Adipose Tissue Secretion Research Articles

Soluble CRTC3: A Newly Identified Protein Released by Adipose Tissue That Is Associated with Childhood Obesity.

CREB-regulated transcription coactivator 3 (CRTC3) is found in adipocytes, where it may promote obesity through disruption of catecholamine signaling. We wished to assess whether CRTC3 is a soluble protein secreted by adipose tissue, explore whether CRTC3 is detectable and quantifiable in the circulation, and ascertain whether CRTC3 serum concentrations are related to metabolic markers in children. Explants of adipose tissue from 12 children were cultured to study adipocyte cell size and the secretion of CRTC3 (immunoblot and ELISA). We also performed a cross-sectional and longitudinal study in 211 asymptomatic prepubertal white children at age 7 years, 115 of whom were followed up at age approximately 10 years. We measured circulating concentrations of CRTC3 and studied associations between serum CRTC3 and metabolic markers. Measurable concentrations of CRTC3 were found in conditioned media of adipose tissue explants and in serum samples. CRTC3 concentrations in visceral adipose tissue were negatively associated with adipocyte cell size and positively related to adipocyte cell number (P < 0.05). In the cross-sectional study, higher CRTC3 concentrations were associated with higher body mass index (P = 0.001), waist circumference (P = 0.003), and systolic blood pressure (P = 0.007) and lower high molecular weight adiponectin (P = 0.003). In the longitudinal study, serum concentrations of CRTC3 at age approximately 7 years were associated with changes in waist circumference (β = 0.254; P = 0.004; r = 0.145) and high molecular weight adiponectin (β=-0.271; P = 0.014; r = 0.101), respectively, at age approximately 10 years. CRTC3, a newly identified protein that is related to childhood obesity, is present in the circulation, partly as a result of adipose tissue secretion. Higher serum CRTC3 concentrations are related to and predict a poorer metabolic profile in children.

Adipose tissue metabolic and inflammatory responses to a mixed meal in lean, overweight and obese men

PurposeMost of what we know about adipose tissue is restricted to observations derived after an overnight fast. However, humans spend the majority of waking hours in a postprandial (fed) state, and it is unclear whether increasing adiposity impacts adipose tissue responses to feeding. The aim of this research was to investigate postprandial responses in adipose tissue across varying degrees of adiposity.MethodsThirty males aged 35–55 years with waist circumference 81–118 cm were divided equally into groups categorized as either lean, overweight or obese. Participants consumed a meal and insulinaemic, glycaemic and lipidaemic responses were monitored over 6 h. Subcutaneous adipose tissue samples were obtained at baseline and after 6 h to examine changes in gene expression and adipose tissue secretion of various adipokines.ResultsFollowing consumption of the meal, insulin and glucose responses were higher with increased adiposity (total AUC effects of group; p = 0.058 and p = 0.027, respectively). At 6 h, significant time effects reflected increases in IL-6 (F = 14.7, p = 0.001) and MCP-1 (F = 10.7, p = 0.003) and reduction in IRS2 adipose tissue gene expression (F = 24.6, p < 0.001), all independent of adiposity. Exvivo adipokine secretion from adipose tissue explants remained largely unchanged after feeding.ConclusionsIncreased systemic measures of postprandial metabolism with greater adiposity do not translate into increased inflammatory responses within adipose tissue. Instead, postprandial adipose tissue changes may represent a normal response to feeding or a (relatively) normalized response with increased adiposity due to either similar net exposure (i.e. per g of adipose) or reduced adipose tissue responsiveness.

Abstract 901: Grape seed extract decreases visceral adiposity and impairs the pro-tumorigenic adipose tissue secretions affecting colorectal cancer growth and progression

