Delivery of sonic hedgehog or glial derived neurotrophic factor to dopamine-rich grafts in a rat model of Parkinson's disease using adenoviral vectors Increased yield of dopamine cells is dependent on embryonic donor age

Encapsulation of young donor age dopaminergic grafts in a GDNF-loaded collagen hydrogel further increases their survival, reinnervation, and functional efficacy after intrastriatal transplantation in hemi-Parkinsonian rats

Biomaterials have been shown to significantly improve the outcome of cellular reparative approaches for Parkinson's disease in experimental studies because of their ability to provide transplanted cells with a supportive microenvironment and shielding from the host immune system. However, given that the margin for improvement in such reparative therapies is considerable, further studies are required to fully investigate and harness the potential of biomaterials in this context. Given that several recent studies have demonstrated improved brain repair in Parkinsonian models when using dopaminergic grafts derived from younger foetal donors, we hypothesized that encapsulating these cells in a supportive biomaterial would further improve their reparative efficacy. Thus, this study aimed to determine the impact of a GDNF-loaded collagen hydrogel on the survival, reinnervation, and functional efficacy of dopaminergic neurons derived from young donors. To do so, hemi-Parkinsonian (6-hydroxydopamine-lesioned) rats received intrastriatal transplants of embryonic day 12 cells extracted from the rat ventral mesencephalon either alone, in a collagen hydrogel, with GDNF, or in a GDNF-loaded collagen hydrogel. Methamphetamine-induced rotational behaviour was assessed at three weekly intervals for a total of 12 weeks, after which rats were sacrificed for postmortem assessment of graft survival. We found that, following intrastriatal transplantation to the lesioned striatum, the GDNF-loaded collagen hydrogel significantly increased the survival (4-fold), reinnervation (5.4-fold), and functional efficacy of the embryonic day 12 dopaminergic neurons. In conclusion, this study further demonstrates the significant potential of biomaterial hydrogel scaffolds for cellular brain repair approaches in neurodegenerative diseases such as Parkinson's disease.

Regulatory Effects of Neuroinflammatory Responses Through Brain-Derived Neurotrophic Factor Signaling in Microglial Cells

Inhibition of microglial over-activation is an important strategy to counter balance neurodegenerative progression. We previously demonstrated that the adenosine monophosphate-activated protein kinase (AMPK) may be a therapeutic target in mediating anti-neuroinflammatory responses in microglia. Brain-derived neurotrophic factor (BDNF) is one of the major neurotrophic factors produced by astrocytes to maintain the development and survival of neurons in the brain, and have recently been shown to modulate homeostasis of neuroinflammation. Therefore, the present study focused on BDNF-mediated neuroinflammatory responses and may provide an endogenous regulation of neuroinflammation. Among the tested neuroinflammation, epigallocatechin gallate (EGCG) and minocycline exerted BDNF upregulation to inhibit COX-2 and proinflammatory mediator expressions. Furthermore, both EGCG and minocycline upregulated BDNF expression in microglia through AMPK signaling. In addition, minocycline and EGCG also increased expressions of erythropoietin (EPO) and sonic hedgehog (Shh). In the endogenous modulation of neuroinflammation, astrocyte-conditioned medium (AgCM) also decreased the expression of COX-2 and upregulated BDNF expression in microglia. The anti-inflammatory effects of BDNF were mediated through EPO/Shh in microglia. Our results indicated that the BDNF-EPO-Shh novel-signaling pathway underlies the regulation of inflammatory responses and may be regarded as a potential therapeutic target in neurodegenerative diseases. This study also reveals a better understanding of an endogenous crosstalk between astrocytes and microglia to regulate anti-inflammatory actions, which could provide a novel strategy for the treatment of neuroinflammation and neurodegenerative diseases.

