Elevated intracellular levels of cAMP induce olfactory ensheathing cells to express GAL-C and GFAP but not MBP

Fire Needle Acupuncture Regulates Wnt/ERK Multiple Pathways to Promote Neural Stem Cells to Differentiate into Neurons in Rats with Spinal Cord Injury

BACKGROUND & OBJECTIVE

NSCs therapy is considered one of the most potential methods for spinal cord injury (SCI).

METHODS

We build the SCI model rats to investigate the therapeutic effect of fire needle acupuncture in improving the locomotor function of SCI rats and its possible mechanism. BBB scale was used for the motor ability of rats. The expression of Nestin, NSE, Gal-C, and GFAP was detected by immunohistochemistry. Wnt, GSK3β, β-catenin, ERK1/2, CyclinD1, and ngn1 were detected by western blot and PCR. The BBB score of both model group (1.20±0.94, 3.12±0.67, 5.34±1.57, 7.12±1.49) and fire needle group (1.70±0.58, 4.50±1.63, 7.53±2.41, 9.24±0.63) gradually increased after SCI. Furthermore, at d10 and d14, the fire needle group showed a significantly high score compared with that in model group at the same time (P<0.05). Fire needle increased Nestin, NSE, and Gal-C expression inhibited GFAP expression after SCI. Also, fire needle could up-regulate Wnt3a, GSK3β, β-catenin, and ngn1, and down-regulate ERK1/2, cyclinD1 gene and protein expression.

CONCLUSION

In conclusion, fire needle could improve lower limb locomotor function of SCI rats. Also, fire needles could promote endogenous NSCs proliferation differentiating into neurons, and the mechanism might be mediated by promoting the activation of Wnt/β-catenin and inhibiting the overexpression of ERK.

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

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

TGF-β1 enhances phagocytic removal of neuron debris and neuronal survival by olfactory ensheathing cells via integrin/MFG-E8 signaling pathway

Olfactory ensheathing cells (OECs) have been shown to be a leading candidate in cell therapies for central nervous system (CNS) injuries and neurodegenerative diseases. Rapid clearance of neuron debris can promote neuronal survival and axonal regeneration in CNS injuries and neurodegenerative diseases. The phagocytic removal of neuron debris by OECs has been shown to contribute to neuronal outgrowth. However, the precise molecular and cellular mechanisms of phagocytic removal of neuron debris by OECs have not been explored. In this study, we found that OECs secreted anti-inflammatory cytokine transforming growth factor β1 (TGF-β1) during the phagocytic removal of neuron debris. TGF-β1 enhanced phagocytic activity of OECs through regulating integrin/MFG-E8 signaling pathway. In addition, TGF-β1 shifted OECs towards a flattened shape with increased cellular area, which might also be involved in the enhancement of phagocytic activity of OECs. Furthermore, the removal of neuron debris by OECs affected neuronal survival and outgrowth. TGF-β1 enhanced the clearance of neuron debris by OECs and increased neuronal survival. These results reveal the role and mechanism of TGF-β1 in enhancing the phagocytic activity of OECs, which will update the understanding of phagocytosis of OECs and improve the therapeutic use of OECs in CNS injuries and neurodegenerative diseases.

Chronic TNFα Exposure Induces Robust Proliferation of Olfactory Ensheathing Cells, but not Schwann Cells

TNFα is persistently elevated in many injury and disease conditions. Previous reports of cytotoxicity of TNFα for oligodendrocytes and their progenitors suggest that the poor endogenous remyelination in patients with traumatic injury or multiple sclerosis may be due in part to persistent inflammation. Understanding the effects of inflammatory cytokines on potential cell therapy candidates is therefore important for evaluating the feasibility of their use. In this study, we assessed the effects of long term exposure to TNFα on viability, proliferation, migration and TNFα receptor expression of cultured rat olfactory ensheathing cells (OECs) and Schwann cells (SCs). Although OECs and SCs transplanted into the CNS produce similar myelinating phenotypes, and might be expected to have similar therapeutic uses, we report that they have very different sensitivities to TNFα. OECs exhibited positive proliferative responses to TNFα over a much broader range of concentrations than SCs. Low TNFα concentrations increased proliferation and migration of both OECs and SCs, but SC number declined in the presence of 100 ng/ml or higher concentrations of TNFα. In contrast, OECs exhibited enhanced proliferation even at high TNFα concentrations (up to 1 µg/ml) and showed no evidence of TNF cytotoxicity even at 4 weeks post-treatment. Furthermore, while both OECs and SCs expressed TNFαR1 and TNFαR2, TNFα receptor levels were downregulated in OECs after exposure to100 ng/ml TNFα for 5-7 days, but were either elevated or unchanged in SCs. These results imply that OECs may be a more suitable cell therapy candidate if transplanted into areas with persistent inflammation.

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.

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.

Combination of olfactory ensheathing cells with local versus systemic cAMP treatment after a cervical rubrospinal tract injury

The failure of CNS axons to regenerate following traumatic injury is due in part to a growth-inhibitory environment in CNS as well as a weak intrinsic neuronal growth response. Olfactory ensheathing cell (OECs) transplants have been reported to create a favorable environment promoting axonal regeneration, remyelination, and functional recovery after spinal cord injury. However, in our previous experiments, OEC transplants failed to promote regeneration of rubrospinal axons through and beyond the site of a dorsolateral funiculus crush in rats. Rubrospinal neurons undergo massive cell atrophy and limited expression of regeneration-associated genes after axotomy. Using the same injury model, we tested the hypothesis that treatment of the red nucleus with cAMP, known to stimulate the intrinsic growth response in other neurons, will promote rubrospinal regeneration in combination with OEC transplants. In addition, we assessed a systemic increase of cAMP using the phosphodiesterase inhibitor rolipram. OECs prevented cavity formation, attenuated astrocytic hypertrophy and the retraction of the axotomized rubrospinal axons, and tended to reduce the overall lesion size. OEC transplantation lowered the thresholds for thermal sensitivity of both forepaws. None of our treatments, alone or in combination, promoted rubrospinal regeneration through the lesion site. However, the systemic elevation of cAMP with rolipram resulted in greater numbers of OECs and axonal density within the graft and improved motor performance in a cylinder test in conjunction with enhanced rubrospinal branching and attenuated astrocytic hypertrophy.

Juvenile and adult olfactory ensheathing cells bundle and myelinate dorsal root ganglion axons in culture

Olfactory ensheathing cells (OEC), which normally associate closely with but do not myelinate axons in situ, myelinate axons in the adult mammalian spinal cord. They are of clinical interest as candidate cells for autologous transplantation but the ability of OEC to myelinate axons in vitro has been controversial. To clarify this issue, we isolated OEC from olfactory bulbs (OB) of juvenile and adult rats expressing GFP and analyzed their ability to myelinate axons. Using a well-defined assay for myelination of dorsal root ganglia (DRG) axons in culture, we found that OEC from juvenile pups associated with and then myelinated DRG axons. OEC assembled into bundles with the axons by 1week and required more than a week before myelination on axons was detected. In contrast, rat Schwann cells did not bundle axons and they formed P0(+) and MBP(+) myelin segments after as little as 1week. Most of the OEC in culture exhibited staining for calponin, a marker that was not found on Schwann cells in culture, whereas in both OEC and Schwann cell populations nearly all cells were positive for p75NTR and GFAP. These results confirm previous reports showing only subtle immunological differences between Schwann cells and OEC. Besides differences in the rate of myelination, we detected two additional functional differences in the interactions of OEC and Schwann cells with DRG axons. First, the diameter of OEC generated myelin was greater than for Schwann cell myelin on DRG axons. Second, OEC but not Schwann cells myelinated DRG axons in the absence of vitamin C. OEC isolated from adult OB were also found to bundle and myelinate DRG axons but the latter occurred only after incubation times of at least 3weeks. The results indicate that adult OEC require longer incubation times than juvenile OEC to myelinate axons and suggest that patterns of myelination by OEC and Schwann cells are distinguishable at least on axons in vitro. This article is part of a Special Issue entitled: Understanding olfactory ensheathing glia and their prospect for nervous system repair.

