Human neural precursor cells express low levels of telomerase in vitro andshow diminishing cell proliferation with extensive axonal outgrowth following transplantation
T. Ostenfeld et al., Human neural precursor cells express low levels of telomerase in vitro andshow diminishing cell proliferation with extensive axonal outgrowth following transplantation, EXP NEUROL, 164(1), 2000, pp. 215-226
Worldwide attention. is presently focused on proliferating populations of n
eural precursor cells as an in vitro source of tissue for neural transplant
ation and brain repair. However, successful neuroreconstruction is continge
nt upon their capacity to integrate within the host CNS and the absence of
tumorigenesis, Here we show that human neural precursor cells express very
low levels of telomerase at early passages (less than 20 population doublin
gs), but that this decreases to undetectable levels at later passages. In c
ontrast, rodent neural precursors express high levels of telomerase at both
early and late passages. The human neural precursors also have telomeres (
approximately 12 kbp) significantly shorter than those of their rodent coun
terparts (approximately 40 kbp), Human neural precursors were then expanded
100-fold prior to intrastriatal transplantation in a rodent model of Parki
nson's disease. To establish the effects of implanted cell number on surviv
al and integration, precursors were transplanted at either 200,000, 1 milli
on, or 2 million cells per animal. Interestingly, the smaller transplants w
ere more likely to extend neuronal fibers and less likely to provoke immune
rejection than the largest transplants in this xenograft model. Cellular p
roliferation continued immediately posttransplantation, but by 20 weeks the
re were virtually no dividing cells within any of the grafts. In contrast,
fiber outgrowth increased gradually over time and often occupied the entire
striatum at 20 weeks postgrafting, Transient expression of tyrosine hydrox
ylase-positive cells within the grafts was found in some animals, hut this
was not sustained at 20 weeks and had no functional effects, For Parkinson'
s disease, the principal aim now is to induce the dopaminergic phenotype in
these cells prior to transplantation. However, given the relative safety p
rofile for these human cells and their capacity to extend fibers into the a
dult rodent brain, they may provide the ideal basis for the repair of other
lesions of the CNS where extensive axonal outgrowth is required. (C) 2000
Academic Press.