Human primary adipocytes exhibit immune cell function: adipocytes prime inflammation independent of macrophages

Background

Obesity promotes inflammation in adipose tissue (AT) and this is implicated in pathophysiological complications such as insulin resistance, type 2 diabetes and cardiovascular disease. Although based on the classical hypothesis, necrotic AT adipocytes (ATA) in obese state activate AT macrophages (ATM) that then lead to a sustained chronic inflammation in AT, the link between human adipocytes and the source of inflammation in AT has not been in-depth and systematically studied. So we decided as a new hypothesis to investigate human primary adipocytes alone to see whether they are able to prime inflammation in AT.

Methods and Results

Using mRNA expression, human preadipocytes and adipocytes express the cytokines/chemokines and their receptors, MHC II molecule genes and 14 acute phase reactants including C-reactive protein. Using multiplex ELISA revealed the expression of 50 cytokine/chemokine proteins by human adipocytes. Upon lipopolysaccharide stimulation, most of these adipocyte-associated cytokines/chemokines and immune cell modulating receptors were up-regulated and a few down-regulated such as (ICAM-1, VCAM-1, MCP-1, IP-10, IL-6, IL-8, TNF-α and TNF-β highly up-regulated and IL-2, IL-7, IL-10, IL-13 and VEGF down-regulated. In migration assay, human adipocyte-derived chemokines attracted significantly more CD4+ T cells than controls and the number of migrated CD4+ cells was doubled after treating the adipocytes with LPS. Neutralizing MCP-1 effect produced by adipocytes reduced CD4+ migration by approximately 30%.

Conclusion

Human adipocytes express many cytokines/chemokines that are biologically functional. They are able to induce inflammation and activate CD4+ cells independent of macrophages. This suggests that the primary event in the sequence leading to chronic inflammation in AT is metabolic dysfunction in adipocytes, followed by production of immunological mediators by these adipocytes, which is then exacerbated by activated ATM, activation and recruitment of immune cells. This study provides novel knowledge about the prime of inflammation in human obese adipose tissue, opening a new avenue of investigations towards obesity-associated type 2 diabetes.

Modulatory role of the ovarian function in neuroimmunoendocrine axis activity

The aim of this study was to evaluate the effect of ovariectomy on the acute-phase response of inflammatory stress. Ex vivo adrenocortical, peripheral mononuclear cell (PMNC) and adipocyte activities were studied in intact and ovariectomized mice. Endotoxemia was mimicked by intraperitoneal administration of bacterial lipopolysaccharide (LPS; 25 mg per mouse) to sham-operated and 21-day ovariectomized mice. Circulating corticosterone, tumor necrosis factor-α (TNFα) and leptin concentrations were monitored before and 30-120 min after the administration of LPS. Additionally, in vitro experiments were performed with isolated corticoadrenal cells, PMNCs and omental adipocytes from sham-operated and ovariectomized mice incubated with specific secretagogues. The results indicate that while ovariectomy enhanced TNFα secretion after in vivo administration of LPS, it reduced corticoadrenal response and abrogated LPS-elicited leptin secretion into the circulation. While the corticoadrenal sensitivity to ACTH stimulation was reduced by ovariectomy, the LPS-induced PMNC response was not affected. Exogenous leptin enhanced baseline PMNC function regardless of surgery. Finally, ovariectomy drastically reduced in vitro adipocyte functionality. Our data support the notion that ovariectomy modified neuroendocrine-immune-adipocyte axis function and strongly suggest that ovarian activity could play a pivotal role in the development of an adequate immune defense mechanism after injury.

Obesity, visceral fat and Crohn's disease

PURPOSE OF REVIEW

Increasing evidence indicates that adipose tissue is an active endocrine organ involved in metabolic syndrome and regulation of inflammation. Visceral fat accumulation is a hallmark of both obesity and Crohn's disease. Here, we present recent data describing the immune properties of intra-abdominal adipose tissue that could link the innate immune response to obesity-related disorders and gut inflammation.

