Long-term benefits of hematopoietic stem cell-based macrophage/microglia delivery of GDNF to the CNS in a mouse model of Parkinson's disease.

Glial cell line-derived neurotrophic factor (GDNF) protects dopaminergic neurons in various models of Parkinson's disease (PD). Cell-based GDNF gene delivery mitigates neurodegeneration and improves both motor and non-motor functions in PD mice. As PD is a chronic condition, this study aims to investigate the long-lasting benefits of hematopoietic stem cell (HSC)-based macrophage/microglia-mediated CNS GDNF (MMC-GDNF) delivery in an MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mouse model. The results indicate that GDNF treatment effectively ameliorated MPTP-induced motor deficits for up to 12 months, which coincided with the protection of nigral dopaminergic neurons and their striatal terminals. Also, the HSC-derived macrophages/microglia were recruited selectively to the neurodegenerative areas of the substantia nigra. The therapeutic benefits appear to involve two mechanisms: (1) macrophage/microglia release of GDNF-containing exosomes, which are transferred to target neurons, and (2) direct release of GDNF by macrophage/microglia, which diffuses to target neurons. Furthermore, the study found that plasma GDNF levels were significantly increased from baseline and remained stable over time, potentially serving as a convenient biomarker for future clinical trials. Notably, no weight loss, altered food intake, cerebellar pathology, or other adverse effects were observed. Overall, this study provides compelling evidence for the long-term therapeutic efficacy and safety of HSC-based MMC-GDNF delivery in the treatment of PD.

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.

High expression of the RET receptor tyrosine kinase and its ligand GDNF identifies a high-risk subset of estrogen receptor positive breast cancer.

PURPOSE: Resistance to endocrine therapy is the primary cause of treatment failure and death in patients with ER-positive (ER +)/luminal breast cancer. Expression and activation of the RET receptor tyrosine kinase may be driving poor outcomes. We aim to identify high-risk patients and druggable pathways for biomarker-based clinical trials. METHODS: We obtained batch-normalized mRNA expression data from Breast Invasive Carcinoma-The Cancer Genome Atlas, PanCancer Atlas (BRCA-TCGA). To determine clinically significant cutoffs for RET expression, patients were grouped at different thresholds for Kaplan-Meier plotting. Differential gene expression (DGE) analysis and enrichment for gene sets was performed. transcriptomic dataset of antiestrogen-treated ER + tumors stratified by clinical response was then analyzed. RESULTS: High RET expression was associated with worse outcomes in patients with ER + tumors, and stratification was enhanced by incorporating GDNF expression. High RET/GDNF patients had significantly lower overall survival (HR = 2.04, p = 0.012), progression-free survival (HR = 2.87, p < 0.001), disease-free survival (HR = 2.67, p < 0.001), and disease-specific survival (HR = 3.53, p < 0.001) than all other ER + patients. High RET/GDNF tumors were enriched for estrogen-independent signaling and targetable pathways including NTRK, PI3K, and KRAS. Tumors with adaptive resistance to endocrine therapy were enriched for gene expression signatures of high RET/GDNF primary tumors. CONCLUSION: Expression and activation of the RET receptor tyrosine kinase may be driving poor outcomes in some patients with ER + breast cancer. ER + patients above the 75th percentile may benefit from clinical trials with tyrosine kinase inhibitors.

Cerebral dopamine neurotrophic factor protects and repairs dopamine neurons by novel mechanism.

Midbrain dopamine neurons deteriorate in Parkinson's disease (PD) that is a progressive neurodegenerative movement disorder. No cure is available that would stop the dopaminergic decline or restore function of injured neurons in PD. Neurotrophic factors (NTFs), e.g., glial cell line-derived neurotrophic factor (GDNF) are small, secreted proteins that promote neuron survival during mammalian development and regulate adult neuronal plasticity, and they are studied as potential therapeutic agents for the treatment of neurodegenerative diseases. However, results from clinical trials of GDNF and related NTF neurturin (NRTN) in PD have been modest so far. In this review, we focus on cerebral dopamine neurotrophic factor (CDNF), an unconventional neurotrophic protein. CDNF delivered to the brain parenchyma protects and restores dopamine neurons in animal models of PD. In a recent Phase I-II clinical trial CDNF was found safe and well tolerated. CDNF deletion in mice led to age-dependent functional changes in the brain dopaminergic system and loss of enteric neurons resulting in slower gastrointestinal motility. These defects in Cdnf-/- mice intriguingly resemble deficiencies observed in early stage PD. Different from classical NTFs, CDNF can function both as an extracellular trophic factor and as an intracellular, endoplasmic reticulum (ER) luminal protein that protects neurons and other cell types against ER stress. Similarly to the homologous mesencephalic astrocyte-derived neurotrophic factor (MANF), CDNF is able to regulate ER stress-induced unfolded protein response (UPR) signaling and promote protein homeostasis in the ER. Since ER stress is thought to be one of the pathophysiological mechanisms contributing to the dopaminergic degeneration in PD, CDNF, and its small-molecule derivatives that are under development may provide useful tools for experimental medicine and future therapies for the treatment of PD and other neurodegenerative protein-misfolding diseases.

