Potential opposite roles of the extracellular signal-regulated kinase (ERK) pathway in autism spectrum and bipolar disorders

A critical review of the impact of candidate copy number variants on autism spectrum disorder

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder (NDD) influenced by genetic, epigenetic, and environmental factors. Recent advancements in genomic analysis have shed light on numerous genes associated with ASD, highlighting the significant role of both common and rare genetic mutations, as well as copy number variations (CNVs), single nucleotide polymorphisms (SNPs) and unique de novo variants. These genetic variations disrupt neurodevelopmental pathways, contributing to the disorder's complexity. Notably, CNVs are present in 10 %-20 % of individuals with autism, with 3 %-7 % detectable through cytogenetic methods. While the role of submicroscopic CNVs in ASD has been recently studied, their association with genomic loci and genes has not been thoroughly explored. In this review, we focus on 47 CNV regions linked to ASD, encompassing 1632 genes, including protein-coding genes and long non-coding RNAs (lncRNAs), of which 659 show significant brain expression. Using a list of ASD-associated genes from SFARI, we detect 17 regions harboring at least one known ASD-related protein-coding gene. Of the remaining 30 regions, we identify 24 regions containing at least one protein-coding gene with brain-enriched expression and a nervous system phenotype in mouse mutants, and one lncRNA with both brain-enriched expression and upregulation in iPSC to neuron differentiation. This review not only expands our understanding of the genetic diversity associated with ASD but also underscores the potential of lncRNAs in contributing to its etiology. Additionally, the discovered CNVs will be a valuable resource for future diagnostic, therapeutic, and research endeavors aimed at prioritizing genetic variations in ASD.

The gut metabolite indole-3-propionic acid activates ERK1 to restore social function and hippocampal inhibitory synaptic transmission in a 16p11.2 microdeletion mouse model

BACKGROUND

Microdeletion of the human chromosomal region 16p11.2 (16p11.2+ / - ) is a prevalent genetic factor associated with autism spectrum disorder (ASD) and other neurodevelopmental disorders. However its pathogenic mechanism remains unclear, and effective treatments for 16p11.2+ / -  syndrome are lacking. Emerging evidence suggests that the gut microbiota and its metabolites are inextricably linked to host behavior through the gut-brain axis and are therefore implicated in ASD development. Despite this, the functional roles of microbial metabolites in the context of 16p11.2+ / -  are yet to be elucidated. This study aims to investigate the therapeutic potential of indole-3-propionic acid (IPA), a gut microbiota metabolite, in addressing behavioral and neural deficits associated with 16p11.2+ / - , as well as the underlying molecular mechanisms.

RESULTS

Mice with the 16p11.2+ / -  showed dysbiosis of the gut microbiota and a significant decrease in IPA levels in feces and blood circulation. Further, these mice exhibited significant social and cognitive memory impairments, along with hyperactivation of hippocampal dentate gyrus neurons and reduced inhibitory synaptic transmission in this region. However, oral administration of IPA effectively mitigated the histological and electrophysiological alterations, thereby ameliorating the social and cognitive deficits of the mice. Remarkably, IPA treatment significantly increased the phosphorylation level of ERK1, a protein encoded by the Mapk3 gene in the 16p11.2 region, without affecting the transcription and translation of the Mapk3 gene.

CONCLUSIONS

Our study reveals that 16p11.2+ / -  leads to a decline in gut metabolite IPA levels; however, IPA supplementation notably reverses the behavioral and neural phenotypes of 16p11.2+ / -  mice. These findings provide new insights into the critical role of gut microbial metabolites in ASD pathogenesis and present a promising treatment strategy for social and cognitive memory deficit disorders, such as 16p11.2 microdeletion syndrome. Video Abstract.

Disrupted extracellular matrix and cell cycle genes in autism-associated Shank3 deficiency are targeted by lithium

The Shank3 gene encodes the major postsynaptic scaffolding protein SHANK3. Its mutation causes a syndromic form of autism spectrum disorder (ASD): Phelan-McDermid Syndrome (PMDS). It is characterized by global developmental delay, intellectual disorders (ID), ASD behavior, affective symptoms, as well as extra-cerebral symptoms. Although Shank3 deficiency causes a variety of molecular alterations, they do not suffice to explain all clinical aspects of this heterogenic syndrome. Since global gene expression alterations in Shank3 deficiency remain inadequately studied, we explored the transcriptome in vitro in primary hippocampal cells from Shank3∆11(-/-) mice, under control and lithium (Li) treatment conditions, and confirmed the findings in vivo. The Shank3∆11(-/-) genotype affected the overall transcriptome. Remarkably, extracellular matrix (ECM) and cell cycle transcriptional programs were disrupted. Accordingly, in the hippocampi of adolescent Shank3∆11(-/-) mice we found proteins of the collagen family and core cell cycle proteins downregulated. In vitro Li treatment of Shank3∆11(-/-) cells had a rescue-like effect on the ECM and cell cycle gene sets. Reversed ECM gene sets were part of a network, regulated by common transcription factors (TF) such as cAMP responsive element binding protein 1 (CREB1) and β-Catenin (CTNNB1), which are known downstream effectors of synaptic activity and targets of Li. These TFs were less abundant and/or hypo-phosphorylated in hippocampi of Shank3∆11(-/-) mice and could be rescued with Li in vitro and in vivo. Our investigations suggest the ECM compartment and cell cycle genes as new players in the pathophysiology of Shank3 deficiency, and imply involvement of transcriptional regulators, which can be modulated by Li. This work supports Li as potential drug in the management of PMDS symptoms, where a Phase III study is ongoing.

Vasopressin as Possible Treatment Option in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is rather common, presenting with prevalent early problems in social communication and accompanied by repetitive behavior. As vasopressin was implicated not only in salt-water homeostasis and stress-axis regulation, but also in social behavior, its role in the development of ASD might be suggested. In this review, we summarized a wide range of problems associated with ASD to which vasopressin might contribute, from social skills to communication, motor function problems, autonomous nervous system alterations as well as sleep disturbances, and altered sensory information processing. Beside functional connections between vasopressin and ASD, we draw attention to the anatomical background, highlighting several brain areas, including the paraventricular nucleus of the hypothalamus, medial preoptic area, lateral septum, bed nucleus of stria terminalis, amygdala, hippocampus, olfactory bulb and even the cerebellum, either producing vasopressin or containing vasopressinergic receptors (presumably V1a). Sex differences in the vasopressinergic system might underline the male prevalence of ASD. Moreover, vasopressin might contribute to the effectiveness of available off-label therapies as well as serve as a possible target for intervention. In this sense, vasopressin, but paradoxically also V1a receptor antagonist, were found to be effective in some clinical trials. We concluded that although vasopressin might be an effective candidate for ASD treatment, we might assume that only a subgroup (e.g., with stress-axis disturbances), a certain sex (most probably males) and a certain brain area (targeting by means of virus vectors) would benefit from this therapy.

