A role for RhoB in synaptic plasticity and the regulation of neuronal morphology

A disease similarity approach identifies short-lived Niemann-Pick type C disease mice with accelerated brain aging as a novel mouse model for Alzheimer's disease and aging research

Since its first description in 1906 by Dr. Alois Alzheimer, Alzheimer's disease (AD) has been the most common type of dementia. Initially thought to be caused by age-associated accumulation of plaques, in recent years, research has increasingly associated AD with lysosomal storage and metabolic disorders, and the explanation of its pathogenesis has shifted from amyloid and tau accumulation to oxidative stress and impaired lipid and glucose metabolism aggravated by hypoxic conditions. However, the underlying mechanisms linking those cellular processes and conditions to disease progression have yet to be defined. Here, we applied a disease similarity approach to identify unknown molecular targets of AD by using transcriptomic data from congenital diseases known to increase AD risk, namely Down Syndrome, Niemann Pick Disease Type C (NPC), and Mucopolysaccharidoses I. We uncovered common pathways, hub genes, and miRNAs across in vitro and in vivo models of these diseases as potential molecular targets for neuroprotection and amelioration of AD pathology, many of which have never been associated with AD. We then investigated common molecular alterations in brain samples from an NPC disease mouse model by juxtaposing them with brain samples of both human and mouse models of AD. Detailed phenotypic and molecular analyses revealed that the NPC mut mouse model can serve as a potential short-lived in vivo model for AD research and for understanding molecular factors affecting brain aging. This research represents the first comprehensive approach to congenital disease association with neurodegeneration and a new perspective on AD research while highlighting shortcomings and lack of correlation in diverse in vitro models. Considering the lack of an AD mouse model that recapitulates the physiological hallmarks of brain aging, the characterization of a short-lived NPC mouse model will further accelerate the research in these fields and offer a unique model for understanding the molecular mechanisms of AD from a perspective of accelerated brain aging.

Unveiling the regulatory role of miRNAs in stroke pathophysiology and diagnosis

Stroke, a major global cause of mortality, leads to a range of problems for those who survive. Besides its brutal events, stroke also tends to have a characteristic of recurrence, making it a complex disease involving intricate regulatory networks. One of the major cellular regulators is the non-coding RNAs (ncRNA), specifically microRNAs (miRNAs), thus the possible functions of miRNAs in the pathogenesis of stroke are discussed as well as the possibility of using miRNA-based therapeutic approaches. Firstly, the molecular mechanisms by which miRNAs regulate vital physiological processes, including synaptic plasticity, oxidative stress, apoptosis, and the integrity of the blood-brain barrier (BBB) are reviewed. The miRNA indirectly impacts stroke outcomes by regulating BBB function and angiogenesis through the targeting of transcription factors and angiogenic factors. In addition, the tendency for some miRNAs to be upregulated in response to hypoxia, which is a prevalent phenomenon in stroke and various neurological disorders, highlights the possibility that it controls hypoxia-inducible factor (HIF) signaling and angiogenesis, thereby influencing the integrity of the BBB as examples of the discussed mechanisms. Furthermore, this review explores the potential therapeutic targets that miRNAs may offer for stroke recovery and highlights their promising capacity to alleviate post-stroke complications. This review provides researchers and clinicians with valuable resources since it attempts to decipher the complex network of miRNA-mediated mechanisms in stroke. Additionally, the review addresses the interplay between miRNAs and stroke risk factors as well as clinical applications of miRNAs as diagnostic and prognostic markers.

A Structural Network Analysis of Neuronal ArhGAP21/23 Interactors by Computational Modeling

RhoGTPase-activating proteins (RhoGAPs) play multiple roles in neuronal development; however, details of their substrate recognition system remain elusive. ArhGAP21 and ArhGAP23 are RhoGAPs that contain N-terminal PDZ and pleckstrin homology domains. In the present study, the RhoGAP domain of these ArhGAPs was computationally modeled by template-based methods and the AlphaFold2 software program, and their intrinsic RhoGTPase recognition mechanism was analyzed from the domain structures using the protein docking programs HADDOCK and HDOCK. ArhGAP21 was predicted to preferentially catalyze Cdc42, RhoA, RhoB, RhoC, and RhoG and to downregulate RhoD and Tc10 activities. Regarding ArhGAP23, RhoA and Cdc42 were deduced to be its substrates, whereas RhoD downregulation was predicted to be less efficient. The PDZ domains of ArhGAP21/23 possess the FTLRXXXVY sequence, and similar globular folding consists of antiparalleled β-sheets and two α-helices that are conserved with PDZ domains of MAST-family proteins. A peptide docking analysis revealed the specific interaction of the ArhGAP23 PDZ domain with the PTEN C-terminus. The pleckstrin homology domain structure of ArhGAP23 was also predicted, and the functional selectivity for the interactors regulated by the folding and disordered domains in ArhGAP21 and ArhGAP23 was examined by an in silico analysis. An interaction analysis of these RhoGAPs revealed the existence of mammalian ArhGAP21/23-specific type I and type III Arf- and RhoGTPase-regulated signaling. Multiple recognition systems of RhoGTPase substrates and selective Arf-dependent localization of ArhGAP21/23 may form the basis of the functional core signaling necessary for synaptic homeostasis and axon/dendritic transport regulated by RhoGAP localization and activities.

Establishment and Application of a Novel In Vitro Model of Microglial Activation in Traumatic Brain Injury

Mechanical impact-induced primary injury after traumatic brain injury (TBI) leads to acute microglial pro-inflammatory activation and consequently mediates neurodegeneration, which is a major secondary brain injury mechanism. However, the detailed pathologic cascades have not been fully elucidated, partially because of the pathologic complexity in animal TBI models. Although there are several in vitro TBI models, none of them closely mimic post-TBI microglial activation. In the present study, we aimed to establish an in vitro TBI model, specifically reconstituting the pro-inflammatory activation and associated neurodegeneration following TBI. We proposed three sets of experiments. First, we established a needle scratch injured neuron-induced microglial activation and neurodegeneration in vitro model of TBI. Second, we compared microglial pro-inflammatory cytokines profiles between the in vitro TBI model and TBI in male mice. Additionally, we validated the role of injured neurons-derived damage-associated molecular patterns in amplifying microglial pro-inflammatory pathways using the in vitro TBI model. Third, we applied the in vitro model for the first time to characterize the cellular metabolic profile of needle scratch injured-neuron-activated microglia, and define the role of metabolic reprogramming in mediating pro-inflammatory microglial activation and mediated neurodegeneration. Our results showed that we successfully established a novel in vitro TBI model, which closely mimics primary neuronal injury-triggered microglial pro-inflammatory activation and mediated neurodegeneration after TBI. This in vitro model provides an advanced and highly translational platform for dissecting interactions in the pathologic processes of neuronal injury-microglial activation-neuronal degeneration cascade, and elucidating the detailed underlying cellular and molecular insights after TBI.SIGNIFICANCE STATEMENT Microglial activation is a key component of acute neuroinflammation that leads to neurodegeneration and long-term neurologic outcome deficits after TBI. However, it is not feasible to truly dissect primary neuronal injury-induced microglia activation, and consequently mediated neurodegeneration in vivo Furthermore, there is currently lacking of in vitro TBI models closely mimicking the TBI primary injury-mediated microglial activation. In this study, we successfully established and validated a novel in vitro TBI model of microglial activation, and for the first time, characterized the cellular metabolic profile of microglia in this model. This novel microglial activation in vitro TBI model will help in elucidating microglial inflammatory activation and consequently associated neurodegeneration after TBI.

