In obesity and weight loss, all roads lead to the mighty macrophage

Two-Pronged Attack: Dual Activation of Fat Reduction Using Near-Infrared-Responsive Nanosandwich for Targeted Anti-Obesity Treatment

Excessive fat accumulation and chronic inflammation are two typical characteristics of obesity. AMP-activated protein kinase (AMPK), a master regulator of energy metabolism, is involved in adipogenesis, lipogenesis, and inflammation modulation in adipose tissue (AT). Thus, effective lipid reduction and anti-inflammation through AMPK regulation play vital roles in treating obesity. Herein, an anti-obesity nanosandwich is fabricated through attaching polymetformin (PolyMet) onto photothermal agent black phosphorus nanosheets (BP). PolyMet activates AMPK to inhibit adipogenesis, promote browning, and mitigate AT inflammation by decreasing macrophage infiltration, repolarizing macrophage phenotype, and downregulating pro-inflammatory cytokines. Additionally, BP induces lipolysis and apoptosis of adipocytes and macrophages through a photothermal effect. By further functionalization using hyaluronic acid (HA) and MMP2 substrate-linking P3 peptide-modified HA (P3-HA), an enhanced anti-obesity effect is obtained by dual-targeting of P3 and HA, and HA-mediated CD44 poly-clustering after MMP2 cleavage. Upon laser irradiation, the designed nanosandwich (P3-HA/PM@BP) effectively inhibits obesity development in obese mice, increases M2/M1 ratio in AT, reduces the serum levels of cholesterol/triglyceride and improves insulin sensitivity, exhibiting promising research potential to facilitate the clinical development of modern anti-obesity therapies.

An anti-inflammatory phenotype in visceral adipose tissue of old lean mice, augmented by exercise

Visceral adipose tissue is an immunogenic tissue, which turns detrimental during obesity by activation of proinflammatory macrophages. During aging, chronic inflammation increases proportional to visceral adipose tissue (VAT) mass and associates with escalating morbidity and mortality. Here, we utilize a mouse model to investigate the inflammatory status of visceral adipose tissue in lean aging mice and assess the effects of exercise training interventions. We randomized adult (11 months; n = 21) and old (23 months; n = 27) mice to resistance training (RT) or endurance training (ET), or to a sedentary control group (S). Strikingly, we observed an anti-inflammatory phenotype in the old mice, consisting of higher accumulation of M2 macrophages and IL-10 expression, compared to the adult mice. In concordance, old mice also had less VAT mass and smaller adipocytes compared to adult mice. In both age groups, exercise training enhanced the anti-inflammatory phenotype and increased PGC1-α mRNA expression. Intriguingly, the brown adipose tissue marker UCP1 was modestly higher in old mice, while remained unchanged by the intervention. In conclusion, in the absence of obesity, visceral adipose tissue possesses a pronounced anti-inflammatory phenotype during aging which is further enhanced by exercise.

Serum leptin levels correlate negatively with the capacity of vitamin D to modulate the in vitro cytokines production by CD4+ T cells in asthmatic patients

Both obesity and low vitamin D levels have been associated with allergic asthma (AA) severity. In the present study, severity of AA was associated with obesity but to the in vitro IgE production. In those patients, higher levels of IL-5, IL-6 and IL-17 were quantified in CD4⁺ T-cell cultures as compared with patients with mild and moderate AA. In addition, the lowest IL-10 levels were detected in the cell cultures from patients with a worse prognosis. Interestingly, the occurrence of AA elevates the plasma levels of leptin, and this adipokine was positively correlated with the release of IL-5, IL-6 and IL-17, but inversely correlated with IL-10 production, by CD4⁺ T-cells from patients. In AA-derived CD4⁺ T-cell cultures, 1,25(OH)2D3 was less efficient at inhibiting IL-5, IL-6 and IL-17 production, and up regulating IL-10 release, as those from healthy subjects. Interestingly, the in vitro immunomodulatory effects of vitamin D were inversely correlated with serum leptin levels. In summary, our findings suggested that obesity, probably due to the overproduction of leptin, negatively impacts AA as it favors imbalance between Th2/Th17 and regulatory phenotypes. The deleterious effects of leptin may also be due to its ability to counter-regulate the immunosuppressive effects of vitamin D.

