A proteomic approach for identification of secreted proteins during the differentiation of 3T3-L1 preadipocytes to adipocytes

Cord lining progenitor cells: potential in vitro adipogenesis model

OBJECTIVE

To investigate the effect of glucose and insulin concentrations on differentiation of umbilical cord lining progenitor cells to adipocyte-like cells (ALCs).

METHODS

Cord lining mesenchymal cells (CLMCs) were isolated from the explant of human umbilical cord amniotic membrane. CLMCs were subjected to differentiation under various culture conditions for 20 days. Lipid droplets were confirmed with Oil Red O staining. Gene expressions of adipsin and peroxisome proliferator-activated receptor gamma (PPARγ) were analyzed using reverse transcription-PCR. Leptin and adiponectin secretions were detected using enzyme-linked immunosorbent assay kit.

RESULTS

CLMCs became irregular, cuboidal-shaped cells that resemble adipocytes, and Oil Red O staining showed the presence of lipid droplets. The gene expressions of PPARγ and adipsin were upregulated. Leptin and adiponectin secretions by naive CLMCs were below the limits of detection. Matured ALCs cultured in low-glucose medium significantly secreted leptin and adiponectin, whereas those in high-glucose medium significantly secreted only leptin. Insulin concentration affects leptin but not adiponectin secretion.

CONCLUSIONS

Under different culture conditions, CLMCs can differentiate into ALCs that resemble adipocytes in either normal-weight or obese individuals. Hence, these ALCs have the potential to be used as an in vitro model to study adipogenesis and obesity, and possibly as a drug discovery model for metabolic disorders.

Hexosamine flux, the O-GlcNAc modification, and the development of insulin resistance in adipocytes

Excess flux through the hexosamine biosynthesis pathway in adipocytes is a fundamental cause of "glucose toxicity" and the development of insulin resistance that leads to type II diabetes. Adipose tissue-specific elevation in hexosamine flux in animal models recapitulates whole-body insulin-resistant phenotypes, and increased hexosamine flux in adipocyte cell culture models impairs insulin-stimulated glucose uptake. Many studies have been devoted to unveiling the molecular mechanisms in adipocytes in response to excess hexosamine flux-mediated insulin resistance. As a major downstream event consuming and incorporating the final product of the hexosamine biosynthesis pathway, dynamic and inducible O-GlcNAc modification is emerging as a modulator of insulin sensitivity in adipocytes. Given that O-GlcNAc is implicated in both insulin-mediated signal transduction and transcriptional events essential for adipocytokine secretion, direct functional studies to pinpoint the roles of O-GlcNAc in the development of insulin resistance via excess flux through hexosamine biosynthesis pathway are needed.

Lipocalin-2 deficiency attenuates insulin resistance associated with aging and obesity

OBJECTIVE

The proinflammatory cytokines/adipokines produced from adipose tissue act in an autocrine and/or endocrine manner to perpetuate local inflammation and to induce peripheral insulin resistance. The present study investigates whether lipocalin-2 deficiency or replenishment with this adipokine has any impact on systemic insulin sensitivity and the underlying mechanisms.

METHODS AND RESULTS

Under conditions of aging or dietary-/genetic-induced obesity, lipocalin-2 knockout (Lcn2-KO) mice show significantly decreased fasting glucose and insulin levels and improved insulin sensitivity compared with their wild-type littermates. Despite enlarged fat mass, inflammation and the accumulation of lipid peroxidation products are significantly attenuated in the adipose tissues of Lcn2-KO mice. Adipose fatty acid composition of these mice varies significantly from that in wild-type animals. The amounts of arachidonic acid (C20:4 n6) are elevated by aging and obesity and are paradoxically further increased in adipose tissue, but not skeletal muscle and liver of Lcn2-KO mice. On the other hand, the expression and activity of 12-lipoxygenase, an enzyme responsible for metabolizing arachidonic acid, and the production of tumor necrosis factor-alpha (TNF-alpha), a critical insulin resistance-inducing factor, are largely inhibited by lipocalin-2 deficiency. Lipocalin-2 stimulates the expression and activity of 12-lipoxygenase and TNF-alpha production in fat tissues. Cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate (CDC), an arachidonate lipoxygenase inhibitor, prevents TNF-alpha expression induced by lipocalin-2. Moreover, treatment with TNF-alpha neutralization antibody or CDC significantly attenuated the differences of insulin sensitivity between wild-type and Lcn2-KO mice.

CONCLUSIONS

Lipocalin-2 deficiency protects mice from developing aging- and obesity-induced insulin resistance largely by modulating 12-lipoxygenase and TNF-alpha levels in adipose tissue.

Mechanisms regulating repression of haptoglobin production by peroxisome proliferator-activated receptor-gamma ligands in adipocytes

Obesity leads to inflammation of white adipose tissue involving enhanced secretion of cytokines and acute-phase proteins in response in part to the accumulation of excess lipids in adipocytes. Haptoglobin is an acute-phase reactant secreted by white adipose tissue and induced by inflammatory cytokines such as TNFalpha. In this study, we investigated the mechanisms regulating haptoglobin expression in adipocytes. Peroxisome proliferator-activated receptor (PPAR)-gamma agonists such as thiazolidinediones (TZDs) as well as non-TZD ligands can repress in vitro and in vivo haptoglobin expression in adipocytes and also prevent its induction by TNFalpha. This action requires direct involvement of PPAR gamma in regulating haptoglobin gene transcription because mutation of critical amino acids within helix 7 of the ligand-binding domain of PPAR gamma prevents repression of the haptoglobin gene by the synthetic ligands. Chromatin immunoprecipitation analysis shows active binding of PPAR gamma to a distal region of the haptoglobin promoter, which contains putative PPAR gamma binding sites. Additionally, PPAR gamma induces transcription of a luciferase reporter gene when driven by the distal promoter region of the haptoglobin gene, and TZD treatment significantly reduces the extent of this induction. Furthermore, the mutated PPAR gamma is incapable of enhancing luciferase activity in these in vitro reporter gene assays. In contrast to other adipokines repressed by TZDs such as resistin and chemerin, repression of haptoglobin does not require either CCAAT/enhancer-binding protein C/EBP alpha or the corepressors C-terminal binding protein 1 or 2. These data are consistent with a model in which synthetic PPAR gamma ligands selectively activate PPAR gamma bound to the haptoglobin gene promoter to arrest haptoglobin gene transcription.

Adipocyte extracellular matrix composition, dynamics and role in obesity

The central role of the adipose tissue in lipid metabolism places specific demands on the cell structure of adipocytes. The protein composition and dynamics of the extracellular matrix (ECM) is of crucial importance for the functioning of those cells. Adipogenesis is a bi-phasic process in which the ECM develops from a fibrillar to a laminar structure as cells move from the commitment phase to the growth phase characterized by storage of vast amounts of triglycerides. Mature adipocytes appear to spend a lot of energy on the maintenance of the ECM. ECM remodeling is mediated by a balanced complement of constructive and destructive enzymes together with their enhancers and inhibitors. ECM remodeling is an energy costing process regulated by insulin, by the energy metabolism, and by mechanical forces. In the obese, overgrowth of adipocytes may lead to instability of the ECM, possibly mediated by hypoxia.

The obesity and inflammatory marker haptoglobin attracts monocytes via interaction with chemokine (C-C motif) receptor 2 (CCR2)

Background

Obesity is a chronic low inflammatory state. In the obesity condition the white adipose tissue (WAT) is massively infiltrated with monocytes/macrophages, and the nature of the signals recruiting these inflammatory cells has yet to be fully elucidated. Haptoglobin (Hp) is an inflammatory marker and its expression is induced in the WAT of obese subjects. In an effort to elucidate the biological significance of Hp presence in the WAT and of its upregulation in obesity we formulated the hypothesis that Hp may serve as a macrophage chemoattractant.

