Abstract
Periodontal ligament contains periodontal ligament stem cells that maintain tissue homeostasis. Targeting hPDLSCs (human periodontal ligament cells) is a promising strategy for repair and regeneration of bone tissue destroyed by periodontal diseases. However, the mechanisms by which PDLSCs differentiate into osteoblasts to form a mineralized matrix is unclear. In this study, we demonstrate for the first time the molecular events that contribute to osteogenic differentiation of PDLSCs. Dentin matrix protein 1 (DMP1) and its receptor, Glucose regulated protein-78 (GRP78), are localized in the progenitor cells of the PDL. Our overall goal is to demonstrate the formation of DMP1-GRP78 complex at the plasma membrane and subsequent protein trafficking and nuclear localization to promote osteogenic differentiation. To study the internalization and routing of the complex, we mimic an in vivo differentiation scenario by stimulating cells with DMP1 and culturing them in the presence of osteogenic differentiation conditions. We first demonstrate the translocation of the ER chaperone protein GRP78 to the plasma membrane during the differentiation process. Total internal reflection microscopy imaging demonstrates the formation and internalization of the receptor- ligand (GRP78-DMP1) complex. Confocal microscopy results show the internalization of the GRP78-DMP1 complex specifically through the caveolin pathway and trafficked through the cell with various endocytic markers such as Rab5 and 7 GTPases to early and late endosomes respectively. DMP1 is ultimately transported to the nucleus where it functions to promote osteogenic differentiation as demonstrated by quantitative Real-Time PCR. This observation is the first report that suggests DMP1 and GRP78 can interact at the plasma membrane, then packaged in vesicles and ultimately DMP1 is routed to the nucleus where it aids in osteogenic differentiation of PDLSCs. Characterizing the osteogenic potential of PDLSCs would favor the development of therapeutic strategies for reconstruction of mineralized tissues destroyed by periodontal diseases.
Highlights
The healthy periodontium, consisting of the gingiva, alveolar bone, periodontal ligament and cementum, functions in anchoring the tooth to the alveolar bone
We demonstrate the osteogenic differentiation of periodontal ligament stem cells (PDLSCs) by utilizing a regulatory matrix molecule Dentin matrix protein 1 (DMP1) and its receptor Glucose regulated protein-78 (GRP78)
We have previously demonstrated that DMP1 in the ECM can be internalized with the aid of its receptor GRP78 localized on the plasma membrane of osteoblasts (Ravindran et al, 2008)
Summary
The healthy periodontium, consisting of the gingiva, alveolar bone, periodontal ligament and cementum, functions in anchoring the tooth to the alveolar bone. In pathological conditions such as periodontal diseases, trauma or excessive force, destruction of the periodontal tissue can occur and result in loss of tooth structure in the adults (Mortazavi and Baharvand, 2016). PDLSCs are capable of differentiating into osteoblasts, cementoblasts and fibroblasts, making them a unique population of adult stem cells (Zhu and Liang, 2015). PDLSCs were used in this study to demonstrate their feasibility in promoting osteogenic differentiation as the adult stem cells from different tissues have unique epigenetic and transcription factors to regulate its function. The regeneration of bone is a complicated process, stem cells have been proven to be advantageous in developing new strategies to overcome these issues
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
