Potential of olfactory ensheathing cells from different sources for spinal cord repair

The role of olfactory ensheathing cells in the repair of nerve injury

Cell transplantation has brought about a breakthrough in the treatment of nerve injuries, and the efficacy of cell transplantation compared to drug and surgical therapies is very exciting. In terms of transplantation targets, the classic cells include neural stem cells (NSCs) and Schwann cells, while a class of cells that can exist and renew throughout the life of the nervous system - olfactory ensheathing cells (OECs) - has recently been discovered in the olfactory system. OECs not only encircle the olfactory nerves but also act as macrophages and play an innate immune role. OECs can also undergo reprogramming to transform into neurons and survive and mature after transplantation. Currently, many studies have confirmed the repairing effect of OECs after transplantation into injured nerves, and safe and effective results have been obtained in clinical trials. However, the specific repair mechanism of OECs among them is not quite clear. For this purpose, we focus here on the repair mechanisms of OECs, which are summarized as follows: neuroprotection, secretion of bioactive factors, limitation of inflammation and immune regulation, promotion of myelin and axonal regeneration, and promotion of vascular proliferation. In addition, integrating the aspects of harvesting, purification, and prognosis, we found that OECs may be more suitable for transplantation than NSCs and Schwann cells, but this does not completely discard the value of these classical cells. Overall, OECs are considered to be one of the most promising transplantation targets for the treatment of nerve injury disorders.

Designing a Clinical Trial with Olfactory Ensheathing Cell Transplantation-Based Therapy for Spinal Cord Injury: A Position Paper

Spinal cord injury (SCI) represents an urgent unmet need for clinical reparative therapy due to its largely irreversible and devastating effects on patients, and the tremendous socioeconomic burden to the community. While different approaches are being explored, therapy to restore the lost function remains unavailable. Olfactory ensheathing cell (OEC) transplantation is a promising approach in terms of feasibility, safety, and limited efficacy; however, high variability in reported clinical outcomes prevent its translation despite several clinical trials. The aims of this position paper are to present an in-depth analysis of previous OEC transplantation-based clinical trials, identify existing challenges and gaps, and finally propose strategies to improve standardization of OEC therapies. We have reviewed the study design and protocols of clinical trials using OEC transplantation for SCI repair to investigate how and why the outcomes show variability. With this knowledge and our experience as a team of biologists and clinicians with active experience in the field of OEC research, we provide recommendations regarding cell source, cell purity and characterisation, transplantation dosage and format, and rehabilitation. Ultimately, this position paper is intended to serve as a roadmap to design an effective clinical trial with OEC transplantation-based therapy for SCI repair.

Recombinant Adenoviruses for Delivery of Therapeutics Following Spinal Cord Injury

The regeneration of nerve tissue after spinal cord injury is a complex and poorly understood process. Medication and surgery are not very effective treatments for patients with spinal cord injuries. Gene therapy is a popular approach for the treatment of such patients. The delivery of therapeutic genes is carried out in a variety of ways, such as direct injection of therapeutic vectors at the site of injury, retrograde delivery of vectors, and ex vivo therapy using various cells. Recombinant adenoviruses are often used as vectors for gene transfer. This review discusses the advantages, limitations and prospects of adenovectors in spinal cord injury therapy.

Considering the Cellular Composition of Olfactory Ensheathing Cell Transplants for Spinal Cord Injury Repair: A Review of the Literature

Olfactory ensheathing cells (OECs) are specialized glia cells of the olfactory system that support the continual regeneration of olfactory neurons throughout adulthood. Owing to their pro-regenerative properties, OECs have been transplanted in animal models of spinal cord injuries (SCI) and trialed in clinical studies on SCI patients. Although these studies have provided convincing evidence to support the continued development of OEC transplantation as a treatment option for the repair of SCI, discrepancies in the reported outcome has shown that OEC transplantation requires further improvement. Much of the variability in the reparative potential of OEC transplants is due to the variations in the cell composition of transplants between studies. As a result, the optimal cell preparation is currently a subject of debate. Here we review, the characterization as well as the effect of the cell composition of olfactory cell transplantation on therapeutic outcome in SCI. Firstly, we summarize and review the cell composition of olfactory cell preparations across the different species studied prior to transplantation. Since the purity of cells in olfactory transplants might affect the study outcome we also examine the effect of the proportions of OECs and the different cell types identified in the transplant on neuroregeneration. Finally, we consider the effect of the yield of cells on neuroregeneration by assessing the cell dose of transplants on therapeutic outcome.