Nogo-A Neutralization Improves Graft Function in a Rat Model of Parkinson's Disease

Transplantation of fetal human ventral mesencephalic (VM) dopaminergic neurons into the striatum is a promising strategy to compensate for the characteristic dopamine deficit observed in Parkinson’s disease (PD). This therapeutic approach, however, is currently limited by the high number of fetuses needed for transplantation and the poor survival and functional integration of grafted dopaminergic neurons into the host brain. Accumulating evidence indicates that contrasting inhibitory signals endowed in the central nervous system (CNS) might support neuronal regeneration. Hence, in the present study we aimed at improving survival and integration of grafted cells in the host brain by neutralizing Nogo-A, one of the most potent neurite growth inhibitors in the CNS. For that purpose, VM tissue cultures were transplanted into rats with a partial 6-hydroxydopamine (6-OHDA) lesion causing a hemi-PD model and concomitantly treated for 2 weeks with intra-ventricular infusion of neutralizing anti-Nogo-A antibodies. Motor behavior using the cylinder test was assessed prior to and after transplantation as functional outcome. At the end of the experimental period the number of dopaminergic fibers growing into the host brain, the number of surviving dopaminergic neurons in the grafts as well as graft size was examined. We found that anti-Nogo-A antibody infusion significantly improved the asymmetrical forelimb use observed after lesions as compared to controls. Importantly, a significantly three-fold higher dopaminergic fiber outgrowth from the transplants was detected in the Nogo-A antibody treated group as compared to controls. Furthermore, Nogo-A neutralization showed a tendency for increased survival of dopaminergic neurons (by two-fold) in the grafts. No significant differences were observed for graft volume and the number of dopaminergic neurons co-expressing G-protein-coupled inward rectifier potassium channel subunit two between groups. In sum, our findings support the view that neutralization of Nogo-A in the host brain may offer a novel and therapeutically meaningful intervention for cell transplantation approaches in PD.

Activation of Sonic Hedgehog Leads to Survival Enhancement of Astrocytes via the GRP78-Dependent Pathway in Mice Infected with Angiostrongylus cantonensis

Angiostrongylus cantonensis infection may cause elevation of ROS and antioxidants in the CSF of infected mice. Astrocytes may protect the surrounding neurons from oxidative stress-induced cell death by secreting Sonic hedgehog (Shh) via the PI3-K/AKT/Bcl-2 pathway. This study was conducted to determine the role of the Shh signaling pathway in A. cantonensis-infected BABL/c mice by coculturing astrocytes with living fifth-stage larvae or soluble antigens. The Shh pathway was activated with corresponding increases in the level of the Shh. Glial fibrillary acidic protein (GFAP) and Shh were increased in astrocyte cocultured with living fifth-stage larvae or soluble antigens. The survival of astrocytes pretreated with Shh was significantly elevated in cocultures with the antigens but reduced by its inhibitor cyclopamine. The expression of GRP78 and Bcl-2 was significantly higher in astrocytes pretreated with recombinant Shh. These findings suggest that the expression of Shh may inhibit cell death by activating Bcl-2 through a GRP78-dependent pathway.

Lentivirus-mediated delivery of sonic hedgehog into the striatum stimulates neuroregeneration in a rat model of Parkinson disease

Parkinson disease (PD) is a progressive neurodegenerative disorder in which the nigrostriatal pathway, consisting of dopaminergic neuronal projections from the substantia nigra to the striatum, degenerates. Viral transduction is currently the most promising in vivo strategy for delivery of therapeutic proteins into the brain for treatment of PD. Sonic hedgehog (Shh) is necessary for cell proliferation, differentiation and neuroprotection in the central nervous system. In this study, we investigated the effects of overexpressed N-terminal product of SHH (SHH-N) in a PD model rat. A lentiviral vector containing SHH-N was stereotactically injected into the striatum 24 h after a striatal 6-OHDA lesion. We found that overexpressed SHH-N attenuated behavioral deficits and reduced the loss of dopamine neurons in the substantia nigra and the loss of dopamine fibers in the striatum. In addition, fluoro-ruby-labeled nigrostriatal projections were also repaired. Together, our results demonstrate the feasibility and efficacy of using the strategy of lentivirus-mediated Shh-N delivery to delay nigrostriatal pathway degeneration. This strategy holds the potential for therapeutic application in the treatment of PD.

