7 research outputs found

    Browning of White Adipose Tissue Uncouples Glucose Uptake from Insulin Signaling

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    <div><p>Presence of thermogenically active adipose tissue in adult humans has been inversely associated with obesity and type 2 diabetes. While it had been shown that insulin is crucial for the development of classical brown fat, its role in development and function of inducible brown-in-white (brite) adipose tissue is less clear. Here we show that insulin deficiency impaired differentiation of brite adipocytes. However, adrenergic stimulation almost fully induced the thermogenic program under these settings. Although brite differentiation of adipocytes as well as browning of white adipose tissue entailed substantially elevated glucose uptake by adipose tissue, the capacity of insulin to stimulate glucose uptake surprisingly was not higher in the brite state. Notably, in line with the insulin-independent stimulation of glucose uptake, our data revealed that brite recruitment results in induction of solute carrier family 2 (GLUT-1) expression in adipocytes and inguinal WAT. These results for the first time demonstrate that insulin signaling is neither essential for brite recruitment, nor is it improved in cells or tissues upon browning.</p></div

    Lack of insulin impairs differentiation but not browning capacity of primary pre-adipocytes.

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    <p>(<b>A</b>) Heatmap showing differential mRNA expression between confluent primary inguinal white adipose tissue (iWAT) precursor cells differentiated for 24 h with white (EtOH treated) or brite (cPGI<sub>2</sub> treated) differentiation cocktail and between absence or presence of insulin (Ins) in the medium. Higher and lower expression is displayed in red and blue, respectively. (n = 3). (<b>B</b>) mRNA expression of UCP-1 and CIDEA or (<b>C</b>) FABP4 and RETN in primary iWAT precursor cells differentiated into white (EtOH treated) or brite (cPGI<sub>2</sub> treated) adipocytes for 8 days with insulin present in the differentiation medium for the indicated timepoints (n = 3). All values in bar graphs are expressed as means ± SEM, #p<0.05, ##p<0.01, ###p<0.001 white (EtOH treated) vs. brite (cPGI<sub>2</sub> treated) cells, *p<0.05, **p<0.01, ***p<0.001 normal conditions vs. insulin deprived conditions.</p

    Brite adipose cells and tissues exhibit elevated glucose uptake independent of insulin stimulation, thereby enhancing glucose clearance from blood.

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    <p>(<b>A, B</b>) <sup>3</sup>H-2-deoxy-D-glucose (3H-2DOG) uptake by primary inguinal white adipose tissue (iWAT) precursor cells (<b>A</b>) absolute or (<b>B</b>) relative to unstimulated basal uptake. Cells were differentiated into white (EtOH treated) or brite (cPGI<sub>2</sub> treated) adipocytes for 8 days and stimulated with different doses of Insulin for 20 minutes. (<b>C, D</b>) Intraperitoneal insulin (Ins) tolerance test (0.5 U/kg body weight insulin) of mice treated with CL316,243 (CL, 1 µg/g/day) or NaCl via s.c. implanted osmotic pumps for 10 days. (<b>C</b>) Absolute blood glucose levels and (<b>D</b>) levels relative to non-insulin-stimulated are shown. (<b>E, F</b>) 3H-2DOG uptake rate into inguinal or abdominal white (iWAT, aWAT) or brown (BAT) adipose tissue and heart of the same mice as in B, C. (<b>E</b>) Absolute uptake and (<b>F</b>) uptake relative to non-insulin-stimulated conditions is shown. Uptake rates were measured 45 minutes after intraperitoneal injection of insulin or vehicle. All values are expressed as means ± SEM, n = 3–6, #p<0.05, ##p<0.01, ###p<0.001 white vs. brite, *p<0.05, **p<0.01, ***p<0.001 no insulin vs. insulin stimulated.</p

    Physiological parameters.

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    <p>(A) Body weight (BW) and (B) adipose tissues weights of T<sub>reg</sub> cell-proficient (PBS) and T<sub>reg</sub> cell-deficient (DT) mice after cold exposure. BAT, brown adipose tissue; scWAT, subcutaneous white adipose tissue, aWAT, abdominal white adipose tissue. (C) Blood glucose, (D) serum non-estherified fatty acids (NEFA) and (E) serum triglycerides in PBS and DT mice. Values are mean ± SD (n = 9–10); *P<0.05 (Student’s t-test).</p

    Genotypical comparison of T<sub>reg</sub> and T<sub>conv</sub> cells isolated from brown adipose tissue (BAT) and spleen tissue (SPL) in cold- and warm-conditioned animals generated with an Illumina Mouse Expression Array.

