Localized striatal delivery of GDNF as a treatment for Parkinson disease

Adenosine and adenosine receptors in metabolic imbalance-related neurological issues

Metabolic syndromes (e.g., obesity) are characterized by insulin resistance, chronic inflammation, impaired glucose metabolism, and dyslipidemia. Recently, patients with metabolic syndromes have experienced not only metabolic problems but also neuropathological issues, including cognitive impairment. Several studies have reported blood-brain barrier (BBB) disruption and insulin resistance in the brain of patients with obesity and diabetes. Adenosine, a purine nucleoside, is known to regulate various cellular responses (e.g., the neuroinflammatory response) by binding with adenosine receptors in the central nervous system (CNS). Adenosine has four known receptors: A1R, A2AR, A2BR, and A3R. These receptors play distinct roles in various physiological and pathological processes in the brain, including endothelial cell homeostasis, insulin sensitivity, microglial activation, lipid metabolism, immune cell infiltration, and synaptic plasticity. Here, we review the recent findings on the role of adenosine receptor-mediated signaling in neuropathological issues related to metabolic imbalance. We highlight the importance of adenosine signaling in the development of therapeutic solutions for neuropathological issues in patients with metabolic syndromes.

Disease-specific interventions: The use of cell and gene therapies for Parkinson disease

Approaches to repair the brain around the loss of the nigrostriatal dopaminergic pathways in Parkinson disease (PD) are not new and have been attempted over many years. However, of late, the situation has moved forward in two main ways. In the case of cell therapies, the ability to make large numbers of authentic midbrain dopaminergic neuroblasts from human pluripotent stem cell sources has turned what was an interesting avenue of research into a major area of investment and trialing, by academics in conjunction with Pharma. In the case of gene therapies, their use around dopamine replacement has waned, as the interest in using them for disease modification targeting PD-specific pathways has grown. In this chapter, we discuss all these developments and the current status of cell and gene therapies for PD.

The promise of the TGF-β superfamily as a therapeutic target for Parkinson's disease

A large body of evidence underscore the regulatory role of TGF-β superfamily in the central nervous system. Components of the TGF-β superfamily modulate key events during embryonic brain development and adult brain tissue injury repair. With respect to Parkinson's disease (PD), TGF-ß signaling pathways are implicated in the differentiation, maintenance and synaptic function of the dopaminergic neurons, as well as in processes related to the activation state of astrocytes and microglia. In vitro and in vivo studies using toxin models, have interrogated on the dopaminotrophic and protective role of the TGF-β superfamily members. The evolution of genetic and animal models of PD that more closely recapitulate the disease condition has made possible the dissection of intracellular pathways in response to TGF-ß treatment. Although the first clinical trials using GDNF did not meet their primary endpoints, substantial work has been carried out to reappraise the TGF-β superfamily's clinical benefit.

Induced Cognitive Impairments Reversed by Grafts of Neural Precursors: A Longitudinal Study in a Macaque Model of Parkinson's Disease

Parkinson's disease (PD) evolves over an extended and variable period in humans; years prior to the onset of classical motor symptoms, sleep and biological rhythm disorders develop, significantly impacting the quality-of-life of patients. Circadian-rhythm disorders are accompanied by mild cognitive deficits that progressively worsen with disease progression and can constitute a severe burden for patients at later stages. The gold-standard 6-methyl-1-methyl-4-phenyl-1,2,3,6-tetrahydropyridin (MPTP) macaque model of PD recapitulates the progression of motor and nonmotor symptoms over contracted periods of time. Here, this multidisciplinary/multiparametric study follows, in five animals, the steady progression of motor and nonmotor symptoms and describes their reversal following grafts of neural precursors in diverse functional domains of the basal ganglia. Results show unprecedented recovery from cognitive symptoms in addition to a strong clinical motor recuperation. Both motor and cognitive recovery and partial circadian rhythm recovery correlate with the degree of graft integration, and in a subset of animals, with in vivo levels of striatal dopaminergic innervation and function. The present study provides empirical evidence that integration of neural precursors following transplantation efficiently restores function at multiple levels in parkinsonian nonhuman primates and, given interindividuality of disease progression and recovery, underlines the importance of longitudinal multidisciplinary assessments in view of clinical translation.

Inhibition of TRPM2 by AG490 Is Neuroprotective in a Parkinson's Disease Animal Model

Parkinson's disease (PD) is characterized by motor impairment and dopaminergic neuronal loss. There is no cure for the disease, and treatments have several limitations. The transient receptor potential melastatin 2 (TRPM2), a calcium-permeable non-selective cation channel, has been reported to be upregulated in neuronal death. However, there are no in vivo studies evaluating TRPM2's role and neuroprotective effects in PD. Here, we test the hypothesis that TRPM2 is upregulated in the 6-hydroxydopamine (6-OHDA) mouse model of PD and that its inhibition, by the AG490, is neuroprotective. For that, AG490 or vehicle were intraperitoneally administered into C57BL/6 mice. Mice then received 6-OHDA into the right striatum. Motor behavior assessments were evaluated 6, 13, and 20 days after surgery using the cylinder and apomorphine-induced rotational testes, and 7, 14, and 21 days after surgery using rotarod test. Brain samples of substantia nigra (SNc) and striatum (CPu) were collected for immunohistochemistry and immunoblotting on days 7 and 21. We showed that TRPM2 protein expression was upregulated in 6-OHDA-treated animals. In addition, AG490 prevented dopaminergic neuron loss, microglial activation, and astrocyte reactivity in 6-OHDA-treated animals. The compound improved motor behaviors and Akt/GSK-3β/caspase-3 signaling. We conclude that TRPM2 inhibition by AG490 is neuroprotective in the 6-OHDA model and that the TRPM2 channel may represent a potential therapeutic target for PD.

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.

Glial Cell Line-Derived Neurotrophic Factor and Focal Ischemic Stroke

Focal ischemic stroke (FIS) is a leading cause of human debilitation and death. Following the onset of a FIS, the brain experiences a series of spatiotemporal changes which are exemplified in different pathological processes. One prominent feature of FIS is the development of reactive astrogliosis and glial scar formation in the peri-infarct region (PIR). During the subacute phase, astrocytes in PIR are activated, referred to as reactive astrocytes (RAs), exhibit changes in morphology (hypotrophy), show an increased proliferation capacity, and altered gene expression profile, a phenomenon known as reactive astrogliosis. Subsequently, the morphology of RAs remains stable, and proliferation starts to decline together with the formation of glial scars. Reactive astrogliosis and glial scar formation eventually cause substantial tissue remodeling and changes in permanent structure around the PIR. Glial cell line-derived neurotrophic factor (GDNF) was originally isolated from a rat glioma cell-line and regarded as a potent survival neurotrophic factor. Under normal conditions, GDNF is expressed in neurons but is upregulated in RAs after FIS. This review briefly describes properties of GDNF, its receptor-mediated signaling pathways, as well as recent studies regarding the role of RAs-derived GDNF in neuronal protection and brain recovery. These results provide evidence suggesting an important role of RA-derived GDNF in intrinsic brain repair and recovery after FIS, and thus targeting GDNF in RAs may be effective for stroke therapy.

