Altered plasma membrane abundance of the sulfatide-binding protein NF155 links glycosphingolipid imbalances to demyelination.

Myelin is a multilayered membrane that tightly wraps neuronal axons, enabling efficient, high-speed signal propagation. The axon and myelin sheath form tight contacts, mediated by specific plasma membrane proteins and lipids, and disruption of these contacts causes devastating demyelinating diseases. Using two cell-based models of demyelinating sphingolipidoses, we demonstrate that altered lipid metabolism changes the abundance of specific plasma membrane proteins. These altered membrane proteins have known roles in cell adhesion and signaling, with several implicated in neurological diseases. The cell surface abundance of the adhesion molecule neurofascin (NFASC), a protein critical for the maintenance of myelin-axon contacts, changes following disruption to sphingolipid metabolism. This provides a direct molecular link between altered lipid abundance and myelin stability. We show that the NFASC isoform NF155, but not NF186, interacts directly and specifically with the sphingolipid sulfatide via multiple binding sites and that this interaction requires the full-length extracellular domain of NF155. We demonstrate that NF155 adopts an S-shaped conformation and preferentially binds sulfatide-containing membranes in cis, with important implications for protein arrangement in the tight axon-myelin space. Our work links glycosphingolipid imbalances to disturbance of membrane protein abundance and demonstrates how this may be driven by direct protein-lipid interactions, providing a mechanistic framework to understand the pathogenesis of galactosphingolipidoses.

Direct fluorescent labeling of NF186 and NaV1.6 in living primary neurons using bioorthogonal click chemistry.

The axon initial segment (AIS) is a highly specialized neuronal compartment that regulates the generation of action potentials and maintenance of neuronal polarity. Live imaging of the AIS is challenging due to the limited number of suitable labeling methods. To overcome this limitation, we established a novel approach for live labeling of the AIS using unnatural amino acids (UAAs) and click chemistry. The small size of UAAs and the possibility of introducing them virtually anywhere into target proteins make this method particularly suitable for labeling of complex and spatially restricted proteins. Using this approach, we labeled two large AIS components, the 186 kDa isoform of neurofascin (NF186; encoded by Nfasc) and the 260 kDa voltage-gated Na+ channel (NaV1.6, encoded by Scn8a) in primary neurons and performed conventional and super-resolution microscopy. We also studied the localization of epilepsy-causing NaV1.6 variants with a loss-of-function effect. Finally, to improve the efficiency of UAA incorporation, we developed adeno-associated viral (AAV) vectors for click labeling in neurons, an achievement that could be transferred to more complex systems such as organotypic slice cultures, organoids, and animal models.

Proteinuria is a key to suspect autoimmune nodopathies.

BACKGROUND AND PURPOSE: Reports of patients who have autoimmune nodopathies concurrent with nephrotic syndrome are increasing. We investigated whether proteinuria could be a biomarker of autoimmune nodopathies. METHODS: Qualitative urinalysis results were retrospectively obtained from 69 patients who were diagnosed with chronic inflammatory demyelinating polyneuropathy (CIDP) at a hospital in Japan. Proteinuria was graded as mild to severe (i.e., mild, 30-99; moderate, 100-299; severe, 300 mg/dL or more) according to the results of the urine dipstick test. Autoantibodies against the paranodal proteins contactin 1 (CNTN1), neurofascin 155 (NF155), and contactin-associated protein 1 (Caspr1) and the nodal protein neurofascin 186 (NF186) were measured, and the predominant IgG subclass was determined by enzyme-linked immunosorbent assay in sera from the 69 patients. RESULTS: Four patients (6%), five patients (7%), and one (1%) patient were positive for anti-CNTN1, anti-NF155, and anti-Caspr1 IgG4 antibodies, respectively. No patients had IgG4 antibodies against NF186. Proteinuria of mild or greater levels was found in three patients with anti-CNTN1 IgG4 and two patients with anti-NF155 IgG4 antibodies. The autoantibody-positive patients more frequently had proteinuria of mild or greater levels than the seronegative patients (p = 0.01). CONCLUSIONS: Proteinuria is a possible biomarker of autoimmune nodopathies associated with autoantibodies targeting CNTN1 or NF155. Urinalysis results should be carefully checked for quick differentiation of autoimmune nodopathies from CIDP. Patients who present with nephrotic syndrome should be tested for anti-CNTN1 IgG4 antibodies, and patients who exhibit mild proteinuria should be tested for anti-NF155 IgG4 antibodies.