Genome-wide translation control analysis of developing human neurons

During neuronal differentiation, neuroprogenitor cells become polarized, change shape, extend axons, and form complex dendritic trees. While growing, axons are guided by molecular cues to their final destination, where they establish synaptic connections with other neuronal cells. Several layers of regulation are integrated to control neuronal development properly. Although control of mRNA translation plays an essential role in mammalian gene expression, how it contributes temporarily to the modulation of later stages of neuronal differentiation remains poorly understood. Here, we investigated how translation control affects pathways and processes essential for neuronal maturation, using H9-derived human neuro progenitor cells differentiated into neurons as a model. Through Ribosome Profiling (Riboseq) combined with RNA sequencing (RNAseq) analysis, we found that translation control regulates the expression of critical hub genes. Fundamental synaptic vesicle secretion genes belonging to SNARE complex, Rab family members, and vesicle acidification ATPases are strongly translationally regulated in developing neurons. Translational control also participates in neuronal metabolism modulation, particularly affecting genes involved in the TCA cycle and glutamate synthesis/catabolism. Importantly, we found translation regulation of several critical genes with fundamental roles regulating actin and microtubule cytoskeleton pathways, critical to neurite generation, spine formation, axon guidance, and circuit formation. Our results show that translational control dynamically integrates important signals in neurons, regulating several aspects of its development and biology.

Function of SYDE C2-RhoGAP family as signaling hubs for neuronal development deduced by computational analysis

Recent investigations of neurological developmental disorders have revealed the Rho-family modulators such as Syde and its interactors as the candidate genes. Although the mammalian Syde proteins are reported to possess GTPase-accelerating activity for RhoA-family proteins, diverse species-specific substrate selectivities and binding partners have been described, presumably based on their evolutionary variance in the molecular organization. A comprehensive in silico analysis of Syde family proteins was performed to elucidate their molecular functions and neurodevelopmental networks. Predicted structural modeling of the RhoGAP domain may account for the molecular constraints to substrate specificity among Rho-family proteins. Deducing conserved binding motifs can extend the Syde interaction network and highlight diverse but Syde isoform-specific signaling pathways in neuronal homeostasis, differentiation, and synaptic plasticity from novel aspects of post-translational modification and proteolysis.

LIM-Kinases in Synaptic Plasticity, Memory, and Brain Diseases

Learning and memory require structural and functional modifications of synaptic connections, and synaptic deficits are believed to underlie many brain disorders. The LIM-domain-containing protein kinases (LIMK1 and LIMK2) are key regulators of the actin cytoskeleton by affecting the actin-binding protein, cofilin. In addition, LIMK1 is implicated in the regulation of gene expression by interacting with the cAMP-response element-binding protein. Accumulating evidence indicates that LIMKs are critically involved in brain function and dysfunction. In this paper, we will review studies on the roles and underlying mechanisms of LIMKs in the regulation of long-term potentiation (LTP) and depression (LTD), the most extensively studied forms of long-lasting synaptic plasticity widely regarded as cellular mechanisms underlying learning and memory. We will also discuss the involvement of LIMKs in the regulation of the dendritic spine, the structural basis of synaptic plasticity, and memory formation. Finally, we will discuss recent progress on investigations of LIMKs in neurological and mental disorders, including Alzheimer’s, Parkinson’s, Williams–Beuren syndrome, schizophrenia, and autism spectrum disorders.

Roles of palmitoylation in structural long-term synaptic plasticity

Long-term potentiation (LTP) and long-term depression (LTD) are important cellular mechanisms underlying learning and memory processes. N-Methyl-d-aspartate receptor (NMDAR)-dependent LTP and LTD play especially crucial roles in these functions, and their expression depends on changes in the number and single channel conductance of the major ionotropic glutamate receptor α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) located on the postsynaptic membrane. Structural changes in dendritic spines comprise the morphological platform and support for molecular changes in the execution of synaptic plasticity and memory storage. At the molecular level, spine morphology is directly determined by actin cytoskeleton organization within the spine and indirectly stabilized and consolidated by scaffold proteins at the spine head. Palmitoylation, as a uniquely reversible lipid modification with the ability to regulate protein membrane localization and trafficking, plays significant roles in the structural and functional regulation of LTP and LTD. Altered structural plasticity of dendritic spines is also considered a hallmark of neurodevelopmental disorders, while genetic evidence strongly links abnormal brain function to impaired palmitoylation. Numerous studies have indicated that palmitoylation contributes to morphological spine modifications. In this review, we have gathered data showing that the regulatory proteins that modulate the actin network and scaffold proteins related to AMPAR-mediated neurotransmission also undergo palmitoylation and play roles in modifying spine architecture during structural plasticity.

The seed of Litchi chinensis fraction ameliorates hippocampal neuronal injury in an Aβ25-35-induced Alzheimer's disease rat model via the AKT/GSK-3β pathway

Context: The seed of Litchi chinensis Sonn., a famous traditional Chinese medicine, was recently reported to enhance cognitive function by inhibiting neuronal apoptosis in rats.Objective: We determined whether the seed of Litchi chinensis fraction (SLF) can ameliorate hippocampal neuronal injury via the AKT/GSK-3β pathway.Materials and methods: We established Alzheimer's disease (AD) model by infusing Aβ_25-35 into the lateral ventricle of Sprague-Dawley (SD) rats and randomly divided into five groups (n = 10): sham, donepezil and SLF (120, 240 and 480 mg/kg/d). Rats were treated by intragastric administration for 28 consecutive days. Spatial learning and memory were evaluated with Morris water maze, while protein expression of AKT, GSK-3β and tau in the hippocampal neurons was measured by Western blotting and immunohistochemistry.Results: On the fifth day, escape latency of the AD model group was 45.78 ± 2.52 s and that of the sham operative group was 15.98 ± 2.32 s. SLF could improve cognitive functions by increasing the number of rats that crossed the platform (p < 0.01), and their platform quadrant dwell time (p < 0.05). The protein expression level of AKT was upregulated (p < 0.001), while that of GSK-3β and tau (p < 0.01) was remarkably downregulated in the hippocampal CA1 area.Discussion and conclusions: To our knowledge, the present study is the first to show that SLF may exert neuroprotective effect in AD rats via the AKT/GSK-3β signalling pathway, thereby serving as evidence for the potential utility of SLF as an effective drug against AD.

Mutations disrupting neuritogenesis genes confer risk for cerebral palsy

In addition to commonly associated environmental factors, genomic factors may cause cerebral palsy. We performed whole-exome sequencing of 250 parent-offspring trios, and observed enrichment of damaging de novo mutations in cerebral palsy cases. Eight genes had multiple damaging de novo mutations; of these, two (TUBA1A and CTNNB1) met genome-wide significance. We identified two novel monogenic etiologies, FBXO31 and RHOB, and showed that the RHOB mutation enhances active-state Rho effector binding while the FBXO31 mutation diminishes cyclin D levels. Candidate cerebral palsy risk genes overlapped with neurodevelopmental disorder genes. Network analyses identified enrichment of Rho GTPase, extracellular matrix, focal adhesion and cytoskeleton pathways. Cerebral palsy risk genes in enriched pathways were shown to regulate neuromotor function in a Drosophila reverse genetics screen. We estimate that 14% of cases could be attributed to an excess of damaging de novo or recessive variants. These findings provide evidence for genetically mediated dysregulation of early neuronal connectivity in cerebral palsy.

