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Study Design

A controlled study to evaluate a new technique for spinal rod fixation after spinal cord injury in rats. Alignment of implanted tissue-engineered scaffolds was assessed radiographically and by magnetic resonance imaging.

Objective

To evaluate the stability of implanted scaffolds and the extent of kyphoscoliotic deformities after spinal fixation.

Summary of Background Data

Biodegradable scaffolds provide an excellent platform for the quantitative assessment of cellular and molecular factors that promote regeneration within the transected cord. Successful delivery of scaffolds to the damaged cord can be hampered by malalignment following transplantation, which in turn, hinders the assessment of neural regeneration.

Methods

Radio-opaque barium sulfate-impregnated poly-lactic-co-glycolic acid scaffolds were implanted into spinal transection injuries in adult rats. Spinal fixation was performed in one group of animals using a metal rod fixed to the spinous processes above and below the site of injury, while the control group received no fixation. Radiographic morphometry was performed after 2 and 4 weeks, and 3-dimensional magnetic resonance microscopy analysis 4 weeks after surgery.

Results

Over the course of 4 weeks, progressive scoliosis was evident in the unfixed group, where a Cobb angle of 8.13 ± 2.03° was measured. The fixed group demonstrated significantly less scoliosis, with a Cobb angle measurement of 1.89 ± 0.75° (P = 0.0004). Similarly, a trend for less kyphosis was evident in the fixed group (7.33 ± 1.68°) compared with the unfixed group (10.13 ± 1.46°). Quantitative measurements of the degree of malalignment of the scaffolds were also significantly less in the fixed group (5 ± 1.23°) compared with the unfixed group (11 ± 2.82°) (P = 0.0143).

Conclusion

Radio-opaque barium sulfate allows for visualization of scaffolds in vivo using radiographic analysis. Spinal fixation was shown to prevent scoliosis, reduce kyphosis, and reduce scaffold malalignment within the transected rat spinal cord. Using a highly optimized model will increase the potential for finding a therapy for restoring function to the injured cord.

The adult spinal cord harbours a population of multipotent neural precursor cells (NPCs) with the ability to replace oligodendrocytes. However, despite this capacity, proliferation and endogenous remyelination is severely limited after spinal cord injury (SCI). In the post-traumatic microenvironment following SCI, endogenous spinal NPCs mainly differentiate into astrocytes which could contribute to astrogliosis that exacerbate the outcomes of SCI. These findings emphasize a key role for the post-SCI niche in modulating the behaviour of spinal NPCs after SCI. We recently reported that chondroitin sulphate proteoglycans (CSPGs) in the glial scar restrict the outcomes of NPC transplantation in SCI by reducing the survival, migration and integration of engrafted NPCs within the injured spinal cord. These inhibitory effects were attenuated by administration of chondroitinase (ChABC) prior to NPC transplantation. Here, in a rat model of compressive SCI, we show that perturbing CSPGs by ChABC in combination with sustained infusion of growth factors (EGF, bFGF and PDGF-AA) optimize the activation and oligodendroglial differentiation of spinal NPCs after injury. Four days following SCI, we intrathecally delivered ChABC and/or GFs for seven days. We performed BrdU incorporation to label proliferating cells during the treatment period after SCI. This strategy increased the proliferation of spinal NPCs, reduced the generation of new astrocytes and promoted their differentiation along an oligodendroglial lineage, a prerequisite for remyelination. Furthermore, ChABC and GF treatments enhanced the response of non-neural cells by increasing the generation of new vascular endothelial cells and decreasing the number of proliferating macrophages/microglia after SCI. In conclusions, our data strongly suggest that optimization of the behaviour of endogenous spinal NPCs after SCI is critical not only to promote endogenous oligodendrocyte replacement, but also to reverse the otherwise detrimental effects of their activation into astrocytes which could negatively influence the repair process after SCI.