Anti-pan-neurofascin antibodies induce subclass-related complement activation and nodo-paranodal damage.

Autoimmune neuropathy associated with antibodies against pan-neurofascin is a new subtype of nodo-paranodopathy. It is relevant because it is associated with high morbidity and mortality. Affected patients often require intensive care unit treatment for several months, and data on the reversibility and long-term prognosis are limited. The pathogenicity including IgG subclass-associated mechanisms has not been unravelled, nor directly compared to anti-neurofascin-155 IgG4-related pathology. Understanding the underlying pathology might have a direct impact on treatment of these severely affected patients. By a multicentre combined prospective and retrospective approach, we provide clinical data of a large cohort of patients with anti-neurofascin-associated neuropathy (n = 18) including longitudinal titre and neurofilament light chain assessment via Ella® and relate clinical data to in vitro pathogenicity studies of anti-neurofascin antibodies. We assessed antibody binding characteristics and the pathogenic effects of anti-pan-neurofascin versus neurofascin-155 antibodies on living myelinating dorsal root ganglia co-cultures. Additionally, we analysed the IgG subclass profile and the complement binding capacity and effector functions considering the effects of intravenous immunoglobulin preparations via enzyme-linked immunosorbent and cell-based assays. In contrast to chronic neurofascin-155 IgG4-associated neuropathy, anti-pan-neurofascin-associated disease presented with a high morbidity and mortality, but as a monophasic and potentially reversible disorder. During follow-up, antibodies were no longer detectable in 8 of 11 patients. Anti-pan-neurofascin had direct access to the nodes of Ranvier in myelinating cultures titre-dependently, most probably inducing this severe phenotype. Antibody preincubation led to impaired paranode formation, destruction of paranodal architecture and alterations on paranodal myelin and sensory neurons in the cultures, with more severe effects than neurofascin-155 antibodies. Besides IgG4, subclass IgG3 was detected and associated with complement binding and cytotoxic effects in vitro. As a possible correlate of axonal damage in vivo, we detected highly increased serum neurofilament light chain levels (sNF-L), correlating to serum C3a. Still, sNF-L was not identified as a marker for poor prognosis, but rather as an intra- and interindividual marker for acuteness, severity and course, with a strong decrease during recovery. Our data provide evidence that anti-pan-neurofascin antibodies directly attack the node and induce severe and acute, but potentially reversible, nodo-paranodal pathology, possibly involving complement-mediated mechanisms. Screening for autoantibodies thus is crucial to identify this subset of patients who benefit from early antibody-depleting therapy. Titre and sNF-L might serve as valuable follow-up parameters. The prospect of a favourable outcome has high relevance for physicians, patients and relatives during months of critical care.

Anti-pan-neurofascin nodopathy: cause of fulminant neuropathy.

Autoimmune nodopathies are inflammatory diseases of the peripheral nervous system with clinical and neurophysiological peculiar characteristics. In this nosological category, we find patients with autoantibodies against Neurofascin 140/186 and 155, Contactin1, and Caspr1 directed precisely towards nodal and paranodal structures. These antibodies are extremely rare and cause severe clinical symptoms. We describe the clinical case of a patient with autoimmune nodopathy caused by the coexistence of anti-neurofascin (NF) 186/140 and 155, characterized by progressive weakness in all limbs leading to tetraplegia, involving cranial nerves, and respiratory insufficiency. Response to first-line treatments was good followed by rapid dramatic clinical relapse. There are few reported cases of anti-pan NF neuropathy in the literature, and they present a clinical phenotype similar to our patient. In these cases, early recognition of clinical red flags of nodopathies and serial neurophysiological studies can facilitate the diagnosis. However, the severe clinical relapse suggests a possible early use of immunosuppressive therapies for this rare category of patients.

