Dead adipocytes, detected as crown-like structures, are prevalent in visceral fat depots of genetically obese mice

Accumulation of visceral fat is a key phenomenon in the onset of obesity-associated metabolic disorders. Macrophage infiltration induces chronic mild inflammation widely considered as a causative factor for insulin resistance and eventually diabetes. We previously showed that >90% of macrophages infiltrating the adipose tissue of obese animals and humans are arranged around dead adipocytes, forming characteristic crown-like structures (CLS). In this study we quantified CLS in visceral and subcutaneous depots from two strains of genetically obese mice, db/db and ob/ob. In both strains, CLS were prevalent in visceral compared with subcutaneous fat. Adipocyte size and CLS density exhibited a positive correlation both in visceral and in subcutaneous depots; however, the finding that adipocyte size was smallest and CLS density highest in visceral fat suggests a different susceptibility of visceral and subcutaneous adipocytes to death. Visceral fat CLS density was 3.4-fold greater in db/db than in ob/ob animals, which at the age at which our experimental strain was used are more prone to glucose metabolic disorders.     

The effects of designed angiopoietin-1 variant on lipid droplet diameter, vascular endothelial cell density and metabolic parameters in diabetic db/db mice

Metabolic syndrome consists of metabolic abnormality with central obesity, hypertriglyceridemia, insulin resistance and hypertension. Adipose tissue has been known as a primary site of insulin resistance and its adipocyte size may be correlated with the degree of insulin resistance. A designed angiopoietin-1, COMP-Angiopoietin-1 (COMP-Ang1), mitigated high-fat diet-induced insulin resistance in skeletal muscle. In this study, we examined effects of COMP-Ang1 on adipocyte droplet size, vascular endothelial cell density in adipose tissue and metabolic parameters in db/db mice by administering COMP-Ang1 or LacZ (as a control) adenovirus. Administration of COMP-Ang1 decreased fat droplet diameter in epididymal and abdominal visceral adipocyte and visceral fat content in db/db mice. The density of vascular endothelial cell in adipose tissue was increased in db/db mice after treatment with COMP-Ang1. Serum resistin and tumor necrosis factor-α level was lower after treatment with COMP-Ang1 in db/db mice. COMP-Ang1 caused a restoration of fasting glycemic control in db/db mice and decreased serum insulin level and insulin resistance measured by HOMA index. These findings indicate that COMP-Ang1 regulates adipocyte fat droplet diameter, vascular endothelial cell density and metabolic parameters in db/db mice.     

Subcutaneous fat modulates insulin sensitivity in mice by regulating TNF-alpha expression in visceral fat.

The distribution of fat in obese persons is related to the risk of developing various metabolic disorders, such as glucose intolerance, dyslipidemia and hypertension, and the combination of these conditions is known as the metabolic syndrome. The aim of this study was to investigate the role of subcutaneous fat in regulating insulin resistance and its influence on TNF-alpha expression in visceral fat, by using mice that were subjected to subcutaneous lipectomy with or without subsequent fat transplantation. After partial subcutaneous lipectomy, mice showed significantly greater accumulation of visceral fat compared with sham-operated control mice. Lipectomy led to higher plasma insulin and lower plasma glucose levels after loading with glucose and insulin, respectively, compared with the levels in control mice. Insulin-induced phosphorylation of IRS-1 was decreased in the skeletal muscles of lipectomized mice. Subcutaneous transplantation of fat pads into lipectomized mice reversed the above-mentioned changes indicating insulin resistance in these animals. The fat storage area of adipocytes and TNF- alpha expression by adipocytes in visceral fat were significantly higher in the lipectomized mice than in controls, while subcutaneous transplantation of fat reduced both the fat storage area and TNF-alpha expression. The insulin resistance of lipectomized mice was also ameliorated by systemic neutralization of TNF-alpha activity using a specific antibody. These findings obtained in mice subjected to subcutaneous lipectomy with/without subsequent fat transplantation indicate that subcutaneous fat regulates systemic insulin sensitivity, possibly through altering fat storage and the expression of TNF-alpha by adipocytes in visceral fat. The balance between accumulation of subcutaneous fat and visceral fat may be important with respect to the occurrence of systemic insulin resistance in the metabolic syndrome.     

