Integrin specificity as a novel strategy for enhancing transplanted stem cell survival and tissue repair in vivo

Abstract

Event Abstract Back to Event Integrin specificity as a novel strategy for enhancing transplanted stem cell survival and tissue repair in vivo Amy Clark1, 2* and Andres J. Garcia1, 2 1 Georgia Institute of Technology, Woodruff School of Mechanical Engineering, United States 2 Georgia Institute of Technology, Petit Institute for Bioengineering and Bioscience, United States Introduction: Despite the promising clinical results for the use of human mesenchymal stem cells (hMSC) in musculoskeletal defect treatment, inadequate control over cell survival, engraftment and fate limits the success of this cell-based therapy. Integrin-mediated cell adhesion plays a central role in tissue formation, maintenance, and repair by providing anchorage forces and triggering signals that regulate cell function. We hypothesize biomaterials presenting integrin-specific adhesive motifs will direct hMSC signaling and specification. The objective of this project is to engineer bioartificial hydrogels presenting integrin-specific ligands as biomimetic cell delivery vehicles for enhanced in vivo engraftment and function – an innovative strategy as it focuses on engineering specificity to integrin receptors to promote survival and cell-based repair without the use of exogenous growth factors. Methods: Early passage hMSC (<4) were transduced to constitutively express firefly luciferase (hMSCFLuc). 4-arm PEG-maleimide was functionalized with one of three ligands: α2β1-binding collagen I-mimetic GFOGER, αvβ3-binding RGD, or non-adhesive RDG peptides and cross-linked with a protease-degradable peptide. 2.5 mm defects were created in the radii of 8-9 week old male NOD scid gamma mice and treated with cell-laden hydrogels containing 15k hMSC. Bioluminescence was monitored using an In Vivo Imaging System (PerkinElmer). New bone formation was evaluated using an in vivo microcomputer tomography scanner (Scanco Medical). Gene expression was evaluated after 1 week in vivo. Total RNA was extracted from cells in the defect space and standardized across all samples. 96 total genes were screened using Fluidigm gene chip technology. Results: Bioluminescence of transplanted hMSCFLuc was monitored after transplantation (Fig 1A). The significantly higher bioluminescent signal in GFOGER/hMSCFLuc-treated defects suggests GFOGER hydrogels support transplanted cell survival and proliferation in vivo whereas the bioluminescent signals for hMSCFLuc delivered in a RGD or RDG hydrogel remained low. GFOGER/hMSC-treated defects exhibited significantly higher bone volume at weeks 4 and 8 compared to RGD and RDG with no statistical difference between groups receiving hMSCFLuc and hMSC (Fig 1B). Differences in gene expression for approximately 60 genes were observed after 1 week in vivo, with statistically higher expression of vascularization and inflammation genes in GFOGER/hMSC treated defects (Fig 2). Conclusions: GFOGER-functionalized PEG hydrogels support enhanced bone formation and hMSC viability in vivo compared to RGD and RDG, possibly via enhanced vascularization These studies are ongoing for immunohistochemical, cytokine, and defect vascularization analyses. This work highlights integrin-specificity as an important consideration in the design of cell delivery vehicles for engraftment and tissue repair. NIH grants R01 AR062368 and R01 AR062920