Abstract Colorectal cancer (CRC) is the third most frequently diagnosed malignancy in the United States. Given the global obesity epidemic, and the fact that obesity is associated with increased CRC risk, incidence and mortality, it is imperative that we discover and develop agents with efficacy against CRC under obese conditions. Thus, an agent with both anti-obesogenic and anti-CRC activities would be ideal to impair different facets of CRC interactions with adipose tissue secretions resulting in CRC chemoprevention under obese conditions. Our extensive in vitro and in vivo studies investigating the benefits of grape seed extract (GSE) consumption against CRC have shown that it exerts strong inhibitory activity in different CRC pre-clinical models. Recently, we also explored GSE potential to modulate the growth promoting tumorigenic secretions of adipocytes on CRC and colon cancer stem cells (CSCs). Results indicated that GSE significantly reduces the growth and invasion promoting effects of both mouse and human adipocytes on these cells which was associated with a decrease in CSC-associated markers and transcription factors. Notably, GSE effects on adipocytes were not due to changes in lipid content, but mechanistic studies showed that GSE causes differential modulation of adipogenesis-related proteins during different stages of adipocyte differentiation and induces the ‘browning’ of adipocytes as evidenced by an increase in UCP1 mRNA level and mitochondriogenesis. To further establish that indeed GSE has the potential to modify adipose tissue secretions, we fed GSE to obese mice and evaluated its anti-obesogenic effect. Briefly, short-term GSE feeding (200mg/ Kg body weight) for two weeks by oral gavage to diet-induced obese mice suppressed body weight, decreased the weight of fat pads, and improved associated metabolic abnormalities. During the high-fat-diet induced hyperlipidemia, GSE normalized total cholesterol in serum with a concomitant increase in high density cholesterol. Furthermore, our findings showed that GSE feeding significantly modulated the serum levels of adipokines/cytokines; specifically, GSE lowered the circulating leptin, resistin, pentraxin-2, lipocalin-2, and IGF-1 serum levels, while increasing IGFBP-1 levels. These results are significant as presence of meta-inflammation in obese people suggests that reversal of white adipose tissue dysfunction and modulation of visceral obese adipose tissue-driven pro-inflammatory adipokines/cytokines signaling provide unique opportunities for the preventive intervention of CRC in obese conditions. Based on these notable biological effects, GSE is a strong candidate agent to be studied further for its potential use against CRC growth and progression under obese conditions. Citation Format: Komal Raina, Sushil Kumar, Dileep Kumar, Ranganatha R. Somasagara, Reenu Punia, Rama Kant, Rajesh Agarwal, Chapla Agarwal. Grape seed extract decreases visceral adiposity and impairs the pro-tumorigenic adipose tissue secretions affecting colorectal cancer growth and progression. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 901. doi:10.1158/1538-7445.AM2015-901

Increased adipose tissue secretion of Fetuin-A, lipopolysaccharide-binding protein and high-mobility group box protein 1 in metabolic syndrome

ObjectiveAdipose Tissue (AT) dysregulation contributes to the pro-inflammatory state and insulin resistance of Metabolic Syndrome (MetS). We examined AT secretion of the hepatokine, Fetuin-A, LBP, sCD14 and HMGB-1, and toll-like receptor 2 and 4 protein levels in MetS and controls. Design and methodsSecreted levels of Fetuin-A, LBP, HMGB-1 and sCD14 and TLR2 and TLR4 protein in AT of controls and MetS patients were assayed. Also mRNA and protein for Fetuin-A, LBP, sCD14 and HMGB-1 were studied in subcutaneous fat depot of mice and during adipocyte differentiation. ResultsSecretion of Fetuin-A, LBP and HMGB-1 from AT were significantly increased in MetS (n = 28) compared to controls (n = 25), even after adjustment for adiposity. There were no significant differences in sCD14. Both LBP and Fetuin-A correlated significantly with HOMA-IR and increased significantly with increasing features of MetS. There was a significant increase in AT TLR2 and TLR4 protein in MetS compared to controls. Expression of Fetuin-A and LBP were significantly higher in subcutaneous white adipose tissue of HFD fed mice as well as in ob/ob mice compared to C57BL6/J control mice (n = 6 per group). Additionally mRNA and protein levels of FetA, LBP and HMGB-1 increased during differentiation of 3T3-L1 adipocytes. ConclusionsWe make the novel observation of increased secretion of Fetuin A, LBP and HMGB-1 from AT and hypothesize that these engage TLRs in AT and other tissues contributing to the pro-inflammatory state and insulin resistance of MetS.

Roles of hepatic glucokinase in intertissue metabolic communication: Examination of novel liver-specific glucokinase knockout mice

Glucokinase is expressed principally in pancreatic β-cells and hepatocytes, and catalyzes the phosphorylation of glucose to glucose-6-phosphate, a rate-limiting step of glycolysis. To better understand the roles of hepatic glucokinase, we generated Gck knockout mice by ablating liver-specific exon 1b. The knockout mice exhibited impaired glucose tolerance, decreased hepatic glycogen content, and reduced Pklr and Fas gene expression in the liver, indicating that hepatic glucokinase plays important roles in glucose metabolism. It has also been reported that hepatic glucokinase regulates the expression of thermogenesis-related genes in brown adipose tissue (BAT) and insulin secretion in response to glucose. However, the liver-specific Gck knockout mice displayed neither altered expression of thermogenesis-related genes in BAT nor impaired insulin secretion by β-cells under a normal chow diet. These results suggest that chronic suppression of hepatic glucokinase has a small influence on intertissue (liver-to-BAT as well as liver-to-β-cell) metabolic communication.

