Chromosomal localization and partial genomic structure of the human peroxisome proliferator activated receptor-gamma (hPPAR gamma) gene

The global perspective on peroxisome proliferator-activated receptor γ (PPARγ) in ectopic fat deposition: A review

Excessive expansion of adipocytes can have unhealthy consequences as excess free fatty acids enter other tissues and cause ectopic fat deposition by resynthesizing triglycerides. This lipid accumulation in various tissues is harmful and can increase the risk of related metabolic diseases such as type II diabetes, cardiovascular disease, and insulin resistance. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily that play a key role in energy metabolism as fatty acid metabolism sensors, and peroxisome proliferator-activated receptor γ (PPARγ) is the main subtype responsible for fat cell differentiation and adipogenesis. In this paper, we introduce the main structure and function of PPARγ and its regulatory role in the process of lipogenesis in the liver, kidney, skeletal muscle, and pancreas. This information can serve as a reference for further understanding the regulatory mechanisms and measures of the PPAR family in the process of ectopic fat deposition.

The Potential Roles of Post-Translational Modifications of PPARγ in Treating Diabetes

The number of patients with type 2 diabetes mellitus (T2DM), which is mainly characterized by insulin resistance and insulin secretion deficiency, has been soaring in recent years. Accompanied by many other metabolic syndromes, such as cardiovascular diseases, T2DM represents a big challenge to public health and economic development. Peroxisome proliferator-activated receptor γ (PPARγ), a ligand-activated nuclear receptor that is critical in regulating glucose and lipid metabolism, has been developed as a powerful drug target for T2DM, such as thiazolidinediones (TZDs). Despite thiazolidinediones (TZDs), a class of PPARγ agonists, having been proven to be potent insulin sensitizers, their use is restricted in the treatment of diabetes for their adverse effects. Post-translational modifications (PTMs) have shed light on the selective activation of PPARγ, which shows great potential to circumvent TZDs' side effects while maintaining insulin sensitization. In this review, we will focus on the potential effects of PTMs of PPARγ on treating T2DM in terms of phosphorylation, acetylation, ubiquitination, SUMOylation, O-GlcNAcylation, and S-nitrosylation. A better understanding of PTMs of PPARγ will help to design a new generation of safer compounds targeting PPARγ to treat type 2 diabetes.

PPARγ and TGFβ-Major Regulators of Metabolism, Inflammation, and Fibrosis in the Lungs and Kidneys

Peroxisome proliferator-activated receptor gamma (PPARγ) is a type II nuclear receptor, initially recognized in adipose tissue for its role in fatty acid storage and glucose metabolism. It promotes lipid uptake and adipogenesis by increasing insulin sensitivity and adiponectin release. Later, PPARγ was implicated in cardiac development and in critical conditions such as pulmonary arterial hypertension (PAH) and kidney failure. Recently, a cluster of different papers linked PPARγ signaling with another superfamily, the transforming growth factor beta (TGFβ), and its receptors, all of which play a major role in PAH and kidney failure. TGFβ is a multifunctional cytokine that drives inflammation, fibrosis, and cell differentiation while PPARγ activation reverses these adverse events in many models. Such opposite biological effects emphasize the delicate balance and complex crosstalk between PPARγ and TGFβ. Based on solid experimental and clinical evidence, the present review summarizes connections and their implications for PAH and kidney failure, highlighting the similarities and differences between lung and kidney mechanisms as well as discussing the therapeutic potential of PPARγ agonist pioglitazone.

The role of polymorphism in various potential genes on polycystic ovary syndrome susceptibility and pathogenesis

Polycystic ovary syndrome (PCOS) is the most common endocrinopathies affecting the early reproductive age in women, whose pathophysiology perplexes many researchers till today. This syndrome is classically categorized by hyperandrogenism and/or hyperandrogenemia, menstrual and ovulatory dysfunction, bulky multi follicular ovaries on Ultrasonography (USG), and metabolic abnormalities such as hyperinsulinemia, dyslipidemia, obesity. The etiopathogenesis of PCOS is not fully elucidated, but it seems that the hypothalamus-pituitary-ovarian axis, ovarian, and/or adrenal androgen secretion may contribute to developing the syndrome. Infertility and poor reproductive health in women's lives are highly associated with elevated levels of androgens. Studies with ovarian theca cells taken from PCOS women have demonstrated increased androgen production due to augmented ovarian steroidogenesis attributed to mainly altered expression of critical enzymes (Cytochrome P450 enzymes: CYP17, CYP21, CYP19, CYP11A) in the steroid hormone biosynthesis pathway. Despite the heterogeneity of PCOS, candidate gene studies are the widely used technique to delineate the genetic variants and analyze for the correlation of androgen biosynthesis pathway and those affecting the secretion or action of insulin with PCOS etiology. Linkage and association studies have predicted the relationship between genetic variants and PCOS risk among families or populations. Several genes have been proposed as playing a role in the etiopathogenesis of PCOS, and the presence of mutations and/or polymorphisms has been discovered, which suggests that PCOS has a vital heritable component. The following review summarizes the influence of polymorphisms in crucial genes of the steroidogenesis pathway leading to intraovarian hyperandrogenism which can result in PCOS.

PPARγ: Potential Therapeutic Target for Ailments Beyond Diabetes and its Natural Agonism

Intense research interests have been observed in establishing PPAR gamma as a therapeutic target for diabetes. However, PPARγ is also emerging as an important therapeutic target for varied disease states other than type 2 diabetes like neurodegenerative disorders, cancer, spinal cord injury, asthma, and cardiovascular problems. Furthermore, glitazones, the synthetic thiazolidinediones, also known as insulin sensitizers, are the largely studied PPARγ agonists and the only ones approved for the treatment of type 2 diabetes. However, they are loaded with side effects like fluid retention, obesity, hepatic failure, bone fractures, and cardiac failure; which restrict their clinical application. Medicinal plants used traditionally are the sources of bioactive compounds to be used for the development of successful drugs and many structurally diverse natural molecules are already established as PPARγ agonists. These natural partial agonists when compared to full agonist synthetic thiazolidinediones led to weaker PPARγ activation with lesser side effects but are not thoroughly investigated. Their thorough characterization and elucidation of mechanistic activity might prove beneficial for counteracting diseases by modulating PPARγ activity through dietary changes. We aim to review the therapeutic significance of PPARγ for ailments other than diabetes and highlight natural molecules with potential PPARγ agonistic activity.

The Role of PPARγ Ligands in Breast Cancer: From Basic Research to Clinical Studies

Peroxisome proliferator-activated receptor gamma (PPARγ), belonging to the nuclear receptor superfamily, is a ligand-dependent transcription factor involved in a variety of pathophysiological conditions such as inflammation, metabolic disorders, cardiovascular disease, and cancers. In this latter context, PPARγ is expressed in many tumors including breast cancer, and its function upon binding of ligands has been linked to the tumor development, progression, and metastasis. Over the last decade, much research has focused on the potential of natural agonists for PPARγ including fatty acids and prostanoids that act as weak ligands compared to the strong and synthetic PPARγ agonists such as thiazolidinedione drugs. Both natural and synthetic compounds have been implicated in the negative regulation of breast cancer growth and progression. The aim of the present review is to summarize the role of PPARγ activation in breast cancer focusing on the underlying cellular and molecular mechanisms involved in the regulation of cell proliferation, cell cycle, and cell death, in the modulation of motility and invasion as well as in the cross-talk with other different signaling pathways. Besides, we also provide an overview of the in vivo breast cancer models and clinical studies. The therapeutic effects of natural and synthetic PPARγ ligands, as antineoplastic agents, represent a fascinating and clinically a potential translatable area of research with regards to the battle against cancer.

