Grafted cerebellar cells in a mouse model of hereditary ataxia express IGF-I system genes and partially restore behavioral function

The Childhood-Onset Neurodegeneration with Cerebellar Atrophy (CONDCA) Disease Caused by AGTPBP1 Gene Mutations: The Purkinje Cell Degeneration Mouse as an Animal Model for the Study of this Human Disease

Recent reports have identified rare, biallelic damaging variants of the AGTPBP1 gene that cause a novel and documented human disease known as childhood-onset neurodegeneration with cerebellar atrophy (CONDCA), linking loss of function of the AGTPBP1 protein to human neurodegenerative diseases. CONDCA patients exhibit progressive cognitive decline, ataxia, hypotonia or muscle weakness among other clinical features that may be fatal. Loss of AGTPBP1 in humans recapitulates the neurodegenerative course reported in a well-characterised murine animal model harbouring loss-of-function mutations in the AGTPBP1 gene. In particular, in the Purkinje cell degeneration (pcd) mouse model, mutations in AGTPBP1 lead to early cerebellar ataxia, which correlates with the massive loss of cerebellar Purkinje cells. In addition, neurodegeneration in the olfactory bulb, retina, thalamus and spinal cord were also reported. In addition to neurodegeneration, pcd mice show behavioural deficits such as cognitive decline. Here, we provide an overview of what is currently known about the structure and functional role of AGTPBP1 and discuss the various alterations in AGTPBP1 that cause neurodegeneration in the pcd mutant mouse and humans with CONDCA. The sequence of neuropathological events that occur in pcd mice and the mechanisms governing these neurodegenerative processes are also reported. Finally, we describe the therapeutic strategies that were applied in pcd mice and focus on the potential usefulness of pcd mice as a promising model for the development of new therapeutic strategies for clinical trials in humans, which may offer potential beneficial options for patients with AGTPBP1 mutation-related CONDCA.

Increases in GFAP immunoreactive astrocytes in the cerebellar molecular layer of young adult CBA/J mice

Background

CBA/J mice are standard experimental animals in auditory studies, and age-related changes in auditory pathways are well documented. However, changes in locomotion-related brain regions have not been systematically explored.

Results

We showed an increase in immunoreactivity for glial fibrillary acidic protein (GFAP) in the cerebellar molecular layer associated with Purkinje cells in mice at 24 weeks of age but not in the younger mice. Increased GFAP immunoreactivity appeared in the form of clusters and distributed multifocally consistent with hyperplasia of astrocytes that were occasionally associated with Purkinje cell degeneration. Three out of 12 animals at 16 and 24 weeks of age exhibited pre-convulsive clinical signs. Two of these 3 animals also showed increased GFAP immunoreactivity in the cerebellum. Rotarod behavioral assessments indicated decreased performance at 24 weeks of age.

Conclusions

These results suggest minimal to mild reactive astrocytosis likely associated with Purkinje cell degeneration in the cerebellum at 24 weeks of age in CBA/J mice. These findings should be taken into consideration prior to using this mouse strain for studying neuroinflammation or aging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42826-021-00100-5.

Task Force Paper On Cerebellar Transplantation: Are We Ready to Treat Cerebellar Disorders with Cell Therapy?

Restoration of damaged central nervous system structures, functional recovery, and prevention of neuronal loss during neurodegenerative diseases are major objectives in cerebellar research. The highly organized anatomical structure of the cerebellum with numerous inputs/outputs, the complexity of cerebellar functions, and the large spectrum of cerebellar ataxias render therapies of cerebellar disorders highly challenging. There are currently several therapeutic approaches including motor rehabilitation, neuroprotective drugs, non-invasive cerebellar stimulation, molecularly based therapy targeting pathogenesis of the disease, and neurotransplantation. We discuss the goals and possible beneficial mechanisms of transplantation therapy for cerebellar damage and its limitations and factors determining outcome.

Daily bone marrow cell transplantations for the management of fast neurodegenerative processes

Cell therapy has been proven to be a promising treatment for fighting neurodegenerative diseases. As neuronal replacement presents undeniable complications, the neuroprotection of live neurons arises as the most suitable therapeutic approach. Accordingly, the earlier the diagnosis and treatment, the better the prognosis. However, these diseases are commonly diagnosed when symptoms have already progressed towards an irreversible degenerative stage. This problem is especially dramatic when neurodegeneration is aggressive and rapidly progresses. One of the most interesting approaches for neuroprotection is the fusion between healthy bone marrow-derived cells and neurons, as the former can provide the latter with regular/protective genes without harming brain parenchyma. So far, this phenomenon has only been identified in Purkinje cells, whose death is the cause of different diseases like cerebellar ataxias. Here we have employed a model of aggressive cerebellar neurodegeneration, the Purkinje Cell Degeneration mouse, to optimize a cell therapy based on bone marrow-derived cell and cell fusion. Our findings show that the substitution of bone marrow in diseased animals by healthy bone marrow, even prior to the onset of neurodegeneration, is not fast enough to stop neuronal loss in time. Conversely, avoiding bone marrow replacement and ensuring a regular supply of healthy cells through continuous, daily transplants, the neurodegenerative milieu of PCD is enough to attract those transplanted elements. Furthermore, in the most affected cerebellar regions, more than a half of surviving neurons undergo a process of cell fusion. Therefore, this method deserves consideration as a means to impede neuronal cell death.

Organization and Histochemical Phenotype of Human Fetal Cerebellar Cells following Transplantation into the Cerebellum of Nude Mice

Previous rodent studies have demonstrated the capacity of cerebellar transplants to organize into trilaminar cell layers typically observed in the normal cerebellum. In Purkinje Cell (PC)-deficient animals, PCs will migrate into the host and form synaptic connections. Recently, fetal cerebellar grafts transplanted into the Purkinje cell degeneration (pcd) mutant mouse were shown to result in an improvement of motor behaviors. These studies indicate the potential therapeutic use of neural transplantation in patients with cerebellar degeneration. In the present study, human fetal cerebellar tissue (8.5 wk postconception) was dissociated and transplanted into the normal cerebellum of nude mice. Six months following transplantation, histological analysis revealed donor cells in recipient mice. Immunostaining for the 28 kDa calcium-binding protein (calbindin) revealed the presence of donor PCs that were organized in discrete cellular layers within the transplant neuropil. In most cases the dendritic processes were oriented in a planar fashion perpendicular to the transplant cell layer. Human neurofilament immunostaining revealed bundles of donor fibers within the core of the transplant and/or at the periphery. These bundles were found to be calbindin positive (PC fibers). Three animals provided evidence of donor PC axon growth ventrally into host white matter, and in one case, this ventral migration reached the deep cerebellar nuclei. Most notable was the development of a pronounced folia-like organization by the implanted cell suspensions. Glial processes within the grafts were aligned perpendicular to the long axis of the transplant folia. These results demonstrate the capacity of human fetal cerebellar cell suspension to reorganize into cell layers typical of the normal cerebellum following transplantation into the rodent cerebellum, and develop an organotypic folia-like organization.

Mutation-related differences in exploratory, spatial, and depressive-like behavior in pcd and Lurcher cerebellar mutant mice

The cerebellum is not only essential for motor coordination but is also involved in cognitive and affective processes. These functions of the cerebellum and mechanisms of their disorders in cerebellar injury are not completely understood. There is a wide spectrum of cerebellar mutant mice which are used as models of hereditary cerebellar degenerations. Nevertheless, they differ in pathogenesis of manifestation of the particular mutation and also in the strain background. The aim of this work was to compare spatial navigation, learning, and memory in pcd and Lurcher mice, two of the most frequently used cerebellar mutants. The mice were tested in the open field for exploration behavior, in the Morris water maze with visible as well as reversal hidden platform tasks and in the forced swimming test for motivation assessment. Lurcher mice showed different space exploration activity in the open field and a lower tendency to depressive-like behavior in the forced swimming test compared with pcd mice. Severe deficit of spatial navigation was shown in both cerebellar mutants. However, the overall performance of Lurcher mice was better than that of pcd mutants. Lurcher mice showed the ability of visual guidance despite difficulties with the direct swim toward a goal. In the probe trial test, Lurcher mice preferred the visible platform rather than the more recent localization of the hidden goal.

Concise review: stem cells for the treatment of cerebellar-related disorders

Embryonic neural transplants have become clinically relevant over the past 25 years for their possible application in the treatment of cerebellum-related neurodegenerative diseases. While highlighting the important role that fetal neural progenitors have in meeting these challenges, we define rationales for all types of cell therapy involving adult stem cells as well as human embryonic stem cells (hESC) and human induced pluripotent stem (iPS) cells. The recent advances in the field of hESC and iPS cells, including their capacity for differentiation toward regional specific neural lineages, could open a new era of transplantation in cell-based therapy for cerebellar ataxias.

Brain regeneration in physiology and pathology: the immune signature driving therapeutic plasticity of neural stem cells

Regenerative processes occurring under physiological (maintenance) and pathological (reparative) conditions are a fundamental part of life and vary greatly among different species, individuals, and tissues. Physiological regeneration occurs naturally as a consequence of normal cell erosion, or as an inevitable outcome of any biological process aiming at the restoration of homeostasis. Reparative regeneration occurs as a consequence of tissue damage. Although the central nervous system (CNS) has been considered for years as a "perennial" tissue, it has recently become clear that both physiological and reparative regeneration occur also within the CNS to sustain tissue homeostasis and repair. Proliferation and differentiation of neural stem/progenitor cells (NPCs) residing within the healthy CNS, or surviving injury, are considered crucial in sustaining these processes. Thus a large number of experimental stem cell-based transplantation systems for CNS repair have recently been established. The results suggest that transplanted NPCs promote tissue repair not only via cell replacement but also through their local contribution to changes in the diseased tissue milieu. This review focuses on the remarkable plasticity of endogenous and exogenous (transplanted) NPCs in promoting repair. Special attention will be given to the cross-talk existing between NPCs and CNS-resident microglia as well as CNS-infiltrating immune cells from the circulation, as a crucial event sustaining NPC-mediated neuroprotection. Finally, we will propose the concept of the context-dependent potency of transplanted NPCs (therapeutic plasticity) to exert multiple therapeutic actions, such as cell replacement, neurotrophic support, and immunomodulation, in CNS repair.

Efficient generation of mature cerebellar Purkinje cells from mouse embryonic stem cells

Mouse embryonic stem cells (ESCs) can generate cerebellar neurons, including Purkinje cells (PCs) and their precursor cells, in a floating culture system called serum-free culture of embryoid body-like aggregates (SFEB) treated with BMP4, Fgf8b, and Wnt3a. Here we successfully established a coculture system that induced the maturation of PCs in ESC-derived Purkinje cell (EDPC) precursors in SFEB, using as a feeder layer a cerebellum dissociation culture prepared from mice at postnatal day (P) 6-8. PC maturation was incomplete or abnormal when the adherent culture did not include feeder cells or when the feeder layer was from neonatal cerebellum. In contrast, EDPCs exhibited the morphology of mature PCs and synaptogenesis with other cerebellar neurons when grown for 4 weeks in coculture system with the postnatal cerebellar feeder. Furthermore, the electrophysiological properties of these EDPCs were compatible with those of native mature PCs in vitro, such as Na(+) or Ca(2+) spikes elicited by current injections and excitatory or inhibitory postsynaptic currents, which were assessed by whole-cell patch-clamp recordings. Thus, EDPC precursors in SFEB can mature into PCs whose properties are comparable with those of native PCs in vitro.

The ataxic Syrian hamster: an animal model homologous to the pcd mutant mouse?

A spontaneous model of cerebellar ataxia in the Syrian hamster is described. Breeding data indicate that the condition is hereditary and that the mode of inheritance is autosomal recessive. Homozygotes are smaller in size than the wild-type but have a normal appearance. Mutants show a moderate ataxia beginning at 7 weeks of age. Although affected adults exhibit significant atrophy in the cerebellum, other parts of the brain appear relatively normal by light microscopy. Mutants lose almost all Purkinje cells by 18 months of age and exhibit a moderate reduction in granule cell density, probably as a consequence of the primary loss of Purkinje cells. In the homozygous hamster brain, Nna1 expression is suppressed, similar to that previously observed in Purkinje cell degeneration (pcd) mutant mice. A phenotypic comparison of ataxic hamsters with the pcd mutant mice suggests that the influence of the causal allele in ataxic hamsters is considerably milder than most of the alleles found in the mutant mice.

The Purkinje cell degeneration (pcd) mouse: an unexpected molecular link between neuronal degeneration and regeneration

The spontaneous autosomal recessive mouse mutation, Purkinje cell degeneration (pcd), was first identified through its ataxic behavior. Since its discovery in the 1970s, the strain has undergone extensive investigation, although another quarter century elapsed until the mutant gene (agtpbp1 a.k.a. Nna1) underlying the pcd phenotype was identified. As Nna1 was initially discovered as a gene induced in motor neurons following axotomy the finding that its loss leads to selective neuronal degeneration points to a novel and unexpected common molecular mechanism contributing to the apparently opposing processes of degeneration and regeneration. The elucidation of this mechanism may of course have significant implications for an array of neurological disorders. Here we will first review the principle features of the pcd phenotype and then discuss the functional implications of more recent findings emanating from the characterization of Nna1, the protein that is lost in pcd. We also provide new data on the genetic dissection of the cell death pathways operative in pcd(3J) mice, proving that granule cell death and Purkinje cell death in these mice have distinct molecular bases. We also provide new information on the structure of mouse Nna1 as well as Nna1 protein levels in pcd(3J) mice.

Intranasal administration of IGF-I improves behavior and Purkinje cell pathology in SCA1 mice

Spinocerebellar ataxia type 1 (SCA1) is a neurodegenerative disease caused by the expansion of polyglutamine repeat within ataxin-1 protein. Cerebellar Purkinje cells are the primary targets of SCA1 pathology. These cells synthesize insulin-like growth factor-I (IGF-I) and express its receptors during their entire life. The aim of present study was to determine if intranasally administered IGF-I to SCA1 transgenic mice suppresses toxic effects of ataxin-1. Two-week old SCA1 heterozygous animals were randomly divided into two treatment groups of IGF-I (30 and 60 microg IGF-I/animal) and a vehicle-treated control group. The wildtype animals served as normal controls. IGF-I or vehicle was administered at 48 h intervals for the total of 10 doses. Animals were then subjected to rotarod test, sacrificed, brains removed and processed for immunohistochemical and Western blot analysis. Radiolabeled IGF-I and bioactive TAT peptide accumulated in the brains of SCA1 mice following intranasal administration validating the use of intranasal route. SCA1 mice showed SCA1 pathology with impaired motor function and downregulation of calcium binding proteins as compared to wildtype mice. However, 30 and 60 microg IGF-I-treated animals showed improved performance on the rotarod as compared to vehicle-treated SCA1 mice with significant improvement (p < 0.05) on day 3 in 60 microg IGF-I group. The immunohistochemical data further showed partial recovery in the expression of calbindin D28k and protein kinase C-gamma in Purkinje cells in IGF-I-treated SCA1 animals. Our results indicate that suppression of ataxin-1-mediated adverse effects by intranasal IGF-I treatment may be of a therapeutic value to treat SCA1.

Neuronal replacement and integration in the rewiring of cerebellar circuits

Repair of CNS injury or degeneration by cell replacement may lead to significant functional recovery only through faithful reconstruction of the original anatomical architecture. This is particularly relevant for point-to-point systems, where precisely patterned connections have to be re-established to regain adaptive function. Despite the major interest recently drawn on cell therapies, little is known about the mechanisms and the potentialities for specific integration of new neurons in the mature CNS. Major findings and concepts about this issue will be reviewed here, with special focus on work dealing with the Purkinje cell transplantation in the rodent cerebellum. These studies show that the adult CNS may provide some efficient information to direct cell engraftment and process outgrowth. On their side, immature cells may be able to induce adaptive changes in their adult partners to facilitate their incorporation in the recipient network. Despite the rather high degree of specific integration achieved in several different CNS regions, these processes are usually defective and long-distance connections are not rewired. Thus, although some potentialities for cell replacement exist in the mature CNS, full incorporation of new neurons in adult circuits is rarely observed. Indeed, intrinsic mechanisms for growth control as well as injury-induced changes in the properties and architecture of the nervous tissue contribute to hamper repair processes. As a consequence, crucial to obtain successful cell replacement and integration in the mature CNS is a deep understanding of the basic biological mechanisms that regulate the interactions between newly added elements and the recipient environment.

Selective rather than inductive mechanisms favour specific replacement of Purkinje cells by embryonic cerebellar cells transplanted to the cerebellum of adult Purkinje cell degeneration (pcd) mutant mice

Cell replacement after neuronal degeneration in the adult CNS depends on the availability of specific cues to direct specification, differentiation and integration of newly born neurons into mature circuits. Following recent reports indicating that neurogenic signals may be reactivated in the adult injured CNS, here we asked whether such signals are expressed in the cerebellum after Purkinje cell degeneration. Thus, we compared the fate of embryonic cerebellar cells transplanted to the cerebella of adult wild-type and Purkinje cell degeneration (pcd) mutant mice. Donor cells were dissected from beta-actin-enhanced green fluorescent protein (EGFP) transgenic mice and transplanted as a single cell suspension. In both hosts, grafted cells generated all major cerebellar phenotypes, with a precise localization in the recipient cortex or white matter. Nevertheless, the phenotypic distributions showed striking quantitative differences. Most notably, in the pcd cerebellum there was a higher amount of Purkinje cells, while other phenotypes were less frequent. Analysis of cell proliferation by 5-bromo-2'-deoxyuridine (BrDU) incorporation revealed that in both hosts mitotic activity was strongly reduced shortly after transplantation, and virtually all donor Purkinje cells were actually generated before grafting. Together, these results indicate that some compensatory mechanisms operate in the pcd environment. However, the very low mitotic rate of transplanted cells suggests that the adult cerebellum, either wild-type or mutant, does not provide instructive neurogenic cues to direct the specification of uncommitted progenitors. Rather, specific replacement in mutant hosts is achieved through selective mechanisms that favour the survival and integration of donor Purkinje cells at the expense of other phenotypes.