Abstract 17843: Visceral Adipose Tissue Secretion of Adiponectin Decreases with Increased Body Mass Index

Introduction: Peripheral adiposity is associated with better metabolic health and higher plasma adiponectin (ADPN) levels. Since ADPN is secreted mainly by adipose tissue (AT), it is intriguing that higher visceral adipose tissue (VAT) is associated with lower ADPN levels and poor metabolic health. Hypothesis: We hypothesized that various AT depots differ in their ability to secrete ADPN. Methods: Paired AT samples (VAT and subcutaneous adipose tissue (SAT)) were collected from 19 subjects (10 women, 15 obese) undergoing elective abdominal surgery. The samples were cultured and the supernatant was collected after 24 hours. ADPN levels released into the supernatant from VAT and SAT were measured using multiplex methods. Subjects were defined as obese or non-obese (NO) based on BMI &gt; or ≤ 30kg/m2 respectively. Obese subjects were further classified as metabolically unhealthy obese (MUO) or metabolically healthy obese (MHO) based on presence or absence of type 2 diabetes mellitus, hypertension, or cardiovascular disease at the time of surgery. Results: Mean ADPN secretion levels from SAT and VAT were similar in NO subjects (17.3 ± 3.4 vs. 9.8 ± 13.0 ng/mL/mg, p=0.5) whereas the mean ADPN secretion was lower from VAT among obese subjects (15.9 ± 0.8 vs. 4.5 ± 0.2 ng/mL/mg, p=0.0002). ADPN secretion decreased from VAT (r=-0.16) and increased from SAT (r=0.33) with increased BMI (Fig.1). When MHO and MUO were compared, ADPN secretion from VAT in MHO was reduced only slightly (16.1 ± 8.2 vs. 4.0 ± 2.0 ng/mL/mg, p=0.07) whereas ADPN secretion was significantly reduced in MUO (15.9 ± 5.3 vs. 4.7 ± 4.6 ng/mL/mg, p=0.003). Conclusions: Reduced ADPN secretion from VAT in subjects with increasing BMI may explain lower circulating ADPN levels in obese individuals. Higher ADPN production from SAT and the relatively preserved secretion of ADPN from VAT may explain metabolic health in some obese individuals. Futures studies will help identify factors that control ADPN secretion from AT.

Modulation of adipose tissue inflammation by FOXP3+ Treg cells, IL-10, and TGF-β in metabolically healthy class III obese individuals

ObjectiveThe objective of this study was to compare the profiles of proinflammatory (interleukin [IL]-6 and tumor necrosis factor [TNF]) and anti-inflammatory (IL-10 and transforming growth factor [TGF]-β) adipokines in the blood, subcutaneous adipose tissue (SAT), and visceral adipose tissue (VAT) of metabolically healthy class III obese individuals and normal-weight controls. MethodsThe serum concentrations (enzyme-linked immunosorbent assay [ELISA]), mRNA expression levels (reverse transcriptase polymerase chain reaction), and adipose tissue secretion (ELISA) of IL-6, TNF, IL-10, and TGF-β were analyzed, as were the mRNA expression of FOXP3 (present in regulatory T cells) and the secretion (Western blotting) of matrix metalloproteinases in the adipose tissue. ResultsThere were no differences in the circulating levels, expression, or secretion of IL-6 and TNF between the groups or tissues. The expression and circulating levels of IL-10 were higher in obese individuals, especially in the SAT. Although the blood concentration of TGF-β was similar between the groups, its expression and secretion levels were higher in the adipose tissues of obese individuals compared with controls. FOXP3 and MMP expression levels were higher in the SAT and VAT of obese individuals, respectively, compared with the controls. ConclusionMetabolically healthy, extremely obese individuals have effective immunoregulation to counter chronic obesity-related inflammation through the increased production of the anti-inflammatory cytokines IL-10 and TGF-β in adipose tissue, especially SAT; the increased presence of FOXP3-positive regulatory T cells; and increases in angiogenesis and adipogenesis induced by TGF-β and MMPs. These regulatory mechanisms could be important in the delayed onset of metabolic complications, even in extremely obese individuals.

