Lineage-restricted neural precursors survive, migrate, and differentiate following transplantation into the injured adult spinal cord

Early graft of neural precursors in spinal cord compression reduces glial cyst and improves function

OBJECTIVE

Spinal cord injury (SCI) often results in irreversible and permanent neurological deficits below the injury site and is considered a pathological state of functional damage to local neurons and axon fibers. There are several experimental treatments to minimize tissue damage, and recently cell transplantation has emerged as a promising approach in spinal cord repair. The authors undertook this study to evaluate grafting of neural tube precursors as a possible therapeutic strategy in a model of spinal cord compression in the mouse.

METHODS

Compression SCI was induced at the T-13 level in adult male mice. Immediately after injury, neural precursor cells (NPs) were transplanted into the SCI lesion cavity in 18 mice; the remaining 19 mice received saline injections into the lesion cavity and were used as controls. Spinal cords were examined 12, 19, and 26 days postinjury to investigate the survival of the NPs and their effects on the cellular environment, glial scar and glial cyst formation, astrogliosis, and microglial activation.

RESULTS

Grafted NPs survived well and integrated into the host spinal cord tissue. Some NPs had differentiated into cells expressing glial and neuronal markers at all 3 end points. Analysis of glial cyst volume showed a lesion volume reduction of 63.2% in the NP-treated mice compared with volume in the injured but untreated mice. There appeared to be no difference in astroglial and microglial activation between untreated mice and treated ones. Sensory and motor tests demonstrated that transplantation of NPs promoted improvement in injured and treated animals compared with controls.

CONCLUSIONS

These results support the therapeutic potential of NPs, demonstrating that they can survive for a long time, differentiate, integrate into the injured spinal cord, and promote functional recovery after SCI.

NADPH-d and Fos reactivity in the rat spinal cord following experimental spinal cord injury and embryonic neural stem cell transplantation

AIMS

The aim of this study is to determine the role of nitric oxide (NO) in neuropathic pain and the effect of embryonic neural stem cell (ENSC) transplantation on NO content in rat spinal cord neurons following spinal cord injury (SCI).

MAIN METHODS

Ninety adult male Sprague-Dawley rats were divided into 3 groups (n=30, each): control (laminectomy), SCI (hemisection at T12-T13 segments) and SCI+ENSC. Each group was further divided into sub-groups (n=5 each) based on the treatment substance (L-NAME, 75 mg/kg/i.p.; L-arginine, 225 mg/kg/i.p.; physiological saline, SF) and duration (2h for acute and 28 days for chronic groups). Pain was assessed by tail flick and Randall-Selitto tests. Fos immunohistochemistry and NADPH-d histochemistry were performed in segments 2 cm rostral and caudal to SCI.

KEY FINDINGS

Tail-flick latency time increased in both acute and chronic L-NAME groups and increased in acute and decreased in chronic L-arginine groups. The number of Fos (+) neurons decreased in acute and chronic L-NAME and decreased in acute L-arginine groups. Following ENSC, Fos (+) neurons did not change in acute L-NAME but decreased in the chronic L-NAME groups, and decreased in both acute and chronic L-arginine groups. NADPH-d (+) neurons decreased in acute L-NAME and increased in L-arginine groups with and without ENSC transplantation.

SIGNIFICANCE

This study confirms the role of NO in neuropathic pain and shows an improvement following ENSC transplantation in the acute phase, observed as a decrease in Fos(+) and NADPH-d (+) neurons in spinal cord segments rostral and caudal to injury.

Gene therapy approaches to enhancing plasticity and regeneration after spinal cord injury

During the past decades, new insights into mechanisms that limit plasticity and functional recovery after spinal cord injury have spurred the development of novel approaches to enhance axonal regeneration and rearrangement of spared circuitry. Gene therapy may provide one means to address mechanisms that underlie the insufficient regenerative response of injured neurons and can also be used to identify factors important for axonal growth. Several genetic approaches aimed to modulate the environment of injured axons, for example by localized expression of growth factors, to enhance axonal sprouting and regeneration and to guide regenerating axons towards their target have been described. In addition, genetic modification of injured neurons via intraparenchymal injection, or via retrograde transport of viral vectors has been used to manipulate the intrinsic growth capacity of injured neurons. In this review we will summarize some of the progress and limitations of cell transplantation and gene therapy to enhance axonal bridging and regeneration across a lesion site, and to maximize the function, collateral sprouting and connectivity of spared axonal systems.

Neurite outgrowth of neural progenitors in presence of inhibitory proteoglycans

Attempts to promote host regeneration after spinal cord injury (SCI) have often resulted in poor axon extension due to formation of a glial scar, which creates a dense physical barrier around the injury and contains molecules that inhibit regeneration and repair of adult injured axons. Previous studies have shown that, while transplants of multipotent neural stem cells (NSC) integrate poorly in the injury site, the use of neuronal-restricted precursor cells (NRP) together with glial-restricted precursor cells (GRP) allow differentiation and integration of neurons, possibly because NRP are able to overcome chondroitin sulfate proteoglycan (CSPG) inhibition. To investigate this possibility, we grew mixed cultures of NRP/GRP on CSPG at inhibitory concentrations, using embryonic hippocampal cultures as controls. We found that NRP/GRP grown on CSPG survive and differentiate into neurons with no significant changes in neurite length, relative to growth on control polylysine substrate, and in contrast to a significant inhibition of axon growth in hippocampal cultures grown on CSPG-coated substrate. There was, however, a significant decrease in neurite number and branching in both cultures, indicating that CSPG also has important effects on neuronal morphology. These data suggest that embryonic neurons supported by glial cells derived from NRP/GRP transplants are less sensitive to inhibitory effects of CSPG in the glial scar, and are thus an appropriate source for neuronal cell replacement and reconnection of damaged circuits after SCI.

Cyclosporin A increases recovery after spinal cord injury but does not improve myelination by oligodendrocyte progenitor cell transplantation

BACKGROUND

Transplantation of oligodendrocyte precursor cells (OPCs) is an attractive therapy for demyelinating diseases. Cyclosporin A (CsA) is one of the foremost immunosuppressive agents and has widespread use in tissue and cell transplantation. However, whether CsA affects survival and differentiation of engrafted OPCs in vivo is unknown. In this study, the effect of CsA on morphological, functional and immunological aspects, as well as survival and differentiation of engrafted OPCs in injured spinal cord was explored.

