Neurite Degeneration Research Articles

High fidelity neuronal networks formed by plasma masking with a bilayer membrane: analysis of neurodegenerative and neuroprotective processes

Spatially defined neuronal networks have great potential to be used in a wide spectrum of neurobiology assays. We present an original technique for the precise and reproducible formation of neuronal networks. A PDMS membrane comprising through-holes aligned with interconnecting microchannels was used during oxygen plasma etching to dry mask a protein rejecting poly(ethylene glycol) (PEG) adlayer. Patterns were faithfully replicated to produce an oxidized interconnected array pattern which supported protein adsorption. Differentiated human SH-SY5Y neuron-like cells adhered to the array nodes with the micron-scale interconnecting tracks guiding neurite outgrowth to produce neuronal connections and establish a network. A 2.0 μm track width was optimal for high-level network formation and node compliance. These spatially standardized neuronal networks were used to analyse the dynamics of acrylamide-induced neurite degeneration and the protective effects of co-treatment with calpeptin or brain derived neurotrophic factor (BDNF).

Study on hydrogen peroxide-induced neurite degeneration and neuroprotective effect of vitamin E

Study on hydrogen peroxide-induced neurite degeneration and neuroprotective effect of vitamin E

The Suppression of CRMP2 Expression by Bone Morphogenetic Protein (BMP)-SMAD Gradient Signaling Controls Multiple Stages of Neuronal Development

The formation of the functional mammalian cerebral cortex requires a concerted control of neurogenesis, neuronal migration, and neuronal morphogenesis. However, molecular mechanisms that control these processes are not well understood. We have found that the BMP signaling downstream transcription factor SMAD1 and CRMP2 (collapsin response mediator protein-2) are inversely and complementarily expressed in the developing neocortex. BMPs can suppress CRMP2 expression in cortical cells. Our ChIP assay demonstrates that both SMAD1 and -4 bind to CRMP2 promoter in the neocortex, and overexpression of SMAD1 and 4 in vivo suppresses CRMP2 expression. RNA interference of CRMP2 and overexpression of dominant negative forms of CRMP2 in utero cause accumulation of multipolar cells in the ventricular, subventricular, and intermediate zones and suppresses neurite outgrowth, suggesting that CRMP2 is required for multipolar to bipolar transition for directional neuronal migration and neurite outgrowth. Thus, our study reveals a novel mechanism that the BMP-SMAD signaling pathway controls neuronal migration and neurite outgrowth by suppressing the transcription of CRMP2.

Familial amyloid precursor protein mutants cause caspase-6-dependent but amyloid β-peptide-independent neuronal degeneration in primary human neuron cultures.

Although familial Alzheimer disease (AD)-associated autosomal dominant mutants have been extensively studied, little is known about the underlying molecular mechanisms of neurodegeneration induced by these mutants in AD. Wild-type, Swedish or London amyloid precursor protein (APP) transfection in primary human neurons induced neuritic beading, in which several co-expressed proteins, such as enhanced green fluorescent protein, red fluorescent protein (RFP)-tau and RFP-ubiquitin, accumulated. APP-induced neuritic beading was dependent on caspase-6 (Casp6), because it was inhibited with 5 μM z-VEID-fmk or with dominant-negative Casp6. Neuritic beading was independent from APP-mediated amyloid β-peptide (Aβ) production, because the APPM596V (APPMV) mutant, which cannot generate Aβ, still induced Casp6-dependent neuritic beading. However, the beaded neurons underwent Casp6- and Aβ-dependent cell death. These results indicate that overexpression of wild-type or mutant APP causes Casp6-dependent but Aβ-independent neuritic degeneration in human neurons. Because Casp6 is activated early in AD and is involved in axonal degeneration, these results suggest that the inhibition of Casp6 may represent an efficient early intervention against familial forms of AD. Furthermore, these results indicate that removing Aβ without inhibiting Casp6 may have little effect in preventing the progressive dementia associated with sporadic or familial AD.

