GDNF-enhanced axonal regeneration and myelination following spinal cord injury is mediated by primary effects on neurons

Injectable alginate hydrogel loaded with GDNF promotes functional recovery in a hemisection model of spinal cord injury

We hypothesized that local delivery of GDNF in spinal cord lesion via an injectable alginate hydrogel gelifying in situ would support spinal cord plasticity and functional recovery. The GDNF release from the hydrogel was slowed by GDNF encapsulation in microspheres compared to non-formulated GDNF (free GDNF). When injected in a rat spinal cord hemisection model, more neurofilaments were observed in the lesion when the rats were treated with free GDNF-loaded hydrogels. More growing neurites were detected in the tissues surrounding the lesion when the animals were treated with GDNF microsphere-loaded hydrogels. Intense GFAP (astrocytes), low βIII tubulin (neural cells) and RECA-1 (endothelial cells) stainings were observed for non-treated lesions while GDNF-treated spinal cords presented less GFAP staining and more endothelial and nerve fiber infiltration in the lesion site. The animals treated with free GDNF-loaded hydrogel presented superior functional recovery compared with the animals treated with the GDNF microsphere-loaded hydrogels and non-treated animals.

Bone marrow stromal cells promote neurite outgrowth of spinal motor neurons by means of neurotrophic factors in vitro

Transplantation of bone marrow stromal cells (BMSCs) into spinal cord injury models has shown significant neural function recovery; however, the underlying mechanisms have not been fully understood. In the present study we examined the effect of BMSCs on neurite outgrowth of spinal motor neuron using an in vitro co-culture system. The ventral horn of the spinal grey matter was harvested from neonatal Sprague-Dawley rats, cultured with BMSCs, and immunostained for neurofilament-200 (NF-200). Neurite outgrowth of spinal motor neurons was measured using Image J software. ELISA was used to quantify neurotrophic factors such as brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF) and nerve growth factor (NGF) in culture media, and antibodies or exogenous neurotrophic factors were used to block or mimic the effect of BMSCs on neurite outgrowth, respectively. The results showed that neurite outgrowth significantly increased in spinal motor neurons after co-cultured with BMSCs, while the secretion level of BDNF, GDNF and NGF was dramatically elevated in co-culture. However, the neurite outgrowth-promoting effect of BMSCs was found to significantly reduced using antibodies to BDNF, GDNF and NGF. In addition, a fraction of BMSCs was found to exhibit NF-200 immunoreactivity. These results indicated that BMSCs could promote neurite outgrowth of motor neurons by means of neurotrophic factors. The findings of the present study provided new cues for the treatment of spinal cord injury.

The protective effects of resveratrol on Schwann cells with toxicity induced by ethanol in vitro

Schwann cells (SCs) are the myelin forming cells in the peripheral nervous system, they play a key role in the pathology of various polyneuropathies and provide trophic support to axons via expression of various neurotrophic factors, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF). Ethanol (EtOH) adversely affected both SCs proliferation and myelin formation in culture. Resveratrol (Res) has been shown to regulate many cellular processes and to display multiple protective and therapeutic effects. Whether Res has protective effects on SCs with EtOH-induced toxicity is still unclear. The protective efficacy of Res on EtOH-treated SCs in vitro was investigated in the present study. Res improved cell viability of the EtOH-treated SCs. Hoechst 33342 staining and terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate nick-end labeling analysis showed that the EtOH-induced apoptosis was inhibited by Res. The effects of Res were blocked by the 5'-adenosine monophosphate-activated protein kinase inhibitor Compound C and the silencing information regulator T1 inhibitor nicotinamide. Res could increase the mRNA and protein levels of BDNF and GDNF in the EtOH-treated SCs. However, the EtOH-induced increase of NGF in the SCs is inhibited by Res. The data from the present study indicate that Res protects SCs from EtOH-induced cell death and regulates the expression of neurotrophicfactors. Res and its derivative may be effective for the treatment of neuropathic diseases induced by EtOH.

