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

Axonal Tract Reconstruction Using a Tissue-Engineered Nigrostriatal Pathway in a Rat Model of Parkinson's Disease

Parkinson's disease (PD) affects 1-2% of people over 65, causing significant morbidity across a progressive disease course. The classic PD motor deficits are caused by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc), resulting in the loss of their long-distance axonal projections that modulate striatal output. While contemporary treatments temporarily alleviate symptoms of this disconnection, there is no approach able to replace the nigrostriatal pathway. We applied microtissue engineering techniques to create a living, implantable tissue-engineered nigrostriatal pathway (TE-NSP) that mimics the architecture and function of the native pathway. TE-NSPs comprise a discrete population of dopaminergic neurons extending long, bundled axonal tracts within the lumen of hydrogel micro-columns. Neurons were isolated from the ventral mesencephalon of transgenic rats selectively expressing the green fluorescent protein in dopaminergic neurons with subsequent fluorescent-activated cell sorting to enrich a population to 60% purity. The lumen extracellular matrix and growth factors were varied to optimize cytoarchitecture and neurite length, while immunocytochemistry and fast-scan cyclic voltammetry (FSCV) revealed that TE-NSP axons released dopamine and integrated with striatal neurons in vitro. Finally, TE-NSPs were implanted to span the nigrostriatal pathway in a rat PD model with a unilateral 6-hydroxydopamine SNpc lesion. Immunohistochemistry and FSCV established that transplanted TE-NSPs survived, maintained their axonal tract projections, extended dopaminergic neurites into host tissue, and released dopamine in the striatum. This work showed proof of concept that TE-NSPs can reconstruct the nigrostriatal pathway, providing motivation for future studies evaluating potential functional benefits and long-term durability of this strategy. This pathway reconstruction strategy may ultimately replace lost neuroarchitecture and alleviate the cause of motor symptoms for PD patients.

New Targets and New Technologies in the Treatment of Parkinson’s Disease: A Narrative Review

Parkinson’s disease (PD) is a progressive neurodegenerative disease, whose main neuropathological finding is pars compacta degeneration due to the accumulation of Lewy bodies and Lewy neurites, and subsequent dopamine depletion. This leads to an increase in the activity of the subthalamic nucleus (STN) and the internal globus pallidus (GPi). Understanding functional anatomy is the key to understanding and developing new targets and new technologies that could potentially improve motor and non-motor symptoms in PD. Currently, the classical targets are insufficient to improve the entire wide spectrum of symptoms in PD (especially non-dopaminergic ones) and none are free of the side effects which are not only associated with the procedure, but with the targets themselves. The objective of this narrative review is to show new targets in DBS surgery as well as new technologies that are under study and have shown promising results to date. The aim is to give an overview of these new targets, as well as their limitations, and describe the current studies in this research field in order to review ongoing research that will probably become effective and routine treatments for PD in the near future.

Concise Review: Recent advances in neuroimaging techniques to assist clinical trials on cell-based therapies in neurodegenerative diseases

Neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), are progressive disorders for which a curative therapy is still lacking. Cell-based therapy aims at replacing dysfunctional cellular populations by repairing damaged tissue and by enriching the microenvironment of selective brain areas, and thus constitutes a promising disease-modifying treatment of neurodegenerative diseases. Scientific research has engineered a wide range of human-derived cellular populations to help overcome some of the logistical, safety, and ethical issues associated with this approach. Open-label studies and clinical trials in human participants have employed neuroimaging techniques, such as positron emission tomography (PET) and magnetic resonance imaging (MRI), to assess the success of the transplantation, to evaluate the functional integration of the implanted tissue into the host environment and to understand the pathophysiological changes associated with the therapy. Neuroimaging has constituted an outcome measure of large, randomized clinical trials, and has given answers to clarify the pathophysiology underlying some of the complications linked with this therapy. Novel PET radiotracers and MRI sequences for the staging of neurodegenerative diseases and to study alterations at molecular level significantly expands the translational potential of neuroimaging to assist pre-clinical and clinical research on cell-based therapy in these disorders. This concise review summarizes the current use of neuroimaging in human studies of cell-based replacement therapy and focuses on future application of PET and MRI techniques to evaluate the pathophysiology and treatment efficacy, as well as to aid patient selection and as an outcome measure to improve treatment success.

Glial cells in intracerebral transplantation for Parkinson's disease

In the last few decades, intracerebral transplantation has grown from a dubious neuroscientific topic to a plausible modality for treatment of neurological disorders. The possibility for cell replacement opens a new field of perspectives in the therapy of neurodegenerative disorders, ischemia, and neurotrauma, with the most lessons learned from intracerebral transplantation in Parkinson's disease. Multiple animal studies and a few small-scale clinical trials have proven the concept of intracerebral grafting, but still have to provide a uniform and highly efficient approach to the procedure, suitable for clinical application. The success of intracerebral transplantation is highly dependent on the integration of the grafted cells with the host brain. In this process, glial cells are clearly more than passive bystanders. They provide transplanted cells with mechanical support, trophics, mediate synapse formation, and participate in graft vascularization. At the same time, glial cells mediate scarring, graft rejection, and neuroinflammation, which can be detrimental. We can use this information to try to understand the mechanisms behind the glial reaction to intracerebral transplantation. Recognizing and utilizing glial reactivity can move translational research forward and provide an insight not only to post-transplantation events but also to mechanisms of neuronal death and degeneration. Knowledge about glial reactivity to transplanted cells could also be a key for optimization of transplantation protocols, which ultimately should contribute to greater patient benefit.

Advantages and Recent Developments of Autologous Cell Therapy for Parkinson's Disease Patients