Adult neural progenitor cells (NPCs) are an attractive source for functional replacement in neurodegenerative diseases and traumatic central nervous systems (CNS) injury. It has been shown that transplantation of neural stem cells or NPCs into the lesioned region partially restores CNS function. However, the capacity of endogenous NPCs in neuronal replacement and functional recovery of spinal cord injury (SCI) is apparently poor. More significantly, the early response of endogenous adult NPCs to SCI remains largely undefined. A comprehensive understanding of the temporal and spatial responses of NPCs to SCI is essential for the development of effective NPC therapy to restore neurological function. To this end, we have analyzed the early organization, distribution, and potential function of NPCs in response to SCI using nestin promoter controlled LacZ reporter transgenic mice. We showed that there was an increase of NPC proliferation, migration, and neurogenesis in adult spinal cord after traumatic compression SCI. The proliferation of NPCs detected by BrdU incorporation and LacZ staining was restricted to the ependymal zone (EZ) of the central canal. During acute SCI, NPCs in the EZ of the central canal migrated vigorously toward the dorsal direction, where the compression lesion is generated. The optimal NPC migration occurred in the adjacent region close to the epicenter. More significantly, there was an increased de novo neurogenesis from NPCs 24 hours after SCI. The enhanced proliferation, migration, and neurogenesis of (from) endogenous NPCs in the adult spinal cord in response to SCI suggest a potential role for NPCs in attempting to restore SCI-mediated neuronal dysfunction.

Endothelial cell (EC) loss and subsequent angiogenesis occurs over the first week after spinal cord injury (SCI). To identify molecular mechanisms that could be targeted with intravenous (i.v.) treatments we determined whether transmembrane A Disintegrin And Metalloprotease (ADAM) proteins are expressed in ECs of the injured spinal cord. ADAMs bind to integrins which are important for EC survival and angiogenesis. Female adult C57Bl/6 mice with a spinal cord contusion had progressively more ADAM8 (CD156) immunostaining in blood vessels and individual ECs between 1 and 28 days following injury. Uninjured spinal cords had little ADAM8 staining. The increase in ADAM8 mRNA and protein was confirmed in spinal cord lysates, and ADAM8 mRNA was present in FACS-enriched ECs. ADAM8 co-localized extensively and exclusively with the EC marker PECAM and also with i.v. injected lectins. I.v. injected isolectin B4 (IB4) labels a subpopulation of blood vessels at and within the injury epicenter 3-7 days after injury, coincident with angiogenesis. Both ADAM8 and the proliferation marker Ki-67 were present in IB4-positive microvessels. ADAM8-positive proliferating cells were seen at the leading end of IB4-positive blood vessels. Angiogenesis was confirmed by BrdU incorporation, binding of i.v. injected nucleolin antibodies, and MT1-MMP immunostaining in a subset of blood vessels. These data suggest that ADAM8 is vascular-selective and plays a role in proliferation and/or migration of ECs during angiogenesis following SCI.

The spontaneous axon regeneration of damaged neurons is limited after spinal cord injury (SCI). Recently, mesenchymal stem cell (MSC) transplantation was proposed as a potential approach for enhancing nerve regeneration that avoids the ethical issues associated with embryonic stem cell transplantation. As SCI is a complex pathological entity, the treatment of SCI requires a multipronged approach. The purpose of the present study was to investigate the functional recovery and therapeutic potential of human MSCs (hMSCs) and polymer in a spinal cord hemisection injury model. Rats were subjected to hemisection injuries and then divided into three groups. Two groups of rats underwent partial thoracic hemisection injury followed by implantation of either polymer only or polymer with hMSCs. Another hemisection-only group was used as a control. Behavioral, electrophysiological and immunohistochemical studies were performed on all rats. The functional recovery was significantly improved in the polymer with hMSC-transplanted group as compared with control at five weeks after transplantation. The results of electrophysiologic study demonstrated that the latency of somatosensory-evoked potentials (SSEPs) in the polymer with hMSC-transplanted group was significantly shorter than in the hemisection-only control group. In the results of immunohistochemical study, β-gal-positive cells were observed in the injured and adjacent sites after hMSC transplantation. Surviving hMSCs differentiated into various cell types such as neurons, astrocytes and oligodendrocytes. These data suggest that hMSC transplantation with polymer may play an important role in functional recovery and axonal regeneration after SCI, and may be a potential therapeutic strategy for SCI.

