Increased iron content in the heart of the Fmr1 knockout mouse.
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ABSTRACT:
SUBMITTER: Talvio K
PROVIDER: S-EPMC8313461 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Fragile X syndrome (FXS) is a neurodevelopmental disorder caused by silencing of the FMR1 gene and subsequent loss of its protein product, fragile X retardation protein (FMRP). One of the most robust neuropathological findings in post-mortem human FXS and Fmr1 KO mice is the abnormal increase in dendritic spine densities, with the majority of spines showing an elongated immature morphology. However, the exact mechanisms of how FMRP can regulate dendritic spine development are still unclear. Abnormal dendritic spines can result from disturbances of multiple factors during neurodevelopment, such as alterations in neuron numbers, position and glial cells. In this study, we undertook a comprehensive histological analysis of the cerebral cortex in Fmr1 KO mice. They displayed significantly fewer neuron and PV-interneuron numbers, along with altered cortical lamination patterns. In terms of glial cells, Fmr1 KO mice exhibited an increase in Olig2-oligodendrocytes, which corresponded to the abnormally higher myelin expression in the corpus callosum. Iba1-microglia were significantly reduced but GFAP-astrocyte numbers and intensity were elevated. Using primary astrocytes derived from KO mice, we further demonstrated the presence of astrogliosis characterized by an increase in GFAP expression and astrocyte hypertrophy. Our findings provide important information on the cortical architecture of Fmr1 KO mice, and insights towards possible mechanisms associated with FXS.
| S-EPMC6570929 | biostudies-literature
Project description:Fragile X syndrome (FXS) is caused by a failure of neuronal cells to express the gene encoding the fragile mental retardation protein (FMRP). Clinical features of the syndrome include intellectual disability, learning impairment, hyperactivity, seizures and anxiety. Fmr1 knockout (KO) mice do not express FMRP and, as a result, reproduce some FXS behavioral abnormalities. While intrinsic and synaptic properties of excitatory cells in various part of the brain have been studied in Fmr1 KO mice, a thorough analysis of action potential characteristics and input-output function of CA1 pyramidal cells in this model is lacking. With a view to determining the effects of the absence of FMRP on cell excitability, we studied rheobase, action potential duration, firing frequency-current intensity relationship and action potential after-hyperpolarization (AHP) in CA1 pyramidal cells of the hippocampus of wild type (WT) and Fmr1 KO male mice. Brain slices were prepared from 8- to 12-week-old mice and the electrophysiological properties of cells recorded. Cells from both groups had similar resting membrane potentials. In the absence of FMRP expression, cells had a significantly higher input resistance, while voltage threshold and depolarization voltage were similar in WT and Fmr1 KO cell groups. No changes were observed in rheobase. The action potential duration was longer in the Fmr1 KO cell group, and the action potential firing frequency evoked by current steps of the same intensity was higher. Moreover, the gain (slope) of the relationship between firing frequency and injected current was 1.25-fold higher in the Fmr1 KO cell group. Finally, AHP amplitude was significantly reduced in the Fmr1 KO cell group. According to these data, FMRP absence increases excitability in hippocampal CA1 pyramidal cells.
| S-EPMC5607184 | biostudies-literature
Project description:The current study aimed to further address important questions regarding the therapeutic efficacy of omega-3 fatty acids for various behavioral and neuroimmune aspects of the Fmr1 phenotype. To address these questions, our experimental design utilized two different omega-3 fatty acid administration timepoints, compared to both standard laboratory chow controls ("Standard") and a diet controlling for the increase in fat content ("Control Fat"). In the first paradigm, post-weaning supplementation (after postnatal day 21) with the omega-3 fatty acid diet ("Omega-3") reversed deficits in startle threshold, but not deficits in prepulse inhibition, and the effect on startle threshold was not specific to the Omega-3 diet. However, post-weaning supplementation with both experimental diets also impaired acquisition of a fear response, recall of the fear memory and contextual fear conditioning compared to the Standard diet. The post-weaning Omega-3 diet reduced hippocampal expression of IL-6 and this reduction of IL-6 was significantly associated with diminished performance in the fear conditioning task. In the perinatal experimental paradigm, the Omega-3 diet attenuated hyperactivity and acquisition of a fear response. Additionally, perinatal exposure to the Control Fat diet (similar to a "Western" diet) further diminished nonsocial anxiety in the Fmr1 knockout. This study provides significant evidence that dietary fatty acids throughout the lifespan can significantly impact the behavioral and neuroimmune phenotype of the Fmr1 knockout model.
