Potential therapeutic targets and biomarkers for seizure: genome‐wide DE miRNA expression profiling of rat brain following exposure to soman

Abstract

The term seizure refers to certain physical or behavioral actions that may occur after an episode of abnormal electrical activity in the brain. Epileptic seizure, one of the major seizure types, affects about 1% of the population currently and has affected about 4% of the population at some point in time. Most of those affected by seizures (nearly 80%) live in developing countries. Soman, also known as GD, is an extremely toxic man‐made organophosphorous chemical. Exposure to GD frequently results in seizures, as well as neuropathological and neurochemical abnormalities in various regions of the rat brain. Small microRNAs (miRNA) are (~22 nt) non‐coding RNAs that regulate the expression of target mRNAs at the post‐transcriptional level. Experimental evidence has demonstrated that miRNAs are involved in heterogeneous brain functions, including neuro‐inflammation, synaptic remodeling, and neuronal death. The purpose of the current study was to search potential therapeutic targets and biomarkers for seizure by sequencing genome‐wide small RNA and identifying differentially expressed (DE) miRNA of the rat brain following exposure to GD. Rats were exposed to either 0.8 LD50 GD or 1.0 LD50 GD versus a saline control group and then evaluated for seizure activity with EEG and also visually. We conducted miRNA profiling studies in brain tissues (hippocampus‐HP, hypothalamus‐HT, piriform cortex‐PIR, thalamus‐TH, amygdala‐AY and medial prefrontal cortex‐mPFC) collected from rats exposed to GD at 72 hours post‐exposure. Principal component analysis indicated good separation in relation to seizure activity. The principal component analysis showed two distinct clusters as per expression profile for all brain regions and AY, PIR and mPFC brain region were clustered together than the other brain tissues. To identify the expression profile of significantly different miRNAs in these brain regions, we performed the moderated t‐test to call differentially expressed (DE) miRNAs. The DE analysis showed total of 276 significant DE miRNAs in rat brain (87 in AY, 166 in PIR and 23 in mPFC) at the 1.0 LD50 of GD exposure concentrations as compared to the control group. After comparison of the seizure activity group to “none” seizure activity (DNS) group, we observed a total of 533 DE miRNAs (123 in AY, 58 in HP, 147 in HT, 249 in PIR, 185 in TH and 19 in mPFC) at 1 LD50 and 0.8 LD50 GD exposures. In conclusion, we identified changes in brain miRNAs (DE miRNA) that clearly distinguish seizures in rats from the control group, “none” seizure activity group and seizure group. These alterations in DE miRNA expression correlate with neuropathological progression and, potentially, with response to experimental treatment. This study provides potential therapeutic targets and biomarkers for the control of seizures. In addition, these data provide important insights into the molecular mechanisms involved in soman‐induced seizure activity and a basis for generating hypotheses about the mechanisms of seizure.