Uncoupling protein-2 controls adiponectin gene expression in adipose tissue through the modulation of reactive oxygen species production

Emerging role and the signaling pathways of uncoupling protein 2 in kidney diseases

OBJECTIVES

Uncoupling protein 2 (UCP2) was involved in the pathogenesis and development of kidney diseases. Many signaling pathways and factors regulate the expression of UCP2. We aimed to investigate the precise role of UCP2 and its signaling pathways in kidney diseases.

METHODS

We summarized the available evidence to yield a more detailed conclusion of the signal transduction pathways of UCP2 and its role in the development and progression of kidney diseases.

RESULTS

UCP2 could interact with 14.3.3 family proteins, mitochondrial phospholipase iPLA2γ, NMDAR, glucokinase, PPARγ2. There existed a signaling pathway between UCP2 and NMDAR, PPARγ. UCP2 can inhibit the ROS production, inflammatory response, and apoptosis, which may protect against renal injury, particularly AKI. Meanwhile UCP2 can decrease ATP production and inhibit the secretion of insulin, which may alleviate chronic renal damages, such as diabetic nephropathy and kidney fibrosis.

CONCLUSIONS

Homeostasis of UCP2 is helpful for kidney health. UCP2 may play different roles in different kinds of renal injury.

Diabesity alters the protective effects of estrogens on endothelial function through adipose tissue secretome

Estrogens have a well-known protective role in the development of the metabolic syndrome. Nevertheless, recent epidemiological data question the cardioprotective effect of estrogens in obese and diabetic women. In this context, white adipose tissue (WAT) becomes dysfunctional, which has an impact on the cardiovascular system. The aim of the study was to elucidate the role of 17β-estradiol (E2) in the interplay between adipose tissue and endothelial function in an animal model of diabesity. We used ZDF (fa/fa) female rats subjected to ovariectomy (OVA), OVA + E2 or sham operated, as well as non-obese non-diabetic ZDF (fa/+) rats. Endothelial function and vascular remodeling markers were assessed in the aorta, while mitochondrial function, oxidative stress, and adiponectin production were analyzed in gonadal WAT. Conditioned media from gonadal WAT explants were used to assess the effects of WAT secretome on HUVEC. Additionally, the adiponectin receptor agonist AdipoRON and E2 were utilized to examine potential interactions. Ovariectomy ameliorated the WAT dysfunction associated to the obese and diabetic state and promoted adiponectin secretion, effects that were linked to a reduction of endothelial dysfunction and inflammatory markers in the aorta of OVA rats and in HUVEC treated with OVA-conditioned media. Our findings provide evidence supporting the idea that in the context of obesity and diabetes, ovariectomy improves WAT secretome and positively impacts endothelial function, suggesting a detrimental role for E2. Additionally, our results point to adiponectin as the primary driver of the effects exerted by ovariectomy on the adipovascular axis.

Immuno-metabolic effect of pancreastatin inhibitor PSTi8 in diet induced obese mice: In vitro and in vivo findings

AIMS

Pancreastatin (PST), an anti-insulin peptide derived from chromogranin A. Its levels increase in cases of obesity, which contributes to adipose tissue inflammation and insulin resistance. This study aims to investigate the immunometabolic effect of PST inhibitor (PSTi8) against PST by using in vitro and in vivo finding.

MAIN METHODS

3T3-L1 cells were differentiated with or without PSTi8, and Oil Red O staining was performed. J774A.1 cells were used for macrophage polarization study. The diet-induced obesity and T2DM model was developed in C57BL/6 mice through high-fat diet for 8 weeks. Alzet osmotic pumps were filled with PSTi8 (release rate: 2 mg/kg/day) and implanted in mice for eight weeks. Further, insulin and glucose tolerance tests were performed. Liver and eWAT sections were stained with hematoxylin and eosin. FACS was used to measure mitochondrial ROS and membrane potential, while Oroboros O2k was used to measure oxygen consumption rate. Immunocytochemistry and qRT-PCR were done for protein and gene expression, respectively.

KEY FINDINGS

PSTi8 inhibited the expression of lipolytic genes and proteins in 3T3-L1 adipocytes. PSTi8 improved the inulin sensitivity, lipid profile, MMP, and OCR levels in the 3T3-L1 adipocyte and eWAT. It also increased the M1 to M2 macrophage polarization in J77A.1 cells and eWAT. Further, PSTi8 attenuated inflammatory CD4⁺ T, CD8⁺ T cells and increased the anti-inflammatory T-reg and eosinophil populations in the eWAT. It also reduced the expression of pro-inflammatory genes like Mcp1, Tnfα, and Il-6.

SIGNIFICANCE

Collectively, PSTi8 exerted its beneficial effect on adipose tissue inflammation and restored energy expenditure against diet-induced obesity.

The interaction between mitochondrial haplogroups (M7a/D) and physical activity on adiponectin in a Japanese population

Mitochondrial haplogroups F, A, and M7a are associated with increased risks of lifestyle diseases, while haplogroups N9 and D are associated with decreased risks of lifestyle diseases or with longevity. The current study determined the existence of interactions between 5 selected haplogroups and physical activity (PA) on total and high-molecular-weight (HMW) adiponectin in 3,994 men and 6,014 women. The interactions between haplogroups (M7a/D) and PA on adiponectin were significant in men (total and HMW: P-interaction = 0.041 and 0.011). The positive association of PA with adiponectin in men carrying haplogroup M7a is attenuated in comparison to men carrying haplogroup D.

Oxidative Phosphorylation Dysfunction Modifies the Cell Secretome

Mitochondrial oxidative phosphorylation disorders are extremely heterogeneous conditions. Their clinical and genetic variability makes the identification of reliable and specific biomarkers very challenging. Until now, only a few studies have focused on the effect of a defective oxidative phosphorylation functioning on the cell’s secretome, although it could be a promising approach for the identification and pre-selection of potential circulating biomarkers for mitochondrial diseases. Here, we review the insights obtained from secretome studies with regard to oxidative phosphorylation dysfunction, and the biomarkers that appear, so far, to be promising to identify mitochondrial diseases. We propose two new biomarkers to be taken into account in future diagnostic trials.

Adipose Tissue and Brain Metabolic Responses to Western Diet-Is There a Similarity between the Two?

Dietary fats and sugars were identified as risk factors for overweight and neurodegeneration, especially in middle-age, an earlier stage of the aging process. Therefore, our aim was to study the metabolic response of both white adipose tissue and brain in middle aged rats fed a typical Western diet (high in saturated fats and fructose, HFF) and verify whether a similarity exists between the two tissues. Specific cyto/adipokines (tumor necrosis factor alpha (TNF-α), adiponectin), critical obesity-inflammatory markers (haptoglobin, lipocalin), and insulin signaling or survival protein network (insulin receptor substrate 1 (IRS), Akt, Erk) were quantified in epididymal white adipose tissue (e-WAT), hippocampus, and frontal cortex. We found a significant increase of TNF-α in both e-WAT and hippocampus of HFF rats, while the expression of haptoglobin and lipocalin was differently affected in the various tissues. Interestingly, adiponectin amount was found significantly reduced in e-WAT, hippocampus, and frontal cortex of HFF rats. Insulin signaling was impaired by HFF diet in e-WAT but not in brain. The above changes were associated with the decrease in brain derived neurotrophic factor (BDNF) and synaptotagmin I and the increase in post-synaptic protein PSD-95 in HFF rats. Overall, our investigation supports for the first time similarities in the response of adipose tissue and brain to Western diet.

Obesity, Bariatric Surgery, and Fractures

CONTEXT

Obesity and its associated comorbidities are a recognized and growing public health problem. For a long time, obesity-associated effects on bone were considered to strengthen the bone, mainly because of the known relationship between body weight and bone mass and the long-term weight-bearing load effect on bone. However, recent epidemiologic studies have shown that obesity may not have a fully protective effect on the occurrence of fragility fractures. The goal of this article is to review updated information on the link between obesity, bariatric surgery, and fractures.

METHODS

The primary source literature for this review was acquired by searching a published database for reviews and articles up to January 2018. Additional references were selected through the in-depth analysis of the relevant studies.

