A ligand for peroxisome proliferator activated receptor gamma inhibits cell growth and induces apoptosis in human liver cancer cells

BACKGROUND AND AIMS: Induction of apoptosis of cancer cells through ligands of nuclear hormone receptors (NHRs) is a new approach in cancer therapy. Recently, one of the NHRs, peroxisome proliferator activated receptor gamma (PPARgamma), has been shown to influence cell growth in certain cancer cells although its effect on hepatocellular carcinoma (HCC) has not been analysed. METHODS: Experiments were conducted using three human liver cancer cell lines, PLC/PRF/5, Hep G2 and HuH-7, in vitro. These cells were exposed to troglitazone, a synthetic ligand for PPARgamma, and the effects on cell growth were analysed. RESULTS: Expression of PPARgamma mRNA was detected in all three liver cancer cell lines. Activation of PPARgamma by troglitazone caused a marked growth inhibition in a dose dependent manner in three hepatoma cell lines. The DNA fragmentation ELISA assay and Hoechst 33258 staining revealed that the growth inhibitory effect by adding troglitazone was due to apoptosis of PLC/PRF/5, which strongly expressed PPARgamma. Troglitazone also induced activation of the cell death protease, caspase 3, but not caspase 8, in PLC/PRF/5 cells. However, expression levels of antiapoptotic factor bcl-2 and apoptosis inducing factor bax were not affected. CONCLUSION: Our study showed that PPARgamma was expressed in human liver cancer cells and that the ligand for PPARgamma, troglitazone, inhibited the growth of these cells by inducing apoptosis through caspase 3 activation, indicating that troglitazone could be potentially useful as an apoptosis inducer for the treatment of HCC.     

Analysis of the peroxisome proliferator activated receptor gamma (PPARgamma) gene in HAIRAN syndrome with obesity

OBJECTIVES: To test the hypothesis that the triad of hyperandrogenism, insulin resistance and acanthosis nigricans (HAIRAN syndrome) in the presence of obesity, also known as type C insulin resistance, is caused by mutations in the gene for peroxisome proliferator activated receptor gamma (PPARgamma), a receptor for the thiazolidinedione drugs that enhance sensitivity to insulin. To investigate possible correlations between mutations in PPARgamma and the degree of insulin resistance. DESIGN: A candidate gene approach to study the molecular basis for a syndrome of obesity; a comparison of genotype with in vivo phenotype. PATIENTS: Fifteen unrelated patients with HAIRAN syndrome and obesity. Controls for the gene analysis: 25 unrelated non-diabetic non-obese individuals. Controls for the metabolic studies: six unrelated patients with type 2 diabetes mellitus and nine unrelated non-diabetic non-obese individuals. MEASUREMENTS: Analysis of polymerase chain reaction (PCR) products of the 7 exons that constitute the entire coding region of both PPARgamma isoforms (PPARgamma1 and PPARgamma2) for single-stranded conformational polymorphisms (SSCP); in exons with variant patterns: restriction fragment length polymorphism (RFLP) analysis; and, where relevant, direct sequencing. Evaluation of insulin resistance using the insulin euglycaemic clamp technique. RESULTS: A synonymous substitution in codon 477 (CACHis --> CATHis) was found in one patient. A missense mutation in codon 12 of PPARgamma2 (CCAPro --> GCAAla) was found in another patient, but not in any of 25 non-diabetic, non-obese control individuals. The patient with the Pro12Ala variant had the highest steady state glucose infusion rate (SSGIR) and most marked suppression of hepatic glucose production rate (HGPR) of all of the patients studied. CONCLUSIONS: Mutations in the PPARgamma gene are unlikely to be major contributors to HAIRAN syndrome with obesity. The Pro12Ala variant may correlate with a lesser degree of insulin resistance in these patients.     

