Quantification of N-CAM and N-cadherin expression in axotomized and crushed rat sciatic nerve

Mesenchymal stem cells derived from bone marrow and adipose tissue for repairing acute sciatic nerve injury in a rabbit model

Peripheral nerve injury is one of the common disabling clinical conditions and around 50% of the cases end up in permanent impairment. Due to the lack of effective treatment options regenerative medicine employing stem cells is being evaluated. The presented study evaluated and compared regeneration potential of mesenchymal stem cells (MSCs) derived from bone marrow (BM) and adipose tissue (AD) in acute rabbit sciatic nerve injury (axonotmesis) model. A total of n = 54 grey giant rabbits were made subject of the study and divided equally into 3 groups: Control, BM-MSCs in Collagen I and AD-MSCs in Collagen I as per the treatment given. Iliac crest BM and omental AD was harvested from the same donor for isolation and culture of MSCs. The repair of sciatic nerve injury was evaluated on days 60 and 90. The clinical and histopathological scores and SEM morphology was better in cell treated groups as compared to the control. Morphology and histological studies revealed injured nerve in different levels of regenerative process. Gene expression was more than double for N-Cadherin in cell treated groups as compared to the control, especially at day 60. Between cell treated groups, BM-MSCs group showed better response as compared to the AD-MSCs, although statistically non-significant (p > 0.05). Incomplete nerve regeneration observed under various diagnostic parameters was in compliance to the incomplete clinical recovery at day 90. It was concluded that MSCs may improve sciatic nerve healing but fall short of complete regeneration at day 90, although BM-MSCs may have an edge over AD-MSCs.

A Review on the Role of Endogenous Neurotrophins and Schwann Cells in Axonal Regeneration

Injury to the peripheral nerve is traditionally referred to acquired nerve injury as they are the result of physical trauma due to laceration, stretch, crush and compression of nerves. However, peripheral nerve injury may not be completely limited to acquired physical trauma. Peripheral nerve injury equally implies clinical conditions like Guillain-Barré syndrome (GBS), Carpal tunnel syndrome, rheumatoid arthritis and diabetes. Physical trauma is commonly mono-neuropathic as it engages a single nerve and produces focal damage, while in the context of pathological conditions the damage is divergent involving a group of the nerve causing polyneuropathy. Damage to the peripheral nerve can cause a diverse range of manifestations from sensory impairment to loss of function with unpredictable recovery patterns. Presently no treatment option provides complete or functional recovery in nerve injury, as nerve cells are highly differentiated and inert to regeneration. However, the regenerative phenotypes in Schwann cells get expressed when a signalling cascade is triggered by neurotrophins. Neurotrophins are one of the promising biomolecules that are released naturally post-injury with the potential to exhibit better functional recovery. Pharmacological intervention modulating the expression of these neurotrophins such as brain-derived neurotrophic factor (BDNF) and pituitary adenylyl cyclase-activating peptide (PACAP) can prove to be a significant treatment option as endogenous compounds which may have remarkable innate advantage showing maximum 'biological relevance'.

Chitosan Micro-Grooved Membranes with Increased Asymmetry for the Improvement of the Schwann Cell Response in Nerve Regeneration

Peripheral nerve injuries are a common condition in which a nerve is damaged, affecting more than one million people every year. There are still no efficient therapeutic treatments for these injuries. Artificial scaffolds can offer new opportunities for nerve regeneration applications; in this framework, chitosan is emerging as a promising biomaterial. Here, we set up a simple and effective method for the production of micro-structured chitosan films by solvent casting, with high fidelity in the micro-pattern reproducibility. Three types of chitosan directional micro-grooved patterns, presenting different levels of symmetricity, were developed for application in nerve regenerative medicine: gratings (GR), isosceles triangles (ISO) and scalene triangles (SCA). The directional patterns were tested with a Schwann cell line. The most asymmetric topography (SCA), although it polarized the cell shaping less efficiently, promoted higher cell proliferation and a faster cell migration, both individually and collectively, with a higher directional persistence of motion. Overall, the use of micro-structured asymmetrical directional topographies may be exploited to enhance the nerve regeneration process mediated by chitosan scaffolds.

Effect of low-intensity pulsed ultrasound on orofacial sensory disturbance following inferior alveolar nerve injury: Role of neurotrophin-3 signaling

Percutaneous treatment of low-intensity pulsed ultrasound (LIPUS) to the site of inferior alveolar nerve (IAN) transection promotes functional regeneration, but the detailed mechanism is unknown. We examined the involvement of neurotrophin-3 (NT-3), which primarily binds with tropomyosin receptor kinase C (TrkC), in functional transected IAN regeneration following LIPUS treatment in rats. Daily LIPUS treatment to the transected IAN was performed, and the mechanical sensitivity of the facial skin was measured for 14 d. On day 5 after IAN transection, the expression of NT-3 in the transected IAN and TrkC-positive trigeminal ganglion neurons were immunohistochemically examined. Further, the effect of TrkC neutralization on the acceleration of facial mechanosensory disturbance restoration due to LIPUS treatment was analyzed. LIPUS treatment to the site of IAN transection significantly facilitated functional recovery from sensory disturbance on facial skin. Schwann cells in the transected IAN expressed NT-3, and LIPUS treatment increased the amount of NT-3. The facilitated recovery from the mechanosensory disturbance by continuous LIPUS treatment was inhibited by the ongoing TrkC neutralization at the IAN transection site. These results suggest that LIPUS treatment accelerates the recovery of orofacial mechanosensory function following IAN transection through the enhancement of NT-3 signaling in the transected IAN.

