Glial growth factor 2 induces proliferation and structural changes in ensheathing cells

Spine impairment in mice high-expressing neuregulin 1 due to LIMK1 activation

The genes encoding for neuregulin1 (NRG1), a growth factor, and its receptor ErbB4 are both risk factors of major depression disorder and schizophrenia (SZ). They have been implicated in neural development and synaptic plasticity. However, exactly how NRG1 variations lead to SZ remains unclear. Indeed, NRG1 levels are increased in postmortem brain tissues of patients with brain disorders. Here, we studied the effects of high-level NRG1 on dendritic spine development and function. We showed that spine density in the prefrontal cortex and hippocampus was reduced in mice (ctoNrg1) that overexpressed NRG1 in neurons. The frequency of miniature excitatory postsynaptic currents (mEPSCs) was reduced in both brain regions of ctoNrg1 mice. High expression of NRG1 activated LIMK1 and increased cofilin phosphorylation in postsynaptic densities. Spine reduction was attenuated by inhibiting LIMK1 or blocking the NRG1–LIMK1 interaction, or by restoring NRG1 protein level. These results indicate that a normal NRG1 protein level is necessary for spine homeostasis and suggest a pathophysiological mechanism of abnormal spines in relevant brain disorders.

Generation of pure cultures of autologous Schwann cells by use of biopsy specimens of the dorsal cutaneous branches of the cervical nerves of young adult dogs

OBJECTIVE To identify an optimal technique for isolation, purification, and amplification of Schwann cells (SCs) from biopsy specimens of the dorsal cutaneous branches of the cervical nerves of dogs. SAMPLE Biopsy specimens of dorsal cervical cutaneous nerves from the cadavers of three 1- to 2-year-old dogs. PROCEDURES Nerve specimens were dissected, predegenerated, and dissociated to isolate single cells. After culture to enhance SC growth, cells were immunopurified by use of magnetic beads. Cell purity was evaluated by assessing expression of cell surface antigens p75 (to detect SCs) and CD90 (to detect fibroblasts). Effects of various concentrations of recombinant human glial growth factor 2 (rhGGF2) on SC proliferation were tested. Cell doubling time was assessed in SC cultures with selected concentrations of rhGGF2. RESULTS Mean ± SD wet weight of nerve fascicles obtained from the biopsy specimens was 16.8 ± 2.8 mg. A mean predegeneration period of 8.6 days yielded approximately 6,000 cells/mg of nerve tissue, and primary culture yielded 43,000 cells/mg of nerve tissue in a mean of 11 days, of which 39.9 ± 9.1% expressed p75. Immunopurification with magnetic beads yielded a mean of 85.4 ± 1.9% p75-positive cells. Two passages of subculture with 10μM cytosine arabinoside further enhanced SC purity to a mean of 97.8 ± 1.2% p75-positive cells. Finally, rhGGF2 supplementation at a range of 40 to 100 ng/mL increased the SC proliferation rate up to 3-fold. CONCLUSIONS AND CLINICAL RELEVANCE SCs could be cultured from biopsy specimens of dorsal cervical cutaneous nerves and purified and expanded to generate adequate numbers for autologous transplants to treat dogs with spinal cord and peripheral nerve injuries.