Parkinson’s Disease (PD) is a progressive degenerative disease characterized by tremor, bradykinesia, rigidity and postural instability. There are approximately 7–10 million PD patients worldwide. Currently, there are no biomarkers available or pharmaceuticals that can halt the dopaminergic neuron degeneration. At the time of diagnosis about 60% of the midbrain dopamine (mDA) neurons have already degenerated, resulting in a depletion of roughly 70% of striatal dopamine (DA) levels and synapses. Symptomatic treatment (e.g., with L-dopa) can initially restore DA levels and motor function, but with time often lead to side-effects like dyskinesia. Deep-brain-stimulation can alleviate these side-effects and some of the motor symptoms but requires repeat procedures and adds limitations for the patients. Restoration of dopaminergic synapses using neuronal cell replacement therapy has shown benefit in clinical studies using cells from fetal ventral midbrain. This approach, if done correctly, increases DA levels and restores synapses, allowing biofeedback regulation between the grafted cells and the host brain. Drawbacks are that it is not scalable for a large patient population and the patients require immunosuppression. Stem cells differentiated in vitro to mDA neurons or progenitors have shown promise in animal studies and is a scalable approach that allows for cryopreservation of transplantable cells and rigorous quality control prior to transplantation. However, all allogeneic grafts require immunosuppression. HLA-donor-matching, reduces, but does not completely eliminate, the need for immunosuppression, and is currently investigated in a clinical trial for PD in Japan. Since immune compatibility is very important in all areas of transplantation, these approaches may ultimately be of less benefit to the patients than an autologous approach. By using the patient’s own somatic cells, reprogrammed to induced pluripotent stem cells (iPSCs) and differentiated to mDA neurons immunosuppression is not required, and may also present with several biological and functional advantages in the patients, as described in this article. The proof-of-principle of autologous iPSC mDA restoration of function has been shown in parkinsonian non-human primates (NHPs), and this can now be investigated in clinical trials in addition to the allogeneic and HLA-matched approaches. In this review, we focus on the autologous approach of cell therapy for PD.

Emerging regenerative medicine and tissue engineering strategies for Parkinson's disease

Parkinson's disease (PD) is the second most common progressive neurodegenerative disease, affecting 1-2% of people over 65. The classic motor symptoms of PD result from selective degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc), resulting in a loss of their long axonal projections to the striatum. Current treatment strategies such as dopamine replacement and deep brain stimulation (DBS) can only minimize the symptoms of nigrostriatal degeneration, not directly replace the lost pathway. Regenerative medicine-based solutions are being aggressively pursued with the goal of restoring dopamine levels in the striatum, with several emerging techniques attempting to reconstruct the entire nigrostriatal pathway-a key goal to recreate feedback pathways to ensure proper dopamine regulation. Although many pharmacological, genetic, and optogenetic treatments are being developed, this article focuses on the evolution of transplant therapies for the treatment of PD, including fetal grafts, cell-based implants, and more recent tissue-engineered constructs. Attention is given to cell/tissue sources, efficacy to date, and future challenges that must be overcome to enable robust translation into clinical use. Emerging regenerative medicine therapies are being developed using neurons derived from autologous stem cells, enabling the construction of patient-specific constructs tailored to their particular extent of degeneration. In the upcoming era of restorative neurosurgery, such constructs may directly replace SNpc neurons, restore axon-based dopaminergic inputs to the striatum, and ameliorate motor deficits. These solutions may provide a transformative and scalable solution to permanently replace lost neuroanatomy and improve the lives of millions of people afflicted by PD.

Homogeneity evaluation of mesenchymal stem cells based on electrotaxis analysis

Stem cell therapy that can restore function to damaged tissue, avoid host rejection and reduce inflammation throughout body without use of immunosuppressive drugs. The established methods were used to identify and to isolate specific stem cell markers by FACS or by immunomagnetic cell separation. The procedures for distinguishing population of stem cells took a time and needed many preparations. Here we suggest an electrotaxis analysis as a new method to evaluate the homogeneity of mesenchymal stem cells which can observe the stem cell population in culture condition and wide use to various types of stem cells. Human mesenchymal stem cell, adipose derived stem cell, tonsil derived stem cell and osteogenic differentiated cells migrated toward anode but the migration speed of differentiated cells was significantly decreased versus that of stem cells. In mixture of stem cells and differentiated cells condition, we identified that the ratio of stem cell versus differentiated cell was matched with the homogeneity evaluation data of stem cells based on electrotaxis analysis. As a result, our evaluation tool has the possibility of the wide use to stem cell homogeneity evaluation and might be used as the stem cell quality control during stem cell culture without any additional antibodies.

Umbilical cord: an unlimited source of cells differentiable towards dopaminergic neurons

Cell replacement therapy utilizing mesenchymal stem cells as its main resource holds great promise for ultimate treatment of human neurological disorders. Parkinson's disease (PD) is a common, chronic neurodegenerative disorder hallmarked by localized degeneration of a specific set of dopaminergic neurons within a midbrain sub-region. The specific cell type and confined location of degenerating neurons make cell replacement therapy ideal for PD treatment since it mainly requires replenishment of lost dopaminergic neurons with fresh and functional ones. Endogenous as well as exogenous cell sources have been identified as candidate targets for cell replacement therapy in PD. In this review, umbilical cord mesenchymal stem cells (UCMSCs) are discussed as they provide an inexpensive unlimited reservoir differentiable towards functional dopaminergic neurons that potentially lead to long-lasting behavioral recovery in PD patients. We also present miRNAs-mediated neuronal differentiation of UCMSCs. The UCMSCs bear a number of outstanding characteristics including their non-tumorigenic, low-immunogenic properties that make them ideal for cell replacement therapy purposes. Nevertheless, more investigations as well as controlled clinical trials are required to thoroughly confirm the efficacy of UCMSCs for therapeutic medical-grade applications in PD.

Merging DBS with viral vector or stem cell implantation: "hybrid" stereotactic surgery as an evolution in the surgical treatment of Parkinson's disease

Parkinson’s disease (PD) is a complex neurodegenerative disorder that is currently managed using a broad array of symptom-based strategies. However, targeting its molecular origins represents the potential to discover disease-modifying therapies. Deep brain stimulation (DBS), a highly successful treatment modality for PD symptoms, addresses errant electrophysiological signaling pathways in the basal ganglia. In contrast, ongoing clinical trials testing gene and cell replacement therapies propose to protect or restore neuronal-based physiologic dopamine transmission in the striatum. Given promising new platforms to enhance target localization—such as interventional MRI-guided stereotaxy—the opportunity now exists to create hybrid therapies that combine DBS with gene therapy and/or cell implantation. In this mini-review, we discuss approaches used for central nervous system biologic delivery in PD patients in previous trials and propose a new set of strategies based on novel molecular targets. A multifaceted approach, if successful, may not only contribute to our understanding of PD pathology but could introduce a new era of disease modification.

Foetal Cell Transplantation for Parkinson's Disease: Focus on Graft-Induced Dyskinesia

Transplantation of dopamine- (DA-) rich foetal ventral mesencephalic cells emerged as a promising therapy for Parkinson's disease (PD), as it allowed significant improvement of motor symptoms in several PD patients in open-label studies. However, double-blind clinical trials have been largely disappointing. The general agreement in the field is that the lack of standardization of tissue collection and preparation, together with the absence of postsurgical immunosuppression, played a key role in the failure of these studies. Moreover, a further complication that emerged in previous studies is the appearance of the so-called graft-induced dyskinesia (GID), in a subset of grafted patients, which resembles dyskinesia induced by L-DOPA but in the absence of medication. Preclinical evidence pointed to the serotonin neurons as possible players in the appearance of GID. In agreement, clinical investigations have shown that grafted tissue may contain a large number of serotonin neurons, in the order of half of the DA cells; moreover, the serotonin 5-HT1A receptor agonist buspirone has been found to produce significant dampening of GID in grafted patients. In this paper, we will review the recent preclinical and clinical studies focusing on cell transplantation for PD and on the mechanisms underlying GID.