Dynamic Environmental Physical Cues Activate Mechanosensitive Responses in the Repair Schwann Cell Phenotype

Schwann cells plastically change in response to nerve injury to become a newly reconfigured repair phenotype. This cell is equipped to sense and interact with the evolving and unusual physical conditions characterizing the injured nerve environment and activate intracellular adaptive reprogramming as a consequence of external stimuli. Summarizing the literature contributions on this matter, this review is aimed at highlighting the importance of the environmental cues of the regenerating nerve as key factors to induce morphological and functional changes in the Schwann cell population. We identified four different microenvironments characterized by physical cues the Schwann cells sense via interposition of the extracellular matrix. We discussed how the physical cues of the microenvironment initiate changes in Schwann cell behavior, from wrapping the axon to becoming a multifunctional denervated repair cell and back to reestablishing contact with regenerated axons.

The transcriptome of anterior regeneration in earthworm Eudrilus eugeniae

The oligochaete earthworm, Eudrilus eugeniae is capable of regenerating both anterior and posterior segments. The present study focuses on the transcriptome analysis of earthworm E. eugeniae to identify and functionally annotate the key genes supporting the anterior blastema formation and regulating the anterior regeneration of the worm. The Illumina sequencing generated a total of 91,593,182 raw reads which were assembled into 105,193 contigs using CLC genomics workbench. In total, 40,946 contigs were annotated against the NCBI nr and SwissProt database and among them, 15,702 contigs were assigned to 14,575 GO terms. Besides a total of 9389 contigs were mapped to 416 KEGG biological pathways. The RNA-Seq comparison study identified 10,868 differentially expressed genes (DEGs) and of them, 3986 genes were significantly upregulated in the anterior regenerated blastema tissue samples of the worm. The GO enrichment analysis showed angiogenesis and unfolded protein binding as the top enriched functions and the pathway enrichment analysis denoted TCA cycle as the most significantly enriched pathway associated with the upregulated gene dataset of the worm. The identified DEGs and their function and pathway information can be effectively utilized further to interpret the key cellular, genetic and molecular events associated with the regeneration of the worm.

p75 and neural cell adhesion molecule 1 can identify pathologic Schwann cells in peripheral neuropathies

OBJECTIVE

Myelinated Schwann cells (SCs) in adult peripheral nerves dedifferentiate into immature cells in demyelinating neuropathies and Wallerian degeneration. This plastic SC change is actively involved in the myelin destruction and clearance as demyelinating SCs (DSCs). In inherited demyelinating neuropathy, pathologically differentiated and dysmyelinated SCs constitute the main nerve pathology.

METHODS

We investigated whether this SC plastic status in human neuropathic nerves could be determined by patient sera to develop disease-relevant serum biomarkers. Based on proteomics analysis of the secreted exosomes from immature SCs, we traced p75 neurotrophin receptor (p75) and neural cell adhesion molecule 1 (NCAM) in the sera of patients with peripheral neuropathy.

RESULTS

Enzyme-linked immunosorbent assay (ELISA) revealed that p75 and NCAM were subtype-specifically expressed in the sera of patients with peripheral neuropathy. In conjunction with these ELISA data, pathological analyses of animal models and human specimens suggested that the presence of DSCs in inflammatory neuropathy and of supernumerary nonmyelinating or dysmyelinating SCs in inherited neuropathy could potentially be distinguished by comparing the expression profiles of p75 and NCAM.

INTERPRETATION

This study indicates that the identification of disease-specific pathological SC stages might be a valuable tool for differential diagnosis of peripheral neuropathies.

Uridine-5'-Triphosphate Partially Blocks Differentiation Signals and Favors a more Repair State in Cultured rat Schwann Cells

Schwann cells (SCs) play a key role in peripheral nerve regeneration. After damage, they respond acquiring a repair phenotype that allows them to proliferate, migrate and redirect axonal growth. Previous studies have shown that Uridine-5'-Triphosphate (UTP) and its purinergic receptors participate in several pathophysiological responses in the nervous system. Our group has previously described how UTP induces the migration of a Schwannoma cell line and promotes wound healing. These data suggest that UTP participates in the signaling involved in the regeneration process. In the present study we evaluated UTP effects in isolated rat SCs and cocultures of SCs and dorsal root ganglia neurons. UTP reduced cAMP-dependent Krox-20 induction in SCs. UTP also reduced the N-cadherin re-expression that occurs when SCs and axons make contact. In myelinating cocultures, a non-significant tendency to a lower expression of P0 and MAG proteins in presence of UTP was observed. We also demonstrated that UTP induced SC migration without affecting cell proliferation. Interestingly, UTP was found to block neuregulin-induced phosphorylation of the ErbB3 receptor, a pathway involved in the regeneration process. These results indicate that UTP could acts as a brake to the differentiation signals, promoting a more migratory state in the repair-SCs.

