Dissection of signaling pathways regulating TrkB-dependent gephyrin clustering.

Introduction: The TrkB receptor is known for its role in regulating excitatory neuronal plasticity. However, accumulating evidence over the past decade has highlighted the involvement of TrkB in regulating inhibitory synapse stability and plasticity, particularly through regulation of the inhibitory scaffold protein gephyrin, although with contradicting results.

Methods: In this study, we extended on these findings by overexpressing rat TrkB mutants deficient in either Shc-or PLCγ-dependent signaling, as well as a kinase-dead mutant, to dissect the contributions of specific TrkB-dependent signaling pathways to gephyrin clustering.

Patient iPSC-derived neural progenitor cells display aberrant cell cycle control, p53, and DNA damage response protein expression in schizophrenia.

Background: Schizophrenia (SCZ) is a severe psychiatric disorder associated with alterations in early brain development. Details of underlying pathomechanisms remain unclear, despite genome and transcriptome studies providing evidence for aberrant cellular phenotypes and pathway deregulation in developing neuronal cells. However, mechanistic insight at the protein level is limited.

Aberrant neuronal connectivity and network activity of neurons derived from patients with idiopathic schizophrenia.

Schizophrenia (SCZ) is a psychiatric disorder with a strong genetic determinant. A major hypothesis to explain disease aetiology comprises synaptic dysfunction associated with excitatory-inhibitory imbalance of synaptic transmission, ultimately contributing to impaired network oscillation and cognitive deficits associated with the disease. Here, we studied the morphological and functional properties of a highly defined co-culture of GABAergic and glutamatergic neurons derived from induced pluripotent stem cells (iPSC) from patients with idiopathic SCZ.

Selective knockdown of GABAA-α2 subunit in the dorsal dentate gyrus in adulthood induces anxiety, learning and memory deficits and impairs synaptic plasticity.

Animal studies and clinical trials suggest that maintenance of gamma-aminobutyric acid (GABA)-ergic activity may be crucial in coping with stressful conditions, anxiety and mood disorders. Drugs highly efficient in promoting anxiolysis were shown to activate this system, particularly via the α2-subunit of type A receptors (GABAA α2). Given the high expression of GABAA α2 in the dentate gyrus (DG) sub-field of the hippocampus, we sought to examine whether manipulation of the α2 subunit in this area will evoke changes in emotional behaviour, memory and learning as well as in synaptic plasticity.

Microglia-neuron interactions in schizophrenia.

Multiple lines of evidence implicate increased neuroinflammation mediated by glial cells to play a key role in neurodevelopmental disorders such as schizophrenia. Microglia, which are the primary innate immune cells of the brain, are crucial for the refinement of the synaptic circuitry during early brain development by synaptic pruning and the regulation of synaptic plasticity during adulthood. Schizophrenia risk factors as genetics or environmental influences may further be linked to increased activation of microglia, an increase of pro-inflammatory cytokine levels and activation of the inflammasome resulting in an overall elevated neuroinflammatory state in patients.

Defined co-cultures of glutamatergic and GABAergic neurons with a mutation in DISC1 reveal aberrant phenotypes in GABAergic neurons.

Background: Mutations in the gene DISC1 are associated with increased risk for schizophrenia, bipolar disorder and major depression. The study of mutated DISC1 represents a well-known and comprehensively characterized approach to understand neuropsychiatric disease mechanisms. However, previous studies have mainly used animal models or rather heterogeneous populations of iPSC-derived neurons, generated by undirected differentiation, to study the effects of DISC1 disruption.

Regulation of synaptic connectivity in schizophrenia spectrum by mutual neuron-microglia interaction.

The examination of post-mortem brain tissue suggests synaptic loss as a central pathological hallmark of schizophrenia spectrum (SCZ), which is potentially related to activated microglia and increased inflammation. Induced pluripotent stem cells serve as a source for neurons and microglia-like cells to address neuron-microglia interactions. Here, we present a co-culture model of neurons and microglia, both of human origin, to show increased susceptibility of neurons to microglia-like cells derived from SCZ patients.

Generation of two induced pluripotent stem cell lines (TMOi001-A-5, TMOi001-A-6) carrying variants in DISC1 exon 2 using CRISPR/Cas9 gene editing.

DISC1 is a scaffold protein involved in key developmental processes such as neuronal migration, differentiation and neurogenesis. Genetic variants of the DISC1 gene have been linked to neuropsychiatric disorders like schizophrenia, bipolar disorder and major depression. Here, we generated two isogenic iPSC lines carrying mutations in DISC1 exon 2 using CRISPR/Cas9 gene editing.