Potential role for peroxisome proliferator activated receptor (PPAR) in preventing colon cancer

BACKGROUND: Peroxisome proliferator activated receptors (PPARs) are nuclear hormone receptors involved in genetic control of many cellular processes. PPAR and PPAR have been implicated in colonic malignancy. Here we provide three lines of evidence suggesting an inhibitory role for PPAR in colorectal cancer development. METHODS: Levels of PPAR mRNA and protein in human colorectal cancers were compared with matched non-malignant mucosa using RNAse protection and western blotting. APC(Min)/+ mice were randomised to receive the PPAR activator methylclofenapate 25 mg/kg or vehicle for up to 16 weeks, and small and large intestinal polyps were quantified by image analysis. The effect of methylclofenapate on serum stimulated mitogenesis (thymidine incorporation), linear cell growth, and annexin V and propidium iodide staining were assessed in human colonic epithelial cells. RESULTS: PPAR (mRNA and protein) expression levels were significantly depressed in colorectal cancer compared with matched non-malignant tissue. Methylclofenapate reduced polyp area in the small intestine from 18.7 mm(2) (median (interquartile range 11.1, 26.8)) to 9.90 (4.88, 13.21) mm(2) (p=0.003) and in the colon from 9.15 (6.31, 10.5) mm(2) to 3.71 (2.71, 5.99) mm(2) (p=0.009). Methylclofenapate significantly reduced thymidine incorporation and linear cell growth with no effect on annexin V or propidium iodide staining. CONCLUSIONS: PPAR may inhibit colorectal tumour progression, possibly via inhibition of proliferation, and may be an important therapeutic target.     

Variation in the gene for human peroxisome proliferator activated receptor gamma (PPARgamma) does not play a major role in the development of morbid obesity

OBJECTIVE: To determine the extent of variation in the gene for peroxisome proliferator activated receptor gamma (PPARgamma) in patients with morbid obesity. SUBJECTS: Two hundred morbidly obese patients who underwent gastric banding surgery and 192 healthy blood donors. Diabetics were excluded. EXPERIMENTAL: The frequency of the P115Q and P12A variants in the PPARgamma gene was determined. Single strand conformational polymorphism (SSCP) analysis was performed on all exons, exon/intron boundaries and part of the promoter of the PPARgamma gene on a sub-group of 67 morbid obese patients. RESULTS: None of the morbid patients or the blood donors were carriers of the P115Q mutation. The frequency of the P12A polymorphism did not differ significantly between morbid obese patients and controls and there was no statistically significant association between P12A and BMI. Male blood donors who were A12A homozygotes had statistically significant higher serum leptin concentrations (P = 0.001). Mutation screening revealed that one patient had a T -->G transversion at -208 in the promoter of PPARgamma-2, two had silent mutations, one a T-->C transition in the third base of codon 144 and the other a C-->T transition in codon 297. The fourth patient had a CGC-->TGC transition in codon 316 resulting in the replacement of an arginine with a cysteine. This mutation was not found in any other morbidly obese patient. CONCLUSION: Variation in the PPARgamma gene is unlikely to play a major role in the development of morbid obesity.     

Effect of peroxisome proliferator activated receptor gamma ligands on growth and gene expression profiles of gastric cancer cells

BACKGROUND AND AIMS: Although peroxisome proliferator activated receptor gamma (PPARgamma) agonists have been implicated in differentiation and growth inhibition of cancer cells, the potential therapeutic and chemopreventive effects on gastric cancer are poorly defined. We examined the in vitro and in vivo effects of PPARgamma ligands on growth of gastric cancer, and the effect of PPARgamma activation on expression of cyclooxygenase 2 (COX-2) and cancer related genes. METHODS: Gastric cell lines (MKN28 and MKN45) were treated with two specific PPARgamma ligands: ciglitazone and 15-deoxy-Delta(12,)(14)-prostaglandin J(2). Cell growth was determined by bromodeoxyuridine incorporation assay and apoptosis was measured by DNA fragmentation. Expression of COX-2 was determined by western blot and real time quantitative polymerase chain reaction (PCR). Expression profiles of cancer related genes were screened with cDNA array. In vivo growth of implanted MKN45 cells in nude mice was monitored after oral treatment with rosiglitazone. RESULTS: PPARgamma ligands suppressed the in vitro growth of MKN45 cells in a dose dependent manner whereas prostacyclin, a PPARdelta agonist, had no growth inhibitory effect. Growth inhibition was more pronounced in MKN45 cells, which was accompanied by DNA fragmentation and downregulation of COX-2. Screening by cDNA microarray showed that PPARgamma ligand treatment was associated with upregulation of bad and p53, and downregulation of bcl-2, bcl-xl, and cyclin E1 in MKN45 cells, which was confirmed by quantitative real time PCR. In contrast, MKN28 cells with lower PPARgamma and COX-2 expression levels had lower growth inhibitory responses to PPARgamma ligands. Microarray experiments only showed induction of the bad gene in MKN28 cells. In vivo growth of MKN45 cells in nude mice was retarded by rosiglitazone. Mean tumour volume in rosiglitazone treated mice was significantly lower than controls at six weeks (p = 0.019) and seven weeks (p = 0.001) after treatment. CONCLUSIONS: PPARgamma ligands suppress both in vitro and in vivo growth of gastric cancer and may play a major role in cancer therapy and prevention.     

