Engraftment,migration and differentiation of neural stem cells in the rat spinal cord following contusion injury

Background aimsSpinal cord injury is a devastating injury that impacts drastically on the victim's quality of life. Stem cells have been proposed as a therapeutic strategy. Neural stem (NS) cells have been harvested from embryonic mouse forebrain and cultured as adherent cells. These NS cells express markers of neurogenic radial glia.MethodsMouse NS cells expressing green fluorescent protein (GFP) were transplanted into immunosupressed rat spinal cords following moderate contusion injury at T9. Animals were left for 2 and 6 weeks then spinal cords were fixed, cryosectioned and analyzed. Stereologic methods were used to estimate the volume and cellular environment of the lesions. Engraftment, migration and differentiation of NS cells were also examined.ResultsNS cells integrated well into host tissue and appeared to migrate toward the lesion site. They expressed markers of neurons, astrocytes and oligodendrocytes at 2 weeks post-transplantation and markers of neurons and astrocytes at the 6-week time-point. NS cells appeared to have a similar morphologic phenotype to radial glia, in particular at the pial surface.ConclusionsAlthough no functional recovery was observed using the Basso Beattie Bresnahan (BBB) locomotor rating scale, NS cells are a potential cellular therapy for treatment of injured spinal cord. They may be used as delivery vehicles for therapeutic proteins because they show an ability to migrate toward the site of a lesion. They may also be used to replace lost or damaged neurons and oligodendrocytes.     

Role of calpain in spinal cord injury: Increased calpain immunoreactivity in rat spinal cord after impact trauma

Impact spinal cord injury (20 g-cm) was induced in rat by weight drop. The immunoreactivity of mcalpain was examined in the lesion and adjacent areas of the cord following trauma. Increased calpain immunoreactivity was evident in the lesion compared to control and the immunostaining intensity progressively increased after injury. The calpain immunoreactivity was also increased in tissue adjacent to the lesion. mCalpain immunoreactivity was significantly stronger in glial and endothelial cells, motor neurons and nerve fibers in the lesion. The calpain immunoreactivity also increased in astrocytes and microglial cells in the adjacent areas. Proliferation of microglia and astrocytes identified by GSA histochemical staining and GFAP immunostaining, respectively, was seen at one and three days after injury. Many motor neurons in the ventral horn showed increased calpain immunoreactivity and were shrunken in the lesion. These studies indicate a pivotal role for calpain and the involvement of glial cells in the tissue destruction in spinal cord injury. Special issue dedicated to Dr. Marion E. Smith.     

Sox11 promotes endogenous neurogenesis and locomotor recovery in mice spinal cord injury

We introduced a lentiviral vector containing the Sox11 gene into injured spinal cords of mice to evaluate the therapeutic potential of Sox11 in spinal cord injury. Sox11 markedly improved locomotor recovery after spinal cord injury and this recovery was accompanied by an up-regulation of Nestin/Doublecortin expression in the injured spinal cord. Sox11 was mainly located in endogenous neural stem cells lining the central canal and in newly-generated neurons in the spinal cord. In addition, Sox 11 significantly induced expressions of BDNF in the spinal cords of LV-Sox11-treated mice. We concluded that Sox11 induced activation of endogenous neural stem cells into neuronal determination and migration within the injured spinal cord. The resultant increase of BDNF at the injured site might form a distinct neurogenic niche which induces a final neuronal differentiation of these neural stem cells. Enhancing Sox11 expression to induce neurogenic differentiation of endogenous neural stem cells after injury may be a promising strategy in restorative therapy after SCI in mammals.     

Regulation of clusterin expression following spinal cord injury

We have investigated the localization and regulation of a putative extracellular chaperone, clusterin, in the rat spinal cord after lesion. In control animals, clusterin is expressed in motoneurons, in meningeal and ependymal cells, and in astrocytes mainly located beneath the pial surface. Beginning at day 2 after hemisection at segmental level C6, clusterin levels increase in GFAP-positive astrocytes within the lesioned segment. Three weeks after trauma, clusterin mRNA and protein are elevated in neurons close to the lesion site and in glial elements within scar tissue and within degenerating fiber tracts rostral and caudal to the lesion. This study provides evidence for a role of clusterin in the subacute and late phase of spinal cord injury.     

