Olfactory ensheathing glial co-grafts improve functional recovery in rats with 6-OHDA lesions

Potential therapeutic effect of olfactory ensheathing cells in neurological diseases: neurodegenerative diseases and peripheral nerve injuries

Neurological diseases are destructive, mainly characterized by the failure of endogenous repair, the inability to recover tissue damage, resulting in the increasing loss of cognitive and physical function. Although some clinical drugs can alleviate the progression of these diseases, but they lack therapeutic effect in repairing tissue injury and rebuilding neurological function. More and more studies have shown that cell therapy has made good achievements in the application of nerve injury. Olfactory ensheathing cells (OECs) are a special type of glial cells, which have been proved to play an important role as an alternative therapy for neurological diseases, opening up a new way for the treatment of neurological problems. The functional mechanisms of OECs in the treatment of neurological diseases include neuroprotection, immune regulation, axon regeneration, improvement of nerve injury microenvironment and myelin regeneration, which also include secreted bioactive factors. Therefore, it is of great significance to better understand the mechanism of OECs promoting functional improvement, and to recognize the implementation of these treatments and the effective simulation of nerve injury disorders. In this review, we discuss the function of OECs and their application value in the treatment of neurological diseases, and position OECs as a potential candidate strategy for the treatment of nervous system diseases.

Novel factor in olfactory ensheathing cell-astrocyte crosstalk: Anti-inflammatory protein α-crystallin B

Astrocytes are key players in CNS neuroinflammation and neuroregeneration that may help or hinder recovery, depending on the context of the injury. Although pro-inflammatory factors that promote astrocyte-mediated neurotoxicity have been shown to be secreted by reactive microglia, anti-inflammatory factors that suppress astrocyte activation are not well-characterized. Olfactory ensheathing cells (OECs), glial cells that wrap axons of olfactory sensory neurons, have been shown to moderate astrocyte reactivity, creating an environment conducive to regeneration. Similarly, astrocytes cultured in medium conditioned by cultured OECs (OEC-CM) show reduced nuclear translocation of nuclear factor kappa-B (NFκB), a pro-inflammatory protein that induces neurotoxic reactivity in astrocytes. In this study, we screened primary and immortalized OEC lines to identify these factors and discovered that Alpha B-crystallin (CryAB), an anti-inflammatory protein, is secreted by OECs via exosomes, coordinating an intercellular immune response. Our results showed that: (a) OEC exosomes block nuclear NFκB translocation in astrocytes while exosomes from CryAB-null OECs could not; (b) OEC exosomes could be taken up by astrocytes, and (c) CryAB treatment suppressed neurotoxicity-associated astrocyte transcripts. Our results indicate CryAB, as well as other factors secreted by OECs, are potential agents that can ameliorate, or even reverse, the growth-inhibitory environment created by neurotoxic reactive astrocytes following CNS injuries.

Macrophage migration inhibitory factor and its binding partner HTRA1 are expressed by olfactory ensheathing cells

Macrophage migration inhibitory factor (MIF) is an important regulator of innate immunity with key roles in neural regeneration and responses to pathogens, amongst a multitude of other functions. The expression of MIF and its binding partners has been characterised throughout the nervous system, with one key exception: the primary olfactory nervous system. Here, we showed in young mice (postnatal day 10) that MIF is expressed in the olfactory nerve by olfactory ensheathing glial cells (OECs) and by olfactory nerve fibroblasts. We also examined the expression of potential binding partners for MIF, and found that the serine protease HTRA1, known to be inhibited by MIF, was also expressed at high levels by OECs and olfactory fibroblasts in vivo and in vitro. We also demonstrated that MIF mediated segregation between OECs and J774a.1 cells (a monocyte/macrophage cell line) in co-culture, which suggests that MIF contributes to the fact that macrophages are largely absent from olfactory nerve fascicles. Phagocytosis assays of axonal debris demonstrated that MIF strongly stimulates phagocytosis by OECs, which indicates that MIF may play a role in the response of OECs to the continual turnover of olfactory axons that occurs throughout life.

Olfactory ensheathing cells improve the survival of porcine neural xenografts in a Parkinsonian rat model

BACKGROUND

Parkinson's disease (PD) features the motor control deficits resulting from irreversible, progressive degeneration of dopaminergic (DA) neurons of the nigrostriatal pathway. Although intracerebral transplantation of human fetal ventral mesencephalon (hfVM) has been proven effective at reviving DA function in the PD patients, this treatment is clinically limited by availability of hfVM and the related ethical issues. Homologous tissues to hfVM, such as porcine fetal ventral mesencephalon (pfVM) thus present a strong clinical potential if immune response following xenotransplantation could be tamed. Olfactory ensheathing cells (OECs) are glial cells showing immunomodulatory properties. It is unclear but intriuging whether these properties can be applied to reducing immune response following neural xenotransplantation of PD.

