Limits to the capacity of transplants of olfactory glia to promote axonal regrowth in the CNS

ROCK Inhibitor Y27632 Induced Morphological Shift and Enhanced Neurite Outgrowth-Promoting Property of Olfactory Ensheathing Cells via YAP-Dependent Up-Regulation of L1-CAM

Olfactory ensheathing cells (OECs) are heterogeneous in morphology, antigenic profiles and functions, and these OEC subpopulations have shown different outcomes following OEC transplantation for central nervous system (CNS) injuries. Morphologically, OECs are divided into two subpopulations, process-bearing (Schwann cells-like) and flattened (astrocytes-like) OECs, which could switch between each other and are affected by extracellular and intracellular factors. However, neither the relationship between the morphology and function of OECs nor their molecular mechanisms have been clarified. In the present study, we first investigated morphological and functional differences of OECs under different cytokine exposure conditions. It demonstrated that OECs mainly displayed a process-bearing shape under pro-inflammatory conditions (lipopolysaccharide, LPS), while they displayed a flattened shape under anti-inflammatory conditions [interleukin-4 (IL-4) and transforming growth factor-β1 (TGF-β1)]. The morphological changes were partially reversible and the Rho-associated coiled-coil-containing protein kinase (ROCK)/F-actin pathway was involved. Functionally, process-bearing OECs under pro-inflammatory conditions showed increased cellular metabolic activity and a higher migratory rate when compared with flattened OECs under anti-inflammatory conditions and significantly promoted neurite outgrowth and extension. Remarkably, the morphological shift towards process-bearing OECs induced by ROCK inhibitor Y27632 enhanced the neurite outgrowth-promoting property of OECs. Furthermore, as the downstream of the ROCK pathway, transcriptional co-activator Yes-associated protein (YAP) mediated morphological shift and enhanced the neurite outgrowth-promoting property of OECs through upregulating the expression of the neural adhesion molecule L1-CAM. Our data provided evidence that OECs with specific shapes correspond to specific functional phenotypes and opened new insights into the potential combination of OECs and small-molecule ROCK inhibitors for the regeneration of CNS injuries.

Pharmacological, Cell, and Gene Therapy Strategies to Promote Spinal Cord Regeneration

In this review, recent studies using pharmacological treatment, cell transplantation, and gene therapy to promote regeneration of the injured spinal cord in animal models will be summarized. Pharmacological and cell transplantation treatments generally revealed some degree of effect on the regeneration of the injured ascending and descending tracts, but further improvements to achieve a more significant functional recovery are necessary. The use of gene therapy to promote repair of the injured nervous system is a relatively new concept. It is based on the development of methods for delivering therapeutic genes to neurons, glia cells, or nonneural cells. Direct in vivo gene transfer or gene transfer in combination with (neuro)transplantation (ex vivo gene transfer) appeared powerful strategies to promote neuronal survival and axonal regrowth following traumatic injury to the central nervous system. Recent advances in understanding the cellular and molecular mechanisms that govern neuronal survival and neurite outgrowth have enabled the design of experiments aimed at viral vector-mediated transfer of genes encoding neurotrophic factors, growth-associated proteins, cell adhesion molecules, and antiapoptotic genes. Central to the success of these approaches was the development of efficient, nontoxic vectors for gene delivery and the acquirement of the appropriate (genetically modified) cells for neurotransplantation. Direct gene transfer in the nervous system was first achieved with herpes viral and E1-deleted adenoviral vectors. Both vector systems are problematic in that these vectors elicit immunogenic and cytotoxic responses. Adeno-associated viral vectors and lentiviral vectors constitute improved gene delivery systems and are beginning to be applied in neuroregeneration research of the spinal cord. Ex vivo approaches were initially based on the implantation of genetically modified fibroblasts. More recently, transduced Schwann cells, genetically modified pieces of peripheral nerve, and olfactory ensheathing glia have been used as implants into the injured spinal cord.

