A role for the Ras signalling pathway in synaptic transmission and long-term memory

Transcriptomics and biochemical evidence of trigonelline ameliorating learning and memory decline in the senescence-accelerated mouse prone 8 (SAMP8) model by suppressing proinflammatory cytokines and elevating neurotransmitter release

In recent years, exploring natural compounds with functional properties to ameliorate aging-associated cognitive decline has become a research priority to ensure healthy aging. In the present study, we investigated the effects of Trigonelline (TG), a plant alkaloid, on memory and spatial learning in 16-week-old senescence-accelerated mouse model SAMP8 using an integrated approach for cognitive and molecular biology aspects. After 30 days of oral administration of TG at the dose of 5 mg/kg/day, the mice were trained in Morris Water Maze task. TG-treated SAMP8 mice exhibited significant improvement in the parameters of escape latency, distance moved, and annulus crossing index. Next, we performed a whole-genome transcriptome profiling of the mouse hippocampus using microarrays. Gene ontology analyses showed that a wide range of biological processes, including nervous system development, mitochondrial function, ATP synthesis, and several signaling pathways related to inflammation, autophagy, and neurotransmitter release, were significantly enriched in TG-treated SAMP8 compared to nontreated. Further, a nonlinear dimensionality reduction technique, Uniform Manifold Approximation and Projection (UMAP), was applied to identify clusters of functions that revealed TG primarily regulated pathways related to inflammation, followed by those involved in neurotransmitter release. In addition, a protein-protein interaction network analysis indicated that TG may exert its biological effects through negatively modulating Traf6-mediated NF-κB activation. Finally, ELISA test showed that TG treatment significantly decreased proinflammatory cytokines- TNFα and IL6 and increased neurotransmitters- dopamine, noradrenaline, and serotonin in mouse hippocampus. Altogether, our integrated bio-cognitive approach highlights the potential of TG in alleviating age-related memory and spatial impairment.

Interactions between Ras and Rap signaling pathways during neurodevelopment in health and disease

The Ras family of small GTPases coordinates tissue development by modulating cell proliferation, cell-cell adhesion, and cellular morphology. Perturbations of any of these key steps alter nervous system development and are associated with neurological disorders. While the underlying causes are not known, genetic mutations in Ras and Rap GTPase signaling pathways have been identified in numerous neurodevelopmental disorders, including autism spectrum, neurofibromatosis, intellectual disability, epilepsy, and schizophrenia. Despite diverse clinical presentations, intersections between these two signaling pathways may provide a better understanding of how deviations in neurodevelopment give rise to neurological disorders. In this review, we focus on presynaptic and postsynaptic functions of Ras and Rap GTPases. We highlight various roles of these small GTPases during synapse formation and plasticity. Based on genomic analyses, we discuss how disease-related mutations in Ras and Rap signaling proteins may underlie human disorders. Finally, we discuss how recent observations have identified molecular interactions between these pathways and how these findings may provide insights into the mechanisms that underlie neurodevelopmental disorders.

Nuclear ERK1/2 signaling potentiation enhances neuroprotection and cognition via Importinα1/KPNA2

Cell signaling is central to neuronal activity and its dysregulation may lead to neurodegeneration and cognitive decline. Here, we show that selective genetic potentiation of neuronal ERK signaling prevents cell death in vitro and in vivo in the mouse brain, while attenuation of ERK signaling does the opposite. This neuroprotective effect mediated by an enhanced nuclear ERK activity can also be induced by the novel cell penetrating peptide RB5. In vitro administration of RB5 disrupts the preferential interaction of ERK1 MAP kinase with importinα1/KPNA2 over ERK2, facilitates ERK1/2 nuclear translocation, and enhances global ERK activity. Importantly, RB5 treatment in vivo promotes neuroprotection in mouse models of Huntington's (HD), Alzheimer's (AD), and Parkinson's (PD) disease, and enhances ERK signaling in a human cellular model of HD. Additionally, RB5-mediated potentiation of ERK nuclear signaling facilitates synaptic plasticity, enhances cognition in healthy rodents, and rescues cognitive impairments in AD and HD models. The reported molecular mechanism shared across multiple neurodegenerative disorders reveals a potential new therapeutic target approach based on the modulation of KPNA2-ERK1/2 interactions.

Upregulation of RasGRF1 ameliorates spatial cognitive dysfunction in mice after chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion (CCH)-mediated cognitive impairment is a serious problem worldwide. However, given its complexity, the underlying mechanisms by which CCH induces cognitive dysfunction remain unclear, resulting in a lack of effective treatments. In this study, we aimed to determine whether changes in the expression of RasGRF1, an important protein associated with cognition and synaptic plasticity, underlie the associated impairments in cognition after CCH. We found that RasGRF1 levels markedly decreased following CCH. Through prediction and validation studies, we observed that miRNA-323-3p was upregulated after CCH and could bind to the 3'-untranslated region of Rasgrf1 mRNA and regulate its expression in vitro. Moreover, the inhibition of miRNA-323-3p upregulated Rasgrf1 expression in the hippocampus after CCH, which was reversed by Rasgrf1 siRNA. This suggests that miRNA-323-3p is an important regulator of Rasgrf1. The Morris water maze and Y maze tests showed that miRNA-323-3p inhibition and Rasgrf1 upregulation improved spatial learning and memory, and electrophysiological measurements revealed deficits in long-term potentiation after CCH that were reversed by Rasgrf1 upregulation. Dendritic spine density and mature mushroom spine density were also improved after miRNA-323-3p inhibition and Rasgrf1 upregulation. Furthermore, Rasgrf1 upregulation by miRNA-323-3p inhibition improved dendritic spine density and mature mushroom spine density and ameliorated the deterioration of synapses and postsynaptic density. Overall, RasGRF1 regulation attenuated cognitive impairment, helped maintain structural and functional synaptic plasticity, and prevented synapse deterioration after CCH. These results suggest that Rasgrf1 downregulation by miRNA-323-3p plays an important role in cognitive impairment after CCH. Thus, RasGRF1 and miRNA-323-3p may represent potential therapeutic targets for cognitive impairment after CCH.

Contributions of extracellular-signal regulated kinase 1/2 activity to the memory trace

The ability to learn from experience and consequently adapt our behavior is one of the most fundamental capacities enabled by complex and plastic nervous systems. Next to cellular and systems-level changes, learning and memory formation crucially depends on molecular signaling mechanisms. In particular, the extracellular-signal regulated kinase 1/2 (ERK), historically studied in the context of tumor growth and proliferation, has been shown to affect synaptic transmission, regulation of neuronal gene expression and protein synthesis leading to structural synaptic changes. However, to what extent the effects of ERK are specifically related to memory formation and stabilization, or merely the result of general neuronal activation, remains unknown. Here, we review the signals leading to ERK activation in the nervous system, the subcellular ERK targets associated with learning-related plasticity, and how neurons with activated ERK signaling may contribute to the formation of the memory trace.

DNA Methylation Analysis of Imprinted Genes in the Cortex and Hippocampus of Cross-Fostered Mice Selectively Bred for Increased Voluntary Wheel-Running

We have previously shown that high runner (HR) mice (from a line genetically selected for increased wheel-running behavior) have distinct, genetically based, neurobiological phenotypes as compared with non-selected control (C) mice. However, developmental programming effects during early life, including maternal care and parent-of-origin-dependent expression of imprinted genes, can also contribute to variation in physical activity. Here, we used cross-fostering to address two questions. First, do HR mice have altered DNA methylation profiles of imprinted genes in the brain compared to C mice? Second, does maternal upbringing further modify the DNA methylation status of these imprinted genes? To address these questions, we cross-fostered all offspring at birth to create four experimental groups: C pups to other C dams, HR pups to other HR dams, C pups to HR dams, and HR pups to C dams. Bisulfite sequencing of 16 imprinted genes in the cortex and hippocampus revealed that the HR line had altered DNA methylation patterns of the paternally imprinted genes, Rasgrf1 and Zdbf2, as compared with the C line. Both fostering between the HR and C lines and sex modified the DNA methylation profiles for the paternally expressed genes Mest, Peg3, Igf2, Snrpn, and Impact. Ig-DMR, a gene with multiple paternal and maternal imprinted clusters, was also affected by maternal upbringing and sex. Our results suggest that differential methylation patterns of imprinted genes in the brain could contribute to evolutionary increases in wheel-running behavior and are also dependent on maternal upbringing and sex.

