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.