Effect of PGE2 induced by compressive and tensile stresses on cementoblast differentiation in vitro.

OBJECTIVE: The aim of the study was to clarify the mechanisms underlying orthodontically induced root resorption by characterizing the role of PGE(2) induced by compressive stress (CS) and tensile stress (TS) on cementoblast metabolism in vitro. DESIGN: Mouse cementoblast cell line OCCM-30 was continuously stimulated with 0.2 KPa CS or 5.0 KPa TS. COX-2 mRNA expression and PGE(2) production were thus quantified. In addition, cells were treated with COX-2 inhibitor and the role of PGE(2) induced by CS or TS on the expression of genes related to cementoblast differentiation was examined. PGE(2) receptors mRNA expression induced by CS or TS was also evaluated. Moreover, cells were treated with exogenous PGE(2) and the role of PGE(2) concentration on matrix mineralization was verified. RESULTS: CS and TS enhanced COX-2 mRNA expression and PGE(2) production. PGE(2) synthesis, however, was markedly induced by CS. Gene expression of bone morphogenetic protein 2 (BMP-2), osteocalcin (OCN) and receptor activator for nuclear factor kappaB ligand (RANKL) was enhanced by CS on an endogenous PGE(2)-mediated manner. Osteoprotegerin (OPG) expression was not affected by CS. Meanwhile, TS up-regulated the expression of BMP-2 and alkaline phosphatase (ALP) on an endogenous PGE(2)-mediated manner. TS down-regulated RANKL mRNA expression, whilst OPG expression was not affected. Moreover, EP4 mRNA expression was considerably enhanced by TS. Regarding PGE(2) concentration, only cells treated with low concentration presented anabolic response. CONCLUSIONS: Gene expression was differentially regulated according to the type of mechanical stimulation applied to cementoblasts. In addition, it is shown that PGE(2) plays an important role on mediating cementoblast mechanosensitivity.