Implantation of Xenogeneic Transgenic Neural Plate Tissues into Parkinsonian Rat Brain

Grafted Miniature-Swine Neural Stem Cells of Early Embryonic Mesencephalic Neuroepithelial Origin can Repair the Damaged Neural Circuitry of Parkinson's Disease Model Rats

Although recent progress in the use of human iPS cell-derived midbrain dopaminergic progenitors is remarkable, alternatives are essential in the strategies of treatment of basal-ganglia-related diseases. Attention has been focused on neural stem cells (NSCs) as one of the possible candidates of donor material for neural transplantation, because of their multipotency and self-renewal characteristics. In the present study, miniature-swine (mini-swine) mesencephalic neuroepithelial stem cells (M-NESCs) of embryonic 17 and 18 days grafted in the parkinsonian rat striatum were assessed immunohistochemically, behaviorally and electrophysiologically to confirm their feasibility for the neural xenografting as a donor material. Grafted mini-swine M-NESCs survived in parkinsonian rat striatum at 8 weeks after transplantation and many of them differentiated into tyrosine hydroxylase (TH)-positive cells. The parkinsonian model rats grafted with mini-swine M-NESCs exhibited a functional recovery from their parkinsonian behavioral defects. The majority of donor-derived TH-positive cells exhibited a matured morphology at 8 weeks. Whole-cell recordings from donor-derived neurons in the host rat brain slices incorporating the graft revealed the presence of multiple types of neurons including dopaminergic. Glutamatergic and GABAergic post-synaptic currents were evoked in the donor-derived cells by stimulation of the host site, suggesting they receive both excitatory and inhibitory synaptic inputs from host area. The present study shows that non-rodent mammalian M-NESCs can differentiate into functionally active neurons in the diseased xenogeneic environment and could improve the parkinsonian behavioral defects over the species. Neuroepithelial stem cells could be an attractive candidate as a source of donor material for neural transplantation.

Vigorous Neuronal Differentiation of Amplified and Grafted Basic Fibroblast Growth Factor-Responsive Neurospheres Derived from Neuroepithelial Stem Cells

Neuroepithelial stem cells (NESCs) have emerged as a possible donor material aimed at neural transplantation for the repair of damaged neural circuitry, particularly because of their propensity to differentiate into neurons. We previously ascertained in vitro that NESCs derived from rat early embryos could be amplified in culture containing basic fibroblast growth factors (bFGF), and that neurospheres grown for 7 days in the culture had a strong tendency to differentiate into neurons. In this report, we analyze immunohistochemically the biological nature of bFGF-responsive neurospheres derived from NESCs. We first succeeded in amplifying the number of NESCs from the mesencephalic neural plate of embryonic day 10 Wistar rats with the addition of bFGF. Grown neurospheres were labeled with bromodeoxyuridine (BrdU) in vitro and were stereotactically transplanted into the right striatum of the normal adult Wistar rat. Two weeks after transplantation, a viable graft in the host brain was observed. While many BrdU/Hu double positive cells were seen in the graft, and a few BrdU/nestin double positive cells were also seen, no BrdU/GFAP double positive cells could be identified. These results suggested that bFGF-responsive neurospheres derived from NESCs demonstrated a propensity to differentiate into neurons in the adult brain environment. Furthermore, following in vitro amplification of the original stem cell number with bFGF, the grown neurospheres preserved their propensity to differentiate vigorously into neurons. NESCs are thus suggested as a feasible candidate for intracerebral grafting donor materials aimed at reconstruction of damaged neural circuits.