RESULTS

We present data showing that overweight and obesity are often encountered in fracture cases. We also analyzed possible reasons and risk factors for fractures associated with overweight and patients with obesity. In addition, this review focuses on the complex effects of dramatic changes in body composition when interpreting dual-energy X-ray absorptiometry readings and findings. Finally, we review the data on the effects and consequences of bariatric surgery on bone metabolism and the risk of fractures in patients undergoing these procedures.

CONCLUSION

Because of various adiposity-induced effects, patients with obesity are at risk for fracture in certain sites. Bariatric surgery increases the risk of fractures in patients undergoing malabsorptive procedures.

Obesity impairs leukocyte-endothelium cell interactions and oxidative stress in humans

BACKGROUND

To evaluate the relationship between leukocyte-endothelial cell interactions and oxidative stress parameters in non-diabetic patients with different grades of obesity.

MATERIAL AND METHODS

For this cross-sectional study, 225 subjects were recruited from January 1, 2014 to December 31, 2016 and divided into groups according to BMI (<30 kg/m² , 30-40 kg/m² and >40 kg/m²). We determined clinical parameters, systemic inflammatory markers, soluble cellular adhesion molecules, leukocyte-endothelium cell interactions-rolling flux, velocity and adhesion-, oxidative stress parameters-total ROS, total superoxide, glutathione-and mitochondrial membrane potential in leukocytes.

RESULTS

We verified that HOMA-IR and hsCRP increased progressively as obesity developed, whereas A1c, IL6 and TNFα were augmented in the BMI > 40 kg/m² group. The cellular adhesion molecule sP-selectin was increased in patients with obesity, while sICAM, total ROS, total superoxide and mitochondrial membrane potential were selectively higher in the BMI > 40 kg/m² group. Obesity induced a progressive decrease in rolling velocity and an enhancement of rolling flux and leukocyte adhesion.

CONCLUSION

Our findings reveal that endothelial dysfunction markers are altered in human obesity and are associated with proinflammatory cytokines and increased oxidative stress parameters.

Association between UCP polymorphisms and adipokines with obesity in Mexican adolescents

BACKGROUND

It has been reported that the uncoupling proteins (UCPs) can contribute to energy metabolism, and are thus involved in the pathogenesis of obesity. The objective of the study was to analyze the association between UCP polymorphisms, clinical parameters and leptin and adiponectin plasma levels in an adolescent population with overweight and obesity.

METHODS

We analyzed the UCP1 -3826 C/T, UCP2-866 G/A, Ala55Val and UCP3 -55 C/T polymorphisms and the levels of adipokines in adolescents with normal weight and with overweight or obesity. The study included 270 students aged between 12 and 18 years categorized according to the percentiles from Mexico City. Adipokines levels were measured by immunoassay methods and the UCP polymorphisms were determined using Taqman real-time polymerase chain reaction (RT-PCR).

RESULTS

No significant differences were found in the UCP polymorphisms in seven inheritance models studied. Most of the significant differences in the clinical parameters were found under a recessive model, the UCP2 -866 polymorphism was associated with diastolic blood pressure (p=0.008), triglycerides (p=0.045), low-density lipoprotein-cholesterol (LDL-C) (p=0.003), high-density lipoprotein-cholesterol (HDL-C) (p=0.050) and plasma levels of leptin (p<0.001). Also, the obese group was found to have higher leptin levels and lower adiponectin levels in GA+AA vs. GG (recessive model).

CONCLUSIONS

This study demonstrated a direct relationship between the clinical characteristics and UCP2-866 in a recessive model, associated with high levels of leptin and decreased levels of adiponectin in an obese or overweight Mexican adolescent population.

Xylobiose Prevents High-Fat Diet Induced Mice Obesity by Suppressing Mesenteric Fat Deposition and Metabolic Dysregulation

Obesity is a public concern and is responsible for various metabolic diseases. Xylobiose (XB), an alternative sweetener, is a major component of xylo-oligosaccharide. The purpose of this study was to investigate the effects of XB on obesity and its associated metabolic changes in related organs. For these studies, mice received a 60% high-fat diet supplemented with 15% d-xylose, 10% XB, or 15% XB as part of the total sucrose content of the diet for ten weeks. Body weight, fat and liver weights, fasting blood glucose, and blood lipids levels were significantly reduced with XB supplementation. Levels of leptin and adipokine were also improved and lipogenic and adipogenic genes in mesenteric fat and liver were down-regulated with XB supplementation. Furthermore, pro-inflammatory cytokines, fatty acid uptake, lipolysis, and β-oxidation-related gene expression levels in mesenteric fat were down-regulated with XB supplementation. Thus, XB exhibited therapeutic potential for treating obesity which involved suppression of fat deposition and obesity-related metabolic disorders.

Association between uncoupling protein 2, adiponectin and resting energy expenditure in obese women with normal and low resting energy expenditure

Obesity is recognized as the most prevalent metabolic disease worldwide. Decreases in energy expenditure may increase risk of obesity. One of the key regulators of energy balance is uncoupling protein2 (UCP2), a transporter protein presents in mitochondrial inner membrane. Moreover, adiponectin is the most abundant adipocytokine, it may play a role in energy metabolism and gene expression of UCP2. The aim of this study was to investigate potential associations between the level of uncoupling protein 2 and adiponectin and their relationship with REE (Resting Energy Expenditure) in obese women with normal and low resting energy expenditure. A total of 49 subjects (women, 25-50 years old), were included in current study, 16 subjects with BMI > 30 and low resting energy expenditure, 17 subjects with BMI > 30 and normal resting energy expenditure and 16 non-obese subjects as a control group. Anthropometric, body composition parameters and resting energy expenditure were measured. Plasma adiponectin, UCP2 protein and total protein in PBMC were determined. Measured resting energy expenditure in obese subjects with low REE was significantly lower than other groups. Plasma adiponectin in the obese subjects with low REE was significantly lower compared to normal weight group. There was a significant relationship between 'UCP2 protein/Total protein' ratio and plasma adiponectin in obese group with low REE and in three groups when we pooled. There was a significant association between REE and plasma adiponectin in three groups when we pooled. There was a significant association between plasma adiponectin and REE. Moreover, there was a significant relationship between UCP2 and REE.

Pharmacologic concentrations of linezolid modify oxidative phosphorylation function and adipocyte secretome

The oxidative phosphorylation system is important for adipocyte differentiation. Therefore, xenobiotics inhibitors of the oxidative phosphorylation system could affect adipocyte differentiation and adipokine secretion. As adipokines impact the overall health status, these xenobiotics may have wide effects on human health. Some of these xenobiotics are widely used therapeutic drugs, such as ribosomal antibiotics. Because of its similarity to the bacterial one, mitochondrial translation system is an off-target for these compounds. To study the influence of the ribosomal antibiotic linezolid on adipokine production, we analyzed its effects on adipocyte secretome. Linezolid, at therapeutic concentrations, modifies the levels of apolipoprotein E and several adipokines and proteins related with the extracellular matrix. This antibiotic also alters the global methylation status of human adipose tissue-derived stem cells and, therefore, its effects are not limited to the exposure period. Besides their consequences on other tissues, xenobiotics acting on the adipocyte oxidative phosphorylation system alter apolipoprotein E and adipokine production, secondarily contributing to their systemic effects.

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Linezolid decreases oxidative phosphorylation system capacity.

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Linezolid reduces adipocyte differentiation from human adipose-derived stem cells.

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Linezolid modifies APOE, adipokine and extracellular matrix proteins levels.

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Linezolid changes DNA methylation of human adipose tissue-derived stem cells.

