Synaptic membrane glycoproteins gp65 and gp55 are new members of the immunoglobulin superfamily

Disfunction of dorsal raphe nucleus-hippocampus serotonergic-HTR3 transmission results in anxiety phenotype of Neuroplastin 65-deficient mice

Anxiety disorders are the most common psychiatric condition, but the etiology of anxiety disorders remains largely unclear. Our previous studies have shown that neuroplastin 65 deficiency (NP65-/-) mice exhibit abnormal social and mental behaviors and decreased expression of tryptophan hydroxylase 2 (TPH2) protein. However, whether a causal relationship between TPH2 reduction and anxiety disorders exists needs to be determined. In present study, we found that replenishment of TPH2 in dorsal raphe nucleus (DRN) enhanced 5-HT level in the hippocampus and alleviated anxiety-like behaviors. In addition, injection of AAV-NP65 in DRN significantly increased TPH2 expression in DRN and hippocampus, and reduced anxiety-like behaviors. Acute administration of exogenous 5-HT or HTR3 agonist SR57227A in hippocampus mitigated anxiety-like behaviors in NP65-/- mice. Moreover, replenishment of TPH2 in DRN partly repaired the impairment of long-term potentiation (LTP) maintenance in hippocampus of NP65-/- mice. Finally, we found that loss of NP65 lowered transcription factors Lmx1b expression in postnatal stage and replenishment of NP65 in DRN reversed the decrease in Lmx1b expression of NP65-/- mice. Together, our findings reveal that NP65 deficiency induces anxiety phenotype by downregulating DRN-hippocampus serotonergic-HTR3 transmission. These studies provide a novel and insightful view about NP65 function, suggesting an attractive potential target for treatment of anxiety disorders.

Neuroplastin splice variants Np55 and Np65: Who is doing the job in macrophages?

Neuroplastin, a paralog of CD147/Basigin, is known as a neuronal cell adhesion molecule and as an auxiliary subunit of plasma membrane calcium ATPases in both neurons and adaptive immune cells. Recently, an interesting study by Ren et al. (2022) provided evidence for an important role of neuroplastin in macrophages during bacterial infection. Here, we critically discuss one aspect of this study, the assignment of this role to Np65 as one of two prominent splice variants of neuroplastin.

Embigin deficiency leads to delayed embryonic lung development and high neonatal mortality in mice

Embigin (Gp70), a receptor for fibronectin and an ancillary protein for monocarboxylate transporters, is known to regulate stem cell niches in sebaceous gland and bone marrow. Here, we show that embigin expression is at high level during early mouse embryogenesis and that embigin is essential for lung development. Markedly increased neonatal mortality of Emb-/- mice can be explained by the compromised lung maturation: in Emb-/- mice (E17.5) the number and the size of the small airways and distal airspace are significantly smaller, there are fewer ATI and ATII cells, and the alkaline phosphatase activity in amniotic fluid is lower. Emb-/- lungs show less peripheral branching already at E12.5, and embigin is highly expressed in lung primordium. Thus, embigin function is essential at early pseudoglandular stage or even earlier. Furthermore, our RNA-seq analysis and Ki67 staining results support the idea that the development of Emb-/- lungs is rather delayed than defected.

Neuroplastin Expression in Male Mice Is Essential for Fertility, Mating, and Adult Testosterone Levels

Male reproduction depends on hormonally driven behaviors and numerous genes for testis development and spermatogenesis. Neuroplastin-deficient (Nptn-/-) male mice cannot sire offspring. By immunohistochemistry, we characterized neuroplastin expression in the testis. Breeding, mating behavior, hormonal regulation, testicular development, and spermatogenesis were analyzed in cell-type specific neuroplastin mutant mice. Leydig, Sertoli, peritubular myoid, and germ cells express Np, but spermatogenesis and sperm number are not affected in Nptn-/- males. Neuroplastin lack from CNS neurons or restricted to spermatogonia or Sertoli cells permitted reproduction. Normal luteinizing hormone (LH) and follicle-stimulating hormone (FSH) blood levels in Nptn-/- males support undisturbed hormonal regulation in the brain. However, Nptn-/- males lack mounting behavior accompanied by low testosterone blood levels. Testosterone rise from juvenile to adult blood levels is absent in Nptn-/- males. LH-receptor stimulation raising intracellular Ca2+ in Leydig cells triggers testosterone production. Reduced Plasma Membrane Ca2+ ATPase 1 (PMCA1) in Nptn-/- Leydig cells suggests that Nptn-/- Leydig cells produce sufficient testosterone for testis and sperm development, but a lack of PMCA-Np complexes prevents the increase from reaching adult blood levels. Behavioral immaturity with low testosterone blood levels underlies infertility of Nptn-/- males, revealing that Np is essential for reproduction.

Neuroplastin 65 deficiency reduces amyloid plaque formation and cognitive deficits in an Alzheimer's disease mouse model

Introduction

Alzheimer's disease (AD) is characterized by increasing cognitive dysfunction, progressive cerebral amyloid beta (Aβ) deposition, and neurofibrillary tangle aggregation. However, the molecular mechanisms of AD pathologies have not been completely understood. As synaptic glycoprotein neuroplastin 65 (NP65) is related with synaptic plasticity and complex molecular events underlying learning and memory, we hypothesized that NP65 would be involved in cognitive dysfunction and Aβ plaque formation of AD. For this purpose, we examined the role of NP65 in the transgenic amyloid precursor protein (APP)/presenilin 1 (PS1) mouse model of AD.

Methods

Neuroplastin 65-knockout (NP65^-/-) mice crossed with APP/PS1 mice to get the NP65-deficient APP/PS1 mice. In the present study, a separate cohort of NP65-deficient APP/PS1 mice were used. First, the cognitive behaviors of NP65-deficient APP/PS1 mice were assessed. Then, Aβ plaque burden and Aβ levels in NP65-deficient APP/PS1 mice were measured by immunostaining and western blot as well as ELISA. Thirdly, immunostaining and western blot were used to evaluate the glial response and neuroinflammation. Finally, protein levels of 5-hydroxytryptamin (serotonin) receptor 3A and synaptic proteins and neurons were measured.

Results

We found that loss of NP65 alleviated the cognitive deficits of APP/PS1 mice. In addition, Aβ plaque burden and Aβ levels were significantly reduced in NP65-deficient APP/PS1 mice compared with control animals. NP65-loss in APP/PS1 mice resulted in a decrease in glial activation and the levels of pro- and anti-inflammatory cytokines (IL-1β, TNF-α, and IL-4) as well as protective matrix YM-1 and Arg-1, but had no effect on microglial phenotype. Moreover, NP65 deficiency significantly reversed the increase in 5-hydroxytryptamine (serotonin) receptor 3A (Htr3A) expression levels in the hippocampus of APP/PS1 mice.

Discussion

These findings identify a previously unrecognized role of NP65 in cognitive deficits and Aβ formation of APP/PS1 mice, and suggest that NP65 may serve as a potential therapeutic target for AD.

The role of neuroplastin65 in macrophage against E. coli infection in mice

BACKGROUND

Innate immune response constitutes the first line of defense against pathogens. Inflammatory responses involve close contact between different populations of cells. These adhesive interactions mediate migration of cells to sites of infection leading the effective action of cells within the lesions. Cell adhesion molecules are critical to controlling immune response mediating cell adhesion or chemotaxis, as well as coordinating actin-based cell motility during phagocytosis and chemotaxis. Recently, a newly discovered neuroplastin (Np) adhesion molecule is found to play an important role in the nervous system. However, there is limited information on Np functions in immune response. To understand how Np is involved in innate immune response, a mouse model of intraperitoneal infection was established to investigate the effect of Np on macrophage-mediated clearance of E. coli infection and its possible molecular mechanisms.

METHODS

Specific deficiency mice with Nptn gene controlling Np65 isoform were employed in this study. The expression levels of mRNA and proteins were detected by qPCR and western blot, or evaluated by flow cytometry. The expression level of NO and ROS were measured with their specific indicators. Cell cycle and apoptosis were detected by specific detection kits. Acid phosphatase activity was measured by flow cytometry after labelling with LysoRed fluorescent probe. Bone marrow derived macrophages (BMDMs) were isolated from bone marrow of mice hind legs. Cell proliferation was detected by CCK8 assay. Cell migration was measured by wound healing assay or transwell assay.

