Adipose triglyceride lipase gene expression in human visceral obesity.

In comparison to subcutaneous (SC) fat, visceral adipose tissue is more sensitive to catecholamine-induced lipolysis and less sensitive to the antilipolytic effects of insulin. Variation in the expression of lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL) have been reported. We therefore hypothesized that expression of adipose triglyceride lipase (ATGL) is different in visceral and SC depot and investigated whether ATGL mRNA expression is related to obesity, fat distribution and insulin sensitivity. ATGL, LPL, and HSL mRNA expression was measured in 85 paired samples of omental and subcutaneous adipose tissue in normal glucose tolerant lean and obese individuals. In addition, we included a subgroup of obese (BMI >30 kg/m2) individuals with either impaired or preserved insulin sensitivity determined by euglycemic-hyperinsulinemic clamps. ATGL mRNA levels are significantly decreased in insulin resistant obese subjects. Independently of body fat mass, omental ATGL mRNA correlates with fasting insulin concentration, glucose uptake during the steady state of the clamp and HSL mRNA expression. In obese, but not in lean subjects, LPL and HSL mRNA expression was significantly higher in omental compared to SC fat. In both depots, HSL mRNA was significantly lower in obese individuals. Visceral HSL mRNA expression is closely related to adipocyte size and fasting plasma insulin concentrations, whereas visceral fat area significantly predicts visceral LPL mRNA expression. ATGL mRNA expression is not significantly different between omental and SC fat. HSL, but not ATGL mRNA expression is closely related to individual and regional differences in adipocyte size. Impaired insulin sensitivity was associated with decreased ATGL and HSL mRNA expression, independently of body fat mass and fat distribution.     

吡格列酮对肥胖大鼠脂肪甘油三酯脂酶表达的调控

观察吡格列酮对高脂饮食诱导胰岛素抵抗大鼠脂肪、肝脏、肌肉三大组织脂肪甘油三酯脂酶(adipose triglyceride lipase,ATGL)表达的变化.结果显示吡格列酮促进胰岛素抵抗大鼠脂肪、肝脏、肌肉三大代谢组织中ATGL的表达.     

Role of hexosamines in insulin resistance and nutrient sensing in human adipose and muscle tissue

It has been proposed that the hexosamine pathway acts as a nutrient-sensing pathway, protecting the cell against abundant fuel supply, and that accumulation of hexosamines represents a biochemical mechanism by which hyperglycemia and hyperlipidemia induce insulin resistance. We hypothesized that if an increased flux through the hexosamine pathway caused insulin resistance in humans, the hexosamine levels should be increased in adipose and/or muscle tissue in insulin-resistant subjects, such as patients with type 2 diabetes and obese individuals. In addition, we reasoned that if the hexosamine pathway were a nutrient-sensing pathway, hexosamine levels in adipose and skeletal muscle tissue should be correlated with levels of circulating nutrients, such as glucose and free fatty acids (FFAs) and leptin concentrations.In a human cross-sectional study of 55 patients [20 with type 2 diabetes mellitus (DM) and 21 normal-lean (NL) and 14 normal-obese (NO) subjects] who underwent hip replacement surgery, adipose and muscle tissue biopsies were obtained and analyzed for levels of hexosamines [UDP-N-acetylglucosamine (UDP-GlcNAc) and UDP-N-acetylgalactosamine] and hexoses (UDP-glucose and UDP-galactose). Fasting plasma glucose, glycosylated hemoglobin, serum insulin and homeostasis model assessment calculations, serum lipids, and leptin were measured on the same day.Hexosamines were not elevated in adipose and muscle tissue of patients with type 2 DM compared with NL and NO subjects (UDP-GlcNac DM vs. NL vs. NO, 3.3 +/- 2.3 vs. 2.2 +/- 2.1 vs. 3.0 +/- 2.0 nmol/g tissue in adipose tissue and 8.1 +/- 2.9 vs. 7.8 +/- 2.8 vs. 7.6 +/- 2.8 nmol/g tissue in muscle tissue, respectively). Hexosamines in adipose tissue were positively correlated with circulating levels of FFA (UDP-GlcNAc, r = 0.33, P < 0.05; UDP-N-acetylgalactosamine, r = 0.41, P < 0.01). Adipose tissue UDP-GlcNAc was correlated with leptin levels (r = 0.33; P < 0.05). No such relationship was identified in muscle tissue.In conclusion, these findings argue against a pathophysiological role of the hexosamine pathway in insulin resistance in humans but support the hypothesis that the hexosamine pathway in adipose tissue, not in muscle, is a FFA-sensing pathway and could be involved in the regulation of leptin expression.     