Increased intramyocellular lipid accumulation in HIV-infected women with fat redistribution.

The human immunodeficiency virus (HIV)-lipodystrophy syndrome is associated with fat redistribution and metabolic abnormalities, including insulin resistance. Increased intramyocellular lipid (IMCL) concentrations are thought to contribute to insulin resistance, being linked to metabolic and body composition variables. We examined 46 women: HIV infected with fat redistribution (n = 25), and age- and body mass index-matched HIV-negative controls (n = 21). IMCL was measured by 1H-magnetic resonance spectroscopy, and body composition was assessed with computed tomography, dual-energy X-ray absorptiometry (DEXA), and magnetic resonance imaging. Plasma lipid profile and markers of glucose homeostasis were obtained. IMCL was significantly increased in tibialis anterior [135.0 +/- 11.5 vs. 85.1 +/- 13.2 institutional units (IU); P = 0.007] and soleus [643.7 +/- 61.0 vs. 443.6 +/- 47.2 IU, P = 0.017] of HIV-infected subjects compared with controls. Among HIV-infected subjects, calf subcutaneous fat area (17.8 +/- 2.3 vs. 35.0 +/- 2.5 cm2, P < 0.0001) and extremity fat by DEXA (11.8 +/- 1.1 vs. 15.6 +/- 1.2 kg, P = 0.024) were reduced, whereas visceral abdominal fat (125.2 +/- 11.3 vs. 74.4 +/- 12.3 cm2, P = 0.004), triglycerides (131.1 +/- 11.0 vs. 66.3 +/- 12.3 mg/dl, P = 0.0003), and fasting insulin (10.8 +/- 0.9 vs. 7.0 +/- 0.9 microIU/ml, P = 0.004) were increased compared with control subjects. Triglycerides (r = 0.39, P = 0.05) and extremity fat as percentage of whole body fat by DEXA (r = -0.51, P = 0.01) correlated significantly with IMCL in the HIV but not the control group. Extremity fat (beta = -633.53, P = 0.03) remained significantly associated with IMCL among HIV-infected patients, controlling for visceral abdominal fat, abdominal subcutaneous fat, and antiretroviral medications in a regression model. These data demonstrate increased IMCL in HIV-infected women with a mixed lipodystrophy pattern, being most significantly associated with reduced extremity fat. Further studies are necessary to determine the relationship between extremity fat loss and increased IMCL in HIV-infected women.     

Obese adipocytes show ultrastructural features of stressed cells and die of pyroptosis

We previously suggested that, in obese animals and humans, white adipose tissue inflammation results from the death of hypertrophic adipocytes; these are then cleared by macrophages, giving rise to distinctive structures we denominated crown-like structures. Here we present evidence that subcutaneous and visceral hypertrophic adipocytes of leptin-deficient (ob/ob and db/db) obese mice exhibit ultrastructural abnormalities (including calcium accumulation and cholesterol crystals), many of which are more common in hyperglycemic db/db versus normoglycemic ob/ob mice and in visceral versus subcutaneous depots. Degenerating adipocytes whose intracellular content disperses in the extracellular space were also noted in obese mice; in addition, increased anti-reactive oxygen species enzyme expression in obese fat pads, documented by RT-PCR and immunohistochemistry, suggests that ultrastructural changes are accompanied by oxidative stress. RT-PCR showed NLRP3 inflammasome activation in the fat pads of both leptin-deficient and high-fat diet obese mice, in which formation of active caspase-1 was documented by immunohistochemistry in the cytoplasm of several hypertrophic adipocytes. Notably, caspase-1 was not detected in FAT-ATTAC transgenic mice, where adipocytes die of apoptosis. Thus, white adipocyte overexpansion induces a stress state that ultimately leads to death. NLRP3-dependent caspase-1 activation in hypertrophic adipocytes likely induces obese adipocyte death by pyroptosis, a proinflammatory programmed cell death.     