IL-3 Control Tau Modifications and Protects Cortical Neurons from Neurodegeneration

Interleukin-3 (IL-3) regulates the proliferation, survival and differentiation of haematopoietic cells via interaction with specific cell-surface receptors. IL-3 is expressed in several non-hematopoietic cell types. Studies have demonstrated the presence of IL-3 in the central nervous system, however, its physiological role in these cells is poorly understood. Previously we have been demonstrated that IL-3 prevents neuronal death induced by fibrillary β amyloid in these cells, by PI 3-kinase and Jak/STAT pathway activation. In this study, we demonstrated that IL-3 significantly reduced Aβ-promoted neurite degeneration and toxicity. Thus, this cytokine provides cellular protection against Aβ neurotoxicity in primary cortical neuronal cells, by modulating microtubular dynamics and prevention of tau cleavage and hyperphosphorylation. We also demonstrates that IL-3 is expressed in the "in vivo" mouse model of AD, Tg2576, which also expresses human AβPP with the Swedish mutation. In summary, these results suggest that IL-3 could play a neuroprotective role in AD.

Modified Immunotherapies Against Alzheimer's Disease: Toward Safer and Effective Amyloid-β Clearance

Alzheimer's disease (AD) is characterized by the deposition of amyloid plaques, loss of neurons, neuritic degeneration, accumulation of fibrillary tangles in neurons, and a progressive loss of cognitive function. Amyloid-β peptide (Aβ) appears to play a pivotal role in the development of AD. Clearance of Aβ from the brain represents an important therapeutic strategy for prevention and treatment of AD. Immunotherapy targeting Aβ is effective to remove the peptide from the brain. However, it is associated with detrimental adverse effects, such as autoimmune meningoencephalitis and microhemorrhage. These are presumably the results of brain infiltration of provoked autoimmune T lymphocytes in response to Aβ vaccination and release of proinflammatory cytokines from microglia activated by the immune complex of Aβ and antibodies. An improvement of the safety of the immunotherapy is a major goal of the immunotherapy study. Here, we review the mechanisms involved in modified immunological strategies, as well as their adverse effects. We discuss the following: the development of B epitope vaccines to avoid activation of autoimmune T lymphocytes; DNA vaccines containing appropriate immunostimulatory and immunomodulatory sequences to induce the desired humoral immune responses; antibody modifications to avoid activation of microglia and subsequent release of proinflammatory cytokines; single chain antibodybased gene therapy; immunotherapy targeting Aβ oligomers; modulation of antibody delivery approach and dose; and application of autoantibodies against Aβ. These ultimately represent future directions of therapeutic approaches toward safer and effective Aβ clearance.

Prevention of oxaliplatin-induced mechanical allodynia and neurodegeneration by neurotropin in the rat model

Oxaliplatin is a key drug for colorectal cancer, but it causes acute peripheral neuropathy (triggered by cold) and chronic neuropathy (sensory and motor neuropathy) in patients. Neurotropin, a non-protein extract from the inflamed rabbit skin inoculated with vaccinia virus, has been used to treat various chronic pains. In the present study, we investigated the effect of neurotropin on the oxaliplatin-induced neuropathy in rats. Repeated administration of oxaliplatin caused cold hyperalgesia from Day 5 to Day 29 and mechanical allodynia from Day 15 to Day 47. Repeated administration of neurotropin relieved the oxaliplatin-induced mechanical allodynia but not cold hyperalgesia, and inhibited the oxaliplatin-induced axonal degeneration in rat sciatic nerve. Neurotropin also inhibited the oxaliplatin-induced neurite degeneration in cultured pheochromocytoma 12 (PC12) and rat dorsal root ganglion (DRG) cells. On the other hand, neurotropin did not affect the oxaliplatin-induced cell injury in rat DRG cells. These results suggest that repeated administration of neurotropin relieves the oxaliplatin-induced mechanical allodynia by inhibiting the axonal degeneration and it is useful for the treatment of oxaliplatin-induced neuropathy clinically.

