Accumulation Of Neurofilaments Research Articles

Peripherin Is a Subunit of Peripheral Nerve Neurofilaments: Implications for Differential Vulnerability of CNS and Peripheral Nervous System Axons

Peripherin, a neuronal intermediate filament protein implicated in neurodegenerative disease, coexists with the neurofilament triplet proteins [neurofilament light (NFL), medium (NFM), and heavy (NFH) chain] but has an unknown function. The earlier peak expression of peripherin than the triplet during brain development and its ability to form homopolymers, unlike the triplet, which are obligate heteropolymers, have supported a widely held view that peripherin and neurofilament triplets form separate filament systems. However, here, we demonstrate that, despite a postnatal decline in expression, peripherin is as abundant as the triplet in the adult PNS and exists in a relatively fixed stoichiometry with these subunits. Peripherin exhibits a distribution pattern identical to those of triplet proteins in sciatic axons and colocalizes with NFL on single neurofilaments by immunogold electron microscopy. Peripherin also coassembles into a single network of filaments containing NFL, NFM, and NFH with and without α-internexin in quadruple- or quintuple-transfected SW13vim(-) cells. Genetically deleting NFL in mice dramatically reduces peripherin content in sciatic axons. Moreover, peripherin mutations has been shown to disrupt the neurofilament network in transfected SW13vim(-) cells. These data show that peripherin and the neurofilament proteins are functionally interdependent. The results strongly support the view that, rather than forming an independent structure, peripherin is a subunit of neurofilaments in the adult PNS. Our findings provide a basis for its close relationship with neurofilaments in PNS diseases associated with neurofilament accumulation.

Distinctive clinicopathological features of 2 large families with amyotrophic lateral sclerosis having L106V mutation in SOD1 gene

A clinicopathological study of 2 families with familial amyotrophic lateral sclerosis was previously reported [1]. The present study continues to investigate these families, with detailed clinical, genetic, and neuropathological studies performed on 24 patients, including 5 autopsy cases of the families. A point mutation at codon 106 (L106V) in the copper/zinc superoxide dismutase-1 (SOD1) gene was identified in the families. Average age at onset was 52.0±9.4years, and initial symptoms were weakness and atrophy in the distal muscles of the lower extremities in most patients. Half of the patients showed neurogenic bladder (overactive bladder) and sensory impairment. The neurophysiological study showed peripheral/central conduction delay. Neuropathological examination revealed severe motor neuron loss with many bizarre reactive astrocytes in the spinal anterior horn. SOD1-immunopositive Lewy body-like hyaline inclusions and aggregation of neurofilaments were observed in the surviving anterior horn cells. Degeneration of the corticospinal tract was relatively minor. In addition, slight but diffuse gliosis was identified in the hypothalamus and medial nucleus of thalamus. Neurogenic bladder, sensory impairment, and degeneration of the hypothalamus and thalamus might be specific features in patients with familial amyotrophic lateral sclerosis with L106V mutation in the SOD1 gene.

CSF markers in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS, 'Lou Gehrig disease') is the most common, progressive, neurodegenerative, motor neuron disease, causing damage to upper and lower motor neurons, leading to paralysis and death within 3-5 years. Majority of ALS cases are sporadic ALS (SALS) and only 5-10 % of cases are familial ALS (FALS). Pathogenesis of ALS is complicated and still unclear, including genetic, glutamate excitotoxicity, oxidative stress, mitochondrial dysfunction, neurofilament accumulation, impaired trophic support, altered glial function, viral infection, immune imbalance and impairment of the blood-brain, blood-spinal cord and blood-cerebrospinal fluid barriers (BBB/BSCB/BCSFB). The CSF analysis is still one of the basic laboratory tools and might reflect pathophysiological alterations in the course of the disease and could provide an insight into disease pathomechanisms. The most important aim of its analysis is evaluation of blood-CSF barrier, which is altered in 46 % of ALS patients. The CSF biomarkers may give insight into ALS pathophysiology and may be useful for early, presymptomatic diagnosis, therapeutic monitoring and the development of new therapeutic strategies. This review summarizes the general concepts of biomarkers in CSF of ALS patients and their potential usefulness in further research.

