Fetal ventral mesencephalon of human and rat origin maintained in vitro and transplanted to 6-hydroxydopamine-lesioned rats gives rise to grafts rich in dopaminergic neurons

Challenges involved in cell therapy for Parkinson's disease using human pluripotent stem cells

Neurons derived from human pluripotent stem cells (hPSCs) provide a valuable tool for studying human neural development and neurodegenerative diseases. The investigation of hPSC-based cell therapy, involving the differentiation of hPSCs into target cells and their transplantation into affected regions, is of particular interest. One neurodegenerative disease that is being extensively studied for hPSC-based cell therapy is Parkinson's disease (PD), the second most common among humans. Various research groups are focused on differentiating hPSCs into ventral midbrain dopaminergic (vmDA) progenitors, which have the potential to further differentiate into neurons closely resembling DA neurons found in the substantia nigra pars compacta (SNpc) after transplantation, providing a promising treatment option for PD. In vivo experiments, where hPSC-derived vmDA progenitor cells were transplanted into the striatum or SNpc of animal PD models, the transplanted cells demonstrated stable engraftment and resulted in behavioral recovery in the transplanted animals. Several differentiation protocols have been developed for this specific cell therapy. However, the lack of a reliable live-cell lineage identification method presents a significant obstacle in confirming the precise lineage of the differentiated cells intended for transplantation, as well as identifying potential contamination by non-vmDA progenitors. This deficiency increases the risk of adverse effects such as dyskinesias and tumorigenicity, highlighting the importance of addressing this issue before proceeding with transplantation. Ensuring the differentiation of hPSCs into the target cell lineage is a crucial step to guarantee precise therapeutic effects in cell therapy. To underscore the significance of lineage identification, this review focuses on the differentiation protocols of hPSC-derived vmDA progenitors developed by various research groups for PD treatment. Moreover, in vivo experimental results following transplantation were carefully analyzed. The encouraging outcomes from these experiments demonstrate the potential efficacy and safety of hPSC-derived vmDA progenitors for PD cell therapy. Additionally, the results of clinical trials involving the use of hPSC-derived vmDA progenitors for PD treatment were briefly reviewed, shedding light on the progress and challenges faced in translating this promising therapy into clinical practice.

Enhanced Vascularization and Survival of Neural Transplants with Ex Vivo Angiogenic Gene Transfer

Restoration of brain function by neural transplants is largely dependent upon the survival of donor neurons. Unfortunately, in both rodent models and human patients with Parkinson's disease the survival rate of transplanted neurons has been poor. We have employed a strategy to increase the availability of nutrients to the transplant by increasing the rate at which blood vessels are formed. Replication-deficient HSV-1 vectors containing the cDNA for human vascular endothelial growth factor (HSVhvegf) and the bacterial β-galacto-sidase gene (HSVlac) have been transduced in parallel into nonadherent neuronal aggregate cultures made of cells from embryonic day 15 rat mesencephalon. Gene expression from HSVlac was confirmed in fixed preparations by staining with X-gal. VEGF expression as determined by sandwich ELISA assay of culture supernatant was up to 322-fold higher in HSVhvegf-infected than HSVlac-infected sister cultures. This peptide was also biologically active, inducing endothelial cell proliferation in vitro. Adult Sprague-Dawley rats received bilateral transplants into the striatum, with HSVlac on one side and HSVhvegf on the other. At defined intervals up to 8 weeks, animals were sacrificed and vibratome sections of the striatum were assessed for various parameters of cell survival and vascularization. Results demonstrate dose-dependent increases in blood vessel density within transplants transduced with HSVhvegf. These transplants were vascularized at a faster rate up to 4 weeks after transplantation. After 8 weeks, the average size of the HSVhvegf-infected transplants was twice that of controls. In particular, the survival of transplanted dopaminergic neurons increased 3.9-fold. Taken together these experiments provide convincing evidence that the rate of vascularization may be a major determinant of neuronal survival that can be manipulated by VEGF gene transduction.