Insulin sensitivity and regional fat gain in response to overfeeding

Although insulin resistance and type 2 diabetes (T2DM) are associated with upper body fat distribution, it is unknown whether insulin resistance predisposes to upper body fat gain or whether upper body fat gain causes insulin resistance. Our objective was to determine whether insulin sensitivity predicts abdominal (subcutaneous and/or visceral) fat gain in normal weight adults. Twenty-eight (15 men) lean (BMI = 22.1 ± 2.5 kg/m(2)), healthy adults underwent ~8 weeks of overfeeding to gain ~4 kg fat. Body composition was assessed before and after overfeeding, using dual-energy X-ray absorptiometry (DXA) and abdominal computed tomography to measure total and regional (visceral, abdominal, and lower body subcutaneous) fat gain. We assessed insulin sensitivity with an intravenous glucose tolerance test (IVGTT) and the 24-h insulin area under the curve (AUC). We found a wide range of insulin sensitivity and a relatively narrow range of body fat distribution in this normal weight cohort. Participants gained 3.8 ± 1.7 kg of body fat (4.6 ± 2.2 kg body weight). The baseline 24-h AUC of insulin concentration was positively correlated with percent body fat (r = 0.43, P < 0.05). The contribution of leg fat gain to total fat gain ranged from 29 to 79%, whereas the contributions of abdominal subcutaneous fat and visceral fat gain to total fat gain ranged from 17 to 69% and -5 to 22%, respectively. Baseline insulin sensitivity, whether measured by an IVGTT (S(i)) or the 24-h AUC insulin, did not predict upper body subcutaneous or visceral fat gain in response to overfeeding. We conclude that reduced insulin sensitivity is not an obligate precursor to upper body fat gain.     

Roles of degree of fat deposition and its localization on VEGF expression in adipocytes

Vascular endothelial growth factor (VEGF) is an important angiogenic factor and is expressed in wide variety of cell types. In this study, we investigated the mechanism of VEGF production in adipocytes in three sets of experiments. First, to clarify the relation between plasma VEGF concentrations and their expressions in adipose tissues, we investigated the genetically obese db/db and KK-Ay mice. Plasma VEGF concentrations in obese mice were significantly higher than in control and were related to adiposity. VEGF expressions in visceral fat were enhanced during growth and were related to fat deposition. Next, to demonstrate the relation between VEGF production and lipid accumulation in adipocytes, we analyzed VEGF mRNA expression and its protein secretion in 3T3-L1 cells. VEGF production was enhanced during lipid accumulation in 3T3-L1 cells after adipocyte conversion. Next, to clarify the role of anatomic localization on VEGF expression in adipocytes, we implanted 3T3-L1 cells into visceral or subcutaneous fat in athymic mice. 3T3-L1 cells implanted into the mesenteric area expressed more VEGF mRNA than that into the subcutaneous area. Plasma VEGF concentration in the mice implanted in visceral fat was higher than in controls. These results suggest that both the anatomic localization and the lipid accumulation are important for the VEGF production in adipocytes.     

Mast cells, macrophages, and crown-like structures distinguish subcutaneous from visceral fat in mice

Obesity is accompanied by adipocyte death and accumulation of macrophages and mast cells in expanding adipose tissues. Considering the differences in biological behavior of fat found in different anatomical locations, we explored the distribution of mast cells, solitary macrophages, and crown-like structures (CLS), the surrogates for dead adipocytes, in subcutaneous and abdominal visceral fat of lean and diet-induced obese C57BL/6 mice. In fat depots of lean mice, mast cells were far less prevalent than solitary macrophages. Subcutaneous fat contained more mast cells, but fewer solitary macrophages and CLS, than visceral fat. Whereas no significant change in mast cell density of subcutaneous fat was observed, obesity was accompanied by a substantial increase in mast cells in visceral fat. CLS became prevalent in visceral fat of obese mice, and the distribution paralleled mast cells. Adipose tissue mast cells contained and released preformed TNF-α, the cytokine implicated in the pathogenesis of obesity-linked insulin resistance. In summary, subcutaneous fat differed from visceral fat by immune cell composition and a lower prevalence of CLS both in lean and obese mice. The increase in mast cells in visceral fat of obese mice suggests their role in the pathogenesis of obesity and insulin resistance.     

Inactivity, exercise, and visceral fat. STRRIDE: a randomized, controlled study of exercise intensity and amount.

