Neurofilaments are obligate heteropolymers in vivo

Antisense Morpholino Oligonucleotides Reduce Neurofilament Synthesis and Inhibit Axon Regeneration in Lamprey Reticulospinal Neurons

The sea lamprey has been used as a model for the study of axonal regeneration after spinal cord injury. Previous studies have suggested that, unlike developing axons in mammal, the tips of regenerating axons in lamprey spinal cord are simple in shape, packed with neurofilaments (NFs), and contain very little F-actin. Thus it has been proposed that regeneration of axons in the central nervous system of mature vertebrates is not based on the canonical actin-dependent pulling mechanism of growth cones, but involves an internal protrusive force, perhaps generated by the transport or assembly of NFs in the distal axon. In order to assess this hypothesis, expression of NFs was manipulated by antisense morpholino oligonucleotides (MO). A standard, company-supplied MO was used as control. Axon retraction and regeneration were assessed at 2, 4 and 9 weeks after MOs were applied to a spinal cord transection (TX) site. Antisense MO inhibited NF180 expression compared to control MO. The effect of inhibiting NF expression on axon retraction and regeneration was studied by measuring the distance of axon tips from the TX site at 2 and 4 weeks post-TX, and counting the number of reticulospinal neurons (RNs) retrogradely labeled by fluorescently-tagged dextran injected caudal to the injury at 9 weeks post-TX. There was no statistically significant effect of MO on axon retraction at 2 weeks post-TX. However, at both 4 and 9 weeks post-TX, inhibition of NF expression inhibited axon regeneration.

Live-cell imaging of neurofilament transport in cultured neurons

Neurofilaments, which are the intermediate filaments of nerve cells, are space-filling cytoskeletal polymers that contribute to the growth of axonal caliber. In addition to their structural role, neurofilaments are cargos of axonal transport that move along microtubule tracks in a rapid, intermittent, and bidirectional manner. Though they measure just 10nm in diameter, which is well below the diffraction limit of optical microscopes, these polymers can reach 100 μm or more in length and are often packed densely, just tens of nanometers apart. These properties of neurofilaments present unique challenges for studies on their movement. In this article, we describe several live-cell fluorescence imaging strategies that we have developed to image neurofilament transport in axons of cultured neurons on short and long timescales. Together, these methods form a powerful set of complementary tools with which to study the axonal transport of these unique intracellular cargos.

Order and disorder in intermediate filament proteins

Intermediate filaments (IFs), important components of the cytoskeleton, provide a versatile, tunable network of self-assembled proteins. IF proteins contain three distinct domains: an α-helical structured rod domain, flanked by intrinsically disordered head and tail domains. Recent studies demonstrated the functional importance of the disordered domains, which differ in length and amino-acid sequence among the 70 different human IF genes. Here, we investigate the biophysical properties of the disordered domains, and review recent findings on the interactions between them. Our analysis highlights key components governing IF functional roles in the cytoskeleton, where the intrinsically disordered domains dictate protein-protein interactions, supramolecular assembly, and macro-scale order.

Biomarkers of inflammation and axonal degeneration/damage in patients with newly diagnosed multiple sclerosis: contributions of the soluble CD163 CSF/serum ratio to a biomarker panel

BACKGROUND

Expression of soluble CD163 (sCD163), a macrophage/microglia biomarker, is increased in inflammatory conditions, and sCD163 levels in the cerebrospinal fluid (CSF) have recently been shown to be elevated in patients with multiple sclerosis (MS): the sCD163 CSF/serum ratio was elevated in patients with relapsing-remitting MS (RRMS), primary progressive MS (PPMS), and clinically isolated syndrome (CIS) compared with symptomatic controls.

OBJECTIVE

To investigate the contributions of the sCD163 CSF/serum ratio to a biomarker panel focusing on inflammation and axonal degeneration in newly diagnosed MS; thus optimising a diagnostic biomarker panel for MS.

METHODS

After a full MS diagnostic work-up, including collection of paired samples of CSF and serum, 125 patients were included in this study. Patients were divided into groups based on their diagnosis, and patients with normal clinical and paraclinical findings were defined as symptomatic controls. Serum and CSF levels, ratios, and indices of sCD163, CXCL13, osteopontin, neopterin, and CSF levels of neurofilament light polypeptide were determined by enzyme-linked immunosorbent assays (ELISAs). For sCD163 the results constitute a post-hoc analysis of already published data.

RESULTS

All tested biomarkers, notably the sCD163 ratio, the CXCL13 ratio, the NEO ratio, the CSF level of NfL, the IgG index, and the serum level of OPN, were significantly correlated to RRMS, PPMS, and/or CIS. The individual biomarkers in single tests had a lower performance than the IgG index, however, their combined receiver operating characteristic (ROC) curve demonstrated excellent diagnostic discriminatory power.

CONCLUSION

The biomarker panel showed distinct profiles for each patient group and could be a valuable tool for clinical differentiation of MS subgroups. The combined ROC analysis showed that sCD163 contributes positively as a diagnostic marker to a panel of established MS biomarkers. Patients with PPMS were demonstrated to have significantly elevated levels of both inflammatory and degenerative markers.

Diffuse axonal injury in brain trauma: insights from alterations in neurofilaments

Traumatic brain injury (TBI) from penetrating or closed forces to the cranium can result in a range of forms of neural damage, which culminate in mortality or impart mild to significant neurological disability. In this regard, diffuse axonal injury (DAI) is a major neuronal pathophenotype of TBI and is associated with a complex set of cytoskeletal changes. The neurofilament triplet proteins are key structural cytoskeletal elements, which may also be important contributors to the tensile strength of axons. This has significant implications with respect to how axons may respond to TBI. It is not known, however, whether neurofilament compaction and the cytoskeletal changes that evolve following axonal injury represent a component of a protective mechanism following damage, or whether they serve to augment degeneration and progression to secondary axotomy. Here we review the structure and role of neurofilament proteins in normal neuronal function. We also discuss the processes that characterize DAI and the resultant alterations in neurofilaments, highlighting potential clues to a possible protective or degenerative influence of specific neurofilament alterations within injured neurons. The potential utility of neurofilament assays as biomarkers for axonal injury is also discussed. Insights into the complex alterations in neurofilaments will contribute to future efforts in developing therapeutic strategies to prevent, ameliorate or reverse neuronal degeneration in the central nervous system (CNS) following traumatic injury.

