Single gene contributions: genetic variants of peroxisome proliferator-activated receptor (isoforms alpha, beta/delta and gamma) and mechanisms of dyslipidemias

Nuclear receptor research in zebrafish

Nuclear receptors (NRs) form a superfamily of transcription factors that can be activated by ligands and are involved in a wide range of physiological processes. NRs are well conserved between vertebrate species. The zebrafish, an increasingly popular animal model system, contains a total of 73 NR genes, and orthologues of almost all human NRs are present. In this review article, an overview is presented of NR research in which the zebrafish has been used as a model. Research is described on the three most studied zebrafish NRs: the estrogen receptors (ERs), retinoic acid receptors (RARs) and peroxisome proliferator-activated receptors (PPARs). The studies on these receptors illustrate the versatility of the zebrafish as a model for ecotoxicological, developmental and biomedical research. Although the use of the zebrafish in NR research is still relatively limited, it is expected that in the next decade the full potential of this animal model will be exploited.

PPARs: regulators of metabolism and as therapeutic targets in cardiovascular disease. Part II: PPAR-β/δ and PPAR-γ

The PPARs are a subfamily of three ligand-inducible transcription factors, which belong to the superfamily of nuclear hormone receptors. In mammals, the PPAR subfamily consists of three members: PPAR-α, PPAR-β/δ and PPAR-γ. PPARs control the expression of a large number of genes involved in metabolic homeostasis, lipid, glucose and energy metabolism, adipogenesis and inflammation. PPARs regulate a large number of metabolic pathways that are implicated in the pathogenesis of metabolic diseases such as metabolic syndrome, Type 2 diabetes mellitus, nonalcoholic fatty liver disease and cardiovascular disease. The aim of this review is to provide up-to-date information about the biochemical and metabolic actions of PPAR-β/δ and PPAR-γ, the therapeutic potential of their agonists currently under clinical development and the cardiovascular disease outcome of clinical trials of PPAR-γ agonists, pioglitazone and rosiglitazone.

The association of nonalcoholic fatty liver disease with genetic polymorphisms: a multicenter study

INTRODUCTION

Growing evidence suggests that multiple factors, such as insulin resistance, nutritional factors, gut microbiota, and hormones released from the adipose tissue, act together on genetically predisposed individuals. We aimed to investigate whether various single-nucleotide polymorphisms (SNPs) play a role in the development of nonalcoholic fatty liver disease (NAFLD) and severity of liver damage in the Anatolian population.

METHODS

Two hundred and sixteen patients with biopsy-proven NAFLD and 150 control participants, aged 18-70 years, were consecutively enrolled in this multicenter study. Blood samples were genotyped for the PNPLA3 (rs738409), IL28B (rs12979860, rs12980275, rs8099917), PPAR-α 227 ALA, PPAR-γ pro 12 ALA, SOD2 C47T, and LOX-1 IVS4-14 polymorphisms using the custom-made LightSNiP assays on a LightCycler 480 II instrument.

RESULTS

Genotypic distributions of PNPLA3 rs738409 SNPs were different between NAFLD and control participants, but not for other SNPs. The PNPLA3 rs738409 GG polymorphism was associated with a 27-fold increased risk of development of NAFLD (odds ratio=27.8, 95% confidence interval: 3.5-218.4; P=0.002). Patients with the PNPLA3 GG genotype had higher nonalcoholic fatty liver disease activity score levels compared with patients with the PNPLA3 CC genotype (P<0.005). NAFLD patients without fibrosis had a higher frequency of IL28B rs12979860 TT and rs12980275 GG genotypes compared with NAFLD patients with fibrosis (P<0.005).

CONCLUSION

The present study proposes that polymorphisms in the PNPLA3 gene have highly predictive value in the development of NAFLD and are independently associated with the severity of liver histology in patients with NAFLD. The results of this study suggest that IL28B rs12979860 TT or rs12980275 GG may play an important protective role against the development of advanced fibrosis and even cirrhosis.

