Rapid disruption of an astrocyte interaction with the extracellular matrix mediated by integrin alpha(6)beta(4) during focal cerebral ischemia/reperfusion

Background and Purpose Integrins participate in cerebral microvascular integrity and signaling during focal ischemia/reperfusion. The integrin subunits alpha(1), alpha(6), and beta(1) are distributed identically on normal cerebral microvessels, Studies in epithelium indicate that integrin alpha(6) beta(4) which interacts with laminin-5 in the basal lamina/extracellular matrix, is unique. This study describes the exact location of alpha(6), beta(4), and alpha(6) beta(4) and that their responses in focal cerebral ischemia are relevant to astrocyte-matrix interactions. Methods The effect of middle cerebral artery occlusion and subsequent reperfusion on the microvascular expression of alpha(6)beta>(4) and laminin-5 in regions of cellular injury (dUTP incorporat tion) was examined in 15 nonhuman primates. Well-characterized antibodies against human alpha(6), beta(4), alpha(6)beta>(4) laminin-5 and laminin-l, endothelial CD31, and vascular markers were measured with computerized video imaging and laser confocal microscopy. Results Integrin alpha(6) beta(4) was localized on astrocytes where it connects with the extracellular matrix at the astrocyte-vessel interface. It represented 59.3 +/- 16.4% of alpha(6) antigen in cerebral microvessels <100 mu m in diameter. By 2 hours of ischemia, the significant reduction in alpha(6) expression (2P<.001) was accompanied by decreases in beta(4)/laminin-5 (0.76 +/- 0.03 to 0.20 +/- 0.09; 2P=.001) and alpha(6) beta(4)/laminin-5 (0.73 +/- 0.18 to 0.25 +/- 0.11; 2P=.001) in the region of dUTP incorporation. Parallel changes in laminin-5 and laminin-1 were less pronounced and coincided by 24 hours. Conclusions This is the first description of a potential role of integrin alpha(6) beta(4) in the brain, where it mediates astrocyte-matrix interactions. The dramatic disappearance of alpha(6) beta(4) relative to its ligands reflects early loss of integrin between the astrocyte and the vessel wall in selected microvessels in response to ischemia.