Neisseria meningitidis Induces Pathology-Associated Cellular and Molecular Changes in Trigeminal Schwann Cells.

Neisseria meningitidis, a common cause of sepsis and bacterial meningitis, infects the meninges and central nervous system (CNS), primarily via paracellular traversal across the blood-brain barrier (BBB) or blood-cerebrospinal fluid barrier. N. meningitidis is often present asymptomatically in the nasopharynx, and the nerves extending between the nasal cavity and the brain constitute an alternative route by which the meningococci may reach the CNS. To date, the cellular mechanisms involved in nerve infection are not fully understood. Peripheral nerve glial cells are phagocytic and are capable of eliminating microorganisms, but some pathogens may be able to overcome this protection mechanism and instead infect the glia, causing cell death or pathology. Here, we show that N. meningitidis readily infects trigeminal Schwann cells (the glial cells of the trigeminal nerve) in vitro in both two-dimensional and three-dimensional cell cultures. Infection of trigeminal Schwann cells may be one mechanism by which N. meningitidis is able to invade the CNS. Infection of the cells led to multinucleation and the appearance of atypical nuclei, with the presence of horseshoe nuclei and the budding of nuclei increasing over time. Using sequential window acquisition of all theoretical mass spectra (SWATH-MS) proteomics followed by bioinformatics pathway analysis, we showed that N. meningitidis induced protein alterations in the glia that were associated with altered intercellular signaling, cell-cell interactions, and cellular movement. The analysis also suggested that the alterations in protein levels were consistent with changes occurring in cancer. Thus, infection of the trigeminal nerve by N. meningitidis may have ongoing adverse effects on the biology of Schwann cells, which may lead to pathology.

Basic insights into Zika virus infection of neuroglial and brain endothelial cells.

Zika virus (ZIKV) has recently emerged as an important human pathogen due to the strong evidence that it causes disease of the central nervous system, particularly microcephaly and Guillain-Barré syndrome. The pathogenesis of disease, including mechanisms of neuroinvasion, may include both invasion via the blood-brain barrier and via peripheral (including cranial) nerves. Cellular responses to infection are also poorly understood. This study characterizes the in vitro infection of laboratory-adapted ZIKV African MR766 and two Asian strains of (1) brain endothelial cells (hCMEC/D3 cell line) and (2) olfactory ensheathing cells (OECs) (the neuroglia populating cranial nerve I and the olfactory bulb; both human and mouse OEC lines) in comparison to kidney epithelial cells (Vero cells, in which ZIKV infection is well characterized). Readouts included infection kinetics, intracellular virus localization, viral persistence and cytokine responses. Although not as high as in Vero cells, viral titres exceeded 104 plaque-forming units (p.f.u.) ml-1 in the endothelial/neuroglial cell types, except hOECs. Despite these substantial titres, a relatively small proportion of neuroglial cells were primarily infected. Immunolabelling of infected cells revealed localization of the ZIKV envelope and NS3 proteins in the cytoplasm; NS3 staining overlapped with that of dsRNA replication intermediate and the endoplasmic reticulum (ER). Infected OECs and endothelial cells produced high levels of pro-inflammatory chemokines. Nevertheless, ZIKV was also able to establish persistent infection in hOEC and hCMEC/D3 cells. Taken together, these results provide basic insights into ZIKV infection of endothelial and neuroglial cells and will form the basis for further study of ZIKV disease mechanisms.

Why are olfactory ensheathing cell tumors so rare?

