Adenovirus Vector-Mediated In Vivo Gene Transfer of Brain-Derived Neurotrophic Factor (BDNF) Promotes Rubrospinal Axonal Regeneration and Functional Recovery after Complete Transection of the Adult Rat Spinal Cord

Trehalose-Carnosine Prevents the Effects of Spinal Cord Injury Through Regulating Acute Inflammation and Zinc(II) Ion Homeostasis

Spinal cord injury (SCI) leads to long-term and permanent motor dysfunctions, and nervous system abnormalities. Injury to the spinal cord triggers a signaling cascade that results in activation of the inflammatory cascade, apoptosis, and Zn(II) ion homeostasis. Trehalose (Tre), a nonreducing disaccharide, and L-carnosine (Car), (β-alanyl-L-histidine), one of the endogenous histidine dipeptides have been recognized to suppress early inflammatory effects, oxidative stress and to possess neuroprotective effects. We report on the effects of the conjugation of Tre with Car (Tre-car) in reducing inflammation in in vitro and in vivo models. The in vitro study was performed using rat pheochromocytoma cells (PC12 cell line). After 24 h, Tre-car, Car, Tre, and Tre + Car mixture treatments, cells were collected and used to investigate Zn²⁺ homeostasis. The in vivo model of SCI was induced by extradural compression of the spinal cord at the T6-T8 levels. After treatments with Tre, Car and Tre-Car conjugate 1 and 6 h after SCI, spinal cord tissue was collected for analysis. In vitro results demonstrated the ionophore effect and chelating features of L-carnosine and its conjugate. In vivo, the Tre-car conjugate treatment counteracted the activation of the early inflammatory cascade, oxidative stress and apoptosis after SCI. The Tre-car conjugate stimulated neurotrophic factors release, and influenced Zn²⁺ homeostasis. We demonstrated that Tre-car, Tre and Car treatments improved tissue recovery after SCI. Tre-car decreased proinflammatory, oxidative stress mediators release, upregulated neurotrophic factors and restored Zn²⁺ homeostasis, suggesting that Tre-car may represent a promising therapeutic agent for counteracting the consequences of SCI.

Application of a New Gene-Cell Construct Based on the Olfactory Mucosa Escheating Cells Transduced with an Adenoviral Vector Encoding Mature BDNF in the Therapy of Spinal Cord Cysts

A gene-cell construct based on rat olfactory mucosa ensheathing cells transduced with an adenoviral vector encoding a mature form of brain neurotrophic factor (mBDNF) was transplanted into post-traumatic cysts of rat spinal cord. Transplantation of the gene-cell construct improved motor activity of the hind limbs and reduced the size of cysts in some animals. However, comparison of the effects of transduced and non-transduced ensheathing cells revealed no significant differences. In parallel in vitro experiments, a decrease in the proliferation of transduced cells compared to non-transduced cells was observed. It is likely that mBDNF reduces proliferation of transduced cells, which can affect their efficiency. The therapeutic efficacy of the new gene-cell construct is most likely provided by the cellular component.

Recombinant Adenoviruses for Delivery of Therapeutics Following Spinal Cord Injury

The regeneration of nerve tissue after spinal cord injury is a complex and poorly understood process. Medication and surgery are not very effective treatments for patients with spinal cord injuries. Gene therapy is a popular approach for the treatment of such patients. The delivery of therapeutic genes is carried out in a variety of ways, such as direct injection of therapeutic vectors at the site of injury, retrograde delivery of vectors, and ex vivo therapy using various cells. Recombinant adenoviruses are often used as vectors for gene transfer. This review discusses the advantages, limitations and prospects of adenovectors in spinal cord injury therapy.

Study of the Therapeutic Efficiency of Transduced Olfactory Ensheathing Cells in Spinal Cord Cysts

Posttraumatic spinal cord cysts are difficult to treat with medication and surgery. Gene-cell therapy is a promising area of treatment for such patients. However, optimal gene-cell construct for this therapy has not been developed. We investigated the therapeutic efficiency of human olfactory ensheathing cells (OECs) transduced by adenoviral vector encoding the mature form of brain-derived neurotrophic factor (mBDNF) in spinal cord cysts. The adenoviral vectors Ad5/35-CAG-mBDNF and Ad5/35-CAG-Fluc were constructed. Spinal cysts were modeled in female Wistar rats. We selected animals at the early and intermediate stages of recovery with scores to 13 according to the Basso, Beattie and Bresnahan (BBB) scale. The efficiency of therapy was evaluated by BBB tests. No cytotoxicity was detected using the Resazurin/AlamarBlue assay for both vectors at multiplicity of infection (MOIs) of 1, 5, and 25. There was an increase in the proliferation of cells treated with Ad5/35-CAG-mBDNF at MOIs of 5 and 25. The hind limb mobility after the transplantation of Ad5/35-CAG-mBDNF- and Ad5/35-CAG-Fluc-transduced human OECs and nontransduced OECs had approximately the same tendency to improve. Cyst reduction was observed with the transplantation of all the samples. Although Ad5/35-CAG-mBDNF-transduced OECs had high BDNF expression levels in vitro, these cells lacked positive effect in vivo because they did not exhibit significant effect concerning functional test when comparing the groups that received the same numbers of OECs. The therapeutic efficiency of transduced OECs appears to be due to the cell component. The autological and tissue-specific human OECs are promising for the personalized cell therapy. It is extremely important to test new gene-cell constructs based on these cells for further clinical use.

Neurotrophin gene therapy to promote survival of spiral ganglion neurons after deafness

Hearing impairment is a major health and economic concern worldwide. Currently, the cochlear implant (CI) is the standard of care for remediation of severe to profound hearing loss, and in general, contemporary CIs are highly successful. But there is great variability in outcomes among individuals, especially in children, with many CI users deriving much less or even marginal benefit. Much of this variability is related to differences in auditory nerve survival, and there has been substantial interest in recent years in exploring potential therapies to improve survival of the cochlear spiral ganglion neurons (SGN) after deafness. Preclinical studies using osmotic pumps and other approaches in deafened animal models to deliver neurotrophic factors (NTs) directly to the cochlea have shown promising results, especially with Brain-Derived Neurotrophic Factor (BDNF). More recent studies have focused on the use of NT gene therapy to force expression of NTs by target cells within the cochlea. This could provide the means for a one-time treatment to promote long-term NT expression and improve neural survival after deafness. This review summarizes the evidence for the efficacy of exogenous NTs in preventing SGN degeneration after hearing loss and reviews the animal research to date suggesting that NT gene therapy can elicit long-term NT expression in the cochlea, resulting in significantly improved SGN and radial nerve fiber survival after deafness. In addition, we discuss NT gene therapy in other non-auditory applications and consider some of the remaining issues with regard to selecting optimal vectors, timing of treatment, and place/method of delivery, etc. that must be resolved prior to considering clinical application.

