Adult rat olfactory nerve ensheathing cells are effective promoters of adult central nervous system neurite outgrowth in coculture

Human placenta-derived mesenchymal stem cells stimulate neuronal regeneration by promoting axon growth and restoring neuronal activity

In the last decades, mesenchymal stem cells (MSCs) have become the cornerstone of cellular therapy due to their unique characteristics. Specifically human placenta-derived mesenchymal stem cells (hPMSCs) are highlighted for their unique features, including ease to isolate, non-invasive techniques for large scale cell production, significant immunomodulatory capacity, and a high ability to migrate to injuries. Researchers are exploring innovative techniques to overcome the low regenerative capacity of Central Nervous System (CNS) neurons, with one promising avenue being the development of tailored mesenchymal stem cell therapies capable of promoting neural repair and recovery. In this context, we have evaluated hPMSCs as candidates for CNS lesion regeneration using a skillful co-culture model system. Indeed, we have demonstrated the hPMSCs ability to stimulate damaged rat-retina neurons regeneration by promoting axon growth and restoring neuronal activity both under normoxia and hypoxia conditions. With our model we have obtained neuronal regeneration values of 10%-14% and axonal length per neuron rates of 19-26, μm/neuron. To assess whether the regenerative capabilities of hPMSCs are contact-dependent effects or it is mediated through paracrine mechanisms, we carried out transwell co-culture and conditioned medium experiments confirming the role of secreted factors in axonal regeneration. It was found that hPMSCs produce brain derived, neurotrophic factor (BDNF), nerve-growth factor (NGF) and Neurotrophin-3 (NT-3), involved in the process of neuronal regeneration and restoration of the physiological activity of neurons. In effect, we confirmed the success of our treatment using the patch clamp technique to study ionic currents in individual isolated living cells demonstrating that in our model the regenerated neurons are electrophysiologically active, firing action potentials. The outcomes of our neuronal regeneration studies, combined with the axon-regenerating capabilities exhibited by mesenchymal stem cells derived from the placenta, present a hopeful outlook for the potential therapeutic application of hPMSCs in the treatment of neurological disorders.

Combined treatment of retinoic acid with olfactory ensheathing cells protect gentamicin-induced SGNs damage in the rat cochlea in vitro

Hearing is mainly dependent on the function of hair cells (HCs) and spiral ganglion neurons (SGNs) which damage or loss of them leads to irreversible hearing loss. Olfactory ensheathing cells (OECs) are specialized glia that forms the fascicles of the olfactory nerve by surrounding the olfactory sensory axons. The OECs, as a regenerating part of the nervous system, play a supporting function in axonal regeneration and express a wide range of growth factors. In addition, retinoic acid (RA) enhances the proliferation and differentiation of these cells into the nerve. In the present study, we co-cultured human OECs (hOECs) with cochlear SGNs in order to determine whether hOECs and RA co-treatment can protect the repair process in gentamycin-induced SGNs damage in vitro. For this purpose, cochlear cultures were prepared from P4 Wistar rats, which were randomly appointed to four groups: normal cultivated SGNs (Control), gentamicin-lesioned SGNs culture (Gent), gentamicin-lesioned SGNs culture treated with OECs (Gent + OECs) and gentamicin-lesioned SGNs culture co-treated with OECs and RA (Gent + OEC& RA). The expression of a specific protein in SGNs was examined using immunohistochemical and Western blotting technique. TUNEl staining was used to detect cell apoptosis. Here, we revealed that combined treatment of OECs and RA protect synapsin and Tuj-1 expression in the lesioned SGNs and attenuate cell apoptosis. These findings suggest that RA co-treatment can enhance efficiency of OECs in repair of SGNs damage induced by ototoxic drug.

The proteome of distal nerves: implication in delayed repair and poor functional recovery

Chronic denervation is one of the key factors that affect nerve regeneration. Chronic axotomy deteriorates the distal nerve stump, causes protein changes, and renders the microenvironment less permissive for regeneration. Some of these factors/proteins have been individually studied. To better delineate the comprehensive protein expression profiles and identify proteins that contribute to or are associated with this detrimental effect, we carried out a proteomic analysis of the distal nerve using an established delayed rat sciatic nerve repair model. Four rats that received immediate repair after sciatic nerve transection served as control, whereas four rats in the experimental group (chronic denervation) had their sciatic nerve repaired after a 12-week delay. All the rats were sacrificed after 16 weeks to harvest the distal nerves for extracting proteins. Twenty-five micrograms of protein from each sample were fractionated in SDS-PAGE gels. NanoLC-MS/MS analysis was applied to the gels. Protein expression levels of nerves on the surgery side were compared to those on the contralateral side. Any protein with a P value of less than 0.05 and a fold change of 4 or higher was deemed differentially expressed. All the differentially expressed proteins in both groups were further stratified according to the biological processes. A PubMed search was also conducted to identify the differentially expressed proteins that have been reported to be either beneficial or detrimental to nerve regeneration. Ingenuity Pathway Analysis (IPA) software was used for pathway analysis. The results showed that 709 differentially expressed proteins were identified in the delayed repair group, with a bigger proportion of immune and inflammatory process-related proteins and a smaller proportion of proteins related to axon regeneration and lipid metabolism in comparison to the control group where 478 differentially expressed proteins were identified. The experimental group also had more beneficial proteins that were downregulated and more detrimental proteins that were upregulated. IPA revealed that protective pathways such as LXR/RXR, acute phase response, RAC, ERK/MAPK, CNTF, IL-6, and FGF signaling were inhibited in the delayed repair group, whereas three detrimental pathways, including the complement system, PTEN, and apoptosis signaling, were activated. An available database of the adult rodent sciatic nerve was used to assign protein changes to specific cell types. The poor regeneration seen in the delayed repair group could be associated with the down-regulation of beneficial proteins and up-regulation of detrimental proteins. The proteins and pathways identified in this study may offer clues for future studies to identify therapeutic targets.

