Adipokine Gene Research Articles

Adipokine genetics: Unbalanced protein secretion by human adipose tissue as a cause of the metabolic syndrome

Subcutaneous and visceral adipose compartments act, not only as fatty acid depots, but also as active endocrine organs that undergo hyperplastic changes and significantly enhance their function in obesity. Akipokines and other proteins secreted by both adipocytes and stromal cells play a central role in peripheral insulin resistance and the metabolic syndrome (MS). Minor alleles of the adipokine genes substantially contribute to MS. The most important consequence of MS is low-level systemic inflammation supported by adipose-specific synthesis of proinflammatory soluble molecules. Proinflammatory signals are secreted into the bloodstream and spread to peripheral tissues that contain their receptors. The signals provided by adipose tissue stimulate the development of secondary complications of MS, including cardiovascular disorders (CVDs) and nonalcoholic fatty liver disease. The review describes the physiological effects of adiponectin, leptin, resistin, visfatin, and apelin and the influence of the minor alleles of the adipokine genes on the development of the secondary complications of MS.

Endotoxaemia leads to major increases in inflammatory adipokine gene expression in white adipose tissue of mice

The proposition that white adipose tissue is involved in the inflammatory response and metabolic dysregulation of endotoxaemia has been examined. Mice were injected with lipopolysaccharide (LPS; 25 mg/kg) and epididymal, perirenal and subcutaneous adipose tissue removed 4 or 24 h later. The expression of genes encoding key inflammation-related adipokines was measured by real-time polymerase chain reaction. At 24 h after the administration of LPS, there was no change in leptin mRNA level, and adiponectin mRNA fell. However, major increases in TNFalpha, MCP-1 (up to 40-fold) and IL-6 (up to 250-fold) mRNA levels were evident; a substantial elevation in these mRNAs occurred by 4 h, and adipose tissue IL-6 protein also increased (three- to eightfold). At 24 h, the responses in the subcutaneous depot were much lower than in epididymal and perirenal adipose tissue, but at 4 h, the subcutaneous tissue showed major increases in IL-6, MCP-1 and TNFalpha gene expression. In contrast to the inflammatory adipokines, the mRNA level of two macrophage markers, F4/80 and MAC-1, was unaltered in adipose tissue during endotoxaemia. Expression of the hypoxia-sensitive transcription factor, HIF-1alpha, gene was increased at both 4 and 24 h, and HIF-1alpha protein was elevated at 4 h, suggesting that the tissue was hypoxic. It is concluded that white adipose tissue may play an important role in the production of inflammatory mediators in endotoxaemia.

Maternal dexamethasone administration and the maturation of perirenal adipose tissue of the neonatal sheep

Maternal dexamethasone administration promotes fetal maturation such that thermoregulation is improved following premature delivery and is thus comparable with a full term birth. In the present study we determined the impact of dexamethasone on both the mothers’ metabolic status together with adipose tissue function in the newborn. Glucocorticoid action, adipokine gene expression and mitochondrial protein abundance were measured in perirenal adipose tissue of neonatal sheep that were born into either a warm (30oC) or cool (15oC) ambient temperature at 140 days of gestation (dGA; term ~147 dGA), either two days after maternal dexamethasone administration, or at 146 dGA for controls. Dexamethasone administration resulted in a reduction in maternal food intake in conjunction with raised plasma cortisol and free triiodothyronine. In offspring of dexamethasone administered mothers, plasma cortisol was lower and non-esterified fatty acids (NEFA) higher than controls. Glucocorticoid receptor (GR), 11β-hydroxysteroid dehydrogenase (11β-HSD1), interleukin-6 and uncoupling protein (UCP)1 and 2 mRNA together with voltage dependent anion channel, cytochrome c protein and UCP1 abundance were all increased by dexamethasone administration and being born into a cool ambient temperature. Gene expression of tumor necrosis factor α, adiponectin and peroxisome proliferator-activated receptor transcription factor γ were unaffected by dexamethasone. The abundance of mRNA for the GR, 11β-HSD1, UCP1 and 2 mRNA together with each protein were positively correlated to plasma NEFA and negatively correlated to plasma cortisol. In conclusion, despite reduced maternal food intake dexamethasone promotes maturation of glucocorticoid action and mitochondrial protein abundance in the newborn, an adaptation dependent on delivery temperature.