Cellular Source of Apolipoprotein E4 Determines Neuronal Susceptibility to Excitotoxic Injury in Transgenic Mice

The lipid transport protein apolipoprotein E (apoE) is abundantly expressed in the brain. Its main isoforms in humans are apoE2, apoE3, and apoE4. ApoE4 is the major known genetic risk factor for Alzheimer's disease and also contributes to the pathogenesis of various other neurological conditions. In the central nervous system, apoE is synthesized by glial cells and neurons, but it is unclear whether the cellular source affects its biological activities. To address this issue, we induced excitotoxic injury by systemic kainic acid injection in transgenic Apoe knockout mice expressing human apoE isoforms in astrocytes or neurons. Regardless of its cellular source, apoE3 expression protected neuronal synapses and dendrites against the excitotoxicity seen in apoE-deficient mice. Astrocyte-derived apoE4, which has previously been shown to have detrimental effects in vitro, was as excitoprotective as apoE3 in vivo. In contrast, neuronal expression of apoE4 was not protective and resulted in loss of cortical neurons after excitotoxic challenge, indicating that neuronal apoE4 promotes excitotoxic cell death. Thus, an imbalance between astrocytic (excitoprotective) and neuronal (neurotoxic) apoE4 expression may increase susceptibility to diverse neurological diseases involving excitotoxic mechanisms.

Gypenosides protects dopaminergic neurons in primary culture against MPP +-induced oxidative injury

Oxidative injury has been implicated in the etiology of Parkinson's disease (PD). Gypenosides (GPs), the saponins extract derived from the Gynostemma pentaphyllum, has various bioactivities. In this study, GPs was investigated for its neuroprotective effects on the 1-methyl-4-phenylpyridinium ion (MPP +)-induced oxidative injury of dopaminergic neurons in primary nigral culture. It was found that GPs pretreatment, cotreatment or posttreatment significantly and dose-dependently attenuated MPP +-induced oxidative damage, reduction of dopamine uptake, loss of tyrosine hydrolase (TH)-immunopositive neurons and degeneration of TH-immunopositive neurites. However, the preventive effect of GPs was more potential than its therapeutical effect. Most importantly, the neuroprotective effect of GPs may be attributed to GPs-induced strengthened antioxidation as manifested by significantly increased glutathione content and enhanced activity of glutathione peroxidase, catalyze and superoxide dismutase in nigral culture. The neuroprotective effects of GPs are specific for dopaminergic neurons and it may have therapeutic potential in the treatment of PD.

Mutant HSPB8 causes motor neuron-specific neurite degeneration

Missense mutations (K141N and K141E) in the α-crystallin domain of the small heat shock protein HSPB8 (HSP22) cause distal hereditary motor neuropathy (distal HMN) or Charcot-Marie-Tooth neuropathy type 2L (CMT2L). The mechanism through which mutant HSPB8 leads to a specific motor neuron disease phenotype is currently unknown. To address this question, we compared the effect of mutant HSPB8 in primary neuronal and glial cell cultures. In motor neurons, expression of both HSPB8 K141N and K141E mutations clearly resulted in neurite degeneration, as manifested by a reduction in number of neurites per cell, as well as in a reduction in average length of the neurites. Furthermore, expression of the K141E (and to a lesser extent, K141N) mutation also induced spheroids in the neurites. We did not detect any signs of apoptosis in motor neurons, showing that mutant HSPB8 resulted in neurite degeneration without inducing neuronal death. While overt in motor neurons, these phenotypes were only very mildly present in sensory neurons and completely absent in cortical neurons. Also glial cells did not show an altered phenotype upon expression of mutant HSPB8. These findings show that despite the ubiquitous presence of HSPB8, only motor neurons appear to be affected by the K141N and K141E mutations which explain the predominant motor neuron phenotype in distal HMN and CMT2L.

Neurotoxic and peripheral neuropathic effects in preclinical and clinical studies of carfilzomib (CFZ), a novel proteasome inhibitor (PI).