RESULTS

We transplanted green fluorescent protein (GFP) expressed OPCs (GFP-OPCs) into injured spinal cords of rats treated with or without CsA (10 mg/kg). Two weeks after cell transplantation, more GFP-positive cells were found in CsA-treated rats than that in vehicle-treated ones. However, the engrafted cells mostly differentiated into astrocytes, but not oligodendrocytes in both groups. In the CsA-treated group, a significant decrease in spinal cord lesion volume along with increase in spared myelin and neurons were found compared to the control group. Such histological improvement correlated well with an increase in behavioral recovery. Further study suggested that CsA treatment could inhibit infiltration of T cells and activation of resident microglia and/or macrophages derived from infiltrating monocytes in injured spinal cords, which contributes to the survival of engrafted OPCs and repair of spinal cord injury (SCI).

CONCLUSIONS

These results collectively indicate that CsA can promote the survival of engrafted OPCs in injured spinal cords, but has no effect on their differentiation. The engrafted cells mostly differentiated into astrocytes, but not oligodendrocytes. The beneficial effect of CsA on SCI and the survival of engrafted cells may be attributed to its neuroprotective effect.

Differentiation of neural precursor cell-derived oligodendrocyte progenitor cells following transplantation into normal and injured spinal cords

Demyelination contributes to the functional deficits after spinal cord injury (SCI). Therefore, remyelination may be an important strategy to facilitate repair after SCI. Oligodendrocyte precursor cells (OPCs) are immature oligodendrocytes and can differentiate into myelin-forming cells of central nervous system under certain conditions. OPC transplantation is an attractive approach for the treatment of demyelinating diseases. In this study, we transplanted OPCs expressing green fluorescent protein (GFP-OPCs) into normal and injured rat spinal cords to evaluate the differentiation of transplanted OPCs in vivo. Unfortunately, the grafted GFP-OPCs, in spinal cord whether normal or injured, were all differentiated into astrocytes, but not oligodendrocytes. Our further study indicated that inflammatory environment might not be the key factor influencing the differentiation of OPCs. Some spinal cord components, such as bone morphogenetic proteins (BMPs), were the major factors that induced OPCs to differentiate into astrocytes. The three types of BMP receptor (BMPRIA, IB and II) could all be detected in OPCs, and the astroglial differentiation of OPCs induced by spinal cord homogenate extract (SCHE) in vitro could be blocked partly by noggin, an antagonist of BMP. These results suggested that the BMPR signal transduction pathway might be one of the key factors which determine the differentiation direction of engrafted OPCs in spinal cord.

Analysis of Dosing Regimen and Reproducibility of Intraspinal Grafting of Human Spinal Stem Cells in Immunosuppressed Minipigs

In recent studies using a rat aortic balloon occlusion model, we have demonstrated that spinal grafting of rat or human neuronal precursors or human postmitotic hNT neurons leads to progressive amelioration of spasticity and rigidity and corresponding improvement in ambulatory function. In the present study, we characterized the optimal dosing regimen and safety profile of human spinal stem cells (HSSC) when grafted into the lumbar spinal cord segments of naive immunosuppressed minipigs. Gottingen-Minnesota minipigs (18–23 kg) were anesthetized with halothane, mounted into a spine-immobilization apparatus, and received five bilateral injections of HSSC delivered in 2, 4, 6, 8, or 10 μl of media targeted into L2-L5 central gray matter (lamina VII). The total number of delivered cells ranged between 2,500 and 100,000 per injection. Animals were immunosuppressed with Prograf® for the duration of study. After cell grafting, ambulatory function was monitored daily using a Tarlov's score. Sensory functions were assessed by mechanically evoked skin twitch test. Animals survived for 6–7 weeks. Three days before sacrifice animals received daily injections of bromodeoxyuridine (100 mg/kg; IV) and were then transcardially perfused with 4% paraformaldehyde. Th12-L6 spinal column was then dissected; the spinal cord was removed and scanned with MRI. Lumbar transverse spinal cord sections were then cut and stained with a combination of human-specific (hNUMA, hMOC, hNSE, hSYN) or nonspecific (DCX, MAP2, GABA, CHAT) antibodies. The total number of surviving cells was estimated using stereological quantification. During the first 12–24 h after cell grafting, a modest motor weakness was observed in three of eight animals but was no longer present at 4 days to 7 weeks. No sensory dysfunction was seen at any time point. Postmortem MRI scans revealed the presence of the individual grafts in the targeted spinal cord areas. Histological examination of spinal cord sections revealed the presence of hNUMA-immunoreactive grafted cells distributed between the base of the dorsal horn and the ventral horn. In all grafts intense hMOC, DCX, and hSYN immunoreactivity in grafted cells was seen. In addition, a rich axodendritic network of DCX-positive processes was identified extending 300–700 μm from the grafts. On average, 45% of hNUMA-positive neurons were GABA immunoreactive. Stereological analysis of hNUMA-positive cells showed an average of 2.5- to 3-fold increase in number of surviving cells compared with the number of injected cells. Analysis of spinal structural morphology showed that in animals injected with more than 50,000 cells/injection or volumes of injectate higher than 6 μl/injection there was tissue expansion and disruption of the local axodendritic network. Based on these data the safe total number of injected cells and volume of injectate were determined to be 30,000 cells delivered in ≤6 μl of media. These data demonstrate that highly reproducible delivery of a potential cell therapeutic candidate into spinal parenchyma can be achieved across a wide range of cell doses by direct intraspinal injections. The resulting grafts uniformly showed robust cell survival and progressive neuronal maturation.

