Adipose tissue-specific PPARgamma deficiency increases resistance to oxidative stress

The impact of PPARγ and ApoE gene polymorphisms on susceptibility to diabetic kidney disease in type 2 diabetes mellitus: a meta-analysis

BACKGROUND

Globally, diabetic kidney disease (DKD) has become the leading cause of end-stage renal disease, imposing substantial social and economic costs. This meta-analysis was designed to provide valuable insights into gene-disease interactions by investigating the potential association between lipid metabolism gene polymorphisms and the risk of DKD.

METHODS

An electronic literature search was conducted on MEDLINE Complete, Web of Science, Embase, and PubMed. A total of 18 studies on the peroxisome proliferator-activated receptor γ (PPARγ) Pro12Ala variant and 20 publications concerning apolipoprotein E (ApoE) gene polymorphism were included in the meta-analysis.

RESULTS

Overall, the PPARγ Pro12Ala polymorphism was found to be significantly associated with a decreased DKD risk (OR = 0.74, 95% CI: 0.62-0.88). In subgroup analysis, Ala carriers were less susceptible to DKD than Pro homozygotes among Asian (OR = 0.73, 95% CI: 0.56-0.95) and Caucasian populations (OR = 0.74, 95% CI: 0.59-0.93). Subgroup analysis stratified by albuminuria categories showed that the PPARγ Pro12Ala polymorphism reduced the risk of both microalbuminuria and macroalbuminuria with corresponding ORs of 0.58 (95% CI: 0.43-0.78) and 0.68 (95% CI: 0.53-0.86). Sensitivity analysis confirmed the robustness of the meta-analysis results. However, publication bias was identified in the subgroup analysis of the Caucasian population. The primary analysis of the ApoE gene polymorphism yielded significant findings, indicating that ApoE ε2/ε2, ApoE ε2/ε3, and ApoE ε2/ε4 genotypes increase the risk of DKD (ε2/ε2 vs. ε3/ε3: OR = 1.93, 95% CI: 1.03-3.61; ε2/ε3 vs. ε3/ε3: OR = 1.63, 95% CI: 1.19-2.25; ε2/ε4 vs. ε3/ε3: OR = 1.87, 95% CI: 1.37-2.55). However, sensitivity analysis suggested that influential and Hardy-Weinberg equilibrium (HWE)-violating studies may impact the overall effect estimates.

CONCLUSIONS

A meta-analysis showed that PPARγ gene polymorphism may be a protective factor for DKD, whereas the ApoE ε2/ε2, ApoE ε2/ε3, and ApoE ε2/ε4 genotypes are associated with an increased risk of DKD. However, the role of ApoE gene polymorphism in susceptibility to DKD is less certain and requires further evaluation.

Adipose tissue homeostasis orchestrates the oxidative, energetic, metabolic and endocrine disruption induced by binge drinking in adolescent rats

Binge drinking (BD) is the most common alcohol consumption model for adolescents, and has recently been related to the generation of high oxidation and insulin resistance (IR). White adipose tissue (WAT) is a target organ for insulin action that regulates whole-body metabolism by secreting adipokines. The present study aimed to analyse the oxidative, inflammatory, energetic and endocrine profile in the WAT of BD-exposed adolescent rats, to obtain an integrative view of insulin secretion and WAT in IR progression. Two groups of male adolescent rats were used: control (n = 8) and BD (n = 8). An intermittent i.p. BD model (20% v/v) was used during 3 consecutive weeks. BD exposure led to a pancreatic oxidative imbalance, which was joint to high insulin secretion by augmenting deacetylase sirtuin-1 (SIRT-1) pancreatic expression and serum adipsin levels. However, BD rats had hyperglycaemia and high homeostasis model assessment of insulin resistance value (HOMA-IR). BD exposure in WAT increased lipid oxidation, as well as decreased insulin receptor substrate 1 (IRS-1) and AKT expression, sterol regulatory element-binding protein 1 (SREBP1), forkhead box O3A (FOXO3a) and peroxisome proliferator-activated receptor γ (PPARγ), and adipocyte size. BD also affected the expression of proteins related to energy balance, such as SIRT-1 and AMP activated protein kinase (AMPK), affecting the adipokine secretion profile (increasing resistin/adiponectin ratio). BD altered the entire serum lipid profile, increasing the concentration of free fatty acids. In conclusion, BD led to an oxidative imbalance and IR process in WAT, which modified the energy balance in this tissue, decreasing the WAT lipogenic/lipolytic ratio, affecting adipokine secretion and the systemic lipid profile, and contributing to the progression of IR. Therefore, WAT is key in the generation of metabolic and endocrine disruption after BD exposure during adolescence in rats. KEY POINTS: Adolescent rat binge drinking (BD) exposure leads to hepatic and systemic oxidative stress (OS) via reactive oxygen species generation, causing hepatic insulin resistance (IR) and altered energy metabolism. In the present study, BD exposure in adolescent rats induces OS in the pancreas, with increased insulin secretion despite hyperglycaemia, indicating a role for IR in white adipose tissue (WAT) homeostasis. In WAT, BD produces IR and an oxidative and energetic imbalance, triggering an intense lipolysis where the serum lipid profile is altered and free fatty acids are increased, consistent with liver lipid accumulation and steatosis. BD exposure heightens inflammation in WAT, elevating pro-inflammatory and reducing anti-inflammatory adipokines, favouring cardiovascular damage. This research provides a comprehensive view of how adolescent BD in rats impacts liver, WAT and pancreas homeostasis, posing a risk for future cardiometabolic complications in adulthood.

Effect of Pesticides on Peroxisome Proliferator-Activated Receptors (PPARs) and Their Association with Obesity and Diabetes

Obesity and diabetes mellitus are considered the most important diseases of the XXI century. Recently, many epidemiological studies have linked exposure to pesticides to the development of obesity and type 2 diabetes mellitus. The role of pesticides and their possible influence on the development of these diseases was investigated by examining the relationship between these compounds and one of the major nuclear receptor families controlling lipid and carbohydrate metabolism: the peroxisome proliferator-activated receptors (PPARs), PPARα, PPARβ/δ, and PPARγ; this was possible through in silico, in vitro, and in vivo assays. The present review aims to show the effect of pesticides on PPARs and their contribution to the changes in energy metabolism that enable the development of obesity and type 2 diabetes mellitus.