Glial cell line-derived neurotrophic factor contributes to alcoholic-induced liver injury by regulating the NF-κB pathway.

BACKGROUND: Alcoholic liver disease (ALD) is associated with high morbidity and mortality worldwide. The pathogenesis of ALD is not completely understood. Although accumulating evidence suggests an important role of glial cell line-derived neurotrophic factor (GDNF) in several diseases, there are no data concerning its role in ALD. This study compared patients with ALD with control subjects and used a mouse model and a cell culture model to investigate the function of GDNF in ALD and its mechanism of action in hepatocyte injury. METHODS: Serum levels of GDNF were measured in 25 patients with ALD and 25 healthy control subjects. A 4-week Lieber-DeCarli ethanol (EtOH) liquid diet combined with the Gao-Binge model was used in the mouse study. Mouse primary hepatocytes and Huh-7 cells were used for cell experiments. The parameters of liver injury, inflammatory cytokines, and lipid metabolism were measured. RESULTS: Patients with alcoholic hepatitis had higher serum GDNF than control subjects. Expression of GDNF mRNA and protein was markedly increased in mice in the chronic-plus-binge ALD mouse model. The level of GDNF mRNA was upregulated in primary hepatic stellate cells isolated from ethanol-fed mouse liver. Ethanol induced GDNF expression in LX2 cells. The levels of inflammatory cytokines (tumor necrosis factor α, interleukin 1ß, and monocyte chemotactic protein 1) were significantly increased after GDNF stimulation in primary hepatocytes and Huh-7 cells. After GDNF stimulation, levels of both p-AKT and p-NF-κB were significantly increased in primary hepatocytes and Huh-7 cells. The NF-κB activity induced by GDNF was significantly decreased by an NF-κB inhibitor, which limited hepatocyte injury and inflammation. CONCLUSIONS: The concentration of GDNF is increased in the circulation of ALD patients. GDNF promotes alcohol-induced liver injury and inflammation via the activation of NF-κB, which mediates hepatocyte injury and inflammatory cytokine expression. Based on these findings, GDNF is a potential therapeutic target for preventing or ameliorating liver injury in ALD.

Low-Intensity Pulsed Ultrasound Enhances Neurotrophic Factors and Alleviates Neuroinflammation in a Rat Model of Parkinson's Disease.

Low-intensity pulsed ultrasound (LIPUS) has also been reported to improve behavioral functions in Parkinson's disease (PD) animal models; however, the effect of LIPUS stimulation on the neurotrophic factors and neuroinflammation has not yet been addressed. PD rat model was built by injection of 6-hydroxydopamine (6-OHDA) in 2 sites in the right striatum. The levels of neurotrophic factors and lipocalin-2 (LCN2)-induced neuroinflammation were quantified using a western blot. Rotational test and cylinder test were conducted biweekly for 8 weeks. When the 6-OHDA + LIPUS and 6-OHDA groups were compared, the locomotor function of the 6-OHDA + LIPUS rats was significantly improved. After LIPUS stimulation, the tyrosine hydroxylase staining density was significantly increased in the striatum and substantia nigra pars compacta (SNpc) of lesioned rats. Unilateral LIPUS stimulation did not increase brain-derived neurotrophic factor in the striatum and SNpc of lesioned rats. In contrast, unilateral LIPUS stimulation increased glial cell line-derived neurotrophic factor (GDNF) protein 1.98-fold unilaterally in the SNpc. Additionally, LCN2-induced neuroinflammation can be attenuated following LIPUS stimulation. Our data indicated that LIPUS stimulation may be a potential therapeutic tool against PD via enhancement of GDNF level and inhibition of inflammatory responses in the SNpc of the brain.