RECENT FINDINGS

Innate immune properties of adipocytes have become well characterized since recent studies described the Toll-like receptor (TLR) expression repertoire and specific TLR ligand responses of adipocytes. Adipokine secretion profiles have also been elucidated both in obese patients, when they may be involved in obesity-associated metabolic disease, and in Crohn's disease. Whereas mesenteric fat hypertrophy and fat wrapping of the bowel are characteristic of Crohn's disease, there exists a paucity of information concerning this important pathophysiological aspect. Our current classical animal models are of limited interest when investigating the role of mesenteric fat in gut inflammation. Recent new alternative disease paradigms could help to design more specific models for elucidating chronic transmural inflammation of the gut.

SUMMARY

Obesity and Crohn's disease share common features with the development of mesenteric fat that may be involved in gut inflammation. Further studies are required to clearly assess the origin and influence of intestinal fat deposits upon gut inflammation, notably during Crohn's disease development.

Pro-inflammatory CD11c+CD206+ adipose tissue macrophages are associated with insulin resistance in human obesity

OBJECTIVE

Insulin resistance and other features of the metabolic syndrome have been causally linked to adipose tissue macrophages (ATMs) in mice with diet-induced obesity. We aimed to characterize macrophage phenotype and function in human subcutaneous and omental adipose tissue in relation to insulin resistance in obesity.

RESEARCH DESIGN AND METHODS

Adipose tissue was obtained from lean and obese women undergoing bariatric surgery. Metabolic markers were measured in fasting serum and ATMs characterized by immunohistology, flow cytometry, and tissue culture studies. RESULTS ATMs comprised CD11c(+)CD206(+) cells in "crown" aggregates and solitary CD11c(-)CD206(+) cells at adipocyte junctions. In obese women, CD11c(+) ATM density was greater in subcutaneous than omental adipose tissue and correlated with markers of insulin resistance. CD11c(+) ATMs were distinguished by high expression of integrins and antigen presentation molecules; interleukin (IL)-1beta, -6, -8, and -10; tumor necrosis factor-alpha; and CC chemokine ligand-3, indicative of an activated, proinflammatory state. In addition, CD11c(+) ATMs were enriched for mitochondria and for RNA transcripts encoding mitochondrial, proteasomal, and lysosomal proteins, fatty acid metabolism enzymes, and T-cell chemoattractants, whereas CD11c(-) ATMs were enriched for transcripts involved in tissue maintenance and repair. Tissue culture medium conditioned by CD11c(+) ATMs, but not CD11c(-) ATMs or other stromovascular cells, impaired insulin-stimulated glucose uptake by human adipocytes.

CONCLUSIONS

These findings identify proinflammatory CD11c(+) ATMs as markers of insulin resistance in human obesity. In addition, the machinery of CD11c(+) ATMs indicates they metabolize lipid and may initiate adaptive immune responses.

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.

Adipose tissue depots of Holstein cows are immune responsive: inflammatory gene expression in vitro

