Death resistant neural progenitors yield mostly neurons: an erythropoietin-dependent process

Traumatic lesions of the cord are characterized by a secondary process of degeneration, that is a complex condition of ischemia-like syndrome and neuroinflammation. We reported that mouse adult neural stem cells, isolated from the subventricular zone (SVZ), accumulate at the site of injury and improve the early rate of hind limb functional recovery, however, few weeks later the transplanted are totally phagocytated by macrophages. In view of such results we aimed at isolating adult neural stem cells after a prolonged ischemic insult, this could provide a population of cells capable of resisting at the unfavourable site of injury. The cellular responses to hypoxia are manifested by activation of the hypoxia-inducible factor-1 (HIF-1), a transcription factor of the basic helix loop-helix family [Huang et al, 1998]. HIF-1 consists of two subunits, one is O2 - regulated HIF-1 alpha subunit, and the other is O2 -independent HIF-1 beta subunit. Under hypoxic conditions, HIF-1 alpha is no longer hydroxylated and the two subunits dimerize and migrate to the nuclei; this results in increased expression of several key target genes such as erythropoietin, vascular endothelial growth factor, tyrosine hydroxylase (TH) and OCT4, which function as regulators of cellular proliferation and differentiation. Here we report the isolation from SVZ of neural precursors at several hours after death of the donor mouse. These cells differentiate mostly in neurons (> 50% of total cells) showing high activation of HIF1α and MAPK with the specific expression of erythropoietin and its receptor. The addition of antibodies to erythropoietin to the specific medium inhibits the differentiation towards the neuronal phenotype and obliterate the voltage sensitive calcium currents. These results suggest that the expression of ischemia-induced EPO signaling is an indispensable precondition to gain and maintain the neuronal morphological and functional phenotype by the death resistant neural precursors. The induction of EPO is of great importance in brain preconditioning and suggest that these cells may represent a possible successful candidate for transplantation into the central nervous system after injury