Interplay between human adipocytes and T lymphocytes in obesity: CCL20 as an adipochemokine and T lymphocytes as lipogenic modulators

Defining macrophage phenotype and function in adipose tissue

In obesity, chronic low-grade inflammation is thought to mediate the effects of increased adipose tissue mass on metabolic comorbidity. Of the different cell types that contribute to obesity-induced inflammation in adipose tissue, this review focuses on macrophages and their monocytes precursors. Mechanisms for monocyte recruitment to adipose tissue, and how both monocytes and macrophages are phenotypically modified in this environment in response to increasing fat mass, are considered. The versatile phenotype of adipose tissue macrophages might contribute not only to inflammatory and metabolic alterations, but could also help to maintain adipose tissue homeostasis in the setting of obesity.

Diabetes resolution and hyperinsulinaemia after metabolic Roux-en-Y gastric bypass

The global prevalence of type 2 diabetes mellitus and impaired glucose metabolism continues to rise in conjunction with the pandemic of obesity. The metabolic Roux-en-Y gastric bypass operation offers the successful resolution of diabetes in addition to sustained weight loss and excellent long-term outcomes in morbidly obese individuals. The procedure consists of the physiological BRAVE effects: (i) Bile flow alteration; (ii) Reduction of gastric size; (iii) Anatomical gut rearrangement and altered flow of nutrients; (iv) Vagal manipulation and (v) Enteric gut hormone modulation. This operation provides anti-diabetic effects through decreasing insulin resistance and increasing the efficiency of insulin secretion. These metabolic outcomes are achieved through weight-independent and weight-dependent mechanisms. These include the foregut, midgut and hindgut mechanisms, decreased inflammation, fat, adipokine and bile metabolism, metabolic modulation, shifts in gut microbial composition and intestinal gluconeogenesis. In a small minority of patients, gastric bypass results in hyperinsulinaemic hypoglycaemia that may lead to nesidioblastosis (pancreatic beta-cell hypertrophy with islet hyperplasia). Elucidating the precise metabolic mechanisms of diabetes resolution and hyperinsulinaemia after surgery can lead to improved operations and disease-specific procedures including 'diabetes surgery'. It can also improve our understanding of diabetes pathogenesis that may provide novel strategies for the management of metabolic syndrome and impaired glucose metabolism.

Immune cells in adipose tissue: key players in metabolic disorders

Obesity, defined as the excess development of adipose tissue, is an important risk factor for metabolic and cardiovascular diseases such as type 2 diabetes, hypertension and atherosclerosis. Over the past few years, metabolic inflammation has emerged as a major process underlying the link between obesity and its associated pathologies. Adipose tissue appears to play a primary and crucial role as a source and site of inflammation. Accumulation of immune cells within adipose tissue occurs in obese conditions. The present review focuses on the relationship between adipose tissue and immune cells, including macrophages, dendritic cells, T and B lymphocytes, and natural killer cells, in both the physiological state and under obese conditions. The factors involved in the accumulation of both myeloid and lymphoid cells in adipose tissue are also described. In addition, the role of adipose-tissue immune cells on adipocyte metabolism and cells of the adipose tissue stromal-vascular fraction are discussed, with particular emphasis on the cross-talk between macrophages and adipocytes, together with recent reports of T lymphocytes in adipose tissue.

Inflammation correlates with markers of T-cell subsets including regulatory T cells in adipose tissue from obese patients