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.

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.

Functional differences and interactions between phenotypic subpopulations of olfactory ensheathing cells in promoting CNS axonal regeneration

We demonstrate that there are significantly more p75 neurotrophin receptor- (NTR)-expressing cells in olfactory ensheathing cell (OEC) primary cultures from olfactory nerve rootlets (ONR), but a greater proportion of O4 antigen- and PSA-NCAM-expressing cells in parallel cultures from the nerve fibre layer of the olfactory bulb (OB). By co-culturing adult rat retinal ganglion cells (RGCs) with OECs derived from either ONR or OB tissue, we compared their neurite regrowth-promoting properties. In phenotypically unsorted cultures, there is greater RGC neurite regrowth on ONR OECs compared to OB OECs. Following immunoselection of ONR cells for p75 NTR, there is increased RGC neurite regrowth on the enriched population compared to the unselected cell population or the p75 NTR depleted population. When p75 NTR-enriched cells from ONR and OB cultures are compared directly, tissue source-related differences are no longer observed. Our previous work implicated a pertussis toxin (PTx)-sensitive G protein-linked signalling pathway in OEC regulation of neurite regrowth. We show that this pathway probably operates in interactions between the p75 NTR-positive and -negative cells; separated populations lose the PTx-mediated enhancement of neurite regrowth-promoting properties seen in mixed cultures. Optimum neurite regrowth is observed when both phenotypes are present in cultures from either ONR or OB, and where glial G-protein signalling is disabled by PTx before co-culture with neurons. We thus propose that p75 NTR-positive cells, whilst being the more effective neurite regrowth promoting subpopulation in isolation, cooperate with negative cells to provide optimum support for axonal regrowth.

Manipulation of olfactory ensheathing cell signaling mechanisms: effects on their support for neurite regrowth from adult CNS neurons in coculture

Pretreatment of olfactory ensheathing cells (OECs) with Pertussis toxin increased the number of subsequently cocultured adult retinal ganglion cells (RGCs) regrowing neurites without affecting neuronal survival. Pertussis toxin (PTx) inactivated an OEC G(i/o) protein as pretreating OECs with the PTx B-oligomer subunit had no effect on RGC neurite regrowth. However, the B-oligomer was responsible for decreasing the marked orientation of neurite regrowth on the OEC substrate. Simultaneous incubation of OECs with PTx and a depolarizing concentration of KCl abolished the increase in neurite regrowth from cocultured RGCs, but exposure to a depolarizing KCl concentration after OECs had been PTx-treated had no effect. Our evidence supports the hypothesis that G-protein-regulated calcium signaling plays a significant role in OEC support for CNS axonal regeneration.

Heterogeneous expression of connexin 36 in the olfactory epithelium and glomerular layer of the olfactory bulb

