RhoGDI phosphorylation by PKC promotes its interaction with death receptor p75NTR to gate axon growth and neuron survival.

How receptors juggle their interactions with multiple downstream effectors remains poorly understood. Here we show that the outcome of death receptor p75NTR signaling is determined through competition of effectors for interaction with its intracellular domain, in turn dictated by the nature of the ligand. While NGF induces release of RhoGDI through recruitment of RIP2, thus decreasing RhoA activity in favor of NFkB signaling, MAG induces PKC-mediated phosphorylation of the RhoGDI N-terminus, promoting its interaction with the juxtamembrane domain of p75NTR, disengaging RIP2, and enhancing RhoA activity in detriment of NF-kB. This results in stunted neurite outgrowth and apoptosis in cerebellar granule neurons. If presented simultaneously, MAG prevails over NGF. The NMR solution structure of the complex between the RhoGDI N-terminus and p75NTR juxtamembrane domain reveals previously unknown structures of these proteins and clarifies the mechanism of p75NTR activation. These results show how ligand-directed competition between RIP2 and RhoGDI for p75NTR engagement determine axon growth and neuron survival. Similar principles are likely at work in other receptors engaging multiple effectors and signaling pathways.

Antibody cross-reactivity between casein and myelin-associated glycoprotein results in central nervous system demyelination.

Multiple sclerosis (MS) is a neuroinflammatory demyelinating disease of the central nervous system (CNS) with a high socioeconomic relevance. The pathophysiology of MS, which is both complex and incompletely understood, is believed to be influenced by various environmental determinants, including diet. Since the 1990s, a correlation between the consumption of bovine milk products and MS prevalence has been debated. Here, we show that C57BL/6 mice immunized with bovine casein developed severe spinal cord pathology, in particular, demyelination, which was associated with the deposition of immunoglobulin G. Furthermore, we observed binding of serum from casein-immunized mice to mouse oligodendrocytes in CNS tissue sections and in culture where casein-specific antibodies induced complement-dependent pathology. We subsequently identified myelin-associated glycoprotein (MAG) as a cross-reactive antigenic target. The results obtained from the mouse model were complemented by clinical data showing that serum samples from patients with MS contained significantly higher B cell and antibody reactivity to bovine casein than those from patients with other neurologic diseases. This reactivity correlated with the B cell response to a mixture of CNS antigens and could again be attributed to MAG reactivity. While we acknowledge disease heterogeneity among individuals with MS, we believe that consumption of cow's milk in a subset of patients with MS who have experienced a previous loss of tolerance to bovine casein may aggravate the disease. Our data suggest that patients with antibodies to bovine casein might benefit from restricting dairy products from their diet.

Prevalence and clinical profiles of anti-myelin-associated glycoprotein neuropathy in Japan: A nationwide survey study of 133 patients.

BACKGROUND AND PURPOSE: The aim of this study was to determine the prevalence of anti-myelin-associated glycoprotein (MAG) neuropathy and the current status of such patients in Japan. METHODS: We conducted a nationwide survey in 2021 using established epidemiological methods. Questionnaires were sent to all neurology and pediatric neurology departments throughout Japan to identify patients with anti-MAG neuropathy. An initial questionnaire was used to determine the number of patients, with a second one used to collect detailed clinical information. RESULTS: The estimated number of patients with anti-MAG neuropathy was 353, with a prevalence of 0.28 per 100,000 and an incidence of 0.05 per 100,000. The detailed clinical profiles of 133 patients were available. The median (range) age of onset was 67 (30-87) years, with a prominent peak in the age range 66-70 years, and the male-to-female ratio was 3.6. Most patients had distal sensory-predominant polyneuropathy, and neuropathic pain (50%), or sensory ataxia (42%), while 18% had Waldenström's macroglobulinemia or multiple myeloma. Intravenous immunoglobulin was the most frequently used treatment (65%), but the response rate was <50%, whereas rituximab was given in 32% of patients, and 64% of these showed improvement. At the last visit, 27% of patients could not walk independently. CONCLUSIONS: This study on anti-MAG neuropathy provides updated insights into the epidemiology of this disease, clinical profiles, and treatment approaches in Japan. Rituximab therapy, used for only one-third of the patients, demonstrated efficacy. During the final visit, a quarter of the patients were unable to walk independently. Further studies are warranted to determine the optimal management of this rare and intractable disorder.