A novel growth-promoting pathway formed by GDNF-overexpressing Schwann cells promotes propriospinal axonal regeneration, synapse formation, and partial recovery of function after spinal cord injury

Descending propriospinal neurons (DPSN) are known to establish functional relays for supraspinal signals, and they display a greater growth response after injury than do the long projecting axons. However, their regenerative response is still deficient due to their failure to depart from growth supportive cellular transplants back into the host spinal cord, which contains numerous impediments to axon growth. Here we report the construction of a continuous growth-promoting pathway in adult rats, formed by grafted Schwann cells overexpressing glial cell line-derived neurotrophic factor (GDNF). We demonstrate that such a growth-promoting pathway, extending from the axonal cut ends to the site of innervation in the distal spinal cord, promoted regeneration of DPSN axons through and beyond the lesion gap of a spinal cord hemisection. Within the distal host spinal cord, regenerated DPSN axons formed synapses with host neurons leading to the restoration of action potentials and partial recovery of function.

GDNF-treated acellular nerve graft promotes motoneuron axon regeneration after implantation into cervical root avulsed spinal cord

It is well known that glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor for motoneurons. We have previously shown that it greatly enhanced motoneuron survival and axon regeneration after implantation of peripheral nerve graft following spinal root avulsion.

AIMS

In the current study, we explore whether injection of GDNF promotes axon regeneration in decellularized nerve induced by repeated freeze-thaw cycles.

METHODS

We injected saline or GDNF into the decellularized nerve after root avulsion in adult Sprague-Dawley rats and assessed motoneuron axon regeneration and Schwann cell migration by retrograde labelling and immunohistochemistry.

RESULTS

We found that no axons were present in saline-treated acellular nerve whereas Schwann cells migrated into GDNF-treated acellular nerve grafts. We also found that Schwann cells migrated into the nerve grafts as early as 4 days after implantation, coinciding with the first appearance of regenerating axons in the grafts. Application of GDNF outside the graft did not induce Schwann cell infiltration nor axon regeneration into the graft. Application of pleiotrophin, a trophic factor which promotes axon regeneration but not Schwann cell migration, did not promote axon infiltration into acellular nerve graft.

CONCLUSIONS

We conclude that GDNF induced Schwann cell migration and axon regeneration into the acellular nerve graft. Our findings can be of potential clinical value to develop acellular nerve grafting for use in spinal root avulsion injuries.

Gamma knife irradiation of injured sciatic nerve induces histological and behavioral improvement in the rat neuropathic pain model

We examined the effects of gamma knife (GK) irradiation on injured nerves using a rat partial sciatic nerve ligation (PSL) model. GK irradiation was performed at one week after ligation and nerve preparations were made three weeks after ligation. GK irradiation is known to induce immune responses such as glial cell activation in the central nervous system. Thus, we determined the effects of GK irradiation on macrophages using immunoblot and histochemical analyses. Expression of Iba-1 protein, a macrophage marker, was further increased in GK-treated injured nerves as compared with non-irradiated injured nerves. Immunohistochemical study of Iba-1 in GK-irradiated injured sciatic nerves demonstrated Iba-1 positive macrophage accumulation to be enhanced in areas distal to the ligation point. In the same area, myelin debris was also more efficiently removed by GK-irradiation. Myelin debris clearance by macrophages is thought to contribute to a permissive environment for axon growth. In the immunoblot study, GK irradiation significantly increased expressions of βIII-tubulin protein and myelin protein zero, which are markers of axon regeneration and re-myelination, respectively. Toluidine blue staining revealed the re-myelinated fiber diameter to be larger at proximal sites and that the re-myelinated fiber number was increased at distal sites in GK-irradiated injured nerves as compared with non-irradiated injured nerves. These results suggest that GK irradiation of injured nerves facilitates regeneration and re-myelination. In a behavior study, early alleviation of allodynia was observed with GK irradiation in PSL rats. When GK-induced alleviation of allodynia was initially detected, the expression of glial cell line-derived neurotrophic factor (GDNF), a potent analgesic factor, was significantly increased by GK irradiation. These results suggested that GK irradiation alleviates allodynia via increased GDNF. This study provides novel evidence that GK irradiation of injured peripheral nerves may have beneficial effects.

Spinal cord regeneration: where fish, frogs and salamanders lead the way, can we follow?

Major trauma to the mammalian spinal cord often results in irreversible loss of function, i.e. paralysis, and current therapies ranging from drugs, implantations of stem cells and/or biomaterials, and electrically stimulated nerve regrowth, have so far offered very limited success in improving quality-of-life. However, in marked contrast with this basic shortcoming of ours, certain vertebrate species, including fish and salamanders, display the amazing ability to faithfully regenerate various complex body structures after injury or ablation, restoring full functionality, even in the case of the spinal cord. Despite the inherently strong and obvious translational potential for improving treatment strategies for human patients, our in-depth molecular-level understanding of these decidedly more advanced repair systems remains in its infancy. In the present review, we will discuss the current state of this field, focusing on recent progress in such molecular analyses using various regenerative species, and how these so far relate to the mammalian situation.

