Understanding the Influence of Target Acquisition on Survival, Integration, and Phenotypic Maturation of Dopamine Neurons within Stem Cell-Derived Neural Grafts in a Parkinson's Disease Model.

Midbrain dopaminergic (DA) neurons include many subtypes characterized by their location, connectivity and function. Surprisingly, mechanisms underpinning the specification of A9 neurons [responsible for motor function, including within ventral midbrain (VM) grafts for treating Parkinson's disease (PD)] over adjacent A10, remains largely speculated. We assessed the impact of synaptic targeting on survival, integration, and phenotype acquisition of dopaminergic neurons within VM grafts generated from fetal tissue or human pluripotent stem cells (PSCs). VM progenitors were grafted into female mice with 6OHDA-lesions of host midbrain dopamine neurons, with some animals also receiving intrastriatal quinolinic acid (QA) injections to ablate medium spiny neurons (MSN), the A9 neuron primary target. While loss of MSNs variably affected graft survival, it significantly reduced striatal yet increased cortical innervation. Consequently, grafts showed reduced A9 and increased A10 specification, with more DA neurons failing to mature into either subtype. These findings highlight the importance of target acquisition on DA subtype specification during development and repair.SIGNIFICANCE STATEMENT Parish and colleagues highlight, in a rodent model of Parkinson's disease (PD), the importance of synaptic target acquisition in the survival, integration and phenotypic specification of grafted dopamine neurons derived from fetal tissue and human stem cells. Ablation of host striatal neurons resulted in reduced dopamine neuron survival within grafts, re-routing of dopamine fibers from striatal to alternate cortical targets and a consequential reduced specification of A9 dopamine neurons (the subpopulation critical for restoration of motor function) and increase in A10 DA neurons.

Hemispheric cortical atrophy and chronic microglial activation following mild focal ischemic stroke in adult male rats.

Animal modeling has played an important role in our understanding of the pathobiology of stroke. The vast majority of this research has focused on the acute phase following severe forms of stroke that result in clear behavioral deficits. Human stroke, however, can vary widely in severity and clinical outcome. There is a rapidly building body of work suggesting that milder ischemic insults can precipitate functional impairment, including cognitive decline, that continues through the chronic phase after injury. Here we show that a small infarction localized to the frontal motor cortex of rats following injection of endothelin-1 results in an essentially asymptomatic state based on motor and cognitive testing, and yet produces significant histopathological change including remote atrophy and inflammation that persists up to 1 year. While there is understandably a major focus in stroke research on mitigating the acute consequences of primary infarction, these results point to progressive atrophy and chronic inflammation as additional targets for intervention in the chronic phase after injury. The present rodent model provides an important platform for further work in this area.

Focal Ischemic Injury to the Early Neonatal Rat Brain Models Cognitive and Motor Deficits with Associated Histopathological Outcomes Relevant to Human Neonatal Brain Injury.

Neonatal arterial ischemic stroke is one of the more severe birth complications. The injury can result in extensive neurological damage and is robustly associated with later diagnoses of cerebral palsy (CP). An important part of efforts to develop new therapies include the on-going refinement and understanding of animal models that capture relevant clinical features of neonatal brain injury leading to CP. The potent vasoconstrictor peptide, Endothelin-1 (ET-1), has previously been utilised in animal models to reduce local blood flow to levels that mimic ischemic stroke. Our previous work in this area has shown that it is an effective and technically simple approach for modelling ischemic injury at very early neonatal ages, resulting in stable deficits in motor function. Here, we aimed to extend this model to also examine the impact on cognitive function. We show that focal delivery of ET-1 to the cortex of Sprague Dawley rats on postnatal day 0 (P0) resulted in impaired learning in a touchscreen-based test of visual discrimination and correlated with important clinical features of CP including damage to large white matter structures.

Axonal Growth of Midbrain Dopamine Neurons is Modulated by the Cell Adhesion Molecule ALCAM Through Trans-Heterophilic Interactions with L1cam, Chl1, and Semaphorins.

