Abstract
During enamel development, formation of hydroxyapatite crystals and regulation of pH in the enamel matrix require massive transport of ions. Both ameloblasts and adjacent dental epithelial cells in the stellate reticulum co-express several transmembrane cotransporters/ion-exchangers for transport of ions across plasma membranes. Gap junctions (GJs) enable intercellular exchanges of ions between neighboring cells. This suggests that the ameloblasts and other cell layers of the enamel organ, form a functional unit. During the bell stage of tooth formation, the non-ameloblast dental epithelium highly expresses the Na-K-Cl cotransporter (Nkcc1). Nkcc1-null mice are associated with enamel hypomineralization and increased expression of GJ protein connexin 43 (Cx43), suggesting that reduced ion transport in the Nkcc1-null mouse is in part compensated by increased intercellular ion transport through GJs. To understand the role of GJs in ion transport and its effect on pH regulation, we examined in a mouse strain in which Cx43 was ablated selectively in DMP1 expressing cells (Cx43flox/flox mice crossed with DMP1-8kb-Cre mice), including ameloblasts. Micro-CT analysis showed that the mineral density at late maturation stage incisal enamel of the Cx43-null mice was 10% less than in controls, whereas that in dentin was unchanged. Maturation stage ameloblasts of mice lacking the pH regulating sodium/bicarbonate transporter NBCe1 (Nbce1-null), or chloride channel Cftr (Cftr-null) were found to have increased Cx43-immunostaining. These results support the possibility that GJs in the ameloblast–papillary complex at the maturation stage contribute to ion transport by enabling passage of ions directly from cells of the papillary layer into ameloblast layer. Increasing the number of GJs may partly compensate the reduction of ion-cotransporters and ion exchangers in dental epithelium.
Highlights
IntroductionEnamel mineralization is an active process, regulated by enamel organ cells, including ameloblasts, stratum intermedium cells, stellate reticulum, and the papillary layer
Dental enamel is the hardest substance in the human body
Our results, which show that the loss of connexin 43 (Cx43) Gap junctions (GJs) only affect enamel mineralization at the late stage of enamel formation, do not support the proposal by Toth et al (2010) that Cx43 GJs may mediate protein deposition required for final matrix mineralization
Summary
Enamel mineralization is an active process, regulated by enamel organ cells, including ameloblasts, stratum intermedium cells, stellate reticulum, and the papillary layer. Secretory stage ameloblasts differentiate from pre-ameloblasts to synthesize and secrete proteins into the matrix space to form the full thickness of matrix, into which long thin hydroxyapatite crystals grow. At the end of the secretion stage, capillaries invaginate the stellate reticulum layer, which overlies ameloblasts, to form the papillary layer, which is rich in capillaries. Expression patterns of the ion exchangers of SLC4A4 (NBCe1) and Na+-K+-ATPase (Lacruz et al, 2010b; Jalali et al, 2014; Wen et al, 2014), in both ameloblasts and papillary cells, suggest that both layers form a functional unit to regulate the hemostasis of ion sodium and potassium exchange to direct matrix mineralization. Changes in the structure of the papillary layer between early and late maturation stages may reflect changing rates of calcification or of resorption of enamel proteins
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