8135 Background: Treatment-induced peripheral neuropathy (TIPN) is a common, frequently debilitating, therapy-limiting complication in multiple myeloma (MM). Chemotherapies associated with TIPN in MM include thalidomide and bortezomib (BTZ). CFZ, a novel, highly selective PI, is structurally and mechanistically distinct from BTZ. In Ph I-II trials single-agent CFZ is active without dose-limiting PN in pts with relapsed and/or refractory (R/R) MM. Here we compare CFZ and BTZ in a neurotoxicity model and report clinical experience with CFZ in R/R MM. Methods: An in vitro neurotoxicity model established with differentiated SH-SY5Y neuroblastoma cells was used to investigate PI effects on neurite degeneration. A possible mechanism was pursued by bioinformatic and biochemical methods. Data were pooled from 2, ongoing Ph II trials of single-agent CFZ in pts with R/R MM, including neuropathy history, baseline neuropathic symptoms and neurological exam findings, prospective neurological exams, and FACT-GOG/NTx pt survey scores. PN adverse event data were also included. Results: Following 24 hrs of exposure to 10 nM BTZ, SH-SY5Y cells showed 40% reduction in neurite length/cell compared to CFZ- or vehicle-treated cells. Both agents induced equivalent proteasomal inhibition suggesting off-target effects induce neurodegeneration. HtrA2/Omi, a mitochondrial serine protease with a role in neuron survival was identified in databases and confirmed as a target of BTZ (IC50 = 3 nM), but not of CFZ (>10 μ M). At screening, 72% of 135 pts had active Grade (G) 1/2 PN; 81% had a history of TIPN. Pts received a mean of 30.4 CFZ doses (range 2–72) and 17% received >10 mo of therapy. New onset PN or PN worsening from baseline was reported in 16% of pts. There were no reports of G4 PN, missed doses, or treatment discontinuations. Only 1 pt was dose-reduced due to PN. Conclusions: In contrast to BTZ TIPN, CFZ-related PN is uncommon and not dose-limiting. In vitro, BTZ induces neurotoxicity in a proteasome-independent manner and potently inhibits a neuronal cell survival factor, HtrA2. These in vitro and clinical data suggest that severe PN is not a PI class effect. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Onyx Bristol-Myers Squibb, Celgene, Facet, Millennium, Novartis, Onyx Onyx Celgene, Johnson & Johnson, Merck, Millennium, Onyx, Ortho, Takeda Bristol-Myers Squibb, Celgene, Facet, Gloucester Pharmaceuticals, Millennium, Novartis, Onyx

Immunohistochemical evidence for macroautophagy in neurones and endothelial cells in Alzheimer's disease

To determine the pathological structures associated with macroautophagy in Alzheimer's disease (AD) and any relationship to disease progression. Immunohistochemistry using antibodies to beclin-1, Atg5 and Atg12, early macroautophagy markers and LC3, the mammalian homologue of the later macroautophagy marker Atg8, were localized in formalin-fixed, paraffin-embedded medial temporal lobe sections of AD cases at variable neuritic disease stages. Double immunofluorescence labelling was used to co-localize these macroautophagy markers with Abeta and phospho-tau (AT8) and correlations performed using Spearman rank tests. Atg12 immunoreactivity in AD was either dispersed in the soma and dendrites or concentrated in tau-immunoreactive dystrophic neurites and some neurofibrillary tangles. Fewer Atg12-immunopositive neurones were observed with longer disease durations. Atg12-immunoreactive endothelial cells were found spatially associated with Abeta-positive plaques, with more Atg12-immunoreactive capillary endothelial cells with higher neuritic disease stage. These findings were confirmed by the other autophagy markers beclin-1, Atg5 and LC3. The data confirm that macroautophagy occurs in neurones undergoing neuritic degeneration in AD, identified early macroautophagy markers in capillary endothelial cells in close proximity to Abeta plaques, and found that evidence for macroautophagy changes with disease progression.

