BDNF overexpression produces a long-term increase in myelin formation in the peripheral nervous system

Positive Allosteric Modulators of Trk Receptors for the Treatment of Alzheimer's Disease

Neurotrophins are important regulators of neuronal and non-neuronal functions. As such, the neurotrophins and their receptors, the tropomyosin receptor kinase (Trk) family of receptor tyrosine kinases, has attracted intense research interest and their role in multiple diseases including Alzheimer's disease has been described. Attempts to administer neurotrophins to patients have been reported, but the clinical trials have so far have been hampered by side effects or a lack of clear efficacy. Thus, much of the focus during recent years has been on identifying small molecules acting as agonists or positive allosteric modulators (PAMs) of Trk receptors. Two examples of successful discovery and development of PAMs are the TrkA-PAM E2511 and the pan-Trk PAM ACD856. E2511 has been reported to have disease-modifying effects in preclinical models, whereas ACD856 demonstrates both a symptomatic and a disease-modifying effect in preclinical models. Both molecules have reached the stage of clinical development and were reported to be safe and well tolerated in clinical phase 1 studies, albeit with different pharmacokinetic profiles. These two emerging small molecules are interesting examples of possible novel symptomatic and disease-modifying treatments that could complement the existing anti-amyloid monoclonal antibodies for the treatment of Alzheimer's disease. This review aims to present the concept of positive allosteric modulators of the Trk receptors as a novel future treatment option for Alzheimer's disease and other neurodegenerative and cognitive disorders, and the current preclinical and clinical data supporting this new concept. Preclinical data indicate dual mechanisms, not only as cognitive enhancers, but also a tentative neurorestorative function.

Knockdown of NCOR2 Inhibits Cell Proliferation via BDNF/TrkB/ERK in NF1-Derived MPNSTs

(1) Background: malignant peripheral nerve sheath tumours (MPNSTs) are aggressive Schwann cell-derived sarcomas with dismal prognoses. Previous studies have shown that nuclear receptor corepressor 2 (NCOR2) plays a vital role in neurodevelopment and in various tumours. However, the impact of NCOR2 on the progression of MPNST remains unclear. (2) Methods: by GEO database, MPNST tissue microarray, and NF1-related tumour tissues and cell lines were used to explore NCOR2 expression level in the MPNSTs. The role and mechanism of NCOR2 in NF1-derived MPNSTs were explored by experiments in vivo and in vitro and by transcriptome high-throughput sequencing. (3) Results: NCOR2 expression is significantly elevated in NF1-derived MPNSTs and is associated with patient 10-year survival time. Knockdown of NCOR2 suppressed NF1-derived MPNST cell proliferation by blocking the cell cycle in the G0/G1 phase. Moreover, decreased NCOR2 expression could down-regulate MAPK signal activity through the BDNF/TrkB pathway. (4) Conclusions: our findings demonstrated that NCOR2 expression is significantly elevated in NF1-derived MPNSTs. NCOR2 knockdown can inhibit NF1-derived MPNST cell proliferation by weakened BDNF/TrkB/ERK signalling. Targeting NF1-derived MPNSTs with TrkB inhibitors, or in combination with ERK inhibitors, may be a novel therapeutic strategy for clinical trials.

Application of neurotrophic and proangiogenic factors as therapy after peripheral nervous system injury

The intrinsic ability of peripheral nerves to regenerate after injury is extremely limited, especially in case of severe injury. This often leads to poor motor function and permanent disability. Existing approaches for the treatment of injured nerves do not provide appropriate conditions to support survival and growth of nerve cells. This drawback can be compensated by the use of gene therapy and cell therapy-based drugs that locally provide an increase in the key regulators of nerve growth, including neurotrophic factors and extracellular matrix proteins. Each growth factor plays its own specific angiotrophic or neurotrophic role. Currently, growth factors are widely studied as accelerators of nerve regeneration. Particularly noteworthy is synergy between various growth factors, that is essential for both angiogenesis and neurogenesis. Fibroblast growth factor 2 and vascular endothelial growth factor are widely known for their proangiogenic effects. At the same time, fibroblast growth factor 2 and vascular endothelial growth factor stimulate neural cell growth and play an important role in neurodegenerative diseases of the peripheral nervous system. Taken together, their neurotrophic and angiogenic properties have positive effect on the regeneration process. In this review we provide an in-depth overview of the role of fibroblast growth factor 2 and vascular endothelial growth factor in the regeneration of peripheral nerves, thus demonstrating their neurotherapeutic efficacy in improving neuron survival in the peripheral nervous system.

Sortilin Modulates Schwann Cell Signaling and Remak Bundle Regeneration Following Nerve Injury

Peripheral nerve regeneration relies on the ability of Schwann cells to support the regrowth of damaged axons. Schwann cells re-differentiate when reestablishing contact with the sprouting axons, with large fibers becoming remyelinated and small nociceptive fibers ensheathed and collected into Remak bundles. We have previously described how the receptor sortilin facilitates neurotrophin signaling in peripheral neurons via regulated trafficking of Trk receptors. This study aims to characterize the effects of sortilin deletion on nerve regeneration following sciatic crush injury. We found that Sort1^–/– mice displayed functional motor recovery like that of WT mice, with no detectable differences in relation to nerve conduction velocities and morphological aspects of myelinated fibers. In contrast, we found abnormal ensheathment of regenerated C-fibers in injured Sort1^–/– mice, demonstrating a role of sortilin for Remak bundle formation following injury. Further studies on Schwann cell signaling pathways showed a significant reduction of MAPK/ERK, RSK, and CREB phosphorylation in Sort1^–/– Schwann cells after stimulation with neurotrophin-3 (NT-3), while Schwann cell migration and myelination remained unaffected. In conclusion, our results demonstrate that loss of sortilin blunts NT-3 signaling in Schwann cells which might contribute to the impaired Remak bundle regeneration after sciatic nerve injury.

Serum brain injury biomarkers are gestationally and post-natally regulated in non-brain injured neonates

BACKGROUND

To determine the association of gestational age (GA) and day of life (DOL) with the circulating serum concentration of six brain injury-associated biomarkers in non-brain injured neonates born between 23 and 41 weeks' GA.

METHODS

In a multicenter prospective observational cohort study, serum CNS-insult, inflammatory and trophic proteins concentrations were measured daily in the first 7 DOL.

RESULTS

Overall, 3232 serum samples were analyzed from 745 enrollees, median GA 32.3 weeks. BDNF increased 3.7% and IL-8 increased 8.9% each week of gestation. VEGF, IL-6, and IL-10 showed no relationship with GA. VEGF increased 10.8% and IL-8 18.9%, each DOL. IL-6 decreased by 15.8% each DOL. IL-10 decreased by 81.4% each DOL for DOL 0-3. BDNF did not change with DOL. Only 49.67% of samples had detectable GFAP and 33.15% had detectable NRGN. The odds of having detectable GFAP and NRGN increased by 53% and 11%, respectively, each week after 36 weeks' GA. The odds of having detectable GFAP and NRGN decreased by 15% and 8%, respectively, each DOL.

CONCLUSIONS

BDNF and IL-8 serum concentrations vary with GA. VEGF and interleukin concentrations are dynamic in the first week of life, suggesting circulating levels should be adjusted for GA and DOL for clinically relevant assessment of brain injury.

IMPACT

Normative data of six brain injury-related biomarkers is being proposed. When interpreting serum concentrations of brain injury biomarkers, it is key to adjust for gestational age at birth and day of life during the first week to correctly assess for clinical brain injury in neonates. Variation in levels of some biomarkers may be related to gestational and postnatal age and not necessarily pathology.