Improvement of cardiometabolic markers after fish oil intervention in young Mexican adults and the role of PPARα L162V and PPARγ2 P12A

Polyunsaturated fatty acids (PUFA) contained in fish oil (FO) are ligands for peroxisome proliferator-activated receptors (PPAR) that may induce changes in cardiometabolic markers. Variation in PPAR genes may influence the beneficial responses linked to FO supplementation in young adults. The study aimed to analyze the effect of FO supplementation on glucose metabolism, circulating lipids and inflammation according to PPARα L162V and PPARγ2 P12A genotypes in young Mexican adults. 191 young, non-smoking subjects between 18 and 40 years were included in a one-arm study. Participants were supplemented with 2.7 g/day of EPA+DHA, during six weeks. Dietary analysis, body composition measurements and indicators for glucose metabolism, circulating lipids, and markers for inflammation were analyzed before and after intervention. An overall decrease in triglycerides (TG) and an increase in HS-ω3 index were observed in all subjects [-4.1 mg/dL, (SD:±51.7), P=.02 and 2.6%, (SD:±1.2), P<.001 respectively]. Mean fasting insulin and glycated hemoglobin (HbA1c%) were significantly decreased in all subjects [-0.547mlU/L, (SD:±10.29), P=.034 and-0.07%, (SD:±0.3), P<.001 respectively], whereas there was no change in body composition, fasting glucose, adiponectin and inflammatory markers. Subjects carrying the minor alleles of PPARα L162V and PPARγ2 P12A had higher responses in reduction of TG and fasting insulin respectively. Interestingly, doses below 2.7 g/day (1.8 g/day) were sufficient to induce a significant reduction in fasting insulin and HbA1c% from baseline (P=.019 and P<.001). The observed responses in triglycerides and fasting insulin in the Mexican population give further evidence of the importance of FO supplementation in young people as an early step towards the prevention of cardiometabolic disease.

Zebrafish as a Model to Study the Role of Peroxisome Proliferating-Activated Receptors in Adipogenesis and Obesity

The Peroxisome Proliferator-Activated Receptors (PPARs) PPARA and PPARD are regulators of lipid metabolism with important roles in energy release through lipid breakdown, while PPARG plays a key role in lipid storage and adipogenesis. The aim of this review is to describe the role of PPARs in lipid metabolism, adipogenesis, and obesity and evaluate the zebrafish as an emerging vertebrate model to study the function of PPARs. Zebrafish are an appropriate model to study human diseases, including obesity and related metabolic diseases, as pathways important for adipogenesis and lipid metabolism which are conserved between mammals and fish. This review synthesizes knowledge on the role of PPARs in zebrafish and focuses on the putative function of PPARs in zebrafish adipogenesis. Using in silico analysis, we confirm the presence of five PPARs (pparaa, pparab, pparda, ppardb, and pparg) in the zebrafish genome with 67–74% identity to human and mouse PPARs. During development, pparda/b paralogs and pparg show mRNA expression around the swim bladder and pancreas, the region where adipocytes first develop, whereas pparg is detectable in adipocytes at 15 days post fertilization (dpf). This review indicates that the zebrafish is a promising model to investigate the specific functions of PPARs in adipogenesis and obesity.

PPARγ mutations, lipodystrophy and diabetes

The focus of this review is the lipodystrophy syndrome caused by mutation in the PPARγ nuclear receptor - partial familial lipodystrophy FPLD3. To provide a broader context for how these mutations act to generate the clinical features of partial lipodystrophy we will review the basic biology of PPARγ and also survey the set PPARγ genetic variants that do not cause lipodystrophy, but are nonetheless associated with clinically related syndromes, specifically type 2 diabetes.