The adeno-associated virus rh10 vector is an effective gene transfer system for chronic spinal cord injury

Treatment options for chronic spinal cord injury (SCI) remain limited due to unfavourable changes in the microenvironment. Gene therapy can overcome these barriers through continuous delivery of therapeutic gene products to the target tissue. In particular, adeno-associated virus (AAV) vectors are potential candidates for use in chronic SCI, considering their safety and stable gene expression in vivo. Given that different AAV serotypes display different cellular tropisms, it is extremely important to select an optimal serotype for establishing a gene transfer system during the chronic phase of SCI. Therefore, we generated multiple AAV serotypes expressing ffLuc-cp156, a fusion protein of firefly luciferase and Venus, a variant of yellow fluorescent protein with fast and efficient maturation, as a reporter, and we performed intraparenchymal injection in a chronic SCI mouse model. Among the various serotypes tested, AAVrh10 displayed the highest photon count on bioluminescence imaging. Immunohistological analysis revealed that AAVrh10 showed favourable tropism for neurons, astrocytes, and oligodendrocytes. Additionally, with AAVrh10, the area expressing Venus was larger in the injury epicentre and extended to the surrounding tissue. Furthermore, the fluorescence intensity was significantly higher with AAVrh10 than with the other vectors. These results indicate that AAVrh10 may be an appropriate serotype for gene delivery to the chronically injured spinal cord. This promising tool may be applied for research and development related to the treatment of chronic SCI.

Local BDNF Delivery to the Injured Cervical Spinal Cord using an Engineered Hydrogel Enhances Diaphragmatic Respiratory Function

We developed an innovative biomaterial-based approach to repair the critical neural circuitry that controls diaphragm activation by locally delivering brain-derived neurotrophic factor (BDNF) to injured cervical spinal cord. BDNF can be used to restore respiratory function via a number of potential repair mechanisms; however, widespread BDNF biodistribution resulting from delivery methods such as systemic injection or lumbar puncture can lead to inefficient drug delivery and adverse side effects. As a viable alternative, we developed a novel hydrogel-based system loaded with polysaccharide-BDNF particles self-assembled by electrostatic interactions that can be safely implanted in the intrathecal space for achieving local BDNF delivery with controlled dosing and duration. Implantation of BDNF hydrogel after C4/C5 contusion-type spinal cord injury (SCI) in female rats robustly preserved diaphragm function, as assessed by in vivo recordings of compound muscle action potential and electromyography amplitudes. However, BDNF hydrogel did not decrease lesion size or degeneration of cervical motor neuron soma, suggesting that its therapeutic mechanism of action was not neuroprotection within spinal cord. Interestingly, BDNF hydrogel significantly preserved diaphragm innervation by phrenic motor neurons (PhMNs), as assessed by detailed neuromuscular junction morphological analysis and retrograde PhMN labeling from diaphragm using cholera toxin B. Furthermore, BDNF hydrogel enhanced the serotonergic axon innervation of PhMNs that plays an important role in modulating PhMN excitability. Our findings demonstrate that local BDNF hydrogel delivery is a robustly effective and safe strategy to restore diaphragm function after SCI. In addition, we demonstrate novel therapeutic mechanisms by which BDNF can repair respiratory neural circuitry.SIGNIFICANCE STATEMENT Respiratory compromise is a leading cause of morbidity and mortality following traumatic spinal cord injury (SCI). We used an innovative biomaterial-based drug delivery system in the form of a hydrogel that can be safely injected into the intrathecal space for achieving local delivery of brain-derived neurotrophic factor (BDNF) with controlled dosing and duration, while avoiding side effects associated with other delivery methods. In a clinically relevant rat model of cervical contusion-type SCI, BDNF hydrogel robustly and persistently improved diaphragmatic respiratory function by enhancing phrenic motor neuron (PhMN) innervation of the diaphragm neuromuscular junction and by increasing serotonergic innervation of PhMNs in ventral horn of the cervical spinal cord. These exciting findings demonstrate that local BDNF hydrogel delivery is a safe and robustly effective strategy to maintain respiratory function after cervical SCI.

Adenovirus vector-mediated ex vivo gene transfer of brain-derived neurotrophic factor (BDNF) tohuman umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) promotescrush-injured rat sciatic nerve regeneration

This study was designed toinvestigate the efficacy of adenovirus vector-mediated brain-derived neurotrophic factor (BDNF) ex vivo gene transfer to human umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) in a rat sciatic nerve crush injury model. BDNF protein and mRNA expression after infection was checked through an enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qRT-PCR). Male Sprague-Dawley rats (200-250g, 6 weeks old) were distributed into threegroups (n=20 each): the control group, UCB-MSC group, and BDNF-adenovirus infected UCB-MSC (BDNF-Ad+UCB-MSC) group. UCB-MSCs (1×10⁶cells/10μl/rat) or BDNF-Ad+UCB-MSCs (1×10⁶cells/10μl/rat)were transplantedinto the rats at the crush site immediately after sciatic nerve injury. Cell tracking was done with PKH26-labeled UCB-MSCs and BDNF-Ad+UCB-MSCs (1×10⁶cells/10μl/rat). The rats were monitored for 4 weeks post-surgery. Results showed that expression of BDNF at both the protein and mRNA levels was higher inthe BDNF-Ad+UCB-MSC group compared to theUCB-MSC group in vitro.Moreover, BDNF mRNA expression was higher in both UCB-MSC group and BDNF-Ad+ UCB-MSC group compared tothe control group, and BDNF mRNA expression in theBDNF-Ad+UCB-MSC group was higher than inboth other groups 5days after surgeryin vivo. Labeled neurons in the dorsal root ganglia (DRG), axon counts, axon density, and sciatic function index were significantly increased in the UCB-MSC and BDNF-Ad+ UCB-MSCgroupscompared to the controlgroup four weeksaftercell transplantation. Importantly,the BDNF-Ad+UCB-MSCgroup exhibited more peripheral nerve regeneration than the other two groups.Our results indicate thatboth UCB-MSCs and BDNF-Ad+UCB-MSCscan improve rat sciatic nerve regeneration, with BDNF-Ad+UCB-MSCsshowing a greater effectthan UCB-MSCs.

Neurotrophic Factors Used to Treat Spinal Cord Injury

The application of neurotrophic factors as a therapy to improve morphological and behavioral outcomes after experimental spinal cord injury (SCI) has been the focus of many studies. These studies vary markedly in the type of neurotrophic factor that is delivered, the mode of administration, and the location, timing, and duration of the treatment. Generally, the majority of studies have had significant success if neurotrophic factors are applied in or close to the lesion site during the acute or the subacute phase after SCI. Comparatively fewer studies have administered neurotrophic factors in order to directly target the somata of injured neurons. The mode of delivery varies between acute injection of recombinant proteins, subacute or chronic delivery using a variety of strategies including osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells, or precursor/stem cells. In this brief review, we summarize the state of play of many of the therapies using these factors, most of which have been undertaken in rodent models of SCI.

