During focal
cerebral ischemia, the degradation of microvessel basal lamina matrix occurs acutely and is associated with
edema formation and microhemorrhage. These events have been attributed to
matrix metalloproteinases (
MMPs). However, both known
protease generation and
ligand specificities suggest other participants. Using cerebral tissues from a non-human primate focal
ischemia model and primary murine brain endothelial cells, astrocytes, and microglia in culture, the effects of active
cathepsin L have been defined. Within 2 hours of
ischemia onset
cathepsin L, but not
cathepsin B, activity appears in the ischemic core, around microvessels, within regions of neuron injury and
cathepsin L expression. In in vitro studies,
cathepsin L activity is generated during experimental
ischemia in microglia, but not astrocytes or endothelial cells. In the acidic ischemic core,
cathepsin L release is significantly increased with time. A novel ex vivo assay showed that
cathepsin L released from microglia during
ischemia degrades microvessel matrix, and interacts with
MMP activity. Hence, the loss of microvessel matrix during
ischemia is explained by microglial
cathepsin L release in the acidic core during injury evolution. The roles of
cathepsin L and its interactions with specific
MMP activities during
ischemia are relevant to strategies to reduce microvessel injury and
hemorrhage.