Gap junctions regulate a variety of cell functions by directly connecting two cells through intercellular channels. Connexins are gap junction channel-forming protein subunits. In this study, we studied the expression of connexin 36 (Cx36) in the olfactory epithelium and olfactory bulb of adult mice. In situ hybridization revealed that mRNA for Cx36 was expressed in the olfactory sensory epithelium, main olfactory bulb and accessory olfactory bulb. Expression of mRNA encoding Cx36 was observed in the olfactory epithelium mainly in ventral and lateral regions of the turbinates. Immunohistochemical determination of Cx36 protein expression showed sparse punctuate staining in the olfactory epithelial layer. Intense Cx36-like immunostaining was found in the olfactory nerve bundles underlying the olfactory epithelium and in the olfactory nerve layer and glomerular layer of the olfactory bulb. Mapping of the intensity of Cx36-like immunofluorescence in glomeruli throughout the main olfactory bulb indicated a heterogeneous distribution. A set of approximately 50 glomeruli located in the anterior and posterior limits of the olfactory bulb was more intensely labeled than other glomeruli. There was intense immunofluorescence signal in the glomerular layer of the accessory olfactory bulb and in the vomeronasal nerve. beta-Galactosidase distribution in the olfactory epithelium and olfactory bulb in Cx36 knockout mice (Deans et al. [2001] Neuron 31:477-485) supported the findings with immunofluorescence. Cx36-like immunofluorescence was absent in the olfactory nerve bundles in Cx36 knockout mice. The immunolocalization of Cx36 to the olfactory and vomeronasal nerves, and a subset of olfactory glomeruli suggest a functional role for Cx36 in odor coding.

Olfactory ensheathing cells: historical perspective and therapeutic potential

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

Intracellular calcium handling in rat olfactory ensheathing cells and its role in axonal regeneration

Intracellular calcium handling by rat olfactory ensheathing cells (OECs) is implicated in their support for regrowth of adult CNS neurites in a coculture model of axonal regeneration. Pretreatment of OECs with BAPTA-AM to sequester glial intracellular calcium ([Ca(2+)](i)) reduces significantly the numbers of cocultured neurons regrowing neurites. The mean resting [Ca(2+)](i) of OECs cultured alone or with neurons was 300 nM in an external solution containing 2.5 mM calcium ([Ca(2+)](o)). In high [K(+)](o) or zero [Ca(2+)](o), resting [Ca(2+)](i) significantly decreased. [Ca(2+)](i) significantly increased when [Ca(2+)](o) was increased to 20 mM, lonomycin, thapsigargin, and thimerosal increased [Ca(2+)](i), and caffeine, ryanodine, and cyclopiazonic acid were without effect. Of the receptor agonists tested, none induced a change in [Ca(2+)](i). The calcium influx induced by high [Ca(2+)](o) was blocked by La(3+) and SKF96365, partially inhibited by Cd(2+), and insensitive to Ni(2+) and nifedipine. Pretreatment of OECs with La(3+) reduced neurite regrowth in cocultures in a concentration-dependent manner over the range that blocked the non-voltage-gated calcium flux through a putative TRP-like channel, which, we propose, is activated in OEC-mediated axonal regeneration.

Functional MRI of congenital hyposmia: brain activation to odors and imagination of odors and tastes

PURPOSE

Our goal was to use functional MRI (fMRI) to define brain activation in response to odors and imagination ("memory") of odors and tastes in patients who never recognized odors (congenital hyposmia).

METHOD

Functional MR brain scans were obtained in nine patients with congenital hyposmia using multislice echo planar imaging (EPI) in response to odors of amyl acetate, menthone, and pyridine and to imagination ("memory") of banana and peppermint odors and to salt and sweet tastes. Functional MR brain scans were compared with those in normal subjects and patients with acquired hyposmia. Activation images were derived using correlation analysis, and ratios of areas of brain activated to total and hemispheric brain areas were calculated. Total and hemispheric activated pixel counts were used to quantitate regional brain activation.

RESULTS

Brain activation in response to odors was present in patients with congenital hyposmia. Activation was significantly lower than in normal subjects and patients with acquired hyposmia and did not demonstrate differential vapor pressure-dependent detection responsiveness or odor response lateralization. Regional activation localization was in anterior frontal and temporal cortex similar to that in normal subjects and patients with acquired hyposmia. Activation in response to presented odors was diverse, with a larger group exhibiting little or no activation with localization only in anterior frontal and temporal cortex and a smaller group exhibiting greater activation with localization extending to more complex olfactory integration sites. "Memory" of odors and tastes elicited activation in the same central nervous system (CNS) regions in which activation in response to presented odors occurred, but responses were significantly lower than in normal subjects and patients with acquired hyposmia and did not lateralize.