Promoting directional axon growth from neural progenitors grafted into the injured spinal cord

Spinal cord injury (SCI) is a devastating condition characterized by disruption of axonal connections, failure of axonal regeneration, and loss of motor and sensory function. The therapeutic promise of neural stem cells has been focused on cell replacement, but many obstacles remain in obtaining neuronal integration following transplantation into the injured CNS. This study investigated the neurotransmitter identity and axonal growth potential of neural progenitors following grafting into adult rats with a dorsal column lesion. We found that using a combination of neuronal and glial restricted progenitors (NRP and GRP) produced graft-derived glutamatergic and GABAergic neurons within the injury site, with minimal axonal extension. Administration of brain-derived neurotrophic factor (BDNF) with the graft promoted modest axonal growth from grafted cells. In contrast, injecting a lentiviral vector expressing BDNF rostral into the injured area generated a neurotrophin gradient and promoted directional growth of axons for up to 9 mm. Animals injected with BDNF lentivirus (at 2.5 and 5.0 mm) showed significantly more axons and significantly longer axons than control animals injected with GFP lentivirus. However, only the 5.0-mm-BDNF group showed a preference for extension in the rostral direction. We concluded that NRP/GRP grafts can be used to produce excitatory and inhibitory neurons, and neurotrophin gradients can guide axonal growth from graft-derived neurons toward putative targets. Together they can serve as a building block for neuronal cell replacement of local circuits and formation of neuronal relays.

Neuronal progenitor transplantation and respiratory outcomes following upper cervical spinal cord injury in adult rats

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 (FSC(D) or FSC(V), 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.

Stem cell therapies for spinal cord injury

Stem cell therapy is a potential treatment for spinal cord injury (SCI), and a variety of different stem cell types have been evaluated in animal models and humans with SCI. No consensus exists regarding the type of stem cell, if any, that will prove to be effective therapeutically. Most data suggest that no single therapy will be sufficient to overcome all the biological complications caused by SCI. Rationales for therapeutic use of stem cells for SCI include replacement of damaged neurons and glial cells, secretion of trophic factors, regulation of gliosis and scar formation, prevention of cyst formation, and enhancement of axon elongation. Most therapeutic approaches that use stem cells involve implantation of these cells into the spinal cord. The attendant risks of stem cell therapy for SCI--including tumor formation, or abnormal circuit formation leading to dysfunction--must be weighed against the potential benefits of this approach. This Review will examine the biological effects of SCI, the opportunities for stem cell treatment, and the types of stem cells that might be used therapeutically. The limited information available on the possible benefits of stem cell therapy to humans will also be discussed.

Long-term fate of allogeneic neural stem cells following transplantation into injured spinal cord

To characterize the fate of allogeneic neural stem cells (NSCs) following transplantation into injured spinal cord, green fluorescent protein (GFP)-NSCs isolated from GFP transgenic Sprague-Dawley rat embryos were transplanted into contused spinal cords of Wistar rats. The GFP-NSCs survived for at least 6 months in injured spinal cord; most of them differentiated rapidly into astrocytes, and a few were able to undergo proliferation. After transplantation, the GFP-NSCs remained in the transplantation site at the early stage, and then migrated along white-matter, and gathered around the injured cavity. At 6 months post-transplantation, CD8 T-lymphocytes infiltrated the spinal cord, and mixed lymphocyte culture from host and donor showed that lymphocytes from the host spleen were primed by allogeneic GFP-NSCs. At 12 months post-transplantation, most GFP cells in the spinal cord lost their morphology and disintegrated. The Basso, Beattie and Bresnahan score and footprint analysis indicated that the improvement of locomotor function in transplanted rats appeared only at the early stage, and was not seen even at 6 months after transplantation All these results suggest that the allogeneic NSCs, after transplantation into injured spinal cord, activate the host immune system. Therefore, if immunosuppressive agents are not used, the grafted allogeneic NSCs, although they can survive for a long time, are subjected to host immune rejection, and the effect of NSCs on functional recovery is limited.

Comparative profiling of microRNA expression between neural stem cells and motor neurons in embryonic spinal cord in rat

Neural stem cells' transplantation has been proposed as a future therapy for spinal cord injury. The challenge is how to make proportionally more neural stem cells differentiate into spinal motor neurons. Recent reports reveal that microRNAs play an important role in regulating stem cell self-renewal and differentiation. The aim of this study was to compare the profiling of microRNA expression between neural stem cells and motor neurons and to find candidate targets that direct differentiation of neural stem cells into motor neurons. We performed a parallel isolation and purification of motor neurons and neural stem cells from the same rat embryonic spinal cord sample. With the high-throughput TaqMan low-density array platform, 44 differentially expressed microRNAs were identified (22 specially expressed microRNAs in motor neurons and neural stem cells, respectively). Using bioinformatic methods, clustering, transcriptional regulation and target genes of differential microRNAs were analyzed. Furthermore, miR-126 specially expressed in cultured motor neurons identified by TaqMan low-density array was significantly elevated in choline acetyltransferase-positive neurons differentiated from the neural stem cells. These findings suggest that specially expressed microRNAs may contribute to the directed differentiation of neural stem cells into motor neurons and are potential targets for therapeutic interventions following spinal cord injury.

A systematic review of cellular transplantation therapies for spinal cord injury

Cell transplantation therapies have become a major focus in pre-clinical research as a promising strategy for the treatment of spinal cord injury (SCI). In this article, we systematically review the available pre-clinical literature on the most commonly used cell types in order to assess the body of evidence that may support their translation to human SCI patients. These cell types include Schwann cells, olfactory ensheathing glial cells, embryonic and adult neural stem/progenitor cells, fate-restricted neural/glial precursor cells, and bone-marrow stromal cells. Studies were included for review only if they described the transplantation of the cell substrate into an in-vivo model of traumatic SCI, induced either bluntly or sharply. Using these inclusion criteria, 162 studies were identified and reviewed in detail, emphasizing their behavioral effects (although not limiting the scope of the discussion to behavioral effects alone). Significant differences between cells of the same "type" exist based on the species and age of donor, as well as culture conditions and mode of delivery. Many of these studies used cell transplantations in combination with other strategies. The systematic review makes it very apparent that cells derived from rodent sources have been the most extensively studied, while only 19 studies reported the transplantation of human cells, nine of which utilized bone-marrow stromal cells. Similarly, the vast majority of studies have been conducted in rodent models of injury, and few studies have investigated cell transplantation in larger mammals or primates. With respect to the timing of intervention, nearly all of the studies reviewed were conducted with transplantations occurring subacutely and acutely, while chronic treatments were rare and often failed to yield functional benefits.

