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

Am J Physiol Heart Circ Physiol. 2005 Aug;289(2):H558-68. doi: 10.1152/ajpheart.01275.2004. Epub 2005 Mar 11.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Blood Cell Count
  • Blood Vessels / pathology
  • Blood-Brain Barrier*
  • Blotting, Western
  • Cell Adhesion
  • Cerebral Infarction / pathology
  • Cerebrovascular Circulation
  • Collagen Type IV / metabolism
  • Endothelium, Vascular / pathology
  • Hemodynamics
  • Inflammation Mediators / metabolism*
  • Ischemic Attack, Transient / enzymology
  • Ischemic Attack, Transient / metabolism*
  • Ischemic Attack, Transient / pathology
  • Ischemic Attack, Transient / physiopathology
  • Leukocytes / enzymology*
  • Matrix Metalloproteinase 2 / metabolism
  • Matrix Metalloproteinase 9 / metabolism*
  • Mice
  • Mice, Knockout
  • Nervous System Diseases / prevention & control
  • Neutrophil Infiltration


  • Collagen Type IV
  • Inflammation Mediators
  • Matrix Metalloproteinase 2
  • Matrix Metalloproteinase 9