Regulation of metabolism by the innate immune system

Grape seed proanthocyanidin extract ameliorates inflammation and adiposity by modulating gut microbiota in high-fat diet mice

SCOPE

Obesity and associated metabolic complications is a worldwide public health issue. Gut microbiota have been recently linked to obesity and its related inflammation. In this study, we have explored the anti-inflammatory effect of grape seed proanthocyanindin extract (GSPE) in the high-fat diet (HFD)-induced obesity and identified the contribution of the gut microbiota to GSPE effects on metabolism.

METHODS AND RESULTS

Mice were fed a normal diet and a high-fat diet with or without GSPE (300 mg/kg body weight/day) by oral gavage for 7 weeks. Supplementation with GSPE significantly decreased plasma levels of inflammatory factors such as TNF-α, IL-6 and MCP-1, companied with ameliorated macrophage infiltration in epidydimal fat and liver tissues. Furthermore, GSPE also reduced epidydimal fat mass and improved insulin sensitivity. 16S rDNA analyses revealed that GSPE supplementation modulated the gut microbiota composition and certain bacteria including Clostridium XIVa, Roseburia and Prevotella. More importantly, depleting gut microbiota by antibiotics treatment abolished the beneficial effects of GSPE on inflammation and adiposity.

CONCLUSION

Our study identifies the novel links between gut microbiota alterations and metabolic benefits by GSPE supplementation, providing possibilities for the prevention and treatment of metabolic disorders by targeting gut microbiota through a potential prebiotic agent GSPE.

Adipose tissue: between the extremes

Adipose tissue represents a critical component in healthy energy homeostasis. It fulfills important roles in whole-body lipid handling, serves as the body's major energy storage compartment and insulation barrier, and secretes numerous endocrine mediators such as adipokines or lipokines. As a consequence, dysfunction of these processes in adipose tissue compartments is tightly linked to severe metabolic disorders, including obesity, metabolic syndrome, lipodystrophy, and cachexia. While numerous studies have addressed causes and consequences of obesity-related adipose tissue hypertrophy and hyperplasia for health, critical pathways and mechanisms in (involuntary) adipose tissue loss as well as its systemic metabolic consequences are far less understood. In this review, we discuss the current understanding of conditions of adipose tissue wasting and review microenvironmental determinants of adipocyte (dys)function in related pathophysiologies.

Myeloid protein tyrosine phosphatase 1B (PTP1B) deficiency protects against atherosclerotic plaque formation in the ApoE-/- mouse model of atherosclerosis with alterations in IL10/AMPKα pathway

Objective

Cardiovascular disease (CVD) is the most prevalent cause of mortality among patients with Type 1 or Type 2 diabetes, due to accelerated atherosclerosis. Recent evidence suggests a strong link between atherosclerosis and insulin resistance due to impaired insulin receptor (IR) signaling. Moreover, inflammatory cells, in particular macrophages, play a key role in pathogenesis of atherosclerosis and insulin resistance in humans. We hypothesized that inhibiting the activity of protein tyrosine phosphatase 1B (PTP1B), the major negative regulator of the IR, specifically in macrophages, would have beneficial anti-inflammatory effects and lead to protection against atherosclerosis and CVD.

Methods

We generated novel macrophage-specific PTP1B knockout mice on atherogenic background (ApoE^−/−/LysM-PTP1B). Mice were fed standard or pro-atherogenic diet, and body weight, adiposity (echoMRI), glucose homeostasis, atherosclerotic plaque development, and molecular, biochemical and targeted lipidomic eicosanoid analyses were performed.

Results

Myeloid-PTP1B knockout mice on atherogenic background (ApoE^−/−/LysM-PTP1B) exhibited a striking improvement in glucose homeostasis, decreased circulating lipids and decreased atherosclerotic plaque lesions, in the absence of body weight/adiposity differences. This was associated with enhanced phosphorylation of aortic Akt, AMPKα and increased secretion of circulating anti-inflammatory cytokine interleukin-10 (IL-10) and prostaglandin E2 (PGE₂), without measurable alterations in IR phosphorylation, suggesting a direct beneficial effect of myeloid-PTP1B targeting.

Conclusions

Here we demonstrate that inhibiting the activity of PTP1B specifically in myeloid lineage cells protects against atherosclerotic plaque formation, under atherogenic conditions, in an ApoE^−/− mouse model of atherosclerosis. Our findings suggest for the first time that macrophage PTP1B targeting could be a therapeutic target for atherosclerosis treatment and reduction of CVD risk.

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PTP1B inhibition as therapy for atherosclerosis/cardiovascular disease is proposed.

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Myeloid-PTP1B mice on ApoE^−/− background (ApoE^−/−/LysM-PTP1B) were generated.

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ApoE^−/−/LysM-PTP1B had improved glucose homeostasis with no body weight differences.

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ApoE^−/−/LysM-PTP1B had lower lipids and protection against atherosclerotic plaques.

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Protection was via a PGE₂/IL-10/AMPKα mechanism.

Type I Interferons Interfere with Liver Glucose Metabolism

The specific immunological components linking metabolic stresses to liver inflammation and systemic metabolic pathologies in obesity are not entirely known. A recent study (Ghazarian et al., 2017) reveals that obesity-induced type I interferon signaling drives the accumulation and activation of intrahepatic CD8⁺ T cells, leading to systemic metabolic deterioration.

Temporal and tissue-specific requirements for T-lymphocyte IL-6 signalling in obesity-associated inflammation and insulin resistance

Low-grade inflammation links obesity to insulin resistance through the activation of tissue-infiltrating immune cells. Interleukin-6 (IL-6) is a crucial regulator of T cells and is increased in obesity. Here we report that classical IL-6 signalling in T cells promotes inflammation and insulin resistance during the first 8 weeks on a high-fat diet (HFD), but becomes dispensable at later stages (after 16 weeks). Mice with T cell-specific deficiency of IL-6 receptor-α (IL-6Rα^T-KO) exposed to a HFD display improved glucose tolerance, insulin sensitivity and inflammation in liver and EWAT after 8 weeks. However, after 16 weeks, insulin resistance in IL-6Rα^T-KO epididymal white adipose tissue (EWAT) is comparable to that of controls, whereas the inflammatory profile is significantly worse. This coincided with a shift from classical T cell IL-6 signalling at 8 weeks, to enhanced IL-6 trans-signalling at 16 weeks. Collectively, our studies reveal that IL-6 action in T cells through classical IL-6 signalling promotes inflammation and insulin resistance early during obesity development, which can be compensated for by enhanced IL-6 trans-signalling at later stages.

Interleukin-6 (IL-6) is increased in obesity and activates T cells to promote inflammation. Here, Xu et al. use mice that lack IL-6 receptors on T cells to uncover the temporal and tissue-specific effects of classic and trans IL-6 signalling on inflammation and insulin resistance on a high-fat diet.