小鼠过氧化物酶体增殖体激活受体γ2重组逆转录病毒载体在NIH3T3细胞中的表达

目的通过应用重组逆转录病毒介导小鼠过氧化物酶体增殖体激活受体γ2(mPPARγ2)基因整合入MH3T3细胞基因组中并进行表达.方法从经测序证实含正确序列mPPARγ2的重组质粒pcDNA3/mPPARγ2中,双酶切下约1.5Kb的mPPARγ2全长cDNA编码序列,亚克隆入逆转录病毒载体pGCEN中构建重组逆转录病毒载体pGCEN/mPPARγ2.pGCEN/mPPARγ2及pGCEN经LipofectAMINE感染病毒包装细胞系PA317细胞,通过筛选PA317细胞G418抗性克隆,收集病毒上清,然后用其感染靶细胞NIH3T3细胞,用免疫荧光染色及Westem印迹方法鉴定mPPARγ2在NIH3T3细胞中的表达情况.结果构建了含mPPARγ2全长cDNA重组逆转录病毒载体,获得了滴度分别为5×104CFU/ml和6×105CFU/ml的pGCEN/mPPARγ2及pGCEN的病毒上清.经鉴定pGCEN/mPPARγ2能有效地感染靶细胞NIH3T3细胞并表达mPPARγ2.结论本研究结果为在体外建立脂肪细胞分化模型及为进一步研究PPARγ2在诱导脂肪细胞分化中的分子机制奠定了基础.     

Cytoprotective effect of tauroursodeoxycholate on hepatocyte apoptosis induced by peroxisome proliferator-activated receptor gamma ligand

Background and Aim:  Peroxisome proliferator-activated receptor gamma (PPARγ) ligands inhibit cell growth and induce apoptosis in various cancer cells. Bile acids are also known to cause hepatocyte apoptosis through nuclear receptor-mediated mechanisms. The aim of this study was to examine the effect of two different bile acid species on the inhibitory action of PPARγ in cell growth with paying attention to the role of the mitogen-activated protein kinase pathway as an underlying mechanism.
Methods:  Immortalized human hepatocytes (OUMS-29) and hepatoma cells (HepG2 and Huh7) were incubated with troglitazone (TGZ), a PPARγ ligand with or without pre-incubation of either hydrophobic glycochenodeoxycholate (GCDC) or hydrophilic tauroursodeoxycholate (TUDC).
Results:  TGZ induced cell apoptosis in all cell types, resulting in the reduction of cell viability. While pre-incubation with GCDC enhanced the apoptotic effects of TGZ, TUDC significantly attenuated it. Both bile acids enhanced p38 and c-Jun N-terminal kinase (JNK) phosphorylation in a similar way, whereas there was more drastic enhancement of extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in the presence of TUDC compared to GCDC. In addition, ERK inhibitors suppressed the action of TUDC against apoptotic effect of TGZ.
Conclusion:  This study demonstrates that TUDC exhibits anti-apoptotic and cytoprotective effects against TGZ-induced cell apoptosis, presumably through the ERK signaling pathway. We speculate that the administration of TUDC might be one of the potential strategies for the hepatotoxicity caused by TGZ.     

