ABSTRACT: Abstract: Stem cell therapies are severely limited by poor cell survival and engraftment rates. A major hurdle to the use of materials for cell delivery is the lack of understanding of material properties that govern transplanted stem cell functionality. Here, we show that synthetic hydrogels presenting integrin-specific peptides enhance the survival, persistence, and osteo-reparative functions of human mesenchymal stem cells (hMSC) transplanted in murine bone defects. Integrin-specific hydrogels regulated hMSC adhesion, paracrine signaling, and osteoblastic differentiation in vitro. Hydrogels presenting GFOGER, a triple helical peptide targeting α2β1 integrin, prolonged hMSC survival and engraftment in a segmental bone defect and resulted in improved bone repair compared to other adhesive and control peptides. Moreover, integrin-specific hydrogels had diverse pleiotropic effects on hMSC reparative activities, modulating in vitro cytokine secretion and in vivo gene expression for effectors associated with inflammation, vascularization, and bone formation. These results demonstrate that integrin specificity can be engineered into synthetic hydrogel systems resulting in improved tissue healing by directing mesenchymal stem cell survival, engraftment, paracrine immunomodulatory potential, and reparative activities. Radial segmental defects were treated with hydrogels functionalized with adhesive peptide and encapsulated hMSC. The tissue within the defect space was explanted at 1 week post-transplantation and stored in RNAlater solution (Qiagen) until further processing. Samples were placed in Qiazol solution (Qiagen), lysed by probe sonication, and homogenized in QIAshredder columns (Qiagen). Total RNA was isolated using an RNAeasy Plus Micro kit (Qiagen), and RNA content and purity were measured by spectrophotometry (NanoDrop 1000). cDNA synthesis was performed on total RNA (100 ng) using the High-Capacity RNA-to-cDNA Kit (Thermo Fisher). Quantitative PCR was performed using Fluidigm 96×96 nanofluidic arrays targeting a set of 96 transcripts (human or murine) to observe changes in bone, survival, inflammation, vascularization, and matrix markers. Primers used are listed in Supplementary Table 4. The genes were pre-amplified in a single 13-cycle PCR reaction for each sample with EvaGreen Mastermix (Fluidigm BioMark) following the manufacturer’s protocol. Sixty-three gene targets resulted in detectable qPCR results. All subsequent statistical analyses were carried out using JMP-Genomics (SAS Institute) using the basic gene expression workflow 62. Raw Ct values were imported into JMP-Genomics and normalized to mean Ct values across all genes for each sample for principal components analysis (PCA), assessment of the biological principal variance component contributions (PVCA), and hierarchical clustering using Ward’s method to identify sub-types of expression profile. Finally, one-way ANOVA was used to detect statistical differences followed by False Discovery Rate analysis using two-state linear step-up procedure of Benjamini, Krieger and Yekutieli. Results are presented as raw Ct values normalized to mean Ct values across all genes for a sample.