Chemotactic TEG3 Cells' Guiding Platforms Based on PLA Fibers Functionalized With the SDF-1α/CXCL12 Chemokine for Neural Regeneration Therapy

(Following spinal cord injury, olfactory ensheathing cell (OEC) transplantation is a promising therapeutic approach in promoting functional improvement. Some studies report that the migratory properties of OECs are compromised by inhibitory molecules and potentiated by chemical concentration differences. Here we compare the attachment, morphology, and directionality of an OEC-derived cell line, TEG3 cells, seeded on functionalized nanoscale meshes of Poly(l/dl-lactic acid; PLA) nanofibers. The size of the nanofibers has a strong effect on TEG3 cell adhesion and migration, with the PLA nanofibers having a 950 nm diameter being the ones that show the best results. TEG3 cells are capable of adopting a bipolar morphology on 950 nm fiber surfaces, as well as a highly dynamic behavior in migratory terms. Finally, we observe that functionalized nanofibers, with a chemical concentration increment of SDF-1α/CXCL12, strongly enhance the migratory characteristics of TEG3 cells over inhibitory substrates.

Impact of Dual Cell Co-culture and Cell-conditioned Media on Yield and Function of a Human Olfactory Cell Line for Regenerative Medicine

Olfactory ensheathing cells (OECs) are a promising candidate therapy for neuronal tissue repair. However, appropriate priming conditions to drive a regenerative phenotype are yet to be determined. We first assessed the effect of using a human fibroblast feeder layer and fibroblast conditioned media on primary rat olfactory mucosal cells (OMCs). We found that OMCs cultured on fibroblast feeders had greater expression of the key OEC marker p75NTR (25.1 ± 10.7 cells/mm²) compared with OMCs cultured on laminin (4.0 ± 0.8 cells/mm², p = 0.001). However, the addition of fibroblast-conditioned media (CM) resulted in a significant increase in Thy1.1 (45.9 ± 9.0 cells/mm² versus 12.5 ± 2.5 cells/mm² on laminin, p = 0.006), an undesirable cell marker as it is regarded to be a marker of contaminating fibroblasts. A direct comparison between human feeders and GMP cell line Ms3T3 was then undertaken. Ms3T3 cells supported similar p75NTR levels (10.7 ± 5.3 cells/mm²) with significantly reduced Thy1.1 expression (4.8 ± 2.1 cells/mm²). Ms3T3 cells were used as feeder layers for human OECs to determine whether observations made in the rat model were conserved. Examination of the OEC phenotype (S100β expression and neurite outgrowth from NG108-15 cells) revealed that co-culture with fibroblast feeders had a negative effect on human OECs, contrary to observations of rat OECs. CM negatively affected rat and human OECs equally. When the best and worst conditions in terms of supporting S100β expression were used in NG108-15 neuron co-cultures, those with the highest S100β expression resulted in longer and more numerous neurites (22.8 ± 2.4 μm neurite length/neuron for laminin) compared with the lowest S100β expression (17.9 ± 1.1 μm for Ms3T3 feeders with CM). In conclusion, this work revealed that neither dual co-culture nor fibroblast-conditioned media support the regenerative OEC phenotype. In our case, a preliminary rat model was not predictive of human cell responses.

Olfactory Ensheathing Cells: A Trojan Horse for Glioma Gene Therapy

BACKGROUND

The olfactory ensheathing cells (OECs) migrate from the peripheral nervous system to the central nervous system (CNS), a critical process for the development of the olfactory system and axonal extension after injury in neural regeneration. Because of their ability to migrate to the injury site and anti-inflammatory properties, OECs were tested against different neurological pathologies, but were never studied in the context of cancer. Here, we evaluated OEC tropism to gliomas and their potential as a "Trojan horse" to deliver therapeutic transgenes through the nasal pathway, their natural route to CNS.

METHODS

OECs were purified from the mouse olfactory bulb and engineered to express a fusion protein between cytosine deaminase and uracil phosphoribosyltransferase (CU), which convert the prodrug 5-fluorocytosine (5-FC) into cytotoxic metabolite 5-fluorouracil, leading to a bystander killing of tumor cells. These cells were injected into the nasal cavity of mice bearing glioblastoma tumors and OEC-mediated gene therapy was monitored by bioluminescence imaging and confirmed with survival and ex vivo histological analysis. All statistical tests were two-sided.

RESULTS

OECs migrated from the nasal pathway to the primary glioma site, tracked infiltrative glioma stemlike cells, and delivered therapeutic transgene, leading to a slower tumor growth and increased mice survival. At day 28, bioluminescence imaging revealed that mice treated with a single injection of OEC-expressing CU and 5-FC had tumor-associated photons (mean [SD]) of 1.08E + 08 [9.7E + 07] vs 4.1E + 08 [2.3E + 08] for control group (P < .001), with a median survival of 41 days vs 34 days, respectively (ratio = 0.8293, 95% confidence interval = 0.4323 to 1.226, P <  .001) (n = 9 mice per group).

CONCLUSIONS

We show for the first time that autologous transplantation of OECs can target and deliver therapeutic transgenes to brain tumors upon intranasal delivery, the natural route of OECs to the CNS, which could be extended to other types of cancer.

The controlled design of electrospun PCL/silk/quercetin fibrous tubular scaffold using a modified wound coil collector and L-shaped ground design for neural repair

Asymmetrically porous and aligned fibrous tubular conduit with selective permeability as a biomimetic neural scaffold was manufactured using polycaprolactone (PCL), silk, and quercetin by a modified electrospinning method. The outer surface of the randomly oriented fibrous scaffold had microscale pores that could prevent fibrous tissue invasion (FTI), but could permeate neurotrophic factors, nutrients, and oxygen. The inner surface of the aligned fibrous scaffold can be favorable for neurite outgrowth, because of their superior neural cell attachment, migration, and directional growth. In vitro and in vivo studies have demonstrated the therapeutic effect of Quercetin, a ubiquitous flavonoid widely distributed in plants, on neuropathy, by modulating the expression of NRF-2-dependent antioxidant responsive elements. In this study, the controlled inner and outer surface geometry of the 0.5, 1.0, and 2.0 wt% quercetin-containing electrospun PCL/silk fibrous tubular scaffold fabricated via a modified wound coil collector and L-shaped ground design (WCC-LG) was characterized by FE-SEM, TEM, FFT, FT-IR, and XRD. In addition, two types of neural cell lines, PC12 and S42, were used to evaluate the cell proliferation rate of the different amount of quercetin-loaded PCL/silk tubular scaffolds.

