CRMP3 is required for hippocampal CA1 dendritic organization and plasticity

The memory enhancing effect of the APP-derived tripeptide Ac-rER is mediated through CRMP2

The diasteromeric (D/L) form of the acetylated tripeptide rER (NH2-D-arg-L-glu-D-arg-COOH), derived from the external domain of amyloid precursor protein, protects against amyloid-β induced memory loss for a passive avoidance task in young chicks and enhances retention for a weak version of the task when injected peripherally up to 12 h prior to training. The tripeptide readily crosses the blood-brain barrier, binds to receptor sites in the brain and is without adverse effects on general behaviour. The mechanisms of its action are unknown, as are its target molecules/pathways. Here, we report the binding partners for Ac-rER are collapsin response mediator protein 2 (CRMP2), syntaxin binding protein 1 and heat shock protein 70. Behavioural studies of the effects of Ac-rER on memory retention confirmed that the effect of Ac-rER is mediated via CRMP2, as anti-CRMP2 antibodies if injected intracranially 30 min pre-training, induced amnesia for the passive avoidance task. However, Ac-rER, if injected prior to the anti-CRMP2, rescues the memory deficits induced by anti-CRMP2 antibodies. As CRMP2 is placed at the junction of many different cellular processes during brain development and in adult neuronal plasticity as well as being implicated in Alzheimer's disease, this strengthens the claim that Ac-rER may be a potential therapeutic agent in Alzheimer's disease, although its precise mode of action remains to be elucidated.

CRMP5 interacts with tubulin to inhibit neurite outgrowth, thereby modulating the function of CRMP2

Collapsin response mediator proteins (CRMPs) are involved in signaling of axon guidance and neurite outgrowth during neural development and regeneration. Among these, CRMP2 has been identified as an important actor in neuronal polarity and axon outgrowth, these activities being correlated with the reorganization of cytoskeletal proteins. In contrast, the function of CRMP5, expressed during brain development, remains obscure. Here, we find that, in contrast to CRMP2, CRMP5 inhibits tubulin polymerization and neurite outgrowth. Knockdown of CRMP5 expression by small interfering RNA confirms its inhibitory functions. CRMP5 forms a ternary complex with MAP2 and tubulin, the latter involving residues 475-522 of CRMP5, exposed at the molecule surface. Using different truncated CRMP5 constructs, we demonstrate that inhibition of neurite outgrowth by CRMP5 is mediated by tubulin binding. When both CRMP5 and CRMP2 are overexpressed, the inhibitory effect of CRMP5 abrogates neurite outgrowth promotion induced by CRMP2, suggesting that CRMP5 acts as a dominant signal. In cultured hippocampal neurons, CRMP5 shows no effect on axon growth, whereas it inhibits dendrite outgrowth and formation, at an early developmental stage, correlated with its strong expression in neurites. At later stages, when dendrites begin to extend, CRMP5 expression is absent. However, CRMP2 is constantly expressed. Overexpression of CRMP5 with CRMP2 inhibits CRMP2-induced outgrowth both on the axonal and dendritic levels. Deficiency of CRMP5 expression enhanced the CRMP2 effect. This antagonizing effect of CRMP5 is exerted through a tubulin-based mechanism. Thus, the CRMP5 binding to tubulin modulates CRMP2 regulation of neurite outgrowth and neuronal polarity during brain development.

Using evolutionary conserved modules in gene networks as a strategy to leverage high throughput gene expression queries

BACKGROUND

Large-scale gene expression studies have not yielded the expected insight into genetic networks that control complex processes. These anticipated discoveries have been limited not by technology, but by a lack of effective strategies to investigate the data in a manageable and meaningful way. Previous work suggests that using a pre-determined seed-network of gene relationships to query large-scale expression datasets is an effective way to generate candidate genes for further study and network expansion or enrichment. Based on the evolutionary conservation of gene relationships, we test the hypothesis that a seed network derived from studies of retinal cell determination in the fly, Drosophila melanogaster, will be an effective way to identify novel candidate genes for their role in mouse retinal development.

METHODOLOGY/PRINCIPAL FINDINGS

Our results demonstrate that a number of gene relationships regulating retinal cell differentiation in the fly are identifiable as pairwise correlations between genes from developing mouse retina. In addition, we demonstrate that our extracted seed-network of correlated mouse genes is an effective tool for querying datasets and provides a context to generate hypotheses. Our query identified 46 genes correlated with our extracted seed-network members. Approximately 54% of these candidates had been previously linked to the developing brain and 33% had been previously linked to the developing retina. Five of six candidate genes investigated further were validated by experiments examining spatial and temporal protein expression in the developing retina.