Safety Assessment of AAV2-hGDNF Administered Via Intracerebral Injection in Rats for Treatment of Parkinson's Disease.

Glial cell line-derived neurotrophic factor (GDNF) is a potent neuroprotective biologic in Parkinson's disease models. Adeno-associated viral vector serotype 2 (AAV2)-human GDNF safety was assessed in rats treated with a single intracerebral dose of vehicle, 6.8 × 108, 6.8 × 109, or 5.2 × 1010 vector genomes (vg)/dose followed by interim sacrifices on day 7, 31, 90, and 376. There were no treatment-related effects observed on food consumption, body weight, hematology, clinical chemistry, coagulation parameters, neurobehavioral parameters, organ weights, or serum GDNF and anti-GDNF antibody levels. Increased serum anti-AAV2 neutralizing antibody titers were observed in the 5.2 × 1010 vg/dose group. Histopathological lesions were observed at the injection site in the 6.8 × 109 vg/dose (day 7) and 5.2 × 1010 vg/dose groups (days 7 and 31) and consisted of gliosis, mononuclear perivascular cuffing, intranuclear inclusion bodies, and/or apoptosis on day 7 and mononuclear perivascular cuffing on day 31. GDNF immunostaining was observed in the injection site in all dose groups through day 376 indicating no detectable impacts of anti-AAV2 neutralizing antibody. There was no evidence of increased expression of calcitonin gene-related peptide or Swann cell hyperplasia in the cervical and lumbar spinal cord or medulla oblongata at the 5.2 × 1010 vg/dose level indicating lack of hyperplastic effects. In conclusion, no systemic toxicity was observed, and the local toxicity observed at the injection site appeared to be reversible demonstrating a promising safety profile of intracerebral AAV2-GDNF delivery. Furthermore, an intracerebral dose of 6.8 × 108 AAV2-GDNF vg/dose was considered to be a no observed adverse effect level in rats.

Combination of Drugs and Cell Transplantation: More Beneficial Stem Cell-Based Regenerative Therapies Targeting Neurological Disorders.

Cell transplantation therapy using pluripotent/multipotent stem cells has gained attention as a novel therapeutic strategy for treating neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease, Huntington's disease, ischemic stroke, and spinal cord injury. To fully realize the potential of cell transplantation therapy, new therapeutic options that increase cell engraftments must be developed, either through modifications to the grafted cells themselves or through changes in the microenvironment surrounding the grafted region. Together these developments could potentially restore lost neuronal function by better supporting grafted cells. In addition, drug administration can improve the outcome of cell transplantation therapy through better accessibility and delivery to the target region following cell transplantation. Here we introduce examples of drug repurposing approaches for more successful transplantation therapies based on preclinical experiments with clinically approved drugs. Drug repurposing is an advantageous drug development strategy because drugs that have already been clinically approved can be repurposed to treat other diseases faster and at lower cost. Therefore, drug repurposing is a reasonable approach to enhance the outcomes of cell transplantation therapies for neurological diseases. Ideal repurposing candidates would result in more efficient cell transplantation therapies and provide a new and beneficial therapeutic combination.

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.

The impact of N-cadherin-ß-catenin signaling on the analgesic effects of glial cell-derived neurotrophic factor in neuropathic pain.

Long-term neuropathic pain can lead to anxiety, depression, and other issues, which seriously affect patients' quality of life. For this reason, it is important to find effective treatments. Studies have shown that glial cell-derived neurotrophic factor (GDNF) can relieve neuropathic pain. However, its mechanism of action is unknown. Our previous study of GDNF suggested that the N-cadherin-ß-catenin transmembrane signaling system might play a role in GDNF transmembrane signaling. Based on this, the current study aimed to produce a neuropathic pain model to confirm the activation of the N-cadherin-ß-catenin signaling system in the spinal dorsal horn under pain conditions and to study the impact of GDNF intrathecal injection on central sensitization of dorsal horn neurons. The results showed that N-cadherin expression, as well as the expression of membrane-associated ß-catenin, was reduced in the dorsal horn of the spinal cord in the chronic pain model. Intrathecal injection of GDNF could reactivate the N-cadherin-ß-catenin system, improve central sensitization, and relieve pain. Knockdown of N-cadherin or ß-catenin could significantly reduce the analgesic effect of GDNF. These results provide clear experimental evidence that the N-cadherin-ß-catenin signaling system participates in the analgesic effect of GDNF in neuropathic pain and help identify transmembrane and intracellular signal transduction mechanisms associated with GDNF's analgesic effects.

