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Body fat is stored in anatomically distinct adipose depots that vary in their cell composition and play specialized roles in systemic metabolic homeostasis via secreted products. Their local effects on nearby tissues (e.g. the gut and visceral adipose tissues) are increasingly recognized and this local crosstalk is being elucidated. The major subcutaneous fat depots, abdominal and gluteal-femoral, exert opposite effects on the risk of metabolic disease. The pace of research into developmental, sex, and genetic determinants of human adipose depot growth and function is rapidly accelerating, providing insight into the pathogenesis of metabolic dysfunction in persons with obesity., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

It has been known adipocytes increase p53 expression and activity in obesity, however, only canonical p53 functions (i.e. senescence and apoptosis) are attributed to inflammation-associated metabolic phenotypes. Whether or not p53 is directly involved in mature adipocyte metabolic regulation remains unclear. Here we show p53 protein expression can be up-regulated in adipocytes by nutrient starvation without activating cell senescence, apoptosis, or a death-related p53 canonical pathway. Inducing the loss of p53 in mature adipocytes significantly reprograms energy metabolism and this effect is primarily mediated through a AMP-activated protein kinase (AMPK) pathway and a novel downstream transcriptional target, lysosomal acid lipase (LAL). The pathophysiological relevance is further demonstrated in a conditional and adipocyte-specific p53 knockout mouse model. Overall, these data support a non-canonical p53 function in the regulation of adipocyte energy homeostasis and indicate that the dysregulation of this pathway may be involved in developing metabolic dysfunction in obesity., Competing Interests: HW, XW, PP, LE, SF, LL No competing interests declared, (© 2020, Wang et al.)

Objective: Adipose tissue cholesterol increases with adipocyte triglyceride content and size during development of obesity. However, how adipocyte cholesterol affects adipocyte function is poorly understood. The aim of this study was to evaluate the role of the cellular cholesterol exporter, Abca1 (ATP-binding cassette transporter A1), on adipose tissue function during diet-induced obesity., Approach and Results: Adiponectin Cre recombinase transgenic mice were crossed with Abca1 flox/flox mice to generate ASKO (adipocyte-specific Abca1 knockout) mice. Control and ASKO mice were then fed a high-fat, high-cholesterol (45% calories as fat and 0.2% cholesterol) diet for 16 weeks. Compared with control mice, ASKO mice had a 2-fold increase in adipocyte plasma membrane cholesterol content and significantly lower body weight, epididymal fat pad weight, and adipocyte size. ASKO versus control adipose tissue had decreased PPARγ (peroxisome proliferator-activated receptor γ) and CCAAT/enhancer-binding protein expression, nuclear SREBP1 (sterol regulatory element-binding protein 1) protein, lipogenesis, and triglyceride accretion but similar Akt activation after acute insulin stimulation. Acute siRNA-mediated Abca1 silencing during 3T3L1 adipocyte differentiation reduced adipocyte Abca1 and PPARγ protein expression and triglyceride content. Systemic stimulated triglyceride lipolysis and glucose homeostasis were similar between control and ASKO mice., Conclusions: Adipocyte Abca1 is a key regulator of adipocyte lipogenesis and lipid accretion, likely because of increased adipose tissue membrane cholesterol, resulting in decreased activation of lipogenic transcription factors PPARγ and SREBP1., (© 2018 American Heart Association, Inc.)

Increased adipocyte size is hypothesized to signal the recruitment of adipose progenitor cells (APCs) to expand tissue storage capacity. To investigate depot and sex differences in adipose growth, male and female C57BL/6J mice (10 wk-old) were challenged with high-fat (HF) or low-fat (LF) diets (D) for 14 wk. The HFD increased gonadal (GON) depot weight by adipocyte hypertrophy and hyperplasia in females but hypertrophy alone in males. In both sexes, inguinal (ING) adipocytes were smaller than GON, and depot expansion was due to hypertrophy. Matrix metalloproteinase 3 (Mmp3), an antiadipogenic factor, and its inhibitor Timps modulate the extracellular matrix remodeling needed for depot expansion. Mmp3 mRNA was depot different (ING > GON), higher in females than males and mainly expressed in APCs. In males, HFD-induced obesity increased tissue and APC Mmp3 mRNA levels and MMP3 protein and enzymatic activity. In females however, HFD significantly decreased MMP3 protein without affecting its mRNA levels. MMP3 activity also decreased (significant in ING). Timp4 mRNA was expressed mainly in adipocytes, and HFD-induced obesity tended to increase the ratio of TIMP4 to MMP3 protein in females, whereas it decreased it in males. Overexpression of Mmp3 in 3T3-L1 preadipocytes or rhMMP3 protein added to primary human preadipocytes inhibited differentiation, whereas rhTIMP4 improved adipogenesis and attenuated the inhibitory effect of rhMMP3. These data suggest that HFD-induced obesity downregulates APC MMP3 expression to trigger adipogenesis, and adipocyte TIMP4 may modulate this process to regulate hyperplastic vs. hypertrophic adipose tissue expansion, fat distribution, and metabolic health in a sex- and depot-dependent manner., (Copyright © 2017 the American Physiological Society.)

Glucocorticoids promote fat accumulation in visceral compared to subcutaneous depots, but the molecular mechanisms involved remain poorly understood. To identify long-term changes in gene expression that are differentially sensitive or responsive to glucocorticoids in these depots, paired samples of human omental (Om) and abdominal subcutaneous (Abdsc) adipose tissues obtained from obese women during elective surgery were cultured with the glucocorticoid receptor agonist dexamethasone (Dex, 0, 1, 10, 25 and 1000 nM) for 7 days. Dex regulated 32% of the 19,741 genes on the array, while 53% differed by Depot and 2.5% exhibited a Depot*Dex concentration interaction. Gene set enrichment analysis showed Dex regulation of the expected metabolic and inflammatory pathways in both depots. Cluster analysis of the 460 transcripts that exhibited an interaction of Depot and Dex concentration revealed sets of mRNAs for which the responses to Dex differed in magnitude, sensitivity or direction between the two depots as well as mRNAs that responded to Dex only in one depot. These transcripts were also clearly depot different in fresh adipose tissue and are implicated in processes that could affect adipose tissue distribution or functions (e.g. adipogenesis, triacylglycerol synthesis and storage, insulin action). Elucidation of the mechanisms underlying the depot differences in the effect of Dex on the expression of specific genes and pathways that regulate adipose function may offer novel insights into understanding the biology of visceral adipose tissues and their links to metabolic health., Competing Interests: The authors have declared that no competing interests exist.

The glucocorticoid-induced leucine zipper (GILZ), a primary target of glucocorticoids, is expressed in human adipocytes, but its importance in adipocyte function is unknown. Because TNFα is increased in obese adipose tissue and antagonizes a number of glucocorticoid actions, we investigated the interplay of these pathways. GILZ knockdown increased and GILZ overexpression decreased interleukin-6 (IL-6) and leptin mRNA and protein secretion. GILZ knockdown increased the magnitude of the glucocorticoid effect on leptin secretion, but did not affect the glucocorticoid suppression of IL-6. Although GILZ silencing decreased adiponectin mRNA levels, it did not affect the amount of adiponectin secreted. GILZ negatively modulated pro-inflammatory signaling pathways, blocking basal and TNFα-stimulated (1 h) p65 nuclear factor κB nuclear translocation and transcriptional activity by binding to p65 in the cytoplasm. GILZ silencing increased basal ERK1/2 and JNK phosphorylation, and decreased MAPK phosphatase-1 protein levels. Longer term TNFα (4 h or 24 h) treatment decreased GILZ expression in human adipocytes. Furthermore, adipose tissue GILZ mRNA levels were reduced in proportion to the degree of obesity and expression of inflammatory markers. Overall, these results suggest that GILZ antagonizes the pro-inflammatory effects of TNFα in human adipocytes, and its downregulation in obesity may contribute to adipose inflammation and dysregulated adipokine production, and thereby systemic metabolism., (Copyright © 2016 by the American Society for Biochemistry and Molecular Biology, Inc.)