METHODS

To determine whether OECs may benefit neural xenografts for PD, different compositions of grafting cells were transplanted into striatum of the PD model rats. We used apomorphine-induced rotational behavior to evaluate effectiveness of the neural grafts on reviving DA function. Immunohistochemistry was applied to investigate the effect of OECs on the survival of neuroxenografts and underlying mechanisms of this effect.

RESULTS

Four weeks following the xenotransplantation, we found that the PD rats receiving pfVM + OECs co-graft exhibited a better improvement in apomorphine-induced rotational behavior compared with those receiving only pfVM cells. This result can be explained by higher survival of DA neurons (tyrosine hydroxylase immunoreactivity) in grafted striatum of pfVM + OECs group. Furthermore, pfVM + OECs group has less immune response (CD3⁺ T cells and OX-6⁺ microglia) around the grafted area compared with pfVM only group. These results suggest that OECs may enhance the survival of the striatal xenografts via dampening the immune response at the grafted sites.

CONCLUSIONS

Using allogeneic OECs as a co-graft material for xenogeneic neural grafts could be a feasible therapeutic strategy to enhance results and applicability of the cell replacement therapy for PD.

miR-124-3p is a chronic regulator of gene expression after brain injury

Traumatic brain injury (TBI) initiates molecular and cellular pathologies that underlie post-injury morbidities, including hippocampus-related memory decline and epileptogenesis. Non-coding small RNAs are master regulators of gene expression with the potential to affect multiple molecular pathways. To evaluate whether hippocampal gene expression networks are chronically regulated by microRNAs after TBI, we sampled the dentate gyrus of rats with severe TBI induced by lateral fluid-percussion injury 3 months earlier. Ingenuity pathway analysis revealed 30 upregulated miR-124-3p targets, suggesting that miR-124-3p is downregulated post-TBI (z-score = - 5.146, p < 0.05). Droplet digital polymerase chain reaction (ddPCR) and in situ hybridization confirmed the chronic downregulation of miR-124-3p (p < 0.05). Quantitative PCR analysis of two targets, Plp2 and Stat3, indicated that their upregulation correlated with the miR-124-3p downregulation (r = - 0.647, p < 0.05; r = - 0.629, p < 0.05, respectively). Immunohistochemical staining of STAT3 confirmed the increased protein expression. STRING analysis showed that 9 of the 30 miR-124-3p targets belonged to a STAT3 network. Reactome analysis and data mining connected the targets especially to inflammation and signal transduction. L1000CDS2 software revealed drugs (e.g., importazole, trichostatin A, and IKK-16) that could reverse the observed molecular changes. The translational value of our data was emphasized by in situ hybridization showing chronic post-traumatic downregulation of miR-124-3p in the dentate gyrus of TBI patients. Analysis of another brain injury model, status epilepticus, highlighted the fact that chronic downregulation of miR-124 is a common phenomenon after brain injury. Together, our findings indicate that miR-124-3p is a chronic modulator of molecular networks relevant to post-injury hippocampal pathologies in experimental models and in humans.

Cranial Pair I: The Olfactory Nerve

The olfactory nerve constitutes the first cranial pair. Compared with other cranial nerves, it depicts some atypical features. First, the olfactory nerve does not form a unique bundle. The olfactory axons join other axons and form several small bundles or fascicles: the fila olfactoria. These fascicles leave the nasal cavity, pass through the lamina cribrosa of the ethmoid bone and enter the brain. The whole of these fascicles is what is known as the olfactory nerve. Second, the olfactory sensory neurons, whose axons integrate the olfactory nerve, connect the nasal cavity and the brain without any relay. Third, the olfactory nerve is composed by unmyelinated axons. Fourth, the olfactory nerve contains neither Schwann cells nor oligodendrocytes wrapping its axons. But it contains olfactory ensheathing glia, which is a type of glia unique to this nerve. Fifth, the olfactory axons participate in the circuitry of certain spherical structures of neuropil that are unique in the brain: the olfactory glomeruli. Sixth, the axons of the olfactory nerve are continuously replaced and their connections in the central nervous system are remodeled continuously. Therefore, the olfactory nerve is subject to lifelong plasticity. Finally seventh, the olfactory nerve can be a gateway for the direct entrance of viruses, neurotoxins and other xenobiotics to the brain. In the same way, it can be used as a portal of entry to the brain for therapeutic substances, bypassing the blood-brain barrier. In this article, we analyze some features of the anatomy and physiology of the first cranial pair. Anat Rec, 302:405-427, 2019. © 2018 Wiley Periodicals, Inc.

Neuroprotective effect of olfactory ensheathing cells co-transfected with Nurr1 and Ngn2 in both in vitro and in vivo models of Parkinson's disease

AIMS

The aim of the study is to evaluate the neuroprotective effects of olfactory ensheathing cells (OECs) with the overexpression of nuclear receptor-related factor 1 (Nurr1) and neurogenin 2 (Ngn2) in experimental models of Parkinson's disease (PD) and to elucidate the potential mechanism underlying the neuroprotective effects of OECs-Nurr1-Ngn2.