Ladder-based resistance training elicited similar ultrastructural adjustments in forelimb and hindlimb peripheral nerves of young adult Wistar rats

To analyze the morphological response induced by high-volume, high-intensity ladder-based resistance training (LRT) on the ultrastructure of the radial (forelimb) and sciatic (hindlimb) nerves of adults Wistar rats. Twenty rats were equally distributed into groups: sedentary (SED) and LRT. After the rodents were subjected to the maximum load (ML) carrying test, the LRT group performed 6-8 progressive climbs (2 × 50% ML, 2 × 75% ML, 2 × 100% ML, and 2 × 100% ML + 30 g) three times per week. After 8 weeks, the radial and sciatic nerves were removed and prepared for transmission electron microscopy. In the radial nerve, myelinated axons cross-sectional area (CSA), unmyelinated axons CSA, myelin sheath thickness, and Schwann cells nuclei area were statistically larger in the LRT group than SED (p < 0.05). Also, the number of microtubules and neurofilaments per field were statistically higher in the LRT group than in SED (p < 0.01). For sciatic nerve, myelinated fibers CSA, unmyelinated axons CSA, myelin sheath thickness, Schwann cells nuclei area, and the number of neurofilaments per field were statistically larger in the LRT group compared to the SED group (p < 0.05). LRT with high-volume and high-intensity effectively induce similar changes in adult Wistar rats' radial and sciatic nerves' ultrastructure.

Physical exercise mitigates neuropathic changes in an animal model for Charcot-Marie-Tooth disease 1X

Inherited neuropathies of the Charcot-Marie-Tooth (CMT) type 1 are still untreatable diseases of the peripheral nervous system. We have previously shown that macrophages substantially amplify neuropathic changes in various mouse models of CMT1 subforms and that targeting innate immune cells substantially ameliorates disease outcome. However, up to date, specific approaches targeting macrophages pharmacologically might entail side effects. Here, we investigate whether physical exercise dampens peripheral nerve inflammation in a model for an X-linked dominant form of CMT1 (CMT1X) and whether this improves neuropathological and clinical outcome subsequently. We found a moderate, but significant decline in the number of macrophages and an altered macrophage activation upon voluntary wheel running. These observations were accompanied by an improved clinical outcome and axonal preservation. Most interestingly, exercise restriction by ~40% accelerated amelioration of clinical outcome and further improved nerve structure by increasing myelin thickness compared to the unrestricted running group. This myelin-preserving effect of limited exercise was accompanied by an elevated expression of brain-derived neurotrophic factor (BDNF) in peripheral nerves, while the expression of other trophic factors like neuregulin-1, glial cell line-derived neurotrophic factor (GDNF) or insulin-like growth factor 1 (IGF-1) were not influenced by any mode of exercise. We demonstrate for the first time that exercise dampens inflammation and improves nerve structure in a mouse model for CMT1, likely leading to improved clinical outcome. Reducing the amount of exercise does not automatically decrease treatment efficacy, reflecting the need of optimally designed exercise studies to achieve safe and effective treatment options for CMT1 patients.

Microglia: The Missing Link to Decipher and Therapeutically Control MS Progression?

Therapeutically controlling chronic progression in multiple sclerosis (MS) remains a major challenge. MS progression is defined as a steady loss of parenchymal and functional integrity of the central nervous system (CNS), occurring independent of relapses or focal, magnetic resonance imaging (MRI)-detectable inflammatory lesions. While it clinically surfaces in primary or secondary progressive MS, it is assumed to be an integral component of MS from the very beginning. The exact mechanisms causing progression are still unknown, although evolving evidence suggests that they may substantially differ from those driving relapse biology. To date, progression is assumed to be caused by an interplay of CNS-resident cells and CNS-trapped hematopoietic cells. On the CNS-resident cell side, microglia that are phenotypically and functionally related to cells of the monocyte/macrophage lineage may play a key role. Microglia function is highly transformable. Depending on their molecular signature, microglia can trigger neurotoxic pathways leading to neurodegeneration, or alternatively exert important roles in promoting neuroprotection, downregulation of inflammation, and stimulation of repair. Accordingly, to understand and to possibly alter the role of microglial activation during MS disease progression may provide a unique opportunity for the development of suitable, more effective therapeutics. This review focuses on the current understanding of the role of microglia during disease progression of MS and discusses possible targets for therapeutic intervention.

Contribution of P2X4 Receptors to CNS Function and Pathophysiology

The release and extracellular action of ATP are a widespread mechanism for cell-to-cell communication in living organisms through activation of P2X and P2Y receptors expressed at the cell surface of most tissues, including the nervous system. Among ionototropic receptors, P2X4 receptors have emerged in the last decade as a potential target for CNS disorders such as epilepsy, ischemia, chronic pain, anxiety, multiple sclerosis and neurodegenerative diseases. However, the role of P2X4 receptor in each pathology ranges from beneficial to detrimental, although the mechanisms are still mostly unknown. P2X4 is expressed at low levels in CNS cells including neurons and glial cells. In normal conditions, P2X4 activation contributes to synaptic transmission and synaptic plasticity. Importantly, one of the genes present in the transcriptional program of myeloid cell activation is P2X4. Microglial P2X4 upregulation, the P2X4+ state of microglia, seems to be common in most acute and chronic neurodegenerative diseases associated with inflammation. In this review, we summarize knowledge about the role of P2X4 receptors in the CNS physiology and discuss potential pitfalls and open questions about the therapeutic potential of blocking or potentiation of P2X4 for different pathologies.

Neuroprotective Effect of Salvianolic Acid A against Diabetic Peripheral Neuropathy through Modulation of Nrf2

Oxidative stress has been recognized as the contributor to diabetic peripheral neuropathy (DPN). Antioxidant strategies have been most widely explored; nevertheless, whether antioxidants alone prevent DPN still remains inconclusive. In the present study, we established an in vitro DPN cell model for drug screening using Schwann RSC96 cells under high glucose (HG) stimulation, and we found that salvianolic acid A (SalA) mitigated HG-induced injury evidenced by cell viability and myelination. Mechanistically, SalA exhibited strong antioxidative effects by inhibiting 1,1-diphenyl-2-picrylhydrazyl (DPPH) and reducing reactive oxygen species (ROS), malondialdehyde (MDA), and oxidized glutathione (GSSG) content, as well as upregulating antioxidative enzyme mRNA expression. In addition, SalA significantly extenuated neuroinflammation with downregulated inflammatory factor mRNA expression. Furthermore, SalA improved the mitochondrial function of HG-injured Schwann cells by scavenging mitochondrial ROS, decreasing mitochondrial membrane potential (MMP), and enhancing ATP production, as well as upregulating oxidative phosphorylation gene expression. More importantly, we identified nuclear factor-E2-related factor 2 (Nrf2) as the upstream regulator which mediated protective effects of SalA on DPN. SalA directly bound to the Kelch domain of Kelch-like ECH-associated protein 1 (Keap1) and thus disrupted the interaction of Nrf2 and Keap1 predicted by LibDock of Discovery Studio. Additionally, SalA significantly inhibited Nrf2 promoter activity and downregulated Nrf2 mRNA expression but without affecting Nrf2 protein expression. Interestingly, SalA upregulated the nuclear Nrf2 expression and promoted Nrf2 nuclear translocation by high content screening assay, which was confirmed to be involved in its antiglucotoxicity effect by the knockdown of Nrf2 in RSC96 cells. In KK-Ay mice, we demonstrated that SalA could effectively improve the abnormal glucose and lipid metabolism and significantly protect against DPN by increasing the mechanical withdrawal threshold and sciatic nerve conduction velocity and restoring the ultrastructural impairment of the injured sciatic nerve induced by diabetes. Hence, SalA protected against DPN by antioxidative stress, attenuating neuroinflammation, and improving mitochondrial function via Nrf2. SalA may be prospective therapeutics for treating DPN.

Enhancement of Motor Function Recovery after Spinal Cord Injury in Mice by Delivery of Brain-Derived Neurotrophic Factor mRNA

Spinal cord injury (SCI) is a debilitating condition that can cause impaired motor function or full paralysis. In the days to weeks following the initial mechanical injury to the spinal cord, inflammation and apoptosis can cause additional damage to the injured tissues. This secondary injury impairs recovery. Brain-derived neurotrophic factor is a secreted protein that has been shown to improve a variety of neurological conditions, including SCI, by promoting neuron survival and synaptic plasticity. This study treated a mouse model of contusion SCI using a single dose of brain-derived neurotrophic factor (BDNF) mRNA nanomicelles prepared with polyethylene glycol polyamino acid block copolymer directly injected into the injured tissue. BDNF levels in the injured spinal cord tissue were approximately doubled by mRNA treatment. Motor function was monitored using the Basso Mouse Scale and Noldus CatWalk Automated Gait Analysis System for 6 weeks post-injury. BDNF-treated mice showed improved motor function recovery, demonstrating the feasibility of mRNA delivery to treat SCI.