Objective: To review recent advances in understanding the cellular mechanisms that regulate fat distribution., Methods: In this review, new insights into depot and sex differences in the developmental origins and growth of adipose tissues as revealed by studies that use new methods, including lineage tracing, are highlighted., Results: Variations in fat distribution during normal growth and in response to alterations in nutritional or hormonal status are driven by intrinsic differences in cells found in each adipose depot. Adipose progenitor cells and preadipocytes in different anatomical adipose tissues derive from cell lineages that determine their capacity for proliferation and differentiation. As a result, rates of hypertrophy and hyperplasia during growth and remodeling vary among depots. The metabolic capacities of adipose cells are also determined by variations in the expression of key transcription factors and non-coding RNAs. These developmental events are influenced by sex chromosomes and hormonal and nutrient signals that determine the adipogenic, metabolic, and functional properties of each depot., Conclusions: These new developments in the understanding of fat distribution provide a sound basis for understanding the association of body shape and health in men and women with and without obesity., (© 2015 The Obesity Society.)

Adipose tissue modifies the development of cardiovascular disease in a complex manner: obesity is a major risk factor, especially when accompanied by a central fat distribution. For that reason the characteristics of visceral adipose tissue have attracted most of the research interest thus far, and measurement of waist circumference is now recommended for everyday clinical practice. However, the direct, causative role of visceral fat in cardiometabolic disease remains to be established. Epidemiological and clinical studies show that accumulation of fat subcutaneously, in the gluteofemoral area, is protective against cardiovascular disease, but the exact molecular mechanisms remain unclear. In the last few years, imaging has allowed the study of smaller fat depots that may interact locally with important tissues: epicardial fat with the myocardium, perivascular fat with the vessel wall and the developing atherosclerotic plaque, and renal sinus fat with the renal artery. Unraveling the heterogeneous fat distribution and metabolic phenotypes in human obesity will facilitate optimal assessment of cardiovascular risk in overweight and obese individuals.

Obesity, defined as excess fat mass, increases risks for multiple metabolic diseases, such as type 2 diabetes, cardiovascular disease and several types of cancer. Over and above fat mass per se, the pattern of fat distribution, android or truncal as compared to gynoid or peripheral, has a profound influence on systemic metabolism and hence risk for metabolic diseases. Increases in upper body adipose tissue (visceral and abdominal subcutaneous) confer an independent risk, while the quantity of gluteofemoral adipose tissue is protective. Variations in the capacity of different depots to store and release fatty acids and to produce adipokines are important determinants of fat distribution and its metabolic consequences. Depot differences in cellular composition and physiology, including innervation and blood flow, likely influence their phenotypic properties. A number of lines of evidence also support the idea that adipocytes from different anatomical depots are intrinsically different as a result of genetic or developmental events. In this chapter, we will review the phenotypic characteristics of different adipose depots and mechanisms that link their depot-specific biology to metabolic complications in men and women., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Purpose of Review: Recent studies demonstrate that adipose tissue undergoes a continuous process of remodeling that is pathologically accelerated in the obese state. Contrary to earlier dogma, adipocytes die and are replaced by newly differentiated ones. This review will summarize recent advances of our knowledge of the mechanisms that regulate adipose tissue remodeling and highlight the influences of obesity, depot, and sex, as well as the relevance of rodent models to humans., Recent Findings: A substantial literature now points to the importance of dynamic changes in adipocyte and immune cell turnover, angiogenesis, and extracellular matrix remodeling in regulating the expandability and functional integrity of this tissue. In obesity, the macrophages are recruited, surrounding dead adipocytes and polarized toward an inflammatory phenotype. The number of dead adipocytes is closely associated with the pathophysiological consequences of obesity, including insulin resistance and hepatic steatosis. Further, there are substantial depot, sex and species differences in the extent of remodeling., Summary: Adipose tissue undergoes a continuous remodeling process that normally maintains tissue health, but may spin out of control and lead to adipocyte death in association with the recruitment and activation of macrophages, and systemic insulin resistance.

This review summarizes recent advances in our understanding of the pre- and posttranscriptional mechanisms that regulate leptin production and secretion in adipocytes. Basal leptin production is proportional to the status of energy stores, i.e., fat cell size, and this is mainly regulated by alterations in leptin mRNA levels. Leptin mRNA levels are regulated by hormones, including glucocorticoids and catecholamines, but little is known about the transcriptional mechanisms involved. Leptin synthesis and secretion is also acutely modulated in response to hormones such as insulin and the availability of metabolic fuels. Acute variations in leptin production over a time course of minutes to hours are mediated at the levels of both translation and secretion. Increases in amino acids and insulin after a meal activate the mammalian target of rapamycin (mTOR) pathway, leading to an increase in specific rates of leptin biosynthesis. Cross-talk among mTOR, PKA, and AMP-activated protein kinase pathways appears to integrate hormonal and nutrient signals that regulate leptin mRNA translation, at least in part through mechanisms involving its 5'- and 3'-untranslated regions. In addition, the rate of leptin secretion from preformed stores in response to hormonal cues is also regulated. Insulin stimulates, and adrenergic agonists inhibit, leptin secretion, and this likely contributes to variations in the magnitude of nutrition-related leptin excursions and oscillations. Overall, the study of leptin production has contributed to a deepening understanding of leptin biology and, more broadly, to our understanding of the cellular and molecular mechanisms by which the adipocyte integrates hormonal and nutrient signals to regulate adipokine production.

Previous studies showed that dietary L-arginine supplementation decreased white fat mass in genetically obese rats. This study tested the effectiveness of L-arginine in diet-induced obesity. Male Sprague-Dawley rats were fed for 15 wk a high-fat (HF) (40% energy) or low-fat (LF) (10% energy) diet beginning at 4 wk of age, resulting in 18% higher body weight gains and 74% higher weights of major white fat pads (retroperitoneal, epididymal, subcutaneous, and mesenteric adipose tissues) in HF than in LF fed rats. Starting at 19 wk of age, rats in each dietary group were supplemented for 12 wk with 1.51% L-arginine-HCl or 2.55% L-alanine (isonitrogenous control) (n = 8 per treatment) in drinking water and arginine groups were individually pair-fed to alanine controls. Despite similar energy intake, absolute weights of white fat pads increased by 98% in control rats over a 12-wk period but only by 35% in arginine-supplemented rats. The arginine treatment reduced the relative weights of white fat pads by 30% and enhanced those of soleus muscle by 13%, extensor digitorum longus muscle by 11%, and brown fat by 34% compared with control rats. Serum concentrations of insulin, adiponectin, growth hormone, corticosterone, triiodothyronine, and thyroxine did not differ between control and arginine-supplemented rats. However, arginine treatment resulted in lower serum concentrations of leptin, glucose, triglycerides, urea, glutamine, and branched-chain amino acids, higher serum concentrations of nitric-oxide metabolites, and improvement in glucose tolerance. Thus, dietary arginine supplementation shifts nutrient partitioning to promote muscle over fat gain and may provide a useful treatment for improving the metabolic profile and reducing body white fat in diet-induced obese rats.

