Gene expression patterns for GDNF and its receptors in the human putamen affected by Parkinson's disease: a real-time PCR study

The Use of Neurotrophic Factors as a Promising Strategy for the Treatment of Neurodegenerative Diseases (Review)

The review considers the use of exogenous neurotrophic factors in the treatment of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, and others. This group of diseases is associated with the death of neurons and dysfunction of the nervous tissue. Currently, there is no effective therapy for neurodegenerative diseases, and their treatment remains a serious problem of modern medicine. A promising strategy is the use of exogenous neurotrophic factors. Targeted delivery of these factors to the nervous tissue can improve survival of neurons during the development of neurodegenerative processes and ensure neuroplasticity. There are methods of direct injection of neurotrophic factors into the nervous tissue, delivery using viral vectors, as well as the use of gene cell products. The effectiveness of these approaches has been studied in numerous experimental works and in a number of clinical trials. Further research in this area could provide the basis for the creation of an alternative treatment for neurodegenerative diseases.

Unraveling the role of glial cell line-derived neurotrophic factor in the treatment of Parkinson's disease

Parkinson's disease is the second most common neurodegenerative condition with its prevalence projected to 8.9 million individuals globally in the year 2019. Parkinson's disease affects both motor and certain non-motor functions of an individual. Numerous research has focused on the neuroprotective effect of the glial cell line-derived neurotrophic factor (GDNF) in Parkinson's disease. Discovered in 1993, GDNF is a neurotrophic factor identified from the glial cells which was found to have selective effects on promoting survival and regeneration of certain populations of neurons including the dopaminergic nigrostriatal pathway. Given this property, recent studies have focused on the exogenous administration of GDNF for relieving Parkinson's disease-related symptoms both at a pre-clinical and a clinical level. This review will focus on enumerating the molecular connection between Parkinson's disease and GDNF and shed light on all the available drug delivery approaches to facilitate the selective delivery of GDNF into the brain paving the way as a potential therapeutic candidate for Parkinson's disease in the future.

Advances in Recombinant Adeno-Associated Virus Vectors for Neurodegenerative Diseases

Recombinant adeno-associated virus (rAAV) vectors are gene therapy delivery tools that offer a promising platform for the treatment of neurodegenerative diseases. Keeping up with developments in this fast-moving area of research is a challenge. This review was thus written with the intention to introduce this field of study to those who are new to it and direct others who are struggling to stay abreast of the literature towards notable recent studies. In ten sections, we briefly highlight early milestones within this field and its first clinical success stories. We showcase current clinical trials, which focus on gene replacement, gene augmentation, or gene suppression strategies. Next, we discuss ongoing efforts to improve the tropism of rAAV vectors for brain applications and introduce pre-clinical research directed toward harnessing rAAV vectors for gene editing applications. Subsequently, we present common genetic elements coded by the single-stranded DNA of rAAV vectors, their so-called payloads. Our focus is on recent advances that are bound to increase treatment efficacies. As needed, we included studies outside the neurodegenerative disease field that showcased improved pre-clinical designs of all-in-one rAAV vectors for gene editing applications. Finally, we discuss risks associated with off-target effects and inadvertent immunogenicity that these technologies harbor as well as the mitigation strategies available to date to make their application safer.

Differential expression of RET and GDNF family receptor, GFR-α1, between striatum and substantia nigra following nigrostriatal lesion: a case for diminished GDNF-signaling

Although glial cell line-derived neurotrophic factor (GDNF) showed efficacy in preclinical and early clinical studies to alleviate parkinsonian signs in Parkinson's disease (PD), later trials did not meet primary endpoints, giving pause to consider further investigation. While GDNF dose and delivery methods may have contributed to diminished efficacy, one crucial aspect of these clinical studies is that GDNF treatment across all studies began ∼8 years after PD diagnosis; a time point representing several years after near 100% depletion of nigrostriatal dopamine markers in striatum and at least 50% in substantia nigra (SN), and is later than the timing of GDNF treatment in preclinical studies. With nigrostriatal terminal loss exceeding 70% at PD diagnosis, we utilized hemi-parkinsonian rats to determine if expression of GDNF family receptor, GFR-α1, and receptor tyrosine kinase, RET, differed between striatum and SN at 1 and 4 weeks following a 6-hydroxydopamine (6-OHDA) lesion. Whereas GDNF expression changed minimally, GFR-α1 expression decreased progressively in striatum and in tyrosine hydroxylase positive (TH+) cells in SN, correlating with reduced TH cell number. However, in nigral astrocytes, GFR-α1 expression increased. RET expression decreased maximally in striatum by 1 week, whereas in the SN, a transient bilateral increase occurred that returned to control levels by 4 weeks. Expression of brain-derived neurotrophic factor (BDNF) or its receptor, TrkB, were unchanged throughout lesion progression. Together, these results reveal that differential GFR-α1 and RET expression between the striatum and SN, and cell-specific differences in GFR-α1 expression in SN, occur during nigrostriatal neuron loss. Targeting loss of GDNF receptors appears critical to enhance GDNF therapeutic efficacy against nigrostriatal neuron loss.

Significance Statement

Although preclinical evidence supports that GDNF provides neuroprotection and improves locomotor function in preclinical studies, clinical data supporting its efficacy to alleviate motor impairment in Parkinson's disease patients remains uncertain. Using the established 6-OHDA hemi-parkinsonian rat model, we determined whether expression of its cognate receptors, GFR-α1 and RET, were differentially affected between striatum and substantia nigra in a timeline study. In striatum, there was early and significant loss of RET, but a gradual, progressive loss of GFR-α1. In contrast, RET transiently increased in lesioned substantia nigra, but GFR-α1 progressively decreased only in nigrostriatal neurons and correlated with TH cell loss. Our results indicate that direct availability of GFR-α1 may be a critical element that determines GDNF efficacy following striatal delivery.

Highlights

GDNF expression was minimally affected by nigrostriatal lesionGDNF family receptor, GFR-α1, progressively decreased in striatum and in TH neurons in SN.GFR-α1 expression decreased along with TH neurons as lesion progressedGFR-α1 increased bilaterally in GFAP+ cells suggesting an inherent response to offset TH neuron lossRET expression was severely reduced in striatum, whereas it increased in SN early after lesion induction.

Recent developments in nucleic acid-based therapies for Parkinson's disease: Current status, clinical potential, and future strategies

Parkinson's disease is the second most common progressive neurodegenerative disease diagnosed mainly based on clinical symptoms caused by loss of nigrostriatal dopaminergic neurons. Although currently available pharmacological therapies provide symptomatic relief, however, the disease continues to progress eventually leading to severe motor and cognitive decline and reduced quality of life. The hallmark pathology of Parkinson's disease includes intraneuronal inclusions known as Lewy bodies and Lewy neurites, including fibrillar α-synuclein aggregates. These aggregates can progressively spread across synaptically connected brain regions leading to emergence of disease symptoms with time. The α-synuclein level is considered important in its fibrillization and aggregation. Nucleic acid therapeutics have recently been shown to be effective in treating various neurological diseases, raising the possibility of developing innovative molecular therapies for Parkinson's disease. In this review, we have described the advancements in genetic dysregulations in Parkinson's disease along with the disease-modifying strategies involved in genetic regulation with particular focus on downregulation of α-synuclein gene using various novel technologies, notably antisense oligonucleotides, microRNA, short interfering RNA, short hairpin RNAs, DNA aptamers, and gene therapy of vector-assisted delivery system-based therapeutics. In addition, the current status of preclinical and clinical development for nucleic acid-based therapies for Parkinson's disease have also been discussed along with their limitations and opportunities.

