Role of the Toll-like receptor 4/NF-kappaB pathway in saturated fatty acid-induced inflammatory changes in the interaction between adipocytes and macrophages.
OBJECTIVE
Previous studies demonstrated that obese adipose tissue is characterized by increased infiltration of macrophages, suggesting that they might represent an important source of inflammation. Using an in vitro coculture system composed of 3T3-L1 adipocytes and RAW264 macrophages, we previously demonstrated that saturated fatty acids (FAs) and tumor necrosis factor (TNF)-alpha derived from adipocytes and macrophages, respectively, play a major role in the coculture-induced inflammatory changes.


RESULTS
Coculture of adipocytes and macrophages resulted in the activation of nuclear factor-kappaB (NF-kappaB), a primary regulator of inflammatory responses, in both cell types. Pharmacological inhibition of NF-kappaB markedly suppressed the coculture-induced production of proinflammatory cytokines and adipocyte lipolysis. Peritoneal macrophages obtained from Toll-like receptor 4 (TLR4) mutant mice exhibited marked attenuation of TNFalpha production in response to saturated FAs. Notably, coculture of hypertrophied adipocytes and TLR4-mutant macrophages resulted in marked inhibition of proinflammatory cytokine production and adipocyte lipolysis. We also observed that endogenous FAs, which are released from adipocytes via the beta3-adrenergic stimulation, resulted in the activation of the TLR4/NF-kappaB pathway.


CONCLUSIONS
These findings suggest that saturated FAs, which are released in large quantities from hypertrophied adipocytes via the macrophage-induced adipocyte lipolysis, serve as a naturally occurring ligand for TLR4, thereby inducing the inflammatory changes in both adipocytes and macrophages through NF-kappaB activation.
Suganami
Takayoshi
T
Department of Molecular Medicine and Metabolism, Medical Research Institute, Tokyo Medical and Dental University, 2-3-10 Kanda-surugadai, Chiyoda-ku, Tokyo 101-0062, Japan.
Tanimoto-Koyama
Kanami
K
Nishida
Junko
J
Itoh
Michiko
M
Yuan
Xunmei
X
Mizuarai
Shinji
S
Kotani
Hidehito
H
Yamaoka
Shoji
S
Miyake
Kensuke
K
Aoe
Seiichiro
S
Kamei
Yasutomi
Y
Ogawa
Yoshihiro
Y
D017667:Adipocytes / Q000187:drug effects / Q000473:pathology*; D000818:Animals; D002450:Cell Communication / Q000187:drug effects*; D002460:Cell Line; D018920:Coculture Techniques; D005227:Fatty Acids / Q000494:pharmacology*; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D006984:Hypertrophy / Q000473:pathology; D007249:Inflammation / Q000473:pathology; D008066:Lipolysis; D008264:Macrophages / Q000187:drug effects / Q000473:pathology*; D051379:Mice; D008817:Mice, Mutant Strains; D016328:NF-kappa B / Q000235:genetics / Q000502:physiology*; D009765:Obesity / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
D005227:Fatty Acids; D005230:Fatty Acids, Nonesterified; D016328:NF-kappa B; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha