Interleukin 37 reverses the metabolic cost of inflammation, increases oxidative respiration, and improves exercise tolerance.

IL-1 family member interleukin 37 (IL-37) has broad antiinflammatory properties and functions as a natural suppressor of innate inflammation. In this study, we demonstrate that treatment with recombinant human IL-37 reverses the decrease in exercise performance observed during systemic inflammation. This effect was associated with a decrease in the levels of plasma and muscle cytokines, comparable in extent to that obtained upon IL-1 receptor blockade. Exogenous administration of IL-37 to healthy mice, not subjected to an inflammatory challenge, also improved exercise performance by 82% compared with vehicle-treated mice (P = 0.01). Treatment with eight daily doses of IL-37 resulted in a further 326% increase in endurance running time compared with the performance level of mice receiving vehicle (P = 0.001). These properties required the engagement of the IL-1 decoy receptor 8 (IL-1R8) and the activation of AMP-activated protein kinase (AMPK), because both inhibition of AMPK and IL-1R8 deficiency abrogated the positive effects of IL-37 on exercise performance. Mechanistically, treatment with IL-37 induced marked metabolic changes with higher levels of muscle AMPK, greater rates of oxygen consumption, and increased oxidative phosphorylation. Metabolomic analyses of plasma and muscles of mice treated with IL-37 revealed an increase in AMP/ATP ratio, reduced levels of proinflammatory mediator succinate and oxidative stress-related metabolites, as well as changes in amino acid and purine metabolism. These effects of IL-37 to limit the metabolic costs of chronic inflammation and to foster exercise tolerance provide a rationale for therapeutic use of IL-37 in the treatment of inflammation-mediated fatigue.

Interleukin-37 suppresses the osteogenic responses of human aortic valve interstitial cells in vitro and alleviates valve lesions in mice.

Calcific aortic valve disease is a chronic inflammatory process, and aortic valve interstitial cells (AVICs) from diseased aortic valves express greater levels of osteogenic factors in response to proinflammatory stimulation. Here, we report that lower cellular levels of IL-37 in AVICs of diseased human aortic valves likely account for augmented expression of bone morphogenetic protein-2 (BMP-2) and alkaline phosphatase (ALP) following stimulation of Toll-like receptor (TLR) 2 or 4. Treatment of diseased AVICs with recombinant human IL-37 suppresses the levels of BMP-2 and ALP as well as calcium deposit formation. In mice, aortic valve thickening is observed when exposed to a TLR4 agonist or a high fat diet for a prolonged period; however, mice expressing human IL-37 exhibit significantly lower BMP-2 levels and less aortic valve thickening when subjected to the same regimens. A high fat diet in mice results in oxidized low-density lipoprotein (oxLDL) deposition in aortic valve leaflets. Moreover, the osteogenic responses in human AVICs induced by oxLDL are suppressed by recombinant IL-37. Mechanistically, reduced osteogenic responses to oxLDL in human AVICs are associated with the ability of IL-37 to inhibit NF-κB and ERK1/2. These findings suggest that augmented expression of osteogenic factors in AVICs of diseased aortic valves from humans is at least partly due to a relative IL-37 deficiency. Because recombinant IL-37 suppresses the osteogenic responses in human AVICs and alleviates aortic valve lesions in mice exposed to high fat diet or a proinflammatory stimulus, IL-37 has therapeutic potential for progressive calcific aortic valve disease.

Interleukin-37 treatment of mice with metabolic syndrome improves insulin sensitivity and reduces pro-inflammatory cytokine production in adipose tissue.