Sarcopenic obesity or obese sarcopenia: A cross talk between age-associated adipose tissue and skeletal muscle inflammation as a main mechanism of the pathogenesis

Sarcopenia, an age-associated decline in skeletal muscle mass coupled with functional deterioration, may be exacerbated by obesity leading to higher disability, frailty, morbidity and mortality rates. In the combination of sarcopenia and obesity, the state called sarcopenic obesity (SOB), some key age- and obesity-mediated factors and pathways may aggravate sarcopenia. This review will analyze the mechanisms underlying the pathogenesis of SOB. In obese adipose tissue (AT), adipocytes undergo hypertrophy, hyperplasia and activation resulted in accumulation of pro-inflammatory macrophages and other immune cells as well as dysregulated production of various adipokines that together with senescent cells and the immune cell-released cytokines and chemokines create a local pro-inflammatory status. In addition, obese AT is characterized by excessive production and disturbed capacity to store lipids, which accumulate ectopically in skeletal muscle. These intramuscular lipids and their derivatives induce mitochondrial dysfunction characterized by impaired β-oxidation capacity and increased reactive oxygen species formation providing lipotoxic environment and insulin resistance as well as enhanced secretion of some pro-inflammatory myokines capable of inducing muscle dysfunction by auto/paracrine manner. In turn, by endocrine manner, these myokines may exacerbate AT inflammation and also support chronic low grade systemic inflammation (inflammaging), overall establishing a detrimental vicious circle maintaining AT and skeletal muscle inflammation, thus triggering and supporting SOB development. Under these circumstances, we believe that AT inflammation dominates over skeletal muscle inflammation. Thus, in essence, it redirects the vector of processes from "sarcopenia→obesity" to "obesity→sarcopenia". We therefore propose that this condition be defined as "obese sarcopenia", to reflect the direction of the pathological pathway.

Bile Acid Control of Metabolism and Inflammation in Obesity, Type 2 Diabetes, Dyslipidemia, and Nonalcoholic Fatty Liver Disease

Bile acids are signaling molecules that coordinately regulate metabolism and inflammation via the nuclear farnesoid X receptor (FXR) and the Takeda G protein-coupled receptor 5 (TGR5). These receptors activate transcriptional networks and signaling cascades controlling the expression and activity of genes involved in bile acid, lipid and carbohydrate metabolism, energy expenditure, and inflammation by acting predominantly in enterohepatic tissues, but also in peripheral organs. In this review, we discuss the most recent findings on the inter-organ signaling and interplay with the gut microbiota of bile acids and their receptors in meta-inflammation, with a focus on their pathophysiologic roles in obesity, type 2 diabetes, dyslipidemia, and nonalcoholic steatohepatitis, and their potential therapeutic applications.

Expression profiling feline peripheral blood monocytes identifies a transcriptional signature associated with type two diabetes mellitus

Diabetes mellitus is a common disease of cats and is similar to type 2 diabetes (T2D) in humans, especially with respect to the role of obesity-induced insulin resistance, glucose toxicity, decreased number of pancreatic β-cells and pancreatic amyloid deposition. Cats have thus been proposed as a valuable translational model of T2D. In humans, inflammation associated with adipose tissue is believed to be central to T2D development, and peripheral blood monocytes (PBM) are important in the inflammatory cascade which leads to insulin resistance and β-cell failure. PBM may thus provide a useful window to study the pathogenesis of diabetes mellitus in cats, however feline monocytes are poorly characterised. In this study, we used the Affymetrix Feline 1.0ST array to profile peripheral blood monocytes from 3 domestic cats with T2D and 3 cats with normal glucose tolerance. Feline monocytes were enriched for genes expressed in human monocytes, and, despite heterogeneous gene expression, we identified a T2D-associated expression signature associated with cell cycle perturbations, DNA repair and the unfolded protein response, oxidative phosphorylation and inflammatory responses. Our data provide novel insights into the feline monocyte transcriptome, and support the hypothesis that inflammatory monocytes contribute to T2D pathogenesis in cats as well as in humans.

Human adipose tissue accumulation is associated with pro-inflammatory changes in subcutaneous rather than visceral adipose tissue

The importance of the involvement of adipose tissue macrophage subpopulations in obesity-related disorders is well known from different animal models, but human data are scarcer. Subcutaneous (n=44) and visceral (n=52) adipose tissues of healthy living kidney donors were obtained during living donor nephrectomy. Stromal vascular fractions were isolated and analysed by flow cytometry using CD14, CD16, CD36 and CD163 antibodies. Total macrophage numbers in subcutaneous adipose tissue increased (P=0.02) with body mass index (BMI), with a similar increase seen in the proportion of phagocytic CD14+CD16+CD36^high macrophages (P<0.01). On the other hand, there was an inverse correlation between anti-inflammatory CD14+CD16-CD163+ macrophages (P<0.05) and BMI. These correlations disappeared after excluding obese subjects (BMI ⩾30 kg m^-2) from the analysis. Interestingly, none of these subpopulations were significantly related to BMI in visceral adipose tissue. Obesity per se is associated with distinct, highly phagocytic macrophage accumulation in human subcutaneous adipose tissue.

Hematopoietic-Derived Galectin-3 Causes Cellular and Systemic Insulin Resistance

In obesity, macrophages and other immune cells accumulate in insulin target tissues, promoting a chronic inflammatory state and insulin resistance. Galectin-3 (Gal3), a lectin mainly secreted by macrophages, is elevated in both obese subjects and mice. Administration of Gal3 to mice causes insulin resistance and glucose intolerance, whereas inhibition of Gal3, through either genetic or pharmacologic loss of function, improved insulin sensitivity in obese mice. In vitro treatment with Gal3 directly enhanced macrophage chemotaxis, reduced insulin-stimulated glucose uptake in myocytes and 3T3-L1 adipocytes and impaired insulin-mediated suppression of glucose output in primary mouse hepatocytes. Importantly, we found that Gal3 can bind directly to the insulin receptor (IR) and inhibit downstream IR signaling. These observations elucidate a novel role for Gal3 in hepatocyte, adipocyte, and myocyte insulin resistance, suggesting that Gal3 can link inflammation to decreased insulin sensitivity. Inhibition of Gal3 could be a new approach to treat insulin resistance.

GPCR-Mediated Signaling of Metabolites

In addition to their bioenergetic intracellular function, several classical metabolites act as extracellular signaling molecules activating cell-surface G-protein-coupled receptors (GPCRs), similar to hormones and neurotransmitters. "Signaling metabolites" generated from nutrients or by gut microbiota target primarily enteroendocrine, neuronal, and immune cells in the lamina propria of the gut mucosa and the liver and, through these tissues, the rest of the body. In contrast, metabolites from the intermediary metabolism act mainly as metabolic stress-induced autocrine and paracrine signals in adipose tissue, the liver, and the endocrine pancreas. Importantly, distinct metabolite GPCRs act as efficient pro- and anti-inflammatory regulators of key immune cells, and signaling metabolites may thus function as important drivers of the low-grade inflammation associated with insulin resistance and obesity. The concept of key metabolites as ligands for specific GPCRs has broadened our understanding of metabolic signaling significantly and provides a number of novel potential drug targets.

