Thioflavin T indicates mitochondrial membrane potential in mammalian cells

Area of Science:

• Biophysics
• Cell Biology
• Biochemistry

Background:

• Thioflavin T (ThT) is a fluorescent dye commonly used to detect protein aggregates in neurodegenerative disease research.
• Recent studies suggest ThT can also indicate membrane potential in bacteria due to its cationic properties.

Purpose of the Study:

• To investigate if ThT fluorescence is linked to mitochondrial membrane potential in mammalian cells.
• To determine the implications of ThT's interaction with mitochondrial membrane potential for its use in live-cell imaging.

Main Methods:

• Localization studies of ThT in HeLa cells using confocal microscopy.
• Co-localization with tetramethylrhodamine methyl ester (TMRM), a known mitochondrial membrane potential indicator.
• Assessment of ThT and TMRM responses to FCCP, a protonophore, to evaluate membrane potential changes.
• Investigating the effect of ThT concentration and blue light exposure on mitochondrial membrane potential.
• Mathematical modeling to understand ThT's photosensitization effect.

Main Results:

• ThT localizes to mitochondria in HeLa cells in a manner dependent on mitochondrial membrane potential.
• ThT fluorescence intensity and temporal responses mirrored TMRM under FCCP treatment.
• A combination of ThT and blue light (405 nm) caused mitochondrial membrane potential depolarization.
• This depolarization effect was additive, depending on both ThT concentration and light intensity.
• Mathematical modeling supported the observed photosensitization mechanism.

Conclusions:

• ThT can function as a mitochondrial membrane potential indicator in mammalian cells under specific conditions (low concentration, low light).
• ThT's use at micromolar concentrations with blue light requires re-evaluation due to potential mitochondrial depolarization.
• This study highlights ThT's utility for future research on mitochondrial membrane potential dynamics and its links to protein aggregation.