Capsaicin ameliorates diabetic retinopathy by inhibiting poldip2-induced oxidative stress

Background

Oxidative stress and the resultant hyperpermeability play a vital role in the pathogenesis of diabetic retinopathy (DR). Poldip2 has been implicated in H₂O₂ production, but the effects of capsaicin on poldip2 have not been reported.

Methods

Diabetic Sprague-Dawley (SD) rats induced with STZ were treated with capsaicin or AAV₉-poldip2-shRNA, and human retinal microvascular endothelial cells (HRMECs) were treated with capsaicin or poldip2 siRNA.

Results

Current data indicated that the expression of PPARγ, poldip2, Nox4, VCAM-1, HIF-1α, and VEGF increased in rat retinas with DR and in HRMECs treated with high glucose. The production of ROS or H₂O₂ in the tissues, serum, and cells increased, and the paracellular permeability of cultured HRMECs with high glucose significantly increased. In addition, overt hyperpermeability of retinal microvessels and increased retinal neovascularization in diabetic rats were observed. However, capsaicin treatment inhibited these increases and suppressed the expression of PPARγ by enhancing its phosphorylation and ubiquitination in the retinas of DR rats. Poldip2 knockdown in HRMECs or its silencing in the retina of DR rats concomitantly led to reduced levels of Nox4, VCAM-1, HIF-1α, VEGF, ROS, and H₂O₂, and the paracellular permeability of HRMECs or the hyperpermeability of retinal microvessels in diabetic rat retinas decreased. Similarly, after PPARγ knockdown in HRMECs, poldip2, Nox4, HIF-1α, VEGF, ROS, and H₂O₂ decreased, and the monolayer paracellular permeability was reduced accordingly.

Conclusion

Capsaicin may ameliorate diabetic retinopathy by activating TRPV1 and suppressing the PPARγ-poldip2-Nox4 pathway.

Different Effects of Low Selenite and Selenium-Nanoparticle Supplementation on Adipose Tissue Function and Insulin Secretion in Adolescent Male Rats

Adolescence is a period of intense growth and endocrine changes, and obesity and insulin-resistance processes during this period have lately been rising. Selenium (Se) homeostasis is related to lipid metabolism depending on the form and dose of Se. This study tests the actions of low-dose selenite and Se nanoparticles (SeNPs) on white (WAT) and brown adipose tissue (BAT) deposition, insulin secretion, and GPx1, IRS-1 and FOXO3a expression in the WAT of adolescent rats as regards oxidative stress, adipocyte length and adipokine secretion. Four groups of male adolescent rats were treated: control (C), low selenite supplementation (S), low SeNP supplementation (NS) and moderate SeNP supplementation (NSS). Supplementation was received orally through water intake; NS and NSS rats received two- and tenfold more Se than C animals, respectively. SeNPs were obtained by reducing Se tetrachloride in the presence of ascorbic acid. For the first time in vivo, it was demonstrated that low selenite supplementation contributed to increased adipogenesis via the insulin signaling pathway and LCN2 modulation, while low SeNP administration prevented fat depots in WAT via the decrease in insulin signaling and FOXO3a autophagy in WAT, lowering inflammation. These effects were independent of GPx1 expression or activity in WAT. These findings provide data for dietary approaches to prevent obesity and/or anorexia during adolescence. These findings may be relevant to future studies looking at a nutritional approach aimed at pre-venting obesity and/or anorexia in adolescence.

A Brief Overview of Oxidative Stress in Adipose Tissue with a Therapeutic Approach to Taking Antioxidant Supplements

One of the leading causes of obesity associated with oxidative stress (OS) is excessive consumption of nutrients, especially fast-foods, and a sedentary lifestyle, characterized by the ample accumulation of lipid in adipose tissue (AT). When the body needs energy, the lipid is broken down into glycerol (G) and free fatty acids (FFA) during the lipolysis process and transferred to various tissues in the body. Materials secreted from AT, especially adipocytokines (interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α)) and reactive oxygen species (ROS), are impressive in causing inflammation and OS of AT. There are several ways to improve obesity, but researchers have highly regarded the use of antioxidant supplements due to their neutralizing properties in removing ROS. In this review, we have examined the AT response to OS to antioxidant supplements focusing on animal studies. The results are inconsistent due to differences in the study duration and diversity in animals (strain, age, and sex). Therefore, there is a need for different studies, especially in humans.

PPARγ gene Pro12Ala variants reduce the risk of obese individuals to non-alcoholic fatty liver: A study in Uygur Chinese population residing in Northwestern China

OBJECTIVE

To investigate the association of polymorphisms of Pro12Ala of peroxisome proliferator-activated receptor gamma (PPARγ) gene with clinical and biochemical parameters in Uygur Chinese population with non-alcoholic fatty liver (NAFLD) METHODS: In this case-control study, we recruited 467 NAFLD cases and 524 controls. Examination of abdominal ultrasound, clinical and biochemical profiles, as well as polymerase chain reaction-restriction fragment length polymorphisms of Pro12Ala of PPARγ gene were performed. The association of PPARγ gene Pro12Ala variants with clinical and biochemical parameters was analyzed.

RESULTS

There was no statistically significant difference between NAFLD and control groups in the frequencies of genotypic and allele distribution (P>0.05), while significantly difference of genotypic (P=0.032) and allele (P=0.015) distribution was found between NAFLD and control groups in the obese. Using logistics multivariate regression analysis by adjusting age, sex, body mass index, diabetes, hyperuricemia and dyslipidemia, both Pro12Ala and Ala12Ala polymorphisms were not associated with the presence of NAFLD. However, above two polymorphisms were found to be related to NAFLD in obesity group (odds ratio=0.442, P=0.031 and odds ratio=0.039, P=0.010, respectively) CONCLUSION: In Uygur Chinese population, PPARr gene Ala variants reduce the risk of NAFLD in obese individuals.

