Increased Adiposity in Annexin A1-Deficient Mice

Production of Annexin A1 (ANXA1), a protein that mediates the anti-inflammatory action of glucocorticoids, is altered in obesity, but its role in modulation of adiposity has not yet been investigated. The objective of this study was to investigate modulation of ANXA1 in adipose tissue in murine models of obesity and to study the involvement of ANXA1 in diet-induced obesity in mice. Significant induction of ANXA1 mRNA was observed in adipose tissue of both C57BL6 and Balb/c mice with high fat diet (HFD)-induced obesity versus mice on chow diet. Upregulation of ANXA1 mRNA was independent of leptin or IL-6, as demonstrated by use of leptin-deficient ob/ob mice and IL-6 KO mice. Compared to WT mice, female Balb/c ANXA1 KO mice on HFD had increased adiposity, as indicated by significantly elevated body weight, fat mass, leptin levels, and adipocyte size. Whereas Balb/c WT mice upregulated expression of enzymes involved in the lipolytic pathway in response to HFD, this response was absent in ANXA1 KO mice. A significant increase in fasting glucose and insulin levels as well as development of insulin resistance was observed in ANXA1 KO mice on HFD compared to WT mice. Elevated plasma corticosterone levels and blunted downregulation of 11-beta hydroxysteroid dehydrogenase type 1 in adipose tissue was observed in ANXA1 KO mice compared to diet-matched WT mice. However, no differences between WT and KO mice on either chow or HFD were observed in expression of markers of adipose tissue inflammation.These data indicate that ANXA1 is an important modulator of adiposity in mice, with female ANXA1 KO mice on Balb/c background being more susceptible to weight gain and diet-induced insulin resistance compared to WT mice, without significant changes in inflammation.     

Deficiency of Interleukin-15 Confers Resistance to Obesity by Diminishing Inflammation and Enhancing the Thermogenic Function of Adipose Tissues

ObjectiveIL-15 is an inflammatory cytokine secreted by many cell types. IL-15 is also produced during physical exercise by skeletal muscle and has been reported to reduce weight gain in mice. Contrarily, our findings on IL-15 knockout (KO) mice indicate that IL-15 promotes obesity. The aim of this study is to investigate the mechanisms underlying the pro-obesity role of IL-15 in adipose tissues.MethodsControl and IL-15 KO mice were maintained on high fat diet (HFD) or normal control diet. After 16 weeks, body weight, adipose tissue and skeletal mass, serum lipid levels and gene/protein expression in the adipose tissues were evaluated. The effect of IL-15 on thermogenesis and oxygen consumption was also studied in primary cultures of adipocytes differentiated from mouse preadipocyte and human stem cells.ResultsOur results show that IL-15 deficiency prevents diet-induced weight gain and accumulation of lipids in visceral and subcutaneous white and brown adipose tissues. Gene expression analysis also revealed elevated expression of genes associated with adaptive thermogenesis in the brown and subcutaneous adipose tissues of IL-15 KO mice. Accordingly, oxygen consumption was increased in the brown adipocytes from IL-15 KO mice. In addition, IL-15 KO mice showed decreased expression of pro-inflammatory mediators in their adipose tissues.ConclusionsAbsence of IL-15 results in decreased accumulation of fat in the white adipose tissues and increased lipid utilization via adaptive thermogenesis. IL-15 also promotes inflammation in adipose tissues that could sustain chronic inflammation leading to obesity-associated metabolic syndrome.     

