The Role of Prostaglandin E2 on Osteoblast Proliferation Induced by Hydroxyapatite

Erwan Sugiatno,Endang Herminajeng,Wihaskoro Sosroseno

doi:10.4236/jbm.2020.81006

Abstract

Objective: Prostaglandin E2 (PGE2) plays a crucial role in regulating bone cell differentiation and proliferation. The aim of the present study was to determine whether PGE2 may regulate osteoblast proliferation induced by hydroxyapatite. Materials and Methods: Osteoblasts (HOS cell line) pre-treated with cyclooxygenase (COX) inhibitors (indomethacin, aspirin and nimesulide) were then cultured. The cells were also pre-treated with or without nimesulide and then cultured with PGE2. The cell cultures were also treated with SQ22536 (adenylyl cyclase inhibitor) and added with Db-cAMP (cAMP analog), and/or PGE2. KT5720 [protein kinase A (PKA) inhibitor.], Db-cAMP and/or forskolin (adenylyl cyclase activator)-treated cultures were used to assess the role of PKA. The role of EP2 and/or EP4 was determined by using EP2 antagonist (PF-04418948) and EP4 antagonist (L-161,982) with PGE2. All cells were cultured with or without hydroxyapatite. The levels of PGE2 and cAMP were detected from the culture supernantants and the cell proliferation was assessed colorimetrically. Results: Nimesulide and indomethacin but not aspirin suppressed partially the cell proliferation but fully PGE2 production. PGE2 abrogated nimesulide-mediated suppression of cell proliferation. The cell proliferation was enhanced by low but suppressed by high concentration of PGE2. Moreover, the SQ22536-mediated suppression of cell proliferation was abolished by Db-cAMP but not PGE2. Conversely, PGE2, Db-cAMP or forskolin failed to eliminate KT5720-mediated suppression of cell proliferation. The effect of PGE2 on cell proliferation and cAMP levels was mediated predominantly via EP2 and to a lesser extent, EP4. The results of the controls for all experiments were significantly lower than hydroxyapatite-stimulated cell cultures. Conclusion: These results suggest thatPGE2, acting via a COX-2-, cAMP-PKA- and both EP2 and EP4-dependent pathway may partially regulate hydroxyapatite-induced human osteoblasts in an autocrine fashion.

Highlights

Prostaglandin E2 (PGE2), a prostanoid produced by the action of cyclooxygenases (COX-1 and COX-2) on arachidonic acid, is known as a potent regulator on bone remodeling, since it has ability to activate osteoclast and osteoblast differentiation and proliferation by binding with its receptors, i.e., EP1, EP2, EP3, and EP4 [1]
This notion is supported by the current study that the suppressive effect of COX-2 inhibitor on osteoblast proliferation even without hydroxyapatite could be abolished by exogenous PGE2, indicating that the COX-2-mediated PGE2 pathway may be a part of the multiple signal transduction networks which regulate osteoblast proliferation and that hydroxyapatite-stimulated PGE2 may further augment this signaling network (Figure 7)
The PGE2 production and partial cell proliferation by human osteoblasts stimulated with hydroxyapatite were a COX-2-dependent mechanism

Summary

Introduction

Prostaglandin E2 (PGE2), a prostanoid produced by the action of cyclooxygenases (COX-1 and COX-2) on arachidonic acid, is known as a potent regulator on bone remodeling, since it has ability to activate osteoclast and osteoblast differentiation and proliferation by binding with its receptors, i.e., EP1, EP2, EP3, and EP4 [1]. It seems plausible that all four PGE2 receptors may play a regulatory role in the dynamic bone remodeling. Bone remodeling at the site of implantation seems to be under regulation of PGE2. The effect of PGE2 on bone remodeling may be dependent on the concentration of this cytokine. This notion was based on the fact that low and high concentration of PGE2 induce bone formation and destruction in the implanted site, respectively [9]

Methods

Results

Discussion

Conclusion