Introduction: Nervous system injuries comprise a diverse group of disorders that include traumatic brain injury\r\n(TBI). The potential of mesenchymal stem cells (MSCs) to differentiate into neural cell types has aroused hope for\r\nthe possible development of autologous therapies for central nervous system injury.\r\nMethods: In this study we isolated and characterized a human peripheral blood derived (HPBD) MSC population\r\nwhich we examined for neural lineage potential and ability to migrate in vitro and in vivo. HPBD CD133+, ATPbinding\r\ncassette sub-family G member 2 (ABCG2)+, C-X-C chemokine receptor type 4 (CXCR4)+ MSCs were\r\ndifferentiated after priming with b-mercaptoethanol (b-ME) combined with trans-retinoic acid (RA) and culture in\r\nneural basal media containing basic fibroblast growth factor (FGF2) and epidermal growth factor (EGF) or coculture\r\nwith neuronal cell lines. Differentiation efficiencies in vitro were determined using flow cytometry or\r\nfluorescent microscopy of cytospins made of FACS sorted positive cells after staining for markers of immature or\r\nmature neuronal lineages. RA-primed CD133+ABCG2+CXCR4+ human MSCs were transplanted into the lateral\r\nventricle of male Sprague-Dawley rats, 24 hours after sham or traumatic brain injury (TBI). All animals were\r\nevaluated for spatial memory performance using the Morris Water Maze (MWM) Test. Histological examination of\r\nsham or TBI brains was done to evaluate MSC survival, migration and differentiation into neural lineages. We also\r\nexamined induction of apoptosis at the injury site and production of MSC neuroprotective factors.\r\nResults: CD133+ABCG2+CXCR4+ MSCs consistently expressed markers of neural lineage induction and were\r\npositive for nestin, microtubule associated protein-1b (MAP-1b), tyrosine hydroxylase (TH), neuron specific nuclear\r\nprotein (NEUN) or type III beta-tubulin (Tuj1). Animals in the primed MSC treatment group exhibited MWM latency\r\nresults similar to the uninjured (sham) group with both groups showing improvements in latency. Histological\r\nexamination of brains of these animals showed that in uninjured animals the majority of MSCs were found in the\r\nlateral ventricle, the site of transplantation, while in TBI rats MSCs were consistently found in locations near the\r\ninjury site. We found that levels of apoptosis were less in MSC treated rats and that MSCs could be shown to\r\nproduce neurotropic factors as early as 2 days following transplantation of cells. In TBI rats, at 1 and 3 months post\r\ntransplantation cells were generated which expressed markers of neural lineages including immature as well as\r\nmature neurons.
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