Intrathecal epigallocatechin gallate treatment improves functional recovery after spinal cord injury by upregulating the expression of BDNF and GDNF

This study aimed to investigate the therapeutic effects of epigallocatechin-3-gallate (EGCG) administered by subarachnoid injection following spinal cord injury (SCI) in rats and to explore the underlying mechanism. Sprague-Dawley rats were randomly divided into four groups of 12 as follows: a sham group (laminectomy only); a control group; a 10 mg/kg EGCG-treated group; and a 20 mg/kg EGCG-treated group. SCI was induced in the rats using the modified weight-drop method (10 g × 4 cm) at the T10 (10th thoracic vertebral) level. EGCG (10 or 20 mg/kg) or vehicle as control was administered by subarachnoid injection at lumbar level 4 immediately after SCI. Locomotor functional recovery was assessed during the four weeks post-operation using open-field locomotor tests and inclined-plane tests. At the end of the study, the segments of spinal cord encompassing the injury site were removed for histopathological analysis. Immunohistochemical and Western blot analyses were performed to observe the expression of: the B cell CLL/lymphoma-2 (Bcl-2), Bcl-2-associated X protein (Bax), brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF). The results showed that the EGCG-treated animals had significantly better recovery of locomotor function, less myelin loss, greater Bcl-2 expression and attenuated Bax expression. In addition, the EGCG treatment significantly increased the expression of BDNF and GDNF after SCI. These findings suggest that EGCG treatment can significantly improve locomotor recovery, and this neuroprotective effect may be related to the up-regulation of BDNF and GDNF, and the inhibition of apoptosis-related proteins. Therefore, EGCG may be a promising therapeutic agent for SCI.

Potential role of growth factors in the management of spinal cord injury

OBJECTIVE

To review central nervous system growth factors and their therapeutic potential and clinical translation into spinal cord injury (SCI), as well as the challenges that have been encountered during clinical development.

METHODS

A systemic review of the available current and historical literature regarding central nervous system growth factors and clinical trials regarding their use in spinal cord injury was conducted.

RESULTS

The effectiveness of administering growth factors as a potential therapeutic strategy for SCI has been tested with the use of brain-derived neurotrophic factor, glial cell-derived neurotrophic factor, neurotrophin 3, and neurotrophin-4/5. Delivery of growth factors to injured SC has been tested by numerous methods. Unfortunately, most of clinical trials at this time are uncontrolled and have questionable results because of lack of efficacy and/or unacceptable side effects.

CONCLUSIONS

There is promise in the use of specific growth factors therapeutically for SCI. However, more studies involving neuronal regeneration and functional recovery are needed, as well the development of delivery methods that allow sufficient quantity of growth factors while restricting their distribution to target sites.

Adult rat mesenchymal stem cells delay denervated muscle atrophy

To evaluate the function of rat mesenchymal stem cells (rMSCs) on denervated gastrocnemius muscles and to address the role of ciliary neurotrophic factor (CNTF) in rMSCs, denervated Wistar rats were separately injected with culture media (sham control), CNTF protein, 2.5 × 10(5) siCNTF-treated rMSCs, 2.5 × 10(5) GFP-transfected rMSCs, or 2.5 × 10(5) untreated rMSCs. Muscle function was assessed at different time points post-surgery. Tibial nerve and gastrocnemius muscle samples were taken at 4, 8, and 12 weeks for histochemistry, and neuromuscular junction repair was also examined by electron microscopy. Fluorescence immunocytochemistry on tissue sections confirmed neurotrophin expression in rMSCs but with little evidence of neuronal differentiation. The engraftment of rMSCs significantly preserved the function of denervated gastrocnemius muscle based both on evaluation of muscle function and direct examination of muscle tissue. Further, the density and depth of the junctional folds were visibly reduced 12 weeks after surgery and transplantation, especially in control group. Knockdown of CNTF expression in rMSCs failed to block muscle preservation, although administration of CNTF protein alone inhibited muscle atrophy, which indicating that delivery of rMSCs could preserve gastrocnemius muscle function following denervation and post-junctional mechanisms involved in the repairing capability of rMSCs.

