Emerging restorative treatments for Parkinson's disease

Prolonged membrane depolarization enhances midbrain dopamine neuron differentiation via epigenetic histone modifications

Understanding midbrain dopamine (DA) neuron differentiation is of importance, because of physiological and clinical implications of this neuronal subtype. We show that prolonged membrane depolarization induced by KCl treatment promotes DA neuron differentiation from neural precursor cells (NPCs) derived from embryonic ventral midbrain (VM). Interestingly, the depolarization-induced increase of DA neuron yields was not abolished by L-type calcium channel blockers, along with no depolarization-mediated change of intracellular calcium level in the VM-derived NPCs (VM-NPCs), suggesting that the depolarization effect is due to a calcium-independent mechanism. Experiments with labeled DA neuron progenitors indicate that membrane depolarization acts at the differentiation fate determination stage and promotes the expression of DA phenotype genes (tyrosine hydroxylase [TH] and DA transporter [DAT]). Recruitment of Nurr1, a transcription factor crucial for midbrain DA neuron development, to the promoter of TH gene was enhanced by depolarization, along with increases of histone 3 acetylation (H3Ac) and trimethylation of histone3 on lysine 4 (H3K4m3), and decreases of H3K9m3 and H3K27m3 in the consensus Nurr1 binding regions of TH promoter. Depolarization stimuli on differentiating VM-NPCs also induced dissociation of methyl CpG binding protein 2 and related repressor complex molecules (repressor element-1 silencing transcription factor corepressor and histone deacetylase 1) from the CpG sites of TH and DAT promoters. Based on these findings, we suggest that membrane depolarization promotes DA neuron differentiation by opening chromatin structures surrounding DA phenotype genes and inhibiting the binding of corepressors, thus allowing transcriptional activators such as Nurr1 to access DA neuron differentiation gene promoter regions.

Mesenchymal stem cells augment neurogenesis in the subventricular zone and enhance differentiation of neural precursor cells into dopaminergic neurons in the substantia nigra of a parkinsonian model

Growing evidence has demonstrated that neurogenesis in the subventricular zone (SVZ) is significantly decreased in Parkinson's disease (PD). Modulation of endogenous neurogenesis would have a significant impact on future therapeutic strategies for neurodegenerative diseases. In the present study, we investigated the augmentative effects of human mesenchymal stem cells (hMSCs) on neurogenesis in a PD model. Neurogenesis was assessed in vitro with 1-methyl-4-phenylpyridinium (MPP(+)) treatment using neural precursor cells (NPCs) isolated from the SVZ and in vivo with a BrdU-injected animal model of PD using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Immunochemical analyses were used to measure neurogenic activity. The number of BrdU-ir cells in the SVZ and the substantia nigra (SN) was significantly increased in the hMSC-treated PD group compared with the MPTP-only-treated group. Double-stained cells for BrdU and tyrosine hydroxylase were notably observed in the SN of hMSC-treated PD animals, and they did not colocalize with the nuclear matrix; however, double-stained cells were not detected in the SN of the MPTP-induced PD animal model. Furthermore, hMSC administration increased the expression of the epidermal growth factor receptor (EGFR) in the SVZ of PD animals, and the coculture of hMSCs significantly increased the release of EGF in the medium of MPP(+)-treated NPCs. The present study demonstrated that hMSC administration significantly augmented neurogenesis in both the SVZ and SN of PD animal models, which led to increased differentiation of NPCs into dopaminergic neurons in the SN. Additionally, hMSC-induced modulation of EGF seems to be an underlying contributor to the enhancement of neurogenesis by hMSCs. The modulation of endogenous adult neurogenesis to repair the damaged PD brain using hMSCs would have a significant impact on future strategies for PD treatment.

Parkinson's disease and mesenchymal stem cells: potential for cell-based therapy

Cell transplantation is a strategy with great potential for the treatment of Parkinson's disease, and many types of stem cells, including neural stem cells and embryonic stem cells, are considered candidates for transplantation therapy. Mesenchymal stem cells are a great therapeutic cell source because they are easy accessible and can be expanded from patients or donor mesenchymal tissues without posing serious ethical and technical problems. They have trophic effects for protecting damaged tissues as well as differentiation ability to generate a broad spectrum of cells, including dopamine neurons, which contribute to the replenishment of lost cells in Parkinson's disease. This paper focuses mainly on the potential of mesenchymal stem cells as a therapeutic cell source and discusses their potential clinical application in Parkinson's disease.

Co-transplantation of macaque autologous Schwann cells and human embryonic nerve stem cells in treatment of macaque Parkinson's disease

OBJECTIVE

To investigate the therapeutic effects of co-transplantation with Schwann cells (SCs) and human embryonic nerve stem cells (NSCs) on macaque Parkinson's disease (PD).

METHODS

Macaque autologous SCs and human embryonic NSCs were adopted for the treatment of macaque PD.

RESULTS

Six months after transplantation, positron emission computerized tomography showed that (18)F-FP-β-CIT was significantly concentrated in the injured striatum in the co-transplanted group. Immunohistochemical staining of transplanted area tissue showed migration of tyroxine hydroxylase positive cells from the transplant area to the surrounding area was significantly increased in the co-transplanted group.

CONCLUSIONS

Co-transplantation of SCs and NSCs could effectively cure PD in macaques. SCs harvested from the autologous peripheral nerves can avoid rejection and the ethics problems, so it is expected to be applied clinically.

