Glial Cell Line-derived Neurotrophic Factor Gene Delivery Research Articles

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.

Non-toxic HSC Transplantation-Based Macrophage/Microglia-Mediated GDNF Delivery for Parkinson’s Disease

Glial cell-line-derived neurotrophic factor (GDNF) is a potent neuroprotective agent in cellular and animal models of Parkinson’s disease (PD). However, CNS delivery of GDNF in clinical trials has proven challenging due to blood-brain barrier (BBB) impermeability, poor diffusion within brain tissue, and large brain size. We report that using non-toxic mobilization-enabled preconditioning, hematopoietic stem cell (HSC) transplantation-based macrophage-mediated gene delivery may provide a solution to overcome these obstacles. Syngeneic bone marrow HSCs were transduced ex vivo with a lentiviral vector expressing macrophage promoter-driven GDNF and transplanted into 14-week-old MitoPark mice exhibiting PD-like impairments. Transplant preconditioning with granulocyte colony-stimulating factor (G-CSF) and AMD3100 was used to vacate bone marrow stem cell niches. Chimerism reached ∼80% after seven transplantation cycles. Transgene-expressing macrophages infiltrated degenerating CNS regions of MitoPark mice (not wild-type littermate controls), resulting in increased GDNF levels in the midbrain. Macrophage GDNF delivery not only markedly improved motor and non-motor dysfunction, but also dramatically mitigated the loss of dopaminergic neurons in both substantia nigra and the ventral tegmental area and preserved axonal terminals in the striatum. Striatal dopamine levels were almost completely restored. Our data support further development of mobilization-enabled HSC transplantation (HSCT)-based macrophage-mediated GDNF gene delivery as a disease-modifying therapy for PD.

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.

GDNF Gene Delivery via a 2-(Dimethylamino)ethyl Methacrylate Based Cyclized Knot Polymer for Neuronal Cell Applications

Nonviral genetic therapeutic intervention strategies for neurological disorders hold great promise, but a lack of vector efficacy, coupled with vector toxicity, continue to hinder progress. Here we report the application of a newly developed class of polymer, distinctly different from conventional branched polymers, as a transfection agent for the delivery of glial cell line derived neurotrophic factor (GDNF) encoding gene. This new 2-(dimethylamino)ethyl methacrylate (DMAEMA) based cyclized knot polymer was studied for neuronal cell transfection applications, in comparison to branched polyethyleneimine (PEI). While showing a similar transfection profile over multiple cell types, the cyclized knot polymer showed far lower toxicity. In addition, transfection of Neu7 astrocytes with the GDNF encoding gene was able to cause neurite outgrowth when cocultured with dorsal root ganglia (DRGs). The cyclized knot polymer assessed here (PD-E 8%PEG), synthesized via a simple one-pot reaction, was shown to have great potential for neuronal gene therapy applications.

Glial Cell Line–Derived Neurotrophic Factor Gene Transfer Exerts Protective Effect on Axons in Sciatic Nerve Following Constriction-Induced Peripheral Nerve Injury

Damage to peripheral nerves following trauma or neurodegenerative diseases often results in various sensory and motor abnormalities and chronic neuropathic pain. The loss of neurotrophic factor support has been proposed to contribute to the development of peripheral neuropathy. The main objective of this study was to investigate the protective effect of glial cell line-derived neurotrophic factor (GDNF) using peripheral gene delivery in a rat model of constriction-induced peripheral nerve injury. In this study, it was shown that mechanical and thermal hypersensitivity increased on the injured limb at day 7 after chronic constrictive injury (CCI) was induced. The neurological changes were correlated with the structural changes and loss of GDNF/Akt signaling, particularly in the distal stump of the injured sciatic nerve. Subsequently, recombinant adenovirus was employed to evaluate the potential of intramuscular GDNF gene delivery to alleviate the CCI-induced nerve degeneration ad neuropathic pain. After CCI for 3 days, intramuscular injection of adenovirus encoding GDNF (Ad-GDNF) restored the protein level and activity of GDNF/Akt signaling pathway in the sciatic nerve. This was associated with an improved myelination profile and behavioral outcomes in animals with CCI. In conclusion, the present study demonstrates the involvement of GDNF loss in the pathogenesis of CCI-induced neuropathic pain and the therapeutic potential of intramuscular GDNF gene delivery for the treatment of peripheral nerve degeneration.