Accumulation of cytotoxic and T-helper (T(h))1 cells together with a loss of regulatory T cells in gonadal adipose tissue was recently shown to contribute to obesity-induced adipose tissue inflammation and insulin resistance in mice. Human data on T-cell populations in obese adipose tissue and their potential functional relevance are very limited. We aimed to investigate abundance and proportion of T-lymphocyte sub-populations in human adipose tissue in obesity and potential correlations with anthropometric data, insulin resistance, and systemic and adipose tissue inflammation. Therefore, we analyzed expression of marker genes specific for pan-T cells and T-cell subsets in visceral and subcutaneous adipose tissue from highly obese patients (BMI >40 kg/m(2), n = 20) and lean to overweight control subjects matched for age and sex (BMI <30 kg/m(2); n = 20). All T-cell markers were significantly upregulated in obese adipose tissue and correlated with adipose tissue inflammation. Proportions of cytotoxic T cells and T(h)1 cells were unchanged, whereas those of regulatory T cells and T(h)2 were increased in visceral adipose tissue from obese compared to control subjects. Systemic and adipose tissue inflammation positively correlated with the visceral adipose abundance of cytotoxic T cells and T(h)1 cells but also regulatory T cells within the obese group. Therefore, this study confirms a potential role of T cells in human obesity-driven inflammation but does not support a loss of protective regulatory T cells to contribute to adipose tissue inflammation in obese patients as suggested by recent animal studies.

Macrophage gene expression is related to obesity and the metabolic syndrome in human subcutaneous fat as well as in visceral fat

AIMS/HYPOTHESIS

Our goal was to identify a set of human adipose tissue macrophage (ATM)-specific markers and investigate whether their gene expression in subcutaneous adipose tissue (SAT) as well as in visceral adipose tissue (VAT) is related to obesity and to the occurrence of the metabolic syndrome.

METHODS

ATM-specific markers were identified by DNA microarray analysis of adipose tissue cell types isolated from SAT of lean and obese individuals. We then analysed gene expression of these markers by reverse transcription quantitative PCR in paired samples of SAT and VAT from 53 women stratified into four groups (lean, overweight, obese and obese with the metabolic syndrome). Anthropometric measurements, euglycaemic-hyperinsulinaemic clamp, blood analysis and computed tomography scans were performed.

RESULTS

A panel of 24 genes was selected as ATM-specific markers based on overexpression in ATM compared with other adipose tissue cell types. In SAT and VAT, gene expression of ATM markers was lowest in lean and highest in the metabolic syndrome group. mRNA levels in the two fat depots were negatively correlated with glucose disposal rate and positively associated with indices of adiposity and the metabolic syndrome.

CONCLUSIONS/INTERPRETATION

In humans, expression of ATM-specific genes increases with the degree of adiposity and correlates with markers of insulin resistance and the metabolic syndrome to a similar degree in SAT and in VAT.

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.

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.

Role of the adipocyte-specific NF-κB activity in the regulation of IP-10 and T cell migration

Infiltration of immune cells into adipose tissue plays a central role in the pathophysiology of obesity-associated low-grade inflammation. The aim of this study was to analyze the role of adipocyte NF-κB signaling in the regulation of the chemokine/adipokine interferon-γ-induced protein 10 kDa (IP-10) and adipocyte-mediated T cell migration. Therefore, the regulation of IP-10 was investigated in adipose tissue of male C57BL/6J mice, primary human and 3T3-L1 preadipocytes/adipocytes. To specifically block the NF-κB pathway, 3T3-L1 cells stably overexpressing a transdominant mutant of IκBα were generated, and the chemical NF-κB inhibitor Bay117082 was used. Adipocyte-mediated T cell migration was assessed by a migration assay. It could be shown that IP-10 expression was higher in mature adipocytes compared with preadipocytes. Induced IP-10 expression and secretion were completely blocked by an NF-κB inhibitor in 3T3-L1 and primary human adipocytes. Stable overexpression of a transdominant mutant of IκBα in 3T3-L1 adipocytes led to an inhibition of basal and stimulated IP-10 expression and secretion. T cell migration was induced by 3T3-L1 adipocyte-conditioned medium, and both basal and induced T cell migration was strongly inhibited by stable overexpression of a transdominant IκBα mutant. In addition, with the use of an anti-IP-10 antibody, a significant decrease of adipocyte-induced T cell migration was shown. In conclusion, in this study, we could demonstrate that the NF-κB pathway is essential for the regulation of IP-10 in 3T3-L1 and primary human adipocytes. Adipocytes rather than preadipocytes contribute to NF-κB-dependent IP-10 expression and secretion. Furthermore, NF-κB-dependent factors and especially IP-10 represent novel signals from adipocytes to induce T cell migration.