| S-EPMC8797197 | biostudies-literature
Project description:Altered neuronal excitability is one of the hallmarks of fragile X syndrome (FXS), but the mechanisms underlying this critical neuronal dysfunction are poorly understood. Here, we find that pyramidal cells in the entorhinal cortex of Fmr1 KO mice, an established FXS mouse model, display a decreased AP threshold and increased neuronal excitability. The AP threshold changes in Fmr1 KO mice are caused by increased persistent sodium current (INaP). Our results indicate that this abnormal INaP in Fmr1 KO animals is mediated by increased mGluR5-PLC-PKC (metabotropic glutamate receptor 5/phospholipase C/protein kinase C) signaling. These findings identify Na(+) channel dysregulation as a major cause of neuronal hyperexcitability in cortical FXS neurons and uncover a mechanism by which abnormal mGluR5 signaling causes neuronal hyperexcitability in a FXS mouse model.
| S-EPMC5055130 | biostudies-literature
Project description:Background: Loss of FMR1 is associated with Fragile X syndrome, amongst the most prevalent inherited intellectual disability. Despite extensive research in this area, previous studies have failed to detect consistent evidence of cognitive impairments in the Morris water maze (MWM) task in the Fmr1 knockout (KO) mouse. However, few studies have examined cognitive flexibility in a reversal form of the MWM task, which may illuminate subtle learning deficits. Methods: Adult male Fmr1 wildtype (WT) and KO mice were bred and tested in the MWM reversal paradigm. The testing paradigm consisted of two blocks per day, with 4 trials per block to locate a hidden platform. After the last trials on the fourth day of testing, the animals were given a probe trial with the platform removed. The following week, the location of the platform was switched to the opposite quadrant and the animals received 2 more days of testing, with 4 blocks in total. Results: As expected, Fmr1 KO mice did not display a learning deficit during the acquisition phase, F genotype (1, 24) = 0.034, p = 0.854, and performed similarly on the probe trial, F genotype (1, 23) = 0.024, p = 0.877. However, during the reversal phase of learning, Fmr1 KO mice showed deficits in their ability to learn the new location of the platform, F genotype (1, 23) = 3.93, p = 0.059. Further independent samples t-testing revealed that KO animals displayed significantly higher latency to reach the hidden platform during the third trial, t(23) = -2.96, p < 0.01. Conclusions: While previous studies have not demonstrated deficits in spatial memory in the Fmr1 KO model, it is possible that the acquisition phase of the task is less sensitive to deficits in learning. Future studies using this model to evaluate therapeutic interventions should consider utilizing the MWM reversal paradigm.
| S-EPMC6051189 | biostudies-literature
Project description:Fragile X syndrome (FXS) is an X-chromosome linked intellectual disability and the most common known inherited single gene cause of autism spectrum disorder (ASD). Building upon demonstrated deficits in neuronal plasticity and spatial memory in FXS, we investigated how spatial information processing is affected in vivo in an FXS mouse model (Fmr1-KO). Healthy hippocampal neurons (so-called place cells) exhibit place-related activity during spatial exploration, and their firing fields tend to remain stable over time. In contrast, we find impaired stability and reduced specificity of Fmr1-KO spatial representations. This is a potential biomarker for the cognitive dysfunction observed in FXS, informative on the ability to integrate sensory information into an abstract representation and successfully retain this conceptual memory. Our results provide key insight into the biological mechanisms underlying cognitive disabilities in FXS and ASD, paving the way for a targeted approach to remedy these.
| S-EPMC5995880 | biostudies-other
Project description:BACKGROUND: This study was designed to test a new approach to drug treatment of autism spectrum disorders (ASDs) in the Fragile X (Fmr1) knockout mouse model. METHODS: We used behavioral analysis, mass spectrometry, metabolomics, electron microscopy, and western analysis to test the hypothesis that the disturbances in social behavior, novelty preference, metabolism, and synapse structure are treatable with antipurinergic therapy (APT). RESULTS: Weekly treatment with the purinergic antagonist suramin (20 mg/kg intraperitoneally), started at 9 weeks of age, restored normal social behavior, and improved metabolism, and brain synaptosomal structure. Abnormalities in synaptosomal glutamate, endocannabinoid, purinergic, and IP3 receptor expression, complement C1q, TDP43, and amyloid β precursor protein (APP) were corrected. Comprehensive metabolomic analysis identified 20 biochemical pathways associated with symptom improvements. Seventeen pathways were shared with human ASD, and 11 were shared with the maternal immune activation (MIA) model of ASD. These metabolic pathways were previously identified as functionally related mediators of the evolutionarily conserved cell danger response (CDR). CONCLUSIONS: The data show that antipurinergic therapy improves the multisystem, ASD-like features of both the environmental MIA, and the genetic Fragile X models. These abnormalities appeared to be traceable to mitochondria and regulated by purinergic signaling.