The glial cells of the primary olfactory nervous system, olfactory ensheathing cells (OECs), are unusual in that they rarely form tumors. Only 11 cases, all of which were benign, have been reported to date. In fact, the existence of OEC tumors has been debated as the tumors closely resemble schwannomas (Schwann cell tumors), and there is no definite method for distinguishing the two tumor types. OEC transplantation is a promising therapeutic approach for nervous system injuries, and the fact that OECs are not prone to tumorigenesis is therefore vital. However, why OECs are so resistant to neoplastic transformation remains unknown. The primary olfactory nervous system is a highly dynamic region which continuously undergoes regeneration and neurogenesis throughout life. OECs have key roles in this process, providing structural and neurotrophic support as well as phagocytosing the axonal debris resulting from turnover of neurons. The olfactory mucosa and underlying tissue is also frequently exposed to infectious agents, and OECs have key innate immune roles preventing microbes from invading the central nervous system. It is possible that the unique biological functions of OECs, as well as the dynamic nature of the primary olfactory nervous system, relate to the low incidence of OEC tumors. Here, we summarize the known case reports of OEC tumors, discuss the difficulties of correctly diagnosing them, and examine the possible reasons for their rare incidence. Understanding why OECs rarely form tumors may open avenues for new strategies to combat tumorigenesis in other regions of the nervous system.

Schwann cell lamellipodia regulate cell-cell interactions and phagocytosis.

Lamellipodia in Schwann cells (SCs) are crucial for myelination, but their other biological functions remain largely uncharacterised. Two types of lamellipodia exist in SCs: axial lamellipodia at the outermost edge of the cell processes, and radial lamellipodia appearing peripherally along the entire cell. We have previously shown that radial lamellipodia on olfactory glia (olfactory ensheathing cells; OECs) promote cell-cell adhesion, contact-mediated migration and phagocytosis. Here we have investigated whether lamellipodia in SCs have similar roles. Using live-cell imaging, we show that the radial lamellipodia in SCs are highly motile, appear at multiple cellular sites and rapidly move in a wave-like manner. We found that axial and radial lamellipodia had strikingly different roles and are regulated by different intracellular pathways. Axial lamellipodia initiated interactions with other SCs and with neurons by contacting radial lamellipodia on SCs, and budding neurites/axons. Most SC-SC interactions resulted in repulsion, and, lamellipodial activity (unlike in OECs) did not promote contact-mediated migration. We show that lamellipodia are crucial for SC-mediated phagocytosis of both axonal debris and bacteria, and demonstrated that inhibition of lamellipodial activity by blocking the Rho/Rac pathways also inhibits phagocytosis. We also show that heregulin, which induces SC differentiation and maturation, alters lamellipodial behaviour but does not affect phagocytic activity. Overall, the results show that SC lamellipodia are important for cell interactions and phagocytosis.

Linckosides enhance proliferation and induce morphological changes in human olfactory ensheathing cells.

Linckosides are members of the steroid glycoside family isolated from the starfish Linckia laevigata. These natural compounds have notable neuritogenic activity and synergistic effects on NGF-induced neuronal differentiation of PC12 cells. Neurogenic factors or molecules that are able to mimic their activities are known to be involved in the survival, proliferation and migration of neurons and glial cells; however how glial cells respond to specific neurogenic molecules such as linckosides has not been investigated. This study aimed to examine the effect of three different linckosides (linckoside A, B and granulatoside A) on the morphological properties, proliferation and migration of human olfactory ensheathing cells (hOECs). The proliferation rate after all the treatments was higher than control as detected by MTS assay. Additionally, hOECs displayed dramatic morphological changes characterized by a higher number of processes after linckoside treatment. Interestingly changes in microtubule organization and expression levels of some early neuronal markers (GAP43 and ßIII-tubulin) were also observed. An increase in the phosphorylation of ERK 1/2 after addition of the compounds suggests that this pathway may be involved in the linckoside-mediated effects particularly those related to morphological changes. These results are the first description of the stimulating effects of linckosides on hOECs and raise the potential for this natural compound or its derivatives to be used to regulate and enhance the therapeutic properties of OECs, particularly for cell transplantation therapies.

The Glia Response after Peripheral Nerve Injury: A Comparison between Schwann Cells and Olfactory Ensheathing Cells and Their Uses for Neural Regenerative Therapies.

