Cellular and functional recovery of Parkinsonian rats after intrastriatal transplantation of carotid body cell aggregates

Protection and Repair of the Nigrostriatal Pathway with Stem-Cell-Derived Carotid Body Glomus Cell Transplants in Chronic MPTP Parkinsonian Model

Antiparkinsonian carotid body (CB) cell therapy has been proven to be effective in rodent and nonhuman primate models of Parkinson’s disease (PD), exerting trophic protection and restoration of the dopaminergic nigrostriatal pathway. These neurotrophic actions are mediated through the release of high levels of glial-cell-line-derived neurotrophic factor (GDNF) by the CB transplant. Pilot clinical trials have also shown that CB autotransplantation can improve motor symptoms in PD patients, although its effectiveness is affected by the scarcity of the grafted tissue. Here, we analyzed the antiparkinsonian efficacy of in vitro-expanded CB dopaminergic glomus cells. Intrastriatal xenografts of rat CB neurospheres were shown to protect nigral neurons from degeneration in a chronic MPTP mouse PD model. In addition, grafts performed at the end of the neurotoxic treatment resulted in the repair of striatal dopaminergic terminals through axonal sprouting. Interestingly, both neuroprotective and reparative effects induced by in vitro-expanded CB cells were similar to those previously reported by the use of CB transplants. This action could be explained because stem-cell-derived CB neurospheres produce similar amounts of GDNF compared to native CB tissue. This study provides the first evidence that in vitro-expanded CB cells could be a clinical option for cell therapy in PD.

Carotid Body and Cell Therapy

During the past decade, the carotid body (CB) has been considered an innovative therapeutic target for the treatment of certain cardiorespiratory and metabolic diseases most of which are sympathetically mediated. It has recently been revealed that CB stem cells provide new target sites for the development of promising cell-based therapies. Specifically, generation of CB progenitors in vitro which can differentiate into functionally active glomus cells may be a useful procedure to produce the cell mass required for replacement cell therapy. Due to their dopaminergic nature, adult glomus cells can be used for an intrastriatal grafting in neurodegenerative brain disorders including Parkinson's disease. The beneficial effect of throphic factors such as glial cell-derived neurotrophic factor synergistically released by the transplanted cells then enables the transplant to survive. Likewise, intracerebral administration of CB cell aggregates or dispersed cells has been tested for the treatment of an experimental model of stroke. The systematic clinical applicability of CB autotransplants following glomectomy in humans is under investigation. In such autotransplantation studies, cell aggregates from unilaterally resected CB might be used as autografts. In addition, stem cells could offer an opportunity for tissue expansion and might settle the issue of small number of glomus cells available for transplantation.

Cellular basis of learning and memory in the carotid body

The carotid body is the primary peripheral chemoreceptor in the body, and critical for respiration and cardiovascular adjustments during hypoxia. Yet considerable evidence now implicates the carotid body as a multimodal sensor, mediating the chemoreflexes of a wide range of physiological responses, including pH, temperature, and acidosis as well as hormonal, glucose and immune regulation. How does the carotid body detect and initiate appropriate physiological responses for these diverse stimuli? The answer to this may lie in the structure of the carotid body itself. We suggest that at an organ-level the carotid body is comparable to a miniature brain with compartmentalized discrete regions of clustered glomus cells defined by their neurotransmitter expression and receptor profiles, and with connectivity to defined reflex arcs that play a key role in initiating distinct physiological responses, similar in many ways to a switchboard that connects specific inputs to selective outputs. Similarly, within the central nervous system, specific physiological outcomes are co-ordinated, through signaling via distinct neuronal connectivity. As with the brain, we propose that highly organized cellular connectivity is critical for mediating co-ordinated outputs from the carotid body to a given stimulus. Moreover, it appears that the rudimentary components for synaptic plasticity, and learning and memory are conserved in the carotid body including the presence of glutamate and GABAergic systems, where evidence pinpoints that pathophysiology of common diseases of the carotid body may be linked to deviations in these processes. Several decades of research have contributed to our understanding of the central nervous system in health and disease, and we discuss that understanding the key processes involved in neuronal dysfunction and synaptic activity may be translated to the carotid body, offering new insights and avenues for therapeutic innovation.

Are Cell-Based Therapies Safe and Effective in the Treatment of Neurodegenerative Diseases? A Systematic Review with Meta-Analysis

Over the past two decades, significant advances have been made in the field of regenerative medicine. However, despite being of the utmost clinical urgency, there remains a paucity of therapeutic strategies for conditions with substantial neurodegeneration such as (progressive) multiple sclerosis (MS), spinal cord injury (SCI), Parkinson's disease (PD) and Alzheimer's disease (AD). Different cell types, such as mesenchymal stromal cells (MSC), neuronal stem cells (NSC), olfactory ensheathing cells (OEC), neurons and a variety of others, already demonstrated safety and regenerative or neuroprotective properties in the central nervous system during the preclinical phase. As a result of these promising findings, in recent years, these necessary types of cell therapies have been intensively tested in clinical trials to establish whether these results could be confirmed in patients. However, extensive research is still needed regarding elucidating the exact mechanism of action, possible immune rejection, functionality and survival of the administered cells, dose, frequency and administration route. To summarize the current state of knowledge, we conducted a systematic review with meta-analysis. A total of 27,043 records were reviewed by two independent assessors and 71 records were included in the final quantitative analysis. These results show that the overall frequency of serious adverse events was low: 0.03 (95% CI: 0.01-0.08). In addition, several trials in MS and SCI reported efficacy data, demonstrating some promising results on clinical outcomes. All randomized controlled studies were at a low risk of bias due to appropriate blinding of the treatment, including assessors and patients. In conclusion, cell-based therapies in neurodegenerative disease are safe and feasible while showing promising clinical improvements. Nevertheless, given their high heterogeneity, the results require a cautious approach. We advocate for the harmonization of study protocols of trials investigating cell-based therapies in neurodegenerative diseases, adverse event reporting and investigation of clinical outcomes.