Glial cell line-derived neurotrophic factor (GDNF) gene delivery protects cortical neurons from dying following a traumatic brain injury

The therapeutic potential of glial cell line-derived neurotrophic factor (GDNF) gene delivery was examined in a rodent model of traumatic brain injury (TBI), the controlled cortical impact (CCI). An adenoviral vector harboring human GDNF (AdGDNF) or green fluorescent protein (AdGFP) was injected unilaterally into the forelimb sensorimotor cortex (FL-SMC) of the rat one week prior to a unilateral CCI. Tests of forelimb function and asymmetry were administered for 2 weeks post-injury. At 2 weeks post-injury, animals were sacrificed and contusion size, neuronal survival, neurodegeneration, and virally-mediated GDNF and GFP protein expression were measured. Rats injected with AdGDNF had significantly smaller contusions, more surviving neurons, and less neurodegeneration than AdGFP injected and uninjected injured animals. GDNF gene delivery also resulted in significantly faster recovery of forelimb coordination and a smaller initial preference for the uninjured forelimb during exploration of the walls of a platform. However, overall recovery of symmetrical forelimb use was not achieved. The discrepancy between neural protection and behavioral recovery suggests that while GDNF gene delivery provided a high degree of protection of damaged cortical neurons in this model of TBI, it may not have fully protected their terminals and synaptic functioning, resulting in only mild protection against behavioral deficits.

Reversible neurochemical changes mediated by delayed intrastriatal glial cell line‐derived neurotrophic factor gene delivery in a partial Parkinson's disease rat model

Efficient protection of dopaminergic neurons against a subsequent 6-hydroxydopamine lesion by glial cell line-derived neurotrophic factor (GDNF) gene delivery has been demonstrated. By contrast, the neurorestorative effects of GDNF administered several weeks after the toxin have been less characterized. In particular, whether these were permanent or dependent on the continuous presence of GDNF remains elusive. A tetracycline-inducible adeno-associated virus (AAV)-1 vector expressing human GDNF cDNA was administered unilaterally in the rat striatum 5 weeks after 6-hydroxydopamine. Rats were treated with doxycycline (dox) or untreated from the day of vector injection until sacrifice (4 or 14 weeks). A sub-group was dox-treated for 7 weeks then untreated until 14 weeks. The motor behavior was assessed by amphetamine-induced rotations and spontaneous forelimb asymmetry. The amounts of tyrosine hydroxylase (TH), serine-40-phosphorylated TH (S40-TH) and aromatic amino acid decarboxylase (AADC) proteins were compared by western blotting and the dopamine levels quantified by high-performance liquid chromatography. Dox-dependent behavioral improvements were demonstrated 4 weeks post-vector injection. At later time points, spontaneous partial recovery was observed in all rats, but no further improvement was found in dox-treated animals. TH levels were significantly increased in dox-treated rats at all time points. By contrast, striatal dopamine and S40-TH were increased at 4 weeks, but not 14 weeks, and AADC remained unchanged. Dox withdrawal after 7 weeks, resulted in TH levels comparable to the controls at 14 weeks. Delayed GDNF gene delivery only transiently improved dopaminergic function. Over the long term, TH was more abundant, but not functional, and the increase was lost when GDNF gene expression was switched off.

