Limk1在FMR1基因敲除小鼠脑组织的表达及意义

目的：通过免疫组化方法观察LIM-kinase 1（Limk1）在不同年龄组的FMR1基因敲除鼠（FMR1 knockout mouse,KO）和野生鼠（wild type mouse,WT）脑组织不同部位的表达差异.方法：取FVB品系新生和生后2、6周KO鼠（KO0d、KO2周和KO6周）,并分别与同龄WT鼠作对照.每组6只通过免疫组化染色,观察Limk1在不同年龄组的KO和WT小鼠脑组织各部位的表达差异.结果：Limk1在新生鼠的海马、皮层、丘脑、小脑表达丰富,以染色阳性纤维为主,染色阳性细胞少见.生后2周、6周小鼠的大脑皮质和海马仅见少量散在弱阳性细胞表达,但在丘脑未定带、腹后外侧核,小脑蒲肯野细胞和脑干前庭蜗神经核可见强阳性细胞表达.各年龄组KO与WT小鼠Limk1在脑区的分布特点基本一致.KO0d、KO2周及KO6周组小脑、蜗神经核Limk1强阳性表达脑区的平均光密度值以及KO2W及KO6W组丘脑部位的阳性细胞计数均高于同龄WT组,差异有统计学意义（P＜0.05）.结论：Limk1在KO与WT小鼠脑组织的表达均有着明显的时空特异性,FMRP能负性调控Limk1表达.     

FMRP Sustains Presynaptic Function via Control of Activity-Dependent Bulk Endocytosis

Synaptic vesicle (SV) recycling is essential for the maintenance of neurotransmission, with a number of neurodevelopmental disorders linked to defects in this process. Fragile X syndrome (FXS) results from a loss of fragile X mental retardation protein (FMRP) encoded by the FMR1 gene. Hyperexcitability of neuronal circuits is a key feature of FXS, therefore we investigated whether SV recycling was affected by the absence of FMRP during increased neuronal activity. We revealed that primary neuronal cultures from male Fmr1 knock-out (KO) rats display a specific defect in activity-dependent bulk endocytosis (ADBE). ADBE is dominant during intense neuronal activity, and this defect resulted in an inability of Fmr1 KO neurons to sustain SV recycling during trains of high-frequency stimulation. Using a molecular replacement strategy, we also revealed that a human FMRP mutant that cannot bind BK channels failed to correct ADBE dysfunction in KO neurons, however this dysfunction was corrected by BK channel agonists. Therefore, FMRP performs a key role in sustaining neurotransmitter release via selective control of ADBE, suggesting intervention via this endocytosis mode may correct the hyperexcitability observed in FXS.SIGNIFICANCE STATEMENT Loss of fragile X mental retardation protein (FMRP) results in fragile X syndrome (FXS), however whether its loss has a direct role in neurotransmitter release remains a matter of debate. We demonstrate that neurons lacking FMRP display a specific defect in a mechanism that sustains neurotransmitter release during intense neuronal firing, called activity-dependent bulk endocytosis (ADBE). This discovery provides key insights into mechanisms of brain communication that occur because of loss of FMRP function. Importantly it also reveals ADBE as a potential therapeutic target to correct the circuit hyperexcitability observed in FXS.     

MPEP Reduces Seizure Severity in Fmr-1 KO mice over Expressing Human A��

Metabotropic glutamate receptor 5 (mGluR₅) regulates the translation of amyloid precursor protein (APP) mRNA. Under resting conditions, mRNA is bound to and translationally repressed by the fragile X mental retardation protein (FMRP). Upon group 1 mGluR activation, FMRP dissociates from the mRNA and translation ensues. APP levels are elevated in the dendrites of primary neuronal cultures as well as in synaptoneurosomes (SN) prepared from embryonic and juvenile fmr-1 knockout (KO) mice, respectively. In order to study the effects of APP and its proteolytic product Aβ on Fragile X syndrome (FXS) phenotypes, we created a novel mouse model (FRAXAD) that over-expresses human APPSwe/Aβ in an fmr-1 KO background. Herein, we assess (1) human APP_Swe and Aβ levels as a function of age in FRAXAD mice, and (2) seizure susceptibility to pentylenetetrazol (PTZ) after mGluR₅ blockade. PTZ-induced seizure severity is decreased in FRAXAD mice pre-treated with the mGluR₅ antagonist MPEP. These data suggest that Aβ contributes to seizure incidence and may be an appropriate therapeutic target to lessen seizure pathology in FXS, Alzheimer''s disease (AD) and Down syndrome (DS) patients.     