The Effect of Transplantation of Olfactory Ensheathing Cells on the Size of Posttraumatic Spinal Cord Cysts

We studied the effect of transplantation of ensheathing cells obtained from the olfactory mucosa of rats and humans on the size of posttraumatic spinal cord cysts. MRI examination showed that transplantation of these cells into experimental posttraumatic cysts of the spinal cord led to a significant decrease in cyst volume and even their complete disappearance in two animals receiving transplantation of rat or human cells. These findings attested to regenerative processes developing as a result of ensheathing cell transplantation. Further studies in this field will be aimed at elucidation of the mechanisms underlying spinal cord regeneration in the area of posttraumatic cysts after transplantation of ensheathing cells.

Comparison of the effects of two therapeutic strategies based on olfactory ensheathing cell transplantation and repetitive magnetic stimulation after spinal cord injury in female mice

Spinal cord injury (SCI) is a debilitating condition, which leads to a permanent loss of functions below the injury site. The events which take place after SCI are characterized by cellular death, release of inhibitory factors, and inflammation. Many therapies have been studied to cure SCI, among them magnetic stimulation aims to reduce the secondary damages in particular by decreasing apoptosis, while, cellular transplantation promotes neuroregeneration by enhancing axonal regrowth. In the present study, we compared individually primary olfactory ensheathing cell (OEC) transplantation and repetitive trans‐spinal magnetic stimulation (rTSMS) and then, we combined these two therapeutic approaches on tissue repair and functional recovery after SCI. To do so, SCIs were performed at Th10 level on female C57BL/6 mice, which were randomized into four groups: SCI, SCI + primary bOECs, SCI + STM, SCI + primary bulbar olfactory ensheathing cells (bOECs) + stimulation (STM). On these animals bioluminescence, immunohistological, and behavioral experiments were performed after SCI. Our results show that rTSMS has beneficial effect on the modulation of spinal scar by reducing fibrosis, demyelination, and microglial cell activation and by increasing the astroglial component of the scar, while, primary bOEC transplantation decreases microglial reactivity. At the opposite, locotronic experiments show that both treatments induce functional recovery. We did not observed any additional effect by combining the two therapeutic approaches. Taken together, the present study indicates that primary bOEC transplantation and rTSMS treatment act through different mechanisms after SCI to induce functional recovery. In our experimental paradigm, the combination of the two therapies does not induce any additional benefit.

Delivery of chondroitinase by canine mucosal olfactory ensheathing cells alongside rehabilitation enhances recovery after spinal cord injury

Spinal cord injury (SCI) can cause chronic paralysis and incontinence and remains a major worldwide healthcare burden, with no regenerative treatment clinically available. Intraspinal transplantation of olfactory ensheathing cells (OECs) and injection of chondroitinase ABC (chABC) are both promising therapies but limited and unpredictable responses are seen, particularly in canine clinical trials. Sustained delivery of chABC presents a challenge due to its thermal instability; we hypothesised that transplantation of canine olfactory mucosal OECs genetically modified ex vivo by lentiviral transduction to express chABC (cOEC-chABC) would provide novel delivery of chABC and synergistic therapy. Rats were randomly divided into cOEC-chABC, cOEC, or vehicle transplanted groups and received transplant immediately after dorsal column crush corticospinal tract (CST) injury. Rehabilitation for forepaw reaching and blinded behavioural testing was conducted for 8 weeks. We show that cOEC-chABC transplanted animals recover greater forepaw reaching accuracy on Whishaw testing and more normal gait than cOEC transplanted or vehicle control rats. Increased CST axon sprouting cranial to the injury and serotonergic fibres caudal to the injury suggest a mechanism for recovery. We therefore demonstrate that cOECs can deliver sufficient chABC to drive modest functional improvement, and that this genetically engineered cellular and molecular approach is a feasible combination therapy for SCI.

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.

Transplantation of activated olfactory ensheathing cells by curcumin strengthens regeneration and recovery of function after spinal cord injury in rats

BACKGROUND AIMS

The pro-regeneration capabilities of olfactory ensheathing cells (OECs) remain controversial. However, little is known regarding whether the transplantation of activated OECs by curcumin (CCM) elicits neural regeneration and functional recovery after spinal cord injury (SCI) in rats, and the possible molecular mechanisms have never been investigated.