Induction of Cytosolic Phospholipase A2α Is Required for Adipose Neutrophil Infiltration and Hepatic Insulin Resistance Early in the Course of High-Fat Feeding

In established obesity, inflammation and macrophage recruitment likely contribute to the development of insulin resistance. In the current study, we set out to explore whether adipose tissue infiltration by neutrophils that occurs early (3 days) after initiating a high-fat diet (HFD) could contribute to the early occurrence of hepatic insulin resistance and to determine the role of cytosolic phospholipase A2α (cPLA2α) in this process. The 3-day HFD caused a significant upregulation of cPLA2α in periepididymal fat and in the liver. A specific antisense oligonucleotide (AS) effectively prevented cPLA2α induction, neutrophil infiltration into adipose tissue (likely involving MIP-2), and protected against 3-day HFD–induced impairment in hepatic insulin signaling and glucose over-production from pyruvate. To sort out the role of adipose neutrophil infiltration independent of cPLA2α induction in the liver, mice were injected intraperitoneally with anti–intracellular adhesion molecule-1 (ICAM-1) antibodies. This effectively prevented neutrophil infiltration without affecting cPLA2α or MIP-2, but like AS, prevented impairment in hepatic insulin signaling, the enhanced pyruvate-to-glucose flux, and the impaired insulin-mediated suppression of hepatic glucose production (assessed by clamp), which were induced by the 3-day HFD. Adipose tissue secretion of tumor necrosis factor-α (TNF-α) was increased by the 3-day HFD, but not if mice were treated with AS or ICAM-1 antibodies. Moreover, systemic TNF-α neutralization prevented 3-day HFD–induced hepatic insulin resistance, suggesting its mediatory role. We propose that an acute, cPLA2α-dependent, neutrophil-dominated inflammatory response of adipose tissue contributes to hepatic insulin resistance and glucose overproduction in the early adaptation to high-fat feeding.

Salivary glands and adipobiology

This review explores the functional relationships between salivary glands and adipose tissue. Since salivary glands, and in particular the submandibular glands, exert profound systemic effects on organs and inflammatory responses outside the gastrointestinal tract, the question arises if these glands also impact the body's physiological response to increases in adipose tissue deposition and secretion. And, if the adipose tissue deposition and secretion impact the salivary gland's physiological response. To date the evidence is relatively weak that salivary glands significantly impact obesity, or that their function is dramatically altered by obesity, and that the measurement of metabolic peptides in saliva will lead to diagnostic and treatment strategies for obesity and related cardiometabolic diseases. Although obesity detrimentally impacts oral health causative linkages and associations have not been conclusively made between periodontitis and obesity. The most intriguing connections between adipobiology and saliva (or salivary glands) have emerged from unexpected quarters. It was recently reported that adiponectin, resistin and visfatin (adipose tissue-derived signaling proteins collectively termed adipokines) are found in saliva and that their amount correlates with that of circulating level of these adipokines. These observations suggest that the introduction of salivary determinations of adipokines may contribute to the study of pathogenesis of various obesity-related diseases. Receptors for adipokines and obesity-related hormones, especially for polypeptide Y (PYY (3-36)), in the mouth and in particular the taste buds, may be a primary signal for satiety. This observation offers new avenues for investigating the physiology of satiety along with potential treatment strategies for obesity. Another unexpected finding, and to date unrelated to obesity - the transplantation of adipose-derived stromal cells has the potential to restore salivary gland function after their destruction by radiation therapy. Adipobiology 2012; 4: 51-58.

Visceral adiposity index is highly associated with adiponectin values and glycaemic disturbances