Upregulation of vascular endothelial growth factor receptors Flt-1 and Flk-1 following acute spinal cord contusion in rats.

To investigate the possible role of vascular endothelial growth factor (VEGF) in the injured spinal cord, we analyzed the distribution and time course of the two tyrosine kinase receptors for VEGF, Flt-1 and Flk-1, in the rat spinal cord following contusion injury using a weight-drop impactor. The semi-quantitative RT-PCR analysis of Flt-1 and Flk-1 in the spinal cord showed slight upregulation of these receptors following spinal cord injury. Although mRNAs for Flt-1 and Flk-1 were constitutively expressed in neurons, vascular endothelial cells, and some astrocytes in laminectomy control rats, their upregulation was induced in association with microglia/macrophages and reactive astrocytes in the vicinity of the lesion within 1 day in rats with a contusion injury and persisted for at least 14 days. The spatiotemporal expression of Flt-1 in the contused spinal cord mirrored that of Flk-1 expression. In the early phase of spinal cord injury, upregulation of Flt-1 and Flk-1 mRNA occurred in microglia/macrophages that infiltrated the lesion. In addition, the expression of both receptors increased progressively in reactive astrocytes within the vicinity of the lesion, predominately in the white matter, and almost all reactive astrocytes coexpressed Flt-1 or Flk-1 and nestin. These results suggest that VEGF may be involved in the inflammatory response and the astroglial reaction to contusion injuries of the spinal cord via specific VEGF receptors.     

In vivo imaging of axonal degeneration and regeneration in the injured spinal cord

The poor response of central axons to transection underlies the bleak prognosis following spinal cord injury. Here, we monitor individual fluorescent axons in the spinal cords of living transgenic mice over several days after spinal injury. We find that within 30 min after trauma, axons die back hundreds of micrometers. This acute form of axonal degeneration is similar in mechanism to the more delayed Wallerian degeneration of the disconnected distal axon, but acute degeneration affects the proximal and distal axon ends equally. In vivo imaging further shows that many axons attempt regeneration within 6-24 h after lesion. This growth response, although robust, seems to fail as a result of the inability of axons to navigate in the proper direction. These results suggest that time-lapse imaging of spinal cord injury may provide a powerful analytical tool for assessing the pathogenesis of spinal cord injury and for evaluating therapies that enhance regeneration.     

Inhibition of Epidermal Growth Factor Receptor Improves Myelination and Attenuates Tissue Damage of Spinal Cord Injury

Preventing demyelination and promoting remyelination of denuded axons are promising therapeutic strategies for spinal cord injury (SCI). Epidermal growth factor receptor (EGFR) inhibition was reported to benefit the neural functional recovery and the axon regeneration after SCI. However, its role in de- and remyelination of axons in injured spinal cord is unclear. In the present study, we evaluated the effects of EGFR inhibitor, PD168393 (PD), on the myelination in mouse contusive SCI model. We found that expression of myelin basic protein (MBP) in the injured spinal cords of PD treated mice was remarkably elevated. The density of glial precursor cells and oligodendrocytes (OLs) was increased and the cell apoptosis in lesions was attenuated after PD168393 treatment. Moreover, PD168393 treatment reduced both the numbers of OX42 + microglial cells and glial fibrillary acidic protein + astrocytes in damaged area of spinal cords. We thus conclude that the therapeutic effects of EGFR inhibition after SCI involves facilitating remyelination of the injured spinal cord, increasing of oligodendrocyte precursor cells and OLs, as well as suppressing the activation of astrocytes and microglia/macrophages.     

