Differentiation of 3T3‐L1 adipocytes with arachidonic acid increases inflammatory markers

Adipose tissue is responsible for insulating internal organs, storing energy for times of negative energy balance, and secreting adipokines into circulation. The major cell types found in adipose tissue include undifferentiated adipocytes (pre‐adipocytes), adipocytes, and adipose tissue macrophages macrophages (ATMs). Adipocytes and ATMs are the major sources of adipokines, adipose tissue cytokines with functions ranging from inflammatory mediators to metabolic regulators. Polyunsaturated fatty acids (PUFAs) have been shown to affect the differentiation and lipid droplet formation in 3T3‐L1 adipocytes, but few studies have examined their effects on inflammatory adipokine production from these cells. Adipocyte differentiation, which is marked by lipid droplet (triacylglycerol; TAG) accumulation, is regulated by various transcription activators, including a splice variant of the nuclear receptor PPAR□. PUFAs are major regulators of PPAR□. For example, the n‐3 PUFA EPA has been shown to have an effect on lipid droplet size through effects on lipid catabolism, as well as mediate reductions in pro‐inflammatory adipokine secretion in favor of anti‐inflammatory secretions. The objectives of this experiment were to determine the effects of n‐3 and ‐6 PUFAs on TAG lipolysis, as measured by free fatty acid (FFA) release, and inflammatory cytokine production, as measured by interleukin (IL)‐6 and macrophage inflammatory protein (MIP)‐1α production. In order to examine these effects, the 3T3‐L1 cells were differentiated in media with 100μM of PUFA treatment (α‐linoleic acid [LA], arachidonic acid [ARA], and EPA), followed by a 6 h, 1μg/mL of lipopolysaccharide (LPS) challenge. Fully differentiated 3T3‐L1 adipocytes under these treatments did not release FFA in quantifiable amounts. The LPS+ARA treatment resulted in significantly higher levels of MIP‐1□ (26.3±2.5 pg/ml) and IL‐6 (146.13±17.0 pg/ml) in conditioned media, compared to control (MIP‐1□:0.55±2.5; IL‐6:0.23±17.0), LPS (MIP‐1□:0.06±2.5; IL‐6:16.5±17.0), and LPS+LA (MIP‐1□:7.5±2.5; IL‐6:27.0±17.0). Cells treated with LPS+EPA released similar amounts of MIP‐1□ (14.9±2.5) but significantly lower amounts of IL‐6 (20.3±17.0) compared to LPS+ARA‐treated cells. These data suggest that differentiating 3T3‐L1 adipocytes in the presence of the n‐6 PUFA ARA results in increased release of LPS‐stimulated IL‐6 and MIP‐1□. These results indicate a role of this n‐6 fatty acid on adipocyte‐derived inflammation. Support or Funding Information Laurie Bukovac Hodgson & David Hodgson Endowed Fund, as well as the Denison Summer Science Research Supply Fund