IL-1 plays an important role in lipid metabolism by regulating insulin levels under physiological conditions

Mature-onset obesity in interleukin-1 receptor I knockout mice

Interleukin-1 (IL-1) is a major mediator of inflammation that exerts its biological activities through the IL-1 type I receptor (IL-1RI). The body weights of IL-1RI(-/-) mice of both sexes started to deviate from those of wild-type mice at 5-6 months of age and were 20% higher at 9 months of age. Visceral and subcutaneous fat mass, measured by dual-energy X-ray absorptiometry and magnetic resonance imaging, was markedly (1.5- to 2.5-fold) increased. Lean body mass and crown-rump length were also slightly (11 and 5%, respectively) increased, as was serum IGF-I. Obese IL-1RI(-/-) mice were insulin resistant, as evidenced by hyperinsulinemia, decreased glucose tolerance, and insulin sensitivity. To elucidate the mechanisms for the development of obesity, young pre-obese IL-1RI(-/-) mice were investigated. They showed decreased suppression of body weight and food intake in response to systemic leptin treatment. The decreased leptin responsiveness was even more pronounced in older obese animals. Moreover, spontaneous locomotor activity and fat utilization, as measured by respiratory quotient, were decreased in pre-obese IL-1RI(-/-) mice. In conclusion, lack of IL-1RI-mediated biological activity causes mature-onset obesity. This obese phenotype is preceded by decreased leptin sensitivity, fat utilization, and locomotor activity.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

Combined interleukin-6 and interleukin-1 deficiency causes obesity in young mice

Proinflammatory cytokines including interleukin (IL)-1 and IL-6 exert pleiotropic effects on the neuro-immuno-endocrine system. Previously, we showed that IL-1 receptor antagonist-deficient (IL-1Ra(-/-)) mice show a lean phenotype due to an abnormal lipid metabolism. On the contrary, it was reported that IL-6(-/-) mice exhibit obesity after 6 months of age. This study sought to assess the roles of IL-1 and IL-6 in body weight homeostasis. We generated mice deficient in IL-6 and IL-1Ra (IL-6(-/-) IL-1Ra(-/-)) and IL-6, IL-1alpha, and IL-1beta (IL-6(-/-) IL-1(-/-)). IL-6(-/-) IL-1Ra(-/-) mice exhibited a lean phenotype, similar to IL-1Ra(-/-) mice. On the other hand, IL-6(-/-) IL-1(-/-) mice became obese as early as 10 weeks of age, while IL-1(-/-) mice and IL-6(-/-) mice were normal at this age. The daily food intake was significantly higher in IL-6(-/-) IL-1(-/-) mice than in IL-6(-/-) IL-1(+/-) mice, while energy expenditure was comparable in these two strains. Acute anorexia induced by peripheral administration of IL-1 was significantly suppressed in IL-6(-/-) IL-1(-/-) mice, but not in IL-1(-/-) mice or IL-6(-/-) mice compared with wild-type mice. These results indicate that IL-1 and IL-6 are both involved in the regulation of body fat in a redundant manner in young mice.

Impact of interleukin-1 and interleukin-6 in murine primary schistosomiasis

BACKGROUND

Immunization with schistosome antigens invariably elicits a plethora of cytokines and, hence, it is reasonable to assume that these cytokines influence host responses to challenge lung-stage larvae and, consequently, the adult worm burden, and may be responsible for the erratic data generally observed in protection studies against schistosome infection.

METHODS

Schistosoma mansoni-infected mice were administered with recombinant interleukin (IL)-1beta or IL-6 to evaluate the impact of cytokines in host responses to lung-stage schistosomula, and subsequent effects on adult worm parameters. Plasma lipid levels were assayed by colorimetric enzymatic tests and antibody responses by ELISA. Cytokine profile in peripheral blood mononuclear cells was evaluated by RT-PCR.