Differential gene expression in the EphA4 knockout spinal cord and analysis of the inflammatory response following spinal cord injury

Mice lacking the axon guidance molecule EphA4 have been shown to exhibit extensive axonal regeneration and functional recovery following spinal cord injury. To assess mechanisms by which EphA4 may modify the response to neural injury a microarray was performed on spinal cord tissue from mice with spinal cord injury and sham injured controls. RNA was purified from spinal cords of adult EphA4 knockout and wild-type mice four days following lumbar spinal cord hemisection or laminectomy only and was hybridised to Affymetrix All-Exon Array 1.0 GeneChips?. While subsequent analyses indicated that several pathways were altered in EphA4 knockout mice, of particular interest was the attenuated expression of a number of inflammatory genes, including Arginase 1, expression of which was lower in injured EphA4 knockout compared to wild-type mice. Immunohistological analyses of different cellular components of the immune response were then performed in injured EphA4 knockout and wildtype spinal cords. While numbers of infiltrating CD3+ T cells were low in the hemisection model, a robust CD11b+ macrophage/microglial response was observed post-injury. There was no difference in the overall number or spread of macrophages/activated microglia in injured EphA4 knockout compared to wild-type spinal cords at 2, 4 or 14 days post-injury, however a lower proportion of Arginase-1 immunoreactive macrophages/activated microglia was observed in EphA4 knockout spinal cords at 4 days post-injury. Subtle alterations in the neuroinflammatory response in injured EphA4 knockout spinal cords may contribute to the regeneration and recovery observed in these mice following injury.     

Anatomical repair of nerve membranes in crushed mammalian spinal cord with polyethylene glycol

Acute damage to axons is manifested as a breach in their membranes, ion exchange across the compromised region, local depolarization, and sometimes conduction block. This condition can worsen leading to axotomy. Using a novel recording chamber, we demonstrate immediate arrest of this process by application of polyethylene glycol (PEG) to a severe compression of guinea pig spinal cord. Variable magnitudes of compound actions potentials (CAPs) were rapidly restored in 100% of the PEG-treated spinal cords. Using a dye exclusion test, in which horseradish peroxidase is imbibed by damaged axons, we have shown that the physiological recovery produced by polyethylene glycol was associated with sealing of compromised axolemmas. Injured axons readily imbibe horseradish peroxidase—but not following sealing of their membranes. The density of nerve fibers taking up the marker is significantly reduced following polyethylene glycol treatment compared to a control group. We further show that all axons—independent of their caliber—are equally susceptible to the compression injury and equally susceptible to polyethylene glycol mediated repair. Thus, polyethylene glycol—induced reversal of permeabilization by rapid membrane sealing is likely the basis for physiological recovery in crushed spinal cords. We discuss the clinical importance of these findings.     

Arylsulfatase B Improves Locomotor Function after Mouse Spinal Cord Injury

Bacterial chondroitinase ABC (ChaseABC) has been used to remove the inhibitory chondroitin sulfate chains from chondroitin sulfate proteoglycans to improve regeneration after rodent spinal cord injury. We hypothesized that the mammalian enzyme arylsulfatase B (ARSB) would also enhance recovery after mouse spinal cord injury. Application of the mammalian enzyme would be an attractive alternative to ChaseABC because of its more robust chemical stability and reduced immunogenicity. A one-time injection of human ARSB into injured mouse spinal cord eliminated immunoreactivity for chondroitin sulfates within five days, and up to 9 weeks after injury. After a moderate spinal cord injury, we observed improvements of locomotor recovery assessed by the Basso Mouse Scale (BMS) in ARSB treated mice, compared to the buffer-treated control group, at 6 weeks after injection. After a severe spinal cord injury, mice injected with equivalent units of ARSB or ChaseABC improved similarly and both groups achieved significantly more locomotor recovery than the buffer-treated control mice. Serotonin and tyrosine hydroxylase immunoreactive axons were more extensively present in mouse spinal cords treated with ARSB and ChaseABC, and the immunoreactive axons penetrated further beyond the injury site in ARSB or ChaseABC treated mice than in control mice. These results indicate that mammalian ARSB improves functional recovery after CNS injury. The structural/molecular mechanisms underlying the observed functional improvement remain to be elucidated.     