Epidural Stimulation Combined with Triple Gene Therapy for Spinal Cord Injury Treatment.

The translation of new therapies for spinal cord injury to clinical trials can be facilitated with large animal models close in morpho-physiological scale to humans. Here, we report functional restoration and morphological reorganization after spinal contusion in pigs, following a combined treatment of locomotor training facilitated with epidural electrical stimulation (EES) and cell-mediated triple gene therapy with umbilical cord blood mononuclear cells overexpressing recombinant vascular endothelial growth factor, glial-derived neurotrophic factor, and neural cell adhesion molecule. Preliminary results obtained on a small sample of pigs 2 months after spinal contusion revealed the difference in post-traumatic spinal cord outcomes in control and treated animals. In treated pigs, motor performance was enabled by EES and the corresponding morpho-functional changes in hind limb skeletal muscles were accompanied by the reorganization of the glial cell, the reaction of stress cell, and synaptic proteins. Our data demonstrate effects of combined EES-facilitated motor training and cell-mediated triple gene therapy after spinal contusion in large animals, informing a background for further animal studies and clinical translation.

Unilateral ex vivo gene therapy by GDNF in epileptic rats.

Temporal lobe epilepsy (TLE) is the most common type of epilepsy in adults. This neurological disorder is characterized by focal seizures originating in the temporal lobe, often with secondary generalization. A variety of pharmacological treatments exist for patients suffering from focal seizures, but systemically administered drugs offer only symptomatic relief and frequently cause unwanted side effects. Moreover, available drugs are ineffective in one third of the epilepsy patients. Thus, developing more targeted and effective treatment strategies for focal seizures, originating from, e.g., the temporal lobe, is highly warranted. In order to deliver potential anti-epileptic agents directly into the seizure focus we used encapsulated cell biodelivery (ECB), a specific type of ex vivo gene therapy. Specifically, we asked whether unilateral delivery of glial cell line-derived neurotrophic factor (GDNF), exclusively into the epileptic focus, would suppress already established spontaneous recurrent seizures (SRS) in rats. Our results show that GDNF delivered by ECB devices unilaterally into the seizure focus in the hippocampus effectively decreases the number of SRS in epileptic rats. Thus, our study demonstrates that focal unilateral delivery of neurotrophic factors, such as GDNF, using ex vivo gene therapy based on ECB devices could be an effective anti-epileptic strategy providing a bases for the development of a novel, alternative, treatment for focal epilepsies.

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

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

Non-viral nucleic acid delivery to the central nervous system and brain tumors.

Gene therapy is a rapidly emerging remedial route for many serious incurable diseases, such as central nervous system (CNS) diseases. Currently, nucleic acid medicines, including DNAs encoding therapeutic or destructive proteins, small interfering RNAs or microRNAs, have been successfully delivered to the CNS with gene delivery vectors using various routes of administration and have subsequently exhibited remarkable therapeutic efficiency. Among these vectors, non-viral vectors are favorable for delivering genes into the CNS as a result of their many special characteristics, such as low toxicity and pre-existing immunogenicity, high gene loading efficiency and easy surface modification. In this review, we highlight the main types of therapeutic genes that have been applied in the therapy of CNS diseases and then outline non-viral gene delivery vectors.

Research on the repairing effect of polylactic acid-trimethylene carbonate/GNDF slow-release catheter on the injured femoral nerve fiber.