Exogenous basic fibroblast growth factor inhibits ER stress-induced apoptosis and improves recovery from spinal cord injury

AIM

To investigate the mechanism of endoplasmic reticulum (ER) stress-induced apoptosis as well as the protective action of basic fibroblast growth factor (bFGF) both in vivo and in vitro.

METHODS AND RESULTS

ER stress-induced apoptosis was involved in the injuries of spinal cord injury (SCI) model rat. bFGF administration improved the recovery and increased the survival of neurons in spinal cord lesions in model rat. The protective effect of bFGF is related to the inhibition of CHOP, GRP78 and caspase-12, which are ER stress-induced apoptosis response proteins. bFGF administration also increased the survival of neurons and the expression of growth-associated protein 43 (GAP43), which is related to neural regeneration. The protective effect of bFGF is related to the activation of downstream signals, PI3K/Akt/GSK-3β and ERK1/2, especially in the ER stress cell model.

CONCLUSIONS

This is the first study to illustrate that the role of bFGF in SCI recovery is related to the inhibition of ER stress-induced cell death via the activation of downstream signals. Our work also suggested a new trend for bFGF drug development in central neural system injuries, which are involved in chronic ER stress-induced apoptosis.

Fluoxetine ameliorates behavioral and neuropathological deficits in a transgenic model mouse of α-synucleinopathy

The term α-synucleinopathies refers to a group of age-related neurological disorders including Parkinson's disease (PD), Dementia with Lewy Bodies (DLB) and Multiple System Atrophy (MSA) that display an abnormal accumulation of alpha-synuclein (α-syn). In contrast to the neuronal α-syn accumulation observed in PD and DLB, MSA is characterized by a widespread oligodendrocytic α-syn accumulation. Transgenic mice expressing human α-syn under the oligodendrocyte-specific myelin basic protein promoter (MBP1-hαsyn tg mice) model many of the behavioral and neuropathological alterations observed in MSA. Fluoxetine, a selective serotonin reuptake inhibitor, has been shown to be protective in toxin-induced models of PD, however its effects in an in vivo transgenic model of α-synucleinopathy remain unclear. In this context, this study examined the effect of fluoxetine in the MBP1-hαsyn tg mice, a model of MSA. Fluoxetine administration ameliorated motor deficits in the MBP1-hαsyn tg mice, with a concomitant decrease in neurodegenerative pathology in the basal ganglia, neocortex and hippocampus. Fluoxetine administration also increased levels of the neurotrophic factors, GDNF (glial-derived neurotrophic factor) and BDNF (brain-derived neurotrophic factor) in the MBP1-hαsyn tg mice compared to vehicle-treated tg mice. This fluoxetine-induced increase in GDNF and BDNF protein levels was accompanied by activation of the ERK signaling pathway. The effects of fluoxetine administration on myelin and serotonin markers were also examined. Collectively these results indicate that fluoxetine may represent a novel therapeutic intervention for MSA and other neurodegenerative disorders.

A new in vitro injury model of mouse neurons induced by mechanical scratching

The mixed culture of neurons and glial cells has been widely used as a mechanical insult model for the study of neuron injury in vitro. However, a better model is desirable to eliminate the interference of glial cells during the study. Here we report a new model with exclusive cerebellar granule neurons (CGNs), which can be used for the study of in vitro neuron injury without involvement of glial cells. We found that after scratching insult, there was a decrease in both the survival rate and vitality of injured CGNs. Meanwhile, pathological changes were observed by electron microscopy. With this new model, we also tested the effects of neurotrophin-3 (NT-3) on neuroprotection. The result showed that the vitality of injured CGNs was enhanced by the administration of NT-3. These findings demonstrate that this new model is useful for investigation of the precise effect of mechanical damage on neurons excluding other factors, and to detect the neuroprotective effect of certain factors on mechanically injured neurons.