Decelerated transport and its mechanism of 2,5-hexanedione on middle-molecular-weight neurofilament in rat dorsal root ganglia cells

Chronic exposure to n-hexane induces peripheral-central axonopathy, mediated by its metabolite 2,5-hexanedione (2,5-HD), in occupational workers and experimental animals, but the underlying mechanism is still unclear. In the current study, we investigated the effects of 2,5-HD on middle-molecular-weight neurofilament (NF-M) axonal transport using live-cell imaging technique in cultured rat dorsal root ganglia (DRG) cells. PA-GFP-NF-M plasmid was transfected into DRG neurons and live-cell imaging was performed to observe the slow axonal transport of NF-M. The levels of cytoskeleton and motor proteins in DRG cells were detected by Western-blot and the concentration of ATP was determined using an ATP Assay Kit. The results showed that 2,5-HD administration resulted in a decrease of NF-M axonal transport and a reduction of three neurofilament subunits levels in DRG cells. Furthermore, 2,5-HD exposure significantly decreased ATP contents and the protein levels of kinesin heavy chain (KHC). These findings indicated that 2,5-HD reduced slow axonal transport, neurofilaments cargoes, motor proteins and ATP energy in rat DRG cells, which may contribute to 2,5-HD-induced neurotoxicity.

Neuroprotective function of 14-3-3 proteins in neurodegeneration

14-3-3 proteins are abundantly expressed adaptor proteins that interact with a vast number of binding partners to regulate their cellular localization and function. They regulate substrate function in a number of ways including protection from dephosphorylation, regulation of enzyme activity, formation of ternary complexes and sequestration. The diversity of 14-3-3 interacting partners thus enables 14-3-3 proteins to impact a wide variety of cellular and physiological processes. 14-3-3 proteins are broadly expressed in the brain, and clinical and experimental studies have implicated 14-3-3 proteins in neurodegenerative disease. A recurring theme is that 14-3-3 proteins play important roles in pathogenesis through regulating the subcellular localization of target proteins. Here, we review the evidence that 14-3-3 proteins regulate aspects of neurodegenerative disease with a focus on their protective roles against neurodegeneration.

Neurofilament light and heavy subunits compared as therapeutic biomarkers in multiple sclerosis

BACKGROUND

Neurofilaments are promising biomarkers in multiple sclerosis (MS) and increased levels in cerebrospinal fluid (CSF) indicate axonal damage or degeneration. In a previous study, neurofilament light chain (NfL) levels in CSF of relapsing remitting (RR) patients with MS were normalized by natalizumab treatment.

AIMS OF THE STUDY

We compared the coherence between NfL and neurofilament heavy chain (NfH(SMI) (35) ) levels in longitudinal CSF samples in a subset of these patients.

METHODS

In 30 patients with RRMS, CSF was obtained prior to and following 12 months of natalizumab treatment. NfH(SMI) (35) was measured by an electrochemiluminescence-based immunoassay. NfL levels were determined previously by the UmanDiagnostics NF-light(®) assay.

RESULTS

NfH(SMI) (35) decreased in 73.3% and NfL in 90% of the patients following natalizumab treatment (32.4 vs 27.4 pg/ml, P = 0.002 and 820 vs 375 pg/ml, P < 0.0001). Patients experiencing a relapse showed higher NfH(SMI) (35) levels compared with patients in remission (47.7 vs 27.6 pg/ml, n = 8, P = 0.001). This difference was less obvious for NfL (1055 vs 725 pg/ml, P = 0.256). In patients in remission, NfL levels were lower following natalizumab treatment (830 vs 365 pg/ml, n = 20, P = 0.0002), whereas the same comparison failed significance for NfH(SMI) (35) (28.3 vs 26.9 pg/ml, P = 0.086).

CONCLUSIONS

We confirm previous findings, indicating reduced axonal damage under natalizumab treatment by measuring NfH(SMI) (35) , using an assay with independent methodology. In comparison with NfH(SMI) (35) , NfL changes were more pronounced and the treatment effect also included patients in remission. Our results suggest that NfL is superior over NfH(SMI) (35) as therapeutic biomarker and is a promising candidate to measure neuroaxonal damage in MS treatment trials.

Molecular cloning and characterization of chicken neuronal intermediate filament protein α-internexin

α-Internexin is one of the neuronal intermediate filament (IF) proteins, which also include low-, middle-, and high-molecular-weight neurofilament (NF) triplet proteins, designated NFL, NFM, and NFH, respectively. The expression of α-internexin occurs in most neurons as they begin differentiation and precedes the expression of the NF triplet proteins in mammals. However, little is known about the gene sequence and physiological function of α-internexin in avians. In this study we describe the molecular cloning of the mRNA sequence encoding the chicken α-internexin (chkINA) protein from embryonic brains. The gene structure and predicted amino acid sequence of chkINA exhibited high similarity to those of its zebrafish, mouse, rat, bovine, and human homologs. Data from transient-transfection experiments show that the filamentous pattern of chkINA was found in transfected cells and colocalized with other endogenous IFs, as demonstrated via immunocytochemistry using a chicken-specific antibody. The expression of chkINA was detected at the early stage of development and increased during the developmental process of the chicken. chkINA was expressed widely in chicken brains and colocalized with NF triplet proteins in neuronal processes, as assessed using immunohistochemistry. We also found that chkINA was expressed abundantly in the developing cerebellum and was the major IF protein in the parallel processes of granule neurons. Thus, we suggest that chkINA is a neuron-specific IF protein that may be a useful marker for studies of chicken brain development.