Lack of axonal sprouting of spared propriospinal fibers caudal to spinal contusion injury is attributed to chronic axonopathy

We have previously shown that a small percentage of long descending propriospinal tract (LDPT) axons are spared, whereas few short thoracic propriospinal (TPS) fibers survive 2 weeks following severe (50 mm weight drop) low thoracic spinal cord contusion injury (SCI). Here, we extended those findings to a moderate (25 mm weight drop) T9 SCI and assessed the effects of this lesion severity on propriospinal tract fibers at different time periods after injury. We anterogradely labeled fibers with fluororuby (FR) or WGA-HRP to determine their location and number 2, 4, 6, and 16 weeks post-SCI. Findings were compared with non-injured controls. At chronic time points, surviving FR-labeled LDPT fibers rostral to the injury remained as reactive endings or as putative regenerative sprouts. Caudal to the injury, spared LDPT fibers ran along a rim of lateral and ventral white matter, and ended as small abnormal-appearing putative terminal boutons or reactive endings within the intermediate gray matter of lumbosacral cord, with little axonal arborization and no evidence of injury-induced sprouting. One striking difference in the WGA-HRP experimental operates was the increased density of labeling of spared axons within the white matter caudal to the injury compared to controls. This labeling pattern was reminiscent of the labeling found after axotomy in studies by others, and raises a question as to contusion injury-induced impaired axonal transport. We hypothesize that axonal sprouting of axons after partial spinal cord injury seen in previous investigations was not found in the present investigation because of the additional pathological effects of contusion injury, similar to what is observed after traumatic brain injury.

Embryonic and adult stem cells promote raphespinal axon outgrowth and improve functional outcome following spinal hemisection in mice

Spinal cord injury (SCI) often results in permanent neurological deficits below the injury site. Serotonergic raphespinal projections promote functional recovery after SCI, but spontaneous regeneration of most severed axons is limited by the glial cyst and scar that form at the lesion site. Stem cell (SC) transplantation offers a promising approach for inducing regeneration through the damaged area. Here we compare the effects of transplantation of embryonic neural precursors (NPs) or adult mesenchymal SCs, both of which are potential candidates for SC therapy. The spinal cord was hemisected at the L2 neuromer in adult mice. Two weeks post-injury, we transplanted neural precursors or mesenchymal SCs into the cord, caudal to the hemisection. Injured mice without a graft served as controls. Mice were tested for functional recovery on a battery of motor tasks, then killed and analysed for survival of grafted cells, for effects of engraftment on the local cellular environment and for the sprouting of serotonergic axons. Both types of SCs survived and were integrated into the host tissue, but only the NPs expressed neuronal markers. All transplanted animals displayed an increased number of serotonin-positive fibres caudal to the hemisection, compared with untreated mice. And both cell types led to improved motor performance. These results point to a therapeutic potential for such cell grafting.

Transplantation of subventricular zone neural precursors induces an endogenous precursor cell response in a rat model of Parkinson's disease

Realistically, future stem cell therapies for neurological conditions including Parkinson's disease (PD) will most probably entail combination treatment strategies, involving both the stimulation of endogenous cells and transplantation. Therefore, this study investigates these two modes of neural precursor cell (NPC) therapy in concert in order to determine their interrelationships in a rat PD model. Human placental alkaline phosphatase (hPAP)-labeled NPCs were transplanted unilaterally into host rats which were subsequently infused ipsilaterally with 6-hydroxydopamine (6-OHDA). The reaction of host NPCs to the transplantation and 6-OHDA was tracked by bromodeoxyuridine (BrdU) labeling. Two weeks after transplantation, in animals transplanted with NPCs we found evidence of elevated host subventricular zone NPC proliferation, neurogenesis, and migration to the graft site. In these animals, we also observed a significant preservation of striatal tyrosine hydroxylase (TH) expression and substantia nigra TH cell number. We have seen no evidence that neuroprotection is a product of dopamine neuron replacement by NPC-derived cells. Rather, the NPCs expressed glial cell line-derived neurotrophic factor (GDNF), sonic hedgehog (Shh), and stromal cell-derived factor 1 alpha (SDF1alpha), providing a molecular basis for the observed neuroprotection and endogenous NPC response to transplantation. In summary, our data suggests plausible synergy between exogenous and endogenous NPC actions, and that NPC implantation before the 6-OHDA insult can create a host microenvironment conducive to stimulation of endogenous NPCs and protection of mature nigral neurons.

Region-specific differentiation potential of adult rat spinal cord neural stem/precursors and their plasticity in response to in vitro manipulation

This study characterized the differentiation of neural stem/precursor cells (NSPCs) isolated from different levels of the spinal cord (cervical vs lumbar cord) and different regions along the neuraxis (brain vs cervical spinal cord) of adult male Wistar enhanced green fluorescent protein rats. The differentiation of cervical spinal cord NSPCs was further examined after variation of time in culture, addition of growth factors, and changes in cell matrix and serum concentration. Brain NSPCs did not differ from cervical cord NSPCs in the percentages of neurons, astrocytes, or oligodendrocytes but produced 26.9% less radial glia. Lumbar cord NSPCs produced 30.8% fewer radial glia and 6.9% more neurons compared with cervical cord NSPCs. Spinal cord NSPC differentiation was amenable to manipulation by growth factors and changes in in vitro conditions. This is the first study to directly compare the effect of growth factors, culturing time, serum concentration, and cell matrix on rat spinal cord NSPCs isolated, propagated, and differentiated under identical conditions.

Bladder function recovery in rats with traumatic spinal cord injury after transplantation of neuronal-glial restricted precursors or bone marrow stromal cells

PURPOSE

We investigated functional recovery of the lower urinary system in rats with spinal cord injury after transplanting neuronal restricted precursors/glial restricted precursors or neural cells derived from bone marrow stromal cells into the injured area of the spinal cord.

MATERIALS AND METHODS

A total of 30 rats underwent experimentation in 4 groups, including group 1--sham operation, group 2--spinal cord injury plus neuronal restricted precursor/glial restricted precursor transplantation, group 3--spinal cord injury plus bone marrow stromal cell transplantation and group 4--spinal cord injury control. All rats in the 4 groups were investigated urodynamically and sacrificed on day 28 after transplantation. The cells transplanted into the injured spinal cord underwent histological investigation.