Altered autophagy in human adipose tissues in obesity

CONTEXT

Autophagy is a housekeeping mechanism, involved in metabolic regulation and stress response, shown recently to regulate lipid droplets biogenesis/breakdown and adipose tissue phenotype.

OBJECTIVE

We hypothesized that in human obesity autophagy may be altered in adipose tissue in a fat depot and distribution-dependent manner.

SETTING AND PATIENTS

Paired omental (Om) and subcutaneous (Sc) adipose tissue samples were used from obese and nonobese (n = 65, cohort 1); lean, Sc-obese and intraabdominally obese (n = 196, cohort 2); severely obese persons without diabetes or obesity-associated morbidity, matched for being insulin sensitive or resistant (n = 60, cohort 3).

RESULTS

Protein and mRNA levels of the autophagy genes Atg5, LC3A, and LC3B were increased in Om compared with Sc, more pronounced among obese persons, particularly with intraabdominal fat accumulation. Both adipocytes and stromal-vascular cells contribute to the expression of autophagy genes. An increased number of autophagosomes and elevated autophagic flux assessed in fat explants incubated with lysosomal inhibitors were observed in obesity, particularly in Om. The degree of visceral adiposity and adipocyte hypertrophy accounted for approximately 50% of the variance in omental Atg5 mRNA levels by multivariate regression analysis, whereas age, sex, measures of insulin sensitivity, inflammation, and adipose tissue stress were excluded from the model. Moreover, in cohort 3, the autophagy marker genes were increased in those who were insulin resistant compared with insulin sensitive, particularly in Om.

CONCLUSIONS

Autophagy is up-regulated in adipose tissue of obese persons, especially in Om, correlating with the degree of obesity, visceral fat distribution, and adipocyte hypertrophy. This may co-occur with insulin resistance but precede the occurrence of obesity-associated morbidity.

The NLRP3 inflammasome instigates obesity-induced inflammation and insulin resistance

Emergence of chronic ‘sterile’ inflammation during obesity in absence of overt infection or autoimmune process is a puzzling phenomenon. The Nod Like Receptor (NLR) family of innate immune cell sensors like the Nlrp3 inflammasome are implicated in recognizing certain non-microbial origin ‘danger–signals’ leading to caspase-1 activation and subsequent IL-1β and IL-18 secretion. We show that reduction in adipose tissue expression of Nlrp3 is coupled with decreased inflammation and improved insulin–sensitivity in obese type-2 diabetic patients. The Nlrp3 inflammasome senses the lipotoxicity–associated ceramide to induce caspase-1 cleavage in macrophages and adipose tissue. Ablation of Nlrp3 prevented the obesity–induced inflammasome activation in fat depots and liver together with enhanced insulin–signalling. Furthermore, elimination of Nlrp3 in obesity reduced IL-18 and adipose tissue IFNγ along with an increase in naïve and reduction in effector adipose tissue T cells. Collectively, these data establish that Nlrp3 inflammasome senses obesity–associated ‘danger–signals’ and contributes to obesity–induced inflammation and insulin–resistance.

Adipose-derived stromal cells: cytokine expression and immune cell contaminants

The present method describes an immunoselection/depletion approach to isolate the native human adipose tissue-derived progenitor cells that are free from endothelial cells and immune cells by the use of magnetic nanobeads and microbeads coupled to antibodies. Moreover, methods to isolate and to analyse the distinct cell populations that constitute the microenvironment of the human adipose tissue progenitor cells, i.e. mature adipocytes, endothelial cells, and macrophages, are mentioned.

