Comparison of messenger RNA distribution for 60 proteins in fat cells vs the nonfat cells of human omental adipose tissue

Reappraisal of Adipose Tissue Inflammation in Obesity

Chronic low-grade inflammation is a central component in the pathogenesis of obesity-related expansion of adipose tissue and complications in other metabolic tissues. Five different signaling pathways are defined as dominant determinants of adipose tissue inflammation: These are increased circulating endotoxin due to dysregulation in the microbiota-gut-brain axis, systemic oxidative stress, macrophage accumulation, and adipocyte death. Finally, the nucleotide-binding and oligomerization domain (NOD) leucine-rich repeat family pyrin domain-containing 3 (NLRP3) inflammasome pathway is noted to be a key regulator of metabolic inflammation. The NLRP3 inflammasome and associated metabolic inflammation play an important role in the relationships among fatty acids and obesity. Several highly active molecules, including primarily leptin, resistin, adiponectin, visfatin, and classical cytokines, are abundantly released from adipocytes. The most important cytokines that are released by inflammatory cells infiltrating obese adipose tissue are tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), monocyte chemoattractant protein 1 (MCP-1) (CCL-2), and IL-1. All these molecules mentioned above act on immune cells, causing local and then general inflammation. Three metabolic pathways are noteworthy in the development of adipose tissue inflammation: toll-like receptor 4 (TLR4)/phosphatidylinositol-3'-kinase (PI3K)/Protein kinase B (Akt) signaling pathway, endoplasmic reticulum (ER) stress-derived unfolded protein response (UPR), and inhibitor of nuclear factor kappa-B kinase beta (IKKβ)-nuclear factor kappa B (NF-κB) pathway. In fact, adipose tissue inflammation is an adaptive response that contributes to a visceral depot barrier that effectively filters gut-derived endotoxin. Excessive fatty acid release worsens adipose tissue inflammation and contributes to insulin resistance. However, suppression of adipose inflammation in obesity with anti-inflammatory drugs is not a rational solution and paradoxically promotes insulin resistance, despite beneficial effects on weight gain. Inflammatory pathways in adipocytes are indeed indispensable for maintaining systemic insulin sensitivity. Cannabinoid type 1 receptor (CB1R) is important in obesity-induced pro-inflammatory response; however, blockade of CB1R, contrary to anti-inflammatory drugs, breaks the links between insulin resistance and adipose tissue inflammation. Obesity, however, could be decreased by improving leptin signaling, white adipose tissue browning, gut microbiota interactions, and alleviating inflammation. Furthermore, capsaicin synthesized by chilies is thought to be a new and promising therapeutic option in obesity, as it prevents metabolic endotoxemia and systemic chronic low-grade inflammation caused by high-fat diet.

In vitro studies of the renin-angiotensin system in human adipose tissue/adipocytes and possible relationship to SARS-CoV-2: a scoping review

The renin-angiotensin system (RAS) operates within adipose tissue. Obesity-related changes can affect adipose RAS, predisposing to hypertension, type 2 diabetes, and possibly severe COVID-19. We evaluated the in vitro research on human adipose RAS and identified gaps in the literature. Medline (Ovid), Embase (Ovid), Web of Science, Scopus, and 1findr were searched to identify relevant studies. Fifty primary studies met our inclusion criteria for analysis. Expression of RAS components (n = 14), role in differentiation (n = 14), association with inflammation (n = 15) or blood pressure (n = 7) were investigated. We found (1) obesity-related changes in RAS were frequently studied (30%); (2) an upswing of articles investigating adipose ACE-2 expression since the COVID-19 pandemic; (3) a paucity of papers on AT2R and Ang (1-7)/MasR which counterbalance Ang II/ART1; (4) weight loss lowered adipose ACE-2 mRNA expression; and (5) angiotensin receptor blockers (ARBs) reduced deleterious effects of angiotensin II. Overall, these studies link Ang II/ATR1 signalling to impaired adipogenesis and a pro-inflammatory dysfunctional adipose tissue, with ATR1 blockade limiting these responses. ACE-2 may mitigate Ang II effects by converting it to Ang(1-7) which binds MasR. More work is needed to understand adipose RAS in various pathologic states such as obesity and COVID-19 infection.T.

Relationship of liver fat content with systemic metabolism and chronic complications in patients with type 2 diabetes mellitus

OBJECTIVE

This study investigated the correlation of liver fat content (LFC) with metabolic characteristics and its association with chronic complications in type 2 diabetes mellitus (T2DM) patients.

METHODS

Eighty-one prospectively enrolled T2DM patients were divided into non-alcoholic fatty liver disease (NAFLD) group and the non-NAFLD group according to the presence of NAFL complications. LFC was determined by MRI IDEAL-IQ Sequence, and patients were divided into 4 groups according to LFC by quartile method. Basic information, metabolic indexes, and occurrence of chronic complications in different groups were analyzed and compared.

RESULTS

BMI, SBP, DBP, TG, ALT, AST, GGT, UA, HbA1c, FCP, 2 h CP, HOMA-IR, and HOMA-IS in the NAFLD group were significantly higher than the non-NAFLD group (P < 0.05). The incidences of chronic complications in the NAFLD group were higher than in the non-NAFLD group but not statistically significant (P > 0.05). BMI, SBP, DBP, TC, TG, ALT, AST, FCP, 2 h CP, HOMA-IR, and HOMA-IS showed significant differences between the patients with different LFC, and these indexes were significantly higher in patients with higher LFC than those with lower LFC (P < 0.05). Moreover, diabetes duration, TC, HOMA-IR, and LFC were the risk factors for ASCVD complications, while diabetes duration, TG, and LDL-C were risk factors for DN complications. Also, diabetes duration and SBP were risk factors for both DR and DPN complications in T2DM patients (P < 0.05).

CONCLUSION

LFC is positively correlated with the severity of the systemic metabolic disorder and chronic complications in T2DM patients.

cDNA Characterization and Expression of Selenium-Dependent CqGPx3 Isoforms in the Crayfish Cherax quadricarinatus under High Temperature and Hypoxia

Glutathione peroxidase 3 (GPx3) is the only extracellular selenoprotein (Sel) that enzymatically reduces H2O2 to H2O and O2. Two GPx3 (CqGPx3) cDNAs were characterized from crayfish Cherax quadricarinatus. The nerve cord CqGPx3a isoform encodes for a preprotein containing an N-terminal signal peptide of 32 amino acid residues, with the mature Sel region of 192 residues and a dispensable phosphorylation domain of 36 residues. In contrast, the pereiopods CqGPx3b codes for a precursor protein with 19 residues in the N-terminal signal peptide, then the mature 184 amino acid residues protein and finally a Pro-rich peptide of 42 residues. CqGPx3 are expressed in cerebral ganglia, pereiopods and nerve cord. CqGPx3a is expressed mainly in cerebral ganglia, antennulae and nerve cord, while CqGPx3b was detected mainly in pereiopods. CqGPx3a expression increases with high temperature and hypoxia; meanwhile, CqGPx3b is not affected. We report the presence and differential expression of GPx3 isoforms in crustacean tissues in normal conditions and under stress for high temperature and hypoxia. The two isoforms are tissue specific and condition specific, which could indicate an important role of CqGPx3a in the central nervous system and CqGPx3b in exposed tissues, both involved in different responses to environmental stressors.