Neural progenitor cell implants in the lesioned medial longitudinal fascicle of adult cats regulate synaptic composition and firing properties of abducens internuclear neurons

Transplants of neural progenitor cells (NPCs) into the injured CNS have been proposed as a powerful tool for brain repair, but, to date, few studies on the physiological response of host neurons have been reported. Therefore, we explored the effects of NPC implants on the discharge characteristics and synaptology of axotomized abducens internuclear neurons, which mediate gaze conjugacy for horizontal eye movements. NPCs were isolated from the subventricular zone of neonatal cats and implanted at the site of transection in the medial longitudinal fascicle of adult cats. Abducens internuclear neurons of host animals showed a complete restoration of axotomy-induced alterations in eye position sensitivity, but eye velocity sensitivity was only partially regained. Analysis of the inhibitory and excitatory components of the discharge revealed a normal re-establishment of inhibitory inputs, but only partial re-establishment of excitatory inputs. Moreover, their inhibitory terminal coverage was similar to that in controls, indicating that there was ultimately no loss of inhibitory synaptic inputs. Somatic coverage by synaptophysin-positive contacts, however, showed intermediate values between control animals and animals that had undergone axotomy, likely due to partial loss of excitatory inputs. We also demonstrated that severed axons synaptically contacted NPCs, most of which were VEGF immunopositive, and that abducens internuclear neurons expressed the VEGF receptor Flk1. Together, our results suggest that VEGF neurotrophic support might underlie the increased inhibitory-to-excitatory balance observed in the postimplant cells. The noteworthy improvement of firing properties of injured neurons following NPC implants indicates that these cells might provide a promising therapeutic strategy after neuronal lesions.

Generation of magnetized olfactory ensheathing cells for regenerative studies in the central and peripheral nervous tissue

As olfactory receptor axons grow from the peripheral to the central nervous system (CNS) aided by olfactory ensheathing cells (OECs), the transplantation of OECs has been suggested as a plausible therapy for spinal cord lesions. The problem with this hypothesis is that OECs do not represent a single homogeneous entity, but, instead, a functionally heterogeneous population that exhibits a variety of responses, including adhesion and repulsion during cell-matrix interactions. Some studies report that the migratory properties of OECs are compromised by inhibitory molecules and potentiated by chemical gradients. In this paper, we report a system based on modified OECs carrying magnetic nanoparticles as a proof of concept experiment enabling specific studies aimed at exploring the potential of OECs in the treatment of spinal cord injuries. Our studies have confirmed that magnetized OECs (i) survive well without exhibiting stress-associated cellular responses; (ii) in vitro, their migration can be modulated by magnetic fields; and (iii) their transplantation in organotypic slices of spinal cord and peripheral nerve showed positive integration in the model. Altogether, these findings indicate the therapeutic potential of magnetized OECs for CNS injuries.

Myelin-associated proteins block the migration of olfactory ensheathing cells: an in vitro study using single-cell tracking and traction force microscopy

Newly generated olfactory receptor axons grow from the peripheral to the central nervous system aided by olfactory ensheathing cells (OECs). Thus, OEC transplantation has emerged as a promising therapy for spinal cord injuries and for other neural diseases. However, these cells do not present a uniform population, but instead a functionally heterogeneous population that exhibits a variety of responses including adhesion, repulsion, and crossover during cell-cell and cell-matrix interactions. Some studies report that the migratory properties of OECs are compromised by inhibitory molecules and potentiated by chemical gradients. Here, we demonstrated that rodent OECs express all the components of the Nogo receptor complex and that their migration is blocked by myelin. Next, we used cell tracking and traction force microscopy to analyze OEC migration and its mechanical properties over myelin. Our data relate the decrease of traction force of OEC with lower migratory capacity over myelin, which correlates with changes in the F-actin cytoskeleton and focal adhesion distribution. Lastly, OEC traction force and migratory capacity is enhanced after cell incubation with the Nogo receptor inhibitor NEP1-40.

Stimulation of olfactory ensheathing cell motility enhances olfactory axon growth

Axons of primary olfactory neurons are intimately associated with olfactory ensheathing cells (OECs) from the olfactory epithelium until the final targeting of axons within the olfactory bulb. However, little is understood about the nature and role of interactions between OECs and axons during development of the olfactory nerve pathway. We have used high resolution time-lapse microscopy to examine the growth and interactions of olfactory axons and OECs in vitro. Transgenic mice expressing fluorescent reporters in primary olfactory axons (OMP-ZsGreen) and ensheathing cells (S100ß-DsRed) enabled us to selectively analyse these cell types in explants of olfactory epithelium. We reveal here that rather than providing only a permissive substrate for axon growth, OECs play an active role in modulating the growth of pioneer olfactory axons. We show that the interactions between OECs and axons were dependent on lamellipodial waves on the shaft of OEC processes. The motility of OECs was mediated by GDNF, which stimulated cell migration and increased the apparent motility of the axons, whereas loss of OECs via laser ablation of the cells inhibited olfactory axon outgrowth. These results demonstrate that the migration of OECs strongly regulates the motility of axons and that stimulation of OEC motility enhances axon extension and growth cone activity.

