P2RX7 inhibitor suppresses exosome secretion and disease phenotype in P301S tau transgenic mice

Zhi Ruan,Jean-Christophe Delpech,Tsuneya Ikezu,Jianqiao Hu,Seiko Ikezu,Srinidhi Venkatesan Kalavai,Alicia A Van Enoo

doi:10.1186/s13024-020-00396-2

Abstract

BackgroundNeuronal accumulation of misfolded microtubule-associated protein tau is a hallmark of neuropathology in Alzheimer’s disease, frontotemporal dementia, and other tauopathies, and has been a therapeutic target. Microglia can spread tau pathology by secreting tau-containing exosomes, although the specific molecular target is yet to be identified for the therapeutic intervention. P2X purinoceptor 7 (P2RX7) is an ATP-gated cation channel, enriched in microglia and triggers exosome secretion. The purpose of the study is to examine the therapeutic effect of an orally applicable, CNS-penetrant P2RX7 specific inhibitor on the early disease stage of a tauopathy mouse model.MethodsThree-months-old P301S tau mice were treated with P2RX7-specific inhibitor GSK1482160 or vehicle for 30 days, followed by behavioral, biochemical and immunohistochemical assessment. GSK1482160 was also tested for exosome secretion from primary cultured murine astrocytes, neurons and microglia in vitro.ResultsOral administration of GSK1482160 significantly reduced accumulation of MC1+ and Alz50+ misfolded tau in hippocampal regions, which was accompanied with reduced accumulation of Tsg101, an exosome marker, in hippocampal neurons. Proximity ligation assay demonstrated complex formation of Alz50+ tau and Tsg101 in hippocampal neurons, which was reduced by GSK1482160. On the other hand, GSK1482160 had no effect on microglial ramification or CD68 expression, which was significantly enhanced in P301S mice, or pro/anti-inflammatory cytokine gene expression. Strikingly, GSK1482160-treated P301S mice show significantly improved working and contextual memory as determined by Y-maze and fear conditioning tests. GSK1482160 also significantly increased accumulation of Tsg101 and CD81 in microglia in vivo, suggesting its suppression of P2RX7-induced exosome secretion from microglia. This effect was confirmed in vitro, as ATP-induced secretion of tau-containing exosome was significantly suppressed by GSK1482160 treatment from primary murine microglia, but not from neurons or astrocytes.DiscussionThe oral administration of P2RX7 inhibition mitigates disease phenotypes in P301S mice, likely by suppressing release of microglial exosomes. P2RX7 could be a novel therapeutic target for the early stage tauopathy development.

Highlights

Neuronal accumulation of misfolded microtubule-associated protein tau is a hallmark of neuropathology in Alzheimer’s disease, frontotemporal dementia, and other tauopathies, and has been a therapeutic target
Among many possible molecules regulating exosome release, we focused on P2X purinoceptor 7 (P2RX7), an ATP-evoked Na+/Ca2+ channel predominantly expressed in microglia [4]
Pharmacological blockade of P2RX7 decreases accumulation of misfolded tau aggregates in P301S mouse brain To determine the effect of pharmacological blockade of P2RX7 on tau pathology development in P301S mice, we performed immunohistochemistry (IHC) and biochemical analysis of tau pathology after GSK1482160 or vehicle administration from 3 months of age for 30 days

Summary

Introduction

Neuronal accumulation of misfolded microtubule-associated protein tau is a hallmark of neuropathology in Alzheimer’s disease, frontotemporal dementia, and other tauopathies, and has been a therapeutic target. The innate immune cells in the central nervous system (CNS), play a pivotal role in spreading tau by releasing exosomes, small extracellular vesicles (EVs: 50–150 nm), which contain and transfer pathological tau in the tauopathy mouse model [1]. Other groups demonstrated that exosomes isolated from a different tau mouse model can spread tau pathology after intracranial injection into the recipient mice [2] and AD-associated BIN1 is critical in microglia-mediated spread of tau pathology via exosome secretion [3]. These evidences support the idea that targeting specific molecules to suppress exosome secretion from microglia may lead to halt tau propagation. The role of P2RX7 has never been examined in the context of tau spread through exosome secretion in tauopathy animal models

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