Isolation of Murine Adipose-Derived Stromal/Stem Cells for Adipogenic Differentiation or Flow Cytometry-Based Analysis

Murine models of obesity or reduced adiposity are a valuable resource for understanding the role of adipocyte dysfunction in metabolic disorders. Adipose tissue stromal vascular cells or primary adipocytes derived from murine adipose tissue and grown in culture are essential tools for studying the mechanisms underlying adipocyte development and function. Herein, we describe methods for the isolation, expansion, and long-term storage of murine adipose-derived stromal/stem cells along with protocols for inducing adipogenesis in this cell population or isolating the adipose stromal vascular fraction cells for flow cytometric analysis.

Catechin attenuates TNF-α induced inflammatory response via AMPK-SIRT1 pathway in 3T3-L1 adipocytes

Chronic inflammation is a fundamental symptom of many diseases. Catechin possesses anti-oxidant and anti-inflammatory properties. However, the mechanism of catechin to prevent inflammation in 3T3-L1 adipocytes caused by TNF-α remains unknown. Therefore, the effects of catechin on the gene expression of cytokines and the activation of cell signals in TNF-α induced 3T3-L1 adipocytes were investigated. The effects of catechin on adipogenesis and cell viability were detected by Oil Red O staining and CCK-8 assay, respectively. The genes expression of cytokines was determined by real-time RT-PCR. The expression of NF-κB, AMPK, FOXO3a and SIRT1 on translation level was determined by western blotting analysis. The results demonstrated that catechin significantly enhanced adipogenesis and cell viability. catechin inhibited the gene expression of pro-inflammatory cytokines including IL-1α, IL-1β, IL-6, IL-12p35, and inflammatory enzymes including iNOS and COX-2, but enhanced the gene expression of anti-inflammatory cytokines including IL-4 and IL-10. Catechin also inhibited the activation of NF-κB, AMPK, FOXO3a and SIRT1, but increased the phosphorylation level of the above factors. All these results indicated that as a potential therapeutic strategy catechin has the ability of attenuating inflammatory response triggered by TNF-α through signaling cascades involved in inflammation and cytokines.

Differential modulation of CXCL8 versus CXCL10, by cytokines, PPAR-gamma, or PPAR-alpha agonists, in primary cells from Graves' disease and ophthalmopathy

BACKGROUND

Thyrocytes secrete CXC chemokines, particularly (C-X-C motif) ligand (CXCL)8 and CXCL10; its physiopathological significance remains unclear. This study investigates the modulation of the secretion of CXCL8 vs. CXCL10, in human primary cells cultures of thyroid follicular cells (TFC) in Graves' disease (GD), and fibroblasts (OF) or preadipocytes (OP) from Graves' ophthalmopathy (GO).

METHODS

Cells were initially incubated with different concentrations of tumor necrosis factor (TNF)α (1, 5, 10 ng/mL). Then, CXCL8 and CXCL10 were measured in the supernatants of TFC, OF or OP cells basally and after 24 h of treatment with interferon (IFN)γ (1000 IU/mL) and/or TNFα (10 ng/mL), in presence/absence of the peroxisome proliferator activated receptor (PPAR)γ agonist pioglitazone (0, 0.1, 1, 5, 10, 20 μM), or the PPARα agonist fenofibrate (5, 10, 50, 100 μM).

RESULTS

CXCL8, not CXCL10, was detected in basal conditions in TFC, OF and OP. CXCL8 secretion increased dose-dependently with increasing concentrations of TNFα. CXCL10 secretion was significantly stimulated by IFNγ (P < 0.01) and not by TNFα, whereas CXCL8 was induced by TNFα (P < 0.01), and inhibited by IFNγ (P < 0.01) in TFC, OF and OP. Combining TNFα and IFNγ, the IFNγ-induced CXCL10 secretion was synergistically increased (P < 0.01) while the TNFα-induced CXCL8 secretion (P < 0.01) was reversed in all cell types. Pioglitazone had no significant effect on the secretion of CXCL8 stimulated by TNFα, while inhibited CXCL10. Fenofibrate, in presence of IFNγ plus TNFα, dose-dependently inhibited both CXCL10 and CXCL8 release.