Transplantation of Embryonic Porcine Neocortical Tissue into Newborn Rats

Several previous studies, suggesting the potential use of embryonic xenografts in the treatment of neurological disorders, indicate that neural growth and axonal guidance factors may function across species. In this light, blocks of fetal porcine neocortex were grafted into small cortical lesion cavities made in newborn rats. Sacrifice at 3–12.5 weeks posttransplantation revealed healthy looking grafts in several animals. Apparent graft rejection evidenced by areas of necrosis and OX1 reactivity was observed in some of the older transplants. Treatment of nursing mothers or of postweaning newborns with cyclosporin A did not appear to promote graft survival. Some transplants grew to extremely large proportions and were characterized by bands of cells and bundles of axons as observed using immunohistochemical staining for pig neurofilament. Neurofilament-positive axons projected from several of the grafts to course through the corpus callosum to the contralateral cortex or to course ipsilaterally within the subcortical white matter, where labeled fibers could be traced to the midbrain crus cerebri in older transplants. Bundles of axons were also observed coursing within the ipsilateral caudate putamen where terminal branching was apparent. The normal course of transplant efferents within the host brain indicates that growing pig axons can respond to rodent axonal guidance factors.

Creatine Supplementation Improves Dopaminergic Cell Survival and Protects against MPP+ Toxicity in an Organotypic Tissue Culture System

Cell replacement therapy using mesencephalic precursor cells is an experimental approach for the treatment of Parkinson's disease (PD). A significant problem associated with this procedure is the poor survival of grafted neurons. Impaired energy metabolism is considered to contribute to neuronal cell death after transplantation. Creatine is a substrate for mitochondrial and cytosolic creatine kinases (CK) and buffers cellular ATP resources. Furthermore, elevated cellular creatine levels facilitate metabolic channeling and show anti-apoptotic properties. Exogenous creatine supplementation therefore might offer a tool for improvement of dopaminergic neuron survival. The present study aimed at investigating the effects of creatine on cell survival of rat embryonic day 14 (E14) ventral mesencephalic neurons grown as organotypic free-floating roller tube (FFRT) cultures. We found that the brain-specific isoform of CK (BB-CK) and the ubiquitous mitochondrial isoform (uMt-CK) are expressed at high levels in FFRT cultures and colocalize with tyrosine hydroxylase immunoreactive (TH-ir) cells. Exposure of these cultures to creatine induced an increase in the content of the BB-CK isotype. Creatine (5 mM) administration starting at day in vitro (DIV) 7 resulted in a significant increase (+35%) in TH-ir cell density at DIV21. In addition, we observed that creatine treatment provided neuroprotection against 1-methyl-4-phenyl pyridinium ion (MPP+)-induced TH-ir cell loss in the FFRT culture system, resulting in a significantly higher density (+19%) of TH-ir neurons in creatine-treated cultures compared to corresponding controls. The decrease of TH-ir neurons in the MPP+-treated group corresponded with an increase in immunoreactivity for active caspase-3, an effect that was not seen in the group receiving creatine supplementation. In conclusion, our data imply that creatine administration is beneficial for the survival of TH-ir neurons encountering harmful conditions.

Additive effect of glial cell line-derived neurotrophic factor and neurotrophin-4/5 on rat fetal nigral explant cultures

Transplantation of embryonic dopaminergic neurons is an experimental therapy for Parkinson's disease, but limited tissue availability and suboptimal survival of grafted dopaminergic neurons impede more widespread clinical application. Glial cell line-derived neurotrophic factor (GDNF) and neurotrophin-4/5 (NT-4/5) exert neurotrophic effects on dopaminergic neurons via different receptor systems. In this study, we investigated possible additive or synergistic effects of combined GDNF and NT-4/5 treatment on rat embryonic (embryonic day 14) nigral explant cultures grown for 8 days. Contrary to cultures treated with GDNF alone, cultures exposed to NT-4/5 and GDNF+NT-4/5 were significantly larger than controls (1.6- and 2.0-fold, respectively) and contained significantly more protein (1.6-fold). Treatment with GDNF, NT-4/5 and GDNF+NT-4/5 significantly increased dopamine levels in the culture medium by 1.5-, 2.5- and 4.7-fold, respectively, compared to control levels, and the numbers of surviving tyrosine hydroxylase-immunoreactive neurons increased by 1.7-, 2.1-, and 3.4-fold, respectively. Tyrosine hydroxylase enzyme activity was moderately increased in all treatment groups compared to controls. Counts of nigral neurons containing the calcium-binding protein, calbindin-D28k, revealed a marked increase in these cells by combined GDNF and NT-4/5 treatment. Western blots for neuron-specific enolase suggested an enhanced neuronal content in cultures after combination treatment, whereas the expression of glial markers was unaffected. The release of lactate dehydrogenase into the culture medium was significantly reduced for GDNF+NT-4/5-treated cultures only. These results indicate that combined treatment with GDNF and NT4/5 may be beneficial for embryonic nigral donor tissue either prior to, or in conjunction with, intrastriatal transplantation in Parkinson's disease.

