ABSTRACT
Copy number variation (CNV) at 7q11.23 causes Williams-Beuren syndrome (WBS) and 7q microduplication syndrome (7Dup), neurodevelopmental disorders (NDDs) featuring intellectual disability accompanied by symmetrically opposite neurocognitive features. Although significant progress has been made in understanding the molecular mechanisms underlying 7q11.23-related pathophysiology, the propagation of CNV dosage across gene expression layers and their interplay remains elusive. Here we uncovered 7q11.23 dosage-dependent symmetrically opposite dynamics in neuronal differentiation and intrinsic excitability. By integrating transcriptomics, translatomics, and proteomics of patient-derived and isogenic induced neurons, we found that genes related to neuronal transmission follow 7q11.23 dosage and are transcriptionally controlled, while translational factors and ribosomal genes are posttranscriptionally buffered. Consistently, we found phosphorylated RPS6 (p-RPS6) downregulated in WBS and upregulated in 7Dup. Surprisingly, p-4EBP was changed in the opposite direction, reflecting dosage-specific changes in total 4EBP levels. This highlights different dosage-sensitive dyregulations of the mTOR pathway as well as distinct roles of p-RPS6 and p-4EBP during neurogenesis. Our work demonstrates the importance of multiscale disease modeling across molecular and functional layers, uncovers the pathophysiological relevance of ribosomal biogenesis in a paradigmatic pair of NDDs, and uncouples the roles of p-RPS6 and p-4EBP as mechanistically actionable relays in NDDs.
Subject(s)
Chromosomes, Human, Pair 7 , DNA Copy Number Variations , Neurons , Humans , Neurons/metabolism , Neurons/pathology , Chromosomes, Human, Pair 7/genetics , Ribosomes/metabolism , Ribosomes/genetics , Neurogenesis/genetics , Williams Syndrome/genetics , Williams Syndrome/metabolism , Williams Syndrome/pathology , Williams Syndrome/physiopathology , Ribosomal Protein S6/metabolism , Ribosomal Protein S6/genetics , TOR Serine-Threonine Kinases/metabolism , TOR Serine-Threonine Kinases/genetics , Male , Cell Differentiation , FemaleABSTRACT
Synaptic abnormalities are a hallmark of several neurological diseases, and clarification of the underlying mechanisms represents a crucial step toward the development of therapeutic strategies. Rett syndrome (RTT) is a rare neurodevelopmental disorder, mainly affecting females, caused by mutations in the X-linked methyl-CpG-binding protein 2 (MECP2) gene, leading to a deep derangement of synaptic connectivity. Although initial studies supported the exclusive involvement of neurons, recent data have highlighted the pivotal contribution of astrocytes in RTT pathogenesis through non-cell autonomous mechanisms. Since astrocytes regulate synapse formation and functionality by releasing multiple molecules, we investigated the influence of soluble factors secreted by Mecp2 knock-out (KO) astrocytes on synapses. We found that Mecp2 deficiency in astrocytes negatively affects their ability to support synaptogenesis by releasing synaptotoxic molecules. Notably, neuronal inputs from a dysfunctional astrocyte-neuron crosstalk lead KO astrocytes to aberrantly express IL-6, and blocking IL-6 activity prevents synaptic alterations.
ABSTRACT
In the last years, the hypothesis that elevated levels of proinflammatory cytokines contribute to the pathogenesis of neurodevelopmental diseases has gained popularity. IL-1 is one of the main cytokines found to be elevated in Autism spectrum disorder (ASD), a complex neurodevelopmental condition characterized by defects in social communication and cognitive impairments. In this study, we demonstrate that mice lacking IL-1 signaling display autistic-like defects associated with an excessive number of synapses. We also show that microglia lacking IL-1 signaling at early neurodevelopmental stages are unable to properly perform the process of synapse engulfment and display excessive activation of mammalian target of rapamycin (mTOR) signaling. Notably, even the acute inhibition of IL-1R1 by IL-1Ra is sufficient to enhance mTOR signaling and reduce synaptosome phagocytosis in WT microglia. Finally, we demonstrate that rapamycin treatment rescues the defects in IL-1R deficient mice. These data unveil an exclusive role of microglial IL-1 in synapse refinement via mTOR signaling and indicate a novel mechanism possibly involved in neurodevelopmental disorders associated with defects in the IL-1 pathway.
