Pharmacological Inhibition of Amyloidogenic APP Processing and Knock-Down of APP in Primary Human Macrophages Impairs the Secretion of Cytokines.

Juan Manuel Maler,Hans-Joachim Knölker,Caroline Göth,Matthias Walter,Philipp Spitzer,Johannes Kornhuber,Philipp Linning,Timo Jan Oberstein

doi:10.3389/fimmu.2020.01967

Juan Manuel Maler, Hans-Joachim Knölker + Show 6 more

Open Access

https://doi.org/10.3389/fimmu.2020.01967

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Abstract

It has been previously shown that the amyloid precursor protein (APP) support the innate immune defense as an immune receptor. Amyloid β (Aβ) peptides seem to have properties of an antimicrobial peptide and can act as opsonines. In APP-deficient mouse models, a reduced secretion of cytokines has been observed. Still, it is unclear whether this can be attributed to the lack of APP or to the missing secretion of Aβ peptides. We inhibited the secretion of Aβ peptides in primary human monocyte derived macrophages with the γ-secretase inhibitor N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenylglycine-t-butyl-ester (DAPT) or the β-secretase inhibitor GL-189. Alternatively, we knocked down APP by transfection with siRNA. We measured tumor necrosis factor α (TNFα), interleukin 6 (IL-6) and interleukin (IL-10) by enzyme linked immunosorbent assay (ELISA) and evaluated the phagocytotic activity by flow cytometry. We observed reduced concentrations of TNFα and IL-6 in the media of APPk/d macrophages and after inhibition of the β-, or γ-secretase, especially after additional immunological activation with lipopolysaccharide (LPS). Secretion of IL-10 was increased after pharmacological inhibition of APP processing when the macrophages were not immunologically activated but was decreased during LPS-induced inflammation in APPk/d macrophages. No changes of the phagocytotic activity were observed. We conclude that macrophage APP and Aβ peptides support the initiation of an immune response and are involved in the regulation of TNFα, IL-6, and IL-10 secretion by human monocyte-derived macrophages.

Highlights

The amyloid precursor protein (APP) is expressed on nearly every cell type and the amyloid β (Aβ) peptides, which are generated by sequential cleavage of APP by the β- and γ-secretase, are known to aggregate to plaques in the brains of patients with Alzheimer’s disease (AD) [1]
We previously reported that monocytes express APP and that its metabolisation into Aβ peptides depends on their immunological activation [22,23,24]
Primary human monocyte derived macrophages were cultivated in serum-free media

Summary

Introduction

The amyloid precursor protein (APP) is expressed on nearly every cell type and the amyloid β (Aβ) peptides, which are generated by sequential cleavage of APP by the β- and γ-secretase, are known to aggregate to plaques in the brains of patients with Alzheimer’s disease (AD) [1]. APP and its cleavage products have been intensely investigated in the context of AD, little is known about their physiological functions and their role within the immune system. Inflammatory processes such as the activation of microglia and peripheral macrophages are increasingly considered in the research of AD pathophysiology [3,4,5]. It is still not clear, whether neuroinflammation is the cause or the consequence of AD and whether it is harmful or beneficial [3, 6, 7]

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