Adeno-Associated Viral Vectors as Versatile Tools for Neurological Disorders: Focus on Delivery Routes and Therapeutic Perspectives

It is without doubt that the gene therapy field is currently in the spotlight for the development of new therapeutics targeting unmet medical needs. Thus, considering the gene therapy scenario, neurological diseases in general and neurodegenerative disorders in particular are emerging as the most appealing choices for new therapeutic arrivals intended to slow down, stop, or even revert the natural progressive course that characterizes most of these devastating neurodegenerative processes. Since an extensive coverage of all available literature is not feasible in practical terms, here emphasis was made in providing some advice to beginners in the field with a narrow focus on elucidating the best delivery route available for fulfilling any given AAV-based therapeutic approach. Furthermore, it is worth nothing that the number of ongoing clinical trials is increasing at a breath-taking speed. Accordingly, a landscape view of preclinical and clinical initiatives is also provided here in an attempt to best illustrate what is ongoing in this quickly expanding field.

Is activation of GDNF/RET signaling the answer for successful treatment of Parkinson's disease? A discussion of data from the culture dish to the clinic

The neurotrophic signaling of glial cell line-derived neurotrophic factor (GDNF) with its canonical receptor, the receptor tyrosine kinase RET, coupled together with the GDNF family receptor alpha 1 is important for dopaminergic neuron survival and physiology in cell culture experiments and animal models. This prompted the idea to try GDNF/RET signaling as a therapeutic approach to treat Parkinson's disease with the hallmark of dopaminergic cell death in the substantia nigra of the midbrain. Despite several clinical trials with GDNF in Parkinson's disease patients, which mainly focused on optimizing the GDNF delivery technique, benefits were only seen in a few patients. In general, the endpoints did not show significant improvements. This suggests that it will be helpful to learn more about the basic biology of this fascinating but complicated GDNF/RET signaling system in the dopaminergic midbrain and about recent developments in the field to facilitate its use in the clinic. Here we will refer to the latest publications and point out important open questions in the field.

Mechanistic Insight from Preclinical Models of Parkinson's Disease Could Help Redirect Clinical Trial Efforts in GDNF Therapy

Parkinson’s disease (PD) is characterized by four pathognomonic hallmarks: (1) motor and non-motor deficits; (2) neuroinflammation and oxidative stress; (3) pathological aggregates of the α-synuclein (α-syn) protein; (4) neurodegeneration of the nigrostriatal system. Recent evidence sustains that the aggregation of pathological α-syn occurs in the early stages of the disease, becoming the first trigger of neuroinflammation and subsequent neurodegeneration. Thus, a therapeutic line aims at striking back α-synucleinopathy and neuroinflammation to impede neurodegeneration. Another therapeutic line is restoring the compromised dopaminergic system using neurotrophic factors, particularly the glial cell-derived neurotrophic factor (GDNF). Preclinical studies with GDNF have provided encouraging results but often lack evaluation of anti-α-syn and anti-inflammatory effects. In contrast, clinical trials have yielded imprecise results and have reported the emergence of severe side effects. Here, we analyze the discrepancy between preclinical and clinical outcomes, review the mechanisms of the aggregation of pathological α-syn, including neuroinflammation, and evaluate the neurorestorative properties of GDNF, emphasizing its anti-α-syn and anti-inflammatory effects in preclinical and clinical trials.

Adeno-Associated Viral Vectors as Versatile Tools for Parkinson's Research, Both for Disease Modeling Purposes and for Therapeutic Uses

It is without any doubt that precision medicine therapeutic strategies targeting neurodegenerative disorders are currently witnessing the spectacular rise of newly designed approaches based on the use of viral vectors as Trojan horses for the controlled release of a given genetic payload. Among the different types of viral vectors, adeno-associated viruses (AAVs) rank as the ones most commonly used for the purposes of either disease modeling or for therapeutic strategies. Here, we reviewed the current literature dealing with the use of AAVs within the field of Parkinson’s disease with the aim to provide neuroscientists with the advice and background required when facing a choice on which AAV might be best suited for addressing a given experimental challenge. Accordingly, here we will be summarizing some insights on different AAV serotypes, and which would be the most appropriate AAV delivery route. Next, the use of AAVs for modeling synucleinopathies is highlighted, providing potential readers with a landscape view of ongoing pre-clinical and clinical initiatives pushing forward AAV-based therapeutic approaches for Parkinson’s disease and related synucleinopathies.

Adeno-Associated Virus Vector for Central Nervous System Gene Therapy

The past several years have witnessed significant advances in the development of therapeutic gene delivery for neurological disorders of the central nervous system (CNS). In particular, genome-wide sequencing analysis has deepened our understanding of mutations that underlie many monogenic disorders, which in turn has contributed to clinical advances involving adeno-associated virus (AAV) vector delivery of replacement genes to treat recessive disorders. Moreover, gene therapy has been further bolstered with advances in genome editing tools that allow researchers to silence, repair, and amend endogenous genes. However, despite strong preclinical and clinical progress, challenges remain, including delivery and safety. Here, we discuss advances in AAV engineering, recent developments in cargo design, and translation of these technologies towards clinical progress.

Exploring the Use of Intracranial and Extracranial (Remote) Photobiomodulation Devices in Parkinson's Disease: A Comparison of Direct and Indirect Systemic Stimulations

In recent times, photobiomodulation has been shown to be beneficial in animal models of Parkinson's disease, improving locomotive behavior and being neuroprotective. Early observations in people with Parkinson's disease have been positive also, with improvements in the non-motor symptoms of the disease being evident most consistently. Although the precise mechanisms behind these improvements are not clear, two have been proposed: direct stimulation, where light reaches and acts directly on the distressed neurons, and remote stimulation, where light influences cells and/or molecules that provide systemic protection, thereby acting indirectly on distressed neurons. In relation to Parkinson's disease, given that the major zone of pathology lies deep in the brain and that light from an extracranial or external photobiomodulation device would not reach these vulnerable regions, stimulating the distressed neurons directly would require intracranial delivery of light using a device implanted close to the vulnerable regions. For indirect systemic stimulation, photobiomodulation could be applied to either the head and scalp, using a transcranial helmet, or to a more remote body part (e.g., abdomen, leg). In this review, we discuss the evidence for both the direct and indirect neuroprotective effects of photobiomodulation in Parkinson's disease and propose that both types of treatment modality, when working together using both intracranial and extracranial devices, provide the best therapeutic option.