Disruption of amygdala Tsc2 in adolescence leads to changed prelimbic cellular activity and generalized fear responses at adulthood in rats.

Adolescence constitutes a period of vulnerability in the emergence of fear-related disorders (FRD), as a massive reorganization occurs in the amygdala-prefrontal cortex network, critical to regulate fear behavior. Genetic and environmental factors during development may predispose to the emergence of FRD at the adult age, but the underlying mechanisms are poorly understood. In the present study, we tested whether a partial knock-down of tuberous sclerosis complex 2 (Tsc2, Tuberin), a risk gene for neurodevelopmental disorders, in the basolateral amygdala (BLA) from adolescence could alter fear-network functionality and create a vulnerability ground to FRD appearance at adulthood.

Human iPSC-Derived Glia as a Tool for Neuropsychiatric Research and Drug Development.

Neuropsychiatric disorders such as schizophrenia or autism spectrum disorder represent a leading and growing burden on worldwide mental health. Fundamental lack in understanding the underlying pathobiology compromises efficient drug development despite the immense medical need. So far, antipsychotic drugs reduce symptom severity and enhance quality of life, but there is no cure available.

Autism Spectrum Disorder Risk Factor Met Regulates the Organization of Inhibitory Synapses.

A common hypothesis explains autism spectrum disorder (ASD) as a neurodevelopmental disorder linked to excitatory/inhibitory (E/I) imbalance in neuronal network connectivity. Mutation of genes including Met and downstream signaling components, e.g.

Functional brain defects in a mouse model of a chromosomal t(1;11) translocation that disrupts DISC1 and confers increased risk of psychiatric illness.

A balanced t(1;11) translocation that directly disrupts DISC1 is linked to schizophrenia and affective disorders. We previously showed that a mutant mouse, named Der1, recapitulates the effect of the translocation upon DISC1 expression. Here, RNAseq analysis of Der1 mouse brain tissue found enrichment for dysregulation of the same genes and molecular pathways as in neuron cultures generated previously from human t(1;11) translocation carriers via the induced pluripotent stem cell route.

Generation and characterization of human induced pluripotent stem cells lines from four patients diagnosed with schizophrenia and one healthy control.

Fibroblasts were isolated from skin biopsies of four patients diagnosed with schizophrenia and from one healthy control. Patient fibroblasts were transfected with five episomal, non-integrative reprogramming vectors to generate human induced pluripotent stem cells (iPSC). Reprogrammed iPSC showed consistent expression of several pluripotency markers, loss of expression of exogenous reprogramming vectors and ability to differentiate into all three germ layers.

The potential of induced pluripotent stem cells for discriminating neurodevelopmental disorders.

Studying human disease-specific processes and mechanisms in vitro is limited by a lack of valid human test systems. Induced pluripotent stem cells (iPSCs) evolve as an important and promising tool to better understand the molecular pathology of neurodevelopmental disorders. Patient-derived iPSCs enable analysis of unique disease mechanisms and may also serve for preclinical drug development.

Interference With Complex IV as a Model of Age-Related Decline in Synaptic Connectivity.

Age-related impairment of mitochondrial function may negatively impact energy-demanding processes such as synaptic transmission thereby triggering cognitive decline and processes of neurodegeneration. Here, we present a novel model for age-related mitochondrial impairment based on partial inhibition of cytochrome c oxidase subunit 4 (Cox4) of complex IV of the respiratory chain. miRNA-mediated knockdown of Cox4 correlated with a marked reduction in excitatory and inhibitory synaptic marker densities and as well as an impairment of neuronal network activity in primary neuronal cultures.

Comparative characterization of human induced pluripotent stem cells (hiPSC) derived from patients with schizophrenia and autism.

Human induced pluripotent stem cells (hiPSC) provide an attractive tool to study disease mechanisms of neurodevelopmental disorders such as schizophrenia. A pertinent problem is the development of hiPSC-based assays to discriminate schizophrenia (SZ) from autism spectrum disorder (ASD) models. Healthy control individuals as well as patients with SZ and ASD were examined by a panel of diagnostic tests.

Neurofascin Knock Down in the Basolateral Amygdala Mediates Resilience of Memory and Plasticity in the Dorsal Dentate Gyrus Under Stress.