Combined Central and Peripheral Demyelination: Two Case Reports.

Combined central and peripheral demyelination (CCPD) is a rare disease characterized by demyelinating lesions in both the central nervous system (CNS) and peripheral nervous system (PNS). CCPD can present with acute, subacute, or chronic onset. The initial symptom may be of CNS origin, PNS origin, or both. The clinical manifestations of CCPD are quite heterogeneous, and there are no well-defined diagnostic criteria. In MRI imaging of CCPD cases, demyelinating lesions can be seen in areas such as the brain, cerebellum, brainstem, optic nerve, and spinal cord. Common electromyography (EMG) findings in patients with CCPD include decreased motor nerve conduction velocities, decreased or absent sensory nerve action potentials, prolonged F-wave latency, and decreased amplitude of compound muscle action potentials. Neurofascin (NF) is a transmembrane protein and anti-neurofascin (anti-NF) antibodies directed against NF can be positive in cases of CCPD. Four main NF polypeptides are produced by alternative splicing: NF 186, NF 180, NF 166, and NF 155. The investigation of anti-NF in CCPD cases is therefore important for etiological considerations. Here, we discussed three cases diagnosed with CCPD based on clinical, neuroimaging, EMG, and anti-NF antibody results in light of the literature.

Crystal structure of Ankyrin-G in complex with a fragment of Neurofascin reveals binding mechanisms required for integrity of the axon initial segment.

The axon initial segment (AIS) has characteristically dense clustering of voltage-gated sodium channels (Nav), cell adhesion molecule Neurofascin 186 (Nfasc), and neuronal scaffold protein Ankyrin-G (AnkG) in neurons, which facilitates generation of an action potential and maintenance of axonal polarity. However, the mechanisms underlying AIS assembly, maintenance, and plasticity remain poorly understood. Here, we report the high-resolution crystal structure of the AnkG ankyrin repeat (ANK repeat) domain in complex with its binding site in the Nfasc cytoplasmic tail that shows, in conjunction with binding affinity assays with serial truncation variants, the molecular basis of AnkG-Nfasc binding. We confirm AnkG interacts with the FIGQY motif in Nfasc, and we identify another region required for their high affinity binding. Our structural analysis revealed that ANK repeats form 4 hydrophobic or hydrophilic layers in the AnkG inner groove that coordinate interactions with essential Nfasc residues, including F1202, E1204, and Y1212. Moreover, we show disruption of the AnkG-Nfasc complex abolishes Nfasc enrichment at the AIS in cultured mouse hippocampal neurons. Finally, our structural and biochemical analysis indicated that L1 syndrome-associated mutations in L1CAM, a member of the L1 immunoglobulin family proteins including Nfasc, L1CAM, NrCAM, and CHL1, compromise binding with ankyrins. Taken together, these results define the mechanisms underlying AnkG-Nfasc complex formation and show that AnkG-dependent clustering of Nfasc is required for AIS integrity.

Super-resolution imaging pinpoints the periodic ultrastructure at the human node of Ranvier and its disruption in patients with polyneuropathy.