The transcriptional response of adipose tissue depots with respect to their immune responsiveness in dairy cows remains largely unknown. Thus, we examined mRNA expression and responsiveness of subcutaneous (SUB) and mesenteric (MES) adipose tissue from nonpregnant dairy cows to a short-term (2 h), in vitro lipopolysaccharide (LPS) challenge (20 microg/mL in physiological saline). Abundance of mRNA for tumor necrosis factor-alpha (TNFA), interleukin-6 (IL6), serum amyloid A3 (SAA3), toll-like receptor 4 (TLR4), monocyte chemoattractant protein-1 (CCL2), and RANTES/chemokine C-C motif ligand 5 (CCL5) were analyzed using quantitative polymerase chain reaction (PCR) from tissue samples collected at slaughter from 5 nonpregnant/nonlactating Holstein cows. Prior to LPS challenge, SAA3 mRNA abundance was greater in MES than SUB tissue. Regardless of depot site, LPS led to greater mRNA abundance of TNFA and IL6 and was more pronounced for IL6 in MES. We also observed a marked increased in expression of CCL2, CCL5, TLR4, IL6, and TNFA in both MES and SUB during the 2-h incubation with saline alone (ie, the control). Because mRNA expression of the apoptotic markers B-cell CLL/lymphoma 2 (BCL2) and tumor protein p53 (TP53) did not differ during the 2-h incubation, it is less likely that the response to saline was a result of increased rate of cell death during incubation. Analysis using semiquantitative PCR of the 16s rRNA gene in cDNA from tissue explants revealed the presence of bacteria likely arising from contamination during sample collection. Furthermore, surfactant medium from about 50% of explant cultures had viable aerobic bacteria without differences between treatments or tissue samples. Thus, the presence of bacteria could partly explain the large increase in inflammatory-related genes after 2-h incubation with saline. The higher SAA3 expression in MES suggests that this acute-phase protein has a role in lipid metabolism and/or transport during an immune challenge. Overall, results provided evidence that adipose depots of dairy cows are capable of synthesizing chemokines and are immune responsive when exposed to inflammatory conditions that can arise from a pathogenic insult or during and soon after parturition.

The c-Jun N-terminal kinase mediates the induction of oxidative stress and insulin resistance by palmitate and toll-like receptor 2 and 4 ligands in 3T3-L1 adipocytes

Saturated fatty acids (SFAs) are known to induce inflammation and insulin resistance in adipocytes through toll-like receptor-4 (Tlr4) signaling, but the mechanisms are not well delineated. Furthermore, the potential roles of Tlr2 and the c-Jun N-terminal kinase (JNK) in inflammation in adipocytes have not been investigated. We demonstrated that palmitate, lipopolysaccharide (LPS), and the toll-like receptor-2 (Tlr2) agonist, zymosan A (ZymA), induced insulin resistance in a time- and dose-dependent manner in 3T3-L1 adipocytes. Corresponding with the reduction of insulin sensitivity was an increased expression of IL-6, as well as activation of the proinflammatory transcription factors, nuclear factor kappa B, and activator protein-1. Reactive oxygen species (ROS) accumulation was also observed in palmitate and Tlr agonist treated adipocytes. The JNK inhibitor, SP600125, attenuated insulin resistance mediated by SFA and Tlr agonists, which corresponded with a diminished proinflammatory response and reduced ROS accumulation. Collectively, these results demonstrated Tlr2 involvement in adipocyte inflammation and therefore implicated the receptor as a potential target for SFA. Moreover, activation of JNK also appeared to be essential to Tlr2-, as well as Tlr4-induced insulin resistance and oxidative stress.

Pioglitazone reduces inflammatory responses of human adipocytes to factors secreted by monocytes/macrophages

Infiltration of monocyte-derived macrophages into adipose tissue may contribute to tissue and systemic inflammation and insulin resistance. We hypothesized that pioglitazone (Pio) could specifically reduce the inflammatory response of adipocytes to factors released by monocytes/macrophages. We show that macrophage factors (Mphi-factors) greatly increase expression levels of proinflammatory adipokines, chemokines, and adhesion molecules in human subcutaneous and visceral adipose tissue (SAT and VAT) as well as in adipocytes (up to several hundredfold of control). Compared with SAT, VAT showed enhanced basal and Mphi-factor-induced inflammatory responses. Mphi-factors also induced greater lipolysis in adipocytes, as assessed by concentrations of glycerol released from the cells (196 +/- 13 vs. 56 +/- 7 microM in control, P < 0.05). Pretreatment of adipose tissue or adipocytes with Pio reduced these responses to Mphi-factors (by 13-86%, P < 0.05) and prevented Mphi-factor suppression of adiponectin expression. Furthermore, Pio pretreatment of adipocytes and macrophages tended to further reduce inflammatory responses of adipocytes to Mphi-factors and monocyte adhesion to Mphi-factor-activated adipocytes. In support of these in vitro data, media conditioned by monocytes isolated from impaired glucose-tolerant subjects treated with Pio (compared with placebo) induced release of lower concentrations of proinflammatory adipokines and glycerol (100 +/- 7 vs. 150 +/- 15 microM, P < 0.05) from adipocytes. In summary, Pio decreases inflammatory responses in adipose tissue/cells induced by monocytes/macrophages by acting on either or both cell types. These beneficial effects of Pio may attenuate proinflammatory responses resulting from monocyte/macrophage infiltration into adipose tissue and suppress tissue inflammation resulting from the interaction between both cell types.

