The common rs9939609 gene variant of the fat mass- and obesity-associated gene FTO is related to fat cell lipolysis

We investigated the rs9939609 single nucleotide polymorphism of the FTO gene in relation to fat cell function and adipose tissue gene expression in 306 healthy women with a wide range in body mass index (18-53 kg/m(2)). Subcutaneous adipose tissue biopsies were taken for fat cell metabolism studies and in a subgroup (n = 90) for gene expression analyses. In homozygous carriers of the T-allele, the in vitro basal (spontaneous) adipocyte glycerol release was increased by 22% (P = 0.007) and the in vivo plasma glycerol level was increased by approximately 30% (P = 0.037) compared with carriers of the A allele. In contrast, there were no genotype effects on catecholamine-stimulated lipolysis or basal or insulin-induced lipogenesis. We found no difference between genotypes for adipose tissue mRNA levels of FTO, hormone-sensitive lipase, adipose triglyceride lipase, perilipin, or CGI-58. Finally, the adipose tissue level of FTO mRNA was increased in obesity (P = 0.002), was similar in subcutaneous and omental adipose tissue, was higher in fat cells than in fat tissue (P = 0.0007), and was induced at an early stage in the differentiation process (P = 0.004). These data suggest a role of the FTO gene in fat cell lipolysis, which may be important in explaining why the gene is implicated in body weight regulation.     

Rosiglitazone controls fatty acid cycling in human adipose tissue by means of glyceroneogenesis and glycerol phosphorylation

Control of fatty acid homeostasis is crucial to prevent insulin resistance. During fasting, the plasma fatty acid level depends on triglyceride lipolysis and fatty acid re-esterification within fat cells. In rodents, Rosiglitazone controls fatty acid homeostasis by stimulating two pathways in the adipocytes, glyceroneogenesis and glycerol phosphorylation, that provide the glycerol 3-phosphate necessary for fatty acid re-esterification. Here, we analyzed the functionality of both pathways for controlling fatty acid release in subcutaneous adipose tissue samples from lean and overweight women before and after Rosiglitazone ex vivo treatment. In controls, pyruvate, used as a substrate of glyceroneogenesis, could contribute to the re-esterification of up to 65% of the fatty acids released after basal lipolysis, whereas glycerol phosphorylation accounted for only 14 +/- 9%. However, the efficiency of glyceroneogenesis diminished as body mass index (BMI) of women increased. After Rosiglitazone treatment, increase of either pyruvate- or glycerol-dependent fatty acid re-esterification was strictly correlated to that of phosphoenolpyruvate carboxykinase and glycerol kinase, the key enzymes of each pathway, but depended on BMI of the women. Whereas the Rosiglitazone responsiveness of glyceroneogenesis was rather constant according to the BMI of the women, glycerol phosphorylation was mostly enhanced in lean women (BMI < 27). Overall, these data indicate that, whereas glyceroneogenesis is more utilized than glycerol phosphorylation for fatty acid re-esterification in human subcutaneous adipose tissue in the physiological situation, both are solicited in response to Rosiglitazone but with lower efficiency when BMI is increased.     

Relationship between the tissue level of cyclic AMP and the fat cell size of human adipose tissue.

The relationship between mean fat cell size, maximal tissue cyclic AMP concentration, and glycerol release was investigated in human subcutaneous adipose tissue incubated in vitro with or without isoprenaline or noradrenaline added at maximal effective concentrations. Basal and stimulated glycerol release and cyclic AMP concentration were each related to the fat cell size. Whether or not the phosphodiesterase inhibitor theophylline was present in the incubation system, basal and noradrenaline-induced cyclic AMP levels were significantly correlated with the fat cell size. The noradrenaline-induced cyclic AMP levels resulted in twice as rapid glycerol release as could be expected from the basal ratio between glycerol release and cyclic AMP. Furthermore, both basal and noradrenaline-induced glycerol release in relation to the cyclic AMP levels were more rapid in enlarge fat cells. It is concluded that basal and catecholamine-induced production of cyclic AMP is related to the fat cell size and that a quantitative relationship exists between rate of lipolysis and maximal tissue levels of cyclic AMP in human adipose tissue. Basal and noradrenaline-induced lipolysis are probably regulated by different mechanisms and the lipolytic sensitivity to cyclic AMP seems increased in large fat cells.     