The role of NEFL in cell growth and invasion in head and neck squamous cell carcinoma cell lines

The neurofilament light polypeptide (NEFL) gene located on chromosome 8q21 is associated with the cancer of several organs and is regarded as a potential tumor suppressor gene. However, the role of the NEFL protein has not yet been studied in cancer cells. Although evidence suggests that there is a correlation between NEFL expression and cancer, studies regarding the role of the NEFL protein have been mostly limited to neurological diseases, such as Charcot-Marie-Tooth's disease (CMT). Most of these studies have not explored the role of NEFL in cancer cell apoptosis and/or invasion. In this study, NEFL expression was manipulated, and apoptosis and invasion were compared in head and neck squamous cell carcinoma cell lines. The results show that the expression of NEFL induces cancer cell apoptosis and inhibits invasion in these cell lines, suggesting that NEFL may play a role in cancer cell apoptosis and invasion.

A comparative study of CSF neurofilament light and heavy chain protein in MS

BACKGROUND

There is a lack of reliable biomarkers of axonal degeneration. Neurofilaments are promising candidates to fulfil this task. We compared two highly sensitive assays to measure two subunits of the neurofilament protein (neurofilament light (NfL) and neurofilament heavy chain (NfH)).

METHODS

We evaluated the analytical and clinical performance of the UmanDiagnostics NF-light(®) enzyme-linked immunosorbent assay (ELISA) in the cerebrospinal fluid (CSF) of a group of 148 patients with clinically isolated syndrome (CIS) or multiple sclerosis (MS), and 72 controls. We compared our results with referring levels of our previously-developed CSF NfH(SMI35) assay.

RESULTS

Exposure to room temperature (up to 8 days) or repetitive thawing (up to 4 thaws) did not influence measurement of NfL concentrations. Values of NfL were higher in all disease stages of CIS/MS, in comparison to controls (p ≤ 0.001). NfL levels correlated with the Expanded Disability Status Scale (EDSS) score in patients with relapsing disease (r(s) = 0.31; p = 0.002), spinal cord relapses and with CSF markers of acute inflammation. The ability of NfL to distinguish patients from controls was greater than that of NfH(SMI35) in both CIS patients (p = 0.001) and all MS stages grouped together (p = 0.035).

CONCLUSIONS

NfL proved to be a stable protein, an important prerequisite for a reliable biomarker, and the NF-light(®) ELISA performed better in discriminating patients from controls, compared with the ECL-NfH(SMI35) immunoassay. We confirmed and expanded upon previous findings regarding neurofilaments as quantitative markers of neurodegeneration. Our results further support the role of neurofilaments as a potential surrogate measure for neuroprotective treatment in MS studies.

Microscopic anatomy: normal structure

A peripheral nerve trunk is composed of nerve fascicles supported in a fibrous collagenous sheath and defined by concentric layers of cells (the perineurium) that separate the contents (the endoneurium) from its fibrous collagen support (the epineurium). In the endoneurium are myelinated and unmyelinated fibers that are axons combined with their supporting Schwann cells to provide physical and electrical connections with end-organs such as muscle fibers and sensory endings. Axons are tubular neuronal extensions with a cytoskeleton of neurotubules and tubulin along which organelles and proteins can travel between the neuronal cell body and the axon terminal. During development some axons enlarge and are covered by a chain of Schwann cells each associated with just one axon. As the axons grow in diameter, the Schwann cells wrap round them to produce a myelin sheath. This consists of many layers of compacted Schwann cell membrane plus some additional proteins. Adjacent myelin segments connect at highly specialized structures, the nodes of Ranvier. Myelin insulates the axon so that the nerve impulse can jump from one node to the next. The region adjacent to the node, the paranodal segment, is the site of myelin terminations on the axolemma. There are connections here between the Schwann cell and the axon via a complex chain of proteins. The Schwann cell cytoplasm in the adjacent segment, the juxtaparanode, contains most of the Schwann cell mitochondria. In addition to the node, continuity of myelin lamellae is broken at intervals along the internode by helical regions of decompaction known as Schmidt-Lanterman incisures; these are seen as paler conical segments in suitably stained microscopical preparations and provide a pathway between the adaxonal and abaxonal cytoplasm. Smaller axons without a myelin sheath conduct very much more slowly and have a more complex relationship with their supporting Schwann cells that has important implications for repair.

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.

Oxidative modification of neurofilament-L and neuronal cell death induced by the catechol neurotoxin, tetrahydropapaveroline

Tetrahydropapaveroline (THP), which is an endogenous neurotoxin, has been suspected to be associated with dopaminergic neurotoxicity of l-DOPA. In this study, we examined oxidative modification of neurofilament-L (NF-L) and neuronal cell death induced by THP. When disassembled NF-L was incubated with THP, protein aggregation was increased in a time- and THP dose-dependent manner. The formation of carbonyl compounds and dityrosine were observed in the THP-mediated NF-L aggregates. Radical scavengers reduced THP-mediated NF-L modification. These results suggest that the modification of NF-L by THP may be due to oxidative damage resulting from the generation of reactive oxygen species (ROS). When THP exposed NF-L was subjected to amino acid analysis, glutamate, proline and lysine residues were found to be particularly sensitive. We also investigated the effects of copper ions on THP-mediated NF-L modification. At a low concentration of THP, copper ions enhanced the modification of NF-L. Treatment of C6 astrocyte cells with THP led to a concentration-dependent reduction in cell viability. When these cells were treated with 100μM THP, the levels of ROS increased 3.5-fold compared with control cells. Furthermore, treatment of cells with THP increased NF-L aggregate formation, suggesting the involvement of NF-L modification in THP-induced cell damage.

