Proteomic Signatures of Human Visceral and Subcutaneous Adipocytes

CONTEXT

Adipose tissue distribution is a key factor influencing metabolic health and risk in obesity-associated comorbidities.

OBJECTIVE

Here we aim to compare the proteomic profiles of mature adipocytes from different depots.

METHODS

Abdominal subcutaneous (SA) and omental visceral adipocytes (VA) were isolated from paired adipose tissue biopsies obtained during bariatric surgery on 19 severely obese women (body mass index > 30 kg/m2) and analyzed using state-of-the-art mass spectrometry. Differential expression analysis and weighted gene co-expression network analysis (WGCNA) were performed to investigate proteome signature properties and to examine a possible association of the protein expression with the clinical data.

RESULTS

We identified 3686 protein groups and found 1140 differentially expressed proteins (adj. P value < 0.05), of which 576 proteins were upregulated in SA and 564 in VA samples. We provide a global protein profile of abdominal SA and omental VA, present the most differentially expressed pathways and processes distinguishing SA from VA, and correlate them with clinical and body composition data. We show that SA are significantly more active in processes linked to vesicular transport and secretion, and to increased lipid metabolism activity. Conversely, the expression of proteins involved in the mitochondrial energy metabolism and translational or biosynthetic activity is higher in VA.

CONCLUSION

Our analysis represents a valuable resource of protein expression profiles in abdominal SA and omental VA, highlighting key differences in their role in obesity.

GPR183 Is Dispensable for B1 Cell Accumulation and Function, but Affects B2 Cell Abundance, in the Omentum and Peritoneal Cavity

B1 cells constitute a specialized subset of B cells, best characterized in mice, which is abundant in body cavities, including the peritoneal cavity. Through natural and antigen-induced antibody production, B1 cells participate in the early defense against bacteria. The G protein-coupled receptor 183 (GPR183), also known as Epstein-Barr virus-induced gene 2 (EBI2), is an oxysterol-activated chemotactic receptor that regulates migration of B cells. We investigated the role of GPR183 in B1 cells in the peritoneal cavity and omentum. B1 cells expressed GPR183 at the mRNA level and migrated towards the GPR183 ligand 7α,25-dihydroxycholesterol (7α,25-OHC). GPR183 knock-out (KO) mice had smaller omenta, but with normal numbers of B1 cells, whereas they had fewer B2 cells in the omentum and peritoneal cavity than wildtype (WT) mice. GPR183 was not responsible for B1 cell accumulation in the omentum in response to i.p. lipopolysaccharide (LPS)-injection, in spite of a massive increase in 7α,25-OHC levels. Lack of GPR183 also did not affect B1a- or B1b cell-specific antibody responses after vaccination. In conclusion, we found that GPR183 is non-essential for the accumulation and function of B1 cells in the omentum and peritoneal cavity, but that it influences the abundance of B2 cells in these compartments.

LYVE1+ macrophages of murine peritoneal mesothelium promote omentum-independent ovarian tumor growth

Two resident macrophage subsets reside in peritoneal fluid. Macrophages also reside within mesothelial membranes lining the peritoneal cavity, but they remain poorly characterized. Here, we identified two macrophage populations (LYVE1hi MHC IIlo-hi CX3CR1gfplo/- and LYVE1lo/- MHC IIhi CX3CR1gfphi subsets) in the mesenteric and parietal mesothelial linings of the peritoneum. These macrophages resembled LYVE1+ macrophages within surface membranes of numerous organs. Fate-mapping approaches and analysis of newborn mice showed that LYVE1hi macrophages predominantly originated from embryonic-derived progenitors and were controlled by CSF1 made by Wt1+ stromal cells. Their gene expression profile closely overlapped with ovarian tumor-associated macrophages previously described in the omentum. Indeed, syngeneic epithelial ovarian tumor growth was strongly reduced following in vivo ablation of LYVE1hi macrophages, including in mice that received omentectomy to dissociate the role from omental macrophages. These data reveal that the peritoneal compartment contains at least four resident macrophage populations and that LYVE1hi mesothelial macrophages drive tumor growth independently of the omentum.

Acute Kidney Ischemic Injury in a Rat Model Treated by Human Omental Mesenchymal Stem Cells

BACKGROUND

Mesenchymal stem cells (MSCs) may provide a novel clinical approach for acute kidney injury (AKI), which represents a severe health care condition. The human omentum is an important source of MSCs. We investigated the effects of human omental mesenchymal stem cells (HO-MSCs) after induction of ischemic AKI in a rat model.

METHODS

The ischemic-reperfusion injury (IRI) was induced at reperfusion following a 45-minute clamping of renal vessels. Twenty animals were used in this study. Each rat was randomly assigned to 1 of 2 groups: G1 (control, n = 10; IRI infusion of phosphate buffer solution) or G2 (HO-MSCs, n = 10; IRI infusion of HO-MSCs). The infusions were performed in the parenchyma at reperfusion. Renal function at 1, 3, 5, and 7 days was assessed. At sacrifice, histologic samples were analyzed by light, and renal injury was graded.

RESULTS

HO-MSCs induced an accelerated renal exocrine functional recovery, demonstrated by biochemical parameters and confirmed by histology showing that histopathological alterations associated with ischemic injury were less severe in cell-treated kidneys as compared with control groups (P < .05). The renal damage degree was significantly less in the animals of the HO-MSC group (P < .0001).

CONCLUSIONS

These results suggest that HO-MSCs could be useful in the treatment of AKI in a rat model with possible potential implication in clinical setting.

Adipocyte-Induced FABP4 Expression in Ovarian Cancer Cells Promotes Metastasis and Mediates Carboplatin Resistance

Adipocytes are critical for ovarian cancer cells to home to the omentum, but the metabolic changes initiated by this interaction are unknown. To this end, we carried out unbiased mass spectrometry-based metabolomic and proteomic profiling of cancer cells cocultured with primary human omental adipocytes. Cancer cells underwent significant proteo-metabolomic alteration(s), typified by changes in the lipidome with corresponding upregulation of lipid metabolism proteins. FABP4, a lipid chaperone protein, was identified as the critical regulator of lipid responses in ovarian cancer cells cocultured with adipocytes. Subsequently, knockdown of FABP4 resulted in increased 5-hydroxymethylcytosine levels in the DNA, downregulation of gene signatures associated with ovarian cancer metastasis, and reduced clonogenic cancer cell survival. In addition, clustered regularly interspaced short palindromic repeats (CRISPR)-mediated knockout of FABP4 in high-grade serous ovarian cancer cells reduced metastatic tumor burden in mice. Consequently, a small-molecule inhibitor of FABP4 (BMS309403) not only significantly reduced tumor burden in a syngeneic orthotopic mouse model but also increased the sensitivity of cancer cells toward carboplatin both in vitro and in vivo. Taken together, these results show that targeting FABP4 in ovarian cancer cells can inhibit their ability to adapt and colonize lipid-rich tumor microenvironments, providing an opportunity for specific metabolic targeting of ovarian cancer metastasis. SIGNIFICANCE: Ovarian cancer metastatic progression can be restricted by targeting a critical regulator of lipid responses, FABP4.

Whole-Tooth Regeneration by Allogeneic Cell Reassociation in Pig Jawbone

IMPACT STATEMENT

The methods developed in this study to manipulate pig tooth germ cells in vitro and in vivo provide a reference for studying whole-tooth regeneration and tooth development in large animals. Of importance, compared with conventional ectopic tooth regeneration, conducted in the omentum, subcutaneous tissues, or kidney capsule (among other locations) with low with immune reactivity in rodent models, this study achieved orthotopic regeneration and development of whole teeth in a large mammal, representing a large stride toward the realization of tooth regenerative therapy for humans with missing teeth.

Personalized Hydrogels for Engineering Diverse Fully Autologous Tissue Implants

Despite incremental improvements in the field of tissue engineering, no technology is currently available for producing completely autologous implants where both the cells and the scaffolding material are generated from the patient, and thus do not provoke an immune response that may lead to implant rejection. Here, a new approach is introduced to efficiently engineer any tissue type, which its differentiation cues are known, from one small tissue biopsy. Pieces of omental tissues are extracted from patients and, while the cells are reprogrammed to become induced pluripotent stem cells, the extracellular matrix is processed into an immunologically matching, thermoresponsive hydrogel. Efficient cell differentiation within a large 3D hydrogel is reported, and, as a proof of concept, the generation of functional cardiac, cortical, spinal cord, and adipogenic tissue implants is demonstrated. This versatile bioengineering approach may assist to regenerate any tissue and organ with a minimal risk for immune rejection.