CONCLUSION

Odors induced CNS activation in patients with congenital hyposmia, which distinguishes olfaction from vision and audition since neither light nor acoustic stimuli induce CNS activation. Odor activation localized to anterior frontal and temporal cortex, consistent with the hypothesis that olfactory pathways are hard-wired into the CNS and that further pathways are undeveloped with primary olfactory system CNS connections but lack of secondary connections. However, some patients exhibited greater odor activation with response localization extending to cingulate and opercular cortex, indicating some olfactory signals impinge on and maintain secondary connections consistent with similar functions in vision and audition. Activation localization of taste "memory" to anterior frontal and temporal cortex is consistent with CNS plasticity and cross-modal CNS reorganization as described for vision and audition. Thus, there are differences and similarities between olfaction, vision, and audition, the differences dependent on unique qualities of olfaction, perhaps due to its diffuse, primitive, fundamental role in survival. Response heterogeneity to odors may reflect heterogeneous genetic abnormalities, independent of anatomic or hormonal changes but dependent on molecular abnormalities in growth factor function interfering with growth factor/stem cell interactions. Patients with congenital hyposmia offer an unique model system not previously explored in which congenital smell lack as measured by fMRI is reflective of congenital dysfunction of a major sensory system.

SCIP/Oct-6, Krox-20, and desert hedgehog mRNA expression during CNS remyelination by transplanted olfactory ensheathing cells

Olfactory ensheathing cells (OECs), although having a separate developmental origin to Schwann cells, are able to generate myelin sheaths following transplantation into areas of CNS demyelination that are remarkably similar to those made by Schwann cells. The transcriptional control of Schwann cell myelination has been well documented, in particular the role of SCIP/Oct-6 and Krox-20. It is not known, however, whether these transcription factors are also expressed when OECs assume a myelinating phenotype. In this study, we addressed this question by using a transplantation approach to generate myelinating OECs and then examined the expression of SCIP/Oct-6 and Krox-20 mRNA by in situ hybridization using oligonucleotide probes. We also examined the expression of desert hedgehog (Dhh), a Schwann cell-derived signaling molecule that is responsible for regulating the development of the connective tissue elements in peripheral nerve, which bear similarities to the morphologies adopted by nonmyelinating transplanted cells. Our results indicate that both Krox-20 and Dhh mRNA are strongly expressed by transplanted OECs, with SCIP mRNA present at much lower levels. The expression of Krox-20 relative to the expression of P0 mRNA by the transplanted OECs is consistent with its playing a similar role in OEC myelination to that in Schwann cell myelination, while the expression of Dhh suggests a possible mechanism for the diverse morphologies that cells adopt following OEC transplantation into the damaged CNS. Taken together, our results provide further evidence for the close similarity of OECs and Schwann cells and suggest that, despite their separate origins, the manner in which they generate a peripheral-type myelin sheath involves similar regulatory mechanisms.

Leukemia inhibitory factor, interleukin-6, and their receptors are expressed transiently in the olfactory mucosa after target ablation