Neuroprotective and behavioral efficacy of nerve growth factor-transfected hippocampal progenitor cell transplants after experimental traumatic brain injury

OBJECT

Immortalized neural progenitor cells derived from embryonic rat hippocampus (HiB5), were transduced ex vivo with the gene for mouse nerve growth factor (NGF) to secrete NGF (NGF-HiB5) at 2 ng/hr/10(5) cells in culture.

METHODS

Fifty-nine male Wistar rats weighing 300 to 370 g each were anesthetized with 60 mg/kg sodium pentobarbital and subjected to lateral fluid-percussion brain injury of moderate severity (2.3-2.4 atm, 34 rats) or sham injury (25 rats). At 24 hours postinjury, 2 microl (150,000 cells/microl) of [3H]thymidine-labeled NGF-HiB5 cells were transplanted stereotactically into three individual sites in the cerebral cortex adjacent to the injury site (14 rats). Separate groups of brain-injured rats received nontransfected (naive [n])-HiB5 cells (12 animals) or cell suspension vehicle (eight animals). One week postinjury, animals underwent neurological evaluation for motor function and cognition (Morris water maze) and were killed for histological, autoradiographic, and immunocytochemical analysis. Viable HiB5 cell grafts were identified in all animals, together with reactive microglia and macrophages located throughout the periinjured parenchyma and grafts (OX-42 immunohistochemistry). Brain-injured animals transplanted with either NGF-HiB5 or n-HiB5 cells displayed significantly improved neuromotor function (p < 0.05) and spatial learning behavior (p < 0.005) compared with brain-injured animals receiving microinjections of vehicle alone. A significant reduction in hippocampal CA3 cell death was observed in brain-injured animals receiving transplants of NGF-HiB5 cells compared with those receiving n-HiB5 cells or vehicle (p < 0.025).

CONCLUSIONS

This study demonstrates that immortalized neural stem cells that have been retrovirally transduced to produce NGF can markedly improve cognitive and neuromotor function and rescue hippocampal CA3 neurons when transplanted into the injured brain during the acute posttraumatic period.

Visualization, direct isolation, and transplantation of midbrain dopaminergic neurons

To visualize and isolate live dopamine (DA)-producing neurons in the embryonic ventral mesencephalon, we generated transgenic mice expressing green fluorescent protein (GFP) under the control of the rat tyrosine hydroxylase gene promoter. In the transgenic mice, GFP expression was observed in the developing DA neurons containing tyrosine hydroxylase. The outgrowth and cue-dependent guidance of GFP-labeled axons was monitored in vitro with brain culture systems. To isolate DA neurons expressing GFP from brain tissue, cells with GFP fluorescence were sorted by fluorescence-activated cell sorting. More than 60% of the sorted GFP(+) cells were positive for tyrosine hydroxylase, confirming that the population had been successfully enriched with DA neurons. The sorted GFP(+) cells were transplanted into a rat model of Parkinson's disease. Some of these cells survived and innervated the host striatum, resulting in a recovery from Parkinsonian behavioral defects. This strategy for isolating an enriched population of DA neurons should be useful for cellular and molecular studies of these neurons and for clinical applications in the treatment of Parkinson's disease.

