Global Transcriptional and Translational Repression in Human-Embryonic-Stem-Cell-Derived Rett Syndrome Neurons

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Rett Syndrome is a neurodevelopmental disorder that arises from mutations in the X-linked gene methyl-CpG binding protein 2 (MeCP2). MeCP2 has a large number of targets and a wide range of functions, suggesting the hypothesis that functional signaling mechanisms upstream of synaptic and circuit maturation may contribute to our understanding of the disorder and provide insight into potential treatment. Here, we show that insulin-like growth factor-1 (IGF1) levels are reduced in young male Mecp2-null (Mecp2 −/y ) mice, and systemic treatment with recombinant human IGF1 (rhIGF1) improves lifespan, locomotor activity, heart rate, respiration patterns, and social and anxiety behavior. Furthermore, Mecp2-null mice treated with rhIGF1 show increased synaptic and activated signaling pathway proteins, enhanced cortical excitatory synaptic transmission, and restored dendritic spine densities. IGF1 levels are also reduced in older, fully symptomatic heterozygous (Mecp2 −/+ ) female mice, and short-term treatment with rhIGF1 in these animals improves respiratory patterns, reduces anxiety levels, and increases exploratory behavior. In addition, rhIGF1 treatment normalizes abnormally prolonged plasticity in visual cortex circuits of adult Mecp2 −/+ female mice. Our results provide characterization of the phenotypic development of Rett Syndrome in a mouse model at the molecular, circuit, and organismal levels and demonstrate a mechanism-based therapeutic role for rhIGF1 in treating Rett Syndrome. molecular therapeutic | respiration | synaptic function | male mice | female mice R ett Syndrome (RTT) is a devastating, rare neurodevelopmental disorder that primarily afflicts girls. Over 90% of individuals with RTT have sporadic mutations in the X-linked gene coding for methyl-CpG binding protein 2 (MeCP2). Affected girls are initially asymptomatic, but later develop a wide range of symptoms. Mouse models of RTT with deletion of Mecp2 recapitulate many of the key physiological, autonomic, motor, and cognitive aspects of the disorder (1, 2).MeCP2 binds widely across the genome and has complex roles that encompass activating or inhibiting gene transcription, repressing methylation, regulating chromatin remodeling, and altering noncoding RNAs (3). This wide range of functions has led to the proposal that a focus on functional signaling pathways is needed to drive an understanding of RTT and its possible therapeutics (1, 2, 4). Several lines of evidence indicate an arrested brain maturation phenotype in RTT, suggesting that loss of functional MeCP2 leads to immature synapses and circuits in the brain (5). Importantly, mouse models have suggested reversibility of specific symptoms once MeCP2 function is restored (6, 7). One well-documented target of MeCP2 is brain-derived neurotrophic factor (BDNF), which is known to be critical for neuronal and synaptic maturation and is down-regulated in Mecp2 mutant mice and RTT patients (8, 9). BDNF exerts influence on neurons and synapses mainly via the phosphoinositide 3-kinase (PI3K)/Akt pathway ...

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confidence: 62%

Functional recovery with recombinant human IGF1 treatment in a mouse model of Rett Syndrome

Castro

Garcia

Kwok

et al. 2014

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167

“…The partial success of rhIGF1 in restoring numerous behavioral and organismal functions disrupted in Mecp2 KO mice (20), the safety and efficacy of rhIGF1 in clinical trials (25)(26)(27)(28), as well as the ability of rhIGF1 to rescue neuronal phenotypes in patientderived neurons (22,23) and astrocytes (24), prompted us to investigate whether Mecp2 knockdown can affect IGF1 expression, and look into additional drugs with potential to mechanistically rescue deficiencies in brain growth factor expression. Here, we show that, in addition to the known deficits in BDNF expression, IGF1 synthesis is reduced in the cerebellum of male Mecp2 KO mice, which is associated with a decreased level of miRNA-processing gene LIN28A and an up-regulation of LIN28A-regulated let-7f miRNA.…”

Section: Discussionmentioning

confidence: 99%

“…Indeed, several studies have demonstrated that IGF1 can rescue molecular signaling, structural and physiological phenotypes in human induced pluripotent stem cell-derived neurons (22,23) and astrocytes (24), and clinical trials of recombinant human IGF1 for RTT have shown favorable safety (25), and safety plus efficacy (26,27) profiles.…”

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confidence: 99%

β2-Adrenergic receptor agonist ameliorates phenotypes and corrects microRNA-mediated IGF1 deficits in a mouse model of Rett syndrome

