Tooth enamel is a highly mineralized hard tissue, uniquely comprised of millions of hexagonal carbonated hydroxyapatite (HAP) crystals. These crystals are very thin and extremely long, which determine excellent mechanical properties of tooth enamel. Mineralized enamel crystals develop from a layer of enamel protein matrix that is predominated by amelogenins (>90%), which forms special nanostructures to modulate crystal formation. Amelogenins are gradually and completely removed by enamel proteinases MMP20 and KLK4 to form highly mineralized enamel at the end of maturation stage. The interactions between crystal, amelogenin and proteinase dynamically and delicately controlled the growth rate, direction and morphology of enamel crystals. We hypothesize that the binding of amelogenin to apatite crystal changes the conformation of amelogenin adsorbed on crystals and results in preferential degradation of amelogenin from crystal surface by proteinases. The amelogenin adsorption and degradation are also specific on different crystal planes, which drive the crystal to elongate primarily along the c axis and widen/thicken along a and b axes in different developmental stages of amelogenesis. In addition, the N-terminal proline 70 is involved in the plane-specific adsorption and degradation of amelogenin. The mutation of the proline (P70T, linked to a type of amelogenesis imperfect) interferes with crystal- amelogenin-proteinase interactions, resulting in abnormal enamel mineralization and morphology.
Three specific aims are proposed to evaluate the hypothesis:
Specific Aim 1, to characterize and compare (001) and (hk0) planes of oriented HAP crystals;
Specific Aim 2, to determine amelogenin-crystal interactions by identifying the binding domains, analyzing binding affinities and kinetics, and investigating the binding patterns of amelogenins on (001) and (hk0) planes of HAP crystals;
Specific Aim 3, To investigate amelogenin-proteinases interactions before and after amelogenin binding to apatite crystals and determine how the interactions affect the growth of crystal. The amelogenin carrying P70T mutation will be also used to test the effects of the mutation on crystal- amelogenin-proteinase interactions. The proposed studies will integrate the roles of HAP, amelogenin and proteinase into an interactive unity, and study how the interactions modulate the enamel crystal growth and morphology. The findings collected in this study will build new concepts to advance our knowledge of the unique principle of amelogenin-mediated crystal growth and help us to better understand the fundamental mechanism of AI. The new concepts may be also useful for future acellular tooth enamel repair and regeneration.

Public Health Relevance

This project will use state of the art techniques to study the mechanism of tooth enamel formation. The proposed studies focus on the enamel crystal growth modulated by interactions between apatite crystals, amelogenin and proteinases during different development stages and the defective growth of crystals in a type of amelogenesis imperfecta.

Agency
National Institute of Health (NIH)
Institute
National Institute of Dental & Craniofacial Research (NIDCR)
Type
Research Project (R01)
Project #
5R01DE015821-07
Application #
8296533
Study Section
Special Emphasis Panel (ZRG1-MOSS-B (02))
Program Officer
Lumelsky, Nadya L
Project Start
2004-03-01
Project End
2015-06-30
Budget Start
2012-07-01
Budget End
2013-06-30
Support Year
7
Fiscal Year
2012
Total Cost
$341,780
Indirect Cost
$84,206
Name
University of California San Francisco
Department
Dentistry
Type
Schools of Dentistry
DUNS #
094878337
City
San Francisco
State
CA
Country
United States
Zip Code
94143
Zhu, Li; Hwang, Peter; Witkowska, H Ewa et al. (2013) Quantitatively and kinetically identifying binding motifs of amelogenin proteins to mineral crystals through biochemical and spectroscopic assays. Methods Enzymol 532:327-41
Khan, Feroz; Liu, Haichuan; Reyes, Aileen et al. (2013) The proteolytic processing of amelogenin by enamel matrix metalloproteinase (MMP-20) is controlled by mineral ions. Biochim Biophys Acta 1830:2600-7
Yoon, Hyesook; Blaber, Sachiko I; Li, Wu et al. (2013) Activation profiles of human kallikrein-related peptidases by matrix metalloproteinases. Biol Chem 394:137-47
Huang, Yulei; Goldberg, Michel; Le, Thuan et al. (2012) Amelogenin exons 8 and 9 encoded peptide enhances leucine rich amelogenin peptide mediated dental pulp repair. Cells Tissues Organs 196:151-60
Khan, Feroz; Li, Wu; Habelitz, Stefan (2012) Biophysical characterization of synthetic amelogenin C-terminal peptides. Eur J Oral Sci 120:113-22
Uskokovic, Vuk; Khan, Feroz; Liu, Haichuan et al. (2011) Hydrolysis of amelogenin by matrix metalloprotease-20 accelerates mineralization in vitro. Arch Oral Biol 56:1548-59
Uskokovic, Vuk; Odsinada, Roselyn; Djordjevic, Sonia et al. (2011) Dynamic light scattering and zeta potential of colloidal mixtures of amelogenin and hydroxyapatite in calcium and phosphate rich ionic milieus. Arch Oral Biol 56:521-32
Zhu, Li; Uskokovic, Vuk; Le, Thuan et al. (2011) Altered self-assembly and apatite binding of amelogenin induced by N-terminal proline mutation. Arch Oral Biol 56:331-6
Uskokovic, V; Castiglione, Z; Cubas, P et al. (2010) Zeta-potential and particle size analysis of human amelogenins. J Dent Res 89:149-53
Zhu, Li; Tanimoto, Kotaro; Le, Thuan et al. (2009) Functional roles of prolines at amelogenin C terminal during tooth enamel formation. Cells Tissues Organs 189:203-6

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