Deficiency in the extracellular signal-regulated kinase 1 (ERK1) protects leptin-deficient mice from insulin resistance without affecting obesity

AIMS/HYPOTHESIS

Extracellular signal-regulated kinase (ERK) activity is increased in adipose tissue in obesity and type 2 diabetes mellitus and strong evidences suggests that it is implicated in the downregulation of insulin signalling and action in the insulin-resistant state. To determine the role of ERK1 in obesity-associated insulin resistance in vivo, we inactivated Erk1 (also known as Mapk3) in obese leptin-deficient mice (ob/ob).

METHODS

Mice of genotype ob/ob-Erk1⁻(/)⁻ were obtained by crossing Erk1⁻(/)⁻ mice with ob/ob mice. Glucose tolerance and insulin sensitivity were studied in 12-week-old mice. Tissue-specific insulin sensitivity, insulin signalling, liver steatosis and adipose tissue inflammation were determined.

RESULTS

While ob/ob-Erk1⁻(/)⁻ and ob/ob mice exhibited comparable body weight and adiposity, ob/ob-Erk1⁻(/)⁻ mice did not develop hyperglycaemia and their glucose tolerance was improved. Hyperinsulinaemic-euglycaemic clamp studies demonstrated an increase in whole-body insulin sensitivity in the ob/ob-Erk1⁻(/)⁻ mice associated with an increase in both insulin-stimulated glucose disposal in skeletal muscles and adipose tissue insulin sensitivity. This occurred in parallel with improved insulin signalling in both tissues. The ob/ob-Erk1⁻(/)⁻ mice were also partially protected against hepatic steatosis with a strong reduction in acetyl-CoA carboxylase level. These metabolic improvements were associated with reduced expression of mRNA encoding inflammatory cytokine and T lymphocyte markers in the adipose tissue.

CONCLUSIONS/INTERPRETATION

Our results demonstrate that the targeting of ERK1 could partially protect obese mice against insulin resistance and liver steatosis by decreasing adipose tissue inflammation and by increasing muscle glucose uptake. Our results indicate that deregulation of the ERK1 pathway could be an important component in obesity-associated metabolic disorders.

Decreased AMP-activated protein kinase activity is associated with increased inflammation in visceral adipose tissue and with whole-body insulin resistance in morbidly obese humans

Inflammation and infiltration of immune cells in white adipose tissue have been implicated in the development of obesity-associated insulin resistance. Likewise, dysregulation of the fuel-sensing enzyme AMP-activated protein kinase (AMPK) has been proposed as a pathogenetic factor for these abnormalities based on both its links to insulin action and its anti-inflammatory effects. In this study, we examined the relationships between AMPK activity, the expression of multiple inflammatory markers in visceral (mesenteric and omental) and abdominal subcutaneous adipose tissue, and whole-body insulin sensitivity in morbidly obese patients (BMI 48±1.9 kg/m(2)) undergoing gastric bypass surgery. AMPK activity was assessed by Western-blots (P-AMPK/T-AMPK) and mRNA levels of various markers of inflammation by qRT-PCR. Patients were stratified as insulin sensitive obese or insulin-resistant obese according to their HOMA-IR values. The results indicate that AMPK activity is lower in visceral than in subcutaneous abdominal adipose tissue of these patients and that this is associated with an increased expression of multiple inflammatory genes. They also revealed that AMPK activity is lower in adipose tissue of obese patients who are insulin resistant (HOMA-IR>2.3) than in BMI-matched insulin sensitive subjects. Furthermore, this difference was evident in all three fat depots. In conclusion, the data suggest that there are close links between reduced AMPK activity and inflammation in white adipose tissue, and whole-body insulin resistance in obese humans. Whether adipose tissue AMPK dysregulation is a causal factor for the development of the inflammation and insulin resistance remains to be determined.

Butyrate and other short-chain fatty acids as modulators of immunity: what relevance for health?

PURPOSE OF REVIEW

High-fiber diets have been shown to reduce plasma concentrations of inflammation markers. Increased production of fermentation-derived short-chain fatty acids (SCFAs) is one of the factors that could exert these positive effects. This review examines the effects of SCFAs on immune cells and discusses the relevance of their effects on systemic inflammation, as frequently seen in obesity.