Targeting Motor End Plates for Delivery of Adenoviruses: An Approach to Maximize Uptake and Transduction of Spinal Cord Motor Neurons

Gene therapy can take advantage of the skeletal muscles/motor neurons anatomical relationship to restrict gene expression to the spinal cord ventral horn. Furthermore, recombinant adenoviruses are attractive viral-vectors as they permit spatial and temporal modulation of transgene expression. In the literature, however, several inconsistencies exist with regard to the intramuscular delivery parameters of adenoviruses. The present study is an evaluation of the optimal injection sites on skeletal muscle, time course of expression and mice’s age for maximum transgene expression in motor neurons. Targeting motor end plates yielded a 2.5-fold increase in the number of transduced motor neurons compared to injections performed away from this region. Peak adenoviral transgene expression in motor neurons was detected after seven days. Further, greater numbers of transduced motor neurons were found in juvenile (3–7 week old) mice as compared with adults (8+ weeks old). Adenoviral injections produced robust transgene expression in motor neurons and skeletal myofibres. In addition, dendrites of transduced motor neurons were shown to extend well into the white matter where the descending motor pathways are located. These results also provide evidence that intramuscular delivery of adenovirus can be a suitable gene therapy approach to treat spinal cord injury.

Chitosan scaffolds induce human dental pulp stem cells to neural differentiation: potential roles for spinal cord injury therapy

Cell-based transplantation strategies hold great potential for spinal cord injury (SCI) repair. Chitosan scaffolds have therapeutic benefits for spinal cord regeneration. Human dental pulp stem cells (DPSCs) are abundant available stem cells with low immunological incompatibility and can be considered for cell replacement therapy. The purpose of this study is to investigate the role of chitosan scaffolds in the neural differentiation of DPSCs in vitro and to assess the supportive effects of chitosan scaffolds in an animal model of SCI. DPSCs were incubated with chitosan scaffolds. Cell viability and the secretion of neurotrophic factors were analyzed. DPSCs incubated with chitosan scaffolds were treated with neural differentiation medium for 14 days and then neural genes and protein markers were analyzed by Western blot and reverse transcription plus the polymerase chain reaction. Our study revealed a higher cell viability and neural differentiation in the DPSC/chitosan-scaffold group. Compared with the control group, the levels of BDNF, GDNF, b-NGF, and NT-3 were significantly increased in the DPSC/chitosan-scaffold group. The Wnt/β-catenin signaling pathway played a key role in the neural differentiation of DPSCs combined with chitosan scaffolds. Transplantation of DPSCs together with chitosan scaffolds into an SCI rat model resulted in the marked recovery of hind limb locomotor functions. Thus, chitosan scaffolds were non-cytotoxic and provided a conducive and favorable microenvironment for the survival and neural differentiation of DPSCs. Transplantation of DPSCs might therefore be a suitable candidate for treating SCI and other neuronal degenerative diseases.

Knockdown of Nogo gene by short hairpin RNA interference promotes functional recovery of spinal cord injury in a rat model

The specific myelin component Nogo protein is one of the major inhibitory molecules of spinal cord axonal outgrowth following spinal cord injury. The present study aimed to investigate the effects of silencing Nogo protein with shRNA interference on the promotion of functional recovery in a rat model with spinal cord hemisection. Nogo-A short hairpin RNAs (Nogo shRNAs) were constructed and transfected into rats with spinal cord hemisection by adenovirus-mediated transfection. Reverse transcription‑polymerase chain reaction and western blotting were performed to analyze the expression of Nogo-A and Growth Associated Protein 43 (GAP-43). In addition, Basso Beattie Bresnahan (BBB) scores were used to assess the functional recovery of rats following spinal cord injury. The results demonstrated that expression of the Nogo‑A gene was observed to be downregulated following transfection and GAP‑43 expression was observed to increase. The BBB scores were increased following treatment with Nogo shRNAs, indicating functional recovery of the injured nerves. Thus, Nogo-A shRNA interference can knockdown Nogo gene expression and upregulate GAP-43 to promote the functional recovery of spinal cord injury in rats. This finding may advance progress toward assisting the regeneration of injured neurons through the use of Nogo-A shRNA.

A Proposal for a Rat Model of Spinal Cord Injury Featuring the Rubrospinal Tract and its Contributions to Locomotion and Skilled Hand Movement

Spinal cord injury and repair is a dynamic field of research. The development of reliable animal models of traumatic spinal cord injury has been invaluable in providing a wealth of information regarding the pathological consequences and recovery potential of this condition. A number of injury models have been instrumental in the elaboration and the validation of therapeutic interventions aimed at reversing this once thought permanent condition. In general, the study of spinal cord injury and repair is made difficult by both its anatomical complexity and the complexity of the behavior it mediates. In this perspective paper, we suggest a new model for spinal cord investigation that simplifies problems related to both the functional and anatomical complexity of the spinal cord. We begin by reviewing and contrasting some of the most common animal models used for investigating spinal cord dysfunction. We then consider two widely used models of spinal deficit-recovery, one involving the corticospinal tracts (CTS) and the other the rubrospinal tract (RST). We argue that the simplicity of the function of the RST makes it a useful model for studying the cord and its functional repair. We also reflect on two obstacles that have hindered progress in the pre-clinical field, delaying translation to the clinical setup. The first is recovery of function without reconnection of the transected descending fibers and the second is the use of behavioral paradigms that are not under the control of the descending fiber pathway under scrutiny.

7,8-dihydroxyflavone, a small molecular TrkB agonist, is useful for treating various BDNF-implicated human disorders

Brain-derived neurotrophic factor (BDNF) regulates a variety of biological processes predominantly via binding to the transmembrane receptor tyrosine kinase TrkB. It is a potential therapeutic target in numerous neurological, mental and metabolic disorders. However, the lack of efficient means to deliver BDNF into the body imposes an insurmountable hurdle to its clinical application. To address this challenge, we initiated a cell-based drug screening to search for small molecules that act as the TrkB agonist. 7,8-Dihydroxyflavone (7,8-DHF) is our first reported small molecular TrkB agonist, which has now been extensively validated in various biochemical and cellular systems. Though binding to the extracellular domain of TrkB, 7,8-DHF triggers TrkB dimerization to induce the downstream signaling. Notably, 7,8-DHF is orally bioactive that can penetrate the brain blood barrier (BBB) to exert its neurotrophic activities in the central nervous system. Numerous reports suggest 7,8-DHF processes promising therapeutic efficacy in various animal disease models that are related to deficient BDNF signaling. In this review, we summarize our current knowledge on the binding activity and specificity, structure-activity relationship, pharmacokinetic and metabolism, and the pre-clinical efficacy of 7,8-DHF against some human diseases.

Localized and sustained release of brain-derived neurotrophic factor from injectable hydrogel/microparticle composites fosters spinal learning after spinal cord injury

Injectable hydrogel allows for sustained delivery of growth factor resulting in spinal mediated learning after injury.

