Olfactory ensheathing cells: their potential use for repairing the injured spinal cord

Progression in translational research on spinal cord injury based on microenvironment imbalance

Spinal cord injury (SCI) leads to loss of motor and sensory function below the injury level and imposes a considerable burden on patients, families, and society. Repair of the injured spinal cord has been recognized as a global medical challenge for many years. Significant progress has been made in research on the pathological mechanism of spinal cord injury. In particular, with the development of gene regulation, cell sequencing, and cell tracing technologies, in-depth explorations of the SCI microenvironment have become more feasible. However, translational studies related to repair of the injured spinal cord have not yielded significant results. This review summarizes the latest research progress on two aspects of SCI pathology: intraneuronal microenvironment imbalance and regenerative microenvironment imbalance. We also review repair strategies for the injured spinal cord based on microenvironment imbalance, including medications, cell transplantation, exosomes, tissue engineering, cell reprogramming, and rehabilitation. The current state of translational research on SCI and future directions are also discussed. The development of a combined, precise, and multitemporal strategy for repairing the injured spinal cord is a potential future direction.

High-Yield Mucosal Olfactory Ensheathing Cells Restore Loss of Function in Rat Dorsal Root Injury

In a previous study, we reported that no axons were crossing from the severed dorsal roots to the spinal cord using the rat dorsal rhizotomy paradigm. The injury caused ipsilateral deficits of forepaw function. An attempt to restore the function by transplanting cells containing 5% olfactory ensheathing cells (OECs) cultured from the olfactory mucosa did not succeed. However, obtaining OECs from the olfactory mucosa has an advantage for clinical application. In the present study, we used the same rhizotomy paradigm, but rats with an injury received cells from a modified mucosal culture containing around 20% OECs mixed in collagen. The forelimb proprioception assessment showed that 80% of the rats receiving the transplants had functional improvement over six weeks of the study. The adhesive removal test showed that the time taken for the rats to notice the adhesive label and remove it almost returned to the normal level after receiving the transplants. Transplanted cells were identified with the expression of green fluorescent protein (ZsGreen). Some regeneration fibres immunostained for neurofilament (NF) or traced by biotinylated dextran amine (BDA) in the injury area were associated with the transplanted cells. The evidence in this study improves the prospect of clinical application using OECs from the olfactory mucosa to treat CNS injuries.

Olfactory ensheathing cells: Unique glial cells promising for treatments of spinal cord injury

Spinal cord injury (SCI) is generally the consequence of physical damage, which may result in devastating consequences such as paraplegia or paralysis. Some certain candidates for SCI repair are olfactory ensheathing cells (OECs), which are unique glial cells located in the transition region of the peripheral nervous system and central nervous system and perform neuron regeneration in the olfactory system throughout life. Culture studies have clarified many properties of OECs, but their mechanisms of actions are not fully understood. Successful results achieved in animal models showcased that SCI treatment with OEC transplants is suitable for clinical trials. However, clinical trials are limited by difficulties like cell acquisition for autograft transplantation. Despite the improvements in both animal and clinical studies so far, there is still insufficient information about the mechanism of actions, adverse effects, proper application methods, effective subtypes, and sources of cells. This review summarizes pre-clinical and clinical literature focused on the cellular characterization of both OECs in vitro and post-transplantation. We highlight the roles and effects of OECs on (a) the injury-induced glial milieu, (b) neuronal growth/regeneration, and (c) functional recovery after injury. Due to the shown benefits of OECs with in vitro and animal studies and a limited number of clinical trials, where safety and effectivity were shown, it is necessary to conduct more studies on OECs to obtain effective and feasible treatment methods.

Using Humidity to Control the Morphology and Properties of Electrospun BioPEGylated Polyhydroxybutyrate Scaffolds

