MicroRNA调控通路与脆性X综合征

本文首先介绍了脆性智力低下蛋白在脆性X综合征发病机制的作用,然后介绍microRNA调控通路研究概况,特别是最近几年其在神经系统疾病研究的一些进展,并进一步阐述microRNA调控通路可能在脆性X综合征的发病机制及进展,从而使读者更深入的了解脆性X综合征的分子发病机制,并通过两者之间关系的研究可能为该病提供新的治疗方法与手段。     

代谢性谷氨酸受体在脆性X综合征树突棘发育中的作用

目的探讨代谢性谷氨酸受体-Ⅰ(mGluR-Ⅰ)在脆性X综合征发病中的作用和mGluR-Ⅰ拮抗剂治疗的机制。方法培养FMR-1基因敲除小鼠(KO)和野生(WT)小鼠海马神经元,给予mGluR-Ⅰ激动剂和拮抗剂进行处理,Western-Blot法检测处理前后脆性X智力低下蛋白(FMRP)和微管相关蛋白1B(MAP1B),共聚焦显微镜观察树突棘的长度和密度。结果KO小鼠海马神经元树突棘长度(1·32±0·79)和MAP1B含量显著高于WT小鼠(1·00±0·62)。mGluR-Ⅰ激动剂干预后,KO和WT小鼠树突棘长度(1·60±0·88和1·33±0·80)和MAP1B均显著增加。mGluR-Ⅰ拮抗后,KO小鼠树突棘长度(0·95±0·57)和MAP1B均显著降低,在WT小鼠未见明显变化。结论脆性X综合征模型鼠由于缺乏FMRP的负性调节作用,导致mGluR-Ⅰ激活的MAP1B过度表达,可能是树突棘异常的主要原因。mGluR-Ⅰ拮抗剂逆转树突棘缺陷可能参与治疗机制。     

脆性X智力低下一号基因缺陷对环磷酸腺苷的影响

目的探讨脆性X智力低下一号基因(FMR1)表达缺失对环磷酸腺苷(cAMP)的影响及其机制。方法通过硝普钠封闭FMR1，建立脆性X综合征细胞模型；研究FMR1表达缺失对cAMP水平及cAMP代谢途径中的两个关键酶[腺苷酸环化酶(AC)及磷酸二酯酶(PDE)]活性的影响。结果在细胞水平，硝普钠可成功地封闭FMR1基因；基因封闭组细胞内cAMP水平明显低于对照组(P=0．000)；该组腺苷酸环化酶的比活力明显低于对照组(P=0．000)，而磷酸二酯酶比活力则无显著改变(P=0．983)。结论FMR1基因表达缺失可导致细胞内cAMP的水平降低，腺苷酸环化酶活性被抑制可能是其降低的原因之一。     

伴有癫痫的脆性X综合征家系1例

脆性X综合征（fragile X syndrome,FXS）是FMR1基因CGG异常重复扩增导致的疾病。本文报告1对经基因检测诊断为FXS的兄弟,2例患者分别为15岁和14岁,均存在语言障碍、智力障碍、注意力缺陷障碍、孤独症谱系障碍和FXS特征性面容等临床表现,其中先证者伴有罕见的晚发性癫痫发作,经左乙拉西坦治疗效果良好,而其弟弟经反复随访未见脑电图异常。该对病例提示FXS临床表型具有多样性和异质性。     

脆性X综合征的神经病学研究进展

脆性X综合征是人类智力低下的常见病因之一.临床表现多种多样,主要为精神发育迟滞、语言及行为障碍、特殊面容和青春期后大睾丸.癫痫为重要临床表现之一,脑电图具有特征性.神经影象学检查提示非特异性改变.小脑蚓后部发育不良可能在孤独样行为发生中起重要作用.树突棘发育不良为主要神经病理发现.     

脆性X综合征与癫痫

脆性X综合征(fragile X syndrome,FXS)是一种最常见的遗传性智力障碍.这种智力障碍疾病主要是由于脆性X智力低下蛋白(fragile X mental retardation protein,FMRP)的缺失引起.FMRP是一种RNA结合蛋白,通过调节与其结合的信使RNA的翻译而调节神经元内的信号传导.很多FXS病人表现出较高的癫痫发作易感性.癫痫是一种慢性神经系统疾病.它的主要症状是反复的癫痫发作.癫痫发作是由大脑神经元的异常高兴奋性和同步放电引起的.FMEP缺失引起的神经元形态异常和神经元内信号传导的异常均可导致癫痫发作.本文结合在FXS和癫痫病两方面上取得研究结果综合分析,探讨FXS病人癫痫高易感性的发病机理,并对其他智力障碍疾病中的癫痫高易感性的机制的研究做一展望.     

