Expression of neurochondrin in the developing and adult mouse brain

Regulation of the evolutionarily conserved muscle myofibrillar matrix by cell type dependent and independent mechanisms

Skeletal muscles play a central role in human movement through forces transmitted by contraction of the sarcomere. We recently showed that mammalian sarcomeres are connected through frequent branches forming a singular, mesh-like myofibrillar matrix. However, the extent to which myofibrillar connectivity is evolutionarily conserved as well as mechanisms which regulate the specific architecture of sarcomere branching remain unclear. Here, we demonstrate the presence of a myofibrillar matrix in the tubular, but not indirect flight (IF) muscles within Drosophila melanogaster. Moreover, we find that loss of transcription factor H15 increases sarcomere branching frequency in the tubular jump muscles, and we show that sarcomere branching can be turned on in IF muscles by salm-mediated conversion to tubular muscles. Finally, we demonstrate that neurochondrin misexpression results in myofibrillar connectivity in IF muscles without conversion to tubular muscles. These data indicate an evolutionarily conserved myofibrillar matrix regulated by both cell-type dependent and independent mechanisms.

A postzygotic de novo NCDN mutation identified in a sporadic FTLD patient results in neurochondrin haploinsufficiency and altered FUS granule dynamics

Frontotemporal dementia (FTD) is a heterogeneous clinical disorder characterized by progressive abnormalities in behavior, executive functions, personality, language and/or motricity. A neuropathological subtype of FTD, frontotemporal lobar degeneration (FTLD)-FET, is characterized by protein aggregates consisting of the RNA-binding protein fused in sarcoma (FUS). The cause of FTLD-FET is not well understood and there is a lack of genetic evidence to aid in the investigation of mechanisms of the disease. The goal of this study was to identify genetic variants contributing to FTLD-FET and to investigate their effects on FUS pathology. We performed whole-exome sequencing on a 50-year-old FTLD patient with ubiquitin and FUS-positive neuronal inclusions and unaffected parents, and identified a de novo postzygotic nonsense variant in the NCDN gene encoding Neurochondrin (NCDN), NM_014284.3:c.1206G > A, p.(Trp402*). The variant was associated with a ~ 31% reduction in full-length protein levels in the patient’s brain, suggesting that this mutation leads to NCDN haploinsufficiency. We examined the effects of NCDN haploinsufficiency on FUS and found that depleting primary cortical neurons of NCDN causes a reduction in the total number of FUS-positive cytoplasmic granules. Moreover, we found that these granules were significantly larger and more highly enriched with FUS. We then examined the effects of a loss of FUS function on NCDN in neurons and found that depleting cells of FUS leads to a decrease in NCDN protein and mRNA levels. Our study identifies the NCDN protein as a likely contributor of FTLD-FET pathophysiology. Moreover, we provide evidence for a negative feedback loop of toxicity between NCDN and FUS, where loss of NCDN alters FUS cytoplasmic dynamics, which in turn has an impact on NCDN expression.

CCCH-zinc finger antiviral protein relieves immunosuppression of T cell induced by avian leukosis virus subgroup J via NLP-PKC-δ-NFAT pathway

CCCH-zinc finger antiviral protein (ZAP) can recognize and induce the degradation of mRNAs and proteins of certain viruses, as well as exert its antiviral activity by activating T cell. However, the mechanism of ZAP mediating T cell activation during virus infection remains unclear. Here, we found a potential function of ZAP that relieves immunosuppression of T cell induced by avian leukosis virus subgroup J (ALV-J) via a novel signaling pathway that involves norbin like protein (NLP), protein kinase C delta (PKC-δ) and nuclear factor of activated T cell (NFAT). Specifically, ZAP expression activated T cells by promoting the dephosphorylation and nuclear translocation of NFAT. Furthermore, knockdown of ZAP weakened the reactivity and antiviral response of T cells. Mechanistically, ZAP reduced PKC-δ activity by up-regulating and reactivating NLP through competitively binding with viral protein. Knockdown of NLP decreased the dephosphorylation of PKC-δ by ZAP expression. Moreover, we showed that knockdown of PKC-δ reduced the phosphorylation levels of NFAT and enhanced its nuclear translocation. Taken together, these data revealed that ZAP relieves immunosuppression caused by ALV-J and mediates T cell activation through NLP-PKC-δ-NFAT pathway. Importance The evolution of host defense system is driven synchronously in the process of resisting virus invasion. Accordingly, host innate defense factors exert effectively work in suppressing virus replication. However, it remains unclear that whether the host innate defense factors are involved in antiviral immune response against the invasion of immunosuppressive viruses. Here, we found that CCCH-type zinc finger antiviral protein (ZAP) effectively worked in resistance on immunosuppression caused by avian leukosis virus subgroup J (ALV-J), a classic immunosuppressive virus. Evidence showed that ZAP released the phosphatase activity of NLP inhibited by ALV-J and further activated NFAT by inactivating PKC-δ. This novel molecular mechanism that ZAP regulates antiviral immune response by mediating NLP-PKC-δ-NFAT pathway has greatly enriched the understanding of the functions of host innate defense factors and provided important scientific ideas and theoretical basis for the research of immunosuppressive virus and antiviral immunity.

