Novel insights into the genetic etiology of pulp stones

Despite the clinical relevance of ectopic pulp calcifications as an obstacle for endodontic treatment, the underlying mechanisms have not been clearly defined. Objectives: We tested the novel hypothesis that pulp stones are a result of an altered function of Twist-1, a nuclear protein. In osteogenesis, Twist-1 partners with Runx2 to control the onset of osteoblast differentiation and mineralization. Since osteoblasts and odontoblasts share a similar genetic profile, it is likely that Twist-1 also controls odontoblast differentiation and function. Methods: Twist-1 mRNA expression in wildtype tissues (brain, calvaria, kidney, liver, lung, molars) at several pre- and postnatal stages was investigated using RT-PCR analysis with Twist-1-specific primers. Sections of Twist-1 (+/-) tissues at day 0, 7, 21, 45, 60 and 120 were prepared. Histologic analysis was performed using H&Es, Masson's trichrome and stains for alkaline phosphatase. In situ-hybridization with RNA-ribobrobes for Col á(I) I and Dspp was carried out. To determine whether Twist-1 protein regulates Dspp expression we performed DNA cotransfection experiments. Results: RT-PCR analysis showed the presence of Twist-1 transcripts in all tissues and stages. Phenotypic studies of Twist-1 (+/-) mice revealed changes in dentition; most striking was the finding of matrix deposits within the pulp. Multiple nonspecific deposits showing a homogenous structure were found within blood vessels, fewer deposits exhibiting dentin-like structure could be observed within the pulp. Alkaline phosphatase activity was increased and spatially extended. The molecular assays imply a regulatory function of Twist-1 on Dspp, a gene specifically expressed in odontoblasts, which is involved in matrix mineralization. Conclusions: These findings suggest a role of Twist-1 in regulating pulpal homeostasis and introduce the new perspective of disordered mineralization as an effect of altered genetic background. This investigation was supported by NIH/NIDCR Grant #DE13368 to Rena D‘Souza and by a grant of the German Academic Exchange Service to Kerstin Galler.