The growth of axons corresponding to different neuronal subtypes is governed by unique expression profiles of molecules on the growth cone. These molecules respond to extracellular cues either locally though cell adhesion interactions or over long distances through diffusible gradients. Here, we report that that the cell adhesion molecule ALCAM (CD166) can act as an extracellular substrate to selectively promote the growth of murine midbrain dopamine (mDA) neuron axons through a trans-heterophilic interaction with mDA-bound adhesion molecules. In mixed-sex primary midbrain cultures, the growth-promoting effect of ALCAM was abolished by neutralizing antibodies for components of the Semaphorin receptor complex Nrp1, Chl1, or L1cam. The ALCAM substrate was also found to modulate the response of mDA neurites to soluble semaphorins in a context-specific manner by abolishing the growth-promoting effect of Sema3A but inducing a branching response in the presence of Sema3C. These findings identify a previously unrecognized guidance mechanism whereby cell adhesion molecules act in trans to modulate the response of axonal growth cones to soluble gradients to selectively orchestrate the growth and guidance of mDA neurons.SIGNIFICANCE STATEMENT The mechanisms governing the axonal connectivity of midbrain dopamine (mDA) neurons during neural development have remained rather poorly understood relative to other model systems for axonal growth and guidance. Here, we report a series of novel interactions between proteins previously not identified in the context of mDA neuronal growth. Significantly, the results suggest a previously unrecognized mechanism involving the convergence in signaling between local, adhesion and long-distance, soluble cues. A better understanding of the molecules and mechanisms involved in establishment of the mDA system is important as a part of ongoing efforts to understand the consequence of conditions that may result from aberrant connectivity and also for cell replacement strategies for Parkinson's disease.

Isolation of LMX1a Ventral Midbrain Progenitors Improves the Safety and Predictability of Human Pluripotent Stem Cell-Derived Neural Transplants in Parkinsonian Disease.

Human pluripotent stem cells (hPSCs) are a promising resource for the replacement of degenerated ventral midbrain dopaminergic (vmDA) neurons in Parkinson's disease. Despite recent advances in protocols for the in vitro generation of vmDA neurons, the asynchronous and heterogeneous nature of the differentiations results in transplants of surprisingly low vmDA neuron purity. As the field advances toward the clinic, it will be optimal, if not essential, to remove poorly specified and potentially proliferative cells from donor preparations to ensure safety and predictable efficacy. Here, we use two novel hPSC knock-in reporter lines expressing GFP under the LMX1A and PITX3 promoters, to selectively isolate vm progenitors and DA precursors, respectively. For each cell line, unsorted, GFP+, and GFP- cells were transplanted into male or female Parkinsonian rodents. Only rats receiving unsorted cells, LMX1A-eGFP+, or PITX3-eGFP- cell grafts showed improved motor function over 6 months. Postmortem analysis revealed small grafts from PITX3-eGFP+ cells, suggesting that these DA precursors were not compatible with cell survival and integration. In contrast, LMX1A-eGFP+ grafts were highly enriched for vmDA neurons, and importantly excluded expansive proliferative populations and serotonergic neurons. These LMX1A-eGFP+ progenitor grafts accelerated behavioral recovery and innervated developmentally appropriate forebrain targets, whereas LMX1A-eGFP- cell grafts failed to restore motor deficits, supported by increased fiber growth into nondopaminergic target nuclei. This is the first study to use an hPSC-derived reporter line to purify vm progenitors, resulting in improved safety, predictability of the graft composition, and enhanced motor function.SIGNIFICANCE STATEMENT Clinical trials have shown functional integration of transplanted fetal-derived dopamine progenitors in Parkinson's disease. Human pluripotent stem cell (hPSC)-derived midbrain progenitors are now being tested as an alternative cell source; however, despite current differentiation protocols generating >80% correctly specified cells for implantation, resultant grafts contain a small fraction of dopamine neurons. Cell-sorting approaches, to select for correctly patterned cells before implantation, are being explored yet have been suboptimal to date. This study provides the first evidence of using 2 hPSC reporter lines (LMX1A-GFP and PITX3-GFP) to isolate correctly specified cells for transplantation. We show LMX1A-GFP+, but not PITX3-GFP+, cell grafts are more predictable, with smaller grafts, enriched in dopamine neurons, showing appropriate integration and accelerated functional recovery in Parkinsonian rats.