MicroRNA-134在FMR1基因敲除鼠脑组织中的表达及意义

目的 观察脆性X综合征(FXS)模型小鼠不同发育时期脑组织中microRNA-134(miR-134)的表达,明确miR-134的表达特点及脆性X智力低下蛋白(FMRP)缺失是否导致miR-134转录的改变. 方法 应用荧光实时定量PCR检测FVB近交系雄性0 d、4、6周(W)龄FMR1基因敲除型(KO)(KO0d、KO4w、KO6w)和同龄野生型(WT)(WT0d、WT4w、WT6w)小鼠脑组织中miR-134的表达(n=5). 结果同龄KO与WT小鼠miR-134的转录表达量差异无统计学意义(P＞0.05);KO6w小鼠脑组织miR-134的转录表达量低于KO0d和KO2w小鼠,WT6w小鼠脑组织miR-134的转录表达量也低于WT0d和WT2w小鼠,差异均有统计学意义(P＜0.05). 结论 FMRp的缺失并未影响miR-134的转录;miR-134的转录表达量在神经系统发育期保持着较高水平,至成年期则下降,提示其在调控神经系统发育中可能起着重要作用.     

脆性X综合征筛选方法的评价

目的 探讨某些脆性X综合征筛选方法在我国的可行性。方法 按Nolin和Laing等报道的筛选标准对10例细胞遗传学检查脆性X阳性及PCR法检测FMR－1基因有CGG异常扩增的智力低下患儿进行评分，并将本组病人的得分和临床表现与筛选标准进行比较。结果 按上述两种筛选标准得分≥5分者占30％；仅1例得分为3分的病人有智力低下家族史。与前述筛选方法比较，本组仅40％符合，即假阴性率高达60％。结论 上述两种方法不适合国内脆性X综合征患儿的筛选。     

Cellular distribution of the fragile X mental retardation protein in the mouse brain

The fragile X mental retardation protein (FMRP) plays an important role in normal brain development. Absence of FMRP results in abnormal neuronal morphologies in a selected manner throughout the brain, leading to intellectual deficits and sensory dysfunction in the fragile X syndrome (FXS). Despite FMRP importance for proper brain function, its overall expression pattern in the mammalian brain at the resolution of individual neuronal cell groups is not known. In this study we used FMR1 knockout and isogenic wildtype mice to systematically map the distribution of FMRP expression in the entire mouse brain. Using immunocytochemistry and cellular quantification analyses, we identified a large number of prominent cell groups expressing high levels of FMRP at the subcortical levels, in particular sensory and motor neurons in the brainstem and thalamus. In contrast, many cell groups in the midbrain and hypothalamus exhibit low FMRP levels. More important, we describe differential patterns of FMRP distribution in both cortical and subcortical brain regions. Almost all major brain areas contain high and low levels of FMRP cell groups adjacent to each other or between layers of the same cortical areas. These differential patterns indicate that FMRP expression appears to be specific to individual neuronal cell groups instead of being associated with all neurons in distinct brain regions, as previously considered. Taken together, these findings support the notion of FMRP differential neuronal regulation and strongly implicate the contribution of fundamental sensory and motor processing at subcortical levels to FXS pathology. J. Comp. Neurol. 525:818–849, 2017. © 2016 Wiley Periodicals, Inc.     

A quantitative homogeneous assay for fragile X mental retardation 1 protein

Background

Hypermethylation of the fragile X mental retardation 1 gene FMR1 results in decreased expression of FMR1 protein FMRP, which is the underlying cause of Fragile X syndrome – an incurable neurological disorder characterized by mental retardation, anxiety, epileptic episodes and autism. Disease-modifying therapies for Fragile X syndrome are thus aimed at treatments that increase the FMRP expression levels in the brain. We describe the development and characterization of two assays for simple and quantitative detection of FMRP protein.

Method

Antibodies coupled to fluorophores that can be employed for time-resolved Förster’s resonance energy transfer were used for the development of homogeneous, one-step immunodetection. Purified recombinant human FMRP and patient cells were used as control samples for assay development.

Results

The assays require small sample amounts, display high stability and reproducibility and can be used to quantify endogenous FMRP in human fibroblasts and peripheral blood mononuclear cells. Application of the assays to FXS patient cells showed that the methods can be used both for the characterization of clinical FXS patient samples as well as primary readouts in drug-discovery screens aimed at increasing endogenous FMRP levels in human cells.