The C-terminal domains of NF-H and NF-M subunits maintain axonal neurofilament content by blocking turnover of the stationary neurofilament network

Newly synthesized neurofilaments or protofilaments are incorporated into a highly stable stationary cytoskeleton network as they are transported along axons. Although the heavily phosphorylated carboxyl-terminal tail domains of the heavy and medium neurofilament (NF) subunits have been proposed to contribute to this process and particularly to stability of this structure, their function is still obscure. Here we show in NF-H/M tail deletion [NF-(H/M)(tailΔ)] mice that the deletion of both of these domains selectively lowers NF levels 3-6 fold along optic axons without altering either rates of subunit synthesis or the rate of slow axonal transport of NF. Pulse labeling studies carried out over 90 days revealed a significantly faster rate of disappearance of NF from the stationary NF network of optic axons in NF-(H/M)(tailΔ) mice. Faster NF disappearance was accompanied by elevated levels of NF-L proteolytic fragments in NF-(H/M)(tailΔ) axons. We conclude that NF-H and NF-M C-terminal domains do not normally regulate NF transport rates as previously proposed, but instead increase the proteolytic resistance of NF, thereby stabilizing the stationary neurofilament cytoskeleton along axons.

2,5-hexanedione altered the degradation of low-molecular-weight neurofilament in rat nerve tissues

Occupational exposure to n-hexane produces a central-peripheral distal axonopathy, which is characterized by giant axonal swellings filled with neurofilaments (NFs). To investigate the change of NFs degradation and their possible role in n-hexane neuropathy, adult male Wistar rats were administered intraperitoneally at a dosage of 400 mg/kg/day 2,5-hexanedione (2,5-HD) for 4 weeks. The time course of low-molecular-weight neurofilament (NF-L) degradation and autophagy-related protein in rat sciatic nerves and spinal cords was determined by Western blotting. The results demonstrated that the administration of 2,5-HD inhibited NF-L degradation to an undetectable level in sciatic nerves. Furthermore, a significant reduction of NF-L degradation in spinal cords was observed in the early stage of 2,5-HD exposure. In the meantime, 2,5-HD significantly decreased the level of Beclin-1, a key autophagy-regulated protein in sciatic nerves of rats while increased the level of P62, a selective substrate of autophagy degrading pathway, which indicated a dysfunctional autophagy in rat nerve tissues. Collectively, our findings suggested that the inhibition of autophagy by 2,5-HD might be responsible for the reduction of NF-L degradation in rat sciatic nerves, and involved in the pathogenesis of 2,5-HD-induced axonopathy.

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.

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.

Expansion of neurofilament medium C terminus increases axonal diameter independent of increases in conduction velocity or myelin thickness

Maturation of the peripheral nervous system requires specification of axonal diameter, which, in turn, has a significant influence on nerve conduction velocity. Radial axonal growth initiates with myelination, and is dependent upon the C terminus of neurofilament medium (NF-M). Molecular phylogenetic analysis in mammals suggested that expanded NF-M C termini correlated with larger-diameter axons. We used gene targeting and computational modeling to test this new hypothesis. Increasing the length of NF-M C terminus in mice increased diameter of motor axons without altering neurofilament subunit stoichiometry. Computational modeling predicted that an expanded NF-M C terminus extended farther from the neurofilament core independent of lysine-serine-proline (KSP) phosphorylation. However, expansion of NF-M C terminus did not affect the distance between adjacent neurofilaments. Increased axonal diameter did not increase conduction velocity, possibly due to a failure to increase myelin thickness by the same proportion. Failure of myelin to compensate for larger axonal diameters suggested a lack of plasticity during the processes of myelination and radial axonal growth.

Assembly properties of lamprey neurofilament subunits and their expression after spinal cord transection

In mammals neurofilaments (NF) are formed by coassembly of three subunits: NFL, NFM, and NFH (light, medium, and heavy). It had been believed that lampreys have only one subunit, NF180. However, a previous study showed that NF180 could not self-assemble but could coassemble with rat NFL, suggesting the existence of additional NF subunits in lamprey. More recently, we cloned three additional NF subunits. These new subunits and NF180 have now been transfected in combinations into SW13cl.2Vim(-) cells, which lack endogenous cytoplasmic intermediate filaments. None of the subunits could self-assemble. No combination of NF subunits could form filaments in the absence of lamprey NFL (L-NFL). Assembly occurred at 28°C, but not at 37°C. L-NFL could form thick NF bundles with NF180 but not with NF132 and NF95, which formed only fine filamentous arrays. To determine which parts of the NF subunits are required for filament or bundle formation, we constructed deletion mutants of NF180 and cotransfected them with L-NFL. As with mammalian NF, only constructs with intact head and core domains could form filaments with L-NFL. However, the full length of NF180 was required to form NF bundles. As with NF180, in situ hybridization indicated that mRNA for L-NFL and NF132 was downregulated in identified reticulospinal neurons by 5 weeks after spinal cord transection, but was reexpressed at 10 weeks selectively in those neurons whose axons have a high probability of regenerating. This is consistent with a possible role of NFs in the mechanism of axon regeneration.

Expressing hNF-LE397K results in abnormal gaiting in a transgenic model of CMT2E

Charcot-Marie-Tooth disease (CMT) is the most commonly inherited peripheral neuropathy. CMT disease signs include distal limb neuropathy, abnormal gaiting, exacerbation of neuropathy, sensory defects and deafness. We generated a novel line of CMT2E mice expressing an hNF-L(E397K) transgene, which displayed muscle atrophy of the lower limbs without denervation, proximal reduction in large caliber axons and decreased nerve conduction velocity. In this study, we showed that hNF-L(E397K) mice developed abnormal gait of the hind limbs. The identification of severe gaiting defects in combination with previously observed muscle atrophy, reduced axon caliber and decreased nerve conduction velocity suggests that hNF-L(E397K) mice recapitulate many of clinical signs associated with CMT2E. Therefore, hNF-L(E397K) mice provide a context for potential therapeutic intervention.

Axonal Charcot-Marie-Tooth disease

PURPOSE OF REVIEW

The aim is to specify the genetic causes of dominantly and recessively inherited axonal forms of Charcot-Marie-Tooth disease (CMT) and review the biological basis for these disorders.

