The center of the spinal cord may be central to its repair

Excitotoxic glutamate levels drive spinal cord ependymal stem cell proliferation and fate specification through CP-AMPAR signaling

The adult spinal cord contains a population of ependymal-derived neural stem/progenitor cells (epNSPCs) that are normally quiescent, but are activated to proliferate, differentiate, and migrate after spinal cord injury. The mechanisms that regulate their response to injury cues, however, remain unknown. Here, we demonstrate that excitotoxic levels of glutamate promote the proliferation and astrocytic fate specification of adult spinal cord epNSPCs. We show that glutamate-mediated calcium influx through calcium-permeable alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors (CP-AMPARs) in concert with Notch signaling increases the proliferation of epNSPCs via pCREB, and induces astrocytic differentiation through Hes1 upregulation. Furthermore, the in vivo targeting of this pathway via positive modulation of AMPARs after spinal cord injury enhances epNSPC proliferation, astrogliogenesis, neurotrophic factor production and increases neuronal survival. Our study uncovers an important mechanism by which CP-AMPARs regulate the growth and phenotype of epNSPCs, which can be targeted therapeutically to harness the regenerative potential of these cells after injury.

Combinatorial lentiviral gene delivery of pro-oligodendrogenic factors for improving myelination of regenerating axons after spinal cord injury

Spinal cord injury (SCI) results in paralysis below the injury and strategies are being developed that support axonal regrowth, yet recovery lags, in part, because many axons are not remyelinated. Herein, we investigated strategies to increase myelination of regenerating axons by overexpression of platelet-derived growth factor (PDGF)-AA and noggin either alone or in combination in a mouse SCI model. Noggin and PDGF-AA have been identified as factors that enhance recruitment and differentiation of endogenous progenitors to promote myelination. Lentivirus encoding for these factors was delivered from a multichannel bridge, which we have previously shown creates a permissive environment and supports robust axonal growth through channels. The combination of noggin+PDGF enhanced total myelination of regenerating axons relative to either factor alone, and importantly, enhanced functional recovery relative to the control condition. The increase in myelination was consistent with an increase in oligodendrocyte-derived myelin, which was also associated with a greater density of cells of an oligodendroglial lineage relative to each factor individually and control conditions. These results suggest enhanced myelination of regenerating axons by noggin+PDGF that act on oligodendrocyte-lineage cells post-SCI, which ultimately led to improved functional outcomes.

[Repair and time-dose factor: The example of spinal cord irradiation]

The question whether a reirradiation is possible, with either curative of palliative intent, is a frequent issue and a true therapeutic challenge, in particular for a critical organ sensitive to cumulative dose, such as the spinal cord. Preclinical experimental data, based on debatable models that are hardly transferable to patients, suggest that there is a possibility of reirradiation, beyond the classical threshold for dose constraints, taking into account the "time-dose factor". Although the underlying biological mechanisms are however uncertain, scarce clinical data seem to confirm that the tolerance of spinal cord to reirradiation does exist, provided that a particular attention to total dose is given. In the context where modern stereotactic irradiation facilities expand therapeutic perspectives, we review the literature on possibilities of reirradiation, through the example of spinal cord reirradiation.

Angiogenic microspheres promote neural regeneration and motor function recovery after spinal cord injury in rats

This study examined sustained co-delivery of vascular endothelial growth factor (VEGF), angiopoietin-1 and basic fibroblast growth factor (bFGF) encapsulated in angiogenic microspheres. These spheres were delivered to sites of spinal cord contusion injury in rats, and their ability to induce vessel formation, neural regeneration and improve hindlimb motor function was assessed. At 2–8 weeks after spinal cord injury, ELISA-determined levels of VEGF, angiopoietin-1, and bFGF were significantly higher in spinal cord tissues in rats that received angiogenic microspheres than in those that received empty microspheres. Sites of injury in animals that received angiogenic microspheres also contained greater numbers of isolectin B4-binding vessels and cells positive for nestin or β III-tubulin (P < 0.01), significantly more NF-positive and serotonergic fibers, and more MBP-positive mature oligodendrocytes. Animals receiving angiogenic microspheres also suffered significantly less loss of white matter volume. At 10 weeks after injury, open field tests showed that animals that received angiogenic microspheres scored significantly higher on the Basso-Beattie-Bresnahan scale than control animals (P < 0.01). Our results suggest that biodegradable, biocompatible PLGA microspheres can release angiogenic factors in a sustained fashion into sites of spinal cord injury and markedly stimulate angiogenesis and neurogenesis, accelerating recovery of neurologic function.

