Human neural progenitor cell transplants into the subthalamic nucleus lead to functional recovery in a rat model of Parkinson’s disease

Derivation of Neural Stem Cells from the Developing and Adult Human Brain

Neural stem cells isolated from the developing and adult brain are an ideal source of cells for use in clinical applications such as cell replacement therapy. The clear advantage of these cells over the more commonly utilised embryonic and pluripotent stem cells is that they are already neurally committed. Of particular importance is the fact that these cells don't require the same level of in vitro culture that can be cost and labour intensive. Foetal neural stem cells can be readily derived from the foetal brain and expand in culture over time. Similarly, adult stem cells have been explored for their potential in vitro and in vivo animal models. In this chapter we identify the progress made in developing these cells as well as the advantages of taking them forward for clinical use.

In Vivo Assessment of Stem Cells for Treating Neurodegenerative Disease: Current Approaches and Future Prospects

In recent years, stem cell-related therapies have been widely applied for treating neurodegenerative disease. Despite their potential, stem cell tracking and imaging techniques for the evaluation of in vivo proof-of-concept (PoC) therapies have not been sufficiently represented in the research area. This review summarizes the recent approaches that have been used for tracking and imaging engrafted stem cells in vivo. Furthermore, we introduce tissue clearing technology that can be applied to develop three-dimensional in vivo experiments. Monitoring stem cell survival and migration and graft-host relationships is a useful strategy to evaluate the therapeutic efficacy of regenerative medicine approaches in neurodegenerative disease.

Purinergic receptors in embryonic and adult neurogenesis

ATP (adenosine 5'-triphosphate), one of the most ancient neurotransmitters, exerts essential functions in the brain, including neurotransmission and modulation of synaptic activity. Moreover, this nucleotide has been attributed with trophic properties and experimental evidence points to the participation of ATP-activated P2X and P2Y purinergic receptors in embryonic brain development as well as in adult neurogenesis for maintenance of normal brain functions and neuroregeneration upon brain injury. We discuss here the available data on purinergic P2 receptor expression and function during brain development and in the neurogenic zones of the adult brain, as well as the insights based on the use of in vitro stem cell cultures. While several P2 receptor subtypes were shown to be expressed during in vitro and in vivo neurogenesis, specific functions have been proposed for P2Y1, P2Y2 metabotropic as well as P2X2 ionotropic receptors to promote neurogenesis. Further, the P2X7 receptor is suggested to function in the maintenance of pools of neural stem and progenitor cells through induction of proliferation or cell death, depending on the microenvironment. Pathophysiological actions have been proposed for this receptor in worsening damage in brain disease. The P2X7 receptor and possibly additional P2 receptor subtypes have been implicated in pathophysiology of neurological diseases including Parkinson's disease, Alzheimer's disease and epilepsy. New strategies in cell therapy could involve modulation of purinergic signaling, either in the achievement of more effective protocols to obtain viable and homogeneous cell populations or in the process of functional engraftment of transplanted cells into the damaged brain. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Adult human olfactory epithelial-derived progenitors: a potential autologous source for cell-based treatment for Parkinson's disease

Human adult olfactory epithelial-derived neural progenitors (hONPs) can differentiate along several neural lineages in response to morphogenic signals in vitro. A previous study optimized the transfection paradigm for the differentiation of hONPs to dopaminergic neurons. This study engrafted cells modified by the most efficient transfection paradigm for dopaminergic neural restriction and pretransfected controls into a unilateral neurotoxin, 6-hydroxydopamine-induced parkinsonian rat model. Approximately 35% of the animals engrafted with hONPs had improved behavioral recovery as demonstrated by the amphetamine-induced rotation test, as well as a corner preference and cylinder paw preference, over a period of 24 weeks. The pre- and post-transfected groups produced equivalent responses, indicating that the toxic host environment supported hONP dopaminergic differentiation in situ. Human fibroblasts used as a cellular control did not diminish the parkinsonian rotational deficits at any point during the study. Increased numbers of tyrosine hydroxylase (TH)-positive cells were detected in the engrafted brains compared with the fibroblast-implanted and medium-only controls. Engrafted TH-positive hONPs were detected for a minimum of 6 months in vivo; they were multipolar, had long processes, and migrated beyond their initial injection sites. Higher dopamine levels were detected in the striatum of behaviorally improved animals than in equivalent regions of their nonrecovered counterparts. Throughout these experiments, no evidence of tumorigenicity was observed. These results support our hypothesis that human adult olfactory epithelial-derived progenitors represent a unique autologous cell type with promising potential for future use in a cell-based therapy for patients with Parkinson's disease.

Protocols for investigating microRNA functions in human neural progenitor cells

Human embryonic stem cells and induced pluripotent stem cells offer great hope for studies of pathogenic mechanisms of disease and cell-based therapies. One powerful approach to manipulate the behaviors of human stem cells and their progenies is through microRNAs (miRNAs), a class of small noncoding RNAs that regulate gene expression at the posttranscriptional level. Each miRNA may target up to hundreds of mRNAs; some are specifically expressed in progenitor cells and affect multiple cellular processes. Here we present experimental protocols for investigating the endogenous functions of specific miRNAs in the proliferation, survival, and migration of human neural progenitor cells derived from embryonic stem cells. These methods may be applicable to protein factors and neural progenitor cells derived from patient-specific induced pluripotent stem cells.