GDNF gene delivery via the p75 NTR receptor rescues injured motor neurons

The retrograde axonal transport mechanism of motor neurons has been exploited to deliver the gene encoding Glial cell line-derived neurotrophic factor (GDNF) into the central nervous system to provide trophic support following injury. A nonviral gene delivery system, consisting of a monoclonal antibody (MC192) that binds the neurotrophic receptor, p75 NTR, coupled to poly- L-lysine, was constructed and used to deliver the gene via a receptor-mediated mechanism. The MC192-poly- l-lysine/pGDNF complex was injected into the hind limb of newborn rats to allow gene expression within motor neurons prior to sciatic nerve transection. In adult rats, the gene delivery complex was administrated in gel foam placed on a transected hypoglossal nerve. We show that the delivered construct is internalized following binding to p75 NTR and is transported into the brain and spinal cord, bypassing the blood–brain barrier. The presence of the GDNF transgene and its transcript could be detected for up to 8 weeks in spinal cord and brain stem. Expression of the GDNF protein rescued 38% of the targeted motor neurons 1 week postinjury in newborn rats while the survival rate in control group was below 12%. In adult rats, neuronal death induced by axotomy was almost completely reversed by the introduction of the transgene (95 ± 3%). Thus, the significant functional outcomes of this novel gene delivery system are demonstrated both in postnatal and adult motor neurons.

Hypothalamic rAAV-mediated GDNF gene delivery ameliorates age-related obesity

Intraventricular delivery of glial cell line-derived neurotrophic factor (GDNF) results in weight loss. We hypothesized that this effect of GDNF was likely mediated via its effects on dopaminergic neurons in the hypothalamus. Continuous rAAV-mediated GDNF expression in the hypothalamus of young and senescent rats resulted in weight loss compared to controls. However, GDNF-induced weight loss was unrelated to alterations in hypothalamic dopamine levels. The weight loss was associated with decreased food intake and increased energy expenditure, but these effects were not mediated by changes in hypothalamic NPY or POMC expression. Moreover, uncoupling protein 1 levels were unchanged in brown adipose tissue (BAT). The reduction in weight and adiposity were as great or greater in the aged rats even though aged rats are generally resistant to weight loss therapies. In summary, central GDNF gene delivery reduces weight and adiposity in young and aged rats through decreased food intake and increased energy expenditure. Our observations in aged rats suggest that GDNF may be especially effective in reducing obesity in aged obese rats.

549. Peripheral Gene Delivery of Glial Cell Line-Derived Neurotrophic Factor Alleviated Neurological Deficits in Diabetic Rats

The neurological deficit in peripheral nerves is one of the major complications associated with diabetes. Deprivation of trophic factors may contribute to the pathogenesis of diabetic neuropathy while restored expression of neurotrophic factors could ameliorate such sensory abnormalities. Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor that effectively prevents neuronal death and restores the synapse conduction during trauma of central nervous system. In the present study, we evaluated the therapeutic potential of GDNF gene delivery for neuropathy in diabetic rats. After injection of streptozotocin for 14 days, a reduction in nerve conduction velocity (NCV) with a concomitant increment in H-reflex was detected in diabetic rats by electrophysiological studies. Single, intramuscular (IM) injection of adenovirus encoding GDNF (Ad-GDNF) led to systemic GDNF expression for at least 35 days. Besides, the declined GDNF level in sciatic nerve was also restored by GDNF gene delivery. After gene delivery for 2-4 weeks, Ad-GDNF-treated rats exhibited a significant increment in NCV (P<0.05) and a concomitant decrease in H-reflex latency (P<0.05) comparing with animals of control groups. IM GDNF gene delivery was well tolerant to diabetic rats without affecting their biochemical parameters Therefore, peripheral GDNF gene delivery may hold potential for treatment of diabetic neuropathy.

Intrathecal gene delivery of glial cell line-derived neurotrophic factor ameliorated paraplegia in rats after spinal ischemia

Paraplegia is a catastrophic complication of thoracic aortic surgery. At present, there is no effective mean to prevent the ischemia-induced spinal cord trauma. Gene delivery of neurotrophic factors may hold promises for prevention of spinal injury. In the present study, we evaluated the effect of glial cell line-derived neurotrophic factor (GDNF) gene delivery on prevention of the pathological changes due to spinal ischemia. Recombinant adenovirus vectors encoding GDNF (Ad-GDNF) and green fluorescent protein (Ad-GFP) were used for gene transfer studies. Treatment with cobalt chloride induced dose-dependent bcl-2 and synaptophysin downregulation in spinal neuronal cells, which could be effectively reversed by GDNF gene transfer. Intrathecal injection of Ad-GDNF led to maximal GDNF expression in spinal cord within 2–7 days. Thus, after intrathecal administration of adenovirus vectors for 3 days, Sprague–Dawley rats received transient aortic occlusion to induce spinal ischemia and were monitored for behavior deficits. The Ad-GDNF-treated rats showed significantly lower paraplegia rate (40%) than that of Ad-GFP- or saline-treated groups (75–85%; P < 0.01). In addition, the Ad-GDNF-treated rats exhibited significantly improved locomotor function comparing with rats of control groups ( P < 0.001). Histological analysis revealed that GDNF gene delivery profoundly attenuated the infiltration of leukocytes in spinal cord after ischemic insults. Furthermore, GDNF gene delivery prominently attenuated the ischemia-induced neuronal loss in dorsal horn lamina VI–VIII and reduction in synaptophysin expression in spinal cords. In conclusion, GDNF gene transfer confers protection to the neuronal cells and synapses networks, thereby alleviated the paraplegia due to spinal ischemia.