CONCLUSION

We first show that TFC, OF, and OP secrete CXCL8 and CXCL10 differentially, sustained by specific proinflammatory cytokines or their combination. This could reflect a different role of the two chemokines in the course of the disease, as CXCL10 could be associated with the initial phase of the disease when IFNγ is preponderant, while CXCL8 could be associated with a later chronic phase of the disease, when TNFα prevails.

Adipose-on-a-chip: a dynamic microphysiological in vitro model of the human adipose for immune-metabolic analysis in type II diabetes

Infiltration of immune cells into adipose tissue is associated with chronic low-grade inflammation in obese individuals. To better understand the crosstalk between immune cells and adipocytes, in vivo-like in vitro models are required. Conventionally transwell culture plates are used for studying the adipocyte-immune cell interaction; however, the static culture nature of this approach falls short of closely recapitulating the physiological environment. Here we present a compartmentalized microfluidic co-culture system which provides a constant-rate of nutrient supply as well as waste removal, resembling the microvascular networks of the in vivo environment. Human adipocytes and U937 cells were co-cultured in close proximity in an enclosed system. The porous barrier between the adjacent compartments comprises an array of microchannels, which enables paracrine interaction between cells in adjacent compartments and improved perfusion-based long term cell feeding. Human pre-adipocytes were fully differentiated into adipocytes on the chip and remained viable for several weeks. Upon co-culturing with immune cells, adipocytes showed a tendency to develop insulin resistance. The immune-metabolic correlation has been studied by monitoring adiponectin and IL-6 expression, as well as glucose uptake upon treatment with insulin. Our microfluidic system can be potentially used to develop physiologically relevant adipose tissue models to study obesity-associated diseases such as insulin resistance and type 2 diabetes and therefore, facilitate drug development to treat these diseases.

Immunophenotyping of Human B Lymphocytes in Blood and in Adipose Tissue

The human obese subcutaneous adipose tissue (SAT) contributes to systemic and B cell intrinsic inflammation, reduced B cell responses, and increased secretion of autoimmune antibodies. Immune cells are recruited to the SAT by chemokines released by both adipocytes and infiltrating immune cells. We describe here the characterization of B lymphocytes from the SAT and blood (control) of obese females undergoing weight reduction surgeries (breast reduction or panniculectomy). We show how to isolate the immune cells from the blood and SAT, how to characterize B cells and their subsets, and how to measure markers of activation and/or transcription factors in SAT-derived B cells and B cell subsets. We also show how to evaluate other immune cell types infiltrating the SAT, including T cells, NK cells, monocyte/macrophages, in order to measure relative proportions of these cell types as compared to the blood.

A long-term maternal diet transition from high-fat diet to normal fat diet during pre-pregnancy avoids adipose tissue inflammation in next generation

Recent studies have suggested that maternal high-fat (HF) diet caused inflammation changes in adipose tissue; however, it remains unclear if maternal diet intervention before pregnancy rescues such effects in offspring. To address this question, female mice were continued on a normal-fat (NF group), or a HF diet (HF group) or transitioned from a HF diet to a NF diet at 1 (H1N group), 5 (H5N group) or 9 weeks (H9N group) prior to pregnancy. Among the three intervention groups, the H9N offspring displayed less and steady body weight gain, and maintained glucose tolerance, whereas the H1N and H5N offspring showed exacerbate these phenotypes. The H1N and H5N, but not the H9N offspring, displayed adipocyte hypertrophy associated with increased expression of genes involved in fat deposition. The H1N and H5N, but not the H9N adipose tissue, displayed increased macrophage infiltration with enhanced expression of inflammatory cytokine genes. In addition, overactivation of the NF-κB and the JNK signaling were observed in the H1N adipose tissue. Overall, our study showed that a long-term but not a short- or medium-term diet intervention before pregnancy released offspring adipose tissue inflammation induced by maternal HF diet, which adds details in our understanding how the maternal environment either promotes or discourages onset of disease in offspring. Clinically, this study is of great value for providing evidence in the design of clinical trials to evaluate the urgently required intervention strategies to minimize the intergenerational cycle of obesity.