Cell-based therapies for Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide, classically characterized by a triad of motor features: bradykinesia, rigidity and resting tremor. Neurodegeneration in PD critically involves the dopaminergic neurons of the substantia nigra pars compacta, which results in a severe reduction in dopamine levels in the dorsal striatum. However, the disease also exhibits extensive non-nigral pathology and as many non-motor as motor features. Nevertheless, owing to the relatively circumscribed nature of the nigrostriatal lesion in PD, dopaminergic cell transplantation has emerged as a potentially reparative therapy for the disease. Sources for such cells are varied and include the developing ventral mesencephalon, several autologous somatic cell types, embryonic stem cells and induced pluripotent stem cells. In this article, we review the origins of dopaminergic transplantation for PD and the emergent hunt for a suitable long-term source of transplantable dopaminergic neurons.

Extrastriatal dopaminergic circuits of the Basal Ganglia

The basal ganglia are comprised of the striatum, the external and internal segment of the globus pallidus (GPe and GPi, respectively), the subthalamic nucleus (STN), and the substantia nigra pars compacta and reticulata (SNc and SNr, respectively). Dopamine has long been identified as an important modulator of basal ganglia function in the striatum, and disturbances of striatal dopaminergic transmission have been implicated in diseases such as Parkinson's disease (PD), addiction and attention deficit hyperactivity disorder. However, recent evidence suggests that dopamine may also modulate basal ganglia function at sites outside of the striatum, and that changes in dopaminergic transmission at these sites may contribute to the symptoms of PD and other neuropsychiatric disorders. This review summarizes the current knowledge of the anatomy, functional effects and behavioral consequences of the dopaminergic innervation to the GPe, GPi, STN, and SNr. Further insights into the dopaminergic modulation of basal ganglia function at extrastriatal sites may provide us with opportunities to develop new and more specific strategies for treating disorders of basal ganglia dysfunction.

VEGF and its receptor-2 involved in neuropathic pain transmission mediated by P2X₂(/)₃ receptor of primary sensory neurons

The pathogenesis of neuropathic pain is complex. P2X₂(/)₃ receptor plays a crucial role in nociception transduction of chronic pain. VEGF inhibitors are effective for pain relief. The present study investigated the effects of VEGF and VEGF receptor-2 (VEGFR2) on the pain transmission in neuropathic pain states that mediated by P2X₂(/)₃ receptor in primary sensory neurons. Chronic constriction injury (CCI) model was used as neuropathic pain model. Sprague-Dawley rats had been randomly divided into sham group, CCI group and CCI rats treated with anti-rVEGF antibody group. Mechanical withdrawal threshold and thermal withdrawal latency were measured. Expressions of VEGF, VEGFR2 and P2X₂(/)₃ in L4-6 dorsal root ganglia (DRG) were detected by immunohistochemistry, RT-PCR and western blot analysis. The mechanical withdrawal threshold and thermal withdrawal latency in CCI group were lower than those in sham group and CCI rats treated with anti-rVEGF antibody group (p<0.05), while VEGF, VEGFR2 and P2X₂(/)₃ receptors' expressions of L4-6 DRG in CCI group were higher than those in the other two groups (p<0.05). The expressions of VEGF, VEGFR2 and P2X₂(/)₃ in L4-6 DRG of CCI rats treated with anti-rVEGF antibody group were decreased compared with those in CCI group (p<0.05). The results show that VEGF and VEGFR2 are involved in the pathogenesis of neuropathic pain and VEGF primarily potentiates pain responses mediated by P2X₂(/)₃ receptor on DRG neurons. Anti-rVEGF treatment in CCI rats may alleviate chronic neuropathic pain by decreasing the expressions of VEGFR2 and P2X₂(/)₃ receptors on DRG neurons to inhibit the transmission of neuropathic pain signaling.

Roadblocks en route to the clinical application of induced pluripotent stem cells

Since the first studies of human embryonic stem cells (hESCs) and, more recently, human induced pluripotent stem cells (hiPSCs), the stem-cell field has been abuzz with the promise that these pluripotent populations will one day be a powerful therapeutic tool. Although it has been proposed that hiPSCs will supersede hESCs with respect to their research and/or clinical potential because of the ease of their derivation and the ability to create immunologically matched iPSCs for each individual patient, recent evidence suggests that iPSCs in fact have several underappreciated characteristics that might mean they are less suitable for clinical application. Continuing research is revealing the similarities, differences and deficiencies of various pluripotent stem-cell populations, and suggests that many years will pass before the clinical utility of hESCs and hiPSCs is realized. There are a plethora of ethical, logistical and technical roadblocks on the route to the clinical application of pluripotent stem cells, particularly of iPSCs. In this Essay, we discuss what we believe are important issues that should be considered when attempting to bring hiPSC-based technology to the clinic.