Probiotics may reduce inflammation by enhancing peroxisome proliferator activated receptor gamma activation in HT-29 cells]

BACKGROUND/AIMS: The peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor highly expressed in the colon which plays an anti-inflammatory role through the inhibition of nuclear factor-kappaB (NF-kappaB) pathway. Probiotics have been shown to exert beneficial effects on inflammatory bowel diseases. However, the exact mechanism by which probiotics exert protection against intestinal inflammation is not well understood. The aims of this study were to evaluate the attenuation of inflammatory response by probiotics in intestinal epithelial cells and to study the association between probiotics and PPARgamma. METHODS: HT-29 human epithelial cells were stimulated with LPS (20 microg/mL) and probiotics, Lactobacillus casei (L. casei) (10(5)-10(7) cfu/mL), or with LPS (20 microg/mL) alone for 24 hours. Interleukin-8 (IL-8), cyclooxygenase-2 (COX-2), toll-like receptor-4 (TLR-4) and PPARgamma mRNA expressions were assessed by RT-PCR. IL-8 protein secretion was measured by ELISA. HT-29 cells were transfected with tk promoter-luciferase plasmid containing a peroxisome proliferator response element (PPRE). After stimulation with L. casei or PPARgamma agonist (15d-PGJ2 or ciglitazone), luciferase activities were measured. RESULTS: LPS induced IL-8, COX-2, TLR-4 mRNA expression, and IL-8 protein secretion in HT-29 cells. Treatment with LPS and L. casei in comparison with LPS stimulation alone lowered IL-8, COX-2, TLR-4 mRNA expression, and IL-8 protein secretion. L. casei increased PPARgamma mRNA expression in dose-dependent manner. L. casei activated PPRE in HT-29 cells transfected with PPRE3-tk-luciferase construct. CONCLUSIONS: Probiotics, L. casei, suppresses the expression of inflammatory mediators in intestinal epithelial cells. The anti-inflammatory action of L. casei might be partially related to PPARgamma activation.     

过氧化物酶体增殖物激活受体γ基因多态性与老年男性骨质疏松的相关性

目的 探讨过氧化物酶体增殖物激活受体γ(PPARγ)基因第6外显子C161→T单核苷酸多态性与老年男性骨质疏松的相关性.方法 采用聚合酶链反应限制性片段长度多态性分析法检测老年男性骨质疏松组、老年男性非骨质疏松组(对照组)的基因频率分布;采用双能X线吸收测定法检测老年男性骨质疏松组及对照组腰椎和股骨上端(大转子、股骨颈)的骨密度;酶联免疫法(ELISA)检测血清骨钙素.结果 PPARγ基因第6外显子C161→T的多态性,有CC、CT和TT 3种基因型,老年男性骨质疏松组携带T等位基因的频率高于对照组,CT+TT分别为40.4%和25.7%(P＜0.05);与对照组比较,老年男性骨质疏松组骨钙素水平、骨密度较低;与CC基因型比较,携带T等位基因型的骨密度更低.结论 PPAR7基因多态性与老年男性骨质疏松有关,T等位基因是老年男性骨质疏松的易感因素.PPARγ可能是骨质疏松的一个候选基因.     

Regulation of carnitine palmitoyltransferase I (CPT-Ialpha) gene expression by the peroxisome proliferator activated receptor gamma coactivator (PGC-1) isoforms

The peroxisome proliferator activated receptor gamma coactivators (PGC-1) have important roles in mitochondrial biogenesis and metabolic control in a variety of tissues. There are multiple isoforms of PGC-1 including PGC-1alpha and PGC-1beta. Both the PGC-1alpha and beta isoforms promote mitochondrial biogenesis and fatty acid oxidation, but only PGC-1alpha stimulates gluconeogenesis in the liver. Carnitine palmitoyltransferase I (CPT-I) is a key enzyme regulating mitochondrial fatty acid oxidation. In these studies, we determined that PGC-1beta stimulated expression of the "liver" isoform of CPT-I (CPT-Ialpha) but that PGC-1beta did not induce pyruvate dehydrogenase kinase 4 (PDK4) which is a regulator of pyruvate metabolism. The CPT-Ialpha gene is induced by thyroid hormone. We found that T3 increased the expression of PGC-1beta and that PGC-1beta enhanced the T3 induction of CPT-Ialpha. The thyroid hormone receptor interacts with PGC-1beta in a ligand dependent manner. Unlike PGC-1alpha, the interaction of PGC-1beta and the T3 receptor does not occur exclusively through the leucine-X-X-leucine-leucine motif in PGC-1beta. We have found that PGC-1beta is associated with the CPT-Ialpha gene in vivo. Overall, our results demonstrate that PGC-1beta is a coactivator in the T3 induction of CPT-Ialpha and that PGC-1beta has similarities and differences with the PGC-1alpha isoform.     