Obesity and the metabolic syndrome are characterized by chronic, low-grade inflammation mainly originating from expanding adipose tissue and resulting in inhibition of insulin signaling and disruption of glycemic control. Transgenic mice expressing human interleukin 37 (IL-37), an anti-inflammatory cytokine of the IL-1 family, are protected against metabolic syndrome when fed a high-fat diet (HFD) containing 45% fat. Here, we examined whether treatment with recombinant IL-37 ameliorates established insulin resistance and obesity-induced inflammation. WT mice were fed a HFD for 22 weeks and then treated daily with IL-37 (1 µg/mouse) during the last 2 weeks. Compared with vehicle only-treated mice, IL-37-treated mice exhibited reduced insulin in the plasma and had significant improvements in glucose tolerance and in insulin content of the islets. The IL-37 treatment also increased the levels of circulating IL-1 receptor antagonist. Cultured adipose tissues revealed that IL-37 treatment significantly decreases spontaneous secretions of IL-1ß, tumor necrosis factor α (TNFα), and CXC motif chemokine ligand 1 (CXCL-1). We also fed mice a 60% fat diet with concomitant daily IL-37 for 2 weeks and observed decreased secretion of IL-1ß, TNFα, and IL-6 and reduced intracellular levels of IL-1α in the liver and adipose tissue, along with improved plasma glucose clearance. Compared with vehicle treatment, these IL-37-treated mice had no apparent weight gain. In human adipose tissue cultures, the presence of 50 pm IL-37 reduced spontaneous release of TNFα and 50% of lipopolysaccharide-induced TNFα. These findings indicate that IL-37's anti-inflammatory effects can ameliorate established metabolic disturbances during obesity.

IL-37 Expression Reduces Lean Body Mass in Mice by Reducing Food Intake.

The human cytokine interleukin (IL)-37 is an anti-inflammatory member of the IL-1 family of cytokines. Transgenic expression of IL-37 in mice protects them from diet-induced obesity and associated metabolic complications including dyslipidemia, inflammation and insulin resistance. The precise mechanism of action leading to these beneficial metabolic effects is not entirely known. Therefore, we aimed to assess in detail the effect of transgenic IL-37 expression on energy balance, including food intake and energy expenditure. Feeding homozygous IL-37 transgenic mice and wild-type (WT) control mice a high-fat diet (HFD; 45% kcal palm fat) for 6 weeks showed that IL-37 reduced body weight related to a marked decrease in food intake. Subsequent mechanistic studies in mice with heterozygous IL-37 expression versus WT littermates, fed the HFD for 18 weeks, confirmed that IL-37 reduces food intake, which led to a decrease in lean body mass, but did not reduce fat mass and plasma lipid levels or alterations in energy expenditure independent of lean body mass. Taken together, this suggests that IL-37 reduces lean body mass by reducing food intake.

Abnormal epigenetic changes during differentiation of human skeletal muscle stem cells from obese subjects.

BACKGROUND: Human skeletal muscle stem cells are important for muscle regeneration. However, the combined genome-wide DNA methylation and expression changes taking place during adult myogenesis have not been described in detail and novel myogenic factors may be discovered. Additionally, obesity is associated with low relative muscle mass and diminished metabolism. Epigenetic alterations taking place during myogenesis might contribute to these defects. METHODS: We used Infinium HumanMethylation450 BeadChip Kit (Illumina) and HumanHT-12 Expression BeadChip (Illumina) to analyze genome-wide DNA methylation and transcription before versus after differentiation of primary human myoblasts from 14 non-obese and 14 obese individuals. Functional follow-up experiments were performed using siRNA mediated gene silencing in primary human myoblasts and a transgenic mouse model. RESULTS: We observed genome-wide changes in DNA methylation and expression patterns during differentiation of primary human muscle stem cells (myoblasts). We identified epigenetic and transcriptional changes of myogenic transcription factors (MYOD1, MYOG, MYF5, MYF6, PAX7, MEF2A, MEF2C, and MEF2D), cell cycle regulators, metabolic enzymes and genes previously not linked to myogenesis, including IL32, metallothioneins, and pregnancy-specific beta-1-glycoproteins. Functional studies demonstrated IL-32 as a novel target that regulates human myogenesis, insulin sensitivity and ATP levels in muscle cells. Furthermore, IL32 transgenic mice had reduced insulin response and muscle weight. Remarkably, approximately 3.7 times more methylation changes (147,161 versus 39,572) were observed during differentiation of myoblasts from obese versus non-obese subjects. In accordance, DNMT1 expression increased during myogenesis only in obese subjects. Interestingly, numerous genes implicated in metabolic diseases and epigenetic regulation showed differential methylation and expression during differentiation only in obese subjects. CONCLUSIONS: Our study identifies IL-32 as a novel myogenic regulator, provides a comprehensive map of the dynamic epigenome during differentiation of human muscle stem cells and reveals abnormal epigenetic changes in obesity.

