A soluble chimeric form of the L1 glycoprotein stimulates neurite outgrowth

Functional Relationships between L1CAM, LC3, ATG12, and Aβ

Abnormal protein accumulations in the brain are linked to aging and the pathogenesis of dementia of various types, including Alzheimer's disease. These accumulations can be reduced by cell indigenous mechanisms. Among these is autophagy, whereby proteins are transferred to lysosomes for degradation. Autophagic dysfunction hampers the elimination of pathogenic protein aggregations that contribute to cell death. We had observed that the adhesion molecule L1 interacts with microtubule-associated protein 1 light-chain 3 (LC3), which is needed for autophagy substrate selection. L1 increases cell survival in an LC3-dependent manner via its extracellular LC3 interacting region (LIR). L1 also interacts with Aβ and reduces the Aβ plaque load in an AD model mouse. Based on these results, we investigated whether L1 could contribute to autophagy of aggregated Aβ and its clearance. We here show that L1 interacts with autophagy-related protein 12 (ATG12) via its LIR domain, whereas interaction with ubiquitin-binding protein p62/SQSTM1 does not depend on LIR. Aβ, bound to L1, is carried to the autophagosome leading to Aβ elimination. Showing that the mitophagy-related L1-70 fragment is ubiquitinated, we expect that the p62/SQSTM1 pathway also contributes to Aβ elimination. We propose that enhancing L1 functions may contribute to therapy in humans.

Fasciclin 2 engages EGFR in an auto-stimulatory loop to promote imaginal disc cell proliferation in Drosophila

How cell to cell interactions control local tissue growth to attain a species-specific organ size is a central question in developmental biology. The Drosophila Neural Cell Adhesion Molecule, Fasciclin 2, is expressed during the development of neural and epithelial organs. Fasciclin 2 is a homophilic-interaction protein that shows moderate levels of expression in the proliferating epithelia and high levels in the differentiating non-proliferative cells of imaginal discs. Genetic interactions and mosaic analyses reveal a cell autonomous requirement of Fasciclin 2 to promote cell proliferation in imaginal discs. This function is mediated by the EGFR, and indirectly involves the JNK and Hippo signaling pathways. We further show that Fasciclin 2 physically interacts with EGFR and that, in turn, EGFR activity promotes the cell autonomous expression of Fasciclin 2 during imaginal disc growth. We propose that this auto-stimulatory loop between EGFR and Fasciclin 2 is at the core of a cell to cell interaction mechanism that controls the amount of intercalary growth in imaginal discs.

A key problem in developmental biology is how species-specific organ size is determined. Control of organ growth occurs at different levels of organization, from the systemic to the cell to cell interaction level. During nervous system development cell contact interactions regulate axon growth. Here, we show that one of the cell adhesion molecules involved in controlling axon growth, the Drosophila NCAM ortholog Fasciclin 2, also controls epithelial organ growth and size. Fasciclin 2 is expressed in highly dynamic but moderate levels during cell proliferation in imaginal discs (precursor epithelial organs of the adult epidermis), and at much higher level in pre-differentiating and differentiating cells in imaginal discs. During imaginal disc growth cell interactions mediated by Fasciclin 2 promote Epidermal Growth Factor Receptor function and cell proliferation. In turn, Epidermal Growth Factor Receptor activity promotes Fasciclin 2 expression, creating a cell autonomous auto-stimulatory loop that maintains cell proliferation. This function of Fasciclin 2 is reciprocal to its reported function in pre-differentiating and differentiating cells in imaginal discs, where it acts as an Epidermal Growth Factor Receptor repressor. Our study suggests that the amount of Fasciclin 2 may determine a threshold to grow or stop growing during epithelial organ development.

Soluble vascular endothelial-cadherin in CSF after subarachnoid hemorrhage

OBJECTIVE

To determine if CSF and plasma levels of soluble vascular endothelial (sVE)-cadherin are associated with functional outcome after subarachnoid hemorrhage (SAH) and to investigate sVE-cadherin effects on microglia.

METHODS

Serial CSF and plasma were collected from prospectively enrolled patients with nontraumatic SAH from a ruptured aneurysm in the anterior circulation and who required an external ventricular drain for clinical indications. Patients with normal-pressure hydrocephalus without SAH served as controls. For prospective assessment of long-term outcomes at 3 and 6 months after SAH, modified Rankin Scale scores (mRS) were obtained and dichotomized into good (mRS ≤ 2) vs poor (mRS > 2) outcome groups. For SAH severity, Hunt and Hess grade was assessed. Association of CSF sVE-cadherin levels with long-term outcomes, HH grade, and CSF tumor necrosis factor (TNF)-α levels were evaluated. sVE-cadherin effects on microglia were also studied.

RESULTS

sVE-cadherin levels in CSF, but not in plasma, were higher in patients with SAH and were associated with higher clinical severity and higher CSF TNF-α levels. Patients with SAH with higher CSF sVE-cadherin levels over time were more likely to develop worse functional outcome at 3 months after SAH. Incubation of cultured microglia with sVE-cadherin resulted in increased inducible nitric oxide synthase, interleukin-1β, reactive oxygen species, cell soma size, and metabolic activity, consistent with microglia activation. Microinjection of sVE-cadherin fragments into mouse brain results in an increased number of microglia surrounding the injection site, compared to injection of denatured vascular endothelial-cadherin fragments.

CONCLUSIONS

These results support the existence of a novel pathway by which sVE-cadherin, released from injured endothelium after SAH, can shift microglia into a more proinflammatory phenotype and contribute to neuroinflammation and poor outcome in SAH.

L1 Cell Adhesion Molecule Overexpression Down Regulates Phosphacan and Up Regulates Structural Plasticity-Related Genes Rostral and Caudal to the Complete Spinal Cord Transection

L1 cell adhesion molecule (L1CAM) supports spinal cord cellular milieu after contusion and compression lesions, contributing to neuroprotection, promoting axonal outgrowth, and reducing outgrowth-inhibitory molecules in lesion proximity. We extended investigations into L1CAM molecular targets and explored long-distance effects of L1CAM rostral and caudal to complete spinal cord transection (SCT) in adult rats. L1CAM overexpression in neurons and glia after Th10/Th11 SCT was achieved using adeno-associated viral vector serotype 5 (AAV5) injected into an L1-lumbar segment immediately after transection. At 5 weeks, a L1CAM mRNA profound decrease detected rostral and caudal to the transection site was alleviated by AAV5-L1CAM treatment, with increased endogenous L1CAM rostral to the SCT. Transected corticospinal tract fibers showed attenuated retraction after treatment, accompanied by a multi-segmental increase of lesion-reduced expression of adenylate cyclase 1 (Adcy1), synaptophysin, growth-associated protein 43, and myelin basic protein genes caudal to transection, and Adcy1 rostral to transection. In parallel, chondroitin sulfate proteoglycan phosphacan elevated after SCT was downregulated after treatment. Low-molecular L1CAM isoforms generated after spinalization indicated the involvement of sheddases in L1CAM processing and long-distance effects. A disintegrin and metalloproteinase (ADAM)10 sheddase immunoreactivity, stronger in AAV5-L1CAM than AAV5- enhanced green fluorescent protein (EGFP)-transduced motoneurons indicated local ADAM10 upregulation by L1CAM. The results suggest that increased L1CAM availability and penetration of diffusible L1CAM fragments post-lesion induce both local and long-distance neuronal and glial responses toward better neuronal maintenance, neurite growth, and myelination. Despite the fact that intervention promoted beneficial molecular changes, kinematic analysis of hindlimb movements showed minor improvement, indicating that spinalized rats require longer L1CAM treatment to regain locomotor functions.

