Isolation of multipotent astroglia form the adult stem cell niche and the injured brain.

Adult neural stem cells, as the source of life-long neurogenesis, reside in the subependymal zone (SEZ) in the lateral wall of the lateral ventricles and in the dentate gyrus of the hippocampus. In both neurogenic regions, subsets of glial fibrillary acidic protein (GFAP) expressing astrocytes are found, that have been shown to act as neural stem cells. So far, it is not known how to distinguish these stem cell astrocytes from other astrocyte populations within the SEZ. Towards this end we decided to isolate a subpopulation of adult SEZ astrocytes that expresses the CD133 by FACS. GFP-positive cells in the SEZ from hGFAP/eGFP mice that were also CD133+ve comprised all neurosphere-initiating cells that were self-renewing and multipotent from the SEZ. Moreover, single cell neurosphere analysis showed 70% efficiency in neurosphere formation. Further more Cre-mediated fate mapping of this double-positive population showed their contribution to adult neurogenesis. Transcriptional profiling of the GFP/CD133-double-positive cells allowed us to a) determine their similarity at the transcriptome level to both ependymal cells AND astrocytes and b) to identify their unique molecular neural stem cell signature. We also discovered that astrocytes outside this neurogenic niche could go some way towards dedifferentiation into neural stem cells. We have previously described (Buffo et al., PNAS 2008) a population of astrocytes in the adult cerebral cortex after stab wound injury that dedifferentiates as far to form multipotent and self-renewing neurospheres. Now we succeeded to establish the factor responsible for this dedifferentiation and sufficient to elicit the dedifferentiation response even in cells that were not exposed to injury. These data will be presented. Taken together, our work allows for the first time, the identification and characterization of the astrocyte sub-types acting as neural stem cells