NRF2, KEAP1 and GSK-3 levels in autism spectrum disorder: a case control study

Recent studies show that oxidative stress has an important role in the etiology of autism. In our study, Nrf2, which is the main regulator of cellular antioxidant response, and Keap1 and Gsk-3β, which are the main proteins that regulate this pathway, were compared between children with autism and healthy controls. To the best of our knowledge, our study is the first in which Nrf2, Keap1 and Gsk-3β levels were evaluated together in children with ASD. In our study, Nrf2 level was found to be lower and Keap1 level higher in children with autism. Although GSK-3β is increased in many psychiatric and neurodegenerative diseases, it was found to be low in the autistic group in accordance with the literature. In conclusion, considering the versatile modulation of the Nrf2 pathway, this article does not provide any mechanistic insight into the pathway, but it suggests that Nrf2, Keap1 and Gsk-3β, which have central roles in oxidative stress, may play a role in the pathophysiology of autism.

The Role of Maternal Immune Activation in the Pathogenesis of Autism: A Review of the Evidence, Proposed Mechanisms and Implications for Treatment

Autism spectrum disorder (ASD) is a neurodevelopmental disease that is characterized by a deficit in social interactions and communication, as well as repetitive and restrictive behaviors. Increasing lines of evidence suggest an important role for immune dysregulation and/or inflammation in the development of ASD. Recently, a relationship between inflammation, oxidative stress, and mitochondrial dysfunction has been reported in the brain tissue of individuals with ASD. Some recent studies have also reported oxidative stress and mitochondrial abnormalities in animal models of maternal immune activation (MIA). This review is focused on the hypothesis that MIA induces microglial activation, oxidative stress, and mitochondrial dysfunction, a deleterious trio in the brain that can lead to neuroinflammation and neurodevelopmental pathologies in offspring. Infection during pregnancy activates the mother’s immune system to release proinflammatory cytokines, such as IL-6, TNF-α, and others. Furthermore, these cytokines can directly cross the placenta and enter the fetal circulation, or activate resident immune cells, resulting in an increased production of proinflammatory cytokines, including IL-6. Proinflammatory cytokines that cross the blood–brain barrier (BBB) may initiate a neuroinflammation cascade, starting with the activation of the microglia. Inflammatory processes induce oxidative stress and mitochondrial dysfunction that, in turn, may exacerbate oxidative stress in a self-perpetuating vicious cycle that can lead to downstream abnormalities in brain development and behavior.

Characterizing Sleep Problems in 16p11.2 Deletion and Duplication

Studies of 16p11.2 copy number variants (CNVs) provide an avenue to identify mechanisms of impairment and develop targeted treatments for individuals with neurodevelopmental disorders. 16p11.2 deletion and duplication phenotypes are currently being ascertained; however, sleep disturbances are minimally described. In this study, we examine sleep disturbance in a well-characterized national sample of 16p11.2 CNVs, the Simons Foundation Autism Research Initiative (SFARI) database of youth and adults (n = 692). Factor analyses and multilevel models of derived sleep questionnaires for youth (n = 345) and adults (n = 347) indicate that 16p11.2 carriers show elevated sleep disturbance relative to community controls. Non-carrier family members also show elevated sleep disturbance. However, sleep duration does not differ between carriers and controls. Further studies of sleep in 16p11.2 are needed.

Elucidation of Abnormal Extracellular Regulated Kinase (ERK) Signaling and Associations with Syndromic and Non-syndromic Autism

Autism is a highly inherited and extremely complex disorder in which results from various cases indicate chromosome anomalies, unusual single-gene mutations, and multiplicative effects of particular gene variants, characterized primarily by impaired speech and social interaction and restricted behavior. The precise etiology of Autism Spectrum Disorder (ASD) is currently unclear. The extracellular signal-regulated kinase (ERK) signaling mechanism affects neurogenesis and neuronal plasticity during the development of the central nervous mechanism. In this regard, the pathway of ERK has recently gained significant interest in the pathogenesis of ASD. The mutation occurs in a few ERK components. Besides, the ERK pathway dysfunction lies in the upstream of modified translation and contributes to synapse pathology in syndromic types of autism. In this review, we highlight the ERK pathway as a target for neurodevelopmental disorder autism. In addition, we summarize the regulation of the ERK pathway with ERK inhibitors in neurological disorders. In conclusion, a better understanding of the ERK signaling pathway provides a range of therapeutic options for autism spectrum disorder.

The Creatine Transporter Unfolded: A Knotty Premise in the Cerebral Creatine Deficiency Syndrome

Creatine provides cells with high-energy phosphates for the rapid reconstitution of hydrolyzed adenosine triphosphate. The eponymous creatine transporter (CRT1/SLC6A8) belongs to a family of solute carrier 6 (SLC6) proteins. The key role of CRT1 is to translocate creatine across tissue barriers and into target cells, such as neurons and myocytes. Individuals harboring mutations in the coding sequence of the human CRT1 gene develop creatine transporter deficiency (CTD), one of the pivotal underlying causes of cerebral creatine deficiency syndrome. CTD encompasses an array of clinical manifestations, including severe intellectual disability, epilepsy, autism, development delay, and motor dysfunction. CTD is characterized by the absence of cerebral creatine, which implies an indispensable role for CRT1 in supplying the brain cells with creatine. CTD-associated variants dramatically reduce or abolish creatine transport activity by CRT1. Many of these are point mutations that are known to trigger folding defects, leading to the retention of encoded CRT1 proteins in the endoplasmic reticulum and precluding their delivery to the cell surface. Misfolding of several related SLC6 transporters also gives rise to detrimental pathologic conditions in people; e.g., mutations in the dopamine transporter induce infantile parkinsonism/dystonia, while mutations in the GABA transporter 1 cause treatment-resistant epilepsy. In some cases, folding defects are amenable to rescue by small molecules, known as pharmacological and chemical chaperones, which restore the cell surface expression and transport activity of the previously non-functional proteins. Insights from the recent molecular, animal and human case studies of CTD add toward our understanding of this complex disorder and reveal the wide-ranging effects elicited upon CRT1 dysfunction. This grants novel therapeutic prospects for the treatment of patients afflicted with CTD, e.g., modifying the creatine molecule to facilitate CRT1-independent entry into brain cells, or correcting folding-deficient and loss-of-function CTD variants using pharmacochaperones and/or allosteric modulators. The latter justifies a search for additional compounds with a capacity to correct mutation-specific defects.

Comprehensive Behavioral Phenotyping of a 16p11.2 Del Mouse Model for Neurodevelopmental Disorders

The microdeletion of copy number variant 16p11.2 is one of the most common genetic mutations associated with neurodevelopmental disorders, such as Autism Spectrum Disorders (ASDs). Here, we describe our comprehensive behavioral phenotyping of the 16p11.2 deletion line developed by Alea Mills on a C57BL/6J and 129S1/SvImJ F1 background (Del^m ). Male and female Del^m mice were tested in developmental milestones as preweanlings (PND2-PND12), and were tested in open field activity, elevated zero maze, rotarod, novel object recognition, fear conditioning, social approach, and other measures during post-weaning (PND21), adolescence (PND42), and adulthood (>PND70). Developmentally, Del^m mice show distinct weight reduction that persists into adulthood. Del^m males also have reduced grasp reflexes and limb strength during development, but no other reflexive deficits whereas Del^m females show limb strength deficits and decreased sensitivity to heat. In a modified version of a rotarod task that measures balance and coordinated motor activity, Del^m males, but not females, show improved performance at high speeds. Del^m males and females also show age-specific reductions in anxiety-like behavior compared with WTs, but neither sex show deficits in a social preference task. When assessing learning and memory, Del^m males and females show age-specific impairments in a novel object or spatial object recognition, but no deficits in contextual fear memory. This work extends the understanding of the behavioral phenotypes seen with 16p11.2 deletion by emphasizing age and sex-specific deficits; important variables to consider when studying mouse models for neurodevelopmental disorders. LAY SUMMARY: Autism spectrum disorder is a common neurodevelopmental disorder that causes repetitive behavior and impairments in social interaction and communication. Here, we assess the effects of one of the most common genetic alterations in ASDs, a deletion of one copy of 29 genes, using a mouse model. These animals show differences in behavior between males and females and across ages compared with control animals, including changes in development, cognition, and motor coordination. Autism Res 2020, 13: 1670-1684. © 2020 International Society for Autism Research and Wiley Periodicals LLC.

