Characterisation of the effect of genetic deletion of MicroRNA-22 on brain structure and functional outcomes in experimental epilepsy
Creators: name: Luiz Fernando Almeida Silva
Publisher: name: Royal College of Surgeons in Ireland
Year: 2020
Subjects: subject: 110903 Central Nervous System
subject: FOS: Clinical medicine
subject: FOS: Clinical medicine

description: Epilepsy is a serious chronic neurological disease that affects over 65 millionpeople worldwide. Temporal lobe epilepsy is the most common form of epilepsy inadults and patients are often refractory to available pharmacotherapy.Unfortunately, antiepileptic drugs only treat the symptoms and do not exertdisease-modifying effects in patients. It is crucial to develop new pharmacologicalapproaches to aid patients with drug-resistant epilepsy as well as the developmentof pharmacotherapy with disease-modifying capability. The pathomechanismsinvolved in the development and maintenance of the epileptic state remainincompletely understood. However, gene profiling and other “omics” techniqueshave revealed large-scale gene expression changes accompany brain insults thatcause epilepsy and the gene expression landscape remains altered in establishedepilepsy. Therefore, identifying key regulators of this gene expression landscapeis critical if we are to develop novel disease-modifying therapies. In line with thisview, miRNAs have emerged as important contributors to the gene expressionlandscape in health and disease through post-transcriptional mechanisms.MiRNAs are small non-coding RNA that function as an additional regulatory layerof gene expression. There is now extensive evidence that multiple miRNAs arealtered in experimental and human epilepsy and that targeting individual miRNAscan influence seizures and neuropathological processes including inflammatorysignalling and gliosis.MiRNA-22 was recently identified as a novel miRNA involved in opposinghyperexcitability in experimental epilepsy, mainly by suppressing the P2rx7receptor which drives microgliosis. As with most other work to date, however, thefunctional evidence is based entirely on oligonucleotide targeting of the miRNA.<br>These offer incomplete silencing of variable duration and have potential off-targeteffects. Genetic evidence for miRNA involvement in epilepsy remains scarce.Therefore, the present thesis focused on obtaining genetic evidence for the role ofmiR-22 in experimental status epilepticus and epilepsy using mice engineered tolack miR-22. These mice were developed on a 129 background strain andtherefore the modelling of epilepsy in this strain was also a focus of studies here.In the first of three Results Chapters, we identified a number of phenotypes in theintra-amygdala kainic acid model of status epilepticus (SE) and epilepsy thatdiffered in 129 mice compared to the standard C57BL/6 strain used. Theseincluded subdued convulsive behaviour and minor variations in the seizurefeatures on the electroencephalogram (EEG). However, neuropathology wassimilar between strains. Importantly, studies characterised for the first time theemergence of epilepsy after intra-amygdala KA-induced SE in a mouse strainbesides the C57BL/6. Overall, the results in this chapter showed that 129 mice aresuitable for use in subsequent studies.The second Results Chapter featured a comprehensive analysis of the brains ofthe miR-22 mice. Overall, the mice show little to no difference, with normalappearing brain structures and neuron and glial populations. A subtle molecularphenotype was noted, however, with increased levels of a miR-22 target. Themice also appear more susceptible to seizures induced by the GABA antagonistPTZ.In the final results Chapter, studies investigated the response of the mice to SE inthe intra-amygdala kainic acid model. A key finding here was that female miR-22-deficient mice had altered responses to SE the first sex difference observed for amiRNA in an epilepsy study.. As a result, epilepsy-monitoring studies were<br>performed on male mice. Long-term telemetry-based EEG monitoring studiesdemonstrated that male miR-22-deficient mice develop a more severe form ofepilepsy compared to wildtype mice, suggesting miR-22 is involved in adapting tobrain injuries, likely by suppressing inflammatory signalling. Studies involving thereintroduction of miR-22 into the knockout mice failed to rescue the phenotype,pointing to limitations in mimic-based miRNA therapies. Finally, gene expressionstudies identified a number of novel genes and pathways disrupted in miR-22-deficient mice that could explain the phenotype and point to novel targets for thefuture.Taken together, the studies in this thesis provide important genetic evidence for arole for miR-22 in the pathomechanisms of epilepsy and point to opportunities aswell as challenges in miRNA-based therapies for the treatment of epilepsy.