Low intensity repetitive transcranial magnetic stimulation does not induce cell survival or regeneration in a mouse optic nerve crush model

Low intensity repetitive Transcranial Magnetic Stimulation (LI-rTMS), a non-invasive form of brain stimulation, has been shown to induce structural and functional brain plasticity, including short distance axonal sprouting. However, the potential for LI-rTMS to promote axonal regeneration following neurotrauma has not been investigated. This study examined the effect of LI-rTMS on retinal ganglion cell (RGC) survival, axon regeneration and levels of BDNF in an optic nerve crush neurotrauma model. Adult C57Bl/6J mice received a unilateral intraorbital optic nerve crush. Mice received 10 minutes of sham (handling control without stimulation) (n=6) or LI-rTMS (n = 8) daily stimulation for 14 days to the operated eye. Immunohistochemistry was used to assess RGC survival (β-3 Tubulin) and axon regeneration across the injury (GAP43). Additionally, BDNF expression was quantified in a separate cohort by ELISA in the retina and optic nerve of injured (optic nerve crush) (sham n = 5, LI-rTMS n = 5) and non-injured mice (sham n = 5, LI-rTMS n = 5) that received daily stimulation as above for 7 days. Following 14 days of LI-rTMS there was no significant difference in mean RGC survival between sham and treated animals (p>0.05). Also, neither sham nor LI-rTMS animals showed GAP43 positive labelling in the optic nerve, indicating that regeneration did not occur. At 1 week, there was no significant difference in BDNF levels in the retina or optic nerves between sham and LI-rTMS in injured or non-injured mice (p>0.05). Although LI-rTMS has been shown to induce structural and molecular plasticity in the visual system and cerebellum, our results suggest LI-rTMS does not induce neuroprotection or regeneration following a complete optic nerve crush. These results help define the therapeutic capacity and limitations of LI-rTMS in the treatment of neurotrauma.

Localized delivery of brain-derived neurotrophic factor-expressing mesenchymal stem cells enhances functional recovery following cervical spinal cord injury

Neurotrophins, such as brain-derived neurotrophic factor (BDNF), are important in modulating neuroplasticity and promoting recovery after spinal cord injury. Intrathecal delivery of BDNF enhances functional recovery following unilateral spinal cord hemisection (SH) at C2, a well-established model of incomplete cervical spinal cord injury. We hypothesized that localized delivery of BDNF-expressing mesenchymal stem cells (BDNF-MSCs) would promote functional recovery of rhythmic diaphragm activity after SH. In adult rats, bilateral diaphragm electromyographic (EMG) activity was chronically monitored to determine evidence of complete SH at 3 days post-injury, and recovery of rhythmic ipsilateral diaphragm EMG activity over time post-SH. Wild-type, bone marrow-derived MSCs (WT-MSCs) or BDNF-MSCs (2×10(5) cells) were injected intraspinally at C2 at the time of injury. At 14 days post-SH, green fluorescent protein (GFP) immunoreactivity confirmed MSCs presence in the cervical spinal cord. Functional recovery in SH animals injected with WT-MSCs was not different from untreated SH controls (n=10; overall, 20% at 7 days and 30% at 14 days). In contrast, functional recovery was observed in 29% and 100% of SH animals injected with BDNF-MSCs at 7 days and 14 days post-SH, respectively (n=7). In BDNF-MSCs treated SH animals at 14 days, root-mean-squared EMG amplitude was 63±16% of the pre-SH value compared with 12±9% in the control/WT-MSCs group. We conclude that localized delivery of BDNF-expressing MSCs enhances functional recovery of diaphragm muscle activity following cervical spinal cord injury. MSCs can be used to facilitate localized delivery of trophic factors such as BDNF in order to promote neuroplasticity following spinal cord injury.

Neurotrophic factors for spinal cord repair: Which, where, how and when to apply, and for what period of time?

A variety of neurotrophic factors have been used in attempts to improve morphological and behavioural outcomes after experimental spinal cord injury (SCI). Here we review many of these factors, their cellular targets, and their therapeutic impact on spinal cord repair in different, primarily rodent, models of SCI. A majority of studies report favourable outcomes but results are by no means consistent, thus a major aim of this review is to consider how best to apply neurotrophic factors after SCI to optimize their therapeutic potential. In addition to which factors are chosen, many variables need be considered when delivering trophic support, including where and when to apply a given factor or factors, how such factors are administered, at what dose, and for how long. Overall, the majority of studies have applied neurotrophic support in or close to the spinal cord lesion site, in the acute or sub-acute phase (0-14 days post-injury). Far fewer chronic SCI studies have been undertaken. In addition, comparatively fewer studies have administered neurotrophic factors directly to the cell bodies of injured neurons; yet in other instructive rodent models of CNS injury, for example optic nerve crush or transection, therapies are targeted directly at the injured neurons themselves, the retinal ganglion cells. The mode of delivery of neurotrophic factors is also an important variable, whether delivered by acute injection of recombinant proteins, sub-acute or chronic delivery using osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells or precursor/stem cells. Neurotrophic factors are often used in combination with cell or tissue grafts and/or other pharmacotherapeutic agents. Finally, the dose and time-course of delivery of trophic support should ideally be tailored to suit specific biological requirements, whether they relate to neuronal survival, axonal sparing/sprouting, or the long-distance regeneration of axons ending in a different mode of growth associated with terminal arborization and renewed synaptogenesis. This article is part of a Special Issue entitled SI: Spinal cord injury.

Neurotrophin strategies for neuroprotection: are they sufficient?

As people are living longer, the prevalance of neurodegenerative diseases continues to rise resulting in huge socio-economic consequences. Despite major advancements in studying the pathophysiology of these diseases and a large number of clinical trials currently there is no effective treatment for these illnesses. All neuroprotective strategies have either failed or have shown only a minimal effect. There has been a major shift in recent years exploring the potential of neuroregenerative approaches. While the concept of using neurotropins for therapeutic purposes has been in existence for many years, new modes of delivery and expression of this family of molecules makes this approach now feasilble. Further neurotropin mimetics and receptor agonists are also being developed. The use of small molecules to induce the expression of neurotropins including repurposing of FDA approved drugs for this approach is another strategy being pursued. In the review we examine these new developments and discuss the potential for such approaches in the context of the pathophysiology of neurodegenerative diseases.

TrkB agonist antibody pretreatment enhances neuronal survival and long-term sensory motor function following hypoxic ischemic injury in neonatal rats

Perinatal hypoxic ischemia (H-I) causes brain damage and long-term neurological impairments, leading to motor dysfunctions and cerebral palsy. Many studies have demonstrated that the TrkB-ERK1/2 signaling pathway plays a key role in mediating the protective effect of brain-derived neurotrophic factor (BDNF) following perinatal H-I brain injury in experimental animals. In the present study, we explored the neuroprotective effects of the TrkB-specific agonist monoclonal antibody 29D7 on H-I brain injury in neonatal rats. First, we found that intracerebroventricular (icv) administration of 29D7 in normal P7 rats markedly increased the levels of phosphorylated ERK1/2 and phosphorylated AKT in neurons up to 24 h. Second, P7 rats received icv administration of 29D7 and subjected to H-I injury induced by unilateral carotid artery ligation and exposure to hypoxia (8% oxygen). We found that 29D7, to a similar extent to BDNF, significantly inhibited activation of caspase-3, a biochemical hallmark of apoptosis, following H-I injury. Third, we found that this 29D7-mediated neuroprotective action persisted at least up to 5 weeks post-H-I injury as assessed by brain tissue loss, implicating long-term neurotrophic effects rather than an acute delay of cell death. Moreover, the long-term neuroprotective effect of 29D7 was tightly correlated with sensorimotor functional recovery as assessed by a tape-removal test, while 29D7 did not significantly improve rotarod performance. Taken together, these findings demonstrate that pretreatment with the TrkB-selective agonist 29D7 significantly increases neuronal survival and behavioral recovery following neonatal hypoxic-ischemic brain injury.