Mineralocorticoid receptor blockade reverses obesity-related changes in expression of adiponectin, peroxisome proliferator-activated receptor-gamma, and proinflammatory adipokines.

In obesity, decreases in adiponectin and increases in proinflammatory adipokines are associated with heart disease. Because adipocytes express mineralocorticoid receptor (MR) and MR blockade reduces cardiovascular inflammation and injury, we tested the hypothesis that MR blockade reduces inflammation and expression of proinflammatory cytokines in adipose tissue and increases adiponectin expression in adipose tissue and hearts of obese mice. We determined the effect of MR blockade (eplerenone, 100 mg/kg per day for 16 weeks) on gene expression in retroperitoneal adipose and heart tissue from obese, diabetic db/db mice (n=8) compared with untreated obese, diabetic db/db mice (n=10) and lean, nondiabetic db/+ littermates (n=11). Expression of tumor necrosis factor-alpha, monocyte chemoattractant protein-1, plasminogen activator inhibitor type 1, and macrophage protein CD68 increased, and expression of adiponectin and peroxisome proliferator-activated receptor-gamma decreased in retroperitoneal adipose tissue from obese versus lean mice. In addition, adiponectin expression in heart was reduced in obese versus lean mice. MR blockade prevented these obesity-related changes in gene expression. Furthermore, treatment of undifferentiated preadipocytes with aldosterone (10(-8) mol/L for 24 hours) increased mRNA levels of tumor necrosis factor-alpha and monocyte chemoattractant protein-1 and reduced mRNA and protein levels of peroxisome proliferator-activated receptor-gamma and adiponectin, supporting a direct aldosterone effect on gene expression. MR blockade reduced expression of proinflammatory and prothrombotic factors in adipose tissue and increased expression of adiponectin in heart and adipose tissue of obese, diabetic mice. These effects on adiponectin and adipokine gene expression may represent a novel mechanism for the cardioprotective effects of MR blockade.

The transcriptional co-activator PGC-1α up regulates apelin in human and mouse adipocytes

By using pangenomic microarray, we identified apelin as a unique adipokine up regulated by the transcriptional co-activator peroxisome proliferator-activated receptor γ (PPARγ) co-activator 1α (PGC-1α) in human white adipocytes. We investigated its regulation in vitro and in vivo. Overexpression of PGC-1α by adenovirus in human adipocytes induces apelin expression and secretion. Pharmacological induction of cAMP, an upstream regulator of endogenous PGC-1α expression, up regulates apelin gene expression and also apelin secretion in human and mice adipocytes. Moreover, during cold exposure in mice, a physiological situation known to induce both cAMP and PGC-1α, apelin expression in adipocytes and plasma levels were increased. This is the first demonstration that PGC-1α is involved in the regulation of an adipokine gene expression and release.

Antioxidative Effects of a New Lychee Fruit-Derived Polyphenol Mixture, Oligonol, Converted into a Low-Molecular Form in Adipocytes

In this study we investigated the antioxidative effects of Oligonol (Amino Up Chemical Co., Ltd., Sapporo, Japan), a new polyphenol, in adipocytes. The levels of reactive oxygen species (ROS) and the expression of adipokine genes decreased in HW mouse white adipocytes upon treatment with Oligonol as compared to control cells. The transcriptional activity of nuclear factor-kappaB (NF-kappaB) and the activation of extracellular signal-regulated kinase (ERK) 1/2 were also down-regulated by Oligonol. In addition, when C57BL/6J mice were fed a high fat diet (HFD) for 5 weeks, the levels of epididymal white adipose tissue (WAT) mass and lipid peroxidation in WAT both increased, but Oligonol intake clearly inhibited such HFD-induced increases. Furthermore, dysregulated expression of genes for adipokines in WAT of mice fed solely a HFD was attenuated by Oligonol intake. These results suggest that Oligonol has antioxidative effects and that it attenuates HFD-induced dysregulated expression of genes for adipokines in adipocytes.

