Role of Serum Amyloid A in Adipocyte-Macrophage Cross Talk and Adipocyte Cholesterol Efflux

Institut National de la Santé et de la Recherche Médicale, U872 team7, Nutriomique, Cordelier Research Center, Paris 75006, France.
The Journal of Clinical Endocrinology and Metabolism (Impact Factor: 6.21). 03/2009; 94(5):1810-7. DOI: 10.1210/jc.2008-2040
Source: PubMed


Acute phase serum amyloid A (A-SAA) is secreted by hepatocytes in response to injury and is regulated by proinflammatory cytokines. In obese humans, adipocytes are also a major contributor to circulating A-SAA levels.
We aimed to investigate the role and regulation of A-SAA in human adipose tissue (AT).
An approach combining microarrays and the FunNet bioinformatics tool was applied to human AT fractions (i.e. adipocytes vs. stroma vascular fraction) to hypothesize genes and functions related to A-SAA. Experiments with human AT from 37 obese subjects and human multipotent adipose-derived stem (hMADS) cells were used to confirm the microarray driven hypotheses.
Microarray analysis highlighted the relationship between A-SAA and stroma vascular fraction inflammatory genes, and between A-SAA and adipocyte-expressed ATP-binding cassette (ABC) transporters. We confirmed that serum amyloid A (SAA) protein is expressed in sc AT of obese subjects (n = 37, body mass index = 49.3 +/- 1.5 kg/m(2)) and showed that SAA protein expression correlated with adipocyte size (R = 0.44; P = 6.10(-3)), macrophage infiltration (R = 0.61; P = 10(-4)), and ABC subfamily A1 protein expression (R = 0.43; P = 9.10(-3)). IL-1beta, TNF-alpha, and human AT macrophage-conditioned medium significantly induced A-SAA secretion (from 2.6 to 7.6 fold) in hMADS cells. Recombinant SAA induced cholesterol ABC subfamily A1-dependent efflux from hMADS adipocytes by 4.3-fold in a dose-dependent manner.
This work provides original insight suggesting that A-SAA is a player in the dialogue between hypertrophied adipocytes and macrophages through its regulation of adipocyte cholesterol efflux.

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    • "SAA is primarily synthesized by hepatocytes [1], and its extra-hepatic sources include leukocytes [2], adipocytes [3], synoviocytes [4], tumor cells [5] and first trimester trophoblast cells [6]. SAA has been shown to play biological roles in lipid metabolism [7], immunomodulation [8]–[10] and cell proliferation [11], [12] and invasion [13]. "
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    • "They exhibit stem cell characteristics, i.e. the capacity to self-renew and differentiate into several cell types at the clonal level, even after longterm expansion. Expanded hMADS cells are able to differentiate under serum-free adipogenic conditions into cells displaying a combination of properties similar, if not identical, to those of native human adipocytes [3] [4]. Altogether, hMADS cells appear to be a powerful cellular model to investigate cell surface marker expression during self-renewal and differentiation. "
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    • "We previously reported that SAA is a player in the dialogue between hypertrophied adipocytes and macrophages through its regulation of adipocyte cholesterol efflux [42]. Taken together, our new data along with the published observation provide further evidence for a central role of SAA in adipocyte-macrophage cross-talks in obesity: 1) SAA increases IL-6 and IL-8 production by adipocytes as well as the chemokine MCP-1, which recruits circulating monocytes into the adipose tissue; 2) SAA increases IL-6, IL-8 and TNFα production by immune cells; 3) SAA displays direct chemoattractant activity in the presence or absence of hyaluronan complexes [15], [33], [41]–[44]. "
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