糖皮质激素对高脂饮食肥胖大鼠棕色脂肪和骨骼肌PGC-1αmRNA表达的影响

实时荧光定量PCR方法检测大鼠棕色脂肪和骨骼肌中PPARγ辅激活因子1α(PGC-1α)mRNA的表达.肥胖大鼠棕色脂肪和骨骼肌中PGC-1α mRNA表达水平低于普通大鼠(均P<0.01);应用高剂量糖皮质激素后普通大鼠和肥胖大鼠棕色脂肪和骨骼肌中PGC-1α mRNA表达水平降低.     

Lipoprotein lipase of adipose tissue and skeletal muscle in human obesity: Response to glucose and to semistarvation

Obesity is frequently associated with elevated plasma levels of triglyceride and very low density lipoproteins (VLDL). It is possible that this could be at least partly attributed to defective removal of triglycerides from circulation. Therefore, we studied the response of tissue lipoprotein lipase (LPL) activity to stimulation by glucose and to suppression by caloric deficiency in subjects with simple obesity and in nonobese controls. A five-hour intravenous infusion of glucose increased the LPL activity in both adipose tissue and skeletal muscle. The average rise was 2.5-fold in nonobese subjects but only 1.8-fold in obese patients (p < 0.05). The decrease of response was similar in obese subjects with and in those without hypertriglyceridemia suggesting that the change was due to obesity as such. During feeding a 400 cal diet for 7 days the LPL activity of obese subjects fell by an average of 50% in adipose tissue and by 40% in skeletal muscle. The decreases are smaller than previously found in nonobese human subjects in a similar experiment. The magnitude of decrease of LPL activity in both tissues was positively correlated with initial enzyme activity but was not influenced by serum triglyceride level. During starvation the HDL cholesterol levels were reduced the change being positively related to simultaneous decreases of LPL activity in adipose tissue and in skeletal muscle. It is concluded that the metabolic regulation of tissue LPL activity (of the heparin-releasable pool) is abnormal in obesity. This may be related to insulin resistance of obese people and it may explain why obese people are basically more prone to develop hypertriglyceridemia than lean ones. The resistance of LPL to caloric restriction in obese subjects could bear on difficulties in reducing the adipose tissue mass.     

Brown adipocyte progenitor population is modified in obese and diabetic skeletal muscle

Brown adipose tissue mitochondria express the unique thermogenic uncoupling protein-1. Recently, brown adipocyte progenitors have been identified in the CD34+ cell population of human skeletal muscle. The aims of this study were firstly to determine if obesity and diabetes have altered amounts of muscle brown adipocyte progenitors and, secondly, to establish if the latter are correlated with clinical parameters of obesity and diabetes. Body mass index (BMI), plasma glucose, insulin, cholesterol and triglycerides as well as homeostasis model assessment were measured in lean (n=10), obese (n=18) and obese-diabetic (n=15) subjects and muscle biopsies were taken from the rectus abdominus. CD34 being also expressed on endothelial cells, we measured CD31, another endothelial marker, and expressed the brown adipocyte progenitors, as the CD34/CD31 mRNA ratio. The latter was significantly reduced in the obese vs lean subjects suggesting a smaller pool of brown adipocyte progenitors. More strikingly, for lean and obese subjects negative correlations were observed between the CD34/CD31 mRNA ratios and BMI, fasting insulin levels and homeostasis model assessment. These correlations highlight the potential physiological relevance of the muscle CD34/CD31 mRNA ratio.     

Relationship between peroxisome proliferator-activated receptor gamma and retinoic acid receptor alpha gene expression in obese human adipose tissue

OBJECTIVE: To investigate in human adipose tissue a possible relationship between per oxisome proliferator-activated receptor gamma (PPARgamma) and retinoic acid receptor alpha (RARalpha) gene expression, two genes involved in the control of adipocyte differentiation. SUBJECTS: Ten lean control women (age 31-60 y, body mass index (BMI) 18-24.7 kg/m(2)) and an obese group of 15 women (age 27-62 y, BMI 30-57.5 kg/m(2)), of whom 10 subjects were in weight-gain phase and five were in weight-loss phase. MEASUREMENTS: We assessed the relative PPARgamma and RARalpha mRNA levels in subcutaneous abdominal adipose tissue using a real-time PCR method. RESULTS: PPARgamma mRNA level were significantly increased (+91%; P<0.01) in obese women compared to lean control women. In the obese group, we observed a PPARgamma mRNA level 42% lower in weight-loss obese than in weight-gain obese subjects. We obtained a positive correlation (r=0.56; P<0.01) between PPARgamma mRNA level and the BMI of all subjects. Relative mRNA abundance level of RARalpha in subcutaneous adipose tissue of obese subjects is significantly lower than in control subjects (-56%, P<0.01), and a negative correlation was found between PPARgamma and RARalpha mRNA levels in subcutaneous adipose tissue of subjects study (r=-0.75; P<0.01). CONCLUSION: Our findings suggest that obesity is associated with an inverse relationship between PPARgamma and RARalpha expressions in human subcutaneous adipose tissue. Modulations of nuclear receptor profile could be an important event in the body's early adaptive mechanisms promoting adipose tissue plasticity and leading to the onset of obesity.     