N-Cadherin is Involved in Neuronal Activity-Dependent Regulation of Myelinating Capacity of Zebrafish Individual Oligodendrocytes In Vivo

Stimulating neuronal activity increases myelin sheath formation by individual oligodendrocytes, but how myelination is regulated by neuronal activity in vivo is still not fully understood. While in vitro studies have revealed the important role of N-cadherin in myelination, our understanding in vivo remains quite limited. To obtain the role of N-cadherin during activity-dependent regulation of myelinating capacity of individual oligodendrocytes, we successfully built an in vivo dynamic imaging model of the Mauthner cell at the subcellular structure level in the zebrafish central nervous system. Enhanced green fluorescent protein (EGFP)-tagged N-cadherin was used to visualize the stable accumulations and mobile transports of N-cadherin by single-cell electroporation at the single-cell level. We found that pentylenetetrazol (PTZ) significantly enhanced the accumulation of N-cadherin in Mauthner axons, a response that was paralleled by enhanced sheath number per oligodendrocytes. By offsetting this phenotype using oligopeptide (AHAVD) which blocks the function of N-cadherin, we showed that PTZ regulates myelination in an N-cadherin-dependent manner. What is more, we further suggested that PTZ influences N-cadherin and myelination via a cAMP pathway. Consequently, our data indicated that N-cadherin is involved in neuronal activity-dependent regulation of myelinating capacity of zebrafish individual oligodendrocytes in vivo.

Transcriptome Analysis on Monocytes from Patients with Neovascular Age-Related Macular Degeneration

Mononuclear phagocytes (MPs), including monocytes/macrophages, play complex roles in age-related macular degeneration (AMD) pathogenesis. We reported altered gene-expression signature in peripheral blood mononuclear cells from AMD patients, and a chemokine receptor signature on AMD monocytes. To obtain comprehensive understanding of MP involvement, particularly in peripheral circulation in AMD, we performed global gene expression analysis in monocytes. We separated monocytes from treatment-naïve neovascular AMD (nvAMD) patients (n = 14) and age-matched controls (n = 15), and performed microarray and bioinformatics analysis. Quantitative real-time PCR was performed on other sets of nvAMD (n = 25), atrophic AMD (n = 21), and controls (n = 28) for validation. This validated microarray genes (like TMEM176A/B and FOSB) tested, including differences between nvAMD and atrophic AMD. We identified 2,165 differentially-expressed genes (P < 0.05), including 79 genes with log2 fold change ≥1.5 between nvAMD and controls. Functional annotation using DAVID and TANGO demonstrated immune response alterations in AMD monocytes (FDR-P <0.05), validated by randomized data comparison (P < 0.0001). GSEA, ISMARA, and MEME analysis found immune enrichment and specific involved microRNAs. Enrichment of differentially-expressed genes in monocytes was found in retina via SAGE data-mining. These genes were enriched in non-classical vs. classical monocyte subsets (P < 0.05). Therefore, global gene expression analysis in AMD monocytes reveals an altered immune-related signature, further implicating systemic MP activation in AMD.

Schwann Cell Contact Guidance versus Boundary -Interaction in Functional Wound Healing along Nano and Microstructured Membranes

Peripheral nerve transection is often encountered after trauma and can lead to long-term/permanent loss of sensor/motor functionality. Here, the effect of pure contact interaction of nano/microgrooved substrates on Schwann cells (SCs) is studied in view of their possible use for nerve-repair applications. Elastomeric gratings (GRs; i.e., alternating lines of ridges and grooves) are developed with different lateral periods (1-20 μm) and depths (0.3-2.5 μm), leading to two distinct cell-material interaction regimes: contact guidance (grating period < cell body diameter) and boundary guidance (grating period ≥ cell body diameter). Here, it is shown that boundary guidance leads to the best single-cell polarization, actin organization, and single-cell directional migration. Remarkably, contact guidance is instead more effective in driving collective SC migration and improves functional wound healing. It is also demonstrated that this behavior is linked to the properties of the SC monolayers on different GRs. SCs on large-period GRs are characterized by N-Cadherin downregulation and enhanced single-cell scattering into the wound with respect to SCs on small-period GRs, indicating a less compact monolayer characterized by looser cell-cell junctions in the boundary guidance regime. The present results provide information on the impact of specific sub-micrometer topographical elements on SC functional response, which can be exploited for nerve-regeneration applications.

Nerve demyelination increases metabotropic glutamate receptor subtype 5 expression in peripheral painful mononeuropathy

Wallerian degeneration or nerve demyelination, arising from spinal nerve compression, is thought to bring on chronic neuropathic pain. The widely distributed metabotropic glutamate receptor subtype 5 (mGluR5) is involved in modulating nociceptive transmission. The purpose of this study was to investigate the potential effects of mGluR5 on peripheral hypersensitivities after chronic constriction injury (CCI). Sprague-Dawley rats were operated on with four loose ligatures around the sciatic nerve to induce thermal hyperalgesia and mechanical allodynia. Primary afferents in dermis after CCI exhibited progressive decreases, defined as partial cutaneous denervation; importantly, mGluR5 expressions in primary afferents were statistically increased. CCI-induced neuropathic pain behaviors through the intraplantar injections of 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a selective mGluR5 antagonist, were dose-dependently attenuated. Furthermore, the most increased mGluR5 expressions in primary afferents surrounded by reactive Schwann cells were observed at the distal CCI stumps of sciatic nerves. In conclusion, these results suggest that nerve demyelination results in the increases of mGluR5 expression in injured primary afferents after CCI; and further suggest that mGluR5 represents a main therapeutic target in developing pharmacological strategies to prevent peripheral hypersensitivities.