Protection of dopamine neurons by CDNF and neurturin variant N4 against MPP+ in dissociated cultures from rat mesencephalon

Parkinson's disease is associated with the loss of dopamine (DA) neurons in ventral mesencephalon. We have previously reported that no single neurotrophic factor we tested protected DA neurons from the dopaminergic toxin 1-methyl-4-phenylpyridinium (MPP+) in dissociated cultures isolated from the P0 rat substantia nigra, but that a combination of five neurotrophic factors was protective. We now report that cerebral DA neurotrophic factor (CDNF) and a variant of neurturin (NRTN), N4, were also not protective when provided alone but were protective when added together. In cultures isolated from the substantia nigra, MPP+ (10 μM) decreased tyrosine hydroxylase-positive cells to 41.7 ± 5.4% of vehicle control. Although treatment of cultures with 100 ng/ml of either CDNF or N4 individually before and after toxin exposure did not significantly increase survival in MPP+-treated cultures, when the two trophic factors were added together at 100 ng/ml each, survival of cells was increased 28.2 ± 6.1% above the effect of MPP+ alone. In cultures isolated from the ventral tegmental area, another DA rich area, a higher dose of MPP+ (1 mM) was required to produce an EC50 in TH-positive cells but, as in the substantia nigra, only the combination of CDNF and N4 (100 ng/ml each) was successful at increasing the survival of these cells compared to MPP+ alone (by 22.5 ± 3.5%). These data support previous findings that CDNF and N4 may be of therapeutic value for treatment of PD, but suggest that they may need to be administered together.

Gene Therapy for Neurodegenerative Diseases: Slowing Down the Ticking Clock

Gene therapy is an emerging and powerful therapeutic tool to deliver functional genetic material to cells in order to correct a defective gene. During the past decades, several studies have demonstrated the potential of AAV-based gene therapies for the treatment of neurodegenerative diseases. While some clinical studies have failed to demonstrate therapeutic efficacy, the use of AAV as a delivery tool has demonstrated to be safe. Here, we discuss the past, current and future perspectives of gene therapies for neurodegenerative diseases. We also discuss the current advances on the newly emerging RNAi-based gene therapies which has been widely studied in preclinical model and recently also made it to the clinic.

GDNF/RET signaling in dopamine neurons in vivo

The glial cell line-derived neurotrophic factor (GDNF) and its canonical receptor Ret can signal both in tandem and separately to exert many vital functions in the midbrain dopamine system. It is known that Ret has effects on maintenance, physiology, protection and regeneration in the midbrain dopamine system, with the physiological functions of GDNF still somewhat unclear. Notwithstanding, Ret ligands, such as GDNF, are considered as promising candidates for neuroprotection and/or regeneration in Parkinson's disease, although data from clinical trials are so far inconclusive. In this review, we discuss the current knowledge of GDNF/Ret signaling in the dopamine system in vivo as well as crosstalk with pathology-associated proteins and their signaling in mammals.

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.

Improving therapeutic potential of GDNF family ligands

The last decade has been a frustrating time for investigators who had envisioned major advances in the treatment of Parkinson’s disease using neurotrophic factors. The first trials of glial cell line–derived neurotrophic factor for treating Parkinson’s disease were very promising. Later blinded control trials were disappointing, not reaching the predetermined outcomes for improvement in motor function. Consideration of the problems in the studies as well as the biology of the neurotrophins used can potentially lead to more effective therapies. Parkinson’s disease presents a multitude of opportunities for the cell biologist wanting to understand its pathology and to find possible new avenues for treatment.

gdnf affects early diencephalic dopaminergic neuron development through regulation of differentiation-associated transcription factors in zebrafish

Glial cell line-derived neurotrophic factor (GDNF) has been reported to enhance dopaminergic neuron survival and differentiation in vitro and in vivo, although those results are still being debated. Glial cell line-derived neurotrophic factor (gdnf) is highly conserved in zebrafish and plays a role in enteric nervous system function. However, little is known about gdnf function in the teleost brain. Here, we employed clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 to impede gdnf function in the maintenance of dopaminergic neuron development. Genotyping of gdnf crispants revealed successful deletions of the coding region with various mutant band sizes and down-regulation of gdnf transcripts at 1, 3 and 7 day(s) post fertilization. Notably, ~20% reduction in ventral diencephalic dopaminergic neuron numbers in clusters 8 and 13 was observed in the gdnf-deficient crispants. In addition, gdnf depletion caused a modest reduction in dopaminergic neurogenesis as determined by 5-ethynyl-2'-deoxyuridine pulse chase assay. These deleterious effects could be partly attributed to deregulation of dopaminergic neuron fate specification-related transcription factors (otp,lmx1b,shha,and ngn1) in both crispants and established homozygous mutants with whole mount in-situ hybridization (WISH) on gdnf mutants showing reduced otpb and lmx1b.1 expression in the ventral diencephalon. Interestingly, locomotor function of crispants was only impacted at 7 dpf, but not earlier. Lastly, as expected, gdnf deficiency heightened crispants vulnerability to 1-methyl-4-phenylpyridinium toxic insult. Our results suggest conservation of teleost gdnf brain function with mammals and revealed the interactions between gdnf and transcription factors in dopaminergic neuron differentiation.

Hyperpolarized 13 C magnetic resonance spectroscopy detects toxin-induced neuroinflammation in mice

Lipopolysaccharide (LPS) is a commonly used agent for induction of neuroinflammation in preclinical studies. Upon injection, LPS causes activation of microglia and astrocytes, whose metabolism alters to favor glycolysis. Assessing in vivo neuroinflammation and its modulation following therapy remains challenging, and new noninvasive methods allowing for longitudinal monitoring would be highly valuable. Hyperpolarized (HP) ¹³ C magnetic resonance spectroscopy (MRS) is a promising technique for assessing in vivo metabolism. In addition to applications in oncology, the most commonly used probe of [1-¹³ C] pyruvate has shown potential in assessing neuroinflammation-linked metabolism in mouse models of multiple sclerosis and traumatic brain injury. Here, we aimed to investigate LPS-induced neuroinflammatory changes using HP [1-¹³ C] pyruvate and HP ¹³ C urea. 2D chemical shift imaging following simultaneous intravenous injection of HP [1-¹³ C] pyruvate and HP ¹³ C urea was performed at baseline (day 0) and at days 3 and 7 post-intracranial injection of LPS (n = 6) or saline (n = 5). Immunofluorescence (IF) analyses were performed for Iba1 (resting and activated microglia/macrophages), GFAP (resting and reactive astrocytes) and CD68 (activated microglia/macrophages). A significant increase in HP [1-¹³ C] lactate production was observed at days 3 and 7 following injection, in the injected (ipsilateral) side of the LPS-treated mouse brain, but not in either the contralateral side or saline-injected animals. HP ¹³ C lactate/pyruvate ratio, without and with normalization to urea, was also significantly increased in the ipsilateral LPS-injected brain at 7 days compared with baseline. IF analyses showed a significant increase in CD68 and GFAP staining at 3 days, followed by increased numbers of Iba1 and GFAP positive cells at 7 days post-LPS injection. In conclusion, we can detect LPS-induced changes in the mouse brain using HP ¹³ C MRS, in alignment with increased numbers of microglia/macrophages and astrocytes. This study demonstrates that HP ¹³ C spectroscopy has substantial potential for providing noninvasive information on neuroinflammation.

Canine neuropathies: powerful spontaneous models for human hereditary sensory neuropathies

In humans, hereditary sensory neuropathies (HSN), also known as hereditary sensory and autonomic neuropathies (HSAN), constitute a clinically and genetically heterogeneous group of disorders characterized by progressive sensory loss, often accompanied by chronic skin ulcerations and nail dystrophic changes. To date, although around 20 genes have already been discovered, they do not explain the genetic causes of all patients. In dogs, similar neuropathies are also diagnosed, several breeds being predisposed to specific forms of the disease. Indeed, the breed specificity of most canine genetic diseases is due to the small numbers of founders and high levels of inbreeding. Recent knowledge and tools developed to study the canine genome efficiently allows deciphering the genetic bases of such diseases. To date, a dozen breeds are recognized to develop specific HSN. For the Border collie and hunting dog breeds, the genes involved have recently been discovered. Other affected breeds thus constitute potential genetic models, with new genes to be found in dogs that can be considered as candidate genes for human HSAN/HSN. Here, we review the different forms of human and canine HSAN/HSN and we present a novel form in Fox terrier cases, highlighting the advantages of the dog model for such rare human diseases.

