It has been recognized that bone marrow stromal cell (BMSC) transplantation has beneficial effects on spinal cord injury in animal models and therapeutic trials. It is hypothesized that BMSCs provide microenvironments suitable for axonal regeneration and secrete some trophic factors to rescue affected cells from degeneration. However, the molecular and cellular mechanisms of the trophic factors involved remain unclear. In the present study, we examined the effects of trophic factors secreted by rat BMSCs using bioassays involving cultured hippocampal neurons. The conditioned medium (CM) as well as non-contact co-culture of BMSCs promoted neurite outgrowth and suppressed TUNEL-positive cells compared to serum-free D-MEM. Protein analyses of the CM by antibody-based protein array analysis and ELISA revealed that the CM contained insulin-like growth factor (IGF)-1, hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF), and transforming growth factor (TGF)-beta1. DNA microarray analysis revealed that neurons highly expressed receptors of IGF-1 and TGF-beta1. However, their expression indices remained unchanged even after the CM treatment. The individual trophic factors mentioned above or their combinations were less effective at promoting neuronal survival and neurite outgrowth than the CM. The present study showed that BMSCs secreted various kinds of molecules into the culture medium including trophic factors to promote neuronal survival and neurite outgrowth. The main trophic factors responsible remain to be elucidated.
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