Birth weight and gender determine expression of adipogenic, lipogenic and adipokine genes in perirenal adipose tissue in the young adult sheep

Epidemiological studies have demonstrated that low birth weight is associated with an increased incidence of visceral obesity and metabolic disorders in later life. In the present study, we have determined the impact of birth weight and gender on gene expression in visceral adipose tissue (VAT) in the young adult sheep. Lambs ( n = 19, birth weight range 2.6–7.55 kg) were born at term and growth monitored for 22.4 ± 0.2 weeks, when body composition was determined by Dual X-ray Absorptiometry (DXA) and samples of VAT and subcutaneous (SCAT) adipose tissue collected. Plasma samples were collected at post-mortem for the determination of free fatty acids (FFA), glucose and insulin concentrations. Peroxisome-Proliferator Activated Receptor-γ (PPARγ), glycerol-3-phosphate dehydrogenase (G3PDH), lipoprotein lipase (LPL), adiponectin and leptin mRNA expression was determined by qRT-PCR. Fractional growth rate in postnatal weeks 1–3 was inversely related to birth weight in both males and females ( R 2 = 0.22, P < 0.05, n = 19). PPARγ mRNA expression in VAT, but not SCAT, was inversely related to birth weight ( R 2 = 0.60, P < 0.01, n = 18). In males, but not females, PPARγ mRNA in VAT was directly related to G3PDH mRNA expression ( R 2 = 0.69, P < 0.01, n = 9). Plasma FFA concentrations were inversely related to birth weight in both males and females ( R 2 = 0.22, P < 0.05, n = 19). These findings demonstrate that low birth weight is associated with an increased expression of a key adipogenic factor in visceral adipose tissue in young adulthood. In males, this is associated with an increased expression of lipogenic genes, and this may contribute to the increased propensity for visceral obesity in low birth weight males compared to females.

Placental restriction of fetal growth decreases IGF1 and leptin mRNA expression in the perirenal adipose tissue of late gestation fetal sheep

Placental restriction (PR) of fetal growth results in a low birth weight and an increased visceral fat mass in postnatal life. We investigated whether PR alters expression of genes that regulate adipogenesis [IGF1, IGF1 receptor (IGF1R), IGF2, IGF2R, proliferator-activated receptor-gamma, retinoid-X-receptor-alpha], adipocyte metabolism (lipoprotein lipase, G3PDH, GAPDH) and adipokine signaling (leptin, adiponectin) in visceral adipose tissue before birth. PR was induced by removal of the majority of endometrial caruncles in nonpregnant ewes before mating. Fetal blood samples were collected from 116 days gestation, and perirenal visceral adipose tissue (PAT) was collected from PR and control fetuses at 145 days. PAT gene expression was measured by quantitative RT-PCR. PR fetuses had a lower weight (PR 2.90 +/- 0.32 kg; control, 5.12 +/- 0.24 kg; P < 0.0001), mean gestational arterial Po(2) (P < 0.0001), plasma glucose (P < 0.01), and insulin concentrations (P < 0.02), than controls. The expression of IGF1 mRNA in PAT was lower in the PR fetuses (PR, 0.332 +/- 0.063; control, 0.741 +/- 0.083; P < 0.01). Leptin mRNA expression in PAT was also lower in PR fetuses (PR, 0.077 +/- 0.009; control, 0.115 +/- 0.013; P < 0.05), although there was no difference in the expression of other adipokine or adipogenic genes in PAT between PR and control fetuses. Thus, restriction of placental and hence, fetal substrate supply results in decreased IGF1 and leptin expression in fetal visceral adipose tissue, which may alter the functional development of the perirenal fat depot and contribute to altered leptin signaling in the growth-restricted newborn and the subsequent emergence of an increased visceral adiposity.