Vision impairment after traumatic brain injury: present knowledge and future directions

Traumatic brain injury (TBI) is a major cause of mortality and morbidity in the USA as well as in the world. As a result of TBI, the visual system is also affected often causing complete or partial visual loss, which in turn affects the quality of life. It may also lead to ocular motor dysfunction, defective accommodation, and impaired visual perception. As a part of the therapeutic strategy, early rehabilitative optometric intervention is important. Orthoptic therapy, medication, stem cell therapy, motor and attention trainings are the available treatment options. Gene therapy is one of the most promising emerging strategies. Use of state-of-the-art nanomedicine approaches to deliver drug(s) and/or gene(s) might enhance the therapeutic efficacy of the present and future modalities. More research is needed in these fields to improve the outcome of this debilitating condition. This review focuses on different visual pathologies caused by TBI, advances in pre-clinical and clinical research, and available treatment options.

Synapse formation: from cellular and molecular mechanisms to neurodevelopmental and neurodegenerative disorders

The precise patterns of neuronal assembly during development determine all functional outputs of a nervous system; these may range from simple reflexes to learning, memory, cognition, etc. To understand how brain functions and how best to repair it after injury, disease, or trauma, it is imperative that we first seek to define fundamental steps mediating this neuronal assembly. To acquire the sophisticated ensemble of highly specialized networks seen in a mature brain, all proliferated and migrated neurons must extend their axonal and dendritic processes toward targets, which are often located at some distance. Upon contact with potential partners, neurons must undergo dramatic structural changes to become either a pre- or a postsynaptic neuron. This connectivity is cemented through specialized structures termed synapses. Both structurally and functionally, the newly formed synapses are, however, not static as they undergo consistent changes in order for an animal to meet its behavioral needs in a changing environment. These changes may be either in the form of new synapses or an enhancement of their synaptic efficacy, referred to as synaptic plasticity. Thus, synapse formation is not restricted to neurodevelopment; it is a process that remains active throughout life. As the brain ages, either the lack of neuronal activity or cell death render synapses dysfunctional, thus giving rise to neurodegenerative disorders. This review seeks to highlight salient steps that are involved in a neuron's journey, starting with the establishment, maturation, and consolidation of synapses; we particularly focus on identifying key players involved in the synaptogenic program. We hope that this endeavor will not only help the beginners in this field to understand how brain networks are assembled in the first place but also shed light on various neurodevelopmental, neurological, neurodegenerative, and neuropsychiatric disorders that involve synaptic inactivity or dysfunction.

L1CAM increases MAP2 expression via the MAPK pathway to promote neurite outgrowth

The neural cell adhesion molecule L1 (L1CAM) promotes neurite outgrowth via mechanisms that are not completely understood, but are known to involve the cytoskeleton. Here, we show that L1 binds directly to the microtubule associated protein 2c (MAP2c). This isoform of MAP2 is predominantly expressed in developing neurons. We found that the mRNA and protein levels of MAP2c, but not of MAP2a/b, are reduced in brains of young adult L1-deficient transgenic mice. We show via ELISA, that MAP2c, but not MAP2a/b, binds directly to the intracellular domain of L1. Remarkably, all these MAP2 isoforms co-immunoprecipitate with L1, suggesting that MAP2a/b associates with L1 via intermediate binding partners. The expression levels of MAP2a/b/c correlate with those of L1 in different brain regions of early postnatal mice, while expression levels of heat shock cognate protein 70 (Hsc70) or actin do not. L1 enhances the expression of MAP2a/b/c in cultured hippocampal neurons depending on activation of the mitogen-activated protein kinase (MAPK) pathway. Deficiency in both L1 and MAP2a/b/c expression results in reduced neurite outgrowth in vitro. We propose that the L1-triggered increase in MAP2a/b/c expression is required to promote neurite outgrowth.

Oriented, multimeric biointerfaces of the L1 cell adhesion molecule: an approach to enhance neuronal and neural stem cell functions on 2-D and 3-D polymer substrates

This article focuses on elucidating the key presentation features of neurotrophic ligands at polymer interfaces. Different biointerfacial configurations of the human neural cell adhesion molecule L1 were established on two-dimensional films and three-dimensional fibrous scaffolds of synthetic tyrosine-derived polycarbonate polymers and probed for surface concentrations, microscale organization, and effects on cultured primary neurons and neural stem cells. Underlying polymer substrates were modified with varying combinations of protein A and poly-D-lysine to modulate the immobilization and presentation of the Fc fusion fragment of the extracellular domain of L1 (L1-Fc). When presented as an oriented and multimeric configuration from protein A-pretreated polymers, L1-Fc significantly increased neurite outgrowth of rodent spinal cord neurons and cerebellar neurons as early as 24 h compared to the traditional presentation via adsorption onto surfaces treated with poly-D-lysine. Cultures of human neural progenitor cells screened on the L1-Fc/polymer biointerfaces showed significantly enhanced neuronal differentiation and neuritogenesis on all protein A oriented substrates. Notably, the highest degree of βIII-tubulin expression for cells in 3-D fibrous scaffolds were observed in protein A oriented substrates with PDL pretreatment, suggesting combined effects of cell attachment to polycationic charged substrates with subcellular topography along with L1-mediated adhesion mediating neuronal differentiation. Together, these findings highlight the promise of displays of multimeric neural adhesion ligands via biointerfacially engineered substrates to "cooperatively" enhance neuronal phenotypes on polymers of relevance to tissue engineering.

Neuronal growth-promoting and inhibitory cues in neuroprotection and neuroregeneration

During development of the nervous system, neurons extend axons over considerable distances in a highly stereospecific fashion in order to innervate their targets in an appropriate manner. This involves the recognition, by the axonal growth cone, of guidance cues that determine the pathway taken by the axons. These guidance cues can act to promote and/or repel growth cone advance. The directed growth of axons is partly governed by cell adhesion molecules (CAMs) on the neuronal growth cone that bind to CAMs on the surface of other axons or nonneuronal cells. In vitro assays have established the importance of the CAMs ((neural cell adhesion molecule NCAM), N-cadherin, and L1) in promoting axonal growth over cells. Compelling evidence implicates the fibroblast growth factor receptor tyrosine kinase as the primary signal transduction molecule in the CAM pathway. CAMs are important constituents of synapses, and they appear to play important and diverse roles in regulating synaptic plasticity associated with learning and memory. Synthetic NCAM peptide mimetics corresponding to the binding site of NCAM for the fibroblast growth factor receptor promote synaptogenesis, enhance presynaptic function, and facilitate memory consolidation. Dimeric versions of functional binding motifs of N-cadherin behave as N-cadherin agonists, promoting both neuritogenesis and neuronal cell survival. Negative extracellular signals that physically direct neurite growth have also been described. The latter include the myelin inhibitory proteins, Nogo, myelin-associated glycoprotein, and oligodendrocyte-myelin glycoprotein. Potentiation of outgrowth-promoting signals, together with antagonism of myelin proteins or their convergent receptor, NgR, and its second messenger pathways, may provide new opportunities in the rational design of treatments for acute brain injury and neurodegenerative disorders.

Growth cone 3-D morphology is modified by distinct micropatterned adhesion substrates

The development, connectivity, and structural plasticity of neuronal networks largely depend on the directional growth of axonal growth cones (GCs). The morphology and 3-D profile of axons and GCs of primary hippocampal neurons, grown onto glass surfaces coated with poly-D-lysine (PDL) and micropatterned with stripes of the adhesion molecule L1 by using the indirect microcontact printing, were investigated. Neurons were fixed at early stages (one to seven days) of in vitro development prior to synapse formation, and analyzed by fluorescence and atomic force microscopy. The latter technique allowed us to investigate the 3-D morphology of the GCs, and detect their morphological rearrangements during axon outgrowth and during contact with the underlying substrate. We found that axons decreased their height-to-width ratio over development in culture, and that this value became particularly low when the axon and the GC proceeded onto a surface containing attracting cues such as L1 with respect to GCs growing onto a nonspecific adhesion substrate such as PDL. Along with this shape change of the axons, GCs lying onto L1 tracks displayed a flattened shape, ideal for sensing and progression, whereas GCs onto areas of nonspecific adhesion displayed more prominent shapes and steeper edges.