PPAR α and PPAR γ polymorphisms as risk factors for dyslipidemia in a Chinese Han population

BACKGROUND

The PPAR α and PPAR γ are the key messengers responsible for the translation of nutritional stimuli into changes for the expression of genes, particularly genes involved in lipid metabolism. However, the associations between PPAR α/γ polymorphisms and lipid serum levels in the general population were rarely studied, and the conclusions were conflicting. The objective was to investigate the associations of the PPAR α and PPAR γ polymorphisms with dyslipidemia.

METHODS

820 subjects were randomly selected from the Prevention of Multiple Metabolic Disorders and MS in Jiangsu Province cohort populations. The logistic regression model was used to examine the association between these polymorphisms and dyslipidemia. SNPstats was used to explore the haplotype association analyses.

RESULTS

In the codominant and log-additive models, rs1800206, rs1805192 and rs3856806 were all associated with dyslipidemia (P < 0.005). When the most common haplotype L-G (established by rs1800206, rs4253778) was treated as the reference group, the V-G haplotype was associated with dyslipidemia (P < 0.001), higher TC and TG levels (P < 0.01). Moreover, when compared to Pro-C haplotype (established by rs1805192, rs3856806), the Pro-T, Ala-C, Ala-T haplotypes were associated with dyslipidemia (p < 0.001). A-T haplotype was associated with higher TC levels, (p < 0.01), and the P-T, A-C, A-T haplotypes were associated with higher TG levels (p < 0.01).

CONCLUSIONS

PPAR α and PPAR γ polymorphisms and haplotypes may be the genetic risk factors for dyslipidemia.

Peroxisome proliferator-activated receptors alpha and gamma2 polymorphisms in nonalcoholic fatty liver disease: a study in Brazilian patients

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) refers to the accumulation of hepatic steatosis in the absence of excess alcohol consumption. The pathogenesis of fatty liver disease and steatohepatitis (NASH) is not fully elucidated, but the common association with visceral obesity, hyperlipidemia, hypertension and type 2 diabetes mellitus (T2DM) suggests that it is the hepatic manifestation of metabolic syndrome. Peroxisome proliferator-activated receptor PPARα and PPARγ are members of a family of nuclear receptors involved in the metabolism of lipids and carbohydrates, adipogenesis and sensitivity to insulin. The objective of this study was to analyze the polymorphisms Leu162Val of PPARα and Pro12Ala of PPARγ as genetic risk factors for the development and progression of NAFLD.

METHODS

One hundred and three NAFLD patients (89 NASH, 14 pure steatosis) and 103 healthy volunteers were included. Single nucleotide polymorphisms (SNPs) Leu162Val and Pro12Ala were analyzed by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP).

RESULTS

NASH patients presented higher BMI, AST and prevalence of T2DM than patients with pure steatosis. A higher prevalence of 12Ala allele was observed in the NASH Subgroup when compared to Control Group. When we grouped NASH and Steatosis Subgroups (NAFLD), we found lower serum glucose and more advanced fibrosis in the Leu162Val SNP. On the other hand, there was no statistical difference in clinical, laboratorial and histological parameters according to the Pro12Ala SNP.

CONCLUSIONS

We documented a lower prevalence of 12Ala allele of gene PPARγ in the NASH Subgroup when compared to Control Group. In NAFLD patients, there were no associations among the occurrence of Pro12Ala SNP with clinical, laboratorial and histological parameters. We also documented more advanced fibrosis in the Leu162Val SNP. The obtained data suggest that Pro12Ala SNP may result in protection against liver injury and that Leu162Val SNP may be involved in the progression of NAFLD.

