CRMP4 and CRMP2 Interact to Coordinate Cytoskeleton Dynamics, Regulating Growth Cone Development and Axon Elongation

CRMP/UNC-33 maintains neuronal microtubule arrays by promoting individual microtubule rescue

Microtubules (MTs) are intrinsically dynamic polymers. In neurons, staggered individual microtubules form stable, polarized acentrosomal MT arrays spanning the axon and dendrite to support long-distance intracellular transport. How the stability and polarity of these arrays are maintained when individual MTs remain highly dynamic is still an open question. Here we visualize MT arrays in vivo in C. elegans neurons with single microtubule resolution. We find that the CRMP family homolog, UNC-33, is essential for the stability and polarity of MT arrays in neurites. In unc-33 mutants, MTs exhibit dramatically reduced rescue after catastrophe, develop gaps in coverage, and lose their polarity, leading to trafficking defects. UNC-33 is stably anchored on the cortical cytoskeleton and forms patch-like structures along the dendritic shaft. These discrete and stable UNC-33 patches concentrate free tubulins and correlate with MT rescue sites. In vitro , purified UNC-33 preferentially associates with MT tips and increases MT rescue frequency. Together, we propose that UNC-33 functions as a microtubule-associated protein (MAP) to promote individual MT rescue locally. Through this activity, UNC-33 prevents the loss of individual MTs, thereby maintaining the coverage and polarity of MT arrays throughout the lifetime of neurons.

Insular cortex stimulation alleviates neuropathic pain through changes in the expression of collapsin response mediator protein 2 involved in synaptic plasticity

In recent studies, brain stimulation has shown promising potential to alleviate chronic pain. Although studies have shown that stimulation of pain-related brain regions can induce pain-relieving effects, few studies have elucidated the mechanisms of brain stimulation in the insular cortex (IC). The present study was conducted to explore the changes in characteristic molecules involved in pain modulation mechanisms and to identify the changes in synaptic plasticity after IC stimulation (ICS). Following ICS, pain-relieving behaviors and changes in proteomics were explored. Neuronal activity in the IC after ICS was observed by optical imaging. Western blotting was used to validate the proteomics data and identify the changes in the expression of glutamatergic receptors associated with synaptic plasticity. Experimental results showed that ICS effectively relieved mechanical allodynia, and proteomics identified specific changes in collapsin response mediator protein 2 (CRMP2). Neuronal activity in the neuropathic rats was significantly decreased after ICS. Neuropathic rats showed increased expression levels of phosphorylated CRMP2, alpha amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR), and N-methyl-d-aspartate receptor (NMDAR) subunit 2B (NR2B), which were inhibited by ICS. These results indicate that ICS regulates the synaptic plasticity of ICS through pCRMP2, together with AMPAR and NR2B, to induce pain relief.

Sinomenine ameliorates fibroblast-like synoviocytes dysfunction by promoting phosphorylation and nuclear translocation of CRMP2

ETHNOPHARMACOLOGICAL RELEVANCE

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial inflammation and arthritic pain. Sinomenine (SIN), derived from the rhizome of Chinese medical herb Qing Teng (scientific name: Sinomenium acutum (Thunb.) Rehd. Et Wils), has a longstanding use in Chinese traditional medicine for treating rheumatoid arthritis. It has been shown to possess anti-inflammatory, analgesic, and immunosuppressive effects with minimal side-effects clinically. However, the mechanisms governing its effects in treatment of joint pathology, especially on fibroblast-like synoviocytes (FLSs) dysfunction, and arthritic pain remains unclear.

AIM

This study aimed to investigate the effect and underlying mechanism of SIN on arthritic joint inflammation and joint FLSs dysfunctions.

MATERIALS AND METHODS

Collagen-induced arthritis (CIA) was induced in rats and the therapeutic effects of SIN on joint pathology were evaluated histopathologically. Next, we conducted a series of experiments using LPS-induced FLSs, which were divided into five groups (Naïve, LPS, SIN 10, 20, 50 μg/ml). The expression of inflammatory factors was measured by qPCR and ELISA. The invasive ability of cells was detected by modified Transwell assay and qPCR. Transwell migration and cell scratch assays were used to assess the migration ability of cells. The distribution and content of relevant proteins were observed by immunofluorescence and laser confocal microscopy, as well as Western Blot and qPCR. FLSs were transfected with plasmids (CRMP2 T514A/D) to directly modulate the post-translational modification of CRMP2 protein and downstream effects on FLSs function was monitored.

RESULTS

SIN alleviated joint inflammation in rats with CIA, as evidenced by improvement of synovial hyperplasia, inflammatory cell infiltration and cartilage damage, as well as inhibition of pro-inflammatory cytokines release from FLSs induced by LPS. In vitro studies revealed a concentration-dependent suppression of SIN on the invasion and migration of FLSs induced by LPS. In addition, SIN downregulated the expression of cellular CRMP2 that was induced by LPS in FLSs, but increased its phosphorylation at residue T514. Moreover, regulation of pCRMP2 T514 by plasmids transfection (CRMP2 T514A/D) significantly influenced the migration and invasion of FLSs. Finally, SIN promoted nuclear translocation of pCRMP2 T514 in FLSs.

CONCLUSIONS

SIN may exert its anti-inflammatory and analgesic effects by modulating CRMP2 T514 phosphorylation and its nuclear translocation of FLSs, inhibiting pro-inflammatory cytokine release, and suppressing abnormal invasion and migration. Phosphorylation of CRMP2 at the T514 site in FLSs may present a new therapeutic target for treating inflammatory joint's destruction and arthritic pain in RA.

Microtubule association of TRIM3 revealed by differential extraction proteomics

The microtubule network is formed from polymerised tubulin subunits and associating proteins, which govern microtubule dynamics and a diverse array of functions. To identify novel microtubule-binding proteins, we have developed an unbiased biochemical assay, which relies on the selective extraction of cytosolic proteins from U2OS cells, while leaving behind the microtubule network. Candidate proteins are linked to microtubules by their sensitivities to the depolymerising drug nocodazole or the microtubule-stabilising drug taxol, which is quantitated by mass spectrometry. Our approach is benchmarked by co-segregation of tubulin and previously established microtubule-binding proteins. We then identify several novel candidate microtubule-binding proteins, from which we have selected the ubiquitin E3 ligase tripartite motif-containing protein 3 (TRIM3) for further characterisation. We map TRIM3 microtubule binding to its C-terminal NHL-repeat region. We show that TRIM3 is required for the accumulation of acetylated tubulin, following treatment with taxol. Furthermore, loss of TRIM3 partially recapitulates the reduction in nocodazole-resistant microtubules characteristic of α-tubulin acetyltransferase 1 (ATAT1) depletion. These results can be explained by a decrease in ATAT1 following depletion of TRIM3 that is independent of transcription.

Rab3A interacts with spastin to regulate neurite outgrowth in hippocampal neurons

Investigating novel mechanisms of neurite outgrowth via cytoskeleton is critical for developing therapeutic strategies against neural disorders. Rab3A is a vesicle-related protein distributed throughout the nervous system, but the detailed mechanism related to cytoskeleton remains largely unknown. Our previous reports show that spastin serves microtubule to regulate neurite outgrowth. Here, we asked whether Rab3A could function via modulating spastin during neuronal development. The results revealed that Rab3A colocalized with spastin in cultured hippocampal neurons. Immunoprecipitation assays showed that Rab3A physically interacted with spastin in rat brain lysates. Rab3A overexpression significantly induced spastin degradation; this effect was reversed by leupeptin- or MG-132- administration, suggesting the lysosomal and ubiquitin-mediated degradation system. Immunofluorescence staining further confirmed that Rab3A and spastin immune-colocalized with the lysosome marker lysotracker. In COS7 cells, Rab3A overexpression significantly downregulated spastin expression and abolished the spastin-mediated microtubule severing. Furthermore, overexpression inhibited while genetic knockdown of Rab3A promoted neurite outgrowth. However, this inhibitory effect on neurite outgrowth in hippocampal neurons could be reversed via co-transfection of spastin, indicating that Rab3A functions via its interaction protein spastin. In general, our data identify an interaction between Rab3A and spastin, and this interaction affects the protein stability of spastin and eliminates its microtubule severing function, thereby modulating neurite outgrowth.