METHODS

Primary OECs were treated with 1μM CCM for 1-3 days. Concomitantly, activated OECs were transplanted into the traumatic spinal cord of Sprague Dawley rats. One to 9 weeks after surgery, the assessment of behavior recovery was made using the Basso, Beattie and Bresnahan (BBB) locomotor scale; electrophysiology tests, such as somatosensory evoked potential (SEP) and motor evoked potential (MEP); and the cylinder test. Pathological study, including hematoxylin and eosin staining and immunofluorescence staining for neurofilaments (NFs), was conducted at 5 weeks post-surgery. In addition, activation profiles of OECs by CCM stimulus were assessed and levels of transglutaminase-2 (TG2) and phosphatidylserine receptor (PSR) in OECs stimulated by CCM were further determined.

RESULTS

CCM remarkably enhanced OEC proliferation, improved cell viability and strengthened secretion of neurotrophins and anti-inflammatory factors. In addition, the levels of TG2 and PSR in CCM-treated OECs were significantly elevated. More importantly, beyond 1 week post-transplantation of CCM-treated OECs into lesioned spinal cord, BBB score and cylinder test score were significantly higher than that seen in the other three groups and a more postponed latent SEP and MEP period was noted. Furthermore, 5 weeks later, numerous, well-arranged NF-positive nerve fibers, lesions with less cavities and reduced levels of pro-inflammatory cytokines were found in activated OEC implantation groups. In addition, the number of NF-positive fibers was significantly improved and the number and area of both cavities and gliotic scars were remarkably decreased compared with the corresponding controls.

CONCLUSIONS

Transplantation of OECs activated by CCM promotes neural regeneration and functional recovery following SCI, the underlying mechanisms of which are intimately associated with the elevated production of neurotrophic factors and anti-inflammatory factors in OECs stimulated by CCM as well as reduced pro-inflammatory cytokines from the post-contusion spinal cord. In addition, OECs activated by CCM were mediated through TG2 and PSR.

Gli3 Regulates Vomeronasal Neurogenesis, Olfactory Ensheathing Cell Formation, and GnRH-1 Neuronal Migration

During mammalian development, gonadotropin-releasing-hormone-1 neurons (GnRH-1ns) migrate from the developing vomeronasal organ (VNO) into the brain asserting control of pubertal onset and fertility. Recent data suggest that correct development of the olfactory ensheathing cells (OEC) is imperative for normal GnRH-1 neuronal migration. However, the full ensemble of molecular pathways that regulate OEC development remains to be fully deciphered. Loss-of-function of the transcription factor Gli3 is known to disrupt olfactory development, however, if Gli3 plays a role in GnRH-1 neuronal development is unclear. By analyzing Gli3 extra-toe mutants (Gli3Xt/Xt), we found that Gli3 loss-of-function compromises the onset of achaete-scute family bHLH transcription factor 1 (Ascl-1)+ vomeronasal progenitors and the formation of OEC in the nasal mucosa. Surprisingly, GnRH-1 neurogenesis was intact in Gli3Xt/Xt mice but they displayed significant defects in GnRH-1 neuronal migration. In contrast, Ascl-1null mutants showed reduced neurogenesis for both vomeronasal and GnRH-1ns but less severe defects in OEC development. These observations suggest that Gli3 is critical for OEC development in the nasal mucosa and subsequent GnRH-1 neuronal migration. However, the nonoverlapping phenotypes between Ascl-1 and Gli3 mutants indicate that Ascl-1, while crucial for GnRH-1 neurogenesis, is not required for normal OEC development. Because Kallmann syndrome (KS) is characterized by abnormal GnRH-1ns migration, we examined whole-exome sequencing data from KS subjects. We identified and validated a GLI3 loss-of-function variant in a KS individual. These findings provide new insights into GnRH-1 and OECs development and demonstrate that human GLI3 mutations contribute to KS etiology.SIGNIFICANCE STATEMENT The transcription factor Gli3 is necessary for correct development of the olfactory system. However, if Gli3 plays a role in controlling GnRH-1 neuronal development has not been addressed. We found that Gli3 loss-of-function compromises the onset of Ascl-1+ vomeronasal progenitors, formation of olfactory ensheathing cells in the nasal mucosa, and impairs GnRH-1 neuronal migration to the brain. By analyzing Ascl-1null mutants we dissociated the neurogenic defects observed in Gli3 mutants from lack of olfactory ensheathing cells in the nasal mucosa, moreover, we discovered that Ascl-1 is necessary for GnRH-1 ontogeny. Analyzing human whole-exome sequencing data, we identified a GLI3 loss-of-function variant in a KS individual. Our data suggest that GLI3 is a candidate gene contributing to KS etiology.