PPAR-α as a key nutritional and environmental sensor for metabolic adaptation

Peroxisome proliferator-activated receptors (PPARs) are transcription factors that belong to the superfamily of nuclear hormone receptors and regulate the expression of several genes involved in metabolic processes that are potentially linked to the development of some diseases such as hyperlipidemia, diabetes, and obesity. One type of PPAR, PPAR-α, is a transcription factor that regulates the metabolism of lipids, carbohydrates, and amino acids and is activated by ligands such as polyunsaturated fatty acids and drugs used to treat dyslipidemias. There is evidence that genetic variants within the PPARα gene have been associated with a risk of the development of dyslipidemia and cardiovascular disease by influencing fasting and postprandial lipid concentrations; the gene variants have also been associated with an acceleration of the progression of type 2 diabetes. The interactions between genetic PPARα variants and the response to dietary factors will help to identify individuals or populations who can benefit from specific dietary recommendations. Interestingly, certain nutritional conditions, such as the prolonged consumption of a protein-restricted diet, can produce long-lasting effects on PPARα gene expression through modifications in the methylation of a specific locus surrounding the PPARα gene. Thus, this review underlines our current knowledge about the important role of PPAR-α as a mediator of the metabolic response to nutritional and environmental factors.

PPARα polymorphisms as risk factors for dyslipidemia in a Brazilian population

BACKGROUND AND AIMS

Peroxisome proliferator-activated receptor α is a nuclear receptor involved in the regulation of several biochemical pathways. Polymorphisms within its gene have been associated with several metabolic traits. We aimed to investigate the association of L162V and Intron 7G>C polymorphisms with serum level markers and common morbidities affecting an older adult/elderly cohort from Cuiaba City, Mato Grosso State, Brazil, as well as to compare the results with a previously studied population from São Paulo City, Brazil.

METHODS AND RESULTS

The studied population consisted of 570 subjects from Cuiaba City, Brazil, who were subjected to clinical interviews and blood collection for laboratory examinations and DNA extraction. Dyslipidemia was defined when participants were taking oral hypolipemiants or those with total cholesterol above 200mg/dL, HDL-c below 40 mg/dL, LDL-c above 130 mg/dL and TG above 150 mg/dL. Restriction fragment length polymorphism polymerase chain reaction (RFLP-PCR) was used for polymorphism genotyping. Individual polymorphism and haplotype data were available for analyses. In the studied sample, allele frequencies were 0.052 and 0.292 for 162V and Intron 7C, respectively. In brief, 162V allele was associated with dyslipidemia (p=0.025), and after correction for alcohol consumption and waist-to-rip ratio, a tendency of association could still be observed (p=0.050). In addition, Intron 7C allele was associated with dyslipidemia even after correction for the same variables (p=0.029). When compared to our previous study from São Paulo, we found some divergences regarding these results, which may be explained by differences between the two populations. Haplotype association analyses revealed an association between L/C haplotype and dyslipidemia (p=0.021) and between V/C haplotype and lower LDL-c levels when compared to L/G haplotype (p=0.044).

CONCLUSION

These results may help to clarify the role of PPARα gene in lipid and lipoprotein metabolism and the evaluation of its polymorphisms and haplotypes as being characterized as genetic risk factors for metabolic disturbances.

Evaluation of single nucleotide polymorphisms of Pro12Ala in peroxisome proliferator-activated receptor-γ and Gly308Ala in tumor necrosis factor-α genes in obese Asian Indians: a population-based study

BACKGROUND

A population-based case control study was performed to determine the associations of Pro12Ala polymorphism in peroxisome proliferator-activated receptor-γ (PPARG) and Gly308Ala polymorphism in tumor necrosis factor-α (TNFA) genes in obese subjects.

PATIENTS AND METHODS

Of 1,400 eligible subjects, ≧20 years, we recruited only 1,127. For extreme phenotype case-control design, we evaluated 201 subjects with body mass index (BMI) ≧30 kg/m(2) (Group 1) and 143 with BMI <20 kg/m(2) (Group 2). Clinical, anthropometric, biochemical, and nutritional details and polymorphisms were estimated.