Motor Unit Pathology in SMA Patients (P03.175)

Objective: To examine the pathology of the motor unit in spinal muscular atrophy (SMA). Background SMA is an inherited motor neuron disease, which often causes early mortality. Although there is currently no disease-modify treatment to offer patients, several drugs show promising effects in SMA mouse models in which the pathology of the motor unit has been well defined. In mice, there are early abnormalities of motor neuron (MN) terminals prior to MN loss with differential susceptibility of certain MN groups. Limited prior studies of human SMA pathology have not characterized early changes of MNs, their axons, or terminals. Design/Methods: At autopsy, spinal cord, nerve roots, phrenic nerve, and skeletal muscle were collected from 14 SMA cases and analyzed with confocal and electron microscopy methods. Results: Vast numbers of small, round myofibers were evident in the psoas, paraspinal, and intercostal muscles, but myofiber size was relatively preserved in diaphragm muscle. Phrenic nerve showed an average of 1830±177 axons/nerve in SMA cases, while ventral roots exhibited a severe reduction in axonal density. Active axonal degeneration was present in ventral roots and phrenic nerve where 3.7±0.45% of axons showed a compacted myelin appearance. Neuromuscular junctions (NMJs) in the diaphragm were often well innervated, but many axon terminals displayed neurofilament aggregation and others were very thin. EM analysis confirmed neurofilament aggregation and reduced density of synaptic vesicles in SMA diaphragm NMJs. Conclusions: These studies show that motor units are differentially affected in human SMA, with phrenic nerve motor neurons innervating the diaphragm less affected than those innervating the paraspinal, intercostal, or proximal limb muscles. The diaphragm may therefore provide important insights into early SMA disease pathology. In this muscle, most NMJs were innervated but structurally abnormal. These studies raise the possibility that the distal motor neuron terminal and axon are the earliest sites of disease pathogenesis in human SMA. Supported by: The SMA Foundation and by R01NS062869 (CJS) from NINDS and by R01-HD054599 (KJS) from NICHD. Disclosure: Dr. Crowder has nothing to disclose. Dr. Polley has nothing to disclose. Dr. Kong has nothing to disclose. Dr. Van Meerbeke has nothing to disclose. Dr. Murphy has nothing to disclose. Dr. Swoboda has received research support from BioMarin Pharmaceuticals and Orphamed, Dr. Crawford has nothing to disclose. Dr. Sumner has nothing to disclose.

Neurofilament Phosphorylation during Development and Disease: Which Came First, the Phosphorylation or the Accumulation?

Posttranslational modification of proteins is a ubiquitous cellular mechanism for regulating protein function. Some of the most heavily modified neuronal proteins are cytoskeletal proteins of long myelinated axons referred to as neurofilaments (NFs). NFs are type IV intermediate filaments (IFs) that can be composed of four subunits, neurofilament heavy (NF-H), neurofilament medium (NF-M), neurofilament light (NF-L), and α-internexin. Within wild type axons, NFs are responsible for mediating radial growth, a process that determines axonal diameter. NFs are phosphorylated on highly conserved lysine-serine-proline (KSP) repeats located along the C-termini of both NF-M and NF-H within myelinated axonal regions. Phosphorylation is thought to regulate aspects of NF transport and function. However, a key pathological hallmark of several neurodegenerative diseases is ectopic accumulation and phosphorylation of NFs. The goal of this review is to provide an overview of the posttranslational modifications that occur in both normal and diseased axons. We review evidence that challenges the role of KSP phosphorylation as essential for radial growth and suggests an alternative role for NF phosphorylation in myelinated axons. Furthermore, we demonstrate that regulation of NF phosphorylation dynamics may be essential to avoiding NF accumulations.