Despite the importance of randomized, dose-response studies for proper evaluation of effective clinical interventions, there have been no dose-response studies on the effects of exercise amount on abdominal obesity, a major risk factor for metabolic syndrome, diabetes, and cardiovascular disease. One hundred seventy-five sedentary, overweight men and women with mild to moderate dyslipidemia were randomly assigned to participate for 6 mo in a control group or for approximately 8 mo in one of three exercise groups: 1) low amount, moderate intensity, equivalent to walking 12 miles/wk (19.2 km) at 40-55% of peak oxygen consumption; 2) low amount, vigorous intensity, equivalent to jogging 12 miles/wk at 65-80% of peak oxygen consumption; or 3) high amount, vigorous intensity, equivalent to jogging 20 miles/wk (32.0 km). Computed tomography scans were analyzed for abdominal fat. Controls gained visceral fat (8.6 +/- 17.2%; P = 0.001). The equivalent of 11 miles of exercise per week, at either intensity, prevented significant accumulation of visceral fat. The highest amount of exercise resulted in decreased visceral (-6.9 +/- 20.8%; P = 0.038) and subcutaneous (-7.0 +/- 10.8%; P < 0.001) abdominal fat. Significant gains in visceral fat over only 6 mo emphasize the high cost of continued inactivity. A modest exercise program, consistent with recommendations from the Centers for Disease Control/American College of Sports Medicine (CDC/ACSM), prevented significant increases in visceral fat. Importantly, a modest increase over the CDC/ACSM exercise recommendations resulted in significant decreases in visceral, subcutaneous, and total abdominal fat without changes in caloric intake.     

Fat and Water 1H MRI to Investigate Effects of Leptin in Obese Mice

Leptin is known to be associated with regulation of body weight and fat content. The effects of exogenous leptin on abdominal visceral (VS) and subcutaneous (SC) fat volume and hepatic fat‐to‐water ratio in leptin‐deficient obese mice were investigated by ¹H magnetic resonance imaging (MRI). Chemical shift‐selected fat and water ¹H MRI of control and leptin‐treated mice were obtained 1 day before treatment and after 7 days of treatment (0.3 mg/kg/day). Hepatic fat‐to‐water ratio and VS fat volume decreased significantly with treatment, whereas SC fat volume did not change. Noninvasive measurement of fat and water content in different body regions using MRI should prove useful for evaluating new drugs for the treatment of obesity and other metabolic disorders.     

Adrenalectomy and steroid treatment in obese (ob/ob) and diabetic (db/db) mice

Adrenalectomy in young obese (ob/ob) and the diabetic (db/db) mouse slowed body weight gain. Treatment of adrenalectomized ob/ob mice with cortisone or deoxycorticosterone acetate (DOCA) significantly increased weight gain in a dose-related manner. Cortisone had no effect on weight gain on lean mice and treatment with dehydroepiandrosterone sulfate was without effect on either ob/ob or lean mice. The increment in body weight of adrenalectomized ob/ob mice treated with corticosterone and DOCA was associated with an increase in body weight and an increase in food intake. When adrenalectomy was performed at twenty-three days of age (five days before weaning), animals carrying the (db/db) genotype remained lighter than their normal littermates. These data document the importance of the adrenal gland and its steroids for the development and maintenance of many features of the obese or diabetes mouse.     

Tissue leptin and plasma insulin are associated with lipoprotein lipase activity in severely obese patients

The development of metabolic complications of obesity has been associated with the existence of depot-specific differences in the biochemical properties of adipocytes. The aim of this study was to investigate, in severely obese men and women, both gender- and depot-related differences in lipoprotein lipase (LPL) expression and activity, as well as the involvement of endocrine and biometric factors and their dependence on gender and/or fat depot. Morbidly obese, nondiabetic, subjects (9 men and 22 women) aged 41.1+/-1.9 years, with a body mass index (BMI) of 54.7+/-1.7 kg/m(2) who had undergone abdominal surgery were studied. Both expression and activity of LPL and leptin expression were determined in adipose samples from subcutaneous and visceral fat depots. In both men and women, visceral fat showed higher LPL mRNA levels as well as lower ob mRNA levels and tissue leptin content than the subcutaneous one. In both subcutaneous and visceral adipose depots, women exhibited higher protein content, decreased fat cell size and lower LPL activity than men. The gender-related differences found in abdominal fat LPL activity could contribute to the increased risk for developing obesity-associated diseases shown by men, even in morbid obesity, in which the massive fat accumulation could mask these differences. Furthermore, the leptin content of fat depots as well as plasma insulin concentrations appear in our population as the main determinants of adipose tissue LPL activity, adjusted by gender, depot and BMI.     