RESULTS

In Group 1, the dietary intake of calories and fats was higher, physical activity was lower, and prevalence of truncal obesity, hypertension, high total cholesterol, low high-density lipoprotein cholesterol, and diabetes was greater than in Group 2. There were no homozygous polymorphisms of either gene. Heterozygous Pro12Ala polymorphism in PPARG was found in 15 (7.5%) subjects in Group 1 and 3 (2.1%) subjects in Group 2 (P = 0.028), and heterozygous Gly308Ala polymorphism in TNFA was found in 19 (9.5%) in Group 1 and 7 (4.9%) in Group 2 (P = 0.115). Presence of heterozygous polymorphism in PPARG and TNFA-predicted obesity with univariate odds ratio ([OR], 95% confidence intervals) of 2.25 (1.32-3.84, P = 0.003) and 1.48 (1.10-1.99, P = 0.009) and with multivariate OR 1.74 (1.03-2.93, P = 0.038) and 1.46 (1.05-2.03, P = 0.024), respectively. The addition of dietary and physical activity variables did not result in significant change.

CONCLUSION

Obese Asian Indians have greater prevalence of heterozygous polymorphisms of Pro12Ala in PPARG and Gly308Ala in TNFA genes.

Peroxisome proliferator-activated receptors, metabolic syndrome and cardiovascular disease

Metabolic syndrome (MetS) is a constellation of risk factors including insulin resistance, central obesity, dyslipidemia and hypertension that markedly increase the risk of Type 2 diabetes (T2DM) and cardiovascular disease (CVD). The peroxisome proliferators-activated receptor (PPAR) isotypes, PPARα, PPARδ/ß and PPARγ are ligand-activated nuclear transcription factors, which modulate the expression of an array of genes that play a central role in regulating glucose, lipid and cholesterol metabolism, where imbalance can lead to obesity, T2DM and CVD. They are also drug targets, and currently, PPARα (fibrates) and PPARγ (thiazolodinediones) agonists are in clinical use for treating dyslipidemia and T2DM, respectively. These metabolic characteristics of the PPARs, coupled with their involvement in metabolic diseases, mean extensive efforts are underway worldwide to develop new and efficacious PPAR-based therapies for the treatment of additional maladies associated with the MetS. This article presents an overview of the functional characteristics of three PPAR isotypes, discusses recent advances in our understanding of the diverse biological actions of PPARs, particularly in the vascular system, and summarizes the developmental status of new single, dual, pan (multiple) and partial PPAR agonists for the clinical management of key components of MetS, T2DM and CVD. It also summarizes the clinical outcomes from various clinical trials aimed at evaluating the atheroprotective actions of currently used fibrates and thiazolodinediones.

Differences in transcriptional activation by the two allelic (L162V Polymorphic) variants of PPARα after Omega-3 fatty acids treatment

Omega-3 fatty acids (FAs) have the potential to regulate gene expression via the peroxisome proliferator-activated receptor α (PPARα); therefore, genetic variations in this gene may impact its transcriptional activity on target genes. It is hypothesized that the transcriptional activity by wild-type L162-PPARα is enhanced to a greater extent than the mutated variant (V162-PPARα) in the presence of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) or a mixture of EPA:DHA. To examine the functional difference of the two allelic variants on receptor activity, transient co-transfections were performed in human hepatoma HepG2 cells activated with EPA, DHA and EPA:DHA mixtures. Results indicate that the addition of EPA or DHA demonstrate potential to increase the transcriptional activity by PPARα with respect to basal level in both variants. Yet, the EPA:DHA mixtures enhanced the transcriptional activity to a greater extent than individual FAs indicating possible additive effects of EPA and DHA. Additionally, the V162 allelic form of PPARα demonstrated consistently lower transcriptional activation when incubated with EPA, DHA or EPA:DHA mixtures than, the wild-type variant. In conclusion, both allelic variants of the PPARα L162V are activated by omega-3 FAs; however, the V162 allelic form displays a lower transcriptional activity than the wild-type variant.