Intra-abdominal White Adipose Tissue Research Articles

Screening and validation of differentially expressed genes in adipose tissue of patients with obesity and type 2 diabetes mellitus.

White adipose tissue (WAT) plays a pivotal role in the onset of type 2 diabetes mellitus (T2DM) and obesity. Despite its significance the underlying pathogenesis and key genes associated with it remain elusive. In our study, we screened the differentially expressed genes (DEGs) in intra-abdominal WAT of T2DM patients with obesity, as well as those with simple obesity, aiming to lay a foundational theory for an in-depth investigation of T2DM pathogenesis and the identification of novel therapeutic targets. Gene expression datasets (GSE16415 and GSE71416) were retrieved from the Gene Expression Omnibus (GEO) database. We employed R for screening DEGs and conducted a functional enrichment analysis using the Metascape database. Combined Lasso regression and Boruta feature selection algorithms were used to identify key DEGs. Subsequently, these were cross-verified using the GSE29231 dataset. Samples and medical records were collected from clinical study participants. The mRNA and protein expressions of the key DEGs were verified using qRT-PCR and western blotting, respectively. We discerned a total of 130 DEGs, with 40 being upregulated and 90 downregulated. Functional and pathway enrichment analyses illuminated that these genes are instrumental in mediating metabolite and energy production, neutrophil-mediated immunity, and other associated biological processes. This includes their involvement in the tricarboxylic acid cycle, glycolysis/gluconeogenesis, peroxisome proliferator-activated receptors, and other signalling pathways. Two genes, CIDEA and FSCN1 emerged as key DEGs. The low expression of CIDEA and high expression of FSCN1 in the T2DM and obesity group were verified in clinical samples (P < 0.05). We established that CIDEA and FSCN1 manifest significant differential expression in T2DM patients who are obese. This suggests their potential as risk assessment markers and therapeutic targets for T2DM.

Wt1 haploinsufficiency induces browning of epididymal fat and alleviates metabolic dysfunction in mice on high-fat diet

Aims/hypothesisDespite a similar fat storing function, visceral (intra-abdominal) white adipose tissue (WAT) is detrimental, whereas subcutaneous WAT is considered to protect against metabolic disease. Recent findings indicate that thermogenic genes, expressed in brown adipose tissue (BAT), can be induced primarily in subcutaneous WAT. Here, we investigate the hypothesis that the Wilms tumour gene product (WT1), which is expressed in intra-abdominal WAT but not in subcutaneous WAT and BAT, suppresses a thermogenic program in white fat cells.MethodsHeterozygous Wt1 knockout mice and their wild-type littermates were examined in terms of thermogenic and adipocyte-selective gene expression. Glucose tolerance and hepatic lipid accumulation in these mice were assessed under normal chow and high-fat diet conditions. Pre-adipocytes isolated from the stromal vascular fraction of BAT were transduced with Wt1-expressing retrovirus, induced to differentiate and analysed for the expression of thermogenic and adipocyte-selective genes.ResultsExpression of the thermogenic genes Cpt1b and Tmem26 was enhanced and transcript levels of Ucp1 were on average more than tenfold higher in epididymal WAT of heterozygous Wt1 knockout mice compared with wild-type mice. Wt1 heterozygosity reduced epididymal WAT mass, improved whole-body glucose tolerance and alleviated severe hepatic steatosis upon diet-induced obesity in mice. Retroviral expression of WT1 in brown pre-adipocytes, which lack endogenous WT1, reduced mRNA levels of Ucp1, Ppargc1a, Cidea, Prdm16 and Cpt1b upon in vitro differentiation by 60–90%. WT1 knockdown in epididymal pre-adipocytes significantly lowered Aldh1a1 and Zfp423 transcripts, two key suppressors of the thermogenic program. Conversely, Aldh1a1 and Zfp423 mRNA levels were increased approximately five- and threefold, respectively, by retroviral expression of WT1 in brown pre-adipocytes.Conclusion/interpretationWT1 functions as a white adipocyte determination factor in epididymal WAT by suppressing thermogenic genes. Reducing Wt1 expression in this and other intra-abdominal fat depots may represent a novel treatment strategy in metabolic disease.Graphical abstract