The endocrine function of adipose tissues in health and cardiometabolic disease

In addition to their role in glucose and lipid metabolism, adipocytes respond differentially to physiological cues or metabolic stress by releasing endocrine factors that regulate diverse processes, such as energy expenditure, appetite control, glucose homeostasis, insulin sensitivity, inflammation and tissue repair. Both energy-storing white adipocytes and thermogenic brown and beige adipocytes secrete hormones, which can be peptides (adipokines), lipids (lipokines) and exosomal microRNAs. Some of these factors have defined targets; for example, adiponectin and leptin signal through their respective receptors that are expressed in multiple organs. For other adipocyte hormones, receptors are more promiscuous or remain to be identified. Furthermore, many of these hormones are also produced by other organs and tissues, which makes defining the endocrine contribution of adipose tissues a challenge. In this Review, we discuss the functional role of adipose tissue-derived endocrine hormones for metabolic adaptations to the environment and we highlight how these factors contribute to the development of cardiometabolic diseases. We also cover how this knowledge can be translated into human therapies. In addition, we discuss recent findings that emphasize the endocrine role of white versus thermogenic adipocytes in conditions of health and disease.

Human adipocytes and CD34+ cells from the stromal vascular fraction of the same adipose tissue differ in their energy metabolic enzyme configuration

Adipose tissue plays a role in energy storage and metabolic balance and is composed of different cell types. The metabolic activity of the tissue itself has been a matter of research for a long time, but comparative data about the energy metabolism of different cell types of human subcutaneous adipose tissue are sparse. Therefore, we compared the activity of major energy metabolic pathways of adipocytes and CD34⁺ cells from the stromal vascular fraction (SVF) separated from the same tissue. This CD34⁺ cell fraction is enriched with adipose tissue-derived mesenchymal progenitors, as they account for the largest proportion of CD34⁺ cells of the SVF. Adipocytes displayed significantly higher mitochondrial enzyme capacities compared to CD34⁺ SVF-cells, as shown by the higher activities of isocitrate dehydrogenase and ß-hydroxyacyl-CoA dehydrogenase. Inversely, the CD34⁺ SVF-cells showed higher capacities for cytosolic carbohydrate metabolism, represented by the activity of glycolysis and the pentose phosphate pathway. Thus, the CD34⁺ SVF-cells may ensure the provision of pentose phosphates and reduction equivalents for the replication of DNA during proliferation. The data indicate that these two cell fractions of the human adipose tissue vary in their metabolic configuration adapted to their physiological demands regarding proliferation and differentiation in vivo.

Molecular Mechanisms of Vaspin Action - From Adipose Tissue to Skin and Bone, from Blood Vessels to the Brain

Visceral adipose tissue-derived serine protease inhibitor (vaspin) or SERPINA12 according to the serpin nomenclature was identified together with other genes and gene products that were specifically expressed or overexpressed in the intra-abdominal or visceral adipose tissue (AT) of the Otsuka Long-Evans Tokushima fatty rat. These rats spontaneously develop visceral obesity, insulin resistance, hyperinsulinemia and -glycemia, as well as hypertension and thus represent a well suited animal model of obesity and related metabolic disorders such as type 2 diabetes.The follow-up study reporting the cloning, expression and functional characterization of vaspin suggested the great and promising potential of this molecule to counteract obesity induced insulin resistance and inflammation and has since initiated over 300 publications, clinical and experimental, that have contributed to uncover the multifaceted functions and molecular mechanisms of vaspin action not only in the adipose, but in many different cells, tissues and organs. This review will give an update on mechanistic and structural aspects of vaspin with a focus on its serpin function, the physiology and regulation of vaspin expression, and will summarize the latest on vaspin function in various tissues such as the different adipose tissue depots as well as the vasculature, skin, bone and the brain.

Adipocytes enhance murine pancreatic cancer growth via a hepatocyte growth factor (HGF)-mediated mechanism

INTRODUCTION

Obesity accelerates the development and progression of pancreatic cancer, though the mechanisms underlying this association are unclear. Adipocytes are biologically active, producing factors such as hepatocyte growth factor (HGF) that may influence tumor progression. We therefore sought to test the hypothesis that adipocyte-secreted factors including HGF accelerate pancreatic cancer cell proliferation.

MATERIAL AND METHODS

Murine pancreatic cancer cells (Pan02 and TGP-47) were grown in a) conditioned medium (CM) from murine F442A preadipocytes, b) HGF-knockdown preadipocyte CM, c) recombinant murine HGF at increasing doses, and d) CM plus HGF-receptor (c-met) inhibitor. Cell proliferation was measured using the MTT assay. ANOVA and t-test were applied; p < 0.05 considered significant.

RESULTS

Wild-type preadipocyte CM accelerated Pan02 and TGP-47 cell proliferation relative to control (59 ± 12% and 34 ± 12%, p < 0.01, respectively). Knockdown of preadipocyte HGF resulted in attenuated proliferation vs. wild type CM in Pan02 cells (35 ± 5% vs. 68 ± 14% greater than control; p < 0.05), but proliferation in TGP-47 cells remained unchanged. Recombinant HGF dose-dependently increased Pan02, but not TGP-47, proliferation (p < 0.05). Inhibition of HGF receptor, c-met, resulted in attenuated proliferation versus control in Pan02 cells, but not TGP-47 cells.

CONCLUSIONS

These experiments demonstrate that adipocyte-derived factors accelerate murine pancreatic cancer proliferation. In the case of Pan02 cells, HGF is responsible, in part, for this proliferation.

Is vaspin related to cardio-metabolic status and autonomic function in early stages of glucose intolerance and in metabolic syndrome?

BACKGROUND

This study aims to assess serum vaspin in early stages of glucose intolerance and in the presence of metabolic syndrome (MetS); and to evaluate vaspin correlation to different cardio-metabolic parameters and autonomic tone in these subjects.

METHODS

185 subjects (80 males and 105 females) of mean age 45.8 ± 11.6 years and mean BMI 31.2 ± 6.3 kg/m(2), divided into groups according to: glucose tolerance, presence of MetS and cardio-vascular autonomic dysfunction (CAD), were enrolled. Glucose tolerance was studied during OGTT. Anthropometric indices, blood pressure, HbA1c, serum lipids, hsCRP, fasting immunoreactive insulin and serum vaspin were measured. Body composition was estimated by impedance analysis. AGEs were assessed by skin fluorescence. CAD was assessed by ANX-3.0.

RESULTS

There was no difference in vaspin levels between the groups according to glucose tolerance, presence of MetS, and CAD. Regression analysis revealed independent association between serum vaspin and total body fat in newly diagnosed type 2 diabetes (NDT2D) group, and between serum vaspin and age and total body fat in MetS group. Vaspin negatively correlated with both sympathetic and parasympathetic activity in normal glucose tolerance (NGT) and just with parasympathetic tone in NGT without MetS.

CONCLUSION

Our results demonstrate no overt fluctuations in vaspin levels in the early stages of glucose intolerance and in MetS. Total body fat seems to be related to vaspin levels in MetS and NDT2D. Our data show negative correlation between vaspin and autonomic function in NGT, as vaspin is associated with parasympathetic activity even in the absence of MetS.

The role of vaspin in the development of metabolic and glucose tolerance disorders and atherosclerosis

In recent years, most research efforts have been focused on studying insulin-sensitizing adipokines. One of the most recently discovered adipokines is vaspin, a visceral adipose tissue-derived serine protease inhibitor. Vaspin levels have been found significantly increased in mice with obesity and insulin resistance. It has been assumed that vaspin serves as an insulin sensitizer with anti-inflammatory effects and might act as a compensatory mechanism in response to decreased insulin sensitivity. Most studies in humans have shown a positive correlation between vaspin gene expression and serum levels, and metabolic syndrome parameters. Vaspin gene expression is influenced by age and gender, and the administration of insulin sensitizers enhances it in mice, whereas the use of metformin decreases serum vaspin levels in humans, probably due to different regulatory mechanisms. Presumably vaspin plays local and endocrine role in the development of initial and advanced atherosclerosis in obese subjects and might be used as a predictor of coronary and cerebrovascular disease. It is believed that vaspin could be regarded as a new link between obesity and related metabolic disorders, including glucose intolerance. The entire understanding of vaspin intimate mechanism of action might enable the development of novel etiology-based treatment strategies, targeting metabolic and glucose tolerance disorders.