The promotive effects of thymosin beta4 on neuronal survival and neurite outgrowth by upregulating L1 expression

Thymosin beta(4) (Tbeta4) is a major actin-sequestering peptide widely distributed in mammalian tissues including the nervous system. The presence of this peptide in the nervous system likely plays a role in synaptogensis, axon growth, cell migration, and plastic changes in dendritic spine. However, the effects of Tbeta4 on the survival of neurons and axonal outgrowth have still not been fully understood. So far it is not clear if the effects of Tbeta4 are associated with L1 functions. In the present study, we hypothesized that Tbeta4-induced up-regulation of L1 synthesis could be involved in the survival and axon outgrowth of cultured spinal cord neurons. To test this hypothesis, primarily cultured neurons were prepared from the mouse spinal cord and treated with various concentrations of Tbeta4 ranging from 0.1 to 10 microg/ml. The analysis of L1 mRNA expression and protein synthesis in neurons was then carried out using RT-PCR and western blot assays, respectively. After the addition of Tbeta4 to cultures, cells were then treated with antibodies against distinct domains of L1-Fc. Subsequently, beta-tubulin III and L1 double-labeled indirect immunofluorescence was carried out. Meanwhile, L1 immunofluorescent reactivity was analyzed and compared in cells treated with Tbeta4. Furthermore, the number of beta-tubulin III-positive cells and neurite lengths were measured. We found that Tbeta4 enhanced L1 expression in a dose-dependent manner, and the highest L1 mRNA and protein synthesis in cells increased by more than 2.1- and 2.3-fold in the presence of Tbeta4 at identical concentrations, respectively. Moreover, it also dose dependently enhanced neurite outgrowth and neuronal survival. Compared to conditions without Tbeta4, the length of neurite and neuronal survival increased markedly in presence of 0.5, 1, and 5 microg/ml Tbeta4, respectively, whereas the effects of Tbeta4 were significantly attenuated or inhibited in the process of L1-Fc antibodies treatment. These above results indicate that the promotive effect of Tbeta4 on the survival and neurite outgrowth of cultured spinal cord neurons might be mediated, at least in part via a stimulation of the production of L1 in the neurons.

Interaction of amyloid precursor protein with contactins and NgCAM in the retinotectal system

The amyloid precursor protein (APP) plays a central role in Alzheimer's disease, but its actions in normal development are not well understood. Here, a tagged APP ectodomain was used to identify extracellular binding partners in developing chick brain. Prominent binding sites were seen in the olfactory bulb and on retinal axons growing into the optic tectum. Co-precipitation from these tissues and tandem mass spectrometry led to the identification of two associated proteins: contactin 4 and NgCAM. In vitro binding studies revealed direct interactions among multiple members of the APP and contactin protein families. Levels of the APP processing fragment, CTFalpha, were modulated by both contactin 4 and NgCAM. In the developing retinotectal system, APP, contactin 4 and NgCAM are expressed in the retina and tectum in suitable locations to interact. Functional assays revealed regulatory effects of both APP and contactin 4 on NgCAM-dependent growth of cultured retinal axons, demonstrating specific functional interactions among these proteins. These studies identify novel binding and functional interactions among proteins of the APP, contactin and L1CAM families, with general implications for mechanisms of APP action in neural development and disease.

Pharmacology of cell adhesion molecules of the nervous system

Cell adhesion molecules (CAMs) play a pivotal role in the development and maintenance of the nervous system under normal conditions. They also are involved in numerous pathological processes such as inflammation, degenerative disorders, and cancer, making them attractive targets for drug development. The majority of CAMs are signal transducing receptors. CAM-induced intracellular signalling is triggered via homophilic (CAM-CAM) and heterophilic (CAM - other counter-receptors) interactions, which both can be targeted pharmacologically. We here describe the progress in the CAM pharmacology focusing on cadherins and CAMs of the immunoglobulin (Ig) superfamily, such as NCAM and L1. Structural basis of CAM-mediated cell adhesion and CAM-induced signalling are outlined. Different pharmacological approaches to study functions of CAMs are presented including the use of specific antibodies, recombinant proteins, and synthetic peptides. We also discuss how unravelling of the 3D structure of CAMs provides novel pharmacological tools for dissection of CAM-induced signalling pathways and offers therapeutic opportunities for a range of neurological disorders.

Therapeutic vaccination for central nervous system repair

1. Vaccination against infectious agents has been heralded as a triumph in modern medicine and, more recently, cancer vaccines have risen in prominence. The present review looks towards the use of vaccine therapy to attenuate damage after injury to the central nervous system (CNS). 2. Significant debility is associated with brain injury, most commonly occurring as a result of physical trauma or stroke. This end result reflects the inability of neurons and axons to regenerate following injury to the CNS. This unconductive environment is due, in large part, to the presence of myelin and oligodendrocyte-related inhibitors of neurite outgrowth. 3. We review how a vaccine-based approach has been variably used to circumvent this issue and promote axonal regeneration and repair following traumatic injury and other neurodegenerative disorders. In addition, emerging evidence suggests that the immune response to injury in the CNS may be manipulated so as to reduce cellular damage. Vaccine-directed approaches using this concept are also outlined.

Alteration of the cell adhesion molecule L1 expression in a specific subset of primary afferent neurons contributes to neuropathic pain

The cell adhesion molecule L1 (L1-CAM) plays important functional roles in the developing and adult nervous systems. Here we show that peripheral nerve injury induced dynamic post-transcriptional alteration of L1-CAM in the rat dorsal root ganglia (DRGs) and spinal cord. Sciatic nerve transection (SCNT) changed the expression of L1-CAM protein but not L1-CAM mRNA. In DRGs, SCNT induced accumulation of the L1-CAM into the surface of somata, which resulted in the formation of immunoreactive ring structures in a number of unmyelinated C-fiber neurons. These neurons with L1-CAM-immunoreactive ring structures were heavily colocalized with phosphorylated p38 MAPK. Western blot analysis revealed the increase of full-length L1-CAM and decrease of fragments of L1-CAM after SCNT in DRGs. Following SCNT, L1-CAM-immunoreactive profiles in the dorsal horn showed an increase mainly in pre-synaptic areas of laminae I–II with a delayed onset and colocalized with growth-associated protein 43. In contrast to DRGs, SCNT increased the proteolytic 80-kDa fragment of L1-CAM and decreased full-length L1-CAM in the spinal cord. The intrathecal injection of L1-CAM antibody for the extracellular domain of L1-CAM inhibited activation of p38 MAPK and emergence of ring structures of L1-CAM immunoreactivity in injured DRG neurons. Moreover, inhibition of extracellular L1-CAM binding by intrathecal administration of antibody suppressed the mechanical allodynia and thermal hyperalgesia induced by partial SCNT. Collectively, these data suggest that the modification of L1-CAM in nociceptive pathways might be an important pathomechanism of neuropathic pain.

