Transgenic mice in the study of ALS: the role of neurofilaments

Intrinsic Disorder as a Natural Preservative: High Levels of Intrinsic Disorder in Proteins Found in the 2600-Year-Old Human Brain

Proteomic analysis revealed the preservation of many proteins in the Heslington brain (which is at least 2600-year-old brain tissue uncovered within the skull excavated in 2008 from a pit in Heslington, Yorkshire, England). Five of these proteins-"main proteins": heavy, medium, and light neurofilament proteins (NFH, NFM, and NFL), glial fibrillary acidic protein (GFAP), and myelin basic (MBP) protein-are engaged in the formation of non-amyloid protein aggregates, such as intermediate filaments and myelin sheath. We used a wide spectrum of bioinformatics tools to evaluate the prevalence of functional disorder in several related sets of proteins, such as the main proteins and their 44 interactors, all other proteins identified in the Heslington brain, as well as the entire human proteome (20,317 manually curated proteins), and 10,611 brain proteins. These analyses revealed that all five main proteins, half of their interactors and almost one third of the Heslington brain proteins are expected to be mostly disordered. Furthermore, most of the remaining Heslington brain proteins are expected to contain sizable levels of disorder. This is contrary to the expected substantial (if not complete) elimination of the disordered proteins from the Heslington brain. Therefore, it seems that the intrinsic disorder of NFH, NFM, NFL, GFAP, and MBP, their interactors, and many other proteins might play a crucial role in preserving the Heslington brain by forming tightly folded brain protein aggregates, in which different parts are glued together via the disorder-to-order transitions.

Assessing neuraxial microstructural changes in a transgenic mouse model of early stage Amyotrophic Lateral Sclerosis by ultra-high field MRI and diffusion tensor metrics

OBJECTIVE

Cell structural changes are one of the main features observed during the development of amyotrophic lateral sclerosis (ALS). In this work, we propose the use of diffusion tensor imaging (DTI) metrics to assess specific ultrastructural changes in the central nervous system during the early neurodegenerative stages of ALS.

METHODS

Ultra-high field MRI and DTI data at 17.6T were obtained from fixed, excised mouse brains, and spinal cords from ALS (G93A-SOD1) mice.

RESULTS

Changes in fractional anisotropy (FA) and linear, planar, and spherical anisotropy ratios (CL, CP, and CS, respectively) of the diffusion eigenvalues were measured in white matter (WM) and gray matter (GM) areas associated with early axonal degenerative processes (in both the brain and the spinal cord). Specifically, in WM structures (corpus callosum, corticospinal tract, and spinal cord funiculi) as the disease progressed, FA, CL, and CP values decreased, whereas CS values increased. In GM structures (prefrontal cortex, hippocampus, and central spinal cord) FA and CP decreased, whereas the CL and CS values were unchanged or slightly smaller. Histological studies of a fluorescent mice model (YFP, G93A-SOD1 mouse) corroborated the early alterations in neuronal morphology and axonal connectivity measured by DTI.

CONCLUSIONS

Changes in diffusion tensor shape were observed in this animal model at the early, nonsymptomatic stages of ALS. Further studies of CL, CP, and CS as imaging biomarkers should be undertaken to refine this neuroimaging tool for future clinical use in the detection of the early stages of ALS.

Modeling hallmark pathology using motor neurons derived from the family and sporadic amyotrophic lateral sclerosis patient-specific iPS cells

Background

Amyotrophic lateral sclerosis (ALS) represents a devastating, progressive, heterogeneous, and the most common motor neuron (MN) disease. To date, no cure has been available for the condition. Studies with transgenic mice have yielded significant results that help us understand the underlying mechanisms of ALS. Nonetheless, none of more than 30 large clinical trials over the past 20 years proved successful, which led some researchers to challenge the validity of the preclinical models.

Methods

Human-induced pluripotent cells (iPSCs) were established by introducing Sendai virus into fibroblast cells. We established TDP-43 HES by inserting CAG-TDP43 (G298S) cassette or the CAG-EGFP cassette into PPP1R12C-locus of human embryonic stem cells (ESC, H9) by TALEN-mediated homologous recombination. iPSCs or HESC were differentiated to motor neurons and non-motor neuron as control. Relevant biomarkers were detected in different differentiated stages. TDP-43 aggregates, neurofilament, and mitochondria analyses were performed.

