Effects of PGE2 on Smad Phosphorylation in Human Dental Pulp Cells

Abstract

When dental pulp is subjected to chronic decay or mild external irritation such as dental attrition or abrasion, hard tissue formation is promoted and reparative dentin is formed. It has been reported that prostaglandin E2 (PGE₂) is able to enhance or inhibit this process,depending on its concentration, but the precise mechanisms are uncertain. Thus, in the present study, we simulated dental pulpitis by PGE₂ stimulation in human dental pulp cells (HDPC), and investigated the effects on Smad dynamics, as well as heat shock protein 70 (HSP70)and Matrix Gla Protein (MGP). HDPC were obtained from unerupted teeth extracted in the course of orthodontic treatment. HDPC were cultured and stimulated with various concentrations of PGE₂, after which totalRNA was extracted and stored at −80℃. Subsequently, mRNA was amplified by PCR and cDNA was synthesized by real-time PCR. Protein levels in lysates from cultured HDPC were assessed by SDS-PAGE and Western blotting. PGE₂ was found to increase HSP70 mRNA levels and decrease MGP mRNA levels in a concentration-dependent manner. Furthermore, phosphorylated-Smad 1/5/8 and Smad 6 levels were higher after PGE₂ treatment. These results indicate that PGE₂ enhances HSP70 mRNA expression in dentalpulp and decreases MGP mRNA expression. PGE₂ stimulation at 1μM also promotes the expression of Smad6, an Anti-Smad, thereby inhibiting Smad1/5/8 phosphorylation, blocking BMP signaling and inhibiting hard tissue formation.