Treating non-motor symptoms of Parkinson's disease with transplantation of stem cells

Parkinson's disease (PD) treatment-based research has focused on developing therapies for the management of motor symptoms. Non-motor symptoms do not respond to treatments targeting motor deficits, thus necessitating an urgent need to develop new modalities that cater to both motor and non-motor deficits. Stem cell transplantation is potentially therapeutic for PD, but the disease non-motor symptoms have been primarily neglected in such cell therapy regimens. Many types of stem cells are currently available for transplantation therapy, including adult tissue (e.g., bone marrow, placenta)-derived mesenchymal stem cells. The fact that mesenchymal stem cells can replace and rescue degenerated dopaminergic and non-dopaminergic cells suggests their potential for the treatment of motor as well as non-motor symptoms of PD, which is discussed in this article.

Therapeutic translation of iPSCs for treating neurological disease

Somatic cellular reprogramming is a fast-paced and evolving field that is changing the way scientists approach neurological diseases. For the first time in the history of neuroscience, it is feasible to study the behavior of live neurons from patients with neurodegenerative diseases, such as Alzheimer's and Parkinson's disease, and neuropsychiatric diseases, such as autism and schizophrenia. In this Perspective, we will discuss reprogramming technology in the context of its potential use for modeling and treating neurological and psychiatric diseases and will highlight areas of caution and opportunities for improvement.

Development of a stereotaxic device for low impact implantation of neural constructs or pieces of neural tissues into the mammalian brain

Implanting pieces of tissue or scaffolding material into the mammalian central nervous system (CNS) is wrought with difficulties surrounding the size of tools needed to conduct such implants and the ability to maintain the orientation and integrity of the constructs during and after their transplantation. Here, novel technology has been developed that allows for the implantation of neural constructs or intact pieces of neural tissue into the CNS with low trauma. By “laying out” (instead of forcibly expelling) the implantable material from a thin walled glass capillary, this technology has the potential to enhance neural transplantation procedures by reducing trauma to the host brain during implantation and allowing for the implantation of engineered/dissected tissues or constructs in such a way that their orientation and integrity are maintained in the host. Such technology may be useful for treating various CNS disorders which require the reestablishment of point-to-point contacts (e.g., Parkinson's disease) across the adult CNS, an environment which is not normally permissive to axonal growth.

Dyskinesias in Parkinson's disease: views from positron emission tomography studies

Levodopa-induced dyskinesias (LIDs) and graft-induced dyskinesias (GIDs) are serious and common complications of Parkinson's disease (PD) management following chronic treatment with levodopa or intrastriatal transplantation with dopamine-rich foetal ventral mesencephalic tissue, respectively. Positron emission tomography (PET) molecular imaging provides a powerful in vivo tool that has been employed over the past 20 years for the elucidation of mechanisms underlying the development of LIDs and GIDs in PD patients. PET used together with radioligands tagging molecular targets has allowed the functional investigation of several systems in the brain including the dopaminergic, serotonergic, glutamatergic, opioid, endocannabinoid, noradrenergic and cholinergic systems. In this article the role of PET imaging in unveiling pathophysiological mechanisms underlying the development of LIDs and GIDs in PD patients is reviewed.

Amniotic fluid stem cells with low γ-interferon response showed behavioral improvement in Parkinsonism rat model

Amniotic fluid stem cells (AFSCs) are multipotent stem cells that may be used in transplantation medicine. In this study, AFSCs established from amniocentesis were characterized on the basis of surface marker expression and differentiation potential. To further investigate the properties of AFSCs for translational applications, we examined the cell surface expression of human leukocyte antigens (HLA) of these cells and estimated the therapeutic effect of AFSCs in parkinsonian rats. The expression profiles of HLA-II and transcription factors were compared between AFSCs and bone marrow-derived mesenchymal stem cells (BMMSCs) following treatment with γ-IFN. We found that stimulation of AFSCs with γ-IFN prompted only a slight increase in the expression of HLA-Ia and HLA-E, and the rare HLA-II expression could also be observed in most AFSCs samples. Consequently, the expression of CIITA and RFX5 was weakly induced by γ-IFN stimulation of AFSCs compared to that of BMMSCs. In the transplantation test, Sprague Dawley rats with 6-hydroxydopamine lesioning of the substantia nigra were used as a parkinsonian-animal model. Following the negative γ-IFN response AFSCs injection, apomorphine-induced rotation was reduced by 75% in AFSCs engrafted parkinsonian rats but was increased by 53% in the control group after 12-weeks post-transplantation. The implanted AFSCs were viable, and were able to migrate into the brain’s circuitry and express specific proteins of dopamine neurons, such as tyrosine hydroxylase and dopamine transporter. In conclusion, the relative insensitivity AFSCs to γ-IFN implies that AFSCs might have immune-tolerance in γ-IFN inflammatory conditions. Furthermore, the effective improvement of AFSCs transplantation for apomorphine-induced rotation paves the way for the clinical application in parkinsonian therapy.

Prolonged maturation culture favors a reduction in the tumorigenicity and the dopaminergic function of human ESC-derived neural cells in a primate model of Parkinson's disease

For the safe clinical application of embryonic stem cells (ESCs) for neurological diseases, it is critical to evaluate the tumorigenicity and function of human ESC (hESC)-derived neural cells in primates. We have herein, for the first time, compared the growth and function of hESC-derived cells with different stages of neural differentiation implanted in the brains of primate models of Parkinson's disease. We herein show that residual undifferentiated cells expressing ESC markers present in the cell preparation can induce tumor formation in the monkey brain. In contrast, a cell preparation matured by 42-day culture with brain-derived neurotrophic factor/glial cell line-derived neurotrophic factor (BDNF/GDNF) treatment did not form tumors and survived as primarily dopaminergic (DA) neurons. In addition, the monkeys with such grafts showed behavioral improvement for at least 12 months. These results support the idea that hESCs, if appropriately matured, can serve as a source for DA neurons without forming any tumors in a primate brain.

