Myelin Formation Research Articles

Human Pulmonary Surfactant Protein SP-A1 Provides Maximal Efficiency of Lung Interfacial Films

Pulmonary surfactant is a lipoprotein complex that reduces surface tension to prevent alveolar collapse and contributes to the protection of the respiratory surface from the entry of pathogens. Surfactant protein A (SP-A) is a hydrophilic glycoprotein of the collectin family, and its main function is related to host defense. However, previous studies have shown that SP-A also aids in the formation and biophysical properties of pulmonary surfactant films at the air-water interface. Humans, unlike rodents, have two genes, SFTPA1 and SFTPA2. The encoded proteins, SP-A1 and SP-A2, differ quantitatively or qualitatively in function. It has been shown that both gene products are necessary for tubular myelin formation, an extracellular structural form of lung surfactant. The goal of this study was to investigate potential differences in the biophysical properties of surfactants containing human SP-A1, SP-A2, or both. For this purpose, we have studied for the first time, to our knowledge, the biophysical properties of pulmonary surfactant from individual humanized transgenic mice expressing human SP-A1, SP-A2, or both SP-A1 and SP-A2, in the captive bubble surfactometer. We observed that pulmonary surfactant containing SP-A1 reaches lower surface tension after postexpansion interfacial adsorption than surfactants containing no SP-A or only SP-A2. Under interfacial compression-expansion cycling conditions, surfactant films containing SP-A1 also performed better, particularly with respect to the reorganization of the films that takes place during compression. On the other hand, addition of recombinant SP-A1 to a surfactant preparation reconstituted from the hydrophobic fraction of a porcine surfactant made it more resistant to inhibition by serum than the addition of equivalent amounts of SP-A2. We conclude that the presence of SP-A1 allows pulmonary surfactant to adopt a particularly favorable structure with optimal biophysical properties.

Cholesterol Biosynthesis Supports Myelin Gene Expression and Axon Ensheathment through Modulation of P13K/Akt/mTor Signaling.

Myelin, which ensheaths and insulates axons, is a specialized membrane highly enriched with cholesterol. During myelin formation, cholesterol influences membrane fluidity, associates with myelin proteins such as myelin proteolipid protein, and assembles lipid-rich microdomains within membranes. Surprisingly, cholesterol also is required by oligodendrocytes, glial cells that make myelin, to express myelin genes and wrap axons. How cholesterol mediates these distinct features of oligodendrocyte development is not known. One possibility is that cholesterol promotes myelination by facilitating signal transduction within the cell, because lipid-rich microdomains function as assembly points for signaling molecules. Signaling cascades that localize to cholesterol-rich regions of the plasma membrane include the PI3K/Akt pathway, which acts upstream of mechanistic target of rapamycin (mTOR), a major driver of myelination. Through manipulation of cholesterol levels and PI3K/Akt/mTOR signaling in zebrafish, we discovered that mTOR kinase activity in oligodendrocytes requires cholesterol. Drawing on a combination of pharmacological and rescue experiments, we provide evidence that mTOR kinase activity is required for cholesterol-mediated myelin gene expression. On the other hand, cholesterol-dependent axon ensheathment is mediated by Akt signaling, independent of mTOR kinase activity. Our data reveal that cholesterol-dependent myelin gene expression and axon ensheathment are facilitated by distinct signaling cascades downstream of Akt. Because mTOR promotes cholesterol synthesis, our data raise the possibility that cholesterol synthesis and mTOR signaling engage in positive feedback to promote the formation of myelin membrane. The speed of electrical impulse movement through axons is increased by myelin, a specialized, cholesterol-rich glial cell membrane that tightly wraps axons. During development, myelin membrane grows dramatically, suggesting a significant demand on mechanisms that produce and assemble myelin components, while it spirally wraps axons. Our studies indicate that cholesterol is necessary for both myelin growth and axon wrapping. Specifically, we found that cholesterol facilitates signaling mediated by the PI3K/Akt/mTOR pathway, a powerful driver of myelination. Because mTOR promotes the expression of genes necessary for cholesterol synthesis, cholesterol formation and PI3K/Akt/mTOR signaling might function as a feedforward mechanism to produce the large amounts of myelin membrane necessary for axon ensheathment.