Unprecedented Potential for Neural Drug Discovery Based on Self-Organizing hiPSC Platforms.

Human induced pluripotent stem cells (hiPSCs) have transformed conventional drug discovery pathways in recent years. In particular, recent advances in hiPSC biology, including organoid technologies, have highlighted a new potential for neural drug discovery with clear advantages over the use of primary tissues. This is important considering the financial and social burden of neurological health care worldwide, directly impacting the life expectancy of many populations. Patient-derived iPSCs-neurons are invaluable tools for novel drug-screening and precision medicine approaches directly aimed at reducing the burden imposed by the increasing prevalence of neurological disorders in an aging population. 3-Dimensional self-assembled or so-called 'organoid' hiPSCs cultures offer key advantages over traditional 2D ones and may well be gamechangers in the drug-discovery quest for neurological disorders in the coming years.

Modelling the dopamine and noradrenergic cell loss that occurs in Parkinson's disease and the impact on hippocampal neurogenesis.

Key pathological features of Parkinson's Disease (PD) include the progressive degeneration of midbrain dopaminergic (DA) neurons and hindbrain noradrenergic (NA) neurons. The loss of DA neurons has been extensively studied and is the main cause of motor dysfunction. Importantly, however, there are a range of 'non-movement' related features of PD including cognitive dysfunction, sleep disturbances and mood disorders. The origins for these non-motor symptoms are less clear, but a possible substrate for cognitive decline may be reduced adult-hippocampal neurogenesis, which is reported to be impaired in PD. The mechanisms underlying reduced neurogenesis in PD are not well established. Here we tested the hypothesis that NA and DA depletion, as occurs in PD, impairs hippocampal neurogenesis. We used 6-hydroxydopamine or the immunotoxin dopamine-ß-hydroxylase-saporin to selectively lesion DA or NA neurons, respectively, in adult Sprague Dawley rats and assessed hippocampal neurogenesis through phenotyping of cells birth-dated using 5-bromo-2'-deoxyuridine. The results showed no difference in proliferation or differentiation of newborn cells in the subgranular zone of the dentate gyrus after NA or DA lesions. This suggests that impairment of hippocampal neurogenesis in PD likely results from mechanisms independent of, or in addition to degeneration of DA and NA neurons.

Transcriptome analysis reveals transmembrane targets on transplantable midbrain dopamine progenitors.

An important challenge for the continued development of cell therapy for Parkinson's disease (PD) is the establishment of procedures that better standardize cell preparations for use in transplantation. Although cell sorting has been an anticipated strategy, its application has been limited by lack of knowledge regarding transmembrane proteins that can be used to target and isolate progenitors for midbrain dopamine (mDA) neurons. We used a "FACS-array" approach to identify 18 genes for transmembrane proteins with high expression in mDA progenitors and describe the utility of four of these targets (Alcam, Chl1, Gfra1, and Igsf8) for isolating mDA progenitors from rat primary ventral mesencephalon through flow cytometry. Alcam and Chl1 facilitated a significant enrichment of mDA neurons following transplantation, while targeting of Gfra1 allowed for robust separation of dopamine and serotonin neurons. Importantly, we also show that mDA progenitors isolated on the basis of transmembrane proteins are capable of extensive, functional innervation of the host striatum and correction of motor impairment in a unilateral model of PD. These results are highly relevant for current efforts to establish safe and effective stem cell-based procedures for PD, where clinical translation will almost certainly require safety and standardization measures in order to deliver well-characterized cell preparations.