Subject(s)
Autism Spectrum Disorder , Autistic Disorder , Animals , Mice , Microglia , TOR Serine-Threonine Kinases , Cytokines , Sirolimus/pharmacology , Synapses , Interleukin-1 , MammalsABSTRACT
In the last two decades, the term synaptopathy has been largely used to underline the concept that impairments of synaptic structure and function are the major determinant of brain disorders, including neurodevelopmental disorders. This notion emerged from the progress made in understanding the genetic architecture of neurodevelopmental disorders, which highlighted the convergence of genetic risk factors onto molecular pathways specifically localized at the synapse. However, the multifactorial origin of these disorders also indicated the key contribution of environmental factors. It is well recognized that inflammation is a risk factor for neurodevelopmental disorders, and several immune molecules critically contribute to synaptic dysfunction. In the present review, we highlight this concept, which we define by the term "immune-synaptopathy," and we discuss recent evidence suggesting a bi-directional link between the genetic architecture of individuals and maternal activation of the immune system in modulating brain developmental trajectories in health and disease.
Subject(s)
Neurodevelopmental Disorders , Humans , Neurodevelopmental Disorders/genetics , Neurodevelopmental Disorders/metabolism , Synapses/metabolism , FamilyABSTRACT
Intracerebral hemorrhages are recognized risk factors for neurodevelopmental disorders and represent early biomarkers for cognitive dysfunction and mental disability, but the pathways leading to their occurrence are not well defined. We report that a single intrauterine exposure of the immunostimulant Poly I:C to pregnant mice at gestational day 9, which models a prenatal viral infection and the consequent maternal immune activation, induces the defective formation of brain vessels and causes intracerebral hemorrhagic events, specifically in male offspring. We demonstrate that maternal immune activation promotes the production of the TGF-ß1 active form and the consequent enhancement of pSMAD1-5 in males' brain endothelial cells. TGF-ß1, in combination with IL-1ß, reduces the endothelial expression of CD146 and claudin-5, alters the endothelium-pericyte interplay resulting in low pericyte coverage, and increases hemorrhagic events in the adult offspring. By showing that exposure to Poly I:C at the beginning of fetal cerebral angiogenesis results in sex-specific alterations of brain vessels, we provide a mechanistic framework for the association between intragravidic infections and anomalies of the neural vasculature, which may contribute to neuropsychiatric disorders.
Subject(s)
Cerebral Hemorrhage , Prenatal Exposure Delayed Effects , Animals , Female , Male , Mice , Pregnancy , Behavior, Animal , Brain/blood supply , Brain/pathology , Cerebral Hemorrhage/pathology , Disease Models, Animal , Endothelial Cells/metabolism , Poly I-C/adverse effects , Prenatal Exposure Delayed Effects/pathology , Transforming Growth Factor beta1/metabolismABSTRACT
Early prenatal inflammatory conditions are thought to be a risk factor for different neurodevelopmental disorders. Maternal interleukin-6 (IL-6) elevation during pregnancy causes abnormal behavior in offspring, but whether these defects result from altered synaptic developmental trajectories remains unclear. Here we showed that transient IL-6 elevation via injection into pregnant mice or developing embryos enhanced glutamatergic synapses and led to overall brain hyperconnectivity in offspring into adulthood. IL-6 activated synaptogenesis gene programs in glutamatergic neurons and required the transcription factor STAT3 and expression of the RGS4 gene. The STAT3-RGS4 pathway was also activated in neonatal brains during poly(I:C)-induced maternal immune activation, which mimics viral infection during pregnancy. These findings indicate that IL-6 elevation at early developmental stages is sufficient to exert a long-lasting effect on glutamatergic synaptogenesis and brain connectivity, providing a mechanistic framework for the association between prenatal inflammatory events and brain neurodevelopmental disorders.