Neuroprotective Potential of a Small Molecule RET Agonist in Cultured Dopamine Neurons and Hemiparkinsonian Rats

BACKGROUND

Parkinson's disease (PD) is a progressive neurological disorder where loss of dopamine neurons in the substantia nigra and dopamine depletion in the striatum cause characteristic motor symptoms. Currently, no treatment is able to halt the progression of PD. Glial cell line-derived neurotrophic factor (GDNF) rescues degenerating dopamine neurons both in vitro and in animal models of PD. When tested in PD patients, however, the outcomes from intracranial GDNF infusion paradigms have been inconclusive, mainly due to poor pharmacokinetic properties.

OBJECTIVE

We have developed drug-like small molecules, named BT compounds that activate signaling through GDNF's receptor, the transmembrane receptor tyrosine kinase RET, both in vitro and in vivo and are able to penetrate through the blood-brain barrier. Here we evaluated the properties of BT44, a second generation RET agonist, in immortalized cells, dopamine neurons and rat 6-hydroxydopamine model of PD.

METHODS

We used biochemical, immunohistochemical and behavioral methods to evaluate the effects of BT44 on dopamine system in vitro and in vivo.

RESULTS

BT44 selectively activated RET and intracellular pro-survival AKT and MAPK signaling pathways in immortalized cells. In primary midbrain dopamine neurons cultured in serum-deprived conditions, BT44 promoted the survival of the neurons derived from wild-type, but not from RET knockout mice. BT44 also protected cultured wild-type dopamine neurons from MPP+-induced toxicity. In a rat 6-hydroxydopamine model of PD, BT44 reduced motor imbalance and seemed to protect dopaminergic fibers in the striatum.

CONCLUSION

BT44 holds potential for further development into a novel, possibly disease-modifying, therapy for PD.

Treating brain diseases using systemic parenterally-administered protein therapeutics: Dysfunction of the brain barriers and potential strategies

The parenteral administration of protein therapeutics is increasingly gaining importance for the treatment of human diseases. However, the presence of practically impermeable blood-brain barriers greatly restricts access of such pharmaceutics to the brain. Treating brain disorders with proteins thus remains a great challenge, and the slow clinical translation of these therapeutics may be largely ascribed to the lack of appropriate brain delivery system. Exploring new approaches to deliver proteins to the brain by circumventing physiological barriers is thus of great interest. Moreover, parallel advances in the molecular neurosciences are important for better characterizing blood-brain interfaces, particularly under different pathological conditions (e.g., stroke, multiple sclerosis, Parkinson's disease, and Alzheimer's disease). This review presents the current state of knowledge of the structure and the function of the main physiological barriers of the brain, the mechanisms of transport across these interfaces, as well as alterations to these concomitant with brain disorders. Further, the different strategies to promote protein delivery into the brain are presented, including the use of molecular Trojan horses, the formulation of nanosystems conjugated/loaded with proteins, protein-engineering technologies, the conjugation of proteins to polymers, and the modulation of intercellular junctions. Additionally, therapeutic approaches for brain diseases that do not involve targeting to the brain are presented (i.e., sink and scavenging mechanisms).

Gene and Cell-Based Therapies for Parkinson's Disease: Where Are We?

Parkinson's disease (PD) is a neurodegenerative disorder that carries large health and socioeconomic burdens. Current therapies for PD are ultimately inadequate, both in terms of symptom control and in modification of disease progression. Deep brain stimulation and infusion therapies are the current mainstay for treatment of motor complications of advanced disease, but these have very significant drawbacks and offer no element of disease modification. In fact, there are currently no agents that are established to modify the course of the disease in clinical use for PD. Gene and cell therapies for PD are now being trialled in the clinic. These treatments are diverse and may have a range of niches in the management of PD. They hold great promise for improved treatment of symptoms as well as possibly slowing progression of the disease in the right patient group. Here, we review the current state of the art for these therapies and look to future strategies in this fast-moving field.

Molecular targets for endogenous glial cell line-derived neurotrophic factor modulation in striatal parvalbumin interneurons

Administration of recombinant glial cell line-derived neurotrophic factor into the putamen has been tested in preclinical and clinical studies to evaluate its neuroprotective effects on the progressive dopaminergic neuronal degeneration that characterizes Parkinson’s disease. However, intracerebral glial cell line-derived neurotrophic factor infusion is a challenging therapeutic strategy, with numerous potential technical and medical limitations. Most of these limitations could be avoided if the production of endogenous glial cell line-derived neurotrophic factor could be increased. Glial cell line-derived neurotrophic factor is naturally produced in the striatum from where it exerts a trophic action on the nigrostriatal dopaminergic pathway. Most of striatal glial cell line-derived neurotrophic factor is synthesized by a subset of GABAergic interneurons characterized by the expression of parvalbumin. We sought to identify molecular targets specific to those neurons and which are putatively associated with glial cell line-derived neurotrophic factor synthesis. To this end, the transcriptomic differences between glial cell line-derived neurotrophic factor-positive parvalbumin neurons in the striatum and parvalbumin neurons located in the nearby cortex, which do not express glial cell line-derived neurotrophic factor, were analysed. Using mouse reporter models, we have defined the genomic signature of striatal parvalbumin interneurons obtained by fluorescence-activated cell sorting followed by microarray comparison. Short-listed genes were validated by additional histological and molecular analyses. These genes code for membrane receptors (Kit, Gpr83, Tacr1, Tacr3, Mc3r), cytosolic proteins (Pde3a, Crabp1, Rarres2, Moxd1) and a transcription factor (Lhx8). We also found the proto-oncogene cKit to be highly specific of parvalbumin interneurons in the non-human primate striatum, thus highlighting a conserved expression between species and suggesting that specific genes identified in mouse parvalbumin neurons could be putative targets in the human brain. Pharmacological stimulation of four G-protein-coupled receptors enriched in the striatal parvalbumin interneurons inhibited Gdnf expression presumably by decreasing cyclic adenosine monophosphate formation. Additional experiments with pharmacological modulators of adenylyl cyclase and protein kinase A indicated that this pathway is a relevant intracellular route to induce Gdnf gene activation. This preclinical study is an important step in the ongoing development of a specific pro-endo-glial cell line-derived neurotrophic factor pharmacological strategy to treat Parkinson’s disease.