Neurotrophic factors and neurodegenerative diseases: a delivery issue

Neurotrophic factors (NTFs) represent one of the most stimulating challenge in neurodegenerative diseases, due to their potential in neurorestoring and neuroprotection. Despite the large number of proofs-of-concept and evidences of their activity, most of the clinical trials, mainly regarding Parkinson's disease and Alzheimer's disease, demonstrated several failures of the therapeutic intervention. A large number of researches were conducted on this hot topic of neuroscience, clearly evidencing the advantages of NTF approach, but evidencing the major limitations in its application. The inability in crossing the blood-brain barrier and the lack of selectivity actually represent some of the most highlighted limits of NTFs-based therapy. In this review, beside an overview of NTF activity versus the main neuropathological disorders, a summary of the most relevant approaches, from invasive to noninvasive strategies, applied for improving NTF delivery to the central nervous systems is critically considered and evaluated.

Optimized quantities of GDNF overexpressed by engineered astrocytes are critical for protection of neuroblastoma cells against 6-OHDA toxicity

Optimized levels of glial cell line-derived neurotrophic factor (GDNF) are critical for protection of dopaminergic neurons against parkinsonian cell death. Recombinant lentiviruses harboring GDNF coding sequence were constructed and used to infect astrocytoma cell line 1321N1. The infected astrocytes overexpressed GDNF mRNA and secreted an average of 2.2 ng/mL recombinant protein as tested in both 2 and 16 weeks post-infection. Serial dilutions of GDNF-enriched conditioned medium from infected astrocytes added to growing neuroblastoma cell line SK-N-MC resulted in commensurate resistance against 6-OHDA toxicity. SK-N-MC cell survival rate rose from 51% in control group to 84% in the cells grown with astro-CM containing 453 pg secreted GDNF, an increase that was highly significant (P < 0.0001). However, larger volumes of the GDNF-enriched conditioned medium failed to improve cell survival and addition of volumes that contained 1,600 pg or more GDNF further reduced survival rate to below 70%. Changes in cell survival paralleled to changes in the percent of apoptotic cell morphologies. These data demonstrate the feasibility of using astrocytes as minipumps to stably oversecrete neurotrophic factors and further indicate that GDNF can be applied to neuroprotection studies in PD pending the optimization of its concentrations.

Delivery of brain-derived neurotrophic factor via nose-to-brain pathway

PURPOSE

To investigate the plausibility of delivering brain-derived neurotrophic factor (BDNF) to brain via nose-to-brain pathway using chitosan as barrier-modulating agent.

METHODS

Effect of different viscosity grades chitosan at different concentrations on permeation of fluorescein isothio-cyanate dextran (FD 40 K) across bovine olfactory mucosa was studied using Franz diffusion cells. Medium viscosity chitosan was used to carry out permeation studies of BDNF. Pharmacokinetic and pharmacodynamic studies were carried out in Sprague dawley rats upon intranasal/i.v administration of different formulations.

RESULTS

Medium viscosity chitosan more efficiently enhanced permeation of FD 40 K across olfactory mucosa compared to other grades. In case of BDNF, medium viscosity chitosan (0.25% w/v) enhanced permeation ~14-fold over control (18.78 ± 16.69 ng/cm(2)). Brain bioavailability of rats administered intranasally with BDNF solution containing chitosan was significantly enhanced ~13-fold compared to rats administered with same concentration of BDNF solution without chitosan. In rats subjected to immobilization stress, BDNF solution containing chitosan significantly decreased immobility time.

CONCLUSIONS

Intranasal formulations containing chitosan as barrier-modulating agent significantly enhanced brain bioavailability of BDNF. Delivery of BDNF was found to counteract stress-induced depression in rats.

The TrkB-positive dopaminergic neurons are less sensitive to MPTP insult in the substantia nigra of adult C57/BL mice

Tyrosine kinase receptors TrkB and TrkC mediate neuroprotective effects of the brain-derived neurotrophic factor (BDNF) and neurotrophins in the dopaminergic nigro-striatal system, but it is obscure about their responses or expression changes in the injured substantia nigra under Parkinson's disease. In present study, immunofluorescence, Fluoro-Jade staining and laser scanning confocal microscopy were applied to investigate distribution and changes of TrkB and TrkC in the dopamine neurons of the substantia nigra by comparison of control and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model. It revealed that TrkB and TrkC-immunoreactivities were substantially localized in cytoplasm and cell membrane of the substantia nigra neurons of control adults. While neurons double-labeled with tyrosine hydroxylase (TH)/TrkB, or TH/TrkC were distributed in a large numbers in the substantia nigra of controls, they apparently went down at 36.2-65.7% of normal level, respectively following MPTP insult. In MPTP model, cell apoptosis or degeneration of nigral neurons were confirmed by caspase-3 and Fluoro-Jade staining. More interestingly, TH/TrkB-positive neurons survived more in cell numbers in comparison with that of TH/TrkC-positive ones in the MPTP model. This study has indicated that TrkB-containing dopamine neurons are less sensitive in the substantia nigra of MPTP mouse model, suggesting that specific organization of Trks may be involved in neuronal vulnerability to MPTP insult, and BDNF-TrkB signaling may play more important role in protecting dopamine neurons and exhibit therapeutic potential for Parkinson's disease.