Evaluation of anti-insulin receptor antibodies as potential novel therapies for human insulin receptoropathy using cell culture models

AIMS/HYPOTHESIS

Bi-allelic loss-of-function mutations in the INSR gene (encoding the insulin receptor [INSR]) commonly cause extreme insulin resistance and early mortality. Therapeutic options are limited, but anti-INSR antibodies have been shown to activate two mutant receptors, S323L and F382V. This study evaluates four well-characterised murine anti-INSR monoclonal antibodies recognising distinct epitopes (83-7, 83-14, 18-44, 18-146) as surrogate agonists for potential targeted treatment of severe insulin resistance arising from insulin receptoropathies.

METHODS

Ten naturally occurring mutant human INSRs with defects affecting different aspects of receptor function were modelled and assessed for response to insulin and anti-INSR antibodies. A novel 3T3-L1 adipocyte model of insulin receptoropathy was generated, permitting conditional knockdown of endogenous mouse Insr by lentiviral expression of species-specific short hairpin (sh)RNAs with simultaneous expression of human mutant INSR transgenes.

RESULTS

All expressed mutant INSR bound to all antibodies tested. Eight mutants showed antibody-induced autophosphorylation, while co-treatment with antibody and insulin increased maximal phosphorylation compared with insulin alone. After knockdown of mouse Insr and expression of mutant INSR in 3T3-L1 adipocytes, two antibodies (83-7 and 83-14) activated signalling via protein kinase B (Akt) preferentially over signalling via extracellular signal-regulated kinase 1/2 (ERK1/2) for seven mutants. These antibodies stimulated glucose uptake via P193L, S323L, F382V and D707A mutant INSRs, with antibody response greater than insulin response for D707A.

CONCLUSIONS/INTERPRETATION

Anti-INSR monoclonal antibodies can activate selected naturally occurring mutant human insulin receptors, bringing closer the prospect of novel therapy for severe insulin resistance caused by recessive mutations.

Allograft Inflammatory Factor-1 Mediates Macrophage-Induced Impairment of Insulin Signaling in Adipocytes

BACKGROUND/AIMS

Allograft inflammatory factor-1 (AIF-1) is an inflammatory cytokine produced mainly by macrophages within human white adipose tissue. Its expression is increased in obese subjects and positively correlated with insulin resistance. The purpose of this study is to characterize the regulatory role of AIF-1 in insulin signaling of adipocyte.

METHODS

AIF-1 was over-expressed via transfection of AIF-1 cDNA into murine RAW 264.7 macrophages, and the constitutive expression of AIF-1 was decreased via transfection of targeting siRNA. Murine 3T3L1 adipocytes were treated with macrophage-conditioned medium or AIF-1 protein. Intracellular lipid accumulation was assayed by oil red O stain. Reactive oxygen species production was determinated by a flow cytometer and adipokine secretion was measured with ELISA. Glucose uptake was detected using the glucose oxidase method and insulin-signal-transduction related molecules were analyzed by Western blot.

RESULTS

Short term (48 h) AIF-1 treatment slightly promoted intracellular lipid storage in differentiating 3T3L1 cells. The protein stimulated reactive oxygen species production, provoked TNFα, IL6, resistin, but suppressed adiponectin release and insulin-stimulated glucose uptake both under normal basal and insulin resistance conditions. Furthermore, AIF-1 induced NF-κB activation, inhibited PPARγ expression, GLUT4 translocation to plasma membrane and Akt phosphorylation.

CONCLUSION

Macrophage-derived AIF-1 up-regulated reactive oxygen species production, adipokine TNFα, IL6, resistin release, and inhibited adiponectin secretion. Moreover, it suppressed insulin-stimulated glucose uptake by down-regulating insulin signaling. Thus, AIF-1 could be related to obesity-related diseases.

Adipocytes affect castration-resistant prostate cancer cells to develop the resistance to cytotoxic action of NK cells with alterations of PD-L1/NKG2D ligand levels in tumor cells

BACKGROUND

Obesity affects prostate cancer (PCa) progression, and the periprostatic adipose tissue adjacent to the prostate is considered a driving force of disease progression. Adipocytes are the main cell population in adipose tissues and their paracrine role contributes to PCa progression, however its implication in modulating immune reactions remains largely unknown. We investigated the adipocyte role in controlling the susceptibility of castration-resistant PCa (CRPC) cells to the cytotoxic action of natural killer (NK) cells.