GLAST-CreERT2 mediated deletion of GDNF increases brain damage and exacerbates long-term stroke outcomes after focal ischemic stroke in mouse model

Focal ischemic stroke (FIS) is a leading cause of human death. Glial scar formation largely caused by reactive astrogliosis in peri-infarct region (PIR) is the hallmark of FIS. Glial cell-derived neurotrophic factor (GDNF) was originally isolated from a rat glioma cell-line supernatant and is a potent survival neurotrophic factor. Here, using CreER^T2 -LoxP recombination technology, we generated inducible and astrocyte-specific GDNF conditional knockout (cKO), that is, GLAST-GDNF^-/- cKO mice to investigate the effect of reactive astrocytes (RAs)-derived GDNF on neuronal death, brain damage, oxidative stress and motor function recovery after photothrombosis (PT)-induced FIS. Under non-ischemic conditions, we found that adult GLAST-GDNF^-/- cKO mice exhibited significant lower numbers of Brdu+, Ki67+ cells, and DCX+ cells in the dentate gyrus (DG) in hippocampus than GDNF floxed (GDNF^f/f ) control (Ctrl) mice, indicating endogenous astrocytic GDNF can promote adult neurogenesis. Under ischemic conditions, GLAST-GDNF^-/- cKO mice had a significant increase in infarct volume, hippocampal damage and FJB+ degenerating neurons after PT as compared with the Ctrl mice. GLAST-GDNF^-/- cKO mice also had lower densities of Brdu+ and Ki67+ cells in the PIR and exhibited larger behavioral deficits than the Ctrl mice. Mechanistically, GDNF deficiency in astrocytes increased oxidative stress through the downregulation of glucose-6-phosphate dehydrogenase (G6PD) in RAs. In summary, our study indicates that RAs-derived endogenous GDNF plays important roles in reducing brain damage and promoting brain recovery after FIS through neural regeneration and suggests that promoting anti-oxidant mechanism in RAs is a potential strategy in stroke therapy.

Possible roles of epigenetics in stem cell therapy for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease with loss of dopaminergic neurons. PD has genetic and epigenetic influences that determine specific changes in the brain. Epigenetic changes result in defective methylation of genes leading to differential gene-expression causing PD. This review provides an overview of stem cell transplantations as potential therapies for PD, with a focus on the epigenetic changes, prior or following transplantation. To date, no reports have addressed epigenetic alterations following stem cell transplantation into the PD brain. Given the potential for affecting the efficacy of stem cell therapy, increased attention needs to be given to the epigenetic processes that occur during stem cell culture and transplantation to maximize the therapeutic potential of stem cells to PD.

The role of Glial cell derived neurotrophic factor in head and neck cancer

Glial cell-derived neurotrophic factor (GDNF) is reported to promote the survival of neurons and salivary gland regeneration after radiation damage. This study investigated the effect of GDNF on cell migration, growth, and response to radiation in preclinical models of head and neck squamous cell carcinoma (HNSCC) and correlated GDNF expression to treatment outcomes in HNSCC patients. Our ultimate goal is to determine whether systemic administration of GDNF at high dose is safe for the management of hyposalivation or xerostomia in HNSCC patients. Three HPV-positive and three HPV-negative cell lines were examined for cell migration, growth, and clonogenic survival in vitro and tumor growth assay in vivo. Immunohistochemical staining of GDNF, its receptors GFRα1 and its co-receptor RET was performed on two independent HNSCC tissue microarrays (TMA) and correlated to treatment outcomes. Results showed that GDNF only enhanced cell migration in two HPV-positive cells at supra-physiologic doses, but not in HPV-negative cells. GDNF did not increase cell survival in the tested cell lines post-irradiation. Likewise, GDNF treatment affected neither tumor growth in vitro nor response to radiation in xenografts in two HPV-positive and two HPV-negative HNSCC models. High stromal expression of GDNF protein was associated with worse overall survival in HPV-negative HNSCC on multivariate analysis in a combined cohort of patients from Stanford University (n = 82) and Washington University (n = 189); however, the association between GDNF gene expression and worse survival was not confirmed in a separate group of HPV-negative HNSCC patients identified from the Cancer Genome Atlas (TCGA) database. Based on these data, we do not believe that GNDF is a safe systemic treatment to prevent or treat xerostomia in HNSCC and a local delivery approach such as intraglandular injection needs to be explored.

Harpagide, a natural product, promotes synaptic vesicle release as measured by nanoelectrode amperometry

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive loss of dopaminergic (DAergic) neurons and low level of dopamine (DA) in the midbrain. Recent studies suggested that some natural products can protect neurons against injury, but their role on neurotransmitter release and the underlying mechanisms remained unknown. In this work, nanoelectrode electrochemistry was used for the first time to quantify DA release inside single DAergic synapses. Our results unambiguously demonstrated that harpagide, a natural product, effectively enhances synaptic DA release and restores DA release at normal levels from injured neurons in PD model. These important protective and curative effects are shown to result from the fact that harpagide efficiently inhibits the phosphorylation and aggregation of α-synuclein by alleviating the intracellular reactive oxygen level, being beneficial for vesicle loading and recycling. This establishes that harpagide offers promising avenues for preventive or therapeutic interventions against PD and other neurodegenerative disorders.

GDNF-expressing macrophages restore motor functions at a severe late-stage, and produce long-term neuroprotective effects at an early-stage of Parkinson's disease in transgenic Parkin Q311X(A) mice

There is an unmet medical need in the area of Parkinson's disease (PD) to develop novel therapeutic approaches that can stop and reverse the underlying mechanisms responsible for the neuronal death. We previously demonstrated that systemically administered autologous macrophages transfected ex vivo to produce glial cell line-derived neurotrophic factor (GDNF) readily migrate to the mouse brain with acute toxin-induced neuroinflammation and ameliorate neurodegeneration in PD mouse models. We hypothesized that the high level of cytokines due to inflammatory process attracted GDNF-expressing macrophages and ensured targeted drug delivery to the PD brain. Herein, we validated a therapeutic potential of GDNF-transfected macrophages in a transgenic Parkin Q311X(A) mice with slow progression and mild brain inflammation. Systemic administration of GDNF-macrophages at a severe late stage of the disease leaded to a near complete restoration of motor functions in Parkin Q311X(A) mice and improved brain tissue integrity with healthy neuronal morphology. Furthermore, intravenous injections of GDNF-macrophages at an early stage of disease resulted in potent sustained therapeutic effects in PD mice for more than a year after the treatment. Importantly, multiple lines of evidence for therapeutic efficacy were observed including: diminished neuroinflammation and α-synuclein aggregation, increased survival of dopaminergic neurons, and improved locomotor functions. In summary, GDNF-transfected macrophages represent a promising therapeutic strategy for PD at both late- and early-stages of the disease.

