Neutralization of interleukin-9 ameliorates experimental stroke by repairing the blood–brain barrier via down-regulation of astrocyte-derived vascular endothelial growth factor-A

Astrocytes mediate the destruction of the blood–brain barrier (BBB) during ischemic stroke (IS). IL-9 is a pleiotropic cytokine that we previously found to be highly expressed in peripheral blood mononuclear cells from patients with IS, and the presence of IL-9 receptors on astrocytes has been reported in the literature. Here, we detected the effect of IL-9 on astrocytes using an anti–IL-9-neutralizing antibody to treat rats with experimental stroke. Supernatants from astrocytes treated with or without oxygen–glucose deprivation and/or IL-9 were incubated with bEnd.3 cell monolayers after blocking the IL-9 receptor on the endothelium. Immunofluorescence staining and Western blot analyses were conducted to observe the change in tight junction proteins (TJPs) in bEnd.3 cells as well as the level of VEGF-A and possible signal pathways in astrocytes. We also applied middle cerebral artery occlusion (MCAO) models to determine the effect of anti–IL-9-neutralizing antibodies on IS. As a result, astrocyte-conditi...