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Xenobiotics, acting on adipocyte oxidative phosphorylation, affect human health.

pNaKtide Attenuates Steatohepatitis and Atherosclerosis by Blocking Na/K-ATPase/ROS Amplification in C57Bl6 and ApoE Knockout Mice Fed a Western Diet

We have previously reported that the α1 subunit of sodium potassium adenosine triphosphatase (Na/K-ATPase), acts as a receptor and an amplifier for reactive oxygen species, in addition to its distinct pumping function. On this background, we speculated that blockade of Na/K-ATPase-induced ROS amplification with a specific peptide, pNaKtide, might attenuate the development of steatohepatitis. To test this hypothesis, pNaKtide was administered to a murine model of NASH: the C57Bl6 mouse fed a “western” diet containing high amounts of fat and fructose. The administration of pNaKtide reduced obesity as well as hepatic steatosis, inflammation and fibrosis. Of interest, we also noted marked improvement in mitochondrial fatty acid oxidation, insulin sensitivity, dyslipidemia and aortic streaking in this mouse model. To further elucidate the effects of pNaKtide on atherosclerosis, similar studies were performed in ApoE knockout mice also exposed to the western diet. In these mice, pNaKtide not only improved steatohepatitis, dyslipidemia, and insulin sensitivity, but also ameliorated significant aortic atherosclerosis. Collectively, this study demonstrates that the Na/K-ATPase/ROS amplification loop contributes significantly to the development and progression of steatohepatitis and atherosclerosis. And furthermore, this study presents a potential treatment, the pNaKtide, for the metabolic syndrome phenotype.

Thyroid hormone-stimulated increases in PGC-1α and UCP2 promote life history-specific endocrine changes and maintain a lipid-based metabolism

Thyroid hormones (THs) regulate metabolism, but are typically suppressed during times of stressful physiological conditions, including fasting. Interestingly, prolonged fasting in northern elephant seal pups is associated with reliance on a lipid-based metabolism and increased levels of circulating THs that are partially attributed to active secretion as opposed to reduced clearance. This apparent paradox is coupled with complementary increases in cellular TH-mediated activity, suggesting that in mammals naturally adapted to prolonged fasting, THs are necessary to support metabolism. However, the functional relevance of this physiological paradox has remained largely unexplored, especially as it relates to the regulation of lipids. To address the hypothesis that TSH-mediated increase in THs contributes to lipid metabolism, we infused early and late-fasted pups with TSH and measured several key genes in adipose and muscle, and plasma hormones associated with regulation of lipid metabolism. TSH infusion increased the mRNA expressions of peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) more than 6.5-fold at 60 min in muscle, and expression of uncoupling protein 2 (UCP2) more than 27-fold during the early fast at 60 min, in adipose. Additionally, during the late fast period, the protein content of adipose CD36 increased 1.1-fold, and plasma nonesterified fatty acid (NEFA) concentrations increased 25% at 120 min, with NEFA levels returning to baseline after 24 h. We show that the TSH-induced increases in THs in fasting pups are functional and likely contribute to the maintenance of a lipid-based metabolism.

Chitosan oligosaccharide affects antioxidant defense capacity and placental amino acids transport of sows

BACKGROUND

Chitosan oligosaccharide (COS) is widely consumed as a functional food due to its multiple health effects, but few studies about COS supplement on placental antioxidant and nutrition transport capacity were reported. Taken pregnant sow as a model, we aimed to investigate the effects of dietary COS supplementation during late gestation on placental amino acids transport and antioxidant defense capacity of sows. From day (d) 85 of gestation to parturition, sixteen pregnant sows were divided into a control group (basal diet without COS supplementation) and a COS group (30 mg COS/kg basal diet). Plasma sample of sow was collected on d 110 of gestation, and placenta tissue was obtained during parturition. Then plasma antioxidant enzyme's activities, the relative level of oxidant stress related genes, amino acids transport related genes and mTOR pathway molecules in placenta were determined.

RESULTS

Results showed that maternal dietary supplementation with COS increased (P < 0.05) plasma total SOD, caused a downtrend in plasma MDA (0.05 < P < 0.10) on d 110 of gestation. Interestingly, the mRNA expression of some antioxidant genes in the placenta were increased (P < 0.05) and pro-inflammatory cytokines were reduced (P < 0.05) by COS supplement, whereas no significant difference was observed in the activities of placental total SOD and CAT between two groups. Additionally, further study demonstrated that COS feeding stimulated mTOR signaling pathway, increased amino acids transporters expression in placenta.

CONCLUSIONS

These observations suggested that COS supplement in sow's diet during late gestation enhanced antioxidant defense capacity of sows, promoted placental amino acids transport, which may contribute to the health of sows and development of fetus during gestation.

Increasing cAMP levels of preadipocytes by cyanidin-3-glucoside treatment induces the formation of beige phenotypes in 3T3-L1 adipocytes

Obesity is a serious health problem and a major risk factor for the onset of several diseases such as heart disease, diabetes, stroke and cancer. The conversion of white adipocytes to brown-like adipocytes, also called beige or brite adipocytes, by pharmacological and dietary compounds has gained attention as an effective treatment for obesity. Cyanidin-3-glucoside (Cy3G), a polyphenolic compound contained in black soybean, blueberry and grape, has several antiobesity effects. However, there are no reports on the role of Cy3G in the induction of differentiation of preadipocytes to beige adipocytes and corresponding phenotypes. Here, the formation of beige adipocyte phenotypes following treatment with Cy3G was evaluated using 3T3-L1 adipocytes. Cy3G induced phenotypic changes to white adipocytes, such as increased multilocular lipid droplets and mitochondrial content. Additionally, the expression of mitochondrial genes (TFAM, SOD2, UCP-1 and UCP-2), UCP-1 protein and beige adipocyte markers (CITED1 and TBX1) in 3T3-L1 adipocytes was increased by Cy3G. Furthermore, Cy3G promoted preadipocyte differentiation by up-regulating of C/EBPβ through the elevation of the intracellular cAMP levels. These results indicated that Cy3G elevates the intracellular cAMP levels, which induces beige adipocyte phenotypes. This is the first report on the effect of Cy3G on induction of differentiation of preadipocytes into beige adipocyte phenotypes.

Interactions between uncoupling protein 2 gene polymorphisms, obesity and alcohol intake on liver function: a large meta-analysed population-based study

BACKGROUND AND OBJECTIVE

Given the role of uncoupling protein 2 (UCP2) in the accumulation of fat in the hepatocytes and in the enhancement of protective mechanisms in acute ethanol intake, we hypothesised that UCP2 polymorphisms are likely to cause liver disease through their interactions with obesity and alcohol intake. To test this hypothesis, we investigated the interaction between tagging polymorphisms in the UCP2 gene (rs2306819, rs599277 and rs659366), alcohol intake and obesity traits such as BMI and waist circumference (WC) on alanine aminotransferase (ALT) and gamma glutamyl transferase (GGT) in a large meta-analysis of data sets from three populations (n=20 242).

DESIGN AND METHODS

The study populations included the Northern Finland Birth Cohort 1966 (n=4996), Netherlands Study of Depression and Anxiety (n=1883) and LifeLines Cohort Study (n=13 363). Interactions between the polymorphisms and obesity and alcohol intake on dichotomised ALT and GGT levels were assessed using logistic regression and the likelihood ratio test.

RESULTS

In the meta-analysis of the three cohorts, none of the three UCP2 polymorphisms were associated with GGT or ALT levels. There was no evidence for interaction between the polymorphisms and alcohol intake on GGT and ALT levels. In contrast, the association of WC and BMI with GGT levels varied by rs659366 genotype (Pinteraction=0.03 and 0.007, respectively; adjusted for age, gender, high alcohol intake, diabetes, hypertension and serum lipid concentrations).

CONCLUSION

In conclusion, our findings in 20 242 individuals suggest that UCP2 gene polymorphisms may cause liver dysfunction through the interaction with body fat rather than alcohol intake.

Dehydroepiandrosterone-enhanced dual specificity protein phosphatase (DDSP) prevents diet-induced and genetic obesity

Dehydroepiandrosterone (DHEA) exerts a wide variety of therapeutic effects against medical disorders, such as diabetes and obesity. However, the molecular basis of DHEA action remains to be clarified. Previously, we reported that DHEA-enhanced dual specificity protein phosphatase, designated DDSP, is one of the target molecules of DHEA. To examine the role of DDSP in DHEA signaling, we generated mice that carry a DDSP transgene in which expression is driven by the CAG promoter (DDSP-Tg). DDSP-Tg mice weighed significantly less than wild-type (WT) control mice when a high fat diet was supplied (p < 0.01). No difference in food-intake or locomotor activity was found between DDSP-Tg and WT mice. Oxygen consumption of DDSP-Tg mice was higher than that of WT mice (p < 0.01), which suggested an increase in basal metabolism in DDSP-Tg mice. To further investigate the role of DDSP in genetic obese mice, DDSP-Tg mice with a db/db background were generated (DDSP-Tg db/db). We observed cancellation of obesity by the db/db mutation and development of a cachexic phenotype in DDSP-Tg db/db mice. In conclusion, our study shows that expression of DDSP leads to prevention of diet-induced and genetic (db/db) obesity. Anti-obese effects of DHEA might be mediated through DDSP, which might be a therapeutic target for intervention of obesity.