Aquaglyceroporins: implications in adipose biology and obesity

Aquaporins (AQPs) are membrane water/glycerol channels that are involved in many physiological processes. Their primary function is to facilitate the bidirectional transfer of water and small solutes across biological membranes in response to osmotic gradients. Aquaglyceroporins, a subset of the AQP family, are the only mammalian proteins with the ability to permeate glycerol. For a long time, AQP7 has been the only aquaglyceroporin associated with the adipose tissue, which is the major source of circulating glycerol in response to the energy demand. AQP7 dysregulation was positively correlated with obesity onset and adipocyte glycerol permeation through AQP7 was appointed as a novel regulator of adipocyte metabolism and whole-body fat mass. Recently, AQP3, AQP9, AQP10 and AQP11 were additionally identified in human adipocytes and proposed as additional glycerol pathways in these cells. This review contextualizes the importance of aquaglyceroporins in adipose tissue biology and highlights aquaglyceroporins' unique structural features which are relevant for the design of effective therapeutic compounds. We also refer to the latest advances in the identification and characterization of novel aquaporin isoforms in adipose tissue. Finally, considerations on the actual progress of aquaporin research and its implications on obesity therapy are suggested.

Expression of genes related to prostaglandin synthesis or signaling in human subcutaneous and omental adipose tissue: depot differences and modulation by adipogenesis

OBJECTIVES

(1) To examine depot-specific PGE2 and PGF2α release and mRNA expression of enzymes or receptors involved in PG synthesis or signaling in human adipose tissues; (2) to identify changes in expression of these transcripts through preadipocyte differentiation; and (3) to examine associations between adipose tissue mRNA expression of these transcripts and adiposity measurements.

METHODS

Fat samples were obtained surgically in women. PGE2 and PGF2α release by preadipocytes and adipose tissue explants was measured. Expression levels of mRNA coding for enzymes or receptors involved in PG synthesis or signaling were measured by RT-PCR.

RESULTS

Cultured preadipocytes and explants from omental fat released more PGE2 and PGF2α than those from the subcutaneous depot and the corresponding transcripts showed consistent depot differences. Following preadipocyte differentiation, expression of PLA2G16 and PTGER3 mRNA was significantly increased whereas COX-1, COX-2, PTGIS, and PTGES mRNA abundance were decreased in both compartments (P ≤ 0.01 for all). Transcripts that were stimulated during adipogenesis were those that correlated best with adiposity measurements.

CONCLUSION

Cells from the omental fat compartment release more PGE2 and PGF2α than those from the subcutaneous depot. Obesity modulates expression of PG-synthesizing enzymes and PG receptors which likely occurs through adipogenesis-induced changes in expression of these transcripts.

Fenofibrate increases serum vaspin by upregulating its expression in adipose tissue

Fenofibrate is a peroxisome proliferator-activated receptor-α that has been clinically used to treat dyslipidemia and insulin resistance. To better understand the molecular mechanisms underlying fenofibrate action, we investigated whether fenofibrate affects serum levels of vaspin, an adipocytokine that has recently been shown to link obesity and insulin resistance. Fenofibrate treatment significantly increased serum vaspin levels of dyslipidemic patients, which correlated with reduced body weight and increased insulin sensitivity. To elucidate the biochemical mechanisms of fenofibrate action, we investigated the effect of fenofibrate on vaspin mRNA and protein expressions in obese rats. Fenofibrate greatly increased vaspin mRNA and protein levels in visceral adipose tissue consisting of retroperitoneal, mesenteric, and periepididymal adipose tissue but not in the subcutaneous adipose tissue, which correlated with increased serum vaspin levels and increased insulin sensitivity in obese rats. Consistent with a direct effect on vaspin expression, fenofibrate treatment significantly increased the mRNA and protein expression levels of vaspin in 3T3-L1 adipocytes. Together, our results demonstrate for the first time that fenofibrate upregulates vaspin expression in dyslipidemic human subjects and suggest that upregulation of vaspin expression in adipocytes may provide a mechanism by which fenofibrate improves insulin sensitivity in dyslipidemic patients.

Prostaglandin (PG) F2 alpha synthesis in human subcutaneous and omental adipose tissue: modulation by inflammatory cytokines and role of the human aldose reductase AKR1B1

INTRODUCTION

PGF2α may be involved in the regulation of adipose tissue function.

OBJECTIVES

1) To examine PGF2α release by primary preadipocytes, mature adipocytes and whole tissue explants from the subcutaneous and omental fat compartments; 2) To assess which PGF synthase is the most relevant in human adipose tissue.

METHODS

Fat samples were obtained by surgery in women. PGF2α release by preadipocytes, adipocytes and explants under stimulation by TNF-α, IL-1β or both was measured. Messenger RNA expression levels of AKR1B1 and AKR1C3 were measured by RT-PCR in whole adipose tissue and cytokine-treated preadipocytes. The effect of AKR1B1 inhibitor ponalrestat on PGF2α synthesis was investigated.

RESULTS

PGF2α release was significantly induced in response to cytokines compared to control in omental (p = 0.01) and to a lesser extent in subcutaneous preadipocytes (p = 0.02). Messenger RNA of COX-2 was significantly higher in omental compared to subcutaneous preadipocytes in response to combined TNF-α and IL-1β (p = 0.01). Inflammatory cytokines increased AKR1B1 mRNA expression and protein levels (p≤0.05), but failed to increase expression levels of AKR1C3 in cultured preadipocytes. Accordingly, ponalrestat blunted PGF2α synthesis by preadipocytes in basal and stimulated conditions (p≤0.05). Women with the highest PGF2α release by omental adipocytes had a higher BMI (p = 0.05), waist circumference (p≤0.05) and HOMAir index (p≤0.005) as well as higher mRNA expression of AKR1B1 in omental (p<0.10) and subcutaneous (p≤0.05) adipose tissue compared to women with low omental adipocytes PGF2α release. Positive correlations were observed between mRNA expression of AKR1B1 in both compartments and BMI, waist circumference as well as HOMAir index (p≤0.05 for all).

CONCLUSION

PGF2α release by omental mature adipocytes is increased in abdominally obese women. Moreover, COX-2 expression and PGF2α release is particularly responsive to inflammatory stimulation in omental preadipocytes. Yet, blockade of PGF synthase AKR1B1 inhibits most of the PGF2α release.

Biophysical assessment of human aquaporin-7 as a water and glycerol channel in 3T3-L1 adipocytes

The plasma membrane aquaporin-7 (AQP7) has been shown to be expressed in adipose tissue and its role in glycerol release/uptake in adipocytes has been postulated and correlated with obesity onset. However, some studies have contradicted this view. Based on this situation, we have re-assessed the precise localization of AQP7 in adipose tissue and analyzed its function as a water and/or glycerol channel in adipose cells. Fractionation of mice adipose tissue revealed that AQP7 is located in both adipose and stromal vascular fractions. Moreover, AQP7 was the only aquaglyceroporin expressed in adipose tissue and in 3T3-L1 adipocytes. By overexpressing the human AQP7 in 3T3-L1 adipocytes it was possible to ascertain its role as a water and glycerol channel in a gain-of-function scenario. AQP7 expression had no effect in equilibrium cell volume but AQP7 loss of function correlated with higher triglyceride content. Furthermore it is also reported for the first time a negative correlation between water permeability and the cell non-osmotic volume supporting the observation that AQP7 depleted cells are more prone to lipid accumulation. Additionally, the strong positive correlation between the rates of water and glycerol transport highlights the role of AQP7 as both a water and a glycerol channel and reflects its expression levels in cells. In all, our results clearly document a direct involvement of AQP7 in water and glycerol transport, as well as in triglyceride content in adipocytes.