Emerging roles of microglial activation and non-motor symptoms in Parkinson's disease

Recent data has indicated that the traditional view of Parkinson's disease (PD) as an isolated disorder of the nigrostriatal dopaminergic system alone is an oversimplification of its complex symptomatology. Aside from classical motor deficits, various non-motor symptoms including autonomic dysfunction, sensory and cognitive impairments as well as neuropsychiatric alterations and sleep disturbances are common in PD. Some of these non-motor symptoms can even antedate the motor problems. Many of them are associated with extranigral neuropathological changes, such as extensive α-synuclein pathology and also neuroinflammatory responses in specific brain regions, i.e. microglial activation, which has been implicated in several aspects of PD pathogenesis and progression. However, microglia do not represent a uniform population, but comprise a diverse group of cells with brain region-specific phenotypes that can exert beneficial or detrimental effects, depending on the local phenotype and context. Understanding how microglia can be neuroprotective in one brain region, while promoting neurotoxicity in another, will improve our understanding of the role of microglia in neurodegeneration in general, and of their role in PD pathology in particular. Since neuroinflammatory responses are in principle modifiable, such approaches could help to identify new targets or adjunctive therapies for the full spectrum of PD-related symptoms.

Bilateral transplantation of allogenic adult human bone marrow-derived mesenchymal stem cells into the subventricular zone of Parkinson's disease: a pilot clinical study

The progress of PD and its related disorders cannot be prevented with the medications available. In this study, we recruited 8 PD and 4 PD plus patients between 5 to 15 years after diagnosis. All patients received BM-MSCs bilaterally into the SVZ and were followed up for 12 months. PD patients after therapy reported a mean improvement of 17.92% during “on” and 31.21% during “off” period on the UPDRS scoring system. None of the patients increased their medication during the follow-up period. Subjectively, the patients reported clarity in speech, reduction in tremors, rigidity, and freezing attacks. The results correlated with the duration of the disease. Those patients transplanted in the early stages of the disease (less than 5 years) showed more improvement and no further disease progression than the later stages (11–15 years). However, the PD plus patients did not show any change in their clinical status after stem cell transplantation. This study demonstrates the safety of adult allogenic human BM-MSCs transplanted into the SVZ of the brain and its efficacy in early-stage PD patients.

Clinical application of stem cell therapy in Parkinson's disease

Cell replacement therapies in Parkinson's disease (PD) aim to provide long-lasting relief of patients' symptoms. Previous clinical trials using transplantation of human fetal ventral mesencephalic (hfVM) tissue in the striata of PD patients have provided proof-of-principle that such grafts can restore striatal dopaminergic (DA-ergic) function. The transplants survive, reinnervate the striatum, and generate adequate symptomatic relief in some patients for more than a decade following operation. However, the initial clinical trials lacked homogeneity of outcomes and were hindered by the development of troublesome graft-induced dyskinesias in a subgroup of patients. Although recent knowledge has provided insights for overcoming these obstacles, it is unlikely that transplantation of hfVM tissue will become routine treatment for PD owing to problems with tissue availability and standardization of the grafts. The main focus now is on producing DA-ergic neuroblasts for transplantation from stem cells (SCs). There is a range of emerging sources of SCs for generating a DA-ergic fate in vitro. However, the translation of these efforts in vivo currently lacks efficacy and sustainability. A successful, clinically competitive SC therapy in PD needs to produce long-lasting symptomatic relief without side effects while counteracting PD progression.

In vivo imaging of the integration and function of nigral grafts in clinical trials

In vivo functional imaging has provided objective evidence for the integration and function of nigral grafts in the brains of patients with Parkinson's disease. Clinical trials with the use of positron emission tomography have shown that transplants of human dopamine-rich fetal ventral mesencephalic tissue can survive, grow, and release dopamine providing motor symptom relief, and also that they can restore brain activation related to movement. Positron emission tomography has aided in the elucidation of the pathophysiology of serious adverse effects, so-called graft-induced dyskinesias. With the use of newly established radioligands, positron emission tomography and single-photon emission computed tomography could help to improve Parkinson's patient selection in future clinical trials by selecting those with better predicted outcomes. Moreover, positron emission tomography could help monitoring postoperational inflammatory processes around the grafted tissue and the effect of immunosuppression. Recent evidence from positron emission tomography has provided insight of how ongoing extrastriatal serotonergic denervation may have relevance to nonmotor symptoms in transplanted Parkinson's disease patients indicating new cell therapy targets for a more complete relief of symptoms. Functional and structural magnetic resonance imaging techniques could help to better assess the integration of nigral graft with the host brain by assessing the restoration of brain activation during movement and of functional and structural connectivity. This knowledge should lead to the development of new, optimized in vivo imaging protocols that could help to better schedule, monitor, and modify the clinical outcomes of future human trials assessing the efficacy of fetal or stem cell therapy in Parkinson's disease.

Efficient generation of A9 midbrain dopaminergic neurons by lentiviral delivery of LMX1A in human embryonic stem cells and induced pluripotent stem cells

Human embryonic stem cells (hESC) and induced pluripotent stem cells (iPSC) offer great hope for in vitro modeling of Parkinson's disease (PD), as well as for designing cell-replacement therapies. To realize these opportunities, there is an urgent need to develop efficient protocols for the directed differentiation of hESC/iPSC into dopamine (DA) neurons with the specific characteristics of the cell population lost to PD, i.e., A9-subtype ventral midbrain DA neurons. Here we use lentiviral vectors to drive the expression of LMX1A, which encodes a transcription factor critical for ventral midbrain identity, specifically in neural progenitor cells. We show that clonal lines of hESC engineered to contain one or two copies of this lentiviral vector retain long-term self-renewing ability and pluripotent differentiation capacity. Greater than 60% of all neurons generated from LMX1A-engineered hESC were ventral midbrain DA neurons of the A9 subtype, compared with ∼10% in green fluorescent protein-engineered controls, as judged by specific marker expression and functional analyses. Moreover, DA neuron precursors differentiated from LMX1A-engineered hESC were able to survive and differentiate when grafted into the brain of adult mice. Finally, we provide evidence that LMX1A overexpression similarly increases the yield of DA neuron differentiation from human iPSC. Taken together, our data show that stable genetic engineering of hESC/iPSC with lentiviral vectors driving controlled expression of LMX1A is an efficient way to generate enriched populations of human A9-subtype ventral midbrain DA neurons, which should prove useful for modeling PD and may be helpful for designing future cell-replacement strategies.