Inhibition of the H3K4 methyltransferase SET7/9 ameliorates peritoneal fibrosis

Transforming growth factor-β1 (TGF-β1) is a major mediator of peritoneal fibrosis and reportedly affects expression of the H3K4 methyltransferase, SET7/9. SET7/9-induced H3K4 mono-methylation (H3K4me1) critically activates transcription of fibrosis-related genes. In this study, we examined the effect of SET7/9 inhibition on peritoneal fibrosis in mice and in human peritoneal mesothelial cells (HPMCs). We also examined SET7/9 expression in nonadherent cells isolated from the effluent of peritoneal dialysis (PD) patients. Murine peritoneal fibrosis was induced by intraperitoneal injection of methylglyoxal (MGO) into male C57/BL6 mice over 21 days. Sinefungin, a SET7/9 inhibitor, was administered subcutaneously just before MGO injection (10 mg/kg). SET7/9 expression was elevated in both MGO-injected mice and nonadherent cells isolated from the effluent of PD patients. SET7/9 expression was positively correlated with dialysate/plasma ratio of creatinine in PD patients. Sinefungin was shown immunohistochemically to suppress expression of mesenchymal cells and collagen deposition, accompanied by decreased H3K4me1 levels. Peritoneal equilibration tests showed that sinefungin attenuated the urea nitrogen transport rate from plasma and the glucose absorption rate from the dialysate. In vitro, sinefungin suppressed TGF-β1-induced expression of fibrotic markers and inhibited H3K4me1. These findings suggest that inhibiting the H3K4 methyltransferase SET7/9 ameliorates peritoneal fibrosis.

A microfluidic chip containing multiple 3D nanofibrous scaffolds for culturing human pluripotent stem cells

In microfluidics-based lab-on-a-chip systems, which are used for investigating the effect of drugs and growth factors on cells, the latter are usually cultured within the device's channels in two-dimensional, and not in their optimal three-dimensional (3D) microenvironment. Herein, we address this shortfall by designing a microfluidic system, comprised of two layers. The upper layer of the system consists of multiple channels generating a gradient of soluble factors. The lower layer is comprised of multiple wells, each deposited with 3D, nanofibrous scaffold. We first used a mathematical model to characterize the fluid flow within the system. We then show that induced pluripotent stem cells can be seeded within the 3D scaffolds and be exposed to a well-mixed gradient of soluble factors. We believe that utilizing such system may enable in the future to identify new differentiation factors, investigate drug toxicity, and eventually allow to perform analyses on patient-specific tissues, in order to fit the appropriate combination and concentration of drugs.

Effects of Rapamycin on the Epithelial-to-mesenchymal Transition of Human Peritoneal Mesothelial Cells

The preservation of the peritoneal membrane is crucial for long-term survival in peritoneal dialysis. Epithelial-to-mesenchymal transition (EMT) is a process demonstrated in mesothelial cells (MC), responsible for negative peritoneal changes and directly related to PD. EMT enables neovascularization and fibrogenic capabilities in MC. Vascular endothelial growth factor (VEGF) is the mediator for neo-vascularization. Rapamycin is a potent immunosuppressor with antifibrotic action in renal allografts and has a demonstrated anti-VEGF effect. We performed this study with the hypothesis that rapamycin may regulate the EMT of MC.

MC from human omentum were cultured. When mesothelial cells reached confluence, some of them were stimulated with r-TGF-ß (1 ng/mL) to induce EMT, co-administered with rapamycin (0.2, 2, 4, 20 and 40 nM). Other groups of cells received similar doses of rapamycin or r-TGF-ß, separately. Cells were analyzed at 6, 24, 48 hours and 7 days. As markers of EMT we included α-SMA, E-cadherin and snail nuclear factor by quantitative RT-PCR.

EMT markers and regulators demonstrated the following changes with rapamycin: E-cadherin (a protective gene for EMT) increased 2.5-fold relative to controls under 40 nM, at 24h. Importantly, rapamycin inhibited snail expression induced by TGF-ß at 6h, whereas TGF-ß increased snail 10fold. At day 7, rapamycin showed no anti-EMT properties. An important decrease in α-SMA expression by MC after rapamycin addition was observed.

In conclusion, rapamycin shows a mild protective effect on EMT, as it increases E-cadherin and decreases α-SMA expression. Consequently, rapamycin might partially regulate the epithelial-to-mesenchymal transition of mesothelial cells.

The Potential of Mesothelial Cells in Tissue Engineering and Regenerative Medicine Applications

Injury to the serosa through injurious agents such as radiation, surgery, infection and disease results in the loss of the protective surface mesothelium and often leads to fibrous adhesion formation. Mechanisms that increase the rate of mesothialisation are therefore actively being investigated in order to reduce the formation of adhesions. These include intraperitoneal delivery of cultured mesothelial cells as well as administration of factors that are known to increase mesothelial proliferation and migration. An exciting alternative that has only recently received attention, is the possible role of mesothelial progenitor cells in the repair and regeneration of denuded serosal areas. Accumulating evidence suggests that such a population exists and under certain conditions is able to form a number of defined cell types indicating a degree of plasticity. Such properties may explain the extensive use of mesothelial cells in various tissue engineering applications including the development of vascular conduits and peripheral nerve replacements. It is likely that with the rapid explosion in the fields of tissue engineering and regenerative medicine, a greater understanding of the potential of mesothelial progenitor cells to repair, replace and possibly regenerate damaged or defective tissue will be uncovered.

Correlation between HSP-72 Expression and IL-8 Secretion in Human Mesothelial Cells

Background

Cytotoxicity of peritoneal dialysis fluid (PDF) and peritoneal inflammation are currently regarded as the two major culprits for chronic mesothelial injury and peritoneal membrane failure. In this study, we correlated induction of HSP-72, as a marker of the cellular stress response, to secretion of IL-8, as a marker for pro-inflammatory cytokines, in mesothelial cells upon sublethal PDF exposure.

Methods

Primary omental cell cultures of human mesothelial cells were subjected to sublethal PDF exposure times (CAPD2, Fresenius, Germany). At the end of a 24 hour recovery period, induction of HSP-72 in the cell homogenate and IL-8 secretion in the supernatant was assessed by immunodensitometry and ELISA, respectively.

Results

PDF exposure times from 15 min to 60 min resulted in progressively increased HSP-72 expression levels (267 vs 320 vs 419% of controls, p<0.05 vs controls) as well as increased IL-8 secretion (323 vs 528 vs 549% of controls, p<0.05 vs controls) with full cell viability (MTT unchanged to control). HSP-72 expression was statistically significantly correlated with IL-8 secretion. Conclusions: The significant correlation between HSP-72 expression and IL-8 secretion suggests that the regulation of pro-inflammatory pathways in mesothelial cells exposed to PDF may represent an integral part of their stress response. Future studies to investigate the cellular regulatory mechanism involved are warranted.

Cathepsin D non-proteolytically induces proliferation and migration in human omental microvascular endothelial cells via activation of the ERK1/2 and PI3K/AKT pathways

Epithelial ovarian cancer (EOC) frequently metastasises to the omentum, a process that requires pro-angiogenic activation of human omental microvascular endothelial cells (HOMECs) by tumour-secreted factors. We have previously shown that ovarian cancer cells secrete a range of factors that induce pro-angiogenic responses e.g. migration, in HOMECs including the lysosomal protease cathepsin D (CathD). However, the cellular mechanism by which CathD induces these cellular responses is not understood. The aim of this study was to further examine the pro-angiogenic effects of CathD in HOMECs i.e. proliferation and migration, to investigate whether these effects are dependent on CathD catalytic activity and to delineate the intracellular signalling kinases activated by CathD. We report, for the first time, that CathD significantly increases HOMEC proliferation and migration via a non-proteolytic mechanism resulting in activation of ERK1/2 and AKT. These data suggest that EOC cancer secreted CathD acts as an extracellular ligand and may play an important pro-angiogenic, and thus pro-metastatic, role by activating the omental microvasculature during EOC metastasis to the omentum.

Characterization of the Extracellular Matrix of Normal and Diseased Tissues Using Proteomics

The extracellular matrix (ECM) is a complex meshwork of insoluble fibrillar proteins and signaling factors interacting together to provide architectural and instructional cues to the surrounding cells. Alterations in ECM organization or composition and excessive ECM deposition have been observed in diseases such as fibrosis, cardiovascular diseases, and cancer. We provide here optimized protocols to solubilize ECM proteins from normal or tumor tissues, digest the proteins into peptides, analyze ECM peptides by mass spectrometry, and interpret the mass spectrometric data. In addition, we present here two novel R-script-based web tools allowing rapid annotation and relative quantification of ECM proteins, peptides, and intensity/abundance in mass spectrometric data output files. We illustrate this protocol with ECMs obtained from two pairs of tissues, which differ in ECM content and cellularity: triple-negative breast cancer and adjacent mammary tissue, and omental metastasis from high-grade serous ovarian cancer and normal omentum. The complete proteomics data set generated in this study has been deposited to the public repository ProteomeXchange with the data set identifier: PXD005554.

