Rett syndrome: Expanding the phenotype

Spectrum of MECP2 gene mutations in a cohort of Indian patients with Rett syndrome: Report of two novel mutations

Rett Syndrome and MeCP2: Linking Epigenetics and Neuronal Function

P196 – 3008: Rett syndrome: Case report

Rett syndrome is a neurological disease of early postnatal brain growth found almost exclusively in girls. Typically girls with Rett syndrome show developmental regression including loss of communication and motor skills, stereotypic hand movements and a deceleration of head growth. The defective gene, methyl CpG binding protein 2 (Rett syndrome) ( MECP2 ) is normally involved in the transcription silencing of genes (turning genes ‘off’): in Rett syndrome, the MECP2 protein does not work properly in approximately half of the patient's cells (heterozygous), leading to the aberrant expression of a cascade of other genes, normally regulated by MECP2.

The lens epithelium derived growth factor p75 (LEDGF/p75) is an emerging oncoprotein identified as a key player in the cellular response to oxidative stress. LEDGF/p75 is induced by oxidative stress and promotes resistance to stress-induced cell death presumably by transcriptionally activating specific stress and survival genes. LEDGF/p75 has a splice variant, p52, which induces cell death when overexpressed. We have shown elevated expression of LEDGF/p75 in advanced stage prostatic adenocarcinomas, most likely as a result of increased oxidative stress in the prostate tumor microenvironment. To understand the mechanisms by which LEDGF/p75 transcriptionally activate stress genes and promotes protection against oxidative stress-induced cell death, it was necessary to identify endogenous cellular interacting partners of this protein. Screening of a transcription factor protein array identified the Methyl CpG binding Protein 2 (MeCP2) as a possible interacting partner of LEDGF/p75. MeCP2 is mutated in patients with Rett syndrome, both activate and repress transcription and has been implicated in prostate tumor growth. This study was designed to validate MeCP2 as an interacting partner of LEDFG/p75 and to explore its influence on LEDGF/p75's function. To examine the interaction of MeCP2 and LEDGF, pull down assays were performed with purified GST-MeCP2 incubated with His-LEDGF/p75 or His-p52, and with GST-MeCP2 or GST-p75 incubated with U2OS cell lysates. The results suggested binding of MeCP2 to both LEDGF/p75 and p52. Co-immunoprecipitation assays using U2OS cell lysates revealed binding of proteins, detected by immunoblotting using specific anti-LEDGF/p75 or MeCP2 antibodies, suggesting interaction of both proteins in the cellular microenvironment. We also examined the intracellular localization of both proteins in U2OS cells by immunofluorescence microscopy. Both MeCP2 and LEDGF/p75 co-localized in the chromatin, showing a similar dense fine speckled staining pattern. To examine if MeCP2 influences LEDGF/p75's transcriptional activity, luciferase reporter assays were performed. Even though LEDGF/p75, p52 and MeCP2 transactivated the Hsp27 promoter (pr) individually, co-expression of LEDGF/p75 with MeCP2 increased Hsp27pr activity, while co-expression of LEDGF/p52 with MeCP2 decreased activity. In addition, LEDGF/p75 overexpression protected PC3 cells from tert-butyl hydrogen peroxide (TBHP) treatment; but siRNA knockdown of MeCP2 in these cells sensitized cells to TBHP treatment compared to control siRNA. In conclusion, our data suggest that LEDGF/p75 and MeCP2 are interacting partners and MeCP2 influences LEDGF/p75's transcription and survival function. Future studies will explore modulating the interaction between LEDGF/p75 and MeCP2 to sensitize prostate cancer cells to therapy-induced cell death. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2945.