IGF-I and bFGF improve dopamine neuron survival and behavioral outcome in parkinsonian rats receiving cultured human fetal tissue strands

To promote dopamine cell survival in human fetal tissue strands transplanted into immunosuppressed 6-OHDA-lesioned rats, we have preincubated tissue in insulin-like growth factor-I (IGF-I, 150 ng/ml) and basic fibroblast growth factor (bFGF, 15 ng/ml) in vitro for 2 weeks. Growth factor treatment did not affect the rate of homovanillic acid production in vitro but increased overall dopamine neuron survival in animals after transplant from 1240 +/- 250 to 2380 +/- 440 neurons (P < 0.05). Animals in the growth factor-treated group had a significantly greater reduction in methamphetamine-induced rotation (66%) compared to control transplants (30%, P < 0.05). We conclude that in vitro preincubation of human fetal tissue strands with IGF-I and bFGF improves dopamine cell survival and the behavioral outcome of transplants.

Influence of time in culture and BDNF pretreatment on survival and function of grafted embryonic rat ventral mesencephalon in the 6-OHDA rat model of Parkinson's disease

Embryonic midbrain can be maintained as free-floating roller tube cultures prior to grafting in experimental Parkinson's disease. We examined the influence of pregrafting culture time and pretreatment with brain-derived neurotrophic factor on graft survival and function. Cultures were prepared from solid pieces of embryonic (E14) rat ventral mesencephalon and maintained 4, 8, or 12 days in vitro with or without brain-derived neurotrophic factor (100 ng/ml) and grafted into the striatum of 6-hydroxydopamine-lesioned rats. Graft survival and function were evaluated by amphetamine-induced rotation behavior, number of tyrosine hydroxylase-immunoreactive neurons, striatal reinnervation, and graft volume. Rats receiving untreated tissue cultured for 4 or 8 days displayed no differences in graft quality, while grafts from 12-day-old cultures contained significantly fewer (P < 0.05) tyrosine hydroxylase-immunoreactive neurons (340 +/- 97, 267 +/- 92, and 62 +/- 19) and displayed a lower survival rate (9.6 +/- 2.7, 7.9 +/- 2.7, and 2.6 +/- 0.8% for 4, 8, and 12 days in vitro, respectively). Only rats grafted with 4- and 8-day-old cultures recovered significantly (P < 0.05) from lesion-induced rotations (69.4 +/- 18.6, 70.3 +/- 13.9, and 23.2 +/- 12.1% for 4, 8, and 12 days in vitro, respectively). Striatal reinnervation decreased with increasing culture time (P < 0.05). Pretreatment of the cultures with brain-derived neurotrophic factor affected only graft-induced fiber reinnervation, which was reduced even after short culture times. We therefore suggest that a storage period of 8 days is well suited to maintain embryonic rat ventral mesencephalon with the free-floating roller tube culture technique prior to transplantation. BDNF pretreatment as a new strategy to improve graft survival and function, however, was not effective.

Nonviral glial cell-derived neurotrophic factor gene transfer enhances survival of cultured dopaminergic neurons and improves their function after transplantation in a rat model of Parkinson's disease

Transplantation of dopaminergic fetal mesencephalic tissue into the striatum is currently being developed for treatment of patients with advanced Parkinson's disease. Ethical concerns regarding the use of human fetal tissue, and the limited availability as well as poor survival and differentiation of dopaminergic neurons after transplantation have reduced the extent and outcome of this approach so far. With the purpose of finding means to increase the yield of dopaminergic neurons in transplants, and to reduce the amount of fetal tissue needed for each transplanted patient, we transfected rat fetal ventral mesencephalic (VM) tissue grown as organotypic free-floating roller tube (FFRT) cultures with a vector encoding human glial cell-derived neurotrophic factor (hGDNF). For transfer of an episomal expression vector (pRep7-GDNF8) a nonviral, nonliposomal cationic transfection technique was applied and optimized. Recombinant hGDNF expression resulted in a higher number of TH-positive neurons in the cultures as measured 6 days after transfection. Ventral mesencephalic cultures expressing hGDNF were then grafted into the striatum of unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats. Grafting of genetically modified VM cultures resulted in earlier functional recovery compared with grafting nontransfected cultures. We conclude that organotypic free-floating roller tube cultures can be successfully transfected to produce hGDNF with effects on TH-expressing neurons in vitro and functional effects after grafting in a rat Parkinson's disease model.