Immunological Functions of the Omentum

The omentum is a visceral adipose tissue with unique immune functions. Although it is primarily an adipose tissue, the omentum also contains lymphoid aggregates, called milky spots (MSs), that contribute to peritoneal immunity by collecting antigens, particulates, and pathogens from the peritoneal cavity and, depending on the stimuli, promoting a variety of immune responses, including inflammation, tolerance, or even fibrosis. Reciprocal interactions between cells in the MS and adipocytes regulate their immune and metabolic functions. Importantly, the omentum collects metastasizing tumor cells and supports tumor growth by immunological and metabolic mechanisms. Here we summarize our current knowledge about the development, organization, and function of the omentum in peritoneal immunity.

Unique cellular interactions between pancreatic cancer cells and the omentum

Pancreatic cancer is a common cause of cancer-related mortality. Omental spread is frequent and usually represents an ominous event, leading to patient death. Omental metastasis has been studied in ovarian cancer, but data on its role in pancreatic cancer are relatively scarce and the molecular biology of this process has yet to be explored. We prepared tissue explants from human omental fat, and used conditioned medium from the explants for various in vitro and in vivo experiments designed to evaluate pancreatic cancer development, growth, and survival. Mass spectrometry identified the fat secretome, and mRNA array identified specific fat-induced molecular alternations in tumor cells. Omental fat increased pancreatic cancer cellular growth, migration, invasion, and chemoresistance. We identified diverse potential molecules secreted by the omentum, which are associated with various pro-tumorigenic biological processes. Our mRNA array identified specific omental-induced molecular alternations that are associated with cancer progression and metastasis. Omental fat increased the expression of transcription factors, mRNA of extracellular matrix proteins, and adhesion molecules. In support with our in vitro data, in vivo experiments demonstrated an increased pancreatic cancer tumor growth rate of PANC-1 cells co-cultured for 24 hours with human omental fat conditioned medium. Our results provide novel data on the role of omental tissue in omental metastases of pancreatic cancer. They imply that omental fat secreted factors induce cellular reprogramming of pancreatic cancer cells, resulting in increased tumor aggressiveness. Understanding the mechanisms of omental metastases may enable us to discover new potential targets for therapy.

Comparative analysis of three human adipocyte size measurement methods and their relevance for cardiometabolic risk

OBJECTIVE

To determine whether adipocyte diameters from three measurement methods are similarly associated with adiposity measurements and cardiometabolic variables.

METHODS

Surgical samples of omental and abdominal subcutaneous adipose tissue were obtained in a sample of 60 women (age 35-59 years; body mass index 20.3-41.1 kg/m² ). Median adipocyte diameter of the main cell population was determined by collagenase digestion, osmium tetroxide fixation, and histological analysis. Adiposity and cardiometabolic risk factors were assessed.

RESULTS

Adipocyte diameter was consistently smaller with formalin fixation than with collagenase digestion, whereas osmium-fixed cells were larger (P < 0.0001, for all). Median adipocyte diameters derived from all methods were intercorrelated (r = 0.46-0.83, P < 0.001 for all). Positive associations were found between adipocyte diameters from all techniques and regional or total adiposity measurements (P < 0.01 for all). Omental adipocyte diameter was positively associated with fasting glucose, insulin, and homeostatic model assessment of insulin resistance (r = 0.30-0.52, P < 0.05 for all), with osmium-fixed cell size as a stronger correlate. Osmium-fixed cell diameter was also a better correlate of plasma adiponectin and leptin.

CONCLUSIONS

Although measurement techniques generated systematic differences in adipocyte size, associations with adiposity were only slightly affected by the technique. Osmium fixation generated stronger associations with cardiometabolic risk factors than collagenase digestion and histological analysis.

Depot Dependent Effects of Dexamethasone on Gene Expression in Human Omental and Abdominal Subcutaneous Adipose Tissues from Obese Women

Glucocorticoids promote fat accumulation in visceral compared to subcutaneous depots, but the molecular mechanisms involved remain poorly understood. To identify long-term changes in gene expression that are differentially sensitive or responsive to glucocorticoids in these depots, paired samples of human omental (Om) and abdominal subcutaneous (Abdsc) adipose tissues obtained from obese women during elective surgery were cultured with the glucocorticoid receptor agonist dexamethasone (Dex, 0, 1, 10, 25 and 1000 nM) for 7 days. Dex regulated 32% of the 19,741 genes on the array, while 53% differed by Depot and 2.5% exhibited a Depot*Dex concentration interaction. Gene set enrichment analysis showed Dex regulation of the expected metabolic and inflammatory pathways in both depots. Cluster analysis of the 460 transcripts that exhibited an interaction of Depot and Dex concentration revealed sets of mRNAs for which the responses to Dex differed in magnitude, sensitivity or direction between the two depots as well as mRNAs that responded to Dex only in one depot. These transcripts were also clearly depot different in fresh adipose tissue and are implicated in processes that could affect adipose tissue distribution or functions (e.g. adipogenesis, triacylglycerol synthesis and storage, insulin action). Elucidation of the mechanisms underlying the depot differences in the effect of Dex on the expression of specific genes and pathways that regulate adipose function may offer novel insights into understanding the biology of visceral adipose tissues and their links to metabolic health.

Characterisation of Cultured Mesothelial Cells Derived from the Murine Adult Omentum

The human omentum has been long regarded as a healing patch, used by surgeons for its ability to immunomodulate, repair and vascularise injured tissues. A major component of the omentum are mesothelial cells, which display some of the characteristics of mesenchymal stem/stromal cells. For instance, lineage tracing studies have shown that mesothelial cells give rise to adipocytes and vascular smooth muscle cells, and human and rat mesothelial cells have been shown to differentiate into osteoblast- and adipocyte-like cells in vitro, indicating that they have considerable plasticity. However, so far, long-term cultures of mesothelial cells have not been successfully established due to early senescence. Here, we demonstrate that mesothelial cells isolated from the mouse omentum could be cultured for more than 30 passages. While epithelial markers were downregulated over passages in the mesothelial cells, their mesenchymal profile remained unchanged. Early passage mesothelial cells displayed clonogenicitiy, expressed several stem cell markers, and up to passage 5 and 13, respectively, could differentiate along the adipogenic and osteogenic lineages, demonstrating stem/progenitor characteristics and differentiation potential.

Impact of the Type of Continuous Insulin Administration on Metabolism in a Diabetic Rat Model

Exogenous insulin is the only treatment available for type 1 diabetic patients and is mostly administered by subcutaneous (SC) injection in a basal and bolus scheme using insulin pens (injection) or pumps (preimplanted SC catheter). Some divergence exists between these two modes of administration, since pumps provide better glycaemic control compared to injections in humans. The aim of this study was to compare the impacts of two modes of insulin administration (single injections of long-acting insulin or pump delivery of rapid-acting insulin) at the same dosage (4 IU/200 g/day) on rat metabolism and tissues. The rat weight and blood glucose levels were measured periodically after treatment. Immunostaining for signs of oxidative stress and for macrophages was performed on the liver and omental tissues. The continuous insulin delivery by pumps restored normoglycaemia, which induced the reduction of both reactive oxygen species and macrophage infiltration into the liver and omentum. Injections controlled the glucose levels for only a short period of time and therefore tissue stress and inflammation were elevated. In conclusion, the insulin administration mode has a crucial impact on rat metabolic parameters, which has to be taken into account when studies are designed.

Differences in the Osteogenic Differentiation Capacity of Omental Adipose-Derived Stem Cells in Obese Patients With and Without Metabolic Syndrome

Multiple studies have suggested that the reduced differentiation capacity of multipotent adipose tissue-derived mesenchymal stem cells (ASCs) in obese subjects could compromise their use in cell therapy. Our aim was to assess the osteogenic potential of omental ASCs and to examine the status of the isolated CD34(negative)-enriched fraction of omental-derived ASCs from subjects with different metabolic profiles. Omental ASCs from normal-weight subjects and subjects with or without metabolic syndrome were isolated, and the osteogenic potential of omental ASCs was evaluated. Additionally, osteogenic and clonogenic potential, proliferation rate, mRNA expression levels of proteins involved in redox balance, and fibrotic proteins were examined in the CD34(negative)-enriched fraction of omental-derived ASCs. Both the omental ASCs and the CD34(negative)-enriched fraction of omental ASCs from subjects without metabolic syndrome have a greater osteogenic potential than those from subjects with metabolic syndrome. The alkaline phosphatase and osteonectin mRNA were negatively correlated with nicotinamide adenine dinucleotide phosphate oxidase-2 mRNA and the mRNA expression levels of the fibrotic proteins correlated positively with nicotinamide adenine dinucleotide phosphate oxidase-5 mRNA and the homeostasis model assessment. Although the population doubling time was significantly higher in subjects with a body mass index of 25 kg/m(2) or greater, only the CD34(negative)-enriched omental ASC fraction in the subjects with metabolic syndrome had a higher population doubling time than the normal-weight subjects. The osteogenic, clonogenic, fibrotic potential, and proliferation rate observed in vitro suggest that omental ASCs from subjects without metabolic syndrome are more suitable for therapeutic osteogenic applications than those from subjects with metabolic syndrome.

