CPNE7 and NFI-C mediate odontoblast differentiation and dentin formation

Abstract

During the process of tooth morphogenesis, numerous signaling molecules and transcription factors mediate odontoblast differentiation and dentin formation through sequential epithelial-mesenchymal interactions. Dentin is formed by odontoblasts which secrete extracellular matrix (ECM) proteins. Among ECM proteins, dentin sialophosphoprotein (DSPP) is the most abundant ECM in dentin. However, the precise function and molecular mechanisms of odontoblast differentiation are still under investigation. In the present study, we investigated biological function and mechanisms of Cpne7 and NFI-C in regulation of odontoblast differentiation. Cpne7 was expressed in preameloblasts and inner enamel epithelium.The secreted Cpne7 was translocated to differentiating odontoblasts. In odontoblasts, Cpne7 promoted odontoblastic markers and mineralized nodule formationin vitro. Moreover, Cpne7 induces the differentiation of dental pulp cells into odontoblasts and dentin formation in vivo. Mechanistically, Cpne7interacted with Nucleolin and Cpne7-Nucleoin complex promoted the expression of Dspp. Zinc deficiency is involved in bone malformations and oral disease. Mice deficient in zinc transporter Zip13 show connective tissue and skeletaldisorders, abnormal incisor teeth, and reduced root dentin formation in the molar teeth and share a morphologically similar phenotype tonuclear factor I-C (NFI-C)-deficient mice. In the present study, we determined the NFI-C signaling on odontoblastdifferentiation and dentin formation with altered zinc concentration. Zinc enhanced the binding efficiency of NFI-C and phosphorylation of Smad2/3(p-Smad2/3) in the cytoplasm. In zinc deficiency, NFI-C accumulated into nucleus, and NFI-C bound to the Dspp promoter and regulated Dspp gene transcription. Furthermore, zinc deficiency condition promotedDSPP expression in odontoblasts and dentin mineralization, while zinc sufficiency condition decreased DSPP expression and slightly delayeddentin mineralization. Taken together, Cpne7 and NFI-C signaling regulate odontoblast differentiation and dentin formation through modulation of Dspp gene transcription.