Expression and secretion of RANTES (CCL5) in human adipocytes in response to immunological stimuli and hypoxia

Obesity and related disorders represent states of systemic low-grade inflammation. Chemokine secretion by adipocytes may initiate leukocyte infiltration in obese adipose tissue and thus mediate an important step in the establishment of chronic immune activation. The chemokine RANTES (regulated upon activation normal T cell expressed and secreted)/CCL5 is a chemoattractant for various leukocyte subsets. This study was designed to examine whether RANTES is expressed and released by human adipocytes and how its expression is regulated. RANTES expression under basal conditions was studied in mature adipocytes. Cells were therefore challenged with lipopolysaccharide (LPS), interferon (IFN)-gamma, interleukin (IL)-4, monocyte chemoattractant protein (MCP)-1 or exposed to low oxygen pressure. RANTES was expressed and secreted constitutively in most samples of mature adipocytes from the omental and the subcutaneous depot. RANTES release was dependent on adipocyte size and also seemed to be higher from cells of obese donors. Hypoxia (4% O (2)) caused an approximately 36% increase of RANTES release. Human adipocytes express the chemokine RANTES and are thus identified as a novel cellular source of this immune mediator. LPS and IFNgamma do not seem to play a significant role for the expression of RANTES in contrast to moderate hypoxia, which points to a distinct role in the innate immune system.

Relation of adipose tissue to metabolic flexibility

Metabolic flexibility is the capacity for skeletal muscle to shift reliance between lipids and glucose during fasting or in response to insulin. We hypothesized that body fat, adipose tissue characteristics, e.g. larger adipocytes, presence of inflammatory gene markers and impaired suppression of non-esterified fatty acids (NEFAs) during insulin infusion might be related to metabolic flexibility. We measured changes in respiratory quotient (DeltaRQ) before and during euglycemic-hyperinsulinemic clamp in healthy young males. Body fat by DXA, laboratory measurements, abdominal subcutaneous adipose tissue biopsies and fat cell size (FCS) were obtained after an overnight fast. Gene expression for 17 adipose tissue genes related to lipid synthesis, uptake, oxidation and storage, lipolysis and inflammation were measured. Reduced metabolic flexibility was associated with higher body fat, larger FCS and impaired insulin suppression of NEFAs. Metabolic flexibility was associated with higher serum adiponectin levels. Lower adipose tissue gene expression for inflammation markers was associated with greater NEFA suppression by insulin and metabolic flexibility. Combined, these results indicate that body fat, larger adipocytes, failure of insulin to suppress NEFAs, decreased adiponectin levels and inflammation markers in adipose tissue are associated with decreased insulin-stimulated glucose uptake and oxidation, which is an important component of reduced metabolic flexibility.

Trypanosoma cruzi infection of cultured adipocytes results in an inflammatory phenotype

