Schwann Cells In Peripheral Nervous System Research Articles

The cytoplasmic tail of myelin protein zero induces morphological changes in lipid membranes

The major myelin protein expressed by the peripheral nervous system Schwann cells is protein zero (P0), which represents 50 % of the total protein content in myelin. This 30-kDa integral membrane protein consists of an immunoglobulin (Ig)-like domain, a transmembrane helix, and a 69-residue C-terminal cytoplasmic tail (P0ct). The basic residues in P0ct contribute to the tight packing of myelin lipid bilayers, and alterations in the tail affect how P0 functions as an adhesion molecule necessary for the stability of compact myelin. Several neurodegenerative neuropathies are related to P0, including the more common Charcot-Marie-Tooth disease (CMT) and Dejerine-Sottas syndrome (DSS) as well as rare cases of motor and sensory polyneuropathy. We found that high P0ct concentrations affected the membrane properties of bicelles and induced a lamellar-to-inverted hexagonal phase transition, which caused bicelles to fuse into long, protein-containing filament-like structures. These structures likely reflect the formation of semicrystalline lipid domains with potential relevance for myelination. Not only is P0ct important for stacking lipid membranes, but time-lapse fluorescence microscopy also shows that it might affect membrane properties during myelination. We further describe recombinant production and low-resolution structural characterisation of full-length human P0. Our findings shed light on P0ct effects on membrane properties, and with the successful purification of full-length P0, we have new tools to study the role of P0 in myelin formation and maintenance in vitro.

Biotargets in neural regeneration

The peripheral nervous system (PNS) exhibits a much larger capacity for regeneration than the central nervous system (CNS). The main reason is that the neurons in PNS still have certain intrinsic capacity for regeneration and the Schwann cells in PNS provide a suitable regeneration microenvironment. Factors that enhance the intrinsic growth potential of adult neurons are key players in the successful repair and regeneration of neurons following injury. Therefore, the full understanding of the mechanism of peripheral nerve regeneration will help us to solve the problems encountered in CNS regeneration. In this review, a number of intrinsic regeneration-promoting mechanisms have been described, including the role of transcription factors [signal transducers and activators of transcription 3 (STAT3), activating transcription factor 3 (ATF3), c-Jun, cyclic AMP response element binding protein (CREB) and Sox] in neuronal regeneration, the regulating factors [the phosphatase and tensin homolog (PTEN)-mTOR, PI3K-glycogen synthesis kinase 3 (GSK3), suppressor of cytokine signaling 3 (SOCS 3), histone deacetylases 5 (HDAC5) and reactive oxygen species (ROS)] for neuronal regeneration, the regulation of non-coding RNA [microRNAs (miRNAs), long-chain non-coding RNAs (lncRNAs) and circular RNAs (circRNAs)] in neuronal regeneration, the regulation of regeneration pathway in neural regeneration and the exosomes in neural regeneration. Finally, the prospect of neural regeneration was discussed, which contributes to greatly broaden the way to study the ability of nerve regeneration, identify more key biotarget molecules in neuronal regeneration, and provide innovative strategies to trigger and enhance the nerve regeneration.

CNS Schwann cells display oligodendrocyte precursor-like potassium channel activation and antigenic expression in vitro

Central nervous system (CNS) injury triggers production of myelinating Schwann cells from endogenous oligodendrocyte precursors (OLPs). These CNS Schwann cells may be attractive candidates for novel therapeutic strategies aiming to promote endogenous CNS repair. However, CNS Schwann cells have been so far mainly characterized in situ regarding morphology and marker expression, and it has remained enigmatic whether they display functional properties distinct from peripheral nervous system (PNS) Schwann cells. Potassium channels (K+) have been implicated in progenitor and glial cell proliferation after injury and may, therefore, represent a suitable pharmacological target. In the present study, we focused on the function and expression of voltage-gated K+ channels Kv(1-12) and accessory β-subunits in purified adult canine CNS and PNS Schwann cell cultures using electrophysiology and microarray analysis and characterized their antigenic phenotype. We show here that K+ channels differed significantly in both cell types. While CNS Schwann cells displayed prominent K D-mediated K+ currents, PNS Schwann cells elicited K(D-) and K(A-type) K+ currents. Inhibition of K+ currents by TEA and Ba2+ was more effective in CNS Schwann cells. These functional differences were not paralleled by differential mRNA expression of Kv(1-12) and accessory β-subunits. However, O4/A2B5 and GFAP expressions were significantly higher and lower, respectively, in CNS than in PNS Schwann cells. Taken together, this is the first evidence that CNS Schwann cells display specific properties not shared by their peripheral counterpart. Both Kv currents and increased O4/A2B5 expression were reminiscent of OLPs suggesting that CNS Schwann cells retain OLP features during maturation.