Cannabinoid Receptor 1 Blockade Attenuates Obesity and Adipose Tissue Type 1 Inflammation Through miR-30e-5p Regulation of Delta-Like-4 in Macrophages and Consequently Downregulation of Th1 Cells

Obesity is characterized by chronic low-grade inflammation that contributes to development of cardiometabolic disorders. Cannabinoid receptor 1 (CB1) antagonists attenuate diet-induced obesity (DIO) and related inflammation, although the precise anti-inflammatory mechanisms involved have not been fully explored. In the current study we used a mouse model of DIO intervention to determine the microRNA (miRNA, miR)-mediated anti-obesity and anti-inflammatory effects of the CB1 antagonist, AM251. DIO mice that were fed high-fat diet (HFD) for 12 weeks were treated with AM251 (10 mg/kg) for an additional 4 weeks. HFD + AM251 mice experienced rapid and prolonged weight loss and reduced inflammatory M1 adipose tissue macrophage (ATM) infiltration. To investigate miRNA-mediated regulation of ATMs, F4/80+ cells from stromal vascular fractions (SVF) of epididymal fat were subjected to miR microarray analysis. Several miRs were differentially expressed in AM251-treated mice that were independent of calorie restriction. Prominently, miR-30e-5p was upregulated in ATMs from HFD + AM251 mice while the miR-30e-5p target, DLL4, was downregulated. Consistent with a decrease in DLL4-Notch signaling, fat storage and pro-inflammatory cytokine/chemokine expression was reduced following AM251 treatment. Furthermore, we found that AM251-treated macrophages can suppress DLL4-mediated Th1 polarization in CD4+ T cells. Together these data demonstrate that blocking CB1 receptors leads to upregulation of miR-30e-5p and down regulation of DLL4 in ATMs, which in turn suppress DLL4-Notch signaling-induced polarization of inflammatory Th1 cells and adipocyte energy storage. This combined effect of ATMs and T cells leads to an anti-inflammatory state and attenuation of DIO. These data support therapeutic potential of miR-30 in the treatment of cardiometabolic disorders.

Infrequent Feeding of Restricted Amounts of Food Induces Stress and Adipose Tissue Inflammation, Contributing to Impaired Glucose Metabolism

Food restriction has been recommended as an effective strategy for body weight loss. However, food restriction can alter biological rhythms and leads to physiological stress. However, relatively little is known about the physiological impact of different methods of food restriction. Therefore, we investigated whether different schedules of restricted food intake induce physiological stress and then contribute to glucose metabolism disorder. C57BL/6 mice were fed a high fat diet (60% fat) for 8 weeks and then randomly divided into three groups: the control group was continuously fed the high fat diet; the two food restriction groups were fed 50% of food consumed by the control mice with one group (FR1) being fed the full amount once a day and the other group (FR2) being fed the same total amount as FR1 twice a day for 3 days. We found increased body weight loss, the serum triglyceride levels, the expression of lipolysis-related genes, and serum corticosterone levels in the FR1 group compared with the FR2 group. The immune cell population infiltrating the adipose tissue and the expression of monocyte chemoattractant protein (MCP-1) and toll-like receptor (TLR-4) mRNA were increased in the FR1 group compared with the control. To determine whether long-term dietary manipulation is associated with metabolic disorders, mice were fed a restricted diet for 3 days alternating with an unrestricted diet for the following 4 days and this was repeated for 8 weeks. The alternating FR1 group showed impaired glucose tolerance compared with the alternating FR2 group. These results indicate that infrequent feeding of restricted amounts of food could induce stress hormones, lipolysis, adipose tissue immune cell infiltration and inflammation, which in turn may promote glucose metabolism disorder.

