Promoting the survival, migration and integration of Schwann cells by over-expression of polysialic acid

Abstract

The poor survival and migration of transplanted Schwann cells (SCs) are major drawbacks for their clinical application in cell therapy for neurotrauma. To overcome such drawbacks we genetically modified SCs to over-express polysialic acid (PSA) by lentiviral vectors-mediated expression of polysialyltransferase ST8SiaIV (PST), to study whether over-expression of PSA could enhance their survival, migration, and integration when transplanted into the spinal cord. It was found that more PSA-expressing SCs (PST/SCs) survived than GFP-expressing SCs (GFP/SCs) after transplantation. In vitro expression of PSA on SCs can partially rescue SCs from cell death induced by serum and growth factor withdrawal. In addition, we found high concentration of ATP (>3 mM) could induce SCs death via P2X7 receptor (P2X7R) activation. Blockade of P2X7Rs with an antagonist completely abolished ATP induced SCs death in vitro and also enhance the survival of grafted SCs in vivo. Interestingly, expression of PSA on SCs was found to partially protect SCs from ATP induced cell death in vitro. PSA expression on SCs did not enhance the motility of transplanted SCs in intact spinal cord. However, in a spinal cord crush injury model PST/SCs transplanted 2.5 mm caudal to the lesion site showed that more cells migrated toward the injury site compared with that of GFP/SCs. Induced expression of PSA in spinal cord further facilitated the infiltration of PST/SCs into the lesion cavity. PST/SCs were also shown to intermingle with the host spinal cells while GFP/SCs formed boundaries with the host tissue. This was confirmed by an in vitro confrontation assay. Furthermore, PST/SCs induced much less expression of GFAP and CSPGs in the surrounding host tissues than GFP/SCs, indicating that expression of PSA on SCs do not cause significant stress response of astrocytes. These results demonstrate that over-expression of PSA on SCs significantly changes their biological properties and makes them more feasible for cell therapy after neurotrauma.