RECENT FINDINGS

SCFAs have been shown to reduce chemotaxis and cell adhesion; this effect is dependent on type and concentration of SCFA. In spite of conflicting results, especially butyrate seems to have an anti-inflammatory effect, mediated by signaling pathways like nuclear factor-κB and inhibition of histone deacetylase. The discrepancies in the results could be explained by differences in cell types used and their proliferative and differentiation status.

SUMMARY

SCFAs show anti-inflammatory effects and seem to have the potency to prevent infiltration of immune cells from the bloodstream in, for example, the adipose tissue. In addition, their ability to inhibit the proliferation and activation of T cells and to prevent adhesion of antigen-presenting cells could be important as it recently has been shown that obesity-associated inflammation might be antigen-dependent. More studies with concentrations in micromolar range are needed to approach more physiological concentrations.

Adipose tissue endothelial cells from obese human subjects: differences among depots in angiogenic, metabolic, and inflammatory gene expression and cellular senescence

OBJECTIVE

Regional differences among adipose depots in capacities for fatty acid storage, susceptibility to hypoxia, and inflammation likely contribute to complications of obesity. We defined the properties of endothelial cells (EC) isolated from subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) biopsied in parallel from obese subjects.

RESEARCH DESIGN AND METHODS

The architecture and properties of the fat tissue capillary network were analyzed using immunohistochemistry and flow cytometry. CD34(+)/CD31(+) EC were isolated by immunoselection/depletion. Expression of chemokines, adhesion molecules, angiogenic factor receptors, as well as lipogenic and senescence-related genes were assayed by real-time PCR. Fat cell size and expression of hypoxia-dependent genes were determined in adipocytes from both fat depots.

RESULTS

Hypoxia-related genes were more highly expressed in VAT than SAT adipocytes. VAT adipocytes were smaller than SAT adipocytes. Vascular density and EC abundance were higher in VAT. VAT-EC exhibited a marked angiogenic and inflammatory state with decreased expression of metabolism-related genes, including endothelial lipase, GPIHBP1, and PPAR gamma. VAT-EC had enhanced expression of the cellular senescence markers, IGFBP3 and γ-H2AX, and decreased expression of SIRT1. Exposure to VAT adipocytes caused more EC senescence-associated β-galactosidase activity than SAT adipocytes, an effect reduced in the presence of vascular endothelial growth factor A (VEGFA) neutralizing antibodies.

CONCLUSIONS

VAT-EC exhibit a more marked angiogenic and proinflammatory state than SAT-EC. This phenotype may be related to premature EC senescence. VAT-EC may contribute to hypoxia and inflammation in VAT.

Adaptive immunity and adipose tissue biology

Studies of immunity typically focus on understanding how hematopoietic cells interact within conventional secondary lymphoid tissues. However, immune reactions and their regulation occur in various environments within the body. Adipose tissue is one tissue that can influence and be influenced by adjacent and embedded lymphocytes. Despite the abundance and wide distribution of such tissue, and despite a growing obesity epidemic, studies of these interactions have been only marginally appreciated in the past. Here, we review advances in understanding of lymphoid structures within adipose tissue, the relationship between adipose tissue and adaptive immune function, and evidence for how this relationship contributes to obesity-associated diseases.

Increased epicardial adipose tissue volume in HIV-infected men and relationships to body composition and metabolic parameters

Epicardial fat accumulation may have important clinical consequences, yet little is known regarding this depot in HIV patients. We compared epicardial fat volume in 78 HIV-infected men and 32 HIV-negative controls. Epicardial fat volume was higher in HIV-infected patients than that in controls (P = 0.04). In HIV patients, epicardial fat volume was strongly associated with visceral adipose tissue area (rho = 0.76, P < 0.0001), fasting glucose (rho = 0.41, P = 0.001) and insulin (rho = 0.44, P = 0.0003). Relationships with glucose and insulin remained significant controlling for age, race, BMI, adiponectin, visceral adipose tissue and antiretroviral therapy. Epicardial fat may be an important fat depot in HIV-infected patients.