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    <p>(A) Gene expression profiles comparing T<sub>reg</sub> (top) or T<sub>conv</sub> (bottom) cell populations between spleen and adipose tissue samples isolated from warm-conditioned animals (left) or between cells isolated from cold vs warm-conditioned animals (right). Numbers indicate genes either up- or downregulated more than 2-fold (cut-off: dotted line), with the number of significantly different (p<0.05) genes shown in brackets with an asterisk. (B) Volcano plot comparing gene expression and significance values between T<sub>reg</sub> and T<sub>conv</sub> genes isolated from BAT in warm-conditioned animals. Key up- or downregulated genes in T<sub>reg</sub> cells are annotated (Foxp3, Il10, Cxcl1/2, Tcf7, Ifng) and serve as quality control to the published consensus T<sub>reg</sub>-cell signature. (C) Hierarchical clustering of the top-30 upregulated genes and the top-10 downregulated genes in warm-conditioned brown adipose tissue T<sub>reg</sub> cells versus spleen T<sub>reg</sub> cells. (D) Comparison of BAT-T<sub>reg</sub>-specific genes with visceral adipose tissue (VAT)-specific genes. We first determined 430 genes to upregulated in BAT warm-conditioned T<sub>reg</sub> cells, with 222 genes being significantly altered (p<0.05). We then overlaid BAT T<sub>reg</sub>-upregulated genes with VAT T<sub>reg</sub> tissue specific expression gene data. 181 genes were matched between both microarary chips, with 169 genes also upregulated in VAT, and only 12 genes specific for BAT (left). The corresponding analysis of the 516 genes upregulated in cold BAT T<sub>reg</sub> cells versus warm spleen T<sub>reg</sub> cells revealed 194 genes to be significantly upregulated. 158 could be matched to VAT T<sub>reg</sub>-specific genes, of which 148 were VAT-specific, whereas only 10 were specific for BAT. P-values indicate the significance of overrepresentation of BAT T<sub>reg</sub>-specific genes in the VAT T<sub>reg</sub> signature. (E) Comparison of VAT-T<sub>reg</sub> specific genes on BAT warm (left) or BAT cold (right) gene signatures. Of 1839 genes specifically overexpressed in VAT T<sub>reg</sub> cells, 1059 were statistically significantly (p<0.05) upregulated. Of these 1059 genes, 829 were also detectable in the BAT T<sub>reg</sub> microarray. When comparing the VAT T<sub>reg</sub> signature to warm BAT T<sub>reg</sub> cells, 660 genes were overrepresented in VAT, whereas cold BAT T<sub>reg</sub> cells show 685 genes to be overrepresented in VAT.</p

    Inflammatory status of adipose tissue.

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    <p>Real-time RT-PCR analysis of (A) brown adipose tissue (BAT) and (B) subcutaneous white adipose tissue of T<sub>reg</sub> cell-proficient (PBS) and T<sub>reg</sub> cell-deficient (DT) mice after cold exposure. Ucp1, uncoupling protein 1; Cidea,cell death-inducing DNA fragmentation factor, alpha subunit-like effector A; Dio2,deiodinase, iodothyronine, type II; Pparg, peroxisome proliferator-activated receptor gamma; Prdm16, PR domain containing 16; Cd68, Cd68 antigen; Ccl2,chemokine (C-C motif) ligand 2; Tnfa, tumor necrosis factor alpha; Ifng, interferon, gamma; Mrc1, mannose receptor, C type 1; Mgl1, macrophage galactose-type C-type lectin 1; Arg1,arginase 1; Il-10, interleukin 10; Il-4, interleukin 4. Data are mean ± SD (n = 9–10); *p<0.05 (Student’s t-test). (C) Representative hematoxylin and eosin (H&E) staining (left) and immunohistochemical anti-MAC-2 staining (right; brown color) in BAT from PBS and DT mice. Scale bar 100 μm. Quantification of MAC-2 positive area (panel below MAC-2 staining) as a percentage of total area.</p
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