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B Transcription Factor and Induces IL-6 and TNF
Expression in 3T3-L1 Adipocytes1
Department of Animal Sciences, Center for Comparative Medicine, Purdue University, West Lafayette, IN 47907-2054
2To whom correspondence should be addressed. E-mail: spurloc0{at}purdue.edu.
Fatty acids and their metabolites regulate gene expression and immunological pathways. Furthermore, obese individuals frequently have increased circulating fatty acid concentrations, and localized inflammation in adipose tissue may facilitate the systemic inflammation associated with the insulin resistance of obesity. Although palmitate induces inflammation (i.e., activates proinflammatory pathways) in myotubes, the effects of fatty acids on inflammatory processes in adipocytes have not been established. Therefore, we examined the potential for palmitate, laurate, and docosahexaenoic acid (DHA) to modulate inflammation in 3T3-L1 adipocytes. Palmitate, but not DHA or laurate, induced nuclear factor 
B (NF-B)-driven luciferase activity and interleukin-6 (IL-6) expression (P < 0.05). Inhibition of fatty acyl Co-A synthase (FACS) with triacsin C suppressed palmitate-induced NF-B activation (P < 0.05), but caused an additive increase in palmitate-induced IL-6 expression (P < 0.05). Disrupting mitogen-activated protein kinase/Erk kinase (MEK) and protein kinase C (PKC) activity with U0126 and Bisindolylmaleimide (Bis), respectively, suppressed palmitate-induced IL-6 expression (P < 0.05), but had no effect on NF-B reporter gene activity (P > 0.05). However, the phosphoinositide-3 kinase (PI3K) inhibitor, wortmannin, alone and additively with palmitate, activated the NF-B reporter gene and induced IL-6 expression (P < 0.05). Palmitate also induced the mRNA expression of tumor necrosis factor 
(TNF) (P < 0.05), but the increase in mRNA abundance was not reflected in a greater protein concentration in the media (P > 0.05). These data indicate that palmitate induces inflammation in adipocytes, and that this is not a generalized effect of all SFA. Furthermore, PI3K may act constitutively to suppress inflammation. Consequently, inhibition of this enzyme may promote and exacerbate the inflammation in adipose tissue that is associated with obesity and insulin resistance.
KEY WORDS: • NF-B • fatty acids • cytokines • adipocyte • inflammation
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