Axonal regeneration in early stages of sciatic nerve crush injury is enhanced by α7nAChR in rats

This study investigated the role of alpha 7 nicotinic acetylcholine receptor (α7nAChR) in axonal regeneration after crush injury to the rat sciatic nerve. The time course of α7nAChR expression following injury was assessed by immunohistochemistry and western blotting, and local inflammation, as indicated by the expression of tumor necrosis factor (TNF)-α, was detected by enzyme-linked immunosorbent assay. Axonal regeneration was evaluated by the pinch-test, morphometric analysis, and by measuring growth-associated protein 43 expressions. Local α7nAChR expression increased on day 1, peaked on day 3, and remained elevated on day 5 following nerve injuries. Prominent α7nAChR immunoreactivity was observed in Schwann cells, endothelial cells of the capillaries, and a small number of inflammatory cells. Application of the selective α7nAChR agonist PNU-282987 decreased TNF-α level and enhanced axonal regeneration, but this effect was blocked by concomitant treatment with methyllycaconitine, a α7nAChR antagonist. The results indicate that the local expression of α7nAChR is increased during the early stages of sciatic nerve injury, and application of a α7nAChR agonist promotes axonal regeneration by suppression of TNF-α-mediated inflammation. The α7nAChR can act as a neuroprotective agent and α7nAChR activation may be a useful therapeutic strategy to treat peripheral nerve injury.

Reproducible mouse sciatic nerve crush and subsequent assessment of regeneration by whole mount muscle analysis

Regeneration in the peripheral nervous system (PNS) is widely studied both for its relevance to human disease and to understand the robust regenerative response mounted by PNS neurons thereby possibly illuminating the failures of CNS regeneration(1). Sciatic nerve crush (axonotmesis) is one of the most common models of peripheral nerve injury in rodents(2). Crushing interrupts all axons but Schwann cell basal laminae are preserved so that regeneration is optimal(3,4). This allows the investigator to study precisely the ability of a growing axon to interact with both the Schwann cell and basal laminae(4). Rats have generally been the preferred animal models for experimental nerve crush. They are widely available and their lesioned sciatic nerve provides a reasonable approximation of human nerve lesions(5,4). Though smaller in size than rat nerve, the mouse nerve has many similar qualities. Most importantly though, mouse models are increasingly valuable because of the wide availability of transgenic lines now allows for a detailed dissection of the individual molecules critical for nerve regeneration(6, 7). Prior investigators have used multiple methods to produce a nerve crush or injury including simple angled forceps, chilled forceps, hemostatic forceps, vascular clamps, and investigator-designed clamps(8,9,10,11,12). Investigators have also used various methods of marking the injury site including suture, carbon particles and fluorescent beads(13,14,1). We describe our method to obtain a reproducibly complete sciatic nerve crush with accurate and persistent marking of the crush-site using a fine hemostatic forceps and subsequent carbon crush-site marking. As part of our description of the sciatic nerve crush procedure we have also included a relatively simple method of muscle whole mount we use to subsequently quantify regeneration.

Spatiotemporal expression profiling of proteins in rat sciatic nerve regeneration using reverse phase protein arrays

Background

Protein expression profiles throughout 28 days of peripheral nerve regeneration were characterized using an established rat sciatic nerve transection injury model. Reverse phase protein microarrays were used to identify the spatial and temporal expression profile of multiple proteins implicated in peripheral nerve regeneration including growth factors, extracellular matrix proteins, and proteins involved in adhesion and migration. This high-throughput approach enabled the simultaneous analysis of 3,360 samples on a nitrocellulose-coated slide.

Results

The extracellular matrix proteins collagen I and III, laminin gamma-1, fibronectin, nidogen and versican displayed an early increase in protein levels in the guide and proximal sections of the regenerating nerve with levels at or above the baseline expression of intact nerve by the end of the 28 day experimental course. The 28 day protein levels were also at or above baseline in the distal segment however an early increase was only noted for laminin, nidogen, and fibronectin. While the level of epidermal growth factor, ciliary neurotrophic factor and fibroblast growth factor-1 and -2 increased throughout the experimental course in the proximal and distal segments, nerve growth factor only increased in the distal segment and fibroblast growth factor-1 and -2 and nerve growth factor were the only proteins in that group to show an early increase in the guide contents. As expected, several proteins involved in cell adhesion and motility; namely focal adhesion kinase, N-cadherin and β-catenin increased earlier in the proximal and distal segments than in the guide contents reflecting the relatively acellular matrix of the early regenerate.

Conclusions

In this study we identified changes in expression of multiple proteins over time linked to regeneration of the rat sciatic nerve both demonstrating the utility of reverse phase protein arrays in nerve regeneration research and revealing a detailed, composite spatiotemporal expression profile of peripheral nerve regeneration.

Protein profiling of anastomosed facial nerve treated with mesenchymal stromal cells

BACKGROUND AIMS

The types of proteins released from mesenchymal stromal cells (MSC) are still unclear. Our aim was to compare apoptosis scores and the expression of myelin-associated glycoprotein (MAG), myelin basic protein (MBP), neural cell adhesion molecule (NCAM)-1,matrix metalloproteinase (MMP)-1A, tissue inhibitor of metalloproteinase (TIMP)-1, TIMP-1/MMP-1A ratio, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), neurotrophin (NT)-3, NT-4, glial cell-derived neurotropic factor (GDNF), leukemia inhibitory factor (LIF), basic fibroblast growth factor (FGF)-2, insulin-like growth factor (IGF)-1, platelet-derived growth factor (PDGF)-α and transforming growth factor (TGF)-β1 in anastomosed facial nerves that had been treated with or without MSC.