RECENT FINDINGS

More than 10 genes that cause axonal CMT have been identified over the past decade. Many of these genes express proteins that are ubiquitously expressed. Clinical phenotypes of many of these disorders are being studied and animal and cellular models of these neuropathies have been created.

SUMMARY

Identification of these new genetic causes of axonal neuropathy has not only been important for patients and their families but it has also provided exciting new information about disease mechanisms involved in neuronal degeneration. These mechanisms extend beyond the field of axonal CMT and have relevance to sensory neuropathies and motor neuron disorders. Therapeutic strategies for some of these are also provided. We hope that this review will be of interest to clinicians and scientists interested in axonal forms of CMT.

Single-stranded noncoding RNAs mediate local epigenetic alterations at gene promoters in rat cell lines

A growing number of noncoding RNAs (ncRNAs) are thought to be involved in sequence-specific alterations of epigenetic processes, mostly causing gene repression. In this study, promoter-associated ncRNAs (pancRNAs >200 nucleotides in size) that were endogenously generated from the sense strand at Map2b, antisense strand at Nefl, and both strands at Vim were investigated regarding their epigenetic potential as positive or negative regulators in rat pheochromocytoma (PC12) and fibroblast (normal rat kidney) cell lines. The respective antisense pancRNAs were associated with several active chromatin marks at the Nefl and Vim promoters. Forced expression of fragments expressing the antisense pancRNAs caused sequence-specific DNA demethylation, whereas a decrease of expression induced methylation of the same sequences. In contrast, perturbing the expression of the two sense pancRNAs did not change the DNA methylation status. These results suggest that a fraction of naturally occurring ncRNAs acts in cis as a single-stranded form and that the transcriptional orientation of pancRNA is important for the establishment of sequence-specific epigenetic modifications consistent with open chromatin structure.

Phosphatidylinositol phosphates directly bind to neurofilament light chain (NF-L) for the regulation of NF-L self assembly

Phosphatidylinositol phosphates (PtdInsPs) are ubiquitous membrane phospholipids that play diverse roles in cell growth and differentiation. To clarify the regulation mechanism acting on neurofilament light chain (NF-L) self assembly, we examined the effects of various PtdInsPs on this process. We found that PtdInsPs, including PI(4,5)P((2)), directly bind to the positively charged Arg(54) of murine NF-L, and this binding promotes NF-L self assembly in vitro. Mutant NF-L (R53A/R54A) proteins lacking binding affinity to PtdInsPs did not have the same effect, but the mutant NF-L proteins showed greater self assembly than the wild-type in the absence of any PtdInsP. These results collectively suggest that Arg(54) plays a pivotal role in NF-L self assembly by binding with PtdInsPs.

Biomarker-based dissection of neurodegenerative diseases

The diagnosis of neurodegenerative diseases within neurology and psychiatry are hampered by the difficulty in getting biopsies and thereby validating the diagnosis by pathological findings. Biomarkers for other types of disease have been readily adopted into the clinical practice where for instance troponins are standard tests when myocardial infarction is suspected. However, the use of biomarkers for neurodegeneration has not been fully incorporated into the clinical routine. With the development of cerebrospinal fluid (CSF) biomarkers that reflect pathological events within the central nervous system (CNS), important clinical diagnostic tools are becoming available. This review summarizes the most promising biomarker candidates that may be used to monitor different types of neurodegeneration and protein inclusions, as well as different types of metabolic changes, in living patients in relation to the clinical phenotype and disease progression over time. Our aim is to provide the reader with an updated lexicon on currently available biomarker candidates, how far they have come in development and how well they reflect pathogenic processes in different neurodegenerative diseases. Biomarkers for specific pathogenetic processes would also be valuable tools both to study disease pathogenesis directly in patients and to identify and monitor the effect of novel treatment strategies.

Muscle pathology without severe nerve pathology in a new mouse model of Charcot-Marie-Tooth disease type 2E

Mutations in neurofilament light (NF-L) have been linked to Charcot-Marie-Tooth disease type 2E (CMT2E) in humans. To provide insight into disease pathogenesis, we developed a novel line of CMT2E mice that constitutively express human NF-L (hNF-L) with a glutamic acid to lysine mutation at position 397 (hNF-L(E397K)). This new line of mice developed signs consistent with CMT2E patients. Disease signs were first observed at 4 months in hNF-L(E397K) mice, and consisted of aberrant hind limb posture, digit deformities, reduced voluntary locomotor activity, reduced motor nerve conduction velocities (MNCVs) and muscle atrophy. Reduced voluntary locomotor activity and muscle pathology occurred without significant denervation, and hNF-L(E397K) mice showed relatively mild signs of nerve pathology. Nerve pathology in hNF-L(E397K) mice was characterized by ectopic accumulations of phosphorylated NFs in motor neuron cell bodies as early as 1 month. Moreover, NF organization was altered in motor and sensory roots, with small motor axons being most affected. Peak axonal diameter was reduced for small motor axons prior to and after the onset of overt phenotypes, whereas large motor axons were affected only after onset, which correlated with reduced MNCVs. Additionally, there was a small reduction in the number of sensory axons in symptomatic hNF-L(E397K) mice. hNF-L(E397K) mice are a novel line of CMT2E mice that recapitulate many of the overt phenotypes observed in CMT2E patients and hNF-L(P22S) mice. The cellular pathology observed in hNF-L(E397K) mice differed from that recently reported in hNF-L(P22S) mice, suggesting that overt CMT2E phenotypes may arise through different cellular mechanisms.