Identification and characterization of a population of motile neurons in long-term cortical culture

The specific phenotypes and progression to maturity of primary cortical neurons in long-term culture correlate well with neurons in vivo. Utilizing a model of neuronal injury in long-term cultures at 21 days in vitro (DIV), we have identified a distinct population of neurons that translocate into the injury site. 5-bromo-2'-deoxyUridine (BrdU) incorporation studies demonstrated that neurons with the capacity to translocate were 21 days old. However, this motile ability is not consistent with the traditional view of the maturation and structural stability of neurons in long-term culture. Therefore, we examined the neurons' cytoskeletal profile using immunocytochemistry, to establish relative stage of maturation and phenotype. Expression of marker proteins including beta-III-tubulin, alpha-internexin, NF-L and NF-M, tau and L1 indicated the neurons were differentiated, and in some cases polarized. The neurons did not immunolabel with NF-H or MAP2, which might suggest they had not reached the level of maturity of other neurons in culture. They did not express the microtubule-associated migration marker doublecortin (DCX). Cytoskeletal disrupting agents were used to further investigate the role of the microtubule cytoskeleton in translocation, and microtubule destabilization significantly enhanced aspects of their motility. Finally, molecular guidance cues affected their motility in a similar manner to that reported for both axon guidance and early neuron migration. Therefore, this study has identified and characterized a population of motile neurons in vitro that have the capacity to migrate into a site of injury. These studies provide new information on the structurally dynamic features of subsets of neurons.

Cell adhesion molecule L1 modulates nerve-growth-factor-induced CGRP-IR fiber sprouting

Overexpression of nerve growth factor (NGF) using adenoviruses (Adts) after spinal cord injury induces extensive regeneration and sprouting of calcitonin-gene-related peptide immunoreactive (CGRP-IR) fibers, whereas overexpression of cell adhesion molecules (CAMs) has no effect on the normal distribution of these fibers. Interestingly, co-expression of cell adhesion molecule L1 and NGF significantly decreases (p<0.0001) CGRP-IR fiber sprouting within the spinal cord, when compared to NGF alone. Co-expression of cell adhesion molecules NCAM or N-cadherin had no effect on NGF-induced CGRP-IR fiber sprouting. These data demonstrate that reduced sprouting is specific to L1 co-expression and not other cell adhesion molecules. In vitro studies carried out to address potential mechanisms show that neurite outgrowth over astrocytes overexpressing L1 in the presence of NGF is comparable to controls, indicating that other factors present in vivo might be involved in the L1-mediated reduction in sprouting. One potential factor is semaphorin 3A (sema3A), which mediates growth cone collapse of CGRP-positive axons. Recent studies have shown that L1 is important in sema3A receptor signaling for cortical neurons. In our study, co-expression of sema3A indeed reduces neurite outgrowth from DRG neurons by about 40% on L1-expressing astrocytes. Based on these results, we hypothesize that overexpression of L1 potentiates sema3A signaling resulting in reduced sprouting.

Semaphorin3A regulates synaptic function of differentiated hippocampal neurons

Semaphorins are major chemorepellents for developing neuronal projections. Their persistent expression at adult stages suggests that they may contribute to the functioning of neuronal circuits. We investigated the functional properties of semaphorin3A (Sema3A) in adult hippocampal neurons, and report that exogenous application of this cue decreases the efficacy of synaptic transmission evoked in the CA1 region of hippocampal slices. In situ hybridization, imaging and biochemical techniques showed that the Sema3A receptor component neuropilin-1 is present at hippocampal synapses and localizes in the presynaptic membrane. In differentiated cultured hippocampal neurons, Sema3A elicited Erk1/2 phosphorylation in somata and neuritic compartments. Furthermore, Sema3A application resulted in a striking reduction of synaptophysin and postsynaptic density 95 puncta without affecting the axon diameter. These observations reveal novel functional potentialities for secreted semaphorins, which suggest that these cues could modulate the morphology and function of synapses in the adult brain.

A conserved role for Drosophila Neuroglian and human L1-CAM in central-synapse formation

BACKGROUND

Drosophila Neuroglian (Nrg) and its vertebrate homolog L1-CAM are cell-adhesion molecules (CAM) that have been well studied in early developmental processes. Mutations in the human gene result in a broad spectrum of phenotypes (the CRASH-syndrome) that include devastating neurological disorders such as spasticity and mental retardation. Although the role of L1-CAMs in neurite extension and axon pathfinding has been extensively studied, much less is known about their role in synapse formation.

RESULTS

We found that a single extracellular missense mutation in nrg(849) mutants disrupted the physiological function of a central synapse in Drosophila. The identified giant neuron in nrg(849) mutants made a synaptic terminal on the appropriate target, but ultrastructural analysis revealed in the synaptic terminal a dramatic microtubule reduction, which was likely to be the cause for disrupted active zones. Our results reveal that tyrosine phosphorylation of the intracellular ankyrin binding motif was reduced in mutants, and cell-autonomous rescue experiments demonstrated the indispensability of this tyrosine in giant-synapse formation. We also show that this function in giant-synapse formation was conserved in human L1-CAM but neither in human L1-CAM with a pathological missense mutation nor in two isoforms of the paralogs NrCAM and Neurofascin.

CONCLUSIONS

We conclude that Nrg has a function in synapse formation by organizing microtubules in the synaptic terminal. This novel synaptic function is conserved in human L1-CAM but is not common to all L1-type proteins. Finally, our findings suggest that some aspects of L1-CAM-related neurological disorders in humans may result from a disruption in synapse formation rather than in axon pathfinding.

Expression, crystallization and preliminary X-ray analysis of the extracellular Ig modules I-IV and F3 modules I-III of the neural cell-adhesion molecule L1

Four amino-terminal immunoglobulin (Ig) modules and three fibronectin type III (F3) modules of the mouse neural cell-adhesion molecule L1 have been expressed in Drosophila S2 cells. The Ig modules I-IV of L1 crystallized in a trigonal space group, with unit-cell parameters a = b = 239.6, c = 99.3 A, and the crystals diffracted X-rays to a resolution of about 3.5 A. The F3 modules I-III of L1 crystallized in a tetragonal space group, with unit-cell parameters a = b = 80.1, c = 131 A, and the crystals diffracted X-rays to 2.8 A resolution. This is a step towards the structure determination of the multimodular constructs of the neural cell-adhesion molecule L1 in order to understand the function of L1 on a structural basis.

Pathological missense mutations of neural cell adhesion molecule L1 affect neurite outgrowth and branching on an L1 substrate

A number of pathological missense mutations of L1CAM have been shown to disrupt L1-L1 homophilic binding and/or affect surface expression. To investigate whether these mutations disrupt L1-mediated neurite outgrowth, cerebellar neurons from L1 knockout mice are transfected with WT human L1 or L1 mutant constructs, and grown on an L1 substrate. Various parameters of neurite growth are quantified. Most L1 mutations do not affect neurite length significantly but several mutations cause a significant decrease in branching. Comparison of these data with data on L1 expression levels and homophilic binding strength show that changes in neurite growth cannot be simply explained by reductions in either of these parameters. Our results suggest that a coreceptor is involved in L1-mediated neurite outgrowth. Some pathological mutations have little effect on L1 mediated neurite growth, so it is unlikely that a failure of L1-mediated neurite outgrowth is the principle cause of brain defects in patients with L1 mutations.

Genetic analysis of an overlapping functional requirement for L1- and NCAM-type proteins during sensory axon guidance in Drosophila

L1- and NCAM-type cell adhesion molecules represent distinct protein families that function as specific receptors for different axon guidance cues. However, both L1 and NCAM proteins promote axonal growth by inducing neuronal tyrosine kinase activity and are coexpressed in subsets of axon tracts in arthropods and vertebrates. We have studied the functional requirements for the Drosophila L1- and NCAM-type proteins, Neuroglian (Nrg) and Fasciclin II (FasII), during postembryonic sensory axon guidance. The rescue of the Neuroglian loss-of-function (LOF) phenotype by transgenically expressed L1- and NCAM-type proteins demonstrates a functional interchangeability between these proteins in Drosophila photoreceptor pioneer axons, where both proteins are normally coexpressed. In contrast, the ectopic expression of Fasciclin II in mechanosensory neurons causes a strong enhancement of the axonal misguidance phenotype. Moreover, our findings demonstrate that this functionally redundant specificity to mediate axon guidance has been conserved in their vertebrate homologs, L1-CAM and NCAM.

