Expression and characterization of disulfide bond use of oligomerized A2-Pancortins: Extracellular matrix constituents in the developing brain

Noelin1 Affects Lateral Mobility of Synaptic AMPA Receptors

Lateral diffusion on the neuronal plasma membrane of the AMPA-type glutamate receptor (AMPAR) serves an important role in synaptic plasticity. We investigated the role of the secreted glycoprotein Noelin1 (Olfactomedin-1 or Pancortin) in AMPAR lateral mobility and its dependence on the extracellular matrix (ECM). We found that Noelin1 interacts with the AMPAR with high affinity, however, without affecting rise- and decay time and desensitization properties. Noelin1 co-localizes with synaptic and extra-synaptic AMPARs and is expressed at synapses in an activity-dependent manner. Single-particle tracking shows that Noelin1 reduces lateral mobility of both synaptic and extra-synaptic GluA1-containing receptors and affects short-term plasticity. While the ECM does not constrain the synaptic pool of AMPARs and acts only extrasynaptically, Noelin1 contributes to synaptic potentiation by limiting AMPAR mobility at synaptic sites. This is the first evidence for the role of a secreted AMPAR-interacting protein on mobility of GluA1-containing receptors and synaptic plasticity.

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Noelin1 interacts with high affinity to AMPA receptors (AMPARs)

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Noelin1 is secreted upon cellular stimulation

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(Extra)synaptic AMPAR mobility, but not channel properties, are affected by Noelin1

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Reducing synaptic AMPAR lateral mobility by Noelin1 limits synaptic plasticity

Proteomic Analysis of the Human Olfactory Bulb

The importance of olfaction to human health and disease is often underappreciated. Olfactory dysfunction has been reported in association with a host of common complex diseases, including neurological diseases such as Alzheimer's disease and Parkinson's disease. For health, olfaction or the sense of smell is also important for most mammals, for optimal engagement with their environment. Indeed, animals have developed sophisticated olfactory systems to detect and interpret the rich information presented to them to assist in day-to-day activities such as locating food sources, differentiating food from poisons, identifying mates, promoting reproduction, avoiding predators, and averting death. In this context, the olfactory bulb is a vital component of the olfactory system receiving sensory information from the axons of the olfactory receptor neurons located in the nasal cavity and the first place that processes the olfactory information. We report in this study original observations on the human olfactory bulb proteome in healthy subjects, using a high-resolution mass spectrometry-based proteomic approach. We identified 7750 nonredundant proteins from human olfactory bulbs. Bioinformatics analysis of these proteins showed their involvement in biological processes associated with signal transduction, metabolism, transport, and olfaction. These new observations provide a crucial baseline molecular profile of the human olfactory bulb proteome, and should assist the future discovery of biomarker proteins and novel diagnostics associated with diseases characterized by olfactory dysfunction.

Mutated olfactomedin 1 in the interphotoreceptor matrix of the mouse retina causes functional deficits and vulnerability to light damage

Olfactomedin 1 (OLFM1) is a secreted glycoprotein and member of the olfactomedin protein family, which is preferentially expressed in various areas throughout the central nervous system. To learn about the functional properties of OLFM1 in the eye, we investigated its localization in the mouse and pig eye. In addition, we analyzed the ocular phenotype of Olfm1 mutant mice in which 52 amino acids were deleted in the central part (M2 region) of OLFM1. OLFM1 was detected in cornea, sclera, retina, and optic nerve of both wild-type and Olfm1 mutant littermates. By immunohistochemistry and double labeling with the lectin peanut agglutinin, OLFM1 was found in the interphotoreceptor matrix (IPM) of mouse and pig retina where it was directly localized to the inner segments of photoreceptors. Western blotting confirmed the presence of the OLFM1 isoforms pancortin 1 (BMY) and pancortin 2 (BMZ) in the IPM. The retinal phenotype of Olfm1 mutant mice did not obviously differ from that of wild-type littermates. In addition, outer nuclear layer (ONL) and total retinal thickness were not different, and the same was true for the area of the optic nerve in cross sections. Functional changes were observed though by electroretinography, which showed significantly lower a- and b-wave amplitudes in Olfm1 mutant mice when compared to age-matched wild-type mice. When light damage experiments were performed as an experimental paradigm of photoreceptor apoptosis, significantly more TUNEL-positive cells were observed in Olfm1 mutant mice 30 h after light exposure. One week after light exposure, the ONL was significantly thinner in Olfm1 mutant mice than in wild-type littermates indicating increased photoreceptor loss. No differences were observed when rhodopsin turnover or ERK1/2 signaling was investigated. We conclude that OLFM1 is a newly identified IPM molecule that serves an important role for photoreceptor homeostasis, which is significantly compromised in the eyes of Olfm1 mutant mice.