METHODS

In seven rats, the buccal branch of the right facial nerve was transected, anastomosed and treated with MSC (anastomosed + MSC group). The left buccal branch was anastomosed only (anastomosed-only group). The left mandibular branch served as an intact nerve group. On days 18-20, the distal segments of the branches were examined in terms of expression of the mentioned proteins and apoptosis scores using polymerase chain reaction (PCR) and terminal deoxynucleotidyl transferase-mediated digoxigenin-UTP nick end labeling (TUNEL) assays.

RESULTS

MSC application significantly increased CNTF, PDGF-α, LIF, TGF-β1, BDNF and NT-3 expression (P < 0.05). MAG expression slightly decreased whereas NCAM-1, MMP-1A and FGF-2 slightly increased(P > 0.05). Changes in other proteins and apoptosis scores were not significant.

CONCLUSIONS

These results suggest that MSC increases expression of CNTF, PDGF-α, LIF,TGF-β1, BDNF and NT-3. MAG, NCAM-1, MMP-1A and FGF-2 expressions were slightly changed in this stage of nerve regeneration. The comparison of apoptotic activity was not conclusive. Overall, it appears that MSC might have differential effects on the mentioned tissue-related proteins and trophic/growth factors.

Neural regeneration

Regeneration of the nervous system requires either the repair or replacement of nerve cells that have been damaged by injury or disease. While lower organisms possess extensive capacity for neural regeneration, evolutionarily higher organisms including humans are limited in their ability to regenerate nerve cells, posing significant issues for the treatment of injury and disease of the nervous system. This chapter focuses on current approaches for neural regeneration, with a discussion of traditional methods to enhance neural regeneration as well as emerging concepts within the field such as stem cells and cellular reprogramming. Stem cells are defined by their ability to self-renew as well as their ability to differentiate into multiple cell types, and hence can serve as a source for cell replacement of damaged neurons. Traditionally, adult stem cells isolated from the hippocampus and subventricular zone have served as a source of neural stem cells for replacement purposes. With the advancement of pluripotent stem cells, including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (iPSCs), new and exciting approaches for neural cell replacement are being developed. Furthermore, with increased understanding of the human genome and epigenetics, scientists have been successful in the direct genetic reprogramming of somatic cells to a neuronal fate, bypassing the intermediary pluripotent stage. Such breakthroughs have accelerated the timing of production of mature neuronal cell types from a patient-specific somatic cell source such as skin fibroblasts or mononuclear blood cells. While extensive hurdles remain to the translational application of such stem cell and reprogramming strategies, these approaches have revolutionized the field of regenerative biology and have provided innovative approaches for the potential regeneration of the nervous system.

Extrinsic and intrinsic determinants of nerve regeneration

After central nervous system (CNS) injury axons fail to regenerate often leading to persistent neurologic deficit although injured peripheral nervous system (PNS) axons mount a robust regenerative response that may lead to functional recovery. Some of the failures of CNS regeneration arise from the many glial-based inhibitory molecules found in the injured CNS, whereas the intrinsic regenerative potential of some CNS neurons is actively curtailed during CNS maturation and limited after injury. In this review, the molecular basis for extrinsic and intrinsic modulation of axon regeneration within the nervous system is evaluated. A more complete understanding of the factors limiting axonal regeneration will provide a rational basis, which is used to develop improved treatments for nervous system injury.

Elevated expression of CAPON and neuronal nitric oxide synthase in the sciatic nerve of rats following constriction injury

Neuronal nitric oxide synthase (nNOS) has been implicated in peripheral nerve lesions and regeneration. The CAPON adaptor protein interacts with the PDZ domain of nNOS, helping to regulate nNOS activity at post-synaptic sites in neurones, but it is not known whether its expression is altered in sciatic nerves after chronic nerve constriction injury. In the present study, the spatiotemporal expression of CAPON was determined in chronically constricted rat sciatic nerves. Similar to the level of protein expression, CAPON mRNA was significantly up-regulated for almost 5weeks following sciatic nerve injury. Immunohistochemistry demonstrated that increased CAPON was found mainly in S-100-positive Schwann cells. In addition, co-immunoprecipitation demonstrated an interaction between CAPON and nNOS in Schwann cells and the interaction was enhanced in injured sciatic nerves. CAPON may be involved in peripheral nerve regeneration through regulation of nNOS activity.

Diffusion tensor imaging of cocaine-treated rodents

Studies in cocaine-dependent human subjects have shown differences in white matter on diffusion tensor imaging (DTI) compared with non-drug-using controls. It is not known whether the differences in fractional anisotropy (FA) seen on DTI in white matter regions of cocaine-dependent humans result from a pre-existing predilection for drug use or purely from cocaine abuse. To study the effect of cocaine on brain white matter, DTI was performed on 24 rats after continuous infusion of cocaine or saline for 4 weeks, followed by brain histology. Voxel-based morphometry analysis showed an 18% FA decrease in the splenium of the corpus callosum (CC) in cocaine-treated animals relative to saline controls. On histology, significant increase in neurofilament expression (125%) and decrease in myelin basic protein (40%) were observed in the same region in cocaine-treated animals. This study supports the hypothesis that chronic cocaine use alters white matter integrity in human CC. Unlike humans, where the FA in the genu differed between cocaine users and non-users, the splenium was affected in rats. These differences between rodent and human findings could be due to several factors that include differences in the brain structure and function between species and/or the dose, timing, and duration of cocaine administration.