Tissue engineering is a promising method for the repair of spinal cord injuries (Review)

Spinal cord injury (SCI) may lead to a devastating and permanent loss of neurological function, which may place a great economic burden on the family of the patient and society. Methods for reducing the death of neuronal cells, inhibiting immune and inflammatory reactions, and promoting the growth of axons in order to build up synapses with the target cells are the focus of current research. Target cells are located in the damaged spinal cord which create a connect with the scaffold. As tissue engineering technology is developed for use in a variety of different areas, particularly the biomedical field, a clear understanding of the mechanisms of tissue engineering is important. This review establishes how this technology may be used in basic experiments with regard to SCI and considers its potential future clinical use.

Newly developed TGF-β2 knock down transgenic mouse lines express TGF-β2 differently and its distribution in multiple tissues varies

Background

Transforming growth factor-betas (TGF-βs), including beta2 (TGF-β2), constitute a superfamily of multifunctional cytokines with important implications in morphogenesis, cell differentiation and tissue remodeling. TGF-β2 is thought to play important roles in multiple developmental processes and neuron survival. However, before we carried out these investigations, a TGF-β2 gene down-regulated transgenic animal model was needed. In the present study, expressional silencing TGF-β2 was achieved by select predesigning interference short hairpin RNAs (shRNAs) targeting mouse TGF-β2 genes.

Results

Four homozygous transgenic offspring were generated by genetic manipulation and the protein expressions of TGF-β2 were detected in different tissues of these mice. The transgenic mice were designated as Founder 66, Founder 16, Founder 53 and Founder 41. The rates of TGF-β2 down-expression in different transgenic mice were evaluated. The present study showed that different TGF-β2 expressions were detected in multiple tissues and protein levels of TGF-β2 decreased at different rates relative to that of wild type mice. The expressions of TGF-β2 proteins in transgenic mice (Founder 66) reduced most by 52%.

Conclusions

The present study generated transgenic mice with TGF-β2 down-regulated, which established mice model for systemic exploring the possible roles of TGF-β2 in vivo in different pathology conditions.

Targeted delivery of TrkB receptor to phrenic motoneurons enhances functional recovery of rhythmic phrenic activity after cervical spinal hemisection

Progressive recovery of rhythmic phrenic activity occurs over time after a spinal cord hemisection involving unilateral transection of anterolateral funiculi at C₂ (SH). Brain-derived neurotrophic factor (BDNF) acting through its full-length tropomyosin related kinase receptor subtype B (TrkB.FL) contributes to neuroplasticity after spinal cord injury, but the specific cellular substrates remain unclear. We hypothesized that selectively targeting increased TrkB.FL expression to phrenic motoneurons would be sufficient to enhance recovery of rhythmic phrenic activity after SH. Several adeno-associated virus (AAV) serotypes expressing GFP were screened to determine specificity for phrenic motoneuron transduction via intrapleural injection in adult rats. GFP expression was present in the cervical spinal cord 3 weeks after treatment with AAV serotypes 7, 8, and 9, but not with AAV2, 6, or rhesus-10. Overall, AAV7 produced the most consistent GFP expression in phrenic motoneurons. SH was performed 3 weeks after intrapleural injection of AAV7 expressing human TrkB.FL-FLAG or saline. Delivery of TrkB.FL-FLAG to phrenic motoneurons was confirmed by FLAG protein expression in the phrenic motor nucleus and human TrkB.FL mRNA expression in microdissected phrenic motoneurons. In all SH rats, absence of ipsilateral diaphragm EMG activity was confirmed at 3 days post-SH, verifying complete interruption of ipsilateral descending drive to phrenic motoneurons. At 14 days post-SH, all AAV7-TrkB.FL treated rats (n = 11) displayed recovery of ipsilateral diaphragm EMG activity compared to 3 out of 8 untreated SH rats (p<0.01). During eupnea, AAV7-TrkB.FL treated rats exhibited 73±7% of pre-SH root mean squared EMG vs. only 31±11% in untreated SH rats displaying recovery (p<0.01). This study provides direct evidence that increased TrkB.FL expression in phrenic motoneurons is sufficient to enhance recovery of ipsilateral rhythmic phrenic activity after SH, indicating that selectively targeting gene expression in spared motoneurons below the level of spinal cord injury may promote functional recovery.

Motoneuron BDNF/TrkB signaling enhances functional recovery after cervical spinal cord injury

A C2 cervical spinal cord hemisection (SH) interrupts descending inspiratory-related drive to phrenic motoneurons located between C3 and C5 in rats, paralyzing the ipsilateral hemidiaphragm muscle. There is gradual recovery of rhythmic diaphragm muscle activity ipsilateral to cervical spinal cord injury over time, consistent with neuroplasticity and strengthening of spared, contralateral descending premotor input to phrenic motoneurons. Brain-derived neurotrophic factor (BDNF) signaling through the tropomyosin related kinase receptor subtype B (TrkB) plays an important role in neuroplasticity following spinal cord injury. We hypothesized that 1) increasing BDNF/TrkB signaling at the level of the phrenic motoneuron pool by intrathecal BDNF delivery enhances functional recovery of rhythmic diaphragm activity after SH, and 2) inhibiting BDNF/TrkB signaling by quenching endogenous neurotrophins with the soluble fusion protein TrkB-Fc or by knocking down TrkB receptor expression in phrenic motoneurons using intrapleurally-delivered siRNA impairs functional recovery after SH. Diaphragm EMG electrodes were implanted bilaterally to verify complete hemisection at the time of SH and 3days post-SH. After SH surgery in adult rats, an intrathecal catheter was placed at C4 to chronically infuse BDNF or TrkB-Fc using an implanted mini-osmotic pump. At 14days post-SH, all intrathecal BDNF treated rats (n=9) displayed recovery of ipsilateral hemidiaphragm EMG activity, compared to 3 out of 8 untreated SH rats (p<0.01). During eupnea, BDNF treated rats exhibited 76±17% of pre-SH root mean squared EMG vs. only 5±3% in untreated SH rats (p<0.01). In contrast, quenching endogenous BDNF with intrathecal TrkB-Fc treatment completely prevented functional recovery up to 14days post-SH (n=7). Immunoreactivity of the transcription factor cAMP response element-binding protein (CREB), a downstream effector of TrkB signaling, increased in phrenic motoneurons following BDNF treatment (n=6) compared to artificial cerebrospinal fluid treatment (n=6; p<0.001). Intrapleural injections of non-sense or TrkB siRNA were administered after SH to specifically target phrenic motoneurons. At 14days post-SH, none out of 9 TrkB siRNA treated rats displayed functional recovery compared to 5 out of 9 non-sense siRNA treated rats. These results indicate that BDNF/TrkB signaling in phrenic motoneuron pool plays a critical role in functional recovery after cervical spinal cord injury.

