Mesial temporal lobe epilepsy (MTLE) is a particularly devastating form of human epilepsy with significant incidence of medical intractability. MicroRNAs (miRs) are small, noncoding RNAs that regulate the posttranscriptional expression of protein-coding mRNAs, which may have key roles in the pathogenesis of MTLE development. To study the dynamic expression patterns of brain-specific miR-124 and miR-134 and inflammation-related miR-132 and miR-21, we performed qPCR on the hippocampi of immature rats at 25 days of age. Expressions were monitored in the three stages of MTEL and in the control hippocampal tissues corresponding to the same timeframes. A similar expression method was applied to hippocampi obtained from children with MTLE and normal controls. The expression patterns of miR-124 and miR-134 nearly showed the same dynamics in the three stages of MTLE development. On the other hand, miR-132 and miR-21 showed significant upregulation in acute and chronic stages, while in the latent stage, miR-132 was upregulated and miR-21 was downregulated. The four miRs were upregulated in hippocampal tissues obtained from children with MTLE. The significant upregulation of miR-124 and miR-134 in the seizure-related stages and children suggested that both can be potential targets for anticonvulsant drugs in the epileptic developing brains, while the different expression patterns of miR-132 and miR-21 may suggest different functions in MTLE pathogenesis.

Summary Purpose:  Increasing evidence indicates that neuroinflammation plays a critical role in the pathogenesis of mesial temporal lobe epilepsy (MTLE). The aim of this study was to investigate the dynamic expression of interleukin (IL)–1β as a proinflammatory cytokine and microRNA (miR)‐146a as a posttranscriptional inflammation‐associated microRNA (miRNA) in the hippocampi of an immature rat model and children with MTLE. Methods:  To study the expression of IL‐1β and miR‐146a, we performed a reverse transcription polymerase chain reaction, Western blot, and real‐time quantitative PCR on the hippocampi of immature rats at 11 days of age. Expression was monitored in the acute, latent, and chronic stages of disease (2 h and 3 and 8 weeks after induction of lithium‐pilocarpine status epilepticus, respectively), and in control hippocampal tissues corresponding to the same timeframes. Similar expression methods were applied to hippocampi obtained from children with MTLE and normal controls. Key Findings:  The expression of IL‐1β and miR‐146a in both children and immature rats with MTLE differs according to the stage of MTLE development. Both IL‐1β and miR‐146a are significantly up‐regulated, but in opposite ways: IL‐1β expression is highest in the acute stage, when expression of miR‐146a is at its lowest level; miR‐146a expression is highest in the latent stage, when IL‐1β expression is at its lowest level. Both IL‐1β and miR‐146a are up‐regulated in the chronic stage, but not as much as in the other stages. Significance:  Our study is the first to focus on the expression of miR‐146a in the immature rat model of lithium‐pilocarpine MTLE and in children with MTLE. We have detected that the expression of proinflammatory cytokine IL‐1β and posttranscriptional inflammation‐associated miR‐146a is variable depending on the disease stage. Furthermore, both IL‐1β and miR‐146a are up‐regulated in immature rats and children with MTLE. Our findings elucidate the role of inflammation in the pathogenesis of MTLE in the immature rat model and children. Therefore, modulation of the IL‐1β–miR‐146a axis may be a novel therapeutic target in the treatment of MTLE.

Recently, the role of inflammation has attracted great attention in the pathogenesis of mesial temporal lobe epilepsy (MTLE), and microRNAs start to emerge as promising new players in MTLE pathogenesis. In this study, we investigated the dynamic expression patterns of tumor necrosis factor alpha (TNF-α) and microRNA-155 (miR-155) in the hippocampi of an immature rat model of status epilepticus (SE) and children with MTLE. The expressions of TNF-α and miR-155 were significantly upregulated in the seizure-related acute and chronic stages of MTLE in the immature rat model and also in children with MTLE. Modulation of TNF-α expression, either by stimulation using myeloid-related protein (MRP8) or lipopolysaccharide or inhibition using lenalidomide on astrocytes, leads to similar dynamic changes in miR-155 expression. Our study is the first to focus on the dynamic expression pattern of miR-155 in the immature rat of SE lithium-pilocarpine model and children with MTLE and to detect their relationship at the astrocyte level. TNF-α and miR-155, having similar expression patterns in the three stages of MTLE development, and their relationship at the astrocyte level may suggest a direct interactive relationship during MTLE development. Therefore, modulation of the TNF-α/miR-155 axis may be a novel therapeutic target for the treatment of MTLE.

Astrocyte activation, associated with the release of pro-inflammatory cytokines interleukin 1-β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α), is a hallmark of multiple brain diseases, including mesial temporal lobe epilepsy. In recent years, several microRNAs have emerged as important controllers of Toll-like receptor (TLR) signaling. In this study, we investigated the effect of miR-132, miR-146a, and miR-155 on myeloid-related protein-8 (MRP8) induced astrocyte-related inflammation. Using quantitative polymerase chain reaction (qPCR) and western blot, we found clear upregulation of TLR4 and downstream inflammatory cytokines, along with dysregulation of miR-132, miR-146a, and miR-155 in in vitro astrocytes after exposing them to different concentrations of MRP8. In addition, we focused on the effect of miR-132 on astrocyte-related inflammation induced by MRP8 via lentiviral infection then evaluated the expression of its possible target genes: acetylcholinesterase (AChE) and interleukin-1 receptor-associated kinase (IRAK4). Our results show that miR-132 is a negative feedback regulator of IL-1β and IL-6, but not TNF-α, by targeting IRAK4. Together, our findings demonstrate the novel role of TLR4-related microRNAs, especially miR-132, in the regulation of MRP8-induced astrocyte activation and highlight the importance of miR-132 in the modulation of innate immune response induced by endogenous ligands in neurological diseases.

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