Adipose tissue inflammation: novel insight into the role of macrophages and lymphocytes

PURPOSE OF REVIEW

Obesity is associated with low-grade chronic inflammation in adipose tissue. This review presents an update on human and rodent studies analyzing the nature of fat-infiltrating immune cells, the time course of adipose tissue infiltration and underlying mechanisms.

RECENT FINDINGS

Intensive studies in rodents have shown that not only cells of the innate immune system traffic into adipose tissue but also various lymphocytes of the adaptive immunity are involved in inflammatory processes in fat. Several studies also provide insight in the order of appearance of macrophages and lymphocytes during the onset of obesity. Adipocytes and preadipocytes are also active players by their secretion of chemotactic adipokines.

SUMMARY

This review summarizes strong evidence for a link between the action of innate and adaptive immune systems in adipose tissue in the context of obesity and metabolism in rodents, but more studies in humans are necessary to relate this topic to human physiology. Targeting different immune cells at different stages of obesity may eventually lead to novel therapeutic approaches for the metabolic syndrome.

Dietary intervention-induced weight loss decreases macrophage content in adipose tissue of obese women

OBJECTIVE

Accumulation of adipose tissue macrophages (ATMs) is observed in obesity and may participate in the development of insulin resistance and obesity-related complications. The aim of our study was to investigate the effect of long-term dietary intervention on ATM content in human adipose tissue.

DESIGN

We performed a multi-phase longitudinal study.

SUBJECTS AND MEASUREMENTS

A total of 27 obese pre-menopausal women (age 39 ± 2 years, body mass index 33.7 ± 0.5 kg m(-2)) underwent a 6-month dietary intervention consisting of two periods: 4 weeks of very low-calorie diet (VLCD) followed by weight stabilization composed of 2 months of low-calorie diet and 3 to 4 months of weight maintenance diet. At baseline and at the end of each dietary period, samples of subcutaneous adipose tissue (SAT) were obtained by needle biopsy and blood samples were drawn. ATMs were determined by flow cytometry using combinations of cell surface markers. Selected cytokine and chemokine plasma levels were measured using enzyme-linked immunosorbent assay. In addition, in a subgroup of 16 subjects, gene expression profiling of macrophage markers in SAT was performed using real-time PCR.

RESULTS

Dietary intervention led to a significant decrease in body weight, plasma insulin and C-reactive protein levels. After VLCD, ATM content defined by CD45+/14+/206+ did not change, whereas it decreased at the end of the intervention. This decrease was associated with a downregulation of macrophage marker mRNA levels (CD14, CD163, CD68 and LYVE-1 (lymphatic vessel endothelial hyaluronan receptor-1)) and plasma levels of monocyte-chemoattractant protein-1 (MCP-1) and CXCL5 (chemokine (C-X-C motif) ligand 5). During the whole dietary intervention, the proportion of two ATM subpopulations distinguished by the CD16 marker was not changed.

CONCLUSION

A 6-month weight-reducing dietary intervention, but not VLCD, promotes a decrease in the number of the whole ATM population with no change in the relative distribution of ATM subsets.

Adipose tissue lymphocytes: types and roles

Besides adipocytes, specialized in lipid handling and involved in energy balance regulation, white adipose tissue (WAT) is mainly composed of other cell types among which lymphocytes represent a non-negligible proportion. Different types of lymphocytes (B, alphabetaT, gammadeltaT, NK and NKT) have been detected in WAT of rodents or humans, and vary in their relative proportion according to the fat pad anatomical location. The lymphocytes found in intra-abdominal, visceral fat pads seem representative of innate immunity, while those present in subcutaneous fat depots are part of adaptive immunity, at least in mice. Both the number and the activity of the different lymphocyte classes, except B lymphocytes, are modified in obesity. Several of these modifications in the relative proportions of the lymphocyte classes depend on the degree of obesity, or on leptin concentration, or even fat depot anatomical location. Recent studies suggest that alterations of lymphocyte number and composition precede the macrophage increase and the enhanced inflammatory state of WAT found in obesity. Lymphocytes express receptors to adipokines while several proinflammatory chemokines are produced in WAT, rendering intricate crosstalk between fat and immune cells. However, the evidences and controversies available so far are in favour of an involvement of lymphocytes in the control of the number of other cells in WAT, either adipocytes or immune cells and of their secretory and metabolic activities. Therefore, immunotherapy deserves to be considered as a promising approach to treat the endocrino-metabolic disorders associated to excessive fat mass development.