Novel alternatively-spliced exons of the VRK2 gene in mouse brain and microglial cells

Common sequence variations in the VRK2 gene contribute to genetic risk for various psychiatric diseases including schizophrenia and major depressive disorder. Despite the clear importance of studying the regulation and function of VRK2 for understanding the causes of these diseases, the organisation and expression of the gene remain poorly characterised. Using reverse-transcriptase-PCR, we have amplifed exons of Vrk2 mRNA from regions of mouse brain, and from different cell classes comprising neurones, astrocytes and microglial cells. We find that Vrk2 mRNA is expressed in all cell types, and that the splicing of the mouse Vrk2 gene is much more complex than previously appreciated. In addition to the predicted alternative splicing (absence/presence) of the penultimate 3 prime exon, we also detected a variety of 5 prime structures, including two novel exons spanning the first characterised exon (exon 1), which we term exons 1a and 1b. While expressed in neurones and astrocytes, exon 1b was not expressed in microglial cells. Expression of transcripts containing exon 1a in microglia was increased by immune stimulation. An additional truncated transcript lacking 7 central exons was also identified. As with the human gene, the results confirm complex patterns of alternative splicing which are likely to be relevant for understanding the physiological and pathological function of the gene in the CNS.

Much More Than a Scaffold: Cytoskeletal Proteins in Neurological Disorders

Recent observations related to the structure of the cytoskeleton in neurons and novel cytoskeletal abnormalities involved in the pathophysiology of some neurological diseases are changing our view on the function of the cytoskeletal proteins in the nervous system. These efforts allow a better understanding of the molecular mechanisms underlying neurological diseases and allow us to see beyond our current knowledge for the development of new treatments. The neuronal cytoskeleton can be described as an organelle formed by the three-dimensional lattice of the three main families of filaments: actin filaments, microtubules, and neurofilaments. This organelle organizes well-defined structures within neurons (cell bodies and axons), which allow their proper development and function through life. Here, we will provide an overview of both the basic and novel concepts related to those cytoskeletal proteins, which are emerging as potential targets in the study of the pathophysiological mechanisms underlying neurological disorders.

Altered expression of microRNA-223 in the plasma of patients with first-episode schizophrenia and its possible relation to neuronal migration-related genes

Recent studies have shown that microRNAs (miRNAs) play a role as regulators of neurodevelopment by modulating gene expression. Altered miRNA expression has been reported in various psychiatric disorders, including schizophrenia. However, the changes in the miRNA expression profile that occur during the initial stage of schizophrenia have not been fully investigated. To explore the global alterations in miRNA expression profiles that may be associated with the onset of schizophrenia, we first profiled miRNA expression in plasma from 17 patients with first-episode schizophrenia and 17 healthy controls using microarray analysis. Among the miRNAs that showed robust changes, the elevated expression of has-miR-223-3p (miR-223) was validated via quantitative reverse transcription-polymerase chain reaction (qRT-PCR) using another independent sample set of 21 schizophrenia patients and 21 controls. To identify the putative targets of miR-223, we conducted a genome-wide gene expression analysis in neuronally differentiated SK-N-SH cells with stable miR-223 overexpression and an in silico analysis. We found that the mRNA expression levels of four genes related to the cytoskeleton or cell migration were significantly downregulated in miR-223-overexpressing cells, possibly due to interactions with miR-223. The in silico analysis suggested the presence of miR-223 target sites in these four genes. Lastly, a luciferase assay confirmed that miR-223 directly interacted with the 3' untranslated regions (UTRs) of all four genes. Our results reveal an increase in miR-223 in plasma during both the first episode and the later stage of schizophrenia, which may affect the expression of cell migration-related genes targeted by miR-223.

Distortion of protein analysis in primary neuronal cultures by serum albumin from culture medium: A methodological approach to improve target protein quantification

BACKGROUND

Primary neuronal cultures underpin diverse neuroscience experiments, including various protein analysis techniques, such as Western blotting, whereby protein extraction from cultured neurons is required. During immunoblotting experiments, we encountered problems due to a highly-abundant protein of 65-70 KDa present in the cell extracts, that interfered with total protein estimation, and immunodetection of target proteins of similar size. Previous research has suggested that serum proteins, specifically albumin, contained within commonly-used culture media, can bind to, or be adsorbed by, generic cell culture plasticware. This residual albumin may then be extracted along with cell proteins.

NEW METHOD

We made simple modifications to wash steps of traditional cell lysis/extraction protocols.

RESULTS

We report that a substantial amount of albumin, accumulated from the standard culture media, is extracted from primary neuronal cultures along with the cellular contents. This contamination can be reduced, without changing the culture conditions, by modifying wash procedures.

COMPARISON WITH EXISTING METHODS

Accumulated albumin from neuronal culture media, in amounts equivalent to cellular contents, can distort data from total protein assays and from the immunoreactive signal from nearby bands on Western blots. By altering wash protocols during protein extraction, these problems can be ameliorated.

CONCLUSIONS

We suggest that the standard extended culture periods for primary neuronal cultures, coupled with the requirement for successive medium changes, may leave them particularly susceptible to cumulative albumin contamination from the culture media used. Finally, we propose the implementation of simple alterations to wash steps in protein extraction protocols which can ameliorate this interference.

miR-19a-mediated downregulation of RhoB inhibits the dephosphorylation of AKT1 and induces osteosarcoma cell metastasis

Osteosarcoma is a primary malignancy that develops in bone, along with serious recurrence and metastasis. As an isoform of Rho family GTPases, RhoB could suppress cell proliferation, invasion, and anti-angiogenesis. But it is not clear how RhoB involves in tumor metastasis. Here we found that expression of RhoB was decreased in osteosarcoma primary samples and cell lines. Ectopic expression of RhoB restrains the migration of osteosarcoma cells in vitro and in vivo, and induces osteosarcoma cell apopotsis. Further study showed that overexpression of RhoB could increase the proportion of B55 in PP2A complex and enhance the dephosphorylation of AKT1 by interacting with B55. Moreover, we demonstrated that miR-19a, which exhibits abnormal expression in highly metastatic osteosarcoma cell lines, could inhibit the expression of RhoB and promote the lung metastasis of osteosarcoma cells in vivo. Our results indicate that miR-19a-mediated RhoB is a critical regulator for the dephosphorylation of AKT1 in osteosarcoma cells. It may have a possible strategy on suppressing osteosarcoma metastasis by miR-19a inhibitory oligonucleotides. The miR-19a/RhoB/AKT1 network may help us to better understand the mechanism of osteosarcoma metastasis.

The Cullin-3-Rbx1-KCTD10 complex controls endothelial barrier function via K63 ubiquitination of RhoB

The RhoA GTPase controls endothelial cell migration, adhesion, and barrier formation but the role of RhoB is unclear. Kovačević et al. now discover that RhoB is ubiquitinated by the CUL3–Rbx1–KCTD10 complex and that this is a prerequisite for lysosomal degradation of RhoB and the maintenance of endothelial barrier integrity. 

RhoGTPases control endothelial cell (EC) migration, adhesion, and barrier formation. Whereas the relevance of RhoA for endothelial barrier function is widely accepted, the role of the RhoA homologue RhoB is poorly defined. RhoB and RhoA are 85% identical, but RhoB’s subcellular localization and half-life are uniquely different. Here, we studied the role of ubiquitination for the function and stability of RhoB in primary human ECs. We show that the K63 polyubiquitination at lysine 162 and 181 of RhoB targets the protein to lysosomes. Moreover, we identified the RING E3 ligase complex Cullin-3–Rbx1–KCTD10 as key modulator of endothelial barrier integrity via its regulation of the ubiquitination, localization, and activity of RhoB. In conclusion, our data show that ubiquitination controls the subcellular localization and lysosomal degradation of RhoB and thereby regulates the stability of the endothelial barrier through control of RhoB-mediated EC contraction.

