Striatal transcriptome of a mouse model of ADHD reveals a pattern of synaptic remodeling

Despite the prevalence and high heritability of Attention-Deficit/Hyperactivity Disorder (ADHD), genetic etiology remains elusive. Clinical evidence points in part to reduced function of the striatum, but which specific genes are differentially expressed and how they sculpt striatal physiology to predispose ADHD are not well understood. As an exploratory tool, a polygenic mouse model of ADHD was recently developed through selective breeding for high home cage activity. Relative to the Control line, the High-Active line displays hyperactivity and motor impulsivity which are ameliorated with amphetamine. This study compared gene expression in the striatum between Control and High-Active mice to develop a coherent hypothesis for how genes might affect striatal physiology and predispose ADHD-like symptoms. To this end, striatal transcriptomes of High-Active and Control mice were analyzed after mice were treated with saline or amphetamines. The pseudogene Gm6180 for n-cofilin (Cfl1) displayed 20-fold higher expression in High-Active mice corresponding with reduced Cfl1 expression suggesting synaptic actin dysregulation. Latrophilin 3 (Lphn3), which is associated with ADHD in human populations and is involved in synapse structure, and its ligand fibronectin leucine rich transmembrane protein 3 (Flrt3), were downregulated in High-Active mice. Multiple genes were altered in High-Active mice in a manner predicted to downregulate the canonical Wnt pathway. A smaller and different set of genes including glyoxalase (Glo1) were differentially regulated in High-Active as compared to Control in response to amphetamine. Together, results suggest genes involved in excitatory synapse regulation and maintenance are downregulated in ADHD-like mice. Consistent with the molecular prediction, stereological analysis of the striatum from a separate set of mice processed for imunohistochemical detection of synaptophysin revealed approximately a 46% reduction in synaptophysin immunoreactivity in High-Active relative to Control. Results provide a new set of molecular targets related to synapse maintenance for the next generation of ADHD medicines.尽管注意缺陷多动障碍（Attention-Deficit/Hyperactivity Disorder, ADHD）患病率高且遗传力显著，但迄今其遗传病因仍未明确。临床研究证据部分提示纹状体（striatum）功能减退，但具体哪些基因存在差异表达，以及这些基因如何通过调控纹状体生理机能增加ADHD易感性，目前仍缺乏清晰认知。作为探索性研究工具，近期一项研究通过对高笼活动小鼠进行选择性繁育，成功构建了ADHD多基因小鼠模型（polygenic mouse model）。与对照组（Control line）相比，高活动组（High-Active line）小鼠表现出多动与运动冲动症状，且该类症状可经苯丙胺（amphetamine）治疗得到缓解。本研究对比了对照组与高活动组小鼠纹状体的基因表达谱，旨在构建连贯的科学假说，阐释基因如何影响纹状体生理机能并诱发ADHD样症状。为此，研究人员分别对经生理盐水或苯丙胺处理的高活动组与对照组小鼠的纹状体转录组（transcriptome）进行了分析。结果显示，n-丝切蛋白（n-cofilin, Cfl1）的假基因（pseudogene）Gm6180在高活动组小鼠中的表达量上调20倍，同时伴随Cfl1本身的表达降低，提示突触肌动蛋白调控异常。Latrophilin 3（LPHN3）在人群中与ADHD发病相关，且参与突触结构构建，其配体纤连蛋白亮氨酸富集跨膜蛋白3（fibronectin leucine rich transmembrane protein 3, Flrt3）在高活动组小鼠中均出现表达下调。高活动组小鼠体内存在多个基因表达异常，其变化模式预示经典Wnt通路（canonical Wnt pathway）被抑制。与对照组相比，高活动组小鼠在接受苯丙胺处理后，另有一组规模更小、构成迥异的基因（包括乙二醛酶glyoxalase, Glo1）出现差异表达。综合所有实验结果，提示与兴奋性突触调节及维持相关的基因在ADHD样症状小鼠中呈现表达下调趋势。与分子层面的预测结果一致，对另一组通过免疫组织化学（immunohistochemical）方法检测突触素（synaptophysin）的小鼠纹状体进行立体学分析（stereological analysis）显示，高活动组小鼠的突触素免疫反应性较对照组降低约46%。本研究结果为下一代ADHD治疗药物开发提供了一系列与突触维持相关的全新分子靶点。