Activation of proteinase 3 contributes to Non-alcoholic Fatty Liver Disease (NAFLD) and insulin resistance.

Activation of inflammatory pathways is known to accompany development of obesity-induced non-alcoholic fatty liver disease (NAFLD), insulin resistance and type 2 diabetes. In addition to caspase-1, the neutrophil serine proteases proteinase 3, neutrophil elastase and cathepsin G are able to process the inactive pro-inflammatory mediators IL-1ß and IL-18 to their bioactive forms, thereby regulating inflammatory responses. In the present study, we investigated whether proteinase 3 is involved in obesity-induced development of insulin resistance and NAFLD. We investigated the development of NAFLD and insulin resistance in mice deficient for neutrophil elastase/proteinase 3 and neutrophil elastase/cathepsin G and in wild-type mice treated with the neutrophil serine proteinase inhibitor human alpha-1 antitrypsin. Expression profiling of metabolically relevant tissues obtained from insulin resistant mice showed that expression of proteinase 3 was specifically upregulated in the liver, whereas neutrophil elastase, cathepsin G and caspase-1 were not. Neutrophil elastase/proteinase 3 deficient mice showed strongly reduced levels of lipids in the liver after fed a high fat diet. Moreover, these mice were resistant to high fat diet-induced weight gain, inflammation and insulin resistance. Injection of proteinase 3 exacerbated insulin resistance in caspase-1(-/-) mice, indicating that proteinase 3 acts independently of caspase-1. Treatment with alpha-1 antitrypsin during the last 10 days of a 16 week high fat diet reduced hepatic lipid content and decreased fasting glucose levels. We conclude that proteinase 3 is involved in NAFLD and insulin resistance and that inhibition of proteinase 3 may have therapeutic potential.

One week treatment with the IL-1 receptor antagonist anakinra leads to a sustained improvement in insulin sensitivity in insulin resistant patients with type 1 diabetes mellitus.

Inflammation associated with obesity is involved in the development of insulin resistance. We hypothesized that anti-inflammatory treatment with the Interleukin-1 receptor antagonist anakinra would improve insulin sensitivity. In an open label proof-of-concept study, we included overweight patients diagnosed with type 1 diabetes with an HbA1c level over 7.5%. Selecting insulin resistant patients with longstanding type 1 diabetes allowed us to study the effects of anakinra on insulin sensitivity. Patients were treated with 100mg anakinra daily for one week. Insulin sensitivity, insulin need and blood glucose profiles were measured before, after one week and after four weeks of follow-up. Fourteen patients completed the study. One week of anakinra treatment led to an improvement of insulin sensitivity, an effect that was sustained for four weeks. Similarly, glucose profiles, HbA1c levels and insulin needs improved. In conclusion, one week of treatment with anakinra improves insulin sensitivity in patients with type 1 diabetes.

IL-1 family members in the pathogenesis and treatment of metabolic disease: Focus on adipose tissue inflammation and insulin resistance.

Obesity is characterized by a chronic, low-grade inflammation that contributes to the development of insulin resistance and type 2 diabetes. Cytokines and chemokines produced by immunocompetent cells influence local as well as systemic inflammation and are therefore critical contributors to the pathogenesis of type 2 diabetes. Hence, cytokines that modulate inflammatory responses are emerging as potential targets for intervention and treatment of the metabolic consequences of obesity. The interleukin-1 (IL-1) family of cytokines and receptors are key mediators of innate inflammatory responses and exhibit both pro- and anti-inflammatory functions. During the last decades, mechanistic insights into how the IL-1 family affects the initiation and progression of obesity-induced insulin resistance have increased significantly. Here, we review the current knowledge and understanding, with emphasis on the therapeutic potential of individual members of the IL-1 family of cytokines for improving insulin sensitivity in patients with diabetes.