NEGR1 and FGFR2 cooperatively regulate cortical development and core behaviours related to autism disorders in mice

Autism spectrum disorders are neurodevelopmental conditions with diverse aetiologies, all characterized by common core symptoms such as impaired social skills and communication, as well as repetitive behaviour. Cell adhesion molecules, receptor tyrosine kinases and associated downstream signalling have been strongly implicated in both neurodevelopment and autism spectrum disorders. We found that downregulation of the cell adhesion molecule NEGR1 or the receptor tyrosine kinase fibroblast growth factor receptor 2 (FGFR2) similarly affects neuronal migration and spine density during mouse cortical development in vivo and results in impaired core behaviours related to autism spectrum disorders. Mechanistically, NEGR1 physically interacts with FGFR2 and modulates FGFR2-dependent extracellular signal-regulated kinase (ERK) and protein kinase B (AKT) signalling by decreasing FGFR2 degradation from the plasma membrane. Accordingly, FGFR2 overexpression rescues all defects due to Negr1 knockdown in vivo. Negr1 knockout mice present phenotypes similar to Negr1-downregulated animals. These data indicate that NEGR1 and FGFR2 cooperatively regulate cortical development and suggest a role for defective NEGR1-FGFR2 complex and convergent downstream ERK and AKT signalling in autism spectrum disorders.

Microarray analysis of gene expression in the diacylglycerol kinase η knockout mouse brain

We have revealed that diacylglycerol kinase η (DGKη)-knockout (KO) mice display bipolar disorder (BPD) remedy-sensitive mania-like behaviors. However, the molecular mechanisms causing the mania-like abnormal behaviors remain unclear. In the present study, microarray analysis was performed to determine global changes in gene expression in the DGKη-KO mouse brain. We found that the DGKη-KO brain had 43 differentially expressed genes and the following five affected biological pathways: "neuroactive ligand-receptor interaction", "transcription by RNA polymerase II", "cytosolic calcium ion concentration", "Jak-STAT signaling pathway" and "ERK1/2 cascade". Interestingly, mRNA levels of prolactin and growth hormone, which are augmented in BPD patients and model animals, were most strongly increased. Notably, all five biological pathways include at least one gene among prolactin, growth hormone, forkhead box P3, glucagon-like peptide 1 receptor and interleukin 1β, which were previously implicated in BPD. Consistent with the microarray data, phosphorylated ERK1/2 levels were decreased in the DGKη-KO brain. Microarray analysis showed that the expression levels of several glycerolipid metabolism-related genes were also changed. Liquid chromatography-mass spectrometry revealed that several polyunsaturated fatty acid (PUFA)-containing phosphatidic acid (PA) molecular species were significantly decreased as a result of DGKη deficiency, suggesting that the decrease affects PUFA metabolism. Intriguingly, the PUFA-containing lysoPA species were markedly decreased in DGKη-KO mouse blood. Taken together, our study provides not only key broad knowledge to gain novel insights into the underlying mechanisms for the mania-like behaviors but also information for developing BPD diagnostics.

Brain mitochondrial proteome alteration driven by creatine deficiency suggests novel therapeutic venues for creatine deficiency syndromes

Creatine (Cr) is a small metabolite with a central role in energy metabolism and mitochondrial function. Creatine deficiency syndromes are inborn errors of Cr metabolism causing Cr depletion in all body tissues and particularly in the nervous system. Patient symptoms involve intellectual disability, language and behavioral disturbances, seizures and movement disorders suggesting that brain cells are particularly sensitive to Cr depletion. Cr deficiency was found to affect metabolic activity and structural abnormalities of mitochondrial organelles; however a detailed analysis of molecular mechanisms linking Cr deficit, energy metabolism alterations and brain dysfunction is still missing. Using a proteomic approach we evaluated the proteome changes of the brain mitochondrial fraction induced by the deletion of the Cr transporter (CrT) in developing mutant mice. We found a marked alteration of the mitochondrial proteomic landscape in the brain of CrT deficient mice, with the overexpression of many proteins involved in energy metabolism and response to oxidative stress. Moreover, our data suggest possible abnormalities of dendritic spines, synaptic function and plasticity, network excitability and neuroinflammatory response. Intriguingly, the alterations occurred in coincidence with the developmental onset of neurological symptoms. Thus, cerebral mitochondrial alterations could represent an early response to Cr deficiency that could be targeted for therapeutic intervention.

Dual-Specificity Phosphatase Regulation in Neurons and Glial Cells

Dual-specificity protein phosphatases comprise a protein phosphatase subfamily with selectivity towards mitogen-activated protein (MAP) kinases, also named MKPs, or mitogen-activated protein kinase (MAPK) phosphatases. As powerful regulators of the intensity and duration of MAPK signaling, a relevant role is envisioned for dual-specificity protein phosphatases (DUSPs) in the regulation of biological processes in the nervous system, such as differentiation, synaptic plasticity, and survival. Important neural mediators include nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) that contribute to DUSP transcriptional induction and post-translational mechanisms of DUSP protein stabilization to maintain neuronal survival and differentiation. Potent DUSP gene inducers also include cannabinoids, which preserve DUSP activity in inflammatory conditions. Additionally, nucleotides activating P2X7 and P2Y₁₃ nucleotide receptors behave as novel players in the regulation of DUSP function. They increase cell survival in stressful conditions, regulating DUSP protein turnover and inducing DUSP gene expression. In general terms, in the context of neural cells exposed to damaging conditions, the recovery of DUSP activity is neuroprotective and counteracts pro-apoptotic over-activation of p38 and JNK. In addition, remarkable changes in DUSP function take place during the onset of neuropathologies. The restoration of proper DUSP levels and recovery of MAPK homeostasis underlie the therapeutic effect, indicating that DUSPs can be relevant targets for brain diseases.