Maintenance of Kidney Metabolic Homeostasis by PPAR Gamma

Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear hormone receptors that control the transcription of specific genes by binding to regulatory DNA sequences. Among the three subtypes of PPARs, PPARγ modulates a broad range of physiopathological processes, including lipid metabolism, insulin sensitization, cellular differentiation, and cancer. Although predominantly expressed in adipose tissue, PPARγ expression is also found in different regions of the kidney and, upon activation, can redirect metabolism. Recent studies have highlighted important roles for PPARγ in kidney metabolism, such as lipid and glucose metabolism and renal mineral control. PPARγ is also implicated in the renin-angiotensin-aldosterone system and, consequently, in the control of systemic blood pressure. Accordingly, synthetic agonists of PPARγ have reno-protective effects both in diabetic and nondiabetic patients. This review focuses on the role of PPARγ in renal metabolism as a likely key factor in the maintenance of systemic homeostasis.

Deciphering the Roles of Thiazolidinediones and PPAR in Bladder Cancer

The use of thiazolidinedione (TZD) therapy in type II diabetic patients has proven useful in the lowering of blood glucose levels. However, recent investigations have shown that there may be potential health concerns associated, including the risk of developing bladder cancer as well as complications in the cardiovasculature. TZDs are ligands for the nuclear receptor PPARγ, and activation causes lipid uptake and insulin sensitization, both of which are critical processes for diabetic patients whose bodies are unable to utilize insulin effectively. Several studies have shown that PPARγ/TZDs decrease IGF-1 levels and, thus, reduce cancer growth in carcinomas such as the pancreas, colon, liver, and prostate. However, other studies have shed light on the potential of the receptor as a biomarker for uroepithelial carcinomas, particularly due to its stimulatory effect on migration of bladder cancer cells. Furthermore, PPARγ may provide the tumor-promoting microenvironment by de novo synthesis of nutrients that are needed for bladder cancer development. In this review, we closely examine the TZD class of drugs and their effects on PPARγ in patient studies along with additional molecular factors that are positive modulators, such as protein phosphatase 5 (PP5), which may have considerable implications for bladder cancer therapy.

Increased peroxisome proliferator-activated receptor γ activity reduces imatinib uptake and efficacy in chronic myeloid leukemia mononuclear cells

Imatinib is actively transported by organic cation transporter-1 (OCT-1) influx transporter, and low OCT-1 activity in diagnostic chronic myeloid leukemia blood mononuclear cells is significantly associated with poor molecular response to imatinib. Herein we report that, in diagnostic chronic myeloid leukemia mononuclear cells and BCR-ABL1⁺ cell lines, peroxisome proliferator-activated receptor γ agonists (GW1929, rosiglitazone, pioglitazone) significantly decrease OCT-1 activity; conversely, peroxisome proliferator-activated receptor γ antagonists (GW9662, T0070907) increase OCT-1 activity. Importantly, these effects can lead to corresponding changes in sensitivity to BCR-ABL kinase inhibition. Results were confirmed in peroxisome proliferator-activated receptor γ-transduced K562 cells. Furthermore, we identified a strong negative correlation between OCT-1 activity and peroxisome proliferator-activated receptor γ transcriptional activity in diagnostic chronic myeloid leukemia patients (n=84; P<0.0001), suggesting that peroxisome proliferator-activated receptor γ activation has a negative impact on the intracellular uptake of imatinib and consequent BCR-ABL kinase inhibition. The inter-patient variability of peroxisome proliferator-activated receptor γ activation likely accounts for the heterogeneity observed in patient OCT-1 activity at diagnosis. Recently, the peroxisome proliferator-activated receptor γ agonist pioglitazone was reported to act synergistically with imatinib, targeting the residual chronic myeloid leukemia stem cell pool. Our findings suggest that peroxisome proliferator-activated receptor γ ligands have differential effects on circulating mononuclear cells compared to stem cells. Since the effect of peroxisome proliferator-activated receptor γ activation on imatinib uptake in mononuclear cells may counteract the clinical benefit of this activation in stem cells, caution should be applied when combining these therapies, especially in patients with high peroxisome proliferator-activated receptor γ transcriptional activity.

A systematic review of genetic variants associated with metabolic syndrome in patients with schizophrenia

Metabolic syndrome (MetS) is a cluster of factors that increases the risk of cardiovascular disease (CVD), one of the leading causes of mortality in patients with schizophrenia. Incidence rates of MetS are significantly higher in patients with schizophrenia compared to the general population. Several factors contribute to this high comorbidity. This systematic review focuses on genetic factors and interrogates data from association studies of genes implicated in the development of MetS in patients with schizophrenia. We aimed to identify variants that potentially contribute to the high comorbidity between these disorders. PubMed, Web of Science and Scopus databases were accessed and a systematic review of published studies was conducted. Several genes showed strong evidence for an association with MetS in patients with schizophrenia, including the fat mass and obesity associated gene (FTO), leptin and leptin receptor genes (LEP, LEPR), methylenetetrahydrofolate reductase (MTHFR) gene and the serotonin receptor 2C gene (HTR2C). Genetic association studies in complex disorders are convoluted by the multifactorial nature of these disorders, further complicating investigations of comorbidity. Recommendations for future studies include assessment of larger samples, inclusion of healthy controls, longitudinal rather than cross-sectional study designs, detailed capturing of data on confounding variables for both disorders and verification of significant findings in other populations. In future, big genomic datasets may allow for the calculation of polygenic risk scores in risk prediction of MetS in patients with schizophrenia. This could ultimately facilitate early, precise, and patient-specific pharmacological and non-pharmacological interventions to minimise CVD associated morbidity and mortality.

Association of PPARγ2 gene variant Pro12Ala polymorphism with hypertension and obesity in the aboriginal Qatari population known for being consanguineous

AIM

The aim of this study was to investigate the association of the Pro12Ala polymorphism of the human peroxisome proliferator-activated receptor gamma 2 (PPARγ2) gene with hypertension and obesity in a highly consanguineous aboriginal Qatari population.

DESIGN

A cross-sectional survey conducted from January 2011-December 2012.

SETTING

Primary health care clinics.

SUBJECTS

A random sample of 1,528 Qatari male and female population older than 20 years of age.

MATERIALS AND METHODS

Data on age, sex, income, level of education, occupation status, body mass index, and blood pressure and lipid profile were obtained. The Pro12Ala in the PPARγ2 gene was detected on the LightCycler® using two specific probes: (Sensor [G] 5'-CTC CTA TTG ACG CAG AAA GCG-FL and PPAR Anchor 5' LC Red 640- TCC TTC ACT GAT ACA CTG TCT GCA AAC ATA TC-PH). Univariate and multivariate logistic regression were performed.

RESULT

Out of a total 1,528 participants, 220 were diagnosed with essential hypertension, and 420 were obese. Participants with consanguinity were significantly higher among hypertensive than normotensive (41.9% versus 30.8%; P=0.001). Altogether, more than three-fourths (89%) of the participants had a wild genotype (Pro12Pro), 9.8% were heterozygous with Pro12Ala, and only 1.2% was homozygous with the Ala12Ala genotype. The frequency of the Pro allele was 94.5% in normotensive versus 90.5% in hypertensive, while the distribution of the Ala allele was 5.5% in normotensive versus 9.5% in the hypertensive group (P=0.001). The odds of hypertension were 1.7 times higher among the participants with the Ala allele as compared to those with the Pro, while adjusting for other potential confounders (adjusted odds ratio 1.69; 95% confidence interval 1.12-2.55; P=0.012). There was no association between the PPARγ2Ala allele and obesity (P=0.740).