Olfactomedin 1 Deficiency Leads to Defective Olfaction and Impaired Female Fertility

Olfactomedin 1 (OLFM1) is a glycoprotein highly expressed in the brain. Olfm1(-/-) female mice were previously reported to have reduced fertility. Previous microarray analysis revealed Olfm1 among the most highly upregulated genes in the uterine luminal epithelium upon embryo implantation, which was confirmed by in situ hybridization. We hypothesized that Olfm1 deficiency led to defective embryo implantation and thus impaired fertility. Indeed, Olfm1(-/-) females had defective embryo implantation. However, Olfm1(-/-) females rarely mated and those that mated rarely became pregnant. Ovarian histology indicated the absence of corpora lutea in Olfm1(-/-) females, indicating defective ovulation. Superovulation using equine chorionic gonadotropin-human chorionic gonadotropin rescued mating, ovulation, and pregnancy, and equine chorionic gonadotropin alone rescued ovulation in Olfm1(-/-) females. Olfm1(-/-) females had a 13% reduction of hypothalamic GnRH neurons but comparable basal serum LH levels and GnRH-induced LH levels compared with wild-type controls. These results indicated no obvious local defects in the female reproductive system and a functional hypothalamic-pituitary-gonadal axis. Olfm1(-/-) females were unresponsive to the effects of male bedding stimulation on pubertal development and estrous cycle. There were 41% fewer cFos-positive cells in the mitral cell layer of accessory olfactory bulb upon male urine stimulation for 90 minutes. OLFM1 was expressed in the main and accessory olfactory systems including main olfactory epithelium, vomeronasal organ, main olfactory bulb, and accessory olfactory bulb, with the highest expression detected in the axon bundles of olfactory sensory neurons. These data demonstrate that defective fertility in Olfm1(-/-) females is most likely a secondary effect of defective olfaction.

Olfactomedin-1 Has a V-shaped Disulfide-linked Tetrameric Structure

Olfactomedin-1 (Olfm1; also known as noelin and pancortin) is a member of the olfactomedin domain-containing superfamily and a highly expressed neuronal glycoprotein important for nervous system development. It binds a number of secreted proteins and cell surface-bound receptors to induce cell signaling processes. Using a combined approach of x-ray crystallography, solution scattering, analytical ultracentrifugation, and electron microscopy we determined that full-length Olfm1 forms disulfide-linked tetramers with a distinctive V-shaped architecture. The base of the “V” is formed by two disulfide-linked dimeric N-terminal domains. Each of the two V legs consists of a parallel dimeric disulfide-linked coiled coil with a C-terminal β-propeller dimer at the tips. This agrees with our crystal structure of a C-terminal coiled-coil segment and β-propeller combination (Olfm1^coil-Olf) that reveals a disulfide-linked dimeric arrangement with the β-propeller top faces in an outward exposed orientation. Similar to its family member myocilin, Olfm1 is stabilized by calcium. The dimer-of-dimers architecture suggests a role for Olfm1 in clustering receptors to regulate signaling and sheds light on the conformation of several other olfactomedin domain family members.

