Study of endoplasmic reticulum stress response in osteogenic differentiation of human periodontal ligament cells

Abstract

The aim of this study was to establish whether endoplasmic reticulum (ER) stress is involved in osteogenic differentiation of periodontal ligament cells (PDLCs) and to better understand the mechanism of PDLCs osteogenic differentiation. PDLCs were isolated from extracted teeth and cultured in presence or absence of osteogenic medium, which can induce osteogenic differentiation of PDLCs. Alkaline phosphatase and alizarin red S staining were performed to characterize the osteogenic differentiation of PDLCs. The mRNA and protein levels of ER stress markers were examined by RT-PCR and Western blot analysis. The data were analyzed with SPSS 17.0 software package. Cell treated with osteogenic medium showed increased expression of alkaline phosphatase, increased matrix, and mineralized nodule formation compared with untreated controls. Treatment with osteogenic induction resulted in up-regulation of genes, such as splicing x-box binding protein-1 (sXBP1), activating transcription factor 4 (ATF4) and glucose-regulated protein 78 (GRP78). The expressions of ER stress protein markers, phosphorylated RNA-activated protein kinase-like ER-resident kinase (p-PERK), phosphorylated eukaryotic initiation factor-2α (p-eIF2α), increased in osteogenic induction cells compared with controls. The results indicate that ER stress response is involved in the process of osteogenic differentiation of PDLCs.