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.

Bioprocessing strategies to enhance the challenging isolation of neuro-regenerative cells from olfactory mucosa

Olfactory ensheathing cells (OECs) are a promising potential cell therapy to aid regeneration. However, there are significant challenges in isolating and characterizing them. In the current study, we have explored methods to enhance the recovery of cells expressing OEC marker p75NTR from rat mucosa. With the addition of a 24-hour differential adhesion step, the expression of p75NTR was significantly increased to 73 ± 5% and 46 ± 18% on PDL and laminin matrices respectively. Additionally, the introduction of neurotrophic factor NT-3 and the decrease in serum concentration to 2% FBS resulted in enrichment of OECs, with p75NTR at nearly 100% (100 ± 0% and 98 ± 2% on PDL and laminin respectively), and candidate fibroblast marker Thy1.1 decreased to zero. Culturing OECs at physiologically relevant oxygen tension (2-8%) had a negative impact on p75NTR expression and overall cell survival. Regarding cell potency, co-culture of OECs with NG108-15 neurons resulted in more neuronal growth and potential migration at atmospheric oxygen. Moreover, OECs behaved similarly to a Schwann cell line positive control. In conclusion, this work identified key bioprocessing fundamentals that will underpin future development of OEC-based cell therapies for potential use in spinal cord injury repair. However, there is still much work to do to create optimized isolation methods.

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.

Harnessing Nanotopography of Electrospun Nanofibrous Nerve Guide Conduits (NGCs) for Neural Tissue Engineering

The anatomical recovery of nerve defects with their neurological functions after an injury caused by diseases or accidents is an important clinical issue. The most efficient surgical technique so far to the nerve defects, which are unrepairable by direct end-to-end suture, can be autograft transplantation. The autograft transplantation, however, has disadvantages including multiple rounds of surgery, a shortage of nerve donor, and function loss at the donor site. Tissue-engineered nerve guide conduits (TENGCs) have emerged as a potential alternative to autologous nerve grafts for nerve regeneration and functional recovery. Various TENGCs researches are being carried out to improve characteristics and enhance functionality such as material selection, biomimetic, topography, and enhancement by the biomolecules additions. Among them, the customizable surface nanotopography of aligned fibrous TENGCs foster neural repair by providing a cell-friendly environment, permissiveness, guidance cues, and directional growth of the cells. Fibrous nerve guide conduits (NGCs) made of longitudinally ordered fibers is a promising candidate for nerve tissue engineering.

Transduction of an immortalized olfactory ensheathing glia cell line with the green fluorescent protein (GFP) gene: Evaluation of its neuroregenerative capacity as a proof of concept

Olfactory ensheathing glia (OEG) cells are known to foster axonal regeneration of central nervous system (CNS) neurons. Several lines of reversibly immortalized human OEG (ihOEG) have been previously established that enabled to develop models for their validation in vitro and in vivo. In this work, a constitutively GFP-expressing ihOEG cell line was obtained, and named Ts14-GFP. Ts14-GFP neuroregenerative ability was similar to that found for the parental line Ts14 and it can be assayed using in vivo transplantation experimental paradigms, after spinal cord or optic nerve damage. Additionally, we have engineered a low-regenerative ihOEG line, hTL2, using lentiviral transduction of the large T antigen from SV40 virus, denominated from now on Ts12. Ts12 can be used as a low regeneration control in these experiments.

Olfactory ensheathing cell-neurite alignment enhances neurite outgrowth in scar-like cultures

The regenerative capacity of adult CNS neurons after injury is strongly inhibited by the spinal cord lesion site environment that is composed primarily of the reactive astroglial scar and invading meningeal fibroblasts. Olfactory ensheathing cell (OEC) transplantation facilitates neuronal survival and functional recovery after a complete spinal cord transection, yet the mechanisms by which this recovery occurs remain unclear. We used a unique multicellular scar-like culture model to test if OECs promote neurite outgrowth in growth-inhibitory areas. Astrocytes were mechanically injured and challenged by meningeal fibroblasts to produce key inhibitory elements of a spinal cord lesion. Neurite outgrowth of postnatal cerebral cortical neurons was assessed on three substrates: quiescent astrocyte control cultures, reactive astrocyte scar-like cultures, and scar-like cultures with OECs. Initial results showed that OECs enhanced total neurite outgrowth of cortical neurons in a scar-like environment by 60%. We then asked if the neurite growth-promoting properties of OECs depended on direct alignment between neuronal and OEC processes. Neurites that aligned with OECs were nearly three times longer when they grew on inhibitory meningeal fibroblast areas and twice as long on reactive astrocyte zones compared to neurites not associated with OECs. Our results show that OECs can independently enhance neurite elongation and that direct OEC-neurite cell contact can provide a permissive substrate that overcomes the inhibitory nature of the reactive astrocyte scar border and the fibroblast-rich spinal cord lesion core.

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.

Cell type- and isotype-specific expression and regulation of β-tubulins in primary olfactory ensheathing cells and Schwann cells in vitro

Olfactory ensheathing cells (OECs) and Schwann cells (SCs) are closely-related cell types with regeneration-promoting properties. Comparative gene expression analysis is particularly relevant since it may explain cell type-specific effects and guide the use of each cell type into special clinical applications. In the present study, we focused on β-tubulin isotype expression in primary adult canine glia as a translational large animal model. β-tubulins so far have been studied mainly in non-neuronal tumors and implied in tumorigenic growth. We show here that primary OECs and SCs expressed βII-V isotype mRNA. Interestingly, βIII-tubulin mRNA and protein expression was high in OECs and low in SCs, while fibroblast growth factor-2 (FGF-2) induced its down-regulation in both cell types to the same extent. This was in contrast to βV-tubulin mRNA which was similarly expressed in both cell types and unaltered by FGF-2. Immunocytochemical analysis revealed that OEC cultures contained a higher percentage of βIII-tubulin-positive cells compared to SC cultures. Addition of FGF-2 reduced the number of βIII-tubulin-positive cells in both cultures and significantly increased the percentage of cells with a multipolar morphology. Taken together, we demonstrate cell type-specific expression (βIII) and isotype-specific regulation (βIII, βV) of β-tubulin isotypes in OECs and SCs. While differential expression of βIII-tubulin in primary glial cell types with identical proliferative behaviour argues for novel functions unrelated to tumorigenic growth, strong βIII-tubulin expression in OECs may help to explain the specific properties of this glial cell type.