A t(3;9)(q25.1;q34.3) translocation leading to OLFM1 fusion transcripts in Gilles de la Tourette syndrome, OCD and ADHD

Gilles de la Tourette syndrome (GTS) is a neuropsychiatric disorder with a strong genetic etiology; however, finding of candidate genes is hampered by its genetic heterogeneity and the influence of non-genetic factors on disease pathogenesis. We report a case of a male patient with GTS, obsessive compulsive disorder, attention-deficit/hyperactivity-disorder, as well as other comorbidities, and a translocation t(3;9)(q25.1;q34.3) inherited from a mother with tics. Mate-pair sequencing revealed that the translocation breakpoints truncated the olfactomedin 1 (OLFM1) gene and two uncharacterized transcripts. Reverse-transcription PCR identified several fusion transcripts in the carriers, and OLFM1 expression was found to be high in GTS-related human brain regions. As OLFM1 plays a role in neuronal development it is a likely candidate gene for neuropsychiatric disorders and haploinsufficiency of OLFM1 could be a contributing risk factor to the phenotype of the carriers. In addition, one of the fusion transcripts may exert a dominant-negative or gain-of-function effect. OLFM1 is unlikely to be a major GTS susceptibility gene as no point mutations or copy number variants affecting OLFM1 were identified in 175 additional patients. The translocation described is thus a unique event, but further studies in larger cohorts are required to elucidate involvement of OLFM1 in GTS pathogenesis.

Structural basis for misfolding in myocilin-associated glaucoma

Olfactomedin (OLF) domain-containing proteins play roles in fundamental cellular processes and have been implicated in disorders ranging from glaucoma, cancers and inflammatory bowel disorder, to attention deficit disorder and childhood obesity. We solved crystal structures of the OLF domain of myocilin (myoc-OLF), the best studied such domain to date. Mutations in myoc-OLF are causative in the autosomal dominant inherited form of the prevalent ocular disorder glaucoma. The structures reveal a new addition to the small family of five-bladed β-propellers. Propellers are most well known for their ability to act as hubs for protein-protein interactions, a function that seems most likely for myoc-OLF, but they can also act as enzymes. A calcium ion, sodium ion and glycerol molecule were identified within a central hydrophilic cavity that is accessible via movements of surface loop residues. By mapping familial glaucoma-associated lesions onto the myoc-OLF structure, three regions sensitive to aggregation have been identified, with direct applicability to differentiating between neutral and disease-causing non-synonymous mutations documented in the human population worldwide. Evolutionary analysis mapped onto the myoc-OLF structure reveals conserved and divergent regions for possible overlapping and distinctive functional protein-protein or protein-ligand interactions across the broader OLF domain family. While deciphering the specific normal biological functions, ligands and binding partners for OLF domains will likely continue to be a challenging long-term experimental pursuit, atomic detail structural knowledge of myoc-OLF is a valuable guide for understanding the implications of glaucoma-associated mutations and will help focus future studies of this biomedically important domain family.

Olfactomedin 1 interacts with the Nogo A receptor complex to regulate axon growth

Olfm1, a secreted highly conserved glycoprotein, is detected in peripheral and central nervous tissues and participates in neural progenitor maintenance, cell death in brain, and optic nerve arborization. In this study, we identified Olfm1 as a molecule promoting axon growth through interaction with the Nogo A receptor (NgR1) complex. Olfm1 is coexpressed with NgR1 in dorsal root ganglia and retinal ganglion cells in embryonic and postnatal mice. Olfm1 specifically binds to NgR1, as judged by alkaline phosphatase assay and coimmunoprecipitation. The addition of Olfm1 inhibited the growth cone collapse of dorsal root ganglia neurons induced by myelin-associated inhibitors, indicating that Olfm1 attenuates the NgR1 receptor functions. Olfm1 caused the inhibition of NgR1 signaling by interfering with interaction between NgR1 and its coreceptors p75NTR or LINGO-1. In zebrafish, inhibition of optic nerve extension by olfm1 morpholino oligonucleotides was partially rescued by dominant negative ngr1 or lingo-1. These data introduce Olfm1 as a novel NgR1 ligand that may modulate the functions of the NgR1 complex in axonal growth.