Specific regulation of NRG1 isoform expression by neuronal activity

Neuregulin 1 (NRG1) is a trophic factor that has been implicated in neural development, neurotransmission, and synaptic plasticity. NRG1 has multiple isoforms that are generated by usage of different promoters and alternative splicing of a single gene. However, little is known about NRG1 isoform composition profile, whether it changes during development, or the underlying mechanisms. We found that each of the six types of NRG1 has a distinct expression pattern in the brain at different ages, resulting in a change in NRG1 isoform composition. In both human and rat, the most dominant are types III and II, followed by either type I or type V, while types IV and VI are the least abundant. The expression of NRG1 isoforms is higher in rat brains at ages of E13 and P5 (in particular type V), suggesting roles in early neural development and in the neonatal critical period. At the cellular level, the majority of NRG1 isoforms (types I, II, and III) are expressed in excitatory neurons, although they are also present in GABAergic neurons and astrocytes. Finally, the expression of each NRG1 isoform is distinctly regulated by neuronal activity, which causes significant increase in type I and IV NRG1 levels. Neuronal activity regulation of type IV expression requires a CRE cis-element in the 5' untranslated region (UTR) that binds to CREB. These results indicate that expression of NRG1 isoforms is regulated by distinct mechanisms, which may contribute to versatile functions of NRG1 and pathologic mechanisms of brain disorders such as schizophrenia.

Novel strategies in brachial plexus repair after traumatic avulsion

Clinical trials in spinal cord injury (SCI) can be affected by many confounding variables including spontaneous recovery, variation in the lesion type and extend. However, the clinical need and the paucity of effective therapies has spawned a large number of animal studies and clinical trials for SCI. In this review, we suggest that brachial plexus avulsion injury, a longitudinal spinal cord lesion, is a simpler model to test methods of spinal cord repair. We explore reconstructive techniques currently explored for the repair of brachial plexus avulsion and focus on the use of olfactory ensheathing cell transplantation as an adjunct treatment in brachial plexus repair.

Efficacy of olfactory ensheathing cells to support regeneration after spinal cord injury is influenced by method of culture preparation

Olfactory ensheathing cells (OEC) have been shown to stimulate regeneration, myelination and functional recovery in different spinal cord injury models. However, recent reports from several laboratories have challenged this treatment strategy. The discrepancy in results could be attributed to many factors including variations in culture protocols. The present study investigates whether the differences in culture preparation could influence neuroprotective and growth-promoting effects of OEC after transplantation into the injured spinal cord. Primary OEC cultures were purified using method of differential cell adhesion (a-OEC) or separated with immunomagnetic beads (b-OEC). After cervical C4 hemisection in adult rats, short-term (3 weeks) or long-term (7 weeks) cultured OEC were transplanted into the lateral funiculus at 1mm rostral and caudal to the transection site. At 3-8 weeks after transplantation, labeled OEC were mainly found in the injection sites and in the trauma zone. Short-term cultured a-OEC supported regrowth of rubrospinal, raphaespinal and CGRP-positive fibers, and attenuated retrograde degeneration in the red nucleus. Short-term cultured b-OEC failed to promote axonal regrowth but increased the density of rubrospinal axons within the dorsolateral funiculus and provided significant neuroprotection for axotomized rubrospinal neurons. In addition, short-term cultured OEC attenuated sprouting of rubrospinal terminals. In contrast, long-term cultured OEC neither enhanced axonal growth nor prevented retrograde cell death. The results suggest that the age of OEC in culture and the method of cell purification could affect the efficacy of OEC to support neuronal survival and regeneration after spinal cord injury. This article is part of a Special Issue entitled: Understanding olfactory ensheathing glia and their prospect for nervous system repair.

Diffusible, membrane-bound, and extracellular matrix factors from olfactory ensheathing cells have different effects on the self-renewing and differentiating properties of neural stem cells

Transplantation of olfactory ensheathing cells (OECs) has been a promising strategy in enhancing central nervous system (CNS) regeneration. However, little is known about the effects of transplanted OECs on the self-renewal, neurogenesis, and oligodendrogenesis of neural stem cells (NSCs), which are known to play a very important role in the repair of damaged CNS tissue. In this study, we investigated the influence of diffusible, membrane-bound, and extracellular matrix factors from OECs on the self-renewal and differentiation properties of NSCs. We found that diffusible factors from cultured OECs promoted self-renewal, whereas the extracellular matrix molecules from OECs increased neurogenesis and oligodendrogenesis of NSCs. Furthermore, we demonstrated that directly coculturing OECs and NSCs inhibited not only self-renewal but also neurogenesis and oligodendrogenesis of NSCs. We propose three models for the interaction between transplanted OECs and endogenous NSCs. Our findings provide new insight into the ability of OECs to promote CNS repair and also indicate potential targets for manipulation of these cells to enhance their restorative ability.