Characterization of a novel proinflammatory effect mediated by BK and the kinin B₂ receptor in human preadipocytes

Obesity and adipose tissue contribute to local and systemic inflammation. However the role of the inflammatory mediator bradykinin (BK) in this context is not known. We therefore evaluated the effect of BK on adipokines secretion in human preadipocytes during the course of differentiation and characterized the receptors involved. Results obtained from antibody array and ELISA experiments showed that several adipokines are released by human preadipocytes under basal conditions while BK specifically stimulated the production of interleukin(IL)-6 and IL-8. The effect of BK diminished with the progression of differentiation, being almost inactive on adipocytes. In preadipocytes, BK also induced a rapid and transient [Ca²⁺](i) mobilization, a rapid and sustained increase in ERK1/2 activation and enhanced forskolin-stimulated cAMP accumulation. BK was without effect on cell proliferation and viability as assessed by bromodeoxyuridine incorporation, WST-1 conversion, or lactate dehydrogenase leakage and was without effect on adipogenesis as measured by triglyceride accumulation, GPDH activity and leptin release. The B₁ receptor agonist, Lys-[des-Arg⁹]-BK, displayed poor activity or was without effect while overall BK effects were prevented by the selective B₂ receptor antagonist, fasitibant chloride, but not by the B₁ selective antagonist, Lys-[Leu⁸][des-Arg⁹]-BK. Immunoblot analysis and immunofluorescence studies showed that the kinin B₂ receptor was essentially expressed at the beginning of the differentiation program. In conclusion, human preadipocytes expressed kinin B₂ receptors linked to multiple signaling pathways, IL-6 and IL-8 production, and BK proinflammatory response in adipose tissue could be prevented by fasitibant chloride.

Chemerin and vaspin: possible targets to treat obesity?

Obesity is one of the main human epidemics today. The increase in fat accumulation, which is associated with obesity, may significantly change the expression of several bioactive molecules known as adipokines. These adipokines interact not only with adipose tissue, but also with metabolically relevant organs such as liver and muscle. Understanding the molecular basics of potential novel targets might help to improve the therapeutic treatment of people who suffer from obesity. Herein we summarize the state of the art of two novel adipokines and their impaired or protective action in obesity: chemerin and vaspin. Their expression patterns, signal transduction activity, and resulting functions within the human body are introduced. We also discuss various possibilities to target these adipokines, which may represent promising new targets for the treatment of obesity by small and synthetic compounds.

Cellular cross-talk between epicardial adipose tissue and myocardium in relation to the pathogenesis of cardiovascular disease

Epicardial and perivascular fat depot size is considered an index of cardiac and visceral obesity. The functional and anatomic proximity of epicardial adipose tissue (EAT) to myocardium has drawn increasing attention in recent years among researchers attempting to elucidate its putative role as an endocrine organ. This includes the role of EAT as a lipid storing depot and as an inflammatory tissue secreting cytokines and chemokines under pathogenic conditions such as cardiovascular diseases. In this review, we discuss the current state of knowledge regarding the potential EAT mediators of inflammation and the paracrine cross-talk between EAT and the underlying myocardium. We also highlight the most recent findings on the causes and correlates of myocardial steatosis/cardiac lipotoxicity and its association with cardiac dysfunction.

Changes in lipid transport-involved proteins of epicardial adipose tissue associated with coronary artery disease

OBJECTIVE

Recent studies have focused on the potential role of epicardial adipose tissue (EAT) in the physiopathology of several metabolic and cardiovascular diseases, especially coronary artery disease (CAD). We aimed to study whether there are differences in the proteome and the secretome between epicardial and subcutaneous adipose tissue (SAT) from patients with and without CAD.

METHODS

EAT and SAT samples were collected from 64 patients undergoing elective cardiac surgery either for coronary artery bypass grafting or valve surgery. One or two-dimensional electrophoresis were performed on tissue samples and media collected at 3, 6, 24 or 48 of tissue culture. Protein identification was performed with mass spectrometry, and the results were then validated with Western blot or enzyme immunoassay. mRNA expression levels were analysed by real time polymerase chain reaction.

RESULTS

The release of several proteins was found to be higher in EAT that in SAT. Remarkably, there were higher levels of apolipoprotein A-I and glutation S-transferase P release, whereas mRNA expression of fatty acid binding protein 4 was lower in EAT. Although apolipoprotein A-I protein quantity in EAT was similar between CAD and non CAD patients, its released levels from this fat pad were lower in CAD.

CONCLUSION

EAT and SAT show different profiles of protein release and a different pattern was also found in samples from patients with CAD. These findings might support the hypothesis that EAT plays an interesting role in the physiopathology of atherosclerosis and CAD.

Serum levels of glutathione peroxidase 3 in overweight and obese subjects from central Mexico

BACKGROUND AND AIMS

Overweight and obesity are considered complex entities in which there are alterations in the concentration of antioxidant enzymes. It has been reported that glutathione peroxidase 3 (GPx3), an extracellular enzyme involved in the reduction of both hydro- and lipoperoxides, shows changes both in gene expression and protein concentration in animal models for type 2 diabetes (T2D) and obesity, but the variability of GPx3 levels in different human populations and under different health conditions are currently unclear. We undertook this study to determine the GPx3 levels in overweight and obese subjects from central Mexico.

METHODS

Biochemical profile (serum glucose, insulin and lipid profile) and GPx3 concentrations were determined in 28 healthy subjects (control) and 133 subjects who were overweight or obese (OW-OB).

RESULTS

The OW-OB group had a higher concentration of triacylglycerides (TAG) compared with the control group (201.2 ± 88.7 vs. 100.3 ± 46.4 mg/dL, p <0.05) and the TAG/high density lipoprotein-cholesterol (HDL-C) index (5.6 ± 2.8 vs. 2.1 ± 1.2, p <0.05), whereas the concentration of HDL-C decreased (38.2 ± 8.7 vs. 50.1 ± 14.5 mg/dL, p <0.05). Serum GPx3 was significantly higher in the OW-OB group than in the control group (175.4 ± 25.4 vs. 143.5 ± 23.1 ng/dL). GPx3 concentration correlated with insulin sensitivity (IS) and the TAG/HDL-C index (Rho = -0.2336 and Rho = 0.2275) (p <0.01).

CONCLUSIONS

The TAG/HDL-C index and serum GPx3 concentration increased in the OW-OB group. In addition, GPx3 had a significant correlation with IS, weight, and the TAG/HDL-C index.

Adipocytokines and the risk of ischemic stroke: the PRIME Study

OBJECTIVE

Adipocytokines are hormones secreted from adipose tissue that possibly link adiposity and the risk of cardiovascular disease, but limited prospective data exist on plasma adipocytokines and ischemic stroke risk. We investigated associations and predictive properties of 4 plasma adipocytokines, namely resistin, adipsin, leptin, and total adiponectin, with regard to incident ischemic stroke in the PRIME Study.

METHODS

A cohort of 9,771 healthy men 50 to 59 years of age at baseline was followed up over a period of 10 years. In a nested case-control study, 95 ischemic stroke cases were matched with 190 controls on age, study center, and date of examination. Hazard ratios (HRs) per standard deviation increase in plasma adipocytokine levels were estimated using conditional logistic regression analysis. The additive value of adipocytokines in stroke risk prediction was evaluated by discrimination and reclassification metrics.

RESULTS

Resistin (HR, 1.88; 95% confidence interval [CI], 1.16-3.03), adipsin (HR, 2.01; 95% CI, 1.33-3.04), and total adiponectin (HR, 1.53; 95% CI, 1.01-2.34), but not leptin, were independent predictors of ischemic stroke. The performance of a traditional risk factor model predicting ischemic stroke was significantly improved by the simultaneous inclusion of resistin, adipsin, and total adiponectin (c-statistic: 0.673 [95% CI, 0.631-0.766] vs 0.826 [95% CI, 0.792-0.892], p < 0.001; net reclassification improvement: 38.1%, p < 0.001).