CONCLUSION

The current study revealed an association between the PPARγ2Ala allele and hypertension in Qatar's population. On the other hand, this study found no association between the Ala allele and obesity.

Distribution and genotype frequency of the C1431T and pro12ala polymorphisms of the peroxisome proliferator activator receptor gamma gene in an Iranian population

BACKGROUND

Peroxisome proliferator activator receptor gamma (PPARγ) is a nuclear transcription factor regulating multiple genes involved in cell growth, differentiation, carbohydrate and lipid metabolism and energy production. Several genetic variations in the PPARγ gene have been identified to be associated with diabetes, obesity, dyslipidemia, insulin resistance, metabolic syndrome and coronary artery disease. The present study was designed to explore the distribution of two common single nucleotide polymorphisms of the PPARγ gene (C1431T and Pro12Ala) in an Iranian population.

MATERIALS AND METHODS

Genotype frequencies for these two polymorphisms were compared for 160 healthy Iranian individuals with reports from other populations. The Genotyping was performed using real-time polymerase chain reaction.

RESULTS

The genotype distribution of the C1431T PPARγ polymorphism was 0.869 for the CC genotype, 0.119 for the CT genotype and 0.013 for uncommon TT genotype. Allelic frequencies were 0.93 for C and 0.07 for T allele respectively. For the Pro12Ala polymorphism of PPARγ gene, genotypic distributions and allelic frequencies were, 0.813 for CC, 0.181 for CG and 0.06 for GG and 0.903 for C and 0.097 for G respectively. Allelic and genotypic frequencies for both polymorphisms of PPARγ gene were in Hardy-Weinberg equilibrium.

CONCLUSIONS

Iran is a country with an ethnically diverse population and a comparison of allelic and genotypic frequencies of PPARγ C1431T and Pro12Ala polymorphisms between our population and others showed significant differences.

PPARgamma: The Portrait of a Target Ally to Cancer Chemopreventive Agents

Peroxisome proliferator-activated receptor-gamma (PPARγ), one of three ligand-activated transcription factors named PPAR, has been identified as a molecular target for cancer chemopreventive agents. PPARγ was initially understood as a regulator of adipocyte differentiation and glucose homeostasis while later on, it became evident that it is also involved in cell differentiation, apoptosis, and angiogenesis, biological processes which are deregulated in cancer. It is now established that PPARγ ligands can induce cell differentiation and yield early antineoplastic effects in several tumor types. Moreover, several bioactive natural products with cancer protecting potential are shown to operate through activation of PPARγ. Overall, PPARγ appears to be a prevalent target ally to cancer chemopreventive agents and therefore pursuing research in this area is of great relevance.

Role of peroxisome proliferator-activated receptor gamma and its ligands in the treatment of hematological malignancies

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a multifunctional transcription factor with important regulatory roles in inflammation, cellular growth, differentiation, and apoptosis. PPARgamma is expressed in a variety of immune cells as well as in numerous leukemias and lymphomas. Here, we review recent studies that provide new insights into the mechanisms by which PPARgamma ligands influence hematological malignant cell growth, differentiation, and survival. Understanding the diverse properties of PPARgamma ligands is crucial for the development of new therapeutic approaches for hematological malignancies.

Association between C1431T polymorphism in peroxisome proliferator-activated receptor-γ gene and coronary artery disease in Chinese Han population

The C1431T polymorphism in peroxisome proliferator-activated receptor-γ (PPARγ) has been shown to be associated with diabetes, obesity, and metabolic syndrome. However, it is unclear whether this polymorphism is associated with coronary artery disease (CAD). Therefore, we conducted a hospital-based case-control study with 864 CAD patients and 1008 controls to explore the association between the PPARγ C1431T polymorphism and risk of CAD in Chinese Han population. Subjects with the variant genotypes (CT + TT) had a 39% decreased risk of CAD relative to CC carriers (adjusted odds ratio, 0.61; 95% confidence interval, 0.49-0.76). Our results suggested that the C1431T polymorphism was associated with a higher body mass index in both CAD patients and controls. Moreover, this polymorphism was also found to be associated with a higher HDL cholesterol level and a lower blood glucose level in CAD patients. In stratified analyses, the T allele was significantly associated with reduced risk of CAD in males, subjects with age <62 years, and non-smokers. In conclusion, the PPARγ C1431T polymorphism is associated with decreased risk of CAD in Chinese Han population.

Association of peroxisome proliferator-activated receptor-gamma 2 Pro12Ala polymorphism with advanced-stage endometriosis

PROBLEM

To investigate whether the peroxisome proliferator-activated receptor (PPAR)-γ2 Pro12Ala polymorphism is associated with a risk of advanced-stage endometriosis in a Korean population.

METHODS OF STUDY

  Case-control study in a collective of 446 patients and 427 controls. The Pro12Ala polymorphism of PPAR-γ2 gene was genotyped using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis.

RESULTS

The distribution of the PPAR-γ2 Pro12Ala polymorphism was different between the advanced-stage endometriosis group and the control group (non-CC rates were 5.2% for patients with advanced endometriosis and 10.1% for the control group, respectively, P = 0.006). The frequency for the Ala-12 allele variant was significantly lower in patients with advanced stage of endometriosis (2.7%) than in the control group (5.3%) (P = 0.006).

CONCLUSION

These findings suggest that the PPAR-γ2 Pro12Ala polymorphism is associated with advanced-stage endometriosis in the Korean population. Unlike results from other studies reported so far, the Ala-12 allele may have protective effects against advanced-stage endometriosis in the Korean population.

Gender differences in the effects of peroxisome proliferator-activated receptor γ2 gene polymorphisms on metabolic adversity in patients with schizophrenia or schizoaffective disorder

OBJECTIVE

Metabolic syndrome (MS) is a major health problem in schizophrenic patients. Peroxisome proliferator-activated receptor γ2 (PPARγ2) is one of the candidate genes responsible for the liability to metabolic problems. In this study, we investigated the effect of the PPARγ2 gene Pro12Ala and C161T polymorphisms on metabolic adversities in patients with schizophrenia or schizoaffective disorder.

METHODS

Metabolic profiles and PPARγ2 gene polymorphisms were determined in 600 patients (309 men and 291 women) with a clinical diagnosis of schizophrenia or schizoaffective disorder. Metabolic indices and components of MS were compared between patients with different Pro12Ala or C161T genotypes.

RESULTS

In the whole population, the allele frequency of 12Ala and 161T was 4.4% and 24.7% respectively. Both polymorphisms had no significant effect on obesity or metabolic-related traits. However, following gender stratification of the data, we found female 12Ala allele carriers were at greater risk of developing abdominal obesity (OR = 4.0, 95% CI = 1.1-14.2, p = 0.04) and hypertension (OR=2.9, 95% CI = 1.2-7.4, p = 0.02) than female 12Ala allele non-carriers. Male 161T allele carriers had lower insulin levels (p = 0.02) and lower high-density lipoprotein cholesterol (HDL-C) (p = 0.05) levels than male 161T allele non-carriers. Moreover, female 161T allele carriers had higher body weight (p = 0.04), waist circumference (p = 0.05), and systolic blood pressure (p = 0.01), and were at greater risk of developing hypertension (OR = 2.0, 95% CI = 1.1-3.5, p = 0.02). Haplotype analyses showed that PPARγ2 gene polymorphisms were significantly associated with HDL-C level in men and blood pressure in women.