Removal of the synaptic targets of olfactory receptor neurons by olfactory bulb ablation results in apoptosis of olfactory receptor neurons and up-regulation of proliferation of their progenitors. This study focuses on the expression of the neuropoietic cytokines leukemia inhibitory factor (LIF) and its receptor (LIFR) and interleukin 6 (IL-6) and its receptor (IL-6R) in intercellular signaling pathways in the olfactory mucosa after target ablation. Olfactory bulbectomy (OBX) resulted in several transient, early-onset, temporally integrated events that were detected immunohistochemically. Macrophages infiltrated the olfactory epithelium (OE) by 16 hours post-OBX. LIF expression was up-regulated transiently at 2 days post-OBX, when up-regulated expression of LIFR also was detected on globose basal cells (GBCs), a subpopulation of which are immediate progenitors of olfactory receptor neurons. GBC proliferation peaked at 3--4 days post-OBX. In the olfactory nerve (ON), LIF-positive and IL-6-positive macrophage infiltration was followed by the transient up-regulation of expression of LIFR, IL-6, and IL-6R in ensheathing cells by 3 days post-OBX. The mRNAs for LIF/LIFR, IL-6/IL-6R, and their common signal-transduction molecule, gp130, in olfactory-nasal mucosa from control mice and from 3-day post-OBX mice were detected with reverse transcriptase-polymerase chain reaction (RT-PCR). Analysis of Northern blot and relative quantitative RT-PCR demonstrated similar temporal patterns of changes in relative mRNA levels for both LIF and IL-6, which were up-regulated by 16 hours post-OBX and peaked at 2--3 days post-OBX. These data indicate that LIF from infiltrating macrophages acts as a mitogen for GBCs and that LIF from infiltrating macrophages and IL-6 from infiltrating macrophages and ensheathing cells act as repair factors in the ON.

In vitro expression and regulation of ciliary neurotrophic factor and its alpha receptor subunit in neonatal rat olfactory ensheathing cells

During development and in the adult, ciliary neurotrophic factor (CNTF) is expressed at high levels in the olfactory system. In the present study, we asked whether neonatal rat olfactory ensheathing cells (OECs) express CNTF- and CNTF receptoralpha (CNTFRalpha)-mRNA in vitro and studied the regulation of both transcripts in response to growth factor and forskolin (FSK) treatment. We show here that OECs in vitro express CNTF and CNTFRalpha-mRNA under control conditions. Administration of FSK increased the expression of CNTFRalpha while lowering the levels of CNTF. Contrary to fibroblast growth factor-2, CNTF did not stimulate the proliferation of OECs. The observation that OECs express both the ligand and part of its receptor complex may indicate that CNTF exerts paracrine and/or autocrine effects in vivo, which apparently do not include the regulation of cell division.

Expression of the non-compact myelin protein 2′,3′-cyclic nucleotide 3′-phosphodiesterase (CNPase) in olfactory bulb ensheathing glia from explant cultures

The non-compact myelin protein 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) may have a unique role in signaling pathways mediated by lipid-protein domains (Kim and Pfeiffer, 1999). We have tested for CNPase in olfactory bulb ensheathing glia (OBEG) in explant cultures. Migrating bipolar and multipolar cells with OBEG typical morphologies were inimunoreactive for both vimentin- and S100-like proteins. Although apparently devoid of myelin basic protein (MBP)-like immunoreactivity, these cells displayed weak but unambiguous CNPase-like immunoreactivity. Our results suggest a further resemblance to myelinating Schwann cells.

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.

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

Ensheathing cells were isolated from neonatal rat olfactory bulbs and cultured in the presence of glial growth factor 2 (GGF2). Proliferation assay showed that at concentrations of up to 60 ng/ml GGF2, ensheathing cells underwent a modest increase in proliferation rate. This stimulation was not maintained at high doses of GGF2 at 100 ng/ml or more. Chemotaxis chambers and scanning electron microscopy were used to determine whether GGF2 was a chemoattractant for ensheathing cells. Although the results showed no chemotactic response to GGF2, ensheathing cells demonstrated structural changes when cultured in the presence of 20 ng/ml GGF2. Ultrastructural observations revealed that GGF2 promoted increased deposition of extracellular matrix on the cell membrane, more cytoskeletal elements in the processes and as a possible consequence, contributed to a more rigid support. Ensheathing cells cultured in the absence of GGF2 often extended thinner and curved processes. Reverse transcription-polymerase chain reaction confirmed the presence of GGF2 transcripts in ensheathing cells, suggesting that ensheathing cells themselves are a source of GGF2.

