Neurotrophic Factor Neurotrophin-4 Regulates Ameloblastin Expression via Full-length TrkB

Abstract

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.Mammalian development is a complex and highly orchestrated process that involves intricate cross-talk between growth factors and other regulatory molecules. The interaction between the epithelium and mesenchyme induces specific molecular and cellular changes that lead to organogenesis. These interactions are particularly crucial during the initiation of the development of ectodermal organs, such as teeth, skin, hair, and mammary and prostate glands (1). The oral epithelium provides the initial signaling for neuronal crest-derived ectomesenchyme development, and then both tissues interact during tooth formation. Various transcription factors, growth factors, and extracellular matrices are expressed by enamel matrix-producing ameloblasts during tooth development (2-4). The principal components of the enamel matrix that are synthesized by secretory ameloblasts can be classified into two major categories, amelogenin (Amel) 2 and non-Amel, which includes ameloblastin (Ambn) and enamelin (Enam) (5). Ambn, also known as amelin or sheathlin, is a tooth-specific glycoprotein that represents the most abundant non-Amel enamel matrix protein. We previously created Ambn-null mice, which develop severe enamel hypoplasia in which ameloblasts detached from the matrix, lost cell polarity, resumed ...

Role of Epithelial-Stem Cell Interactions during Dental Cell Differentiation

“…5D) may also contribute to dental epithelial cell differentiation of iPS cells. A previous our reported that NT-4 induced Ambn expression in dental epithelium, while NT-4 knock-out mice showed delayed expression of enamel matrices in the early stage of ameloblast differentiation (29). In the present study, the presence of the anti-NT-4 neutralizing antibody or Noggin in conditioned medium from SF2-24 cells inhibited Ambn expression, but not that of CK14 (Fig.…”

“…9D), indicating that Ambn may be necessary for differentiation of iPS cells into dental epithelium. Previously, we showed that neurotrophic factor NT-4 is important for the differentiation of ameloblasts (29). To examine the effect of NT-4 on dental epithelial cell differentiation by iPS cells, we analyzed the expressions of Ambn and CK14 in iPS cells cultured with SF2-24-conditioned medium in the presence of K252a (inhibitor of neurotrophic receptor Trk), PD98059 (MEK inhibitor), anti-NT-4 neutralizing antibody, or Noggin (BMP antagonist).…”

Network-Based Method for Identifying Co-Regeneration Genes in Bone, Dentin, Nerve and Vessel Tissues

“…The following gene AMBN (ENSP00000313809) has already been analyzed above as a co-regenerative gene for bone and dentin. During AMBN-mediated dentin development, such gene has also been identified to participate in the development of surrounding nerves [76]. In 2008, a specific study [76] on dental tissues confirmed that as the downstream of a specific neuron development associated factor neurotrophin-4, AMBN may also participate in nerve development associated biological processes.…”

“…During AMBN-mediated dentin development, such gene has also been identified to participate in the development of surrounding nerves [76]. In 2008, a specific study [76] on dental tissues confirmed that as the downstream of a specific neuron development associated factor neurotrophin-4, AMBN may also participate in nerve development associated biological processes. RARS (ENSP00000231572), as a functional co-regeneration associated gene has already been analyzed in Section 4.1, can be confirmed its potential role during the co-regeneration of bone and dentin.…”

MAPK mediates Hsp25 signaling in incisor development

“…Several studies have found that MAPK signaling is involved in during mouse tooth and oral development (Abe et al 2007;Cho et al 2008;Xu et al 2008). Furthermore ERK1/2 and MEK concerned proliferation and diVerentiation of the dental epithelium and odontogenic tissues (Kumamoto and Ooya 2007;Yoshizaki et al 2008). However, the roles of pERK and pMEK during mouse incisor developmental stage, the relationship between MAPK and other proteins in the incisor, and the MAPK mechanisms involved in ameloblast diVerentiation and proliferation are not well understood.…”