Olfactory glia enhance neonatal axon regeneration

Olfactory ensheathing cells (OECs) migrate with olfactory axons that extend from the nasal epithelium into the olfactory bulb. Unlike other glia, OECs are thought to migrate ahead of growing axons instead of following defined axonal paths. However it remains unknown how the presence of axons and OECs influences the growth and migration of each other during regeneration. We have developed a regeneration model in neonatal mice to examine whether (i) the presence of OECs ahead of olfactory axons affects axonal growth and (ii) the presence of olfactory axons alters the distribution of OECs. We performed unilateral bulbectomy to ablate olfactory axons followed by methimazole administration to further delay neuronal growth. In this model OECs filled the cavity left by the bulbectomy before new axons extended into the cavity. We found that delaying axon growth increased the rate at which OECs filled the cavity. The axons subsequently grew over a significantly larger region and formed more distinct fascicles and glomeruli in comparison with growth in animals that had undergone only bulbectomy. In vitro, we confirmed (i) that olfactory axon growth was more rapid when OECs were more widely distributed than the axons and (ii) that OECs migrated faster in the absence of axons. These results demonstrate that the distribution of OECs can be increased by repressing by growth of olfactory axons and that olfactory axon growth is significantly enhanced if a permissive OEC environment is present prior to axon growth.

Effect of Neurotrophin-3 Genetically Modified Olfactory Ensheathing Cells Transplantation on Spinal Cord Injury

Transplantation of olfactory ensheathing cells (OECs) has emerged as a very promising therapy for spinal cord injury (SCI). Also, local delivery of NT-3 can counteract pathological events and induce a regenerative response after SCI. Supplement of exogenetic NT-3 might be a new approach to SCI repair. In this study, we examined the therapeutic effect of rat NT-3 gene-modified OECs transplantation on SCI. Rat NT-3 gene was transfected into OECs using a retroviral system. The engineered NT-3-OECs were tested for their ability to express and secrete biologically active NT-3 in vitro. Then NT-3-OECs were implanted into contused T9 spinal cord of the adult rats. Their ability of survival and NT-3 production was examined. The effect of axon regeneration was evaluated at the morphological level and promotion of locomotor functional recovery were assessed. The result showed that genetically modified OECs were capable of surviving and producing NT-3 in vivo to significantly improve the recovery after SCI.

Therapeutic potential of olfactory ensheathing cells in neurodegenerative diseases

The regenerative capacity of the olfactory system has generated interest in potential clinical application of cells from the olfactory epithelium in the treatment of neurodegenerative diseases. Experimental evidence from animal models and clinical studies suggest that transplantation of olfactory ensheathing cells (OEC), specialized glia in the olfactory system, may be therapeutically useful in neurodegenerative diseases such as spinal cord injury and stroke. This review article describes the different experimental approaches in OEC transplantation. We also discuss the possible effects of OEC implantation on the underlying pathophysiology in neurological disease, including neuroplasticity. Our recent study of this particular population of cells has disclosed some of the molecular basis of the regenerative mechanism of OECs. In summary OECs produce several neurotrophic factors such as stromal cell-derived factor 1alpha and brain-derived neurotrophic factor and enhance axonal regeneration to promote neuroplasticity in neurodegenerative diseases.

Ex vivo non-viral vector-mediated neurotrophin-3 gene transfer to olfactory ensheathing glia: effects on axonal regeneration and functional recovery after implantation in rats with spinal cord injury

OBJECTIVE

Combine olfactory ensheathing glia (OEG) implantation with ex vivo non-viral vector-based neurotrophin-3 (NT-3) gene therapy in attempting to enhance regeneration after thoracic spinal cord injury (SCI).

METHODS

Primary OEG were transfected with cationic liposome-mediated recombinant plasmid pcDNA3.1(+)-NT3 and subsequently implanted into adult Wistar rats directly after the thoracic spinal cord (T9) contusion by the New York University impactor. The animals in 3 different groups received 4x10(5) OEG transfected with pcDNA3.1(+)-NT3 or pcDNA3.1(+) plasmids, or the OEGs without any plasmid transfection, respectively; the fourth group was untreated group, in which no OEG was implanted.

