Tau toxicity is gated through the 306VQIVYK311 domain but through mechanisms not entirely dependent on Tau aggregation

Disease-modifying therapies for Tauopathies like Alzheimer’s disease have targeted Tau hyperphosphorylation and aggregation, as both pathological manifestations are implicated in Tau-mediated toxicity. More recently there has been a renewed interest in Tau conformation which appears to influence its toxic potential. However, the impact of Tau hyper-phosphorylation on its eventual conformation and toxic potential is less well known. Leveraging the genetic tractability of Drosophila , we generated multiple inducible human Tau transgenes with altered phosphorylation status and/or aggregation propensity. Their individual and combined impact was tested in vivo by quantifying Tau misfolding, accumulation and neurodegeneration in the aging fly nervous system. Results showed that phospho-mimicking Tau (hTau2N4R ^E14 ) induced profound neurodegeneration, supporting a neurotoxic role for phosphorylation. However, deletion of the aggregation-promoting ³⁰⁶ VQIVYK ³¹¹ motif in the microtubule-binding region altered the conformation of Tau and neurotoxicity was completely abolished. Intriguingly, overt aggregation of Tau into large filaments, detectable as high molecular weight species in biochemical preps, was not significantly reduced. Moreover, a peptide inhibitor targeting this same motif, that we have previously shown to promote off-pathway Tau aggregation, efficaciously reduced Tau-mediated behavioural deficits in aging Drosophila . Collectively we show that neurodegeneration mediated by Tau hyper-phosphorylation is gated via at least one aggregation-promoting motif of the protein, whether through a direct impact on Tau aggregation or through suppression of other mechanisms of toxicity mediated through this domain. Targeting the ³⁰⁶ VQIVYK ³¹¹ domain reduces the ability of hyper-phosphorylated Tau species to acquire the pathological conformation responsible for inducing neurotoxicity. This highlights the primacy of blocking the ³⁰⁶ VQIVYK ³¹¹ domain of Tau to alter Tau conformation, in emerging therapeutics, perhaps without the need to clear phosphorylated species.