METHODS

Using primary NK cells as the NK cell source, NK cell cytotoxicities to CRPC cells, either control media treated or adipocyte-conditioned media (CM) treated, were tested in lactate dehydrogenase (LDH) release-based assays. The levels of programmed death receptor ligand (PD-L1) and NK group 2D (NKG2D) ligands in adipocyte CM-treated CRPC cells were analyzed in qPCR analyses. Effects of blocking adipocyte action on altering PD-L1/NKG2D ligand levels and the susceptibility of CRPC cells to NK cell cytotoxicity were investigated.

RESULTS

We found NK cell cytotoxicity to CRPC cells decreases when tumor cells are treated with adipocyte CM associated with PD-L1 and NKG2D ligand level alterations. Further, we discovered that the JAK/Stat3 signaling pathway was responsible for the adipocyte CM effect. Two adipokine molecules, IL-6 and leptin, were shown to be important in activation of the JAK/Stat3 signaling in CRPC cells to modulate the PD-L1/NKG2D ligand level alteration. Adding the inhibitors of JAK/Stat3 signaling or neutralizing antibodies of IL-6 or leptin increased the susceptibility of CRPC cells to NK cell action.

CONCLUSIONS

Blocking the adipocyte effect by inhibiting the IL-6/leptin-JAK/Stat3 signaling axis may enhance NK cell mediated immunity to CRPC cells and this strategy may help to develop future therapeutics to treat obese PCa patients.

Correlation study between osteoporosis and hematopoiesis in the context of adjuvant chemotherapy for breast cancer

This retrospective study attempts to establish if a correlation exists between osteoporosis and hematopoiesis before and after adjuvant chemotherapy in the context of non-metastatic breast cancer. Osteoporosis is interpreted both as a direct marker of osteoblastic decline and as an indirect marker of increased bone marrow adiposity within the hematopoietic microenvironment. Patients from the “Centre du Sein” at CHUV (Centre Hospitalier Universitaire Vaudois) undergoing adjuvant chemotherapy were included in this study. Evolution of blood counts was studied in correlation with the osteoporosis status. Toxicity of chemotherapy was coded according to published probability of febrile neutropenia. One hundred forty-three women were included: mean age 52.1 ± 12.5 years, mean BMI (body mass index) 24.4 ± 4.1. BMD (bone mineral density) scored osteoporotic in 32% and osteopenic in 45%. Prior to chemotherapy, BMD was positively correlated with neutrophil (p < 0.001) and thrombocyte (p = 0.01) count; TBS (trabecular bone score) was not correlated with blood count. After the first cycle of chemotherapy, an increase of one point in TBS correlated with a decrease of 57% on the time to reach leucocyte nadir (p = 0.004). There was a positive correlation between BMD and risk of infection (p < 0.001). Our data demonstrates an association between osteoporosis and lower blood counts in a younger cohort than previously published, extending it for the first time to neutrophil counts in females. Our results suggest that the healthier the bone, the earlier the lowest leucocyte count value, prompting further research on this area.

Adapting to obesity with adipose tissue inflammation

Adipose tissue not only has an important role in the storage of excess nutrients but also senses nutrient status and regulates energy mobilization. An overall positive energy balance is associated with overnutrition and leads to excessive accumulation of fat in adipocytes. These cells respond by initiating an inflammatory response that, although maladaptive in the long run, might initially be a physiological response to the stresses obesity places on adipose tissue. In this Review, we characterize adipose tissue inflammation and review the current knowledge of what triggers obesity-associated inflammation in adipose tissue. We examine the connection between adipose tissue inflammation and the development of insulin resistance and catecholamine resistance and discuss the ensuing state of metabolic inflexibility. Finally, we review the current and potential new anti-inflammatory treatments for obesity-associated metabolic disease.

