Vilborg Palsdottir

Glucagon-like peptide 1 receptor induced suppression of food intake, and body weight is mediated by central IL-1 and IL-6

Significance There is a growing interest in the gut- and hindbrain-produced hormone glucagon-like peptide 1 (GLP-1), and GLP-1–targeting drugs are in clinical trials for treatment of obesity, and already in the clinic for treatment of type 2 diabetes. Therefore, the implications of information arising from our study are clinically relevant and considerable. GLP-1 receptor stimulation decreases feeding and body weight likely via the CNS, effects of unquestioned scientific and clinical importance, considering the alarming rates of obesity. Despite this, there is scarce information about the mediators and mechanisms behind the effects of GLP-1. In this study, we found surprising evidence that two cytokines, interleukin-6 and interleukin-1, mediate antiobesity effects of GLP-1 receptor stimulation at the level of the CNS. Glucagon-like peptide 1 (GLP-1), produced in the intestine and the brain, can stimulate insulin secretion from the pancreas and alleviate type 2 diabetes. The cytokine interleukin-6 (IL-6) may enhance insulin secretion from β-cells by stimulating peripheral GLP-1 production. GLP-1 and its analogs also reduce food intake and body weight, clinically beneficial actions that are likely exerted at the level of the CNS, but otherwise are poorly understood. The cytokines IL-6 and interleukin 1β (IL-1β) may exert an anti-obesity effect in the CNS during health. Here we found that central injection of a clinically used GLP-1 receptor agonist, exendin-4, potently increased the expression of IL-6 in the hypothalamus (11-fold) and the hindbrain (4-fold) and of IL-1β in the hypothalamus, without changing the expression of other inflammation-associated genes. Furthermore, hypothalamic and hindbrain interleukin-associated intracellular signals [phosphorylated signal transducer and activator of transcription-3 (pSTAT3) and suppressor of cytokine signaling-1 (SOCS1)] were also elevated by exendin-4. Pharmacologic disruption of CNS IL-1 receptor or IL-6 biological activity attenuated anorexia and body weight loss induced by central exendin-4 administration in a rat. Simultaneous blockade of IL-1 and IL-6 activity led to a more potent attenuation of exendin-4 effects on food intake. Mice with global IL-1 receptor gene knockout or central IL-6 receptor knockdown showed attenuated decrease in food intake and body weight in response to peripheral exendin-4 treatment. GLP-1 receptor activation in the mouse neuronal Neuro2A cell line also resulted in increased IL-6 expression. These data outline a previously unidentified role of the central IL-1 and IL-6 in mediating the anorexic and body weight loss effects of GLP-1 receptor activation.

Inter-relation between Interleukin (IL)-1, IL-6 and Body Fat Regulating Circuits of the Hypothalamic Arcuate Nucleus

Interleukin (IL)‐1 and IL‐6 are immune modulating cytokines that also affect metabolic function because both IL‐1 receptor I deficient (IL‐1RI−/−) and IL‐6 deficient (IL‐6−/−) mice develop late‐onset obesity and leptin resistance. Both IL‐1 and IL‐6 appear to target the central nervous system (CNS) to increase energy expenditure. The hypothalamic arcuate nucleus (ARC) is a major relay between the periphery and CNS in body fat regulation (e.g. by being a target of leptin). The present study aimed to investigate the possible mechanisms responsible for the effects exerted by endogenous IL‐1 and IL‐6 on body fat at the level of the ARC, as well as possible interactions between IL‐1 and IL‐6. Therefore, we measured the gene expression of neuropeptides of the ARC involved in energy balance in IL‐1RI−/− and IL‐6−/− mice. We also investigated the interactions between expression of IL‐1 and IL‐6 in these mice, and mapped IL‐6 receptor α (IL‐6Rα) in the ARC. The expression of the obesity promoting peptide neuropeptide Y (NPY), found in the ARC, was increased in IL‐1RI−/− mice. The expression of NPY and agouti‐related peptide (AgRP), known to be co‐expressed with NPY in ARC neurones, was increased in cold exposed IL‐6−/− mice. IL‐6Rα immunoreactivity was densely localised in the ARC, especially in the medial part, and was partly found in NPY positive cell bodies and also α‐melanocyte‐stimulating hormone positive cell bodies. The expression of hypothalamic IL‐6 was decreased in IL‐1RI−/− mice, whereas IL‐1ß expression was increased in IL‐6−/− mice. The results of the present study indicate that depletion of the activity of the fat suppressing cytokines IL‐1 and IL‐6 in knockout mice can increase the expression of the obesity promoting neuropeptide NPY in the ARC. Depletion of IL‐1 activity suppresses IL‐6 expression, and IL‐6Rα‐like immunoreactivity is present in neurones in the medial ARC, including neurones containing NPY. Therefore, IL‐6, IL‐1 and NPY/AgRP could interact at the level of the hypothalamic ARC in the regulation of body fat.