Labeling of olfactory ensheathing glial cells with fluorescent tracers for neurotransplantation

Development of cell-based treatment strategies for repair of the injured nervous system requires cell tracing techniques to follow the fate of transplanted cells and their interaction with the host tissue. The present study investigates the efficacy of fluorescent cell tracers Fast Blue, PKH26, DiO and CMFDA for long-term labeling of olfactory ensheathing glial cells (OEC) in culture and following transplantation into the rat spinal cord. All tested dyes produced very efficient initial labeling of p75-positive OEC in culture. The number of Fast Blue-positive cells remained largely unchanged during the first 4 weeks but only about 21% of the cells retained tracer 6 weeks after labeling. In contrast, the number of cells labeled with PKH26 and DiO was reduced to 51-55% after 2 weeks in culture and reached 8-12% after 4-6 weeks. CMFDA had completely disappeared from the cells 2 weeks after labeling. AlamarBlue assay showed that among four tested tracers only CMFDA reduced proliferation rate of the OEC. After transplantation into spinal cord, Fast Blue-labeled OEC survived for at least 8 weeks but demonstrated very limited migration from the injection sites. Additional immunostaining with glial and neuronal markers revealed signs of dye leakage from the transplanted cells resulted in weak labeling of microglia and spinal neurons. The results show that Fast Blue is an efficient cell marker for cultured OEC. However, transfer of the dye from the transplanted cells to the host tissue should be considered and correctly interpreted.

Xenografts of expanded primate olfactory ensheathing glia support transient behavioral recovery that is independent of serotonergic or corticospinal axonal regeneration in nude rats following spinal cord transection

Transplantation of olfactory ensheathing glial cells (OEG) may improve the outcome from spinal cord injury. Proof-of-principle studies in primates are desirable and the feasibility and efficacy of using in vitro expanded OEG should be tested. An intermediate step between the validation of rodent studies and human clinical trials is to study expanded primate OEG (POEG) xenografts in immunotolerant rodents. In this study the time course to generate purified POEG was evaluated as well as their survival, effect on damaged axons of the corticospinal and serotonergic systems, tissue sparing, and chronic locomotor recovery following transplantation. Fifty-seven nude rats underwent T9/10 spinal cord transection. Thirty-eight rats received POEG, 19 controls were injected with cell medium, and 10 received lentivirally-GFP-transfected POEG. Histological evaluation was conducted at 6 weeks, 8 weeks, 14 weeks and 23-24 weeks. Of these 57 rats, 18 were studied with 5-HT immunostaining, 16 with BDA anterograde CST labeling, and six were used for transmission electron microscopy. In grafted animals, behavioral recovery, sprouting and limited regeneration of 5-HT fibers, and increased numbers of proximal collateral processes but not regeneration of CST fibers was observed. Grafted animals had less cavitation in the spinal cord stumps than controls. Behavioral recovery peaked at three months and then declined. Five POEG-transplanted animals that had shown behavioral recovery underwent retransection and behavioral scores did not change significantly, suggesting that long tract axonal regeneration did not account for the locomotor improvement. At the ultrastructural level presumptive POEG were found to have direct contacts with astrocytes forming the glia limitans, distinct from those formed by Schwann cells. At 6 weeks GFP expression was detected in cells within the lesion site and within nerve roots but did not match the pattern of Hoechst nuclear labeling. At 3.5 months only GFP-positive debris in macrophages could be detected. Transplanted POEG support behavioral recovery via mechanisms that appear to be independent of long tract regeneration.