RESULTS

The lethal dose of E. coli infection in Np65^-/- mice dropped to the half of lethal dose in WT mice. The bacterial load in the spleen, kidney and liver from Np65^-/- mice were significantly higher than that from WT mice, which were due to the dramatic reduction of NO and ROS production in phagocytes from Np65^-/- mice. Np65 gene deficiency remarkably impaired phagocytosis and function of lysosome in macrophage. Furthermore, Np65 molecule was involved in maturation and proliferation, even in migration and chemotaxis of BMDM in vitro.

CONCLUSION

This study for the first time demonstrates that Np is involved in multi-function of phagocytes during bacterial infection, proposing that Np adhesion molecule plays a critical role in clearing pathogen infection in innate immunity.

Ca2+ signaling in postsynaptic neurons: Neuroplastin-65 regulates the interplay between plasma membrane Ca2+ ATPases and ionotropic glutamate receptors

Upon postsynaptic glutamate receptor activation, the cytosolic Ca²⁺ concentration rises and initiates signaling and plasticity in spines. The plasma membrane Ca²⁺ ATPase (PMCA) is a major player to limit the duration of cytosolic Ca²⁺ signals. It forms complexes with the glycoprotein neuroplastin (Np) isoforms Np55 and Np65 and functionally interplays with N-methyl-D-aspartate (NMDA)-type ionotropic glutamate receptors (iGluNRs). Moreover, binding of the Np65-specific extracellular domain to Ca²⁺-permeable GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-type ionotropic glutamate receptors (iGluA1Rs) was found to be required for long-term potentiation (LTP). However, the link between PMCA and iGluRs function to regulate cytosolic Ca²⁺ signals remained unclear. Here, we report that Np65 coordinates PMCA and iGluRs' functions to modulate the duration and amplitude of cytosolic Ca²⁺ transients in dendrites and spines of hippocampal neurons. Using live-cell Ca²⁺ imaging, acute pharmacological treatments, and GCaMP5G-expressing hippocampal neurons, we discovered that endogenous or Np65-promoted PMCA activity contributes to the restoration of basal Ca²⁺ levels and that this effect is dependent on iGluR activation. Super-resolution STED and confocal microscopy revealed that electrical stimulation increases the abundance of synaptic neuroplastin-PMCA complexes depending on iGluR activation and that low-rate overexpression of Np65 doubled PMCA levels and decreased cell surface levels of GluN2A and GluA1 in dendrites and Shank2-positive glutamatergic synapses. In neuroplastin-deficient hippocampi, we observed reduced PMCA and unchanged GluN2B levels, while GluN2A and GluA1 levels were imbalanced. Our electrophysiological data from hippocampal slices argues for an essential interplay of PMCA with GluN2A- but not with GluN2B-containing receptors upon induction of synaptic plasticity. Accordingly, we conclude that Np65 may interconnect PMCA with core players of glutamatergic neurotransmission to fine-tune the Ca²⁺ signal regulation in basal synaptic function and plasticity.

Retrograde Amnesia - A Question of Disturbed Calcium Levels?

Retrograde amnesia is the inability to remember events or information. The successful acquisition and memory of information is required before retrograde amnesia may occur. Often, the trigger for retrograde amnesia is a traumatic event. Loss of memories may be caused in two ways: either by loss/erasure of the memory itself or by the inability to access the memory, which is still present. In general, memories and learning are associated with a positive connotation although the extinction of unpleasant experiences and memories of traumatic events may be highly welcome. In contrast to the many experimental models addressing learning deficits caused by anterograde amnesia, the incapability to acquire new information, retrograde amnesia could so far only be investigated sporadically in human patients and in a limited number of model systems. Apart from models and diseases in which neurodegeneration or dementia like Alzheimer’s disease result in loss of memory, retrograde amnesia can be elicited by various drugs of which alcohol is the most prominent one and exemplifies the non-specific effects and the variable duration. External or internal impacts like traumatic brain injury, stroke, or electroconvulsive treatments may similarly result in variable degrees of retrograde amnesia. In this review, I will discuss a new genetic approach to induce retrograde amnesia in a mouse model and raise the hypothesis that retrograde amnesia is caused by altered intracellular calcium homeostasis. Recently, we observed that neuronal loss of neuroplastin resulted in retrograde amnesia specifically for associative memories. Neuroplastin is tightly linked to the expression of the main Ca²⁺ extruding pumps, the plasma membrane calcium ATPases (PMCAs). Therefore, neuronal loss of neuroplastin may block the retrieval and storage of associative memories by interference with Ca²⁺ signaling cascades. The possibility to elicit retrograde amnesia in a controlled manner allows to investigate the underlying mechanisms and may provide a deeper understanding of the molecular and circuit processes of memory.

Neuroplastin genetically interacts with Cadherin 23 and the encoded isoform Np55 is sufficient for cochlear hair cell function and hearing

Mammalian hearing involves the mechanoelectrical transduction (MET) of sound-induced fluid waves in the cochlea. Essential to this process are the specialised sensory cochlear cells, the inner (IHCs) and outer hair cells (OHCs). While genetic hearing loss is highly heterogeneous, understanding the requirement of each gene will lead to a better understanding of the molecular basis of hearing and also to therapeutic opportunities for deafness. The Neuroplastin (Nptn) gene, which encodes two protein isoforms Np55 and Np65, is required for hearing, and homozygous loss-of-function mutations that affect both isoforms lead to profound deafness in mice. Here we have utilised several distinct mouse models to elaborate upon the spatial, temporal, and functional requirement of Nptn for hearing. While we demonstrate that both Np55 and Np65 are present in cochlear cells, characterisation of a Np65-specific mouse knockout shows normal hearing thresholds indicating that Np65 is functionally redundant for hearing. In contrast, we find that Nptn-knockout mice have significantly reduced maximal MET currents and MET channel open probabilities in mature OHCs, with both OHCs and IHCs also failing to develop fully mature basolateral currents. Furthermore, comparing the hearing thresholds and IHC synapse structure of Nptn-knockout mice with those of mice that lack Nptn only in IHCs and OHCs shows that the majority of the auditory deficit is explained by hair cell dysfunction, with abnormal afferent synapses contributing only a small proportion of the hearing loss. Finally, we show that continued expression of Neuroplastin in OHCs of adult mice is required for membrane localisation of Plasma Membrane Ca2+ ATPase 2 (PMCA2), which is essential for hearing function. Moreover, Nptn haploinsufficiency phenocopies Atp2b2 (encodes PMCA2) mutations, with heterozygous Nptn-knockout mice exhibiting hearing loss through genetic interaction with the Cdh23ahl allele. Together, our findings provide further insight to the functional requirement of Neuroplastin for mammalian hearing.

Neuroplastin in Neuropsychiatric Diseases

Molecular mechanisms underlying neuropsychiatric and neurodegenerative diseases are insufficiently elucidated. A detailed understanding of these mechanisms may help to further improve medical intervention. Recently, intellectual abilities, creativity, and amnesia have been associated with neuroplastin, a cell recognition glycoprotein of the immunoglobulin superfamily that participates in synapse formation and function and calcium signaling. Data from animal models suggest a role for neuroplastin in pathways affected in neuropsychiatric and neurodegenerative diseases. Neuroplastin loss or disruption of molecular pathways related to neuronal processes has been linked to various neurological diseases, including dementia, schizophrenia, and Alzheimer's disease. Here, we review the molecular features of the cell recognition molecule neuroplastin, and its binding partners, which are related to neurological processes and involved in learning and memory. The emerging functions of neuroplastin may have implications for the treatment of diseases, particularly those of the nervous system.