Results

In this study, using iPSCs-derived human MN from an ALS patient with a TDP43 G298S mutation and two sporadic ALS patients, we showed that both sporadic and familial ALS were characterized by TDP-43 aggregates in the surviving MN. Significantly higher neurofilament (NF) inclusion was also found in ALS MN compared with wild-type (WT) GM15 controls (P < 0.05). The neurite mitochondria density was significantly lower in ALS MN than that in the control MNs. Transgenesis of TDP-43 G298S into AAVS locus in human embryonic stem cells reproduced phenotype of patient-derived G289S MN. By challenging MNs with a proteasome inhibitor, we found that MNs were more vulnerable to MG132, with some accompanying phenotype changes, such as TDP43 translocation, NF inclusion, mitochondria distribution impairment, and activation of caspase3.

Conclusions

Our results suggested that changes in TDP43 protein, NF inclusion, and distribution impairment of mitochondria are common early pathology both in familial and sporadic ALS. These findings will help us gain insight into the pathogenesis of the condition and screen relevant drugs for the disease.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1048-1) contains supplementary material, which is available to authorized users.

Murine Models of Sepsis and Trauma: Can We Bridge the Gap?

Sepsis and trauma are both leading causes of death in the United States and represent major public health challenges. Murine models have largely been used in sepsis and trauma research to better understand the pathophysiological changes that occur after an insult and to develop potential life-saving therapeutic agents. Mice are favorable subjects for this type of research given the variety of readily available strains including inbred, outbred, and transgenic strains. In addition, they are relatively easy to maintain and have a high fecundity. However, pharmacological therapies demonstrating promise in preclinical mouse models of sepsis and trauma often fail to demonstrate similar efficacy in human clinical trials, prompting considerable criticism surrounding the capacity of murine models to recapitulate complex human diseases like sepsis and traumatic injury. Fundamental differences between the two species include, but are not limited to, the divergence of the transcriptomic response, the mismatch of temporal response patterns, differences in both innate and adaptive immunity, and heterogeneity within the human population in comparison to the homogeneity of highly inbred mouse strains. Given the ongoing controversy, this narrative review aims to not only highlight the historical importance of the mouse as an animal research model but also highlight the current benefits and limitations of the model as it pertains to sepsis and trauma. Lastly, this review will propose future directions that may promote further use of the model.

Sigma-1 Receptor in Motoneuron Disease

Amyotrophic Lateral Sclerosis (ALS ) is a neurodegenerative disease affecting spinal cord and brain motoneurons , leading to paralysis and early death. Multiple etiopathogenic mechanisms appear to contribute in the development of ALS , including glutamate excitotoxicity, oxidative stress , protein misfolding, mitochondrial defects, impaired axonal transport, inflammation and glial cell alterations. The Sigma-1 receptor is highly expressed in motoneurons of the spinal cord, particularly enriched in the endoplasmic reticulum (ER) at postsynaptic cisternae of cholinergic C-terminals. Several evidences point to participation of Sigma-1R alterations in motoneuron degeneration. Thus, mutations of the transmembrane domain of the Sigma-1R have been described in familial ALS cases. Interestingly, Sigma-1R KO mice display muscle weakness and motoneuron loss. On the other hand, Sigma-1R agonists promote neuroprotection and neurite elongation through activation of protein kinase C on motoneurons in vitro and in vivo after ventral root avulsion. Remarkably, treatment of SOD1 mice, the most usual animal model of ALS , with Sigma-1R agonists resulted in significantly enhanced motoneuron function and preservation, and increased animal survival. Sigma-1R activation also reduced microglial reactivity and increased the glial expression of neurotrophic factors. Two main interconnected mechanisms seem to underlie the effects of Sigma-1R manipulation on motoneurons: modulation of neuronal excitability and regulation of calcium homeostasis. In addition, Sigma-1R also contributes to regulating protein degradation, and reducing oxidative stress. Therefore, the multi-functional nature of the Sigma-1R represents an attractive target for treating aspects of ALS and other motoneuron diseases .