Dissociative role for dorsal hippocampus in mediating heroin self-administration and relapse through CDK5 and RhoB signaling revealed by proteomic analysis

Addiction is characterized by drug craving, compulsive drug taking and relapse, which is attributed to aberrant neuroadaptation in brain regions implicated in drug addiction, induced by changes in gene and protein expression in these regions after chronic drug exposure. Accumulating evidence suggests that the dorsal hippocampus (DH) plays an important role in mediating drug-seeking and drug-taking behavior and relapse. However, the molecular mechanisms underlying these effects of the DH are unclear. In the present study, we employed a label-free quantitative proteomic approach to analyze the proteins altered in the DH of heroin self-administering rats. A total of 4015 proteins were quantified with high confidence, and 361 proteins showed significant differences compared with the saline control group. Among them, cyclin-dependent kinase 5 (CDK5) and ras homolog family member B (RhoB) were up-regulated in rats with a history of extended access to heroin. Functionally, inhibition of CDK5 in the DH enhanced heroin self-administration, indicating that CDK5 signaling in the DH acts as a homeostatic compensatory mechanism to limit heroin-taking behavior, whereas blockade of the Rho-Rho kinase (ROCK) pathway attenuated context-induced heroin relapse, indicating that RhoB signaling in the DH is required for the retrieval (recall) of addiction memory. Our findings suggest that manipulation of CDK5 signaling in the DH may be essential in determining vulnerability to opiate taking, whereas manipulation of RhoB signaling in the DH may be essential in determining vulnerability to relapse. Overall, the present study suggests that the DH can exert dissociative effects on heroin addiction through CDK5 and RhoB signaling.

MiR-194 is involved in morphogenesis of spiral ganglion neurons in inner ear by rearranging actin cytoskeleton via targeting RhoB

Many microRNAs participate in the development, differentiation and function preservation of the embryonic and adult inner ear, but many details still need to be elucidated regarding the numerous microRNAs in the inner ear. Based on previous investigations on the microRNA profile in the inner ear, we confirmed that several microRNAs are expressed in the inner ear, and we detected the spatial expression of these microRNAs in the neonatal mouse inner ear. Then we focused on miR-194 for its specific expression with a dynamic spatiotemporal pattern during inner ear development. Overexpression of miR-194 in cultured spiral ganglion cells significantly affected the dendrites of differentiated neurons, with more branching and obviously dispersed nerve fibres. Furthermore, the cytoskeleton of cultured cells was markedly affected, as disordered actin filaments resulting from miR-194 overexpression and enhanced filaments resulting from miR-194 knockdown were observed. Together with the bioinformatic methods, the RT-qPCR and western blot results showed that RhoB is a candidate target of miR-194 in the morphogenesis of spiral ganglion neurons. Additionally, the double luciferase reporter system was used to identify RhoB as a novel target of miR-194. Finally, the inhibition of RhoB activation by Clostridium difficile toxin B disturbed the organization of the actin filament, similar to the effects of miR-194 overexpression. In summary, we investigated microRNA expression in the mouse inner ear, and demonstrated that miR-194 is dynamically expressed during inner ear development; importantly, we found that miR-194 affects neuron morphogenesis positively through Rho B-mediated F-actin rearrangement.

Determination of dendritic spine morphology by the striatin scaffold protein STRN4 through interaction with the phosphatase PP2A

Dendritic spines are heterogeneous and exist with various morphologies. Altered spine morphology might underlie the cognitive deficits in neurodevelopmental disorders such as autism, but how different subtypes of dendritic spines are selectively maintained along development is still poorly understood. Spine maturation requires spontaneous activity of N-methyl-d-aspartate (NMDA) receptor and local dendritic protein synthesis. STRN4 (also called zinedin) belongs to the striatin family of scaffold proteins, and some of the potential striatin-interacting proteins are encoded by autism risk genes. Although previous studies have demonstrated their localization in dendritic spines, the function of various striatin family members in the neuron remains unknown. Here, we demonstrate that Strn4 mRNA is present in neuronal dendrites, and the local expression of STRN4 protein depends on NMDA receptor activation. Notably, STRN4 is preferentially expressed in mushroom spines, and STRN4 specifically maintains mushroom spines but not thin spines and filopodia through interaction with the phosphatase PP2A. Our findings have therefore unraveled the local expression of STRN4 as a novel mechanism for the control of dendritic spine morphology.

Selective depletion of tumour suppressors Deleted in Colorectal Cancer (DCC) and neogenin by environmental and endogenous serine proteases: linking diet and cancer

BACKGROUND

The related tumour suppressor proteins Deleted in Colorectal Cancer (DCC) and neogenin are absent or weakly expressed in many cancers, whereas their insertion into cells suppresses oncogenic behaviour. Serine proteases influence the initiation and progression of cancers although the mechanisms are unknown.

METHODS

The effects of environmental (bacterial subtilisin) and endogenous mammalian (chymotrypsin) serine proteases were examined on protein expression in fresh, normal tissue and human neuroblastoma and mammary adenocarcinoma lines. Cell proliferation and migration assays (chemoattraction and wound closure) were used to examine cell function. Cells lacking DCC were transfected with an ectopic dcc plasmid.

RESULTS

Subtilisin and chymotrypsin selectively depleted DCC and neogenin from cells at nanomolar concentrations without affecting related proteins. Cells showed reduced adherence and increased migration, but after washing they re-attached within 24 h, with recovery of protein expression. These effects are induced by chymotryptic activity as they are prevented by chymostatin and the soybean Bowman-Birk inhibitor typical of many plant protease inhibitors.

CONCLUSIONS

Bacillus subtilis, which secretes subtilisin is widely present in soil, the environment and the intestinal contents, while subtilisin itself is used in meat processing, animal feed probiotics and many household cleaning agents. With chymotrypsin present in chyme, blood and tissues, these proteases may contribute to cancer development by depleting DCC and neogenin. Blocking their activity by Bowman-Birk inhibitors may explain the protective effects of a plant diet. Our findings identify a potential non-genetic contribution to cancer cell behaviour which may explain both the association of processed meats and other factors with cancer incidence and the protection afforded by plant-rich diets, with significant implications for cancer prevention.

Morphine-Associated Contextual Cues Induce Structural Plasticity in Hippocampal CA1 Pyramidal Neurons

In people with a prior history of opioid misuse, cues associated with previous drug intake can trigger relapse even after years of abstinence. Examining the processes that lead to the formation and maintenance of the memories between cues/context and the opioid may help to discover new therapeutic candidates to treat drug-seeking behavior. The hippocampus is a brain region essential for learning and memory, which has been involved in the mechanisms underlying opioid cravings. The formation of memories and associations are thought to be dependent on synaptic strengthening associated with structural plasticity of dendritic spines. Here, we assess how dendritic spines in the CA1 region of the hippocampus are affected by morphine-conditioning training. Our results show that morphine pairing with environmental cues (ie, the conditioned place preference (CPP) apparatus) triggers a significant decrease in the number of thin dendritic spines in the hippocampus. Interestingly, this effect was observed regardless of the expression of a conditioned response when mice were trained using an unpaired morphine CPP design and was absent when morphine was administered in the home cage. To investigate the mechanism underlying this structural plasticity, we examined the role of Rho GTPase in dendritic spine remodeling. We found that synaptic expression of RhoA increased with morphine conditioning and blocking RhoA signaling prevented the expression of morphine-induced CPP. Our findings uncover novel mechanisms in response to morphine-associated environmental cues and the underlying alterations in spine plasticity.