Inverse relationship between body mass index and mitochondrial oxidative phosphorylation capacity in human subcutaneous adipocytes

Obesity is characterized by a substantial increase in adipose tissue that may contribute to energy balance. Recently, obesity was suggested to be associated with impaired mitochondrial function in adipocytes. In this study, we investigated the following: 1) the respiratory capacities of mitochondria isolated from mature adipocytes of female subjects whose body mass index (BMI) values were distributed over a wide range and 2) the amounts of electron transport chain complexes in these mitochondria. Fat cells were isolated from adipose tissue specimens by collagenase digestion. Mitochondria were isolated from these fat cells, and their respiratory capacity was determined using a Clark-type electrode. Fat cells were also sorted on the basis of their size into large and small fractions to assess their respiration. Western blot analyses were performed to quantify respiratory chain complex components. We also examined mitochondrial activity development during differentiation using human Simpson-Golabi-Behmel syndrome cells. Our results showed that mitochondrial respiratory capacities in adipocytes were inversely associated with BMI values but were independent of cell size. Western blot analyses revealed significantly fewer complex I and IV components in adipose tissues from obese compared with nonobese women. These results suggest that differences at the level of respiratory chain complexes might be responsible for the deterioration of respiratory capacity in obese individuals. In particular, electron transport at the level of complexes I and IV seems to be most affected.

FGF21 expression and release in muscle cells: involvement of MyoD and regulation by mitochondria-driven signalling

Although the liver is generally considered the main site of production of FGF21 (fibroblast growth factor-21), high FGF21 levels have been found to be associated with neuromuscular mitochondrial genetic diseases, and there are indications that the muscle may be a relevant site of FGF21 production under conditions of muscular mitochondrial stress. In the present study, we found that expression and release of FGF21 was associated with myogenic differentiation, and we identified MyoD as a major controller of FGF21 gene transcription. Mimicking mitochondrial dysfunction using respiratory chain/oxidative phosphorylation inhibitors resulted in enhanced expression and release of FGF21 by muscle cells. The increased production of reactive oxygen species, subsequent induction of p38 MAPK (mitogen-activated protein kinase) and activation of an ATF2 (activating transcription factor 2)-binding site at the proximal promoter region of the FGF21 gene was found to be a major mechanism linking mitochondrial dysfunction with enhanced FGF21 gene transcription in myogenic cells. The myogenic factor MyoD was required for the induction of FGF21 gene transcription by mitochondrial dysfunction, thus explaining the preferential response of muscle cells to mitochondrial dysfunction-induced FGF21 expression and secretion. FGF21 release by muscle cells in response to mitochondrial alterations may represent a physiological mechanism by which the sensing of internal energetic status by muscles results in the release of FGF21 to favour systemic metabolic adaptations.

Enhanced ROS production and oxidative damage in subcutaneous white adipose tissue mitochondria in obese and type 2 diabetes subjects

Oxidative stress in the insulin target tissues has been implicated in the pathophysiology of type 2 diabetes. The study has examined the oxidative stress parameters in the mitochondria of subcutaneous white adipose tissue from obese and non-obese subjects with or without type 2 diabetes. An accumulation of protein carbonyls, fluorescent lipid peroxidation products, and malondialdehyde occurs in the adipose tissue mitochondria of obese type 2 diabetic, non-diabetic obese, and non-obese diabetic subjects with the maximum increase noticed in the obese type 2 diabetes patients and the minimum in non-obese type 2 diabetics. The mitochondria from obese type 2 diabetics, non-diabetic obese, and non-obese type 2 diabetics also produce significantly more reactive oxygen species (ROS) in vitro compared to those of controls, and apparently the mitochondrial ROS production rate in each group is proportional to the respective load of oxidative damage markers. Likewise, the mitochondrial antioxidant enzymes like superoxide dismutase and glutathione peroxidase show decreased activities most markedly in obese type 2 diabetes subjects and to a lesser degree in non-obese type 2 diabetes or non-diabetic obese subjects in comparison to control. The results imply that mitochondrial dysfunction with enhanced ROS production may contribute to the metabolic abnormality of adipose tissue in obesity and diabetes.

Impact of UCP2 polymorphism on long-term exercise-mediated changes in adipocytokines and markers of metabolic syndrome

BACKGROUND AND AIMS

Variations in genes involved in energy expenditure affect aerobic exercise efficiency, but it remains unclear whether the effect of aerobic exercise on adipocytokines is modified by the obesity-associated genotypes in the uncoupling protein 2 gene (UCP2). The purpose of this study was to assess whether genetic variation in UCP2 may affect exercise-mediated changes in adipocytokines and markers of metabolic syndrome in postmenopausal obese women.

METHODS

Forty-two sedentary postmenopausal obese women (age 52.74 ± 6.39 years) participated in this study. Participants were encouraged to train for 3 days a week, for 6 months, for 60 min per session of treadmill walking/running at 60 % [Formula: see text]. Subjects were genotyped for the 45-bp insertion/deletion (I/D) polymorphism in the 3'-untranslated region (UTR) of UCP2.

RESULTS

Among the subjects, 23 (57.1 %) and 19 (42.9 %), were deletion homozygotes (DD) and ID heterozygotes, respectively. For DD homozygotes, body weight, body mass index (BMI), % body fat, and waist circumference, and body weight, BMI, and waist circumference of ID heterozygotes, were significantly decreased after the exercise program. There were no significant changes in metabolic markers in individuals with the ID genotype, whereas insulin and HOMA-IR in individuals with the DD genotype were significantly decreased after the exercise program. In DD homozygotes, but not in ID heterozygotes, adiponectin was significantly increased, and leptin, TNF-α, and IL-6 were significantly decreased after exercise training.

CONCLUSIONS

Exercise-mediated changes in insulin resistance and adiponectin levels may be affected by genotypes in the 3'UTR I/D polymorphism in UCP2 in postmenopausal obese women.

Maternal omega-3 fatty acid intake increases placental labyrinthine antioxidant capacity but does not protect against fetal growth restriction induced by placental ischaemia-reperfusion injury

Placental oxidative stress plays a key role in the pathophysiology of several placenta-related disorders. Oxidative stress occurs when excess reactive oxygen species (ROS) damages cellular components, an outcome limited by antioxidant enzymes; mitochondrial uncoupling protein 2 (UCP2) also limits ROS production. We recently reported that maternal dietary omega-3 polyunsaturated fatty acid (n-3 PUFA) supplementation reduced placental oxidative damage and enhanced fetal and placental growth in the rats. Here, we examined the effect of n-3 PUFAs on placental antioxidant defences and whether n-3 PUFA supplementation could prevent growth restriction induced by placental ischaemia-reperfusion (IR), a known inducer of oxidative stress. Rats were fed either standard or high-n-3 PUFA diets from day 1 of pregnancy. Placentas were collected on days 17 and 22 in untreated pregnancies (term=day 23) and at day 22 following IR treatment on day 17. Expression of several antioxidant enzyme genes (Sod1, Sod2, Sod3, Cat, Txn1 and Gpx3) and Ucp2 was measured by quantitative RT-PCR in the placental labyrinth zone (LZ) and junctional zone (JZ). Cytosolic superoxide dismutase (SOD), mitochondrial SOD and catalase (CAT) activities were also analyzed. Maternal n-3 PUFA supplementation increased LZ mRNA expression of Cat at both gestational days (2- and 1.5-fold respectively; P<0.01) and female Sod2 at day 22 (1.4-fold, P<0.01). Cytosolic SOD activity increased with n-3 PUFA supplementation at day 22 (1.3-fold, P<0.05). Sod1 and Txn1 expression decreased marginally (30 and 22%, P<0.05). JZ antioxidant defences were largely unaffected by diet. Despite increased LZ antioxidant defences, maternal n-3 PUFA supplementation did not protect against placental IR-induced growth restriction of the fetus and placental LZ.