Neuroplastin expression is essential for hearing and hair cell PMCA expression

Hearing deficits impact on the communication with the external world and severely compromise perception of the surrounding. Deafness can be caused by particular mutations in the neuroplastin (Nptn) gene, which encodes a transmembrane recognition molecule of the immunoglobulin (Ig) superfamily and plasma membrane Calcium ATPase (PMCA) accessory subunit. This study investigates whether the complete absence of neuroplastin or the loss of neuroplastin in the adult after normal development lead to hearing impairment in mice analyzed by behavioral, electrophysiological, and in vivo imaging measurements. Auditory brainstem recordings from adult neuroplastin-deficient mice (Nptn^-/-) show that these mice are deaf. With age, hair cells and spiral ganglion cells degenerate in Nptn^-/- mice. Adult Nptn^-/- mice fail to behaviorally respond to white noise and show reduced baseline blood flow in the auditory cortex (AC) as revealed by single-photon emission computed tomography (SPECT). In adult Nptn^-/- mice, tone-evoked cortical activity was not detectable within the primary auditory field (A1) of the AC, although we observed non-persistent tone-like evoked activities in electrophysiological recordings of some young Nptn^-/- mice. Conditional ablation of neuroplastin in Nptn^{lox/loxEmx1Cre} mice reveals that behavioral responses to simple tones or white noise do not require neuroplastin expression by central glutamatergic neurons. Loss of neuroplastin from hair cells in adult Nptn^{Δlox/loxPrCreERT} mice after normal development is correlated with increased hearing thresholds and only high prepulse intensities result in effective prepulse inhibition (PPI) of the startle response. Furthermore, we show that neuroplastin is required for the expression of PMCA 2 in outer hair cells. This suggests that altered Ca²⁺ homeostasis underlies the observed hearing impairments and leads to hair cell degeneration. Our results underline the importance of neuroplastin for the development and the maintenance of the auditory system.

Heteromeric Solute Carriers: Function, Structure, Pathology and Pharmacology

Solute carriers form one of three major superfamilies of membrane transporters in humans, and include uniporters, exchangers and symporters. Following several decades of molecular characterisation, multiple solute carriers that form obligatory heteromers with unrelated subunits are emerging as a distinctive principle of membrane transporter assembly. Here we comprehensively review experimentally established heteromeric solute carriers: SLC3-SLC7 amino acid exchangers, SLC16 monocarboxylate/H⁺ symporters and basigin/embigin, SLC4A1 (AE1) and glycophorin A exchanger, SLC51 heteromer Ost α-Ost β uniporter, and SLC6 heteromeric symporters. The review covers the history of the heteromer discovery, transporter physiology, structure, disease associations and pharmacology - all with a focus on the heteromeric assembly. The cellular locations, requirements for complex formation, and the functional role of dimerization are extensively detailed, including analysis of the first complete heteromer structures, the SLC7-SLC3 family transporters LAT1-4F2hc, b^0,+AT-rBAT and the SLC6 family heteromer B⁰AT1-ACE2. We present a systematic analysis of the structural and functional aspects of heteromeric solute carriers and conclude with common principles of their functional roles and structural architecture.

The amino-terminal domain of GluA1 mediates LTP maintenance via interaction with neuroplastin-65

Long-term potentiation (LTP) has long been considered as an important cellular mechanism for learning and memory. LTP expression involves NMDA receptor-dependent synaptic insertion of AMPA receptors (AMPARs). However, how AMPARs are recruited and anchored at the postsynaptic membrane during LTP remains largely unknown. In this study, using CRISPR/Cas9 to delete the endogenous AMPARs and replace them with the mutant forms in single neurons, we have found that the amino-terminal domain (ATD) of GluA1 is required for LTP maintenance. Moreover, we show that GluA1 ATD directly interacts with the cell adhesion molecule neuroplastin-65 (Np65). Neurons lacking Np65 exhibit severely impaired LTP maintenance, and Np65 deletion prevents GluA1 from rescuing LTP in AMPARs-deleted neurons. Thus, our study reveals an essential role for GluA1/Np65 binding in anchoring AMPARs at the postsynaptic membrane during LTP.

The Interaction of TRAF6 With Neuroplastin Promotes Spinogenesis During Early Neuronal Development

Correct brain wiring depends on reliable synapse formation. Nevertheless, signaling codes promoting synaptogenesis are not fully understood. Here, we report a spinogenic mechanism that operates during neuronal development and is based on the interaction of tumor necrosis factor receptor-associated factor 6 (TRAF6) with the synaptic cell adhesion molecule neuroplastin. The interaction between these proteins was predicted in silico and verified by co-immunoprecipitation in extracts from rat brain and co-transfected HEK cells. Binding assays show physical interaction between neuroplastin’s C-terminus and the TRAF-C domain of TRAF6 with a K_d value of 88 μM. As the two proteins co-localize in primordial dendritic protrusions, we used young cultures of rat and mouse as well as neuroplastin-deficient mouse neurons and showed with mutagenesis, knock-down, and pharmacological blockade that TRAF6 is required by neuroplastin to promote early spinogenesis during in vitro days 6-9, but not later. Time-framed TRAF6 blockade during days 6–9 reduced mEPSC amplitude, number of postsynaptic sites, synapse density and neuronal activity as neurons mature. Our data unravel a new molecular liaison that may emerge during a specific window of the neuronal development to determine excitatory synapse density in the rodent brain.

Cross-Talk between Fibroblast Growth Factor Receptors and Other Cell Surface Proteins

Fibroblast growth factors (FGFs) and their receptors (FGFRs) constitute signaling circuits that transmit signals across the plasma membrane, regulating pivotal cellular processes like differentiation, migration, proliferation, and apoptosis. The malfunction of FGFs/FGFRs signaling axis is observed in numerous developmental and metabolic disorders, and in various tumors. The large diversity of FGFs/FGFRs functions is attributed to a great complexity in the regulation of FGFs/FGFRs-dependent signaling cascades. The function of FGFRs is modulated at several levels, including gene expression, alternative splicing, posttranslational modifications, and protein trafficking. One of the emerging ways to adjust FGFRs activity is through formation of complexes with other integral proteins of the cell membrane. These proteins may act as coreceptors, modulating binding of FGFs to FGFRs and defining specificity of elicited cellular response. FGFRs may interact with other cell surface receptors, like G-protein-coupled receptors (GPCRs) or receptor tyrosine kinases (RTKs). The cross-talk between various receptors modulates the strength and specificity of intracellular signaling and cell fate. At the cell surface FGFRs can assemble into large complexes involving various cell adhesion molecules (CAMs). The interplay between FGFRs and CAMs affects cell–cell interaction and motility and is especially important for development of the central nervous system. This review summarizes current stage of knowledge about the regulation of FGFRs by the plasma membrane-embedded partner proteins and highlights the importance of FGFRs-containing membrane complexes in pathological conditions, including cancer.

Neuroplastin 65 modulates anxiety- and depression-like behavior likely through adult hippocampal neurogenesis and central 5-HT activity

Neuroplastin 65 (Np65) is a brain-specific cell adhesion molecule that is highly expressed in the hippocampus, amygdala, and cortex, regions of the brain that are associated with memory and emotions. However, the role of Np65 in regulation of emotional behavior is still unclear. In the present study, we show that Np65 knock-out (Np65 KO) mice display enhanced anxiety-like behavior, a reduction in some aspects of depressive-like behaviors, and increased sociability and memory. Biochemical investigations revealed that Np65 KO mice show increased adult-born neurons and proliferation in the hippocampus. In addition, the level of 5-hydroxytryptamine (5-HT) in the hippocampus was reduced. The expression of tryptophan hydroxylase 2 in the brainstem and the expression of the 5-HT_3A receptor were also decreased. Electrophysiological recordings confirmed an impaired maintenance of long-term potentiation in the hippocampus of Np65 KO mice. Together, our findings uncover a role for Np65 in regulating anxiety- and depressive-like behaviors and suggest that Np65 may be essential for the maintenance of emotional stability, indicating that it might be an attractive potential target for treatment of psychiatric disorders.

