The Role of Enamel Matrix Protein Amelotin on Biomineralization

Dental caries is one of the most common chronic diseases of people worldwide. Despite recent advances in oral health care and restorative dentistry, the problem of dental caries and erosion remains unresolved due to the lack of knowledge of the natural biomineralization process of tooth tissues. Dental enamel plays a crucial role in preventing the tooth from destruction. However, if damaged or lost, it cannot be regenerated. Understanding the molecular mechanisms behind formation of enamel would not only make restoration of the tissue possible, but would also provide new insights for optimum design of calcium phosphate based biomaterials for dental and orthopedic applications. Amelotin (AMTN) is a recently discovered protein that is primarily expressed during the maturation stage of enamel formation and is localized at the cell-mineral interface on the surface enamel layer. In vivo studies using transgenic mice suggest a direct regulatory function for AMTN in enamel biomineralization. The aim of this PhD project was to test this hypothesis using different in vitro model systems of mineralization. I first showed that recombinant human (rh) AMTN accelerates hydroxyapatite mineralization in a dose-dependent manner when dissolved in the mineralization SBF buffer. Inactivation of a conserved SSEEL motif resulted in significant reduction in the mineralizing ability of the full-length molecule. I also evaluated the importance of phosphorylation in mineralization by testing a synthetic peptide containing a short sequence of AMTN including phosphorylated SSEEL in the crystallization assay and showed that it promoted mineralization albeit to a lesser degree than rh-AMTN. Detailed characterization of secretory enamel matrix in overexpressor mice showed rapid and uncontrolled mineralization. I also tested the mineralizing ability of AMTN in an established osteoblast cell line and demonstrated that AMTN transfected or introduced in the culture media in the recombinant form both accelerate the formation of mineralized nodules. AMTN molecules embedded in collagen gel matrix were also able to mineralize the collagen material in the SBF buffer within a few hours. The findings of this PhD project provide solid evidence that AMTN is a promoter of hydroxyapatite mineralization and likely a key player in the establishment of surface enamel layer.

Department dc:contributor.department

Dentistry

Year dc:date.issued

2015

Author dc:creator

• Abbarin, Nastaran

Advisor dc:contributor.advisor

• Ganss, Bernhard

• Amelotin
• Biomineralization
• Dental caries
• Enamel
• Matrix proteins

Handle dc:identifier.uri

http://hdl.handle.net/1807/75613

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/75613