The survival of neural precursor cell grafts is influenced by in vitro expansion.

Embryonic neural precursor cells (ENPs) provide a potential alternative for transplantation in neurodegenerative diseases, as they can be expanded in culture, avoiding many of the practical obstacles that limit the application of transplanting primary neurones. However, grafts of ENPs into animal models show variable survival and limited differentiation into neurones. The effect of expansion time on their ability to survive and differentiate may be an important factor in this and has not been examined directly. In these experiments, murine and human ENPs were expanded for short (4 weeks) and long (20 weeks) periods before transplantation into the adult rat striatum. Whereas grafts of both short- and long-term expanded human ENPs survived for 4 weeks following transplantation, by 20 weeks all long-term expanded grafts had disappeared. Murine ENPs behaved similarly: only grafts of short-term expanded ENPs survived at 12 weeks following transplantation. RT-PCR analysis of ENP cultures after 4 and 20 weeks of expansion demonstrated changes in expression of a number of different groups of genes. We conclude that long-term expansion of ENPs profoundly impairs their ability to survive long-term after transplantation into the adult brain. This has implications for the potential use of these cells for neural transplantation strategies.

Transplantation of expanded neural precursor cells from the developing pig ventral mesencephalon in a rat model of Parkinson's disease.

Neural precursor cell populations can be expanded in vitro under the influence of growth factors, and may be of use to replace cells lost to neurodegenerative conditions such as the dopaminergic neurons in Parkinson's disease (PD). We explore here whether expanding neural precursor cells from the region in which nigral dopaminergic neurones emerge in normal development renders them more likely to differentiate into TH-positive neurones when transplanted in a rat model of PD. Embryonic neural precursor cells (ENPs) were isolated from the developing pig ventral mesencephalon (VM) at two different gestational ages and were implanted into the striatum or the substantia nigra of cyclosporin A-immunosuppressed, 6-hydroxydopamine-lesioned rats, which were sacrificed 9 or 18 weeks later. The properties of ENPs varied according to the gestational age of the donor: ENPs that expanded robustly and survived transplantation could be derived from E22 VM, but not from E27 VM. ENPs developed into neurones that displayed diffuse fibre projections, including those appropriate for the implantation site. However, behaviourally significant numbers of TH-positive neurones were not seen. A rejection response was apparent in most animals by 18 weeks. These data show that donor age is an important variable when deriving ENPs for transplantation. Furthermore, derivation of ENPs from the VM at the time of normal dopaminergic neurogenesis is inadequate to ensure functional dopaminergic grafts on transplantation.

GABAergic immunoreactivity is predominant in neurons derived from expanded human neural precursor cells in vitro.

Neural precursor cells have been previously isolated from the developing human nervous system and their properties studied both in vitro and in transplantation paradigms in vivo. However, their ability to differentiate into neurons of different neurochemical phenotypes remains poorly defined. In this study, the default in vitro neuronal differentiation of hENPs derived from five different regions of the human embryonic brain (cerebral cortex, striatum, cerebellum, ventral mesencephalon, and spinal cord) was studied after varying periods of time in culture. The results were directly compared to those from similarly prepared murine ENPs. hENPs prepared from all five regions showed a significant reduction in the number of neurons generated at each passage, such that by passage 4 only between 5 and 10% of cells spontaneously adopted a neuronal phenotype after differentiation in vitro. A similar observation was obtained with murine ENPs. hENPs prepared from more caudal parts of the developing neuroaxis generated fewer neurons compared to the more rostral regions. The only neuronal phenotype identified in these cultures was GABA, with 15-60% of the neurons immunopositive for this neurotransmitter. Thus there appears to be important differences between hENPs dependent on region of origin and time in vitro under standard culture conditions, forming decreasing numbers of neurons with increasing time in culture and more caudal sites of harvest, and with the major identifiable neurotransmitter being GABA. Such characterisation is important in the process of learning how to manipulate the neuronal phenotype of these cells.