Subject(s)
Hippocampus/metabolism , Interleukin-6/biosynthesis , Maternal Exposure , Neurons/metabolism , Prenatal Exposure Delayed Effects , Synapses/metabolism , Animals , Cytokines/biosynthesis , Disease Models, Animal , Disease Susceptibility , Female , Hippocampus/physiopathology , Inflammation Mediators/metabolism , Mice , Pregnancy , Signal Transduction , Synaptic TransmissionABSTRACT
MECP2 mutations cause Rett syndrome (RTT), a severe and progressive neurodevelopmental disorder mainly affecting females. Although RTT patients exhibit delayed onset of symptoms, several evidences demonstrate that MeCP2 deficiency alters early development of the brain. Indeed, during early maturation, Mecp2 null cortical neurons display widespread transcriptional changes, reduced activity, and defective morphology. It has been proposed that during brain development these elements are linked in a feed-forward cycle where neuronal activity drives transcriptional and morphological changes that further increase network maturity. We hypothesized that the enhancement of neuronal activity during early maturation might prevent the onset of RTT-typical molecular and cellular phenotypes. Accordingly, we show that the enhancement of excitability, obtained by adding to neuronal cultures Ampakine CX546, rescues transcription of several genes, neuronal morphology, and responsiveness to stimuli. Greater effects are achieved in response to earlier treatments. In vivo, short and early administration of CX546 to Mecp2 null mice prolongs lifespan, delays the disease progression, and rescues motor abilities and spatial memory, thus confirming the value for RTT of an early restoration of neuronal activity.
Subject(s)
Methyl-CpG-Binding Protein 2 , Rett Syndrome , Animals , Brain/metabolism , Female , Humans , Methyl-CpG-Binding Protein 2/genetics , Methyl-CpG-Binding Protein 2/metabolism , Mice , Neurons/metabolism , Phenotype , Rett Syndrome/geneticsABSTRACT
The immune system actively regulates brain activity through the engagement of immune cells and immunomodulatory molecules. In this issue of Immunity, Klawonn et al. show that the activation of microglia in the striatum triggers an IL-6-mediated autocrine loop and the release of prostaglandins, which in turn induce a negative affective state via the stimulation of medium spiny neurons.
Subject(s)
Microglia , NeuronsABSTRACT
[This corrects the article DOI: 10.1371/journal.ppat.1008654.].
ABSTRACT
Chloride homeostasis, the main determinant factor for the dynamic tuning of GABAergic inhibition during development, has emerged as a key element altered in a wide variety of brain disorders. Accordingly, developmental disorders such as schizophrenia, Autism Spectrum Disorder, Down syndrome, epilepsy, and tuberous sclerosis complex (TSC) have been associated with alterations in the expression of genes codifying for either of the two cotransporters involved in the excitatory-to-inhibitory GABA switch, KCC2 and NKCC1. These alterations can result from environmental insults, including prenatal stress and maternal separation which share, as common molecular denominator, the elevation of pro-inflammatory cytokines. In this review we report and systemize recent research articles indicating that different perinatal environmental perturbations affect the expression of chloride transporters, delaying the developmental switch of GABA signaling, and that inflammatory cytokines, in particular interleukin 1ß, may represent a key causal factor for this phenomenon. Based on literature data, we provide therefore a unifying conceptual framework, linking environmental hits with the excitatory-to-inhibitory GABA switch in the context of brain developmental disorders.