Adipose triglyceride lipase and hormone-sensitive lipase protein expression in subcutaneous adipose tissue is decreased after an isoenergetic low-fat high-complex carbohydrate diet in the metabolic syndrome

The objective was to determine the contribution of dietary fat quantity and composition to lipolysis and lipolytic gene expression in humans in relation to obesity, insulin resistance, and the metabolic syndrome (MetS). Men and women with the MetS were randomly assigned to one of four isoenergetic diets: a high-fat saturated fat diet (n=10), a high-fat monounsaturated fat diet (n=7), and two low-fat high-complex carbohydrate (LFHCC) diets, one supplemented with 1.24g/day long-chain n-3 PUFA (LFHCC: n=7, LFHCCn-3: n=8). Subcutaneous adipose tissue biopsies were taken before and after the 12-week dietary intervention period. ATGL and HSL mRNA and protein expression was determined. Whole body rate of appearance of free fatty acids (Ra(FFA)) was determined by intravenous infusion of [(2)H(2)]-palmitate in a subgroup of men (n=20). Adipose tissue ATGL and HSL mRNA and protein expression was not affected by alterations in dietary fat composition. Pooled analysis comparing the low- and high-fat diets showed that ATGL and HSL protein expression was significantly reduced after the LFHCC diets (P=.04), irrespective of long-chain n-3 PUFA. Moreover, LFHCC diets lowered fasting insulin, HOMA(IR), and (LDL)-cholesterol concentrations (P≤.05). Changes in ATGL and HSL protein expression was positively associated with changes in whole body Ra(FFA) (P<.03). The low-fat high-complex carbohydrate diets reduced ATGL and HSL protein expression and significantly improved circulating lipids and insulin sensitivity. Under isoenergetic conditions, dietary fat quantity, rather than composition, may be most important for modulating subcutaneous adipose tissue ATGL and HSL protein expression.     

Adipose tissue lipoprotein lipase in chronic hemodialysis: role in plasma triglyceride metabolism.

The role of adipose tissue lipoprotein lipase (LPL) in the pathogenesis of hypertriglyceridemia in uremic patients receiving maintenance hemodialysis was evaluated. The fasting level of adipose tissue LPL activity was reduced below normal (3.4 +/- 2.5 microU/106 cells; n = 23; mean +/- SD) in hypertriglyceridemic dialysis patients (1.5 +/- 0.8; P less than 0.01; n = 15) and did not differ from normal in normotriglyceridemic dialysis patients (2.5 +/- 2.4; P = NS; n = 13). The enzyme activity increased as a function of relative body weight in normotriglyceridemic hemodialysis patients (r = 0.21; P less than 0.05) but not in the hypertriglyceridemic group (r = 0.21; P = NS). There was an abnormal response of LPL to feeding in the hypertriglyceridemic dialysis patients. The postprandial level of LPL was significantly lower in hypertriglyceridemic dialysis patients (2.2 +/- 1.0; n = 9) than in normotriglyceridemic dialysis patients (3.9 +/- 1.9; P less than 0.05; n = 10) or normal controls (4.8 +/- 1.8; P less than 0.01; n = 12). Whereas the postprandial change in LPL was inversely related to the fasting enzyme activity in normotriglyceridemic dialysis patients (r = 0.74; P less than 0.02; n = 10) and in normal controls (r = 0.58; P less than 0.05; n = 12), no such relationship existed in hypertriglyceridemic dialysis patients (r = 0.17; P = NS; n = 9). Furthermore, fasting plasma triglyceride levels in the entire group of dialysis patients were a function of the postprandial level of LPL activity (rs = 0.574; P less than 0.02; n = 19). Since the level of LPL 1) is below normal in both the fasted and fed state in the hypertriglyceridemic hemodialysis patients, 2) is normal in both the fasted and fed state in the normotriglyceridemic hemodialysis patients, and 3) in the fed state is inversely correlated with the fasting plasma triglyceride concentration in the entire group of hemodialysis patients, it is proposed that adipose tissue LPL plays a role in the etiology of hypertriglyceridemia in hemodialysis patients.     