Neurofilament depletion improves microtubule dynamics via modulation of Stat3/stathmin signaling

In neurons, microtubules form a dense array within axons, and the stability and function of this microtubule network is modulated by neurofilaments. Accumulation of neurofilaments has been observed in several forms of neurodegenerative diseases, but the mechanisms how elevated neurofilament levels destabilize axons are unknown so far. Here, we show that increased neurofilament expression in motor nerves of pmn mutant mice, a model of motoneuron disease, causes disturbed microtubule dynamics. The disease is caused by a point mutation in the tubulin-specific chaperone E (Tbce) gene, leading to an exchange of the most C-terminal amino acid tryptophan to glycine. As a consequence, the TBCE protein becomes instable which then results in destabilization of axonal microtubules and defects in axonal transport, in particular in motoneurons. Depletion of neurofilament increases the number and regrowth of microtubules in pmn mutant motoneurons and restores axon elongation. This effect is mediated by interaction of neurofilament with the stathmin complex. Accumulating neurofilaments associate with stathmin in axons of pmn mutant motoneurons. Depletion of neurofilament by Nefl knockout increases Stat3–stathmin interaction and stabilizes the microtubules in pmn mutant motoneurons. Consequently, counteracting enhanced neurofilament expression improves axonal maintenance and prolongs survival of pmn mutant mice. We propose that this mechanism could also be relevant for other neurodegenerative diseases in which neurofilament accumulation and loss of microtubules are prominent features.

Amyotrophic lateral sclerosis: Current perspectives from basic research to the clinic

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive degeneration of upper and lower motoneurons, leading to muscle weakness and paralysis, and finally death. Considerable recent advances have been made in basic research and preclinical therapeutic attempts using experimental models, leading to increasing clinical and translational research in the context of this disease. In this review we aim to summarize the most relevant findings from a variety of aspects about ALS, including evaluation methods, animal models, pathophysiology, and clinical findings, with particular emphasis in understanding the role of every contributing mechanism to the disease for elucidating the causes underlying degeneration of motoneurons and the development of new therapeutic strategies.

Gene expression profiling of two distinct neuronal populations in the rodent spinal cord

Background

In the field of neuroscience microarray gene expression profiles on anatomically defined brain structures are being used increasingly to study both normal brain functions as well as pathological states. Fluorescent tracing techniques in brain tissue that identifies distinct neuronal populations can in combination with global gene expression profiling potentially increase the resolution and specificity of such studies to shed new light on neuronal functions at the cellular level.

Methodology/Principal Findings

We examine the microarray gene expression profiles of two distinct neuronal populations in the spinal cord of the neonatal rat, the principal motor neurons and specific interneurons involved in motor control. The gene expression profiles of the respective cell populations were obtained from amplified mRNA originating from 50–250 fluorescently identified and laser microdissected cells. In the data analysis we combine a new microarray normalization procedure with a conglomerate measure of significant differential gene expression. Using our methodology we find 32 genes to be more expressed in the interneurons compared to the motor neurons that all except one have not previously been associated with this neuronal population. As a validation of our method we find 17 genes to be more expressed in the motor neurons than in the interneurons and of these only one had not previously been described in this population.

Conclusions/Significance

We provide an optimized experimental protocol that allows isolation of gene transcripts from fluorescent retrogradely labeled cell populations in fresh tissue, which can be used to generate amplified aRNA for microarray hybridization from as few as 50 laser microdissected cells. Using this optimized experimental protocol in combination with our microarray analysis methodology we find 49 differentially expressed genes between the motor neurons and the interneurons that reflect the functional differences between these two cell populations in generating and transmitting the motor output in the rodent spinal cord.

Dynamic endogenous association of neurofilament mRNAs with K-homology domain ribonucleoproteins in developing cerebral cortex

The low, middle, and high molecular mass neurofilament subunit proteins (NF-L, NF-M, and NF-H) co-polymerize to form neurofilaments (NFs). During development, NF subunit expression is highly regulated, and in neurodegenerative disease, aberrant regulation of this expression can lead to the formation of harmful aggregates. NF expression in both development and disease is under significant post-transcriptional control, but the specific ribonucleoproteins (RNPs) involved are only poorly understood. Previously, mass spectrometry on affinity purified proteins from rat brain identified three K-homology (KH) domain RNPs - hnRNP K, hnRNP E1, hnRNP E2 - as being capable of binding NF-M RNA. In the current study, to determine whether these RNPs associate with NF mRNAs endogenously, we performed a co-immunoprecipitation assay on homogenates of postnatal and developing rat cerebral cortex. We found that all three NF mRNAs indeed associated endogenously with these RNPs and that the degree of this association changed during postnatal development, a period when NF expression is under significant post-transcriptional control. The degree of these associations changed independently of the abundance of either the RNPs or the NF messages, indicating that the RNA-protein interactions themselves are directly regulated. This study is consistent with a model whereby these RNPs and NF mRNAs are components of a dynamic post-transcriptional regulatory module that influences the cytoskeletal compositions of neurons.