Insulin-like growth factor-I improves cerebellar dysfunction but does not prevent cerebellar neurodegeneration in the calcium channel mutant mouse, leaner

The effects of insulin-like growth factor-I (IGF-I) on cerebellar dysfunction and neurodegeneration were investigated in leaner mice, which exhibit cerebellar ataxia and neurodegeneration related to P/Q-type calcium channel mutations. Leaner mice showed significantly reduced serum and cerebellar IGF-I concentrations compared to wild-type mice at postnatal day 30. Behavioral assessment of leaner mice injected with IGF-I subcutaneously for 4 weeks showed partially improved cerebellar function. Histological analysis of IGF-I treated leaner cerebella showed no difference in the number of dying Purkinje cells compared to control leaner cerebella. These results further support potential use of IGF-I as a therapeutic aid for cerebellar ataxia related to calcium channel mutations. Nonetheless, IGF-I administration does not rescue dying cerebellar neurons, which suggests that the beneficial effects of IGF-I may have been achieved through surviving cerebellar neurons.

Spinocerebellar degeneration

The spinocerebellar degenerations/ataxias (SCAs) are a diverse group of rare, slowly progressive, neurological diseases, often inherited but of incompletely understood pathophysiology, which affect the cerebellum and its related pathways. They have few animal models and share no reliable biomarkers. They have, as yet, no universally validated rating scale for use in clinical trials. In the past 25 years, there have been, at most, 18 controlled (Class 1) trials for ataxia, which have focused on neurotransmitter mechanisms. There is currently only one National Institute of Neurological Disorders and Stroke-sponsored drug trial for ataxia (Phase I study of idebenone in Friedreich's ataxia). There are, as yet, no FDA-approved drugs for SCA. Current treatment practices encompass rehabilitation interventions and off-label use of symptomatic medications [1,2].

Pluripotent stem cells identified in multiple murine tissues

Pluripotential stem cells (PSCs) have been recently described in many tissues including skeletal muscle, brain, and bone marrow. However, the true nature of these cells is still unclear, and their precise definition has yet to be determined. We hypothesized that a common, rare population of PSCs with a broad tissue differentiation potential can be identified in multiple murine tissues and that these cells are capable of transdifferentiation into cells of different primordial germ layer origins in response to diverse microenvironmental cues. To examine this hypothesis, we isolated phenotypically defined cells from murine skeletal muscle and cultured these cells under different conditions tailored to promote differentiation into several cell types including myocytes. We report here that in conditions permissive for hematopoietic differentiation, muscle-derived CD45(-)Sca-1(+)c-kit(-) cells differentiated into cells expressing hematopoietic-specific mRNA; while in conditions promoting myogenic, neuronal, and adipocytic differentiation, cells morphologically typical of these cell types expressing tissue-specific markers were identified 9-14 days in culture. When CD45(-)Sca-1(+)c-kit(-) cells from muscle or bone marrow were transplanted intracerebellarly into Purkinje cell degenerative (pcd) mice, the behavior of these mice improved 28 days after transplantation relative to mice injected with vehicle alone, suggesting that these cells contributed to the appearance of functional neuronal cells that may have improved the ataxic condition characteristic of these mice. Phenotypic analysis of single cell suspensions prepared from brain, blood, and intestinal epithelium revealed the presence of CD45(-)Sca-1(+)c-kit(-) cells in varying degrees. These studies suggest that a phenotypically common, multipotent cell can be identified in different tissues and that this cell may represent a universal pluripotent stem cell residing at different levels in multiple murine tissues.

28. Embryonic and adult stem cell therapy

Stem cells are characterized by the ability to remain undifferentiated and to self-renew. Embryonic stem cells derived from blastocysts are pluripotent (able to differentiate into many cell types). Adult stem cells, which were traditionally thought to be monopotent multipotent, or tissue restricted, have recently also been shown to have pluripotent properties. Adult bone marrow stem cells have been shown to be capable of differentiating into skeletal muscle, brain microglia and astroglia, and hepatocytes. Stem cell lines derived from both embryonic stem and embryonic germ cells (from the embryonic gonadal ridge) are pluripotent and capable of self-renewal for long periods. Therefore embryonic stem and germ cells have been widely investigated for their potential to cure diseases by repairing or replacing damaged cells and tissues. Studies in animal models have shown that transplantation of fetal, embryonic stem, or embryonic germ cells may be able to treat some chronic diseases. In this review, we highlight recent developments in the use of stem cells as therapeutic agents for three such diseases: Diabetes, Parkinson disease, and congestive heart failure. We also discuss the potential use of stem cells as gene therapy delivery cells and the scientific and ethical issues that arise with the use of human stem cells.

Neurotrophic factors for the investigation and treatment of movement disorders

Neurotrophic factors (NFs) are proteins that enhance neuronal survival, differentiation, neurotransmitter function and resistance to neurotoxins and lesions. For these reasons the NFs are considered as a new potential therapeutic tool for the treatment of neurodegenerative disorders, a group of diseases that produce the most important cause for disability in the Western world. Some NFs prevent or even reverse the behavioral, biochemical, pharmacological and histological abnormalities observed in several in vitro and in vivo models of neurodegenerative disorders, namely Parkinson's disease. Several NFs have been investigated in primate models of neurological disorders and some of them have been used for patients with these diseases. The results so far obtained in humans have been disappointing for several reasons, including technical problems for delivery, unbearable side effects or lack of efficacy. Future approaches for the use of NFs in humans should include the following: (1) Investigation of the putative compounds in animal models more related to the pathophysiology of each disease, such as in genetic models of neurodegenerative diseases; (2) New methods of delivery including genetic engineering by viral vectors and administration through implantable devices; (3) More precise methods of continuous response evaluation, including the novel neuroimaging techniques; (4) Investigation of the effects of behavioral stimulation and conventional pharmacotherapy on the metabolism of NFs.