Lipoprotein lipase activity of adipose tissue and skeletal muscle in insulin-deficient human diabetes

Summary We have previously shown that lipoprotein lipase (LPL) activity of tissues is an important determinant not only of plasma VLDL levels but also of HDL-cholesterol. Studies were designed to investigate whether the serum lipoprotein alterations in uncontrolled insulin-deficient diabetes can be accounted for by changes in LPL activity of tissues. The heparin-releasable LPL activity was determined from biopsy samples of adipose tissue and skeletal muscle in 16 patients with newly detected untreated insulin-deficient diabetes and in 16 age-, sex- and body weight-matched healthy control subjects. Repeat assays were carried out after the patients had been on insulin treatment for an average of two weeks and when the diabetes was well controlled. When untreated the patients had increased concentrations of triglycerides and cholesterol in whole serum and in VLDL and LDL while the HDL cholesterol level was lower than that of controls (p<0.01). The cholesterol/triglyceride ratio in each of the three lipoproteins was similar in patients and controls. While untreated the diabetic patients had significantly reduced mean LPL activity both in adipose tissue (average 34% of control mean, p<0.001) and in skeletal muscle (average 45% of control mean, p<0.05). In the whole group HDL-cholesterol was positively correlated with adipose tissue LPL activity (r=+0.58, p<0.001) while log serum total triglyceride and log VLDL-triglyceride showed significant negative correlations with LPL activity of both adipose tissue and skeletal muscle. After initiation of insulin treatment the LPL activity increased significantly (p<0.01) in both tissues but was still subnormal after 2 weeks. At the same time the VLDL and LDL concentrations had returned to normal while the HDL-cholesterol remained low. The results suggest that the increase of VLDL and LDL triglyceride and the decrease of HDL-cholesterol present in uncontrolled insulin-deficient diabetes are, at least partly, accounted for by decreased LPL activity of tissues. The restoration of tissue LPL and of serum HDL-cholesterol by insulin are relatively slow processes. The results are consistent with the hypothesis that HDL-cholesterol concentration is dependent on the efficiency of removal of triglyceride-rich lipoproteins from the circulation.     

Expression of fatty-acid-handling proteins in human adipose tissue in relation to obesity and insulin resistance

