Lamivudine modulates the expression of neurological impairment-related genes and LINE-1 retrotransposons in brain tissues of a down syndrome mouse model

Elevated activity of retrotransposons is increasingly recognized to be implicated in a wide range of neurodegenerative and neurodevelopmental diseases, including Down syndrome (DS), which is the most common chromosomal condition causing intellectual disability globally. Previous research by our group has revealed that treatment with lamivudine, a reverse transcriptase inhibitor, improved neurobehavioral phenotypes and completely rescued hippocampaldependent recognition memory in a DS mouse model, Ts65Dn. We hypothesized that retrotransposition rates would increase in the Ts65Dn mouse model, and lamivudine could block retrotransposons. We analyzed the differentially expressed long interspersed element-1 (LINE-1 or L1) mapping on MMU16 and 17, and showed for the first time that retrotransposition could be associated with Ts65Dn's pathology, as misregulation of L1 was found in brain tissues associated with trisomy. In the cerebral cortex, 6 out of 26 upregulated L1s in trisomic treated mice were located in the telomeric region of MMU16 near Ttc3, Kcnj6, and Dscam genes. In the hippocampus, one upregulated L1 element in trisomic treated mice was located near the Fgd4 gene on MMU16. Moreover, two downregulated L1s rescued after treatment with lamivudine were located in the intronic region of Nrxn1 (MMU17) and Snhg14 (MMU7), implicated in a variety of neurodegenerative disorders. To gain further insight into the mechanism of this improvement, we here analyzed the gene expression profile in the hippocampus and cerebral cortex of trisomic mice treated and no-treated with lamivudine compared to their wild-type littermates. We found that treatment with lamivudine rescued the expression of 24% of trisomic genes in the cortex (located on mouse chromosome (MMU) 16 and 17) and 15% in the hippocampus (located in the human chromosome 21 orthologous regions), with important DS candidate genes such as App and Ets2, rescued in both regions. Overall design: To gain insight into the mechanism by which lamivudine improved the neurobehavioral profile in trisomic mice we analyzed the gene expression profile in the hippocampus and cerebral cortex of trisomic treated and no-treated mice compared to their wild type littermates. We performed bulk RNA-seq profiling

逆转录转座子（retrotransposons）的异常激活日益被证实与多种神经退行性及神经发育性疾病密切相关，其中包括唐氏综合征（Down syndrome, DS）——这是全球范围内最常见的引发智力障碍的染色体疾病。本团队此前的研究表明，采用逆转录酶抑制剂拉米夫定（lamivudine）处理唐氏综合征Ts65Dn小鼠模型，可改善其神经行为表型，并完全挽救其海马依赖的识别记忆功能。我们据此提出假说：Ts65Dn小鼠模型中的逆转录转座速率会升高，而拉米夫定可阻断逆转录转座子的活性。我们对定位在小鼠染色体（MMU）16和17上的差异表达长散在核元件-1（long interspersed element-1, LINE-1或L1）进行了分析，首次证实逆转录转座可能与Ts65Dn的病理机制相关——三体脑组织中存在L1的调控异常。在大脑皮层中，三体模型经拉米夫定处理后上调的26个L1元件中有6个定位于MMU16的端粒区域，紧邻Ttc3、Kcnj6及Dscam基因；在海马体中，三体模型经处理后上调的1个L1元件定位于MMU16上的Fgd4基因附近。此外，经拉米夫定处理后恢复正常表达的2个下调L1元件分别位于Nrxn1（MMU17）和Snhg14（MMU7）的内含子区域，这两个基因均与多种神经退行性疾病相关。为进一步阐明该改善效应的分子机制，我们对比分析了经拉米夫定处理、未处理的三体小鼠及其野生型同窝仔鼠的海马体与大脑皮层的基因表达谱。结果发现，拉米夫定处理可挽救皮层中24%的三体基因（定位于小鼠染色体16和17）的表达，以及海马体中15%的三体基因（定位于人类21号染色体同源区域）的表达；其中App和Ets2等关键唐氏综合征候选基因在两个脑区中均实现了表达挽救。总体实验设计：为探究拉米夫定改善三体小鼠神经行为表型的分子机制，我们对经拉米夫定处理、未处理的三体小鼠及其野生型同窝仔鼠的海马体与大脑皮层开展了基因表达谱分析，具体采用批量RNA测序（bulk RNA-seq）技术完成。