Optic nerve regeneration in polyglycolic acid–chitosan conduits coated with recombinant L1-Fc

Autografts have been extensively studied to facilitate optic nerve (ON) regeneration in animal experiments, but the clinical application of this approach to aid autoregeneration has not yet been attempted. This study aims to explore the guided regeneration by an artificial polyglycolic acid-chitosan conduit coated with recombinant L1-Fc. Consistent with previous studies; in vitro assay showed that both chitosan, a natural biomaterial, and the neural cell adhesion molecule L1-Fc enhanced neurite outgrowth. Rat optic nerve transection was used as an in vivo model. The implanted PGA-chitosan conduit was progressively degraded and absorbed, accompanied by significant axonal regeneration as revealed by immunohistochemistry, anterograde and retrograde tracing. The polyglycolic acid-chitosan conduit coated with L1-Fc showed more effective to promote axonal regeneration and remyelination. Taken together, our observations demonstrated that the L1-Fc coated PGA-chitosan conduits provided a compatible and supportive canal to guild the injured nerve regeneration and remyelination.

Binding partners L1 cell adhesion molecule and the ezrin-radixin-moesin (ERM) proteins are involved in development and the regenerative response to injury of hippocampal and cortical neurons

Regeneration of the adult central nervous system may require recapitulation of developmental events and therefore involve the re-expression of developmentally significant proteins. We have investigated whether the L1 cell adhesion molecule, and its binding partner, the ezrin-radixin-moesin (ERM) proteins are involved in the neuronal regenerative response to injury. Hippocampal and cortical neurons were cultured in vitro on either an L1 substrate or poly-L-lysine, and ERM and other neuronal proteins were localized immunocytochemically both developmentally and following neurite transection of neurons maintained in long-term culture. Activated ERM was localized to growth cones up to 7 days in vitro but relatively mature cultures (21 days in vitro) were devoid of active ERM proteins. However, ERM proteins were localized to the growth cones of sprouting neuronal processes that formed several hours after neurite transection. In addition, the L1 substrate, relative to poly-L-lysine, resulted in significantly longer regenerative neurites, as well as larger growth cones with more filopodia. Furthermore, neurons derived from the cortex formed significantly longer post-injury neurite sprouts at 6 h post-injury than hippocampal derived neurons grown on both substrates. We have demonstrated that L1 and the ERM proteins are involved in the neuronal response to injury, and that neurons derived from the hippocampus and cortex may have different post-injury regenerative neurite sprouting abilities.

Neuroglian and FasciclinII can promote neurite outgrowth via the FGF receptor Heartless

To further investigate the role of the Drosophila cell adhesion molecules (CAMs), we have developed an in vitro assay that allows us to test the contribution individual CAMs make to promote outgrowth of specific Drosophila neurons. The extension of primary cultured neurons on a substrate of purified recombinant CAM is measured. We show that both FasciclinII and Neuroglian are able to promote outgrowth of FasciclinII or Neuroglian expressing neurons, respectively. Furthermore, this growth promotion activity is provided when the CAMs are presented both in a substrate bound or soluble form. We also show that the signal provided by the CAMs acts via the Heartless fibroblast growth factor receptor (FGFR) as outgrowth is reduced to basal levels in the presence of an FGFR inhibitor or if Heartless function is missing from the neurons.

Extracellular Ig domains 1 and 2 of Robo are important for ligand (Slit) binding

Robo, the receptor for the midline repellent Slit, is a member of the cell adhesion molecule (CAM) Ig superfamily. We have recently demonstrated that members of the Robo family (Robo1 and Robo2) interact homophilically and heterophilically, thereby functioning to promote neurite outgrowth. Here, we describe a series of in vitro experiments to dissect the Robo ligand-interacting domains by deleting specific extracellular regions of the Robo1 molecule, generating a series of mutant proteins. Using these, we demonstrate that Ig domains 1 and 2 of Robo1 are important for Robo-Slit interaction and provide functional data using the Slit-mediated olfactory bulb repulsion assay. To investigate whether homophilic binding properties of Robo are domain specific, we used Robo1-Fc mutant deletion proteins in an aggregation assay and observed a reduction in homophilic binding when any one Ig or all the fibronectin domains were deleted, although homophilic binding was never completely abolished.

Regulation of pontine neurite morphology by target-derived signals

The molecular cues that regulate neurite morphology within the target environment are key to the formation of complex neural circuitry. During development of the ponto-cerebellar projection, pontine fibers sprout and form elaborate arbors within the inner cerebellar layer prior to arrival of their target cells, the cerebellar granule neurons. Here, we describe the biochemical fractionation of two granule neuron-derived factors that stimulate elaboration of pontine neurites. These factors were identified using a dissociated pontine bioassay and biochemically fractionated from granule cell (GC) conditioned medium (GCCM). One of the factors, STIM1, is a protein with a molecular weight greater than 30 kDa that is distinct from known neurotrophins. The other, STIM2, is a small, protease-resistant molecule with an estimated molecular weight below 1 kDa. We show that these factors stimulate pontine neurite elongation both independently and cooperatively and thus may contribute to the formation of elaborate pontine arbors within the cerebellar cortex.

A dimeric version of the short N-cadherin binding motif HAVDI promotes neuronal cell survival by activating an N-cadherin/fibroblast growth factor receptor signalling cascade

The HAVDI and INPISGQ sequences have been identified as functional binding motifs in extracellular domain 1 (ECD1) of N-cadherin. Cyclic peptides containing a tandem repeat of the individual motifs function as N-cadherin agonists and stimulate neurite outgrowth. We now show that the cyclic peptide N-Ac-CHAVDINGHAVDIC-NH2 (SW4) containing the HAVDI sequence in tandem is efficacious also in promoting the in vitro survival of several populations of central nervous system neurons in paradigms where fibroblast growth factor-2 (FGF-2) is active. SW4 supported the survival of rat postnatal cerebellar granule neurons plated in serum-free medium and limited the death of differentiated granule neurons induced to die by switch to low K+ medium. In addition, SW4 rescued embryonic hippocampal and cortical neurons from injury caused by glutamic acid excitotoxicity. The neuroprotective effects of SW4 displayed a concentration dependence similar to those inducing neuritogenesis, were inhibited by a monomeric version of the same motif and by a specific FGF receptor antagonist (PD173074), and were not mimicked by the linear peptide. Inhibitors of the phosphatidylinositol 3-kinase (PI 3-kinase), MAP kinase, and p38 kinase signalling pathways did not interfere with SW4 function. These data suggest that SW4 functions by binding to and clustering N-cadherin in neurons and thereby activating and N-cadherin/FGF receptor signalling cascade, and propose that such agonists may represent a starting point for the development of therapeutic agents promoting neuronal cell survival and regeneration.

LIMK1 regulates Golgi dynamics, traffic of Golgi-derived vesicles, and process extension in primary cultured neurons

In this study, we examined the subcellular distribution and functions of LIMK1 in developing neurons. Confocal microscopy, subcellular fractionation, and expression of several epitope-tagged LIMK1 constructs revealed that LIMK1 is enriched in the Golgi apparatus and growth cones, with the LIM domain required for Golgi localization and the PDZ domain for its presence at neuritic tips. Overexpression of wild-type LIMK1 suppresses the formation of trans-Golgi derived tubules, and prevents cytochalasin D-induced Golgi fragmentation, whereas that of a kinase-defective mutant has the opposite effect. Transfection of wild-type LIMK1 accelerates axon formation and enhances the accumulation of Par3/Par6, insulin-like growth factor (IGF)1 receptors, and neural cell adhesion molecule (NCAM) at growth cones, while inhibiting the Golgi export of synaptophysin-containing vesicles. These effects were dependent on the Golgi localization of LIMK1, paralleled by an increase in cofilin phosphorylation and phalloidin staining in the region of the Golgi apparatus, and prevented by coexpression of constitutive active cofilin. The long-term overexpression of LIMK1 produces growth cone collapse and axon retraction, an effect that is dependent on its growth cone localization. Together, our results suggest an important role for LIMK1 in axon formation that is related with its ability to regulate Golgi dynamics, membrane traffic, and actin cytoskeletal organization.