Cellular messenger molecules mediating addictive drug-induced cognitive impairment: cannabinoids, ketamine, methamphetamine, and cocaine

Background

Cognitive impairment is a commonly reported symptom with increasing life spans. Numerous studies have focused on identifying precise targets to relieve or reduce cognitive impairment; however, its underlying mechanism remains elusive. Most patients or animals exposed to addictive drugs exhibit cognitive impairment. Accordingly, the present review discusses the molecular changes induced by addictive drugs to clarify potential mechanisms that mediate cognitive impairments.

Main body

We investigated changes in cognitive function using four drugs: cannabinoids, ketamine, methamphetamine, and cocaine. Chronic administration of most addictive drugs reduces overall cognitive functions, such as working, spatial, and long-term recognition memories. Levels of several transcription factors involved in neuronal differentiation, as well as functional components of neurotransmitter receptors in neuronal cells, are reportedly altered. In addition, inflammatory factors showed a generally increasing trend. These impairments could be mediated by neuroinflammation, synaptic activity, and neuronal plasticity.

Conclusion

This review outlines the effects of acute or chronic drug use and potential molecular alterations in the central nervous system. In the central nervous system, addictive drug-induced changes in molecular pathways associated with cognitive function might play a pivotal role in elucidating the pathogenesis of cognitive impairment.

Rac-maninoff and Rho-vel: The symphony of Rho-GTPase signaling at excitatory synapses

Synaptic connections between neurons are essential for every facet of human cognition and are thus regulated with extreme precision. Rho-family GTPases, molecular switches that cycle between an active GTP-bound state and an inactive GDP-bound state, comprise a critical feature of synaptic regulation. Rho-GTPases are exquisitely controlled by an extensive suite of activators (GEFs) and inhibitors (GAPs and GDIs) and interact with many different signalling pathways to fulfill their roles in orchestrating the development, maintenance, and plasticity of excitatory synapses of the central nervous system. Among the mechanisms that control Rho-GTPase activity and signalling are cell surface receptors, GEF/GAP complexes that tightly regulate single Rho-GTPase dynamics, GEF/GAP and GEF/GEF functional complexes that coordinate multiple Rho-family GTPase activities, effector positive feedback loops, and mutual antagonism of opposing Rho-GTPase pathways. These complex regulatory mechanisms are employed by the cells of the nervous system in almost every step of development, and prominently figure into the processes of synaptic plasticity that underlie learning and memory. Finally, misregulation of Rho-GTPases plays critical roles in responses to neuronal injury, such as traumatic brain injury and neuropathic pain, and in neurodevelopmental and neurodegenerative disorders, including intellectual disability, autism spectrum disorder, schizophrenia, and Alzheimer's Disease. Thus, decoding the mechanisms of Rho-GTPase regulation and function at excitatory synapses has great potential for combatting many of the biggest current challenges in mental health.

KRAS mutation: from undruggable to druggable in cancer

Cancer is the leading cause of death worldwide, and its treatment and outcomes have been dramatically revolutionised by targeted therapies. As the most frequently mutated oncogene, Kirsten rat sarcoma viral oncogene homologue (KRAS) has attracted substantial attention. The understanding of KRAS is constantly being updated by numerous studies on KRAS in the initiation and progression of cancer diseases. However, KRAS has been deemed a challenging therapeutic target, even "undruggable", after drug-targeting efforts over the past four decades. Recently, there have been surprising advances in directly targeted drugs for KRAS, especially in KRAS (G12C) inhibitors, such as AMG510 (sotorasib) and MRTX849 (adagrasib), which have obtained encouraging results in clinical trials. Excitingly, AMG510 was the first drug-targeting KRAS (G12C) to be approved for clinical use this year. This review summarises the most recent understanding of fundamental aspects of KRAS, the relationship between the KRAS mutations and tumour immune evasion, and new progress in targeting KRAS, particularly KRAS (G12C). Moreover, the possible mechanisms of resistance to KRAS (G12C) inhibitors and possible combination therapies are summarised, with a view to providing the best regimen for individualised treatment with KRAS (G12C) inhibitors and achieving truly precise treatment.

Potential roles of imprinted genes in the teratogenic effects of alcohol on the placenta, somatic growth, and the developing brain

Despite several decades of research and prevention efforts, fetal alcohol spectrum disorders (FASD) remain the most common preventable cause of neurodevelopmental disabilities worldwide. Animal and human studies have implicated fetal alcohol-induced alterations in epigenetic programming as a chief mechanism in FASD. Several studies have demonstrated fetal alcohol-related alterations in methylation and expression of imprinted genes in placental, brain, and embryonic tissue. Imprinted genes are epigenetically regulated in a parent-of-origin-specific manner, in which only the maternal or paternal allele is expressed, and the other allele is silenced. The chief functions of imprinted genes are in placental development, somatic growth, and neurobehavior-three domains characteristically affected in FASD. In this review, we summarize the growing body of literature characterizing prenatal alcohol-related alterations in imprinted gene methylation and/or expression and discuss potential mechanistic roles for these alterations in the teratogenic effects of prenatal alcohol exposure. Future research is needed to examine potential physiologic mechanisms by which alterations in imprinted genes disrupt development in FASD, which may, in turn, elucidate novel targets for intervention. Furthermore, mechanistic alterations in imprinted gene expression and/or methylation in FASD may inform screening assays that identify individuals with FASD neurobehavioral deficits who may benefit from early interventions.

Exome array identifies functional exonic biomarkers for pediatric dental caries

BACKGROUND

Pediatric dental caries is common among Arab children, however we are still searching for possible genes and molecular mechanisms that influence caries development.

AIM

To identity genetic predispositions of dental caries among Saudi children with high DMFT (Decayed, Missing, and Filled Teeth).

DESIGN

This case-control study analysed putative functional exonic-variants (n = 243,345) to study the molecular genetics of pediatric caries with high dmft index, 8.75 ± 4.16 on Arab-ancestry subjects with primary dentition (n = 111; 76 cases, dmft>5 and 35 controls, dmft = 0).

RESULTS

Pediatric caries is significantly associated with single nucleotide polymorphisms (SNP) in the GRIN2B-rs4764039C (p-value = 2.03 × 10^-08) and CFH-rs1065489G (p-value = 8.26 × 10^-08) genes, even after Bonferroni correction. Irregular tooth brushing habits (p = 0.0404) and irregular dental visits (p = 0.0050) are significantly associated with caries. Functional enrichment analysis of significant genes is associated with calcium-activated chloride channel, Staphylococcus aureus infection, and N-linked glycosylation.

CONCLUSION

Genetic predispositions are found to be significantly associated with the high prevalence of pediatric caries, which is a disorder of multigene-environment interaction. The significant functional exonic variants identified can be biomarkers for the early diagnosis of pediatric dental caries in Arabs.