Concise Review: Bridging the Gap: Novel Neuroregenerative and Neuroprotective Strategies in Spinal Cord Injury

Spinal cord injuries (SCIs) result in devastating lifelong disability for patients and their families. The initial mechanical trauma is followed by a damaging secondary injury cascade involving proapoptotic signaling, ischemia, and inflammatory cell infiltration. Ongoing cellular necrosis releases ATP, DNA, glutamate, and free radicals to create a cytotoxic postinjury milieu. Long-term regeneration of lost or injured networks is further impeded by cystic cavitation and the formation of an inhibitory glial-chondroitin sulfate proteoglycan scar. In this article, we discuss important neuroprotective interventions currently applied in clinical practice, including surgical decompression, blood pressure augmentation, and i.v. methylprednisolone. We then explore exciting translational therapies on the horizon, such as riluzole, minocycline, fibroblast growth factor, magnesium, and hypothermia. Finally, we summarize the key neuroregenerative strategies of the next decade, including glial scar degradation, Rho-ROCK inhibition, cell-based therapies, and novel bioengineered adjuncts. Throughout, we emphasize the need for combinatorial approaches to this multifactorial problem and discuss relevant studies at the forefront of translation. We conclude by providing our perspectives on the future direction of SCI research.

SIGNIFICANCE

Spinal cord injuries (SCIs) result in devastating, lifelong disability for patients and their families. This article discusses important neuroprotective interventions currently applied in clinical practice, including surgical decompression, blood pressure augmentation, and i.v. methylprednisolone. Translational therapies on the horizon are discussed, such as riluzole, minocycline, fibroblast growth factor, magnesium, and hypothermia. The key neuroregenerative strategies of the next decade are summarized, including glial scar degradation, Rho-ROCK inhibition, cell-based therapies, and novel bioengineered adjuncts. The need for combinatorial approaches to this multifactorial problem is emphasized, relevant studies at the forefront of translation are discussed, and perspectives on the future direction of SCI research are presented.

Concise review: reactive astrocytes and stem cells in spinal cord injury: good guys or bad guys?

Spinal cord injury (SCI) usually results in long lasting locomotor and sensory neuron degeneration below the injury. Astrocytes normally play a decisive role in mechanical and metabolic support of neurons, but in the spinal cord they cause injury, exerting well-known detrimental effects that contribute to glial scar formation and inhibition of axon outgrowth. Cell transplantation is considered a promising approach for replacing damaged cells and promoting neuroprotective and neuroregenerative repair, but the effects of the grafted cells on local tissue and the regenerative properties of endogenous neural stem cells in the injured spinal cord are largely unknown. During the last 2 decades cumulative evidence from diverse animal models has indicated that reactive astrocytes in synergy with transplanted cells could be beneficial for injury in multiple ways, including neuroprotection and axonal growth. In this review, we specifically focus on the dual opposing roles of reactive astrocytes in SCI and how they contribute to the creation of a permissive environment when combined with transplanted cells as the influential components for a local regenerative niche. Modulation of reactive astrocyte function might represent an extremely attractive new therapy to enhance the functional outcomes in patients.

Transplantation of neural stem cells clonally derived from embryonic stem cells promotes recovery after murine spinal cord injury