Infection with Trypanosoma cruzi, the etiologic agent of Chagas disease is accompanied by an intense inflammatory reaction. Our laboratory group has identified adipose tissue as one of the major sites of inflammation during disease progression. Because adipose tissue is composed of many cell types, we were interested in investigating whether the adipocyte per se was a source of inflammatory mediators in this infection. Cultured adipocytes were infected with the Tulahuen strain of T. cruzi for 48-96 h. Immunoblot and quantitative PCR (qPCR) analyses demonstrated an increase in the expression of proinflammatory cytokines and chemokines, including interleukin (IL)-1 beta, interferon-gamma, tumor necrosis factor-alpha, CCL2, CCL5, and CXCL10 as well as an increase in the expression of Toll-like receptors-2 and 9 and activation of the notch pathway. Interestingly, caveolin-1 expression was reduced while cyclin D1 and extracellular signal-regulated kinase (ERK) expression was increased. The expression of PI3kinase and the activation of AKT (phosphorylated AKT) were increased suggesting that infection may induce components of the insulin/IGF-1 receptor cascade. There was an infection-associated decrease in adiponectin and peroxisome proliferator-activated receptor-gamma (PPAR-gamma). These data provide a mechanism for the increase in the inflammatory phenotype that occurs in T. cruzi-infected adipocytes. Overall, these data implicate the adipocyte as an important target of T. cruzi, and one which contributes significantly to the inflammatory response observed in Chagas disease.

Interferon-gamma, a Th1 cytokine, regulates fat inflammation: a role for adaptive immunity in obesity

Adipose tissue (AT) can accumulate macrophages and secrete several inflammatory mediators. Despite its pivotal role in the progression of chronic inflammatory processes such as atherosclerosis, the adaptive role of immunity in obesity remains poorly explored. Visceral AT of diet-induced obese C57BL/6 mice had higher numbers of both CD4(+) and CD8(+) T cells than lean controls, monitored by flow cytometry. When stimulated in vitro, T cells from obese AT produced more interferon (IFN)gamma than those from controls. AT from obese animals also had more cells expressing I-A(b), a mouse class II histocompatibility marker implicated in antigen presentation, as determined by immunostaining. Differentiated 3T3-L1 cells stimulated with recombinant IFNgamma or T-helper 1-derived supernatant produced several chemokines and their mRNAs. Obese IFNgamma-deficient animals had significantly reduced AT expression of mRNA-encoding inflammatory genes such as tumor necrosis factor-alpha and monocyte chemoattractant protein-1, decreased AT inflammatory cell accumulation, and better glucose tolerance than control animals consuming the same diet. Obese mice doubly deficient for IFNgamma receptor and apolipoprotein (Apo)E on a mixed 129SvEv/C57BL/6 (129/B6) genetic background, despite exhibiting similar AT mRNA levels of tumor necrosis factor-alpha and monocyte chemoattractant protein-1 as 129/B6-ApoE(-/-) controls, had decreased expression of important T cell-related genes, such as IFNgamma-inducible protein-10 and I-A(b), and lower plasma triglycerides and glucose. These results indicate a role for T cells and IFNgamma, a prototypical T-helper 1 cytokine, in regulation of the inflammatory response that accompanies obesity.

Cell surface expression of stem cell antigen-1 (Sca-1) distinguishes osteo-, chondro-, and adipoprogenitors in fetal mouse calvaria

The flat bones of the skull (calvaria) develop by balanced cell proliferation and differentiation in the calvarial sutures and the bone tips. As the brain grows and the calvaria expand, cells within the sutures must remain undifferentiated to maintain suture patency, but osteoprogenitors also need to be recruited into the osteogenic fronts. The exact identity of calvarial osteoprogenitors is currently not known. We used immunomagnetic cell sorting to isolate Sca-1+ and Sca-1(-) cells from fetal mouse calvaria and determined their differentiation potential in in vitro differentiation asssays and in vivo subcutaneous transplantations. Cells within the Sca-1+ cell fraction have a higher adipogenic potential, whereas cells within the Sca-1(-) cell fraction have a higher osteogenic and chondrogenic potential. The Sca-1(-) fraction retains its chondrogenic potential after in vitro expansion but not its osteogenic potential. The Sca-1+ fraction does not retain its adipogenic potential after in vitro expansion. Subcutaneous transplantation resulted in islands of bone and cartilage in implants that had been seeded with Sca-1(-) cells. In conclusion, immunomagnetic cell sorting with Sca-1 antibodies can be used to separate a Sca-1+ cell fraction with adipogenic potential from a Sca-1(-) cell fraction with osteogenic and chondrogenic potential. Isolation of pure populations of calvarial adipoprogenitors, osteoprogenitors, and chondroprogenitors will be beneficial for cellular studies of calvarial development, adipogenesis, osteogenesis, and chondrogenesis. Calvaria-derived osteogenic cell populations may be useful in craniofacial tissue regeneration and repair.