Flavonoid fisetin reverses impaired hippocampal synaptic plasticity and cognitive function by regulating the function of AMPARs in a male rat model of schizophrenia

Cognitive deficits are the core feature of schizophrenia and effective treatment strategies are still missing. Previous studies have reported that fisetin promotes long-term potentiation (LTP) and cognitive function in normal rodents and other model animals of neurological diseases. The aim of this study was to assess the effect of fisetin on synaptic plasticity and cognitive deficits caused by a brief disruption of N-methyl-D-aspartate receptors (NMDARs) with dizocilpine (MK-801) during early development in rats. The cognitive performance was examined by the Morris water maze task and a fear conditioning test. Hippocampal synaptic plasticity was investigated by field potential recording. The expression of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs) and cognition-related proteins was measured by western blotting. We found that intraperitoneal administration of fisetin rescued hippocampus-dependent spatial and contextual fear memory in MK-801 rats. In parallel with these behavioral results, fisetin treatment in MK-801 rats reversed the impairment of hippocampal LTP. At the molecular level, fisetin treatment selectively increased the phosphorylation and surface expression of AMPA receptor subunit 1 (GluA1) in MK-801-treated rats. Moreover, fisetin restored the phosphorylation levels of calcium-calmodulin-dependent kinaseII (CaMKII), cAMP response element-binding protein (CREB), and the extracellular signal-regulated kinase (ERK1/2) in MK-801-treated rats. Collectively, our findings demonstrate that fisetin treatment can reverse the deficits of hippocampal synaptic plasticity and memory in a male rat model of schizophrenia by restoring the phosphorylation and surface expression of AMPAR GluA1 subunit, suggesting fisetin as a promising therapeutic candidate for schizophrenia-associated cognitive deficits.

Ras GEF Mouse Models for the Analysis of Ras Biology and Signaling

Animal models have become in recent years a crucial tool to understand the physiological and pathological roles of many cellular proteins. They allow analysis of the functional consequences of [1] complete or partial (time- or organ-limited) removal of specific proteins (knockout animals), [2] the exchange of a wild-type allele for a mutant or truncated version found in human illnesses (knock-in), or [3] the effect of overexpression of a given protein in the whole body or in specific organs (transgenic mice). In this regard, the study of phenotypes in Ras GEF animal models has allowed researchers to find specific functions for otherwise very similar proteins, uncovering their role in physiological contexts such as memory formation, lymphopoiesis, photoreception, or body homeostasis. In addition, mouse models have been used to unveil the functional role of Ras GEFs under pathological conditions, including Noonan syndrome, skin tumorigenesis, inflammatory diseases, diabetes, or ischemia among others. In the following sections, we will describe the methodological approaches employed for Ras GEF animal model analyses, as well as the main discoveries made.

Proteomic signature of the Dravet syndrome in the genetic Scn1a-A1783V mouse model

BACKGROUND

Dravet syndrome is a rare, severe pediatric epileptic encephalopathy associated with intellectual and motor disabilities. Proteomic profiling in a mouse model of Dravet syndrome can provide information about the molecular consequences of the genetic deficiency and about pathophysiological mechanisms developing during the disease course.

METHODS

A knock-in mouse model of Dravet syndrome with Scn1a haploinsufficiency was used for whole proteome, seizure, and behavioral analysis. Hippocampal tissue was dissected from two- (prior to epilepsy manifestation) and four- (following epilepsy manifestation) week-old male mice and analyzed using LC-MS/MS with label-free quantification. Proteomic data sets were subjected to bioinformatic analysis including pathway enrichment analysis. The differential expression of selected proteins was confirmed by immunohistochemical staining.

RESULTS

The findings confirmed an increased susceptibility to hyperthermia-associated seizures, the development of spontaneous seizures, and behavioral alterations in the novel Scn1a-A1873V mouse model of Dravet syndrome. As expected, proteomic analysis demonstrated more pronounced alterations following epilepsy manifestation. In particular, proteins involved in neurotransmitter dynamics, receptor and ion channel function, synaptic plasticity, astrogliosis, neoangiogenesis, and nitric oxide signaling showed a pronounced regulation in Dravet mice. Pathway enrichment analysis identified several significantly regulated pathways at the later time point, with pathways linked to synaptic transmission and glutamatergic signaling dominating the list.

CONCLUSION

In conclusion, the whole proteome analysis in a mouse model of Dravet syndrome demonstrated complex molecular alterations in the hippocampus. Some of these alterations may have an impact on excitability or may serve a compensatory function, which, however, needs to be further confirmed by future investigations. The proteomic data indicate that, due to the molecular consequences of the genetic deficiency, the pathophysiological mechanisms may become more complex during the course of the disease. As a result, the management of Dravet syndrome may need to consider further molecular and cellular alterations. Ensuing functional follow-up studies, this data set may provide valuable guidance for the future development of novel therapeutic approaches.

Impaired contextual fear conditioning in RasGRF2 mutant mice is likely Ras-ERK-dependent

Ras/Raf/MEK/ERK (Ras-ERK) signaling has been shown to play an important role in fear acquisition. However, little information is known regarding the mechanisms that contribute to the regulation of this pathway in terms of the learning of conditioned fears. Ras Guanine Nucleotide Releasing Factor 2 (RasGRF2) is one of two guanine nucleotide exchange factors (GEF) that regulates the Ras-ERK signaling pathway in a Ca²⁺-dependent manner via control of the cycling of Ras isoforms between an inactive and active state. Here we sought to determine the role of RasGRF2 on contextual fear conditioning in RasGRF2 knockout (KO) and their wild type (WT) counterparts. Male KO and WT mice underwent a single session of contextual fear conditioning (12 min, 4 unsignaled shocks), followed by either daily 12-min retention trials or the molecular analysis of Ras activation and pERK1/2 activity. KO mice showed an impaired acquisition of contextual fear, as demonstrated by reduced freezing during fear conditioning and 24-hr retention tests relative to WT mice. Ras analysis following fear conditioning demonstrated a reduction in Ras activation in the hippocampus as well as a reduction in pERK1/2 in the CA1 region of the hippocampus in KO mice, suggesting that the decrease in fear conditioning in KO mice is at least in part due to the impairment of Ras-ERK signaling in the hippocampus during learning. These data indicate a role for RasGRF2 in contextual fear conditioning in mice that may be Ras-ERK-dependent.

MMP-9 Signaling Pathways That Engage Rho GTPases in Brain Plasticity

The extracellular matrix (ECM) has been identified as a critical factor affecting synaptic function. It forms a functional scaffold that provides both the structural support and the reservoir of signaling molecules necessary for communication between cellular constituents of the central nervous system (CNS). Among numerous ECM components and modifiers that play a role in the physiological and pathological synaptic plasticity, matrix metalloproteinase 9 (MMP-9) has recently emerged as a key molecule. MMP-9 may contribute to the dynamic remodeling of structural and functional plasticity by cleaving ECM components and cell adhesion molecules. Notably, MMP-9 signaling was shown to be indispensable for long-term memory formation that requires synaptic remodeling. The core regulators of the dynamic reorganization of the actin cytoskeleton and cell adhesion are the Rho family of GTPases. These proteins have been implicated in the control of a wide range of cellular processes occurring in brain physiology and pathology. Here, we discuss the contribution of Rho GTPases to MMP-9-dependent signaling pathways in the brain. We also describe how the regulation of Rho GTPases by post-translational modifications (PTMs) can influence these processes.

Pedigree-Based Gene Mapping Supports Previous Loci and Reveals Novel Suggestive Loci in Specific Language Impairment

Purpose Specific language impairment (SLI) is characterized by a delay in language acquisition despite a lack of other developmental delays or hearing loss. Genetics of SLI is poorly understood. The purpose of this study is to identify SLI genetic loci through family-based linkage mapping. Method We performed genome-wide parametric linkage analysis in six families segregating with SLI. An age-appropriate standardized omnibus language measure was used to categorically define the SLI phenotype. Results A suggestive linkage region replicated a previous region of interest with the highest logarithm of odds (LOD) score of 2.40 at 14q11.2-q13.3 in Family 489. A paternal parent-of-origin effect associated with SLI and language phenotypes on a nonsynonymous single nucleotide polymorphism (SNP) in NOP9 (14q12) was reported previously. Linkage analysis identified a new SLI locus at 15q24.3-25.3 with the highest parametric LOD score of 3.06 in Family 315 under a recessive mode of inheritance. Suggestive evidence of linkage was also revealed at 4q31.23-q35.2 in Family 300, with the highest LOD score of 2.41. Genetic linkage was not identified in the other three families included in parametric linkage analysis. Conclusions These results are the first to report genome-wide suggestive linkage with a total language standard score on an age-appropriate omnibus language measure across a wide age range. Our findings confirm previous reports of a language-associated locus on chromosome 14q, report new SLI loci, and validate the pedigree-based parametric linkage analysis approach to mapping genes for SLI. Supplemental Material https://doi.org/10.23641/asha.13203218.

