Clinical neurotransplantation protocol for Huntington's and Parkinson's disease.

PURPOSE: The concept of transplantation of neuronal cells to treat Huntington's and Parkinson's diseases is based on the proven principle that dopaminergic and GABA-ergic progenitor neurons (from the human developing ventral mesencephalon and whole ganglionic eminence) can survive, differentiate and functionally integrate into an allogenic host brain. However, several donor and host-specific variables play a major role in the safety and outcome of this procedure. In this paper, we seek to summarize an updated neural transplantation protocol, based on our institutional experience and many years of collaboration with other neurotransplantation centers. METHODS: We present a detailed clinical neurotransplantation protocol for Parkinson's (PD) and Huntington's (HD) diseases with special emphasis in understanding the anatomical relationships of the human fetal tissue that are relevant for selection of the desired cell populations. RESULTS: Two detailed step-wise neurotransplantation protocols are presented, outlining strategies facilitating the avoidance of possible procedure-related complications. CONCLUSIONS: In this paper we delineated some crucial technical factors enabling the execution of a safe and effective neural transplantation. The protocols presented here might contribute to further development of the experimental clinical neurotransplantation towards a routine therapeutic procedure.

Fetal dopaminergic transplantation trials and the future of neural grafting in Parkinson's disease.

Clinical use of allografts of fetal ventral mesencephalic tissue as a treatment to replace dopaminergic neurons in patients with Parkinson's disease was first done more than 20 years ago. Since then, many patients have received transplants, with variable results. During this time, our knowledge of Parkinson's disease has changed and the nature and extent of problems associated with the disorder have been better defined. Our understanding on how best to implement this cell-replacement strategy for patients has grown, but gaining this insight has entailed critical reappraisal of data from transplant trials that have already been undertaken.

Long-term survival of solid embryonic cerebellar grafts in Lurcher mice.

Lurcher mutant mice represent a natural model of olivocerebellar degeneration. They serve as a tool to study pathogenesis, the functional impact of the degeneration as well as therapeutic approaches. Wild type littermates are used as healthy controls. Neurotransplantation may be a promising method of therapy for neurodegenerative diseases. The aim of this work was to compare the long-term survival rate of the solid embryonic cerebellar graft in adult Lurcher mutant and wild type mice of the B6CBA strain and to assess the fundamental structural features of the graft. The graft was obtained from 12-day-old GFP mouse embryos. The brains of host mice were examined histologically 6 months after the transplantation. The graft was identified according to its GFP fluorescence. The graft presence and structure was assessed. The graft survived in all 14 Lurcher mice and in 12 of the 14 wild type mice. Cell migration and fibre sprouting from the graft were poor. No marked differences in the graft morphology between Lurcher mutant and wild type mice were found. The graft survival and appearance were similar to those after a shorter period described in a previous study. This suggests that during the 6 months, no intensive or commonly occurring processes changing the graft had proceeded and that the Lurcher mutant cerebellum niche had no strong influence over the fate of the solid cerebellar graft.

Rewiring the brain with cell transplantation in Parkinson's disease.

Cell replacement therapy has been proposed as a means to replace lost dopaminergic neurons in Parkinson's disease (PD). In most studies, the transplanted cells have been placed within the target site, the striatum, and not within the lesioned site, the substantia nigra, as the adult nigrostriatal pathway was thought to constitute a non-permissive environment for long distance axonal outgrowth of transplanted neuroblasts. Here, we discuss recent findings showing that intranigral transplanted dopaminergic neuroblasts can form axonal projections to the striatum, resulting in increased striatal dopamine levels and ameliorating behavioral deficits in animal models of PD. Such findings have raised new hopes and opened new avenues for cell replacement therapy in patients with PD.

The promise of an interneuron-based cell therapy for epilepsy.

Of the nearly 3 million Americans diagnosed with epilepsy, approximately 30% are unresponsive to current medications. Recent data has shown that early postnatal transplantation of interneuronal precursor cells increases GABAergic inhibition in the host brain and dramatically suppresses seizure activity in epileptic mice. In this review, we will highlight findings from seizure-prone mice and humans that demonstrate the link between dysfunctional GABAergic inhibition and hyperexcitability. In particular, we will focus on rodent models of temporal lobe epilepsy, the most common and difficult to treat form of the disease, and interneuronopathies, an emerging classification. A wealth of literature showing a causal link between reduced GABA-mediated inhibition and seizures has directed our efforts to recover the loss of inhibition via transplantation of interneuronal precursors. Numerous related studies have explored the anticonvulsant potential of cell grafts derived from a variety of brain regions, yet the mechanism underlying the effect of such heterogeneous cell transplants is unknown. In discussing our recent findings and placing them in context with what is known about epilepsy, and how related transplant approaches have progressed, we hope to initiate a frank discussion of the best path toward the translation of this approach to patients with intractable forms of epilepsy.

