title: Down-regulation of endogenous amyloid precursor protein processing due to cellular aging.
abstract: Processing of amyloid precursor protein (APP) is a well acknowledged central pathogenic mechanism in Alzheimer disease. However, influences of age-associated cellular alterations on the biochemistry of APP processing have not been studied in molecular detail so far. Here, we report that processing of endogenous APP is down-regulated during the aging of normal human fibroblasts (IMR-90). The generation of intracellular APP cleavage products C99, C83, and AICD gradually declines with increasing life span and is accompanied by a reduced secretion of soluble APP (sAPP) and sAPPalpha. Further, the maturation of APP was reduced in senescent cells, which has been shown to be directly mediated by age-associated increased cellular cholesterol levels. Of the APP processing secretases, protein levels of constituents of the gamma-secretase complex, presenilin-1 (PS1) and nicastrin, were progressively reduced during aging, resulting in a progressive decrease in gamma-secretase enzymatic activity. ADAM10 (a disintegrin and metalloprotease 10) and BACE (beta-site APP-cleaving enzyme) protein levels exhibited no age-associated regulation, but interestingly, BACE enzymatic activity was increased in aged cells. PS1 and BACE are located in detergent-resistant membranes (DRMs), well structured membrane microdomains exhibiting high levels of cholesterol, and caveolin-1. Although total levels of both structural components of DRMs were up-regulated in aged cells, their particular DRM association was decreased. This age-dependent membrane modification was associated with an altered distribution of PS1 and BACE between DRM and non-DRM fractions, very likely affecting their APP processing potential. In conclusion, we have found a significant modulation of endogenous APP processing and maturation in human fibroblasts caused by age-associated alterations in cellular biochemistry.
authors.affiliation: Institute for Physiological Chemistry and Pathobiochemistry, Johannes Gutenberg University Mainz, 55099 Mainz, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kern
authors.forename: Birgit
authors.initials: B
authors.lastname: Roempp
authors.forename: Kai
authors.initials: K
authors.lastname: Prager
authors.forename: Jochen
authors.initials: J
authors.lastname: Walter
authors.forename: Christian
authors.initials: C
authors.lastname: Behl
mesh_terms: D053829:Amyloid Precursor Protein Secretases; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D016282:Aspartic Acid Endopeptidases; D002460:Cell Line; D016922:Cellular Senescence; D002784:Cholesterol / Q000502:physiology; D010450:Endopeptidases / Q000032:analysis / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology; D006801:Humans; D008562:Membrane Glycoproteins / Q000032:analysis; D021962:Membrane Microdomains / Q000378:metabolism; D008565:Membrane Proteins / Q000032:analysis / Q000378:metabolism; D053764:Presenilin-1; D011499:Protein Processing, Post-Translational
chemical_list: D016564:Amyloid beta-Protein Precursor; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C508853:PSEN1 protein, human; D053764:Presenilin-1; C413604:nicastrin protein; D002784:Cholesterol; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human