UCSF

Ameloblasts continuously differentiate from epithelial stem cells to maturation stage ameloblasts, modulating and directing the formation of a mineralized enamel matrix. Calcium is required for enamel mineralization, however, as in other epithelial tissues; calcium may also be a modulator for ameloblast differentiation. Several studies have suggested a role for the calcium sensing receptor (CaSR) in ameloblast differentiation. Hypothesis: Calcium regulates ameloblast differentiation through the activity of the calcium sensing receptor. Methods: A primary ameloblast cell culture model was used to determine whether calcium could direct ameloblast differentiation, cellular morphology, and gene expression. Gene expression in response to calcium was assessed via microarray analysis. In vivo studies using K14-Cre-CaSR-/- mice treated with a normal diet, low calcium diet or high fluoride diet were completed to determine the role of the CaSR on ameloblast differentiation. Enamel formation, mineralization, and ameloblast differentiation were imaged by microCT, histochemistry, and immunohistochemistry. Gene expression was compared by qPCR. Results: In vitro primary cell culture data showed that elevated levels of calcium could induce mineralization, changes in cell morphology and gene expression related to dose and time of exposure. Primary ameloblast lineage cells is very heterogeneous, with a proportion of stellate reticulum cells, which accounts for the high levels of collagen Type I levels found in the microarray study. In vivo K14-Cre-CaSR-/- mouse model data showed earlier enamel formation compared to wild type mice, with no effects on ameloblast morphology and gene expression. The early enamel formation phenotype in K14-Cre-CaSR-/- mice was enhanced in the presence of fluoride and in the absence of calcium in the diet. Conclusion: Calcium can modulate expression of extracellular matrix proteins in a mixed primary cell culture. CaSR activity can influence the timing of enamel formation, but has a limited role in regulating ameloblast differentiation. Calcium mediated changes in gene expression and ameloblast cellular function appears to be controlled through mechanisms other than CaSR.