Results

We demonstrated by chemotaxis assay that Hp is able to attract chemokine (C-C motif) receptor 2 (CCR2)-transfected pre-B lymphocytes and monocytes in a dose-dependent manner. Moreover, Hp-mediated migration of monocytes is impaired by CCR2-specific inhibition or previous cell exposure to monocyte chemoattractant protein 1 (MCP1) (also known as CCR2 ligand or chemokine (C-C motif) ligand 2 (CCL2)). Downstream effects of Hp/CCR2 interaction were also investigated: flow cytometry proved that monocytes treated with Hp show reduced CCR2 expression on their surface; Hp interaction induces calcium release that is reduced upon pretreatment with CCR2 antagonist; extracellular signal-regulated kinase (ERK)1/2, a signal transducer activated by CCR2, is phosphorylated following Hp treatment and this phosphorylation is reduced when cells are pretreated with a specific CCR2 inhibitor. Consistently, blocking the ERK1/2 pathway with U0126, the selective inhibitor of the ERK upstream mitogen-activated protein (MAP)-ERK kinase (MEK), results in a dramatic reduction (by almost 100%) of the capability of Hp to induce monocyte migration.

Conclusions

Our data show that Hp is a novel monocyte chemoattractant and that its chemotactic potential is mediated, at least in part. by its interaction with CCR2.

Pigment epithelium-derived factor suppresses adipogenesis via inhibition of the MAPK/ERK pathway in 3T3-L1 preadipocytes

We previously reported that circulating levels of pigment epithelium-derived factor (PEDF), a newly identified adipokine, are increased in patients with type 2 diabetes, correlating with body mass index. However, the role of PEDF in adipogenesis remains elusive. In the present study, we have investigated the effects and mechanisms of PEDF on adipocyte differentiation in 3T3-L1 preadipocytes. Differentiation of 3T3-L1 preadipocytes was induced in the presence or absence of human recombinant PEDF protein. The effects of PEDF on adipogenic gene expression, mitotic clonal expansion (MCE), and MAPK activation were investigated. Physiological concentrations of human PEDF protein inhibited adipocyte differentiation, evidenced by decreased lipid accumulation, downregulation of adipocyte markers, and inhibition of master adipogenic transcription factors such as C/EBP-alpha and PPARgamma. The antiadipogenic effects of PEDF were observed only when PEDF was added to the cells on day 0, but not on day 3 during differentiation, suggesting that PEDF targets some early adipogenic events. Similarly, overexpression of PEDF by adenovirus attenuated adipocyte differentiation. Further studies revealed that PEDF, or U-0126, a specific MAPK/ERK inhibitor, sequentially inhibited the early activation of ERK and MCE. Moreover, PEDF attenuated expression and the phosphorylation of C/EBP-beta at Thr(188), an essential step for transcriptional activation of C/EBP-beta. In addition, PEDF expression was decreased significantly in the first 24 h during adipocyte differentiation, suggesting that downregulation of PEDF may be essential for the initiation of MCE and adipogenesis. We conclude that PEDF inhibits adipogenesis in 3T3-L1 preadipocytes partially because of inhibition of the MAPK/ERK signaling pathway and MCE.

Pigment epithelium-derived factor inhibits lysosomal degradation of Bcl-xL and apoptosis in HepG2 cells

Pigment epithelium-derived factor (PEDF) has several biological actions on tumor cells, but its effects are cell-type dependent. The aim of this study was to examine the pathophysiological role of PEDF in hepatocellular carcinoma (HCC). PEDF expression was examined in various hepatoma cell lines and human HCC tissues, and was seen in various hepatoma cell lines including HepG2 cells. In human HCC tissues, PEDF expression was higher than in adjacent non-HCC tissues. In addition, serum PEDF levels were higher in HCC patients than in non-HCC patients, and curative treatment of HCC caused significant reductions in serum PEDF levels compared with pretreatment levels. In vitro experiments, camptothecin (CPT) was used to induce apoptosis and the effect of PEDF was investigated by knockdown of the PEDF gene in CPT-treated HepG2 cells. Knockdown of the PEDF gene enhanced CPT-induced apoptosis, simultaneously down-regulating Bcl-xL expression in HepG2 cells. Expression of apoptosis-related molecules and effects of bafilomycin A1 on CPT-induced apoptosis were also examined in PEDF gene knockdown HepG2 cells. Treatment with bafilomycin A1 suppressed CPT-induced decreases in Bcl-xL expression and increases in apoptosis in PEDF gene knockdown HepG2 cells. PEDF may, therefore, exert anti-apoptotic effects through inhibition of lysosomal degradation of Bcl-xL in CPT-treated HepG2 cells.

Quantitative analysis of secretome from adipocytes regulated by insulin

Adipocyte is not only a central player involved in storage and release of energy, but also in regulation of energy metabolism in other organs via secretion of peptides and proteins. During the pathogenesis of insulin resistance and type 2 diabetes, adipocytes are subjected to the increased levels of insulin, which may have a major impact on the secretion of adipokines. We have undertaken cleavable isotope-coded affinity tag (cICAT) and label-free quantitation approaches to identify and quantify secretory factors that are differentially secreted by 3T3-L1 adipocytes with or without insulin treatment. Combination of cICAT and label-free results, there are 317 proteins predicted or annotated as secretory proteins. Among these secretory proteins, 179 proteins and 53 proteins were significantly upregulated and down-regulated, respectively. A total of 77 reported adipokines were quantified in our study, such as adiponectin, cathepsin D, cystatin C, resistin, and transferrin. Western blot analysis of these adipokines confirmed the quantitative results from mass spectrometry, and revealed individualized secreting patterns of these proteins by increasing insulin dose. In addition, 240 proteins were newly identified and quantified as secreted proteins from 3T3-L1 adipocytes in our study, most of which were up-regulated upon insulin treatment. Further comprehensive bioinformatics analysis revealed that the secretory proteins in extracellular matrix-receptor interaction pathway and glycan structure degradation pathway were significantly upregulated by insulin stimulation.

Identification of astrocyte secreted proteins with a combination of shotgun proteomics and bioinformatics

Astrocytes are important regulators of normal brain function in mammals, including roles in synaptic signaling, synapse formation, and neuronal health and survival. Many of these functions are executed via secreted proteins. To analyze the astrocyte secretome, a combination of shotgun proteomics and bioinformatics was employed to analyze conditioned media from primary murine astrocyte cultures. Both two- and one-dimensional LC-MS/MS were used to analyze astrocyte secreted proteins, resulting in the identification of over 420 proteins. To refine our results, the intracellular protein contaminants were removed in silico using a cytoplasmic control. In additional rounds of refinement, putative secreted proteins were subjected to analysis by SignalP, SecretomeP, and gene ontology analysis, yielding a refined list of 187 secreted proteins. In conclusion, the use of shotgun proteomics combined with multiple rounds of data refinement produced a high quality catalog of astrocyte secreted proteins.