Axonal Degeneration Is Regulated by the Apoptotic Machinery or a NAD+-Sensitive Pathway in Insects and Mammals

Selective degeneration of neuronal projections and neurite pruning are critical for establishment and maintenance of functional neural circuits in both insects and mammals. However, the molecular mechanisms that govern developmental neurite pruning versus injury-induced neurite degeneration are still mostly unclear. Here, we show that the effector caspases 6 and 3 are both expressed within axons and that, on trophic deprivation, they exhibit distinct modes of activation. Surprisingly, inhibition of caspases is not sufficient for axonal protection and a parallel modulation of a NAD(+)-sensitive pathway is required. The proapoptotic protein BAX is a key element in both pathways as its genetic ablation protected sensory axons against developmental degeneration both in vitro and in vivo. Last, we demonstrate that both pathways are also involved in developmental dendritic pruning in Drosophila. More specifically, the mouse Wld(S) (Wallerian degeneration slow) protein, which is mainly composed of the full-length sequence of the NAD(+) biosynthetic Nmnat1 enzyme, can suppress dendritic pruning in C4da (class IV dendritic arborization) sensory neurons in parallel to the fly effector caspases. These findings indicate that two distinct autodestruction pathways act separately or in concert to regulate developmental neurite pruning.

Hallmark cellular pathology of Alzheimer’s disease induced by mutant human tau expression in cultured Aplysia neurons

The mechanisms underlying neurodegenerative diseases are the outcome of pathological alterations of evolutionary conserved molecular and cellular cascades. For this reason, Drosophila and C. elegans serve as useful model systems to study various aspects of neurodegenerative diseases. Here, we introduce the advantageous use of cultured Aplysia neurons (which express over 100 disease-related gene homologs shared with mammals), as a platform to study cell biological processes underlying the generation of tauopathy. Using live confocal imaging to follow cytoskeletal elements, autophagosomes, lysosomes, anterogradely and retrogradely transported organelles, complemented with electron microscopy, we demonstrate that the expression of mutant human tau in cultured Aplysia neurons leads to the development of hallmark Alzheimer disease (AD) pathologies. These include a reduction in the number of microtubules and their redistribution, impaired organelle transport, a dramatic accumulation of macro-autophagosomes and lysosomes, compromised neurite morphology and degeneration. Our study demonstrates the accessibility of the platform for long-term live imaging and quantification of subcellular pathological cascades leading to tauopathy. Based on the present study, it is conceivable that this system can also be used to screen for reagents that alter the pathological cascades.

Truncated beta-amyloid peptide channels provide an alternative mechanism for Alzheimer's Disease and Down syndrome.

Full-length amyloid beta peptides (Abeta(1-40/42)) form neuritic amyloid plaques in Alzheimer's disease (AD) patients and are implicated in AD pathology. However, recent transgenic animal models cast doubt on their direct role in AD pathology. Nonamyloidogenic truncated amyloid-beta fragments (Abeta(11-42) and Abeta(17-42)) are also found in amyloid plaques of AD and in the preamyloid lesions of Down syndrome, a model system for early-onset AD study. Very little is known about the structure and activity of these smaller peptides, although they could be the primary AD and Down syndrome pathological agents. Using complementary techniques of molecular dynamics simulations, atomic force microscopy, channel conductance measurements, calcium imaging, neuritic degeneration, and cell death assays, we show that nonamyloidogenic Abeta(9-42) and Abeta(17-42) peptides form ion channels with loosely attached subunits and elicit single-channel conductances. The subunits appear mobile, suggesting insertion of small oligomers, followed by dynamic channel assembly and dissociation. These channels allow calcium uptake in amyloid precursor protein-deficient cells. The channel mediated calcium uptake induces neurite degeneration in human cortical neurons. Channel conductance, calcium uptake, and neurite degeneration are selectively inhibited by zinc, a blocker of amyloid ion channel activity. Thus, truncated Abeta fragments could account for undefined roles played by full length Abetas and provide a unique mechanism of AD and Down syndrome pathologies. The toxicity of nonamyloidogenic peptides via an ion channel mechanism necessitates a reevaluation of the current therapeutic approaches targeting the nonamyloidogenic pathway as avenue for AD treatment.