RESULTS

S. mansoni infection elicited, at the time of parasite residency in the lung, significant increase in free fatty acids (FA) and decrease in cholesterol plasma levels in C57BL/6 and CD1 mice, and stimulation of mRNA expression for cytokines of T helper type (Th) 2 in BALB/c, Th1 in C57BL/6, and Th1/Th2 in CD1 mice. However, no specific antibody production was evident in any mouse strain. In BALB/c mice, exogenous IL-1beta-related plasma free FA level significant increase, stimulation of expression of IL-1 and IL-12 mRNA, and considerable increase in percent of specific antibody-producing mice were associated with significant reduction in adult worm burden and egg load. In contrast, exogenous IL-1beta elicited decrease in free FA plasma levels, and down-regulation of cytokines' mRNA expression in C57BL/6 and CD1 mice, changes associated with aggravation of the worm burden. Likewise, exogenous IL-6 failed to stimulate increase in plasma free FA levels or percent of antibody-producing mice except in BALB/c mice, effects that were protective for the host in BALB/c and for the parasite in C57BL/6 and CD1 mice.

CONCLUSION

These findings were discussed in relation to the erratic data of protection experiments with schistosome subunit antigens in different mouse strains.

A polymorphism of the interleukin 1 receptor antagonist is not associated with polycystic ovary syndrome in Caucasian women

In a prospective case-control study we investigated the association of a common polymorphism of the interleukin 1 receptor antagonist gene (IL-1 RA) with the occurrence and the clinical characteristics of polycystic ovary syndrome (PCOS). Allele frequencies did not vary statistically significantly among women with PCOS and healthy controls or within the PCOS group with respect to their clinical characteristics.

Interleukin-1 receptor antagonist is upregulated during diet-induced obesity and regulates insulin sensitivity in rodents

AIMS/HYPOTHESIS

The IL-1 receptor antagonist (IL-1Ra) is an anti-inflammatory cytokine known to antagonise the actions of IL-1. We have previously shown that IL-1Ra is markedly upregulated in the serum of obese patients, is correlated with BMI and insulin resistance, and is overexpressed in the white adipose tissue (WAT) of obese humans. The aim of this study was to examine the role of IL-1Ra in the regulation of glucose homeostasis in rodents.

METHODS

We assessed the expression of genes related to IL-1 signalling in the WAT of mice fed a high-fat diet, as well as the effect of Il1rn (the gene for IL-1Ra) deletion and treatment with IL-1Ra on glucose homeostasis in rodents.

RESULTS

We show that the expression of Il1rn and the gene encoding the inhibitory type II IL-1 receptor was upregulated in diet-induced obesity. The blood insulin:glucose ratio was significantly lower in Il1rn ( -/- )animals, which is compatible with an increased sensitivity to insulin, reinforced by the fact that the insulin content and pancreatic islet morphology of Il1rn ( -/- ) animals were normal. In contrast, the administration of IL-1Ra to normal rats for 5 days led to a decrease in the whole-body glucose disposal due to a selective decrease in muscle-specific glucose uptake.

CONCLUSIONS/INTERPRETATION

The expression of genes encoding inhibitors of IL-1 signalling is upregulated in the WAT of mice with diet-induced obesity, and IL-1Ra reduces insulin sensitivity in rats through a muscle-specific decrease in glucose uptake. These results suggest that the markedly increased levels of IL-1Ra in human obesity might contribute to the development of insulin resistance.

