Abstract
Saturated fatty acids (SFAs) are known to induce inflammation and insulin resistance
in adipocytes through toll-like receptor-4 (Tlr4) signaling, but the mechanisms are
not well delineated. Furthermore, the potential roles of Tlr2 and the c-Jun N-terminal
kinase (JNK) in inflammation in adipocytes have not been investigated. We demonstrated
that palmitate, lipopolysaccharide (LPS), and the toll-like receptor-2 (Tlr2) agonist,
zymosan A (ZymA), induced insulin resistance in a time- and dose-dependent manner
in 3T3-L1 adipocytes. Corresponding with the reduction of insulin sensitivity was
an increased expression of IL-6, as well as activation of the proinflammatory transcription
factors, nuclear factor kappa B, and activator protein-1. Reactive oxygen species
(ROS) accumulation was also observed in palmitate and Tlr agonist treated adipocytes.
The JNK inhibitor, SP600125, attenuated insulin resistance mediated by SFA and Tlr
agonists, which corresponded with a diminished proinflammatory response and reduced
ROS accumulation. Collectively, these results demonstrated Tlr2 involvement in adipocyte
inflammation and therefore implicated the receptor as a potential target for SFA.
Moreover, activation of JNK also appeared to be essential to Tlr2-, as well as Tlr4-induced
insulin resistance and oxidative stress.
Key words
adipose tissue - obesity - cytokines - chemokines
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Correspondence
M. E. Spurlock
Department of Food Science and Human Nutrition
Iowa State University
50011 Ames
USA
Telefon: +1/515/294 50 38
Fax: +1/515/294 61 93
eMail: mspurloc@iastate.edu