Differential Dissection of the Rat E16 Ventral Mesencephalon and Survival and Reinnervation of the 6-Ohda-Lesioned Striatum by a Subset of Aldehyde Dehydrogenase-Positive th Neurons

Exercise Promotes Neurite Extensions from Grafted Dopaminergic Neurons in the Direction of the Dorsolateral Striatum in Parkinson's Disease Model Rats

Background:

Cell transplantation is expected to be a promising treatment for Parkinson’s disease (PD), in which re-innervation of the host striatum by grafted dopamine (DA) neurons is essential. In particular, the dorsolateral part of the striatum is important because it is the target of midbrain A9 DA neurons, which are degenerated in PD pathology. The effect of exercise on the survival and maturation of grafted neurons has been reported in several neurological disease models, but never in PD models.

Objective:

We investigated how exercise influences cell transplantation for PD, especially from the viewpoint of cell survival and neurite extensions.

Methods:

Ventral mesencephalic neurons from embryonic (E12.5) rats were transplanted into the striatum of adult 6-OHDA-lesioned rats. The host rats then underwent treadmill training as exercise after the transplantation. Six weeks after the transplantation, they were sacrificed, and the grafts in the striatum were analyzed.

Results:

The addition of exercise post-transplantation significantly increased the number of surviving DA neurons. Moreover, it promoted neurite extensions from the graft toward the dorsolateral part of the striatum.

Conclusions:

This study indicates a beneficial effect of exercise after cell transplantation in PD.

Dopamine transporter neuroimaging accurately assesses the maturation of dopamine neurons in a preclinical model of Parkinson's disease

BACKGROUND

Significant developments in stem cell therapy for Parkinson's disease (PD) have already been achieved; however, methods for reliable assessment of dopamine neuron maturation in vivo are lacking. Establishing the efficacy of new cellular therapies using non-invasive methodologies will be critical for future regulatory approval and application. The current study examines the utility of neuroimaging to characterise the in vivo maturation, innervation and functional dopamine release of transplanted human embryonic stem cell-derived midbrain dopaminergic neurons (hESC-mDAs) in a preclinical model of PD.

METHODS

Female NIH RNu rats received a unilateral stereotaxic injection of 6-OHDA into the left medial forebrain bundle to create the PD lesion. hESC-mDA cell and sham transplantations were carried out 1 month post-lesion, with treated animals receiving approximately 4 × 10⁵ cells per transplantation. Behavioural analysis, [¹⁸F]FBCTT and [¹⁸F]fallypride microPET/CT, was conducted at 1, 3 and 6 months post-transplantation and compared with histological characterisation at 6 months.

RESULTS

PET imaging revealed transplant survival and maturation into functional dopaminergic neurons. [¹⁸F]FBCTT-PET/CT dopamine transporter (DAT) imaging demonstrated pre-synaptic restoration and [¹⁸F]fallypride-PET/CT indicated functional dopamine release, whilst amphetamine-induced rotation showed significant behavioural recovery. Moreover, histology revealed that the grafted cells matured differently in vivo producing high- and low-tyrosine hydroxylase (TH) expressing cohorts, and only [¹⁸F]FBCTT uptake was well correlated with differentiation.

CONCLUSIONS

This study provides further evidence for the value of in vivo functional imaging for the assessment of cell therapies and highlights the utility of DAT imaging for the determination of early post-transplant cell maturation and differentiation of hESC-mDAs.

Grafted Neural Precursors Integrate Into Mouse Striatum, Differentiate and Promote Recovery of Function Through Release of Erythropoietin in MPTP-Treated Mice