Angiogenesis and neurogenesis are coupled processes. Using a coculture system, we tested the hypothesis that cerebral endothelial cells activated by ischemia enhance neural progenitor cell proliferation and differentiation, while neural progenitor cells isolated from the ischemic subventricular zone promote angiogenesis. Coculture of neural progenitor cells isolated from the subventricular zone of the adult normal rat with cerebral endothelial cells isolated from the stroke boundary substantially increased neural progenitor cell proliferation and neuronal differentiation and reduced astrocytic differentiation. Conditioned medium harvested from the stroke neural progenitor cells promoted capillary tube formation of normal cerebral endothelial cells. Blockage of vascular endothelial growth factor receptor 2 suppressed the effect of the endothelial cells activated by stroke on neurogenesis as well as the effect of the supernatant obtained from stroke neural progenitor cells on angiogenesis. These data suggest that angiogenesis couples to neurogenesis after stroke and vascular endothelial growth factor likely mediates this coupling.

The purpose of this study was to evaluate the effects of fibrin scaffolds on subacute rat spinal cord injury (SCI). Long Evans rats were anesthetized and underwent a dorsal hemisection injury, two weeks later the injury site was re-exposed, scar tissue was removed, and a fibrin scaffold was implanted into the wound site. An effective method for fibrin scaffold implantation following subacute SCI was investigated based on the presence of fibrin within the lesion site and morphological analysis 1 week after implantation. Pre-polymerized fibrin scaffolds were found to be present within the lesion site 1 week after treatment and were used for the remainder of the study. Fibrin scaffolds were then implanted for 2 and 4 weeks, after which spinal cords were harvested and evaluated using markers for neurons, astrocytes, and chondroitin sulfate proteoglycans. Compared to untreated control, the fibrin-treated group had significantly higher levels of neural fiber staining in the lesion site at 2 and 4 weeks after treatment, and the accumulation of glial fibrillary acidic protein (GFAP) positive reactive astrocytes surrounding the lesion was delayed. These results show that fibrin is conducive to regeneration and cellular migration, and illustrates the advantage of using fibrin as a scaffold for drug delivery and cell-based therapies for SCI.

Intraspinal microstimulation (ISMS) involves the implantation of microwires into the spinal cord below the level of an injury to excite neural networks involved in the control of locomotion in the lower limbs. The goal of this study was to examine the potential spinal cord damage that might occur with chronic ISMS. We employed functional measures of force recruitment and immunohistochemical processing of serial spinal cord sections to evaluate any damage induced by spinal transection, implantation of ISMS arrays, and electrical stimulation of 4 hours/day for 30 days. Functional measurements showed no change in force recruitment following transection and chronic ISMS, indicating no changes to underlying neural networks. The implantation of sham intraspinal microwires produced a spatially-limited increase in the density of microglia/macrophages and GFAP+ astrocytes adjacent to the microwire tracks, indicating a persistent immune response. Most importantly, these results were not different from those around microwires that were chronically pulsed with charge levels up to 48 nC/phase. Likewise, measurements of neuronal density indicated no decrease in neuronal cell bodies in the ventral grey matter surrounding ISMS microwires (243.6/mm2 ± 35.3/mm2) compared to tissue surrounding sham microwires (207.8/mm2 ± 38.8/mm2). We conclude that the implantation of intraspinal microwires and chronic application of ISMS are well tolerated by spinal cord tissue.

The host response to spinal cord injury can lead to an ischemic environment that can induce cell death and limits cell transplantation approaches to promote spinal cord regeneration. Spinal cord bridges that provide a localized and sustained release of VEGF and FGF-2 were investigated for their ability to promote angiogenesis and nerve growth within the injury. Bridges were fabricated by fusion of poly(lactide-co-glycolide) microspheres using a gas foaming/particulate leaching technique, and proteins were incorporated by encapsulation into the microspheres and/or mixing with the microspheres before foaming. Compared to the mixing method, encapsulation reduced the losses during leaching and had a slower protein release, while VEGF was released more rapidly than FGF-2. In vivo implantation of bridges loaded with VEGF enhanced the levels of VEGF within the injury at one week, and bridges releasing VEGF and FGF-2 increased the infiltration of endothelial cells and the formation of blood vessel at 6 weeks post implantation. Additionally, substantial neurofilament staining was observed within the bridge; however, no significant difference was observed between bridges with or without protein. Bridges releasing angiogenic factors may provide an approach to overcome an ischemic environment that limits regeneration and cell transplantation based approaches.

