Wnt/β-Catenin Signaling Mediates Osteoblast Differentiation Triggered by Peptide-induced α5β1 Integrin Priming in Mesenchymal Skeletal Cells

• Published in: The Journal of biological chemistry 2015-03, Vol.290 (11), p.6903-6912
• Main Authors: Saidak, Zuzana, Le Henaff, Carole, Azzi, Sofia, Marty, Caroline, Da Nascimento, Sophie, Sonnet, Pascal, Marie, Pierre J.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; beta Catenin - metabolism; Bone; Bone and Bones - drug effects; Bone and Bones - metabolism; Bone and Bones - pathology; Bone Diseases, Metabolic - drug therapy; Bone Diseases, Metabolic - metabolism; Bone Diseases, Metabolic - pathology; Cell Differentiation; Cell Differentiation - drug effects; Cell Line; CRRETAWAC; Humans; Integrin; Integrin alpha5beta1 - metabolism; Life Sciences; Mesenchymal Stem Cells - cytology; Mesenchymal Stem Cells - drug effects; Mesenchymal Stem Cells - metabolism; Mice; Oligopeptides - chemistry; Oligopeptides - pharmacology; Oligopeptides - therapeutic use; Osteoblast; Osteoblasts - cytology; Osteoblasts - drug effects; Osteoblasts - metabolism; Osteogenesis - drug effects; Osteopenic Mice; Phosphatidylinositol 3-Kinases - metabolism; Signal Transduction; Wnt Signaling; Wnt Signaling Pathway - drug effects
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M114.621219

The α5β1 integrin is a key fibronectin (FN) receptor that binds to RGD-containing peptides to mediate cell adhesion. We previously reported that α5β1 integrin promotes osteogenic differentiation in mesenchymal skeletal cells (MSCs), but the underlying mechanisms are not fully understood. In this study, we determined the signaling mechanisms induced by α5β1 integrin interaction with its high-affinity ligand CRRETAWAC in murine and human MSCs and in vivo. We show that cyclized CRRETAWAC fully displaced MSC adhesion to FN, whereas related peptides lacking the full RRET sequence produced a partial displacement, indicating that RRET acts as an RGD-like sequence that is required to antagonize FN-mediated cell adhesion. However, all peptides increased focal adhesion kinase phosphorylation, OSE2 transcriptional activity, osteoblast gene expression, and matrix mineralization in MSCs, indicating that peptide-induced α5β1 integrin priming can promote osteogenic differentiation independently of the RRET sequence. Biochemical analyses showed that peptide-induced α5β1 integrin priming transiently increased PI3K/Akt phosphorylation and promoted Wnt/β-catenin transcriptional activity independently of RRET. Consistently, pharmacological inhibition of PI3K activity reduced osteoblast differentiation and abolished Wnt regulatory gene expression induced by α5β1 integrin priming. In vivo, systemic delivery of cyclized GACRETAWACGA linked to (DSS)6 to allow delivery to bone-forming sites for 6 weeks increased serum osteocalcin levels and improved long bone mass and microarchitecture in SAMP-6 senescent osteopenic mice. The results support a mechanism whereby α5β1 integrin priming by high-affinity ligands integrates Wnt/β-catenin signaling to promote osteoblast differentiation independently of cell adhesion, which could be used to improve bone mass and microarchitecture in the aging skeleton. Background: The mechanisms whereby α5β1 integrin triggers osteogenesis are poorly understood. Results: CRRETAWAC-mediated α5β1 integrin priming promotes osteoblast differentiation via PI3K/Wnt/β-catenin signaling independently of the RGD-like REET sequence. Systemic delivery of the α5β1 integrin-priming peptide improved long bone microarchitecture in senescent osteopenic mice. Conclusion: Wnt signaling mediates osteoblast differentiation induced by peptide-mediated α5β1 integrin priming. Significance: A novel mechanism underlying α5β1 integrin-mediated osteoblast differentiation is provided