Electrospinning produces nanofibrous scaffolds with potential for tissue engineering and wound repair. Spinning parameters control scaffold morphology and properties. BioPEGylation of polyhydroxybutyrate (PHB) introduces terminal hydrophilic groups into the hydrophobic chain, making this natural-synthetic hybrid copolymer more susceptible to humidity. Varying the humidity from 10 to 50% RH during electrospinning had a relatively little effect on polyhydroxybutyrate (PHB) average fiber and pore diameters, which remained around 3.0 and 8.7 μm, respectively. In contrast, fiber and pore diameters for electrospun bioPEGylated PHB scaffolds varied significantly with humidity, peaking at 30% RH (5.5 and 14.1 μm, respectively). While scaffolds showed little change, hydrophobicity decreased linearly with humidity during electrospinning. Compared to solvent-cast films, electrospun scaffolds showed significantly greater average cell spread. A 108% increase for olfactory ensheathing cells (OECs) cultivated on bioPEGylated PHB scaffolds was proportionally greater than their counterparts on electrospun PHB scaffolds, (70%). OECS grown on BioPEGylated PHB scaffolds were over twice the size, 260 ± 20 μm diameter, than those on PHB electrospun scaffolds, 110 ± 18 μm diameter. Electrospun scaffolds also promoted cell health compared to their solvent-cast counterparts, with increases in the mitochondrial activity of 165 ± 13 and 196 ± 13% for PHB and bioPEGylated PHB, respectively. OECS cultivated on electrospun scaffolds of bioPEGylated PHB had significantly better membrane integrities compared to their counterparts on solvent-cast films, 47 ± 5% reducing to 17 ± 6%. The combination of bioPEGylation and humidity during electrospinning permitted significant controllable changes to scaffold morphology and properties. These changes resulted in the significantly greater promotion of cell growth on electrospun bioPEGylated PHB scaffolds compared to their solvent-cast counterparts and electrospun PHB.

Olfactory Ensheathing Cells express both Ghrelin and Ghrelin Receptor in vitro: a new hypothesis in favor of a neurotrophic effect

Olfactory Ensheathing Cells (OECs) are glial cells able to secrete different neurotrophic growth factors and thus promote axonal growth, also acting as a mechanical support. In the olfactory system, during development, they drive the non-myelinated axons of the Olfactory Receptor Neurons (ORNs) towards the Olfactory Bulb (OB). Ghrelin (Ghre), a gut-brain peptide hormone, and its receptor (GHS-R 1a) are expressed in different parts of the central nervous system. In the last few years, this peptide has stimulated particular interest as results show it to be a neuroprotective factor with antioxidant, anti-inflammatory and anti-apoptotic properties. Our previous studies showed that OB mitral cells express Ghre, thus being able to play an important role in regulating food behavior in response to odors. In this study, we investigated the presence of Ghre and GHS-R 1a in primary mouse OECs. The expression of both Ghre and its receptor was assessed by an immunocytochemical technique, Western Blot and Polymerase Chain Reaction (PCR) analysis. Our results demonstrated that OECs are able to express both Ghre and GHS-R 1a and that these proteins are detectable after extensive passages in vitro; in addition, PCR analysis further confirmed these data. Therefore, we can hypothesize that Ghre and GHS-R 1a interact with a reinforcement function, in the peripheral olfactory circuit, providing a neurotrophic support to the synaptic interaction between ORNs and mitral cells.

Transplantation of cultured olfactory mucosal cells rescues optic nerve axons in a rat glaucoma model

PURPOSE

To determine whether transplantation of olfactory mucosal cells (OMCs) is able to rescue the loss of optic nerve axons after the intraocular pressure (IOP) is elevated in rats.

METHODS

The IOP was raised by injection of magnetic microspheres into the anterior chamber of the eye. OMCs cultured from the adult olfactory mucosa were transplanted into the region of the optic disc.

RESULTS

We demonstrated that although the raised IOP returned to its normal level at six weeks, there was an irreversible 58% loss of optic nerve axons in the control group. However, the loss of the axons was reduced to 23% in the group with the transplanted OMCs. The Pattern Electroretinograms (pERG) showed that the decrement of the voltage amplitudes in association with the raised IOP was significantly alleviated in the group with transplantation of OMC.

CONCLUSIONS

Transplantation of OMCs is able to rescue loss of optic nerve axons induced by raised IOP in the rats. The pERG recording suggested that the functional activities of the axons are also protected.

TRANSLATIONAL RELEVANCE

The results demonstrated the ability of the transplanted OMCs to protect against the loss of the optic nerve axons and the loss of function caused by raised IOPs. The findings provide a basis for future human clinical trials by autografting OMCs from autologous nasal epithelial biopsies to treat or delay glaucoma diseases.

Clinical translation of stem cell based interventions for spinal cord injury - Are we there yet?