Isolation of Adipogenic and Fibro-Inflammatory Stromal Cell Subpopulations from Murine Intra-Abdominal Adipose Depots

The stromal-vascular fraction (SVF) of white adipose tissue (WAT) is remarkably heterogeneous and consists of numerous cell types that contribute functionally to the expansion and remodeling of WAT in adulthood. A tremendous barrier to studying the implications of this cellular heterogeneity is the inability to readily isolate functionally distinct cell subpopulations from WAT SVF for in vitro and in vivo analyses. Single-cell sequencing technology has recently identified functionally distinct fibro-inflammatory and adipogenic PDGFRβ+ perivascular cell subpopulations in intra-abdominal WAT depots of adult mice. Fibro-inflammatory progenitors (termed, "FIPs") are non-adipogenic collagen producing cells that can exert a pro-inflammatory phenotype. PDGFRβ+ adipocyte precursor cells (APCs) are highly adipogenic both in vitro and in vivo upon cell transplantation. Here, we describe multiple methods for the isolation of these stromal cell subpopulations from murine intra-abdominal WAT depots. FIPs and APCs can be isolated by fluorescence-activated cell sorting (FACS) or by taking advantage of biotinylated antibody-based immunomagnetic bead technology. Isolated cells can be used for molecular and functional analysis. Studying the functional properties of stromal cell subpopulation in isolation will expand our current knowledge of adipose tissue remodeling under physiological or pathological conditions on the cellular level.

Epiregulin induces leptin secretion and energy expenditure in high-fat diet-fed mice.

Adipokine leptin regulates neuroendocrine circuits that control energy expenditure, thermogenesis and weight loss. However, canonic regulators of leptin secretion, such as insulin and malonyl CoA, do not support these processes. We hypothesize that epiregulin (EREG), a growth factor that is secreted from fibroblasts under thermogenic and cachexia conditions, induces leptin secretion associated with energy dissipation. The effects of EREG on leptin secretion were studied ex vivo, in the intra-abdominal white adipose tissue (iAb WAT) explants, as well as in vivo, in WT mice with diet-induced obesity (DIO) and in ob/ob mice. These mice were pair fed a high-fat diet and treated with intraperitoneal injections of EREG. EREG increased leptin production and secretion in a dose-dependent manner in iAb fat explants via the EGFR/MAPK pathway. After 2 weeks, the plasma leptin concentration was increased by 215% in the EREG-treated group compared to the control DIO group. EREG-treated DIO mice had an increased metabolic rate and core temperature during the active dark cycle and displayed cold-induced thermogenesis. EREG treatment reduced iAb fat mass, the major site of leptin protein production and secretion, but did not reduce the mass of the other fat depots. In the iAb fat, expression of genes supporting mitochondrial oxidation and thermogenesis was increased in EREG-treated mice vs control DIO mice. All metabolic and gene regulation effects of EREG treatment were abolished in leptin-deficient ob/ob mice. Our data revealed a new role of EREG in induction of leptin secretion leading to the energy expenditure state. EREG could be a potential target protein to regulate hypo- and hyperleptinemia, underlying metabolic and immune diseases.

The role of adipose tissue in the pathogenesis of Crohn's disease.

Crohn's disease (CD) is a chronic, immune system-mediated inflammatory disease affecting gastrointestinal (GI) tract. The pathogenesis of the intestinal lesions is not entirely explained and understood: excessive activation of the immune system may come as a result of the interaction of environmental, genetic and infectious factors and the mediation of abnormal intestinal flora. The main objective of the current study is to further identify the role of adipose tissue in the pathogenesis of CD. Alterations in body fat distribution, accumulation of intra-abdominal white adipose tissue (WAT) and mesenteric obesity are well-known features of CD. Up to date, data concerning the role of WAT in the pathogenesis of CD is limited with only a few studies on the relationship between WAT and the course of the disease, as well as pro- and anti-inflammatory cytokine profile and general immune system functioning. In this review, we focus on the importance of physiological and pathophysiological WAT functions and secreted adipokines, which seem to have a vital role in the inflammatory and fibrotic processes in CD sufferers.

