Leucine-rich amelogenin peptide induces osteogenesis by activation of the Wnt pathway

Abstract

We previously showed that one of the amelogenin splicing isoforms, Leucine-rich Amelogenin Peptide (LRAP), induced osteogenic differentiation of mouse embryonic stem cells; however, the signaling pathway(s) activated by LRAP remained unknown. Here, we demonstrated that the canonical Wnt/β-catenin signaling is activated upon LRAP treatment, as evidenced by elevated β-catenin level and increased Wnt reporter gene activity. Furthermore, a specific Wnt inhibitor sFRP-1 completely blocks the LRAP-mediated Wnt signaling. However, exogenous recombinant Wnt3a alone was less effective at osteogenic induction of mouse ES cells in comparison to LRAP. Using a quantitative real-time PCR array, we discovered that LRAP treatment up-regulated the expression of Wnt agonists and down-regulated the expression of Wnt antagonists. We conclude that LRAP activates the canonical Wnt signaling pathway to induce osteogenic differentiation of mouse ES cells through the concerted regulation of Wnt agonists and antagonists.

Amelogenin Peptide Extract Increases Differentiation and Angiogenic and Local Factor Production and Inhibits Apoptosis in Human Osteoblasts

“…In contrast to the four peaks found in the original fractionation [29], here we found that Fraction C contained just two peaks, one of 43 amino acids and the other one corresponding to 45 amino acids in length, which correspond to the previously reported TRAP species [28]. The LRAP portion of amelogenin has been shown to induce osteogenesis in vivo [49] and osteoblast maturation in vitro [50,51], but the effect of Fraction C, containing the TRAP portion, was unclear. In the current study, we provide evidence that primary human osteoblasts and osteoblast-like cells are sensitive to the Fraction C and that this active peptide increases osteoblast maturation.…”

Cytomegalovirus Induces Stage-Dependent Enamel Defects and Misexpression of Amelogenin, Enamelin and Dentin Sialophosphoprotein in Developing Mouse Molars

“…Given that canonical Wnt/ ␤ -catenin signaling regulates tooth shape and root formation [Yamashiro et al, 2007;Liu et al, 2008;Nemoto et al, 2009], the significantly higher ␤ -catenin expression in Bell stage-infected molars as compared to Cap stage-infected molars likely mediates the improved tooth morphology and root formation. Furthermore, since amelogenins activate the canonical Wnt/ ␤ -catenin pathway [Matsuzawa et al, 2009;Warotayanont et al, 2009] and Wnt/ ␤ -catenin signaling regulates Dspp transcript expression [Yamashiro et al, 2007], the significantly higher Dspp expression in Bell stage-infected molars may be due, in part, to the significantly approximately 25-30% higher (p ! 0.001) Amelx and ␤ -catenin transcript expression.…”

“…However, amelogenin transcripts and proteins have also been found in odontoblasts, pulp cells and cementoblasts in developing teeth [Oida et al, 2002;Veis, 2003;Papagerakis et al, 2003Papagerakis et al, , 2005, as well as in tissues not related to odontogenesis (for example, brain cells, hematopoietic cells and chondrogenic/osteogenic cells) [for review, see Deutsch et al, 2006]. In vitro and in vivo studies have clearly demonstrated that amelogenins have signaling properties [Hoang et al, 2002;Veis, 2003;Tompkins et al, 2005Tompkins et al, , 2006Zeichner-David et al, 2006;Ye et al, 2006;Matsuzawa et al, 2009;Warotayanont et al, 2009].…”

Wnt Proteins in Mineralized Tissue Development and Homeostasis

“…Certain isoforms of amelogenin, the predominant protein product of ameloblasts, have been shown to have signaling capability [34]. Notably, several studies have shown amelogenin signaling is effected, in part, through canonical Wnt signaling mechanisms as evidenced by the ability of full-length amelogenin and an amelogenin-spliced isoform, leucine-rich amelogenin peptide (LRAP), to induce increased protein levels of β-catenin and stimulate Wnt reporter gene activity [35,36]. A subsequent study has revealed LRAP stimulation of bone marrow stem cells induced osteogenesis with activation of the Wnt signaling pathway observed [37].The expression of Wnt10b by these cells was detected and the osteogenic activity of LRAP was inhibited by application of sFRP1.…”