Nod2 and Nod2-regulated microbiota protect BALB/c mice from diet-induced obesity and metabolic dysfunction

Genetics plays a central role in susceptibility to obesity and metabolic diseases. BALB/c mice are known to be resistant to high fat diet (HFD)-induced obesity, however the genetic cause remains unknown. We report that deletion of the innate immunity antibacterial gene Nod2 abolishes this resistance, as Nod2^−/− BALB/c mice developed HFD-dependent obesity and hallmark features of metabolic syndrome. Nod2^−/− HFD mice developed hyperlipidemia, hyperglycemia, glucose intolerance, increased adiposity, and steatosis, with large lipid droplets in their hepatocytes. These changes were accompanied by increased expression of immune genes in adipose tissue and differential expression of genes for lipid metabolism, signaling, stress, transport, cell cycle, and development in both adipose tissue and liver. Nod2^−/− HFD mice exhibited changes in the composition of the gut microbiota and long-term treatment with antibiotics abolished diet-dependent weight gain in Nod2^−/− mice, but not in wild type mice. Furthermore, microbiota from Nod2^−/− HFD mice transferred sensitivity to weight gain, steatosis, and hyperglycemia to wild type germ free mice. In summary, we have identified a novel role for Nod2 in obesity and demonstrate that Nod2 and Nod2-regulated microbiota protect BALB/c mice from diet-induced obesity and metabolic dysfunction.

Obesity promotes prolonged ovalbumin-induced airway inflammation modulating T helper type 1 (Th1), Th2 and Th17 immune responses in BALB/c mice

Clinical and epidemiological studies indicate that obesity affects the development and phenotype of asthma by inducing inflammatory mechanisms in addition to eosinophilic inflammation. The aim of this study was to assess the effect of obesity on allergic airway inflammation and T helper type 2 (Th2) immune responses using an experimental model of asthma in BALB/c mice. Mice fed a high-fat diet (HFD) for 10 weeks were sensitized and challenged with ovalbumin (OVA), and analyses were performed at 24 and 48 h after the last OVA challenge. Obesity induced an increase of inducible nitric oxide synthase (iNOS)-expressing macrophages and neutrophils which peaked at 48 h after the last OVA challenge, and was associated with higher levels of interleukin (IL)-4, IL-9, IL-17A, leptin and interferon (IFN)-γ in the lungs. Higher goblet cell hyperplasia was associated with elevated mast cell influx into the lungs and trachea in the obese allergic mice. In contrast, early eosinophil influx and lower levels of IL-25, thymic stromal lymphopoietin (TSLP), CCL11 and OVA-specific immunoglobulin (IgE) were observed in the obese allergic mice in comparison to non-obese allergic mice. Moreover, obese mice showed higher numbers of mast cells regardless of OVA challenge. These results indicate that obesity affects allergic airway inflammation through mechanisms involving mast cell influx and the release of TSLP and IL-25, which favoured a delayed immune response with an exacerbated Th1, Th2 and Th17 profile. In this scenario, an intense mixed inflammatory granulocyte influx, classically activated macrophage accumulation and intense mucus production may contribute to a refractory therapeutic response and exacerbate asthma severity.

Neutrophils as protagonists and targets in chronic inflammation

Traditionally, neutrophils have been acknowledged to be the first immune cells that are recruited to an inflamed tissue and have mainly been considered in the context of acute inflammation. By contrast, their importance during chronic inflammation has been studied in less depth. This Review aims to summarize our current understanding of the roles of neutrophils in chronic inflammation, with a focus on how they communicate with other immune and non-immune cells within tissues. We also scrutinize the roles of neutrophils in wound healing and the resolution of inflammation, and finally, we outline emerging therapeutic strategies that target neutrophils.

Negative Regulation of Type 2 Immunity

Type 2 immunity encompasses the mechanisms through which the immune system responds to helminths and an array of environmental substances such as allergens. In the developing world, billions of individuals are chronically infected with endemic parasitic helminths. In comparison, in the industrialized world, millions of individuals suffer from dysregulated type 2 immunity, referred to clinically as atopic diseases including asthma, allergic rhinitis, and atopic dermatitis. Thus, type 2 immunity must be carefully regulated to mount protective host responses yet avoid inappropriate activation and immunopathology. In this review, we describe the key players and connections at play in type 2 responses and focus on the emerging mechanisms involved in the negative regulation of type 2 immunity.

Aberrant Expression of FBXO2 Disrupts Glucose Homeostasis Through Ubiquitin-Mediated Degradation of Insulin Receptor in Obese Mice

Insulin resistance is a critical factor in the development of metabolic disorders, including type 2 diabetes (T2DM). However, its molecular mechanisms remain incompletely understood. In this study, we found that F-box only protein 2 (FBXO2), a substrate recognition component of the Skp1-Cul1-F-box protein (SCF) E3 ubiquitin ligase complex, was upregulated in livers of obese mice. Furthermore, using a protein purification approach combined with high-performance liquid chromatography/tandem mass spectrometry, we carried out a system-wide screening of FBXO2 substrates, in which the insulin receptor (IR) was identified as a substrate for FBXO2. SCF^FBXO2 acts as an E3 ligase targeting the IR for ubiquitin-dependent degradation to regulate insulin signaling integrity. As a result, adenovirus-mediated overexpression of FBXO2 in healthy mice led to hyperglycemia, glucose intolerance, and insulin resistance, whereas ablation of FBXO2 alleviated diabetic phenotypes in obese mice. Therefore, our results identify SCF^FBXO2 as an E3 ligase for the IR in the liver, which might provide a novel therapeutic target for treating T2DM and related metabolic disorders.

New targets to alleviate skeletal muscle inflammation: role of microRNAs regulated by adiponectin

Muscle inflammation worsens metabolic disorders as well as devastating myopathies. The hormone adiponectin (ApN) has emerged has a master regulator of inflammation/immunity in several tissues including the skeletal muscle. In this work, we explore whether microRNAs regulated by ApN may represent novel mechanisms for controlling muscle inflammation. By screening arrays, we found miR-711 as a strong candidate for mediating ApN action. Thus, ApN-knockout mice showed decreased muscular expression of miR-711 together with enhanced inflammation/oxidative stress markers, while mice overexpressing ApN showed increased miR-711 levels. Likewise, electrotransfer of the ApN gene in muscle of ApN-knockout mice upregulated miR-711 while reducing inflammation and oxidative stress. Similar data were obtained in murine C2C12 cells or in human primary myotubes treated with ApN. MiR-711 overexpression downregulated several components of the Toll-like receptor-4 (TLR4) pathway, which led to repression of NF-κB activity and downstream pro-inflammatory cytokines. MiR-711 blockade had opposite effects. Moreover, muscle electrotransfer of pre-miR-711 recapitulated in vivo the anti-inflammatory effects observed in vitro. Thus, miR-711, which is upregulated by ApN represses TLR4 signaling, acting therefore as a major mediator of the anti-inflammatory action of ApN. This novel miRNA and its related target genes may open new therapeutic perspectives for controlling muscle inflammation.