CONCLUSIONS

We did not find an association of PPARγ2 gene polymorphisms with MS or obesity in our schizophrenia sample. But further analyses by gender stratification revealed gender-specific differences in the effect of different PPARγ2 genotypes on certain metabolic adversities in these patients.

Distribution of peroxisome proliferator-activated receptor-gamma polymorphisms in Chinese and Dutch patients with inflammatory bowel disease

BACKGROUND

As peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is frequently expressed in colon, its genetic polymorphism may play a role in the etiology of inflammatory bowel disease (IBD). The aims of the present study were to determine the distribution of PPAR-gamma polymorphisms Pro12Ala and C161T and to explore the association between the PPAR-gamma genotypes and phenotypes of IBD patients.

METHODS

A total of 244 IBD patients [212 ulcerative colitis (UC) and 32 Crohn's disease (CD)] and 220 controls in the Chinese population and 603 IBD patients (302 UC and 301 CD) and 180 controls in the white Dutch population were enrolled in the study. The phenotypes of Chinese IBD patients were grouped according to disease location. The PPAR-gamma polymorphisms Pro12Ala and C161T were genotyped by PCR-based methods.

RESULTS

In the Chinese population, T carriers of the PPAR-gamma C161T polymorphism were more common in UC patients than in the controls [37.7% vs. 25.5%, odds ratio 1.77, 95% confidence interval 1.18-2.68, P = 0.007], whereas Ala carriers of the Pro12Ala polymorphism showed no significant association in UC patients, but there was a significant association of Ala carriers with more extensive disease among the UC patients (P = 0.002); Pro12Ala and C161T genotypes did not show any associations with CD patients. No associations were found for the PPAR-gamma C161T SNP studied in the Dutch IBD population.

CONCLUSIONS

Our study showed the potential association between the PPAR-gamma C161T polymorphism and UC patients in the central Chinese population. This finding was not replicated in the Dutch population. Further studies are necessary to explore the functional implication of the PPAR-gamma C161T polymorphism in Chinese UC patients.

Association between two common polymorphisms of PPARgamma gene and metabolic syndrome families in a Chinese population

BACKGROUND AND AIMS

We investigated the association between the two common polymorphisms, C1431T and Pro12Ala of PPARgamma gene, and metabolic syndrome (MS) in a Chinese population.

METHODS

We included 423 subjects with MS and families without MS. Subjects were divided into three groups: MS probands and first- and second-degree relatives of probands, spouses and controls. Each group was then divided into two subgroups according to genotype (Pro/Pro and Pro/Ala for Pro12Ala, CC and CT + TT for 1431C/T). Anthropometric indices, fasting plasma glucose, lipid profile, Sv1 + Rv5 of electrocardiogram and single nucleotide polymorphisms were detected.

RESULTS

Frequencies of C1431T genotypes, but not Pro12Ala, were different among the three groups. MS patients with Pro/Ala genotype had higher fasting blood sugar (FBS) levels and Sv1 + Rv5. Controls with Ala allele had lower total cholesterol levels. In relatives, Ala carriers had higher high-density lipoprotein cholesterol (HDL-c) levels. BMI of the different groups were not significant. MS patients with T allele had higher FBS and Sv1 + Rv5. In relatives of MS subjects, T-allele carriers had lower blood uric acid, creatinine and higher HDL-c levels and Sv1 + Rv5.

CONCLUSIONS

C1431T, but not Pro12Ala polymorphisms, are associated with MS in a Chinese population. In MS patients, Ala allele and T allele are both associated with higher fasting blood sugar and higher left ventricular voltage. In controls, Ala carriers have lower total cholesterol. In MS relatives, Ala carriers had higher HDL-c levels and T-allele carriers had lower uric acid, creatinine and higher HDL-c levels and left ventricular voltage.

Peroxisome proliferator-activated receptor gamma overexpression suppresses growth and induces apoptosis in human multiple myeloma cells

PURPOSE

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a transcription factor that regulates immune and inflammatory responses. Our laboratory has shown that normal and malignant B cells, including multiple myeloma, express PPARgamma. Moreover, certain PPARgamma ligands can induce apoptosis in multiple myeloma cells. Because PPARgamma ligands can also have PPARgamma-independent effects, the role of PPARgamma in B-cell malignancies remains poorly understood. To further understand the role of PPARgamma, we examined the functional consequences of its overexpression in human multiple myeloma.

EXPERIMENTAL DESIGN

In the present work, we developed a lentiviral vector for PPARgamma gene delivery. We transduced multiple myeloma cells with a lentivirus-expressing PPARgamma and studied the involvement of this receptor on cell growth and viability.

RESULTS

PPARgamma overexpression decreased multiple myeloma cell proliferation and induced spontaneous apoptosis even in the absence of exogenous ligand. These PPARgamma-overexpressing cells were dramatically more sensitive to PPARgamma ligand-induced apoptosis compared with uninfected or LV-empty-infected cells. Apoptosis was associated with the down-regulation of antiapoptotic proteins X-linked inhibitor of apoptosis protein and myeloid cell leukemia-1 as well as induction of caspase-3 activity. Importantly, PPARgamma overexpression-induced cell death was not abrogated by coincubation with bone marrow stromal cells (BMSC), which are known to protect multiple myeloma cells from apoptosis. Additionally, PPARgamma overexpression in multiple myeloma or BMSC inhibited both basal and multiple myeloma-induced interleukin-6 production by BMSC.

CONCLUSIONS

Our results indicate that PPARgamma negatively controls multiple myeloma growth and viability in part through inhibition of interleukin-6 production by BMSC. As such, PPARgamma is a viable therapeutic target in multiple myeloma.

Peroxisome proliferator-activated receptor gamma overexpression and knockdown: impact on human B cell lymphoma proliferation and survival

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a multifunctional transcription factor that regulates adipogenesis, immunity and inflammation. Our laboratory previously demonstrated that PPARgamma ligands induce apoptosis in malignant B cells. While malignant B lineage cells such as B cell lymphoma express PPARgamma, its physiological function remains unknown. Herein, we demonstrate that silencing PPARgamma expression by RNAi in human Burkitt's type B lymphoma cells increased basal and mitogen-induced proliferation and survival, which was accompanied by enhanced NF-kappaB activity and increased expression of Bcl-2. These cells also had increased survival upon exposure to PPARgamma ligands and exhibited a less differentiated phenotype. In contrast, PPARgamma overexpression in B lymphoma cells inhibited cell growth and decreased their proliferative response to mitogenic stimuli. These cells were also more sensitive to PPARgamma-ligand induced growth arrest and displayed a more differentiated phenotype. Collectively, these findings support a regulatory role for PPARgamma in the proliferation, survival and differentiation of malignant B cells. These findings further suggest the potential of PPARgamma as a therapeutic target for B cell malignancy.

