Antibody-mediated clearance of tau in primary mouse microglial cultures requires Fc\u03b3-receptor binding and functional lysosomes

Christian Rungsted Andersson,Jan Torleif Pedersen,Jeffrey B Stavenhagen,Bente Finsen,Nina Rosenqvist,Jeppe Falsig,Fredrik Kartberg,Søren Christensen

doi:10.1038/s41598-019-41105-4

Christian Rungsted Andersson, Jan Torleif Pedersen + Show 6 more

Open Access

https://doi.org/10.1038/s41598-019-41105-4

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Abstract

Neurodegenerative diseases such as Alzheimer’s disease are characterized by the progressive spreading and accumulation of hyper-phosphorylated tau protein in the brain. Anti-tau antibodies have been shown to reduce tau pathology in in vivo models and antibody-mediated clearance of tau exerted by microglia has been proposed as a contributing factor. By subjecting primary microglia cultured in vitro to anti-phospho-tau antibodies in complex with pathological tau, we show that microglia internalise and degrade tau in a manner that is dependent on FcγR interaction and functional lysosomes. It has recently been discussed if anti-tau antibody effector-functions are required for induction of tau clearance. Using antibodies with compromised FcγR binding and non-compromised control antibodies we show that antibody effector functions are required for induction of microglial clearance of tau. Understanding the inflammatory consequences of targeting microglia using therapeutic antibodies is important when developing these molecules for clinical use. Using RNA sequencing, we show that treatment with anti-tau antibodies increases transcription of mRNA encoding pro-inflammatory markers, but that the mRNA expression profile of antibody-treated cells differ from the profile of LPS activated microglia. We further demonstrate that microglia activation alone is not sufficient to induce significant tau clearance.

Highlights

Tauopathies such as Alzheimer’s disease, frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), and progressive supra-nuclear palsy (PSP) are diseases characterised by the intra-neuronal spreading of pathological forms of the microtubule associated protein tau through anatomically connected areas of the brain[1,2,3]
We showed that immune complexes resulted in transcriptional up-regulation of mRNA encoding the marker of early endosomes (Eea 1) in a manner that depended on FcR interaction indicating uptake through the endolysosomal pathway (Fig. 4I)
To validate the findings and to indicate if ubiquitin-mediated degradation could be involved in antibody-mediated tau clearance, we investigated the mRNA levels of Ubiquitin-Binding Domain (UBD) adaptor proteins known to link ubiquitin-bound substrates to proteasomal and autophagosomal degradation[37]

Summary

Introduction

Tauopathies such as Alzheimer’s disease, frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), and progressive supra-nuclear palsy (PSP) are diseases characterised by the intra-neuronal spreading of pathological forms of the microtubule associated protein tau through anatomically connected areas of the brain[1,2,3]. The physiological role of tau is to stabilise the dynamic microtubule scaffold which requires frequent re-organization as part of a range of cellular homeostatic processes such as axonal transport and maintenance of cellular morphology as well as during neuronal development and synaptogenesis[4,5,6,7,8]. This requires interactions with microtubules dynamically regulated, in part, by phosphorylation of tau at several identified phosphorylation sites in the protein reducing its affinity for microtubules[2,9,10]. These markers are associated with microglial activation, this term should be used with caution as the microglia activation is not an all/nothing response, but rather covers a spectrum of activation patterns[27,28]

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