Opposing Morphogenetic Defects on Dendrites and Mossy Fibers of Dentate Granular Neurons in CRMP3-Deficient Mice.

Collapsin response mediator proteins (CRMPs) are highly expressed in the brain during early postnatal development and continue to be present in specific regions into adulthood, especially in areas with extensive neuronal plasticity including the hippocampus. They are found in the axons and dendrites of neurons wherein they contribute to specific signaling mechanisms involved in the regulation of axonal and dendritic development/maintenance. We previously identified CRMP3's role on the morphology of hippocampal CA1 pyramidal dendrites and hippocampus-dependent functions. Our focus here was to further analyze its role in the dentate gyrus where it is highly expressed during development and in adults. On the basis of our new findings, it appears that CRMP3 has critical roles both in axonal and dendritic morphogenesis of dentate granular neurons. In CRMP3-deficient mice, the dendrites become dystrophic while the infrapyramidal bundle of the mossy fiber shows aberrant extension into the stratum oriens of CA3. This axonal misguided projection of granular neurons suggests that the mossy fiber-CA3 synaptic transmission, important for the evoked propagation of the activity of the hippocampal trisynaptic circuitry, may be altered, whereas the dystrophic dendrites may impair the dynamic interactions with the entorhinal cortex, both expected to affect hippocampal function.

Mapping CRMP3 domains involved in dendrite morphogenesis and voltage-gated calcium channel regulation.

Although hippocampal neurons are well-distinguished by the morphological characteristics of their dendrites and their structural plasticity, the mechanisms involved in regulating their neurite initiation, dendrite growth, network formation and remodeling are still largely unknown, in part because the key molecules involved remain elusive. Identifying new dendrite-active cues could uncover unknown molecular mechanisms that would add significant understanding to the field and possibly lead to the development of novel neuroprotective therapy because these neurons are impaired in many neuropsychiatric disorders. In our previous studies, we deleted the gene encoding CRMP3 in mice and identified the protein as a new endogenous signaling molecule that shapes diverse features of the hippocampal pyramidal dendrites without affecting axon morphology. We also found that CRMP3 protects dendrites against dystrophy induced by prion peptide PrP(106-126). Here, we report that CRMP3 has a profound influence on neurite initiation and dendrite growth of hippocampal neurons in vitro. Our deletional mapping revealed that the C-terminus of CRMP3 probably harbors its dendritogenic capacity and supports an active transport mechanism. By contrast, overexpression of the C-terminal truncated CRMP3 phenocopied the effect of CRMP3 gene deletion with inhibition of neurite initiation or decrease in dendrite complexity, depending on the stage of cell development. In addition, this mutant inhibited the activity of CRMP3, in a similar manner to siRNA. Voltage-gated calcium channel inhibitors prevented CRMP3-induced dendritic growth and somatic Ca(2+) influx in CRMP3-overexpressing neurons was augmented largely via L-type channels. These results support a link between CRMP3-mediated Ca(2+) influx and CRMP3-mediated dendritic growth in hippocampal neurons.

Matrix-binding vascular endothelial growth factor (VEGF) isoforms guide granule cell migration in the cerebellum via VEGF receptor Flk1.

Vascular endothelial growth factor (VEGF) regulates angiogenesis, but also has important, yet poorly characterized roles in neuronal wiring. Using several genetic and in vitro approaches, we discovered a novel role for VEGF in the control of cerebellar granule cell (GC) migration from the external granule cell layer (EGL) toward the Purkinje cell layer (PCL). GCs express the VEGF receptor Flk1, and are chemoattracted by VEGF, whose levels are higher in the PCL than EGL. Lowering VEGF levels in mice in vivo or ectopic VEGF expression in the EGL ex vivo perturbs GC migration. Using GC-specific Flk1 knock-out mice, we provide for the first time in vivo evidence for a direct chemoattractive effect of VEGF on neurons via Flk1 signaling. Finally, using knock-in mice expressing single VEGF isoforms, we show that pericellular deposition of matrix-bound VEGF isoforms around PC dendrites is necessary for proper GC migration in vivo. These findings identify a previously unknown role for VEGF in neuronal migration.