PPAR-alpha dependent regulation of vanin-1 mediates hepatic lipid metabolism.

BACKGROUND & AIMS: Peroxisome proliferator-activated receptor alpha (PPARα) is a key regulator of hepatic fat oxidation that serves as an energy source during starvation. Vanin-1 has been described as a putative PPARα target gene in liver, but its function in hepatic lipid metabolism is unknown. METHODS: We investigated the regulation of vanin-1, and total vanin activity, by PPARα in mice and humans. Furthermore, the function of vanin-1 in the development of hepatic steatosis in response to starvation was examined in Vnn1 deficient mice, and in rats treated with an inhibitor of vanin activity. RESULTS: Liver microarray analyses reveals that Vnn1 is the most prominently regulated gene after modulation of PPARα activity. In addition, activation of mouse PPARα regulates hepatic- and plasma vanin activity. In humans, consistent with regulation by PPARα, plasma vanin activity increases in all subjects after prolonged fasting, as well as after treatment with the PPARα agonist fenofibrate. In mice, absence of vanin-1 exacerbates the fasting-induced increase in hepatic triglyceride levels. Similarly, inhibition of vanin activity in rats induces accumulation of hepatic triglycerides upon fasting. Microarray analysis reveal that the absence of vanin-1 associates with gene sets involved in liver steatosis, and reduces pathways involved in oxidative stress and inflammation. CONCLUSIONS: We show that hepatic vanin-1 is under extremely sensitive regulation by PPARα and that plasma vanin activity could serve as a readout of changes in PPARα activity in human subjects. In addition, our data propose a role for vanin-1 in regulation of hepatic TG levels during fasting.

Combined B- and T-cell deficiency does not protect against obesity-induced glucose intolerance and inflammation.

Obesity-induced inflammation is associated with insulin resistance and morphologically characterized by macrophage influx into the adipose tissue. Recently, various other immune cells, including B- and T-cells, have been shown to participate in modulating adipose tissue inflammation during the development of obesity. We show that HFD-feeding modulates the influx of B and T-cells into adipose tissue of obese animals, suggestive of a role of the adaptive immune system in the development of adipose tissue inflammation. Despite a lower bodyweight after HFD-feeding, gene expression levels of CD68, F4/80 and MCP-1 in white adipose tissue were enhanced in SCID animals that lack B- and T-cells. Moreover, conditioned medium from adipose tissue explants of HFD-fed SCID mice revealed increased release of IL-6 and CXCL1 compared to WT animals. Compared to WT mice, glucose tolerance was impaired in B- and T-cell deficient mice after HFD-feeding. Thus, complete B- and T-cell deficiency does not protect against HFD-induced adipose tissue inflammation and glucose intolerance. In contrast, SCID mice showed an increased pro-inflammatory status at the level of the adipose tissue in some cytokines. Our findings suggest that a delicate balance between various B- and T-cell populations controls adipose tissue inflammation.

Circulating interleukin-37 declines with aging in healthy humans: relations to healthspan indicators and IL37 gene SNPs.