Changes in beclin-1 and micro-calpain expression in tri-ortho-cresyl phosphate-induced delayed neuropathy

Tri-ortho-cresyl phosphate (TOCP) can cause toxic neuropathy known as organophosphate-induced delayed neuropathy (OPIDN), which is pathologically characterized by the swollen axon containing aggregations of neurofilaments, microtubules, and multivesicular vesicles. Autophagy is a self-degradative process which plays a housekeeping role in removing misfolded proteins and damaged organelles. The current study was designed to investigate the possible roles of autophagy in the pathogenesis of OPIDN. Adult hens were treated with a dose of 750mg/kg TOCP by gavage, or injected subcutaneously with 60mg/kg phenylmethanesulfonyl fluoride (PMSF) dissolved in DMSO 24h earlier and subsequently treated with TOCP, then sacrificed on the time-points of 0, 1, 5, 10, and 21 days after dosing of TOCP respectively. The levels of beclin-1 and μ-calpain in tibial nerves and spinal cords were determined by immunoblotting. The results showed that in both tissues TOCP increased the expression of μ-calpain while decreased that of beclin-1. When given before TOCP administration, PMSF pretreatment could protect hens against the delayed neuropathy. In the meantime, pretreatment with PMSF reduced calpain expression below basal and increased beclin-1 expression above basal in tibial nerve, whereas it simply returned calpain and beclin-1 expression to their basal levels in spinal cord. In conclusion, the intoxication of TOCP was associated with a significant change of beclin-1 in hen nervous tissues, which suggested that disruption of autophagy-regulated machinery in neurons might be involved in the pathogenesis of OPIDN.

14-3-3 proteins interact with neurofilament protein-L and regulate dynamic assembly of neurofilaments

Neurofilament protein-L (NF-L) is the core component of neurofilaments. Recent studies indicate that the NF-L mutations reported in human Charcot-Marie-Tooth (CMT) disease lead to the formation of NF-L aggregates and result in axon degeneration of motor and sensory neurons, which are thought to be the cause of CMT disease type 2E. In the present study, we investigated the dynamic regulation of NF-L assembly and the mechanism of aggregate formation of CMT NF-L mutants. We report that 14-3-3 proteins interact with NF-L in a phosphorylation-dependent manner. Investigation of mutations of phospho-serine sites at the head domain of NF-L revealed that several phosphorylation sites, particularly Ser43 and Ser55, were important for 14-3-3 binding. 14-3-3 overexpression resulted in a significant increase in the dynamic exchange rate of NF-L subunits and induced striking disassembly of neurofilaments. CMT NF-L mutants, particularly those with mutations in the Pro8 and Pro22 sites of the NF-L head domain, led to substantially diminished interaction between 14-3-3 and NF-L, which resulted in the formation of NF-L aggregates and the disruption of the neurofilament co-assembly of NF-L and NF-M. However, aggregate formation in CMT NF-L mutants was downregulated by 14-3-3 overexpression. Taken together, these results suggest the important role of 14-3-3 in the dynamic regulation of NF-L assembly, and in the capacity to prevent the formation of NF-L aggregates. Thus, the 14-3-3 proteins are a possible molecular target for CMT disease therapy.

Dynein Dysfunction Disrupts Intracellular Vesicle Trafficking Bidirectionally and Perturbs Synaptic Vesicle Docking via Endocytic Disturbances: A Potential Mechanism Underlying Age-Dependent Impairment of Cognitive Function

Although genetic studies have demonstrated that β-amyloid protein (Aβ) plays a pivotal role in Alzheimer's disease (AD) pathogenesis, how aging contributes to AD onset remains unclear. Moreover, growing evidence suggests that Aβ-independent mechanisms, such as altered intracellular signaling cascades and impaired neurotransmitter release, also are likely involved in this process. Cytoplasmic dynein, a microtubule-based motor protein, mediates minus end-directed vesicle transport via interactions with dynactin, another microtubule-associated protein. We previously showed that normal aging attenuates the interaction between dynein-dynactin complexes in monkey brain and that dynein dysfunction reproduces age-dependent endocytic disturbances, resulting in intracellular Aβ accumulation. In this study, we report that dynein dysfunction disrupts not only retrograde transport of neurotrophic receptors but also anterograde transport of synaptic vesicles, which occurs concomitantly with an increase in Rab3 GTPase levels. Additionally, synaptic vesicle docking was perturbed via enhanced endocytosis. Dynein dysfunction also induced neuritic swelling, which is accompanied by a significant accumulation of neurofilaments. Moreover, we also confirmed that the dynein dysfunction-related disturbances are associated with aging in monkey brains and that age-dependent endocytic disturbances precede Aβ abnormality. These findings suggest that dynein dysfunction can alter neuronal activity via endocytic disturbances and may underlie age-dependent impairment of cognitive function. Moreover, in the presence of other risk factors, such as intracellular Aβ accumulation, dynein dysfunction may contribute to the development of AD.