RESULTS

NT-3 production was seen increased both ex vivo and in vivo in pcDNA3.1(+)-NT3 transfected OEGs. Three months after implantation of NT-3-transfected OEGs, behavioral analysis revealed that the hindlimb function of SCI rats was improved. All spinal cords were filled with regenerated neurofilament-positive axons. Retrograde tracing revealed enhanced regenerative axonal sprouting.

CONCLUSION

Non-viral vector-mediated genetic engineering of OEG was safe and more effective in producing NT-3 and promoting axonal outgrowth followed by enhancing SCI recovery in rats.

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.

Nogo enhances the adhesion of olfactory ensheathing cells and inhibits their migration

The migration of olfactory ensheathing cells (OECs) is essential for pioneering the olfactory nerve pathway during development and for promoting axonal regeneration when implanted into the injured central nervous system (CNS). In the present study, recombinant Nogo-66 enhanced the adhesion of OECs and inhibited their migration. Using immunocytochemistry and western blot, we showed that the Nogo-66 receptor (NgR) was expressed on OECs. When NgR was released from the cell surface with phosphatidylinositol-specific phospholipase C or neutralized by NgR antibody, the effect of Nogo-66 on OEC adhesion and migration was markedly attenuated. Nogo-66 was found to promote the formation of focal adhesion in OECs and inhibited their membrane protrusion through the activation of RhoA. Furthermore, the co-culture migration assay demonstrated that OEC motility was significantly restricted by Nogo-A expressed on Cos7 cell membranes or oligodendrocytes. Moreover, treatment with anti-NgR antibody facilitated migration of implanted OECs in a spinal cord hemisection injury model. Taken together, we demonstrate, for the first time, that Nogo, a myelin-associated inhibitor of axon regeneration in the CNS, enhances the adhesion and inhibits the migration of OECs via NgR regulation of RhoA.

Olfactory ensheathing glia and spinal cord injury: basic mechanisms to transplantation

The adult CNS, unlike its counterpart the peripheral nervous system (PNS), has little ability to repair itself after traumatic injury. Therefore, neurotrauma involving the brain or spinal cord has severe and long-lasting functional consequences for injured patients, as well as a massive financial and social impact on the affected families and the community at large. In particular, spinal cord injury (SCI) has provided scientists and clinicians with a challenging problem. In attempts to improve outcomes following SCI, numerous mammalian research models have been developed. Many of these models involve either transection or contusion injuries in rodents and experimental therapies include the transplantation of a range of cell types isolated from either the PNS or CNS. The authors focus on a cell type isolated from the olfactory system; olfactory ensheathing cells (OECs). Some basic tenets of olfactory cell biology, key preclinical results suggesting a role for OECs in stimulating spinal cord repair and the strengths and limitations of this potential therapy are discussed. The current and future status of OEC transplantation in the treatment of human SCI is also considered.

Morphological and functional plasticity of olfactory ensheathing cells

In the primary olfactory pathway, olfactory ensheathing cells (OECs) extend processes to envelop bundles of olfactory axons as they course towards their termination in the olfactory bulb. The expression of growth-promoting adhesion and extracellular matrix molecules by OECs, and their spatially close association with olfactory axons are consistent with OECs being involved in promoting and guiding olfactory axon growth. Because of this, OECs have been employed as a possible tool for inducing axonal regeneration in the injured adult CNS, resulting in significant functional recovery in some animal models and promising outcomes from early clinical applications. However, fundamental aspects of OEC biology remain unclear. This brief review discusses some of the experimental data that have resulted in conflicting views with regard to the identity of OECs. We present here recent findings which support the notion of OECs as a single but malleable phenotype which demonstrate extensive morphological and functional plasticity depending on the environmental stimuli. The review includes a discussion of the normal functional role of OECs in the developing primary olfactory pathway as well as their interaction with regenerating axons and reactive astrocytes in the novel environment of the injured CNS. The use of OECs to induce repair in the injured nervous system reflects the functional plasticity of these cells. Finally, we will explore the possibility that recent microarray data could point to OECs assuming an innate immune function or playing a role in modulating neuroinflammation.