Proteome differences between brown and white fat mitochondria reveal specialized metabolic functions

Mitochondria are functionally specialized in different tissues, and a detailed understanding of this specialization is important to elucidate mitochondrial involvement in normal physiology and disease. In adaptive thermogenesis, brown fat converts mitochondrial energy to heat, whereas tissue-specific functions of mitochondria in white fat are less characterized. Here we apply high-resolution quantitative mass spectrometry to directly and accurately compare the in vivo mouse mitochondrial proteomes of brown and white adipocytes. Their proteomes are substantially different qualitatively and quantitatively and are furthermore characterized by tissue-specific protein isoforms, which are modulated by cold exposure. At transcript and proteome levels, brown fat mitochondria are more similar to their counterparts in muscle. Conversely, white fat mitochondria not only selectively express proteins that support anabolic functions but also degrade xenobiotics, revealing a protective function of this tissue. In vivo comparison of organellar proteomes can thus directly address functional questions in metabolism.

Metabolism and secretory function of white adipose tissue: effect of dietary fat

Approximately 40% of the total energy consumed by western populations is represented by lipids, most of them being ingested as triacylglycerols and phospholipids. The focus of this review is to analyze the effect of the type of dietary fat on white adipose tissue metabolism and secretory function, particularly on haptoglobin, TNF-α, plasminogen activator inhibitor-1 and adiponectin secretion. Previous studies have demonstrated that the duration of the exposure to the high-fat feeding, amount of fatty acid present in the diet and the type of fatty acid may or may not have a significant effect on adipose tissue metabolism. However, the long-term or short-term high fat diets, especially rich in saturated fatty acids, probably by activation of toll-like receptors, stimulated the expression of proinflammatory adipokines and inhibited adiponectin expression. Further studies are needed to investigate the cellular mechanisms by which dietary fatty acids affect white adipose tissue metabolism and secretory functions.

Differential estimation of CKD using creatinine- versus cystatin C-based estimating equations by category of body mass index

BACKGROUND

Adiposity is associated with cystatin C. Cystatin C-based glomerular filtration rate (GFR) equations may result in overestimation of chronic kidney disease (CKD) prevalence at greater body mass index (BMI) levels.

STUDY DESIGN

Cross-sectional.

SETTING & PARTICIPANTS

6,709 US adult Third National Health and Nutrition Examination Survey participants.

FACTOR

BMI.

OUTCOME

Absolute percentage of difference in prevalence of stage 3 or 4 CKD between creatinine- and cystatin C-based estimating equations by level of BMI.

MEASUREMENTS

Normal weight, overweight, and obesity were defined as BMI of 18.5 to less than 25.0, 25 to less than 30.0, and 30 kg/m(2) or greater, respectively. Stage 3 or 4 CKD (estimated glomerular filtration rate [eGFR], 15 to 59 mL/min/1.73 m(2)) was defined using the 4-variable creatinine-based Modification of Diet in Renal Disease Study equation (eGFR(MDRD)); cystatin C level, age, sex, and race equation (eGFR(CysC,age,sex,race)); cystatin C-only equation (eGFR(CysC)); cystatin C level of 1.12 mg/L or greater (increased cystatin C); and an equation incorporating serum creatinine level, cystatin C level, age, sex, and race (eGFR(Cr,CysC,age,sex,race)).

RESULTS

Differences in stage 3 or 4 CKD prevalence estimates between eGFR(CysC,age,sex,race), eGFR(CysC), and increased cystatin C, separately, and eGFR(MDRD) were greater at higher BMI levels. Specifically, compared with estimates derived using eGFR(MDRD) for normal-weight, overweight, and obese participants, estimated prevalences of stage 3 or 4 CKD were 2.1%, 3.0%, and 6.5% greater when estimated by using eGFR(CysC,age,sex,race) (P trend = 0.005); 0.1%, 0.6%, and 2.2% greater for eGFR(CysC) (P trend = 0.03); 2.9%, 5.2%, and 9.5% greater for increased cystatin C (P trend < 0.001); and -0.1%, -0.4%, and 0.0% greater for eGFR(Cr,CysC,age,sex,race), respectively (P trend = 0.7).

LIMITATIONS

No gold-standard measure of GFR was available.

CONCLUSIONS

BMI may influence the estimated prevalence of stage 3 or 4 CKD when cystatin C-based equations are used.

Temporal profiling of the adipocyte proteome during differentiation using a five-plex SILAC based strategy

The adipose tissue has important secretory and endocrine functions in humans. The regulation of adipocyte differentiation has been actively pursued using transcriptomic methods over the last several years. Quantitative proteomics has emerged as a promising approach to obtain temporal profiles of biological processes such as differentiation. Stable isotope labeling with amino acids in cell culture (SILAC) is a simple and robust method for labeling proteins in vivo. Here, we describe the development and application of a five-plex SILAC experiment using four different heavy stable isotopic forms of arginine to study the nuclear proteome and the secretome during the course of adipocyte differentiation. Tandem mass spectrometry analysis using a quadrupole time-of-flight instrument resulted in identification of a total 882 proteins from these two proteomes. Of these proteins, 427 were identified on the basis of one or more arginine-containing peptides that allowed quantitation. In addition to previously reported molecules that are differentially expressed during the process of adipogenesis (e.g., adiponectin and lipoprotein lipase), we identified several proteins whose differential expression during adipocyte differentiation has not been documented previously. For example, THO complex 4, a context-dependent transcriptional activator in the T-cell receptor alpha enhancer complex, showed highest expression at middle stage of adipogenesis, while SNF2 alpha, a chromatin remodeling protein, was downregulated upon initiation of adipogenesis and remained so during subsequent time points. This study using a 5-plex SILAC to investigate dynamics illustrates the power of this approach to identify differentially expressed proteins in a temporal fashion.

Adipose proteome analysis: focus on mediators of insulin resistance

As is well known, adipose tissue is an important site for lipid metabolism and insulin-responsive glucose uptake. The recent discovery of the endocrine function of adipose tissue and the association of obesity with chronic low-grade inflammation in adipose tissue has reinforced the concept of the central role of adipose tissue in mediating obesity-linked insulin resistance and metabolic dysregulation. The study of adipose cells has provided new insights into the mechanism underlying insulin resistance as well as the therapeutic strategies for diabetes. Numerous efforts have been made in identifying key molecular regulators of insulin action and metabolism, including the utilization of advanced proteomics technology. Various proteomic approaches have been applied to identify the adipose secretome, protein-expression profiling and post-translational modifications in adipose cells in the pathological state. In this review, we summarize the recent advances in the proteomics of adipose tissue, and discuss the identified proteins that potentially play important roles in insulin resistance and diabetes.

Depot-specific adipocyte cell lines reveal differential drug-induced responses of white adipocytes--relevance for partial lipodystrophy

Intra-abdominal (IA) fat functionally differs from subcutaneous (SC) adipose tissue, likely contributing to its stronger association with obesity-induced morbidity and to differential response to medications. Drug-induced partial lipodystrophy, like in response to antiretroviral agents, is an extreme manifestation of the different response of different fat depots, with loss of SC but not IA. Investigating depot-specific adipocyte differences is limited by the low accessibility to IA fat and by the heterogenous cell population comprising adipose tissue. Here, we aimed at utilizing immortalized preadipocyte cell lines from IA (epididymal) or SC (inguinal) fat to investigate whether they differentially respond to the HIV protease inhibitor nelfinavir. Preadipocytes were readily amenable to adipogenesis, as evidenced by lipid accumulation, expression of adipose-specific genes, measurable lipolysis, and insulin responsiveness. Leptin secretion was higher by the SC line, consistent with known differences between IA and SC fat. As previously reported, nelfinavir inhibited adipogenesis downstream of C/EBPbeta, but similarly in both cell lines. In contrast, nelfinavir's capacity to diminish insulin signaling, decrease leptin secretion, enhance basal lipolysis, and decrease expression of the lipid droplet-associated protein perilipin occurred more robustly and/or at lower nelfinavir concentrations in the SC line. This was despite similar intracellular concentrations of nelfinavir (23.8 +/- 5.6 and 33.6 +/- 12.2 microg/mg protein for inguinal and epididymal adipocytes, respectively, P = 0.46). The cell lines recapitulated depot-differential effects of nelfinavir observed in differentiated primary preadipocytes and with whole tissue explants. Thus, we report the use of fat depot-specific adipocyte cell lines for unraveling depot-differential responses to a drug causing partial lipodystrophy.