Experimental therapy for neurofibromatosis I shows promise

Experimental therapy for neurofibromatosis I shows promise

Purification and transfection of cochlear Schwann cells

Schwann cells line nerve fibers in the peripheral nervous system (PNS) and synthesize myelin. In addition, they support neuronal survival, neurite growth and regeneration. In dissociated cultures of postnatal mouse spiral ganglia, regenerating neurites spontaneously associate with Schwann cells. However, the mechanisms and consequences of interactions between cochlear Schwann cells and spiral ganglion neurites have not been examined. Further, the similarities and differences between cochlear Schwann cells and other PNS Schwann cells have not been studied. Experiments to examine these questions will rely on the ability to purify and characterize cochlear Schwann cells. Here we present methods for purifying Schwann cells from postnatal mouse cochleas and for transfecting them with expression plasmids. Dissociated spiral ganglia were plated on poly- d-lysine/laminin in medium containing neurotrophins, leukemia inhibitory factor (LIF), N2 supplement and serum and maintained for 5 days. Cells were harvested with trypsin/EDTA and subjected to an immuno-magnetic purification procedure. After 24 h in vitro, cultures were >85% Schwann cells. Nucleofection of purified Schwann cells with pMax-green fluorescent protein (pMax-GFP) plasmid, or with pEGFP-C-vimentin plasmid returned >45% transfection efficiency. These methods will allow the in-depth characterization of cochlear Schwann cells and an evaluation of their biochemical, functional, and genetic mechanisms that may promote neurite growth from the spiral ganglion.

Expression of dominant-negative and chimeric subunits reveals an essential role for β1 integrin during myelination

Myelination represents a remarkable example of cell specialization and cell-cell interaction in development. During this process, axons are wrapped by concentric layers of cell membrane derived either from central nervous system (CNS) oligodendrocytes or peripheral nervous system Schwann cells. In the CNS, oligodendrocytes elaborate a membranous extension with an area of more than 1000 times that of the cell body [1]. The mechanisms regulating this change in cell shape remain poorly understood. Signaling mechanisms regulated by cell surface adhesion receptors of the integrin family represent likely candidates. Integrins link the extracellular environment of the cell with both intracellular signaling molecules and the cytoskeleton and have been shown to regulate the activity of GTPases implicated in the control of cell shape [2]. Our previous work has established that oligodendrocytes and their precursors express a limited repertoire of integrins [3, 4]. One of these, the α6β1 laminin receptor, can interact with laminin-2 substrates to enhance oligodendrocyte myelin membrane formation in cell culture [5]. However, these experiments do not address the important question of integrin function during myelination in vivo, nor do they define the respective roles of the α and β subunits in the signaling pathways involved. Here, we use a dominant-negative approach to provide, for the first time, evidence that β1 integrin function is required for myelination in vivo and use chimeric integrins to dissect apart the roles of the extracellular and cytoplasmic domains of the α6 subunit in the signaling pathways of myelination.

Glial fibrillary acidic protein mRNA isotypes: expression in vitro and in vivo.