Soluble form of amyloid precursor protein regulates proliferation of progenitors in the adult subventricular zone

The amyloid precursor protein (APP) is a type I transmembrane protein of unknown physiological function. Its soluble secreted form (sAPP) shows similarities with growth factors and increases the in vitro proliferation of embryonic neural stem cells. As neurogenesis is an ongoing process in the adult mammalian brain, we have investigated a role for sAPP in adult neurogenesis. We show that the subventricular zone (SVZ) of the lateral ventricle, the largest neurogenic area of the adult brain, is a major sAPP binding site and that binding occurs on progenitor cells expressing the EGF receptor. These EGF-responsive cells can be cultured as neurospheres (NS). In vitro, EGF provokes soluble APP (sAPP) secretion by NS and anti-APP antibodies antagonize the EGF-induced NS proliferation. In vivo, sAPP infusions increase the number of EGF-responsive progenitors through their increased proliferation. Conversely, blocking sAPP secretion or downregulating APP synthesis decreases the proliferation of EGF-responsive cells, which leads to a reduction of the pool of progenitors. These results reveal a new function for sAPP as a regulator of SVZ progenitor proliferation in the adult central nervous system.

Characterization of Gicerin/MUC18/CD146 in the rat nervous system

Gicerin is a cell adhesion molecule of an immunoglobulin (Ig) superfamily isolated from a chicken. It shows homophilic and heterophilic binding activities and has two isoforms. s-Gicerin which has small cytoplasmic domain and the same extracellular domain as l-gicerin shows stronger cell adhesion activity. In the chick nervous system, gicerin expression is only observed in the developmental stage when neurons extend neurites and migrate. In other tissues, gicerin participates in the tissue regeneration or oncogenesis. In this report, we identified two isoforms of rat gicerin corresponding to chicken and we concluded that gicerin is a homologue of human CD146/MUC18/MCAM. Next we generated antibody to characterize a rat gicerin in the nervous system. Gicerin is expressed in the hippocampal cells, Purkinje cells, and sensory neurons of a spinal chord of an adult rat, while expressed most abundantly in the lung. In addition to this, its expression in the hippocampus was increased by electroconvulsive shock, suggesting some role in the mature nervous system. And we also showed neurite promotion activity of gicerin from hippocampal neurons.

Patterning axonal guidance molecules using a novel strategy for microcontact printing

We present here a two-step strategy for micropatterning proteins on a substrate to control neurite growth in culture. First, conventional microcontact printing is used to prepare a micropattern of protein A, which binds the Fc fragment of immunoglobulins. Then, a chimeric protein, consisting of the extracellular domain of a guidance protein recombinantly linked to the Fc fragment of IgG (prepared using conventional molecular techniques), is applied from solution. The chimeric protein binds to the patterned protein A, taking on its geometric pattern. Using this method, we have micropatterned the extracellular domain of the cell adhesion molecule, L1 (as an L1-Fc chimera) and demonstrated that it retains its ability to selectively guide axonal growth. L1-Fc micropatterned on a background of poly-L-lysine resulted in selective growth of the axons on the micropattern, whereas the somata and dendrites were unresponsive. Substrates bearing simultaneous micropatterns of L1-Fc and poly-L-lysine on a background of untreated glass were also created. Using this approach, cell body position was controlled by manipulating the dimensions of the poly-L-lysine pattern, and the dendrites were constrained to the poly-L-lysine pattern, while the axons grew preferentially on L1-Fc. The two-step microcontact printing method allows preparation of substrates that contain guidance proteins in geometric patterns with resolution of approximately 1 microm. This method should be broadly applicable to many classes of proteins.

Regionally specific expression of L1 and sialylated NCAM in the retinofugal pathway of mouse embryos

We have examined expression of L1 and the polysialic acid-associated form of the neural cell adhesion molecule (PSA-NCAM) in mouse embryos during the major period of axon growth in the retinofugal pathway to determine whether they are expressed in patterns that relate to the changes in axon organization in the pathway. Immunostaining for L1 and PSA-NCAM was found on all axons in the retina and the optic stalk. In the chiasm, while L1 immunoreactivity remained high on the axons, PSA-NCAM staining was obviously reduced. At the threshold of the optic tract, L1 immunoreactivity was maintained only in a subpopulation of axons, whereas PSA-NCAM staining was dramatically elevated in axons at the caudal part of the tract. Further investigations of the tract showed that both L1 and PSA-NCAM were preferentially expressed on the dorsal but not ventral optic axons, indicating a regionally specific change of both adhesion molecules on the axons at the chiasm-tract junction. Moreover, intense PSA-NCAM expression was also observed in the tract of postoptic commissure (TPOC), which lies immediately caudal to the optic tract. Immunohistochemical and retrograde tracing studies showed that these PSA-NCAM-positive axons arose from a population of cells rostral to the CD44-positive chiasmatic neurons. These findings indicate that, in addition to the chiasmatic neurons, these PSA-NCAM-positive diencephalic cells also contribute axons to the TPOC. These early generated commissural axons together with the regionally specific pattern of cell adhesion molecule expression on the optic axons may control formation of the partial retinotopic axon order in the optic tract through homophilic or heterophilic interactions that involve PSA-NCAM.

Soluble cell adhesion molecule L1-Fc promotes locomotor recovery in rats after spinal cord injury

Previous studies suggest that the cell adhesion molecule L1 promotes neurite growth by neutralizing white matter associated inhibitors of axonal growth. We made a soluble chimeric dimer by linking mouse L1 to human Fc. This L1-Fc construct (40 microg/mL) markedly facilitated neurite outgrowth, as well as neuronal adhesion to white matter on frozen sections of spinal cord. We applied L1-Fc intrathecally (200 microg/mL at 0.5 microL/h) to rat spinal cords for 2 weeks after a 25-mm weight drop contusion of the T13 spinal cord. Initial experiments indicated that L1-Fc is present in the spinal cord after 2 weeks of intrathecal infusion and significantly improved locomotor recovery by 6-12 weeks after injury. We then randomized 45 rats to intrathecal infusion of L1-Fc (L1), phosphate-buffered saline controls (PBS), and a mouse monoclonal IgM antibody (M1). By 12 weeks after injury, L1-treated rats recovered significantly (p < 0.005) better locomotor function (BBB score 10.57 +/- 0.25, n = 14) than PBS-treated rats (BBB score 9.00 +/- 0.33, n = 14) or M1-treated (BBB score 8.71 +/- 0.16, n = 14). Only two rats of 22 treated with saline recovered weight-supported ambulation. Of 20 L1-Fc-treated rats, however, 18 recovered weight-supported walking by 12 weeks. The L1-Fc-treated rats also showed more consistent hindlimb contact placing than saline controls. We injected biotinylated dextran amine (BDA) into the motor cortices of 14 rats treated with L1-Fc to label corticospinal axons, comparing these with 13 rats treated with saline. In saline-treated rats, BDA-labeled corticospinal axons often grew up to the impact edge and occasionally into the impact site. L1-treated rats showed longer corticospinal tract growth at the injury site. Three rats had BDA-labeled axons that extended beyond the impact center. One L1-Fc-treated rat showed axonal extension and synapse formation in cord distal to the injury. These results indicate that soluble L1-Fc promotes axonal growth and functional recovery after spinal cord injury. However, the limited corticospinal tract growth across the injury site cannot account for the observed locomotor recovery. Thus, L1 may be stimulating growth of other motor tracts or protecting axons and neurons. More studies are required to elucidate the mechanisms of L1-Fc-induced locomotor recovery.