Microarray Analysis of Gene Expression Changes in Neuroplastin 65-Knockout Mice: Implications for Abnormal Cognition and Emotional Disorders

Neuroplastin 65 (Np65) is an immunoglobulin superfamily cell adhesion molecule involved in synaptic formation and plasticity. Our recent study showed that Np65-knockout (KO) mice exhibit abnormal cognition and emotional disorders. However, the underlying mechanisms remain unclear. In this study, we found 588 differentially-expressed genes in Np65-KO mice by microarray analysis. RT-PCR analysis also revealed the altered expression of genes associated with development and synaptic structure, such as Cdh1, Htr3a, and Kcnj9. In addition, the expression of Wnt-3, a Wnt protein involved in development, was decreased in Np65-KO mice as evidenced by western blotting. Surprisingly, MRI and DAPI staining showed a significant reduction in the lateral ventricular volume of Np65-KO mice. Together, these findings suggest that ablation of Np65 influences gene expression, which may contribute to abnormal brain development. These results provide clues to the mechanisms underlying the altered brain functions of Np65-deficient mice.

Promoter interactome of human embryonic stem cell-derived cardiomyocytes connects GWAS regions to cardiac gene networks

Long-range chromosomal interactions bring distal regulatory elements and promoters together to regulate gene expression in biological processes. By performing promoter capture Hi-C (PCHi-C) on human embryonic stem cell-derived cardiomyocytes (hESC-CMs), we show that such promoter interactions are a key mechanism by which enhancers contact their target genes after hESC-CM differentiation from hESCs. We also show that the promoter interactome of hESC-CMs is associated with expression quantitative trait loci (eQTLs) in cardiac left ventricular tissue; captures the dynamic process of genome reorganisation after hESC-CM differentiation; overlaps genome-wide association study (GWAS) regions associated with heart rate; and identifies new candidate genes in such regions. These findings indicate that regulatory elements in hESC-CMs identified by our approach control gene expression involved in ventricular conduction and rhythm of the heart. The study of promoter interactions in other hESC-derived cell types may be of utility in functional investigation of GWAS-associated regions.

Neuroplastin deletion in glutamatergic neurons impairs selective brain functions and calcium regulation: implication for cognitive deterioration

The cell adhesion molecule neuroplastin (Np) is a novel candidate to influence human intelligence. Np-deficient mice display complex cognitive deficits and reduced levels of Plasma Membrane Ca²⁺ ATPases (PMCAs), an essential regulator of the intracellular Ca²⁺ concentration ([iCa²⁺]) and neuronal activity. We show abundant expression and conserved cellular and molecular features of Np in glutamatergic neurons in human hippocampal-cortical pathways as characterized for the rodent brain. In Nptn^{lox/loxEmx1Cre} mice, glutamatergic neuron-selective Np ablation resulted in behavioral deficits indicating hippocampal, striatal, and sensorimotor dysfunction paralleled by highly altered activities in hippocampal CA1 area, sensorimotor cortex layers I-III/IV, and the striatal sensorimotor domain detected by single-photon emission computed tomography. Altered hippocampal and cortical activities correlated with reduction of distinct PMCA paralogs in Nptn^{lox/loxEmx1Cre} mice and increased [iCa²⁺] in cultured mutant neurons. Human and rodent Np enhanced the post-transcriptional expression of and co-localized with PMCA paralogs in the plasma membrane of transfected cells. Our results indicate Np as essential for PMCA expression in glutamatergic neurons allowing proper [iCa²⁺] regulation and normal circuit activity. Neuron-type-specific Np ablation empowers the investigation of circuit-coded learning and memory and identification of causal mechanisms leading to cognitive deterioration.

Increased Susceptibility to Ischemic Brain Injury in Neuroplastin 65-Deficient Mice Likely via Glutamate Excitotoxicity

Cell adhesion molecules (CAMs) are involved in synaptic plasticity and neuronal survival in the adult brain. Neuroplastin 65 (Np65), one member of the immunoglobulin superfamily of CAMs, is brain-specific and highly expressed in rodent forebrain. The roles of Np65 in synaptic plasticity have been confirmed, however, whether Np65 affects neuronal survival remains unknown. To address this gap, we generated, to our knowledge, the first Np65 knockout (KO) mice. By occluding middle cerebral artery to perform ischemic stroke model, we showed that Np65 KO mice exhibited more severe neurological deficits and larger infarction volume measured by TTC staining and more apoptotic cells confirmed by TUNEL staining compared to wild type (WT) mice. Besides, western blot analysis showed that the vesicular glutamate transporter-1(VGluT1), and N-Methyl D-Aspartate receptors, including NR1, NR2A, and NR2B were significantly increased in Np65 KO mice compared with WT mice. In contrast, vesicular gamma amino butyric acid transporter (VGAT) levels were unchanged in two genotypes after stroke. Additionally, phosphorylated-extracellular signal-regulated kinase 1/2 levels were significantly increased in Np65 KO mice compared with WT mice after stroke. Together, these results suggest that Np65 KO mice may be more susceptible to ischemic events in the brain.

Genetically Induced Retrograde Amnesia of Associative Memories After Neuroplastin Ablation

BACKGROUND

Neuroplastin cell recognition molecules have been implicated in synaptic plasticity. Polymorphisms in the regulatory region of the human neuroplastin gene (NPTN) are correlated with cortical thickness and intellectual abilities in adolescents and in individuals with schizophrenia.

METHODS

We characterized behavioral and functional changes in inducible conditional neuroplastin-deficient mice.

RESULTS

We demonstrate that neuroplastins are required for associative learning in conditioning paradigms, e.g., two-way active avoidance and fear conditioning. Retrograde amnesia of learned associative memories is elicited by inducible neuron-specific ablation of Nptn gene expression in adult mice, which shows that neuroplastins are indispensable for the availability of previously acquired associative memories. Using single-photon emission computed tomography imaging in awake mice, we identified brain structures activated during memory recall. Constitutive neuroplastin deficiency or Nptn gene ablation in adult mice causes substantial electrophysiologic deficits such as reduced long-term potentiation. In addition, neuroplastin-deficient mice reveal profound physiologic and behavioral deficits, some of which are related to depression and schizophrenia, which illustrate neuroplastin's essential functions.

CONCLUSIONS

Neuroplastins are essential for learning and memory. Retrograde amnesia after an associative learning task can be induced by ablation of the neuroplastin gene. The inducible neuroplastin-deficient mouse model provides a new and unique means to analyze the molecular and cellular mechanisms underlying retrograde amnesia and memory.

Xkr8 phospholipid scrambling complex in apoptotic phosphatidylserine exposure

Xk-related protein (Xkr) 8, a protein carrying 10 transmembrane regions, is essential for scrambling phospholipids during apoptosis. Here, we found Xkr8 as a complex with basigin (BSG) or neuroplastin (NPTN), type I membrane proteins in the Ig superfamily. In BSG(-/-)NPTN(-/-) cells, Xkr8 localized intracellularly, and the apoptosis stimuli failed to expose phosphatidylserine, indicating that BSG and NPTN chaperone Xkr8 to the plasma membrane to execute its scrambling activity. Mutational analyses of BSG showed that the atypical glutamic acid in the transmembrane region is required for BSG's association with Xkr8. In cells exposed to apoptotic signals, Xkr8 was cleaved at the C terminus and the Xkr8/BSG complex formed a higher-order complex, likely to be a heterotetramer consisting of two molecules of Xkr8 and two molecules of BSG or NPTN, suggesting that this cleavage causes the formation of a larger complex of Xkr8-BSG/NPTN for phospholipid scrambling.

Identification of an S100A8 Receptor Neuroplastin-β and its Heterodimer Formation with EMMPRIN

We previously reported a positive feedback loop between S100A8/A9 and proinflammatory cytokines mediated by extracellular matrix metalloproteinase inducer, an S100A9 receptor. Here, we identify neuroplastin-β as an unreported S100A8 receptor. Neuroplastin-β and extracellular matrix metalloproteinase inducer form homodimers and a heterodimer, and they are co-localized on the surface of cultured normal human keratinocytes. Knockdown of both receptors suppressed cell proliferation and proinflammatory cytokine induction. Upon stimulation with S100A8, neuroplastin-β recruited GRB2 and activated extracellular signal-regulated kinase, resulting in keratinocyte proliferation. Keratinocyte proliferation in response to inflammatory stimuli was accelerated in involucrin promoter-driven S100A8 transgenic mice. Further, S100A8 and S100A9 were strongly up-regulated and co-localized in lesional skin of atopic dermatitis patients. Our results indicate that neuroplastin-β and extracellular matrix metalloproteinase inducer form a functional heterodimeric receptor for S100A8/A9 heterodimer, followed by recruitment of specific adaptor molecules GRB2 and TRAF2, and this signaling pathway is involved in activation of both keratinocyte proliferation and skin inflammation in atopic skin. Suppression of this pathway might have potential for treatment of skin diseases associated with chronic inflammation such as atopic dermatitis.