Aims/hypothesis Protein-mediated trans-membrane and intracellular fatty acid trafficking are becoming increasingly recognised as biochemically and physiologically important concepts. Obesity and insulin resistance are polygenic disorders, heavily influenced by environmental and life-style factors, and are virtually always associated with disturbed fatty acid metabolism in adipose and other tissues. The aim of this study was to investigate mRNA expression levels of fatty-acid-handling proteins in adipose tissue in relation to markers of genetic and acquired obesity and insulin resistance.Methods We quantified mRNA expression of subcutaneous adipose tissue fatty-acid-handling proteins (ALBP, KLBP, FATP1, FATP4, CD36, ACS1) in 17 monozygotic twin-pairs with a range of intra-pair differences () in BMI and detailed measures of obesity and insulin resistance, allowing influences of genetic and non-genetic factors to be distinguished.Results In acquired obesity FATP4 expression was up-regulated independently of genetic background (FATP4 versus BMI; r=0.50, p=0.04; FATP4 versus body fat; r=0.59, p=0.01). Similarly, CD36 and FATP1 expression correlated with acquired differences in HDL cholesterol and non-esterified fatty acid concentrations respectively. Moreover, FATP4 and CD36 expression levels correlated with measures of obesity and insulin resistance that are influenced by both genetic and non-genetic factors (FATP4 versus BMI: r=0.53, p=0.0001; FATP4 versus body fat: r=0.51, p=0.002; FATP4 versus homeostasis model assessment [HOMA]: r=0.49, p=0.001; CD36 versus BMI: r=0.50, p=0.02; CD36 versus body fat: r=0.63, p=0.001; CD36 versus HOMA: r=0.34, p=0.06).Conclusions/interpretation These findings indicate that expression of specific adipose tissue fatty-acid-handling proteins is related to obesity and insulin resistance, and that, in particular, FATP4 plays a role in acquired obesity. Our results suggest that facilitated fatty acid trafficking is a physiologically and pathologically relevant phenomenon in man.Abbreviations ACS acyl-CoA synthase - ALBP adipocyte lipid-binding protein - FABP fatty-acid-binding protein - FATP fatty acid transport protein - HOMA homeostasis model assessment - KLBP keratinocyte lipid-binding protein - MZ monozygotic - TBP TATA-box binding protein - TG triglycerideThis revised version was published online in June 2004 with corrections to title and author addresses.     

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.     

脂肪组织巨噬细胞浸润与胰岛素抵抗

肥胖是一种低度炎性反应状态.近年来发现肥胖个体脂肪组织中巨噬细胞的浸润显著增加,并有研究表明脂肪组织的炎性反应因子主要由浸润的巨噬细胞分泌.目前对脂肪组织巨噬细胞的来源以及影响其浸润的因素还有争论.研究发现,巨噬细胞可以通过抑制脂肪细胞分化,增加炎性反应因子的表达等导致胰岛素抵抗的发生、发展.     

FKBP5 expression in human adipose tissue increases following dexamethasone exposure and is associated with insulin resistance

Objective

To study effects of dexamethasone on gene expression in human adipose tissue aiming to identify potential novel mechanisms for glucocorticoid-induced insulin resistance.

Materials/methods

Subcutaneous and omental adipose tissue, obtained from non-diabetic donors (10 M/15 F; age: 28–60 years; BMI: 20.7–30.6 kg/m²), was incubated with or without dexamethasone (0.003–3 μmol/L) for 24 h. Gene expression was assessed by microarray and real time-PCR and protein expression by immunoblotting.

Results

FKBP5 (FK506-binding protein 5) and CNR1 (cannabinoid receptor 1) were the most responsive genes to dexamethasone in both subcutaneous and omental adipose tissue (~ 7-fold). Dexamethasone increased FKBP5 gene and protein expression in a dose-dependent manner in both depots. The gene product, FKBP51 protein, was 10-fold higher in the omental than in the subcutaneous depot, whereas the mRNA levels were similar. Higher FKBP5 gene expression in omental adipose tissue was associated with reduced insulin effects on glucose uptake in both depots. Furthermore, FKBP5 gene expression in subcutaneous adipose tissue was positively correlated with serum insulin, HOMA-IR and subcutaneous adipocyte diameter and negatively with plasma HDL-cholesterol. FKBP5 SNPs were found to be associated with type 2 diabetes and diabetes-related phenotypes in large population-based samples.

Conclusions

Dexamethasone exposure promotes expression of FKBP5 in adipose tissue, a gene that may be implicated in glucocorticoid-induced insulin resistance.     