Role of innate lymphoid cells in obesity and metabolic disease (Review)

The immune system has previously been demonstrated to be associated with the pathophysiological development of metabolic abnormalities. However, the mechanisms linking immunity to metabolic disease remain to be fully elucidated. It has previously been suggested that innate lymphoid cells (ILCs) may be involved in the progression of numerous types of metabolic diseases as these cells act as suppressors and promoters for obesity and associated conditions, and are particularly involved in adipose tissue inflammation, which is a major feature of metabolic imbalance. Group 2 ILCs (ILC2s) have been revealed as anti‑obese immune regulators by secreting anti‑inflammatory cytokines and promoting the polarization of M2 macrophages, whereas group 1 ILCs (ILC1s), including natural killer cells, may promote adipose tissue inflammation via production of interferon‑γ, which in turn polarizes macrophages toward the M1 type. The majority of studies to date have demonstrated the pathological association between ILCs and obesity in the context of adipose tissue inflammation, whereas the roles of ILCs in other organs which participate in obesity development have not been fully characterized. Therefore, identifying the roles of all types of ILCs as central components mediating obesity‑associated inflammation, is of primary concern, and may lead to the discovery of novel preventative and therapeutic interventions.

Therapeutic silencing of fat-specific protein 27 improves glycemic control in mouse models of obesity and insulin resistance

Obesity is a component of the metabolic syndrome, mechanistically linked to diabetes, fatty liver disease, and cardiovascular disease. Proteins that regulate the metabolic fate of intracellular lipid droplets are potential therapeutic candidates to treat obesity and its related consequences. CIDEC (cell death-inducing DFFA-like effector C), also known in mice as Fsp27 (fat-specific protein 27), is a lipid droplet-associated protein that prevents lipid mobilization and promotes intracellular lipid storage. The consequences of complete loss of FSP27 on hepatic metabolism and on insulin resistance are controversial, as both healthy and deleterious lipodystrophic phenotypes have been reported in Fsp27^−/− mice. To test whether therapeutic silencing of Fsp27 might be useful to improve obesity, fatty liver, and glycemic control, we used antisense oligonucleotides (ASOs) in both nutritional (high-fat diet) and genetic (leptin-deficient ob/ob) mouse models of obesity, hyperglycemia, and hepatosteatosis. We show that partial silencing Fsp27 in either model results in the robust decrease in visceral fat, improved insulin sensitivity and whole-body glycemic control, and tissue-specific changes in transcripts controlling lipid oxidation and synthesis. These data suggest that partial reduction of FSP27 activity (e.g., using ASOs) might be exploited therapeutically in insulin-resistant obese or overweight patients.

Isolated exopolysaccharides from Lactobacillus rhamnosus GG alleviated adipogenesis mediated by TLR2 in mice

The fibroblast cell line of 3T3-L1 was used as a cell model for screening and evaluating the feasibility of probiotic components in improving animal lipid metabolisms. The extracts from 12 Lactobacillus strains caused significantly reduced triacylglycerol (TAG) accumulation but with severe inflammation induction in 3T3-L1 adipocytes. Interestingly, exopolysaccharides (EPS) from LGG (Lactobacillus rhamnosus GG) significantly decreased the TAG accumulation without any inflammation. The anti-obesity effect of EPS was confirmed in high-fat-diets feeding mice. Fat pads of mice injected with EPS (50 mg/kg) every two days for two weeks were significantly reduced with much smaller adipocytes, compared with the counterparts. The levels of TAG and cholesterol ester in liver, as well as serum TAG, were decreased in EPS injected mice. In addition, down-regulated inflammation was observed in adipose tissue and liver. Interestingly, the expression of TLR2 in adipose tissue and 3T3-L1 cells was significantly increased by EPS addition. Moreover, the reverse of TAG accumulation in TLR2 knockdown 3T3-L1 in the presence of EPS confirmed that the inhibition effect of EPS on adipogenesis was mediated by TLR2. EPS from LGG has the potential for therapeutic development to intervene lipid metabolic disorders in mammals.

Major role of adipocyte prostaglandin E2 in lipolysis-induced macrophage recruitment