Delivery of chemotropic proteins and improvement of dopaminergic neuron outgrowth through a thixotropic hybrid nano-gel

Chemotropic proteins guide neuronal projections to their final target during embryo development and are useful to guide axons of neurons used in transplantation therapies. Site-specific delivery of the proteins however is needed for their application in the brain to avoid degradation and pleiotropic affects. In the present study we report the use of Poly (ethylene glycol)-Silica (PEG-Si) nanocomposite gel with thixotropic properties that make it injectable and suitable for delivery of the chemotropic protein semaphorin 3A. PEG-Si gel forms a functional gradient of semaphorin that enhances axon outgrowth of dopaminergic neurons from rat embryos or differentiated from stem cells in culture. It is not cytotoxic and its properties allowed its injection into the striatum without inflammatory response in the short term. Long term implantation however led to an increase in macrophages and glial cells. The inflammatory response could have resulted from non-degraded silica particles, as observed in biodegradation assays.

Pleiotrophin over-expression provides trophic support to dopaminergic neurons in parkinsonian rats

Background

Pleiotrophin is known to promote the survival and differentiation of dopaminergic neurons in vitro and is up-regulated in the substantia nigra of Parkinson's disease patients. To establish whether pleiotrophin has a trophic effect on nigrostriatal dopaminergic neurons in vivo, we injected a recombinant adenovirus expressing pleiotrophin in the substantia nigra of 6-hydroxydopamine lesioned rats.

Results

The viral vector induced pleiotrophin over-expression by astrocytes in the substantia nigra pars compacta, without modifying endogenous neuronal expression. The percentage of tyrosine hydroxylase-immunoreactive cells as well as the area of their projections in the lesioned striatum was higher in pleiotrophin-treated animals than in controls.

Conclusions

These results indicate that pleiotrophin over-expression partially rescues tyrosine hydroxylase-immunoreactive cell bodies and terminals of dopaminergic neurons undergoing 6-hydroxydopamine-induced degeneration.

Oct4-induced reprogramming is required for adult brain neural stem cell differentiation into midbrain dopaminergic neurons

Neural stem cells (NSCs) lose their competency to generate region-specific neuronal populations at an early stage during embryonic brain development. Here we investigated whether epigenetic modifications can reverse the regional restriction of mouse adult brain subventricular zone (SVZ) NSCs. Using a variety of chemicals that interfere with DNA methylation and histone acetylation, we showed that such epigenetic modifications increased neuronal differentiation but did not enable specific regional patterning, such as midbrain dopaminergic (DA) neuron generation. Only after Oct-4 overexpression did adult NSCs acquire a pluripotent state that allowed differentiation into midbrain DA neurons. DA neurons derived from Oct4-reprogrammed NSCs improved behavioural motor deficits in a rat model of Parkinson's disease (PD) upon intrastriatal transplantation. Here we report for the first time the successful differentiation of SVZ adult NSCs into functional region-specific midbrain DA neurons, by means of Oct-4 induced pluripotency.

Optimizing functional imaging protocols for assessing the outcome of fetal cell transplantation in Parkinson's disease

Clinical trials aiming to assess the safety and efficacy of fetal cell transplantation in Parkinson's disease rely on the hypothesis that the grafted tissue will survive and grow, restore striatal dopaminergic neurotransmission, improve the connectivity between striatum, thalamus and cortex and, thereby, produce long-lasting clinical improvement while avoiding the development of adverse effects. Although transplantation of human fetal ventral mesencephalic tissue has been reported as one of the most effective reparative therapies in Parkinson's disease patients to date, different studies have shown inconsistent results causing a paucity of new trials over the last decade. However, during this period, functional imaging alongside other scientific developments from clinical observations and animal work has significantly aided in understanding the mechanisms responsible for the success or failure of grafting human fetal tissue. Recent advances in functional imaging including both positron emission tomography and functional magnetic resonance imaging could be proven useful in vivo tools for the development and assessment of new clinically competitive trials. In this commentary we discuss how an optimized functional imaging protocol could assist new clinical trials using fetal cell transplantation in Parkinson's disease.

Functions of the nigrostriatal dopaminergic synapse and the use of neurotransplantation in Parkinson's disease

While pharmaceutical options remain the overwhelmingly accepted treatment of choice for neurological and psychiatric diseases, significant accomplishments in regenerative neuroscience research have demonstrated the potential of cellular and synaptic functional repair in future therapies. Parkinson's disease stands out as an example in which repair by dopaminergic neurons appears a viable potential therapy. This article describes the basic neurobiological underpinnings of the rationale for cell therapy for Parkinson's disease and the challenges ahead for the use of regenerative medicine in the treatment for this disease.

Tracking stem cell differentiation in the setting of automated optogenetic stimulation

Membrane depolarization has been shown to play an important role in the neural differentiation of stem cells and in the survival and function of mature neurons. Here, we introduce a microbial opsin into ESCs and develop optogenetic technology for stem cell engineering applications, with an automated system for noninvasive modulation of ESC differentiation employing fast optogenetic control of ion flux. Mouse ESCs were stably transduced with channelrhodopsin-2 (ChR2)-yellow fluorescent protein and purified by fluorescence activated cell sorting (FACS). Illumination of resulting ChR2-ESCs with pulses of blue light triggered inward currents. These labeled ESCs retained the capability to differentiate into functional mature neurons, assessed by the presence of voltage-gated sodium currents, action potentials, fast excitatory synaptic transmission, and expression of mature neuronal proteins and neuronal morphology. We designed and tested an apparatus for optically stimulating ChR2-ESCs during chronic neuronal differentiation, with high-speed optical switching on a custom robotic stage with environmental chamber for automated stimulation and imaging over days, with tracking for increased expression of neural and neuronal markers. These data point to potential uses of ChR2 technology for chronic and temporally precise noninvasive optical control of ESCs both in vitro and in vivo, ranging from noninvasive control of stem cell differentiation to causal assessment of the specific contribution of transplanted cells to tissue and network function.

Neuron-like differentiation of bone marrow-derived mesenchymal stem cells

PURPOSE

Mesenchymal stem cells (MSCs) are multipotent and give rise to distinctly differentiated cells from all three germ layers. Neuronal differentiation of MSC has great potential for cellular therapy. We examined whether the cluster of mechanically made, not neurosphere, could be differentiated into neuron-like cells by growth factors, such as epidermal growth factor (EGF), hepatocyte growth factor (HGF), and vascular endothelial growth factor (VEGF).

MATERIALS AND METHODS

BMSCs grown confluent were mechanically separated with cell scrapers and masses of separated cells were cultured to form cluster BMSCs. As described here cluster of BMSCs were differentiated into neuron-like cells by EGF, HGF, and VEGF. Differentiated cells were analyzed by means of phase-contrast inverted microscopy, reverse transcriptase-polymerase chain reaction (RT-PCR), immunofluorescence, and immunocytochemistry to identify the expression of neural specific markers.