Hypothalamic integration of immune function and metabolism

The immune and neuroendocrine systems are closely involved in the regulation of metabolism at peripheral and central hypothalamic levels. In both physiological (meals) and pathological (infections, traumas and tumors) conditions immune cells are activated responding with the release of cytokines and other immune mediators (afferent signals). In the hypothalamus (central integration), cytokines influence metabolism by acting on nucleus involved in feeding and homeostasis regulation leading to the acute phase response (efferent signals) aimed to maintain the body integrity. Peripheral administration of cytokines, inoculation of tumor and induction of infection alter, by means of cytokine action, the normal pattern of food intake affecting meal size and meal number suggesting that cytokines acted differentially on specific hypothalamic neurons. The effect of cytokines-related cancer anorexia is also exerted peripherally. Increase plasma concentrations of insulin and free tryptophan and decrease gastric emptying and d-xylose absorption. In addition, in obesity an increase in interleukin (IL)-1 and IL-6 occurs in mesenteric fat tissue, which together with an increase in corticosterone, is associated with hyperglycemia, dyslipidemias and insulin resistance of obesity-related metabolic syndrome. These changes in circulating nutrients and hormones are sensed by hypothalamic neurons that influence food intake and metabolism. In anorectic tumor-bearing rats, we detected upregulation of IL-1beta and IL-1 receptor mRNA levels in the hypothalamus, a negative correlation between IL-1 concentration in cerebro-spinal fluid and food intake and high levels of hypothalamic serotonin, and these differences disappeared after tumor removal. Moreover, there is an interaction between serotonin and IL-1 in the development of cancer anorexia as well as an increase in hypothalamic dopamine and serotonin production. Immunohistochemical studies have shown a decrease in neuropeptide Y (NPY) and dopamine (DA) and an increase in serotonin concentration in tumor-bearing rats, in first- and second-order hypothalamic nuclei, while tumor resection reverted these changes and normalized food intake, suggesting negative regulation of NPY and DA systems by cytokines during anorexia, probably mediated by serotonin that appears to play a pivotal role in the regulation of food intake in cancer. Among the different forms of therapy, nutritional manipulation of diet in tumor-bearing state has been investigated. Supplementation of tumor bearing rats with omega-3 fatty acid vs. control diet delayed the appearance of tumor, reduced tumor-growth rate and volume, negated onset of anorexia, increased body weight, decreased cytokines production and increased expression of NPY and decreased alpha-melanocyte-stimulating hormone (alpha-MSH) in hypothalamic nuclei. These data suggest that omega-3 fatty acid suppressed pro-inflammatory cytokines production and improved food intake by normalizing hypothalamic food intake-related peptides and point to the possibility of a therapeutic use of these fatty acids. The sum of these data support the concept that immune cell-derived cytokines are closely related with the regulation of metabolism and have both central and peripheral actions, inducing anorexia via hypothalamic anorectic factors, including serotonin and dopamine, and inhibiting NPY leading to a reduction in food intake and body weight, emphasizing the interconnection of the immune and neuroendocrine systems in regulating metabolism during infectious process, cachexia and obesity.

Decreased fat mass in interleukin-1 receptor antagonist-deficient mice: impact on adipogenesis, food intake, and energy expenditure

Interleukin (IL)-1 is a regulator of inflammation but is also implicated in the control of energy homeostasis. Because the soluble IL-1 receptor antagonist (IL-1Ra) is markedly increased in the serum of obese patients and is overexpressed in white adipose tissue in obesity, we studied the metabolic consequences of genetic IL-1Ra ablation in mice. We have shown that IL-1Ra-/- mice have a lean phenotype due to decreased fat mass, related to a defect in adipogenesis and increased energy expenditure. The adipocytes were smaller in these animals, and the expression of genes involved in adipogenesis was reduced. Energy expenditure as measured by indirect calorimetry was elevated, and weight loss in response to a 24-h fast was increased in IL-1Ra-/- animals compared with wild-type mice. Lipid oxidation of IL-1Ra-/- mice was higher during the light period, reflecting their reduction in diurnal food intake. Interestingly, IL-1Ra-/- and IL-1Ra+/- mice presented an attenuation in high-fat diet-induced caloric hyperphagia, indicating a better adaptation to hypercaloric alimentation, which is in line with the role of IL-1Ra as a mediator of leptin resistance. Taken together, we show that IL-1Ra is an important regulator of adipogenesis, food intake, and energy expenditure.

Adipose tissue: a regulator of inflammation

Adipose tissue is a highly active organ. In addition to storing calories as triglycerides, it also secretes a large variety of proteins, including cytokines, chemokines and hormone-like factors, such as leptin, adiponectin and resistin. Intriguingly, many, if not most, of these adipose-derived proteins have dual actions; cytokines have both immunomodulatory functions and act as systemic or auto-/paracrine regulators of metabolism, while proteins such as leptin and adiponectin are regulators of both metabolism and inflammation. The production of pro-atherogenic chemokines by adipose tissue is of particular interest since their local secretion, e.g. by perivascular adipose depots, may provide a novel mechanistic link between obesity and the associated vascular complications.

The dependence of serum interleukin-6 level on PPAR-alpha polymorphism in men with coronary atherosclerosis

BACKGROUND

The association between L162V polymorphism in the gene for peroxisome proliferator activated receptor (PPAR) alpha and the development of coronary heart disease was examined.

METHODS

PPAR-alpha polymorphism was determined in 48 men with angiographically confirmed coronary atherosclerosis and in 51 healthy men.