Obesity induces accumulation of adipose tissue macrophages (ATMs), which contribute to both local and systemic inflammation and modulate insulin sensitivity. Adipocyte lipolysis during fasting and weight loss also leads to ATM accumulation, but without proinflammatory activation suggesting distinct mechanisms of ATM recruitment. We examined the possibility that specific lipid mediators with anti-inflammatory properties are released from adipocytes undergoing lipolysis to induce macrophage migration. In the present study, we showed that conditioned medium (CM) from adipocytes treated with forskolin to stimulate lipolysis can induce migration of RAW 264.7 macrophages. In addition to FFAs, lipolytic stimulation increased release of prostaglandin E2(PGE2) and prostaglandin D2(PGD2), reflecting cytosolic phospholipase A2α activation and enhanced cyclooxygenase (COX) 2 expression. Reconstituted medium with the anti-inflammatory PGE2potently induced macrophage migration while different FFAs and PGD2had modest effects. The ability of CM to induce macrophage migration was abolished by treating adipocytes with the COX2 inhibitor sc236 or by treating macrophages with the prostaglandin E receptor 4 antagonist AH23848. In fasted mice, macrophage accumulation in adipose tissue coincided with increases of PGE2levels and COX1 expression. Collectively, our data show that adipocyte-originated PGE2with inflammation suppressive properties plays a significant role in mediating ATM accumulation during lipolysis.

The complex immunological and inflammatory network of adipose tissue in obesity

A number of approaches have been utilized in the prevention, management, and treatment of obesity, including, surgery, medication, diet, exercise, and overall lifestyle changes. Despite these interventions, the prevalence of obesity and the various disorders related to it is growing. In obesity, there is a constant state of chronic low-grade inflammation which is characterized by activation and infiltration of pro-inflammatory immune cells and a dysregulated production of high levels of pro-inflammatory cytokines. This pro-inflammatory milieu contributes to insulin resistance, type-2 diabetes, cardiovascular disease, and other related co-morbidities. The roles of the innate (macrophages, neutrophils, eosinophils, mast cells, NK cells, MAIT cells) and the adaptive (CD4 T cells, CD8 T cells, regulatory T cells, and B cells) immune responses and the roles of adipokines and cytokines in adipose tissue inflammation and obesity are discussed. An understanding of the crosstalk between the immune system and adipocytes may shed light in better treatment modalities for obesity and obesity-related diseases.

Transcriptional profiling of rat white adipose tissue response to 2,3,7,8-tetrachlorodibenzo-ρ-dioxin

Polychlorinated dibenzodioxins are environmental contaminants commonly produced as a by-product of industrial processes. The most potent of these, 2,3,7,8-tetrachlorodibenzo-ρ-dioxin (TCDD), is highly lipophilic, leading to bioaccumulation. White adipose tissue (WAT) is a major site for energy storage, and is one of the organs in which TCDD accumulates. In laboratory animals, exposure to TCDD causes numerous metabolic abnormalities, including a wasting syndrome. We therefore investigated the molecular effects of TCDD exposure on WAT by profiling the transcriptomic response of WAT to 100μg/kg of TCDD at 1 or 4days in TCDD-sensitive Long-Evans (Turku/AB; L-E) rats. A comparative analysis was conducted simultaneously in identically treated TCDD-resistant Han/Wistar (Kuopio; H/W) rats one day after exposure to the same dose. We sought to identify transcriptomic changes coinciding with the onset of toxicity, while gaining additional insight into later responses. More transcriptional responses to TCDD were observed at 4days than at 1day post-exposure, suggesting WAT shows mostly secondary responses. Two classic AHR-regulated genes, Cyp1a1 and Nqo1, were significantly induced by TCDD in both strains, while several genes involved in the immune response, including Ms4a7 and F13a1 were altered in L-E rats alone. We compared genes affected by TCDD in rat WAT and human adipose cells, and observed little overlap. Interestingly, very few genes involved in lipid metabolism exhibited altered expression levels despite the pronounced lipid mobilization from peripheral fat pads by TCDD in L-E rats. Of these genes, the lipolysis-associated Lpin1 was induced slightly over 2-fold in L-E rat WAT on day 4.

Nutrient and immune sensing are obligate pathways in metabolism, immunity, and disease

The growth and survival of multicellular organisms depend upon their abilities to acquire and metabolize nutrients, efficiently store and harness energy, and sense and fight infection. Systems for sensing and using nutrients have consequently coevolved alongside systems for sensing and responding to danger signals, including pathogens, and share many of the same cell signaling proteins and networks. Diets rich in carbohydrates and fats can overload these systems, leading to obesity, metabolic dysfunction, impaired immunity, and cardiovascular disease. Excessive nutrient intake promotes adiposity, typically altering adipocyte function and immune cell distribution, both of which trigger metabolic dysfunction. Here, we discuss novel mechanistic links between metabolism and immunity that underlie metabolic dysfunction in obesity. We aim to stimulate debate about how the endocrine and immune systems are connected through autocrine, paracrine, and neuroendocrine signaling in sophisticated networks that are only now beginning to be resolved. Understanding the expression and action of signaling proteins, together with modulating their receptors or pattern recognition using agonists or antagonists, will enable rational intervention in immunometabolism that may lead to novel treatments for obesity and metabolic dysfunction.