Recent advances in basic science in research related to spinal cord injury (SCI) and regeneration have led to a variety of novel experimental therapeutics designed to promote functionally effective axonal regrowth and sprouting. Stem cell and other cellular interventions have gained lot of attention due to their immense potential of regeneration. These interventions have been tested for their efficacy in case of SCI both at the pre-clinical and clinical level. In this review we critically discuss the published literature on the cellular interventions for SCI and their clinical applications with respect to the strength of evidence established by these studies. The need to curb unethical practice of offering unproven stem cell "therapies" for SCI at a global level is also discussed.

Combinatorial Therapies After Spinal Cord Injury: How Can Biomaterials Help?

Traumatic spinal cord injury (SCI) results in an immediate loss of motor and sensory function below the injury site and is associated with a poor prognosis. The inhibitory environment that develops in response to the injury is mainly due to local expression of inhibitory factors, scarring and the formation of cystic cavitations, all of which limit the regenerative capacity of endogenous or transplanted cells. Strategies that demonstrate promising results induce a change in the microenvironment at- and around the lesion site to promote endogenous cell repair, including axonal regeneration or the integration of transplanted cells. To date, many of these strategies target only a single aspect of SCI; however, the multifaceted nature of SCI suggests that combinatorial strategies will likely be more effective. Biomaterials are a key component of combinatorial strategies, as they have the potential to deliver drugs locally over a prolonged period of time and aid in cell survival, integration and differentiation. Here we summarize the advantages and limitations of widely used strategies to promote recovery after injury and highlight recent research where biomaterials aided combinatorial strategies to overcome some of the barriers of spinal cord regeneration.

Direct conversion of mouse fibroblasts to GABAergic neurons with combined medium without the introduction of transcription factors or miRNAs

Degeneration or loss of GABAergic neurons frequently may lead to many neuropsychiatric disorders such as epilepsy and autism spectrum disorders. So far no clinically effective therapies can slow and halt the progression of these diseases. Cell-replacement therapy is a promising strategy for treatment of these neuropsychiatric diseases. Although increasing evidence showed that mammalian somatic cells can be directly converted into functional neurons using specific transcription factors or miRNAs via virus delivery, the application of these induced neurons is potentially problematic, due to integration of vectors into the host genome, which results in the disruption or dysfunction of nearby genes. Here, we show that mouse fibroblasts could be efficiently reprogrammed into GABAergic neurons in a combined medium composed of conditioned medium from neurotrophin-3 modified Olfactory Ensheathing Cells (NT3-OECs) plus SB431542, GDNF and RA. Following 3 weeks of induction, these cells derived from fibroblasts acquired the morphological and phenotypical GABAerigic neuronal properties, as demonstrated by the expression of neuronal markers including Tuj1, NeuN, Neurofilament-L, GABA, GABA receptors and GABA transporter 1. More importantly, these converted cells acquired neuronal functional properties such as synapse formation and increasing intracellular free calcium influx when treated with BayK, a specific activator of L-type calcium channel. Therefore, our findings demonstrate for the first time that fibroblasts can be directly converted into GABAergic neurons without ectopic expression of specific transcription factors or miRNA. This study may provide a promising cell source for the application of cell replacement therapy in neuropsychiatric disorders.

Autologous Olfactory Lamina Propria Transplantation for Chronic Spinal Cord Injury: Three-Year Follow-Up Outcomes From a Prospective Double-Blinded Clinical Trial

We did a clinical trial to determine whether olfactory mucosa lamina propria (OLP) transplants promote regeneration and functional recovery in chronic human spinal cord injury (SCI). The trial randomized 12 subjects to OLP transplants (n = 8) or control sham surgery (n = 4). The subjects received magnetic resonance imaging (MRI), electromyography (EMG), urodynamic study (UDS), American Spinal Injury Association impairment scale (AIS), and other functional assessments. OLP-transplanted subjects recovered more motor, sensory, and bladder function compared to sham-operated subjects. At 3 years after OLP transplant, one patient improved from AIS A to C and another recovered from AIS A to B, two recovered more than three segmental sensory levels, two had less spasticity, two had altered H-reflexes and SSEP, two regained bladder and anorectal sensation and had improved bladder compliance on UDS. OLP-treated patients had partial or complete tissue bridges at the injury site compared to cavitary gaps in sham-operated patients. The limited recovery suggests that OLP transplants alone do not have significant benefits but may provide a rationale for larger randomized trials or combination therapies.