ERK signalling: a master regulator of cell behaviour, life and fate

The proteins extracellular signal-regulated kinase 1 (ERK1) and ERK2 are the downstream components of a phosphorelay pathway that conveys growth and mitogenic signals largely channelled by the small RAS GTPases. By phosphorylating widely diverse substrates, ERK proteins govern a variety of evolutionarily conserved cellular processes in metazoans, the dysregulation of which contributes to the cause of distinct human diseases. The mechanisms underlying the regulation of ERK1 and ERK2, their mode of action and their impact on the development and homeostasis of various organisms have been the focus of much attention for nearly three decades. In this Review, we discuss the current understanding of this important class of kinases. We begin with a brief overview of the structure, regulation, substrate recognition and subcellular localization of ERK1 and ERK2. We then systematically discuss how ERK signalling regulates six fundamental cellular processes in response to extracellular cues. These processes are cell proliferation, cell survival, cell growth, cell metabolism, cell migration and cell differentiation.

RasGRF1 participates in the protective effect of tanshinone IIA on depressive like behaviors of a chronic unpredictable mild stress induced mouse model

Tanshinone IIA (Tan IIA) is reported to have neuroprotective effects to suppress cell apoptosis of cortical neurons induced by Aβ_25-35 through inhibiting oxidative stress. Nevertheless, few studies have investigated the effects of Tan IIA on depressive disorder. Here, we aimed to measure the effects of Tan IIA on chronic unpredictable mild stress (CUMS) induced mouse model and its underlying mechanism. For 28 days, mice were subjected to CUMS while Tan IIA was administered once daily at doses of 0, 1, 2.5, 5, or 10 mg/kg. CUMS exposure increased depressive-like behaviors, as indicated by increased immobility time in the forced swim and tail suspension tests, decreased sucrose preference in the sucrose preference test, and reduced exploratory behavior in the open field test. All of these behaviors were reversed dose-dependently by Tan IIA treatment. Oxidative stress was determined by measuring malondialdehyde, glutathione peroxidase, and superoxide dismutase activity and total antioxidant capacity. Levels of pro-inflammatory factors IL-1β and IL-18, cAMP response element binding protein and brain derived neurotrophic factor were detected by ELISA and western blot assay, respectively. The results showed that CUMS increased oxidative stress and pro-inflammatory factors and decreased levels of cAMP response element binding protein and brain-derived neurotrophic factor. Tan IIA treatment again reversed these effects. Importantly, RasGRF1 expression increased in CUMS-exposed mice but decreased after Tan IIA administration. Using RasGRF1^-/- mice to determine the role of RasGRF1 in mice exposed to CUMS, we found that knockdown of RasGRF1 reversed the effects of CUMS on mice, just like Tan IIA. These results indicate that Tan IIA may reverse depressive-like behaviors in CUMS-exposed mice by regulating RasGRF1.

Genetic variants linked to myopic macular degeneration in persons with high myopia: CREAM Consortium

Purpose

To evaluate the roles of known myopia-associated genetic variants for development of myopic macular degeneration (MMD) in individuals with high myopia (HM), using case-control studies from the Consortium of Refractive Error and Myopia (CREAM).

Methods

A candidate gene approach tested 50 myopia-associated loci for association with HM and MMD, using meta-analyses of case-control studies comprising subjects of European and Asian ancestry aged 30 to 80 years from 10 studies. Fifty loci with the strongest associations with myopia were chosen from a previous published GWAS study. Highly myopic (spherical equivalent [SE] ≤ -5.0 diopters [D]) cases with MMD (N = 348), and two sets of controls were enrolled: (1) the first set included 16,275 emmetropes (SE ≤ -0.5 D); and (2) second set included 898 highly myopic subjects (SE ≤ -5.0 D) without MMD. MMD was classified based on the International photographic classification for pathologic myopia (META-PM).

Results

In the first analysis, comprising highly myopic cases with MMD (N = 348) versus emmetropic controls without MMD (N = 16,275), two SNPs were significantly associated with high myopia in adults with HM and MMD: (1) rs10824518 (P = 6.20E-07) in KCNMA1, which is highly expressed in human retinal and scleral tissues; and (2) rs524952 (P = 2.32E-16) near GJD2. In the second analysis, comprising highly myopic cases with MMD (N = 348) versus highly myopic controls without MMD (N = 898), none of the SNPs studied reached Bonferroni-corrected significance.

Conclusions

Of the 50 myopia-associated loci, we did not find any variant specifically associated with MMD, but the KCNMA1 and GJD2 loci were significantly associated with HM in highly myopic subjects with MMD, compared to emmetropes.

The Inhibition of RasGRF2, But Not RasGRF1, Alters Cocaine Reward in Mice

Ras/Raf/MEK/ERK (Ras-ERK) signaling has been implicated in the effects of drugs of abuse. Inhibitors of MEK1/2, the kinases upstream of ERK1/2, have been critical in defining the role of the Ras-ERK cascade in drug-dependent alterations in behavioral plasticity, but the Ras family of small GTPases has not been extensively examined in drug-related behaviors. We examined the role of Ras Guanine Nucleotide Releasing Factor 1 (RasGRF1) and 2 (RasGRF2), upstream regulators of the Ras-ERK signaling cascade, on cocaine self-administration (SA) in male mice. We first established a role for Ras-ERK signaling in cocaine SA, demonstrating that pERK1/2 is upregulated following SA in C57BL/6N mice in striatum. We then compared RasGRF1 and RasGRF2 KO mouse lines, demonstrating that cocaine SA in RasGRF2 KO mice was increased relative to WT controls, whereas RasGRF1 KO and WT mice did not differ. This effect in RasGRF2 mice is likely mediated by the Ras-ERK signaling pathway, as pERK1/2 upregulation following cocaine SA was absent in RasGRF2 KO mice. Interestingly, the lentiviral knockdown of RasGRF2 in the NAc had the opposite effect to that in RasGRF2 KO mice, reducing cocaine SA. We subsequently demonstrated that the MEK inhibitor PD325901 administered peripherally prior to cocaine SA increased cocaine intake, replicating the increase seen in RasGRF2 KO mice, whereas PD325901 administered into the NAc decreased cocaine intake, similar to the effect seen following lentiviral knockdown of RasGRF2. These data indicate a role for RasGRF2 in cocaine SA in mice that is ERK-dependent, and suggest a differential effect of global versus site-specific RasGRF2 inhibition.SIGNIFICANCE STATEMENT Exposure to drugs of abuse activates a variety of intracellular pathways, and following repeated exposure, persistent changes in these pathways contribute to drug dependence. Downstream components of the Ras-ERK signaling cascade are involved in the acute and chronic effects of drugs of abuse, but their upstream mediators have not been extensively characterized. Here we show, using a combination of molecular, pharmacological, and lentiviral techniques, that the guanine nucleotide exchange factor RasGRF2 mediates cocaine self-administration via an ERK-dependent mechanism, whereas RasGRF1 has no effect on responding for cocaine. These data indicate dissociative effects of mediators of Ras activity on cocaine reward and expand the understanding of the contribution of Ras-ERK signaling to drug-taking behavior.