Two-step grafting significantly enhances the survival of foetal dopaminergic transplants and induces graft-derived vascularisation in a 6-OHDA model of Parkinson's disease

Following transplantation of foetal primary dopamine (DA)-rich tissue for neurorestaurative treatment of Parkinson's disease (PD), only 5-10% of the functionally relevant DAergic cells survive both in experimental models and in clinical studies. The current work tested how a two-step grafting protocol could have a positive impact on graft survival. DAergic tissue is divided in two portions and grafted in two separate sessions into the same target area within a defined time interval. We hypothesized that the first graft creates a "DAergic" microenvironment or "nest" similar to the perinatal substantia nigra that stimulates and protects the second graft. 6-OHDA-lesioned rats were sequentially transplanted with wild-type (GFP-, first graft) and transgenic (GFP+, second graft) DAergic cells in time interims of 2, 5 or 9days. Each group was further divided into two sub-groups receiving either 200k (low cell number groups: 2dL, 5dL, 9dL) or 400k cells (high cell number groups: 2dH, 5dH, 9dH) as first graft. During the second transplantation, all groups received the same amount of 200k GFP+ cells. Controls received either low or high cell numbers in one single session (standard protocol). Drug-induced rotations, at 2 and 6weeks after grafting, showed significant improvement compared to the baseline lesion levels without significant differences between the groups. Rats were sacrificed 8weeks after transplantation for post-mortem histological assessment. Both two-step groups with the time interval of 2days (2dL and 2dH) showed a significantly higher survival of DAergic cells compared to their respective standard control group (2dL, +137%; 2dH, +47%). Interposing longer intervals of 5 or 9days resulted in the loss of statistical significance, neutralising the beneficial two-step grafting effect. Furthermore, the transplants in the 2dL and 2dH groups had higher graft volume and DA-fibre-density values compared to all other two-step groups. They also showed intense growth of GFP+ vessels - completely absent in control grafts - in regions where the two grafts overlap, indicating second-graft derived angiogenesis. In summary, the study shows that two-step grafting with a 2days time interval significantly increases DAergic cell survival compared to the standard protocol. Furthermore, our results demonstrate, for the first time, a donor-derived neoangiogenesis, leading to a new understanding of graft survival and development in the field of cell-replacement therapies for neurodegenerative diseases.

Trophic and proliferative effects of Shh on motor neurons in embryonic spinal cord culture from wildtype and G93A SOD1 mice

Background

The developmental morphogen sonic hedgehog (Shh) may continue to play a trophic role in the support of terminally-differentiated motor neurons, of potential relevance to motor neuron disease. In addition, it may support the proliferation and differentiation of endogenous stem cells along motor neuronal lineages. As such, we have examined the trophic and proliferative effects of Shh supplementation or Shh antagonism in embryonic spinal cord cell cultures derived from wildtype or G93A SOD1 mice, a mouse model of amyotrophic lateral sclerosis.

Results

Shh supported survival, and stimulated growth of motor neurons, neurite outgrowth, and neurosphere formation in primary culture derived from both G93A SOD1 and WT mice. Shh increased the percentage of ciliated motor neurons, especially in G93A SOD1 culture. Shh-treated cultures showed increased neuronal proliferation compared to controls and especially cyclopamine treated cultures, from G93A SOD1 and WT mice. Moreover, Shh enhanced cell survival and differentiation of motor neuron precursors in WT culture.

Conclusions

Shh is neurotrophic to motor neurons and has mitogenic effects in WT and mSOD1 G93A culture in vitro.

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

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

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.