Neuregulin 1 type III/ErbB signaling is crucial for Schwann cell colonization of sympathetic axons

Analysis of Schwann cell (SC) development has been hampered by the lack of growing axons in many commonly used in vitro assays. As a consequence, the molecular signals and cellular dynamics of SC development along peripheral axons are still only poorly understood. Here we use a superior cervical ganglion (SCG) explant assay, in which axons elongate after treatment with nerve growth factor (NGF). Migration as well as proliferation and apoptosis of endogenous SCG-derived SCs along sympathetic axons were studied in these cultures using pharmacological interference and time-lapse imaging. Inhibition of ErbB receptor tyrosine kinases leads to reduced SC proliferation, increased apoptosis and thereby severely interfered with SC migration to distal axonal sections and colonization of axons. Furthermore we demonstrate that SC colonization of axons is also strongly impaired in a specific null mutant of an ErbB receptor ligand, Neuregulin 1 (NRG1) type III. Taken together, using a novel SC development assay, we demonstrate that NRG1 type III serves as a critical axonal signal for glial ErbB receptors that drives SC development along sympathetic axons.

Multifunctional, multichannel bridges that deliver neurotrophin encoding lentivirus for regeneration following spinal cord injury

Therapeutic strategies following spinal cord injury must address the multiple barriers that limit regeneration. Multiple channel bridges have been developed that stabilize the injury following implantation and provide physical guidance for regenerating axons. These bridges have now been employed as a vehicle for localized delivery of lentivirus. Implantation of lentivirus loaded multiple channel bridges produced transgene expression that persisted for at least 4 weeks. Expression was maximal at the implant at the earliest time point, and decreased with increasing time of implantation, as well as rostral and caudal to the bridge. Immunohistochemical staining indicated transduction of macrophages, Schwann cells, fibroblasts, and astrocytes within the bridge and adjacent tissue. Subsequently, the delivery of lentivirus encoding the neurotrophic factors NT-3 or BDNF significantly increased the extent of axonal growth into the bridge relative to empty scaffolds. In addition to promoting axon growth, the induced expression of neurotrophic factors led to myelination of axons within the channels of the bridge, where the number of myelinated axons was significantly enhanced relative to control. Combining gene delivery with biomaterials to provide physical guidance and create a permissive environment can provide a platform to enhance axonal growth and promote regeneration.

The correlation among the dynamic change of Zn2+, ZnT-1, and brain-derived neurotrophic factor after acute spinal cord injury in rats

Zinc plays an important role in regulating the expression of brain-derived neurotrophic factor (BDNF) and its receptor in nervous system, but the correlation among Zn(2+), zinc transporter, and BDNF in spinal cord injuries (SCI) is not fully understood. The purpose of this study was to investigate the expression of Zn(2+), zinc transporter 1 (ZnT-1), and BDNF, as well as their correlation in spinal cord-injured rats. One hundred Wistar male rats were divided into two groups: sham-operated group (as control group) and model group. Spinal cord injury was induced in model groups by hemisection of T9 on the left side. Compared with the control group, the serum zinc levels in SCI model group were significantly decreased after surgery, but zinc concentrations in spinal cord were increased gradually. The mRNA levels of ZnT-1 and BDNF were significantly increased in SCI model group, and there is a positive correlation between them (Spearman rho = 0.381, P = 0.0204). The correlation found between BDNF and ZnT-1 allows us to speculate that these two factors may be physiologically co-regulated, which may provide an idea for the treatment of SCI.

Immortalized adult rodent Schwann cells as in vitro models to study diabetic neuropathy

We have established spontaneously immortalized Schwann cell lines from normal adult mice and rats and murine disease models. One of the normal mouse cell lines, IMS32, possesses some biological properties of mature Schwann cells and high proliferative activities. The IMS32 cells under hyperglycemic and/or hyperlipidemic conditions have been utilized to investigate the pathogenesis of diabetic neuropathy, especially the polyol pathway hyperactivity, glycation, increased oxidative stress, and reduced synthesis of neurotrophic factors. In addition to the mouse cell lines, our current study focuses on the characterization of a normal rat cell line, IFRS1, under normal and high glucose conditions. These Schwann cell lines can be valuable tools for exploring the detailed mechanisms leading to diabetic neuropathy and novel therapeutic approaches against that condition.