过氧化物酶体增殖物激活受体-γ在炎症性肠病中的表达及意义

目的 观察过氧化物酶体增殖物激活受体-γ(PPAR-γ)在炎症性肠病(IBD)中的表达,探讨其可能的意义.方法 采用免疫组织化学方法检测28例克罗恩病(CD)患者、38例溃疡性结肠炎(UC)患者及30例健康对照肠道组织中PPAR-γ蛋白的表达,并进一步分析PPAR-γ蛋白与IBD临床特征的关系.结果 PPAR-γ在UC患者中表达阳性率为34.21% (13/38),明显低于正常对照63.33%(19/30) 及CD患者60.71%(17/28)(P<0.05);PPAR-γ蛋白表达与UC疾病活动性明显相关(P<0.05),与UC严重程度、病变部位及CD临床特征无明显相关(P>0.05).结论 PPAR-γ蛋白在UC肠道组织中表达降低,且与疾病活动性明显相关.提示PPAR-γ可能在UC发生、发展中发挥重要作用.     

Ligand-activated peroxisome proliferator activated receptor gamma alters placental morphology and placental fatty acid uptake in mice

The nuclear receptor peroxisome proliferator activated receptor gamma (PPARgamma) is essential for murine placental development. We previously showed that activation of PPARgamma in primary human trophoblasts enhances the uptake of fatty acids and alters the expression of several proteins associated with fatty acid trafficking. In this study we examined the effect of ligand-activated PPARgamma on placental development and transplacental fatty acid transport in wild-type (wt) and PPARgamma(+/-) embryos. We found that exposure of pregnant mice to the PPARgamma agonist rosiglitazone for 8 d (embryonic d 10.5-18.5) reduced the weights of wt, but not PPARgamma(+/-) placentas and embryos. Exposure to rosiglitazone reduced the thickness of the spongiotrophoblast layer and the surface area of labyrinthine vasculature, and altered expression of proteins implicated in placental development. The expression of fatty acid transport protein 1 (FATP1), FATP4, adipose differentiation related protein, S3-12, and myocardial lipid droplet protein was enhanced in placentas of rosiglitazone-treated wt embryos, whereas the expression of FATP-2, -3, and -6 was decreased. Additionally, rosiglitazone treatment was associated with enhanced accumulation of the fatty acid analog 15-(p-iodophenyl)-3-(R, S)-methyl pentadecanoic acid in the placenta, but not in the embryos. These results demonstrate that in vivo activation of PPARgamma modulates placental morphology and fatty acid accumulation.     

Adipocytes differentiation of NIH3T3 cells induced by peroxisome proliferator activation receptor gamma 2 expression]

OBJECTIVE: To express the mouse peroxisome proliferator activated receptor gamma 2(mPPAR gamma 2) in NIH3T3 cells mediated by the recombinant retrovirus and study its function. METHODS: mPPAR gamma 2 gene digested from the recombinant plasmid pcDNA3/mPPAR gamma 2 and confirmed to contain the target gene segment with fluorescence-sequencing was subcloned into retrovirus vector pGCEN to generate the recombinant retrovirus pGCEN/mPPAR gamma 2. The recombinant retrovirus pGCEN/mPPAR gamma 2 and pGCEN were packaged with PA317 cells and anti-G418 clones of PA317 cells were selected. Viral supernatants were collected and used to infect NIH3T3 cells. Peroxisome proliferator activated receptor gamma 2 (PPAR gamma 2)-expressing NIH3T3 cells cultured in the differentiation media containing PPAR gamma activator ETYA were induced into adipocytes. RESULTS: The recombinant retrovirus pGCEN/mPPAR gamma 2 was constructed, 5 x 10(4) CFU/ml of the viral supernatants containing pGCEN/mPPAR gamma 2 and 6 x 10(5) CFU/ml of the viral supernatants containing pGCEN were obtained. mPPAR gamma 2 was expressed in NIH3T3 cells mediated by the recombinant retrovirus. Lipid accumulation obviously existed in PPAR gamma 2-expressing NIH3T3 cells at 10 days postdifferentiation and the lipid-containing cells morphologically resembled the mature adipocytes in vivo. CONCLUSION: An adipocyte differentiation model in vitro was established. The work is the basis for further researches on the molecular mechanism of adipocyte differentiation induced by PPAR gamma 2.     