Peroxisome proliferator-activated receptors (PPARs) and the human skin: importance of PPARs in skin physiology and dermatologic diseases

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily that regulate lipid, glucose, and amino acid metabolism. More recently, PPARs and corresponding ligands have been shown in skin and other organs to regulate important cellular functions, including cell proliferation and differentiation, as well as inflammatory responses. These new functions identify PPARs and corresponding ligands as potential targets for the treatment of various skin diseases and other disorders. It has been shown that in inflammatory skin disorders, including hyperproliferative psoriatic epidermis and the skin of patients with atopic dermatitis, the expression of both PPARalpha and PPARgamma is decreased. This observation suggests the possibility that PPARalpha and PPARgamma activators, or compounds that positively regulate PPAR gene expression, may represent novel NSAIDs for the topical or systemic treatment of common inflammatory skin diseases such as atopic dermatitis, psoriasis, and allergic contact dermatitis. Moreover, recent findings indicate that PPAR-signaling pathways may act as a promising therapeutic target for the treatment of hyperproliferative skin diseases including skin malignancies. Studies in non-diabetic patients suggest that oral thiazolidinediones, which are synthetic ligands of PPARgamma, not only exert an antidiabetic effect but also may be beneficial for moderate chronic plaque psoriasis by suppressing proliferation and inducing differentiation of keratinocytes; furthermore, they may even induce cell growth arrest, apoptosis, and terminal differentiation in various human malignant tumors. It has been reported that PPARalpha immunoreactivity is reduced in human keratinocytes of squamous cell carcinoma (SCC) and actinic keratosis (AK), while PPARdelta appears to be upregulated. Additionally, the microvessel density is significantly higher in AK and SCC that express high levels of PPARdelta. PPARdelta has been demonstrated to have an anti-apoptotic role and to maintain survival and differentiation of epithelial cells, whereas PPARalpha and PPARgamma activators induce differentiation and inhibit proliferation and regulate apoptosis. In melanoma, the growth inhibitory effect of PPARgamma activation is independent of apoptosis and seems to occur primarily through induction of cell cycle arrest in the G1 phase of the cell cycle or induction of re-differentiation. PPARalpha activation causes inhibition of migration of melanoma cells and anchorage-independent growth, whereas primary tumor growth remains unaltered. In clinical trials of gemfibrozil, a PPARalpha ligand, significantly fewer patients treated with this lipid-lowering drug were diagnosed with melanoma as compared to those in the control group. In conclusion, an increasing body of evidence indicates that PPAR signaling pathways may represent interesting therapeutic targets for a broad variety of skin disorders, including inflammatory skin diseases such as psoriasis and atopic dermatitis, and skin malignancies.

The non-genomic crosstalk between PPAR-gamma ligands and ERK1/2 in cancer cell lines

Peroxisome proliferator activated receptors (PPARs) are members of the nuclear receptor superfamily acting as transcription factors. PPAR-gamma, one of the three PPAR subtypes, is expressed in many malignant and non-malignant cells and tissues. PPAR-gamma ligands influence cancer biology via both genomic as well as non-genomic events. The non-genomic action of PPAR-gamma ligands, including the activation of MAPK signaling pathways, is under intense investigation. In the presence of PPAR-gamma ligands, a rapid phosphorylation of ERK1/2 is observed in many cancer cell lines. Activated ERK1/2 elicits rapid, non-genomic cellular effects and can directly repress PPAR-gamma transcriptional activity by phosphorylation. This paper reviews the interrelation of PPAR-gamma ligands and activated ERK1/2, in relation to their antineoplastic actions in cancer cell lines, which may offer the potential for improved anticancer therapies.

Present concepts and future outlook: function of peroxisome proliferator-activated receptors (PPARs) for pathogenesis, progression, and therapy of cancer

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily of transcriptional regulators that regulate lipid, glucose, and amino acid metabolism. In recent studies it also has been shown that these receptors are implicated in tumor progression, cellular differentiation, and apoptosis and modulation of their function is therefore considered as a potential target for cancer prevention and treatment. PPAR ligands and other agents influencing PPAR signalling pathways have been shown to reveal chemopreventive potential by mediating tumor suppressive activities in a variety of human cancers and could represent a potential novel strategy to inhibit tumor carcinogenesis and progression. This review summarizes the currently available data on the roles of PPARs in relation to the processes of cell differentiation and carcinogenesis as well as their role as promising future therapeutic targets.

International Union of Pharmacology. LXI. Peroxisome proliferator-activated receptors

The three peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors of the nuclear hormone receptor superfamily. They share a high degree of structural homology with all members of the superfamily, particularly in the DNA-binding domain and ligand- and cofactor-binding domain. Many cellular and systemic roles have been attributed to these receptors, reaching far beyond the stimulation of peroxisome proliferation in rodents after which they were initially named. PPARs exhibit broad, isotype-specific tissue expression patterns. PPARalpha is expressed at high levels in organs with significant catabolism of fatty acids. PPARbeta/delta has the broadest expression pattern, and the levels of expression in certain tissues depend on the extent of cell proliferation and differentiation. PPARgamma is expressed as two isoforms, of which PPARgamma2 is found at high levels in the adipose tissues, whereas PPARgamma1 has a broader expression pattern. Transcriptional regulation by PPARs requires heterodimerization with the retinoid X receptor (RXR). When activated by a ligand, the dimer modulates transcription via binding to a specific DNA sequence element called a peroxisome proliferator response element (PPRE) in the promoter region of target genes. A wide variety of natural or synthetic compounds was identified as PPAR ligands. Among the synthetic ligands, the lipid-lowering drugs, fibrates, and the insulin sensitizers, thiazolidinediones, are PPARalpha and PPARgamma agonists, respectively, which underscores the important role of PPARs as therapeutic targets. Transcriptional control by PPAR/RXR heterodimers also requires interaction with coregulator complexes. Thus, selective action of PPARs in vivo results from the interplay at a given time point between expression levels of each of the three PPAR and RXR isotypes, affinity for a specific promoter PPRE, and ligand and cofactor availabilities.

Association of two polymorphisms in the peroxisome proliferator-activated receptor-gamma gene with adenomyosis, endometriosis, and leiomyomata in Japanese women

OBJECTIVE

The peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a nuclear hormone receptor that plays an important role in many diseases. This study investigated whether two polymorphisms (Pro12Ala in exon B and C161T in exon 6) of the PPAR-gamma2 gene are related to adenomyosis, endometriosis, or leiomyomata.

METHODS

A total of 390 patients with adenomyosis, endometriosis, and/or leiomyomata were classified into four groups: 103 patients with adenomyosis (21 adenomyosis only and 82 adenomyosis with endometriosis and/or leiomyomata), 95 patients with endometriosis only, 100 patients with leiomyomata only, and 92 patients with endometriosis and leiomyomata.

RESULTS

There was no association between distribution of genotype or allele frequencies for the PPAR-gamma Pro12Ala polymorphism and the presence of adenomyosis, endometriosis, and/or leiomyomata. However, compared with results for controls, the PPAR-gamma 161CC genotype and 161C allele frequencies were significantly increased in patients with adenomyosis (genotype: chi2 = 8.185, corrected P value [Pc] = .0169; allele: chi2 = 8.337, Pc = .0155) and in patients with endometriosis (genotype: chi2 = 6.748, Pc = .0375; allele: chi2 = 6.413, Pc = .0453).

CONCLUSION

The results suggest that the PPAR-gamma 161CC genotype could be a genetic risk factor for adenomyosis and endometriosis, whereas the Pro12Ala polymorphism was not associated with these estrogen-dependent benign uterine diseases in a Japanese population.