L-4F treatment reduces adiposity, increases adiponectin levels, and improves insulin sensitivity in obese mice

We hypothesized that the apolipoprotein mimetic peptide L-4F, which induces arterial anti-oxidative enzymes and is vasoprotective in a rat model of diabetes, would ameliorate insulin resistance and diabetes in obese mice. L-4F (2 mg/kg/d) administered to ob/ob mice for 6 weeks limited weight gain without altering food intake, decreased visceral (P < 0.02) and subcutaneous (P < 0.045) fat content, decreased plasma IL-1beta and IL-6 levels (P < 0.05) and increased insulin sensitivity, resulting in decreased glucose (P < 0.001) and insulin (P < 0.036) levels. In addition, L-4F treatment increased aortic and bone marrow heme oxygenase (HO) activity and decreased aortic and bone marrow superoxide production (P < 0.001). L-4F treatment increased serum adiponectin levels (P < 0.037) and decreased adipogenesis in mouse bone marrow (P < 0.039) and in cultures of human bone marrow-derived mesenchymal stem cells (P < 0.022). This was manifested by reduced adiposity, improved insulin sensitivity, improved glucose tolerance, increased plasma adiponectin levels, and reduced IL-1beta and IL-6 levels in obese mice. This study highlights the existence of a temporal relationship between HO-1 and adiponectin that is positively affected by L-4F in the ob/ob mouse model of diabetes, resulting in the amelioration of the deleterious effects of diabetes.     

Low-dose GH supplementation reduces the TLR2 and TNF-alpha expressions in visceral fat

The increased population of TLR2/TNF-α co-expressing adipocytes is associated with the development of insulin resistance. We have herein shown the significance of low-dose growth hormone (GH) supplementation for the regulation of TLR2 and TNF-α expressions in visceral fat using different kinds of mouse models fed with a high-fat diet. Low-dose GH supplementation reduced the increased population of TLR2/TNF-α co-expressing adipocytes in high-fat fed mice. The neutralization of IGF-1 abolished the effect of GH supplementation on the TLR2 expression using GH-overexpressing mice. IGF-1, but not GH, inhibited the FFA-induced TLR2 and TNF-α expression in 3T3-L1 cells. Finally, low-dose GH supplementation reduced the TLR2 expression without an obvious change in the visceral fat volume in ob/ob mice. These results indicate that low-dose GH supplementation possibly inhibits the high-fat induced change of the adipocytes to TLR2/TNF-α co-expressing cells through the action of IGF-1.     

Hepatic glycogen metabolism in the db/db mouse

Summary Knowledge of the metabolic changes that occur in insulin-resistant type 2 diabetes is relatively lacking compared to insulin-deficient type 1 diabetes. This paper summarizes the importance of the C57BL/KsJ-db/db mouse as a model of type 2 diabetes, and illustrates the effects that insulin-deficient and insulin-resistant states have on hepatic glycogen metabolism. A longitudinal study of db/db mice of ages 2–15 weeks revealed that significant changes in certain parameters of hepatic glycogen metabolism occur during this period. The liver glycogen levels were similar between diabetic and control mice. However, glycogen particles from db/db mice were on average smaller in mass and had shorter exterior and interior chain lengths. Total phosphorylase and phosphorylase a activities were elevated in the genetically diabetic mice. This was primarily due to an increase in the amount of enzymic protein apparently the result of a decreased rate of degradation. It was not possible to find a consistent alteration in glycogen synthase activity in the db/db mice. Glycogen synthase and phosphorylase from diabetic liver revealed some changes in kinetic properties in the form of a decrease in V_max, and altered sensitivity to inhibitors like ATP. The altered glycogen structure in db/db mice may have contributed to changes in the activities and properties of glycogen synthase and phosphorylase. The exact role played by hormones (insulin and glucagon) in these changes is not clear but further studies should reveal their contributions. The db/db mouse provides a good model for type 2 diabetes and for fluctuating insulin and glucagon ratios. Its use should clarify the regulation of hepatic glycogen metabolism and other metabolic processes known to be controlled by these hormones. The other animal models of type 2 diabetes, ob/ob mouse and fatty Zucker (fa/fa) rat, show similar impairment of hepatic glycogen metabolism. The concentrations of glycogen metabolizing enzymes are high and in vitro studies indicate enhanced rate of glycogen synthesis and breakdown. However, streptozotocin-induced diabetic animals and BB rats which resemble insulin-deficient type 1 diabetes are characterized by decreased glycogen turnover as a result of reduction in the levels of glycogen metabolizing enzymes.     

