Leukocyte-derived matrix metalloproteinase-9 mediates blood-brain barrier breakdown and is proinflammatory after transient focal cerebral ischemia

Abstract

Results of recent studies reveal vascular and neuroprotective effects of matrix metalloproteinase-9 (MMP-9) inhibition and MMP-9 gene deletion in experimental stroke. However, the cellular source of MMP-9 produced in the ischemic brain and the mechanistic basis of MMP-9-mediated brain injury require elucidation. In the present study, we used MMP-9-/- mice and chimeric knockouts lacking either MMP-9 in leukocytes or in resident brain cells to test the hypothesis that MMP-9 released from leukocytes recruited to the brain during postischemic reperfusion contributes to this injury phenotype. We also tested the hypothesis that MMP-9 promotes leukocyte recruitment to the ischemic brain and thus is proinflammatory. The extent of blood-brain barrier (BBB) breakdown, the neurological deficit, and the volume of infarction resulting from transient focal stroke were abrogated to a similar extent in MMP-9-/- mice and in chimeras lacking leukocytic MMP-9 but not in chimeras with MMP-9-containing leukocytes. Zymography and Western blot analysis from these chimeras confirmed that the elevated MMP-9 expression in the brain at 24 h of reperfusion is derived largely from leukocytes. MMP-9-/- mice exhibited a reduction in leukocyte-endothelial adherence and a reduction in the number of neutrophils plugging capillaries and infiltrating the ischemic brain during reperfusion; microvessel immunopositivity for collagen IV was also preserved in these animals. These latter results document proinflammatory actions of MMP-9 in the ischemic brain. Overall, our findings implicate leukocytes, most likely neutrophils, as a key cellular source of MMP-9, which, in turn, promotes leukocyte recruitment, causes BBB breakdown secondary to microvascular basal lamina proteolysis, and ultimately contributes to neuronal injury after transient focal stroke.

Multiple expression of matrix metalloproteinases in murine neurocysticercosis: Implications for leukocyte migration through multiple central nervous system barriers

“…Thus, enhanced expression of various MMPs in inflammatory infiltrates of animals infected with M. corti likely sustains accumulation of additional leukocytes by facilitating further extravasation through vasculature as well as through the ECM. In particular, the high expression and activity of MMP-8 in this model contrasts reports from most of the findings in other CNS disorders where MMP-2, -3 and -9 appear to be the main players in the pathological process [1,21,28,62,63]. In murine NCC, MMP-8 cleaved both gelatin and collagen, and it was detected in most of the areas analyzed, indicating its crucial role during the course of this infectious disease.…”

“…These multifunctional capabilities suggest that several members of this family are involved in the inflammatory process, and our results showing upregulation of multiple MMPs at the RNA level support this hypothesis albeit distinguishing between pro-and active MMPs is essential. Infiltrating leukocytes have been shown to be a major source of MMPs in distinct CNS disorders [21,25,31,55,59]. However, studies in this area have generally focused on a particular MMP and enzymatic activity, mostly cleavage of gelatin.…”

Metformin ameliorates BSCB disruption by inhibiting neutrophil infiltration and MMP‐9 expression but not direct TJ proteins expression regulation

“…It is widely accepted that in CNS disease, the increased MMP‐9 primarily come from infiltrating neutrophils 15, 16, 17. Removing neutrophils from the circulation prior to SCI with an anti‐neutrophil serum significantly reduces MMP‐9 level, which indicates that the increase in MMP‐9 after SCI come from neutrophils 17.…”

Treatment with Evasin-3 Reduces Atherosclerotic Vulnerability for Ischemic Stroke, but Not Brain Injury in Mice

“…12,13 Animals were scored neurologically, according to a 6-point scale: 0 ¼ no apparent neurologic deficit, 1 ¼ contra lateral forelimb flexion, 2 ¼ decreased grip of the contra lateral forelimb, 3 ¼ spontaneous movement in all directions, but contra lateral circling if pulled by tail, 4 ¼ spontaneous contra lateral circling, and 5 ¼ death. [14][15][16] Infarct Volume and Brain Edema Measurements Brains were cut in 20 mm coronal sections from the anterior to the posterior side. Every 150 mm, the brain sections were stained with a solution of 0.5% cresyl violet.…”