Early Developmental Marginal Zinc Deficiency Affects Neurogenesis Decreasing Neuronal Number and Altering Neuronal Specification in the Adult Rat Brain

During pregnancy, a decreased availability of zinc to the fetus can disrupt the development of the central nervous system leading to defects ranging from severe malformations to subtle neurological and cognitive effects. We previously found that marginal zinc deficiency down-regulates the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway and affects neural progenitor cell (NPC) proliferation. This study investigated if marginal zinc deficiency during gestation in rats could disrupt fetal neurogenesis and affect the number and specification of neurons in the adult offspring brain cortex. Rats were fed a marginal zinc deficient or adequate diet throughout gestation and until postnatal day (P) 2, and subsequently the zinc adequate diet until P56. Neurogenesis was evaluated in the offspring at embryonic day (E)14, E19, P2, and P56 measuring parameters of NPC proliferation and differentiation by Western blot and/or immunofluorescence. At E14 and E19, major signals (i.e., ERK1/2, Sox2, and Pax6) that stimulate NPC proliferation and self-renewal were markedly downregulated in the marginal zinc deficient fetal brain. These alterations were associated to a lower number of Ki67 positive cells in the ventricular (VZs) and subventricular zones (SVZs). Following the progression of NPCs into intermediate progenitor cells (IPCs) and into neurons, Pax6, Tbr2 and Tbr1 were affected in the corresponding areas of the brain at E19 and P2. The above signaling alterations led to a lower density of neurons and a selective decrease of glutamatergic neurons in the young adult brain cortex exposed to maternal marginal zinc deficiency from E14 to P2. Current results supports the concept that marginal zinc deficiency during fetal development can disrupt neurogenesis and alter cortical structure potentially leading to irreversible neurobehavioral impairments later in life.

Disruption of mTOR and MAPK pathways correlates with severity in idiopathic autism

The molecular signature underlying autism spectrum disorder remains largely unknown. This study identifies differential expression of mTOR and MAPK pathways in patients affected by mild and severe idiopathic autism. A total of 55 subjects were enrolled, of which 22 were typically developing individuals and 33 were patients aged between 3 and 11 years, with autism spectrum disorder. A detailed history, including physical examination, developmental evaluation, mental health history and autism diagnostic observation schedule were performed for each patient. Components of the mTOR and MAPK signalling pathways were analysed from peripheral blood at the protein level. Patients were then stratified according to their clinical phenotypes, and the molecular profiling was analysed in relation to the degree of autism severity. In this cohort of patients, we identified increased activity of mTOR and the MAPK pathways, key regulators of synaptogenesis and protein synthesis. Specifically, rpS6, p-eIF4E, TSC1 and p-MNK1 expression discriminated patients according to their clinical diagnosis, suggesting that components of protein synthesis signalling pathways might constitute a molecular signature of clinical severity in autism spectrum disorder.

The cAMP responsive element-binding (CREB)-1 gene increases risk of major psychiatric disorders

Bipolar disorder (BPD), schizophrenia (SCZ) and unipolar major depressive disorder (MDD) are primary psychiatric disorders sharing substantial genetic risk factors. We previously reported that two single-nucleotide polymorphisms (SNPs) rs2709370 and rs6785 in the cAMP responsive element-binding (CREB)-1 gene (CREB1) were associated with the risk of BPD and abnormal hippocampal function in populations of European ancestry. In the present study, we further expanded our analyses of rs2709370 and rs6785 in multiple BPD, SCZ and MDD data sets, including the published Psychiatric Genomics Consortium (PGC) genome-wide association study, the samples used in our previous CREB1 study, and six additional cohorts (three new BPD samples, two new SCZ samples and one new MDD sample). Although the associations of both CREB1 SNPs with each illness were not replicated in the new cohorts (BPD analysis in 871 cases and 1089 controls (rs2709370, P=0.0611; rs6785, P=0.0544); SCZ analysis in 1273 cases and 1072 controls (rs2709370, P=0.230; rs6785, P=0.661); and MDD analysis in 129 cases and 100 controls (rs2709370, P=0.114; rs6785, P=0.188)), an overall meta-analysis of all included samples suggested that both SNPs were significantly associated with increased risk of BPD (11 105 cases and 51 331 controls; rs2709370, P=2.33 × 10^-4; rs6785, P=6.33 × 10^-5), SCZ (34 913 cases and 44 528 controls; rs2709370, P=3.96 × 10^-5; rs6785, P=2.44 × 10^-5) and MDD (9369 cases and 9619 controls; rs2709370, P=0.0144; rs6785, P=0.0314), with the same direction of allelic effects across diagnostic categories. We then examined the impact of diagnostic status on CREB1 mRNA expression using data obtained from independent brain tissue samples, and observed that the mRNA expression of CREB1 was significantly downregulated in psychiatric patients compared with healthy controls. The protein-protein interaction analyses showed that the protein encoded by CREB1 directly interacted with several risk genes of psychiatric disorders identified by GWAS. In conclusion, the current study suggests that CREB1 might be a common risk gene for major psychiatric disorders, and further investigations are necessary.

Pharmacological Inhibition of ERK Signaling Rescues Pathophysiology and Behavioral Phenotype Associated with 16p11.2 Chromosomal Deletion in Mice

The human 16p11.2 microdeletion is one of the most common gene copy number variations linked to autism, but the pathophysiology associated with this chromosomal abnormality is largely unknown. The 593 kb deletion contains the ERK1 gene and other genes that converge onto the ERK/MAP kinase pathway. Perturbations in ERK signaling are linked to a group of related neurodevelopmental disorders hallmarked by intellectual disability, including autism. We report that mice harboring the 16p11.2 deletion exhibit a paradoxical elevation of ERK activity, cortical cytoarchitecture abnormalities and behavioral deficits. Importantly, we show that treatment with a novel ERK pathway inhibitor during a critical period of brain development rescues the molecular, anatomical and behavioral deficits in the 16p11.2 deletion mice. The ERK inhibitor treatment administered to adult mice ameliorates a subset of these behavioral deficits. Our findings provide evidence for potential targeted therapeutic intervention in 16p11.2 deletion carriers.SIGNIFICANCE STATEMENT The ERK/MAPK pathway is genetically linked to autism spectrum disorders and other syndromes typified by intellectual disability. We provide direct evidence connecting the ERK/MAP kinases to the developmental abnormalities in neurogenesis and cortical cytoarchitecture associated with the 16p11.2 chromosomal deletion. Most importantly, we demonstrate that treatment with a novel ERK-specific inhibitor during development rescues aberrant cortical cytoarchitecture and restores normal levels of cell-cycle regulators during cortical neurogenesis. These treatments partially reverse the behavioral deficits observed in the 16p11.2del mouse model, including hyperactivity, memory as well as olfaction, and maternal behavior. We also report a rescue of a subset of these deficits upon treatment of adult 16p11.2del mice. These data provide a strong rationale for therapeutic approaches to this disorder.

Brain-specific functional relationship networks inform autism spectrum disorder gene prediction

Autism spectrum disorder (ASD) is a neuropsychiatric disorder with strong evidence of genetic contribution, and increased research efforts have resulted in an ever-growing list of ASD candidate genes. However, only a fraction of the hundreds of nominated ASD-related genes have identified de novo or transmitted loss of function (LOF) mutations that can be directly attributed to the disorder. For this reason, a means of prioritizing candidate genes for ASD would help filter out false-positive results and allow researchers to focus on genes that are more likely to be causative. Here we constructed a machine learning model by leveraging a brain-specific functional relationship network (FRN) of genes to produce a genome-wide ranking of ASD risk genes. We rigorously validated our gene ranking using results from two independent sequencing experiments, together representing over 5000 simplex and multiplex ASD families. Finally, through functional enrichment analysis on our highly prioritized candidate gene network, we identified a small number of pathways that are key in early neural development, providing further support for their potential role in ASD.

