Role of integrins in the peripheral nervous system

Axonal transport deficits in the pathogenesis of diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is a chronic and prevalent metabolic disease that gravely endangers human health and seriously affects the quality of life of hyperglycemic patients. More seriously, it can lead to amputation and neuropathic pain, imposing a severe financial burden on patients and the healthcare system. Even with strict glycemic control or pancreas transplantation, peripheral nerve damage is difficult to reverse. Most current treatment options for DPN can only treat the symptoms but not the underlying mechanism. Patients with long-term diabetes mellitus (DM) develop axonal transport dysfunction, which could be an important factor in causing or exacerbating DPN. This review explores the underlying mechanisms that may be related to axonal transport impairment and cytoskeletal changes caused by DM, and the relevance of the latter with the occurrence and progression of DPN, including nerve fiber loss, diminished nerve conduction velocity, and impaired nerve regeneration, and also predicts possible therapeutic strategies. Understanding the mechanisms of diabetic neuronal injury is essential to prevent the deterioration of DPN and to develop new therapeutic strategies. Timely and effective improvement of axonal transport impairment is particularly critical for the treatment of peripheral neuropathies.

Engineering Nanofiber Scaffolds with Biomimetic Cues for Differentiation of Skin-Derived Neural Crest-like Stem Cells to Schwann Cells

Our laboratory reported the derivation of neural crest stem cell (NCSC)-like cells from the interfollicular epidermis of the neonatal and adult epidermis. These keratinocyte (KC)-derived Neural Crest (NC)-like cells (KC-NC) could differentiate into functional neurons, Schwann cells (SC), melanocytes, and smooth muscle cells in vitro. Most notably, KC-NC migrated along stereotypical pathways and gave rise to multiple NC derivatives upon transplantation into chicken embryos, corroborating their NC phenotype. Here, we present an innovative design concept for developing anisotropically aligned scaffolds with chemically immobilized biological cues to promote differentiation of the KC-NC towards the SC. Specifically, we designed electrospun nanofibers and examined the effect of bioactive cues in guiding KC-NC differentiation into SC. KC-NC attached to nanofibers and adopted a spindle-like morphology, similar to the native extracellular matrix (ECM) microarchitecture of the peripheral nerves. Immobilization of biological cues, especially Neuregulin1 (NRG1) promoted the differentiation of KC-NC into the SC lineage. This study suggests that poly-ε-caprolactone (PCL) nanofibers decorated with topographical and cell-instructive cues may be a potential platform for enhancing KC-NC differentiation toward SC.

Identification of hub genes in the subacute spinal cord injury in rats

Background

Spinal cord injury (SCI) is a common trauma in clinical practices. Subacute SCI is mainly characterized by neuronal apoptosis, axonal demyelination, Wallerian degeneration, axonal remodeling, and glial scar formation. It has been discovered in recent years that inflammatory responses are particularly important in subacute SCI. However, the mechanisms mediating inflammation are not completely clear.

Methods

The gene expression profiles of GSE20907, GSE45006, and GSE45550 were downloaded from the GEO database. The models of the three gene expression profiles were all for SCI to the thoracic segment of the rat. The differentially expressed genes (DEGs) and weighted correlation network analysis (WGCNA) were performed using R software, and functional enrichment analysis and protein–protein interaction (PPI) network were performed using Metascape. Module analysis was performed using Cytoscape. Finally, the relative mRNA expression level of central genes was verified by RT-PCR.

Results

A total of 206 candidate genes were identified, including 164 up-regulated genes and 42 down-regulated genes. The PPI network was evaluated, and the candidate genes enrichment results were mainly related to the production of tumor necrosis factors and innate immune regulatory response. Twelve core genes were identified, including 10 up-regulated genes and 2 down-regulated genes. Finally, seven hub genes with statistical significance in both the RT-PCR results and expression matrix were identified, namely Itgb1, Ptprc, Cd63, Lgals3, Vav1, Shc1, and Casp4. They are all related to the activation process of microglia.

Conclusion

In this study, we identified the hub genes and signaling pathways involved in subacute SCI using bioinformatics methods, which may provide a molecular basis for the future treatment of SCI.

Peripheral Nerve Development and the Pathogenesis of Peripheral Neuropathy: the Sorting Point

Nerve development requires a coordinated sequence of events and steps to be accomplished for the generation of functional peripheral nerves to convey sensory and motor signals. Any abnormality during development may result in pathological structure and function of the nerve, which evolves in peripheral neuropathy. In this review, we will briefly describe different steps of nerve development while we will mostly focus on the molecular mechanisms involved in radial sorting of axons, one of these nerve developmental steps. We will summarize current knowledge of molecular pathways so far reported in radial sorting and their possible interactions. Finally, we will describe how disruption of these pathways may result in human neuropathies.

Determination of the transcriptional level of long non-coding RNA NEAT-1, downstream target microRNAs, and genes targeted by microRNAs in diabetic neuropathy patients

BACKGROUND

Diabetic neuropathy (DN) is one of the microvascular complications of diabetes that leads to peripheral sensorimotor and autonomic nervous system damages. In this study, we first examined the expression of lncRNA NEAT-1 and its downstream microRNAs, miR-183-5p, miR-433-3p, and then examined mRNA expression of ITGA4, ITGB1, SESN1, and SESN3 as the downstream targets of miR-183-5p, miR-433-3p.

METHODS

The blood sample was obtained from a total of 40 patients with type 2 diabetes (20 DN patients and 20 non-DN diabetic cases) and ten healthy individuals. After RNA extraction from peripheral blood samples and cDNA synthesis, expression measurements were performed by the RT-qPCR technique.

RESULTS

Our results showed that the expression level of lncRNA NEAT-1 was significantly higher, and the expression level of miR-183-5p was significantly lower in DN patients compared to the healthy control group. Besides, the expression level of miR-433-3p was significantly lower, and the mRNA expression of ITGA4, SESN1, and SESN3 was significantly higher in DN patients compared to the diabetes group. The ROC curve analysis showed that the miR-183-5p with high levels of accuracy could discriminate DN patients from healthy control (AUC = 0.836) and NEAT-1, SESN1, SESN3, ITGA4 have a high ability to distinguish DN from non-DN patients (AUC = 0.701, 0.772, 0.815 and 0.780, respectively).

CONCLUSION

It seems that the NEAT-1 probably targets miR-183-5p and miR-433-3p, as a result of which the expression of ITGA4, SESN1, and SESN3 is affected. Dysregulated expression of NEAT-1 and related miRNAs and genes might be involved in the pathogenesis of DN.

