Osteopontin and its Integrin Receptor α v β 3 Are Upregulated During Formation of the Glial Scar After Focal Stroke

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Abstract
Background and Purpose—Microglia and astrocytes in the peri-infarct region are activated in response to focal stroke. A critical function of activated glia is formation of a protective barrier that ultimately forms a new glial-limiting membrane. Osteopontin, a provisional matrix protein expressed during wound healing, is induced after focal stroke. The present study was performed to determine the spatial and temporal expression of osteopontin and its integrin receptor αvβ3 during formation of the peri-infarct gliotic barrier and subsequent formation of a new glial-limiting membrane. Methods—Spontaneously hypertensive rats (n=19) were subjected to permanent occlusion of the middle cerebral artery and killed 3, 6, and 24 hours and 2, 5, and 15 days after occlusion. The spatial and temporal expression of osteopontin mRNA was determined by in situ hybridization, and that of osteopontin ligand and its integrin receptor αvβ3 was determined by immunohistochemistry. Results—Osteopontin mRNA was expressed de novo in the peri-infarct region from 3 to 48 hours; by 5 days osteopontin mRNA expression was restricted to the infarct. Osteopontin protein was expressed by peri-infarct microglia beginning at 24 hours and by microglia/macrophages at 48 hours in the infarct. Integrin receptor αvβ3 was expressed in peri-infarct astrocytes at 5 and 15 days. Conclusions—Early microglial/macrophage expression of osteopontin mRNA defines the borders and final infarct area at 24 hours. At 5 days osteopontin ligand is at a distance from the peri-infarct astrocytes expressing integrin receptor αvβ3. By 15 days astrocytes expressing integrin receptor αvβ3 are localized in an osteopontin-rich region concomitant with formation of the new glial-limiting membrane. The de novo expression and interaction of osteopontin ligand with its receptor integrin αvβ3 suggest a role in wound healing after focal stroke.

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