Long-term exposure to GDNF induces dephosphorylation of Ret, AKT, and ERK1/2, and is ineffective at protecting midbrain dopaminergic neurons in cellular models of Parkinson's disease

Glial cell line-derived neurotrophic factor (GDNF) promotes differentiation, proliferation, and survival in different cell types, including dopaminergic neurons. Thus, GDNF has been proposed as a promising neuroprotective therapy in Parkinson's disease. Although findings from cellular and animal models of Parkinson's disease were encouraging, results emerging from clinical trials were not as good as expected, probably due to the inappropriate administration protocols. Despite the growing information on GDNF action mechanisms, many aspects of its pharmacological effects are still unclear and data from different studies are still contradictory. Considering that GDNF action mechanisms are mediated by its receptor tyrosine kinase Ret, which activates PI3K/AKT and MAPK/ERK signaling pathways, we aimed to investigate Ret activation and its effect over both signaling pathways in midbrain cell cultures treated with GDNF at different doses (0.3, 1, and 10 ng/ml) and times (15 min, 24 h, 24 h (7 days), and 7 continuous days). The results showed that short-term or acute (15 min, 24 h, and 24 h (7 days)) GDNF treatment in rat midbrain neurons increases Tyrosine hydroxylase (TH) expression and the phosphorylation levels of Ret (Tyr 1062), AKT (Ser 473), ERK1/2 (Thr202/Tyr204), S6 (Ser 235/236), and GSK3-β (Ser 9). However, the phosphorylation level of these kinases, TH expression, and dopamine uptake, decreased below basal levels after long-term or prolonged treatment with 1 and 10 ng/ml GDNF (7 continuous days). Our data suggest that long-term GDNF treatment inactivates the receptor by an unknown mechanism, affecting its neuroprotective capacity against degeneration caused by 6-OHDA or rotenone, while short-term exposure to GDNF promoted dopaminergic cell survival. These findings highlight the need to find new and more effective long-acting therapeutic approaches for disorders in which GDNF plays a beneficial role, including Parkinson's disease. In this regard, it is necessary to propose new GDNF treatment guidelines to regulate and control its long-term expression levels and optimize the clinical use of this trophic factor in patients with Parkinson's disease.

Implantation of glial cell line-derived neurotrophic factor-expressing adipose tissue-derived stromal cells in a rat Parkinson's disease model

In previous studies, the effects of glial cell line-derived neurotrophic factor (GDNF) expressing adipose tissue-derived stromal cells (ADSCs) on Parkinson's disease (PD) models have been studied but have not been elucidated. The present study aims to investigate this phenomenon and trace their differentiation in vivo. In our study, ADSCs were harvested from adult Sprague-Dawley rats, then genetically modified into GDNF-expressing system by lentivirus. The secretion of GDNF from the transduced cells was titrated by enzyme-linked immunosorbent assay (ELISA). Cellular differentiation in vitro was observed after induction. To examine survival and differentiation in vivo, they were injected into the striatum of 6-hydroxydopamine-lesioned rats, whose apomorphine-induced rotations were examined 2, 7, 14 and 21d after grafting. It's found that GDNF-expressing ADSCs can differentiate into neuron-like cells in vitro. Moreover, engrafted GDNF-expressing ADSCs survived at least 90 days post-grafting and differentiated into dopaminergic neuron-like cells. Most importantly, these cells drastically improved the clinical symptoms of PD rats. In conclusion, ADSCs can be efficiently engineered by lentivirus system and deliver a therapeutic level of the transgene to target tissues. GDNF-ADSCs can improve behavior phenotype in the rat PD model. Moreover, ADSCs is a more readily available source of dopaminergic neurons, though a more effective procedure needs to be developed to enrich the number of differentiation.

The carotid body: a physiologically relevant germinal niche in the adult peripheral nervous system

Oxygen constitutes a vital element for the survival of every single cell in multicellular aerobic organisms like mammals. A complex homeostatic oxygen-sensing system has evolved in these organisms, including detectors and effectors, to guarantee a proper supply of the element to every cell. The carotid body represents the most important peripheral arterial chemoreceptor organ in mammals and informs about hypoxemic situations to the effectors at the brainstem cardiorespiratory centers. To optimize organismal adaptation to maintained hypoxemic situations, the carotid body has evolved containing a niche of adult tissue-specific stem cells with the capacity to differentiate into both neuronal and vascular cell types in response to hypoxia. These neurogenic and angiogenic processes are finely regulated by the niche and by hypoxia itself. Our recent data on the cellular and molecular mechanisms underlying the functioning of this niche might help to comprehend a variety of different diseases coursing with carotid body failure, and might also improve our capacity to use these stem cells for the treatment of neurological disease. Herein, we review those data about the recent characterization of the carotid body niche, focusing on the study of the phenotype and behavior of multipotent stem cells within the organ, comparing them with other well-documented neural stem cells within the adult nervous system.

Long-term immunosuppression for CNS mouse xenotransplantation: Effects on nigrostriatal neurodegeneration and neuroprotective carotid body cell therapy

BACKGROUND

The use of long-term immunosuppressive treatments on neural transplantation has been controversial during the last decades. Although nowadays there is a consensus about the necessity of maintaining a permanent state of immunosuppression to preserve the survival of cerebral grafts, little is known about the effects that chronic immunosuppression produces both on the neurodegenerative process and on transplants function.

METHODS

Here, we establish a new immunosuppressive protocol, based on the discontinuous administration of CsA (15 mg/kg; s.c.) and prednisone (20 mg/kg; s.c.), to produce long-term immunosuppression in mice. Using this treatment, we analyse the effects that long-term immunosuppression induces in a chronic 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP) model of parkinsonism and on the neuroprotective and neurorestorative anti-parkinsonian actions exerted by rat carotid body (CB) xenografts.

RESULTS

This protocol preserves the survival of rat CB xenotransplants maintaining the general wellness of the grafted mice. Although permanent immunosuppression does not prevent the MPTP-induced cell death of nigral neurons and the consequent degeneration of dopaminergic striatal innervation, allowing for its use as Parkinson's disease (PD) model, it reduces the microglial activation and slightly declines the striatal damage. Moreover, we reported that chronic administration of immunosuppressant drugs does not alter the neuroprotective and restorative anti-parkinsonian actions of rat CB xenografts into parkinsonian mice.