Familial Alzheimer's disease-associated presenilin 1 mutants promote γ-secretase cleavage of STIM1 to impair store-operated Ca2+ entry

Some forms of familial Alzheimer's disease (FAD) are caused by mutations in presenilins (PSs), catalytic components of a γ-secretase complex that cleaves target proteins, including amyloid precursor protein (APP). Calcium (Ca(2+)) dysregulation in cells with these FAD-causing PS mutants has been attributed to attenuated store-operated Ca(2+) entry [SOCE; also called capacitative Ca(2+) entry (CCE)]. CCE occurs when STIM1 detects decreases in Ca(2+) in the endoplasmic reticulum (ER) and activates ORAI channels to replenish Ca(2+) stores in the ER. We showed that CCE was attenuated by PS1-associated γ-secretase activity. Endogenous PS1 and STIM1 interacted in human neuroblastoma SH-SY5Y cells, patient fibroblasts, and mouse primary cortical neurons. Forms of PS1 with FAD-associated mutations enhanced γ-secretase cleavage of the STIM1 transmembrane domain at a sequence that was similar to the γ-secretase cleavage sequence of APP. Cultured hippocampal neurons expressing mutant PS1 had attenuated CCE that was associated with destabilized dendritic spines, which were rescued by either γ-secretase inhibition or overexpression of STIM1. Our results indicate that γ-secretase activity may physiologically regulate CCE by targeting STIM1 and that restoring STIM1 may be a therapeutic approach in AD.

Dependence receptor involvement in subtilisin-induced long-term depression and in long-term potentiation

The serine protease subtilisin induces a form of long-term depression (LTD) which is accompanied by a reduced expression of the axo-dendritic guidance molecule Unco-ordinated-5C (Unc-5C). One objective of the present work was to determine whether a loss of Unc-5C function contributed to subtilisin-induced LTD by using Unc-5C antibodies in combination with the pore-forming agents Triton X-100 (0.005%) or streptolysin O in rat hippocampal slices. In addition we have assessed the effect of subtilisin on the related dependence receptor Deleted in Colorectal Cancer (DCC) and used antibodies to this protein for functional studies. Field excitatory postsynaptic potentials (fEPSPs) were analyzed in rat hippocampal slices and protein extracts were used for Western blotting. Subtilisin produced a greater loss of DCC than of Unc-5C, but the antibodies had no effect on resting excitability or fEPSPs and did not modify subtilisin-induced LTD. However, antibodies to DCC but not Unc-5C did reduce the amplitude of theta-burst long-term potentiation (LTP). In addition, two inhibitors of endocytosis - dynasore and tat-gluR2(3Y) - were tested and, although the former compound had no effect on neurophysiological responses, tat-gluR2(3Y) did reduce the amplitude of subtilisin-induced LTD without affecting the expression of DCC or Unc-5C but with some loss of PostSynaptic Density Protein-95. The results support the view that the dependence receptor DCC may be involved in LTP and suggest that the endocytotic removal of a membrane protein or proteins may contribute to subtilisin-induced LTD, although it appears that neither Unc-5C nor DCC are involved in this process.

Deletion of JMJD2B in neurons leads to defective spine maturation, hyperactive behavior and memory deficits in mouse

JMJD2B is a histone demethylase enzyme that regulates gene expression through demethylation of H3K9me3. Although mutations of JMJD2B have been suggested to be responsible for neurodevelopmental disorders, the function of JMJD2B in the central nervous system (CNS) remains to be elucidated. Here we show that JMJD2B has a critical role in the development of the CNS. We observed JMJD2B expression, which was especially strong in the hippocampus, throughout the CNS from embryonic periods through adulthood. We generated neuron-specific JMJD2B-deficient mice using the cre-loxP system. We found an increase in total spine number, but a decrease in mature spines, in the CA1 region of the hippocampus. JMJD2B-deficient mice exhibited hyperactive behavior, sustained hyperactivity in a novel environment, deficits in working memory and spontaneous epileptic-like seizures. Together these observations indicate that JMJD2B mutant mice display symptoms reminiscent of neurodevelopmental disorders. Our findings provide evidence for the involvement of histone demethylation in the formation of functional neural networks during development.

RNA Sequencing Reveals the Alteration of the Expression of Novel Genes in Ethanol-Treated Embryoid Bodies

Fetal alcohol spectrum disorder is a collective term representing fetal abnormalities associated with maternal alcohol consumption. Prenatal alcohol exposure and related anomalies are well characterized, but the molecular mechanism behind this phenomenon is not well characterized. In this present study, our aim is to profile important genes that regulate cellular development during fetal development. Human embryonic carcinoma cells (NCCIT) are cultured to form embryoid bodies and then treated in the presence and absence of ethanol (50 mM). We employed RNA sequencing to profile differentially expressed genes in the ethanol-treated embryoid bodies from NCCIT vs. EB, NCCIT vs. EB+EtOH and EB vs. EB+EtOH data sets. A total of 632, 205 and 517 differentially expressed genes were identified from NCCIT vs. EB, NCCIT vs. EB+EtOH and EB vs. EB+EtOH, respectively. Functional annotation using bioinformatics tools reveal significant enrichment of differential cellular development and developmental disorders. Furthermore, a group of 42, 15 and 35 transcription factor-encoding genes are screened from all of the differentially expressed genes obtained from NCCIT vs. EB, NCCIT vs. EB+EtOH and EB vs. EB+EtOH, respectively. We validated relative gene expression levels of several transcription factors from these lists by quantitative real-time PCR. We hope that our study substantially contributes to the understanding of the molecular mechanism underlying the pathology of alcohol-mediated anomalies and ease further research.

Novel functions for ADF/cofilin in excitatory synapses - lessons from gene-targeted mice

Actin filaments (F-actin) are the major structural component of excitatory synapses. In excitatory synapses, F-actin is enriched in presynaptic terminals and in postsynaptic dendritic spines, and actin dynamics - the spatiotemporally controlled assembly and disassembly of F-actin - have been implicated in pre- and postsynaptic physiology, additionally to their function in synapse morphology. Hence, actin binding proteins that control actin dynamics have moved into the focus as regulators of synapse morphology and physiology. Actin depolymerizing proteins of the ADF/cofilin family are important regulators of actin dynamics, and several recent studies highlighted the relevance of cofilin 1 for dendritic spine morphology, trafficking of postsynaptic glutamate receptors, and synaptic plasticity. Conversely, almost nothing was known about the synaptic function of ADF, a second ADF/cofilin family member present at excitatory synapses, and it remained unknown whether ADF/cofilin is relevant for presynaptic physiology. To comprehensively characterize the synaptic function of ADF/cofilin we made use of mutant mice lacking either ADF or cofilin 1 or both proteins. Our analysis revealed presynaptic defects (altered distribution and enhanced exocytosis of synaptic vesicles) and behavioral abnormalities reminiscent of attention deficit-hyperactivity disorder in double mutants that were not present in single mutants. Hence, by exploiting gene-targeted mice, we demonstrated the relevance of ADF for excitatory synapses, and we unraveled novel functions for ADF/cofilin in presynaptic physiology and behavior.