Mellios

Woodson

Garcia

et al. 2014

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Rett syndrome is a severe childhood onset neurodevelopmental disorder caused by mutations in methyl-CpG-binding protein 2 (MECP2), with known disturbances in catecholamine synthesis. Here, we show that treatment with the β2-adrenergic receptor agonist clenbuterol increases survival, rescues abnormalities in respiratory function and social recognition, and improves motor coordination in young male Mecp2-null (Mecp2 −/y ) mice. Importantly, we demonstrate that short-term treatment with clenbuterol in older symptomatic female heterozygous (Mecp2 −/+ ) mice rescues respiratory, cognitive, and motor coordination deficits, and induces an anxiolytic effect. In addition, we reveal abnormalities in a microRNA-mediated pathway, downstream of brain-derived neurotrophic factor that affects insulin-like growth factor 1 (IGF1) expression in Mecp2 −/y mice, and show that treatment with clenbuterol restores the observed molecular alterations. Finally, cotreatment with clenbuterol and recombinant human IGF1 results in additional increases in survival in male null mice. Collectively, our data support a role for IGF1 and other growth factor deficits as an underlying mechanism of Rett syndrome and introduce β2-adrenergic receptor agonists as potential therapeutic agents for the treatment of the disorder.let-7f | LIN28A

“…With recent insights into the affinity of MeCP2 for mCA and hmCG, a major next step is to integrate this knowledge of MeCP2 binding specificity with in vitro and in vivo biochemical data and gene-expression analysis in MeCP2 mutants to build models of how MeCP2 functions to modulate transcription in vivo. A few studies already have begun to probe how MeCP2 functions with DNA methylation to regulate transcription by comparing the alterations in gene expression that occur in the brain of Mecp2 knockout mice with profiles of hydroxymethylation in the brain (38,58).…”

Section: Toward a Model Of Gene Regulation By Mch Hmc And Mecp2mentioning

confidence: 99%

Reading the unique DNA methylation landscape of the brain: Non-CpG methylation, hydroxymethylation, and MeCP2

Kinde

Gabel

Gilbert

et al. 2015

208

191

DNA methylation at CpG dinucleotides is an important epigenetic regulator common to virtually all mammalian cell types, but recent evidence indicates that during early postnatal development neuronal genomes also accumulate uniquely high levels of two alternative forms of methylation, non-CpG methylation and hydroxymethylation. Here we discuss the distinct landscape of DNA methylation in neurons, how it is established, and how it might affect the binding and function of protein readers of DNA methylation. We review studies of one critical reader of DNA methylation in the brain, the Rett syndrome protein methyl CpG-binding protein 2 (MeCP2), and discuss how differential binding affinity of MeCP2 for non-CpG and hydroxymethylation may affect the function of this methyl-binding protein in the nervous system.M ethylation of cytosines at the carbon 5 position (5-methylcytosine, mC) constitutes the most common covalent modification of vertebrate genomic DNA. Traditionally, cytosine methylation in vertebrate genomes has been viewed as largely restricted to CpG dinucleotide (CG) sequences, providing a stable epigenetic mark that mediates long-term transcriptional silencing. Indeed, 60-90% of all CGs are methylated in mammalian genomes, and CG methylation (mCG) has been shown to play critical roles in genomic imprinting, X-chromosome inactivation, cellular differentiation, and development (1). In addition, the disruption of cellular DNA methylation patterns has been linked to human disease, including multiple cancers (2, 3).Evidence that DNA methylation has a uniquely important role in the brain emerged almost two decades ago with the discovery of the prominent methyl-DNA-binding protein, methyl-CpG-binding protein 2 (MeCP2), and the later identification that mutations in MeCP2 give rise to the X-linked neurological disorder Rett syndrome (RTT) (4-6). Subsequent studies also have identified neurodevelopmental disorders associated with mutations in DNA methyltransferases (7), suggesting that both the enzymatic "writers" of DNA methylation patterns and the "readers" of these marks have important roles in the brain. In this context, new studies from several laboratories have uncovered extensive cytosine modification in the brain beyond mCG. Non-CG methylation (CH methylation or mCH, in which H = A, C, or T) is now appreciated to accumulate in the human and mouse brain postnatally, reaching levels similar to that of mCG in the neuronal genome (8, 9). Moreover, oxidation of mC by the ten-eleven translocation (Tet) family of dioxygenases leads to the selective accumulation of 5-hydroxymethylcytosine (hmC) in the adult brain, together with its more highly oxidized derivatives 5-formylcytosine and 5-carboxylcytosine (10, 11). This finding suggests that hmC may act as an intermediate in an active DNA demethylation pathway, though growing evidence also suggests that hmC may serve as a stable neuronal epigenetic mark in its own right (12).The discovery of these previously unidentified brain-enriched forms of DNA methylation provides...