Chondroitinase improves midbrain pathway reconstruction by transplanted dopamine progenitors in Parkinsonian mice.

Within the adult central nervous system the lack of guidance cues together with the presence of inhibitory molecules produces an environment that is restrictive to axonal growth following injury. Consequently, while clinical trials in Parkinson's disease (PD) patients have demonstrated the capacity of fetal-derived dopamine neurons to survive, integrate and alleviate symptoms, the non-permissive host environment has contributed to the incomplete re-innervation of the target tissue by ectopic grafts, and even more noticeable, the poor reconstruction of the midbrain dopamine pathways following homotopic midbrain grafting. One such inhibitory molecule is the chondroitin sulfate proteoglycan (CSPG), a protein that has been shown to impede axonal growth during development and after injury. Digestion of CSPGs, by delivery of the bacterial enzyme chondroitinase ABC (ChABC), can improve axonal regrowth following a number of neural injuries. Here we examined whether ChABC could similarly improve axonal growth of transplanted dopamine neurons in an animal model of PD. Acute delivery of ChABC, into the medial forebrain bundle, degraded CSPGs along the nigrostriatal pathway. Simultaneous homotopic transplantation of dopaminergic progenitors, into the ventral midbrain of ChABC treated PD mice, had no effect on graft survival but resulted in enhanced axonal growth along the nigrostriatal pathway and reinnervation of the striatum, compared to control grafted mice. This study demonstrates that removal of axonal growth inhibitory molecules could significantly enhance dopaminergic graft integration, thereby holding implications for future approaches in the development of cell replacement therapies for Parkinsonian patients.

Reconstruction of brain circuitry by neural transplants generated from pluripotent stem cells.

Pluripotent stem cells (embryonic stem cells, ESCs, and induced pluripotent stem cells, iPSCs) have the capacity to generate neural progenitors that are intrinsically patterned to undergo differentiation into specific neuronal subtypes and express in vivo properties that match the ones formed during normal embryonic development. Remarkable progress has been made in this field during recent years thanks to the development of more refined protocols for the generation of transplantable neuronal progenitors from pluripotent stem cells, and the access to new tools for tracing of neuronal connectivity and assessment of integration and function of grafted neurons. Recent studies in brains of neonatal mice or rats, as well as in rodent models of brain or spinal cord damage, have shown that ESC- or iPSC-derived neural progenitors can be made to survive and differentiate after transplantation, and that they possess a remarkable capacity to extend axons over long distances and become functionally integrated into host neural circuitry. Here, we summarize these recent developments in the perspective of earlier studies using intracerebral and intraspinal transplants of primary neurons derived from fetal brain, with special focus on the ability of human ESC- and iPSC-derived progenitors to reconstruct damaged neural circuitry in cortex, hippocampus, the nigrostriatal system and the spinal cord, and we discuss the intrinsic and extrinsic factors that determine the growth properties of the grafted neurons and their capacity to establish target-specific long-distance axonal connections in the damaged host brain.

State of the Art in Sub-Phenotyping Midbrain Dopamine Neurons.

Dopaminergic neurons in the ventral tegmental area (VTA) and the substantia nigra pars compacta (SNpc) comprise around 75% of all dopaminergic neurons in the human brain. While both groups of dopaminergic neurons are in close proximity in the midbrain and partially overlap, development, function, and impairments in these two classes of neurons are highly diverse. The molecular and cellular mechanisms underlying these differences are not yet fully understood, but research over the past decade has highlighted the need to differentiate between these two classes of dopaminergic neurons during their development and in the mature brain. This differentiation is crucial not only for understanding fundamental circuitry formation in the brain but also for developing therapies targeted to specific dopaminergic neuron classes without affecting others. In this review, we summarize the state of the art in our understanding of the differences between the dopaminergic neurons of the VTA and the SNpc, such as anatomy, structure, morphology, output and input, electrophysiology, development, and disorders, and discuss the current technologies and methods available for studying these two classes of dopaminergic neurons, highlighting their advantages, limitations, and the necessary improvements required to achieve more-precise therapeutic interventions.