Reduction of retrograde axonal transport associated-proteins motor proteins, dynein and dynactin in the spinal cord and cerebral cortex of hens by tri-ortho-cresyl phosphate (TOCP)

Tri-ortho-cresyl phosphate (TOCP) can cause a type of neurotoxicity known as organophosphate-induced delayed neuropathy (OPIDN). The characteristic axonal swelling containing aggregations of neurofilaments, microtubules, and multivesicular vesicles is consistent with a disturbance of axonal transport. We hypothesized that there existed a disturbance of molecular motor in the pathogenesis of OPIDN. In the present study, adult hens were treated with a dosage of 750mg/kg TOCP by gavage, or pretreated 24h earlier with phenylmethanesulfonyl fluoride (PMSF) and subsequently with TOCP, then sacrificed on the time-points of 0, 1, 5, 10, and 21days after dosing of TOCP, respectively. The level of kinesin-1, dynein, and dynactin in spinal cords and cerebral cortexes of hens was determined. Immunoblotting analysis showed a progressive decline of dynein and dynactin in spinal cords after dosing TOCP. Furthermore, a significant reduction in dynactin and dynein was observed in cerebral cortexes at several time-points post dosing TOCP. In contrast, no significant changes of kinesin-1 were observed throughout the period of experiment. When given before TOCP administration, PMSF could inhibit TOCP-induced motor protein disruption, while it protected hens against the delayed neuropathy. In conclusion, the reduction of the motor proteins, dynein and dynactin, might be associated with the disruption of retrograde neuronal axonal transport in OPIDN.

Axonopathy is associated with complex axonal transport defects in a model of multiple sclerosis.

Multiple sclerosis (MS) is an inflammatory and neurodegenerative disease characterized by myelin and axonal pathology. In a viral model of MS, we tested whether axonopathy initiation and development are based on an impaired transport of neurofilaments. Spinal cords of Theiler's murine encephalomyelitis virus (TMEV)-infected and mock-infected mice and TMEV infected neuroblastoma N1E-115 cells were analyzed by microarray analysis, light microscopy and electron and laser confocal microscopy. In vivo axonal accumulation of non-phosphorylated neurofilaments after TMEV infection revealed a temporal development caused by the impairments of the axonal traffic consisting of the downregulation of kinesin family member 5A, dynein cytoplasmic heavy chain 1, tau-1 and β-tubulin III expression. In addition, alterations of the protein metabolism were also noticed. In vitro, the TMEV-infected N1E-115 cells developed tandem-repeated swellings similar to in vivo alterations. Furthermore, the hypothesis of an underlying axonal self-destruction program involving nicotinamide adenine dinucleotide depletion was supported by molecular findings. The obtained data indicate that neurofilament accumulation in TME is mainly the result of dysregulation of their axonal transport machinery and impairment of neurofilament phosphorylation and protein metabolism. The present findings allow a more precise understanding of the complex interactions responsible for initiation and development of axonopathies in inflammatory degenerative diseases.

