Activity-dependent BDNF release and TRPC signaling is impaired in hippocampal neurons of Mecp2 mutant mice

Dysfunction of the neurotrophin brain-derived neurotrophic factor (BDNF) is implicated in Rett syndrome (RTT), but the state of its releasable pool and downstream signaling in mice lacking methyl-CpG-binding protein-2 (Mecp2) is unknown. Here, we show that membrane currents and dendritic Ca2+ signals evoked by recombinant BDNF or an activator of diacylglycerol (DAG)-sensitive transient receptor potential canonical (TRPC) channels are impaired in CA3 pyramidal neurons of symptomatic Mecp2 mutant mice. TRPC3 and TRPC6 mRNA and protein levels are lower in Mecp2 mutant hippocampus, and chromatin immunoprecipitation (ChIP) identified Trpc3 as a target of MeCP2 transcriptional regulation. BDNF mRNA and protein levels are also lower in Mecp2 mutant hippocampus and dentate gyrus granule cells, which is reflected in impaired activity-dependent release of endogenous BDNF estimated from TRPC currents and dendritic Ca2+ signals in CA3 pyramidal neurons. These results identify the gene encoding TRPC3 channels as a MeCP2 target and suggest a potential therapeutic strategy to boost impaired BDNF signaling in RTT.Fil: Li, Wei. University of Alabama at Birmingahm; Estados UnidosFil: Calfa, Gaston Diego. University of Alabama at Birmingahm; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Farmacología Experimental de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Farmacología Experimental de Córdoba; ArgentinaFil: Larimore, Jennifer. Agnes Scott College. Biology Department and Neuroscience Program; Estados UnidosFil: Pozzo-Miller, Lucas. Agnes Scott College. Biology Department and Neuroscience Program; Estados Unido

#4 - Endosomal Proteins in Neurodevelopmental Disorders

Rett Syndrome is a neurodevelopmental disorder that primarily affects females and is detected at 6-18 months of age. Rett Syndrome results from a mutations in the methyl-CpG binding protein 2 gene (MECP2) which is found on the X chromosome. Its mutation results in impairment in cognitive, sensory, emotional, motor and autonomic functions. Schizophrenia is also a neurodevelopmental disorder with onset in adulthood, however there is no single genetic cause. Endosomal proteins have been implicated in both disorders through GWAS studies and animal models, suggesting a common molecular mechanism shared between these neurodevelopmental disorders. Previous research in our lab has demonstrated a disruption in endosomal trafficking in animal models of both disorders. This study explores the levels and localization of endosomal proteins in coronal brain sections for mice models for these neurodevelopmental disorders. Using immunohistochemistry, we will examine protein levels in the hippocampus and cortex for endosomal trafficking markers. We will also use whole-brain derived synaptosomes and western blots to examine the subcellular levels of these endosomal markers. Our data demonstrate a reduction of endosomal proteins in the hippocampus of mouse models of neurodevelopmental disorders. Future studies will include investigations into the affected cargo being mis-trafficked in these disorders

The Endosome Localized Arf-GAP AGAP1 Modulates Dendritic Spine Morphology Downstream of the Neurodevelopmental Disorder Factor Dysbindin

AGAP1 is an Arf1 GTPase activating protein that interacts with the vesicle-associated protein complexes adaptor protein 3 (AP-3) and Biogenesis of Lysosome Related Organelles Complex-1 (BLOC-1). Overexpression of AGAP1 in non-neuronal cells results in an accumulation of endosomal cargoes, which suggests a role in endosome-dependent traffic. In addition, AGAP1 is a candidate susceptibility gene for two neurodevelopmental disorders, autism spectrum disorder (ASD) and schizophrenia (SZ); yet its localization and function in neurons have not been described. Here, we describe that AGAP1 localizes to axons, dendrites, dendritic spines, and synapses, colocalizing preferentially with markers of early and recycling endosomes. Functional studies reveal overexpression and down-regulation of AGAP1 affects both neuronal endosomal trafficking and dendritic spine morphology, supporting a role for AGAP1 in the recycling endosomal trafficking involved in their morphogenesis. Finally, we determined the sensitivity of AGAP1 expression to mutations in the DTNBP1 gene, which is associated with neurodevelopmental disorder, and found that AGAP1 mRNA and protein levels are selectively reduced in the null allele of the mouse orthologue of DTNBP1. We postulate that endosomal trafficking contributes to the pathogenesis of neurodevelopmental disorders affecting dendritic spine morphology, and thus excitatory synapse structure and function

MeCP2 Regulates the Synaptic Expression of a Dysbindin-BLOC-1 Network Component in Mouse Brain and Human Induced Pluripotent Stem Cell-Derived Neurons

