HYPOXIA‐INDUCED ASTROCYTES PROMOTE THE MIGRATION OF NEURAL PROGENITOR CELLS VIA VASCULAR ENDOTHELIAL FACTOR, STEM CELL FACTOR, STROMAL‐DERIVED FACTOR‐1α AND MONOCYTE CHEMOATTRACTANT PROTEIN‐1 UPREGULATION IN VITRO

SUMMARY The aim of the present study was to examine if and how rat hypoxia‐induced astrocytes affect the migration of neural progenitor cells (NPC) and to investigate the expression patterns of some chemokines, such as vascular endothelial growth factor (VEGF), stem cell factor (SCF), stromal‐derived factor‐1α (SDF‐1α), fractalkine and monocyte chemoattractant protein‐1 (MCP‐1) in hypoxia‐induced astrocytes and their contribution to NPC migration in vitro . Costar Transwell inserts were used for the chemotaxis assay and quantified changes in the chemokines mRNA for between 0 h and 24 h posthypoxia were tested using real‐time quantitative reverse transcriptase‐polymerase chain reaction (RT‐PCR) analysis. The results showed that the chemotaxis of astrocyte cells exposed to hypoxia for 18 h reached a peak value, whereas the chemotaxis of astrocytes exposed to hypoxia for 24 h began to decrease compared with those exposed to hypoxia for 18 h. Hypoxia upregulated chemokine VEGF, SCF, SDF‐1α and MCP‐1 expression in a time‐dependent manner but downregulated fractalkine expression in astrocytes. In addition, the time points of the peak expressions for VEGF, SCF, SDF‐1α and MCP‐1 were similar to the time point of maximum NPC migration. Specific inhibitors that block the binding of specific chemokines to its receptors were used for analysing the contribution of the chemokine to NPC migration. When VEGF, SCF, SDF‐1α and MCP‐1 were each inhibited independently, NPC migration was reduced. When they were inhibited together, NPC migration was obviously inhibited compared with both the control and single‐block cultures, which implies that the migratory effect of hypoxia‐induced astrocytes was synergetic by several chemokines. In conclusion, we demonstrated the time‐dependent manner of NPC migration promotion by hypoxia‐induced astrocytes. We also provide evidence that soluble factors, such as VEGF, SCF, SDF‐1α and MCP‐1, released from astrocytes, direct the migration of NPC under hypoxic circumstances. Given that astrocytes were activated to all hypoxia–ischaemia diseases, these results indicate an important role for astrocytes in directing NPC replacement therapy in the central nervous system.