Association of the PRO12ALA polymorphism of the PPAR-gamma2 gene with oxidized low-density lipoprotein and cardiolipin autoantibodies in nondiabetic and type 2 diabetic subjects

G Allele of the rs1801282 Polymorphism in PPARγ Gene Confers an Increased Risk of Obesity and Hypercholesterolemia, While T Allele of the rs3856806 Polymorphism Displays a Protective Role Against Dyslipidemia: A Systematic Review and Meta-Analysis

BACKGROUND

The relationships between the rs1801282 and rs3856806 polymorphisms in nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) gene and obesity indexes as well as serum lipid levels have been extensively investigated in various studies, but the results were inconsistent and even contradictory.

METHODS

PubMed, Google Scholar, Embase, Cochrane Library, Web of Science, Wanfang, CNKI and VIP databases were searched for eligible studies. The random-effTPDEects model was used, and standardized mean difference (SMD) with 95% confidence interval (CI) was calculated to estimate the differences in obesity indexes and serum lipid levels between the subjects with different genotypes in a dominant model. Heterogeneity among studies was assessed by Cochran's x²-based Q-statistic test. Publication bias was identified by using Begg's test.

RESULTS

One hundred and twenty studies (70,317 subjects) and 33 studies (18,353 subjects) were identified in the analyses for the rs1801282 and rs3856806 polymorphisms, respectively. The G allele carriers of the rs1801282 polymorphism had higher levels of body mass index (SMD = 0.08 kg/m², 95% CI = 0.04 to 0.12 kg/m², p < 0.001), waist circumference (SMD = 0.12 cm, 95% CI = 0.06 to 0.18 cm, p < 0.001) and total cholesterol (SMD = 0.07 mmol/L, 95% CI = 0.02 to 0.11 mmol/L, p < 0.01) than the CC homozygotes. The T allele carriers of the rs3856806 polymorphism had lower levels of low-density lipoprotein cholesterol (SMD = -0.09 mmol/L, 95% CI = -0.15 to -0.03 mmol/L, p < 0.01) and higher levels of high-density lipoprotein cholesterol (SMD = 0.06 mmol/L, 95% CI = 0.02 to 0.10 mmol/L, p < 0.01) than the CC homozygotes.

CONCLUSIONS

The meta-analysis suggests that the G allele of the rs1801282 polymorphism confers an increased risk of obesity and hypercholesterolemia, while the T allele of the rs3856806 polymorphism displays a protective role against dyslipidemia, which can partly explain the associations between these polymorphisms and cardiovascular disease.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/, identifier [CRD42022319347].

The Ala allele in the PPAR-gamma2 gene is associated with reduced risk of type 2 diabetes mellitus in Caucasians and improved insulin sensitivity in overweight subjects

The purpose of the present study was to identify the association of the Pro12Ala polymorphism in the PPAR-gamma2 gene with diabetes, insulinaemia and insulin resistance. A meta-analysis study was carried out based on studies conducted in the last 10 years, using the databases PubMed, ISI Web of Knowledge, High Wire Press and Scielo, and the reference lists of the obtained articles. We included original studies that showed the relationship between the Pro12Ala polymorphism in the PPAR-gamma2 gene and type 2 diabetes mellitus (T2DM), insulinaemia and insulin resistance. Statistical analyses were conducted using the program RevMAn 5.0. The Mantel-Haenszel test was used to estimate the OR and the 95 % CI of the dichotomous variable, while the standardised effect size was used to estimate the average standardised mean difference and 95 % CI of continuous variables. The studies were subgrouped by ethnicity and overweight status. Forty-one studies were analysed, including a global sample of 30 612 subjects. We found a significant association of the Ala allele with the lowest risk of T2DM in Caucasians (OR 0.80; 95 % CI 0.65, 0.98), lower serum insulin (standardised effect size: - 0.05; 95 % CI - 0.09, - 0.00; P = 0.04), and greater sensitivity to insulin in overweight individuals (homeostasis model assessment of insulin resistance standardised effect size: - 0.07; 95 % CI - 0.13, - 0.01; P = 0.02). Considering that the Pro12Ala polymorphism in the PPAR-gamma2 gene is one of the factors related to insulin sensitivity, the present study demonstrated a significant effect of the Ala allele on lower development of T2DM in Caucasians and greater sensitivity to insulin in overweight subjects.