Opinion: neural stem cell therapy for neurological diseases: dreams and reality

There is a pressing need for treatments for neurodegenerative diseases. Hopes have been raised by the prospect of neural stem cell therapy; however, despite intense research activities and media attention, stem cell therapy for neurological disorders is still a distant goal. Effective strategies must be developed to isolate, enrich and propagate homogeneous populations of neural stem cells, and to identify the molecules and mechanisms that are required for their proper integration into the injured brain. This article examines these requirements, discusses the results obtained so far, and considers the steps that need to be taken to provide instruction to donor cells and to elucidate the neurogenic potential of the adult central nervous system environment.

Highly efficient and specific gene transfer to Purkinje cells in vivo using a herpes simplex virus I amplicon

The transduction of cerebellar neurons in vivo with herpes simplex virus 1 (HSV-1) amplicon carrying the lacZ gene has been investigated after injection of the vector in the cerebellar cortex, ventricles, and inferior olive of adult rats. Injection into the cerebellar cortex resulted in transduction of Purkinje cells near the needle tract and injection into the ventricles yielded no transduced neurons. In contrast, high transduction efficiency was achieved by vector injection into the inferior olive, resulting in one of three positive Purkinje cells all over the ipsilateral and contralateral cerebellar hemispheres. Because neurons in the deep cerebellar nuclei are also transduced, we suggest that the vector is delivered from the inferior olive to the cerebellar nuclei and then to Purkinje cells by retrograde axonal transport. Expression of the lacZ gene within Purkinje cells was surprisingly persistent and was maintained at the same level for at least 40 days. Importantly, no signs of either toxicity or inflammation were observed in the cerebellum after vector injection, except for the borders of the needle tract where some reactive astrocytes were detected. Indeed, motor coordination of treated animals was entirely normal, as assessed by the rota-rod test. These results demonstrate that HSV-1 amplicon vectors can effect safe and stable transgene expression in Purkinje cells in vivo, raising the possibility of using these vectors for long-term gene therapy of human cerebellar disorders.

Multilineage differentiation from human embryonic stem cell lines

Stem cells are unique cell populations with the ability to undergo both self-renewal and differentiation. A wide variety of adult mammalian tissues harbors stem cells, yet "adult" stem cells may be capable of developing into only a limited number of cell types. In contrast, embryonic stem (ES) cells, derived from blastocyst-stage early mammalian embryos, have the ability to form any fully differentiated cell of the body. Human ES cells have a normal karyotype, maintain high telomerase activity, and exhibit remarkable long-term proliferative potential, providing the possibility for unlimited expansion in culture. Furthermore, they can differentiate into derivatives of all three embryonic germ layers when transferred to an in vivo environment. Data are now emerging that demonstrate human ES cells can initiate lineage-specific differentiation programs of many tissue and cell types in vitro. Based on this property, it is likely that human ES cells will provide a useful differentiation culture system to study the mechanisms underlying many facets of human development. Because they have the dual ability to proliferate indefinitely and differentiate into multiple tissue types, human ES cells could potentially provide an unlimited supply of tissue for human transplantation. Though human ES cell-based transplantation therapy holds great promise to successfully treat a variety of diseases (e.g., Parkinson's disease, diabetes, and heart failure) many barriers remain in the way of successful clinical trials.

Radial glial cell line C6-R integrates preferentially in adult white matter and facilitates migration of coimplanted neurons in vivo

C6-R is a cell line derived from C6 glioma cells that exhibits key properties of radial glia including the ability to support neuronal migration in culture. To explore its potential use in promoting neuronal migration in vivo, we analyzed the behavior of C6-R cells in the intact and injured adult rat CNS. At 6-11 days postimplantation at the splenium of the corpus callosum, green fluorescent protein-labeled C6-R cells were observed primarily in either the corpus callosum or the hippocampus in the brain, and in the spinal cord they migrated more extensively in the white matter than in the grey matter. To determine whether C6-R cells retain their ability to promote neuronal migration in vivo, they were coinjected with labeled neurons into adult brain. When rat embryonic neurons were coimplanted with C6-R cells, the neurons and C6-R cells comigrated through a much larger volume than neurons alone or neurons coimplanted with fibroblasts. In brains preinjured with ibotenic acid, C6-R cells as well as coimplanted neurons distributed widely within the lesion site and migrated into adjacent brain tissue, while transplants with neurons alone were restricted primarily to the lesion site. The results suggest that radial glial cell lines can serve as a scaffold for neuronal migration that may facilitate development of experimental models for neural transplantation and regeneration.

Mutant mice as a model for cerebellar ataxia

Not later than two synapses after their arrival in the cerebellar cortex all excitatory afferent signals are subsequently transformed into inhibitory ones. Guaranteed by the exceedingly ordered and stereotyped synaptic arrangement of its cellular elements, the cerebellar cortex transmits this inhibitory result of cerebellar integration exclusively via Purkinje cells (PCs) in a precise temporal succession directly onto the target neurons of the deep cerebellar and vestibular nuclei. Thus the cerebellar cortex seems to produce a temporal pattern of inhibitory influence on these target neurons that modifies their excitatory action in such a way that an activation of muscle fibers occurs which progressively integrates the intended motion into the actual condition of the motoric inventory. In consequence, disturbances that affect this cerebellar inhibition will cause uncoordinated, decomposed and ataxic movements, commonly referred to as cerebellar ataxia. Electrophysiological investigations using different cerebellar mouse mutants have shown that alterations in the cerebellar inhibitory input in the target nuclei lead to diverse neuronal responses and to different consequences for the behavioural phenotype. A dependence between the reconstitution of inhibition and the behavioural outcome seems to exist. Obviously two different basic mechanisms are responsible for these observations: (1) ineffective inhibition on target neurons by surviving PCs; and (2) enhancement of intranuclear inhibition in the deep cerebellar and vestibular nuclei. Which of the two strategies evolves is dependent upon the composition of the residual cell types in the cerebellum and on the degree of PC input loss in a given area of the target nuclei. Motor behaviour seems to deteriorate under the first of these mechanisms whereas it may benefit from the second. This is substantiated by stereotaxic removal of the remaining PC input, which eliminates the influence of the first mechanism and is able to induce the second strategy. As a consequence, motor performance improves considerably. In this review, results leading to the above conclusions are presented and links forged to human cerebellar diseases.

