BDNF gene transfer to the mammalian brain using CNS-derived neural precursors

Neural stem cell lines represent a homogeneous source of cells for genetic, developmental, and gene transfer and repair studies in the nervous system. Since both gene transfer of neurotrophic factors and cell replacement stra tegie are of immediate interest for therapeutical purposes, we have generat ed BDNF-secreting neural stem cell lines and investigated to what extent di fferent endogenous levels of BDNF expression affect in vitro survival, prol iferation differentiation of these cells. Also, we have investigated the in vivo effects of such BDNF gene transfer procedure in the rat neostriatum. Hippocampus- and cerebellum-derived cell lines reacted differently to manip ulations aimed at varying their levels of BDNF production. Over-expression of BDNF enhanced survival of both cell types, in a serum-deprivation assay. Conversely, and ruling out unspecific effects, expression of an antisense version of BDNF resulted in compromised survival of cerebellum-derived cell s, and in a lethal phenotype in hippocampal progenitors. These data indicat e that endogenous BDNF level strongly influences the in vitro survival of t hese cells. These effects are more pronounced for hippocampus- than for cer ebellum-derived progenitors. Hippocampus-derived BDNF overproducers showed no major change in their capacity to differentiate towards a neuronal pheno type in vitro. In contrast, cerebellar progenitors overproducing BDNF did n ot differentiate into neurons, whereas cells expressing the antisense BDNF construct generated cells with morphological features of neurons and expres sing immunological neuronal markers. Taken together these results provide e vidence that BDNF controls both the in vitro survival and differentiation o f neural stem cells. After in vivo transplantation of BDNF-overproducing ce lls to the rat neostriatum, these survived better than the control ones, an d induced the expected neurotrophic effects on cholinergic neurons. However , long-term (3 months) administration of BDNF resulted in detrimental effec ts, at this location. These findings may be of importance for the understan ding of brain development, for the design of therapeutic neuro-regenerative strategies, and for cell replacement and gene therapy studies.