Cortactin and Spine Dysfunction in Fragile X

描述（由申请人提供）：自闭症是一种毁灭性的疾病，对患者，他们的家庭和国家经济造成重大损失。没有治疗方法 认知损伤（例如，学习和记忆缺陷），影响超过75%的自闭症患者。在许多自闭症相关疾病和自闭症合并症的模型中，如脆性X、Rett和Angelman Syndrome，树突棘形态存在显著异常，这与长时程增强（LTP）稳定性受损有关，LTP是记忆编码的突触机制。总之，这些发现表明，脊柱肌动蛋白细胞骨架的缺陷可能是不同起源的自闭症相关疾病的认知缺陷的基础。脊柱异常和LTP损伤在脆性X综合征（FXS）的Fmr 1敲除（KO）小鼠模型中得到了最好的表征，FXS是一种与自闭症具有高（~30%）共病性的疾病。具体而言，这些突变体表现出缺陷的信号转导通过Rac GT3，稳定的活性驱动的变化，在脊柱丝状（F）肌动蛋白，巩固LTP。申请人的研究已经证明，在LTP诱导后，通过肌动球蛋白和微管系统稳定肌动蛋白网络分支点并保护F-肌动蛋白免于降解的棘蛋白corneumn的运动在Fmr 1-KO棘上受损。这表明科斯中的F-肌动蛋白稳定性缺陷可能反映了向皮质激素的信号传导的干扰。拟议的研究将建立在这些发现的基础上，以测试以下特定假设：（a）调节蛋白质亚细胞运动的异常coronin丝氨酸磷酸化和乙酰化，两者都起源于单个分子损伤，并导致科斯中LTP诱导后运动受损的表型;以及（B）学习（体内）激活WT而非KO小鼠中的这些突触过程。有三个具体目标。目标1将测试在科斯中突触Ras或PP 2A的基础水平或活化是否受损（这两种靶点均影响皮质素磷酸化和乙酰化途径）。目的2将测试通过MAPK和/或HDAC 6的信号传导（其有助于皮质素丝氨酸磷酸化和乙酰化）是否是活性诱导的皮质素易位所必需的。海马区依赖性空间学习激活WT中皮质素的突触信号传导，并且如果这种信号传导在体内Fmr 1-科斯中减弱或缺失。通过询问与F-肌动蛋白稳定性受损相关的突触机制，并确定这些异常是否也存在于行为动物中，拟议的研究将有助于我们理解正常和FXS模型小鼠的突触可塑性，并为FXS和其他自闭症患者的记忆功能正常化提供治疗靶点。最后，Aim 3将测试是否视丘依赖性空间学习激活WT中皮质素的突触信号，以及这种信号在体内Fmr 1-科斯中是否减弱或缺失。通过询问与F-肌动蛋白稳定性受损相关的突触机制，并确定这些异常是否也存在于行为动物中，拟议的研究将有助于我们理解正常和FXS模型小鼠的突触可塑性，并为FXS和其他自闭症患者的记忆功能正常化提供治疗靶点。

DESCRIPTION (provided by applicant): Autism is a devastating condition which takes a significant toll on patients, their families, and the national economy. There are no treatments for cognitive impairments (e.g., learning and memory deficits) that affect over 75% of autistic patients. In models of many autism-associated disorders and conditions with comorbidity for autism, such Fragile X, Rett, and Angelman Syndromes, there are significant abnormalities in dendritic spine morphology, which are associated with impairments in the stabilization of long-term potentiation (LTP), a synaptic mechanism of memory encoding. Together, these findings suggest that defects in the spine actin cytoskeleton may underlie cognitive deficits in autism-associated conditions of different origin. Spine abnormalities and LTP impairments are best characterized in the Fmr1-knockout (KO) mouse model of fragile X syndrome (FXS), a condition with high (~30%) comorbidity for autism. Specifically, these mutants exhibit defects in signaling through Rac GTPase, stabilization of activity-driven changes in spine filamentous (F) actin, and consolidation of LTP. Studies by the applicant have demonstrated that movement of cortactin, a spine protein which stabilizes actin network branch points and protects F-actin from degradation, via both actomyosin and microtubule systems, is impaired at Fmr1-KO spines following LTP-induction. This suggests that the F- actin stabilization deficits in KOs may reflect disturbances in signaling to cortactin. The proposed research will build on these findings to test the specific hypotheses that (a) abnormal cortactin serine phosphorylation and acetylation, which regulate the protein's subcellular movement, both originate from a single molecular impairment and contribute to the phenotype of impaired movement following LTP induction in KOs and that (b) learning (in vivo) activates these synaptic processes in WT but not KO mice. There are 3 specific aims. Aim 1 will test if basal levels or activation of synaptic Ras or PP2A are impaired in KOs (both of these targets influence the cortactin phosphorylation and acetylation paths). Aim 2 will test if signaling through MAPK and/or HDAC6, which contribute to cortactin serine phosphorylation and acetylation, are necessary for activity- induced cortactin translocation. hippocampus-dependent spatial learning activates synaptic signaling to cortactin in the WTs and if this signaling is attenuated or absent in Fmr1-KOs in vivo. Through interrogating synaptic mechanisms associated with impairments in F-actin stabilization and determining if these abnormalities are also present in the behaving animal, the proposed studies will contribute to our understanding of synaptic plasticity in both normal and FXS model mice and offer therapeutic targets for normalization of memory function in FXS and other autistic conditions. Finally, Aim 3 will test if hippocampus-dependent spatial learning activatessynaptic signaling to cortactin in the WTs and if this signaling is attenuated or absent in Fmr1-KOs in vivo. Through interrogating synaptic mechanisms associated with impairments in F-actin stabilization and determining if these abnormalities are also present in the behaving animal, the proposed studies will contribute to our understanding of synaptic plasticity in both normal and FXS model mice and offer therapeutic targets for normalization of memory function in FXS and other autistic conditions.