Neurotrophic factor neurotrophin-4 regulates ameloblastin expression via full-length TrkB.
Neurotrophic factors play an important role in the development and maintenance of not only neural but also nonneural tissues. Several neurotrophic factors are expressed in dental tissues, but their role in tooth development is not clear. Here, we report that neurotrophic factor neurotrophin (NT)-4 promotes differentiation of dental epithelial cells and enhances the expression of enamel matrix genes. Dental epithelial cells from 3-day-old mice expressed NT-4 and three variants of TrkB receptors for neurotrophins (full-length TrkB-FL and truncated TrkB-T1 and -T2). Dental epithelial cell line HAT-7 expressed these genes, similar to those in dental epithelial cells. We found that NT-4 reduced HAT-7 cell proliferation and induced the expression of enamel matrix genes, such as ameloblastin (Ambn). Transfection of HAT-7 cells with the TrkB-FL expression construct enhanced the NT-4-mediated induction of Ambn expression. This enhancement was blocked by K252a, an inhibitor for Trk tyrosine kinases. Phosphorylation of ERK1/2, a downstream molecule of TrkB, was induced in HAT-7 cells upon NT-4 treatment. TrkB-FL but not TrkB-T1 transfection increased the phosphorylation level of ERK1/2 in NT-4-treated HAT-7 cells. These results suggest that NT-4 induced Ambn expression via the TrkB-MAPK pathway. The p75 inhibitor TAT-pep5 decreased NT-4-mediated induction of the expression of Ambn, TrkB-FL, and TrkB-T1, suggesting that both high affinity and low affinity neurotrophin receptors were required for NT-4 activity. We found that NT-4-null mice developed a thin enamel layer and had a decrease in Ambn expression. Our results suggest that NT-4 regulates proliferation and differentiation of the dental epithelium and promotes production of the enamel matrix.
Section of Pediatric Dentistry, Kyushu University, Fukuoka 812-8582, Japan; Section of Orthodontics, Division of Oral Health, Growth, and Development, Faculty of Dental Science, Kyushu University, Fukuoka 812-8582, Japan.
Keigo
K
Yoshizaki
Section of Pediatric Dentistry, Kyushu University, Fukuoka 812-8582, Japan.
Shinya
S
Yamamoto
Section of Pediatric Dentistry, Kyushu University, Fukuoka 812-8582, Japan.
Aya
A
Yamada
Section of Pediatric Dentistry, Kyushu University, Fukuoka 812-8582, Japan.
Kenji
K
Yuasa
Section of Pediatric Dentistry, Kyushu University, Fukuoka 812-8582, Japan.
Tsutomu
T
Iwamoto
Nagasaki University Graduate School of Biomedical Sciences, Nagasaki 852-8521, Japan.
Emiko
E
Fukumoto
Department of Oral Anatomy II, Iwate Medical College School of Dentistry, Morioka, Iwate 020-8505, Japan.
Hidemitsu
H
Harada
Department of Molecular and Cellular Biochemistry, Osaka University Graduate School of Dentistry, Suita, Osaka 565-0871, Japan.
Masahiro
M
Saito
Section of Orthodontics, Division of Oral Health, Growth, and Development, Faculty of Dental Science, Kyushu University, Fukuoka 812-8582, Japan.
Akihiko
A
Nakasima
Section of Pediatric Dentistry, Kyushu University, Fukuoka 812-8582, Japan.
Kazuaki
K
Nonaka
Craniofacial Developmental Biology and Regeneration Branch, NIDCR, National Institutes of Health, Bethesda, Maryland 20892.
Yoshihiko
Y
Yamada
Section of Pediatric Dentistry, Kyushu University, Fukuoka 812-8582, Japan; Division of Pediatric Dentistry, Department of Oral Health and Development Sciences, Tohoku University Graduate School of Dentistry, Sendai, Miyagi 980-8575, Japan. Electronic address: fukumoto@mail.tains.tohoku.ac.jp.
Satoshi
S
Fukumoto
D000818:Animals; D001921:Brain / Q000378:metabolism; D002460:Cell Line; D003746:Dental Enamel Proteins / Q000096:biosynthesis*; D004847:Epithelial Cells / Q000378:metabolism; D005786:Gene Expression Regulation; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009414:Nerve Growth Factors / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D051381:Rats; D020813:Receptor, trkB / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014070:Tooth / Q000196:embryology
C490889:AMBN protein, human; D003746:Dental Enamel Proteins; D009414:Nerve Growth Factors; D020813:Receptor, trkB; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; C073922:neurotrophin 4