Submitted on February 26, 2007
Accepted on February 12, 2008
JNK- and I
B-dependent pathways regulate MCP-1, not adiponectin, release from artificially hypertrophied 3T3-L1 adipocytes preloaded with palmitate in vitro
Kazuto Takahashi1, Shinya Yamaguchi1, Tatsuhiro Shimoyama1, Hiroyuki Seki1, Hidenori Katsuta1, Kaoru Miyokawa1, Toshiaki Tanaka1, Katsuhiko Yoshimoto1, Hideki Ohno2, Shinya Nagamatsu3, and Hitoshi Ishida1*
1 Third Department of Internal Medicine, Kyorin University School of Medicine, Mitaka, Tokyo, Japan
2 Molecular Predictive Medicine and Sport Science, Kyorin University School of Medicine, Mitaka, Tokyo, Japan
3 Biochemistry, Kyorin University School of Medicine, Mitaka, Tokyo, Japan
* To whom correspondence should be addressed. E-mail: ishida{at}kyorin-u.ac.jp.
Obese conditions increase the expression of adipocytokine monocyte chemoattractant protein-1 (MCP-1) in adipose tissue, as well as increasing 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. This increased MCP-1 expression was enhanced by adding exogenous tumor necrosis factor-
(TNF-) (17.8-fold vs. control, p<0.01) rather than interleukin-1
(IL-1) (2.6-fold vs. control, p<0.01). However, endogenous TNF- and IL-1 release was not affected in hypertrophied cells, suggesting these endogenous cytokines do not mediated 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 I
B phosphorylation inhibitors BAY 11-7085 and BMS-345541 (p<0.01). MCP-1 secretion was not affected by PPAR-
antagonists assayed. Adiponectin, another adipocytokine studied in parallel, also showed increased release in hypertrophied relative to control cells. But in contrast to MCP-1, adiponectin release was significantly suppressed by both exogenous TNF- and IL-1, as well as by PPAR- antagonists bisphenol A diglycidyl ether and T0070907 (p<0.01). JNK inhibitors and IB 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 IB signaling. In contrast, the parallel increase in adiponectin expression appears to be related to the PPAR- ligand properties of palmitate.