RESULTS

The frequency of the V allele of the L162V polymorphism was four times higher in men with atherosclerosis (0.25 in studied group and 0.06 in controls). The polymorphism was not associated with changes in body mass index, lipid pattern, serum adhesion molecules, or vasoactive agents concentrations. The effect of the polymorphism on the serum interleukin-6 level (IL-6) was observed (p<0.01). The serum IL-6 level was higher in homozygotic than in heterozygotic subjects (p<0.02). Multivariate regression analysis showed the existence of a relationship between simvastatin therapy and serum IL-6 level (r=0.83; p<0.05) in the homozygotic men. While in homozygotic patients with atherosclerosis a negative linear correlation between serum IL-6 and NO concentration was shown, in heterozygotic men positive correlations between IL-6 or HDL cholesterol and adhesion molecule levels were found.

CONCLUSION

L162V polymorphism in the gene for PPAR-alpha seems to be associated with atherosclerosis through a mechanism including regulation of the IL-6 level.

Interactions of metabolic hormones, adipose tissue and exercise

Physiological and psychological systems work together to determine energy intake and output, and thus maintain adipose tissue. In addition, adipose tissue secretes leptin and cytokines, which induces satiety and has been linked to catecholamines, cortisol, insulin, human growth hormone, thyroid hormones, gonadotropin and lipolysis. Thus, adipose tissue is acted upon by a number of physiological stimuli, including hormones, and simultaneously, is an active component in the regulation of its own lipid content. All of the hormones mentioned above are associated with each other and respond to exercise and exercise training. Thus, exercise is one of the major links between the hormonal modulators of energy intake and output. It appears that the sympathetic nervous system and the catecholamines are key components facilitating the lipolytic activity during exercise. These two neuroendocrine factors directly affect adipose metabolism and metabolic hormones that influence adipose metabolism. Acute low- and moderate-intensity exercise causes hormonal changes that facilitate lipolytic activity. Exercise training reduces these hormonal responses, but the sensitivity to these hormones increases so that lipolysis may be facilitated. Large amounts of adipose tissue blunt the metabolic hormonal responses to exercise, but the sensitivity of these hormones is increased; thus maintaining normal lipolytic activity. Although the physiological role of the endocrine system during exercise and training is significant, other training effects may have as great, or greater influence on lipolytic activity in adipose tissue.

Homeostatic alterations induced by interleukin-1β microinjection into the orbitofrontal cortex in the rat

The present experiments were designed to elucidate the effect of direct orbitofrontal cortical administration of interleukin-1beta (IL-1beta) on the homeostatic regulation. Short- and long-term food intakes (FI), water intakes and body temperature (BT) were measured before and after a bilateral microinjection of IL-1beta (with or without paracetamol /P/ pretreatment) into the orbitofrontal cortex (OBF) of Wistar rats, and the effects were compared with those found in vehicle-treated and i.p. injected IL-1beta, IL-1beta+P or control animals. In addition, blood glucose levels (BGLs), along a glucose tolerance test, and plasma concentrations of insulin, leptin, cholesterol, triglycerides and urate were determined in cytokine treated and control rats. Short-term FI was suppressed after orbitofrontal cortical or peripheral application of IL-1beta. In the long-term FI, however, there was no significant difference among the groups. Cytokine microinjection into the OBF, similar to the i.p. administration, was also followed by a significant increase in BT. Pretreatment with P failed to influence the anorexigenic and hyperthermic effects of the centrally administered IL-1beta. The sugar load led to a diabetes-like prolonged elevation of BGL in the IL-1beta treated animals. Following cytokine administration, plasma levels of insulin and that of triglycerides were found decreased, whereas that of uric acid increased. The present findings confirm that the OBF is one of the neural routes through which IL-1beta exerts modulatory effect on the central homeostatic regulation.

Interleukin-6 in neurons of the pterygopalatine ganglion of the rat

An indirect immunofluorescence method was used to study the pterygopalatine nerve ganglion in rats with the aim of determining the identification and locations within it of neurons expressing IL-6. A low density of IL-6-immunoreactive cells was seen in the cranial area of the ganglion; the medial surface and caudal area contained occasional cells demonstrating nuclear fluorescence; rarer groups of cells, organized into chains, were seen in the intermediate part of the ganglion on its lateral margin contacting the maxillary nerve.

