Possible involvement of PI3K-dependent pathways in the increased VEGF120 release from osteoblastic cells preloaded with palmitate in vitro.
It have been reported that abnormal bone metabolism often occurs in patients with type 2 diabetes, but the underlying mechanisms remain to be elucidated. In recent years dyslipidemia (hyperlipidemia) has been presumed to have an influence on bone metabolism. In addition, the involvements of VEGF and MCP-1 derived from osteoblasts in bone abnormal metabolism were also observed. Thus, we investigated the pathogenic mechanism of this abnormal bone metabolism, which is included in the regulation of VEGF and MCP-1 secretions from osteoblasts, by using UMR-106 osteosarcoma cells as an osteoblast cell model and treating them with palmitate in order to mimic a state of hyperlipidemia. Palmitate-preloaded cells showed the significant increase of VEGF120 release (1.8-fold vs. control cells, p<0.01). Moreover, the treatment with palmitate significantly increased VEGF-A mRNA with the maximal 2.5-fold upregulation at 12h after the treatment (p<0.01). However, MCP-1 release was not affected by palmitate. Moreover, the amplified VEGF120 secretion with palmitate was significantly decreased by the treatment with TLR4 antagonist or PI3K pathway inhibitors, LY294002 and wortmannin (p<0.01, respectively). On the other hand, the stimulation with TNF-α, which osteoclasts were able to release, significantly enhanced MCP-1 secretion (p<0.01), but had no effect on VEGF120. On the contrary IL-1β amplified VEGF120 release (p<0.01), but not MCP-1. These results suggest that palmitate can increase VEGF120 release from UMR-106 osteosarcoma cells, which is accelerated at the transcriptional level, and this increase of VEGF120 release may be mediated though, at least partly, TLR4 and the PI3K pathways. In addition, we also verified that TNF-α and IL-1β, which are considered to be derived from osteoclasts, amplified the secretions of MCP-1 and VEGF120 from UMR-106 cells, respectively.
Third Department of Internal Medicine, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
Rie
R
Moriya
Third Department of Internal Medicine, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
Kazuto
K
Takahashi
Third Department of Internal Medicine, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
Atsuko
A
Kitahara
Third Department of Internal Medicine, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
Hirohisa
H
Onuma
Third Department of Internal Medicine, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
Keiko
K
Handa
Third Department of Internal Medicine, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
Yoshikazu
Y
Sumitani
Third Department of Internal Medicine, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
Toshiaki
T
Tanaka
Third Department of Internal Medicine, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
Hidenori
H
Katsuta
Third Department of Internal Medicine, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
Susumu
S
Nishida
Third Department of Internal Medicine, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
Eiji
E
Itagaki
Third Department of Internal Medicine, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
Kouichi
K
Inukai
Third Department of Internal Medicine, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan. Electronic address: ishida@ks.kyorin-u.ac.jp.
Hitoshi
H
Ishida
D000818:Animals; D045744:Cell Line, Tumor; D018932:Chemokine CCL2 / Q000378:metabolism; D006949:Hyperlipidemias / Q000235:genetics / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010168:Palmitates / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism*
C491766:Ccl2 protein, rat; D018932:Chemokine CCL2; D010168:Palmitates; D012333:RNA, Messenger; C495347:Tlr4 protein, rat; D051197:Toll-Like Receptor 4; D042461:Vascular Endothelial Growth Factor A; C467498:vascular endothelial growth factor A, rat; D019869:Phosphatidylinositol 3-Kinases
MCP-1; Osteoblast; VEGF(120)