[Cell surface antigen expression of orbital preadipocytes between patients with thyroid-associated ophthalmopathy and healthy adults]

OBJECTIVE

To study the cell surface antigen expression of orbital preadipocytes between patients with thyroid-associated ophthalmopathy (TAO) and healthy adults.

METHODS

Tissue culture Methods were used in the cell culture of orbital preadipocytes in patients with TAO and healthy adults. Flow cytometry was used to analyze the expression of CD29, CD44, CD49d, and HLA-DR in these 2 cells.

RESULTS

Positive expressions were examined in orbital preadipocytes of patients with TAO and healthy adults. The orbital preadipocytes of patients with TAO had a higher expression of HLA-DR than that of healthy adults.

CONCLUSION

The orbital preadipocytes of patients with TAO and healthy adults cultured by tissue cultured Methods both belong to mesenchymal stem cells, and the former may participate in the orbital inflammation.

BM cells giving rise to MSC in culture have a heterogeneous CD34 and CD45 phenotype

BACKGROUND

Mesenchymal stromal cells (MSC) isolated from adult human BM are characterized by their fibroblast-like morphology, adherent growth and capacity to differentiate into adipocytes, osteocytes, chondrocytes, cardiomyocytes and neuroprogenitors. After culturing these cells in vitro, they express the cell-surface molecules CD44, CD90, SH2 and SH3, and are negative for CD34 and the hematopoietic marker CD45. The aim of this study was to characterize the in vivo phenotype of MSC relative to the expression of CD34 and CD45.

METHODS

BM mononuclear cells were stained with Ab against both molecules and separated into the CD34(+), CD34(-), CD45(+) CD34(+), CD45(high+) CD34(-), CD45(med,low+) CD34(-) and CD45(-) CD34(-) subpopulations, which were then cultured under the same conditions and analyzed for growth of MSC.

RESULTS

A small population of MSC arose from the CD45(+) CD34(+) fraction, although the majority was obtained from the CD45(-) CD34(-) subpopulation. MSC from all fractions could be differentiated into adipocytes and osteocytes. In addition, MSC from the CD34(+) and CD34(-) fractions were shown to differentiate into chondrocytes. After in vitro culture, MSC from both fractions possessed the same phenotype, which was negative for CD34 and CD45.

DISCUSSION

MSC from the CD45(+) CD34(+) fraction change their phenotype under in vitro conditions.

Obesity-associated mouse adipose stem cell secretion of monocyte chemotactic protein-1

Studies showed that monocyte chemotactic protein-1 (MCP-1) concentrations are increased in obesity. In our current study, we demonstrate that plasma MCP-1 level in leptin-deficient ob/ob mice is significantly higher than in lean mice. Furthermore, we determined that basal adipose tissue MCP-1 mRNA levels are significantly higher in ob/ob mice compared with lean mice. To determine the mechanisms underlying obesity-associated increases in plasma and adipose tissue MCP-1 levels, we determined adipose tissue cell type sources of MCP-1 production. Our data show that adipose tissue stem cells (CD34(+)), macrophages (F4/80(+)), and stromal vascular fraction (SVF) cells express significantly higher levels of MCP-1 compared with adipocytes under both basal and lipopolysaccharide (LPS)-stimulated conditions. Furthermore, basal and LPS-induced MCP-1 secretion levels were the same for both adipose F4/80(+) and CD34(+) cells, whereas adipose CD34(+) cells have twofold higher cell numbers (30% of total SVF cells) compared with F4/80(+) macrophages (15%). Our data also show that CD34(+) cells from visceral adipose tissue depots secrete significantly higher levels of MCP-1 ex vivo when compared with CD34(+) cells from subcutaneous adipose tissue depots. Taken together, our data suggest that adipose CD34(+) stem cells may play an important role in obesity-associated increases in plasma MCP-1 levels.