Partial Reconstruction of the Nigrostriatal Circuit along a Preformed Molecular Guidance Pathway

The overall goal of our research is to establish a preformed molecular guidance pathway to direct the growth of dopaminergic axons from embryonic ventral mesencephalon (VM), tissue placed within the substantia nigra (SN), into the striatum to reconstruct the nigrostriatal pathway in a hemi-Parkinson's disease rat model. Guidance pathways were prepared by injecting lentivirus encoding either GFP or a combination of glial-cell-line-derived neurotrophic factor (GDNF) with either GDNF family receptor α1 (GFRα1) or netrin1. In another cohort of animals, adeno-associated virus (AAV) encoding brain-derived neurotrophic factor (BDNF) was injected within the striatum after guidance pathway formation. GDNF combined with either GFRα1 or netrin significantly increased growth of dopaminergic axons out of transplants and along the pathway, resulting in a significant reduction in the number of amphetamine-induced rotations. Retrograde tract tracing showed that the dopaminergic axons innervating the striatum were from A9 neurons within the transplant. Increased dopaminergic innervation of the striatum and improved behavioral recovery were observed with the addition of BDNF. Preformed guidance pathways using a combination of GDNF and netrin1 can be used to reconstruct the nigrostriatal pathway and improve motor recovery.

Materials Science and Design Principles of Growth Factor Delivery Systems in Tissue Engineering and Regenerative Medicine

Growth factors (GFs) are signaling molecules that direct cell development by providing biochemical cues for stem cell proliferation, migration, and differentiation. GFs play a key role in tissue regeneration, but one major limitation of GF-based therapies is dosage-related adverse effects. Additionally, the clinical applications and efficacy of GFs are significantly affected by the efficiency of delivery systems and other pharmacokinetic factors. Hence, it is crucial to design delivery systems that provide optimal activity, stability, and tunable delivery for GFs. Understanding the physicochemical properties of the GFs and the biomaterials utilized for the development of biomimetic GF delivery systems is critical for GF-based regeneration. Many different delivery systems have been developed to achieve tunable delivery kinetics for single or multiple GFs. The identification of ideal biomaterials with tunable properties for spatiotemporal delivery of GFs is still challenging. This review characterizes the types, properties, and functions of GFs, the materials science of widely used biomaterials, and various GF loading strategies to comprehensively summarize the current delivery systems for tunable spatiotemporal delivery of GFs aimed for tissue regeneration applications. This review concludes by discussing fundamental design principles for GF delivery vehicles based on the interactive physicochemical properties of the proteins and biomaterials.

Neurotrophic factors hold promise for the future of Parkinson's disease treatment: is there a light at the end of the tunnel?

Parkinson's disease (PD) is the second most common neurodegenerative disorder and is characterized by a spectrum of clinicopathologic signs and a complex etiology. PD results from the degeneration of dopaminergic (DAergic) neurons in the substantia nigra. Current therapies for PD are only able to alleviate symptoms without stopping disease progression. In addition, the available therapeutic strategies do not have long-lasting effects. Furthermore, these therapies cause different ranges of adverse side effects. There is great interest in neurotrophic factors (NTFs) due to their ability to promote the survival of different neural cells. These factors are divided into four families: neurotrophins, neurokines, the glial cell line-derived NTF family of ligands, and the newly recognized cerebral DA NTF/mesencephalic astrocyte-derived NTF family. The protective and therapeutic effects of these factors on DAergic neurons make them suitable for the prevention of progressive cell loss in PD. Based on the above premise, we focus on the protective effects of NTFs, especially CDNF and MANF, on nigrostriatal DAergic neurons in PD.

Combination of cell transplantation and glial cell line-derived neurotrophic factor-secreting encapsulated cells in Parkinson's disease

A major limitation of cell transplantation for Parkinson's disease (PD) is the mediocre survival of the grafted cells. Facilitating graft survival may improve the functional outcomes of the transplanted cells. Here, we discuss our observations that combination of rat fetal ventral mesencephalic (VM) tissue and encapsulated cells that secrete glial cell line-derived neurotrophic factor (GDNF) enhanced graft function in an animal model of PD. We described significant 2-fold increase in the number of tyrosine hydroxylase immunoreactive (TH-ir) cells per graft, as well as 1.7-fold and 9-fold increments in TH-ir fiber outgrowth into the host brain and toward the capsule with combined transplants and GDNF capsules as opposed to the VM transplants and mock-capsule group. These findings demonstrate that encapsulated GDNF-secreting cells improve graft survival that may optimize functional benefits for the treatment of PD.

Simultaneous Transplantation of Fetal Ventral Mesencephalic Tissue and Encapsulated Genetically Modified Cells Releasing GDNF in a Hemi-Parkinsonian Rat Model of Parkinson's Disease

Transplantation of fetal ventral mesencephalic (VM) neurons for Parkinson’s disease (PD) is limited by poor survival and suboptimal integration of grafted tissue into the host brain. In a 6-hydroxydopamine rat model of PD, we investigated the feasibility of simultaneous transplantation of rat fetal VM tissue and polymer-encapsulated C2C12 myoblasts genetically modified to produce glial cell line–derived neurotrophic factor (GDNF) or mock-transfected myoblasts on graft function. Amphetamine-induced rotations were assessed prior to transplantation and 2, 4, 6 and 9 wk posttransplantation. We found that rats grafted with VM transplants and GDNF capsules showed a significant functional recovery 4 wk after implantation. In contrast, rats from the VM transplant and mock-capsule group did not improve at any time point analyzed. Moreover, we detected a significantly higher number of tyrosine hydroxylase immunoreactive (TH-ir) cells per graft (2-fold), a tendency for a larger graft volume and an overall higher TH-ir fiber outgrowth into the host brain (1.7-fold) in the group with VM transplants and GDNF capsules as compared to the VM transplant and mock-capsule group. Most prominent was the TH-ir fiber outgrowth toward the capsule (9-fold). Grafting of GDNF-pretreated VM transplants in combination with the implantation of GDNF capsules resulted in a tendency for a higher TH-ir fiber outgrowth into the host brain (1.7-fold) as compared to the group transplanted with untreated VM transplants and GDNF capsules. No differences between groups were observed for the number of surviving TH-ir neurons or graft volume. In conclusion, our findings demonstrate that simultaneous transplantation of fetal VM tissue and encapsulated GDNF-releasing cells is feasible and support the graft survival and function. Pretreatment of donor tissue with GDNF may offer a way to further improve cell transplantation approaches for PD.

Ultrasound-Triggered Effects of the Microbubbles Coupled to GDNF Plasmid-Loaded PEGylated Liposomes in a Rat Model of Parkinson's Disease

Background: The purpose of this study was to investigate ultrasound-triggered effects of PEGylated liposomes-coupled microbubbles mediated gene transfer of glial cell line-derived neurotrophic factor (GDNF) plasmid (PLs-GDNF-MBs) on behavioral deficits and neuron loss in a rat model of Parkinson's disease (PD).