Aging is characterized by declines in physiological function that increase risk of age-associated diseases and limit healthspan, mediated in part by chronic low-grade inflammation. Interleukin (IL)-37 suppresses inflammation in pathophysiological states but has not been studied in the context of aging in otherwise healthy humans. Thus, we investigated associations between IL-37 and markers of healthspan in 271 young (18-39 years; n = 41), middle-aged (40-64 years; n = 162), and older (65 + years; n = 68) adults free of overt clinical disease. After conducting a thorough validation of AdipoGen's IL-37 ELISA, we found that plasma IL-37 is lower in older adults (young: 339 ± 240, middle-aged: 345 ± 234; older: 258 ± 175 pg/mL; P = 0.048), despite elevations in pro-inflammatory markers. As such, the ratios of circulating IL-37 to pro-inflammatory markers were considerably lower in older adults (e.g., IL-37 to C-reactive protein: young, 888 ± 918 vs. older, 337 ± 293; P = 0.02), indicating impaired IL-37 responsiveness to a pro-inflammatory state with aging and consistent with the notion of immunosenescence. These ratios were related to multiple indicators of healthspan, including positively to cardiorespiratory fitness (P < 0.01) and negatively to markers of adiposity, blood pressure, and blood glucose (all P < 0.05). Lastly, we correlated single-nucleotide polymorphisms (SNPs) in the IL37 and ILR8 (the co-receptor for IL-37) genes and found that variants in IL37 SNPs tended to be associated with blood pressure and adiposity (P = 0.08-0.09) but did not explain inter-individual variability in circulating IL-37 concentrations across age (P ≥ 0.23). Overall, our findings provide novel insights into a possible role of IL-37 in biological aging in humans.

Interleukin-37 improves T-cell-mediated immunity and chimeric antigen receptor T-cell therapy in aged backgrounds.

Aging-associated declines in innate and adaptive immune responses are well documented and pose a risk for the growing aging population, which is predicted to comprise greater than 40 percent of the world's population by 2050. Efforts have been made to improve immunity in aged populations; however, safe and effective protocols to accomplish this goal have not been universally established. Aging-associated chronic inflammation is postulated to compromise immunity in aged mice and humans. Interleukin-37 (IL-37) is a potent anti-inflammatory cytokine, and we present data demonstrating that IL-37 gene expression levels in human monocytes significantly decline with age. Furthermore, we demonstrate that transgenic expression of interleukin-37 (IL-37) in aged mice reduces or prevents aging-associated chronic inflammation, splenomegaly, and accumulation of myeloid cells (macrophages and dendritic cells) in the bone marrow and spleen. Additionally, we show that IL-37 expression decreases the surface expression of programmed cell death protein 1 (PD-1) and augments cytokine production from aged T-cells. Improved T-cell function coincided with a youthful restoration of Pdcd1, Lat, and Stat4 gene expression levels in CD4+ T-cells and Lat in CD8+ T-cells when aged mice were treated with recombinant IL-37 (rIL-37) but not control immunoglobin (Control Ig). Importantly, IL-37-mediated rejuvenation of aged endogenous T-cells was also observed in aged chimeric antigen receptor (CAR) T-cells, where improved function significantly extended the survival of mice transplanted with leukemia cells. Collectively, these data demonstrate the potency of IL-37 in boosting the function of aged T-cells and highlight its therapeutic potential to overcome aging-associated immunosenescence.

Short-term interleukin-37 treatment improves vascular endothelial function, endurance exercise capacity, and whole-body glucose metabolism in old mice.

Aging is associated with vascular endothelial dysfunction, reduced exercise tolerance, and impaired whole-body glucose metabolism. Interleukin-37 (IL-37), an anti-inflammatory cytokine of the interleukin-1 family, exerts salutary physiological effects in young mice independent of its inflammation-suppressing properties. Here, we assess the efficacy of IL-37 treatment for improving physiological function in older age. Old mice (26-28 months) received daily intraperitoneal injections of recombinant human IL-37 (recIL-37; 1 µg/200 ml PBS) or vehicle (200 ml PBS) for 10-14 days. Vascular endothelial function (ex vivo carotid artery dilation to increasing doses of acetylcholine, ACh) was enhanced in recIL-37 vs. vehicle-treated mice via increased nitric oxide (NO) bioavailability (all p < .05); this effect was accompanied by enhanced ACh-stimulated NO production and reduced levels of reactive oxygen species in endothelial cells cultured with plasma from IL-37-treated animals (p < .05 vs. vehicle plasma). RecIL-37 treatment increased endurance exercise capacity by 2.4-fold, which was accompanied by a 2.9-fold increase in the phosphorylated AMP-activated kinase (AMPK) to AMPK ratio (i.e., AMPK activation) in quadriceps muscle. RecIL-37 treatment also improved whole-body insulin sensitivity and glucose tolerance (p < .05 vs. vehicle). Improvements in physiological function occurred without significant changes in plasma, aortic, and skeletal muscle pro-inflammatory proteins (under resting conditions), whereas pro-/anti-inflammatory IL-6 was greater in recIL-37-treated animals. Plasma metabolomics analysis revealed that recIL-37 treatment altered metabolites related to pathways involved in NO synthesis (e.g., increased L-arginine and citrulline/arginine ratio) and fatty acid metabolism (e.g., increased pantothenol and free fatty acids). Our findings provide experimental support for IL-37 therapy as a novel strategy to improve diverse physiological functions in old age.

