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.

IntroductionThe abnormal hyperphosphorylation of the microtubule-associated protein tau plays a crucial role in neurodegeneration in Alzheimer's disease (AD) and other tauopathies.MethodsHighly specific and selective anti-pS396-tau antibodies have been generated using peptide immunization with screening against pathologic hyperphosphorylated tau from rTg4510 mouse and AD brains and selection in in vitro and in vivo tau seeding assays.ResultsThe antibody C10.2 bound specifically to pS396-tau with an IC50 of 104 pM and detected preferentially hyperphosphorylated tau aggregates from AD brain with an IC50 of 1.2 nM. C10.2 significantly reduced tau seeding of P301L human tau in HEK293 cells, murine cortical neurons, and mice. AD brain extracts depleted with C10.2 were not able to seed tau in vitro and in vivo, demonstrating that C10.2 specifically recognized pathologic seeding-competent tau.DiscussionTargeting pS396-tau with an antibody like C10.2 may provide therapeutic benefit in AD and other tauopathies.