Roles of LIM kinases in central nervous system function and dysfunction

LIM kinase 1 (LIMK1) and LIM kinase 2 (LIMK2) regulate actin dynamics by phosphorylating cofilin. In this review, we outline studies that have shown an involvement of LIMKs in neuronal function and we detail some of the pathways and molecular mechanisms involving LIMKs in neurodevelopment and synaptic plasticity. We also review the involvement of LIMKs in neuronal diseases and emphasize the differences in the regulation of LIMKs expression and mode of action. We finally present the existence of a cofilin-independent pathway also involved in neuronal function. A better understanding of the differences between both LIMKs and of the precise molecular mechanisms involved in their mode of action and regulation is now required to improve our understanding of the physiopathology of the neuronal diseases associated with LIMKs.

Consistent and reproducible staining of glia by a modified Golgi-Cox method

BACKGROUND

Golgi-Cox staining is a powerful histochemical approach which has been used extensively to visualize the morphology of neurons and glia. However, its usage as a first-choice method is hindered by its uncertain nature, diminished consistency and lengthy staining duration. The FD Rapid GolgiStain™ Kit (FD Neurotechnologies, Inc., USA) has been developed by employing the Golgi-Cox approach. It is a simple, reliable and reproducible way of performing Golgi impregnation for the analysis of neuronal morphology.

NEW METHOD

We report here simple modifications to the manufacturer's protocol which enable reproducible and reliable staining of glial cells.

RESULTS

Exposure of brain tissue to 4% paraformaldehyde (PFA) during perfusion followed by postfixation with 8% glutaraldehyde in 4% PFA led to only glial cells being stained, whereas in the absence of postfixation both neurons and glia were stained with unclear morphology. Additionally, we found that impregnation at 26°C±1 was critical to attain uniform staining.

COMPARISON WITH EXISTING METHOD

Our modified Golgi-Cox approach is consistent and reproducible and affords uniform glial staining throughout the brain.

CONCLUSION

As this protocol stains only a small percentage of cells, it is suitable for the analysis of individual cells.

ADF/cofilin: a crucial regulator of synapse physiology and behavior

Actin filaments (F-actin) are the major structural component of excitatory synapses, being present in presynaptic terminals and in postsynaptic dendritic spines. In the last decade, it has been appreciated that actin dynamics, the assembly and disassembly of F-actin, is crucial not only for the structure of excitatory synapses, but also for pre- and postsynaptic physiology. Hence, regulators of actin dynamics take a central role in mediating neurotransmitter release, synaptic plasticity, and ultimately behavior. Actin depolymerizing proteins of the ADF/cofilin family are essential regulators of actin dynamics, and a number of recent studies highlighted their crucial functions in excitatory synapses. In dendritic spines, ADF/cofilin activity is required for spine enlargement during initial long-term potentiation (LTP), but needs to be switched off during spine stabilization and LTP consolidation. Conversely, active ADF/cofilin is needed for spine pruning during long-term depression (LTD). Moreover, ADF/cofilin controls activity-induced synaptic availability of glutamate receptors, and exocytosis of synaptic vesicles. These data show that the activity of ADF/cofilin in synapses needs to be spatially and temporally tightly controlled through several upstream regulatory pathways, which have been identified recently. Hence, ADF/cofilin-controlled actin dynamics emerged as a critical and central regulator of synapse physiology. In this review, I will summarize and discuss our current knowledge on the roles of ADF/cofilin in synapse physiology and behavior, by focusing on excitatory synapses of the mammalian central nervous system.

Rho family GTPases: key players in neuronal development, neuronal survival, and neurodegeneration

The Rho family of GTPases belongs to the Ras superfamily of low molecular weight (∼21 kDa) guanine nucleotide binding proteins. The most extensively studied members are RhoA, Rac1, and Cdc42. In the last few decades, studies have demonstrated that Rho family GTPases are important regulatory molecules that link surface receptors to the organization of the actin and microtubule cytoskeletons. Indeed, Rho GTPases mediate many diverse critical cellular processes, such as gene transcription, cell–cell adhesion, and cell cycle progression. However, Rho GTPases also play an essential role in regulating neuronal morphology. In particular, Rho GTPases regulate dendritic arborization, spine morphogenesis, growth cone development, and axon guidance. In addition, more recent efforts have underscored an important function for Rho GTPases in regulating neuronal survival and death. Interestingly, Rho GTPases can exert either a pro-survival or pro-death signal in neurons depending upon both the cell type and neurotoxic insult involved. This review summarizes key findings delineating the involvement of Rho GTPases and their effectors in the regulation of neuronal survival and death. Collectively, these results suggest that dysregulation of Rho family GTPases may potentially underscore the etiology of some forms of neurodegenerative disease such as amyotrophic lateral sclerosis.

Ablation of ErbB4 from excitatory neurons leads to reduced dendritic spine density in mouse prefrontal cortex

Dendritic spine loss is observed in many psychiatric disorders, including schizophrenia, and likely contributes to the altered sense of reality, disruption of working memory, and attention deficits that characterize these disorders. ErbB4, a member of the EGF family of receptor tyrosine kinases, is genetically associated with schizophrenia, suggesting that alterations in ErbB4 function contribute to the disease pathology. Additionally, ErbB4 functions in synaptic plasticity, leading us to hypothesize that disruption of ErbB4 signaling may affect dendritic spine development. We show that dendritic spine density is reduced in the dorsomedial prefrontal cortex of ErbB4 conditional whole-brain knockout mice. We find that ErbB4 localizes to dendritic spines of excitatory neurons in cortical neuronal cultures and is present in synaptic plasma membrane preparations. Finally, we demonstrate that selective ablation of ErbB4 from excitatory neurons leads to a decrease in the proportion of mature spines and an overall reduction in dendritic spine density in the prefrontal cortex of weanling (P21) mice that persists at 2 months of age. These results suggest that ErbB4 signaling in excitatory pyramidal cells is critical for the proper formation and maintenance of dendritic spines in excitatory pyramidal cells.

ADF/Cofilin Controls Synaptic Actin Dynamics and Regulates Synaptic Vesicle Mobilization and Exocytosis

Actin is a regulator of synaptic vesicle mobilization and exocytosis, but little is known about the mechanisms that regulate actin at presynaptic terminals. Genetic data on LIMK1, a negative regulator of actin-depolymerizing proteins of the ADF/cofilin family, suggest a role for ADF/cofilin in presynaptic function. However, synapse physiology is fully preserved upon genetic ablation of ADF in mice, and n-cofilin mutant mice display defects in postsynaptic plasticity, but not in presynaptic function. One explanation for this phenomenon is overlapping functions of ADF and n-cofilin in presynaptic physiology. Here, we tested this hypothesis and genetically removed ADF together with n-cofilin from synapses. In double mutants for ADF and n-cofilin, synaptic actin dynamics was impaired and more severely affected than in single mutants. The resulting cytoskeletal defects heavily affected the organization, mobilization, and exocytosis of synaptic vesicles in hippocampal CA3-CA1 synapses. Our data for the first time identify overlapping functions for ADF and n-cofilin in presynaptic physiology and vesicle trafficking. We conclude that n-cofilin is a limiting factor in postsynaptic plasticity, a function which cannot be substituted by ADF. On the presynaptic side, the presence of either ADF or n-cofilin is sufficient to control actin remodeling during vesicle release.