Contribution of the dihydropyrimidinase-like proteins family in synaptic physiology and in neurodevelopmental disorders

The dihydropyrimidinase-like (DPYSL) proteins, also designated as the collapsin response mediators (CRMP) proteins, constitute a family of five cytosolic phosphoproteins abundantly expressed in the developing nervous system but down-regulated in the adult mouse brain. The DPYSL proteins were initially identified as effectors of semaphorin 3A (Sema3A) signaling and consequently involved in regulation of growth cone collapse in young developing neurons. To date, it has been established that DPYSL proteins mediate signals for numerous intracellular/extracellular pathways and play major roles in variety of cellular process including cell migration, neurite extension, axonal guidance, dendritic spine development and synaptic plasticity through their phosphorylation status. The roles of DPYSL proteins at early stages of brain development have been described in the past years, particularly for DPYSL2 and DPYSL5 proteins. The recent characterization of pathogenic genetic variants in DPYSL2 and in DPYSL5 human genes associated with intellectual disability and brain malformations, such as agenesis of the corpus callosum and cerebellar dysplasia, highlighted the pivotal role of these actors in the fundamental processes of brain formation and organization. In this review, we sought to establish a detailed update on the knowledge regarding the functions of DPYSL genes and proteins in brain and to highlight their involvement in synaptic processing in later stages of neurodevelopment, as well as their particular contribution in human neurodevelopmental disorders (NDDs), such as autism spectrum disorders (ASD) and intellectual disability (ID).

CRMP2 and CRMP4 are required for the formation of commissural tracts in the developing zebrafish forebrain

Axonal connections between the two sides of the brain are essential for processing sensorimotor functions, especially in animals with bilateral symmetry. The anterior commissure and post-optic commissure are two crucial axonal projections that develop early in the zebrafish central nervous system. In this study, we characterized the function of collapsin response mediator protein 2 (CRMP2) and CRMP4 in patterning the development of the anterior and post-optic commissures by analyzing morpholino-knockdown zebrafish morphants and CRISPR/Cas9-edited gene-knockout mutants. We observed a loss of commissural structures or a significant reduction in axon bundles connecting the two hemispheres, but the defects could be largely recovered by co-injecting CRMP2 or CRMP4 mRNA. Loss of both CRMP2 and CRMP4 function resulted in a synergistic increase in the number of commissural defects. To elucidate the mechanism by which CRMP2 and CRMP4 provide guidance cues for the development of the anterior and post-optic commissures, we included neuropilin 1a (Nrp1a) morphants and double morphants (CRMP2/Nrp1a and CRMP4/Nrp1a) for analysis. Our experimental results indicated that CRMP2 and CRMP4 might mediate their activities through the common semaphorin 3/Nrp1a signaling pathway. This article is protected by copyright. All rights reserved.

CRMP4 is required for the positioning and maturation of newly generated neurons in adult mouse hippocampus

Adult neurogenesis is a phenomenon in which neural stem cells differentiate and mature to generate new neurons in the adult brain. In mammals, the sites where adult neurogenesis occurs are limited to the subgranular zone (SGZ) of the hippocampal dentate gyrus and the subventricular zone. In the hippocampus, newly generated neurons migrate into the granule cell layer (GCL) and are integrated into neural circuits. Previous studies have revealed that CRMP4, a member of the CRMP family, is expressed in immature neurons in the hippocampal SGZ of the adult brain. However, the role of CRMP4 in adult neurogenesis is unknown. To study the role of CRMP4 in hippocampal adult neurogenesis, we compared adult neurogenesis between wild type and CRMP4-/- mice. In CRMP4-/- mice, the number of doublecortin (DCX)-positive cells was comparable to that in wild-type mice, and some DCX-positive cells were ectopically located in the granule cell layer, suggesting that CRMP4 is involved in the migration of adult neurogenesis. In addition, the number of calretinin-positive new neurons in the SGZ was significantly increased, whereas the number of EdU/NeuN-double positive neurons was decreased in CRMP4-/- mice, suggesting that CRMP4 plays an important role in neuronal maturation. Because CRMP4 is expressed in immature neurons, its expression may regulate the migration from the SGZ to the GCL during neuronal maturation in hippocampal adult neurogenesis.

Effect of Muscle Extract and Graphene Oxide on Muscle Structure of Chicken Embryos

Simple Summary

Genetic selection of broilers increased muscle growth; however, very fast growth can lead to pathological conditions caused by the deficiency of nutrients. The number of muscle cells is mainly formed during the embryonic period, and consequently, in ovo supplementation of proteins to embryos may impact future muscle structure. We hypothesized that proteins from chicken embryo muscle extract (CEME) caused by the unique, natural composition and biocompatibility can supply additional proteins. However, supplemented proteins are actively metabolized, which may reduce their utilization for improved muscle synthesis. Nevertheless, CEME can be transported and protected by graphene oxide (GO). The objective of the present work was to investigate the effects of in ovo-injected CEME and the complex of GO-CEME on embryonic cell cultures and the growth of chicken embryo hind limb muscle. Toxicity and cell proliferation were measured in vitro with cell cultures and mortality, morphology, histology, and blood biochemistry in vivo with embryos. CEME increased the number of cells and nuclei in muscle, but the complex GO-CEME did not further improve the muscle structure. The results indicate a vital role of CEME as in ovo enhancer of muscle development in broilers.

Abstract

The effects of CEME and it complex with GO injected in ovo on the growth and development of chicken embryo hindlimb muscle were investigated. First, the preliminary in vitro study on primary muscle precursor cell culture obtained from a nine-day-old chicken embryo was performed to assess toxicity (MTT assay) of CEME, GO (100 ppm) and it complex with different concentrations (1, 2, 5, and 10 wt.%). The effect on cell proliferation was investigated by BrdU assay. CEME at concentrations 1–5% increased cell proliferation, but not the complex with GO. In vitro cytotoxicity was highest in 10% and GO groups. Next, the main experiment with chicken embryos was performed with CEME, GO and it complex injected in ovo on day one of embryogenesis. On day 20 of embryogenesis survival, morphological development, histological structure of the muscle, and biochemical parameters of blood serum of the embryos were measured. No negative effect on mortality, body weight, or biochemistry of blood after use of CEME or GO-CEME complexes was observed. Interestingly, the slight toxicity of GO, observed in in vitro studies, was not observed in vivo. The use of CEME at the levels of 2% and 5% improved the structure of the lower limb muscle by increasing the number of cells, and the administration of 2% CEME increased the number of nuclei visible in the stained cross-section of the muscle. The complex GO-CEME did not further improve the muscle structure. The results indicate that CEME can be applied as an in ovo enhancer of muscle development in broilers.

CRMP4-mediated fornix development involves Semaphorin-3E signaling pathway

Neurodevelopmental axonal pathfinding plays a central role in correct brain wiring and subsequent cognitive abilities. Within the growth cone, various intracellular effectors transduce axonal guidance signals by remodeling the cytoskeleton. Semaphorin-3E (Sema3E) is a guidance cue implicated in development of the fornix, a neuronal tract connecting the hippocampus to the hypothalamus. Microtubule-associated protein 6 (MAP6) has been shown to be involved in the Sema3E growth-promoting signaling pathway. In this study, we identified the collapsin response mediator protein 4 (CRMP4) as a MAP6 partner and a crucial effector in Sema3E growth-promoting activity. CRMP4-KO mice displayed abnormal fornix development reminiscent of that observed in Sema3E-KO mice. CRMP4 was shown to interact with the Sema3E tripartite receptor complex within detergent-resistant membrane (DRM) domains, and DRM domain integrity was required to transduce Sema3E signaling through the Akt/GSK3 pathway. Finally, we showed that the cytoskeleton-binding domain of CRMP4 is required for Sema3E's growth-promoting activity, suggesting that CRMP4 plays a role at the interface between Sema3E receptors, located in DRM domains, and the cytoskeleton network. As the fornix is affected in many psychiatric diseases, such as schizophrenia, our results provide new insights to better understand the neurodevelopmental components of these diseases.

Beyond Neuronal Microtubule Stabilization: MAP6 and CRMPS, Two Converging Stories

The development and function of the central nervous system rely on the microtubule (MT) and actin cytoskeletons and their respective effectors. Although the structural role of the cytoskeleton has long been acknowledged in neuronal morphology and activity, it was recently recognized to play the role of a signaling platform. Following this recognition, research into Microtubule Associated Proteins (MAPs) diversified. Indeed, historically, structural MAPs—including MAP1B, MAP2, Tau, and MAP6 (also known as STOP);—were identified and described as MT-binding and -stabilizing proteins. Extensive data obtained over the last 20 years indicated that these structural MAPs could also contribute to a variety of other molecular roles. Among multi-role MAPs, MAP6 provides a striking example illustrating the diverse molecular and cellular properties of MAPs and showing how their functional versatility contributes to the central nervous system. In this review, in addition to MAP6’s effect on microtubules, we describe its impact on the actin cytoskeleton, on neuroreceptor homeostasis, and its involvement in signaling pathways governing neuron development and maturation. We also discuss its roles in synaptic plasticity, brain connectivity, and cognitive abilities, as well as the potential relationships between the integrated brain functions of MAP6 and its molecular activities. In parallel, the Collapsin Response Mediator Proteins (CRMPs) are presented as examples of how other proteins, not initially identified as MAPs, fall into the broader MAP family. These proteins bind MTs as well as exhibiting molecular and cellular properties very similar to MAP6. Finally, we briefly summarize the multiple similarities between other classical structural MAPs and MAP6 or CRMPs.In summary, this review revisits the molecular properties and the cellular and neuronal roles of the classical MAPs, broadening our definition of what constitutes a MAP.