Apheresis in Autoimmune Encephalitis and Autoimmune Dementia

Autoimmune encephalitis (AE) is a rapidly progressive inflammatory neurological disease. Underlying autoantibodies can bind to neuronal surfaces and synaptic proteins resulting in psychiatric symptoms, focal neurological signs, autonomic dysfunction and cognitive decline. Early and effective treatment is mandatory to reduce clinical symptoms and to achieve remission. Therapeutic apheresis, involving both plasma exchange (PE) and immunoadsorption (IA), can rapidly remove pathogenic antibodies from the circulation, thus representing an important first-line treatment in AE patients. We here review the most relevant studies regarding therapeutic apheresis in AE, summarizing the outcome for patients and the expanding clinical spectrum of treatment-responsive clinical conditions. For example, patients with slowly progressing cognitive impairment suggesting a neurodegenerative dementia can have underlying autoantibodies and improve with therapeutic apheresis. Findings are encouraging and have led to the first ongoing clinical studies assessing the therapeutic effect of IA in patients with anti-neuronal autoantibodies and the clinical presentation of dementia. Therapeutic apheresis is an established and well tolerated option for first-line therapy in AE and, potentially, other antibody-mediated central nervous system diseases.

Generation of a human Neurochondrin deficient iPSC line KICRi002-A-3 using CRISPR/Cas9

The role of Neurochondrin (NCDN) in humans is not well understood. Mice with a conditional Ncdn knock-out show epileptic seizures, depressive-like behaviours and impaired spatial learning. Using CRISPR/Cas9, we generated a Neurochondrin deficient human iPSC line KICRi002-A-3 carrying a homozygous 752 bp deletion / 2 bp insertion in the NCDN gene. The iPSC line maintained a normal 46,XY karyotype, expressed pluripotency markers and exhibited capability to differentiate into the three germ layers in vitro. Off-target editing was excluded and Neurochondrin expression was not detectable. The iPSC line offers a valuable resource to study the role of Neurochondrin during human neurogenesis.

Encephalopathy Associated With Neurochondrin Autoantibodies

We determined the prevalence of autoantibodies against an extended number of established and novel neural antigens in children and adolescents with suspected autoimmune encephalitis, epilepsy, single seizures, or marked epileptiform activity in electroencephalography (EEG). Prospectively, 103 patients were recruited aged between 0 and 18 years and 104 controls. A panel of 35 autoantibodies against neural cell-surface and intracellular antigens was screened. Sixteen of 103 patients (15.5%) showed a positive result for 1 or more autoantibodies, compared to 6 of 104 controls (5.8%, P = .02). Neurochondrin was identified as a possible new target of autoantibodies in 3 patients within this cohort, but none in controls. The patients showed severe behavioral disturbances, memory and cognitive impairment, episodes of reduced responsiveness, but no seizures, and normal MRI. Clinical findings, course, and treatment response of these 3 patients are presented.

Neurochondrin neurological autoimmunity

Objectives

To describe the neurologic spectrum and treatment outcomes for neurochondrin-IgG positive cases identified serologically in the Mayo Clinic Neuroimmunology Laboratory.

Methods

Archived serum and CSF specimens previously scored positive for IgGs that stained mouse hippocampal tissue in a nonuniform synaptic pattern by immunofluorescence assay (89 among 616,025 screened, 1993–2019) were reevaluated. Antibody characterization experiments revealed specificity for neurochondrin, confirmed by recombinant protein assays.