Epidermal growth factor receptor in adult retinal neurons of rat, mouse, and human

During development, the epidermal growth factor receptor (EGFR) regulates proliferation and differentiation of many types of cells, including precursors of neurons and glia. In the adult, EGFR continues to drive the growth and differentiation of epithelial cells but is absent from glia in the CNS. However, the localization and functions of EGFR in adult neurons are not well defined. By using immunohistochemistry and Western blotting, we have identified EGFR and its ligands in adult retinal ganglion cells in the normal rat, mouse, and human retina. EGFR and its ligands were also present in certain other adult retinal neurons, for example, horizontal cells and amacrine cells, and had different distribution patterns among these species. In addition, we found that EGFR was expressed in the rat retinal ganglion cell line RGC-5. One of the EGFR ligands, EGF, caused a cell shape change and increased neurofilament phosphorylation in RGC-5 cells. The expression of EGFR in postmitotic, terminally differentiated adult retinal neurons suggests that EGFR has pleiotropic functions. In addition to the conventional mitogenic role in adult epithelial cells, EGFR must serve a different, nonmitogenic function in adult neurons. Our work localizes EGFR and its ligands in the adult retinas of several species as a step toward investigating the nonmitogenic functions of EGFR in adult neurons.

Protein accumulation in traumatic brain injury

Traumatic brain injury (TBI) is one of the most devastating diseases in our society, accounting for a high percentage of mortality and disability. A major consequence of TBI is the rapid and long-term accumulation of proteins. This process largely reflects the interruption of axonal transport as a result of extensive axonal injury. Although many proteins are found accumulating after TBI, three have received particular attention; beta-amyloid precursor protein and its proteolytic products, amyloid-beta (Abeta) peptides, neurofilament proteins, and synuclein proteins. Massive coaccumulations of all of these proteins are found in damaged axons throughout the white matter after TBI. Additionally, these proteins form aggregates in other neuronal compartments and in brain parenchyma after brain trauma. Interestingly, TBI is also an epigenetic risk factor for developing neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease. Here, the similarities and differences of these accumulations with pathologies of neurodegenerative diseases will be explored. In addition, the potential deleterious roles of protein accumulations on functional outcome and progressive neurodegeneration following TBI will be examined.

Selective loss of trans-acting instability determinants of neurofilament mRNA in amyotrophic lateral sclerosis spinal cord

Neurofilament (NF) aggregates in motor neurons are a key neuropathological feature of amyotrophic lateral sclerosis (ALS). We have previously observed an alteration in the stoichiometry of NF subunit steady state mRNA levels in ALS spinal motor neurons using in situ hybridization and proposed that this led to aggregate formation. We have now examined the levels of NF mRNA in whole tissue homogenates of spinal cord using the RNase protection assay and real time reverse transcriptase-PCR and observed significant elevations of NF mRNA level in ALS. Compared with age-matched control, we observed a greater stability of heterogeneously expressed NFL mRNA in the presence of ALS spinal cord homogenates. Heat denaturing or protease K digestion of the control homogenates increased the stability of the NFL mRNA to levels observed in ALS homogenate. Increased NFL mRNA stability was also induced by increasing the percentage of ALS homogenate in an admixture of control and ALS homogenates. These observations suggest the presence of trans-acting NFL mRNA-destabilizing elements in control but not in ALS spinal cord homogenates. This was confirmed in gel retardation assays. We also observed that the destabilizing elements interact with the 3'-untranslated region of NFL mRNA. These findings suggest that the trans-acting NFL-destabilizing elements are selectively suppressed in ALS homogenates, resulting in an increased stability and level of NFL mRNA.

Neurofilaments and neurological disease

Neurofilaments are one of the major components of the neuronal cytoskeleton and are responsible for maintaining the calibre of axons. They are modified by post-translational changes that are regulated in complex fashions including by the interaction with neighbouring glial cells. Neurofilament accumulations are seen in several neurological diseases and neurofilament mutations have now been associated with Charcot-Marie-Tooth disease, Parkinson's disease and amyotrophic lateral sclerosis. In this review, we discuss the structure, normal function and molecular pathology of neurofilaments.

