TNF-α inhibits BMP-induced osteoblast differentiation through activating SAPK/JNK signaling

• Published in: Biochemical and biophysical research communications 2007-05, Vol.356 (4), p.1004-1010
• Main Authors: Mukai, Tomoyuki, Otsuka, Fumio, Otani, Hiroyuki, Yamashita, Misuzu, Takasugi, Koji, Inagaki, Kenichi, Yamamura, Masahiro, Makino, Hirofumi
• Format: Article
• Language: English
• Subjects: Animals; Bone morphogenetic protein (BMP); Bone Morphogenetic Proteins - administration & dosage; C2C12; Cell Differentiation - drug effects; Cell Line; Dose-Response Relationship, Drug; Drug Combinations; MAP Kinase Signaling System - drug effects; MAP Kinase Signaling System - physiology; Mice; Mitogen-activated protein (MAP) kinase; Myoblasts - cytology; Myoblasts - drug effects; Myoblasts - physiology; Osteoblast; Osteoblasts - cytology; Osteoblasts - drug effects; Osteoblasts - physiology; Tumor necrosis factor (TNF)-α; Tumor Necrosis Factor-alpha - administration & dosage
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2007.03.099

The cellular mechanism by which TNF-α 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-α. 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-α. BMP-induced Smad1,5,8 phosphorylation of C2C12 cells was suppressed by TNF-α signaling. In addition, cDNA array analysis showed an increased expression of inhibitory Smad6 by TNF-α. MAP kinase analysis showed that ERK1/ERK2 and SAPK/JNK phosphorylation were selectively activated by TNF-α 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-α effects on BMP-induced osteoblast differentiation demonstrated by Id-1-promoter activity as well as Runx2 and osteocalcin mRNA levels. Collectively, TNF-α elicits BMP-induced osteogenic inhibition by suppressing BMP-Smad signaling pathway, at least in part, through SAPK/JNK activation and Smad6 upregulation.