Absence of Neuroplastin-65 Affects Synaptogenesis in Mouse Inner Hair Cells and Causes Profound Hearing Loss

The Neuroplastin gene encodes two synapse-enriched protein isoforms, Np55 and Np65, which are transmembrane glycoproteins that regulate several cellular processes, including the genesis, maintenance, and plasticity of synapses. We found that an absence of Np65 causes early-onset sensorineural hearing loss and prevented the normal synaptogenesis in inner hair cells (IHCs) in the newly identified mouse mutant pitch. In wild-type mice, Np65 is strongly upregulated in the cochlea from around postnatal day 12 (P12), which corresponds to the onset of hearing. Np65 was specifically localized at the presynaptic region of IHCs. We found that the colocalization of presynaptic IHC ribbons and postsynaptic afferent terminals is greatly reduced in pitch mutants. Moreover, IHC exocytosis is also reduced with mutant mice showing lower rates of vesicle release. Np65 appears to have a nonessential role in vision. We propose that Np65, by regulating IHC synaptogenesis, is critical for auditory function in mammals.

SIGNIFICANCE STATEMENT

In the mammalian cochlea, the sensory inner hair cells (IHCs) encode auditory information. They do this by converting sound wave-induced mechanical motion of their hair bundles into an electrical current. This current generates a receptor potential that controls release of glutamate neurotransmitter from their ribbon synapses onto the auditory afferent fiber. We show that the synapse-enriched protein Np65, encoded by the Neuroplastin gene, is localized at the IHC presynaptic region. In mutant mice, absence of Np65 causes early-onset sensorineural hearing loss and prevents normal neurotransmitter release in IHCs and colocalization of presynaptic ribbons with postsynaptic afferents. We identified Neuroplastin as a novel deafness gene required for ribbon synapse formation and function, which is critical for sound perception in mammals.

Neuroplastin 65 mediates cognitive functions via excitatory/inhibitory synapse imbalance and ERK signal pathway

Neuroplastin 65 (NP65) is a brain-specific glycoprotein component of synaptic membrane, which is predominantly located in the forebrain such as the cortex, amygdala and striatum and hippocampus. Previous studies have shown that NP65 is implicated in synaptic plasticity, so it was hypothesized to play roles in cognitive functions. To test this hypothesis, we generated NP65 knock-out (KO) mice and found that the null mice exhibited enhanced hippocampus-dependent learning and memory as manifested by Morris water maze test and step-through passive avoidance test, but showed anxiety-like behaviors as manifested by open field test and light/dark exploration test. In addition, molecular and cellular studies revealed several alterations including: (1) the enhanced ratio of excitatory to inhibitory synapses; (2) increased expression of NMDA receptors NR2A; (3) enhanced activation of ERK signaling; (4) lowered number of the mushroom- and bifurcate-shaped dendritic spines in NP65 KO mice. Together, our findings suggest that NP65 may mediate cognitive functions.

The Neuroplastin adhesion molecules: key regulators of neuronal plasticity and synaptic function

The Neuroplastins Np65 and Np55 are neuronal and synapse-enriched immunoglobulin superfamily molecules that play important roles in a number of key neuronal and synaptic functions including, for Np65, cell adhesion. In this review we focus on the physiological roles of the Neuroplastins in promoting neurite outgrowth, regulating the structure and function of both inhibitory and excitatory synapses in brain, and in neuronal and synaptic plasticity. We discuss the underlying molecular and cellular mechanisms by which the Neuroplastins exert their physiological effects and how these are dependent upon the structural features of Np65 and Np55, which enable them to bind to a diverse range of protein partners. In turn this enables the Neuroplastins to interact with a number of key neuronal signalling cascades. These include: binding to and activation of the fibroblast growth factor receptor; Np65 trans-homophilic binding leading to activation of p38 MAPK and internalization of glutamate (GluR1) receptor subunits; acting as accessory proteins for monocarboxylate transporters, thus affecting neuronal energy supply, and binding to GABAA α1, 2 and 5 subunits, thus regulating the composition and localization of GABAA receptors. An emerging theme is the role of the Neuroplastins in regulating the trafficking and subcellular localization of specific binding partners. We also discuss the involvement of Neuroplastins in a number of pathophysiological conditions, including ischaemia, schizophrenia and breast cancer and the role of a single nucleotide polymorphism in the human Neuroplastin (NPTN) gene locus in impairment of cortical development and cognitive functions. Neuroplastins are neuronal cell adhesion molecules, which induce neurite outgrowth and play important roles in synaptic maturation and plasticity. This review summarizes the functional implications of Neuroplastins for correct synaptic membrane protein localization, neuronal energy supply, expression of LTP and LTD, animal and human behaviour, and pathophysiology and disease. It focuses particularly on Neuroplastin binding partners and signalling mechanisms, and proposes perspectives for future research on these important immunoglobulin superfamily members.

Structure of excitatory synapses and GABAA receptor localization at inhibitory synapses are regulated by neuroplastin-65

Formation, maintenance, and activity of excitatory and inhibitory synapses are essential for neuronal network function. Cell adhesion molecules (CAMs) are crucially involved in these processes. The CAM neuroplastin-65 (Np65) highly expressed during periods of synapse formation and stabilization is present at the pre- and postsynaptic membranes. Np65 can translocate into synapses in response to electrical stimulation and it interacts with subtypes of GABAA receptors in inhibitory synapses. Here, we report that in the murine hippocampus and in hippocampal primary culture, neurons of the CA1 region and the dentate gyrus (DG) express high Np65 levels, whereas expression in CA3 neurons is lower. In neuroplastin-deficient (Np(-/-)) mice the number of excitatory synapses in CA1 and DG, but not CA3 regions is reduced. Notably this picture is mirrored in mature Np(-/-) hippocampal cultures or in mature CA1 and DG wild-type (Np(+/+)) neurons treated with a function-blocking recombinant Np65-Fc extracellular fragment. Although the number of GABAergic synapses was unchanged in Np(-/-) neurons or in mature Np65-Fc-treated Np(+/+) neurons, the ratio of excitatory to inhibitory synapses was significantly lower in Np(-/-) cultures. Furthermore, GABAA receptor composition was altered at inhibitory synapses in Np(-/-) neurons as the α1 to α2 GABAA receptor subunit ratio was increased. Changes of excitatory and inhibitory synaptic function in Np(-/-) neurons were confirmed evaluating the presynaptic release function and using patch clamp recording. These data demonstrate that Np65 is an important regulator of the number and function of synapses in the hippocampus.

The neuroplastins: multifunctional neuronal adhesion molecules--involvement in behaviour and disease

The neuroplastins np65 and np55 are neuronal and synapse-enriched immunoglobulin (Ig) superfamily cell adhesion molecules that contain 3 and 2 Ig domains, respectively. Np65 is neuron specific whereas np55 is expressed in many tissues. They are multifunctional proteins whose physiological roles are defined by the partner proteins they bind to and the signalling pathways they activate. The neuroplastins are implicated in activity-dependent long-term synaptic plasticity. Thus neuroplastin-specific antibodies and a recombinant peptide inhibit long-term potentiation in hippocampal neurones. This is mediated by activation of the p38MAP kinase signalling pathway, resulting in the downregulation of the surface expression of GluR1 receptors. Np65, but not np55, exhibits trans-homophilic binding. Both np65 and np55 induce neurite outgrowth and both activate the FGF receptor and associated downstream signalling pathways. Np65 binds to and colocalises with GABA(A) receptor subtypes and may play a role in anchoring them to specific synaptic and extrasynaptic sites. Most recently the neuroplastins have been shown to chaperone and support the monocarboxylate transporter MCT2 in transporting lactate across the neuronal plasma membrane. Thus the neuroplastins are multifunctional adhesion molecules which support neurite outgrowth, modulate long-term activity-dependent synaptic plasticity, regulate surface expression of GluR1 receptors, modulate GABA(A) receptor localisation, and play a key role in delivery of monocarboxylate energy substrates both to the synapse and to extrasynaptic sites. The diverse functions and range of signalling pathways activated by the neuroplastins suggest that they are important in modulating behaviour and in relation to human disease.

