Calcium Transport in HAT-7 Cells: A Cellular Model of Amelogenesis
Kádár Kristóf György
Theoretical and Translational Medicine
Dr. Kellermayer Miklós
SE Elméleti Orvostudományi Központ, Beznák Aladár terem
2025-12-16 14:00:00
Physiology and Pathophysiology of the Regulation of Fluids and Electrolyte Homeostasis
Dr. Zsembery Ákos
Dr. Zsembery Ákos
Dr. Ruisanchez Éva
Dr. Szentandrássy Norbert
Dr. Várnai Péter
Vasziné Dr. Szabó Enikő
Dr. Miklós Zsuzsanna
Enamel, the most highly mineralized tissue in the human body, covers the crown of teeth and provides mechanical resilience during mastication. It is formed by specialized epithelial cells, the ameloblasts, which disappear after eruption, leaving enamel acellular, avascular, inert, and non-regenerative. Since Ca2+ is the predominant mineral component, one of the key functions of ameloblasts is Ca2+ transport to the mineralization front. Although several channels and transporters have been identified, the precise mechanisms of Ca2+ transport during amelogenesis remain largely unresolved. TRPM7, a channel with a known role in Ca2+, Zn2+, and Mg2+ homeostasis, is abundantly expressed in ameloblasts, and TRPM7 deficiency leads to enamel hypomineralization.
Because ameloblasts are lost after eruption, functional modeling of transport dynamics requires in vitro model systems. HAT-7 ameloblast cells, previously shown to form polarized monalayer with vectorial bicarbonate transport, were therefore used to investigate the role of TRPM7 in Ca2+ transport. This thesis focused on: (1) identifying the functional presence, Ca²⁺ conductance, and pH sensitivity of TRPM7 in HAT-7 cells, and (2) examining purinergic and cholinergic receptor activity in 3D cultures of these cells.
HAT-7 cells expressed TRPM7 at both mRNA and protein levels and displayed TRPM7-like transmembrane currents in whole-cell patch-clamp recording. sensitive to extracellular acidfication. TRPM7 activators (mibefradil and naltriben) induced Ca2+ influx, which was further enhanced by intracellular acidification, indicating functional and pH-sensitive TRPM7 channels in unpolarized cells. In polarized monolayers, mibefradil evoked Ca2+ responses predominantly at the apical membrane, suggesting polarized distribution of TRPM7 proteins. In 3D spheroid cultures, HAT-7 cells exhibited purinergic Ca²⁺ signaling characteristic of P2Y2/P2Y4 receptors, whereas no functional muscarinic or nicotinic acetylcholine receptors were detected.
Taken together, HAT-7 cells abundantly express functional TRPM7 channels with Ca2+ conductance modulated by intra- and extracellular pH. This suggests a potential link between environmental pH changes and Ca2+ transport during amelogenesis. Therefore, HAT-7 ameloblasts, cultured as unpolarised, polarized or 3D speroid culture could serve as a physiologically relevant in vitro model for investigating ion transport mechanisms in enamel formation.