AHSG gene variant is associated with leanness among Swedish men

Alpha(2) Heremans-Schmid glycoprotein (AHSG) is a plasma protein inhibiting the activity of the insulin receptor tyrosine kinase. Ahsg knock-out mice have increased insulin sensitivity and are resistant to diet-induced obesity. We hypothesized that functional variants of the AHSG gene segregating in the human population would reflect variation in body mass index (BMI). We genotyped 356 overweight or obese (BMI: 37.2 [25.0-66.5] kg/m(2)) and 148 lean (BMI: 23.7 [23.4-24.9] kg/m(2)) otherwise healthy Swedish men for three non-synonymous single-nucleotide polymorphisms (SNPs) within exon 6 (rs4917) and exon 7 (rs4918 and Arg299Cys) and one SNP in intron 1 (rs2593813) of the AHSG gene. The G/G genotype for rs2593813 was more common among lean than among obese and overweight individuals (odds ratio = 2.01, P = 0.009), whereas rs2593813 was in strong linkage disequilibrium (|D'| > or = 0.97) with rs4917 and rs4918. Homozygosity for the rs2593813:G-rs4917:Met-rs4918:Ser haplotype conferred an increased risk for leanness (odds ratio=1.90, P = 0.027). rs4917:Met and rs4918:Ser have previously been associated with lower AHSG protein level. A common variant of AHSG, previously associated with a lower AHSG protein level, is thus more common among lean than obese and overweight men, supporting the results from Ahsg knock-out mice, namely, that AHSG modulates body mass.

Deficiency of interleukin-1 receptor antagonist deteriorates fatty liver and cholesterol metabolism in hypercholesterolemic mice

Although the anti-inflammatory effect of interleukin-1 (IL-1) receptor antagonist (IL-1Ra) has been described, the contribution of this cytokine to cholesterol metabolism remains unclear. Our aim was to ascertain whether deficiency of IL-1Ra deteriorates cholesterol metabolism upon consumption of an atherogenic diet. IL-1Ra-deficient mice (IL-1Ra(-/-)) showed severe fatty liver and portal fibrosis containing many inflammatory cells following 20 weeks of an atherogenic diet when compared with wild type (WT) mice. Expectedly, the levels of total cholesterol in IL-1Ra(-/-) mice were significantly increased, and the start of lipid accumulation in liver was observed earlier when compared with WT mice. Real-time PCR analysis revealed that IL-1Ra(-/-) mice failed to induce mRNA expression of cholesterol 7alpha-hydroxylase, which is the rate-limiting enzyme in bile acid synthesis, with concurrent up-regulation of small heterodimer partner 1 mRNA expression. Indeed, IL-1Ra(-/-) mice showed markedly decreased bile acid excretion, which is elevated in WT mice to maintain cholesterol level under atherogenic diet feeding. Therefore, we conclude that the lack of IL-1Ra deteriorates cholesterol homeostasis under atherogenic diet-induced inflammation.

Short-term resistance to diet-induced obesity in A/J mice is not associated with regulation of hypothalamic neuropeptides

To investigate the mechanisms underlying long-term resistance of the A/J mouse strain to diet-induced obesity, we studied, over a period of 4 wk, the expression of uncoupling proteins in brown adipose tissue and the expression of hypothalamic neuropeptides known to regulate energy homeostasis and then used microarray analysis to identify other potentially important hypothalamic peptides. Despite increased caloric intake after 2 days of high-fat feeding, body weights of A/J mice remained stable. On and after 1 wk of high-fat feeding, A/J mice adjusted their food intake to consume the same amount of calories as mice fed a low-fat diet; thus their body weight and insulin, corticosterone, free fatty acid, and glucose levels remained unchanged for 4 wk. We found no changes in hypothalamic expression of several orexigenic and/or anorexigenic neuropeptides known to play an important role in energy homeostasis for the duration of the study. Uncoupling protein-2 mRNA expression in brown adipose tissue, however, was significantly upregulated after 2 days of high-fat feeding and tended to remain elevated for the duration of the 4-wk study. Gene array analysis revealed that several genes are up- or downregulated in response to 2 days and 1 wk of high-fat feeding. Real-time PCR analysis confirmed that expression of the hypothalamic IL-1 pathway (IL-1beta, IL-1 type 1 and 2 receptors, and PPM1b/PP2C-beta, a molecule that has been implicated in the inhibition of transforming growth factor-beta-activated kinase-1-mediated IL-1 action) is altered after 2 days, but not 1 wk, of high-fat feeding. The role of additional molecules discovered by microarray analysis needs to be further explored in the future.

