The focus of this supplement is to determine if cathepsin K is essential for proper dental enamel formation. The original application (R01 DE016276) focused on defining how enamelysin (matrix metalloproteinase-20;MMP20) processes enamel proteins and focused on determining how such processing allows for proper enamel development. This supplemental application extends and enhances the original studies because it is focused on identifying the function of a protease (cathepsin K) that is well known for its role in bone remodeling, but was heretofore not known as expressed by enamel producing cells (ameloblasts). During amelogenesis, enamel matrix proteins are degraded and removed to generate the virtually protein-free mineral of mature enamel. Proteolytic processing is critical for enamel formation as homozygous mutation of either of the resident enamel proteases, MMP20 or kallikrein-4 (KLK4), results in defective hypomineralized enamel. The long-term goal of our research is to achieve a better understanding of protein degradation and removal as dental enamel attains its final hardened form. In this supplemental application we provide preliminary data demonstrating that cathepsin K is expressed by ameloblasts and that its expression increases as enamel development progresses. We also show that cathepsin K rapidly degrades recombinant amelogenin in vitro. Notably, we discovered that cathepsin K null mice have significantly reduced enamel hardness when compared to controls. Thus, we hypothesize that cathepsin K actively participates in the degradation of enamel matrix proteins that are resorbed by maturation stage ameloblasts. The overall objective of this proposal is to determine if cathepsin K is an essential protease for proper dental enamel development. To this end, we will identify the location of total and active cathepsin K within the developing tooth (Aim 1). We will localize cathepsin K in mouse incisors by use of immunogold labeling and will identify the location of active cathepsin K by use of a catalytic histochemical assay.
In Aim 2 we will determine if enamel development is altered in the cathepsin K null mouse. Tooth morphology, volume, and density will be examined by radiography and microCT analysis. Enamel crystal structure and mineral surface characteristics will be characterized by nanoindentation and SEM. Results from these studies will accomplish our overall objective of understanding if, and/or to what extent, cathepsin K plays a role in enamel development. We will also further our knowledge of how enamel starts as a protein rich tissue, but ends as a virtually protein-free mineralized hard tissue. Relevance to public health: These studies will lead to a better understanding of how dental enamel forms on teeth. This knowledge is a necessary first step to eventually understand how to treat individuals with genetically malformed dental enamel. At the outset, the genes required for enamel formation should be known and well characterized. These studies are also necessary to enhance the possibility that tissue engineering techniques will eventually provide therapeutic interventions.

Public Health Relevance

Little is known about how enamel matrix proteins are degraded and removed from maturing dental enamel. We show that the cells (ameloblasts) responsible for enamel formation, express an enzyme (cathepsin K) that degrades proteins. This proposal seeks to demonstrate that cathepsin K plays an essential role in enamel formation by degrading enamel matrix proteins as the proteins are removed from the maturing enamel.

Agency
National Institute of Health (NIH)
Institute
National Institute of Dental & Craniofacial Research (NIDCR)
Type
Research Project (R01)
Project #
3R01DE016276-04S1
Application #
7818106
Study Section
Special Emphasis Panel (ZRG1-MOSS-K (95))
Program Officer
Wan, Jason
Project Start
2009-09-21
Project End
2012-06-30
Budget Start
2009-09-21
Budget End
2012-06-30
Support Year
4
Fiscal Year
2009
Total Cost
$316,252
Indirect Cost
Name
Forsyth Institute
Department
Type
DUNS #
062190616
City
Cambridge
State
MA
Country
United States
Zip Code
02142
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Bartlett, J D; Simmer, J P (2015) New perspectives on amelotin and amelogenesis. J Dent Res 94:642-4
Bartlett, John D; Simmer, James P (2014) Kallikrein-related peptidase-4 (KLK4): role in enamel formation and revelations from ablated mice. Front Physiol 5:240
Pugach, Megan K; Ozer, Fusun; Mulmadgi, Raj et al. (2014) Shear bond strength of dentin and deproteinized enamel of amelogenesis imperfecta mouse incisors. Pediatr Dent 36:130-6
Sarkar, Juni; Simanian, Emil J; Tuggy, Sarah Y et al. (2014) Comparison of two mouse ameloblast-like cell lines for enamel-specific gene expression. Front Physiol 5:277
Shin, Masashi; Hu, Yuanyuan; Tye, Coralee E et al. (2014) Matrix metalloproteinase-20 over-expression is detrimental to enamel development: a Mus musculus model. PLoS One 9:e86774
Guan, Xiaomu; Bidlack, Felicitas B; Stokes, Nicole et al. (2014) E-cadherin can replace N-cadherin during secretory-stage enamel development. PLoS One 9:e102153
Yamakoshi, Yasuo; Simmer, James P; Bartlett, John D et al. (2013) MMP20 and KLK4 activation and inactivation interactions in vitro. Arch Oral Biol 58:1569-77
Wang, S-K; Hu, Y; Simmer, J P et al. (2013) Novel KLK4 and MMP20 mutations discovered by whole-exome sequencing. J Dent Res 92:266-71
Pugach, M K; Suggs, C; Li, Y et al. (2013) M180 amelogenin processed by MMP20 is sufficient for decussating murine enamel. J Dent Res 92:1118-22

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