Identification Of Small Peptides In Human Cerebrospinal Fluid Upon Amyloid-Beta Degradation

Background: Arnyloid-P (AP) degradation in brains of Alzheimer disease patients is a crucial focus for the clarification of disease pathogenesis. Nevertheless, the mechanisms underlying AP degradation in the human brain remain unclear. Objective: This study aimed to quantify the levels of small C-terminal AP fragments generated upon A3 degradation in human cerebrospinal fluid (CSF). Methods: A fraction containing small peptides was isolated and purified from human CSF by high-pressure liquid chromatography. Degradation products of AP C termini were identified and measured by liquid chromatography-tandem mass spectrometry. The C terminal fragments of AP in the conditioned medium of cultured cells transfected with the Swedish variant of I3APP (sw (3APP) were analyzed. These fragments in brains of PS1I213T knock-in transgenic mice, overexpressing sw PAPP, were also analyzed. Results: The peptide fragments GGW and GW, produced by the cleavage of AP40, were identified in human CSF as well as in the brains ofthe transgenic mice and in the conditioned medium of the cultured cells. Relative to A1340 levels, GGW and GW levels were 7.6 0.81 and 1.5 0.18%, respectively, in human CSF. Levels of the GGW fragment did not increase by the introduction of genes encoding neprilysin and insulin-degrading enzyme to the cultured cells. Conclusion: Our results indicate that a substantial amount of A1340 in human brains is degraded via a neprilysin- or insulin-degrading enzyme-independent pathway. (C) 2017 S. Karger AG, Basel