Endogenous lipid antigens for invariant natural killer T cells hold the reins in adipose tissue homeostasis

The global obesity epidemic and its associated co-morbidities, including type 2 diabetes, cardiovascular disease and certain types of cancers, have drawn attention to the pivotal role of adipocytes in health and disease. Besides their 'classical' function in energy storage and release, adipocytes interact with adipose-tissue-resident immune cells, among which are lipid-responsive invariant natural killer T (iNKT) cells. The iNKT cells are activated by lipid antigens presented by antigen-presenting cells as CD1d/lipid complexes. Upon activation, iNKT cells can rapidly secrete soluble mediators that either promote or oppose inflammation. In lean adipose tissue, iNKT cells elicit a predominantly anti-inflammatory immune response, whereas obesity is associated with declining iNKT cell numbers. Recent work showed that adipocytes act as non-professional antigen-presenting cells for lipid antigens. Here, we discuss endogenous lipid antigen processing and presentation by adipocytes, and speculate on how these lipid antigens, together with 'environmental factors' such as tissue/organ environment and co-stimulatory signals, are able to influence the fate of adipose-tissue-resident iNKT cells, and thereby the role of these cells in obesity and its associated pathologies.

A role for PFKFB3/iPFK2 in metformin suppression of adipocyte inflammatory responses

Metformin improves obesity-associated metabolic dysregulation, but has controversial effects on adipose tissue inflammation. The objective of the study is to examine the direct effect of metformin on adipocyte inflammatory responses and elucidate the underlying mechanisms. Adipocytes were differentiated from 3T3-L1 cells and treated with metformin at various doses and for different time periods. The treated cells were examined for the proinflammatory responses, as well as the phosphorylation states of AMPK and the expression of PFKFB3/iPFK2. In addition, PFKFB3/iPFK2-knockdown adipocytes were treated with metformin and examined for changes in the proinflammatory responses. The following results were obtained from the study. Treatment of adipocytes with metformin decreased the effects of lipopolysaccharide on inducing the phosphorylation states of JNK p46 and on increasing the mRNA levels of IL-1β and TNFα. In addition, treatment with metformin increased the expression of PFKFB3/iPFK2, but failed to significantly alter the phosphorylation states of AMPK. In PFKFB3/iPFK2-knockdown adipocytes, treatment with metformin did not suppress the proinflammatory responses as did it in control adipocytes. In conclusion, metformin has a direct effect on suppressing adipocyte proinflammatory responses in an AMPK-independent manner. Also, metformin increases adipocyte expression of PFKFB3/iPFK2, which is involved in the anti-inflammatory effect of metformin.

Immunological Functions of the Omentum

The omentum is a visceral adipose tissue with unique immune functions. Although it is primarily an adipose tissue, the omentum also contains lymphoid aggregates, called milky spots (MSs), that contribute to peritoneal immunity by collecting antigens, particulates, and pathogens from the peritoneal cavity and, depending on the stimuli, promoting a variety of immune responses, including inflammation, tolerance, or even fibrosis. Reciprocal interactions between cells in the MS and adipocytes regulate their immune and metabolic functions. Importantly, the omentum collects metastasizing tumor cells and supports tumor growth by immunological and metabolic mechanisms. Here we summarize our current knowledge about the development, organization, and function of the omentum in peritoneal immunity.

CREG1 heterozygous mice are susceptible to high fat diet-induced obesity and insulin resistance

Cellular repressor of E1A-stimulated genes 1 (CREG1) is a small glycoprotein whose physiological function is unknown. In cell culture studies, CREG1 promotes cellular differentiation and maturation. To elucidate its physiological functions, we deleted the Creg1 gene in mice and found that loss of CREG1 leads to early embryonic death, suggesting that it is essential for early development. In the analysis of Creg1 heterozygous mice, we unexpectedly observed that they developed obesity as they get older. In this study, we further studied this phenotype by feeding wild type (WT) and Creg1 heterozygote (Creg1^+/-) mice a high fat diet (HFD) for 16 weeks. Our data showed that Creg1^+/- mice exhibited a more prominent obesity phenotype with no change in food intake compared with WT controls when challenged with HFD. Creg1 haploinsufficiency also exacerbated HFD-induced liver steatosis, dyslipidemia and insulin resistance. In addition, HFD markedly increased pro-inflammatory cytokines in plasma and epididymal adipose tissue in Creg1^+/- mice as compared with WT controls. The activation level of NF-κB, a major regulator of inflammatory response, in epididymal adipose tissue was also elevated in parallel with the cytokines in Creg1^+/- mice. These pro-inflammatory responses elicited by CREG1 reduction were confirmed in 3T3-L1-derived adipocytes with CREG1 depletion by siRNA transfection. Given that adipose tissue inflammation has been shown to play a key role in obesity-induced insulin resistance and metabolic syndrome, our results suggest that Creg1 haploinsufficiency confers increased susceptibility of adipose tissue to inflammation, leading to aggravated obesity and insulin resistance when challenged with HFD. This study uncovered a novel function of CREG1 in metabolic disorders.

