Effect of Compressive Force on TGF-β1/2 Signaling Pathway in MC3T3-E1 Cells

Transforming growth factor (TGF)-beta are strongly associated with osteoblast differentiation. Mechanical stress including compressive force (CF) also involve in osteoblast differentiation via the alteration of the expression of bone-specific transcription factors, namely Runx2 and Osterix. However, the role of TGF-beta s in mediating the effects of CF on osteoblasts remains unclear. In the present study, we examined the effects of CF on the expression of TGF-beta 1, TGF-beta 2, TGF-beta type 1 and 2 receptor (T beta r1 and T beta r2), and Runx2 and Osterix in osteoblasts: We also investigated the effects of CF on the phosphorylation of Smad2, Smad3 and p38; which were located on the downstream of T beta rs. Effect of T beta r inhibitor (LY2109761) on expression of Runx2 and Osterix, and phosphorylation of Smad2, Smad3 and p38 were additionally examined Cultured MC3T3-E1 osteoblast-like cells were subjected, or not, to continuous CF (1.0 g/ cm(2) or 2.0 g/cm(2)) for 1-9 h. TGF-beta 1, TGF-beta 2, T beta r1, T beta r2, Runx2 and Osterix expression were measured by real-time polymerase chain reaction and Western blot analysis. Phosphorylation levels of Smad2, Smad3 and p38 were determined by Western blot analysis. The mRNA and protein expression of TGF-beta 1 and TGF-beta 2 were significantly increased by 1.0 g/cm(2), but not 2.0 g/cm(2), CF for 3-6 h, relative to control cells; T beta r1 and T beta r2 expression were unaffected by either CF condition. The 1.0 g/cm(2) CF also increased the phosphorylation of Smad2, Smad3 and p38 and the expression of Runx2 and Osterix, and these increases were attenuated by pretreatment with LY2109761. The present findings indicate that 1.0 g/cm(2) CF can induce bone-specific transcription factors via autocrine action of CF-induced TGF-beta signaling in osteoblasts.