Culture conditions affect proliferative responsiveness of olfactory ensheathing glia to neuregulins

Olfactory ensheathing glia (OEG) have been used to improve outcome after experimental spinal cord injury and are being trialed clinically. Their rapid proliferation in vitro is essential to optimize clinical application, with neuregulins (NRG) being potential mitogens. We examined the effects of NRG-1beta, NRG-2alpha, and NRG3 on proliferation of p75-immunopurified adult OEG. OEG were grown in serum-containing medium with added bovine pituitary extract and forskolin (added mitogens) or in serum-containing medium (no added mitogens). Cultures were switched to chemically defined medium (no added mitogens or serum), NRG added and OEG proliferation assayed using BrdU. OEG grown initially with added mitogens were not responsive to added NRGs and pre-exposure to forskolin and pituitary extract increased basal proliferation rates so that OEG no longer responded to added NRG. However, NRG promoted proliferation but only if cells were initially grown in mitogen-free medium. Primary OEG express ErbB2, ErbB3, and small levels of ErbB4 receptors; functional blocking indicates that ErbB2 and ErbB3 are the main NRG receptors utilized in the presence of NRG-1beta. The long-term stimulation of OEG proliferation by initial culture conditions raises the possibility of manipulating OEG before therapeutic transplantation.

Comparison of cell populations derived from canine olfactory bulb and olfactory mucosal cultures

OBJECTIVE

To evaluate the numbers and proportions of olfactory ensheathing cells (OECs) in cell cultures derived from the olfactory bulb (OB) and olfactory mucosa of dogs.

ANIMALS

7 dogs.

PROCEDURES

OB tissue and olfactory mucosa from the nasal cavity and frontal sinus were obtained from euthanatized dogs and prepared for cell culture. At 7, 14, and 21 days of culture in vitro, numbers and proportions of OECs, astrocytes, and fibroblasts were determined via immunocytochemistry. Antibody against the low-affinity nerve growth factor receptor p75 was used to identify OECs, antibody against glial fibrillary acidic protein was used to identify astrocytes, and antibody against fibronectin was used to identify fibroblasts.

RESULTS

Cultured OECs derived from the olfactory mucosa of the nasal cavity and frontal sinus had similar characteristics. However, whereas OECs in the OB cell cultures constituted approximately 50% of the cells at 7 days and approximately 75% at 21 days the proportion of OECs in cultures derived from both mucosal types was much lower, with approximately 40% OECs at 7 days and approximately 25% at 21 days. Analysis of OEC numbers revealed that these changes were accompanied by corresponding decreases and increases in the population of cells with fibronectin receptors.

CONCLUSIONS AND CLINICAL RELEVANCE

Although olfactory mucosal cell cultures yielded a sufficient number of OECs for spinal cord transplantation procedures in dogs, modification of culture conditions would be required to ensure that the derived cell population contained a sufficient proportion of OECs.

Neuregulin-1 isoform induces mitogenesis, KCa and Ca2+ currents in PC12 cells. A comparison with sciatic nerve conditioned medium

Neuregulin-1 (NRG-1) is an active component found in sciatic nerve conditioned medium (CM). NRG-1 is a growth and differentiation factor shown to have an effect on neuritogenesis and survival of neural cells. PC12 cells chronically treated with NRG-1 (beta1 isoform) show an increase in proliferation under low-serum condition (2.5% fetal bovine serum and 1.25% horse serum) and serum deprivation, without visible morphological changes. NRG-1 and CM treatments of PC12 cells induced an increase of voltage-activated Ca2+ currents and large-conductance calcium-activated K+ currents (KCa). AG825, a specific inhibitor for erbB2 receptor, abolishes KCa current, though Ca2+ currents were not inhibited. These results showed that NRG-1 is capable of inducing functional changes but is not sufficient on its own to have an effect on cell morphology.