Neuromedin beta: P73T polymorphism in overweight and obese subjects

Neuromedin beta (NMB) is a member of the bombesin-like peptide family expressed in brain, gastrointestinal tract, pancreas, adrenals and adipose tissue. The aim of our study was to compare the frequency of P73T polymorphism in overweight and obese patients (37 men: age 50.6+/-11.7 years, BMI 41.1+/-7.8 kg/m(2); 255 women: age 49.0+/-11.9 years, BMI 37.9+/-6.8 kg/m(2)) with that of healthy normal weight subjects (51 men: age 28.2+/-7.1 years, BMI 22.3+/-2.0 kg/m(2); 104 women: age 29.1+/-9.1 years, BMI 21.5+/-1.9 kg/m(2)) and to investigate the polymorphism's influence on anthropometric, nutritional and psychobehavioral parameters in overweight/obese patients both at the baseline examination and at a control visit carried out 2.5 years later, regardless of the patient s compliance with the weight reduction program. No significant differences in the genotype distribution were demonstrated between normal weight and overweight/obese subjects. Male T allele non-carriers compared to T allele carriers had higher energy (p=0.009), protein (p=0.018) and fat (p=0.002) intakes and hunger score (p=0.015) at the beginning of treatment. Male T allele non-carriers had a more favorable response to weight management at the follow-up, as they exhibited a significant reduction in waist circumference, energy intake and depression score as well as a significant increase in dietary restraint. No significant differences between carriers and non-carriers were demonstrated in women at the baseline examination. Both female T allele carriers and non-carriers demonstrated similar significant changes in nutritional parameters and in restraint score at the follow-up. Nevertheless, only female non-carriers showed a significant decrease in the hunger score.     

Binding specificity of siglec7 to disialogangliosides of renal cell carcinoma: possible role of disialogangliosides in tumor progression

The G protein beta3 subunit (GNB3) 825T allele is predictive of enhanced Gi protein activation. Studying the influence of C825T allele status on cellular in vitro immune responses towards recall antigens and interleukin-2 stimulation we observed a 2-4-fold, significantly increased proliferation in homozygous 825T (TT) vs. C825 allele (CC) carriers. Furthermore, lymphocyte chemotaxis and CD4(+) T cell counts of individuals with TT+TC genotypes were significantly enhanced compared to the CC genotype. In summary, it appears that C825T allele status is highly predictive of immunocompetence and could be a candidate gene in disorders associated with inadequate immune response.     

G蛋白β亚单位C825T基因多态性与原发性高血压的相关性研究

分析大规模日本人群的G蛋白β亚单位基因（GNB3,C825T-Gprotein β3 subunit C825T）多态性与原发性高血压病（essential hypertension,EH）的关系。采集日本同一个地区健康体检人群为研究对象,共4,830例,其中高血压组（HT：2,092例）,正常血压组（NT：2,738例）。对体检对象做：体重指数（BMI）、吸烟,饮酒等环境因素和血浆胆固醇、甘油三酯等血液生化指标的测量。并用Taqman—PCR化学分析方法对GNB3基因的C825T多态性进行分型检测。GNB3基因的C825T多态性符合Hardy—Weinberg平衡遗传规律。在HT与NT之间,CC、CT、TT遗传表型的频率为NT：24．8％,47．8％和27．4％;HT：22．9％,51．7％和25．4％。C等位基因频率分别为NT：48．72％及HT：48．78％;C825T基因型在HT及NT组之间有显著性差异,基因型频率CC／CT＋TT：P=0．027;OR：1．169;CI95％：1．019～1．341;等位基因频率在两组之间也有统计学差异。C,T：P=0．001;OR：1．154;CI95％：1．064—1．252。CT＋TT基因型携带者发生EH病的危险性为CC基因型携带者的1．169倍（OR）。GNB3基因的C825T的T等位基因EH发病危险是C的1．154倍。GNB3的C825T基因多态性可能是日本人群EH的一个候选基因。     