Subject(s)
Symporters , gamma-Aminobutyric Acid , Chlorides/metabolism , Developmental Disabilities , Female , Humans , Inflammation , Maternal Deprivation , Pregnancy , Prenatal Exposure Delayed Effects , Symporters/geneticsABSTRACT
Prion protein (PrP) mutations are linked to genetic prion diseases, a class of phenotypically heterogeneous neurodegenerative disorders with invariably fatal outcome. How mutant PrP triggers neurodegeneration is not known. Synaptic dysfunction precedes neuronal loss but it is not clear whether, and through which mechanisms, disruption of synaptic activity ultimately leads to neuronal death. Here we show that mutant PrP impairs the secretory trafficking of AMPA receptors (AMPARs). Specifically, intracellular retention of the GluA2 subunit results in synaptic exposure of GluA2-lacking, calcium-permeable AMPARs, leading to increased calcium permeability and enhanced sensitivity to excitotoxic cell death. Mutant PrPs linked to different genetic prion diseases affect AMPAR trafficking and function in different ways. Our findings identify AMPARs as pathogenic targets in genetic prion diseases, and support the involvement of excitotoxicity in neurodegeneration. They also suggest a mechanistic explanation for how different mutant PrPs may cause distinct disease phenotypes.
Subject(s)
Calcium/metabolism , Neurons/metabolism , PrPSc Proteins/metabolism , Receptors, AMPA/metabolism , Synapses/metabolism , Animals , Cell Death/physiology , Mice , Permeability , Protein Transport/physiologyABSTRACT
The process of neurotransmitter release is central to the control of cell-to-cell communication in brain. SNAP-25 is a component of the SNARE complex, which, together with syntaxin-1 and synaptobrevin, mediates synaptic vesicle fusion with the plasma membrane. The genetic ablation of the protein or its proteolytic cleavage by botulinum neurotoxins results in a complete block of synaptic transmission. In the last years, several evidences have indicated that SNAP-25 also plays additional modulatory roles in neurotransmission through the control of voltage-gated calcium channels and presynaptic calcium ion concentration. Consistently, reduced levels of the protein affect presynaptic calcium homeostasis and result in pathologically enhanced glutamate exocytosis. The SNAP-25-dependent alterations of synaptic calcium dynamics may have direct impact on the development of neuropsychiatric disorders where the Snap-25 gene has been found to be involved.
Subject(s)
Calcium/metabolism , Exocytosis/physiology , Neurons/metabolism , Neurotransmitter Agents/metabolism , Synaptosomal-Associated Protein 25/metabolism , Animals , Homeostasis/physiology , Humans , Neuronal Plasticity/physiologyABSTRACT
Control of synapse number and function in the developing central nervous system is critical to the formation of neural circuits. Astrocytes play a key role in this process by releasing factors that promote the formation of excitatory synapses. Astrocyte-secreted thrombospondins (TSPs) induce the formation of structural synapses, which however remain post-synaptically silent, suggesting that completion of early synaptogenesis may require a two-step mechanism. Here, we show that the humoral innate immune molecule Pentraxin 3 (PTX3) is expressed in the developing rodent brain. PTX3 plays a key role in promoting functionally-active CNS synapses, by increasing the surface levels and synaptic clustering of AMPA glutamate receptors. This process involves tumor necrosis factor-induced protein 6 (TSG6), remodeling of the perineuronal network, and a ß1-integrin/ERK pathway. Furthermore, PTX3 activity is regulated by TSP1, which directly interacts with the N-terminal region of PTX3. These data unveil a fundamental role of PTX3 in promoting the first wave of synaptogenesis, and show that interplay of TSP1 and PTX3 sets the proper balance between synaptic growth and synapse function in the developing brain.
Subject(s)
C-Reactive Protein/physiology , Extracellular Matrix/metabolism , Integrin beta1/metabolism , Nerve Tissue Proteins/physiology , Receptors, AMPA/metabolism , Synapses/physiology , Animals , Astrocytes/metabolism , Brain/growth & development , Brain/metabolism , C-Reactive Protein/genetics , CHO Cells , Cells, Cultured , Cricetinae , Cricetulus , Extracellular Matrix/genetics , Mice , Mice, Inbred C57BL , Nerve Tissue Proteins/genetics , Neuronal Plasticity/genetics , Protein Transport/genetics , Thrombospondin 1/metabolismABSTRACT
The neurovascular unit (NVU) is the most important biological barrier between vascular districts and central nervous system (CNS) parenchyma, which maintains brain homeostasis, protects the CNS from pathogens penetration, and mediates neuroimmune communication. T lymphocytes migration across the blood-brain barrier is heavily affected in different brain diseases, representing a major target for novel drug development. In vitro models of NVU could represent a primary tool to investigate the molecular events occurring at this interface. To move toward the establishment of personalized therapies, a patient-related NVU-model is set, incorporating human primary astrocytes integrated into a microfluidic platform. The model is morphologically and functionally characterized, proving to be an advantageous tool to investigate human T lymphocytes transmigration and thus the efficacy of potential novel drugs affecting this process.