Long-Term Safety of GDNF Gene Delivery in the Retina

Purpose: To examine retinal function after the long-term, gene therapy–delivered expression of exogenous glial cell line–derived neurotrophic factor (GDNF). Methods: Forty Sprague-Dawley rats each received an intravitreal injection of recombinant adeno-associated virus expressing GDNF (rAAV-GDNF) in their right eye. The left eye was untreated. One year after viral transduction in ocular tissues, retinal morphology and function were compared between rAAV-GDNF–injected and normal naïve eyes. Synthesis and accumulation of GDNF within the retina were immunohistologically confirmed using enzyme-linked immunosorbent assay. Morphological analyses included light microscope examination of retinal sections and the counting of retinal ganglion cells. Inflammation by infiltration of leukocytes in retina was assessed immunohistochemically. Retinal function was assessed using electroretinography. Results: GDNF expression was confirmed. There was no obvious abnormality in retinal section or increased infiltration by leukocytes after retinal transduction of rAAV-GDNF for 1 year. Counts of retinal ganglion cells were not decreased in rAAV-GDNF–injected eyes. There were no statistical differences in amplitude as well as latency of the electroretinogram-determined a- and b-waves between transduced and untreated eyes. Conclusions: Long-term expression of GDNF within the eyes can be achieved by intravitreal injection of rAAV vectors in the absence of morphological or functional deficits in the retina.

Motoneurons crave glial cell line-derived neurotrophic factor

This is a commentary on the developmental and therapeutic relevance of recent studies in the glial fibrillary acid protein (GFAP)-glial cell line-derived neurotrophic factor (GDNF) transgenic mouse reported by Zhao et al. (2004). This interesting study demonstrated that increased expression of GDNF in astrocytes increases the number of neighboring motoneurons of certain motoneuron subpopulations by diminishing programmed cell death during development. In addition, astrocyte-derived GDNF was shown to protect facial motoneurons from injury-induced cell death. Since this is the first direct demonstration that secretion of GDNF from astrocytes in the CNS can affect motoneuron development in utero and motoneuron survival after axotomy, novel approaches for motor neuron disease are suggested. The known target neurons that respond to GDNF are reviewed, as are studies using GDNF gene delivery in animal models of amyotrophic lateral sclerosis (ALS). It is postulated that GDNF is a factor to which many motoneurons respond along their whole extent from soma to axon to terminal.

Adenoviral vector-mediated delivery of glial cell line-derived neurotrophic factor provides neuroprotection in the aged parkinsonian rat.

1. The long-term delivery of neurotrophic factors to specific regions of the central nervous system via gene therapy offers a new strategy for the treatment of neurodegenerative disorders. 2. The neurotrophic factor glial cell line-derived neurotrophic factor (GDNF) is a potent dopaminergic (DA) trophic factor that ameliorates the behavioural and histological consequences of lesioning DA neurons in rodent and primate models of Parkinson's disease. 3. Glial cell line-derived neurotrophic factor gene therapy may have a potential use in the clinical treatment of Parkinson's disease. 4. We examined whether injection of an adenoviral vector encoding human GDNF preproprotein (Ad GDNF) could protect the rat nigrostriatal DA system from progressive neuronal degeneration. Because Parkinson's disease occurs primarily in the elderly population, we studied the effect of GDNF gene delivery in an aged rat model of Parkinson's disease. 5. In the aged (20 month) Fischer 344 rat, Ad GDNF was injected either near DA cell bodies in the substantia nigra (SN) or at the DA terminals in the striatum. One week following gene delivery, the neurotoxin 6-hydroxydopamine (6-OHDA) was injected unilaterally into the striatum to cause progressive degeneration of the DA neurons. 6. Injection of GDNF vector into either the striatum or the SN provided significant cell protection against 6-OHDA. However, only striatal injection of Ad GDNF protected against the development of behavioural and neurochemical changes that occur in the DA-depleted brain. 7. The results of this study are reviewed here and the behavioural and cellular effects of GDNF gene delivery into striatal versus mesencephalic sites are discussed.