Cell intrinsic and extrinsic factors contribute to enhance neural circuit reconstruction following transplantation in Parkinsonian mice.

Cell replacement therapy for Parkinson's disease has predominantly focused on ectopic transplantation of fetal dopamine (DA) neurons into the striatum as a means to restore neurotransmission, rather than homotopic grafts into the site of cell loss, which would require extensive axonal growth. However, ectopic grafts fail to restore important aspects of DA circuitry necessary for controlled basal ganglia output, and this may underlie the suboptimal and variable functional outcomes in patients. We recently showed that DA neurons in homotopic allografts of embryonic ventral mesencephalon (VM) can send long axonal projections along the nigrostriatal pathway in order to innervate forebrain targets, although the extent of striatal reinnervation remains substantially less than can be achieved with ectopic placement directly into the striatal target. Here, we examined the possible benefits of using younger VM donor tissue and over-expression of glial cell-derived neurotrophic factor (GDNF) in the striatal target to improve the degree of striatal innervation from homotopic grafts. Younger donor tissue, collected on embryonic day (E)10, generated 4-fold larger grafts with greater striatal targeting, compared to grafts generated from more conventional E12 donor VM. Over-expression of GDNF in the host brain also significantly increased DA axonal growth and striatal innervation. Furthermore, a notable increase in the number and proportion of A9 DA neurons, essential for functional recovery, was observed in younger donor grafts treated with GDNF. Behavioural testing confirmed functional integration of younger donor tissue and demonstrated that improved motor function could be attributed to both local midbrain and striatal innervation. Together, these findings suggest there is significant scope for further development of intra-nigral grafting as a restorative approach for Parkinson's disease.

Generation of striatal projection neurons extends into the neonatal period in the rat brain.

Substantial advances have been made in the last decade on our understanding of the basic physiology underlying neurogenesis in the postnatal mammalian brain. The bulk of the work in this area has been based on analysis of the adult brain. Relatively less is known about the capacity for neurogenesis in specific structures within the neonatal brain. Here we report that the production of medium spiny striatal projection neurons extends into the early neonatal period under normal physiological conditions in the rat brain. Birth-dating of newborn cells with bromodeoxyuridine at postnatal days 0, 2 and 5 showed a peak production close to birth, which sharply declined at the later time-points. Additionally, there was a low-level but stable contribution of neurons with interneuron identity over the same time-period. Importantly, retroviral labelling of new striatal projection neurons with green fluorescent protein showed long-term survival and terminal differentiation with characteristic morphology, including highly elaborated spiny dendrites, and appropriate axonal targeting of the globus pallidus and midbrain. This latent period of striatal neurogenesis in the early neonatal brain represents an interesting target for regenerative approaches aimed at restoring striatal circuitry in perinatal pathologies, such as hypoxic and ischaemic damage associated with cerebral palsy.

Glycogen synthase kinase 3ß and activin/nodal inhibition in human embryonic stem cells induces a pre-neuroepithelial state that is required for specification to a floor plate cell lineage.

The floor plate is one of the major organizers of the developing nervous system through its secretion of sonic hedgehog (Shh). Although the floor plate is located within the neural tube, the derivation of the floor plate during development is still debatable and some studies suggest that floor plate cells are specified by Shh in a temporarily restricted window different to neuroepithelial cells. Using human embryonic stem cells (hESC) as a model of neurogenesis, we sought to determine how floor plate cells may be temporarily specified by SHH signaling during human embryogenesis. We found that inhibition of both GSK3ß and activin/nodal pathways in hESC induces a cellular state of SOX2+/PAX6- expression, we describe as "pre-neuroepithelial." Exposure of SHH during this pre-neuroepithelial period causes the expression of GLI transcription factors to function as activators and consequently upregulate expression of the floor plate marker, FOXA2, while also supressing PAX6 expression to inhibit neuroepithelial fate. FOXA2+ cells were able to efficiently generate mesencephalic dopaminergic neurons, a floor plate derivative. Overall, this study demonstrates a highly efficient system for generating floor plate cells from hESC and, most importantly, reveals that specification of floor plate cells is temporally dependent, whereby it occurs prior to the onset of PAX6 expression, within a pre-neuroepithelial stage.