Present research aims to investigate the repairing effect of polylactic acid-trimethylene carbonate/GNDF slow-release catheter on the injured femoral nerve fiber. Adult SD male rats as the subjects were divided into two groups, the GDNF group and the control group, and received the surgery to remove the nerve from the exposed left femoral nerves. Thereafter, rats in the GNDF group and the control group received the GNDF or normal saline, and we evaluated the changes in rats, including the morphological, functional and electrophysiological changes of regenerated nerves. Regenerated axons were found in each group, but enormous regeneration of axons was only identified in GDNF group. Further analysis showed that: At the 4th, 8th and 12th weeks, areas of the regenerated nerves in GDNF group were (0.95±0.06) mm2, (1.14±0.07) mm2 and (1.22±0.06) mm2, respectively; in the control group, these were (0.15±0.01) mm2, (0.25±0.07) mm2 and (0.52±0.05) mm2, respectively. These showed that the outcome of GDNF group was superior to that of control group. In GDNF group, quantities of the myelinated fiber were (0.8119×104±0.0637×104), (1.3371×104±0.0460×104) and (1.7669×104±0.0542×104); while in control group, these were (0.2179×104±0.0097×104), (0.3490×104±0.0329×104) and (0.7737×l04±0.0788×104). Again, these results also indicated that the outcome of GDNF group was superior to that of the control group (p<0.05). In GDNF group, the average diameters of myelinated fibers were (2.25±0.17) µm, (2.42±0.14) µm and (2.80±0.10) µm, which were significantly better than (1.24±0.08) µm, (1.43±0.14) µm and (1.82±0.14) µm in the control group. Degrees of fiber myelination in the GDNF group were (0.71±0.03), (0.64±0.03) and (0.6l±0.0l), respectively, which were also significantly higher than (0.02±0.01), (0.04±0.01) and (0.06±0.02) in the control group (p<0.01). At the 12th week after surgery, HE staining was performed to observe the histological changes in quadriceps femoris for evaluation of atrophy in each group. In the GDNF group, significant amelioration was found in the atrophy of quadriceps femoris with an average area of myofiber of (84.95±3.92) %, while the area of the control group was (57.95±5.78) %, suggesting that the outcome of the GDNF group was better than that of the control group (p<0.05). Electrophysiological examination of nerves was employed to detect the recovery of neurological functions after repair of nerve defect. At the 4th, 8th and 12th weeks after surgery, CMAP amplitudes in the GDNF group were (9.34±0.52) mV, (14.40±0.69) mV and (19.18±0.48) mV, significantly better than (0.39±0.07) mV, (1.44±0.41) mV and (9.27±0.40) in the control group (p<0.01). Polylactic acid-trimethylene carbonate/GNDF slow-release catheter can accelerate the functional recovery of injured nerves, thus promoting the regeneration efficiency of femoral nerves.

Systemic injection of AAV9-GDNF provides modest functional improvements in the SOD1G93A ALS rat but has adverse side effects.

Injecting proteins into the central nervous system that stimulate neuronal growth can lead to beneficial effects in animal models of disease. In particular, glial cell line-derived neurotrophic factor (GDNF) has shown promise in animal and cell models of Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis (ALS). Here, systemic AAV9-GDNF was delivered via tail vein injections to young rats to determine whether this could be a safe and functional strategy to treat the SOD1G93A rat model of ALS and, therefore, translated to a therapy for ALS patients. We found that GDNF administration in this manner resulted in modest functional improvement, whereby grip strength was maintained for longer and the onset of forelimb paralysis was delayed compared to non-treated rats. This did not, however, translate into an extension in survival. In addition, ALS rats receiving GDNF exhibited slower weight gain, reduced activity levels and decreased working memory. Collectively, these results confirm that caution should be applied when applying growth factors such as GDNF systemically to multiple tissues.

Structural changes in the inner ear over time studied in the experimentally deafened guinea pig.

Today a cochlear implant (CI) may significantly restore auditory function, even for people with a profound hearing loss. Because the efficacy of a CI is believed to depend mainly on the remaining population of spiral ganglion neurons (SGNs), it is important to understand the timeline of the degenerative process of the auditory neurons following deafness. Guinea pigs were transtympanically deafened with neomycin, verified by recording auditory brainstem responses (ABRs), and then sacrificed at different time points. Loss of SGNs as well as changes in cell body and nuclear volume were estimated. To study the effect of delayed treatment, a group of animals that had been deaf for 12 weeks was implanted with a stimulus electrode mimicking a CI, after which they received a 4-week treatment with glial cell-derived neurotrophic factor (GDNF). The electrical responsiveness of the SGNs was measured by recording electrically evoked ABRs. There was a rapid degeneration during the first 7 weeks, shown as a significant reduction of the SGN population. The degenerative process then slowed, and there was no difference in the amount of remaining neurons between weeks 7 and 18. © 2016 The Authors Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Current disease modifying approaches to treat Parkinson's disease.