Experimental reconstruction of the injured spinal cord

Injury to the spinal cord, with its pathological sequelae, results in a permanent neurological deficit. With currently available tools at hand, there is very little that clinicians can do to treat such a condition with the view of helping patients with spinal cord injury (SCI). On the other hand, in the last 20 years experimental research has brought new insights into the pathophysiology of spinal cord injury; we can divide the time course into 3 phases: primary injury (the time of traumatic impact and the period immediately afterwards), the secondary phase (cell death, inflammation, ischemia), and the chronic phase (scarring, demyelination, cyst formation). Increased knowledge about the pathophysiology of SCI can stimulate the development of new therapeutic modalities and approaches, which may be feasible in the future in clinical practice. Some of the most promising experimental therapies include: neurotrophic factors, enzymes and antibodies against inhibitory molecules (such as Nogo), activated macrophages, stem cells and bridging scaffolds. Their common goal is to reconstitute the damaged tissue in order to recover the lost function. In the current review, we focus on some of the recent developments in experimental SCI research.

In vitro neural differentiation of bone marrow stromal cells induced by cocultured olfactory ensheathing cells

Bone marrow stromal cells (BMSCs) could be induced to differentiate into neural cells under certain conditions, nevertheless, optimal protocols that could be reproducible and reliable in generating transplantable BMSCs in vitro are still not available. We studied for the first time the neural differentiation of BMSCs induced by coculturing with olfactory ensheathing cells (OECs). BMSCs and OECs were isolated from bone marrow and nasal olfactory lamina propria of adult SD rats respectively, then brought to coculture with transwell culture dishes. At various time points (0h, 6h, 12h, 24h, 72h, 1 week and 2 weeks post-coculture), BMSCs were morphologically observed and processed for immunofluorescence and reverse transcription-polymerase chain reaction (RT-PCR). The number of cells assuming neural morphology dramatically increased at 1- and 2-week-post-coculture, so as the number of immunoreactive cells labeled by neural markers NSE, beta-III-tubulin, MAP2, GFAP and p75(NTR). Our findings demonstrate that BMSCs can efficiently differentiate into neural cells when coculturing with OECs, and the present protocol provides an alternative neurogenesis pathway for generating sufficient numbers of neural cells from BMSCs.

Combined transplantation of neural stem cells and olfactory ensheathing cells improves the motor function of rats with intracerebral hemorrhage

OBJECTIVE

To investigate the effects of combined transplantation of neural stem cells (NSC) and olfactory ensheathing cells (OEC) on the motor function of rats with intracerebral hemorrhage.

METHODS

In three days after a rat model of caudate nucleus hemorrhage was established, NSCs and OEC, NSC, OEC (from embryos of Wistar rats) or normal saline were injected into hematomas of rats in combined transplantation group, NSC group, OEC group, and control group, respectively. Damage of neural function was scored before and in 3, 7, 14, 30 days after operation. Tissue after transplantation was observed by immunocytochemistry staining.

RESULTS

The scores for the NSC, OEC and co-transplantation groups were significantly lower in 14 and 30 days after operation than in 3 days after operation (P < 0.05). The scores for the NSC and OEC groups were significantly lower than those for the control group only in 30 days after operation (P < 0.05), while the difference for the NSC-OEC group was significant in 14 days after operation (P < 0.05). Immunocytochemistry staining revealed that the transplanted OEC and NSC could survive, migrate and differentiate into neurons, astrocytes, and oligodendrocytes. The number of neural precursor cells was greater in the NSC and combined transplantation groups than in the control group. The number of neurons differentiated from NSC was significantly greater in the co-transplantation group than in the NSC group.

CONCLUSION

Co-transplantation of NSC and OEC can promote the repair of injured tissue and improve the motor function of rats with intracerebral hemorrhage.