PPARgamma gene C161T substitution is associated with reduced risk of coronary artery disease and decreased proinflammatory cytokine expression

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a transcription factor implicated in the expression of proinflammatory cytokines in atheroma-associated cells, and the expression of proinflammatory cytokines, such as tumor necrosis factor alpha (TNF-alpha) and matrix metalloproteinases (MMPs), represents a critical step in atherogenesis and atherosclerosis. In this study, we test the hypothesis of whether a polymorphism corresponding to C161T substitution in exon 6 of the PPARgamma gene may affect the expression of proinflammatory cytokines and the onset of coronary artery diseases (CADs) in a Chinese population.

METHODS

We have studied distribution of the PPARgamma C161T substitution at exon 6 in 247 patients with CAD and 214 patients with chest pain syndrome. The plasma concentrations of MMP-9 and TNF-alpha were measured by enzyme-linked immunosorbent assay.

RESULTS

The results showed that the frequencies of the CC, CT, and TT genotypes were 61.9%, 34.0%, and 4.1% in CAD, and 51.4%, 45.3%, and 3.3% in chest pain syndrome, respectively. There was a significant association between the PPARgamma C161T polymorphism and CAD. The T allele carriers (CT + TT) had significantly reduced CAD risk compared with the CC homozygotes (odds ratio 0.547, 95% CI 0.327-0.831, P = .012) in a logistic regression model after controlling known independent factors for CAD. The CC homozygotes also had increased MMP-9 and TNF-alpha levels compared with T allele carriers. Moreover, the CC homozygotes were more susceptible to acute coronary syndrome than T allele carriers.

CONCLUSIONS

PPARgamma C161T polymorphism was associated with angiographically documented CAD in a Chinese population. The T allele of the PPARgamma gene might have a protective effect on the progression of CAD and reduce the onset of acute coronary syndrome, which might be associated with the decreased expression of MMP-9 and TNF-alpha in patients with CAD.

Heterogeneous effect of peroxisome proliferator-activated receptor gamma2 Ala12 variant on type 2 diabetes risk

Conflicting results have been reported regarding whether the PPARgamma2 Pro12Ala polymorphism plays a role in the risk of type 2 diabetes (T2D), suggesting genetic heterogeneity. To investigate this issue, a meta-analysis of 41 published and 2 unpublished studies (a total of 42,910 subjects) was conducted. Ala12 carriers had a 19% T2D risk reduction, but this association was highly heterogeneous (p = 0.005). A great proportion (48%) of heterogeneity was explained by the controls' BMI, with risk reduction being greater when BMI was lower. Risk reduction of Ala12 carriers in Asia (35%) was higher than in Europe (15%, p = 0.02) and tended to be higher than in North America (18%, p = 0.10). Difference between Asians and Europeans was no longer significant (p = 0.15) after adjusting for the controls' BMI. Studies from Europe were still heterogeneous (p = 0.02) with risk reduction in Ala12 carriers being progressively smaller (test for trend in the odds ratios, p = 0.02) from Northern (26% reduction, p < 0.0001) to Central (10%, p = 0.04) and Southern (0%, p = 0.94) Europe. In conclusion, in our meta-analysis, the reduced risk of T2D in Ala12 carriers is not homogeneous. It is greater in Asia than in Europe and, among Europeans, it is higher in Northern Europe, barely significant in Central Europe, and nonexistent in Southern Europe.

