Inhibition of MicroRNA‐155 Supports Endothelial Tight Junction Integrity Following Oxygen‐Glucose Deprivation

BACKGROUND: Brain microvascular endothelial cells form a highly selective blood brain barrier regulated by the endothelial tight junctions. Cerebral ischemia selectively targets tight junction protein complexes, which leads to significant damage to cerebral microvasculature. Short noncoding molecules called microRNAs are implicated in the regulation of various pathological states, including endothelial barrier dysfunction. In the present study, we investigated the influence of microRNA‐155 (miR‐155) on the barrier characteristics of human primary brain microvascular endothelial cells (HBMECs). METHODS AND RESULTS: Oxygen‐glucose deprivation was used as an in vitro model of ischemic stroke. HBMECs were subjected to 3 hours of oxygen‐glucose deprivation, followed by transfections with miR‐155 inhibitor, mimic, or appropriate control oligonucleotides. Intact normoxia control HBMECs and 4 oxygen‐glucose deprivation–treated groups of cells transfected with appropriate nucleotide were subjected to endothelial monolayer electrical resistance and permeability assays, cell viability assay, assessment of NO and human cytokine/chemokine release, immunofluorescence microscopy, Western blot, and polymerase chain reaction analyses. Assessment of endothelial resistance and permeability demonstrated that miR‐155 inhibition improved HBMECs monolayer integrity. In addition, miR‐155 inhibition significantly increased the levels of major tight junction proteins claudin‐1 and zonula occludens protein‐1, while its overexpression reduced these levels. Immunoprecipitation and colocalization analyses detected that miR‐155 inhibition supported the association between zonula occludens protein‐1 and claudin‐1 and their stabilization at the HBMEC membrane. Luciferase reporter assay verified that claudin‐1 is directly targeted by miR‐155. CONCLUSIONS: Based on these results, we conclude that miR‐155 inhibition–induced strengthening of endothelial tight junctions after oxygen‐glucose deprivation is mediated via its direct target protein claudin‐1.