Dysregulated CRMP Mediates Circadian Deficits in a Drosophila Model of Fragile X Syndrome

Fragile X syndrome (FXS) is the leading inherited cause of intellectual disability, resulting from the lack of functional fragile X mental retardation protein (FMRP), an mRNA binding protein mainly serving as a translational regulator. Loss of FMRP leads to dysregulation of target mRNAs. The Drosophila model of FXS show an abnormal circadian rhythm with disruption of the output pathway downstream of the clock network. Yet the FMRP targets involved in circadian regulation have not been identified. Here, we identified collapsing response mediator protein (CRMP) mRNA as a target of FMRP. Knockdown of pan-neuronal CRMP expression ameliorated the circadian defects and abnormal axonal structures of clock neurons (ventral lateral neurons) in dfmr1 mutant flies. Furthermore, specific reduction of CRMP in the downstream output insulin-producing cells attenuated the aberrant circadian behaviors. Molecular analyses revealed that FMRP binds with CRMP mRNA and negatively regulates its translation. Our results indicate that CRMP is an FMRP target and establish an essential role for CRMP in the circadian output in FXS Drosophila.

Inhibition of RhoA Activity Does Not Rescue Synaptic Development Abnormalities and Long-Term Cognitive Impairment After Sevoflurane Exposure

General anesthetics interfere with dendritic development and synaptogenesis, resulting in cognitive impairment in the developing animals. RhoA signal pathway plays important roles in dendritic development by regulating cytoskeleton protein such as tubulin and actin. However, it's not clear whether RhoA pathway is involved in inhaled general anesthetics sevoflurane-induced synaptic development abnormalities and long-term cognitive dysfunction. Rats at postnatal day 7 (PND7) were injected intraperitoneally with RhoA pathway inhibitor Y27632 or saline 20 min before exposed to 2.8% sevoflurane for 4 h. The apoptosis-related proteins and RhoA/CRMP2 pathway proteins in the hippocampus were measured 6 h after sevoflurane exposure. Cognitive functions were evaluated by the open field test on PND25 rats and contextual fear conditioning test on PND32-33 rats. The dendritic morphology and density of dendritic spines in the pyramidal neurons of hippocampus were determined by Golgi staining and the synaptic plasticity-related proteins were also measured on PND33 rats. Long term potentiation (LTP) from hippocampal slices was recorded on PND34-37 rats. Sevoflurane induced caspase-3 activation, decreased the ratio of Bcl-2/Bax and increased TUNEL-positive neurons in hippocampus of PND7 rats, which were attenuated by inhibition of RhoA. However, sevoflurane had no significant effects on activity of RhoA/CRMP2 pathway. Sevoflurane disturbed dendritic morphogenesis, reduced the number of dendritic spines, decreased proteins expression of PSD-95, drebrin and synaptophysin, inhibited LTP in hippocampal slices and impaired memory ability in the adolescent rats, while inhibition of RhoA activity did not rescue the changes above induced by sevoflurane. RhoA signal pathway did not participate in sevoflurane-induced dendritic and synaptic development abnormalities and cognitive dysfunction in developing rats.

Somatostatin Ameliorates β-Amyloid-Induced Cytotoxicity via the Regulation of CRMP2 Phosphorylation and Calcium Homeostasis in SH-SY5Y Cells

Somatostatin is involved in the regulation of multiple signaling pathways and affords neuroprotection in response to neurotoxins. In the present study, we investigated the role of Somatostatin-14 (SST) in cell viability and the regulation of phosphorylation of Collapsin Response Mediator Protein 2 (CRMP2) (Ser522) via the blockade of Ca²⁺ accumulation, along with the inhibition of cyclin-dependent kinase 5 (CDK5) and Calpain activation in differentiated SH-SY5Y cells. Cell Viability and Caspase 3/7 assays suggest that the presence of SST ameliorates mitochondrial stability and cell survival pathways while augmenting pro-apoptotic pathways activated by Aβ. SST inhibits the phosphorylation of CRMP2 at Ser522 site, which is primarily activated by CDK5. Furthermore, SST effectively regulates Ca²⁺ influx in the presence of Aβ, directly affecting the activity of calpain in differentiated SH-SY5Y cells. We also demonstrated that SSTR2 mediates the protective effects of SST. In conclusion, our results highlight the regulatory role of SST in intracellular Ca²⁺ homeostasis. The neuroprotective role of SST via axonal regeneration and synaptic integrity is corroborated by regulating changes in CRMP2; however, SST-mediated changes in the blockade of Ca²⁺ influx, calpain expression, and toxicity did not correlate with CDK5 expression and p35/25 accumulation. To summarize, our findings suggest two independent mechanisms by which SST mediates neuroprotection and confirms the therapeutic implications of SST in AD as well as in other neurodegenerative diseases where the effective regulation of calcium homeostasis is required for a better prognosis.

p39-associated Cdk5 activity regulates dendritic morphogenesis

Dendrites, branched structures extending from neuronal cell soma, are specialized for processing information from other neurons. The morphogenesis of dendritic structures is spatiotemporally regulated by well-orchestrated signaling cascades. Dysregulation of these processes impacts the wiring of neuronal circuit and efficacy of neurotransmission, which contribute to the pathogeneses of neurological disorders. While Cdk5 (cyclin-dependent kinase 5) plays a critical role in neuronal dendritic development, its underlying molecular control is not fully understood. In this study, we show that p39, one of the two neuronal Cdk5 activators, is a key regulator of dendritic morphogenesis. Pyramidal neurons deficient in p39 exhibit aberrant dendritic morphology characterized by shorter length and reduced arborization, which is comparable to dendrites in Cdk5-deficient neurons. RNA sequencing analysis shows that the adaptor protein, WDFY1 (WD repeat and FYVE domain-containing 1), acts downstream of Cdk5/p39 to regulate dendritic morphogenesis. While WDFY1 is elevated in p39-deficient neurons, suppressing its expression rescues the impaired dendritic arborization. Further phosphoproteomic analysis suggests that Cdk5/p39 mediates dendritic morphogenesis by modulating various downstream signaling pathways, including PI3K/Akt-, cAMP-, or small GTPase-mediated signaling transduction pathways, thereby regulating cytoskeletal organization, protein synthesis, and protein trafficking.

The lncRNA MALAT1/miR-30/Spastin Axis Regulates Hippocampal Neurite Outgrowth

Spastin, a microtubule-severing enzyme, is important for neurite outgrowth. However, the mechanisms underlying the post-transcriptional regulation of spastin during microtubule-related processes are largely unknown. We demonstrated that the spastin expression level is controlled by a long non-coding RNA (lncRNA) metastasis-associated lung adenocarcinoma transcript 1 (MALAT1)/microRNA-30 (miR-30) axis during neurite outgrowth. The miR-30 expression level decreased in hippocampal neurons with increasing days in culture, and miR-30 overexpression suppressed while miR-30 inhibition promoted neurite outgrowth in hippocampal neurons. Spastin was validated as a target gene of miR-30 using the luciferase reporter assay. The protein expression, microtubule severing activity, and neurite promoting effect of spastin were suppressed by the overexpression of miR-30 mimics and increased by miR-30 inhibitors. MALAT1 expression increased during neurite outgrowth and MALAT1 silencing impaired neurite outgrowth. miR-30 was a sponge target of MALAT1 and MALAT1/miR-30 altered neurite outgrowth in hippocampal neurons. MALAT1 overexpression reversed the inhibitory effect of miR-30 on the activity of a luciferase reporter construct containing spastin, as well as spastin mRNA and protein expression, indicating that spastin was a downstream effector of MALAT1/miR-30. The MALAT1/miR-30 cascade also modulated spastin-induced microtubule severing, and the MALAT1/miR-30/spastin axis regulated neurite outgrowth in hippocampal neurons. This study suggests a new mechanism governing neurite outgrowth in hippocampal neurons involving MALAT1/miR-30-regulated spastin expression.

Loss of Collapsin Response Mediator Protein 4 Attenuates 6-Hydroxydopamine-Induced Impairments in a Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is a chronic neurodegenerative disorder characterized by impaired motor symptoms induced by the degeneration of dopaminergic neurons of the substantia nigra pars compacta (SNc). Many factors are speculated to operate in the mechanism of PD, including oxidative stress, mitochondrial dysfunction, abnormal protein handling, and PD induced apoptosis. Besides, researchers have recently shown that inflammatory secretions may engage neighboring cells such as astrocytes, which then induce autocrine and paracrine responses that amplify the inflammation, leading to neurodegeneration. In the present study, we analyzed the neuroprotective and anti-inflammatory effects of collapsin response mediator protein 4 (CRMP4) deletion in 6-hydroxydopamine (6-OHDA)-injected male mice, as well as its effects on motor impairments. Our findings indicated that the deletion of CRMP4 could maintain the TH-positive fibers in the striatum and the TH-positive cells in SNc, attenuate the inflammatory responses, and improve motor coordination and rotational behavior. Furthermore, based on our findings at the early time points, we hypothesized that primary differences between the Crmp4+/+ and Crmp4-/- mice may occur in microglia instead of neurons. Although further work should be carried out to clarify the specific role of CRMP4 in the pathogenesis of PD, our findings suggest that it could be a possible target for the treatment of PD.