Inhibition of ERK1/2 pathway suppresses adiponectin secretion via accelerating protein degradation by Ubiquitin-proteasome system: relevance to obesity-related adiponectin decline

OBJECTIVE

Predominantly secreted by adipose tissue, adiponectin possesses insulin-sensitizing, anti-atherogenic, anti-inflammatory, and anti-angiogenic properties. Paradoxically, obesity is associated with declined plasma adiponectin levels; however, the underlying mechanisms remain elusive. In this study, we investigated the mechanistic involvement of MEK/ERK1/2 pathway in obesity-related adiponectin decrease.

MATERIALS/METHODS

C57 BL/6 mice exposed to a high-fat diet (HFD) were employed as animal obesity model. Both fully-differentiated 3T3-L1 and mouse primary adipocytes were used in the in vitro experiments.

RESULTS

Obesity and plasma adiponectin decline induced by prolonged HFD exposure were associated with suppressed ERK1/2 activation in adipose tissue. In adipocytes, specific inhibition of MEK/ERK1/2 pathway decreased intracellular and secretory adiponectin levels, whereas adiponectin gene expression was increased, suggesting that MEK/ERK1/2 inhibition may promote adiponectin protein degradation. Cycloheximide (CHX)-chase assay revealed that MEK/ERK1/2 inhibition accelerated adiponectin protein degradation, which was prevented by MG132, a potent proteasome inhibitor. Immunoprecipitation assay showed that intracellular MEK/ERK1/2 activity was negatively associated with ubiquitinated adiponectin protein levels. Consistently, long-term HFD feeing in mice increased ubiquitinated adiponectin levels in the epididymal fat pads.

CONCLUSIONS

Adipose tissue MEK/ERK1/2 activity can differentially regulate adiponectin gene expression and protein abundance and its suppression in obesity may play a mechanistic role in obesity-related plasma adiponectin decline.

Mitochondrial dysfunction leads to impairment of insulin sensitivity and adiponectin secretion in adipocytes

Adipocytes play an integrative role in the regulation of energy metabolism and glucose homeostasis in the human body. Functional defects in adipocytes may cause systemic disturbance of glucose homeostasis. Recent studies revealed mitochondrial abnormalities in the adipose tissue of patients with type 2 diabetes. In addition, patients with mitochondrial diseases usually manifest systemic metabolic disorder. However, it is unclear how mitochondrial dysfunction in adipocytes affects the regulation of glucose homeostasis. In this study, we induced mitochondrial dysfunction and overproduction of reactive oxygen species (ROS) by addition of respiratory inhibitors oligomycin A and antimycin A and by knockdown of mitochondrial transcription factor A (mtTFA), respectively. We found an attenuation of the insulin response as indicated by lower glucose uptake and decreased phosphorylation of Akt upon insulin stimulation of adipocytes with mitochondrial dysfunction. Furthermore, the expression of glucose transporter 4 (Glut4) and secretion of adiponectin were decreased in adipocytes with increased ROS generated by defective mitochondria. Moreover, the severity of insulin insensitivity was correlated with the extent of mitochondrial dysfunction. These results suggest that higher intracellular ROS levels elicited by mitochondrial dysfunction resulted in impairment of the function of adipocytes in the maintenance of glucose homeostasis through attenuation of insulin signaling, downregulation of Glut4 expression, and decrease in adiponectin secretion. Our findings substantiate the important role of mitochondria in the regulation of glucose homeostasis in adipocytes and also provide a molecular basis for the explanation of the manifestation of diabetes mellitus or insulin insensitivity in a portion of patients with mitochondrial diseases such as MELAS or MERRF syndrome.

Maternal dexamethasone administration and the maturation of perirenal adipose tissue of the neonatal sheep

Maternal dexamethasone administration promotes fetal maturation such that thermoregulation is improved following premature delivery and is thus comparable with a full term birth. In the present study we determined the impact of dexamethasone on both the mothers' metabolic status together with adipose tissue function in the newborn. Glucocorticoid action, adipokine gene expression and mitochondrial protein abundance were measured in perirenal adipose tissue of neonatal sheep that were born into either a warm (30 degrees C) or cool (15 degrees C) ambient temperature at 140 days of gestation (dGA; term approximately 147 dGA), either two days after maternal dexamethasone administration, or at 146 dGA for controls. Dexamethasone administration resulted in a reduction in maternal food intake in conjunction with raised plasma cortisol and free triiodothyronine. In offspring of dexamethasone administered mothers, plasma cortisol was lower and non-esterified fatty acids (NEFA) higher than controls. Glucocorticoid receptor (GR), 11beta-hydroxysteroid dehydrogenase (11beta-HSD1), interleukin-6 and uncoupling protein (UCP)1 and 2 mRNA together with voltage dependent anion channel, cytochrome c protein and UCP1 abundance were all increased by dexamethasone administration and being born into a cool ambient temperature. Gene expression of tumor necrosis factor alpha, adiponectin and peroxisome proliferator-activated receptor transcription factor gamma were unaffected by dexamethasone. The abundance of mRNA for the GR, 11beta-HSD1, UCP1 and 2 mRNA together with each protein were positively correlated to plasma NEFA and negatively correlated to plasma cortisol. In conclusion, despite reduced maternal food intake dexamethasone promotes maturation of glucocorticoid action and mitochondrial protein abundance in the newborn, an adaptation dependent on delivery temperature.

Mitochondrial dysfunction in white adipose tissue

Although mitochondria in brown adipose tissue and their role in non-shivering thermogenesis have been widely studied, we have only a limited understanding of the relevance of mitochondria in white adipose tissue (WAT) for cellular homeostasis of the adipocyte and their impact upon systemic energy homeostasis. A better understanding of the regulatory role that white adipocyte mitochondria play in the regulation of whole-body physiology becomes increasingly important. WAT mitochondrial biogenesis can effectively be induced pharmacologically using a number of agents, including PPARγ agonists. Through their ability to influence key biochemical processes central to the adipocyte, such as fatty acid (FA) esterification and lipogenesis, as well as their impact upon the production and release of key adipokines, mitochondria play a crucial role in determining systemic insulin sensitivity.

Systems biology of antioxidants

Understanding the role of oxidative injury will allow for therapy with agents that scavenge ROS (reactive oxygen species) and antioxidants in the management of several diseases related to free radical damage. The majority of free radicals are generated by mitochondria as a consequence of the mitochondrial cycle, whereas free radical accumulation is limited by the action of a variety of antioxidant processes that reside in every cell. In the present review, we provide an overview of the mitochondrial generation of ROS and discuss the role of ROS in the regulation of endothelial and adipocyte function. Moreover, we also discuss recent findings on the role of ROS in sepsis, cerebral ataxia and stroke. These results provide avenues for the therapeutic potential of antioxidants in a variety of diseases.

Uncoupling protein-2 (UCP2) gene expression in subcutaneous and omental adipose tissue of Asian Indians: Relationship to adiponectin and parameters of metabolic syndrome

Objective

UCP2 is a mitochondrial membrane transporter expressed in white adipose tissue and involved in regulation of energy balance. In this present study, we examined the depot specific comparison of UCP2 gene expression in different metabolic states, in order to explore the potential role of UCP2 in human obesity and diabetes. We also determined UCP2’s association with adiponectin and insulin resistance with different parameters of the metabolic syndrome.

Methods

Subcutaneous adipose tissue (SAT) and omental adipose tissues (OAT) were obtained from 69 subjects, including 23 non-obese controls, 26 obese and 20 obese T2DM patients. Metabolic syndrome and other clinical features were studied. Adiponectin and UCP2 gene expression was quantitated by Real Time Reverse Transcriptase Polymerase Chain Reaction (RT-PCR).

Results

UCP2 gene expression was significantly reduced in obese and diabetic patients compared with controls. Interestingly, we found that UCP2 gene expression was reduced more in omental fat compared with subcutaneous fat and this effect was observed only in males but not in females. Partial correlation analysis showed significant association with the obesity parameters waist circumference, insulin and HOMA-IR, the lipid parameter triglyceride and the adipokine adiponectin.