Negative regulation of myelination: relevance for development, injury, and demyelinating disease

Dedifferentiation of myelinating Schwann cells is a key feature of nerve injury and demyelinating neuropathies. We review recent evidence that this dedifferentiation depends on activation of specific intracellular signaling molecules that drive the dedifferentiation program. In particular, we discuss the idea that Schwann cells contain negative transcriptional regulators of myelination that functionally complement positive regulators such as Krox-20, and that myelination is therefore determined by a balance between two opposing transcriptional programs. Negative transcriptional regulators should be expressed prior to myelination, downregulated as myelination starts but reactivated as Schwann cells dedifferentiate following injury. The clearest evidence for a factor that works in this way relates to c-Jun, while other factors may include Notch, Sox-2, Pax-3, Id2, Krox-24, and Egr-3. The role of cell-cell signals such as neuregulin-1 and cytoplasmic signaling pathways such as the extracellular-related kinase (ERK)1/2 pathway in promoting dedifferentiation of myelinating cells is also discussed. We also review evidence that neurotrophin 3 (NT3), purinergic signaling, and nitric oxide synthase are involved in suppressing myelination. The realization that myelination is subject to negative as well as positive controls contributes significantly to the understanding of Schwann cell plasticity. Negative regulators are likely to have a major role during injury, because they promote the transformation of damaged nerves to an environment that fosters neuronal survival and axonal regrowth. In neuropathies, however, activation of these pathways is likely to be harmful because they may be key contributors to demyelination, a situation which would open new routes for clinical intervention.

E-cadherin expression in postnatal Schwann cells is regulated by the cAMP-dependent protein kinase a pathway

Expression of E-cadherin in the peripheral nervous system is a highly regulated process that appears postnatally in concert with the development of myelinating Schwann cell lineage. As a major component of autotypic junctions, E-cadherin plays an important role in maintaining the structural integrity of noncompact myelin regions. In vivo, the appearance of E-cadherin in postnatal Schwann cell is accompanied by the disappearance of N-cadherin, suggesting reciprocal regulation of the two cadherins during Schwann cell development. The molecular signal that regulates the cadherin switch in Schwann cell is unclear. Using a neuron-Schwann cell co-culture system, here we show that E-cadherin expression is induced by components on the axonal membrane. We also show that the axonal effect is mediated through cAMP-dependent protein kinase A (cAMP-PKA) activation in the Schwann cell: (1) inhibition of cAMP-PKA blocks axon-induced E-cadherin expression and (2) cAMP elevation in the Schwann cell is sufficient to induce E-cadherin expression. In addition, cAMP-dependent E-cadherin expression is promoted by contact between adjacent Schwann cell membranes, suggesting its role in autotypic junction formation during myelination. Furthermore, cAMP-induced E-cadherin expression is accompanied by suppression of N-cadherin expression. Therefore, we propose that axon-dependent activation of cAMP-PKA serves as a signal that promotes cadherin switch during postnatal development of Schwann cells.

Level and localization of polysialic acid is critical for early peripheral nerve regeneration

PolySia, the most striking post-translational modification of the neural cell adhesion molecule, is down-regulated during postnatal development. After peripheral nerve lesion, polySia is located on neuronal and glial cells normally not synthesizing polySia. However, structural consequences of reduced polySia content for peripheral nerve regeneration have not yet been clear. Furthermore, the contribution of sialyltransferases ST8SiaII and ST8SiaIV for the up-regulation of polySia has not been studied so far. In order to investigate the impact of polySia on regeneration processes of myelinated axons, we examined mouse mutants retaining only one functional sialyltransferase allele. In the absence of ST8SiaII, quantification of myelinated axons revealed a significant decrease in number and size of regenerated fibers without impairment of remyelination. In contrast, St8SiaIV deficiency resulted in increased fiber outgrowth and axonal maturation. Western blot analysis demonstrated that both ST8SiaII and St8SiaIV direct up-regulation of polySia. Cell-specific induction of polySia in myelinating Schwann cells and on regenerated axons in the presence of ST8SiaIV, but not ST8SiaII, indicates that not only the amount of polySia but also its cellular localization has a high impact on the regeneration progress of peripheral nerves.

In vitro cell alignment obtained with a Schwann cell enriched microstructured nerve guide with longitudinal guidance channels

Therapeutic benefits of autologous nerve grafting in repair of peripheral nerve lesions have not been reached using any alternative nerve guide. Nevertheless, issues of co-morbidity and limited availability of donor nerves urgently ask for a need of bioartificial nerve guides which could either replace or complement autologous nerve grafts. It is increasingly appreciated that optimal nerve guides comprise both physical and molecular cues in support of peripheral axon regeneration. Now, we present a collagen-based microstructured 3D nerve guide containing numerous longitudinal guidance channels with dimensions resembling natural endoneurial tubes. Moreover, these nerve guides could be functionalized by Schwann cell (SC) seeding. Viable SCs did not only adhere to the nerve guide, but also migrated throughout the guidance channels. Of particular importance was the observation that SCs within the guidance channels formed cellular columns reminiscent of "Bands of Büngner", which are crucial structures in the natural process of peripheral nerve regeneration during the Wallerian degeneration. We, therefore, conclude that our orientated 3D nerve guides (decorated with SCs) with their physical and molecular properties may hold great promise in the repair of peripheral nerve lesion and serve as a basis for future experimental regeneration studies.

