Glial Cell Line-derived Neurotrophic Factor Release 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.

Electroacupuncture Promotes Functional Recovery after Facial Nerve Injury in Rats by Regulating Autophagy via GDNF and PI3K/mTOR Signaling Pathway.

To explore the mechanism of electroacupuncture (EA) in promoting recovery of the facial function with the involvement of autophagy, glial cell line-derived neurotrophic factor (GDNF), and phosphatidylinositol-3-kinase (PI3K)/mammalian target of rapamycin (mTOR) signaling pathway. Seventy-two male Sprague-Dawley rats were randomly allocated into the control, sham-operated, facial nerve injury (FNI), EA, EA+3-methyladenine (3-MA), and EA+GDNF antagonist groups using a random number table, with 12 rats in each group. An FNI rat model was established with facial nerve crushing method. EA intervention was conducted at Dicang (ST 4), Jiache (ST 6), Yifeng (SJ 17), and Hegu (LI 4) acupoints for 2 weeks. The Simone's 10-Point Scale was utilized to monitor the recovery of facial function. The histopathological evaluation of facial nerves was performed using hematoxylin-eosin (HE) staining. The levels of Beclin-1, light chain 3 (LC3), and P62 were detected by immunohistochemistry (IHC), immunofluorescence, and reverse transcription-polymerase chain reaction, respectively. Additionally, IHC was also used to detect the levels of GDNF, Rai, PI3K, and mTOR. The facial functional scores were significantly increased in the EA group than the FNI group (P<0.05 or P<0.01). HE staining showed nerve axons and myelin sheaths, which were destroyed immediately after the injury, were recovered with EA treatment. The expressions of Beclin-1 and LC3 were significantly elevated and the expression of P62 was markedly reduced in FNI rats (P<0.01); however, EA treatment reversed these abnormal changes (P<0.01). Meanwhile, EA stimulation significantly increased the levels of GDNF, Rai, PI3K, and mTOR (P<0.01). After exogenous administration with autophagy inhibitor 3-MA or GDNF antagonist, the repair effect of EA on facial function was attenuated (P<0.05 or P<0.01). EA could promote the recovery of facial function and repair the facial nerve damages in a rat model of FNI. EA may exert this neuroreparative effect through mediating the release of GDNF, activating the PI3K/mTOR signaling pathway, and further regulating the autophagy of facial nerves.

Glial cell line derived neurotrophic factor in brain repair after focal ischemic stroke.

Glial cell line derived neurotrophic factor in brain repair after focal ischemic stroke.

GDNF to the rescue: GDNF delivery effects on motor neurons and nerves, and muscle re-innervation after peripheral nerve injuries.

Peripheral nerve injuries commonly occur due to trauma, like a traffic accident. Peripheral nerves get severed, causing motor neuron death and potential muscle atrophy. The current golden standard to treat peripheral nerve lesions, especially lesions with large (≥ 3 cm) nerve gaps, is the use of a nerve autograft or reimplantation in cases where nerve root avulsions occur. If not tended early, degeneration of motor neurons and loss of axon regeneration can occur, leading to loss of function. Although surgical procedures exist, patients often do not fully recover, and quality of life deteriorates. Peripheral nerves have limited regeneration, and it is usually mediated by Schwann cells and neurotrophic factors, like glial cell line-derived neurotrophic factor, as seen in Wallerian degeneration. Glial cell line-derived neurotrophic factor is a neurotrophic factor known to promote motor neuron survival and neurite outgrowth. Glial cell line-derived neurotrophic factor is upregulated in different forms of nerve injuries like axotomy, sciatic nerve crush, and compression, thus creating great interest to explore this protein as a potential treatment for peripheral nerve injuries. Exogenous glial cell line-derived neurotrophic factor has shown positive effects in regeneration and functional recovery when applied in experimental models of peripheral nerve injuries. In this review, we discuss the mechanism of repair provided by Schwann cells and upregulation of glial cell line-derived neurotrophic factor, the latest findings on the effects of glial cell line-derived neurotrophic factor in different types of peripheral nerve injuries, delivery systems, and complementary treatments (electrical muscle stimulation and exercise). Understanding and overcoming the challenges of proper timing and glial cell line-derived neurotrophic factor delivery is paramount to creating novel treatments to tend to peripheral nerve injuries to improve patients’ quality of life.