Involvement of IL-1 family proteins in p38 linked cellular senescence of mouse embryonic fibroblasts

Senescence of mammalian cultured cells is essentially organized by a machinery of cell division and cellular stresses induced by various extracellular stimuli. Here, we show that in mouse embryonic fibroblasts (MEFs) culture in vitro, expression of an inflammatory cytokine, interleukin-1beta (IL-1beta) and its antagonist, IL-1 receptor antagonist (IL-1Ra) are induced by senescence. The kinetics of IL-1beta-expression was similar to that of p38 activation during MEFs culture. We also found a distinguishable accelerated senescence in cell growth in IL-1Ra deficient MEFs culture. Our results suggest that IL-1beta signaling pathway is involved in activation of p38 linked cellular senescence.

Regulatory effects of interleukin (IL)-1, interferon-beta, and IL-4 on the production of IL-1 receptor antagonist by human adipose tissue

Adipose tissue is the source of production and site of action of several pro- and antiinflammatory cytokines. We have recently shown that white adipose tissue (WAT) is a major producer of the antiinflammatory IL-1 receptor antagonist (IL-1Ra). Because IL-1Ra serum levels are elevated 7-fold in human obesity and an excess of this protein has been implicated in the acquired resistance to leptin and insulin, we investigated the regulation of IL-1Ra in human WAT. We demonstrate that IL-1Ra is mainly produced by adipocytes, rather than the stromal fraction of WAT, and that IL-1alpha and beta, as well as interferon-beta (IFN-beta), strongly up-regulate the expression and secretion of IL-1Ra in WAT. Moreover, human WAT expresses the receptors and proteins known to be required for the action of IL-1 (IL-1 receptor type I, IL-1 receptor accessory protein) and IFN-beta (IFN-alpha/beta receptor subunits 1 and 2). Finally, human WAT actively secretes these regulatory cytokines, suggesting that they up-regulate IL-1Ra through a local autocrine/paracrine action, which is hypothesized to play a regulatory role in adipogenesis and metabolism.

The intricate interface between immune system and metabolism

Increasing experimental evidence indicates that several factors that influence metabolism also play a role in the regulation of immune responses. Dissection of the interface connecting the metabolic and immune systems has recently gained wide interest. Particular focus has been on certain cytokines [interleukin-1 (IL-1), IL-6, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma)], hormones (leptin and insulin), neuropeptides (corticotropin-releasing hormone and alpha-melanocyte-stimulating hormone), immune-related proteins (zinc-alpha2-glycoprotein and attractin and/or mahogany), transcription factors (peroxisome-proliferator-activated receptors) and glucose metabolism. A better knowledge of the intricate network of interactions among energy regulation, immune surveillance and vital organ functions could in the near future lead to valuable strategies for therapeutic intervention in several immune-mediated diseases.

Lack of interleukin-1 receptor antagonist modulates plaque composition in apolipoprotein E-deficient mice

OBJECTIVE

Interleukin (IL)-1 plays an important role in atherosclerosis. IL-1 receptor antagonist (IL-1Ra) is an endogenous inhibitor of IL-1. However, the role of IL-1Ra in the development of atherosclerosis is poorly understood.

METHODS AND RESULTS

Mice that lacked IL-1Ra (IL-1Ra-/-) were crossed with apolipoprotein E-deficient (E-/-) mice and formation of atherosclerotic lesions was analyzed after 16 weeks or 32 weeks consumption of a normal chow diet. This study focused on the comparison of atherosclerotic lesion between IL-1Ra+/+/apoE-/- (n=12) and IL-1Ra(+/-)/apoE-/- mice (n=12), because of the significantly leaner phenotype in IL-1Ra-/-/apoE-/- mice compared with the others. Interestingly, atherosclerotic lesion size in IL-1Ra+/-/apoE-/- mice at age 16 weeks was significantly increased (30%) compared with IL-1Ra+/+/apoE-/- mice (P<0.05). At 32 weeks, the differences of lesion size between these mice failed to achieve statistical significance. However, immunostaining demonstrated an 86% (P<0.0001) increase in the MOMA-2-stained lesion area of IL-1Ra+/-/apoE-/- mice. In addition, alpha-actin staining in these lesions was significantly decreased (-15%) compared with those in IL-1Ra+/+/apoE-/- mice (P<0.05).

CONCLUSIONS

These results suggest an important role of IL-1Ra in the suppression of lesion development during early atherogenesis and furthermore indicate its role in the modulation of plaque composition.