The node of Ranvier is the key element in saltatory conduction along myelinated axons, but its specific protein organization remains elusive in the human species. To shed light on nanoscale anatomy of the human node of Ranvier in health and disease, we assessed human nerve biopsies of patients with polyneuropathy by super-resolution fluorescence microscopy. We applied direct stochastic optical reconstruction microscopy (dSTORM) and supported our data by high-content confocal imaging combined with deep learning-based analysis. As a result, we revealed a âˆ¼ 190 nm periodic protein arrangement of cytoskeletal proteins and axoglial cell adhesion molecules in human peripheral nerves. In patients with polyneuropathy, periodic distances increased at the paranodal region of the node of Ranvier, both at the axonal cytoskeleton and at the axoglial junction. In-depth image analysis revealed a partial loss of proteins of the axoglial complex (Caspr-1, neurofascin-155) in combination with detachment from the cytoskeletal anchor protein ß2-spectrin. High content analysis showed that such paranodal disorganization occurred especially in acute and severe axonal neuropathy with ongoing Wallerian degeneration and related cytoskeletal damage. We provide nanoscale and protein-specific evidence for the prominent, but vulnerable role of the node of Ranvier for axonal integrity. Furthermore, we show that super-resolution imaging can identify, quantify and map elongated periodic protein distances and protein interaction in histopathological tissue samples. We thus introduce a promising tool for further translational applications of super resolution microscopy.

Growing Spectrum of Autoimmune Nodopathies.

PURPOSE OF REVIEW: Recognition of node of Ranvier as the site of injury in inflammatory neuropathies contributed to discovery of antibodies against the nodal/paranodal structures. These antibodies mediate a unique type of inflammatory neuropathies that are different from typical chronic inflammatory demyelinating polyneuropathy. This review discusses the advancements made in the field of autoimmune neuropathies secondary to antibodies to nodal and paranodal proteins. RECENT FINDINGS: Neuropathies caused by antibodies to nodal-paranodal antigens including neurofascin 186, neurofascin 155, contactin1, and contactin-associated protein1 were termed as autoimmune nodopathies (AN) in 2021. Since the initial description almost a decade ago, newer cohorts have expanded the clinical spectrum of AN. In addition to IgG4, other subclasses of IgG such as IgG1/IgG3 have been identified, particularly in relation to acute presentations and anti-pan neurofascin antibody disease. In vitro and in vivo studies have also supported antibody-mediated pathogenicity of many of these biomarkers. Antibodies to nodal-paranodal antigens have emerged as a biomarker for a novel type of immune-mediated neuropathies. These antibodies have distinct pathogenic mechanisms and produce a unique set of clinicopathologic features. Their clinical profile and treatment may also vary depending on the antibody isotype. B cell depleting therapies are effective in managing some of these patients.

Clinical and pathophysiological implications of autoantibodies in autoimmune neuropathies.

Autoimmune neuropathies are a heterogeneous group of rare and disabling diseases in which the immune system targets peripheral nervous system antigens and that respond to immune therapies. This review focuses on Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, multifocal motor neuropathy, polyneuropathy associated with IgM monoclonal gammopathy, and autoimmune nodopathies. Autoantibodies targeting gangliosides, proteins in the node of Ranvier, and myelin-associated glycoprotein have been described in these disorders, defining subgroups of patients with similar clinical features and response to therapy. This topical review describes the role of these autoantibodies in the pathogenesis of autoimmune neuropathies and their clinical and therapeutic importance.

Intra-amygdala metaplasticity modulation of fear extinction learning.

The amygdala is a key brain region involved in emotional memory formation. It is also responsible for memory modulation in other brain areas. Under extreme conditions, amygdala modulation may lead to the generation of abnormal plasticity and trauma-related psychopathologies. However, the amygdala itself is a dynamic brain region, which is amenable to long-term plasticity and is affected by emotional experiences. These alterations may modify the way the amygdala modulates activity and plasticity in other related brain regions, which in turn may alter the animal's response to subsequent challenges in what could be termed as "Behavioral metaplasticity."Because of the reciprocal interactions between the amygdala and other emotion processing regions, such as the medial prefrontal cortex (mPFC) or the hippocampus, experience-induced intra-amygdala metaplasticity could lead to alterations in mPFC-dependent or hippocampus-dependent behaviors. While initiated by alterations within the basolateral amygdala (BLA), such alterations in other brain regions may come to be independent of BLA modulation, thus establishing what may be termed "Trans-regional metaplasticity." In this article, we review evidence supporting the notions of intra-BLA metaplasticity and how this may develop into "Trans-regional metaplasticity." Future research is needed to understand how such dynamic metaplastic alterations contribute to developing psychopathologies, and how this knowledge may be translated into promoting novel interventions in psychopathologies associated with fear, stress, and trauma.

