Disturbance of NFI-C Gene Induces Apoptosis and Cell-growth-Arrest in Odontoblasts

Objective: Our previous studies have demonstrated that nuclear factor I-C (NFI-C) null mice developed short molar roots which contain aberrant odontoblasts and abnormal dentin formation. Based on these findings, studies were performed to uncover the underlying mechanism of NFI-C function in odontoblasts. Methods: We examined the expression of TGFβ-RI and p-Smad2/3 in incisors from normal and Nfic (-/-) mice by immunohistochemistry and western blot. Proliferation and apoptosis of the cells were investigated by BrdU and Tunel POD staining. Expression of cell-growth related genes and proteins was evaluated by RT-PCR and western blot. Result: Disturbance of the Nfic gene increased the expression of TGFβ-RI and p-Smad2/3 in aberrant odontoblasts and sub-odontoblastic pulpal cells. Cell proliferation analysis of both cervical loop and ectomesenchymal cells of the Nfic (-/-) mice revealed a significantly decreased proliferation activity compared to normal mice. Nfic (-/-) primary pulp cells showed increased expression of p21 and p16, but decreased expression of cyclin D1 and cyclin B1, strongly suggesting a cell growth arrest when the Nfic gene function was disturbed. Aberrant odontoblasts and sub-odontoblastic cells in Nfic (-/-) mice exhibited an increased apoptotic activity. Further, Nfic (-/-) primary pulp cells increased not only the expression of Fas and FasL but also the activation of caspase-8 and -3, while the cleaved form of Bid was hardly detected. Conclusion: These results indicate that disturbance of the Nfic gene suppresses odontogenic cell proliferation and induces apoptosis of aberrant odontoblasts by up-regulating the expression of TGFβ-RI and its downstream signaling molecules during root formation, contributing to the formation of short roots. This work was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MOST)(No. M10646010002-06N4601-00210)