Identification of novel APP/Abeta isoforms in human cerebrospinal fluid.
BACKGROUND
Aggregation of beta-amyloid (Abeta) into oligomers and plaques is the central pathogenic mechanism in Alzheimer's disease (AD). Abeta is produced from the amyloid precursor protein (APP) by beta- and gamma-secretases, whereas, in the nonamyloidogenic pathway, alpha-secretase cleaves within the Abeta sequence, and thus precludes Abeta formation. A lot of research has focused on Abeta production and the neurotoxic 42-amino-acid form of Abeta (Abeta1-42), while less is known about the nonamyloidogenic pathway and how Abeta is degraded.


OBJECTIVE
To study the Abeta metabolism in man by searching for novel Abeta peptides in cerebrospinal fluid (CSF).


METHODS
Immunoprecipitation, using an anti-Abeta antibody, 6E10, was combined with either matrix-assisted laser desorption/ionization time-of-flight mass spectrometry or nanoflow liquid chromatography and tandem mass spectrometry.


RESULTS
We identified 12 truncated APP/Abeta peptides in the CSF, all of which end at amino acid 15 in the Abeta sequence, i.e. 1 amino acid before the proposed alpha-secretase site. Of these 12 APP/Abeta peptides, 11 are novel peptides and start N-terminally of the beta-secretase site. The most abundant APP/Abeta peptide starts 25 amino acids before the beta-secretase site, APP/Abeta (-25 to 15), and had a concentration of approximately 80 pg/ml. The identity of all the APP/Abeta peptides was verified in a cohort of AD patients and controls. A first pilot study also showed that the intensity of several APP/Abeta peaks in CSF was higher in AD cases than in controls.


CONCLUSIONS
These data suggest an enzymatic activity that cleaves the precursor protein in a specific manner that may reflect a novel metabolic pathway for APP and Abeta.
Portelius
Erik
E
Clinical Neurochemistry Laboratory, Department of Neuroscience and Physiology, University of Göteborg, Sahlgrenska University Hospital, Mölndal, Sweden. erik.portelius@neuro.gu.se
Brinkmalm
Gunnar
G
Tran
Ai Jun
AJ
Zetterberg
Henrik
H
Westman-Brinkmalm
Ann
A
Blennow
Kaj
K
D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000134:cerebrospinal fluid*; D000595:Amino Acid Sequence; D053829:Amyloid Precursor Protein Secretases / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000134:cerebrospinal fluid* / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000134:cerebrospinal fluid* / Q000378:metabolism; D002853:Chromatography, Liquid; D005260:Female; D006801:Humans; D047468:Immunoprecipitation; D008297:Male; D008969:Molecular Sequence Data; D010865:Pilot Projects; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D053829:Amyloid Precursor Protein Secretases