Purification and in vitro characterization of adult canine olfactory ensheathing cells

Olfactory ensheathing cells (OECs) are known to promote neural repair under experimental conditions. The experimental focus has so far been almost entirely on rodent OECs (rOECs), and hence whether human OECs (humOECs) display similar properties is unclear. Studies on larger mammals as an "intermediate" model may be helpful for translating the experimental evidence gathered so far into novel therapeutic strategies. In the present study, we purified adult canine OECs (caOECs) from the olfactory bulb and analyzed their in vitro properties with respect to antigen expression, proliferation, and differentiation. Secondary caOECs shared the expression of marker molecules and the reactivity toward growth factors, with rOECs and humOECs. CaOECs were positively immunostained for the low affinity neurotrophin receptor p75, GFAP, and O4 and proliferated in response to fibroblast growth factor-2 and heregulin-1beta. No decline in proliferation was noted at higher passages (>8). The effects of forskolin, which neither increased proliferation nor stimulated the expression of O4, were clearly different from those on rOECs. Moreover, caOECs displayed their typical spindle-shaped morphology only upon growth factor/forskolin addition, whereas mitotically quiescent caOECs had a flattened morphology. Thus, caOECs can readily be purified from adult canine olfactory bulb and expanded by using established OEC mitogens. The behavior of caOECs toward forskolin suggests that caOECs and humOECs share a number of properties amd implies the presence of common intracellular signalling pathways. CaOECs therefore represent a suitable model system relevant for humOECs in neural repair studies.

Alginate hydrogel and matrigel as potential cell carriers for neurotransplantation

Development of biosynthetic conduits carrying extracellular matrix molecules and cell lines expressing neurotrophic growth factors represents a novel and promising strategy for spinal cord and peripheral nerve repair. In the present in vitro study, the compatibility and growth-promoting effects of (i) alginate hydrogel, (ii) alginate hydrogel complemented with fibronectin, and (iii) matrigel were compared between olfactory ensheathing cells (OECs), Schwann cells (SCs), and bone marrow stromal cells (BMSCs). Neurite outgrowth from embryonic dorsal root ganglia (DRG) neurons was used to assess the efficacy of the hydrogels alone or in combination with cultured cells to promote axonal regeneration. The result showed that alginate hydrogel transformed OECs, SCs, and BMSCs into atypical cells with spherical shape and inhibited their metabolic activity. Combination of alginate hydrogel with fibronectin promoted only OECs proliferation. Alginate hydrogel also inhibited outgrowth of DRG neurites, although this effect was attenuated by addition of fibronectin, SCs, or BMSCs. In contrast, matrigel stimulated cell proliferation, preserved the typical morphological features of the cultured cells and induced massive sprouting of DRG neurites. Addition of cultured cells to matrigel did not further improve DRG neurite outgrowth. The present findings suggest that addition of extracellular matrix should be considered when engineering biosynthetic scaffolds on the basis of alginate hydrogels.

Galanin inhibits the proliferation of glial olfactory ensheathing cells

The effect of galanin (GAL) on neural proliferation was studied in this article using olfactory ensheathing cells (OECs). OECs were isolated from newborn rat olfactory bulb and cultured in vitro. RT-PCR was used to determine the expression of GAL and its receptors in these cells. MTT analysis and LDH assay were used to detect the effects of GAL and the agonist, antagonist of GAL receptors on the proliferation of OECs. Results show that OECs express mRNAs for GAL and GAL receptor2 (GalR2) but not for the two other GAL receptors, GalR1 and GalR3. In addition, GAL and two receptor agonists, GAL1-11 and GAL2-11, can inhibit the proliferation of OECs significantly, but cause no cytotoxicity in the OECs population. Moreover, the influence can be blocked by M35, a nonspecific antagonist of GAL receptors. It is suggested that GAL is an inhibitory factor in regulating OECs proliferation.

