(554c) Engineering Microenvironments to Regulate Mesenchymal Stem Cell Secretome

Improved understanding of stem cell biology has resulted in widespread investigation of the therapeutic potential of mesenchymal stem cells (MSCs) for developing cell-based therapies for restoration of tissue/organ integrity. While classically the therapeutic benefit of mesenchymal stem cells (MSCs) was attributed to their broad plasticity and ability to act as tissue-specific progenitors, low engraftment and retention rate of MSCs at the target site refutes the hypothesis that the donor cells can functionally integrate with the damaged tissue to facilitate the repair or regeneration process. Instead, mounting evidence attributes the soluble factors secreted by these cells to the therapeutic effects of stem cells. This diverse array of biomolecules including cytokines, chemokines, angiogenic factors, growth factors, extracellular matrix proteases, and hormones known as “secretome” is believed to play critical role in the regulation of numerous physiological processes. While the microenvironmental cues play an important role in orchestrating the commitment decisions of MSCs, not much is known how they influence the secretory profile of MSCs.

In this study, gelatin methacrylate (GelMA) based scaffolds were developed with stiffness ranging from 1kPa to 25 kPa. Our results indicated that human bone marrow-derived MSCs seeded on GelMA matrices exhibited enhanced proliferation and elongated spindle shaped morphology (confocal imaging via phalloidin staining) with increasing matrix stiffness. For correlating the secretory activity of MSCs with matrix stiffness, the conditioned media was collected and concentration of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and platelet derived growth factor (PDGF) in the media was measured by ELISA. It was observed that MSCs prefer a matrix of optimal stiffness for maximal release of VEGF(180 pg/1000 cells). However, no statistical difference was observed in secretion pattern of bFGF and PDGF with changes in matrix mechanics. Enhanced pro-angiogenic signaling of MSC secretome was further confirmed by the angiogenesis assay. For the purpose, Matrigel culture of human umbilical vein endothelial cells (HUVECs) in the presence of conditioned media collected from MSCs grown on matrices of varying stiffness was carried out. Tube area in the presence of conditioned media collected from MSCs seeded on optimized matrix stiffness was found to be significantly higher. MSCs were then plated on matrices of same stiffness but varying GelMA concentration. Variation in GelMA concentration did not have any significant impact on pro-angiogenic signaling of MSCs. These observations suggest that harnessing MSC secretome by manipulating matrix mechanics may potentially be a reasonable approach for enhancing the therapeutic capacity of MSCs.

This study was funded by Alternatives Research and Development Foundation and University of Michigan-Dearborn Office of Sponsored Research.