Enamel: Molecular identity of its transepithelial ion transport system

Abstract

Enamel is the most calcified tissue in vertebrates. It differs from bone in a number of characteristics including its origin from ectodermal epithelium, lack of remodeling capacity by the enamel forming cells, and absence of collagen. The enamel-forming cells known as ameloblasts, choreograph first the synthesis of a unique protein-rich matrix, followed by the mineralization of this matrix into a tissue that is ~95% mineral. To do this, ameloblasts arrange the coordinated movement of ions across a cell barrier while removing matrix proteins and monitoring extracellular pH using a variety of buffering systems to enable the growth of carbonated apatite crystals. Although our knowledge of these processes and the molecular identity of the proteins involved in transepithelial ion transport has increased in the last decade, it remains limited compared to other cells. Here we present an overview of the evolution and development of enamel, its differences with bone, and describe the ion transport systems associated with ameloblasts.

CRAC channels in dental enamel cells

“…Growth of enamel crystals takes place in the extracellular space only, near the apical (distal) pole of the ameloblasts, which are heavily polarized cells [13]. This extracellular space is largely inaccessible to ions and molecules unless these are transiting through the ameloblasts [13, 14]. In this space, there is an aqueous solution whose composition is largely modulated by the cells, differing from the ionic composition of serum and thereby confirming the status of the enamel fluid as a specialized microenvironment [15].…”

Defense Mechanisms Against Acid Exposure by Dental Enamel Formation, Saliva and Pancreatic Juice Production

“…However, many studies have been published on the matter using fine structural hard and soft tissue examinations, histological studies, also applying genetic knock-out of genes and studies investigating the chemical composition of enamel. Based on these works, four recent reviews have been published that nicely cover our present knowledge on amelogenesis [ 4 , 102 - 104 ].…”

Integrative Temporo-Spatial, Mineralogic, Spectroscopic, and Proteomic Analysis of Postnatal Enamel Development in Teeth with Limited Growth

“…While much is known about the major proteins and minerals involved in tooth enamel formation, it has become increasingly obvious that amelogenesis is more complex than a mixture of an aqueous enamel protein solution with a combination of calcium and phosphate ions, subjected to enzymatic protein digestion and gradual removal of water over time. Recent studies have illustrated the importance of ion transport mechanisms for mineral transport (Hubbard, 2000 ; Paine et al, 2001 ; Lacruz, 2017 ), the effect of pH modulation through regulatory molecules (Takagi et al, 1998 ; Lacruz et al, 2010 ; Moradian-Oldak, 2012 ; Robinson, 2014 ) and the role of junctional proteins such as cadherins for ameloblast movement (Bartlett and Smith, 2013 ; Guan et al, 2014 ). These molecules and events are only one part of a process that ensures a gradual deposition of minerals at the dentin-enamel junction throughout amelogenesis and their step-wise conversion into hydroxyapatite crystals and alignment into enamel prisms into one of the most fascinating biomaterials found in nature.…”