Collapsin Response Mediator Protein 2 and Endophilin2 Coordinate Regulation of AMPA Receptor GluA1 Subunit Recycling

The dynamic trafficking of AMPA receptors (AMPARs), which enables the endocytosis, recycling, and exocytosis of AMPARs, is crucial for synaptic plasticity. Endophilin2, which directly interacts with the GluA1 subunit of AMPARs, plays an important role in AMPAR endocytosis. Collapsin response mediator protein 2 (CRMP2) promotes the maturation of the dendritic spine and can transfer AMPARs to the membrane. Although the mechanisms of AMPAR endocytosis and exocytosis are well known, the exact molecular mechanisms underlying AMPAR recycling remain unclear. Here, we report a unique interaction between CRMP2 and endophilin2. Our results showed that overexpression of CRMP2 and endophilin2 increased the amplitude and frequency of miniature excitatory synaptic currents (mEPSCs) and modestly enhanced AMPAR levels in hippocampal neurons. Furthermore, the CRMP2 and endophilin2 overexpression phenotype failed to occur when the interaction between these two proteins was inhibited. Further analysis revealed that this interaction was regulated by CRMP2 phosphorylation. The phosphorylation of CRMP2 inhibited its interaction with endophilin2; this was mainly affected by the phosphorylation of Thr514 and Ser518 by glycogen synthase kinase (GSK) 3β. CRMP2 phosphorylation increased degradation and inhibited the surface expression of AMPAR GluA1 subunits in cultured hippocampal neurons. However, the dephosphorylation of CRMP2 inhibited degradation and promoted the surface expression of AMPAR GluA1 subunits in cultured hippocampal neurons. Taken together, our data demonstrated that the interaction between CRMP2 and endophilin2 was conductive to the recycling of AMPA receptor GluA1 subunits in hippocampal neurons.

Dihydropyrimidinase-related protein 5 controls glioblastoma stem cell characteristics as a biomarker of proneural-subtype glioblastoma stem cells

Glioblastoma (GBM) is the most aggressive and malignant brain tumor, resulting in a poor prognosis. The current therapy for GBM consists in concurrent radiation and chemotherapy following removal of the tumor. Although the therapy prolongs patient survival, recurrence often occurs. The major cause of tumor recurrence is thought to be GBM stem cells (GSCs), which aid the development of chemo-radiotherapy resistance, and can self-renew and aberrantly differentiate. Therefore, GSCs should be targeted to eradicate the tumor and prevent recurrence. Transcriptomic analysis has categorized GBM into proneural (PN), mesenchymal and classical subtypes, and the outcome of recurrence and prognosis markedly depends on subtype. To identify specific GSC markers, the present study analyzed public microarray and RNA-seq data and identified dihydropyrimidinase-related protein 5 (DRP5) as a candidate GSC marker. DRP5 is known to mediate semaphorin 3A signaling and is involved in the regulation of neurite outgrowth and axon guidance during neuronal development. In the present study, DRP5 was specifically upregulated in the PN-subtype GSCs and served crucial roles in maintaining GSC properties, including tumor sphere formation, stem cell marker expression and xenograft tumor growth. Furthermore, bioinformatics analysis revealed that DRP5 expression was positively correlated with signatures of stemness, including Notch, Hedgehog and Wnt/β-catenin expression, which are also known to be positively correlated with PN-subtype gene signatures. Conversely, DRP5 expression was negatively correlated with NF-κB and signal transducer and activator of transcription 3 stemness signatures, which are negatively correlated with PN-subtype gene signatures. Taken together, these findings suggested that DRP5 was specifically expressed in PN-subtype GSCs and may be used as a functional marker of PN-subtype GSCs.

Genome-Wide Analysis Identifies NURR1-Controlled Network of New Synapse Formation and Cell Cycle Arrest in Human Neural Stem Cells

Nuclear receptor-related 1 (Nurr1) protein has been identified as an obligatory transcription factor in midbrain dopaminergic neurogenesis, but the global set of human NURR1 target genes remains unexplored. Here, we identified direct gene targets of NURR1 by analyzing genome-wide differential expression of NURR1 together with NURR1 consensus sites in three human neural stem cell (hNSC) lines. Microarray data were validated by quantitative PCR in hNSCs and mouse embryonic brains and through comparison to published human data, including genome-wide association study hits and the BioGPS gene expression atlas. Our analysis identified ~40 NURR1 direct target genes, many of them involved in essential protein modules such as synapse formation, neuronal cell migration during brain development, and cell cycle progression and DNA replication. Specifically, expression of genes related to synapse formation and neuronal cell migration correlated tightly with NURR1 expression, whereas cell cycle progression correlated negatively with it, precisely recapitulating midbrain dopaminergic development. Overall, this systematic examination of NURR1-controlled regulatory networks provides important insights into this protein's biological functions in dopamine-based neurogenesis.

Low Incidence of High-Grade Pancreatic Intraepithelial Neoplasia Lesions in a Crmp4 Gene-Deficient Mouse Model of Pancreatic Cancer

Pancreatic intraepithelial neoplasia (PanIN), the most common premalignant lesion of the pancreas, is a histologically well-defined precursor to invasive pancreatic ductal adenocarcinoma (PDAC). However, the molecular mechanisms underlying the progression of PanINs have not been fully elucidated. Previously, we demonstrated that the expression of collapsin response mediator protein 4 (CRMP4) in PDAC was associated with poor prognosis. The expression of CRMP4 was also augmented in a pancreatitis mouse model. However, the role of CRMP4 in the progression of PanIN lesions remains uncertain. In the present study, we examined the relationship between CRMP4 expression and progression of PanIN lesions using genetically engineered mouse models. PanIN lesions were induced by peritoneal injection of the cholecystokinin analog caerulein in LSL-KRAS^G12D; Pdx1-Cre (KC-Crmp4 wild-type, WT) mice and LSL-KRAS^G12D; Pdx1-Cre; Crmp4^−/− (KC-Crmp4 knockout, KO) mice. We analyzed pancreatic tissue sections from these mice and evaluated PanIN grade by hematoxylin and eosin staining. CRMP4 expression was examined and the cellular components assessed by immunohistochemistry using antibodies against CRMP4, CD3, and α-smooth muscle actin (SMA). The incidence of high-grade PanIN in KC-Crmp4 WT mice was higher than that in KC-Crmp4 KO animals. CRMP4 was expressed not only in epithelial cells but also in αSMA-positive cells in stromal areas of PanIN lesions. The CRMP4 expression in stromal areas correlated with PanIN grade in WT mice. These results suggested that the expression of CRMP4 in stromal cells may underlie the incidence or progression of PanIN.

Fluoxetine exposure for more than 2 days decreases the neuronal plasticity mediated by CRMP2 in differentiated PC12 cells

BACKGROUND

Recent studies indicate that antidepressants treatment restores neuronal plasticity. In contrast, some researchers claim that serotonergic antidepressants, including fluoxetine (FLU), may exacerbate neuronal plasticity, which is contradictory and rarely studied. Since almost those studies exposed cells with drugs for 1-2 days as treatment models of antidepressants, it is possible that FLU exposure for longer periods would have opposite effects on neuronal plasticity.

RESULTS

In the present study, we examined the effects of FLU exposure (up to 3 days) on the neuronal plasticity in differentiated PC12 cells. The cell viability shown a slight decrease at day 2 (93.5 ± 3.5 %), followed by a highly significant decrease at day 3(71.4 ± 4.4 %). As previously reported, neuronal plasticity was significantly upregulated by FLU exposure at day 1. However, the neurite length, activity-regulated cytoskeleton-associated protein (Arc) and c-Fos mRNA were inhibited with FLU exposure at day 3. Similarly, the expression of tubulin, which play important roles in the neuronal plasticity, was the same result. Furthermore, we found α-tubulin interacted with collapsing response mediator protein 2(CRMP2), which is related to neuronal plasticity, and the regulation of CRMP2 activity influenced the neurite length, Arc, c-Fos and tubulin expression.

CONCLUSIONS

The results demonstrated that neuronal plasticity was increased by FLU exposure at day 1, but exposure with FLU for more than 2 days had opposite effect on it. The reduction in neuronal plasticity with FLU exposure for more than 2 days might be involved in some aspects of the therapeutic effect of antidepressant on depression.