Reliable cell purification and determination of cell purity: crucial aspects of olfactory ensheathing cell transplantation for spinal cord repair

Transplantation of olfactory ensheathing cells, the glia of the primary olfactory nervous system, has been trialed for spinal cord injury repair with promising but variable outcomes in animals and humans. Olfactory ensheathing cells can be harvested either from the lamina propria beneath the neuroepithelium in the nasal cavity, or from the olfactory bulb in the brain. As these areas contain several other cell types, isolating and purifying olfactory ensheathing cells is a critical part of the process. It is largely unknown how contaminating cells such as fibroblasts, other glial cell types and supporting cells affect olfactory ensheathing cell function post-transplantation; these cells may also cause unwanted side-effects. It is also, however, possible that the presence of some of the contaminant cells can improve outcomes. Here, we reviewed the last decade of olfactory ensheathing cell transplantation studies in rodents, with a focus on olfactory ensheathing cell purity. We analyzed how purification methods and resultant cell purity differed between olfactory mucosa- and olfactory bulb-derived cell preparations. We analyzed how the studies reported on olfactory ensheathing cell purity and which criteria were used to define cells as olfactory ensheathing cells. Finally, we analyzed the correlation between cell purity and transplantation outcomes. We found that olfactory bulb-derived olfactory ensheathing cell preparations are typically purer than mucosa-derived preparations. We concluded that there is an association between high olfactory ensheathing cell purity and favourable outcomes, but the lack of olfactory ensheathing cell-specific markers severely hampers the field.

Survival and Integration of Transplanted Olfactory Ensheathing Cells are Crucial for Spinal Cord Injury Repair: Insights from the Last 10 Years of Animal Model Studies

Olfactory ensheathing cells (OECs), the glial cells of the primary olfactory nervous system, support the natural regeneration of the olfactory nerve that occurs throughout life. OECs thus exhibit unique properties supporting neuronal survival and growth. Transplantation of OECs is emerging as a promising treatment for spinal cord injury; however, outcomes in both animals and humans are variable and the method needs improvement and standardization. A major reason for the discrepancy in functional outcomes is the variability in survival and integration of the transplanted cells, key factors for successful spinal cord regeneration. Here, we review the outcomes of OEC transplantation in rodent models over the last 10 years, with a focus on survival and integration of the transplanted cells. We identify the key factors influencing OEC survival: injury type, source of transplanted cells, co-transplantation with other cell types, number and concentration of cells, method of delivery, and time of transplantation after the injury. We found that two key issues are hampering optimization and standardization of OEC transplantation: lack of (1) reliable methods for identifying transplanted cells, and (2) three-dimensional systems for OEC delivery. To develop OEC transplantation as a successful and standardized therapy for spinal cord injury, we must address these issues and increase our understanding of the complex parameters influencing OEC survival.

Inhibition of ADAMTS-4 Expression in Olfactory Ensheathing Cells Enhances Recovery after Transplantation within Spinal Cord Injury

Spinal cord injury (SCI) induces permanent loss of sensitive and motor functions below the injury level. To date, a wide variety of cells has been used as biotherapies to cure SCI in different animal paradigms. Specifically, olfactory ensheathing cells (OECs) is one of the most promising. Indeed, OECs have been shown to enhance recovery in many animal studies. Moreover, OECs transplantation has been applied to a paraplegic patient and have shown beneficial effects. However, it has been reported that the significant level of recovery varies among different patients. Therefore, it is of primary importance to enhance the regenerative efficiency of OECs for better translations. Recently, it has been shown that inhibiting ADAMTS4 expression in glial cells in vitro increases their synthesis of neurotrophic factors. We hypothesized that the expression of neurotrophic factors secreted by OECs can be increased by the deletion of ADAMTS4. Taking advantage of ADAMTS4^-/- mouse line, we produce ADAMTS4 deficient primary OEC cultures and then we investigated their regenerative potential after SCI. By using quantitative polymerase chain reaction, bioluminescence imaging, measurement of locomotor activity, electrophysiological studies, and immunohistochemistry, our results show that ADAMTS4^-/- olfactory bulb OEC (bOECs) primary cultures upregulate their trophic factor expression in vitro, and that the transplantation of ADAMTS4^-/- bOECs in a severe SCI model increases functional recovery and tissue repair in vivo. Altogether, our study reveals, for the first time, that primary bOEC cultures transplantation can be potentialized by inhibition of the expression of ADAMTS4.

