**Josephine C. Ferreon 1,\*, Antrix Jain 2, Kyoung-Jae Choi 1, Phoebe S. Tsoi 1, Kevin R. MacKenzie 1,3, Sung Yun Jung <sup>4</sup> and Allan Chris Ferreon 1,\***


Received: 8 April 2018; Accepted: 2 May 2018; Published: 4 May 2018

**Abstract:** Neuropathological aggregates of the intrinsically disordered microtubule-associated protein Tau are hallmarks of Alzheimer's disease, with decades of research devoted to studying the protein's aggregation properties both in vitro and in vivo. Recent demonstrations that Tau is capable of undergoing liquid-liquid phase separation (LLPS) reveal the possibility that protein-enriched phase separated compartments could serve as initiation sites for Tau aggregation, as shown for other amyloidogenic proteins, such as the Fused in Sarcoma protein (FUS) and TAR DNA-binding protein-43 (TDP-43). Although truncation, mutation, and hyperphosphorylation have been shown to enhance Tau LLPS and aggregation, the effect of hyperacetylation on Tau aggregation remains unclear. Here, we investigate how the acetylation of Tau affects its potential to undergo phase separation and aggregation. Our data show that the hyperacetylation of Tau by p300 histone acetyltransferase (HAT) disfavors LLPS, inhibits heparin-induced aggregation, and impedes access to LLPS-initiated microtubule assembly. We propose that Tau acetylation prevents the toxic effects of LLPS-dependent aggregation but, nevertheless, contributes to Tau loss-of-function pathology by inhibiting Tau LLPS-mediated microtubule assembly.

**Keywords:** intrinsically disordered protein; membrane-less organelle; neurodegenerative disease; p300 HAT acetylation; post-translational modification; protein aggregation; Tau fibrillation