Peri-ovarian adipose tissue contributes to intraovarian control during folliculogenesis in mice.

Peri-ovarian adipose tissue (POAT) is a kind of intra-abdominal white adipose tissue that is present surrounding the ovaries in rodents. Recent studies demonstrated that POAT-deficient mice displayed a phenotype of delayed antral follicular development, for which decreases in serum estrogen, serum FSH and FSHR levels were responsible. However, folliculogenesis is regulated by endocrine signals and also modulated by a number of locally produced intraovarian factors whose acts are both autocrine and paracrine. Here, we used a model of surgical removal of POAT unilaterally and contralateral ovaries as controls, as both were under the same endocrine control, to assess the paracrine effect of the POAT on folliculogenesis. Surgical removal of unilateral POAT resulted in delayed antral follicular development and the increased number of atretic follicles, accompanied by decreased levels of intraovarian adipokines and growth factors, lipid accumulation and steroidogenic enzyme expression. POAT-deficient ovaries displayed compensatory increased expressions of intraovarian genes, such as Vegf and Adpn for angiogenesis, Acc, Fasn, and Gapdh involved in lipogenesis and Fshr in response to FSH stimulation. Furthermore, we demonstrated that removal of POAT promoted follicular apoptosis, caused retention of cytoplasmic YAP and inhibited PTEN-AKT-mTOR activation. These alterations were observed only in the POAT-deficient ovaries but not in the contralateral ovaries (with POAT), which suggests that a paracrine interaction between POAT and ovaries is important for normal folliculogenesis.

Depot-specific and GH-dependent regulation of IGF binding protein-4, pregnancy-associated plasma protein-A, and stanniocalcin-2 in murine adipose tissue

IntroductionPregnancy-associated plasma protein-A (PAPP-A) stimulates insulin-like growth factor (IGF)-I action through proteolytic cleavage of IGF binding protein-4 (IGFBP-4). Recently, stanniocalcin-2 (STC2) was discovered as an inhibitor of PAPP-A. Most members of the IGF system are expressed in adipose tissue (AT), but there is a relative paucity of information on the distribution of IGFBP-4, PAPP-A, and STC2 in different AT depots. Since IGF-I expression in AT is highly GH-dependent, we used bovine GH transgenic (bGH) and GH receptor knockout (GHR−/−) mice to investigate AT depot-specific expression patterns of IGFBP-4, PAPP-A, and STC2, and whether the regulation is GH-dependent. MethodsSeven-month-old male bGH, GHR−/− and wild type (WT) control mice were used. Body composition was determined, and subcutaneous, epididymal, retroperitoneal, mesenteric and brown adipose tissue (BAT) depots were collected. RNA expression of Igfbp4, Pappa, and Stc2 was assessed by reverse transcription quantitative PCR and IGFBP-4 protein by Western blotting. ResultsIgfbp4, Pappa, and Stc2 RNA levels were differentially expressed in an AT depot-dependent manner in WT mice. Igfbp4 RNA levels were significantly higher in all white AT depots than in BAT. Pappa was most highly expressed in the mesenteric depot: levels were 7.5-fold higher in mesenteric than in subcutaneous AT (p < .001). Although intraabdominal in origin, epididymal and retroperitoneal Pappa expression levels were 69% and 68% lower, respectively, as compared to mesenteric levels (p < .001). Stc2 RNA expression was significantly higher in all intraabdominal white AT as compared to subcutaneous AT and BAT; levels in epididymal, retroperitoneal, and mesenteric were all more than three-fold higher than in subcutaneous AT (p < .001) and 12-fold higher than in BAT (p < .001). Gene expression patterns in bGH and GHR−/− mice mimicked those in WT mice, suggesting that GH does not affect the transcription of the STC2-PAPP-A-IGFBP-4-axis in AT. However, proteins levels of intact IGFBP-4 were significantly increased in bGH mice and decreased in GHR−/− mice, whereas the PAPP-A-generated IGFBP-4 fragment level was unaltered. ConclusionExpression of Igfbp4, Pappa, and Stc2 differ between AT depots and is generally higher in white AT than in BAT. The transcription appears to occur in a GH-independent manner, whereas IGFBP-4 protein levels are highly influenced by altered GH activity.