RESULTS

For the group with growth factors, the shapes of neuron-like cells was observable a week later, and two weeks later, most cells were similar in shape to neuron-like cells. Particularly, in the group with chemical addition, various shapes of filament structures were seen among the cells. These culture conditions induced MSCs to exhibit a neural cell phenotype, expressing several neuro-glial specific markers.

CONCLUSION

bone marrow-derived mesenchymal stem cells (BMSCs) could be easily induced to form clusters using mechanical scraping, not neurospheres, which in turn could differentiate further into neuron-like cells and might open an attractive possibility for clinical cell therapy for neurodegenerative diseases. In the future, we consider that neuron-like cells differentiated from clusters of BMSCs are needed to be compared and analyzed on a physiological and molecular biological level with preexisting neuronal cells, and studies on the possibility of their transplantation and differentiation capability in animal models are further required.

Stem cell challenges in the treatment of neurodegenerative disease

Neurodegenerative diseases result from the gradual and progressive loss of neural cells and lead to nervous system dysfunction. The rapidly advancing stem cell field is providing attractive alternative options for fighting these diseases. Results have provided proof of principle that cell replacement can work in humans with Parkinson's disease (PD). However, three clinical studies of cell transplantation were published that found no net benefit, while patients in two of the studies developed dyskinesias that persisted despite reductions in treatment. Induced pluripotent stem cells (iPSC) have major potential advantages because patient-specific neuroblasts are suitable for transplantation, avoid immune reactions, and can be produced without the use of human ES cells (hESC). Although iPSCs have not been successfully used in clinical trials for PD, patients with amyotrophic lateral sclerosis (ALS) were treated with autologous stem cells and, though they had some degree of decline one year after treatment, they were still improved compared with the preoperative period or without any drug therapy. In addition, neural stem cells (NSCs), via brain-derived neurotrophic factor (BDNF), have been shown to ameliorate complex behavioral deficits associated with widespread Alzheimer's disease (AD) pathology in a transgenic mouse model of AD. So far, the FDA lists 18 clinical trials treating multiple sclerosis (MS), but most are in preliminary stages. This article serves as an overview of recent studies in stem cell and regenerative approaches to the above chronic neurodegenerative disorders. There are still many obstacles to the use of stem cells as a cure for neurodegenerative disease, especially because we still don't fully understand the true mechanisms of these diseases. However, there is hope in the potential of stem cells to help us learn and understand a great deal more about the mechanisms underlying these devastating neurodegenerative diseases.

Differentiation of human ES and Parkinson's disease iPS cells into ventral midbrain dopaminergic neurons requires a high activity form of SHH, FGF8a and specific regionalization by retinoic acid

The cardinal motor symptoms of Parkinson's disease (PD) are caused by the vulnerability to dysfunction and degeneration of ventral midbrain (VM) dopaminergic (DA) neurons. A major limitation for experimental studies of current ES/iPS cell differentiation protocols is the lack of VM DA neurons with a stable phenotype as defined by an expression marker code of FOXA2/TH/β-tubulin. Here we demonstrate a combination of three modifications that were required to produce VM DA neurons. Firstly, early and specific exposure to 10(-)(8)M (low dose) retinoic acid improved the regional identity of neural progenitor cells derived from human ES cells, PD or healthy subject-specific iPS cells. Secondly, a high activity form of human sonic hedgehog established a sizeable FOXA2(+) neural progenitor cell population in vitro. Thirdly, early exposure to FGF8a, rather than Fgf8b, and WNT1 was required for robust differentiation of the FOXA2(+) floor plate-like human neural progenitor cells into FOXA2(+) DA neurons. FOXA2(+) DA neurons were also generated when this protocol was adapted to feeder-free conditions. In summary, this new human ES and iPS cell differentiation protocol using FGF8a, WNT1, low dose retinoic acid and a high activity form of SHH can generate human VM DA neurons that are required for relevant new bioassays, drug discovery and cell based therapies for PD.

Axon responses of embryonic stem cell-derived dopaminergic neurons to semaphorins 3A and 3C

Class 3 Semaphorins are a subfamily of chemotropic molecules implicated in the projection of dopaminergic neurons from the ventral mesencephalon and in the formation of the nigrostriatal pathway (NSP) during embryonic development. In humans, loss of mesencephalic dopaminergic neurons leads to Parkinson's disease (PD). Cell replacement therapy with dopaminergic neurons generated from embryonic stem cells (ES-TH(+)) is being actively explored in models of PD. Among several requisites for this approach to work are adequate reconstruction of the NSP and correct innervation of normal striatal targets by dopaminergic axons. In this work, we characterized the response of ES-TH(+) neurons to semaphorins 3A, 3C, and 3F and compared it with that of tyrosine hidroxylase-positive neurons (TH(+)) obtained from embryonic ventral mesencephalon (VM-TH(+)). We observed that similar proportions of ES-TH(+) and VM-TH(+) neurons express semaphorin receptors neuropilins 1 and 2. Furthermore, the axons of both populations responded very similarly to semaphorin exposure: semaphorin 3A increased axon length, and semaphorin 3C attracted axons and increased their length. These effects were mediated by neuropilins, insofar as addition of blocking antibodies against these proteins reduced the effects on axonal growth and attraction, and only TH(+) axons expressing neuropilins responded to the semaphorins analyzed. The observations reported here show phenotypic similarities between VM-TH(+) and ES-TH(+) neurons and suggest that semaphorins 3A and 3C could be employed to guide axons of grafted ES-TH(+) in therapeutic protocols for PD.

Cell-based therapeutic approaches for Parkinson's disease: progress and perspectives

Motor dysfunctions in Parkinson's disease are believed to be primarily due to the degeneration of dopaminergic neurons located in the substantia nigra pars compacta. Because a single-type cell population is depleted, Parkinson's disease is considered a primary target for cell replacement-based therapeutic strategies. Extensive studies have confirmed transplantation of donor neurons could be beneficial, yet identifying an alternative cell source is clearly essential. Human embryonic stem cells (hESCs) have been proposed as a renewable source of dopaminergic neurons for transplantation in Parkinson's disease; other potential sources could include neural stem cells (hNSCs) and adult mesenchymal stem cells (hMSCs). However, numerous difficulties avert practical application of stem cell-based therapeutic approaches for the treatment of Parkinson's disease. Among the latter, ethical, safety (including xeno- and tumor formation-associated risks) and technical issues stand out. This review aims to provide a balanced and updated outlook on various issues associated with stem cells in regard to their potential in the treatment of Parkinson's disease. Essential features of the individual stem cell subtypes, principles of available differentiation protocols, transplantation, and safety issues are discussed extensively.