A critical role of spinal Shank2 proteins in NMDA-induced pain hypersensitivity

Background

Self-injurious behaviors (SIBs) are devastating traits in autism spectrum disorder (ASD). Although deficits in pain sensation might be one of the contributing factors underlying the development of SIBs, the mechanisms have yet to be addressed. Recently, the Shank2 synaptic protein has been considered to be a key component in ASD, and mutations of SHANK2 gene induce the dysfunction of N-methyl-D-aspartate (NMDA) receptors, suggesting a link between Shank2 and NMDA receptors in ASD. Given that spinal NMDA receptors play a pivotal role in pain hypersensitivity, we investigated the possible role of Shank2 in nociceptive hypersensitivity by examining changes in spontaneous pain following intrathecal NMDA injection in Shank2−/− (Shank2 knock-out, KO) mice.

Results

Intrathecal NMDA injection evoked spontaneous nociceptive behaviors. These NMDA-induced nociceptive responses were significantly reduced in Shank2 KO mice. We also observed a significant decrease of NMDA currents in the spinal dorsal horn of Shank2 KO mice. Subsequently, we examined whether mitogen-activated protein kinase or AKT signaling is involved in this reduced pain behavior in Shank2 KO mice because the NMDA receptor is closely related to these signaling molecules. Western blotting and immunohistochemistry revealed that spinally administered NMDA increased the expression of a phosphorylated form of extracellular signal-regulated kinase (p-ERK) which was significantly reduced in Shank2 KO mice. However, p38, JNK, or AKT were not changed by NMDA administration. The ERK inhibitor, PD98059, decreased NMDA-induced spontaneous pain behaviors in a dose-dependent manner in wild-type mice. Moreover, it was found that the NMDA-induced increase in p-ERK was primarily colocalized with Shank2 proteins in the spinal cord dorsal horn.

Conclusion

Shank2 protein is involved in spinal NMDA receptor-mediated pain, and mutations of Shank2 may suppress NMDA-ERK signaling in spinal pain transmission. This study provides new clues into the mechanisms underlying pain deficits associated with SIB and deserves further study in patients with ASD.

Rare deleterious mutations are associated with disease in bipolar disorder families

Bipolar disorder (BD) is a common, complex and heritable psychiatric disorder characterized by episodes of severe mood swings. The identification of rare, damaging genomic mutations in families with BD could inform about disease mechanisms and lead to new therapeutic interventions. To determine whether rare, damaging mutations shared identity-by-descent in families with BD could be associated with disease, exome sequencing was performed in multigenerational families of the NIMH BD Family Study followed by in silico functional prediction. Disease association and disease specificity was determined using 5090 exomes from the Sweden-Schizophrenia (SZ) Population-Based Case-Control Exome Sequencing study. We identified 14 rare and likely deleterious mutations in 14 genes that were shared identity-by-descent among affected family members. The variants were associated with BD (P<0.05 after Bonferroni's correction) and disease specificity was supported by the absence of the mutations in patients with SZ. In addition, we found rare, functional mutations in known causal genes for neuropsychiatric disorders including holoprosencephaly and epilepsy. Our results demonstrate that exome sequencing in multigenerational families with BD is effective in identifying rare genomic variants of potential clinical relevance and also disease modifiers related to coexisting medical conditions. Replication of our results and experimental validation are required before disease causation could be assumed.

Acamprosate in a mouse model of fragile X syndrome: modulation of spontaneous cortical activity, ERK1/2 activation, locomotor behavior, and anxiety

BACKGROUND

Fragile X Syndrome (FXS) occurs as a result of a silenced fragile X mental retardation 1 gene (FMR1) and subsequent loss of fragile X mental retardation protein (FMRP) expression. Loss of FMRP alters excitatory/inhibitory signaling balance, leading to increased neuronal hyperexcitability and altered behavior. Acamprosate (the calcium salt of N-acetylhomotaurinate), a drug FDA-approved for relapse prevention in the treatment of alcohol dependence in adults, is a novel agent with multiple mechanisms that may be beneficial for people with FXS. There are questions regarding the neuroactive effects of acamprosate and the significance of the molecule's calcium moiety. Therefore, the electrophysiological, cellular, molecular, and behavioral effects of acamprosate were assessed in the Fmr1^-/y (knock out; KO) mouse model of FXS controlling for the calcium salt in several experiments.

METHODS

Fmr1 KO mice and their wild-type (WT) littermates were utilized to assess acamprosate treatment on cortical UP state parameters, dendritic spine density, and seizure susceptibility. Brain extracellular-signal regulated kinase 1/2 (ERK1/2) activation was used to investigate this signaling molecule as a potential biomarker for treatment response. Additional adult mice were used to assess chronic acamprosate treatment and any potential effects of the calcium moiety using CaCl₂ treatment on behavior and nuclear ERK1/2 activation.

RESULTS

Acamprosate attenuated prolonged cortical UP state duration, decreased elevated ERK1/2 activation in brain tissue, and reduced nuclear ERK1/2 activation in the dentate gyrus in KO mice. Acamprosate treatment modified behavior in anxiety and locomotor tests in Fmr1 KO mice in which control-treated KO mice were shown to deviate from control-treated WT mice. Mice treated with CaCl₂ were not different from saline-treated mice in the adult behavior battery or nuclear ERK1/2 activation.

CONCLUSIONS

These data indicate that acamprosate, and not calcium, improves function reminiscent of reduced anxiety-like behavior and hyperactivity in Fmr1 KO mice and that acamprosate attenuates select electrophysiological and molecular dysregulation that may play a role in the pathophysiology of FXS. Differences between control-treated KO and WT mice were not evident in a recognition memory test or in examination of acoustic startle response/prepulse inhibition which impeded conclusions from being made about the treatment effects of acamprosate in these instances.

Wnt and GSK3 Signaling Pathways in Bipolar Disorder: Clinical and Therapeutic Implications

The neurobiology of bipolar disorder, a chronic and systemic ailment is not completely understood. The bipolar phenotype manifests in myriad ways, and psychopharmacological agents like lithium have long term beneficial effects. The enzyme glycogen synthase kinase 3 (GSK3) has come into focus, as lithium and several other mood stabilizing medications inhibit its activity. This kinase and its key upstream modulator, Wnt are dysregulated in mood disorders and there is a growing impetus to delineate the chief substrates involved in the development of these illnesses. In May 2016, a comprehensive literature search was undertaken which revealed that there is over activity of GSK3 in bipolar disorder with deleterious downstream effects like proinflammatory status, increased oxidative stress, and circadian dysregulation leading to declining neurotrophic support and enhanced apoptosis of neural elements. By developing specific GSK3 inhibitors the progressive worsening in bipolar disorder can be forestalled with improved prospects for the sufferers.