No Association Between a Genetic Variant of FOXO3 and Risk of Type 2 Diabetes Mellitus in the Elderly Population of North India

Aging can be considered an evolutionary process that is modulated by various genetic and biochemical processes. Therefore the genetic variants may interplay a role in human longevity as well as age related illness. Forkhead Box O (FOXO) gene is one of the major defensive genes that are known for ameliorating lifespan. FOXO proteins act as nuclear transcription factors that facilitate the action of insulin or insulin-like growth factor (IGF-1) in various physiological processes. The rationale of our study is to find out association between genetic variant rs2253310 of FOXO3 and risk of Type 2 Diabetes Mellitus (T2DM) in elderly population. This case control study involved 172 age sex matched elderly subjects while patients were recruited as per IDF criteria. Clinical, biochemical, ELISA methods were employed for assesement of clinical samples while Taqman method was used for genotyping analysis. Our results revealed that there was no significant difference in genotypic and allelic frequencies for the tested SNP (p > 0.05) between elderly T2DM patients and controls. The SNP rs2253310 was not associated with risk of T2DM in any genetic model. Also no association was found among the studied group between FOXO3 variant and HOMA-IR, HOMA-B index and Fasting plasma glucose. Serum level of inflammatory markers like CRP and TNF-α was significantly higher in patients but its not associated with SNP rs2253310. Our study concluded that, this intronic longevity-associated variant rs2253310 in FOXO3 is not associated with type 2 diabetes in geriatric patients of northern India.

Selenium and Selenoproteins in Adipose Tissue Physiology and Obesity

Selenium (Se) homeostasis is tightly related to carbohydrate and lipid metabolism, but its possible roles in obesity development and in adipocyte metabolism are unclear. The objective of the present study is to review the current data on Se status in obesity and to discuss the interference between Se and selenoprotein metabolism in adipocyte physiology and obesity pathogenesis. The overview and meta-analysis of the studies on blood Se and selenoprotein P (SELENOP) levels, as well as glutathione peroxidase (GPX) activity in obese subjects, have yielded heterogenous and even conflicting results. Laboratory studies demonstrate that Se may modulate preadipocyte proliferation and adipogenic differentiation, and also interfere with insulin signaling, and regulate lipolysis. Knockout models have demonstrated that the selenoprotein machinery, including endoplasmic reticulum-resident selenoproteins together with GPXs and thioredoxin reductases (TXNRDs), are tightly related to adipocyte development and functioning. In conclusion, Se and selenoproteins appear to play an essential role in adipose tissue physiology, although human data are inconsistent. Taken together, these findings do not support the utility of Se supplementation to prevent or alleviate obesity in humans. Further human and laboratory studies are required to elucidate associations between Se metabolism and obesity.

Longevity-Associated Forkhead Box O3 (FOXO3) Single Nucleotide Polymorphisms are Associated with Type 2 Diabetes Mellitus in Chinese Elderly Women

Background

This study aimed to investigate the association of single nucleotide polymorphisms (SNPs) of Forkhead box O3 (FOXO3) gene with type 2 diabetes mellitus (T2D).

Material/Methods

A total of 843 elderly residents from east China were enrolled in this study, which included 426 patients with type 2 diabetes and 417 controls. Four SNPs were analyzed by qPCR. Genotype frequencies of the 4 SNPs in FOXO3 of the patients and controls were analyzed using logistic regression analysis. The association between each SNP and clinical indicators was analyzed by linear regression analysis.

Results

None of the 4 FOXO3 variants, rs13217795, rs2764264, rs2802292, and rs13220810, were associated with the risk of type 2 diabetes compared to controls. However, rs13217795, rs2764264, and rs2802292 were associated with lower blood glucose levels. Notably, further subgroup analysis indicated that the longevity-associated alleles of FOXO3 SNP (rs13217795, rs2764264, and rs2802292) were associated with lower blood glucose levels in women (TC versus TT, −0.724 mmol/L, P=0.005; CC versus TT, −1.093 mmol/L, P=0.03; TC versus TT, −0.801 mmol/L, P=0.002; CC versus TT, −1.212 mmol/L, P=0.001; TG versus TT, −0.754 mmol/L, P=0.004; and GG versus TT, −1.150 mmol/L, P=0.001) but not in men.

Conclusions

The results indicated that longevity-associated FOXO3 variants were correlated with lower blood glucose levels in elderly women with type 2 diabetes in east China.

Altered levels of sirtuin genes (SIRT1, SIRT2, SIRT3 and SIRT6) and their target genes in adipose tissue from individual with obesity

INTRODUCTION

Sirtuins regulate energy metabolism and insulin sensitivity through their ability to act as energy sensors and regulators in several metabolic tissues.

AIM

To evaluate the expression levels of sirtuin genes SIRT1, SIRT2, SIRT3 and SIRT6 and their target genes (PPAR-α, PGC1-α, NRF1, DGAT1, PPAR-γ and FOXO3a) in subcutaneous adipose tissue collected from individuals with normoweight, overweight and obesity.

METHODS

Adipose tissue samples, obtained by lipoaspiration during liposuction surgery, were processed to obtain RNA, which was reverse-transcribed to cDNA. Then, we measured the expression levels of each gene by qPCR.

RESULTS

We found differences in the mRNA expression of SIRT1, SIRT2, SIRT3 and SIRT6 and their target genes (PPAR-α, PGC1-α, NRF1, DGAT1, PPAR-γ and FOXO3a) in adipose tissue from overweight or obese subjects when compared to normoweight subjects. All genes analyzed, except SIRT2, showed correlation with BMI.

CONCLUSIONS

Our findings in human subcutaneous adipose tissue show that increased body mass index modifies the expression of genes encoding sirtuins and their target genes, which are metabolic regulators of adipose tissue. Therefore, these could be used as biomarkers to predict the ability of adipose tissue to gain mass of adipose tissue.

