Amyloidogenic Processing of Human Amyloid Precursor Protein in Hippocampal Neurons Devoid of Cathepsin D

Paul Saftig,Christoph Peters,Kurt Von Figura,Katleen Craessaerts,Fred Van Leuven,Bart De Strooper

doi:10.1074/jbc.271.44.27241

Abstract

betaA4-Amyloid peptide, the main component of the amyloid plaques in the brain of Alzheimer's disease patients is produced from amyloid precursor protein (APP) by proteolytical processing. Several lines of evidence suggest a direct role for cathepsin D, the major endosomal/lysosomal aspartic endopeptidase, in betaA4-amyloid peptide generation. Here we tested this hypothesis using primary cultures of hippocampal neurons derived from cathepsin D-deficient (knock out) mice and expressing wild-type human APP and two clinical APP variants via recombinant Semliki Forest virus. We demonstrate APP secretory processing, production of carboxyl-terminal amyloid fragments, and secretion of the betaA4-amyloid peptide in the complete absence of cathepsin D. The results rule out cathepsin D as a critical component of alpha-, beta-, or gamma-secretase and therefore as a primary target for drugs aimed at decreasing the betaA4-amyloid peptide burden in Alzheimer's disease.

Highlights

␤A4-Amyloid peptide, the main component of the amyloid plaques in the brain of Alzheimer’s disease patients is produced from amyloid precursor protein (APP) by proteolytical processing
Primary cultures of hippocampal neurons were established from individual E17 mouse embryos produced by heterozygous matings of mice with one defective cathepsin D gene allele [32]
Wild-type Human APP Processing—A set of previously characterized specific APP antibodies, summarized in Fig. 2A, was used to analyze the metabolism of APP in recombinant SFVinfected cathepsin Dϩ/ϩ and cathepsin DϪ/Ϫ hippocampal neurons derived from littermate embryos

Summary

Introduction

␤A4-Amyloid peptide, the main component of the amyloid plaques in the brain of Alzheimer’s disease patients is produced from amyloid precursor protein (APP) by proteolytical processing. Several lines of evidence suggest a direct role for cathepsin D, the major endosomal/ lysosomal aspartic endopeptidase, in ␤A4-amyloid peptide generation We tested this hypothesis using primary cultures of hippocampal neurons derived from cathepsin D-deficient (knock out) mice and expressing wild-type human APP and two clinical APP variants via recombinant Semliki Forest virus. Accumulating evidence has implicated cathepsin D as the ␤or ␥-secretase involved in the amyloidogenic processing of APP [17,18,19,20,21,22,23,24,25,26,27,28] This aspartyl proteinase is present in all mammalian species and is expressed in most tissues (18, 29 –32). A set of antibodies was used to identify different intermediates of APP metabolism in these cells

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Conclusion