Hematological and acute-phase responses to diet-induced obesity in IL-6 KO mice

Obesity is associated with chronic inflammation and elevated levels of IL-6. The role of IL-6 in induction of acute-phase proteins and modulation of hematological responses has been demonstrated in models of inflammation and aging, but not in obesity. We hypothesized that IL-6 is necessary to regulate the acute-phase response and hematological changes associated with diet-induced obesity (DIO) in mice. Feeding a 60%kcal/fat diet for 13 weeks to C57BL6 WT male mice induced a significant increase in IL-6 expression in visceral adipose tissue (VAT), but not liver, compared to mice fed chow diet. Significantly elevated IL-6 levels were present in the peritoneal lavage fluid, but not plasma, of DIO compared to lean mice. A comparable degree of obesity, hepatomegaly, hyperleptinemia, VAT inflammation and insulin resistance was observed in DIO WT and IL-6 KO mice compared to WT and KO mice fed chow diet. Significant leukocytosis was observed in DIO WT but not DIO KO mice compared to lean groups. A significant reduction in platelet counts, without alterations in platelet size, percentage of circulating reticulated platelets and number of bone marrow megakaryocytes, was present in DIO KO mice compared to each other group. Hepatic expression of thrombopoietin was comparable in each group, with DIO WT and KO mice having reduced VAT expression compared to lean mice. Lean KO mice had significantly elevated plasma levels of thrombopoietin compared to each other group, whereas liver-associated thrombopoietin levels were comparable in each group. Deficiency of IL-6 resulted in blunted hepatic induction of the acute-phase protein serum amyloid A-1, whereas expression of hepcidin-1 and -2, LPS-binding protein, ceruloplasmin, plasminogen activator inhibitor-1 and thrombospondin-1 was IL-6-independent. In conclusion, in the absence of overt metabolic alterations, IL-6 modulates leukocytosis, thrombopoiesis and induction of SAA-1, but not other acute-phase proteins in obese mice.     

Obesity in Insulin Receptor Substrate‐2–Deficient Mice: Disrupted Control of Arcuate Nucleus Neuropeptides

Objectives : Disturbances in insulin signaling have been shown to induce obesity and/or hyperphagia in brain insulin receptor or insulin receptor substrate‐2 (IRS‐2) knockout (KO) mice. This study aimed to examine the central and peripheral mechanisms underlying the phenotype in IRS‐2 KO mice. Research Methods and Procedures : We measured the histological characterization of adipose tissues, mRNA levels of pro‐opiomelanocortin, agouti‐related protein, and neuropeptide Y in the hypothalamus and uncoupling proteins (UCPs) in peripheral tissues of IRS‐2 KO mice. Results : Female IRS‐2 KO mice showed increased daily food intake. Body weight and adiposity were increased in both sexes, although these differences were more pronounced in female than in male IRS‐2 KO mice. Both male and female IRS‐2 KO mice showed decreased UCP1 mRNA expression in brown adipose tissue with defective thermoregulation, and UCP2 mRNA expression was increased in the white adipose tissue of female knockout mice. Furthermore, arcuate nucleus mRNA expression of pro‐opiomelanocortin, was decreased in both male and female IRS‐2 KO mice, whereas expression of agouti‐related protein and neuropeptide Y were increased in female IRS‐2 KO mice. Discussion : In IRS‐2 KO mice, disrupted control of hypothalamic neuropeptide levels and UCP mRNA expression may contribute to the development of obesity.     

Adipose and liver expression of interleukin (IL)-1 family members in morbid obesity and effects of weight loss

Morbid obesity is associated with a state of chronic inflammation. Interleukin-1 family (IL-1F) cytokine members are produced by human adipose tissue in obesity. Whereas certain IL-1F members such as IL-1β or IL-18 are potently proinflammatory, others such as IL-1 receptor antagonist (IL-1Ra) or IL-37 (formerly IL-1F7) are antiinflammatory. The NLRP3 inflammasome plays a key role in the processing of bioactive IL-1β and IL-18. We investigated the effect of excessive weight loss on subcutaneous adipose tissue and liver expression of IL-1α, IL-1β, IL-18, IL-1Ra, IL-37 and NLRP3. Twenty-one severely obese patients undergoing laparoscopic adjustable gastric banding were studied. Tissue samples were collected before and 6 months after laparoscopic adjustable gastric banding surgery. mRNA expression of all studied IL-1F members, but especially of IL-37, was much higher in subcutaneous/visceral adipose tissue compared with their liver expression. Subcutaneous adipose tissue mRNA expression of IL-1β decreased significantly after extensive weight loss; expression of IL-18 and IL-1Ra did not change, whereas IL-37 expression increased. Weight loss led to a significant reduction in liver IL-1β, IL-18 and IL-1Ra expression, whereas hepatic IL-37 mRNA expression remained stable. Adipose/liver NLRP3 inflammasome and IL-1α expression were not affected by weight loss. Tissue expression of IL-1β, IL-18 and IL-37 were significantly higher in subcutaneous/visceral adipose tissue compared with the liver. In conclusion, expression of IL-1F members is more pronounced in adipose compared with liver tissue in patients with severe obesity. Excessive weight loss changes the adipose and liver expression profile of IL-1F members toward a more antiinflammatory direction.     