Peripheral Nerve Regeneration Is Independent From Schwann Cell p75NTR Expression

Schwann cell reprogramming and differentiation are crucial prerequisites for neuronal regeneration and re-myelination to occur following injury to peripheral nerves. The neurotrophin receptor p75NTR has been identified as a positive modulator for Schwann cell myelination during development and implicated in promoting nerve regeneration after injury. However, most studies base this conclusion on results obtained from complete p75NTR knockout mouse models and cannot dissect the specific role of p75NTR expressed by Schwann cells. In this present study, a conditional knockout model selectively deleting p75NTR expression in Schwann cells was generated, where p75NTR expression is replaced with that of an mCherry reporter. Silencing of Schwann cell p75NTR expression was confirmed in the sciatic nerve in vivo and in vitro, without altering axonal expression of p75NTR. No difference in sciatic nerve myelination during development or following sciatic nerve crush injury was observed, as determined by quantification of both myelinated and unmyelinated nerve fiber densities, myelinated axonal diameter and myelin thickness. However, the absence of Schwann cell p75NTR reduced motor nerve conduction velocity after crush injury. Our data indicate that the absence of Schwann cell p75NTR expression in vivo is not critical for axonal regrowth or remyelination following sciatic nerve crush injury, but does play a key role in functional recovery. Overall, this represents the first step in redefining the role of p75NTR in the peripheral nervous system, suggesting that the Schwann cell-axon unit functions as a syncytium, with the previous published involvement of p75NTR in remyelination most likely depending on axonal/neuronal p75NTR and/or mutual glial-axonal interactions.

A microfluidic platform to study the effects of GDNF on neuronal axon entrapment

BACKGROUND

One potential treatment strategy to enhance axon regeneration is transplanting Schwann Cells (SCs) that overexpress glial cell line-derived neurotrophic factor (GDNF). Unfortunately, constitutive GDNF overexpression in vivo can result in failure of regenerating axons to extend beyond the GDNF source, a phenomenon termed the "candy-store" effect. Little is known about the mechanism of this axon entrapment in vivo.

NEW METHOD

We present a reproducible in vitro culture platform using a microfluidic device to model axon entrapment and investigate mechanisms by which GDNF causes axon entrapment. The device is comprised of three culture chambers connected by two sets of microchannels, which prevent cell soma from moving between chambers but allow neurites to grow between chambers. Neurons from dorsal root ganglia were seeded in one end chamber while the effect of different conditions in the other two chambers was used to study neurite entrapment.

RESULTS

The results showed that GDNF-overexpressing SCs (G-SCs) can induce axon entrapment in vitro. We also found that while physiological levels of GDNF (100 ng/mL) promoted neurite extension, supra-physiological levels of GDNF (700 ng/mL) induced axon entrapment.

COMPARISON WITH EXISTING METHOD

All previous work related to the "candy-store" effect were done in vivo. Here, we report the first in vitro platform that can recapitulate the axonal entrapment and investigate the mechanism of the phenomenon.

CONCLUSIONS

This platform facilitates investigation of the "candy-store" effect and shows the effects of high GDNF concentrations on neurite outgrowth.

Changes in miRNA-132 and miR-124 levels in non-treated and citalopram-treated patients with depression

BACKGROUND

Neurotrophins including brain-derived neurotropic factor (BDNF) are implicated in the pathogenesis of major depressive disorder (MDD). Yet, the roles of brain-specific BDNF-related miRNAs miR-132 and miR-124 are unclear.

METHODS

We enrolled 45 treatment-free patients with MDD, 32 citalopram-treated patients with MDD, and 32 healthy control subjects. Participants were assessed with the Hamilton Depression Scale (HAMD) and Hamilton Anxiety Scale (HAMA). In a case-control sub-study, we followed 14 treatment-free patients who were subsequently treated with citalopram for 2 months. Enzyme-linked immunosorbent assay was used to detect plasma BDNF, and real-time polymerase chain reaction was used to quantify relative plasma miR-132 and miR-124 expression.

RESULTS

Patients with MDD had significantly higher HAMA and HAMD scores than the control group, with the highest scores in the treatment-free MDD group. Plasma miR-132 in the treatment-free MDD group was 2.4-fold that in the control group and significantly higher than that in the citalopram-treated MDD group. Plasma miR-124 in the treatment-free MDD and citalopram-treated MDD groups was 1.8-fold and 4-fold that in the control group, respectively. Compared to the control group, plasma BDNF levels were increased in both MDD groups, but not significantly different between them. There was a positive correlation between miR-132 and HAMD and HAMA scores, whereas no significant correlations were identified for plasma miR-124 or BDNF.

LIMITATIONS

The range of neurotrophin-related MiRNAs and the number of follow-up cases were limited.

CONCLUSIONS

BDNF and miR-124 in plasma increase with depression and antidepressants. Plasma MiR-132 might be an indication for depression status.

Genome expression profiling predicts the molecular mechanism of peripheral myelination

The present study aimed to explore the molecular mechanism of myelination in the peripheral nervous system (PNS) based on genome expression profiles. Microarray data (GSE60345) was acquired from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were integrated and subsequently subjected to pathway and term enrichment analysis. A protein-protein interaction network was constructed and the top 200 DEGs according to their degree value were further subjected to pathway enrichment analysis. A microRNA (miR)-target gene regulatory network was constructed to explore the role of miRs associated with PNS myelination. A total of 783 upregulated genes and 307 downregulated genes were identified. The upregulated DEGs were significantly enriched in the biological function of complement and coagulation cascades, cytokine-cytokine receptor interactions and cell adhesion molecules. Pathways significantly enriched by the downregulated DEGs included the cell cycle, oocyte meiosis and the p53 signaling pathway. In addition, the upregulated DEGs among the top 200 DEGs were significantly enriched in natural killer (NK) cell mediated cytotoxicity and the B cell receptor (BCR) signaling pathway, in which Fc γ receptor (FCGR), ras-related C3 botulinum toxin substrate 2 (RAC2) and 1-phosphatidylinositol-4,5-bisphosphate phosphodiesterase γ-2 (PLCG2) were involved. miR-339-5p, miR-10a-5p and miR-10b-5p were identified as having a high degree value and may regulate the target genes TOX high mobility group box family member 4 (Tox4), DNA repair protein XRCC2 (Xrcc2) and C5a anaphylatoxin chemotactic receptor C5a2 (C5ar2). NK cell mediated cytotoxicity and the BCR pathway may be involved in peripheral myelination by targeting FCGR, RAC2 and PLCG2. The downregulation of oocyte meiosis, the cell cycle and the cellular tumor antigen p53 signaling pathway suggests decreasing schwann cell proliferation following the initiation of myelination. miR-339-5p, miR-10a-5p and miR-10b-5p may play important roles in PNS myelination by regulating Tox4, Xrcc2 and C5ar2.

