Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX, USA.
Department of Biology, University of Houston, Houston, TX, USA.
Mol Neurobiol. 2018 Jun;55(6):4529-4542. doi: 10.1007/s12035-017-0666-4. Epub 2017 Jul 8.
Behavioral intervention therapy has proven beneficial in the treatment of autism and intellectual disabilities (ID), raising the possibility of certain changes in molecular mechanisms activated by these interventions that may promote learning. Fragile X syndrome (FXS) is a neurodevelopmental disorder characterized by autistic features and intellectual disability and can serve as a model to examine mechanisms that promote learning. FXS results from mutations in the fragile X mental retardation 1 gene (Fmr1) that prevents expression of the Fmr1 protein (FMRP), a messenger RNA (mRNA) translation regulator at synapses. Among many other functions, FMRP organizes a complex with the actin cytoskeleton-regulating small Rho GTPase Rac1. As in humans, Fmr1 KO mice lacking FMRP display autistic-like behaviors and deformities of actin-rich synaptic structures in addition to impaired hippocampal learning and synaptic plasticity. These features have been previously linked to proper function of actin remodeling proteins that includes Rac1. An important step in Rac1 activation and function is its translocation to the membrane, where it can influence synaptic actin cytoskeleton remodeling during hippocampus-dependent learning. Herein, we report that Fmr1 KO mouse hippocampus exhibits increased levels of membrane-bound Rac1, which may prevent proper learning-induced synaptic changes. We also determine that increasing training intensity during fear conditioning (FC) training restores contextual memory in Fmr1 KO mice and reduces membrane-bound Rac1 in Fmr1 KO hippocampus. Increased training intensity also results in normalized long-term potentiation in hippocampal slices taken from Fmr1 KO mice. These results point to interventional treatments providing new therapeutic options for FXS-related cognitive dysfunction.
行为干预疗法已被证明对自闭症和智力障碍(ID)的治疗有益,这使得这些干预措施激活的分子机制发生某些变化成为可能,而这些变化可能会促进学习。脆性 X 综合征(FXS)是一种神经发育障碍,其特征为自闭症特征和智力障碍,并可作为研究促进学习的机制的模型。FXS 是由脆性 X 智力低下 1 基因(Fmr1)的突变引起的,该突变阻止了 Fmr1 蛋白(FMRP)的表达,FMRP 是突触处的信使 RNA(mRNA)翻译调节剂。除了其他许多功能外,FMRP 还与调节小 Rho GTPase Rac1 的肌动蛋白细胞骨架调节复合物一起发挥作用。与人类一样,缺乏 FMRP 的 Fmr1 KO 小鼠表现出类似自闭症的行为和富含肌动蛋白的突触结构畸形,此外还存在海马体学习和突触可塑性受损的情况。这些特征先前与包括 Rac1 在内的肌动蛋白重塑蛋白的正常功能有关。Rac1 的激活和功能的重要步骤是其向膜的易位,在海马体依赖性学习过程中,它可以影响突触肌动蛋白细胞骨架重塑。在此,我们报告 Fmr1 KO 小鼠海马体中膜结合 Rac1 的水平增加,这可能会阻止适当的学习诱导的突触变化。我们还确定,在恐惧条件反射(FC)训练期间增加训练强度可以恢复 Fmr1 KO 小鼠的上下文记忆,并减少 Fmr1 KO 海马体中的膜结合 Rac1。增加训练强度还会导致取自 Fmr1 KO 小鼠的海马切片中的长时程增强正常化。这些结果表明,干预性治疗为 FXS 相关认知功能障碍提供了新的治疗选择。
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