CONCLUSIONS/SIGNIFICANCE

We present an effective strategy for pursuing a systems biology approach that utilizes an evolutionary comparative framework between two model organisms, fly and mouse. Future implementation of this strategy will be useful to determine the extent of network conservation, not just gene conservation, between species and will facilitate the use of prior biological knowledge to develop rational systems-based hypotheses.

Advanced microscopy techniques for quantitative analysis in neuromorphology and neuropathology research: current status and requirements for the future

Visualizing neuromorphology and in particular neuropathology has been the focus of many researchers in the quest to solve the numerous questions that are still remaining related to several neurological and neuropsychiatric diseases. Over the last years, intense research into microscopy techniques has resulted in the development of various new types of microscopes, software imaging systems, and analysis programs. This review briefly discusses some key techniques, such as confocal stereology and automated neuron tracing and reconstruction, and their applications in neuroscience research. Special emphasis is placed on needs for further developments, such as the demand for higher-throughput analyses in quantitative neuromorphology. These developments will advance basic neuroscience research as well as pharmaceutical and biotechnology research and development.

Collapsin response mediator protein 4a (CRMP4a) is upregulated in motoneurons of mutant SOD1 mice and can trigger motoneuron axonal degeneration and cell death

Embryonic motoneurons from mutant SOD1 (mSOD1) mouse models of amyotrophic lateral sclerosis (ALS), but not wild-type motoneurons, can be triggered to die by exposure to nitric oxide (NO), leading to activation of a motoneuron-specific signaling pathway downstream of the death receptor Fas/CD95. To identify effectors of mSOD1-dependent cell death, we performed a proteomic analysis. Treatment of cultured mSOD1 motoneurons with NO led to a 2.5-fold increase in levels of collapsin response mediator protein 4a (CRMP4a). In vivo, the percentage of mSOD1 lumbar motoneurons expressing CRMP4 in mSOD1 mice increased progressively from presymptomatic to early-onset stages, reaching a maximum of 25%. Forced adeno-associated virus (AAV)-mediated expression of CRMP4a in wild-type motoneurons in vitro triggered a process of axonal degeneration and cell death affecting 60% of motoneurons, whereas silencing of CRMP4a in mSOD1 motoneurons protected them from NO-induced death. In vivo, AAV-mediated overexpression of CRMP4a but not CRMP2 led to the death of 30% of the lumbar motoneurons and an 18% increase in denervation of neuromuscular junctions in the gastrocnemius muscle. Our data identify CRMP4a as a potential early effector in the neurodegenerative process in ALS.

Resilience against predator stress and dendritic morphology of amygdala neurons

Individual differences in coping response lie at the core of vulnerability to conditions like post-traumatic stress disorder (PTSD). Like humans, not all animals exposed to severe stress show lasting change in affect. Predator stress is a traumatic experience inducing long-lasting fear, but not in all rodents. Thus, individual variation may be a cross species factor driving responsiveness to stressful events. The present study investigated neurobiological bases of variation in coping with severe stress. The amygdala was studied because it modulates fear and its function is affected by stress. Moreover, stress-induced plasticity of the amygdala has been related to induction of anxiety, a comorbid symptom of psychiatric conditions like PTSD. We exposed rodents to predator stress and grouped them according to their adaptability based on a standard anxiety test (the elevated plus maze). Subsequently we investigated if well-adapted (less anxious) and mal-adapted (extremely anxious) stressed animals differed in the structure of dendritic trees of their output neurons of the right basolateral amygdala (BLA). Two weeks after exposure to stress, well-adapted animals showed low anxiety levels comparable to unstressed controls, whereas mal-adapted animals were highly anxious. In these same animals, Golgi analysis revealed that BLA neurons of well-adapted rats exhibited more densely packed and shorter dendrites than neurons of mal-adapted or unstressed control animals, which did not differ. These data suggest that dendritic hypotrophy in the BLA may be a resilience marker against lasting anxiogenic effects of predator stress.