Erythropoietin-releasing neural precursor cells (Er-NPCs) are a subclass of subventricular zone-derived neural progenitors, capable of surviving for 6 hr after death of donor. They present higher neural differentiation. Here, Er-NPCs were studied in animal model of Parkinson's disease. Dopaminergic degeneration was caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine intraperitoneal administration in C57BL/6 mice. The loss of function was evaluated by specific behavioral tests. Er-NPCs (2.5 × 10⁵) expressing the green fluorescent protein were administered by stereotaxic injection unilaterally in the left striatum. At the end of observational research period (2 weeks), most of the transplanted Er-NPCs were located in the striatum, while several had migrated ventrally and caudally from the injection site, up to ipsilateral and contralateral substantia nigra. Most of transplanted cells had differentiated into dopaminergic, cholinergic, or GABAergic neurons. Er-NPCs administration also promoted a rapid functional improvement that was already evident at the third day after cells administration. This was accompanied by enhanced survival of nigral neurons. These effects were likely promoted by Er-NPCs-released erythropoietin (EPO), since the injection of Er-NPCs in association with anti-EPO or anti-EPOR antibodies had completely neutralized the recovery of function. In addition, intrastriatal administration of recombinant EPO mimics the effects of Er-NPCs. We suggest that Er-NPCs, and cells with similar properties, may represent good candidates for cellular therapy in neurodegenerative disorders of this kind.

The A9 dopamine neuron component in grafts of ventral mesencephalon is an important determinant for recovery of motor function in a rat model of Parkinson's disease

Grafts of foetal ventral mesencephalon, used in cell replacement therapy for Parkinson’s disease, are known to contain a mix of dopamine neuronal subtypes including the A9 neurons of the substantia nigra and the A10 neurons of the ventral tegmental area. However, the relative importance of these subtypes for functional repair of the brain affected by Parkinson’s disease has not been studied thoroughly. Here, we report results from a series of grafting experiments where the anatomical and functional properties of grafts either selectively lacking in A9 neurons, or with a typical A9/A10 composition were compared. The results show that the A9 component of intrastriatal grafts is of critical importance for recovery in tests on motor performance, in a rodent model of Parkinson’s disease. Analysis at the histological level indicates that this is likely to be due to the unique ability of A9 neurons to innervate and functionally activate their target structure, the dorsolateral region of the host striatum. The findings highlight dopamine neuronal subtype composition as a potentially important parameter to monitor in order to understand the variable nature of functional outcome better in transplantation studies. Furthermore, the results have interesting implications for current efforts in this field to generate well-characterized and standardized preparations of transplantable dopamine neuronal progenitors from stem cells.

Neuronal cell replacement in Parkinson's disease

Transplantation of foetal dopamine neurons into the striatum of Parkinson's disease patients can provide restoration of the dopamine system and alleviate motor deficits. However, cellular replacement is associated with several problems. As with pharmacological treatments, cell therapy can lead to disabling abnormal involuntary movements (dyskinesias). The exclusion of serotonin and GABA neurons, and enrichment of substantia nigra (A9) dopamine neurons, may circumvent this problem. Furthermore, although grafted foetal dopamine neurons can survive in Parkinson's patients for more than a decade, the occurrence of Lewy bodies within such transplanted cells and reduced dopamine transporter and tyrosine hydroxylase expression levels indicate that grafted cells are associated with pathology. It will be important to understand if such abnormalities are host- or graft induced and to develop methods to ensure survival of functional dopamine neurons. Careful preparation of cellular suspensions to minimize graft-induced inflammatory responses might influence the longevity of transplanted cells. Finally, a number of practical and ethical issues are associated with the use of foetal tissue sources. Thus, future cell therapy is aiming towards the use of embryonic stem cell or induced pluripotent stem cell derived dopamine neurons.