Current tissue engineering and novel therapeutic approaches to axonal regeneration following spinal cord injury using polymer scaffolds

This review highlights current tissue engineering and novel therapeutic approaches to axonal regeneration following spinal cord injury. The concept of developing 3-dimensional polymer scaffolds for placement into a spinal cord transection model has recently been more extensively explored as a solution for restoring neurologic function after injury. Given the patient morbidity associated with respiratory compromise, the discrete tracts in the spinal cord conveying innervation for breathing represent an important and achievable therapeutic target. The aim is to derive new neuronal tissue from the surrounding, healthy cord that will be guided by the polymer implant through the injured area to make functional reconnections. A variety of naturally derived and synthetic biomaterial polymers have been developed for placement in the injured spinal cord. Axonal growth is supported by inherent properties of the selected polymer, the architecture of the scaffold, permissive microstructures such as pores, grooves or polymer fibres, and surface modifications to provide improved adherence and growth directionality. Structural support of axonal regeneration is combined with integrated polymeric and cellular delivery systems for therapeutic drugs and for neurotrophic molecules to regionalize growth of specific nerve populations.

Unique in vivo properties of olfactory ensheathing cells that may contribute to neural repair and protection following spinal cord injury

Olfactory ensheathing cells (OECs) are specialized glial cells that guide olfactory receptor axons from the nasal mucosa into the brain where they make synaptic contacts in the olfactory bulb. While a number of studies have demonstrated that in vivo transplantation of OECs into injured spinal cord results in improved functional outcome, precise cellular mechanisms underlying this improvement are not fully understood. Current thinking is that OECs can encourage axonal regeneration, provide trophic support for injured neurons and for angiogenesis, and remyelinate axons. However, Schwann cell (SC) transplantation also results in significant functional improvement in animal models of spinal cord injury. In culture SCs and OECs share a number of phenotypic properties such as expression of the low affinity NGF receptor (p75). An important area of research has been to distinguish potential differences in the in vivo behavior of OECs and SCs to determine if one cell type may offer greater advantage as a cellular therapeutic candidate. In this review we focus on several unique features of OECs when they are transplanted into the spinal cord.

Single-cell printing to form three-dimensional lines of olfactory ensheathing cells

Biological laser printing (BioLP) is a unique tool capable of printing high resolution two- and three-dimensional patterns of living mammalian cells, with greater than 95% viability. These results have been extended to primary cultured olfactory ensheathing cells (OECs), harvested from adult Sprague-Dawley rats. OECs have been found to provide stimulating environments for neurite outgrowth in spinal cord injury models. BioLP is unique in that small load volumes ( approximately microLs) are required to achieve printing, enabling low numbers of OECs to be harvested, concentrated and printed. BioLP was used to form several 8 mm lines of OECs throughout a multilayer hydrogel scaffold. The line width was as low as 20 microm, with most lines comprising aligned single cells. Fluorescent confocal microscopy was used to determine the functionality of the printed OECs, to monitor interactions between printed OECs, and to determine the extent of cell migration throughout the 3D scaffold. High-resolution printing of low cell count, harvested OECs is an important advancement for in vitro study of cell interactions and functionality. In addition, these cell-printed scaffolds may provide an alternative for spinal cord repair studies, as the single-cell patterns formed here are on relevant size scales for neurite outgrowth.

Multipotent stem and progenitor cells of the olfactory epithelium

In recent decades, a wide spectrum of fetal and embryonic stem and progenitor cells were used for cell therapy of diseases of the central nervous system, but the olfactory glial ensheathing cells exhibited certain advantages due to their biological properties and capacity to stimulate regeneratory processes in spinal injury. The therapeutic effect of a heterogeneous complex of olfactory epithelial cells is more pronounced; apart from glial ensheathing cells, this complex includes fibroblasts, Schwann cells, stem and progenitor cells of this structure. The use of minimally invasive methods for isolation of human olfactory epithelial tissue is important for clinical practice, because they provide cells for autologous transplantation and rule out graft rejection immune reaction and the risk of transmission viral infection and transfer of genetic defects, which can be associated with allotransplantation.

Repair of neural pathways by olfactory ensheathing cells

Damage to nerve fibre pathways results in a devastating loss of function, due to the disconnection of nerve fibres from their targets. However, some recovery does occur and this has been correlated with the formation of new (albeit abnormal) connections. The view that an untapped growth potential resides in the adult CNS has led to various attempts to stimulate the repair of disconnectional injuries. A key factor in the failure of axonal regeneration in the CNS after injury is the loss of the aligned glial pathways that nerve fibres require for their elongation. Transplantation of cultured adult olfactory ensheathing cells into lesions is being investigated as a procedure to re-establish glial pathways permissive for the regeneration of severed axons.

