Lefterov Iliya, Schug Jonathan, Mounier Anais, Nam Kyong Nyon, Fitz Nicholas F, Koldamova Radosveta
Department of Environmental & Occupational Health, University of Pittsburgh, Pittsburgh, PA 15219, USA.
Institute for Diabetes, Obesity and Metabolism, University of Pennsylvania, Philadelphia, PA 19104, USA; Functional Genomics Core, Department of Genetics, University of Pennsylvania, Philadelphia, PA 19104, USA.
Neurobiol Dis. 2015 Oct;82:132-140. doi: 10.1016/j.nbd.2015.05.019. Epub 2015 Jun 10.
We have recently demonstrated that short term bexarotene treatment of APP/PS1 mice significantly improves their cognitive performance. While there were no changes in plaque load, or insoluble Aβ levels in brain, biochemical analysis strongly suggested improved clearance of soluble Aβ, including Aβ oligomers. To get further insight into molecular mechanisms underlying this therapeutic effect, we explored genome-wide differential gene expression in brain of bexarotene and control treated APP/PS1 mice. We performed high throughput massively parallel sequencing on mRNA libraries generated from cortices of bexarotene or vehicle treated APP/PS1 mice and compared the expression profiles for differential gene expression. Gene Ontology (GO) Biological Process categories with the highest fold enrichment and lowest False Discovery Rate (FDR) are clustered in GO terms immune response, inflammatory response, oxidation-reduction and immunoglobulin mediated immune response. Chromatin immunoprecipitation (ChIP) followed by ChIP-QPCR, and RT-QPCR expression assays were used to validate select genes, including Trem2, Tyrobp, Apoe and Ttr, differentially expressed in response to Retinoid X Receptor (RXR) activation. We found that bexarotene significantly increased the phagocytosis of soluble and insoluble Aβ in BV2 cells. The results of our study demonstrate that in AD model mice expressing human APP, gene networks up-regulated in response to RXR activation by the specific, small molecule, ligand bexarotene may influence diverse regulatory pathways that are considered critical for cognitive performance, inflammatory response and Aβ clearance, and may provide an explanation of the bexarotene therapeutic effect at the molecular level. This study also confirms that unbiased massive parallel sequencing approaches are useful and highly informative for revealing brain molecular and cellular mechanisms underlying responses to activated nuclear hormone receptors in AD animal models.
我们最近证明，短期使用贝沙罗汀治疗APP/PS1小鼠可显著改善其认知能力。虽然脑内斑块负荷或不溶性Aβ水平没有变化，但生化分析强烈表明可溶性Aβ（包括Aβ寡聚体）的清除得到改善。为了进一步深入了解这种治疗效果的分子机制，我们探究了贝沙罗汀和对照处理的APP/PS1小鼠脑内全基因组差异基因表达。我们对从贝沙罗汀或载体处理的APP/PS1小鼠皮质产生的mRNA文库进行了高通量大规模平行测序，并比较了差异基因表达的表达谱。基因本体（GO）生物过程类别中富集倍数最高且错误发现率（FDR）最低的聚集在免疫应答、炎症应答、氧化还原和免疫球蛋白介导的免疫应答等GO术语中。采用染色质免疫沉淀（ChIP）后进行ChIP-QPCR以及RT-QPCR表达分析来验证选定的基因，包括Trem2、Tyrobp、Apoe和Ttr，这些基因在视黄酸X受体（RXR）激活后差异表达。我们发现贝沙罗汀显著增加了BV2细胞中可溶性和不溶性Aβ的吞噬作用。我们的研究结果表明，在表达人APP的AD模型小鼠中，由特定小分子配体贝沙罗汀激活RXR后上调的基因网络可能影响多种对认知能力、炎症应答和Aβ清除至关重要的调节途径，并可能在分子水平上解释贝沙罗汀的治疗效果。这项研究还证实，无偏倚的大规模平行测序方法对于揭示AD动物模型中对活化核激素受体反应的脑分子和细胞机制是有用且信息丰富的。