Methods: The unloaded PLs-MBs were characterized for particle size, concentration and zeta potential. PD rat model was established by a unilateral 6-hydroxydopamine (6-OHDA) lesion. Rotational, climbing pole, and suspension tests were used to evaluate behavioral deficits. The immunohistochemical staining of tyrosine hydroxylase (TH) and dopamine transporter (DAT) was used to assess the neuron loss. The expression levels of GDNF and nuclear receptor-related factor 1 (Nurr1) were determined by western blot and qRT-PCR analysis.

Results: The particle size of PLs-MBs was gradually increased, while the concentration and absolute zeta potential were gradually decreased in a time-dependent manner after injection. 6-OHDA elevated amphetamine-induced rotations and decreased the TH and DAT immunoreactivity compared to sham group. However, these effects were blocked by the PLs-GDNF-MBs. In addition, the mRNA and protein expression levels of GDNF and Nurr1 were increased after PLs-GDNF-MBs treatment.

Conclusions: The delivery of PLs-GDNF-MBs into the brains using MRI-guided focused ultrasound alleviates the behavioral deficits and neuron loss in the rat model of PD.

Exercise-Induced Neuroprotection of the Nigrostriatal Dopamine System in Parkinson's Disease

Epidemiological studies indicate that physical activity and exercise may reduce the risk of developing Parkinson's disease (PD), and clinical observations suggest that physical exercise can reduce the motor symptoms in PD patients. In experimental animals, a profound observation is that exercise of appropriate timing, duration, and intensity can reduce toxin-induced lesion of the nigrostriatal dopamine (DA) system in animal PD models, although negative results have also been reported, potentially due to inappropriate timing and intensity of the exercise regimen. Exercise may also minimize DA denervation-induced medium spiny neuron (MSN) dendritic atrophy and other abnormalities such as enlarged corticostriatal synapse and abnormal MSN excitability and spiking activity. Taken together, epidemiological studies, clinical observations, and animal research indicate that appropriately dosed physical activity and exercise may not only reduce the risk of developing PD in vulnerable populations but also benefit PD patients by potentially protecting the residual DA neurons or directly restoring the dysfunctional cortico-basal ganglia motor control circuit, and these benefits may be mediated by exercise-triggered production of endogenous neuroprotective molecules such as neurotrophic factors. Thus, exercise is a universally available, side effect-free medicine that should be prescribed to vulnerable populations as a preventive measure and to PD patients as a component of treatment. Future research needs to establish standardized exercise protocols that can reliably induce DA neuron protection, enabling the delineation of the underlying cellular and molecular mechanisms that in turn can maximize exercise-induced neuroprotection and neurorestoration in animal PD models and eventually in PD patients.

Nanoformulation: A Useful Therapeutic Strategy for Improving Neuroprotection and the Neurorestorative Potential in Experimental Models of Parkinson's Disease

Parkinson's disease (PD) is the second most frequent neurodegenerative disorder, but current therapies are only symptomatic. Experimental models are necessary to go deeper in the comprehension of pathophysiological mechanism and to assess new therapeutic strategies. The unilateral 6-hydroxydopamine (6-OHDA) lesion either in medial forebrain bundle (MFB) or into the striatum in rats affords to study various stages of PD depending on the evolution time lapsed. A promising alternative to address the neurodegenerative process is the use of neurotrophic factors; but its clinical use has been limited due to its short half-life and rapid degradation after in vivo administration, along with difficulties for crossing the blood-brain barrier (BBB). Tyrosine hydroxylase (TH) immunostaining revealed a significant decrease of the TH-immunopositive striatal volume in 6-OHDA group from rostral to caudal one. The loss of TH-ir neurons and axodendritic network (ADN) was higher in caudal sections showing a selective vulnerability of the topological distributed dopaminergic system. In addition to a remarkable depletion of dopamine in the nigrostriatal system, the administration of 6-OHDA into MFB induces some other neuropathological changes such as an increase of glial fibrillary acidic protein (GFAP) positive cells in substantia nigra (SN) as well as in striatum. Intrastriatal implantation of micro- or nanosystems delivering neurotrophic factor in parkinsonized rats for bypassing BBB leads to a significative functional and morphological recovery. Neurorestorative morphological changes (preservation of the TH-ir cells and ADN) along the rostrocaudal axis of caudoputamen complex and SN have been probed supporting a selective recovering after the treatment as well. Others innovative therapeutic strategies, such as the intranasal delivery, have been recently assessed in order to search the NTF effects. In addition some others methodological key points are reviewed.

Metformin lowers α-synuclein phosphorylation and upregulates neurotrophic factor in the MPTP mouse model of Parkinson's disease

In spite of the massive research for the identification of neurorestorative or neuroprotective intervention for curing Parkinson's disease (PD), there is still lack of clinically proven neuroprotective agents. Metformin, a common anti-hyperglycemic drug has been known to possess neuroprotective properties. However, specific mechanisms by which metformin protects neurons from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity remain to be elucidated. In this study, we assessed the neuroprotective effects of metformin in the subchronic MPTP model of PD, and explored its feasible mechanisms for neuroprotection. Animals received saline or MPTP injection (30 mg/kg/day) for the first 7 days, and then saline or metformin (200 mg/kg/day) for the next 7 days. Immunohistochemical stainings showed that metformin rescued the tyrosine hydroxylase-positive neurons and attenuated astroglial activation in the nigrostriatal pathway. In parallel, metformin restored dopamine depletion and behavioral impairments exerted by MPTP. Western blot analysis revealed that metformin ameliorated MPTP-induced α-synuclein phosphorylation which was accompanied by increased methylation of protein phosphatase 2A (PP2A), a phosphatase related to α-synuclein dephosphorylation. Moreover, the metformin regimen significantly increased the level of brain derived neurotrophic factor in the substantia nigra, and activated signaling pathways related to cell survival. Proof of concept study revealed that inhibition of PP2A or tropomyosin receptor kinase B reversed neuroprotective property of metformin in SH-SY5Y cells. Our results indicate that metformin provides neuroprotection against MPTP neurotoxicity, which might be mediated by inhibition of α-synuclein phosphorylation and induction of neurotrophic factors.