Analysis of organ physiology in transgenic mice

The increasing availability of transgenic mouse models of gene deletion and human disease has mandated the development of creative approaches to characterize mouse phenotype. The mouse presents unique challenges to phenotype analysis because of its small size, habits, and inability to verbalize clinical symptoms. This review describes strategies to study mouse organ physiology, focusing on the cardiovascular, pulmonary, renal, gastrointestinal, and neurobehavioral systems. General concerns about evaluating mouse phenotype studies are discussed. Monitoring and anesthesia methods are reviewed, with emphasis on the feasibility and limitations of noninvasive and invasive procedures to monitor physiological parameters, do cannulations, and perform surgical procedures. Examples of phenotype studies are cited to demonstrate the practical applications and limitations of the measurement methods. The repertoire of phenotype analysis methods reviewed here should be useful to investigators involved in or contemplating the use of mouse models.

Neurotrophic factors in neurodegenerative disorders: model of Parkinson's disease

Neurotrophic factors are compounds that enhance neuronal survival and differentiation. Most of these compounds exert their pharmacological actions on selective types of neurons, and therefore, are considered promising new therapeutic agents for the treatment of different neurodegenerative disorders characterized by selective degeneration of certain neuronal groups. Those compounds have been used in humans for several neurological disorders including amyotrophic lateral sclerosis--ciliary derived neurotrophic factor (CNTF) and brain derived neurotrophic factor (BDNF), Alzheimer's disease and peripheral neuropathy--nerve growth factor (NGF) and Parkinson's disease (PD)--glial derived neurotrophic factor (GDNF). In spite of well founded clinical experiments by previous experimental work in animal models some of these trials have been negative. For instance, animal models of PD have shown that several neurotrophic factors, including GDNF and other compounds, reduce apoptosis and increase resistance of dopamine neurons to neurotoxins in vitro. These compounds prevent or recover the damage to dopamine neurons of rodents and primates produced by chemical or mechanical acute lesions including 6-OH-DA, MPTP, methamphetamine and axotomy. The differences between the promising results obtained in experimental models and the lack of clinical results or excessive toxicity found in humans could be attributed to the following reasons: (a) Lack of relevance between the pathogenesis of the experimental lesion and the corresponding neurodegenerative disorder. (b) Poor correlation between results obtained in acute, self-limited, selective deficit produced to experimental animals and those available in more complex, chronic and progressive disorders involving patients. (c) Inadequate delivery of the active product to the target area in the human brain. (d) Poor information from acute experiments in animals which does not predict long-term effects of chronic infusion in humans. Further experimental work, therefore, is needed to transfer these neurotrophic factors to the clinic.

Cerebellar allografts survive and transiently alleviate ataxia in a transgenic model of spinocerebellar ataxia type-1

Spinocerebellar ataxia type 1 (SCA-1) is one of several neurodegenerative diseases, including Huntington's disease, spinobulbar muscular atrophy, dentatorubral-pallidoluysian atrophy, and SCA-2, SCA-3, SCA-6, and SCA-7, each caused by an expanded number of CAG repeats in the coding region of their respective genes. The mechanism by which the resulting proteins are pathogenic is unknown. Clinical trials of neural transplants in Huntington's disease patients are under way. While initial reports are encouraging, definitive evidence of graft survival in patients despite the ongoing disease process is not possible with current imaging techniques. Transplants in primates have shown long-term survival of striatal grafts and recovery of function, but have used lesioning to model Huntington's phenotypically. Studies of striatal grafts in a transgenic mouse model of Huntington's have not yet shown a behavioral benefit. We describe a behavioral benefit of cerebellar grafts in a transgenic model of SCA-1 in which the ataxic phenotype results from expression of an expanded ataxin-1 protein. Mice were transplanted at an age when their ataxic phenotype is just becoming evident. Compared with sham-operated littermates, grafted mice showed better performance on multiple behavioral tests of cerebellar function. Differences persisted for 10 to 12 weeks posttransplant, after which there was a progressive decline in motor performance. At 20 weeks postsurgery, donor Purkinje cell survival was evident in 9 of 12 graft recipients. These results indicate that transplants can have behavioral benefits and grafts can survive long-term despite the ongoing pathological process in a brain actively expressing an expanded polyglutamine protein.

Establishment and properties of neural stem cell clones: plasticity in vitro and in vivo

The study of the basic physiology of the neural precursors generated during brain development is driven by two inextricably linked goals. First, such knowledge is instrumental to our understanding of how the high degree of cellular complexity of the mature central nervous system (CNS) is generated, and how to dissect the steps of proliferation, fate commitment, and differentiation that lead early pluripotent neural progenitors to give rise to mature CNS cells. Second, it is hoped that the isolation, propagation, and manipulation of brain precursors and, particularly, of multipotent neural stem cells (NSCs), will lead to therapeutic applications in neurological disorders. The debate is still open concerning the most appropriate definition of a stem cell and on how it is best identified, characterized, and manipulated. By adopting an operational definition of NSCs, we review some of the basic findings in this area and elaborate on their potential therapeutic applications. Further, we discuss recent evidence from our two groups that describe, based on that rigorous definition, the isolation and propagation of clones of NSCs from the human fetal brain and illustrate how they have begun to show promise for neural cell replacement and molecular support therapy in models of degenerative CNS diseases. The extensive propagation and engraftment potential of human CNS stem cells may, in the not-too-distant-future, be directed towards genuine clinical therapeutic ends, and may open novel and multifaceted strategies for redressing a variety of heretofore untreatable CNS dysfunctions.