The great roundleaf bat (Hipposideros armiger) as a good model for cold-induced browning of intra-abdominal white adipose tissue.

BackgroundInducing beige fat from white adipose tissue (WAT) is considered to be a shortcut to weight loss and increasingly becoming a key area in research into treatments for obesity and related diseases. However, currently, animal models of beige fat are restricted to rodents, where subcutaneous adipose tissue (sWAT, benign WAT) is more liable to develop into the beige fat under specific activators than the intra-abdominal adipose tissue (aWAT, malignant WAT) that is the major source of obesity related diseases in humans.MethodsHere we induced beige fat by cold exposure in two species of bats, the great roundleaf bat (Hipposideros armiger) and the rickett's big-footed bat (Myotis ricketti), and compared the molecular and morphological changes with those seen in the mouse. Expression of thermogenic genes (Ucp1 and Pgc1a) was measured by RT-qPCR and adipocyte morphology examined by HE staining at three adipose locations, sWAT, aWAT and iBAT (interscapular brown adipose tissue).ResultsExpression of Ucp1 and Pgc1a was significantly upregulated, by 729 and 23 fold, respectively, in aWAT of the great roundleaf bat after exposure to 10°C for 7 days. Adipocyte diameters of WATs became significantly reduced and the white adipocytes became brown-like in morphology. In mice, similar changes were found in the sWAT, but much lower amounts of changes in aWAT were seen. Interestingly, the rickett's big-footed bat did not show such a tendency in beige fat.ConclusionsThe great roundleaf bat is potentially a good animal model for human aWAT browning research. Combined with rodent models, this model should be helpful for finding therapies for reducing harmful aWAT in humans.

Adipose tissue mitochondrial dysfunction triggers a lipodystrophic syndrome with insulin resistance, hepatosteatosis, and cardiovascular complications.

Mitochondrial dysfunction in adipose tissue occurs in obesity, type 2 diabetes, and some forms of lipodystrophy, but whether this dysfunction contributes to or is the result of these disorders is unknown. To investigate the physiological consequences of severe mitochondrial impairment in adipose tissue, we generated mice deficient in mitochondrial transcription factor A (TFAM) in adipocytes by using mice carrying adiponectin-Cre and TFAM floxed alleles. These adiponectin TFAM-knockout (adipo-TFAM-KO) mice had a 75-81% reduction in TFAM in the subcutaneous and intra-abdominal white adipose tissue (WAT) and interscapular brown adipose tissue (BAT), causing decreased expression and enzymatic activity of proteins in complexes I, III, and IV of the electron transport chain (ETC). This mitochondrial dysfunction led to adipocyte death and inflammation in WAT and a whitening of BAT. As a result, adipo-TFAM-KO mice were resistant to weight gain, but exhibited insulin resistance on both normal chow and high-fat diets. These lipodystrophic mice also developed hypertension, cardiac hypertrophy, and cardiac dysfunction. Thus, isolated mitochondrial dysfunction in adipose tissue can lead a syndrome of lipodystrophy with metabolic syndrome and cardiovascular complications.