The clinical features of combined central and peripheral demyelination and antibodies against the node of Ranvier.

BACKGROUND: Combined central and peripheral demyelination (CCPD) is a disease of inflammatory demyelination that affects central and peripheral nerves simultaneously or temporally separated. OBJECTIVES: This study evaluated the clinical characteristics and the existence of antinodal/paranodal antibodies in patients with CCPD. METHODS: We reviewed the clinical manifestations, laboratory tests, electrophysiological examinations, neuroimaging findings, treatment, and prognosis of 31 patients with CCPD. Using a live cell-based assay, we tested antinodal/paranodal antibodies. RESULTS: The most common symptoms were motor weakness (83.3%), hyporeflexia (63.3%), and sphincter disturbance (58.1%). In total, 16.6% of patients had impaired vision symptoms, whereas 33.3% of patients had abnormal visual-evoked potentials (VEPs). A total of 21.1% (4/19) of patients were positive for anti-AQP4 (aquaporin 4) antibodies, 20.0% (2/10) of patients were positive for anti-NF155 (neurofascin-155) antibodies, and 10.0% (1/10) of patients were positive for anti-MAG (myelin-associated glycoprotein) antibodies. The effective rates of intravenous corticosteroids, intravenous immunoglobulins, and rituximab were 72.2%, 37.5%, and 100%, respectively. At the illness peak, 75% of patients with CCPD had an mRS (modified Rankin Scale) score of 4 or greater. In remission, 37.5% had an mRS score of 4 or greater. CONCLUSION: The clinical manifestations of patients with CCPD are highly heterogeneous. We recommend testing antinodal/paranodal antibodies for patients with CCPD.

Clinical features of Guillain-Barré syndrome with anti-neurofascin 155 antibody.

OBJECTIVE: Anti-neurofascin 155 (NF155) antibody has been discovered in chronic demyelinating conditions. However, the positive rate and clinical description were insufficient in acute demyelinating conditions, such as Guillain-Barré syndrome (GBS). This study aimed to explore the positive rate of anti-NF155 antibody in GBS patients and determine whether there were unique clinical characteristics in these patients. MATERIALS & METHODS: Serum anti-NF155 antibody was detected from 94 GBS patients and 50 sex- and age-matched healthy controls using cell-based assay and tissue-based assay with immunostaining of mouse teased sciatic nerve fibers. Clinical characteristics, laboratory data, and electrophysiology examinations were retrospectively collected. RESULTS: Seven of 94 (7.45%) GBS patients were positive for anti-NF155 antibody, and the main IgG subclass was IgG1. Compared with anti-NF155 antibody-negative GBS patients, anti-NF155 antibody-positive GBS patients had a higher GBS disability score at nadirs (p = .010), higher modified Erasmus GBS outcome score (p = .022), higher rate of abnormal compound motor action potential (CMAP) amplitude (p = .002), higher frequency of prolonged F-wave latency (p < .001), lower frequency of abnormal sensory conduction velocity (p < .001) and sensory nerve action potential amplitude (p < .001), more axonal type (p = .040), and poorer therapeutic effect (p = .017). CONCLUSIONS: Anti-NF155 antibody exists in a small portion of GBS patients. Anti-NF155 antibody-positive GBS patients possibly have a more severe clinical course, less sensory nerves involved, higher proportion of axonal type, poorer therapeutic effect, and worse prognosis, but the pathogenicity of the anti-NF155 antibody in GBS needs further study.

Accumulation of Neurofascin at Nodes of Ranvier Is Regulated by a Paranodal Switch.