RESULTS

Transplanted cells (neuronal and glial restricted precursors, and bone marrow stromal cells) were found to maintain a presence in the injured spinal cord area. Baseline pressure, maximum capacity, mean uninhibited contraction amplitude, mean voiding pressure, voided volume and post-void residual volume were significantly better in groups 2 and 3 than in group 4, while baseline pressure in group 2 was better than that in group 3. We found no significant difference among the groups according to mean uninhibited contraction frequency.

CONCLUSIONS

Although neuronal/glial restricted precursor transplanted rats seemed to have more improvement, all rats in groups 2 and 3 showed some significant improvement in lower urinary system function. On the other hand, the level of this improvement was far from complete functional recovery.

Grafting of human bone marrow stromal cells into spinal cord injury: a comparison of delivery methods

STUDY DESIGN

Three groups of 6 rats received subtotal cervical spinal cord hemisections followed with marrow stromal cell (MSC) transplants by lumbar puncture (LP), intravenous delivery (IV), or direct injection into the injury (control). Animals survived for 4 or 21 days.

OBJECTIVE

Cell therapy is a promising strategy for the treatment of spinal cord injury (SCI). The mode of cell delivery is crucial for the translation to the clinic. Injections directly into the parenchyma may further damage already compromised tissue; therefore, less invasive methods like LP or IV delivery are preferable.

SUMMARY OF BACKGROUND DATA

Human MSC are multipotent mesenchymal adult stem cells that have a potential for autologous transplantation, obviating the need for immune suppression. Although previous studies have established that MSC can be delivered to the injured spinal cord by both LP and IV, the efficacy of cell delivery has not been directly compared with respect to efficacy of delivery and effects on the host.

METHODS

Purified MSC from a human donor were transplanted into the CSF at the lumbar region (LP), into the femoral vein (IV), or directly into the injury (control). After sacrifice, spinal cord sections were analyzed for MSC graft size, tissue sparing, host immune response, and glial scar formation, using specific antibodies and Nissl-myelin staining.

RESULTS

LP delivery of MSC to the injured spinal cord is superior to IV delivery. Cell engraftment and tissue sparing were significantly better after LP delivery, and host immune response after LP delivery was reduced compared with IV delivery.

CONCLUSION

LP is an ideal minimally invasive technique to deliver cellular transplants to the injured spinal cord. It is superior to IV delivery and, together with the potential for autologous transplantation, lends itself for clinical application.

Endogenous neural progenitor cells as therapeutic target after spinal cord injury

Growing knowledge about the role of neural progenitor cells supports the hope that stem cell-based therapeutic approaches aimed at restoring function in the lesioned central nervous system can be established. Possible therapies for promoting recovery after spinal cord injury include stimulating the formation of neurons and glial cells by endogenous progenitor cells. This article reviews the current knowledge about the nature of adult progenitor cells in the intact and injured spinal cord and summarizes possibilities and limitations of cellular replacement strategies based on manipulations of endogenous spinal cord progenitor cells and their environment.

Stem cell delivery by lumbar puncture as a therapeutic alternative to direct injection into injured spinal cord

Object

Using cellular transplants to treat spinal cord injury is a promising therapeutic strategy, but transplants grafted directly into the injury site can further damage the already compromised cord. To avoid additional trauma and to simplify translation to the clinic, it is advantageous to use less invasive delivery methods.

Methods

The authors compared the efficacy of intrathecal cell delivery at the lumbar region (lumbar puncture [LP]) to direct injection into a thoracic contusion injury using a mixed population of lineage-restricted neural precursor cells.

Results

Direct injection resulted in a higher volume of neural precursor cells located throughout the injury site, whereas fewer LP-delivered cells accumulated at the dorsal aspect of the injured cord. Both grafting methods were neuroprotective, resulting in reduction of injury size and greater tissue sparing compared with controls. Functional recovery was evaluated by assessing motor and bladder function. Animals that received cells via direct injection performed significantly better in the open-field locomotor test than did operated controls, while LP-treated animals showed intermediate recovery of function that did not differ statistically from that of either operated controls or directly injected animals. Bladder function, however, was significantly improved in both directly injected and LP-treated animals.

Conclusion

Grafting of stem cells via LP resulted in localized accumulation of cells at the injury site, neuroprotection, and modest recovery of function. Further optimization of the LP procedure by increasing the number of cells that are delivered and determining the optimal delivery schedule may further improve recovery to levels comparable to direct injection.

Glial precursor cell transplantation therapy for neurotrauma and multiple sclerosis

Traumatic injury to the brain or spinal cord and multiple sclerosis (MS) share a common pathophysiology with regard to axonal demyelination. Despite advances in central nervous system (CNS) repair in experimental animal models, adequate functional recovery has yet to be achieved in patients in response to any of the current strategies. Functional recovery is dependent, in large part, upon remyelination of spared or regenerating axons. The mammalian CNS maintains an endogenous reservoir of glial precursor cells (GPCs), capable of generating new oligodendrocytes and astrocytes. These GPCs are upregulated following traumatic or demyelinating lesions, followed by their differentiation into oligodendrocytes. However, this innate response does not adequately promote remyelination. As a result, researchers have been focusing their efforts on harvesting, culturing, characterizing, and transplanting GPCs into injured regions of the adult mammalian CNS in a variety of animal models of CNS trauma or demyelinating disease. The technical and logistic considerations for transplanting GPCs are extensive and crucial for optimizing and maintaining cell survival before and after transplantation, promoting myelination, and tracking the fate of transplanted cells. This is especially true in trials of GPC transplantation in combination with other strategies such as neutralization of inhibitors to axonal regeneration or remyelination. Overall, such studies improve our understanding and approach to developing clinically relevant therapies for axonal remyelination following traumatic brain injury (TBI) or spinal cord injury (SCI) and demyelinating diseases such as MS.

