Neuroinflammatory responses and blood-brain barrier injury in chronic alcohol exposure: role of purinergic P2 x 7 Receptor signaling

Alcohol consumption leads to neuroinflammation and blood-brain barrier (BBB) damage, resulting in neurological impairment. We previously demonstrated that ethanol-induced disruption of barrier function in human brain endothelial cells was associated with mitochondrial injury, increased ATP and extracellular vesicle (EV) release, and purinergic receptor P2 x 7R activation. Therefore, we aimed to evaluate the effect of P2 x 7R blockade on peripheral and neuro-inflammation in ethanol-exposed mice. In a chronic intermittent ethanol (CIE)-exposed mouse model, P2 x 7R was inhibited by two different methods: Brilliant Blue G (BBG) or gene knockout. We assessed blood ethanol concentration (BEC), brain microvessel gene expression by using RT2 PCR array, plasma P2 x 7R and P-gp, serum ATP, EV-ATP, number of EVs, and EV mtDNA copy numbers. An RT2 PCR array of brain microvessels revealed significant upregulation of proinflammatory genes involved in apoptosis, vasodilation, and platelet activation in CIE-exposed wild-type animals, which were decreased 15-50-fold in BBG-treated-CIE-exposed animals. Plasma P-gp levels and serum P2 x 7R shedding were significantly increased in CIE-exposed animals. Pharmacological or genetic suppression of P2 x 7R decreased receptor shedding to levels equivalent to those in control group. The increase in EV number and EV-ATP content in the CIE-exposed mice was significantly reduced by P2 x 7R inhibition. CIE mice showed augmented EV-mtDNA copy numbers which were reduced in EVs after P2 x 7R inhibition or receptor knockout. These observations suggested that P2 x 7R signaling plays a critical role in ethanol-induced brain injury. Increased extracellular ATP, EV-ATP, EV numbers, and EV-mtDNA copy numbers highlight a new mechanism of brain injury during alcohol exposure via P2 x 7R and biomarkers of such damage. In this study, for the first time, we report the in vivo involvement of P2 x 7R signaling in CIE-induced brain injury.