Adipose tissue remodeling in rats exhibiting fructose-induced obesity

To explore the effect of a fructose-rich diet on morphological and functional changes in white adipose tissue (WAT) that could contribute to the development of insulin resistance. Adult sedentary rats were fed a fructose-rich diet for 8weeks. Glucose tolerance test was carried out together with measurement of plasma triglycerides, non-esterified fatty acids and lipid peroxidation. In subcutaneous abdominal and intra-abdominal WAT, number and size of adipocytes together with cellular insulin sensitivity and lipolytic activity were assessed. Rats fed a fructose-rich diet exhibited a significant increase in plasma insulin, triglycerides, non-esterified fatty acids and lipid peroxidation, together with significantly increased body lipids and epididymal and mesenteric WAT, compared to controls. Mean adipocyte volume in subcutaneous abdominal WAT was significantly lower, while mean adipocyte volume in intra-abdominal WAT was significantly higher, in rats fed a fructose-rich diet compared to controls. A significant increase in larger adipocytes and a significant decrease in smaller adipocytes were found in intra-abdominal WAT in rats fed a fructose-rich diet compared to controls. Insulin's ability to inhibit lipolysis was blunted in subcutaneous abdominal and intra-abdominal adipocytes from fructose-fed rats. Accordingly, lower p-Akt/Akt ratio was found in WAT in rats fed a fructose-rich diet compared to controls. Long-term consumption of high levels of fructose elicits remarkable morphological and functional modifications, particularly in intra-abdominal WAT, that are highly predictive of obesity and insulin resistance and that contribute to the worsening of metabolic alterations peculiar in a fructose-rich, hypolipidic diet.

Adipose-derived stem cells enhance tissue regeneration of gastrotomy closure

BackgroundThe aim of this study was to examine whether transplantation of adipose-derived stem cells (ADSCs) improves healing of a gastrotomy closure in rats. In digestive surgery, anastomotic leakage is a serious postoperative complication and anastomotic stenosis may reduce quality of life. Recent studies have suggested that ADSCs play material roles in intestinal healing, acceleration of angiogenesis, and reduction of fibrosis, and treatment with ADSCs may improve healing. Materials and methodsADSCs were isolated from intra-abdominal white adipose tissue of 40 male Wistar rats (weight 300 g) in four groups (n = 10 each). Gastrotomy closures were prepared surgically in all rats. Controls were treated with phosphate-buffered saline injection and sacrificed 7 d (group 1) or 28 d (group 3) after the surgery. Other animals were treated with locally autotransplanted ADSCs (labeled by CM-DiI) and sacrificed 7 d (group 2) or 28 d (group 4) after the surgery. Histopathologic features were evaluated in the four groups. ResultsInjection of ADSCs significantly enhanced angiogenesis and collagen deposition after 7 d, indicating improved healing of the gastrotomy closure. In contrast, ADSC transplantation significantly reduced collagen deposition after 28 d. The bursting pressure was higher in the transplant groups after 7 d. ConclusionsADSCs enhance tissue regeneration in gastrotomy closures by accelerating angiogenesis and fibrosis in the early healing period. In the late period, ADSCs prevent excessive fibrosis and assist in regeneration of tissues that closely resemble the native structure. These results suggest that therapy with transplanted ADSCs might improve postoperative complications in digestive surgery.

Opa3, a novel regulator of mitochondrial function, controls thermogenesis and abdominal fat mass in a mouse model for Costeff syndrome

The interrelationship between brown adipose tissue (BAT) and white adipose tissue (WAT) is emerging as an important factor in obesity, but the effect of impairing non-shivering thermogenesis in BAT on lipid storage in WAT remains unclear. To address this, we have characterized the metabolic phenotype of a mouse model for Costeff syndrome, in which a point mutation in the mitochondrial membrane protein Opa3 impairs mitochondrial activity. Opa3(L122P) mice displayed an 80% reduction in insulin-like growth factor 1, postnatal growth retardation and hepatic steatosis. A 90% reduction in uncoupling protein 1 (UCP1) expression in interscapular BAT was accompanied by a marked reduction in surface body temperature, with a 2.5-fold elevation in interscapular BAT mass and lipid storage. The sequestration of circulating lipid into BAT resulted in profound reductions in epididymal and retroperitoneal WAT mass, without affecting subcutaneous WAT. The histological appearance and intense mitochondrial staining in intra-abdominal WAT suggest significant 'browning', but with UCP1 expression in WAT of Opa3(L122P) mice only 62% of that in wild-type littermates, any precursor differentiation does not appear to result in thermogenically active beige adipocytes. Thus, we have identified Opa3 as a novel regulator of lipid metabolism, coupling lipid uptake with lipid processing in liver and with thermogenesis in BAT. These findings indicate that skeletal and metabolic impairment in Costeff syndrome may be more significant than previously thought and that uncoupling lipid uptake from lipid metabolism in BAT may represent a novel approach to controlling WAT mass in obesity.

