Interaction of enamel matrix proteins with human periodontal ligament cells

OBJECTIVES: It has recently been shown that enamel matrix derivative (EMD) components (Fraction C, containing <6 kDa peptides (mainly a 5.3 kDa tyrosine-rich amelogenin peptide (TRAP)), and Fraction A, containing a mixture of >6 kDa peptides (including a leucine-rich amelogenin peptide (LRAP))) differentially regulate osteogenic differentiation of periodontal ligament (PDL) cells. The present study examined whether EMD and the EMD Fractions (i) bind and internalize into PDL cells and (ii) precipitate and form insoluble complexes on PDL cells. MATERIALS AND METHODS: Biotin-labelled EMD/EMD Fractions were incubated with PDL cells under various different culture conditions and confocal and electron microscopies were carried out to examine the binding and intracellular trafficking of these proteins. RESULTS: The results reported here show, for the first time, that at least some components in Fraction A and the TRAP peptide in Fraction C can bind and be internalized by human PDL cells via receptor-mediated endocytosis. In addition, Fraction A was found to form insoluble aggregate-like structures on PDL cells, whereas Fraction C was soluble in culture media. CONCLUSION: Soluble amelogenin isoform TRAP appears to be internalizing into a subset of PDL cells. Moreover, TRAP uptake is most likely controlled by receptor-mediated endocytosis. CLINICAL RELEVANCE: Information on interaction between PDL cells and EMD/TRAP might prove useful in designing targeted interventions (i.e. use of chemically prepared soluble amelogenin peptides) to repair/regenerate periodontal tissues. Such interventions can also (i) avoid the use of rather crude animal-derived enamel matrix protein (EMP)/EMD preparation and (ii) preparation of cost-effective and more controlled chemically synthesized amelogenin peptides for the clinical use. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00784-015-1510-8) contains supplementary material, which is available to authorized users.