No evidence for chronic demyelination in spared axons after spinal cord injury in a mouse

The pattern of remyelination after traumatic spinal cord injury remains elusive, with animal and human studies reporting partial to complete demyelination followed by incomplete remyelination. In the present study, we found that spared rubrospinal tract (RST) axons of passage traced with actively transported dextrans and examined caudally to the lesion 12 weeks after mouse spinal cord contusion injury were fully remyelinated. Spared axons exhibited a marginally reduced myelin thickness and significantly shorter internodes. CASPR (contactin-associated protein) and K(v)1.2 channels were used to identify internodes and paranodal protein distribution properties were used as an index of myelin integrity. This is the first time the CNS myelin internode length was measured in a mouse. To better understand the significance of shortened internodes and thinner myelin in spared axons, we modeled conduction properties using McIntyre's et al. model of myelinated axons. Mathematical modeling predicted a 21% decrease in the conduction velocity of remyelinated RST axons attributable to shortened internodes. To determine whether demyelination could be present on axons exhibiting a pathological transport system, we used the retroviral reporter system. Virally delivered green fluorescent protein unveiled a small population of dystrophic RST axons that persist chronically with evident demyelination or abnormal remyelination. Collectively, these data show that lasting demyelination in spared axons is rare and that remyelination of axons of passage occurs in the chronically injured mouse spinal cord.

Transplanted neural progenitor cells survive and differentiate but achieve limited functional recovery in the lesioned adult rat spinal cord

Endogenous repair after injury in the adult CNS is limited by a number of factors including cellular loss, inflammation, cavitation and glial scarring. Spinal cord neural progenitor cells (SCNPCs) may provide a valuable cellular source for promoting repair following spinal cord injury. SCNPCs are multipotent, can be expanded in vitro, have the capacity to differentiate into CNS cell lineages and are capable of long-term survival following transplantation. Aims & Method: To determine the extent to which SCNPCs may contribute to spinal cord repair SCNPCs isolated from rat fetal spinal cord were expanded ex vivo and transplanted into the adult rat spinal cord after a dorsal column crush lesion. Results: The survival and distribution of transplanted cells were examined at 24 h, 1, 2 and 6 weeks after injury. Transplanted cells were identified at all time points, located mainly at the lesion perimeter, indicating good post-transplant cell survival. Furthermore, SCNPCs maintained their ability to differentiate in vivo, with approximately 40% differentiating into cells with a glial morphology, whilst 8% displayed a neural morphology. Transplanted animals were also assessed on a number of behavioral tasks measuring sensorimotor and proprioceptive function to determine the extent to which SCNPC transplants might attenuate lesion-induced functional deficits. SCNPCs failed to promote significant functional recovery, with a small improvement observed in only one of the four tasks employed, primarily related to improvements in sensory function. Tracing of the corticospinal tract and ascending dorsal column pathway revealed no regeneration of the axons beyond the lesion site. Conclusions: These data indicate that, although transplanted SCNPCs show good survival in the spinal cord injury environment, combination with other treatment strategies is likely to be required for these cells to fully exert their therapeutic potential.

Stem cells: a revolution in therapeutics-recent advances in stem cell biology and their therapeutic applications in regenerative medicine and cancer therapies

Basic and clinical research accomplished during the last few years on embryonic, fetal, amniotic, umbilical cord blood, and adult stem cells has constituted a revolution in regenerative medicine and cancer therapies by providing the possibility of generating multiple therapeutically useful cell types. These new cells could be used for treating numerous genetic and degenerative disorders. Among them, age-related functional defects, hematopoietic and immune system disorders, heart failures, chronic liver injuries, diabetes, Parkinson's and Alzheimer's diseases, arthritis, and muscular, skin, lung, eye, and digestive disorders as well as aggressive and recurrent cancers could be successfully treated by stem cell-based therapies. This review focuses on the recent advancements in adult stem cell biology in normal and pathological conditions. We describe how these results have improved our understanding on critical and unique functions of these rare sub-populations of multipotent and undifferentiated cells with an unlimited self-renewal capacity and high plasticity. Finally, we discuss some major advances to translate the experimental models on ex vivo and in vivo expanded and/or differentiated stem cells into clinical applications for the development of novel cellular therapies aimed at repairing genetically altered or damaged tissues/organs in humans. A particular emphasis is made on the therapeutic potential of different tissue-resident adult stem cell types and their in vivo modulation for treating and curing specific pathological disorders.

Establishment of a canine spinal cord injury model induced by epidural balloon compression

A model that provides reproducible, submaximal yet sufficient spinal cord injury is needed to allow experiments leading to development of therapeutic techniques and prediction of clinical outcome to be conducted. This study describes an experimental model for spinal cord injury that uses three different volumes of balloon inflation and durations of compression to create a controlled gradation outcome in adult dogs. Twenty-seven mongrel dogs were used for this study. A 3-french embolectomy catheter was inserted into the epidural space through a left hemilaminectomy hole at the L₄ vertebral arch. Balloons were then inflated with 50, 100, or 150 µl of a contrast agent at the L1 level for 6, 12, or 24 h and spinal canal occlusion (SCO) measured using computed tomography. Olby score was used to evaluate the extent of spinal cord injury and a histopathologic examination was conducted 1 week after surgery. The SCO of the 50, 100, and 150 µl inflations was 22-46%, 51-70%, and 75-89%, respectively (p < 0.05). Olby scores were diminished significantly by a combination of the level of SCO and duration of inflation in all groups. Olby scores in the groups of 150 µl-12 h, 150 µl-24 h, and 100 µl-24 h were 0.5, 0, and 1.7, respectively. Based on these results, a SCO > 50% for 24 h, and > 75% for 12 h induces paraplegia up to a week after spinal cord injury.

An overview of tissue engineering approaches for management of spinal cord injuries

Severe spinal cord injury (SCI) leads to devastating neurological deficits and disabilities, which necessitates spending a great deal of health budget for psychological and healthcare problems of these patients and their relatives. This justifies the cost of research into the new modalities for treatment of spinal cord injuries, even in developing countries. Apart from surgical management and nerve grafting, several other approaches have been adopted for management of this condition including pharmacologic and gene therapy, cell therapy, and use of different cell-free or cell-seeded bioscaffolds. In current paper, the recent developments for therapeutic delivery of stem and non-stem cells to the site of injury, and application of cell-free and cell-seeded natural and synthetic scaffolds have been reviewed.