Multichanneled Nerve Guidance Conduit with Spatial Gradients of Neurotrophic Factors and Oriented Nanotopography for Repairing the Peripheral Nervous System

Peripheral nerve injuries, causing sensory and motor impairment, affect a great number of patients annually. It is therefore important to incorporate different strategies to promote nerve healing. Among the treatment options, however, the efficacy of nerve conduits is often compromised by their lack of living cells, insufficient growth factors, and absence of the extracellular matrix (ECM)-like structure. To improve the functional recovery, we aimed to develop a natural biodegradable multichanneled scaffold characterized with aligned electrospun nanofibers and neurotrophic gradient (MC/AN/NG) to guide axon outgrowth. The gelatin-based conduits mimicked the fascicular architecture of natural nerve ECM. The multichanneled (MC) scaffolds, cross-linked with microbial transglutaminase, possessed sustainable mechanical stability. Meanwhile, the release profile of dual neurotrophic factors, nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), exhibited a temporal-controlled manner. In vitro, the differentiated neural stem cells effectively extended their neurites along the aligned nanofibers. Besides, in the treated group, the cell density increased in high NGF concentration regions of the gradient membrane, and the BDNF significantly promoted myelination. In a rabbit sciatic nerve transection in vivo model, the MC/AN/NG scaffold showed superior nerve recovery and less muscle atrophy comparable to autograft. By integrating multiple strategies to promote peripheral nerve regeneration, the MC/AN/NG scaffolds as nerve guidance conduits showed promising results and efficacious treatment alternatives for autologous nerve grafts.

Dynamic impact of brief electrical nerve stimulation on the neural immune axis-polarization of macrophages toward a pro-repair phenotype in demyelinated peripheral nerve

Demyelinating peripheral nerves are infiltrated by cells of the monocyte lineage, including macrophages, which are highly plastic, existing on a continuum from pro-inflammatory M1 to pro-repair M2 phenotypic states. Whether one can therapeutically manipulate demyelinated peripheral nerves to promote a pro-repair M2 phenotype remains to be elucidated. We previously identified brief electrical nerve stimulation (ES) as therapeutically beneficial for remyelination, benefits which include accelerated clearance of macrophages, making us theorize that ES alters the local immune response. Thus, the impact of ES on the immune microenvironment in the zone of demyelination was examined. Adult male rat tibial nerves were focally demyelinated via 1% lysophosphatidyl choline (LPC) injection. Five days later, half underwent 1 hour 20 Hz sciatic nerve ES proximal to the LPC injection site. ES had a remarkable and significant impact, shifting the macrophage phenotype from predominantly pro-inflammatory/M1 toward a predominantly pro-repair/M2 one, as evidenced by an increased incidence of expression of M2-associated phenotypic markers in identified macrophages and a decrease in M1-associated marker expression. This was discernible at 3 days post-ES (8 days post-LPC) and continued at the 5 day post-ES (10 days post-LPC) time point examined. ES also affected chemokine (C-C motif) ligand 2 (CCL2; aka MCP-1) expression in a manner that correlated with increases and decreases in macrophage numbers observed in the demyelination zone. The data establish that briefly increasing neuronal activity favorably alters the immune microenvironment in demyelinated nerve, rapidly polarizing macrophages toward a pro-repair phenotype, a beneficial therapeutic concept that may extend to other pathologies. GLIA 2016;64:1546-1561.

Finding novel distinctions between the sAPPα-mediated anabolic biochemical pathways in Autism Spectrum Disorder and Fragile X Syndrome plasma and brain tissue

Autism spectrum disorder (ASD) and Fragile X syndrome (FXS) are developmental disorders. No validated blood-based biomarkers exist for either, which impedes bench-to-bedside approaches. Amyloid-β (Aβ) precursor protein (APP) and metabolites are usually associated with Alzheimer’s disease (AD). APP cleavage by α-secretase produces potentially neurotrophic secreted APPα (sAPPα) and the P3 peptide fragment. β-site APP cleaving enzyme (BACE1) cleavage produces secreted APPβ (sAPPβ) and intact Aβ. Excess Aβ is potentially neurotoxic and can lead to atrophy of brain regions such as amygdala in AD. By contrast, amygdala is enlarged in ASD but not FXS. We previously reported elevated levels of sAPPα in ASD and FXS vs. controls. We now report elevated plasma Aβ and total APP levels in FXS compared to both ASD and typically developing controls, and elevated levels of sAPPα in ASD and FXS vs. controls. By contrast, plasma and brain sAPPβ and Aβ were lower in ASD vs. controls but elevated in FXS plasma vs. controls. We also detected age-dependent increase in an α-secretase in ASD brains. We report a novel mechanistic difference in APP pathways between ASD (processing) and FXS (expression) leading to distinct APP metabolite profiles in these two disorders. These novel, distinctive biochemical differences between ASD and FXS pave the way for blood-based biomarkers for ASD and FXS.

Transplantation of neural stem cells clonally derived from embryonic stem cells promotes recovery after murine spinal cord injury

The pathology of spinal cord injury (SCI) makes it appropriate for cell-based therapies. Treatments using neural stem cells (NSCs) in animal models of SCI have shown positive outcomes, although uncertainty remains regarding the optimal cell source. Pluripotent cell sources such as embryonic stem cells (ESCs) provide a limitless supply of therapeutic cells. NSCs derived using embryoid bodies (EB) from ESCs have shown tumorigenic potential. Clonal neurosphere generation is an alternative method to generate safer and more clinically relevant NSCs without the use of an EB stage for use in cell-based therapies. We generated clonally derived definitive NSCs (dNSCs) from ESC. These cells were transplanted into a mouse thoracic SCI model. Embryonic stem cell-derived definitive neural stem cell (ES-dNSC)-transplanted mice were compared with controls using behavioral measures and histopathological analysis of tissue. In addition, the role of remyelination in injury recovery was investigated using transmission electron microscopy. The SCI group that received ES-dNSC transplantation showed significant improvements in locomotor function compared with controls in open field and gait analysis. The cell treatment group had a significant enhancement of spared neural tissue. Immunohistological assessments showed that dNSCs differentiated primarily to oligodendrocytes. These cells were shown to express myelin basic protein, associate with axons, and support nodal architecture as well as display proper compact, multilayer myelination in electron microscopic analysis. This study provides strong evidence that dNSCs clonally derived from pluripotent cells using the default pathway of neuralization improve motor function after SCI and enhance sparing of neural tissue, while remaining safe and clinically relevant.

Adipose-Derived Stem Cells Expressing the Neurogenin-2 Promote Functional Recovery After Spinal Cord Injury in Rat

Neurogenin2 (Ngn2) is a proneural gene that directs neuronal differentiation of progenitor cells during development. This study aimed to investigate whether the use of adipose-derived stem cells (ADSCs) over-expressing the Ngn2 transgene (Ngn2-ADSCs) could display the characteristics of neurogenic cells and improve functional recovery in an experimental rat model of SCI. ADSCs from rats were cultured and purified in vitro, followed by genetically modified with the Ngn2 gene. Forty-eight adult female Sprague-Dawley rats were randomly assigned to three groups: the control, ADSCs, and Ngn2-ADSCs groups. The hind-limb motor function of all rats was recorded using the Basso, Beattie, and Bresnahan locomotor rating scale for 8 weeks. Moreover, hematoxylineosin staining and immunohistochemistry were also performed. After neural induction, positive expression rate of NeuN in Ngn2-ADSCs group was upon 90 %. Following transplantation, a great number of ADSCs was found around the center of the injury spinal cord at 1 and 4 weeks, which improved retention of tissue at the lesion site. Ngn2-ADSCs differentiated into neurons, indicated by the expression of neuronal markers, NeuN and Tuj1. Additionally, transplantation of Ngn2-ADSCs upregulated the trophic factors (brain-derived neurotrophic factor and vascular endothelial growth factor), and inhibited the glial scar formation, which was indicated by immunohistochemistry with glial fibrillary acidic protein. Finally, Ngn2-ADSCs-treated animals showed the highest functional recovery among the three groups. These findings suggest that transplantation of Ngn2-overexpressed ADSCs promote the functional recovery from SCI, and improve the local microenvironment of injured cord in a more efficient way than that with ADSCs alone.