Stem cells in human neurodegenerative disorders--time for clinical translation?

Stem cell-based approaches have received much hype as potential treatments for neurodegenerative disorders. Indeed, transplantation of stem cells or their derivatives in animal models of neurodegenerative diseases can improve function by replacing the lost neurons and glial cells and by mediating remyelination, trophic actions, and modulation of inflammation. Endogenous neural stem cells are also potential therapeutic targets because they produce neurons and glial cells in response to injury and could be affected by the degenerative process. As we discuss here, however, significant hurdles remain before these findings can be responsibly translated to novel therapies. In particular, we need to better understand the mechanisms of action of stem cells after transplantation and learn how to control stem cell proliferation, survival, migration, and differentiation in the pathological environment.

Lack of functional relevance of isolated cell damage in transplants of Parkinson's disease patients

Postmortem analyses from clinical neural transplantation trials of several subjects with Parkinson's disease revealed surviving grafted dopaminergic neurons after more than a decade. A subset of these subjects displayed isolated dopaminergic neurons within the grafts that contained Lewy body-like structures. In this review, we discuss why this isolated cell damage is unlikely to affect the overall graft function and how we can use these observations to help us to understand age-related neurodegeneration and refine our future cell replacement therapies.

Prospects of stem cell therapy for replacing dopamine neurons in Parkinson's disease

In Parkinson's disease (PD), the main pathology is a loss of nigrostriatal dopamine (DA) neurons. Clinical trials with intrastriatal transplantation of human embryonic mesencephalic tissue have shown that grafted DA neurons reinnervate the striatum, restore striatal DA release and, in some patients, induce major clinical benefit. Stem cells could provide an unlimited source of DA neurons for transplantation. Recent studies demonstrate that cells with properties of mesencephalic DA neurons can be produced from stem cells of different sources including reprogrammed somatic cells. However, as we discuss here, it remains to be shown that these cells can provide efficient functional reinnervation and behavioral recovery in animal PD models. Moreover, a clinically competitive cell therapy for PD will require better criteria for patient selection, improved functional efficacy of grafts by a tailor-made transplantation procedure providing optimum repair of the patient's DA system and strategies to prevent dyskinesias and tumor formation.

Bone marrow-derived mesenchymal stem cell therapy as a candidate disease-modifying strategy in Parkinson's disease and multiple system atrophy

Parkinson's disease (PD) and multiple system atrophy (MSA) are neurodegenerative diseases representative of α-synucleinopathies characterized pathologically by α-synuclein-abundant Lewy bodies and glial cytoplasmic inclusions, respectively. Embryonic stem cells, fetal mesencephalic neurons, and neural stem cells have been introduced as restorative strategies in PD animals and patients, but ethical and immunological problems as well as the serious side effects of tumorigenesis and disabling dyskinesia have limited clinical application of these stem cells. Meanwhile, cell therapy using mesenchymal stem cells (MSCs) is attractive clinically because these cells are free from ethical and immunological problems. MSCs are present in adult bone marrow and represent <0.01% of all nucleated bone marrow cells. MSCs are themselves capable of multipotency, differentiating under appropriate conditions into chondrocytes, skeletal myocytes, and neurons. According to recent studies, the neuroprotective effect of MSCs is mediated by their ability to produce various trophic factors that contribute to functional recovery, neuronal cell survival, and stimulation of endogenous regeneration and by immunoregulatory properties that not only inhibit nearly all cells participating in the immune response cell-cell-contact-dependent mechanism, but also release various soluble factors associated with immunosuppressive activity. However, the use of MSCs as neuroprotectives in PD and MSA has seldom been studied. Here we comprehensively review recent advances in the therapeutic roles of MSCs in PD and MSA, especially focusing on their neuroprotective properties and use in disease-modifying therapeutic strategies.

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.

Molecular and cellular determinants for generating ES-cell derived dopamine neurons for cell therapy

Embryonic stem (ES) cells can generate midbrain dopaminergic (DA) neuronal phenotypes in vitro and have been successfully applied to restore function in animal models of Parkinson's disease (PD). How can we best integrate our growinginsight into the regulatory cascade of transcription factors guiding midbrain specification to further improve the in vitro differentiation of midbrain DA neurons for cell therapy of PD? To characterize the differentiation of authentic DA neurons in vitro, expression patterns of the numerous midbrain-characteristic markers need to be investigated. When using forced gene expression, such factors have to be closely monitored to avoid generation of nonphysiological cell types. Fluorescent markers such as Pitx3-GFP, TH-GFP, Sox1-GFP or surface antigens have proven useful for elimination of unwanted cell types by cell sorting, thereby averting tumors and increasing the DA fraction for transplantation studies. The importance of appropriate timing during application of extrinsic factors and the influence of cell-cell interactions in the dish has to be taken into account. This conceptual synopsis outlines current objectives, progress, but also challenges, in deriving midbrain DA neurons from pluripotent stem cells for clinical and scientific applications.

Fate mapping and lineage analyses demonstrate the production of a large number of striatal neuroblasts after transforming growth factor alpha and noggin striatal infusions into the dopamine-depleted striatum

Infusion of transforming growth factor alpha (TGFalpha) into the adult dopamine (DA)-depleted striatum generates a local population of nestin(+)/proliferating cell nuclear antigen (PCNA)(+) newborn cells. The precise origin and fate of these new striatal cells are unknown, making it difficult to direct them for neural repair in Parkinson's disease. Experiments in rats using 5-bromo-2'-deoxyuridine (BrdU) to label neural progenitor cells showed that during TGFalpha infusion in the DA-depleted striatum, newborn striatal cells formed a homogeneous population of precursors, with the majority coexpressing nestin, Mash1, Olig2, and epidermal growth factor receptor, consistent with the phenotype of multipotent C cells. Upon TGFalpha pump withdrawal, the subventricular zone (SVZ) was repopulated by neuroblasts. Strikingly, during this period, numerous clusters of doublecortin(+)/polysialylated neuronal cell adhesion molecule(+) neuroblasts were also produced in the ipsilateral medial striatum. In parallel, striatal BrdU(+)/glial fibrillary acidic protein(+) astrocytes were generated, but no BrdU(+)/O4(+)/CNPase(+) oligodendrocytes were generated. Infusion of the neuralizing bone morphogenetic protein antagonist noggin after TGFalpha pump withdrawal increased the neuroblast-to-astrocyte ratio among new striatal cells by blocking glial differentiation but did not alter striatal neurogenesis. At no time or treatment condition were differentiated neurons generated, including DA neurons. Using 6-hydroxydopamine-lesioned nestin-CreER(T2)/R26R-YFP mice that allow genetic fate-mapping of SVZ nestin(+) cells, we show that TGFalpha-generated striatal cells originate from SVZ nestin(+) precursors that confirmed data from the rats on the phenotype and fate of striatal nestin(+)/PCNA(+) cells upon TGFalpha withdrawal. This work demonstrates that a large population of multipotent striatal C-like cells can be generated in the DA-depleted striatum that do not spontaneously differentiate into DA neurons.