Clinical, epidemiological, and genetic evidence suggest overlapping pathogenic mechanisms between autism spectrum disorder (ASD) and schizophrenia. We tested this hypothesis by asking if mutations in the ASD gene MECP2 which cause Rett syndrome affect the expression of genes encoding the schizophrenia risk factor dysbindin, a subunit of the biogenesis of lysosome-related organelles complex-1 (BLOC-1), and associated interacting proteins. We measured mRNA and protein levels of key components of a dysbindin interaction network by, quantitative real time PCR and quantitative immunohistochemistry in hippocampal samples of wild-type and Mecp2 mutant mice. In addition, we confirmed results by performing immunohistochemistry of normal human hippocampus and quantitative qRT-PCR of human inducible pluripotent stem cells (iPSCs)-derived human neurons from Rett syndrome patients. We defined the distribution of the BLOC-1 subunit pallidin in human and mouse hippocampus and contrasted this distribution with that of symptomatic Mecp2 mutant mice. Neurons from mutant mice and Rett syndrome patients displayed selectively reduced levels of pallidin transcript. Pallidin immunoreactivity decreased in the hippocampus of symptomatic Mecp2 mutant mice, a feature most prominent at asymmetric synapses as determined by immunoelectron microcopy. Pallidin immunoreactivity decreased concomitantly with reduced BDNF content in the hippocampus of Mecp2 mice. Similarly, BDNF content was reduced in the hippocampus of BLOC-1 deficient mice suggesting that genetic defects in BLOC-1 are upstream of the BDNF phenotype in Mecp2 deficient mice. Our results demonstrate that the ASD-related gene Mecp2 regulates the expression of components belonging to the dysbindin interactome and these molecular differences may contribute to synaptic phenotypes that characterize Mecp2 deficiencies and ASD.Fil: Larimore, Jennifer. Agnes Scott College; Estados UnidosFil: Ryder, Pearl V.. University of Emory; Estados UnidosFil: Kim, Kun Yong. University of Yale. School of Medicine; Estados UnidosFil: Ambrose, L. Alex. Agnes Scott College; Estados UnidosFil: Chapleau, Christopher. University Of Alabama; Estados UnidosFil: Calfa, Gaston Diego. University Of Alabama; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gross, Christina. University of Emory; Estados UnidosFil: Bassell, Gary J.. University of Emory; Estados UnidosFil: Pozzo Miller, Lucas. University Of Alabama; Estados UnidosFil: Smith, Yoland. University of Emory; Estados UnidosFil: Talbot, Konrad. The Pennsylvania State University; Estados UnidosFil: Park, In Hyun. University of Yale. School of Medicine; Estados UnidosFil: Faundez, Victor. University of Emory; Estados Unido

Modulation of dendritic spine development and plasticity by BDNF and vesicular trafficking: fundamental roles in neurodevelopmental disorders associated with mental retardation and autism

The process of axonal and dendritic development establishes the synaptic circuitry of the central nervous system (CNS) and is the result of interactions between intrinsic molecular factors and the external environment. One growth factor that has a compelling function in neuronal development is the neurotrophin brain-derived neurotrophic factor (BDNF). BDNF participates in axonal and dendritic differentiation during embryonic stages of neuronal development, as well as in the formation and maturation of dendritic spines during postnatal development. Recent studies have also implicated vesicular trafficking of BDNF via secretory vesicles, and both secretory and endosomal trafficking of vesicles containing synaptic proteins, such as neurotransmitter and neurotrophin receptors, in the regulation of axonal and dendritic differentiation, and in dendritic spine morphogenesis. Several genes that are either mutated or deregulated in neurodevelopmental disorders associated with mental retardation have now been identified, and several mouse models of these disorders have been generated and characterized. Interestingly, abnormalities in dendritic and synaptic structure are consistently observed in human neurodevelopmental disorders associated with mental retardation, and in mouse models of these disorders as well. Abnormalities in dendritic and synaptic differentiation are thought to underlie altered synaptic function and network connectivity, thus contributing to the clinical outcome. Here, we review the roles of BDNF and vesicular trafficking in axonal and dendritic differentiation in the context of dendritic and axonal morphological impairments commonly observed in neurodevelopmental disorders associated with mental retardation

Final Report on the National Biological Survey- State of Illinois Partnership

ID: 8753; issued December 15, 1996INHS Technical Report prepared for US National Biological Servic

Sex‐dimorphic effects of biogenesis of lysosome‐related organelles complex‐1 deficiency on mouse perinatal brain development

The function(s) of the Biogenesis of Lysosome-related Organelles Complex-1 (BLOC-1) during brain development is to date largely unknown. Here, we investigated how its absence alters the trajectory of postnatal brain development using as model the pallid mouse. Most of the defects observed early postnatally in the mutant mice were more prominent in males than in females and in the hippocampus. Male mutant mice, but not females, had smaller brains as compared to sex-matching wild types at postnatal day 1 (P1), this deficit was largely recovered by P14 and P45. An abnormal cytoarchitecture of the pyramidal cell layer of the hippocampus was observed in P1 pallid male, but not female, or juvenile mice (P45), along with severely decreased expression levels of the radial glial marker Glutamate-Aspartate Transporter. Transcriptomic analyses showed that the overall response to the lack of functional BLOC-1 was more pronounced in hippocampi at P1 than at P45 or in the cerebral cortex. These observations suggest that absence of BLOC-1 renders males more susceptible to perinatal brain maldevelopment and although most abnormalities appear to have been resolved in juvenile animals, still permanent defects may be present, resulting in faulty neuronal circuits, and contribute to previously reported cognitive and behavioral phenotypes in adult BLOC-1-deficient mice