The matricellular protein SPARC/osteonectin as a newly identified factor up-regulated in obesity

Alterations in the expression level of genes may contribute to the development and pathophysiology of obesity. To find genes differentially expressed in adipose tissue during obesity, we performed suppression subtractive hybridization on epididymal fat mRNA from goldthioglucose (GTG) obese mice and from their lean littermates. We identified the secreted protein acidic and rich in cysteine (SPARC), a protein that mediates cell-matrix interactions and plays a role in modulation of cell adhesion, differentiation, and angiogenesis. SPARC mRNA expression in adipose tissue was markedly increased (between 3- and 6-fold) in three different models of obesity, i.e. GTG mice, ob/ob mice, and AKR mice, after 6 weeks of a high fat diet. Immunoblotting of adipocyte extracts revealed a similar increase in protein level. Using a SPARC-specific ELISA, we demonstrated that SPARC is secreted by isolated adipocytes. We found that insulin administration to mice increased SPARC mRNA in the adipose tissue. Food deprivation had no effect on SPARC expression, but after high fat refeeding SPARC mRNA levels were significantly increased. Our results reveal both hormonal and nutritional regulation of SPARC expression in the adipocyte, and importantly, its alteration in obesity. Finally, we show that purified SPARC increased mRNA levels of plasminogen activator inhibitor 1 (PAI-1) in cultured rat adipose tissue suggesting that elevated adipocyte expression of SPARC might contribute to the abnormal expression of PAI-1 observed in obesity. We propose that SPARC is a newly identified autocrine/paracrine factor that could affect key functions in adipose tissue physiology and pathology.     

Role of IL-6 in Exercise Training- and Cold-Induced UCP1 Expression in Subcutaneous White Adipose Tissue

Expression of brown adipose tissue (BAT) associated proteins like uncoupling protein 1 (UCP1) in inguinal WAT (iWAT) has been suggested to alter iWAT metabolism. The aim of this study was to investigate the role of interleukin-6 (IL-6) in exercise training and cold exposure-induced iWAT UCP1 expression. The effect of daily intraperitoneal injections of IL-6 (3 ng/g) in C57BL/6 mice for 7 days on iWAT UCP1 expression was examined. In addition, the expression of UCP1 in iWAT was determined in response to 3 days of cold exposure (4°C) and 5 weeks of exercise training in wild type (WT) and whole body IL-6 knockout (KO) mice. Repeated injections of IL-6 in C57BL/6 mice increased UCP1 mRNA but not UCP1 protein content in iWAT. Cold exposure increased iWAT UCP1 mRNA content similarly in IL-6 KO and WT mice, while exercise training increased iWAT UCP1 mRNA in WT mice but not in IL-6 KO mice. Additionally, a cold exposure-induced increase in iWAT UCP1 protein content was blunted in IL-6 KO mice, while UCP1 protein content in iWAT was lower in both untrained and exercise trained IL-6 KO mice than in WT mice. In conclusion, repeated daily increases in plasma IL-6 can increase iWAT UCP1 mRNA content and IL-6 is required for an exercise training-induced increase in iWAT UCP1 mRNA content. In addition IL-6 is required for a full induction of UCP1 protein expression in response to cold exposure and influences the UCP1 protein content iWAT of both untrained and exercise trained animals.     

