Dynamic expression of neurotrophin receptors during in vitro differentiation of human neural stem cells.

Since NGF is an essential factor regulating survival and differentiation of neuronal progenitors in the peripheral and central nervous system, the aim of our study was to investigate whether NGF and its receptors are involved in the differentiation of human neural stem cells in vitro. Human neural stem/ progenitor cells derived from foetal cortex were cultured as neurospheres in defined conditions with mitogens and induced to differentiate by plating without mitogens on adherent surfaces with or without NGF. The differentiation stages and cell phenotypes were identified by the expression of neural markers such as Pax6, nestin, vimentin and GFAP for neuroepithelial and radial glial cells, and betaIII-tubulin, MAP2 and ChAT for neuronal cells. These cell populations were analyzed for the expression of the NGF specific receptor TrkA and the pan-neurotrophin receptor p75. The data obtained using RT-PCR and Real-Time PCR, double and triple immunofluorescence analyzed by confocal microscopy and flow-cytometry indicated that the expression of TrkA and p75 was not homogeneous in human stem/progenitor cells and their temporal expression was correlated with the differentiation stage and cell phenotype. TrkA and p75 were both expressed in neurospheres, in nestin positive cells, but after their plating, while p75 was not expressed, TrkA was highly up-regulated in the radial glial cells co-expressing vimentin and GFAP. This temporal expression of NGF receptors indicates a different NGF dependence of human progenitor cells and suggests that NGF can regulate differentiation of human neural stem and progenitor cells towards specific neuronal populations. Dr Nat is a recipient of a CNR-NATO fellowship. published in FENS Forum Abstracts, vol. 3, 2006. Ref.: FENS Abstr., vol.3, A124.12, 2006