INTERPRETATION

Higher plasma levels of resistin, adipsin, and total adiponectin were associated with an increased 10-year risk of ischemic stroke among healthy middle-aged men. Resistin, adipsin, and total adiponectin provided incremental value over traditional risk factors for the prediction of ischemic stroke risk.

Vaspin in obesity and diabetes: pathophysiological and clinical significance

Vaspin (visceral adipose tissue-derived serpin; serpinA12) was originally identified as an adipokine, which is predominantly secreted from visceral adipose tissue in Otsuka Long-Evans Tokushima fatty (OLETF), an animal model of obesity and type 2 diabetes. Consistent with that higher vaspin serum concentrations and increased vaspin mRNA expression in human adipose tissue were found to be associated with obesity, insulin resistance, and type 2 diabetes in humans. However, the mechanisms how vaspin secretion may be linked to deterioration of glucose metabolism and insulin sensitivity are not entirely understood. Vaspin serum concentrations show a food intake-related diurnal variation. Vaspin is also expressed in the skin, hypothalamus, pancreatic islets, and stomach. Administration of vaspin to obese mice improves glucose tolerance, insulin sensitivity, and reduces food intake. Until now molecular target(s) of vaspin and its mode of action are unknown. Thus, identification of the proteases, which are inhibited by vaspin may lead to the development of novel strategies in the treatment of obesity, diabetes and insulin resistance. This review discusses the clinical relevance of vaspin in the pathophysiology of obesity and type 2 diabetes.

The mRNA-binding protein Zfp36 is upregulated by β-adrenergic stimulation and represses IL-6 production in 3T3-L1 adipocytes

Obesity produces a chronic inflammatory state that contributes to the development of diabetes and atherosclerosis. In obese humans, fat depot adipocytes and macrophages produce inflammatory cytokines and other factors which exert unfavorable local and systemic immune responses. The expression of many cytokines is modulated at the post-transcriptional level by mRNA-binding proteins which recognize AU-rich elements (AREs) in the 3'-untranslated regions (3'-UTR) of these transcripts. One such protein, zinc finger protein 36 (Zfp36), is known to destabilize target mRNAs leading to decreased cytokine expression. Few regulators of Zfp36 expression in adipocytes have been described and mRNA targets of Zfp36 in adipocytes are largely unknown. We found that macrophage-derived inflammatory stimuli enhanced endogenous Zfp36 expression in 3T3-L1 adipocytes. Furthermore, the β-adrenergic receptor agonist isoproterenol (Iso) and the glucocorticoid dexamethasone (Dex) each enhanced Zfp36 expression in adipocytes, the former most likely via a cyclic adenosine monophosphate (cAMP)-dependent pathway. By contrast, Zfp36 expression in murine macrophages (RAW 264.7) was not enhanced by exposure to Dex but was stimulated by retinoic acid (RA). Zfp36 inhibited basal and lipopolysaccharide (LPS)-stimulated interleukin-6 (IL-6) expression in adipocytes. These data reveal important and cell type-specific modulators of Zfp36 expression in adipocytes and macrophages and identify Zfp36 as a potent repressor of adipocyte-derived IL-6. Furthermore, this work identifies new factors that stimulate adipocyte Zfp36 expression that are neither classically inflammatory nor mitogenic. Upregulating an mRNA-binding protein for therapeutic purposes may provide a novel mechanistic approach with which to treat diverse inflammatory disorders including common conditions associated with obesity.

Correlative studies on the effects of obesity, diabetes and hypertension on gene expression in omental adipose tissue of obese women

OBJECTIVE

A major consequence of obesity is the enormous expansion of and enhanced inflammatory response seen in visceral adipose tissue. I hypothesized that the expression of inflammatory markers in visceral omental fat would correlate with the extent of visceral adiposity as measured by waist circumference or body mass index and that diabetes and hypertension, defined as subjects taking anti-hypertensive drugs, would be associated with changes in mRNA expression in visceral fat.

DESIGN AND METHODS

The expression of 106 mRNAs by RT-PCR was examined in observational studies using extracts of omental fat of obese women undergoing bariatric surgery as well as the circulating levels of some adipokines. We also compared the mRNA levels of 65 proteins in omental fat removed during gastric bypass surgery of women with and without hypertension and those with type 2 diabetes.

RESULTS

Out of 106 mRNAs the expression of 10 mRNAs in omental fat of women not taking anti-hypertensive drugs correlated with waist circumference while 7 different mRNAs had significant correlations with circulating glucose. The correlations of waist circumference with mRNA expression were abolished, except for interleukin (IL)-1 receptor antagonist (IL-1RA), in women taking anti-hypertensive drugs. The correlations of blood glucose with omental fat mRNA expression were abolished, except for that of Akt1 and Akt2, in women taking anti-hypertensive drugs. However, the expression of 4 different mRNAs in omental fat was affected by circulating glucose in subjects taking anti-hypertensive drugs. The circulating levels of IL-1 RA, but not fatty acid binding protein 4, adipsin and phospholipase A2, correlated with both waist circumference and mRNA expression in omental fat.

CONCLUSION

In female bariatric surgery patients, the mRNA expression of some proteins in omental fat was affected by the degree of obesity, whereas hypertension and diabetes affected a separate set of mRNAs.Nutrition and Diabetes (2011) 1, e17; doi:10.1038/nutd.2011.14; published online 26 September 2011.

Hypoxia-induced inflammatory cytokine secretion in human adipose tissue stromovascular cells

AIMS

Hypoxia has been implicated as a cause of adipose tissue inflammation in obesity, although the inflammatory response of human adipose tissue to hypoxia is not well understood. The goal of this study was to define in vitro inflammatory responses of human adipose tissue to hypoxia and identify molecular mechanisms of hypoxia-induced inflammation.

METHODS

The inflammatory milieu and responses of visceral (VAT) and subcutaneous (SAT) adipose tissue explants and purified stromovascular cells (SVFs) from obese and lean humans were studied in an in vitro hypoxic culture system using quantitative real-time PCR, ELISA, western blotting, immunofluorescence microscopy, flow cytometry and immunohistochemistry.

RESULTS

Human adipose tissue in obesity demonstrates an increased leucocyte infiltrate that is greater in VAT than SAT and involves macrophages, T cells and natural killer (NK) cells. Hypoxic culture regulates inflammatory cytokine secretion and transcription of metabolic stress response genes in human adipose tissue SVF. Adipocyte diameter is increased and adipose tissue capillary density is decreased in obese participants. Inhibition of c-Jun terminal kinase (JNK) or p38 significantly attenuates hypoxia-induced SVF inflammatory responses. Hypoxia induces phosphorylation of p38 in adipose tissue.

CONCLUSIONS

Human adipose tissue in obesity is characterised by a depot-specific inflammatory cell infiltrate that involves not only macrophages, but also T cells and NK cells. Hypoxia induces inflammatory cytokine secretion by human adipose tissue SVF, the primary source of which is adipose tissue macrophages. These data implicate p38 in the regulation of hypoxia-induced inflammation and suggest that alterations in adipocyte diameter and adipose tissue capillary density may be potential underlying causes of adipose tissue hypoxia.

Tools for the identification of bioactives impacting the metabolic syndrome: screening of a botanical extract library using subcutaneous and visceral human adipose-derived stem cell-based assays

Plant extracts continue to represent an untapped source of renewable therapeutic compounds for the treatment and prevention of illnesses including chronic metabolic disorders. With the increase in worldwide obesity and its related morbidities, the need for identifying safe and effective treatments is also rising. As such, use of primary human adipose-derived stem cells represents a physiologically relevant cell system to screen for bioactive agents in the prevention and treatment of obesity and its related complications. By using these cells in a primary screen, the risk and cost of identifying artifacts due to interspecies variation and immortalized cell lines is eliminated. We demonstrate that these cells can be formatted into 384-well high throughput screens to rapidly identify botanical extracts that affect lipogenesis and lipolysis. Additionally, counterscreening with human primary stem cells from distinct adipose depots can be routinely performed to identify tissue specific responses. In our study, over 500 botanical extracts were screened and 16 (2.7%) were found to affect lipogenesis and 4 (0.7%) affected lipolysis.