Intracerebral injections of DNA nanoparticles encoding for a therapeutic gene provide partial neuroprotection in an animal model of neurodegeneration

This study reports proof of concept for administering compacted DNA nanoparticles (DNPs) intracerebrally as a means to protect against neurotoxin-induced neurodegeneration of dopamine (DA) neurons. In this study we used DNPs that encoded for human glial cell line-derived neurotrophic factor (hGDNF); GDNF is a potent neurotrophic factor for DA neurons. Intracerebral injections of DNPs into the striatum and/or substantia nigra were performed 1 week before treatment with a neurotoxin. We observed that the number of surviving DA cells, the density of DA fiber terminals and recovery of motor function were greater in animals injected with GDNF-encoding DNPs than in control animals receiving DNPs encoding for an inert reporter gene. The results of these studies are one of the first to demonstrate that a non-viral, synthetic nanoparticle can be used to deliver therapeutic genes to cells in the brain as a means to protect cells against neurotoxin-induced neurodegeneration.

Impact of the Secretome of Human Mesenchymal Stem Cells on Brain Structure and Animal Behavior in a Rat Model of Parkinson's Disease

Research in the last decade strongly suggests that mesenchymal stem cell (MSC)‐mediated therapeutic benefits are mainly due to their secretome, which has been proposed as a possible therapeutic tool for the treatment of Parkinson's disease (PD). Indeed, it has been shown that the MSC secretome increases neurogenesis and cell survival, and has numerous neuroprotective actions under different conditions. Additionally, using dynamic culturing conditions (through computer‐controlled bioreactors) can further modulate the MSC secretome, thereby generating a more potent neurotrophic factor cocktail (i.e., conditioned medium). In this study, we have characterized the MSC secretome by proteomic‐based analysis, investigating its therapeutic effects on the physiological recovery of a 6‐hydroxidopamine (6‐OHDA) PD rat model. For this purpose, we injected MSC secretome into the substantia nigra (SNc) and striatum (STR), characterizing the behavioral performance and determining histological parameters for injected animals versus untreated groups. We observed that the secretome potentiated the increase of dopaminergic neurons (i.e., tyrosine hydroxylase‐positive cells) and neuronal terminals in the SNc and STR, respectively, thereby supporting the recovery observed in the Parkinsonian rats’ motor performance outcomes (assessed by rotarod and staircase tests). Finally, proteomic characterization of the MSC secretome (through combined mass spectrometry analysis and Bioplex assays) revealed the presence of important neuroregulatory molecules, namely cystatin C, glia‐derived nexin, galectin‐1, pigment epithelium‐derived factor, vascular endothelial growth factor, brain‐derived neurotrophic factor, interleukin‐6, and glial cell line‐derived neurotrophic factor. Overall, we concluded that the use of human MSC secretome alone was able to partially revert the motor phenotype and the neuronal structure of 6‐OHDA PD animals. This indicates that the human MSC secretome could represent a novel therapeutic for the treatment of PD. Stem Cells Translational Medicine2017;6:634–646

Ret is essential to mediate GDNF's neuroprotective and neuroregenerative effect in a Parkinson disease mouse model

Glial cell line-derived neurotrophic factor (GDNF) is a potent survival and regeneration-promoting factor for dopaminergic neurons in cell and animal models of Parkinson disease (PD). GDNF is currently tested in clinical trials on PD patients with so far inconclusive results. The receptor tyrosine kinase Ret is the canonical GDNF receptor, but several alternative GDNF receptors have been proposed, raising the question of which signaling receptor mediates here the beneficial GDNF effects. To address this question we overexpressed GDNF in the striatum of mice deficient for Ret in dopaminergic neurons and subsequently challenged these mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Strikingly, in this established PD mouse model, the absence of Ret completely abolished GDNF's neuroprotective and regenerative effect on the midbrain dopaminergic system. This establishes Ret signaling as absolutely required for GDNF's effects to prevent and compensate dopaminergic system degeneration and suggests Ret activation as the primary target of GDNF therapy in PD.

Microtubule: A Common Target for Parkin and Parkinson’s Disease Toxins

Parkinson’s disease (PD) is characterized by the selective loss of nigral dopaminergic (DA) neurons, which have long axons enriched with microtubules. Depolymerization of microtubules by PD toxins such as rotenone disrupts vesicular transport. The ensuing accumulation of vesicles in the cell body leads to increased cytosolic concentration of dopamine due to leakage of the vesicles. Elevated oxidative stress induced by dopamine oxidation may thus trigger the selective demise of DA neurons. Many strategies have been developed to protect DA neurons by stabilizing microtubules either directly or through intracellular signaling cascades. On the other hand, parkin, one of the most frequently mutated genes in PD, encodes for a protein-ubiquitin E3 ligase that strongly binds to microtubules. Parkin stabilizes microtubules through three domains that provide strong and independent interactions with tubulin and microtubules. These interactions anchor parkin on microtubules and may facilitate its E3 ligase activity on misfolded proteins transported along microtubules. Thus, parkin and rotenone, two prominent genetic and environmental factors linked to PD, act in an opposing manner on the same molecular target in the cell, microtubules, whose destruction underlies the selective vulnerability of dopaminergic neurons.

Comparative Analysis of the Effects of Neurotrophic Factors CDNF and GDNF in a Nonhuman Primate Model of Parkinson's Disease

Cerebral dopamine neurotrophic factor (CDNF) belongs to a newly discovered family of evolutionarily conserved neurotrophic factors. We demonstrate for the first time a therapeutic effect of CDNF in a unilateral 6-hydroxydopamine (6-OHDA) lesion model of Parkinson’s disease in marmoset monkeys. Furthermore, we tested the impact of high chronic doses of human recombinant CDNF on unlesioned monkeys and analyzed the amino acid sequence of marmoset CDNF. The severity of 6-OHDA lesions and treatment effects were monitored in vivo using ¹²³I-FP-CIT (DaTSCAN) SPECT. Quantitative analysis of ¹²³I-FP-CIT SPECT showed a significant increase of dopamine transporter binding activity in lesioned animals treated with CDNF. Glial cell line-derived neurotrophic factor (GDNF), a well-characterized and potent neurotrophic factor for dopamine neurons, served as a control in a parallel comparison with CDNF. By contrast with CDNF, only single animals responded to the treatment with GDNF, but no statistical difference was observed in the GDNF group. However, increased numbers of tyrosine hydroxylase immunoreactive neurons, observed within the lesioned caudate nucleus of GDNF-treated animals, indicate a strong bioactive potential of GDNF.

Neurotrophic factors in Parkinson's disease are regulated by exercise: Evidence-based practice

We carried out a qualitative review of the literature on the influence of forced or voluntary exercise in Parkinson's Disease (PD)-induced animals, to better understand neural mechanisms and the role of neurotrophic factors (NFs) involved in the improvement of motor behavior. A few studies indicated that forced or voluntary exercise may promote neuroprotection, through upregulation of NF expression, against toxicity of drugs that simulate PD. Forced training, such as treadmill exercise and forced-limb use, adopted in most studies, in addition to voluntary exercise on a running wheel are suitable methods for NFs upregulation.