Transplantation de cellules gliales olfactives après traumatisme médullaire

Over recent years, a certain number of experimental investigations have studied the effect of the transplantation of olfactory ensheathing glial cells (OEC) after spinal traumatism in animal, the rat in particular. Some of these studies have reported improvements in motor (mainly locomotor, postural and respiratory) and sensory function. While these new data provide additional support for the interest of the strategy of EOC transplantation to minimise the incapacitating effects of spinal pathologies in clinical therapy, it nonetheless remains necessary to continue experiments on animal models in order to better understand and master certain important points: beneficial effects according to the nature and composition of the transplants; therapeutic impact according to the type of pathology and the nature of the traumatism; influence of the dose effect; migration of the transplanted OECs (distance, pathways); active principles of the transplants; beneficial effect on various functions, in particular at the level of the vesico-sphincteric area; long-term innocuousness; long-term posttraumatic efficacy. Although therapeutic trials are in progress in certain countries (Australia, China, Portugal), it would nonetheless appear essential that these somewhat obscure points should be better understood before any clinical application might be seriously envisaged, in order to respect the principles of precaution, maximum efficacy and observance of the prevailing ethical rules.

Transplantation de cellules gliales olfactives après traumatisme médullaire

Ensheathing olfactory glial cells (OEC) can be considered, with stem cells, as the other most important cell type for developing therapeutic cellular transplantation strategies following lesion of the central nervous system (CNS) and particularly in the case of spinal cord injury. OECs are macroglial cells whose precursors are located in the olfactory mucosa. OEC ensheath the axons of the sensory olfactory neurons, from the peripheral mucosa to the central olfactory bulbs. These glial cells constitute one of the rare macroglial cells which, after removal in the adult mammal, can survive in culture and multiply. After post-traumatic transplantation in the CNS, these cells have induced several instances of functional recovery after injury of different neural systems. The "OEC transplantation effect" consists in modifying the central inhibitory environment to make it more propitious for axonal regrowth and cell survival (reduction of the glial scar; releasing of numerous survival and neurotrophic factors, and of surface, extracellular matrix and adhesion molecules). In addition to the fact that OEC can ensheath and/or myelinate central axons, migrate in the CNS and accompany the growing axons over a relatively long distance, they also can be obtained from olfactory mucosa. OEC thus constitute a preferential candidate for autologous transplantation for the purposes of repair.

Olfactory ensheathing cells and spinal cord repair

The olfactory ensheathing cell is a specialized glial cell that assists in growth of the axons of the olfactory sensory neurons as they are generated and regenerated throughout adult life. There is increasing evidence in animal models that transplantation of olfactory ensheathing cell promotes recovery after transplantation into the injured spinal cord. Olfactory ensheathing cell transplants have promoted regrowth of axons across the injury site and led to recovery of functional behaviours including climbing, walking, reaching, and breathing. Most evidence comes from olfactory ensheathing cells derived from the olfactory bulb. This is an impractical site for human biopsy compared to the easy accessibility of olfactory ensheathing cells from the olfactory mucosa in the nose. Our experiments demonstrated that nasal olfactory ensheathing cells led to functional improvement after complete spinal cord transaction in rat. After devising methods to grow human olfactory ensheathing cells from nasal biopsy we recently initiated a Phase I clinical trial of transplantation into the human paraplegic spinal cord.

Cell death and axon regeneration of Purkinje cells after axotomy: challenges of classical hypotheses of axon regeneration

Although adult mammalian neurons are able to regenerate their axons in the peripheral nervous system under certain conditions, they are not able to do it in the central nervous system. The environment surrounding the severed axons appears to be a key factor for axon regeneration. Many studies aiming to enhance axon regeneration in the CNS of adult mammals have successfully manipulated this environment by adding growth permissive molecules and/or neutralizing growth inhibitory molecules. In both cases, the number of axons able to regenerate was low and the different neuronal populations were not equal in their regenerative response, suggesting that manipulation of the environment is not always sufficient. This is particularly well illustrated in the cerebellar system, in which axotomized inferior olivary neurons regenerate when confronted with a permissive environment, whereas mature Purkinje cells do not. The intrinsic ability of a neuron to regenerate its axon is generally correlated with the intensity of its reaction to axotomy (expression of molecules, probability to die). Furthermore, molecules such as GAP-43 (growth-associated molecule) and c-Jun are involved in both axon regeneration and cell death suggesting that these two processes are linked. Surprisingly, Purkinje cells lose their capacity to regenerate their axon (even in the absence of myelin) during development before losing their capacity to react to an axotomy by cell death. These results emphasize the different reactions to axotomy between neuron types and underline that in Purkinje cells, the two cell decisions (axon regeneration and cell death) are differently regulated and therefore not part of the same signaling pathway.