Melanin and melanogenesis in adipose tissue: possible mechanisms for abating oxidative stress and inflammation?

Obesity has become a worldwide epidemic and can lead to multiple chronic diseases. Adipose tissue is increasingly thought to play an active role in obesity-related pathologies such as insulin resistance and non-alcoholic fatty liver disease. Obesity has been strongly associated with systemic inflammation and, to a lesser degree, with oxidative stress, although the causal relationships among these factors are unclear. A recent study demonstrating an expression of the components of the melanogenic pathway and the presence of melanin in visceral adipose has raised questions regarding the possible role of melanogenesis in adipose tissue. As this study also found larger amounts of melanin in the adipose tissue of obese patients relative to lean ones, we hypothesize that melanin, a pigment known for its antioxidant and anti-inflammatory properties, may scavenge reactive oxygen species and abate oxidative stress and inflammation in adipose tissue. This review considers the evidence to support such a hypothesis, and speculates on the role of melanin within adipocytes. Furthermore, we consider whether the α-melanocyte-stimulating hormone or its synthetic analogues could be used to stimulate melanin production in adipocytes, should the hypothesis be supported in future experiments.

Expression of osteoprotegerin in human fat tissue; implications for chronic kidney disease

BACKGROUND

Premature vascular calcification (or rather ossification) significantly contributes to morbidity and mortality in patients with chronic kidney disease stage 5 (CKD-5) and is linked to dysregulation of bone remodelling proteins. Recent evidence of a cross-talk between bone and fat tissue urged us to investigate whether the calcification/ossification-associated factors osteoprotegerin (OPG) and alpha-2-HS-glycoprotein (AHSG) are expressed in human uremic subcutaneous adipose tissue (SAT) and if the expression differs from nonuremic SAT.

MATERIALS AND METHODS

Abdominal SAT biopsies were obtained from 38 patients with CKD-5 [16 women, 58 (22-73) years old] during the surgical insertion of a peritoneal dialysis catheter and 20 controls [11 females, 56 (40-77) years old] undergoing elective hernia repair or laparoscopic cholecystectomy. Real-time polymerase chain reaction (PCR) quantifications were performed followed by immunohistochemical staining and serum protein concentration measurements. Relative mRNA expression and protein concentrations were evaluated together with clinical parameters. An additional 59 patients with CKD-5 were included for replication of statistical analyses.

RESULTS

OPG but not AHSG mRNAs were detected in SAT, which were also positively immunolabelled for OPG. OPG mRNA levels were reduced (P = ·0001) and serum OPG concentrations were elevated (P < 0·0001), both about twofold, in patients compared to controls. Circulating OPG increased in proportion to BMI.

CONCLUSIONS

Human SAT expresses OPG but not AHSG, and OPG expression is reduced in patients with CKD-5 when compared to controls, despite increased circulating protein levels.

Proteome of human subcutaneous adipose tissue stromal vascular fraction cells versus mature adipocytes based on DIGE

Adipose tissue contains a heterogeneous population of mature adipocytes, endothelial cells, immune cells, pericytes, and preadipocytic stromal/stem cells. To date, a majority of proteomic analyses have focused on intact adipose tissue or isolated adipose stromal/stem cells in vitro. In this study, human subcutaneous adipose tissue from multiple depots (arm and abdomen) obtained from female donors was separated into populations of stromal vascular fraction cells and mature adipocytes. Out of 960 features detected by 2-D gel electrophoresis, a total of 200 features displayed a 2-fold up- or down-regulation relative to each cell population. The protein identity of 136 features was determined. Immunoblot analyses comparing SVF relative to adipocytes confirmed that carbonic anhydrase II was up-regulated in both adipose depots while catalase was up-regulated in the arm only. Bioinformatic analyses of the data set determined that cytoskeletal, glycogenic, glycolytic, lipid metabolic, and oxidative stress related pathways were highly represented as differentially regulated between the mature adipocytes and stromal vascular fraction cells. These findings extend previous reports in the literature with respect to the adipose tissue proteome and the consequences of adipogenesis. The proteins identified may have value as biomarkers for monitoring the physiology and pathology of cell populations within subcutaneous adipose depots.

Serum adiponectin and vaspin levels in rheumatoid arthritis

BACKGROUND AND AIMS

The risks of insulin resistance and accelerated atherosclerosis are increased in chronic inflammatory diseases including rheumatoid arthritis (RA). Adipo-(cyto)kines are associated with insulin resistance, atherosclerosis and inflammation. This study aimed to determine serum adiponectin and vaspin levels and their associations with the predictors of atherosclerosis in RA and Behcet's disease (BD).

METHODS

The study involved 56 patients with RA, 37 patients with BD, and 29 healthy controls (HC). Serum adiponectin and vaspin levels, homeostasis model assessment for insulin resistance (HOMA-IR) index, and common carotid intima-media thickness (IMT) were determined.

RESULTS

Serum adiponectin levels in both patient groups and serum vaspin level in only the RA group were higher, whereas serum vaspin level was lower in the active BD subgroup, compared to the HC group. However, adiponectin and vaspin levels were correlated with neither HOMA-IR index nor IMT in the RA group. Adiponectin level was correlated with DAS-28 and IL-6 level in the RA group, and it was higher in the active BD subgroup than in the inactive BD subgroup and the HC group.

CONCLUSIONS

Adiponectin and vaspin levels are higher in RA but associated with neither HOMA-IR index nor IMT. Adiponectin is related with disease activity remarks in RA and BD. Therefore, it may be suggested that adiponectin may be involved in the regulation of inflammatory responses in inflammatory diseases. Moreover, in contrast to in RA, vaspin level declines in active BD, and these results suggest that different chronic inflammatory diseases exert different influences on either adipokines.

The stromal-vascular fraction of adipose tissue contributes to major differences between subcutaneous and visceral fat depots

Adipose tissue represents a complex tissue both in terms of its cellular composition, as it includes mature adipocytes and the various cell types comprising the stromal-vascular fraction (SVF), and in relation to the distinct biochemical, morphological and functional characteristics according to its anatomical location. Herein, we have characterized the proteomic profile of both mature adipocyte and SVF from human visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) fat depots in order to unveil differences in the expression of proteins which may underlie the distinct association of VAT and SAT to several pathologies. Specifically, 24 proteins were observed to be differentially expressed between SAT SVF versus VAT SVF from lean individuals. Immunoblotting and RT-PCR analysis confirmed the differential regulation of the nuclear envelope proteins lamin A/C, the membrane-cytoskeletal linker ezrin and the enzyme involved in retinoic acid production, aldehyde dehydrogenase 1A2, in the two fat depots. In sum, the observation that proteins with important cell functions are differentially distributed between VAT and SAT and their characterization as components of SVF or mature adipocytes pave the way for future research on the molecular basis underlying diverse adipose tissue-related pathologies such as metabolic syndrome or lipodystrophy.