Widespread alterations in the synaptic proteome of the adolescent cerebral cortex following prenatal immune activation in rats

An increasing number of studies have revealed associations between pre- and perinatal immune activation and the development of schizophrenia and autism spectrum disorders (ASDs). Accordingly, neuroimmune crosstalk has a considerably large impact on brain development during early ontogenesis. While a plethora of heterogeneous abnormalities have already been described in established maternal immune activation (MIA) rodent and primate animal models, which highly correlate to those found in human diseases, the underlying molecular background remains obscure. In the current study, we describe the long-term effects of MIA on the neocortical pre- and postsynaptic proteome of adolescent rat offspring in detail. Molecular differences were revealed in sub-synaptic fractions, which were first thoroughly characterized using independent methods. The widespread proteomic examination of cortical samples from offspring exposed to maternal lipopolysaccharide administration at embryonic day 13.5 was conducted via combinations of different gel-based proteomic techniques and tandem mass spectrometry. Our experimentally validated proteomic data revealed more pre- than postsynaptic protein level changes in the offspring. The results propose the relevance of altered synaptic vesicle recycling, cytoskeletal structure and energy metabolism in the presynaptic region in addition to alterations in vesicle trafficking, the cytoskeleton and signal transduction in the postsynaptic compartment in MIA offspring. Differing levels of the prominent signaling regulator molecule calcium/calmodulin-dependent protein kinase II in the postsynapse was validated and identified specifically in the prefrontal cortex. Finally, several potential common molecular regulators of these altered proteins, which are already known to be implicated in schizophrenia and ASD, were identified and assessed. In summary, unexpectedly widespread changes in the synaptic molecular machinery in MIA rats were demonstrated which might underlie the pathological cortical functions that are characteristic of schizophrenia and ASD.

Pathway Network Analyses for Autism Reveal Multisystem Involvement, Major Overlaps with Other Diseases and Convergence upon MAPK and Calcium Signaling

We used established databases in standard ways to systematically characterize gene ontologies, pathways and functional linkages in the large set of genes now associated with autism spectrum disorders (ASDs). These conditions are particularly challenging—they lack clear pathognomonic biological markers, they involve great heterogeneity across multiple levels (genes, systemic biological and brain characteristics, and nuances of behavioral manifestations)—and yet everyone with this diagnosis meets the same defining behavioral criteria. Using the human gene list from Simons Foundation Autism Research Initiative (SFARI) we performed gene set enrichment analysis with the Kyoto Encyclopedia of Genes and Genomes (KEGG) Pathway Database, and then derived a pathway network from pathway-pathway functional interactions again in reference to KEGG. Through identifying the GO (Gene Ontology) groups in which SFARI genes were enriched, mapping the coherence between pathways and GO groups, and ranking the relative strengths of representation of pathway network components, we 1) identified 10 disease-associated and 30 function-associated pathways 2) revealed calcium signaling pathway and neuroactive ligand-receptor interaction as the most enriched, statistically significant pathways from the enrichment analysis, 3) showed calcium signaling pathways and MAPK signaling pathway to be interactive hubs with other pathways and also to be involved with pervasively present biological processes, 4) found convergent indications that the process “calcium-PRC (protein kinase C)-Ras-Raf-MAPK/ERK” is likely a major contributor to ASD pathophysiology, and 5) noted that perturbations associated with KEGG’s category of environmental information processing were common. These findings support the idea that ASD-associated genes may contribute not only to core features of ASD themselves but also to vulnerability to other chronic and systemic problems potentially including cancer, metabolic conditions and heart diseases. ASDs may thus arise, or emerge, from underlying vulnerabilities related to pleiotropic genes associated with pervasively important molecular mechanisms, vulnerability to environmental input and multiple systemic co-morbidities.

RYR2, PTDSS1 and AREG genes are implicated in a Lebanese population-based study of copy number variation in autism

Autism Spectrum Disorders (ASDs) are a group of neurodevelopmental disorders characterized by ritualistic-repetitive behaviors and impaired verbal and non-verbal communication. Objectives were to determine the contribution of genetic variation to ASDs in the Lebanese. Affymetrix Cytogenetics Whole-Genome 2.7 M and CytoScan(™) HD Arrays were used to detect CNVs in 41 Lebanese autistic children and 35 non-autistic, developmentally delayed and intellectually disabled patients. 33 normal participants were used as controls. 16 de novo CNVs and 57 inherited CNVs, including recognized pathogenic 16p11.2 duplications and 2p16.3 deletions were identified. A duplication at 1q43 classified as likely pathogenic encompasses RYR2 as a potential ASD candidate gene. This previously identified CNV has been classified as both pathogenic, and, of uncertain significance. A duplication of unknown significance at 10q11.22, proposed as a modulator for phenotypic disease expression in Rett syndrome, was also identified. The novel potential autism susceptibility genes PTDSS1 and AREG were uncovered and warrant further genetic and functional analyses. Previously described and novel genetic targets in ASD were identified in Lebanese families with autism. These findings may lead to improved diagnosis of ASDs and informed genetic counseling, and may also lead to untapped therapeutic targets applicable to Lebanese and non-Lebanese patients.

Plasticity-related genes in brain development and amygdala-dependent learning

Learning about motivationally important stimuli involves plasticity in the amygdala, a temporal lobe structure. Amygdala-dependent learning involves a growing number of plasticity-related signaling pathways also implicated in brain development, suggesting that learning-related signaling in juveniles may simultaneously influence development. Here, we review the pleiotropic functions in nervous system development and amygdala-dependent learning of a signaling pathway that includes brain-derived neurotrophic factor (BDNF), extracellular signaling-related kinases (ERKs) and cyclic AMP-response element binding protein (CREB). Using these canonical, plasticity-related genes as an example, we discuss the intersection of learning-related and developmental plasticity in the immature amygdala, when aversive and appetitive learning may influence the developmental trajectory of amygdala function. We propose that learning-dependent activation of BDNF, ERK and CREB signaling in the immature amygdala exaggerates and accelerates neural development, promoting amygdala excitability and environmental sensitivity later in life.

Photoperiodic and circadian bifurcation theories of depression and mania

Seasonal effects on mood have been observed throughout much of human history.  Seasonal changes in animals and plants are largely mediated through the changing photoperiod (i.e., the photophase or duration of daylight).  We review that in mammals, daylight specifically regulates SCN (suprachiasmatic nucleus) circadian organization and its control of melatonin secretion.  The timing of melatonin secretion interacts with gene transcription in the pituitary pars tuberalis to modulate production of TSH (thyrotropin), hypothalamic T3 (triiodothyronine), and tuberalin peptides which modulate pituitary production of regulatory gonadotropins and other hormones.  Pituitary hormones largely mediate seasonal physiologic and behavioral variations.  As a result of long winter nights or inadequate illumination, we propose that delayed morning offset of nocturnal melatonin secretion, suppressing pars tuberalis function, could be the main cause for winter depression and even cause depressions at other times of year.  Irregularities of circadian sleep timing and thyroid homeostasis contribute to depression.  Bright light and sleep restriction are antidepressant and conversely, sometimes trigger mania.  We propose that internal desynchronization or bifurcation of SCN circadian rhythms may underlie rapid-cycling manic-depressive disorders and perhaps most mania.  Much further research will be needed to add substance to these theories.