Ontogeny and polarization of macrophages in inflammation: blood monocytes versus tissue macrophages

The explosion of new information in recent years on the origin of macrophages in the steady-state and in the context of inflammation has opened up numerous new avenues of investigation and possibilities for therapeutic intervention. In contrast to the classical model of macrophage development, it is clear that tissue-resident macrophages can develop from yolk sac-derived erythro-myeloid progenitors, fetal liver progenitors, and bone marrow-derived monocytes. Under both homeostatic conditions and in response to pathophysiological insult, the contribution of these distinct sources of macrophages varies significantly between tissues. Furthermore, while all of these populations of macrophages appear to be capable of adopting the polarized M1/M2 phenotypes, their respective contribution to inflammation, resolution of inflammation, and tissue repair remains poorly understood and is likely to be tissue- and disease-dependent. A better understanding of the ontology and polarization capacity of macrophages in homeostasis and disease will be essential for the development of novel therapies that target the inherent plasticity of macrophages in the treatment of acute and chronic inflammatory disease.

Adipose tissue-resident regulatory T cells: phenotypic specialization, functions and therapeutic potential

Foxp3(+)  CD4(+) regulatory T (Treg) cells, recognized to be one of the most important defences of the human body against an inappropriate immune response, have recently gained attention from those outside immunology thanks to the compelling evidence for their capability to exert non-canonical immune functions in a variety of tissues in health and disease. The recent discovery of the differences between tissue-resident Treg cells and those derived from lymphoid organs is affecting the mindset of many investigators now questioning the broad applicability of observations originally based on peripheral blood/lymphoid organ cells. So far, the best characterized 'Treg flavour' comes from studies focused on their role in suppressing adipose tissue inflammation and obesity-driven insulin resistance. Adipose tissue derived Treg cells are distinct from their counterparts in lymphoid organs based on their transcriptional profile, T-cell receptor repertoire, and cytokine and chemokine receptor expression pattern. These cells are abundant in visceral adipose tissue of lean mice but their number is greatly reduced in insulin-resistant animal models of obesity. Interestingly, peroxisome-proliferator-activated receptor γ expression by visceral adipose tissue Treg cells is crucial for their accumulation, phenotype and function in the fat and surprisingly necessary for complete restoration of insulin sensitivity in obese mice by the anti-diabetic drug Pioglitazone. This review surveys recent findings relating to the unique phenotype and function of adipose tissue-resident Treg cells, speculates on the nature of their dynamics in lean and obese mouse models, and analyses their potential therapeutic application in the treatment of type 2 diabetes.

IκB kinase activity drives fetal lung macrophage maturation along a non-M1/M2 paradigm

In preterm infants, exposure to inflammation increases the risk of bronchopulmonary dysplasia, a chronic, developmental lung disease. Although macrophages are the key cells that initiate lung inflammation, less is known about lung macrophage phenotype and maturation. We hypothesized that fetal lung macrophages mature into distinct subpopulations during mouse development, and that activation could influence macrophage maturation. Expression of the fetal macrophage markers CD68, CD86, CD206, Ym1, fibrinogen-like protein 2, and indolamine-2, 3-dioxygenase was developmentally regulated, with each marker having different temporal patterns. Flow cytometry analysis showed macrophages within the fetal lung were less diverse than the distinctly separate subpopulations in newborn and adult lungs. Similar to adult alveolar macrophages, fetal lung macrophages responded to the TLR4 agonist LPS and the alternative activation cytokines IL-4 and IL-13. Using a macrophage-specific constitutively active IκB Kinase transgenic model (IKFM), we demonstrated that macrophage activation increased proinflammatory gene expression and reduced the response of fetal lung macrophages to IL-4 and IL-13. Activation also increased fetal lung macrophage proliferation. Fetal IKFM lungs contained increased percentages of more mature, CD11b(low)F4/80(high) cells that also expressed higher levels of the alternative activation markers CD204 and CD206. Development of fetal lung macrophages into mature alveolar macrophages may therefore include features of both proinflammatory and alternative activation paradigms.