Cerebrospinal fluid dendritic cells infiltrate the brain parenchyma and target the cervical lymph nodes under neuroinflammatory conditions.

BACKGROUND: In many neuroinflammatory diseases, dendritic cells (DCs) accumulate in several compartments of the central nervous system (CNS), including the cerebrospinal fluid (CSF). Myeloid DCs invading the inflamed CNS are thus thought to play a major role in the initiation and perpetuation of CNS-targeted autoimmune responses. We previously reported that, in normal rats, DCs injected intra-CSF migrated outside the CNS and reached the B-cell zone of cervical lymph nodes. However, there is yet no information on the migratory behavior of CSF-circulating DCs under neuroinflammatory conditions. METHODOLOGY/PRINCIPAL FINDINGS: To address this issue, we performed in vivo transfer experiments in rats suffering from experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. EAE or control rats were injected intra-CSF with bone marrow-derived myeloid DCs labeled with the fluorescent marker carboxyfluorescein diacetate succinimidyl ester (CFSE). In parallel experiments, fluorescent microspheres were injected intra-CSF to EAE rats in order to track endogenous antigen-presenting cells (APCs). Animals were then sacrificed on day 1 or 8 post-injection and their brain and peripheral lymph nodes were assessed for the presence of microspheres(+) APCs or CFSE(+) DCs by immunohistology and/or FACS analysis. Data showed that in EAE rats, DCs injected intra-CSF substantially infiltrated several compartments of the inflamed CNS, including the periventricular demyelinating lesions. We also found that in EAE rats, as compared to controls, a larger number of intra-CSF injected DCs reached the cervical lymph nodes. This migratory behavior was accompanied by an accentuation of EAE clinical signs and an increased systemic antibody response against myelin oligodendrocyte glycoprotein, a major immunogenic myelin antigen. CONCLUSIONS/SIGNIFICANCE: Altogether, these results indicate that CSF-circulating DCs are able to both survey the inflamed brain and to reach the cervical lymph nodes. In EAE and maybe multiple sclerosis, CSF-circulating DCs may thus support the immune responses that develop within and outside the inflamed CNS.

Abnormal expression of truncated CRMP-1 protein in the brain cortex of MPSIIIB mice.

Mucopolysaccharidosis IIIB is a lysosomal disease characterized by a severe neurological deterioration, the pathophysiological mechanisms of which are poorly understood. Recently FGF pathway was shown to be altered leading us to explore a downstream target involved in brain development: the collapsin response mediator protein-1 (CRMP-1). CRMP-1 transcript level was normal but a cleavage of CRMP-1 was observed with an abnormal expression of the truncated form until adult age. This truncated CRMP-1 protein could play a role in post-natal cortex maturation and be involved in neuronal alterations occurring in lysosomal diseases.

Processing and nuclear localization of CRMP2 during brain development induce neurite outgrowth inhibition.

Collapsin response mediator proteins (CRMPs) are believed to play a crucial role in neuronal differentiation and axonal outgrowth. Among them, CRMP2 mediates axonal guidance by collapsing growth cones during development. This activity is correlated with the reorganization of cytoskeletal proteins. CRMP2 is implicated in the regulation of several intracellular signaling pathways. Two subtypes, A and B, and multiple cytosolic isoforms of CRMP2B with apparent masses between 62 and 66 kDa have previously been reported. Here, we show a new short isoform of 58 kDa, expressed during brain development, derived from C-terminal processing of the CRMP2B subtype. Although full-length CRMP2 is restricted to the cytoplasm, using transfection experiments, we demonstrate that a part of the short isoform is found in the nucleus. Interestingly, at the tissue level, this short CRMP2 is also found in a nuclear fraction of brain extract. By mutational analysis, we demonstrate, for the first time, that nuclear translocation occurs via nuclear localization signal (NLS) within residues Arg(471)-Lys(472) in CRMP2 sequence. The NLS may be unmasked after C-terminal processing; thereby, this motif may be surface-exposed. This short CRMP2 induces neurite outgrowth inhibition in neuroblastoma cells and suppressed axonal growth in cultured cortical neurons, whereas full-length CRMP2 promotes neurite elongation. The NLS-mutated short isoform, restricted to the cytoplasm, abrogates both neurite outgrowth and axon growth inhibition, indicating that short nuclear CRMP2 acts as a dominant signal. Therefore, post-transcriptional processing of CRMP2 together with its nuclear localization may be an important key in the regulation of neurite outgrowth in brain development.

