Effect of cleidocranial dysplasia‐related novel mutation of RUNX2 on characteristics of dental pulp cells and tooth development

Abstract

Cleidocranial dysplasia (CCD) is an autosomal-dominant disorder caused by a lack of function of one or more alleles of the RUNX2 gene. Mutations of the RUNX2 gene were analyzed in a family with CCD, and a novel nonsense mutation was identified, c. 1096G > T, p.E366X, which was predicted to cause a number of potential dysfunctions. Western blot analysis showed that the novel mutation created a shortened protein product, which lost 155 aa in the C-terminal domain. The mutant protein was detected to be localized mostly in the cytoplasm, not in the nucleus, which demonstrated that transport of the RUNX2 protein into the nucleus was disturbed by the p.E366X mutation. For the first time, RUNX2(+/m) dental pulp cells (DPCs) were isolated from two permanent incisors of the CCD patient. Compared to RUNX2(+/+) controls, RUNX2(+/m) DPCs presented an impeded progression from the G1 to the S phase in the cell cycle, a lower rate of proliferation, weaker ability of calcification, and distinct ultrastructure. More interestingly, the ultrastructural analysis and energy dispersive X-ray spectrometry (EDS) analysis showed that the CCD tooth exhibited insufficient mineralization of enamel and dentin. This study suggests that the truncated RUNX2 mutant protein may be responsible for the alterations of RUNX2(+/m) DPCs, and RUNX2 gene may be involved in dental development by affecting the cell growth and differentiation, which provides new insights into understanding of dental abnormalities in CCD patients.