Cell transplantation in Parkinson's disease: problems and perspectives.

PURPOSE OF REVIEW: We review recent experiments conducted using embryonic tissue and stem cell transplants in experimental models of Parkinson's disease. We also highlight the challenges which remain to be met in order for cell therapy to become clinically effective and safe. RECENT FINDINGS: The outcome of previous clinical transplantation trials was variable in terms of motor recovery. We discuss whether transplants can mitigate L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesias and consider the risk factors which predispose to graft-induced dyskinesias. In addition, we introduce Transeuro, a new European Union-funded multicenter consortium which plans to perform transplantation trials.Stem cells have emerged as an alternative source for the generation of dopaminergic precursors. We briefly outline progress made in the use of human embryonic stem cells and focus predominantly on the emerging field of induced pluripotency. We conclude by introducing the exciting and novel method of direct reprogramming which involves the conversion of fibroblasts to neurons without inducing a pluripotent state. SUMMARY: The area of cell transplantation has been revitalized by the identification of parameters which predispose patients to graft-induced dyskinesias and by the emergence of novel methods of generating dopaminergic neurons. Hopefully, the Transeuro clinical trials will give further impetus and act as a stepping stone to future trials employing stem-cell-derived neurons.

Neurotrophic support of midbrain dopaminergic neurons.

In this chapter we review work on neurotrophic factors for midbrain dopaminergic neurons mainly from the past decade, with a focus on neurotrophins and fibroblast growth factors. We summarize data obtained from animal models of Parkinson's disease, review analyses of neurotrophin, neurotrophin receptor and FGF-2 knockout mice and put these into context with data obtained from patients with Parkinson's disease and from postmortem studies. We provide a brief overview on several other factors (EGF, TGF-alpha, IGF, CNTF, PDGF, interleukins) and their capacity to promote survival and protect lesioned DAergic neurons. TGF-betas are reviewed in a separate chapter (Roussa et al, this volume).

The R6 lines of transgenic mice: a model for screening new therapies for Huntington's disease.

Huntington's disease (HD) is a hereditary neurodegenerative disorder caused by an expanded CAG repeat in the HD gene that results in cortical and striatal degeneration, and mutant huntingtin aggregation. Current treatments are unsatisfactory. R6 transgenic mice replicate many features of the human condition, show early onset of symptoms and fast disease progression, being one of the most used models for therapy screening. Here we review the therapies that have been tested in these mice: environmental enrichment, inhibition of histone deacetylation and methylation, inhibition of misfolding and oligomerization, transglutaminase inhibition, rescue of metabolic impairment, amelioration of the diabetic phenotype, use of antioxidants, inhibition of excitotoxicity, caspase inhibition, transplantation, genetic manipulations, and restoration of neurogenesis. Although many of these treatments were beneficial in R6 mice, they may not be as effective in HD patients, and thus the search for a combination of therapies that will rescue the human condition continues.

Stem cell transplantation: a promising therapy for Parkinson's disease.

Parkinson's disease is one of the most common neurodegenerative diseases caused by the loss of dopaminergic neurons in the substantia nigra pars compacta. Pharmacological therapies are valuable but suffer from two main drawbacks: side effects and loss of efficacy with disease progression. Surgical treatment is no better than drugs. Transplantation of embryonic mesencephalic tissue has emerged as a therapeutic alternative, but the unstable efficiency and the shortage of embryonic donors limit its clinical application. Recent advances in stem cell research inspire our hope that stem cell transplantation to replace degenerated neurons may be a promising therapy for Parkinson's disease. There are three sources of stem cells currently in testing: embryonic stem cells, neural stem cells, and mesenchymal stem cells. The stem cell transplantation in the animal model of Parkinson's disease proves that it is capable of relieving symptoms and restoring damaged brain function. Future stem cell research should focus not only on ameliorating the symptoms of Parkinson's disease but also on neuroprotection or neurorescue that can favorably modify the natural course and slow the progression of the disease.

Olfactory ensheathing glia: their contribution to primary olfactory nervous system regeneration and their regenerative potential following transplantation into the injured spinal cord.