MATERIALS AND METHODS

In vitro study, OECs-Nurr1-Ngn2 conditioned medium (CM) was added to MPP⁺-treated PC12 cells for 24h, and then the viability of PC12 cells, oxidative stress and apoptosis were detected. In vivo study, 48 male Sprague-Dawley (SD) rats were randomly divided into four groups. OECs/VMCs and OECs-Nurr1-Ngn2/VMCs groups were transplanted with 2×10⁵ cells each of OECs or OECs-Nurr1-Ngn2 and VMCs into the right striatum one week after a unilateral 6-OHDA lesion. Control and PD groups were injected with 0.9% NaCl and 0.2% ascorbic acid into the same region. Rotational behavior was determined at 2, 4, 6 and 8weeks after injection or implantation in all groups. Neuronal differentiation markers, oxidative stress- and apoptosis-related indicators were detected at 8weeks post-grafting.

KEY FINDINGS

OECs-Nurr1-Ngn2 increased the viability of PC12 cells, inhibited oxidative stress and apoptosis, and these effects could be reversed by pre-treatment of k252a, a TrkB receptor inhibitor. The behavioral deficits of PD rat were ameliorated by the transplantation of OECs-Nurr1-Ngn2/VMCs.

SIGNIFICANCE

These results suggest that OECs-Nurr1-Ngn2 exhibits substantial neuroprotective, anti-oxidant, and anti-apoptotic effects against PD via the up-regulation of the neurotrophic factor-TrkB pathway.

KA-bridged transplantation of mesencephalic tissue and olfactory ensheathing cells in a Parkinsonian rat model

The pathology of Parkinson's disease (PD) results mainly from nigrostriatal pathway damage. Unfortunately, commonly used PD therapies do not repair the disconnected circuitry. It has been reported that using kainic acid (KA, an excitatory amino acid) in bridging transplantation may be useful to generate an artificial tract and reconstruct the nigrostriatal pathway in 6-hydroxydopamine (6-OHDA) lesioned rats. In this study, we used KA bridging and a co-graft of rat olfactory ensheathing cells (OECs) and rat E14 embryonic ventral mesencephalic (VM) tissue to restore the nigrostriatal pathway of the PD model rats. The methamphetamine-induced rotational behaviour, 4-[¹⁸ F]-ADAM (a selectively serotonin transporter radioligand)/micro-PET imaging, and immunohistochemistry were used to assess the effects of the transplantation. At 9 weeks post-grafting in PD model rats, the results showed that the PD rats undergoing VM tissue and OECs co-grafts (VM-OECs) exhibited better motor recovery compared to the rats receiving VM tissue transplantation only. The striatal uptake of 4-[¹⁸ F]-ADAM and tyrosine hydroxylase immunoreactivity (TH-ir) of the grafted area in the VM-OECs group were also more improved than those of the VM alone group. These results suggested that OECs may enhance the survival of the grafted VM tissue and facilitate the recovery of motor function after VM transplantation. Moreover, OECs possibly promote the elongation of dopaminergic and serotonergic axon in the bridging graft. Copyright © 2015 John Wiley & Sons, Ltd.

PET Imaging of Serotonin Transporters With 4-[(18)F]-ADAM in a Parkinsonian Rat Model With Porcine Neural Xenografts

Parkinson's disease (PD) is a neurodegenerative disease characterized by a loss of dopaminergic neurons in the nigrostriatal pathway. Apart from effective strategies to halt the underlying neuronal degeneration, cell replacement now offers novel prospects for PD therapy. Porcine embryonic neural tissue has been considered an alternative source to human fetal grafts in neurodegenerative disorders because its use avoids major practical and ethical issues. This study was undertaken to evaluate the effects of embryonic day 27 (E27) porcine mesencephalic tissue transplantation in a PD rat model using animal positron emission tomography (PET) coupled with 4-[(18)F]-ADAM, a serotonin transporter (SERT) imaging agent. The parkinsonian rat was induced by injecting 6-hydroxydopamine into the medial forebrain bundle (MFB) of the right nigrostriatal pathway. The apomorphine-induced rotation behavioral test and 4-[(18)F]-ADAM/animal PET scanning were carried out following 6-OHDA lesioning. At the second week following 6-OHDA lesioning, the parkinsonian rat rotates substantially on apomorphine-induced contralateral turning. In addition, the mean striatal-specific uptake ratio (SUR) of 4-[(18)F]-ADAM decreased by 44%. After transplantation, the number of drug-induced rotations decreased markedly, and the mean SUR of 4-[(18)F]-ADAM and the level of SERT immunoreactivity (SERT-ir) in striatum were partially restored. The mean SUR level was restored to 71% compared to that for the contralateral intact side, which together with the abundant survival of tyrosine hydroxylase (TH) neurons accounted for functional recovery at the fourth week postgraft. In regard to the extent of donor-derived cells, we found the neurons of the xenografts from E27 transgenic pigs harboring red fluorescent protein (RFP) localized with TH-ir cells and SERT-ir in the grafted area. Thus, transplanted E27 porcine mesencephalic tissue may restore dopaminergic and serotonergic systems in the parkinsonian rat. The 4-[(18)F]-ADAM/animal PET can be used to detect serotonergic neuron loss in PD and monitor the efficacy of therapy.

