Activation of periodontal ligament cell cytodifferentiation by juxtacrine signaling from cementoblasts

BACKGROUND: New cementum forms from existing cementum during periodontal tissue regeneration, indicating that cementoblasts may interact with progenitor cells in the periodontal ligament to enhance cementogenesis. However, the molecular mechanisms of this process are currently unknown. This study aims to clarify the role of cell-cell interactions between cementoblasts and periodontal ligament cells in differentiation into cementoblasts. METHODS: To analyze the role of human cementoblast-like cells (HCEMs) on human periodontal ligament cells (HPDLs), we mixed cell suspensions of enhanced green fluorescent protein-tagged HPDLs and HCEMs, and then seeded and cultured them in single wells (direct co-cultures). We sorted co-cultured HPDLs and analyzed their characteristics, including the expression of cementum-related genes. In addition, we cultured HPDLs and HCEMs in a non-contact environment using a culture system composed of an upper insert and a lower well separated by a semi-permeable membrane (indirect co-cultures), and similar analysis was performed. Gene expression of integrin-binding sialoprotein (IBSP) in cementoblasts was confirmed in mouse periodontal tissues. We also investigated the effect of Wingless-type (Wnt) signaling on the differentiation of HPDLs into cementoblasts. RESULTS: Direct co-culture of HPDLs with HCEMs significantly upregulated the expression of cementoblast-related genes in HPDLs, whereas indirect co-culture exerted no effect. Wnt3A stimulation significantly upregulated IBSP expression in HPDLs, whereas inhibition of canonical Wnt signaling suppressed the effects of co-culture. CONCLUSION: Our results suggest that direct cell interactions with cementoblasts promote periodontal ligament cell differentiation into cementoblasts. Juxtacrine signaling via the canonical Wnt pathway plays a role in this interaction.