Results

IgG in serum (9) or CSF (4) from 8 patients yielded identical neuron-restricted CNS patterns, most pronounced in hippocampus (stratum lucidum in particular), cerebellum (Purkinje cells and molecular layer), and amygdala. All were neurochondrin-IgG positive. Five were women; median symptom onset age was 43 years (range, 30–69). Of 7 with clinical data, 6 presented with rapidly progressive cerebellar ataxia, brainstem signs, or both; 1 had isolated unexplained psychosis 1 year prior. Five of 6 had cerebellar signs, 4 with additional brainstem symptoms or signs (eye movement abnormalities, 3; dysphagia, 2; nausea and vomiting, 1). One patient with brainstem signs (vocal cord paralysis and VII nerve palsy) had accompanying myelopathy (longitudinally extensive abnormality on MRI; aquaporin-4-IgG and myelin oligodendrocyte glycoprotein-IgG negative). The 7th patient had small fiber neuropathy only. Just 1 of 7 had contemporaneous cancer (uterine). Six patients with ataxia or brainstem signs received immunotherapy, but just 1 remained ambulatory. At last follow-up, 5 had MRI evidence of severe cerebellar atrophy.

Conclusion

In our series, neurochondrin autoimmunity was usually accompanied by a nonparaneoplastic rapidly progressive rhombencephalitis with poor neurologic outcomes. Other phenotypes and occasional paraneoplastic causes may occur.

Neurochondrin is a neuronal target antigen in autoimmune cerebellar degeneration

OBJECTIVE

To report on a novel neuronal target antigen in 3 patients with autoimmune cerebellar degeneration.

METHODS

Three patients with subacute to chronic cerebellar ataxia and controls underwent detailed clinical and neuropsychological assessment together with quantitative high-resolution structural MRI. Sera and CSF were subjected to comprehensive autoantibody screening by indirect immunofluorescence assay (IFA) and immunoblot. Immunoprecipitation with lysates of hippocampus and cerebellum combined with mass spectrometric analysis was used to identify the autoantigen, which was verified by recombinant expression in HEK293 cells and use in several immunoassays. Multiparameter flow cytometry was performed on peripheral blood and CSF, and peripheral blood was subjected to T-cell receptor spectratyping.

RESULTS

Patients presented with a subacute to chronic cerebellar and brainstem syndrome. MRI was consistent with cortical and cerebellar gray matter atrophy associated with subsequent neuroaxonal degeneration. IFA screening revealed strong immunoglobulin G1 reactivity in sera and CSF with hippocampal and cerebellar molecular and granular layers, but not with a panel of 30 recombinantly expressed established neural autoantigens. Neurochondrin was subsequently identified as the target antigen, verified by IFA and immunoblot with HEK293 cells expressing human neurochondrin as well as the ability of recombinant neurochondrin to neutralize the autoantibodies' tissue reaction. Immune phenotyping revealed intrathecal accumulation and activation of B and T cells during the acute but not chronic phase of the disease. T-cell receptor spectratyping suggested an antigen-specific T-cell response accompanying the formation of antineurochondrin autoantibodies. No such neurochondrin reactivity was found in control cohorts of various neural autoantibody-associated neurologic syndromes, relapsing-remitting multiple sclerosis, cerebellar type of multiple system atrophy, hereditary cerebellar ataxias, other neurologic disorders, or healthy donors.

CONCLUSION

Neurochondrin is a neuronal target antigen in autoimmune cerebellar degeneration.

Norbin Stimulates the Catalytic Activity and Plasma Membrane Localization of the Guanine-Nucleotide Exchange Factor P-Rex1