The fatty acid transporter FAT/CD36 is upregulated in subcutaneous and visceral adipose tissues in human obesity and type 2 diabetes

BACKGROUND: Long-chain fatty acids (LCFAs) cross the plasma membrane via a protein-mediated mechanism involving one or more LCFA-binding proteins. Among these, FAT/CD36 has been identified as key LCFA transporter in the heart and skeletal muscle, where it is regulated acutely and chronically by insulin. In skeletal muscle, FAT/CD36 expression and/or subcellular distribution is altered in obesity and type 2 diabetes. There is limited information as to whether the expression of this protein is also altered in subcutaneous and/or visceral adipose tissue depots in human obesity or type 2 diabetes. OBJECTIVES: To compare (a) the expression of FAT/CD36 in subcutaneous and visceral adipose tissue depots in lean, overweight, and obese individuals and in type 2 diabetics, (b) to determine whether the protein expression of FAT/CD36 in these depots is associated with the severity of insulin resistance (type 2 diabetes>obese>overweight/lean) and (c) whether FAT/CD36 protein expression in these adipose tissue depots is associated with alterations in circulating substrates and hormones. SUBJECTS: Subjects who were undergoing abdominal surgery and who were lean (n=10; three men, seven women), overweight (n=10; three men, seven women) or obese (n=7; one man, six women), or who had been diagnosed with type 2 diabetes (n=5; one man, four women) participated in this study. MEASUREMENTS: Subcutaneous and visceral adipose tissue samples, as well as blood samples, were obtained from the subjects while under general anesthesia. Adipose tissue samples were analyzed for FAT/CD36 using Western blotting. Serum samples were analyzed for glucose, insulin, FFA and leptin. BMI was also calculated. RESULTS: Subcutaneous adipose tissue FAT/CD36 expression was upregulated by +58, +76 and +150% in overweight, obese and type 2 diabetics, respectively. Relative to subcutaneous adipose tissue, visceral adipose tissue FAT/CD36 expression was upregulated in lean (+52%) and overweight subjects (+30%). In contrast, in obese subjects and type 2 diabetics, no difference in FAT/CD36 protein expression was observed between their subcutaneous and visceral adipose tissue depots (P>0.05). The subcutaneous adipose tissue FAT/CD36 expression (R=0.85) and the visceral adipose tissue FAT/CD36 expression (R=0.77) were associated with alteration in BMI and circulating glucose and insulin. CONCLUSIONS: Subcutaneous adipose tissue FAT/CD36 expression is upregulated in obesity and type 2 diabetes. As FAT/CD36 expression is not different in lean, overweight and obese subjects, and was only increased in type 2 diabetics, it appears that visceral adipose tissue FAT/CD36 may respond in a less dynamic manner to metabolic disturbances than subcutaneous adipose tissue FAT/CD36.     