We report a 3-year-old girl with characteristic clinical, electroencephalographic and neuroradiological features of Rett syndrome (RS) - an X-linked dominant, neurodevelopmental disorder caused by mutation in methyl-CpG binding protein 2 (MECP2) gene. It predominantly affects females and is one of the commonest causes of mental retardation in females. It is characterized by progressive loss of intellectual functioning, fine and gross motor skills and communicative abilities, deceleration of head growth, and the development of stereotypic hand movements, occurring after a period of normal development. A 3-year-old girl was brought from our neighboring country with progressive loss of milestones. She had a normal development till one year of age when she gradually lost her motor milestones and started socially withdrawing from her surroundings. She also started excessive hand playing which were stereotypical and repetitive. She was microcephalic and had marked postural hypotonia. Her electroencephalography and magnetic resonance imaging showed the characteristic change associated with RS. These clinical features support the diagnosis of RS even though genetic analysis was not done. This is the first case report of RS from Pakistan.

Mutations in MECP2 cause the neurodevelopmental disorder Rett syndrome. MECP2 codes for methyl CpG binding protein 2 (MECP2), a transcriptional regulator that activates genetic programs for experience-dependent plasticity. Many neural and behavioral symptoms of Rett syndrome may result from dysregulated timing and thresholds for plasticity. As a model of adult plasticity, we examine changes to auditory cortex inhibitory circuits in female mice when they are first exposed to pups; this plasticity facilitates behavioral responses to pups emitting distress calls. Brainwide deletion of Mecp2 alters expression of markers associated with GABAergic parvalbumin interneurons (PVins) and impairs the emergence of pup retrieval. We hypothesized that loss of Mecp2 in PVins disproportionately contributes to the phenotype. Here, we find that deletion of Mecp2 from PVins delayed the onset of maternal retrieval behavior and recapitulated the major molecular and neurophysiological features of brainwide deletion of Mecp2 We observed that when PVin-selective mutants were exposed to pups, auditory cortical expression of PVin markers increased relative to that in wild-type littermates. PVin-specific mutants also failed to show the inhibitory auditory cortex plasticity seen in wild-type mice on exposure to pups and their vocalizations. Finally, using an intersectional viral genetic strategy, we demonstrate that postdevelopmental loss of Mecp2 in PVins of the auditory cortex is sufficient to delay onset of maternal retrieval. Our results support a model in which PVins play a central role in adult cortical plasticity and may be particularly impaired by loss of Mecp2 SIGNIFICANCE STATEMENT Rett syndrome is a neurodevelopmental disorder that includes deficits in both communication and the ability to update brain connections and activity during learning (plasticity). This condition is caused by mutations in the gene MECP2 We use a maternal behavioral test in mice requiring both vocal perception and neural plasticity to probe the role of Mecp2 in social and sensory learning. Mecp2 is normally active in all brain cells, but here we remove it from a specific population (parvalbumin neurons). We find that this is sufficient to delay learned behavioral responses to pups and recreates many deficits seen in whole-brain Mecp2 deletion. Our findings suggest that parvalbumin neurons specifically are central to the consequences of loss of Mecp2 activity and yield clues as to possible mechanisms by which Rett syndrome impairs brain function.

Editor—Rett syndrome (RTT, MIM 312750) is a progressive neurological disorder, occurring almost exclusively in females during their first two years of life . RTT is one of the most common...

Brain protein changes in Mecp2 mouse mutant models: Effects on disease progression of Mecp2 brain specific gene reactivation

Methyl CpG-binding protein 2 (MeCP2) is an epigenetic reader of DNA methylation with high abundance in the brain. While genetic mutations occur across different protein domains of MeCP2, the T158M mutation is amongst the most frequent MeCP2 mutations. MeCP2 is encoded by the MECP2/Mecp2 gene located on the X chromosome. In humans, MECP2 mutations cause Rett Syndrome, a debilitating neurodevelopmental disorder in females, with very rare cases presenting in males. Despite the generation of different transgenic mouse lines with MeCP2 mutations, the sex-dependent phenotypic and molecular impact of common MeCP2 mutations in mouse models of disease remains largely unexplored. Here, we focus on the MeCP2 T158M mutation using Mecp2tm4.1Bird/J transgenic mice (referred to as Mecp2T158M), and report that Mecp2T158M mutant mice display sex-specific molecular, behavioural, and phenotypic characteristics when compared to wild-type controls. Our data indicates sex- and brain-region-dependent impacts on the expression of MeCP2, synaptic proteins, cytoskeletal markers, and autophagy factors. Our findings demonstrate that the phenotypic and molecular characteristics of this mouse model may relate to the clinical manifestation in human patients with Rett Syndrome.