Collapsin Response Mediator Protein 4 (CRMP4) Facilitates Wallerian Degeneration and Axon Regeneration following Sciatic Nerve Injury

In contrast to neurons in the CNS, damaged neurons from the peripheral nervous system (PNS) regenerate, but this process can be slow and imperfect. Successful regeneration is orchestrated by cytoskeletal reorganization at the tip of the proximal axon segment and cytoskeletal disassembly of the distal segment. Collapsin response mediator protein 4 (CRMP4) is a cytosolic phospho-protein that regulates the actin and microtubule cytoskeleton. During development, CRMP4 promotes growth cone formation and dendrite development. Paradoxically, in the adult CNS, CRMP4 impedes axon regeneration. Here, we investigated the involvement of CRMP4 in peripheral nerve injury in male and female Crmp4^−/− mice following sciatic nerve injury. We find that sensory axon regeneration and Wallerian degeneration are impaired in Crmp4^−/− mice following sciatic nerve injury. In vitro analysis of dissociated dorsal root ganglion (DRG) neurons from Crmp4^−/− mice revealed that CRMP4 functions in the proximal axon segment to promote the regrowth of severed DRG neurons and in the distal axon segment where it facilitates Wallerian degeneration through calpain-dependent formation of harmful CRMP4 fragments. These findings reveal an interesting dual role for CRMP4 in proximal and distal axon segments of injured sensory neurons that coordinately facilitate PNS axon regeneration.

Collapsin Response Mediator Proteins: Novel Targets for Alzheimer's Disease

Numerous experimental and postmortem studies have increasingly reported dystrophic axons and dendrites, and alterations of dendritic spine morphology and density in the hippocampus as prominent changes in the early stages of Alzheimer's disease (AD). Furthermore, these alterations tend to correlate well with the progressive cognitive decline observed in AD. For these reasons, and because these neurite structures have a capacity to re-grow, re-establish lost connections, and are critical for learning and memory, there is compelling evidence to suggest that therapeutic interventions aimed at preventing their degradation or promoting their regrowth may hold tremendous promise in preventing the progression of AD. In this regard, collapsin response mediator proteins (CRMPs), a family of phosphoproteins playing a major role in axon guidance and dendritic growth, are especially interesting. The roles these proteins play in neurons and immune cells are reviewed here.

The oligodendrocyte growth cone and its actin cytoskeleton: A fundamental element for progenitor cell migration and CNS myelination

Cells of the oligodendrocyte (OLG) lineage engage in highly motile behaviors that are crucial for effective central nervous system (CNS) myelination. These behaviors include the guided migration of OLG progenitor cells (OPCs), the surveying of local environments by cellular processes extending from differentiating and pre-myelinating OLGs, and during the process of active myelin wrapping, the forward movement of the leading edge of the myelin sheath's inner tongue along the axon. Almost all of these motile behaviors are driven by actin cytoskeletal dynamics initiated within a lamellipodial structure that is located at the tip of cellular OLG/OPC processes and is structurally as well as functionally similar to the neuronal growth cone. Accordingly, coordinated stoichiometries of actin filament (F-actin) assembly and disassembly at these OLG/OPC growth cones have been implicated in directing process outgrowth and guidance, and the initiation of myelination. Nonetheless, the functional importance of the OLG/OPC growth cone still remains to be fully understood, and, as a unique aspect of actin cytoskeletal dynamics, F-actin depolymerization and disassembly start to predominate at the transition from myelination initiation to myelin wrapping. This review provides an overview of the current knowledge about OLG/OPC growth cones, and it proposes a model in which actin cytoskeletal dynamics in OLG/OPC growth cones are a main driver for morphological transformations and motile behaviors. Remarkably, these activities, at least at the later stages of OLG maturation, may be regulated independently from the transcriptional gene expression changes typically associated with CNS myelination.

Dysregulation of CRMP2 Post-Translational Modifications Drive Its Pathological Functions

Collapsin response mediator proteins (CRMPs) are a family of ubiquitously expressed, homologous phosphoproteins best known for coordinating cytoskeletal formation and regulating cellular division, migration, polarity, and synaptic connection. CRMP2, the most studied of the five family members, is best known for its affinity for tubulin heterodimers and function in regulating the microtubule network. These functions are tightly regulated by post-translational modifications including phosphorylation, SUMOylation, oxidation, and O-GlcNAcylation. While CRMP2's physiological functions rely mostly on its non-phosphorylated state, dysregulation of CRMP2 phosphorylation and SUMOylation has been reported to be involved in the pathophysiology of multiple diseases including cancer, chronic pain, spinal cord injury, neurofibromatosis type 1, and others. Here, we provide a consolidated update on what is known about CRMP2 signaling and function, first focusing on axonal growth and neuronal polarity, then illustrating the link between dysregulated CRMP2 post-translational modifications and diseases. We additionally discuss the roles of CRMP2 in non-neuronal cells, both in the CNS and regions of the periphery. Finally, we offer thoughts on the therapeutic implications of modulating CRMP2 function in a variety of diseases.

Both GSK-3β/CRMP2 and CDK5/CRMP2 pathways participate in the protection of dexmedetomidine against propofol-induced learning and memory impairment in neonatal rats

Dexmedetomidine has been reported to ameliorate propofol-induced neurotoxicity in neonatal animals. However, the underlying mechanism is still undetermined. Glycogen synthase kinase-3β (GSK-3β), cycline dependent kinase-5 (CDK5) and Rho-kinase (RhoA) pathways play critical roles in neuronal development. The present study is to investigate whether GSK-3β, CDK5 and RhoA pathways are involved in the neuroprotection of dexmedetomidine. Seven-day-old (P7) Sprague-Dawley rats were anesthetized with propofol for 6 h. Dexmedetomidine at various concentrations were administered before propofol exposure. Neuroapoptosis, the neuronal proliferation and the level of neurotransmitter in the hippocampus were evaluated. The effects of GSK-3β inhibitor SB415286, CDK5 inhibitor roscovitine or RhoA inhibitor Y276321 on propofol-induced neurotoxicity were assessed. Propofol induced apoptosis in the hippocampal neurons and astrocytes, inhibited neuronal proliferation in the DG region, down-regulated the level of γ-aminobutyric acid (GABA) and glutamate in the hippocampus, and impaired long-term cognitive function. These harmful effects were reduced by pretreatment with 50 μg·kg-1 dexmedetomidine. Moreover, propofol activated GSK-3β and CDK5 pathways, but not RhoA pathway, by reducing the phosphorylation of GSK-3β (ser 9), increasing the expression of CDK5 activator P25 and increasing the phosphorylation of their target sites on CRMP2 shortly after exposure. These effects were reversed by pretreatment with 50 μg·kg-1 dexmedetomidine. Furthermore, SB415286 and roscovitine, not Y276321, attenuated the propofol-induced neuroapoptosis, brain cell proliferation inhibition, GABA and glutamate downregulation, and learning and memory dysfunction. Our results indicate that dexmedetomidine reduces propofol-induced neurotoxicity and neurocognitive impairment via inhibiting activation of GSK-3β/CRMP2 and CDK5/CRMP2 pathways in the hippocampus of neonatal rats.

Crmp4-KO Mice as an Animal Model for Investigating Certain Phenotypes of Autism Spectrum Disorders

Previous research has demonstrated that the collapsin response mediator protein (CRMP) family is involved in the formation of neural networks. A recent whole-exome sequencing study identified a de novo variant (S541Y) of collapsin response mediator protein 4 (CRMP4) in a male patient with autism spectrum disorder (ASD). In addition, Crmp4-knockout (KO) mice show some phenotypes similar to those observed in human patients with ASD. For example, compared with wild-type mice, Crmp4-KO mice exhibit impaired social interaction, abnormal sensory sensitivities, broader distribution of activated (c-Fos expressing) neurons, altered dendritic formation, and aberrant patterns of neural gene expressions, most of which have sex differences. This review summarizes current knowledge regarding the role of CRMP4 during brain development and discusses the possible contribution of CRMP4 deficiencies or abnormalities to the pathogenesis of ASD. Crmp4-KO mice represent an appropriate animal model for investigating the mechanisms underlying some ASD phenotypes, such as impaired social behavior, abnormal sensory sensitivities, and sex-based differences, and other neurodevelopmental disorders associated with sensory processing disorders.

Genetic inhibition of CRMP2 phosphorylation at serine 522 promotes axonal regeneration after optic nerve injury

Axonal degeneration occurs in various neurological diseases and traumatic nerve injury, and axonal regeneration is restricted by inhibitory factors in the central nervous system. Cyclin-dependent kinase 5 and glycogen synthase kinase 3β (GSK3β) are activated by one of those inhibitors, and collapsin response mediator protein 2 (CRMP2) is phosphorylated by both kinases. We previously developed a CRMP2 knock-in (CRMP2 KI) mouse line, in which CRMP2 phosphorylation at Ser 522 is inhibited. Because CRMP2 KI mice showed promotion of axonal regeneration after spinal cord injury, we hypothesized that CRMP2 KI mice would show higher axonal regeneration after optic nerve injury. In this study, we first show that depolymerization of microtubules after optic nerve crush (ONC) injury was suppressed in CRMP2 KI mice. Loss of retinal ganglia cells was also reduced after ONC. We found that protein level of GAP43, a marker of regenerative axons, was higher in the optic nerve from CRMP2KI than that from wild type 4 weeks after of ONC. We further observed increased numbers of axons labeled by tracer in the optic nerve after ONC in CRMP2 KI mice. These results suggest that inhibition of phosphorylation of CRMP2 suppresses axonal degeneration and promotes axonal regeneration after optic nerve injury.