Understanding and modeling regional specification of the human ganglionic eminence.

Inhibitory neurons originating from the ventral forebrain are associated with several neurological conditions. Distinct ventral forebrain subpopulations are generated from topographically defined zones; lateral-, medial- and caudal ganglionic eminences (LGE, MGE and CGE), yet key specification factors often span across developing zones contributing to difficulty in defining unique LGE, MGE or CGE profiles. Here we use human pluripotent stem cell (hPSC) reporter lines (NKX2.1-GFP and MEIS2-mCherry) and manipulation of morphogen gradients to gain greater insight into regional specification of these distinct zones. We identified Sonic hedgehog (SHH)-WNT crosstalk in regulating LGE and MGE fate and uncovered a role for retinoic acid signaling in CGE development. Unraveling the influence of these signaling pathways permitted development of fully defined protocols that favored generation of the three GE domains. These findings provide insight into the context-dependent role of morphogens in human GE specification and are of value for in vitro disease modeling and advancement of new therapies.

Efficient production of mesencephalic dopamine neurons by Lmx1a expression in embryonic stem cells.

Signaling factors involved in CNS development have been used to control the differentiation of embryonic stem cells (ESCs) into mesencephalic dopamine (mesDA) neurons, but tend to generate a limited yield of desired cell type. Here we show that forced expression of Lmx1a, a transcription factor functioning as a determinant of mesDA neurons during embryogenesis, effectively can promote the generation of mesDA neurons from mouse and human ESCs. Under permissive culture conditions, 75%-95% of mouse ESC-derived neurons express molecular and physiological properties characteristic of bona fide mesDA neurons. Similar to primary mesDA neurons, these cells integrate and innervate the striatum of 6-hydroxy dopamine lesioned neonatal rats. Thus, the enriched generation of functional mesDA neurons by forced expression of Lmx1a may be of future importance in cell replacement therapy of Parkinson disease.

Creation of GMP-Compliant iPSCs From Banked Umbilical Cord Blood.

Many clinical trials are in progress using cells derived from induced pluripotent stem cells (iPSC) for immunotherapies and regenerative medicine. The success of these new therapies is underpinned by the quality of the cell population used to create the iPSC lines, along with the creation of iPSCs in a fully Good Manufacturing Practice (GMP)-compliant environment such that they can be used safely and effectively in the clinical setting. Umbilical cord blood (CB) from public cord blood banks is an excellent source of starting material for creation of iPSCs. All CB units are manufactured under GMP-conditions, have been screened for infectious diseases, with known family and medical history of the donor. Furthermore, the HLA tissue typing is known, thereby allowing identification of CB units with homozygous HLA haplotypes. CB cells are naïve with less exposure to environmental insults and iPSC can be generated with high efficiency. We describe a protocol that can be adopted by those seeking to create clinical-grade iPSC from banked CB. This protocol uses a small volume of thawed CB buffy to first undergo ex-vivo expansion towards erythroid progenitor cells, which are then used for reprogramming using the CytoTune™-iPS 2.0 Sendai Reprogramming Kit. Resultant iPSC lines are tested to confirm pluripotency, genomic integrity, and stability. Cells are maintained in a feeder-free, xeno-free environment, using fully defined, commercially available reagents. Adoption of this protocol, with heed given to tips provided, allows efficient and robust creation of clinical-grade iPSC cell lines from small volumes of cryopreserved CB.