Severe neuromuscular denervation of clinically relevant muscles in a mouse model of spinal muscular atrophy

Spinal muscular atrophy (SMA), a motoneuron disease caused by a deficiency of the survival of motor neuron (SMN) protein, is characterized by motoneuron loss and muscle weakness. It remains unclear whether widespread loss of neuromuscular junctions (NMJs) is involved in SMA pathogenesis. We undertook a systematic examination of NMJ innervation patterns in >20 muscles in the SMNΔ7 SMA mouse model. We found that severe denervation (<50% fully innervated endplates) occurs selectively in many vulnerable axial muscles and several appendicular muscles at the disease end stage. Since these vulnerable muscles were located throughout the body and were comprised of varying muscle fiber types, it is unlikely that muscle location or fiber type determines susceptibility to denervation. Furthermore, we found a similar extent of neurofilament accumulation at NMJs in both vulnerable and resistant muscles before the onset of denervation, suggesting that neurofilament accumulation does not predict subsequent NMJ denervation. Since vulnerable muscles were initially innervated, but later denervated, loss of innervation in SMA may be attributed to defects in synapse maintenance. Finally, we found that denervation was amendable by trichostatin A (TSA) treatment, which increased innervation in clinically relevant muscles in TSA-treated SMNΔ7 mice. Our findings suggest that neuromuscular denervation in vulnerable muscles is a widespread pathology in SMA, and can serve as a preparation for elucidating the biological basis of synapse loss, and for evaluating therapeutic efficacy.

A 6-year-old girl with progressive ataxia

A 6-year-old girl with progressive ataxia

The spinal muscular atrophy mouse model, SMAΔ7, displays altered axonal transport without global neurofilament alterations

Spinal muscular atrophy (SMA) is a neurodegenerative disease resulting from decreased levels of survival motor neuron 1 (SMN1) protein. Reduced SMN1 levels are linked to pathology at neuromuscular junctions (NMJs), which includes decreased vesicle density and organization, decreased quantal release, increased endplate potential duration, and neurofilament (NF) accumulations. This work presents a first study towards defining molecular alterations that may lead to the development of NMJ pathology in SMA. Fast, anterograde transport of synaptic vesicle 2 (SV2-c) and synaptotagmin (Syt1) proteins was reduced 2days prior to the observed decrease in synaptic vesicle density. Moreover, reduced accumulation of SV2-c or Syt1 was not due to reduced protein expression or reduced kinesin activity. Dynein levels were reduced at times that are consistent with NF accumulations at NMJs. Furthermore, NF distribution, from cell body to sciatic nerve, appeared normal in SMA∆7 mice. Taken together, these results suggest that reduced axonal transport may provide a mechanistic explanation for reduced synaptic vesicle density and concomitant synaptic transmission defects, while providing evidence that suggests NF accumulations result from local NMJ alterations to NFs.

Axonal Protection by 17β-Estradiol through Thioredoxin-1 in Tumor Necrosis Factor-Induced Optic Neuropathy

Axonal degeneration often leads to the death of neuronal cell bodies. Previous studies demonstrated the substantial protective role of 17β-estradiol (E2) in several types of neuron. However, most studies examined cell body protection, and the role of 17β-E2 in axonal degeneration of retinal ganglion cells (RGC) remains unclear. In this study, we showed the presence of thioredoxin-1 (Trx1) in the optic nerve axons and found that the levels of Trx1 protein were significantly decreased in isolated RGC and the optic nerve after intravitreal injection of TNF, which was shown previously to induce optic nerve degeneration and subsequent loss of RGC. These changes were concomitant with disorganization of the microtubules with neurofilament accumulation, which were blocked by 17β-E2 implantation. 17β-E2 treatment also totally abolished TNF-induced decreases in Trx1 protein levels in isolated RGC and the optic nerve. The induction of Trx1 by 17β-E2 in the optic nerve was significantly inhibited by simultaneous injection of Trx1 small interfering RNA (siRNA) with TNF. Up-regulation of Trx1 by 17β-E2 in RGC-5 cells was prevented by Trx1 siRNA treatment. 17β-E2 significantly prevented TNF-induced axonal loss, and this axonal-protective effect was inhibited by intravitreal injection of Trx1 siRNA. This finding was also supported by the quantification of microtubules and neurofilaments. These results suggest that a Trx1 decrease in RGC bodies and their axons may be associated with TNF-induced optic nerve axonal degeneration. Axonal protection by 17β-E2 may be related to its regulatory effect on Trx1 induction.