Capillary Isoelectric Focusing Immunoassay for Fat Cell Differentiation Proteomics

Profiling cellular proteome is critical to understanding signal integration during cell fate determination. In this study, the capability of capillary isoelectric focusing (cIEF) immunoassays to detect post-translational modifications (PTM) of protein isoforms is demonstrated. cIEF immunoassays exhibit protein detection sensitivity at up to 5 orders of magnitude higher than traditional methods. This detection ultra-sensitivity permits proteomic profiling of several nanograms of tissue samples. cIEF immunoassays are employed to simultaneously profile three protein kinases during fat cell differentiation: cGMP-dependent protein kinase type I (PKG-I) of the nitric oxide (NO) signaling pathway, protein kinase B (Akt) of the insulin signaling pathway, and extracellular signal-regulated kinase (ERK) of the mitogen-activated protein kinase (MAPK) signaling pathway. Interestingly, a switch in the expression level of PKG- isoforms is observed during fat cell differentiation. While both PKG-Iα and PKG-Iβ isoforms are present in preadipocytes, only PKG-Iβ isoform is expressed in adipocytes. On the other hand, the phosphorylation level increases for Akt while decreases for ERK1 and ERK2 following the maturation of preadipocytes into adipocytes. Taken together, cIEF immunoassay provides a highly sensitive means to study fat cell differentiation proteomics. cIEF immunoassay should be a powerful proteomics tool to study complex protein signal integration in biological systems.

Comparison of Stromal/Stem Cells Isolated from Human Omental and Subcutaneous Adipose Depots: Differentiation and Immunophenotypic Characterization

The emerging field of regenerative medicine has identified adipose tissue as an abundant source of stromal/stem cells for tissue engineering applications. Therefore, we have compared the differentiation and immunophenotypic features of adipose-derived stromal/stem cells (ASC) isolated from either omental or subcutaneous adipose depots. Human tissue samples were obtained from bariatric and plastic surgical practices at a university-affiliated teaching hospital and a private practice, respectively, with informed patient consent. Primary cultures of human ASC were isolated from adipose specimens within 24 h of surgery and culture expanded in vitro. The passaged ASC were induced to undergo adipogenic or osteogenic differentiation as assessed by histochemical methods or evaluated for surface antigen expression profiles by flow cytometry. ASC yields per unit weight of tissue were comparable between omental and subcutaneous depots. At passage 0, the immunophenotype of omental and subcutaneous ASC were not significantly different with the exception of CD105 and endoglin, a component of the transforming growth factor β receptor. The adipogenic differentiation of omental ASC was less robust than that of subcutaneous ASC based on in vitro histochemical and PCR assays. Although the yield and immunophenotype of ASC from omental adipose depots resembled that of subcutaneous ASC, omental ASC displayed significantly reduced adipogenic differentiation capacity following chemical induction. Further studies are necessary to evaluate and optimize the differentiation function of omental ASC in vitro and in vivo. Pending such analyses, omental ASC should not be used interchangeably with subcutaneous ASC for regenerative medical applications.

Plasticity of human dedifferentiated adipocytes toward endothelial cells

The process of cellular differentiation in terminally differentiated cells is thought to be irreversible, and these cells are thought to be incapable of differentiating into distinct cell lineages. Our previous study showed that mature adipocytes represent an alternative source of mesenchymal stem cells. Here, results showed the capacity of mature adipocytes to differentiate into endothelial-like cells, using the ability of these cells to revert into an immature phase without any relievable chromosomal alterations. Mature adipocytes were isolated from human omental and subcutaneous fat and were dedifferentiated in vitro. The resulting cells were subcultivated for endothelial differentiation and were analyzed for their expression of specific genes and proteins. Endothelial-like cells were harvested from the differentiation medium and were traditionally cultured to evaluate the endothelial markers and the karyotype. Cells cultured in specific medium formed tube-like structures and expressed several endothelial marker genes and proteins. The endothelial-like cells expressed significantly higher levels of vascular endothelium growth factor receptor 2, vascular endothelial cadherin, Von Willebrand factor, and CD133 than the untreated cells. These cells were positively stained for CD31 and vascular endothelial cadherin, markers of mature endothelial cells. Moreover, the low-density lipoprotein-uptake assay demonstrated a functionally endothelial differentiation of these cells. When these cells were harvested and reseeded in basal medium, they lost the endothelial markers and reacquired the typical mesenchymal stem cell markers and the ability to expand in a short time period. Moreover, karyotype analysis showed that these cells reverted into an immature phase without any karyotype alterations. In conclusion, the results showed that adipocytes exhibited a great plasticity toward the endothelial lineage, suggesting their possible use in cell therapy applications for vascular disease.

Preferential expression of PAPPA in human preadipocytes from omental fat

Fat distribution differs between individuals, and those with visceral fat predominance develop metabolic profiles that increase the risk of adverse cardiovascular events. This is due, in part, to the proinflammatory state associated with visceral obesity as well as depot-specific adipogenesis. The IGF system is important in adipose tissue development and metabolic function. Pregnancy-associated plasma protein A (PAPPA) is a novel zinc metalloproteinase that regulates local IGF availability. The first aim of this study was to characterize PAPPA mRNA and protein expression in primary cultures of human preadipocytes isolated from omental, mesenteric, and subcutaneous depots. PAPPA expression was significantly increased in omental preadipocytes compared with mesenteric and subcutaneous preadipocytes. The second aim of this study was to investigate the factors regulating PAPPA expression, focusing on proinflammatory cytokines and resveratrol that have been shown to have negative and positive effects, respectively, on metabolism and diet-induced obesity. Treatment of cultured primary human preadipocytes with tumor necrosis factor α and interleukin 1β led to significant increases in PAPPA expression. Activated pathways mediating cytokine-induced PAPPA expression include the nuclear factor κB pathway and the MAPK family, particularly c-Jun NH2-terminal kinase and p38 MAPK. Resveratrol, a polyphenolic compound with beneficial cardiometabolic effects, significantly downregulated PAPPA expression under basal and stimulated conditions. Effects of resveratrol on PAPPA appeared to be mediated through pathways independent of silent mating type information regulation 2 homolog 1 (SIRT1) and AMP kinase activation. Depot-specific PAPPA expression in human preadipocytes may contribute to a depot-specific function.

Prostaglandin (PG) F2 alpha synthesis in human subcutaneous and omental adipose tissue: modulation by inflammatory cytokines and role of the human aldose reductase AKR1B1

INTRODUCTION

PGF2α may be involved in the regulation of adipose tissue function.

OBJECTIVES

1) To examine PGF2α release by primary preadipocytes, mature adipocytes and whole tissue explants from the subcutaneous and omental fat compartments; 2) To assess which PGF synthase is the most relevant in human adipose tissue.

METHODS

Fat samples were obtained by surgery in women. PGF2α release by preadipocytes, adipocytes and explants under stimulation by TNF-α, IL-1β or both was measured. Messenger RNA expression levels of AKR1B1 and AKR1C3 were measured by RT-PCR in whole adipose tissue and cytokine-treated preadipocytes. The effect of AKR1B1 inhibitor ponalrestat on PGF2α synthesis was investigated.

RESULTS

PGF2α release was significantly induced in response to cytokines compared to control in omental (p = 0.01) and to a lesser extent in subcutaneous preadipocytes (p = 0.02). Messenger RNA of COX-2 was significantly higher in omental compared to subcutaneous preadipocytes in response to combined TNF-α and IL-1β (p = 0.01). Inflammatory cytokines increased AKR1B1 mRNA expression and protein levels (p≤0.05), but failed to increase expression levels of AKR1C3 in cultured preadipocytes. Accordingly, ponalrestat blunted PGF2α synthesis by preadipocytes in basal and stimulated conditions (p≤0.05). Women with the highest PGF2α release by omental adipocytes had a higher BMI (p = 0.05), waist circumference (p≤0.05) and HOMAir index (p≤0.005) as well as higher mRNA expression of AKR1B1 in omental (p<0.10) and subcutaneous (p≤0.05) adipose tissue compared to women with low omental adipocytes PGF2α release. Positive correlations were observed between mRNA expression of AKR1B1 in both compartments and BMI, waist circumference as well as HOMAir index (p≤0.05 for all).

CONCLUSION

PGF2α release by omental mature adipocytes is increased in abdominally obese women. Moreover, COX-2 expression and PGF2α release is particularly responsive to inflammatory stimulation in omental preadipocytes. Yet, blockade of PGF synthase AKR1B1 inhibits most of the PGF2α release.