Examination of the relationship between astrocyte morphology and laminar boundaries in the molecular layer of adult dentate gyrus

Astrocytes are known to play an integral role in the development of compartmental boundaries in the brain and in the creation of trauma-induced boundaries. However, the physical relationship between astrocytes and such boundaries in the adult brain is less clear. If astrocytes do respect or play an ongoing role in maintaining such boundaries, a correlation between the position of such a boundary and the morphology of neighboring astrocytes might be observable. In this study, we examined the distribution of astrocytes with respect to the laminar boundaries compartmentalizing afferents to the dentate gyrus molecular layer. In addition, we attempted to determine whether astrocyte morphology is influenced by these laminar boundaries. To this end, protoplasmic astrocytes in the adult rat dentate gyrus were revealed with fluorescent tracer dyes and subsequently analyzed with respect to laminar boundaries demarcated by means of immunolabeling for the lamina-specific molecules EphA4 and neural cell adhesion molecule (N-CAM). We find that astrocyte distribution is influenced by the boundary separating the associational/commissural and perforant path afferents. In addition, we show that astrocytes in this region are polarized in their morphology, unlike typically stellate astrocytes, but that the laminar boundaries themselves do not appear to confer this morphology. This polarized morphology, however acquired, may have import for the functioning of astrocytes within the highly organized composition of the dentate gyrus molecular layer and for the overall microphysiology of this and other brain regions.

N-cadherin mediates retinal lamination, maintenance of forebrain compartments and patterning of retinal neurites

The complex, yet highly ordered and predictable, structure of the neural retina is one of the most conserved features of the vertebrate central nervous system. In all vertebrate classes, retinal neurons are organized into laminae with each neuronal class adopting specific morphologies and patterns of connectivity. Using genetic analyses in zebrafish, we demonstrate that N-cadherin (Ncad) has several distinct and crucial functions during the establishment of retinal organization. Although the location of cell division is disorganized in embryos with reduced or no Ncad function, different classes of retinal neurons are generated. However, these neurons fail to organize into correct laminae, most probably owing to compromised adhesion between retinal cells. In addition, amacrine cells exhibit exuberant and misdirected outgrowth of neurites that contributes to severe disorganization of the inner plexiform layer. Retinal ganglion cells also exhibit defects in process outgrowth, with axons exhibiting fasciculation defects and adopting incorrect ipsilateral trajectories. At least some of these defects are likely to be due to a failure to maintain compartment boundaries between eye, optic nerve and brain. Although in vitro studies have implicated Fgf receptors in modulating the axon outgrowth promoting properties of Ncad, most aspects of the Ncad mutant phenotype are not phenocopied by treatments that block Fgf receptor function.

Biochemical and ultrastructural analyses of IgLON cell adhesion molecules, Kilon and OBCAM in the rat brain

Kilon (kindred of IgLON) and opioid-binding cell adhesion molecule belong to the IgLON subgroup of immunoglobulin superfamily together with the limbic system-associated membrane protein and neurotrimin. In the present study, we have analyzed biochemical and ultrastructural characterization of Kilon and opioid-binding cell adhesion molecule such as regional and developmental expression patterns, light and electron microscopic localization, and intermolecular interactions. Western blotting revealed a widespread distribution pattern of Kilon with high expression levels in the olfactory bulb, cerebral cortex, diencephalon, hippocampus, and cerebellum and low expression levels in the medulla oblongata and spinal cord. In contrast, opioid-binding cell adhesion molecule showed a regionally restricted expression pattern with high levels only in the cerebral cortex and hippocampus. Expression of Kilon and opioid-binding cell adhesion molecule was increased gradually during postnatal development and maintained until adulthood. Light microscopic immunohistochemistry demonstrated that the localization of opioid-binding cell adhesion molecule and Kilon coincided well with that of vesicle-associated membrane protein 2, a synaptic marker protein, in the cerebral cortex and hippocampus of adult brain. In the cerebellum, Kilon-immunoreactive puncta were observed to colocalize well with that of vesicle-associated membrane protein 2, while opioid-binding cell adhesion molecule immunoreactivity was observed only at part of synaptic glomeruli in the granular layer and rare in the molecular layer. Electron microscopic analysis revealed that Kilon and opioid-binding cell adhesion molecule immunoreactivity was observed mainly at postsynaptic sites of dendritic and somatic synapses in adult cerebral cortex and hippocampus. Only trace levels of Kilon and opioid-binding cell adhesion molecule were detected in the soluble fraction of a cortical homogenate, although a substantial amount of F3 was present in the soluble fraction. A binding analysis using a cross-linker and the immunoprecipitation technique demonstrated that Kilon and opioid-binding cell adhesion molecule interacted heterophilically and homophilically. These findings show that Kilon and opioid-binding cell adhesion molecule are clearly distinguishable from each other in regional expression and localization, and binding patterns. These differences possibly represent diverse functions of each IgLON molecule.

Soluble dimeric prion protein binds PrP(Sc) in vivo and antagonizes prion disease

Conversion of cellular prion protein (PrP(C)) into a pathological conformer (PrP(Sc)) is thought to be promoted by PrP(Sc) in a poorly understood process. Here, we report that in wild-type mice, the expression of PrP(C) rendered soluble and dimeric by fusion to immunoglobulin Fcgamma (PrP-Fc(2)) delays PrP(Sc) accumulation, agent replication, and onset of disease following inoculation with infective prions. In infected PrP-expressing brains, PrP-Fc(2) relocates to lipid rafts and associates with PrP(Sc) without acquiring protease resistance, indicating that PrP-Fc(2) resists conversion. Accordingly, mice expressing PrP-Fc(2) but lacking endogenous PrP(C) are resistant to scrapie, do not accumulate PrP-Fc(2)(Sc), and do not transmit disease to others. These results indicate that various PrP isoforms engage in a complex in vivo, whose distortion by PrP-Fc(2) affects prion propagation and scrapie pathogenesis. The unique properties of PrP-Fc(2) suggest that soluble PrP derivatives may represent a new class of prion replication antagonists.

Rho kinase inhibition enhances axonal regeneration in the injured CNS

Myelin-associated inhibitors limit axonal regeneration in the injured brain and spinal cord. A common target of many neurite outgrowth inhibitors is the Rho family of small GTPases. Activation of Rho and a downstream effector of Rho, p160ROCK, inhibits neurite outgrowth. Here, we demonstrate that Rho is directly activated by the myelin-associated inhibitor Nogo-66. Using a binding assay to measure Rho activity, we detected increased levels of GTP Rho in PC12 and dorsal root ganglion (DRG) cell lysates after Nogo-66 stimulation. Rho activity levels were not affected by Amino-Nogo stimulation. Rho inactivation with C3 transferase promotes neurite outgrowth of chick DRG neurons in vitro, but with the delivery method used here, it fails to promote neurite outgrowth after corticospinal tract (CST) lesions in the adult rat. Inhibition of p160ROCK with Y-27632 also promotes neurite outgrowth on myelin-associated inhibitors in vitro. Furthermore, Y-27632 enhances sprouting of CST fibers in vivo and accelerates locomotor recovery after CST lesions in adult rats.

