title: Identification of Small Peptides in Human Cerebrospinal Fluid upon Amyloid-β Degradation.
abstract: Amyloid-β (Aβ) degradation in brains of Alzheimer disease patients is a crucial focus for the clarification of disease pathogenesis. Nevertheless, the mechanisms underlying Aβ degradation in the human brain remain unclear.
  
  
  
  This study aimed to quantify the levels of small C-terminal Aβ fragments generated upon Aβ degradation in human cerebrospinal fluid (CSF).
  
  
  
  A fraction containing small peptides was isolated and purified from human CSF by high-pressure liquid chromatography. Degradation products of Aβ C termini were identified and measured by liquid chromatography-tandem mass spectrometry. The C-terminal fragments of Aβ in the conditioned medium of cultured cells transfected with the Swedish variant of βAPP (sw βAPP) were analyzed. These fragments in brains of PS1 I213T knock-in transgenic mice, overexpressing sw βAPP, were also analyzed.
  
  
  
  The peptide fragments GGVV and GVV, produced by the cleavage of Aβ40, were identified in human CSF as well as in the brains of the transgenic mice and in the conditioned medium of the cultured cells. Relative to Aβ40 levels, GGVV and GVV levels were 7.6 ± 0.81 and 1.5 ± 0.18%, respectively, in human CSF. Levels of the GGVV fragment did not increase by the introduction of genes encoding neprilysin and insulin-degrading enzyme to the cultured cells.
  
  
  
  Our results indicate that a substantial amount of Aβ40 in human brains is degraded via a neprilysin- or insulin-degrading enzyme-independent pathway.
authors.affiliation: Psychiatry, Department of Integrated Medicine, Division of Internal Medicine, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Mizuta
authors.forename: Kanta
authors.initials: K
authors.lastname: Yanagida
authors.forename: Takashi
authors.initials: T
authors.lastname: Kodama
authors.forename: Takeshi
authors.initials: T
authors.lastname: Tomonaga
authors.forename: Mako
authors.initials: M
authors.lastname: Takami
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Oyama
authors.forename: Takashi
authors.initials: T
authors.lastname: Kudo
authors.forename: Manabu
authors.initials: M
authors.lastname: Ikeda
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Takeda
authors.forename: Shinji
authors.initials: S
authors.lastname: Tagami
authors.forename: Masayasu
authors.initials: M
authors.lastname: Okochi
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000134:cerebrospinal fluid* / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism; D055879:Gene Knock-In Techniques; D057809:HEK293 Cells / Q000378:metabolism; D006801:Humans; D007339:Insulysin / Q000378:metabolism; D008822:Mice, Transgenic; D015260:Neprilysin / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D059748:Proteolysis
chemical_list: C545487:APP protein, human; D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D010446:Peptide Fragments; D015260:Neprilysin; D007339:Insulysin