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

A coculture method is described for ensheathing glial cells from adult rat olfactory nerve, serving as a substrate for the regrowth of neurites from adult rat retinal ganglion cells. Immunocytochemically identified phenotypes present in primary cultures of olfactory nerve cells are described, and their ability to promote neurite outgrowth is compared with neonatal astrocytes and Schwann cells, with other nonglial cells, and with laminin. Ensheathing cell cultures were more effective than any other substrate tested and also directed the orientation of regrowing neurites. In comparison with cultured Schwann cells, which released neurotrophic factors into the culture medium, there was no evidence of a similar activity in ensheathing cell cultures. Combinations of ensheathing cell-conditioned medium and substrates of laminin, merosin, or 3T3 cells also failed to show the release of factors enhancing either survival or neurite outgrowth from retinal ganglion cells. Evidence is presented for a partial inhibition of neurite outgrowth in the presence of calcium channel antagonists or an intracellular calcium-chelating reagent. This provides evidence for a contribution from an intracellular calcium signaling mechanism, possibly implicating ensheathing cell adhesion molecules in promoting neurite outgrowth.

Primary culture of adult mouse olfactory receptor neurons

Olfactory receptor neurons (ORNs) are unique because they can be replaced by stem cells throughout life. Previous studies have demonstrated that adult mouse olfactory epithelium (OE) injured by exposure to ZnSO4 through nasal irrigation can stimulate stem cell mitotic activity in situ, which continues when placed in culture. We report on an improved ZnSO4 delivery method, mist inhalation, which produces more consistent and greater yields of OE cells. Cultures established following this method contained bipolar, nest, fusiform, and giant cells. The bipolar cells usually underwent asymmetric process development. Some bipolar cells reacted positively to neuron-specific antibodies and were immunonegative for keratin and glia-specific proteins, suggesting that they were ORNs. Those that were negative for the neuron-specific proteins may represent either neuron progenitors or olfactory ensheathing cells. The fusiform cells were relatively small and undifferentiated, exposure to brain-derived neurotrophic factor resulted in their decrease and an increase in bipolar cells. Therefore, they might be the stem cells. The nest cells had morphological characteristics of epithelia and bound keratin antibodies. The giant cells had the morphology of epithelial cells but were negative for keratin; they may represent a unique cell population induced by the ZnSO4. These results indicate that the major cell types of intact OE are present in our cultures, and each retains characteristics found in situ. The mist inhalation method provides an in vitro population of adult mitotically active neurons for study.

Olfactory ensheathing glia: properties and function

The failure of regenerating axons to grow within the adult mammalian central nervous system (CNS) does not apply to the olfactory bulb (OB). In this structure, normal and transected olfactory axons are able to enter, regenerate, and reestablish lost synaptic contacts with their targets, throughout the lifetime of the organism. A remarkable difference between an axonal growth-permissive structure such as the OB and the remaining CNS resides in the presence of ensheathing glia in the former. These cells exhibit phenotypic and functional properties known to be involved in the process of axonal elongation that may explain the permissibility of the OB to axonal growth. In addition, transplants of ensheathing glia were successfully used to promote axonal regeneration within the injured adult CNS. The axonal growth-promoting properties of ensheathing glia make the study of this cell type interesting to provide an insight into the mechanisms underlying the process of axonal regeneration. Therefore, in this article we review the developmental, morphologic, immunocytochemical, and functional properties presented by this unique glial cell type, and correlate them with the axonal growth-promoting ability of ensheathing glia. In addition, we provide some evidence of the potentiality that ensheathing glia might have as a promoter of axonal regeneration within the injured nervous system.