Ultrastructural study of the primary olfactory pathway inMacaca fascicularis

Olfactory ensheathing glial cells (OEGs) interact with a wide repertoire of cell types and support extension of olfactory axons (OAs) within the olfactory pathway. OEGs are thought to exclude OAs from contact with all other cells between the olfactory epithelium and the glomerulus of the olfactory bulb. These properties have lead to testing to determine whether OEGs support axonal growth following transplantation. The cellular interactions of transplanted OEGs will probably resemble those that occur within the normal pathway where interactions between OEGs and fibroblasts are prominent. No previous primate studies have focused on these interactions, knowledge of which is important if clinical application is envisioned. We describe the detailed intercellular interactions of OAs with supporting cells throughout the olfactory epithelium, the lamina propria, the fila olfactoria, and the olfactory nerve layer by using transmission electron microscopy in adult Macaca fascicularis. Patterns of OEG ensheathment and variations of the endo- and perineurium formed by olfactory nerve fibroblasts are described. OAs mainly interacted with horizontal basal cells, OEGs, and astrocytes. At both transitional ends of the pathway seamless intercellular interactions were observed, and fibroblast processes were absent. Perineurial cells produced surface basal lamina; however, endoneurial, epineurial, and meningeal fibroblasts did not. Perineurial cells contained intermediate filaments and were distinct from other fibroblasts and meningeal cells. OAs had direct contacts with astrocytes near the glia limitans. The properties of OEGs differed depending on whether astrocytic or fibroblastic processes were present. This indicates the importance of the cellular milieu in the structure and function of OEGs in primates.

Phrenic rehabilitation and diaphragm recovery after cervical injury and transplantation of olfactory ensheathing cells

Functional respiratory recovery was evaluated by recording diaphragm and phrenic nerve activity several months after cervical cord hemisection followed by olfactory ensheathing cell (OEC) transplantation. The intact side was taken as a control in each rat. Sham-transplanted rats did not recover respiratory activity from the ipsilateral lesioned side. By contrast, ipsilateral phrenic and diaphragmatic activities recovered in transplanted rats amounted to 80.7% and 73% of their controls, respectively. After contralateral acute C1 section eliminating any contralateral influence from crossed compensatory pathways, the ipsilateral phrenic activity remained at 57.5% of the control, indicating that the phrenic recovery originated from the ipsilateral side. Supralesional stimulation in these rats elicited sublesional ipsilateral postsynaptic phrenic responses showing that transplantation helped ipsilateral fibers to again transmit nervous messages to the phrenic target, leading to substantial functional recovery. The origin of mechanisms involved in respiratory recovery (regeneration, resurrection, sprouting, sparing, demasking of latent pathways) is discussed.

Central nervous system lesions that can and those that cannot be repaired with the help of olfactory bulb ensheathing cell transplants

Growth-promoting macroglia (aldynoglia) with growth properties and immunological markers similar to Schwann cells, are found in loci of the mammalian CNS where axon regeneration occurs throughout life, like the olfactory sytem, hypothalamus-hypophysis and the pineal gland. Contrary to Schwann cells, aldynoglia mingle freely with astrocytes and can migrate in brain and spinal cord. Transplantation of cultured and immunopurified olfactory ensheathing cells (OECs) in the spinal cord after multiple central rhizotomy, promoted sensory and central axon growth and partial functional restoration, judging by anatomical, electrophysiological and behavioural criteria. OEC transplants suppressed astrocyte reactivity, thus generally favouring axon growth after a lesion. However, the functional repair promoted by OEC transplants was partial in the best cases, depending on lesion type and location. Cyst formation after photochemical cord lesion was partially prevented but neither the corticospinal tract, interrupted by a mild contusion, nor the sectioned medial longitudinal fascicle, did regrow after OEC transplantation in the injured area.

Olfactory ensheathing cells promote collateral axonal branching in the injured adult rat spinal cord

In recent years, injection of olfactory ensheathing cells (ECs) into the spinal cord has been used as an experimental strategy to promote regeneration of injured axons. In this study, we have compared the effects of transplanting encapsulated ECs with those injected directly into the spinal cord. The dorsal columns of adult rats were cut at T(8-9) and rats in experimental groups received either EC-filled porous polymer capsules or culture medium (CM)-filled capsules with ECs injected at the injury site. Control rats were in three groups: (1) uninjured, (2) lesion with transplantation of CM-filled capsules and (3) lesion with transplantation of CM-filled capsules and injections of CM. Three weeks after injury, Fluororuby was injected into the hindlimb motor and somatosensory cortex to label corticospinal neurons. Observations indicated that there were a few regenerating fibres, up to 10, in the EC-treated groups. In rats that received encapsulated ECs, regenerating fibres were present in close association with the capsule. Rats that received EC injections demonstrated a significant increase in the number of collateral branches from the intact ventral corticospinal tract (vCST) compared with the corresponding control, CM-injected group (P=0.003), while a trend for increased collateral branches was observed in rats that received encapsulated ECs (P=0.07).