The neuroplastin adhesion molecules are accessory proteins that chaperone the monocarboxylate transporter MCT2 to the neuronal cell surface

BACKGROUND

The neuroplastins np65 and np55 are two synapse-enriched immunoglobulin (Ig) superfamily adhesion molecules that contain 3 and 2 Ig domains respectively. Np65 is implicated in long term, activity dependent synaptic plasticity, including LTP. Np65 regulates the surface expression of GluR1 receptor subunits and the localisation of GABA(A) receptor subtypes in hippocampal neurones. The brain is dependent not only on glucose but on monocarboxylates as sources of energy. The. monocarboxylate transporters (MCTs) 1-4 are responsible for the rapid proton-linked translocation of monocarboxylates including pyruvate and lactate across the plasma membrane and require association with either embigin or basigin, proteins closely related to neuroplastin, for plasma membrane expression and activity. MCT2 plays a key role in providing lactate as an energy source to neurons.

METHODOLOGY/FINDINGS

Here we use co-transfection of neuroplastins and monocarboxylate transporters into COS-7 cells to demonstrate that neuroplastins can act as ancillary proteins for MCT2. We also show that Xenopus laevis oocytes contain endogenous neuroplastin and its knockdown with antisense RNA reduces the surface expression of MCT2 and associated lactate transport. Immunocytochemical studies show that MCT2 and the neuroplastins are co-localised in rat cerebellum. Strikingly neuroplastin and MCT2 are enriched in the same parasagittal zebrin II-negative stripes.

CONCLUSIONS

These data strongly suggest that neuroplastins act as key ancillary proteins for MCT2 cell surface localisation and activity in some neuronal populations, thus playing an important role in facilitating the uptake of lactate for use as a respiratory fuel.

Neuroplastin expression in the hippocampus of mice lacking complex gangliosides

We report changes in neuroplastin gene and protein expression in the hippocampus of B4galnt1 null mice, which lacks complex ganglioside structures, compared with that of wild-type mice. Neuroplastin mRNA expression was significantly higher in the hippocampi of B4galnt1 null mice than in wild-type mice. Moreover, Western blot analysis shows increased neuroplastin protein levels of neuroplastin-55 isoform in B4galnt1 null hippocampal homogenates. Immunohistochemistry revealed a substantially different distribution of neuroplastin immunoreactivity in sagittal sections of the hippocampi derived from B4galnt1 null in comparison with those from wild-type mice. Most strikingly, B4galnt1 null mice had relatively little neuroplastin immunoreactivity in the pyramidal layer of CA1 and CA3, whereas wild-type mice had strong neuroplastin staining of pyramidal cells. Results of this study support the hypothesis that alterations of brain ganglioside expression influence the expression of neuroplastin. As both neuroplastin and gangliosides have important roles in synaptic transmission, synaptic plasticity, and neurite outgrowth, it will be of particular interest to unravel the molecular mechanisms underlying the relationship between ganglioside composition and neuroplastin transcript and protein expression in the mammalian nervous system.

The cell adhesion molecule neuroplastin-65 is a novel interaction partner of γ-aminobutyric acid type A receptors

γ-Aminobutyric acid type A (GABA(A)) receptors are pentameric ligand-gated ion channels that mediate fast inhibition in the central nervous system. Depending on their subunit composition, these receptors exhibit distinct pharmacological properties and differ in their ability to interact with proteins involved in receptor anchoring at synaptic or extra-synaptic sites. Whereas GABA(A) receptors containing α1, α2, or α3 subunits are mainly located synaptically where they interact with the submembranous scaffolding protein gephyrin, receptors containing α5 subunits are predominantly found extra-synaptically and seem to interact with radixin for anchorage. Neuroplastin is a cell adhesion molecule of the immunoglobulin superfamily that is involved in hippocampal synaptic plasticity. Our results reveal that neuroplastin and GABA(A) receptors can be co-purified from rat brain and exhibit a direct physical interaction as demonstrated by co-precipitation and Förster resonance energy transfer (FRET) analysis in a heterologous expression system. The brain-specific isoform neuroplastin-65 co-localizes with GABA(A) receptors as shown in brain sections as well as in neuronal cultures, and such complexes can either contain gephyrin or be devoid of gephyrin. Neuroplastin-65 specifically co-localizes with α1 or α2 but not with α3 subunits at GABAergic synapses. In addition, neuroplastin-65 also co-localizes with GABA(A) receptor α5 subunits at extra-synaptic sites. Down-regulation of neuroplastin-65 by shRNA causes a loss of GABA(A) receptor α2 subunits at GABAergic synapses. These results suggest that neuroplastin-65 can co-localize with a subset of GABA(A) receptor subtypes and might contribute to anchoring and/or confining GABA(A) receptors to particular synaptic or extra-synaptic sites, thus affecting receptor mobility and synaptic strength.

The retinal specific CD147 Ig0 domain: from molecular structure to biological activity

CD147 is a type I transmembrane protein that is involved in inflammatory diseases, cancer progression, and multiple human pathogens utilize CD147 for efficient infection. CD147 expression is so high in several cancers that it is now used as a prognostic marker. The two primary isoforms of CD147 that are related to cancer progression have been identified, differing in their number of immunoglobulin (Ig)-like domains. These include CD147 Ig1-Ig2, which is ubiquitously expressed in most tissues, and CD147 Ig0-Ig1-Ig2, which is retinal specific and implicated in retinoblastoma. However, little is known in regard to the retinal specific CD147 Ig0 domain despite its potential role in retinoblastoma. We present the first crystal structure of the human CD147 Ig0 domain and show that the CD147 Ig0 domain is a crystallographic dimer with an I-type domain structure, which maintained in solution. Furthermore, we have utilized our structural data together with mutagenesis to probe the biological activity of CD147-containing proteins, both with and without the CD147 Ig0 domain, within several model cell lines. Our findings reveal that the CD147 Ig0 domain is a potent stimulator of interleukin-6 and suggest that the CD147 Ig0 domain has its own receptor distinct from that of the other CD147 Ig-like domains, CD147 Ig1-Ig2. Finally, we show that the CD147 Ig0 dimer is the functional unit required for activity and can be disrupted by a single point mutation.

Neuroplastin-55 binds to and signals through the fibroblast growth factor receptor

Neuroplastin (Np) is a glycoprotein belonging to the immunoglobulin superfamily of cell adhesion molecules (CAMs) and existing in two isoforms, Np55 and Np65, named according to their molecular weights. The extracellular part of Np65 contains three immunoglobulin (Ig)-like modules (Ig1, Ig2, and Ig3), whereas Np55 lacks the Ig1 module. Of these two isoforms, only Np65 is involved in homophilic interactions resulting in cell adhesion, whereas the role of Np55 is poorly understood. The present study reports for the first time the crystal structure of the ectodomain of Np55 at 1.95-A resolution and demonstrates that Np55 binds to and activates the fibroblast growth factor receptor 1 (FGFR1). Furthermore, we identify a sequence motif in the Ig2 module of Np55 interacting with FGFR1 and show that a synthetic peptide encompassing this motif, termed narpin, binds to and activates FGFR1. We show that both Np55 and the narpin peptide induce neurite outgrowth through FGFR1 activation and that Np55 increases synaptic calcium concentration in an FGFR1-dependent manner. Moreover, we demonstrate that narpin has an antidepressive-like effect in rats subjected to the forced swim test, suggesting that Np55-induced signaling may be involved in synaptic plasticity in vivo. Owczarek, S., Kiryushko, D., Larsen, M. H., Kastrup, J. S., Gajhede, M., Sandi, C., Berezin, V., Bock, E., Soroka, V. Neuroplastin-55 binds to and signals through the fibroblast growth factor receptor.