Ethanol exposure depletes hepatic pigment epithelium-derived factor, a novel lipid regulator

BACKGROUND & AIMS

Ethanol abuse can lead to hepatic steatosis and evolve into cirrhosis and hepatocellular carcinoma. Pigment epithelium-derived factor (PEDF) is a multifunctional secreted glycoprotein that is expressed by hepatocytes. Proteomic, experimental, and clinical studies implicate PEDF's role in lipid regulation. Because matrix metalloproteinase (MMP)-2/9 activity regulates PEDF levels, we investigated whether PEDF degradation by MMPs has a permissive role in ethanol-induced hepatic steatosis.

METHODS

PEDF levels were examined in liver biopsy specimens from patients with ethanol-induced steatosis. Hepatic PEDF levels and MMP activity were assessed in 2 animal models of ethanol feeding (rats on an alcohol-containing liquid diet and mice given intragastric infusion of ethanol). The consequences of PEDF depletion in the liver were examined in PEDF-null mice.

RESULTS

Liver biopsy samples from patients with ethanol-induced steatosis had reduced PEDF levels, compared with normal liver samples. Ethanol-fed animals had histologic steatosis and increased liver triglyceride content (P< .05), as well as reduced levels of hepatic PEDF and increased MMP-2/9 activity. Ethanol-exposed hepatic lysates degraded PEDF in a MMP-2/9-dependent manner, and liver sections demonstrated abundant MMP-2/9 activity in situ. Addition of recombinant PEDF to PEDF-null hepatocytes, reduced their triglyceride content.

CONCLUSIONS

Ethanol exposure leads to marked loss of hepatic PEDF in human livers and in 2 animal models of ethanol feeding. Loss of PEDF contributes to the accumulation of lipids in ethanol-induced hepatic steatosis.

Serum levels of pigment epithelium-derived factor (PEDF) are positively associated with visceral adiposity in Japanese patients with type 2 diabetes

BACKGROUND

Pigment epithelium-derived factor (PEDF) inhibits endothelial cell injury. Further, serum levels of PEDF are elevated in the metabolic syndrome. These observations suggest that PEDF may be elevated as a counter-system against vascular cell damage in the metabolic syndrome. However, little is known about the regulation of PEDF in patients with diabetes. In order to clarify the determinants of serum PEDF, here, we examined the relationship between the 1-year changes in PEDF levels and those in anthropometric and metabolic variables in type 2 diabetic patients.

METHODS

Eighty-six consecutive outpatients with type 2 diabetes underwent a complete history and physical examination, determination of blood chemistries, and serum levels of PEDF at baseline and 1 year after. PEDF gene expression in cultured subcutaneous or omental adipocytes were analysed by quantitative real-time reverse transcription-polymerase chain reactions.

RESULTS

Multiple regression analyses revealed that waist circumference, triglycerides, creatinine, and TNF-alpha were independently associated with PEDF. Further, the percent changes in serum levels of PEDF during 1-year observational periods were positively correlated with those of BMI. In addition, PEDF mRNA levels in cultured adipocytes were increased in parallel to the BMI values of subjects from whom adipocytes were derived, especially in omental adipocytes.

CONCLUSION

These results demonstrated that serum levels of PEDF were positively associated with metabolic components and TNF-alpha in Japanese patients with type 2 diabetes. Our present study suggests that PEDF may be generated from adipose tissues and play some role in visceral obesity in type 2 diabetic patients.

Novel insights into adipogenesis from omics data

Obesity, the excess accumulation of adipose tissue, is one of the most pressing health problems in both the Western world and in developing countries. Adipose tissue growth results from two processes: the increase in number of adipocytes (hyperplasia) that develop from precursor cells, and the growth of individual fat cells (hypertrophy) due to incorporation of triglycerides. Adipogenesis, the process of fat cell development, has been extensively studied using various cell and animal models. While these studies pointed out a number of key factors involved in adipogenesis, the list of molecular components is far from complete. The advance of high-throughput technologies has sparked many experimental studies aimed at the identification of novel molecular components regulating adipogenesis. This paper examines the results of recent studies on adipogenesis using high-throughput technologies. Specifically, it provides an overview of studies employing microarrays for gene expression profiling and studies using gel based and non-gel based proteomics as well as a chromatin immunoprecipitation followed by microarray analysis (ChIP-chip) or sequencing (ChIP-seq). Due to the maturity of the technology, the bulk of the available data was generated using microarrays. Therefore these data sets were not only reviewed but also underwent meta analysis. The review also shows that large-scale omics technologies in conjunction with sophisticated bioinformatics analyses can provide not only a list of novel players, but also a global view on biological processes and molecular networks. Finally, developing technologies and computational challenges associated with the data analyses are highlighted, and an outlook on the questions not previously addressed is provided.

Serum levels of pigment epithelium-derived factor (PEDF) are an independent determinant of insulin resistance in patients with essential hypertension

We have previously found that serum level of pigment epithelium-derived factor (PEDF) is increased in proportion to the accumulation of the number of components of metabolic syndrome in general population. However, the link between PEDF and insulin resistance in hypertensive patients remains unclear. We investigated here whether serum PEDF level was associated with insulin resistance in hypertensive patients. Ninety-seven consecutive outpatients with essential hypertension underwent a complete history and physical examination, determination of blood chemistries, including serum PEDF. In multiple regression analyses, BMI, age (inversely) and PEDF were independently correlated with homeostasis model assessment of insulin resistance (HOMA-IR). When age- and sex-adjusted PEDF levels were stratified by HOMA-IR tertiles, a linear and significant trend was observed. These results demonstrated that serum level of PEDF was an independent determinant of HOMA-IR in patients with essential hypertension. PEDF may play a role in insulin resistance in hypertensive patients.

Identification of differentially expressed genes in a porcine in vivo model of adipogenesis using suppression subtractive hybridization

Although they provide valuable information, in vitro models of adipocyte development often require high doses of hormones and growth factors, which may influence gene expression and adipocyte differentiation patterns. To overcome these problems, a novel in vivo model of adipose tissue development was used to characterize genes involved in adipogenesis. The suppression subtractive hybridization technique was used to identify genes showing differential expression between the adipose tissue of a day 90 gestating sow, which is enriched in adipocytes, and day 90 fetal adipose tissue, which is enriched in preadipocytes. A total of 149 expressed sequence tags corresponding to identified genes and tentative consensus sequences emerged. Thirty-seven clones matched expressed sequence tags or genomic DNA sequences and six novel sequences were also identified. Adipogenesis-related genes were identified, many of which have never been reported to be expressed in mammalian adipose tissue, and may play a role in regulation of adipose tissue differentiation. Validation of differentially expressed genes was confirmed for perilipin, monocyte to macrophage differentiation-associated, myocilin, paraoxonase 3, stearoyl-CoA desaturase, angiotensinogen and adiponectin genes using real-time RT-PCR.