Glial cell line-derived neurotrophic factor-secreting genetically modified human bone marrow-derived mesenchymal stem cells promote recovery in a rat model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by progressive degeneration of nigrostriatal dopaminergic (DA) neurons. The therapeutic potential of glial cell line-derived neurotrophic factor (GDNF), the most potent neurotrophic factor for DA neurons, has been demonstrated in many experimental models of PD. However, chronic delivery of GDNF to DA neurons in the brain remains an unmet challenge. Here, we report the effects of GDNF-releasing Notch-induced human bone marrow-derived mesenchymal stem cells (MSC) grafted into striatum of the 6-hydroxydopamine (6-OHDA) progressively lesioned rat model of PD. Human MSC, obtained from bone marrow aspirates of young, healthy adult volunteers, were transiently transfected with the intracellular domain of the Notch1 gene (NICD) to generate SB623 cells. SB623 cells expressing GDNF and/or humanized Renilla green fluorescent protein (hrGFP) following lentiviral transduction or nontransduced cells were stereotaxically placed into rat striatum 1 week after a unilateral partial 6-OHDA striatal lesion. At 4 weeks, rats that had received GDNF-transduced SB623 cells had significantly decreased amphetamine-induced rotation compared with control rats, although this effect was not observed in rats that received GFP-transduced or nontransduced SB623 cells. At 5 weeks, rejuvenated tyrosine hydroxylase-immunoreactive (TH-IR) fibers that appeared to be host DA axons were observed in and around grafts. This effect was more prominent in rats that received GDNF-secreting cells and was not observed in controls. These observations suggest that human bone-marrow derived MSC, genetically modified to secrete GDNF, hold potential as an allogeneic or autologous stem cell therapy for PD.

Graft and host interactions following transplantation of neural stem cells to organotypic striatal cultures

AIMS

To investigate neural stem cell (NSC) interactions with striatal tissue following engraftment and the effects of growth factors.

MATERIALS & METHODS

Organotypic striatal slice cultures established from neonatal rats were used as an ex vivo model system. Survival, integration and differentiation of grafted NSCs from the previously generated C17.2 clone and host tissue response were investigated weekly for 28 days in vitro. To direct grafted cells towards a neuronal lineage, the role of growth factor supplementation and serum-free culturing conditions was studied using neural stem cells overexpressing neurotrophin-3 and Neurobasal/B27 culture medium.

RESULTS

Following engraftment, NSCs gradually integrated morphologically and formed a part of the host 3D cytoarchitecture. Compared with nongrafted cultures, NSC engraftment increased the overall survival of the organotypic cultures by 39%, and reduced the host cell necrosis by more than 80% (from 2.1 ± 0.5% to 0.3 ± 0.1%), the host cell apoptosis by more than 60% (from 1.4 ± 0.4% to 0.5 ± 0.1%) and the reactions to mechanical trauma by 30% (estimated by nestin and glial fibrillary acidic protein immunohistochemistry) 7 days after engraftment. Elevated neurotrophin-3 production in NSCs and serum-free culturing conditions directed grafted NSCs towards a neuronal lineage as indicated by increased Tuj1 and Map2ab expression. However, this did not alter the survival of organotypic cultures.

CONCLUSIONS

NSC engraftment was associated with rescue of imperiled host cells and reduction of host cell gliosis. These NSC effects were not related to the addition of growth factors, suggesting that other factors are involved in the supportive effects of the host following NSC engraftment.

Cell transplantation in Parkinson's disease: problems and perspectives

PURPOSE OF REVIEW

We review recent experiments conducted using embryonic tissue and stem cell transplants in experimental models of Parkinson's disease. We also highlight the challenges which remain to be met in order for cell therapy to become clinically effective and safe.

RECENT FINDINGS

The outcome of previous clinical transplantation trials was variable in terms of motor recovery. We discuss whether transplants can mitigate L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesias and consider the risk factors which predispose to graft-induced dyskinesias. In addition, we introduce Transeuro, a new European Union-funded multicenter consortium which plans to perform transplantation trials.Stem cells have emerged as an alternative source for the generation of dopaminergic precursors. We briefly outline progress made in the use of human embryonic stem cells and focus predominantly on the emerging field of induced pluripotency. We conclude by introducing the exciting and novel method of direct reprogramming which involves the conversion of fibroblasts to neurons without inducing a pluripotent state.

SUMMARY

The area of cell transplantation has been revitalized by the identification of parameters which predispose patients to graft-induced dyskinesias and by the emergence of novel methods of generating dopaminergic neurons. Hopefully, the Transeuro clinical trials will give further impetus and act as a stepping stone to future trials employing stem-cell-derived neurons.

Nucleus accumbens-derived glial cell line-derived neurotrophic factor is a retrograde enhancer of dopaminergic tone in the mesocorticolimbic system

Spontaneous firing of ventral tegmental area (VTA) dopamine (DA) neurons provides ambient levels of DA in target areas such as the nucleus accumbens (NAc) and the prefrontal cortex (PFC). Here we report that the glial cell line-derived neurotrophic factor (GDNF), produced in one target region, the NAc, is retrogradely transported by DA neurons to the VTA where the growth factor positively regulates the spontaneous firing activity of both NAc- and PFC-projecting DA neurons in a mechanism that requires the activation of the mitogen-activated protein kinase (MAPK) pathway. We also show that the consequence of GDNF-mediated activation of the MAPK signaling cascade in the VTA is an increase in DA overflow in the NAc. Together, these results demonstrate that NAc-produced GDNF serves as a retrograde enhancer that upregulates the activity of the mesocorticolimbic DA system.