Nanofibrous bicomponent scaffolds for the dual delivery of NGF and GDNF: controlled release of growth factors and their biological effects

Electrospun fibrous scaffolds capable of providing dual growth factor delivery in a controlled manner have distinctive advantages for tissue engineering. In this study, we have investigated the formation, structure, and characteristics/properties of fibrous bicomponent scaffolds for the dual delivery of glial cell line-derived neurotrophic factor (GDNF) and nerve growth factor (NGF) for peripheral nerve tissue regeneration. GDNF and NGF were incorporated into core-shell structured poly(lactic-co-glycolic acid) (PLGA) and poly (d,l-lactic acid) (PDLLA) nanofibers, respectively, through emulsion electrospinning. Using dual-source dual-power electrospinning, bicomponent scaffolds composed of GDNF/PLGA fibers and NGF/PDLLA fibers with different fiber component ratios were produced. The structure, properties, and in vitro release behavior of mono- and bicomponent scaffolds were systematically investigated. Concurrent and sustained release of GDNF and NGF from bicomponent scaffolds was achieved and their release profiles could be tuned. In vitro biological investigations were conducted. Rat pheochromocytoma cells were found to attach, spread, and proliferate on all scaffolds. The release of growth factors from scaffolds could induce much improved neurite outgrowth and neural differentiation. GDNF and NGF released from GDNF/PLGA scaffolds and NGF/PDLLA scaffolds, respectively, could induce dose-dependent neural differentiation separately. GDNF and NGF released from bicomponent scaffolds exerted a synergistic effect on promoting neural differentiation.

Ginsenoside Rg1-induced activation of astrocytes promotes functional recovery via the PI3K/Akt signaling pathway following spinal cord injury

AimsTo determine whether ginsenoside Rg1 is involved in scratch wound healing through altered expression of related molecules in astrocytes and improved functional recovery after spinal cord injury (SCI). Materials and methodsAstrocytes were isolated from rats, followed by Rg1 treatment. The wound healing test was performed to observe the scratch wound healing in different groups. The expression of nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF), basic fibroblast growth factor (bFGF), and components of the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway were detected by western blot. Reverse transcription–polymerase chain reaction (RT-PCR) was used to measure the altered expression of laminin (LN) and fibronectin (FN). A revised Allen's method for the SCI model was performed, followed by Rg1 treatment. Then, functional scoring was conducted to evaluate the functional recovery. Hematoxylin-eosin (HE) staining showed changes in the void area. Finally, western blot assessed the expression of glial fibrillary acidic protein (GFAP) and chondroitin sulfate proteoglycans (CSPGs). Key findingsRg1 mediated scratch wound healing through inducing an increased release of LN, FN, NGF, GDNF, and bFGF in vitro. Additionally, Rg1 activated the PI3K/Akt signaling pathway and promoted the functional recovery of hindlimb movement in rats. Furthermore, Rg1 significantly reduced the void area and downregulated the expression of GFAP and CSPGs. SignificanceRg1 not only enhanced the scratch wound repair in vitro through the release of astroglial neurotrophic factors, adhesion factors, and inhibitory factors, but it also improved the functional recovery in vivo following SCI.

Long-gap peripheral nerve repair through sustained release of a neurotrophic factor in nonhuman primates.

