Plasma kallikrein (PK) is activated during
hemorrhage and has been implicated in cerebral vascular permeability and
edema. To further characterize the potential effects of PK on the brain that may follow cerebral
vascular injury, we have utilized a proteomics approach to search for novel PK substrates in the astrocyte secretome. Extracellular
proteins released by astrocytes are critical mediators of cerebral homeostasis, including roles in synapse function and vascular integrity. We identified 1,108
proteins in astrocyte condition medium and 295 of these were annotated as secreted
proteins. The total abundance of nine
proteins was changed
after treatment with PK. Characterization of the secreted
proteins revealed low molecular weight fragments for 59
proteins in
conditioned media exposed to PK that were not observed in untreated controls. The most striking finding from this study was the appearance of fragmentation of 26 extracellular matrix-associated
proteins including
collagen isoforms 1-6 and11,
nidogen-1 and -2,
lysyl oxidase-like
protein 1, and
matrix metalloproteinase 19 in the presence of PK. We also demonstrated that PK induced the fragmentation of non-matrix
proteins, including
apolipoprotein E. This report further characterizes the astrocyte secretome and identifies novel potential targets of PK-induced proteolysis that may contribute to its effects on the brain following
vascular injury.