From molecular to nanotechnology strategies for delivery of neurotrophins: emphasis on brain-derived neurotrophic factor (BDNF)

Neurodegenerative diseases represent a major public health problem, but beneficial clinical treatment with neurotrophic factors has not been established yet. The therapeutic use of neurotrophins has been restrained by their instability and rapid degradation in biological medium. A variety of strategies has been proposed for the administration of these leading therapeutic candidates, which are essential for the development, survival and function of human neurons. In this review, we describe the existing approaches for delivery of brain-derived neurotrophic factor (BDNF), which is the most abundant neurotrophin in the mammalian central nervous system (CNS). Biomimetic peptides of BDNF have emerged as a promising therapy against neurodegenerative disorders. Polymer-based carriers have provided sustained neurotrophin delivery, whereas lipid-based particles have contributed also to potentiation of the BDNF action. Nanotechnology offers new possibilities for the design of vehicles for neuroprotection and neuroregeneration. Recent developments in nanoscale carriers for encapsulation and transport of BDNF are highlighted.

BDNF: the career of a multifaceted neurotrophin in spinal cord injury

Brain-derived neurotrophic factor (BDNF) has been identified as a potent promoter of neurite growth, a finding that has led to an ongoing exploration of this neurotrophin as a potential treatment for spinal cord injury. BDNF's many effects in the nervous system make it an excellent candidate for neuroprotective strategies as well as for promoting axonal regeneration, plasticity and re-myelination. In addition, neuronal activity and physical exercise can modulate the expression of BDNF, suggesting that non-invasive means to increase BDNF levels might exist. Nonetheless, depending on the location, amount and duration of BDNF delivery, this potent neurotrophin can also have adverse effects, such as modulation of nociceptive pathways or contribution to spasticity. Taken together, the benefits and possible risks require careful assessment when considering this multifaceted neurotrophin as a treatment option for spinal cord injury.

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.

Site-specific gene transfer into the rat spinal cord by photomechanical waves

Nonviral, site-specific gene delivery to deep tissue is required for gene therapy of a spinal cord injury. However, an efficient method satisfying these requirements has not been established. This study demonstrates efficient and targeted gene transfer into the spinal cord by using photomechanical waves (PMWs), which were generated by irradiating a black laser absorbing rubber with 532-nm nanosecond Nd:YAG laser pulses. After a solution of plasmid DNA coding for enhanced green fluorescent protein (EGFP) or luciferase was intraparenchymally injected into the spinal cord, PMWs were applied to the target site. In the PMW application group, we observed significant EGFP gene expression in the white matter and remarkably high luciferase activity only in the spinal cord segment exposed to the PMWs. We also assessed hind limb movements 24 h after the application of PMWs based on the Basso-Beattie-Bresnahan (BBB) score to evaluate the noninvasiveness of this method. Locomotor evaluation showed no significant decrease in BBB score under optimum laser irradiation conditions. These findings demonstrated that exogenous genes can be efficiently and site-selectively delivered into the spinal cord by applying PMWs without significant locomotive damage.

Impaired arpeggio movement in skilled reaching by rubrospinal tract lesions in the rat: a behavioral/anatomical fractionation

Spinal cord injury damaging the rubrospinal tract (RST) interferes with skilled forelimb movement, but identification of the precise role of the RST in this behavior is impeded by the difficulty of surgically isolating the RST from other pathways running within the lateral funiculus (LF). The present study used a skilled reaching task and a behavioral/anatomical dissection method to identify the contribution of the RST to skilled forelimb movement. Rats were trained on the skilled reaching task and subjected to lesions of the LF. Based on histological evaluation, the animals were assigned to large, medium, or small LF lesion size groups. End point and arm/hand/digit movements were subsequently identified for each group. Success was impaired in all groups, but the impairment was not related to lesion size. Frame-by-frame qualitative analysis of the video recordings revealed that large LF lesions abolished the elements of digits close, digits open, arpeggio, grasp, supination 2, and release. Medium LF lesions interfered with a subset of the movement elements that were shown to be affected by the large LF lesions, namely arpeggio and grasp. Only the arpeggio movement was compromised after small LF lesions. The results show that not only does the LF contribute to skilled reaching, but because the RST was likely to have been damaged in all lesion groups, the RST is more involved in hand rotation than in digit use. The results are discussed in relation to the fiber tracts that are likely to be damaged in the different LF lesion groups.

Preferential and bidirectional labeling of the rubrospinal tract with adenovirus-GFP for monitoring normal and injured axons

The rodent rubrospinal tract (RST) has been studied extensively to investigate regeneration and remodeling of central nervous system (CNS) axons. Currently no retrograde tracers can specifically label rubrospinal axons and neurons (RSNs). The RST can be anterogradely labeled by injecting tracers into the red nucleus (RN), but accurately locating the RN is a technical challenge. Here we developed a recombinant adenovirus carrying a green fluorescent protein reporter gene (Adv-GFP) which can preferentially, intensely, and bi-directionally label the RST. When Adv-GFP was injected into the second lumbar spinal cord, the GFP was specifically transported throughout the entire RST, with peak labeling seen at 2 weeks post-injection. When Adv-GFP was injected directly into the RN, GFP was anterogradely transported throughout the RST. Following spinal cord injury (SCI), injection of Adv-GFP resulted in visualization of GFP in transected, spared, or sprouted RST axons bi-directionally. Thus Adv-GFP could be used as a novel tool for monitoring and evaluating strategies designed to maximize RST axonal regeneration and remodeling following SCI.

Deoxygedunin, a natural product with potent neurotrophic activity in mice

Gedunin, a family of natural products from the Indian neem tree, possess a variety of biological activities. Here we report the discovery of deoxygedunin, which activates the mouse TrkB receptor and its downstream signaling cascades. Deoxygedunin is orally available and activates TrkB in mouse brain in a BDNF-independent way. Strikingly, it prevents the degeneration of vestibular ganglion in BDNF −/− pups. Moreover, deoxygedunin robustly protects rat neurons from cell death in a TrkB-dependent manner. Further, administration of deoxygedunin into mice displays potent neuroprotective, anti-depressant and learning enhancement effects, all of which are mediated by the TrkB receptor. Hence, deoxygedunin imitates BDNF's biological activities through activating TrkB, providing a powerful therapeutic tool for treatment of various neurological diseases.