Effects of Chronic Scopolamine Treatment on Cognitive Impairments and Myelin Basic Protein Expression in the Mouse Hippocampus.

Myelin plays an important role in learning and memory, and degradation of myelin is a key feature in the pathogenesis of neurological disorders involving cognitive dysfunction. Myelin basic protein (MBP) is one of the most abundant structural proteins in myelin and is essential for myelin formation and compaction. In this study, we first examined changes in the distribution of MBP-immunoreactive myelinated fibers and MBP levels according to hippocampal subregion in mice following chronic systemic treatment with 1mg/kg scopolamine (SCO) for 4weeks. We found that SCO-induced cognitive impairments, as assayed by the water maze and passive avoidance tests, were significantly reduced 1week after SCO treatment and the impairments were maintained without any hippocampal neuronal loss. MBP-immunoreactive myelinated fibers were easily detected in the stratum radiatum and lacunosum-moleculare of the hippocampus proper (CA1-3 region) and in the molecular and polymorphic layers of the dentate gyrus. The distribution of MBP-immunoreactive myelinated fibers was not altered 1week after SCO treatment. However, the density of MBP-immunoreactive myelinated fibers was significantly decreased 2weeks after SCO treatment; thereafter, the density gradually, though not significantly, decreased with time. In addition, the changing pattern of MBP levels in the hippocampus following SCO treatment corresponded to immunohistochemical changes. In brief, this study shows that chronic systemic treatment with SCO induced significant degradation of MBP in the hippocampus without neuronal loss at least 2weeks after SCO treatment, although cognitive impairments occurred 1week after SCO treatment.

Three-dimensional scaffolds seeded with NeuroD1-modified neural stem cells for repair of spinal cord injury

Objective To investigate the role of three-dimensional scaffolds seeded with NeuroD1-modified neural stem cells (NSCs) for repair of spinal cord injury in rats. Methods A new three-dimensional bio-printer was used to make bionic spinal cord scaffolds. NSCs are transduced with retrovirus vectors encoding NeuroD1 to express transgenes in high levels. Forty healthy female SD rats were divided into control group, scaffold group, scaffold+ NSCs-green fluorescent protein (GFP) group and scaffold+ NSCs-NeuroD1 group with 10 rats per group, according to the random number table. Spinal cord injury in rats was induced using the electric controlled cortical impactor. A week later, the control group was excised 3 mm spinal cord at the injury site under microscope. RT-PCR was used to confirm the construction of NeuroD1 overexpressing NSCs. Survival and differentiation of transplanted NSCs were detected with fluorescent staining. Rat neurological motor function was evaluated with BBB score at postoperative 1, 2, 4, 6 and 8 weeks. Rat electrophysiological changes were observed by monitoring motion evoked potential and sensory evoked potential at 8 weeks. Results RT-PCR results confirmed the successful reconstruction of NeuroD1-overexpressing NSCs. BBB score in scaffold+ NSCs-NeuroD1 group was the highest and had significant differences compared to other three groups (P<0.05). Electrophysiological results showed the motor and sensory in scaffold+ NSCs-NeuroD1 group had the shortest latencies and highest amplitudes, which revealed significant differences compared to other three groups (P<0.05). Immunofluorescence staining showed GFP cells in scaffold+ NSCs-NeuroD1 group at 8 weeks, which differentiated into neurons and astrocytes. GAP-43 was positively stained, and myelin formation was detected. Conclusion Three-dimensional scaffolds seeded with NeuroD1-modified NSCs can promote nerve loop reconstruction in spinal cord injury rats, and accelerate recovery of motor and sensory function. Key words: Spinal cord injuries; Neural stem cells; Bionic scaffold

YAP and TAZ control peripheral myelination and the expression of laminin receptors in Schwann cells.