Multiple neurofilament subunits are present in lamprey CNS

In mammals, there are three neurofilament (NF) subunits (NF-L, NF-M, and NF-H), but it was thought that only a single NF, NF180, exists in lamprey. However, NF180 lacked the ability to self-assemble, suggesting that like mammalian NFs, lamprey NFs are heteropolymers, and that additional NF subunits may exist. The present study provides evidence for the existence of a lamprey NF-L homolog (L-NFL). Genes encoding two new NF-M isoforms (NF132 and NF95) also have been isolated and characterized. With NF180, this makes three NF-M-like isoforms. In situ hybridization showed that all three newly cloned NFs are expressed in spinal cord neurons and in spinal-projecting neurons of the brainstem. Like NF180, there were no KSP multiphosphorylation repeat motifs in the tail regions of NF132 or NF95. NF95 was highly identical to homologous parts of NF180, sharing 2 common pieces of DNA with it. Northern blots suggested that NF95 may be expressed at very low levels in older larvae. The presence of L-NFL in lamprey CNS may support the hypothesis that as in mammals, NFs in lamprey are obligate heteropolymers, in which NF-L is a required subunit.

Phosphorylation-mediated conformational changes in the mouse neurofilament architecture: insight from a neurofilament brush model

Neurofilaments (NFs) are important cytoskeletal filaments that consist of long flexible C-terminal tails that are abundant with charges. The tails attain additional negative charges through serine phosphorylation of Lys-Ser-Pro (KSP) repeat motifs that are particularly found in neurofilament heavy (NF-H) and neurofilament medium (NF-M) proteins. These side-arm protrusions mediate the interaction between neighboring filaments and maintain axonal diameter. However, the precise role of NF proteins and their phosphorylation in regulating interfilament distances and axonal diameter still remains unclear. In this regard, a recent gene replacement study revealed that the phosphorylation of mouse NF-M KSP repeats does not affect axonal cytoarchitecture, challenging the conventional viewpoint on the role of NF phosphorylation. To better understand the effect of phosphorylation, particularly NF-M phosphorylation, we applied a computational method to reveal phosphorylation-mediated conformational changes in mouse NF architecture. We employed a three-dimensional sequence-based coarse-grained NF brush model to perform Monte Carlo simulations of mouse NF by using the sequence and stoichiometry of mouse NF proteins. Our result shows that the phosphorylation of mouse NF-M does not change the radial extension of NF-M side arms under a salt-free condition and in ionic solution, highlighting a structural factor that supports the notion that NF-M KSP phosphorylation has no effect on the axonal diameter of mouse. On the other hand, significant phosphorylation-mediated conformational changes were found in NF-H side arms under the salt-free condition, while the changes in ionic solution are not significant. However, NF-H side arms are found at the periphery of mouse NF architecture, implying a role in linking neighboring filaments.

Transgenic mouse models of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory demyelinating disease affecting the central nervous system (CNS) and a frequent cause of neurological disability in young adults. Multifocal inflammatory lesions in the CNS white matter, demyelination, oligodendrocyte loss, axonal damage, as well as astrogliosis represent the histological hallmarks of the disease. These pathological features of MS can be mimicked, at least in part, using animal models. This review discusses the current concepts of the immune effector mechanisms driving CNS demyelination in murine models. It highlights the fundamental contribution of transgenesis in identifying the mediators and mechanisms involved in the pathophysiology of MS models.

Conformational dynamics of neurofilament side-arms

The side-arms of neurofilaments (NFs) have been proposed to be highly disordered, leading to entropic repulsion that modulates interfilament spacing. To gain further insight into the dynamics and organization of the side-arms, we performed molecular dynamics simulations of neurofilament brushes using a coarse-grained model. The density profiles for three NF proteins, NF-L, NF-M, and phosphorylated NF-H (NF-HP), grafted to planar surfaces were calculated and examined as a function of component (salt, residues) and as a function of charge. Analysis of these profiles reveals that the NF with the shortest side arm, NF-L, is disproportionately long compared to the other NFs. The reason for difference is that NF-L is effectively a strong polyelectrolyte, while NF-M and NF-HP are effectively weaker polyelectrolytes. Further, we find cross-correlations between neurofilament side-arms within the brush, even for the NF-L polymers. These correlations occur because of strong attractions between the long sequence repeats of negative residues and the long postive residue repeats and impart a time average structure of the neurofilament brush that deviates from an ideal polymer in a theta solvent.

Syncoilin modulates peripherin filament networks and is necessary for large-calibre motor neurons

Syncoilin is an atypical type III intermediate filament (IF) protein, which is expressed in muscle and is associated with the dystrophin-associated protein complex. Here, we show that syncoilin is expressed in both the central and peripheral nervous systems. Isoform Sync1 is dominant in the brain, but isoform Sync2 is dominant in the spinal cord and sciatic nerve. Peripherin is a type III IF protein that has been shown to colocalise and interact with syncoilin. Our analyses suggest that syncoilin might function to modulate formation of peripherin filament networks through binding to peripherin isoforms. Peripherin is associated with the disease amyotrophic lateral sclerosis (ALS), thus establishing a link between syncoilin and ALS. A neuronal analysis of the syncoilin-null mouse (Sync(-/-)) revealed a reduced ability in accelerating treadmill and rotarod tests. This phenotype might be attributable to the impaired function of extensor digitorum longus muscle and type IIb fibres caused by a shift from large- to small-calibre motor axons in the ventral root.

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.

Anti-alpha-internexin autoantibody from neuropsychiatric lupus induce cognitive damage via inhibiting axonal elongation and promote neuron apoptosis

BACKGROUND

Neuropsychiatric systemic lupus erythematosus (NPSLE) is a major complication for lupus patients, which often leads to cognitive disturbances and memory loss and contributes to a significant patient morbidity and mortality. The presence of anti-neuronal autoantibodies (aAbs) has been identified; as examples, anti-NMDA receptors and anti-Ribsomal P aAbs have been linked to certain pathophysiological features of NPSLE.