No association of defined variability in leptin, leptin receptor, adiponectin, proopiomelanocortin and ghrelin gene with food preferences in the Czech population

Background: Previously, it has been reported that mutations in the genes encoding for adipokines may be associated with impaired food intake and may serve as potential obesity biomarkers. The aim of this study was to investigate the possible associations of defined variability in leptin, leptin receptor, adiponectin, proopiomelanocortin and ghrelin genes with food preferences in the obese and non-obese Czech population and evaluate their potential as the obesity susceptibility genes.Patients and Methods: Using PCR followed by restriction analysis, we studied 185 volunteers. Basic anthropometrical characteristics associated to obesity were measured and the food intake was monitored using a 7-day record method. In the group of obese individuals, a subset of 34 morbidly obese patients was studied for plasma leptin and soluble leptin receptor levels.Results: None of the examined polymorphisms was associated to anthropometrical or demographic characteristics of the study subjects. The Gln223Arg polymorphism within the leptin receptor gene was significantly associated with lower plasma leptin levels (the RR genotype being more frequent in patients with lower plasma leptin levels; P = 0.001). No associations of the examined polymorphisms with food preferences was observed.Conclusions: Based on our results, the examined polymorphisms in the adipokine genes do not seem to be the major risk factor for obesity development in the Czech population nor significantly affect food preferences.

Valproic Acid and CEBPα-Mediated Regulation of Adipokine Gene Expression in Hypothalamic Neurons and 3T3-L1 Adipocytes

Background/Aims: Valproic acid (VPA) is the drug of choice for treating epilepsy, but has the unwanted effects of inducing weight gain and increasing the risk of developing insulin resistance. The mechanism through which these side effects occur is unknown. VPA inhibits histone deacetylase (HDAC), but also decreases the transcriptional activity of CCAAT enhancer binding protein α (CEBPα). Given the possible association between VPA, CEBPα and adipokine gene regulation, we hypothesized that they would alter the expression of resistin (rstn), fasting-induced adipose factor (fiaf) and suppressor of cytokine signaling-3 (socs-3), genes implicated in the development of leptin and insulin resistance. Methods: We investigated the effects of VPA (1 mM; 24 or 48 h) on gene expression using real-time RT-PCR in 3 distinct models: N-1 hypothalamic neurons, 3T3-L1 adipocytes and male CD-1 mice. Subsequently, cells were treated with 5 nM of the more specific HDAC inhibitor trichostatin A (TSA). CEBPα expression was also modified in N-1 neurons using either RNA interference (RNAi) or an overexpression vector to evaluate its effects on target gene expression. Results: In N-1 neurons, VPA induced significant increases in CEBPα and socs-3, but inhibited rstn and fiaf gene expression. In contrast, TSA induced rstn and socs-3, but inhibited fiaf. VPA also induced the expression of CEBPαin 3T3-L1 adipocytes, but had no effect on other target genes, and TSA suppressed fiaf and socs-3.Subsequently, CEBPα was overexpressed (24 h) or silenced using RNAi (24 and 48 h) in N-1 neurons. The silencing of CEBPα led to significant decreases in rstn mRNA, but increased fiaf and socs-3 expression, whereas its overexpression had the opposite effect. When male CD-1 mice were treated with either a single (100 mg/kg; 24 h), or multiple (200 mg/kg; 72 h) daily injections of VPA, no changes in body weight or gene expression were detected in either hypothalamic or adipose tissues. Conclusions: In summary, these experiments reveal a potentially important role for CEBPα in the regulation of hypothalamic gene expression in N-1 neurons and suggest that it might modulate central energy metabolism. Although VPA also modified hypothalamic gene expression in vitro, it remains to be determined whether it has similar effects in vivo.