Structural features and functional domains of amassin-1, a cell-binding olfactomedin protein

Amassin-1 mediates a rapid cell adhesion that tightly adheres sea urchin coelomocytes (body cavity immunocytes) together. Three major structural regions exist in amassin-1: a short beta region, 3 coiled coils, and an olfactomedin domain. Amassin-1 contains 8 disulfide-bonded cysteines that, upon reduction, render it inactive. Truncated forms of recombinant amassin-1 were expressed and purified from Pichia pastoris and their disulfide bonding and biological activities investigated. Expressed alone, the olfactomedin domain contained 2 intramolecular disulfide bonds, existed in a monomeric state, and inhibited amassin-1-mediated clotting of coelomocytes by a calcium-dependent cell-binding activity. The N-terminal beta region, containing 3 cysteines, was not required for clotting activity. The coiled coils may dimerize amassin-1 in a parallel orientation through a homodimerizing disulfide bond. Neither amassin-1 fragments that were disulfide-linked as dimers or that were engineered to exist as dimers induced coelomocytes clotting. Clotting required higher multimeric states of amassin-1, possibly tetramers, which occurred through the N-terminal beta region and (or) the first segment of coiled coils.

Secreted gliomedin is a perinodal matrix component of peripheral nerves

The interaction between gliomedin and the axonodal cell adhesion molecules (CAMs) neurofascin and NrCAM induces the clustering of Na⁺ channels at the nodes of Ranvier. We define new interactions of gliomedin that are essential for its clustering activity. We show that gliomedin exists as both transmembrane and secreted forms that are generated by proteolytic cleavage of the protein, and that only the latter is detected at the nodes of Ranvier. The secreted extracellular domain of gliomedin binds to Schwann cells and is incorporated into the extracellular matrix (ECM) in a heparin-dependent manner, suggesting the involvement of heparan sulfate proteoglycans (HSPGs). Furthermore, we show that the N-terminal region of gliomedin serves as an oligomerization domain that mediates self-association of the molecule, which is required for its binding to neurofascin and NrCAM. Our results indicate that the deposition of gliomedin multimers at the nodal gap by binding to HSPGs facilitates the clustering of the axonodal CAMs and Na⁺ channels.

Pancortin-2 interacts with WAVE1 and Bcl-xL in a mitochondria-associated protein complex that mediates ischemic neuronal death

The actin-modulating protein Wiskott-Aldrich syndrome protein verprolin homologous-1 (WAVE1) and a novel CNS-specific protein, pancortin, are highly enriched in adult cerebral cortex, but their functions are unknown. Here we show that WAVE1 and pancortin-2 interact in a novel cell death cascade in adult, but not embryonic, cerebral cortical neurons. Focal ischemic stroke induces the formation of a protein complex that includes pancortin-2, WAVE1, and the anti-apoptotic protein Bcl-xL. The three-protein complex is associated with mitochondria resulting in increased association of Bax with mitochondria, cytochrome c release, and neuronal apoptosis. In pancortin null mice generated using a Cre-loxP system, ischemia-induced WAVE1-Bcl-xL interaction is diminished, and cortical neurons in these mice are protected against ischemic injury. Thus, pancortin-2 is a mediator of ischemia-induced apoptosis of neurons in the adult cerebral cortex and functions in a novel mitochondrial/actin-associated protein complex that sequesters Bcl-xL.

β-dystrobrevin, a kinesin-binding receptor, interacts with the extracellular matrix components pancortins

The dystrobrevins (alpha and beta) are components of the dystrophin-associated protein complex (DPC), which links the cytoskeleton to the extracellular matrix and serves as a scaffold for signaling proteins. The precise functions of the beta-dystrobrevin isoform, which is expressed in nonmuscle tissues, have not yet been determined. To gain further insights into the role of beta-dystrobrevin in brain, we performed a yeast two-hybrid screen and identified pancortin-2 as a novel beta-dystrobrevin-binding partner. Pancortins-1-4 are neuron-specific olfactomedin-related glycoproteins, highly expressed during brain development and widely distributed in the mature cerebral cortex of the mouse. Pancortins are important constituents of the extracellular matrix and are thought to play an essential role in neuronal differentiation. We characterized the interaction between pancortin-2 and beta-dystrobrevin by in vitro and in vivo association assays and mapped the binding site of pancortin-2 on beta-dystrobrevin to amino acids 202-236 of the beta-dystrobrevin molecule. We also found that the domain of interaction for beta-dystrobrevin is contained in the B part of pancortin-2, a central region that is common to all four pancortins. Our results indicate that beta-dystrobrevin could interact with all members of the pancortin family, implying that beta-dystrobrevin may be involved in brain development. We suggest that dystrobrevin, a motor protein receptor that binds kinesin heavy chain, might play a role in intracellular transport of pancortin to specific sites in the cell.