Severe injuries to peripheral nerves are challenging to repair. Standard-of-care treatment for nerve gaps >2 to 3 centimeters is autografting; however, autografting can result in neuroma formation, loss of sensory function at the donor site, and increased operative time. To address the need for a synthetic nerve conduit to treat large nerve gaps, we investigated a biodegradable poly(caprolactone) (PCL) conduit with embedded double-walled polymeric microspheres encapsulating glial cell line-derived neurotrophic factor (GDNF) capable of providing a sustained release of GDNF for >50 days in a 5-centimeter nerve defect in a rhesus macaque model. The GDNF-eluting conduit (PCL/GDNF) was compared to a median nerve autograft and a PCL conduit containing empty microspheres (PCL/Empty). Functional testing demonstrated similar functional recovery between the PCL/GDNF-treated group (75.64 ± 10.28%) and the autograft-treated group (77.49 ± 19.28%); both groups were statistically improved compared to PCL/Empty-treated group (44.95 ± 26.94%). Nerve conduction velocity 1 year after surgery was increased in the PCL/GDNF-treated macaques (31.41 ± 15.34 meters/second) compared to autograft (25.45 ± 3.96 meters/second) and PCL/Empty (12.60 ± 3.89 meters/second) treatment. Histological analyses included assessment of Schwann cell presence, myelination of axons, nerve fiber density, and g-ratio. PCL/GDNF group exhibited a statistically greater average area occupied by individual Schwann cells at the distal nerve (11.60 ± 33.01 μm2) compared to autograft (4.62 ± 3.99 μm2) and PCL/Empty (4.52 ± 5.16 μm2) treatment groups. This study demonstrates the efficacious bridging of a long peripheral nerve gap in a nonhuman primate model using an acellular, biodegradable nerve conduit.

Ellagic acid supports neuron by regulating astroglia Nrf2.

Astroglia support neuron by providing substrates for neuronal metabolism, glutamate clearance, and antioxidative protection. Nuclear factor erythroid 2-related factor 2 (Nrf2) participates in the antioxidative defense response. Also, Nrf2 signaling is recognized to activate the neurotrophic pathway to replace/protect damaged organelles. Ellagic acid (EA), an extraction component of fruits and nuts, presents many pharmacological activities such as anti-inflammation, antioxidation, and neuroprotection. However, few studies have been focused on the neurotrophic properties of EA. Our study investigated whether EA could increase neuronal survival and the target cells. Thus, primary neuron-enriched cultures and primary astroglia-enriched cultures were applied to detect whether EA-elicited neurotrophic effects were mediated by astroglia Nrf2. This study indicated that EA promoted neuronal survival. Further, astroglia Nrf2 participate in EA-elicited neuronal survival with the following scenarios. First, EA elicited astroglia proliferation, glial cell line-derived neurotrophic factor (GDNF) release, and Nrf2 activation. Second, after silencing astroglia Nrf2, EA-induced astrogliosis, GDNF release, and neuronal survival disappeared. Thus, EA-mediated astroglia Nrf2 activation is important to enhance neurotrophic effects on neurons, which might provide new insights for neurodegenerative disease.

Glial cell line-derived neurotrophic factor as a treatment after spinal cord injury.

Glial cell line-derived neurotrophic factor as a treatment after spinal cord injury.

Development and characterization of cores–shell poly(lactide-co-glycolide)-chitosan microparticles for sustained release of GDNF

The microencapsulation of bioactive neurotrophic factors in biodegradable poly(lactide-co-glycolide) (PLGA) microspheres has been a promising tool in the treatment of various nervous system disorders. However, challenges still exist; the PLGA burst drug release and acidic degradation products often limit clinical application. In this study, cores–shell PLGA-chitosan microparticles (MPs) were fabricated with a single shell of chitosan and multi-cores of PLGA using a re-emulsification method. The glial cell line-derived neurotrophic factor (GDNF) was encapsulated at the PLGA cores of the cores–shell MPs. The cores–shell MPs prepared by different chitosan concentrations showed a rough surface, and the particle mean size varied between 32.3 and 45.2μm. The fluorescence images indicated that Nile red-stained PLGA microspheres were uniformly distributed in the cores–shell MPs. Compared with PLGA microspheres, the cores–shell MPs were able to reduce the initial burst release of GDNF and neutralize the acidity of PLGA degradation products, which could be modulated by changing the chitosan concentrations. Further differentiation of PC12 cells toward a neuronal phenotype in vitro indicated that the cores–shell MPs were capable of maintaining the bioactivity of GDNF during preparation. Taken together, these findings highlight the possibility of using cores–shell PLGA-chitosan MPs for the sustained release of GDNF, which offers potential applications in nerve injury repair.