Effects of Embryonic Neural Stem Cell Transplantation on DNA Damage in the Brain and Spinal Cord Following Spinal Cord Injury

Embryonic neural stem cell (ENSC) transplantation is used experimentally for the improvement of spinal cord repair following spinal cord injury (SCI). However, the effects of such intervention on oxidative stress and cell death remain unknown. We used in vivo Comet assay in the acute and chronic SCI groups compared with the SCI+ENSC transplantation groups of experimental rats in order to evaluate DNA damage in the spinal cord. Chronic SCI resulted in the generation of oxidative DNA damage in the spinal cord brain and kidneys, as indicated by high Comet assay parameters, including the percentage of DNA in the tail (T%, or TD), tail moment (TM), and tail length (TL). The DNA damage levels significantly decreased after ENSC transplantation in the spinal cords of acute and chronic SCI groups within the lesion site and rostrally and caudally to the injury, and in the brains and kidneys of the chronic SCI group. Thus, ENSC transplantation is found to be an effective tool for limitation of DNA damage following spinal cord injury.     

The Cell Neural Adhesion Molecule Contactin-2 (TAG-1) Is Beneficial for Functional Recovery after Spinal Cord Injury in Adult Zebrafish

The cell neural adhesion molecule contactin-2 plays a key role in axon extension and guidance, fasciculation, and myelination during development. We thus asked, whether contactin-2 is also important in nervous system regeneration after trauma. In this study, we used an adult zebrafish spinal cord transection model to test the functions of contactin-2 in spinal cord regeneration. The expression patterns of contactin-2 at different time points after spinal cord injury were studied at the mRNA level by qPCR and in situ hybridization, and contactin-2 protein levels and immunohistological localization were detected by Western blot and immunofluorescence analyses, respectively. Contactin-2 mRNA and protein levels were increased along the central canal at 6 days and 11 days after spinal cord injury, suggesting a requirement for contactin-2 in spinal cord regeneration. Co-localization of contactin-2 and islet-1 (a motoneuron marker) was observed in spinal cords before and after injury. To further explore the functions of contactin-2 in regeneration, an anti-sense morpholino was used to knock down the expression of contactin-2 protein by application at the time of injury. Motion analysis showed that inhibition of contactin-2 retarded the recovery of swimming functions when compared to standard control morpholino. Anterograde and retrograde tracing at 6 weeks after injury showed that knock down of contactin-2 inhibited axonal regrowth from NMLF neurons beyond lesion site. The combined observations indicate that contactin-2 contributes to locomotor recovery and successful regrowth of axons after spinal cord injury in adult zebrafish.     

Rapid, widespread, and longlasting induction of nestin contributes to the generation of glial scar tissue after CNS injury

Neuronal regeneration does generally not occur in the central nervous system (CNS) after injury, which has been attributed to the generation of glial scar tissue. In this report we show that the composition of the glial scar after traumatic CNS injury in rat and mouse is more complex than previously assumed: expression of the intermediate filament nestin is induced in reactive astrocytes. Nestin induction occurs within 48 hours in the spinal cord both at the site of lesion and in degenerating tracts and lasts for at least 13 months. Nestin expression is induced with similar kinetics in the crushed optic nerve. In addition to the expression in reactive astrocytes, we also observed nestin induction within 48 hours after injury in cells close to the central canal in the spinal cord, while nestin expressing cells at later timepoints were found progressively further out from the central canal. This dynamic pattern of nestin induction after injury was mimicked by lacZ expressing cells in nestin promoter/lacZ transgenic mice, suggesting that defined nestin regulatory regions mediate the injury response. We discuss the possibility that the spatiotemporal pattern of nestin expression reflects a population of nestin positive cells, which proliferates and migrates from a region close to the central canal to the site of lesion in response to injury.     

The mechanical properties of neonatal rat spinal cord in vitro,and comparisons with adult

A number of studies have investigated the mechanical properties of adult spinal cord under tension, however it is not known whether age has an effect on these properties. This is of interest to those aiming to understand the clinical differences between adults and children with spinal cord injury (e.g. severity and recovery), and those developing experimental or computational models for paediatric spinal cord injury. Entire spinal cords were freshly harvested from neonatal rats (14 days) and tested in vitro under uniaxial tension at a range of strain rates (0.2, 0.02, 0.002/s) to a range of strains (2%, 3.5%, 5%), with relaxation responses being recorded for 15 min. These mechanical properties were compared to previously reported data from similar experiments on adult rat spinal cords, and the peak stress and the stress after 15 min of relaxation were found to be significantly higher for spinal cords from adults than neonates (p<0.001). A non-linear viscoelastic model was developed and was observed to adequately predict the mechanical behaviour of this tissue. The model developed in this study may be of use in computational models of paediatric spinal cord. The significant differences between adult and neonatal spinal cord properties may explain the higher initial severity of spinal cord injury in children and may have implications for the development of experimental animal models for paediatric spinal cord injury, specifically for those aiming to match the injury severity with adult experimental models.     