Transient lysosomal activation is essential for p75 nerve growth factor receptor expression in myelinated Schwann cells during Wallerian degeneration

Myelinated Schwann cells in the peripheral nervous system express the p75 nerve growth factor receptor (p75NGFR) as a consequence of Schwann cell dedifferentiation during Wallerian degeneration. p75NGFR has been implicated in the remyelination of regenerating nerves. Although many studies have shown various mechanisms underlying Schwann cell dedifferentiation, the molecular mechanism contributing to the re-expression of p75NGFR in differentiated Schwann cells is largely unknown. In the present study, we found that lysosomes were transiently activated in Schwann cells after nerve injury and that the inhibition of lysosomal activation by chloroquine or lysosomal acidification inhibitors prevented p75NGFR expression at the mRNA transcriptional level in an ex vivo Wallerian degeneration model. Lysosomal acidification inhibitors suppressed demyelination, but not axonal degeneration, thereby suggesting that demyelination mediated by lysosomes may be an important signal for inducing p75NGFR expression. Tumor necrosis factor-α (TNF-α) has been suggested to be involved in regulating p75NGFR expression in Schwann cells. In this study, we found that removing TNF-α in vivo did not significantly suppress the induction of both lysosomes and p75NGFR. Thus, these findings suggest that lysosomal activation is tightly correlated with the induction of p75NGFR in demyelinating Schwann cells during Wallerian degeneration.

GDNF modifies reactive astrogliosis allowing robust axonal regeneration through Schwann cell-seeded guidance channels after spinal cord injury

Reactive astrogliosis impedes axonal regeneration after injuries to the mammalian central nervous system (CNS). Here we report that glial cell line-derived neurotrophic factor (GDNF), combined with transplanted Schwann cells (SCs), effectively reversed the inhibitory properties of astrocytes at graft-host interfaces allowing robust axonal regeneration, concomitant with vigorous migration of host astrocytes into SC-seeded semi-permeable guidance channels implanted into a right-sided spinal cord hemisection at the 10th thoracic (T10) level. Within the graft, migrated host astrocytes were in close association with regenerated axons. Astrocyte processes extended parallel to the axons, implying that the migrated astrocytes were not inhibitory and might have promoted directional growth of regenerated axons. In vitro, GDNF induced migration of SCs and astrocytes toward each other in an astrocyte-SC confrontation assay. GDNF also enhanced migration of astrocytes on a SC monolayer in an inverted coverslip migration assay, suggesting that this effect is mediated by direct cell-cell contact between the two cell types. Morphologically, GDNF administration reduced astrocyte hypertrophy and induced elongated process extension of these cells, similar to what was observed in vivo. Notably, GDNF treatment significantly reduced production of glial fibrillary acidic protein (GFAP) and chondroitin sulfate proteoglycans (CSPGs), two hallmarks of astrogliosis, in both the in vivo and in vitro models. Thus, our study demonstrates a novel role of GDNF in modifying spinal cord injury (SCI)-induced astrogliosis resulting in robust axonal regeneration in adult rats.

Clinical and experimental advances in regeneration of spinal cord injury

Spinal cord injury (SCI) is one of the major disabilities dealt with in clinical rehabilitation settings and is multifactorial in that the patients suffer from motor and sensory impairments as well as many other complications throughout their lifetimes. Many clinical trials have been documented during the last two decades to restore damaged spinal cords. However, only a few pharmacological therapies used in clinical settings which still have only limited effects on the regeneration, recovery speed, or retraining of the spinal cord. In this paper, we will introduce recent clinical trials, which performed pharmacological treatments and cell transplantations for patients with SCI, and evaluate recent in vivo studies for the regeneration of injured spinal cord, including stem-cell transplantation, application of neurotrophic factors and suppressor of inhibiting factors, development of biomaterial scaffolds and delivery systems, rehabilitation, and the combinations of these therapies to evaluate what can be appropriately applied in the future to the patients with SCI.

Simvastatin treatment improves functional recovery after experimental spinal cord injury by upregulating the expression of BDNF and GDNF

The aim of this study was to determine the therapeutic efficacy of simvastatin treatment starting 1 day after spinal cord injury (SCI) in rat and to investigate the underlying mechanism. Spinal cord injury was induced in adult female Sprague-Dawley rats after laminectomy at T9-T10. Then additionally with sham group (laminectomy only) the SCI animals were randomly divided into 3 groups: vehicle-treated group; 5-mg/kg simvastatin-treated group; and 10-mg/kg simvastatin-treated group. Simvastatin or vehicle was administered orally at 1 day after SCI and then daily for 5 weeks. Locomotor functional recovery was assessed during 8 weeks postoperation by performing open-field locomotor test and inclined-plane test. At the end of study, motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) were assessed to evaluate the integrity of spinal cord pathways. Then, the animals were killed, and 1-cm segments of spinal cord encompassing the injury site were removed for histopathological analysis. Immunohistochemistry was performed to observe the expression of brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF) in the spinal cord. Results show that the simvastatin-treated animals showed significantly better locomotor function recovery, better electrophysiological outcome, less myelin loss, and higher expression of BDNF and GDNF. These findings suggest that simvastatin treatment starting 1 day after SCI can significantly improve locomotor recovery, and this neuroprotective effect may be related to the upregulation of BDNF and GDNF. Therefore, simvastatin may be useful as a promising therapeutic agent for SCI.