Protein tyrosine phosphatase 4A3 (PTP4A3/PRL-3) promotes the aggressiveness of human uveal melanoma through dephosphorylation of CRMP2

Uveal melanoma (UM) is an aggressive tumor in which approximately 50% of patients develop metastasis. Expression of the PTP4A3 gene, encoding a phosphatase, is predictive of poor patient survival. PTP4A3 expression in UM cells increases their migration in vitro and invasiveness in vivo. Here, we show that CRMP2 is mostly dephosphorylated on T514 in PTP4A3 expressing cells. We also demonstrate that inhibition of CRMP2 expression in UM cells expressing PTP4A3 increases their migration in vitro and invasiveness in vivo. This phenotype is accompanied by modifications of the actin microfilament network, with shortened filaments, whereas cells with a inactive mutant of the phosphatase do not show the same behavior. In addition, we showed that the cell cytoplasm becomes stiffer when CRMP2 is downregulated or PTP4A3 is expressed. Our results suggest that PTP4A3 acts upstream of CRMP2 in UM cells to enhance their migration and invasiveness and that a low level of CRMP2 in tumors is predictive of poor patient survival.

Molecular basis of the functions of the mammalian neuronal growth cone revealed using new methods

The neuronal growth cone is a highly motile, specialized structure for extending neuronal processes. This structure is essential for nerve growth, axon pathfinding, and accurate synaptogenesis. Growth cones are important not only during development but also for plasticity-dependent synaptogenesis and neuronal circuit rearrangement following neural injury in the mature brain. However, the molecular details of mammalian growth cone function are poorly understood. This review examines molecular findings on the function of the growth cone as a result of the introduction of novel methods such superresolution microscopy and (phospho)proteomics. These results increase the scope of our understating of the molecular mechanisms of growth cone behavior in the mammalian brain.

Dexmedetomidine Ameliorates the Neurotoxicity of Sevoflurane on the Immature Brain Through the BMP/SMAD Signaling Pathway

Numerous studies have demonstrated that general anesthetics might damage the nervous system, thus, the effect of general anesthetics on the developing brain has attracted much attention. Dexmedetomidine (Dex) exhibits a certain neuroprotective effect, but the mechanism is obscure. In our study, pregnant rats on gestational day 20 (G20) were exposed to 3% sevoflurane for 2 h or 4 h, and the neuronal apoptosis in hippocampal CA1 region of the offspring rats was detected by quantification of TUNEL positive cells and cleaved-caspase3 (cl-caspase3). Different doses of Dex were intraperitoneally injected before sevoflurane anesthesia; then, the expression of apoptotic-related proteins including BCL-2, BAX and cl-caspase3 as well as amyloid precursor protein (APP, a marker of axonal injury), p-CRMP-2 and CRMP-2 were measured at postnatal days 0, 1and 3 (P0, P1, and P3, respectively). As an antagonist of the bone morphgenetic proteins (BMP) receptor, DMH1 was co-administered with sevoflurane plus Dex to investigate whether BMP/SMAD is associated with the neuroprotective effects of Dex. The results showed that prenatal sevoflurane anesthesia for 4 h activated apoptosis transiently, as manifested by the caspase3 activity peaked on P1 and disappeared on P3. In addition, the expressions of APP and p-CRMP-2/CRMP-2 in postnatal rat hippocampus were significantly increased, which revealed that prenatal sevoflurane anesthesia caused axonal injury of offspring. The long-term learning and memory ability of offspring rats was also impaired after prenatal sevoflurane anesthesia. These damaging effects of sevoflurane could be mitigated by Dex and DMH1 reversed the neuroprotective effect of Dex. Our results indicated that prenatal exposure to 3% sevoflurane for 4 h increased apoptosis and axonal injury, even caused long-term learning and memory dysfunction in the offspring rats. Dex dose-dependently reduced sevoflurane- anesthesia-induced the neurotoxicity by activating the BMP/SMAD signaling pathway.

DPYSL3 modulates mitosis, migration, and epithelial-to-mesenchymal transition in claudin-low breast cancer

Mass spectrometry-based proteogenomics of patient-derived xenografts (PDXs) identified dihydropyrimidinase-like-3 (DPYSL3) as a multilevel (RNA/protein/phosphoprotein) expression outlier specific to a claudin-low (CLOW) PDX. DPYSL3 has established functions in neural cell migration and axon outgrowth but is understudied in breast cancer. Here, we demonstrate that loss of DPYSL3 promotes cell-cycle arrest, multinucleation, and collapse of the vimentin microfilament network associated with increased phospho-vimentin. DPYSL3 is also a negative regulator of p21-activated kinase (PAK) and suppresses epithelial-to-mesenchymal transition (EMT). In turn, EMT regulators induce DPYSL3, suggesting that DPYSL3 provides negative feedback on EMT. DPYSL3 therefore serves as a biomarker for CLOW tumors that exhibit PAK-dependent motility and EMT and is also susceptible to therapeutic approaches that promote vimentin phosphorylation during mitosis.

A Clinical Proteomic Tumor Analysis Consortium (CPTAC) proteogenomic analysis prioritized dihydropyrimidinase-like-3 (DPYSL3) as a multilevel (RNA/protein/phosphoprotein) expression outlier specific to the claudin-low (CLOW) subset of triple-negative breast cancers. A PubMed informatics tool indicated a paucity of data in the context of breast cancer, which further prioritized DPYSL3 for study. DPYSL3 knockdown in DPYSL3-positive (DPYSL3+) CLOW cell lines demonstrated reduced proliferation, yet enhanced motility and increased expression of epithelial-to-mesenchymal transition (EMT) markers, suggesting that DPYSL3 is a multifunctional signaling modulator. Slower proliferation in DPYSL3-negative (DPYSL3−) CLOW cells was associated with accumulation of multinucleated cells, indicating a mitotic defect that was associated with a collapse of the vimentin microfilament network and increased vimentin phosphorylation. DPYSL3 also suppressed the expression of EMT regulators SNAIL and TWIST and opposed p21 activated kinase 2 (PAK2)-dependent migration. However, these EMT regulators in turn induce DPYSL3 expression, suggesting that DPYSL3 participates in negative feedback on EMT. In conclusion, DPYSL3 expression identifies CLOW tumors that will be sensitive to approaches that promote vimentin phosphorylation during mitosis and inhibitors of PAK signaling during migration and EMT.

Spastin Interacts with CRMP5 to Promote Neurite Outgrowth by Controlling the Microtubule Dynamics

Changing the microtubule dynamics is sufficient to alter the axon and dendrite specification and development. Spastin participates in the growth and regeneration of neurites by severing microtubules into small segments, and collapsin response mediator protein 5 (CRMP5) provides structural support and serves as a track for cargo transport by promoting microtubule polymerization. Nevertheless, how spastin and CRMP5 cooperate to regulate neurite outgrowth by controlling the microtubule dynamics needs to be elucidated. In our present study, spastin interacted with CRMP5 in vitro and in vivo. The binding domains for the spastin and CRMP5 interaction were the N-terminal fragment of spastin (residues 270-328) and the C-terminal fragment of CRMP5 (residues 472-564). Spastin and its truncation mutants, including the microtubule-binding domain (MTBD) and ATPases associated with diverse cellular activities (AAA) domain, were necessary for the severing of microtubules. Furthermore, we demonstrated that microtubule polymerization of CRMP5 interfered with the microtubule-severing function of spastin. Knocking down either spastin or CRMP5 inhibited neurite outgrowth in hippocampal neurons. However, co-transfected spastin and CRMP5 promoted the outgrowth of neurites including dendrites and axons. Taken together, our data support a model in which the spastin interaction with CRMP5 promotes neurite outgrowth by controlling the microtubule dynamics.

CRMP2 and CRMP4 Are Differentially Required for Axon Guidance and Growth in Zebrafish Retinal Neurons

Axons are directed to their correct targets by guidance cues during neurodevelopment. Many axon guidance cues have been discovered; however, much less known is about how the growth cones transduce the extracellular guidance cues to intracellular responses. Collapsin response mediator proteins (CRMPs) are a family of intracellular proteins that have been found to mediate growth cone behavior in vitro; however, their roles in vivo in axon development are much less explored. In zebrafish embryos, we find that CRMP2 and CRMP4 are expressed in the retinal ganglion cell layer when retinal axons are crossing the midline. Knocking down CRMP2 causes reduced elongation and premature termination of the retinal axons, while knocking down CRMP4 results in ipsilateral misprojections of retinal axons that would normally project to the contralateral brain. Furthermore, CRMP4 synchronizes with neuropilin 1 in retinal axon guidance, suggesting that CRMP4 might mediate the semaphorin/neuropilin signaling pathway. These results demonstrate that CRMP2 and CRMP4 function differentially in axon development in vivo.