CONCLUSIONS

This new immunosuppressive protocol provides a new murine model to assay the long-term effects of cerebral xenografts and offer a pharmacological alternative to the commonly used genetic immunodeficient mice, allowing the use of genetically modified mice as hosts. In addition, it will permit the experimental analysis of the effects produced by human CB xenografts in the chronic PD murine model, with the final aim of using CB allografts as an option of cell therapy in PD patients.

Striking parallels between carotid body glomus cell and adrenal chromaffin cell development

Carotid body glomus cells mediate essential reflex responses to arterial blood hypoxia. They are dopaminergic and secrete growth factors that support dopaminergic neurons, making the carotid body a potential source of patient-specific cells for Parkinson's disease therapy. Like adrenal chromaffin cells, which are also hypoxia-sensitive, glomus cells are neural crest-derived and require the transcription factors Ascl1 and Phox2b; otherwise, their development is little understood at the molecular level. Here, analysis in chicken and mouse reveals further striking molecular parallels, though also some differences, between glomus and adrenal chromaffin cell development. Moreover, histology has long suggested that glomus cell precursors are ‘émigrés’ from neighbouring ganglia/nerves, while multipotent nerve-associated glial cells are now known to make a significant contribution to the adrenal chromaffin cell population in the mouse. We present conditional genetic lineage-tracing data from mice supporting the hypothesis that progenitors expressing the glial marker proteolipid protein 1, presumably located in adjacent ganglia/nerves, also contribute to glomus cells. Finally, we resolve a paradox for the ‘émigré’ hypothesis in the chicken - where the nearest ganglion to the carotid body is the nodose, in which the satellite glia are neural crest-derived, but the neurons are almost entirely placode-derived - by fate-mapping putative nodose neuronal 'émigrés' to the neural crest.

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Glomus cell precursors express the neuron-specific marker Elavl3/4 (HuC/D).

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Developing glomus cells express multiple ‘sympathoadrenal' genes.

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Glomus cell development requires Hand2 and Sox4/11, but not Ret or Tfap2b.

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Multipotent progenitors with a glial phenotype contribute to glomus cells.

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Fate-mapping resolves a paradox for the ganglionic 'émigré' hypothesis in birds.

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

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

GDNF-based therapies, GDNF-producing interneurons, and trophic support of the dopaminergic nigrostriatal pathway. Implications for Parkinson's disease

The glial cell line-derived neurotrophic factor (GDNF) is a well-established trophic agent for dopaminergic (DA) neurons in vitro and in vivo. GDNF is necessary for maintenance of neuronal morphological and neurochemical phenotype and protects DA neurons from toxic damage. Numerous studies on animal models of Parkinson’s disease (PD) have reported beneficial effects of GDNF on nigrostriatal DA neuron survival. However, translation of these observations to the clinical setting has been hampered so far by side effects associated with the chronic continuous intra-striatal infusion of recombinant GDNF. In addition, double blind and placebo-controlled clinical trials have not reported any clinically relevant effect of GDNF on PD patients. In the past few years, experiments with conditional Gdnf knockout mice have suggested that GDNF is necessary for maintenance of DA neurons in adulthood. In parallel, new methodologies for exogenous GDNF delivery have been developed. Recently, it has been shown that a small population of scattered, electrically interconnected, parvalbumin positive (PV+) GABAergic interneurons is responsible for most of the GDNF produced in the rodent striatum. In addition, cholinergic striatal interneurons appear to be also involved in the modulation of striatal GDNF. In this review, we summarize current knowledge on brain GDNF delivery, homeostasis, and its effects on nigrostriatal DA neurons. Special attention is paid to the therapeutic potential of endogenous GDNF stimulation in PD.

Neurotrophic Properties, Chemosensory Responses and Neurogenic Niche of the Human Carotid Body

The carotid body (CB) is a polymodal chemoreceptor that triggers the hyperventilatory response to hypoxia necessary for the maintenance of O(2) homeostasis essential for the survival of organs such as the brain or heart. Glomus cells, the sensory elements in the CB, are also sensitive to hypercapnia, acidosis and, although less generally accepted, hypoglycemia. Current knowledge on CB function is mainly based on studies performed on lower mammals, but the information on the human CB is scant. Here we describe the structure, neurotrophic properties, and cellular responses to hypoxia and hypoglycemia of CBs dissected from human cadavers. The adult CB parenchyma contains clusters of chemosensitive glomus (type I) and sustentacular (type II) cells as well as nestin-positive progenitor cells. This organ also expresses high levels of the dopaminotrophic glial cell line-derived neurotrophic factor (GDNF). GDNF production and the number of progenitor and glomus cells were preserved in the CBs of human subjects of advanced age. As reported for other mammalian species, glomus cells responded to hypoxia by external Ca(2+)-dependent increase of cytosolic [Ca(2+)] and quantal catecholamine release. Human glomus cells are also responsive to hypoglycemia and together the two stimuli, hypoxia and hypoglycemia, can potentiate each other's effects. The chemo-sensory responses of glomus cells are also preserved at an advanced age. Interestingly, a neurogenic niche similar to that recently described in rodents is also preserved in the adult human CB. These new data on the cellular and molecular physiology of the CB pave the way for future pathophysiological studies involving this organ in humans.

Cell based therapies in Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disorder after Alzheimer’s disease. It is characterized by bradykinesia, hypokinesia/ akinesia, rigidity, tremor, and postural instability, caused by dopaminergic (DA) striatal denervation. The prevalence of PD increases from 50 years of age with steep rise after age 60 years. Current treatment of PD relies heavily on replacing lost dopamine either with its precursor L-dopa or dopamine agonists (ropinirole, pramipexole, bromocriptine, lisuride etc). Other pharmacological measures like catechol-O-methyltrasferase (COMT) inhibitors like entacopone, telcapone and monoamine oxidase B (MAO-B) inhibitors like selegiline and rasagiline are also useful, while L-dopa remains the gold standard in the treatment of PD. Emerging therapies are focusing on cell based therapeutics derived from various sources.