Peripherally-derived olfactory ensheathing cells do not promote primary afferent regeneration following dorsal root injury

Olfactory ensheathing cells (OECs) may support axonal regrowth, and thus might be a viable treatment for spinal cord injury (SCI); however, peripherally-derived OECs remain untested in most animal models of SCI. We have transplanted OECs from the lamina propria (LP) of mice expressing green fluorescent protein (GFP) in all cell types into immunosuppressed rats with cervical or lumbar dorsal root injuries. LP-OECs were deposited into either the dorsal root ganglion (DRG), intact or injured dorsal roots, or the dorsal columns via the dorsal root entry zone (DREZ). LP-OECs injected into the DRG or dorsal root migrated centripetally, and migration was more extensive in the injured root than in the intact root. These peripherally deposited OECs migrated within the PNS but did not cross the DREZ; similarly, large- or small-caliber primary afferents were not seen to regenerate across the DREZ. LP-OEC deposition into the dorsal columns via the DREZ resulted in a laminin-rich injection track: due to the pipette trajectory, this track pierced the glia limitans at the DREZ. OECs migrated centrifugally through this track, but did not traverse the DREZ; axons entered the spinal cord via this track, but were not seen to reenter CNS tissue. We found a preferential association between CGRP-positive small- to medium-diameter afferents and OEC deposits in injured dorsal roots as well as within the spinal cord. In the cord, OEC deposition resulted in increased angiogenesis and altered astrocyte alignment. These data are the first to demonstrate interactions between sensory axons and peripherally-derived OECs following dorsal root injury.

Lysophosphatidic acid regulates the proliferation and migration of olfactory ensheathing cells in vitro

Olfactory ensheathing cells (OECs) are a unique type of macroglia with axonal growth-promoting properties. However, our understanding of the factors that regulate OECs is at early stages. Lysophosphatidic acid (LPA) is a lipid that influences diverse functions in the nervous system. Recent studies suggest that glial cells, including astrocytes and Schwann cells, are important targets of LPA. However, the influences of LPA on OECs are not known. To address if LPA can influence OECs, we examined effects of LPA on the proliferation and migration of OECs and intracellular effector events. Initially, we observed that OECs expressed the genes for LPA1, LPA2, and LPA3 receptors. When OECs were treated with LPA, we observed stimulated proliferation and migration of OECs. Treatment of OECs with LPA also induced actin cytoskeleton reorganization and focal adhesion assembly. These effects of LPA were blocked by treatment with C3 exoenzyme or Y-27632, which inhibit Rho-GTPase and Rho-associated kinase, respectively. Effects of LPA on OEC proliferation were blocked by the MEK inhibitors PD098059 and U0126 and by the phosphotidylinositol 3-kinase (PI 3-K) inhibitors LY0294002 and wortmannin. These results show that LPA acts via Rho-GTPase, MAPK, and PI 3-K signaling cascades to influence OEC proliferation, migration, and cytoskeleton assembly.

Ex vivo adenoviral vector-mediated neurotrophin gene transfer to olfactory ensheathing glia: effects on rubrospinal tract regeneration, lesion size, and functional recovery after implantation in the injured rat spinal cord

The present study uniquely combines olfactory ensheathing glia (OEG) implantation with ex vivo adenoviral (AdV) vector-based neurotrophin gene therapy in an attempt to enhance regeneration after cervical spinal cord injury. Primary OEG were transduced with AdV vectors encoding rat brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), or bacterial marker protein beta-galactosidase (LacZ) and subsequently implanted into adult Fischer rats directly after unilateral transection of the dorsolateral funiculus. Implanted animals received a total of 2 x 105 OEG that were subjected to transduction with neurotrophin-encoding AdV vector, AdV-LacZ, or no vector, respectively. At 4 months after injury, lesion volumes were smaller in all OEG implanted rats and significantly reduced in size after implantation of neurotrophin-encoding AdV vector-transduced OEG. All OEG grafts were filled with neurofilament-positive axons, and AdV vector-mediated expression of BDNF by implanted cells significantly enhanced regenerative sprouting of the rubrospinal tract. Behavioral analysis revealed that OEG-implanted rats displayed better locomotion during horizontal rope walking than unimplanted lesioned controls. Recovery of hind limb function was also improved after implantation of OEG that were transduced with a BDNF- or NT-3-encoding AdV vector. Hind limb performance during horizontal rope locomotion did directly correlate with lesion size, suggesting that neuroprotective effects of OEG implants contributed to the level of functional recovery. Thus, our results demonstrate that genetic engineering of OEG not only resulted in a cell that was more effective in promoting axonal outgrowth but could also lead to enhanced recovery after injury, possibly by sparing of spinal tissue.