Transplanted neurons alter the course of neurodegenerative disease in Lurcher mutant mice

Embryonic cerebellar, neocortical, and striatal tissues derived from NSE-LacZ transgenic mice were transplanted into the right cerebellar hemisphere of 8- to 10-day-old Lurcher or wild-type mice. Host mice survived for 30-90 days and the transplanted tissue was examined by light microscopy using Nissl staining, X-gal histochemistry, and immunohistochemistry for calcium binding protein and glutamic acid decarboxylase. Transplantation of cerebellar tissue, but not neocortical or striatal progenitors, resulted in robust infiltration of the lurcher mutant host cerebellar cortex by transgenic Purkinje neurons. Deep to the infiltrated molecular layer, the host granular layer was thicker and denser than the mutant granular layer, but transgenic cells did not contribute to the spared granular layer. The host inferior olivary complex consistently exhibited a noticeable bilateral asymmetry in Nissl-stained sections. A quantitative analysis of the olivary complex was performed in 10 90-day-old host mice. The results indicate that the left inferior olivary complex of 90-day-old host mice contained more neurons than the right inferior olive of the host mice and contained more neurons than was observed in 90-day-old Lurcher control mice. Analysis by olivary subdivision indicates that increased neuron numbers were present in all subdivisions of the host left inferior olive. These studies confirm the specific attractive effect of the mutant cerebellar cortex on transplanted Purkinje neuron progenitors and indicate that neural transplants may survive the neurodegenerative period to interact with developing host neural systems. The unilateral rescue of Lurcher inferior olivary neurons in cerebellar transplant hosts indicates that transplanted neurons may interact with diseased host neural circuits to reduce transneuronal degeneration in the course of a neurodegenerative disease.

Purkinje cell transplants in Shaker mutant rats with hereditary Purkinje cell degeneration and ataxia

Shaker mutant rats are characterized by the adult-onset degeneration of cerebellar anterior lobe Purkinje cells and temporally correlated development of ataxia and tremor. Normal E-13 Purkinje cells were transplanted into the anterior cerebellum in adult shaker mutant rats to study donor/host interactions in an animal with adult-onset heredodegeneration. Donor Purkinje cells from extraparenchymal transplant sites migrated radially into the host molecular layer and differentiated. Donor Purkinje cell dendrites expanded to fill the host molecular layer, spinous processes were apparent, and axonal projections into the host gray and white matter were observed. Donor Purkinje cells remaining in the extraparenchymal transplant sites differentiated if they were located relatively close to the host cerebellum. Donor Purkinje cells located intraparenchymally in the host white matter or granule cell layer survived, but were stunted in their development. The orthogonal movement of donor Purkinje cells away from transplant sites in the host cerebellum was spatially restricted. The findings from this study indicate that host cerebellar cortex with adult-onset heredodegeneration of Purkinje cells supports the survival and differentiation of transplanted normal embryonic Purkinje cells.

Dependence of parvalbumin expression on Purkinje cell input in the deep cerebellar nuclei

A complete loss of Purkinje cell (PC) input leads to an increase in expression of the calcium-binding protein parvalbumin (Parv) in neurons of the deep cerebellar nuclei (DCN) of PC degeneration (pcd) mutants. To verify this apparent dependence of Parv expression on PC input in the DCN, the patterns of expression in five other cerebellar mutants (weaver, staggerer, leaner, nervous, and lurcher) with differing grades and chronologies of PC loss were compared. Degree and time course of PC loss and the subsequent denervation of DCN neurons were monitored by using Calbindin D-28k (Calb) immunocytochemistry. Similar to pcd mice, somatal Parv in lurcher mutants increased massively throughout the cerebellar nuclei. In nervous and leaner mutants, somatal Parv was restricted to almost completely denervated nuclear areas, whereas areas with appreciable remnants of PC input were spared. The first appearance of Parv+ somata was closely correlated with the time course of PC degeneration--postnatal day 19 in lurcher mutants and postnatal day 23 in nervous mutants. In staggerer mice, neurons immunopositive for Parv as well as for Calb were present in outer DCN areas, likely representing ectopic PCs rather than DCN neurons. No Parv+ DCN somata were found in weaver mutants at any time. In conclusion, increased expression of somatal Parv in DCN neurons is not restricted to the specific histopathology in pcd mutants but is a common mechanism that is dependent on the topography and severeness of PC-input loss. The functional significance of the Parv increase and its possible contribution to the degree of motor disability among the different mutants are discussed.

Expression of cerebellar specific glutamate and GABAA receptor subunits in heterotopic cerebellar grafts

In the cerebellum, up- and downregulation of specific GABAA and NMDA receptor subunits coincide with granule cell migration and differentiation. In this study, in situ hybridization techniques with GABAA and NMDA receptor subunit specific probes were employed to assess whether the molecular phenotype of heterotopically grafted cerebellar granule cells corresponds to that of normal cerebellum. The cerebellar anlage of rat fetuses was stereotactically grafted into the rostral striatum of adult rats. Eight weeks after transplantation, analysis demonstrated acquisition of an adult differentiation status reflected by abundant GABAA alpha 6 and NR2C mRNA expression in granule cells. Complete lack of NR2B transcripts, molecular markers of immature granule cells, argues against persistence of undifferentiated cells. The data suggest that intrinsic cell-autonomous factors largely determine the molecular commitment of granule cells and that a restricted specific environment is not necessary to promote granule cell differentiation.

Cerebellar Grafts Partially Reverse Amino Acid Receptor Changes Observed in the Cerebellum of Mice with Hereditary Ataxia: Quantitative Autoradiographic Studies