Probenecid Disrupts a Novel Pannexin 1-Collapsin Response Mediator Protein 2 Interaction and Increases Microtubule Stability

Neurite formation relies on finely-tuned control of the cytoskeleton. Here we identified a novel protein-protein interaction between the ion and metabolite channel protein Pannexin 1 (Panx1) and collapsin response mediator protein 2 (Crmp2), a positive regulator of microtubule polymerization and stabilization. Panx1 and Crmp2 co-precipitated from both Neuro-2a (N2a) cells and mouse ventricular zone (VZ) tissue. In vitro binding assays between purified proteins revealed the interaction occurs directly between the Panx1 C-terminus (Panx1 CT) and Crmp2. Because Crmp2 is a well-established microtubule-stabilizing protein, and we previously observed a marked increase in neurite formation following treatment with the Panx1 blocker, probenecid, in N2a cells and VZ neural precursor cells (NPCs), we investigated the impact of probenecid on the Panx1-Crmp2 interaction. Probenecid treatment significantly disrupted the Panx1-Crmp2 interaction by both immunoprecipitation (IP) and proximity ligation analysis, without altering overall Crmp2 protein expression levels. In the presence of probenecid, Crmp2 was concentrated at the distal ends of growing neurites. Moreover, probenecid treatment increased tubulin polymerization and microtubule stability in N2a cells. These results reveal that probenecid disrupts a novel interaction between Panx1 and the microtubule stabilizer, Crmp2, and also increases microtubule stability.

Phosphorylation and SUMOylation of CRMP2 regulate the formation and maturation of dendritic spines

The posttranslational modifications of CRMP2 play an important role in axon outgrowth, cell polarization and dendritic morphogenesis. However, whether CRMP2 and its posttranslational modifications are involved in dendritic spine development specifically is not completely clear. Here, we show that CRMP2 can promote the formation and maturation of dendritic spines in cultured hippocampal neurons. Overexpression of CRMP2 results in an increase in the density of spines especially the mushroom-shape spines. The amplitude and frequency of miniature excitatory postsynaptic currents (mEPSCs) are both enhanced and the intensity of PSD95 is strengthened in the neurons with CRMP2 overexpression. Furthermore, dephosphorylation of CRMP2 at Thr514 and deSUMOylation at Lys374 can further promote the formation and maturation of dendritic spines, whereas, no cross-talk is found between these two posttranslational modifications in the regulation of dendritic spine formation and maturation. Taken together, our data support a model in which phosphorylation and SUMOylation modification of CRMP2 independently promote the formation and maturation of dendritic spines and participate in the process of dendritic spine plasticity.

Human CRMP4 mutation and disrupted Crmp4 expression in mice are associated with ASD characteristics and sexual dimorphism

Autism spectrum disorders (ASD) are more common among boys than girls. The mechanisms responsible for ASD symptoms and their sex differences remain mostly unclear. We previously identified collapsin response mediator protein 4 (CRMP4) as a protein exhibiting sex-different expression during sexual differentiation of the hypothalamic sexually dimorphic nucleus. This study investigated the relationship between the sex-different development of autistic features and CRMP4 deficiency. Whole-exome sequencing detected a de novo variant (S541Y) of CRMP4 in a male ASD patient. The expression of mutated mouse CRMP4 S540Y, which is homologous to human CRMP4 S541Y, in cultured hippocampal neurons derived from Crmp4-knockout (KO) mice had increased dendritic branching, compared to those transfected with wild-type (WT) Crmp4, indicating that this mutation results in altered CRMP4 function in neurons. Crmp4-KO mice showed decreased social interaction and several alterations of sensory responses. Most of these changes were more severe in male Crmp4-KO mice than in females. The mRNA expression levels of some genes related to neurotransmission and cell adhesion were altered in the brain of Crmp4-KO mice, mostly in a gender-dependent manner. These results indicate a functional link between a case-specific, rare variant of one gene, Crmp4, and several characteristics of ASD, including sexual differences.

Endophilin2 Interacts with GluA1 to Mediate AMPA Receptor Endocytosis Induced by Oligomeric Amyloid-β

Amyloid-β (Aβ) plays an important role in Alzheimer's disease (AD), as oligomeric Aβ induces loss of postsynaptic AMPA receptors (AMPARs) leading to cognitive deficits. The loss of postsynaptic AMPARs is mediated through the clathrin-dependent endocytosis pathway, in which endophilin2 is one of the important regulatory proteins. Endophilin2, which is enriched in both the pre- and postsynaptic membrane, has previously been reported to be important for recycling of synaptic vesicles at the presynaptic membrane. However, the role of endophilin2 in oligomeric Aβ-induced postsynaptic AMPAR endocytosis is not well understood. In this study, we show that endophilin2 does not affect constitutive AMPAR endocytosis. Endophilin2 knockdown, but not overexpression, resisted oligomeric Aβ-induced AMPAR dysfunction. Moreover, endophilin2 colocalized and interacted with GluA1, a subunit of AMPAR, to regulate oligomeric Aβ-induced AMPAR endocytosis. Thus, we have determined a role of endophilin2 in oligomeric Aβ-induced postsynaptic AMPAR dysfunction, indicating possible directions for preventing the loss of AMPARs in cognitive impairment and providing evidence for the clinical treatment of AD.

Cyclin-dependent kinase 5/Collapsin response mediator protein 2 pathway may mediate sevoflurane-induced dendritic development abnormalities in rat cortical neurons

Sevoflurane has been reported to induce neurotoxicity and cognitive impairment in the developing brains. However, the underlying molecular mechanisms remain poorly understood. Recent studies have demonstrated aberrant cyclin-dependent kinase 5 (CDK5) activity is implicated in inhaled anesthetic-induced neurotoxicity. CDK5/CRMP2 signaling is involved in the cortical and hippocampal dendritic development. The aim of present study is to investigate whether the CDK5/CRMP2 pathway mediates sevoflurane-induced dendritic development abnormalities. Rat primary cortical neurons were treated with 4% sevoflurane for 6h, the CDK5 inhibitor roscovitine or the vehicle (0.3% DMSO) was administered 12h before sevoflurane or carrying gases exposure. Cortical neurons were harvested for further analysis 0h, 12h and 24h after exposure. Sevoflurane exposure for 6h did not reduce cell viability and slightly increased the expression of cleaved caspase-3. Sevoflurane induced abnormal CDK5 activation by increasing the expression of its activator p25 and promoted the phosphorylation of CRMP2 (Ser522). The increased phospho-CRMP2 (Ser522) was mainly distributed in the cytoplasm of cortical neurons. Sevoflurane significantly reduced the number of primary dendrites and the number of branching points; whereas it did not influence the total dendritic length. Suppression of CDK5 activation with roscovitine attenuated neuronal apoptosis, hyperphosphorylation of CRMP2 (Ser522) and dendritic development abnormalities induced by sevoflurane. Our results indicate that activation of the CDK5/CRMP2 pathway may mediate sevoflurane-induced dendritic development abnormalities in the cortical neurons. The physiological significance of these findings remains to be determined.

DRP5 is involved in cancer cell growth and predicts poor prognosis in human osteosarcoma

Osteosarcoma is an extremely aggressive primary malignant bone tumor of childhood. Collapsin response mediator proteins (CRMPs), which are highly expressed in the developing nervous system, were recently shown to be associated with cancer development. However, the relationship between DRP5 (CRMP5) and osteosarcoma has not been evaluated. In this study, we investigated the role of DRP5 in the regulation of osteosarcoma growth. DRP5 mRNA and protein levels were significantly upregulated in human osteosarcoma cell lines and associated with increased migration and invasion. Genetic knockdown of DRP5 markedly suppressed the expression of matrix metalloproteinase (MMP)‐2 and MMP‐9. DRP5 silencing significantly inhibited osteosarcoma cell growth in vitro and in a xenograft mouse model in vivo. Microarray immunohistochemical analysis of osteosarcoma specimens and Kaplan–Meier analysis showed that patients with high DRP5 protein expression had shorter overall survival than those with low DRP5 levels. Taken together, these results suggest that DRP5 plays a critical role in the regulation of osteosarcoma and could be a potential therapeutic target and prognostic factor in osteosarcoma.

