The X-Linked Intellectual Disability Protein IL1RAPL1 Regulates Dendrite Complexity.

Mutations and deletions of the interleukin-1 receptor accessory protein like 1 (IL1RAPL1) gene, located on the X chromosome, are associated with intellectual disability (ID) and autism spectrum disorder (ASD). IL1RAPL1 protein is located at the postsynaptic compartment of excitatory synapses and plays a role in synapse formation and stabilization. Here, using primary neuronal cultures and Il1rapl1-KO mice, we characterized the role of IL1RAPL1 in regulating dendrite morphology. In Il1rapl1-KO mice we identified an increased number of dendrite branching points in CA1 and CA2 hippocampal neurons associated to hippocampal cognitive impairment. Similarly, induced pluripotent stem cell-derived neurons from a patient carrying a null mutation of the IL1RAPL1 gene had more dendrites. In hippocampal neurons, the overexpression of full-length IL1RAPL1 and mutants lacking part of C-terminal domains leads to simplified neuronal arborization. This effect is abolished when we overexpressed mutants lacking part of N-terminal domains, indicating that the IL1RAPL1 extracellular domain is required for regulating dendrite development. We also demonstrate that PTPδ interaction is not required for this activity, while IL1RAPL1 mediates the activity of IL-1ß on dendrite morphology. Our data reveal a novel specific function for IL1RAPL1 in regulating dendrite morphology that can help clarify how changes in IL1RAPL1-regulated pathways can lead to cognitive disorders in humans.SIGNIFICANCE STATEMENT Abnormalities in the architecture of dendrites have been observed in a variety of neurodevelopmental, neurodegenerative, and neuropsychiatric disorders. Here we show that the X-linked intellectual disability protein interleukin-1 receptor accessory protein like 1 (IL1RAPL1) regulates dendrite morphology of mice hippocampal neurons and induced pluripotent stem cell-derived neurons from a patient carrying a null mutation of IL1RAPL1 gene. We also found that the extracellular domain of IL1RAPL1 is required for this effect, independently of the interaction with PTPδ, but IL1RAPL1 mediates the activity of IL-1ß on dendrite morphology. Our data reveal a novel specific function for IL1RAPL1 in regulating dendrite morphology that can help clarify how changes in IL1RAPL1-regulated pathways can lead to cognitive disorders in humans.

Novel IL1RAPL1 mutations associated with intellectual disability impair synaptogenesis.

Mutations in interleukin-1 receptor accessory protein like 1 (IL1RAPL1) gene have been associated with non-syndromic intellectual disability (ID) and autism spectrum disorder. This protein interacts with synaptic partners like PSD-95 and PTPδ, regulating the formation and function of excitatory synapses. The aim of this work was to characterize the synaptic consequences of three IL1RAPL1 mutations, two novel causing the deletion of exon 6 (Δex6) and one point mutation (C31R), identified in patients with ID. Using immunofluorescence and electrophysiological recordings, we examined the effects of IL1RAPL1 mutant over-expression on synapse formation and function in cultured rodent hippocampal neurons. Δex6 but not C31R mutation leads to IL1RAPL1 protein instability and mislocalization within dendrites. Analysis of different markers of excitatory synapses and sEPSC recording revealed that both mutants fail to induce pre- and post-synaptic differentiation, contrary to WT IL1RAPL1 protein. Cell aggregation and immunoprecipitation assays in HEK293 cells showed a reduction of the interaction between IL1RAPL1 mutants and PTPδ that could explain the observed synaptogenic defect in neurons. However, these mutants do not affect all cellular signaling because their over-expression still activates JNK pathway. We conclude that both mutations described in this study lead to a partial loss of function of the IL1RAPL1 protein through different mechanisms. Our work highlights the important function of the trans-synaptic PTPδ/IL1RAPL1 interaction in synaptogenesis and as such in ID in the patients.

Rescuing epileptic and behavioral alterations in a Dravet syndrome mouse model by inhibiting eukaryotic elongation factor 2 kinase (eEF2K).

BACKGROUND: Dravet Syndrome is a severe childhood pharmaco-resistant epileptic disorder mainly caused by mutations in the SCN1A gene, which encodes for the α1 subunit of the type I voltage-gated sodium channel (NaV1.1), that causes imbalance between excitation and inhibition in the brain. We recently found that eEF2K knock out mice displayed enhanced GABAergic transmission and tonic inhibition and were less susceptible to epileptic seizures. Thus, we investigated the effect of inhibition of eEF2K on the epileptic and behavioral phenotype of Scn1a ± mice, a murine model of Dravet Syndrome. METHODS: To elucidate the role of eEF2K pathway in the etiopathology of Dravet syndrome we generated a new mouse model deleting the eEF2K gene in Scn1a ± mice. By crossing Scn1a ± mice with eEF2K-/- mice we obtained the three main genotypes needed for our studies, Scn1a+/+ eEF2K+/+ (WT mice), Scn1a ± eEF2K+/+ mice (Scn1a ± mice) and Scn1a ± eEF2K-/- mice, that were fully characterized for EEG and behavioral phenotype. Furthermore, we tested the ability of a pharmacological inhibitor of eEF2K in rescuing EEG alterations of the Scn1a ± mice. RESULTS: We showed that the activity of eEF2K/eEF2 pathway was enhanced in Scn1a ± mice. Then, we demonstrated that both genetic deletion and pharmacological inhibition of eEF2K were sufficient to ameliorate the epileptic phenotype of Scn1a ± mice. Interestingly we also found that motor coordination defect, memory impairments, and stereotyped behavior of the Scn1a ± mice were reverted by eEF2K deletion. The analysis of spontaneous inhibitory postsynaptic currents (sIPSCs) suggested that the rescue of the pathological phenotype was driven by the potentiation of GABAergic synapses. LIMITATIONS: Even if we found that eEF2K deletion was able to increase inhibitory synapses function, the molecular mechanism underlining the inhibition of eEF2K/eEF2 pathway in rescuing epileptic and behavioral alterations in the Scn1a ± needs further investigations. CONCLUSIONS: Our data indicate that pharmacological inhibition of eEF2K could represent a novel therapeutic intervention for treating epilepsy and related comorbidities in the Dravet syndrome.

