Synergistic MAPT mutations as a platform to uncover modifiers of tau pathogenesis

The natively unfolded tau protein is extremely soluble, which poses challenges when modeling neurofibrillary tangle (NFT) pathology in Alzheimers disease (AD). To overcome this hurdle, we combined P301L and S320F mutations (PL-SF) to generate a rapid and reliable platform to expedite the discovery of factors that modulate tau aggregation. Using this model, we evaluated heat-shock proteins (Hsp), traditionally linked to tau pathology, but whose role in AD remains enigmatic and controversial. In primary neurons, expression of Hsp70, but not Hsc70 or Hsp90, exacerbated tau aggregation. Conversely, lowering of Hsp70 by shRNA or a chaperone-deficient tau mutant (PL-SF-4delta) reduced tau phosphorylation and abrogated tau aggregation, highlighting Hsp70 as a key driver of tau aggregation. Functionally, mature aggregate-bearing neurons showed deficits in neuronal firing and network communication, while chaperone-binding deficient tau variants displayed reduced tau pathology and restored network properties. This study provides a powerful cell intrinsic model for accelerated tau aggregation, which can be harnessed to identify regulators of tau aggregation as promising therapeutic targets.