Common variants of NRG1 and ITGB4 confer risk of Hirschsprung disease in Han Chinese population

BACKGROUND

Hirschsprung disease (HSCR) is a neurodevelopmental disorder with a strong genetic component. Common variants of NRG1 contributed to HSCR risk in Asians, and rare variants of ERBB2 and ITGB4 were found to be associated with HSCR. ERBB2 and ITGB4 are partners of Nrg1/ErbB pathway, which is important in HSCR pathogenesis. We aimed to investigate whether common variants in NRG1, ERBB2 and ITGB4 were associated with HSCR in Chinese Han population.

METHODS

We genotype 17 single nucleotide polymorphisms (SNPs) of NRG1, ERBB2 and ITGB4 in 420 HSCR patients and 1665 controls, and performed association analysis.

RESULTS

We validated associations of two NRG1 SNPs rs7835688 (P_Allelic = 2.2 × 10^-20, OR = 2.21, 95%CI = 1.86-2.62) and rs16879552 (P_Allelic = 5.6 × 10^-9, OR = 1.57, 95%CI = 1.35-1.83) with risk to HSCR. SNP rs3744000 located 5' upstream of ITGB4 showed association with HSCR (P_Allelic = 2.4 × 10^-3, OR = 1.27, 95%CI = 1.09-1.49). Four SNPs of ERBB2 exhibited no association.

CONCLUSIONS

Our results suggested that common variation of ITGB4 and NRG1 conferred risk to HSCR in Chinese Han population, which further highlighted Nrg-1/ErbB pathway involving in the pathogenesis of HSCR.

Mechanosensation in traumatic brain injury

Traumatic brain injury (TBI) is distinct from other neurological disorders because it is induced by a discrete event that applies extreme mechanical forces to the brain. This review describes how the brain senses, integrates, and responds to forces under both normal conditions and during injury. The response to forces is influenced by the unique mechanical properties of brain tissue, which differ by region, cell type, and sub-cellular structure. Elements such as the extracellular matrix, plasma membrane, transmembrane receptors, and cytoskeleton influence its properties. These same components also act as force-sensors, allowing neurons and glia to respond to their physical environment and maintain homeostasis. However, when applied forces become too large, as in TBI, these components may respond in an aberrant manner or structurally fail, resulting in unique pathological sequelae. This so-called "pathological mechanosensation" represents a spectrum of cellular responses, which vary depending on the overall biomechanical parameters of the injury and may be compounded by repetitive injuries. Such aberrant physical responses and/or damage to cells along with the resulting secondary injury cascades can ultimately lead to long-term cellular dysfunction and degeneration, often resulting in persistent deficits. Indeed, pathological mechanosensation not only directly initiates secondary injury cascades, but this post-physical damage environment provides the context in which these cascades unfold. Collectively, these points underscore the need to use experimental models that accurately replicate the biomechanics of TBI in humans. Understanding cellular responses in context with injury biomechanics may uncover therapeutic targets addressing various facets of trauma-specific sequelae.

Secretion of a mammalian chondroitinase ABC aids glial integration at PNS/CNS boundaries

Schwann cell grafts support axonal growth following spinal cord injury, but a boundary forms between the implanted cells and host astrocytes. Axons are reluctant to exit the graft tissue in large part due to the surrounding inhibitory environment containing chondroitin sulphate proteoglycans (CSPGs). We use a lentiviral chondroitinase ABC, capable of being secreted from mammalian cells (mChABC), to examine the repercussions of CSPG digestion upon Schwann cell behaviour in vitro. We show that mChABC transduced Schwann cells robustly secrete substantial quantities of the enzyme causing large-scale CSPG digestion, facilitating the migration and adhesion of Schwann cells on inhibitory aggrecan and astrocytic substrates. Importantly, we show that secretion of the engineered enzyme can aid the intermingling of cells at the Schwann cell-astrocyte boundary, enabling growth of neurites over the putative graft/host interface. These data were echoed in vivo. This study demonstrates the profound effect of the enzyme on cellular motility, growth and migration. This provides a cellular mechanism for mChABC induced functional and behavioural recovery shown in in vivo studies. Importantly, we provide in vitro evidence that mChABC gene therapy is equally or more effective at producing these effects as a one-time application of commercially available ChABC.

Schwann Cell Migration through Magnetic Actuation Mediated by Fluorescent-Magnetic Bifunctional Fe3O4·Rhodamine 6G@Polydopamine Superparticles

Peripheral nerve injuries always cause dysfunction but without ideal strategies to assist the treatment and recovery successfully. The primary way to repair the peripheral nerve injuries is to bridge the lesions by promoting axon regeneration. Schwann cells acting as neuroglial cells play a pivotal role during axonal regeneration. The orderly and organized migration of Schwann cells is beneficial for the extracellular matrix connection and Büngner bands formation, which greatly promote the regeneration of axons by offering mechanical support and growth factors. Thus, the use of Schwann cells as therapeutic cells offers us an attractive method for neurorepair therapies, and the ability to direct and manipulate Schwann cell migration and distribution is of great significance in the field of cell therapy in regards to the repair and regeneration of the peripheral nerve. Herein, we design and characterize a type of novel fluorescent-magnetic bifunctional Fe₃O₄·Rhodamine 6G (R6G)@polydopamine (PDA) superparticles (SPs) and systematically study the biological behaviors of Fe₃O₄·R6G@PDA SP uptake by Schwann cells. The results demonstrate that our tailor-made Fe₃O₄·R6G@PDA SPs can be endocytosed by Schwann cells and then highly magnetize Schwann cells by virtue of their excellent biocompatibility. Furthermore, remote-controlling and noninvasive magnetic targeting migration of Schwann cells can be achieved on the basis of the high magnetic responsiveness of Fe₃O₄·R6G@PDA SPs. At the end, gene expression profile analysis is performed to explore the mechanism of Schwann cells' magnetic targeting migration. The results indicate that cells can sense external magnetic mechanical forces and transduce into intracellular biochemical signaling, which stimulate gene expression associated with Schwann cell migration.

αvβ3 Integrin Antagonists Enhance Chemotherapy Response in an Orthotopic Pancreatic Cancer Model

Pancreatic cancer decreases survival time and quality of life because of drug resistance and peripheral neuropathy during conventional treatment. This study was undertaken to investigate whether αvβ3 integrin receptor antagonist compounds NDAT and XT199 can suppress the development of cisplatin resistance and cisplatin-induced peripheral neuropathy in an orthotopic pancreatic SUIT2-luc cancer cell mouse model. Anticancer effects of these compounds and their combination with cisplatin were assessed in this tumor mouse model with bioluminescent signaling and histopathology, and a cytokine assay was used to examine expression of inflammatory cytokines IL-1β, IL-6, IL-10, and TNF-α from plasma samples. To determine the neuroprotective effects of the compounds on cisplatin-induced peripheral neuropathy, behavioral hind-limb posture of the mice was evaluated. The combination therapy of NDAT or XT199 with cisplatin elicited greater inhibition of tumor growth and increased tumor necrosis compared to cisplatin alone. NDAT and XT199 in combination with cisplatin significantly decreased expression of pro-inflammatory cytokines IL-1β, IL-6, and TNF-α and significantly increased expression of anti-inflammatory cytokine IL-10 in comparison to cisplatin alone. Cisplatin-treated groups showed stocking-glove hind-limb posture, whereas NDAT and XT199 with cisplatin-treated groups displayed normal hind-limb posture. Results clearly suggest that NDAT and XT199 treatment with cisplatin that inactivates NF-κB may contribute to increased antitumor and anti-inflammatory efficacy as well as alleviate cisplatin-mediated loss of motor function in this pancreatic tumor mouse model.