Traumatic brain injury induces adipokine gene expression in rat brain

Traumatic brain injury (TBI) induces cachexia and neuroinflammation which profoundly impact patient recovery. Adipokine genes such as leptin ( ob), resistin ( rstn) and fasting-induced adipose factor ( fiaf) are implicated in energy metabolism and body weight control and are also associated with chronic low grade inflammation. Since central rstn and fiaf expression was increased following hypoxic/ischemic brain injury, we hypothesized that these genes would also be induced in the rat brain following TBI. Realtime RT-PCR detected a 2–2.5-fold increase in ob mRNA in the ipsilateral cortex and thalamus 12 h following lateral fluid percussion (FP)-induced brain injury. Fiaf mRNA was elevated 5–7.5-fold in cortex, hippocampus and thalamus, and modest increases were also detectable in the contralateral brain. Remarkably, rstn mRNA was elevated in ipsilateral (150-fold) and in contralateral (50-fold) hippocampus. To test whether these changes were part of an inflammatory response to TBI we also examined the effects of an intracerebral injection of lipopolysaccharide (LPS). We determined that central injection of LPS produced some, but not all, of the changes seen after TBI. For example, in contrast to the stimulatory influence of TBI, LPS had no effect on ob expression in any brain region, though fiaf and rstn mRNA levels were significantly elevated in both ipsi- and contralateral cortex. In conclusion: (a) brain-derived adipokines could be involved in the acute pathology of traumatic brain injury partly through modulation of central inflammatory responses, but also via leptin-mediated neuroprotective effects and (b) TBI-induced brain adipokines may induce the metabolic changes observed following neurotrauma.

Postnatal Programming of Glucocorticoid Metabolism in Rats Modulates High-Fat Diet–Induced Regulation of Visceral Adipose Tissue Glucocorticoid Exposure and Sensitivity and Adiponectin and Proinflammatory Adipokines Gene Expression in Adulthood

Alterations of the perinatal environment, which lead to increased prevalence of the metabolic syndrome in adulthood, program an upregulation of systemic and/or adipose tissue glucocorticoid metabolism (11 beta-hydroxysteroid dehydrogenase type 1 [11 beta-HSD-1]-induced corticosterone reactivation). We hypothesized that postnatal programming could modulate high-fat diet-induced adipose tissue dysregulation in adulthood. We compared the effects of chronic (since weaning) high- or low-fat diet in postnatally normofed (control) or overfed (programmed) rats. Postnatal programming accentuated high-fat diet-induced overweight, insulin resistance, glucose intolerance, and decrease in circulating and epididymal adipose tissue adiponectin. Neither manipulation altered liver function. Postnatal programming or high-fat diet increased systemic corticosterone production, which was not further modified when both manipulations were associated. Postnatal programming suppressed high-fat diet-induced decrease in mesenteric adipose tissue (MAT) glucocorticoid sensitivity and triggered high-fat diet-induced increase in MAT glucocorticoid exposure, subsequent to enhanced MAT 11 beta-HSD-1 gene expression. MAT tumor necrosis factor (TNF)-alpha, TNF-receptor 1, interleukin (IL)-6, resistin, and plasminogen activator inhibitor-1 mRNAs were not changed by high-fat feeding in control rats and showed a large increase in programmed animals, with this effect further enhanced by high-fat diet for TNF-alpha and IL-6. Our data show for the first time that postnatal manipulation programs high-fat diet-induced upregulation of MAT glucocorticoid exposure, sensitivity, and inflammatory status and therefore reveal the pivotal role of the environment during the perinatal period on the development of diet-induced adipose tissue dysregulation in adulthood. They also urge the need for clinical trials with specific 11 beta-HSD-1 inhibitors.

