Neprilysin Degrades Both Amyloid β Peptides 1-40 and 1-42 Most Rapidly and Efficiently among Thiorphan- and Phosphoramidon-sensitive Endopeptidases

Abstract

To identify the amyloid β peptide (Aβ) 1-42-degrading enzyme whose activity is inhibited by thiorphan and phosphoramidon in vivo, we searched for neprilysin (NEP) homologues and cloned neprilysin-like peptidase (NEPLP) α, NEPLP β, and NEPLP γ cDNAs. We expressed NEP, phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PEX), NEPLPs, and damage-induced neuronal endopeptidase (DINE) in 293 cells as 95- to 125-kDa proteins and found that the enzymatic activities of PEX, NEPLP α, and NEPLP β, as well as those of NEP and DINE, were sensitive to thiorphan and phosphoramidon. Among the peptidases tested, NEP degraded both synthetic and cell-secreted Aβ1-40 and Aβ1-42 most rapidly and efficiently. PEX degraded cold Aβ1-40 and NEPLP α degraded both cold Aβ1-40 and Aβ1-42, although the rates and the extents of the digestion were slower and less efficient than those exhibited by NEP. These data suggest that, among the endopeptidases whose activities are sensitive to thiorphan and phosphoramidon, NEP is the most potent Aβ-degrading enzyme in vivo. Therefore, manipulating the activity of NEP would be a useful approach in regulating Aβ levels in the brain.