Acupuncture does not ameliorate metabolic disturbances in the P450 aromatase inhibitor-induced rat model of polycystic ovary syndrome

NEW FINDINGS

What is the central question of this study? The effectiveness of low-frequency electroacupuncture in the treatment of metabolic disorders associated with polycystic ovary syndrome (PCOS), an endocrine-metabolic disorder characterized by an imbalance in sex steroid production, is controversial. What is the main finding and its importance? In a rat model of PCOS induced by the inhibition of P450 aromatase, low-frequency electroacupuncture increased low-density lipoprotein-cholesterol but did not improve the insulin resistance or the adipose tissue dysfunction, suggesting that a balance of sex steroids is needed to restore the metabolic function in this rat model of PCOS. Low-frequency electroacupuncture restores sex steroid synthesis and sympathetic activity in women with polycystic ovary syndrome, which may ameliorate its metabolic disturbances, probably by modulating sympathetic nerve activity or sex steroid synthesis. We investigated whether low-frequency electroacupuncture regulates the metabolic function to the same extent as treatment with estradiol or β-adrenergic blocking in a rat model of polycystic ovary syndrome induced by a P450 aromatase inhibitor (letrozole). Letrozole (200 μg day^-1 ) or placebo pellets were implanted in prepubertal Wistar rats. Six weeks thereafter, rats were treated for 5-6 weeks with the following: low-frequency electroacupuncture (5 days per week); a β-adrenergic blocker (propranolol hydrochloride, 0.1 mg kg^-1 , 5 days per week); or 17β-estradiol (2.0 μg) every fourth day. Body weight development, body composition, locomotor activity, insulin sensitivity, tissue-specific glucose uptake, lipid profile, adipocyte size, serum concentrations of adiponectin and insulin, and gene expression in inguinal fat were measured. All treatments increased circulating levels of low-density lipoprotein-cholesterol. Estradiol treatment restored locomotor activity and increased insulin sensitivity but did not modify the glucose uptake in muscle and fat. An upregulation of genes related to insulin sensitivity and downregulation of genes related to adipogenesis were observed in subcutaneous adipose tissue from rats exposed to letrozole. Only estradiol treatment normalized the expression of these genes. In conclusion, low-frequency electroacupuncture increased low-density lipoprotein-cholesterol without affecting insulin sensitivity or adipose tissue function, which could suggest effects on hepatic lipid regulation, probably mediated by the action of estradiol or the β-adrenergic pathway.

Stem cell death and survival in heart regeneration and repair

Cardiovascular diseases are major causes of mortality and morbidity. Cardiomyocyte apoptosis disrupts cardiac function and leads to cardiac decompensation and terminal heart failure. Delineating the regulatory signaling pathways that orchestrate cell survival in the heart has significant therapeutic implications. Cardiac tissue has limited capacity to regenerate and repair. Stem cell therapy is a successful approach for repairing and regenerating ischemic cardiac tissue; however, transplanted cells display very high death percentage, a problem that affects success of tissue regeneration. Stem cells display multipotency or pluripotency and undergo self-renewal, however these events are negatively influenced by upregulation of cell death machinery that induces the significant decrease in survival and differentiation signals upon cardiovascular injury. While efforts to identify cell types and molecular pathways that promote cardiac tissue regeneration have been productive, studies that focus on blocking the extensive cell death after transplantation are limited. The control of cell death includes multiple networks rather than one crucial pathway, which underlies the challenge of identifying the interaction between various cellular and biochemical components. This review is aimed at exploiting the molecular mechanisms by which stem cells resist death signals to develop into mature and healthy cardiac cells. Specifically, we focus on a number of factors that control death and survival of stem cells upon transplantation and ultimately affect cardiac regeneration. We also discuss potential survival enhancing strategies and how they could be meaningful in the design of targeted therapies that improve cardiac function.

The PPARγ2 Pro12Ala variant is protective against progression of nephropathy in people with type 2 diabetes

Objective

Cross-sectional studies suggest the association between diabetic nephropathy and the PPARγ2 Pro12Ala polymorphism of the peroxisome proliferator-activated receptor γ2 (PPARγ2). Prospective data are limited to microalbuminuria and no information on renal function is available to date. The present study evaluates the association between the Pro12Ala polymorphism of PPARγ2 and the progression of albuminuria and decay in glomerular filtration rate (GFR) in type 2 diabetes.

Patients and measurements

We studied 256 patients with an average 5-year follow-up. Among others, urinary albumin excretion rate (UAER) was measured on spot sample, GFR was estimated with the CKD-EPI Equation.

Results

Baseline UAER and GFR were similar for carriers or non-carriers of the polymorphism. At follow-up no significant changes from baseline were observed for UAER or eGFR in carriers of the Pro12Ala polymorphism whereas a significant increase in UAER [17 (11.3-37.9) versus 24.5 (13.8-49.9) μg/mg, p < 0.006)] and a significant reduction in the eGFR (82.8 ± 14.5 versus 80.3 ± 17.3 ml/min/1.73, m² p = 0.02), were observed in non carriers of the Pro12Ala polymorphism. Progression of nephropathy - defined according to a combined end point of UAER and eGFR- i.e. doubling of baseline UAER to at least 100 μg/mg, or new onset microalbuminuria, or progression from micro to macroalbuminuria, or 25% reduction of eGFR, or annualized eGFR decline >3 ml/min/year - was significantly less frequent in Ala carriers than non carriers (11.4% vs 35.8%; p < 0.01); HR adjusted for baseline age, AER, eGFR, HbA1c, diabetes duration and blood pressure was 0.32 (0.12-0.80).

Conclusions

This study found that among patients with type 2 diabetes, the PPARγ2 Pro12Ala polymorphism is protective against progression of nephropathy and decay of renal function independent of major confounders.

Pro12Ala polymorphism of the PPARγ2 gene interacts with a mediterranean diet to prevent telomere shortening in the PREDIMED-NAVARRA randomized trial

BACKGROUND

The gene variant Pro/Ala (rs1801282) in the PPARγ2 has been associated with lower cardiovascular risk and greater benefit from lifestyle interventions. This polymorphism also seems to be associated with longer lifespan, but no information on telomere length (TL) is available. Our aim was to study the association between the Ala allele and changes in TL in high cardiovascular risk subjects and the potential interaction with a Mediterranean dietary pattern.