Visceral Adiposity Index (VAI) is a gender-specific mathematical index estimated with the use of simple anthropometric (body mass index and waist circumference) and biochemical (triglycerides and high density lipoprotein cholesterol) parameters. Recent studies have shown that VAI reflects accurately the degree of visceral adiposity and insulin resistance. However, up to now, VAI has not been evaluated if it correlates with carbohydrate metabolism disorders, as well as with adipokine secretion from the fat mass. In a cohort of 308 out of 414 adult Saudi subjects screened for the study, detailed personal medical history, anthropometrics and metabolic/hormonal profiles were obtained. Additionally, the circulating concentrations of several circulating adipokines, namely adiponectin, leptin, tumour necrosis factor-α (TNF-α) and resistin, were measured. Stepwise multivariate analysis showed that VAI was the sole determinant of adiponectin levels (R(2) =0·07, beta±SE: -0·25±0·05), while BMI and female gender predicted leptin levels (R(2) =0·26, 0·10±0·01 and 0·61±0·15, respectively). Furthermore, the presence of impaired fasting glucose (IFG)/diabetes was predicted only by age and VAI. We report for the first time the direct relations of VAI with adipose tissue secretion, as well as with functional glycaemic disorders. Because VAI is estimated easily with data obtained in everyday practice, it could be used as an indirect index of adiponectin levels and the risk of impaired glucose metabolism.

Leptin differentially regulate STAT3 activation in ob/ob mouse adipose mesenchymal stem cells

BackgroundLeptin-deficient ob/ob mice exhibit adipocyte hypertrophy and hyperplasia as well as elevated adipose tissue and systemic inflammation. Multipotent stem cells isolated from adult adipose tissue can differentiate into adipocytes ex vivo and thereby contribute toward increased adipocyte cell numbers, obesity, and inflamm ation. Currently, information is lacking regarding regulation of adipose stem cell numbers as well as leptin-induced inflammation and its signaling pathway in ob/ob mice.MethodsUsing leptin deficient ob/ob mice, we investigated whether leptin injection into ob/ob mice increases adipose stem cell numbers and adipose tissue inflammatory marker MCP-1 mRNA and secretion levels. We also determined leptin mediated signaling pathways in the adipose stem cells.ResultsWe report here that adipose stem cell number is significantly increased following leptin injection in ob/ob mice and with treatment of isolated stem cells with leptin in vitro. Leptin also up-regulated MCP-1 secretion in a dose- and time-dependent manner. We further showed that increased MCP-1 mRNA levels were due to increased phosphorylation of Signal Transducer and Activator of Transcription 3 (STAT3) Ser727 but not STAT3 Tyr705 phosphorylation, suggesting differential regulation of MCP-1 gene expression under basal and leptin-stimulated conditions in adipose stem cells.ConclusionsTaken together, these studies demonstrate that leptin increases adipose stem cell number and differentially activates STAT3 protein resulting in up-regulation of MCP-1 gene expression. Further studies of mechanisms mediating adipose stem cell hyperplasia and leptin signaling in obesity are warranted and may help identify novel anti-obesity target strategies.

Autophagy Activity Is Up-Regulated in Adipose Tissue of Obese Individuals and Modulates Proinflammatory Cytokine Expression

Autophagy, an evolutionary conserved process aimed at recycling damaged organelles and protein aggregates in the cell, also modulates proinflammatory cytokine production in peripheral blood mononuclear cells. Because adipose tissue inflammation accompanied by elevated levels of proinflammatory cytokines is characteristic for the development of obesity, we hypothesized that modulation of autophagy alters adipose tissue inflammatory gene expression and secretion. We tested our hypothesis using ex vivo and in vivo studies of human and mouse adipose tissue. Levels of the autophagy marker LC3 were elevated in sc adipose tissue of obese vs. lean human subjects and positively correlated to both systemic insulin resistance and morphological characteristics of adipose tissue inflammation. Similarly, autophagic activity levels were increased in adipose tissue of obese and insulin resistant animals as compared with lean mice. Inhibition of autophagy by 3-methylalanine in human and mouse adipose tissue explants led to a significant increase in IL-1β, IL-6, and IL-8 mRNA expression and protein secretion. Noticeably, the enhancement in IL-1β, IL-6, and keratinocyte-derived chemoattractant (KC) by inhibition of autophagy was more robust in the presence of obesity. Similar results were obtained by blocking autophagy using small interfering RNA targeted to ATG7 in human Simpson-Golabi-Behmel syndrome adipocytes. Our results demonstrate that autophagy activity is up-regulated in the adipose tissue of obese individuals and inhibition of autophagy enhances proinflammatory gene expression both in adipocytes and adipose tissue explants. Autophagy may function to dampen inflammatory gene expression and thereby limit excessive inflammation in adipose tissue during obesity.