SUPPRESSION OF MAFS EXPRESSION BY THE SIRNA TECHNIQUE ALTERS THE GENE PROFILE RELATED TO PANCREATIC ENDOCRINE HORMONE AND ADIPOCYTOKINE IN VIVO AND IN VITRO

One of the large maf molecules, mafA, is a strong transactivator of insulin, and other mafs, including mafB and c-maf, have been found to be involved in the regulation of pancreatic development and function. In a previous study we established an mRNA interference technique that makes it possible to modify the level of targeted mRNAs in the mouse in vivo. An expression vector carrying synthetic maf-siRNA was rapidly injected into the tail vein of 8-week-old-mice (Hydrodynamic method), and the resulting alteration of the gene profile was analyzed with a microarray system. Suppression of the mafA mRNA level in the pancreas by siRNA resulted in down-regulation of insulin and glucagon mRNA and of the mRNA of the adipocytokines adipsin and adiponectin. Thus, mafA is likely to be involved in the regulation of adipocytokines as well as pancreatic endocrine hormone. In a preliminary experiment we found that transfection of adipocytes with mafA siRNA in vitro attenuated adipocyte differentiation and downregulated adipokine gene expression. On the other hand, the c-maf expression level in the pancreas of c-maf-siRNA-treated mice was approximately 50% reduced in comparison with stop-siRNA-treated animals. Microarray analysis revealed down-regulation of expression of the insulin and glucagon genes in the pancreas of siRNA-treated mice, while Ddit3 and Nurp1 (Ddit3 having a p53 binding site, encodes an inhibitor of C/EBP and Nurp1 is a transcriptional cofactor activated in acinar cells of pancreatitis) were upregulated, and HSP8 expression was down-regulated. Moreover, several genes coding kallikrein 1-related peptidase (Klk1b4, Klk1b8, Klk1b11 and Klk1b24), that locate on kallikrein 1 locus (chr.19q13.3-13.4) and code serin protease protein without proven kininogenase activity were down-regulated in the pancreas. This study demonstrated that reduction of mafA and c-maf RNA levels altered expression of genes that code pancreatic hormones, including insulin and glucagon. The results of this study also suggest that mafA may regulate several adipocytokines in the pancreas and that c-maf may not only regulate endocrine hormones in the pancreas but serine proteases as well. Taken together, the findings in this study suggested there the involvement of a network of transcriptional factors, mafs, pancreatic endocrine hormones, and adipocytokines in glucose and lipid metabolism.

Increased Maternal Nutrition Increases Leptin Expression in Perirenal and Subcutaneous Adipose Tissue in the Postnatal Lamb

The present study tested the hypothesis that exposure to an increased level of maternal nutrition before birth results in altered expression of adipogenic, lipogenic, and adipokine genes in adipose tissue in early postnatal life. Pregnant ewes were fed either at or approximately 50% above maintenance energy requirements during late pregnancy, and quantitative RT-PCR was used to measure peroxisome proliferator-activated receptor (PPAR)-gamma, lipoprotein lipase (LPL), glycerol-3-phosphate-dehydrogenase (G3PDH), adiponectin, and leptin mRNA expression in perirenal (PAT) and sc adipose tissue (SCAT) in the offspring on postnatal d 30. Relative SCAT mass was higher in lambs of well-fed ewes (40.0 +/- 4.0 vs. 22.8 +/- 3.3 g/kg, P < 0.05) and was directly related to plasma insulin in the first 24 h after birth and to G3PDH and LPL expression. The expression of leptin mRNA in both the SCAT and PAT depots was higher (P < 0.05) in lambs of well-fed ewes. PPARgamma adiponectin, LPL, and G3PDH mRNA expression were not, however, different between well-fed and control groups in either depot. Relative PPARgamma expression in SCAT was directly related to plasma insulin concentrations in the first 24 h after birth (r(2) = 0.23; P < 0.05), and G3PDH and LPL expressions were also positively correlated with PPARgamma expression (r(2) = 0.27; P < 0.05). We have demonstrated that exposure to increased prenatal nutrition increases leptin expression at 1 month of age in both PAT and SCAT. The results of this study provide evidence that the nutritional environment before and immediately after birth can influence the development of adipose tissue in early postnatal life.