A dangerous duo in adipose tissue: high-mobility group box 1 protein and macrophages

High-mobility group box 1 (HMGB1) protein first made headlines 40 years ago as a non-histone nuclear protein that regulates gene expression. Not so long ago, it was also shown that HMGB1 has an additional surprising function. When released into the extracellular milieu, HMGB1 triggers an inflammatory response by serving as an endogenous danger signal. The pro-inflammatory role of HMGB1 is now well-established and has been associated with several diseases, including sepsis, rheumatoid arthritis, and atherosclerosis. Yet very little is known about its role in obesity, wherein adipose tissue is typified by a persistent, smoldering inflammatory response instigated by high macrophage infiltrate that potentiates the risk of obesity-associated comorbidities. This mini-review focuses on the putative causal relationship between HMGB1 and macrophage pro-inflammatory activation in pathologically altered adipose tissue associated with obesity.

Immunometabolic role of long-chain omega-3 fatty acids in obesity-induced inflammation

Inflammation links obesity with the development of insulin resistance. Macrophages and phagocytic immune cells communicate with metabolic tissues to direct an inflammatory response caused by overnutrition and expanding adipose tissue. Marine-derived omega-3 fatty acids, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), modulate inflammatory signalling events, providing various anti-inflammatory and cardioprotective benefits. Moreover, EPA and DHA may improve insulin sensitivity by generating proresolving lipid mediators and promoting alternatively activated macrophages. This review will assess the role of EPA and DHA in ameliorating obesity-induced inflammation, evaluating clinical evidence and mechanisms of action. The pathophysiology of insulin resistance resulting from obesity-induced inflammation will be discussed, highlighting the relationship between metabolism and immunity, and in particular, how EPA and DHA work with both systems to modulate immunometabolic complications and chronic disease.

An inhibitor of phospholipase A2 group IIA modulates adipocyte signaling and protects against diet-induced metabolic syndrome in rats

Obesity, type 2 diabetes, and cardiovascular disease correlate with infiltration to adipose tissue of different immune cells, with uncertain influences on metabolism. Rats were fed a diet high in carbohydrates and saturated fats to develop diet-induced obesity over 16 weeks. This nutritional overload caused overexpression and secretion of phospholipase A(2) group IIA (pla2g2a) from immune cells in adipose tissue rather than adipocytes, whereas expression of adipose-specific phospholipase A(2) (pla2g16) was unchanged. These immune cells produce prostaglandin E(2) (PGE(2)), which influences adipocyte signaling. We found that a selective inhibitor of human pla2g2a (5-(4-benzyloxyphenyl)-(4S)-(phenyl-heptanoylamino)-pentanoic acid [KH064]) attenuated secretion of PGE(2) from human immune cells stimulated with the fatty acid, palmitic acid, or with lipopolysaccharide. Oral administration of KH064 (5 mg/kg/day) to rats fed the high-carbohydrate, high-fat diet prevented the overexpression of pla2g2a and the increased macrophage infiltration and elevated PGE(2) concentrations in adipose tissue. The treatment also attenuated visceral adiposity and reversed most characteristics of metabolic syndrome, producing marked improvements in insulin sensitivity, glucose intolerance, and cardiovascular abnormalities. We suggest that pla2g2a may have a causal relationship with chronic adiposity and metabolic syndrome and that its inhibition in vivo may be a valuable new approach to treat obesity, type 2 diabetes, and metabolic dysfunction in humans.

