Peptide Design for Mesenchymal Stem Cell Specific Attachment on Apatite Surfaces for Bone Tissue Regeneration.

Abstract

Over 2 million bone grafting procedures are performed annually worldwide for the treatment of bone defects. Cell transplantation therapies are promising alternatives to conventional auto-, allo-, and xenograft therapies. Successfully delivering stem and progenitor cells to the defect site requires biomaterials that support and guide reconstruction. Biomaterial functionalization with extracellular matrix derivatives to improve adhesion and guide tissue regeneration lacks specificity towards particular regenerative cell populations. In order to direct cell specific adhesion to specific biomaterial surface chemistries, we used a combinatorial phage display strategy to identify 2 sequences, 1 with high affinity towards apatite (VTK) and a second with high affinity to clonally derived mesenchymal stem cells (MSC) from human bone marrow stroma (DPI) and combined the two sequences into a dual-functioning peptide (DPI-VTK). Dual-functioning peptide DPI-VTK exhibited greater apatite binding compared to single peptide controls (p < 0.01). Mesenchymal stem cells on DPI-VTK coated apatite substrates exhibited greater adhesion strength compared to pre-osteoblasts and fibroblasts (p <0.01). DPI-VTK also increased MSC spreading (p < 0.001) and proliferation (p < 0.001) compared to apatite controls while supporting differentiation on apatite substrates. Competitive inhibition revealed RGD-binding integrin involvement in MSC attachment to DPI-VTK. MSC driven bone formation, cellularity and vascularization in a subcutaneous mouse model were greater on DPI-VTK coated PLGA-mineral composite scaffolds compared to VTK (p < 0.017) and uncoated controls (p <0.001) and acellular peptide-coated controls (p <0.002). Taken together, DPI-VTK improves MSC specific attachment and subsequent adhesion on mineralized substrates driving greater proliferation and bone formation compared to acellular and non-peptide coated controls. A vast array of biomaterials and multitude of regenerative cell sources are available for tissue regeneration applications. As tissue engineering shifts from developing technologies to meet general clinical challenges to addressing more focused clinical applications, there will be an increased need for delivering cell specific cues to material surfaces with defined surface chemistries. Combinatorial phage display is a powerful platform to enable focused cell based tissue regeneration through the discovery of cell specific and material specific peptide sequences.