Objective: We examined the relationship between the expression of thrombospondin (TSP)1, an antiangiogenic factor and regulator of transforming growth factor-beta activity, obesity, adipose inflammation, and insulin resistance., Research Design and Methods: TSP1 gene expression was quantified in subcutaneous adipose tissue (SAT) of 86 nondiabetic subjects covering a wide range of BMI and insulin sensitivity, from visceral adipose (VAT) and SAT from 14 surgical patients and from 38 subjects with impaired glucose tolerance randomized to receive either pioglitazone or metformin for 10 weeks. An adipocyte culture system was also used to assess the effects of pioglitazone and coculture with macrophages on TSP1 gene expression., Results: TSP1 mRNA was significantly associated with obesity (BMI) and insulin resistance (low insulin sensitivity index). Relatively strong positive associations were seen with markers of inflammation, including CD68, macrophage chemoattractant protein-1, and plasminogen activator inhibitor (PAI)-1 mRNA (r >/= 0.46, P = 0.001 for each), that remained significant after controlling for BMI and S(i). However, TSP1 mRNA was preferentially expressed in adipocyte fraction, whereas inflammatory markers predominated in stromal vascular fraction. Coculture of adipocytes and macrophages augmented TSP1 gene expression and secretion from both cell types. Pioglitazone (not metformin) treatment resulted in a 54% decrease (P < 0.04) in adipose TSP gene expression, as did in vitro pioglitazone treatment of adipocytes., Conclusions: TSP1 is a true adipokine that is highly expressed in obese, insulin-resistant subjects; is highly correlated with adipose inflammation; and is decreased by pioglitazone. TSP1 is an important link between adipocytes and macrophage-driven adipose tissue inflammation and may mediate the elevation of PAI-1 that promotes a prothrombotic state.

Central obesity and the accumulation of visceral fat are risk factors for the development of type 2 diabetes and cardiovascular disease. Omentin is a protein expressed and secreted from visceral but not subcutaneous adipose tissue that increases insulin sensitivity in human adipocytes. To determine the impact of obesity-dependent insulin resistance on the regulation of two omentin isoforms, gene expression and plasma levels were measured in lean, overweight, and obese subjects. Omentin 1 was shown to be the major circulating isoform in human plasma. Lean subjects had significantly higher plasma omentin 1 levels than obese and overweight subjects. In addition, higher plasma omentin 1 levels were detected in women compared with men. Plasma omentin 1 levels were inversely correlated with BMI, waist circumference, leptin levels, and insulin resistance as measured by homeostasis model assessment and positively correlated with adiponectin and HDL levels. Both omentin 1 and omentin 2 gene expression were decreased with obesity and were highly correlated with each other in visceral adipose tissue. In summary, decreased omentin levels are associated with increasing obesity and insulin resistance. Therefore, omentin levels may be predictive of the metabolic consequences or co-morbidities associated with obesity.

Context: Visfatin (VF) is a recently described adipokine preferentially secreted by visceral adipose tissue (VAT) with insulin mimetic properties., Objective: The aim of this study was to examine the association of VF with insulin sensitivity, intramyocellular lipids (IMCL), and inflammation in humans., Design and Patients: VF mRNA was examined in paired samples of VAT and abdominal sc adipose tissue (SAT) obtained from subjects undergoing surgery. Plasma VF and VF mRNA was also examined in SAT and muscle tissue, obtained by biopsy from well-characterized subjects with normal or impaired glucose tolerance, with a wide range in body mass index (BMI) and insulin sensitivity (S(I))., Setting: The study was conducted at a University Hospital and General Clinical Research Center., Intervention: S(I) was measured, and fat and muscle biopsies were performed. In impaired glucose tolerance subjects, these procedures were performed before and after treatment with pioglitazone or metformin., Main Outcome Measures: We measured the relationship between VF and obesity, S(I), adipose tissue inflammation, IMCL, and response to insulin sensitizers., Results: No significant difference in VF mRNA was seen between SAT and VAT depots. VAT VF mRNA associated positively with BMI, whereas SAT VF mRNA decreased with BMI. SAT VF correlated positively with S(I), and the association of SAT VF mRNA with S(I) was independent of BMI. IMCL and markers of inflammation (adipose CD68 and plasma TNFalpha) were negatively associated with SAT VF. Impaired glucose tolerance subjects treated with pioglitazone showed no change in SAT VF mRNA despite a significant increase in S(I). Plasma VF and muscle VF mRNA did not correlate with BMI or S(I) or IMCL, and there was no change in muscle VF with either pioglitazone or metformin treatments., Conclusion: SAT VF is highly expressed in lean, more insulin-sensitive subjects and is attenuated in subjects with high IMCL, low S(I), and high levels of inflammatory markers. VAT VF and SAT VF are regulated oppositely with BMI.

Background: Obesity is associated with low-grade chronic inflammation, and serum markers of inflammation are independent risk factors for cardiovascular disease (CVD). However, the molecular and cellular mechanisms that link obesity to chronic inflammation and CVD are poorly understood., Methods and Findings: Acute-phase serum amyloid A (A-SAA) mRNA levels, and A-SAA adipose secretion and serum levels were measured in obese and nonobese individuals, obese participants who underwent weight-loss, and persons treated with the insulin sensitizer rosiglitazone. Inflammation-eliciting activity of A-SAA was investigated in human adipose stromal vascular cells, coronary vascular endothelial cells and a murine monocyte cell line. We demonstrate that A-SAA was highly and selectively expressed in human adipocytes. Moreover, A-SAA mRNA levels and A-SAA secretion from adipose tissue were significantly correlated with body mass index (r = 0.47; p = 0.028 and r = 0.80; p = 0.0002, respectively). Serum A-SAA levels decreased significantly after weight loss in obese participants (p = 0.006), as well as in those treated with rosiglitazone (p = 0.033). The magnitude of the improvement in insulin sensitivity after weight loss was significantly correlated with decreases in serum A-SAA (r = -0.74; p = 0.034). SAA treatment of vascular endothelial cells and monocytes markedly increased the production of inflammatory cytokines, e.g., interleukin (IL)-6, IL-8, tumor necrosis factor alpha, and monocyte chemoattractant protein-1. In addition, SAA increased basal lipolysis in adipose tissue culture by 47%., Conclusions: A-SAA is a proinflammatory and lipolytic adipokine in humans. The increased expression of A-SAA by adipocytes in obesity suggests that it may play a critical role in local and systemic inflammation and free fatty acid production and could be a direct link between obesity and its comorbidities, such as insulin resistance and atherosclerosis. Accordingly, improvements in systemic inflammation and insulin resistance with weight loss and rosiglitazone therapy may in part be mediated by decreases in adipocyte A-SAA production.