Regulatory Eosinophils in Inflammation and Metabolic Disorders

Eosinophils are potent effector cells implicated in allergic responses and helminth infections. Responding to stimuli, they release their granule-derived cytotoxic proteins and are involved in inflammatory processes. However, under homeostatic conditions, eosinophils are abundantly present in the intestine and are constantly in contact with the gut microbiota and maintain the balance of immune responses without inflammation. This situation indicates that intestinal eosinophils have an anti-inflammatory function unlike allergic eosinophils. In support of this notion, some papers have shown that eosinophils have different phenotypes depending on the site of residence and are a heterogeneous cell population. Recently, it was reported that eosinophils in the small intestine and adipose tissue, respectively, contribute to homeostasis of intestinal immune responses and metabolism. Accordingly, in this review, we summarize new functions of eosinophils demonstrated in recent studies and discuss their homeostatic functions.

Maresin 1 improves insulin sensitivity and attenuates adipose tissue inflammation in ob/ob and diet-induced obese mice

The beneficial actions of n-3 fatty acids on obesity-induced insulin resistance and inflammation have been related to the synthesis of specialized proresolving lipid mediators (SPMs) like resolvins. The aim of this study was to evaluate the ability of one of these SPMs, maresin 1 (MaR1), to reverse adipose tissue inflammation and/or insulin resistance in two models of obesity: diet-induced obese (DIO) mice and genetic (ob/ob) obese mice. In DIO mice, MaR1 (2 μg/kg; 10 d) reduced F4/80-positive cells and expression of the proinflammatory M1 macrophage phenotype marker Cd11c in white adipose tissue (WAT). Moreover, MaR1 decreased Mcp-1, Tnf-α, and Il-1β expression, upregulated adiponectin and Glut-4, and increased Akt phosphorylation in WAT. MaR1 administration (2 μg/kg; 20 d) to ob/ob mice did not modify macrophage recruitment but increased the M2 macrophage markers Cd163 and Il-10. MaR1 reduced Mcp-1, Tnf-α, Il-1β, and Dpp-4 and increased adiponectin gene expression in WAT. MaR1 treatment also improved the insulin tolerance test of ob/ob mice and increased Akt and AMPK phosphorylation in WAT. These data suggest that treatment with MaR1 can counteract the dysfunctional inflamed WAT and could be useful to improve insulin sensitivity in murine models of obesity.-Martínez-Fernández, L., González-Muniesa, P., Laiglesia, L. M., Sáinz, N., Prieto-Hontoria, P. L., Escoté, X., Odriozola, L., Corrales, F. J., Arbones-Mainar, J. M., Martínez, J. A., Moreno-Aliaga, M. J. Maresin 1 improves insulin sensitivity and attenuates adipose tissue inflammation in ob/ob and diet-induced obese mice.

Genome-wide analysis identifies colonic genes differentially associated with serum leptin and insulin concentrations in C57BL/6J mice fed a high-fat diet

Obesity-induced chronic inflammation is known to increase the risk of ulcerative colitis, Crohn's disease, and colorectal cancer. Accumulating evidence suggests that leptin and insulin are key molecules linking obesity with diseases of the lower intestine. Here, we identified serum phenotype-associated genes in the colon of diet-induced obese mice as early biomarkers of obesity-associated colonic diseases. C57BL/6J mice were fed with either normal diet (ND, 15% of fat calories) or high-fat diet (HFD, 45% of fat calories) for 8 weeks. Serum concentrations of insulin, insulin-like growth factor-1 (IGF-1), leptin, and adiponectin were measured as obesity-related phenotypic markers. Genome-wide gene expression profiles of colon tissue were determined, followed by statistical analyses to detect differentially expressed and serum phenotype-associated genes. HFD-fed mice showed higher serum concentrations of leptin (P < 0.001) and insulin (P < 0.01) than those in the ND group, whereas serum IGF-1 and adiponectin concentrations did not differ between the two dietary groups. Among differentially expressed genes affected by HFD, 135, 128, 110, and 341 genes were associated with serum levels of leptin, insulin, IGF-1, and adiponectin, respectively. We identified 17 leptin-associated genes and 4 insulin-associated genes that inversely responded to HFD and ND. Among these, leptin-associated Peli3 (Pellino E3 ubiquitin protein ligase family member 3), Creb1 (cAMP responsive element binding protein 1), and Enpp2 (ectonucleotide pyrophosphatase/phosphodiesterase 2, autotaxin) and insulin-associated Centg1 (AGAP2, ArfGAP with GTPase domain) are reported to play a role either in obesity or colonic diseases. mRNA expression of these genes was validated by RT-qPCR. Our data suggest Peli3, Creb1, Enpp2, and Centg1 as potential early biomarker candidates for obesity-induced pathophysiological changes in the colon. Future studies verifying the function of these candidates are needed for the prevention, early detection, and treatment of colon diseases.

Ginsenoside Rb2 enhances the anti-inflammatory effect of ω-3 fatty acid in LPS-stimulated RAW264.7 macrophages by upregulating GPR120 expression

Recent studies confirm that chronic low-grade inflammation is closely associated with metabolic syndromes, and anti-inflammatory therapy is a potential approach for treating cardiovascular diseases and type 2 diabetes. Accumulating evidence suggests that GPR120 activation is a feasible solution to ameliorating chronic inflammation and improving glucose metabolism. In this study we investigated whether ginsenoside Rb2 (Rb2), which exhibited regulatory activities in glucose and lipid metabolism, affected GPR120 expression in lipopolysaccharide (LPS)-activated mouse macrophage RAW264.7 cells, and examined the contribution of GPR120 activation to reducing the LPS-induced inflammatory response. LPS (100 ng/mL) activated the macrophages, resulting in dramatic increases in TNF-α, IL-6, IL-1β and NO production. Treatment with a ω-3 fatty acid α-linolenic acid (ALA, 50 μmol/L) produced moderate reduction in LPS-stimulated inflammatory cytokines and NO production (TNF-α and IL-6 were decreased by 46% and 42%, respectively). Pre-incubation with Rb2 (1 or 10 μmol/L) for 12 h before ALA treatment dramatically amplified the inhibitory effects of ALA (TNF-α and IL-6 were decreased by 74% and 86%, respectively). Compared to the treatment with ALA alone, pre-incubation with Rb2 resulted in a more prominent reduction in LPS-stimulated expression of iNOS and COX-2 and LPS-stimulated IKK/NF-κB phosphorylation and MAPK pathway activation. Rb2 (0.1-100 μmol/L) dose- and time-dependently increased both mRNA and protein expression of GPR120 in RAW264.7 cells, but treatment with Rb2 alone did not exert anti-inflammatory effect in LPS-activated RAW264.7 cells. In RAW264.7 cells transfected with GPR120 shRNA, the ameliorating effects of Rb2 on LPS-induced inflammation were abolished. In conclusion, Rb2 exerts anti-inflammatory effect in LPS-stimulated mouse macrophage RAW264.7 cells in vitro by increasing GPR120 expression and subsequently enhancing ω-3 fatty acid-induced GPR120 activation.