Increased Adipocyte Size, Macrophage Infiltration, and Adverse Local Adipokine Profile in Perirenal Fat in Cushing's Syndrome.

OBJECTIVE: To analyze changes in fat cell size, macrophage infiltration, and local adipose tissue adipokine profiles in different fat depots in patients with active Cushing's syndrome. METHODS: Subcutaneous (SC) and perirenal (PR) adipose tissue of 10 patients with Cushing's syndrome was compared to adipose tissue of 10 gender-, age-, and BMI-matched controls with regard to adipocyte size determined by digital image analysis on hematoxylin and eosin stainings, macrophage infiltration determined by digital image analysis on CD68 stainings, and adipose tissue leptin and adiponectin levels using fluorescent bead immunoassays and ELISA techniques. RESULTS: Compared to the controls, mean adipocyte size was larger in PR adipose tissue in patients. The percentage of macrophage infiltration of the PR adipose tissue and PR adipose tissue lysate leptin levels were higher and adiponectin levels were lower in SC and PR adipose tissue lysates in patients. The adiponectin levels were also lower in the SC adipose tissue supernatants of patients. Associations were found between the severity of hypercortisolism and PR adipocyte size. CONCLUSIONS: Cushing's syndrome is associated with hypertrophy of PR adipocytes and a higher percentage of macrophage infiltration in PR adipose tissue. These changes are associated with an adverse local adipokine profile.

Genetic and pharmacological inhibition of vanin-1 activity in animal models of type 2 diabetes.

Vanins are enzymes that convert pantetheine to pantothenic acid (vitamin B5). Insights into the function of vanins have evolved lately, indicating vanin-1 to play a role in inflammation, oxidative stress and cell migration. Moreover, vanin-1 has recently gained attention as a novel modulator of hepatic glucose and lipid metabolism. In the present study, we investigated the role of vanin-1 in the development of hepatic steatosis and insulin resistance in animal models of obesity and diabetes. In addition, we evaluated the potency of RR6, a novel pharmacological vanin-1 inhibitor, as an anti-diabetic drug. Increased vanin activity was observed in plasma and liver of high fat diet (HFD)-induced obese mice, as well as ZDF-diabetic rats. Ablation of vanin-1 (Vnn1(-/-) mice) mildly improved glucose tolerance and insulin sensitivity in HFD-fed mice, but had no effects on body weight, hepatic steatosis or circulating lipid levels. Oral administration of RR6 for 8 days completely inhibited plasma vanin activity, but did not affect hepatic glucose production, insulin sensitivity or hepatic steatosis in ZDF-diabetes rats. In conclusion, absence of vanin-1 activity improves insulin sensitivity in HFD-fed animals, yet short-term inhibition of vanin activity may have limited value as an anti-diabetic strategy.

Reduced large elastic artery stiffness with regular aerobic exercise in middle-aged and older adults: potential role of suppressed nuclear factor κ B signalling.