Docosahexaenoic acid induces glial cell-line derived neurotrophic factor release in C6 glioma cells: Implications of antidepressant effects for docosahexaenoic acid

Dietary deficiency of n-3 polyunsaturated fatty acids (PUFAs) is involved in the pathophysiology and etiology of major depressive disorder. Supplementation with docosahexaenoic acid (DHA) exerts antidepressant-like effect; however, the molecular mechanism of DHA action remains unclear. Here we examined the effects of DHA on the modulation of glial cell line-derived neurotrophic factor (GDNF), which is essential for neural development, plasticity, neurogenesis, and survival. We demonstrated that DHA treatment significantly increased GDNF release in a concentration dependent manner in rat C6 glioma cells (C6 cells) and primary cultured rat astrocytes, which is also associated with increased expression of GDNF mRNA. Furthermore, the DHA-induced GDNF production was inhibited by mitogen activated protein kinase (MEK) inhibitor and protein kinase C (PKC) inhibitor, but not protein kinase A (PKA) inhibitor and p38 mitogen-activated protein kinase (MAPK) inhibitor. DHA-induced extracellular signal-regulated kinase (ERK) activation is dependent on the PKC, as demonstrated by its reversibility after pretreatment with PKC inhibitor. Moreover, fibroblast growth factor receptor (FGFR inhibitor) but not epidermal growth factor receptor (EGFR) inhibitor blocked the activation of ERK induced by DHA treatment. DHA-induced GDNF production was also blocked by FGFR inhibitor, suggesting that FGFR is also involved in ERK activation-mediated GDNF production induced by DHA. Our study demonstrates that DHA-induced release of GDNF, mediated by PKC and FGFR-dependent on ERK activation, may contribute to the antidepressant-like effect of DHA.

Encapsulated cell device approach for combined electrical stimulation and neurotrophic treatment of the deaf cochlea

Profound hearing impairment can be overcome by electrical stimulation (ES) of spiral ganglion neurons (SGNs) via a cochlear implant (CI). Thus, SGN survival is critical for CI efficacy. Application of glial cell line-derived neurotrophic factor (GDNF) has been shown to reduce SGN degeneration following deafness. We tested a novel method for local, continuous GDNF-delivery in combination with ES via a CI. The encapsulated cell (EC) device contained a human ARPE-19 cell-line, genetically engineered for secretion of GDNF. In vitro, GDNF delivery was stable during ES delivered via a CI. In the chronic in vivo part, cats were systemically deafened and unilaterally implanted into the scala tympani with a CI and an EC device, which they wore for six months. The implantation of control devices (same cell-line not producing GDNF) had no negative effect on SGN survival. GDNF application without ES led to an unexpected reduction in SGN survival, however, the combination of GDNF with initial, short-term ES resulted in a significant protection of SGNs. A tight fibrous tissue formation in the scala tympani of the GDNF-only group is thought to be responsible for the increased SGN degeneration, due to mechanisms related to an aggravated foreign body response. Furthermore, the fibrotic encapsulation of the EC device led to cell death or cessation of GDNF release within the EC device during the six months in vivo. In both in vitro and in vivo, fibrosis was reduced by CI stimulation, enabling the neuroprotective effect of the combined treatment. Thus, fibrous tissue growth limits treatment possibilities with an EC device. For a stable and successful long-term neurotrophic treatment of the SGN via EC devices in human CI users, it would be necessary to make changes in the treatment approach (provision of anti-inflammatories), the EC device surface (reduced cell adhesion) and the ES (initiation prior to fibrosis formation).