Neuroprotective properties of mildronate, a small molecule, in a rat model of Parkinson's disease

Previously, we have found that mildronate [3-(2,2,2-trimethylhydrazinium) propionate dihydrate], a small molecule with charged nitrogen and oxygen atoms, protects mitochondrial metabolism that is altered by inhibitors of complex I and has neuroprotective effects in an azidothymidine-neurotoxicity mouse model. In the present study, we investigated the effects of mildronate in a rat model of Parkinson's disease (PD) that was generated via a unilateral intrastriatal injection of the neurotoxin 6-hydroxydopamine (6-OHDA). We assessed the expression of cell biomarkers that are involved in signaling cascades and provide neural and glial integration: the neuronal marker TH (tyrosine hydroxylase); ubiquitin (a regulatory peptide involved in the ubiquitin-proteasome degradation system); Notch-3 (a marker of progenitor cells); IBA-1 (a marker of microglial cells); glial fibrillary acidic protein, GFAP (a marker of astrocytes); and inducible nitric oxide synthase, iNOS (a marker of inflammation). The data show that in the 6-OHDA-lesioned striatum, mildronate completely prevented the loss of TH, stimulated Notch-3 expression and decreased the expression of ubiquitin, GFAP and iNOS. These results provide evidence for the ability of mildronate to control the expression of an array of cellular proteins and, thus, impart multi-faceted homeostatic mechanisms in neurons and glial cells in a rat model of PD. We suggest that the use of mildronate provides a protective effect during the early stages of PD that can delay or halt the progression of this neurodegenerative disease.

Novel D3 dopamine receptor-preferring agonist D-264: Evidence of neuroprotective property in Parkinson's disease animal models induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and lactacystin

Parkinson's disease (PD), a progressive neurodegenerative movement disorder, is known to be caused by diverse pathological conditions resulting from dysfunction of the ubiquitin-proteasome system (UPS), mitochondria, and oxidative stress leading to preferential nigral dopamine (DA) neuron degeneration in the substantia nigra. In the present study, we evaluated the novel D3 receptor-preferring agonist D-264 in a mouse model of PD to evaluate its neuroprotective properties against both the nigrostriatal dopaminergic toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)- and the proteasome inhibitor lactacystin-induced dopaminergic degeneration. C57BL/6 male mice either were given MPTP by intraperitoneal injection twice per day for 2 successive days at a dose 20 mg/kg or were microinjected with lactacystin bilaterally (1.25 microg/side) into the medial forebrain bundle (MFB). Pretreatment with D-264 (1 mg/kg and 5 mg/kg, intraperitoneally, once per day), started 7 days before administration of MPTP or lactacystin. We found that D-264 significantly improved behavioral performance, attenuated both MPTP- and lactacystin-induced DA neuron loss, and blocked proteasomal inhibition and microglial activation in the substantia nigra (SN). Furthermore, D-264 treatment was shown to increase the levels of brain-derived neurotrophic factor (BDNF) and glial cell line-derived factor (GDNF) in MPTP- and lactacystin-treated mice, possibly indicating, at least in part, the mechanism of neuroprotection by D-264. Furthermore, pretreatment with the D3 receptor antagonist U99194 significantly altered the effect of neuroprotection conferred by D-264. Collectively, our study demonstrates that D-264 can prevent neurodegeneration induced by the selective neurotoxin MPTP and the UPS inhibitor lactacystin. The results indicate that D-264 could potentially serve as a symptomatic and neuroprotective treatment agent for PD.

Astrocytes and therapeutics for Parkinson's disease

Astrocytes play direct, active, and critical roles in mediating neuronal survival and function in various neurodegenerative disorders. This role of astrocytes is well illustrated in amyotrophic lateral sclerosis (ALS), in which the removal of glutamate from the extracellular space by astrocytes confers neuroprotection, whereas astrocytic release of soluble toxic molecules promotes neurodegeneration. In recent years, this context-dependent dual role of astrocytes has also been documented in experimental models of Parkinson's disease. The present review addresses these studies and some potential mechanisms by which astrocytes may influence the neurodegenerative processes in Parkinson's disease, and in particular examines how astrocytes confer neuroprotection either through the removal of toxic molecules from the extracellular space or through the release of trophic factors and antioxidant molecules. In contrast, under pathological conditions, astrocytes release proinflammatory cytokines and other toxic molecules that are detrimental to dopaminergic neurons. These emerging roles of astrocytes in the pathogenesis of Parkinson's disease constitute an exciting development with promising novel therapeutic targets.

Progress and prospects: stem cells and neurological diseases

The central nervous system has limited capacity of regenerating lost tissue in slowly progressive, degenerative neurological conditions such as Parkinson's disease (PD), Alzheimer's disease or Huntington's disease (HD), or in acute injuries resulting in rapid cell loss for example, in cerebrovascular damage (for example, stroke) or spinal cord injury. Although the adult brain contains small numbers of stem cells in restricted areas, they do not contribute significantly to functional recovery. Transplantation of stem cells or stem cell-derived progenitors has long been seen as a therapeutic solution to repair the damaged brain. With the advent of the induced pluripotent stem cells technique a new and potentially better source for transplantable cells may be available in future. This review aims to highlight current strategies to replace lost cellular populations in neurodegenerative diseases with the focus on HD and PD and traumatic brain injuries such as stroke, discussing many of the technical and biological issues associated with central nervous system cell transplantation.

Brain injury activates microglia that induce neural stem cell proliferation ex vivo and promote differentiation of neurosphere-derived cells into neurons and oligodendrocytes

Brain damage, such as ischemic stroke, enhances proliferation of neural stem/progenitor cells (NSPCs) in the subventricular zone (SVZ). To date, no reliable in vitro systems, which can be used to unravel the potential mechanisms underlying this lesion-induced effect, have been established. Here, we developed an ex vivo method to investigate how the proliferation of NSPCs changes over time after experimental stroke or excitotoxic striatal lesion in the adult rat brain by studying the effects of microglial cells derived from an injured brain on NSPCs. We isolated NSPCs from the SVZ of brains with lesions and analyzed their growth and differentiation when cultured as neurospheres. We found that NSPCs isolated from the brains 1-2 weeks following injury consistently generated more and larger neurospheres than those harvested from naive brains. We attributed these effects to the presence of microglial cells in NSPC cultures that originated from injured brains. We suggest that the effects are due to released factors because we observed increased proliferation of NSPCs isolated from non-injured brains when they were exposed to conditioned medium from cultures containing microglial cells derived from injured brains. Furthermore, we found that NSPCs derived from injured brains were more likely to differentiate into neurons and oligodendrocytes than astrocytes. Our ex vivo system reliably mimics what is observed in vivo following brain injury. It constitutes a powerful tool that could be used to identify factors that promote NSPC proliferation and differentiation in response to injury-induced activation of microglial cells, by using tools such as proteomics and gene array technology.