P-Rex1 is a guanine-nucleotide exchange factor (GEF) that activates the small G protein (GTPase) Rac1 to control Rac1-dependent cytoskeletal dynamics, and thus cell morphology. Three mechanisms of P-Rex1 regulation are currently known: (i) binding of the phosphoinositide second messenger PIP₃, (ii) binding of the Gβγ subunits of heterotrimeric G proteins, and (iii) phosphorylation of various serine residues. Using recombinant P-Rex1 protein to search for new binding partners, we isolated the G-protein-coupled receptor (GPCR)-adaptor protein Norbin (Neurochondrin, NCDN) from mouse brain fractions. Coimmunoprecipitation confirmed the interaction between overexpressed P-Rex1 and Norbin in COS-7 cells, as well as between endogenous P-Rex1 and Norbin in HEK-293 cells. Binding assays with purified recombinant proteins showed that their interaction is direct, and mutational analysis revealed that the pleckstrin homology domain of P-Rex1 is required. Rac-GEF activity assays with purified recombinant proteins showed that direct interaction with Norbin increases the basal, PIP₃- and Gβγ-stimulated Rac-GEF activity of P-Rex1. Pak-CRIB pulldown assays demonstrated that Norbin promotes the P-Rex1-mediated activation of endogenous Rac1 upon stimulation of HEK-293 cells with lysophosphatidic acid. Finally, immunofluorescence microscopy and subcellular fractionation showed that coexpression of P-Rex1 and Norbin induces a robust translocation of both proteins from the cytosol to the plasma membrane, as well as promoting cell spreading, lamellipodia formation, and membrane ruffling, cell morphologies generated by active Rac1. In summary, we have identified a novel mechanism of P-Rex1 regulation through the GPCR-adaptor protein Norbin, a direct P-Rex1 interacting protein that promotes the Rac-GEF activity and membrane localization of P-Rex1.

Three axonal projection routes of individual pyramidal cells in the ventral CA1 hippocampus

Pyramidal cells of the ventral hippocampal CA1 area have numerous and diverse distant projections to other brain regions including the temporal and parietal association areas, visual, auditory, olfactory, somatosensory, gustatory, and visceral areas, and inputs to the amygdalar and prefrontal-orbital-agranular insular region. In addition, their differential expression of proteins like calbindin provides further indications for cellular diversity. This raises the possibility that the pyramidal cells may form subpopulations participating in different brain circuitries. To address this hypothesis we applied the juxtacellular labeling technique to fill individual pyramidal cells in the ventral hippocampus with neurobiotin in urethane anesthetized rats. For each labeled pyramidal cell we determined soma location, dendritic arborizations and selective expression of calbindin and norbin. Reconstruction and mapping of long-range axonal projections were made with the Neurolucida system. We found three major routes of ventral CA1 pyramidal cell projections. The classical pathway run caudo-ventrally across and innervating the subiculum, further to the parahippocampal regions and then to the deep and superficial layers of entorhinal cortex. The other two pathways avoided subiculum by branching from the main axon close to the soma and either traveled antero- and caudo-ventrally to amygdaloid complex, amygdalopiriform-transition area and parahippocampal regions or run antero-dorsally through the fimbria-fornix to the septum, hypothalamus, ventral striatum and olfactory regions. We found that most pyramidal cells investigated used all three major routes to send projecting axons to other brain areas. Our results suggest that the information flow through the ventral hippocampus is distributed by wide axonal projections from the CA1 area.

Changes in the molecular phenotype of nucleus pulposus cells with intervertebral disc aging

Intervertebral disc (IVD) disorder and age-related degeneration are believed to contribute to low back pain. Cell-based therapies represent a promising strategy to treat disc degeneration; however, the cellular and molecular characteristics of disc cells during IVD maturation and aging still remain poorly defined. This study investigated novel molecular markers and their age-related changes in the rat IVD. Affymetrix cDNA microarray analysis was conducted to identify a new set of genes characterizing immature nucleus pulposus (NP) cells. Among these markers, select neuronal-related proteins (Basp1, Ncdn and Nrp-1), transcriptional factor (Brachyury T), and cell surface receptors (CD24, CD90, CD155 and CD221) were confirmed by real-time PCR and immunohistochemical (IHC) staining for differential expression between IVD tissue regions and among various ages (1, 12 and 21 months). NP cells generally possessed higher levels of mRNA or protein expression for all aforementioned markers, with the exception of CD90 in anulus fibrosus (AF) cells. In addition, CD protein (CD24 and CD90) and Brachyury (T) expression in immature disc cells were also confirmed via flow cytometry. Similar to IHC staining, results revealed a higher percentage of immature NP cells expressing CD24 and Brachyury, while higher percentage of immature AF cells was stained positively for CD90. Altogether, this study identifies that tissue-specific gene expression and age-related differential expression of the above markers do exist in immature and aged disc cells. These age-related phenotype changes provide a new insight for a molecular profile that may be used to characterize NP cells for developing cell-based regenerative therapy for IVD regeneration.