The paranodal junctions flank mature nodes of Ranvier and provide a barrier between ion channels at the nodes and juxtaparanodes. These junctions also promote node assembly and maintenance by mechanisms that are poorly understood. Here, we examine their role in the accumulation of NF186, a key adhesion molecule of PNS and CNS nodes. We previously showed that NF186 is initially targeted/accumulates via its ectodomain to forming PNS (hemi)nodes by diffusion trapping, whereas it is later targeted to mature nodes by a transport-dependent mechanism mediated by its cytoplasmic segment. To address the role of the paranodes in this switch, we compared accumulation of NF186 ectodomain and cytoplasmic domain constructs in WT versus paranode defective (i.e., Caspr-null) mice. Both pathways are affected in the paranodal mutants. In the PNS of Caspr-null mice, diffusion trapping mediated by the NF186 ectodomain aberrantly persists into adulthood, whereas the cytoplasmic domain/transport-dependent targeting is impaired. In contrast, accumulation of NF186 at CNS nodes does not undergo a switch; it is predominantly targeted to both forming and mature CNS nodes via its cytoplasmic domain and requires intact paranodes. Fluorescence recovery after photobleaching analysis indicates that the paranodes provide a membrane diffusion barrier that normally precludes diffusion of NF186 to nodes. Linkage of paranodal proteins to the underlying cytoskeleton likely contributes to this diffusion barrier based on 4.1B and ßII spectrin expression in Caspr-null mice. Together, these results implicate the paranodes as membrane diffusion barriers that regulate targeting to nodes and highlight differences in the assembly of PNS and CNS nodes.SIGNIFICANCE STATEMENT Nodes of Ranvier are essential for effective saltatory conduction along myelinated axons. A major question is how the various axonal proteins that comprise the multimeric nodal complex accumulate at this site. Here we examine how targeting of NF186, a key nodal adhesion molecule, is regulated by the flanking paranodal junctions. We show that the transition from diffusion-trapping to transport-dependent accumulation of NF186 requires the paranodal junctions. We also demonstrate that these junctions are a barrier to diffusion of axonal proteins into the node and highlight differences in PNS and CNS node assembly. These results provide new insights into the mechanism of node assembly and the pathophysiology of neurologic disorders in which impaired paranodal function contributes to clinical disability.

The prevalence of anti-neurofascin-155 antibodies in patients with neuromyelitis optica spectrum disorders.

Anti-neurofascin-155 (NF155) antibodies have been observed in two cases with neuromyelitis optica spectrum disorders (NMOSD). This study investigated the prevalence of anti-NF155 antibodies in patients with NMOSD and the clinical features of anti-NF155 antibody-positive patients. Sera from 129 patients with NMOSD were screened with anti-NF155 antibodies by cell-based assay (CBA) and re-examined using immunostaining of teased mouse sciatic nerve fibres. Fifty-six patients with multiple sclerosis (MS) and 50 healthy controls (HC) were also enrolled for detecting anti-NF155 antibodies. A total of 12.40% (16 of 129) of patients with NMOSD were positive for anti-NF155 antibodies confirmed by both CBA and immunostaining. Immunoglobulin (Ig) G1 was the predominant subclass. However, none of 56 MS patients or 50 HC were positive for anti-NF155 antibodies. Anti-NF155 antibody-positive NMOSD patients had a higher proportion of co-existing with autoimmune diseases (p < 0.001) and higher positive rates of serum non-organ-specific autoantibodies, including anti-SSA antibodies (p < 0.001), anti-SSB antibodies (p = 0.008), anti-Ro-52 antibodies (p < 0.001) and rheumatoid factor (p < 0.001). Five anti-NF155 antibody-positive NMOSD patients who took part in the nerve conduction study showed mildly abnormal results. Differences in some nerve conduction study parameters were observed between anti-NF155 antibody-positive and negative patients. Anti-NF155 antibodies occurred in a small proportion of NMOSD patients. Anti-NF155 antibody-positive NMOSD patients tended to co-exist with autoimmune diseases.