Rap1GAP interacts with RET and suppresses GDNF-induced neurite outgrowth

Glial cell line-derived neurotrophic factor (GDNF) was originally recognized for its ability to promote survival of midbrain dopaminergic neurons, but it has since been demonstrated to be crucial for the survival and differentiation of many neuronal subpopulations, including motor neurons, sympathetic neurons, sensory neurons and enteric neurons. To identify possible effectors or regulators of GDNF signaling, we performed a yeast two-hybrid screen using the intracellular domain of RET, the common signaling receptor of the GDNF family, as bait. Using this approach, we identified Rap1GAP, a GTPase-activating protein (GAP) for Rap1, as a novel RET-binding protein. Endogenous Rap1GAP co-immunoprecipitated with RET in neural tissues, and RET and Rap1GAP were co-expressed in dopaminergic neurons of the mesencephalon. In addition, overexpression of Rap1GAP attenuated GDNF-induced neurite outgrowth, whereas suppressing the expression of endogenous Rap1GAP by RNAi enhanced neurite outgrowth. Furthermore, using co-immunoprecipitation analyses, we found that the interaction between RET and Rap1GAP was enhanced following GDNF treatment. Mutagenesis analysis revealed that Tyr981 in the intracellular domain of RET was crucial for the interaction with Rap1GAP. Moreover, we found that Rap1GAP negatively regulated GNDF-induced ERK activation and neurite outgrowth. Taken together, our results suggest the involvement of a novel interaction of RET with Rap1GAP in the regulation of GDNF-mediated neurite outgrowth.

Ectopic Dopaminergic Progenitor Cells from En1+/Otx2lacZ Transgenic Mice Survive and Functionally Reinnervate the Striatum Following Transplantation in a Rat Model of Parkinson's Disease

Cell-based therapies for Parkinson's disease (PD) using neural stem cells to replace the lost dopamine neurons is currently an intense area of research. In this study we have evaluated the restorative potential of ectopic dopaminergic (DA) neurons derived from the rostral hindbrain (RH) of En1 +/Otx2lacZ transgenic mice. The genetic modification of the DA progenitor domain in the En1 +/Otx2lacZ mice is a gain of function, resulting in the enlargement of the area containing DA neurons, as well as an increase in their absolute number in the midbrain/hindbrain region. Amphetamine-induced rotation performed after cell transplantation into the unilaterally 6-hydroxydopamine-lesioned rat striatum revealed that animals with transgenic RH-derived DA grafts exhibited functional recovery similar to transgenic and wild-type ventral mesencephalon (VM)-derived DA grafts. Morphological analyses revealed equivalent numbers of surviving DA neurons from both homotopic VM- and ectopic RH-derived grafts from transgenic donors with low numbers of surviving serotonergic (5-HT) neurons. Conversely, grafts derived from wild-type donors contained predominantly surviving DA neurons or 5-HT neurons when they were prepared from the VM or RH, respectively. The study demonstrates the pattern of survival and functional potential of ectopic DA neurons derived from the RH of En1 +/Otx2lacZ transgenic mice and that cell transplantation is an important neurobiological tool to characterize newly generated DA neural stem cells in vivo.

What can pluripotent stem cells teach us about neurodegenerative diseases?

Neurodegenerative diseases represent a growing public health challenge. Current medications treat symptoms, but none halt or retard neurodegeneration. The recent advent of pluripotent cell biology has opened new avenues for neurodegenerative disease research. The greatest potential for induced pluripotent cells derived from affected individuals is likely to be their utility for modeling and understanding the mechanisms underlying neurodegenerative processes, and for searching for new treatments, including cell replacement therapies. However, much work remains to be done before pluripotent cells can be used for preclinical and clinical applications. Here we discuss the challenges of generating specific neural cell subtypes from pluripotent stem cells, the use of pluripotent stem cells to model both cell-autonomous and non-cell-autonomous mechanisms of neurodegeneration, whether adult-onset neurodegeneration can be emulated in short-term cultures and the hurdles of cell replacement therapy. Progress in these four areas will substantially accelerate effective application of pluripotent stem cells.

Foxa2 and Nurr1 synergistically yield A9 nigral dopamine neurons exhibiting improved differentiation, function, and cell survival

Effective dopamine (DA) neuron differentiation from neural precursor cells (NPCs) is prerequisite for precursor/stem cell-based therapy of Parkinson's disease (PD). Nurr1, an orphan nuclear receptor, has been reported as a transcription factor that can drive DA neuron differentiation from non-dopaminergic NPCs in vitro. However, Nurr1 alone neither induces full neuronal maturation nor expression of proteins found specifically in midbrain DA neurons. In addition, Nurr1 expression is inefficient in inducing DA phenotype expression in NPCs derived from certain species such as mouse and human. We show here that Foxa2, a forkhead transcription factor whose role in midbrain DA neuron development was recently revealed, synergistically cooperates with Nurr1 to induce DA phenotype acquisition, midbrain-specific gene expression, and neuronal maturation. Thus, the combinatorial expression of Nurr1 and Foxa2 in NPCs efficiently yielded fully differentiated nigral (A9)-type midbrain neurons with clearly detectable DA neuronal activities. The effects of Foxa2 in DA neuron generation were observed regardless of the brain regions or species from which NPCs were derived. Furthermore, DA neurons generated by ectopic Foxa2 expression were more resistant to toxins. Importantly, Foxa2 expression resulted in a rapid cell cycle exit and reduced cell proliferation. Consistently, transplantation of NPCs transduced with Nurr1 and Foxa2 generated grafts enriched with midbrain-type DA neurons but reduced number of proliferating cells, and significantly reversed motor deficits in a rat PD model. Our findings can be applied to ongoing attempts to develop an efficient and safe precursor/stem cell-based therapy for PD.

