Bone marrow stromal cells promoting corticospinal axon growth through the release of humoral factors in organotypic cocultures in neonatal rats

Object. The transplantation of bone marrow stromal cells (BMSCs) is considered to be an alternative treatment to promote central nervous system regeneration, but the precise mechanisms of this regeneration after transplantation of BMSCs have not been clarified. In the present study, the authors assessed the effects of BMSC transplantation on corticospinal axon growth quantitatively, and they analyzed the mechanism of central nervous system regeneration in the injured and BMSC-treated spinal cord using the organotypic coculture system. Methods. Bone marrow stromal cells derived from green fluorescent protein-expressing transgenic Sprague-Dawley rats were transplanted to the organotypic coculture system in which brain cortex and spinal cord specimens obtained in neonatal Sprague-Dawley rats were used. The axon growth from the cortex to the spinal cord was assessed quantitatively, using anterograde tracing with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate. To identify the differentiation of transplanted BMSCs, immunohistochemical examinations were performed. In addition, BMSCs were analyzed using reverse transcriptase polymerase chain reaction (RT-PCR) for mRNA expression of the growth factors. The transplantation of BMSCs beneath the membrane, where the transplanted cells did not come into direct contact with the cultured tissue, promoted corticospinal axon growth to the same extent as transplantation of BMSCs on the tissues. The RT-PCR showed that the transplanted BMSCs expressed the mRNA of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF). Conclusions. These findings strongly suggest that Immoral factors expressed by BMSCs, including BDNF and VEGF, participate in regeneration of the central nervous system after transplantation of these cells.