Stim1 Regulates Enamel Mineralization and Ameloblast Modulation

Abstract

Loss-of-function mutations in the Ca release-activated Ca channel genes ORAI1 and STIM1 abolish store-operated Ca entry (SOCE) and result in ectodermal dysplasia with amelogenesis imperfecta. However, because of the limited availability of patient tissue, analyses of enamel mineralization or possible changes in ameloblast function or morphology have not been possible. Here, we generated mice with ectodermal tissue-specific deletion of Stim1 ( Stim1 cKO [conditional knockout]), Stim2 ( Stim2 cKO), and Stim1 and Stim2 ( Stim1/2 cKO) and analyzed their enamel phenotypes as compared with those of control ( Stim1/2) animals. Ablation of Stim1 and Stim1/2 but not Stim2 expression resulted in chalky enamel and severe attrition at the incisor tips and molar cusps. Stim1 and Stim1/2 cKO, but not Stim2 cKO, demonstrated inferior enamel mineralization with impaired structural integrity, whereas the shape of the teeth and enamel thickness appeared to be normal in all animals. The gene expression levels of the enamel matrix proteins Amelx and Ambn and the enamel matrix proteases Mmp20 and Klk4 were not altered by the abrogation of SOCE in Stim1/2 cKO mice. The morphology of ameloblasts during the secretory and maturation stages was not significantly altered in either the incisors or molars of the cKO animals. However, in Stim1 and Stim1/2 cKO incisors, the alternating modulation of maturation-stage ameloblasts between the smooth- and ruffle-ended cell types continued beyond the regular cycle and extended to the areas corresponding to the zone of postmodulation ameloblasts in the teeth of control animals. These results indicate that SOCE is essential for proper enamel mineralization, in which Stim1 plays a critical role during the maturation process.

CRAC channels in dental enamel cells

“…Interestingly, both studies showed that altered SOCE in these mouse models did not have a major impact on the expression of enamel genes [12, 55]. This is in contrast to in vitro data using two different enamel cell lines (LS8 and HAT-7) [44, 46], which demonstrated a decrease in transcript levels of, among others, Amelx and Ambn.…”

“…Collectively, our data showed that disrupting SOCE had profound effects on cell metabolism, redox system, and impaired enamel mineralization, functions that are understudied in enamel biology [55]. A later study by Furukawa et al reported on Stim1/2-deficent mice using a similar approach to analyze the dental phenotype [12]. Although the data presented in this study was more limited than in the report by Eckstein et al[11], their findings overall agree with our study supporting the critical role of Stim1/2 in enamel mineralization.…”

“…Although the data presented in this study was more limited than in the report by Eckstein et al[11], their findings overall agree with our study supporting the critical role of Stim1/2 in enamel mineralization. The Furukawa et al study, however, also presented murine data following the conditional deletion of Stim1 and Stim2 genes independently [12]. Deletion of Stim1 but not Stim2 resulted in decreased enamel mineralization, suggesting that Stim1 is the key SOCE player in enamel cells [12].…”

“…The Furukawa et al study, however, also presented murine data following the conditional deletion of Stim1 and Stim2 genes independently [12]. Deletion of Stim1 but not Stim2 resulted in decreased enamel mineralization, suggesting that Stim1 is the key SOCE player in enamel cells [12]. …”

“…It soon became apparent that CRAC channel deficiencies, named CRAC channelopathy, had a profound impact on many tissues and organs, including dental enamel [6–9]. These clinical reports, and subsequent functional data including the study of CRAC-deficient mouse models [10–12], firmly stablished CRAC channels as key elements in Ca 2+ transport and signaling in enamel. This elegant system that monitors the refilling of intracellular Ca 2+ stores also participating in Ca 2+ signaling has provided clarity regarding the pathway for Ca 2+ influx in enamel cells, which had been unresolved.…”