Cortical spreading depression (CSD) develops during experimental stroke and within normal and traumatically-injured human brain. Recently, matrix metalloproteinases (MMP) have been implicated in stroke pathogenesis and in the integrity of the neurovascular unit by degrading matrix proteins, enhancing blood brain barrier (BBB) permeability and brain edema, and promoting hemorrhage after tPA administration. Although brain injury or vascular mechanisms provide triggers, we recently found that intense neuronal and glial depolarization during a single CSD activates MMP-9 for at least 72 hr and promotes perivascular plasma protein leakage. We propose 4 aims to explore the novel hypothesis that MMP activation during CSD is caused in part by neuronal and glial activation directly and contributes to the development of edema in ischemia and BBB disruption in normal brain.
Aim 1 will confirm and extend preliminary data establishing CSD as a trigger for MMP activation and will identify relevant isoforms and cells of origin.
Aim 2 will test the hypothesis that CSD is accompanied by leakage of plasma protein caused by MMP activation and will extend preliminary data showing that, (1) permeability of 8kD dextran and Evans blue increases within ipsilateral vessels and that, (2) antigenicity of endothelial harder antigen and laminin is decreased by MMP-dependent mechanisms after CSD.
Aim 3 will examine upstream mechanisms triggering MMP activation during CSD. Because nitric oxide (NO) S-nitrosylates the MMP active site to promote activation, we will examine whether CSD-induced NO generation triggers S-nitrosylated MMP activation and if so, examine the relevant NOS isoform promoting MMP activation by using selective NOS knockout mice. We will also examine the importance of NFkappaB pathway in the transcriptional regulation of CSD-induced MMP and the expression of TIMP-1, as a regulator of MMP-9 activity after CSD.
Aim 4 will examine the consequences of CSD-induced MMP activation during ischemia and explore the contributions of MMPs to vascular permeability changes both within the ischemic lesion and in remote brain areas. Using mutant mice lacking MMP-8 expressed on leukocytes, we propose to determine the extent to which MMP-8 causes CSD-induced BBB disruption in ischemic and non-ischemic tissue, and examine the potential for CSD-induced MMP-9 activation by MMP-8 dependent mechanisms in leukocytes. By so doing, we intend to explore ways in which neuronal activity during cerebral ischemia modulates the extracellular matrix and neurovascular unit and contribute to tissue injury.
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