Matrix metalloproteinase-9 and spontaneous hemorrhage in an animal model of cerebral amyloid angiopathy.

We examined the potential role of the extra-cellular matrix-degrading enzyme, matrix metalloproteinase-9 (MMP-9), in the pathogenesis of cerebral amyloid angiopathy (CAA)-induced spontaneous hemorrhage. The amyloid-beta peptide (Abeta) induced the synthesis, release and activation of MMP-9 in murine cerebral endothelial cells, resulting in increased extracellular matrix degradation. Furthermore, extensive MMP-9 immunoreactivity was observed in CAA-vessels with evidence of microhemorrhage in aged APPsw transgenic mice, but not detected in aged wild type or young APPsw mice. These results suggest that increased vascular MMP-9 expression, stimulated by Abeta, may play a role in the pathogenesis of spontaneous intracerebral hemorrhage in patients with CAA.