Genetic expression profile of olfactory ensheathing cells is distinct from that of Schwann cells and astrocytes

Olfactory ensheathing cells (OECs) accompany the axons of olfactory receptor neurons, which regenerate throughout life, from the olfactory mucosa into the olfactory bulb. OECs have shown widely varying efficacy in repairing the injured nervous system. Analysis of the transcriptome of OECs will help in understanding their biology and will provide tools for investigating the mechanisms of their efficacy and interactions with host tissues in lesion models. In this study, we compared the transcriptional profile of cultured OECs with that of Schwann cells (SCs) and astrocytes (ACs), two glial cell types to which OECs have similarities. Two biological replicates of RNA from cultured OECs, SCs, and ACs were hybridized to long oligo rat 5K arrays against a common reference pool of RNA (50% cultured fibroblast RNA and 50% neonatal rat brain RNA). Transcriptional profiles were analyzed by hierarchical clustering, Principal Components Analysis, and the Venn diagram. The three glial cell types had similarly increased or decreased expression of numerous transcripts compared with the reference. However, OECs were distinguishable from both SCs and ACs by a modest number of transcripts, which were significantly enriched or depleted. Furthermore, OECs and SCs were more closely related to each other than to ACs. Expression of selected transcripts not previously characterized in OECs, such as Lyz, Timp2, Gro1 (Cxcl1), Ccl2 (MCP1), Ctgf, and Cebpb, was validated by real-time reverse transcription-polymerase chain reaction (RT-PCR); immunohistochemistry in cultured OECs, SCs, and ACs, and adult tissues was performed to demonstrate their expression at the protein level.

Neurotrophin 3 promotes purification and proliferation of olfactory ensheathing cells from human nose

Several studies have demonstrated the potential of olfactory ensheathing cells for the repair of central and peripheral nerve injury. However, the majority of these studies have been performed with olfactory ensheathing cells derived from the olfactory bulbs, situated inside the skull. A more clinically relevant source of olfactory ensheathing cells is the olfactory mucosa, located in the nose. To be successful, an autologous transplant of nasal ensheathing glia would require a large number of purified cells. To address this issue, we have focused our research on three neurotrophic factors, namely nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin 3 (NT3). We show here that their respective receptors, TrkA, TrkB, TrkC, as well as p75(NTR) (the low affinity NGF receptor), are expressed in vitro by the nasal ensheathing cells; the three neurotrophins promote purification and proliferation of these glial cells, with an optimal concentration of 50 ng/ml; and human ensheathing cells can be easily biopsied and highly purified using a serum-free medium supplemented with NT3. This technique opens the door for clinical trials in which nasal ensheathing cells will be autotransplanted in humans suffering from nerve injury.

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).

Ciliary neurotrophic factor in the olfactory bulb of rats and mice

Ciliary neurotrophic factor (CNTF) is primarily regarded as an astrocytic lesion factor, promoting neuronal survival and influencing plasticity processes in deafferented areas of the CNS. Postnatal loss of neurons in CNTF-deficient mice indicates a function of the factor also under physiological conditions. In the olfactory bulb, where neurogenesis, axo- and synaptogenesis continue throughout life, CNTF content is constitutively high. The cellular localization of CNTF in the rat olfactory bulb is not fully resolved, and species differences between mouse and rat are not yet characterized. In the present study, four different CNTF antibodies and double immunolabeling with specific markers for glial and neuronal cells were used to study the cellular localization of CNTF in rat and mouse olfactory bulb. Specificity of the detection was checked with tissue from CNTF-deficient mice, and investigations were complemented by immunolocalization of reporter protein in mice synthesizing beta-galactosidase under control of the CNTF promoter (CNTF lacZ-knock-in mice). In both species, CNTF localized to ensheathing cell nuclei, cell bodies and axon-enveloping processes. Additionally, individual axons of olfactory neurons were CNTF immunoreactive. Both CNTF protein content and immunoreaction intensity were lower in mice than in rats. Scattered lightly CNTF-reactive cells were found in the granular and external plexiform layers in rats. Some CNTF-positive cells were associated with immunoreactivity for the polysialylated form of the neural cell adhesion molecule, which is expressed by maturing interneurons derived from the rostral migratory stream. In CNTF lacZ-knock-in mice, beta-galactosidase reactivity was found in ensheathing cells of the olfactory nerve layer, and in cells of the glomerular, external plexiform and granular layers. The study proves that CNTF is localized in glial and neuronal structures in the rodent olfactory bulb. Results in mice provide a basis for investigations concerning the effects of a lack of the factor in CNTF-deficient mice.