Molecular pathway of pancreatic cancer-associated neuropathic pain.

The pancreas is a heterocrine gland that has both exocrine and endocrine parts. Most pancreatic cancer begins in the cells that line the ducts of the pancreas and is called pancreatic ductal adenocarcinoma (PDAC). PDAC is the most encountered pancreatic cancer type. One of the most important characteristic features of PDAC is neuropathy which is primarily due to perineural invasion (PNI). PNI develops tumor microenvironment which includes overexpression of fibroblasts cells, macrophages, as well as angiogenesis which can be responsible for neuropathy pain. In tumor microenvironment inactive fibroblasts are converted into an active form that is cancer-associated fibroblasts (CAFs). Neurotrophins they also increase the level of Substance P, calcitonin gene-related peptide which is also involved in pain. Matrix metalloproteases are the zinc-associated proteases enzymes which activates proinflammatory interleukin-1ß into its activated form and are responsible for release and activation of Substance P which is responsible for neuropathic pain by transmitting pain signal via dorsal root ganglion. All the molecules and their role in being responsible for neuropathic pain are described below.

Gangliosides as Siglec ligands.

The structure of a sialoglycan can be translated into to a biological response when it binds to a specific endogenous lectin. Among endogenous sialic acid-binding lectins in humans are those comprising the 15-member Siglec family, most of which are expressed on overlapping sets of immune cells. Endogenous Siglec ligands are sialoglycolipids (gangliosides) and/or sialoglycoproteins, on cell surfaces or in the extracellular milieu, that bind to and initiate signaling by cell surface Siglecs. In the nervous system, where gangliosides are the predominant sialoglycans, Siglec-4 (myelin-associated glycoprotein) on myelinating cells binds to gangliosides GD1a and GT1b on nerve cell axons to ensure stable and productive axon-myelin interactions. In the immune system, Siglec-7 on natural killer cells binds to gangliosides GD3 and GD2 to inhibit immune signaling. Expression of GD3 and GD2 on cancer cells can lead to tumor immune evasion. Siglec-1 (sialoadhesin, CD169) on macrophages binds to gangliosides on tumors and enveloped viruses. This may enhance antigen presentation in some cases, or increase viral distribution in others. Several other Siglecs bind to gangliosides in vitro, the biological significance of which has yet to be fully established. Gangliosides, which are found on all human cells and tissues in cell-specific distributions, are functional Siglec ligands with varied roles driving Siglec-mediated signaling.

Entrapment partly participates in the longitudinal progression of neuropathy with anti-MAG antibodies.

Neuropathy with anti-myelin-associated glycoprotein (MAG) antibodies commonly demonstrates distal-dominant prolongation of nerve conduction. However, recent electrophysiological studies have shown that distal motor demyelination is not always a distinct feature. We aimed to elucidate whether the longitudinal progression of nerve impairment occurs in a distal-dominant manner. Seven patients with neuropathy with anti-MAG antibodies were enrolled. Sequential nerve conduction studies revealed nerve conduction reduction only at the wrist segment in the median nerve of the patients, but not in the ulnar nerve. Median nerve entrapment at the wrist may play a role in longitudinal disease progression in neuropathy with anti-MAG antibodies.

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.

Possible Contribution of Altered Cholinergic Activity in the Visual Cortex in Visual Hallucinations in Parkinson's Disease.