Motor and Sensory Deficits in the teetering Mice Result from Mutation of the ESCRT Component HGS

Neurons are particularly vulnerable to perturbations in endo-lysosomal transport, as several neurological disorders are caused by a primary deficit in this pathway. In this report, we used positional cloning to show that the spontaneously occurring neurological mutation teetering (tn) is a single nucleotide substitution in hepatocyte growth factor-regulated tyrosine kinase substrate (Hgs/Hrs), a component of the endosomal sorting complex required for transport (ESCRT). The tn mice exhibit hypokenesis, muscle weakness, reduced muscle size and early perinatal lethality by 5-weeks of age. Although HGS has been suggested to be essential for the sorting of ubiquitinated membrane proteins to the lysosome, there were no alterations in receptor tyrosine kinase levels in the central nervous system, and only a modest decrease in tropomyosin receptor kinase B (TrkB) in the sciatic nerves of the tn mice. Instead, loss of HGS resulted in structural alterations at the neuromuscular junction (NMJ), including swellings and ultra-terminal sprouting at motor axon terminals and an increase in the number of endosomes and multivesicular bodies. These structural changes were accompanied by a reduction in spontaneous and evoked release of acetylcholine, indicating a deficit in neurotransmitter release at the NMJ. These deficits in synaptic transmission were associated with elevated levels of ubiquitinated proteins in the synaptosome fraction. In addition to the deficits in neuronal function, mutation of Hgs resulted in both hypermyelinated and dysmyelinated axons in the tn mice, which supports a growing body of evidence that ESCRTs are required for proper myelination of peripheral nerves. Our results indicate that HGS has multiple roles in the nervous system and demonstrate a previously unanticipated requirement for ESCRTs in the maintenance of synaptic transmission.

Endocytic trafficking involves the internalization, endosomal sorting and lysosomal degradation of cell surface cargo. Many factors involved in endosomal sorting in mammalian cells have been identified, and mutations in these components are associated with a variety of neurological disorders. While the function of endosomal sorting components has been intensely studied in immortalized cell lines, it is not known what role these factors play in endosomal sorting in the nervous system. In this study, we show that the teetering (tn) gene encodes the hepatocytegrowth factor regulated tyrosine kinasesubstrate (Hgs), a core component of the endosomal sorting pathway. The tn mice exhibit several signs of motor neuron disease, including reduced muscle mass, muscle weakness and motor abnormalities. Although HGS is predicted to be required for the lysosomal degradation of receptor tyrosine kinases, there was no change in the levels of receptor tyrosine kinases in the spinal cords of the tn mice. Instead, we found that HGS is required for synaptic transmission at the neuromuscular junction and for the proper myelination of the peripheral nervous system.

Transcriptional Regulation of Brain-Derived Neurotrophic Factor (BDNF) by Methyl CpG Binding Protein 2 (MeCP2): a Novel Mechanism for Re-Myelination and/or Myelin Repair Involved in the Treatment of Multiple Sclerosis (MS)

Multiple sclerosis (MS) is a chronic progressive, neurological disease characterized by the targeted immune system-mediated destruction of central nervous system (CNS) myelin. Autoreactive CD4+ T helper cells have a key role in orchestrating MS-induced myelin damage. Once activated, circulating Th1-cells secrete a variety of inflammatory cytokines that foster the breakdown of blood-brain barrier (BBB) eventually infiltrating into the CNS. Inside the CNS, they become reactivated upon exposure to the myelin structural proteins and continue to produce inflammatory cytokines such as tumor necrosis factor α (TNFα) that leads to direct activation of antibodies and macrophages that are involved in the phagocytosis of myelin. Proliferating oligodendrocyte precursors (OPs) migrating to the lesion sites are capable of acute remyelination but unable to completely repair or restore the immune system-mediated myelin damage. This results in various permanent clinical neurological disabilities such as cognitive dysfunction, fatigue, bowel/bladder abnormalities, and neuropathic pain. At present, there is no cure for MS. Recent remyelination and/or myelin repair strategies have focused on the role of the neurotrophin brain-derived neurotrophic factor (BDNF) and its upstream transcriptional repressor methyl CpG binding protein (MeCP2). Research in the field of epigenetic therapeutics involving histone deacetylase (HDAC) inhibitors and lysine acetyl transferase (KAT) inhibitors is being explored to repress the detrimental effects of MeCP2. This review will address the role of MeCP2 and BDNF in remyelination and/or myelin repair and the potential of HDAC and KAT inhibitors as novel therapeutic interventions for MS.

Combining acellular nerve allografts with brain-derived neurotrophic factor transfected bone marrow mesenchymal stem cells restores sciatic nerve injury better than either intervention alone

In this study, we chemically extracted acellular nerve allografts from bilateral sciatic nerves, and repaired 10-mm sciatic nerve defects in rats using these grafts and brain-derived neurotrophic factor transfected bone marrow mesenchymal stem cells. Experiments were performed in three groups: the acellular nerve allograft bridging group, acellular nerve allograft + bone marrow mesenchymal stem cells group, and the acellular nerve allograft + brain-derived neurotrophic factor transfected bone marrow mesenchymal stem cells group. Results showed that at 8 weeks after bridging, sciatic functional index, triceps wet weight recovery rate, myelin thickness, and number of myelinated nerve fibers were significantly changed in the three groups. Variations were the largest in the acellular nerve allograft + brain-derived neurotrophic factor transfected bone marrow mesenchymal stem cells group compared with the other two groups. Experimental findings suggest that chemically extracted acellular nerve allograft combined nerve factor and mesenchymal stem cells can promote the restoration of sciatic nerve defects. The repair effect seen is better than the single application of acellular nerve allograft or acellular nerve allograft combined mesenchymal stem cell transplantation.

Hyaluronan tetrasaccharide exerts neuroprotective effect and promotes functional recovery after acute spinal cord injury in rats

The objective of this study was to explore the therapeutic efficiency of hyaluronan tetrasaccharide (HA4) treatment after spinal cord injury (SCI) in rats and to investigate the underlying mechanism. Locomotor functional and electrophysiological evaluations revealed that the behavioral function of rats in the HA4-treated group was significantly improved compared with the vehicle-treated group. The expression of brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF), cluster determinant (CD44) and Toll-like receptor-4 (TLR-4) was obviously upregulated in the HA4-treated group than that in the sham and vehicle-treated group. Furthermore, HA4 could induce BDNF and VEGF expression in the astrocytes in vitro. In addition, the high expression of BDNF and VEGF could be inhibited by blocking CD44 and TLR-4. These findings indicate that HA4 could be useful as a promising therapeutic agent for SCI and might exert the effect by interaction with the CD44 and TLR-4.

Delayed nerve stimulation promotes axon-protective neurofilament phosphorylation, accelerates immune cell clearance and enhances remyelination in vivo in focally demyelinated nerves

Rapid and efficient axon remyelination aids in restoring strong electrochemical communication with end organs and in preventing axonal degeneration often observed in demyelinating neuropathies. The signals from axons that can trigger more effective remyelination in vivo are still being elucidated. Here we report the remarkable effect of delayed brief electrical nerve stimulation (ES; 1 hour @ 20 Hz 5 days post-demyelination) on ensuing reparative events in a focally demyelinated adult rat peripheral nerve. ES impacted many parameters underlying successful remyelination. It effected increased neurofilament expression and phosphorylation, both implicated in axon protection. ES increased expression of myelin basic protein (MBP) and promoted node of Ranvier re-organization, both of which coincided with the early reappearance of remyelinated axons, effects not observed at the same time points in non-stimulated demyelinated nerves. The improved ES-associated remyelination was accompanied by enhanced clearance of ED-1 positive macrophages and attenuation of glial fibrillary acidic protein expression in accompanying Schwann cells, suggesting a more rapid clearance of myelin debris and return of Schwann cells to a nonreactive myelinating state. These benefits of ES correlated with increased levels of brain derived neurotrophic factor (BDNF) in the acute demyelination zone, a key molecule in the initiation of the myelination program. In conclusion, the tremendous impact of delayed brief nerve stimulation on enhancement of the innate capacity of a focally demyelinated nerve to successfully remyelinate identifies manipulation of this axis as a novel therapeutic target for demyelinating pathologies.