Abstract

Nitric oxide (NO) is an important regulator of vasodilation and angiogenesis in the central nervous system (CNS). Signaling initiated by the membrane receptor CD47 antagonizes vasodilation and angiogenesis by inhibiting synthesis of cyclic guanosine monophosphate (cGMP). We recently found that deletion of CD47 led to significant functional locomotor improvements, enhanced angiogenesis, and increased epicenter microvascular perfusion in mice after moderate contusive spinal cord injury (SCI). We tested the hypothesis that improving NO/cGMP signaling within the spinal cord immediately after injury would increase microvascular perfusion, angiogenesis, and functional recovery, with an acute, 7-day administration of the cGMP phosphodiesterase 5 (PDE5) inhibitor sildenafil. PDE5 expression is localized within spinal cord microvascular endothelial cells and smooth muscle cells. While PDE5 antagonism has been shown to increase angiogenesis in a rat embolic stroke model, sildenafil had no significant effect on angiogenesis at 7 days post-injury after murine contusive SCI. Sildenafil treatment increased cGMP concentrations within the spinal cord and improved epicenter microvascular perfusion. Basso Mouse Scale (BMS) and Treadscan analyses revealed that sildenafil treatment had no functional consequence on hindlimb locomotor recovery. These data support the hypothesis that acutely improving microvascular perfusion within the injury epicenter by itself is an insufficient strategy for improving functional deficits following contusive SCI.

Despite extensive gray matter loss following spinal cord injury (SCI), little attention has been given to neuronal replacement strategies and their effects on specific functional circuits in the injured spinal cord. In the present study, we assessed breathing behavior and phrenic nerve electrophysiological activity following transplantation of microdissected dorsal or ventral pieces of rat fetal spinal cord tissue (FSCD or FSCV, respectively) into acute, cervical (C2) spinal hemisections. Transneuronal tracing demonstrated connectivity between donor neurons from both sources and the host phrenic circuitry. Phrenic nerve recordings revealed differential effects of dorsally- vs. ventrally-derived neural progenitors on ipsilateral phrenic nerve recovery and activity. These initial results suggest that local gray matter repair can influence motoneuron function in targeted circuits following spinal cord injury and that outcomes will be dependent on the properties and phenotypic fates of the donor cells employed.

Summary:

Due to the varied and numerous changes in spinal cord tissue following injury, successful treatment for repair may involve strategies combining neuroprotection (pharmacological prevention of some of the damaging intracellular cascades that lead to secondary tissue loss), axonal regeneration promotion (cell transplantation, genetic engineering to increase growth factors, neutralization of inhibitory factors, reduction in scar formation), and rehabilitation. Our goal has been to find effective combination strategies to improve outcome after injury to the adult rat thoracic spinal cord. Combination interventions tested have been implantation of Schwann cells (SCs) plus neuroprotective agents and growth factors administered in various ways, olfactory ensheathing cell (OEC) implantation, chondroitinase addition, or elevation of cyclic AMP. The most efficacious strategy in our hands for the acute complete transection/SC bridge model, including improvement in locomotion [Basso, Beattie, Bresnahan Scale (BBB)], is the combination of SCs, OECs, and chondroitinase administration (BBB 2.1 vs 6.6, 3 times more myelinated axons in the SC bridge, increased serotonergic axons in the bridge and beyond, and significant correlation between the number of bridge myelinated axons and functional improvement). We found the most successful combination strategy for a subacute spinal cord contusion injury (12.5–mm, 10–g weight, MASCIS impactor) to be SCs and elevation of cyclic AMP (BBB 10.4 vs 15, significant increases in white matter sparing, in myelinated axons in the implant, and in responding reticular formation and red and raphe nuclei, and a significant correlation between the number of serotonergic fibers and improvement in locomotion). Thus, in two injury paradigms, these combination strategies as well as others studied in our laboratory have been found to be more effective than SCs alone and suggest ways in which clinical application may be developed.