Catalpol attenuates MPTP induced neuronal degeneration of nigral-striatal dopaminergic pathway in mice through elevating glial cell derived neurotrophic factor in striatum

The protective effect of an iridoid catalpol extracted and purified from the traditional Chinese medicinal herb Rehmannia glutinosa on the neuronal degeneration of nigral-striatal dopaminergic pathway was studied in a chronic 1-methyl-4-phenyl-1,2,3,4-tetrahydropyridine (MPTP)/probenecid C57BL/6 mouse model and in 1-methyl-4-phenylpyridimium (MPP(+)) intoxicated cultured mesencephalic neurons. Rotarod performance revealed that the locomotor ability of mice was significantly impaired after completion of model production and maintained thereafter for at least 4 weeks. Catalpol orally administered for 8 weeks (starting from the second week of model production) dose dependently improved the locomotor ability. HPLC revealed that catalpol significantly elevated striatal dopamine levels without changing the metabolite/dopamine ratios. Nor did it bind to dopamine receptors. Therefore it is unlikely that catalpol resembles any of the known compounds for treating Parkinsonism. Instead, catalpol dose dependently raised the tyrosine hydroxylase (TH) neuron number in substantia nigra pars compacta (SNpc), the striatal dopamine transporter (DAT) density and the striatal glial cell derived neurotrophic factor (GDNF) protein level. Linear regression revealed that both the TH neuron number and DAT density were positively correlated to the GDNF level. In the cultured mesencephalic neurons, MPP(+) decreased the dopaminergic neuron number and shortened the neurite length, whereas catalpol showed protective effect dose dependently. Furthermore, the expression of GDNF mRNA was up-regulated by catalpol to a peak nearly double of normal control in neurons intoxicated with MPP(+) for 24 h but not in normal neurons. The GDNF receptor tyrosine kinase RET inhibitor 4-amino-5-(4-methyphenyl)-7-(t-butyl)-pyrazolo-[3,4-d]pyrimidine (PP1) abolished the protective effect of catalpol either partially (TH positive neuron number) or completely (neurite length). Taken together, catalpol improves locomotor ability by attenuating the neuronal degeneration of nigral-striatal dopaminergic pathway, and this attenuation is at least partially through elevating the striatal GDNF expression.

Lentiviral vector-mediated gene transfer and RNA silencing technology in neuronal dysfunctions

Lentiviral-mediated gene transfer in vivo or in cultured mammalian neurons can be used to address a wide variety of biological questions, to design animal models for specific neurodegenerative pathologies, or to test potential therapeutic approaches in a variety of brain disorders. Lentiviruses can infect nondividing cells, thereby allowing stable gene transfer in postmitotic cells such as mature neurons. An important contribution has been the use of inducible vectors: the same animal can thus be used repeatedly in the doxycycline-on or -off state, providing a powerful mean for assessing the function of a gene candidate in a disorder within a specific neuronal circuit. Furthermore, lentivirus vectors provide a unique tool to integrate siRNA expression constructs with the aim to locally knockdown expression of a specific gene, enabling to assess the function of a gene in a very specific neuronal pathway. Lentiviral vector-mediated delivery of short hairpin RNA results in persistent knockdown of gene expression in the brain. Therefore, the use of lentiviruses for stable expression of siRNA in brain is a powerful aid to probe gene functions in vivo and for gene therapy of diseases of the central nervous system. In this chapter, I review the applications of lentivirus-mediated gene transfer in the investigation of specific gene candidates involved in major brain disorders and neurodegenerative processes. Major applications have been in polyglutamine disorders, such as synucleinopathies and Parkinson's disease, or in investigating gene function in Huntington's disease, dystonia, or muscular dystrophy. Recently, lentivirus gene transfer has been an invaluable tool for evaluation of gene function in behavioral disorders such as drug addiction and attention-deficit hyperactivity disorder or in learning and cognition.

Monocytes deliver bioactive nerve growth factor through a brain capillary endothelial cell-monolayer in vitro and counteract degeneration of cholinergic neurons

Alzheimer's disease is an age-dependent brain disorder, characterized by progressive memory deficits and cognitive decline and loss of cholinergic neurons. Nerve growth factor (NGF) is the most potent protein to protect cholinergic neurons against degeneration. However, problems of delivery to the brain limit the therapeutical use of NGF. The aim of the present study was to test, if primary rat monocytes can be loaded with recombinant NGF and pass an in vitro monolayer of brain capillary endothelial cells (BCEC), release NGF, and support the cholinergic neurons in an organotypic brain slice model. Monocytes were isolated from rat blood by negative magnetic selection, loaded with recombinant NGF using Bioporter. The monocytes adhered and migrated through an in vitro rat BCEC-monolayer. NGF released at the basolateral side counteracted degeneration of cholinergic basal nucleus of Meynert neurons. In conclusion, our present study shows a proof-of-principle, that primary monocytes secreting NGF might be useful tools to deliver NGF into the brain, however, further in vivo studies are necessary.