Myelination is essential for nervous system function. Schwann cells interact with neurons and the basal lamina to myelinate axons, using known receptors, signals and transcription factors. In contrast, the transcriptional control of axonal sorting and the role of mechanotransduction in myelination are largely unknown. Yap and Taz are effectors of the Hippo pathway that integrate chemical and mechanical signals in cells. We describe a previously unknown role for the Hippo pathway in myelination. Using conditional mutagenesis in mice we show that Taz is required in Schwann cells for radial sorting and myelination, and that Yap is redundant with Taz. Yap/Taz are activated in Schwann cells by mechanical stimuli, and regulate Schwann cell proliferation and transcription of basal lamina receptor genes, both necessary for proper radial sorting of axons and subsequent myelination. These data link transcriptional effectors of the Hippo pathway and of mechanotransduction to myelin formation in Schwann cells.

α-Synuclein-induced myelination deficit defines a novel interventional target for multiple system atrophy.

Multiple system atrophy (MSA) is a rare atypical parkinsonian disorder characterized by a rapidly progressing clinical course and at present without any efficient therapy. Neuropathologically, myelin loss and neurodegeneration are associated with α-synuclein accumulation in oligodendrocytes, but underlying pathomechanisms are poorly understood. Here, we analyzed the impact of oligodendrocytic α-synuclein on the formation of myelin sheaths to define a potential interventional target for MSA. Post-mortem analyses of MSA patients and controls were performed to quantify myelin and oligodendrocyte numbers. As pre-clinical models, we used transgenic MSA mice, a myelinating stem cell-derived oligodendrocyte-neuron co-culture, and primary oligodendrocytes to determine functional consequences of oligodendrocytic α-synuclein overexpression on myelination. We detected myelin loss accompanied by preserved or even increased numbers of oligodendrocytes in post-mortem MSA brains or transgenic mouse forebrains, respectively, indicating an oligodendrocytic dysfunction in myelin formation. Corroborating this observation, overexpression of α-synuclein in primary and stem cell-derived oligodendrocytes severely impaired myelin formation, defining a novel α-synuclein-linked pathomechanism in MSA. We used the pro-myelinating activity of the muscarinic acetylcholine receptor antagonist benztropine to analyze the reversibility of the myelination deficit. Transcriptome profiling of primary pre-myelinating oligodendrocytes demonstrated that benztropine readjusts myelination-related processes such as cholesterol and membrane biogenesis, being compromised by oligodendrocytic α-synuclein. Additionally, benztropine restored the α-synuclein-induced myelination deficit of stem cell-derived oligodendrocytes. Strikingly, benztropine also ameliorated the myelin deficit in transgenic MSA mice, resulting in a prevention of neuronal cell loss. In conclusion, this study defines the α-synuclein-induced myelination deficit as a novel and crucial pathomechanism in MSA. Importantly, the reversible nature of this oligodendrocytic dysfunction opens a novel avenue for an intervention in MSA.

The fatty acid chain elongase, Elovl1, is required for kidney and swim bladder development during zebrafish embryogenesis

Very long chain fatty acids are required for sphingolipid synthesis, lipid homeostasis, myelin formation, epidermal permeability, and retinal function. Seven different enzymes are known to be involved in the elongation cycle of fatty acids, with different chain-length specificities. Elovl1 is one of those enzymes whose function has been linked mainly to the synthesis of sphingolipids and the epidermal barrier. However, the role of Elovl1 in organogenesis is not clear. In zebrafish, 2 Elovl1 genes, elovl1a and elovl1b, are highly expressed in the swim bladder, and elovl1b is also expressed in the kidney. We found that both elovl1 knockdown embryos contain increased levels of long chain fatty acids from carbon number 14 to 20 as compared to control embryos. Oil-Red-O staining shows that yolk lipid consumption is greatly reduced, whereas lipid droplets accumulate within the swim bladder. Notably, knockdown of either elovl1a or elovl1b affects the expression of genes involved in swim bladder development and impairs inflation of the swim bladder. Consistent with its expression in the pronephros, knockdown of elovl1b alone affects the expression of genes required for kidney development and reduces renal clearance. Our findings strongly suggest that both elovl1 genes are a key determinant of swim bladder and kidney development in zebrafish, which may be comparatively applicable to lung and kidney development in humans.