CRMP3 is required for hippocampal CA1 dendritic organization and plasticity.

In vitro studies have pointed to the collapsin response mediator proteins (CRMPs) as key regulators of neurite outgrowth and axonal differentiation. CRMP3 is expressed mostly in the nervous system during development but remains at high levels in the hippocampus of adults. To explore CRMP3 function in vivo, we generated mice with targeted disruption of the CRMP3 gene. Immunohistochemistry and Golgi staining of CA1 showed abnormal dendrite and spine morphogenesis in the hippocampus of CRMP3-deficient mice. Apical dendrites displayed an increase in undulation and a reduction in length and branching points. Basal dendrites also exhibited a reduction in length with an alteration in soma stem distribution and an increased number of thick dendrites localized in stratum oriens (SO). Long-term potentiation (LTP) was impaired in this area. These data indicate an important role for CRMP3 in dendrite arborization, guide-posts navigation, and neuronal plasticity.

A diagnostic marker set for invasion, proliferation, and aggressiveness of prolactin pituitary tumors.

Although most pituitary tumors are benign, some are invasive or aggressive. In the absence of specific markers of malignancy, only tumors with metastases are considered malignant. To identify markers of invasion and aggressiveness, we focused on prolactin (PRL) tumors in the human and rat. Using radiology and histological methods, we classified 25 human PRL tumors into three groups (non-invasive, invasive, and aggressive-invasive) and compared them with a model of transplantable rat PRL tumors with benign and malignant lineages. Combining histological(mitoses and labeling for Ki-67, P53, pituitary transforming tumor gene (PTTG), and polysialic acid neural cell adhesion molecule) and transcriptomic (microarrays and q-RTPCR) methods with clinical data (post-surgical outcome with case-control statistical analysis), we found nine genes implicated in invasion (ADAMTS6, CRMP1, and DCAMKL3) proliferation (PTTG, ASK, CCNB1, AURKB, and CENPE), or pituitary differentiation (PITX1) showing differential expression in the three groups of tumors (P = 0.015 to 0.0001). A case-control analysis, comparing patients in remission (9 controls) and patients with persistent or recurrent tumors (14 cases) revealed that eight out of the nine genes were differentially up- or downregulated (P = 0.05 to 0.002), with only PTTG showing no correlation with clinical course (P = 0.258). These combined histological and transcriptomic analyses improve the pathological diagnosis of PRL tumors, indicating a reliable procedure for predicting tumor aggressiveness and recurrence potential. The similar gene profiles found between non-invasive human and benign rat tumors, as well as between aggressive-invasive human and malignant rat tumors provide new insights into malignancy in human pituitary tumors.

Glutamatergic alterations in the cortex of genetic absence epilepsy rats.

