Trps1 Represses Mineralization through Regulation of Phosphate Homeostasis Genes

Objective: Mineralization is a process whereby crystals of calcium phosphate are laid down within a protein scaffold of the extracellular matrix. The balance of inorganic pyrophosphate and phosphate is critical for the regulation of this process and is maintained both systemically and in the local cellular environment. In our previous studies, we demonstrated that Col1a1-Trps1 transgenic mice that overexpress Trps1 specifically in odontoblasts and osteoblasts present with severe impairment of dentin mineralization. The aim of this study is to elucidate the molecular mechanism of Trps1-mediated repression of odontoblast function.

Methods: The 17IIA11 preodontoblastic cell line, which is capable of producing mineralizing matrix when cultured in differentiation conditions, was used to generate a Trps1-overexpressing line. Effects of Trps1 overexpression on mineralization were evaluated by alkaline phosphatase and alizarin red staining. Changes in gene expression patterns were analyzed by an Affimetrix Mouse Exon 1.0 ST Array and confirmed by qRT-PCR and immunofluorescence. Additionally, expression of selected genes was analyzed in teeth of Col1a1-Trps1 transgenic mice.

Results:  Overexpression of Trps1 in the 17IIA11 preodontoblastic cell line resulted in impaired mineralization, thus confirming that Trps1 represses odontoblast function both in vitro and in vivo.  Analyses of gene expression revealed significant down-regulation of multiple genes involved in mineralization. In particular, aberrant expression of genes involved in phosphate metabolism was detected in 17IIA11 cells overexpressing Trps1 and in odontoblasts of Col1a1-Trps1 transgenic mice.

Conclusion:  Collectively, these results indicate that Trps1 has a repressive role in mature secretory odontoblasts, and that this repressive function might be mediated through genes involved in phosphate metabolism.

Support: NIH/NIAMSR03AR057128, NIDCR-5T32DE017607DART