In vivo and in vitro studies indicate that beta-adrenergic receptor agonists decrease leptin release from fat cells in as little as 30 min. Our objective was to determine whether alterations in leptin biosynthesis or secretion were involved in the short-term adrenergic regulation of leptin in human and rat adipose tissue. Isoproterenol (Iso) decreased leptin release from incubated adipose tissue of both nonobese and obese subjects to similar extent (-28 vs. -21% after 3 h). Inhibition of protein synthesis with cycloheximide did not block the effect of Iso on leptin release from human adipose tissue, suggesting that the Iso effect is independent of leptin synthesis. Iso also tended to increase tissue leptin content at the end of the 3-h incubation, as expected from the observed inhibition of release. Consistent with a posttranslational mechanism, Iso treatment did not affect leptin mRNA levels or relative rate of leptin biosynthesis as directly assessed by [35S]methionine incorporation into immunoprecipitable leptin. In contrast to these results in human adipose tissues, Iso did not decrease basal leptin release from rat adipose tissue. However, Iso did decrease insulin-stimulated leptin release by inhibiting the ability of insulin to increase leptin biosynthesis without detectably affecting leptin mRNA levels. Thus, in both human and rat, adrenergic regulation of posttranscriptional events (secretion in humans, translation in rats) may contribute to the rapid decline in circulating leptin that occurs when the sympathetic nervous system is activated, such as during fasting and cold exposure. Furthermore, the rat does not provide an ideal model to study mechanisms of cellular leptin regulation in humans.

Objective: Perilipins are phosphoproteins that are localized to the surface of triacylglycerol droplets within adipocytes where they regulate the rate of lipolysis. We sought to determine the effects of severe obesity and depot [omental (Om) vs. subcutaneous (Sc)] on perilipin expression in the adipose tissue of individuals., Research Methods and Procedures: Samples of Om and Sc adipose tissues obtained at surgery from severely obese subjects and fat aspirations from nonobese subjects were analyzed for perilipin protein and mRNA levels by Northern and Western analysis., Results: Perilipin A (periA) was the major perilipin expressed in adipose tissues. periA mRNA relative abundance was significantly lower in Sc adipose tissue from severely obese compared to that from nonobese subjects. Western blotting of adipose tissue extracts showed that periA protein levels expressed relative to tissue protein or fat cell surface area were significantly lower ( approximately -40%) in abdominal Sc adipose tissue from severely obese compared to that from nonobese subjects. However, the calculated mass of perilipin per fat cell did not differ between the two groups. Perilipin mRNA levels were higher in Sc compared to Om adipose tissue from obese individuals (p < 0.025; n = 26; 17 women, 9 men); however, periA protein levels did not differ. In addition, perilipin protein, but not mRNA, levels were higher in Sc adipose tissue from obese men than from women (p < 0.025)., Discussion: Variations in perilipin expression may contribute to the higher basal lipolytic rates observed in obese compared to nonobese individuals and in obese women compared to obese men.

Adipose tissue remodeling and dysfunction, characterized by elevated inflammation and insulin resistance, play a central role in obesity-related development of type 2 diabetes (T2D) and cardiovascular diseases. Long intergenic non-coding RNAs (lincRNAs) are important regulators of cellular functions. Here, we describe the functions of linc-ADAIN (adipose anti-inflammatory), an adipose lincRNA that is downregulated in white adipose tissue of obese humans. We demonstrate that linc-ADAIN knockdown (KD) increases KLF5 and interleukin-8 (IL-8) mRNA stability and translation by interacting with IGF2BP2. Upregulation of KLF5 and IL-8, via linc-ADAIN KD, leads to an enhanced adipogenic program and adipose tissue inflammation, mirroring the obese state, in vitro and in vivo. KD of linc-ADAIN in human adipose stromal cell (ASC) hTERT adipocytes implanted into mice increases adipocyte size and macrophage infiltration compared to implanted control adipocytes, mimicking hallmark features of obesity-induced adipose tissue remodeling. linc-ADAIN is an anti-inflammatory lincRNA that limits adipose tissue expansion and lipid storage. [Display omitted] • linc-ADAIN expression increases during adipocyte differentiation • linc-ADAIN is suppressed in white adipose tissue of obese humans • Knockdown of linc-ADAIN leads to increased inflammation and sustained adipogenesis • linc-ADAIN knockdown increases IL-8 and KLF5 mRNA, important genes for adipogenesis O'Reilly et al. investigate a long non-coding RNA, named linc-adipose anti-inflammatory (linc-ADAIN), and its role in adipose inflammation and maturation of fat cells (adipocytes). They show that linc-ADAIN 's expression is suppressed in adipose tissue of obese humans and that linc-ADAIN regulates inflammation as well as maturation and size of fat cells. [ABSTRACT FROM AUTHOR]

Objective: Lower body fat is associated with diminishing cardiometabolic risk. Physiological differences between gluteofemoral and abdominal subcutaneous adipocyte functions are known, but the molecular basis for depot differences in adipocyte function is poorly understood. The objective of this study was to identify depot differences in microRNA (miRNA) expression in human abdominal and gluteofemoral subcutaneous adipose tissues and their implication in gene regulation.Methods: Abdominal and gluteofemoral adipose tissue aspirates obtained from 18 participants (9 male and 9 female, age 30 ± 1.5 y, BMI 27.3 ± 1.23 kg/m2 ) were analyzed for miRNA expression profiles by next-generation DNA sequencing. The raw reads were mapped to miRBase 17, and differentially expressed miRNAs were confirmed by qRT-PCR. The hsa-mimic-miR196a was transfected into cultured abdominal preadipocytes isolated from five women with obesity. Target gene expression was evaluated by RT-qPCR.Results: Among the 640 miRNAs detected in adipose tissue, miR196a2, miR196a1, miR196b, and miR204 showed a higher expression in the gluteofemoral depot (fold change = 2.7, 2.3, 1.7, and 2.3, respectively) independent of sex. Bioinformatic analyses and human primary preadipocyte transfection with miR196 suggested that the differentially expressed miRNAs could directly or indirectly modulate homeobox (HOX) gene expression.Conclusions: The miR196 gene family could play an important role in the regulation of HOX gene expression in subcutaneous adipose tissue and in fat distribution variation. [ABSTRACT FROM AUTHOR]

Objective To investigate the effects of short-term GH administration on abdominal subcutaneous adipocyte size and CT attenuation in men with abdominal obesity. Design 6-week, randomized, double-blind, placebo-controlled study of GH (starting dose 2 μg/kg/d) vs placebo of 15 abdominally obese men (mean age: 34 ± 6 years; mean BMI: 37.7 ± 6.1 kg/m 2 , mean IGF-1 SDS: − 1.9 ± 0.5) who underwent abdominal subcutaneous adipose tissue (SAT) aspirations to determine adipocyte size, CTs for body composition and measures of glucose tolerance at baseline and 6 weeks. GH dosing was titrated to target IGF-1 levels in the upper normal age-appropriate range. Results GH administration decreased subcutaneous abdominal adipocyte size compared to placebo. Adipocyte size was positively associated with 120-min glucose and HOMA-IR and inversely associated with peak-stimulated GH and CT attenuation. CT attenuation of SAT was inversely associated with 120-min glucose and HOMA-IR and increased following GH administration. Conclusion In men with abdominal obesity, subcutaneous abdominal adipocyte size is positively associated with measures of impaired glucose tolerance and administration of GH at doses that raise IGF-1 levels within the normal range, decreases abdominal subcutaneous adipocyte size, suggesting that GH administration improves the health of adipose tissue. Clinical trials number: NCT00131378 [ABSTRACT FROM AUTHOR]