Inhibition of N-cadherin and beta-catenin function reduces axon-induced Schwann cell proliferation

N-cadherin and beta-catenin are involved in cell adhesion and cell cycle in tumor cells and neural crest. Both are expressed at key stages of Schwann cell (SC) development, but little is known about their function in the SC lineage. We studied the role of these molecules in adult rat derived SC-embryonic dorsal root ganglion cocultures by using low-Ca(2+) conditions and specific blocking antibodies to interfere with N-cadherin function and by using small interfering RNA (siRNA) to decrease beta-catenin expression in both SC-neuron cocultures and adult rat-derived SC monocultures. N-cadherin blocking conditions decreased SC-axon association and reduced axon-induced SC proliferation. In SC monocultures, beta-catenin reduction diminished the proliferative response of SCs to the mitogen beta1-heregulin, and, in SC-DRG cocultures, beta-catenin reduction inhibited axon-contact-dependent SC proliferation. Stimulation of SC cultures with beta1-heregulin increased total beta-catenin protein amount, phosphorylation of GSK-3beta and beta-catenin presence in nuclear extracts. In conclusion, our findings suggest a previously unrecognized contribution of beta-catenin and N-cadherin to axon-induced SC proliferation.

Purinergic receptor signaling regulates N-cadherin expression in primary astrocyte cultures

Extracellular ATP exerts both short-term and long-term effects in the CNS by stimulating cell-surface purinergic receptors. Here we have examined the effect of purinergic receptor activation on N-cadherin expression, a calcium-dependent cell adhesion molecule involved in many processes, including glia-glia and axon-glia interactions. When primary cultures of rat cortical astrocytes were treated with ATP, N-cadherin protein expression increased in a time- and concentration-dependent manner. In addition, ATP treatment caused an increase in N-cadherin immunoreactivity in both the cytoplasm and on the cell surface membrane. Interestingly, experiments with cycloheximide revealed that relocalization of N-cadherin to the cell surface membrane were independent of protein synthesis. The ATP-induced increase in N-cadherin protein expression was blocked by reactive blue 2 and 8-(p-sulfophenyl)-theophylline, suggesting involvement of both P2 and P1 purinergic receptors, respectively. In addition, N-cadherin expression was partially blocked when signaling from purinergic receptors to extracellular signal regulated protein kinase or Akt was inhibited by 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene or wortmannin, respectively. By using an in vitro model of traumatic CNS injury, we found that N-cadherin expression was increased when astrocytes were subjected to rapid and reversible mechanical strain. The findings presented here demonstrate a role for extracellular ATP, purinergic receptors and protein kinase signaling in regulating N-cadherin expression and suggest a role for this mechanism in cell-cell interactions.

Antibodies neutralizing Nogo-A increase pan-cadherin expression and motor recovery following spinal cord injury in rats

STUDY DESIGN

A rat model of spinal cord injury was used to test the hypothesis that Nogo-A monoclonal antibody (NEP1-40) promotes morphologic and functional recoveries of injured spinal cord.

OBJECTIVE

Nogo-A is a myelin-associated neurite outgrowth inhibitory protein, which blocks elongation nerve fibers and limits neuronal regeneration after central nervous system injury.

METHODS

Forty-four rats were utilized and allocated into control (vehicle) and NEP1-40-treated groups. In all animals, the spinal cord was hemi-transected at Th-10 and phosphate-buffered saline solution was immediately applied on the injured area in the control group. NEP1-40 solution was immediately applied on the hemi-transected area in the treatment group. Each group was subdivided into three subgroups according to the postsurgical day of killing (3, 8 and 21 days). The spinal cords were removed for analysis.

RESULTS

Motor scores in the NEP1-40-treated groups were significantly higher than those in the vehicle groups both at 8 and 21 days post injury. Immunohistochemical staining for pan-cadherin, a marker of neuronal cell adhesion and axonal sprouting, revealed a significant increase in staining in the NEP1-40 treatment group at 8 and 21 days post injury. Transmission electron microscopical evaluation revealed degeneration of the myelin and loss of cytoarchitectural organization in the axons of controls. Better preservation and normal histologic features were observed in the NEP1-40-treated groups.

CONCLUSION

We have demonstrated improved preservation of injured axons and significant pan-cadherin expression after NEP1-40 treatment after the spinal cord injury. Inhibition of Nogo-A may improve the capacity for neuronal regeneration after spinal cord injury.