The 16p11.2 deletion mouse model of autism exhibits altered cortical progenitor proliferation and brain cytoarchitecture linked to the ERK MAPK pathway

Autism spectrum disorders are complex, highly heritable neurodevelopmental disorders affecting ∼1 in 100 children. Copy number variations of human chromosomal region 16p11.2 are genetically linked to 1% of autism-related disorders. This interval contains the MAPK3 gene, which encodes the MAP kinase, ERK1. Mutations in upstream elements regulating the ERK pathway are genetically linked to autism and other disorders of cognition including the neuro-cardio-facial cutaneous syndromes and copy number variations. We report that a murine model of human 16p11.2 deletion exhibits a reduction in brain size and perturbations in cortical cytoarchitecture. We observed enhanced progenitor proliferation and premature cell cycle exit, which are a consequence of altered levels of downstream ERK effectors cyclin D1 and p27(Kip1) during mid-neurogenesis. The increased progenitor proliferation and cell cycle withdrawal resulted in premature depletion of progenitor pools, altering the number and frequency of neurons ultimately populating cortical lamina. Specifically, we found a reduced number of upper layer pyramidal neurons and an increase in layer VI corticothalamic projection neurons, reflecting the altered cortical progenitor proliferation dynamics in these mice. Importantly, we observed a paradoxical increase in ERK signaling in mid-neurogenesis in the 16p11.2del mice, which is coincident with the development of aberrant cortical cytoarchitecture. The 16p11.2del mice exhibit anxiety-like behaviors and impaired memory. Our findings provide evidence of ERK dysregulation, developmental abnormalities in neurogenesis, and behavioral impairment associated with the 16p11.2 chromosomal deletion.

BDNF stimulation of protein synthesis in cortical neurons requires the MAP kinase-interacting kinase MNK1

Although the MAP kinase-interacting kinases (MNKs) have been known for >15 years, their roles in the regulation of protein synthesis have remained obscure. Here, we explore the involvement of the MNKs in brain-derived neurotrophic factor (BDNF)-stimulated protein synthesis in cortical neurons from mice. Using a combination of pharmacological and genetic approaches, we show that BDNF-induced upregulation of protein synthesis requires MEK/ERK signaling and the downstream kinase, MNK1, which phosphorylates eukaryotic initiation factor (eIF) 4E. Translation initiation is mediated by the interaction of eIF4E with the m(7)GTP cap of mRNA and with eIF4G. The latter interaction is inhibited by the interactions of eIF4E with partner proteins, such as CYFIP1, which acts as a translational repressor. We find that BDNF induces the release of CYFIP1 from eIF4E, and that this depends on MNK1. Finally, using a novel combination of BONCAT and SILAC, we identify a subset of proteins whose synthesis is upregulated by BDNF signaling via MNK1 in neurons. Interestingly, this subset of MNK1-sensitive proteins is enriched for functions involved in neurotransmission and synaptic plasticity. Additionally, we find significant overlap between our subset of proteins whose synthesis is regulated by MNK1 and those encoded by known FMRP-binding mRNAs. Together, our data implicate MNK1 as a key component of BDNF-mediated translational regulation in neurons.

An evo-devo approach to thyroid hormones in cerebral and cerebellar cortical development: etiological implications for autism

The morphological alterations of cortical lamination observed in mouse models of developmental hypothyroidism prompted the recognition that these experimental changes resembled the brain lesions of children with autism; this led to recent studies showing that maternal thyroid hormone deficiency increases fourfold the risk of autism spectrum disorders (ASD), offering for the first time the possibility of prevention of some forms of ASD. For ethical reasons, the role of thyroid hormones on brain development is currently studied using animal models, usually mice and rats. Although mammals have in common many basic developmental principles regulating brain development, as well as fundamental basic mechanisms that are controlled by similar metabolic pathway activated genes, there are also important differences. For instance, the rodent cerebral cortex is basically a primary cortex, whereas the primary sensory areas in humans account for a very small surface in the cerebral cortex when compared to the associative and frontal areas that are more extensive. Associative and frontal areas in humans are involved in many neurological disorders, including ASD, attention deficit-hyperactive disorder, and dyslexia, among others. Therefore, an evo-devo approach to neocortical evolution among species is fundamental to understand not only the role of thyroid hormones and environmental thyroid disruptors on evolution, development, and organization of the cerebral cortex in mammals but also their role in neurological diseases associated to thyroid dysfunction.

Long-term memory deficits are associated with elevated synaptic ERK1/2 activation and reversed by mGluR5 antagonism in an animal model of autism

A significant proportion of patients with autism exhibit some degree of intellectual disability. The BTBR T(+) Itpr3(tf)/J mouse strain exhibits behaviors that align with the major diagnostic criteria of autism. To further evaluate the BTBR strain's cognitive impairments, we quantified hippocampus-dependent object location memory (OLM) and found that one-third of the BTBR mice exhibited robust memory, whereas the remainder did not. Fluorescence deconvolution tomography was used to test whether synaptic levels of activated extracellular signal-regulated kinase 1/2 (ERK1/2), a protein that contributes importantly to plasticity, correlate with OLM scores in individual mice. In hippocampal field CA1, the BTBRs had fewer post-synaptic densities associated with high levels of phosphorylated (p-) ERK1/2 as compared with C57BL/6 mice. Although counts of p-ERK1/2 immunoreactive synapses did not correlate with OLM performance, the intensity of synaptic p-ERK1/2 immunolabeling was negatively correlated with OLM scores across BTBRs. Metabotropic glutamate receptor (mGluR) 5 signaling activates ERK1/2. Therefore, we tested whether treatment with the mGluR5 antagonist MPEP normalizes synaptic and learning measures in BTBR mice: MPEP facilitated OLM and decreased synaptic p-ERK1/2 immunolabeling intensity without affecting numbers of p-ERK1/2+ synapses. In contrast, semi-chronic ampakine treatment, which facilitates memory in other models of cognitive impairment, had no effect on OLM in BTBRs. These results suggest that intellectual disabilities associated with different neurodevelopmental disorders on the autism spectrum require distinct therapeutic strategies based on underlying synaptic pathology.

Dual-specificity phosphatases as molecular targets for inhibition in human disease

SIGNIFICANCE

The dual-specificity phosphatases (DUSPs) constitute a heterogeneous group of cysteine-based protein tyrosine phosphatases, whose members exert a pivotal role in cell physiology by dephosphorylation of phosphoserine, phosphothreonine, and phosphotyrosine residues from proteins, as well as other non-proteinaceous substrates.

RECENT ADVANCES

A picture is emerging in which a selected group of DUSP enzymes display overexpression or hyperactivity that is associated with human disease, especially human cancer, making feasible targeted therapy approaches based on their inhibition. A panoply of molecular and functional studies on DUSPs have been performed in the previous years, and drug-discovery efforts are ongoing to develop specific and efficient DUSP enzyme inhibitors. This review summarizes the current status on inhibitory compounds targeting DUSPs that belong to the MAP kinase phosphatases-, small-sized atypical-, and phosphatases of regenerating liver subfamilies, whose inhibition could be beneficial for the prevention or mitigation of human disease.

CRITICAL ISSUES

Achieving specificity, potency, and bioavailability are the major challenges in the discovery of DUSP inhibitors for the clinics. Clinical validation of compounds or alternative inhibitory strategies of DUSP inhibition has yet to come.

FUTURE DIRECTIONS

Further work is required to understand the dual role of many DUSPs in human cancer, their function-structure properties, and to identify their physiologic substrates. This will help in the implementation of therapies based on DUSPs inhibition.