Aquaporin 1 - a novel player in spinal cord injury

The role of water channel aquaporin 1 (AQP-1) in uninjured or injured spinal cords is unknown. AQP-1 is weakly expressed in neurons and gray matter astrocytes, and more so in white matter astrocytes in uninjured spinal cords, a novel finding. As reported before, AQP-1 is also present in ependymal cells, but most abundantly in small diameter sensory fibers of the dorsal horn. Rat contusion spinal cord injury (SCI) induced persistent and significant four- to eightfold increases in AQP-1 levels at the site of injury (T10) persisting up to 11 months post-contusion, a novel finding. Delayed AQP-1 increases were also found in cervical and lumbar segments, suggesting the spreading of AQP-1 changes over time after SCI. Given that the antioxidant melatonin significantly decreased SCI-induced AQP-1 increases and that hypoxia inducible factor-1α was increased in acutely and chronically injured spinal cords, we propose that chronic hypoxia contributes to persistent AQP-1 increases after SCI. Interestingly; AQP-1 levels were not affected by long-lasting hypertonicity that significantly increased astrocytic AQP-4, suggesting that the primary role of AQP-1 is not regulating isotonicity in spinal cords. Based on our results we propose possible novel roles for AQP-1 in the injured spinal cords: (i) in neuronal and astrocytic swelling, as AQP-1 was increased in all surviving neurons and reactive astrocytes after SCI and (ii) in the development of the neuropathic pain after SCI. We have shown that decreased AQP-1 in melatonin-treated SCI rats correlated with decreased AQP-1 immunolabeling in the dorsal horns sensory afferents, and with significantly decreased mechanical allodynia, suggesting a possible link between AQP-1 and chronic neuropathic pain after SCI.     

Changes in Glial Cell Line-derived Neurotrophic Factor Expression in the Rostral and Caudal Stumps of the Transected Adult Rat Spinal Cord

Limited information is available regarding the role of endogenous Glial cell line-derived neurotrophic factor (GDNF) in the spinal cord following transection injury. The present study investigated the possible role of GDNF in injured spinal cords following transection injury (T₉–T₁₀) in adult rats. The locomotor function recovery of animals by the BBB (Basso, Beattie, Bresnahan) scale score showed that hindlimb support and stepping function increased gradually from 7 days post operation (dpo) to 21 dpo. However, the locomotion function in the hindlimbs decreased effectively in GDNF-antibody treated rats. GDNF immunoreactivty in neurons in the ventral horn of the rostral stump was stained strongly at 3 and 7 dpo, and in the caudal stump at 14 dpo, while immunostaining in astrocytes was also seen at all time-points after transection injury. Western blot showed that the level of GDNF protein underwent a rapid decrease at 7 dpo in both stumps, and was followed by a partial recovery at a later time-point, when compared with the sham-operated group. GDNF mRNA-positive signals were detected in neurons of the ventral horn, especially in lamina IX. No regenerative fibers from corticospinal tract can be seen in the caudal segment near the injury site using BDA tracing technique. No somatosensory evoked potentials (SEP) could be recorded throughout the experimental period as well. These findings suggested that intrinsic GDNF in the spinal cord could play an essential role in neuroplasticity. The mechanism may be that GDNF is involved in the regulation of local circuitry in transected spinal cords of adult rats.     

