Cell-secreted matrices perpetuate the bone-forming phenotype of differentiated mesenchymal stem cells

Prior to transplantation, mesenchymal stem/stromal cells (MSCs) can be induced toward the osteoblastic phenotype using a cocktail of soluble supplements. However, there is little evidence of differentiated MSCs directly participating in bone formation, suggesting that MSCs may either die or revert in phenotype upon transplantation. Cell-secreted decellularized extracellular matrices (DMs) are a promising platform to confer bioactivity and direct cell fate through the presentation of a complex and physiologically relevant milieu. Therefore, we examined the capacity of biomimetic DMs to preserve the mineral-producing phenotype upon withdrawal of the induction stimulus. Regardless of induction duration, ranging up to 6 weeks, MSCs exhibited up to a 5-fold reduction in osteogenic markers within 24 h following stimulus withdrawal. We show that seeding osteogenically induced MSCs on DMs yields up to 2-fold more calcium deposition than tissue culture plastic, and this improvement is at least partially mediated by increasing actin cytoskeletal tension via the ROCK II pathway. MSCs on DMs also secreted 25% more vascular endothelial growth factor (VEGF), a crucial endogenous proangiogenic factor that is abrogated during MSC osteogenic differentiation. The deployment of DMs into a subcutaneous ectopic site enhanced the persistence of MSCs 5-fold, vessel density 3-fold, and bone formation 2-fold more than MSCs delivered without DMs. These results underscore the need for deploying MSCs using biomaterial platforms such as DMs to preserve the in vitro-acquired mineral-producing phenotype and accelerate the process of bone repair.