Two recurring problems with stem/neural progenitor cell (NPC) transplantation therapies for spinal cord injury (SCI) are poor cell survival and uncontrolled cell differentiation. The current study evaluated the viability and differentiation of embryonic stem cell-derived neural progenitor cells (ESNPCs) transplanted within fibrin scaffolds containing growth factors (GFs) and a heparin-binding delivery system (HBDS) to enhance cell survival and direct differentiation into neurons. Mouse ESNPCs were generated from mouse embryonic stem cells (ESCs) using a 4−/4+ retinoic acid (RA) induction protocol that resulted in a population of cells that was 70% nestin positive NPCs. The ESNPCs were transplanted directly into a rat subacute dorsal hemisection lesion SCI model. ESNPCs were either encapsulated in a fibrin scaffold; encapsulated in fibrin containing the HBDS, neurotrophin-3 (NT-3) and platelet derived growth factor (PDGF-AA); or encapsulated in fibrin scaffolds with NT-3 and PDGF-AA without the HBDS. We report that the combination of GFs and fibrin scaffold (without HBDS) enhanced the total number of ESNPCs present in the treated spinal cords and increased the number of ESNPC-derived NeuN positive neurons 8 weeks after transplantation. All experimental groups treated with ESNPCs exhibited an increase in behavioral function 4 weeks after transplantation. In a subset of animals, the ESNPCs over-proliferated as evidenced by SSEA-1 positive/Ki67 positive ESCs found at 4 and 8 weeks. These results demonstrate the potential of tissue-engineered fibrin scaffolds to enhance the survival of NPCs and highlight the need to purify cell populations used in therapies for SCI.

Vessels are a critical and necessary component of most tissues, and there has been substantial research investigating vessel formation and stabilization. Several groups have investigated coculturing endothelial cells with a second cell type to promote formation and stabilization of vessels. Some have noted that long-term vessels derived from implanted cocultures are often chimeric consisting of both host and donor cells. The questions arise as to whether the coculture cell might impact the chimeric nature of the microvessels and can modulate the density of donor cells over time. If long-term engineered microvessels are primarily of host origin, any impairment of the host's angiogenic ability has significant implications for the long-term success of the implant. If one can modulate the host versus donor response, one may be able to overcome a host's angiogenic impairment. Furthermore, if one can modulate the donor contribution, one may be able to engineer microvascular networks to deliver molecules a patient lacks systemically for long times. To investigate the impact of the cocultured cell on the host versus donor contributions of endothelial cells in engineered microvascular networks, we varied the ratio of the neural progenitors to endothelial cells in subcutaneously implanted poly(ethylene glycol)/poly-L-lysine hydrogels. We found that the coculture of neural progenitors with endothelial cells led to the formation of chimeric host-donor vessels, and the ratio of neural progenitors has a significant impact on the long term residence of donor endothelial cells in engineered microvascular networks in vivo even though the neural progenitors are only present transiently in the system. We attribute this to the short term paracrine signaling between the two cell types. This suggests that one can modulate the host versus donor contributions using short-term paracrine signaling which has broad implications for the application of engineered microvascular networks and cellular therapy more broadly.

To ensure survival of engineered implantable tissues thicker than approximately 2–3 mm, convection of nutrients and waste products to enhance the rate of transport will be required. Creating a network of vessels in vitro, before implantation (prevascularization), is one potential strategy to achieve this aim. In this study, we developed three-dimensional engineered vessel networks in vitro by coculture of endothelial cells (ECs) and fibroblasts in a fibrin gel for 7 days. Vessels formed by cord blood endothelial progenitor cell–derived ECs (EPC-ECs) in the presence of a high density of fibroblasts created an interconnected tubular network within 4 days, compared with 5–7 days in the presence of a low density of fibroblasts. Vessels derived from human umbilical vein ECs (HUVECs) in vitro showed similar kinetics. Implantation of the prevascularized tissues into immune-compromised mice, however, revealed a dramatic difference in the ability of EPC-ECs and HUVECs to form anastomoses with the host vasculature. Vascular beds derived from EPC-ECs were perfused within 1 day of implantation, whereas no HUVEC vessels were perfused at day 1. Further, while almost 90% of EPC-EC–derived vascular beds were perfused at day 3, only one-third of HUVEC-derived vascular beds were perfused. In both cases, a high density of fibroblasts accelerated anastomosis by 2–3 days. We conclude that both EPC-ECs and a high density of fibroblasts significantly accelerate the rate of functional anastomosis, and that prevascularizing an engineered tissue may be an effective strategy to enhance convective transport of nutrients in vivo.