GPR30 Activation Contributes to the Puerarin-Mediated Neuroprotection in MPP+-Induced SH-SY5Y Cell Death.

The neuroprotective action of puerarin in Parkinson's disease (PD) models has been well investigated. However, the mechanisms involved in protection have not been completely understood. G protein-coupled receptor 30 (GPR30) is a G protein-coupled estrogen receptor and considered a potential target in the neuroprotection against PD. In this study, we investigated whether puerarin prevented against 1-methyl-4-phenylpyridinium (MPP+)-induced cell death via GPR30. Our results showed that the GPR30 agonist, G1, exhibited puerarin-mediated neuroprotection against MPP+-induced cell death of SH-SY5Y cells. This protective action was reversed by the GPR30 antagonist. Moreover, a time- and concentration-dependent effect of puerarin on GPR30 expression was verified at the protein level but not at the mRNA level. Further, we showed that an mTor-dependent new GPR30 synthesis contributed to the protection conferred by puerarin. Finally, glial cell line-derived neurotrophic factor (GDNF) levels were enhanced by puerarin and G1 in both control and MPP+-lesioned cells via GPR30. Taken together, our data strongly suggest that puerarin prevents MPP+-induced cell death via facilitating GPR30 expression and GDNF release.

Deconstructing the Iboga Alkaloid Skeleton: Potentiation of FGF2-induced Glial Cell Line-Derived Neurotrophic Factor Release by a Novel Compound.

Modulation of growth factor signaling pathways in the brain represents a new experimental approach to treating neuropsychiatric disorders such as depression, anxiety, and addiction. Neurotrophins and growth factors exert synaptic, neuronal, and circuit level effects on a wide temporal range, which suggests a possibility of rapid and lasting therapeutic effects. Consequently, identification of small molecules that can either enhance the release of growth factors or potentiate their respective pathways will provide a drug-like alternative to direct neurotrophin administration or viral gene delivery and thus represents an important frontier in chemical biology and drug design. Glial cell line-derived neurotrophic factor (GDNF), in particular, has been implicated in marked reduction of alcohol consumption in rodent addiction models, and the natural product ibogaine, a substance used traditionally in ritualistic ceremonies, has been suggested to increase the synthesis and release of GDNF in the dopaminergic system in rats. In this report, we describe a novel iboga analog, XL-008, created by unraveling the medium size ring of the ibogamine skeleton, and its ability to induce release of GDNF in C6 glioma cells. Additionally, XL-008 potentiates the release of GDNF induced by fibroblast growth factor 2 (FGF2), another neurotrophin implicated in major depressive disorder, increasing potency more than 2-fold (from 7.85 ± 2.59 ng/mL to 3.31 ± 0.98 ng/mL) and efficacy more than 3-fold. The GDNF release by both XL-008 and the FGF2/XL-008 mixture was found to be mediated through the MEK and PI3K signaling pathways but not through PLCγ in C6 glioma cells.

Ethylene Oxide Sterilization Preserves Bioactivity and Attenuates Burst Release of Encapsulated Glial Cell Line Derived Neurotrophic Factor from Tissue Engineered Nerve Guides For Long Gap Peripheral Nerve Repair.

Synthetic nerve guides are widely utilized to reconstruct peripheral nerve defects that are less than three centimeters. However, there are no clinically available nerve guides that are approved to promote repair over long gaps (>3 cm). Many currently available guides are unable to sustain large defect regeneration either because of limitations in fabrication or short degradation times in vivo. Furthermore, current clinically available nerve guides do not contain neurotrophic factor delivery systems to promote nerve tissue regeneration over long gaps. The purpose of this paper is to describe the manufacturing parameters and sterilization procedures of a 5.2 cm poly(caprolactone) nerve conduit with embedded polymeric microspheres that encapsulate glial cell line-derived neurotrophic factor (GDNF) for implantation into a preclinical rhesus macaque 5 cm median nerve defect model. Nerve conduits were sterilized with room temperature ethylene oxide (RT EtO) and assessed for morphology as well as maintenance of porosity. Release kinetics and bioactivity of GDNF were also assessed in RT EtO sterilized guides. Scanning electron microscopy indicated that RT EtO treatment did not affect morphology and porosity percentage of nerve guides. Furthermore, RT EtO had no effect on GDNF bioactivity based on Schwannoma cell migration studies. RT EtO guides exhibited significantly slowed GDNF release compared to GDNF release from nonsterile guides indicating that EtO treatment may enhance the long-term delivery kinetics of GDNF from polymeric microspheres within the nerve guide.

