ENAMEL WITH OVEREXPRESSED AMELOBLASTIN

Developmental defects of enamel include molar-incisor hypomineralization (MIH). This condition affects thequality and quantity of enamel and severely disrupts oral functions in children with loss of occlusion, toothsensitivity and increased caries susceptibility. Children with MIH have greater needs for dental treatmentthroughout their life and often exhibit dental behavioral management problems. MIH is found in manydifferent populations worldwide with a prevalence ranging from 2.4% to 40.2%. The enamel organepithelium is affected by unknown factors resulting in MIH. The pathophysiology of MIH is not understood.Therapeutic options are limited to conventional therapy with fluoride applications, restorations often withpoor retention and extractions. Enamel formation into the hardest mineral is promoted by enamel matrixproteins. One of the enamel proteins is ameloblastin (Ambn) accounting for 5% of the enamel proteins. Inhypomineralized enamel, the mineral content does not reach the necessary concentration. Ambn wasidentified in hypomineralized enamel of extracted teeth, but it is not clear if it plays a role in thepathogenesis of MIH. We have developed a mouse model to study the effect of Ambn overexpression inMIH-like enamel in enamel organ epithelium. When Ambn is overexpressed, the enamel in these micedisplays white, demarcated ?patches? that fracture easily from the dentin. The MIH mouse model will serveto dissect the cellular and molecular events in enamel hypomineralization to identify strategies for thediagnosis, prevention and therapy of hypomineralized enamel.We have developed transgenic mice with demarcated, MIH-like lesions in enamel. Our preliminary resultsshow that the lesions enlarge as the ameloblastin (Ambn) concentration increases. Normally, enamel matrixis rapidly processed, degraded and internalized by ameloblasts, but when Ambn is overexpressed, theenamel matrix lingers on and the accumulation of mineral is hampered, manifesting as hypomineralizedenamel. We have developed tools to accurately quantify mineral content and enamel volume with microCTmethods. In a transcriptome analysis of enamel organ epithelium pathways for enamel matrix, enzymaticdegradation, protein trafficking and ion handling were dysregulated. Our overall hypothesis is thatoverexpressed ameloblastin influences the mechanisms of enamel formation resulting in MIH lesions inenamel. In SA1 we will determine the onset of demarcated opacities within the phased formation of enamel inmice overexpressing Ambn. In SA2, we will determine the biological pathways of endocytosis of enamelproteins in vivo and in vitro as a consequence of ameloblastin overexpression. In SA3, we will determine ifendocytosis of overexpressed Ambn can be promoted in Ambn mice by increasing the enzymatic activity inthe enamel matrix. For the proposed studies a team of clinician scientists, experts in quantitative imaging,proteomics and bioinformatics has been assembled for unique interaction and novel approaches.