The peripheral nervous system (PNS) exhibits a much larger capacity for regeneration than the central nervous system (CNS). One reason for this difference is the difference in glial cell types between the two systems. PNS glia respond rapidly to nerve injury by clearing debris from the injury site, supplying essential growth factors and providing structural support; all of which enhances neuronal regeneration. Thus, transplantation of glial cells from the PNS is a very promising therapy for injuries to both the PNS and the CNS. There are two key types of PNS glia: olfactory ensheathing cells (OECs), which populate the olfactory nerve, and Schwann cells (SCs), which are present in the rest of the PNS. These two glial types share many similar morphological and functional characteristics but also exhibit key differences. The olfactory nerve is constantly turning over throughout life, which means OECs are continuously stimulating neural regeneration, whilst SCs only promote regeneration after direct injury to the PNS. This review presents a comparison between these two PNS systems in respect to normal physiology, developmental anatomy, glial functions and their responses to injury. A thorough understanding of the mechanisms and differences between the two systems is crucial for the development of future therapies using transplantation of peripheral glia to treat neural injuries and/or disease.

Burkholderia pseudomallei Rapidly Infects the Brain Stem and Spinal Cord via the Trigeminal Nerve after Intranasal Inoculation.

Infection with Burkholderia pseudomallei causes melioidosis, a disease with a high mortality rate (20% in Australia and 40% in Southeast Asia). Neurological melioidosis is particularly prevalent in northern Australian patients and involves brain stem infection, which can progress to the spinal cord; however, the route by which the bacteria invade the central nervous system (CNS) is unknown. We have previously demonstrated that B. pseudomallei can infect the olfactory and trigeminal nerves within the nasal cavity following intranasal inoculation. As the trigeminal nerve projects into the brain stem, we investigated whether the bacteria could continue along this nerve to penetrate the CNS. After intranasal inoculation of mice, B. pseudomallei caused low-level localized infection within the nasal cavity epithelium, prior to invasion of the trigeminal nerve in small numbers. B. pseudomallei rapidly invaded the trigeminal nerve and crossed the astrocytic barrier to enter the brain stem within 24 h and then rapidly progressed over 2,000 µm into the spinal cord. To rule out that the bacteria used a hematogenous route, we used a capsule-deficient mutant of B. pseudomallei that does not survive in the blood and found that it also entered the CNS via the trigeminal nerve. This suggests that the primary route of entry is via the nerves that innervate the nasal cavity. We found that actin-mediated motility could facilitate initial infection of the olfactory epithelium. Thus, we have demonstrated that B. pseudomallei can rapidly infect the brain and spinal cord via the trigeminal nerve branches that innervate the nasal cavity.

Burkholderia pseudomallei Capsule Exacerbates Respiratory Melioidosis but Does Not Afford Protection against Antimicrobial Signaling or Bacterial Killing in Human Olfactory Ensheathing Cells.

Melioidosis, caused by the bacterium Burkholderia pseudomallei, is an often severe infection that regularly involves respiratory disease following inhalation exposure. Intranasal (i.n.) inoculation of mice represents an experimental approach used to study the contributions of bacterial capsular polysaccharide I (CPS I) to virulence during acute disease. We used aerosol delivery of B. pseudomallei to establish respiratory infection in mice and studied CPS I in the context of innate immune responses. CPS I improved B. pseudomallei survival in vivo and triggered multiple cytokine responses, neutrophil infiltration, and acute inflammatory histopathology in the spleen, liver, nasal-associated lymphoid tissue, and olfactory mucosa (OM). To further explore the role of the OM response to B. pseudomallei infection, we infected human olfactory ensheathing cells (OECs) in vitro and measured bacterial invasion and the cytokine responses induced following infection. Human OECs killed >90% of the B. pseudomallei in a CPS I-independent manner and exhibited an antibacterial cytokine response comprising granulocyte colony-stimulating factor, tumor necrosis factor alpha, and several regulatory cytokines. In-depth genome-wide transcriptomic profiling of the OEC response by RNA-Seq revealed a network of signaling pathways activated in OECs following infection involving a novel group of 378 genes that encode biological pathways controlling cellular movement, inflammation, immunological disease, and molecular transport. This represents the first antimicrobial program to be described in human OECs and establishes the extensive transcriptional defense network accessible in these cells. Collectively, these findings show a role for CPS I in B. pseudomallei survival in vivo following inhalation infection and the antibacterial signaling network that exists in human OM and OECs.