Norbin: A promising central nervous system regulator

Norbin, a neurite-outgrowth promoting protein, has been found to interact with and regulate several membrane proteins, including metabotropic glutamate receptor 5 (mGluR5). The disruption of both Norbin alleles leads to early embryonic death between 3.5 and 6.5 day post coitus.1 Forebrain specific Norbin knockout (KO) mice are defective in synaptic plasticity,2 an interesting feature considering that Norbin was initially discovered in the context of chemical-induced long term potentiation (LTP),3 a form of synaptic plasticity extensively studied in the context of learning and memory.4 The behavioral phenotypes associated with Norbin conditional KO suggest reduced mGluR5 function. Because of its fundamental functions, Norbin is emerging as a key neuronal regulator. The aim of the present review is to summarize current knowledge about Norbin while emphasizing its role in the nervous system.

Proteomic analysis of cathepsin B- and L-deficient mouse brain lysosomes

Cathepsins B and L are lysosomal cysteine proteases which have been implicated in a variety of pathological processes such as cancer, tumor angiogenesis, and neurodegeneration. However, only a few protein substrates have thus far been described and the mechanisms by which cathepsins B and L regulate cell proliferation, invasion, and apoptosis are poorly understood. Combined deficiency of both cathepsins results in early-onset neurodegeneration in mice reminiscent of neuronal ceroid lipofuscinoses in humans. Therefore, we intended to quantify accumulated proteins in brain lysosomes of double deficient mice. A combination of subcellular fractionation and LC-MS/MS using isobaric tagging for relative and absolute quantitation (iTRAQ) allowed us to simultaneously assess wildtype and cathepsin B(-/-)L(-/-) cerebral lysosomes. Altogether, 19 different proteins were significantly increased in cathepsin B(-/-)L(-/-) lysosomes. Most elevated proteins had previously been localized to neuronal biosynthetic, recycling/endocytic or lysosomal compartments. A more than 10-fold increase was observed for Rab14, the Delta/Notch-like epidermal growth factor-related receptor (DNER), calcyon, and carboxypeptidase E. Intriguingly, immunohistochemistry demonstrated that Rab14 and DNER specifically stain swollen axons in double deficient brains. Since dense accumulations of expanded axons are the earliest phenotypic and pathognomonic feature of cathepsin B(-/-)L(-/-) brains, our data suggest a role for cathepsins B and L in recycling processes during axon outgrowth and synapse formation in the developing postnatal central nervous system.

Interaction of neurochondrin with the melanin-concentrating hormone receptor 1 interferes with G protein-coupled signal transduction but not agonist-mediated internalization

Screening of a human brain cDNA library using the C-terminal tail of the melanin-concentrating hormone receptor 1 (MCHR1) as bait in a yeast two-hybrid assay resulted in the identification of the neurite-outgrowth related factor, neurochondrin. This interaction was verified in overlay, pulldown, and co-immunoprecipitation assays. Deletion mapping confined the binding to the C terminus of neurochondrin and to the proximal C terminus of MCHR1, a region known to be involved in G protein binding and signal transduction. This region of the MCHR1 is also able to interact with the actin- and intermediate filament-binding protein, periplakin. Interactions of MCHR1 with neurochondrin and periplakin were competitive, indicating that these two proteins bind to overlapping regions of MCHR1. Although neurochondrin did not interfere with melanin-concentrating hormone-mediated internalization of the receptor, it did inhibit G protein-coupled signal transduction via both Galpha(i/o) and Galpha(q/11) family G proteins as measured by each of melanin-concentrating hormone-induced G protein-activated inwardly rectifying K(+) channel activity of voltage-clamped amphibian oocytes, by calcium mobilization in transfected mammalian cells, and by reduction in the capacity of melanin-concentrating hormone to promote binding of [(35)S]guanosine 5'-3-O-(thio)triphosphate to both Galpha(o1) and Galpha(11). Immunohistochemistry revealed co-expression of neurochondrin and MCHR1 within the rodent brain, suggesting that neurochondrin may be involved in the regulation of MCHR1 signaling and play a role in modulating melanin-concentrating hormone-mediated functions in vivo.