Cognitive deficits in animal models of basal ganglia disorders

The two most common neurological disorders of the basal ganglia are Parkinson's disease (PD) and Huntington's disease (HD). The most overt symptoms of these diseases are motoric, reflecting the loss of the striatal medium spiny neurons in HD and ascending substantia nigra dopaminergic cells in PD. However, both disease processes induce insidious psychiatric and cognitive syndromes that can manifest well in advance of the onset of motor deficits. These early deficits provide an opportunity for prophylactic therapeutic intervention in order to retard disease progression from the earliest possible point. In order to exploit this opportunity, animal models of HD and PD are being probed for the specific cognitive deficits represented in the disease states. At the neuronal level, these deficits are typically, but not exclusively, mediated by disruption of parallel corticostriatal loops that integrate motor information with sensory and higher order, "executive" cognitive functions. Dysfunction in these systems can be probed with sensitive behavioural tests that selectively probe these cognitive functions in mouse models with focal lesions of striatal or cortical regions, or of specific neurotransmitter systems. Typically these tests were designed and validated in rats. With the advent of genetically modified mouse models of disease, validated tests provide an opportunity to screen mouse models of disease for early onset cognitive deficits. This review seeks to draw together the literature on cognitive deficits in HD and PD, to determine the extent to which these deficits are represented in the current animal models of disease, and to evaluate the viability of selecting cognitive deficits as potential therapeutic targets. This article is part of a Special Issue entitled 'Animal Models'.

A Simple Breeding Protocol for the Procurement of Accurately Staged Rat Donor Embryos for Neural Transplantation

Obtaining accurately staged rat embryos can be difficult because of the variety of breeding protocols employed and because precise staging cannot be confirmed until excision of the embryos from the dam. The detection of estrus, pairing of animals, and confirmation of pregnancies is generally left to commercial suppliers, as in-house breeding can be laborious and unpredictable. Here we describe a simple, reliable in-house breeding protocol for the generation of accurately staged embryos as assessed by measurements of average crown to rump length (CRL).

Frontiers in the surgical treatment of Parkinson's disease

Despite the continued refinement of medical and surgical therapies, the treatment of Parkinson's disease (PD) remains challenging. Current treatment strategies are largely focused on managing the motor symptoms of the disease, either by dopamine-based medications or, in advanced stages, by the application of deep brain stimulation to more stably alter the function of the basal ganglia. Important advances have been made in the last decade, but unfortunately a number of the motor symptoms of late-stage PD remain poorly treated, and while currently available therapies address the symptoms of the disease, they fail to alter the course of the disease itself. This has spurred basic and clinical exploration on a number of fronts. Several centers have examined novel stimulation targets to treat refractory symptoms of gait difficulty and axial imbalance. Basic and clinical researchers are examining whether the use of deep brain stimulation might slow the progress of the disease and thus be a useful neuroprotective therapy if initiated earlier in the progression of the disease. An expanded understanding of the genetic and cellular events that underlie PD has led some researchers to explore the use of neurotrophic factors or genetic restoration to preserve threatened neuronal populations. Finally, there has been much research on the use of fetal mesencephalic or stem cell populations to restore dopaminergic function. In this report, we will examine each of these potential new surgical therapies and the promise they may hold for the future treatment of PD.

A Rat Embryo Staging Scale for the Generation of Donor Tissue for Neural Transplantation

In rat models of Parkinson's and Huntington's diseases, embryonic neural cells obtained from embryos of specified ages can be implanted into the brain to partially restore both physiology and function. However, in litters produced using overnight mating protocols (often from commercial suppliers), the embryonic age can be difficult to determine precisely. As a result, embryonic size based on crown to rump length (CRL) is usually a more reliable method of embryo staging than the day of mating. This approach is not without difficulty. There are a number of rat staging scales in the literature, none of which deal with donor ages younger than E13, and there are discrepancies between scales at some donor ages. In the present article, we have devised a short mating-period protocol to produce precisely aged embryos. We show that CRL is a highly accurate, reproducible index of donor age and we present an updated embryonic staging scale for Sprague-Dawley (CD) rats that includes donor ages younger than those previously reported.

Immunology of neurological gene therapy: how T cells modulate viral vector-mediated therapeutic transgene expression through immunological synapses