Differing phagocytic capacities of accessory and main olfactory ensheathing cells and the implication for olfactory glia transplantation therapies.

The rodent olfactory systems comprise the main olfactory system for the detection of odours and the accessory olfactory system which detects pheromones. In both systems, olfactory axon fascicles are ensheathed by olfactory glia, termed olfactory ensheathing cells (OECs), which are crucial for the growth and maintenance of the olfactory nerve. The growth-promoting and phagocytic characteristics of OECs make them potential candidates for neural repair therapies such as transplantation to repair the injured spinal cord. However, transplanting mixed populations of glia with unknown properties may lead to variations in outcomes for neural repair. As the phagocytic capacity of the accessory OECs has not yet been determined, we compared the phagocytic capacity of accessory and main OECs in vivo and in vitro. In normal healthy animals, the accessory OECs accumulated considerably less axon debris than main OECs in vivo. Analysis of freshly dissected OECs showed that accessory OECs contained 20% less fluorescent axon debris than main OECs. However, when assayed in vitro with exogenous axon debris added to the culture, the accessory OECs phagocytosed almost 20% more debris than main OECs. After surgical removal of one olfactory bulb which induced the degradation of main and accessory olfactory sensory axons, the accessory OECs responded by phagocytosing the axon debris. We conclude that while accessory OECs have the capacity to phagocytose axon debris, there are distinct differences in their phagocytic capacity compared to main OECs. These distinct differences may be of importance when preparing OECs for neural transplant repair therapies.

Pathogens penetrating the central nervous system: infection pathways and the cellular and molecular mechanisms of invasion.

The brain is well protected against microbial invasion by cellular barriers, such as the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB). In addition, cells within the central nervous system (CNS) are capable of producing an immune response against invading pathogens. Nonetheless, a range of pathogenic microbes make their way to the CNS, and the resulting infections can cause significant morbidity and mortality. Bacteria, amoebae, fungi, and viruses are capable of CNS invasion, with the latter using axonal transport as a common route of infection. In this review, we compare the mechanisms by which bacterial pathogens reach the CNS and infect the brain. In particular, we focus on recent data regarding mechanisms of bacterial translocation from the nasal mucosa to the brain, which represents a little explored pathway of bacterial invasion but has been proposed as being particularly important in explaining how infection with Burkholderia pseudomallei can result in melioidosis encephalomyelitis.

Nedd4-2 (NEDD4L) controls intracellular Na(+)-mediated activity of voltage-gated sodium channels in primary cortical neurons.

Nedd4-2, a HECT (homologous with E6-associated protein C-terminus)-type ubiquitin protein ligase, has been implicated in regulating several ion channels, including Navs (voltage-gated sodium channels). In Xenopus oocytes Nedd4-2 strongly inhibits the activity of multiple Navs. However, the conditions under which Nedd4-2 mediates native Nav regulation remain uncharacterized. Using Nedd4-2-deficient mice, we demonstrate in the present study that in foetal cortical neurons Nedd4-2 regulates Navs specifically in response to elevated intracellular Na(+), but does not affect steady-state Nav activity. In dorsal root ganglia neurons from the same mice, however, Nedd4-2 does not control Nav activities. The results of the present study provide the first physiological evidence for an essential function of Nedd4-2 in regulating Navs in the central nervous system.

Spatial and developmental heterogeneity of calcium signaling in olfactory ensheathing cells.

