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Patients with cleidocranial dysplasia (CCD) caused by mutations in RUNX2 have severe dental anomalies, including delayed or absent eruption of permanent teeth. This requires painful and expensive surgical/orthodontic intervention because of the absence of medicine for this condition. Here, we demonstrate that nicotinamide, a vitamin B3 and class III histone deacetylase inhibitor, significantly improves delayed tooth eruption in Runx2 +/- mice, a well-known CCD animal model, through the restoration of decreased osteoclastogenesis. We also found that Csf1 mRNA and protein levels were significantly reduced in Runx2 +/- osteoblasts as compared with wild type whereas RANKL and OPG levels had no significant difference between wild type and Runx2 +/- osteoblasts. The nicotinamide-induced restoration of osteoclastogenesis of bone marrow-derived macrophages in Runx2 +/- mice was due to the increased expression of RUNX2 and CSF1 and increased RANKL/OPG ratio. RUNX2 directly regulated Csf1 mRNA expression via binding to the promoter region of the Csf1 gene. In addition, nicotinamide enhanced the RUNX2 protein level and transacting activity posttranslationally with Sirt2 inhibition. Taken together, our study shows the potential and underlying molecular mechanism of nicotinamide for the treatment of delayed tooth eruption by using the Runx2 +/- murine model, suggesting nicotinamide as a candidate therapeutic drug for dental abnormalities in patients with CCD.

Objective: Mutations in the RUNX2 gene, a master regulator of bone formation, have been identified in cleidocranial dysplasia (CCD) patients. CCD is a rare autosomal-dominant disease characterized by the delayed closure of cranial sutures, defects in clavicle formation, and supernumerary teeth. The purposes of this study were to identify genetic causes of two CCD nuclear families and to report their clinical phenotypes., Materials and Methods: We identified two CCD nuclear families and performed mutational analyses to clarify the underlying molecular genetic etiology., Results: Mutational analysis revealed a novel nonsense mutation (c.273T>A, p.L93X) in family 1 and a de novo missense one (c.673C>T, p.R225W) in family 2. Individuals with a nonsense mutation showed maxillary hypoplasia, delayed eruption, multiple supernumerary teeth, and normal stature. In contrast, an individual with a de novo missense mutation in the Runt domain showed only one supernumerary tooth and short stature., Conclusions: Mutational and phenotypic analyses showed that the severity of mutations on the skeletal system may not necessarily correlate with that of the disruption of tooth development.