Human adipose tissue microvascular endothelial cells secrete PPARγ ligands and regulate adipose tissue lipid uptake
Silvia Gogg, Annika Nerstedt, Jan Boren, Ulf Smith
Silvia Gogg, Annika Nerstedt, Jan Boren, Ulf Smith
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Research Article Cell biology

Human adipose tissue microvascular endothelial cells secrete PPARγ ligands and regulate adipose tissue lipid uptake

Abstract

Human adipose cells cannot secrete endogenous PPARγ ligands and are dependent on unknown exogenous sources. We postulated that the adipose tissue microvascular endothelial cells (aMVECs) cross-talk with the adipose cells for fatty acid (FA) transport and storage and also may secrete PPARγ ligands. We isolated aMVECs from human subcutaneous adipose tissue and showed that in these cells, but not in (pre)adipocytes from the same donors, exogenous FAs increased cellular PPARγ activation and markedly increased FA transport and the transporters FABP4 and CD36. Importantly, aMVECs only accumulated small lipid droplets and could not be differentiated to adipose cells and are not adipose precursor cells. FA exchange between aMVECs and adipose cells was bidirectional, and FA-induced PPARγ activation in aMVECs was dependent on functional adipose triglyceride lipase (ATGL) protein while deleting hormone-sensitive lipase in aMVECs had no effect. aMVECs also released lipids to the medium, which activated PPARγ in reporter cells as well as in adipose cells in coculture experiments, and this positive cross-talk was also dependent on functional ATGL in aMVECs. In sum, aMVECs are highly specialized endothelial cells, cannot be differentiated to adipose cells, are adapted to regulating lipid transport and secreting lipids that activate PPARγ, and thus, regulate adipose cell function.

Authors

Silvia Gogg, Annika Nerstedt, Jan Boren, Ulf Smith

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Figure 1

Effects of free fatty acids (FA).

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Effects of free fatty acids (FA). (A) FA transport: aMVECs were incubate...
(A) FA transport: aMVECs were incubated for 24 hours without (basal condition; BAS) or with 300 μM OA followed by 60 minutes starvation, but with maintained OA, as indicated. The FA transport assay (Quencher-Based Technology assay) was performed as described in Methods. The results, expressed as relative fluorescence units (RFU), are the means of data from 4 experiments. *P < 0.05 compared with BAS. (B–D) Regulation of lipid transporters: aMVECs and HUVECs were incubated without (BAS) or with 300 μM OA or 5 μM ROSI for 24 hours. Quantitative real-time PCR (qRT-PCR) of FABP4 (B), CD36 (C), and PPARγ (D) expressed as mRNA/18S rRNA ratio; n = 8 aMVECs or n = 5 HUVECs. *P < 0.05; **P < 0.01; ***P < 0.001 compared with BAS. (B and C) The bottom images show representative Western blots of the protein level of FABP4 (B) and CD36 (C). (E and F) Effect of a PPARγ inhibitor in aMVECs: Cells were incubated for 24 hours without (BAS) or with 300 μM OA or 5 μM ROSI, alone or in the presence of 1 μM T0070907(T007). qRT-PCR of FABP4 (E) and CD36 (F); n = 6. *P < 0.05 compared with OA alone. (G) OA in cMVECs: The cardiac microvascular cells were starved and incubated without (BAS) or with 300 μM OA for 24 hours. qRT-PCR of CD36, FABP4, and PPARγ, n = 5. (H) Effect of VEGF in aMVECs: Cells were starved and incubated without (BAS) or with 100 μM hrVEGF-B for 24 hours. qRT-PCR in aMVECs for CD36 and FABP4; n = 7. (I) Comparative mRNA expression of PPARγ in HUVECs, PAs, and aMVECs. Data are from at least 5 experiments. *P < 0.05; **P < 0.01 compared with HUVECs. In all graphs bars represent mean ± SEM. Wilcoxon’s signed-rank test (A), Kruskal-Wallis test (B–D and G–I), and 1-way ANOVA (E and F).