Lipocalin prostaglandin D synthase and PPARγ2 coordinate to regulate carbohydrate and lipid metabolism in vivo.

Mice lacking Peroxisome Proliferator-Activated Receptor γ2 (PPARγ2) have unexpectedly normal glucose tolerance and mild insulin resistance. Mice lacking PPARγ2 were found to have elevated levels of Lipocalin prostaglandin D synthase (L-PGDS) expression in BAT and subcutaneous white adipose tissue (WAT). To determine if induction of L-PGDS was compensating for a lack of PPARγ2, we crossed L-PGDS KO mice to PPARγ2 KO mice to generate Double Knock Out mice (DKO). Using DKO mice we demonstrated a requirement of L-PGDS for maintenance of subcutaneous WAT (scWAT) function. In scWAT, DKO mice had reduced expression of thermogenic genes, the de novo lipogenic program and the lipases ATGL and HSL. Despite the reduction in markers of lipolysis in scWAT, DKO mice had a normal metabolic rate and elevated serum FFA levels compared to L-PGDS KO alone. Analysis of intra-abdominal white adipose tissue (epididymal WAT) showed elevated expression of mRNA and protein markers of lipolysis in DKO mice, suggesting that DKO mice may become more reliant on intra-abdominal WAT to supply lipid for oxidation. This switch in depot utilisation from subcutaneous to epididymal white adipose tissue was associated with a worsening of whole organism metabolic function, with DKO mice being glucose intolerant, and having elevated serum triglyceride levels compared to any other genotype. Overall, L-PGDS and PPARγ2 coordinate to regulate carbohydrate and lipid metabolism.

Cirsimarin, a potent antilipogenic flavonoid, decreases fat deposition in mice intra-abdominal adipose tissue

We previously reported that the flavonoid cirsimarin exerts in vitro a strong lipolytic activity on isolated adipocytes. This study was therefore designed to evaluate in vivo the effects of cirsimarin on white adipose tissue (WAT) accretion in mice. Male CD1 mice were injected daily with either vehicle (intraperitoneal (i.p.)) or cirsimarin (25 or 50 mg kg(-1) per day, i.p.) for 18 days. Mice were killed and fat pads weighted. Epididymal fat pads were used for cellularity measurement. Effects of cirsimarin treatment on lipolysis and lipogenesis in WAT were assessed. Mice treated with 25 or 50 mg kg(-1) per day cirsimarin showed a decrease in retroperitoneal (-29 and -37% respectively, P<0.005) and epididymal (-25 and -28% respectively, P<0.005) fat pad weights compared with controls. This effect was restricted to intra-abdominal WAT as no difference was noticed for subcutaneous inguinal WAT. The decrease in intra-abdominal WAT accretion was due to a decrease in adipose cell diameter (-5 and -8% for 25 and 50 mg kg(-1) per day cirsimarin, respectively) resulting in a 14 and 35% decrease in adipose cell volume while no change was noticed in total adipocyte number. Direct injection of cirsimarin (50 mg kg(-1)) to rats did not trigger lipolysis. In contrast, cirsimarin showed in vivo as well as in vitro a strong antilipogenic activity, which may be the critical aspect of its effects on fat accretion in mice. The inhibitory concentration 50% of cirsimarin on lipogenic activity in isolated adipocytes was found to be 1.28±0.04 μM. Cirsimarin given orally reduced intra-abdominal fat accretion in mice. Cirsimarin exerts potent antilipogenic effect and decreases adipose tissue deposition in mice. Cirsimarin could therefore be a potential candidate for the treatment of obesity.

