Matrix Metalloproteinase 2 (MMP-2) Degrades Soluble Vasculotropic Amyloid-β E22Q and L34V Mutants, Delaying Their Toxicity for Human Brain Microvascular Endothelial Cells

Patients carrying mutations within the amyloid-beta (A beta) sequence develop severe early-onset cerebral amyloid angiopathy with some of the related variants manifesting primarily with hemorrhagic phenotypes. Matrix metalloproteases (MMPs) are typically associated with blood brain barrier disruption and hemorrhagic transformations after ischemic stroke. However, their contribution to cerebral amyloid angiopathy-related hemorrhage remains unclear. Human brain endothelial cells challenged with A beta synthetic homologues containing mutations known to be associated in vivo with hemorrhagic manifestations (A beta E22Q and A beta L34V) showed enhanced production and activation of MMP-2, evaluated via Multiplex MMP antibody arrays, gel zymography, and Western blot, which in turn proteolytically cleaved in situ the A beta peptides. Immunoprecipitation followed by mass spectrometry analysis highlighted the generation of specific C-terminal proteolytic fragments, in particular the accumulation of A beta-(1-16), a result validated in vitro with recombinant MMP-2 and quantitatively evaluated using deuterium-labeled internal standards. Silencing MMP-2 gene expression resulted in reduced A beta degradation and enhanced apoptosis. Secretion and activation of MMP-2 as well as susceptibility of the A beta peptides to MMP-2 degradation were dependent on the peptide conformation, with fibrillar elements of A beta E22Q exhibiting negligible effects. Our results indicate that MMP-2 release and activation differentially degrades A beta species, delaying their toxicity for endothelial cells. However, taking into consideration MMP ability to degrade basement membrane components, these protective effects might also undesirably compromise blood brain barrier integrity and precipitate a hemorrhagic phenotype.