Future of cell and gene therapies for Parkinson's disease

The experimental field of restorative neurology continues to advance with implantation of cells or transfer of genes to treat patients with neurological disease. Both strategies have generated a consensus that demonstrates their capacity for structural and molecular brain modification in the adult brain. However, both approaches have yet to successfully address the complexities to make such novel therapeutic modalities work in the clinic. Prior experimental cell transplantation to patients with PD utilized dissected pieces of fetal midbrain tissue, containing mixtures of cells and neuronal types, as donor cells. Stem cell and progenitor cell biology provide new opportunities for selection and development of large batches of specific therapeutic cells. This may allow for cell composition analysis and dosing to optimize the benefit to an individual patient. The biotechnology used for cell and gene therapy for treatment of neurological disease may eventually be as advanced as today's pharmaceutical drug-related design processes. Current gene therapy phase 1 safety trials for PD include the delivery of a growth factor (neurturin via the glial cell line-derived neurotrophic factor receptor) and a transmitter enzyme (glutamic acid decarboxylase and aromatic acid decarboxylase). Many new insights from cell biological and molecular studies provide opportunities to selectively express or suppress factors relevant to neuroprotection and improved function of neurons involved in PD. Future gene and cell therapies are likely to coexist with classic pharmacological therapies because their use can be tailored to individual patients' underlying disease process and need for neuroprotective or restorative interventions.

Human embryonic stem cell therapy for Parkinson's disease

Human embryonic stem cells (hESCs) may serve as the most enduring source of transplantable cells for Parkinson's disease patients. Accumulating experience in the transplantation of fetal midbrain tissue or cells into Parkinson's disease patients has set the stage for hESC therapy, but has also opened new controversies on the value and appropriate design of cell therapy. hESCs can be directed to differentiate into nigral dopaminergic neurons with high efficiency. The clinical use of hESCs will depend on their growth in controlled conditions, on whether safety can be proven, and on improving the survival of hESC-derived dopaminergic neurons in the host brain.

Correlation between quantitative imaging and behavior in unilaterally 6-OHDA-lesioned rats

We evaluated correlation between neurochemical and functional alterations of the nigrostriatal dopaminergic system in rat brains lesioned with 6-hydroxydopamine (6-OHDA), that model hemi-Parkinson's disease (PD), by using three different quantitative in vivo and in vitro methods. Rats unilaterally lesioned with different doses of 6-OHDA underwent two types of in vivo experiments: (1) a rotational behavioral study with methamphetamine (MAP) or apomorphine (APO); and (2) a positron emission tomography (PET) study with [11C]PE2I (radioligand for dopamine transporters) or [11C]raclopride (radioligand for dopamine D2 receptors). An in vitro autoradiographic study with the same radioligands was also conducted. The number of rotations after the MAP or APO injection increased with increased doses of 6-OHDA. The in vitro and in vivo binding of [11C]PE2I dose-dependently decreased in response to the 6-OHDA injections, while that of [11C]raclopride dose-dependently increased. There was a significant negative hyperbolic correlation between the number of rotations after MAP injection and the binding of [11C]PE2I. In contrast, there was a significant positive linear correlation between the number of rotations after APO injections and the binding of [11C]raclopride. These results robustly reveal a molecular pharmacological basis of parkinsonian symptoms in animal models of PD, and indicate the utility and validity of in vivo PET measurements in assessing pre- and post-synaptic dopaminergic functions.

Cell type analysis of functional fetal dopamine cell suspension transplants in the striatum and substantia nigra of patients with Parkinson's disease

We report the first post-mortem analysis of two patients with Parkinson's disease who received fetal midbrain transplants as a cell suspension in the striatum, and in one case also in the substantia nigra. These patients had a favourable clinical evolution and positive 18F-fluorodopa PET scans and did not develop motor complications. The surviving transplanted dopamine neurons were positively identified with phenotypic markers of normal control human substantia nigra (n = 3), such as tyrosine hydroxylase, G-protein-coupled inward rectifying current potassium channel type 2 (Girk2) and calbindin. The grafts restored the cell type that provides specific dopaminergic innervation to the most affected striatal regions in the parkinsonian brain. Such transplants were able to densely reinnervate the host putamen with new dopamine fibres. The patients received only 6 months of standard immune suppression, yet by post-mortem analysis 3-4 years after surgery the transplants appeared only mildly immunogenic to the host brain, by analysis of microglial CD45 and CD68 markers. This study demonstrates that, using these methods, dopamine neuronal replacement cell therapy can be beneficial for patients with advanced disease, and that changing technical approaches could have a favourable impact on efficacy and adverse events following neural transplantation.