The potential therapeutic applications of olfactory ensheathing cells in regenerative medicine

Olfactory ensheathing cells (OECs) are unique glia cells restricted to the primary olfactory system including the olfactory mucosa, olfactory nerve, and the outer nerve layer of the olfactory bulb. OECs guide growing olfactory axons from the neurons of the nasal cavity olfactory mucosa to the olfactory bulb to connect both the peripheral nervous system (PNS) and central nervous system (CNS). Based on these specialized abilities of OECs, transplantation of OECs to injury sites has been widely investigated for their potential therapeutic applications in neural repair in different injuries. In this article, we reviewed the properties of OECs and their roles in olfactory regeneration and in treatment of different injuries including spinal cord injury, PNS injury, and stroke and neurodegenerative diseases.

Oxidation of survival factor MEF2D in neuronal death and Parkinson's disease

AIMS

Dysfunction of myocyte enhancer factor 2D (MEF2D), a key survival protein and transcription factor, underlies the pathogenic loss of dopaminergic (DA) neurons in Parkinson's disease (PD). Both genetic factors and neurotoxins associated with PD impair MEF2D function in vitro and in animal models of PD. We investigated whether distinct stress conditions target MEF2D via converging mechanisms.

RESULTS

We showed that exposure of a DA neuronal cell line to 6-hyroxydopamine (6-OHDA), which causes PD in animals models, led to direct oxidative modifications of MEF2D. Oxidized MEF2D bound to heat-shock cognate protein 70 kDa, the key regulator for chaperone-mediated autophagy (CMA), at a higher affinity. Oxidative stress also increased the level of lysosomal-associated membrane protein 2A (LAMP2A), the rate-limiting receptor for CMA substrate flux, and stimulated CMA activity. These changes resulted in accelerated degradation of MEF2D. Importantly, 6-OHDA induced MEF2D oxidation and increased LAMP2A in the substantia nigra pars compacta region of the mouse brain. Consistently, the levels of oxidized MEF2D were much higher in postmortem PD brains compared with the controls. Functionally, reducing the levels of either MEF2D or LAMP2A exacerbated 6-OHDA-induced death of the DA neuronal cell line. Expression of an MEF2D mutant that is resistant to oxidative modification protected cells from 6-OHDA-induced death.

INNOVATION

This study showed that oxidization of survival protein MEF2D is one of the pathogenic mechanisms involved in oxidative stress-induced DA neuronal death.

CONCLUSION

Oxidation of survival factor MEF2D inhibits its function, underlies oxidative stress-induced neurotoxicity, and may be a part of the PD pathogenic process.

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.

Electrospun polyhydroxybutyrate and poly(L-lactide-co-ε-caprolactone) composites as nanofibrous scaffolds

Electrospinning can produce nanofibrous scaffolds that mimic the architecture of the extracellular matrix and support cell attachment for tissue engineering applications. In this study, fibrous membranes of polyhydroxybutyrate (PHB) with various loadings of poly(L-lactide-co-ε-caprolactone) (PLCL) were successfully prepared by electrospinning. In comparison to PLCL scaffolds, PLCL blends with PHB exhibited more irregular fibre diameter distributions and higher average fibre diameters but there were no significant differences in pore size. PLCL/PHB scaffolds were more hydrophilic (<120°) with significantly reduced tensile strength (ca. 1 MPa) compared to PLCL scaffolds (150.9 ± 2.8° and 5.8 ± 0.5 MPa). Increasing PLCL loading in PHB/PLCL scaffolds significantly increased the extension at break, (4-6-fold). PLCL/PHB scaffolds supported greater adhesion and proliferation of olfactory ensheathing cells (OECs) than those exhibiting asynchronous growth on culture plates. Mitochondrial activity of cells cultivated on the electrospun blended membranes was enhanced compared to those grown on PLCL and PHB scaffolds (212, 179, and 153%, resp.). Analysis showed that PLCL/PHB nanofibrous membranes promoted cell cycle progression and reduced the onset of necrosis. Thus, electrospun PLCL/PHB composites promoted adhesion and proliferation of OECs when compared to their individual PLCL and PHB components suggesting potential in the repair and engineering of nerve tissue.

