Insulin-like Growth Factor (IGF)-1 treatment stabilizes the microvascular cytoskeleton under ischemic conditions

Abstract

Our previous studies showed that Insulin-like Growth Factor (IGF)-1 reduced blood brain barrier permeability and decreased infarct volume caused by middle cerebral artery occlusion (MCAo) in middle aged female rats. Similarly, cultures of primary brain microvessel endothelial cells from middle-aged female rats and exposed to stroke-like conditions (oxygen glucose deprivation; OGD) confirmed that IGF-1 reduced dye transfer across this cell monolayer. Surprisingly, IGF-1 did not attenuate endothelial cell death caused by OGD. To reconcile these findings, the present study tested the hypothesis that, at the earliest phase of ischemia, IGF-1 promotes barrier function by increasing anchorage and stabilizing cell geometry of surviving endothelial cells. Cultures of human brain microvessel endothelial cells were subject to oxygen-glucose deprivation (OGD) in the presence of IGF-1, IGF-1 + JB-1 (IGFR inhibitor) or vehicle. OGD disrupted the cell monolayer and reduced cell-cell interactions, which was preserved in IGF-1-treated cultures and reversed by concurrent treatment with JB-1. IGF-1-mediated preservation of the endothelial monolayer was reversed with LY294002 treatment, but not by Rapamycin, indicating that IGF-1 s actions on cell-cell contacts are likely mediated via the PI3K pathway. In vivo, microvessel morphology was evaluated in middle-aged female rats that were subjected to ischemia by MCAo, and treated ICV with IGFI, IGF-1 + JB-1, or artificial CSF (aCSF; vehicle) after reperfusion. Compared to vehicle controls, IGF-1 treated animals displayed larger microvessel diameters in the peri-infarct area and increased staining density for vinculin, an anchorage protein. Both these measures were reversed by concurrent IGF-1 + JB-1 treatment. Moreover these effects were restricted to 24 h after ischemia-reperfusion and no treatment effects were seen at 5d post stroke. Collectively, these data suggest that in the earliest hours during ischemia, IGF-1 promotes receptor-mediated anchorage of endothelial cells, and its actions may be accurately characterized as vasculoprotective.

Keywords: Blood brain barrier; Brain microvascular endothelial cells; Cerebral ischemia; Intercellular spaces; Oxygen-glucose deprivation; Vinculin.