Constant Conversion Rate of Endolysosomes Revealed by a pH-Sensitive Fluorescent Probe

Endolysosome dynamics plays an important role in autophagosome biogenesis. Hence, imaging the subcellular dynamics of endolysosomes using high-resolution fluorescent imaging techniques would deepen our understanding of autophagy and benefit the development of pharmaceuticals against endosomerelated diseases. Taking advantage of the intramolecular charge transfer mechanism, herein we report a cationic quinolinium-based fluorescent probe (PyQPMe) that exhibits excellent pH-sensitive fluorescence in endolysosomes at different stages of interest. A systematic photophysical and computational study on PyQPMe was carried out to rationalize its highly pH-dependent absorption and emission spectra. The large Stokes shift and strong fluorescence intensity of PyQPMe can effectively reduce the background noise caused by excitation light and microenvironments and provide a high signal-to-noise ratio for high-resolution imaging of endolysosomes. By applying PyQPMe as a small molecular probe in live cells, we were able to reveal a constant conversion rate from early endosomes to late endosomes/lysosomes during autophagy at the submicron level.

Automated summary

Endolysosome dynamics is crucial for autophagosome biogenesis. A cationic quinolinium-based fluorescent probe (PyQPMe) with pH-sensitive fluorescence in endolysosomes is reported here, enabling high-resolution imaging and deepening understanding of autophagy. The probe's large Stokes shift and strong fluorescence intensity reduce background noise, providing a high signal-to-noise ratio for imaging. Application of PyQPMe revealed a constant conversion rate from early to late endosomes/lysosomes during autophagy at the submicron level.