Adipose Depots Possess Unique Developmental Gene Signatures

We have previously demonstrated that subcutaneous and intra-abdominal adipose tissue show different patterns of expression for developmental genes (Shox2, En1, Tbx15 Hoxa5, Hoxc8, and Hoxc9), and that the expression level of Tbx15 and Hoxa5 in humans correlated with the level of obesity and fat distribution. To further explore the role of these developmental genes in adipose tissue, we have characterized their expression in different adipose depots in mice, and studied their regulation in obesity and by fasting. Developmental and adipogenic gene expression was compared in two subcutaneous and three intra-abdominal white adipose tissue (WAT) depots as well as brown adipose tissue (BAT) from lean or obese mice in a fed or fasting state. Each of these six adipose depots display a unique pattern of developmental gene expression, whereas expression of adipogenic transcription factors PPARgamma2 C/EBPalpha, beta, and Delta showed constant expression levels in all depots. Expression levels of developmental genes were similar in obese (ob/ob and high-fat diet (HFD)) and lean mice in most depots. Fasting systematically decreased expression of Hoxc8, PPARgamma2, and increased C/EBPDelta in both lean and ob/ob mice, but produced only variable changes in the expression of other developmental and adipogenic genes. These data indicate that each fat depot has a unique developmental gene expression signature, which is largely independent of nutritional state. This finding further supports a fundamental role of developmental genes in fat distribution and the development and/or function of specific adipose tissue depots.

Peroxisome Proliferator-activated Receptor γ Stimulation of Adipocyte ApoE Gene Transcription Mediated by the Liver Receptor X Pathway

Peroxisome proliferator-activated receptor (PPARgamma) agonists increase insulin sensitivity in humans and are useful for treating human diabetes. Treatment with these agonists leads to increased apoE expression and triglyceride accumulation in adipocytes. The importance of apoE for adipocyte triglyceride accumulation is demonstrated by observations that triglyceride accumulation is impaired in apoE knockout adipocytes treated with PPARgamma agonists. The current studies investigate the molecular mechanism for PPARgamma stimulation of the adipocyte apoE gene and demonstrate that the liver receptor X (LXR) response element within an apoE gene downstream enhancer is required for the apoE response to PPARgamma agonists. The response of the apoE gene to treatment with PPARgamma agonists was delayed beyond 12 h suggesting the involvement of an intermediary pathway. The combined addition of PPARgamma and LXR agonists did not increase apoE response beyond that observed with addition of either alone. Deletion or mutation of the LXR response element completely eliminated the adipocyte apoE gene response to a PPARgamma agonist. Chromatin immunoprecipitation analyses performed using isolated adipocytes, or adipose tissue from mice treated with PPARgamma agonists, showed increased LXR binding to the apoE gene after PPARgamma agonist treatment. Knockdown of LXR expression completely eliminated the increase in apoE message, protein, and triglyceride in response to PPARgamma stimulation. The LXR response element has been previously shown to mediate sterol responsiveness of the apoE gene, and apoE expression plays an important role in adipocyte triglyceride balance. The current observations suggest that the PPARgamma-LXR-apoE regulatory cascade could be an important molecular link for cross-talk between adipocyte triglyceride and cholesterol homeostasis.

Resistin increases islet blood flow and decreases subcutaneous adipose tissue blood flow in anaesthetized rats

Resistin is an adipokine which has been suggested to participate in the induction of insulin resistance associated with type 2 diabetes. The aim of the present study was to investigate whether acute administration of resistin influences tissue blood perfusion in rats. Resistin was administered as an intravenous infusion of 7.5 microg h(-1) (1.5 mL h(-1)) for 30 min to rats anaesthetized with thiobutabarbital. A microsphere technique was used to estimate the blood flow to six different depots of white adipose tissue (WAT), brown adipose tissue (BAT), as well as to the pancreas, islets, duodenum, colon, kidneys, adrenal glands and liver. Resistin administration led to an increased blood flow to the pancreas and islets and a decrease in subcutaneous WAT and BAT. Intra-abdominal white adipose tissue blood flow and that to other organs were not affected. Acute administration of resistin markedly affects the blood perfusion of both the pancreas and subcutaneous white adipose tissue depots. At present it is unknown whether resistin exerts a direct effect on the vasculature, or works through local or systemic activation of endothelial cells and/or macrophages. The extent to which this might contribute to the insulin resistance caused by resistin is yet unknown.