Identification of novel tumor antigens with patient-derived immune-selected antibodies

The identification of tumor antigens capable of eliciting an immune response in vivo may be an effective method to identify therapeutic cancer targets. We have developed a method to identify such antigens using frozen tumor-draining lymph node samples from breast cancer patients. Immune responses in tumor-draining lymph nodes were identified by immunostaining lymph node sections for B-cell markers (CD20&CD23) and Ki67 which revealed cell proliferation in germinal center zones. Antigen-dependent somatic hypermutation (SH) and clonal expansion (CE) were present in heavy chain variable (VH) domain cDNA clones obtained from these germinal centers, but not from Ki67 negative germinal centers. Recombinant VH single-domain antibodies were used to screen tumor proteins and affinity select potential tumor antigens. Neuroplastin (NPTN) was identified as a candidate breast tumor antigen using proteomic identification of affinity selected tumor proteins with a recombinant VH single chain antibody. NPTN was found to be highly expressed in approximately 20% of invasive breast carcinomas and 50% of breast carcinomas with distal metastasis using a breast cancer tissue array. Additionally, NPTN over-expression in a breast cancer cell line resulted in a significant increase in tumor growth and angiogenesis in vivo which was related to increased VEGF production in the transfected cells. These results validate NPTN as a tumor-associated antigen which could promote breast tumor growth and metastasis if aberrantly expressed. These studies also demonstrate that humoral immune responses in tumor-draining lymph nodes can provide antibody reagents useful in identifying tumor antigens with applications for biomarker screening, diagnostics and therapeutic interventions.

Comparative genomics of human-like Schistosoma japonicum genes indicates a putative mechanism for host-parasite relationship

Schistosoma japonicum causes schistosomiasis in humans and livestock in the Asia-Pacific region. We assembled more than 43,700 S. japonicum expressed sequence tags and conducted comparative genomic analyses between S. japonicum and its human host. Some schistosome genes showed exceptionally high similarity in nucleotide sequence to their human homologues, of which five exhibited anomalous phylogeny and human codon usage bias. The most plausible explanation for their presence is horizontal gene transfer from host to parasite. Functional evidence suggests that S. japonicum might exploit host endocrine and immune signals for cell development and maturation via these host-like genes.

Basigin/EMMPRIN/CD147 mediates neuron-glia interactions in the optic lamina of Drosophila

Basigin, an IgG family glycoprotein found on the surface of human metastatic tumors, stimulates fibroblasts to secrete matrix metalloproteases (MMPs) that remodel the extracellular matrix, and is thus also known as Extracellular Matrix MetalloPRotease Inducer (EMMPRIN). Using Drosophila we previously identified novel roles for basigin. Specifically, photoreceptors of flies with basigin eyes show misplaced nuclei, rough ER and mitochondria, and swollen axon terminals, suggesting cytoskeletal disruptions. Here we demonstrate that basigin is required for normal neuron-glia interactions in the Drosophila visual system. Flies with basigin mutant photoreceptors have misplaced epithelial glial cells within the first optic neuropile, or lamina. In addition, epithelial glia insert finger-like projections--capitate projections (CPs)--sites of vesicle endocytosis and possibly neurotransmitter recycling. When basigin is missing from photoreceptors terminals, CP formation between glia and photoreceptor terminals is disrupted. Visual system function is also altered in flies with basigin mutant eyes. While photoreceptors depolarize normally to light, synaptic transmission is greatly diminished, consistent with a defect in neurotransmitter release. Basigin expression in photoreceptor neurons is required for normal structure and placement of glia cells.

Molecular neuropathology of temporal lobe epilepsy: complementary approaches in animal models and human disease tissue

Patients with temporal lobe epilepsies (TLE) frequently develop pharmacoresistance to antiepileptic treatment. In individuals with drug-refractory TLE, neurosurgical removal of the epileptogenic focus provides a therapy option with high potential for seizure control. Biopsy specimens from TLE patients constitute unique tissue resources to gain insights in neuropathological and molecular alterations involved in human TLE. Compared to human tissue specimens in most neurological diseases, where only autopsy material is available, the bioptic tissue samples from pharmacoresistant TLE patients open rather exceptional preconditions for molecular biological, electrophysiological as well as biochemical experimental approaches in human brain tissue, which cannot be carried out in postmortem material. Pathological changes in human TLE tissue are multiple and relate to structural and cellular reorganization of the hippocampal formation, selective neurodegeneration, and acquired changes of expression and distribution of neurotransmitter receptors and ion channels, underlying modified neuronal excitability. Nevertheless, human TLE tissue specimens have some limitations. For obvious reasons, human TLE tissue samples are only available from advanced, drug-resistant stages of the disease. However, in many patients, a transient episode of status epilepticus (SE) or febrile seizures in childhood can induce multiple structural and functional alterations that after a latency period result in a chronic epileptic condition. This latency period, also referred to as epileptogenesis, cannot be studied in human TLE specimens. TLE animal models may be particularly helpful in order to shed characterize new molecular pathomechanisms related to epileptogenesis and open novel therapeutic strategies for TLE. Here, we will discuss experimental approaches to unravel molecular-neuropathological aspects of TLE and highlight characteristics and potential of molecular studies in human and/or experimental TLE.

The immunolocalization of the synaptic glycoprotein neuroplastin differs substantially between the human and the rodent brain

Neuroplastin is a cell adhesion molecule of the immunoglobulin superfamily that exists in two splice isoforms, np65/np55, and that was reported to play a prominent role in synaptic plasticity processes. The splice isoform np65 associates with synapses in an activity-dependent manner and has been shown to play a role for the induction of hippocampal long-term potentiation in rodents. We have therefore analyzed the distribution of neuroplastins in human brain. Neuroplastin is present in many neuronal cell types of the forebrain and cerebellum and immunoreactive label covers the cell soma, neurites and also puncta in the neuropil were visible. Interestingly, we found some remarkable species differences in the expression patterns of neuroplastins between the human and the rodent brain. In human brain np65 is prominently present in cerebellum while np55 is the predominant isoform in mouse and rat cerebellum. Moreover, the parasagittal stripe-type of staining seen with np55 in mouse cerebellum is not found in human brain. In addition we found no segregation of np65 immunolabel in hippocampal subregions like it was reported previously for the rat. These results might indicate different cellular functions of the molecule in different species.

Association study of putative promoter polymorphisms in the neuroplastin gene and schizophrenia

A previous study revealed a number of methamphetamine (METH) and phencyclidine (PCP)-reactive tags in a rat brain through serial analysis of gene expression. The present study extends this previous study by investigating whether two genes, which deduced from METH/PCP-reactive tags, were identified as those encoding human transmembrane proteins of the immunoglobulin (Ig) superfamily, neuroplastin (NPTN) and basigin (BSG), confer genetic susceptibility to schizophrenia by analyzing single nucleotide polymorphisms (SNPs). There were nominally significant differences between the two groups in their allelic frequencies (T Ins/Del, chi2=4.910, d.f.=1, P=0.040) and genotypic distributions (T/T or T/Del, chi2=5.116, d.f.=1, P=0.036) of rs3840846 in the 5'-upstream of NPTN. The two groups differed significantly also in their allelic frequencies (G/T, chi2=4.229, d.f.=1, P=0.044), but not genotypic distributions of rs3743500 in the 5'-upstream of NPTN. The haplotypes constructed from the three SNPs (rs3840846, rs3826047 and rs3743500, in order) in the 5'-upstream of NPTN showed a significant association with schizophrenia (permutation P=0.036), in that T-G-T (permutation P=0.028) and del-G-G (permutation P=0.040) were under-represented and over-represented, respectively, in schizophrenia. A reporter construct driven by the 5'-upstream region containing any haplotype consisting of the three SNPs had substantial transcriptional activity. Notably, a reporter construct containing a haplotype T-G-T had significantly lower transcriptional activity as compared with one having a haplotype T-G-G or T-A-G. There was no significant difference between the two groups regarding allelic frequencies, genotypic distribution or the adopted SNP-combinatory haplotype for BSG. These results suggest that NPTN may be involved in genetic susceptibility to schizophrenia.