The Relation Between Long-Term Synaptic Plasticity at Glutamatergic Synapses in the Amygdala and Fear Learning in Adult Heterozygous BDNF-Knockout Mice

Brain-derived neurotrophic factor (BDNF) heterozygous knockout mice (BDNF+/- mice) show fear learning deficits from 3 months of age onwards. Here, we addressed the question how this learning deficit correlates with altered long-term potentiation (LTP) in the cortical synaptic input to the lateral amygdala (LA) and at downstream intra-amygdala synapses in BDNF+/- mice. Our results reveal that the fear learning deficit in BDNF+/- mice was not paralleled by a loss of LTP, neither at cortical inputs to the LA nor at downstream intra-amygdala glutamatergic synapses. As we did observe early fear memory (30 min after training) in BDNF+/- mice while long-term memory (24 h post-training) was absent, the stable LTP in cortico-LA and downstream synapses is in line with the intact acquisition of fear memories. Ex vivo recordings in acute slices of fear-conditioned wildtype (WT) mice revealed that fear learning induces long-lasting changes at cortico-LA synapses that occluded generation of LTP 4 and 24 h after training. Overall, our data show that the intact LTP in the tested amygdala circuits is consistent with intact acquisition of fear memories in both WT and BDNF+/- mice. In addition, the lack of learning-induced long-term changes at cortico-LA synapses in BDNF+/- mice parallels the observed deficit in fear memory consolidation.

Maternal Gastrointestinal Nematode Infection Up-regulates Expression of Genes Associated with Long-Term Potentiation in Perinatal Brains of Uninfected Developing Pups

Establishment of neural networks critical for memory and cognition begins during the perinatal period but studies on the impact of maternal infection are limited. Using a nematode parasite that remains in the maternal intestine, we tested our hypothesis that maternal infection during pregnancy and early lactation would alter perinatal brain gene expression, and that the anti-inflammatory nature of this parasite would promote synaptic plasticity and long-term potentiation. Brain gene expression was largely unaffected two days after birth, but in seven-day old pups, long-term potentiation and four related pathways essential for the development of synaptic plasticity, cognition and memory were up-regulated in pups of infected dams. Interestingly, our data suggest that a lowering of Th1 inflammatory processes may underscore the apparent beneficial impact of maternal intestinal infection on long-term potentiation.

Microtopography of fear memory consolidation and extinction retrieval within prefrontal cortex and amygdala

RATIONALE

The precise neural circuitry that encodes fear memory and its extinction within the brain are not yet fully understood. Fearful memories can be persistent, resistant to extinction, and associated with psychiatric disorders, especially post-traumatic stress disorder (PTSD). Here, we investigated the microtopography of neurons activated during the recall of an extinguished fear memory, as well as the influence of time on this microtopography.

METHODS

We used the plasticity-related phosphorylated mitogen-activated protein kinase (pMAPK) to identify neurons activated in the recall of consolidated and extinguished auditory Pavlovian fear memories in rats. Quantitatively matched brain regions were used to investigate activity in the amygdala and prefrontal cortex.

RESULTS

Recall of a consolidated, nonextinguished auditory fear memory resulted in a significantly greater number of activated neurons located in the dorsolateral subdivision of the lateral amygdala (LADL) when recalled 24 h after consolidation but not when recalled 7 days later. We found that the recall of an extinction memory was associated with pMAPK activation in the ventrolateral subdivision of the lateral amygdala (LAVL). Next, we showed that the pattern of pMAPK expression in the prelimbic cortex differed spatially following temporal variation in the recall of that memory. The deep and superficial layers of the pre-limbic cortex were engaged in recent recall of a fear memory, but only the superficial layers were recruited if the recall occurred 7 days later.

CONCLUSIONS

Collectively, our findings demonstrate a functional microtopography of auditory fear memory during consolidation and extinction at the microanatomical level within the lateral amygdala and medial prefrontal cortex.

RasGRF1 mediates brain-derived neurotrophic factor-induced axonal growth in primary cultured cortical neurons

The appropriate development and regulation of neuronal morphology are important to establish functional neuronal circuits and enable higher brain function of the central nervous system. R-Ras, a member of the Ras family of small GTPases, plays crucial roles in the regulation of axonal morphology, including outgrowth, branching, and guidance. GTP-bound activated R-Ras reorganizes actin filaments and microtubules through interactions with its downstream effectors, leading to the precise control of axonal morphology. However, little is known about the upstream regulatory mechanisms for R-Ras activation in neurons. In this study, we found that brain-derived neurotrophic factor (BDNF) has a positive effect on endogenous R-Ras activation and promotes R-Ras-mediated axonal growth. RNA interference knockdown and overexpression experiments revealed that RasGRF1, a guanine nucleotide exchange factor (GEF) for R-Ras, is involved in BDNF-induced R-Ras activation and the promotion of axonal growth. Phosphorylation of RasGRF1 by protein kinase A at Ser916/898 is needed for the full activation of its GEF activity and to facilitate Ras signaling. We observed that BDNF treatment markedly increased this phosphorylation. Our results suggest that BDNF is one of the critical extrinsic regulators for R-Ras activation, and that RasGRF1 is an intrinsic key mediator for BDNF-induced R-Ras activation and R-Ras-mediated axonal morphological regulation.

Spatial learning and long-term memory impairments in RasGrf1 KO, Pttg1 KO, and double KO mice

BACKGROUND

RasGrf1 is a guanine-nucleotide releasing factor that enhances Ras activity. Human PTTG1 is an oncoprotein found in pituitary tumors and later identified as securin, a protein isolated from yeast with a reported role in chromosome separation. It has been suggested that RasGrf1 is an important upstream component of signal transduction pathways regulating Pttg1 expression and controlling beta cell development and their physiological response. At memory formation level, there are contradictory data regarding the role of RasGrf1, while Pttg1 has not been previously studied. Both proteins are expressed in the mammalian hippocampus, which is one of the key brain areas for spatial learning and memory.

OBJECTIVE

The aim of this work was to study a potential link between RasGrf1 and Pttg1 in memory formation.

METHOD

Spatial learning and memory test in the Pttg1 KO, RasGrf1 KO, and Pttg1-RasGrf1 double KO and their correspondent WT mice using a Barnes maze.

RESULTS

In comparison with the WT control mice, Pttg1 KO mice learned how to solve the task in a less efficient way, suggesting problems in memory consolidation. RasGrf1 KO mice performance was similar to controls, and they learned to use the best searching strategy. Double KO mice reached a better spatial learning level than WT.

CONCLUSION

A role for Pttg1 in memory consolidation/formation is suggested, while our RasGrf1 KO mice do not show hippocampus associated memory defects.

ERK/MAPK signaling and autism spectrum disorders

The MAPK pathway is a prominent intracellular signaling pathway regulating various intracellular functions. Components of this pathway are mutated in a related collection of congenital syndromes collectively referred to as neuro-cardio-facio-cutaneous syndromes (NCFC) or Rasopathies. Recently, it has been appreciated that these disorders are associated with autism spectrum disorders (ASD). In addition, idiopathic ASD has also implicated the MAPK signaling cascade as a common pathway that is affected by many of the genetic variants that have been found to be linked to ASDs. This chapter describes the components of the MAPK pathway and how it is regulated. Furthermore, this chapter will highlight the various functions of the MAPK pathway during both embryonic development of the central nervous system (CNS) and its roles in neuronal physiology and ultimately, behavior. Finally, we will summarize the perturbations to MAPK signaling in various models of autism spectrum disorders and Rasopathies to highlight how dysregulation of this pivotal pathway may contribute to the pathogenesis of autism.

