title: Alzheimer's presenilin 1 modulates sorting of APP and its carboxyl-terminal fragments in cerebral neurons in vivo.
abstract: Studies in continuously cultured cells have established that familial Alzheimer's disease (FAD) mutant presenilin 1 (PS1) delays exit of the amyloid precursor protein (APP) from the trans-Golgi network (TGN). Here we report the first description of PS1-regulated APP trafficking in cerebral neurons in culture and in vivo. Using neurons from transgenic mice or a cell-free APP transport vesicle biogenesis system derived from the TGN of those neurons, we demonstrated that knocking-in an FAD-associated mutant PS1 transgene was associated with delayed kinetics of APP arrival at the cell surface. Apparently, this delay was at least partially attributable to impaired exit of APP from the TGN, which was documented in the cell-free APP transport vesicle biogenesis assay. To extend the study to APP and carboxyl terminal fragment (CTF) trafficking to cerebral neurons in vivo, we performed subcellular fractionation of brains from APP transgenic mice, some of which carried a second transgene encoding an FAD-associated mutant form of PS1. The presence of the FAD mutant PS1 was associated with a slight shift in the subcellular localization of both holoAPP and APP CTFs toward iodixanol density gradient fractions that were enriched in a marker for the TGN. In a parallel set of experiments, we used an APP : furin chimeric protein strategy to test the effect of artificially forcing TGN concentration of an APP : furin chimera that could be a substrate for beta- and gamma-cleavage. This chimeric substrate generated excess Abeta42 when compared with wildtype APP. These data indicate that the presence of an FAD-associated mutant human PS1 transgene is associated with redistribution of the APP and APP CTFs in brain neurons toward TGN-enriched fractions. The chimera experiment suggests that TGN-enrichment of a beta-/gamma-secretase substrate may play an integral role in the action of mutant PS1 to elevate brain levels of Abeta42.
authors.affiliation: Farber Institute for Neurosciences and the Department of Neurology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA. samgandy@earthlink.net
authors.forename: Sam
authors.initials: S
authors.lastname: Gandy
authors.forename: Yun-wu
authors.initials: YW
authors.lastname: Zhang
authors.forename: Annat
authors.initials: A
authors.lastname: Ikin
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Schmidt
authors.forename: Alexey
authors.initials: A
authors.lastname: Bogush
authors.forename: Efrat
authors.initials: E
authors.lastname: Levy
authors.forename: Roxanne
authors.initials: R
authors.lastname: Sheffield
authors.forename: Ralph A
authors.initials: RA
authors.lastname: Nixon
authors.forename: Francesca-Fang
authors.initials: FF
authors.lastname: Liao
authors.forename: Paul M
authors.initials: PM
authors.lastname: Mathews
authors.forename: Huaxi
authors.initials: H
authors.lastname: Xu
authors.forename: Michelle E
authors.initials: ME
authors.lastname: Ehrlich
mesh_terms: D000544:Alzheimer Disease / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D016229:Amyloid beta-Peptides / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000378:metabolism* / Q000503:physiopathology; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D050506:Mutant Chimeric Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D009474:Neurons / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D053764:Presenilin-1 / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D019076:Transgenes / Q000235:genetics; D015854:Up-Regulation / Q000502:physiology; D021601:trans-Golgi Network / Q000378:metabolism
chemical_list: D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D050506:Mutant Chimeric Proteins; D010446:Peptide Fragments; D053764:Presenilin-1; C075222:amyloid beta-protein (1-42); D005182:Flavin-Adenine Dinucleotide