Hypoxic Preconditioning Combined with Microbubble-Mediated Ultrasound Effect on MSCs Promote SDF-1/CXCR4 Expression and its Migration Ability: An In Vitro Study

Our objective is to investigate the promoting effect of hypoxic preconditioning combined with microbubble (MB)-mediated ultrasound (US) on the SDF-1/CXCR4 expression and the migration ability of mesenchymal stem cells (MSCs). Based on the uniform design, the parameters of MB-mediated US, such as the total treatment time (T), acoustic intensity (Q), and the dosage of MBs, were optimized firstly. The results were assessed by regression analysis. Using the optimum irradiation parameters, the concentration of SDF-1 in the supernatant, the expression levels of membrane CXCR4, and the cell viability of hypoxic MSCs or normoxic MSCs were compared. The in vitro transwell migration assay was performed as well. The best combination of parameters for more SDF-1 secretion and less MSCs death was T = 30 s, A = 0.6 W/cm(2), and MB = 10(6)/ml. After 24 h of hypoxic preconditioning, the expression of SDF-1 and surface CXCR4 was increased in the hypoxic MSC group as compared to the normoxic MSC group (P < 0.05). On the basis of that, MB-mediated US could further upregulate the expression of SDF-1/CXCR4 with the optimum parameters (P < 0.05), while the cell viability was only decreased by about 9-10 % compared to the untreated groups. The number of successfully migrated cells was also the largest in the hypoxic preconditioning combined with MB-mediated US group than all the other groups. The results obtained indicate the combination of hypoxic preconditioning, and MB-mediated US can upregulate the SDF-1/CXCR4 expression and improve the migration ability in MSCs.