The systemic administration of oleoylethanolamide exerts neuroprotection of the nigrostriatal system in experimental Parkinsonism

Oleoylethanolamide (OEA) is an agonist of the peroxisome proliferator-activated receptor α (PPARα) and has been described to exhibit neuroprotective properties when administered locally in animal models of several neurological disorder models, including stroke and Parkinson's disease. However, there is little information regarding the effectiveness of systemic administration of OEA on Parkinson's disease. In the present study, OEA-mediated neuroprotection has been tested on in vivo and in vitro models of 6-hydroxydopamine (6-OH-DA)-induced degeneration. The in vivo model was based on the intrastriatal infusion of the neurotoxin 6-OH-DA, which generates Parkinsonian symptoms. Rats were treated 2 h before and after the 6-OH-DA treatment with systemic OEA (0.5, 1, and 5 mg/kg). The Parkinsonian symptoms were evaluated at 1 and 4 wk after the development of lesions. The functional status of the nigrostriatal system was studied through tyrosine-hydroxylase (TH) and hemeoxygenase-1 (HO-1, oxidation marker) immunostaining as well as by monitoring the synaptophysin content. In vitro cell cultures were also treated with OEA and 6-OH-DA. As expected, our results revealed 6-OH-DA induced neurotoxicity and behavioural deficits; however, these alterations were less severe in the animals treated with the highest dose of OEA (5 mg/kg). 6-OH-DA administration significantly reduced the striatal TH-immunoreactivity (ir) density, synaptophysin expression, and the number of nigral TH-ir neurons. Moreover, 6-OH-DA enhanced striatal HO-1 content, which was blocked by OEA (5 mg/kg). In vitro, 0.5 and 1 μM of OEA exerted significant neuroprotection on cultured nigral neurons. These effects were abolished after blocking PPARα with the selective antagonist GW6471. In conclusion, systemic OEA protects the nigrostriatal circuit from 6-OH-DA-induced neurotoxicity through a PPARα-dependent mechanism.

Cellular properties and chemosensory responses of the human carotid body

The carotid body (CB) is the major peripheral arterial chemoreceptor in mammals that mediates the acute hyperventilatory response to hypoxia. The CB grows in response to sustained hypoxia and also participates in acclimatisation to chronic hypoxaemia. Knowledge of CB physiology at the cellular level has increased considerably in recent times thanks to studies performed on lower mammals, and rodents in particular. However, the functional characteristics of human CB cells remain practically unknown. Herein, we use tissue slices or enzymatically dispersed cells to determine the characteristics of human CB cells. The adult human CB parenchyma contains clusters of chemosensitive glomus (type I) and sustentacular (type II) cells as well as nestin-positive progenitor cells. This organ also expresses high levels of the dopaminotrophic glial cell line-derived neurotrophic factor (GDNF). We found that GDNF production and the number of progenitor and glomus cells were preserved in the CBs of human subjects of advanced age. Moreover, glomus cells exhibited voltage-dependent Na(+), Ca(2+) and K(+) currents that were qualitatively similar to those reported in lower mammals. These cells responded to hypoxia with an external Ca(2+)-dependent increase of cytosolic Ca(2+) and quantal catecholamine secretion, as reported for other mammalian species. Interestingly, human glomus cells are also responsive to hypoglycaemia and together these two stimuli can potentiate each other's effects. The chemosensory responses of glomus cells are also preserved at an advanced age. These new data on the cellular and molecular physiology of the CB pave the way for future pathophysiological studies involving this organ in humans.

Cografting of carotid body cells improves the long-term survival, fiber outgrowth and functional effects of grafted dopaminergic neurons

AIMS

A major limiting factor for cell therapy in Parkinson's disease is that the survival of grafted dopaminergic neurons is very poor, which may be improved by administration of GDNF, for which the carotid body is a good source.

MATERIALS & METHODS

Rats with total unilateral dopaminergic denervation were grafted with a cell suspension of rat dopaminergic neuroblasts with or without cell aggregates from the rat carotid body. At 1, 2 and 3 months after grafting, the rats were tested in the cylinder and the rotometer and killed 4 months after grafting.

RESULTS

We observed that the survival of dopaminergic neurons and graft-derived dopaminergic innervation were higher in rats that received mixed grafts. Both grafted groups showed complete recovery in the amphetamine-induced rotation test. However, rats with cografts performed significantly better in the cylinder test.

CONCLUSION

Cografting of carotid body cells may constitute a useful strategy for cell therapy in Parkinson's disease.

Stem cells and regenerative therapies for Parkinson's disease

Currently the mainstay of Parkinson's disease (PD) therapy is the pharmacological replacement of the loss of the dopaminergic nigrostriatal pathway using drugs such as dopamine agonists and levodopa. Whilst these drugs effectively ameliorate some of the motor features of PD, they do not improve many of the nonmotor features that arise secondary to pathology outside of this system, nor do they slow the progressive neurodegeneration that is a characteristic of the disease. Regenerative therapies for PD seek to fill this therapeutic gap, with cell transplantation being the most explored approach to date. A number of different cell sources have been used in this therapeutic approach, but to date, the most successful has been the use of fetal ventral mesencephalic (VM) tissue that contains within it the developing nigral dopaminergic cells. Cell transplantation for PD was pioneered in the 1980-1990s, with several successful open-label trials of fetal VM transplantation in patients with relatively advanced PD. Whilst these findings were not replicated in two subsequent double-blind sham-surgery controlled trials, there were reasons to explain this outside of the one drawn at the time that these therapies are ineffective. Indeed all these studies have provided evidence that following the transplantation of fetal VM tissue, dopaminergic cells can survive long term, produce dopamine, and bring about clinical improvements in younger patients over many years. The use of fetal tissue, irrespective of its true efficacy, will never become a widely available therapy for PD for a host of practical and ethical reasons, and thus much work has been put in recently to exploring the utility of stem cells as a source of nigral dopaminergic neurons. In this respect, the advent of embryonic stem cell and induced pluripotent cells has heralded a new era in cell therapy for PD, and several groups have now demonstrated that these cells can form dopaminergic neurons which improve functional deficits in animal models of PD. Whilst encouraging, problems with respect to the immunogenicity and tumorigenicity of these cells means that they will need to be used in the clinic cautiously. Other regenerative therapies in PD have been tried over the years and include the use of trophic factors. This has primarily involved glial cell line-derived neurotrophic factor (GDNF) and again has produced mixed clinical effects, and in order to try and resolve this, a new trial of intraputamenal GDNF is now being planned. In addition, a new trial for platelet derived growth factor as a treatment for PD has just completed recruitment, and PYM50028 (Cogane) an oral agent shown in animal models to reduce the effects of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) lesioning by the induction of growth factors is currently under investigation in a multicentre Phase II trial. Overall, there are a number of promising new regenerative therapies being developed and tested in PD, although the true long-term efficacy of any of these in large numbers of patients is still not known.