BACKGROUND: In absence epilepsy, the neuronal hyper-excitation and hyper-synchronization, which induce spike and wave discharges in a cortico-thalamic loop are suspected to be due to an imbalance between GABA and glutamate (GLU) neurotransmission. In order to elucidate the role played by GLU in disease outcome, we measured cortical and thalamic extracellular levels of GLU and GABA. We used an in vivo quantitative microdialysis approach (no-net-flux method) in an animal model of absence epilepsy (GAERS). In addition, by infusing labelled glutamate through the microdialysis probe, we studied in vivo glutamate uptake in the cortex and thalamus in GAERS and non-epileptic control (NEC) rats. Expression of the vesicular glutamate transporters VGLUT1 and VGLUT2 and a synaptic component, synaptophysin, was also measured. RESULTS: Although extracellular concentrations of GABA and GLU in the cortex and thalamus were not significantly different between GAERS and NEC rats, cortical GLU uptake was significantly decreased in unrestrained awake GAERS. Expression of VGLUT2 and synaptophysin was increased in the cortex of GAERS compared to NEC rats, but no changes were observed in the thalamus. CONCLUSION: The specific decrease in GLU uptake in the cortex of GAERS linked to synaptic changes suggests impairment of the glutamatergic terminal network. These data support the idea that a change in glutamatergic neurotransmission in the cortex could contribute to hyperexcitability in absence epilepsy.

Transient alterations in granule cell proliferation, apoptosis and migration in postnatal developing cerebellum of CRMP1-/- mice.

Collapsin response mediator proteins (CRMPs) consist of five homologous cytosolic proteins that participate in signal transduction involved in a variety of physiological events. CRMP1 is highly expressed during brain development; however, its functions remains unclear. To gain insight into its function, we generated CRMP1(-/-) mice with a knock-in LacZ gene. No gross anatomical changes or behavioral alterations were observed. Expression of CRMP1 was examined by the expression of the knocked-in LacZ gene, in situ hybridization with riboprobes and by imunohistochemistry. CRMP1 was found to be highly expressed in the developing the cerebellum, olfactory bulbs, hypothalamus and retina. In adults, expression level was high in the olfactory bulbs and hippocampus but very low in the retina and cerebellum and undetectable in hypothalamus. To study potential roles of CRMP1, we focused on cerebellum development. CRMP1(-/-) mice showed a decrease in the number of granule cells migrating out of explants of developing cerebellum, as did treatment of the explants from normal mice with anti-CRMP1 specific antibodies. CRMP1(-/-) mice showed a decrease in granule cell proliferation and apoptosis in external granule cell layers in vivo. Adult cerebellum of CRMP1(-/-) did not show any abnormalities.

IQGAP1 protein specifies amplifying cancer cells in glioblastoma multiforme.

The accurate identification and thorough characterization of tumorigenic cells in glioblastomas are essential to enhance our understanding of their malignant behavior and for the design of strategies that target this important cell population. We report here that, in rat brain, the scaffolding protein IQGAP1 is a marker of brain nestin+ amplifying neural progenitor cells. In a rat model of glioma, IQGAP1 also characterizes a subpopulation of nestin+ amplifying tumor cells in glioblastoma-like tumors but not in tumors with oligodendroglioma features. We next confirmed that IQGAP1 represents a new marker that may help to discriminate human glioblastoma from oligodendrogliomas. In human glioblastoma exclusively, IQGAP1 specifies a subpopulation of amplifying nestin+ cancer cells. Neoplastic IQGAP1+ cells from glioblastoma can be expanded in culture and possess all the characteristics of cancer stem-like progenitors. The similarities between amplifying neural progenitors and glioblastoma amplifying cancer cells may have significant implications for understanding the biology of glioblastoma.

Rat choroid plexuses contain myeloid progenitors capable of differentiation toward macrophage or dendritic cell phenotypes.

