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FASEB J. 2020 Feb;34(2):2465-2482. doi: 10.1096/fj.201902347R. Epub 2019 Dec 27.

Mouse brain proteomics establishes MDGA1 and CACHD1 as in vivo substrates of the Alzheimer protease BACE1.

Author information

1
German Center for Neurodegenerative Diseases (DZNE), Munich, Germany.
2
Neuroproteomics, School of Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany.
3
Institute of Pathology, University of Bern, Switzerland.
4
Division of Neurogeriatrics, Department of NVS, Center for Alzheimer Research, Karolinska Institutet, Stockholm, Sweden.
5
Department of Immunology, The Weizmann Institute of Science, Rehovot, Israel.
6
Institute of Pathology, Technical University of Munich, Munich, Germany.
7
School of Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany.
8
Department of Neurology, Ludwig Maximilian University of Munich, Munich, Germany.
9
Institute of Developmental Genetics, Helmholtz Zentrum München, Neuherberg, Germany.
10
Genome Engineering, German Center for Neurodegenerative Diseases (DZNE), Munich, Germany.
11
Developmental Genetics, School of Life Sciences Weihenstephan, Technical University of Munich, Freising, Germany.
12
Munich Cluster for Systems Neurology (SyNergy), Munich, Germany.
13
German Research Center for Environmental Health, Institute for Diabetes and Obesity, Monoclonal Antibody Core Facility, Helmholtz Zentrum München, Neuherberg, Germany.
14
Core Facility Monoclonal Antibodies, German Center for Neurodegenerative Diseases (DZNE), Munich, Germany.
15
Department of Neuroanatomy, Institute of Anatomy and Cell Biology, Faculty of Medicine, University of Freiburg, Germany.
16
Center for Basics in Neuromodulation (NeuroModulBasics), Faculty of Medicine, University of Freiburg, Germany.
17
Department of Ophthalmology, Ludwig Maximilian University of Munich, Munich, Germany.
18
Faculty of Medicine, ICAR3R - Interdisciplinary Centre for 3Rs in Animal Research, Justus-Liebig-University, Giessen, Germany.
19
Neuroscience Center, Institute of Clinical Neuroanatomy, Goethe University, Frankfurt am Main, Germany.
20
Frankfurt Institute for Advanced Studies, Frankfurt am Main, Germany.

Abstract

The protease beta-site APP cleaving enzyme 1 (BACE1) has fundamental functions in the nervous system. Its inhibition is a major therapeutic approach in Alzheimer's disease, because BACE1 cleaves the amyloid precursor protein (APP), thereby catalyzing the first step in the generation of the pathogenic amyloid beta (Aβ) peptide. Yet, BACE1 cleaves numerous additional membrane proteins besides APP. Most of these substrates have been identified in vitro, but only few were further validated or characterized in vivo. To identify BACE1 substrates with in vivo relevance, we used isotope label-based quantitative proteomics of wild type and BACE1-deficient (BACE1 KO) mouse brains. This approach identified known BACE1 substrates, including Close homolog of L1 and contactin-2, which were found to be enriched in the membrane fraction of BACE1 KO brains. VWFA and cache domain-containing protein 1 (CACHD)1 and MAM domain-containing glycosylphosphatidylinositol anchor protein 1 (MDGA1), which have functions in synaptic transmission, were identified and validated as new BACE1 substrates in vivo by immunoblots using primary neurons and mouse brains. Inhibition or deletion of BACE1 from primary neurons resulted in a pronounced inhibition of substrate cleavage and a concomitant increase in full-length protein levels of CACHD1 and MDGA1. The BACE1 cleavage site in both proteins was determined to be located within the juxtamembrane domain. In summary, this study identifies and validates CACHD1 and MDGA1 as novel in vivo substrates for BACE1, suggesting that cleavage of both proteins may contribute to the numerous functions of BACE1 in the nervous system.

KEYWORDS:

SILAC; gamma-secretase; inhibitory synapse; retina; secretase

PMID:
31908000
DOI:
10.1096/fj.201902347R

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