Report of a fulminant anti-pan-neurofascin-associated neuropathy responsive to rituximab and bortezomib.

Inflammatory neuropathies with pathogenic involvement of the nodes of Ranvier through autoantibodies have been increasingly characterized in the past years. The so-called anti-pan-NF-associated neuropathies caused by the simultaneous existence of anti-Neurofascin-186/-140 and -155-antibodies are extremely rare and cause life-threatening symptoms. Therapeutic strategies are needed as symptoms may be life-threatening and may not respond to standard first-line CIDP treatment. We report a case of a 52-year-old male with a rare anti-pan-neurofascin (NF) (-155, -186/-140)-associated neuropathy. The initial presentation was subacute with mild paresthesia leading to a fulminant "locked-in"-like syndrome requiring mechanical ventilation within the first eight weeks despite treatment with intravenous immunoglobulins. Nerve conduction studies revealed non-excitable nerves with acute spontaneous activity in electromyography. High titers of anti-Neurofascin-155, -186/-140-antibodies were detected in serum and cerebrospinal fluid. A combination of aggressive immunotherapy consisting of intravenous immunoglobulins, plasma exchange, rituximab and bortezomib resulted in clinical improvement with ambulation and non-detectable anti-neurofascin-antibodies within the following 3 months. The follow-up nerve conduction studies showed normalized amplitudes of the peripheral nerves with signs of reinnervation in electromyography. We conclude that an early aggressive immunotherapy consisting of a combination of rituximab and bortezomib could be considered as a therapeutic option for anti-pan-NF-associated neuropathies.

Neurofascin antibodies in chronic inflammatory demyelinating polyradiculoneuropathy: from intrinsic genetic background to clinical manifestations.

There are bunch of autoantibodies, particularly autoantibodies against proteins located at the node of Ranvier, have been discovered and transformed the clinical management of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Neurofascin (NF) plays an important role in both the nodal and paranodal regions of the node of Ranvier. In this review, we focus on the two characteristic forms of neurofascin: NF186 and NF155, comparing the similarities and differences between them, reviewing the current knowledge on genetic backgrounds, pathogenesis, clinical manifestations, and management of patients with anti-neurofascin positive CIDP. Autoantibodies against neurofascin were mainly IgG4 isotype. Mutation of NFASC gene in human causes severe neurodevelopment disorders, and HLA DRB1*15 may be a strong risk factor for the development of anti-NF155 antibodies. Motor impairment, sensory ataxia, and tremor were the typical presentations of patients with anti-NF155+ CIDP, while tetraplegia and cranial nerve involvement were more common in patients with anti-NF186+ CIDP. Recent studies have depicted a relatively clear picture of anti-NF155+ CIDP, and the strong clinical correlation of NF186 with CIDP remains unclear. The genetic background of neurofascin will assist in future explorations.

From PNS to CNS: characteristics of anti-neurofascin 186 neuropathy in 16 cases.

INTRODUCTION: Neurofascin (NF) is critical for the formation and maintenance of Ranvier nodes. NF186, the neuronal form of NF, localizes in the initial segment of axon and Ranvier node. NF186 antibody has been detected in demyelinating diseases of both central nervous system (CNS) and peripheral nervous system (PNS). AIMS: To evaluate the clinical features of patients with anti-NF186 IgG neuropathy. METHODS: Sixteen patients (16/138) with serum-positive anti-NF186 IgG were included and divided into groups of either CNS or PNS-involved according to their clinical manifestations. Anti-NF186 IgG was detected by cell-based assays. RESULTS: In 7 patients who were confirmed to have CNS involvement, the most frequent symptoms were dizziness (57%) and vision impairment (43%); lesions in centrum semiovale, cerebellum, and meninges were shown by magnetic resonance imaging (MRI). In comparison, limb weakness (78%) and numbness (78%) were the most common symptoms in PNS-involved patients; axonal loss and demyelination were confirmed by nerve conduction examinations. Elevated level of cerebrospinal fluid (CSF) protein was found in 12 cases without statistically significant difference between the CNS and PNS groups. Meanwhile, CSF white blood cell counts were found significantly elevated in CNS-involved patients compared with patients of PNS group. Thirteen patients received immunomodulating treatments, and patients with chronic onset and progressive course showed poor response to the therapies. CONCLUSIONS: Patients with anti-NF186 IgG neuropathy showed no specific symptoms or signs. It is worth noting that quite a few patients show CNS-impaired signs only, and cranial MRI is essential for the screening of CNS involvement.

