4-Amino-3′,4′-dihydroxychalcone Increases Tau Dynamics in Phase-Separated Droplets and Inhibits Tau Aggregation

The aggregation of the microtubule-associated protein tau is a distinctive characteristic of several neurodegenerative disorders like Alzheimer's disease and frontotemporal dementia. Small-molecule inhibitors have been investigated as a potential therapy for tau aggregation-related diseases. Here, we identified 4-Amino-3',4'-dihydroxychalcone (4-ADHC), a substituted aminochalcone, as an inhibitor of different stages of tau aggregation, namely, liquid-liquid phase separation, oligomerization, and filamentation. Size exclusion chromatography, absorbance, and fluorescence spectroscopic experiments suggested that 4-ADHC bound to purified tau. The dissociation constant for the binding of 4-ADHC to tau was determined to be 5.1 ± 0.8 μM using surface plasmon resonance. The compound potently inhibited heparin and arachidonic acid-induced tau aggregation in vitro. However, 4-ADHC neither inhibited tubulin polymerization nor the enzymatic activity of alcohol dehydrogenase and alkaline phosphatase. Fluorescence recovery after photobleaching experiments showed that 4-ADHC increased tau dynamics in phase-separated droplets, suggesting that the compound impeded the maturation of the droplets by increasing their liquid-like behavior. Further, atomic force microscopy, dot blot assay, and dynamic light scattering experiments demonstrated that the compound suppressed tau oligomerization. In addition, 4-ADHC inhibited tau filamentation and disaggregated preformed filaments. Thus, 4-ADHC is a candidate for developing potent tau aggregation inhibitors.