Cell transplantation approaches to retinal ganglion cell neuroprotection in glaucoma

Glaucoma is a complex neurodegenerative disease that involves interactions among multiple signaling pathways, ultimately leading to progressive retinal ganglion cell (RGC) death. The development of neuroprotective approaches to glaucoma therapy could preserve vision by modulating these pathologic pathways or by acting directly on RGCs to attenuate cell death and maintain function. Intraocular cell transplantation is being evaluated as one approach to achieve sustained RGC neuroprotection. Unlike traditional pharmacological approaches, transplanted cells might be capable of simultaneously targeting multiple pro-survival pathways via local delivery of secreted factors and/or via modulation of the intraocular microenvironment. Elucidating the mechanisms by which different cell types attenuate RGC death in models of glaucoma may uncover additional novel mechanisms of neuroprotection. In this review, we will discuss the rationale for transplantation-based approaches to neuroprotection for glaucoma and explore the various mechanisms of action proposed to account for RGC neuroprotection achieved by two distinct cell classes that have been studied most extensively for this purpose: glial cells and mesenchymal stem cells.

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.

RhoA-ROCK-Myosin pathway regulates morphological plasticity of cultured olfactory ensheathing cells

Olfactory ensheathing cells (OECs) are glial cells in the olfactory system with morphological and functional plasticity. Cultured OECs have the flattened and process-bearing shape. Reversible changes have been found between these two morphological phenotypes. However, the molecular mechanism underlying the regulation of their morphological plasticity remains elusive. Using RhoA FRET biosensor, we found that the active RhoA signal mainly distributed in the lamellipodia and/or filopodia of OECs. Local disruption of these active RhoA distributions led to the morphological change from the flattened into process-bearing shape and promoted process outgrowth. Furthermore, RhoA pathway inhibitors, Toxin-B, C3, Y-27632 or over-expression of DN-RhoA blocked serum-induced morphological change of OECs from the process-bearing into flattened shape, whereas the activation of RhoA pathway by lysophosphatidic acid (LPA) promoted the morphological change from the process-bearing into flattened shape. Finally, ROCK-Myosin-F-actin as a downstream of RhoA pathway was involved in morphological plasticity of OECs. Taken together, these results suggest that RhoA-ROCK-Myosin pathway mediates the morphological plasticity of cultured OECs in response to extracellular cues.

Expression of plasminogen activator inhibitor-1 by olfactory ensheathing glia promotes axonal regeneration

Olfactory ensheathing glia (OEG) cells are known to facilitate repair following axotomy of adult neurons, although the molecular mechanisms involved are not fully understood. We previously identified plasminogen activator inhibitor-1 (PAI-1), proteinase-activated receptor-1 (PAR-1), and thrombomodulin (TM) as candidates to regulate rat OEG-dependent axonal regeneration. In this study, we have validated the involvement of these proteins in promoting axonal regeneration by immortalized human OEGs. We studied the effect of silencing these proteins in OEGs on their capacity to promote the regeneration of severed adult retinal ganglion cells (RGCs) axons. Our results support the role of glial PAI-1 as a downstream effector of PAR-1 in promoting axon regeneration. In contrast, we found that TM inhibits OEG induced-axonal regeneration. We also assessed the signaling pathways downstream of PAR-1 that might modulate PAI-1 expression, observing that specifically inhibiting Gα(i), Rho kinase, or PLC and PKC downregulated the expression of PAI-1 in OEGs, with a concomitant reduction in OEG-dependent axon regeneration in adult RGCs. Our findings support an important role for the thrombin system in regulating adult axonal regeneration by OEGs.

Survival of retinal ganglion cells in slice culture provides a rapid screen for olfactory ensheathing cell preparations

Transplants of olfactory ensheathing cells (OECs) cultured from the olfactory bulb are able to induce structural regeneration of severed central axons and return of function in rat models. For clinical purposes it would be preferable to obtain the cells from the more accessible olfactory mucosa in the nasal lining. However, in our laboratory preparations cultures from mucosal samples yielded around 5% of OECs compared with the 50% obtained from samples cultured from the bulb, and when transplanted these mucosal cell preparations were less effective at repair. There are a number of manipulations which may increase the OEC content and the effectiveness of mucosal preparations, but in vivo transplantation would be a highly labour intensive method for evaluating them. As a candidate for a high throughput assay to screen for beneficial effects of modifications to mucosal cells we here report the effects of co-culture of the cells with retinal explants. Both bulbar and mucosal cell preparations prolong the survival of the explants. Counts of the surviving retinal ganglion cells, identified by beta-III-tubulin immunohistochemistry and by their axon trajectory, show that the bulbar cell preparations have around twice the potency of those from the mucosa. This in vitro system, therefore, provides a bioassay that discriminates bulbar and mucosal cell preparations, and a useful tool for evaluating the functional effects of manipulations of cultured mucosal preparations.

Olfactory ensheathing cell membrane properties are shaped by connectivity

Olfactory ensheathing cells (OECs) have been repeatedly implicated in mediating plasticity, particularly in situ in the olfactory nerve in which they support the extension of olfactory sensory neuron (OSN) axons from the olfactory epithelium to the olfactory bulb (OB). OECs are specialized glia whose processes surround OSN axon fascicles within the olfactory nerve and across the OB surface. Despite their purported importance in promoting axon extension, and following transplants, little is known about either morphology or biophysical properties of OECs in situ. In particular, cell-cell interactions that may influence OEC function are largely unexplored. Here, we studied OEC connectivity and morphology in slice preparations, preserving tissue structure and cell-cell interactions. Our analyses showed that OECs form a matrix of cellular projections surrounding axons, unique among glia, and express high levels of connexin-43. Lucifer Yellow injections revealed selective dye coupling among small subgroups of OECs. Two types of OECs were biophysically distinguished with whole-cell voltage-clamp recordings: (1) with low-input resistance (R(i)), linear current profiles, and frequently dye coupled; and (2) with high R(i), nonlinear current profiles, and infrequent dye coupling. Pharmacological blockade of gap junctions changed OEC membrane properties such that linear OECs became nonlinear. Double recordings indicated that the appearance of the nonlinear current profile was associated with the loss of electrical coupling between OECs. We conclude that the diversity of OEC current profiles can be explained by differences in gap-junction connectivity and discuss implications of this diversity for OEC influences on axon growth and excitability.