Comment on: Hosagai et al. (2007) Adipose Tissue Hypoxia in Obesity and Its Impact on Adipocytokine Dysregulation: Diabetes 56:901–911

We noted with interest the article (1) where evidence for hypoxia in white adipose tissue (WAT) of two mouse models of obesity was presented. This study indicated that the expression of some adipokine genes, including leptin and plasminogen activator inhibitor-1, are increased in WAT of obese animals, that adiponectin is decreased, and that the effects mirrored those in studies on mouse 3T3-L1 cells (1). These findings are consistent with …

Short Communication Single nucleotide polymorphisms in five adipokine genes in dairy cattle populations

Genetic diversity in candidate genes for fitness and production traits was explored in three populations of dairy cattle. The study focused on adipokines, including leptin (LEP), tumor necrosis factor alpha (TNF), interleukin-8 (IL8) and interleukin-10 (IL10) as candidate genes. The three populations of interest included young Jersey and Holstein (modern Holstein) sires, and Holstein sires born prior to 1970 (traditional Holstein). Pools of DNA representing each sire group were used as template to generate PCR products for sequencing and identification of single nucleotide polymorphisms (SNP). Sequences of PCR products were assembled and SNPs identified using Sequencher 4.5 software. One SNP representing each gene and a previously reported SNP in LEP were selected for genotyping across all bulls. A multiplexed genotyping assay was developed using the ABI PRISM SNaPshot Multiplex Kit. Allele and genotypic frequencies were determined for each sire group, and genotypic frequencies were in agreement with Hardy-Weinberg equilibrium. Allele frequencies were compared among sire groups using the chi-square test. A significant difference between Jersey and Holstein was observed for all genes, and modern and traditional Holstein groups differed for the previously described LEP and IL10 SNP. Although allele frequency differences between modern and traditional Holsteins may reflect the effect of selection pressure for production traits on these genomic regions, random genetic drift or sampling bias could also have contributed to the observed differences. Keywords: Fitness traits; genetic markers; adipokines; dairy cattle South African Journal of Animal Science Vol. 37 (3) 2007: pp.154-157

Capsaicin, a spicy component of hot peppers, modulates adipokine gene expression and protein release from obese-mouse adipose tissues and isolated adipocytes, and suppresses the inflammatory responses of adipose tissue macrophages

Adipokines are involved in the obesity-induced chronic inflammatory response that plays a crucial role in the development of obesity-related pathologies such as type II diabetes and atherosclerosis. We here demonstrate that capsaicin, a naturally occurring phytochemical, can suppress obesity-induced inflammation by modulating adipokine release from and macrophage behavior in obese mice adipose tissues. Capsaicin inhibited the expressions of IL-6 and MCP-1 mRNAs and protein release from the adipose tissues and adipocytes of obese mice, whereas it enhanced the expression of the adiponectin gene and protein. The action of capsaicin is associated with NF-κB inactivation and/or PPARγ activation. Moreover, capsaicin suppressed not only macrophage migration induced by the adipose tissue-conditioned medium, but also macrophage activation to release proinflammatory mediators. Capsaicin may be a useful phytochemical for attenuating obesity-induced inflammation and obesity-related complications.

Adipokine Gene Expression in a Novel Hypothalamic Neuronal Cell Line: Resistin-Dependent Regulation of Fasting-Induced Adipose Factor and SOCS-3