Deletion of CD1d in Adipocytes Aggravates Adipose Tissue Inflammation and Insulin Resistance in Obesity

Adipose tissue inflammation is an important factor in obesity that promotes insulin resistance. Among various cell types in adipose tissue, immune cells actively regulate inflammatory responses and affect whole-body energy metabolism. In particular, invariant natural killer T (iNKT) cells contribute to mitigating dysregulation of systemic energy homeostasis by counteracting obesity-induced inflammation in adipose tissue. However, the molecular mechanisms by which adipose iNKT cells become activated and mediate anti-inflammatory roles in obese adipose tissue have not been thoroughly understood yet. In the current study, we demonstrate that adipocyte CD1d plays a key role in the stimulation of adipose iNKT cells, leading to anti-inflammatory responses in high-fat diet (HFD)-fed mice. Accordingly, adipocyte-specific CD1d-knockout (CD1d^ADKO) mice showed reduced numbers of iNKT cells in adipose tissues and decreased responses to α-galactosylceramide-induced iNKT cell activation. Additionally, HFD-fed CD1d^ADKO mice revealed reduced interleukin-4 expression in adipose iNKT cells and aggravated adipose tissue inflammation and insulin resistance. Collectively, these data suggest that adipocytes could selectively stimulate adipose iNKT cells to mediate anti-inflammatory responses and attenuate excess proinflammatory responses in obese adipose tissue.

Adipose Tissue-Specialized Immunologic Features Might Be the Potential Therapeutic Target of Prospective Medicines for Obesity

Excessive lipid accumulation in adipose tissue is either the source of obesity or the cause and result of chronic local inflammation, and recent studies indicate that the accumulation may induce many other specialized immunologic features with macrophages and epidemic diseases. We analyze the effective stages of immune cells in adipose tissue, including macrophage recruitment, macrophage polarization, and macrophage-like phenotype preadipocyte possession to find optimal sites as drug targets. Subsequently, some main signaling pathways are summarized in this review, including the AMP-activated protein kinase (AMPK) pathway, the JNK signaling pathway, and a novel one, the Notch signaling pathway. We illustrate all these points in order to determine the general pathogenesis of chronic low-grade local inflammation in adipose tissue and the related signaling pathways. In addition, signal-associated prospective compounds, such as berberine, are summarized and discussed with potential targets in pathogenesis. This might provide some possible thoughts and novel therapies for studying chronic inflammatory diseases, such as insulin resistance and type 2 diabetes mellitus.

Riboflavin Reduces Pro-Inflammatory Activation of Adipocyte-Macrophage Co-culture. Potential Application of Vitamin B2 Enrichment for Attenuation of Insulin Resistance and Metabolic Syndrome Development

Due to the progressive increase in the incidence of obese and overweight individuals, cardiometabolic syndrome has become a worldwide pandemic in recent years. Given the immunomodulatory properties of riboflavin, the current study was performed to investigate the potency of riboflavin in reducing obesity-related inflammation, which is the main cause of insulin resistance, diabetes mellitus 2 or arteriosclerosis. We determined whether pretreatment with a low dose of riboflavin (10.4–1000 nM) affected the pro-inflammatory activity of adipocyte-macrophage co-culture (3T3 L1-RAW 264.7) following lipopolysaccharide stimulation (LPS; 100 ng/mL) which mimics obesity-related inflammation. The apoptosis of adipocytes and macrophages as well as tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), interleukin 1beta (IL-1β), monocyte chemotactic protein 1 (MCP-1), high-mobility group box 1 (HMGB1), transforming growth factor–beta 1 (TGFβ), interleukin 10 (IL-10), inducible nitric oxide synthase (iNOS), nitric oxide (NO), matrix metalloproteinase 9 (MMP-9), tissue inhibitor of metalloproteinases-1 (TIMP-1) expression and release, macrophage migration and adipokines (adiponectin and leptin) were determined. Our results indicated an efficient reduction in pro-inflammatory factors (TNFα, IL-6, MCP-1, HMGB1) upon culture with riboflavin supplementation (500–1000 nM), accompanied by elevation in anti-inflammatory adiponectin and IL-10. Moreover, macrophage migration was reduced by the attenuation of chemotactic MCP-1 release and degradation of the extracellular matrix by MMP-9. In conclusion, riboflavin effectively inhibits the pro-inflammatory activity of adipocyte and macrophage co-cultures, and therefore we can assume that its supplementation may reduce the likelihood of conditions associated with the mild inflammation linked to obesity.