Different epidermal growth factor receptor signaling pathways in neurons and astrocytes activated by extracellular matrix after spinal cord injury

Spinal cord injury (SCI) is a serious central nervous system (CNS) trauma that results in permanent and severe disability. The extracellular matrix (ECM) can affect the activation of extracellular signal-regulated kinase 1/2 (ERK_1/2) by interacting with the ERK integrin subunits. In this study, we built a model of SCI with glial fibrillary acidic protein-green fluorescent protein (GFAP-GFP) and thymus cell antigen 1-yellow fluorescent protein-H (Thy1-YFPH) in mice that express specific transgenes in their astrocytes or neurons. Then, we collected spinal cord neurons or astrocytes by fluorescence-activated cell sorting (FACS). In this way, we investigated the SCI-induced phosphorylation of ERK_1/2 and epidermal growth factor receptor (EGFR) in neurons and astrocytes, and we discovered that the SCI-induced EGFR signaling pathways differed between neurons and astrocytes. In the present study, we found that the Src-dependent phosphorylation of EGFR induced by SCI occurred only in neurons, not in astrocytes. This phenomenon may be due to the involvement of Thy-1, which promoted the binding between Src and EGFR in neurons after SCI. In addition, the expression of the integrin subunits after SCI differed between neurons and astrocytes. Our present study shows that the EGFR signaling pathway triggered by SCI in neurons differed from the EGFR signaling pathway triggered in astrocytes, a finding that may help to pave the way for clinical trials of therapies that inhibit EGFR signaling pathways after SCI.

Kindlin-1 Regulates Astrocyte Activation and Pain Sensitivity in Rats With Neuropathic Pain

BACKGROUND AND OBJECTIVES

Astrocyte activation has been implicated in the pathogenesis of neuropathic pain, but the involvement of kindlin-1 in astrocyte activation and neuropathic pain has not yet been illustrated. Using a chronic constriction injury (CCI) rat model of neuropathic pain, we investigated the expression levels of kindlin-1 during neuropathic pain and the influences of kindlin-1 on regulating pain sensitivity.

METHODS

Neuropathic pain was induced in rats by CCI of the sciatic nerve. Rats were randomly assigned to 4 groups: sham operation, CCI, CCI + kindlin-1 short hairpin RNA (shRNA), and CCI + kindlin-1 groups. Animals in the CCI + kindling-1 shRNA and CCI + kindlin-1 groups were given kindlin-1 shRNA or kindlin-1 virus infection to reduce or overexpress kindlin-1, respectively. Kindlin-1 expression was persistently increased in rats 10 days after CCI. A large proportion of glial fibrillary acidic protein (GFAP)-positive astrocytes expressed kindlin-1 in spinal cord tissues of rats after CCI.

RESULTS

Compared with the sham operation group, CCI animals exhibited increased GFAP expression and GFAP-positive astrocytes in the spinal cord. Down-regulation of kindlin-1 reduced the up-regulation of GFAP in the spinal cord, whereas overexpression of kindlin-1 promoted elevation of GFAP levels. Kindlin-1 silencing elevated the mechanical and thermal pain thresholds of CCI rats (P < 0.05). However, overexpression of kindlin-1 aggravated CCI-induced pain sensitivity.

CONCLUSIONS

Kindlin-1 may regulate pain sensitivity by affecting activated astrocytes in the spinal cord. Inhibition of kindlin-1 may provide a novel paradigm for the management of neuropathic pain.

Detailed Protocols for the Isolation, Culture, Enrichment and Immunostaining of Primary Human Schwann Cells

This chapter emphasizes detailed protocols for the effective establishment of highly enriched human Schwann cell cultures and their characterization via immunostaining. The Schwann cells are isolated from immediately dissociated fascicle tissue and expanded prior to purification. Two purification methods are described that use either fluorescence-activated cell sorting for the Schwann cell marker TNR16 (p75^NTR) or a less-manipulative two-step enrichment exploiting the differential adhesion properties of Schwann cells and fibroblasts, which is especially useful for low Schwann cell numbers. In addition, a method to determine Schwann cell purity via stained cytospin slides is introduced. Together with an immunofluorescence staining procedure for the combined analysis of extra- and intracellular markers, this chapter provides a solid basis to study human primary Schwann cells.

Glutamate signals through mGluR2 to control Schwann cell differentiation and proliferation

Rapid saltatory nerve conduction is facilitated by myelin structure, which is produced by Schwann cells (SC) in the peripheral nervous system (PNS). Proper development and degeneration/regeneration after injury requires regulated phenotypic changes of SC. We have previously shown that glutamate can induce SC proliferation in culture. Here we show that glutamate signals through metabotropic glutamate receptor 2 (mGluR2) to induce Erk phosphorylation in SC. mGluR2-elicited Erk phosphorylation requires ErbB2/3 receptor tyrosine kinase phosphorylation to limit the signaling cascade that promotes phosphorylation of Erk, but not Akt. We found that Gβγ and Src are involved in subcellular signaling downstream of mGluR2. We also found that glutamate can transform myelinating SC to proliferating SC, while inhibition of mGluR2 signaling can inhibit demyelination of injured nerves in vivo. These data suggest pathophysiological significance of mGluR2 signaling in PNS and its possible therapeutic importance to combat demyelinating disorders including Charcot-Marie-Tooth disease.

Current and future immunotherapy targets in autoimmune neurology

Randomized controlled treatment trials of autoimmune neurologic disorders are generally lacking and data pertaining to treatment are mostly derived from expert opinion, large case series, and anecdotal reports. The treatment of autoimmune neurologic disorders comprises oncologic therapy (where appropriate) and immunotherapy. In this chapter, we first describe the standard acute and chronic immunotherapies and provide a practical overview of their use in the clinic (mechanisms of action, dosing, monitoring, and side effects). Novel approaches to treatment of autoimmune neurologic disorders, through new drug discovery or repurposing, are dependent on improved mechanistic understanding of immunopathology. Such approaches, with emphasis on monoclonal antibodies, are discussed using the paradigm of three autoimmune neurologic disorders whose immunopathogenesis is better understood, specifically myasthenia gravis, neuromyelitis optica, and chronic inflammatory demyelinating polyradiculoneuropathy. It is important to realize that the treatment strategy and management plan must be individualized for each patient. In general these are influenced by the following: clinical severity, antibody type, presence or absence of cancer, and prior treatment response, if known.

