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Abstract Runt-related transcription factor 2 (Runx2)-deficient mice can be used to model congenital tooth agenesis in humans. Conversely, uterine sensitization-associated gene-1 (Usag-1)-deficient mice exhibit supernumerary tooth formation. Arrested tooth formation can be restored by crossing both knockout-mouse strains; however, it remains unclear whether topical inhibition of Usag-1 expression can enable the recovery of tooth formation in Runx2-deficient mice. Here, we tested whether inhibiting the topical expression of Usag-1 can reverse arrested tooth formation after Runx2 abrogation. The results showed that local application of Usag-1 Stealth small interfering RNA (siRNA) promoted tooth development following Runx2 siRNA-induced agenesis. Additionally, renal capsule transplantation of siRNA-loaded cationized, gelatin-treated mouse mandibles confirmed that cationized gelatin can serve as an effective drug-delivery system. We then performed renal capsule transplantation of wild-type and Runx2-knockout (KO) mouse mandibles, treated with Usag-1 siRNA, revealing that hindered tooth formation was rescued by Usag-1 knockdown. Furthermore, topically applied Usag-1 siRNA partially rescued arrested tooth development in Runx2-KO mice, demonstrating its potential for regenerating teeth in Runx2-deficient mice. Our findings have implications for developing topical treatments for congenital tooth agenesis.

Abstract Analysis of various genetically modified mice, with supernumerary teeth, has revealed the following two intrinsic molecular mechanisms that increase the number of teeth. One plausible explanation for supernumerary tooth formation is the rescue of tooth rudiments. Topical application of candidate molecules could lead to whole tooth formation under suitable conditions. Congenital tooth agenesis is caused by the cessation of tooth development due to the deletion of the causative gene and suppression of its function. The arrest of tooth development in Runx2 knockout mice, a mouse model of congenital tooth agenesis, is rescued in double knockout mice of Runx2 and Usag-1. The Usag-1 knockout mouse is a supernumerary model mouse. Targeted molecular therapy could be used to generate teeth in patients with congenital tooth agenesis by stimulating arrested tooth germs. The third dentition begins to develop when the second successional lamina is formed from the developing permanent tooth in humans and usually regresses apoptotically. Targeted molecular therapy, therefore, seems to be a suitable approach in whole-tooth regeneration by the stimulation of the third dentition. A second mechanism of supernumerary teeth formation involves the contribution of odontogenic epithelial stem cells in adults. Cebpb has been shown to be involved in maintaining the stemness of odontogenic epithelial stem cells and suppressing epithelial-mesenchymal transition. Odontogenic epithelial stem cells are differentiated from one of the tissue stem cells, enamel epithelial stem cells, and odontogenic mesenchymal cells are formed from odontogenic epithelial cells by epithelial-mesenchymal transition. Both odontogenic epithelial cells and odontogenic mesenchymal cells required to form teeth from enamel epithelial stem cells were directly induced to form excess teeth in adults. An approach for the development of targeted therapeutics has been the local application of monoclonal neutralizing antibody/siRNA with cationic gelatin for USAG-1 or small molecule for Cebpb.

Runt-related transcription factor 2 (Runx2)-deficient mice can be used to model congenital tooth agenesis in humans. Conversely, uterine sensitization-associated gene-1 (Usag-1)-deficient mice exhibit supernumerary tooth formation. Arrested tooth formation can be restored by crossing both knockout-mouse strains; however, it remains unclear whether topical inhibition of Usag-1 expression can enable the recovery of tooth formation in Runx2-deficient mice. Here, we tested whether inhibiting the topical expression of Usag-1 can reverse arrested tooth formation after Runx2 abrogation. The results showed that local application of Usag-1 Stealth small interfering RNA (siRNA) promoted tooth development following Runx2 siRNA-induced agenesis. Additionally, renal capsule transplantation of siRNA-loaded cationized, gelatin-treated mouse mandibles confirmed that cationized gelatin can serve as an effective drug-delivery system. We then performed renal capsule transplantation of wild-type and Runx2-knockout (KO) mouse mandibles, treated with Usag-1 siRNA, revealing that hindered tooth formation was rescued by Usag-1 knockdown. Furthermore, topically applied Usag-1 siRNA partially rescued arrested tooth development in Runx2-KO mice, demonstrating its potential for regenerating teeth in Runx2-deficient mice. Our findings have implications for developing topical treatments for congenital tooth agenesis. [ABSTRACT FROM AUTHOR]