The interface between the blood and the cerebrospinal fluid (CSF) is formed by the choroid plexuses (CPs), which are specialized structures located within the brain ventricles. They are composed of a vascularized stroma surrounded by a tight epithelium that controls molecular and cellular traffic between the blood and the CSF. Cells expressing myeloid markers are present within the choroidal stroma. However, the exact identity, maturation state, and functions of these CP-associated myeloid cells are not fully clarified. We show here that this cell population contains immature myeloid progenitors displaying a high proliferative potential. Thus, in neonate rats and, to a lesser extent, in adult rats, cultured CP stroma cells form large colonies of macrophages, in response to M-CSF or GM-CSF, while, under the same conditions, peripheral blood monocytes do not. In addition, under GM-CSF treatment, free-floating colonies of CD11c(+) monocytic cells are generated which, when restimulated with GM-CSF and IL-4, differentiate into OX62(+)/MHC class II(+) dendritic cells. Interestingly, in CP stroma cultures, myeloid cells are found in close association with fibroblastic-like cells expressing the neural stem-cell marker nestin. Similarly, in the developing brain, macrophages and nestin(+) fibroblastic cells accumulate in vivo within the choroidal stroma. Taken together, these results suggest that the CP stroma represents a niche for myeloid progenitors and may serve as a reservoir for brain macrophages.

High pathogenicity of wild-type measles virus infection in CD150 (SLAM) transgenic mice.

Measles virus (MV) infection causes an acute childhood disease, associated in certain cases with infection of the central nervous system and development of a severe neurological disease. We have generated transgenic mice ubiquitously expressing the human protein SLAM (signaling lymphocytic activation molecule), or CD150, recently identified as an MV receptor. In contrast to all other MV receptor transgenic models described so far, in these mice infection with wild-type MV strains is highly pathogenic. Intranasal infection of SLAM transgenic suckling mice leads to MV spread to different organs and the development of an acute neurological syndrome, characterized by lethargy, seizures, ataxia, weight loss, and death within 3 weeks. In addition, in this model, vaccine and wild-type MV strains can be distinguished by virulence. Furthermore, intracranial MV infection of adult transgenic mice generates a subclinical infection associated with a high titer of MV-specific antibodies in the serum. Finally, to analyze new antimeasles therapeutic approaches, we created a recombinant soluble form of SLAM and demonstrated its important antiviral activity both in vitro and in vivo. Taken together, our results show the high susceptibility of SLAM transgenic mice to MV-induced neurological disease and open new perspectives for the analysis of the implication of SLAM in the neuropathogenicity of other morbilliviruses, which also use this molecule as a receptor. Moreover, this transgenic model, in allowing a simple readout of the efficacy of an antiviral treatment, provides unique experimental means to test novel anti-MV preventive and therapeutic strategies.

Brain protection at the blood-cerebrospinal fluid interface involves a glutathione-dependent metabolic barrier mechanism.

The choroid plexuses (CPs) form a protective interface between the blood and the ventricular cerebrospinal fluid (CSF). To probe into the pathways by which CPs provide brain protection, we sought to evaluate the efficiency of glutathione conjugation in this barrier as a mechanism to prevent the entry of blood-borne electrophilic, potentially toxic compounds into the CSF, and we investigated the fate of the resulting metabolites. Rat CPs, as well as human CPs from both fetal and adult brains, displayed high glutathione-S-transferase activities. Using an in vitro model of the blood-CSF barrier consisting of choroidal epithelial cells cultured in a two-chambered device, we showed that glutathione conjugation can efficiently prevent the entry of 1-chloro-2,4-dinitrobenzene (CDNB) into the CSF, a model for electrophilic compounds. The duration of this enzymatic protection was set by the concentration of CDNB to which the epithelium was exposed, and this barrier effect was impaired only on severe epithelial intracellular glutathione and cysteine depletion. The conjugate was excreted from the choroidal cells in a polarized manner, mostly at the blood-facing membrane, via a high-capacity transport process, which is not a rate-limiting step in this detoxification pathway, and which may involve transporters of the ATP-binding cassette c(Abcc) and/or solute carrier 21 (Slc21) families. Supplying the choroidal epithelium at the blood-facing membrane with a therapeutically relevant concentration of N-acetylcysteine sustained this neuroprotective effect. Thus, glutathione conjugation at the CP epithelium coupled with the basolateral efflux of the resulting metabolites form an efficient blood-CSF enzymatic barrier, which can be enhanced by pharmacologically increasing glutathione synthesis within the epithelial cells.