Identification of Japanese encephalitis virus-inducible genes in mouse brain and characterization of GARG39/IFIT2 as a microtubule-associated protein

Several mouse central nervous system genes have been identified that are differentially regulated during Japanese encephalitis virus (JEV) infection, including those which have not been reported to be induced by any other neurotropic virus. Interestingly, approximately 80 % of JEV-inducible genes identified in this study are also induced by Sindbis virus, indicating activation of common host signalling pathways by these two viruses, despite their diverse life cycles. One of these, the glucocorticoid attenuated response gene 39 (GARG39, also known as IFIT2, ISG54 and MuP54) was characterized further. It was demonstrated that GARG39 protein interacts with microtubules in vitro, co-localizes with beta-tubulin in vivo and is enriched in the mitotic spindle of non-neuronal cells undergoing mitosis. While GARG39 was known for a long time as an inflammation-inducible glucocorticoid attenuated protein, its identification as a microtubule-associated protein in this study suggests a possible role for this protein in cell proliferation, virion assembly/transport and microtubule dynamics.

Optimedin induces expression of N-cadherin and stimulates aggregation of NGF-stimulated PC12 cells

Optimedin, also known as olfactomedin 3, belongs to a family of olfactomedin domain-containing proteins. It is expressed in neural tissues and Pax6 is involved in the regulation of its promoter. To study possible effects of optimedin on the differentiation of neural cells, we produced stably transfected PC12 cell lines expressing optimedin under a tetracycline-inducible promoter. Cells expressing high levels of optimedin showed higher growth rates and stronger adhesion to the collagen extracellular matrix as compared with control PC12 cells. After stimulation with nerve growth factor (NGF), optimedin-expressing cells demonstrated elevated levels of N-cadherin, beta-catenin, alpha-catenin and occludin as compared with stimulated, control PC12 cells. Expression of optimedin induced Ca(2+)-dependent aggregation of NGF-stimulated PC12 cells and this aggregation was blocked by the expression of N-cadherin siRNA. Expression of optimedin also changed the organization of the actin cytoskeleton and inhibited neurite outgrowth in NGF-stimulated PC12 cells. We suggest that expression of optimedin stimulates the formation of adherent and tight junctions on the cell surface and this may play an important role in the differentiation of the brain and retina through the modulation of cytoskeleton organization, cell-cell adhesion and migration.

The glycoprotein hGC-1 binds to cadherin and lectins

Human granulocyte colony stimulating factor stimulated clone-1 (hGC-1, also known as GW112, OLM4, and hOlfD) is an olfactomedin-related glycoprotein of unknown function. We performed a series of biochemical studies to characterize its function. Using hGC-1 purified from baculovirus Sf9 cells we demonstrated that hGC-1 is a secreted glycoprotein containing N-linked carbohydrate chains and forms disulfide-bonded multimers. It binds to cell surfaces and to the locutions ricinus communis agglutinin I, concanavalin A and wheat germ agglutinin. Purified hGC-1 enhanced NIH3T3 and 293T/17 cell spreading and attachment, as did hGC-1-enriched culture supernatants of 293T/17 cells transfected with an hGC-1 expression vector. Coimmunoprecipitation studies demonstrated that hGC-1 interacts with cadherin in 293T/17 cells. This interaction depends on the C-terminal olfactomedin domain, but does not require the five well-conserved cysteine residues. However, cysteine residues at 83, 85, 246 and 437 are essential for secretion, and cysteine 226 is critical for hGC-1 multimer formation. Our studies demonstrated that hGC-1, an extracellular matrix glycoprotein, facilitates cell adhesion. Its potential interaction with endogenous cell surface lectins and cadherin may mediate this function.