Omega-3 fatty acid deficiency disrupts endocytosis, neuritogenesis, and mitochondrial protein pathways in the mouse hippocampus

Omega-3 fatty acid (n-3 FA) deficiency is an environmental risk factor for schizophrenia, yet characterization of the consequences of deficiency at the protein level in the brain is limited. We aimed to identify the protein pathways disrupted as a consequence of chronic n-3 deficiency in the hippocampus of mice. Fatty acid analysis of the hippocampus following chronic dietary deficiency revealed a 3-fold decrease (p < 0.001) in n-3 FA levels. Label free LC-MS/MS analysis identified and profiled 1008 proteins, of which 114 were observed to be differentially expressed between n-3 deficient and control groups (n = 8 per group). The cellular processes that were most implicated were neuritogenesis, endocytosis, and exocytosis, while specific protein pathways that were most significantly dysregulated were mitochondrial dysfunction and clathrin mediated endocytosis (CME). In order to characterize whether these processes and pathways are ones influenced by antipsychotic medication, we used LC-MS/MS to test the differential expression of these 114 proteins in the hippocampus of mice chronically treated with the antipsychotic agent haloperidol. We observed 23 of the 114 proteins to be differentially expressed, 17 of which were altered in the opposite direction to that observed following n-3 deficiency. Overall, our findings point to disturbed synaptic function, neuritogenesis, and mitochondrial function as a consequence of dietary deficiency in n-3 FA. This study greatly aids our understanding of the molecular mechanism by which n-3 deficiency impairs normal brain function, and provides clues as to how n-3 FA exert their therapeutic effect in early psychosis.

Physiological roles of Rho and Rho effectors in mammals

Rho GTPase is a master regulator controlling cytoskeleton in multiple contexts such as cell migration, adhesion and cytokinesis. Of several Rho GTPases in mammals, the best characterized is the Rho subfamily including ubiquitously expressed RhoA and its homologs RhoB and RhoC. Upon binding GTP, Rho exerts its functions through downstream Rho effectors, such as ROCK, mDia, Citron, PKN, Rhophilin and Rhotekin. Until recently, our knowledge about functions of Rho and Rho effectors came mostly from in vitro studies utilizing cultured cells, and their physiological roles in vivo were largely unknown. However, gene-targeting studies of Rho and its effectors have now unraveled their tissue- and cell-specific roles and provide deeper insight into the physiological function of Rho signaling in vivo. In this article, we briefly describe previous studies of the function of Rho and its effectors in vitro and then review and discuss recent studies on knockout mice of Rho and its effectors.

An ASK1-p38 signalling pathway mediates hydrogen peroxide-induced toxicity in NG108-15 neuronal cells

Reactive oxygen species (ROS) are believed to be involved in many forms of neurodegeneration, including ischaemic infarct damage and Alzheimer's disease. Despite the known involvement of p38 and JNK MAP kinases in mediating apoptosis and cell death in a variety of cell types, the details of the signalling pathways activated in neuronal cells by ROS are poorly characterised. Recently TAK1 (MAP3K7), a kinase upstream of JNK and p38, has attracted attention as a possible mediator of ischaemic cell death. This study tested the hypothesis that hydrogen peroxide (H2O2), which produces ROS, induces apoptosis in the NG108-15 neuronal cell line via activation of either TAK1 or the related kinase ASK1 (MAP3K5). H2O2 caused a concentration-dependent reduction in cell viability associated with caspase 3 activation. Loss of cell viability was inhibited by a selective caspase 3 inhibitor, and by the p38 inhibitor SB203580, but was not affected by the JNK inhibitor SP600125. The selective TAK1 inhibitor 5Z-7-oxozeaenol (5Z-7) exacerbated the loss of cell viability, whereas the ASK1 inhibitor NQDI-1 completely prevented caspase activation and cell death. These results show that pharmacological inhibition of ASK1 is neuroprotective, implicating an ASK1-p38 signalling pathway in ROS-induced apoptosis in neurones. The results also imply that the role of TAK1 may be neuroprotective rather than pro-degenerative.

Estrogen promotes learning-related plasticity by modifying the synaptic cytoskeleton

Estrogen's acute, facilitatory effects on glutamatergic transmission and long-term potentiation (LTP) provide a potential explanation for the steroid's considerable influence on behavior. Recent work has identified mechanisms underlying these synaptic actions. Brief infusion of 17ß-estradiol (E2) into adult male rat hippocampal slices triggers actin polymerization within dendritic spines via a signaling cascade beginning with the GTPase RhoA and ending with inactivation of the filament-severing protein cofilin. Blocking this sequence, or actin polymerization itself, eliminates E2's effects on synaptic physiology. Notably, the theta burst stimulation used to induce LTP activates the same signaling pathway as E2 plus events that stabilize the reorganization of the sub-synaptic cytoskeleton. These observations suggest that E2 elicits a partial form of LTP, resulting in an increase of fast excitatory postsynaptic potentials (EPSPs) and a reduction in the threshold for lasting synaptic changes. While E2's effects on the cytoskeleton could be direct, results described here indicate that the hormone activates synaptic tropomyosin-related kinase B (TrkB) receptors for brain-derived neurotrophic factor (BDNF), a releasable neurotrophin that stimulates the RhoA to cofilin pathway. It is therefore possible that E2 acts via transactivation of neighboring receptors to modify the composition and structure of excitatory contacts. Finally, there is the question of whether a loss of acute synaptic actions contributes to the memory problems associated with estrogen depletion. Initial tests found that ovariectomy in middle-aged rats disrupts RhoA signaling, actin polymerization, and LTP consolidation. Acute applications of E2 reversed these defects, a result consistent with the idea that disturbances to actin management are one cause of behavioral effects that emerge with reductions in steroid levels.

The role of small GTPases in neuronal morphogenesis and polarity

The highly dynamic remodeling and cross talk of the microtubule and actin cytoskeleton support neuronal morphogenesis. Small RhoGTPases family members have emerged as crucial regulators of cytoskeletal dynamics. In this review we will comprehensively analyze findings that support the participation of RhoA, Rac, Cdc42, and TC10 in different neuronal morphogenetic events ranging from migration to synaptic plasticity. We will specifically address the contribution of these GTPases to support neuronal polarity and axonal elongation.

Prenatal activation of Toll-like receptors-3 by administration of the viral mimetic poly(I:C) changes synaptic proteins, N-methyl-D-aspartate receptors and neurogenesis markers in offspring

Background

There is mounting evidence for a neurodevelopmental basis for disorders such as autism and schizophrenia, in which prenatal or early postnatal events may influence brain development and predispose the young to develop these and related disorders. We have now investigated the effect of a prenatal immune challenge on brain development in the offspring. Pregnant rats were treated with the double-stranded RNA polyinosinic:polycytidylic acid (poly(I:C); 10 mg/kg) which mimics immune activation occurring after activation of Toll-like receptors-3 (TLR3) by viral infection. Injections were made in late gestation (embryonic days E14, E16 and E18), after which parturition proceeded naturally and the young were allowed to develop up to the time of weaning at postnatal day 21 (P21). The brains of these animals were then removed to assess the expression of 13 different neurodevelopmental molecules by immunoblotting.

Results

Measurement of cytokine levels in the maternal blood 5 hours after an injection of poly(I:C) showed significantly increased levels of monocyte chemoattractant protein-1 (MCP-1), confirming immune activation. In the P21 offspring, significant changes were detected in the expression of GluN1 subunits of NMDA receptors, with no difference in GluN2A or GluN2B subunits or the postsynaptic density protein PSD-95 and no change in the levels of the related small GTPases RhoA or RhoB, or the NMDA receptor modulator EphA4. Among presynaptic molecules, a significant increase in Vesicle Associated Membrane Protein-1 (VAMP-1; synaptobrevin) was seen, with no change in synaptophysin or synaptotagmin. Proliferating Cell Nuclear Antigen (PCNA), as well as the neurogenesis marker doublecortin were unchanged, although Sox-2 levels were increased, suggesting possible changes in the rate of new cell differentiation.