Effects of endurance exercise training, metformin, and their combination on adipose tissue leptin and IL-10 secretion in OLETF rats

Adipose tissue inflammation plays a role in cardiovascular (CV) and metabolic diseases associated with obesity, insulin resistance, and type 2 diabetes mellitus (T2DM). The interactive effects of exercise training and metformin, two first-line T2DM treatments, on adipose tissue inflammation are not known. Using the hyperphagic, obese, insulin-resistant Otsuka Long-Evans Tokushima Fatty (OLETF) rat model, we tested the hypothesis that treadmill training, metformin, or a combination of these reduces the secretion of proinflammatory cytokines from adipose tissue. Compared with Long-Evans Tokushima Otsuka (LETO) control rats (L-Sed), sedentary OLETF (O-Sed) animals secreted significantly greater amounts of leptin from retroperitoneal adipose tissue. Conversely, secretion of interleukin (IL)-10 by O-Sed adipose tissue was lower than that in L-Sed animals. Examination of leptin and IL-10 secretion from adipose tissue in OLETF groups treated with endurance exercise training (O-EndEx), metformin treatment (O-Met), and a combination of these (O-E+M) from 20 to 32 wk of age indicated that 1) leptin secretion from adipose tissue was reduced in O-Met and O-E+M, but not O-EndEx animals; 2) adipose tissue IL-10 secretion was increased in O-EndEx and O-E+M but not in O-Met animals; and 3) only the combined treatment (O-E+M) displayed both a reduction in leptin secretion and an increase in IL-10 secretion. Leptin and IL-10 concentrations in adipose tissue-conditioned buffers were correlated with their plasma concentrations, adipocyte diameters, and total adiposity. Overall, this study indicates that exercise training and metformin have additive influences on adipose tissue secretion and plasma concentrations of leptin and IL-10.

Adipose Tissue Secretion and Expression of Adipocyte-Produced and Stromavascular Fraction-Produced Adipokines Vary during Multiple Phases of Weight-Reducing Dietary Intervention in Obese Women

Obesity is associated with altered plasma levels of adipokines involved in the development of insulin resistance and obesity-related metabolic disturbances. The aim was to investigate diet-induced changes in adipokine production in sc abdominal adipose tissue (SAT) during a 6-month, multiphase, weight-reducing dietary intervention. Forty-eight obese women followed a dietary intervention consisting of a very low-calorie diet (VLCD) (1 month), followed by a weight-stabilization (WS) period, which consisted of a low-calorie diet (2 months), and a weight-maintenance diet (3 months). Before and at the end of the VLCD and WS, samples of plasma and SAT were obtained. In a subgroup of 26 women, secretion of adipokines was determined in SAT explants, and in a subgroup of 22 women, SAT mRNA expression was measured. Body weight decreased and insulin sensitivity increased during the intervention. Plasma levels, SAT mRNA expression, and secretion rates of adipocyte-produced adipokines (leptin, serum amyloid A, and haptoglobin) decreased during the VLCD and increased during the WS period. Adipokines produced mainly from stroma-vascular cells (IL-6, IL-8, IL-10, IL-1Ra, TNFα, plasminogen activator inhibitor-1, and monocyte chemoattractant protein-1) increased or remained unchanged during VLCD and decreased to levels equal to or lower than prediet levels during the WS period. The diet-induced changes in homeostasis model assessment of insulin resistance correlated with changes in leptin plasma levels during VLCD, WS, and the entire dietary intervention period. Diet-induced regulation of adipokine production in SAT differs according to their cellular origin (adipocytes vs. stroma-vascular cells) and diet phase (VLCD vs. WS). Insulin-sensitivity changes were associated only with those of plasma leptin.

Obesidomics: contribution of adipose tissue secretome analysis to obesity research

Obesity is presently reaching pandemic proportions and it is becoming a major health concern in developed and developing countries due to its comorbidities like type II diabetes, cardiovascular pathologies, and some cancers. The discovery of the adipose tissue role as an endocrine gland able to secrete adipokines that affects whole-body energy homeostasis has become a key break-through toward a better molecular understanding of obesity. Among the known adipokines involved in the regulation of energy metabolism very few have been clearly seen as central regulators of insulin sensitivity, metabolism, and energy homeostasis. Thus, the discovery and characterization of new adipocyte-derived factors is still in progress. Proteomics technology has emerged as a useful tool to analyze adipose tissue secretion (secretome) dynamics giving a wider picture into the molecular events that control body weight. Besides the identification of new secreted proteins, the advantage of using this approach is the possibility to detect post-translational modifications and protein interactions that generally cannot be predicted by genome studies. In this review, we summarize the recent efforts to identify new bioactive adipokines by proteomics especially in pathological situations such as obesity.