Objective Insulin signaling plays a unique role in the regulation of energy homeostasis and the impairment of insulin action is associated with altered lipid metabolism, obesity, and Type 2 Diabetes. The main aim of this study was to provide further insight into the regulatory mechanisms governing the insulin signaling pathway by investigating the role of non-proteolytic ubiquitination in insulin-mediated activation of AKT. Methods The molecular mechanism of AKT regulation through ubiquitination is first dissected in vitro in 3T3-L1 preadipocytes and then validated in vivo using mice with adipo-specific deletion of GPS2, an endogenous inhibitor of Ubc13 activity (GPS2-AKO mice). Results Our results indicate that K63 ubiquitination is a critical component of AKT activation in the insulin signaling pathway and that counter-regulation of this step is provided by GPS2 preventing AKT ubiquitination through inhibition of Ubc13 enzymatic activity. Removal of this negative checkpoint, through GPS2 downregulation or genetic deletion, results in sustained activation of insulin signaling both in vitro and in vivo . As a result, the balance between lipid accumulation and utilization is shifted toward storage in the adipose tissue and GPS2-AKO mice become obese under normal laboratory chow diet. However, the adipose tissue of GPS2-AKO mice is not inflamed, the levels of circulating adiponectin are elevated, and systemic insulin sensitivity is overall improved. Conclusions Our findings characterize a novel layer of regulation of the insulin signaling pathway based on non-proteolytic ubiquitination of AKT and define GPS2 as a previously unrecognized component of the insulin signaling cascade. In accordance with this role, we have shown that GPS2 presence in adipocytes modulates systemic metabolism by restricting the activation of insulin signaling during the fasted state, whereas in absence of GPS2, the adipose tissue is more efficient at lipid storage, and obesity becomes uncoupled from inflammation and insulin resistance. [ABSTRACT FROM AUTHOR]

The triglyceride (TG) transfer activity of microsomal triglyceride transfer protein (MTP) is essential for lipoprotein assembly in the liver and intestine; however, its function in adipose tissue, which does not assemble lipoproteins, is unknown. Here we have elucidated the function of MTP in adipocytes. We demonstrated that MTP is present on lipid droplets in human adipocytes. Adipose-specific MTP deficient (A- Mttp −/− ) male and female mice fed an obesogenic diet gained less weight than Mttp f/f mice, had less fat mass, smaller adipocytes and were insulin sensitive. A- Mttp −/− mice showed higher energy expenditure than Mttp f/f mice. During a cold challenge, A- Mttp −/− mice maintained higher body temperature by mobilizing more fatty acids. Biochemical studies indicated that MTP deficiency de-repressed adipose triglyceride lipase (ATGL) activity and increased TG lipolysis. Both wild type MTP and mutant MTP deficient in TG transfer activity interacted with and inhibited ATGL activity. Thus, the TG transfer activity of MTP is not required for ATGL inhibition. C-terminally truncated ATGL that retains its lipase activity interacted less efficiently than full-length ATGL. Our findings demonstrate that adipose-specific MTP deficiency increases ATGL-mediated TG lipolysis and enhances energy expenditure, thereby resisting diet-induced obesity. We speculate that the regulatory function of MTP involving protein-protein interactions might have evolved before the acquisition of TG transfer activity in vertebrates. Adipose-specific inhibition of MTP-ATGL interactions may ameliorate obesity while avoiding the adverse effects associated with inhibition of the lipid transfer activity of MTP. • Adipose specific MTP knockout mice gain less weight on an obesogenic diet. • Adipose specific MTP knockout mice adapt better to cold challenge. • Adipocyte MTP regulates basal lipolysis by inhibiting ATGL. • Lipid transfer activity of MTP is not essential to inhibit ATGL activity. • MTP inhibits ATGL activity by direct protein-protein interactions. [ABSTRACT FROM AUTHOR]

Objective: Growth hormone (GH) administration reduces abdominal, but not lower body, fat mass. To gain insight into the underlying mechanisms, this study examined the expression of the GH receptor (GHR) and some of its targets in abdominal and gluteal adipose tissue.Methods: GHR and GH targets in the lipolytic pathway were assessed (quantitative PCR/Western blotting) in adipose aspirates from premenopausal women [n = 15, age 26.9 ± 6.1 years, body mass index (BMI) 28.0 ± 6.8 kg/m(2) ] and men (n = 28, age 29.2 ± 7.0 years, BMI 26.9 ± 3.7 kg/m(2) ).Results: GHR mRNA expression was lower in the gluteal depot when compared with the abdominal depot (P = 0.01). Abdominal GHR correlated negatively with age and BMI, whereas gluteal GHR was associated with lower waist-to-hip ratio (WHR), that is, pear shape. In both sites, GHR mRNA correlated strongly with genes important for the regulation of lipolysis: adipose tissue triglyceride lipase (ATGL), hormone-sensitive lipase, perilipin, and CIDEA (all P < 0.001), independently of BMI, WHR, age, and sex. GHR protein was lower in the gluteal fat when compared with the abdominal fat (P = 0.03) and correlated with ATGL protein in the gluteal depot (P < 0.001).Conclusions: GHR levels correlate with levels of lipases and lipid droplet-associated proteins crucial for lipolysis. Thus, higher GHR expression in the abdominal depot when compared with the gluteal depot may underlie the in vivo effect of GH to specifically reduce abdominal adipose tissue mass. [ABSTRACT FROM AUTHOR]

Objective Peripheral lower body fat is associated with lower cardiometabolic risk. Physiological differences in gluteal compared with abdominal subcutaneous (sc) adipocyte functions are known but the molecular basis for depot differences in adipocyte function is poorly understood. Our goal is to identify novel gene regulatory pathways that underlie the heterogeneity of human fat distribution. Methods Abdominal and gluteal adipose tissue aspirates obtained from 35 subjects (age = 30 ± 1.6 years; BMI = 27.3 ± 1.3 kg/m2) were analyzed using Illumina microarrays and confirmed by RT-PCR. The HOTAIR gene was stably transfected into primary cultured human abdominal sc preadipocytes using a lentivirus and effects on adipogenic differentiation were analyzed. Results A long noncoding RNA, HOTAIR that was expressed in gluteal but not in Abd sc adipose tissue was identified. This difference was retained throughout in vitro differentiation and was maximal at day 4. Ectopic expression of HOTAIR in abdominal preadipocytes produced an increase in differentiation as reflected by a higher percentage of differentiated cells, and increased expression of key adipogenic genes including PPARγ and LPL. Conclusions HOTAIR is expressed in gluteal adipose and may regulate key processes in adipocyte differentiation. The role of this lncRNA in determining the metabolic properties of gluteal compared with abdominal adipocytes merits further study. [ABSTRACT FROM AUTHOR]

High concentrations of TNF within obese adipose tissue increase basal lipolysis and antagonize insulin signaling. Adipocytes of the obese are also exposed to elevated levels of glucocorticoids (GCs), which antagonize TNF actions in many cell types. We tested the hypothesis that TNF decreases sensitivity to the antilipolytic effect of insulin and that GCs antagonize this effect in differentiated human adipocytes. Lipolysis and expression levels of lipolytic proteins were measured after treating adipocytes with TNF, dexamethasone (DEX), or DEX + TNF for up to 48 h. TNF not only increased basal lipolysis, it caused resistance to the antilipolytic effects of insulin in human adipocytes. DEX alone did not significantly affect lipolysis. Cotreatment with DEX blocked TNF induction of basal lipolysis and insulin resistance by antagonizing TNF stimulation of PKA-mediated phosphorylation of hormonesensitive lipase (HSL) at Ser563 and Ser660 and perilipin. TNF did not affect perilipin, HSL, or phosphodiesterase-3B mass but paradoxically suppressed adipose tissue triglyceride lipase expression, and this effect was blocked by DEX. The extent to which GCs can restrain the lipolytic actions of TNF may both diminish the potentially deleterious effects of excess lipolysis and contribute to fat accumulation in obesity. [ABSTRACT FROM AUTHOR]