Postnatal deficiency of essential fatty acids in mice results in resistance to diet-induced obesity and low plasma insulin during adulthood

Our objective was to investigate the long-term metabolic effects of postnatal essential fatty acid deficiency (EFAD). Mouse dams were fed an EFAD diet or an isoenergetic control diet 4 days before delivery and throughout lactation. The pups were weaned to standard diet (STD) and were later subdivided into two groups: receiving high fat diet (HFD) or STD. Body composition, energy expenditure, food intake and leptin levels were analyzed in adult offspring. Blood glucose and plasma insulin concentrations were measured before and during a glucose tolerance test. EFAD offspring fed STD were leaner with lower plasma leptin and insulin concentrations compared to controls. EFAD offspring fed HFD were resistant to diet-induced obesity, had higher energy expenditure and lower levels of plasma leptin and insulin compared to controls. These results indicate that the fatty acid composition during lactation is important for body composition and glucose tolerance in the adult offspring.

iTiH-5 Expression in Human adipose Tissue is increased in Obesity

Adipocytes secrete many proteins that regulate metabolic functions. The gene inter‐α (globulin) inhibitor H5 (ITIH‐5) encodes a secreted protein and is known to be expressed abundantly in the placenta. However, using gene expression profiles data we observed high expression of ITIH‐5 in adipose tissue. The aim of this study was to test the hypothesis that ITIH‐5 is strongly expressed in human adipocytes and adipose tissue, and is related to obesity and clinical metabolic variables. ITIH‐5 adipose tissue mRNA expression was analyzed with DNA microarray and real‐time PCR, and its association with clinical variables was examined. ITIH‐5 protein expression was analyzed using western blot. ITIH‐5 mRNA expression was abundant in human adipose tissue, adipocytes, and placenta, and higher in subcutaneous (sc) compared to omental adipose tissue (P < 0.0001). ITIH‐5 mRNA and protein expression in sc adipose tissue were higher in obese compared to lean subjects (P < 0.0001 and P < 0.001, respectively). ITIH‐5 mRNA expression was reduced after diet‐induced weight loss (P < 0.0001). ITIH‐5 mRNA expression was associated with anthropometry and clinical metabolic variables. In conclusion, ITIH‐5 is highly expressed in sc adipose tissue, increased in obesity, down regulated after weight loss, and associated with measures of body size and metabolism. Together, this indicates that ITIH‐5 merits further investigation as a regulator of human metabolism.