Stem cell therapy for Parkinson's disease

Transplantation of human fetal dopamine (DA) neurons to patients with Parkinson's disease (PD) has given proof of the principle that new neurons can survive for at least a decade, and then functionally integrate and provide significant symptomatic relief. Unfortunately, the ethical, technical, and practical limitations of using fetal DA neurons as the source for cell transplantation in PD, in combination with the development of unwanted grafting-related side effects, have put a halt to the spread of this treatment into clinical practice. Hopefully, recent advances in the fields of stem cell biology and adult neurogenesis research will lead totamen in new exciting ways to better understand and control the biological parameters necessary for achieving safe and successful neuronal replacement in PD patients.

Midbrain-derived neural stem cells: from basic science to therapeutic approaches

Neural stem cells (NSCs) are a subtype of tissue-specific progenitor cells capable of extended self-renewal and the ability to generate all major cell types of nervous tissue, such as neurons, astroglia and oligodendroglial cells. Recent studies suggest that salient patterning in anterior-posterior and dorsal-ventral axes occurs early, concomitantly with neural induction and therefore stem cells and restricted precursors exhibit regionalization. Fetal mesencephalic NSCs can be isolated and expanded in vitro for many months while retaining their potential to differentiate into glia and neurons, with a subset of neurons displaying all the major properties of mature functional dopaminergic neurons. Since Parkinson's disease (PD) is characterized by the loss of a specific type of dopaminergic cells, the prospect of replacing the missing or damaged cells is very attractive in PD. Thus, mesencephalic NSCs might serve as a new and continuous source of dopaminergic neurons for regenerative strategies in this neurodegenerative disorder. This review discusses new data concerning the cell biology and therapeutic potential of NSCs derived from the midbrain region of the central nervous system.

Fetal lateral ganglionic eminence attracts one of two morphologically different types of tyrosine hydroxylase-positive nerve fibers formed by cultured ventral mesencephalon

The purpose of this study was to investigate the influence of fetal lateral ganglionic eminence (LGE) on nerve fiber outgrowth formed by fetal ventral mesencephalon (VM). Organotypic tissue cultures of fetal VM and LGE plated as single or cocultures were employed. Survival time was 3-21 days in vitro. Nerve fiber outgrowth and migration of astrocytes were analyzed using immunohistochemistry for tyrosine hydroxylase (TH) and S100. In addition, cultures were labeled with the TUNEL technique and with antibodies directed against neurofilament (NF) in order to study apoptosis and retraction of nerve fibers, respectively. The results revealed two morphologically different types of TH-positive outgrowth growing into the substrate. The initially formed TH-positive outgrowth radiated continuously without changing direction, while a second wave of TH-positive outgrowth became obvious when the initial growth already had reached a distance of approximately 1000 microm. The second wave of TH-positive outgrowth radiated from the tissue, but at a certain distance changed direction and formed a network surrounding the culture. The initially formed TH-positive growth was not associated with the presence of S100-positive astrocytes and avoided to grow into the LGE. At longer time points the first wave of TH-positive nerve fibers appeared dotted, with disrupted NF-immunoreactive fibers and in most cultures these long distance growing fibers had disappeared at 21 days in vitro. The second wave of TH-positive nerve fibers was growing onto a layer of glia and never reached the distance of the first wave. LGE became innervated by TH-positive fibers at the time point for when the second wave of TH-positive growth had been initiated, and the innervation appeared in TH-dense patches that also showed a high density of S100-positive astrocytes. Significantly increased TUNEL activity within LGE portion of cocultures was observed when TH-positive fibers entered the LGE and formed patches. In conclusion, two morphologically different types of TH-positive outgrowth were found and the initially formed fibers neither targeted the LGE nor were they guided by glial cells, but their potential to grow for long distances was high.