The immunological challenges of cell transplantation for the treatment of Parkinson's disease

Dopaminergic cell transplantation is an experimental therapy for Parkinson's disease (PD). It has many potential theoretical advantages over current treatment strategies such as providing continuous local dopaminergic replenishment, eliminating motor fluctuations and medication-induced dyskinesias, slowing down disease progression or even reversing disease pathology in the host. Recent studies also show that dopaminergic cell transplants provide long-term neuromodulation in the basal ganglia that simulates the combined effects of oral dopaminergic therapy and surgical therapies like deep brain stimulation, the contemporary therapeutic approach to advanced PD. However, dopaminergic cell transplantation in PD as not been optimized and current experimental techniques have many drawbacks. In published experiments to date of attempted dopaminergic grafting in PD, the major challenges are unacceptable graft-induced dyskinesias or failure of such grafts to exceed the benefits afforded by sham surgery. A deleterious host immune response to the transplant has been implicated as a major putative cause for these adverse outcomes. This article focuses on recent advances in understanding the immunology of the transplantation in PD and possible methods to overcome adverse events such that we could translate cell replacement strategies into viable clinical treatments in the future.

Peripheral chemoreceptors: function and plasticity of the carotid body

The discovery of the sensory nature of the carotid body dates back to the beginning of the 20th century. Following these seminal discoveries, research into carotid body mechanisms moved forward progressively through the 20th century, with many descriptions of the ultrastructure of the organ and stimulus-response measurements at the level of the whole organ. The later part of 20th century witnessed the first descriptions of the cellular responses and electrophysiology of isolated and cultured type I and type II cells, and there now exist a number of testable hypotheses of chemotransduction. The goal of this article is to provide a comprehensive review of current concepts on sensory transduction and transmission of the hypoxic stimulus at the carotid body with an emphasis on integrating cellular mechanisms with the whole organ responses and highlighting the gaps or discrepancies in our knowledge. It is increasingly evident that in addition to hypoxia, the carotid body responds to a wide variety of blood-borne stimuli, including reduced glucose and immune-related cytokines and we therefore also consider the evidence for a polymodal function of the carotid body and its implications. It is clear that the sensory function of the carotid body exhibits considerable plasticity in response to the chronic perturbations in environmental O2 that is associated with many physiological and pathological conditions. The mechanisms and consequences of carotid body plasticity in health and disease are discussed in the final sections of this article.

Cell-based therapies for Parkinson's disease

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

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

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

Cells therapy for Parkinson's disease--so close and so far away

One of the strategies of treating Parkinson's disease (PD) is the replacement of lost neurons in the substantia nigra with healthy dapamingergic cells. Potential sources for cells range from autologous grafts of dopamine secreting cells, fetal ventral mesencephalon tissue, to various stem cell types. Over the past quarter century, many experimental replacement therapies have been tried on PD animal models as well as human patients, yet none resulted in satisfactory outcomes that warrant wide applications. Recent progress in stem cell biology has shown that nuclear transfer embryonic stem cells (ntES) or induced pluripotent stem cells (iPS) derived cells can be used to successfully treat rodent PD models, thus solving the problem of immunorejection and paving the way for future autologous transplantations for treating PD. Meanwhile, however, post mortem analysis of patients who received fetal brain cell transplantation revealed that implanted cells are prone to degeneration just like endogenous neurons in the same pathological area, indicating long-term efficacy of cell therapy of PD needs to overcome the degenerating environment in the brain. A better understanding of neurodegeneration in the midbrain appeared to be a necessary step in developing new cell therapies in Parkinson's disease. It is likely that future cell replacement will focus on not only ameliorating symptoms of the disease but also trying to slow the progression of the disease by either neuroprotection or restoring the micro-environment in the midbrain.

The neuroprotective effect of dental pulp cells in models of Alzheimer's and Parkinson's disease

Aim of the present study was to investigate the neuroprotective effect of dental pulp cells (DPCs) in in vitro models of Alzheimer and Parkinson disease. Primary cultures of hippocampal and ventral mesencephalic neurons were treated for 24 h with amyloid beta (Abeta(1-42)) peptide 1-42 and 6-OHDA, respectively. DPCs isolated from adult rat incisors were previously cultured in tissue culture inserts and added to the neuron cultures 2 days prior to neurotoxin treatment. Cell viability was assessed by the MTT assay. The co-culture with DPCs significantly attenuated 6-OHDA and Abeta(1-42)-induced toxicity in primary cultures of mesencephalic and hippocampal neurons, and lead to an increase in neuronal viability in untreated cultures, suggesting a neurotrophic effect in both models. Furthermore, human dental pulp cells expressed a neuronal phenotype and produced the neurotrophic factors NGF, GDNF, BDNF, and BMP2 shown by microarray screening and antibody staining for the representative proteins. DPCs protected primary neurons in in vitro models of Alzheimer's and Parkinson's disease and can be viewed as possible candidates for studies on cell-based therapy.