OBJECTIVE: Up to one-third of patients with Parkinson's disease (PD) experience visual hallucinations (VHs). Lewy bodies are sparse in the visual cortices and seem unlikely to explain the hallucinations. Some neuroimaging studies have found that perfusion is reduced in the occipital lobe in individuals with VHs. Recent work has suggested that decreased cholinergic input may directly lead to the decreased perfusion. The investigators hypothesized that individuals with PD and VHs would have biochemical evidence of reduced microvascular perfusion and reduced cholinergic activity in areas of the brain that process visual images. METHODS: Tissue from Brodmann's area (BA) 18 and BA 19 was obtained from a well-characterized cohort matched for age, gender, and postmortem interval in 69 individuals (PD without VHs, N=11; PD without dementia plus VHs N=10, N=10; PD with dementia plus VHs, N=16; and control subjects, N=32). Von Willebrand factor, vascular endothelial growth factor A, and myelin-associated glycoprotein:proteolipid protein-1 (MAG:PLP1) ratio-a measure of tissue oxygenation relative to metabolic demand, acetylcholinesterase (AChE), butyrylcholinesterase (BChE), choline acetyltransferase, and α-synuclein-were quantified by enzyme-linked immunosorbent assay. The primary outcome was the MAG:PLP1 ratio. RESULTS: There was no biochemical evidence of chronic hypoperfusion in PD, although microvessel density was decreased in ventral BA 18 and BA 19. There was no between-group difference in BChE in either dorsal BA 18 or BA 19. AChE concentration was reduced in individuals with PD compared with control subjects in dorsal and ventral BA 18 and dorsal BA 19, and it was increased in ventral BA 19. These changes were most marked in the PD plus VHs group. CONCLUSIONS: These results suggest that changes in cholinergic activity rather than chronic hypoperfusion may underlie VHs in PD.

Nerve Hypertrophy and Altered Diffusion in Anti-Myelin-Associated Glycoprotein Neuropathy Detected by Brachial Plexus Magnetic Resonance Neurography.

INTRODUCTION: This study assessed the morphological changes and diffusion tensor imaging (DTI)-derived parameters of the brachial plexus using magnetic resonance neurography (MRN) in patients with anti-myelin-associated glycoprotein (anti-MAG) neuropathy. METHODS: Eight patients with anti-MAG neuropathy underwent MRN of the brachial plexus with 3-dimensional (3D) short tau inversion recovery (STIR) and DTI sequences. Two neuroradiologists and a neurologist qualitatively assessed nerve hypertrophy on 3D STIR MRN. The cross-sectional area (CSA) of the nerve roots was measured. Quantitative analyses of fractional anisotropy (FA) and axial, radial, and mean diffusivity (AD, RD, and MD) were obtained after postprocessing on DTI and manual segmentation. RESULTS: There was nerve hypertrophy in 37.5% of the patients with anti-MAG neuropathy. All patients with anti-MAG neuropathy with nerve hypertrophy were refractory to rituximab therapy. The CSA of the nerve roots was inversely correlated with FA and positively correlated with MD and RD. FA decreased in the nerve roots and inversely correlated with disease duration. CONCLUSIONS: Nerve hypertrophy appears in the proximal portion of peripheral nerves, such as the brachial plexus, in patients with anti-MAG neuropathy. Altered diffusion in the nerve roots might be associated with the loss of myelin integrity due to the demyelination process in anti-MAG neuropathy.

The Effects of Insulin on Immortalized Rat Schwann Cells, IFRS1.

Schwann cells play an important role in peripheral nerve function, and their dysfunction has been implicated in the pathogenesis of diabetic neuropathy and other demyelinating diseases. The physiological functions of insulin in Schwann cells remain unclear and therefore define the aim of this study. By using immortalized adult Fischer rat Schwann cells (IFRS1), we investigated the mechanism of the stimulating effects of insulin on the cell proliferation and expression of myelin proteins (myelin protein zero (MPZ) and myelin basic protein (MBP). The application of insulin to IFRS1 cells increased the proliferative activity and induced phosphorylation of Akt and ERK, but not P38-MAPK. The proliferative potential of insulin-stimulated IFRS1 was significantly suppressed by the addition of LY294002, a PI3 kinase inhibitor. The insulin-stimulated increase in MPZ expression was significantly suppressed by the addition of PD98059, a MEK inhibitor. Furthermore, insulin-increased MBP expression was significantly suppressed by the addition of LY294002. These findings suggest that both PI3-K/Akt and ERK/MEK pathways are involved in insulin-induced cell growth and upregulation of MPZ and MBP in IFRS1 Schwann cells.