Gene therapy has been shown to be a powerful new approach to the treatment of brain diseases. Brain neurodegenerations, brain tumors, inherited brain diseases, and autoimmune disorders are currently recognized as proper targets for gene therapeutics. Advances in the development of viral vectors (especially improvements in their immune profiles), the capacity to regulate transgene expression, and identification of appropriate therapeutic constructs have made the transition into clinical trials for gene therapy possible. One particular remaining challenge is the immune response that could be raised against either the viral vectors themselves or any regulatory or therapeutic transgenes. Because of the structure of brain immune responses, viral gene transfer into the brain can, under certain circumstances, be invisible to the systemic immune response and thus not generate a deleterious immune attack. If, however, the systemic immune system is primed against any vector antigen, the systemic immune response eliminates transgene expression and thus curtails the therapeutic efficacy of gene therapy. Mechanistic studies of brain immune responses indicate that the adaptive arm of the immune system may indeed be able to kill transduced cells. To move neurological gene therapy into the clinic in an effective and safe manner, these are the developments needed: novel viral vectors that either display a reduced capacity to stimulate an adaptive immune response or become invisible to the immune system after the delivery of the vector genome to the nucleus of transduced cells, and ways either to steer the immune response away from cytotoxic responses or to induce tolerance to gene therapy products.

Improved survival of young donor age dopamine grafts in a rat model of Parkinson's disease

In an attempt to improve the survival of implanted dopamine cells, we have readdressed the optimal embryonic donor age for dopamine grafts. In a rat model of Parkinson's disease, animals with unilateral 6-hydroxydopamine lesions of the median forebrain bundle received dopamine-rich ventral mesencephalic grafts derived from embryos of crown to rump length 4, 6, 9, or 10.5 mm (estimated embryonic age (E) 11, E12, E13 and E14 days post-coitus, respectively). Grafts derived from 4 mm embryos survived poorly, with less than 1% of the implanted dopamine cells surviving. Grafts derived from 9 mm and 10.5 mm embryos were similar to those seen in previous experiments with survival rates of 8% and 7% respectively. The best survival was seen in the group that received 6 mm grafts, which were significantly larger than all other graft groups. Mean dopamine cell survival in the 6 mm group (E12) was 36%, an extremely high survival rate for primary, untreated ventral mesencephalic grafts applied as a single placement, and more than fivefold larger than the survival rate observed in the 10.5 mm (E14) group. As E12 ventral mesencephalic tissues contain few, if any, differentiated dopamine cells we conclude that the large numbers of dopamine cells seen in the 6 mm grafts must have differentiated post-implantation. We consider the in vivo conditions which allow this differentiation to occur, and the implications for the future of clinical trials based on dopamine cell replacement therapy.

Pleiotrophin promotes functional recovery after neural transplantation in rats

Pleiotrophin promotes survival of dopaminergic neurons in vitro. To investigate whether pleiotrophin promotes survival of grafted dopaminergic neurons in vivo, donor cells from ventral mesencephalon were treated with pleiotrophin (100 ng/ml) during cell preparation and grafted into striatum of hemi-Parkinson model rats. Functional recovery in methamphetamine-induced rotations was improved, and more tyrosine hydroxylase-positive cells survived in the striatum in the pleiotrophin-treated group. Pleiotrophin addition to cells just before transplantation also resulted in better functional recovery; however, no caspase-3 activation was seen during cell preparation. Interestingly, the effect of pleiotrophin on the survival was additive to that of glial-cell line-derived neutropic factor. These results revealed that pleiotrophin had effects on donor cells in neural transplantation in vivo.

An investigation of the problem of two-layered immunohistochemical staining in paraformaldehyde fixed sections

In sections of paraformaldehyde fixed brain tissue, stained using immunohistochemical methods, the distribution of staining within the sections is not uniform. Whilst stained cells are seen at the top and bottom surfaces, the central thicknesses of the sections contain little or no immunoreactivity. This presents a major problem for quantification, as each section contains a population of cells that is not visualized by the staining method. Following extensive investigation of this phenomenon, we report that the failure of full thickness, immunohistochemical staining is not a failure of the immunohistochemical methodology per se, nor is it related directly to the thickness of the sections used. Rather, the problem lies in the chemistry of the tissue itself, and originates during fixation of the tissues using paraformaldehyde-based perfusion methods, which render the cell membranes impermeable to one or more components of the staining protocol. We show that this impermeability is affected by addition of membrane-disrupting agents to the fixative, and by a reduction of exposure to paraformaldehyde during fixation. The present investigation contributes to the development of new fixation protocols, optimised for use in both immunohistochemical methods and morphometric analyses.