Long-term fate of neural precursor cells following transplantation into developing and adult CNS

Successful strategies for transplantation of neural precursor cells for replacement of lost or dysfunctional CNS cells require long-term survival of grafted cells and integration with the host system, potentially for the life of the recipient. It is also important to demonstrate that transplants do not result in adverse outcomes. Few studies have examined the long-term properties of transplanted neural precursor cells in the CNS, particularly in non-neurogenic regions of the adult. The aim of the present study was to extensively characterize the fate of defined populations of neural precursor cells following transplantation into the developing and adult CNS (brain and spinal cord) for up to 15 months, including integration of graft-derived neurons with the host. Specifically, we employed neuronal-restricted precursors and glial-restricted precursors, which represent neural precursor cells with lineage restrictions for neuronal and glial fate, respectively. Transplanted cells were prepared from embryonic day-13.5 fetal spinal cord of transgenic donor rats that express the marker gene human placental alkaline phosphatase to achieve stable and reliable graft tracking. We found that in both developing and adult CNS grafted cells showed long-term survival, morphological maturation, extensive distribution and differentiation into all mature CNS cell types (neurons, astrocytes and oligodendrocytes). Graft-derived neurons also formed synapses, as identified by electron microscopy, suggesting that transplanted neural precursor cells integrated with adult CNS. Furthermore, grafts did not result in any apparent deleterious outcomes. We did not detect tumor formation, cells did not localize to unwanted locations and no pronounced immune response was present at the graft sites. The long-term stability of neuronal-restricted precursors and glial-restricted precursors and the lack of adverse effects suggest that transplantation of lineage-restricted neural precursor cells can serve as an effective and safe replacement therapy for CNS injury and degeneration.

Genetic Manipulation of Neural Stem Cells for Transplantation into the Injured Spinal Cord

The injured adult spinal cord is not conducive for neuronal regeneration and neurogenesis. Engrafted neural precursor cells (NPCs) differentiate largely into astroglia, with only a very small percentage becoming neurons (which might replace injured neurons) or oligodendroglia (which might improve injury induced demyelination of spared neurons). Several recent attempts have been made to enhanced neurogenesis or oligodendroglia differentiation of transplanted NPCs by genetic manipulation. These include exogenous expression of noggin, with the idea of antagonizing the astroglia differentiation promoting Bone Morphogenetic Proteins (BMPs). Direct attempts to enhance neurogenesis have also been made in transgenic over-expression of neurogenic basic helix-loop-helix transcription factors. These experiments resulted in some interesting observations, which we discuss here in the light of recent advances in development of cell-based engraftment therapy for spinal cord injuries.

Combining motor training with transplantation of rat bone marrow stromal cells does not improve repair or recovery in rats with thoracic contusion injuries

Previous studies have demonstrated that either transplantation of bone marrow stromal cells (MSC) or physical exercise regimens can elicit limited functional recovery following spinal cord injury, presumably through different mechanisms. The present study examined whether transplantation of MSC derived from transgenic Fischer alkaline phosphatase (AP) rats, in combination with exercise, would have synergistic effects leading to recovery of function that is greater than either alone. Adult female Sprague-Dawley rats received a moderate thoracic contusion injury and were divided into three groups: operated controls (Op-Control), MSC transplant recipients (MSC), and MSC transplant recipients plus exercise (MSC+Ex). Nine days after contusion, a Vitrogen matrix +/-one million MSC was injected into the lesion site in all animals. Immunosuppression with high doses of Cyclosporine A, required for MSC survival, was provided for all animals. Passive hindlimb exercise on motorized bicycles was applied 1 h/day, 3 days/week to the MSC+Ex group. A battery of behavioral tests was performed weekly to assess motor and sensory functions in all 3 groups for 12 weeks. Morphological evaluation included MSC survival, evidence of axonal growth into grafts, phenotypic analysis of MSC, and lesion/transplant size. The weight of the medial gastrocnemius muscle, a hindlimb muscle activated during stance, was used to identify extent of atrophy. No differences in motor recovery were found among the three groups. MSC survived 3 months after transplantation, indicating that the immunosuppression treatment was successful. The extent of survival was variable, and there was no correlation between MSC survival and behavioral scores. The matrix persisted, filling the lesion cavity, and some axons grew into the lesion/matrix but to a similar extent in all groups. There was no difference in lesion/matrix size among groups, indicating no neuroprotective effect on the host provided by the treatments. Immunocytochemical analysis provided no evidence that MSC differentiated into neurons, astrocytes or oligodendrocytes. Muscle mass of the medial gastrocnemius was diminished in the Op-Control group indicating significant atrophy, but was partially preserved in both the MSC and MSC+Ex groups. Our results indicate that combining the beneficial effects of rat MSC and this exercise protocol was not sufficient to enhance behavioral recovery.

Functional considerations of stem cell transplantation therapy for spinal cord repair

Stem cells hold great promise for therapeutic repair after spinal cord injury (SCI). This review compares the current experimental approaches taken towards a stem cell-based therapy for SCI. It critically evaluates stem cell sources, injury paradigms, and functional measurements applied to detect behavioral changes after transplantation into the spinal cord. Many of the documented improvements do not exclusively depend on lineage-specific cellular differentiation. In most of the studies, the functional tests used cannot unequivocally demonstrate how differentiation of the transplanted cells contributes to the observed effects. Standardized cell isolation and transplantation protocols could facilitate the assessment of the true contribution of various experimental parameters on recovery. We conclude that at present embryonic stem (ES)-derived cells hold the most promise for therapeutic utility, but that non-neural cells may ultimately be optimal if the mechanism of possible transdifferentiation can be elucidated.

Concise review: recent advances on the significance of stem cells in tissue regeneration and cancer therapies

In this study, we report on recent advances on the functions of embryonic, fetal, and adult stem cell progenitors for tissue regeneration and cancer therapies. We describe new procedures for derivation and maturation of these stem cells into the tissue-specific cell progenitors. The localization of the adult stem cells and their niches, as well as their implication in the tissue repair after injuries and during cancer progression, are also described. The emphasis is on the interactions among certain developmental signaling factors, such as hormones, epidermal growth factor, hedgehog, Wnt/beta-catenin, and Notch. These factors and their pathways are involved in the stringent regulation of the self-renewal and/or differentiation of adult stem cells. Novel strategies for the treatment of both diverse degenerating disorders, by cell replacement, and some metastatic cancer types, by molecular targeting multiple tumorigenic signaling elements in cancer progenitor cells, are also illustrated.