Recent advances in cell-based therapy for Parkinson disease

In this review, the authors discuss recent advances in the field of cell therapy for Parkinson disease (PD). They compare and contrast recent clinical trials using fetal dopaminergic neurons. They attribute differences in cell preparation techniques, cell type specification, and immunosuppression as reasons for variable outcome and for some of the side effects observed in these clinical trials. To address ethical, practical, and technical issues related to the use of fetal cell sources, alternative sources of therapeutic dopaminergic neurons are being developed. The authors describe the progress in enrichment and purification strategies of stem cell-derived dopaminergic midbrain neurons. They conclude that recent advances in cell therapy for PD will create a viable long-term treatment option for synaptic repair for this debilitating disease.

Dopamine neurons implanted into people with Parkinson's disease survive without pathology for 14 years

Postmortem analysis of five subjects with Parkinson's disease 9-14 years after transplantation of fetal midbrain cell suspensions revealed surviving grafts that included dopamine and serotonin neurons without pathology. These findings are important for the understanding of the etiopathogenesis of midbrain dopamine neuron degeneration and future use of cell replacement therapies.

Targeting axon growth from neuronal transplants along preformed guidance pathways in the adult CNS

To re-establish neuronal circuits lost after CNS injury, transplanted neurons must be able to extend axons toward their appropriate targets. Such growth is highly restricted within the adult CNS attributable to the expression of inhibitory molecules and general lack of guidance cues to direct axon growth. This environment typically induces random patterns of growth and aberrant innervation, if growth occurs at all. To target the growth of axons from neuronal transplants, we are using viral vectors to create guidance pathways before neuronal transplantation. In this study, we transplanted postnatal rat dorsal root ganglia neurons into the corpus callosum of adult rats. Replication-incompetent adenoviruses encoding growth or guidance factors were injected along the desired pathway 1 week before cell transplantation, allowing time for sufficient protein expression by host glial cells. With expression of nerve growth factor (NGF) and basic fibroblast growth factor, sensory axons were able to grow along the corpus callosum, across the midline, and toward an NGF-expressing target in either the contralateral striatum or cortex: a distance of 7-8 mm including a 90 degree turn from white matter into gray matter. Furthermore, expression of semaphorin 3A slightly dorsal and lateral to the turning point increased the number of axons turning into the striatal target. These results show that judicious expression of neuron-specific chemoattractant and chemorepellant molecules using viral vectors can support and target axon growth from neuronal transplants in the adult CNS.

Human stem cells for CNS repair

Although most peripheral tissues have at least a limited ability for self-repair, the central nervous system (CNS) has long been known to be relatively resistant to regeneration. Small numbers of stem cells have been found in the adult brain but do not appear to be able to affect any significant recovery following disease or insult. In the last few decades, the idea of being able to repair the brain by introducing new cells to repair damaged areas has become an accepted potential treatment for neurodegenerative diseases. This review focuses on the suitability of various human stem cell sources for such treatments of both slowly progressing conditions, such as Parkinson's disease, Huntington's disease and multiple sclerosis, and acute insult, such as stroke and spinal cord injury. Despite stem cell transplantation having now moved a step closer to the clinic with the first trials of autologous mesenchymal stem cells, the effects shown are moderate and are not yet at the stage of development that can fulfil the hopes that have been placed on stem cells as a means to replace degenerating cells in the CNS. Success will depend on careful investigation in experimental models to enable us to understand not just the practicalities of stem cell use, but also the underlying biological principles.

Influence of cell preparation and target location on the behavioral recovery after striatal transplantation of fetal dopaminergic neurons in a primate model of Parkinson's disease

Surgeries involving transplantation of fetal dopamine (DA) neurons into the caudate-putamen of patients with Parkinson's disease (PD) have been performed in various clinical trials to examine a potential restoration of motor function. The absence of studies in non-human primates to define the best transplantation protocols have lead to the use of a broad variety of techniques that potentially could have a major impact on the clinical outcome. The effects of using different cell and tissue preparation, and surgical targets, remain unknown. For this purpose, 20 St. Kitts African Green Monkeys (AFG) rendered parkinsonian by i.m. injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were balanced into 4 groups and unilaterally grafted in the (a) caudate or (b) putamen with fetal ventral mesencephalic (VM) tissue as (c) solid pieces or as a (d) cell suspension. By 9 months post-transplantation all animals showed significant and similar behavioral improvement as determined by a UPDRS based PD scale. Postmortem analyses showed that VM transplants survived in all animals. They were located in both surgical target sites, producing a broad DA reinnervation of the targeted nuclei that could also extend to the non-grafted nucleus on the ipsilateral side. Although no differences between groups were found in survival of DA neurons or degree of DA reinnervation, there was a significant correlation between striatal reinnervation and behavioral recovery only in animals transplanted in the putamen surgical target. Additionally, there was in general a stronger glial reaction to solid grafts than to cell suspensions. These studies provide data for the optimal time course, cell preparation and surgical targets for systematic examinations of both potential benefits and side effects of dopamine neuron cell transplantation in primate models of PD.

Differential effects on forelimb grasping behavior induced by fetal dopaminergic grafts in hemiparkinsonian rats

Skilled forelimb movements depend on an intact dopaminergic (DA) neurotransmission and are substantially impaired in the unilateral rat model of Parkinson's disease. It has remained unclear, however, to what extent reaching and grasping movements can be influenced by intrastriatal transplantation of fetal DA neurons. Here an extensive behavioral assessment of skilled forelimb movement patterns in hemiparkinsonian and DA-grafted rats was carried out. Good DA graft survival was accompanied by a compensation of drug-induced rotational asymmetries. Interestingly, skilled forelimb use was significantly improved in transplanted animals as compared to lesion-only animals in the staircase test. Qualitative analysis of single forelimb reaching movement components revealed dissociable patterns of graft effects: while some movement components in grafted animals improved, others remained unchanged or even deteriorated. These findings provide novel insights into the complex interactions of graft-derived restoration of DA neurotransmission and skilled forelimb behavior.