TNF-α impairs endothelial function in adipose tissue resistance arteries of mice with diet-induced obesity

We tested the hypothesis that high fat (HF) feeding results in endothelial dysfunction in resistance arteries of epididymal white adipose tissue (eWAT) and is mediated by adipose tissue inflammation. When compared with normal chow (NC)-fed mice (n = 17), HF-fed male B6D2F1 mice were glucose intolerant and insulin resistant as assessed by glucose tolerance test (area under the curve; HF, 18,174 ± 1,889 vs. NC, 15,814 ± 666 mg·dl(-1)·min(-1); P < 0.05) and the homeostatic model assessment (HF, 64.1 ± 4.3 vs. NC, 85.7 ± 6.4; P = 0.05). HF diet-induced metabolic dysfunction was concomitant with a proinflammatory eWAT phenotype characterized by greater macrophage infiltration (HF, 3.9 ± 0.8 vs. NC, 0.8 ± 0.4%; P = 0.01) and TNF-α (HF, 22.6 ± 4.3 vs. NC, 11.4 ± 2.5 pg/dl; P < 0.05) and was associated with resistance artery dysfunction, evidenced by impaired endothelium-dependent dilation (EDD) (maximal dilation; HF, 49.2 ± 10.7 vs. NC, 92.4 ± 1.4%; P < 0.01). Inhibition of nitric oxide (NO) synthase by N(ω)-nitro-L-arginine methyl ester (L-NAME) reduced dilation in NC (28.9 ± 6.3%; P < 0.01)- and tended to reduce dilation in HF (29.8 ± 9.9%; P = 0.07)-fed mice, eliminating the differences in eWAT artery EDD between NC- and HF-fed mice, indicative of reduced NO bioavailability in eWAT resistance arteries after HF feeding. In vitro treatment of excised eWAT arteries with recombinant TNF-α (rTNF) impaired EDD (P < 0.01) in NC (59.7 ± 10.9%)- but not HF (59.0 ± 9.3%)-fed mice. L-NAME reduced EDD in rTNF-treated arteries from both NC (21.9 ± 6.4%)- and HF (29.1 ± 9.2%)-fed mice (both P < 0.01). In vitro treatment of arteries with a neutralizing antibody against TNF-α (abTNF) improved EDD in HF (88.2 ± 4.6%; P = 0.05)-fed mice but was without effect on maximal dilation in NC (89.0 ± 5.1%)-fed mice. L-NAME reduced EDD in abTNF-treated arteries from both NC (25.4 ± 7.5%)- and HF (27.1 ± 16.8%)-fed mice (both P < 0.01). These results demonstrate that inflammation in the visceral adipose tissue resulting from diet-induced obesity impairs endothelial function and NO bioavailability in the associated resistance arteries. This dysfunction may have important implications for adipose tissue blood flow and appropriate tissue function.

Inflamed tumor-associated adipose tissue is a depot for macrophages that stimulate tumor growth and angiogenesis

Tumor-associated stroma is typified by a persistent, non-resolving inflammatory response that enhances tumor angiogenesis, growth and metastasis. Inflammation in tumors is instigated by heterotypic interactions between malignant tumor cells, vascular endothelium, fibroblasts, immune and inflammatory cells. We found that tumor-associated adipocytes also contribute to inflammation. We have analyzed peritumoral adipose tissue in a syngeneic mouse melanoma model. Compared to control adipose tissue, adipose tissue juxtaposed to implanted tumors exhibited reduced adipocyte size, extensive fibrosis, increased angiogenesis and a dense macrophage infiltrate. A mouse cytokine protein array revealed up-regulation of inflammatory mediators including IL-6, CXCL1, MCP-1, MIP-2 and TIMP-1 in peritumoral versus counterpart adipose tissues. CD11b(+) macrophages contributed strongly to the inflammatory activity. These macrophages were isolated from peritumoral adipose tissue and found to over-express ARG1, NOS2, CD301, CD163, MCP-1 and VEGF, which are indicative of both M1 and M2 polarization. Tumors implanted at a site distant from subcutaneous, anterior adipose tissue were strongly growth-delayed, had fewer blood vessels and were less populated by CD11b(+) macrophages. In contrast to normal adipose tissue, micro-dissected peritumoral adipose tissue explants launched numerous vascular sprouts when cultured in an ex vivo model. Thus, inflamed tumor-associated adipose tissue fuels the growth of malignant cells by acting as a proximate source for vascular endothelium and activated pro-inflammatory cells, in particular macrophages.