Subject(s)
Astrocytes/metabolism , Blood-Brain Barrier/metabolism , Microfluidic Analytical Techniques , Models, Cardiovascular , Models, Neurological , Astrocytes/cytology , Blood-Brain Barrier/cytology , Humans , Primary Cell CultureABSTRACT
In the last 15 years, groundbreaking genetic progress has underlined a convergence onto coherent synaptic pathways for most psychiatric and neurodevelopmental disorders, which are now collectively called "synaptopathies." However, the modest size of inheritance detected so far indicates a multifactorial etiology for these disorders, underlining the key contribution of environmental effects to them. Inflammation is known to influence the risk and/or severity of a variety of synaptopathies. In particular, pro-inflammatory cytokines, produced and released in the brain by activated astrocytes and microglia, may play a pivotal role in these pathologies. Although the link between immune system activation and defects in cognitive processes is nowadays clearly established, the knowledge of the molecular mechanisms by which inflammatory mediators specifically hit synaptic components implicated in synaptopathies is still in its infancy. This review summarizes recent evidence showing that the pro-inflammatory cytokine interleukin-1ß (IL-1ß) specifically targets synaptopathy molecular substrate, leading to memory defects and pathological processes. In particular, we describe three specific pathways through which IL-1ß affects (1) synaptic maintenance/dendritic complexity, (2) spine morphology, and (3) the excitatory/inhibitory balance. We coin the term immune synaptopathies to identify this class of diseases.
ABSTRACT
During differentiation, neurons progressively restrict their fate repressing the expression of specific genes. Here we describe the involvement in such developmental steps of the methyl-CpG binding protein 2 (MeCP2), an epigenetic factor that participates to chromatin folding and transcriptional regulation. We previously reported that, due to transcriptional impairments, the maturation of Mecp2 null neurons is delayed. To evaluate whether this could stem from altered progenitors proliferation and differentiation, we investigated whether lack of Mecp2 affects these features both in vitro and in vivo. We show that in Mecp2 null embryonic cortexes the expression of genes defining the identity of proliferating neuroprogenitors is enriched and that their permanence in the G1 phase is prolonged. Moreover, the number of cells transitioning from a stage of maturation to a more mature one is increased in Mecp2 null embryonic cortices, in line with the central role of G1 for cell identity refinement. We thus suggest that, possibly due to the lack of proper transcriptional control normally exerted by Mecp2, fate refinement is impaired in developing null cells. We propose that the maturation delay affecting the developing Mecp2 null cortex originates, at least in part, from deranged mechanisms of cell fate refinement.