METHODS AND RESULTS

A total of 521 subjects (55-80 years) participating in the Prevención con Dieta Mediterránea randomized trial were genotyped. Changes in TL, measured by quantitative real-time polymerase chain reaction (PCR), were assessed over 5 years of a nutritional intervention, which promoted adherence to the Mediterranean diet (MeDiet). Interestingly, Ala carriers showed lower telomere shortening after 5 years compared with the Pro/Pro genotype (P=0.031). This association was modulated by MeDiet because those Ala carriers who reported better conformity to the MeDiet exhibited increased TL (P<0.001). Moreover, a reduction in carbohydrate intake (≤9.5 g/d) resulted in increased TL among Ala carriers. Notably, an apparent gene-diet interaction was found through the observed changes in the MUFA+PUFA/carbohydrates ratio: as this ratio increased, TL lengthening was detected to a greater extent in the Ala carriers compared with the Pro/Pro subjects (P for interaction <0.001).

CONCLUSIONS

The Pro12Ala polymorphism is associated with TL homeostasis after 5 years follow-up in subjects at high cardiovascular risk. In addition, a higher adherence to the MeDiet pattern strengthens the prevention of telomere shortening among Ala carriers.

CLINICAL TRIAL REGISTRATION

www.controlled-trials.com; Unique Identifier: ISRCTN35739639.

Meta-analysis of associations between the peroxisome proliferator-activated receptor-γ Pro12Ala polymorphism and susceptibility to nonalcoholic fatty liver disease, rheumatoid arthritis, and psoriatic arthritis

INTRODUCTION

The purpose of this study was to examine whether a Proline (Pro)-to-Alanine (Ala) exchange at codon 12 (Pro12Ala) polymorphism of the peroxisome proliferator-activated receptor-gamma (PPARγ) is associated with susceptibility to nonalcoholic fatty liver disease (NAFLD), rheumatoid arthritis (RA), and psoriatic arthritis (PsA).

METHODS

A meta-analysis was conducted on the association between the PPARγ Pro12Ala polymorphism and NAFLD, RA, and PsA.

RESULTS

Nine studies, including five on NAFLD, two on RA, and two on PsA, were available for the meta-analysis consisting of 8082 cases and 3790 controls. The meta-analysis revealed no association between the Ala allele of the PPARγ Pro12Ala polymorphism and NAFLD (odds ratios [OR]=0.936, 95% confidence interval [CI]=0.672-1.302, p=0.693). However, stratification by ethnicity indicated an association between the Ala allele and NAFLD in East Asians (OR=0.700, 95% CI=0.496-0.987, p=0.042), but not in Europeans (OR=1.128, 95% CI=0.863-1.475, p=0.378). Analysis using the dominant model showed the same Ala allele pattern in East Asians and Europeans (OR=0.688, 95% CI=0.484-0.978, p=0.037; OR=1.051, 95% CI=0.782-1.413, p=0.742), demonstrating a significant association between the Ala allele and NAFLD in East Asians. The meta-analysis revealed no association between the Ala allele and RA in East Asians (OR=0.467, 95% CI=0.188-1.161, p=0.101), and no association was found between the Ala allele and PsA in Europeans (OR=0.869, 95% CI=0.465-1.627, p=0.662).

CONCLUSIONS

Our meta-analysis demonstrates that the PPARγ Pro12Ala polymorphism is associated with susceptibility to NAFLD in East Asians, but not in European populations.

Genetics of oxidative stress in obesity

Obesity is a multifactorial disease characterized by the excessive accumulation of fat in adipose tissue and peripheral organs. Its derived metabolic complications are mediated by the associated oxidative stress, inflammation and hypoxia. Oxidative stress is due to the excessive production of reactive oxygen species or diminished antioxidant defenses. Genetic variants, such as single nucleotide polymorphisms in antioxidant defense system genes, could alter the efficacy of these enzymes and, ultimately, the risk of obesity; thus, studies investigating the role of genetic variations in genes related to oxidative stress could be useful for better understanding the etiology of obesity and its metabolic complications. The lack of existing literature reviews in this field encouraged us to gather the findings from studies focusing on the impact of single nucleotide polymorphisms in antioxidant enzymes, oxidative stress-producing systems and transcription factor genes concerning their association with obesity risk and its phenotypes. In the future, the characterization of these single nucleotide polymorphisms (SNPs) in obese patients could contribute to the development of controlled antioxidant therapies potentially beneficial for the treatment of obesity-derived metabolic complications.

Immunometabolism in obese asthmatics: are we there yet?

Obesity is now recognised as a worldwide epidemic. The recent International Association for the Study of Obesity/International Obesity Taskforce (IASO/IOTF) analysis estimates that approximately 1.0 billion adults are currently overweight and a further 475 million are obese. Obesity has huge psychosocial impact with obese children and adolescents facing discrimination and stigmatization in many areas of their lives leading to body dissatisfaction, low self-esteem and depression. Indeed, obesity is recognised as an important risk factor for the development of several chronic diseases such as hypertension, cancer, asthma and metabolic syndrome. Chronic low grade systemic inflammation is considered as a hallmark of obesity and may possibly explain the link between obesity and chronic disease, in particular the increased incidence, prevalence and severity of asthma in obese individuals. There is now strong evidence for infiltration of immune and inflammatory cells into adipose tissue that drives systemic inflammation and subsequent end organ damage. In addition to adipocytes, the key adipose tissue resident immune cells are macrophages and mast cells. Immunometabolism, as an emerging field of investigation, explores the pivotal role of these immune cells in translating immunological changes to metabolic effects in obesity. Abundance of free fatty acids, along with other inflammatory cytokines shift the balance of metabolic homeostasis to pro-inflammatory status by influencing the development of inflammatory cell lineage, which, further exhibits distinct functional phenotypes. There is emerging evidence for macrophage activation and functional polarization of an anti-inflammatory M₂ phenotype towards a pro-inflammatory M₁ phenotype of macrophages in obese adipose tissue. Similarly, studies in both obese humans and murine models reveal the pathognomic presence of an increased number of mast cells in visceral adipose tissue. These suggest a possible contribution of mast cells to the unique metabolome of obese asthma. This review examines proposed multilevel interactions between metabolic and immune systems in obese asthmatics that underlie the negative effects of obesity and may offer significant therapeutic promise.

