Effect of astroglial cells on hypoxia-induced permeability in PBMEC cells

Abstract

An in vitro model of the blood-brain barrier (BBB), consisting of porcine brain-derived microvascular endothelial cells (PBMEC), was used to evaluate the effect of astrocytes in the BBB disruption during hypoxia. Hypoxia-induced hyperpermeability was decreased significantly in a coculture model of astroglia cells, either astrocytes or C6 glioma cells, with PBMEC and, to the same extent, when glia cell-conditioned medium was used. Corresponding to effects on hypoxia-induced hyperpermeability, astrocyte- and C6 cell-conditioned medium diminished hypoxia-induced vascular endothelial growth factor (VEGF) mRNA and protein expression, which recently was shown to be responsible for hypoxia-induced permeability changes in vitro. The effect on hypoxia-induced hyperpermeability and VEGF expression was specific for astroglia cells because conditioned medium from bovine smooth muscle cells (BSMC) did not show any effect. Immunocytochemistry revealed that 24 h of hypoxia disrupted the continuity of the tight junction protein, zonula occludens-1 (ZO-1), which lines the cytoplasmic face of intact tight junctions. These changes were prevented when hypoxia was performed in glia cell-conditioned medium. Results suggest that astrocytes protect the BBB from hypoxia-induced paracellular permeability changes by decreasing hypoxia-induced VEGF expression in microvascular endothelial cells.

Cerebral microvascular changes in permeability and tight junctions induced by hypoxia-reoxygenation

“…3). This is supported by other studies examining the hypoxic effects on localization of ZO-1 in BMECs (20). These disruptions in TJ proteins at cell-to-cell contact sites correlate with increased paracellular permeability and changes seen in actin distribution patterns (i.e., stress tangles).…”

“…Those monolayers with resistance values Ͼ120 ⍀ ⅐ cm 2 were used to assess the permeability effects of hypoxia and reoxygenation on BBMEC monolayers. The passage of [ 14 C]sucrose (a paracellular marker) across the BBMEC monolayer was employed because this method is more sensitive for detecting small changes in permeability compared with TEER measurements (20).…”

Strengthening tight junctions of retinal microvascular endothelial cells by pericytes under normoxia and hypoxia involving angiopoietin-1 signal way

“…It was observed in our study that hypoxia decreased occludin and ZO-1 staining along cells boundaries and increased both staining in cytoplasm, which is consistent with previous results in porcine brain microvessel ECs. 31 The possible mechanism may be the selective phosphorylation of key components of occludin and ZO-1, as protein phosphorylation plays a key role in the regulation of protein function. 32 Under hypoxia, production of ATP is markedly reduced, inhibiting the activity of phosphorylation.…”

Blood—Brain Barrier Breakdown Involves Four Distinct Stages of Vascular Damage in Various Models of Experimental Focal Cerebral Ischemia

“…5,9 As these sealing structures are responsible for the maintenance of the BBB under physiologic conditions, loss of BBB function after stroke or associated with reperfusion is consequently attributed to dysfunctional TJs leading to an increased permeability of affected vessels, although respective data are often derived from in vitro models. [10][11][12][13] However, using the translationally relevant thromboembolic stroke model in rats, our group has recently shown that ischemia-related BBB breakdown is predominantly a result of an endothelial cell damage while TJs proteins remained detectable by immunofluorescence labeling. 14 This concept is further supported by recent data from other groups suggesting that BBB opening may also occur independently of altered TJs by an opening of endothelial connexin-43 hemichannels, which mediates endothelial swelling and cellular damage, thereby increasing BBB permeability.…”