Sensory-motor deficits and neurofilament disorganization in gigaxonin-null mice

BackgroundGiant Axonal Neuropathy (GAN) is a fatal neurodegenerative disorder with early onset characterized by a severe deterioration of the peripheral and central nervous system, involving both the motor and the sensory tracts and leading to ataxia, speech defect and intellectual disabilities. The broad deterioration of the nervous system is accompanied by a generalized disorganization of the intermediate filaments, including neurofilaments in neurons, but the implication of this defect in disease onset or progression remains unknown. The identification of gigaxonin, the substrate adaptor of an E3 ubiquitin ligase, as the defective protein in GAN allows us to now investigate the crucial role of the gigaxonin-E3 ligase in sustaining neuronal and intermediate filament integrity. To study the mechanisms controlled by gigaxonin in these processes and to provide a relevant model to test the therapeutic approaches under development for GAN, we generated a Gigaxonin-null mouse by gene targeting.ResultsWe investigated for the first time in Gigaxonin-null mice the deterioration of the motor and sensory functions over time as well as the spatial disorganization of neurofilaments. We showed that gigaxonin depletion in mice induces mild but persistent motor deficits starting at 60 weeks of age in the 129/SvJ-genetic background, while sensory deficits were demonstrated in C57BL/6 animals. In our hands, another gigaxonin-null mouse did not display the early and severe motor deficits reported previously. No apparent neurodegeneration was observed in our knock-out mice, but dysregulation of neurofilaments in proximal and distal axons was massive. Indeed, neurofilaments were not only more abundant but they also showed the abnormal increase in diameter and misorientation that are characteristics of the human pathology.ConclusionsTogether, our results show that gigaxonin depletion in mice induces mild motor and sensory deficits but recapitulates the severe neurofilament dysregulation seen in patients. Our model will allow investigation of the role of the gigaxonin-E3 ligase in organizing neurofilaments and may prove useful in understanding the pathological processes engaged in other neurodegenerative disorders characterized by accumulation of neurofilaments and dysfunction of the Ubiquitin Proteasome System, such as Amyotrophic Lateral Sclerosis, Huntington's, Alzheimer's and Parkinson's diseases.

Differential expression of c-Ret in motor neurons versus non-neuronal cells is linked to the pathogenesis of ALS

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by selective degeneration of motor neurons throughout the central nervous systems. Non-cell autonomous damage induced by glial cells is linked to the selective susceptibility of motor neurons in ALS, but the mechanisms underlying this phenomenon are not known. We found that the expression of non-phosphorylated and phosphorylated forms (tyrosine (Tyr) residue 905, 1016, and 1062) of c-Ret, a member of the glial cell line-derived neurotrophic factor (GDNF) receptor, are altered in motor neurons of the lumbar spinal cord in ALS transgenic (G93A) mice and ALS (G93A) cell line models. Phosphorylated forms of c-Ret were colocalized with neurofilament aggregates in motor neurons of ALS mice. Consistent with the in vivo data, levels of non-phosphorylated and phosphorylated c-Ret (Tyr 905, 1016, and 1062) were decreased by oxidative stress in motor neuronal cells (NSC-34). Non-phosphorylated and phosphorylated forms of c-Ret immunoreactivity were markedly elevated in active microglia of ALS mice. Our findings suggest that constitutive oxidative stress modulates c-Ret function, thereby reducing GDNF signaling in motor neurons. Furthermore, the induction of c-Ret expression in microglia may contribute to non-cell autonomous cell death of motor neurons by available GDNF in ALS.