Identification and characterization of novel peroxisome proliferator-activated receptor-gamma (PPAR-gamma) transcriptional variants in pig and human

The peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a member of the steroid/thyroid/retinoid receptor superfamily, and is primarily expressed in fat tissue. To date, two major PPAR-gamma isoforms have been identified in pig, PPAR-gamma1 and PPAR-gamma2. Porcine PPAR-gamma1a consists of two leader exons, designated A1 and A2, followed by six exons containing the open reading frame. Here, we report the isolation and characterization of three novel PPAR-gamma1 transcripts. PPAR-gamma1b is derived from exon A1, with exon A2 spliced out. PPAR-gamma1c and PPAR-gamma1d are derived from the new exon, A', containing exon A2 (gamma1c) or without exon A2 (gamma1d). Based on PCR analysis of PAC clones that included sequences from the 5'-untranslated region of the PPAR-gamma gene, the new A' exon is located between the known exons A1 and A2. We also isolated the human homologue to exon A', as well as the two new PPAR-gamma1c and -gamma1d splice variants, from human adipose tissue. Studies of the expression of porcine PPAR-gamma by real time reverse transcription-polymerase chain reaction analysis show that transcripts derived from exon A1 were not expressed at significantly different levels in visceral fat (lamina subserosa) or subcutaneous fat (back fat, inner and outer layer). In contrast, exon A'-derived transcripts were expressed at progressively higher levels in the inner and outer layers of subcutaneous fat than in visceral fat. The same expression pattern was also observed for PPAR-gamma2. We hypothesize that there are three promoters, which differentially regulate PPAR-gamma1 and PPAR-gamma2 gene expression, depending on the specific localization of the fat tissue.

Insulin and oleic acid increase PPARgamma2 expression in cultured mouse hepatocytes

Hepatic PPARgamma expression is increased in several animal models of diabetes and obesity, and liver-specific overexpression of PPARgamma induces liver steatosis. The aim of this study was to investigate the regulation of PPARgamma expression in primary mouse hepatocytes. PPARgamma2, but not PPARgamma1, was up-regulated by insulin and to a lesser extent by oleic acid. Insulin increased transcription of the PPARgamma2 gene via phosphatidylinositol 3-kinase activation. The PPARgamma agonist, rosiglitazone, increased PPARgamma2 expression, but not PPARgamma1, only in the presence of insulin. Also aP2 mRNA expression was induced by rosiglitazone to a higher degree in the presence of insulin, while acyl-CoA oxidase was increased independently of insulin. In summary, PPARgamma2 is increased in hepatocytes by oleic acid and insulin. These results may help to understand the regulation of PPARgamma expression in liver, which possibly plays a role in the development of liver steatosis.

The C161-->T polymorphism in peroxisome proliferator-activated receptor gamma, but not P12A, is associated with insulin resistance in Hispanic and non-Hispanic white women: evidence for another functional variant in peroxisome proliferator-activated receptor gamma

The P12A variant in the peroxisome proliferator-activated receptor gamma (PPARgamma) gene has been intensely studied for association with obesity-related or type-2 diabetes-related traits; however, the results have been somewhat inconsistent in different populations. We genotyped a large cohort of Hispanic and non-Hispanic white individuals from the San Luis Valley Diabetes Study for P12A and another common variant, C161-->T, in the PPARgamma gene to determine if these sites were associated with fasting glucose, insulin, free fatty acid levels, insulin sensitivity, or body fat. There were no statistically significant frequency differences at these two sites between Hispanic and non-Hispanic individuals. No significant association with the metabolic phenotypes was observed for either of the polymorphisms in men; however, in women, significant associations were shown between the C161-->T variant and fasting insulin (P=.008) and the homeostasis model assessment of insulin resistance (HOMA IR; P=.007). After adjusting for age, smoking, fat mass, and skin reflectance, linear regression showed that C161-->T explained 1.5% of the variation in both fasting insulin (P=.031) and HOMA IR (P=.028) whereas P12A contributed only 0.04% (fasting insulin, P=.268) and 0.02% (HOMA IR, P=.418) to the total trait variation. In the San Luis Valley Diabetes Study female patients, C161-->T appears to be a better predictor of fasting insulin levels and insulin resistance than P12A although the effect of this variant is small. These results support the hypothesis that C161-->T is in linkage disequilibrium with unidentified functional variation in PPARgamma or in a linked gene. This could explain some of the inconsistencies in the P12A association studies as the allele frequency and level of linkage disequilibrium of another functional polymorphism in the region could vary in different populations.

[PPAR gamma: a novel pharmacological target against retinal and choroidal neovascularization]

PPARg (peroxisome proliferator-activated receptor gamma) is a nuclear receptor that regulates the transcription of numerous genes involved in the differentiation, proliferation and apoptosis of various cell types. It was initially discovered in adipocytes as a differentiation agent, then was characterized in vascular endothelium and recently in choroidal and retinal endothelial cells. Agonists that bind to PPARgamma and stimulate its transcriptional activity are endogenous lipids such as lysophosphatidic acid and 15-d-PGJ2 as well as the synthetic pharmacological compounds, thiazolidinediones, used for treating type 2 diabetes. These ligands prevent choroidal and retinal neovascularization in several experimental animal models, notably through the inhibition of vascular endothelial growth factor (VEGF) receptor expression. Because of the high affinity and the low molecular weight of agonists, suitable for good bioavailability, PPARgamma could potentially be a novel pharmacological target of angiostatic agents, particularly useful to treat age-related macular degeneration and diabetic retinopathy.

Gender specific association of genetic variation in peroxisome proliferator-activated receptor (PPAR)γ-2 with longevity

Long-lived subjects have been shown to have peculiar anthropometric features (i.e. lower body mass index (BMI)) and metabolic parameters (i.e. improved insulin sensitivity). Life style and a genetic background potentially protective against the age-related metabolic derangement might contribute to such a particular phenotype. Peroxisome proliferator-activated receptor (PPAR)gamma-2 is an important regulator of adipose tissue metabolism, insulin sensitivity and inflammatory response. Thus, the potential role of genetic variability at Pro/Ala loci of PPARG gene on longevity was studied in 222 long-lived subjects and 250 aged subjects. We found a different Pro/Ala genotype frequency distribution between long-lived and aged men subjects, long-lived men having an increased frequency of Pro/Ala genotype (20 vs 8.5%); no differences was found when allele and genotype distribution of Pro/Ala gene polymorphism were analyzed in the two age group of women. Interestingly, subjects with Pro/Ala polymorphism had significantly lower BMI than Ala/Ala and Pro/Pro polymorphism. In conclusion, our study demonstrated that paraoxonase Pro/Ala gene polyporphism is associated with human longevity. Such an effect is probably due to the effect of Pro/Ala polymorphism on body composition and appears to be gender specific.

Association of peroxisome proliferator–activated receptor gamma 2 Pro-12-Ala polymorphism with endometriosis

We explored the association of the PPAR-gamma2 (peroxisome proliferator-activated receptor) Pro-12-Ala polymorphism with endometriosis in a case-control study with 51 women with endometriosis stages I-IV and 55 control women without endometriosis. The 12-Pro allele of PPAR-gamma2 may have protective effects avoiding the development and progression of endometriosis.

