Endoplasmic Reticulum Stress Response is Involved in Osteogenic Differentiation of Human Periodontal Ligament Cells

Objectives: Periodontal ligament cells (PDLCs) have osteogeinc differentiation potential, which plays a key role in periodontal regeneration. However, the mechanism remains unclear. Endoplasmic reticulum (ER) stress response, which is an essential adaptive cellular response to cellular stress conditions, is thought to regulate cells’ protein synthesis and even be associated with bone formation. The aim of this study is to establish whether ER stress is involved in osteogenic differentiation of PDLCs to better understand the mechanism of PDLCs osteogenic differentiation.
Methods: PDLCs were isolated from extracted teeth and cultured in presence or absence of osteogenic medium, which can induce osteogenic differentiation of PDLCs in vitro. Alkaline phosphatase and Alizarin red S staining were performed to characterize the osteogenic differentiation of PDLCs. Real-time polymerase chain reactions (RT-PCR) were performed to analyze the expression of several genes involved in PDLCs osteogenic differentiation. The mRNA and protein levels of ER stress markers were examined by RT-PCR and western blot analysis.
Results:
Osteogenic medium treated cells showed increased expression of alkaline phosphatase, increase matrix, and mineralized nodule formation when compared with untreated controls. Treatment with osteogenic induction resulted in the up-regulation of genes, such as osteocalcin (OCN), bone sialoprotein (BSP), type Ⅰ collagen-A (COL-ⅠA), 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 the 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.
Conclusions: These results indicate that ER stress response is involved in the process of osteogenic differentiation of PDLCs.