Localization and function of the anion exchanger Ae2 in developing teeth and orofacial bone in rodents

Abstract

To explore functions of anion exchanger 2 (Ae2) in the development of bones and teeth we examined the distribution of Ae2 in cells involved in formation of teeth and surrounding bone in young hamsters, mice and rats. In all three species strongest immunostaining for Ae2 was obtained in basolateral membranes of maturation ameloblasts and in osteoclasts resorbing bone. In hamsters a weaker staining was also seen in the Golgi apparatus of secretory ameloblasts, young osteoblasts and osteocytes, odontoblasts and fibroblasts of the forming periodontal ligament. In adult Ae2a,b-/- mice, in which Ae2 targeted disruption precluded the expression of Ae2a, Ae2b1 and Ae2b2 isoforms, the immunostaining for Ae2 in ameloblasts and osteoclasts was totally abolished. Enamel formation was abnormal but teeth erupted, osteoclasts in jaw bone were functional and structure of dentin and bone was normal. In another mouse model, Ae2-/- mice in which expression of all five Ae2 isoforms was disrupted, teeth failed to erupt and the alveolar bone proved poorly formed with giant but apparently functional osteoclasts. Our data indicate that basolaterally located Ae2a, Ae2b1, or Ae2b2 (or a combination of these) is present in maturation ameloblasts critical for the cells’ normal functioning. While isoforms of AE2 were also present in basolateral membranes of osteoclasts they proved not critical to osteoclast resorption of orofacial bone. Poorly formed bone and the failure of teeth to erupt seen in the Ae2-/- mice with gene disruption affecting all isoforms may result from secondary (systemic) changes that are different from Ae2a,b-/- mice.

Ion transporters in secretory and cyclically modulating ameloblasts: a new hypothesis for cellular control of preeruptive enamel maturation

“…In our data the labeling intensity of AE2 was markedly reduced in SA cells compared with RA cells in accordance with a weak or negative immunostaining of AE2 in SA bands of mouse incisors observed by Bronckers et al (5). In AE2 a,bdeficient mice, Lyaruu et al (25) have demonstrated that absence of AE2 a,b interferes with the final mineralization of enamel, resulting in less mineral and more protein than in wild-type enamel.…”

“…So far, few papers have dealt with the presence of a limited number of pumps, channels, or exchangers in the enamel organ (5,24,25,31,32,45).…”

SLC4A2-mediated Cl − /HCO 3 − exchange activity is essential for calpain-dependent regulation of the actin cytoskeleton in osteoclasts

“…The milder phenotype of Slc4a2a,b −/− mice could reflect compensatory expression of SLC4A2c, differences in genetic background, or discrepant functions for SLC4A2 isoforms in other skeletal cells or tissues with hormonal and metabolic effects on bone. Supporting this last possibility are observations that SLC4A2 is expressed and functional in osteoblasts, ameloblasts, and the gut and kidney (15)(16)(17)29). Taken together, these studies left uncertain the relative role of SLC4A2 within the osteoclast for its potential broader function in other cells involved in bone homeostasis.…”

Amelogenins as Potential Buffers during Secretory-stage Amelogenesis

“…Dewaxed and rehydrated paraffin sections were washed in Tris-buffered saline (TBS). Anti-Ae2 staining required retrieval in 10 mM citrate buffer (pH 6.0) overnight at 60ºC (Bronckers et al 2009). Staining in extracellular enamel matrix with anti-porcine amelogenins sections required retrieval in 0.5 mM EGTA in 10-mM Tris (pH 9.0) at 60°C for 5 h. Endogenous peroxidase was inactivated by 5-minute incubation in Dual Endogenous Enzyme Block (EnVision kit, DakoCytomation, Glostrup, Denmark), then washed in TBS and blocked with normal goat sera.…”

“…The mineral density was determined by microcomputed tomography (microCT), and the enamel composition by quantitative electron probe x-ray microanalysis (EPMA). Changes in pH in forming enamel were assessed by staining with methyl-red solution and immunolocalization of anion exchanger-2 (Ae2), a critical pH regulator in maturation ameloblasts (Bronckers et al 2009;Lyaruu et al 2014). …”