Genetic epidemiology of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late onset, rapidly progressive and ultimately fatal neurological disorder, caused by the loss of motor neurons in the brain and spinal cord. Familial aggregation of ALS, with an age-dependent but high penetrance, is a major risk factor for ALS. Familial ALS (FALS) is clinically and genetically heterogeneous. Three genes and linkage to four additional gene loci have been identified so far and may either predominantly lead to ALS (ALSI-ALS6) or cause multisystem neurodegeneration with ALS as an occasional symptom (tauopathies, ALS-dementia complex). This review presents a tentative classification of the "major" ALS genes and ALS "susceptibility" genes, that may act as susceptibility factors for neurodegeneration in interaction with other genetic or environmental risk factors. Considering that mutations in ALS genes explain approximately 10% of familial as well as sporadic ALS, and most remaining cases of the discase are thought to result form the interaction of several genes and environmental factors, ALS is a paradigm for multifactorial discases.

Intracellular glycosylation and development

O-linked N-acetylglucosamine (O-GlcNAc) is a highly dynamic post-translational modification of cytoplasmic and nuclear proteins. Although the function of this abundant modification is yet to be definitively elucidated, all O-GlcNAc proteins are phosphoproteins. Further, the serine and threonine residues substituted with O-GlcNAc are often sites of, or close to sites of, protein phosphorylation. This implies that there may be a dynamic interplay between these two post-translational modifications to regulate protein function. In this review, the functions of some of the proteins that are modified by O-GlcNAc will be considered in the context of the potential role of the O-GlcNAc modification. Furthermore, predictions will be made as to how cellular function and developmental regulation might be affected by changes in O-GlcNAc levels.

Role of oxidative stress and antioxidants in neurodegenerative diseases

Neurodegenerative diseases (NDD) are a group of illness with diverse clinical importance and etiologies. NDD include motor neuron disease such as amyotrophic lateral sclerosis (ALS), cerebellar disorders, Parkinson's disease (PD), Huntington's disease (HD), cortical destructive Alzheimer's disease (AD) and Schizophrenia. Numerous epidemiological and experimental studies provide many risk factors such as advanced age, genetic defects, abnormalities of antioxidant enzymes, excitotoxicity, cytoskeletal abnormalities, autoimmunity, mineral deficiencies, oxidative stress, metabolic toxicity, hypertension and other vascular disorders. Growing body of evidence implicates free radical toxicity, radical induced mutations and oxidative enzyme impairment and mitochondrial dysfunction due to congenital genetic defects in clinical manifestations of NDD. Accumulation of oxidative damage in neurons either primarily or secondarily may account for the increased incidence of NDD such as AD, ALS and stroke in aged populations. The molecular mechanisms of neuronal degeneration remain largely unknown and effective therapies are not currently available. Recent interest has focused on antioxidants such as carotenoids and in particular lycopene, a potent antioxidant in tomatoes and tomato products, flavonoids and vitamins as potentially useful agents in the management of human NDD. The pathobiology of neurodegenerative disorders with emphasis on genetic origin and its correlation with oxidative stress of neurodegenerative disorders will be reviewed and the reasons as to why brain constitutes a vulnerable site of oxidative damage will be discussed. The article will also discuss the potential free radical scavenger, mechanism of antioxidant action of lycopene and the need for the use of antioxidants in the prevention of NDD.

Familial amyotrophic lateral sclerosis

The increasing complexity of the pathways implicated in the pathogenesis of familial amyotrophic lateral sclerosis (ALS) has stimulated intensive research in many directions. Genetic analysis of familial ALS has yielded six loci and one disease gene (SOD1), initially suggesting a role for free radicals in the disease process, although the mechanisms through which the mutant exerts toxicity and results in selective motor neuron death remain uncertain. Numerous studies have focused on structural elements of the affected cell, emphasizing the role of neurofilaments and peripherin and their functional disruption in disease. Other topics examined include cellular homeostasis of copper and calcium, particularly in the context of oxidative stress and the processes of protein aggregation, glutamate excitotoxicity, and apoptosis. It has become evident that there is considerable interplay between these mechanisms and, as the role of each is established, a common picture may emerge, enabling the development of more targeted therapies. This study discusses the main areas of investigation and reviews the findings.