How to drain without lymphatics? Dendritic cells migrate from the cerebrospinal fluid to the B-cell follicles of cervical lymph nodes.

The lack of draining lymphatic vessels in the central nervous system (CNS) contributes to the so-called "CNS immune privilege." However, despite such a unique anatomic feature, dendritic cells (DCs) are able to migrate from the CNS to cervical lymph nodes through a yet unknown pathway. In this report, labeled bone marrow-derived myeloid DCs were injected stereotaxically into the cerebrospinal fluid (CSF) or brain parenchyma of normal rats. We found that DCs injected within brain parenchyma migrate little from their site of injection and do not reach cervical lymph nodes. In contrast, intra-CSF-injected DCs either reach cervical lymph nodes or, for a minority of them, infiltrate the subventricular zone, where neural stem cells reside. Surprisingly, DCs that reach cervical lymph nodes preferentially target B-cell follicles rather than T-cell-rich areas. This report sheds a new light on the specific role exerted by CSF-infiltrating DCs in the control of CNS-targeted immune responses.

A role for the neuronal protein collapsin response mediator protein 2 in T lymphocyte polarization and migration.

The semaphorin-signaling transducer collapsin response mediator protein 2 (CRMP2) has been identified in the nervous system where it mediates Sema3A-induced growth cone navigation. In the present study, we provide first evidence that CRMP2 is present in the immune system and plays a critical role in T lymphocyte function. CRMP2 redistribution at the uropod in polarized T cells, a structural support of lymphocyte motility, suggests that it may regulate T cell migration. This was evidenced in primary T cells by small-interfering RNA-mediated CRMP2 gene silencing and blocking Ab, as well as CRMP2 overexpression in Jurkat T cells tested in a chemokine- and semaphorin-mediated transmigration assay. Expression analysis in PBMC from healthy donors showed that CRMP2 is enhanced in cell subsets bearing the activation markers CD69+ and HLA-DR+. Heightened expression in T lymphocytes of patients suffering from neuroinflammatory disease with enhanced T cell-transmigrating activity points to a role for CRMP2 in pathogenesis. The elucidation of the signals and mechanisms that control this pathway will lead to a better understanding of T cell trafficking in physiological and pathological situations.

Impairment of blood-cerebrospinal fluid barrier properties by retrovirus-activated T lymphocytes: reduction in cerebrospinal fluid-to-blood efflux of prostaglandin E2.

The choroid plexus epithelium forms the interface between the blood and the CSF. In conjunction with the tight junctions restricting the paracellular pathway, polarized specific transport systems in the choroidal epithelium allow a fine regulation of CSF-borne biologically active mediators. The highly vascularized stroma delimited by the choroidal epithelium can be a reservoir for retrovirus-infected or activated immune cells. In this work, new insight in the implication of the blood-CSF barrier in neuroinfectious and inflammatory diseases is provided by using a differentiated cellular model of the choroidal epithelium, exposed to infected T lymphocytes. We demonstrate that T cells activated by a retroviral infection, but not non-infected cells, reduce the transporter-mediated CSF-to-blood efflux of organic anions, in particular that of the potent pro-inflammatory prostaglandin PGE2, via the release of soluble factors. A moderate alteration of the paracellular permeability also occurs. We identified the viral protein Tax, oxygenated free radicals, matrix-metalloproteinases and pro-inflammatory cytokines as active molecules released during the exposure of the epithelium to infected T cells. Among them, tumour necrosis factor and interleukin 1 are directly involved in the mechanism underlying the decrease in some choroidal organic anion efflux. Given the strong involvement of CSF-borne PGE2 in sickness behaviour syndrome, these data suggest that the blood-CSF barrier plays an important role in the pathophysiology of neuroinflammation and neuroinfection, via changes in the transport processes controlling the CSF biodisposition of PGE2.

Specific alteration of the expression of selected hypothalamic neuropeptides during acute and late mouse brain infection using a morbillivirus: relevance to the late-onset obesity?