Expression of adrenomedullin in adipose tissue of lean and obese women

OBJECTIVE: Adrenomedullin (AM), a potent vasodilatator and antioxidative peptide, was shown recently to be expressed by adipose tissue. The aim of our study was to investigate the precise localization of AM within human adipose tissue, and to examine AM regulation in obesity. DESIGN: Subcutaneous (SC) and omental (OM) adipose tissues from 9 lean and 13 obese women were profiled for AM expression changes. Preadipocytes from human adipose tissue were isolated and differentiated under defined adipogenic conditions. METHODS: AM expression was analyzed by immunohistochemistry, in situ hybridization and quantitative RT-PCR. RESULTS: A strong AM expression was observed in vessel walls, stromal cell clusters and isolated stromal cells, some of them being CD 68 positive, whereas mature adipocytes were not labeled. Calcitonin receptor-like receptor and receptor activity-modifying proteins (RAMP) 2 and RAMP 3 were expressed in vessel walls. In vitro, preadipocytes of early differentiation stages spontaneously secreted AM. No difference in AM localization was found between SC and OM adipose tissue. AM levels in SC tissue did not differ between lean and obese subjects. By contrast, AM levels in OM tissue were significantly higher in obese as compared with lean women. Moreover, we found a positive relationship between OM AM and tumor necrosis factor alpha mRNA levels and AM-immunoreactive area in OM tissue followed the features of the metabolic syndrome. CONCLUSION: Stromal cells from human adipose tissue, including macrophages, produce AM. Its synthesis increased in the OM territory during obesity and paralleled the features of the metabolic syndrome. Therefore, AM should be considered as a new member of the adipokine family.     

Effects of cannabinoid receptors on skeletal muscle oxidative pathways

The endocannabinoids, a recently discovered endogenous, lipid derived, signaling system regulating energy metabolism, have effects on central and peripheral energy metabolism predominantly via the cannabinoid receptor type 1 (CB1). CB1 is expressed centrally in the hypothalamus and nucleus accumbens and peripherally in adipocytes and skeletal muscle. This study determined the effect of endocannabinoids on the expression of genes regulating energy metabolism in human skeletal muscle. Primary cultures of myotubes (lean and obese; n=3/group) were treated with the cannabinoid receptor agonist, anandamide (AEA) (0.2 and 5microM) and the CB1 specific antagonist AM251 (0.2 and 5microM) separately and in combination for 24h. The expression of mRNA for AMP-activated protein kinase (AMPK) alpha 1 (alpha1) and alpha 2 (alpha2), pyruvate dehydrogenase kinase 4 (PDK4) and peroxisome proliferator-activated receptor-gamma co-activator-1alpha (PGC-1alpha) were determined using 'Real Time' RT-PCR. AMPKalpha1 mRNA increased in lean and obese myotubes in response to AM251 (P<0.05). AEA inhibited the effect of AM251 on AMPKalpha1 mRNA levels in myotubes from lean and obese subjects (P<0.05); the dose-response curve was shifted to the left in the obese. In response to AM251, irrespective of the presence of AEA, PDK4 expression was decreased in lean and obese myotubes (P<0.05). Taken together these data suggest that endocannabinoids regulate pathways affecting skeletal muscle oxidation, effects particularly evident in myotubes from obese individuals.     

AMP-activated protein kinase is not down-regulated in human skeletal muscle of obese females

Obesity in humans is associated with lipid accumulation in skeletal muscle, insulin and leptin resistance, and type 2 diabetes. AMP-activated protein kinase (AMPK) is an important regulator of fatty acid (FA) metabolism in skeletal muscle. To address the hypothesis that lipid accumulation in skeletal muscle of obese subjects may be due to down-regulation of AMPK, we measured mRNA and protein levels of AMPK isoforms, AMPKalpha1 and -alpha2 activity, AMPK kinase activity, acetyl-coenzyme A carboxylase (ACCbeta) expression and phosphorylation, and FA metabolism in biopsies of rectus abdominus muscle from lean and obese women. We also examined the effect of 5-aminoimidazole-4-carboxamide riboside (AICAR) on AMPK activity and the effects of AICAR and leptin on FA metabolism. Skeletal muscle of obese subjects had increased total FA uptake and triglyceride esterification, and leptin failed to stimulate FA oxidation. However, AMPK mRNA and protein expression, AMPKalpha1 and -alpha2 activities, AMPK kinase activity, ACCbeta phosphorylation, and FA oxidation were similar in lean and obese subjects. Moreover, AICAR increased AMPKalpha2 activity, ACCbeta phosphorylation, and palmitate oxidation to a similar degree in muscle from lean and obese subjects. We conclude that the abnormal lipid metabolism and leptin resistance of skeletal muscle of obese subjects is not due to down-regulation of AMPK. In addition, the similar stimulation by AICAR of AMPK in skeletal muscle of lean and obese subjects suggests that direct pharmacological activation of AMPK may be a therapeutic approach for stimulating FA oxidation in the treatment of human obesity.     