Functional Characterization of DNA Methylation in the Oligodendrocyte Lineage.

Oligodendrocytes derive from progenitors (OPCs) through the interplay of epigenomic and transcriptional events. By integrating high-resolution methylomics, RNA-sequencing, and multiple transgenic lines, this study defines the role of DNMT1 in developmental myelination. We detected hypermethylation of genes related to cell cycle and neurogenesis during differentiation of OPCs, yet genetic ablation of Dnmt1 resulted in inefficient OPC expansion and severe hypomyelination associated with ataxia and tremors in mice. This phenotype was not caused by lineage switch or massive apoptosis but was characterized by a profound defect of differentiation associated with changes in exon-skipping and intron-retention splicing events and by the activation of an endoplasmic reticulum stress response. Therefore, loss of Dnmt1 in OPCs is not sufficient to induce a lineage switch but acts as an important determinant of the coordination between RNA splicing and protein synthesis necessary for myelin formation.

Microenvironmental regulation of oligodendrocyte replacement and remyelination in spinal cord injury.

Myelin is a proteolipid sheath enwrapping axons in the nervous system that facilitates signal transduction along the axons. In the central nervous system (CNS), oligodendrocytes are specialized glial cells responsible for myelin formation and maintenance. Following spinal cord injury (SCI), oligodendroglia cell death and myelin damage (demyelination) cause chronic axonal damage and irreparable loss of sensory and motor functions. Accumulating evidence shows that replacement of damaged oligodendrocytes and renewal of myelin (remyelination) are promising approaches to prevent axonal degeneration and restore function following SCI. Neural precursor cells (NPCs) and oligodendrocyte progenitor cells (OPCs) are two main resident cell populations in the spinal cord with innate capacities to foster endogenous oligodendrocyte replacement and remyelination. However, due to the hostile microenvironment of SCI, the regenerative capacity of these endogenous precursor cells is conspicuously restricted. Activated resident glia, along with infiltrating immune cells, are among the key modulators of secondary injury mechanisms that create a milieu impermissible to oligodendrocyte differentiation and remyelination. Recent studies have uncovered inhibitory roles for astrocyte-associated molecules such as matrix chondroitin sulfate proteoglycans (CSPGs), and a plethora of pro-inflammatory cytokines and neurotoxic factors produced by activated microglia/macrophages. The quality of axonal remyelination is additionally challenged by dysregulation of the supportive growth factors required for maturation of new oligodendrocytes and axo-oligodendrocyte signalling. Careful understanding of factors that modulate the activity of endogenous precursor cells in the injury microenvironment is a key step in developing efficient repair strategies for remyelination and functional recovery following SCI.

G protein-coupled receptor 37 is a negative regulator of oligodendrocyte differentiation and myelination.

While the formation of myelin by oligodendrocytes is critical for the function of the central nervous system, the molecular mechanism controlling oligodendrocyte differentiation remains largely unknown. Here we identify G protein-coupled receptor 37 (GPR37) as an inhibitor of late-stage oligodendrocyte differentiation and myelination. GPR37 is enriched in oligodendrocytes and its expression increases during their differentiation into myelin forming cells. Genetic deletion of Gpr37 does not affect the number of oligodendrocyte precursor cells, but results in precocious oligodendrocyte differentiation and hypermyelination. The inhibition of oligodendrocyte differentiation by GPR37 is mediated by suppression of an exchange protein activated by cAMP (EPAC)-dependent activation of Raf-MAPK-ERK1/2 module and nuclear translocation of ERK1/2. Our data suggest that GPR37 regulates central nervous system myelination by controlling the transition from early-differentiated to mature oligodendrocytes.

The Activators of Cyclin-Dependent Kinase 5 p35 and p39 Are Essential for Oligodendrocyte Maturation, Process Formation, and Myelination.