Isoprenoids and protein prenylation: implications in the pathogenesis and therapeutic intervention of Alzheimer's disease

The mevalonate-isoprenoid-cholesterol biosynthesis pathway plays a key role in human health and disease. The importance of this pathway is underscored by the discovery that two major isoprenoids, farnesyl and geranylgeranyl pyrophosphate, are required to modify an array of proteins through a process known as protein prenylation, catalyzed by prenyltransferases. The lipophilic prenyl group facilitates the anchoring of proteins in cell membranes, mediating protein-protein interactions and signal transduction. Numerous essential intracellular proteins undergo prenylation, including most members of the small GTPase superfamily as well as heterotrimeric G proteins and nuclear lamins, and are involved in regulating a plethora of cellular processes and functions. Dysregulation of isoprenoids and protein prenylation is implicated in various disorders, including cardiovascular and cerebrovascular diseases, cancers, bone diseases, infectious diseases, progeria, and neurodegenerative diseases including Alzheimer's disease (AD). Therefore, isoprenoids and/or prenyltransferases have emerged as attractive targets for developing therapeutic agents. Here, we provide a general overview of isoprenoid synthesis, the process of protein prenylation and the complexity of prenylated proteins, and pharmacological agents that regulate isoprenoids and protein prenylation. Recent findings that connect isoprenoids/protein prenylation with AD are summarized and potential applications of new prenylomic technologies for uncovering the role of prenylated proteins in the pathogenesis of AD are discussed.

Association of RASgrf1 methylation with epileptic seizures

DNA methylation, one of the mechanisms of epigenetic regulation, has been suggested to be related with epilepsy. RASgrf1 is a paternally imprinted gene and has a differentially methylated region (DMR) at the promoter that can silence gene expression. We have previously observed the down-regulation of RASgrf1 in the temporal neocortex of epilepsy patients and in the hippocampus of epileptic animals. Here, we further explored the dynamic change (1-day acute period, 10-day latent period and 45-day chronic phase) of DNA methylation and RASgrf1 expression after acute epileptic seizures in kainic acid (KA)-treated mice, and we observed the impact of N-phthalyl-L-tryptophan (RG108), a DNA methyltransferase (DNMT) inhibitor, on an acute epileptic model by polymerase chain reaction (PCR), western blotting, and bisulfite sequencing PCR (BSP). The results directly showed that the methylation of the RASgrf1 promoter gradually increased and reached a maximal level at the latent period, with subsequent suppression of RASgrf1 mRNA and protein expression levels, which reached a minimum level in the chronic phase. RG108 inhibited the increased methylation of the RASgrf1 gene, with significant inhibition occurring at the latent period, and restored RASgrf1 expression levels in the chronic phase. In addition, we demonstrated that RG108 could suppress acute epileptic seizures in KA-treated mice and epileptic discharges in 4-aminopyridine (4-AP)-treated hippocampal slices. These findings demonstrate that RASgrf1 is closely associated with epilepsy via the aberrant methylation of RASgrf1, and regulating the methylation status of relevant genes might be an intriguing topic in future research on epilepsy.

Neurofibromatosis type 1 alternative splicing is a key regulator of Ras/ERK signaling and learning behaviors in mice

Appropriate activation of the Ras/extracellular signal-regulated kinase (ERK) protein signaling cascade within the brain is crucial for optimal learning and memory. One key regulator of this cascade is the Nf1 Ras GTPase activating protein (RasGAP), which attenuates Ras/ERK signaling by converting active Ras is bound to guanosine triphosphate, activating Ras into inactive Ras is bound to guanosine diphosphate, inactivating Ras. A previous study using embryonic stem cells and embryonic stem cell-derived neurons indicated that Nf1 RasGAP activity is modulated by the highly regulated alternative splicing of Nf1 exon 23a. In this study, we generated Nf123aIN/23aIN mice, in which the splicing signals surrounding Nf1 exon 23a were manipulated to increase exon inclusion. Nf123aIN/23aIN mice are viable and exon 23a inclusion approaches 100% in all tissues, including the brain, where the exon is normally almost completely skipped. Ras activation and phosphorylation of ERK1/2 downstream of Ras are both greatly increased in Nf123aIN/23aIN mouse brain lysates, confirming that exon 23a inclusion inhibits Nf1 RasGAP activity in vivo as it does in cultured cells. Consistent with the finding of altered Ras/ERK signaling in the brain, Nf123aIN/23aIN mice showed specific deficits in learning and memory compared with Nf1+/+ mice. Nf123aIN/23aIN mice performed poorly on the T-maze and Morris water maze tests, which measure short- and long-term spatial memory, respectively. In addition, Nf123aIN/23aIN mice showed abnormally elevated context-dependent fear and a diminished ability to extinguish a cued fear response, indicating defective associative fear learning. Therefore, the regulated alternative splicing of Nf1 is an important mechanism for fine-tuning Ras/ERK signaling as well as learning and memory in mice.

Ras-GRF2 regulates nestin-positive stem cell density and onset of differentiation during adult neurogenesis in the mouse dentate gyrus

Various parameters of neurogenesis were analyzed in parallel in the two neurogenic areas (the Dentate Gyrus[DG] and the Subventricular Zone[SVZ]/Rostral Migratory Stream[RMS]/Main Olfactory Bulb[MOB] neurogenic system) of adult WT and KO mouse strains for the Ras-GRF1/2 genes (Ras-GRF1-KO, Ras-GRF2-KO, Ras-GRF1/2-DKO). Significantly reduced numbers of doublecortin[DCX]-positive cells were specifically observed in the DG, but not the SVZ/RMS/MOB neurogenic region, of Ras-GRF2-KO and Ras-GRF1/2-DKO mice indicating that this novel Ras-GRF2-dependent phenotype is spatially restricted to a specific neurogenic area. Consistent with a role of CREB as mediator of Ras-GRF2 function in neurogenesis, the density of p-CREB-positive cells was also specifically reduced in all neurogenic regions of Ras-GRF2-KO and DKO mice. Similar levels of early neurogenic proliferation markers (Ki67, BrdU) were observed in all different Ras-GRF genotypes analyzed but significantly elevated levels of nestin-immunolabel, particularly of undifferentiated, highly ramified, A-type nestin-positive neurons were specifically detected in the DG but not the SVZ/RMS/MOB of Ras-GRF2-KO and DKO mice. Together with assays of other neurogenic markers (GFAP, Sox2, Tuj1, NeuN), these observations suggest that the deficit of DCX/p-CREB-positive cells in the DG of Ras-GRF2-depleted mice does not involve impaired neuronal proliferation but rather delayed transition from the stem cell stage to the differentiation stages of the neurogenic process. This model is also supported by functional analyses of DG-derived neurosphere cultures and transcriptional characterization of the neurogenic areas of mice of all relevant Ras-GRF genotypes suggesting that the neurogenic role of Ras-GRF2 is exerted in a cell-autonomous manner through a specific transcriptional program.

Tau exacerbates excitotoxic brain damage in an animal model of stroke

Neuronal excitotoxicity induced by aberrant excitation of glutamatergic receptors contributes to brain damage in stroke. Here we show that tau-deficient (tau^−/−) mice are profoundly protected from excitotoxic brain damage and neurological deficits following experimental stroke, using a middle cerebral artery occlusion with reperfusion model. Mechanistically, we show that this protection is due to site-specific inhibition of glutamate-induced and Ras/ERK-mediated toxicity by accumulation of Ras-inhibiting SynGAP1, which resides in a post-synaptic complex with tau. Accordingly, reducing SynGAP1 levels in tau^−/− mice abolished the protection from pharmacologically induced excitotoxicity and middle cerebral artery occlusion-induced brain damage. Conversely, over-expression of SynGAP1 prevented excitotoxic ERK activation in wild-type neurons. Our findings suggest that tau mediates excitotoxic Ras/ERK signaling by controlling post-synaptic compartmentalization of SynGAP1.

Excitotoxicity contributes to neuronal injury following stroke. Here the authors show that tau promotes excitotoxicity by a post-synaptic mechanism, involving site-specific control of ERK activation, in a mouse model of stroke.