The pathology of spinal cord injury (SCI) makes it appropriate for cell-based therapies. Treatments using neural stem cells (NSCs) in animal models of SCI have shown positive outcomes, although uncertainty remains regarding the optimal cell source. Pluripotent cell sources such as embryonic stem cells (ESCs) provide a limitless supply of therapeutic cells. NSCs derived using embryoid bodies (EB) from ESCs have shown tumorigenic potential. Clonal neurosphere generation is an alternative method to generate safer and more clinically relevant NSCs without the use of an EB stage for use in cell-based therapies. We generated clonally derived definitive NSCs (dNSCs) from ESC. These cells were transplanted into a mouse thoracic SCI model. Embryonic stem cell-derived definitive neural stem cell (ES-dNSC)-transplanted mice were compared with controls using behavioral measures and histopathological analysis of tissue. In addition, the role of remyelination in injury recovery was investigated using transmission electron microscopy. The SCI group that received ES-dNSC transplantation showed significant improvements in locomotor function compared with controls in open field and gait analysis. The cell treatment group had a significant enhancement of spared neural tissue. Immunohistological assessments showed that dNSCs differentiated primarily to oligodendrocytes. These cells were shown to express myelin basic protein, associate with axons, and support nodal architecture as well as display proper compact, multilayer myelination in electron microscopic analysis. This study provides strong evidence that dNSCs clonally derived from pluripotent cells using the default pathway of neuralization improve motor function after SCI and enhance sparing of neural tissue, while remaining safe and clinically relevant.

An Examination of the Mechanisms by which Neural Precursors Augment Recovery following Spinal Cord Injury: A Key Role for Remyelination

The mechanisms by which neural precursor cells (NPCs) enhance functional recovery from spinal cord injury (SCI) remain unclear. Spinal cord injured rats were transplanted with wild-type mouse NPCs, shiverer NPCs unable to produce myelin, dead NPCs, or media. Most animals also received minocycline, cyclosporine, and perilesional infusion of trophins. Motor function was graded according to the BBB scale. H&E/LFB staining was used to assess gray and white matter, cyst, and lesional tissue. Mature oligodendrocytes and ED1+ inflammatory cells were quantitated. Confocal and electron microscopy were used to assess the relationship between the transplanted cells and axons. Pharmacotherapy and trophin infusion preserved gray matter, white matter, and oligodendrocytes. Trophin infusion also significantly increased cyst and lesional tissue volume as well as inflammatory infiltrate, and functional recovery was reduced. Animals transplanted with wild-type NPCs showed greatest functional recovery; animals transplanted with shiverer NPCs performed the worst. Wild-type NPCs remyelinated host axons. Shiverer NPCs ensheathed axons but did not produce MBP. These results suggest that remyelination by NPCs is an important contribution to functional recovery following SCI. Shiverer NPCs may prevent remyelination by endogenous cells capable of myelin formation. These findings suggest that remyelination is an important therapeutic target following SCI.

Beneficial effects of melatonin combined with exercise on endogenous neural stem/progenitor cells proliferation after spinal cord injury

Endogenous neural stem/progenitor cells (eNSPCs) proliferate and differentiate into neurons and glial cells after spinal cord injury (SCI). We have previously shown that melatonin (MT) plus exercise (Ex) had a synergistic effect on functional recovery after SCI. Thus, we hypothesized that combined therapy including melatonin and exercise might exert a beneficial effect on eNSPCs after SCI. Melatonin was administered twice a day and exercise was performed on a treadmill for 15 min, six days per week for 3 weeks after SCI. Immunohistochemistry and RT-PCR analysis were used to determine cell population for late response, in conjunction with histological examination and motor function test. There was marked improvement in hindlimb function in SCI+MT+Ex group at day 14 and 21 after injury, as documented by the reduced size of the spinal lesion and a higher density of dendritic spines and axons; such functional improvements were associated with increased numbers of BrdU-positive cells. Furthermore, MAP2 was increased in the injured thoracic segment, while GFAP was increased in the cervical segment, along with elevated numbers of BrdU-positive nestin-expressing eNSPCs in the SCI+MT+Ex group. The dendritic spine density was augmented markedly in SCI+MT and SCI+MT+Ex groups. These results suggest a synergistic effect of SCI+MT+Ex might create a microenvironment to facilitate proliferation of eNSPCs to effectively replace injured cells and to improve regeneration in SCI.