Subject(s)
Cerebral Cortex/cytology , Cerebral Cortex/embryology , Gene Expression Regulation, Developmental/genetics , Methyl-CpG-Binding Protein 2/deficiency , Neurons/pathology , Animals , Basic Helix-Loop-Helix Transcription Factors/metabolism , Bromodeoxyuridine , Cells, Cultured , Cyclin D1/metabolism , Deoxyuridine/analogs & derivatives , Deoxyuridine/toxicity , Embryo, Mammalian/cytology , Embryo, Mammalian/drug effects , Epidermal Growth Factor/pharmacology , Female , Fibroblast Growth Factors/pharmacology , Luminescent Proteins/genetics , Luminescent Proteins/metabolism , Male , Methyl-CpG-Binding Protein 2/genetics , Mice , Mice, Transgenic , Nerve Tissue Proteins/metabolism , Neurogenesis/drug effects , Neurogenesis/genetics , Pregnancy , Proliferating Cell Nuclear Antigen/metabolism , RNA, MessengerABSTRACT
BACKGROUND: The association between maternal infection and neurodevelopmental defects in progeny is well established, although the biological mechanisms and the pathogenic trajectories involved have not been defined. METHODS: Pregnant dams were injected intraperitoneally at gestational day 9 with polyinosinic:polycytidylic acid. Neuronal development was assessed by means of electrophysiological, optical, and biochemical analyses. RESULTS: Prenatal exposure to polyinosinic:polycytidylic acid causes an imbalanced expression of the Na+-K+-2Cl- cotransporter 1 and the K+-Cl- cotransporter 2 (KCC2). This results in delayed gamma-aminobutyric acid switch and higher susceptibility to seizures, which endures up to adulthood. Chromatin immunoprecipitation experiments reveal increased binding of the repressor factor RE1-silencing transcription (also known as neuron-restrictive silencer factor) to position 509 of the KCC2 promoter that leads to downregulation of KCC2 transcription in prenatally exposed offspring. Interleukin-1 receptor type I knockout mice, which display braked immune response and no brain cytokine elevation upon maternal immune activation, do not display KCC2/Na+-K+-2Cl- cotransporter 1 imbalance when implanted in a wild-type dam and prenatally exposed. Notably, pretreatment of pregnant dams with magnesium sulfate is sufficient to prevent the early inflammatory state and the delay in excitatory-to-inhibitory switch associated to maternal immune activation. CONCLUSIONS: We provide evidence that maternal immune activation hits a key neurodevelopmental process, the excitatory-to-inhibitory gamma-aminobutyric acid switch; defects in this switch have been unequivocally linked to diseases such as autism spectrum disorder or epilepsy. These data open the avenue for a safe pharmacological treatment that may prevent the neurodevelopmental defects caused by prenatal immune activation in a specific pregnancy time window.
Subject(s)
Cerebral Cortex/physiology , Epilepsy/etiology , Excitatory Postsynaptic Potentials/physiology , Inhibitory Postsynaptic Potentials/physiology , Pregnancy Complications/immunology , Prenatal Exposure Delayed Effects/etiology , gamma-Aminobutyric Acid , Animals , Cell Culture Techniques , Disease Models, Animal , Embryo, Mammalian , Female , Mice, Inbred C57BL , Mice, Knockout , Patch-Clamp Techniques , Pregnancy , Receptors, Interleukin-1 Type I , Symporters , K Cl- CotransportersABSTRACT
The classical view of multiple sclerosis (MS) pathogenesis states that inflammation-mediated demyelination is responsible for neuronal damage and loss. However, recent findings show that impairment of neuronal functions and demyelination can be independent events, suggesting the coexistence of other pathogenic mechanisms. Due to the inflammatory milieu, subtle alterations in synaptic function occur, which are probably at the basis of the early cognitive decline that often precedes the neurodegenerative phases in MS patients. In particular, it has been reported that inflammation enhances excitatory synaptic transmission while it decreases GABAergic transmission in vitro and ex vivo. This evidence points to the idea that an excitation/inhibition imbalance occurs in the inflamed MS brain, even though the exact molecular mechanisms leading to this synaptic dysfunction are as yet not completely clear. Along this line, we observed that acute treatment of primary hippocampal neurons in culture with pro-inflammatory cytokines leads to an increased phosphorylation of synapsin I (SynI) by ERK1/2 kinase and to an increase in the frequency of spontaneous synaptic vesicle release events, which is prevented by SynI deletion. In vivo, the ablation of SynI expression is protective in terms of disease progression and neuronal damage in the experimental autoimmune encephalomyelitis mouse model of MS. Our results point to a possible key role in MS pathogenesis of the neuronal protein SynI, a regulator of excitation/inhibition balance in neuronal networks.