Alcohol-induced blood-brain barrier dysfunction is mediated via inositol 1,4,5-triphosphate receptor (IP₃R)-gated intracellular calcium release

The blood-brain barrier (BBB) formed by brain microvascular endothelial cells (BMVEC), pericytes and astrocytes controls the transport of ions, peptides and leukocytes in and out of the brain. Tight junctions (TJ) composed of TJ proteins (occludin, claudins and zonula occludens) ensure the structural integrity of the BMVEC monolayer. Neuropathologic studies indicated that the BBB was impaired in alcohol abusers; however, the underlying mechanism of BBB dysfunction remains elusive. Using primary human BMVEC, we previously demonstrated that oxidative stress induced by ethanol (EtOH) metabolism in BMVEC activated myosin light chain kinase (MLCK), resulting in the enhanced phosphorylation of either cytoskeletal or TJ proteins, and in BBB impairment. We proposed that EtOH metabolites stimulated inositol 1,4,5-triphosphate receptor (IP₃R)-operated intracellular calcium (Ca²⁺) release, thereby causing the activation of MLCK in BMVEC. Indeed, treatment of primary human BMVEC with EtOH or its metabolites resulted in the increased expression of IP₃R protein and IP₃R-gated intracellular Ca²⁺ release. These functional changes paralleled MLCK activation, phosphorylation of cytoskeletal/TJ proteins, loss of BBB integrity, and enhanced leukocyte migration across BMVEC monolayers. Inhibition of either EtOH metabolism or IP₃R activation prevented BBB impairment. These findings suggest that EtOH metabolites act as signaling molecules for the activation of MLCK via the stimulation of IP₃R-gated intracellular Ca²⁺ release in BMVEC. These putative events can lead to BBB dysfunction in the setting of alcoholism, and to neuro-inflammatory disorders promoting leukocyte migration across the BBB.