Rapid disruption of an astrocyte interaction with the extracellular matrix mediated by integrin alpha 6 beta 4 during focal cerebral ischemia/reperfusion.
OBJECTIVE
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 incorporation) was examined in 15 nonhuman primates. Well-characterized antibodies against human alpha 6, beta 4, alpha 6 beta 4, laminin-5 and laminin-1, 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 microns 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 integrity between the astrocyte and the vessel wall in selected microvessels in response to ischemia.
Wagner
S
S
Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, Calif. 92037, USA.
Tagaya
M
M
Koziol
J A
JA
Quaranta
V
V
del Zoppo
G J
GJ
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D000954:Antigens, Surface / Q000502:physiology*; D001253:Astrocytes / Q000502:physiology*; D001808:Blood Vessels / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D002545:Brain Ischemia / Q000378:metabolism / Q000503:physiopathology*; D015815:Cell Adhesion Molecules / Q000378:metabolism; D005109:Extracellular Matrix / Q000502:physiology*; D039503:Integrin alpha6; D039161:Integrin alpha6beta4; D039663:Integrin beta4; D016023:Integrins / Q000378:metabolism / Q000502:physiology*; D008297:Male; D008833:Microcirculation; D010215:Papio; D012016:Reference Values; D015427:Reperfusion Injury / Q000378:metabolism / Q000503:physiopathology*; D014018:Tissue Distribution; D000097794:Kalinin
D015703:Antigens, CD; D000954:Antigens, Surface; D015815:Cell Adhesion Molecules; D039503:Integrin alpha6; D039161:Integrin alpha6beta4; D039663:Integrin beta4; D016023:Integrins; D000097794:Kalinin