Abstract: Women have more body fat than men, but in contrast to the deleterious metabolic consequences of the central obesity typical of men, the pear-shaped body fat distribution of many women is associated with lower cardiometabolic risk. To understand the mechanisms regulating adiposity and adipose tissue distribution in men and women, significant research attention has focused on comparing adipocyte morphological and metabolic properties, as well as the capacity of preadipocytes derived from different depots for proliferation and differentiation. Available evidence points to possible intrinsic, cell autonomous differences in preadipocytes and adipocytes, as well as modulatory roles for sex steroids, the microenvironment within each adipose tissue, and developmental factors. Gluteal-femoral adipose tissues of women may simply provide a safe lipid reservoir for excess energy, or they may directly regulate systemic metabolism via release of metabolic products or adipokines. We provide a brief overview of the relationship of fat distribution to metabolic health in men and women, and then focus on mechanisms underlying sex differences in adipose tissue biology. [ABSTRACT FROM AUTHOR]

Glucocorticoids (GC) are powerful regulators of adipocyte differentiation, metabolism, and endocrine function and promote the development of upper body obesity, especially visceral fat stores. To provide a comprehensive understanding of how GC affect adipose tissue and adipocyte function, we analyzed patterns of gene expression (HG U95 Affymetrix arrays) after culture of abdominal subcutaneous (Abd sc) and omental (Om) adipose tissues from severely obese subjects (3 F, 1 M) in the presence of insulin or insulin (7 nM) plus dexamethasone (Dex, 25 nM) for 7 days. About 20% (561 genes in Om and 569 genes in sc) of 2,803 adipose expressed genes were affected by long-term GC. While most of the genes (90%) were commonly regulated by Dex in both depots, 26 in Om and 34 in Abd sc were affected by Dex in only one depot. 60% of the commonly upregulated genes were involved in metabolic pathways and were expressed mainly in adipocytes. Dex suppressed genes in immune/inflammatory (IL-6, IL-8, and MCP-1, expressed in nonadipocytes) and proapoptotic pathways, yet induced genes related to the acute-phase response (SAA, factor D, haptoglobin, and RBP4, expressed in adipocytes) and stress/defense response. Functional classification analysis showed that Dex also induced expression levels of 22 transcription factors related to insulin action and lipogenesis (LXRα, STAT5α, SREBP1, and FoxO1) and immunity/adipogenesis (TSC22D3) while suppressing 17 transcription factors in both depots. Overall, these studies reveal the powerful effects of GC on gene networks that regulate many key functions in human adipose tissue. [ABSTRACT FROM AUTHOR]

Lee M-J, Fried SK. Integration of hormonal and nutrient signals that regulate leptin synthesis and secretion. Am J Physiol Endocrinol Metab 296: E1230-E1238, 2009. First published March 24, 2009; doi:10.1152/ajpendo.90927.2008.-This review summarizes recent advances in our understanding of the preand posttranscriptional mechanisms that regulate leptin production and secretion in adipocytes. Basal leptin production is proportional to the status of energy stores, i.e., fat cell size, and this is mainly regulated by alterations in leptin mRNA levels. Leptin mRNA levels are regulated by hormones, including glucocorticoids and catecholamines, but little is known about the transcriptional mechanisms involved. Leptin synthesis and secretion is also acutely modulated in response to hormones such as insulin and the availability of metabolic fuels. Acute variations in leptin production over a time course of minutes to hours are mediated at the levels of both translation and secretion. Increases in amino acids and insulin after a meal activate the mammalian target of rapamycin (mTOR) pathway, leading to an increase in specific rates of leptin biosynthesis. Cross-talk among mTOR, PKA, and AMPactivated protein kinase pathways appears to integrate hormonal and nutrient signals that regulate leptin mRNA translation, at least in part through mechanisms involving its 5'and 3-untranslated regions. In addition, the rate pf leptin secretion from preformed stores in response to hormonal cues is also regulated. Insulin stimulates, and adrenergic agonists inhibit, leptin secretion, and this likely contributes to variations in the magnitude of nutrition-related leptin excursions and oscillations. Overall, the study of leptin production has contributed to a deepening understanding of leptin biology and, more broadly, to our understanding of the cellular and molecular mechanisms by which the adipocyte integrates hormonal and nutrient signals to regulate adipokine production. [ABSTRACT FROM AUTHOR]

OBJECTIVE--Accumulation of intracellular lipid droplets (LDs) in non-adipose tissues is recognized as a strong prognostic factor for the development of insulin resistance in obesity. LDs are coated with perilipin, adipose differentiation-related protein, tail interacting protein of 47 kd (PAT) proteins that are thought to regulate LD turnover by modulating lipolysis. Our hypothesis is that PAT proteins modulate LD metabolism and therefore insulin resistance. RESEARCH DESIGN AND METHODS--We used a cell culture model (murine AML12 loaded with oleic acid) and small interfering RNA to directly assess the impact of PAT proteins on LD accumulation, lipid metabolism, and insulin action. PAT proteins associated with excess fat deposited in livers of diet-induced obese (DIO) mice were also measured. RESULTS--Cells lacking PAT proteins exhibited a dramatic increase in LD size and a decrease in LD number. Further, the lipolytic rate increased by ∼2- to 2.5-fold in association with increased adipose triglyceride lipase (ATGL) at the LD surface. Downregulation of PAT proteins also produced insulin resistance, as indicated by decreased insulin stimulation of Akt phosphorylation (P < 0.001). Phosphoinositide-dependent kinase-1 and phosphoinositide 3-kinase decreased, and insulin receptor substrate-1 307 phosphorylation increased. Increased lipids in DIO mice livers were accompanied by changes in PAT composition but also increased ATGL, suggesting a relative PAT deficiency. CONCLUSIONS--These data establish an important role for PAT proteins as surfactant at the LD surface, packaging lipids in smaller units and restricting access of lipases and thus preventing insulin resistance. We suggest that a deficiency of PAT proteins relative to the quantity of ectopic fat could contribute to cellular dysfunction in obesity and type 2 diabetes. Diabetes 57:2037-2045, 2008 [ABSTRACT FROM AUTHOR]

Serum leptin levels are upregulated in proportion to body fat and also increase over the short term in response to meals or insulin. To understand the mechanisms involved, we assessed leptin synthesis and secretion in samples of adipose tissue from subjects with a wide range of BMI. Tissue leptin content and relative rates of leptin biosynthesis, as determined by metabolic labeling, were highly correlated with each other and with BMI and fat cell size. To understand mechanisms regulating leptin synthesis in obesity, we used biosynthetic labeling to directly assess the effects of insulin and glucocorticoids (dexamethasone) on leptin synthesis and secretion in human adipose tissue. Chronic treatment (1-2 days in organ culture) with insulin increased relative rates of leptin biosynthesis without affecting leptin mRNA levels. In contrast, dexamethasone increased leptin mRNA and biosynthesis in parallel. Acute treatment with insulin or dexamethasone (added during 1-h preincubation and 45-min pulse labeling) did not affect relative rates of leptin biosynthesis, but pulse-chase studies showed that addition of insulin nearly doubled the release of [35S]leptin after a 1-h chase. We conclude that the higher leptin stores in adipose tissue of obese humans are maintained by chronic effects of insulin and glucocorticoids acting at pre- and posttranslational levels and that the ability of insulin to increase the release of preformed leptin may contribute to short-term variations in circulating leptin levels. [ABSTRACT FROM AUTHOR]