Glial fibrillary acidic protein (GFAP) and its mRNA, primarily expressed in astrocytes, are also expressed in peripheral nervous system Schwann cells as well as in certain non-neural tissues. Schwann cells express a GFAP mRNA (GFAP-beta) which differs from the CNS-type mRNA (GFAP-alpha) by the presence of an extended 5' untranslated region. We have developed a polymerase chain reaction assay which allows distinction of these two GFAP mRNAs, as well as quantitative analysis of their levels. In the cultured rat Schwannoma cell line RT4-D6, GFAP-beta was the major GFAP mRNA species, accounting for at least 75% of total GFAP (alpha + beta) mRNA. GFAP-beta was also detected in primary rat astrocyte cultures, where it constituted approximately 5% of the total GFAP mRNA, as well as in RNA samples prepared from normal rat cerebral cortex, and from hamster and human brain. In rat cortex, the temporal expression of GFAP-beta mRNA paralleled that of total GFAP mRNA, with plateau levels reached between postnatal days 15 and 20. In astrocyte cultures, the relative levels of GFAP-alpha and -beta mRNAs were differentially regulated by exposure to interferon-gamma (10 to 25 units/ml), which caused an increase in GFAP-beta levels while at the same time no change or a small decrease in total GFAP levels. In rat brain cortical slices, 4 hr exposure to 25 units/ml interferon-gamma decreased total GFAP mRNA levels over tenfold, while GFAP-beta levels were unaffected. These data indicate that a second form of the GFAP mRNA is expressed in astrocytes both in vivo and in vitro and provide evidence for independent regulation of these two GFAP mRNA species.

Novel E-cadherin-mediated adhesion in peripheral nerve: Schwann cell architecture is stabilized by autotypic adherens junctions.

Previous studies (Blank, W. F., M. B. Bunge, and R. P. Bunge. 1974. Brain Res. 67:503-518) showed that Schwann cell paranodal membranes were disrupted in calcium free medium suggesting that cadherin mediated mechanisms may operate to maintain the integrity of the paranodal membrane complex. Using antibodies against the fifth extracellular domain of E-cadherin, we now show by confocal laser and electron immunomicroscopy that E-cadherin is a major adhesive glycoprotein in peripheral nervous system Schwann cells. E-Cadherin is not found, however, in compact myelin bilayers. Rather, it is concentrated at the paranodes, in Schmidt-Lanterman incisures, and at the inner and outer loops. At these loci, E-cadherin is associated with subplasmalemmal electron densities that coordinate in register across several cytoplasmic turns of a single Schwann cell. F-Actin and beta-catenin, two proteins implicated in cellular signaling, also co-localize to E-cadherin positive sites. These complexes are autotypic adherens-type junctions that are confined to the plasma membrane synthesized by a single Schwann cell; E-cadherin was never observed between two Schwann cells, nor between Schwann cells and the axon. Our findings demonstrate that E-cadherin and its associated proteins are essential components in the architecture of the Schwann cell cytoplasmic channel network, and suggest that this network has specialized functions in addition to those required for myelinogenesis.

Implants of Cultured Schwann Cells Support Axonal Growth in the Central Nervous System of Adult Rats

Growing axons require an appropriate substrate on which to elongate. In the peripheral nervous system Schwann cells provide this substrate, and in the developing central nervous system (CNS) astrocytes are involved. In the adult CNS damaged axons do not normally regenerate but they can grow through peripheral nerve grafts. Also, they can grow along sheets of implanted Schwann cells or astrocytes. This study examines the ability of dissociated suspensions of Schwann cells and astrocytes to support axonal growth when implanted into the brains of adult rats. Schwann cells and astrocytes are cultured from near-term rat fetuses or newborn pups. They are transferred to polycarbonate tubes, and one end of each tube is inserted into the dorsal thalamus. The other end is secured extracranially. After 4 weeks to 6 months, the tubes are filled with tissue and are well vascularized. Evidence that Schwann cells support axonal growth comes from retrograde labeling studies in which horseradish peroxidase is applied to the extracranial ends of the tubes. In addition, immunolabeling reveals axon-like fibers inside the tubes using three neuron-specific antibodies. Finally, electron microscopy shows that these tubes contain small peripheral nerve-like structures consisting of myelinated and unmyelinated axons and a perineurial wrapping. Tubes filled with astrocytes contain less tissue than Schwann cell tubes and cells in the brain could not be retrogradely labeled by applying HRP to the extracranial ends. However, immunocytochemical studies reveal axon-like fibers extending for several millimeters into these tubes although few, if any, reach the external end.