Decrease in Vascular Integrin Immunoreactivity and Selective Loss of Capillaries During Rat Focal Cerebral Ischemia and Reperfusion
The β1-integrin cell adhesion molecules are the principal endothelial receptors for basal lamina components like collagen and laminin and contribute to the microvascular integrity. During cerebral ischemia and reperfusion the basal lamina antigens disappear, the vascular permeability is impaired, and edema and petechial hemorrhages develop. The current study investigates the localization of β1-integrins in the normal rat brain and after middle cerebral artery occlusion and reperfusion (MCAO/R). In the normal brain, there was only clear immunoreactivity for the α1, α6 and β1 integrins on endothelia, and for α4 on astrocytes. The α6-immunoreactivity was stronger on larger vessels, while α1β1 stained all vessels similarly. Western blotting confirmed the expression of the integrin subunits. Ultrastructurally, integrins were located on the luminal and on the abluminal side of the endothelia and on perivascular cells. Following 3-hours of cerebral ischemia and reperfusion intervals of 0, 9 and 24 hours (I3R0, I3R9 and I3R24, n=15), the number and staining intensity of immunoreactive vessels in the ischemic area were compared to the contralateral side and classified according to their diameters. There was a moderate reduction in the number of the β1-immunoreactive capillaries (6μm to 9μm) by –12% at I3R0 and –15% at I3R9 that greatly decreased to –43% at I3R24 (all p<0.05), all other vessel sizes remained unaffected. The β1-staining intensity decreased homogeneously over all vessel sizes by –4% to –6% at I3R0, –8% to –12% at I3R9 and –16% to –23% at I3R24 (p<0.05). The vascular staining for α1 was affected similarly but less pronounced. Interestingly, the α6-positive capillaries also were reduced by –21% at I3R24 (p<0.05), but the decrease of the α6-staining intensity was confined to vessels larger than 15μm (–15% at I3R24, p<0.05). The diameter-selective loss of vascular integrin presentation points to a size-specific interaction between the endothelium and the basal lamina. The prominent capillar vulnerability may largely account for the impairment of the microvascular integrity during ischemia and reperfusion.