Microtubule-regulating proteins and cAMP-dependent signaling in neuroblastoma differentiation

Neurons are highly differentiated cells responsible for the conduction and transmission of information in the nervous system. The proper function of a neuron relies on the compartmentalization of their intracellular domains. Differentiated neuroblastoma cells have been extensively used to study and understand the physiology and cell biology of neuronal cells. Here, we show that differentiation of N1E-115 neuroblastoma cells is more pronounced upon exposure of a chemical analog of cyclic AMP (cAMP), db-cAMP. We next analysed the expression of key microtubule-regulating proteins in differentiated cells and the expression and activation of key cAMP players such as EPAC, PKA and AKAP79/150. Most of the microtubule-promoting factors were up regulated during differentiation of N1E-115 cells, while microtubule-destabilizing proteins were down regulated. We observed an increase in tubulin post-translational modifications related to microtubule stability. As expected, db-cAMP increased PKA- and EPAC-dependent signalling. Consistently, pharmacological modulation of EPAC activity instructed cell differentiation, number of neurites, and neurite length in N1E-115 cells. Moreover, disruption of the PKA-AKAP interaction reduced these morphometric parameters. Interestingly, PKA and EPAC act synergistically to induce neuronal differentiation in N1E-115. Altogether these results show that the changes observed in the differentiation of N1E-115 cells proceed by regulating several microtubule-stabilizing factors, and the acquisition of a neuronal phenotype is a process involving concerted although independent functions of EPAC and PKA.

Understanding the pathophysiology of schizophrenia: Contributions from the Melbourne Psychiatric Brain Bank

The Melbourne Psychiatric Brain Bank came into existence 25years ago. This review focusses on lines of research that have used tissue from the Brain Bank over periods of time. Hence there is a discussion on the significance of changes in levels of serotonin 2A receptors in the cortex of patients with schizophrenia and the relevance of such changes with regards to the pathophysiology of the disorder. The extensive contribution made by studies using tissue from the Melbourne Psychiatric Brain Bank to understanding the role of muscarinic receptors in the pathophysiology and treatment of schizophrenia is summarised. Finally, findings using brain bank tissue and "omics" technologies are reviewed. In each case, findings using tissue from the Melbourne Psychiatric Brain Bank is placed in context with research carried out on human postmortem CNS in schizophrenia and with findings in other lines of research that can help explain the causes or consequences of changes in CNS molecular cytoarchitecture. This timely review of data from the Melbourne Psychiatric Brain Bank reinforces the challenges faced in trying to increase our understanding of the molecular pathophysiology of schizophrenia. Continuing to increase our understanding of the disorder is important as a precursor to identifying new drug targets that can be exploited to improve the treatment of a disorder where treatment resistance remains a significant problem (Millan et al., 2016).

Deciphering the Role of Emx1 in Neurogenesis: A Neuroproteomics Approach

Emx1 has long been implicated in embryonic brain development. Previously we found that mice null of Emx1 gene had smaller dentate gyri and reduced neurogenesis, although the molecular mechanisms underlying this defect was not well understood. To decipher the role of Emx1 gene in neural regeneration and the timing of its involvement, we determine the frequency of neural stem cells (NSCs) in embryonic and adult forebrains of Emx1 wild type (WT) and knock out (KO) mice in the neurosphere assay. Emx1 gene deletion reduced the frequency and self-renewal capacity of NSCs of the embryonic brain but did not affect neuronal or glial differentiation. Emx1 KO NSCs also exhibited a reduced migratory capacity in response to serum or vascular endothelial growth factor (VEGF) in the Boyden chamber migration assay compared to their WT counterparts. A thorough comparison between NSC lysates from Emx1 WT and KO mice utilizing 2D-PAGE coupled with tandem mass spectrometry revealed 38 proteins differentially expressed between genotypes, including the F-actin depolymerization factor Cofilin. A global systems biology and cluster analysis identified several potential mechanisms and cellular pathways implicated in altered neurogenesis, all involving Cofilin1. Protein interaction network maps with functional enrichment analysis further indicated that the differentially expressed proteins participated in neural-specific functions including brain development, axonal guidance, synaptic transmission, neurogenesis, and hippocampal morphology, with VEGF as the upstream regulator intertwined with Cofilin1 and Emx1. Functional validation analysis indicated that apart from the overall reduced level of phosphorylated Cofilin1 (p-Cofilin1) in the Emx1 KO NSCs compared to WT NSCs as demonstrated in the western blot analysis, VEGF was able to induce more Cofilin1 phosphorylation and FLK expression only in the latter. Our results suggest that a defect in Cofilin1 phosphorylation induced by VEGF or other growth factors might contribute to the reduced neurogenesis in the Emx1 null mice during brain development.

CRMP4 regulates dendritic growth and maturation via the interaction with actin cytoskeleton in cultured hippocampal neurons

CRMP family proteins (CRMPs) are critical for neurite outgrowth and maturation in the developing nervous system. However, the distinct roles of CRMP isoforms remain to be elucidated, especially in dendritic development. Here, we show that CRMP4 is sufficient and necessary for dendritic growth and maturation in cultured hippocampal neurons. Overexpression of CRMP4 promotes and genetic knockdown of CRMP4 inhibits the amount of dendritic tips, total dendritic length, spine density, and the frequency but not amplitude of miniature excitatory synaptic current. By GST-pulldown assay, we reveal that CRMP4 interacts with actin cytoskeleton by its C-terminal region, but not by N-terminal. Overexpression of actin-interacting region of CRMP4 promoted dendritic growth and maturation as CRMP4 wildtype. Taken together, these results suggest that CRMP4 is involved in dendritic development via the interaction with actin cytoskeleton in hippocampal neurons.

CRMPs Function in Neurons and Glial Cells: Potential Therapeutic Targets for Neurodegenerative Diseases and CNS Injury

Neurodegeneration in the adult mammalian central nervous system (CNS) is fundamentally accelerated by its intrinsic neuronal mechanisms, including its poor regenerative capacity and potent extrinsic inhibitory factors. Thus, the treatment of neurodegenerative diseases faces many obstacles. The degenerative processes, consisting of axonal/dendritic structural disruption, abnormal axonal transport, release of extracellular factors, and inflammation, are often controlled by the cytoskeleton. From this perspective, regulators of the cytoskeleton could potentially be a therapeutic target for neurodegenerative diseases and CNS injury. Collapsin response mediator proteins (CRMPs) are known to regulate the assembly of cytoskeletal proteins in neurons, as well as control axonal growth and neural circuit formation. Recent studies have provided some novel insights into the roles of CRMPs in several inhibitory signaling pathways of neurodegeneration, in addition to its functions in neurological disorders and CNS repair. Here, we summarize the roles of CRMPs in axon regeneration and its emerging functions in non-neuronal cells, especially in inflammatory responses. We also discuss the direct and indirect targeting of CRMPs as a novel therapeutic strategy for neurological diseases.

Deletion of collapsin response mediator protein 4 results in abnormal layer thickness and elongation of mitral cell apical dendrites in the neonatal olfactory bulb

Collapsin response mediator protein 4 (CRMP4), a member of the CRMP family, is involved in the pathogenesis of neurodevelopmental disorders such as schizophrenia and autism. Here, we first compared layer thickness of the olfactory bulb between wild-type (WT) and CRMP4-knockout (KO) mice. The mitral cell layer (MCL) was significantly thinner, whereas the external plexiform layer (EPL) was significantly thicker in CRMP4-KO mice at postnatal day 0 (PD0) compared with WTs. However, differences in layer thickness disappeared by PD14. No apoptotic cells were found in the MCL, and the number of mitral cells (MCs) identified with a specific marker (i.e. Tbx21 antibody) did not change in CRMP4-KO neonates. However, DiI-tracing showed that the length of mitral cell apical dendrites was greater in CRMP4-KO neonates than in WTs. In addition, expression of CRMP4 mRNA in WT mice was most abundant in the MCL at PD0 and decreased afterward. These results suggest that CRMP4 contributes to dendritic elongation. Our in vitro studies showed that deletion or knockdown of CRMP4 resulted in enhanced growth of MAP2-positive neurites, whereas overexpression of CRMP4 reduced their growth, suggesting a new role for CRMP4 as a suppressor of dendritic elongation. Overall, our data suggest that disruption of CRMP4 produces a temporary alteration in EPL thickness, which is constituted mainly of mitral cell apical dendrites, through the enhanced growth of these dendrites.

Proteomic and Microscopic Strategies towards the Analysis of the Cytoskeletal Networks in Major Neuropsychiatric Disorders

Mental health disorders have become worldwide health priorities. It is estimated that in the next 20 years they will account for a 16 trillion United State dollars (US$) loss. Up to now, the underlying pathophysiology of psychiatric disorders remains elusive. Altered cytoskeleton proteins expression that may influence the assembly, organization and maintenance of cytoskeletal integrity has been reported in major depressive disorders, schizophrenia and to some extent bipolar disorders. The use of quantitative proteomics, dynamic microscopy and super-resolution microscopy to investigate disease-specific protein signatures holds great promise to improve our understanding of these disorders. In this review, we present the currently available quantitative proteomic approaches use in neurology, gel-based, stable isotope-labelling and label-free methodologies and evaluate their strengths and limitations. We also reported on enrichment/subfractionation methods that target the cytoskeleton associated proteins and discuss the need of alternative methods for further characterization of the neurocytoskeletal proteome. Finally, we present live cell imaging approaches and emerging dynamic microscopy technology that will provide the tools necessary to investigate protein interactions and their dynamics in the whole cells. While these areas of research are still in their infancy, they offer huge potential towards the understanding of the neuronal network stability and its modification across neuropsychiatric disorders.