Search

Alterations of the extracellular matrix contribute to adipose tissue dysfunction in metabolic disease. We studied the role of matrix density in regulating human adipocyte phenotype in a tunable hydrogel culture system. Lipid accumulation was maximal in intermediate hydrogel density of 5 weight %, relative to 3% and 10%. Adipogenesis and lipid and oxidative metabolic gene pathways were enriched in adipocytes in 5% relative to 3% hydrogels, while fibrotic gene pathways were enriched in 3% hydrogels. These data demonstrate that the intermediate density matrix promotes a more adipogenic, less fibrotic adipocyte phenotype geared towards increased lipid and aerobic metabolism. These observations contribute to a growing literature describing the role of matrix density in regulating adipose tissue function. [ABSTRACT FROM AUTHOR]

Obesity-associated type 2 diabetes (DM) leads to adipose tissue dysfunction. Lumican is a proteoglycan implicated in obesity, insulin resistance (IR), and adipocyte dysfunction. Using human visceral adipose tissue (VAT) from subjects with and without DM, we studied lumican effects on adipocyte function. Lumican was increased in VAT and adipocytes in DM. Lumican knockdown in adipocytes decreased lipolysis and improved adipogenesis and insulin sensitivity in VAT adipocytes in DM, while treatment with human recombinant lumican increased lipolysis and impaired insulin-sensitivity in an ERK-dependent manner. We demonstrate that lumican impairs adipocyte metabolism, partially via ERK signalling, and is a potential target for developing adipose tissue-targeted therapeutics in DM. [ABSTRACT FROM AUTHOR]

Subcutaneous (SAT) and visceral (VAT) adipose tissues have distinct metabolic phenotypes. We hypothesized that the extracellular matrix (ECM) regulates depot-specific differences in adipocyte metabolic function inmurine obesity. VAT and SAT preadipocytes from lean or obese mice were subject to adipogenic differentiation in standard 2D culture on plastic tissue culture plates or in 3D culture in ECM, followed by metabolic profiling. Adipocytes from VAT relative to SATmanifested impaired insulin-stimulated glucose uptake and decreased adipogenic capacity. In 3D-ECM-adipocyte culture, ECM regulated adipocyte metabolism in a depot-specific manner, with SAT ECM rescuing defects in glucose uptake and adipogenic gene expression in VAT adipocytes, while VAT ECM impaired adipogenic gene expression in SAT adipocytes. These findings demonstrate that ECM-adipocyte crosstalk regulates depot-specific differences in adipocyte metabolic dysfunction in murine obesity. [ABSTRACT FROM AUTHOR]

Objective: The relationship between adipose tissue fibrosis, adipocyte hypertrophy, and preadipocyte hyperplasia in the context of obesity and the correlation of these tissue-based phenomena with systemic metabolic disease are poorly defined. The goal of this study was to clarify the relationship between adipose tissue fibrosis, adipocyte hypertrophy, and preadipocyte hyperplasia in human obesity and determine the correlation of these adipose-tissue based phenomena with diabetes.Methods: Visceral and subcutaneous adipose tissues from humans with obesity collected during bariatric surgery were studied with QRTPCR, immunohistochemistry, and flow cytometry for expression of collagens and fibrosis-related proteins, adipocyte size, and preadipocyte frequency. Results were correlated with clinical characteristics including diabetes status.Results: Fibrosis was decreased, hypertrophy was increased, and preadipocyte frequency and fibrotic gene expression were decreased in adipose tissues from diabetic subjects compared to non-diabetic subjects. These differences were greater in visceral compared to subcutaneous adipose tissue.Conclusions: These data are consistent with the hypothesis that adipose tissue fibrosis in the context of human obesity limits adipocyte hypertrophy and is associated with a reciprocal increase in adipocyte hyperplasia, with beneficial effects on systemic metabolism. These findings suggest adipose tissue fibrosis as a potential target for manipulation of adipocyte metabolism. [ABSTRACT FROM AUTHOR]

Objective Natural killer (NK) cells are understudied in the context of metabolic disease and obesity. The goal of this study was to define the effect of NK cell ablation on systemic inflammation and glucose homeostasis in murine obesity. Methods A transgenic murine model was used to study the effect of NK cell ablation on systemic inflammation and glucose homeostasis in the context of diet-induced obesity using flow cytometry, QRTPCR, and glucose tolerance and insulin sensitivity testing. Results NK cell ablation achieved a three to fourfold decrease in NK cells but had no effect on T-cell levels in adipose tissues and spleen. NK cell ablation was associated with decreased total macrophage infiltration in intra-abdominal adipose tissue, but macrophage infiltration in subcutaneous adipose tissue and spleen was unaffected. NK cell ablation was associated with modest improvement in insulin sensitivity but had no effect on tissue transcript levels of inflammatory cytokines. Conclusions NK cells play a role in promoting intra-abdominal adipose tissue macrophage infiltration and systemic insulin resistance in obesity. [ABSTRACT FROM AUTHOR]

Abstract: Objective: Adipose tissue inflammation is a cause of obesity-related metabolic disease. Natural killer (NK) cells are an understudied cell type in the context of obesity. The goal of this study was to determine the phenotype of human adipose tissue NK cells. Methods: We used flow cytometry phenotyping to study adipose tissue and peripheral blood NK cells from obese and lean humans. Results: Human adipose tissue NK cells, relative to peripheral blood NK cells, express increased levels of activation markers. Adipose tissue NK cells also demonstrate an activated phenotype in obese relative to lean subjects, with increased expression of the activating receptor NKG2D. Conclusions: These data are the first detailed phenotypic characterization of human adipose tissue NK cells, and suggest a role for NK cells in adipose tissue inflammation in obesity. [Copyright &y& Elsevier]