Adipose tissue expression of the glycerol channel aquaporin-7 gene is altered in severe obesity but not in type 2 diabetes

CONTEXT: Aquaporin-7 is required for efflux of glycerol from adipocytes and influences whole-body glucose homeostasis in animal studies. OBJECTIVE: Our objective was to test the hypothesis that AQP7 gene expression levels may be affected by presence of obesity and type 2 diabetes in humans. DESIGN: The obesity study cohort consisted of 12 lean, 22 nonseverely obese, and 13 severely obese subjects. The type 2 diabetes study cohort consisted of 17 lean and 39 obese type 2 diabetic patients. Circulating levels of plasma soluble proteins monocyte chemoattractant protein-1, TNF receptors 1 and 2, and IL-6 and glycerol were measured. The sc adipose tissue gene expression of AQP7, MCP-1, IL-6, TNFalpha, PPARgamma, and SREBP1c genes was measured by real-time PCR. AQP7 gene mutation analysis was performed. RESULTS: Severely obese women showed lower AQP7 expression levels compared with lean and nonseverely obese (P < 0.001). Moreover, circulating glycerol concentration was lower in severely obese subjects, but no correlation with AQP7 adipose tissue expression was observed. AQP7 expression was negatively related with proinflammatory genes (for monocyte chemoattractant protein-1, r = -0.203 and P = 0.044; for TNFalpha, r = -0.209 and P = 0.036). Concerning adipogenic factors, AQP7 expression levels were found to be positively determined by PPARgamma mRNA expression levels (r = 0.265; P = 0.012). AQP7 expression did not show differences regarding the presence of type 2 diabetes. CONCLUSION: Expression of AQP7 is down-regulated in women with severe obesity. The expression of this glycerol channel is not affected by type 2 diabetes.     

Reduced plasma visfatin/pre-B cell colony-enhancing factor in obesity is not related to insulin resistance in humans

CONTEXT: Visfatin was recently identified as a protein highly expressed and secreted in adipose tissue with insulin-mimetic effect and is a candidate hormone to help explain the association among adipose tissue expansion, insulin resistance, and type 2 diabetes. OBJECTIVE: The objective of the study was to assess expression of visfatin in lean and obese subjects and in sc and visceral adipose tissue and moreover to explore the role of visfatin on insulin resistance in humans. DESIGN: We measured circulating visfatin and its mRNA expression in sc adipose tissue (SAT) in lean and obese subjects. Furthermore, we measured visfatin mRNA in visceral adipose (VAT) and SAT by quantitative RT-PCR. Finally, plasma visfatin and its mRNA in SAT were measured under free fatty acid-induced insulin resistance in healthy subjects. RESULTS: Plasma visfatin and its mRNA in SAT were significantly lower in obese subjects, compared with normal-weight controls. Both circulating visfatin and SAT visfatin mRNA were negatively correlated with body mass index, whereas no correlation was found with homeostasis model assessment. Significantly higher visfatin mRNA was found in VAT of obese subjects, compared with lean controls. Interestingly, visfatin mRNA in VAT was positively correlated with BMI. Elevation of free fatty acid induced a condition of insulin resistance but did not affect either circulating visfatin or its mRNA. CONCLUSIONS: Our findings show that, in human obesity, plasma visfatin is reduced, whereas visfatin mRNA is differentially regulated in SAT and VAT. Visfatin is not related to insulin resistance either as assessed by homeostasis model assessment or during lipid infusion.     

Human adipose tissue cannabinoid receptor 1 gene expression is not related to fat cell function or adiponectin level

CONTEXT: The cannabinoid receptor 1 gene (CNR1) is implicated in adipocyte function. OBJECTIVE: We investigated human adipose tissue CNR1 mRNA in relation to obesity, clinical and metabolic variables, adipocyte function, and adiponectin (ADIPOQ) levels. METHODS: We assessed sc fat biopsies from 96 obese and nonobese subjects and omental fat biopsies from 82 obese and nonobese subjects. RESULTS: The sc and omental adipose CNR1 gene expression were similar in obese and nonobese subjects. No association between either sc or omental adipose CNR1 mRNA levels and body mass index, waist circumference, plasma levels of glucose and insulin, lipids, or blood pressure was found. The sc and omental maximal adrenergic lipolytic activation as well as lipolytic adrenoceptor sensitivity were not related to CNR1 gene expression. Lipogenesis in sc adipocytes also showed no association with CNR1 mRNA levels. Finally, no relation was found between adipose CNR1 gene expression and ADIPOQ mRNA, adipose tissue adiponectin secretion, or circulating adiponectin. CONCLUSION: We found no association of human adipose tissue CNR1 mRNA expression with measures of body fat, metabolic parameters, fat cell function, or ADIPOQ expression. These data do not suggest a major role of human adipose CNR1 in fat cell function or metabolic disease development.     