Parkinson's disease (PD is a progressive neurological disorder characterized by the degeneration and death of midbrain dopamine and non-dopamine neurons in the brain leading to motor dysfunctions and other symptoms, which seriously influence the quality of life of PD patients. The drug L-dopa can alleviate the motor symptoms in PD, but so far there are no rational therapies targeting the underlying neurodegenerative processes. Despite intensive research, the molecular mechanisms causing neuronal loss are not fully understood which has hampered the development of new drugs and disease-modifying therapies. Neurotrophic factors are by virtue of their survival promoting activities attract candidates to counteract and possibly halt cell degeneration in PD. In particular, studies employing glial cell line-derived neurotrophic factor (GDNF) and its family member neurturin (NRTN), as well as the recently described cerebral dopamine neurotrophic factor (CDNF) and the mesencephalic astrocyte-derived neurotrophic factor (MANF) have shown positive results in protecting and repairing dopaminergic neurons in various models of PD. Other substances with trophic actions in dopaminergic neurons include neuropeptides and small compounds that target different pathways impaired in PD, such as increased cell stress, protein handling defects, dysfunctional mitochondria and neuroinflammation. In this review, we will highlight the recent developments in this field with a focus on trophic factors and substances having the potential to beneficially influence the viability and functions of dopaminergic neurons as shown in preclinical or in animal models of PD.

Glial cell line-derived neurotrophic factor protects against high-fat diet-induced hepatic steatosis by suppressing hepatic PPAR-γ expression.

Glial cell line-derived neurotrophic factor (GDNF) protects against high-fat diet (HFD)-induced hepatic steatosis in mice, however, the mechanisms involved are not known. In this study we investigated the effects of GDNF overexpression and nanoparticle delivery of GDNF in mice on hepatic steatosis and fibrosis and the expression of genes involved in the regulation of hepatic lipid uptake and de novo lipogenesis. Transgenic overexpression of GDNF in liver and other metabolically active tissues was protective against HFD-induced hepatic steatosis. Mice overexpressing GDNF had significantly reduced P62/sequestosome 1 protein levels suggestive of accelerated autophagic clearance. They also had significantly reduced peroxisome proliferator-activated receptor-γ (PPAR-γ) and CD36 gene expression and protein levels, and lower expression of mRNA coding for enzymes involved in de novo lipogenesis. GDNF-loaded nanoparticles were protective against short-term HFD-induced hepatic steatosis and attenuated liver fibrosis in mice with long-standing HFD-induced hepatic steatosis. They also suppressed the liver expression of steatosis-associated genes. In vitro, GDNF suppressed triglyceride accumulation in Hep G2 cells through enhanced p38 mitogen-activated protein kinase-dependent signaling and inhibition of PPAR-γ gene promoter activity. These results show that GDNF acts directly in the liver to protect against HFD-induced cellular stress and that GDNF may have a role in the treatment of nonalcoholic fatty liver disease.

Glial cell line-derived neurotrophic factor-induced mice liver defatting: A novel strategy to enable transplantation of steatotic livers.

Moderate macrovesicular steatosis (>30%), which is present in almost 50% of livers considered for transplantation, increases the risk of primary graft dysfunction. Our previously published data showed that glial cell line-derived neurotrophic factor (GDNF) is protective against high-fat diet (HFD)-induced hepatic steatosis in mice. Hence, we hypothesized that perfusion of steatotic livers with GDNF may reduce liver fat content before transplantation. Livers from 8 weeks of regular diet (RD) and of HFD-fed mice were perfused ex vivo for 4 hours with either vehicle, GDNF, or a previously described defatting cocktail. The liver's residual fat was quantified colorimetrically using a triglyceride (TG) assay kit and by Oil Red O (ORO) and Nile red/Hoechst staining. Liver tissue injury was assessed by using a lactate dehydrogenase (LDH) activity assay. In vitro induction of lipolysis in HepG2 cells was assessed by measuring glycerol and free fatty acid release. ORO staining showed significantly more steatosis in livers from HFD-fed mice compared with RD-fed mice (P < 0.001). HFD livers perfused with GDNF had significantly less steatosis than those not perfused (P = 0.001) or perfused with vehicle (P < 0.05). GDNF is equally effective in steatotic liver defatting compared to the defatting cocktail; however, GDNF induces less liver damage than the defatting cocktail. These observations were consistent with data obtained from assessment of liver TG content. Assessment of liver injury revealed significant hepatocyte injury in livers perfused with the control defatting cocktail but no evidence of injury in livers perfused with either GDNF or vehicle. In vitro, GDNF reduced TG accumulation in HepG2 cells and stimulated increased TG lipolysis. In conclusion, GDNF can decrease mice liver fat content to an acceptable range and could be a potential defatting agent before liver transplantation.