Functional recovery after the transplantation of neurally differentiated mesenchymal stem cells derived from bone marrow in a rat model of spinal cord injury

This study was designed to investigate functional recovery after the transplantation of mesenchymal stem cells (MSCs) or neurally differentiated MSCs (NMSCs) derived from bone marrow in a rat model of spinal cord injury (SCI). Sprague-Dawley rats were subjected to incomplete SCI using an NYU impactor to create a free drop contusion at the T9 level. The SCI rats were then classified into three groups; MSCs, NMSCs, and phosphate-buffered saline (PBS)-treated groups. The cells or PBS were administrated 1 week after SCI. Basso-Beattie-Bresnahan (BBB) locomotor rating scores were measured at 1-week intervals for 9 weeks. Somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) were also recorded 8 weeks after transplantation. While transplantation of MSCs led to a clear tendency of motor recovery, NMSC-treated rats had significantly improved BBB scores and showed significantly shortened initial latency, N1 latency, and P1 latency of the SSEPs compared to PBS controls. In addition, 5-bromo-2-deoxyuridine (BrdU)-prelabeled MSCs costained for BrdU and glial fibrillary acidic protein (GFAP) or myelin basic protein (MBP) were found rostrally and caudally 5 mm each from the epicenter of the necrotic cavity 4 weeks after transplantation. These results suggest that neurally differentiated cells might be an effective therapeutic source for functional recovery after SCI.

Role of neurotrophins in recovery of phrenic motor function following spinal cord injury

Many individuals who sustain a cervical spinal cord injury are unable to maintain adequate ventilation due to diaphragm muscle paralysis. These patients become dependent on mechanical ventilators and this situation is associated with ongoing problems with pulmonary clearance, infections, and lung injury leading to significant morbidity and reduced life expectancy. Therefore, functional recovery of rhythmic phrenic activity and the ability to generate expulsive forces would dramatically affect the quality of life of patients with cervical spinal cord injury. Neurotrophins are very promising in that they have been shown to play an important role in modulating functional neuroplasticity. Specifically, brain-derived neurotrophic factor (BDNF) acting via the tropomyosin-related kinase receptor type B (TrkB) has been implicated in neuroplasticity following spinal cord injury. Our central hypothesis is that functional recovery of rhythmic phrenic activity after cervical spinal cord injury is enhanced by an increase in BDNF/TrkB signaling in phrenic motoneurons, providing a novel therapeutic target for patients.

Plasmid releasing multiple channel bridges for transgene expression after spinal cord injury

The regeneration of tissues with complex architectures requires strategies that promote the appropriate cellular processes, and can direct their organization. Plasmid-loaded multiple channel bridges were engineered for spinal cord regeneration with the ability to support and direct cellular processes and promote gene transfer at the injury site. The bridges were manufactured with a gas foaming technique, and had multiple channels with controllable diameter and encapsulated plasmid. Initial studies investigating bridge implantation subcutaneously (SC) indicated transgene expression in vivo for 44 days, with gene expression dependent upon the pore size of the bridge. In the rat spinal cord, bridges implanted into a lateral hemisection supported substantial cell infiltration, aligned cells within the channels, axon growth across the channels, and high levels of transgene expression at the implant site with decreasing levels rostral and caudal. Immunohistochemistry revealed that the transfected cells at the implant site were present in both the pores and channels of the bridge and were mainly identified as Schwann cells, fibroblasts, and macrophages, in descending order of transfection. This synergy between gene delivery and the scaffold architecture may enable the engineering of tissues with complex architectures.

Temporal changes in the level of neurotrophins in the spinal cord and associated precentral gyrus following spinal hemisection in adult Rhesus monkeys

Neurotrophins (NTs) appear to be crucial for the survival and potential regeneration of injured neurons. However, their temporal changes and remote regulations following spinal cord injury (SCI) have been only partially determined, especially in primates. In this study, ELISA was performed on the extracts of injured spinal cord and the associated precentral gyrus contralateral to the site of spinal cord hemisection to investigate the temporal changes in the levels of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) in adult rhesus monkeys subjected to T8 spinal hemisection. Animals were allowed to survive 3, 7, 14, 30 and 90 days post-operation (dpo). In the spinal cord, the levels of NGF, BDNF and NT-3 sharply decreased between 3 and 7dpo. Thereafter, the levels of NGF and BDNF were transiently elevated while NT-3 level continuously increased and recovered to normal level at 30dpo. In the contralateral precentral gyrus (cPG), only the NT-3 level was altered and in fact elevated above the normal value. No obvious changes were observed in NT-4 level in any of the regions studied. Taken together, the present findings indicated that intrinsic NGF, BDNF and NT-3 may play a local role in the responses to the SCI in primates. Especially, the increase of NT-3 level occurred continuously in both the cPG and the spinal cord pointed to a possible transportation of NT-3 to the cord following SCI.

Neurotrophic factor expression in newborns with myelomeningocele: preliminary data

BACKGROUND

Neurotrophic factors play a crucial role in the stimulation of sprouting, synaptic plasticity and reorganization after spinal cord damage. The aim of this study was to investigate the expression of some neurotrophic factors [brain derived neurotrophic factor (BDNF), glial derived neurotrophic factor (GDNF), and nerve growth factor (NGF)] in the cerebrospinal fluid (CSF) of newborns with myelomeningocele (MMC) and to determine their correlations with this malformation.

METHODS

To measure the expression of BDNF, GDNF, and NGF, we collected CSF samples of six newborns during the neurosurgical operation to correct the open MMC and of 10 matched controls. Endogenous neurotrophic factor levels were quantified using a two-site immuno-enzymatic assay. The statistical analysis was performed using the Mann-Whitney two-tailed two-sample test.

FINDINGS

In the CSF of patients analysis of neurotrophic factor expression showed a significant increase of BDNF, GDNF, and NGF compared to the mean level of the control group (445.8+/-82.3, 86.5+/-2.6, and 59.9+/-6.2 pg/mL, respectively, respect to 10.2+/-5.9, 19.9+/-11.3, and 15.3+/-2.6 pg/mL) (p<0.001).

INTERPRETATION

Our study shows an over-expression of neurotrophic factors in the CSF of newborns with MMC. This neurotrophin up-regulation may stimulate axonal sprouting and synaptic reorganization of the damaged neural cells at the site of spinal cord lesion. The neurotrophic factor up-regulation may represent a particularly important biochemical markers of spinal cord damage and might be associated with the severity of spine injury in MMC patients.

Adenovirus vector-mediated ex vivo gene transfer of brain-derived neurotrophic factor to bone marrow stromal cells promotes axonal regeneration after transplantation in completely transected adult rat spinal cord

The aim of this study was to evaluate the efficacy in adult rat completely transected spinal cord of adenovirus vector-mediated brain-derived neurotrophic factor (BDNF) ex vivo gene transfer to bone marrow stromal cells (BMSC). BMSC were infected with adenovirus vectors carrying beta-galactosidase (AxCALacZ) or BDNF (AxCABDNF) genes. The T8 segment of spinal cord was removed and replaced by graft containing Matrigel alone (MG group) or Matrigel and BMSC infected by AxCALacZ (BMSC-LacZ group) or AxCABDNF (BMSC-BDNF group). Axons in the graft were evaluated by immunohistochemistry and functional recovery was assessed with BBB locomotor scale. In the BMSC-BDNF group, the number of fibers positive for growth associated protein-43, tyrosine hydroxylase, and calcitonin gene-related peptide was significantly larger than numbers found for the MG and BMSC-LacZ groups. Rats from BMSC-BDNF and BMSC-LacZ groups showed significant recovery of hind limb function compared with MG rats; however, there was no significant difference between groups in degree of functional recovery. These findings demonstrate that adenovirus vector-mediated ex vivo gene transfer of BDNF enhances the capacity of BMSC to promote axonal regeneration in this completely transected spinal cord model; however, BDNF failed to enhance hind limb functional recovery. Further investigation is needed to establish an optimal combination of cell therapy and neurotrophin gene transfer for cases of spinal cord injury.

