Mesial temporal lobe epilepsy (mTLE) is a debilitating disease characterized by recurrent seizures originating from temporal lobe structures such as the hippocampus. The pathogenic mechanisms underlying mTLE are incompletely understood but include changes in the expression of non-coding RNAs in affected brain regions. Previous work indicates that some of these changes may be selective to specific sub-cellular compartments, but the full extent of these changes and how these sub-cellular compartments themselves are affected remains largely unknown. Here, we performed small RNA sequencing (RNA-seq) of sub-cellular fractions of hippocampal tissue from mTLE patients and controls to determine nuclear and cytoplasmic expression levels of microRNAs (miRNAs). This showed differential expression of miRNAs and isomiRs, several of which displayed enriched nuclear expression in mTLE. Subsequent analysis of miR-92b, the most strongly deregulated miRNA in the nucleus, showed accumulation of this miRNA in the nucleolus in mTLE and association with snoRNAs. This prompted us to further study the nucleolus in human mTLE which uncovered several defects, such as altered nucleolar size or shape, mis-localization of nucleolar proteins, and deregulation of snoRNAs, indicative of nucleolar stress. In a rat model of epilepsy, nucleolar phenotypes were detected in the latency period before the onset of spontaneous seizures, suggesting that nucleolar changes may contribute to the development of seizures and mTLE. Overall, these data for the first time implicate nucleolar defects in the pathogenesis of mTLE and provide a valuable framework for further defining the functional consequences of altered sub-cellular RNA profiles in this disease.

内侧颞叶癫痫 （mTLE） 是一种使人衰弱的疾病，其特征是源自颞叶结构（如海马体）的反复发作。mTLE 的致病机制尚不完全清楚，但包括受影响大脑区域中非编码 RNA 表达的变化。以前的研究表明，其中一些变化可能对特定的亚细胞区室具有选择性，但这些变化的全部程度以及这些亚细胞区室本身如何受到影响在很大程度上仍然未知。在这里，我们对 mTLE 患者和对照的海马组织亚细胞组分进行了小 RNA 测序 （RNA-seq），以确定 microRNA （miRNA） 的细胞核和细胞质表达水平。这显示了 miRNA 和 isomiR 的差异表达，其中一些在 mTLE 中显示出丰富的核表达。随后对细胞核中最强失调的 miR-92b 的分析显示，该 miRNA 在 mTLE 的核仁中积累并与 snoRNA 相关。这促使我们进一步研究人类 mTLE 中的核仁，发现了几个缺陷，例如核仁大小或形状的改变、核仁蛋白的错误定位以及 snoRNA 的失调，这表明核仁应激。在大鼠癫痫模型中，在自发性癫痫发作前的潜伏期检测到核仁表型，表明核仁变化可能有助于癫痫发作和 mTLE 的发展。总体而言，这些数据首次表明核仁缺陷与 mTLE 的发病机制有关，并为进一步确定该疾病中亚细胞 RNA 谱改变的功能后果提供了一个有价值的框架。