Abstract
The Leucine Rich Amelogenin Peptide (LRAP) is a product of alternative splicing of the amelogenin gene. As full length amelogenin, LRAP has been shown, in precipitation experiments, to regulate hydroxyapatite (HAP) crystal formation depending on its phosphorylation status. However, very few studies have questioned the impact of its phosphorylation status on enamel mineralization in biological models. Therefore, we have analyzed the effect of phosphorylated (+P) or non-phosphorylated (−P) LRAP on enamel formation in ameloblast-like cell lines and ex vivo cultures of murine postnatal day 1 molar germs. To this end, the mineral formed was analyzed by micro-computed tomography, Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy, Selected Area Electon Diffraction imaging. Amelogenin gene transcription was evaluated by qPCR analysis. Our data show that, in both cells and germ cultures, LRAP is able to induce an up-regulation of amelogenin transcription independently of its phosphorylation status. Mineral formation is promoted by LRAP(+P) in all models, while LRAP(–P) essentially affects HAP crystal formation through an increase in crystal length and organization in ameloblast-like cells. Altogether, these data suggest a differential effect of LRAP depending on its phosphorylation status and on the ameloblast stage at the time of treatment. Therefore, LRAP isoforms can be envisioned as potential candidates for treatment of enamel lesions or defects and their action should be further evaluated in pathological models.
Highlights
Dental Enamel is the outermost layer of the teeth and the most mineralized structure in the vertebrates, since it is constituted of at least 95% minerals
This study shows a differential effect of the Leucine Rich Amelogenin Peptide (LRAP) peptide on enamel formation, depending on its phosphorylation status in in vitro and ex vivo culture models
The LRAP peptide has proven of interest thanks to its signaling properties as well as its apparent effect on crystal growth and structure (Shaw et al, 2004; Beniash et al, 2009; Le Norcy et al, 2011a,b; WiedemannBidlack et al, 2011; Moradian-Oldak, 2012; Kwak et al, 2016, 2017)
Summary
Dental Enamel is the outermost layer of the teeth and the most mineralized structure in the vertebrates, since it is constituted of at least 95% minerals. Its microstructure is composed of nanorod-like hydroxyapatite (HA) crystals arranged in a highly organized unit called the enamel prism or rod. Prism high organization leads to enamel robust mechanical properties for tissue protection against cariogenic bacteria and mechanical force upon tooth function. Enamel is formed through synthesis, growth, and organization of these rods by specialized cells, the ameloblasts, throughout the process of amelogenesis. Ameloblasts are once and for all, degraded during the process of tooth eruption and they cannot regenerate and actively repair by themselves. In view of the high prevalence of dental caries and enamel defects, enamel regeneration, and repair has become a target for developing biomimetic therapeutic approaches (Cao et al, 2014; Ruan and Moradian-Oldak, 2015; Snead, 2015)
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