Selective inhibition of anti-MAG IgM autoantibody binding to myelin by an antigen-specific glycopolymer.

Anti-myelin-associated glycoprotein (MAG) neuropathy is a disabling autoimmune peripheral neuropathy that is caused by circulating monoclonal IgM autoantibodies directed against the human natural killer-1 (HNK-1) epitope. This carbohydrate epitope is highly expressed on adhesion molecules such as MAG, a glycoprotein present in myelinated nerves. We previously showed the therapeutic potential of the glycopolymer poly(phenyl disodium 3-O-sulfo-ß-d-glucopyranuronate)-(1→3)-ß-d-galactopyranoside (PPSGG) in selectively neutralizing anti-MAG IgM antibodies in an immunological mouse model and ex vivo with sera from anti-MAG neuropathy patients. PPSGG is composed of a biodegradable backbone that multivalently presents a mimetic of the HNK-1 epitope. In this study, we further explored the pharmacodynamic properties of the glycopolymer and its ability to inhibit the binding of anti-MAG IgM to peripheral nerves. The polymer selectively bound anti-MAG IgM autoantibodies and prevented the binding of patients' anti-MAG IgM antibodies to myelin of non-human primate sciatic nerves. Upon PPSGG treatment, neither activation nor inhibition of human and murine peripheral blood mononuclear cells nor alteration of systemic inflammatory markers was observed in mice or ex vivo in human peripheral blood mononuclear cells. Intravenous injections of PPSGG to mice immunized against the HNK-1 epitope removed anti-MAG IgM antibodies within less than 1 hr, indicating a fast and efficient mechanism of action as compared to a B-cell depletion with anti-CD20. In conclusion, these observations corroborate the therapeutic potential of PPSGG for an antigen-specific treatment of anti-MAG neuropathy. Read the Editorial Highlight for this article on page 465.

Anti-MAG IgM: differences in antibody tests and correlation with clinical findings.

OBJECTIVES: Anti-myelin-associated glycoprotein (MAG) antibody is associated with clinically heterogeneous polyneuropathies. Our purpose was to compare neuropathy phenotypes identified by different anti-MAG tests' results. METHODS: Cohort study: Sera from 40 neuropathy anti-MAG EIA positive patients were tested for anti-MAG by Western blot (WB), for anti-peripheral nerve myelin (PNM) on monkey nerve by immunofluorescence assay (IFA), and for anti-HNK1 on rat CNS slices by IFA. Anti-sulfatide antibodies, for comparison, were also tested by EIA. RESULTS: Among 40 anti-MAG EIA positive sera, 85% also had anti-PNM IFA reactivity and 67.5% bind HNK1 on rat CNS. Anti-HNK1 positive patients had the classical predominantly distal acquired demyelinating symmetric (DADS) neuropathy with a benign course, while anti-PNM positive but anti-HNK1 negative patients had predominantly axonal neuropathy with a high frequency of anti-sulfatide reactivity and the worst long-term prognosis. Anti-MAG EIA positive patients without anti-PNM or anti-HNK1 IFA reactivity had a CIDP-like polyneuropathy. CONCLUSION: Different methods to test for anti-MAG antibodies identify different clinical and electrophysiological findings, as well as long-term outcome. HNK1 reactivity is the strongest marker of DADS.

Selective in vivo removal of pathogenic anti-MAG autoantibodies, an antigen-specific treatment option for anti-MAG neuropathy.

