STAT6 mediates the effect of ethanol on neuroinflammatory response in TBI

Traumatic brain injury (TBI) and ethanol intoxication (EI) frequently coincide, particularly in young subjects. However, the mechanisms of their interaction remain poorly understood. Among other pathogenic pathways, TBI induces glial activation and neuroinflammation in the hippocampus, resulting in acute and chronic hippocampal dysfunction. In this regard, we investigated the role of EI affecting these responses unfolding after TBI. We used a blunt, weight-drop approach to model TBI in mice. Male mice were pre-administered with ethanol or vehicle to simulate EI. The neuroinflammatory response in the hippocampus was assessed by monitoring the expression levels of >20 cytokines, the phosphorylation status of transcription factors and the phenotype of microglia and astrocytes. We used AS1517499, a brain-permeable STAT6 inhibitor, to elucidate the role of this pathway in the EI/TBI interaction. We showed that TBI causes the elevation of IL-33, IL-1β, IL-38, TNF-α, IFN-α, IL-19 in the hippocampus at 3 h time point and concomitant EI results in the dose-dependent downregulation of IL-33, IL-1β, IL-38, TNF-α and IL-19 (but not of IFN-α) and in the selective upregulation of IL-13 and IL-12. EI is associated with the phosphorylation of STAT6 and the transcription of STAT6-controlled genes. Moreover, ethanol-induced STAT6 phosphorylation and transcriptional activation can be recapitulated in vitro by concomitant exposure of neurons to ethanol, depolarization and inflammatory stimuli (simulating the acute trauma). Acute STAT6 inhibition prevents the effects of EI on IL-33 and TNF-α, but not on IL-13 and negates acute EI beneficial effects on TBI-associated neurological impairment. Additionally, EI is associated with reduced microglial activation and astrogliosis as well as preserved synaptic density and baseline neuronal activity 7 days after TBI and all these effects are prevented by acute administration of the STAT6 inhibitor concomitant to EI. EI concomitant to TBI exerts significant immunomodulatory effects on cytokine induction and microglial activation, largely through the activation of STAT6 pathway, ultimately with beneficial outcomes.