METHODS AND FINDINGS

In the current study, we used a proteomic approach to identify an intermediate neurofilament alpha-internexin (INA) as a pathogenetically relevant autoantigen in NPSLE. The significance of this finding was then validated in an expanded of a cohort of NPSLE patients (n = 67) and controls (n = 270) by demonstrating that high titers of anti-INA aAb was found in both the serum and cerebrospinal fluid (CSF) of approximately 50% NPSLE. Subsequently, a murine model was developed by INA immunization that resulted in pronounced cognitive dysfunction that mimicked features of NPSLE. Histopathology in affected animals displayed cortical and hippocampal neuron apoptosis. In vitro studies further demonstrated that anti-INA Ab mediated neuronal damage via inhibiting axonal elongation and eventually driving the cells to apoptosis.

CONCLUSIONS

Taken together, this study identified a novel anti-neurofilament aAb in NPSLE, and established a hitherto undescribed mechanism of aAb-mediated neuron damage that could have relevance to the pathophysiology of NPSLE.

Neurofilament localization and phosphorylation in the developing inner ear of the rat

Detailed understanding of neurofilament protein distribution in the inner ear can shed light on regulatory mechanisms involved in neuronal development of this tissue. We assessed the spatio-temporal changes in the distribution of neurofilaments in the developing rat inner ear between embryonic day 12 and 30 days after birth, using antibodies against phosphorylated as well as non-phosphorylated light (NFL), medium (NFM) and heavy (NFH) neurofilament subunits. Our results show that during development, the onset of neurofilament expression in the rat inner ear is on embryonic day 12, earlier than previously shown. We demonstrate that neurofilament subunits of different molecular weight emerge in a developmental stage-dependent order. In addition, we determined that neurofilaments of the vestibular nerve mature earlier than neurofilaments of the cochlear nerve. Cochlear neurofilament maturation progresses in a gradient from base to apex, and from inner to outer hair cells. The sequential pattern of neurofilament expression we describe may help understand the consequences of certain mutations, and contribute to develop therapeutic strategies.

How the projection domains of NF-L and alpha-internexin determine the conformations of NF-M and NF-H in neurofilaments

Making use of a numerical self-consistent field method and polymer brush concepts, we model the solvated corona of neurofilaments (NF) composed of projection domains (unstructured tails) of constituent proteins. Projections are modeled with amino acid resolution. We focus on the importance of the two shortest ones (alpha-internexin and NF-L) in regulating the conformations of the two longer ones (NF-M and NF-H) in an isolated NF. We take the wild-type NF with no alpha-internexin as the reference, for which the phosphorylation-induced translocation of M- and H-tails has been examined previously. We demonstrate that a subbrush of L-tails creates an electrostatic potential profile with an approximately parabolic shape. An experimentally relevant (2:1) ratio of L- to alpha-projections reduces the charge density of the L subbrush and shifts the translocation transition of the H-tails to slightly higher degrees of phosphorylation. Replacing all L-tails by alpha-projections destroys the substructure of the NF corona and this alters the NF response to the phosphorylation of long tails.

Variation of the neurofilament medium KSP repeat sub-domain across mammalian species: implications for altering axonal structure

The evolution of larger mammals resulted in a corresponding increase in peripheral nerve length. To ensure optimal nervous system functionality and survival, nerve conduction velocities were likely to have increased to maintain the rate of signal propagation. Increases of conduction velocities may have required alterations in one of the two predominant properties that affect the speed of neuronal transmission: myelination or axonal diameter. A plausible mechanism to explain faster conduction velocities was a concomitant increase in axonal diameter with evolving axonal length. The carboxy terminal tail domain of the neurofilament medium subunit is a determinant of axonal diameter in large caliber myelinated axons. Sequence analysis of mammalian orthologs indicates that the neurofilament medium carboxy terminal tail contains a variable lysine-serine-proline (KSP) repeat sub-domain flanked by two highly conserved sub-domains. The number of KSP repeats within this region of neurofilament medium varies among species. Interestingly, the number of repeats does not change within a species, suggesting that selective pressure conserved the number of repeats within a species. Mapping KSP repeat numbers onto consensus phylogenetic trees reveals independent KSP expansion events across several mammalian clades. Linear regression analyses identified three subsets of mammals, one of which shows a positive correlation in the number of repeats with head-body length. For this subset of mammals, we hypothesize that variations in the number of KSP repeats within neurofilament medium carboxy terminal tail may have contributed to an increase in axonal caliber, increasing nerve conduction velocity as larger mammals evolved.

A novel recessive Nefl mutation causes a severe, early-onset axonal neuropathy

OBJECTIVE

To report the first cases of a homozygous recessive mutation in NEFL, the gene that encodes the light subunit of neurofilaments.

METHODS

Clinical and electrophysiologic data were evaluated, and a sural nerve biopsy from one affected child was examined by immunohistochemistry and electron microscopy. The ability of the mutant protein to form filaments was characterized in an established cell culture system.

RESULTS

Four of five siblings developed of a severe, progressive neuropathy beginning in early childhood. Serial nerve conduction studies showed progressively reduced amplitudes with age and pronounced slowing at all ages. Visual-evoked responses were slowed in three children, indicating that central nervous system axons were subclinically involved. All four affected children were homozygous for a nonsense mutation at glutamate 210 (E210X) in the NEFL gene; both parents were heterozygous carriers. A sural nerve biopsy from an affected patient showed markedly reduced numbers of myelinated axons; the remaining myelinated axons were small and lacked intermediate filaments. The E210X mutant protein did not form an intermediate filament network and did not interfere with the filament formation by wild-type human light subunit of neurofilaments in SW-13 vim(-) cells.

INTERPRETATION

This is the first demonstration of a recessive NEFL mutation, which appears to cause a simple loss of function, resulting in a severe, early-onset axonal neuropathy with unique features. These results confirm that neurofilaments are the main determinant of axonal caliber and conduction velocity, and demonstrate for the first time that neurofilaments are required for the maintenance of myelinated peripheral nervous system axons.