Feasibility of Using Early Mesencephalic Neural Plate for Intracerebral Grafting

The purpose of this study was to elucidate the biological significance and the possibility of intracerebral grafting of neuroepithelial stem cells derived from the mesencephalic neural plate. Immunohistological studies of embryonic day 10.5 (E10.5) Wister rats revealed strong nestin expression in the mesencephalic part of the neural plate. Mesencephalic neural plates removed from E10.5 rats were processed to either tissue or cell dissociation culture. They were cultured in vitro under various conditions and were analyzed 7 days after the primary culture. When they were cultured as a tissue, cell proliferation and differentiation into neurons extending long neurites were obvious in a serum-free medium, in a medium containing 3% serum, and in a medium containing 20 ng/ml epidermal growth factor. On the other hand, in a medium containing 10 ng/ml basic fibroblast growth factor (bFGF), both vigorous cell proliferation and sphere formation were recognized. Furthermore, marked neurite growth was rarely seen in this culture. When they were plated in a dissociation culture, cell proliferation and neurosphere generation were also recognized only in a medium containing bFGF, depending on the initial cell concentration. The spheres, generated 7 days after the primary cell culture, were positively stained by nestin. These data suggested that bFGF was able to amplify the stem cell population present in the mesencephalic neural plate derived from early embryos. This might make it possible to obtain a large number of stem cells as donor material for neural transplantation on demand.

The X-gal caution in neural transplantation studies

Cell transplantation into host brain requires a reliable cell marker to trace lineage and location of grafted cells in host tissue. The lacZ gene encodes the bacterial (E. coli) enzyme beta-galactosidase (beta-gal) and is commonly visualized as a blue intracellular precipitate following its incubation with a substrate, "X gal," in an oxidation reaction. LacZ is the "reporter gene" most commonly employed to follow gene expression in neural tissue or to track the fate of transplanted exogenous cells. If the reaction is not performed carefully-with adequate optimization and individualization of various parameters (e.g.. pH, concentration of reagents, addition of chelators, composition of fixatives) and the establishment of various controls--then misleading nonspecific background X-gal positivity can result, leading to the misidentification of cells. Some of this background results from endogenous nonbacterial beta-gal activity in discrete populations of neurons in the mammalian brain; some results from an excessive oxidation reaction. Surprisingly, few articles have empha sized how to recognize and to eliminate these potential confounding artifacts in order to maximize the utility and credibility of this histochemical technique as a cell marker. We briefly review the phenomenon in general, discuss a specific case that illustrates how an insufficiently scrutinized X-gal positivity can be a pitfall in cell transplantation studies, and then provide recommendations for optimizing the specificity and reliability of this histochemical reaction for discerning E. coli beta-gal activity.

Differentiation and angiogenesis of central nervous system stem cells implanted with mesenchyme into ischemic rat brain

After cerebral infarction, necrosis in neural tissues is not usually repaired or reconstructed by the injured brain. We therefore examined the effects on postinfarction repair of implanting central nervous system (CNS) stem cells together with mesenchyme, because CNS stem cells can be expected to adapt and survive in the adult brain. Cerebral infarction was induced by the Koizumi-Longa method, using the adult male spontaneous hypertensive rat model. Reperfusion was performed an hour after middle cerebral artery occlusion. The rat mesencephalic neural plate at the early somite stage (embryonic day 10.5) together with the adjacent ventral mesenchymal tissues was dissected out under the microscope and immediately implanted into the ischemic rat striatum. One month later, the cognitive function was evaluated by the Morris water maze method. Histologic and immunohistochemical examinations of the graft were made with hematoxylin-eosin (H&E), neurofilament-200, and tyrosine hydroxylase (TH) stains. In the water maze study, mean latency times required to reach an escape platform in the implanted animals with surviving grafts were found to be shorter than in those without grafts, but longer than in normal animals. In the spatial probe trial, the number of animals seen to cross the area in the pool where the platform had been located was greater in the implanted rats with surviving grafts than in other groups. Multiple vascularization in the grafted area was observed histologically in H&E-stained tissues, and neurofilament-200-positive cells were recognized in the graft. TH staining revealed within the graft many immunoreactive neuron-like cell bodies with long dendrites. It was suggested that grafted CNS stem cells with mesenchyme may survive and differentiate into mature CNS tissue within the adult ischemic rat brain, constructing vessels in and around the grafts, and may therefore have the potential to be effective in the recovery of the cognitive function of the rat model.