Diabetic neuropathy and nerve regeneration

Diabetic neuropathy is the most common peripheral neuropathy in western countries. Although every effort has been made to clarify the pathogenic mechanism of diabetic neuropathy, thereby devising its ideal therapeutic drugs, neither convinced hypotheses nor unequivocally effective drugs have been established. In view of the pathologic basis for the treatment of diabetic neuropathy, it is important to enhance nerve regeneration as well as prevent nerve degeneration. Nerve regeneration or sprouting in diabetes may occur not only in the nerve trunk but also in the dermis and around dorsal root ganglion neurons, thereby being implicated in the generation of pain sensation. Thus, inadequate nerve regeneration unequivocally contributes to the pathophysiologic mechanism of diabetic neuropathy. In this context, the research on nerve regeneration in diabetes should be more accelerated. Indeed, nerve regenerative capacity has been shown to be decreased in diabetic patients as well as in diabetic animals. Disturbed nerve regeneration in diabetes has been ascribed at least in part to all or some of decreased levels of neurotrophic factors, decreased expression of their receptors, altered cellular signal pathways and/or abnormal expression of cell adhesion molecules, although the mechanisms of their changes remain almost unclear. In addition to their steady-state changes in diabetes, nerve injury induces injury-specific changes in individual neurotrophic factors, their receptors and their intracellular signal pathways, which are closely linked with altered neuronal function, varying from neuronal survival and neurite extension/nerve regeneration to apoptosis. Although it is essential to clarify those changes for understanding the mechanism of disturbed nerve regeneration in diabetes, very few data are now available. Rationally accepted replacement therapy with neurotrophic factors has not provided any success in treating diabetic neuropathy. Aside from adverse effects of those factors, more rigorous consideration for their delivery system may be needed for any possible success. Although conventional therapeutic drugs like aldose reductase (AR) inhibitors and vasodilators have been shown to enhance nerve regeneration, their efficacy should be strictly evaluated with respect to nerve regenerative capacity. For this purpose, especially clinically, skin biopsy, by which cutaneous nerve pathology including nerve regeneration can be morphometrically evaluated, might be a safe and useful examination.

The FGF receptor uses the endocannabinoid signaling system to couple to an axonal growth response

A key role for DAG lipase activity in the control of axonal growth and guidance in vitro and in vivo has been established. For example, DAG lipase activity is required for FGF-stimulated calcium influx into neuronal growth cones, and this response is both necessary and sufficient for an axonal growth response. The mechanism that couples the hydrolysis of DAG to the calcium response is not known. The initial hydrolysis of DAG at the sn-1 position (by DAG lipase) will generate 2-arachidonylglycerol, and this molecule is well established as an endogenous cannabinoid receptor agonist in the brain. In the present paper, we show that in rat cerebellar granule neurons, CB1 cannabinoid receptor antagonists inhibit axonal growth responses stimulated by N-cadherin and FGF2. Furthermore, three CB1 receptor agonists mimic the N-cadherin/FGF2 response at a step downstream from FGF receptor activation, but upstream from calcium influx into cells. In contrast, we could find no evidence for the CB1 receptor coupling the TrkB neurotrophin receptor to an axonal growth response in the same neurons. The observation that the CB1 receptor can couple the activated FGF receptor to an axonal growth response raises novel therapeutic opportunities.

Prion protein as trans-interacting partner for neurons is involved in neurite outgrowth and neuronal survival

Many uncertainties remain regarding the physiological function of the prion protein PrP and the consequences of its conversion into the pathological scrapie isoform in prion diseases. Here, we show for the first time that different signal transduction pathways are involved in neurite outgrowth and neuronal survival elicited by PrP in cell culture of primary neurons. These pathways include the nonreceptor Src-related family member p59(Fyn), PI3 kinase/Akt, cAMP-dependent protein kinase A, and MAP kinase. Regulation of Bcl-2 and Bax expression also correlates with the survival effect elicited by PrP. The combined results, along with our observation that PrP carries the recognition molecule-related HNK-1 carbohydrate, argue strongly for a role of the molecule in neural recognition by interacting with yet unknown heterophilic neuronal receptors, as shown by comparison of neurite outgrowth from neurons of PrP-deficient and wild-type mice.

Intracellular signaling by the neural cell adhesion molecule

Cell adhesion molecules are known to play far more complex roles than mechanically attaching one cell to an adjacent cell or to components of the extracellular matrix. Thus, important roles for cell adhesion molecules in the regulation of intracellular signaling pathways have been revealed. In this review, we discuss the present knowledge about signaling pathways activated upon homophilic binding of the neural cell adhesion molecule (NCAM). Homophilic NCAM binding leads to activation of a signal transduction pathway involving Ca2+ through activation of the fibroblast growth factor receptor, and to activation of the mitogen-activated protein kinase pathway. In addition, cyclic adenosine monophosphate and protein kinase A are involved in NCAM-mediated signaling. Among these pathways the possibility exists of cross talk or convergence, of which different possible mediators have been suggested. Finally, several downstream effector molecules leading to NCAM-mediated cellular endpoints have been demonstrated, including transcription factors and regulators of the cytoskeleton.

Cell adhesion molecules during inner ear and hair cell development, including notch and its ligands

Cellular adhesion plays a key role in a number of unique developmental events, including proliferation, cell fate, morphogenesis, neurite outgrowth, fasciculation, and synaptogensis. The number of families of molecules that can mediate cell adhesion and the number of members of each of those families has continued to increase over time. Moreover, the potential for the formation of different pairs of heterodimers with different binding specificities, and for both homo- and hetero-dimeric interactions suggest that a vast number of specific signaling events can be mediated through the expression of different combinations of adhesion factors at different developmental time points. By comparison with the number of known adhesion molecules and their potential effects, our understanding of the role of adhesion in ear development is extremely limited. The patterns of expression for some adhesion molecules have been determined for some aspects of inner ear development. Similarly, with a few exceptions, functional data to indicate the roles of these adhesion molecules are also lacking. However, a consideration of even the limited existing data must lead to the conclusion that adhesion molecules play key roles in all aspects of the development of the auditory system. Unique expression domains for different groups of adhesion molecules within the developing otocyst and ear strongly suggest a role in the determination of different cellular domains. Similarly, the specific expression of adhesion molecules on developing neurites and their target hair cells, suggests a key role for adhesion in the establishment of neuronal connections and possible the development of tonotopy. Finally, the recent demonstration that Cdh23 and Pcdh15 play specific roles in the formation of the hair cell stereociliary bundle provides compelling evidence for the importance of adhesion molecules in the development of stereocilia. With the imminent completion of the mouse genome, it seems likely that the number of adhesion molecules can soon be fixed and that it will then be possible to generate a more comprehensive map of expression of these molecules within the developing inner ear. At the same time, the generation of new transgenic and molecular technologies promises to provide researchers with new tools to examine the specific effects of different adhesion molecules during inner ear development.

Costimulation of T cell receptor-triggered IL-2 production by Jurkat T cells via fibroblast growth factor receptor 1 upon its engagement by CD56

Recent studies have demonstrated that neural cell adhesion molecule (NCAM) is involved in multiple adhesive interactions with several different classes of ligands on the cell surface and in the extracellular matrix. One of these ligands is fibroblast growth factor receptor (FGFR) that is expressed on neural cells. While it is known that CD56 is a molecular isoform of NCAM expressed on human NK cells and a subset of T cells, it remains poorly characterized, with its ligand unidentified. Therefore, we were prompted to examine if CD56 molecules on NK cells interact with FGFR expressed on T cells. We demonstrate that ligation of FGFR1 beta on J.C2-14 Jurkat T cells by CD56 on fixed NK-92 cells costimulates TCR/CD3-triggered IL-2 production. CD56-binding mAbs inhibited the costimulatory effect of NK-92 cells in 50-75%. Flow cytometric analysis and cell adhesion assays showed that FGFR1 beta/Fc and FGFR2 beta/Fc chimeric proteins bind to NK-92 cells. The binding of FGFR1 beta/Fc protein to CD56 molecules was verified by immunoprecipitation of CD56 with anti-CD56 mAb followed by Western blotting with FGFR1 beta/Fc. These findings suggest that ligation of FGFR1 by CD56 may contribute to the interaction between NK cells and T cells that we have postulated in our previous studies.