The regulation of oligodendrocyte development and myelin formation in the CNS is poorly defined. Multiple signals influence the rate and extent of CNS myelination, including the noncanonical cyclin-dependent kinase 5 (Cdk5) whose functions are regulated by its activators p35 and p39. Here we show that selective loss of either p35 or p39 perturbed specific aspects of oligodendrocyte development, whereas loss of both p35 and p39 completely inhibited the development of mature oligodendrocytes and myelination. In the absence of p35, oligodendrocyte differentiation was delayed, process outgrowth was truncated in vitro, and the patterning and extent of myelination were perturbed in the CNS of p35(-/-) mice. In the absence of p39, oligodendrocyte maturation was transiently affected both in vitro and in vivo. However, loss of both p35 and p39 in oligodendrocyte lineage cells completely inhibited oligodendrocyte progenitor cell differentiation and myelination both in vitro and after transplantation into shiverer slice cultures. Loss of p35 and p39 had a more profound effect on oligodendrocyte development than simply the loss of Cdk5 and could not be rescued by Cdk5 overexpression. These data suggest p35 and p39 have specific and overlapping roles in oligodendrocyte development, some of which may be independent of Cdk5 activation.

Sphingosine kinase inhibition ameliorates chronic hypoperfusion-induced white matter lesions

White matter lesions (WML) are thought to contribute to vascular cognitive impairment in elderly patients. Growing evidence show that failure of myelin formation arising from the disruption of oligodendrocyte progenitor cell (OPC) differentiation is a cause of chronic vascular white matter damage. The sphingosine kinase (SphK)/sphingosine-1-phosphate (S1P) signaling pathway regulates oligodendroglia differentiation and function, and is known to be altered in hypoxia. In this study, we measured SphK, S1P as well as markers of WML, hypoxia and OPC (NG2) in a mouse bilateral carotid artery stenosis (BCAS) model of chronic cerebral hypoperfusion. Our results indicated that BCAS induced hypoxia inducible factor (HIF)-1α, Sphk2, S1P, and NG2 up-regulation together with accumulation of WML. In contrast, BCAS mice treated with the SphK inhibitor, SKI-II, showed partial reversal of SphK2, S1P and NG2 elevation and amelioration of WML. In an in vitro model of hypoxia, SKI-II reversed the suppression of OPC differentiation. Our study suggests a mechanism for hypoperfusion-associated WML involving HIF-1α-SphK2-S1P-mediated disruption of OPC differentiation, and proposes the SphK signaling pathway as a potential therapeutic target for white matter disease.

Learning delays in a mouse model of Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is a heterogeneous neurodevelopmental disorder with core symptoms of atypical social interactions and repetitive behaviors. It has also been reported that individuals with ASD have difficulty with multisensory integration, and this may disrupt higher-order cognitive abilities such as learning and social communication. Impairments in the integration of sensory information could in turn reflect diminished cross-modal white matter connectivity. Moreover, the genetic contribution in ASD appears to be strong, with heritability estimates as high as 90%. However, no single gene has been identified, and over 1000 risk genes have been reported. One of these genes – contactin-associated-like-protein 2 (CNTNAP2) – was first associated with Specific Language Impairment, and more recently has been linked to ASD. CNTNAP2 encodes a cell adhesion protein regulating synaptic signal transmission. To better understand the behavioral and biological underlying mechanisms of ASD, a transgenic mouse model was created with a genetic knockout (KO) of the rodent homolog Cntnap2. Initial studies on this mouse revealed poor social interactions, behavioral perseveration, and reduced vocalizations—all strongly resembling human ASD symptoms. Cntnap2 KO mice also show abnormalities in myelin formation, consistent with a hypo-connectivity model of ASD. The current study was designed to further assess the behavioral phenotype of this mouse model, with a focus on learning and memory. Cntnap2 KO and wild-type mice were tested on a 4/8 radial arm water maze for 14 consecutive days. Error scores (total, working memory, reference memory, initial and repeated reference memory), latency and average turn angle were independently assessed using a 2×14 repeated measures ANOVA. Results showed that Cntnap2 KO mice exhibited significant deficits in working and reference memory during the acquisition period of the task. During the retention period (i.e., after asymptote in errors), Cntnap2 KO mice performed comparably to wild-type mice. These findings suggest that CNTNAP2 may influence the development of neural systems important to learning and cross-modal integration, and that disruption of this function could be associated with delayed learning in ASD.

