The anion exchanger Ae2 is required for enamel maturation in mouse teeth

Abstract

One of the mechanisms by which epithelial cells regulate intracellular pH is exchanging bicarbonate for Cl − . We tested the hypothesis that in ameloblasts the anion exchanger-2 (Ae2) is involved in pH regulation during maturation stage amelogenesis. Quantitative X-ray microprobe mineral content analysis, scanning electron microscopy, histology, micro-computed tomography and Ae2 immunolocalisation analyses were applied to Ae2-deficient and wild-type mouse mandibles. Immunolocalisation of Ae2 in wild-type mouse incisors showed a very strong expression of Ae2 in the basolateral membranes of the maturation stage ameloblasts. Strikingly, zones of contiguous ameloblasts were found within the maturation stage in which Ae2 expression was extremely low as opposed to neighbouring cells. Maturation stage ameloblasts of the Ae2 a,b −/− mice failed to stain for Ae2 and showed progressive disorganisation as enamel development advanced. Maturation stage enamel of the Ae2 a,b −/− mice contained substantially less mineral and more protein than wild-type enamel as determined by quantitative X-ray microanalysis. Incisor enamel was more severely affected than molar enamel. Scanning electron microscopy revealed that the rod-inter-rod structures of the Ae2 a,b −/− mice incisor enamel were absent. Mineral content of dentine and bone of Ae2 a,b −/− mice was not significantly different from wild-type mice. The enamel from knockout mouse teeth wore down much faster than that from wild-type litter mates. Basolateral bicarbonate secretion via the anionic exchanger Ae2 is essential for mineral growth in the maturation stage enamel. The observed zonal expression of Ae2 in the maturation stage ameloblasts is in line with a model for cyclic proton secretion during maturation stage amelogenesis.

Molecular physiology and genetics of Na+-independent SLC4 anion exchangers

“…However, hepatobiliary epithelial cells exhibit apical (Aranda et al, 2004;Martinez-Anso et al, 1994) or subapical (Tietz et al, 2003) immunolocalization of AE2. Apical membrane AE2 was also detected in the ameloblast of the Ae2 a,b -/-mouse (Paine et al, 2008) in unfixed sections, but without the accompanying Ae2 -/-tissue controls included in the study detecting lateral localization in the complete Ae2 knockout mouse (Lyaruu et al, 2008).…”

“…It is also expressed throughout the nephron, but most abundantly in the medullary thick ascending limb and the inner medullary collecting duct. AE2 is a major Cl -/HCO 3 -exchanger of the osteoclast contralacunar membrane Josephsen et al, 2009) and in the lateral membrane of dental secretory ameloblasts (Lyaruu et al, 2008). However, hepatobiliary epithelial cells exhibit apical (Aranda et al, 2004;Martinez-Anso et al, 1994) or subapical (Tietz et al, 2003) immunolocalization of AE2.…”

“…The grossly normal Ae2 a,b -/-mouse exhibits male infertility associated with testicular dysplasia (Medina et al, 2003). However, the Ae2 a,b -/-mouse is also hypomorphic for other phenotypes of the complete knockout mouse, including osteopetrosis (Josephsen et al, 2009), failure of dental enamelization (Lyaruu et al, 2008), and reduced stimulated gastric acid secretion in the setting of preserved basal acid secretion, accompanied by chronic, mild mucosal degeneration (Recalde et al, 2006).…”

The Impact of Fluoride on Ameloblasts and the Mechanisms of Enamel Fluorosis

“…The importance of pH regulation in enamel formation has been emphasized in recent studies of alterations to functional exchangers, co-transporters, and chloride channels found to be present in ameloblasts (Wright et al, 1996a,b;Lyaruu et al, 2008a;Paine et al, 2008;Bronckers et al, 2009). Mutations in or deletions of these molecules present enamel phenotypes quite similar to those seen in enamel fluorosis (without hypermineralization lines), and suggest that these genes are potential factors that may be related to susceptibility to fluoride.…”

Neuropathology and Craniofacial Lesions of Osteopetrotic Red Angus Calves

“…6,22 Normal dental eruption with failure of enamelization and with disorganized ameloblasts is reported in 1 SLC4A2 knockout strain. 28 A useful gross diagnostic feature of osteopetrosis in affected Angus calves is unerupted teeth with crowding and abnormal alignment, combined with brachygnathia. Histologic changes were most marked in premolars and molars, with dysplastic intermingling of dentin, enamel, cementum, and bone at the base of the pulp chamber, which resulted in dental ankylosis.…”