Survival-enhancing of spiral ganglion cells under influence of olfactory ensheathing cells by direct cellular contact

The efficacy of cochlear implantation is primarily associated with the quantity and health of the remaining spiral ganglion cells (SGCs). Olfactory ensheathing cells (OECs) are capable of expressing a variety of growth factors and adhesion molecules, playing an important role in enhancing cellular survival. To investigate the effect of OECs on the survival of SGCs, co-cultures of OECs and SGCs were developed in this study. In addition, OECs conditioned medium (OEC-CM) was employed to culture SGCs in contrast with the co-cultures. OECs were identified immunocytochemically by low-affinity nerve growth factor receptor p75 (P75NTR) and glial fibrillary acidic protein (GFAP), while SGCs were stained with neuron-specific markerbetaIII-tubulin. SGCs survival was assessed in different conditions. To explore the underlying mechanism, growth factors, adhesion molecules and their receptors were investigate using RT-PCR. Our results indicate that the co-cultures of OECs and SGCs can be successfully established and that both OECs and OEC-CM promote SGCs survival in vitro. SGCs survival was most enhanced when co-cultured with OECs. Both Olfactory bulb (OB) and OECs were proved to express BMP-4 and NCAM while BMPR-1A and a7 integrin were also detected in cochlea and SGCs. In conclusion, our results suggest that enhancement in co-cultures is in part due to direct cellular contact. Transplantation of OECs may be a cell-based therapy for the application of neurotrophic factors to the inner ear.

Morphological and biomolecular characterization of the neonatal olfactory bulb ensheathing cell line

Cell transplantation therapy has raised a great interest in the perspective of its employment for nerve tissue repair. Among the various cell populations proposed, olfactory ensheathing glial cells have raised great interest over recent years, especially in the perspective of their employment for neural repair because of their homing capacity in both central and peripheral nervous system. This paper is aimed to provide an in vitro characterization of the NOBEC (neonatal olfactory bulb ensheathing cell) line that was obtained from primary cells dissociated from rat neonatal olfactory bulb (OB) and immortalized by retroviral transduction of SV40 large T antigen. Light and electron microscopy investigation showed that NOBECs are a homogeneous cell population both at structural and ultrastructural level. RT-PCR, Western blotting and immunocytochemistry showed that NOBECs express the glial markers S100, GFAP (Glial Fibrillar Acid Protein) and p75NGFR as well as NRG1 (neuregulin-1) and ErbB1-2-3 receptors; while they are negative for ErbB4. Yet, NOBECs exhibit a high proliferation and migration basal activity and can be transducted with vectors carrying GFP (green fluorescent protein) and NRG1 cDNA. Functional stimulation by means of NRG1-III-beta3 overexpression through viral transduction induced a significant increase in cell proliferation rate while it had no effect on cell migration. Altogether, these results show that NOBEC cell line retain glial features both morphologically and functionally, responding to the NRG1/ErbB-mediated gliotrophic stimulus, and represents thus a good tool for in vitro assays of glial cell manipulation and for in vivo experimental studies of glial cell transplantation in the central and peripheral nervous system.

Olfactory ensheathing cells represent an optimal substrate for hippocampal neurons: an in vitro study

Olfactory ensheathing cells (OECs) are cells that display Schwann cell or astrocyte-like properties. They are a source of growth factors and adhesion molecules which play a very important role as neuronal support enhancing cellular survival. Over the past 10 years, OECs have emerged as a leading reparative candidate, when transplanted into the injured spinal cord, having shown significant promise in the regeneration of spinal cord lesions. In this study we assessed the efficacy of OECs on the survival and neurite outgrowth of hippocampal neurons in vitro. Co-cultures of OECs and hippocampal of postnatal rats were successfully established and cells were immunocytochemically characterized. Some hippocampal cultures were added with growth factors, as bFGF, NGF and GDNF. Furthermore, conditioned medium from OECs cultures was used to feed some hippocampal neurons coverslips. Our results show that in co-cultures of hippocampal neurons and OECs the number of neurons and their neurite outgrowth were significantly increased in comparison with controls. Moreover, we showed that NGF and GDNF promoted a more positive effect in both neuronal survival and neurite outgrowth than bFGF. OEC-conditioned media stimulated both the neuronal survival and dense neurite outgrowth. These data indicate that OECs, as a source of growth factors, can promote the survival and the neurite outgrowth of hippocampal neurons in vitro and that bFGF, NGF and GDNF support them differently. Therefore, as OECs and their secreted growth factors appear to exert a neuroprotective effect for functional restoration and for neural plasticity in neurodegenerative disorders, they might be considered an approach for functional recovery.

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.

Mouse olfactory ensheathing glia enhance axon outgrowth on a myelin substrate in vitro

Olfactory ensheathing glia (OEG) express cell adhesion molecules and secrete growth factors that support newly generated olfactory axons and are a promising therapeutic treatment to facilitate axonal regeneration after spinal cord injury (SCI). To study the molecular mechanisms underlying the ability of OEG to enhance axonal outgrowth, we designed an outgrowth assay using spinal cord myelin as a substrate to mimic an injury environment. We asked if olfactory bulb-derived OEG could enhance outgrowth of dorsal root ganglion (DRG) axons on myelin. When grown on myelin alone DRG axons have limited outgrowth potential. However, when OEG are co-cultured with DRG on myelin, twice as many neurons generate axons and their average length is almost twice that grown on myelin alone. We used this OEG/DRG co-culture to determine if a cell adhesion molecule expressed by OEG, L1, and a factor secreted by OEG, brain-derived neurotrophic factor (BDNF), contribute to the ability of OEG to enhance axonal outgrowth on myelin. Using OEG and DRG from L1 mutant mice we found that L1 expression does not contribute to OEG growth promotion. However, both BDNF and its receptor, TrkB, contribute to OEG-enhanced axon regeneration as function-blocking antisera against either component significantly decreased outgrowth of DRG axons. Additional BDNF further enhanced DRG axon growth on myelin alone and on myelin co-cultured with OEG. This simple mouse outgrowth model can be used to determine the molecules that contribute to OEG-enhancement of axonal outgrowth, test therapeutic compounds, and compare the outgrowth potential of other treatments for SCI.

