RUNX2 mutation reduces osteogenic differentiation of dental follicle cells in cleidocranial dysplasia

Disturbed permanent tooth eruption is common in cleidocranial dysplasia (CCD), a skeletal disorder caused by heterozygous mutation of RUNX2, but the mechanism underlying is still unclear. As it is well known that dental follicle cells (DFCs) play a critical role in tooth eruption, the changed biological characteristics of DFCs might give rise to disturbance of permanent tooth eruption in CCD patients. Thus, primary DFCs from one CCD patient and normal controls were collected to investigate the effect of RUNX2 mutation on the bone remodeling activity of DFCs and explore the mechanism of impaired permanent tooth eruption in this disease. Conservation and secondary structure analysis revealed that the RUNX2 mutation (c.514delT, p.172fs) found in the present CCD patient was located in the highly conserved RUNT domain and converted the structure of RUNX2. After osteogenic induction, we found that the mineralised capacity of DFCs and the expression of osteoblast-related genes, including RUNX2, ALP, OSX, OCN and Col I alpha 1, in DFCs was severely interfered by the RUNX2 mutation found in CCD patients. To investigate whether the osteogenic deficiency of DFCs from the CCD patient can be rescued by RUNX2 restoration, we performed 'rescue' experiments. Surprisingly, the osteogenic deficiency and the abnormal expression of osteoblast-associated genes in DFCs from the CCD patient were almost rescued by overexpression of wild-type RUNX2 using lentivirus. All these findings indicate that RUNX2 mutation can reduce the osteogenic capacity of DFCs through inhibiting osteoblast-associated genes, thereby disturbing alveolar bone formation, which serves as a motive force for tooth eruption. This effect may provide valuable explanations and implications for the mechanism of delayed permanent tooth eruption in CCD patients.