α-Naphthoflavone Increases Lipid Accumulation in Mature Adipocytes and Enhances Adipocyte-Stimulated Endothelial Tube Formation.

Mei-Lin Wang,Yue-Hwa Chen,Shyh-Hsiang Lin,Yuan-Yu Hou

doi:10.3390/nu7053166

Abstract

The aryl hydrocarbon receptor (AhR) is a ligand-activated factor that regulates biological effects associated with obesity. The AhR agonists, such as environmental contaminants 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and β-naphthoflavone (BNF), inhibit preadipocyte differentiation and interfere with the functions of adipose tissue, whereas the antagonist may have opposite or protective effects in obesity. This study investigated the effects of α-naphthoflavone (α-NF), an AhR antagonist, on adipogenesis- and angiogenesis-associated factors in mature adipocytes and on cross-talk of mature adipocytes with endothelial cells (ECs). Besides, the roles of the AhR on lipid accumulation and on secretion of vascular endothelial growth factor were also determined by introducing siRNA of AhR. Differentiated 3T3-L1 cells were treated with α-naphthoflavone (α-NF) (1–5 μM) for 16 h. Lipid accumulation and the expressions of AhR-associated factors in the cells were determined. The interaction between adipocytes and ECs was investigated by cultivating ECs with conditioned medium (CM) from α-NF-treated mature adipocytes, followed by the determination of endothelial tube formation. The results showed that α-NF significantly increased triglyceride (TG) accumulation in mature adipocytes, which was associated with increased expression of hormone-sensitive lipase (HSL), estrogen receptor (ER), as well as decreased expression of AhR, AhR nuclear translocator (ARNT), cytochrome P4501B1 (CYP1B1), and nuclear factor erythroid-2-related factor (NRF-2) proteins. In addition, CM stimulated formation of tube-like structures in ECs, and α-NF further enhanced such stimulation in association with modulated the secretions of various angiogenic mediators by mature adipocytes. Similarly, increased TG accumulation and vascular endothelial growth factor (VEGF) secretion were observed in AhR-knockout cells. In conclusion, α-NF increased TG accumulation in mature adipocytes and enhanced mature adipocyte-stimulated tube formation in ECs, suggesting that the AhR may suppress obesity-induced adverse effects, and α-NF abolished the protective effects of the AhR.

Highlights

Obesity is a consequence of excessive storage of lipid in white adipose tissue (WAT), which contains preadipocytes, mature adipocytes, endothelial cells (ECs), and macrophages
Dulbecco’s modified Eagle’s medium (DMEM), sodium bicarbonate, fetal bovine serum (FBS), calf serum, trypan blue, and trypsin were obtained from Gibco (Grand Island, NY, USA). α-NF was dissolved in dimethyl sulfoxide (DMSO), and the concentration of DMSO in culture media was 0.1% (v/v)
Because vascular endothelial growth factor (VEGF) expression is positively correlated to the size of adipocytes [40], and is enhanced by Interleukin 6 (IL-6) [41], α-NF increased production of VEGF and IL-6 may be explained by the increased lipid accumulation in mature adipocytes. All of these mediators were indicated to be proangiogenic, these results suggest that the amounts of VEGF and IL-6 released from mature adipocytes are higher, which may act more potently on angiogenic pathways than the other cytokines

Summary

Introduction

Obesity is a consequence of excessive storage of lipid in white adipose tissue (WAT), which contains preadipocytes, mature adipocytes, endothelial cells (ECs), and macrophages. Obesity is accompanied by adipogenesis, the process that involves preadipocyte differentiation and lipid accumulation, leading to increases in adipocyte size [1,2]. As massive amounts of lipids accumulate in WATs in obesity, intimate interactions may exist between mature adipocytes and adjacent vascular ECs, which may contribute to the physiological and pathological characteristics of adipose tissues, including the occurrence of different metabolic disorders and cancers [6,7]. Aryl hydrocarbon receptor (AhR) is a cytosolic ligand-activated transcription factor that participates in a variety of metabolic processes, including detoxification and adipogenesis. With the assistance of the aryl hydrocarbon translocator protein (ARNT), named hypoxia-inducible factor (HIF)-1β, the activated AhR modulates expressions of various genes involved in xenobiotic-metabolizing pathways, such as cytochrome

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