Treatment with the noradrenaline re-uptake inhibitor atomoxetine alone and in combination with the α2-adrenoceptor antagonist idazoxan attenuates loss of dopamine and associated motor deficits in the LPS inflammatory rat model of Parkinson's disease

The impact of treatment with the noradrenaline (NA) re-uptake inhibitor atomoxetine and the α₂-adrenoceptor (AR) antagonist idazoxan in an animal model of Parkinson's disease (PD) was assessed. Concurrent systemic treatment with atomoxetine and idazoxan, a combination which serves to enhance the extra-synaptic availability of NA, exerts anti-inflammatory and neuroprotective effects following delivery of an inflammatory stimulus, the bacterial endotoxin, lipopolysaccharide (LPS) into the substantia nigra. Lesion-induced deficits in motor function (akinesia, forelimb-use asymmetry) and striatal dopamine (DA) loss were rescued to varying degrees depending on the treatment. Treatment with atomoxetine following LPS-induced lesion to the substantia nigra, yielded a robust anti-inflammatory effect, suppressing microglial activation and expression of the pro-inflammatory cytokine TNF-α whilst increasing the expression of neurotrophic factors. Furthermore atomoxetine treatment prevented loss of tyrosine hydroxylase (TH) positive nigral dopaminergic neurons and resulted in functional improvements in motor behaviours. Atomoxetine alone was sufficient to achieve most of the observed effects. In combination with idazoxan, an additional improvement in the impairment of contralateral limb use 7 days post lesion and a reduction in amphetamine-mediated rotational asymmetry 14 days post-lesion was observed, compared to atomoxetine or idazoxan treatments alone. The results indicate that increases in central NA tone has the propensity to regulate the neuroinflammatory phenotype in vivo and may act as an endogenous neuroprotective mechanism where inflammation contributes to the progression of DA loss. In accordance with this, the clinical use of agents such as NA re-uptake inhibitors and α₂-AR antagonists may prove useful in enhancing the endogenous neuroimmunomodulatory potential of NA in conditions associated with brain inflammation.

A Parkinson's disease gene, DJ-1, repairs brain injury through Sox9 stabilization and astrogliosis

Defects in repair of damaged brain accumulate injury and contribute to slow-developing neurodegeneration. Here, we report that a deficiency of DJ-1, a Parkinson's disease (PD) gene, delays repair of brain injury due to destabilization of Sox9, a positive regulator of astrogliosis. Stereotaxic injection of ATP into the brain striatum produces similar size of acute injury in wild-type and DJ-1-knockout (KO) mice. However, recovery of the injury is delayed in KO mice, which is confirmed by 9.4T magnetic resonance imaging and tyrosine hydroxylase immunostaining. DJ-1 regulates neurite outgrowth from damaged neurons in a non-cell autonomous manner. In DJ-1 KO brains and astrocytes, Sox9 protein levels are decreased due to enhanced ubiquitination, resulting in defects in astrogliosis and glial cell-derived neurotrophic factor/ brain-derived neurotrophic factor expression in injured brain and astrocytes. These results indicate that DJ-1 deficiency causes defects in astrocyte-mediated repair of brain damage, which may contribute to the development of PD.

Complementary proteomic approaches reveal mitochondrial dysfunction, immune and inflammatory dysregulation in a mouse model of Gulf War Illness

Purpose

Long‐term consequences of combined pyridostigmine bromide (PB) and permethrin (PER) exposure in C57BL6/J mice using a well‐characterized mouse model of exposure to these Gulf War (GW) agents were explored at the protein level.

Experimental design

We used orthogonal proteomic approaches to identify pathways that are chronically impacted in the mouse CNS due to semiacute GW agent exposure early in life. These analyses were performed on soluble and membrane‐bound protein fractions from brain samples using two orthogonal isotopic labeling LC‐MS/MS proteomic approaches—stable isotope dimethyl labeling and iTRAQ.

Results

The use of these approaches allowed for greater coverage of proteins than was possible by either one alone and revealed both distinct and overlapping datasets. This combined analysis identified changes in several mitochondrial, as well as immune and inflammatory pathways after GW agent exposure.

Conclusions and clinical relevance

The work discussed here provides insight into GW agent exposure dependent mechanisms that adversely affect mitochondrial function and immune and inflammatory regulation. Collectively, our work identified key pathways which were chronically impacted in the mouse CNS following acute GW agent exposure, this may lead to the identification of potential targets for therapeutic intervention in the future.

Long‐term consequences of combined PB and PER exposure in C57BL6/J mice using a well‐characterized mouse model of exposure to these GW agents were explored at the protein level. Expanding on earlier work, we used orthogonal proteomic approaches to identify pathways that are chronically impacted in the mouse CNS due to semiacute GW agent exposure early in life. These analyses were performed on soluble and membrane‐bound protein fractions from brain samples using two orthogonal isotopic labeling LC‐MS/MS proteomic approaches—stable isotope dimethyl labeling and iTRAQ. The use of these approaches allowed for greater coverage of proteins than was possible by either one alone and revealed both distinct and overlapping datasets. This combined analysis identified changes in several mitochondrial, as well as immune and inflammatory pathways after GW agent exposure. The work discussed here provides insight into GW agent exposure dependent mechanisms that adversely affect mitochondrial function and immune and inflammatory regulation at 5 months postexposure to PB + PER.

Glial Cell Line-Derived Neurotrophic Factor Gene Delivery in Parkinson's Disease: A Delicate Balance between Neuroprotection, Trophic Effects, and Unwanted Compensatory Mechanisms

Glial cell line-derived neurotrophic factor (GDNF) and Neurturin (NRTN) bind to a receptor complex consisting of a member of the GDNF family receptor (GFR)-α and the Ret tyrosine kinase. Both factors were shown to protect nigro-striatal dopaminergic neurons and reduce motor symptoms when applied terminally in toxin-induced Parkinson's disease (PD) models. However, clinical trials based on intraputaminal GDNF protein administration or recombinant adeno-associated virus (rAAV)-mediated NRTN gene delivery have been disappointing. In this review, several factors that could have limited the clinical benefits are discussed. Retrograde transport of GDNF/NRTN to the dopaminergic neurons soma is thought to be necessary for NRTN/GFR-α/Ret signaling mediating the pro-survival effect. Therefore, the feasibility of treating advanced patients with neurotrophic factors is questioned by recent data showing that: (i) tyrosine hydroxylase-positive putaminal innervation has almost completely disappeared at 5 years post-diagnosis and (ii) in patients enrolled in the rAAV-NRTN trial more than 5 years post-diagnosis, NRTN was almost not transported to the substantia nigra pars compacta. In addition to its anti-apoptotic and neurotrophic properties, GDNF also interferes with dopamine homeostasis via time and dose-dependent effects such as: stimulation of dopamine neuron excitability, inhibition of dopamine transporter activity, tyrosine hydroxylase phosphorylation, and inhibition of tyrosine hydroxylase transcription. Depending on the delivery parameters, the net result of this intricate network of regulations could be either beneficial or deleterious. In conclusion, further unraveling of the mechanism of action of GDNF gene delivery in relevant animal models is still needed to optimize the clinical benefits of this new therapeutic approach. Recent developments in the design of regulated viral vectors will allow to finely adjust the GDNF dose and period of administration. Finally, new clinical studies in less advanced patients are warranted to evaluate the potential of AAV-mediated neurotrophic factors gene delivery in PD. These will be facilitated by the demonstration of the safety of rAAV administration into the human brain.