Advances in gene therapy for movement disorders

After nearly 20 years of preclinical experimentation with various gene delivery approaches in animal models of Parkinson's disease (PD), clinical trials are finally underway. The risk/benefit ratio for these procedures is now generally considered acceptable under approved protocols. The current vehicle for gene delivery to the human brain is recombinant adeno-associated viral vector, which is nonpathogenic and non-self-amplifying. Candidate genes tested in PD patients encode 1) glutamic acid decarboxylase, which is injected into the subthalamic nucleus to catalyze biosynthesis of the inhibitory neurotransmitter gamma-aminobutyric acid and so essentially mimic deep brain stimulation of this nucleus; 2) aromatic l-amino acid decarboxylase, which converts l-dopa to dopamine; and 3) neurturin, a member of the glial cell line-derived neurotrophic factor family. Unraveling the genetic underpinnings of PD could allow gene therapy to go beyond modulating neurotransmission or providing trophic effects to dopaminergic neurons by delivering a specific missing or defective gene. For example, the parkin gene (PARK2) is linked to recessively inherited PD due to loss of function mutations; it prevents alpha-synuclein-induced degeneration of nigral dopaminergic neurons in rats and nonhuman primates. On the other hand, for dominantly inherited Huntington's disease (HD), in which an expanded polyglutamine tract imparts to the protein huntingtin a toxic gain of function, repressing expression of the mutant allele in the striatum using RNA interference technology mitigates pathology and delays the phenotype in a mouse model. Here we review the current state of preclinical and clinical gene therapy studies conducted in PD and HD.

Glia-like stem cells sustain physiologic neurogenesis in the adult mammalian carotid body

Neurogenesis is known to occur in the specific niches of the adult mammalian brain, but whether germinal centers exist in the neural-crest-derived peripheral nervous system is unknown. We have discovered stem cells in the adult carotid body (CB), an oxygen-sensing organ of the sympathoadrenal lineage that grows in chronic hypoxemia. Production of new neuron-like CB glomus cells depends on a population of stem cells, which form multipotent and self-renewing colonies in vitro. Cell fate mapping experiments indicate that, unexpectedly, CB stem cells are the glia-like sustentacular cells and can be identified using glial markers. Remarkably, stem cell-derived glomus cells have the same complex chemosensory properties as mature in situ glomus cells. They are highly dopaminergic and produce glial cell line-derived neurotrophic factor. Thus, the mammalian CB is a neurogenic center with a recognizable physiological function in adult life. CB stem cells could be potentially useful for antiparkinsonian cell therapy.

The search for a curative cell therapy in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder, characterised by the progressive loss of dopaminergic neurons in the substantia nigra, and typically treated by dopamine replacement. This treatment, although very effective in the early stages of the disease, is not curative and has side-effects. As such there has been a search for a more definitive treatment for this condition, which has mainly concentrated on replacing the lost neurons with neural grafts. Possible cell sources for replacement range from autologous grafts of dopamine secreting cells to allografts of fetal ventral mesencephalon and neural precursor cells derived from fetal tissue or embryonic stem cells. Some of these cells have been the subject of clinical trials, which to date have produced disparate outcomes. Therefore, whilst cell therapies remain a promising treatment for PD, there is need for further refinement of the techniques involved in this experimental procedure, before any new trials in patients are undertaken.

The future of cell therapies in the treatment of Parkinson's disease

Parkinson's disease (PD) is a common neurological disorder of the brain which has as a part of its core pathology the progressive degeneration of the dopaminergic nigrostriatal pathway. Therefore, cell therapies that aim to restore this degenerated dopaminergic network represent a promising strategy in helping to cure PD. In this review, the authors start by discussing the progress of research on the use of fetal ventral mesencephalic (VM) tissue in transplantation therapies in PD, both from the clinical and experimental perspectives. Then the issues pertinent to its adoption in the clinic are discussed, including the ethical and practical problems with its use, the varied composition of VM tissue that is implanted with the graft and how this may account for some of the problems seen in the clinical trials using this tissue, especially graft-induced dyskinesia. Finally other promising sources of tissue for PD cell therapy are described, including mesenchymal and embryonic stem cells, before concluding on what is the best approach to the cellular repair of the parkinsonian brain.

Human embryonic stem cell-derived neural precursors as a continuous, stable, and on-demand source for human dopamine neurons

Human embryonic stem (hES) cells can be guided to differentiate into ventral midbrain-type neural precursor (NP) cells that proliferate in vitro by specific mitogens. We investigated the potential of these NP cells derived from hES cells (hES-NP) for the large-scale generation of human dopamine (DA) neurons for functional analyses and therapeutic applications. To address this, hES-NP cells were expanded in vitro for 1.5 months with six passages, and their proliferation and differentiation properties determined over the NP passages. Interestingly, the total hES-NP cell number was increased by > 2 x 10(4)-folds over the in vitro period without alteration of phenotypic gene expression. They also sustained their differentiation capacity toward neuronal cells, exhibiting in vitro pre-synaptic DA neuronal functionality. Furthermore, the hES-NP cells can be cryopreserved without losing their proliferative and developmental potential. Upon transplantation into a Parkinson's disease rat model, the multi-passaged hES-NP cells survived, integrated into the host striatum, and differentiated toward the neuronal cells expressing DA phenotypes. A significant reduction in the amphetamine-induced rotation score of Parkinson's disease rats was observed by the cell transplantation. Taken together, these findings indicate that hES-NP cell expansion is exploitable for a large-scale generation of experimental and transplantable DA neurons of human-origin.

Carotid body autotransplantation in Parkinson disease: a clinical and positron emission tomography study

BACKGROUND

Carotid body (CB) glomus cells are highly dopaminergic and express the glial cell line derived neurotrophic factor. The intrastriatal grafting of CB cell aggregates exerts neurotrophic actions on nigrostriatal neurons in animal models of Parkinson disease (PD).

OBJECTIVE

We conducted a phase I-II clinical study to assess the feasibility, long term safety, clinical and neurochemical effects of intrastriatal CB autotransplantation in patients with PD.

METHODS

Thirteen patients with advanced PD underwent bilateral stereotactic implantation of CB cell aggregates into the striatum. They were assessed before surgery and up to 1-3 years after surgery according to CAPIT (Core Assessment Programme for Intracerebral Transplantation) and CAPSIT-PD (Core Assessment Programme for Surgical Interventional Therapies in Parkinson's Disease) protocols. The primary outcome measure was the change in video blinded Unified Parkinson's Disease Rating Scale III score in the off-medication state. Seven patients had 18F-dopa positron emission tomography scans before and 1 year after transplantation.