Tricyclic Antidepressant Amitriptyline-induced Glial Cell Line-derived Neurotrophic Factor Production Involves Pertussis Toxin-sensitive Gαi/o Activation in Astroglial Cells

Further elaborating the mechanism of antidepressants, beyond modulation of monoaminergic neurotransmission, this study sought to elucidate the mechanism of amitriptyline-induced production of glial cell line-derived neurotrophic factor (GDNF) in astroglial cells. Previous studies demonstrated that an amitriptyline-evoked matrix metalloproteinase (MMP)/FGF receptor (FGFR)/FGFR substrate 2α (FRS2α)/ERK cascade is crucial for GDNF production, but how amitriptyline triggers this cascade remains unknown. MMP is activated by intracellular mediators such as G proteins, and this study sought to clarify the involvement of G protein signaling in amitriptyline-evoked GDNF production in rat C6 astroglial cells (C6 cells), primary cultured rat astrocytes, and normal human astrocytes. Amitriptyline-evoked GDNF mRNA expression and release were inhibited by pertussis toxin (PTX), a Gα(i/o) inhibitor, but not by NF449, a Gα(s) inhibitor, or YM-254890, a Gαq inhibitor. The activation of the GDNF production cascade (FGFR/FRS2α/ERK) was also inhibited by PTX. Deletion of Gα(ο1) and Gα(i3) by RNAi demonstrated that these G proteins play important roles in amitriptyline signaling. G protein activation was directly analyzed by electrical impedance-based biosensors (CellKey(TM) assay), using a label-free (without use of fluorescent proteins/probes or radioisotopes) and real time approach. Amitriptyline increased impedance, indicating Gα(i/o) activation that was suppressed by PTX treatment. The impedance evoked by amitriptyline was not affected by inhibitors of the GDNF production cascade. Furthermore, FGF2 treatment did not elicit any effect on impedance, indicating that amitriptyline targets PTX-sensitive Gα(i/o) upstream of the MMP/FGFR/FRS2α/ERK cascade. These results suggest novel targeting for the development of antidepressants.

Controlled release of glial cell line-derived neurotrophic factor from poly(ε-caprolactone) microspheres.

Glial cell line-derived neurotrophic factor (GDNF), a growth factor expressed in the central nervous system, promotes the survival of both dopaminergic and motor neurons, making it a promising candidate for neurodegenerative disease therapy. Although GDNF is currently being evaluated in clinical trials for the treatment of Parkinson's disease (PD), the current delivery method using catheter implantation has certain limitations in terms of delivering GDNF safely and effectively. As a proof of concept, we encapsulated GDNF into poly(ε-caprolactone) (PCL) microspheres to enable controlled drug release for 25days. First, microspheres were loaded with bovine serum albumin (BSA) to determine the optimal fabrication conditions necessary to achieve the desired release rates of protein. BSA was then used as a carrier protein to preserve GDNF activity during the fabrication process in the presence of organic solvents. GDNF-encapsulated microspheres were created and characterized using scanning electron microscopy. Next, the in vitro release of GDNF along with microsphere morphology was tracked over 25days. Finally, the bioactivity of the released GDNF was confirmed using PC12 cells. This work demonstrates the potential of such microspheres for the delivery of bioactive GDNF with the end goal of developing a suitable, clinically relevant formulation for injection to appropriate regions of the brain in PD patients.