Noelins modulate the timing of neuronal differentiation during development

Noelins comprise a family of extracellular proteins with proposed roles in neural and neural crest development. Here, we show that a previously uncharacterized family member, Noelin-4, functions to maintain neural precursors in an undifferentiated state and biases ectoderm toward a neural fate. We show that Noelin-4 is induced by the neurogenic genes X-ngnr-1 and XNeuroD. Over-expression of Noelin-4 causes expansion of the neural plate at the expense of neural crest and epidermis. Although there is an apparent increase in the neural precursor pool, no increase was noted in differentiated neurons. Later, derivatives such as the neural tube and retina appear enlarged. We show biochemically that Noelin-4 protein is glycosylated and secreted and that it interacts with Noelin-1, an isoform previously found to promote differentiation in neuralized animal caps. Accordingly, the neural precursor expansion activity of Noelin-4 is reversed by co-expression of Noelin-1. Our finding that Noelin isoforms can bind to and antagonize one another suggests that interacting Noelin isoforms may play a role in regulating timing of differentiation.

Elucidation of subfamily segregation and intramolecular coevolution of the olfactomedin-like proteins by comprehensive phylogenetic analysis and gene expression pattern assessment

The categorization of genes by structural distinctions relevant to biological characteristics is very important for understanding of gene functions and predicting functional implications of uncharacterized genes. It was absolutely necessary to deploy an effective and efficient strategy to deal with the complexity of the large olfactomedin-like (OLF) gene family sharing sequence similarity but playing diversified roles in many important biological processes, as the simple highest-hit homology analysis gave incomprehensive results and led to inappropriate annotation for some uncharacterized OLF members. In light of evolutionary information that may facilitate the classification of the OLF family and proper association of novel OLF genes with characterized homologs, we performed phylogenetic analysis on all 116 OLF proteins currently available, including two novel members cloned by our group. The OLF family segregated into seven subfamilies and members with similar domain compositions or functional properties all fell into relevant subfamilies. Furthermore, our Northern blot analysis and previous studies revealed that the typical human OLF members in each subfamily exhibited tissue-specific expression patterns, which in turn supported the segregation of the OLF subfamilies with functional divergence. Interestingly, the phylogenetic tree topology for the OLF domains alone was almost identical with that of the full-length tree representing the unique phylogenetic feature of full-length OLF proteins and their particular domain compositions. Moreover, each of the major functional domains of OLF proteins kept the same phylogenetic feature in defining similar topology of the tree. It indicates that the OLF domain and the various domains in flanking non-OLF regions have coevolved and are likely to be functionally interdependent. Expanded by a plausible gene duplication and domain couplings scenario, the OLF family comprises seven evolutionarily and functionally distinct subfamilies, in which each member shares similar structural and functional characteristics including the composition of coevolved and interdependent domains. The phylogenetically classified and preliminarily assessed subfamily framework may greatly facilitate the studying on the OLF proteins. Furthermore, it also demonstrated a feasible and reliable strategy to categorize novel genes and predict the functional implications of uncharacterized proteins based on the comprehensive phylogenetic classification of the subfamilies and their relevance to preliminary functional characteristics.

In-vitro study of the activity of ciprofloxacin alone and in combination against strains of Pseudomonas aeruginosa with multiple antibiotic resistance

Ciprofloxacin appears to have useful activity against Pseudomonas aeruginosa. We have studied its in-vitro activity against ten strains of Ps. aeruginosa with multiple antibiotic resistance. We have confirmed that ciprofloxacin is very active against Ps. aeruginosa with minimal inhibitory concentrations ranging from 0.07 to 0.7 mg/l. Killing curves show ciprofloxacin to be rapidly bactericidal with no regrowth after 24 h. Checkerboard studies with ciprofloxacin in combination with gentamicin, azlocillin and ceftazidime show no consistent interaction. These studies suggest that ciprofloxacin should prove a useful antibiotic in treating infections caused by multiresistant Ps. aeruginosa.