RH, Meininger V, Camu W, Rouleau GA. A novel locus for familial amyotrophic lateral sclerosis, on chromosome 18q

Amyotrophic lateral sclerosis (ALS) is an adult-onset degenerative disorder characterized by the death of motor neurons in the cortex, brain stem, and spinal cord. Despite intensive research the basic pathophysiology of ALS remains unclear. Although most cases are sporadic, approximately 10% of ALS cases are familial (FALS). Mutations in the Cu/Zn superoxide dismutase (SOD1) gene cause approximately 20% of FALS. The gene(s) responsible for the remaining 80% of FALS remain to be found. Using a large European kindred without SOD1 mutation and with classic autosomal dominant adult-onset ALS, we have identified a novel locus by performing a genome scan and linkage analysis. The maximum LOD score is 4.5 at recombination fraction 0.0, for polymorphism D18S39. Haplotype analysis has identified a 7.5-cM, 8-Mb region of chromosome 18q21, flanked by markers D18S846 and D18S1109, as a novel FALS locus.

Further evidence that neurofilament light chain gene mutations can cause Charcot-Marie-Tooth disease type 2E

A missense mutation in the neurofilament light chain gene (NEFL, NF-L) at chromosome 8p21 was recently reported in a single Charcot-Marie-Tooth type 2 family (CMT2). This new CMT2 variant is designated CMT2E. The NEFL gene mutation showed co-segregation with the disease phenotype and is thus most likely the disease-causing mutation. However, the possibility that it is a closely linked rare polymorphism can not be ruled out with certainty. We observed a novel NEFL missense mutation in a second CMT family, providing supporting evidence that CMT2E is caused by NEFL gene mutations.

The gene encoding gigaxonin, a new member of the cytoskeletal BTB/kelch repeat family, is mutated in giant axonal neuropathy

Disorganization of the neurofilament network is a prominent feature of several neurodegenerative disorders including amyotrophic lateral sclerosis (ALS), infantile spinal muscular atrophy and axonal Charcot-Marie-Tooth disease. Giant axonal neuropathy (GAN, MIM 256850), a severe, autosomal recessive sensorimotor neuropathy affecting both the peripheral nerves and the central nervous system, is characterized by neurofilament accumulation, leading to segmental distension of the axons. GAN corresponds to a generalized disorganization of the cytoskeletal intermediate filaments (IFs), to which neurofilaments belong, as abnormal aggregation of multiple tissue-specific IFs has been reported: vimentin in endothelial cells, Schwann cells and cultured skin fibroblasts, and glial fibrillary acidic protein (GFAP) in astrocytes. Keratin IFs also seem to be alterated, as most patients present characteristic curly or kinky hairs. We report here identification of the gene GAN, which encodes a novel, ubiquitously expressed protein we have named gigaxonin. We found one frameshift, four nonsense and nine missense mutations in GAN of GAN patients. Gigaxonin is composed of an amino-terminal BTB (for Broad-Complex, Tramtrack and Bric a brac) domain followed by a six kelch repeats, which are predicted to adopt a beta-propeller shape. Distantly related proteins sharing a similar domain organization have various functions associated with the cytoskeleton, predicting that gigaxonin is a novel and distinct cytoskeletal protein that may represent a general pathological target for other neurodegenerative disorders with alterations in the neurofilament network.

Reduced expression and altered distribution of neurofilaments in neurons cultured in thyroid hormone-deficient medium

The effect of thyroid hormone (TH) deficiency on the expression of neurofilament (NF) proteins and their intracellular distribution has been examined in primary cultures of neurons from embryonic rat cerebra. Northern blot analysis showed that in TH-deficient (THdef) neurons, the expression of all three NF mRNAs (NF-L, NF-M and NF-H) are retarded by 50-70% at days 7, 15 and 25 of culture compared with their TH-supplemented (THsup) counterparts. Western blot analysis also showed a decline of 60-80% in the expression of all the NF-proteins at all time points. Immunofluorescent staining of neurons from THdef and THsup cultures at days 7, 15, and 25 with monoclonal anti NF-L antibody showed that with age, TH deficiency reduced the localization of NF-L in the cell body with a corresponding increase in the hillock and proximal axon region. The present neuronal culture system offers an excellent experimental model for studying the biochemical events responsible for the altered NF pathology in degenerating neurons.

