Molecular Pathogenesis of Dentinogenesis Imperfecta Associated with Dentin Sialophosphoprotein Mutations

Dentin sialophosphoprotein (DSPP) is abundantly expressed by odontoblasts, and transiently expressed by ameloblasts. The mutations in DSPP gene can cause dentinogenesis imperfecta (DGI) type II (DGI-II) and III (DGI-III), as well as dentin dysplasia (DD) type II (DD-II). To date, 42 DSPP mutations in humans have been identified. However, the molecular pathogenesis has not been determined. We used CRISPR/Cas9 technology to generate a Dspp-KI (knock-in) mouse model, carrying P19L mutation equivalent to the c.50C>T, p.P17L mutation in humans. Compared with wild-type control, the Dsppᴾ¹⁹ᴸ/+ and Dsppᴾ¹⁹ᴸ/ᴾ¹⁹ᴸ (mutant) mice displayed enlarged dental pulp and thinner pulp chamber roof dentin at an early stage, representing DGI-III in humans. With age, the mutant mice showed partial pulp obliteration and thickened pulp chamber floor dentin, resembling DGI-II in humans. The mutant mice also exhibited lower dentin density, defective enamel quality, and compromised dentinoenamel junction. The pathological morphology of odontoblasts and ameloblasts, and the impaired odontoblast processes were observed. Hence, the Dspp-KI mice recapitulated the dentin and enamel phenotypes in human DGI patients. In addition, we discovered reduced DSPP mRNA and accumulated DSPP protein in the odontoblasts and ameloblasts of the mutant mice. The intracellularly accumulated DSPP retained in the endoplasmic reticulum (ER), and activated unfolded protein response (UPR). A UPR branch, inositol-requiring enzyme-1 (IRE1) pathway, was highly activated in the pulp cells of the mutant mice. The activation of IRE1 specifically inhibited the synthesis of DSPP protein during the accumulation of DSPP. Thus, UPR, especially IRE1, may play a major role in DGI associated with DSPP mutations. In summary, we generated a Dspp-KI mouse model recapitulating human DGI, and showed that UPR elicited by the DSPP mutation played a major role in DGI. Further elucidation of the molecular pathogenesis may offer insights for potential treatment plans for DGI