Abstract

Spinal cord injury (SCI) results in immediate disruption of the spinal vascular network, triggering an ischemic environment and initiating secondary degeneration. Promoting angiogenesis and vascular stability through the induction of vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1), respectively, provides a possible therapeutic approach in treating SCI. We examined whether supplementing the injured environment with these two factors, which are significantly reduced following injury, has an effect on lesion size and functional outcome. Sustained delivery of both VEGF165 and Ang-1 was realized using viral vectors based on the adeno-associated virus (AAV), which were injected directly into the lesion epicenter immediately after injury. Our results indicate that the combined treatment with VEGF and Ang-1 resulted in both reduced hyperintense lesion volume and vascular stabilization, as determined by magnetic resonance imaging (MRI). Western blot analysis indicated that the viral vector expression was maintained into the chronic phase of injury, and that the use of the AAV vectors did not exacerbate infiltration of microglia into the lesion epicenter. The combined treatment with AAV-VEGF and AAV-Ang-1 improved locomotor recovery in the chronic phase of injury. These results indicate that combining angiogenesis with vascular stabilization may have potential therapeutic applications following SCI.

Loss and damage to blood vessels are thought to contribute to secondary tissue loss after spinal cord injury. Integrins might be therapeutic targets to protect the vasculature and/or promote angiogenesis, as their activation can promote tubule formation and survival of endothelial cells in vitro. Here, we show that immunostaining with an antibody against the α1β1 integrin heterodimer is present only in blood vessels from postnatal day 1 (P1) through adulthood in Sprague-Dawley rats. After a spinal cord contusion at T9 in adults, the area of α1β1 integrin positive blood vessels increases within 11 mm from the injury site at 3 days post-injury and remains prominent within the injured core only at 7 days. Staining for the α6β1 integrin heterodimer increases in blood vessels between P10 and adulthood and is present in preganglionic neurons of the intermediolateral cell column (IML) at all ages. The α6β1 integrin is also expressed by motor neurons postnatally, and oligodendrocyte precursors (OPCs), as previously reported. After the contusion, the area of α6β1 stained blood vessels was increased at 3 days and most prominently, 1 mm from the injury site, followed by a significant reduction at 7 days, when α6β1 integrin staining is most prominent around the injured core. Staining is also present in a subset of microglia and/or macrophages. These results raise the possibility that α1β1 and α6β1 integrins in blood vessels might be targeted to reduce blood vessel loss and promote angiogenesis, which may promote tissue sparing after spinal cord injury.

The aim of this article is to analyze the effects of the molecular basis of vascular events following spinal cord injury and their contribution in pathogenesis.

First of all, we reviewed the anatomy of spinal cord vessels.

The pathophysiology of spinal cord injuries revealed two types of pathogenic mechanisms. The primary event, the mechanic trauma, results in a disruption of neural and vascular structures into the spinal cord. It is followed by secondary pathogenesis that leads to the progression of the initial lesion. We reviewed vascular responses following spinal cord injury, focusing on both primary and secondary events. The intraparenchymal hemorrhage is a direct consequence of trauma; it has a typical pattern of distribution into the contused spinal cord, inside the gray matter and, it is radially extended into the white matter. The intraparenchymal hemorrhage is restricted to the dorsal columns, into adjacent rostral and caudal spinal segments. Distribution of chronic lesions overlaps the pattern of the early intraparenchymal hemorrhage. We described the mechanisms of action, role, induction and distribution of the heme oxygenase isoenzymes 1 and 2. Posttraumatic inflammatory response contributes to secondary pathogenesis. We analyzed the types of cells participating in the inflammatory response, the moment of appearance after the injury, the decrease in number, and the nature of their actions. The disruption of the blood–spinal cord barrier is biphasic. It exposes the spinal cord to inflammatory cells and to toxic effects of other molecules. Endothelin 1 mediates oxidative stress into the spinal cord through the modulation of spinal cord blood flow. The role of matrix metalloproteinases in blood–spinal cord barrier disruption, inflammation, and angiogenesis are reviewed.