An atypical role for collapsin response mediator protein 2 (CRMP-2) in neurotransmitter release via interaction with presynaptic voltage-gated calcium channels

Collapsin response mediator proteins (CRMPs) specify axon/dendrite fate and axonal growth of neurons through protein-protein interactions. Their functions in presynaptic biology remain unknown. Here, we identify the presynaptic N-type Ca(2+) channel (CaV2.2) as a CRMP-2-interacting protein. CRMP-2 binds directly to CaV2.2 in two regions: the channel domain I-II intracellular loop and the distal C terminus. Both proteins co-localize within presynaptic sites in hippocampal neurons. Overexpression in hippocampal neurons of a CRMP-2 protein fused to enhanced green fluorescent protein caused a significant increase in Ca(2+) channel current density, whereas lentivirus-mediated CRMP-2 knockdown abolished this effect. Interestingly, the increase in Ca(2+) current density was not due to a change in channel gating. Rather, cell surface biotinylation studies showed an increased number of CaV2.2 at the cell surface in CRMP-2-overexpressing neurons. These neurons also exhibited a significant increase in vesicular release in response to a depolarizing stimulus. Depolarization of CRMP-2-enhanced green fluorescent protein-overexpressing neurons elicited a significant increase in release of glutamate compared with control neurons. Toxin block of Ca(2+) entry via CaV2.2 abolished this stimulated release. Thus, the CRMP-2-Ca(2+) channel interaction represents a novel mechanism for modulation of Ca(2+) influx into nerve terminals and, hence, of synaptic strength.

Proteomic profiling of the insoluble fractions in the rat hippocampus post-propofol anesthesia

Cognitive dysfunction after propofol anesthesia has been previously found. The underlying mechanisms of this sequel remain unclear. Insoluble proteins as major targets of anesthetics participated in various pathophysiological processes. This study aimed to provide evidence that changes in insoluble proteome in rat hippocampus may be involved in molecular mechanism of cognitive dysfunction following propofol anesthesia. Proteins extracted from rat hippocampus were separated by two-dimensional electrophoresis (2-DE). Their expression patterns were observed at 1, 6, 24 h and 7 days after 3 h of propofol anesthesia. Differentially expressed protein spots among groups were submitted to matrix-assisted laser desorption/ionization time of flight mass spectrometer (MALDI-TOF MS) assay and peptide mass fingerprinting (PMF) identification. Identified proteins were further analyzed through Gene Ontology (GO). Results of 2-DE were selectively assayed using Western blot and RT-PCR. Fifty-nine differentially expressed proteins were detected, among which 43 were identified through MALDI-TOF MS. Most identified proteins were distributed in organelles and membranes. According to biological process category, 27 proteins were involved in metabolic process, 19 in developmental process, 14 in stimulus-response, and 21 in biological regulation. Most changes took place within 24 h, with more down-regulation within 6 h. Twelve proteins did not restore to the basic level until the 7th day after propofol anesthesia. Expressions of insoluble proteome dynamically changed following propofol anesthesia. Down-regulations at early stage might produce depressive effects, which may be involved in molecular mechanism of cognitive dysfunction after propofol anesthesia.

Characterization of the role of full-length CRMP3 and its calpain-cleaved product in inhibiting microtubule polymerization and neurite outgrowth

Collapsin response mediator proteins (CRMPs) are key modulators of cytoskeletons during neurite outgrowth in response to chemorepulsive guidance molecules. However, their roles in adult injured neurons are not well understood. We previously demonstrated that CRMP3 underwent calcium-dependent N-terminal protein cleavage during excitotoxicity-induced neurite retraction and neuronal death. Here, we report findings that the full-length CRMP3 inhibits tubulin polymerization and neurite outgrowth in cultured mature cerebellar granule neurons, while the N-terminal truncated CRMP3 underwent nuclear translocation and caused a significant nuclear condensation. The N-terminal truncated CRMP3 underwent nuclear translocation through nuclear pores. Nuclear protein pull-down assay and mass spectrometry analysis showed that the N-terminal truncated CRMP3 was associated with nuclear vimentin. In fact, nuclear-localized CRMP3 co-localized with vimentin during glutamate-induced excitotoxicity. However, the association between the truncated CRMP3 and vimentin was not critical for nuclear condensation and neurite outgrowth since over-expression of truncated CRMP3 in vimentin null neurons did not alleviate nuclear condensation and neurite outgrowth inhibition. Together, these studies showed CRMP3's role in attenuating neurite outgrowth possibility through inhibiting microtubule polymerization, and also revealed its novel association with vimentin during nuclear condensation prior to neuronal death.