Inhibitory Effect of Methyl 2-(4'-Methoxy-4'-oxobutanamide) Benzoate from Jerusalem Artichoke (Helianthus tuberosus) on the Inflammatory Paracrine Loop between Macrophages and Adipocytes

The interaction between macrophages and adipocytes is known to aggravate inflammation of the adipose tissue, leading to decreased insulin sensitivity. Hence, attenuation of the inflammatory paracrine loop between macrophages and adipocytes is deemed essential to ameliorate insulin resistance and diabetes mellitus type 2. Methyl 2-(4'-methoxy-4'-oxobutanamide) benzoate (compound 1), a newly isolated compound from Jerusalem srtichoke (JA), has not been biologically characterized yet. Here, we investigated whether JA-derived compound 1 attenuates the inflammatory cycle between RAW 264.7 macrophages and 3T3-L1 adipocytes. Compound 1 suppressed the inflammatory response of RAW 264.7 cells to lipopolysaccharide through decreased secretion of IL-1β, IL-6, and TNF-α. Moreover, the mRNA expression of TNF-α, IL-6, IL-1β, MCP-1, and Rantes and MAPK pathway activation in 3T3-L1 adipocytes, incubated in macrophage-conditioned media, were inhibited. These findings suggest an anti-inflammatory effect of a newly extracted compound against adipose tissue inflammation and insulin resistance.

Increased Interleukin-32 Levels in Obesity Promote Adipose Tissue Inflammation and Extracellular Matrix Remodeling: Effect of Weight Loss

Interleukin (IL)-32 is a recently described cytokine involved in the regulation of inflammation. We aimed to explore whether IL-32 could function as an inflammatory and angiogenic factor in human obesity and obesity-associated type 2 diabetes. Samples obtained from 90 subjects were used in the study. Obese patients exhibited higher expression levels of IL-32 in visceral adipose tissue (AT) as well as in subcutaneous AT and peripheral blood mononuclear cells. IL32 was mainly expressed by stromovascular fraction cells, and its expression was significantly enhanced by inflammatory stimuli and hypoxia, whereas no changes were found after the incubation with anti-inflammatory cytokines. The addition of exogenous IL-32 induced the expression of inflammation and extracellular matrix-related genes in human adipocyte cultures, and IL32-silenced adipocytes showed a downregulation of inflammatory genes. Furthermore, adipocyte-conditioned media obtained from obese patients increased IL32 gene expression in human monocyte cultures, whereas the adipocyte-conditioned media from lean volunteers had no effect on IL32 mRNA levels. These findings provide evidence, for the first time, about the inflammatory and remodeling properties of IL-32 in AT, implicating this cytokine in obesity-associated comorbidities.

Thiazolidinedione (Pioglitazone) Blocks P. gingivalis- and F. nucleatum, but not E. coli, Lipopolysaccharide (LPS)-induced Interleukin-6 (IL-6) Production in Adipocytes

An elevated level of C-reactive protein (CRP) predicts the future development of coronary heart disease. Periodontitis appears to up-regulate CRP. CRP is produced by hepatocytes in response to interleukin-6 (IL-6). A major source of IL-6 in obese subjects is adipocytes. We hypothesized that lipopolysaccharide (LPS) from periodontal pathogens stimulated adipocytes to produce IL-6, and that the production was suppressed by the drugs targeted against insulin resistance, thiazolidinedione (pioglitazone), since this agent potentially showed an anti-inflammatory effect. Mouse 3T3-L1 adipocytes were stimulated with E. coli, P. gingivalis, and F. nucleatum LPS. The IL-6 concentration in culture supernatants was measured. All LPS stimulated adipocytes to produce IL-6. Although pioglitazone changed adipocyte appearance from large to small, and completely suppressed P. gingivalis and F. nucleatum LPS-induced IL-6 production, E. coli LPS-induced IL-6 production was not efficiently blocked. Thus, pioglitazone completely blocked periodontal-bacteria-derived LPS-induced IL-6 production in adipocytes, a major inducer of CRP.