Association of GNB3 gene C825T polymorphism with coronary heart disease

The C825T polymorphism in the gene encoding the G protein beta 3 subunit (GNB3) causes enhanced G protein activation and the increased in vitro cell proliferation. We investigated the association of gene GNB3 C825T polymorphism with coronary artery disease (CAD) in the Russian population. A total of 313 patients with CAD diagnosed on the basis of clinical studies and coronary angyography were examined. The control group included 132 individuals that lacked clinical CAD symptoms and had matching profile of coronary artery disease risk factors. Blood pressure was measured using standard protocols. Increased levels of diastolic and systolic pressure was observed in both groups. The allele and genotype frequencies of this polimorphic marker were significantly higher in the CAD patients than in control. We found that the frequency of allele C and gen-. otype CC was significantly higher in the CAD patients (OR = 1.55; P = 0.0079; OR = 1.63; P = 0.0215, respectively), which suggests higher risk of this pathology in carriers of allele C and genotype CC. Thus, in the Russian population coronary artery disease is associated with GNB3 allele C and genotype CC.     

Lack of Association between Human G‐Protein β3 Subunit Variant and Overweight in Japanese Workers*

We examined the association of the G‐protein β3 subunit gene (GNB3) C825T polymorphism with overweight in Japanese workers. This cross‐sectional study used multivariate analysis to investigate whether a polymorphism in the C825T polymorphism was associated independently with overweight when factors such as age and lifestyle were taken into account. The study in 1453 men and 1172 women involved identifying subjects with the C825T genotype using the polymerase chain reaction, followed by restriction fragment‐length polymorphism analysis. Overweight was defined as a BMI ≥25 kg/m². Genotype distributions for C825T in overweight men (CC = 80, CT = 162, TT = 80) and women (CC = 52, CT = 91, TT = 40) were not significantly different from normal‐weight men (CC = 278, CT = 588, TT = 265) and women (CC = 242, CT = 549, TT = 198). The allele distributions were also not significantly different between either sex. The power of the study was estimated as 98% in men and 81% in women based on the allelic frequencies reported in a previous positive study in Chinese subjects. Multiple logistic regression analysis showed that the genotype was not significantly associated with overweight. In conclusion, this study indicated that the GNB3 C825T polymorphism is not a significant factor for overweight in Japanese people.     

Association of GNB3 C825T polymorphism with plasma electrolyte balance and susceptibility to hypertension

The role of G-protein activation in cardiovascular disorders is well-known. G-protein β3 subunit (GNB3) C825T polymorphism is associated with increased intracellular signal transduction. We investigated the role of the variant in plasma sodium and potassium concentrations and association with hypertension. 345 healthy controls and 455 patients with essential hypertension were enrolled. Plasma renin activity and aldosterone concentration were measured. The variant, typed by SNaPshot, was analyzed on an ABI Prism 3100 Genetic Analyzer and GeneScan. The TT genotype and T allele were over-represented in the patients (p < 0.001, p < 0.0001). Multiple-logistic regression disclosed that the risk of hypertension was significantly greater for TT (p < 0.0001, OR = 6.1, CI = 2.9-12.7). One-way ANOVA revealed that hypertensive T-allele carriers (CT+TT), compared to non-carriers (CC), had a greater body mass index (BMI), mean arterial pressure (MAP) and PAC (p = 0.01, p = 0.01, p < 0.0001, respectively); while the patients with 825TT risk genotype showed higher plasma sodium and lower potassium (p < 0.0001, each). The results strongly emphasize, not only the role of C825T polymorphism by the induction of increased G-protein activity and enhancement of Na/h exchangers, but also the association with higher plasma sodium and lower potassium levels, high BMI and susceptibility to hypertension.     

