Injectable hydrogel delivery plus preconditioning of mesenchymal stem cells: exploitation of SDF-1/CXCR4 axis toward enhancing the efficacy of stem cells’ homing

Clinical applications of mesenchymal stem cells (MSCs) rely on their capacity to home in on and engraft in the appropriate target injury tissues for the long term. However, their homing efficiency has been observed to be very poor because of the lack or modifications of homing factors SDF-1a and CXCR4 receptor. Hence, this study was designed to investigate the homing and retention of pretreated human adipose tissuederived MSCs (hASCs) from three different delivery routes in response to SDF-1a released from chitosan-based injectable hydrogels. After stimulation of ASCs with a hypoxia mimicking agents, overexpression and functionality of CXCR4 was analyzed by flowcytometric analysis (FACS), transwell migration assay and qPCR. Then, the homing/retention of pretreated DiI-labeled hASCs were compared through three different in vivo delivery routes, two weeks after transplantation in Wistar Rats. The cells were tracked histologically by fluorescent microscope, and by PCR for humanspecific CXCR4 gene. Results showed CXCR4 has dynamic expression and pretreatment of hASCs significantly up-regulates CXCR4, led to increase in vitro migration capacity toward 100ng/ml SDF-1a, and in vivo homing into the subcutaneously implanted hydrogel releasing SDF-1a. Furthermore, it seems that SDF1a is particularly important in the retention of ASCs, in addition to its chemoattraction role. In summary, the delivery route in which the ASCs were mixed with the hydrogel