Caspase-1 deficiency promotes high-fat diet-induced adipose tissue inflammation and the development of obesity

Caspase-1 is a cysteine protease responsible for the processing of the proinflammatory cytokine interleukin-1β and activated by the formation of inflammasome complexes. Although several investigations have found a link between diet-induced obesity and caspase-1, the relationship remains controversial. Here, we found that mice deficient in caspase-1 were susceptible to high-fat diet-induced obesity with increased adiposity as well as normal lipid and glucose metabolism. Caspase-1 deficiency clearly promoted the infiltration of inflammatory macrophages and increased the production of C-C motif chemokine ligand 2 (CCL2) in the adipose tissue. The dominant cellular source of CCL2 was stromal vascular fraction rather than adipocytes in the adipose tissue. These findings demonstrate a critical role of caspase-1 in macrophage-driven inflammation in the adipose tissue and the development of obesity. These data provide novel insights into the mechanisms underlying inflammation in the pathophysiology of obesity.

IL-17A synergistically enhances TNFα-induced IL-6 and CCL20 production in 3T3-L1 adipocytes

Interleukin-17A (IL-17A) is known to induce inflammatory responses and to be involved in the pathogenesis of not only autoimmune diseases, but also several metabolic and infectious diseases. In this study, IL-17A is shown to induce IL-6 expression in 3T3-L1 mature adipocytes. Interestingly, we found that IL-17A synergistically amplified TNFα-induced secretion of IL-6 and upregulation of IL-17RA expression in 3T3-L1 adipocytes. Its synergistic effects on IL-6 production were inhibited by pre-treatment with inhibitors of IκBα and JNK. Furthermore, IL-17A cooperatively enhanced LPS-mediated IL-6 production in 3T3-L1 adipocytes co-cultured with RAW264.7 macrophages. In addition, IL-17A also enhanced CCL20 production in 3T3-L1 adipocytes stimulated with TNFα or co-cultured with LPS-stimulated RAW macrophages. In high-fat diet-fed mouse epididymal adipose tissues, IL-17RA and RORγt mRNA levels were significantly increased and the serum level of CCL20 was also upregulated. Taken together, these data show that, in adipose tissues, IL-17A contributes to exacerbating insulin resistance-enhancing IL-6 production and promotes the infiltration of Th17 cells in cooperation with TNFα; these findings represent a novel hypothesis for the association between IL-17A-producing cells and type 2 diabetes.

Pro-inflammatory Macrophages suppress PPARγ activity in Adipocytes via S-nitrosylation

Peroxisome proliferator-activated receptor-γ (PPARγ) is a ligand-activated nuclear receptor and plays an essential role in insulin signaling. Macrophage infiltration into adipose tissue is a character of metabolic inflammation and closely related to insulin resistance in type 2 diabetes. The mechanism by which pro-inflammatory macrophages cause insulin resistance remains to be elucidated. Here we showed that co-culture with macrophages significantly suppressed the transcriptional activity of PPARγ on its target genes in 3T3-L1 preadipocytes and diabetic primary adipocytes, depending on inducible nitric oxide synthase (iNOS). We further showed that PPARγ underwent S-nitrosylation in response to nitrosative stress. Mass-spectrometry and site-directed mutagenesis revealed that S-nitrosylation at cysteine 168 was responsible for the impairment of PPARγ function. Extended exposure to NO instigated the proteasome-dependent degradation of PPARγ. Consistently, in vivo evidence revealed an association of the decreased PPARγ protein level with increased macrophage infiltration in visceral adipose tissue (VAT) of obese diabetic db/db mice. Together, our results demonstrated that pro-inflammatory macrophages suppressed PPARγ activity in adipocytes via S-nitrosylation, suggesting a novel mechanism linking metabolic inflammation with insulin resistance.