Abstract TP96: Functional Recovery and White Matter Repair After Exosomes Administration in Different Experimental Animal Models of Stroke

Introduction: Extracellular vesicles such as exosomes has opened a new field of research. Exosomes are able to transfer DNAs, mRNAs, microRNAs, non-coding RNAs, proteins, trophic factors and lipids associated with brain plasticity enhancement after stroke. Aim: To investigate white matter repair after exosomes administration in two experimental models of subcortical stroke: ischemic and hemorrhage. Material/Methods: Subcortical ischemic stroke was induced by Endothelin-1 and Collagenase IV was used to induce subcortical hemorrhagic stroke into striatum. Intravenous exosomes or saline only were administrated at 24h after cerebral infarct as treatment. Exosomes were isolated from culture of adipose mesenchymal stem cell and they were characterized by Nanoshight, Electronic microscope, Western blot and Immunofluorescence. Proteins contained into exosomes were analyzed by Orbitrab. We analyzed functional recovery by Rotarod, beam walking and Rogers tests. Lesion volume and tract connectivity were studied by magnetic resonance image. Anterograde and retrograde tracers were used to analyze axonal sprouting. Myelin formation was analyzed by cryomielin. Results: Proteomics analysis of exosomes identified more than 1400 proteins, many of them involved in intercellular communication. DiI labeled-Exosomes were detected in brain and peripheral organs (liver, lung and spleen). After 28 days, treated groups showed smaller functional deficit compared to control groups in both hemorrhagic and ischemic models. Moreover, treated group showed an increase in tract connectivity at 7 and 28 days compared to control groups. Also, animals which received exosomes showed an increase axonal sprouting and myelin formation at 28 days after stroke in both hemorrhagic and ischemic stroke. The treated groups also showed higher levels of white matter-associated markers in the injured area than the control groups. Conclusion: White matter integrity in different subcortical strokes is in part restored by exosomes treatment, probably mediated by repair molecular factors implicated in axonal sprouting, remyelination and oligodendrogenesis. These findings are associated with improved functional recovery in both kinds of strokes.

Adipose-Derived Stem Cells Promote Peripheral Nerve Regeneration In Vivo without Differentiation into Schwann-Like Lineage.

During recent decades, multipotent stem cells were found to reside in the adipose tissue, and these adipose-derived stem cells were shown to play beneficial roles, like those of Schwann cells, in peripheral nerve regeneration. However, it has not been well established whether adipose-derived stem cells offer beneficial effects to peripheral nerve injuries in vivo as Schwann cells do. Furthermore, the in situ survival and differentiation of adipose-derived stem cells after transplantation at the injured peripheral nerve tissue remain to be fully elucidated. Adipose-derived stem cells and Schwann cells were transplanted with gelatin hydrogel tubes at the artificially blunted sciatic nerve lesion in mice. Neuroregenerative abilities of them were comparably estimated. Cre-loxP-mediated fate tracking was performed to visualize survival in vivo of transplanted adipose-derived stem cells and to investigate whether they differentiated into Schwann linage cells at the peripheral nerve injury site. The transplantation of adipose-derived stem cells promoted regeneration of axons, formation of myelin, and restoration of denervation muscle atrophy to levels comparable to those achieved by Schwann cell transplantation. The adipose-derived stem cells survived for at least 4 weeks after transplantation without differentiating into Schwann cells. Transplanted adipose-derived stem cells did not differentiate into Schwann cells but promoted peripheral nerve regeneration at the injured site. The neuroregenerative ability was comparable to that of Schwann cells. Adipose-derived stem cells at an undifferentiated stage may be used as an alternative cell source for autologous cell therapy for patients with peripheral nerve injury.