Novel axonal distribution of neurofilament-H phosphorylated at the glycogen synthase kinase 3beta-phosphorylation site in its E-segment

The Ser493 residue in the E-segment of the rat neurofilament heavy chain (NF-H) is phosphorylated by glycogen synthase kinase 3beta (GSK3 beta) in vitro and in spinal cord. We examined Ser493 phosphorylation by analyzing developmental changes and cellular distribution of phospho-Ser493 using phosphorylation-site-specific antibodies. This residue was phosphorylated in NF-H prepared from human, rat, and mouse spinal cord, all species in which the amino acid sequence of NF-H is known. Phosphorylated Ser493 appeared on postnatal day 2 in rat brain, at the same time when NF-H is first detected. It gradually increased together with the increase in total NF-H during brain development. Phospho-Ser493 was detected on the phosphorylated form of NF-H at multiple Lys-Ser-Pro (KSP) repeats, which are distributed mainly in axons. In rat ventral horn, phosphorylated Ser493 was localized in axons but not in cell bodies or dendrites. However, the distributions of phosphorylated Ser493 and KSP phosphorylation in axons were not identical. Ser493 was continuously phosphorylated at nodes of Ranvier, whereas the KSP sites were dephosphorylated. Ser493 was also phosphorylated in unmyelinated regions of optic nerve axons. A biochemical difference in phosphorylation between Ser493 and KSP repeats was also found; the subtle phosphorylation at Ser493 was detected in NF-H unphosphorylated at the KSP repeats by immunoblotting cerebral cortex extracts. These results indicate that Ser493 in the NF-H E-segment is a novel site that is phosphorylated in both the myelinated and the unmyelinated regions of axons.

Neurofilament ELISA validation

BACKGROUND

Neurofilament proteins (Nf) are highly specific biomarkers for neuronal death and axonal degeneration. As these markers become more widely used, an inter-laboratory validation study is required to identify assay criteria for high quality performance.

METHODS

The UmanDiagnostics NF-light (R)enzyme-linked immunoabsorbent assays (ELISA) for the neurofilament light chain (NfL, 68kDa) was used to test the intra-assay and inter-laboratory coefficient of variation (CV) between 35 laboratories worldwide on 15 cerebrospinal fluid (CSF) samples. Critical factors, such as sample transport and storage, analytical delays, reaction temperature and time, the laboratories' accuracy and preparation of standards were documented and used for the statistical analyses.

RESULTS

The intra-laboratory CV averaged 3.3% and the inter-laboratory CV 59%. The results from the test laboratories correlated with those from the reference laboratory (R=0.60, p<0.0001). Correcting for critical factors improved the strength of the correlation. Differences in the accuracy of standard preparation were identified as the most critical factor. Correcting for the error introduced by variation in the protein standards improved the correlation to R=0.98, p<0.0001 with an averaged inter-laboratory CV of 14%. The corrected overall inter-rater agreement was subtantial (0.6) according to Fleiss' multi-rater kappa and Gwet's AC1 statistics.

CONCLUSION

This multi-center validation study identified the lack of preparation of accurate and consistent protein standards as the main reason for a poor inter-laboratory CV. This issue is also relevant to other protein biomarkers based on this type of assay and will need to be solved in order to achieve an acceptable level of analytical accuracy. The raw data of this study is available online.

Dynamic changes of neuroskeletal proteins in DRGs underlie impaired axonal maturation and progressive axonal degeneration in type 1 diabetes

We investigated mechanisms underlying progressive axonal dysfunction and structural deficits in type 1 BB/Wor-rats from 1 week to 10 month diabetes duration. Motor and sensory conduction velocities were decreased after 4 and 6 weeks of diabetes and declined further over the remaining 9 months. Myelinated sural nerve fibers showed progressive deficits in fiber numbers and sizes. Structural deficits in unmyelinated axonal size were evident at 2 month and deficits in number were present at 4 mo. These changes were preceded by decreased availability of insulin, C-peptide and IGF-1 and decreased expression of neurofilaments and β-III-tubulin. Upregulation of phosphorylating stress kinases like Cdk5, p-GSK-3β, and p42/44 resulted in increased phosphorylation of neurofilaments. Increasing activity of p-GSK-3β correlated with increasing phosphorylation of NFH, whereas decreasing Cdk5 correlated with diminishing phosphorylation of NFM. The data suggest that impaired neurotrophic support results in sequentially impaired synthesis and postranslational modifications of neuroskeletal proteins, resulting in progressive deficits in axonal function, maturation and size.

Phenylmethylsulfonyl fluoride protects against the degradation of neurofilaments in tri-ortho-cresyl phosphate (TOCP) induced delayed neuropathy

Tri-ortho-cresyl phosphate (TOCP) is an organophosphorus ester, which can cause a type of neurotoxicity known as organophosphate-induced delayed neuropathy (OPIDN). Our recent study has shown that the enhanced degradation of neurofilament (NF) in peripheral nerve of hens is an early event of TOCP-induced OPIDN (Song et al., 2009). The main objective of this investigation is to study the effect of TOCP administration on NF content and NF degradation when OPIDN is blocked by pretreatment with phenylmethylsulfonyl fluoride (PMSF). The hens were pretreated 24h earlier with PMSF and subsequently treated with a single dosage of 750 mg/kg TOCP, then sacrificed on the corresponding time points of 0, 1, 5, 10, and 21 days after dosing TOCP, respectively. The tibial nerves were dissected, homogenized, and centrifuged at 100,000 x g. The level of NF triplet protein in both pellet and supernatant fractions of tibial nerves was determined. Western blotting analysis showed a significant increase of three NF subunits in hens treated with PMSF and TOCP compared with the control. These changes were observed within 24h of PMSF administration and then followed by an obvious recovery. Furthermore, accompanied with the increase of NF content, a significant decline in NF-L degradation rate was observed in both fractions of tibial nerves. Taken together, these results demonstrated the pretreatment with PMSF could inhibit TOCP-induced NF degradation while it protected hens against the development of OPIDN, which suggested the inhibition of NF-associated protease in peripheral nerves might be an underlying protective mechanism of PMSF against OPIDN.