Neurotropic viruses are involved in pathologies of the central nervous system, triggering transient or irreversible disorders, such as neurological diseases or homeostasis imbalance. In experimental animals, viruses have been shown to cause obesity, a complex disease depending on multiple factors, including genetic susceptibility and environmental components. Using a mouse model of virally induced obesity following brain infection by the Canine Distemper Virus (CDV), a morbillivirus closely related to the human measles virus, we investigated the modulation of expression of several hypothalamic neuropeptides known to intervene in the regulation of body weight and energy expenditure, both during the acute and late stages of infection. During the acute stage, while viral replication occurs, we found a dramatic decrease of expressions of neuropeptides, in particular neuropeptide Y, melanin-concentrating hormone (MCH), hypocretin, vasopressin and tachykinins, the magnitude of which seemed to be linked to the viral burden and the individual susceptibility. The effect of the virus, however, varied with the hypothalamic nucleus and neuropeptide involved, suggesting that certain circuits were affected while others remained intact. During the late stage of infection, marked recovery to the initial hypothalamic levels of peptide expression was seen in a number of lean animals, suggesting recovery of homeostasis equilibrium. Interestingly, some neuropeptidergic systems remained disturbed in mice exhibiting obese phenotype, arguing for their involvement in triggering/maintaining obesity. Even though our data could not fully explain the viral-induced obesity, they may be helpful in understanding the molecular events associated with obesity and in investigating therapeutic alternatives.

Involvement of collapsin response mediator proteins in the neurite extension induced by neurotrophins in dorsal root ganglion neurons.

The pattern of sensory neuron extensions and connections is established during embryonic development through complex and varied guidance cues that control motility of growth cones and neurite morphogenesis. Semaphorins and neurotrophins are molecules that act as such cues. Collapsin response mediator proteins (CRMPs) are thought to be part of the semaphorin signal transduction pathway implicated in semaphorin-induced growth cone collapse. In this report, we present evidence that CRMPs are also involved in the neurite extension controlled by neurotrophins. We found that specific antibodies and the dominant-negative mutant protein for CRMP2 both potentiated the neurite extension induced by NGF, while specific antibodies and the corresponding mutant protein for CRMP1 both abolished the neurite extension induced by NT3. Our data suggest that CRMP2 has a negative effect on neurite extension induced by NGF and CRMP1 participates in the neurite formation/extension induced by NT3. These results point to a function for CRMPs in the regulation of neurite outgrowth induced by neurotrophins in sensory neurons.

Semaphorin CD100 from activated T lymphocytes induces process extension collapse in oligodendrocytes and death of immature neural cells.

An inappropriate cross talk between activated T lymphocytes infiltrating the CNS and neural cells can sustain the onset and progression of demyelination and axonal degeneration in neuroinflammatory diseases. To mimic this deleterious cross talk, we designed an experimental paradigm consisting of transient cocultures of T lymphocytes chronically activated by retrovirus infection (not virus productive) with human multipotent neural precursors or primary oligodendrocytes from rat brain. We showed that activated T lymphocytes induced apoptotic death of multipotent neural progenitors and immature oligodendrocytes after a progressive collapse of their process extensions. These effects were reminiscent of those induced by brain semaphorin on neural cells. Blockade by specific Abs of soluble CD100 (sCD100)/semaphorin 4D released by activated T cells, or treatment with rsCD100, demonstrated that this immune semaphorin has the ability to collapse oligodendrocyte process extensions and to trigger neural cell apoptosis, most likely through receptors of the plexin family. The specific presence of sCD100 in the cerebrospinal fluid and of CD100-expressing T lymphocytes in the spinal cord of patients suffering with neuroinflammatory demyelination pointed to the potential pathological effect of sCD100 in the CNS. Thus, our results show that CD100 is a new important element in the deleterious T cell-neural cell cross talk during neuroinflammation and suggest its role in demyelination or absence of remyelination in neuroinflammatory diseases including multiple sclerosis and human T lymphotropic virus type 1-associated myelopathy.