Implantation of olfactory ensheathing cells promotes neuroplasticity in murine models of stroke

Murine olfactory ensheathing cells (OECs) promote central nervous system axonal regeneration in models of spinal cord injury. We investigated whether OECs could induce a neuroplastic effect to improve the neurological dysfunction caused by hypoxic/ischemic stress. In this study, human OECs/olfactory nerve fibroblasts (hOECs/ONFs) specifically secreted trophic factors including stromal cell-derived factor-1alpha (SDF-1alpha). Rats with intracerebral hOEC/ONF implantation showed more improvement on behavioral measures of neurological deficit following stroke than control rats. [18F]fluoro-2-deoxyglucose PET (FDG-PET) showed increased glucose metabolic activity in the hOEC/ONF-treated group compared with controls. In mice, transplanted hOECs/ONFs and endogenous homing stem cells including intrinsic neural progenitor cells and bone marrow stem cells colocalized with specific neural and vascular markers, indicating stem cell fusion. Both hOECs/ONFs and endogenous homing stem cells enhanced neuroplasticity in the rat and mouse ischemic brain. Upregulation of SDF-1alpha and CXCR4 in hOECs/ONFs promoted neurite outgrowth of cocultured primary cortical neurons under oxygen glucose deprivation conditions and in stroke animals through upregulation of cellular prion protein (PrP C) expression. Therefore, the upregulation of SDF-1alpha and the enhancement of CXCR4 and PrP C interaction induced by hOEC/ONF implantation mediated neuroplastic signals in response to hypoxia and ischemia.

Evaluation of neurite outgrowth anisotropy using a novel application of circular analysis

Precise axon growth is required for making proper connections in development and after injury. One method of studying axon guidance and growth is through in vitro outgrowth assays that present controlled microenvironments. In this study, we applied circular statistical methods to evaluate directional neurite response. Visualization of data on a circular scale allows more accurate representation of the data, as neurite angles are inherently expressed on a circle. Here, the direction of neurite outgrowth from dorsal root ganglia derived neurons on different substrate types was quantitatively measured. Further, simulations of datasets with known circular parameters reflecting expected neurite angle distributions from different substrate types were also generated. Circular statistical methods were utilized and compared to linear statistical models widely used in the neuroscience literature. For small samples, Rao's spacing test showed the smallest occurrence of Type I errors (false positives) when tested against simulated uniform distributions. V-test and Rayleigh's test showed highest statistical power when tested against a unimodal distribution with known and unknown mean direction, respectively. For bimodal samples, Watson's U(2)-test showed the highest statistical power. Overall, circular statistical uniformity tests showed higher statistical power than linear non-parametric tests, particularly for small samples (n=5). Circular analysis methods represent a useful tool for evaluation of directionality of neurite outgrowth with applications including: (1) assessment of neurite outgrowth potential; (2) determination of isotropy of cellular responses to single and multiple cues and (3) determination of the relative strengths of cues present in a complex environment.

Olfactory ensheathing glia: Their contribution to primary olfactory nervous system regeneration and their regenerative potential following transplantation into the injured spinal cord

Olfactory ensheathing glia (OEG) are a specialized type of glia that guide primary olfactory axons from the neuroepithelium in the nasal cavity to the brain. The primary olfactory system is able to regenerate after a lesion and OEG contribute to this process by providing a growth-supportive environment for newly formed axons. In the spinal cord, axons are not able to restore connections after an injury. The effects of OEG transplants on the regeneration of the injured spinal cord have been studied for over a decade. To date, of all the studies using only OEG as a transplant, 41 showed positive effects, while 13 studies showed limited or no effects. There are several contradictory reports on the migratory and axon growth-supporting properties of transplanted OEG. Hence, the regenerative potential of OEG has become the subject of intense discussion. In this review, we first provide an overview of the molecular and cellular characteristics of OEG in their natural environment, the primary olfactory nervous system. Second, their potential to stimulate regeneration in the injured spinal cord is discussed. OEG influence scar formation by their ability to interact with astrocytes, they are able to remyelinate axons and promote angiogenesis. The ability of OEG to interact with scar tissue cells is an important difference with Schwann cells and may be a unique characteristic of OEG. Because of these effects after transplantation and because of their role in primary olfactory system regeneration, the OEG can be considered as a source of neuroregeneration-promoting molecules. To identify these molecules, more insight into the molecular biology of OEG is required. We believe that genome-wide gene expression studies of OEG in their native environment, in culture and after transplantation will ultimately reveal unique combinations of molecules involved in the regeneration-promoting potential of OEG.

A novel neurotransmitter-independent communication pathway between axons and glial cells

Recent studies have provided evidence that transmitters released by neurons can activate glial receptors and stimulate calcium signalling in glial cells. Glial calcium signalling, in turn, may affect neuronal performance such as long-term changes in synaptic efficacy. Olfactory ensheathing cells (OECs) are a special glial cell type in vertebrates and insects and promote axon growth in the developing and mature nervous system. Physiological properties of OECs, however, have not been studied so far in detail. We measured changes in the calcium concentration in OECs of the moth Manduca sexta, in situ and in vivo. Electrical stimulation of olfactory receptor neurons in pupae or odour stimulation of receptor neurons in adults resulted in calcium transients in OECs. Olfactory receptor axons release acetylcholine; however, application of acetylcholine or other transmitters such as glutamate, GABA or nitric oxide did not induce calcium transients in OECs. Upon nerve stimulation, extracellular potassium rose by several millimolar as measured with potassium-sensitive microelectrodes. When potassium in the perfusion saline was increased from 4 to 10 mM or higher, voltage-dependent calcium transients in OECs that resembled stimulation-induced calcium transients were evoked. Blocking neuronal potassium channels with TEA reduced both the stimulation-induced increases in extracellular potassium and the calcium transients in OECs, whereas calcium transients in receptor axons were augmented. Our results show for the first time that accumulation of potassium, released by electrically active axons, is sufficient to evoke voltage-dependent calcium influx into glial cells, whereas neurotransmitters appear not to be involved in this neuron-glia communication in Manduca.