Lentivirus-Mediated RNA Interference Targeting RhoA Slacks the Migration, Proliferation, and Myelin Formation of Schwann Cells

RhoA, a member of Rho GTPases family, is known to play an important role in remodeling actin cytoskeleton. During the development of the peripheral nervous system (PNS), Schwann cells undergo proliferation, migration, and radial sorting and finally wrap the related axons compactly to form myelin sheath. All these processes involve actin cytoskeletal remodeling. However, the role of RhoA on Schwann cell during development is still unclear. To address this question, we first used a lentiviral vector-mediated short hairpin (sh) RNA targeting RhoA to knock down the expression of RhoA in the cultured Schwann cells in vitro. Effects of RhoA on Schwann cell proliferation and migration were examined by BrdU assay and transwell assay, respectively. Results of the present study indicated that downregulated RhoA expression in cultured Schwann cells significantly slacked the cells' capabilities of migration and proliferation. Then, we investigated the role of RhoA in the developing rat sciatic nerves. Immunohistology and Western blotting showed that RhoA was mainly expressed in Schwann cells in the sciatic nerves and was peaked at 2weeks postnatal then kept in low level up to 8weeks. In the subjected rats whose sciatic nerves were microinjected with lentiviral vectors at postnatal 3days, we found that the lentiviruses mainly transfected Schwann cells, and the RhoA expression in the transfected Schwann cells was significantly knocked down. Four weeks after lentivirus microinjection, immunohistology and transmission electron microscopy illustrated that RhoA knockdown resulted in hypomyelination and significant decrease of the thickness of myelin in the transfected area. Overall data of current study suggested that RhoA plays a critical role in Schwann cell biology and is essential for myelination in developing peripheral nerve.

Ecotropic Murine Leukemia Virus Infection of Glial Progenitors Interferes with Oligodendrocyte Differentiation: Implications for Neurovirulence.

Certain murine leukemia viruses (MLVs) are capable of inducing fatal progressive spongiform motor neuron disease in mice that is largely mediated by viral Env glycoprotein expression within central nervous system (CNS) glia. While the etiologic mechanisms and the glial subtypes involved remain unresolved, infection of NG2 glia was recently observed to correlate spatially and temporally with altered neuronal physiology and spongiogenesis. Since one role of NG2 cells is to serve as oligodendrocyte (OL) progenitor cells (OPCs), we examined here whether their infection by neurovirulent (FrCasE) or nonneurovirulent (Fr57E) ecotropic MLVs influenced their viability and/or differentiation. Here, we demonstrate that OPCs, but not OLs, are major CNS targets of both FrCasE and Fr57E. We also show that MLV infection of neural progenitor cells (NPCs) in culture did not affect survival, proliferation, or OPC progenitor marker expression but suppressed certain glial differentiation markers. Assessment of glial differentiation in vivo using transplanted transgenic NPCs showed that, while MLVs did not affect cellular engraftment or survival, they did inhibit OL differentiation, irrespective of MLV neurovirulence. In addition, in chimeric brains, where FrCasE-infected NPC transplants caused neurodegeneration, the transplanted NPCs proliferated. These results suggest that MLV infection is not directly cytotoxic to OPCs but rather acts to interfere with OL differentiation. Since both FrCasE and Fr57E viruses restrict OL differentiation but only FrCasE induces overt neurodegeneration, restriction of OL maturation alone cannot account for neuropathogenesis. Instead neurodegeneration may involve a two-hit scenario where interference with OPC differentiation combined with glial Env-induced neuronal hyperexcitability precipitates disease. A variety of human and animal retroviruses are capable of causing central nervous system (CNS) neurodegeneration manifested as motor and cognitive deficits. These retroviruses infect a variety of CNS cell types; however, the specific role each cell type plays in neuropathogenesis remains to be established. The NG2 glia, whose CNS functions are only now emerging, are a newly appreciated viral target in murine leukemia virus (MLV)-induced neurodegeneration. Since one role of NG2 glia is that of oligodendrocyte progenitor cells (OPCs), we investigated here whether their infection by the neurovirulent MLV FrCasE contributed to neurodegeneration by affecting OPC viability and/or development. Our results show that both neurovirulent and nonneurovirulent MLVs interfere with oligodendrocyte differentiation. Thus, NG2 glial infection could contribute to neurodegeneration by preventing myelin formation and/or repair and by suspending OPCs in a state of persistent susceptibility to excitotoxic insult mediated by neurovirulent virus effects on other glial subtypes.