Central (visceral) obesity is more closely associated with insulin resistance, type 2 diabetes, and cardiovascular disease than is peripheral [subcutaneous (sc)] obesity, but the underlying mechanism for this pathophysiological difference is largely unknown. To understand the molecular basis of this difference, we sequenced 10,437 expressed sequence tags (ESTs) from a human omental fat cDNA library and discovered a novel visceral fat depot-specific secretory protein, which we have named omentin. Omentin ESTs were more abundant than many known adipose genes, such as perilipin, adiponectin, and leptin in the cDNA library. Protein sequence analysis indicated that omentin mRNA encodes a peptide of 313 amino acids, containing a secretory signal sequence and a fibrinogen-related domain. Northern analysis demonstrated that omentin mRNA was predominantly expressed in visceral adipose tissue and was barely detectable in sc fat depots in humans and rhesus monkeys. Quantative real-time PCR showed that omentin mRNA was expressed in stromal vascular cells, but not fat cells, isolated from omental adipose tissue, with > 150-fold less in sc cell fractions. Accordingly, omentin protein was secreted into the culture medium of omental, but not sc, fat explants. Omentin was detectable in human serum by Western blot analysis. Addition of recombinant omentin in vitro did not affect basal but enhanced insulin-stimulated glucose uptake in both sc (47%, n = 9, P = 0.003) and omental (∼30%, n = 3, P < 0.05) human adipocytes. Omentin increased Akt phosphorylation in the absence and presence of insulin. In conclusion, omentin is a new adipokine that is expressed in omental adipose tissue in humans and may regulate insulin action. [ABSTRACT FROM AUTHOR]

Background: Obesity is associated with low-grade chronic inflammation, and serum markers of inflammation are independent risk factors for cardiovascular disease (CVD). However, the molecular and cellular mechanisms that link obesity to chronic inflammation and CVD are poorly understood. Methods and Findings: Acute-phase serum amyloid A (A-SAA) mRNA levels, and A-SAA adipose secretion and serum levels were measured in obese and nonobese individuals, obese participants who underwent weight-loss, and persons treated with the insulin sensitizer rosiglitazone. Inflammation-eliciting activity of A-SAA was investigated in human adipose stromal vascular cells, coronary vascular endothelial cells and a murine monocyte cell line. We demonstrate that A-SAA was highly and selectively expressed in human adipocytes. Moreover, A-SAA mRNA levels and A-SAA secretion from adipose tissue were significantly correlated with body mass index (r = 0.47; p = 0.028 and r = 0.80; p = 0.0002, respectively). Serum A-SAA levels decreased significantly after weight loss in obese participants (p = 0.006), as well as in those treated with rosiglitazone (p = 0.033). The magnitude of the improvement in insulin sensitivity after weight loss was significantly correlated with decreases in serum A-SAA (r = −0.74; p = 0.034). SAA treatment of vascular endothelial cells and monocytes markedly increased the production of inflammatory cytokines, e.g., interleukin (IL)-6, IL-8, tumor necrosis factor alpha, and monocyte chemoattractant protein-1. In addition, SAA increased basal lipolysis in adipose tissue culture by 47%. Conclusions: A-SAA is a proinflammatory and lipolytic adipokine in humans. The increased expression of A-SAA by adipocytes in obesity suggests that it may play a critical role in local and systemic inflammation and free fatty acid production and could be a direct link between obesity and its comorbidities, such as insulin resistance and atherosclerosis. Accordingly, improvements in systemic inflammation and insulin resistance with weight loss and rosiglitazone therapy may in part be mediated by decreases in adipocyte A-SAA production. [ABSTRACT FROM AUTHOR]

Examines the relation of the association between abdominal deposition of adipose tissue and morbidities accompanying obesity to high rates of free fatty acid release from enlarged intra-abdominal stores. Investigation of cellular mechanisms; Comparison of rates of triacylglycerol (TG) synthesis in women and men; Effect of the stimulation of lipolysis.

The essential amino acid leucine serves as a signal that activates protein synthesis. A new study by in this issue of Cell Metabolism shows that raising circulating leucine by blocking leucine breakdown drives a futile cycle of protein synthesis and degradation that contributes to higher-energy expenditure, resistance to dietary obesity, and improved insulin sensitivity. [Copyright &y& Elsevier]

Glucocorticoids (GC) are powerful modulators of adipose tissue function, and GC action varies in human visceral and sc adipose tissues. To establish if alterations in GC action are secondary to alterations in its receptor, and post-receptor events, we assessed the tissue-specific expression of glucocorticoid receptor (GR) translational isoforms (A-D). Direct GR isoforms exert diverse and partially non-overlapping effects of GC on gene expression. GRA/B (94-91kDa) and GR D (54 kDa) were major translational isoforms expressed in human adipose tissue. The expression of the more transcriptionally active A/B form was higher in subcutaneous than omentum, while D form was similar (n=5). Because GC action is regulated by inflammatory cytokines in other cell types and tumor necrosis factor alpha (TNF) expression in adipose tissue is increased in human obesity, we examined whether TNF modulates glucocorticoid receptor expression and activity in human adipose tissue. TNF treatment (3 ng/ml, 2d) of subcutaneous adipose tissue fragments in organ culture increased GRα expression levels but simultaneously increased GRα phosphorylational at serine 226 (+82% in ratio to total GR p<0.05, n=4), a post-translational modification known to decrease GR activity. In addition, TNF decreased GR serine 211 phosphorylation (ligand dependent) (ratio to total, +8.9 fold without TNF vs. +4.5 fold with TNF, n=3) and attenuated the magnitude of GC effects on key target genes (glucocortieoid induced leucine zipper (GILZ) and PEPCK). TNF also decreased sensitivity and responsiveness to stimulatory effects of GC on lipoprotein lipase (LPL) activity. These effects on LPL were partially blocked by a JNK inhibitor (SP600125, 25 µM) while p38 or ERK1/2 inhibitors were ineffective. Collectively, these data indicate TNF regulates the expression and activity of the GR in human adipose tissue at translational and post-translational levels. Further, depot- and/or obesity-related differences in TNF in obesity may regulate GR activity. [ABSTRACT FROM AUTHOR]

Retinol binding protein 4 (RBP4) was overexpressed in adipose tissue of Glut4 KO mice, and elevated RBP4 has been associated with insulin resistance in mouse and human studies. To determine the relationship between RBP4 and obesity, insulin resistance, and other markers of insulin resistance in humans, RBP4 gene expression measured by real-time RT-PCR and blood levels measured by ELISA and Western blotting were studied in adipose tissue and muscle of 85 non-diabetic humans over a wide range of BMI (19-55 Kg/m²) and S[sub I] (1.02-26.77 x 10[sup -5] x min[sup -1]/pM), and RBP4 expression was also measured from visceral (VAT) and subcutaneous adipose tissue (SAT) from 16 surgical patients. RBP4 expression was 3-fold higher in SAT vs VAT (p<0.005), and RBP4 was 7-fold higher in the adipocyte (vs stromal) fraction, and undetectable in preadipocytes. Neither SAT RBP4 expression nor blood RBP4 level showed a significant relationship with BMI or S[sub I]. However, there was a strong positive correlation between RBP4 mRNA and the inflammation markers MCP1 (r=0.42, p<0.0001) and CD68 (r=0.46, p<0.0001)). Adipose GLUT4 mRNA was also highly associated with RBP4 (r=0.53, p<0.0001). These relationships remained significant after adjustment for BMI and St. Impaired glucose tolerant subjects were treated with pioglitazone, resulting in an increase in S[sub 1] along with a 60% increase in RBP4 expression, but no change in plasma RBP4. The in vitro treatment of cultured adipocytes with pioglitazone yielded a similar increase in RBP4 mRNA. Hence, RBP4 expression in humans was not significantly associated with obesity or insulin resistance, and actually increased with TZD treatment. However, RBP4 was associated with inflammatory markers and GLUT 4 expression, suggesting a complex role in metabolic syndrome. [ABSTRACT FROM AUTHOR]