Double gene therapy with granulocyte colony-stimulating factor and vascular endothelial growth factor acts synergistically to improve nerve regeneration and functional outcome after sciatic nerve injury in mice

Peripheral-nerve injuries are a common clinical problem and often result in long-term functional deficits. Reconstruction of peripheral-nerve defects is currently undertaken with nerve autografts. However, there is a limited availability of nerves that can be sacrificed and the functional recovery is never 100% satisfactory. We have previously shown that gene therapy with vascular endothelial growth factor (VEGF) significantly improved nerve regeneration, neuronal survival, and muscle activity. Our hypothesis is that granulocyte colony-stimulating factor (G-CSF) synergizes with VEGF to improve the functional outcome after sciatic nerve transection. The left sciatic nerves and the adjacent muscle groups of adult mice were exposed, and 50 or 100 μg (in 50 μl PBS) of VEGF and/or G-CSF genes was injected locally, just below the sciatic nerve, and transferred by electroporation. The sciatic nerves were transected and placed in an empty polycaprolactone (PCL) nerve guide, leaving a 3-mm gap to challenge nerve regeneration. After 6 weeks, the mice were perfused and the sciatic nerve, the dorsal root ganglion (DRG), the spinal cord and the gastrocnemius muscle were processed for light and transmission electron microscopy. Treated animals showed significant improvement in functional and histological analyses compared with the control group. However, the best results were obtained with the G-CSF+VEGF-treated animals: quantitative analysis of regenerated nerves showed a significant increase in the number of myelinated fibers and blood vessels, and the number of neurons in the DRG and motoneurons in the spinal cord was significantly higher. Motor function also showed that functional recovery occurred earlier in animals receiving G-CSF+VEGF-treatment. The gastrocnemius muscle showed an increase in weight and in the levels of creatine phosphokinase, suggesting an improvement of reinnervation and muscle activity. These results suggest that these two factors acted synergistically and optimized the nerve repair potential, improving regeneration after a transection lesion.

Fluoxetine ameliorates behavioral and neuropathological deficits in a transgenic model mouse of α-synucleinopathy

The term α-synucleinopathies refers to a group of age-related neurological disorders including Parkinson's disease (PD), Dementia with Lewy Bodies (DLB) and Multiple System Atrophy (MSA) that display an abnormal accumulation of alpha-synuclein (α-syn). In contrast to the neuronal α-syn accumulation observed in PD and DLB, MSA is characterized by a widespread oligodendrocytic α-syn accumulation. Transgenic mice expressing human α-syn under the oligodendrocyte-specific myelin basic protein promoter (MBP1-hαsyn tg mice) model many of the behavioral and neuropathological alterations observed in MSA. Fluoxetine, a selective serotonin reuptake inhibitor, has been shown to be protective in toxin-induced models of PD, however its effects in an in vivo transgenic model of α-synucleinopathy remain unclear. In this context, this study examined the effect of fluoxetine in the MBP1-hαsyn tg mice, a model of MSA. Fluoxetine administration ameliorated motor deficits in the MBP1-hαsyn tg mice, with a concomitant decrease in neurodegenerative pathology in the basal ganglia, neocortex and hippocampus. Fluoxetine administration also increased levels of the neurotrophic factors, GDNF (glial-derived neurotrophic factor) and BDNF (brain-derived neurotrophic factor) in the MBP1-hαsyn tg mice compared to vehicle-treated tg mice. This fluoxetine-induced increase in GDNF and BDNF protein levels was accompanied by activation of the ERK signaling pathway. The effects of fluoxetine administration on myelin and serotonin markers were also examined. Collectively these results indicate that fluoxetine may represent a novel therapeutic intervention for MSA and other neurodegenerative disorders.

An in vivo characterization of trophic factor production following neural precursor cell or bone marrow stromal cell transplantation for spinal cord injury

Cellular transplantation strategies for repairing the injured spinal cord have shown consistent benefit in preclinical models, and human clinical trials have begun. Interactions between transplanted cells and host tissue remain poorly understood. Trophic factor secretion is postulated a primary or supplementary mechanism of action for many transplanted cells, however, there is little direct evidence to support trophin production by transplanted cells in situ. In the present study, trophic factor expression was characterized in uninjured, injured-untreated, injured-treated with transplanted cells, and corresponding control tissue from the adult rat spinal cord. Candidate trophic factors were identified in a literature search, and primers were designed for these genes. We examined in vivo trophin expression in 3 paradigms involving transplantation of either brain or spinal cord-derived neural precursor cells (NPCs) or bone marrow stromal cells (BMSCs). Injury without further treatment led to a significant elevation of nerve growth factor (NGF), leukemia inhibitory factor (LIF), insulin-like growth factor-1 (IGF-1), and transforming growth factor-β1 (TGF-β1), and lower expression of vascular endothelial growth factor isoform A (VEGF-A) and platelet-derived growth factor-A (PDGF-A). Transplantation of NPCs led to modest changes in trophin expression, and the co-administration of intrathecal trophins resulted in significant elevation of the neurotrophins, glial-derived neurotrophic factor (GDNF), LIF, and basic fibroblast growth factor (bFGF). BMSCs transplantation upregulated NGF, LIF, and IGF-1. NPCs isolated after transplantation into the injured spinal cord expressed the neurotrophins, ciliary neurotrophic factor (CNTF), epidermal growth factor (EGF), and bFGF at higher levels than host cord. These data show that trophin expression in the spinal cord is influenced by injury and cell transplantation, particularly when combined with intrathecal trophin infusion. Trophins may contribute to the benefits associated with cell-based repair strategies for spinal cord injury.

In vitro characterization of trophic factor expression in neural precursor cells

In cellular transplantation strategies for repairing the injured central nervous system, interactions between transplanted neural precursor cells (NPCs) and host tissue remain incompletely understood. Although trophins may contribute to the benefits observed, little research has explored this possibility. Candidate trophic factors were identified, and primers were designed for these genes. Template RNA was isolated from 3 NPC sources, and also from bone marrow stromal cells (BMSCs) and embryonic fibroblasts as comparative controls. Quantitative polymerase chain reaction was performed to determine the effect of cell source, passaging, cellular differentiation, and environmental changes on trophin factor expression in NPCs. Results were analyzed with multivariate statistical analyses. NPCs, BMSCs, and fibroblasts each expressed trophic factors in unique patterns. Trophic factor expression was similar among NPCs whether harvested from rat or mouse, brain or spinal cord, or their time in culture. The expression of neurotrophin NT-3, NT-4/5, glial-derived neurotrophic factor, and insulin-like growth factor-1 decreased with time in culture. Induced differentiation of NPCs led to a marked and statistically significant increase in the expression of trophic factors. Culture conditions and environmental changes were also associated with significant changes in trophin expression. These results suggest that trophins could contribute to the benefits associated with transplantation of NPCs as well as BMSCs. Trophic factor expression changes with NPC differentiation and environmental conditions, which could have important implications with regard to their behavior after in vivo transplantation.

Phosphodiesterase-5 is a therapeutic target for peripheral neuropathy in diabetic mice

Peripheral neuropathy is a common and major complication of diabetes, the underlying mechanisms of which are not fully understood. Using a mouse model of type II diabetes, the present study investigated the role of phosphodiesterase-5 (PDE5) in peripheral neuropathy. BKS.Cg-m+/+Leprdb/J (db/db) mice were treated with sildenafil, a specific inhibitor of PDE5, at doses of 2 and 10 mg/kg or saline. Levels of PDE5 and morphometric parameters in sciatic nerve tissue as well as the motor and sensory function were measured in these mice. In diabetic mice, PDE5 expression in sciatic nerve tissue was significantly upregulated, whereas the myelin sheath thickness, myelin basic protein (MBP), and subcutaneous nerve fibers were significantly reduced. Treatment with sildenafil significantly improved neurological function, assayed by motor and sensory conducting velocities and thermal and mechanical noxious stimuli, concomitantly with increases in myelin sheath thickness, MBP levels, and subcutaneous nerve fibers. In vitro, hyperglycemia upregulated PDE5 in Schwann cells and reduced Schwann cell proliferation, migration, and expression of brain-derived neurotrophic factor (BDNF). Blockage of PDE5 with sildenafil increased cyclic guanosine monophosphate (cGMP) and completely abolished the effect of hyperglycemia on Schwann cells. Sildenafil upregulated cGMP-dependent protein kinase G I (PKGI), whereas inhibition of PKGI with a PKG inhibitor, KT5823, suppressed the inhibitory effect of sildenafil on Schwann cells. These data indicate that hyperglycemia substantially upregulates PDE5 expression and that the cGMP/PKG signaling pathway activated by sildenafil mediates the beneficial effects of sildenafil on diabetic peripheral neuropathy.