The adipocyte as an endocrine cell

Adipose tissue contains many cell types. Among the more abundant are adipocytes, preadipocytes, immune cells, and endothelial cells. During times of excess caloric intake, these cells have to adjust and remodel to accommodate the increased demand for triglyceride storage. Based on a comprehensive analysis of the total adipose tissue secretome, this article focuses on three areas of adipokine biology: (1) How does the adipocyte interact with the extracellular matrix over the course of obesity? (2) Does the adipocyte, per se, play a role in the innate immune response? (3) How is the angiogenic profile of adipose tissue linked to the development of insulin resistance? The authors present a comprehensive overview of all of the currently available secreted adipose tissue products that have been identified at the protein level.

Differential screening identifies transcripts with depot-dependent expression in white adipose tissues

Background

The co-morbidities of obesity are tied to location of excess fat in the intra-abdominal as compared to subcutaneous white adipose tissue (WAT) depot. Genes distinctly expressed in WAT depots may impart depot-dependent physiological functions. To identify such genes, we prepared subtractive cDNA libraries from murine subcutaneous (SC) or intra-abdominal epididymal (EP) white adipocytes.

Results

Differential screening and qPCR validation identified 7 transcripts with 2.5-fold or greater enrichment in EP vs. SC adipocytes. Boc, a component of the hedgehog signaling pathway demonstrated highest enrichment (~12-fold) in EP adipocytes. We also identified a dramatic enrichment in SC adipocytes vs. EP adipocytes and in SC WAT vs. EP WAT for transcript(s) for the major urinary proteins (Mups), small secreted proteins with pheromone functions that are members of the lipocalin family. Expression of Boc and Mup transcript was further assessed in murine tissues, adipogenesis models, and obesity. qPCR analysis reveals that EP WAT is a major site of expression of Boc transcript. Furthermore, Boc transcript expression decreased in obese EP WAT with a concomitant upregulation of Boc transcript in the obese SC WAT depot. Assessment of the Boc binding partner Cdon in adipose tissue and cell fractions thereof, revealed transcript expression similar to Boc; suggestive of a role for the Boc-Cdon axis in WAT depot function. Mup transcripts were predominantly expressed in liver and in the SC and RP WAT depots and increased several thousand-fold during differentiation of primary murine preadipocytes to adipocytes. Mup transcripts were also markedly reduced in SC WAT and liver of ob/ob genetically obese mice compared to wild type.

Conclusion

Further assessment of WAT depot-enriched transcripts may uncover distinctions in WAT depot gene expression that illuminate the physiological impact of regional adiposity.

Whitening effect of adipose-derived stem cells: a critical role of TGF-beta 1

It has been demonstrated that adipose-derived stem cells (ADSCs) secrete cytokines and exhibit diverse pharmacological actions. The present study examined the unknown pharmacological action of ADSCs regarding whitening effects. A conditioned medium of ADSCs (ADSC-CM) was harvested and the whitening effect of ADSC-CM was studied in melanoma B16 cells. ADSC-CM treatment inhibited the synthesis of melanin and the activity of tyrosinase in a dose dependent manner. To clarify the underlying mechanisms of the whitening action of ADSCs, protein levels of melanogenic proteins were measured by Western blot. Although expressions of microphthalmia-associated transcription factor and tyrosinase-related protein 2 (TRP2) remained unchanged, those of tyrosinase and TRP1 were down-regulated. Transforming growth factor-beta1 (TGF-beta 1), a potent regulator of melanogenic proteins, was neutralized by the addition of a blocking antibody to ADSC-CM, and down-regulated expression of tyrosinase and TRP1 was almost reversed. Collectively, these results indicate that secretary factors of ADSC inhibit melanin synthesis by down-regulating the expression of tyrosinase and TRP1, which are mainly mediated by TGF-beta1.

Proteomic analysis for inhibitory effect of chitosan oligosaccharides on 3T3-L1 adipocyte differentiation

In the present study, we performed a differential proteomic analysis using 2-DE combined with MS to clarify the molecular mechanism for the suppressive effect of chitosan oligosaccharides (CO) during differentiation of adipocyte 3T3-L1. Cell differentiation was significantly inhibited by CO at the concentration of 4 mg/mL. Protein mapping of adipocyte homogenates by 2-DE revealed that numerous protein spots were differentially altered in response to CO treatment. Out of 50 identified proteins showing significant alterations, six were up-regulated and 44 were down-regulated by CO treatment in comparison to control mature adipocytes. Among them, most of the proteins are associated with lipid metabolism, cytoskeleton, and redox regulation, in which the levels of farnesyl diphosphate synthetase (FDS), dedicator of cytokinesis 9 (DOCK9), and chloride intracellular channel 1 (CLIC1) were significantly reduced (>two-fold) with CO treatment. These results have not previously been examined in the context of adipogenesis, and thus can be used as novel biomarkers. Taken together with immunoblot analysis, it was concluded that the inhibitory effect of CO on adipocyte differentiation was mediated by C/EBPalpha and PPARgamma pathway through significant downregulations of important adipogenic molecules such as fatty acid binding protein and glucose transporter 4.

Characterization of human mesenchymal stem cell secretome at early steps of adipocyte and osteoblast differentiation

Background

It is well established that adipose tissue plays a key role in energy storage and release but is also a secretory organ and a source of stem cells. Among different lineages, stem cells are able to differentiate into adipocytes and osteoblasts. As secreted proteins could regulate the balance between both lineages, we aimed at characterizing the secretome of human multipotent adipose-derived stem cell (hMADS) at an early step of commitment to adipocytes and osteoblasts.

Results

A proteomic approach, using mono-dimensional electrophoresis and tandem mass spectrometry, allowed us to identify a total of 73 proteins at day 0 and day 3 of adipocyte and osteoblast differentiation. Analysis of identified proteins showed that 52 % corresponded to classical secreted proteins characterized by a signal peptide, that 37 % previously described in the extracellular compartment were devoid of signal peptide and that 11 % neither exhibited a signal peptide nor had been previously described extracellularly. These proteins were classified into 8 clusters according to their function. Quantitative analysis has been performed for 8 candidates: PAI-1, PEDF, BIGH3, PTX3, SPARC, ENO1, GRP78 and MMP2. Among them, PAI-1 was detected at day 0 and day 3 of osteoblast differentiation but never in adipocyte secretome. Furthermore we showed that PAI-1 mRNA was down-regulated in the bone of ovariectomized mice.

Conclusion

Given its regulation during the early events of hMADS cell differentiation and its status in ovariectomized mice, PAI-1 could play a role in the adipocyte/osteoblast balance and thus in bone diseases such as osteoporosis.

The role of lipocalin 2 in the regulation of inflammation in adipocytes and macrophages

Adipose tissue-derived cytokines (adipokines) are associated with the development of inflammation and insulin resistance. However, which adipokine(s) mediate this linkage and the mechanisms involved during obesity is poorly understood. Through proteomics and microarray screening, we recently identified lipocalin 2 (LCN 2) as an adipokine that potentially connects obesity and its related adipose inflammation. Herein we show that the levels of LCN2 mRNA are dramatically increased in adipose tissue and liver of ob/ob mice and primary adipose cells isolated from Zucker obese rats, and thiazolidinedione administration reduces LCN2 expression. Interestingly, addition of LCN2 induces mRNA levels of peroxisome proliferator-activated receptor-gamma (PPARgamma) and adiponectin. Reducing LCN2 gene expression causes decreased expression of PPARgamma and adiponectin, slightly reducing insulin-stimulated Akt2 phosphorylation at Serine 473 in 3T3-L1 adipocytes. LCN2 administration to 3T3-L1 cells attenuated TNFalpha-effect on glucose uptake, expression of PPARgamma, insulin receptor substrate-1, and glucose transporter 4, and secretion of adiponectin and leptin. When added to macrophages, LCN2 suppressed lipopolysaccharide-induced cytokine production. Our data suggest that LCN2, as a novel autocrine and paracrine adipokine, acts as an antagonist to the effect of inflammatory molecules on inflammation and secretion of adipokines.