Microvascular dysfunction, loss of vascular support, ischaemia and sub-acute vascular instability in surviving blood vessels contribute to secondary injury following SCI (spinal cord injury). Neither the precise temporal profile of the cellular dynamics of spinal microvasculature nor the potential molecular effectors regulating this plasticity are well understood. TGFβ (transforming growth factor β) isoforms have been shown to be rapidly increased in response to SCI and CNS (central nervous system) ischaemia, but no data exist regarding their contribution to microvascular dysfunction following SCI. To examine these issues, in the present study we used a model of focal spinal cord ischaemia/reperfusion SCI to examine the cellular response(s) of affected microvessels from 30 min to 14 days post-ischaemia. Spinal endothelial cells were isolated from affected tissue and subjected to focused microarray analysis of TGFβ-responsive/related mRNAs 6 and 24 h post-SCI. Immunohistochemical analyses of histopathology show neuronal disruption/loss and astroglial regression from spinal microvessels by 3 h post-ischaemia, with complete dissolution of functional endfeet (loss of aquaporin-4) by 12 h post-ischaemia. Coincident with this microvascular plasticity, results from microarray analyses show 9 out of 22 TGFβ-responsive mRNAs significantly up-regulated by 6 h post-ischaemia. Of these, serpine 1/PAI-1 (plasminogen-activator inhibitor 1) demonstrated the greatest increase (>40-fold). Furthermore, uPA (urokinase-type plasminogen activator), another member of the PAS (plasminogen activator system), was also significantly increased (>7.5-fold). These results, along with other select up-regulated mRNAs, were confirmed biochemically or immunohistochemically. Taken together, these results implicate TGFβ as a potential molecular effector of the anatomical and functional plasticity of microvessels following SCI.

This study investigated whether delayed treatment of spinal cord injury with controlled release of neurotrophin-3 (NT-3) from fibrin scaffolds can stimulate enhanced neural fiber sprouting. Long Evans rats received a T9 dorsal hemisection spinal cord injury. Two weeks later, the injury site was re-exposed, and either a fibrin scaffold alone, a fibrin scaffold containing a heparin-based delivery system with different concentrations of NT-3 (500 and 1000 ng/mL), or a fibrin scaffold containing 1000 ng/mL of NT-3 (no delivery system) was implanted into the injury site. The injured spinal cords were evaluated for morphological differences using markers for neurons, astrocytes, and chondroitin sulfate proteoglycans 2 weeks after treatment. The addition of 500 ng/mL of NT-3 with the delivery system resulted in an increase in neural fiber density compared to fibrin alone. These results demonstrate that the controlled release of NT-3 from fibrin scaffolds can enhance neural fiber sprouting even when treatment is delayed 2 weeks following 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.

The present study was undertaken to examine multifaceted therapeutic effects of vascular endothelial growth factor (VEGF) in a rat spinal cord injury (SCI) model, focusing on its capability to stimulate proliferation of endogenous glial progenitor cells. Neural stem cells (NSCs) can be genetically modified to efficiently transfer therapeutic genes to diseased CNS. We adopted an ex vivo approach using immortalized human NSC line (F3 cells) to achieve stable and robust expression of VEGF in the injured spinal cord. Transplantation of NSCs retrovirally transduced to overexpress VEGF (F3.VEGF cells) at 7 days after contusive SCI markedly elevated the amount of VEGF in the injured spinal cord tissue compared to injection of PBS or F3 cells without VEGF. Concomitantly, phosphorylation of VEGF receptor flk-1 increased in F3.VEGF group. Stereological counting of BrdU+ cells revealed that transplantation of F3.VEGF significantly enhanced cellular proliferation at 2 weeks after SCI. The number of proliferating NG2+ glial progenitor cells (NG2+/BrdU+) was also increased by F3.VEGF. Furthermore, transplantation of F3.VEGF increased the number of early proliferating cells that differentiated into mature oligodendrocytes, but not astrocytes, at 6 weeks after SCI. F3.VEGF treatment also increased the density of blood vessels in the injured spinal cord and enhanced tissue sparing. These anatomical results were accompanied by improved BBB locomotor scores. The multifaceted effects of VEGF on endogenous gliogenesis, angiogenesis, and tissue sparing could be utilized to improve functional outcomes following SCI.