The Yin and Yang of nucleic acid-based therapy in the brain

The post-genomic era has unveiled the existence of a large repertory of non-coding RNAs and repetitive elements that play a fundamental role in cellular homeostasis and dysfunction. These may represent unprecedented opportunities to modify gene expression at the right time in the correct space in vivo, providing an almost unlimited reservoir of new potential pharmacological agents. Hijacking their mode of actions, the druggable genome can be extended to regulatory RNAs and DNA elements in a scalable fashion. Here, we discuss the state-of-the-art of nucleic acid-based drugs to treat neurodegenerative diseases. Beneficial effects can be obtained by inhibiting (Yin) and increasing (Yang) gene expression, depending on the disease and the drug target. Together with the description of the current use of inhibitory RNAs (small inhibitory RNAs and antisense oligonucleotides) in animal models and clinical trials, we discuss the molecular basis and applications of new classes of activatory RNAs at transcriptional (RNAa) and translational (SINEUP) levels.

Developing therapeutically more efficient Neurturin variants for treatment of Parkinson's disease

In Parkinson's disease midbrain dopaminergic neurons degenerate and die. Oral medications and deep brain stimulation can relieve the initial symptoms, but the disease continues to progress. Growth factors that might support the survival, enhance the activity, or even regenerate degenerating dopamine neurons have been tried with mixed results in patients. As growth factors do not pass the blood-brain barrier, they have to be delivered intracranially. Therefore their efficient diffusion in brain tissue is of crucial importance. To improve the diffusion of the growth factor neurturin (NRTN), we modified its capacity to attach to heparan sulfates in the extracellular matrix. We present four new, biologically fully active variants with reduced heparin binding. Two of these variants are more stable than WT NRTN in vitro and diffuse better in rat brains. We also show that one of the NRTN variants diffuses better than its close homolog GDNF in monkey brains. The variant with the highest stability and widest diffusion regenerates dopamine fibers and improves the conditions of rats in a 6-hydroxydopamine model of Parkinson's disease more potently than GDNF, which previously showed modest efficacy in clinical trials. The new NRTN variants may help solve the major problem of inadequate distribution of NRTN in human brain tissue.

Protection of cultured dopamine neurons from MPP(+) requires a combination of neurotrophic factors

Parkinson's disease is a progressive neurodegenerative disorder, caused in part by the loss of dopamine (DA) neurons in the substantia nigra (SN). Neurotrophic factors have been shown to increase the basal survival of DA neurons in vitro, as well as to protect the neurons from some toxins under certain in vitro conditions and in animal models. Although these factors have often been tested individually, they have rarely been studied in combinations. We therefore examined the effect of such combinations after acute exposure to the toxin 1-methyl-4-phenylpyridinium (MPP(+) ) using dissociated postnatal rat midbrain cultures isolated from SN and ventral tegmental area (VTA). We found that significant loss of DA neurons in the SN occurred with an LC50 of between 1 and 10 μm, whereas the LC50 of DA neurons from the VTA was approximately 1000-fold higher. We did not observe neuroprotection against MPP(+) by individual exposure to glial cell-line derived neurotrophic factor (GDNF), brain derived neurotrophic factor (BDNF), transforming growth factor beta (TGFβ), basic fibroblast growth factor (FGF-2) or growth/differentiation factor 5 (GDF5) at concentrations of 100 or 500 ng/mL. Combinations of two, three or four neurotrophic factors were also ineffective. However, when the SN cultures were exposed to a combination of all five neurotrophic factors, each at a concentration of 100 ng/mL, we observed a 30% increase in DA neuron survival in the presence of 10 and 500 μm MPP(+) . These results may be relevant to the use of neurotrophic factors as therapeutic treatments for Parkinson's disease.

Does the Cerebrospinal Fluid Reflect Altered Redox State But Not Neurotrophic Support Loss in Parkinson's Disease?

Alteration in neurotrophic factors support and antioxidant defenses in the central nervous system (CNS) along with deficit of ferritin have been associated with idiopathic Parkinson's disease (PD). The objectives were to analyze in the cerebrospinal fluid (CSF) of patients with PD and controls the following: (i) the levels of the neuroprotectant factors glial cell line-derived neurotrophic factor, persephin, neurturin, and brain-derived neurotrophic factor, (ii) the levels of transforming growth factor-β1 (TGFβ1) and transforming growth factor-β2 (TGFβ2), proinflammatory factors, (iii) the activity of the antioxidant enzymes glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferase (GST), catalase, superoxide dismutases (SODs), and peroxiredoxins (PRDxs), and (iv) ferritin levels. The study revealed that, among neurotrophic factors, only TGFβ1 levels were found to be enhanced in patients with PD (early, p < 0.05; advanced, p < 0.02). Regarding antioxidant enzymes, the activity of GPx, catalase, and PRDxs, all hydrogen peroxide scavengers, was found to be significantly reduced in patients (GPx, p < 0.001; catalase, p < 0.01; PRDxs, p < 0.01, one-way analysis of variance). Finally, ferritin content in CSF was significantly diminished over time in patients (early, p < 0.01, -49%; advanced, p < 0.001, -80.7%). Our observations lead to the hypothesis that parkinsonian patients suffer from a serious disturbance of redox state in the CNS, as evaluated through the CSF, characterized by reduced hydrogen peroxide scavenging and iron storage.

Persistent astrocyte activation in the fragile X mouse cerebellum

BACKGROUND

Fragile X Syndrome, the most common single gene cause of autism, results from loss of the RNA-binding protein FMRP. Although FMRP is highly expressed in neurons, it has also recently been identified in glia. It has been postulated that in the absence of FMRP, abnormal function of non-neuronal cells may contribute to the pathogenesis of the disorder. We previously demonstrated reduced numbers of oligodendrocyte precursor cells and delayed myelination in the cerebellum of fragile X (Fmr1) knockout mice.

METHODS

We used quantitative western blotting and immunocytochemistry to examine the status of astrocytes and microglia in the cerebellum of Fmr1 mice during development and in adulthood.

RESULTS

We report increased expression of the astrocyte marker GFAP in the cerebellum of Fmr1 mice starting in the second postnatal week and persisting in to adulthood. At 2 weeks postnatal, expression of Tumor Necrosis Factor Receptor 2 (TNFR2) and Leukemia Inhibitory Factor (LIF) were elevated in the Fmr1 KO cerebellum. In adults, expression of TNFR2 and the glial marker S100β were also elevated in Fmr1 knockouts, but LIF expression was not different from wild-type mice. We found no evidence of microglial activation or neuroinflammation at any age examined.

CONCLUSIONS

These findings demonstrate an atypical pattern of astrogliosis in the absence of microglial activation in Fmr1 knockout mouse cerebellum. Enhanced TNFR2 and LIF expression in young mice suggests that changes in the expression of astrocytic proteins may be an attempt to compensate for delayed myelination in the developing cerebellum of Fmr1 mice.