Methods of olfactory ensheathing cell harvesting from the olfactory mucosa in dogs

Olfactory ensheathing cells are thought to support regeneration and remyelination of damaged axons when transplanted into spinal cord injuries. Following transplantation, improved locomotion has been detected in many laboratory models and in dogs with naturally-occurring spinal cord injury; safety trials in humans have also been completed. For widespread clinical implementation, it will be necessary to derive large numbers of these cells from an accessible and, preferably, autologous, source making olfactory mucosa a good candidate. Here, we compared the yield of olfactory ensheathing cells from the olfactory mucosa using 3 different techniques: rhinotomy, frontal sinus keyhole approach and rhinoscopy. From canine clinical cases with spinal cord injury, 27 biopsies were obtained by rhinotomy, 7 by a keyhole approach and 1 with rhinoscopy. Biopsy via rhinoscopy was also tested in 13 cadavers and 7 living normal dogs. After 21 days of cell culture, the proportions and populations of p75-positive (presumed to be olfactory ensheathing) cells obtained by the keyhole approach and rhinoscopy were similar (~4.5 x 10⁶ p75-positive cells; ~70% of the total cell population), but fewer were obtained by frontal sinus rhinotomy. Cerebrospinal fluid rhinorrhea was observed in one dog and emphysema in 3 dogs following rhinotomy. Blepharitis occurred in one dog after the keyhole approach. All three biopsy methods appear to be safe for harvesting a suitable number of olfactory ensheathing cells from the olfactory mucosa for transplantation within the spinal cord but each technique has specific advantages and drawbacks.

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.

The Impact of Tissue Storage Conditions on Rat Olfactory Ensheathing Cell Yield and the Future Clinical Implications

Trauma causes spinal cord injury, and the devastating consequences of the injury are due to the failure of the damaged central nervous system (CNS) axons to regenerate. Previous studies have shown that olfactory ensheathing cells (OECs) are a unique type of glial cell and they can promote regeneration of CNS axons to aid recovery after spinal cord injury. Transplantation of OECs, in particular from the olfactory bulb (OB), is considered one of the most promising therapeutic strategies for the repair of CNS injuries, including spinal cord injury. Transplantation of OECs can be autologous or allogenic. Here we focused on the less invasive and more error-proof allograft approach which needs a collection of donor OB tissue for OEC production. In this study, we investigated the effects on the yield and proportions of OECs and olfactory nerve fibroblasts (ONFs) from storing OB tissue in various media for periods of 24 and 48 hours. The OEC yield contributes to the viability of a successful cell transplant. We concluded that storing OB tissue for a period longer than 24 hours negatively impacted the total cell number and subsequently the OEC population. This study provides useful information for future clinical applications.

Enhancing the Therapeutic Potential of Olfactory Ensheathing Cells in Spinal Cord Repair Using Neurotrophins

Autologous olfactory ensheathing cell (OEC) transplantation is a promising therapy for spinal cord injury; however, the efficacy varies between trials in both animals and humans. The main reason for this variability is that the purity and phenotype of the transplanted cells differs between studies. OECs are susceptible to modulation with neurotrophic factors, and thus, neurotrophins can be used to manipulate the transplanted cells into an optimal, consistent phenotype. OEC transplantation can be divided into 3 phases: (1) cell preparation, (2) cell administration, and (3) continuous support to the transplanted cells in situ. The ideal behaviour of OECs differs between these 3 phases; in the cell preparation phase, rapid cell expansion is desirable to decrease the time between damage and transplantation. In the cell administration phase, OEC survival and integration at the injury site, in particular migration into the glial scar, are the most critical factors, along with OEC-mediated phagocytosis of cellular debris. Finally, continuous support needs to be provided to the transplantation site to promote survival of both transplanted cells and endogenous cells within injury site and to promote long-term integration of the transplanted cells and angiogenesis. In this review, we define the 3 phases of OEC transplantation into the injured spinal cord and the optimal cell behaviors required for each phase. Optimising functional outcomes of OEC transplantation can be achieved by modulation of cell behaviours with neurotrophins. We identify the key growth factors that exhibit the strongest potential for optimizing the OEC phenotype required for each phase.

Cell therapy for spinal cord injury with olfactory ensheathing glia cells (OECs)

