Engineering Organelle-Specific Molecular Viscosimeters Using Aggregation-Induced Emission Luminogens for Live Cell...

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Imaging

Background:

• Subcellular viscosity is a critical indicator of cellular health and function.
• Existing methods for measuring intracellular viscosity are limited.
• Tetraphenylethene (TPE) derivatives offer potential for developing advanced fluorescent probes.

Purpose of the Study:

• To engineer novel tetraphenylethene (TPE)-based fluorescent probes for selective measurement of viscosity in mitochondria and lysosomes.
• To characterize the optical properties of these probes in vitro and in living cells.
• To investigate changes in organelle viscosity during cellular processes like mitophagy.

Main Methods:

• Synthesis and characterization of two TPE-based fluorescent probes, one with mitochondrial specificity (pyridinium group) and another with lysosome-targeting ability (indole ring).
• Evaluation of probe fluorescence response to varying viscosity in vitro.
• In situ imaging of mitochondrial and lysosomal viscosity in living cells under stimulated conditions.
• Monitoring viscosity changes during mitophagy using the developed probes.

Main Results:

• The engineered TPE probes exhibit weak emission in low-viscosity environments and significantly enhanced emission in high-viscosity environments due to restricted intramolecular motion.
• The pyridinium-containing probe demonstrated mitochondrial specificity, while the indole-containing probe targeted lysosomes.
• The probes successfully visualized viscosity variations in mitochondria and lysosomes in living cells.
• A novel finding revealed an increase in both mitochondrial and lysosomal viscosity during mitophagy.

Conclusions:

• Tetraphenylethene (TPE) has been successfully engineered into specific fluorescent molecular viscosimeters for mitochondria and lysosomes.
• These probes offer desirable properties including aqueous solubility, red-shifted emission, and organelle specificity.
• The study provides the first direct evidence of increased mitochondrial and lysosomal viscosity during mitophagy, offering new insights into this cellular process.