Regulation of myelin structure and conduction velocity by perinodal astrocytes.

The speed of impulse transmission is critical for optimal neural circuit function, but it is unclear how the appropriate conduction velocity is established in individual axons. The velocity of impulse transmission is influenced by the thickness of the myelin sheath and the morphology of electrogenic nodes of Ranvier along axons. Here we show that myelin thickness and nodal gap length are reversibly altered by astrocytes, glial cells that contact nodes of Ranvier. Thrombin-dependent proteolysis of a cell adhesion molecule that attaches myelin to the axon (neurofascin 155) is inhibited by vesicular release of thrombin protease inhibitors from perinodal astrocytes. Transgenic mice expressing a dominant-negative fragment of VAMP2 in astrocytes, to reduce exocytosis by 50%, exhibited detachment of adjacent paranodal loops of myelin from the axon, increased nodal gap length, and thinning of the myelin sheath in the optic nerve. These morphological changes alter the passive cable properties of axons to reduce conduction velocity and spike-time arrival in the CNS in parallel with a decrease in visual acuity. All effects were reversed by the thrombin inhibitor Fondaparinux. Similar results were obtained by viral transfection of tetanus toxin into astrocytes of rat corpus callosum. Previously, it was unknown how the myelin sheath could be thinned and the functions of perinodal astrocytes were not well understood. These findings describe a form of nervous system plasticity in which myelin structure and conduction velocity are adjusted by astrocytes. The thrombin-dependent cleavage of neurofascin 155 may also have relevance to myelin disruption and repair.

Biallelic mutations in neurofascin cause neurodevelopmental impairment and peripheral demyelination.

Axon pathfinding and synapse formation are essential processes for nervous system development and function. The assembly of myelinated fibres and nodes of Ranvier is mediated by a number of cell adhesion molecules of the immunoglobulin superfamily including neurofascin, encoded by the NFASC gene, and its alternative isoforms Nfasc186 and Nfasc140 (located in the axonal membrane at the node of Ranvier) and Nfasc155 (a glial component of the paranodal axoglial junction). We identified 10 individuals from six unrelated families, exhibiting a neurodevelopmental disorder characterized with a spectrum of central (intellectual disability, developmental delay, motor impairment, speech difficulties) and peripheral (early onset demyelinating neuropathy) neurological involvement, who were found by exome or genome sequencing to carry one frameshift and four different homozygous non-synonymous variants in NFASC. Expression studies using immunostaining-based techniques identified absent expression of the Nfasc155 isoform as a consequence of the frameshift variant and a significant reduction of expression was also observed in association with two non-synonymous variants affecting the fibronectin type III domain. Cell aggregation studies revealed a severely impaired Nfasc155-CNTN1/CASPR1 complex interaction as a result of the identified variants. Immunofluorescence staining of myelinated fibres from two affected individuals showed a severe loss of myelinated fibres and abnormalities in the paranodal junction morphology. Our results establish that recessive variants affecting the Nfasc155 isoform can affect the formation of paranodal axoglial junctions at the nodes of Ranvier. The genetic disease caused by biallelic NFASC variants includes neurodevelopmental impairment and a spectrum of central and peripheral demyelination as part of its core clinical phenotype. Our findings support possible overlapping molecular mechanisms of paranodal damage at peripheral nerves in both the immune-mediated and the genetic disease, but the observation of prominent central neurological involvement in NFASC biallelic variant carriers highlights the importance of this gene in human brain development and function.