Therapeutic interventions after spinal cord injury

Spinal cord injury (SCI) can lead to paraplegia or quadriplegia. Although there are no fully restorative treatments for SCI, various rehabilitative, cellular and molecular therapies have been tested in animal models. Many of these have reached, or are approaching, clinical trials. Here, we review these potential therapies, with an emphasis on the need for reproducible evidence of safety and efficacy. Individual therapies are unlikely to provide a panacea. Rather, we predict that combinations of strategies will lead to improvements in outcome after SCI. Basic scientific research should provide a rational basis for tailoring specific combinations of clinical therapies to different types of SCI.

Autologous olfactory glial cell transplantation is reliable and safe in naturally occurring canine spinal cord injury

Intraspinal transplantation of olfactory glial cells (OGC) has produced well-defined beneficial effects in experimental rodent models of spinal cord injury (SCI) and therefore has considerable promise as a treatment for severe SCI in human patients. In this study, we used clinical canine cases of severe SCI to determine whether derivation and transplantation of OGC from an autologous source was feasible. From the nerve fiber layer of a single olfactory bulb, we were able to generate 5 x 10(6) cells from each patient within 3 weeks. Of this population, 72% were p75(+) OGC, 20% were meningeal cells, and the remainder mainly astrocytes. Intraspinal transplantation was not associated with any observable long- or short-term complications.

La réparation nerveuse périphérique : 30 siècles de recherche

INTRODUCTION

Nerve injury compromises sensory and motor functions. Techniques of peripheral nerve repair are based on our knowledge regarding regeneration. Microsurgical techniques introduced in the late 1950s and widely developed for the past 20 years have improved repairs. However, functional recovery following a peripheral mixed nerve injury is still incomplete.

STATE OF ART

Good motor and sensory function after nerve injury depends on the reinnervation of the motor end plates and sensory receptors. Nerve regeneration does not begin if the cell body has not survived the initial injury or if it is unable to initiate regeneration. The regenerated axons must reach and reinnervate the appropriate target end-organs in a timely fashion. Recovery of motor function requires a critical number of motor axons reinnervating the muscle fibers. Sensory recovery is possible if the delay in reinnervation is short. Many additional factors influence the success of nerve repair or reconstruction. The timing of the repair, the level of injury, the extent of the zone of injury, the technical skill of the surgeon, and the method of repair and reconstruction contribute to the functional outcome after nerve injury.

CONCLUSION

This review presents the recent advances in understanding of neural regeneration and their application to the management of primary repairs and nerve gaps.

Defining the role of olfactory ensheathing cells in facilitating axon remyelination following damage to the spinal cord

Olfactory ensheathing cells (OECs) are unique cells that are responsible for the successful regeneration of olfactory axons throughout the life of adult mammals. More than a decade of research has shown that implantation of OECs may be a promising therapy for damage to the nervous system, including spinal cord injury. Based on this research, several clinical trials worldwide have been initiated that use autologous transplantation of olfactory tissue containing OECs into the damaged spinal cord of humans. However, research from several laboratories has challenged the widely held belief that OECs are directly responsible for myelinating axons and promoting axon regeneration. The purpose of this review is to provide a working hypothesis that integrates several current ideas regarding the mechanisms of the beneficial effects of OECs. Specifically, OECs promote axon regeneration and functional recovery indirectly by augmenting the endogenous capacity of host Schwann cells to invade the damaged spinal cord. Together with Schwann cells, OECs create a 3-dimensional matrix that provides a permissive microenvironment for successful axon regeneration in the adult mammalian central nervous system.

Potential stem cell therapy and application in neurotrauma

Traumatic brain injury results from a sudden and external physical insult to the head, which is often accompanied by motor and cognitive impairment. Neurotrauma is characterized not only by focal abnormalities, but rather by multifocal, or even global structural and functional disturbances of the brain network. The impact initially causes necrotic cell death in the underlying tissue, followed by apoptotic cell death in the surrounding tissue due to multiple subsequent events, such as ischemia, excitotoxicity and altered gene expression. These pathological conditions are associated with high morbidity and mortality. Despite the high medical and economical relevance of neurotrauma there are currently no sufficient treatments. Supplementary therapeutic strategies have to be established. Many types of stem cells have the ability to engraft diffusely and become integral members of structures throughout the host CNS. Intrinsic factors appear to derive spontaneously from stem cells and seem to be capable of neuroprotective and/or neuroregenerative functions. Furthermore stem cells can be readily engineered to express specific genes. Such observations suggest that stem cells might participate in reconstructing the molecular and cellular milieu of traumatized brains. In this paper, the state of stem cell research is reviewed and its possible application in neurotrauma will be discussed.