Eukaryotic Elongation Factor 2 Kinase a Pharmacological Target to Regulate Protein Translation Dysfunction in Neurological Diseases.

Two major processes tightly regulate protein synthesis, the initiation of mRNA translation and elongation phase that mediates the movement of ribosomes along the mRNA. The elongation phase is a high energy-consuming process, and is mainly regulated by the eukaryotic elongation factor 2 kinase (eEF2K) activity that phosphorylates and inhibits eEF2, the only known substrate of the kinase. eEF2K activity is closely regulated by several signaling pathways because the translation elongation phase strongly influences the cellular energy demand and can change the expression of specific proteins in different tissues. An increasing number of recent findings link eEF2k over activation to an array of human diseases, such as atherosclerosis, pulmonary arterial hypertension, progression of solid tumors, and some major neurological disorders. Several neurological studies suggest that eEF2K is a valuable target in treating epilepsy, depression and major neurodegenerative diseases. Despite eEF2k is an ubiquitous and conserved protein, it has been proved that its deletion does not affect development in animal models and in general cell viability. Therefore, it is possible to postulate that inhibiting its function may not cause serious side effects. In addition, eEF2K is a peculiar kinase molecularly different from most of other mammalian kinases and new compounds that inhibit eEF2K should not necessarily interfere with other important protein kinases. In this review we will critically summarize the evidence supporting the role of the altered eEF2K/eEF2 pathway in defined neurological diseases and its implications in curing these diseases in animal models, and possibly in humans, by targeting eEF2K activity.

Modelling genetic mosaicism of neurodevelopmental disorders in vivo by a Cre-amplifying fluorescent reporter.

Genetic mosaicism, a condition in which an organ includes cells with different genotypes, is frequently present in monogenic diseases of the central nervous system caused by the random inactivation of the X-chromosome, in the case of X-linked pathologies, or by somatic mutations affecting a subset of neurons. The comprehension of the mechanisms of these diseases and of the cell-autonomous effects of specific mutations requires the generation of sparse mosaic models, in which the genotype of each neuron is univocally identified by the expression of a fluorescent protein in vivo. Here, we show a dual-color reporter system that, when expressed in a floxed mouse line for a target gene, leads to the creation of mosaics with tunable degree. We demonstrate the generation of a knockout mosaic of the autism/epilepsy related gene PTEN in which the genotype of each neuron is reliably identified, and the neuronal phenotype is accurately characterized by two-photon microscopy.

Oligodendrocytes in Development, Myelin Generation and Beyond.

Oligodendrocytes are the myelinating cells of the central nervous system (CNS) that are generated from oligodendrocyte progenitor cells (OPC). OPC are distributed throughout the CNS and represent a pool of migratory and proliferative adult progenitor cells that can differentiate into oligodendrocytes. The central function of oligodendrocytes is to generate myelin, which is an extended membrane from the cell that wraps tightly around axons. Due to this energy consuming process and the associated high metabolic turnover oligodendrocytes are vulnerable to cytotoxic and excitotoxic factors. Oligodendrocyte pathology is therefore evident in a range of disorders including multiple sclerosis, schizophrenia and Alzheimer's disease. Deceased oligodendrocytes can be replenished from the adult OPC pool and lost myelin can be regenerated during remyelination, which can prevent axonal degeneration and can restore function. Cell population studies have recently identified novel immunomodulatory functions of oligodendrocytes, the implications of which, e.g., for diseases with primary oligodendrocyte pathology, are not yet clear. Here, we review the journey of oligodendrocytes from the embryonic stage to their role in homeostasis and their fate in disease. We will also discuss the most common models used to study oligodendrocytes and describe newly discovered functions of oligodendrocytes.

The Synaptic and Neuronal Functions of the X-Linked Intellectual Disability Protein Interleukin-1 Receptor Accessory Protein Like 1 (IL1RAPL1).

Since the first observation that described a patient with a mutation in IL1RAPL1 gene associated with intellectual disability in 1999, the function of IL1RAPL1 has been extensively studied by a number of laboratories. In this review, we summarize all the major data describing the synaptic and neuronal functions of IL1RAPL1 and recapitulate most of the genetic deletion identified in humans and associated to intellectual disability (ID) and autism spectrum disorders (ASD). All the data clearly demonstrate that IL1RAPL1 is a synaptic adhesion molecule localized at the postsynaptic membrane. Mutations in IL1RAPL1 gene cause either the absence of the protein or the production of a dysfunctional protein. More recently it has been demonstrated that IL1RAPL1 regulated dendrite formation and mediates the activity of IL-1ß on dendrite morphology. All these data will possibly contribute to identifying therapies for patients carrying mutations in IL1RAPL1 gene.