Microenvironmental Fingerprint of Maturing Tau Condensates from Spectral and Lifetime Phasor Analysis of a Solvatochromic Dye

In a study published in <source f3323c55-3ff>, researchers unveiled a novel multimodal phasor-based framework for imaging the changes in solvatochromic dye ACDAN's microenvironment during the progression of liquid-liquid phase-separated Tau condensates. This framework combines spectral and lifetime analysis to provide a comprehensive view of the dye's response to the varying environments within the assemblies.

The solvatochromic dye ACDAN demonstrated distinct spectral characteristics when exposed to water, glycerol, and ethanol, which indicates that each solvent influenced the dye's excited-state behavior differently. Its fluorescence lifetime, however, distinguished water from the organic solvents but did not differentiate glycerol from ethanol, suggesting that the two observables respond to the same environmental change in disparate ways.

When the researchers applied the ACDAN framework to well-characterized Tau condensates, they observed a gradual decrease in the dye's spectral phasor angle and an increase in its phase-derived lifetime over time. This suggests that the microenvironments within the Tau assemblies are becoming more restricted as the maturation process advances. By 4 hours after incubation, differences between the condensates became apparent, and by 48 hours, pronounced spatial heterogeneity was observed within the assemblies.

Interestingly, the researchers found that when using the fluorogenic probe Thioflavin T, the dye predominantly responded to its environment through its fluorescence lifetime, with only minor spectral changes. In contrast, ACDAN reported microenvironmental changes in both coordinates, providing a more comprehensive understanding of the dye's response.

In conclusion, the study demonstrates that the multimodal framework successfully characterizes the changes in the fluorescence response of ACDAN across Tau assembly maturation while preserving their spatial distribution. This approach offers a powerful tool for understanding the complex behavior of solvatochromic dyes within liquid-liquid phase-separated systems.