Long-term structural brain changes in adult rats after mild ischaemic stroke.

Preclinical studies of remote degeneration have largely focused on brain changes over the first few days or weeks after stroke. Accumulating evidence suggests that neurodegeneration occurs in other brain regions remote to the site of infarction for months and even years following ischaemic stroke. Brain atrophy appears to be driven by both axonal degeneration and widespread brain inflammation. The evolution and duration of these changes are increasingly being described in human studies, using advanced brain imaging techniques. Here, we sought to investigate long-term structural brain changes in a model of mild focal ischaemic stroke following injection of endothlin-1 in adult Long-Evans rats (n = 14) compared with sham animals (n = 10), over a clinically relevant time-frame of 48 weeks. Serial structural and diffusion-weighted MRI data were used to assess dynamic volume and white matter trajectories. We observed dynamic regional brain volume changes over the 48 weeks, reflecting both normal changes with age in sham animals and neurodegeneration in regions connected to the infarct following ischaemia. Ipsilesional cortical volume loss peaked at 24 weeks but was less prominent at 36 and 48 weeks. We found significantly reduced fractional anisotropy in both ipsi- and contralesional motor cortex and cingulum bundle regions of infarcted rats (P < 0.05) from 4 to 36 weeks, suggesting ongoing white matter degeneration in tracts connected to but distant from the stroke. We conclude that there is evidence of significant cortical atrophy and white matter degeneration up to 48 weeks following infarct, consistent with enduring, pervasive stroke-related degeneration.

A combined cell and gene therapy approach for homotopic reconstruction of midbrain dopamine pathways using human pluripotent stem cells.

Midbrain dopamine (mDA) neurons can be replaced in patients with Parkinson's disease (PD) in order to provide long-term improvement in motor functions. The limited capacity for long-distance axonal growth in the adult brain means that cells are transplanted ectopically, into the striatal target. As a consequence, several mDA pathways are not re-instated, which may underlie the incomplete restoration of motor function in patients. Here, we show that viral delivery of GDNF to the striatum, in conjunction with homotopic transplantation of human pluripotent stem-cell-derived mDA neurons, recapitulates brain-wide mDA target innervation. The grafts provided re-instatement of striatal dopamine levels and correction of motor function and also connectivity with additional mDA target nuclei not well innervated by ectopic grafts. These results demonstrate the remarkable capacity for achieving functional and anatomically precise reconstruction of long-distance circuitry in the adult brain by matching appropriate growth-factor signaling to grafting of specific cell types.

Lentiviral delivery of meteorin protects striatal neurons against excitotoxicity and reverses motor deficits in the quinolinic acid rat model.

Meteorin is a newly discovered secreted protein involved in both glial and neuronal cell differentiation, as well as in cerebral angiogenesis during development; but effects in the adult nervous system are unknown. The growth factor-like properties and expression of Meteorin during the development of the nervous system raises the possibility that it might possess important neuroprotective or regenerative capabilities. This report is the first demonstration that Meteorin has potent neuroprotective effects in vivo. Lentiviral-mediated striatal delivery of Meteorin to rats two weeks prior to injections of quinolinic acid (QA) dramatically reduced the loss of striatal neurons. The cellular protection afforded by Meteorin was associated with normalization of neurological performance on spontaneous forelimb placing and cylinder behavioral tests and a complete protection against QA-induced weight loss. These benefits were comparable in magnitude to those obtained with lentiviral-mediated delivery of ciliary neurotrophic factor (CNTF), a protein with known neuroprotective properties in the same model system. In naive animals, endogenous levels of both Meteorin and CNTF were increased in glial cells in response to QA lesion indicating that Meteorin may exert its protective effects as part of the reactive gliosis cascade in the injured brain. In summary, these data demonstrate that Meteorin strongly protects striatal neurons and deserves additional evaluation as a novel therapeutic for the treatment of neurological disorders with an excitotoxic component such as Huntington's Disease.