Adipose tissue adiponectin production and adiponectin serum concentration in human obesity and insulin resistance

The role of adiponectin production for the circulating protein concentration in human obesity and insulin resistance is unclear. We measured serum concentration and sc adipose tissue secretion rate of adiponectin in 77 obese and 23 nonobese women with a varying degree of insulin sensitivity. The serum adiponectin concentration was similar in both groups. In obesity, adiponectin adipose tissue secretion rate per weight unit was reduced by 30% (P = 0.01), whereas total body fat secretion rate was increased by 100% (P < 0.0001). In the group being most insulin resistant (1/3), serum concentration (P < 0.001) and adipose tissue secretion rate per tissue weight (P < 0.05) were reduced, whereas total body fat secretion rate was increased (P < 0.01), by about 30%. The adipose tissue secretion rate of adiponectin was related to the serum concentration (P = 0.005) but explained only about 10% of the interindividual variation in circulating adiponectin and insulin sensitivity. The plasma adiponectin half life was long, 2.5 h. In conclusion, the role of protein secretion for the circulating concentration of adiponectin and insulin sensitivity under these conditions is minor because adiponectin turnover rate is slow. Although increased in obesity and insulin resistance, total body production of adiponectin is insufficient to raise the circulating concentration, may be due to reduced secretion rate per tissue unit.     

Growth arrest-specific 6 modulates adiponectin expression and insulin resistance in adipose tissue

Aims/IntroductionObesity is characterized by disturbed adipocytokine expression and insulin resistance in adipocytes. Growth arrest‐specific 6 (GAS6) is a gene encoding the Gas6 protein, which is expressed in fibroblasts, and its related signaling might be associated with adipose tissue inflammation, glucose intolerance and insulin resistance. The aim of this study was to investigate the associations among Gas6, adipocytokines and insulin resistance in adipocytes.Materials and MethodsMature Simpson Golabi Behmel Syndrome adipocytes were treated with high levels of insulin to mimic insulin resistance, and were examined for the expressions of Gas6, cytokines and adipocytokines from preadipocytes in differentiation. In an animal study, high‐fat diet‐induced obese mice were used to verify the Gas6 expression in vitro.ResultsDuring the differentiation of adipocytes, the expression of Gas6 gradually decreased, and was obviously downregulated with adipocyte inflammation and insulin resistance. Gas6 levels were found to be in proportion to the expression of adiponectin, which has been regarded as closely relevant to improved insulin sensitivity after metformin treatment. Similar results were also confirmed in the animal study.ConclusionsOur results suggest that Gas6 might modulate the expression of adiponectin, and might therefore be associated with insulin resistance in adipose tissues.     

Adipose tissue compartments and insulin resistance in overweight-obese Caucasian men

We examined the association between insulin resistance and adipose tissue compartments in overweight/obese men. Total intra-abdominal, intraperitoneal, retroperitoneal, total subcutaneous, anterior subcutaneous and posterior subcutaneous abdominal adipose tissue (PSAAT) masses (total intra-abdominal fat TIAATM, IPATM, RPATM, TSAATM, ASAATM and PSAATM, respectively) were quantified in 51 overweight/obese men using magnetic resonance imaging (MRI). Total adipose tissue mass (TATM) was also determined using bioelectrical impedance. Insulin resistance was estimated by homeostasis model assessment (HOMA) score. In univariate regression analysis, all fat compartments, with the exception of RPATM, were significantly and positively correlated with the HOMA score. The positive correlation between HOMA score and both IPATM and anterior subcutaneous adipose tissue mass was independent of obesity status. After adjusting total for TATM, only IPATM was significantly correlated with HOMA score (partial r=0.38, P<0.01). In stepwise regression, IPATM was the best predictor of HOMA score. In multivariate regression models including age, obesity status, non-esterified fatty acid (NEFAs) levels, triglycerides and energy expenditure, IPATM remained a significant positive predictor (P<0.05) of HOMA score. In overweight/obese men intraperitoneal AT is the fat compartment that best predicts the degree of insulin resistance. This association appears to be independent of age, total body fat mass and obesity status.