Enamel Defects Associated With Dentin Sialophosphoprotein Mutation in Mice

• Published in: Frontiers in physiology 2021-09, Vol.12, p.724098-724098
• Main Authors: Liang, Tian, Xu, Qian, Zhang, Hua, Wang, Suzhen, Diekwisch, Thomas G. H., Qin, Chunlin, Lu, Yongbo
• Format: Article
• Language: English
• Subjects: ameloblasts; amelogenesis; cell differentiation; enamel; mineralization; Physiology; tooth development
• ISSN: 1664-042X; 1664-042X
• DOI: 10.3389/fphys.2021.724098

Dentin sialophosphoprotein (DSPP) is an extracellular matrix protein that is highly expressed in odontoblasts, but only transiently expressed in presecretory ameloblasts during tooth development. We previously generated a knockin mouse model expressing a mouse equivalent (DSPP, p.P19L) of human mutant DSPP (p.P17L; referred to as “ Dspp P19L/+ ”), and reported that Dspp P19L/+ and Dspp P19L/P19L mice manifested a dentin phenotype resembling human dentinogenesis imperfecta (DGI). In this study, we analyzed pathogenic effects of mutant P19L-DSPP on enamel development in Dspp P19L/+ and Dspp P19L/P19L mice. Micro-Computed Tomography (μCT) analyses of 7-week-old mouse mandibular incisors showed that Dspp P19L/P19L mice had significantly decreased enamel volume and/or enamel density at different stages of amelogenesis examined. Acid-etched scanning electron microscopy (SEM) analyses of mouse incisors demonstrated that, at the mid-late maturation stage of amelogenesis, the enamel of wild-type mice already had apparent decussating pattern of enamel rods, whereas only minute particulates were found in Dspp P19L/+ mice, and no discernible structures in Dspp P19L/P19L mouse enamel. However, by the time that incisor enamel was about to erupt into oral cavity, distinct decussating enamel rods were evident in Dspp P19L/+ mice, but only poorly-defined enamel rods were revealed in Dspp P19L/P19L mice. Moreover, μCT analyses of the mandibular first molars showed that Dspp P19L/+ and Dspp P19L/P19L mice had a significant reduction in enamel volume and enamel density at the ages of 2, 3, and 24weeks after birth. Backscattered and acid-etched SEM analyses revealed that while 3-week-old Dspp P19L/+ mice had similar pattern of enamel rods in the mandibular first molars as age-matched wild-type mice, no distinct enamel rods were observed in Dspp P19L/P19L mice. Yet neither Dspp P19L/+ nor Dspp P19L/P19L mice showed well-defined enamel rods in the mandibular first molars by the age of 24weeks, as judged by backscattered and acid-etched SEM. In situ hybridization showed that DSPP mRNA level was markedly reduced in the presecretory ameloblasts, but immunohistochemistry revealed that DSP/DSPP immunostaining signals were much stronger within the presecretory ameloblasts in Dspp mutant mice than in wild-type mice. These results suggest that mutant P19L-DSPP protein caused developmental enamel defects in mice, which may be associated with intracellular retention of mutant DSPP in the