Rab27a/Slp2-a complex is involved in Schwann cell myelination.

Myelination of Schwann cells in the peripheral nervous system is an intricate process involving myelin protein trafficking. Recently, the role and mechanism of the endosomal/lysosomal system in myelin formation were emphasized. Our previous results demonstrated that a small GTPase Rab27a regulates lysosomal exocytosis and myelin protein trafficking in Schwann cells. In this present study, we established a dorsal root ganglion (DRG) neuron and Schwann cell co-culture model to identify the signals associated with Rab27a during myelination. First, Slp2-a, as the Rab27a effector, was endogenously expressed in Schwann cells. Second, Rab27a expression significantly increased during Schwann cell myelination. Finally, Rab27a and Slp2-a silencing in Schwann cells not only reduced myelin protein expression, but also impaired formation of myelin-like membranes in DRG neuron and Schwann cell co-cultures. Our findings suggest that the Rab27a/Slp2-a complex affects Schwann cell myelination in vitro.

Motor nerve conduction parameters in patients with iron deficiency anemia

Background: Worldwide, iron deficiency anemia (IDA) is the most common nutritional problem. Iron is very essential and has many important functions in brain energy metabolism, neurotransmitter function, and myelin formation. IDA may cause nerve dysfunctions. Aims and Objectives: The purpose of the present study was to investigate the effects of IDA on peripheral motor nerve function. Materials and Methods: A total of 40 individuals (25 females and 15 males) with IDA in the age range of 20-50 years from the Department of Medicine, SRM Medical College, as the study group and 30 participants (20 females and 10 males) without anemia as the control group were enrolled into this cross-sectional study. Patients with history of diabetes mellitus, neuromuscular, metabolic, vasculitic, or rheumatologic diseases and those taking medications that may alter central or peripheral nerve function were excluded from the study. The motor nerve conduction parameters, viz., distal latency, amplitude of compound muscle action potential (CMAP), and motor nerve conduction velocity (MNCV) were recorded bilaterally in median, ulnar, and posterior tibial nerves using standard protocols and settings. Values from patients were compared with those of controls by unpaired student’s t-test and one-way ANOVA. Results: The observations revealed significantly prolonged distal motor latencies, reduced CMAP amplitudes, and slowed MNCV in the peripheral nerves in IDA. Conclusion: The results indicated that the alteration in motor conduction parameters in IDA might be due to various functional and structural changes in peripheral nerves associated with iron deficiency.

MOBP levels are regulated by Fyn kinase and affect the morphological differentiation of oligodendrocytes.

Oligodendrocytes are the myelinating glial cells of the central nervous system (CNS). Myelin is formed by extensive wrapping of oligodendroglial processes around axonal segments, which ultimately allows a rapid saltatory conduction of action potentials within the CNS and sustains neuronal health. The non-receptor tyrosine kinase Fyn is an important signaling molecule in oligodendrocytes. It controls the morphological differentiation of oligodendrocytes and is an integrator of axon-glial signaling cascades leading to localized synthesis of myelin basic protein (MBP), which is essential for myelin formation. The abundant myelin-associated oligodendrocytic basic protein (MOBP) resembles MBP in several aspects and has also been reported to be localized as mRNA and translated in the peripheral myelin compartment. The signals initiating local MOBP synthesis are so far unknown and the cellular function of MOBP remains elusive. Here, we show, by several approaches in cultured primary oligodendrocytes, that MOBP synthesis is stimulated by Fyn activity. Moreover, we reveal a new function for MOBP in oligodendroglial morphological differentiation.