Anti-MAG (myelin-associated glycoprotein) neuropathy is a disabling autoimmune peripheral neuropathy caused by monoclonal IgM autoantibodies that recognize the carbohydrate epitope HNK-1 (human natural killer-1). This glycoepitope is highly expressed on adhesion molecules, such as MAG, present in myelinated nerve fibers. Because the pathogenicity and demyelinating properties of anti-MAG autoantibodies are well established, current treatments are aimed at reducing autoantibody levels. However, current therapies are primarily immunosuppressive and lack selectivity and efficacy. We therefore hypothesized that a significant improvement in the disease condition could be achieved by selectively neutralizing the pathogenic anti-MAG antibodies with carbohydrate-based ligands mimicking the natural HNK-1 glycoepitope 1. In an inhibition assay, a mimetic (2, mimHNK-1) of the natural HNK-1 epitope blocked the interaction of MAG with pathogenic IgM antibodies from patient sera but with only micromolar affinity. Therefore, considering the multivalent nature of the MAG-IgM interaction, polylysine polymers of different sizes were substituted with mimetic 2. With the most promising polylysine glycopolymer PL84(mimHNK-1)45 the inhibitory effect on patient sera could be improved by a factor of up to 230,000 per epitope, consequently leading to a low-nanomolar inhibitory potency. Because clinical studies indicate a correlation between the reduction of anti-MAG IgM levels and clinical improvement, an immunological surrogate mouse model for anti-MAG neuropathy producing high levels of anti-MAG IgM was developed. The observed efficient removal of these antibodies with the glycopolymer PL84(mimHNK-1)45 represents an important step toward an antigen-specific therapy for anti-MAG neuropathy.

Physiological Exploration of the Long Term Evolutionary Selection against Expression of N-Glycolylneuraminic Acid in the Brain.

All vertebrate cell surfaces display a dense glycan layer often terminated with sialic acids, which have multiple functions due to their location and diverse modifications. The major sialic acids in most mammalian tissues are N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc), the latter being derived from Neu5Ac via addition of one oxygen atom at the sugar nucleotide level by CMP-Neu5Ac hydroxylase (Cmah). Contrasting with other organs that express various ratios of Neu5Ac and Neu5Gc depending on the variable expression of Cmah, Neu5Gc expression in the brain is extremely low in all vertebrates studied to date, suggesting that neural expression is detrimental to animals. However, physiological exploration of the reasons for this long term evolutionary selection has been lacking. To explore the consequences of forced expression of Neu5Gc in the brain, we have established brain-specific Cmah transgenic mice. Such Neu5Gc overexpression in the brain resulted in abnormal locomotor activity, impaired object recognition memory, and abnormal axon myelination. Brain-specific Cmah transgenic mice were also lethally sensitive to a Neu5Gc-preferring bacterial toxin, even though Neu5Gc was overexpressed only in the brain and other organs maintained endogenous Neu5Gc expression, as in wild-type mice. Therefore, the unusually strict evolutionary suppression of Neu5Gc expression in the vertebrate brain may be explained by evasion of negative effects on neural functions and by selection against pathogens.

Serum and cerebrospinal neurofilament light chain levels in patients with acquired peripheral neuropathies.

Neurofilament light chain (NFL) levels reflect axonal damage in different inflammatory and neurodegenerative central nervous system conditions, in correlation with disease severity. Our aim was to determine the possible diagnostic and prognostic value of serum and cerebrospinal fluid (CSF) NFL levels in subjects with different forms of acquired peripheral neuropathies (PN). Paired serum and CSF samples of 25 patients with acquired PN were analysed for NFL using an ultrasensitive technique (Quanterix, Simoa, Lexington, MA, USA) and compared with a group of 25 age-matched healthy subjects. Demographic, clinical, CSF and neurophysiological data were reviewed. Cases with Guillain-Barré syndrome (N = 5), multifocal motor neuropathy (N = 3), chronic inflammatory demyelinating polyneuropathy (CIDP) and variants (N = 12), anti-myelin-associated glycoprotein (MAG) neuropathy (N = 3), both CIDP and anti-MAG neuropathy (N = 1), and non-systemic vasculitic neuropathy (N = 1) were studied. NFL levels were significantly (P < 0.001) increased in patients with PN and were higher in the CSF (median: 1407 pg/mL, range: 140.2-12 661) than in serum (median: 31.52 pg/mL, range: 4.33-1178). A statistically significant correlation was observed between serum and CSF levels in cases with blood-nerve-barrier damage (r = 0.71, P < 0.01), and between serum NFL levels and disease activity at sampling (r = 0.52, P < 0.01) and at last follow-up (r = 0.53, P < 0.01) in all subjects. The increase of NFL values in both serum and CSF of patients with acquired PN and the significant correlation between serum NFL levels, disease severity and final outcome support the possible role of NFL as disease activity and prognostic biomarker also in peripheral nervous system disorders.

