title: Endogenous APP accumulates in synapses after BACE1 inhibition.
abstract: BACE1-mediated cleavage of APP is a pivotal step in the production of the Alzheimer related Aβ peptide and inhibitors of BACE1 are currently in clinical development for the treatment of Alzheimer disease (AD). While processing and trafficking of APP has been extensively studied in non-neuronal cells, the fate of APP at neuronal synapses and in response to reduced BACE1 activity has not been fully elucidated. Here we examined the consequence of reduced BACE1 activity on endogenous synaptic APP by monitoring N- and C-terminal APP epitopes by immunocytochemistry. In control rodent primary hippocampal neuron cultures, labeling with antibodies directed to N-terminal APP epitopes showed a significant overlap with synaptic vesicle markers (SV2 or synaptotagmin). In contrast, labeling with antibodies directed to C-terminal epitopes of APP showed only a limited overlap with these proteins. In neurons derived from BACE1-deficient mice, and in control neurons treated with a BACE1 inhibitor, both the N-terminal and the C-terminal APP labeling overlapped significantly with synaptic vesicle markers. Moreover, BACE1 inhibition increased the proximity between the APP C-terminus and SV2 as shown by a proximity ligation assay. These results, together with biochemical observations, indicate that BACE1 can regulate the levels of full-length APP at neuronal synapses.
authors.affiliation: Department of Neuroscience, Karolinska Institutet, S-171 77 Stockholm, Sweden.
authors.forename: Saket Milind
authors.initials: SM
authors.lastname: Nigam
authors.affiliation: Department of Neuroscience, Karolinska Institutet, S-171 77 Stockholm, Sweden.
authors.forename: Shaohua
authors.initials: S
authors.lastname: Xu
authors.affiliation: Department of Neuroscience, Karolinska Institutet, S-171 77 Stockholm, Sweden.
authors.forename: Frauke
authors.initials: F
authors.lastname: Ackermann
authors.affiliation: Department of Neuroscience, Karolinska Institutet, S-171 77 Stockholm, Sweden.
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Gregory
authors.affiliation: AlzeCure, Karolinska Institutet Science Park, S-141 57 Huddinge, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Lundkvist
authors.affiliation: Department of Cell and Molecular Biology, Karolinska Institutet, S-171 77 Stockholm, Sweden.
authors.forename: Urban
authors.initials: U
authors.lastname: Lendahl
authors.affiliation: Department of Neuroscience, Karolinska Institutet, S-171 77 Stockholm, Sweden. Electronic address: lennart.brodin@ki.se.
authors.forename: Lennart
authors.initials: L
authors.lastname: Brodin
mesh_terms: D053829:Amyloid Precursor Protein Secretases / Q000037:antagonists & inhibitors* / Q000235:genetics; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000037:antagonists & inhibitors* / Q000235:genetics; D002478:Cells, Cultured; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009025:Morpholines / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000187:drug effects* / Q000378:metabolism
chemical_list: C581009:4-(4-(3-methylmorpholin-4-yl)-6-(1-(methylsulfonyl)cyclopropyl)pyrimidin-2-yl)-1H-indole; D016564:Amyloid beta-Protein Precursor; D009025:Morpholines; D011743:Pyrimidines; D053829:Amyloid Precursor Protein Secretases; D016282:Aspartic Acid Endopeptidases; C509282:Bace1 protein, mouse; C509281:Bace1 protein, rat
keywords: APP; BACE1; Immunocytochemistry; Proximity ligation assay; Synapse; Synaptic vesicle