Low power laser irradiation alters gene expression of olfactory ensheathing cells in vitro

BACKGROUND AND OBJECTIVES

Both photobiomodulation (PBM) and olfactory ensheathing cells (OECs) transplantation improve recovery following spinal cord injury. However, neither the combination of these two therapies nor the effect of light on OECs has been reported. The purpose of this study was to determine the effect of light on OEC activity in vitro.

MATERIALS AND METHODS

OECs were purified from adult rat olfactory bulbs and exposed to 810 nm light (150 mW; 0, 0.2, or 68 J/cm(2)). After 7-21 days in vitro, cells underwent immunocytochemistry or RNA extraction and RT-PCR.

RESULTS

Analysis of immunolabeling revealed a significant decrease in fibronectin expression in the cultures receiving 68 J/cm(2). Analysis of gene expression revealed a significant (P < 0.05) increase in brain derived neurotrophic factor (BDNF), glial derived neurotrophic factor (GDNF), and collagen expression in the 0.2 J/cm(2) group in comparison to the non-irradiated and 68 J/cm(2) groups. OEC proliferation was also found to significantly increase in both light treated groups in comparison to the control group (P < 0.001).

CONCLUSIONS

These results demonstrate that low and high dosages of PBM alter OEC activity, including upregulation of a number of neurotrophic growth factors and extracellular matrix proteins known to support neurite outgrowth. Therefore, the application of PBM in conjunction with OEC transplantation warrants consideration as a potential combination therapy for spinal cord injury.

Cellular transplantation strategies for spinal cord injury and translational neurobiology

Basic science advances in spinal cord injury and regeneration research have led to a variety of novel experimental therapeutics designed to promote functionally effective axonal regrowth and sprouting. Among these interventions are cell-based approaches involving transplantation of neural and non-neural tissue elements that have potential for restoring damaged neural pathways or reconstructing intraspinal synaptic circuitries by either regeneration or neuronal/glial replacement. Notably, some of these strategies (e.g., grafts of peripheral nerve tissue, olfactory ensheathing glia, activated macrophages, marrow stromal cells, myelin-forming oligodendrocyte precursors or stem cells, and fetal spinal cord tissue) have already been translated to the clinical arena, whereas others have imminent likelihood of bench-to-bedside application. Although this progress has generated considerable enthusiasm about treating what once was thought to be a totally incurable condition, there are many issues to be considered relative to treatment safety and efficacy. The following review reflects on different experimental applications of intraspinal transplantation with consideration of the underlying pathological, pathophysiological, functional, and neuroplastic responses to spinal trauma that such treatments may target along with related issues of procedural and biological safety. The discussion then moves to an overview of ongoing and completed clinical trials to date. The pros and cons of these endeavors are considered, as well as what has been learned from them. Attention is primarily directed at preclinical animal modeling and the importance of patterning clinical trials, as much as possible, according to laboratory experiences.

Neural tissue engineering: strategies for repair and regeneration

Nerve regeneration is a complex biological phenomenon. In the peripheral nervous system, nerves can regenerate on their own if injuries are small. Larger injuries must be surgically treated, typically with nerve grafts harvested from elsewhere in the body. Spinal cord injury is more complicated, as there are factors in the body that inhibit repair. Unfortunately, a solution to completely repair spinal cord injury has not been found. Thus, bioengineering strategies for the peripheral nervous system are focused on alternatives to the nerve graft, whereas efforts for spinal cord injury are focused on creating a permissive environment for regeneration. Fortunately, recent advances in neuroscience, cell culture, genetic techniques, and biomaterials provide optimism for new treatments for nerve injuries. This article reviews the nervous system physiology, the factors that are critical for nerve repair, and the current approaches that are being explored to aid peripheral nerve regeneration and spinal cord repair.