Effect of VEGF on neural differentiation of human embryonic stem cells in vitro

The effects of vascular endothelial growth factor (VEGF) on neural differentiation of human embryonic stem cells (hESCs) in vitro and the possible mechanism were observed. The hESCs lines, TJMU1 and TJMU2, were established and stored by our laboratory. hESCs differentiated into neuronal cells through embryonic body formation. In this induction process, hESCs were divided into three groups: group A, routine induction; group B, routine induction+10 ng/mL VEGF; group C, routine induction+10 ng/mL VEGF+10 ng/mL VEGFR2/Fc. OCT4, Nestin and GFAP in each group were detected by RT-PCR, and the cells expressing Nestin and GFAP were counted by immunofluorescence. The percentage of Nestin positive cells in group B was significantly higher than in groups A and C, while the percentage of GFAP positive cells in group B was significantly lower than in groups A and C (P<0.01). There was no significant difference between groups A and C (P>0.05). It was concluded that VEGF, via VEGFR2, stimulated the neural differentiation of hESCs in vitro.

Role and therapeutic potential of VEGF in the nervous system

The development of the nervous and vascular systems constitutes primary events in the evolution of the animal kingdom; the former provides electrical stimuli and coordination, while the latter supplies oxygen and nutrients. Both systems have more in common than originally anticipated. Perhaps the most striking observation is that angiogenic factors, when deregulated, contribute to various neurological disorders, such as neurodegeneration, and might be useful for the treatment of some of these pathologies. The prototypic example of this cross-talk between nerves and vessels is the vascular endothelial growth factor or VEGF. Although originally described as a key angiogenic factor, it is now well established that VEGF also plays a crucial role in the nervous system. We describe the molecular properties of VEGF and its receptors and review the current knowledge of its different functions and therapeutic potential in the nervous system during development, health, disease and in medicine.

Human neural stem cell grafts in the spinal cord of SOD1 transgenic rats: differentiation and structural integration into the segmental motor circuitry

Cell replacement strategies for degenerative and traumatic diseases of the nervous system depend on the functional integration of grafted cells into host neural circuitry, a condition necessary for the propagation of physiological signals and, perhaps, targeting of trophic support to injured neurons. We have recently shown that human neural stem cell (NSC) grafts ameliorate motor neuron disease in SOD1 transgenic rodents. Here we study structural aspects of integration of neuronally differentiated human NSCs in the motor circuitry of SOD1 G93A rats. Human NSCs were grafted into the lumbar protuberance of 8-week-old SOD1 G93A rats; the results were compared to those on control Sprague-Dawley rats. Using pre-embedding immuno-electron microscopy, we found human synaptophysin (+) terminals contacting the perikarya and proximal dendrites of host alpha motor neurons. Synaptophysin (+) terminals had well-formed synaptic vesicles and were associated with membrane specializations primarily in the form of symmetrical synapses. To analyze the anatomy of motor circuits engaging differentiated NSCs, we injected the retrograde transneuronal tracer Bartha-pseudorabies virus (PRV) or the retrograde marker cholera toxin B (CTB) into the gastrocnemius muscle/sciatic nerve of SOD1 rats before disease onset and also into control rats. With this tracing, NSC-derived neurons were labeled with PRV but not CTB, a pattern suggesting that PRV entered NSC-derived neurons via transneuronal transfer from host motor neurons but not via direct transport from the host musculature. Our results indicate an advanced degree of structural integration, via functional synapses, of differentiated human NSCs into the segmental motor circuitry of SOD1-G93A rats.

Survival, differentiation, and migration of bioreactor-expanded human neural precursor cells in a model of Parkinson disease in rats

Object

Fetal tissue transplantation for Parkinson disease (PD) has demonstrated promising results in experimental and clinical studies. However, the widespread clinical application of this therapeutic approach is limited by a lack of fetal tissue. Human neural precursor cells (HNPCs) are attractive candidates for transplantation because of their long-term proliferation activity. Furthermore, these cells can be reproducibly expanded in a standardized fashion in suspension bioreactors. In this study the authors sought to determine whether the survival, differentiation, and migration of HNPCs after transplantation depended on the region of precursor cell origin, intracerebral site of transplantation, and duration of their expansion.

Methods

Human neural precursor cells were isolated from the telencephalon, brainstem, ventral mesencephalon, and spinal cord of human fetuses 8–10 weeks of gestational age, and their differentiation potential characterized in vitro. After expansion in suspension bioreactors, the HNPCs were transplanted into the striatum and substantia nigra of parkinsonian rats. Histological analyses were performed 7 weeks posttransplantation.

Results

The HNPCs isolated from various regions of the neuraxis demonstrated diverse propensities to differentiate into astrocytes and neurons and could all successfully expand under standardized conditions in suspension bioreactors. At 7 weeks posttransplantation, survival and migration were significantly greater for HNPCs obtained from the more rostral brain regions. The HNPCs differentiated predominantly into astrocytes after transplantation into the striatum or substantia nigra regions, and thus no behavioral improvement was observed.

Conclusions

Understanding the regional differences in HNPC properties is prerequisite to their application for PD cell restoration strategies.