MR imaging of lineage-restricted neural precursors following transplantation into the adult spinal cord

Neural precursor cell (NPC) transplantation is a promising strategy for treatment of CNS injuries and neurodegenerative disorders because of potential for cell replacement. An important element of future clinical applications is development of a non-invasive procedure to follow NPC fate. We show that neuronal-restricted precursors (NRPs) and glial-restricted precursors (GRPs), NPCs with lineage restrictions for neurons and glia, respectively, can be labeled in vitro with the superparamagnetic iron oxide contrast agent Feridex. Following engraftment into intact adult spinal cord, labeled cells robustly survived in white and gray matter and migrated selectively along white matter tracts up to 5 mm. Localization of cells was reliably established using ex vivo magnetic resonance imaging of spinal cords. Imaging coincided with histological detection of iron and the human alkaline phosphatase transgene in most grafting sites, including the stream of migrating cells. Following transplantation, magnetically labeled cells exhibited mature morphologies and differentiated into neurons, astrocytes, and oligodendrocytes, similar to grafts of unlabeled NRPs and GRPs. Interestingly, Feridex-labeled cells, but not unlabeled cells, induced influx of ED1-positive macrophages/microglia. Small numbers of these phagocytic cells took up iron from grafted cells, while the majority of Feridex label was found in transplanted cells. We conclude that Feridex labeling does not inhibit NPC differentiation and can be used to reliably localize NPCs by MRI following engraftment into adult CNS, with the possible exception of areas of rapidly proliferating cells. The present results are relevant for MR-guided clinical application of transplantation strategies in treatment of spinal cord injury and other CNS pathologies.

Potential of stem cell based therapy and tissue engineering in the regeneration of the central nervous system

The insufficiency of self-repair and regeneration of the central nervous system (CNS) leads to difficulty of rehabilitation of the injured brain. In the past few decades, the significant progress in cell therapy and tissue engineering has contributed to the functional recovery of the CNS to a great extent. The present review focuses on the potential role of stem cell based therapy and tissue engineering in the regeneration of the CNS.

Transplantation of neuronal and glial restricted precursors into contused spinal cord improves bladder and motor functions, decreases thermal hypersensitivity, and modifies intraspinal circuitry

Transplanting neuronal and glial restricted precursors (NRP/GRP) into a midthoracic injury 9 d after contusion improved bladder and motor function, diminished thermal hypersensitivity, and modified lumbosacral circuitry compared with operated controls (OP-controls). Histological analysis showed that NRP/GRP survived, filled the lesion site, differentiated into neurons and glia, and migrated selectively. Volume of spinal cord spared was increased in NRP/GRP recipients, suggesting local protection. Bladder areflexia developed in both operated groups, but NRP/GRP recipients exhibited an accelerated recovery, with decreased micturition pressure and fewer episodes of detrusor hyperreflexia. Because noradrenergic receptors proliferate after spinal injury and descending noradrenergic pathways contribute to regulation of bladder control, we examined the effects of administering an alpha-1A-adrenergic antagonist, Tamsulosin, on urodynamics. This improved all cystometric parameters in both operated groups, and micturition pressure in NRP/GRP rats recovered to normal levels. Both operated groups initially showed increased sensitivity to a thermal stimulus applied to the tail; the NRP/GRP rats showed significant improvement over time. NRP/GRP grafts also produced greater recovery of hindlimb function in several tests, although both groups showed persistent and similar deficits in locomotion on a grid. Because bladder, hindlimb, and tail sensory and motor functions are organized through lumbosacral cord, we examined descending and primary afferent projections at L6-S1. The density of serotonergic, noradrenergic, and corticotrophin releasing factor-positive fibers increased in the NRP/GRP group compared with OP-controls, suggesting some sparing and/or sprouting of these modulatory pathways. Immunocytochemical staining density of dorsal root axons in the dorsal horn increased in the OP-controls but appeared normal in the NRP/GRP group. Synaptophysin immunoreactivity in the lumbosacral dorsal horn was similar among groups, consistent with restoration of synaptic density in both groups of operated animals but by different pathways. We suggest that local protection provided by NRP/GRP resulted in increased sparing/sprouting of descending pathways, which prevented sprouting by dorsal root axons, and that this modification in lumbosacral circuitry contributes to the recovery of function.

Long-term fate of neural precursor cells following transplantation into developing and adult CNS

Successful strategies for transplantation of neural precursor cells for replacement of lost or dysfunctional CNS cells require long-term survival of grafted cells and integration with the host system, potentially for the life of the recipient. It is also important to demonstrate that transplants do not result in adverse outcomes. Few studies have examined the long-term properties of transplanted neural precursor cells in the CNS, particularly in non-neurogenic regions of the adult. The aim of the present study was to extensively characterize the fate of defined populations of neural precursor cells following transplantation into the developing and adult CNS (brain and spinal cord) for up to 15 months, including integration of graft-derived neurons with the host. Specifically, we employed neuronal-restricted precursors and glial-restricted precursors, which represent neural precursor cells with lineage restrictions for neuronal and glial fate, respectively. Transplanted cells were prepared from embryonic day-13.5 fetal spinal cord of transgenic donor rats that express the marker gene human placental alkaline phosphatase to achieve stable and reliable graft tracking. We found that in both developing and adult CNS grafted cells showed long-term survival, morphological maturation, extensive distribution and differentiation into all mature CNS cell types (neurons, astrocytes and oligodendrocytes). Graft-derived neurons also formed synapses, as identified by electron microscopy, suggesting that transplanted neural precursor cells integrated with adult CNS. Furthermore, grafts did not result in any apparent deleterious outcomes. We did not detect tumor formation, cells did not localize to unwanted locations and no pronounced immune response was present at the graft sites. The long-term stability of neuronal-restricted precursors and glial-restricted precursors and the lack of adverse effects suggest that transplantation of lineage-restricted neural precursor cells can serve as an effective and safe replacement therapy for CNS injury and degeneration.