| S-EPMC4334917 | biostudies-literature
Project description:BackgroundFragile X syndrome (FXS) is an intellectual disability attributable to loss of fragile X protein (FMRP). We previously demonstrated that FMRP binds mRNAs targeted for nonsense-mediated mRNA decay (NMD) and that FMRP loss results in hyperactivated NMD and inhibition of neuronal differentiation in human stem cells.ResultsWe show here that NMD is hyperactivated during the development of the cerebral cortex, hippocampus, and cerebellum in the Fmr1-knockout (KO) mouse during embryonic and early postnatal periods. Our findings demonstrate that NMD regulates many neuronal mRNAs that are important for mouse brain development.ConclusionsWe reveal the abnormal regulation of these mRNAs in the Fmr1-KO mouse, a model of FXS, and highlight the importance of early intervention.
| S-EPMC8597091 | biostudies-literature
Project description:Fragile X syndrome (FXS) is the most prevalent inherited cause of autism and is accompanied by behavioral and sensory deficits. Errors in the wiring of the brain during early development likely contribute to these deficits, but the underlying mechanisms are unclear. Spontaneous activity patterns, which are required for fine-tuning neuronal networks before the senses become active, are perturbed in rodent models of FXS. Here, we investigated spontaneous network activity patterns in the developing visual cortex of the Fmr1 knockout mouse using in vivo calcium imaging during the second postnatal week, before eye opening. We found that while the frequency, mean amplitude and duration of spontaneous network events were unchanged in the knockout mouse, pair-wise correlations between neurons were increased compared to wild type littermate controls. Further analysis revealed that interneuronal correlations were not generally increased, rather that low-synchronization events occurred relatively less frequently than high-synchronization events. Low-, but not high-, synchronization events have been associated with retinal inputs previously. Since we found that spontaneous retinal waves were normal in the knockout, our results suggest that peripherally driven activity is underrepresented in the Fmr1 KO visual cortex. Therefore, we propose that central gating of retinal inputs may be affected in FXS and that peripherally and centrally driven activity patterns are already unbalanced before eye opening in this disorder.
| S-EPMC6775252 | biostudies-literature
Project description:The enzyme retinol saturase (RetSat) catalyzes the saturation of all-trans-retinol to produce (R)-all-trans-13,14-dihydroretinol. As a peroxisome proliferator-activated receptor (PPAR) gamma target, RetSat was shown to be required for adipocyte differentiation in the 3T3-L1 cell culture model. To understand the mechanism involved in this putative proadipogenic effect of RetSat, we studied the consequences of ablating RetSat expression on retinoid metabolism and adipose tissue differentiation in RetSat-null mice. Here, we report that RetSat-null mice have normal levels of retinol and retinyl palmitate in liver, serum, and adipose tissue, but, in contrast to wild-type mice, are deficient in the production of all-trans-13,14-dihydroretinol from dietary vitamin A. Despite accumulating more fat, RetSat-null mice maintained on either low-fat or high-fat diets gain weight and have similar rates of food intake as age- and gender-matched wild-type control littermates. This increased adiposity of RetSat-null mice is associated with up-regulation of PPARgamma, a key transcriptional regulator of adipogenesis, and also its downstream target, fatty acid-binding protein 4 (FABP4/aP2). On the basis of these results, we propose that dihydroretinoids produced by RetSat control physiological processes that influence PPARgamma activity and regulate lipid accumulation in mice.-Moise, A. R., Lobo, G. P., Erokwu, B., Wilson, D. L., Peck, D., Alvarez, S., Domínguez, M., Alvarez, R., Flask, C. A., de Lera, A. R., von Lintig, J., Palczewski, K. Increased adiposity in the retinol saturase-knockout mouse.
| S-EPMC2845435 | biostudies-literature