Regulatory expression of Neurensin-1 in the spinal motor neurons after mouse sciatic nerve injury

Axonal regeneration after crush injury of the sciatic nerve has been intensely studied for the elucidation of molecular and cellular mechanisms. Neurite extension factor1 (Nrsn1) is a unique membranous protein that has a microtubule-binding domain and is specifically expressed in neurons. Our studies have shown that Nrsn1 is localized particularly in actively extending neurites, thus playing a role in membrane transport to the growing distal ends of extending neurites. To elucidate the possible role of Nrsn1 during peripheral axonal regeneration, we examined the expression of Nrsn1 mRNA by in situ hybridization and Nrsn1 localization by immunocytochemistry, using a mouse model. The results revealed that during the early phase of axonal regeneration of motor nerves, Nrsn1 mRNA is upregulated in the injured motor neuron. Nrsn1 is localized in the cell bodies of motor neurons and at the growing distal ends of regenerating axons. These results indicate that Nrsn1 plays an active role in axonal regeneration as well as in embryonic development.

Expression and localization of the cell adhesion molecule SgIGSF during regeneration of the olfactory epithelium in mice

Spermatogenic immunoglobulin superfamily (SgIGSF) is a cell adhesion molecule originally discovered in mouse testis. SgIGSF is expressed not only in spermatogenic cells but also in lung and liver epithelial cells and in neurons and glia of the central and peripheral nervous systems. In the present study, we examined the expression and localization of SgIGSF in mouse olfactory epithelium before and after transection of the olfactory nerves, by RT-PCR, Western blotting and immunohistochemistry. In normal olfactory mucosa, SgIGSF showed 100 kDa in molecular weight, which was identical with that in the lung but different from that in the brain. SgIGSF was expressed on the membrane of all olfactory, sustentacular and basal cells, but more abundantly in the apical portions of the olfactory epithelium where the dendrites of olfactory cells are in contact with sustentacular cells. After olfactory nerve transection, mature olfactory cells disappeared in 4 days but were regenerated around 7–15 days by proliferation and differentiation of basal cells into mature olfactory cells through the step of immature olfactory cells. During this period, both the mRNA and protein for SgIGSF showed a transient increase, with peak levels at 7 days and 11 days, respectively, after the transection. Immunohistochemistry showed that the enriched immunoreactivity for SgIGSF at 7–11 days was localized primarily to the membrane of immature olfactory cells. These results suggested that, during regeneration of the olfactory epithelium, the adhesion molecule SgIGSF plays physiological roles in differentiation, migration, and maturation of immature olfactory cells.

Role of N-cadherin in Schwann cell precursors of growing nerves

In the present paper, we determine the localization and developmental regulation of N-cadherin in embryonic rat nerves and examine the role of N-cadherin in this system. We also identify a major transition in the architecture of embryonic nerves and relating it to N-cadherin expression. We find that in early embryonic nerves, N-cadherin is primarily expressed in Schwann cell precursors. Pronounced expression is seen at distal nerve fronts where these cells associate with growth cones, and the proximal nerve ends, in boundary cap cells. Unexpectedly, N-cadherin is downregulated as precursors generate Schwann cells, coinciding with the time at which most axons make target connections. Therefore, glial N-cadherin expression is essentially restricted to the period of axon outgrowth. We also provide evidence that N-cadherin supports the formation of contacts between Schwann cell precursors and show that these cells are a favorable substrate for axon growth, unlike N-cadherin-negative Schwann cells. Induction of N-cadherin expression in Schwann cells by neuregulin-1 restores their ability to form contacts and support axon growth. Finally, we show that the loss of glial N-cadherin during embryonic nerve development is accompanied by a transformation of nerve architecture, involving the appearance of endoneurial connective tissue space, fibroblasts, Schwann cell basal lamina, and blood vessels. Because N-cadherin is likely to promote the extensive glial contacts typical of the compact embryonic nerve, we suggest that N-cadherin loss at the time of Schwann cell generation allows endoneurial space to appear between the glial cells, a development that eventually permits the extensive interactions between connective tissue and individual axon-Schwann cell units necessary for myelination.

Induction of parathyroid hormone-related peptide following peripheral nerve injury: Role as a modulator of Schwann cell phenotype

Parathyroid hormone-related peptide (PTHrP) is widely distributed in the rat nervous system, including the peripheral nervous system, where its function is unknown. PTHrP mRNA expression has recently been shown to be significantly elevated following axotomy of sympathetic ganglia, although the role of PTHrP was not investigated. The role of PTHrP in peripheral nerve injury was investigated in this study using the sciatic nerve injury model and dorsal root ganglion (DRG) explant model of nerve regeneration. We find that PTHrP is a constitutively secreted peptide of proliferating Schwann cells and that the PTHrP receptor (PTH1R) mRNA is expressed in isolated DRG and in sciatic nerve. Using the sciatic nerve injury model, we show that PTHrP is significantly upregulated in DRG and in sciatic nerve. In addition, in situ hybridization revealed significant localization of PTHrP mRNA to Schwann cells in the injured sciatic nerve. We also find that PTHrP causes a dramatic increase in the number of Schwann cells that align with and bundle regrowing axons in explants, characteristic of immature, dedifferentiated Schwann cells. In addition to stimulating migration of Schwann cells along the axonal membrane, PTHrP also stimulates migration on a type 1 collagen matrix. Furthermore, treatment of purified Schwann cell cultures with PTHrP results in the rapid phosphorylation of the cAMP response element protein, CREB. We propose that PTHrP acts by promoting the dedifferentiation of Schwann cells, a critical requirement for successful nerve regeneration and an effect consistent with known PTHrP functions in other cellular differentiation programs.