Metabolic signaling functions of ER-mitochondria contact sites: role in metabolic diseases

Beyond the maintenance of cellular homeostasis and the determination of cell fate, ER-mitochondria contact sites, defined as mitochondria-associated membranes (MAM), start to emerge as an important signaling hub that integrates nutrient and hormonal stimuli and adapts cellular metabolism. Here, we summarize the established structural and functional features of MAM and mainly focus on the latest breakthroughs highlighting a crucial role of organelle crosstalk in the control of metabolic homeostasis. Lastly, we discuss recent studies that have revealed the importance of MAM in not only metabolic diseases but also in other pathologies with disrupted metabolism, shedding light on potential common molecular mechanisms and leading hopefully to novel treatment strategies.

Immunologic impact of the intestine in metabolic disease

Obesity and diabetes are associated with increased chronic low-grade inflammation and elevated plasma glucose levels. Although inflammation in the fat and liver are established features of obesity-associated insulin resistance, the intestine is emerging as a new site for immunologic changes that affect whole-body metabolism. Specifically, microbial and dietary factors incurred by diet-induced obesity influence underlying innate and adaptive responses of the intestinal immune system. These responses affect the maintenance of the intestinal barrier, systemic inflammation, and glucose metabolism. In this Review we propose that an understanding of the changes to the intestinal immune system, and how these changes influence systemic immunity and glucose metabolism in a whole-body integrative and a neuronal-dependent network, will unveil novel intestinal pathologic and therapeutic targets for diabetes and obesity.

Skeletal muscle inflammation and insulin resistance in obesity

Obesity is associated with chronic inflammation, which contributes to insulin resistance and type 2 diabetes mellitus. Under normal conditions, skeletal muscle is responsible for the majority of insulin-stimulated whole-body glucose disposal; thus, dysregulation of skeletal muscle metabolism can strongly influence whole-body glucose homeostasis and insulin sensitivity. Increasing evidence suggests that inflammation occurs in skeletal muscle in obesity and is mainly manifested by increased immune cell infiltration and proinflammatory activation in intermyocellular and perimuscular adipose tissue. By secreting proinflammatory molecules, immune cells may induce myocyte inflammation, adversely regulate myocyte metabolism, and contribute to insulin resistance via paracrine effects. Increased influx of fatty acids and inflammatory molecules from other tissues, particularly visceral adipose tissue, can also induce muscle inflammation and negatively regulate myocyte metabolism, leading to insulin resistance.

Inflammatory mechanisms linking obesity and metabolic disease

There are currently over 1.9 billion people who are obese or overweight, leading to a rise in related health complications, including insulin resistance, type 2 diabetes, cardiovascular disease, liver disease, cancer, and neurodegeneration. The finding that obesity and metabolic disorder are accompanied by chronic low-grade inflammation has fundamentally changed our view of the underlying causes and progression of obesity and metabolic syndrome. We now know that an inflammatory program is activated early in adipose expansion and during chronic obesity, permanently skewing the immune system to a proinflammatory phenotype, and we are beginning to delineate the reciprocal influence of obesity and inflammation. Reviews in this series examine the activation of the innate and adaptive immune system in obesity; inflammation within diabetic islets, brain, liver, gut, and muscle; the role of inflammation in fibrosis and angiogenesis; the factors that contribute to the initiation of inflammation; and therapeutic approaches to modulate inflammation in the context of obesity and metabolic syndrome.

Latent Inflammation and Insulin Resistance in Adipose Tissue

Obesity is a growing problem in modern society and medicine. It closely associates with metabolic disorders such as type 2 diabetes mellitus (T2DM) and hepatic and cardiovascular diseases such as nonalcoholic fatty liver disease, atherosclerosis, myocarditis, and hypertension. Obesity is often associated with latent inflammation; however, the link between inflammation, obesity, T2DM, and cardiovascular diseases is still poorly understood. Insulin resistance is the earliest feature of metabolic disorders. It mostly develops as a result of dysregulated insulin signaling in insulin-sensitive cells, as compared to inactivating mutations in insulin receptor or signaling proteins that occur relatively rare. Here, we argue that inflammatory signaling provides a link between latent inflammation, obesity, insulin resistance, and metabolic disorders. We further hypothesize that insulin-activated PI3-kinase pathway and inflammatory signaling mediated by several IκB kinases may constitute negative feedback leading to insulin resistance at least in the fat tissue. Finally, we discuss perspectives for anti-inflammatory therapies in treating the metabolic diseases.

Hypothalamic Insulin Resistance in Obesity: Effects on Glucose Homeostasis

The central link between obesity and type 2 diabetes is the development of insulin resistance. To date, it is still not clear whether hyperinsulinemia causes insulin resistance, which underlies the pathogenesis of obesity-associated type 2 diabetes, owing to the sophisticated regulatory mechanisms that exist in the periphery and in the brain. In recent years, accumulating evidence has demonstrated the existence of insulin resistance within the hypothalamus. In this review, we have integrated the recent discoveries surrounding both central and peripheral insulin resistance to provide a comprehensive overview of insulin resistance in obesity and the regulation of systemic glucose homeostasis. In particular, this review will discuss how hyperinsulinemia and hyperleptinemia in obesity impair insulin sensitivity in tissues such as the liver, skeletal muscle, adipose tissue, and the brain. In addition, this review highlights insulin transport into the brain, signaling pathways associated with hypothalamic insulin receptor expression in the regulation of hepatic glucose production, and finally the perturbation of systemic glucose homeostasis as a consequence of central insulin resistance. We also suggest future approaches to overcome both central and peripheral insulin resistance to treat obesity and type 2 diabetes.

Elevated Serum Cyclophilin B Levels Are Associated with the Prevalence and Severity of Metabolic Syndrome

OBJECTIVE

Inflammation plays a central role in the pathogenesis of metabolic syndrome (MetS). Cyclophilin B (CypB) can be constitutively secreted in response to inflammatory stimuli and oxidative stress, participating in tissue or systemic inflammation. We investigated the relationship between CypB and MetS in both humans and mice.

METHODS

Serum CypB levels were determined in 211 subjects with MetS and 292 subjects without MetS (non-MetS) (133 healthy controls and 159 high-risk subjects with one to two MetS components). Additionally, CypB expression in metabolic organs was examined in mice fed with high-fat diet (HFD) and genetically obese (ob/ob) mice.

RESULTS

Serum CypB level was significantly higher in MetS subjects compared with both groups of non-MetS subjects (193.80 ± 83.22 vs. 168.38 ± 65.01 vs. 124.26 ± 47.83 ng/mL, P < 0.001). Particularly, serum CypB level was significantly higher in subjects with hypertension, central obesity, diabetes mellitus or hyperglycemia, elevated levels of triglycerides, or reduced levels of high-density lipoprotein than in those without. Moreover, CypB was positively associated with the number of MetS components (r = 0.404, P < 0.001), indicating that a higher serum CypB level reflected more severe MetS. Multivariate regression revealed that a one SD increase in CypB was associated with an odds ratio of 1.506 (1.080-2.101, P = 0.016) for MetS prevalence after adjusting for age, gender, conventional risk factors, and medication. Stratified analyses by age and gender demonstrated that subjects >60 years old with higher CypB levels were more likely to have MetS, and the risk for MetS was higher and more significant in women compared with men. Additionally, CypB expression levels were lower at baseline and dramatically enhanced in metabolic organs (such as the liver) and visceral and subcutaneous adipose tissue from HFD-induced obese mice and ob/ob mice.