Vestibular Schwann cells are a distinct subpopulation of peripheral glia with specific sensitivity to growth factors and extracellular matrix components

Vestibular nerve Schwann cells are predisposed to develop schwannoma. While knowledge concerning this condition has greatly improved, little is known about properties of normal vestibular Schwann cells. In an attempt to understand this predisposition, we evaluated cell density regulation and proliferative features of these cells taken from 6-day-old rats. Data were compared to those obtained with sciatic Schwann cells. In both vestibular and sciatic 7-day-old cultures, Schwann cells appear as bipolar or flattened cells. However, sciatic and vestibular cells greatly differ in other aspects: on poly-L-lysine coating, sciatic cells specifically synthesize myelin basic protein, while expression of P0 mRNAs is restricted to some vestibular cells. Laminin increases sciatic cell density but not that of vestibular cells. Fibronectin selectively enhances the proliferation of vestibular Schwann cells and lacks an effect on sciatic ones. Comparison of cell density changes between sciatic and vestibular cells shows that they are sensitive to two different sets of growth factors. Progesterone and FGF-2 combined with forskolin selectively enhance the cell density of sciatic glia, while IGF-1 and GDNF specifically increase vestibular cell density. Furthermore, BrdU incorporation assays indicate that GDNF is also a mitogen for vestibular cells. Altogether, vestibular Schwann cells display phenotypic features and responsiveness to exogenous signals that are significantly different from sciatic Schwann cells, suggesting that vestibular glia form a subpopulation of Schwann cells.

Immortalized olfactory ensheathing glia promote axonal regeneration of rat retinal ganglion neurons

Olfactory bulb ensheathing glia (OEG) have attracted special attention during the last few years because of their unique properties in promoting regeneration of adult mammalian central nervous system (CNS) components. However the molecular and cellular characteristics responsible for this capacity remain to be revealed. Such studies are presently hindered by the lack of a plentiful source of homogenous OEG. Thus the availability of immortalized OEG lines maintaining the regenerative characteristics of the primary cultures would represent an unlimited source of OEG for use not only in biochemical analyses of neuroregenerative mechanisms but also to characterize their regenerative properties in models in culture and in vivo. We have immortalized primary rat OEG using the SV40 large T antigen expressed from a constitutive cellular promotor, and report here the isolation and characterization of clonal lines. These OEG clonal lines were comparable to primary OEG and Schwann cells in the promotion of axonal regeneration of mature rat retinal ganglion neurons (RGN) but, significantly, this culture assay system more closely reflects the in vivo reparative properties of OEG on transected nerves than other assays of neuritogenesis in that it revealed OEG cells to promote the growth of a larger number of long axons than Schwann cells. Using this assay we were able to grade our OEG lines for their neuroregenerative capacity, opening the possibility of identifying molecules with correlative expression levels in these cells. Our preliminary characterization revealed that the expression level of a classical OEG marker, the p75-NGF receptor, does not correlate with neuroregenerative capacity.

Olfactory Ensheathing Glia: Drivers of Axonal Regeneration in the Central Nervous System?

Olfactory ensheathing glia (OEG) accompany olfactory growing axons in their entry to the adult mammalian central nervous system (CNS). Due to this special characteristic, considerable attention has been focused on the possibility of using OEG for CNS regeneration. OEG present a large heterogeneity in culture with respect to their cellular morphology and expressed molecules. The specific characteristics of OEG responsible for their regenerative properties have to be defined. These properties probably result from the combination of several factors: molecular composition of the membrane (expressing adhesion molecules as PSA-NCAM, L1 and/or others) combined with their ability to reduce glial scarring and to accompany new growing axons into the host CNS. Their capacity to produce some neurotrophic factors might also account for their ability to produce CNS regeneration.