Adipogenic and lipolytic effects of chronic glucocorticoid exposure

Glucocorticoids have been proposed to be both adipogenic and lipolytic in action within adipose tissue, although it is unknown whether these actions can occur simultaneously. Here we investigate both the in vitro and in vivo effects of corticosterone (Cort) on adipose tissue metabolism. Cort increased 3T3-L1 preadipocyte differentiation in a concentration-dependent manner, but did not increase lipogenesis in adipocytes. Cort increased lipolysis within adipocytes in a concentration-dependent manner (maximum effect at 1-10 μM). Surprisingly, removal of Cort further increased lipolytic rates (～320% above control, P < 0.05), indicating a residual effect on basal lipolysis. mRNA and protein expression of adipose triglyceride lipase and phosphorylated status of hormone sensitive lipase (Ser563/Ser660) were increased with 48 h of Cort treatment. To test these responses in vivo, Sprague-Dawley rats were subcutaneously implanted with wax pellets with/without Cort (300 mg). After 10 days, adipose depots were removed and cultured ex vivo. Both free fatty acids and glycerol concentrations were elevated in fed and fasting conditions in Cort-treated rats. Despite increased lipolysis, Cort rats had more visceral adiposity than sham rats (10.2 vs. 6.9 g/kg body wt, P < 0.05). Visceral adipocytes from Cort rats were smaller and more numerous than those in sham rats, suggesting that adipogenesis occurred through preadipocyte differentiation rather than adipocyte hypertrophy. Visceral, but not subcutaneous, adipocyte cultures from Cort-treated rats displayed a 1.5-fold increase in basal lipolytic rates compared with sham rats (P < 0.05). Taken together, our findings demonstrate that chronic glucocorticoid exposure stimulates both lipolysis and adipogenesis in visceral adipose tissue but favors adipogenesis primarily through preadipocyte differentiation.     

Larger anti-adipogenic effect of angiotensin II on omental preadipose cells of obese humans

Objective: The ability to form new adipose cells is important to adipose tissue physiology; however, the mechanisms controlling the recruitment of adipocyte progenitors are poorly understood. A role for locally generated angiotensin II in this process is currently proposed. Given that visceral adipose tissue reportedly expresses higher levels of angiotensinogen compared with other depots and the strong association of augmented visceral fat mass with the adverse consequences of obesity, we studied the role of angiotensin II in regulating adipogenic differentiation in omental fat of obese and non‐obese humans. Research Methods and Procedures: The angiotensin II effect on adipose cell formation was evaluated in human omental adipocyte progenitor cells that were stimulated to adipogenic differentiation in vitro. The adipogenic response was measured by the activity of the differentiation marker glycerol‐3‐phosphate dehydrogenase. Results: Angiotensin II reduced the adipogenic response of adipocyte progenitor cells, and the extent of the decrease correlated directly with the subjects’ BMI (p = 0.01, R² = 0.30). A 56.3 ± 3.4% and 44.5 ± 2.7% reduction of adipogenesis was found in obese and non‐obese donors’ cells, respectively (p < 0.01). The effect of angiotensin II was reversed by type 1 angiotensin receptor antagonist losartan. Discussion: A greater anti‐adipogenic response to angiotensin II in omental adipose progenitor cells from obese subjects opens a venue to understand the deregulation of visceral fat tissue cellularity that has been associated with severe functional abnormalities of the obese condition.     

Evolution of the sensitivity of isolated adipocytes of ewes to the lipolytic effects of different stimuli during pregnancy and lactation

Four successive biopsies of omental adipose tissue were performed at 43,100,140 days and during the 3rd week of lactation on 6 "Pré-Alpes" ewes. Using isolated adipocyte incubation, we studied the evolution of both basal lipolysis and stimulated lipolysis in response to different stimuli during these physiologic periods. The basal lipolysis increased from 53 +/- 10 micrograms glycerol/4 hr incubation/g total lipids (TL) at 43 days of pregnancy and 55 +/- 11 micrograms/4 hr/g TL at 100 days of pregnancy to a maximum value of 204 +/- 10 micrograms/4 h/g TL observed one week before parturition. Basal lipolysis remained at a high level during lactation: 153 +/- 27 micrograms/4 hr/g TL. The sensitivity of the fat cells to the lipolytic effects of isoproterenol, theophylline and adenosine-deaminase evolved with profiles comparable to that observed for basal lipolysis. The threshold concentration of stimuli necessary to observe an effect was decreased and the maximum response was increased. Bovine growth hormone (bGH) did not exhibit a direct lipolytic effect during pregnancy and lactation. Nevertheless, bGH provoked a significant potentiation of 20% of the lipolysis stimulated by isoproterenol and theophylline at 43 and 100 days of pregnancy. Ovine placental lactogene hormone (oPL) did not modulate, directely or undirectely, lipolysis.     

