0.060 mg/ml per kg body weight twice a week for 4 weeks. We found that intra-tracheal exposure of LPS resulted in a dose-dependent pattern of chronic lung hyperinflation and hypertrophy, increased alveolar enlargement, reduced vascular endothelial growth factor (VEGF) and elevated tissue inhibitor of metalloproteinases (TIMP)-1 levels in bronchoalveolar lavage (BAL) fluid, and early changes of leukocyte influx and interferon (IFN)-γ levels in bronchoalveolar lavage (BAL) fluid. PPAR-γ agonist ameliorated these changes related with the dose used. LPS-induced lung disease model shows some similarities with human disease, and PPAR-γ agonist may be an alternative for COPD therapy.     

Peroxisome proliferator-activated receptor (PPAR) alpha and PPARbeta/delta,but not PPARgamma,modulate the expression of genes involved in cardiac lipid metabolism

Long-chain fatty acids (FA) coordinately induce the expression of a panel of genes involved in cellular FA metabolism in cardiac muscle cells, thereby promoting their own metabolism. These effects are likely to be mediated by peroxisome proliferator-activated receptors (PPARs). Whereas the significance of PPARalpha in FA-mediated expression has been demonstrated, the role of the PPARbeta/delta and PPARgamma isoforms in cardiac lipid metabolism is unknown. To explore the involvement of each of the PPAR isoforms, neonatal rat cardiomyocytes were exposed to FA or to ligands specific for either PPARalpha (Wy-14,643), PPARbeta/delta (L-165041, GW501516), or PPARgamma (ciglitazone and rosiglitazone). Their effect on FA oxidation rate, expression of metabolic genes, and muscle-type carnitine palmitoyltransferase-1 (MCPT-1) promoter activity was determined. Consistent with the PPAR isoform expression pattern, the FA oxidation rate increased in cardiomyocytes exposed to PPARalpha and PPARbeta/delta ligands, but not to PPARgamma ligands. Likewise, the FA-mediated expression of FA-handling proteins was mimicked by PPARalpha and PPARbeta/delta, but not by PPARgamma ligands. As expected, in embryonic rat heart-derived H9c2 cells, which only express PPARbeta/delta, the FA-induced expression of genes was mimicked by the PPARbeta/delta ligand only, indicating that FA also act as ligands for the PPARbeta/delta isoform. In cardiomyocytes, MCPT-1 promoter activity was unresponsive to PPARgamma ligands. However, addition of PPARalpha and PPARbeta/delta ligands dose-dependently induced promoter activity. Collectively, the present findings demonstrate that, next to PPARalpha, PPARbeta/delta, but not PPARgamma, plays a prominent role in the regulation of cardiac lipid metabolism, thereby warranting further research into the role of PPARbeta/delta in cardiac disease.     

Effects of ligand activation of peroxisome proliferator-activated receptor gamma in human prostate cancer

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear hormone receptor that plays a key role in the differentiation of adipocytes. Activation of this receptor in liposarcomas and breast and colon cancer cells also induces cell growth inhibition and differentiation. In the present study, we show that PPARgamma is expressed in human prostate adenocarcinomas and cell lines derived from these tumors. Activation of this receptor with specific ligands exerts an inhibitory effect on the growth of prostate cancer cell lines. Further, we show that prostate cancer and cell lines do not have intragenic mutations in the PPARgamma gene, although 40% of the informative tumors have hemizygous deletions of this gene. Based on our preclinical data, we conducted a phase II clinical study in patients with advanced prostate cancer using troglitazone, a PPARgamma ligand used for the treatment of type 2 diabetes. Forty-one men with histologically confirmed prostate cancer and no symptomatic metastatic disease were treated orally with troglitazone. An unexpectedly high incidence of prolonged stabilization of prostate-specific antigen was seen in patients treated with troglitazone. In addition, one patient had a dramatic decrease in serum prostate-specific antigen to nearly undetectable levels. These data suggest that PPARgamma may serve as a biological modifier in human prostate cancer and its therapeutic potential in this disease should be further investigated.     

衰老对肌肉组织中过氧化体增殖物激活型受体-γ及葡萄糖转运子-4基础表达水平的影响

目的　观察衰老对肌肉组织中过氧化体增殖物激活型受体 γ(PPARγ)及葡萄糖转运子 4 (GLUT 4 )基础表达水平的影响,探讨其在胰岛素抵抗形成中的意义。方法　用Bergman创立的最小模型技术评价青年鼠(10～12周龄)和老年鼠(2 4月龄)的胰岛素敏感性,采用半定量逆转录聚合酶链反应(RT PCR)法检测肌肉组织中PPARγ1和PPARγ2 mRNA及GLUT 4mRNA的表达水平。结果　与青年鼠组比较,老年鼠组存在明显的胰岛素抵抗[胰岛素抵抗指数:(11.4 9±6 .92 )vs(5 .2 8±1.94 ) ,P <0 .0 5 ;胰岛素敏感指数:- (0 .0 5±0 .0 3)vs - (0 .0 2±0 .0 2 ) ,P <0 .0 5 ]。用RT PCR方法检测到骨骼肌中PPARγ1和PPARγ2 mRNA均有表达,而以PPARγ1mRNA为主要表达形式;与青年鼠组比较,老年鼠组PPARγ1mRNA [(0 .79±0 .0 4 ) vs(0 .5 2±0 .0 3) ,P <0 .0 1]及GLUT 4mRNA[(0 .73±0 .0 4 )vs(0 .6 1±0 .0 3) ,P <0 .0 5 ]的表达水平均明显降低。结论　衰老降低肌肉组织中PPARγmRNA及GLUT 4mRNA的基础表达水平,直接或间接使骨骼肌糖代谢作用受损,可能参与胰岛素抵抗的形成。