Blast exposure causes redistribution of phosphorylated neurofilament subunits in neurons of the adult rat brain

There is little information on threshold levels and critical time factors for blast exposures, although brain damage after a blast has been established both clinically and experimentally. Moreover, the cellular pathophysiology of the brain response is poorly characterized. This study employs a rat model for blast exposure to investigate effects on the neuronal cytoskeleton. Exposure in the range of 154 kPa/198 dB or 240 kPa/202 dB has previously been shown neither to cause visual damage to the brain, nor to affect the neuronal populations, as revealed with routine histology. Here, the brains were investigated immunohistochemically from 2 h to 21 days after blast exposure. A monoclonal antibody was used which detects only the phosphorylated epitope of the heavy subunit of the neurofilament proteins (p-NFH). This epitope is normally restricted to axons, that is, not demonstrable in the perikarya. Eighteen hours after exposure in the 240-kPa/202-dB range, p-NFH immunoreactivity accumulated in neuronal perikarya in layers II-IV of the temporal cortex and of the cingulate and the piriform cortices, the dentate gyrus and the CA1 region of the hippocampus. At the same time, the p-NFH immunoreactivity disappeared from the axons and dendrites of cerebral cortex neurons. The most pronounced immunostaining of neuronal perikarya was found in the hemisphere, which faced the blast source. The perikaryal accumulation of p-NFH was present also at 7 days but the neuronal perikarya had become negative at 21 days, at which time the axons again displayed p-NFH immunoreactivity. Exposure in the range of 154 kPa/198 dB caused similar, although less marked accumulation of p-NFH immunoreactivity in the neuronal perikarya. The findings are interpreted to show a dephosphorylation of NFHs in axons and dendrites and a piling up of p-NFHs in the perikarya due to disturbed axonal transport.

Pathogenesis of amyotrophic lateral sclerosis: a critical review

Amyotrophic lateral sclerosis is a neurodegenerative disease with unknown pathogenesis. It is a relatively common disorder of adults (2-4 per 100,000 incidence) and leads to death from respiratory failure. There is no cure at this time, and available treatment and management can at best extend survival to a modest degree. Increasing our understanding of the pathogenesis of this disease is essential to the development of more effective treatments. The level of research interest is very high, and yearly reviews of the literature are helpful in assessing progress.

Neurofilament functions in health and disease

Transgenic approaches have recently been used to investigate the functions of neuronal intermediate filaments. Gene knockout studies have demonstrated that neurofilaments are not required for axogenesis and that individual neurofilament proteins play distinct roles in filament assembly and in the radial growth of axons. The involvement of neurofilaments in disease is supported by the discovery of novel mutations in the neurofilament heavy gene from cases of amyotrophic lateral sclerosis and by reports of neuronal death in mouse models expressing neurofilament and alpha-internexin transgenes. However, mouse studies have shown that axonal neurofilaments are not required for pathogenesis caused by mutations in superoxide dismutase and that increasing perikaryal levels of neurofilament proteins may even confer protection in this disease.

Disruption of type IV intermediate filament network in mice lacking the neurofilament medium and heavy subunits

To clarify the role of the neurofilament (NF) medium (NF-M) and heavy (NF-H) subunits, we generated mice with targeted disruption of both NF-M and NF-H genes. The absence of the NF-M subunit resulted in a two- to threefold reduction in the caliber of large myelinated axons, whereas the lack of NF-H subunits had little effect on the radial growth of motor axons. In NF-M-/- mice, the velocity of axonal transport of NF light (NF-L) and NF-H proteins was increased by about two-fold, whereas the steady-state levels of assembled NF-L were reduced. Although the NF-M or NF-H subunits are each dispensable for the formation of intermediate filaments, the absence of both subunits in double NF-M; NF-H knockout mice led to a scarcity of intermediate filament structures in axons and to a marked approximately twofold increase in the number of microtubules. Protein analysis indicated that the levels of NF-L and alpha-internexin proteins were reduced dramatically throughout the nervous system. Immunohistochemistry of spinal cord from the NF-M-/-;NF-H-/- mice revealed enhanced NF-L staining in the perikaryon of motor neurons but a weak NF-L staining in axons. In addition, axonal transport studies carried out by the injection of [35S]methionine into spinal cord revealed after 30 days very low levels of newly synthesized NF-L proteins in the sciatic nerve of NF-M-/-;NF-H-/- mice. The combined results demonstrate a requirement of the high-molecular-weight subunits for the assembly of type IV intermediate filament proteins and for the efficient translocation of NF-L proteins into the axonal compartment.