CONCLUSION

Increased CypB levels were significantly and independently associated with the presence and severity of MetS, indicating that CypB could be used as a novel biomarker and clinical predictor of MetS.

S100A8/A9 (Calprotectin), Interleukin-6, and C-Reactive Protein in Obesity and Diabetes before and after Roux-en-Y Gastric Bypass Surgery

BACKGROUND

In obesity, which is a major contributor to insulin resistance and diabetes, the circulating level of S100A8/A9 (calprotectin) is elevated and declines after Roux-en-Y gastric bypass surgery (RYGB). However, studies on S100A8/A9 and the pathophysiological mechanisms in insulin resistance and diabetes are few and contradictory.

METHODS

We studied 48 subjects who underwent RYGB, comprising a non-diabetic control group and two diabetic groups in whom diabetes either regressed or persisted, 6-12 months post-surgically. S100A8/A9, interleukin 6 (IL-6) as well as other inflammatory and diabetes-related markers were measured pre- and post-surgically.

RESULTS

Significant and similar decreases of BMI were found in all groups. S100A8/A9 and IL-6 decreased significantly in the group with diabetes remission and in the control group, but not in the group with persistent diabetes. The relative changes in S100A8/A9 and IL-6 correlated significantly (r = 0.905, p = 0.005) only in the group with persistent diabetes. In contrast, leukocyte count and C-reactive protein correlated significantly to S100A8/A9 only in the control group.

CONCLUSION

Our study is suggestive of S100A8/A9 and IL-6 being related to a persistent diabetes status post-surgically and of different pathophysiological mechanisms being involved in the post-surgical changes in the three groups, despite similar decreases in BMI.

Role of T Lymphocytes in Type 2 Diabetes and Diabetes-Associated Inflammation

Although a critical role of adaptive immune system has been confirmed in driving local and systemic inflammation in type 2 diabetes and promoting insulin resistance, the underlying mechanism is not completely understood. Inflammatory regulation has been focused on innate immunity especially macrophage for a long time, while increasing evidence suggests T cells are crucial for the development of metabolic inflammation and insulin resistance since 2009. There was growing evidence supporting the critical implication of T cells in the pathogenesis of type 2 diabetes. We will discuss the available effect of T cells subsets in adaptive immune system associated with the procession of T2DM, which may unveil several potential strategies that could provide successful therapies in the future.

Mitochondrial fat oxidation is essential for lipid-induced inflammation in skeletal muscle in mice

Inflammation, lipotoxicity and mitochondrial dysfunction have been implicated in the pathogenesis of obesity-induced insulin resistance and type 2 diabetes. However, how these factors are intertwined in the development of obesity/insulin resistance remains unclear. Here, we examine the role of mitochondrial fat oxidation on lipid-induced inflammation in skeletal muscle. We used skeletal muscle-specific Cpt1b knockout mouse model where the inhibition of mitochondrial fatty acid oxidation results in accumulation of lipid metabolites in muscle and elevated circulating free fatty acids. Gene expression of pro-inflammatory cytokines, chemokines, and cytokine- and members of TLR-signalling pathways were decreased in Cpt1b^m−/− muscle. Inflammatory signalling pathways were not activated when evaluated by multiplex and immunoblot analysis. In addition, the inflammatory response to fatty acids was reduced in primary muscle cells derived from Cpt1b^m−/− mice. Gene expression of Cd11c, the M1 macrophage marker, was decreased; while Cd206, the M2 macrophage marker, was increased in skeletal muscle of Cpt1b^m−/− mice. Finally, expression of pro-inflammatory markers was decreased in white adipose tissue of Cpt1b^m−/− mice. We show that the inflammatory response elicited by elevated intracellular lipids in skeletal muscle is repressed in Cpt1b^m−/− mice, strongly supporting the hypothesis that mitochondrial processing of fatty acids is essential for the lipid-induction of inflammation in muscle.

Gal3 Links Inflammation and Insulin Resistance

The connection between obesity-induced insulin resistance and inflammation is established, but targeting inflammatory mediators like TNF-α and IL-1β have had limited success improving insulin sensitivity in patients. Now, Li et al. (2016) indicate that galectin-3 could be a targetable link between inflammation and insulin sensitivity.

Effect of the Interplay Between Genetic and Behavioral Risks on Survival After Age 75

OBJECTIVES

To explore the association between genes that may be related to human mortality, taking into account the possible contribution of morbidity, and investigate whether lifestyle behaviors may attenuate genetic risk.

DESIGN

Twenty-five-year population-based cohort study.

SETTING

Kungsholmen cohort, Stockholm, Sweden.

PARTICIPANTS

Individuals aged 75 and older (N = 1,229).

MEASUREMENTS

The associations between single-nucleotide variations in 14 genes (previously associated with mortality or to diseases linked to mortality), relevant lifestyle risk behaviors (smoking; mental, physical, or social inactivity; moderate or poor social network), and mortality were estimated using Cox regression.

RESULTS

People with allelic variation in four genes related to cardiovascular diseases and metabolism were more likely to die: apolipoprotein (APO)C1 GG and AG carriers, APOE ɛ4 carriers, insulin-degrading enzyme (IDE) TC carriers, and phosphatidylinositol 3-kinase (PI3KCB) GG carriers. Individuals with multiple adverse alleles had 62% higher mortality rate than those with none. In contrast, people with no risk behaviors (low-risk profile) had 65% lower mortality rate than people with all examined risk behaviors (high-risk profile). Combining the genetic and environmental factors, it was found that, independent of genetic profile, individuals with a low-risk profile had up to 64% lower mortality rate than those with a moderate high- or high-risk profile and at least one genetic risk factor.

CONCLUSION

This study supports and expands evidence that genetic variations in APOE, IDE, and PI3KCB are associated with lower mortality rate, although lifestyle behaviors can modulate their effects.

Adipose Recruitment and Activation of Plasmacytoid Dendritic Cells Fuel Metaflammation

In obese individuals, visceral adipose tissue (VAT) is the seat of chronic low-grade inflammation (metaflammation), but the mechanistic link between increased adiposity and metaflammation largely remains unclear. In obese individuals, deregulation of a specific adipokine, chemerin, contributes to innate initiation of metaflammation by recruiting circulating plasmacytoid dendritic cells (pDCs) into VAT through chemokine-like receptor 1 (CMKLR1). Adipose tissue-derived high-mobility group B1 (HMGB1) protein activates Toll-like receptor 9 (TLR9) in the adipose-recruited pDCs by transporting extracellular DNA through receptor for advanced glycation end products (RAGE) and induces production of type I interferons (IFNs). Type I IFNs in turn help in proinflammatory polarization of adipose-resident macrophages. IFN signature gene expression in VAT correlates with both adipose tissue and systemic insulin resistance (IR) in obese individuals, which is represented by ADIPO-IR and HOMA2-IR, respectively, and defines two subgroups with different susceptibility to IR. Thus, this study reveals a pathway that drives adipose tissue inflammation and consequent IR in obesity.