Substratum preferences of motor and sensory neurons in postnatal and adult rats

After peripheral nerve injuries, damaged axons can regenerate but functional recovery is limited by the specific reinnervation of targets. In this study we evaluated if motor and sensory neurites have a substrate preference for laminin and fibronectin in postnatal and adult stages. In postnatal dorsal root ganglia (DRG) explants, sensory neurons extended longer neurites on collagen matrices enriched with laminin (~50%) or fibronectin (~35%), whereas motoneurons extended longer neurites (~100%) in organotypic spinal cord slices embedded in fibronectin-enriched matrix. An increased percentage of parvalbumin-positive neurites (presumptive proprioceptive) vs. neurofilament-positive neurites was also found in DRG in fibronectin-enriched matrix. To test if the different preference of neurons for extracellular matrix components was maintained in vivo, these matrices were used to fill a chitosan guide to repair a 6-mm gap in the sciatic nerve of adult rats. However, the number of regenerating motor and sensory neurons after 1 month was similar between groups. Moreover, none of the retrotraced sensory neurons in DRG was positive for parvalbumin, suggesting that presumptive proprioceptive neurons had poor regenerative capabilities compared with other peripheral neurons. Using real-time PCR we evaluated the expression of α5β1 (receptor for fibronectin) and α7β1 integrin (receptor for laminin) in spinal cord and DRG 2 days after injury. Postnatal animals showed a higher increase of α5β1 integrin, whereas both integrins were similarly expressed in adult neurons. Therefore, we conclude that motor and sensory axons have a different substrate preference at early postnatal stages but this difference is lost in the adult.

Pathophysiology and biomarkers in chronic inflammatory demyelinating polyradiculoneuropathies

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is an acquired dysimmune disorder characterized by strong heterogeneity in terms of clinical manifestations, prognostic and response to treatment. To date, its pathophysiology and potential target antigens are not totally identified despite substantial progress in the understanding of the involved molecular mechanisms. Recent researches in the field have underlined the importance of cell-mediated immunity (lymphocytesT CD4+, CD8+ and macrophages), the breakdown of blood-nerve barrier, a failure of T-cell regulation, and the disruption of nodal and paranodal organization at the node of Ranvier. This last point is possibly mediated by autoantibodies towards axoglial adhesion molecules which may disrupt sodium and potassium voltage-gated channels clustering leading to a failure of saltatory conduction and the apparition of conduction blocks. The purpose of this article is to overview the main pathophysiologic mechanisms and biomarkers identified in CIDP.

Loss of focal adhesions in glia disrupts both glial and photoreceptor axon migration in the Drosophila visual system

Many aspects of glial development are regulated by extracellular signals, including those from the extracellular matrix (ECM). Signals from the ECM are received by cell surface receptors, including the integrin family. Previously, we have shown that Drosophila integrins form adhesion complexes with Integrin-linked kinase and talin in the peripheral nerve glia and have conserved roles in glial sheath formation. However, integrin function in other aspects of glial development is unclear. The Drosophila eye imaginal disc (ED) and optic stalk (OS) complex is an excellent model with which to study glial migration, differentiation and glia-neuron interactions. We studied the roles of the integrin complexes in these glial developmental processes during OS/eye development. The common beta subunit βPS and two alpha subunits, αPS2 and αPS3, are located in puncta at both glia-glia and glia-ECM interfaces. Depletion of βPS integrin and talin by RNAi impaired the migration and distribution of glia within the OS resulting in morphological defects. Reduction of integrin or talin in the glia also disrupted photoreceptor axon outgrowth leading to axon stalling in the OS and ED. The neuronal defects were correlated with a disruption of the carpet glia tube paired with invasion of glia into the core of the OS and the formation of a glial cap. Our results suggest that integrin-mediated extracellular signals are important for multiple aspects of glial development and non-autonomously affect axonal migration during Drosophila eye development.

Pathogenesis of Guillain–Barré syndrome

Guillain-Barre syndrome is a postinfectious disorder caused by an aberrant immune response to an infectious pathogen, resulting in an autoimmune disease. As with other autoimmune diseases of infectious nature, the intricate balance of the numerous factors involved in the immune response may determine the outcome of the interaction between the microbe and host. Recent studies focusing on the role of cytokines and its network of related mediators and receptors suggest that any imbalance may make a significant contribution to the outcome of the infectious disease process. Better understanding of the pathogenesis of Guillain-Barre syndrome may lead to the discovery of newer therapeutics and may also serve as a model for studying other autoimmune diseases.

Neuregulin-1/glial growth factor stimulates Schwann cell migration by inducing α5 β1 integrin-ErbB2-focal adhesion kinase complex formation

After peripheral nerve injury, Schwann cells gain a migratory phenotype and remodel their extracellular matrix to provide a supportive environment for axonal regeneration. The soluble neuregulin-1 isoform, that is, glial growth factor (GGF), is expressed in regenerating axons of injured peripheral nerves and regulates Schwann cell motility by activating the ErbB family of tyrosine kinase receptors, but how GGF/ErbB signaling contributes to Schwann cell motility remains unclear. Here, we show that GGF stimulates Schwann cell migration by inducing the formation of a protein complex containing the fibronectin receptor α5β1 integrin, ErbB2, and focal adhesion kinase (FAK). ErbB2 co-localizes and co-immunoprecipitates with the focal complex members including α5β1 integrin and FAK after GGF treatment. These effects of GGF appear to involve FAK activation, which occurs downstream of ErbB2 stimulation. RNAi-mediated down-regulation of α5 integrin expression in primary cultured Schwann cells resulted in significantly decreased interaction between FAK and ErbB2, as well as decreased GGF-induced migration. An increase in the α5β1 integrin-ErbB2-FAK complex formation was observed in injured nerve Schwann cells, but not uninjured control. Taken together, these data suggest that GGF plays an important modulatory role in Schwann cell migration after nerve crush by inducing α5β1 integrin-ErbB2-FAK complex formation.