Bidirectional changes in water-maze learning following recombinant adenovirus-associated viral vector (rAAV)-mediated brain-derived neurotrophic factor expression in the rat hippocampus

Alterations in hippocampal brain-derived neurotrophic factor (BDNF) expression have been implicated in the pathogenesis of emotional and cognitive dysfunction. Here, we induced BDNF overexpression in the rat hippocampus using recombinant adenovirus-associated viral (rAAV) vectors, and studied its long-term (2 months postinduction) effects on anxiety-related behaviour, exploration in the open field, and spatial learning in the water maze. Although the treatment successfully led to substantial elevation of hippocampal BDNF levels, its effect on spatial learning was bidirectional: a subset of rAAV-induced BDNF-overexpressing rats performed well above control level, whereas the rest were clearly impaired. This behavioural distinction corresponded to two markedly different levels of BDNF overexpression. The increase in dorsal hippocampal BDNF content achieved in the 'water-maze-impaired' subgroup was twice that attained in the 'water-maze-improved' rats. Although neither subgroup of rAAV-induced BDNF-overexpressing rats differed from controls in the open field, the 'water-maze-impaired' subgroup also showed a significant anxiolytic effect. Our results suggest that hippocampal BDNF elevation significantly affects cognitive and emotional behaviours, but the direction and magnitude of the effects critically depend on the precise levels of overexpression. This factor must be taken into account in future studies examining the functional consequences of hippocampal BDNF overexpression.

Granulocyte Colony-Stimulating Factor Attenuates Neuronal Death and Promotes Functional Recovery After Spinal Cord Injury in Mice

Granulocyte colony-stimulating factor (G-CSF) is a protein that stimulates differentiation, proliferation, and survival of granulocytic lineage cells. Recently, a neuroprotective effect of G-CSF was reported in a model of cerebral infarction. The aim of the present study was to elucidate the potential therapeutic effect of G-CSF for spinal cord injury (SCI) in mice. We found that G-CSF is neuroprotective against glutamate-induced cell death of cerebellar granule neurons in vitro. Moreover, we used a mouse model of compressive SCI to examine the neuroprotective potential of G-CSF in vivo. Histologic assessment with cresyl violet staining revealed that the number of surviving neurons in the injured spinal cord was significantly increased in G-CSF-treated mice. Immunohistochemistry for neuronal apoptosis revealed that G-CSF suppressed neuronal apoptosis after SCI. Moreover, administration of G-CSF promoted hindlimb functional recovery. Examination of signaling pathways downstream of the G-CSF receptor suggests that G-CSF might promote functional recovery by inhibiting neuronal apoptosis after SCI. G-CSF is currently used in the clinic for hematopoietic stimulation, and its ongoing clinical trial for brain infarction makes it an appealing molecule that could be rapidly placed into trials for patients with acute SCI.

Rescue of rat anterior horn neurons after spinal cord injury by retrograde transfection of adenovirus vector carrying brain-derived neurotrophic factor gene

We investigated the efficacy of retrograde gene delivery via the sternomastoid muscle of recombinant adenovirus vector (AdV) carrying brain-derived neurotrophic factor (BDNF) gene for the rescue of injured rat spinal cord. One hundred-thirty five adult Sprague-Dawley rats were used in the study with a standard weight-compression technique to produce spinal cord injury. AdV-BDNF gene or AdV-beta-galactosidase (AdV-LacZ) gene was injected into the sternomastoid muscle immediately after traumatic C4 segment spinal cord injury. AdV-BDNF was successfully appeared in the injured cervical spinal cord following injection into the sternomastoid muscle. BDNF expression in the anterior horn neurons of the cervical spinal cord reached peak levels at 1-2 weeks; and the expression persisted at significant levels for approximately 4 weeks after injury. AdV-BDNF transfection was associated with increased numbers of intact neurons as confirmed by Nissl, cholineacetyltransferase (ChAT), and acetylcholine esterase (AChE) staining especially from 2 weeks after injury, compared with the AdV-LacZ injected rats. Our results suggest that in vivo targeted retrograde AdV-BDNF-gene delivery may enhance neuronal survival following traumatic injury of the spinal cord.

Spinal gene transfer using ultrasound and microbubbles

Spinal gene therapy is a promising option for treating various spinal-related disorders. Several previous studies using viral vectors reported successful transfer of therapeutic genes into the spinal nerve system. However, because of the considerable immunogenicity related to the use of viruses, non-viral gene transfer still needs to be developed. One possible approach is the combined use of ultrasound and echo-contrast microbubbles. The present study shows that this method can be applied for targeted intrathecal gene delivery. We intrathecally injected a mixture of plasmid-DNA encoded with luciferase and commercially available albumin microbubbles by needle puncture at the lower lumbar intervertebral space in mice. Subsequent percutaneous ultrasonication on the lumbar vertebrae significantly enhanced the luciferase expression, analyzed by imaging luciferin bioluminescence, in the dorsal meningeal cells at the insonated region. No apparent neurological damages were induced by the present spinal interventions. In addition to the general benefits of the combined use of ultrasound and microbubbles, our approach can offer some advantages specific to spinal gene transfection including minimal invasiveness of simple percutaneous dural puncture, targetability due to the limited access of ultrasound waves through anatomical apertures of the vertebrae, and possible paracrine delivery of therapeutic molecules to the spinal nerve system.

Novel agonist monoclonal antibodies activate TrkB receptors and demonstrate potent neurotrophic activities

Tyrosine kinase receptor B (TrkB) mediates neurotrophic effects of brain-derived neurotrophic factor (BDNF) to increase neuronal survival, differentiation, synaptic plasticity, and neurogenesis. The therapeutic potential of TrkB activation using BDNF has been demonstrated well in several preclinical models of CNS diseases, validating TrkB as a promising drug target. Therefore, we aimed to develop TrkB-specific receptor agonists by using a monoclonal antibody approach. After generation of hybridoma clones and assessment of their binding and functional activity, we identified five mouse monoclonal antibodies that show highly selective binding to TrkB and that induce robust activation of TrkB signaling. Epitope mapping studies using competition analysis showed that each of the monoclonal antibodies recognizes a unique binding site on TrkB, some of which are distinct from BDNF docking sites. These antibodies behave as true agonists based on their ability to both activate proximal and secondary signaling molecules downstream of TrkB receptors and promote neuronal survival and neurite outgrowth. The binding affinities and the functional efficacy of these antibodies are comparable to those of BDNF, whereas they do not bind to the p75 low-affinity neurotrophin receptor at all. Therefore, they could represent novel reagents to explore the pathophysiological roles of TrkB and its potential therapeutic utility in treating CNS disorders.