Adipokines such as leptin, resistin, and fasting-induced adipose factor (FIAF) are secreted by adipocytes, but their expression is also detectable in the brain and pituitary. The role of central adipokines remains elusive, but we speculate that they may modulate those hypothalamic signaling pathways that control energy homeostasis. Here we describe experiments to test this in which we exploited a novel hypothalamic neuronal cell line (N-1) that expresses a variety of neuropeptides and receptors that are known to be implicated in appetite regulation. Using real-time RT-PCR, we confirmed that N-1 neurons express resistin (rstn) and fiaf, as well as suppressor of cytokine signaling-3 (socs-3), a feedback inhibitor of leptin signaling. Treating N-1 cells with recombinant resistin (200 ng/ml, 30 min) reduced both fiaf (25%, p < 0.005) and socs-3 (29%, p < 0.005) mRNA levels, and similar reductions in fiaf (40%, p < 0.001) and socs-3 (25%, p < 0.001) resulted following the overexpression of resistin. Conversely, when RNA interference (RNAi) was used to reduce endogenous rstn levels (–60%, p < 0.005), fiaf and socs-3 expression was increased (46 and 65% respectively, p < 0.005). A similar reduction in rstn mRNA was achieved using RNAi in differentiated 3T3-L1 adipocytes, and this manipulation also reduced fiaf and socs-3 expression (–53, –21 and –20% respectively, p < 0.005). In contrast, although RNAi successfully reduced fiaf mRNA by 50% (p < 0.001) in N-1 cells and 40% (p < 0.001) in 3T3-L1 cells, there was no effect on rstn or socs-3 mRNA. These data suggest that resistin exerts a novel autocrine/paracrine control over fiaf and socs-3 expression in both 3T3-L1 adipocytes and N-1 neurons. Such a mechanism could be part of the central feedback system that modulates the effects of adipokines, and other adiposity signals, implicated in hypothalamic energy homeostasis. However, it remains to be determined whether these in vitro results can be translated to the control of adipokine expression in brain and adipose tissue.

Systems genetics: elucidating networks that underlie heritable variation in adipose function

Excess adipose tissue not only physically stresses the organism but also disrupts homeostasis through release of adipokines. Our long term goal is to determine how heritable differences in adipose function impact risk for obesity and its consequences. We employ systems genetics, anchoring phenotypic variation to naturally occurring genetic polymorphisms in two mouse genetic reference populations (GRP): recombinant inbred BXD (C57BL/6J X DBA/2J) strains, and a panel of eight genetically diverse strains that are progenitors for the collaborative cross (CC), an emergent GRP. Body and fat pad weights, plasma hormone profiles and expression of adipokine genes were measured in males of 24 BXD strains and in both sexes of the CC parental strains. Our current progress demonstrates: adiposity is highly correlated with expression of some adipokines (e.g., leptin, r2= 0.628; p=0.00001), but not others (e.g., visfatin, r2=0.0109, p=0.944); a subset of tightly intercorrelated adipokines are regulated independent of adiposity; and sexually dimorphic relationships exist among adipokines and adipose mass. Ongoing assay of adiposity in emerging generations of CC mice confirms that this new GRP will provide physiological diversity reflective of its genetic diversity and on par with that in a human population, highlighting its utility as a tool to dissect the molecular factors that control adipose function.

Overexpression of renin in the liver impairs glucose tolerance

Animal and clinical studies have pointed to a potential role of the Renin Angiotensin System (RAS) in diabetes. However, mechanisms underlying this association are not completely understood. The objective of this work is to dissect the mechanisms by which overexpression of RAS mediates glucose intolerance, using a transgenic mouse model overexpressing renin in the liver (RenTg; Caron et al., 2002), resulting in constitutively elevated plasma angiotensin II (Ang II). Twenty week-old RenTg mice exhibit significantly impaired glucose tolerance and fasting insulinemia, despite normal glycemia, leptinemia and adiponectinemia, as compared to their wild type littermates. Although adipokine gene expression did not differ across genotypes, the type 2 Ang II receptor was markedly down-regulated in adipose tissue of RenTg mice. Comparative proteomics of adipose tissue from these mice indicates a genotype-dependent differential expression of several proteins associated with diabetes and glucose metabolism. We are currently studying these candidate proteins to identify their role in RAS-induced diabetes. These studies demonstrate that overexpression of renin impairs glucose tolerance and further support the role of RAS in the pathogenesis of diabetes. Future studies will dissect mechanism(s) and tissue(s) linking RAS to diabetes. This work was supported by the TN agricultural experiment station and by the Office of Science, U.S. Dept. of Energy.