Serum amyloid A–containing HDL binds adipocyte-derived versican and macrophage-derived biglycan, reducing its antiinflammatory properties
Chang Yeop Han, Inkyung Kang, Mohamed Omer, Shari Wang, Tomasz Wietecha, Thomas N. Wight, Alan Chait
Chang Yeop Han, Inkyung Kang, Mohamed Omer, Shari Wang, Tomasz Wietecha, Thomas N. Wight, Alan Chait
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Research Article Cell biology Inflammation

Serum amyloid A–containing HDL binds adipocyte-derived versican and macrophage-derived biglycan, reducing its antiinflammatory properties

Abstract

The ability of HDL to inhibit inflammation in adipocytes and adipose tissue is reduced when HDL contains serum amyloid A (SAA) that is trapped by proteoglycans at the adipocyte surface. Because we recently found that the major extracellular matrix proteoglycan produced by hypertrophic adipocytes is versican, whereas activated adipose tissue macrophages produce mainly biglycan, we further investigated the role of proteoglycans in determining the antiinflammatory properties of HDL. The distributions of versican, biglycan, apolipoprotein A1 (the major apolipoprotein of HDL), and SAA were similar in adipose tissue from obese mice and obese human subjects. Colocalization of SAA-enriched HDL with versican and biglycan at the cell surface of adipocyte and peritoneal macrophages, respectively, was blocked by silencing these proteoglycans, which also restored the antiinflammatory property of SAA-enriched HDL despite the presence of SAA. Similar to adipocytes, normal HDL exerted its antiinflammatory function in macrophages by reducing lipid rafts, reactive oxygen species generation, and translocation of Toll-like receptor 4 and NADPH oxidase 2 into lipid rafts, effects that were not observed with SAA-enriched HDL. These findings imply that SAA present in HDL can be trapped by adipocyte-derived versican and macrophage-derived biglycan, thereby blunting HDL’s antiinflammatory properties.

Authors

Chang Yeop Han, Inkyung Kang, Mohamed Omer, Shari Wang, Tomasz Wietecha, Thomas N. Wight, Alan Chait

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Figure 2

Versican colocalizes with HDL isolated from AgNO3-injected mice at the cell surface of 3T3-L1 adipocytes.

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Versican colocalizes with HDL isolated from AgNO3-injected mice at the c...
Free SAA and HDL from PBS- or AgNO3-injected C57BL/6 mice were isolated. Some adipocytes were transfected with siRNA specific for versican (Vcan) for 3 days. After exposure to free SAA (15 μg/mL) and/or these HDL preparations (50 μg protein/mL) for 6 hours, 3T3-L1 adipocytes were fixed in 2% formalin for 5 minutes. After extensively washing, (A) APOA1 and versican were stained using anti-versican (shown in red) and anti-APOA1 (shown in green) antibodies, or (B) SAA and versican were stained using anti-versican (shown in red) and anti-SAA (shown in green) antibodies and photographed by fluorescence microscopy (Nikon Eclipse 80i, original magnification, ×200). Cell nuclei were counterstained with DAPI (blue). Cell morphology was shown by phase-contrast photography (left). Merged fluorescence (overlay) is shown in yellow. (C) Some adipocytes were transfected with siRNA specific for versican (Vcan) for 3 days, or (D) preadipocytes from adipocyte-specific Vcan-deficient (Vcan–/–) or WT control (Vcan+/+) mice were differentiated into adipocytes. After that, HDL (50 μg protein/mL) was added for 6 hours. After extensive washing, the adipocytes were incubated with or without palmitate (250 μmol/L) for 24 hours before measurement of Saa3, Ccl2, Il1b, and Il6 gene expression. Data are representative of 3 independent experiments (n = 4) with mean ± SEM. *P < 0.001 vs. control HDL. ANOVA and Bonferroni’s post hoc test.