GDNF gene delivery to injured adult CNS motor neurons promotes axonal growth, expression of the trophic neuropeptide CGRP, and cellular protection

Glial-cell-line--derived neurotrophic factor (GDNF) has been identified as a potent survival and differentiation factor for several neuronal populations in the central nervous system (CNS), but to date, distinct effects of GDNF on motor axon growth and regeneration in the adult have not been demonstrated. In the present study, ex vivo gene delivery was used to directly examine whether GDNF can influence axonal growth, expression of neuronal regeneration-related genes, and sustain the motor neuronal phenotype after adult CNS injury. Adult Fischer 344 rats underwent unilateral transections of the hypoglossal nerve, followed by intramedullary grafts of fibroblasts genetically modified to secrete GDNF. Control animals received lesions and grafts of cells expressing a reporter gene. Two weeks later, GDNF gene delivery (1) robustly promoted the growth of lesioned hypoglossal motor axons, (2) altered the expression and intracellular trafficking of the growth-related protein calcitonin gene-related peptide (CGRP), and (3) significantly sustained the cholinergic phenotype in 84 +/- 6% of hypoglossal neurons compared with 39 +/- 6% in control animals (P < 0.001). This is the first neurotrophic factor identified to increase the in vivo expression of the trophic peptide CGRP and the first report that GDNF promotes motor axonal growth in vivo in the adult CNS. Taken together with previous in vitro studies, these findings serve as the foundation for a model wherein GDNF and CGRP interact in a paracrine manner to regulate neuromuscular development and regeneration.

Glial Cell Line-Derived Neurotrophic Factor (GDNF) Gene Delivery Protects Dopaminergic Terminals from Degeneration

Previously, we observed that injection of an adenoviral (Ad) vector expressing glial cell line-derived neurotrophic factor (GDNF) into the striatum, but not the substantia nigra (SN), prior to a partial 6-OHDA lesion protects dopaminergic (DA) neuronal function and prevents the development of behavioral impairment in the aged rat. This suggests that striatal injection of AdGDNF maintains nigrostriatal function either by protecting DA terminals or by stimulating axonal sprouting to the denervated striatum. To distinguish between these possible mechanisms, the present study examines the effect of GDNF gene delivery on molecular markers of DA terminals and neuronal sprouting in the aged (20 month) rat brain. AdGDNF or a control vector coding for β-galactosidase (AdLacZ) was injected unilaterally into either the striatum or the SN. One week later, rats received a unilateral intrastriatal injection of 6-OHDA on the side of vector injection. Two weeks postlesion, rats injected with AdGDNF into either the striatum or the SN exhibited a reduction in the area of striatal denervation and increased binding of the DA transporter ligand [125I]IPCIT in the lesioned striatum compared to control animals. Furthermore, injections of AdGDNF into the striatum, but not the SN, increased levels of tyrosine hydroxylase mRNA in lesioned DA neurons in the SN and prevented the development of amphetamine-induced rotational asymmetry. In contrast, the level of T1 α-tubulin mRNA, a marker of neuronal sprouting, was not increased in lesioned DA neurons in the SN following injection of AdGDNF either into the striatum or into the SN. These results suggest that GDNF gene delivery prior to a partial lesion ameliorates damage caused by 6-OHDA in aged rats by inhibiting the degeneration of DA terminals rather than by inducing sprouting of nigrostriatal axons.

