Expression and localization of amelotin, laminin γ2 and odontogenesis-associated phosphoprotein (ODAPH) on the basal lamina and junctional epithelium

Ameloblastin and its multifunctionality in amelogenesis: A review

Extracellular matrix proteins play crucial roles in the formation of mineralized tissues like bone and teeth via multifunctional mechanisms. In tooth enamel, ameloblastin (Ambn) is one such multifunctional extracellular matrix protein implicated in cell signaling and polarity, cell adhesion to the developing enamel matrix, and stabilization of prismatic enamel morphology. To provide a perspective for Ambn structure and function, we begin this review by describing dental enamel and enamel formation (amelogenesis) followed by a description of enamel extracellular matrix. We then summarize the established domains and motifs in Ambn protein, human amelogenesis imperfecta cases, and genetically engineered mouse models involving mutated or null Ambn. We subsequently delineate in silico, in vitro, and in vivo evidence for the amphipathic helix in Ambn as a proposed cell-matrix adhesive and then more recent in vitro evidence for the multitargeting domain as the basis for dynamic interactions of Ambn with itself, amelogenin, and membranes. The multitargeting domain facilitates tuning between Ambn-membrane interactions and self/co-assembly and supports a likely overall role for Ambn as a matricellular protein. We anticipate that this review will enhance the understanding of multifunctional matrix proteins by consolidating diverse mechanisms through which Ambn contributes to enamel extracellular matrix mineralization.

Role of junctional epithelium in maintaining dento-gingival adhesion and periodontal health

The dento-gingival junction comprises multiple epithelia including the junctional epithelium (JE), which is the most coronally-located structural element of the dento-gingival junction that demarcates external from internal periodontal environments. After tooth eruption into the oral cavity, a specialized basal lamina is formed that provides a firm attachment of the JE to the enamel. This attachment prevents microbial species and oral debris from entering subjacent periodontal tissues. Here we discuss the expression of certain JE adhesion molecules and enamel proteins that maintain the health of the dento-gingival junction but that are perturbed in the pathogenesis of periodontitis. We also consider how evolutionary processes have influenced the development of the JE as a specialized adhesion that is well-suited for protection of the dento-gingival junction. A detailed understanding of the biology of the JE will deepen current models of dento-gingival adhesion, potentially clarify inter-patient variability of susceptibility to periodontitis and help to identify new roles of enamel proteins in periodontal regeneration.

Odontogenesis-Associated Phosphoprotein (ODAPH) Overexpression in Ameloblasts Disrupts Enamel Formation via Inducing Abnormal Mineralization of Enamel in Secretory Stage

Odontogenesis-associated phosphoprotein (ODAPH) is a recently discovered enamel matrix protein. Our previous study demonstrated that knockouting out Odaph in mice resulted in enamel hypomineralization. To further investigate the effect of Odaph on enamel mineralization, we constructed an Odaph overexpression mouse model, controlled by an amelogenin promoter. Our histological analysis of OdaphTg mice revealed that the enamel layer was thinner than in WT mice. An uneven, thinner enamel layer was confirmed using micro-computed tomography (uCT). It was subsequently found that the Tomes' processes lost their normal morphology, resulting in the loss of the enamel prism structure. These results indicate that Odaph overexpression in ameloblasts led to enamel dysplasia. In conjunction with this, Odaph overexpression hindered Amelx secretion, and may result in endoplasmic reticulum stress. Interestingly, uCT revealed that enamel had higher mineral density at the secretory stage; due to this, we did the histological staining for the mineralization-related proteins Alkaline phosphatase (ALPL) and Runt-related transcription factor 2 (RUNX2). It was observed that these proteins were up-regulated in OdaphTg mice versus WT mice, indicating that Odaph overexpression led to abnormal enamel mineralization. To confirm this, we transfected ameloblast-like cell line (ALC) with Odaph overexpression lentivirus in vitro and identified that both Alpl and Runx2 were strikingly upregulated in OE-mus-Odaph versus OE-NC cells. We concluded that the ectopic overexpression of Odaph in ameloblasts led to abnormal enamel mineralization. In summary, Odaph profoundly influences amelogenesis by participating in enamel mineralization.