Upregulation of fibronectin and the alpha 5 beta 1 and alpha v beta 3 integrins on blood vessels within the cerebral ischemic penumbra

Following focal cerebral ischemia, blood vessels in the ischemic border, or penumbra, launch an angiogenic response. In light of the critical role for fibronectin in angiogenesis, and the observation that fibronectin and its integrin receptors are strongly upregulated on angiogenic vessels in the hypoxic CNS, the aim of this study was to establish whether angiogenic vessels in the ischemic CNS also show this response. Focal cerebral ischemia was established in C57/Bl6 mice by middle cerebral artery occlusion (MCA: O), and brain tissue analyzed 7 days following re-perfusion, a time at which angiogenesis is ongoing. Within the ischemic core, immunofluorescent (IF) studies demonstrated vascular expression of MECA-32, a marker of leaky cerebral vessels, and vascular breakdown, defined by loss of staining for the endothelial marker, CD31, and the vascular adhesion molecules, laminin, dystroglycan and alpha 6 integrin. Within the ischemic penumbra, dual-IF with CD31 and Ki67 revealed the presence of proliferating endothelial cells, indicating ongoing angiogenesis. Significantly, vessels in the ischemic penumbra showed strong upregulation of fibronectin and the fibronectin receptors, alpha 5 beta 1 and alpha v beta 3 integrins. Taken together with our recent finding that the alpha 5 beta 1 integrin plays an important role in promoting cerebral angiogenesis in response to hypoxia, these results suggest that stimulation of the fibronectin- alpha 5 beta 1 integrin signaling pathway may provide a novel approach to amplifying the intrinsic angiogenic response to cerebral ischemia.