Nerve conduit scaffolds for discrete delivery of two neurotrophic factors

Axonal repair and regeneration remain critical due to lack of appropriate delivery systems for efficient release of neurotrophic factors (NTFs). Recently, we have demonstrated the synergistic activity of nerve growth factor (NGF) and glial cell line-derived neurotrophic factor (GDNF) on axonal regeneration. Combined delivery of GDNF and NGF with individually controlled release kinetics may be crucial for exploiting their synergistic action on axonal elongation in animals. For engineering discrete NTF release kinetics, we have developed several nerve conduits (NCs) using collagen (Col) and silk fibroin (SF); the NC were made of Col or SF alone, or of Col and SF layers, or of Col/SF blends, all loaded with GDNF and NGF. All NC types provided sustained combined release of NGF and GDNF over 28days. NC made of combinations of Col and SF showed reduced burst and more sustained dual release of GDNF and NGF. SF/Col-based NC scaffolds provide an adaptable delivery system for growth factors and hold potential for nerve regeneration and possibly for other tissue engineering applications.

The Effects of Progesterone on Glial Cell Line-derived Neurotrophic Factor Secretion from C6 Glioma Cells.

Progesterone is a steroid hormone whose biology has been greatly studied within the confines of reproductive function. In recent years, the neuroprotective effects of progesterone have attracted growing interest. Glial cell line-derived neurotrophic factor (GDNF), is a neurotrophic factor which plays a crucial role in the development and maintenance of distinct sets of central and peripheral neurons. In the present study, we investigated the potential implication of GDNF in the neuroprotective action of progesterone. Cultured rat C6 glioma cells were treated with progesterone (100 nm, 1 µM, and 10 µM) or its vehicle. After 24, 36, 48 and 72 hr, GDNF protein levels were measured in the cell-conditioned media and cell lysates using a GDNF ELISA kit. Cell numbers were determined by a cell-counting assay kit. Forty-eight hr treatment with progesterone (10 µM) resulted in a significant elevation of GDNF secretion from C6 glioma cells that remained elevated up to 72 hr. The intracellular content of GDNF and cell numbers were not affected by progesterone treatment. Stimulation of GDNF release from glial cells appears as a potential mechanism through which progesterone exerts its neuroprotective effects.

IB4(+) nociceptors mediate persistent muscle pain induced by GDNF

Skeletal muscle is a well-known source of glial cell line-derived neurotrophic factor (GDNF), which can produce mechanical hyperalgesia. Since some neuromuscular diseases are associated with both increased release of GDNF and intense muscle pain, we explored the role of GDNF as an endogenous mediator in muscle pain. Intramuscularly injected GDNF induced a dose-dependent (0.1-10 ng/20 μl) persistent (up to 3 wk) mechanical hyperalgesia in the rat. Once hyperalgesia subsided, injection of prostaglandin E(2) at the site induced a prolonged mechanical hyperalgesia (>72 h) compared with naïve rats (<4 h; hyperalgesic priming). Selective neurotoxic destruction of IB4(+) nociceptors attenuated both GDNF hyperalgesia and hyperalgesic priming. Ergonomic muscular injury induced by eccentric exercise or mechanical vibration increased muscle GDNF levels at 24 h, a time point where rats also exhibited marked muscle hyperalgesia. Intrathecal antisense oligodeoxynucleotides to mRNA encoding GFRα1, the canonical binding receptor for GDNF, reversibly inhibited eccentric exercise- and mechanical vibration-induced muscle hyperalgesia. Finally, electrophysiological recordings from nociceptors innervating the gastrocnemius muscle in anesthetized rats, revealed significant increase in response to sustained mechanical stimulation after local GDNF injection. In conclusion, these data indicate that GDNF plays a role as an endogenous mediator in acute and induction of chronic muscle pain, an effect likely to be produced by GDNF action at GFRα1 receptors located in IB4(+) nociceptors.