Metabolic characteristics of human subcutaneous abdominal adipose tissue after overnight fast

Subcutaneous abdominal adipose tissue is one of the largest fat depots and contributes the major proportion of circulating nonesterified fatty acids (NEFA). Little is known about aspects of human adipose tissue metabolism in vivo other than lipolysis. Here we collated data from 331 experiments in 255 healthy volunteers over a 23-year period, in which subcutaneous abdominal adipose tissue metabolism was studied by measurements of arterio-venous differences after an overnight fast. NEFA and glycerol were released in a ratio of 2.7:1, different (P < 0.001) from the value of 3.0 that would indicate no fatty acid re-esterification. Fatty acid re-esterification was 10.2 ± 1.4%. Extraction of triacylglycerol (TG) (fractional extraction 5.7 ± 0.4%) indicated intravascular lipolysis by lipoprotein lipase, and this contributed 21 ± 3% of the glycerol released. Glucose uptake (fractional extraction 2.6 ± 0.3%) was partitioned around 20-25% for provision of glycerol 3-phosphate and 30% into lactate production. There was release of lactate and pyruvate, with extraction of the ketone bodies 3-hydroxybutyrate and acetoacetate, although these were small numerically compared with TG and glucose uptake. NEFA release (expressed per 100 g tissue) correlated inversely with measures of fat mass (e.g., with BMI, r(s) = -0.24, P < 0.001). We examined within-person variability. Systemic NEFA concentrations, NEFA release, fatty acid re-esterification, and adipose tissue blood flow were all more consistent within than between individuals. This picture of human adipose tissue metabolism in the fasted state should contribute to a greater understanding of adipose tissue physiology and pathophysiology.     

Parathyroid hormone-induced lipolysis in human adipose tissue

Relative lipolytic activity of human parathyroid hormone-(1-34) (hPTH-(1-34], hPTH-(3-34), desamino-Ser1-hPTH-(1-34), and rat PTH-(1-34) was compared in human subcutaneous adipose tissues in vitro. Human PTH-(1-34), rat PTH-(1-34), and desamino-Ser1-hPTH-(1-34) stimulated in vitro lipolysis significantly above basal level at the concentration of 10(-6) M. Average increments of lipolytic rate were 2.39, 1.82, and 0.87 mumol/g per 2 hr, respectively, being significantly different among the three groups. On the other hand, hPTH-(3-34)-induced lipolytic rate was 0.83 +/- 0.18 mumol/g per 2 hr, not significantly different from the basal level (0.71 +/- 0.20 mumol/g per 2 hr). The effect of hPTH-(3-34) on glycerol release stimulated by hPTH-(1-34), isoproterenol, or forskolin was subsequently investigated. Human PTH-(3-34) produced a dose-dependent inhibition of hPTH-(1-34)-stimulated lipolysis. In contrast, isoproterenol- and forskolin-induced lipolytic rates were not influenced by hPTH-(3-34). The effect of propranolol on hPTH-(1-34)- or isoproterenol-induced lipolysis was also studied. Propranolol dose-dependently inhibited isoproterenol-induced lipolysis but had no effect on lipolysis stimulated by hPTH-(1-34). These results suggest that the amino acids at positions 1 (serine) and 2 (valine) of PTH are critical for the stimulation of lipolysis in human adipose tissue. Human PTH-(1-34) causes lipolysis after binding to receptors distinct from beta-adrenergic receptors of fat cells and possibly hPTH-(3-34) inhibits hPTH-(1-34)-stimulated lipolysis by competing at the level of PTH receptor.     

