Divergent dysregulation of gene expression in Fmr1 and Tsc2 knockout mouse models of autism spectrum disorders

Fragile X syndrome and tuberous sclerosis are genetic syndromes that both have a high rate of co-morbidity with autism spectrum disorders. Several lines of evidences suggest that these two monogenic disorders may converge at a molecular level through the dysfunction of activity-dependent synaptic plasticity. We utilized mouse models of these monogenic disorders to identify genome-wide transcriptional changes in cerebellum and blood and characterize the (dis-)similarity of their molecular signatures. Differentially expressed genes and enriched pathways were distinct for the two mouse models examined, with the exception of immune system related pathways. In the cerebellum of the Fmr1 knockout (Fmr1-KO) model, the neuroactive ligand receptor interaction pathway and gene sets associated with synaptic plasticity such as long term potentiation, gap junction, and axon guidance were the most significantly perturbed pathways. The phosphatidylinositol signaling pathway was significantly dysregulated in both blood and brain of Fmr1-KO mice. In both the blood and brain of the Tsc2 heterozygous mouse model, immune system related pathways, genes encoding ribosomal proteins, and glycolipid metabolism pathways were significantly perturbed. Our data suggest that distinct molecular pathways may be involved in autism spectrum disorders with known but different genetic causes, and that blood gene expression profiles of Fmr1-knockout and Tsc2+/- mice mirror some, but not all, of the perturbed molecular pathways in the brain. For the Fmr1-KO model, 10 mice, consisting of 5 KO and 5 WT mice, were profiled. Thus, 10 pairs of blood and cerebella samples were profiled. Likewise, for the Tsc+/- model, 3 transgenic and 3 WT mice were sacrificed and paired blood and cerebella samples were prepared for gene expression profiling. All samples were profiled using the Affymetrix Mouse Gene ST 1.0 ST arrays. Three factors—tissue (i.e. blood vs. cerebellum), treatment (i.e. knockout vs. wildtype), and genetic background (Fmr1-KO vs. Tsc2+/-)—were analyzed with analysis of variance (ANOVA). Subsequently, we compared blood and brain gene expression changes in Fmr1 and Tsc2 knockout mice models using WT littermates as controls using t-tests with unequal variances. The false discovery rate (FDR) was calculated using Storey and Tibshirani’s method.脆性X综合征（Fragile X syndrome）与结节性硬化症（tuberous sclerosis）均为与自闭症谱系障碍（autism spectrum disorders）共病率较高的遗传综合征。多项证据显示，这两种单基因遗传病（monogenic disorders）可能通过活动依赖性突触可塑性（activity-dependent synaptic plasticity）功能异常在分子层面实现通路汇聚。本研究使用上述单基因遗传病的小鼠模型，鉴定小脑（cerebellum）与血液中的全基因组转录组变化，并解析二者分子特征的异同。在所分析的两种小鼠模型中，差异表达基因（differentially expressed genes）与富集通路（enriched pathways）均存在显著差异，仅免疫系统相关通路除外。在Fmr1基因敲除（Fmr1 knockout，缩写Fmr1-KO）模型的小脑中，神经活性配体-受体相互作用通路（neuroactive ligand receptor interaction pathway），以及与突触可塑性相关的基因集（如长时程增强（long term potentiation）、缝隙连接（gap junction）与轴突导向（axon guidance））为受扰动最显著的通路。磷脂酰肌醇信号通路（phosphatidylinositol signaling pathway）在Fmr1-KO小鼠的血液与脑组织中均出现显著失调。在Tsc2杂合子（Tsc2 heterozygous）小鼠模型的血液与脑组织中，免疫系统相关通路、核糖体蛋白编码基因及糖脂代谢通路（glycolipid metabolism pathways）均出现显著扰动。本研究数据表明，针对已知但遗传病因不同的自闭症谱系障碍，可能涉及不同的分子通路；同时Fmr1基因敲除与Tsc2+/-小鼠的血液基因表达谱（gene expression profiles）可部分反映脑组织中受扰动的分子通路，但并非全部。针对Fmr1-KO模型，本研究共纳入10只小鼠，其中5只为基因敲除型、5只为野生型（wildtype，缩写WT），共计完成10对血液与小脑样本的表达谱分析。同理，针对Tsc2+/-模型，本研究处死3只转基因杂合子与3只野生型小鼠，制备成对的血液与小脑样本以开展基因表达谱分析。所有样本均使用Affymetrix Mouse Gene ST 1.0 ST基因芯片完成表达谱检测。本研究采用方差分析（analysis of variance，缩写ANOVA）分析三个因素：组织类型（即血液与小脑）、处理方式（即基因敲除与野生型）及遗传背景（即Fmr1-KO与Tsc2+/-）。随后，本研究以野生型同窝小鼠作为对照，采用方差不齐t检验比较Fmr1与Tsc2基因敲除小鼠模型的血液及脑组织基因表达变化。本研究采用Storey与Tibshirani方法计算错误发现率（false discovery rate，缩写FDR）。