Genetic regulatory elements introduced into neural stem and progenitor cell populations

Genetic modification of neural stem cells

Neural stem cells (NSCs) are the main vehicle for genetic and molecular therapies in the central nervous system (CNS). The sustainability of NSCs has been ensured through genetic manipulation both in vitro and in vivo. NSC lines have also been immortalized and controlled for cell growth in similar fashion. Their potential to differentiate and their genetic plasticity make them the modality of choice for cellular transplantation. After transplantation, NSCs also exhibit inherent long-distance migratory capabilities and a remarkable capacity to integrate into brain structures. This makes NSCs the ideal candidate for delivery and expression of therapeutic genes. Mouse models of CNS diseases have already demonstrated the efficacy of such NSC-mediated treatment, and further investigations are underway to bridge the gap into true clinical application. Finally, the imaging possibilities with NSC transplants are endless, and they will be a pivotal component to safe and effective human transplantation. This paper provides an overview on NSCs and the various methods in which they have been genetically manipulated for biological investigation.

Tissue-engineering approaches for axonal guidance

Owing to the profound impact of nervous system damage, extensive studies have been carried out aimed at facilitating axonal regeneration following injury. Tissue engineering, as an emerging and rapidly growing field, has received extensive attention for nervous system axonal guidance. Numerous engineered substrates containing oriented extracellular matrix molecules, cells or channels have displayed potential of supporting axonal regeneration and functional recovery. Most attempts are focused on seeking new biomaterials, new cell sources, as well as novel designs of tissue-engineered neuronal bridging devices, to generate safer and more efficacious neuronal tissue repairs.

Progress in cerebral transplantation of expanded neuronal stem cells

OBJECT

Given the success and limitations of human fetal primary neural tissue transplantation, neuronal stem cells (NSCs) that can be adequately expanded in culture have been the focus of numerous attempts to develop a superior source of replacement cells for restorative neurosurgery. To clarify recent progress toward this goal, the transplantation into the adult brain of NSCs, expanded in vitro before grafting, was reviewed.

METHODS

Neuronal stem cells can be expanded from a variety of sources, including embryos, fetuses, adult bone marrow, and adult brain tissue. Recent investigations of each of these expanded stem cell types have generated a large body of information along with a great number of unanswered questions regarding the ability of these cells to replace damaged neurons. Expanded NSCs offer many advantages over their primary tissue predecessors, but also may exhibit different functional abilities as grafted cells. Because expanded NSCs will most likely ultimately replace primary tissue grafting in clinical trials, this review was undertaken to focus solely on this distinct body of work and to summarize clearly the existing preclinical data regarding the in vivo successes, limits, and unknowns of using each expanded NSC type when transplanted into the adult brain.

CONCLUSIONS

Embryonic stem cell-derived cells have demonstrated appropriate neuronal phenotypes after transplantation into nonneurogenic areas of the adult brain. Understanding the mechanisms responsible for this may lead to similar success with less studied adult neuronal progenitor cells, which offer the potential for autologous NSC transplantation with less risk of tumorigenesis.

AF5, a CNS cell line immortalized with an N-terminal fragment of SV40 large T: growth, differentiation, genetic stability, and gene expression

Central nervous system progenitor cells that are self-renewing in culture and also differentiate under controlled conditions are potentially useful for developmental studies and for cell-based therapies. We characterized growth and plasticity properties and gene expression in a rat mesencephalic cell line, AF5, that was immortalized with an N-terminal fragment of SV40 large T (T155g). For over 150 population doublings in culture, the growth rate of AF5 cells remained steady, the cells remained responsive to bFGF, and telomerase activity and telomere lengths were unchanged. While karyotype analyses revealed some chromosomal abnormalities, these were also unchanged over time; additionally, no mutations in p53 gene sequences were found, and wild-type p53 activation was normal. AF5 cells produced PDGF, TGFbeta1, TGFbeta2, and bFGF. Similar to primary progenitor cells, AF5 cells retained their plasticity in culture; they could be propagated in an undifferentiated state as "neurospheres" in serum-free media or as adherent cultures in serum-containing media, and they differentiated when allowed to become confluent. Adherent subconfluent actively growing cultures expressed a marker for immature neurons, nestin, while few cells expressed the mature neuronal cell marker betaIII-tubulin. Confluent cultures ceased growing, developed differentiated morphologies, contained few or no nestin-expressing cells, and acquired betaIII-tubulin expression. Global gene expression was examined using a 15,000 gene microarray, comparing exponential growth with and without bFGF stimulation, and the differentiated state. The AF5 cell line exhibited stable genetic and growth properties over extended periods of time, while retaining the ability to differentiate in vitro. These data suggest that the AF5 cell line may be useful as an in vitro model system for studies of neural differentiation.