Abstract: Adipose tissue macrophages are important mediators of inflammation and insulin resistance in obesity. IFN-γ is a central regulator of macrophage function. The role of IFN-γ in regulating systemic inflammation and insulin resistance in obesity is unknown. We studied obese IFN-γ knockout mice to identify the role of IFN-γ in regulating inflammation and insulin sensitivity in obesity. IFN-γ-knockout C57Bl/6 mice and wild-type control litter mates were maintained on normal chow or a high fat diet for 13 weeks and then underwent insulin sensitivity testing then sacrifice and tissue collection. Flow cytometry, intracellular cytokine staining, and QRTPCR were used to define tissue lymphocyte phenotype and cytokine expression profiles. Adipocyte size was determined from whole adipose tissue explants examined under immunofluorescence microscopy. Diet-induced obesity induced systemic inflammation and insulin resistance, along with a pan-leukocyte adipose tissue infiltrate that includes macrophages, T-cells, and NK cells. Obese IFN-γ-knockout animals, compared with obese wild-type control animals, demonstrate modest improvements in insulin sensitivity, decreased adipocyte size, and an M2-shift in ATM phenotype and cytokine expression. These data suggest a role for IFN-γ in the regulation of inflammation and glucose homeostasis in obesity though multiple potential mechanisms, including effects on adipogenesis, cytokine expression, and macrophage phenotype. [Copyright &y& Elsevier]

Obesity is a major health crisis, and diabetes is one of its most serious sequelae. Obesity is associated with a state of chronic systemic inflammation that is a primary etiologic factor in the development of insulin resistance and diabetes. This inflammatory state is based in adipose tissue and mediated in large part by tissue macrophages and their cytokine and adipokine products. Recent research has identified specific molecular mediators of the link between inflammation and insulin resistance in obesity. Study of these mediators and the specific mechanisms underlying inflammation and insulin resistance in obesity holds the promise for novel pharmacotherapy for obesity-related metabolic disease. [ABSTRACT FROM AUTHOR]

Obesity-related type 2 diabetes (DM) is a major public health concern. Adipose tissue metabolic dysfunction, including fibrosis, plays a central role in DM pathogenesis. Obesity is associated with changes in adipose tissue extracellular matrix (ECM), but the impact of these changes on adipose tissue mechanics and their role in metabolic disease is poorly defined. This study utilized atomic force microscopy (AFM) to quantify difference in elasticity between human DM and non-diabetic (NDM) visceral adipose tissue. The mean elastic modulus of DM adipose tissue was twice that of NDM adipose tissue (11.50 kPa vs. 4.48 kPa) to a 95% confidence level, with significant variability in elasticity of DM compared to NDM adipose tissue. Histologic and chemical measures of fibrosis revealed increased hydroxyproline content in DM adipose tissue, but no difference in Sirius Red staining between DM and NDM tissues. These findings support the hypothesis that fibrosis, evidenced by increased elastic modulus, is enhanced in DM adipose tissue, and suggest that measures of tissue mechanics may better resolve disease-specific differences in adipose tissue fibrosis compared with histologic measures. These data demonstrate the power of AFM nanoindentation to probe tissue mechanics, and delineate the impact of metabolic disease on the mechanical properties of adipose tissue. [ABSTRACT FROM AUTHOR]

Dynamic changes of adipose tissue leukocytes, including adipose tissue macrophage (ATM) and adipose tissue dendritic cells (ATDCs), contribute to obesity-induced inflammation and metabolic disease. However, clear discrimination between ATDC and ATM in adipose tissue has limited progress in the field of immunometabolism. In this study, we use CD64 to distinguish ATM and ATDC, and investigated the temporal and functional changes in these myeloid populations during obesity. Flow cytometry and immunostaining demonstrated that the definition of ATM as F4/80+CD11b+ cells overlaps with other leukocytes and that CD45+CD64+ is specific for ATM. The expression of core dendritic cell genes was enriched in CD11c+CD64- cells (ATDC), whereas core macrophage genes were enriched in CD45+CD64+ cells (ATM). CD11c+CD64- ATDCs expressed MHC class II and costimulatory receptors, and had similar capacity to stimulate CD4+ T cell proliferation as ATMs. ATDCs were predominantly CD11b+ conventional dendritic cells and made up the bulk of CD11c+ cells in adipose tissue with moderate high-fat diet exposure. Mixed chimeric experiments with Ccr2-/- mice demonstrated that high-fat diet-induced ATM accumulation from monocytes was dependent on CCR2, whereas ATDC accumulation was less CCR2 dependent. ATDC accumulation during obesity was attenuated in Ccr7-/- mice and was associated with decreased adipose tissue inflammation and insulin resistance. CD45+CD64+ ATM and CD45+CD64-CD11c+ ATDCs were identified in human obese adipose tissue and ATDCs were increased in s.c. adipose tissue compared with omental adipose tissue. These results support a revised strategy for unambiguous delineation of ATM and ATDC, and suggest that ATDCs are independent contributors to adipose tissue inflammation during obesity. [ABSTRACT FROM AUTHOR]