Olfactory ensheathing cells exert a trophic effect on the hypothalamic neurons in vitro

Olfactory ensheathing cells (OECs) constitute an usual population of glial cells sharing properties with both Schwann cells (SC) of peripheral nervous system (PNS) and astrocytes of the central nervous system (CNS). They express a high level of growth factors which play a very important role as neuronal support. Recent evidence in literature suggests that OECs may facilitate axonal regeneration in the injured nervous system. In this study, we developed an in vitro model to evaluate the neurotrophic effect of OECs on the survival and axonal outgrowth of hypothalamic neurons. Co-cultures of OECs and hypothalamus neuronal cells of postnatal rats were successfully established and cells were immunocytochemically characterized. Furthermore, some neuronal cultures were added with NGF, bFGF and GDNF to compare with the co-cultures. Our results indicate that in co-cultures of hypothalamic neurons and OECs, the number of neurons was significantly increased compared to control cultures exhibiting a dense axonal outgrowth. Moreover, we show that NGF promoted a major neuronal survival than bFGF and GDNF, while bFGF and GDNF exerted an evidence axonal and dendritic outgrowth compared to NGF. In conclusion, these data suggest that OECs have the capacity to promote the survival and axonal outgrowth of hypothalamic neurons in vitro and that bFGF, NGF and GDNF differentially support hypothalamic neurons promoting and enhancing the neuronal survival and outgrowth. Therefore, the OECs are a source of growth factors and might be considered a better approach for functional recovery and growth factors might exert a neuroprotective effect in neurodegenerative disorders.

Axon-glia communication evokes calcium signaling in olfactory ensheathing cells of the developing olfactory bulb

Olfactory ensheathing cells (OECs) accompany receptor axons in the olfactory nerve and promote axonal growth into the central nervous system. The mechanisms underlying the communication between axons and OECs, however, have not been studied in detail yet. We investigated the effect of activity-dependent neuronal transmitter release on Ca(2+) signaling of OECs in acute mouse olfactory bulb slices using confocal Ca(2+) imaging. TTX-sensitive axonal activity upon electrical nerve stimulation triggers a rise in cytosolic Ca(2+) in OECs, which can be mimicked by application of DHPG, an agonist of metabotropic glutamate receptors (mGluRs). Both stimulation- and DHPG-induced Ca(2+) transients in OECs were abolished by depletion of intracellular Ca(2+) stores with cyclopiazonic acid (CPA). The mGluR(1)-specific antagonist CPCCOEt completely inhibited DHPG-evoked Ca(2+) transients, but reduced stimulation-induced Ca(2+) transients only partly, suggesting the involvement of another neurotransmitter. Application of ATP evoked CPA-sensitive Ca(2+) transients in OECs, which were inhibited by the P2Y(1)-specific antagonist MRS2179. Co-application of CPCCOEt and MRS2179 almost completely blocked the stimulation-induced Ca(2+) transients, indicating that they were mediated by mGluR(1) and P2Y(1) receptors. Our results show that OECs are able to respond to olfactory nerve activity with an increase in cytosolic Ca(2+) due to glutamate and ATP release.

Olfactory ensheathing cells express smooth muscle α-actin in vitro and in vivo

One strategy for spinal cord repair after injury that has moved quickly from the research laboratory to the clinic is the implantation of olfactory ensheathing cells (OECs). These unique glial cells of the olfactory system have been associated with axonal remyelination and regeneration after grafting into spinalized animals. Despite these promising observations, there remains a lack of direct empirical evidence of the exact fate of OECs after intraspinal implantation, in large part because of a surprising paucity of defined biomarkers that unequivocally distinguish these cells from phenotypically similar Schwann cells. Here we provide direct neurochemical proof that OECs, both in vitro and in vivo, express smooth muscle alpha-actin. That OECs synthesize this contractile protein (and a variety of actin-binding proteins including caldesmon) provides compelling evidence that these cells are, in fact, quite different from Schwann cells. The identification of several smooth muscle-related proteins in OECs points to a new appreciation of the structural and functional features of this population of olfactory glia. These biomarkers can now be used to elucidate the fate of OECs after intraspinal implantation, in particular assessing whether smooth muscle alpha-actin-expressing OECs are capable of facilitating axon remyelination and regeneration.

BDNF production by olfactory ensheathing cells contributes to axonal regeneration of cultured adult CNS neurons

Olfactory ensheathing cells (OECs) are the main glial cell type that populates mammalian olfactory nerves. These cells have a great capacity to promote the regeneration of axons when transplanted into the injured adult mammalian CNS. However, little is still known about the molecular mechanisms they employ in mediating such a task. Brain-derived neurotrophic factor (BDNF) was identified as a candidate molecule in a genomic study that compared three functionally different OEC populations: Early passage OECs (OEC Ep), Late passage OECs (OEC Lp) and the OEC cell line TEG3 [Pastrana, E., Moreno-Flores, M.T., Gurzov, E.N., Avila, J., Wandosell, F., Diaz-Nido, J., 2006. Genes associated with adult axon regeneration promoted by olfactory ensheathing cells: a new role for matrix metalloproteinase 2. J. Neurosci. 26, 5347-5359]. We have here set out to determine the role played by BDNF in the stimulation of axon outgrowth by OECs. We compared the extracellular BDNF levels in the three OEC populations and show that it is produced in significant amounts by the OECs that can stimulate axon regeneration in adult retinal neurons (OEC Ep and TEG3) but it is absent from the extracellular medium of OEC Lp cells which lack this capacity. Blocking BDNF signalling impaired axonal regeneration of adult retinal neurons co-cultured with TEG3 cells and adding BDNF increased the proportion of adult neurons that regenerate their axons on OEC Lp monolayers. Combining BDNF with other extracellular proteins such as Matrix Metalloproteinase 2 (MMP2) further augmented this effect. This study shows that BDNF production by OECs plays a direct role in the promotion of axon regeneration of adult CNS neurons.