Hepatocyte growth factor is a mitogen for olfactory ensheathing cells

Hepatocyte growth factor (HGF) is a potent mitogen for mature hepatocytes, and it has multi-functional effects in a variety of cells in various organs. HGF stimulates DNA synthesis and promotes cell migration and morphogenesis in several cell types including the olfactory system. To characterize the potential mitogenic activity of HGF that might contribute to olfactory ensheathing cell (OEC) proliferation, we tested the ability of HGF to stimulate OEC division in vitro. OECs were obtained from adult rat olfactory bulbs and cultured in serum-free medium, and were identified by double immunostaining for p75 and S-100 antibodies. DNA synthesis assayed by pulsing BrdU for 24 hr showed that HGF at the concentration of 5-100 ng/ml elicited a 5-10-fold increase of OEC proliferation. By immunocytochemical analysis, we demonstrated that c-Met-immunoreactivity was present in cultured OECs, and c-Met anti-serum significantly sequestered the activity of HGF on OECs proliferation, suggesting that HGF-induced proliferation of OECs is mediated by the c-Met receptor. The mitogenic activity of HGF was potentiated by addition of heregulin (HRG), but inhibited by addition of forskolin. These results demonstrate that HGF is a novel mitogen for rat OECs in vitro, and HGF/c-Met system is involved in regulating OECs growth and development.

Cultured olfactory ensheathing cells express nerve growth factor, brain-derived neurotrophic factor, glia cell line-derived neurotrophic factor and their receptors

In the primary olfactory pathway axons of olfactory neurons (ONs) are accompanied by ensheathing cells (ECs) as the fibres course towards the olfactory bulb. Ensheathing cells are thought to play an important role in promoting and guiding olfactory axons to their appropriate target. In recent years, studies have shown that transplants of ECs into lesions in the central nervous system (CNS) are able to stimulate the growth of axons and in some cases restore functional connections. In an attempt to identify a possible mechanism underlying EC support for olfactory nerve growth and CNS axonal regeneration, this study investigated the production of growth factors and expression of corresponding receptors by these cells. Three techniques immunohistochemistry, enzyme linked immunosorbent assay (ELISA) and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to assess growth factor expression in cultured ECs. Immunohistochemistry showed that ECs expressed nerve growth factor (NGF), brain derived neurotrophic factor (BDNF) and glial cell-line derived neurotrophic factor (GDNF). ELISA confirmed the intracellular presence of NGF and BDNF and showed that, compared to BDNF, about seven times as much NGF was secreted by ECs. RT-PCR analysis demonstrated expression of mRNA for NGF, BDNF, GDNF and neurturin (NTN). In addition, ECs also expressed the receptors trkB, GFRalpha-1 and GFRalpha-2. The results of the experiments show that ECs express a number of growth factors and that BDNF in particular could act both in a paracrine and autocrine manner.

Neurotrophic factors in the primary olfactory pathway

The number of identified growth factors continues to increase rapidly with many being implicated in the development of the nervous system, although for most of them the autocrine and paracrine pathways of cellular regulation still remain to be elucidated. The primary olfactory pathway, consisting of the olfactory epithelium and olfactory bulb, is presented here as a very useful model for the analysis of growth factor function. Review of the available literature suggests that a large proportion of neuroactive growth factors and their receptors are present in the olfactory epithelium or olfactory bulb. Furthermore, the primary olfactory pathway is one of the most plastic in the nervous system with neurogenesis continuing to contribute new sensory neurones in the olfactory epithelium and new interneurones in the olfactory bulb throughout adult life. The rich diversity of growth factors and their receptors in the olfactory system indicates that it will be useful in elucidating how these molecules regulate the formation of the nervous system. The olfactory epithelium in particular is proving useful as a model for the actions of growth factors in directing the neuronal lineage from stem cell to mature neurone.