Obesity, innate immunity and gut inflammation

PURPOSE OF REVIEW

The purpose of this review is to present recent data on how obesity-associated conditions may affect innate immunity and its role in the development of gut inflammation.

RECENT FINDINGS

Here we present studies that demonstrate the participation of adipose tissue components in the generation of inflammation. More specifically, we describe increases in the release of proinflammatory cytokines during obesity as well as the expression of receptors involved in innate immune responses by adipocytes. Furthermore, we present data on the involvement of adipose tissue-specific molecules (adipokines) in the generation of an environment that is favorable for diseases with an immune cause and in some cases (leptin) directly contribute to the development of inflammatory bowel disease. Finally, we present evidence supporting a putative association between obesity and gut inflammation through the link of inflammation with angiogenesis and neovascularization and the favorable conditions created for these responses in obesity.

SUMMARY

We believe that obesity-related systemic changes may create conditions that predispose to the development of gut inflammation or even worsen the progression of ongoing disease.

Integrating the immune system with the regulation of growth and efficiency

Muscle growth in meat animals is a complex process governed by integrated signals emanating from multiple endocrine and immune cells. A generalized phenomenon among meat animal industries is that animals commonly fail to meet their genetic potential for growth in commercial production settings. Recent evidence indicates that adipocytes and myofibers are equipped with functional pattern recognition receptors and are capable of responding directly to the corresponding pathogens and other receptor ligands. Thus, these cells are active participants in the innate immune response and, as such, produce a number of immune and metabolic regulators, including proinflammatory cytokines and adiponectin. Specifically, the transcription factor, nuclear factor kappa B, is activated in adipocytes and muscle cells by bacterial lipopolysaccharide and certain saturated fatty acids, which are potent agonists for the Toll-like receptor-4 pattern recognition receptor. Receptor activation results in the local production of interleukin-6 and tumor necrosis factor-alpha, and creates a local environment by which these cytokines regulate both metabolic and immunological pathways. However, adipocytes are also the predominant source of the antiinflammatory hormone, adiponectin, which suppresses the activation of nuclear factor kappa B and the production of proinflammatory cytokines. The molecular ability to recognize antigens and produce regulatory molecules strategically positions adipocytes and myofibers to regulate growth locally and to reciprocally regulate metabolism in peripheral tissues.

Inhibitory effect of naringenin chalcone on inflammatory changes in the interaction between adipocytes and macrophages

Obese adipose tissue is characterized by an enhanced infiltration of macrophages. It is considered that the paracrine loop involving monocyte chemoattractant protein (MCP)-1 and tumor necrosis factor (TNF)-alpha between adipocytes and macrophages establishes a vicious cycle that augments the inflammatory changes and insulin resistance in obese adipose tissue. Polyphenols, which are widely distributed in fruit and vegetables, can act as antioxidants and some of them are also reported to have anti-inflammatory properties. Tomato is one of the most popular and extensively consumed vegetable crops worldwide, which also contains many flavonoids, mainly naringenin chalcone. We investigated the effect of flavonoids, including naringenin chalcone, on the production of proinflammatory mediators in lipopolysaccharide (LPS)-stimulated macrophages and in the interaction between adipocytes and macrophages. Naringenin chalcone inhibited the production of TNF-alpha, MCP-1, and nitric oxide (NO) by LPS-stimulated RAW 264 macrophages in a dose-dependent manner. Coculture of 3T3-L1 adipocytes and RAW 264 macrophages markedly enhanced the production of TNF-alpha, MCP-1, and NO compared with the control cultures; however, treatment with naringenin chalcone dose-dependently inhibited the production of these proinflammatory mediators. These results indicate that naringenin chalcone exhibits anti-inflammatory properties by inhibiting the production of proinflammatory cytokines in the interaction between adipocytes and macrophages. Naringenin chalcone may be useful for ameliorating the inflammatory changes in obese adipose tissue.