Conclusion

Reduced UCP2 gene expression in obese and diabetic patients and its association with obesity parameters and HOMA-IR confirms its role as a candidate gene in the study of obesity and diabetes in our population. Also, its association with triglycerides implicates its role in lipid metabolism. An association between adiponectin and UCP2 gene expression may provide us with an innovative therapeutic strategy to prevent obesity related diseases, like diabetes and CVD.

Uncoupling protein-2 protects endothelial function in diet-induced obese mice

RATIONALE

Previous studies indicate uncoupling protein-2 (UCP2) as an antioxidant defense against endothelial dysfunction in hypertension. UCP2 also regulates insulin secretion and action. However, the role of UCP2 in endothelial dysfunction associated with diabetes and obesity is unclear.

OBJECTIVE

UCP2 protects against endothelial dysfunction induced by high-fat diet through inhibition of reactive oxygen species (ROS) production, and subsequent increase of nitric oxide bioavailability.

METHODS AND RESULTS

Endothelium-dependent relaxation (EDR) in aortae and mesenteric arteries in response to acetylcholine was measured in wire myograph. Flow-mediated vasodilatation in 2(nd)-order mesenteric arteries was measured in pressure myograph. ROS production is measured by CM-H(2)DCFDA and DHE fluorescence. High-glucose exposure reduced EDR in mouse aortae, which was exaggerated in UCP2 knockout (KO) mice, whereas UCP2 overexpression by adenoviral infection (AdUCP2) restored the impaired EDR. Impairment of EDR and flow-mediated vasodilatation in aortae and mesenteric arteries from high-fat diet-induced obese mice (DIO) was exaggerated in UCP2KO DIO mice compared with wild-type DIO littermates, whereas AdUCP2 i.v. injection restored both EDR and flow-mediated vasodilatation in DIO mice. Improved EDR in mesenteric arteries was inhibited by nitric oxide synthase inhibitor. UCP2 overexpression also inhibited intracellular ROS production in the en face endothelium of aorta and mesenteric artery of DIO mice, whereas UCP2 deficiency enhanced ROS production.

CONCLUSIONS

UCP2 preserves endothelial function through increasing nitric oxide bioavailability secondary to the inhibition of ROS production in the endothelium of obese diabetic mice.

ApoA1: mimetic peptide reverses adipocyte dysfunction in vivo and in vitro via an increase in heme oxygenase (HO-1) and Wnt10b

Insulin resistance is a risk factor in the development of type 2 diabetes and is a major cause of atherosclerosis. Reduction in heme oxygenase (HO-1) has been shown to exacerbate vascular dysfunction and insulin resistance in obese mice and involves a decrease in adiponectin levels. Adiponectin is released from mesenchymal stem cell (MSC)-derived adipocytes, its levels are decreased in type 2 diabetes. We hypothesized that the apoA1 mimetic peptide, L-4F, will target the expression of the HO-1-adiponectin axis and reverse adipocyte dysfunction both in vivo and in vitro. The administration of L-4F [2 mg/Kg/daily (i.p.) for 4-week to 8-week-old obese (ob) mice restored adipocyte function, increased adiponectin release (p < 0.05) and decreased the levels of IL-1 and IL-6 (p < 0.05)]. These perturbations were associated with an increase in insulin sensitivity (p < 0.01 vs. untreated ob mice) and decreased glucose levels (309 + 42 vs. 201 + 8 mg/d after L-4F treatment). Treatment of both mesenchymal stem cell (MSC)-derived adipocytes with L-4F (50 μg/ml) increased adiponectin (p < 0.05), decreased IL-1 and IL-6 (p < 0.05) levels and increased MSC-derived adipocyte cell numbers by 50% in S phase (p < 0.05). MSC-derived adipocytes treated with L-4F increased WNT10b and decreased Peg 1/Mest. Inhibition of HO activity reversed the decrease in the adipogenic response gene, Peg 1/Mest. An increase of HO-1 expression by L-4F increased insulin-receptor phosphorylation. These findings support the hypothesis that L-4F increases early adipocyte markers, HO-1-adiponectin, WNT10b and decreases Peg1/Mest, negative regulators of adipocyte differentiation.

A/ASP/VAL allele combination of IGF1R, IRS2, and UCP2 genes is associated with better metabolic profile, preserved energy expenditure parameters, and low mortality rate in longevity

A large array of gene involved in human longevity seems to be in relationship with insulin/IGF1 pathway. However, if such genes interact each other, or with other genes, to reduce the age-related metabolic derangement and determine the long-lived phenotype has been poorly investigated. Thus, we tested the role of interchromosomal interactions among IGF1R, IRS2, and UCP2 genes on the probability to reach extreme old age in 722 unrelated Italian subjects (401 women and 321 men; mean age, 62.83 ± 25.30 years) enrolled between 1998 and 1999. In particular, the G/A-IGF1R, Gly/Asp-IRS2, and Ala/Val-UCP2 allele combination was tested for association with longevity, metabolic profile and energy expenditure parameters. The effect on all-cause and cause-specific mortality rate was also assessed after a mean follow-up of 6 years. The analysis revealed that AAV allele combination is associated with a decreased all-cause mortality risk (HR, 0.72; 95% CI, 0.63-0.91; p = 0.03) and with a higher probability to reach the extreme of old age (OR, 3.185; 95% CI, 1.63-6.19; p = 0.0006). The analysis also revealed lower HOMA-IR (Diff, -0.532, 95% CI, 0.886-0.17; p = 0.003), higher respiratory quotient (Diff, 0.0363, 95% CI, 0.014-0.05; p = 0.001), and resting metabolic rate (Diff, 101.80693, 95% CI, -5.26-204.278; p = 0.038) for AAV allele combination. In conclusion, A-IGF1R/Asp-IRS2/Val-UCP2 allele combination is associated with a decreased all-cause mortality risk and with an increased chance of longevity. Such an effect is probably due to the combined effect of IGF1R, IRS2, and UCP2 genes on energy metabolism and on the age-related metabolic remodeling capacity.

Thymidine kinase 2 deficiency-induced mitochondrial DNA depletion causes abnormal development of adipose tissues and adipokine levels in mice

Mammal adipose tissues require mitochondrial activity for proper development and differentiation. The components of the mitochondrial respiratory chain/oxidative phosphorylation system (OXPHOS) are encoded by both mitochondrial and nuclear genomes. The maintenance of mitochondrial DNA (mtDNA) is a key element for a functional mitochondrial oxidative activity in mammalian cells. To ascertain the role of mtDNA levels in adipose tissue, we have analyzed the alterations in white (WAT) and brown (BAT) adipose tissues in thymidine kinase 2 (Tk2) H126N knockin mice, a model of TK2 deficiency-induced mtDNA depletion. We observed respectively severe and moderate mtDNA depletion in TK2-deficient BAT and WAT, showing both tissues moderate hypotrophy and reduced fat accumulation. Electron microscopy revealed altered mitochondrial morphology in brown but not in white adipocytes from TK2-deficient mice. Although significant reduction in mtDNA-encoded transcripts was observed both in WAT and BAT, protein levels from distinct OXPHOS complexes were significantly reduced only in TK2-deficient BAT. Accordingly, the activity of cytochrome c oxidase was significantly lowered only in BAT from TK2-deficient mice. The analysis of transcripts encoding up to fourteen components of specific adipose tissue functions revealed that, in both TK2-deficient WAT and BAT, there was a consistent reduction of thermogenesis related gene expression and a severe reduction in leptin mRNA. Reduced levels of resistin mRNA were found in BAT from TK2-deficient mice. Analysis of serum indicated a dramatic reduction in circulating levels of leptin and resistin. In summary, our present study establishes that mtDNA depletion leads to a moderate impairment in mitochondrial respiratory function, especially in BAT, causes substantial alterations in WAT and BAT development, and has a profound impact in the endocrine properties of adipose tissues.