Delayed transplantation of precursor cell-derived astrocytes provides multiple benefits in a rat model of Parkinsons

In addition to dopaminergic neuron loss, it is clear that Parkinson disease includes other pathological changes, including loss of additional neuronal populations. As a means of addressing multiple pathological changes with a single therapeutically-relevant approach, we employed delayed transplantation of a unique class of astrocytes, GDAs(BMP), that are generated in vitro by directed differentiation of glial precursors. GDAs(BMP) produce multiple agents of interest as treatments for PD and other neurodegenerative disorders, including BDNF, GDNF, neurturin and IGF1. GDAs(BMP) also exhibit increased levels of antioxidant pathway components, including levels of NADPH and glutathione. Delayed GDA(BMP) transplantation into the 6-hydroxydopamine lesioned rat striatum restored tyrosine hydroxylase expression and promoted behavioral recovery. GDA(BMP) transplantation also rescued pathological changes not prevented in other studies, such as the rescue of parvalbumin(+) GABAergic interneurons. Consistent with expression of the synaptic modulatory proteins thrombospondin-1 and 2 by GDAs(BMP), increased expression of the synaptic protein synaptophysin was also observed. Thus, GDAs(BMP) offer a multimodal support cell therapy that provides multiple benefits without requiring prior genetic manipulation.

Secretion of nerve growth factor, brain-derived neurotrophic factor, and glial cell-line derived neurotrophic factor in co-culture of four cell types in cerebrospinal fluid-containing medium

The present study co-cultured human embryonic olfactory ensheathing cells, human Schwann cells, human amniotic epithelial cells and human vascular endothelial cells in complete culture medium-containing cerebrospinal fluid. Enzyme linked immunosorbent assay was used to detect nerve growth factor, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor secretion in the supernatant of co-cultured cells. Results showed that the number of all cell types reached a peak at 7-10 days, and the expression of nerve growth factor, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor peaked at 9 days. Levels of secreted nerve growth factor were four-fold higher than brain-derived neurotrophic factor, which was three-fold higher than glial cell line-derived neurotrophic factor. Increasing concentrations of cerebrospinal fluid (10%, 20% and 30%) in the growth medium caused a decrease of neurotrophic factor secretion. Results indicated co-culture of human embryonic olfactory ensheathing cells, human Schwann cells, human amniotic epithelial cells and human vascular endothelial cells improved the expression of nerve growth factor, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor. The reduction of cerebrospinal fluid extravasation at the transplant site after spinal cord injury is beneficial for the survival and secretion of neurotrophic factors from transplanted cells.

The cortical and striatal gene expression profile of 100 hz electroacupuncture treatment in 6-hydroxydopamine-induced Parkinson's disease model

Electroacupuncture (EA), especially high-frequency EA, has frequently been used as an alternative therapy for Parkinson disease (PD) and is reportedly effective for alleviating motor symptoms in patients and PD models. However, the molecular mechanism underlying its effectiveness is not completely understood. To implement a full-scale search for the targets of 100 Hz EA, we selected rat models treated with 6-hydroxydopamine into the unilateral MFB, which mimic end-stage PD. High-throughput microarray analysis was then used to uncover the regulated targets in the cortex and striatum after 4-week EA treatment. In the differentially regulated transcripts, the proportion of recovered expression profiles in the genes, the functional categories of targets in different profiles, and the affected pathways were analyzed. Our results suggested that the recovery of homeostasis in the transcript network and many regulated functional clusters in the cortex and striatum after EA treatment may contribute to the behavioral improvement of PD rats.

Co-transplantation of olfactory ensheathing cells from mucosa and bulb origin enhances functional recovery after peripheral nerve lesion

Olfactory ensheathing cells (OECs) represent an interesting candidate for cell therapy and could be obtained from olfactory mucosa (OM-OECs) or olfactory bulbs (OB-OECs). Recent reports suggest that, depending on their origin, OECs display different functional properties. We show here the complementary and additive effects of co-transplanting OM-OECs and OB-OECs after lesion of a peripheral nerve. For this, a selective motor denervation of the laryngeal muscles was performed by a section/anastomosis of the recurrent laryngeal nerve (RLN). Two months after surgery, recovery of the laryngeal movements and synkinesis phenonema were analyzed by videolaryngoscopy. To complete these assessments, measure of latency and potential duration were determined by electrophysiological recordings and myelinated nerve fiber profiles were defined based on toluidine blue staining. To explain some of the mechanisms involved, tracking of GFP positive OECs was performed. It appears that transplantation of OM-OECs or OB-OECs displayed opposite abilities to improve functional recovery. Indeed, OM-OECs increased recuperation of laryngeal muscles activities without appropriate functional recovery. In contrast, OB-OECs induced some functional recovery by enhancing axonal regrowth. Importantly, co-transplantation of OM-OECs and OB-OECs supported a major functional recovery, with reduction of synkinesis phenomena. This study is the first which clearly demonstrates the complementary and additive properties of OECs obtained from olfactory mucosa and olfactory bulb to improve functional recovery after transplantation in a nerve lesion model.