Conclusion

This study provides novel quantitative detection methods for FMRP in FXS patient cells. Importantly, due to the simplicity of the assay protocol, the method is suited to be used in screening applications to identify compounds or genetic interventions that result in increased FMRP levels in human cells.     

BDNF regulates the expression of fragile X mental retardation protein mRNA in the hippocampus

Both fragile X mental retardation protein (FMRP) and brain-derived neurotrophic factor (BDNF) are implicated in the maturation of neurons and in the higher cognitive functions. We have investigated whether FMRP and BDNF are reciprocally regulated in neurons. Exposure of cultured hippocampal neurons to BDNF, but not to NT-3, reduced FMR1 mRNA levels to 84.8% of control at 4 h and the levels were back to baseline by 24 h or 4 days. Furthermore, expression of FMR1 mRNA was reduced (82.4% of control) in vivo in the hippocampus of transgenic mice overexpressing TrkB receptors, and a small but significant (5.1%) decrease was also detected in FMRP protein levels. In contrast, the expression patterns of BDNF and TrkB mRNAs were not altered in FMRP-deficient mice compared to wild-type mice. Our data provide evidence that BDNF via TrkB signaling decreases FMRP expression and suggest a role for FMRP in BDNF-induced synaptic plasticity.     

The mGluR theory of fragile X mental retardation

Many of the diverse functional consequences of activating group 1 metabotropic glutamate receptors require translation of pre-existing mRNA near synapses. One of these consequences is long-term depression (LTD) of transmission at hippocampal synapses. Loss of fragile X mental retardation protein (FMRP), the defect responsible for fragile X syndrome in humans, increases LTD in mouse hippocampus. This finding is consistent with the growing evidence that FMRP normally functions as a repressor of translation of specific mRNAs. Here we present a theory that can account for diverse neurological and psychiatric aspects of fragile X syndrome, based on the assumption that many of the protein-synthesis-dependent functions of metabotropic receptors are exaggerated in fragile X syndrome. The theory suggests new directions for basic research as well as novel therapeutic approaches for the treatment of humans with fragile X, the most frequent inherited cause of mental retardation and an identified cause of autism.     

Sensory stimulation increases cortical expression of the fragile X mental retardation protein in vivo

Fragile X syndrome is a common cause of mental retardation that results from the absence of the fragile X mental retardation protein (FMRP), an RNA binding protein whose function remains unclear. Recent in vitro work has demonstrated that the protein is translated near the synapse in an activity dependent manner [33]. We therefore asked whether expression of FMRP might be altered by neuronal activity in vivo. Using immunoblots of different sub-cellular fractions of the rat somatosensory cortex, we show that the levels of FMRP increase significantly following unilateral whisker stimulation, a model of experience dependent plasticity. This increase is greatest between 2 and 8 h after the stimulus and is seen in both a synaptosomal fraction as well as a sub-cellular fraction enriched for polyribosomal complexes. In contrast, detectable levels of FMRP within the somatosensory cortex show either a decrease or no change after a kainic acid induced seizure compared to water treated controls. Our findings demonstrate that FMRP expression levels are modulated in vivo in response to neuronal activity and suggest a role for FMRP in activity dependent plasticity.     

Proteomic analyses of nucleus laminaris identified candidate targets of the fragile X mental retardation protein

The avian nucleus laminaris (NL) is a brainstem nucleus necessary for binaural processing, analogous in structure and function to the mammalian medial superior olive. In chickens (Gallus gallus), NL is a well‐studied model system for activity‐dependent neural plasticity. Its neurons have bipolar extension of dendrites, which receive segregated inputs from two ears and display rapid and compartment‐specific reorganization in response to unilateral changes in auditory input. More recently, fragile X mental retardation protein (FMRP), an RNA‐binding protein that regulates local protein translation, has been shown to be enriched in NL dendrites, suggesting its potential role in the structural dynamics of these dendrites. To explore the molecular role of FMRP in this nucleus, we performed proteomic analysis of NL, using micro laser capture and liquid chromatography tandem mass spectrometry. We identified 657 proteins, greatly represented in pathways involved in mitochondria, translation and metabolism, consistent with high levels of activity of NL neurons. Of these, 94 are potential FMRP targets, by comparative analysis with previously proposed FMRP targets in mammals. These proteins are enriched in pathways involved in cellular growth, cellular trafficking and transmembrane transport. Immunocytochemistry verified the dendritic localization of several proteins in NL. Furthermore, we confirmed the direct interaction of FMRP with one candidate, RhoC, by in vitro RNA binding assays. In summary, we provide a database of highly expressed proteins in NL and in particular a list of potential FMRP targets, with the goal of facilitating molecular characterization of FMRP signaling in future studies.