Adipocyte-specific deficiency of angiotensinogen decreases plasma angiotensinogen concentration and systolic blood pressure in mice

Previous studies demonstrated that overexpression of angiotensinogen (AGT) in adipose tissue increased blood pressure. However, the contribution of endogenous AGT in adipocytes to the systemic renin-angiotensin system (RAS) and blood pressure control is undefined. To define a role of adipocyte-derived AGT, mice with loxP sites flanking exon 2 of the AGT gene (Agt(fl/fl)) were bred to transgenic mice expressing Cre recombinase under the control of an adipocyte fatty acid-binding protein 4 promoter (aP2) promoter to generate mice with adipocyte AGT deficiency (Agt(aP2)). AGT mRNA abundance in adipose tissue and AGT secretion from adipocytes were reduced markedly in adipose tissues of Agt(aP2) mice. To determine the contribution of adipocyte-derived AGT to the systemic RAS and blood pressure control, mice were fed normal laboratory diet for 2 or 12 mo. In males and females of each genotype, body weight and fat mass increased with age. However, there was no effect of adipocyte AGT deficiency on body weight, fat mass, or adipocyte size. At 2 and 12 mo of age, mice with deficiency of AGT in adipocytes had reduced plasma concentrations of AGT (by 24-28%) compared with controls. Moreover, mice lacking AGT in adipocytes exhibited reduced systolic blood pressures compared with controls (Agt(fl/fl), 117 ± 2; Agt(aP2), 110 ± 2 mmHg; P < 0.05). These results demonstrate that adipocyte-derived AGT contributes to the systemic RAS and blood pressure control.

Twist1 in Human White Adipose Tissue and Obesity

Twist1 is a transcription factor implicated in the regulation of TNFα signaling and was recently shown to be highly expressed in both human and murine adipose tissue, but its role in obesity is unknown. Our objective was to assess the expression of twist1 in human white adipose tissue (WAT), its relationship to obesity and insulin sensitivity, and how it modifies TNFα-mediated inflammation in adipocytes. Twist mRNA levels were measured in WAT from 130 nonobese and obese subjects, and its relation to clinical parameters was assessed. Twist1 expression was measured before and after weight loss as well as in different adipose regions. Human in vitro differentiated adipocytes were treated with TNFα under control conditions or after twist1 gene silencing by RNA interference. Gene expression and secretion of proinflammatory proteins were measured. Twist1 expression was low in obese subjects and increased after weight loss. Twist1 mRNA levels correlated with adiponectin levels and inversely with insulin resistance as well as adipocyte volume (P < 0.001 for all). Low twist1 expression associated with a hypertrophic adipose tissue and high secretion of TNFα and monocyte chemoattractant protein-1 from WAT. Finally, twist1 silencing in human adipocytes enhanced TNFα-induced monocyte chemoattractant protein-1 expression and secretion, which was paralleled by an increase in the mRNA expression of the nuclear factor-κB gene RelA. Low twist1 expression in human WAT correlates with obesity and an insulin-resistant phenotype, which may be mediated by an increased sensitivity to the proinflammatory effect of TNFα.

Adipokines and dietary interventions in human obesity

Obesity is a multisystem disorder associated with cardiovascular and metabolic complications. According to recent studies, it is characterized as a condition of low-grade inflammation with altered adipose tissue function and secretion of various adipokines. One of the strategies in obesity treatment is dietary intervention (DI) that could modulate cytokine levels in a favourable way. The aim of this review was to summarize the results of studies performed in the last 13 years investigating DI programmes accompanied with weight loss in relation to profile of adipokines at different level (adipose tissue mRNA, adipose tissue secretion and circulating level) and identify whether modulations of adipokines are implicated in the positive effects of DIs. The overall finding is that DIs leading to 5-10% weight loss modulate production of certain adipokines and generally induce improvement of clinical parameters, e.g. insulin sensitivity, but the amelioration of obesity complications is not coherent with the pattern of adipokine regulation, except maybe for leptin. Global analysis of the adipose tissue secretome and measurement of panels of adipokines may prove more informative than studies on individual molecules.