Lower expression of adiponectin mRNA in visceral adipose tissue in lean and obese subjects

Adiponectin is an adipocyte-specific protein suggested to play a role in mediating the metabolic effects of obesity. In the present study, we investigated adiponectin mRNA levels in both visceral and subcutaneous abdominal adipose tissue (AT) from lean and obese subjects. Investigations on both "fresh" fat biopsies and incubations of AT fragments were performed. Regional differences in the effects of the cytokine interleukin-1beta (IL-1beta) were investigated. Adiponectin gene expression was 33% lower in visceral AT than in subcutaneous AT of lean subjects (P < 0.05), and 28% lower in obese subjects, albeit non-significant (P = 0.3). In both lean and obese subjects adiponectin mRNA expression in incubated AT fragments was significantly lower in visceral AT than in subcutaneous AT (lean: P < 0.01; obese: P < 0.05). No difference was found in adiponectin mRNA levels in gluteal compared to abdominal subcutaneous AT. IL-1beta suppressed adiponectin mRNA levels substantially in both subcutaneous and visceral AT. In conclusion, adiponectin gene expression is lower in visceral AT than in subcutaneous abdominal AT, suggesting subcutaneous AT to be more important for circulating adiponectin levels.     

The leptin-like effects of 3-d peripheral administration of a melanocortin agonist are more marked in genetically obese Zucker (fa/fa) than in lean rats

The effects of a 3-d peripheral administration of an alpha-MSH agonist, MTII, on body weight and the expression of uncoupling proteins (UCPs) and carnitine palmitoyltransferase-1 were determined in lean and genetically obese fa/fa rats by comparing MTII-treated animals with two different control groups, one being ad libitum fed, the other pair-fed to the amount of food consumed by MTII-treated rats. MTII treatment of lean and obese rats lowered food intake and body weight, the effects being more marked in obese than in lean rats. In both groups, MTII administration suppressed the increased plasma FFA levels brought about by food restriction. In lean rats, MTII prevented the decrease in brown adipose tissue UCP1, UCP2, and UCP3 expression and muscle UCP3 occurring during food restriction. In obese animals, MTII markedly increased brown adipose tissue (7-fold) and muscle (2.5-fold) UCP3 expression. The decrease in liver carnitine palmitoyltransferase-1 elicited by food restriction in lean and obese rats was prevented by MTII administration. In summary, the effects of MTII resemble those of leptin and are more marked in obese than in lean animals, in keeping with their reported reduced endogenous melanocortin tone. Melanocortin agonists may be useful in the treatment of obesity associated with impaired leptin signaling.     

Effects of obesity and weight loss on the expression of proteins involved in fatty acid metabolism in human adipose tissue

OBJECTIVE: Disturbances in adipocyte lipolysis in obesity may contribute to elevated circulating non-esterified fatty acid (NEFA) concentrations and insulin resistance. In experimental models, NEFA metabolism is influenced by adipocyte proteins such as adipocyte and keratinocyte lipid binding proteins (aP2/ALBP and mal1/KLBP) and fatty acid translocase (CD36). We investigated the effect of obesity and weight loss on the expression of these proteins in human subcutaneous adipose tissue. STUDY DESIGN AND SUBJECTS: Subcutaneous adipose tissue was obtained from 12 obese (body mass index (BMI) 42.4+/-1.6 kg/m(2)) and 12 lean (23.4+/-0.6 kg/m(2)) subjects. The obese subjects underwent gastric banding and biopsies were taken again after 2 y following a significant weight reduction (BMI 32.8+/-1.4 kg/m(2)). Adipose tissue proteins were quantified by Western blotting. RESULTS: Differential expression of ALBP, KLBP and CD36 was observed in lean and weight-reduced subjects compared with obese individuals. This resulted in a significantly lower ALBP/KLBP ratio in lean and weight-reduced individuals compared to obese subjects. Furthermore there was a significant influence of gender on this ratio. Moreover, the commonly used internal standard protein actin was expressed significantly higher in lean compared to obese individuals. CONCLUSION: The relative content of ALBP and KLBP in human adipose tissue changes with obesity, weight loss and gender indicating differential regulation. Differing responses in the expression patterns of adipose tissue proteins capable of binding NEFAs in response to weight changes suggest a potential importance in the development of obesity-associated complications.