A dual role of TGF-beta in human osteoclast differentiation mediated by Smad1 versus Smad3 signaling

Abstract

TGF-beta 1 is highly expressed in the synovial tissue of patients with rheumatoid arthritis and is known as a cytokine that plays an important role in tissue repair and immune cell regulation. However, the role of TGF-beta 1 is still unclear in osteoclastogenesis. In this study, we examined the effect of TGF-beta 11 on osteoclast differentiation and the underlying mechanism using healthy human peripheral blood monocytes. TGF-beta 1 was found to inhibit osteoclast differentiation and decrease the expression of osteoclast-specific genes such as acid phosphatase 5, tartrate resistant and cathepsin K. Levels of NFAT1, an important transcription factor in osteoclastogenesis, were also reduced. In addition, TGF-beta 11 suppressed receptor activator of NF-x13 (RANK) ligand-induced NF-kappa B and p38 MAPK signaling. Inhibition of osteoclast differentiation by TGF-beta 1 was reversed by 1 pM SB431542 (an inhibitor of ALK4/5/7), which inhibited TGF-beta 1-induced phosphorylation of SMAD1, but not that of SMAD3. TGF-beta 1 also restricted RANK expression, and this was partially reversed by 1 pM SB431542. In contrast, the inhibition of SMAD3 by SIS3 (an inhibitor of SMAD3) reduced the osteoclast formation. TGF-f31 has both inhibitory and stimulatory effects on human osteoclast differentiation, and that these opposing functions are mediated by SMAD1 and SMAD3 signaling, respectively.