Morphological plasticity of olfactory ensheathing cells is regulated by cAMP and endothelin-1

Olfactory ensheathing cells (ECs) are a promising tool for the repair of injury in the adult central nervous system. However, important aspects of the cell biology of ECs remain unclear, such as whether ECs exist as a single population or as two subpopulations with Schwann cell-like and astrocyte-like characteristics. The morphologies of these subpopulations are used as defining characteristics, yet ECs are known to be morphologically plastic. To elucidate this apparent inconsistency, we investigated the morphological plasticity of ECs in culture. We defined purified ECs as immunopositive for both p75 neurotrophin receptor and glial fibrillary acidic protein. In MEM (D)-valine modification + 10% dialyzed fetal calf serum, 87%-90% of ECs displayed a flat morphology. In three different serum-free media (N2 medium, neurobasal medium + B27 supplement, and DMEM/F-12 medium + G5 supplement), 78%-84% of ECs displayed process-bearing morphology. Ensheathing cells switched reversibly between these morphologies within a day of the serum conditions being changed. Exposure to 1 nM endothelin-1 in serum-free medium prevented the switch from flat to process-bearing morphology, while 1 mM dibutyryl cAMP accelerated this change. The effects of both agents were completely reversible and similar to that reported for astrocytes. Both flat and process-bearing ECs were immunopositive for brain-derived neurotrophic factor, nerve growth factor, neurotrophin-4, and TrkB but not TrkA. Together, these results suggest that ECs exist as a single morphologically plastic population.

Use of a cell line to investigate olfactory ensheathing cell-enhanced axonal regeneration

Olfactory ensheathing cells (OECs), a unique type of macroglia required for normal olfactory axonal regeneration throughout the lifetime of an individual, have been shown to have regeneration-enhancing properties when used to treat various neuronal injuries. Availability of OECs is a hurdle facing future clinical use of the cells for spinal cord injury (SCI) therapy. The number of OECs that can realistically be harvested from each animal is limited, and ensuring a pure cell population is difficult. We have begun to characterize a nonsyngeneic strain of OECs, i.e., from a homogenous OEC clonal cell line (nOECs). The purpose of this study was to determine whether nOECs have the same properties and provide the same functional recovery after SCI, as primary cultures of OECs. The results indicate that nOECs survive in vivo, produce growth-promoting proteins, and possess regeneration-promoting capabilities. Spinal cord injured rats that were treated with nOECs performed significantly better on functional tests than injured control animals beginning at 5 weeks after operation. In summary, evidence of nOEC regeneration-promoting capabilities suggests that this cell line can be used as potential therapy in SCI research.

Recent advances in pathophysiology and treatment of spinal cord injury

Thirty years ago, patients with spinal cord injury (SCI) and their families were told "nothing can be done" to improve function. Since the SCI patient population is reaching normal life expectancy through better health care, it has become an obviously worthwhile enterprise to devote considerable research effort to SCI. Targets for intervention in SCI toward improved function have been identified using basic research approaches and can be simplified into a list: (1) reduction of edema and free-radical production, (2) rescue of neural tissue at risk of dying in secondary processes such as abnormally high extracellular glutamate concentrations, (3) control of inflammation, (4) rescue of neuronal/glial populations at risk of continued apoptosis, (5) repair of demyelination and conduction deficits, (6) promotion of neurite growth through improved extracellular environment, (7) cell replacement therapies, (8) efforts to bridge the gap with transplantation approaches, (9) efforts to retrain and relearn motor tasks, (10) restoration of lost function by electrical stimulation, and (11) relief of chronic pain syndromes. Currently, over 70 clinical trials are in progress worldwide. Consequently, in this millennium, unlike in the last, no SCI patient will have to hear "nothing can be done."

Stem cells in the treatment of amyotrophic lateral sclerosis (ALS)

Until fairly recently, interest in stem cells was restricted to neurobiology studies on the principles of embryonic development. This situation has changed rapidly in the last few years when neuronal stems and precursors were isolated in vitro, thus allowing expansion and controlled differentiation of selective populations of neuronal cells. This theoretically unlimited reserve would then supply specific cells for transplantation in diseases characterized by widespread degeneration of selective cell populations as motor neurons in Amyotrophic Lateral Sclerosis (ALS). The recent evidence of cell transdifferentiation has further amplified the potential therapeutic use of stem cells. Stem cell technology is at an early stage but the desperate need for a therapy in ALS patients may legitimize clinical trials in absence of conclusive scientific evidence. This paper discusses the premises for stem cell therapy in ALS.