Assessment 13

Introduction

Several reviews present data to support the hypothesis that noncoding RNAs have the potential to serve as a diagnostic marker for epilepsy. Additionally, because noncoding RNAs play an integral function in the disease process, they may also serve as a therapeutic target to cure epilepsy.  In these two respects, noncoding RNAs are worth discussing.

In the US, there are approximately 3 million Americans living with epilepsy and each year approximately 150,000 more are diagnosed with this disease (https://www.epilepsyallianceamerica.org).  Of these, roughly 30-50%, depending on the type of epilepsy, are not helped with medications and many on medications are dissatisfied due to drug-related side effects.  Therefore, it is postulated that this embarrassing gap in effective therapy is largely due to a lack of noninvasive biomarkers coupled with a modest understanding of the molecular instigators of epilepsy.  Here is where research may help.

Noncoding RNAs

High school biology taught that one gene produces one protein and that genes via this principle dictate our heredity e.g. who we are.  Furthermore, genes (actually DNA molecules) transcribe their information to another smaller molecule, RNA, which then translates DNA’s instructions precisely into a specific protein.  Scientists now know that this pathway is tightly regulated by many factors, one of which is noncoding RNA, the subject of this blog. 

Thus noncoding RNA is a RNA molecule but as its name implies, it does not code for a protein.  Instead, noncoding RNAs control which proteins are made and how much is made. Interestingly, certain classes of noncoding RNAs regulate other noncoding RNAs.  The bottom line is that noncoding RNAs are essential for the normal health of all cells.  However, when they exist in excess or in lesser amounts compared to normal, gene regulation falls apart, essential proteins are not made and pathology ensues.

Role in epilepsy

The role of noncoding RNAs in epilepsy has been extensively studied in animal models of epilepsy and largely confirmed with tissues surgically removed in patients with intractable, drug-resistant epilepsy. In animal models and human tissues, the majority of disease-associated regulating RNAs are present in abnormally high amounts. Therefore, they are instrumental in supporting a pro-inflammatory milieu, damaging neuronal structure and encouraging neuronal cell death.  These are changes essential for initiation and continuance of epilepsy (see Blog 12).

Noncoding RNAs as a noninvasive biomarker for epilepsy

There is a desperate need for noninvasive biomarkers of epilepsy.  Briefly, a biomarker is a measurement of a pathological process and/or a biomarker indicates the response to a therapeutic/surgical intervention.   To date, the seizure, observed clinically or by EEG, is the only validated biomarker (see Blog 7 for issues) for epilepsy.   Because noncoding RNAs are small molecules, they exit the cell and appear in body fluids e.g. blood.  Present day instrumentation is capable of detecting very low levels of circulating noncoding RNAs.  Studies confirm that variations in blood levels of disease-associated noncoding RNAs mimic changes in the brain, making them a potentially valuable noninvasive biomarker for detection/diagnosis of epilepsy.

There have been a number of studies in man with the objective of assessing the role of noncoding RNAs as a diagnostic noninvasive biomarker.  Many show that certain regulating RNAs measured in serum, plasma or cerebrospinal fluid are indicative of specific epilepsies compared to normal controls.  Some studies measured noncoding RNAs as a biomarker for drug-resistant epilepsy.  In all studies, the select or disease-associated noncoding RNAs were statistically significantly changed from controls and hence have potential to accurately characterize the epilepsy.

Noncoding RNAs as a target to cure epilepsy

Data show that certain disease-associated noncoding RNAs create instability severe enough to ferment inflammation and cause neuronal death. This ignites the beginning stages of epilepsy. Thus, noncoding RNAs represent potential targets for future therapy.  Several anti-noncoding RNA therapies e.g. antisense oligonucleotides, anti-microRNA, microRNA mimics, microRNA sponges (Manna et al., 2022), are currently in development in animal models and could prove valuable to patients with epilepsy.

Issues to overcome

There is little doubt that noncoding RNAs will become useful diagnostic biomarkers and therapeutic targets in the future.  However, several hurdles remain.  One is standardization.  There is the need to develop valid universal methods to allow critical comparison of results between separate studies and different laboratories.  Studies also need to improve on sensitivity and specificity.  “Sensitivity measures the proportion of correctly identified subjects having the specific condition or disease. Specificity measures the proportion of correctly identified subjects not having the disease (Pitkanen et al., 2019).  From well-designed studies, scientists can use these measurement to determine acceptable values. Also, larger studies in man are clearly essential.

Conclusions

Understanding the  role of noncoding RNAs in health and disease is an important endeavor.  Noncoding RNAs are key regulators of gene expression and aberrant regulation leads to dysfunction and disease.  Results from animal models of epilepsy and various studies in patients with epilepsy strongly indicate epilepsy-associated noncoding RNAs could become reliable diagnostic biomarkers for the disease as well as future therapeutic targets.

Select References (Pubmed)

Manna I et al., Non-Coding RNAs: New Biomarkers and Therapeutic Targets for Temporal Lobe Epilepsy. Int. J. Mol. Sci. 23, 3063, 2022.

Papadelis C, Perry MS. Localizing the Epileptogenic Zone with Novel  Biomarkers. Semin Pediatr Neurol 39:100919,  2021.

Pitkanen A. et al., Epilepsy biomarkers – Toward etiology and pathology specificity. Neurobiol Dis. 123: 42–58, 2019.

Some studies in man

Wang X et al., Serum microRNA-4521 is a potential biomarker for focal cortical dysplasia with refractory epilepsy. Neurochem Res 41  :905-12, 2016.

Yan S et al., Altered microRNA profiles in plasma exosomes from mesial temporal lobe epilepsy with hippocampal sclerosis. Oncotarget 8:  4136–4146, 2017.

An N et al,. Elevated serum miR-106b and miR- 146a in patients with focal and generalized epilepsy. Epilepsy Res 127:  311–316, 2016.

Sun J. et al.,  Identification of serum miRNAs differentially expressed in human epilepsy at seizure onset and post-seizure. Mol. Med. Rep 14:  5318–5324, 2016.