Mechanisms underlying cognitive deficits in a mouse model for Costello Syndrome are distinct from other RASopathy mouse models

RASopathies, characterized by germline mutations in genes encoding proteins of the RAS-ERK signaling pathway, show overlapping phenotypes, which manifest themselves with a varying severity of intellectual disability. However, it is unclear to what extent they share the same downstream pathophysiology that underlies the cognitive deficits. Costello syndrome (CS) is a rare RASopathy caused by activating mutations in the HRAS gene. Here we investigated the mechanisms underlying the cognitive deficits of HRas G12V/G12V mice. HRas G12V/G12V mice showed robust upregulation of ERK signaling, neuronal hypertrophy, increased brain volume, spatial learning deficits, and impaired mGluR-dependent long-term depression (LTD). In contrast, long-term potentiation (LTP), which is affected in other RASopathy mouse models was unaffected. Treatment with lovastatin, a HMG-CoA-Reductase inhibitor which has been shown to rescue the behavioral phenotypes of mouse models of NF1 and Noonan syndrome, was unable to restore ERK signaling and the cognitive deficits of HRas G12V/G12V mice. Administration of a potent mitogen-activated protein kinase (MEK) inhibitor rescued the ERK upregulation and the mGluR-LTD deficit of HRas G12V/G12V mice, but failed to rescue the cognitive deficits. Taken together, this study indicates that the fundamental molecular and cellular mechanisms underlying the cognitive aspects of different RASopathies are remarkably distinct, and may require disease specific treatments.

Blood transcriptomic comparison of individuals with and without autism spectrum disorder: A combined-samples mega-analysis

Blood-based microarray studies comparing individuals affected with autism spectrum disorder (ASD) and typically developing individuals help characterize differences in circulating immune cell functions and offer potential biomarker signal. We sought to combine the subject-level data from previously published studies by mega-analysis to increase the statistical power. We identified studies that compared ex vivo blood or lymphocytes from ASD-affected individuals and unrelated comparison subjects using Affymetrix or Illumina array platforms. Raw microarray data and clinical meta-data were obtained from seven studies, totaling 626 affected and 447 comparison subjects. Microarray data were processed using uniform methods. Covariate-controlled mixed-effect linear models were used to identify gene transcripts and co-expression network modules that were significantly associated with diagnostic status. Permutation-based gene-set analysis was used to identify functionally related sets of genes that were over- and under-expressed among ASD samples. Our results were consistent with diminished interferon-, EGF-, PDGF-, PI3K-AKT-mTOR-, and RAS-MAPK-signaling cascades, and increased ribosomal translation and NK-cell related activity in ASD. We explored evidence for sex-differences in the ASD-related transcriptomic signature. We also demonstrated that machine-learning classifiers using blood transcriptome data perform with moderate accuracy when data are combined across studies. Comparing our results with those from blood-based studies of protein biomarkers (e.g., cytokines and trophic factors), we propose that ASD may feature decoupling between certain circulating signaling proteins (higher in ASD samples) and the transcriptional cascades which they typically elicit within circulating immune cells (lower in ASD samples). These findings provide insight into ASD-related transcriptional differences in circulating immune cells. © 2016 Wiley Periodicals, Inc.

Severe Intellectual Disability and Enhanced Gamma-Aminobutyric Acidergic Synaptogenesis in a Novel Model of Rare RASopathies

BACKGROUND

Dysregulation of Ras-extracellular signal-related kinase (ERK) signaling gives rise to RASopathies, a class of neurodevelopmental syndromes associated with intellectual disability. Recently, much attention has been directed at models bearing mild forms of RASopathies whose behavioral impairments can be attenuated by inhibiting the Ras-ERK cascade in the adult. Little is known about the brain mechanisms in severe forms of these disorders.

METHODS

We performed an extensive characterization of a new brain-specific model of severe forms of RASopathies, the KRAS^12V mutant mouse.

RESULTS

The KRAS^12V mutation results in a severe form of intellectual disability, which parallels mental deficits found in patients bearing mutations in this gene. KRAS^12V mice show a severe impairment of both short- and long-term memory in a number of behavioral tasks. At the cellular level, an upregulation of ERK signaling during early phases of postnatal development, but not in the adult state, results in a selective enhancement of synaptogenesis in gamma-aminobutyric acidergic interneurons. The enhancement of ERK activity in interneurons at this critical postnatal time leads to a permanent increase in the inhibitory tone throughout the brain, manifesting in reduced synaptic transmission and long-term plasticity in the hippocampus. In the adult, the behavioral and electrophysiological phenotypes in KRAS^12V mice can be temporarily reverted by inhibiting gamma-aminobutyric acid signaling but not by a Ras-ERK blockade. Importantly, the synaptogenesis phenotype can be rescued by a treatment at the developmental stage with Ras-ERK inhibitors.

CONCLUSIONS

These data demonstrate a novel mechanism underlying inhibitory synaptogenesis and provide new insights in understanding mental dysfunctions associated to RASopathies.

NMDAR dependent intracellular responses associated with cocaine conditioned place preference behavior

The aim of this study was to investigate the intracellular responses associated with the acquisition and expression of cocaine-context associations. ERK (extracellular regulated kinase), CREB (cAMP responsive element binding protein), FosB and ΔFosB proteins were of particular interest due to their involvement in cocaine reward and in synaptic plasticity underlying learning and memory. We used the conditioned place preference (CPP) paradigm, which employs a Pavlovian conditioning procedure to establish an association between a drug-paired environment and the drug's rewarding effects, to study the role of these signaling pathways in cocaine-context associations. N-methyl-D-aspartate receptor (NMDAR) antagonism prior to cocaine administration during conditioning blocked the acquisition of cocaine CPP and reduced Nucleus Accumbens (NAc) phosphorylated-ERK (pERK) and phosphorylated CREB (pCREB) levels following the CPP test (drug-free). We also show that cocaine-induced increases in Caudate Putamen (CPu) FosB and ΔFosB levels are decreased after MK-801 pre-treatment during conditioning. In addition, our results provide evidence for the involvement of striatal SIRT (Silent Information Regulator of Transcription) proteins in cocaine-CPP. These results will aid in the advancement of general knowledge about the molecular formation and retrieval of cocaine-associated memories that can be used in the future when designing treatments for cocaine addiction that target both prevention and relapse.

Homer, Spikar, and Other Drebrin-Binding Proteins in the Brain

Drebrin is a major F-actin-binding protein in the brain. In the past two decades, many drebrin-binding proteins in addition to F-actin have been identified in several research fields including neuroscience, oncology, and immunology. Among the drebrin-binding proteins, there are various kinds of proteins including scaffold proteins, nuclear proteins, phosphatases, microtubule-binding proteins, G-actin-binding proteins, gap junction proteins, chemokine receptors, and cell-adhesion-related proteins. The interaction between drebrin and its binding partners seems to play important roles in higher brain functions, because drebrin is involved in the pathogenesis of some neurological diseases with cognitive defects. In this chapter, we will first review the interaction of Homer and spikar with drebrin, particularly focusing on spine morphogenesis and synaptic function. Homer contributes to spine morphogenesis by cooperating with shank and activated Cdc42 small GTPase, suggesting a novel signaling pathway comprising Homer, drebrin, shank, and Cdc42 for spine morphogenesis. Drebrin sequesters spikar in the cytoplasm and stabilizes it in dendritic spines, leading to spine formation. Finally, we will introduce some other drebrin-binding proteins including end-binding protein 3 (EB3), profilin, progranulin, and phosphatase and tensin homologue (PTEN). These proteins are involved in Alzheimer's disease and cancer. Therefore, further studies on drebrin and its binding proteins will be of great importance to elucidate the pathologies of various diseases and may contribute to their medical treatment and diagnostics development.