Causal relationship between obesity-related traits and TLR4-driven responses at the maternal-fetal interface

AIMS/HYPOTHESIS

Obesity triggers complex inflammatory networks within the innate immune system. During pregnancy, the placenta amplifies the low-grade inflammation through activation of Toll-like receptor 4 (TLR4) signalling pathways. The purpose of this study was to investigate the impact of obesity on placental TLR4 expression and inflammatory signals. The secondary aim was to analyse the placental cell type responsible for TLR4 activation.

METHODS

Thirty-nine women recruited at term-scheduled Caesarean section were grouped according to their pre-gravid BMI (<25 kg/m(2) and >30 kg/m(2)). Placenta, venous maternal and cord blood were obtained at delivery for analysis. Data were analysed with linear regression and Spearman's rank correlation coefficient analysis.

RESULTS

TLR4, IL6 and IL8 expression was increased three- to ninefold (p < 0.001) in the placenta of obese vs lean women. There was a positive correlation between placental TLR4 and maternal systemic and placental IL6 and IL8 concentrations. Placental TLR4 expression was correlated with maternal pre-gravid BMI, insulin resistance index, plasma insulin and C-reactive protein (r = 0.57, 0.31, 0.35, 0.53, respectively; p < 0.001) but not with plasma glucose, maternal age, gestational age and gestational weight gain (r < 0.2; p > 0.1). TLR4 was located in both trophoblast and macrovascular endothelial cells lining fetal vasculature. Lipopolysaccharide-induced TLR4 activation was more robust in trophoblasts than in endothelial vascular cells (100-fold vs tenfold; p < 0.001).

CONCLUSIONS/INTERPRETATION

Trophoblastic TLR4 is strongly implicated in the propagation of placental inflammation. Placental inflammation is related to maternal metabolic conditions such as pre-gravid BMI, whilst gestational weight gain or gestational age are not. These results implicate the pre-gravid condition as a significant contributor to metabolic inflammation in late pregnancy.

Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) has become a major cause of cirrhosis and liver-related deaths worldwide. NASH is strongly associated with obesity and the metabolic syndrome, conditions that cause lipid accumulation in hepatocytes (hepatic steatosis). It is not well understood why some, but not other, individuals with hepatic steatosis develop NASH. The factors that determine whether or not NASH progresses to cirrhosis are also unclear. This review summarizes key components of NASH pathogenesis and discusses how inherent and acquired variations in regulation of these processes impact the risk for NASH and NASH cirrhosis.

Lipotoxic lethal and sublethal stress signaling in hepatocytes: relevance to NASH pathogenesis

The accumulation of lipids is a histologic and biochemical hallmark of obesity-associated nonalcoholic fatty liver disease (NAFLD). A subset of NALFD patients develops progressive liver disease, termed nonalcoholic steatohepatitis, which is characterized by hepatocellular apoptosis and innate immune system-mediated inflammation. These responses are orchestrated by signaling pathways that can be activated by lipids, directly or indirectly. In this review, we discuss palmitate- and lysophosphatidylcholine (LPC)-induced upregulation of p53-upregulated modulator of apoptosis and cell-surface expression of the death receptor TNF-related apoptosis-inducing ligand receptor 2. Next, we review the activation of stress-induced kinases, mixed lineage kinase 3, and c-Jun N-terminal kinase, and the activation of endoplasmic reticulum stress response and its downstream proapoptotic effector, CAAT/enhancer binding homologous protein, by palmitate and LPC. Moreover, the activation of these stress signaling pathways is linked to the release of proinflammatory, proangiogenic, and profibrotic extracellular vesicles by stressed hepatocytes. This review discusses the signaling pathways induced by lethal and sublethal lipid overload that contribute to the pathogenesis of NAFLD.

Obesity as a risk factor for malignant melanoma and non-melanoma skin cancer

The dramatic increases in incidence of both obesity and many cancers including skin cancer emphasize the need to better understand the pathophysiology of both conditions and their connections. Melanoma is considered the fastest growing cancer and rates of non-melanoma skin cancer have also increased over the last decade. The molecular mechanisms underlying the association between obesity and skin cancer are not clearly understood but emerging evidence points to changes in the tumor microenvironment including aberrant cell signaling and genomic instability in the chronic inflammatory state many obese individuals experience. This article reviews the literature linking obesity to melanoma and non-melanoma skin cancer.

Causality of small and large intestinal microbiota in weight regulation and insulin resistance

OBJECTIVE

The twin pandemics of obesity and Type 2 diabetes (T2D) are a global challenge for health care systems. Changes in the environment, behavior, diet, and lifestyle during the last decades are considered the major causes. A Western diet, which is rich in saturated fat and simple sugars, may lead to changes in gut microbial composition and physiology, which have recently been linked to the development of metabolic diseases.

METHODS

We will discuss evidence that demonstrates the influence of the small and large intestinal microbiota on weight regulation and the development of insulin resistance, based on literature search.

RESULTS

Altered large intestinal microbial composition may promote obesity by increasing energy harvest through specialized gut microbes. In both large and small intestine, microbial alterations may increase gut permeability that facilitates the translocation of whole bacteria or endotoxic bacterial components into metabolic active tissues. Moreover, changed microbial communities may affect the production of satiety-inducing signals. Finally, bacterial metabolic products, such as short chain fatty acids (SCFAs) and their relative ratios, may be causal in disturbed immune and metabolic signaling, notably in the small intestine where the surface is large. The function of these organs (adipose tissue, brain, liver, muscle, pancreas) may be disturbed by the induction of low-grade inflammation, contributing to insulin resistance.

CONCLUSIONS

Interventions aimed to restoring gut microbial homeostasis, such as ingestion of specific fibers or therapeutic microbes, are promising strategies to reduce insulin resistance and the related metabolic abnormalities in obesity, metabolic syndrome, and type 2 diabetes. This article is part of a special issue on microbiota.

Geranylgeranyl pyrophosphate performs as an endogenous regulator of adipocyte function via suppressing the LXR pathway

Isoprenoids such as geranylgeranyl pyrophosphate (GGPP) influence various biological processes. Here we show that GGPP inhibits adipocyte differentiation via the liver X receptors (LXRs) pathway. Intracellular GGPP levels and GGPP synthase (Ggps) mRNA expression increases during adipocyte differentiation. Ggps expression also increases in white adipose tissue of obese mice. GGPP addition reduces the expression of adipogenic marker genes such as adipocyte fatty acid binding protein, peroxisome proliferator-activated receptor γ, and insulin-stimulated glucose uptake. Similarly, over-expressing Ggps inhibits adipocyte differentiation. In contrast, Ggps knockdown promotes adipocyte differentiation. Inhibition of adipocyte differentiation by GGPP was partially reduced by LXR agonist T0901317. Furthermore, Ggps knockdown up-regulates LXR target genes during adipocyte differentiation. These results suggest that GGPP may act as an endogenous regulator of adipocyte differentiation and maturation through a mechanism partially dependent on the LXR pathway.