Comparison of human adipose-derived stem cells isolated from subcutaneous, omental, and intrathoracic adipose tissue depots for regenerative applications

Adipose tissue is an abundant source of multipotent progenitor cells that have shown promise in regenerative medicine. In humans, fat is primarily distributed in the subcutaneous and visceral depots, which have varying biochemical and functional properties. In most studies to date, subcutaneous adipose tissue has been investigated as the adipose-derived stem cell (ASC) source. In this study, we sought to develop a broader understanding of the influence of specific adipose tissue depots on the isolated ASC populations through a systematic comparison of donor-matched abdominal subcutaneous fat and omentum, and donor-matched pericardial adipose tissue and thymic remnant samples. We found depot-dependent and donor-dependent variability in the yield, viability, immunophenotype, clonogenic potential, doubling time, and adipogenic and osteogenic differentiation capacities of the ASC populations. More specifically, ASCs isolated from both intrathoracic depots had a longer average doubling time and a significantly higher proportion of CD34(+) cells at passage 2, as compared with cells isolated from subcutaneous fat or the omentum. Furthermore, ASCs from subcutaneous and pericardial adipose tissue demonstrated enhanced adipogenic differentiation capacity, whereas ASCs isolated from the omentum displayed the highest levels of osteogenic markers in culture. Through cell culture analysis under hypoxic (5% O(2)) conditions, oxygen tension was shown to be a key mediator of colony-forming unit-fibroblast number and osteogenesis for all depots. Overall, our results suggest that depot selection is an important factor to consider when applying ASCs in tissue-specific cell-based regenerative therapies, and also highlight pericardial adipose tissue as a potential new ASC source.

[Primary culturing and effects of insulin glargine on proliferation, differentiation of human preadipocytes from subcutaneous and omental adipose tissue]

OBJECTIVE

To compare the morphological and functional differences of human primary preadipocytes from different fat depots and explore the effects of insulin glargine on their proliferation and differentiation.

METHODS

Primary preadipocytes isolated from human subcutaneous and omental adipose tissue by collagenase I were passaged in vitro.Inverted phase contrast microscope was used to observe the morphological differences of two kinds of preadipocytes. Then two kinds of preadipocytes were cultured or induced to differentiation with different doses of insulin glargine. The methyl thiazolyl tetrazolium (MTT) assay was used to detect their proliferative differences.Reverse transcription-polymerase chain reaction (RT-PCR) was used to observe the effects of insulin on adipogenic gene expression.

RESULTS

(1) Both preadipocytes could be successfully cultured from adipose tissue and amplified in vitro.Subcutaneous preadipocytes were more slender and proliferated more quickly while omental preadipocytes were polygonal and aged easily.(2) MTT results showed that insulin glargine could inhibit the proliferation of omental preadipocytes in a dose-dependent fashion. After 72 h incubation, compared with negative control, the absorbance (A) value of 1000 nmol/L insulin glargine group decreased greatly (0.144 ± 0.021 vs 0.267 ± 0.040, P < 0.01). But it had no effect on subcutaneous preadipocytes (0.305 ± 0.045 vs 0.350 ± 0.037, P > 0.05). (3) Insulin at 500 nmol/L was a suitable concentration for inducing differentiation.RT-PCR analysis showed that, for subcutaneous adipocytes, adipogenic genes such as peroxisome proliferator-activated receptor gamma (PPARγ) (F = 31.31, P < 0.01) and CCAAT enhancer binding protein α (C/EBPα) (F = 9.86, P < 0.05) had the highest mRNA expression while preadipocytes gene Pref-1 had the lowest expression at this concentration. But insulin dose had no obvious effect on PPARγ or C/EBPα mRNA (P > 0.05) for omental adipocytes.

CONCLUSION

Insulin glargine could inhibit the proliferation of omental preadipocytes, and enhance the differentiation of subcutaneous and omental preadipocytes.

Characterization of peritoneal dialysis effluent-derived cells: diagnosis of peritoneal integrity

To assess the integrity of the peritoneal membrane, we characterized the functionality of the cellular components derived from peritoneal dialysis effluent (PDE). About 3 % of all cells collected from the PDE attached to the plastic dish, and 97.1 ± 3.1 % of the adherent cells expressed CK-18 (PDE-HPMC). A typical cobble-stone-like morphology under neutralized PD solution was obtained over 65 out of 74 primary cultures (88 %) while only 53 % under acidic PD solution in a previous report by Yanez-Mo et al. However, 26.6 ± 10.3 % of PDE-HPMC expressed the EMT marker α-SMA. Transepithelial resistance (TER) as a marker of cell polarity was 34 % lower than that of omentum-derived(OM)-HPMC. We found a significant decrease in the rate of PDE-HPMC proliferation compared to OM-HPMC, accompanied by a significant increase of cell area within the tertiary passage. Comparison of TER, α-SMA and SA-β-Gal between CAPD durations suggests that cell polarity weakens with increased duration of CAPD, reflecting the occurrence of EMT and cell senescence. We conclude that functional characterization of cellular components in PDE reflects how well the peritoneum is preserved.

Zinc supplementation attenuates high glucose-induced epithelial-to-mesenchymal transition of peritoneal mesothelial cells

Zinc (Zn) plays an important role in preventing many types of epithelial-to-mesenchymal transition (EMT)-driven fibrosis in vivo. But its function in the EMT of the peritoneal mesothelial cells (PMCs) remains unknown. Here, we studied the Zn effect on the high glucose (HG)-induced EMT in the rat PMCs (RPMCs) and the underlying molecular mechanisms. We found that Zn supplementation significantly inhibited TGF-β1 and ROS production, and attenuated the HG-induced EMT in the RPMCs, likely through inhibition of MAPK, NF-κB, and TGF-β/Smad pathways.

Zinc inhibits high glucose-induced apoptosis in peritoneal mesothelial cells

Zinc (Zn) plays an important role in influencing many types of apoptosis. However, its function in apoptosis in peritoneal mesothelial cells (PMCs) remains unknown. Here, we studied the effects of Zn on high glucose (HG)-induced apoptosis in rat PMCs (RPMCs) and examined the underlying molecular mechanisms. We found that Zn supplementation inhibited HG-induced RPMC apoptosis significantly, by attenuating reactive oxygen species (ROS) production, inhibiting HG-induced sFasR and sFasL over-expression, caspase-8 and caspase-3 activation, and inhibiting release of cytochrome c from mitochondria to the cytosol. Further analysis revealed that Zn supplementation facilitated cell survival through activation of the phosphatidylinositol 3-kinase/Akt signaling pathway and MAPK/ERK pathways. These results indicate that Zn can inhibit apoptosis in HG-induced RPMCs by several independent mechanisms, including an indirect antioxidative effect and probably by inhibition of caspase-8 and caspase-3 activation.

The ghrelin O-acyltransferase-ghrelin system reduces TNF-α-induced apoptosis and autophagy in human visceral adipocytes

AIMS/HYPOTHESIS

Proinflammatory and proapoptotic cytokines such as TNF-α are upregulated in human obesity. We evaluated the association between ghrelin isoforms (acylated and desacyl ghrelin) and TNF-α in obesity and obesity-associated type 2 diabetes, as well as the potential role of ghrelin in the control of apoptosis and autophagy in human adipocytes.

METHODS

Plasma concentrations of the ghrelin isoforms and TNF-α were measured in 194 participants. Ghrelin and ghrelin O-acyltransferase (GOAT) levels were analysed by western-blot, immunohistochemistry and real-time PCR in 53 biopsies of human omental adipose tissue. We also determined the effect of acylated and desacyl ghrelin (10 to 1,000 pmol/l) on TNF-α-induced apoptosis and autophagy-related molecules in omental adipocytes.

RESULTS

Circulating concentrations of acylated ghrelin and TNF-α were increased, whereas desacyl ghrelin levels were decreased in obesity-associated type 2 diabetes. Ghrelin and GOAT were produced in omental and subcutaneous adipose tissue. Visceral adipose tissue from obese patients with type 2 diabetes showed higher levels of GOAT, increased adipocyte apoptosis and increased expression of the autophagy-related genes ATG5, BECN1 and ATG7. In differentiating human omental adipocytes, incubation with acylated and desacyl ghrelin reduced TNF-α-induced activation of caspase-8 and caspase-3, and cell death. In addition, acylated ghrelin reduced the basal expression of the autophagy-related genes ATG5 and ATG7, while desacyl ghrelin inhibited the TNF-α-induced increase of ATG5, BECN1 and ATG7 expression.

CONCLUSIONS/INTERPRETATION

Apoptosis and autophagy are upregulated in human visceral adipose tissue of patients with type 2 diabetes. Acylated and desacyl ghrelin reduce TNF-α-induced apoptosis and autophagy in human visceral adipocytes.

Cellular basis of tissue regeneration by omentum

The omentum is a sheet-like tissue attached to the greater curvature of the stomach and contains secondary lymphoid organs called milky spots. The omentum has been used for its healing potential for over 100 years by transposing the omental pedicle to injured organs (omental transposition), but the mechanism by which omentum helps the healing process of damaged tissues is not well understood. Omental transposition promotes expansion of pancreatic islets, hepatocytes, embryonic kidney, and neurons. Omental cells (OCs) can be activated by foreign bodies in vivo. Once activated, they become a rich source for growth factors and express pluripotent stem cell markers. Moreover, OCs become engrafted in injured tissues suggesting that they might function as stem cells.