Chronic demyelinating neuropathy with anti-myelin-associated glycoprotein antibody without any detectable M-protein.

Previous case reports and studies have shown that anti-myelin-associated glycoprotein (MAG) antibody can be detected in patients with polyneuropathy without any detectable M-protein. Nevertheless, the frequency of and related factors have not yet been adequately investigated. The objectives of this study are to examine the prevalence of anti-MAG antibody in patients with demyelinating neuropathy without M-protein and to determine their clinical characteristics. From January, 2004, to September, 2016, consecutive patients with chronic demyelinating neuropathy were recruited. Anti-MAG antibody presence was tested at the first evaluation. We determined the prevalence of anti-MAG antibody without M-protein among included patients and evaluated the clinical characteristics. A total of 44 patients were included in the present study (12 women; median age at first visit 60 years [interquartile range 47-67 years]; median duration between onset and first visit 9 months [3-26 months]). M-protein was found in eight patients (18%) at the first evaluation. Anti-MAG antibody was present in 2 of remaining 36 (5.6 [95% confidence interval 0-13.0] %) patients without M-protein. Patients with anti-MAG antibody exhibited slowly progressive and distal dominant neuropathy with elevated serum IgM levels and refractory to immunotherapy. There were no differences in clinical features between patients having anti-MAG antibody without M-protein, and those with M-protein. One patient with the anti-MAG antibody showed a delayed appearance of M-protein during a 4-year follow-up after diagnosis. The prevalence of the anti-MAG antibody in chronic demyelinating neuropathy without any detectable M-protein was 5.6%. Anti-MAG antibody may be detectable earlier than M-protein.

Sialic Acids on Varicella-Zoster Virus Glycoprotein B Are Required for Cell-Cell Fusion.

Varicella-zoster virus (VZV) is a member of the human Herpesvirus family that causes varicella (chicken pox) and zoster (shingles). VZV latently infects sensory ganglia and is also responsible for encephalomyelitis. Myelin-associated glycoprotein (MAG), a member of the sialic acid (SA)-binding immunoglobulin-like lectin family, is mainly expressed in neural tissues. VZV glycoprotein B (gB) associates with MAG and mediates membrane fusion during VZV entry into host cells. The SA requirements of MAG when associating with its ligands vary depending on the specific ligand, but it is unclear whether the SAs on gB are involved in the association with MAG. In this study, we found that SAs on gB are essential for the association with MAG as well as for membrane fusion during VZV infection. MAG with a point mutation in the SA-binding site did not bind to gB and did not mediate cell-cell fusion or VZV entry. Cell-cell fusion and VZV entry mediated by the gB-MAG interaction were blocked by sialidase treatment. N-glycosylation or O-glycosylation inhibitors also inhibited the fusion and entry mediated by gB-MAG interaction. Furthermore, gB with mutations in N-glycosylation sites, i.e. asparagine residues 557 and 686, did not associate with MAG, and the cell-cell fusion efficiency was low. Fusion between the viral envelope and cellular membrane is essential for host cell entry by herpesviruses. Therefore, these results suggest that SAs on gB play important roles in MAG-mediated VZV infection.

Novel molecular insights into the critical role of sulfatide in myelin maintenance/function.