A hidden residential cell in the lung

Eosinophils are classically known as proinflammatory cells, as they are equipped with a variety of preformed cytotoxic mediators and have been shown to definitively contribute to asthma. The connection between eosinophils and asthma development has led to a new class of asthma therapeutics based on blocking eosinophils with humanized antibodies that neutralize IL-5, a potent eosinophil growth, activation, and survival factor. Yet, recent studies have led to an increasing appreciation that eosinophils have a variety of homeostatic functions, including immunomodulation. In this issue of the JCI, Mesnil et al. identify a notable population of lung-resident eosinophils and demonstrate that, compared with traditional eosinophils, these cells have distinct characteristics, including nuclear structure, surface markers, IL-5 independence, and immunoregulatory function that is capable of polarizing adaptive immune responses, at least in vitro. Thus, these results reinforce a key homeostatic role for this enigmatic cell population, particularly in residing and regulating immunity in the lung.

Transgenic overexpression of VEGF-C induces weight gain and insulin resistance in mice

Obesity comprises great risks for human health, contributing to the development of other diseases such as metabolic syndrome, type 2 diabetes and cardiovascular disease. Previously, obese patients were found to have elevated serum levels of VEGF-C, which correlated with worsening of lipid parameters. We recently identified that neutralization of VEGF-C and -D in the subcutaneous adipose tissue during the development of obesity improves metabolic parameters and insulin sensitivity in mice. To test the hypothesis that VEGF-C plays a role in the promotion of the metabolic disease, we used K14-VEGF-C mice that overexpress human VEGF-C under control of the keratin-14 promoter in the skin and monitored metabolic parameters over time. K14-VEGF-C mice had high levels of VEGF-C in the subcutaneous adipose tissue and gained more weight than wildtype littermates, became insulin resistant and had increased ectopic lipid accumulation at 20 weeks of age on regular mouse chow. The metabolic differences persisted under high-fat diet induced obesity. These results indicate that elevated VEGF-C levels contribute to metabolic deterioration and the development of insulin resistance, and that blockade of VEGF-C in obesity represents a suitable approach to alleviate the development of insulin resistance.

Colonic Macrophages "Remote Control" Adipose Tissue Inflammation and Insulin Resistance

The early events linking diet-induced adipose tissue inflammation and insulin resistance remain poorly understood. In this issue of Cell Metabolism, Kawano et al. (2016) show that infiltration of colonic pro-inflammatory macrophages orchestrated by the intestinal CCL2/CCR2 axis kick-starts this process during high-fat-diet feeding.

Targeting adipose tissue in the treatment of obesity-associated diabetes

Adipose tissue regulates numerous physiological processes, and its dysfunction in obese humans is associated with disrupted metabolic homeostasis, insulin resistance and type 2 diabetes mellitus (T2DM). Although several US-approved treatments for obesity and T2DM exist, these are limited by adverse effects and a lack of effective long-term glucose control. In this Review, we provide an overview of the role of adipose tissue in metabolic homeostasis and assess emerging novel therapeutic strategies targeting adipose tissue, including adipokine-based strategies, promotion of white adipose tissue beiging as well as reduction of inflammation and fibrosis.

Chronic Inflammation and γδ T Cells

The epithelial tissues of the skin, lungs, reproductive tract, and intestines are the largest physical barriers the body has to protect against infection. Epithelial tissues are woven with a matrix of immune cells programed to mobilize the host innate and adaptive immune responses. Included among these immune cells are gamma delta T lymphocytes (γδ T cells) that are unique in their T cell receptor usage, location, and functions in the body. Stress reception by γδ T cells as a result of traumatic epithelial injury, malignancy, and/or infection induces γδ T cell activation. Once activated, γδ T cells function to repair tissue, induce inflammation, recruit leukocytes, and lyse cells. Many of these functions are mediated via the production of cytokines and growth factors upon γδ T cell activation. Pathogenesis of many chronic inflammatory diseases involves γδ T cells; some of which are exacerbated by their presence, while others are improved. γδ T cells require a delicate balance between their need for acute inflammatory mediators to function normally and the detrimental impact imparted by chronic inflammation. This review will focus on the recent progress made in understanding how epithelial γδ T cells influence the pathogenesis of chronic inflammatory diseases and how a balance between acute and chronic inflammation impacts γδ T cell function. Future studies will be important to understand how this balance is achieved.

Regulation of metabolic health and adipose tissue function by group 2 innate lymphoid cells

Adipose tissue (AT) is home to an abundance of immune cells. With chronic obesity, inflammatory immune cells accumulate and promote insulin resistance and the progression to type 2 diabetes mellitus. In contrast, recent studies have highlighted the regulation and function of immune cells in lean, healthy AT, including those associated with type 2 or "allergic" immunity. Although traditionally activated by infection with multicellular helminthes, AT type 2 immunity is active independently of infection, and promotes tissue homeostasis, AT "browning," and systemic insulin sensitivity, protecting against obesity-induced metabolic dysfunction and type 2 diabetes mellitus. In particular, group 2 innate lymphoid cells (ILC2s) are integral regulators of AT type 2 immunity, producing the cytokines interleukin-5 and IL-13, promoting eosinophils and alternatively activated macrophages, and cooperating with and promoting AT regulatory T (Treg) cells. In this review, we focus on the recent developments in our understanding of group 2 innate lymphoid cell cells and type 2 immunity in AT metabolism and homeostasis.

Cathelicidin suppresses lipid accumulation and hepatic steatosis by inhibition of the CD36 receptor

BACKGROUND AND OBJECTIVES

Obesity is a global epidemic which increases the risk of the metabolic syndrome. Cathelicidin (LL-37 and mCRAMP) is an antimicrobial peptide with an unknown role in obesity. We hypothesize that cathelicidin expression correlates with obesity and modulates fat mass and hepatic steatosis.

MATERIALS AND METHODS

Male C57BL/6 J mice were fed a high-fat diet. Streptozotocin was injected into mice to induce diabetes. Experimental groups were injected with cathelicidin and CD36 overexpressing lentiviruses. Human mesenteric fat adipocytes, mouse 3T3-L1 differentiated adipocytes and human HepG2 hepatocytes were used in the in vitro experiments. Cathelicidin levels in non-diabetic, prediabetic and type II diabetic patients were measured by enzyme-linked immunosorbent assay.

RESULTS

Lentiviral cathelicidin overexpression reduced hepatic steatosis and decreased the fat mass of high-fat diet-treated diabetic mice. Cathelicidin overexpression reduced mesenteric fat and hepatic fatty acid translocase (CD36) expression that was reversed by lentiviral CD36 overexpression. Exposure of adipocytes and hepatocytes to cathelicidin significantly inhibited CD36 expression and reduced lipid accumulation. Serum cathelicidin protein levels were significantly increased in non-diabetic and prediabetic patients with obesity, compared with non-diabetic patients with normal body mass index (BMI) values. Prediabetic patients had lower serum cathelicidin protein levels than non-diabetic subjects.

CONCLUSIONS

Cathelicidin inhibits the CD36 fat receptor and lipid accumulation in adipocytes and hepatocytes, leading to a reduction of fat mass and hepatic steatosis in vivo. Circulating cathelicidin levels are associated with increased BMI. Our results demonstrate that cathelicidin modulates the development of obesity.