Smn deficiency causes neuritogenesis and neurogenesis defects in the retinal neurons of a mouse model of spinal muscular atrophy

The eye is an excellent model for the study of neuronal development and pathogenesis of central nervous system disorders because of its relative ease of accessibility and the well-characterized cellular makeup. We have used this model to study spinal muscular atrophy (SMA), an autosomal recessive neuromuscular disease caused by deletions or mutations in the survival of motor neuron 1 gene (SMN1). We have investigated the expression pattern of mouse Smn mRNA and protein in the neural retina and the optic nerve of wild type mice. Smn protein is present in retinal ganglion cells and amacrine cells within the neural retina as well as in glial cells in the optic nerve. Histopathological analysis in phenotype stage SMA mice revealed that Smn deficiency is associated with a reduction in ganglion cell axon and glial cell number in the optic nerve, as well as compromised cellular processes and altered organization of neurofilaments in the neural retina. Whole mount preparation and retinal neuron primary culture provided further evidence of abnormal synaptogenesis and neurofilament accumulation in the neurites of Smn-deficient retinal neurons. A subset of amacrine cells is absent, in a cell-autonomous fashion, in the retina of SMA mice. Finally, the retinas of SMA mice have altered electroretinograms. Altogether, our study has demonstrated defects in axodendritic outgrowth and cellular composition in Smn-depleted retinal neurons, indicating a role for Smn in neuritogenesis and neurogenesis, and providing us with an insight into pathogenesis of SMA.

Distal to proximal development of peripheral nerves requires the expression of neurofilament heavy

At the initiation of radial growth, neurofilaments are likely to consist primarily of neurofilament light and medium as neurofilament heavy expression is developmentally delayed. To better understand the role of neurofilament heavy in structuring axons, axonal diameter and neurofilament organization were measured in proximal and distal segments of the sciatic nerve and along the entire length of the phrenic nerve. Deletion of neurofilament heavy reduced axonal diameters and neurofilament number in proximal nerve segments. However, neurofilament spacing was greater in proximal versus distal phrenic nerve segments. Taken together, these results suggest that loss of neurofilament heavy reduces radial growth in proximal axonal segments by reducing the accumulation of neurofilaments. As neurofilament heavy expression is developmentally delayed, these results suggest that without neurofilament heavy, the neurofilament network is established in a distal to proximal gradient perhaps to allow distal axonal segments to develop prior to proximal segments.

Aluminum induces neurofilament aggregation by stabilizing cross-bridging of phosphorylated c-terminal sidearms

Exposure to neurotoxin aluminum neurotoxicity is accompanied by the perikaryal accumulation of tangles of phosphorylated neurofilaments (NFs). We examined their formation and reversibility under cell-free conditions. AlCl 3 induced dose-dependent formation of NF aggregates, ultimately incorporating 100% of detectable NFs. The same concentration of CaCl 2 induced approximately 25% of NFs to form longitudinal dimers and did not induce aggregation. AlCl 3 induced similar percentages of aggregates in the presence or absence of CaCl 2, and CaCl 2 could not reduce pre-formed aggregates. CaCl 2-induced dimers and AlCl 3-induced aggregates were prevented by prior NF dephosphorylation. While CaCl 2-induced dimers were dissociated by phosphatase treatment, AlCl 3-induced aggregates were only reduced by approximately 50%, suggesting that aggregates may sequester phosphorylation sites. Since phosphatases regulate NF phosphorylation within perikarya, inhibition of NF dephosphorylation by aluminum would promote perikaryal NF phosphorylation and foster precocious phospho-dependent NF–NF associations. These findings are consistent with the notion that prolonged interactions induced among phospho-NFs by the trivalent aluminum impairs axonal transport and promotes perikaryal aggregation.

Application of autologous bone marrow stem cells in giant axonal neuropathy

Giant axonal neuropathy is a rare disorder of autosomal recessive inheritance, morphologically characterized by accumulation of neurofilaments in enlargements of preterminal regions of central and peripheral axons. We present a 7-year-old girl with thick and tightly curled lackluster hair suffering from giant axonal neuropathy. The diagnosis was confirmed on the brain MRI which showed white matter abnormalities in the anterior and posterior periventricular regions as well as the cerebellar white matter. In view of the same, the patient was given intrathecal autologous bone marrow-derived stem cell therapy as part of the neuroregenerative rehabilitation therapy protocol. The patient showed functional improvements in her disability after receiving the therapy. A detailed case report is presented here with.