Clinical neurofunctional rehabilitation of a cat with spinal cord injury after hemilaminectomy and autologous stem cell transplantation

Stem cell-based therapy has been investigated in a number of degenerative and traumatic diseases, including spinal cord injury. In the present study, we investigated the use of autologous mesenchymal stem cells in the functional rehabilitation of a domestic cat presenting a compressive L1-L5 fracture. Bone marrow cells collected by puncture of the iliac crest were cultured to obtain mesenchymal stem cells three weeks before surgery. Hemilaminectomy was performed, followed by injection of the mesenchymal stem cells in the injured area. Clinical evaluation of the animal prior to surgery showed absence of pain, muscular tonus, and panniculi reflexes. Seven days after surgery and cell transplantation the examination revealed a progressive recovery of the panniculus reflexes and of the responses to superficial and deep pain stimuli despite the low proprioceptive and hyperreflexic ataxic hind limbs. Physiotherapy protocols were applied for clinical rehabilitation after surgery. The cat's first steps, three-minute weight-bearing, and intestine and urinary bladder partial reestablishment were observed 75 days post-surgery. Our results indicate the therapeutic potential of mesenchymal stem cells in chronic spinal cord injuries.

Stem cell-based therapy for spinal cord injury

Stem cells (SCs) represent a new therapeutic approach for spinal cord injury (SCI) by enabling improved sensory and motor functions in animal models. The main goal of SC-based therapy for SCI is the replacement of neurons and glial cells that undergo cell death soon after injury. Stem cells are able to promote remyelination via oligodendroglia cell replacement to produce trophic factors enhancing neurite outgrowth, axonal elongation, and fiber density and to activate resident or transplanted progenitor cells across the lesion cavity. While several SC transplantation strategies have shown promising yet partial efficacy, mechanistic proof is generally lacking and is arguably the largest impediment toward faster progress and clinical application. The main challenge ahead is to spur on cooperation between clinicians, researchers, and patients in order to define and optimize the mechanisms of SC function and to establish the ideal source/s of SCs that produce efficient and also safe therapeutic approaches.

An in vivo characterization of trophic factor production following neural precursor cell or bone marrow stromal cell transplantation for spinal cord injury

Cellular transplantation strategies for repairing the injured spinal cord have shown consistent benefit in preclinical models, and human clinical trials have begun. Interactions between transplanted cells and host tissue remain poorly understood. Trophic factor secretion is postulated a primary or supplementary mechanism of action for many transplanted cells, however, there is little direct evidence to support trophin production by transplanted cells in situ. In the present study, trophic factor expression was characterized in uninjured, injured-untreated, injured-treated with transplanted cells, and corresponding control tissue from the adult rat spinal cord. Candidate trophic factors were identified in a literature search, and primers were designed for these genes. We examined in vivo trophin expression in 3 paradigms involving transplantation of either brain or spinal cord-derived neural precursor cells (NPCs) or bone marrow stromal cells (BMSCs). Injury without further treatment led to a significant elevation of nerve growth factor (NGF), leukemia inhibitory factor (LIF), insulin-like growth factor-1 (IGF-1), and transforming growth factor-β1 (TGF-β1), and lower expression of vascular endothelial growth factor isoform A (VEGF-A) and platelet-derived growth factor-A (PDGF-A). Transplantation of NPCs led to modest changes in trophin expression, and the co-administration of intrathecal trophins resulted in significant elevation of the neurotrophins, glial-derived neurotrophic factor (GDNF), LIF, and basic fibroblast growth factor (bFGF). BMSCs transplantation upregulated NGF, LIF, and IGF-1. NPCs isolated after transplantation into the injured spinal cord expressed the neurotrophins, ciliary neurotrophic factor (CNTF), epidermal growth factor (EGF), and bFGF at higher levels than host cord. These data show that trophin expression in the spinal cord is influenced by injury and cell transplantation, particularly when combined with intrathecal trophin infusion. Trophins may contribute to the benefits associated with cell-based repair strategies for spinal cord injury.

In vitro characterization of trophic factor expression in neural precursor cells

In cellular transplantation strategies for repairing the injured central nervous system, interactions between transplanted neural precursor cells (NPCs) and host tissue remain incompletely understood. Although trophins may contribute to the benefits observed, little research has explored this possibility. Candidate trophic factors were identified, and primers were designed for these genes. Template RNA was isolated from 3 NPC sources, and also from bone marrow stromal cells (BMSCs) and embryonic fibroblasts as comparative controls. Quantitative polymerase chain reaction was performed to determine the effect of cell source, passaging, cellular differentiation, and environmental changes on trophin factor expression in NPCs. Results were analyzed with multivariate statistical analyses. NPCs, BMSCs, and fibroblasts each expressed trophic factors in unique patterns. Trophic factor expression was similar among NPCs whether harvested from rat or mouse, brain or spinal cord, or their time in culture. The expression of neurotrophin NT-3, NT-4/5, glial-derived neurotrophic factor, and insulin-like growth factor-1 decreased with time in culture. Induced differentiation of NPCs led to a marked and statistically significant increase in the expression of trophic factors. Culture conditions and environmental changes were also associated with significant changes in trophin expression. These results suggest that trophins could contribute to the benefits associated with transplantation of NPCs as well as BMSCs. Trophic factor expression changes with NPC differentiation and environmental conditions, which could have important implications with regard to their behavior after in vivo transplantation.