MS2 phage ribonucleoproteins as exogenous internal control for RT-qPCR data normalization in gene expression study of developing rat brain

The most popular strategy for normalization of RT-qPCR data involves presenting them in comparison with expression of "housekeeping" genes. However, the required stable expression of the control genes is not always achievable. As an alternative, we used ribonucleoprotein phage particles as an exogenous internal control and demonstrated that this type of normalization provides a simple and reliable method for quantification in RT-qPCR experiments. Using phage-based normalization, we analyzed mRNA levels of three popular housekeeping genes coding β-actin, glyceraldehyde-3-phosphate dehydrogenase, and ribosomal protein L30 and showed high variability in their expression patterns during rat brain development, indicating that they should not be used as controls in gene expression studies of the developing brain either individually or in combination. Using phage-based controls, we showed interstrain differences and age-related changes in the expression of genes involved in proteoglycan biosynthesis and degradation in developing brain of senescence-accelerated OXYS rats and control Wistar rats.

Increased brain bio-distribution and chemical stability and decreased immunogenicity of an engineered variant of GDNF

Several lines of evidence indicate that Glial cell line-derived neurotrophic factor (GDNF) is a trophic factor for dopaminergic neurons. Direct parenchymal administration of GDNF is robustly neuroprotective and neurorestorative in multiple neurotoxin-based animal models (rat and non-human primate (NHP)) of Parkinson's Disease (PD), suggesting its potential as a therapeutic agent. Although small, open-label clinical trials of intra-putamenal administration of bacteria-derived, full length, wild type GDNF (GDNFwt) were efficacious in improving standardized behavioral scores, a double-blinded, randomized controlled trial failed to do so. We hypothesize that the lack of clinical efficacy of GDNFwt in the larger randomized trial was due to poor bio-distribution in the putamen and/or poor chemical stability while in the delivery device for prolonged time periods at 37°C. The development of neutralizing antibodies in some patients may also have been a contributing factor. GDNFv is an engineered form of GDNFwt, expressed and purified from mammalian cells, designed to overcome these limitations, including removal of the N-terminal heparin-binding domain to improve its diffusivity in brain parenchyma by reducing its binding to extracellular matrix (ECM), and key amino acid substitutions to improve chemical stability. Intra-striatal administration of a single injection of GDNFv in the rat produced significantly greater brain distribution than GDNFwt, consistent with reduced binding to ECM. Using liquid chromatography/mass spectrometry (LS/MS) methods GDNFv was shown to have improved chemical stability compared to GDNFwt when stored at 37°C for 4weeks. In addition, GDNFv resulted in lower predicted clinical immunogenicity compared to GDNFwt, as demonstrated by reduced CD4+ T cell proliferation and reduced IL-2-induced secretion in peripheral blood mononucleated cells collected from volunteers representing the world's major histocompatibility complex (MHC) haplotypes. GDNFv was demonstrated to be pharmacologically equivalent to GDNFwt in the key parameters in vitro of GFRα1 receptor binding, c-Ret phosphorylation, neurite outgrowth, and in vivo in its ability to increase dopamine turnover (DA). GDNFv protected dopamine nerve terminals and neurons in a 6-hydroxy-dopamine (6-OHDA) rat model. In summary, we empirically demonstrate the superior properties of GDNFv compared to GDNFwt through enhanced bio-distribution and chemical stability concurrently with decreased predicted clinical immunogenicity while maintaining pharmacological and neurotrophic activity. These data indicate that GDNFv is an improved version of GDNF suitable for clinical assessment as a targeted regenerative therapy for PD.

Astrocytic metabolic and inflammatory changes as a function of age

This study examines age-dependent metabolic-inflammatory axis in primary astrocytes isolated from brain cortices of 7-, 13-, and 18-month-old Sprague–Dawley male rats. Astrocytes showed an age-dependent increase in mitochondrial oxidative metabolism respiring on glucose and/or pyruvate substrates; this increase in mitochondrial oxidative metabolism was accompanied by increases in COX3/18SrDNA values, thus suggesting an enhanced mitochondrial biogenesis. Enhanced mitochondrial respiration in astrocytes limits the substrate supply from astrocytes to neurons; this may be viewed as an adaptive mechanism to altered cellular inflammatory–redox environment with age. These metabolic changes were associated with an age-dependent increase in hydrogen peroxide generation (largely ascribed to an enhanced expression of NOX2) and NFκB signaling in the cytosol as well as its translocation to the nucleus. Astrocytes also displayed augmented responses with age to inflammatory cytokines, IL-1β, and TNFα. Activation of NFκB signaling resulted in increased expression of nitric oxide synthase 2 (inducible nitric oxide synthase), leading to elevated nitric oxide production. IL-1β and TNFα treatment stimulated mitochondrial oxidative metabolism and mitochondrial biogenesis in astrocytes. It may be surmised that increased mitochondrial aerobic metabolism and inflammatory responses are interconnected and support the functionality switch of astrocytes, from neurotrophic to neurotoxic with age.

Effects of naringin, a flavanone glycoside in grapefruits and citrus fruits, on the nigrostriatal dopaminergic projection in the adult brain

Recently, we have demonstrated the ability of naringin, a well-known flavanone glycoside of grapefruits and citrus fruits, to prevent neurodegeneration in a neurotoxin model of Parkinson's disease. Intraperitoneal injection of naringin protected the nigrostriatal dopaminergic projection by increasing glial cell line-derived neurotrophic factor expression and decreasing the level of tumor necrosis factor-alpha in dopaminergic neurons and microglia, respectively. These results suggest that naringin can impart to the adult dopaminergic neurons the ability to produce glial cell line-derived neurotrophic factor against Parkinson's disease with anti-inflammatory effects. Based on these results, we would like to describe an important perspective on its possibility as a therapeutic agent for Parkinson's disease.

Tumour necrosis factor alpha-induced neuronal loss is mediated by microglial phagocytosis

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TNF-α induces neuronal loss in culture without neuronal necrosis or apoptosis.

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TNF-α induces microglial phagocytosis, and the neuronal loss requires microglia.

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Neuronal loss requires the microglial vitronectin receptor, P2Y₆ receptor and MFG-E8.

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Blocking these phagocytic receptors leaves viable neurons.

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TNF-α induced phagoptosis might contribute to neuroinflammatory pathologies.

Tumour necrosis factor-α (TNF-α) is a pro-inflammatory cytokine, expressed in many brain pathologies and associated with neuronal loss. We show here that addition of TNF-α to neuronal–glial co-cultures increases microglial proliferation and phagocytosis, and results in neuronal loss that is prevented by eliminating microglia. Blocking microglial phagocytosis by inhibiting phagocytic vitronectin and P2Y₆ receptors, or genetically removing opsonin MFG-E8, prevented TNF-α induced loss of live neurons. Thus TNF-α appears to induce neuronal loss via microglial activation and phagocytosis of neurons, causing neuronal death by phagoptosis.