OBJECTIVE: Aortic pulse-wave velocity (aPWV) increases with age and is a strong independent predictor of incident cardiovascular diseases (CVDs) in healthy middle-aged and older adults. aPWV is lower in middle-aged and older adults who perform regular aerobic exercise than in their sedentary peers. As exercise is associated with reduced systemic inflammation, we hypothesized that suppression of the pro-inflammatory transcription factor nuclear factor κ B (NFκB) may mediate this process. METHODS: aPWV was measured in young sedentary [n = 10, blood pressure (BP) 108 ±â€Š3/59 ±â€Š2 mmHg; mean ± SEM], middle-aged and older sedentary (n = 9, 124 ±â€Š7/73 ±â€Š5 mmHg) and middle-aged and older aerobic exercise-trained (n = 12, 110 ±â€Š4/67 ±â€Š2 mmHg) healthy, nonhypertensive men and women. RESULTS: Baseline aPWV increased with age [626 ±â€Š14 (young sedentary) vs. 859 ±â€Š49 (middle-aged and older sedentary) cm/s, P < 0.001] but was 20% lower in middle-aged and older trained (686 ±â€Š30 cm/s) than in middle-aged and older sedentary (P < 0.005). Short-term (4 days  x  2500-4500 mg) treatment with the NFκB inhibitor salsalate (randomized, placebo-controlled cross-over design) reduced aPWV (to 783 ±â€Š44 cm/s, P < 0.05) without changing BP (P = 0.40) or heart rate (P = 0.90) in middle-aged and older sedentary, but had no effect in young sedentary (623 ±â€Š19) or middle-aged and older trained (699 ±â€Š30). Following salsalate treatment, aPWV no longer was significantly different in middle-aged and older sedentary vs. middle-aged and older trained (P = 0.29). The reduction in aPWV with salsalate administration was inversely related to baseline (placebo) aPWV (r = -0.60, P < 0.001). CONCLUSION: These results support the hypothesis that suppressed NFκB signalling may partially mediate the lower aortic stiffness in middle-aged and older adults who regularly perform aerobic exercise. Because aPWV predicts incident cardiovascular events in this population, this suggests that tonic suppression of NFκB signalling in middle-aged and older exercising adults may potentially lower cardiovascular risk.

TLR-3 is present in human adipocytes, but its signalling is not required for obesity-induced inflammation in adipose tissue in vivo.

Innate immunity plays a pivotal role in obesity-induced low-grade inflammation originating from adipose tissue. Key receptors of the innate immune system including Toll-like receptors-2 and -4 (TLRs) are triggered by nutrient excess to promote inflammation. The role of other TLRs in this process is largely unknown. In addition to double-stranded viral mRNA, TLR-3 can also recognize mRNA from dying endogenous cells, a process that is frequently observed within obese adipose tissue. Here, we identified profound expression of TLR-3 in adipocytes and investigated its role during diet-induced obesity. Human adipose tissue biopsies (n=80) and an adipocyte cell-line were used to study TLR-3 expression and function. TLR-3-/- and WT animals were exposed to a high-fat diet (HFD) for 16 weeks to induce obesity. Expression of TLR-3 was significantly higher in human adipocytes compared to the non-adipocyte cells part of the adipose tissue. In vitro, TLR-3 expression was induced during differentiation of adipocytes and stimulation of the receptor led to elevated expression of pro-inflammatory cytokines. In vivo, TLR-3 deficiency did not significantly influence HFD-induced obesity, insulin sensitivity or inflammation. In humans, TLR-3 expression in adipose tissue did not correlate with BMI or insulin sensitivity (HOMA-IR). Together, our results demonstrate that TLR-3 is highly expressed in adipocytes and functionally active. However, TLR-3 appears to play a redundant role in obesity-induced inflammation and insulin resistance.

MAP3K8 (TPL2/COT) affects obesity-induced adipose tissue inflammation without systemic effects in humans and in mice.

