UBC Theses and Dissertations
The role of alpha v beta 6 integrin in enamel biomineralization Mohazab, Leila
Tooth enamel has the highest degree of biomineralization of all vertebrate hard tissues. During the secretory stage of enamel formation, ameloblasts deposit an extracellular matrix that is in direct contact with ameloblast plasma membrane. Although it is known that integrins mediate cell-matrix adhesion and regulate cell signaling in most cell types, the receptors that regulate ameloblast adhesion and matrix production are not well characterized. Thus, we hypothesized that αvβ6 integrin is expressed in ameloblasts where it regulates biomineralization of enamel. Human and mouse ameloblasts were found to express both β6 integrin mRNA and protein. The maxillary incisors of Itgb6-/- mice lacked yellow pigment and their mandibular incisors appeared chalky and rounded. Molars of Itgb6-/- mice showed signs of reduced mineralization and severe attrition. The mineral-to-protein ratio in the incisors was signiﬁcantly reduced in Itgb6-/- enamel, mimicking hypomineralized amelogenesis imperfecta. Interestingly, amelogenin-rich extracellular matrix abnormally accumulated between the ameloblast layer of Itgb6-/- mouse incisors and the forming enamel surface, and also between ameloblasts. This accumulation was related to increased synthesis of amelogenin, rather than to reduced removal of the matrix proteins. This was conﬁrmed in cultured ameloblast-like cells, which did not use αvβ6 integrin as an endocytosis receptor for amelogenins, although it participated in cell adhesion on this matrix indirectly via endogenously produced matrix proteins. In summary, integrin αvβ6 is expressed by ameloblasts and it plays a crucial role in regulating amelogenin deposition/turnover and subsequent enamel biomineralization.
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