We used quantitative autoradiography of [3H]CNQX (200 nM), [3H]muscimol (13 nM), and [3H]flunitrazepam (10 nM) binding to study the distribution of non-NMDA and GABAA receptors in the cerebellum of pcd mutant mice with unilateral cerebellar grafts. Nonspecific binding was determined by incubation with 1 mM Glu, 200 μM GABA, or 1 μM clonazepam, respectively. Saturation parameters were defined in wild-type and mutant cerebella. In mutants, non-NMDA receptors were reduced by 38% in the molecular layer and by 47% in the granule cell layer. The reduction of non-NMDA receptors in the pcd cerebellar cortex supports their localization on Purkinje cells. [3H] CNQX binding sites were visualized at higher density in grafts that had migrated to the cerebellar cortex of the hosts (4.1 and 11.0 pmol/mg protein, respectively, at 23 and 37 days after grafting) than in grafts arrested intraparen-chymally (2.6 and 6.2 pmol/mg protein, respectively, at 23 and 37 days after grafting). The pattern of expression of non-NMDA receptors in cortical vs. parenchymal grafts suggests a possible regulation of their levels by transacting elements from host parallel fibers. GABAA binding levels in the grafts for both ligands used were similar to normal molecular layer. Binding was increased in the deep cerebellar nuclei of pcd mutants: the increase in [3H]muscimol binding over normal was 215% and the increase in [3H]flunitrazepam binding was 89%. Such increases in the pcd deep cerebellar nuclei may reflect a denervation-induced supersensitivity subsequent to the loss of Purkinje axon terminal innervation. In the deep nuclei of pcd mutants with unilateral cerebellar grafts, [3H]muscimol binding was 31% lower in the grafted side than in the contralateral nongrafted side at 37 days after transplantation; [3H]fluni-trazepam binding was also lower in the grafted side by 15% compared to the nongrafted side. Such changes in GABAA receptors suggest a significant, albeit partial, normalizing trend of cerebellar grafts on the state of postsynaptic supersensitive receptors in the host cerebellar nuclei.

Decreased IGF-I gene expression during the apoptosis of Purkinje cells in pcd mice

Insulin-like growth factor I (IGF-I) plays a potential functional role in cerebellar development in the rat, as indicated by its spatio-temporally coordinated expression with the IGF-I receptor (IGFR-I), IGF binding protein (IGFBP) 2 and 5 during the postnatal critical growth period. Although IGF-I promotes the survival of cultured cerebellar neurons, its role during cerebellar development in vivo is unclear. Growth factor deprivation has been shown to trigger apoptosis, the developmental cell death which, if abnormal, may lead to various pathological states. To understand the involvement of IGF-I in Purkinje cell survival, we examined mRNA expression of IGF-I, IGFR-I, IGFBP 2 and 5 in the Purkinje cell degeneration (pcd) mice. During pcd cerebellar development, Purkinje cells rapidly degenerate leading to their almost complete depletion by adult life. IGF system mRNA expression was studied during Purkinje cell death in the pcd mutants (pcd/pcd) at postnatal day (D) 11, 17, 24 and adult. At D11 and D17, no significant difference of the IGF-I system mRNA expression was observed between the normal and pcd/pcd cerebellum. At D24, a significant decrease of IGF-I mRNA was found in the apoptotic Purkinje cells in the pcd/pcd cerebellum, which was accompanied by a severe astrogliosis and activation of astrocytic IGF-I expression. In the adult pcd/pcd cerebellum, with few Purkinje cells remaining, many granule cells underwent apoptosis. In conclusion, decreased IGF-I mRNA expression was correlated with Purkinje cell apoptosis in pcd cerebellum. Whether the decrease of IGF-I mRNA expression is the cause or result of the Purkinje cell degeneration needs to be further elucidated.

The role of the insulin-like growth factors in the central nervous system

Increasing evidence strongly supports a role for insulin-like growth factor-I (IGF-I) in central nervous system (CNS) development. IGF-I, IGF-II, the type IIGF receptor (the cell surface tyrosine kinase receptor that mediates IGF signals), and some IGF binding proteins (IGFBPs; secreted proteins that modulate IGF actions) are expressed in many regions of the CNS beginning in utero. The expression pattern of IGF system proteins during brain growth suggests highly regulated and developmentally timed IGF actions on specific neural cell populations. IGF-I expression is predominantly in neurons and, in many brain regions, peaks in a fashion temporally coincident with periods in development when neuron progenitor proliferation and/or neuritic outgrowth occurs. In contrast, IGF-II expression is confined mainly to cells of mesenchymal and neural crest origin. While expression of type I IGF receptors appears ubiquitous, that of IGFBPs is characterized by regional and developmental specificity, and often occurs coordinately with peaks of IGF expression. In vitro IGF-I has been shown to stimulate the proliferation of neuron progenitors and/or the survival of neurons and oligodendrocytes, and in some cultured neurons, to stimulate function. Transgenic (Tg) mice that overexpress IGF-I in the brain exhibit postnatal brain overgrowth without anatomic abnormality (20-85% increases in weight, depending on the magnitude of expression). In contrast, Tg mice that exhibit ectopic brain expression of IGFBP-1, an inhibitor of IGF action when present in molar excess, manifest postnatal brain growth retardation, and mice with ablated IGF-I gene expression, accomplished by homologous recombination, have brains that are 60% of normal size as adults. Taken together, these in vivo studies indicate that IGF-I can influence the development of most, if not all, brain regions, and suggest that the cerebral cortex and cerebellum are especially sensitive to IGF-I actions. IGF-I's growth-promoting in vivo actions result from its capacity to increase neuron number, at least in certain populations, and from its potent stimulation of myelination. These IGF-I actions, taken together with its neuroprotective effects following CNS and peripheral nerve injury, suggest that it may be of therapeutic benefit in a wide variety of disorders affecting the nervous system.

Neuronal progenitors as tools for cell replacement in the nervous system

The clinical prospect of using neural precursor cells for reconstructive approaches in the nervous system has received strong impetus from a recent series of important experimental findings. Transplantation studies in the developing brain have demonstrated that migration and differentiation of neural precursor cells are regulated predominantly by environmental signals. Several observations suggest that the mature CNS retains at least some of these guidance cues. These findings, together with recent evidence for the persistence of neural stem cells in the adult mammalian brain, have made precursor cell recruitment a new focus in CNS reconstruction.

The cerebellar model of neural grafting: structural integration and functional recovery

A synopsis is presented of the recent history of cerebellar tissue transplantation over the past 25 years. The properties of growth and differentiation of cerebellar grafts placed intraocularly or intracranially are reviewed, as well as the interaction of heterotopic and orthotopic grafts with the host brain. Particular emphasis is placed on the use of ataxic mouse mutants as recipients of donor cerebellar tissue for the correction of their structural deficits and the functional recovery of behavioural responses.