Extracellular matrix-associated gene expression in adult sensory neuron populations cultured on a laminin substrate

Background

In our previous investigations of the role of the extracellular matrix (ECM) in promoting neurite growth we have observed that a permissive laminin (LN) substrate stimulates differential growth responses in subpopulations of mature dorsal root ganglion (DRG) neurons. DRG neurons expressing Trk and p75 receptors grow neurites on a LN substrate in the absence of neurotrophins, while isolectin B4-binding neurons (IB4⁺) do not display significant growth under the same conditions. We set out to determine whether there was an expression signature of the LN-induced neurite growth phenotype. Using a lectin binding protocol IB4⁺ neurons were isolated from dissociated DRG neurons, creating two groups - IB4⁺ and IB4^-. A small-scale microarray approach was employed to screen the expression of a panel of ECM-associated genes following dissociation (t=0) and after 24 hr culture on LN (t=24LN). This was followed by qRT-PCR and immunocytochemistry of selected genes.

Results

The microarray screen showed that 36 of the 144 genes on the arrays were consistently expressed by the neurons. The array analyses showed that six genes had lower expression in the IB4+ neurons compared to the IB4- cells at t=0 (CTSH, Icam1, Itgβ1, Lamb1, Plat, Spp1), and one gene was expressed at higher levels in the IB4⁺ cells (Plaur). qRT-PCR was carried out as an independent assessment of the array results. There were discrepancies between the two methods, with qRT-PCR confirming the differences in Lamb1, Plat and Plaur, and showing decreased expression of AdamTs1, FN, and Icam in the IB4⁺ cells at t=0. After 24 hr culture on LN, there were no significant differences detected by qRT-PCR between the IB4⁺ and IB4^- cells. However, both groups showed upregulation of Itgβ1 and Plaur after 24 hr on LN, the IB4⁺ group also had increased Plat, and the IB4^- cells showed decreased Lamb1, Icam1 and AdamTs1. Further, the array screen also detected a number of genes (not subjected to qRT-PCR) expressed similarly by both populations in relatively high levels but not detectably influenced by time in culture (Bsg, Cst3, Ctsb, Ctsd, Ctsl, Mmp14, Mmp19, Sparc. We carried out immunohistochemistry to confirm expression of proteins encoded by a number of these genes.

Conclusions

Our results show that 1B4⁺ and IB4^- neurons differ in the expression of several genes that are associated with responsiveness to the ECM prior to culturing (AdamTs1, FN, Icam1, Lamb1, Plat, Plaur). The data suggest that the genes expressed at higher levels in the IB4^- neurons could contribute to the initial growth response of these cells in a permissive environment and could also represent a common injury response that subsequently promotes axon regeneration. The differential expression of several extracellular matrix molecules (FN, Lamb1, Icam) may suggest that the IB4^- neurons are capable of maintaining /secreting their local extracellular environment which could aid in the regenerative process. Overall, these data provide new information on potential targets that could be manipulated to enhance axonal regeneration in the mature nervous system.

Lck tyrosine kinase mediates β1-integrin signalling to regulate Schwann cell migration and myelination

The interaction between laminin and β1-integrin on the surface of Schwann cells regulates Schwann cell proliferation, maturation and differentiation. However, the signalling mediators that fine-tune these outcomes are not fully elucidated. Here we show that lymphoid cell kinase is the crucial effector of β1-integrin signalling in Schwann cells. Lymphoid cell kinase is activated after laminin treatment of Schwann cells, while downregulation of β1-integrin with short interfering RNAs inhibits lymphoid cell kinase phosphorylation. Treatment of Schwann cells with a selective lymphoid cell kinase inhibitor reveals a pathway that involves paxillin and CrkII, which ultimately elevates Rac-GTP levels to induce radial lamellipodia formation. Inhibition of lymphoid cell kinase in Schwann cell-dorsal root ganglion cocultures and dorsal root ganglions from Lck(-/-) mice show a reduction of Schwann cell longitudinal migration, reduced myelin formation and internode length. Finally, Lck(-/-) mice exhibit delays in myelination, thinner myelin with abnormal g-ratios and aberrant myelin outfoldings. Our data implicate lymphoid cell kinase as a major regulator of cytoskeletal dynamics, migration and myelination in the peripheral nervous system.

Polarization and myelination in myelinating glia

Myelinating glia, oligodendrocytes in central nervous system and Schwann cells in peripheral nervous system, form myelin sheath, a multilayered membrane system around axons enabling salutatory nerve impulse conduction and maintaining axonal integrity. Myelin sheath is a polarized structure localized in the axonal side and therefore is supposed to be formed based on the preceding polarization of myelinating glia. Thus, myelination process is closely associated with polarization of myelinating glia. However, cell polarization has been less extensively studied in myelinating glia than other cell types such as epithelial cells. The ultimate goal of this paper is to provide insights for the field of myelination research by applying the information obtained in polarity study in other cell types, especially epithelial cells, to cell polarization of myelinating glia. Thus, in this paper, the main aspects of cell polarization study in general are summarized. Then, they will be compared with polarization in oligodendrocytes. Finally, the achievements obtained in polarization study for epithelial cells, oligodendrocytes, and other types of cells will be translated into polarization/myelination process by Schwann cells. Then, based on this model, the perspectives in the study of Schwann cell polarization/myelination will be discussed.

Biophysical stimulation induces demyelination via an integrin-dependent mechanism

OBJECTIVE

Chronic nerve compression (CNC) injuries occur when peripheral nerves are subjected to sustained mechanical forces, with increasing evidence implicating Schwann cells as key mediators. Integrins, a family of transmembrane adhesion molecules that are capable of intracellular signaling, have been implicated in a variety of biological processes such as myelination and nerve regeneration. In this study, we seek to define the physical stimuli mediating demyelination and to determine whether integrin plays a role in the demyelinating response.

METHODS

We used a previously described in vitro model of CNC injury where myelinating neuron-Schwann cell cocultures were subjected to independent manipulations of hydrostatic pressure, hypoxia, and glucose deprivation in a custom bioreactor. We assessed whether demyelination increased in response to applied manipulation and determined whether integrin-associated signaling cascades are upregulated.

RESULTS

Biophysical stimulation of neural tissue induced demyelination and Schwann cell proliferation without neuronal or glial cytotoxicity or apoptosis. Although glucose deprivation and hypoxia independently had minor effects on myelin stability, together they potentiated the demyelinating effects of hydrostatic compression, and in combination, significantly destabilized myelin. Biophysical stimuli transiently increased phosphorylation of the integrin-associated tyrosine kinase Src within Schwann cells. Silencing this integrin signaling cascade blocked Src activation and prevented pressure-induced demyelination. Colocalization analysis indicated that Src is localized within Schwann cells.

INTERPRETATION

These results indicate that myelin is sensitive to CNC injury and support the novel concept that myelinating cocultures respond directly to mechanical loading via activating an integrin signaling cascade.

