Maturation stage enamel malformations in Amtn and Klk4 null mice

Matrix Biol. 2016 May-Jul:52-54:219-233. doi: 10.1016/j.matbio.2015.11.007. Epub 2015 Nov 24.

Abstract

Amelotin (AMTN) and kallikrein-4 (KLK4) are secreted proteins specialized for enamel biomineralization. We characterized enamel from wild-type, Amtn(-/-), Klk4(-/-), Amtn(+/-)Klk4(+/-) and Amtn(-/-)Klk4(-/-) mice to gain insights into AMTN and KLK4 functions during amelogenesis. All of the null mice were healthy and fertile. The mandibular incisors in Amtn(-/-), Klk4(-/-) and Amtn(-/-)Klk4(-/-) mice were chalky-white and chipped. No abnormalities except in enamel were observed, and no significant differences were detected in enamel thickness or volume, or in rod decussation. Micro-computed tomography (μCT) maximum intensity projections localized the onset of enamel maturation in wild-type incisors distal to the first molar, but mesial to this position in Amtn(-/-), Klk4(-/-) and Amtn(-/-)Klk4(-/-) mice, demonstrating a delay in enamel maturation in Amtn(-/-) incisors. Micro-CT detected significantly reduced enamel mineral density (2.5 and 2.4gHA/cm(3)) in the Klk4(-/-) and Amtn(-/-)Klk4(-/-) mice respectively, compared with wild-type enamel (3.1gHA/cm(3)). Backscatter scanning electron microscopy showed that mineral density progressively diminished with enamel depth in the Klk4(-/-) and Amtn(-/-)Klk4(-/-) mice. The Knoop hardness of the Amtn(-/-) outer enamel was significantly reduced relative to the wild-type and was not as hard as the middle or inner enamel. Klk4(-/-) enamel hardness was significantly reduced at all levels, but the outer enamel was significantly harder than the inner and middle enamel. Thus the hardness patterns of the Amtn(-/-) and Klk4(-/-) mice were distinctly different, while the Amtn(-/-)Klk4(-/-) outer enamel was not as hard as in the Amtn(-/-) and Klk4(-/-) mice. We conclude that AMTN and KLK4 function independently, but are both necessary for proper enamel maturation.

Keywords: Ameloblasts; Amelotin; Kallikrein-4; Knoop hardness; Null mice; μCT.

Publication types

  • Review
  • Research Support, Non-U.S. Gov't
  • Research Support, N.I.H., Extramural

MeSH terms

  • Amelogenesis*
  • Animals
  • Dental Enamel / abnormalities*
  • Dental Enamel / diagnostic imaging
  • Dental Enamel Proteins / genetics*
  • Incisor
  • Kallikreins / genetics*
  • Mice
  • Mice, Knockout
  • Microscopy, Electron, Scanning
  • Molar
  • Tooth Calcification
  • X-Ray Microtomography

Substances

  • Amtn protein, mouse
  • Dental Enamel Proteins
  • Kallikreins
  • kallikrein 4