Abstract 1419: Adipocytes protect leukemia cells from L-asparaginase treatment

Abstract Obesity increases cancer incidence and mortality. This is also true for acute lymphoblastic leukemia (ALL). L-Asparaginase (ASNase), an important front-line drug in leukemia treatment, acts through the hydrolysis of asparagine (ASN) and glutamine (GLN) into aspartic acid and glutamic acid. As lymphoblastic leukemia cells are highly dependent on these two non-essential amino acids, ASNase leads to decreased protein synthesis, cell cycle arrest, and apoptosis. We have previously shown that obesity impairs ASNase treatment in C57BL/J mice transplanted with syngeneic leukemia cells. The present study was designed to elucidate how obesity protects ALL cells from this drug. The effects of adipocytes on ALL ASNase resistance were examined in vitro using co-cultures with 3T3-L1 adipocytes and ALL cells, separated by TransWells. Differentiated 3T3-L1 adipocytes significantly protected ALL cells from a 3-day treatment with ASNase, compared to undifferentiated 3T3-L1 fibroblasts or no feeder layer (viable cells after ASNase treatment: 3.1 ± 1.2 fold greater than no feeder layer, 2.1 ± 0.6 greater than fibroblast feeder layer, p&amp;lt;0.05, n=6). Since ASNase acts through the hydrolysis of both ASN and GLN, we next determined whether the protection afforded by adipocytes was through the secretion of one or both of these amino acids. Seven human leukemia cell lines (RCH-ACV, SEM, BV-173, Nalm 6, K562, SD-1, and RS4;11) were tested for their ability to proliferate in media lacking either of these two amino acids. Compared to complete media, six had significantly decreased proliferation in media lacking GLN (n=4, p&amp;lt;.05), while only one (RS4;11) showed dependence on ASN. The GLN-dependent SD-1's and ASN-dependent RS4;11's were plated in TransWells over undifferentiated 3T3-L1 fibroblasts, 3T3-L1 adipocytes, and no feeder layer in media lacking both amino acids. Differentiated 3T3-L1 adipocytes significantly protected both cell lines from amino acid starvation (RS4;11: 3.6 ± 0.4 fold greater than no feeder, 2.0 ± 0.3 fold great than fibroblasts, p&amp;lt;.05, n=3; SD-1: 4.2 ± 2.4 fold greater than feeder, 4.0 ± 1.0 fold greater than fibroblasts, p&amp;lt;.05, n=3). Furthermore, we determined that adipocytes secrete both amino acids over a 72 hour period (media concentration of ASN after 24, 48, and 72 hours: 34 uM, 166 uM, 369 uM; GLN: 0, 42, 85 uM, respectively). Most importantly GLN and ASN depleted media decreased mTOR signaling (measured by p70s6k phosphorylation), conditioning of this media by adipocytes for 48 hours reversed this effect. The current data demonstrate that adipocytes directly protect leukemia cells from ASNase treatment. We have demonstrated that adipocytes increase leukemia survival in media starved of ASN and/or GLN, secrete ASN and GLN, and enhance mTOR signaling in amino acid starved leukemia cells. Thus, obesity may impair the effects of ASNase on leukemia cells through adipose tissue secretion of both ASN and GLN. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1419.

Differential Regulation of IL‐27 Expression during Inflammatory Stress in Adipocytes

Obesity can lead to insulin resistance by mechanisms involving macrophage infiltration of adipose tissue and adipocyte secretion of inflammatory adipokines that mediate systemic inflammation and disease. Interleukin‐27 is a heterodimeric cytokine encoded by independent p28 and EBI3 genes. While recent reports have demonstrated regulation of IL‐27 in antigen presenting cells, little information regarding IL‐27 in other cell types has emerged. Using 3T3‐L1 adipocytes stimulated with proinflammatory stimuli as a model of inflammatory stress, we demonstrate similar basal expression of p28 and EBI3 in undifferentiated preadipocytes (PAs) relative to mature adipocytes (ADs). Exposure of PAs to 100 pM tumor necrosis factor α (TNFα) resulted in marked, transient induction of p28 and EBI3 gene expression peaking at 4 hrs and 18 hrs, respectively. Interestingly, neither gene was induced equivalently in ADs following TNFα stimulation. Using specific inhibitors of pertinent signaling pathways, we determined that p28 and EBI3 were predominantly downstream of NFκB. However, the refractory nature of both genes in ADs was not likely due to differences in upstream signaling pathways that were similarly activated in PAs and ADs. These findings demonstrate that IL‐27 gene expression is regulated in PAs in response to inflammatory stress and that both p28 and EBI3 become refractory to such stress as PAs mature into ADs.