TGF-beta/BMP Pathway Dysregulation in Radicular Dentin Dysplasia EOE

 

The TGF-beta/BMP family is critical for primary tooth development (odontogenesis) and subsequent mineralized extracellular matrix formation (dentin and enamel). Transgenic mice studies have shown members of this signaling pathway regulate epithelial-mesenchymal interactions during tooth and root formation. Cells of the enamel organ epithelium (EOE) contribute to the formation of Hertwig’s epithelial root sheath that is essential to root development. Radicular dentin dysplasia (RDD) is a rare inherited disorder that results in incomplete or absent root formation in both dentition. We have identified a nuclear factor I-C (NFI-C) alteration associated with a novel autosomal recessive (AR) form of RDD. NFI-C, a member of NFI gene family, functions as a transcription factor and has been shown to be critical for root development in mice. Objective: To describe the NFI-C mutation related to its biological function in root formation and determine its role in the TGF-beta/BMP signaling dysregulation in AR-RDD EOE cells. Methods: Primary cultures of EOE cells from an AR-RDD patient and normal control (age- and sex-matched) were expanded and used for matrix mineralization studies, immunocytochemistry and TGF-beta/BMP signaling pathway PCR array analysis. Results: Morphologically, the AD-RDD EOE cells represent a heterogenous population of with similar patterns of alkaline phosphatase (ALP) expression to control EOE cells. Furthermore, the AR-RDD mutation did not alter the expression pattern and nuclear translocation of the NFI-C protein. However, TGF-b/BMP signaling pathway genes were dysregulated in AR-RDD EOE cells compared to control. Of the 84 genes related to TGF-beta/BMP-mediated signal transduction tested 34 were down-regulated and 4 up-regulated greater than 2 fold. Many of these genes (including BMP4) are important in epithelial-mesenchymal interactions leading to root development. Conclusions: Our studies indicate that the NFI-C mutation associated with AR-RDD interferes with normal TGF-beta/BMP signaling cascade critical for root formation allowing novel downstream target genes to be identified. Support: UAB-SOD-IOHR/NIDCR-5T32DE01607DART/F30DE0180803(EL)/F30DE021945(AG).