Adipokines and redox signaling: impact on fatty liver disease

Adipokines (adipose tissue cytokines) are polypeptide factors secreted by adipose tissue in a highly regulated manner. The 'classical' adipokines (leptin, adiponectin, and resistin) are expressed only by adipocytes, but other adipokines have been shown to be released by resident and infiltrating macrophages, as well as by components of the vascular stroma. Indeed, adipose tissue inflammation is known to be associated with a modification in the pattern of adipokine secretion. Several studies indicate that adipokines can interfere with hepatic injury associated with fatty infiltration, differentially modulating steatosis, inflammation, and fibrosis. Moreover, plasma levels of adipokines have been investigated in patients with nonalcoholic fatty liver disease in order to establish correlations with the underlying state of insulin resistance and with the type and severity of hepatic damage. In this Forum article, we provide a review of recent data that suggest a significant role for oxidative stress, reactive oxygen species, and redox signaling in mediating actions of adipokines that are relevant in the pathogenesis of nonalcoholic fatty liver disease, including hepatic insulin resistance, inflammation, and fibrosis.

Mitochondrial pathophysiology and type 2 diabetes mellitus

Over the last decades, substantial progress has been made in defining the molecular events and relevant tissues controlling insulin action and the potential defects that lead to insulin resistance and later on Type 2 diabetes mellitus (T2DM). Mitochondrial dysfunction has been postulated as a common mechanism implicated in the development of insulin resistance and T2DM aetiology. Since then there has been growing interest in this area of research and many studies have addressed whether mitochondrial function/dysfunction is implicated in the progression of T2DM or if it is just a consequence. Mitochondria are adjusted to the specific needs of the tissue and to the environmental interactions or pathophysiological state that it encounters. This review offers a current state of the subject in a tissue specific approach. We will focus our attention on skeletal muscle, liver, and white adipose tissue as the main insulin sensitive organs. Hypothalamic mitochondrial function will be also discussed.

Adipose tissue biology and HIV-infection

HIV-1/highly active antiretroviral therapy-associated lipodystrophy syndrome (HALS) is an adipose tissue redistribution disorder characterized by subcutaneous adipose tissue lipoatrophy, sometimes including visceral adipose tissue hypertrophy and accumulation of dorsocervical fat ('buffalo hump'). The pathophysiology of HALS appears to be multifactorial and several key pathophysiological factors associated with HALS have been identified. These include mitochondrial dysfunction, adipocyte differentiation disturbances, high adipocyte lipolysis, and adipocyte apoptosis. These alterations in adipose tissue biology expand to involve systemic metabolism through alterations in endocrine functions of adipose tissue (via disturbed adipokine release), enhanced production of pro-inflammatory cytokines and excessive free fatty-acid release due to lipolysis. The deleterious action of some antiretroviral drugs is an important factor in eliciting these alterations in adipose tissue. However, HIV-1 infection-related events and HIV-1-encoded proteins also contribute directly to the complex development of HALS through effects on adipocyte biology, or indirectly through the promotion of local inflammation in adipose tissue.

Effects of chronic intermittent hypoxia on genioglossus in rats

OBJECTIVE

The objective of this study was to investigate the effects of chronic intermittent hypoxia (CIH) on genioglossal ultrastructure and mitochondrial function as well as the intervention role of adiponectin (Ad).

METHODS

Forty-two Wistar rats were randomly divided into three groups with 14 rats in each. Rats in group A were kept breathing normal air, while rats in both groups B and C received the same CIH environment (a 2-min cycle, 1 min on, 1 min off with a nadir O(2) at 4-5%, 8 h/day for successive 5 weeks). However, rats in group C was given regular intravenous Ad injection (10 μg per time, twice a week for successive 5 weeks). A simultaneous intravenous injection of saline (0.5 ml per time) was carried in groups A and B. At the end of experiment, the genioglossal ultrastructure, the serum adiponectin levels, the mitochondrial membrane potential (ΔΨ(m)), and activities of respiratory chain complexes I and IV in mitochondrion of genioglossal cells were compared among groups.

RESULTS

Serum Ad level was significantly lower in group B than that in group A (P < 0.01). In group B, there were genioglussal myofibril discontinuities, lysis of myofilament, edema of mitochondria, and disruption of cristae, vacuolus, and lysis of some mitochondria. These pathological changes were less significant in group C. The relative value of ΔΨ(m) was the lowest in group B but the highest in group A (P < 0.01), with group B in between. The concentrations of mitochondrial complexes I and IV in group B were the lowest but became higher and higher from group C to A, with a significant difference among groups (all P < 0.05).

CONCLUSION

CIH could lead to hypoadiponectinemia, impaired genioglossal ultrastructure, and mitochondrial dysfunction. These changes could be improved by supplement of Ad.

Balancing mitochondrial redox signaling: a key point in metabolic regulation

Mitochondrial reactive oxygen species (mROS) have emerged as signaling molecules in physiology primarily as a result of studies of uncoupling mechanisms in mitochondrial respiration. The discovery that this mechanism negatively regulates mROS generation in many cell types has drawn the attention of the scientific community to the pathological consequences of excess mROS production. From reports of the energetic fluxes in cells grown under normal conditions, the hypothesis that mROS are an integrated physiological signal of the metabolic status of the cell has emerged. Here, we consider recent studies that support this point of view in two key nutrient sensors of the body, beta cells and the hypothalamus, which are the main coordinators of endocrine and nervous controls of energy metabolism and adipose tissue, which is of paramount importance in controlling body weight and, therefore, the development of obesity and type 2 diabetes. In this context, finely balanced mROS production may be at the core of proper metabolic maintenance, and unbalanced mROS production, which is largely documented, might be an important trigger of metabolic disorders.

Coenzyme Q as an antiadipogenic factor

Coenzyme Q (CoQ) is not only the single antioxidant synthesized in humans but also an obligatory element of mitochondrial functions. We have previously reported CoQ deficiency in white adipose tissue of ob/ob mice. We sought to determine (i) whether this deficit exists in all species and its relevance in human obesity and (ii) to what extent CoQ could be involved in adipocyte differentiation. Here we identified in rodents as well as in humans a specific very strong nonlinear negative correlation between CoQ content in subcutaneous adipose tissue and obesity indexes. This striking correlation reveals a threshold value similar in both species. This relative deficit in CoQ content in adipose tissue rapidly took place during the time course of high-fat-diet-induced obesity in mice. Adipocyte differentiation was assessed in vitro using the preadipocyte 3T3-F442A cell line. When CoQ synthesis was inhibited by a pharmacological approach using chlorobenzoic acid, this strongly triggered adipose differentiation. In contrast, adipogenesis was strongly inhibited when a long-term increase in CoQ content was obtained by overexpressing human 4-hydroxy benzoate acid polyprenyltransferase gene. Altogether, these data suggest that a strict level of CoQ remains essential for adipocyte differentiation, and its impairment is associated with obesity.

Dynamic regulation of mitochondrial network and oxidative functions during 3T3-L1 fat cell differentiation

Mitochondria have been shown to be impaired in insulin resistance-related diseases but have not been extensively studied during the first steps of adipose cell development. This study was designed to determine the sequence of changes of the mitochondrial network and function during the first days of adipogenesis. 3T3-L1 preadipocytes were differentiated into adipocytes without using glitazone compounds. At days 0, 3, 6, 9, and 12, mitochondrial network imaging, mitochondrial oxygen consumption, membrane potential, and oxidative phosphorylation efficiency were assessed in permeabilized cells. Gene and protein expressions related to fatty acid metabolism and mitochondrial network were also determined. Compared to preadipocytes (day 0), new adipocytes (days 6 and 9) displayed profound changes of their mitochondrial network that underwent fragmentation and redistribution around lipid droplets. Drp1 and mitofusin 2 displayed a progressive increase in their gene expression and protein content during the first 9 days of differentiation. In parallel with the mitochondrial network redistribution, mitochondria switched to uncoupled respiration with a tendency towards decreased membrane potential, with no variation of mtTFA and NRF1 gene expression. The expression of PGC1α and NRF2 genes and genes involved in lipid oxidation (UCP2, CD36, and CPT1) was increased. Reactive oxygen species (ROS) production displayed a nadir at day 6 with a concomitant increase in antioxidant enzyme gene expression. This 3T3-L1-based in vitro model of adipogenesis showed that mitochondria adapted to the increased number of lipid droplets by network redistribution and uncoupling respiration. The timing and regulation of lipid oxidation-associated ROS production appeared to play an important role in these changes.