Short-term low-frequency electrical stimulation enhanced remyelination of injured peripheral nerves by inducing the promyelination effect of brain-derived neurotrophic factor on Schwann cell polarization

Electrical stimulation (ES) has been found to aid repair of nerve injuries and have been shown to increase and direct neurite outgrowth during stimulation. However, the effect of ES on peripheral remyelination after nerve damage has been investigated less well, and the mechanism underlying its action remains unclear. In the present study, the crush-injured sciatic nerves in rats were subjected to 1 hr of continuous ES (20 Hz, 100 microsec, 3 V). Electron microscopy and nerve morphometry were performed to investigate the extent of regenerated nerve myelination. The expression profiles of P0, Par-3, and brain-derived neurotrophic factor (BDNF) in the injuried sciatic nerves and in the dorsal root ganglion neuron/Schwann cell cocultures were examined by Western blotting. Par-3 localization in the sciatic nerves was determined by immunohistochemistry to demonstrate Schwann cell polarization during myelination. We reported that 20-Hz ES increased the number of myelinated fibers and the thickness myelin sheath at 4 and 8 weeks postinjury. P0 level in the ES-treated groups, both in vitro and in vivo, was enhanced compared with the controls. The earlier peak of Par-3 in the ES-treated groups indicated an earlier initiation of Schwann cell myelination. Additionally, ES significantly elevated BDNF expression in nerve tissues and in cocultures. ES on the site of nerve injury potentiates axonal regrowth and myelin maturation during peripheral nerve regeneration. Furthermore, the therapeutic actions of ES on myelination are mediated via enhanced BDNF signals, which drive the promyelination effect on Schwann cells at the onset of myelination.

Brain-derived neurotrophic factor promotes central nervous system myelination via a direct effect upon oligodendrocytes

The extracellular factors that are responsible for inducing myelination in the central nervous system (CNS) remain elusive. We investigated whether brain-derived neurotrophic factor (BDNF) is implicated, by first confirming that BDNF heterozygous mice exhibit delayed CNS myelination during early postnatal development. We next established that the influence of BDNF upon myelination was direct, by acting on oligodendrocytes, using co-cultures of dorsal root ganglia neurons and oligodendrocyte precursor cells. Importantly, we found that BDNF retains its capacity to enhance myelination of neurons or by oligodendrocytes derived from p75NTR knockout mice, indicating the expression of p75NTR is not necessary for BDNF-induced myelination. Conversely, we observed that phosphorylation of TrkB correlated with myelination, and that inhibiting TrkB signalling also inhibited the promyelinating effect of BDNF, suggesting that BDNF enhances CNS myelination via activating oligodendroglial TrkB-FL receptors. Together, our data reveal a previously unknown role for BDNF in potentiating the normal development of CNS myelination, via signalling within oligodendrocytes.

Simvastatin treatment improves functional recovery after experimental spinal cord injury by upregulating the expression of BDNF and GDNF

The aim of this study was to determine the therapeutic efficacy of simvastatin treatment starting 1 day after spinal cord injury (SCI) in rat and to investigate the underlying mechanism. Spinal cord injury was induced in adult female Sprague-Dawley rats after laminectomy at T9-T10. Then additionally with sham group (laminectomy only) the SCI animals were randomly divided into 3 groups: vehicle-treated group; 5-mg/kg simvastatin-treated group; and 10-mg/kg simvastatin-treated group. Simvastatin or vehicle was administered orally at 1 day after SCI and then daily for 5 weeks. Locomotor functional recovery was assessed during 8 weeks postoperation by performing open-field locomotor test and inclined-plane test. At the end of study, motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) were assessed to evaluate the integrity of spinal cord pathways. Then, the animals were killed, and 1-cm segments of spinal cord encompassing the injury site were removed for histopathological analysis. Immunohistochemistry was performed to observe the expression of brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF) in the spinal cord. Results show that the simvastatin-treated animals showed significantly better locomotor function recovery, better electrophysiological outcome, less myelin loss, and higher expression of BDNF and GDNF. These findings suggest that simvastatin treatment starting 1 day after SCI can significantly improve locomotor recovery, and this neuroprotective effect may be related to the upregulation of BDNF and GDNF. Therefore, simvastatin may be useful as a promising therapeutic agent for SCI.

Over-expression of alpha-synuclein in the nervous system enhances axonal degeneration after peripheral nerve lesion in a transgenic mouse strain

Wallerian degeneration in peripheral nerves occurs after a traumatic insult when the distal nerve part degenerates while peripheral macrophages enter the nerve stump and remove the accruing debris by phagozytosis. We used an experimental model to investigate the effect of either the absence or over-expression of alpha-synuclein (alpha-syn) after transecting the sciatic nerves of mice. alpha-Synuclein is a major component of Lewy bodies and its aggregation results in a premature destruction of nerve cells. It has also been found present in different peripheral nerves but its role in the axon remains still unclear. Following sciatic nerve transection in different mouse strains, we investigated the numbers of invading macrophages, the amounts of remaining myelin and axons 6 days after injury. All mice showed clear signs of Wallerian degeneration, but transgenic mice expressing human wild-type alpha-syn showed lower numbers of invading macrophages, less preserved myelin and significantly lower numbers of preserved axons in comparison with either knockout mice or a mouse strain with a spontaneous deletion of alpha-syn. The use of protein aggregation filtration blots and paraffin-embedded tissue blots displayed depositions of alpha-syn aggregates within sciatic nerve axons of transgenic mice. Thicker myelin sheaths and higher numbers of mitochondria were detected in old alpha-syn transgenic mice. In a human sural nerve, alpha-syn could also be identified within axons. Thus, alpha-syn and its aggregates are not only a component of Lewy bodies and synapses but also of axons and these aggregates might interfere with axonal transport. alpha-Synuclein transgenic mice represent an appropriate model for investigations on axonal transport in neurodegenerative diseases.

Expression of NGF and GDNF family members and their receptors during peripheral nerve development and differentiation of Schwann cells in vitro

Ligands of NGF and GDNF families of neurotrophic factors have important functions in the development of the vertebrate peripheral nervous system (PNS). It has been established that they also play key roles in the regeneration of PNS. Expression patterns of NGF and GDNF family members and their receptors have mostly been analyzed during regeneration, and less during development of the PNS. We describe the expression of mRNAs encoding these neurotrophic factors and their receptors during development of rat sciatic nerve and in three modes of differentiation of cultured rat Schwann cells. Our results demonstrate specific expression patterns of NGF and GDNF family ligands and their receptors during differentiation of Schwann cells in vivo and in vitro.

BDNF mRNA expression is significantly upregulated in vestibular schwannomas and correlates with proliferative activity

The expression of neurotrophic factors, such as artemin, glial cell line-derived neurotrophic factor (GDNF), neurturin, transforming growth factors (TGF)-beta1/beta2 and brain-derived neurotrophic factor (BDNF), is enhanced in vestibular schwannomas compared to peripheral nerves. Furthermore, this upregulation may correlate with mitotic activity. Vestibular schwannoma arising from Schwann cells of the vestibular nerve are mostly benign and slow-growing. Most of the pathogenic mechanisms regulating the vestibular schwannoma growth process are unknown. An impaired growth regulation and imbalance between mitosis and apoptosis can be assumed. However, molecular mechanisms interfering with regulation of the vestibular schwannoma growth also modulated by mitogenic factors have to be identified. Neurotrophic factors are involved in regulation of developmental processes in neuronal tissues and regeneration after peripheral nerve trauma and also reveal mitogenic effects on glial cell populations. Gene expression profiles of artemin, BDNF, GDNF, TGF-beta1/beta2 and Ret were determined in the vestibular schwannoma in comparison to the peripheral nerve tissues by using semiquantitative RT-PCR. The expression data were correlated to the proliferation-associated Ki-67 labelling index. A significant higher BDNF expression was observed in the vestibular schwannoma, whereas gene expression of artemin and GDNF was upregulated in peripheral nerves. The correlation between LI and BDNF, TGF-beta1 and Ret was found to be significant in the vestibular schwannoma. Our results demonstrate a coherence between BDNF expression and proliferative activity in the vestibular schwannoma. Based on these results, we propose a pivotal role for BDNF in modulating the vestibular schwannoma growth.