Olfactory ensheathing glia (OEG) are a specialized type of glia that guide primary olfactory axons from the neuroepithelium in the nasal cavity to the brain. The primary olfactory system is able to regenerate after a lesion and OEG contribute to this process by providing a growth-supportive environment for newly formed axons. In the spinal cord, axons are not able to restore connections after an injury. The effects of OEG transplants on the regeneration of the injured spinal cord have been studied for over a decade. To date, of all the studies using only OEG as a transplant, 41 showed positive effects, while 13 studies showed limited or no effects. There are several contradictory reports on the migratory and axon growth-supporting properties of transplanted OEG. Hence, the regenerative potential of OEG has become the subject of intense discussion. In this review, we first provide an overview of the molecular and cellular characteristics of OEG in their natural environment, the primary olfactory nervous system. Second, their potential to stimulate regeneration in the injured spinal cord is discussed. OEG influence scar formation by their ability to interact with astrocytes, they are able to remyelinate axons and promote angiogenesis. The ability of OEG to interact with scar tissue cells is an important difference with Schwann cells and may be a unique characteristic of OEG. Because of these effects after transplantation and because of their role in primary olfactory system regeneration, the OEG can be considered as a source of neuroregeneration-promoting molecules. To identify these molecules, more insight into the molecular biology of OEG is required. We believe that genome-wide gene expression studies of OEG in their native environment, in culture and after transplantation will ultimately reveal unique combinations of molecules involved in the regeneration-promoting potential of OEG.

Survival, migration and neuronal differentiation of human fetal striatal and cortical neural stem cells grafted in stroke-damaged rat striatum.

Stroke is a neurodegenerative disorder and the leading cause of disability in adult humans. Treatments to support efficient recovery in stroke patients are lacking. Several studies have demonstrated the ability of grafted neural stem cells (NSCs) to partly improve impaired neurological functions in stroke-subjected animals. Recently, we reported that NSCs from human fetal striatum and cortex exhibit region-specific differentiation in vitro, but survive, migrate and form neurons to a similar extent after intrastriatal transplantation in newborn rats. Here, we have transplanted the same cells into the stroke-damaged striatum of adult rats. The two types of NSCs exhibited a similar robust survival (30%) at 1 month after transplantation, and migrated throughout the damaged striatum. Striatal NSCs migrated farther and occupied a larger volume of striatum. In the transplantation core, cells were undifferentiated and expressed nestin and, to a lesser extent, also GFAP, betaIII-tubulin, DCX and calretinin, markers of immature neural lineage. Immunocytochemistry using markers of proliferation (p-H3 and Ki67) revealed a very low content of proliferating cells (<1%) in the grafts. Human cells outside the transplantation core differentiated, exhibited mature neuronal morphology and expressed mature neuronal markers such as HuD, calbindin and parvalbumin. Interestingly, striatal NSCs generated a greater number of parvalbumin+ and calbindin+ neurons. Virtually none of the grafted cells differentiated into astrocytes or oligodendrocytes. Based on these data, human fetal striatum- and cortex-derived NSCs could be considered potentially safe and viable for transplantation, with strong neurogenic potential, for further exploration in animal models of stroke.

Chronic transplantation of olfactory ensheathing cells promotes partial recovery after complete spinal cord transection in the rat.

The goal of this study was to ascertain whether olfactory ensheathing cells (OECs) were able to promote axonal regeneration and functional recovery when transplanted 45 days after complete transection of the thoracic spinal cord in adult rats. OECs promoted partial restitution of supraspinal pathways evaluated by motor evoked potentials and modest recovery of hindlimb movements. In addition, OEC grafts reduced lumbar reflex hyperexcitability from the first month after transplantation. Histological results revealed that OECs facilitated corticospinal and raphespinal axons regrowth through the injury site and into the caudal spinal cord segments. Interestingly, raphespinal but not corticospinal fibers regenerated long distances through the gray matter and reached the lower lumbar segments (L5) of the spinal cord. However, delayed OEC grafts failed to reduce posttraumatic astrogliosis. In conclusion, the beneficial effects found in the present study further support the use of OECs for treating chronic spinal cord injuries.

Nerve growth factor in treatment and pathogenesis of Alzheimer's disease.

The etiology of Alzheimer's disease (AD) is still unknown. In addition, this terrible neurodegenerative disease will increase exponentially over the next two decades due to longer lifespan and an aging "baby-boomer" generation. All treatments currently approved for AD have moderate efficacy in slowing the rate of cognitive decline in patients, and no efficacy in halting progression of the disease. Hence, there is an urgent need for new drug targets and delivery methods to slow or reverse the progression of AD. One molecule that has received much attention in its potential therapeutic role in AD is nerve growth factor (NGF). This review will demonstrate data from humans and animals which promote NGF as a potential therapeutic target by (1) outlining the hypothesis behind using NGF for the treatment of AD, (2) reviewing both the normal and AD altered signaling pathways and effects of NGF in the central nervous system (CNS), and (3) examining the results of NGF treatment obtained from animal models of AD and AD patients.