Olfactory ensheathing cells (OECs) are specialized glial cells in the mammalian olfactory system supporting growth of axons from the olfactory epithelium into the olfactory bulb. OECs in the olfactory bulb can be subdivided into OECs of the outer nerve layer and the inner nerve layer according to the expression of marker proteins and their location in the nerve layer. In the present study, we have used confocal calcium imaging of OECs in acute mouse brain slices and olfactory bulbs in toto to investigate physiological differences between OEC subpopulations. OECs in the outer nerve layer, but not the inner nerve layer, responded to glutamate, ATP, serotonin, dopamine, carbachol, and phenylephrine with increases in the cytosolic calcium concentration. The calcium responses consisted of a transient and a tonic component, the latter being mediated by store-operated calcium entry. Calcium measurements in OECs during the first three postnatal weeks revealed a downregulation of mGluR(1) and P2Y(1) receptor-mediated calcium signaling within the first 2 weeks, suggesting that the expression of these receptors is developmentally controlled. In addition, electrical stimulation of sensory axons evoked calcium signaling via mGluR(1) and P2Y(1) only in outer nerve layer OECs. Downregulation of the receptor-mediated calcium responses in postnatal animals is reflected by a decrease in amplitude of stimulation-evoked calcium transients in OECs from postnatal days 3 to 21. In summary, the results presented reveal striking differences in receptor responses during development and in axon-OEC communication between the two subpopulations of OECs in the olfactory bulb.

Liraglutide modulates adhesion molecules and enhances cell properties in three-dimensional cultures of olfactory ensheathing cells.

Cell transplantation using olfactory ensheathing cells (OECs) is a promising approach for nerve repair but there are numerous limitations with their delivery method. Three-dimensional (3D) cell culture systems potentially offer a powerful approach for cell production and delivery options. To further optimise the use of OECs, strategies to promote cell viability and maintain cell behaviours in 3D cultures become important. We previously demonstrated an anti-diabetic drug, liraglutide, could modulate OEC migration and re-model extracellular matrix in two-dimensional (2D) cultures. In the present study, we further investigated its beneficial effects in our 3D culture system using primary OECs. OECs treated with liraglutide at 100 nM showed improved cell viability and had modulated expression of N-cadherin and ß1-integrin (two important cell adhesion molecules). When formed into 3D spheroids, the pre-treated OECs generated spheroids with an increased volume and a decreased cell density compared to control spheroids. OECs that subsequently migrated out of the liraglutide pre-treated spheroids had higher capacity for migration with increased duration and length, which was attributed to a reduction in the pauses during the migration. Moreover, OECs that migrated out from liraglutide spheroids had a more bipolar morphology consistent with higher migratory capacity. In summary, liraglutide improved the viability of OECs, modulated cell adhesion molecules, and resulted in stable 3D cell constructs which conferred enhanced migratory capacity on the OECs. Overall, liraglutide may potentially improve the therapeutic use of OECs for neural repair by enhancing the generation of stable 3D constructs and increasing the migratory behaviour of OECs.

Two phases of replacement replenish the olfactory ensheathing cell population after injury in postnatal mice.

Olfactory ensheathing cells (OECs) support the regeneration of olfactory sensory neurons throughout life, however, it remains unclear how OECs respond to a major injury. We have examined the proliferation and migration of OECs following unilateral bulbectomy in postnatal mice. S100ß-DsRed and OMP-ZsGreen transgenic mice were used to visualize OECs and olfactory neurons, respectively, and we used the thymidine analogue ethynyl deoxyuridine (EdU) to identify cells that were proliferating at the time of administration. Following unilateral bulbectomy, there was an initial phase of OEC proliferation throughout the olfactory pathway with a peak of proliferation occurring 2 to 7 days after the injury. A second phase of proliferation also occurred in which precursors localized within the olfactory mucosa divided to replenish the OEC population. We then tracked the positions of OECs that had proliferated and found that there was a progressive increase in OECs in the cavity for at least 12 to 16 days after injury which could not be accounted for solely by local proliferation of OECs within the cavity. These results suggest that OECs migrated from the peripheral olfactory nerve to populate the mass of cells that filled cavity left by bulbectomy. Our results demonstrate that following injury to the olfactory nervous system, the OEC population is replenished by migration of cells that arise from both local proliferation of OECs throughout the olfactory nerve pathway as well as from precursor cells in the olfactory mucosa.

