Transforming Growth Factor β2 Regulates Growth and Differentiation of Pulp Cells via ALK5/Smad2/3

Transforming growth factor β (TGF-β) may regulate the biological activities of dental pulp cells. We found that human dental pulp cells expressed TGF-β1, TGF-β2, and a little amount of TGF-β3 messenger RNA (mRNA). The exposure of pulp cells to TGF-β2 induced the phosphorylation of Smad2/3, Smad1/5/8, and extracellular regulated-kinase 1/2 (ERK1/2) as observed by Western blotting. Exposure to TGF-β2 decreased the alkaline phosphatase (ALP) mRNA expression and enzyme activity. Pretreatment of pulp cells with SB431542 (an inhibitor of TGF-β ALK-4, ALK-5, and ALK-7 receptors) but not U0126 (a MEK1 inhibitor) prevented the inhibition of viable cell number, ALP activity, and mRNA expression by TGF-β2 in dental pulp cells. These results suggest that TGF-β may affect the growth and differentiation of dental pulp cells via an autocrine fashion by activation of the ALK/Smad2/3-signal transduction pathways. TGF-β2 possibly regulates the differentiation of pulp cell at specific stages synergistically with other factors.