Abstract
Targeting specific populations of host cells with chemotactic and adhesion factors is a promising strategy for inducing bone regeneration without the use of exogenous cells. Two peptide sequences have been derived from phage display: the mesenchymal stem cell (MSC) binding DPI (DPIYALSWSGMA) sequence and the apatite binding VTK (VTKHLNQISQSY) sequence. When combined into the dual-functional sequence, DPI-VTK increases the adhesion strength of MSCs to apatite surfaces and the amount of bone formation with transplanted MSCs. Because many adhesion molecules can stimulate chemotaxis, and cell adhesion to peptide DPI-VTK is mediated by integrins also critical to migration, we hypothesized that DPI-VTK serves as an MSC-specific chemotactic factor and can increase bone regeneration by promoting the osteogenesis of the migrated host MSCs in vivo. In transwell assays, induced pluripotent stem cell-derived human MSCs (p < 0.0001) and primary mouse calvarial cells (p < 0.0001) showed significantly increased migration in vitro when DPI-VTK was used as a chemoattractant. Further characterization of DPI-VTK binding cells from mouse calvaria using flow cytometry showed specificity toward cells expressing MSC markers (CD29, CD73, CD90, CD105, CD106, Sca-1, CD44, and CD200). When conjugated to a mineralized scaffold in vivo, DPI-VTK increased the migration of CD90 and CD200 positive cells (p < 0.05) and increased bone formation versus no-peptide controls (p < 0.05). These results demonstrate the utility of phage display in creating multifunctional peptides that can increase migration, adhesion, and bone formation in vivo, a strategy that could be applied to numerous different cell types and systems. Results advance biomaterials-based bone regeneration in two ways-demonstrating the ability of the phage-derived peptides to increase the migration of MSCs in vivo and increase host-mediated bone regeneration-potentially bypassing cell transplantation.