The prospects of achieving regeneration in the central nervous system (CNS) have changed, as most recent findings indicate that several species, including humans, can produce neurons in adulthood. Studies targeting this property may be considered as potential therapeutic strategies to respond to injury or the effects of demyelinating diseases in the CNS. While CNS trauma may interrupt the axonal tracts that connect neurons with their targets, some neurons remain alive, as seen in optic nerve and spinal cord (SC) injuries (SCIs). The devastating consequences of SCIs are due to the immediate and significant disruption of the ascending and descending spinal pathways, which result in varying degrees of motor and sensory impairment. Recent therapeutic studies for SCI have focused on cell transplantation in animal models, using cells capable of inducing axon regeneration like Schwann cells (SchCs), astrocytes, genetically modified fibroblasts and olfactory ensheathing glia cells (OECs). Nevertheless, and despite the improvements in such cell-based therapeutic strategies, there is still little information regarding the mechanisms underlying the success of transplantation and regarding any secondary effects. Therefore, further studies are needed to clarify these issues. In this review, we highlight the properties of OECs that make them suitable to achieve neuroplasticity/neuroregeneration in SCI. OECs can interact with the glial scar, stimulate angiogenesis, axon outgrowth and remyelination, improving functional outcomes following lesion. Furthermore, we present evidence of the utility of cell therapy with OECs to treat SCI, both from animal models and clinical studies performed on SCI patients, providing promising results for future treatments.

Transplanted olfactory ensheathing cells restore retinal function in a rat model of light-induced retinal damage by inhibiting oxidative stress

There is still not an effective treatment for continuous retinal light exposure and subsequent photoreceptor degeneration. Olfactory ensheathing cell (OEC) transplantation has been shown to be neuroprotective in spinal cord, and optic nerve injury and retinitis pigmentosa. However, whether OECs protect rat photoreceptors against light-induced damage and how this may work is unclear. Thus, to elucidate this mechanism, purified rat OECs were grafted into the subretinal space of a Long-Evans rat model with light-induced photoreceptor damage. Light exposure decreased a- and b- wave amplitudes and outer nuclear layer (ONL) thickness, whereas the ONL of rats exposed to light for 24 h after having received OEC transplants in their subretinal space was thicker than the PBS control and untreated groups. A- and b- wave amplitudes from electroretinogram of OEC-transplanted rats were maintained until 8 weeks post OEC transplantation. Also, transplanted OECs inhibited formation of reactive oxygen species in retinas exposed to light. In vitro experiments showed that OECs had more total antioxidant capacity in a co-cultured 661W photoreceptor cell line, and cells were protected from damage induced by hydrogen-peroxide. Thus, transplanted OECs preserved retinal structure and function in a rat model of light-induced degeneration by suppressing retinal oxidative stress reactions.

Olfactory Ensheathing Cell Transplantation in Experimental Spinal Cord Injury: Effect size and Reporting Bias of 62 Experimental Treatments: A Systematic Review and Meta-Analysis

Olfactory ensheathing cell (OEC) transplantation is a candidate cellular treatment approach for human spinal cord injury (SCI) due to their unique regenerative potential and autologous origin. The objective of this study was, through a meta-epidemiologic approach, (i) to assess the efficacy of OEC transplantation on locomotor recovery after traumatic experimental SCI and (ii) to estimate the likelihood of reporting bias and/or missing data. A study protocol was finalized before data collection. Embedded into a systematic review and meta-analysis, we conducted a literature research of databases including PubMed, EMBASE, and ISI Web of Science from 1949/01 to 2014/10 with no language restrictions, screened by two independent investigators. Studies were included if they assessed neurobehavioral improvement after traumatic experimental SCI, administrated no combined interventions, and reported the number of animals in the treatment and control group. Individual effect sizes were pooled using a random effects model. Details regarding the study design were extracted and impact of these on locomotor outcome was assessed by meta-regression. Missing data (reporting bias) was determined by Egger regression and Funnel-plotting. The primary study outcome assessed was improvement in locomotor function at the final time point of measurement. We included 49 studies (62 experiments, 1,164 animals) in the final analysis. The overall improvement in locomotor function after OEC transplantation, measured using the Basso, Beattie, and Bresnahan (BBB) score, was 20.3% (95% CI 17.8–29.5). One missing study was imputed by trim and fill analysis, suggesting only slight publication bias and reducing the overall effect to a 19.2% improvement of locomotor activity. Dose-response ratio supports neurobiological plausibility. Studies were assessed using a 9-point item quality score, resulting in a median score of 5 (interquartile range [IQR] 3–5). In conclusion, OEC transplantation exerts considerable beneficial effects on neurobehavioral recovery after traumatic experimental SCI. Publication bias was minimal and affirms the translational potential of efficacy, but safety cannot be adequately assessed. The data justify OECs as a cellular substrate to develop and optimize minimally invasive and safe cellular transplantation paradigms for the lesioned spinal cord embedded into state-of-the-art Phase I/II clinical trial design studies for human SCI.

This meta-analysis study examines the effects of transplanting olfactory ensheathing cells in rodents with experimental spinal cord injury, finding evidence for significant recovery and identifying aspects of the procedure that influence the effect size.

