Responses of Endothelial Cell and Astrocyte Matrix-Integrin Receptors to Ischemia Mimic Those Observed in the Neurovascular Unit

Abstract

Background and Purpose-Apposition of endothelial cells and astrocyte foot processes to the basal lamina matrix is postulated to underlie the cerebral microvessel permeability barrier. Focal cerebral ischemia induces rapid loss of select matrix-binding integrins from both cell compartments in the nonhuman primate. This study is the first to examine the conditions underlying integrin loss from these cell-types during ischemia in vitro and their relation to the changes in vivo. Methods-The impact of normoxia or standardized oxygen-glucose deprivation on integrin expression by murine primary cerebral endothelial cells and astrocytes grown on matrix substrates (collagen IV, laminin, and perlecan) of the basal lamina were quantitatively assessed by flow cytometry. Results-Endothelial cell expression of the ␤1 and ␣5 subunits significantly increased on all matrix ligands, whereas astrocytes displayed modest significant decreases in ␣5 and ␣6 subunits. Oxygen-glucose deprivation produced a further significant increase in subunit ␤1 expression by both cell types, but a clear decrease in both ␣1 and ␣6 subunits by murine astrocytes. Conclusions-Ischemia in vitro significantly increased endothelial cell ␤1 expression, which is consistent with the increase in ␤1 transcription by microvessels peripheral to the ischemic core. The loss of ␣1 and ␣6 integrins from murine astrocytes is identical to that seen in the nonhuman primate in vivo. These findings establish both isolated murine cerebral endothelial cells and astrocytes as potential integrin response cognates of microvascular cells of the neurovascular unit in primates, and allow determination of the mechanisms of their changes to ischemia.

Heterogeneity in the penumbra

“…Microvessels in the ischemic striatum expressed increased b 1 subunit transcripts in boundaries around central regions devoid of b 1 integrin transcription. To help explain these observations, in vitro integrin b 1 subunit mRNA expression increased when murine brain endothelial cells (grown on collagen type IV, laminin, or perlecan) were exposed to moderate oxygen-glucose deprivation (experimental ischemia) (Milner et al, 2008). Hence, the regions of endothelial cell response in the striatum of the nonhuman primate can be interpreted as multiple 'mini-penumbras' made up of areas of b 1 integrin mRNA upregulation on the edges of each core region and absent b 1 integrin expression in 'mini-cores' because of the failure of transcription and translation in the areas of infarction ( Figure 4A) (Tagaya et al, , 2001).…”

The Rapid Decrease in Astrocyte-Associated Dystroglycan Expression by Focal Cerebral Ischemia is Protease-Dependent

“…Nearly pure cultures of mouse astrocytes were obtained as described previously (Milner and ffrench-Constant, 1994) and by us (Milner et al, 2008). Brains from postnatal mice pups (less than 2 days old) were cleaned of meninges and external blood vessels, minced, and dissociated for 1 h in the same enzymatic solution as for endothelial cells.…”

Interendothelial Claudin-5 Expression Depends on Cerebral Endothelial Cell–Matrix Adhesion by β1-Integrins

“…Basal lamina matrix composition can determine integrin receptor expression by cerebral endothelial cells (Milner et al, 2008a). Recent work has suggested that tight junction expression and function may also be related to the composition of the matrix that endothelial cells are exposed to.…”