Omentum consists of a variety of phenotypically and functionally distinctive cells. To understand the mechanism of tissue repair support by the omentum in more detail, we analyzed the cell subsets derived from the omentum on immune and inflammatory responses. Our data demonstrate that the omentum contains at least two groups of cells that support tissue repair, immunomodulatory myeloid derived suppressor cells and omnipotent stem cells that are indistinguishable from mesenchymal stem cells. Based on these data, we propose that the omentum is a designated organ for tissue repair and healing in response to foreign invasion and tissue damage.

Using gene expression to predict differences in the secretome of human omental vs. subcutaneous adipose tissue

The objective of this study was to characterize differences in the secretome of human omental compared with subcutaneous adipose tissue using global gene expression profiling. Gene expression was measured using Affymetrix microarrays (Affymetrix, Santa Clara, CA) in subcutaneous and omental adipose tissue in two independent experiments (n = 5 and n = 3 independent subjects; n = 16 arrays in total, 2 for each subject). Predictive bioinformatic algorithms were employed to identify secreted proteins. Microarray analysis identified 22 gene probe sets whose expression was significantly different with a fold change (FC) greater than 5 in expression in both experiments between omental and subcutaneous adipose tissue. Using bioinformatic predictive programs 11 of these 22 probe sets potentially coded for secreted proteins. Pathway network analysis of the secreted proteins showed that three of the proteins are part of a common pathway network. These proteins gremlin 1 (GREM1), pleiotrophin (PTN), and secretory leukocyte peptidase inhibitor (SLPI) are expressed respectively 43×, 23×, and 5× in omental adipose tissue relative to subcutaneous adipose tissue as determined by real-time PCR. The presence of GREM1, PTN, and SLPI protein in human adipose tissue was confirmed by western blotting. All three proteins are expressed in the human Simpson-Golabi-Behmel syndrome (SGBS) preadipocyte cell line. The expression of GREM1, PTN, and SLPI changed with the differentiation of the preadipocytes into mature adipocytes. Gene expression coupled with predictive bioinformatic algorithms have identified several genes coding for secreted proteins which are expressed differently in omental adipose tissue compared to subcutaneous adipose tissue proving a valid alternative approach to help further define the adipocyte secretome.

mTOR inhibition with rapamycin causes impaired insulin signalling and glucose uptake in human subcutaneous and omental adipocytes

Rapamycin is an immunosuppressive agent used after organ transplantation, but its molecular effects on glucose metabolism needs further evaluation. We explored rapamycin effects on glucose uptake and insulin signalling proteins in adipocytes obtained via subcutaneous (n=62) and omental (n=10) fat biopsies in human donors. At therapeutic concentration (0.01 μM) rapamycin reduced basal and insulin-stimulated glucose uptake by 20-30%, after short-term (15 min) or long-term (20 h) culture of subcutaneous (n=23 and n=10) and omental adipocytes (n=6 and n=7). Rapamycin reduced PKB Ser473 and AS160 Thr642 phosphorylation, and IRS2 protein levels in subcutaneous adipocytes. Additionally, it reduced mTOR-raptor, mTOR-rictor and mTOR-Sin1 interactions, suggesting decreased mTORC1 and mTORC2 formation. Rapamycin also reduced IR Tyr1146 and IRS1 Ser307/Ser616/Ser636 phosphorylation, whereas no effects were observed on the insulin stimulated IRS1-Tyr and TSC2 Thr1462 phosphorylation. This is the first study to show that rapamycin reduces glucose uptake in human adipocytes through impaired insulin signalling and this may contribute to the development of insulin resistance associated with rapamycin therapy.

TGFbeta family members are key mediators in the induction of myofibroblast phenotype of human adipose tissue progenitor cells by macrophages

Objective

The present study was undertaken to characterize the remodeling phenotype of human adipose tissue (AT) macrophages (ATM) and to analyze their paracrine effects on AT progenitor cells.

Research Design and Methods

The phenotype of ATM, immunoselected from subcutaneous (Sc) AT originating from subjects with wide range of body mass index and from paired biopsies of Sc and omental (Om) AT from obese subjects, was studied by gene expression analysis in the native and activated states. The paracrine effects of ScATM on the phenotype of human ScAT progenitor cells (CD34⁺CD31⁻) were investigated.

Results

Two main ATM phenotypes were distinguished based on gene expression profiles. For ScAT-derived ATM, obesity and adipocyte-derived factors favored a pro-fibrotic/remodeling phenotype whereas the OmAT location and hypoxic culture conditions favored a pro-angiogenic phenotype. Treatment of native human ScAT progenitor cells with ScATM-conditioned media induced the appearance of myofibroblast-like cells as shown by expression of both α-SMA and the transcription factor SNAIL, an effect mimicked by TGFβ1 and activinA. Immunohistochemical analyses showed the presence of double positive α-SMA and CD34 cells in the stroma of human ScAT. Moreover, the mRNA levels of SNAIL and SLUG in ScAT progenitor cells were higher in obese compared with lean subjects.

Conclusions

Human ATM exhibit distinct pro-angiogenic and matrix remodeling/fibrotic phenotypes according to the adiposity and the location of AT, that may be related to AT microenvironment including hypoxia and adipokines. Moreover, human ScAT progenitor cells have been identified as target cells for ScATM-derived TGFβ and as a potential source of fibrosis through their induction of myofibroblast-like cells.

Cyanidin-3-O-β-glucoside and protocatechuic acid exert insulin-like effects by upregulating PPARγ activity in human omental adipocytes

OBJECTIVE

Insulin resistance (IR) represents an independent risk factor for metabolic, cardiovascular, and neoplastic disorders. Preventing/attenuating IR is a major objective to be reached to preserve population health. Because many insulin-sensitizing drugs have shown unwanted side effects, active harmless compounds are sought after. Dietary anthocyanins have been demonstrated to ameliorate hyperglycemia and insulin sensitivity. This study aimed at investigating whether cyanidin-3-O-β-glucoside (C3G) and its metabolite protocatechuic acid (PCA) might have a role in glucose transport activation in human omental adipocytes and 3T3-L1 cells.

RESEARCH DESIGN AND METHODS

In cells treated with 50 µmol/L C3G and 100 µmol/L PCA, [(3)H]-2-deoxyglucose uptake, GLUT4 translocation by immunoblotting, adiponectin secretion, and peroxisome proliferator-activated receptor-γ (PPARγ) activation by enzyme-linked immunosorbent assay kits were evaluated. Parallel experiments were carried out in murine adipocyte 3T3-L1. To define the role of PPARγ in modulating polyphenol effects, small interfering RNA technique and PPARγ antagonist were used to inhibit transcription factor activity.

RESULTS

C3G and PCA increased adipocyte glucose uptake (P < 0.05) and GLUT4 membrane translocation (P < 0.01). Significant increases (P < 0.05) in nuclear PPARγ activity, as well as in adiponectin and GLUT4 expressions (P < 0.01), were also shown. It is interesting that PPARγ inhibition counteracted the polyphenol-induced adiponectin and GLUT4 upregulations, suggesting a direct involvement of PPARγ in this process.

CONCLUSIONS

Our study provides evidence that C3G and PCA might exert insulin-like activities by PPARγ activation, evidencing a causal relationship between this transcription factor and adiponectin and GLUT4 upregulation. Dietary polyphenols could be included in the preventive/therapeutic armory against pathological conditions associated with IR.

The in vitro toxicity of peritoneal dialysis fluid

OBJECTIVE

To investigate the toxicity of peritoneal dialysis fluid (PDF) components on peritoneal changes in primary human mesothelial cell.

MATERIAL AND METHOD

To investigate the mechanism of changes, primary human peritoneal mesothelial cells (HPMCs) were isolated from human omental tissue and were exposed for 15 hours with the various concentrations of conventional PDF and various PDF components. The mesothelial injury was determined by calculating a ratio of supernatant and total intracellular LDH while mesothelial apoptosis was assessed and counted by positive TUNEL staining and flow cytometry, respectively.

RESULTS

PDF caused mesothelial detachment, de-differentiation, cell injuries, and apoptosis and this depended on the concentrations of PDF. The acidic condition and high glucose concentration likely played a major role in the HPMC injuries and detachment while individual PDF component could not yield mesothelial apoptosis as severe as the whole PDF effects. Thus, the additive effects of PDF composition, instead of the effect of each component, contributed to dialysis-related HPMC damages.

CONCLUSION

PDF showed concentration dependent fashion-induced HPMC injury, dedifferentiation, and apoptosis. All of the abnormalities occurred by the additive effects of PDF components.