A Mathematical Model of the Immune System's Role in Obesity-Related Chronic Inflammation

Obesity is quickly becoming a pandemic. The low-grade chronic inammation associated with obesity leads to health risks such as cancer, heart disease, and type 2 diabetes mellitus. To better understand the progression of obesityrelated chronic inammation, mice were fed either a high fat or low fat diet over 140 days. At days 0, 35, 70, and 140, the percentages of macrophage subsets, CD4+ T cells, and regulatory-T cells inltrating the intra-abdominal white adipose tissue (WAT) were examined. Monocyte chemoattractant protein-1 (MCP-1) mRNA expression in WAT was also quantied. Additionally, glucosenormalizing ability was examined by administering peritoneal glucose tolerance tests. This research was conducted during a ten-week research experience for undergraduates. A group of eight undergraduate students participated: Pablo D

Localized proton magnetic resonance spectroscopy of lipids in adipose tissue at high spatial resolution in mice in vivo

We describe a localized proton magnetic resonance spectroscopy ((1)H-MRS) method for in vivo measurement of lipid composition in very small voxels (1.5 mm x 1.5 mm x 1.5 mm) in adipose tissue in mice. The method uses localized point-resolved spectroscopy to collect (1)H spectra from voxels in intra-abdominal white adipose tissue (WAT) and brown adipose tissue (BAT) deposits. Nonlinear least-squares fits of the spectra in the frequency domain allow for accurate calculation of the relative amount of saturated, monounsaturated, and polyunsaturated fatty acids. All spectral data are corrected for spin-spin relaxation. The data show BAT of NMRI mice to be significantly different from BAT of NMRI nu/nu mice in all aspects except for the fraction of monounsaturated fatty acids (FM); for WAT, only the FM is different. BAT and WAT of NMRI mice differ in the amount of saturated and di-unsaturated fatty acids. This method provides a potential tool for studying lipid metabolism in small animal models of disease during the initiation, progression, and manifestation of obesity-related disorders in vivo. Our results clearly demonstrate that localized (1)H-MRS of adipose tissue in vivo is possible at high spatial resolution with voxel sizes down to 3.4 ml.

Carboxylesterase 3 (EC 3.1.1.1) Is a Major Adipocyte Lipase

Hydrolysis of triglycerides is central to energy homeostasis in white adipose tissue (WAT). Hormone-sensitive lipase (HSL) was previously felt to mediate all lipolysis in WAT. Surprisingly, HSL-deficient mice show active HSL-independent lipolysis, suggesting that other lipase(s) also mediate triglyceride hydrolysis. To clarify this, we used functional proteomics to detect non-HSL lipase(s) in mouse WAT. After cell fractionation of intraabdominal WAT, most non-HSL neutral lipase activity is localized in the 100,000 x g infranatant and fat cake fractions. By oleic acid-linked agarose chromatography of infranatant followed by elution in a 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid gradient, we identified two peaks of esterase activity using p-nitrophenyl butyrate as a substrate. One of the peaks contained most of the lipase activity. In the corresponding fractions, gel permeation chromatography and SDS-PAGE, followed by tandem mass spectrometric analysis of excised Coomassie Blue-stained peptides, revealed carboxylesterase 3 (triacylglycerol hydrolase (TGH); EC 3.1.1.1). TGH is also the principle lipase of WAT fat cake extracts. Partially purified WAT TGH had lipase activity as well as lesser but detectable neutral cholesteryl ester hydrolase activity. Western blotting of subcellular fractions of WAT and confocal microscopy of fibroblasts following in vitro adipocytic differentiation are consistent with a distribution of TGH to endoplasmic reticulum, cytosol, and the lipid droplet. TGH is responsible for a major part of non-HSL lipase activity in WAT in vitro and may mediate some or all HSL-independent lipolysis in adipocytes.