JNK- and IkappaB-dependent pathways regulate MCP-1 but not adiponectin release from artificially hypertrophied 3T3-L1 adipocytes preloaded with palmitate in vitro.
Obese conditions increase the expression of adipocytokine monocyte chemoattractant protein-1 (MCP-1) in adipose tissue as well as MCP-1 plasma levels. To investigate the mechanism behind increased MCP-1, we used a model in which 3T3-L1 adipocytes were artificially hypertrophied by preloading with palmitate in vitro. As observed in obesity, under our model conditions, palmitate-preloaded cells showed significantly increased oxidative stress and increased MCP-1 expression relative to control cells. This increased MCP-1 expression was enhanced by adding exogenous tumor necrosis factor-alpha (TNF-alpha; 17.8-fold vs. control cells, P < 0.01) rather than interleukin-1beta (IL-1beta; 2.6-fold vs. control cells, P < 0.01). However, endogenous TNF-alpha and IL-1beta release was not affected in hypertrophied cells, suggesting that these endogenous cytokines do not mediate hypertrophy-induced increase in MCP-1. MCP-1 secretion from hypertrophied cells was significantly decreased by treatment with antioxidant N-acetyl-cysteine, JNK inhibitors SP600125 and JIP-1 peptide, and IkappaB phosphorylation inhibitors BAY 11-7085 and BMS-345541 (P < 0.01). MCP-1 secretion was not affected by peroxisome proliferator-activated receptor-gamma (PPARgamma) antagonists assayed. Adiponectin, another adipocytokine studied in parallel, also showed increased release in hypertrophy relative to control cells. But in contrast to MCP-1, adiponectin release was significantly suppressed by both exogenous TNF-alpha and IL-1beta as well as by PPARgamma antagonists bisphenol A diglycidyl ether and T0070907 (P < 0.01). JNK inhibitors and IkappaB phosphorylation inhibitors showed no significant effect on adiponectin. We conclude that adipocyte hypertrophy through palmitate loading causes oxidative stress, which in turn increases MCP-1 expression and secretion through JNK and IkappaB signaling. In contrast, the parallel increase in adiponectin expression appears to be related to the PPARgamma ligand properties of palmitate.
Takahashi
Kazuto
K
Third Department of Internal Medicine, Kyorin University School of Medicine, Tokyo, Japan.
Yamaguchi
Shinya
S
Shimoyama
Tatsuhiro
T
Seki
Hiroyuki
H
Miyokawa
Kaoru
K
Katsuta
Hidenori
H
Tanaka
Toshiaki
T
Yoshimoto
Katsuhiko
K
Ohno
Hideki
H
Nagamatsu
Shinya
S
Ishida
Hitoshi
H
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D052242:Adiponectin / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D048429:Cell Size / Q000187:drug effects; D018932:Chemokine CCL2 / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D051550:I-kappa B Kinase / Q000502:physiology*; D053583:Interleukin-1beta / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000502:physiology*; D051379:Mice; D047495:PPAR gamma / Q000378:metabolism / Q000502:physiology; D010168:Palmitates / Q000494:pharmacology*; D015398:Signal Transduction / Q000502:physiology*; D014280:Triglycerides / Q000096:biosynthesis; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D052242:Adiponectin; C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; D053583:Interleukin-1beta; D047495:PPAR gamma; D010168:Palmitates; D014280:Triglycerides; D014409:Tumor Necrosis Factor-alpha; D006861:Hydrogen Peroxide; D051550:I-kappa B Kinase; D048031:JNK Mitogen-Activated Protein Kinases