Chronic low-grade inflammation in adipose tissue often accompanies obesity, leading to insulin resistance and increasing the risk for metabolic diseases. MAP3K8 (TPL2/COT) is an important signal transductor and activator of pro-inflammatory pathways that has been linked to obesity-induced adipose tissue inflammation. We used human adipose tissue biopsies to study the relationship of MAP3K8 expression with markers of obesity and expression of pro-inflammatory cytokines (IL-1ß, IL-6 and IL-8). Moreover, we evaluated obesity-induced adipose tissue inflammation and insulin resistance in mice lacking MAP3K8 and WT mice on a high-fat diet (HFD) for 16 weeks. Individuals with a BMI >30 displayed a higher mRNA expression of MAP3K8 in adipose tissue compared to individuals with a normal BMI. Additionally, high mRNA expression levels of IL-1ß, IL-6 and IL-8, but not TNF -α, in human adipose tissue were associated with higher expression of MAP3K8. Moreover, high plasma SAA and CRP did not associate with increased MAP3K8 expression in adipose tissue. Similarly, no association was found for MAP3K8 expression with plasma insulin or glucose levels. Mice lacking MAP3K8 had similar bodyweight gain as WT mice, yet displayed lower mRNA expression levels of IL-1ß, IL-6 and CXCL1 in adipose tissue in response to the HFD as compared to WT animals. However, MAP3K8 deficient mice were not protected against HFD-induced adipose tissue macrophage infiltration or the development of insulin resistance. Together, the data in both human and mouse show that MAP3K8 is involved in local adipose tissue inflammation, specifically for IL-1ß and its responsive cytokines IL-6 and IL-8, but does not seem to have systemic effects on insulin resistance.

Glucose kinetics in the collagen-induced arthritis model: an all-in-one model to assess both efficacy and metabolic side effects of glucocorticoids.

Prednisolone and other glucocorticoids (GCs) are potent anti-inflammatory drugs, but chronic use is hampered by metabolic side effects. Therefore, there is an urgent medical need for improved GCs that are as effective as classical GCs but have a better safety profile. A well-established model to assess anti-inflammatory efficacy is the chronic collagen-induced arthritis (CIA) model in mice, a model with features resembling rheumatoid arthritis. Models to quantify undesired effects of glucocorticoids on glucose kinetics are less well-established. Recently, we have described a model to quantify basal blood glucose kinetics using stably-labeled glucose. In the present study, we have integrated this blood glucose kinetic model in the CIA model to enable quantification of both efficacy and adverse effects in one animal model. Arthritis scores were decreased after treatment with prednisolone, confirming the anti-inflammatory properties of GCs. Both inflammation and prednisolone induced insulin resistance as insulin secretion was strongly increased whereas blood glucose concentrations and hepatic glucose production were only slightly decreased. This insulin resistance did not directly resulted in hyperglycemia, indicating a highly adaptive compensatory mechanism in these mice. In conclusion, this 'all-in-one' model allows for studying effects of (novel) GC compounds on the development of arthritis and glucose kinetics in a single animal. This integrative model provides a valuable tool for investigating (drug-induced) metabolic dysregulation in an inflammatory setting.

IL-37 protects against obesity-induced inflammation and insulin resistance.

Cytokines of the IL-1 family are important modulators of obesity-induced inflammation and the development of systemic insulin resistance. Here we show that IL-1 family member IL-37, recently characterized as an anti-inflammatory cytokine, ameliorates obesity-induced inflammation and insulin resistance. Mice transgenic for human IL-37 (IL-37tg) exhibit reduced numbers of adipose tissue macrophages, increased circulating levels of adiponectin and preserved glucose tolerance and insulin sensitivity after 16 weeks of HFD. In vitro treatment of adipocytes with recombinant IL-37 reduces adipogenesis and activates AMPK signalling. In humans, elevated steady-state IL-37 adipose tissue mRNA levels are positively correlated with insulin sensitivity and a lower inflammatory status of the adipose tissue. These findings reveal IL-37 as an important anti-inflammatory modulator during obesity-induced inflammation and insulin resistance in both mice and humans, and suggest that IL-37 is a potential target for the treatment of obesity-induced insulin resistance and type 2 diabetes.