The anti-inflammatory and antibacterial basis of human omental defense: selective expression of cytokines and antimicrobial peptides

BACKGROUND

The wound healing properties of the human omentum are well known and have extensively been exploited clinically. However, the underlying mechanisms of these effects are not well understood. We hypothesize that the omentum tissue promotes wound healing via modulation of anti-inflammatory pathways, and because the omentum is rich in adipocytes, the adipocytes may modulate the anti-inflammatory response. Factors released by human omentum may affect healing, inflammation and immune defense.

METHODOLOGY

Six human omentum tissues (non obese, free from malignancy, and any other systemic disorder) were obtained during diagnostic laparoscopies having a negative outcome. Healthy oral mucosa (obtained from routine oral biopsies) was used as control. Cultured adipocytes derived from human omentum were exposed to lipopolysaccharide (LPS) (1-50 ng/mL) for 12-72 hours to identify the non-cytotoxic doses. Levels of expression (mRNA and protein) were carried out for genes associated with pro- and anti-inflammatory cytokine responses and antibacterial/antimicrobial activity using qRT-PCR, western blotting, and cell-based ELISA assays.

RESULTS

The study shows significant higher levels of expression (mRNA and protein) of several specific cytokines, and antibacterial peptides in the omentum tissues when compared to oral sub-mucosal tissues. In the validation studies, primary cultures of adipocytes, derived from human omentum were exposed to LPS (5 and 10 ng/mL) for 24 and 48 h. The altered expressions were more pronounced in cultured adipocytes cells when exposed to LPS as compared to the omentum tissue.

CONCLUSIONS/SIGNIFICANCE

Perhaps, this is the first report that provides evidence of expressional changes in pro- and anti-inflammatory cytokines and antibacterial peptides in the normal human omentum tissue as well as adipocytes cultured from this tissue. The study provides new insights on the molecular and cellular mechanisms of healing and defense by the omentum, and suggests the potential applicability of cultured adipocytes derived from the omentum for future therapeutic applications.

Adipocyte morphometric evaluation and angiogenesis in the omentum transposed to the breast: a preliminary study

OBJECTIVE

The purpose of this study was to describe the probable mechanism of the volume increase of laparoscopically harvested omentum flaps used to treat breast deformities.

METHODS

A histological analysis of omentum samples was performed to study the volume increase of laparoscopically harvested omentum flaps. Samples were harvested immediately after the transposition of the omentum from the abdominal cavity to the breast region and during the second surgical procedure for breast symmetrization of eight patients submitted to the transposition of the omentum flap. Changes in the morphometric measurements of the adipocytes (perimeter, diameter, and area), microvascular density (as measured by the CD31 endothelial marker), and immunohistochemical expression of VEGF were documented.

RESULTS

The increases in adipocyte size and microvascular density were statistically significant (P < 0.012). The expression levels of VEGF were lower in the second set of samples when compared to the first set, but the differences were not statistically significant (P < 0.093).

CONCLUSION

These results demonstrate an increase in cellular volume as measured by adipocyte perimeter, diameter, and area. Moreover, the increase in the number of vessels in the second set of samples suggests that neoangiogenesis was stimulated by the initial increase in VEGF expression levels observed in the first set of samples. The increase in VEGF expression in the flap may have been caused by adipocyte hypertrophy resulting from neoangiogenesis.

[Immunophenotypic comparison of adipose-derived mesenchymal stem cells from the greater omentums and subcutaneous adipose tissues of rats]

OBJECTIVE

To compare the adipose-derived mesenchymal stem cells (ADMSCs) isolated from the greater omentums and subcutaneous adipose tissues of rats for their characteristics in cell morphology, growth kinetics and immunophenotypes.

METHODS

ADMSCs were isolated from the greater omentums and inguinal fat pads of 6 SD rats and cultured in vitro. The morphologies of the ADMSCs were observed using phase-contrast microscopy, and their growth curves were generated and the doubling times determined. The phenotypic marker profiles including CD11b, CD29, CD45, CD49d, CD90 and CD106 of the ADMSCs in the fourth passage were determined using flow cytometry.

RESULTS

The ADMSCs harvested from the greater omentums and inguinal fat pads showed almost identical morphologies. The growth curves and the mean doubling time of the ADMSCs from the two different sources showed no obvious difference. With similar positivity rates for CD11b, CD29, CD106 and CD90, the two ADMSCs exhibited different expression rates of CD45 and CD49d.

CONCLUSIONS

The immunophenotypic characteristics of the ADMSCs from the greater omentums and subcutaneous adipose tissues are not totally identical.

Tissue-engineering bone from omentum

Tissue engineering of bone is an interesting field of research. Many approaches to bone tissue engineering such as from bone marrow stromal cells in vitro have been reported. Furthermore, a model of vascularized tissue-engineered bone flap has been reported. However, there has been no report of bone tissue engineering using omentum. We present a study of tissue engineering of bone from omentum in a rabbit model. The omentum, which was elevated based on the right gastroepiploic vessels, was wrapped by the periosteum from cranial bone in the abdomen of rabbits. We harvested the omentum thus wrapped 1, 2, 4, 6, 8, 12, or 24 weeks after surgery. Within 1 week after surgery, woven bone was formed and clusters of osteoblasts were observed. At 8 weeks, medullization, including the presence of granulocytes, was confirmed. This technique might prove useful for creating tissue-engineered bone flaps for reconstructive surgery.

Analysis of angiotensin II- and ACTH-driven mineralocorticoid functions and omental adiposity in a non-genetic, hyperadipose female rat phenotype

The hypothalamic damage induced by neonatal treatment with monosodium L -glutamate (MSG) induces several metabolic abnormalities, resulting in a rat hyperleptinemic-hyperadipose phenotype. This study was conducted to explore the impact of the neonatal MSG treatment, in the adult (120 days old) female rat on: (a) the in vivo and in vitro mineralocorticoid responses to ACTH and angiotensin II (AII); (b) the effect of leptin on ACTH- and AII-stimulated mineralocorticoid secretions by isolated corticoadrenal cells; and (c) abdominal adiposity characteristics. Our data indicate that, compared with age-matched controls, MSG rats displayed: (1) enhanced and reduced mineralocorticoid responses to ACTH and AII treatments, respectively, effects observed in both in vivo and in vitro conditions; (2) adrenal refractoriness to the inhibitory effect of exogenous leptin on ACTH-stimulated aldosterone output by isolated adrenocortical cells; and (3) distorted omental adiposity morphology and function. This study supports that the adult hyperleptinemic MSG female rat is characterized by enhanced ACTH-driven mineralocorticoid function, impaired adrenal leptin sensitivity, and disrupted abdominal adiposity function. MSG rats could counteract undesirable effects of glucocorticoid excess, by developing a reduced AII-driven mineralocorticoid function. Thus, chronic hyperleptinemia could play a protective role against ACTH-mediated allostatic loads in the adrenal leptin resistant, MSG female rat phenotype.

Dehydroepiandrosterone (DHEA) treatment in vitro inhibits adipogenesis in human omental but not subcutaneous adipose tissue

Dehydroepiandrosterone (DHEA), a precursor sex steroid, circulates in sulphated form (DHEAS). Serum DHEAS concentrations are inversely correlated with metabolic syndrome components and in vivo/in vitro studies suggest a role in modulating adipose mass. To investigate further, we assessed the in vitro biological effect of DHEA in white (3T3-L1) and brown (PAZ6) preadipocyte cell lines and human primary preadipocytes. DHEA (from 10(-8)M) caused concentration-dependent proliferation inhibition of 3T3-L1 and PAZ6 preadipocytes. Cell cycle analysis demonstrated unaltered apoptosis but indicated blockade at G1/S or G2/M in 3T3-L1 and PAZ6, respectively. Preadipocyte cell-line adipogenesis was not affected. In human primary subcutaneous and omental preadipocytes, DHEA significantly inhibited proliferation from 10(-8)M. DHEA 10(-7)M had opposing effects on adipogenesis in the two fat depots. Subcutaneous preadipocyte differentiation was unaffected or increased whereas omental preadipocytes showed significantly reduced adipogenesis. We conclude that DHEA exerts fat depot-specific differences which modulate body composition by limiting omental fat production.

Human adipose tissue macrophages: m1 and m2 cell surface markers in subcutaneous and omental depots and after weight loss

CONTEXT

Macrophages accumulate in adipose tissue and possibly participate in metabolic complications in obesity. Macrophage number varies with adipose tissue site and weight loss, but whether this is accompanied by phenotypic changes is unknown.

OBJECTIVE

The objective of the study was to characterize the activation state of adipose tissue macrophages in human obesity.

DESIGN/SETTING

We performed a single-center prospective study.

