TNF-alpha inhibits BMP-induced osteoblast differentiation through activating SAPK/JNK signaling.
The cellular mechanism by which TNF-alpha inhibits osteoblastic differentiation induced by BMPs was investigated using mouse myoblast C2C12 cells expressing functional BMP receptors and Smad signaling molecules except ALK-6. Osteoblast transformation in response to BMP-2 was morphologically suppressed by TNF-alpha. Expression of biological markers for osteoblasts including Runx2 and osteocalcin, alkaline phosphatase activity, and parathyroid hormone (PTH) responsiveness shown by PTH-induced cAMP production were readily activated by BMP-2, -4, -6, and -7. The BMP-induced osteoblastic phenotype was dose-dependently inhibited by TNF-alpha. BMP-induced Smad1,5,8 phosphorylation of C2C12 cells was suppressed by TNF-alpha signaling. In addition, cDNA array analysis showed an increased expression of inhibitory Smad6 by TNF-alpha. MAP kinase analysis showed that ERK1/ERK2 and SAPK/JNK phosphorylation were selectively activated by TNF-alpha regardless of the presence of BMP ligands. BMPs had no effect on expression levels of TNF type 1 and 2 receptors. Notably, inhibition of SAPK/JNK restored TNF-alpha effects on BMP-induced osteoblast differentiation demonstrated by Id-1-promoter activity as well as Runx2 and osteocalcin mRNA levels. Collectively, TNF-alpha elicits BMP-induced osteogenic inhibition by suppressing BMP-Smad signaling pathway, at least in part, through SAPK/JNK activation and Smad6 upregulation.
Mukai
Tomoyuki
T
Department of Medicine and Clinical Science, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Okayama City 700-8558, Japan.
Otsuka
Fumio
F
Otani
Hiroyuki
H
Yamashita
Misuzu
M
Takasugi
Koji
K
Inagaki
Kenichi
K
Yamamura
Masahiro
M
Makino
Hirofumi
H
D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000008:administration & dosage*; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D032446:Myoblasts / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage*
D019485:Bone Morphogenetic Proteins; D004338:Drug Combinations; D014409:Tumor Necrosis Factor-alpha