RESULTS

Clinical amelioration in the primary outcome measure was observed in 10 of 12 blindly analysed patients, which was maximal at 6-12 months after transplantation (5-74%). Overall, mean improvement at 6 months was 23%. In the long term (3 years), 3 of 6 patients still maintained improvement (15-48%). None of the patients developed off-period dyskinesias. The main predictive factors for motor improvement were the histological integrity of the CB and a milder disease severity. We observed a non-significant 5% increase in mean putaminal 18F-dopa uptake but there was an inverse relationship between clinical amelioration and annual decline in putaminal 18F-dopa uptake (r = -0.829; p = 0.042).

CONCLUSIONS

CB autotransplantation may induce clinical effects in patients with advanced PD which seem partly related to the biological properties of the implanted glomus cells.

Transplantation of immortalized mesencephalic progenitors (CSM14.1 cells) into the neonatal parkinsonian rat caudate putamen

The present study analyzed whether grafts of the mesencephalic progenitor cell line CSM14.1 into the neonatal rat caudate putamen (CPu) differentiate into neurons and whether this is accompanied by a functional improvement in 6-hydroxydopamine (6-OHDA)-lesioned animals. As in previous studies, a neuronal differentiation of CSM14.1 cells transplanted into the CPu of adult animals could not be observed, so we here used neonatal rats, because graft location and host age seemingly are crucial parameters for neural transplant differentiation and integration. Rats bilaterally lesioned at postnatal day 1 by intraventricular 6-OHDA-injections 2 days later received 100,000 CSM14.1 cells prelabelled with the fluorescent dye PKH26 into the right CPu. Five weeks after grafting, the cylinder test was performed, and the data compared with data from age-matched intact controls and bilaterally lesioned-only animals. Brain slices immunostained for tyrosine hydroxylase (TH) were quantified by optical densitometry. We observed a significant preference of left forelimb use exclusively in transplanted animals. In these rats, TH-containing perikarya were found in the grafted CPu, presumedly leading to the significant increase of TH-immunoreactive fibers in this region. Moreover, confocal laser microscopy revealed a differentiation of transplanted PKH26-labelled CSM14.1 cells into neuronal nuclei antigen or TH-immunoreactive cells. Thus, CSM14.1 cells differentiate into TH-containing neurons, which most probably contribute to the preferred forelimb use, indicating a functional integration of CSM14.1 cells into the host basal ganglia loops during early postnatal development. These findings that are in contrast to observations in adult rats suggest instructive cues for neuronal differentiation and integration given by the neonatal microenvironment.

Modification of the number and phenotype of striatal dopaminergic cells by carotid body graft

In non-human primates, striatal tyrosine hydroxylase-immunoreactive (TH-ir) cells are increased in number after dopamine depletion and in response to trophic factor delivery. As carotid body cells contain the dopaminotrophic glial cell line-derived neurotrophic factor (GDNF), we evaluated the number, morphology and neurochemistry of these TH-ir cells, in the anterior and posterior striatum of five monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) which received a graft of carotid body cell aggregates (CBCA) (n = 3) or sham surgery (n = 2), and six MPTP-monkeys that were sacrificed 6 months and 3 years after the last MPTP dose [MPTP I (n = 3) and MPTP II (n = 3), respectively]. Three intact monkeys served as controls. A disability rating scale was used for the assessment of parkinsonism in all lesioned animals, both before and after surgery. For the neurochemical examination, tissue sections were double-labelled with antibodies to TH, dopamine transporter, dopa decarboxylase-67, vesicular monoamine transporter 2, glutamic acid decarboxylase -67, calbindin, parvalbumin, calretinin, neuronal nitric oxide synthase and GDNF. Only animals receiving CBCA graft showed a moderate but significant recovery of parkinsonism that persisted 12 months after the graft. The grafted striatum contained the greatest TH-ir cell density (120.4 +/- 10.3 cells/100 mm2), while the control striatum displayed the lowest (15.4 +/- 6.8 cells/100 mm2), and MPTP I, MPTP II and sham-operated monkeys showed a similar intermediate value (66.1 +/- 6.2, 58.3 +/- 17.2 and 57.7 +/- 7.0 cells/100 mm2, respectively). In addition, in the post-commissural striatum, only CBCA graft induced a significant increase in the TH-ir cell density compared to control animals (47.9 +/- 15.9 and 7.9 +/- 3.2, respectively). Phenotypically, TH-ir cells were striatal dopaminergic interneurons. However, in the grafted animals, the phenotype was different from that in control, MPTP and sham-operated monkeys, with the appearance of TH/GDNF-ir cells and the emergence of two TH-ir subpopulations of different size as the two main differentiating features. Our data confirm and extend previous studies demonstrating that striatal CBCA grafts produce a long-lasting motor recovery of MPTP-monkeys along with an increase in the number and phenotype changes of the striatal TH-ir interneurons, probably by the action of the trophic factors contained in carotid body cells. The increased number of striatal TH-ir cells observed in the grafted striatum may contribute to the improvement of parkinsonism observed after the graft.