Amyloid precursor protein expression is upregulated in adipocytes in obesity

The aim of this study was to determine whether amyloid precursor protein (APP) is expressed in human adipose tissue, dysregulated in obesity, and related to insulin resistance and inflammation. APP expression was examined by microarray expression profiling of subcutaneous abdominal adipocytes (SAC) and cultured preadipocytes from obese and nonobese subjects. Quantitative real-time PCR (QPCR) was performed to confirm differences in APP expression in SAC and to compare APP expression levels in adipose tissue, adipocytes, and stromal vascular cells (SVCs) from subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) specimens. Adipose tissue samples were also examined by western blot and immunofluorescence confocal microscopy. Microarray studies demonstrated that APP mRNA expression levels were higher in SAC (approximately 2.5-fold) and preadipocytes (approximately 1.4) from obese subjects. Real-time PCR confirmed increased APP expression in SAC in a separate group of obese compared with nonobese subjects (P=0.02). APP expression correlated to in vivo indices of insulin resistance independently of BMI and with the expression of proinflammatory genes, such as monocyte chemoattractant protein-1 (MCP-1) (R=0.62, P=0.004), macrophage inflammatory protein-1alpha (MIP-1alpha) (R=0.60, P=0.005), and interleukin-6 (IL-6) (R=0.71, P=0.0005). Full-length APP protein was detected in adipocytes by western blotting and APP and its cleavage peptides, Abeta40 and Abeta42, were observed in SAT and VAT by immunofluorescence confocal microscopy. In summary, APP is highly expressed in adipose tissue, upregulated in obesity, and expression levels correlate with insulin resistance and adipocyte cytokine expression levels. These data suggest a possible role for APP and/or Abeta in the development of obesity-related insulin resistance and adipose tissue inflammation.     

Interleukin-6 derived from cutaneous deficiency of stearoyl-CoA desaturase- 1 may mediate metabolic organ crosstalk among skin,adipose tissue and liver

Stearoyl-CoA desaturase 1 (SCD1), a lipogenic enzyme that adds a double bond at the delta 9 position of stearate (C18: 0) and palmitate (C16: 0), has been proven to be important in the development of obesity. Mice with skin-specific deficiency of SCD1 (SKO) display increased whole-body energy expenditure, which is protective against adiposity from a high-fat diet because it improves glucose clearance, insulin sensitivity, and hepatic steatosis. Of note, these mice also display elevated levels of the “pro-inflammatory” plasma interleukin-6 (IL-6). In whole skin of SKO mice, IL-6 mRNA levels are increased, and protein expression is evident in hair follicle cells and in keratinocytes. Recently, the well-known role of IL-6 in causing white adipose tissue lipolysis has been linked to indirectly activating the gluconeogenic enzyme pyruvate carboxylase 1 in the liver, thereby increasing hepatic glucose production. In this study, we suggest that skin-derived IL-6 leads to white adipose tissue lipolysis, which contributes to the lean phenotype of SKO mice without the incidence of meta-inflammation that is associated with IL-6 signaling.     

Differential regulation of leptin expression and function in A/J vs. C57BL/6J mice during diet-induced obesity

Obesity-resistant (A/J) and obesity-prone (C57BL/6J) mice were weaned onto low-fat (LF) or high-fat (HF) diets and studied after 2, 10, and 16 wk. Despite consuming the same amount of food, A/J mice on the HF diet deposited less carcass lipid and gained less weight than C57BL/6J mice over the course of the study. Leptin mRNA was increased in white adipose tissue (WAT) in both strains on the HF diet but to significantly higher levels in A/J compared with C57BL/6J mice. Uncoupling protein 1 (UCP1) and UCP2 mRNA were induced by the HF diet in brown adipose tissue (BAT) and WAT of A/J mice, respectively, but not in C57BL/6J mice. UCP1 mRNA was also significantly higher in retroperitoneal WAT of A/J compared with C57BL/6J mice. The ability of A/J mice to resist diet-induced obesity is associated with a strain-specific increase in leptin, UCP1, and UCP2 expression in adipose tissue. The findings indicate that the HF diet does not compromise leptin-dependent regulation of adipocyte gene expression in A/J mice and suggest that maintenance of leptin responsiveness confers resistance to diet-induced obesity.