Transplantation of neuronal-primed human bone marrow mesenchymal stem cells in hemiparkinsonian rodents

Bone marrow-derived human mesenchymal stem cells (hMSCs) have shown promise in in vitro neuronal differentiation and in cellular therapy for neurodegenerative disorders, including Parkinson' disease. However, the effects of intracerebral transplantation are not well defined, and studies do not agreed on the optimal neuronal differentiation method. Here, we investigated three growth factor-based neuronal differentiation procedures (using FGF-2/EGF/PDGF/SHH/FGF-8/GDNF), and found all to be capable of eliciting an immature neural phenotype, in terms of cell morphology and gene/protein expression. The neuronal-priming (FGF-2/EGF) method induced neurosphere-like formation and the highest NES and NR4A2 expression by hMSCs. Transplantation of undifferentiated and neuronal-primed hMSCs into the striatum and substantia nigra of 6-OHDA-lesioned hemiparkinsonian rats revealed transient graft survival of 7 days, despite the reported immunosuppressive properties of MSCs and cyclosporine-immunosuppression of rats. Neither differentiation of hMSCs nor induction of host neurogenesis was observed at injection sites, and hMSCs continued producing mesodermal fibronectin. Strategies for improving engraftment and differentiation post-transplantation, such as prior in vitro neuronal-priming, nigral and striatal grafting, and co-transplantation of olfactory ensheathing cells that promote neural regeneration, were unable to provide advantages. Innate inflammatory responses (Iba-1-positive microglia/macrophage and GFAP-positive astrocyte activation and accumulation) were detected around grafts within 7 days. Our findings indicate that growth factor-based methods allow hMSC differentiation toward immature neuronal-like cells, and contrary to previous reports, only transient survival and engraftment of hMSCs occurs following transplantation in immunosuppressed hemiparkinsonian rats. In addition, suppression of host innate inflammatory responses may be a key factor for improving hMSC survival and engraftment.

A meta-analysis of microarray-based gene expression studies of olfactory bulb-derived olfactory ensheathing cells

Genome wide transcriptional profiling and large scale proteomics have emerged as two powerful methods to dissect the molecular properties of specific neural tissues or cell types on a global scale. Several genome-wide transcriptional profiling and proteomics studies have been published on cultured olfactory ensheathing cells (OEC). In this article we present a meta-analysis of all five published and publicly available micro-array gene expression datasets of cultured early-passage-OB-OEC with other cell types (Schwann cells, late-passage-OB-OEC, mucosa-OEC, an OEC cell line, and acutely dissected OEC). The aim of this meta-analysis is to identify genes and molecular pathways that are found in multiple instead of one isolated study. 454 Genes were detected in at least three out of five microarray datasets. In this "Top-list", genes involved in the biological processes "growth of neurites", "blood vessel development", "migration of cells" and "immune response" were strongly overrepresented. By applying network analysis tools, molecular networks were constructed and Hub-genes were identified that may function as key genes in the above mentioned interrelated processes. We also identified 7 genes (ENTPD2, MATN2, CTSC, PTHLH, GLRX1, COL27A1 and ID2) with uniformly higher or lower expression in early-passage-OB-OEC in all five microarray comparisons. These genes have diverse but intriguing roles in neuroprotection, neurite extension and/or tissue repair. Our meta-analysis provides novel insights into the molecular basis of OB-OEC-mediated neural repair and can serve as a repository for investigators interested in the molecular biology of OEC. This article is part of a Special Issue entitled: Understanding olfactory ensheathing glia and their prospect for nervous system repair.

Olfactory ensheathing cells promote neurite outgrowth from co-cultured brain stem slice

Cell therapy aiming at the replacement of degenerated neurons is a very attractive approach. By using an established in vitro organotypic brain stem (BS) slice culture we screen for candidate donor cells, some of them being further functionally assessed in in vivo models of sensorineural hearing loss. Both in vitro and in vivo systems show that implanted cells face challenges of survival, targeted migration, differentiation and functional integration with the host tissue. Low success rates are possibly due to the lack of necessary neurotrophic factors, adhesion molecules and guiding cues. Olfactory ensheathing cells (OECs) have been shown to express a number of neurotrophic factors and to promote axonal growth through cell to cell interactions. In the present study we co-cultured OECs with organotypic BS slice in order to see if OECs can serve as a facilitator when screening candidate donor cells in an organotypic culture setup. Here we show that OECs when co-cultured with the auditory BS slice not only promote neurite outgrowth from the cochlear nucleus (CN) region of the BS slice but also support cells by having BS slice axons growing along their processes. These findings further suggest that OECs may enhance survival and targeted migration of candidate donor cells suitable for cell therapy in vitro and in vivo. This article is part of a Special Issue entitled: Understanding olfactory ensheathing glia and their prospect for nervous system repair.

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.