Impairment of cocaine-mediated behaviours in mice by clinically relevant Ras-ERK inhibitors

Ras-ERK signalling in the brain plays a central role in drug addiction. However, to date, no clinically relevant inhibitor of this cascade has been tested in experimental models of addiction, a necessary step toward clinical trials. We designed two new cell-penetrating peptides - RB1 and RB3 - that penetrate the brain and, in the micromolar range, inhibit phosphorylation of ERK, histone H3 and S6 ribosomal protein in striatal slices. Furthermore, a screening of small therapeutics currently in clinical trials for cancer therapy revealed PD325901 as a brain-penetrating drug that blocks ERK signalling in the nanomolar range. All three compounds have an inhibitory effect on cocaine-induced ERK activation and reward in mice. In particular, PD325901 persistently blocks cocaine-induced place preference and accelerates extinction following cocaine self-administration. Thus, clinically relevant, systemically administered drugs that attenuate Ras-ERK signalling in the brain may be valuable tools for the treatment of cocaine addiction.

DOI:http://dx.doi.org/10.7554/eLife.17111.001

Synaptic GluN2B/CaMKII-α Signaling Induces Synapto-Nuclear Transport of ERK and Jacob

A central pathway in synaptic plasticity couples N-Methyl-D-Aspartate-receptor (NMDAR)-signaling to the activation of extracellular signal-regulated kinases (ERKs) cascade. ERK-dependency has been demonstrated for several forms of synaptic plasticity as well as learning and memory and includes local synaptic processes but also long-distance signaling to the nucleus. It is, however, controversial how NMDAR signals are connected to ERK activation in dendritic spines and nuclear import of ERK. The synapto-nuclear messenger Jacob couples NMDAR-dependent Ca²⁺-signaling to CREB-mediated gene expression. Protein transport of Jacob from synapse to nucleus essentially requires activation of GluN2B-containing NMDARs. Subsequent phosphorylation and binding of ERK1/2 to and ERK-dependent phosphorylation of serine 180 in Jacob encodes synaptic but not extrasynaptic NMDAR activation. In this study we show that stimulation of synaptic NMDAR in hippocampal primary neurons and induction of long-term potentiation (LTP) in acute slices results in GluN2B-dependent activation of CaMKII-α and subsequent nuclear import of active ERK and serine 180 phosphorylated Jacob. On the contrary, no evidence was found that either GluN2A-containing NMDAR or RasGRF2 are upstream of ERK activation and nuclear import of Jacob and ERK.

Molecular mechanism linking BDNF/TrkB signaling with the NMDA receptor in memory: the role of Girdin in the CNS

It is well known that synaptic plasticity is the cellular mechanism underlying learning and memory. Activity-dependent synaptic changes in electrical properties and morphology, including synaptogenesis, lead to alterations of synaptic strength, which is associated with long-term potentiation (LTP). Brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (TrkB) signaling is involved in learning and memory formation by regulating synaptic plasticity. The phosphatidylinositol 3-kinase (PI3-K)/Akt pathway is one of the key signaling cascades downstream BDNF/TrkB and is believed to modulate N-methyl-d-aspartate (NMDA) receptor-mediated synaptic plasticity. However, the molecular mechanism underlying the connection between these two key players in synaptic plasticity remains largely unknown. Girders of actin filament (Girdin), an Akt substrate that directly binds to actin filaments, has been shown to play a role in neuronal migration and neuronal development. Recently, we identified Girdin as a key molecule involved in regulating long-term memory. It was demonstrated that phosphorylation of Girdin by Akt contributed to the maintenance of LTP by linking the BDNF/TrkB signaling pathway with NMDA receptor activity. These findings indicate that Girdin plays a pivotal role in a variety of processes in the CNS. Here, we review recent advances in our understanding about the roles of Girdin in the CNS and focus particularly on neuronal migration and memory.

D1 Dopamine Receptor Supersensitivity in the Dopamine-Depleted Striatum Animal Model of Parkinson’s Disease

Dopamine acts in the striatum principally through the D1 and D2 dopamine receptor subtypes, which are segregated to the direct and indirect striatal projection neurons, respectively. As a consequence, degeneration of the dopamine input to the striatum results in opposing affects in these pathways. The resulting functional imbalance is thought to be responsible for the bradykinesia of Parkinson’s disease, which may be temporarily normalized by dopamine replacement therapy. However, direct striatal projection neurons become irreversibly supersensitive to D1 dopamine receptor activation, despite the fact that there is an actual decrease in receptor number. Recent studies show that this D1-supersensitive response results from a switch from the normal D1-mediated activation of protein-kinase A to an aberrant activation of ERK1/2/MAPkinase. This switch in D1-receptor-mediated regulation of protein kinase systems responsible for neuronal plasticity is suggested to underlie dyskinesia produced by L-DOPA treatment of Parkinson’s disease.

Cell type-specific roles of RAS-MAPK signaling in learning and memory: Implications in neurodevelopmental disorders

The RAS-mitogen-activated protein kinase (MAPK) signaling pathway plays critical roles in brain function, including learning and memory. Mutations of molecules in the RAS-MAPK pathway are associated with a group of disorders called RASopathies, which include Noonan syndrome, neurofibromatosis type 1, Costello syndrome, Noonan syndrome with multiple lentigines, Legius syndrome, and cardio-facio-cutaneous syndrome. RASopathies share certain clinical symptoms, including craniofacial abnormalities, heart defects, delayed growth, and cognitive deficits such as learning disabilities, while each individual syndrome also displays unique phenotypes. Recent studies using mouse models of RASopathies showed that each disorder may have a distinct molecular and cellular etiology depending on the cellular specificity of the mutated molecules. Here, we review the cell-type specific roles of the regulators of the RAS-MAPK pathway in cognitive function (learning and memory) and their contribution to the development of RASopathies. We also discussed recent technical advances in analyzing cell type-specific transcriptomes and proteomes in the nervous system. Understanding specific mechanisms for these similar but distinct disorders would facilitate the development of mechanism-based individualized treatment for RASopathies.

New Perspectives on Genomic Imprinting, an Essential and Multifaceted Mode of Epigenetic Control in the Developing and Adult Brain

Mammalian evolution entailed multiple innovations in gene regulation, including the emergence of genomic imprinting, an epigenetic regulation leading to the preferential expression of a gene from its maternal or paternal allele. Genomic imprinting is highly prevalent in the brain, yet, until recently, its central roles in neural processes have not been fully appreciated. Here, we provide a comprehensive survey of adult and developmental brain functions influenced by imprinted genes, from neural development and wiring to synaptic function and plasticity, energy balance, social behaviors, emotions, and cognition. We further review the widespread identification of parental biases alongside monoallelic expression in brain tissues, discuss their potential roles in dosage regulation of key neural pathways, and suggest possible mechanisms underlying the dynamic regulation of imprinting in the brain. This review should help provide a better understanding of the significance of genomic imprinting in the normal and pathological brain of mammals including humans.

RASGRF2 controls nuclear migration in postnatal retinal cone photoreceptors

Detailed immunocytochemical analyses comparing wild-type (WT), GRF1-knockout (KO), GRF2-KO and GRF1/2 double-knockout (DKO) mouse retinas uncovered the specific accumulation of misplaced, 'ectopic' cone photoreceptor nuclei in the photoreceptor segment (PS) area of retinas from GRF2-KO and GRF1/2-DKO, but not of WT or GRF1-KO mice. Localization of ectopic nuclei in the PS area of GRF2-depleted retinas occurred postnatally and peaked between postnatal day (P)11 and P15. Mechanistically, the generation of this phenotype involved disruption of the outer limiting membrane and intrusion into the PS layer by cone nuclei displaying significant perinuclear accumulation of signaling molecules known to participate in nuclear migration and cytoskeletal reorganization, such as PAR3, PAR6 and activated, phosphorylated forms of PAK, MLC2 and VASP. Electroretinographic recordings showed specific impairment of cone-mediated retinal function in GRF2-KO and GRF1/2-DKO retinas compared with WT controls. These data identify defective cone nuclear migration as a novel phenotype in mouse retinas lacking GRF2 and support a crucial role of GRF2 in control of the nuclear migration processes required for proper postnatal development and function of retinal cone photoreceptors.