The migration of olfactory ensheathing cells during development and regeneration.

The primary olfactory nervous system is unique in that it continuously renews itself and regenerates after injury. These properties are attributed to the presence of olfactory glia, termed olfactory ensheathing cells (OECs). Evidence is now emerging that individual OEC populations exist with distinct anatomical localisations and physiological properties, but their differential roles have not been determined. Unlike other glia, OECs can migrate from the periphery into the central nervous system, and organised OEC migration can enhance axonal extension after injury. Despite this, the mechanisms regulating OEC migration are largely unknown. Here, we provide an overview of the roles of OECs in development and adulthood. We review the latest research describing the differences between individual OEC subpopulations and discuss potential regulatory mechanisms for OEC guidance and migration. Using advanced time lapse techniques, we have obtained novel insights into how OECs behave in a complex multicellular environment which we discuss here with particular focus on cell-cell interactions. Significantly, transplantation of OECs constitutes a promising novel therapy for nerve injuries, but results are highly variable and the method needs improvement. We here review the roles of transplanted OECs in neural repair of damaged neuronal tracts distinct from the primary olfactory nervous system.

The carbohydrate CT1 is expressed in topographically fixed glomeruli in the mouse olfactory bulb.

Cell surface carbohydrates define subpopulations of primary olfactory neurons whose axons terminate in select glomeruli in the olfactory bulb. The combination of carbohydrates present on axon subpopulations has been proposed to confer a unique identity that contributes to the establishment of the olfactory topographic map. We have identified a novel subpopulation of primary olfactory neurons in mice that express blood group carbohydrates with GalNAc-ß1,4[NeuAcα 2,3]Galß1 residues recognised by the CT1 antibody. The CT1 carbohydrate has been shown to modulate adhesion of nerve terminals to the extracellular matrix and to synaptic proteins. The axons of the CT1-positive primary olfactory neurons terminate in a subpopulation of glomeruli in the olfactory bulb. Four lines of evidence support the view that CT1 glomeruli are topographically fixed. First, CT1 glomeruli were restricted predominantly to the dorsomedial olfactory bulb and were absent from large patches of the ventrolateral bulb. Second, similar distributions were observed for CT1 glomeruli on both the left and right olfactory bulbs of each animal, and between animals. Third, CT1 glomeruli were typically present as small clusters of 2-4 glomeruli. Fourth, a single CT1 glomerulus was always apposed to the glomeruli innervated by axons expressing the M72 odorant receptor. We also show that the CT1 carbohydrate is lost in gain-of-function transgenic mice over-expressing the blood group A glycosyltransferase in which there is aberrant targeting of M72 axons. Taken together, these results suggest that the CT1 carbohydrate, together with other carbohydrates, contributes to axon guidance during the establishment of the olfactory topographic map.

Correction of aberrant axon growth in the developing mouse olfactory bulb.

During development of the primary olfactory system, sensory axons project from the nasal cavity to the glomerular layer of the olfactory bulb. In the process axons can branch inappropriately into several glomeruli and sometimes over-shoot the glomerular layer, entering the deeper external plexiform layer. However in the adult, axons are rarely observed within the external plexiform layer. While chemorepulsive cues are proposed to restrict axons to the glomerular layer in the embryonic animal, these cues are clearly insufficient for all axons in the postnatal animal. We hypothesised that the external plexiform layer is initially an environment in which axons are able to grow but becomes increasingly inhibitory to axon growth in later postnatal development. We have determined that rather than having short localised trajectories as previously assumed, many axons that enter the external plexiform layer had considerable trajectories and projected preferentially along the ventro-dorsal and rostro-caudal axes for up to 950 µm. With increasing age, fewer axons were detected within the external plexiform layer but axons continued to be present until P17. Thus the external plexiform layer is initially an environment in which axons can extensively grow. We next tested whether the external plexiform layer became increasingly inhibitory to axon growth by microdissecting various layers of the olfactory bulb and preparing protein extracts. When assayed using olfactory epithelium explants of the same embryonic age, primary olfactory axons became increasingly inhibited by extract prepared from the external plexiform layer of increasingly older animals. These results demonstrate that primary olfactory axons can initially grow extensively in the external plexiform layer, but that during postnatal development inhibitory cues are upregulated that reduce axon growth within the external plexiform layer.