Development of biomaterial scaffold for nerve tissue engineering: Biomaterial mediated neural regeneration

Neural tissue repair and regeneration strategies have received a great deal of attention because it directly affects the quality of the patient's life. There are many scientific challenges to regenerate nerve while using conventional autologous nerve grafts and from the newly developed therapeutic strategies for the reconstruction of damaged nerves. Recent advancements in nerve regeneration have involved the application of tissue engineering principles and this has evolved a new perspective to neural therapy. The success of neural tissue engineering is mainly based on the regulation of cell behavior and tissue progression through the development of a synthetic scaffold that is analogous to the natural extracellular matrix and can support three-dimensional cell cultures. As the natural extracellular matrix provides an ideal environment for topographical, electrical and chemical cues to the adhesion and proliferation of neural cells, there exists a need to develop a synthetic scaffold that would be biocompatible, immunologically inert, conducting, biodegradable, and infection-resistant biomaterial to support neurite outgrowth. This review outlines the rationale for effective neural tissue engineering through the use of suitable biomaterials and scaffolding techniques for fabrication of a construct that would allow the neurons to adhere, proliferate and eventually form nerves.

Microtransplantation of Dopaminergic Cell Suspensions: Further Characterization and Optimization of Grafting Parameters

Intracerebral transplantation of dopaminergic (DA) cells is currently further explored as a potential restorative therapy for Parkinson's disease (PD). However, before they can be considered for a more widespread clinical use a number of critical issues have to be resolved, including an optimized transplantation protocol. This study has been performed in a rat 6-hydroxydopamine model of PD and is based on the microtransplantation approach. The results demonstrate a reduced survival (threefold) for a single cell suspension of E14 rat ventral mesencephalon compared to a fragment suspension when a metal cannula is used for implantation. However, fragment suspensions result in a more variable graft survival and ectopically placed cells along the implantation tract. When a glass capillary is used for implantation, the survival of the single cell suspension (so-called “micrograft”) improved by fourfold (vs. single cells/metal cannula) and is superior to the combination of the metal cannula and fragment suspension (+40%). The micrografts show a reduced variability in DA neuron survival as well as fewer ectopically placed cells. Moreover, the implantation time can significantly be reduced from 19 to 7 min in micrografted animals without a compromise in DA graft survival and functional behavioral outcome. Using the microtransplantation approach graft size can be tailored effectively by varying the density of the final cell suspension at least between 11,000 and 320,000 cells/μl, resulting in comparable survival of tyrosine hydroxylase (TH)-positive neurons in the range of 2–4%. With this approach no more than 100 surviving TH-positive neurons are necessary to produce functional effects in the amphetamine-induced rotation test. Interestingly, we found that DA micrografts into lesion striatum present 20% higher survival rates of TH neurons in comparison to the intact striatum. In summary, these results provide further evidence for the usefulness of the microtransplantation approach and allow for a more precise and tailored adaptation of the implantation parameters for further studies on DA, and possibly also other neural-, glial-, and stem cell-derived grafts.

How to improve the survival of the fetal ventral mesencephalic cell transplanted in Parkinson's disease?

It has been extensively confirmed that fetal ventral mesencephalic cell (VMC) transplantation can ameliorate the symptoms of Parkinson's disease (PD). But there are still several problems to be resolved before the extensive clinical application of this technology. The major limitations are the poor survival of grafted dopamine (DA) neurons and restricted dopaminergic reinnervation of host striatum. Some attempts have been made to solve these problems including use of some trophic factor and co-transplantation with neural/paraneural origins. The purpose of this review is to overview advances of the means improving the survival of grafts and their current limitations.

K252a prevents nigral dopaminergic cell death induced by 6-hydroxydopamine through inhibition of both mixed-lineage kinase 3/c-Jun NH2-terminal kinase 3 (JNK3) and apoptosis-inducing kinase 1/JNK3 signaling pathways

It is well documented that the mitogen-activated protein kinase pathway plays a pivotal role in rats with 6-hydroxydopamine (6-OHDA)-induced unilateral lesion in the nigrostriatal system. Our recent studies have shown that mixed-lineage kinase 3 (MLK3) and apoptosis-inducing kinase 1 (ASK1) are all involved in neuronal cell death induced by ischemia, which is mediated by the MLK3/c-Jun NH2-terminal kinase 3 (JNK3) and ASK1/JNK signaling pathway. To investigate whether these pathways are correlated with 6-OHDA-induced lesion as well, we examined the phosphorylation of MLK3, ASK1, and JNK3 in 6-OHDA rats. The results showed that both MLK3 and ASK1 could activate JNK3 and then subsequently enhance the neuronal death through its downstream pathways (i.e., nuclear and non-nuclear pathway). K252a have wide-range effects including Trk inhibition, MLK3 inhibition, and activation of phosphatidylinositol 3 kinase and mitogen-activated protein kinase kinase signaling pathways through interactions with distinct targets and is a well known neuroprotective compound. We found that K252a could protect dopaminergic neurons against cell program death induced by 6-OHDA lesion, and the phenotypes of 6-OHDA rat model treated with K252a were partial rescued. The inhibition of K252a on the activation of MLK3/JNK3 and ASK1/JNK3 provided a link between 6-OHDA lesion and stress-activated kinases. It suggested that both proapoptotic MLK3/JNK3 and ASK1/JNK3 cascade may play an important role in dopaminergic neuronal death in 6-OHDA insult. Thus, the JNK3 signaling may eventually emerge as a prime target for novel therapeutic approaches to treatment of Parkinson disease, and K252a may serve as a potential and important neuroprotectant in therapeutic aspect in Parkinson disease.