Long-term controlled GDNF over-expression reduces dopamine transporter activity without affecting tyrosine hydroxylase expression in the rat mesostriatal system

The dopamine (DA) transporter (DAT) is a plasma membrane glycoprotein expressed in dopaminergic (DA-) cells that takes back DA into presynaptic neurons after its release. DAT dysfunction has been involved in different neuro-psychiatric disorders including Parkinson's disease (PD). On the other hand, numerous studies support that the glial cell line-derived neurotrophic factor (GDNF) has a protective effect on DA-cells. However, studies in rodents show that prolonged GDNF over-expression may cause a tyrosine hydroxylase (TH, the limiting enzyme in DA synthesis) decline. The evidence of TH down-regulation suggests that another player in DA handling, DAT, may also be regulated by prolonged GDNF over-expression, and the possibility that this effect is induced at GDNF expression levels lower than those inducing TH down-regulation. This issue was investigated here using intrastriatal injections of a tetracycline-inducible adeno-associated viral vector expressing human GDNF cDNA (AAV-tetON-GDNF) in rats, and doxycycline (DOX; 0.01, 0.03, 0.5 and 3mg/ml) in the drinking water during 5weeks. We found that 3mg/ml DOX promotes an increase in striatal GDNF expression of 12× basal GDNF levels and both DA uptake decrease and TH down-regulation in its native and Ser40 phosphorylated forms. However, 0.5mg/ml DOX promotes a GDNF expression increase of 3× basal GDNF levels with DA uptake decrease but not TH down-regulation. The use of western-blot under non-reducing conditions, co-immunoprecipitation and in situ proximity ligation assay revealed that the DA uptake decrease is associated with the formation of DAT dimers and an increase in DAT-α-synuclein interactions, without changes in total DAT levels or its compartmental distribution. In conclusion, at appropriate GDNF transduction levels, DA uptake is regulated through DAT protein-protein interactions without interfering with DA synthesis.

FGF9-induced changes in cellular redox status and HO-1 upregulation are FGFR-dependent and proceed through both ERK and AKT to induce CREB and Nrf2 activation

Our previous studies demonstrated that fibroblast growth factor 9 (FGF9) protects cortical and dopaminergic neurons from 1-methyl-4-phenylpyridinium (MPP(+))-induced oxidative insult by upregulation of γ-glutamylcysteine synthetase (γ-GCS) and heme oxygenase-1 (HO-1). However, the mechanisms responsible for FGF9-induced γ-GCS and HO-1 upregulation remain uncharacterized. In the present study, we demonstrate the signaling pathways by which FGF9 upregulates HO-1 and γ-GCS expression. We found that FGF9-induced HO-1 and γ-GCS expression was prevented by PD173014, an inhibitor of the FGF receptor (FGFR). FGF9 treatment induced the phosphorylation of FGFR downstream signals of extracellular signal-regulated kinase 1/2 (ERK1/2) and AKT in a dose- and time-dependent manner. The inhibition of MEK/ERK1/2 or PI3K/AKT activity by U0126 or wortmannin, but not the inhibition of phospholipase Cγ by U73122, prevented FGF9-induced γ-GCS and HO-1 upregulation, changes in cellular redox status, and neuroprotection against MPP(+) toxicity in primary cortical and dopaminergic neurons. Furthermore, FGF9 treatment enhanced the promoter activity of the cAMP-response element binding protein (CREB) and nuclear factor erythroid-derived 2-like 2 (Nrf2), and this phenomenon was blocked by PD173014 or U0126 or wortmannin. Knockdown of CREB and Nrf2 by shRNA blocked FGF9-induced γ-GCS and HO-1 upregulation, but not ERK and AKT phosphorylation. An in vivo study consistently showed that FGF9 overexpression using a lentivirus delivery system induced ERK1/2 phosphorylation and HO-1 upregulation and protected dopaminergic neurons against MPP(+) toxicity in rat substantia nigra. These results indicate that FGF9-induced HO-1 and γ-GCS upregulation is mediated by binding to FGFR and activation of two parallel downstream signaling pathways, ERK and AKT, which reconverge to induce CREB and Nrf2 transcriptional activity.

Quantitative high-throughput gene expression profiling of human striatal development to screen stem cell-derived medium spiny neurons

A systematic characterization of the spatio-temporal gene expression during human neurodevelopment is essential to understand brain function in both physiological and pathological conditions. In recent years, stem cell technology has provided an in vitro tool to recapitulate human development, permitting also the generation of human models for many diseases. The correct differentiation of human pluripotent stem cell (hPSC) into specific cell types should be evaluated by comparison with specific cells/tissue profiles from the equivalent adult in vivo organ. Here, we define by a quantitative high-throughput gene expression analysis the subset of specific genes of the whole ganglionic eminence (WGE) and adult human striatum. Our results demonstrate that not only the number of specific genes is crucial but also their relative expression levels between brain areas. We next used these gene profiles to characterize the differentiation of hPSCs. Our findings demonstrate a temporal progression of gene expression during striatal differentiation of hPSCs from a WGE toward an adult striatum identity. Present results establish a gene expression profile to qualitatively and quantitatively evaluate the telencephalic hPSC-derived progenitors eventually used for transplantation and mature striatal neurons for disease modeling and drug-screening.

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.

Tricyclic antidepressant treatment evokes regional changes in neurotrophic factors over time within the intact and degenerating nigrostriatal system

In addition to alleviating depression, trophic responses produced by antidepressants may regulate neural plasticity in the diseased brain, which not only provides symptomatic benefit but also potentially slows the rate of disease progression in Parkinson's disease (PD). Recent in vitro and in vivo data provide evidence that neurotrophic factors such as brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) may be key mediators of the therapeutic response to antidepressants. As such, we conducted a cross-sectional time-course study to determine whether antidepressant-mediated changes in neurotrophic factors occur in relevant brain regions in response to amitriptyline (AMI) treatment before and after intrastriatal 6-hydroxydopamine (6OHDA). Adult male Wistar rats were divided into seven cohorts and given daily injections (i.p.) of AMI (5mg/kg) or saline throughout the duration of the study. In parallel, various cohorts of intact or parkinsonian animals were sacrificed at specific time points to determine the impact of AMI treatment on trophic factor levels in the intact and degenerating nigrostriatal system. The left and right hemispheres of the substantia nigra, striatum, frontal cortex, piriform cortex, hippocampus, and anterior cingulate cortex were dissected, and BDNF and GDNF levels were measured with ELISA. Results show that chronic AMI treatment elicits effects in multiple brain regions and differentially regulates levels of BDNF and GDNF depending on the region. Additionally, AMI halts the progressive degeneration of dopamine (DA) neurons elicited by an intrastriatal 6-OHDA lesion. Taken together, these results suggest that AMI treatment elicits significant trophic changes important to DA neuron survival within both the intact and degenerating nigrostriatal system.