Inhibition of UDP/P2Y6 purinergic signaling prevents phagocytosis of viable neurons by activated microglia in vitro and in vivo

Microglia activated through Toll-like receptor (TLR)-2 or -4 can cause neuronal death by phagocytosing otherwise-viable neurons—a form of cell death called “phagoptosis.” UDP release from neurons has been shown to provoke microglial phagocytosis of neurons via microglial P2Y₆ receptors, but whether inhibition of this process affects neuronal survival is unknown. We tested here whether inhibition of P2Y₆ signaling could prevent neuronal death in inflammatory conditions, and whether UDP signaling can induce phagoptosis of stressed but viable neurons. We find that delayed neuronal loss and death in mixed neuronal/glial cultures induced by the TLR ligands lipopolysaccharide (LPS) or lipoteichoic acid was prevented by: apyrase (to degrade nucleotides), Reactive Blue 2 (to inhibit purinergic signaling), or MRS2578 (to specifically block P2Y₆ receptors). In each case, inflammatory activation of microglia was not affected, and the rescued neurons remained viable for at least 7 days. Blocking P2Y₆ receptors with MRS2578 also prevented phagoptosis of neurons induced by 250 nM amyloid beta 1–42, 5 μM peroxynitrite, or 50 μM 3-morpholinosydnonimine (which releases reactive oxygen and nitrogen species). Furthermore, the P2Y₆ receptor agonist UDP by itself was sufficient to stimulate microglial phagocytosis and to induce rapid neuronal loss that was prevented by eliminating microglia or inhibiting phagocytosis. In vivo, injection of LPS into rat striatum induced microglial activation and delayed neuronal loss and blocking P2Y₆ receptors with MRS2578 prevented this neuronal loss. Thus, blocking UDP/P2Y₆ signaling is sufficient to prevent neuronal loss and death induced by a wide range of stimuli that activate microglial phagocytosis of neurons.

Traumatic white matter injury and glial activation: from basic science to clinics

An improved understanding and characterization of glial activation and its relationship with white matter injury will likely serve as a novel treatment target to curb post injury inflammation and promote axonal remyelination after brain trauma. Traumatic brain injury (TBI) is a significant public healthcare burden and a leading cause of death and disability in the United States. Particularly, traumatic white matter (WM) injury or traumatic axonal injury has been reported as being associated with patients' poor outcomes. However, there is very limited data reporting the importance of glial activation after TBI and its interaction with WM injury. This article presents a systematic review of traumatic WM injury and the associated glial activation, from basic science to clinical diagnosis and prognosis, from advanced neuroimaging perspective. It concludes that there is a disconnection between WM injury research and the essential role of glia which serve to restore a healthy environment for axonal regeneration following WM injury. Particularly, there is a significant lack of non-invasive means to characterize the complex pathophysiology of WM injury and glial activation in both animal models and in humans. An improved understanding and characterization of the relationship between glia and WM injury will likely serve as a novel treatment target to curb post injury inflammation and promote axonal remyelination.

6-Hydroxydopamine induces distinct alterations in GDF5 and GDNF mRNA expression in the rat nigrostriatal system in vivo

Growth/differentiation factor (GDF)5 and glial cell line-derived neurotrophic factor (GDNF) are neurotrophic factors that promote the survival of midbrain dopaminergic neurons in vitro and in vivo. Both factors have potent neurotrophic and neuroprotective effects in rat models of Parkinson's disease (PD) and represent promising new therapies for PD. The aim of this study was to investigate the expression of GDF5, GDNF and their receptors in the nigrostriatal dopaminergic system in rat models of PD. It found that endogenous GDF5, GDNF and their receptors are differentially expressed in two 6-hydroxydopamine lesion models of PD. In both striatal and medial forebrain bundle (MFB) lesion models, striatal levels of GDF5 mRNA increased at 10 days post-lesion, while GDNF mRNA levels in the nigrostriatal system decreased after 10 and 28 days. Midbrain mRNA levels for both GDF5 receptors transiently increased after striatal lesion, whereas those of two GDNF receptors decreased at later time-points in both models. Despite the fact that exogenous GDF5 and GDNF have comparable effects on dopaminergic neurons in vitro and in vivo, their endogenous responses to neurotoxic injury are different. This highlights the importance of studying neurotrophic factor expression at distinct disease stages and in various animal models of PD.

Gene expression profiling analysis of the putamen for the investigation of compensatory mechanisms in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is affecting 5 million people worldwide, but the response mechanisms of the striatum are still unclear. Therefore, identification of gene expression alterations in the striatum will greatly assist the development of novel therapy strategies.

METHODS

We performed a comprehensive gene expression analysis in 15 PD patients and 15 normal controls to identify differentially expressed genes (DEGs) using the expression profile GSE20291 from Gene Expression Omnibus (GEO). Gene Ontology (GO) analysis and Kyoto Encyclopedia of Gene and Genome (KEGG) pathway enrichment analysis were used to define functions and pathways altered in PD. Protein-protein interaction network was constructed to find out the modules with close interactions.

RESULTS

Total715 DEGs including 268 up-regulated and 447 down-regulated genes were obtained. GO functional enrichment analysis indicated that the genes related with neurons function and cell morphogenesis might be changed upon PD. KEGG pathway enrichment analysis showed that most of the genes were enriched in the nodes of Gap junction, calcium signaling pathway, phosphatidylinositol signaling system, long-term potentiation, Alzheimer's disease and GnRH signaling pathway. Protein-protein interaction network and module analysis suggested that some apoptosis related genes, such as PRKCA, CDC42 and BCL2 may play critical roles in striatal neurons growth.

CONCLUSION

Intrinsic striatal tyrosine hydroxylase interneurons growth may be promoted by changes in several genes expression and thus reduce the functional excitatory synapses.

[Levodopa in the treatment of Parkinson disease -- yesterday and today]

Levodopa has an established position in the treatment of Parkinson's disease for the last 40 years. It is still called a gold standard therapy. The treatment is relatively easy in the first uncomplicated stage of Parkinson's disease, but the results of many studies performed in recent years showed that the time of treatment initiation and the mode of initial treatment may influence the course of disease in following years. At the late stages the levodopa treatment is a challenge due to the changes in reactivity to single doses as a result of changes in its pharmacokinetics, reactivity of dopamine receptors and progressive loss of dopaminergic neurons. This review paper aims to show the recent views on treatment of Parkinson's disease with levodopa still being a core of this therapy.

Gene therapy for the treatment of Parkinson's disease: the nature of the biologics expands the future indications

The pharmaceutical industry's development of therapeutic medications for the treatment of Parkinson's disease (PD) endures, as a result of the continuing need for better agents, and the increased clinical demand due to the aging population. Each new drug offers advantages and disadvantages to patients when compared to other medical offerings or surgical options. Deep brain stimulation (DBS) has become a standard surgical remedy for the effective treatment of select patients with PD, for whom most drug regimens have failed or become refractory. Similar to DBS as a surgical option, gene therapy for the treatment of PD is evolving as a future option. In the four different PD gene therapy approaches that have reached clinical trials investigators have documented an excellent safety profile associated with the stereotactic delivery, viral vectors and doses utilized, and transgenes expressed. In this article, we review the clinically relevant gene therapy strategies for the treatment of PD, concentrating on the published preclinical and clinical results, and the likely mechanisms involved. Based on these presentations, we advance an analysis of how the nature of the gene therapy used may eventually expand the scope and utility for the management of PD.

