Effects of GDF5 overexpression on embryonic rat dopaminergic neurones in vitro and in vivo.

Transplantation of embryonic dopaminergic neurones has shown promise for the treatment of Parkinson's disease (PD), but this approach is limited by the poor survival of the transplanted cells. Exogenous dopaminergic neurotrophic factors such as growth/differentiation factor 5 (GDF5) have been found to enhance the survival of transplanted dopaminergic neurones. However, this approach is limited by the rapid degradation of such factors in vivo; thus, methods for long-term delivery of these factors are under investigation. The present study shows, using optimised lipid-mediated transfection procedures, that overexpression of GDF5 significantly improves the survival of dopaminergic neurones in cultures of embryonic day (E) 13 rat ventral mesencephalon (VM) and protects them against 6-hydroxydopamine (6-OHDA)-induced toxicity. In another experiment, E13 VM cells were transfected with GDF5 after 1 day in vitro (DIV), then transplanted into 6-OHDA-lesioned adult rat striata after 2 DIV. The survival of these E13 VM dopaminergic neurones after transfection and transplantation was as least as high as that of freshly dissected E14 VM dopaminergic neurones, demonstrating that transfection was not detrimental to these cells. Furthermore, GDF5-overexpressing E13 VM transplants significantly reduced amphetamine-induced rotational asymmetry in the lesioned rats. This study shows that lipid-mediated transfection in vitro prior to transplantation is a valid approach for the introduction of neurotrophic proteins such as GDF5, as well as lending further support to the potential use of GDF5 in neuroprotective therapy for PD.

TAT-PAX6 protein transduction in neural progenitor cells: a novel approach for generation of dopaminergic neurones in vitro.

Neural stem cells (NSCs) have the potential to be used for the treatment of Parkinson's disease (PD), as they can be expanded, manipulated and differentiated in vitro to generate dopaminergic neurones which are suitable for transplantation. Since NSCs have a tendency to follow an astrocytic lineage after differentiation in vitro, researchers are investigating ways to induce a neuronal phenotype in these cells. In this study, the human immunodeficiency virus 1 (HIV-1) transactivator of transcription (TAT) protein transduction domain (PTD) system was used in an attempt to promote neuronal differentiation in rodent NSCs. A fusion protein that incorporated both the TAT PTD and the Pax6 protein (a determinant of neurogenesis) was created and added to the differentiation phase of embryonic day (E) 12 rat ventral mesencephalic (VM) neurosphere cultures. Subsequently, application of dopaminergic growth factors (GFs) was used in an attempt to induce the newly-generated neuronal progenitors to adopt a dopaminergic phenotype. In addition, a technique involving the differentiation of intact neurospheres (instead of the differentiation of neurosphere-derived dissociated cells) was investigated for its ability to promote dopaminergic neurogenesis. Immunocytochemical analysis of the differentiated neurosphere cultures indicated that both of these techniques had a significant effect on the emergence of dopaminergic neurones. Moreover, upon combination of these techniques, a further increase in dopaminergic neuronal generation was observed. Based on the findings of the present study, it is clear that NSCs are greatly influenced by their environment and that optimised in vitro conditions can support the potential of these cells to differentiate into dopaminergic neurones.