Background

Neural stem/progenitor cells (NPCs) can differentiate into neurons, astrocytes and oligodendrocytes. NPCs are considered valuable for the cell therapy of injuries in the central nervous system (CNS). However, when NPCs are transplanted into the adult mammalian spinal cord, they mostly differentiate into glial lineage. The same results have been observed for endogenous NPCs during spinal cord injury. However, little is known about the mechanism of such fate decision of NPCs.

Methodology/Principal Findings

In the present study, we have found that myelin protein and Nogo-66 promoted the differentiation of NPCs into glial lineage. NgR and mTOR-Stat3 pathway were involved in this process. Releasing NgR from cell membranes or blocking mTOR-STAT3 could rescue the enhanced glial differentiation by Nogo-66.

Conclusions/Significance

These results revealed a novel function of Nogo-66 in the fate decision of NPCs. This discovery could have profound impact on the understanding of CNS development and could improve the therapy of CNS injuries.

The adult mammalian spinal cord contains neural stem and/or progenitor cells that slowly multiply throughout life and differentiate exclusively into glia. The contribution of adult progenitors to repair has been highlighted in recent studies, demonstrating extensive cell proliferation and gliogenesis following central nervous system (CNS) trauma. The present experiments aimed to determine the relative roles of endogenously dividing progenitor cells versus quiescent progenitor cells in posttraumatic gliogenesis. Using the mitotic indicator bromodeoxyuridine (BrdU) and a retroviral vector, we found that, in the adult female Fisher 344 rat, endogenously dividing neural progenitors are acutely vulnerable in response to T8 dorsal hemisection spinal cord injury. We then studied the population of cells that divide postinjury in the injury epicenter by delivering BrdU or retrovirus at 24 hours after spinal cord injury. Animals were euthanized at five timepoints postinjury, ranging from 6 hours to 9 weeks after BrdU delivery. At all timepoints, we observed extensive proliferation of ependymal and periependymal cells that immunohistochemically resembled stem/progenitor cells. BrdU+ incorporation was noted to be prominent in NG2-immunoreactive progenitors that matured into oligodendrocytes, and in a transient population of microglia. Using a green fluorescence protein (GFP) hematopoietic chimeric mouse, we determined that 90% of the dividing cells in this early proliferation event originate from the spinal cord, whereas only 10% originate from the bone marrow. Our results suggest that dividing, NG2-expressing progenitor cells are vulnerable to injury, but a separate, immature population of neural stem and/or progenitor cells is activated by injury and rapidly divides to replace this vulnerable population.

Spinal cord injury (SCI) has been regarded clinically as an irreversible damage caused by tissue contusion due to a blunt external force. Past research had focused on the analysis of the pathogenesis of secondary injury that extends from the injury epicenter to the periphery, as well as tissue damage and neural cell death associated with secondary injury. Recent studies, however, have proven that neural stem (progenitor) cells are also present in the brain and spinal cord of adult mammals including humans. Analyses using spinal cord injury models have also demonstrated active dynamics of cells expressing several stem cell markers, and methods aiming at functional reconstruction by promoting the potential self-regeneration capacity of the spinal cord are being explored. Furthermore, reconstruction of the neural circuit requires not only replenishment or regeneration of neural cells but also regeneration of axons. Analysis of the tissue microenvironment after spinal cord injury and research aiming to remove axonal regeneration inhibitors have also made progress. SCI is one of the simplest central nervous injuries, but its pathogenesis is associated with diverse factors, and further studies are required to elucidate these complex interactions in order to achieve spinal cord regeneration and functional reconstruction.