Efficient generation of midbrain and hindbrain neurons from mouse embryonic stem cells

Embryonic stem (ES) cells are clonal cell lines derived from the inner cell mass of the developing blastocyst that can proliferate extensively in vitro and are capable of adopting all the cell fates in a developing embryo. Clinical interest in the use of ES cells has been stimulated by studies showing that isolated human cells with ES properties from the inner cell mass or developing germ cells can provide a source of somatic precursors. Previous studies have defined in vitro conditions for promoting the development of specific somatic fates, specifically, hematopoietic, mesodermal, and neurectodermal. In this study, we present a method for obtaining dopaminergic (DA) and serotonergic neurons in high yield from mouse ES cells in vitro. Furthermore, we demonstrate that the ES cells can be obtained in unlimited numbers and that these neuron types are generated efficiently. We generated CNS progenitor populations from ES cells, expanded these cells and promoted their differentiation into dopaminergic and serotonergic neurons in the presence of mitogen and specific signaling molecules. The differentiation and maturation of neuronal cells was completed after mitogen withdrawal from the growth medium. This experimental system provides a powerful tool for analyzing the molecular mechanisms controlling the functions of these neurons in vitro and in vivo, and potentially for understanding and treating neurodegenerative and psychiatric diseases.

Genetic regulatory elements introduced into neural stem and progenitor cell populations

The genetic manipulation of neural cells has advantage in both basic biology and medicine. Its utility has provided a clearer understanding of how the survival, connectivity, and chemical phenotype of neurones is regulated during, and after, embryogenesis. Much of this achievement has come from the recent generation by genetic means of reproducible and representative supplies of precursor cells which can then be analyzed in a variety of paradigms. Furthermore, advances made in the clinical use of transplantation for neurodegenerative disease have created a demand for an abundant, efficacious and safe supply of neural cells for grafting. This review describes how genetic methods, in juxtaposition to epigenetic means, have been used advantageously to achieve this goal. In particular, we detail how gene transfer techniques have been developed to enable cell immortalization, manipulation of cell differentiation and commitment, and the controlled selection of cells for purification or safety purposes. In addition, it is now also possible to genetically modify antigen presentation on cell surfaces. Finally, there is detailed the transfer of therapeutic products to discrete parts of the central nervous system (CNS), using neural cells as elegant and sophisticated delivery vehicles. In conclusion, once the epigenetic and genetic controls over neural cell production, differentiation and death have been more fully determined, providing a mixture of hard-wired elements and more flexibly expressed characteristics becomes feasible. Optimization of the contributions and interactions of these two controlling systems should lead to improved cell supplies for neurotransplantation.

Survival and integration of transplanted postmitotic human neurons following experimental brain injury in immunocompetent rats

OBJECT

Limitations regarding cell homogeneity and survivability do not affect neuronlike hNT cells, which are derived from a human teratocarcinoma cell line (Ntera2) that differentiates into postmitotic neurons with exposure to retinoic acid. Because NT2N neurons survive longer than 1 year after transplantation into nude mice brains, the authors grafted these cells into the brains of immunocompetent rats following lateral fluid-percussion brain injury to determine the long-term survivability of NT2N cell grafts in cortices damaged by traumatic brain injury (TBI) and the therapeutic effect of NT2N neurons on cognitive and motor deficits.

METHODS

Seventy-two adult male Sprague-Dawley rats, each weighing between 340 and 370 g, were given an anesthetic agent and subjected to lateral fluid percussion brain injury of moderate severity (2.2-2.5 atm in 46 rats) or to surgery without TBI (shamoperation, 26 rats). Twenty-four hours postinjury, 10(5) NT2N cells (24 injured animals) or 3 microl of vehicle (22 injured and 14 control animals) was stereotactically implanted into the periinjured or control cerebral cortex. Motor function was assessed at weekly intervals and all animals were killed at 2 or 4 weeks after their posttraumatic learning ability was assessed using a Morris water maze paradigm. Viable NT2N grafts were routinely observed to extend human neural cell adhesion molecule-(MOC-1)immunoreactive processes into the periinjured cortex at 2 and 4 weeks posttransplantation, although no significant improvement in motor or cognitive function was noted. Inflammation identified around the transplant at both time points was assessed by immunohistochemical identification of macrophages (ED-1) and microglia (isolectin B4).

