Sequential Abeta degradation by the matrix metalloproteases MMP-2 and MMP-9 [Protein Synthesis and Degradation]

April 20th, 2015 by Hernandez-Guillamon, M., Mawhirt, S., Blais, S., Montaner, J., Neubert, T. A., Rostagno, A., Ghiso, J.

Matrix metalloproteases MMP-2 and MMP-9 have been implicated in the physiologic catabolism of Alzheimer amyloid-β (Aβ). Conversely, their association with vascular amyloid deposits, blood-brain barrier disruption, and hemorrhagic transformations after ischemic stroke also highlights their involvement in pathologic processes. To better understand this dichotomy, recombinant human (rh) MMP-2 and MMP-9 were incubated with Aβ40 and Aβ42 and the resulting proteolytic fragments assessed via immunoprecipitation and quantitative mass spectrometry. Both MMPs generated Aβ fragments truncated only at the C-terminus, ending at positions 34, 30 and 16. Using deuterated homologues as internal standards, we observed limited and relatively slow degradation of Aβ42 by rhMMP-2 while the enzyme cleaved >80% of Aβ40 during the first hour of incubation. rhMMP-9 was significantly less effective, particularly in degrading Aβ1-42, although the targeted peptide bonds were identical. Using Aβ1-34 and Aβ1-30, we demonstrated that these peptides are also substrates for both MMPs, cleaving Aβ1-34 to produce Aβ1-30 first and Aβ1-16 subsequently. Consistent with the kinetics observed with full-length Aβ, rhMMP-9 degraded only a minute fraction of Aβ1-34 and was even less effective in producing Aβ1-16. Further degradation of Aβ1-16 by either MMP-2 or MMP-9 was not observed even after prolonged incubation times. Notably, all MMP-generated C-terminally truncated Aβ fragments were highly soluble, did not exhibit fibrillogenic properties or induce cytotoxicity in human cerebral microvascular endothelial or neuronal cells supporting the notion that these truncated Aβ species are associated with clearance mechanisms rather than being key elements in the fibrillogenesis process.