Genetic Variance in Uncoupling Protein 2 in Relation to Obesity, Type 2 Diabetes, and Related Metabolic Traits: Focus on the Functional -866G>A Promoter Variant (rs659366)

Uncoupling proteins (UCPs) are mitochondrial proteins able to dissipate the proton gradient of the inner mitochondrial membrane when activated. This decreases ATP-generation through oxidation of fuels and may theoretically decrease energy expenditure leading to obesity. Evidence from Ucp((-/-)) mice revealed a role of UCP2 in the pancreatic β-cell, because β-cells without UCP2 had increased glucose-stimulated insulin secretion. Thus, from being a candidate gene for obesity UCP2 became a valid candidate gene for type 2 diabetes mellitus. This prompted a series of studies of the human UCP2 and UCP3 genes with respect to obesity and diabetes. Of special interest was a promoter variant of UCP2 situated 866bp upstream of transcription initiation (-866G>A, rs659366). This variant changes promoter activity and has been associated with obesity and/or type 2 diabetes in several, although not all, studies. The aim of the current paper is to summarize current evidence of association of UCP2 genetic variation with obesity and type 2 diabetes, with focus on the -866G>A polymorphism.

Chronically increased glucose uptake by adipose tissue leads to lactate production and improved insulin sensitivity rather than obesity in the mouse

AIMS/HYPOTHESIS

In adipocytes, triacylglycerol synthesis depends on the formation of glycerol 3-phosphate, which originates either from glucose, through glycolysis, or from lactate, through glyceroneogenesis. However, glucose is traditionally viewed as the main precursor of the glycerol backbone and thus, enhanced glucose uptake would be expected to result in increased triacylglycerol synthesis and contribute to obesity.

METHODS

To further explore this issue, we generated a mouse model with chronically increased glucose uptake in adipose tissue by expressing Gck, which encodes the glucokinase enzyme.

RESULTS

Here we show that the production of high levels of glucokinase led to increased adipose tissue glucose uptake and lactate production, improved glucose tolerance and higher whole-body and skeletal muscle insulin sensitivity. There was no parallel increase in glycerol 3-phosphate synthesis in vivo, fat accumulation or obesity. Moreover, at high glucose concentrations, in cultured fat cells overproducing glucokinase, glycerol 3-phosphate synthesis from pyruvate decreased, while glyceroneogenesis increased in fat cells overproducing hexokinase II.

CONCLUSIONS/INTERPRETATIONS

These findings indicate that the absence of glucokinase inhibition by glucose 6-phosphate probably led to increased glycolysis and blocked glyceroneogenesis in the mouse model. Furthermore, this study suggests that under physiological conditions, when blood glucose increases, glyceroneogenesis may prevail over glycolysis for triacylglycerol formation because of the inhibition of hexokinase II by glucose 6-phosphate. Together these results point to the indirect pathway (glucose to lactate to glycerol 3-phosphate) being key for fat deposition in adipose tissue.

Uncoupling protein 2 G(-866)A polymorphism: a new gene polymorphism associated with C-reactive protein in type 2 diabetic patients

Background

This study evaluated the relationship between the G(-866)A polymorphism of the uncoupling protein 2 (UCP2) gene and high-sensitivity C reactive protein (hs-CRP) plasma levels in diabetic patients.

Methods

We studied 383 unrelated people with type 2 diabetes aged 40-70 years. Anthropometry, fasting lipids, glucose, HbA1c, and hs-CRP were measured. Participants were genotyped for the G (-866)A polymorphism of the uncoupling protein 2 gene.

Results

Hs-CRP (mg/L) increased progressively across the three genotype groups AA, AG, or GG, being respectively 3.0 ± 3.2, 3.6 ± 5.0, and 4.8 ± 5.3 (p for trend = 0.03). Since hs-CRP values were not significantly different between AA and AG genotype, these two groups were pooled for further analyses. Compared to participants with the AA/AG genotypes, homozygotes for the G allele (GG genotype) had significantly higher hs-CRP levels (4.8 ± 5.3 vs 3.5 ± 4.7 mg/L, p = 0.01) and a larger proportion (53.9% vs 46.1%, p = 0.013) of elevated hs-CRP (> 2 mg/L). This was not explained by major confounders such as age, gender, BMI, waist circumference, HbA1c, smoking, or medications use which were comparable in the two genotype groups.

Conclusions

The study shows for the first time, in type 2 diabetic patients, a significant association of hs-CRP levels with the G(-866)A polymorphism of UCP2 beyond the effect of major confounders.

Antioxidant defenses in the rat placenta in late gestation: increased labyrinthine expression of superoxide dismutases, glutathione peroxidase 3, and uncoupling protein 2

Placental oxidative stress plays a key role in the pathophysiology of placenta-related disorders, most notably preeclampsia (PE) and intrauterine growth restriction (IUGR). Oxidative stress occurs when accumulation of reactive oxygen species (ROS) damages DNA, proteins and lipids, an outcome that is limited by antioxidant enzymes; mitochondrial uncoupling protein 2 (UCP2) may also limit oxidative stress by reducing ROS production. Here we characterized placental antioxidant defenses during normal gestation and following glucocorticoid-induced IUGR. Placentas were collected on Days 16 and 22 of normal rat pregnancy (term = Day 23) and at Day 22 after dexamethasone treatment from Day 13. Expression of several genes encoding antioxidant enzymes (Sod1, Sod2, Sod3, Cat, Gpx3, Txn1, Txnrd1, Txnrd2, and Txnrd3) and Ucp2 was measured by quantitative RT-PCR in the labyrinth (LZ) and junctional zones (JZ) of the placenta. Expression of Sod1 and Ucp2 mRNAs and the activity of xanthine oxidase, a source of ROS, all increased from Days 16 to 22 in both placental zones, whereas Sod2 and Gpx3 increased only in the rapidly growing LZ. In contrast, Sod3 and Txnrd1 expression fell in the LZ over this period, whereas total superoxide dismutase activity remained stable. Dexamethasone treatment reduced fetal-placental growth and LZ expression of Ucp2 but increased JZ expression of Txn1. Indices of placental oxidative damage (TBARS, F(2)-isoprostanes, and 8-OHdG) did not change with gestational age or dexamethasone, indicative of adequate antioxidant protection. Overall, our data suggest that the rat placenta is protected from oxidative stress by the dynamic zone- and stage-dependent expression of antioxidant defense genes.

Involvement of adiponectin-SIRT1-AMPK signaling in the protective action of rosiglitazone against alcoholic fatty liver in mice

The development of alcoholic fatty liver is associated with reduced adipocyte-derived adiponectin levels, decreased hepatic adiponectin receptors, and deranged hepatic adiponectin signaling in animals. Peroxisomal proliferator-activated receptor-gamma (PPAR-gamma) plays a key role in the regulation of adiponectin in adipose tissue. The aim of the present study was to test the ability of rosiglitazone, a known PPAR-gamma agonist, to reverse the inhibitory effects of ethanol on adiponectin expression and its hepatic signaling, and to attenuate alcoholic liver steatosis in mice. Mice were fed modified Lieber-DeCarli ethanol-containing liquid diets for 4 wk or pair-fed control diets. Four groups of mice were given a dose of either 3 or 10 mg.kg body wt(-1).day(-1) of rosiglitazone with or without ethanol in their diets for the last 2 wk of the feeding study. Coadministration of rosiglitazone and ethanol increased the expression and circulating levels of adiponectin and enhanced the expression of hepatic adiponectin receptors (AdipoRs) in mice. These increases correlated closely with the activation of a hepatic sirtuin 1 (SIRT1)-AMP-activated kinase (AMPK) signaling system. In concordance with stimulated SIRT1-AMPK signaling, rosiglitazone administration enhanced expression of fatty acid oxidation enzymes, normalized lipin 1 expression, and blocked elevated expression of genes encoding lipogenic enzymes which, in turn, led to increased fatty acid oxidation, reduced lipogenesis, and alleviation of steatosis in the livers of ethanol-fed mice. Enhanced hepatic adiponectin-SIRT1-AMPK signaling contributes, at least in part, to the protective action of rosiglitazone against alcoholic fatty liver in mice.