Neuroprotective effects of GDNF-expressing human amniotic fluid cells

Brain injury continues to be one of the leading causes of disability worldwide. Despite decades of research, there is currently no pharmacologically effective treatment for preventing neuronal loss and repairing the brain. As a result, novel therapeutic approaches, such as cell-based therapies, are being actively pursued to repair tissue damage and restore neurological function after injury. In this study, we examined the neuroprotective potential of amniotic fluid (AF) single cell clones, engineered to secrete glial cell derived neurotrophic factor (AF-GDNF), both in vitro and in a surgically induced model of brain injury. Our results show that pre-treatment with GDNF significantly increases cell survival in cultures of AF cells or cortical neurons exposed to hydrogen peroxide. Since improving the efficacy of cell transplantation depends on enhanced graft cell survival, we investigated whether AF-GDNF cells seeded on polyglycolic acid (PGA) scaffolds could enhance graft survival following implantation into the lesion cavity. Encouragingly, the AF-GDNF cells survived longer than control AF cells in serum-free conditions and continued to secrete GDNF both in vitro and following implantation into the injured motor cortex. AF-GDNF implantation in the acute period following injury was sufficient to activate the MAPK/ERK signaling pathway in host neural cells in the peri-lesion area, potentially boosting endogenous neuroprotective pathways. These results were complemented with promising trends in beam walk tasks in AF-GDNF/PGA animals during the 7 day timeframe. Further investigation is required to determine whether significant behavioural improvement can be achieved at a longer timeframe.

Enhanced efficacy of the CDNF/MANF family by combined intranigral overexpression in the 6-OHDA rat model of Parkinson's disease

Cerebral Dopamine Neurotrophic Factor (CDNF) and Mesencephalic Astrocyte-derived Neurotrophic factor (MANF) are members of a recently discovered family of neurotrophic factors (NTFs). Here, we used intranigral or intrastriatal lentiviral vector-mediated expression to evaluate their efficacy at protecting dopaminergic function in the 6-OHDA model of Parkinson's disease (PD). In contrast to the well-studied Glial-Derived Neurotrophic Factor (GDNF), no beneficial effects were demonstrated by striatal overexpression of either protein. Interestingly, nigral overexpression of CDNF decreased amphetamine-induced rotations and increased tyroxine hydroxylase (TH) striatal fiber density but had no effect on numbers of TH(+) cells in the SN. Nigral MANF overexpression had no effect on amphetamine-induced rotations or TH striatal fiber density but resulted in a significant preservation of TH(+) cells. Combined nigral overexpression of both factors led to a robust reduction in amphetamine-induced rotations, greater increase in striatal TH-fiber density and significant protection of TH(+) cells in the SN. We conclude that nigral CDNF and MANF delivery is more efficacious than striatal delivery. This is also the first study to demonstrate that combined NTF can have synergistic effects that result in enhanced neuroprotection, suggesting that multiple NTF delivery may be more efficacious for the treatment of PD than the single NTF approaches attempted so far.

GDNF-transfected macrophages produce potent neuroprotective effects in Parkinson's disease mouse model

The pathobiology of Parkinson's disease (PD) is associated with the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) projecting to the striatum. Currently, there are no treatments that can halt or reverse the course of PD; only palliative therapies, such as replacement strategies for missing neurotransmitters, exist. Thus, the successful brain delivery of neurotrophic factors that promote neuronal survival and reverse the disease progression is crucial. We demonstrated earlier systemically administered autologous macrophages can deliver nanoformulated antioxidant, catalase, to the SNpc providing potent anti-inflammatory effects in PD mouse models. Here we evaluated genetically-modified macrophages for active targeted brain delivery of glial cell-line derived neurotropic factor (GDNF). To capitalize on the beneficial properties afforded by alternatively activated macrophages, transfected with GDNF-encoded pDNA cells were further differentiated toward regenerative M2 phenotype. A systemic administration of GDNF-expressing macrophages significantly ameliorated neurodegeneration and neuroinflammation in PD mice. Behavioral studies confirmed neuroprotective effects of the macrophage-based drug delivery system. One of the suggested mechanisms of therapeutic effects is the release of exosomes containing the expressed neurotropic factor followed by the efficient GDNF transfer to target neurons. Such formulations can serve as a new technology based on cell-mediated active delivery of therapeutic proteins that attenuate and reverse progression of PD, and ultimately provide hope for those patients who are already significantly disabled by the disease.

Neurotrophic factor GDNF promotes survival of salivary stem cells

Stem cell-based regenerative therapy is a promising treatment for head and neck cancer patients that suffer from chronic dry mouth (xerostomia) due to salivary gland injury from radiation therapy. Current xerostomia therapies only provide temporary symptom relief, while permanent restoration of salivary function is not currently feasible. Here, we identified and characterized a stem cell population from adult murine submandibular glands. Of the different cells isolated from the submandibular gland, this specific population, Lin-CD24+c-Kit+Sca1+, possessed the highest capacity for proliferation, self renewal, and differentiation during serial passage in vitro. Serial transplantations of this stem cell population into the submandibular gland of irradiated mice successfully restored saliva secretion and increased the number of functional acini. Gene-expression analysis revealed that glial cell line-derived neurotrophic factor (Gdnf) is highly expressed in Lin-CD24+c-Kit+Sca1+ stem cells. Furthermore, GDNF expression was upregulated upon radiation therapy in submandibular glands of both mice and humans. Administration of GDNF improved saliva production and enriched the number of functional acini in submandibular glands of irradiated animals and enhanced salisphere formation in cultured salivary stem cells, but did not accelerate growth of head and neck cancer cells. These data indicate that modulation of the GDNF pathway may have potential therapeutic benefit for management of radiation-induced xerostomia.

Heterotopic mucosal engrafting procedure for direct drug delivery to the brain in mice

Delivery of therapeutics into the brain is impeded by the presence of the blood-brain barrier (BBB) which restricts the passage of polar and high molecular weight compounds from the bloodstream and into brain tissue. Some direct delivery success in humans has been achieved via implantation of transcranial catheters; however this method is highly invasive and associated with numerous complications. A less invasive alternative would be to dose the brain through a surgically implanted, semipermeable membrane such as the nasal mucosa that is used to repair skull base defects following endoscopic transnasal tumor removal surgery in humans. Drug transfer though this membrane would effectively bypass the BBB and diffuse directly into the brain and cerebrospinal fluid. Inspired by this approach, a surgical approach in mice was developed that uses a donor septal mucosal membrane engrafted over an extracranial surgical BBB defect. This model has been shown to effectively allow the passage of high molecular weight compounds into the brain. Since numerous drug candidates are incapable of crossing the BBB, this model is valuable for performing preclinical testing of novel therapies for neurological and psychiatric diseases.