Age-Related Lesions in the Cerebrum in Middle-Aged Female Cynomolgus Monkeys

Alzheimer's disease (AD) in humans is a progressive neurogenic disease that can be linked with such characteristic pathological findings in the cerebrum as senile plaques (SPs), neurofibrillary tangles (NFTs), cerebral amyloid angiopathy (CAA), and neuronal loss. In the present study, the authors investigated the age-related morphological changes in 12 middle-aged and 12 young cynomolgus monkeys. Low numbers of neurons and astrocytes in the hippocampal region in cynomolgus monkeys accompanied ageing, and there was a high number of microglial cells; however, no clearly neurotoxic abnormalities due to beta-amyloid were noted before the age of 20 years. The onset of SPs and CAA in the cerebrum in cynomolgus monkeys can occur before the age of 20 years. SPs were almost all categorized as diffuse plaques (DPs); they did not have amyloid cores and were unaccompanied by neuritic degeneration. In cynomolgus monkeys, SPs (DPs) occur before the appearance of CAA. From the above, it was concluded that cynomolgus monkeys showed pathological changes due to ageing similar to those related to Alzheimer's disease in humans, even before they were 20 years old.

Endogenous Nmnat2 Is an Essential Survival Factor for Maintenance of Healthy Axons

Author SummaryIn a normally functioning neuron, the cell body supplies the axon with materials needed to keep it healthy. This complex logistical activity breaks down completely after injury and often becomes compromised in neurodegenerative diseases, leading to degeneration of the isolated axon. Whilst there are probably many important cargoes delivered from the cell body that isolated axons cannot exist without indefinitely, proteins that are short-lived will be depleted first, so loss of these proteins is likely to act as a trigger for degeneration. Using clues from a mutant mouse whose axons are protected from such degeneration, we have identified delivery of Nmnat2, a protein with an important enzyme activity, as a limiting factor in axon survival. Importantly, Nmnat2 is very labile and its levels decline rapidly in injured axons before they start to degenerate. Even uninjured axons degenerate in a similar way without it. These properties are consistent with loss of Nmnat2 being a natural stimulus for axon degeneration, and it might therefore be a suitable target for therapeutic intervention.

How do soluble oligomers of amyloid β-protein impair hippocampal synaptic plasticity?

How do soluble oligomers of amyloid β-protein impair hippocampal synaptic plasticity?

Neural-specific Deletion of FIP200 Leads to Cerebellar Degeneration Caused by Increased Neuronal Death and Axon Degeneration

FIP200 (FAK family-interacting protein of 200 kDa) is a conserved protein recently identified as a potential mammalian counterpart of yeast autophagy protein Atg17. However, it remains unknown whether mammalian FIP200 regulates autophagy in vivo. Here we show that neural-specific deletion of FIP200 resulted in cerebellar degeneration accompanied by progressive neuronal loss, spongiosis, and neurite degeneration in the cerebellum. Furthermore, deletion of FIP200 led to increased apoptosis in cerebellum as well as accumulation of ubiquitinated protein aggregates without any deficiency in proteasome catalytic functions. We also observed an increased p62/SQSTM1 accumulation in the cerebellum and reduced autophagosome formation as well as accumulation of damaged mitochondria in the mutant mice. Lastly, analysis of cerebellar neurons in vitro showed reduced JNK activation and increased susceptibility to serum deprivation-induced apoptosis in cerebellar neurons from the mutant mice. Taken together, these results provide strong genetic evidence for a role of FIP200 in the regulation of neuronal homeostasis through its function in autophagy in vivo.

Vitamin E Prevent Neurite Degeneration in Hydrogen Peroxide Treated Neurons

Vitamin E Prevent Neurite Degeneration in Hydrogen Peroxide Treated Neurons