LAUSR

The function of mammalian periodontal tissues depends on the presence of a non-mineralized periodontal ligament juxtaposed in between mineralized tooth anchorage tissues alveolar bone and root cementum. In the present study we have hypothesized that the Wnt antagonist SFRP1 is an essential regulator of periodontal tissue mineral homeostasis. Our immunoreactions and Western blot data demonstrated that SFRP1 was substantially higher expressed in periodontal ligament fibroblasts than in surrounding alveolar bone progenitors and cementoblasts. SFRP1 was also detected at higher levels in PDL fibroblasts than in dental follicle cells, but the difference was less pronounced. Preferential H3K4me3 active histone mark enrichment on the SFRP1 promoter and a lack of H3K27me3 repression was most dramatic in PDL progenitors, to a lesser degree in dental follicle cells, and not detected in alveolar bone progenitors and cementoblasts. Selective inhibition of SFRP1 using a small molecule inhibitor WAY-316606 demonstrated that SFRP1 block increased PDL cell mineralization and mineralization gene expression such as β-catenin, alkaline phosphatase, osteocalcin, collagen I, and RUNX2. The effect of SFRP1 inhibition on PDL cell mineral homeostasis was confirmed by RNA silencing. These studies also demonstrated that SFRP1 knockdown promotes PDL differentiation through histone H3K4me3-mediated activation of RUNX2 and SP7. Finally, when SFRP1 inhibition and silencing studies were performed using alveolar bone progenitors instead of PDL progenitors, there was little effect on mineralized state control and gene expression, with the exception of osteocalcin, which was dramatically upregulated upon SFRP1 silencing. Together, the results of our study document the highly specific role of the Wnt inhibitor SFRP1 in maintaining the non-mineralized state of periodontal ligament progenitors.