PARTICIPANTS/INTERVENTIONS

Paired biopsies of sc and omental adipose tissue were obtained during gastric surgery in 16 premenopausal obese women (aged 41.1 +/- 8.6 yr; body mass index 43.8 +/- 3.4 kg/m(2)). Subcutaneous adipose tissue biopsies were obtained 3 months later in obese subjects and in 10 nonobese women (aged 43.3 +/- 3.5 yr; body mass index 22.5 +/- 0.75 kg/m(2)). The number of macrophages stained with CD40, CD206, and CD163 surface markers was determined by immunochemistry.

MAIN OUTCOMES

The number of CD40(+) macrophages significantly increased with obesity and in omental vs. sc adipose tissue in obese women. No significant changes in CD163(+) and CD206(+) macrophage counts was found with obesity and fat pad anatomical location. Three months after gastric surgery, the ratio of CD40(+) to CD206(+) macrophages was 2-fold lower than before surgery in the sc adipose tissue of obese subjects (P < 0.001) due to a concomitant decrease of CD40(+) and increase of CD206(+) macrophages counts.

CONCLUSION

We suggest that the activation state of adipose tissue macrophages is weighted toward M1 over M2 status in obese subjects and switch to a less proinflammatory profile 3 months after gastric bypass.

Primary differences in lipolysis between human omental and subcutaneous adipose tissue observed using in vitro differentiated adipocytes

Catecholamine-induced lipolysis is elevated in omental as compared to subcutaneous adipocytes due to primary differences between the two cell types (i.e., they have different progenitor cells). Whether there is regional variation in atrial natriuretic peptide (ANP)-induced lipolysis is unknown. We studied whether beta-adrenoceptor signaling to lipolysis and ANP-induced lipolysis are involved in the primary differences in lipolysis. In vitro experiments on differentiated preadipocytes from human subcutaneous and omental adipose tissue were performed. The cells were kept in culture for a relative long duration, so any influence of local environment and circulation in the various adipose tissue depots could be excluded. Using beta1-, beta2-, and beta3-adenoceptor agonists, lipolysis was found to be significantly higher in omental as compared to subcutaneous differentiated preadipocytes. Forskolin and dibutyryl cAMP, which act at post-adrenoceptor levels, did not show any regional difference. There was no regional difference in ANP-induced lipolysis. Gene expression of beta1- and beta3-adrenoceptors was higher and beta2-adrenoceptor expression was lower in the omental cells. Omental fat cells have an increased beta-adrenoceptor-mediated lipolysis principally due to primary differences in the early event that couples beta-adrenoceptor subtypes to G-proteins. ANP-induced lipolysis is not subject to primary regional variation.

Fat depot-specific impact of visceral obesity on adipocyte adiponectin release in women

Our objective was to examine omental and subcutaneous adipocyte adiponectin release in women. We tested the hypothesis that adiponectin release would be reduced to a greater extent in omental than in subcutaneous adipocytes of women with visceral obesity. Omental and subcutaneous adipose tissue samples were obtained from 52 women undergoing abdominal hysterectomies (age: 47.1 +/- 4.8 years; BMI: 26.7 +/- 4.7 kg/m(2)). Adipocytes were isolated and their adiponectin release in the medium was measured over 2 h. Measures of body fat accumulation and distribution were obtained using dual-energy X-ray absorptiometry and computed tomography, respectively. Adiponectin release by omental and subcutaneous adipocytes was similar in lean individuals; however, in subsamples of obese or visceral obese women, adiponectin release by omental adipocytes was significantly reduced while that of subcutaneous adipocytes was not affected. Omental adipocyte adiponectin release was significantly and negatively correlated with total body fat mass (r = -0.47, P < 0.01), visceral adipose tissue area (r = -0.50, P < 0.01), omental adipocyte diameter (r = -0.43, P < 0.01), triglyceride levels (r = -0.32, P < or = 0.05), cholesterol/high-density lipoprotein (HDL)-cholesterol (r = -0.31, P < or = 0.05), fasting glucose (r = -0.39, P < or = 0.01), fasting insulin (r = -0.36, P < or = 0.05), homeostasis model assessment index (r = -0.39, P < or = 0.01), and positively associated with HDL-cholesterol concentrations (r = 0.33, P < or = 0.05). Adiponectin release from subcutaneous cells was not associated with any measure of adiposity, lipid profile, or glucose homeostasis. In conclusion, compared to subcutaneous adipocyte adiponectin release, omental adipocyte adiponectin release is reduced to a greater extent in visceral obese women and better predicts obesity-associated metabolic abnormalities.

Expression and secretion of RANTES (CCL5) in human adipocytes in response to immunological stimuli and hypoxia

Obesity and related disorders represent states of systemic low-grade inflammation. Chemokine secretion by adipocytes may initiate leukocyte infiltration in obese adipose tissue and thus mediate an important step in the establishment of chronic immune activation. The chemokine RANTES (regulated upon activation normal T cell expressed and secreted)/CCL5 is a chemoattractant for various leukocyte subsets. This study was designed to examine whether RANTES is expressed and released by human adipocytes and how its expression is regulated. RANTES expression under basal conditions was studied in mature adipocytes. Cells were therefore challenged with lipopolysaccharide (LPS), interferon (IFN)-gamma, interleukin (IL)-4, monocyte chemoattractant protein (MCP)-1 or exposed to low oxygen pressure. RANTES was expressed and secreted constitutively in most samples of mature adipocytes from the omental and the subcutaneous depot. RANTES release was dependent on adipocyte size and also seemed to be higher from cells of obese donors. Hypoxia (4% O (2)) caused an approximately 36% increase of RANTES release. Human adipocytes express the chemokine RANTES and are thus identified as a novel cellular source of this immune mediator. LPS and IFNgamma do not seem to play a significant role for the expression of RANTES in contrast to moderate hypoxia, which points to a distinct role in the innate immune system.

Differences in lipogenesis and lipolysis in obese and non-obese adult human adipocytes

It has been proposed that differences in adipocyte function and/or metabolism between obese and lean individuals may manifest themselves in functional adipose tissue abnormalities that lead to metabolic disorders in obesity. We studied lipogenesis and lipolysis of omental adipocytes from obese (OB) and non-obese (NOB) humans. The specific activity of the lipogenic marker enzyme G3PDH was 50% lower in total adipocytes of OB compared to that of NOB subjects. Omental adipocytes from OB subjects also had lower basal lipolytic levels, and a lower lipolytic response to beta-adrenergic stimulus. Cholesterol depletion of adipocyte plasma membrane using methyl b-cyclodextrin caused a lipolytic effect on adipocytes of both groups together, but when obese and lean subjects were analyzed separately, the response was significant only in the obese. We present evidence of a different lipogenic and lipolytic profile in obese individuals' omental adipocytes, and propose a relevant role of plasma membrane cholesterol, where the impact of its removal in OB and NOB adipocyte lipolysis differs.

Comparison of messenger RNA distribution for 60 proteins in fat cells vs the nonfat cells of human omental adipose tissue

The messenger RNA (mRNA) distribution of 60 proteins was examined in the 3 fractions obtained by collagenase digestion (fat cells and the nonfat cells comprising the tissue remaining after collagenase digestion [matrix] and the stromovascular cells) of omental adipose tissue obtained from morbidly obese women undergoing bariatric surgery. Fat cells were enriched by at least 3-fold as compared with nonfat cells in the mRNAs for retinol binding protein 4, angiotensinogen, adipsin, glutathione peroxidase 3, uncoupling protein 2, peroxisome proliferator-activated receptor gamma, cell death-inducing DFFA-like effector A, fat-specific protein 27, 11beta-hydroxysteroid dehydrogenase 1, glycerol channel aquaporin 7, NADPH:quinone oxidoreductase 1, cyclic adenosine monophosphate phosphodiesterase 3B, glyceraldehyde-3-phosphate dehydrogenase, insulin receptor, and amyloid A1. Fat cells were also enriched by at least 26-fold in the mRNAs for proteins involved in lipolysis such as hormone-sensitive lipase, lipoprotein lipase, adipose tissue triglyceride lipase, and FAT/CD36. The relative distribution of mRNAs in cultured preadipocytes was also compared with that of in vitro differentiated adipocytes derived from human omental adipose tissue. Cultured preadipocytes had far lower levels of the mRNAs for inflammatory proteins than the nonfat cells of omental adipose tissue. The nonfat cells were enriched by at least 5-fold in the mRNAs for proteins involved in the inflammatory response such as tumor necrosis factor alpha, interleukin lbeta, cyclooxygenase 2, interleukin 24, interleukin 6, and monocyte chemoattractant protein 1 plus the mRNAs for osteopontin, vaspin, endothelin, angiotensin II receptor 1, butyrylcholinesterase, lipocalin 2, and plasminogen activator inhibitor 1. The cells in the adipose tissue matrix were enriched at least 3-fold as compared with the isolated stromovascular cells in the mRNAs for proteins related to the inflammatory response, as well as osteopontin and endothelial nitric oxide synthase. We conclude that the mRNAs for inflammatory proteins are primarily present in the nonfat cells of human omental adipose tissue.