Type 2 diabetes: Gaining insight into the disease process using proteomics

The incidence of diabetes mellitus is growing rapidly, with an increasing disease related morbidity and mortality. This is caused by macro- and microvascular complications, as a consequence of the often late diagnosis of type 2 diabetes (T2D), but especially by the difficulties to control glucose homeostasis due to the progressive nature of the disease. T2D is moreover a dual disease, with components of beta-cell failure and components of insulin resistance in peripheral organs, such as liver, fat, and muscle. Understanding the pathogenesis of the disease by gaining insight into the molecular pathways involved in both phenomena is one of the major assets of proteomic approaches. Moreover, proteomics and peptidomics may provide us with robust biomarkers for beta-cell failure, insulin resistance in pheripheral organs, but also for the development of diabetic complications. This review focuses on the knowledge gained by use of proteomic and peptidomic techniques in the study of the pathophysiology of T2D and in the attempts to discover new therapeutic targets.

Defining the regulated secreted proteome of rodent adipocytes upon the induction of insulin resistance

Insulin resistance defines the metabolic syndrome and precedes, as well is the hallmark of, type II diabetes. Adipocytes, besides being a major site for energy storage, are endocrine in nature and secrete a variety of proteins, adipocytokines (adipokines), that can modulate insulin sensitivity, inflammation, obesity, hypertension, food intake (anorexigenic and orexigenic), and general energy homeostasis. Recent data demonstrates that increased intracellular glycosylation of proteins via O-GlcNAc can induce insulin resistance and that a rodent model with genetically elevated O-GlcNAc levels in muscle and fat displays hyperleptinemia. The link between O-GlcNAc levels, insulin resistance, and adipocytokine secretion is further explored here. First, with the use of immortalized and primary rodent adipocytes, the secreted proteome of differentiated adipocytes is more fully elucidated by the identification of 97 and 203 secreted proteins, respectively. Mapping of more than 80 N-linked glycosylation sites on adipocytokines from the cell lines further defines this proteome. Importantly, adipocytokines that are modulated when cells are shifted from insulin responsive to insulin resistant conditions are determined. By the use of two protocols for inducing insulin resistance, classical hyperglycemia with chronic insulin exposure and pharmacological elevation of O-GlcNAc levels, several proteins are identified that are regulated in a similar fashion under both conditions including HCNP, Quiescin Q6, Angiotensin, lipoprotein lipase, matrix metalloproteinase 2, and slit homologue 3. Detection of these potential prognostic/diagnostic biomarkers for metabolic syndrome, type II diabetes, and the resulting complications of both diseases further establishes the central role of the O-GlcNAc modification of intracellular proteins in the pathophysiology of these conditions.

Decreased serum lipocalin-2 levels in human immunodeficiency virus-infected patients: increase during highly active anti-retroviral therapy

Although neutrophil gelatinase-associated lipocalin (NGAL) may play a pivotal role in the innate immune response, there are currently no data on NGAL levels in human immunodeficiency virus (HIV)-infected patients. In this study we aimed to examine the regulation of NGAL in HIV infection. The regulation of NGAL in HIV infection was examined by different experimental approaches, including studies in peripheral blood and mononuclear cells (MNC) from bone marrow aspirates before and during highly active anti-retroviral therapy (HAART). We found that: before initiating HAART, HIV-infected patients (n = 37) had significantly decreased serum NGAL levels compared with healthy controls (n = 26); (ii) during HAART, there was a gradual and significant increase in NGAL concentrations reaching levels comparable to those in healthy controls after 12 months; (iii) this increase was seen primarily in virological responders to HAART (HIV RNA level <200 copies/ml after 24 months); (iv) phytohaemagglutinin-stimulated NGAL release in MNC cells from bone marrow aspirates was decreased in untreated HIV-infected patients compared with healthy controls, but increased after 26 weeks on HAART; and (v) there was a significant positive correlation between neutrophil counts and NGAL levels at all time-points during HAART. We have shown decreased NGAL levels in HIV-infected patients, potentially reflecting decreased number and function of neutrophils as well as impaired bone marrow myelopoiesis. These abnormalities were reversed by successful HAART. Our findings underscore further the involvement of neutrophils and innate immunity in HIV-related immunodeficiency.

Inflammatory biomarkers associated with obesity and insulin resistance: a focus on lipocalin-2 and adipocyte fatty acid-binding protein

Obesity is an important risk factor for a cluster of metabolic and cardiovascular diseases, including insulin resistance, Type 2 diabetes, nonalcoholic fatty liver disease and atherosclerosis. Systemic low-grade inflammation, characterized by elevated circulating concentrations of proinflammatory factors, has recently been proposed to be a key mediator that links obesity with its medical complications. Adipose tissue is now recognized as the major contributor to systemic inflammation associated with obesity. As obesity develops, adipose tissue is infiltrated with activated macrophages. The 'inflamed' adipose tissue secretes a large number of proinflammatory adipokines and/or cytokines, which can act either in an autocrine manner to perpetuate local inflammation or in an endocrine manner to induce insulin resistance and endothelial dysfunction. In this review, we summarize recent advances in several newly identified adipose tissue-derived inflammatory factors, with the focus on lipocalin-2 and adipocyte fatty acid-binding protein (A-FABP). Both lipocalin-2 and A-FABP possess lipid-binding properties and are important integrators of metabolic and inflammatory pathways. A growing body of evidence from experimental, epidemiological and genetic studies suggests that both lipocalin-2 and A-FABP represent a novel class of serum biomarkers for risk prediction and therapeutic intervention of obesity-related medical complications.

Cardiotrophin-1 is expressed in adipose tissue and upregulated in the metabolic syndrome

Adipose tissue is a target for cardiotrophin-1 (CT-1), a cytokine member of the IL-6 family of cytokines that is involved in cardiac growth and dysfunction. However, it is unknown whether adipocytes are a source of CT-1 and whether CT-1 is overexpressed in diseases characterized by increased fat depots [i.e., the metabolic syndrome (MS)]. Thus this work aimed 1) to test whether adipose tissue expresses CT-1 and whether CT-1 expression can be modulated and 2) to compare serum CT-1 levels in subjects with and without MS diagnosed by National Cholesterol Education Program Adult Treatment Panel III criteria. Gene and protein expression of CT-1 was determined by real-time RT-PCR, ELISA, and Western blotting. CT-1 expression progressively increased, along with differentiation time from preadipocyte to mature adipocyte in 3T3-L1 cells. CT-1 expression was enhanced by glucose in a dose-dependent manner in these cells. mRNA and protein CT-1 expression was also demonstrated in human adipose biopsies. Immunostaining showed positive staining in adipocytes. Finally, increased CT-1 serum levels were observed in patients with MS compared with control subjects (127 +/- 9 vs. 106 +/- 4 ng/ml, P < 0.05). Circulating levels of CT-1 were associated with glucose levels (r = 0.2, P < 0.05). Taken together, our data suggest that adipose tissue can be recognized as a source of CT-1, which could account for the high circulating levels of CT-1 in patients with MS.

