Store-operated Ca2+ entry controls ameloblast cell function and enamel development
Miriam Eckstein, Martin Vaeth, Cinzia Fornai, Manikandan Vinu, Timothy G. Bromage, Meerim K. Nurbaeva, Jessica L. Sorge, Paulo G. Coelho, Youssef Idaghdour, Stefan Feske, Rodrigo S. Lacruz
Miriam Eckstein, Martin Vaeth, Cinzia Fornai, Manikandan Vinu, Timothy G. Bromage, Meerim K. Nurbaeva, Jessica L. Sorge, Paulo G. Coelho, Youssef Idaghdour, Stefan Feske, Rodrigo S. Lacruz
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Research Article Bone biology Cell biology

Store-operated Ca2+ entry controls ameloblast cell function and enamel development

Abstract

Loss-of-function mutations in stromal interaction molecule 1 (STIM1) impair the activation of Ca2+ release–activated Ca2+ (CRAC) channels and store-operated Ca2+ entry (SOCE), resulting in a disease syndrome called CRAC channelopathy that is characterized by severe dental enamel defects. The cause of these enamel defects has remained unclear given a lack of animal models. We generated Stim1/2K14cre mice to delete STIM1 and its homolog STIM2 in enamel cells. These mice showed impaired SOCE in enamel cells. Enamel in Stim1/2K14cre mice was hypomineralized with decreased Ca content, mechanically weak, and thinner. The morphology of SOCE-deficient ameloblasts was altered, showing loss of the typical ruffled border, resulting in mislocalized mitochondria. Global gene expression analysis of SOCE-deficient ameloblasts revealed strong dysregulation of several pathways. ER stress genes associated with the unfolded protein response were increased in Stim1/2-deficient cells, whereas the expression of components of the glutathione system were decreased. Consistent with increased oxidative stress, we found increased ROS production, decreased mitochondrial function, and abnormal mitochondrial morphology in ameloblasts of Stim1/2K14cre mice. Collectively, these data show that loss of SOCE in enamel cells has substantial detrimental effects on gene expression, cell function, and the mineralization of dental enamel.

Authors

Miriam Eckstein, Martin Vaeth, Cinzia Fornai, Manikandan Vinu, Timothy G. Bromage, Meerim K. Nurbaeva, Jessica L. Sorge, Paulo G. Coelho, Youssef Idaghdour, Stefan Feske, Rodrigo S. Lacruz

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Figure 8

Schematic showing the effect of store-operated Ca2+ entry deficiency in enamel.

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Schematic showing the effect of store-operated Ca2+ entry deficiency in ...
(A) WT maturation-stage ameloblast showing a well-developed ruffled border (RB) at the apical end where the Na+/Ca2+/K+ exchanger NCKX4 is localized. In these cells, depletion of endoplasmic reticulum (ER) Ca2+ stores results in the activation of the ER Ca2+ sensors STIM1 and STIM2 resulting in sustained Ca2+ entry via Orai1 and refilling of ER stores. Normal Ca2+homeostasis and the Ca2+ extrusion system critically contribute to the proper mineralization of enamel. (B) In STIM1/STIM2–deficient cells, depletion of ER Ca2+stores does not result in appropriate activation of STIM1 and STIM2, and hence Ca2+ entry via Orai1 is impaired, resulting in Ca2+-induced ER stress. The subsequent activation of the unfolded protein response (UPR) mechanism helps mediate this cell stress and can prevent cell death. In enamel cells deficient of STIM1 and STIM2, UPR-associated genes Bip/Grp78 and RCAN1 are upregulated. CHOP is also upregulated, which can affect the glutathione system (GSH) affecting normal S-glutathionylation of actin, preventing the normal development of the RB. Mitochondria become mislocalized as a result. Mitochondria morphology is disrupted, possibly associated with RCAN1 upregulation or with a decreased glutathione system, leading to increased ROS and abnormal mitochondrial bioenergetics. Dysfunction of STIM1 and STIM2 results in severe enamel hypomineralization and softer enamel, which increases tooth wear.