Age-related changes in cell density and the proliferation rate of olfactory ensheathing cells in the lamina propria of postnatal mouse olfactory mucosa

We investigated age-related changes in the distribution and proliferation of olfactory ensheathing cells (OECs) in postnatal mouse olfactory mucosa. In contrast to reported data on other glial cell types in the peripheral and central nervous systems, OEC cell density in the olfactory nerve bundles in the lamina propria remained almost constant from 10 days through 16 months of age. Electron microscopy of the nerve bundles revealed that axon packing density also was constant during that period. These findings suggest that the ratio of the number of OECs to the unit length of the olfactory neuron axons ensheathed by them does not change markedly throughout the lifetime of mice in an undisturbed condition. By contrast, OEC proliferative density decreased rapidly in the 10-day to 1-month-old period, showing a significant difference, and for the rest of life remained at low level, similar to previous values reported for other glial cell types.

Genes associated with adult axon regeneration promoted by olfactory ensheathing cells: a new role for matrix metalloproteinase 2

The molecular mechanisms used by olfactory ensheathing cells (OECs) to promote repair in the damaged adult mammalian CNS remain unknown. Thus, we used microarrays to analyze three OEC populations with different capacities to promote axonal regeneration in cultured rat retinal neurons. Gene expression in "long-term cultured OECs" that do not stimulate adult axonal outgrowth was compared with that of "primary olfactory ensheathing cells" and the immortalized OEC cell line TEG3. In this way, we identified a number of candidate genes that might play a role in promoting adult axonal regeneration. Among these genes, it was striking that both the matrix metalloproteinase 2 (MMP2) and an inhibitor of this protease were represented. The disruption of MMP2 activity in TEG3 cells impaired their capacity to trigger axon regeneration in cultured adult retinal neurons. Furthermore, the MMP2 protein was detected in grafts of OECs that elicited robust axonal regeneration in the injured spinal cord of adult rats in vivo. These data suggest that MMP2 does indeed participate in adult axonal regeneration induced by OECs.

Adult olfactory ensheathing glia promote the long-distance growth of adult retinal ganglion cell neurites in vitro

In vivo, transplanted adult olfactory ensheathing glia (OEG) and adult Schwann cells (SC) can support the regrowth of at least some transected axons within adult CNS neuropil. In the present study, we developed an in vitro adult rat retinal explant model to explore the influence of primary adult SC and OEG on retinal ganglion cell (RGC) neurite regrowth in the presence of glial cells endogenous to the retina. Retinal quadrants were plated RGC-side down onto aclar hats coated with either pure collagen (type 1), collagen with OEG, collagen with SCs, or collagen coated with both OEG and SCs. Regrowing retinal neurites extended onto the pure collagen substrate, largely in association with astrocytes that migrated out from the explants (mean number of neurites: 144+/-65 SEM). The additional presence of OEG (669+/-122), but not SCs (97+/-41), supported the regrowth of significantly greater numbers of RGC neurites. Furthermore, this OEG-stimulated regeneration was over significantly greater distances; >68% of neurites extended >500 microm from the explant, compared with explants plated onto SCs or collagen alone (15% and 29%, respectively). When OEG and SCs were co-cultured the number of regenerating neurites was reduced (397+/-81) compared with the pure OEG treatment. Analysis of explants on pure collagen substrates fed with media conditioned by purified OEG or SC showed no increase in neurite outgrowth compared with control treatments, suggesting that the enhanced growth in the presence of OEG is a contact-mediated effect. The observed differences between the abilities of OEG and SC to support the growth of CNS-derived fibers in the presence of astrocytes support the suggestion that OEG may be better suited for direct transplantation into CNS neuropil following injury.

Neurite outgrowth promoting effects of enriched and mixed OEC/ONF cultures

Olfactory ensheathing cell (OEC) transplants stimulate axon regeneration and partial functional recovery after spinal cord injury. However, it remains unclear whether enriched OEC or mixed transplants of OEC and olfactory nerve fibroblasts (ONF) are optimal for stimulating axon regrowth. The neurite outgrowth stimulating effects of enriched OEC, ONF, and mixed OEC/ONF cultures on neonatal cerebral cortical neurons were compared using co-cultures. We show that (1) OEC are more neurite outgrowth promoting than ONF, and (2) ONF do not enhance the neurite outgrowth stimulating effects of OEC in mixed OEC/ONF cultures. Hence, our data indicate that there is no preference for the use of enriched OEC or mixed OEC/ONF cultures with respect to stimulation of neurite growth in vitro.

Lamina propria and olfactory bulb ensheathing cells exhibit differential integration and migration and promote differential axon sprouting in the lesioned spinal cord

Olfactory bulb-derived (central) ensheathing cell (OB OEC) transplants have shown significant promise in rat models of spinal cord injury, prompting the use of lamina propria-derived (peripheral) olfactory ensheathing cells (LP OECs) in both experimental and clinical trials. Although derived from a common embryonic precursor, both sources of OECs reside in different nervous system compartments postnatally, and their ability to promote regeneration and efficacy after transplantation may differ depending on both their source and mode of transplantation. Here, we have purified green fluorescent protein-expressing LP and OB OECs, assayed their biological differences in vitro, and transplanted them acutely either directly into or rostral and caudal to a dorsolateral funiculus crush. LP and OB OECs exhibit multiple morphological and antigenic similarities in vitro, and, after transplantation, they both attenuate lesion and cavity formation and promote angiogenesis, endogenous Schwann cell infiltration, and axonal sprouting. However, an increased mitotic rate and migratory ability of LP OECs in vitro was reflected in vivo by their superior ability to migrate within the spinal cord, reduce cavity formation and lesion size, and differentially stimulate outgrowth of axonal subpopulations compared with OB OECs. An undesired behavior (autotomy) was also significantly enhanced by LP OEC, over OB OEC, transplantation. These results suggest that LP and OB OECs exhibit intrinsic biological differences that, after transplantation into the lesioned CNS, result in differences in postlesion spinal cord neuropathology and anatomical and behavioral regeneration outcomes that also vary depending on direct versus rostrocaudal transplantation.