The developmental pattern of the RAS/RAF/Erk1/2 pathway in the BTBR autism mouse model

BTBR mice exhibit several autistic-like behaviors and are currently used as a model for understanding mechanisms that may be responsible for the pathogenesis of autism. Ras/Raf/ERK1/2 signaling has been suggested to play an important role in neural development, learning, memory, and cognition. Two studies reported that a deletion of a locus on chromosome 16 containing the mitogen-activated protein kinase 3 (MAPK3) gene, which encodes ERK1, is associated with autism. In the present study, Ras/Raf/ERK1/2 signaling was found to be up-regulated in BTBR mice relative to matched control B6 mice, to further suggest involvement in the pathogenesis of autism. To further characterize the developmental pattern of Ras/Raf/ERK1/2 signaling, varying stages during development were sampled to reveal an up-regulation in newborn and 2-week old BTBR mice relative to age-matched B6 mice. By the age of 3-week, Ras/Raf/ERK1/2 signaling in the brain of BTBR mice was unaltered relative to B6 mice, with this trend maintained in 6-week samples. These results suggest that the alteration of Ras/Raf/ERK signaling in the early developmental stages in mice could contribute to the noted autistic phenotype. Furthermore, these findings support the value of BTBR mice to serve as a human analog for autistic etiological research and aid in a better understanding of the developmental mechanisms of autism.

Shank mutant mice as an animal model of autism

In this review, we focus on the role of the Shank family of proteins in autism. In recent years, autism research has been flourishing. With genetic, molecular, imaging and electrophysiological studies being supported by behavioural studies using animal models, there is real hope that we may soon understand the fundamental pathology of autism. There is also genuine potential to develop a molecular-level pharmacological treatment that may be able to deal with the most severe symptoms of autism, and clinical trials are already underway. The Shank family of proteins has been strongly implicated as a contributing factor in autism in certain individuals and sits at the core of the alleged autistic pathway. Here, we analyse studies that relate Shank to autism and discuss what light this sheds on the possible causes of autism.

Revisiting the relationship between autism and schizophrenia: toward an integrated neurobiology

Schizophrenia and autism have been linked since their earliest descriptions. Both are disorders of cerebral specialization originating in the embryonic period. Genetic, molecular, and cytologic research highlights a variety of shared contributory mechanisms that may lead to patterns of abnormal connectivity arising from altered development and topology. Overt behavioral pathology likely emerges during or after neurosensitive periods in which resource demands overwhelm system resources and the individual's ability to compensate using interregional activation fails. We are at the threshold of being able to chart autism and schizophrenia from the inside out. In so doing, the door is opened to the consideration of new therapeutics that are developed based upon molecular, synaptic, and systems targets common to both disorders.

Minireview: Targeting GPCR Activated ERK Pathways for Drug Discovery

It has become clear in recent years that multiple signal transduction pathways are employed upon GPCR activation. One of the major cellular effectors activated by GPCRs is extracellular signal-regulated kinase (ERK). Both G-protein and β-arrestin mediated signaling pathways can lead to ERK activation. However, depending on activation pathway, the subcellular destination of activated ERK1/2 may be different. G-protein -dependent ERK activation results in the translocation of active ERK to the nucleus, whereas ERK activated via an arrestin-dependent mechanism remains largely in the cytoplasm. The subcellular location of activated ERK1/2 determines the downstream signaling cascade. Many substrates of ERK1/2 are found in the nucleus: nuclear transcription factors that participate in gene transcription, cell proliferation and differentiation. ERK1/2 substrates are also found in cytosol and other cellular organelles: they may play roles in translation, mitosis, apoptosis and cross-talk with other signaling pathways. Therefore, determining specific subcellular locations of activated ERK1/2 mediated by GPCR ligands would be important in correlating signaling pathways with cellular physiological functions. While GPCR-stimulated selective ERK pathway activation has been studied in several receptor systems, exploitation of these different signaling cascades for therapeutics has not yet been seriously pursued. Many old drug candidates were identified from screens based on G-protein signaling assays, and their activity on β-arrestin signaling pathways being mostly unknown, especially regarding their subcellular ERK pathways. With today’s knowledge of complicated GPCR signaling pathways, drug discovery can no longer rely on single-pathway approaches. Since ERK activation is an important signaling pathway and associated with many physiological functions, targeting the ERK pathway, especially specific subcellular activation pathways should provide new avenues for GPCR drug discovery.

Putative role of glycogen as a peripheral biomarker of GSK3β activity

Glycogen synthase kinase 3-β (GSK3β) has a pivotal role in several intracellular signaling cascades that are involved in gene transcription, cytoskeletal reorganization, energy metabolism, cell cycle regulation, and apoptosis. This kinase has pleiotropic functions, and the importance of its activity has recently been shown in neurons and platelets. In addition to its regulatory function in several physiological events, changes in GSK3β activity have been associated with many psychiatric and neurodegenerative illnesses, such as Alzheimer's disease, schizophrenia and autism-spectrum disorders. Beside the reports of its involvement in several pathologies, it has become increasingly apparent that GSK3β might be a common therapeutic target for different classes of psychiatric drugs, and also that the GSK3β ratio may be a useful parameter to determine the biochemical changes that might occur during antidepressant treatment. Although GSK3β is commonly described as a key enzyme in a plethora of signaling cascades, originally it was identified as playing an important role in the regulation of glycogen synthesis, given its ability to inactivate glycogen synthase (GS) by phosphorylation. Acting as a constitutively active kinase, GSK3β phosphorylates GS, which results in a decrease of glycogen production. GSK3β phosphorylation increases glycogen synthesis and storage, while its dephosphorylation decreases glycogen synthesis. Inactivation of GSK3β leads to dephosphorylation of GS and increase in glycogen synthesis in the adipose tissue, muscle and liver. Glycogen levels are reduced by antidepressant treatment, and this effect seems to be related to an effect of drugs on GSK3β activity. Peripherally, glycogen is also abundantly found in platelets, where it is considered a major energy source, required for a variety of its functions, including the release reaction. Recently, analysis of platelets from patients with late-life major depression showed that active forms of GSK3β expression were upregulated by continuous treatment with sertraline. Here, we hypothesized that the quantification of glycogen in platelets might be used as a peripheral biomarker of GSK3β activity. Since it has been recently demonstrated that the modulation of GSK3β activity causes changes in glycogen stores, the glycogen levels in platelets could be used to assay the effects of drugs that have this kinase as a target, or diseases where its activity is affected. In conclusion, we hypothesized that the determination of glycogen peripherally may be useful to indicate a change in the activity of this enzyme, providing a faster and non-invasive approach to guide the therapeutic procedures for the patient.

Protein tyrosine phosphatase variants in human hereditary disorders and disease susceptibilities

Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism to steer normal development and physiological functioning of multicellular organisms. Phosphotyrosine dephosphorylation is exerted by members of the super-family of protein tyrosine phosphatase (PTP) enzymes and many play such essential roles that a wide variety of hereditary disorders and disease susceptibilities in man are caused by PTP alleles. More than two decades of PTP research has resulted in a collection of PTP genetic variants with corresponding consequences at the molecular, cellular and physiological level. Here we present a comprehensive overview of these PTP gene variants that have been linked to disease states in man. Although the findings have direct bearing for disease diagnostics and for research on disease etiology, more work is necessary to translate this into therapies that alleviate the burden of these hereditary disorders and disease susceptibilities in man.