Corpus callosum size and shape alterations in individuals with bipolar disorder and their first-degree relatives

Reductions in the size of the corpus callosum (CC) have been described in patients with bipolar disorder (BD), although the contribution of genetic factors to these changes is unclear. We previously showed a global thinning of the CC in BD patients, and found those with a family history of affective disorders had a larger CC than those without. In this study, we compared callosal size and shape in 180 individuals: 70 with BD, 45 of their first-degree relatives, and 75 healthy controls. The callosum was extracted from a mid-sagittal slice from T1-weighted magnetic resonance images, and its total area, length and curvature were compared across groups. A non-parametric permutation method was used to examine for alterations in width of the callosum along 39 points. Validating our previous findings, a significant global reduction in callosal thickness was seen in BD patients, with a disproportionate thinning in the anterior body. First-degree relatives did not differ in callosal size or shape from controls. In BD patients, duration of illness and age were associated with thinning in the anterior body; BD patients on lithium treatment showed a thicker anterior mid-body than those on other psychotropics. Global and regional thinning of the callosum is seen in BD but not in their first-degree relatives. This suggests that CC abnormalities are linked to disease expression in BD and may not represent a marker of familial predisposition.

BDNF exerts contrasting effects on peripheral myelination of NGF-dependent and BDNF-dependent DRG neurons

Although brain-derived neurotrophic factor (BDNF) has been shown to promote peripheral myelination during development and remyelination after injury, the precise mechanisms mediating this effect remain unknown. Here, we determine that BDNF promotes myelination of nerve growth factor-dependent neurons, an effect dependent on neuronal expression of the p75 neurotrophin receptor, whereas BDNF inhibits myelination of BDNF-dependent neurons via the full-length TrkB receptor. Thus, BDNF exerts contrasting effects on Schwann cell myelination, depending on the complement of BDNF receptors that are expressed by different subpopulations of dorsal root ganglion neurons. These results demonstrate that BDNF exerts contrasting modulatory roles in peripheral nervous system myelination, and that its mechanism of action is acutely regulated and specifically targeted to neurons.

Brain-derived neurotrophic factor effects on oligodendrocyte progenitors of the basal forebrain are mediated through trkB and the MAP kinase pathway

Previous work has indicated that BDNF increases the differentiation of basal forebrain (BF) oligodendrocytes (OLGs) in culture through the mediation of trkB and the MAPK pathway (Du et al. [ 2006a, b] Mol. Cell. Neurosci. 31:366-375; J. Neurosci. Res. 84:1692-1702). In the present work, effects of BDNF on BF OLG progenitor cells (OPCs) were examined. BDNF increased DNA synthesis of OPCs, as assessed by thymidine and bromodeoxyuridine incorporation. Effects of BDNF on DNA synthesis were mediated through the trkB receptor and not the p75 receptor, as shown by inhibitors that block neurotrophin binding to the receptors and by the phosphorylation of trkB. TrkB can activate the mitogen- activated protein kinase (MAPK), phosphatidylinositol-3 kinase (PI3-K), and phospholipase C-gamma (PLC-gamma) pathways. BDNF elicited the phosphorylation of MAPK and Akt, a kinase downstream of PI3K, but not PLC-gamma in OPCs. Through the use of specific inhibitors to the MAPK and PI3-K pathways, it was found that the MAPK pathway was responsible for the effect of BDNF on DNA synthesis. These data indicate that BDNF affects OPC proliferation and development through the mediation of trkB and the MAPK pathway.

Physiological role of basic FGF in peripheral nerve development and regeneration: potential for reconstruction approaches

According to expression studies and functional analyses in mutant mice and in rats, FGF-2 appears to be specifically involved during development of peripheral nerves and in de-/re-generating processes at the lesion site and in spinal ganglia. In the absence of FGF receptor (FGFR)3, axonal and myelin diameters of peripheral nerves are significantly reduced, suggesting that FGFR3 physiologically regulates axonal development. The normally occurring neuronal cell death in spinal ganglia after peripheral nerve axotomy does not take place in FGF-2 and FGFR3-deleted mice, respectively, suggesting that injury-induced apoptosis is mediated via FGF-2 binding to FGFR3. According to a bimodal function of FGF-2, lesion-induced neuron death in rat spinal ganglia can be prevented by application of FGF-2 to the proximal nerve stump, which could be mediated via FGFR1/2. At the lesion site, FGF-2 appears to be involved in stimulating Schwann cell proliferation, promoting neurite outgrowth, especially of sensory nerve fibers, and regulating remyelination.

Deletion of the mouse RegIIIbeta (Reg2) gene disrupts ciliary neurotrophic factor signaling and delays myelination of mouse cranial motor neurons

A large number of cytokines and growth factors support the development and subsequent maintenance of postnatal motor neurons. RegIIIbeta, also known as Reg2 in rat and HIP/PAP1 in humans, is a member of a family of growth factors found in many areas of the body and previously shown to play an important role in both the development and regeneration of subsets of motor neurons. It has been suggested that RegIIIbeta expressed by motor neurons is both an obligatory intermediate in the downstream signaling of the leukemia inhibitory factor/ciliary neurotrophic factor (CNTF) family of cytokines, maintaining the integrity of motor neurons during development, as well as a powerful influence on Schwann cell growth during regeneration of the peripheral nerve. Here we report that in mice with a deletion of the RegIIIbeta gene, motor neuron survival was unaffected up to 28 weeks after birth. However, there was no CNTF-mediated rescue of neonatal facial motor neurons after axotomy in KO animals when compared with wild-type. In mice, RegIIIbeta positive motor neurons are concentrated in cranial motor nuclei that are involved in the patterning of swallowing and suckling. We found that suckling was impaired in RegIIIbeta KO mice and correlated this with a significant delay in myelination of the hypoglossal nerve. In summary, we propose that RegIIIbeta has an important role to play in the developmental fine-tuning of neonatal motor behaviors mediating the response to peripherally derived cytokines and growth factors and regulating the myelination of motor axons.

Developmental loss of NT-3 in vivo results in reduced levels of myelin-specific proteins, a reduced extent of myelination and increased apoptosis of Schwann cells

This work investigates the role of NT-3 in peripheral myelination. Recent articles, based in vitro, propose that NT-3 acting through its high-affinity receptor TrkC may act to inhibit myelin formation by enhancing Schwann cell motility and/or migration. Here, we investigate this hypothesis in vivo by examining myelination formation in NT-3 mutant mice. On the day of birth, soon after the onset of myelination, axons showed normal ensheathment by Schwann cells, no change in the proportion of axons which had begun to myelinate, and no change in either myelin thickness or number of myelin lamellae. However in postnatal day 21 mice, when myelination is substantially complete, we observed an unexpected reduction in mRNA and protein levels for MAG and P(0), and in myelin thickness. This is the opposite result to that predicted from previous in vitro studies, where removal of an inhibitory NT-3 signal would have been expected to enhance myelination. These results suggest that, in vivo, the importance of NT-3 as a major support factor for Schwann cells (Meier et al., (1999) J Neurosci 19:3847-3859) over-rides its potential role as an myelin inhibitor, with the net effect that loss of NT-3 results in degradation of Schwann cell functions, including myelination. In support of this idea, Schwann cells of NT-3 null mutants showed increased expression of activated caspase-3. Finally, we observed significant reduction in width of the Schwann cell periaxonal collar in NT-3 mutant animals suggesting that loss of NT-3 and resulting reduction in MAG levels may alter signaling at the axon-glial interface.