Extracellular tau induces microglial phagocytosis of living neurons in cell cultures. Issue 3 (29th December 2019)

• Record Type: Journal Article
• Authors: Pampuscenko, Katryna; Morkuniene, Ramune; Sneideris, Tomas; Smirnovas, Vytautas; Budvytyte, Rima; Valincius, Gintaras; Brown, Guy C.; Borutaite, Vilmante
• Is Part Of: Journal of neurochemistry. Volume 154:Issue 3(2020)
• Page Start: 316
• Page End: 329
• Publication Date: 2019-12-29
• Subjects: Alzheimer's disease -- cell death -- neuroinflammation -- phagocytosis -- tau protein; Neurochemistry -- Periodicals; 616.8042
• DOI: 10.1111/jnc.14940
• Languages: English
• ISSNs: 0022-3042

Abstract

Abstract: Tau is a microtubule‐associated protein, found at high levels in neurons, and its aggregation is associated with neurodegeneration. Recently, it was found that tau can be actively secreted from neurons, but the effects of extracellular tau on neuronal viability are unclear. In this study, we investigated whether extracellular tau 2N4R can cause neurotoxicity in primary cultures of rat brain neurons and glial cells. Cell cultures were examined for neuronal loss, death, and phosphatidylserine exposure, as well as for microglial phagocytosis by fluorescence microscopy. Aggregation of tau 2N4R was assessed by atomic force microscopy. We found that extracellular addition of tau induced a gradual loss of neurons over 1–2 days, without neuronal necrosis or apoptosis, but accompanied by proliferation of microglia in the neuronal‐glial co‐cultures. Tau addition caused exposure of the 'eat‐me' signal phosphatidylserine on the surface of living neurons, and this was prevented by elimination of the microglia or by inhibition of neutral sphingomyelinase. Tau also increased the phagocytic activity of pure microglia, and this was blocked by inhibitors of neutral sphingomyelinase or protein kinase C. The neuronal loss induced by tau was prevented by inhibitors of neutral sphingomyelinase, protein kinase C or the phagocytic receptor MerTK, or by eliminating microglia from the cultures. The data suggest that extracellular tau induces primary phagocytosis of stressed neurons by activated microglia, and identifies multiple ways in which the neuronal loss induced by tau can be prevented. Abstract : Microtubule‐associated protein tau is found in neurons, but can be also secreted. Effects of extracellular tau on neuronal viability are not clear. We show here that extracellular addition of tau stimulated phagocytic activity of microglia and caused microglia‐dependent exposure of phosphatidylserine on neurons leading to loss of neurons in mixed neuronal‐glial cultures prepared from rats' cerebella. Inhibitors of protein kinase C (Ro 32–0432) and neutral sphingomyelinase (GW4869) blocked tau‐induced phagocytic activity of microglia. In neurons, GW4869 blocked phosphatidylserine exposure. Both inhibitors, as well as Mer‐tyrosine‐kinase inhibitor UNC569 or elimination of microglia prevented extracellular tau‐induced neuronal loss. The data suggest that extracellular tau induces primary phagocytosis of stressed neurons by activated microglia, and identifies multiple ways in which the neuronal loss induced by tau can be prevented.