Long-term muscle-derived cell culture: multipotency and susceptibility to cell death stimuli

Improvement in the yield of adult organism stem cells, and the ability to manage their differentiation and survival potential are the major goals in their application in regenerative medicine and in the adult stem cell research. We have demonstrated that adult rabbit muscle-derived cell lines with an unlimited proliferative potential in vitro can differentiate into myogenic, osteogenic, adipogenic and neurogenic lineages. Studies of cell survival in vitro showed that differentiated cells, except neurogenic ones, are more resistant to apoptosis inducers compared to proliferating cells. Resistance to death signals correlated with the level of protein kinase AKT phosphorylation. Skeletal muscle-derived cell lines can be multipurpose tools in therapy. Enhanced resistance of differentiated cells to certain types of damage shows their potential for long-term survival and maintenance in an organism. This article was published online on 29 January 2013. An error was subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected 6 March 2013.

Carbonic anhydrase III regulates peroxisome proliferator-activated receptor-γ2

Carbonic anhydrase III (CAIII) is an isoenzyme of the CA family. Because of its low specific anhydrase activity, physiological functions in addition to hydrating CO(2) have been proposed. CAIII expression is highly induced in adipogenesis and CAIII is the most abundant protein in adipose tissues. The function of CAIII in both preadipocytes and adipocytes is however unknown. In the present study we demonstrate that adipogenesis is greatly increased in mouse embryonic fibroblasts (MEFs) from CAIII knockout (KO) mice, as demonstrated by a greater than 10-fold increase in the induction of fatty acid-binding protein-4 (FABP4) and increased triglyceride formation in CAIII(-/-) MEFs compared with CAIII(+/+) cells. To address the underlying mechanism, we investigated the expression of the two adipogenic key regulators, peroxisome proliferator-activated receptor-γ2 (PPARγ2) and CCAAT/enhancer binding protein-α. We found a considerable (approximately 1000-fold) increase in the PPARγ2 expression in the CAIII(-/-) MEFs. Furthermore, RNAi-mediated knockdown of endogenous CAIII in NIH 3T3-L1 preadipocytes resulted in a significant increase in the induction of PPARγ2 and FABP4. When both CAIII and PPARγ2 were knocked down, FABP4 was not induced. We conclude that down-regulation of CAIII in preadipocytes enhances adipogenesis and that CAIII is a regulator of adipogenic differentiation which acts at the level of PPARγ2 gene expression.

PPARG gene Pro12Ala variant contributes to the development of non-alcoholic fatty liver in middle-aged and older Chinese population

Oxidative stress has been suggested to contribute to the development of non-alcoholic fatty liver disease (NAFLD). Peroxisome proliferator-activated receptor gamma (PPAR-γ) heterozygous mice and Pro12Ala (C/G) polymorphism in PPARG exhibited increased resistance to oxidative stress. Smoking increases the production of reactive oxygen species, which could accelerates oxidative stress under overnutrition. To explore whether the C/G polymorphism, alone or in combination with smoking, may promote the development of non-alcoholic fatty liver, a case-control study was performed in 903 Chinese subjects. Among the study population, 436 patients with B-mode ultrasound-proven NAFLD (318 with steatosis hepatis I°, 90 with steatosis hepatis II° and 28 with steatosis hepatis III°) and 467 controls were genotyped by using TaqMan allelic discrimination assays. After adjusting for confounders, the C/C genotype significantly associated with NAFLD (OR=1.87, 95%CI 1.13-2.85, p=0.009); smoking was also an independent risk factor for NAFLD (OR=1.69, 95%CI 1.18-2.43, p=0.025). In addition, we found possible synergistic effects, the higher risk group (smokers with the C/C genotype) showed 3.75 times higher risk of NAFLD than the low-risk group (non-smokers with C/G genotype) in a multiple logistic analysis after adjusting for the confounders (p<0.001), but no departure from additivity was found. Our results indicated that the C/C genotype and smoking were significant independent risk factors for NAFLD. The possible synergistic effects of genotype and smoking may promote the development of NAFLD by aggravating oxidative stress, which supports the hypothesis that oxidative stress contributes to the development of NAFLD.

Role of PPARg2 transcription factor in thiazolidinedione-induced insulin sensitization

OBJECTIVES

Adipose tissue is the key regulator of energy balance, playing an active role in lipid storage and metabolism and may be a dynamic buffer to control fatty acid flux. Peroxisome proliferator-activated receptor gamma isoform-2 (PPARg2), an isoform of the nuclear hormone receptor superfamily, has been implicated in almost all aspects of human metabolic alterations such as obesity, insulin resistance, type-2 diabetes and dyslipidaemia. The PPARg2 isoform is highly present in adipose tissue where it functions as a thrifty phenotype, which promotes adipocyte differentiation and triglyceride storage. Thiazolidinediones, antidiabetic drugs, induce insulin sensitivity by controlling adipokines. The thiazolidinediones bind with PPARg2 in adipocytes and exert an agonist effect by enhancing adipogenesis and fatty acid uptake. Thiazolidinediones stimulate PPARg2, by which they down-regulate tumour necrosis factor-α, leptin, interleukin-6 and plasminogen and also enhance insulin sensitivity. The aim of this work is to define role of PPARg2 transcription factor in thiazolidinedione-induced insulin sensitization.

KEY FINDINGS

The PPARg2 alters the transcription of the target gene. This altered gene transcription results in the up-regulation of insulin-sensitizing factors and down-regulation of insulin-resistant factors. The variant Pro12Ala of the PPARg2 gene is an important modulator in metabolic control in the body. Thiazolidinediones stimulate PPARg2 transcription factor by which PPARg2 binds to responsive elements located in the promoter regions of many genes and modulates their transcriptive activity. There is a strong mutual relationship between receptor binding and agonism, which is evidence of the insulin-sensitizing target of thiazolidinediones in PPARg2. This evidently increases the biological potency of the glucose-lowering effect of thiazolidinediones in vivo as well as their antidiabetic activity.

CONCLUSIONS

PPARg2 transcription factor plays an important role in treatment of type-2 diabetes with thiazolidindiones. The variant Pro12Ala of the PPARg2 gene promotes the activity of thiazolidinediones in minimizing insulin resistance. Transcriptional activity of Pro12Ala variant improves the activity of insulin. Thus thiazolidinediones promote the phosphorylation of PPARg2 to induce insulin sensitivity.