Identification of novel GDNF isoforms and cis-antisense GDNFOS gene and their regulation in human middle temporal gyrus of Alzheimer disease

Primate-specific genes and isoforms could provide insight into human brain diseases. Our bioinformatic analysis revealed that there are possibly five isoforms of human GDNF gene with different pre- and pro-regions by inter- and intra-exon splicing. By using TaqMan primer probe sets, designed between exons, we verified the expression of all isoforms. Furthermore, a novel GDNFOS gene was found to be transcribed from the opposite strand of GDNF gene. GDNFOS gene has four exons that are spliced into different isoforms. GDNFOS1 and GDNFOS2 are long noncoding RNAs, and GDNFOS3 encodes a protein of 105 amino acids. To study human GDNF and GDNFOS regulation in neurodegenerative diseases, the protein and mRNA levels were measured by Western blot and RT-quantitative PCR, respectively, in postmortem middle temporal gyrus (MTG) of Alzheimer disease (AD) and Huntington disease (HD) patients in comparison with those of normal controls. In the MTG of AD patients, the mature GDNF peptide was down-regulated; however, the transcript of GDNF isoform from human exon 2 was up-regulated, whereas that of the conserved isoform from exon 1 remained unchanged in comparison with those of normal controls. In contrast, the mature GDNF peptide and the isoform mRNA levels were not changed in the MTG of HD. The findings of novel GDNF and GDNFOS isoforms and differences in tissue expression patterns dysregulated in AD brains may further reveal the role of endogenous GDNF in human brain diseases.

Is GDNF beneficial in Parkinson disease?

Glial cell line-derived neurotrophic factor (GDNF) has proved efficacious in treatment of neurodegeneration in toxin-induced models of Parkinson disease (PD), but clinical trials have been equivocal. Do the results of a recent study—suggesting that GDNF is ineffective in an α-synuclein-overexpression PD model—exclude GDNF as a therapy for PD?

Regulation of the severity of neuroinflammation and demyelination by TLR-ASK1-p38 pathway

Apoptosis signal-regulating kinase 1 (ASK1) is an evolutionarily conserved mitogen-activated protein kinase (MAPK) kinase kinase which plays important roles in stress and immune responses. Here, we show that ASK1 deficiency attenuates neuroinflammation in experimental autoimmune encephalomyelitis (EAE), without affecting the proliferation capability of T cells. Moreover, we found that EAE upregulates expression of Toll-like receptors (TLRs) in activated astrocytes and microglia, and that TLRs can synergize with ASK1-p38 MAPK signalling in the release of key chemokines from astrocytes. Consequently, oral treatment with a specific small molecular weight inhibitor of ASK1 suppressed EAE-induced autoimmune inflammation in both spinal cords and optic nerves. These results suggest that the TLR-ASK1-p38 pathway in glial cells may serve as a valid therapeutic target for autoimmune demyelinating disorders including multiple sclerosis.

Therapeutic efficacy of intranasally delivered mesenchymal stem cells in a rat model of Parkinson disease

Safe and effective cell delivery remains one of the main challenges in cell-based therapy of neurodegenerative disorders. Graft survival, sufficient enrichment of therapeutic cells in the brain, and avoidance of their distribution throughout the peripheral organs are greatly influenced by the method of delivery. Here we demonstrate for the first time noninvasive intranasal (IN) delivery of mesenchymal stem cells (MSCs) to the brains of unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats. IN application (INA) of MSCs resulted in the appearance of cells in the olfactory bulb, cortex, hippocampus, striatum, cerebellum, brainstem, and spinal cord. Out of 1 × 10⁶ MSCs applied intranasally, 24% survived for at least 4.5 months in the brains of 6-OHDA rats as assessed by quantification of enhanced green fluorescent protein (EGFP) DNA. Quantification of proliferating cell nuclear antigen-positive EGFP-MSCs showed that 3% of applied MSCs were proliferative 4.5 months after application. INA of MSCs increased the tyrosine hydroxylase level in the lesioned ipsilateral striatum and substantia nigra, and completely eliminated the 6-OHDA-induced increase in terminal deoxynucleotidyl transferase (TdT)-mediated 2'-deoxyuridine, 5'-triphosphate (dUTP)-biotin nick end labeling (TUNEL) staining of these areas. INA of EGFP-labeled MSCs prevented any decrease in the dopamine level in the lesioned hemisphere, whereas the lesioned side of the control animals revealed significantly lower levels of dopamine 4.5 months after 6-OHDA treatment. Behavioral analyses revealed significant and substantial improvement of motor function of the Parkinsonian forepaw to up to 68% of the normal value 40-110 days after INA of 1 × 10⁶ cells. MSC-INA decreased the concentrations of inflammatory cytokines-interleukin-1β (IL-1β), IL-2, -6, -12, tumor necrosis factor (TNF), interferon-γ (IFN-γ, and granulocyte-macrophage colony-stimulating factor (GM-CSF)-in the lesioned side to their levels in the intact hemisphere. IN administration provides a highly promising noninvasive alternative to the traumatic surgical procedure of transplantation and allows targeted delivery of cells to the brain with the option of chronic application.

Enhanced dopamine transporter activity in middle-aged Gdnf heterozygous mice

Glial cell line-derived neurotrophic factor (GDNF) supports the viability of midbrain dopamine (DA) neurons that degenerate in Parkinson's disease. Middle-aged, 12 month old, Gdnf heterozygous (Gdnf(+/-)) mice have diminished spontaneous locomotor activity and enhanced synaptosomal DA uptake compared with wild type mice. In this study, dopamine transporter (DAT) function in middle-aged, 12 month old Gdnf(+/-) mice was more thoroughly investigated using in vivo electrochemistry. Gdnf(+/-) mice injected with the DAT inhibitor, nomifensine, exhibited significantly more locomotor activity than wild type mice. In vivo electrochemistry with carbon fiber microelectrodes demonstrated enhanced clearance of DA in the striatum of Gdnf(+/-) mice, suggesting greater surface expression of DAT than in wild type littermates. Additionally, 12 month old Gdnf(+/-) mice expressed greater D(2) receptor mRNA and protein in the striatum than wild type mice. Neurochemical analyses of striatal tissue samples indicated significant reductions in DA and a faster DA metabolic rate in Gdnf(+/-) mice than in wild type mice. Altogether, these data support an important role for GDNF in the regulation of uptake, synthesis, and metabolism of DA during aging.

Peripheral nerve pericytes modify the blood-nerve barrier function and tight junctional molecules through the secretion of various soluble factors

The objectives of this study were to establish pure blood-nerve barrier (BNB) and blood-brain barrier (BBB)-derived pericyte cell lines of human origin and to investigate their unique properties as barrier-forming cells. Brain and peripheral nerve pericyte cell lines were established via transfection with retrovirus vectors incorporating human temperature-sensitive SV40 T antigen (tsA58) and telomerase. These cell lines expressed several pericyte markers such as α-smooth muscle actin, NG2, platelet-derived growth factor receptor β, whereas they did not express endothelial cell markers such as vWF and PECAM. In addition, the inulin clearance was significantly lowered in peripheral nerve microvascular endothelial cells (PnMECs) through the up-regulation of claudin-5 by soluble factors released from brain or peripheral nerve pericytes. In particular, bFGF secreted from peripheral nerve pericytes strengthened the barrier function of the BNB by increasing the expression of claudin-5. Peripheral nerve pericytes may regulate the barrier function of the BNB, because the BNB does not contain cells equivalent to astrocytes which regulate the BBB function. Furthermore, these cell lines expressed several neurotrophic factors such as NGF, BDNF, and GDNF. The secretion of these growth factors from peripheral nerve pericytes might facilitate axonal regeneration in peripheral neuropathy. Investigation of the characteristics of peripheral nerve pericytes may provide novel strategies for modifying BNB functions and promoting peripheral nerve regeneration.