Body weight homeostat that regulates fat mass independently of leptin in rats and mice

Significance The only known homeostatic regulator of fat mass is the leptin system. We hypothesized that there is a second homeostat regulating body weight with an impact on fat mass. In this study we have added and removed weight loads from experimental animals and measured the effects on the biological body weight. The results demonstrate that there is a body weight homeostat that regulates fat mass independently of leptin. As the body weight-reducing effect of increased loading was dependent on osteocytes, we propose that there is a sensor for body weight in the long bones of the lower extremities acting as “body scales.” This is part of a body weight homeostat, “gravitostat,” that keeps body weight and body fat mass constant. Subjects spending much time sitting have increased risk of obesity but the mechanism for the antiobesity effect of standing is unknown. We hypothesized that there is a homeostatic regulation of body weight. We demonstrate that increased loading of rodents, achieved using capsules with different weights implanted in the abdomen or s.c. on the back, reversibly decreases the biological body weight via reduced food intake. Importantly, loading relieves diet-induced obesity and improves glucose tolerance. The identified homeostat for body weight regulates body fat mass independently of fat-derived leptin, revealing two independent negative feedback systems for fat mass regulation. It is known that osteocytes can sense changes in bone strain. In this study, the body weight-reducing effect of increased loading was lost in mice depleted of osteocytes. We propose that increased body weight activates a sensor dependent on osteocytes of the weight-bearing bones. This induces an afferent signal, which reduces body weight. These findings demonstrate a leptin-independent body weight homeostat (“gravitostat”) that regulates fat mass.

Dietary Polyunsaturated Fatty Acids Increase Survival and Decrease Bacterial Load during Septic Staphylococcus aureus Infection and Improve Neutrophil Function in Mice

ABSTRACT Severe infection, including sepsis, is an increasing clinical problem that causes prolonged morbidity and substantial mortality. At present, antibiotics are essentially the only pharmacological treatment for sepsis. The incidence of resistance to antibiotics is increasing; therefore, it is critical to find new therapies for sepsis. Staphylococcus aureus is a major cause of septic mortality. Neutrophils play an important role in the defense against bacterial infections. We have shown that a diet with high levels of dietary saturated fatty acids decreases survival in septic mice, but the mechanisms behind this remain elusive. The aim of the present study was to investigate how the differences in dietary fat composition affect survival and bacterial load after experimental septic infection and neutrophil function in uninfected mice. We found that, after S. aureus infection, mice fed a polyunsaturated high-fat diet (HFD-P) for 8 weeks had increased survival and decreased bacterial load during sepsis compared with mice fed a saturated high-fat diet (HFD-S), similar to mice fed a low-fat diet (LFD). Uninfected mice fed HFD-P had a higher frequency of neutrophils in bone marrow than mice fed HFD-S. In addition, mice fed HFD-P had a higher frequency of neutrophils recruited to the site of inflammation in response to peritoneal injection of thioglycolate than mice fed HFD-S. Differences between the proportion of dietary protein and carbohydrate did not affect septic survival at all. In conclusion, polyunsaturated dietary fat increased both survival and efficiency of bacterial clearance during septic S. aureus infection. Moreover, this diet increased the frequency and chemotaxis of neutrophils, key components of the immune response to S. aureus infections.

Preproglucagon neurons in the hindbrain have IL-6 receptor-α and show Ca2+ influx in response to IL-6

Neuronal circuits in the hypothalamus and hindbrain are of importance for control of food intake, energy expenditure, and fat mass. We have recently shown that treatment with exendin-4 (Ex-4), an analog of the proglucagon-derived molecule glucagon-like peptide 1 (GLP-1), markedly increases mRNA expression of the cytokine interleukin-6 (IL-6) in the hypothalamus and hindbrain and that this increase partly mediates the suppression of food intake and body weight by Ex-4. Endogenous GLP-1 in the central nervous system (CNS) is produced by preproglucagon (PPG) neurons of the nucleus of the solitary tract (NTS) in the hindbrain. These neurons project to various parts of the brain, including the hypothalamus. Outside the brain, IL-6 stimulates GLP-1 secretion from the gut and pancreas. In this study, we aim to investigate whether IL-6 can affect GLP-1-producing PPG neurons in the nucleus of the solitary tract (NTS) in mouse hindbrain via the ligand binding part of the IL-6 receptor, IL-6 receptor-α (IL-6Rα). Using immunohistochemistry, we found that IL-6Rα was localized on PPG neurons of the NTS. Recordings of these neurons in GCaMP3/GLP-1 reporter mice showed that IL-6 enhances cytosolic Ca(2+) concentration in neurons capable of expressing PPG. We also show that the Ca(2+) increase originates from the extracellular space. Furthermore, we found that IL-6Rα was localized on cells in the caudal hindbrain expressing immunoreactive NeuN (a neuronal marker) or CNP:ase (an oligodendrocyte marker). In summary, IL-6Rα is present on PPG neurons in the NTS, and IL-6 can stimulate these cells by increasing influx of Ca(2+) to the cytosol from the extracellular space.