Association analysis of common variants in FOXO3 with type 2 diabetes in a South Indian Dravidian population

Recent studies have identified common variants in forkhead box O3 gene (FOXO3) to be strongly associated with longevity in different populations. But studies have not been carried out to analyse the role of common variants in FOXO3 with type 2 diabetes. Since type 2 diabetes is an age related disorder and FOXO proteins play an important role in the regulation of metabolism, we studied the role of common variants in FOXO3 for association with type 2 diabetes. The study was carried out in 994 type 2 diabetic samples and 984 normoglycemic control samples from a South Indian Dravidian population. In our analysis, we found that there was no association between any of the selected SNPs in FOXO3 with type 2 diabetes. Analysis of these SNPs with diabetes related biochemical and clinical parameters also did not reveal any significant association. Haplotype association of SNPs in FOXO3 with type 2 diabetes was observed, but the frequency of the haplotypes was considerably lower and they do not remain significant after correction for multiple testing. In conclusion, we did not observe any association of SNPs in FOXO3 with type 2 diabetes and related parameters suggesting an entirely different mechanism by which these SNPs influence longevity. However additional studies in other populations are required to completely rule out the association of common variants in FOXO3 with type 2 diabetes.

Transcriptional regulatory program in wild-type and retinoblastoma gene-deficient mouse embryonic fibroblasts during adipocyte differentiation

Background

Although many molecular regulators of adipogenesis have been identified a comprehensive catalogue of components is still missing. Recent studies showed that the retinoblastoma protein (pRb) was expressed in the cell cycle and late cellular differentiation phase during adipogenesis. To investigate this dual role of pRb in the early and late stages of adipogenesis we used microarrays to perform a comprehensive systems-level analysis of the common transcriptional program of the classic 3T3-L1 preadipocyte cell line, wild-type mouse embryonic fibroblasts (MEFs), and retinoblastoma gene-deficient MEFs (Rb-/- MEFs).

Findings

Comparative analysis of the expression profiles of 3T3-L1 cells and wild-type MEFs revealed genes involved specifically in early regulation of the adipocyte differentiation as well as secreted factors and signaling molecules regulating the later phase of differentiation. In an attempt to identify transcription factors regulating adipogenesis, bioinformatics analysis of the promoters of coordinately and highly expressed genes was performed. We were able to identify a number of high-confidence target genes for follow-up experimental studies. Additionally, combination of experimental data and computational analyses pinpointed a feedback-loop between Pparg and Foxo1.

To analyze the effects of the retinoblastoma protein at the transcriptional level we chose a perturbated system (Rb-/- MEFs) for comparison to the transcriptional program of wild-type MEFs. Gene ontology analysis of 64 deregulated genes showed that the Rb-/- MEF model exhibits a brown(-like) adipocyte phenotype. Additionally, the analysis results indicate a different or additional role for pRb family member involvement in the lineage commitment.

Conclusion

In this study a number of commonly modulated genes during adipogenesis in 3T3-L1 cells and MEFs, potential transcriptional regulation mechanisms, and differentially regulated targets during adipocyte differentiation of Rb-/- MEFs could be identified. These data and the analysis provide a starting point for further experimental studies to identify target genes for pharmacological intervention and ultimately remodeling of white adipose tissue into brown adipose tissue.

Effect of antioxidant supplementation on insulin sensitivity in response to endurance exercise training

While production of reactive oxygen and nitrogen species (RONS) is associated with some of the beneficial adaptations to regular physical exercise, it is not established whether RONS play a role in the improved insulin-stimulated glucose uptake in skeletal muscle obtained by endurance training. To assess the effect of antioxidant supplementation during endurance training on insulin-stimulated glucose uptake, 21 young healthy (age 29 ± 1 y, BMI 25 ± 3 kg/m(2)) men were randomly assigned to either an antioxidant [AO; 500 mg vitamin C and 400 IU vitamin E (α-tocopherol) daily] or a placebo (PL) group that both underwent a supervised intense endurance-training program 5 times/wk for 12 wk. A 3-h euglycemic-hyperinsulinemic clamp, a maximal oxygen consumption (Vo(2max)) and maximal power output (P(max)) test, and body composition measurements (fat mass, fat-free mass) were performed before and after the training. Muscle biopsies were obtained for determination of the concentration and activity of proteins regulating glucose metabolism. Although plasma levels of vitamin C (P < 0.05) and α-tocopherol (P < 0.05) increased markedly in the AO group, insulin-stimulated glucose uptake increased similarly in both the AO (17.2%, P < 0.05) and the PL (18.9%, P < 0.05) group in response to training. Vo(2max) and P(max) also increased similarly in both groups (time effect, P < 0.0001 for both) as well as protein content of GLUT4, hexokinase II, and total Akt (time effect, P ≤ 0.05 for all). Our results indicate that administration of antioxidants during strenuous endurance training has no effect on the training-induced increase in insulin sensitivity in healthy individuals.

Pro12Ala polymorphism in the PPARG gene contributes to the development of diabetic nephropathy in Chinese type 2 diabetic patients

OBJECTIVE

Oxidative stress is a major contributing factor in the development of diabetic nephropathy. Peroxisome proliferator-activated receptor gamma heterozygous mice and Pro12Ala polymorphism in PPARG exhibited increased resistance to oxidative stress. Smoking increases the production of reactive oxygen species, which accelerates oxidative stress under hyperglycemia. To determine whether the Pro12Ala polymorphism, alone or in combination with smoking, contributes to the development of diabetic nephropathy, a case-control study was performed in 760 Chinese patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Among patients, 532 had diabetic nephropathy with microalbuminuria (n = 245) or overt albuminuria (n = 287), and 228 did not show either of these symptoms but had had diabetes for > or =10 years and were not undergoing anti-hypertension treatment.