Applications of proteomics to the study of adipose tissue

Determination of the complex secretory proteome of adipocytes and its metabolic changes induced by drug treatment such as insulin or rosiglitazone is possible with the advanced proteomics technologies described herein. To study the secreted proteins of adipocytes, a 2D- liquid chromatography/mass spectrometry/mass spectrometry protocol has been established. With the use of reversed-phase high-performance liquid chromatography, intact proteins were separated in the first dimension into eight fractions, then digested with Lys-C and trypsin. Comparative differences after drug treatment were assessed using 18O proteolytic labeling strategies. With the advent of more and more sophisticated instrumentation and data analysis tools, protocols like this one will likely become standard tools for scientists in the research fields of endocrinology, obesity, and diabetes. These protocols enable researchers to study the dynamic drug-induced changes in a comprehensive and systematic manner that was inconceivable just a few years ago.

Recent advances in protein profiling of tissues and tissue fluids

Creating protein profiles of tissues and tissue fluids, which contain secreted proteins and peptides released from various cells, is critical for biomarker discovery as well as drug and vaccine target selection. It is extremely difficult to obtain pure samples from tissues or tissue fluids, however, and identification of complex protein mixtures is still a challenge for mass spectrometry analysis. Here, we summarize recent advances in techniques for extracting proteins from tissues for mass spectrometry profiling and imaging. We also introduce a novel technique using a capillary ultrafiltration (CUF) probe to enable in vivo collection of proteins from the tissue microenvironment. The CUF probe technique is compared with existing sampling techniques, including perfusion, saline wash, fine-needle aspiration and microdialysis. In this review, we also highlight quantitative mass spectrometric proteomic approaches with, and without, stable-isotope labels. Advances in quantitative proteomics will significantly improve protein profiling of tissue and tissue fluid samples collected by CUF probes.

The adipokine lipocalin 2 is regulated by obesity and promotes insulin resistance

OBJECTIVE

We identified lipocalin 2 (Lcn2) as a gene induced by dexamethasone and tumor necrosis factor-alpha in cultured adipocytes. The purpose of this study was to determine how expression of Lcn2 is regulated in fat cells and to ascertain whether Lcn2 could be involved in metabolic dysregulation associated with obesity.

RESEARCH DESIGN AND METHODS

We examined Lcn2 expression in murine tissues and in 3T3-L1 adipocytes in the presence and absence of various stimuli. We used quantitative Western blotting to observe Lcn2 serum levels in lean and obese mouse models. To assess effects on insulin action, we used retroviral delivery of short hairpin RNA to reduce Lcn2 levels in 3T3-L1 adipocytes.

RESULTS

Lcn2 is highly expressed by fat cells in vivo and in vitro. Expression of Lcn2 is elevated by agents that promote insulin resistance and is reduced by thiazolidinediones. The expression of Lcn2 is induced during 3T3-L1 adipogenesis in a CCAAT/enhancer-binding protein-dependent manner. Lcn2 serum levels are elevated in multiple rodent models of obesity, and forced reduction of Lcn2 in 3T3-L1 adipocytes improves insulin action. Exogenous Lcn2 promotes insulin resistance in cultured hepatocytes.

CONCLUSIONS

Lcn2 is an adipokine with potential importance in insulin resistance associated with obesity.

Evidence supporting antioxidant action of adipose-derived stem cells: protection of human dermal fibroblasts from oxidative stress

BACKGROUND

Mesenchymal stem cells within the stromal-vascular fraction of subcutaneous adipose tissue, adipose-derived stem cells (ADSCs), produced soluble factors and they exhibit diverse pharmacological effects in skin biology.

OBJECTIVE

The present study examines the protective effect of ADSCs for human dermal fibroblasts (HDFs) through anti-oxidation in a tert-butyl hydroperoxide (tbOOH) induced oxidative injury model.

METHODS AND RESULTS

The conditioned medium of ADSCs (ADSC-CM) was harvested and tested for antioxidant action. ADSC-CM had an antioxidant effect as potent as 100 microM ascorbic acid and various antioxidant proteins were detected in ADSC-CM by proteomic analysis. Morphological change and cell survival assay revealed that incubation with ADSC-CM aided HDFs to resist free radicals induced by tbOOH. In addition, activities of superoxide dismutase and glutathione peroxidase were enhanced in the ADSC-CM treated HDFs which confirmed the study hypothesis that ADSCs protect HDFs through antioxidant action. In a cell cycle analysis, ADSC-CM treatment reversed the apoptotic cell death induced by tbOOH and caused a decrease of sub-G1 cells with respect to untreated cells. The anti-apoptotic effect of ADSC-CM was also reproduced by caspase-3 activity assay.

CONCLUSION

These results suggest that ADSCs have potent antioxidant activity and protect HDFs from oxidative injury by decreasing apoptotic cells. Therefore, ADSCs and ADSC-CM are good candidates for control and prevention of skin damage from free radicals in various skin conditions.

Wound healing effect of adipose-derived stem cells: a critical role of secretory factors on human dermal fibroblasts

BACKGROUND

Adipose-derived stem cells (ADSCs) are a population of pluripotent cells, which have characteristics similar to bone marrow-derived mesenchymal stem cells. Whereas ADSCs have potential applications for the repair and regeneration of various damaged tissues, few studies have dealt with the effect of ADSCs on fibroblasts, which play a key role in skin biology.

OBJECTIVE

In this study, we investigated the possible roles of ADSCs in skin wound healing process, especially in the aspect of fibroblast activation-proliferation, collagen synthesis and migratory properties.

METHODS AND RESULTS

ADSCs promoted human dermal fibroblast (HDF) proliferation, not only by cell-to-cell direct contact, which was confirmed by co-culture experiment, but also by paracrine activation through secretory factors, resolved by transwell co-culture and culturing with conditioned medium of ADSCs (ADSC-CM). ADSC-CM enhanced the secretion of type I collagen in HDFs by regulating the mRNA levels of extracellular matrix (ECM) proteins: up-regulation of collagen type I, III and fibronectin and down-regulation of MMP-1. Moreover, ADSC-CM showed stimulatory effect on migration of HDFs in in vitro wound healing models. Additional to those in vitro evidences, wound healing effect of ADSCs was also verified with in vivo animal study, resulted that ADSCs significantly reduced the wound size and accelerated the re-epithelialization from the edge.

CONCLUSION

Collectively, these data suggest that ADSC is constitutionally well suited for dermal wound healing and secretory factors derived from ADSCs promote wound healing via HDFs and ADSCs can be used for the treatment of photoaging and wound healing.

Adipose-derived stem cells for regenerative medicine

The emerging field of regenerative medicine will require a reliable source of stem cells in addition to biomaterial scaffolds and cytokine growth factors. Adipose tissue represents an abundant and accessible source of adult stem cells with the ability to differentiate along multiple lineage pathways. The isolation, characterization, and preclinical and clinical application of adipose-derived stem cells (ASCs) are reviewed in this article.

Identification of proteins from feeder conditioned medium that support human embryonic stem cells

The maintenance of undifferentiated human embryonic stem cells (hESC) requires feeder cells, either in co-culture or feeder-free with conditioned medium (CM) from the feeders. In this study, we compared the CM of a supporting primary mouse embryonic feeder (MEF) and an isogenic but non-supporting MEF line (DeltaE-MEF) in order to gain an insight to the differential expression profile of secreted factors. Using two-dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ionization-time of flight (MALDI) tandem mass spectrometry, 13 protein identities were found to be downregulated in DeltaE-MEF compared to MEF, of which 4 were found to be soluble factors and 3 proteins were membrane-associated or related to the extracellular matrix. In addition, four other proteins were identified to be differentially expressed in MEF-CM using high pressure liquid chromatography (HPLC) and cytokine arrays. In functional experiments where CM was replaced with six of the factors identified, hESC were able to proliferate for five continuous passages whilst maintaining 68-82% and 74-98% expression of pluripotent markers, Oct-4 and Tra-1-60, respectively. Using proteomic tools, important proteins from CM that supports hESC culture have been identified, which when replaced with recombinant proteins, continue to support undifferentiated hESC growth in a feeder-free culture platform.

