The leucine-rich amelogenin peptide alters the amelogenin null enamel phenotype

Abstract

Introduction: The amelogenin proteins secreted by ameloblasts during dental enamel development are required for normal enamel structure. Amelx null (KO) mice have hypoplastic, disorganized enamel similar to that of human patients with mutations in the AMELX gene, and provide a model system for studies of the enamel defect amelogenesis imperfecta. Because many amelogenin proteins are present in developing enamel due to RNA alternative splicing and proteolytic processing, understanding the function of individual amelogenins has been challenging.

Purpose: Our objective was to better understand the role of LRAP, a 59 amino acid leucine-rich amelogenin peptide, in the development of enamel.

Approach: Teeth from transgenic mice that express LRAP under control of the Amelx regulatory regions were analyzed for mechanical properties, and transgenic males were mated with female KO mice. Male offspring with a null background that were transgene positive or transgene negative were compared to determine phenotypic differences using microcomputed tomography (microCT) and scanning electron microscopy (SEM).

Results: Nanoindentation revealed no differences between LRAP transgenic and wild-type murine enamel. Using microCT, LRAPKO enamel volume and density measurements were similar to those from KO mice. However, in etched samples examined by SEM, the organization of the enamel rod pattern was altered by the presence of the LRAP transgene.

Conclusions: The presence of LRAP leads to changes in enamel appearance compared to enamel from KO mice. Expression of a combination of amelogenin transgenes in KO mice may lead to rescue of the individual characteristics of normal enamel.

Fig. 1.

SEM images of fractured incisors. a TgLRAP incisor showing enamel rods characteristic of normal enamel structure. b KO incisor with aprismatic enamel lacking rod structure.

Fig. 2.

SEM images of etched KO teeth. Incisor (a) and molar (b), with a layer of aprismatic enamel adjacent to the junction with dentin.

Fig. 3.

SEM images of etched TgLRAPKO teeth. Incisor (a) and molar (b), both of which reveal some prismatic organization in the enamel layer.

Fig. 4.

SEM image of etched TgLRAPKO incisor, showing some prismatic structure at higher magnification.