过氧化物酶体增殖物激活受体γ与肝纤维化关系的研究进展

过氧化物酶体增殖物激活受体（peroxisome proliferator activated receptors，PPARs）属Ⅱ型核激素受体超家族成员，1990年首先由Issemann等从小鼠肝脏克隆得到，因其被过氧化物酶体增殖物活化后能诱导肝脏过氧化物酶体增殖而得名。迄今已发现PPARα、β和γ3种亚型，β亚型又称δ亚型；它们在结构、功能及组织分布上均有差异。PPARs具有多种生物学效应，已知PPARs与许多慢性疾病如肥胖、糖尿病、动脉硬化和癌症等的发生有关。PPARs也是重要的肝脏代谢调节分子，肝星状细胞（HSC）表达PPARγ。本文就PPARγ与肝纤维化关系的研究进展作一综述。     

The peroxisome proliferator-activated receptor gamma ligand troglitazone induces apoptosis and p53 in rat granulosa cells

PPARgamma is expressed in both the rodent and human ovary, but the endogenous activation state of PPARgamma in the ovary and its normal role in ovarian function remain unclear. Here, we investigated mRNA and protein expression as well as DNA-binding activity of PPARgamma during follicle growth and luteinization in the immature, gonadotropin-primed rat model. Gel shift analysis demonstrated binding of ovarian PPAR to a consensus peroxisome proliferator response element (PPRE) that was supershifted with an antibody specific for PPARgamma, but not with antibodies specific for PPARalpha or beta/delta. PPARgamma expression and DNA-binding activity was highest 0-12 h post-PMSG, but declined during later stages of follicle growth (24-36 h post-PMSG). Administration of hCG induced a decline in PPARgamma mRNA, protein, and DNA-binding activity beginning at 4 h. Treatment of preovulatory granulosa cells with the PPARgamma ligand troglitazone (1-10 microM) in vitro decreased cell viability, increased sub-G1 apoptosis, and reduced DNA synthesis. Troglitazone induced p53 protein expression and decreased bcl-2 mRNA, suggesting possible mechanisms for troglitazone-induced apoptosis. These data indicate that PPARgamma is in the ovary is capable of binding DNA in the absence of pharmacological activation and provide evidence for a possible physiologic role for this receptor in regulating granulosa cell survival.     

过氧化物酶体增殖物激活受体γ及其配体调节大鼠肺纤维化的作用机制

目的探讨过氧化物酶体增殖物激活受体γ（PPARγ）及其配体在博莱霉素诱导大鼠肺纤维化中的作用及参与机制。方法将24只雄性SD大鼠随机分为4组,即生理盐水对照组、罗格列酮对照组、博莱霉素组、罗格列酮干预组,经气管内注射博莱霉素建立肺纤维化模型。采用Masson染色观察肺组织形态学变化;碱水解法检测肺组织中羟脯氨酸含量;免疫组化及荧光定量RT-PCR检测PPARγ、MMP-9和TGF-β1的表达。结果气管内注入博莱霉素后,肺组织中羟脯氨酸含量、胶原沉积、MMP-9、TGF-β1及PPARγ表达较生理盐水对照组增加（P均〈0.05）;给予罗格列酮干预后,除PPARγ表达进一步增加,上述指标均下降（P均〈0.05）。相关性分析显示,博莱霉素组PPARγ蛋白水平与MMP-9和TGF-β1mRNA表达分别呈负相关（P均〈0.05）。结论 PPARγ参与了肺纤维化的发生;PPARγ及其配体罗格列酮可能通过抑制TGF-β1、MMP-9转录,从而减少胶原沉积,延缓博莱霉素诱导的肺纤维化进程。