Cortical microcircuit dysfunction as a result of MET deficiency: a link to autism

描述（由申请人提供）：自闭症谱系障碍（ASD）影响多达1/150的儿童。它是一种复杂的发育障碍，其特征在于社交缺陷、语言障碍和兴趣受限（Newschaffer等人，2007; Levitt和坎贝尔，2009）。遗传连锁技术最近揭示，患有ASD的个体在MET受体酪氨酸激酶（下文称为MET）的基因的启动子区中具有突变的可能性是三倍，这导致MET表达降低（Campbel et al.，2006; Campbel等人，2007年）。MET信号传导通路对于大脑皮层的正常发育是重要的（Powell等人，2001; Powell等人，2003; Levitt等人，2004; Gutierrez等人，2004年）。干扰这一通路会以多种方式影响皮质发育。然而，仍然未知的是，在何种程度上的皮质回路的功能组织受到MET功能障碍。ASD研究特别感兴趣的是额叶皮层的突触组织，其涉及行为和执行功能的许多高阶认知方面。有证据表明ASD中皮质区域之间的长距离连接不足（Horwitz等人，198; Courchesne和Pierce，2005; Kana等人，2007年）。从这个角度来看，ASD是一种皮质回路的紊乱。有人提出，ASD的地方连通性也过度加强（Courchesne和Pierce，2005年），但这一点尚未得到直接测量。MET敲除（MET-KO）小鼠的可用性将使我能够测量由于干扰MET信号通路而导致的突触连接的变化。我推测额叶皮层的局部突触连接由于MET-KO而过度加强。我将通过用高通量电路映射技术测量皮质纹状体神经元的电路异常来测试这一假设（Weiler等人，2008; Yu等人，2008; Wood等人，2009，安德森2010）。我将专注于皮质纹状体神经元，因为这些神经元向其他皮质区域提供长距离输入（Wilson，1987; Reiner等人，2003），并且投射是连接额叶皮层与基底神经节和丘脑的环中的关键组分，对于行为的选择和启动是重要的（阿尔宾等人，1989年）。了解MET-KO中皮质连接性的改变将是表征与ASD相关的皮质回路疾病性质的重要一步。这将为理解ASD大脑变化的机制提供基础。 公共卫生相关性：每150名儿童中就有1名被诊断患有自闭症谱系障碍（ASD），这是一种复杂的发育障碍，其特征是社会交往异常，语言缺陷和兴趣受限。有证据表明ASD患者的额叶皮层回路发生了改变，但迄今为止，尚未获得非综合征型ASD患者突触连接的详细细胞水平分辨率。我们将描述ASD皮质回路功能障碍小鼠模型的皮质回路，这将对额叶皮质突触组织差异的潜在机制产生重要的见解，并有助于理解ASD患者大脑中发生的变化。

DESCRIPTION (provided by applicant): Autism spectrum disorder (ASD) affects as many as 1 in 150 children. It is a complex developmental disorder characterized by social deficits, language impairment, and restricted interests (Newschaffer et al., 2007; Levitt and Campbell, 2009). Genetic linkage techniques recently revealed that individuals with ASD are three times more likely to have a mutation in the promoter region of the gene for MET receptor tyrosine kinase (hereafter MET), which results in reduced MET expression (Campbel et al., 2006; Campbel et al., 2007). The MET signaling pathway is important for the normal development of the cerebral cortex (Powell et al., 2001; Powell et al., 2003; Levitt et al., 2004; Gutierrez et al., 2004). Interference with this pathway affects cortical development in a number of ways. Still unknown however, is the extent to which the functional organization of cortical circuits is affected by MET dysfunction. Of particular interest to ASD research is the synaptic organization of the frontal cortex, which is involved in many higher order cognitive aspects of behavior and executive functioning. Evidence suggests long-range under-connectivity between cortical areas in ASD (Horwitz et al., 198; Courchesne and Pierce, 2005; Kana et al., 2007). From this view, ASD is a disorder of cortical circuits. It has been proposed that there is also an over-strengthening of local connectivity in ASD (Courchesne and Pierce, 2005), but this has yet to be directly measured. The availability of a MET- knockout (MET-KO) mouse will allow me to measure changes in synaptic connectivity that result from interference with the MET signaling pathway. I hypothesize that local synaptic connections in frontal cortex are over-strengthened as a result of MET- KO. I will test this hypothesis by measuring the circuit abnormalities of corticostriatal neurons with high throughput circuit mapping techniques (Weiler et al., 2008; Yu et al., 2008; Wood et al., 2009, Anderson 2010). I will focus on corticostriatal neurons because these neurons provide long-range input to other cortical areas (Wilson, 1987; Reiner et al., 2003) and the projection is a key component in loops linking the frontal cortex with the basal ganglia and the thalamus important for the selection and initiation of behavior (Albin et al., 1989). Understanding altered cortical connectivity in MET-KO will be an important step towards characterizing the nature of cortical circuit disorders associated with ASD. It will provide a basis for understanding the mechanisms underlying the changes to the brain in ASD. PUBLIC HEALTH RELEVANCE: As many 1 in 150 children are diagnosed with autism spectrum disorder (ASD), which is a complex developmental disorder characterized by abnormal social interactions, language deficits, and restricted interests. Evidence implicates alterations to the circuits of the frontal cortex in ASD, but to date, no detailed, cell-level resolution of synaptic connectivity in non-syndromic ASD has been obtained. We will characterize the cortical circuits of a mouse model of cortical circuit dysfunction in ASD, which will yield important insight into the mechanism underlying differences in the synaptic organization of the frontal cortex, and help understand the changes that occur in the brains of people with ASD.