Trophic factor induction of human umbilical cord blood cells in vitro and in vivo

The mononuclear fraction of human umbilical cord blood (HUCBmnf) is a mixed cell population that multiple research groups have shown contains cells that can express neural proteins. In these studies, we have examined the ability of the HUCBmnf to express neural antigens after in vitro exposure to defined media supplemented with a cocktail of growth and neurotrophic factors. It is our hypothesis that by treating the HUCBmnf with these developmentally-relevant factors, we can expand the population, enhance the expression of neural antigens and increase cell survival upon transplantation. Prior to growth factor treatment in culture, expression of stem cell antigens is greater in the non-adherent HUCBmnf cells compared to the adherent cells (p < 0.05). Furthermore, treatment of the non-adherent cells with growth factors, increases BrdU incorporation, especially after 14 days in vitro (DIV). In HUCBmnf-embryonic mouse striata co-culture, a small number of growth factor treated HUCBmnf cells were able to integrate into the growing neural network and express immature (nestin and TuJ1) and mature (GFAP and MAP2) neural markers. Treated HUCBmnf cells implanted in the subventricular zone predominantly expressed GFAP although some grafted HUCBmnf cells were MAP2 positive. While short-term treatment of HUCBmnf cells with growth and neurotrophic factors enhanced proliferative capacity in vitro and survival of the cells in vivo, the treatment regimen employed was not enough to ensure long-term survival of HUCBmnf-derived neurons necessary for cell replacement therapies for neurodegenerative diseases.

Implantation of pure cultured olfactory ensheathing cells in an animal model of parkinsonism

BACKGROUND

Implantation of neural cells has been proposed as a therapeutic strategy for repairing the injured or diseased brain. In the present study we have examined the potential of olfactory ensheathing cells (OEC) to promote brain repair after surgical implantation in a rodent model of parkinsonism.

METHODS

Neonatal OECs were implanted in the striatum after a 6-hydroxydopamine lesion of the ipsilateral substantia nigra. Amphetamine-induced rotational asymmetry scores were determined 48 hours before and 4, 6 and 8 weeks after OEC implantation. The density of immunostaining for tyrosine hydroxylase and synaptophysin in the striatum and the number of tyrosine hydroxylase-positive cells remaining in the substantia nigra were also determined.

RESULTS

Rotational asymmetry scores were similar in OEC-implanted and vehicle-treated groups at all time points examined, and at each time were similar to those observed prior to implantation. Levels of striatal tyrosine-hydroxylase and synaptophysin immunoreactivity were similar in OEC- and vehicle-treated groups. The number of tyrosine-hydroxylase-positive cells in the substantia nigra was similar in both groups indicating that severity of the lesion was similar. Visualisation of GFP-labelled OECs one week after implantation in a separate group of animals revealed the cells to be located in the area immediately surrounding the needle tract.

CONCLUSION

This study demonstrates that implantation of OECs alone is not sufficient to promote tissue repair and functional recovery in a rodent model of parkinsonism. The results add to a growing number of studies that propose a caveat for the use of pure OECs as a neurosurgical strategy for the treatment of brain disease or injury.

The isolation of neural stem cells from the olfactory bulb of Parkinson's disease model

Hyposmia is one of the characteristic symptoms of PD. We isolated the neurosphere forming cells (NSFCs) from the olfactory bulb (OB) after dopaminergic neuronal loss induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which is a model of Parkinson's disease. We used BrdU to label dividing cells and isolated NSFCs from the OB of adult mice with or without MPTP to confirm the function of OB in PD models. Seven days after MPTP treatment, BrdU-positive cells were significantly increased in the OB, especially in the glomerular layer (GL) and the subependymal zone (SEZ). The number of neurospheres derived from the adult OB was not decreased in groups receiving MPTP, instead, it was significantly increased at 21 days post-injection and only returned to control levels 40 days after MPTP administration. We also evaluated the differentiation of NSFCs into neural subtypes and found that these NSFCs could be well infected with retrovirus. Adult neurogenesis may be enhanced as a repair system in the tyrosine hydroxylase (TH) positive cells of the OB after MPTP administration. The isolation of neural stem cells from the OB after MPTP administration has helped to establish the cellular basis of neurogenesis and supports a role for the transplant-mediated treatment of PD.