Spinal cord injury converts into a debilitating disease affecting millions of chronic patients worldwide. Despite increased molecular knowledge over the last decades, no causal pharmacological or cellular therapy has proven effective so far. Due to their unique regenerative capabilities and their autologous origin, olfactory ensheathing cells (OECs) constitute an appealing candidate for topical cell transplantation. In contrast to few and heterogeneous experimental reports of OEC transplantation after spinal cord injury in humans, a considerable number of preclinical studies have been conducted applying OEC transplantation in rodent models. We set out to conduct a systematic review and meta-analysis to assess preclinical efficacy of OEC transplantation. We detected a significant overall increase of functional neurological recovery in animals after OEC transplantation compared to the control group. This effect was not distorted by publication bias. We identified several specific hallmarks of the cell transplantation procedure that determine the effect size of the transplantation. Our findings delineate conditions for optimized OEC transplantation into lesioned spinal cords and its relevance for effective translation to human trials.

Co-transplantation of autologous OM-MSCs and OM-OECs: a novel approach for spinal cord injury

Spinal cord injury (SCI) is a disastrous injury that leads to motor and sensory dysfunctions in patients. In recent years, co-transplantation has become an increasingly used therapeutic treatment for patients with SCI. Both mesenchymal stem cells (MSCs) and olfactory-ensheathing cells (OECs) have been adopted to ameliorate SCI, with promising outcomes. Remarkable effects on the rehabilitation of patients with SCI have been achieved using MSCs. Olfactory mucosa (OM) MSCs from human OM are one of the most ideal cell resources for auto-transplantation in clinical application owing to their a high proliferation rate and multipotent capability. In addition, OECs derived from OM have been used to improve functional recovery of SCI and resulted in promising functional recovery in years. Accordingly, co-transplantation of OM-MSCs coupled with OM-OECs has been adopted to improve the recovery of SCI. Here we reviewed the reported applications of OM-MSCs and OM-OECs for SCI treatment and proposed that a novel combined strategy using both autologous OM-MSCs and OM-OECs would achieve a better approach for the treatment of SCI.

Immunocytochemical characterisation of ensheathing glia in the olfactory and vomeronasal systems of Ambystoma mexicanum (Caudata: Ambystomatidae)

The olfactory and vomeronasal systems of vertebrates are characterised by neurogenesis occurring throughout life. The regenerative ability of olfactory receptor neurons relies on specific glial cells, the olfactory and vomeronasal axon-surrounding cells. Numerous studies have examined mammalian olfactory ensheathing cells which are considered potential candidates for spinal cord injury repair using cell-based therapy. With regard to non-mammalian vertebrates, limited information is available on these glial cells in fish, and there is no information on them in terrestrial anamniotes, the amphibians. In the present research, we studied the immunocytochemical characteristics of axon-surrounding cells in Ambystoma mexicanum. Urodeles have relatively simple olfactory and vomeronasal systems, and represent a good model for studying ensheathing cells in extant representatives of basal tetrapods. Sections from the decalcified heads of A. mexicanum were immunocytochemically processed for the detection of proteins used in research on mammalian olfactory-ensheathing cells. S100, GFAP and NCAM were clearly observed. p75NTR, Gal-1 and PSA-NCAM showed weak staining. No vimentin immunopositivity was observed. The corresponding areas of the olfactory and vomeronasal pathways displayed the same staining characteristics, with the exception of Gal-1, p75NTR and PSA-NCAM in the mucosae. The degree of marker expression was not uniform throughout the sensory pathways. In contrast to fish, both olfactory and vomeronasal nerves displayed uniform staining intensity. This study showed that some markers for mammalian and fish-ensheathing glia are also applicable in urodeles. The olfactory systems of vertebrates show similarities, and also clear dissimilarities. Further investigations are required to ascertain the functional significance of these regional and interspecific differences.