The cell adhesion molecule neuroplastin-65 inhibits hippocampal long-term potentiation via a mitogen-activated protein kinase p38-dependent reduction in surface expression of GluR1-containing glutamate receptors

Neuroplastin-65 is a brain-specific, synapse-enriched member of the immunoglobulin (Ig) superfamily of cell adhesion molecules. Previous studies highlighted the importance of neuroplastin-65 for long-term potentiation (LTP), but the mechanism was unclear. Here, we show how neuroplastin-65 activation of mitogen-activated protein kinase p38 (p38MAPK) modified synapse strength by altering surface glutamate receptor expression. Organotypic hippocampal slice cultures treated with the complete extracellular fragment of neuroplastin-65 (FcIg1-3) sustained an increase in the phosphorylation of p38MAPK and an inability to induce LTP at hippocampal synapses. The LTP block was reversed by application of the p38MAPK inhibitor SB202190, suggesting that p38MAPK activation occurred downstream of neuroplastin-65 binding and upstream of the loss of LTP. Further investigation revealed that the mechanism underlying neuroplastin-65-dependent prevention of LTP was a p38MAPK-dependent acceleration of the loss of surface-exposed glutamate receptor subunits that was reversed by pretreatment with the p38MAPK inhibitor SB202190. Our results indicate that neuroplastin-65 binding and associated stimulation of p38MAPK activity are upstream of a mechanism to control surface glutamate receptor expression and thereby influence plasticity at excitatory hippocampal synapses.

Basigin (EMMPRIN/CD147) interacts with integrin to affect cellular architecture

Basigin, an IgG family glycoprotein found on the surface of human metastatic tumors, stimulates fibroblasts to secrete matrix metalloproteases that remodel the extracellular matrix. Using Drosophila melanogaster we identify intracellular, matrix metalloprotease-independent, roles for basigin. Specifically, we found that basigin, interacting with integrin, is required for normal cell architecture in some cell types. Basigin promotes cytoskeletal rearrangements and the formation of lamellipodia in cultured insect cells. Loss of basigin from photoreceptors leads to misplaced nuclei, rough ER and mitochondria, as well as to swollen axon terminals. These changes in intracellular structure suggest cytoskeletal disruptions. These defects can be rescued by either fly or mouse basigin. Basigin and integrin colocalize to cultured cells and to the visual system. Basigin-mediated changes in the architecture of cultured cells require integrin binding activity. Basigin and integrin interact genetically to affect cell structure in the animal, possibly by forming complexes at cell contacts that help organize internal cell structure.

5A11/Basigin Gene Products Are Necessary for Proper Maturation and Function of the Retina

5A11/Basigin gene products are important membrane glycoproteins for development and maturation of the retina. The gene encodes two immunoglobulin-like, membrane-bound glycoproteins as a result of splice variation. The smaller protein product, named 5A11/Basigin, is expressed by many tissues within the mouse, whereas the larger protein product, named 5A11/Basigin-2, is expressed only by the photoreceptor cells (PCs) of the retina. Mice in which the gene for 5A11/Basigin has been deleted have several abnormalities, including blindness from the time of eye opening with subsequent degeneration of the PCs. Studies by this laboratory suggest that a developmental deficiency is the underlying cause of the blindness. However, definitive biological functions for 5A11/Basigin and 5A11/Basigin-2 have yet to be defined. It is known that 5A11/Basigin is multifunctional and can interact with several different proteins. Preliminary studies indicate that 5A11/Basigin-2 may be multifunctional as well. Studies by this laboratory and others have demonstrated that 5A11/Basigin (and probably 5A11/Basigin-2) acts as a chaperone for monocarboxylate transporter-1 (MCT-1) translocation to the cell membrane. We have proposed that a lactate metabolon exists within the retina and functions to shuttle lactate, an energy source, from glial cells to the PCs. This metabolon is not present within 5A11/Basigin null mouse retinas, which may be the underlying cause of the retinal dysfunction and subsequent degeneration. Further studies will be necessary to determine which of the functions are critical for proper development of the retina.

Lectin affinity as an approach to the proteomic analysis of membrane glycoproteins

The aim was to determine the proportion of membrane glycoproteins captured using concanavalin A or wheat germ agglutinin lectin affinity chromatography. Digests of the isolated proteins were separated by reversed-phase liquid chromatography and analyzed by matrix-assisted laser desorption tandem mass spectrometry. The two lectins identified different groups of proteins with a broad range of molecular mass and p/ values, including a number of proteins that overlapped the two groups. Approximately 30% of the proteins were positively identified as containing domains that were predicted using standard bioinformatics methods to be characteristic of integral membrane proteins. This approach represents an effective method of surveying the membrane protein pool of mammalian cells for subsequent proteomic analysis.

Molecular profiling of temporal lobe epilepsy: comparison of data from human tissue samples and animal models

The advent of gene chip technology and the era of functional genomics have initially been accompanied by huge anticipations to quickly unravel the molecular pathogenesis of multifactorial diseases. Expectations have, today, given way to some concerns about this non-hypothesis driven approach. However, the careful and controlled application of expression microarrays in concert with refined bioinformatic tools may provide novel insights in major disorders particularly of highly complex organs such as the central nervous system (CNS). Epilepsies are among the most frequent CNS disorders affecting approximately 1.5% of the population worldwide. In temporal lobe epilepsy (TLE), the seizure origin typically involves the hippocampal formation, a structure located in the mesial temporal lobe. Many TLE patients develop pharmacoresistance, i.e. seizures can no more be controlled by antiepileptic drugs. In order to achieve seizure control, surgical removal of the epileptogenic focus has been established as successful therapeutic strategy. Hippocampal biopsy tissue of pharmacoresistant TLE patients represents an excellent substrate to analyze molecular mechanisms related to structural and cellular reorganization in epilepsy. The complexity of alterations in TLE hippocampi suggests numerous genes and signaling cascades to be involved in the pathogenesis. By microarrays, genome wide expression profiles can be constituted from TLE tissues. However, hippocampi of pharmacoresistant TLE patients represent an advanced stage of the disease. Early stages of epilepsy development are not available for functional genome analysis in humans. Animal models of TLE appear particularly helpful to study molecular mechanisms of highly dynamic processes such as the development of hyperexcitability and pharmacoresistance. In this review, we summarize recent data of gene expression profiles in human and experimental TLE and discuss the relevance of novel tools for bioinformatic analysis and data mining.

Functional genomics and target gene validation in experimental and human disease

In contrast to rare monogenic disorders related to mutations in distinct genes, frequent multifactorial diseases including complex neuronal disorders as well as neoplasms involve expression changes in a multitude of genes. The integration of data derived from human disease tissue and of animal models by data mining constitutes a recent approach to increase the pathogenetic significance of target genes. Functional validation by animal models represents a key step to develop new treatment pathways for common disorders.:

Comparison of neuroplastin and synaptic marker protein expression in acute and cultured organotypic hippocampal slices from rat

Organotypic hippocampal slice cultures can be used to study hippocampal biochemistry and physiology over a chronic period on the days to weeks timescale. In order to validate the organotypic hippocampal slice culture for our ongoing studies of synaptic function, we have compared, using Western blotting, the levels of a number of synaptic proteins from in vitro organotypic hippocampal slice cultures with those from in vivo hippocampal slices prepared from age-matched controls. We chose to follow the developmental expression of the neuroplastin (np) family of immunoglobulin related cell adhesion molecules (CAMs), np65, a brain specific isoform highly expressed in hippocampal neurones and np55 a more widely expressed isoform and two synaptic marker proteins, synaptophysin, a pre-synaptic marker and post-synaptic density protein-95, PSD95, a post-synaptic marker. All showed increasing expression over the developmental time period, both in vivo and in vitro. The level of both neuroplastins was also consistent between the in vivo and in vitro preparations, whereas the level of PSD95 was markedly increased in the organotypic hippocampal slice cultures while the level of synaptophysin was slightly decreased. Whilst these findings may indicate some differences in the composition and organisation of synapses, the developmental expression profiles of these synaptic proteins within organotypic hippocampal slice cultures suggests they are a valid model for the study of synapse function and development in vitro.