Estradiol Alters Hippocampal Gene Expression during the Estrous Cycle

Estrogen (E2) modulates a wide range of neural functions such as spine formation, synaptic plasticity, and neurotransmission in the hippocampus. Dendritic spines and synapse numbers in hippocampal neurons of female rats cyclically fluctuate across the estrous cycle, but the key genes responsible for these fluctuations are still unknown. In order to address this question, we explore the hippocampal transcriptome via RNA-sequencing (RNA-seq) at the proestrus (<b>PE</b>) and estrus (<b>ES</b>) stages in female rats. At standard fold-change selection criteria, 37 differentially expressed genes (<b>DEGs</b>) were found in PE vs. ES groups (FDR adjusted <i>p</i>-value (q)&lt;0.05). The transcriptional changes identified by RNA-seq were confirmed by quantitative real-time PCR. To gain insight into the function of the DEGs, the E2-regulated genes were annotated by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes database (KEGG). Based on GO and KEGG pathways, the identified DEGs of PE vs. ES stages are involved in extracellular matrix formation, regulation of actin cytoskeleton, oxidative stress, neuroprotection, immune system, oligodendrocyte maturation and myelination, signal transduction pathways, growth factor signaling, retinoid signaling, aging, cellular process, metabolism and transport. The profiles of the gene expression in the hippocampus identified at the PE vs. ES stages were compared with the gene expression profiles in ovariectomized (OVX) rats receiving E2 replacement via RNA-seq and qPCR. The profiles of gene expression between the OVX+E2 and the estrous cycle were different and the possible causes were discussed.

雌激素（Estrogen, E2）可调控海马体的诸多神经功能，包括棘突形成、突触可塑性以及神经传递。雌性大鼠海马神经元的树突棘与突触数量会随发情周期呈周期性波动，但介导此类波动的关键基因仍未明确。
为解答这一科学问题，本研究针对雌性大鼠的发情前期（proestrus, PE）与发情期（estrus, ES）两个阶段，通过RNA测序（RNA-seq）技术分析其海马体转录组。按照标准倍数变化筛选标准，在PE组与ES组的对比中共鉴定出37个差异表达基因（differentially expressed genes, DEGs），其经错误发现率（FDR）校正后的p值（q值）均小于0.05。RNA-seq检测到的转录组变化，经实时定量聚合酶链式反应（qPCR）验证属实。
为解析DEGs的功能，本研究通过基因本体论（Gene Ontology, GO）与京都基因与基因组百科全书（Kyoto Encyclopedia of Genes and Genomes, KEGG）数据库对E2调控基因进行注释。基于GO与KEGG通路富集分析结果，PE与ES阶段的差异表达基因主要参与细胞外基质形成、肌动蛋白细胞骨架调控、氧化应激、神经保护、免疫系统功能、少突胶质细胞成熟与髓鞘形成、信号转导通路、生长因子信号通路、类视黄醇信号通路、衰老进程、细胞生理过程、代谢与物质转运等生物学过程。
本研究还将PE与ES阶段鉴定得到的海马基因表达谱，与接受雌激素替代治疗的去卵巢（ovariectomized, OVX）大鼠的基因表达谱通过RNA-seq与qPCR进行了对比分析。结果显示，OVX+E2组与发情周期组的基因表达谱存在显著差异，本研究对其潜在成因展开了讨论。