CD36 regulates fatty acid composition and sensitivity to insulin in 3T3-L1 adipocytes

In the current study, we tested a hypothesis that CD36 fatty acid (FA) transporter might affect insulin sensitivity by indirect effects on FA composition of adipose tissue. We examined the effects of CD36 downregulation by RNA interference in 3T3-L1 adipocytes on FA transport and composition and on sensitivity to insulin action. Transfected 3T3-L1 adipocytes, without detectable CD36 protein, showed reduced neutral lipid levels and significant differences in FA composition when levels of essential FA and their metabolites were lower or could not be detected including gamma linolenic (C18:3 n6), eicosadienic (C20:2 n6), dihomo-gamma linolenic (C20:3 n6), eicosapentaenoic (EPA) (C20:5 n3), docosapentaenoic (DPA) (C22:5 n3), and docosahexaenoic (DHA) (C22:6 n3) FA. Transfected 3T3-L1 adipocytes exhibited a significantly higher n6/n3 FA ratio, reduced 5-desaturase and higher 9-desaturase activities. These lipid profiles were associated with a significantly reduced insulin-stimulated glucose uptake (4.02+/-0.1 vs. 8.42+/-0.26 pmol.10(-3) cells, P=0.001). These findings provide evidence that CD36 regulates FA composition thereby affecting sensitivity to insulin action in 3T3-L1 adipocytes.

C-reactive protein inhibits adiponectin gene expression and secretion in 3T3-L1 adipocytes

C-reactive protein (CRP) is considered as one of the most sensitive markers of inflammation. The aim of the present study is to investigate the effects of CRP on the production of adiponectin in 3T3-L1 adipocytes. Northern and western blot analysis revealed that CRP treatment inhibited adiponectin mRNA expression and secretion in a dose- and time-dependent manner. Co-incubation of adipocytes with rosiglitazone and CRP decreased induction of adiponectin gene expression by rosiglitazone. However, luciferase reporter assays did not show that CRP affected the activity of approximately 2.1 kb adiponectin gene promoter, which was increased by rosiglitazone alone. Pharmacological inhibition of phosphatidylinositol (PI)-3 kinase by LY294002 partially reversed inhibition of adiponectin gene expression by CRP. These results collectively suggest that CRP suppresses adiponectin gene expression partially through the PI-3 kinase pathway, and that decreased production of adiponectin might represent a mechanism by which CRP regulates insulin sensitivity.

Acute and selective inhibition of adipocyte glyceroneogenesis and cytosolic phosphoenolpyruvate carboxykinase by interferon gamma

Interferon gamma (IFN-gamma) was previously shown to promote fatty acid (FA) release from adipose tissue (AT). Net lipolysis is an equilibrium between triglyceride breakdown and FA re-esterification. The latter requires activated glyceroneogenesis for glycerol-3-phosphate synthesis and increased cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C), the key enzyme in this pathway. We wondered whether glyceroneogenesis and PEPCK-C would be IFN-gamma targets. We injected mice with IFN-gamma, and exposed either AT explants and isolated adipocytes from humans and mice or 3T3-F442A adipocytes to IFN-gamma before monitoring expression of genes involved in lipid metabolism and the metabolic consequences. We show that IFN-gamma induces a large increase in FA release without affecting glycerol output and decreases [1-(14)C]-pyruvate incorporation into lipids, thus demonstrating that FA re-esterification is reduced due to diminished glyceroneogenesis. A series of mRNA encoding proteins involved in FA metabolism remained unaffected by IFN-gamma, while that of PEPCK-C was rapidly and drastically lowered. IFN-gamma effect opposed that of the beta-agonist isoproterenol and of 8-Br-cAMP. In IFN-gamma-treated mice, PEPCK-C gene expression was decreased in AT, but not in liver or kidney. Thus, IFN-gamma exerts a tissue-specific action in rodents and humans, having glyceroneogenesis and the PEPCK-C gene as selective targets to intensify FA release from adipocytes.