A role for myeloid miR-155 in regulating hypoxia induced seizures in neonatal C57BL/J6 mice

Hypoxic ischaemic injury (HIE) in the neonatal brain has significant consequences on neurodevelopment and increases the occurrence of neurological deficits in infants. HIE is also a leading cause of neonatal seizures. Therapeutic options for the treatment of HIE are very limited. Hypoxia-ischemia directly damages brain tissue in a primary-wave of injury which activates a cascade of events triggering local and systemic inflammatory responses, driven by the innate immune system, which contribute to a significant secondary-wave of injury taking place as early as 6 hours post-hypoxia-ischaemia. Levels of the well documented inflammatory microRNA, miR-155 are elevated in rodent seizure and epilepsy models. Here, we assessed the impact of, miR-155 deletion in myeloid cells, on regulating inflammation and seizure severity in a preclinical model of neonatal hypoxia-induced seizures (Hypoxia-Sz). Wildtype miR-155 (miR-155+/+LysMCre) mice were compared to a mouse line in which miR-155 was deleted in myeloid cells (miR-155fl/fl LysMCre). We demonstrate significant upregulation of miR-155 target genes, brain-derived neurotrophic factor (bdnf), arginase-2 (arg-2), ship-1 and socs-1 in miR-155fl/fl LysMCre mice compared to controls at various time points following Hypoxia-Sz. Conversely, we report decreased mRNA levels of pro-inflammatory cytokines IL-1{beta} and IL-6 and lower protein levels of IL-1{beta} in miR-155fl/fl LysMCre mice as compared to WTs. Myeloid miR-155 deletion significantly reduced behavioural seizure severity score, reduced electrographically (EEG) measured seizure frequency and seizure burden as compared to mice to wildtypes, suggesting miR-155 regulation of seizure occurrence in this model. Behavioural tests for motor functions at 5 weeks post Hypoxia-Sz demonstrated differences between genotypes. Excitingly this work highlights that inhibition of miR-155, specifically in myeloid cells, may hold therapeutic benefit for both seizures and comorbidities associated with hypoxic brain injury.