Activation of the amygdala is one of the hallmarks of acute stress reactions and a central element of the negative impact of stress on hippocampus-dependent memory and cognition. Stress-induced psychopathologies, such as posttraumatic stress disorder, exhibit a sustained hyperactivity of the amygdala, triggered at least in part by deficits in GABAergic inhibition that lead to shifts in amygdalo-hippocampal interaction. Here, we have utilized lentiviral knock down of neurofascin to reduce GABAergic inhibition specifically at the axon initial segment (AIS) of principal neurons within the basolateral amygdala (BLA) of rats.

Perturbation of GABAergic Synapses at the Axon Initial Segment of Basolateral Amygdala Induces Trans-regional Metaplasticity at the Medial Prefrontal Cortex.

GABAergic synapses in the basolateral amygdala (BLA) play an important role in fear memory generation. We have previously reported that reduction in GABAergic synapses innervating specifically at the axon initial segment (AIS) of principal neurons of BLA, by neurofascin (NF) knockdown, impairs fear extinction. BLA is bidirectionally connected with the medial prefrontal cortex (mPFC), which is a key region involved in extinction of acquired fear memory.

GABAergic Synapses at the Axon Initial Segment of Basolateral Amygdala Projection Neurons Modulate Fear Extinction.

Inhibitory synaptic transmission in the amygdala has a pivotal role in fear learning and its extinction. However, the local circuits formed by GABAergic inhibitory interneurons within the amygdala and their detailed function in shaping these behaviors are not well understood. Here we used lentiviral-mediated knockdown of the cell adhesion molecule neurofascin in the basolateral amygdala (BLA) to specifically remove inhibitory synapses at the axon initial segment (AIS) of BLA projection neurons.

Receptor tyrosine kinase EphA7 is required for interneuron connectivity at specific subcellular compartments of granule cells.

Neuronal transmission is regulated by the local circuitry which is composed of principal neurons targeted at different subcellular compartments by a variety of interneurons. However, mechanisms that contribute to the subcellular localisation and maintenance of GABAergic interneuron terminals are poorly understood. Stabilization of GABAergic synapses depends on clustering of the postsynaptic scaffolding protein gephyrin and its interaction with the guanine nucleotide exchange factor collybistin.

Dentate Gyrus Local Circuit is Implicated in Learning Under Stress--a Role for Neurofascin.

The inhibitory synapses at the axon initial segment (AIS) of dentate gyrus granular cells are almost exclusively innervated by the axo-axonic chandelier interneurons. However, the role of chandelier neurons in local circuitry is poorly understood and controversially discussed. The cell adhesion molecule neurofascin is specifically expressed at the AIS.

Organisation and control of neuronal connectivity and myelination by cell adhesion molecule neurofascin.

The neuronal cell adhesion molecule neurofascin is expressed in highly complex temporally and spatially regulated patterns. Accordingly, many different functions have been described including control of neurite outgrowth, clustering of protein complexes at the axon initial segments as well as at the nodes of Ranvier and axoglial contact formation at paranodal segments. At the molecular level, neurofascin provides a link between extracellular interactions of many different interaction partners and cytoskeletal components or signal transduction.

Stress modulation of hippocampal activity--spotlight on the dentate gyrus.

The effects of stress on learning and memory are diverse, ranging from impairment to facilitation. Many studies emphasize the major role of the hippocampus, mainly its CA1 and CA3 areas, in the process of memory formation under emotional and stressful conditions. In the current review, we summarize work which suggests that the dentate gyrus (DG) of the hippocampus is likely to play a pivotal role in defining the impact of stress on hippocampal functioning.

A comprehensive small interfering RNA screen identifies signaling pathways required for gephyrin clustering.

The postsynaptic scaffold protein gephyrin is clustered at inhibitory synapses and serves for the stabilization of GABA(A) receptors. Here, a comprehensive kinome-wide siRNA screen in a human HeLa cell-based model for gephyrin clustering was used to identify candidate protein kinases implicated in the stabilization of gephyrin clusters. As a result, 12 hits were identified including FGFR1 (FGF receptor 1), TrkB, and TrkC as well as components of the MAPK and mammalian target of rapamycin (mTOR) pathways.

Regulation of adhesion by flexible ectodomains of IgCAMs.

To perform their diverse biological functions the adhesion activities of the cell adhesion molecules of the immunoglobulin superfamily (IgCAMs) might be regulated by local clustering, proteolytical shedding of their ectodomains or rapid recycling to and from the plasma membrane. Another form of regulation of adhesion might be obtained through flexible ectodomains of IgCAMs which adopt distinct conformations and which in turn modulate their adhesion activity. Here, we discuss variations in the conformation of the extracellular domains of CEACAM1 and CAR that might influence their binding and signaling activities.