Intrastriatal transplantation of GDNF-engineered BMSCs and its neuroprotection in lactacystin-induced Parkinsonian rat model

The potential value of glial cell line-derived neurotrophic factor (GDNF) in treating Parkinson's disease (PD) remains controversial. In order to evaluate the therapeutic effect of GDNF-engineered bone marrow stromal cells (BMSCs) in parkinsonian rat model, GDNF-BMSCs and LacZ-BMSCs were transplanted into striatum and followed by Lactacystin lesioning at median forebrain bundles 1 week later. We observed that the intrastriatal transplantation of GDNF-BMSCs could significantly rescue the dopaminergic neurons from lactacystin-induced neurotoxicity with regard to behavioral recovery, tyrosine hydroxylase level in nigra and striatum, and striatal dopamine level. We interpret the outcomes that intrastriatal transplantation of GDNF-BMSCs might be beneficial in the treatment of PD.

Insect GDNF:TTC fusion protein improves delivery of GDNF to mouse CNS

With a view toward improving delivery of exogenous glial cell line-derived neurotrophic factor (GDNF) to CNS motor neurons in vivo, we evaluated the bioavailability and pharmacological activity of a recombinant GDNF:tetanus toxin C-fragment fusion protein in mouse CNS. Following intramuscular injection, GDNF:TTC but not recombinant GDNF (rGDNF) produced strong GDNF immunostaining within ventral horn cells of the spinal cord. Intrathecal infusion of GDNF:TTC resulted in tissue concentrations of GDNF in lumbar spinal cord that were at least 150-fold higher than those in mice treated with rGDNF. While levels of immunoreactive choline acetyltransferase and GFRalpha-1 in lumbar cord were not altered significantly by intrathecal infusion of rGNDF, GDNF:TTC, or TTC, only rGDNF and GDNF:TTC caused significant weight loss following intracerebroventricular infusion. These studies indicate that insect cell-derived GDNF:TTC retains its bi-functional activity in mammalian CNS in vivo and improves delivery of GDNF to spinal cord following intramuscular- or intrathecal administration.

Future directions: use of interventional MRI for cell-based therapy of Parkinson disease

Transplantation of neural cells for the treatment of neurologic disorders has garnered much attention and considerable enthusiasm from patients and physicians alike. Cell-based therapies have been proposed for a wide range of central nervous system pathologies ranging from stroke and trauma to demyelinating disorders and neurodegenerative diseases. Notably, cell transplantation for Parkinson disease (PD) has become even more attractive with the rapid advances in derivation of dopaminergic neurons from human embryonic stem cells. This article briefly reviews some of the relevant issues regarding the transplantation of cells for treatment of PD and hypothesizes how interventional MRI may be useful to optimize the surgical delivery of cells for PD and other central nervous system disorders.

Brain-derived neurotrophic factor in neurodegenerative diseases

Changes in the levels and activities of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), have been described in a number of neurodegenerative disorders, including Huntington disease, Alzheimer disease and Parkinson disease. It is only in Huntington disease, however, that gain-of-function and loss-of-function experiments have linked BDNF mechanistically with the underlying genetic defect. Altogether, these studies have led to the development of experimental strategies aimed at increasing BDNF levels in the brains of animals that have been genetically altered to mimic the aforementioned human diseases, with a view to ultimately influencing the clinical treatment of these conditions. In this article, we will review the current knowledge about the involvement of BDNF in a number of neurodegenerative diseases, with particular emphasis on Huntington disease, and will provide the rationale for and discuss the problems in proposing BDNF treatment as a beneficial and feasible therapeutic approach in the clinic.

Survival and early functional integration of dopaminergic progenitor cells following transplantation in a rat model of Parkinson's disease

Dopaminergic (DA) grafts in rat models of Parkinson's disease (PD) have previously been derived from embryonic day (E) 14 grafts. Because there is an increasing interest in the restorative capacity of DA stem and progenitor cells, in the present study we examined the survival and early and late functional behavioral effects of DA progenitor cells derived from E12, E13, E14, and E15 grafts transplanted into rats with unilateral 6-hydroxydopamin lesions. DA transplant-induced functional recovery was already observed in postural balancing reactions after 10 days and in stepping behavior after 13 days, that is, in spontaneous complex behaviors, and later, after 16 days, in the amphetamine-induced rotation test. Three distinct patterns of functional recovery could be observed at 6-9 weeks posttransplantation. First, behavioral improvements in drug-induced rotational asymmetry, stepping, and skilled forelimb behavior were directly related to DA neuron survival and TH-positive fiber reinnervation. Second, recovery in postural balancing reactions was closely related to a specific developmental time window of donor age, for example, only seen in E13 and E14 grafts. Finally, no functional graft effects were seen in the table lift test. Interestingly, DA neuron graft survival, TH-positive fiber outgrowth, and graft volume were significantly influenced by the developmental time window in which the DA progenitor cells were dissected from the ventral mesencephalon, that is, from E12, E13, E14, or E15 rat embryos. These data highlight the complexity of graft-host interactions and provide novel insights into the dynamics of DA progenitor graft-mediated functional recovery in animal models of Parkinson's disease.