CONCLUSIONS

Long-term survival and integration of NT2N cells in the periinjured cortex of immunocompetent rats provides the researcher with an important cellular system that can be used to study maturation, regulation, and neurite outgrowth of transplanted neurons following TBI.

Rat fetal ventral mesencephalon grown as solid tissue cultures: influence of culture time and BDNF treatment on dopamine neuron survival and function

Free-floating roller tube (FFRT) cultures of fetal rat and human nigral tissue are a means for tissue storage prior to grafting in experimental Parkinson's disease. In the present study, FFRT cultures prepared from embryonic-day-14 rat ventral mesencephalon were maintained for 4, 8, 12, or 16 days in vitro (DIV) in the presence or absence (controls) of BDNF [100 ng/ml]. The dopamine content in the culture medium, analyzed by HPLC, was significantly higher (4-5 fold) in the BDNF group at DIV 8 and DIV 12 compared to the corresponding control levels (40 pg/ml). The number of tyrosine hydroxylase immunoreactive neurons was significantly higher for BDNF treated cultures (2729+/-300) at DIV 8, as compared to controls (1679+/-217). At DIV 12, the culture volume was significantly increased by BDNF (1.05+/-0.12 vs. 0.71+/-0.04 mm3). Similar results were obtained for total protein. Western blot analysis demonstrated increasing signals for GFAP with increasing time in culture, but levels for control and BDNF treated cultures did not differ at any time-point investigated. In conclusion, it is suggested that the time window for effective storage of dopaminergic tissue prior to grafting can be extended by using the FFRT culture technique and that the in vitro storage may be further prolonged by treatment with BDNF.

Transplantation of expanded mesencephalic precursors leads to recovery in parkinsonian rats

In vitro expansion of central nervous system (CNS) precursors might overcome the limited availability of dopaminergic neurons in transplantation for Parkinson's disease, but generating dopaminergic neurons from in vitro dividing precursors has proven difficult. Here a three-dimensional cell differentiation system was used to convert precursor cells derived from E12 rat ventral mesencephalon into dopaminergic neurons. We demonstrate that CNS precursor cell populations expanded in vitro can efficiently differentiate into dopaminergic neurons, survive intrastriatal transplantation and induce functional recovery in hemiparkinsonian rats. The numerical expansion of primary CNS precursor cells is a new approach that could improve both the ethical and the technical outlook for the use of human fetal tissue in clinical transplantation.

Implants of polymer-encapsulated genetically modified cells releasing glial cell line-derived neurotrophic factor improve survival, growth, and function of fetal dopaminergic grafts

Neural transplantation as an experimental therapy for Parkinsonian patients has been shown to be effective in several clinical trials. Further benefit, however, may be expected if the grafting is combined with a treatment of neurotrophic factors thus improving the survival and growth of grafted embryonic dopaminergic neurons. Continuous trophic support may be needed and therefore requires the long-term delivery of neurotrophic factors to the brain. We demonstrate here that the implantation of polymer-encapsulated cells genetically engineered to continuously secrete glial cell line-derived neurotrophic factor to the adult rat striatum improves dopaminergic graft survival and function. Near complete compensation of 6-hydroxydopamine-induced rotation was already achieved within 3 weeks postgrafting in rats that received glial cell line-derived neurotrophic factor-releasing capsules in addition to dopaminergic cell grafts of cultured tissue. Rats without trophic factor supply showed only little recovery at the same time point and sham grafted rats showed no recovery. The number of tyrosine hydroxylase-immunoreactive cells per graft was increased 2.6-fold in the presence of glial cell line-derived neurotrophic factor 6 weeks postgrafting. Similarly, tyrosine hydroxylase-immunoreactive fibers around the graft were increased by 53%. Moreover, these fibers showed a preferential growth towards the trophic factor-releasing capsule. Taken together, these results provide evidence that encapsulated genetically engineered cells are an effective means of long-term trophic factor supply into the adult rat brain and that the delivery of glial cell line-derived neurotrophic factor can sustain dopaminergic graft function and survival.