Extracellular matrix molecules enhance the neurotrophic effect of Schwann cell-like differentiated adipose-derived stem cells and increase cell survival under stress conditions

Since the first reports of induction of adipose-derived stem cells (ASC) into neuronal and glial cell phenotypes, expectations have increased regarding their use in tissue engineering applications for nerve repair. Cell adhesion to extracellular matrix (ECM) is a basic feature of survival, differentiation, and migration of Schwann cells (SC) during nerve regeneration, and fibronectin and laminin are two key molecules of this process. Interaction between ECM and SC-like differentiated ASC (dASC) could potentially improve the neurotrophic potential of the stem cells. We have investigated the effect of ECM molecules on SC-like dASC in terms of proliferation, adhesion, and cell viability. Fibronectin and laminin did not affect the proliferation of dASC when compared with cell adherent tissue culture plastic, but significantly improved viability and cell attachment when dASC were exposed to apoptotic conditions. To assess the influence of the ECM molecules on dASC neurotrophic activity, dASC were seeded onto ECM-coated culture inserts suspended above dorsal root ganglia (DRG) sensory neurons. Neurite outgrowth of DRG neurons was enhanced when dASC were seeded on fibronectin and laminin when compared with controls. When DRG neurons and dASC were in direct contact on the various surfaces there was significantly enhanced neurite outgrowth and coculture with laminin-conditioned dASC produced the longest neurites. Compared with primary SCs, dASC grown on laminin produced similar levels of neurite outgrowth in the culture insert experiments but neurite length was shorter in the direct contact groups. Anti β1 integrin blocking antibody could inhibit baseline and dASC evoked neurite elongation but had no effect on outgrowth mediated by laminin-conditioned dASC. ECM molecules had no effect on the levels of nerve growth factor and brain-derived neurotrophic factor secretion from dASC. The results of the study suggest that ECM molecules can significantly improve the potential of dASC for nerve regeneration.

Downstream effector molecules in successful peripheral nerve regeneration

The robust axon regeneration that occurs following peripheral nerve injury is driven by transcriptional activation of the regeneration program and by the expression of a wide range of downstream effector molecules from neuropeptides and neurotrophic factors to adhesion molecules and cytoskeletal adaptor proteins. These regeneration-associated effector molecules regulate the actin-tubulin machinery of growth-cones, integrate intracellular signalling and stimulatory and inhibitory signals from the local environment and translate them into axon elongation. In addition to the neuronally derived molecules, an important transcriptional component is found in locally activated Schwann cells and macrophages, which release a number of cytokines, growth factors and neurotrophins that support neuronal survival and axonal regeneration and that might provide directional guidance cues towards appropriate peripheral targets. This review aims to provide a comprehensive up-to-date account of the transcriptional regulation and functional role of these effector molecules and of the information that they can give us with regard to the organisation of the regeneration program.

Extrinsic cellular and molecular mediators of peripheral axonal regeneration

The ability of injured peripheral nerves to regenerate and reinnervate their original targets is a characteristic feature of the peripheral nervous system (PNS). On the other hand, neurons of the central nervous system (CNS), including retinal ganglion cell (RGC) axons, are incapable of spontaneous regeneration. In the adult PNS, axonal regeneration after injury depends on well-orchestrated cellular and molecular processes that comprise a highly reproducible series of degenerative reactions distal to the site of injury. During this fine-tuned process, named Wallerian degeneration, a remodeling of the distal nerve fragment prepares a permissive microenvironment that permits successful axonal regrowth originating from the proximal nerve fragment. Therefore, a multitude of adjusted intrinsic and extrinsic factors are important for surviving neurons, Schwann cells, macrophages and fibroblasts as well as endothelial cells in order to achieve successful regeneration. The aim of this review is to summarize relevant extrinsic cellular and molecular determinants of successful axonal regeneration in rodents that contribute to the regenerative microenvironment of the PNS.

Vimentin phosphorylation by Cdc2 in Schwann cell controls axon growth via β1-integrin activation

Although preconditioning injury on the peripheral nerve induces axonal regenerative capacity in neurons, it is not known whether similar lesion effects occur in glial cells. Here we demonstrate that Schwann cells are activated by peripheral nerve preinjury and primed to mediate axon regeneration. Cdc2, which was induced from Schwann cells after sciatic nerve injury, phosphorylated vimentin almost exclusively in the distal nerve area. Phospho-vimentin-positive Schwann cells showed increased migration activity and were in close contact with process outgrowth of co-cultured neurons. Vimentin phosphorylation by Cdc2 was involved in β1-integrin activation leading to FAK phoshorylation and associated with Erk1/2 activation in Schwann cells. Neurite outgrowth of dorsal root ganglion neurons was increased by co-culture with activated Schwann cells, in which phospho-vimentin signaling was transmitted into β1-integrin activation. Then neurite outgrowth was suppressed by genetic depletion of phospho-vimentin and β1 integrin as well as inhibition of vimentin phosphorylation by Cdc2 inhibitor purvalanol A. The sciatic nerve graft harboring activated Schwann cells into the spinal cord induced Schwann cell migration beyond the graft-host barrier and facilitated regeneration of spinal axons, which was inhibited by purvalanol A pretreatment of the graft. This is the first report to our knowledge demonstrating that activation of phospho-vimentin linked to β1-integrin pathway may mediate transcellular signaling to promote axon growth.

Integrin activation promotes axon growth on inhibitory chondroitin sulfate proteoglycans by enhancing integrin signaling

Chondroitin sulfate proteoglycans (CSPGs) are upregulated after CNS lesions, where they inhibit axon regeneration. In order for axon growth and regeneration to occur, surface integrin receptors must interact with surrounding extracellular matrix molecules. We have explored the hypothesis that CSPGs inhibit regeneration by inactivating integrins and that forcing integrins into an active state might overcome this inhibition. Using cultured rat sensory neurons, we show that the CSPG aggrecan inhibits laminin-mediated axon growth by impairing integrin signaling via decreasing phosphorylated FAK (pFAK) and pSrc levels, without affecting surface integrin levels. Forcing integrin activation and signaling by manganese or an activating antibody TS2/16 reversed the inhibitory effect of aggrecan on mixed aggrecan/laminin surfaces, and enhanced axon growth from cultured rat sensory neurons (manganese) and human embryonic stem cell-derived motoneurons (TS2/16). The inhibitory effect of Nogo-A can also be reversed by integrin activation. These results suggest that inhibition by CSPGs can act via inactivation of integrins, and that activation of integrins is a potential method for improving axon regeneration after injury.