Peroxisome proliferator-activated receptor-gamma represses GLUT4 promoter activity in primary adipocytes, and rosiglitazone alleviates this effect

The synthetic thiazolidinedione ligands of peroxisome proliferator-activated receptor-gamma (PPARgamma) improve insulin sensitivity in type II diabetes and induce GLUT4 mRNA expression in fat and muscle. However, the molecular mechanisms involved are still unclear. We studied the regulatory effects of PPARgamma and its ligands on GLUT4 gene expression in primary rat adipocytes and CHO-K1 cells cotransfected with PPARgamma and the GLUT4 promoter reporter. PPARgamma1 and PPARgamma2 repressed the activity of the GLUT4 promoter in a dose-dependent manner. Whereas this repression was augmented by the natural ligand 15Delta-prostaglandin J2, it was completely alleviated by rosiglitazone (Rg). Ligand binding-defective mutants PPARgamma1-L468A/E471A and PPARgamma2-L496A/E499A retained the repression effect, which was unaffected by Rg, whereas the PPARgamma2-S112A mutant exhibited a 50% reduced capacity to repress GLUT4 promoter activity. The -66/+163 bp GLUT4 promoter region was sufficient to mediate PPARgamma inhibitory effects. The PPARgamma/retinoid X receptor-alpha heterodimer directly bound to this region, whereas binding was abolished in the presence of Rg. Thus, we show that PPARgamma represses transcriptional activity of the GLUT4 promoter via direct and specific binding of PPARgamma/retinoid X receptor-alpha to the GLUT4 promoter. This effect requires an intact Ser112 phosphorylation site on PPARgamma and is completely alleviated by Rg, acting via its ligand-binding domain. These data suggest a novel mechanism by which Rg exerts its antidiabetic effects via detaching PPARgamma from the GLUT4 gene promoter, thus leading to increased GLUT4 expression and enhanced insulin sensitivity.

Pro12Ala of the peroxisome proliferator-activated receptor-gamma2 gene is associated with lower serum insulin levels in nonobese African Americans: the Atherosclerosis Risk in Communities Study

Recent research suggests that the Pro12Ala variant in peroxisome proliferator-activated receptor-gamma2 (PPAR-gamma2) is associated with diabetes- and obesity-related traits, and that its effects may be modified by obesity status. We characterized this variant in a population-based sample of 1,441 middle-aged African-American individuals with respect to diabetes-, obesity-, and other cardiovascular-related traits, both cross-sectionally and prospectively. The overall frequency of Ala12 was 1.9% (95% CI 1.5-2.5%), significantly lower than in Caucasian populations. Consistent with previous findings in Caucasians, African Americans with type 2 diabetes tended to be less likely to have the Pro/Ala genotype than those without (odds ratio [OR] 0.64, 95% CI 0.34-1.20); however, this OR was not statistically significant. Among nonobese individuals, the Pro/Ala genotype was associated with significantly lower ln(insulin) (P = 0.001), lower ln(HOMA-IR) (homeostasis model assessment of insulin resistance) (P = 0.002), higher fasting glucose-to-insulin ratio (P = 0.005), and lower diastolic blood pressure (P = 0.02). Among overweight individuals (BMI 25-29.9 kg/m(2)), the Pro/Ala genotype was associated with greater BMI (P = 0.02), waist-to-hip ratio (P = 0.01), and waist circumference (P = 0.04). Among obese individuals, there was no association between any of the diabetes- or obesity-related traits and the Pro12Ala PPAR-gamma2 variant. We conclude that among nonobese African Americans, the Pro/Ala genotype is associated with markers of greater insulin sensitivity.

The peroxisome proliferator-activated receptor-gamma2 gene polymorphism (Pro12Ala) beneficially influences insulin resistance and its tracking from childhood to adulthood: the Bogalusa Heart Study

The peroxisome proliferator-activated receptor (PPAR)-gamma2 gene polymorphism Pro12Ala has been associated with increased insulin sensitivity in some but not all studies. Little is known about its effect on the tracking of insulin resistance status over time. These aspects were examined in a community-based sample of 686 white young adults, aged 20-38 years, and 426 white children, aged 4-17 years, and a subsample of a cohort (n = 362) who participated both as children and adults, with an average follow-up period of 13.4 years. Insulin resistance was measured by the homeostasis model assessment of insulin resistance (HOMA-IR) using fasting insulin and glucose. The frequency of the variant Ala12 allele was 0.104 in whites vs. 0.017 in blacks. After adjusting for sex, age, and BMI, adult subjects with the genotype Pro/Pro, Pro/Ala, and Ala/Ala, respectively, showed significant decreasing trends in fasting insulin (11.7, 10.3, and 8.8 micro U/ml; P = 0.002) and HOMA-IR (2.4, 2.1, and 1.7; P = 0.006). Similar but nonsignificant trends were noted in childhood. A significant genotype-BMI interaction effect on insulin (P = 0.020), glucose (P = 0.007), and HOMA-IR (P = 0.001) was found in adulthood, with carriers versus noncarriers showing attenuated association with BMI. The genotype-BMI interaction effect on these variables tended to be similar in childhood. With respect to tracking over time, of individuals in the top age- and sex-specific quartile of HOMA-IR in childhood, 48.7% (38/78) of noncarriers vs. 16.7% (2/12) of the carriers (P = 0.035) remained in the same quartile in adulthood. A similar trend was observed for insulin (2/13 vs. 35/77, P = 0.037). In conclusion, the Pro12Ala polymorphism of the PPAR-gamma2 gene beneficially influences insulin resistance and its tracking from childhood to adulthood. Further, the Ala12 allele attenuates the adverse association between adiposity and insulin resistance measures.

The Pro12Ala PPARgamma2 gene missense mutation is associated with obesity and insulin resistance in Swedish middle-aged men

BACKGROUND

A missense mutation in exon B of the adipocyte-specific isoform peroxisome proliferator-activated receptor-gamma2 (PPARgamma2) has recently been described, leading to the substitution of proline to alanine at codon 12, which causes a reduction in the transcriptional activity of PPARgamma2. The Pro12Ala PPARgamma2 polymorphism has been variably associated with obesity, insulin sensitivity, and dyslipidemia.

AIMS AND METHODS

In the present study, we addressed the hypothesis that the Pro12Ala variant is associated with obesity and estimates of insulin, glucose, and lipid metabolism as well as circulating hormones including salivary cortisol in 284 unrelated Swedish men born in 1944. The subjects were genotyped by using PCR amplification of exon B of the PPARgamma2 gene followed by digestion with the restriction enzyme BstUI.

RESULTS

Tests for differences between the PPARgamma2 genotypes revealed that the PPARgamma2 Ala homozygotes (n = 6) had higher body mass index (P = 0.022), abdominal sagittal diameter (P = 0.038), and nearly 3 times higher fasting insulin levels (P < 0.001) as well as higher HOMA insulin-resistance index (P = 0.011) compared to the PPARgamma2 Pro homozygotes (n = 186). This association was independent of body mass and fat distribution. In addition, subjects with the Ala/Ala genotype had lower total cholesterol (P = 0.012) as well as a trend toward lower high- and low-density lipoprotein cholesterol (P = 0.071 and P = 0.095) compared to the other PPARgamma2 genotypes.

CONCLUSION

In summary, these findings both confirm and expand the current notion that the PPARgamma2 gene might play a role in the etiology of obesity and that genetic variability in PPARgamma2 is associated with variations in body fat mass and insulin sensitivity.