Macrophages, meta-inflammation, and immuno-metabolism

Current research depicts specific modes of immunity and energy metabolism as being interrelated at the molecular, cellular, organ and organism level. Hence, whereas M2 (alternatively-activated) macrophages dominate insulin-sensitive adipose tissue in the lean, M1-skewed (classically-activated) macrophages accumulate in parallel to adiposity in the obese, and promote inflammation and insulin resistance, that is, meta-inflammation. The latest frontier of immuno-metabolism explores the coregulation of energy metabolism and immune function within hematopoietic cells. M1-skewed macrophages are sustained in edematous, hypoxic tissues by anaerobic glycolysis, whereas mitochondrial biogenesis and respiration dominates in M2 cells. We review the underlying mechanisms and the consequences of the transition from M2 to M1 predominance in adipose tissue, as well as the extracellular signals and transcription factors that control macrophage phenotypes and impose distinct metabolic modes.

Low-grade adipose tissue inflammation in patients with mild-to-moderate chronic obstructive pulmonary disease

BACKGROUND

Low-grade systemic inflammation is common in chronic obstructive pulmonary disease (COPD), but its source remains unclear. Adipose tissue is a potent producer of inflammatory mediators and may contribute to systemic inflammation in COPD, possibly via hypoxia.

OBJECTIVE

We studied the influence of COPD and exercise-induced oxygen desaturation on adipose tissue inflammation (ATI) and its contribution to systemic inflammation.

DESIGN

Subcutaneous adipose tissue biopsies were investigated in 28 clinically stable COPD patients [forced expiratory volume in 1 s: 58 ± 16% predicted; BMI (in kg/m(2)): 24.9 ± 2.9] and 15 age-, sex-, and body composition-matched healthy control subjects. Fat mass was measured with dual-energy X-ray absorptiometry. Patients were prestratified by oxygen desaturation assessed by incremental cycle ergometry. The adipocyte size and adipose tissue expression of 19 inflammatory and hypoxia-related genes were measured, and adipose tissue macrophages (ATMs) were histologically quantified. Systemic inflammatory markers included C-reactive protein (CRP) and a panel of 20 adipokines.

RESULTS

COPD patients had comparable fat mass but higher CRP and HOMA-IR than did control subjects. COPD patients and control subjects had comparable adipose tissue gene expression, adipocyte size, ATM infiltration, and systemic adipokine concentrations. Desaturating COPD patients had no different ATI status than did nondesaturating COPD patients. COPD patients with high CRP had significantly greater ATM infiltration than did patients with low CRP, which was independent of BMI and fat mass.

CONCLUSIONS

In COPD patients, mild-to-moderate COPD, per se, does not enhance ATI or its contribution to systemic inflammation compared with in well-matched healthy control subjects. However, to our knowledge, our study provides a first indication for a possible role of ATMs in the systemic inflammatory response in COPD that requires additional investigation. This trial was registered at www.trialregister.nl as NTR1402.

Lysine acetylation in obesity, diabetes and metabolic disease

Histone acetyltransferases (HATs) and histone deacetylases (HDACs) mediate acetylation and deacetylation of histone proteins and transcription factors. There is abundant evidence that these enzymes regulate the acetylation state of many cytoplasmic proteins, including lysine residues in important metabolic enzymes. Lysine acetylation regulates major cellular functions as a common post-transcriptional modification of proteins, conserved from prokaryotes to humans. In this article, we refer to HATs and HDACs broadly as lysine acetyltransferases (KATs) and deacetylases (KDACs). Lysine acetylation is vitally important in both immunological and metabolic pathways and may regulate the balance between energy storage and expenditure. Obesity, type II diabetes and cardiovascular disease (metabolic syndrome) are widely recognised as features of a chronic low-grade inflammatory state, involving significant alterations in primary immunometabolism. Identifying effective therapeutic and preventive options to treat this multi-factorial syndrome has proven to be very challenging, with an emerging focus on developing anti-inflammatory agents that can combat adiposity and metabolic disease. Here, we summarise current evidence and understanding of innate immune and metabolic pathways relevant to adiposity and metabolic disease regulated by lysine acetylation. Developing this understanding in greater detail may facilitate strategic development of novel and enzyme-specific lysine deacetylase modulators that regulate both metabolic and immune systems.