Epicardial fat gene expression after aerobic exercise training in pigs with coronary atherosclerosis: relationship to visceral and subcutaneous fat

Epicardial adipose tissue (EAT) is contiguous with coronary arteries and myocardium and potentially may play a role in coronary atherosclerosis (CAD). Exercise is known to improve cardiovascular disease risk factors. The purpose of this study was to investigate the effect of aerobic exercise training on the expression of 18 genes, measured by RT-PCR and selected for their role in chronic inflammation, oxidative stress, and adipocyte metabolism, in peri-coronary epicardial (cEAT), peri-myocardial epicardial (mEAT), visceral abdominal (VAT), and subcutaneous (SAT) adipose tissues from a castrate male pig model of familial hypercholesterolemia with CAD. We tested the hypothesis that aerobic exercise training for 16 wk would reduce the inflammatory profile of mRNAs in both components of EAT and VAT but would have little effect on SAT. Exercise increased mEAT and total heart weights. EAT and heart weights were directly correlated. Compared with sedentary pigs matched for body weight to exercised animals, aerobic exercise training reduced the inflammatory response in mEAT but not cEAT, had no effect on inflammatory genes but preferentially decreased expression of adiponectin and other adipocyte-specific genes in VAT, and had no effect in SAT except that IL-6 mRNA went down and VEGFa mRNA went up. We conclude that 1) EAT is not homogeneous in its inflammatory response to aerobic exercise training, 2) cEAT around CAD remains proinflammatory after chronic exercise, 3) cEAT and VAT share similar inflammatory expression profiles but different metabolic mRNA responses to exercise, and 4) gene expression in SAT cannot be extrapolated to VAT and heart adipose tissues in exercise intervention studies.

Human epicardial adipokine messenger RNAs: comparisons of their expression in substernal, subcutaneous, and omental fat

We compared the gene expression of inflammatory and other proteins by real-time quantitative polymerase chain reaction in epicardial, substernal (mediastinal) and subcutaneous sternal, upper abdominal, and leg fat from coronary bypass patients and omental (visceral) fat from extremely obese women undergoing bariatric surgery. We hypothesized that (1) epicardial fat would exhibit higher expression of inflammatory messenger RNAs (mRNAs) than substernal and subcutaneous fat and (2) epicardial mRNAs would be similar to those in omental fat. Epicardial fat was clearly different from substernal fat because there was a far higher expression of haptoglobin, prostaglandin D(2) synthase, nerve growth factor beta, the soluble vascular endothelial growth factor receptor (FLT1), and alpha1 glycoprotein but not of inflammatory adipokines such as monocyte chemoattractant protein-1, interleukin (IL)-8, IL-1beta, tumor necrosis factor alpha, serum amyloid A, plasminogen activator inhibitor-1, or adiponectin despite underlying coronary atherosclerosis. However, the latter inflammatory adipokines as well as most other mRNAs were overexpressed in epicardial fat as compared with the subcutaneous depots except for IL-8, fatty acid binding protein 4, the angiotensin II receptor 1, IL-6, and superoxide dismutase-2. Relative to omental fat, about one third of the genes were expressed at the same levels, whereas monocyte chemoattractant protein-1, cyclooxygenase-2, plasminogen activator inhibitor-1, IL-1beta, and IL-6 were expressed at far lower levels in epicardial fat. In conclusion, epicardial fat does not appear to be a potentially more important source of inflammatory adipokines than substernal mediastinal fat. Furthermore, the expression of inflammatory cytokines such as IL-6 and IL-1beta is actually higher in omental fat from obese women without coronary atherosclerosis. The data do not support the hypothesis that most of the inflammatory adipokines are expressed at high levels in epicardial fat of humans.

Rab11a and its binding partners regulate the recycling of the ß1-adrenergic receptor

ß1-adrenergic receptors (ß1-AR) are internalized in response to agonists and then recycle back for another round of signaling. The serine 312 to alanine mutant of the ß1-AR (S312A) is internalized but does not recycle. We determined that WT ß1-AR and S312A were internalized initially to an early sorting compartment because they colocalized by >70% with the early endosomal markers rab5a and early endosomal antigen-1 (EEA1). Subsequently, the WT ß1-AR trafficked via rab4a-expressing sorting endosomes to recycling endosomes. In recycling endosomes WT ß1-AR were colocalized by >70% with the rab11 GTPase. S312A did not colocalize with either rab4a or rab11, instead they exited from early endosomes to late endosomes/lysosomes in which they were degraded. Rab11a played a prominent role in recycling of the WT ß1-AR because dominant negative rab11a inhibited, while constitutively active rab11a accelerated the recycling of the ß1-AR. Next, we determined the effect of each of the rab11-interacting proteins on trafficking of the WT ß1-AR. The recycling of the ß1-AR was markedly inhibited when myosin Vb, FIP2, FIP3 and rabphillin were knocked down. These data indicate that rab11a and a select group of its binding partners play a prominent role in recycling of the human ß1-AR.

Release of inflammatory mediators by human adipose tissue is enhanced in obesity and primarily by the nonfat cells: a review

This paper considers the role of putative adipokines that might be involved in the enhanced inflammatory response of human adipose tissue seen in obesity. Inflammatory adipokines [IL-6, IL-10, ACE, TGFbeta1, TNFalpha, IL-1beta, PAI-1, and IL-8] plus one anti-inflammatory [IL-10] adipokine were identified whose circulating levels as well as in vitro release by fat are enhanced in obesity and are primarily released by the nonfat cells of human adipose tissue. In contrast, the circulating levels of leptin and FABP-4 are also enhanced in obesity and they are primarily released by fat cells of human adipose tissue. The relative expression of adipokines and other proteins in human omental as compared to subcutaneous adipose tissue as well as their expression in the nonfat as compared to the fat cells of human omental adipose tissue is also reviewed. The conclusion is that the release of many inflammatory adipokines by adipose tissue is enhanced in obese humans.

Release of 12 adipokines by adipose tissue, nonfat cells, and fat cells from obese women

The relative release in vitro of endothelin-1, zinc-alpha2-glycoprotein (ZAG), lipocalin-2, CD14, RANTES (regulated on activation, normal T cell expressed and secreted protein), lipoprotein lipase (LPL), osteoprotegerin (OPG), fatty acid-binding protein 4 (FABP-4), visfatin/PBEF/Nampt, glutathione peroxidase-3 (GPX-3), intracellular cell adhesion molecule 1 (ICAM-1), and amyloid A was examined using explants of human adipose tissue as well as the nonfat cell fractions and adipocytes from obese women. Over a 48-h incubation the majority of the release of LPL was by fat cells whereas that of lipocalin-2, RANTES, and ICAM-1 was by the nonfat cells present in human adipose tissue. In contrast appreciable amounts of OPG, amyloid A, ZAG, FABP-4, GPX-3, CD14, and visfatin/PBEF/Nampt were released by both fat cells and nonfat cells. There was an excellent correlation (r = 0.75) between the ratios of adipokine release by fat cells to nonfat cells over 48 h and the ratio of their mRNAs in fat cells to nonfat cells at the start of the incubation. The total release of ZAG, OPG, RANTES, and amyloid A by incubated adipose tissue explants from women with a fat mass of 65 kg was not different from that by women with a fat mass of 29 kg. In contrast that of ICAM-1, FABP-4, GPX-3, visfatin/PBEF/Nampt, CD14, lipocalin-2, LP, and endothelin-1 was significantly greater in tissue from women with a total fat mass of 65 kg.

Dexamethasone and the inflammatory response in explants of human omental adipose tissue

Dexamethasone is a synthetic glucocorticoid that is a potent anti-inflammatory agent. The present studies examined the changes in gene expression of 64 proteins in human omental adipose tissue explants incubated for 48h both in the absence and presence of dexamethasone as well as the release of 8 of these proteins that are putative adipokines. The proteins were chosen because they are inflammatory response proteins in other cells, are key regulatory proteins or are proteins with known functions. About 50% were significantly up-regulated while about 10% were unchanged and the remaining 40% were down-regulated. Dexamethasone significantly up-regulated the expression of about 33% of the proteins but down-regulated the expression of about 12% of the proteins. We conclude that dexamethasone is a selective anti-inflammatory agent since it inhibits only about one-fourth of the proteins up-regulated during in vitro incubation of human omental adipose tissue.