RESULTS

After adjustment for confounders, the Pro/Pro genotype was significantly associated with diabetic nephropathy (odds ratio 2.30 [95% CI 1.18-4.45], P = 0.014); smoking was also an independent risk factor for diabetic nephropathy (1.99 [1.08-3.68], P = 0.029). In addition, we identified possible synergistic effects; i.e., the high-risk group (smokers with the Pro/Pro genotype) showed 4.52 times higher risk (1.78-11.48, P = 0.002) of diabetic nephropathy than the low-risk group (nonsmokers with the Pro/Ala genotype) in a multiple logistic regression analysis controlled for the confounders.

CONCLUSIONS

Our results indicated that the Pro/Pro genotype and smoking were significant independent risk factors for diabetic nephropathy. The possible synergistic effects of genotype and smoking may aggravate oxidative stress and contribute to the development of diabetic nephropathy.

Transcriptomic analysis identifies Foxo3A as a novel transcription factor regulating mesenchymal stem cell chrondrogenic differentiation

Multipotent mesenchymal stromal cells (MSC) are progenitor cells able to differentiate into several lineages including chondrocytes, and thus represent a suitable source of cells for cartilage engineering. However, the control of MSC differentiation to hypertrophy is a crucial step for the clinical application of MSC in cartilage repair where a stable chondrogenic phenotype without transition to terminal differentiation is the goal to achieve. This study aims at identifying new factors that may regulate this process. Using microarrays, we compared the transcriptional profiles of human MSC and MSC-derived chondrocytes obtained after culture in micropellets. After chondrogenesis induction, 676 genes were upregulated, among which five transcription factors not yet associated with chondrocyte differentiation of adult stem cells. These factors, in particular Foxo3A, are strongly expressed at day 21 and in mature chondrocytes. We investigated the role of Foxo3A using RNA interference. Our results revealed an important role of Foxo3A in the differentiation process of MSC toward chondrogenic fate, both in early and late stages. Indeed, stable Foxo3A knockdown tends to increase cell survival and decrease apoptosis, mainly in early stages of chondrogenesis. Importantly, we show that the loss of Foxo3A in MSC results in an increased expression level of markers specific for mature (aggrecan, collagen II) and hypertrophic (collagen X) chondrocytes. Therefore, our findings suggest that upregulation of Foxo3A over the course of chondrogenic differentiation plays a dual role, mainly inhibiting the differentiation process toward hypertrophy and promoting cell apoptosis.

Ppargamma2 is a key driver of longevity in the mouse

Aging involves a progressive physiological remodeling that is controlled by both genetic and environmental factors. Many of these factors impact also on white adipose tissue (WAT), which has been shown to be a determinant of lifespan. Interrogating a transcriptional network for predicted causal regulatory interactions in a collection of mouse WAT from F2 crosses with a seed set of 60 known longevity genes, we identified a novel transcriptional subnetwork of 742 genes which represent thus-far-unknown longevity genes. Within this subnetwork, one gene was Pparg (Nr1c3), an adipose-enriched nuclear receptor previously not associated with longevity. In silico, both the PPAR signaling pathway and the transcriptional signature of Pparγ agonist rosiglitazone overlapped with the longevity subnetwork, while in vivo, lowered expression of Pparg reduced lifespan in both the lipodystrophic Pparg1/2-hypomorphic and the Pparg2-deficient mice. These results establish Pparγ2 as one of the determinants of longevity and suggest that lifespan may be rather determined by a purposeful genetic program than a random process.

The progression of aging is controlled by both genetic and environmental factors. Many of these factors are present also in adipose tissue, which itself has been shown to determine lifespan. Applying advanced bioinformatics methods on a large mouse gene expression data set, we identified Pparg (Nr1c3), an important metabolic controller that regulates the expression of many other genes particularly in adipose tissue, to be associated with longevity. This association was verified in experimental mouse models where the lowered expression of Pparg reduced lifespan. In addition to Pparg, our analysis identified >700 potential novel aging genes in mouse adipose tissue. More generally, these findings suggest that lifespan may not be a random process but controlled by a purposeful genetic program.

ACP1 genotype, glutathione reductase activity, and riboflavin uptake affect cardiovascular risk in the obese

Erythrocyte acid phosphatase (ACP locus 1), also known as low-molecular-weight protein tyrosine phosphatase, has previously been associated to glycemia, dyslipidemia, and obesity. In this study, ACP1 genotype and activity were tested in 318 women aged 19 to 83 (mean, 51.74 +/- 13.44) years. ACP1 genotype was found to directly correlate to glutathione reductase activity (P < .001) and levels of low-density lipoprotein cholesterol (P = .038). Glutathione reductase activity was in turn found to correlate to a series of cardiovascular risk factors such as systolic arterial pressure (P < .001), total cholesterol levels (P = .018), and low-density lipoprotein cholesterol levels (P = .039). A possible protective effect of ACP1 genotype AA against these cardiovascular risk factors was observed in this study. Furthermore, this work hypothesizes that nutritional riboflavin uptake becomes more crucial as body mass index increases, to counteract oxidative stress and minimize cardiovascular risk. This might be especially true in ACP1 genotypes AC, BC, and CC, which might possibly show the least endogenous protection against oxidative stress.

PPARγ2 polymorphism and human health

The nuclear hormone receptor peroxisome proliferator activated receptor gamma (PPARγ) is an important transcription factor regulating adipocyte differentiation, lipid and glucose homeostasis, and insulin sensitivity. Numerous genetic mutations of PPARγ have been identified and these mutations positively or negatively regulate insulin sensitivity. Among these, a relatively common polymorphism of PPARγ, Pro12Ala of PPARγ2, the isoform expressed only in adipose tissue has been shown to be associated with lower body mass index, enhanced insulin sensitivity, and resistance to the risk of type 2 diabetes in human subjects carrying this mutation. Subsequent studies in different ethnic populations, however, have revealed conflicting results, suggesting a complex interaction between the PPARγ2 Pro12Ala polymorphism and environmental factors such as the ratio of dietary unsaturated fatty acids to saturated fatty acids and/or between the PPARγ2 Pro12Ala polymorphism and genetic factors such as polymorphic mutations in other genes. In addition, this polymorphic mutation in PPARγ2 is associated with other aspects of human diseases, including cancers, polycystic ovary syndrome, Alzheimer disease and aging. This review will highlight findings from recent studies.