In vivo lipolysis in adipose tissue from two anatomical locations measured by microdialysis

In this study, the difference in lipolytic response in inguinal subcutaneous and epididymal adipose tissues of male Sprague-Dawley rats was assessed in vivo by microdialysis. Probes were perfused with Ringer solution in which increasing concentrations of isoproterenol (10(-7) - 10(-4) mol/L) were added. Glycerol release, expressed as extracellular glycerol concentration, was used as lipolytic index. The effect of isoproterenol on local blood flow was investigated using the ethanol technique. No differences were found in the interstitial glycerol concentration between both adipose tissues under basal conditions. When isoproterenol was perfused, a dose-response increase in glycerol production was induced in both tissues. Interstitial glycerol concentration from epididymal adipose tissue was higher than that of inguinal subcutaneous depot at all isoproterenol concentrations. No vasodilatory effect of isoproterenol was found. These results suggest that epididymal adipose tissue is more responsive in vivo to beta-adrenergic lipolysis stimulation than is subcutaneous fat pad from the inguinal region.     

AMPD1 gene polymorphism and the vasodilatory response to ischemia

Peripheral vasculature resistance can play an important role in affecting blood pressure and the development of cardiovascular disease. A better understanding of the genes that encode vasodilators, such as adenosine, will provide insight into the mechanisms underlying cardiovascular disease. We tested whether the adenosine monophosphate deaminase-1 (AMPD1) C34T gene polymorphism was associated with the vasodilatory response to ischemia in Caucasian females aged 18-35 years. Blood samples (n = 58) were analyzed for the C34T variant and resulted in the following genotype groups: CC (n = 45) and CT (n = 13). Mean blood pressure (MBP), heart rate, and forearm blood flow (FBF) measured by venous occlusion plethysmography were measured at baseline and at 1 (peak FBF), 2 and 3 min of vasodilation during reactive hyperemia following 5 min of arm ischemia. To control for interindividual variability in baseline FBF and forearm vascular resistance (FVR) the percent change in FBF and FVR were calculated for each min. The percent decrease in FVR was significantly greater in the CT compared to the CC genotype group (-40+/-4% vs. -24+/-3%, P = 0.01) during the 2nd min of reactive hyperemia. The percent increase in FBF tended to be greater in the CT compared to the CC genotype group (+69+/-9% vs. +42+/-9%, P = 0.07) during the 2nd min of reactive hyperemia after adjustment for percent body fat. Consistent with previous findings of increased production of adenosine during exercise in individuals carrying a T allele, our findings suggest that the AMPD1 C34T polymorphism is associated with vasodilatory response to ischemia in the peripheral vasculature because individuals with the T allele had a greater vasodilatory response to ischemia.     

Effects of 2-deoxy-D-glucose, oligomycin and theophylline on in vitro glycerol metabolism in rat adipose tissue: response to insulin and epinephrine.

The effects of 2-deoxy-D-glucose (2DG), oligomycin and theophylline on the in vitro production and metabolism of glycerol and its response to insulin and epinephrine were studied in epididymal fat pads from fed rats. 2-DG failed to affect basal or epinephrine stimulated glycerol production but it decreased the uptake of 1-14 C-glycerol by the tissue and its conversion to glyceride-glycerol. Oligomycin also failed to affect the basal production of glycerol but it inhibited the effect of epinephrine on this parameter as well as the uptake and utilization of 1-14-C-glycerol. Theophylline enhanced the production of glycerol by the tissue and this effect was not further augmented by epinephrine. Theophyline also inhibited the uptake and utilization of 1-14C-glycerol; the most pronounced effect of theophylline was observed in the formation of 14C-fatty acids from 1-14C-glycerol in the presence of glucose. Insulin, but not epinephrine, decreased the inhibitory effect of theophylline on glycerol utilization. It is concluded that these compounds affect more intensely the ability of adipose tissue to metabolize glycerol than to release it through lipolysis. The pathway for glycerol utilization in adipose tissue appears to be more sensitive to changes in the availability of ATP than the mechanisms responsible for the release of glycerol from the tissue.