Comparison of Olfactory Bulbar and Mucosal Cultures in a Rat Rhizotomy Model

In an ongoing clinical trial, a spinal injured patient who received a transplant of autologous cells cultured from the olfactory bulb is showing greater functional benefit than three previous patients with transplants of mucosal origin. Previous laboratory studies of transplantation into rat spinal cord injuries show that the superior reparative benefits of bulbar over mucosal cultures are associated with regeneration of severed corticospinal tract fibers over a bridge of olfactory ensheathing cells (OECs) formed across the injury site. In a rat rhizotomy paradigm, we reported that transplantation of bulbar cell cultures also enables severed axons of the C6–T1 dorsal roots to regenerate across a bridge of OECs into the spinal cord and restore electrophysiological transmission and forepaw grasping during a climbing test. We now report a repeat of the same rhizotomy procedure in 25 rats receiving cells cultured from olfactory mucosal biopsies. In no case did the transplanted cells form a bridging pathway. No axons crossed from the severed roots to the spinal cord, and there was no restoration of forepaw grasping. This suggests that the superior clinical benefit in the patient receiving bulbar cell transplants is due to regeneration of severed fibers across the injury site, and this correlates with imaging and the pattern of functional recovery. Using present culture protocols, the yield of OECs from bulbar biopsies is around 50%, but that from mucosal biopsies is less than 5%. Improving the yield of OECs from mucosal biopsies might avoid the necessity for the intracranial approach to obtain bulbar cells.

Synergic effects of EPI-NCSCs and OECs on the donor cells migration, the expression of neurotrophic factors, and locomotor recovery of contused spinal cord of rats

Cell-based therapy is a promising strategy for the repair of spinal cord injury (SCI), and the synergic effects of donor cells are emphasized in recent years. In this study, epidermal neural crest stem cells (EPI-NCSCs) and olfactory ensheathing cells (OECs) were transplanted into the contused spinal cord of rats separately or jointly at 1 week after injury. At 3 and 9 weeks posttransplantation, migration of the donor cells, expression of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) and functional recovery of the contused cord were determined by techniques of histopathology, quantitative real-time polymerase chain reaction (qPCR), immunohistochemistry and Basso-Beattie-Bresnahan (BBB) score. The results showed that the migration and distribution of EPI-NCSCs in vivo were promoted by OECs at 3 weeks after transplantation, but they vanished at 9 weeks. The expression of BDNF and GDNF was significantly increased by co-transplantation at molecular and protein level. Although the expression of both factors in EPI-NCSCs- and OECs-injected group was lower than in co-injected group, it was higher than in control groups. Similarly, the best locomotor recovery of the contused cord was acquired from co-injected animals. As we know, this is the first time to study the synergic effects of EPI-NCSCs and OECs, and the data indicates that donor cells migration, expression of neurotrophic factors (NTFs), and recovery of motor function can be improved by EPI-NCSCs and OECs synergistically.

Understanding the neural repair-promoting properties of olfactory ensheathing cells

Olfactory ensheathing glial cells (OECs) are a specialized type of glia that form a continuously aligned cellular pathway that actively supports unprecedented regeneration of primary olfactory axons from the periphery into the central nervous system. Implantation of OECs stimulates neural repair in experimental models of spinal cord, brain and peripheral nerve injury and delays disease progression in animal models for neurodegenerative diseases like amyotrophic lateral sclerosis. OECs implanted in the injured spinal cord display a plethora of pro-regenerative effects; they promote axonal regeneration, reorganize the glial scar, remyelinate axons, stimulate blood vessel formation, have phagocytic properties and modulate the immune response. Recently genome wide transcriptional profiling and proteomics analysis combined with classical or larger scale "medium-throughput" bioassays have provided novel insights into the molecular mechanism that endow OECs with their pro-regenerative properties. Here we review these studies and show that the gaps that existed in our understanding of the molecular basis of the reparative properties of OECs are narrowing. OECs express functionally connected sets of genes that can be linked to at least 10 distinct processes directly relevant to neural repair. The data indicate that OECs exhibit a range of synergistic cellular activities, including active and passive stimulation of axon regeneration (by secretion of growth factors, axon guidance molecules and basement membrane components) and critical aspects of tissue repair (by structural remodeling and support, modulation of the immune system, enhancement of neurotrophic and antigenic stimuli and by metabolizing toxic macromolecules). Future experimentation will have to further explore the newly acquired knowledge to enhance the therapeutic potential of OECs.

ADAMTS proteoglycanases in the physiological and pathological central nervous system

ADAMTS-1, -4, -5 and -9 belong to ‘a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)’ family and more precisely to the proteoglycanases subgroup based on their common ability to degrade chondroitin sulfate proteoglycans. They have been extensively investigated for their involvement in inflammation-induced osteoarthritis, and a growing body of evidence indicates that they may be of key importance in the physiological and pathological central nervous system (CNS). In this review, we discuss the deregulated expression of ADAMTS proteoglycanases during acute CNS injuries, such as stroke and spinal cord injury. Then, we provide new insights on ADAMTS proteoglycanases mediating synaptic plasticity, neurorepair, angiogenesis and inflammation mechanisms. Altogether, this review allows us to propose that ADAMTS proteoglycanases may be original therapeutic targets for CNS injuries.