Peroxisome proliferator activated receptor gamma (PPARγ) as a therapeutic target for improvement of cognitive performance in Fragile-X

Rare disorders leading to intellectual disability, such as Fragile X syndrome (FXS) alter synaptic plasticity. Ligand identification of orphan nuclear receptors has led to the discovery of many signaling pathways and has revealed a direct link of nuclear receptors with human conditions such as mental retardation and neurodegenerative diseases. PPARγ agonists can act as neuroprotective agents, promoting synaptic plasticity and neurite outgrowth. Therefore, selective PPARγ agonists are good candidates for therapeutic evaluation in intellectual disabilities. Preliminary results suggest that PPARγ agonists such as Pioglitazone, Rosiglitazone and synthetic agonist, GW1929, are used as the therapeutic agent in neurological disorders. These components interact with intracellular transduction signals (e.g. GSK3β, PI3K/Akt, Wnt/β-Catenin, Rac1 and MMP-9). It seems that interaction with these pathways can improve memory recognition in FXS animal models. The present hypothesis consists of enhancing synaptic plasticity that may then rescue the learning and memory in FXS. This will open many new therapeutic avenues for a variety of human diseases.     

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.     

Males but not females show differences in calbindin immunoreactivity in the dorsal thalamus of the mouse model of fragile X syndrome

Fragile X syndrome (FXS), the most common form of inherited mental retardation, is caused by the loss of the Fmr1 gene product, fragile X mental retardation protein. Here we analyze the immunohistochemical expression of calcium‐binding proteins in the dorsal thalamus of Fmr1 knockout mice of both sexes and compare it with that of wildtype littermates. The spatial distribution pattern of calbindin‐immunoreactive cells in the dorsal thalamus was similar in wildtype and knockout mice but there was a notable reduction in calbindin‐immunoreactive cells in midline/intralaminar/posterior dorsal thalamic nuclei of male Fmr1 knockout mice. We counted the number of calbindin‐immunoreactive cells in 18 distinct nuclei of the dorsal thalamus. Knockout male mice showed a significant reduction in calbindin‐immunoreactive cells (range: 36–67% lower), whereas female knockout mice did not show significant differences (in any dorsal thalamic nucleus) when compared with their wildtype littermates. No variation in the calretinin expression pattern was observed throughout the dorsal thalamus. The number of calretinin‐immunoreactive cells was similar for all experimental groups as well. Parvalbumin immunoreactivity was restricted to fibers and neuropil in the analyzed dorsal thalamic nuclei, and presented no differences between genotypes. Midline/intralaminar/posterior dorsal thalamic nuclei are involved in forebrain circuits related to memory, nociception, social fear, and auditory sensory integration; therefore, we suggest that downregulation of calbindin protein expression in the dorsal thalamus of male knockout mice should be taken into account when analyzing behavioral studies in the mouse model of FXS. J. Comp. Neurol. 521:894–911, 2013. © 2012 Wiley Periodicals, Inc.     

The effects of prenatal H1N1 infection at E16 on FMRP,glutamate, GABA,and reelin signaling systems in developing murine cerebellum

Prenatal viral infection has been identified as a potential risk factor for the development of neurodevelopmental disorders such as schizophrenia and autism. Additionally, dysfunction in gamma‐aminobutyric acid, Reelin, and fragile X mental retardation protein (FMRP)–metabotropic glutamate receptor 5 signaling systems has also been demonstrated in these two disorders. In the current report, we have characterized the developmental profiles of selected markers for these systems in cerebella of mice born to pregnant mice infected with human influenza (H1N1) virus on embryonic day 16 or sham‐infected controls using SDS‐PAGE and Western blotting techniques and evaluated the presence of abnormalities in the above‐mentioned markers during brain development. The cerebellum was selected in light of emerging evidence that it plays roles in learning, memory, and emotional processing—all of which are disrupted in autism and schizophrenia. We identified unique patterns of gene and protein expression at birth (postnatal day 0 [P0]), childhood (P14), adolescence (P35), and young adulthood (P56) in both exposed and control mouse progeny. We also identified significant differences in protein expression for FMRP, very‐low‐density lipoprotein receptor, and glutamic acid decarboxylase 65 and 67 kDa proteins at specific postnatal time points in cerebella of the offspring of exposed mice. Our results provide evidence of disrupted FMRP, glutamatergic, and Reelin signaling in the exposed mouse offspring that explains the multiple brain abnormalities observed in this animal model. © 2016 Wiley Periodicals, Inc.     

Dissociation of social and nonsocial anxiety in a mouse model of fragile X syndrome

Anxiety is a common symptom in fragile X patients. However, an anxiety-prone phenotype in mouse models of fragile X syndrome is not clear. In most studies of fmr1 knockout mice, decreased anxiety-like responses in exploratory-based models are found, but mice also exhibit abnormal social interactions. We hypothesize the coexistence of elevated social anxiety and reduced nonsocial anxiety in fmr1 knockout mice. In the present study, we applied an automated three-chambered social approach method and the elevated zero maze test to further investigate social interactions and general anxiety, respectively. Results indicate lower levels of both social approach behavior and response to social novelty in fmr1 knockout mice compared with wild-type littermates in the social interaction test. In the elevated zero maze, fmr1 knockout mice spent a greater percent time in open quadrants than wild-type mice, suggesting reduced nonsocial anxiety. These findings support the hypothesis that social and nonsocial anxiety can be dissociated and that in the fragile X mouse model, behavior consistent with hyper-social anxiety coexists with hypo-nonsocial anxiety.