In-depth analysis of the adipocyte proteome by mass spectrometry and bioinformatics

Adipocytes are central players in energy metabolism and the obesity epidemic, yet their protein composition remains largely unexplored. We investigated the adipocyte proteome by combining high accuracy, high sensitivity protein identification technology with subcellular fractionation of nuclei, mitochondria, membrane, and cytosol of 3T3-L1 adipocytes. We identified 3,287 proteins while essentially eliminating false positives, making this one of the largest high confidence proteomes reported to date. Comprehensive bioinformatics analysis revealed that the adipocyte proteome, despite its specialized role, is very complex. Comparison with microarray data showed that the mRNA abundance of detected versus non-detected proteins differed by less than 2-fold and that proteomics covered as large a proportion of the insulin signaling pathway. We used the Endeavour gene prioritization algorithm to associate a number of factors with vesicle transport in response to insulin stimulation, a key function of adipocytes. Our data and analysis can serve as a model for cellular proteomics. The adipocyte proteome is available as supplemental material and from the Max-Planck Unified Proteome database.

Characterization of the Human Visceral Adipose Tissue Secretome

Adipose tissue is an endocrine organ involved in storage and release of energy but also in regulation of energy metabolism in other organs via secretion of peptide and protein hormones (adipokines). Especially visceral adipose tissue has been implicated in the development of metabolic syndrome and type 2 diabetes. Factors secreted by the stromal-vascular fraction contribute to the secretome and modulate adipokine secretion by adipocytes. Therefore, we aimed at the characterization of the adipose tissue secretome rather than the adipocyte cell secretome. The presence of serum proteins and intracellular proteins from damaged cells, released during culture, may dramatically influence the dynamic range of the sample and thereby identification of secreted proteins. Part of the study was therefore dedicated to the influence of the culture setup on the quality of the final sample. Visceral adipose tissue was cultured in five experimental setups, and the quality of resulting samples was evaluated in terms of protein concentration and protein composition. The best setup involved one wash after the 1st h in culture followed by two or three additional washes within an 8-h period, starting after overnight culture. Thereafter tissue was maintained in culture for an additional 48-114 h to obtain the final sample. For the secretome experiment, explants were cultured in media containing L-[(13)C(6),(15)N(2)]lysine to validate the origin of the identified proteins (adipose tissue- or serum-derived). In total, 259 proteins were identified with > or =99% confidence. 108 proteins contained a secretion signal peptide of which 70 incorporated the label and were considered secreted by adipose tissue. These proteins were classified into five categories according to function. This is the first study on the (human) adipose tissue secretome. The results of this study contribute to a better understanding of the role of adipose tissue in whole body energy metabolism and related diseases.

Plasma concentration of pigment epithelium-derived factor in patients with diabetic retinopathy

CONTEXT

Pigment epithelium-derived factor (PEDF) is a strong inhibitor of angiogenesis. Eyes with diabetic retinopathy have low levels of ocular PEDF; however, the PEDF levels in the blood of diabetics have still not been determined.

OBJECTIVES

Our objective was to determine the plasma levels of PEDF in diabetic patients and to determine the relationship with the stage of the diabetic retinopathy.

DESIGN AND SETTING

This study was designed as a cross-sectional, institutional study.

PATIENTS OR OTHER PARTICIPANTS

A total of 145 Japanese were studied; 112 had type 2 diabetes mellitus, and 33 were healthy controls.

INTERVENTION

There was no intervention.

MAIN OUTCOME MEASURES

The plasma level of PEDF was measured by ELISA, and the stage of diabetic retinopathy was determined by ophthalmic examinations. Clinical systemic status of diabetic patients was also examined.

RESULTS

The plasma PEDF level in diabetic patients (6.68 +/- 0.54 microg/ml; mean +/- sem) was significantly higher than that in controls (4.38 +/- 0.59 microg/ml, P = 0.03), and the level was especially high in patients with proliferative diabetic retinopathy (7.78 +/- 0.98 microg/ml; n = 45; P = 0.005). The gender (P = 0.03), blood urea nitrogen (P = 0.005), and triglycerides (P = 0.04) were significant and independent determinants of plasma PEDF levels in diabetic patients.

CONCLUSIONS

The PEDF level in the plasma was significantly elevated in diabetic patients, especially those with proliferative diabetic retinopathy. High levels of PEDF in the plasma may be related to the progression of diabetic retinopathy.

Cell Cycle Genes PEDF and CDKN1C in Growing Deer Antlers

Deer antlers are the only mammalian appendage to display an annual cycle of full regeneration. The growth phase in antler involves the rapid proliferation of several tissues types, including epidermis, dermis, cartilage, bone, blood vessels, and nerves. Antlers thus provide an excellent model to study the developmental regulation of these tissues. We describe here the identification of two genes, pigment epithelium-derived factor (PEDF) and cyclin-dependent kinase inhibitor 1C (CDKN1C), both of which are known to be involved in cell proliferation and differentiation. These genes were identified as the result of screening an expressed sequence tag database derived from a cDNA library enriched for sequences from the growing antler tip. PEDF mRNA was detected in developing skin, cartilage, and bone during endochondral ossification. PEDF mRNA was not detected within endothelial cells that exhibited positive immunoreactivity to a CD146 antibody. CDKN1C mRNA was expressed by only the immature chondrocytes within the precartilage region. These results suggested that PEDF and CDKN1C are important genes involved in cell proliferation and differentiation during antler growth.

Adipokine gene expression in brain and pituitary gland

The brain has been recognized as a prominent site of peptide biosynthesis for more than 30 years, and many neuropeptides are now known to be common to gut and brain. With these precedents in mind it is remarkable that adipose-derived peptides like leptin have attracted minimal attention as brain-derived putative neuromodulators of energy balance. This review outlines the evidence that several adipose-specific genes are also expressed in the central nervous system and pituitary gland. We, and others, confirmed that the genes for leptin, resistin, adiponectin, FIAF (fasting-induced adipose factor) and adiponutrin are expressed and regulated in these tissues. For example, leptin mRNA was readily detectable in human, rat, sheep and pig brain, but not in the mouse. Leptin expression in rat brain and pituitary was regulated through development, by food restriction, and following traumatic brain injury. In contrast, hypothalamic resistin mRNA was unaffected by age or by fasting, but was significantly depleted by food restriction in mouse pituitary gland. Similar results were seen in the ob/ob mouse, and we noted a marked reduction in resistin-positive hypothalamic nerve fibres. Resistin and fiaf mRNA were also upregulated in hypoxic/ischaemic mouse brain. Our studies on the regulation of neuronal adipokines were greatly aided by the availability of clonal hypothalamic neuronal cell lines. One of these, N-1, expresses both rstn and fiaf together with several other neuropeptides and receptors involved in energy homeostasis. Selective silencing of rstn revealed an autocrine/paracrine regulatory system, mediated through socs-3 expression that may influence the feedback effects of insulin and leptin in vivo. A similar convergence of signals in the pituitary gland could also influence anterior pituitary hormone secretion. In conclusion, the evidence is suggestive that brain and pituitary-derived adipokines represent a local regulatory circuit that may fine tune the feedback effects of adipose hormones in the control of energy balance.