Deficiency of G protein‐coupled receptor Gpr111/Adgrf2 causes enamel hypomineralization in mice by alteration of the expression of kallikrein‐related peptidase 4 (Klk4) during pH cycling process

Abstract

Enamel is formed by the repetitive secretion of a tooth‐specific extracellular matrix and its decomposition. Calcification of the enamel matrix via hydroxyapatite (HAP) maturation requires pH cycling to be tightly regulated through the neutralization of protons released during HAP synthesis. We found that Gpr115, which responds to changes in extracellular pH, plays an important role in enamel formation. Gpr115‐deficient mice show partial enamel hypomineralization, suggesting that other pH‐responsive molecules may be involved. In this study, we focused on the role of Gpr111/Adgrf2, a duplicate gene of Gpr115, in tooth development. Gpr111 was highly expressed in mature ameloblasts. Gpr111‐KO mice showed enamel hypomineralization. Dysplasia of enamel rods and high carbon content seen in Gpr111‐deficient mice suggested the presence of residual enamel matrices in enamel. Depletion of Gpr111 in dental epithelial cells induced the expression of ameloblast‐specific protease, kallikrein‐related peptidase 4 (Klk4), suggesting that Gpr111 may act as a suppressor of Klk4 expression. Moreover, reduction of extracellular pH to 6.8 suppressed the expression of Gpr111, while the converse increased Klk4 expression. Such induction of Klk4 was synergistically enhanced by Gpr111 knockdown, suggesting that proper enamel mineralization may be linked to the modulation of Klk4 expression by Gpr111. Furthermore, our in vitro suppression of Gpr111 and Gpr115 expression indicated that their suppressive effect on calcification was additive. These results suggest that both Gpr111 and Gpr115 respond to extracellular pH, contribute to the expression of proteolytic enzymes, and regulate the pH cycle, thereby playing important roles in enamel formation.

S100a6 knockdown promotes the differentiation of dental epithelial cells toward the epidermal lineage instead of the odontogenic lineage

“…Matrices such as Ambn and Amelx are important for the initiation of calcification, whereas enzymes such as Klk4 are important for hypercalcification. Therefore, an appropriate dose of protease is essential for enamel formation, and deficiency or excess of Klk4 causes enamel dysplasia 8,66 . In the present study, Ambn , Amelx , and Klk4 were upregulated during ameloblast differentiation; however, S100a6 knockdown suppressed Ambn and Amelx expression (Figure 5A).…”

“…(A) (B) dysplasia. 8,66 In the present study, Ambn, Amelx, and Klk4 were upregulated during ameloblast differentiation; however, S100a6 knockdown suppressed Ambn and Amelx expression (Figure 5A). The suppression of Ambn and Amelx suggests that the loss of S100a6 inhibited the difof ameloblasts.…”

“…[4][5][6][7] Calcification is performed using the enamel matrix as a scaffold, 4,5 which is later degraded by proteases such as matrix metalloproteinase-20 and kallikrein-related peptidase 4 (Klk4) to enhance calcification. Although extensive studies have been performed on the differentiation of the dental epithelium into mature ameloblasts, 8,9 the calcification process remains poorly understood.…”