Altered Pulpal Mineralization Potential Associated with Radicular Dentin Dysplasia

Radicular dentin dysplasia (RDD) is a rare disorder resulting in abrogated tooth root formation and premature tooth exfoliation. This disease often presents with mild to severe crown pulpal calcification with lack of radicular dentin. Our laboratory has identified a NFIC alteration associated with a novel autosomal recessive (AR) form of RDD. NFI-C is a transcription factor essential for normal root development. Nfic-deficient mice exhibit aberrant odontoblasts, missing molar roots with no radicular dentin, exfoliation of molars, and severely deformed incisors. During odontogenesis, the TGF-β/BMP signaling pathway and non-collagenous SIBLING proteins have been shown to play critical roles in regulating odontoblast cytodifferentiation and matrix formation and mineralization. Objective: To determine the differentiation potential and mineralization pattern of AR-RDD dental pulp (DP) cells in context to the identified NFIC mutation. Methods: DP cultures were established from AR-RDD patient samples and compared with age- and sex-matched controls. Total RNA was isolated from samples and processed for comprehensive gene array analysis using Affymetrix Human Exon 1.0 ST platform. Data were analyzed using GeneSpring GX11 Analysis. Selected gene expression differences were validated using qRT-PCR and/or Western blot analysis. Alizarin Red staining was performed at two-day intervals for 14 days to examine mineralization potential. Results: DP cells were able to differentiate into odontoblast-like cells associated with matrix mineralization. AR-RDD microarray analysis revealed 718 genes downregulated and 1022 upregulated (> 2-fold change). qRT-PCR confirmed that COL1A1, IL-6, LTBP1, LTBP4, TGFBRI, and TGIF1 were significantly downregulated, whereas ALP, BMPR1B, DSPP, and OPN were significantly upregulated. Conclusions: These results suggest that NFI-C plays an important role in the regulation of genes critical for matrix mineralization and associated signaling during odontoblast cytodifferentiation. Disruption of these finely-tuned events coordinating  dentinogenesis and subsequent root formation might explain the enhanced pulpal calcification and defects in root development that characterize AR-RDD. Support: NIDCR-T-32DE017607DART/1F30DE021945(AG).