Calcium Sets the Clock in Ameloblasts

Raed Said; Liubov Lobanova; Silvana Papagerakis; Petros Papagerakis

doi:10.3389/fphys.2020.00920

Calcium Sets the Clock in Ameloblasts

Front Physiol. 2020 Jul 31:11:920. doi: 10.3389/fphys.2020.00920. eCollection 2020.

Authors

Raed Said^{1

2}, Liubov Lobanova², Silvana Papagerakis³, Petros Papagerakis^{1

2}

Affiliations

¹ Department of Anatomy, Physiology and Pharmacology, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada.
² College of Dentistry, University of Saskatchewan, Saskatoon, SK, Canada.
³ Department of Surgery, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada.

Abstract

Background: Stromal interaction molecule 1 (STIM1) is one of the main components of the store operated Ca²⁺ entry (SOCE) signaling pathway. Individuals with mutated STIM1 present severely hypomineralized enamel characterized as amelogenesis imperfecta (AI) but the downstream molecular mechanisms involved remain unclear. Circadian clock signaling plays a key role in regulating the enamel thickness and mineralization, but the effects of STIM1-mediated AI on circadian clock are unknown.

Objectives: The aim of this study is to examine the potential links between SOCE and the circadian clock during amelogenesis.

Methods: We have generated mice with ameloblast-specific deletion of Stim1 (Stim1 ^fl/fl/Amelx-iCre^+/+, Stim1 cKO) and analyzed circadian gene expression profile in Stim1 cKO compared to control (Stim1 ^fl/fl/Amelx-iCre^-/-) using ameloblast micro-dissection and RNA micro-array of 84 circadian genes. Expression level changes were validated by qRT-PCR and immunohistochemistry.

Results: Stim1 deletion has resulted in significant upregulation of the core circadian activator gene Brain and Muscle Aryl Hydrocarbon Receptor Nuclear Translocation 1 (Bmal1) and downregulation of the circadian inhibitor Period 2 (Per2). Our analyses also revealed that SOCE disruption results in dysregulation of two additional circadian regulators; p38α mitogen-activated protein kinase (MAPK14) and transforming growth factor-beta1 (TGF-β1). Both MAPK14 and TGF-β1 pathways are known to play major roles in enamel secretion and their dysregulation has been previously implicated in the development of AI phenotype.

Conclusion: These data indicate that disruption of SOCE significantly affects the ameloblasts molecular circadian clock, suggesting that alteration of the circadian clock may be partly involved in the development of STIM1-mediated AI.

Keywords: STIM1; ameloblast; amelogenesis; amelogenesis imperfecta; calcium; circadian clock; enamel; store operated Ca2+ channels.