Neural progenitors isolated from newborn rat spinal cords differentiate into neurons and astroglia

Permanent functional deficit in patients with spinal cord injury (SCI) is in part due to severe neural cell death. Therefore, cell replacement using stem cells and neural progenitors that give rise to neurons and glia is thought to be a potent strategy to promote tissue repair after SCI. Many studies have shown that stem cells and neural progenitors can be isolated from embryonic, postnatal and adult spinal cords. Recently, we isolated neural progenitors from newborn rat spinal cords. In general, the neural progenitors grew as spheres in culture, and showed immunoreactivity to a neural progenitor cellular marker, nestin. They were found to proliferate and differentiate into glial fibrillary acidic protein-positive astroglia and multiple neuronal populations, including GABAergic and cholinergic neurons. Neurotrophin 3 and neurotrophin 4 enhanced the differentiation of neural progenitors into neurons. Furthermore, the neural progenitors that were transplanted into contusive spinal cords were found to survive and have migrated in the spinal cord rostrally and caudally over 8 mm to the lesion center 7 days after injury. Thus, the neural progenitors isolated from newborn rat spinal cords in combination with neurotrophic factors may provide a tool for cell therapy in SCI patients.     

Permissive role of Cdc2 activity induced from astrocytes in neurite outgrowth

Following spinal cord injury, glial cells are recognized as major environmental factors hampering axon's regenerative responses. However, recent studies suggested that, in certain circumstances, reactive astrocytes may have a permissive role for axonal regeneration and functional recovery. Here, we report that Cdc2 activation in astrocytes is positively linked to axon growth. Cdc2 was strongly, but transiently, induced from reactive astrocytes within and around the injury cavity. Cdc2 levels in primary, non‐neuronal cells prepared from injured spinal cord were up‐regulated by extending the pre‐injury period. Cdc2‐mediated vimentin phosphorylation was strongly induced in astrocytes after long‐term culture (7 days, LTC) as compared with short‐term culture (3 days, STC). Induction levels of phospho‐vimentin in LTC astrocytes were positively associated with increased neurite outgrowth in co‐cultured dorsal root ganglion neurons. β3 integrin mRNA was induced in LTC astrocytes and activation of β3 integrin was regulated by Cdc2 activity. Furthermore, genetic depletion and pharmacological blockade experiments demonstrate that activation of Cdc2 and β3 integrin in LTC astrocytes is required for neurite outgrowth. Our data suggest that the Cdc2 pathway may play an important role in determining phenotypic expression of astrocytes such that astrocytes provide permissive environments for axonal regeneration following spinal cord injury.     

BMP inhibition enhances axonal growth and functional recovery after spinal cord injury

Bone morphogenetic proteins (BMPs) are multifunctional growth factors that belong to the transforming growth factor-β superfamily. BMPs regulate several crucial aspects of embryonic development and organogenesis. The reemergence of BMPs in the injured adult CNS suggests their involvement in the pathogenesis of the lesion. Here, we demonstrate that BMPs are potent inhibitors of axonal regeneration in the adult spinal cord. The expression of BMP-2/4 is elevated in oligodendrocytes and astrocytes around the injury site following spinal cord contusion. Intrathecal administration of noggin – a soluble BMP antagonist—leads to enhanced locomotor activity and reveals significant regrowth of the corticospinal tract after spinal cord contusion. Thus, BMPs play a role in inhibiting axonal regeneration and limiting functional recovery following injury to the CNS.     

Viability-dependent promoting action of adult neural precursors in spinal cord injury

The aim of the study was the assessment of the effects of adult neural stem cell (NSC) transplantation in a mouse model of spinal cord injury (SCI). The contusion injury was performed by means of the Infinite Horizon Device to allow the generation of reproducible traumatic lesion to the cord. We administered green fluorescent-labeled (GFP-)NSCs either by intravenous (i.v.) injection or by direct transplantation into the spinal cord (intraspinal route). We report that NSCs significantly improved recovery of hind limb function and greatly attenuated secondary degeneration. The i.v. route of NSC administration yielded better recovery than the intraspinal route of administration. About 2% of total i.v.-administered NSCs homed to the spinal cord injury site, and survived almost undifferentiated; thus the positive effect of NSC treatment cannot be ascribed to damaged tissue substitution. The NSCs homing to the injury site triggered, within 48 h, a large increase of the expression of neurotrophic factors and chemokines. One wk after transplantation, exogenous GFP-NSCs still retained their proliferation potential and produced neurospheres when recovered from the lesion site and cultured in vitro. At a later time, GFP-NSC were phagocytated by macrophages. We suggest that the process of triggering the recovery of function might be strongly related to the viability of GFP-NSC, still capable ex vivo of producing neurospheres, and their ability to modify the lesion environment in a positive fashion.