Rett syndrome is a neurodevelopmental disorder and an important cause of mental retardation and autistic behavior in girls and in a small group of boys. In 1999, mutation of the methyl-CpG binding protein 2 (MECP2) gene encoding a transcriptional repressor on the X chromosome was found to cause Rett syndrome. Since this discovery, significant research has focused on the elucidation of its specific role in the central nervous system. Recent studies revealed that MECP2 is expressed in more differentiated neurons rather than in less differentiated neuroblasts and that MECP2 is involved in the maturation and maintenance of neurons, including dendritic arborization and axonal projections, rather than in early cell fate decisions in the mammalian brain. In this review, we summarize recent findings regarding regional, temporal, and cell type-specific MECP2 expression in the central nervous system; neurobiologic abnormalities in MECP2 -mutant mice; and MECP2 target genes in the central nervous system.

Several X-linked neurodevelopmental disorders including Rett syndrome, induced by mutations in the MECP2 gene, and fragile X syndrome (FXS), caused by mutations in the FMR1 gene, share autism-related features. The mRNA coding for methyl CpG binding protein 2 (MeCP2) has previously been identified as a substrate for the mRNA-binding protein, fragile X mental retardation protein (FMRP), which is silenced in FXS. Here, we report a homeostatic relationship between these two key regulators of gene expression in mouse models of FXS (Fmr1 Knockout (KO)) and Rett syndrome (MeCP2 KO). We found that the level of MeCP2 protein in the cerebral cortex was elevated in Fmr1 KO mice, whereas MeCP2 KO mice displayed reduced levels of FMRP, implicating interplay between the activities of MeCP2 and FMRP. Indeed, knockdown of MeCP2 with short hairpin RNAs led to a reduction of FMRP in mouse Neuro2A and in human HEK-293 cells, suggesting a reciprocal coupling in the expression level of these two regulatory proteins. Intra-cerebroventricular injection of an adeno-associated viral vector coding for FMRP led to a concomitant reduction in MeCP2 expression in vivo and partially corrected locomotor hyperactivity. Additionally, the level of MeCP2 in the posterior cortex correlated with the severity of the hyperactive phenotype in Fmr1 KO mice. These results demonstrate that MeCP2 and FMRP operate within a previously undefined homeostatic relationship. Our findings also suggest that MeCP2 overexpression in Fmr1 KO mouse posterior cerebral cortex may contribute to the fragile X locomotor hyperactivity phenotype.

Rett syndrome (RTT) is a neurodevelopmental disorder caused predominantly by loss-of-function mutations in the gene Methyl-CpG-binding protein 2 (MECP2), which encodes the MeCP2 protein. RTT is a MECP2-related disorder, along with MECP2 duplication syndrome (MDS), caused by gain-of-function duplications of MECP2. Nearly two decades of research have advanced our knowledge of MeCP2 function in health and disease. The following review will discuss MeCP2 protein function and its dysregulation in the MECP2-related disorders RTT and MDS. This will include a discussion of the genetic underpinnings of these disorders, specifically how sporadic X-chromosome mutations arise and manifest in specific populations. We will then review current diagnostic guidelines and clinical manifestations of RTT and MDS. Next, we will delve into MeCP2 biology, describing the dual landscapes of methylated DNA and its reader MeCP2 across the neuronal genome as well as the function of MeCP2 as a transcriptional modulator. Following this, we will outline common MECP2 mutations and genotype-phenotype correlations in both diseases, with particular focus on mutations associated with relatively mild disease in RTT. We will also summarize decades of disease modeling and resulting molecular, synaptic, and behavioral phenotypes associated with RTT and MDS. Finally, we list several therapeutics in the development pipeline for RTT and MDS and available evidence of their safety and efficacy.