Acute sublethal global hypoxia induces transient increase of GAP-43 immunoreactivity in the striatum of neonatal rats

We assessed immunoreactivity (IR) in the cerebral cortex (CC), hippocampus (Hipp), and striatum (ST) of a growth-associated protein, GAP-43, and of proteins of the synaptic vesicle fusion complex: VAMP-2, Syntaxin-1, and SNAP-25 (SNARE proteins) throughout postnatal development of rats after submitting the animals to acute global postnatal hypoxia (6.5% O(2), 70 min) at postnatal day 4 (PND4). In the CC only the IR of the SNARE protein SNAP-25 increased significantly with age. The hypoxic animals showed the same pattern of IR for SNAP-25, although with lower levels at PND11, and also a significant increase of VAMP-2. SNAP-25 (control): PND11 P < 0.001 vs. PND18, 25, and 40, SNAP-25 (hypoxic): P < 0.001 vs. PND18, 25, and 40; VAMP-2 (hypoxic): P < 0.05 PND11 vs. PND18, and P < 0.01 vs. PND25 and PND40; one-way ANOVA and Bonferroni post-test. In the Hipp, SNAP-25 and syntaxin-1 increased significantly with age, reaching a plateau at PND25 through PND40 in control animals (one-way ANOVA: syntaxin-1: P = 0.043; Bonferroni: NS; SNAP-25: P = 0.013; Bonferroni: P < 0.01 PND11 vs. PND40). Hypoxic rats showed higher levels of significance in the one-way ANOVA than controls (syntaxin-1: P = 0.009; Bonferroni: P < 0.05 PND11 vs. PND25 and P < 0.001 PND11 vs. PND40). In the ST, GAP-43 differed significantly among hypoxic and control animals and the two-way ANOVA revealed significant differences with age (F = 3.23; P = 0.037) and treatment (F = 4.84; P = 0.036). VAMP-2 expression also reached statistical significance when comparing control and treated animals (F = 6.25, P = 0.018) without changes regarding to age. Elevated plus maze test performed at PND40 indicated a lower level of anxiety in the hypoxic animals. At adulthood (12 weeks) learning, memory and locomotor abilities were identical in both groups of animals. With these results, we demonstrate that proteins of the presynaptic structures of the ST are sensitive to acute disruption of homeostatic conditions, such as a temporary decrease of the O(2) concentration. Modifications in the activity of these proteins could contribute to the long term altered responses to stress due to acute hypoxic insult in the neonatal period.

Transplantation of autologous sympathetic neurons as a potential strategy to restore metabolic functions of the damaged nigrostriatal dopamine nerve terminals in Parkinson's disease

Grafting of catecholamine-producing cells can be a possible therapeutic strategy for attenuating motor symptoms in Parkinson's disease (PD). The potential of autologous sympathetic neurons has been investigated as a donor for cell therapy of PD. The clinical trials of autotransplantation of sympathetic ganglion cells in PD have revealed that the grafts increase the duration of L-DOPA (L-dihydroxy phenyl alanine)-induced beneficial effects, and that the graft-mediated effect is detectable during a follow-up period of at least 1 year postgrafting. In an in vitro analysis of the ability of human sympathetic neurons to release catecholamines, although DA was not detectable under basal conditions, DA levels were significantly increased upon exposure to exogenous L-DOPA. Furthermore, animal experiments with xenografting of human sympathetic ganglionic neurons in the DA-denervated striatum of rats demonstrated that a significant increase in striatal DA levels is noted after systemic L-DOPA treatment, and that the DA levels remain high for longer periods of time in the grafted rats than in control animals with sham surgery. The L-DOPA-induced rise of striatal DA levels was significantly attenuated when given reserpine pretreatment. This suggests that DA derived from exogenously administered L-DOPA is subjected to, at least in part, vesicular storage in grafted sympathetic neurons. Histological examinations indeed showed that the grafts express aromatic-L-amino acid decarboxylase and vesicular monoamine transporter-2, both of which are important molecules for the synthesis and the storage of DA, respectively. Taken together, grafted sympathetic neurons can provide a site for both the conversion of exogenous L-DOPA to DA and the storage of the synthesized DA in the DA-denervated striatum. This might be an explanation for a mechanism by which sympathetic neuron autografts can increase the duration of L-DOPA effects in PD patients. This review article summarizes the clinical effect of transplantation of autologous sympathetic neurons in PD and discusses the underlying mechanism for the effect based on experimental evidence previously obtained.

Neuroprotection by transgenic expression of glucose-6-phosphate dehydrogenase in dopaminergic nigrostriatal neurons of mice

Oxidative damage to dopaminergic nigrostriatal (DNS) neurons plays a central role in the pathogenesis of Parkinson's disease (PD). Glucose-6-phosphate dehydrogenase (G6PD) is a key cytoprotective enzyme that provides NADPH, the major source of the reducing equivalents of a cell. Mutations of this enzyme are the most common enzymopathies worldwide. We have studied in vivo the role of G6PD overexpressed specifically in the DNS pathway and show that the increase of G6PD activity in the soma and axon terminals of DNS neurons, separately from other neurons or glial cells, protects them from parkinsonism. Analysis of DNS neurons by histological, neurochemical, and functional methods showed that even a moderate increase of G6PD activity rendered transgenic mice more resistant than control littermates to the toxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The neuroprotective action of G6PD was also observed in aged animals despite that they had a greater susceptibility to MPTP. Therefore, overexpression of G6PD in dopaminergic neurons or pharmacological activation of the native enzyme should be considered as potential therapeutic strategies to PD.

Selective glial cell line-derived neurotrophic factor production in adult dopaminergic carotid body cells in situ and after intrastriatal transplantation

Glial cell line-derived neurotrophic factor (GDNF) exerts a notable protective effect on dopaminergic neurons in rodent and primate models of Parkinson's disease (PD). The clinical applicability of this therapy is, however, hampered by the need of a durable and stable GDNF source allowing the safe and continuous delivery of the trophic factor into the brain parenchyma. Intrastriatal carotid body (CB) autografting is a neuroprotective therapy potentially useful in PD. It induces long-term recovery of parkinsonian animals through a trophic effect on nigrostriatal neurons and causes amelioration of symptoms in some PD patients. Moreover, the adult rodent CB has been shown to express GDNF. Here we show, using heterozygous GDNF/lacZ knock-out mice, that unexpectedly CB dopaminergic glomus, or type I, cells are the source of CB GDNF. Among the neural or paraneural cells tested, glomus cells are those that synthesize and release the highest amount of GDNF in the adult rodent (as measured by standard and in situ ELISA). Furthermore, GDNF expression by glomus cells is maintained after intrastriatal grafting and in CB of aged and parkinsonian 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated animals. Thus, glomus cells appear to be prototypical abundant sources of GDNF, ideally suited to be used as biological pumps for the endogenous delivery of trophic factors in PD and other neurodegenerative diseases.