Genetics of leptin and obesity: a HuGE review

Leptin is an important regulator of the mass of adipose tissue and of body weight; it operates by inhibiting food intake and stimulating energy expenditure. Some polymorphic genes involved in the regulation of leptin-the leptin gene (LEP A19G), the leptin receptor gene (LEPR Q223R, K109R, and K656N), and the peroxisome proliferator-activated receptor-gamma gene (PPARG P12A and C161T)--have been investigated as possible factors associated with obesity. Allelic frequencies of these polymorphisms show ethnic variation. The authors performed a meta-analysis of the available data on the association between these polymorphisms and obesity based on case-control studies. Odds ratios and 95% confidence intervals for obesity associated with leptin polymorphisms were calculated by using both fixed- and random-effects models. Results suggest no evidence of association between the genes under study and obesity. The lack of association could be due to the complex pathogenesis of obesity, which involves a number of genetic and environmental factors. Large studies including testing of multiple genes in both obese and lean subjects, with epidemiologic data on dietary habits in different ethnic groups, are necessary to better understand the role of leptin in regulating weight in human populations.

Peroxisome proliferator-activated receptor-gamma calls for activation in moderation: lessons from genetics and pharmacology

The peroxisome proliferator-activated receptor gamma (PPARgamma) is a prototypical member of the nuclear receptor superfamily and integrates the control of energy, lipid, and glucose homeostasis. PPARgamma can bind a variety of small lipophilic compounds derived from metabolism and nutrition. These ligands, in turn, determine cofactor recruitment to PPARgamma, regulating the transcription of genes in a variety of metabolic pathways. PPARgamma is the main target of the thiazolidinedione class of insulin-sensitizing drugs, which are currently a mainstay of therapy for type 2 diabetes. However, this therapy has a number of side effects. Here, we review the clinical consequences of PPARgamma polymorphisms in humans, as well as several studies in mice using general or tissue-specific knockout techniques. We also discuss the recent pharmacological literature describing a variety of new PPARgamma partial agonists and antagonists, as well as pan-PPAR agonists. The results of these studies have added to the understanding of PPARgamma function, allowing us to hypothesize a general mechanism of PPARgamma action and speculate on future trends in the use of PPARgamma as a target in the treatment of type II diabetes.

Are phospholipid-binding antibodies implicated in the pathogenesis of diabetic microangiopathy?

Diabetic retinopathy (DR) is a major cause of blindness in the working population of the Western world and there is no doubt that its prevalence is strongly related to the duration of diabetes and the glycemic control. However, although intensive diabetes management, with the goal of achieving near-normal glycemia, has been shown to prevent and/or delay the onset of DR, there is now ample of evidence that the development of this microangiopathy is a multifactorial process in which genetic, metabolic, haemostatic and growth factors play an important role. Moreover, given the suggestions that immunological mechanisms might have a role in the pathogenesis of diabetic microangiopathy via immune complex deposition, it has been hypothesized that antiphospholipid antibodies (A-Ab) directed against endothelial antigens could be responsible for initiating vascular injury. In particular, not only A-Ab production was found to be increased in patients with overt nephropathy or macroangiopathy but also Lupus Anticoagulant positivity, representing an intersection point between immune and haemostatic alterations, has been highlighted as a potential and additional risk factor in the pathogenesis of microangiopathy in type 1 diabetics. Moreover, given the high levels of activated protein C, endothelin-1 and thrombo-modulin that have been observed in normo-albuminuric and uncomplicated patients, it has been concluded that the vascular endothelium shifts pathologically from an antithrombotic to a prothrombotic state even in the early phases of the disease. This condition was found to be more pronounced in subjects with anticardiolipin positivity and/or high circulating immune complexes concentrations, since they possess the ability not only to induce platelet activation and aggregation but also to activate the complement system via the classical pathway. Therefore, a potential synergism between generation of autoantibodies, haemostatic alterations and endothelial stress has been suggested, a stimulating hypothesis that needs further studies to be clarified in its complexity.