Clearance Of Amyloid-Beta Peptide By Neuronal And Non-Neuronal Cells: Proteolytic Degradation By Secreted And Membrane Associated Proteases

Deposition of amyloid-beta peptide (A beta) in the brain is an early and invariant feature of all forms of Alzheimer's disease (AD). As for all proteins or peptides, the steady-state level of A,8 peptide is determined not only by its production, but also by its degradation. So, overactive proteases involved in generating A beta from amyloid precursor protein or underactive A beta-degrading enzymes could lead to abnormal A beta deposition in the brain. Since in the sporadic forms of AD (90% of all AD cases) an impaired clearance of A,8 appears to be at the origin of its aggregation and tissue deposition, we have investigated its proteolytic degradation by several neuronal and non-neuronal cells. In this report, we show that these cell types exhibit a similar profile of A beta-degradation by cell-surface and secreted proteases which were respectively characterized as metallo- and serine proteases. By using a combination of the liquid chromatography/on-line mass spectrometry, we demonstrate that: (i)-the membrane associated protease(s) hydrolizes A,840 essentially at Lys(28)down arrow Gly(28), Phe(19)down arrow Phe(20) and Val(18)down arrow Phe(19) bonds; and (ii)-the secreted protease(s) cleaves the generating fragments A beta(1-28), A beta(1-19), A beta(1-18) at His(14)down arrow Gln(15) bond and also A beta(1-28) at Phe(20 down arrow)Ala(21) and AsP23 down arrow Val(24) sites. This is the first time our results define a proteolytic degradation process of A,640 that appears to be independent of the cell type and may represent a general pattern of its enzymatic clearance.