The involvement of platelet-derived growth factor receptors and insulin-like growth factor-I receptors signaling during mineralized nodule formation by human periodontal ligament cells

Background and objective: Periodontal ligament cells are regarded to have the capacity to differentiate into cementoblasts or osteoblasts, and are capable of forming a mineralized nodule in vitro. However, the precise mechanisms are unclear. Here we evaluated the possible involvement of growth factor receptors, such as the platelet-derived growth factor receptor (PDGFR), insulin-like growth factor-I receptor (IGF-IR), and epidermal growth factor receptor (EGFR) on periodontal ligament cells and their ligands during periodontal ligament cells differentiation in vitro. Methods: Human periodontal ligament cells were differentiated via culturing in the presence of dexamethasone, ascorbic acid, and β-glycerophosphate for mineralized nodule formation, characterized by von Kossa staining. Expressions of receptors and their ligands were analyzed by flow cytometry/reverse transcription-polymerase chain reaction. Results: During the differentiation, PDGFR-α was held at a lower level compared with the control. PDGFR-β, however, was maintained at a slightly higher level that was reversed to the control level when mineralized nodules formed. In contrast, IGF-IR and EGFR were not substantially different from the control. The mineralized nodule formation was strongly inhibited by a PDGFR kinase blocker (AG1295 and AG1296), partially inhibited by an IGF-IR kinase blocker (I-Ome-AG538 and AG1024), and not inhibited by an EGFR kinase blocker (AG99). PDGF-A, PDGF-C, PDGF-D, IGF-I, and IGF-II, but not PDGF-B, were expressed on the control as well as dexamethasone/ascorbic acid-treated periodontal ligament cells during mineralized nodule formation; however, the pattern of their expressions was quite different. Conclusion: These findings suggest that a pathway of PDGFs/PDGFR and IGFs/IGF-IR on periodontal ligament cells are involved during mineralized nodule formation, and that PDGFs and IGFs expressed by periodontal ligament cells may contribute to the formation.