The inflammatory response seen when human omental adipose tissue explants are incubated in primary culture is not dependent upon albumin and is primarily in the nonfat cells

Background

The present studies were designed to investigate the changes in gene expression during in vitro incubation of human visceral omental adipose tissue explants as well as fat cells and nonfat cells derived from omental fat.

Methods

Adipose tissue was obtained from extremely obese women undergoing bariatric surgery. Explants of the tissue as well as fat cells and the nonfat cells derived by digestion with collagenase were incubated for 20 minutes to 48 h. The expression of interleukin 1β [IL-1β], tumor necrosis factor α [TNFα], interleukin 8 [IL-8], NFκB₁p50 subunit, hypoxia-inducible factor 1α [HIF1α], omentin/intelectin, and 11β-hydroxysteroid dehydrogenase 1 [11β-HSD1] mRNA were measured by qPCR as well as the release of IL-8 and TNFα.

Results

There was an inflammatory response at 2 h in explants of omental adipose tissue that was reduced but not abolished in the absence of albumin from the incubation buffer for IL-8, IL-1β and TNFα. There was also an inflammatory response with regard to upregulation of HIF1α and NFκB1 gene expression that was unaffected whether albumin was present or absent from the medium. In the nonfat cells derived by a 2 h collagenase digestion of omental fat there was an inflammatory response comparable but not greater than that seen in tissue. The exception was HIF1α where the marked increase in gene expression was primarily seen in intact tissue. The inflammatory response was not seen with respect to omentin/intelectin. Over a subsequent 48 h incubation there was a marked increase in IL-8 mRNA expression and IL-8 release in adipose tissue explants that was also seen to the same extent in the nonfat cells incubated in the absence of fat cells.

Conclusion

The marked inflammatory response seen when human omental adipose tissue is incubated in vitro is reduced but not abolished in the presence of albumin with respect to IL-1β, TNFα, IL-8, and is primarily in the nonfat cells of adipose tissue.

Functional analyses reveal the greater potency of preadipocytes compared with adipocytes as endothelial cell activator under normoxia, hypoxia, and TNFalpha exposure

Obesity is associated with a state of chronic low-grade inflammation. Immune cells accumulate in white adipose tissue (WAT). The vascular endothelium plays an interactive role in these infiltration and inflammatory processes. Mature and hypertrophic adipocytes are considered as the major adipogenic cell type secreting proinflammatory cytokines in WAT. In contrast, the proinflammatory capacity of preadipocytes and their role in endothelial cell activation have been neglected so far. To gain new insights into this molecular and cellular cross-talk, we examined the proinflammatory expression and secretion of normoxia, hypoxia, and TNFalpha-treated human preadipocytes and adipocytes (SGBS cells) and their impact on human microvascular endothelial cell (HMEC-1) function. In this study, stimulation of HMEC-1 with conditioned media (CM) from preadipocytes increased endothelial ICAM-1 expression and monocyte adhesion but not adipocyte-CM. After hypoxia and TNFalpha stimulation of SGBS cells, adipocyte-CM induced and preadipocyte-CM enhanced the monocyte adhesion. Concordantly, the expression of proinflammatory adipokines was considerably higher in preadipocytes than in adipocytes. SGBS-CM upregulated the phosphorylation of three MAPK pathways, STAT1/3, and c-Jun in HMEC-1, whereas the NF-kappaB pathway was not affected. Inhibitor experiments showed that monocyte/endothelial cell-cell adhesion and endothelial ICAM-1 expression was JNK and JAK-1/STAT1/3 pathway dependent and revealed IL-6 as a major mediator in CM increasing monocyte/endothelial cell-cell adhesion via the STAT1/3 pathway. Our study shows that preadipocytes rather than adipocytes operate as potent activators of endothelial cells. This can be enhanced in preadipocytes and induced in adipocytes by TNFalpha and hypoxia in a manner similar to what may occur in WAT in the etiology of obesity.

Regulation of visceral adipose tissue-derived serine protease inhibitor by nutritional status, metformin, gender and pituitary factors in rat white adipose tissue

Visceral adipose tissue-derived serine protease inhibitor (vaspin) is a recently discovered adipocytokine mainly secreted from visceral adipose tissue, which plays a main role in insulin sensitivity. In this study, we have investigated the regulation of vaspin gene expression in rat white adipose tissue (WAT) in different physiological (nutritional status, pregnancy, age and gender) and pathophysiological (gonadectomy, thyroid status and growth hormone deficiency) settings known to be associated with energy homeostasis and alterations in insulin sensitivity. We have determined vaspin gene expression by real-time PCR. Vaspin was decreased after fasting and its levels were partially recovered after leptin treatment. Chronic treatment with metformin increased vaspin gene expression. Vaspin mRNA expression reached the highest peak at 45 days in both sexes after birth and its expression was higher in females than males, but its levels did not change throughout pregnancy. Finally, decreased levels of growth hormone and thyroid hormones suppressed vaspin expression. These findings suggest that WAT vaspin mRNA expression is regulated by nutritional status, and leptin seems to be the nutrient signal responsible for those changes. Vaspin is influenced by age and gender, and its expression is increased after treatment with insulin sensitizers. Finally, alterations in pituitary functions modify vaspin levels. Understanding the molecular mechanisms regulating vaspin will provide new insights into the pathogenesis of the metabolic syndrome.

Increased adipose tissue expression of lipocalin-2 in obesity is related to inflammation and matrix metalloproteinase-2 and metalloproteinase-9 activities in humans

Lipocalin-2 (LCN2) is a novel adipokine with potential roles in obesity, insulin resistance, and inflammation. The aim of the present work was to evaluate the effect of obesity on circulating concentrations and gene and protein expression levels of LCN2 in human visceral adipose tissue (VAT) as well as its involvement in inflammation. VAT biopsies from 47 subjects were used in the study. Real-time PCR and Western-blot analyses were performed to quantify levels of LCN2 in VAT as well as the association with other genes implicated in inflammatory pathways. Forty-four serum samples were used to analyze the circulating concentrations of LCN2. Zymography analysis was used to determine the activity of matrix metalloproteinase (MMP) in VAT. Obese patients exhibited increased mRNA (p < 0.0001) and protein (p = 0.017) expression levels of LCN2 compared to lean subjects. Although no differences in plasma LCN2 concentrations were observed, increased circulating LCN2/MMP-9 complex levels were found (p = 0.038) in the obese group. Moreover, obese individuals showed increased (p < 0.01) activity of MMP-2 and MMP-9/LCN2 complex, while a positive correlation (p < 0.01) between MMP-2 and MMP-9 activities and BMI was observed. Gene and protein expression levels of LCN2 in VAT were positively associated with inflammatory markers (p < 0.01). These findings represent the first observation that mRNA and protein levels of LCN2 are increased in human VAT of obese subjects. Furthermore, LCN2 is associated with MMP-2 and MMP-9 activities as well as with pro-inflammatory markers suggesting its potential involvement in the low-grade chronic inflammation accompanying obesity.

Stimulation of human omental adipose tissue lipolysis by growth hormone plus dexamethasone

Growth hormone [GH] administration results in a reduction in adiposity of humans that is attributed to stimulation of lipolysis. We examined the effect of direct addition of human GH, in both the absence and presence of dexamethasone [Dex], as well as that of interferon beta on lipolysis by omental adipose tissue explants from obese women incubated for 48h in primary culture. There was a significant stimulation of lipolysis by GH in the presence of Dex but not by Dex or GH alone. There was also a significant further stimulation by GH in the presence of Dex of hormone-sensitive lipase, perilipin, lipoprotein lipase and beta1 adrenergic receptor mRNA. We conclude that the direct lipolytic effect of GH is accompanied by an increase in HSL mRNA in the presence of DEX, but GH also increased the mRNAs for other proteins that could explain all or part of its lipolytic action.