The effect of ponalrestat on sorbitol levels in the lens of obese and diabetic mice

Sorbitol levels were determined in lens of genetically obese (ob/ob) and diabetic (db/db) mice, as well as in lean mice (+/db, +/ob) made diabetic by administration of streptozotocin (STZ). Treatment of lean mice with STZ resulted in hypoinsulinemia, whereas the ob/ob and db/db mice were hyperinsulinemic. Hyperglycemia was present in STZ-treated +/db and +/ob mice and in db/db mice, whereas relative euglycemia was observed in ob/ob mice and untreated +/db and +/ob mice. Sorbitol levels were elevated in lens tissue of db/db mice and STZ-treated +/db. In contrast, no changes in sorbitol content were observed in ob/ob mice and +/ob mice treated with STZ, suggesting that aldose reductase activity in lens of this animal model is considerably less than that present in db/db mice. Oral treatment of db/db mice and STZ-treated +/db mice with Ponalrestat reduced hyperglycemia-induced sorbitol accumulation significantly in lens, indicating that aldose reductase inhibitors may ameliorate long-term complications associated with sorbitol accumulation in diabetes.     

Visceral fat and liver fat are independent predictors of metabolic risk factors in men

We examined the independent associations among abdominal adipose tissue (AT), liver fat, cardiorespiratory fitness (CRF), and lipid variables in 161 Caucasian men who had a wide variation in adiposity. We measured AT and liver fat by computed tomography and CRF by a maximal exercise test on a treadmill. Visceral AT remained a significant (P or= 0.05) correlate of any lipid variable after control for visceral AT and CRF. Furthermore, subdivision of subcutaneous AT into deep and superficial depots did not alter these observations. Visceral AT was the strongest correlate of liver fat and remained so after control for abdominal subcutaneous AT, CRF, and alcohol consumption (r = -0.34, P < 0.01). In contrast, abdominal subcutaneous AT and CRF were not significant (P > 0.10) correlates of liver fat after control for visceral AT. Visceral AT remained a significant (P < 0.01) correlate of TG, HDL-C, and TC/HDL-C independent of liver fat. However, liver fat was also a significant correlate (P 相似文献   

Reduction of food intake and weight gain by the ob protein requires a specific secondary structure and is reversible.

BACKGROUND: Obesity, the condition of excessive accumulation of fat is a poorly understood disorder and is a risk factor for type II diabetes, hypertension, and hyperlipidaemia. Recently, a putative mouse obese gene was cloned and its product, termed ob protein, was shown to be involved in the regulation of body weight. MATERIALS AND METHODS: Bacterial and insect cells were used for expression of recombinant mouse ob protein. Amino-terminal sequence analysis and site-directed mutagenesis were used to identify and characterize the mature form of ob protein. Genetically obese mice and wild-type rats were used to determine the biological activity of ob protein. RESULTS: Mouse ob protein is synthesized as a precursor molecule, the mature form of which was found in mouse serum. Biochemical analysis identified the processing site in the ob precursor molecule and an intramolecular disulfide bond in the mature form that is necessary for activity. Reduction of food intake and weight gain after administration of ob protein to genetically obese mice and wild-type rats is reversible. DISCUSSION: This study demonstrates that ob protein is a secreted satiety factor which regulates body weight and reduces food intake even in animals with no genetic body weight abnormalities. The failure of ob protein to effect these parameters in db/db mice supports the hypothesis that these mice are deficient in a signaling molecule that normally responds to the ob protein.