Mapping of the fibroblast growth factors in human white adipose tissue

CONTEXT

Fibroblast growth factors (FGFs) regulate the development of white adipose tissue (WAT). However, the secretion and cellular origin of individual FGFs in WAT as well as the influence of obesity are unknown.

OBJECTIVE

Our objective was to map FGFs in human sc WAT, the cellular source, and association with obesity.

DESIGN

Secretion, mRNA, and circulatory levels of FGFs in human abdominal sc WAT from nonobese and obese donors were examined by microarray, real-time quantitative PCR, and ELISA. The activity of FGFs in cultured human adipocytes was determined by phosphorylation assays.

RESULTS

Expression of five FGFs (FGF1, FGF2, FGF7, FGF9, and FGF18) and FGF homologous factor (FHF2) was identified in WAT. Only FGF1 was released in a time-dependent manner from sc WAT, and fat cells were the major source of FGF1 secretion. FGF1 expression increased and FGF2 decreased during adipocyte differentiation. Furthermore, FGF1 was not secreted into the circulation. Although FGF1 levels were 2-fold increased in obesity, they were unaltered by weight reduction. Only FGF1 and FGF2 induced a marked concentration-dependent phosphorylation of p44/42 in cultured human adipocytes.

CONCLUSIONS

Of the investigated FGFs, only FGF1 is secreted from sc WAT and predominantly so from the adipocyte fraction. The activity in adipocyte cultures and lack of secretion into the circulation suggest that FGF1 acts as an auto- or paracrine factor. FGF1 levels are increased in obesity but unaffected by weight reduction, suggesting a primary defect in obese individuals. In conclusion, FGF1 may play a superior role among the FGFs in sc WAT and obesity development.

The role of chemokines in recruitment of immune cells to the artery wall and adipose tissue

The role of the immune system is to recognize pathogens, tumor cells or dead cells and to react with a very specific and localized response. By taking advantage of a highly sophisticated system of chemokines and chemokine receptors, leukocytes such as neutrophils, macrophages, and T-lymphocytes are targeted to the precise location of inflammation. While this is a beneficial process for acute infection and inflammation, recruitment of immune cells to sites of chronic inflammation can be detrimental. It is becoming clear that these inflammatory cells play a significant role in the initiation and progression of metabolic disorders such as atherosclerosis and insulin resistance by infiltrating the artery wall and adipose tissue (AT), respectively. Data from human studies indicate that elevated plasma levels of chemokines are correlated with these metabolic diseases. Recruitment of macrophages to the artery wall is well known to be one of the first steps in early atherosclerotic lesion formation. Likewise, recruitment of macrophages to AT is thought to contribute to insulin resistance associated with obesity. Based on this knowledge, much recent work in these areas has focused on the role of chemokines in attracting immune cells (monocytes/macrophages in particular) to these 2 sites. Thus, understanding the potential for chemokines to contribute to metabolic disease can help direct studies of chemokines as therapeutic targets. In this article, we will review current literature regarding the role of chemokines in atherosclerosis and obesity-related insulin resistance. We will focus on novel work showing that chemokine secretion from endothelial cells, platelets, and adipocytes can contribute to immune cell recruitment, with a diagram showing the time course of chemokine expression and leukocyte recruitment to AT. We will also highlight a few of the less-commonly known chemokine-chemokine receptor pairs. Finally, we will discuss the potential for chemokines as therapeutic targets for treatment of atherosclerosis and insulin resistance.