TRPC channel-mediated neuroprotection by PDGF involves Pyk2/ERK/CREB pathway

Platelet-derived growth factor-BB (PDGF) has been reported to provide tropic support for neurons in the central nervous system. The protective role of PDGF on dopaminergic neurons, especially in the context of HIV-associated dementia (HAD), however, remains largely unknown. Here, we show that exogenous PDGF was neuroprotective against toxicity induced by HIV-1 Tat in primary midbrain neurons. Furthermore, we report the involvement of transient receptor potential canonical (TRPC) channels in PDGF-mediated neuroprotection. TRPC channels are Ca(2+)-permeable, nonselective cation channels with a variety of physiological functions. Blocking TRPC channels with either a blocker or short-interfering RNAs (specific for TRPC 5 and 6) in primary neurons resulted in suppression of both PDGF-mediated neuroprotection as well as elevations in intracellular Ca(2+). PDGF-mediated neuroprotection involved parallel but distinct ERK/CREB and PI3K/Akt pathways. TRPC channel blocking also resulted in suppression of PDGF-induced Pyk2/ERK/CREB activation, but not Akt activation. Relevance of these findings in vivo was further corroborated by intrastriatal injections of PDGF and HIV-1 Tat in mice. Administration of PDGF was able to rescue the dopaminergic neurons in the substantia nigra from Tat-induced neurotoxicity. This effect was attenuated by pre-treatment of mice with the TRP blocker, thus underscoring the novel role of TRPC channels in the neuroprotection mediated by PDGF.

PDGF-mediated protection of SH-SY5Y cells against Tat toxin involves regulation of extracellular glutamate and intracellular calcium

The human immunodeficiency virus (HIV-1) protein Tat has been implicated in mediating neuronal apoptosis, one of the hallmark features of HIV-associated dementia (HAD). Mitigation of the toxic effects of Tat could thus be a potential mechanism for reducing HIV toxicity in the brain. In this study we demonstrated that Tat-induced neurotoxicity was abolished by NMDA antagonist-MK801, suggesting the role of glutamate in this process. Furthermore, we also found that pretreatment of SH-SY5Y cells with PDGF exerted protection against Tat toxicity by decreasing extracellular glutamate levels. We also demonstrated that extracellular calcium chelator EGTA was able to abolish PDGF-mediated neuroprotection, thereby underscoring the role of calcium signaling in PDGF-mediated neuroprotection. We also showed that Erk signaling pathway was critical for PDGF-mediated protection of cells. Additionally, blocking calcium entry with EGTA resulted in suppression of PDGF-induced Erk activation. These findings thus underscore the role of PDGF-mediated calcium signaling and Erk phosphorylation in the protection of cells against HIV Tat toxicity.

Absence of striatal newborn neurons with mature phenotype following defined striatal and cortical excitotoxic brain injuries

Experimental stroke and excitotoxic brain lesion to the striatum increase the proliferation of cells residing within the ventricular wall and cause subsequent migration of newborn neuroblasts into the lesioned brain parenchyma. In this study, we clarify the different events of neurogenesis following striatal or cortical excitotoxic brain lesions in adult rats. Newborn cells were labeled by intraperitoneal injection of bromo-deoxy-uridine (BrdU), or by green fluorescent protein (GFP)-expressing lentiviral vectors injected into the subventricular zone (SVZ). We show that only neural progenitors born the first 5 days in the SVZ reside and expand within this neurogenic niche over time, and that these early labeled cells are more prone to migrate towards the striatum as neuroblasts. However, these neuroblasts could not mature into NeuN+ neurons in the striatum. Furthermore, we found that cortical lesions, close or distant from the SVZ, could not upregulate SVZ cell proliferation nor promote neurogenesis. Our study demonstrates that both the time window for labeling proliferating cells and the site of lesion are crucial when assessing neurogenesis following brain injury.

A new perspective on the treatment of aromatic L-amino acid decarboxylase deficiency

The final step in production of the neurotransmitters dopamine and serotonin is catalyzed by aromatic l-amino acid decarboxylase (AADC). AADC deficiency is a debilitating genetic condition that results in a deficit in these neurotransmitters, and manifests in infancy as a severe movement disorder with developmental delay. Response to current treatments is often disappointing. We have reviewed the literature to look for improvements to the current treatment strategy and also for new directions for AADC deficiency treatment. There may be differences in the mode of action, side-effect risk and effectiveness between different dopamine agonists and monoamine oxidase inhibitors currently used for AADC deficiency treatment. The range of these drugs used requires re-evaluation as some may have greater efficacy than others. Pyridoxal 5'-phosphate, the AADC cofactor may stabilize AADC and could increase AADC activity. Pyridoxal 5'-phosphate could have advantages as a treatment instead of pyridoxine. Atypical neuroleptics and peripheral AADC inhibitors both increase AADC activity in vivo and could be a future direction for AADC deficiency treatment and related conditions. Parkinson's disease gene therapy to deliver and express the human AADC gene in striatum is being tested in humans. Consequently gene therapy for AADC deficiency could be a realistic aim however an animal model of AADC deficiency is important for further progression.

Pluripotent stem cells as new drugs? The example of Parkinson's disease

Cell replacement therapy is a widely discussed novel concept of medical treatment. The increased knowledge in the stem cell field, particularly pluripotent stem cells, potentially provides powerful tools for this therapeutic concept. A large number of disease characterized by the loss of functional cells are potential candidates for cell replacement therapy and, in this regards, Parkinson's disease is of particular interest. It is one of the most prevalent neurodegenerative diseases caused by the loss of dopaminergic neurons in the Substantia nigra pars compacta. Pharmacological therapies are valuable but suffer from the progressive decline of efficacy as the disease progresses. Cell therapy application has emerged about two decades ago as a valid therapeutic alternative and recent advances in stem cell research suggest that pluripotent stem cell transplantation may be a promising approach to replace degenerated neurons in Parkinson's disease. Various sources of pluripotent stem cells (PSC) currently tested in animal models of Parkinson's disease have proven their efficacy in relieving symptoms and restoring damaged brain function. This review summarizes and discusses the important challenges that actually must be solved before the first studies of PSC transplantation can be undertaken into humans.