Advances in Electrospun Nerve Guidance Conduits for Engineering Neural Regeneration.

Injuries to the peripheral nervous system result in devastating consequences with loss of motor and sensory function and lifelong impairments. Current treatments have largely relied on surgical procedures, including nerve autografts to repair damaged nerves. Despite improvements to the surgical procedures over the years, the clinical success of nerve autografts is limited by fundamental issues, such as low functionality and mismatching between the damaged and donor nerves. While peripheral nerves can regenerate to some extent, the resultant outcomes are often disappointing, particularly for serious injuries, and the ongoing loss of function due to poor nerve regeneration is a serious public health problem worldwide. Thus, a successful therapeutic modality to bring functional recovery is urgently needed. With advances in three-dimensional cell culturing, nerve guidance conduits (NGCs) have emerged as a promising strategy for improving functional outcomes. Therefore, they offer a potential therapeutic alternative to nerve autografts. NGCs are tubular biostructures to bridge nerve injury sites via orienting axonal growth in an organized fashion as well as supplying a supportively appropriate microenvironment. Comprehensive NGC creation requires fundamental considerations of various aspects, including structure design, extracellular matrix components and cell composition. With these considerations, the production of an NGC that mimics the endogenous extracellular matrix structure can enhance neuron-NGC interactions and thereby promote regeneration and restoration of function in the target area. The use of electrospun fibrous substrates has a high potential to replicate the native extracellular matrix structure. With recent advances in electrospinning, it is now possible to generate numerous different biomimetic features within the NGCs. This review explores the use of electrospinning for the regeneration of the nervous system and discusses the main requirements, challenges and advances in developing and applying the electrospun NGC in the clinical practice of nerve injuries.

Neuron-fibrous scaffold interfaces in the peripheral nervous system: a perspective on the structural requirements.

The nerves of the peripheral nervous system are not able to effectively regenerate in cases of severe neural injury. This can result in debilitating consequences, including morbidity and lifelong impairments affecting the quality of the patient's life. Recent findings in neural tissue engineering have opened promising avenues to apply fibrous tissue-engineered scaffolds to promote tissue regeneration and functional recovery. These scaffolds, known as neural scaffolds, are able to improve neural regeneration by playing two major roles, namely, by being a carrier for transplanted peripheral nervous system cells or biological cues and by providing structural support to direct growing nerve fibers towards the target area. However, successful implementation of scaffold-based therapeutic approaches calls for an appropriate design of the neural scaffold structure that is capable of up- and down-regulation of neuron-scaffold interactions in the extracellular matrix environment. This review discusses the main challenges that need to be addressed to develop and apply fibrous tissue-engineered scaffolds in clinical practice. It describes some promising solutions that, so far, have shown to promote neural cell adhesion and growth and a potential to repair peripheral nervous system injuries.

Designing Olfactory Ensheathing Cell Transplantation Therapies: Influence of Cell Microenvironment.

Olfactory ensheathing cell (OEC) transplantation is emerging as a promising treatment option for injuries of the nervous system. OECs can be obtained relatively easily from nasal biopsies, and exhibit several properties such as secretion of trophic factors, and phagocytosis of debris that facilitate neural regeneration and repair. But a major limitation of OEC-based cell therapies is the poor survival of transplanted cells which subsequently limit their therapeutic efficacy. There is an unmet need for approaches that enable the in vitro production of OECs in a state that will optimize their survival and integration after transplantation into the hostile injury site. Here, we present an overview of the strategies to modulate OECs focusing on oxygen levels, stimulating migratory, phagocytic, and secretory properties, and on bioengineering a suitable environment in vitro.