Long-term effects of perinatal essential fatty acid deficiency on anxiety-related behavior in mice.

Dietary essential fatty acids have been shown to regulate behavioral and cognitive functions in rodents. However, the long-term effect on behavior, besides memory and learning, of essential fatty acid deficiency (EFAD), i.e., lack of n-3 and n-6 fatty acids, during the perinatal period has not been investigated. Therefore, pregnant C57Bl/6 mice were given either an EFAD or an isoenergetic control diet from gestational day 16 and throughout lactation. The female offspring were given standard chow from 3 weeks of age, and at 12 to 14 weeks of age, open-field, object recognition, light-dark transition, elevated plus maze, and social interaction tests were performed. The brain glycerophospholipid fatty acid composition was investigated in 3-week-old and adult offspring by gas chromatography. The differences observed in behavior were indicative of lower anxiety in the EFAD mice compared to controls illustrated by more time spent in the open arms of the elevated plus maze (+ 41%, p < .05) and in the light compartment in the light-dark transition test (+ 63%, p < .05). The proportion of total n-3 fatty acids, especially 22:6n-3 in the brain, was lower with a compensatory increase in the proportion of total n-6 fatty acids, foremost 22:5n-6, in the EFAD mice compared to controls at 3 weeks of age. In the adult brains the fatty acid composition was normalized. In conclusion, our data show that EFAD during the perinatal period results in short-term alterations of fatty acid composition in brain and decreased anxiety in adult life.

Prenatal essential fatty acid deficiency in mice results in long-term gender-specific effects on body weight and glucose metabolism

Essential fatty acids are important for normal growth and development in early life. However, the long-term effects of prenatal essential fatty acid deficiency (EFAD) on the adult metabolism remain to be determined. The aim of this study was to investigate the effects of an EFAD diet given to mice during late gestation on body weight and body composition, and metabolism in the adult offspring. Pregnant dams were given an EFAD or a control diet during the last 10 days of gestation. After delivery, all mice were fed normal chow and the body weight of the offspring was measured weekly. Furthermore, food intake, energy expenditure and intraperitoneal glucose tolerance were analysed in the adult offspring in addition to body composition (analysed by dual-energy X-ray absorptiometry), plasma levels of leptin, triglycerides and cholesterol. The body weight was lower in the EFAD offspring as compared to the controls during the first 4 weeks of age, and remained lower in the females throughout the study. Lean body mass and plasma leptin levels were also lower in the female EFAD offspring as compared to the controls. Male EFAD offspring were found to have higher fasting glucose and insulin levels as well as higher insulin levels during the glucose tolerance test compared to the controls. However, no differences were found in blood lipids, food intake or energy expenditure between EFAD and control mice of either gender. These results demonstrate that an EFAD diet given during the last 10 days of gestation results in long-term gender-specific effects on body weight and insulin sensitivity in the adult offspring.

Metabolic profiles of fat and glucose differ by gender in healthy 8-year-olds

Objective:  The aim was to investigate if metabolic markers were associated with anthropometry and weight increase in healthy 8‐year‐olds.