Cerebroside sulfotransferase (CST) catalyzes the production of sulfatide, a major class of myelin-specific lipids. CST knockout (CST(-/-) ) mice in which sulfatide is completely depleted are born healthy, but display myelin abnormalities and progressive tremors starting at 4-6 weeks of age. Although these phenotypes suggest that sulfatide plays a critical role in myelin maintenance/function, the underlying mechanisms remain largely unknown. We analyzed the major CNS myelin proteins and the major lipids enriched in the myelin in a spatiotemporal manner. We found a one-third reduction of the major compact myelin proteins (myelin basic protein, myelin basic protein, and proteolipid protein, PLP) and an equivalent post-developmental loss of myelin lipids, providing the molecular basis behind the thinner myelin sheaths. Our lipidomics data demonstrated that the observed global reduction of myelin lipid content was not because of an increase of lipid degradation but rather to the reduction of their synthesis by oligodendrocytes. We also showed that sulfatide depletion leads to region-specific effects on non-compact myelin, dramatically affecting the paranode (neurofascin 155) and the major inner tongue myelin protein (myelin-associated glycoprotein). Moreover, we demonstrated that sulfatide promotes the interaction between adjacent PLP extracellular domains, evidenced by a progressive decline of high molecular weight PLP complexes in CST(-/-) mice, providing an explanation at a molecular level regarding the uncompacted myelin sheaths. Finally, we proposed that the dramatic losses of neurofascin 155 and PLP interactions are responsible for the progressive tremors and eventual ataxia. In summary, we unraveled novel molecular insights into the critical role of sulfatide in myelin maintenance/function. Cerebroside sulfotransferase (CST) catalyzes the production of sulfatide, a major class of myelin-specific lipids. CST knockout (CST(-/-) ) mice in which sulfatide is completely depleted are born healthy, but display myelin abnormalities We show in our study that sulfatide depletion leads to losses of myelin proteins and lipids, and impairment of myelin functions, unraveling novel molecular insights into the critical role of sulfatide in myelin maintenance/function.

hnRNP A1 and secondary structure coordinate alternative splicing of Mag.

Myelin-associated glycoprotein (MAG) is a major component of myelin in the vertebrate central nervous system. MAG is present in the periaxonal region of the myelin structure, where it interacts with neuronal proteins to inhibit axon outgrowth and protect neurons from degeneration. Two alternatively spliced isoforms of Mag mRNA have been identified. The mRNA encoding the shorter isoform, known as S-MAG, contains a termination codon in exon 12, while the mRNA encoding the longer isoform, known as L-MAG, skips exon 12 and produces a protein with a longer C-terminal region. L-MAG is required in the central nervous system. How inclusion of Mag exon 12 is regulated is not clear. In a previous study, we showed that heteronuclear ribonucleoprotein A1 (hnRNP A1) contributes to Mag exon 12 skipping. Here, we show that hnRNP A1 interacts with an element that overlaps the 5' splice site of Mag exon 12. The element has a reduced ability to interact with the U1 snRNP compared with a mutant that improves the splice site consensus. An evolutionarily conserved secondary structure is present surrounding the element. The structure modulates interaction with both hnRNP A1 and U1. Analysis of splice isoforms produced from a series of reporter constructs demonstrates that the hnRNP A1-binding site and the secondary structure both contribute to exclusion of Mag exon 12.

Distal acquired demyelinating symmetric (DADS) neuropathy associated with colorectal adenocarcinoma.

INTRODUCTION: Paraneoplastic neuropathies are well recognized as a remote effect of cancer, and subacute sensory neuronopathy is a recognized syndrome. Demyelinating neuropathies are relatively rare. Distal acquired demyelinating symmetric (DADS) neuropathy associated with lymphoproliferative disease has been reported previously. We present the association of DADS neuropathy with solid tumor. METHODS: We report the clinical presentation, electrophysiology, and progress of DADS neuropathy in a patient later found to have colorectal adenocarcinoma. RESULTS: A patient presented with subacute onset of symmetric distal sensory and motor symptoms. Electrophysiology was typical of DADS neuropathy. Anti-MAG antibodies were initially positive at low titer, and indirect immunofluorescence analysis for anti-nuclear antibodies revealed autoantibodies to centromere nuclear protein-F (CENP-F). There was clinical and electrophysiologic resolution after tumor resection. CONCLUSIONS: This case describes the presentation of DADS neuropathy as a paraneoplastic syndrome in a patient later found to have colorectal adenocarcinoma.