Construction of pathways to promote axon growth within the adult central nervous system

Inducing significant axon growth or regeneration after spinal cord injury has been difficult, primarily due to the poor growth supportive environment and low intrinsic growth ability of neurons within the CNS. Neurotrophins alone have been shown to readily induce regeneration of sensory axons after dorsal root lesions, however if neurotrophin gradients are expressed within the spinal cord these axons fail to terminate within appropriate target regions. Under such conditions, addition of a "stop" signal reduces growth into deeper dorsal laminae to support more specific targeting. Such neurotrophin gradients alone lose their effectiveness when lesions are within the spinal cord, requiring a combined treatment regime. Construction of pathways using combined treatments support good regeneration when they increase the intrinsic growth properties of neurons, provide a bridge across the lesion site, and supply a growth supportive substrate to induce axon growth out of the bridge and back into the host. Neurotrophin gradients distal to the bridge greatly enhance axon outgrowth. In disorders where neuronal circuits are lost, construction of preformed growth supportive pathways sustain long distance axon growth from a neuronal transplant to distal target locations.

Synergistic effects of NGF, CNTF and GDNF on functional recovery following sciatic nerve injury in rats

PURPOSE

To investigate the synergistic effects of nerve growth factor (NGF), ciliary neurotrophic factor (CNTF) and glia cell line-derived neurotrophic factor (GDNF) on survival and growth of sensory neurons and motoneurons, as well as on the functional recovery following sciatic nerve injury in rats.

METHODS

Experimental rats and neurons were randomized into 8 groups: NGF group, CNTF group, GDNF group, NGF+CNTF group, CNTF+GDNF group, NGF+GDNF group, NGF+CNTF+GDNF group and control group. Each group received local intramuscular injection of indicated NTFs according to the treatment protocol. The sciatic nerve function index (SFI), nerve conduction velocity and wet weight recovery rate of gastrocnemius muscle were tested to evaluate the functional recovery in vivo. A 2 (presence or absence of NGF) x 2 (presence or absence of CNTF) x 2 (presence or absence of GDNF) analysis of variance (ANOVA) was used to examine the main effects and interactions among NGF, CNTF and GDNF, and one-way ANOVA was calculated for multiple comparison.

RESULTS

NGF and GDNF acted significantly on the survival of sensory neuron and motoneuron, respectively. CNTF was a dominant factor promoting cell body development, and GDNF had the most powerful effect on neurite outgrowth and elongation of sensory neurons and motoneurons. Combined administration of the three factors resulted in optimal functional recovery following sciatic nerve injury in rats.

CONCLUSIONS

It is demonstrated that differential and complementary biological effects of various neurotrophic factors contribute to synergistic promotion of nervous function recovery.

Oligodendrocyte-spinal cord explant co-culture: an in vitro model for the study of myelination

The in vitro models developed to investigate the growth and myelination of axons, such as dorsal root ganglion (DRG)-Schwann cell co-culture, DRG-oligodendrocyte co-culture and central nervous system (CNS) neuron-oligodendrocyte co-culture, have provided an effective way to reveal the mechanisms that underlie the interaction between neurons and myelin-forming cells. In order to better understand the complex process of myelination during CNS development and spinal cord repair, we established a rat spinal cord neuron-oligodendrocyte co-culture model. In this co-culture system, the spinal cord explants were used as the source of neurons, and the oligodendrocytes were induced from GFP-oligodendrocyte precursor cells (GFP-OPCs). The results showed that the GFP-oligodendrocytes that differentiated from GFP-OPCs in co-culture attached to the neurites growing out from the spinal cord explants and formed myelin structures. As the oligodendrocytes expressed GFP, and the neuron somas remained in the explants, the interaction between oligodendrocytes and neurites in co-culture were observed clearly and dynamically without immunostaining.