This study was conducted to test the hypothesis that dietary arginine supplementation can reduce fat mass in diet-induced obesity. Male Sprague-Dawley rats were fed low- or high-fat diets for 15 wks. Thereafter, the resultant lean or obese rats continued their respective diets and received drinking water containing either 1.51% arginine-HCl or 2.55% alanine (isonitrogenous control) for 12 wks. High-fat diet increased the mass of retroperitoneal (RP), epididymal, subcutaneous and mesenteric fat by 49-96% compared to the low-fat diet, and arginine reduced the mass of these fat pads by 20-40% (P<0.01). Arginine treatment decreased adipocyte sizes, plasma glucose, triglyceride and leptin levels, increased basal lipolysis and improved glucose tolerance (P<0.05). Arginine stimulated glucose oxidation in muscles as well as oleic acid oxidation in muscles and RP fat (P<0.05). The mRNA levels for hepatic FAS and SCD-I were reduced but those for AMPK and CPT-I as well as skeletal muscle CPT-I were increased by arginine treatment (P<0.05). Hepatic AMPK protein as well as AMPK and ACC activation were increased 2-, 5- and 2.5-fold, respectively, by arginine (P<0.01). These findings indicate that dietary arginine supplementation regulates expression of key genes/proteins involved the metabolism of energy substrates, thereby reducing excess fat and improving insulin sensitivity in rats. [ABSTRACT FROM AUTHOR]

Abstract: Central obesity is associated with insulin resistance and dyslipidemia. Thus, the mechanisms that control fat distribution and its impact on systemic metabolism have importance for understanding the risk for diabetes and cardiovascular disease. Hypercortisolemia at the systemic (Cushing's syndrome) or local levels (due to adipose-specific overproduction via 11β-hydroxysteroid dehydrogenase 1) results in the preferential expansion of central, especially visceral fat depots. At the same time, peripheral subcutaneous depots can become depleted. The biochemical and molecular mechanisms underlying the depot-specific actions of glucocorticoids (GCs) on adipose tissue function remain poorly understood. GCs exert pleiotropic effects on adipocyte metabolic, endocrine and immune functions, and dampen adipose tissue inflammation. GCs also regulate multiple steps in the process of adipogenesis. Acting synergistically with insulin, GCs increase the expression of numerous genes involved in fat deposition. Variable effects of GC on lipolysis are reported, and GC can improve or impair insulin action depending on the experimental conditions. Thus, the net effect of GC on fat storage appears to depend on the physiologic context. The preferential effects of GC on visceral adipose tissue have been linked to higher cortisol production and glucocorticoid receptor expression, but the molecular details of the depot-dependent actions of GCs are only beginning to be understood. In addition, increasing evidence underlines the importance of circadian variations in GCs in relationship to the timing of meals for determining their anabolic actions on the adipocyte. In summary, although the molecular mechanisms remain to be fully elucidated, there is increasing evidence that GCs have multiple, depot-dependent effects on adipocyte gene expression and metabolism that promote central fat deposition. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease. [Copyright &y& Elsevier]

Menopause is associated with increased adiposity and greater risk of metabolic disease. In the ovariectomized (OVX) rodent model of menopause, increased adiposity is prevented by estrogen (E2) replacement, reflecting both anorexigenic and potentially metabolic actions of E2. To elucidate metabolic and molecular mechanisms by which E2 regulates fat storage and fat mobilization independently of reduced energy intake, C57 BL/6 mice were ovariectomized, randomized to estrogen (OVX-E2) or control pellet implants (OVX-C), and pairfed for 40 days. E2 treatment was associated with reduced adipose mass and adipocyte size and down-regulation of lipogenic genes in adipocytes under the control of sterol-regulatory element-binding protein 1c. Adipocytes of OVX-E2 mice contained »3-fold more perilipin protein than adipocytes of pairfed control (OVX) mice, and this difference was associated with enhanced ex vivo lipolytic response to catecholamines and with greater levels of serum-free fatty acids following fasting. As in adipose tissue, E2 decreased the expression of lipogenic genes in liver and skeletal muscle. In the latter, E2 appears to promote the partitioning of free fatty acids toward oxidation and away from triglyceride storage by up-regulating the expression of peroxisome proliferation activator receptor-δ and its downstream targets and also by directly and rapidly activating AMP-activated protein kinase. Thus, novel genomic and non-genomic actions of E2 promote leanness in OVX mice independently of reduced energy intake. [ABSTRACT FROM AUTHOR]

Previous studies have indicated a relationship between cocaine- and amphetamine-related transcript (CART) and leptin. The present study used quantitative PCR and in situ hybridization to examine this CART–leptin relationship in different animal models. With CART injection, the function of this pathway was also investigated. The results demonstrate that CART mRNA in the arcuate nucleus (ARC) was significantly increased in subjects fed a high-fat diet (HFD) compared to low-fat diet (LFD). It was also elevated in obese vs. lean rats and in normal-weight obesity-prone vs. obesity-resistant rats. In each group tested, CART mRNA in the ARC was positively correlated specifically with circulating levels of leptin. Its close association specifically with leptin was further supported by a stimulatory effect of this hormone on CART expression. This leptin–CART relationship in the ARC, in contrast, was less consistent or undetectable in the paraventricular nucleus and lateral hypothalamus. Central injection of CART peptide (55–102) increased circulating non-esterified fatty acid levels and decreased lipoprotein lipase activity in adipose tissue. These results suggest that, on a fat-rich diet, this leptin–CART pathway originating in the ARC inhibits excessive body fat accrual by causing a shift from lipid storage toward lipid mobilization. [Copyright &y& Elsevier]

: ObjectiveThe aim of the present study was to assess the effects of grape seed extract (GSE) on the fat-metabolizing enzymes pancreatic lipase, lipoprotein lipase, and hormone-sensitive lipase in vitro and evaluate its potential application as a treatment for obesity.: MethodsCrushed grape seeds were extracted in ethanol, and the extract was assayed for the measurement of inhibitory effects on pancreatic lipase and lipoprotein lipase activities and on lipolysis of 3T3-L1 adipocytes.: ResultsThe GSE rich in bioactive phytochemicals showed inhibitory activity on the fat-metabolizing enzymes pancreatic lipase and lipoprotein lipase, thus suggesting that GSE might be useful as a treatment to limit dietary fat absorption and the accumulation of fat in adipose tissue. The observed reduction in intracellular lipolytic activity of cultured 3T3-L1 adipocytes may reduce the levels of circulating free fatty acids that have been linked to insulin resistance in obese patients.: ConclusionThe GSE rich in compounds that inhibit lipases may provide a safe, natural, and cost-effective weight control treatment. [Copyright &y& Elsevier]