Toward full restoration of synaptic and terminal function of the dopaminergic system in Parkinson's disease by stem cells

New therapeutic nonpharmacological methodology in Parkinson's disease (PD) involves cell and synaptic renewal or replacement to restore function of neuronal systems, including the dopaminergic (DA) system. Using fetal DA cell therapy in PD patients and laboratory models, it has been demonstrated that functional motor deficits associated with parkinsonism can be reduced. Similar results have been observed in animal models with stem cell-derived DA neurons. Evidence obtained from transplanted PD patients further shows that the underlying disease process does not destroy transplanted fetal DA cells, although degeneration of the host nigrostriatal system continues. The optimal DA cell regeneration system would reconstitute a normal neuronal network capable of restoring feedback-controlled release of DA in the nigrostriatal system. The success of cell therapy for PD is limited by access to preparation and development of highly specialized dopaminergic neurons found in the A9 and A10 region of the substantia nigra pars compacta as well as the technical and surgical steps associated with the transplantation procedure. Recent laboratory work has focused on using stem cells as a starting point for deriving the optimal DA cells to restore the nigrostriatal system. Ultimately, understanding the cell biological principles necessary for generating functional DA neurons can provide many new avenues for better treatment of patients with PD.

Isolation and transplantation of dopaminergic neurons and neural stem cells

Although transplantation of mesencephalic tissue is considered a promising therapy for Parkinson's disease (PD), its clinical use is still restricted to a very few cases. A major limiting factor of this therapy is the difficulty of obtaining sufficient quantities of viable embryonic mesencephalic tissue. To overcome this limitation, techniques to produce dopaminergic (DA) neurons in vitro have been developed. However, these cultures are likely to contain a variety of unidentified cells, which must be removed before implantation. Specific cell-surface markers to sort DA neurons or their precursors are not available. We have developed an alternative strategy, by which these cells can be labeled with green fluorescent protein and isolated with fluorescent activated cell sorter. Transplantation of the sorted cells resulted in recovery of a rat model of the PD. This strategy should be useful for developing new therapies for PD.

Embryonic stem cells develop into functional dopaminergic neurons after transplantation in a Parkinson rat model

Although implantation of fetal dopamine (DA) neurons can reduce parkinsonism in patients, current methods are rudimentary, and a reliable donor cell source is lacking. We show that transplanting low doses of undifferentiated mouse embryonic stem (ES) cells into the rat striatum results in a proliferation of ES cells into fully differentiated DA neurons. ES cell-derived DA neurons caused gradual and sustained behavioral restoration of DA-mediated motor asymmetry. Behavioral recovery paralleled in vivo positron emission tomography and functional magnetic resonance imaging data demonstrating DA-mediated hemodynamic changes in the striatum and associated brain circuitry. These results demonstrate that transplanted ES cells can develop spontaneously into DA neurons. Such DA neurons can restore cerebral function and behavior in an animal model of Parkinson's disease.

Viability and survival of hNT neurons determine degree of functional recovery in grafted ischemic rats

We recently reported behavioral improvements following intrastriatal transplantation of cryopreserved cultured human neuroteratocarcinoma-derived cells (hNT neurons) in rats with cerebral ischemia induced by occlusion of the middle cerebral artery. In the present study, the viability and survival of hNT neurons were evaluated immediately prior to the transplantation surgery and at 3 months post-transplantation in ischemic rats. Cryopreserved hNT neurons were routinely thawed, and trypan blue exclusion viability counts revealed 52-95% viable hNT neurons before transplantation. Monthly behavioral tests, starting at 1 month and extending to 3 months post-transplantation, revealed that ischemic animals that were intrastriatally transplanted with hNT neurons (approximately 40000) and treated with an immunosuppressive drug displayed normalization of asymmetrical motor behavior compared with ischemic animals that received medium alone. Within-subject comparisons of cell viability and subsequent behavioral changes revealed that a high cell viability just prior to transplantation surgery correlated highly with a robust and sustained functional improvement in the transplant recipient. Furthermore, histological analysis of grafted brains revealed a positive correlation between number of surviving hNT neurons and degree of functional recovery. In concert with similar reports on fetal tissue transplantation, we conclude that high cell viability is an important criterion for successful transplantation of cryopreserved neurons derived from cell lines to enhance graft-induced functional effects.