Autoimmune diseases of the peripheral nervous system

Autoimmune-mediated diseases targeting the peripheral nerve represent a group of disorders often associated with high clinical disability. At present, therapeutic options are limited. The application of innovative and cutting-edge technologies to the study of immune-mediated disorders of the peripheral nervous system (PNS) have generated a better understanding of underlying principles of the organization of the immune network present in the peripheral nerve and its dialogue with the systemic immune system. These insights may foster the development of specific and highly effective therapies for autoimmune diseases of the peripheral nerve. Of great interest in this context is the application of monoclonal antibodies, such as rituximab or alemtuzumab, which in small observational studies provided promising clinical results. But also other immunomodulatory or immunosuppressive drugs used in other indications currently find their way to PNS autoimmunity. Clearly, prospective controlled clinical trials are warranted before making firm conclusions on the feasibility of these innovative therapeutic approaches for treating immune-mediated disease of the peripheral nerve.

SH3TC2, a protein mutant in Charcot-Marie-Tooth neuropathy, links peripheral nerve myelination to endosomal recycling

Patients with Charcot-Marie-Tooth neuropathy and gene targeting in mice revealed an essential role for the SH3TC2 gene in peripheral nerve myelination. SH3TC2 expression is restricted to Schwann cells in the peripheral nervous system, and the gene product, SH3TC2, localizes to the perinuclear recycling compartment. Here, we show that SH3TC2 interacts with the small guanosine triphosphatase Rab11, which is known to regulate the recycling of internalized membranes and receptors back to the cell surface. Results of protein binding studies and transferrin receptor trafficking are in line with a role of SH3TC2 as a Rab11 effector molecule. Consistent with a function of Rab11 in Schwann cell myelination, SH3TC2 mutations that cause neuropathy disrupt the SH3TC2/Rab11 interaction, and forced expression of dominant negative Rab11 strongly impairs myelin formation in vitro. Our data indicate that the SH3TC2/Rab11 interaction is relevant for peripheral nerve pathophysiology and place endosomal recycling on the list of cellular mechanisms involved in Schwann cell myelination.

[Peripheral nervous system and grounds for the neural insult in leprosy]

The mechanism of interaction between Mycobacterium leprae and neural cells has not been elucidated so far. No satisfactory interpretation exists as to the bacterium tropism to the peripheral nervous system in particular. The present study is a review of the micro-physiology of the extracellular apparatus attached to Schwann cells, as well as on the description of morphological units probably involved in the process of the binding to the bacterial wall.

Roles of channels and receptors in the growth cone during PNS axonal regeneration

Neurons in the peripheral nervous system (PNS) are known to maintain a regenerative capacity and will normally regenerate their axons within a permissive growth environment. The success of regeneration in the PNS largely depends on maintenance of the supportive basal lamina membrane, efficient removal of axonal and myelin debris by macrophages and Schwann cells, expression of neurotrophic factors by Schwann cells, and up-regulation of the intrinsic growth program in PNS neurons. The PNS regenerative process is well characterized through initial Wallerian degeneration followed by axonal sprouting, formation of neuronal growth cones, active axonal growth to the target, and finally sensory and motor functional recovery. The initiation and maintenance of active growth cones during peripheral nerve regeneration recapitulate many aspects of early neural development and are achieved through the activation of complex signaling cascades, involving various receptors, channels, cytoplasmic signaling cascades, as well as transcriptional and translational programs. This review focuses on roles of cell surface ion channels and receptors in the growth cone during Wallerian degeneration and axon regeneration in the PNS.

Understanding the mechanisms of entrapment neuropathies. Review article

Compression neuropathies are highly prevalent, debilitating conditions with variable functional recovery following surgical decompression. Due to the limited amount of human nerve tissue available for analysis, a number of animal models have been created to help investigators understand the molecular and cellular pathogenesis of chronic nerve compression (CNC) injury. Evidence suggests that CNC injury induces concurrent Schwann cell proliferation and apoptosis in the early stages of the disorder. These proliferating Schwann cells downregulate myelin proteins, leading to local demyelination and remyelination in the region of injury. In addition, the downregulation of myelin proteins, in particular myelin-associated glycoprotein, allows for axonal sprouting. Interestingly, these changes occur in the absence of both morphological and electrophysiological evidence of axonal damage. This is in direct contrast to acute injuries, such as transection or crush, which are characterized by axonal injury followed by Wallerian degeneration. Because the accepted trigger for Schwann cell dedifferentiation is axonal injury, an alternate mechanism for Schwann response must exist in CNC injury. In vitro studies of pure Schwann cells have shown that these cells can respond directly to mechanical stimuli by downregulating myelin proteins and proliferating. These studies suggest that although the reciprocal relationship between neurons and glial cells is maintained, chronic nerve compression injury is a Schwann cell-mediated disease.

Peripheral sensory axon growth: from receptor binding to cellular signaling

Regeneration following axonal injury of the adult peripheral sensory nervous system is heavily influenced by factors located in a neuron's extracellular environment. These factors include neurotrophins, such as Nerve Growth Factor (NGF) and the extracellular matrix, such as laminin. The presence of these molecules in the peripheral nervous system (PNS) is a major contributing factor for the dichotomy between regenerative capacities of central vs. peripheral neurons. Although PNS neurons are capable of spontaneous regeneration, this response is critically dependent on many different factors including the type, location and severity of the injury. In this article, we will focus on the plasticity of adult dorsal root ganglion (DRG) sensory neurons and how trophic factors and the extracellular environment stimulate the activation of intracellular signaling cascades that promote axonal growth in adult dorsal root ganglion neurons.

Regulation of Schwann cell function by the extracellular matrix

Laminins and collagens are extracellular matrix proteins that play essential roles in peripheral nervous system development. Laminin signals regulate Schwann cell proliferation and survival as well as actin cytoskeleton dynamics, which are essential steps for radial sorting and myelination of peripheral axons by Schwann cells. Collagen and their receptors promote Schwann cell adhesion, spreading, and myelination as well as neurite outgrowth. In this article, we will review the recent advances in the studies of laminin and collagen function in Schwann cell development.

Conditional deletion of the Itgb4 integrin gene in Schwann cells leads to delayed peripheral nerve regeneration

Several different integrins participate in the complex interactions that promote repair of the peripheral nervous system. The role of the integrin alpha6beta4 in peripheral nerve regeneration was investigated in mice by cre-mediated deletion of the Itgb4 (beta4) gene in Schwann cells. After a crush lesion of the sciatic nerve, the recovery of motor, but not that of sensory, nerve function in beta4(-/-) mice was delayed. Immunostaining of neurofilament-200 showed that there also is a significant reduction in the number of newly outgrowing nerve sprouts in beta4(-/-) mice. Morphometric quantitative measurements revealed that fewer axons are myelinated in the nonlesioned beta4(-/-) nerves. After a sciatic nerve crush lesion, beta4(-/-) mice did not only have fewer myelinated axons compared with lesioned wild-type nerve, but their axons also showed a higher g-ratio and a thinner myelin sheath, pointing at reduced myelination. This study revealed that the beta4 protein remains expressed in the early stages of peripheral regeneration, albeit at levels lower than those before the lesion was inflicted, and showed that laminin deposition is not altered in the absence of beta4. These results together demonstrate that integrin alpha6beta4 plays an essential role in axonal regeneration and subsequent myelination.