Biosynthesis of carnosine in primary cultures of rat olfactory bulb

Primary cultures of glia cells obtained from adult rat olfactory bulb synthesize carnosine (beta-alanyl histidine). The rate of synthesis increases the older the culture is and is enhanced by the addition of dibutyrylcyclic-AMP (dBcAMP) to the medium. Millimolar concentrations of this agent intensify galactocerebroside (GalC) staining compared to control cultures. Removal of GalC positive cells through antibody and complement cell killing decreases carnosine synthesis to a minimum. Cultures prepared from olfactory bulb of new-born rats contain neuron specific enolase (NSE) positive neurons and GalC positive ensheathing cells. Such cultures produce carnosine. When switched to nerve growth factor (NGF) depleted medium containing dBcAMP the share of neurons in the culture decreases drastically with time and concomitantly an increase of the relative rate of carnosine synthesis is observed. After 1 week in such medium the cultures contain almost no NSE positive cells. Virtually all cells express glial fibrillary acidic protein (GFAP) and are GalC positive. These data suggest that carnosine is synthesized by the ensheathing cells of the olfactory bulb and not by olfactory neurons.

Schwann cell-like myelination following transplantation of an olfactory bulb-ensheathing cell line into areas of demyelination in the adult CNS

In this study we have transplanted a clonal olfactory bulb-ensheathing cell line into focal areas of the rat spinal cord which contain demyelinated axons but neither oligodendrocytes nor astrocytes. The cell line was created by retroviral incorporation of the temperature-sensitive Tag gene into FACS-sorted 04+ cells from 7-day-old rat pup olfactory bulb. The spinal cord lesions were obtained by injecting small volumes of ethidium bromide into the dorsal white matter of spinal cord previously exposed to 40 Grays of X-irradiation. Many of the axons were remyelinated by PO+ myelin sheaths 21 days after transplantation. Light and electron microscopy revealed cells engaging and myelinating axons in a manner highly reminiscent of Schwann cells within similar lesions. GFAP+ cells were also present within the lesion. This study provides the first in vivo evidence that olfactory bulb-ensheathing cells are able to produce peripheral-type myelin sheaths around axons of the appropriate diameter.

Spontaneous immortalisation of ensheathing cells from adult rat olfactory nerve

In this report, we describe the isolation of a cell line, Rolf B1.T, from cultures of adult rat olfactory nerve cells. Rolf B1.T cells have an antigenic phenotype which closely resembles that of olfactory ensheathing cells. In routine culture conditions, Rolf B1.T cells constitutively express glial fibrillary acidic protein, S1OO, the low-affinity neurotrophin receptor p75 NGF, laminin, tenascin, and the neural cell adhesion molecule (N-CAM); a variable proportion of the cells also express cadherin, which is regulated by local culture conditions and is associated positively with cell proliferation status. We provide evidence that the association may be indirect and linked to a related parameter such as local cell density. Rolf B1.T cells arose from a population of less well-differentiated cells after a spontaneous immortalisation event. The cells retain many characteristics of normal cells, are dependent on serum growth factors for their proliferation, and fail to grow in semi-solid agar. Rolf B1.T cells support the regrowth of neurites from adult retinal ganglion cells in vitro in a heterologous co-culture system and will have potential value in investigations into the mechanisms of glial support for axonal regeneration from adult mammalian central neurons.

Olfactory ensheathing cells do not require L-ascorbic acid in vitro to assemble a basal lamina or to myelinate dorsal root ganglion neurites

Ensheathing cells reside within both the PNS and CNS portions of the primary olfactory pathway and provide a glial covering and support for the unmyelinated olfactory axons. In vivo, these ensheathing cells express a mixture of astrocyte-specific and Schwann cell-specific phenotypic features. When grown in vitro in the presence of DRG neurons however, these ensheathing cells were observed to myelinate DRG neurites. The purpose of the present study was to determine whether ensheathing cells, like Schwann cells, require the addition of ascorbic acid to the medium in order to assemble a basal lamina and a myelin sheath. Our findings indicate that ensheathing cells can myelinate DRG neurites regardless of whether ascorbic acid is included in the growth medium and that these glial cells can assemble a basal lamina in the absence of added ascorbic acid. It appears from these results that Schwann cells and ensheathing cells have different growth media requirements for the assembly of a basal lamina.