The peroxisome proliferator-activated receptor-gamma2 Pro12Ala polymorphism

Peroxisome proliferator-activated receptor (PPAR)-gamma is a transcription factor with a key role in adipocyte differentiation. The Ala allele of the common Pro12Ala polymorphism in the isoform PPAR-gamma2 is associated with reduced risk for type 2 diabetes. The effect on the individual is weak, but because of a prevalence of >75% of the high-risk Pro allele, the population-attributable risk is enormous. The in vivo effects of the polymorphism are secondary to alterations in adipose tissue, where PPAR-gamma2 is predominantly expressed. Moderate reduction in transcriptional activity of PPAR-gamma as a result of the polymorphism modulates production and release of adipose-derived factors. Both decreased release of insulin-desensitizing free fatty acids, tumor necrosis factor-alpha, and resistin and increased release of the insulin-sensitizing hormone adiponectin result in secondary improvement of insulin sensitivity of glucose uptake and suppression of glucose production. The population effect of this polymorphism may be modulated by environmental or genetic factors such as obesity, ethnicity, ratio of unsaturated to saturated fatty acids, and genetic background. Once diabetes has developed, the protective effect of the Ala allele may be lost, since increased vascular complications and more pronounced beta-cell dysfunction have been reported. These observations, however, are currently unexplained. In conclusion, the Pro12Ala polymorphism in PPAR-gamma2 represents the first genetic variant with a broad impact on the risk of common type 2 diabetes. The precise understanding of its mechanism may lead to novel diagnostic, preventive, and therapeutic approaches for improving the management of type 2 diabetes.

The role of peroxisome proliferator-activated receptor gamma in diabetes and obesity

Peroxisome proliferator-activated receptor gamma (PPAR gamma) is a nuclear receptor, which upon activation with various natural and synthetic ligands, stimulates the transcription of genes responsible for growth and differentiation of adipocytes. Furthermore, PPAR gamma is the receptor for the insulin-sensitizing thiazolidinediones, which are commonly used for the treatment of type 2 diabetes. Rare inactivating mutations of the gene encoding PPAR gamma are associated with insulin resistance type 2 diabetes, and hypertension, whereas a rare gain of function mutation causes extreme obesity. A common polymorphism (Pro12Ala) of the adipose tissue-specific gamma 2 isoform is associated with increased insulin sensitivity and decreased risk of developing type 2 diabetes. These findings indicate a central role of PPAR gamma in fat cell biology and in the pathophysiology of obesity, diabetes, and insulin resistance.

Identification of novel genes differentially expressed in omental fat of obese subjects and obese type 2 diabetic patients

Obesity is associated with an increased risk for developing type 2 diabetes, insulin resistance, hypertension, dyslipidemia, cardiovascular disease, respiratory dysfunction, and certain forms of cancer. Insulin resistance in many type 2 diabetic patients is the result of increased visceral adiposity. To identify novel genes implicated in type 2 diabetes and/or obesity and to elucidate the molecular mechanisms underlying both diseases, we analyzed gene expression in omental fat from lean and obese nondiabetic subjects and obese type 2 diabetic patients using mRNA differential display and subtracted library techniques. After screening over 13,800 subtracted cDNA clones and 6,912 cDNA amplification products, we identified 2,078 cDNAs that showed potential differential expression in the omental fat of lean versus obese nondiabetic subjects versus obese type 2 diabetic patients. Data analysis showed that 70.7% of these clones corresponded to unknown genes (26.7% matched express sequence tags [ESTs]) and 29.3% corresponded to known genes. Reverse Northern and classic Northern analyses further confirmed that the expression of five of these cDNA clones was elevated in obese nondiabetic subjects and obese type 2 diabetic patients. Four candidate genes were further evaluated for tissue distribution, which showed expression primarily in adipose and skeletal muscle tissue, and chromosomal localization. We concluded that both mRNA differential display and subtracted cDNA libraries are powerful tools for identifying novel genes implicated in the pathogenesis of obesity and type 2 diabetes.

Deletion at 3p25.3-p23 is frequently encountered in endocrine pancreatic tumours and is associated with metastatic progression

For several reasons, chromosome 3p is thought to be involved in the pathogenesis of sporadic endocrine pancreatic tumours (EPTs): von Hippel-Lindau's disease (VHL gene at 3p25.5) is associated with EPTs; 3p is frequently involved in solid human tumours; and comparative genomic hybridization has identified frequent losses at 3p in EPTs. This study investigated 99 benign and malignant tumours, including 20 metastases, from 82 patients, by microsatellite loss of heterozygosity (LOH) analysis and fluorescence in situ hybridization (FISH) in order to evaluate the importance of chromosome 3p deletions in the molecular pathogenesis and biological behaviour of EPTs, to elaborate a common region of deletion, and to narrow down putative tumour suppressor gene loci. Allelic losses of 3p were found in 58/99 (58.6%) of tumours in 45/82 (54.9%) patients; analysis of seven microsatellite markers (3p26-p21) revealed a common region of LOH at 3p25.3-p23. The LOH frequency was significantly higher in malignant than in benign neoplasms (70.2% versus 28.0%; p=0.001). In addition, a strong correlation was found between the loss of alleles on chromosome 3p and clinically metastatic disease (LOH of 73.7% in metastasizing versus 41.5% in non-metastasizing tumours; p=0.008). EPTs from these patients showed a tendency towards losing large parts or the entire short arm of chromosome 3 with tumour progression. Furthermore, FISH analysis revealed complete loss of chromosome 3 in ten out of 37 EPTs (27%). These results indicate that a putative tumour suppressor gene at 3p25.3-p23 may play a role in the oncogenesis of sporadic EPTs and that losses of larger centromeric regions are associated with metastatic progression.

Peroxisome proliferator-activated receptor-gamma2 P12A and type 2 diabetes in Canadian Oji-Cree

Among the Oji-Cree of northern Ontario, we previously identified a novel variant in the HNF1A gene, namely G319S, that was strongly associated with type 2 diabetes. However, the majority of subjects with diabetes did not have the HNF1A S319 variant, suggesting that there might be other genetic determinants of diabetes susceptibility. In the course of sequencing candidate genes in diabetic subjects who were homozygous for HNF1A G319/G319, we found that some of them had the PPARG A12 variant. After genotyping PPARG in the entire adult Oji-Cree population, we found that: 1) PPARG A12 was strongly associated with type 2 diabetes in women, but not men; 2) among women, the odds of being affected for carriers of PPARG A12 compared with noncarriers was 2.3 (95% confidence interval, 1.4-3.8); and 3) among women, affected carriers of PPARG A12 had a significantly earlier age-of-onset and/or age-at-diagnosis compared with noncarriers. When taken together with the previously reported association of diabetes with HNF1A in both men and women, the gender-specific association with PPARG A12 confirms that type 2 diabetes is etiologically complex in the Oji-Cree and that at least two genes are involved in determining susceptibility to the disease in these people.

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.

Peroxisome proliferator-activated receptor gamma gene locus is related to body mass index and lipid values in healthy nonobese subjects

The peroxisome proliferator-activated receptor gamma (PPARgamma) gene has been implicated in morbid obesity and is important to lipid and carbohydrate metabolism. However, the relevance of gene variations in healthy nonobese subjects has not been defined. We recruited monozygotic and dizygotic healthy nonobese twin subjects to test the hypothesis that the PPARgamma gene is important to body mass index and lipid concentrations in healthy nonobese subjects. Both linkage and association strategies were used in the same dizygotic twins. The PPARgamma gene locus was linked (P<0.01) to high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and body mass index as quantitative traits. A biallelic variant in the PPARgamma gene was associated with high-density lipoprotein cholesterol and body mass index (P<0.05). We also looked for linkage between the same variables and the retinoic X receptor gene locus. This locus was linked to total and low-density lipoprotein cholesterol as well as triglycerides. We conclude that the PPARgamma gene is highly relevant to lipid metabolism and body mass index, not only in the morbidly obese but also in healthy nonobese subjects. The same appears to be true for its binding partner. Sequencing these genes in twins would serve to identify gene variations contributing to body mass index and lipid concentrations in healthy nonobese subjects.