Intravenous immunoglobulins in the treatment of immune neuropathies

PURPOSE OF REVIEW

The aim of this review is to describe the value of high-dose polyclonal intravenous immunoglobulins as a treatment option in autoimmune disorders affecting the peripheral nervous system.

RECENT FINDINGS

A randomized placebo-controlled trial in patients with chronic inflammatory demyelinating polyradiculoneuropathy revealed short-term and long-term efficacy and safety of intravenous immunoglobulins as a treatment option for the chronically inflamed peripheral nervous system. Case reports suggest that the subcutaneous administration of immunoglobulins may represent a convenient alternative.

SUMMARY

Intravenous immunoglobulin represents an effective and safe treatment option in patients with autoimmune-mediated diseases affecting the peripheral nerves.

Integrin beta 4 in neural cells

Integrin beta 4, one of the heterodimeric receptors, is expressed predominantly on epithelial cells. It is concentrated at the basement membrane zone, where it localizes to specialized adhesion structures called hemidesmosomes. In addition to its adhesive functions, novel insights have emerged regarding the specific roles of integrin beta 4 in their attachment to extracellular matrix and in their signal transduction pathways within the central nervous system (CNS) and peripheral nervous system in the past few years. It has been reported that integrin beta 4 is expressed in several kinds of neural cells including astrocyte, Schwann cells, neurons, and neural stem cells. In the mean while, it is expressed by some Schwann cells in the peripheral nervous system and mediated the Mycobacterium leprae invade the peripheral nervous system to reach the Schwann cells. This review highlights recent progress in the function and regulation of integrin beta 4 in neural cells.

Integrin signaling is integral to regeneration

The inability of the adult injured mammalian spinal cord to successfully regenerate is not well understood. Studies suggest that both extrinsic and intrinsic factors contribute to regeneration failure. In this review, we focus on intrinsic factors that impact regeneration, in particular integrin receptors and their downstream signaling pathways. We discuss studies that address the impact of integrins and integrin signaling pathways on growth cone guidance and motility and how lessons learned from these studies apply to spinal cord regeneration in vivo.

p38 Mitogen-activated protein kinase regulates myelination

The p38 mitogen-activated protein kinase family is emerging as a crucial signaling molecule for a vast number of cellular functions including cell migration, proliferation, and differentiation. The function of p38 in myelination has only been recently addressed. Using pyridinyl imidazole-based p38 alpha/beta selective inhibitors, we have reported a critical role for this kinase in the regulation of myelination, specifically, in controlling the differentiation of Schwann cells, and oligodendrocytes, the myelinating glia of the peripheral and central nervous systems, respectively. These compounds inhibited the accumulation of myelin-cell-specific markers, including myelin-specific glycosphingolipids, myelin-associated glycoprotein, and myelin basic protein. More significantly, myelination of dorsal root ganglia neurons by oligodendrocytes was irreversibly blocked by p38 inhibitors. Our current studies are focusing on the molecular mechanisms by which p38 regulates oligodendrocyte and Schwann cell differentiation and its role in models of myelination and remyelination.

Molecular design and characterization of the neuron-microelectrode array interface

Electrophysiological activities of neuronal networks can be recorded on microelectrode arrays (MEAs). This technique requires tight coupling between MEA-surfaces and cells. Therefore, this study investigated the interface between DRG neurons and MEA-surface materials after adsorption of neurite promoting proteins: laminin-111, fibronectin, L1Ig6 and poly-l-lysine. Moreover, substrate-induced effects on neuronal networks with time were analyzed. The thickness of adsorbed protein layers was found between approximately 1 nm for poly-l-lysine and approximately 80 nm for laminin-111 on platinum, gold and silicon nitride. The neuron-to-substrate interface was characterized by Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and SEM after in situ focused-ion-beam milling demonstrating that the ventral cell membrane adhered inhomogeneously to laminin-111 or L1Ig6 surfaces. Tight areas of 20-30 nm and distant areas <1 microm alternated and even tightest areas did not correlate with the physical thickness of the protein layers. This study illustrates the difficulties to predict cell-to-material interfaces that contribute substantially to the success of in vitro or in vivo systems. Moreover, focused ion beam (FIB)/SEM is explored as a new technique to analyze such interfaces.

From bench to bedside--experimental rationale for immune-specific therapies in the inflamed peripheral nerve

Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy are autoimmune-mediated inflammatory diseases of the PNS. In recent years, substantial progress has been made towards understanding the immune mechanisms that underlie these conditions, in large part through the study of experimental models. Here, we review the available animal models that partially mimic human Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy, and discuss the wide range of therapeutic approaches that have been successfully established in these models of inflammatory neuropathies. Transfer of this preclinical knowledge to patients has been far less successful, and inflammatory neuropathies are still associated with significant morbidity and mortality. We will summarize successful therapeutic trials in human autoimmune neuropathies to provide a vantage point for the transfer of experimental treatment strategies to clinical practice in immune-mediated diseases of the peripheral nerve.

Developmental abnormalities in the nerves of peripheral myelin protein 22-deficient mice

Peripheral myelin protein 22 (PMP22) is a tetraspan glycoprotein whose misexpression is associated with a family of hereditary peripheral neuropathies. In a recent report, we have characterized a novel PMP22-deficient mouse model in which the first two coding exons were replaced by the lacZ reporter. To investigate further the myelin abnormalities in the absence of PMP22, sciatic nerves and dorsal root ganglion (DRG) neuron explant cultures from PMP22-deficient mice were studied at various stages of myelination. Throughout the first 3 months of postnatal development, myelin protein and beta4 integrin levels are dramatically reduced, whereas p75 and beta1 integrin remain elevated. By immunostaining, the distributions of several glial proteins, including beta4 integrin, the voltage-gated potassium channel Kv1.1, and E-cadherin, are altered. Schwann cells from PMP22-deficient mice are able to produce limited amounts of myelin in DRG explant cultures, yet the internodal segments are dramatically fewer and shorter. The comparison of PMP22-deficient mice with other PMP22 mutant models reveals that the decrease in beta4 integrin is specific to an absence of PMP22. Furthermore, whereas lysosome-associated membrane protein 1 and ubiquitin are notably up-regulated in nerves of PMP22-deficient mice, heat shock protein 70 levels remain constant or decrease compared with wild-type or PMP22 mutant samples. Together these results support a role for PMP22 in the early events of peripheral nerve myelination. Additionally, although myelin abnormalities are a commonality among PMP22 neuropathic models, the underlying subcellular mechanisms are distinct and depend on the specific genetic abnormality.