Could Extracellular microRNAs act as a novel biomarkers of temporal lobe epilepsy?
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Epilepsy diagnosis is always a challenging process. A detailed clinical history is the main tool used for diagnosis and classification; however, it is often incomplete and misleading. Electroencephalography and neuroimaging have their role in assisting the diagnosis but, still, they cannot confirm or rule out epilepsy. This is reflected clinically as a high figure of epilepsy misdiagnosis, where about one third of patients are being misdiagnosed. The identification of a reliable molecular biomarker for epilepsy will not only allow for a definitive diagnosis of seizures and epilepsy but as well help in the disease classification, individualize the treatment options and predict prognosis and comorbidities.
MicroRNAs have recently emerged as a promising class of biomarkers. These are small, endogenous RNA molecules that regulate gene expression by interfering with the translation of their target mRNA. The identification of microRNAs in various body fluids, their stability as well as their tissue specificity opens up a new field for biomarker studies in epilepsy. The main aim of the present study was to investigate the expression and dysregulation of microRNAs in biofluid samples of temporal lobe epilepsy patients and evaluate their possible role as diagnostic biomarkers. To achieve this aim, the study began by investigating the stability and inter-personal variabilities of extracellular microRNAs in healthy controls. The first goal was to identify any difference in extracellular microRNA profiles between morning-afternoon and male-female samples and to confirm the stability of these molecules in plasma samples overtime. Standardization of sample collection and processing techniques, RNA extraction and profiling methods and defining a protocol for optimal data analysis of genome-wide microRNA profiles were also among the important goals. The obtained results showed that microRNA levels were very consistent between males and females and at different time points confirming their suitability for biomarker studies.
Next, a multiphase case-control study was performed to investigate the ability of plasma microRNAs to differentiate temporal lobe epilepsy patients from healthy controls as well as to track the occurrence of seizures. Plasma microRNA profile was explored using dual platform design (RNA-sequencing and QuantStudioTM 12K Flex OpenArray system) which increased the confidence in the identified signature. Furthermore, the inclusion of pre- and post-seizure samples in the study allowed the identification of microRNAs with biomarker potential for both temporal lobe epilepsy and seizure. The dysregulation of several microRNAs was identified in the discovery phase and confirmed in the validation phase of the study. The performance of the dysregulated microRNAs as biomarkers was also investigated with miR-654-3p was best in differentiating temporal lobe epilepsy from controls. Moreover, reduced plasma levels of miR-328-3p and miR-27a-3p in post-seizure samples indicated a high performance of both microRNAs in identifying patients presented after a recent seizure episode.
Finally, microRNA expression and dysregulation in cerebrospinal fluid of temporal lobe epilepsy and status epilepticus patients was explored. Cerebrospinal fluid offers a unique source of microRNA biomarkers with the advantage of being in close contact with the sites of pathology. Differential expression of 20 microRNAs was detected between patient groups and controls. A validation phase included an expanded cohort and samples from patients with other neurological diseases. The study identified lower levels of miR-19b-3p in temporal lobe epilepsy patients compared to controls, status epilepticus and other neurological diseases. Levels of miR-451a were higher in status epilepticus compared to other groups whereas miR-21-5p was different in status epilepticus compared to temporal lobe epilepsy but not to other neurological diseases.
In conclusion, the present study indicates the presence of a set of dysregulated microRNAs in plasma and cerebrospinal fluid of temporal lobe epilepsy patients that can be utilized clinically as diagnostic and prognostic epilepsy biomarkers.