Cellular treatments for spinal cord injury: the time is right for clinical trials

More than 1 million people in the United States live with a spinal cord injury (SCI). Despite medical advances, many patients with SCIs still experience substantial neurological disability, with loss of motor, sensory, and autonomic function. Cell therapy is ideally suited to address the multifactorial nature of the secondary events following SCI. Remarkable advances in our understanding of the pathophysiology of SCI, structural and functional magnetic resonance imaging, image-guided micro-neurosurgical techniques, and transplantable cell biology have enabled the use of cell-based regenerative techniques in the clinic. It is important to note that there are more than a dozen recently completed, ongoing, or recruiting cell therapy clinical trials for SCI that reflect the views of many key stakeholders. The field of regenerative neuroscience has reached a stage in which the clinical trials are scientifically and ethically justified. Although experimental models and analysis methods and techniques continue to evolve, no model will completely replicate the human condition. It is recognized that more work with cervical models of contusive/compressive SCI are required in parallel with clinical trials. It is also important that the clinical translation of advances made through well-established and validated experimental approaches in animal models move forward to meet the compelling needs of individuals with SCI and to advance the field of regenerative neuroscience. However, it is imperative that such efforts at translation be done in the most rigorous and informed fashion to determine safety and possible efficacy, and to provide key information to clinicians and basic scientists, which will allow improvements in regenerative techniques and the validation and refinement of existing preclinical animal models and research approaches. The field of regenerative neuroscience should not be stalled at the animal model stage, but instead the clinical trials need to be focused, safe, and ethical, backed up by a robust, translationally relevant preclinical research strategy.

Reaction of endogenous progenitor cells in a rat model of posttraumatic syringomyelia

OBJECT

Endogenous stem cells theoretically could replace lost tissue and repair deficits caused by syringes. In this study the authors quantitatively examined 1) whether neural progenitor cells exist in an adult rat model of posttraumatic syringomyelia (PTS); 2) and if so, how long an active population of progenitor cells can persist; 3) whether the cell population's location is associated with the syrinx; 4) the degree of differentiation of the progenitor cells; and 5) the phenotypic fate of the progenitor cells.

METHODS

Wistar rats were divided into intact, sham-operated, and experimental syrinx groups. Animals in each group were equally subdivided according to 4 time points: 7, 14, 28, and 56 days post-syrinx induction. Rats in the experimental syrinx group underwent a C-7 and T-1 laminectomy and then received 0.5 μl of a 24-mg/ml quisqualic acid spinal cord injection at the C-8 level to mimic an excitotoxic injury with an initial cyst, and 10 μl of a 250-mg/ml kaolin injection into the subarachnoid space at the C-8 level to create arachnoiditis. The proliferation, distribution, and differentiation of endogenous progenitor cells were identified immunocytochemically.

RESULTS

The authors observed a 20-fold increase in progenitor cells excluding inflammatory cells in the 1st 2 weeks post-syrinx induction. The cells persisted for at least 56 days, and 80% of them were located in the gray matter along the border of cysts. They included neural multipotential progenitor cells, oligodendroglial progenitor cells, and astrocytes.

CONCLUSIONS

Data in this study provide evidence for proliferation, distribution, and differentiation of endogenous progenitor cells in a model of PTS in adult rats. These progenitor cells proliferate rapidly, extend for long periods, and are mainly located in the gray matter along the border of syringes. Neural multipotential progenitor cells are expected to be associated with reparative and regenerative mechanisms of PTS. Glial cells are involved in the formation of a glial scar barrier that surrounds the syrinx and may prevent cyst enlargement. The authors' findings suggest that neural progenitor cells play a protective role in PTS.