Olfactory ensheathing cells: historical perspective and therapeutic potential

Olfactory ensheathing cells (OECs) are the glial cells that ensheath the axons of the first cranial nerve. They are attracting increasing attention from neuroscientists as potential therapeutic agents for use in the repair of spinal cord injury and as a source of myelinating glia for use in remyelinating axons in demyelinating diseases such as multiple sclerosis. This review mainly addresses the cell biological aspects of OECs pertinent to addressing two questions. Namely, where do OECs fit into the groupings of central nervous system (CNS)/peripheral nervous system (PNS) glial cells and should OECs be viewed as a clinically relevant alternative to Schwann cells in the treatment of spinal cord injury? The evidence indicates that OECs are indeed a clinically relevant alternative to Schwann cells. However, much more work needs to be done before we can even come close to answering the first question as to the lineage and functional relationship of OECs to the other types of CNS and PNS glial cells.

Viral vector-mediated gene expression in olfactory ensheathing glia implants in the lesioned rat spinal cord

Implantation of olfactory ensheathing glia (OEG) is a promising strategy to augment long-distance regeneration in the injured spinal cord. In this study, implantation of OEG following unilateral hemisection of the dorsal cervical spinal cord was combined with ex vivo gene transfer techniques. We report, to our knowledge for the first time, that purified cultures of primary OEG are capable of expressing a foreign gene following adenoviral (AdV) and lentiviral (LV) vector-mediated gene transfer. OEG implants subjected to AdV vector-mediated gene transfer expressed high levels of transgenic protein in both intact and lesioned spinal cord at 7 days after implantation. However, the levels of transgene expression gradually declined between 7 and 30 days after implantation in lesioned spinal cord. Infection with LV vectors resulted in stable transduction of primary OEG cultures and transgene expression persisted for at least 4 months after implantation. Genetic engineering of OEG opens the possibility of expressing additional neurotrophic genes and create optimal 'bridging' substrates to support spinal axon regeneration. Furthermore, stable transduction of OEG allows us to reliably study the behaviour of implanted cells and to obtain better understanding of their regeneration supporting properties.

In early development of the rat mRNA for the major myelin protein P(0) is expressed in nonsensory areas of the embryonic inner ear, notochord, enteric nervous system, and olfactory ensheathing cells

The myelin protein P(0) has a major structural role in Schwann cell myelin, and the expression of P(0) protein and mRNA in the Schwann cell lineage has been extensively documented. We show here, using in situ hybridization, that the P(0) gene is also activated in a number of other tissues during embryonic development. P(0) mRNA is first detectable in 10-day-old embryos (E10) and is at this time seen only in cells in the cephalic neural crest and in the otic placode/pit. P(0) expression continues in the otic vesicle and at E12 P(0) expression in this structure largely overlaps with expression of another myelin gene, proteolipid protein. In the developing ear at E14, P(0) expression is complementary to expression of serrate and c-ret mRNAs, which later are expressed in sensory areas of the inner ear, while expression of bone morphogenetic protein (BMP)-4 and P(0), though largely complementary, shows small areas of overlap. P(0) mRNA and protein are detectable in the notochord from E10 to at least E13. In addition to P(0) expression in a subpopulation of trunk crest cells at E11/E12 and in Schwann cell precursors thereafter, P(0) mRNA is also present transiently in a subpopulation of cells migrating in the enteric neural crest pathway, but is down-regulated in these cells at E14 and thereafter. P(0) is also detected in the placode-derived olfactory ensheathing cells from E13 and is maintained in the adult. No signal is seen in cells in the melanocyte migration pathway or in TUJ1 positive neuronal cells in tissue sections. The activation of the P(0) gene in specific tissues outside the nervous system was unexpected. It remains to be determined whether this is functionally significant, or whether it is an evolutionary relic, perhaps reflecting ancestral use of P(0) as an adhesion molecule.