Conclusions

The results reveal the induction by prenatal poly(I:C) of selective molecular changes in the brains of P21 offspring, affecting primarily molecules associated with neuronal development and synaptic transmission. These changes may contribute to the behavioural abnormalities that have been reported in adult animals after exposure to poly(I:C) and which resemble symptoms seen in schizophrenia and related disorders.

Role of RhoB in the regulation of pulmonary endothelial and smooth muscle cell responses to hypoxia

RATIONALE

RhoA and Rho kinase contribute to pulmonary vasoconstriction and vascular remodeling in pulmonary hypertension. RhoB, a protein homologous to RhoA and activated by hypoxia, regulates neoplastic growth and vasoconstriction but its role in the regulation of pulmonary vascular function is not known.

OBJECTIVE

To determine the role of RhoB in pulmonary endothelial and smooth muscle cell responses to hypoxia and in pulmonary vascular remodeling in chronic hypoxia-induced pulmonary hypertension.

METHODS AND RESULTS

Hypoxia increased expression and activity of RhoB in human pulmonary artery endothelial and smooth muscle cells, coincidental with activation of RhoA. Hypoxia or adenoviral overexpression of constitutively activated RhoB increased actomyosin contractility, induced endothelial permeability, and promoted cell growth; dominant negative RhoB or manumycin, a farnesyltransferase inhibitor that targets the vascular function of RhoB, inhibited the effects of hypoxia. Coordinated activation of RhoA and RhoB maximized the hypoxia-induced stress fiber formation caused by RhoB/mammalian homolog of Drosophila diaphanous-induced actin polymerization and RhoA/Rho kinase-induced phosphorylation of myosin light chain on Ser19. Notably, RhoB was specifically required for hypoxia-induced factor-1α stabilization and for hypoxia- and platelet-derived growth factor-induced cell proliferation and migration. RhoB deficiency in mice markedly attenuated development of chronic hypoxia-induced pulmonary hypertension, despite compensatory expression of RhoA in the lung.

CONCLUSIONS

RhoB mediates adaptational changes to acute hypoxia in the vasculature, but its continual activation by chronic hypoxia can accentuate vascular remodeling to promote development of pulmonary hypertension. RhoB is a potential target for novel approaches (eg, farnesyltransferase inhibitors) aimed at regulating pulmonary vascular tone and structure.

Morphological and functional reversal of phenotypes in a mouse model of Rett syndrome

Rett syndrome is a neurological disorder caused by mutation of the X-linked MECP2 gene. Mice lacking functional Mecp2 display a spectrum of Rett syndrome-like signs, including disturbances in motor function and abnormal patterns of breathing, accompanied by structural defects in central motor areas and the brainstem. Although routinely classified as a neurodevelopmental disorder, many aspects of the mouse phenotype can be effectively reversed by activation of a quiescent Mecp2 gene in adults. This suggests that absence of Mecp2 during brain development does not irreversibly compromise brain function. It is conceivable, however, that deep-seated neurological defects persist in mice rescued by late activation of Mecp2. To test this possibility, we have quantitatively analysed structural and functional plasticity of the rescued adult male mouse brain. Activation of Mecp2 in ∼70% of neurons reversed many morphological defects in the motor cortex, including neuronal size and dendritic complexity. Restoration of Mecp2 expression was also accompanied by a significant improvement in respiratory and sensory-motor functions, including breathing pattern, grip strength, balance beam and rotarod performance. Our findings sustain the view that MeCP2 does not play a pivotal role in brain development, but may instead be required to maintain full neurological function once development is complete.

Molecular changes associated with hippocampal long-lasting depression induced by the serine protease subtilisin-A

The serine protease subtilisin-A (SubA) induces a form of long-term depression (LTD) of synaptic transmission in the rat hippocampus, and molecular changes associated with SubA-induced LTD (SubA-LTD) were explored by using recordings of evoked postsynaptic potentials and immunoblotting. SubA-LTD was prevented by a selective inhibitor of SubA proteolysis, but the same inhibitor did not affect LTD induced by electrical stimulation or activation of metabotropic glutamate receptors. SubA-LTD was reduced by the protein kinase inhibitors genistein and lavendustin A, although not by inhibitors of p38 mitogen-activated protein kinase, glycogen synthase kinase-3, or protein phosphatases. It was also reduced by (RS)-α-methyl-4-carboxyphenylglycine, a broad-spectrum antagonist at metabotropic glutamate receptors. Inhibition of the Rho kinase enzyme Rho-associated coiled-coil kinase reduced SubA-LTD, although inhibitors of the RhoGTPase-activating enzymes farnesyl transferase and geranylgeranyl transferase did not. In addition, a late phase of SubA-LTD was dependent on new protein synthesis. There was a small, non-significant difference in SubA-LTD between wild-type and RhoB(-/-) mice. Marked decreases were seen in the levels of Unc-5H3, a protein that is intimately involved in the development and plasticity of glutamatergic synapses. Smaller changes were noted, at higher concentrations of SubA, in Unc-5H1, vesicle-associated membrane protein-1 (synaptobrevin), and actin, with no changes in the levels of synaptophysin, synaptotagmin, RhoA, or RhoB. None of these changes was associated with LTD induced electrically or by the metabotropic glutamate receptor agonist (RS)-3,5-dihydroxyphenylglycine. These results indicate that SubA induces molecular changes that overlap with other forms of LTD, but that the overall molecular profile of SubA-LTD is quite different.

Signalling pathways underlying structural plasticity of dendritic spines

Synaptic plasticity, or changes in synaptic strength, is thought to underlie learning and memory. Imaging studies, mainly in brain slices, have revealed that long-term synaptic plasticity of excitatory synapses in hippocampal neurons is coupled with structural plasticity of dendritic spines, which is thought to be essential for inducing and regulating functional plasticity. Using pharmacological and genetic manipulation, the signalling network underlying structural plasticity has been extensively studied. Furthermore, the recent advent of fluorescence resonance energy transfer (FRET) imaging techniques has provided a readout of the dynamics of signal transduction in dendritic spines undergoing structural plasticity. These studies reveal the signalling pathways relaying Ca²⁺ to the functional and structural plasticity of dendritic spines.

Altered apoptotic responses in neurons lacking RhoB GTPase

Caspase 3 activation has been linked to the acute neurotoxic effects of central nervous system damage, as in traumatic brain injury or cerebral ischaemia, and also to the early events leading to long-term neurodegeneration, as in Alzheimer's disease. However, the precise mechanisms activating caspase 3 in neuronal injury are unclear. RhoB is a member of the Rho GTPase family that is dramatically induced by cerebral ischaemia or neurotrauma, both in preclinical models and clinically. In the current study, we tested the hypothesis that RhoB might directly modulate caspase 3 activity and apoptotic or necrotic responses in neurons. Over-expression of RhoB in the NG108-15 neuronal cell line or in cultured corticohippocampal neurons elevated caspase 3 activity without inducing overt toxicity. Cultured corticohippocampal neurons from RhoB knockout mice did not show any differences in sensitivity to a necrotic stimulus - acute calcium ionophore exposure - compared with neurons from wild-type mice. However, corticohippocampal neurons lacking RhoB exhibited a reduction in the degree of DNA fragmentation and caspase 3 activation induced by the apoptotic agent staurosporine, in parallel with increased neuronal survival. Staurosporine induction of caspase 9 activity was also suppressed. RhoB knockout mice showed reduced basal levels of caspase 3 activity in the adult brain. These data directly implicate neuronal RhoB in caspase 3 activation and the initial stages of programmed cell death, and suggest that RhoB may represent an attractive target for therapeutic intervention in conditions involving elevated caspase 3 activity in the central nervous system.