Adenovirus-mediated glial cell line–derived neurotrophic factor gene delivery reduces motor neuron injury after transient spinal cord ischemia in rabbits

Objective: Glial cell line–derived neurotrophic factor (GDNF) has protective effects on various injuries involving the central and peripheral nervous systems in vitro and vivo. However, the possible protective effect of GDNF on spinal cord ischemia and the exact mechanism involved in the ameliorative effect of GDNF on ischemic spinal cord injuries are not fully understood. Therefore, we investigated the possible protective effect of the adenovirus-mediated GDNF gene delivery on transient spinal cord ischemia in rabbits. Methods: The adenoviral vector (lacZ gene as a control or GDNF gene contained) was injected directly into the lumbar spinal cord via a needle inserted into the dorsal spine 2 days before the animal was subjected to 15 minutes of spinal cord ischemia induced by infrarenal aortic occlusion. In situ terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick-end labeling (TUNEL staining) was performed, and temporal profiles of the GDNF and caspase-3 (caspase-3 is the marker of apoptotic change) immunoreactivity were investigated. Results: In the control rabbit, the majority of motor neurons showed selective cell death at 7 days of reperfusion. Immunocytochemistry showed that in situ TUNEL staining was selectively detected at 2 days of reperfusion in motor neuron nuclei. GDNF and caspase-3 were selectively induced in the motor neuron cells at 8 hours of reperfusion. In the GDNF-treated group, a large population of motor neuron cells was still surviving at 7 days after having been subjected to 15 minutes of ischemia. Unlike the control group, the GDNF-treated group expressed GDNF persistently. Induction of TUNEL staining and immunoreactivity for caspase-3 were greatly reduced by the GDNF treatment. Conclusion: These results suggest that the reduction in motor neuron death by GDNF was greatly associated with a reduction in DNA fragmentation and apoptotic signals of the caspase-3 cascade; they further suggest a great potential for gene therapy for paraplegic patients in the future. (J Thorac Cardiovasc Surg 2000;120:1148-57)

Gene transfer for neuroprotection in animal models of Parkinson's disease and amyotrophic lateral sclerosis.

Glial cell line-derived neurotrophic factor (GDNF) is a potent survival factor for motoneurons (MN) and dopaminergic (DA) neurons, neurons which selectively die in amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD). GDNF gene delivery has been studied in rodent models of ALS and PD. In a mouse model of ALS, implantation of myoblasts retrovirally transduced with GDNF into hindlimb muscles at 6 weeks of age, i.e. prior to the onset of disease symptoms, increased the number of large MNs that maintained projections to treated muscles at 18 weeks of age. GDNF-treated mice also performed better on tests of motor function and had a delayed onset of disease. In a progressive degeneration rat model of PD, effects of in vivo GDNF gene therapy using an adenoviral vector (AdGDNF) were studied in young and aged rats. AdGDNF protected DA neurons against the neurotoxin, 6-hydroxydopamine (6-OHDA), and was effective whether injected either before or after 6-OHDA damage had commenced. However, if AdGDNF was injected prior to 6-OHDA, it was most effective in protecting against DA-dependent changes in the brain when injected near the terminals of the DA neurons. In contrast, if 6-OHDA damage had already commenced, AdGDNF was most effective if injected near the DA soma. These studies suggest that GDNF gene delivery into specific sites in the CNS or into muscle where MNs have access to secreted GDNF may slow the progression of PD and ALS, respectively. Neurotrophic factor gene therapy offers novel interventions not only for PD and ALS, but also other neurodegenerative diseases and injuries to the nervous system.

Glial cell line-derived neurotrophic factor (GDNF) as a defensive molecule for neurodegenerative disease: a tribute to the studies of Antonia Vernadakis on neuronal–glial interactions

Research stemming from interests in neuronal–glial interactions has led to the identification of a number of novel trophic factors, such as the dopaminergic neurotrophic factor glial cell line-derived neurotrophic factor (GDNF). Delivery of the GDNF gene to rat models of Parkinson’s disease suggests a potential clinical use of GDNF gene therapy for humans with this disease. This review article briefly summarizes the history of GDNF and the effects of GDNF gene delivery prior to or after a lesion of the rat nigrostriatal system.