Rett syndrome is a neurodevelopmental disorder caused by loss-of-function mutations in MECP2, the gene encoding the transcriptional regulator methyl-CpG-binding protein 2 (MeCP2). Mecp2 deletion in mice results in an imbalance of excitation and inhibition in hippocampal neurons, which affects 'Hebbian' synaptic plasticity. We show that Mecp2-deficient neurons also lack homeostatic synaptic plasticity, likely due to reduced levels of EEA1, a protein involved in AMPA receptor endocytosis. Expression of EEA1 restored homeostatic synaptic plasticity in Mecp2-deficient neurons, providing novel targets of intervention in Rett syndrome. Rett syndrome is a neurodevelopmental disorder caused by loss-of-function mutations in MECP2, the gene encoding the transcriptional regulator methyl-CpG-binding protein 2 (MeCP2). Deletion of Mecp2 in mice results in an imbalance of synaptic excitation and inhibition in hippocampal pyramidal neurons, which affects 'Hebbian' long-term synaptic plasticity. Since the excitatory-inhibitory balance is maintained by homeostatic mechanisms, we examined the role of MeCP2 in homeostatic synaptic plasticity (HSP) at excitatory synapses. Negative feedback HSP, also known as synaptic scaling, maintains the global synaptic strength of individual neurons in response to sustained alterations in neuronal activity. Hippocampal neurons from Mecp2 knockout (KO) mice do not show the characteristic homeostatic scaling up of the amplitude of miniature excitatory postsynaptic currents (mEPSCs) and of synaptic levels of the GluA1 subunit of AMPA-type glutamate receptors after 48h silencing with the Na+ channel blocker tetrodotoxin. This deficit in HSP is bidirectional because Mecp2 KO neurons also failed to scale down mEPSC amplitudes and GluA1 synaptic levels after 48h blockade of type A GABA receptor (GABAA R)-mediated inhibition with bicuculline. Consistent with the role of synaptic trafficking of AMPA-type of glutamate receptors in HSP, Mecp2 KO neurons have lower levels of early endosome antigen 1 (EEA1), a protein involved in AMPA-type glutamate receptor endocytosis. In addition, expression of EEA1 in Mecp2 KO neurons reduced mEPSC amplitudes to wild-type levels, and restored synaptic scaling down of mEPSC amplitudes after 48h blockade of GABAA R-mediated inhibition with bicuculline. The identification of a molecular deficit in HSP in Mecp2 KO neurons provides potentially novel targets of intervention for improving hippocampal function in Rett syndrome individuals.

Rett syndrome (RS) is an X-linked neurodevelopmental disorder mostly involving mutations in the gene for methyl-CpG-binding protein 2 (MECP2). Ganglioside abnormalities were previously found in cerebrum and cerebellum in RS patients. We evaluated total lipid distribution in cerebrum/brainstem, hippocampus, and cerebellum in male mice carrying either the Mecp2 (tm1.1Bird) knockout mutation or the Mecp2 (308/y) deletion mutation. The concentration of the neuronal enriched ganglioside GD1a was significantly lower in the cerebrum/brainstem of Mecp2 (tm1.1Bird) mice than in that of age matched controls, but was not reduced in the Mecp2 (308/y) mice. No other differences in brain lipid content, including myelin-enriched cerebrosides, were detected in mice with either type of Mecp2 mutation. These findings indicate that the poor motor performance previously reported in the RS mutant mice is not associated with major brain lipid abnormalities and that most previous brain lipid abnormalities observed in RS patients were not observed in the Mecp2 (tm1.1Bird) or the Mecp2 (308/y) RS mice.