STIM1 a Calcium Sensor Promotes the Assembly of an ECM that Contains Extracellular Vesicles and Factors that Modulate Mineralization

Bone and dentin development requires temporal and spatial deposition of calcium phosphate mineral. Several proteins work in coordination and contribute to this tightly regulated process. STIM1 (Stromal interaction molecule 1) is one such protein that has been recently identified to function in bone and enamel mineralization. STIM1 is a calcium sensor localized on the ER membrane and is well recognized for its physiological role in maintaining calcium homeostasis. We have demonstrated earlier that DMP1 stimulation of preosteoblasts and preodontoblasts stimulate calcium release from internal Ca2+ stores and this store depletion is sensed by STIM1. Store-operated calcium entry (SOCE) is one of the major Ca2+ influx mechanisms following store depletion in the ER. To demonstrate a role for STIM1 in dentin matrix mineralization, we generated transgenic DPSCs in which STIM1 was either overexpressed or silenced. These cells were characterized for their differentiation potential by gene expression analysis, Alizarin Red staining and the topology of the matrix examined by Field Emission Scanning Electron Microscopy (FESEM). Results suggest upregulation of genes involved in mineralization and increased calcium deposition with STIM1 overexpression. FESEM results demonstrate that STIM1 overexpression resulted in release of large amount of extracellular microvesicles and promoted matrix mineralization. Interestingly, knockdown of STIM1 resulted in release of fewer microvesicles and less mineral deposits in the ECM. Reduced dentin thickness, malformed and highly porous alveolar bone of STIM-1 null mice confirmed the role of STIM1 in the formation of calcified tissues. Overall, STIM1 is a crucial molecule in biomineralization as STIM1 can influence intracellular Ca2+ oscillations and thus provide a signal for activation of upstream and downstream effectors to promote precursor cell differentiation and matrix mineralization.