Ratiometric probe with optimized permeability for visualizing lysosomal acidification during autophagy

Abstract

Lysosomal pH plays indispensable roles in regulating the activity of lysosomal hydrolases, and is involved in crucial biological procedures including autophagy. Fluorescent probes for lysosomal pH were significant molecular tools to investigate lysosomal pH regulation. In this work, we have designed a new fluorophore to respond to pH in a ratiometric manner based on intramolecular charge transfer (ICT) mechanism. By modifying different alkyl chains on the dye, we have obtained a novel ratiometric probe for lysosomal pH with optimized membrane permeability. The probe could stain lysosomes, and was capable of monitoring lysosomal pH in a ratiometric manner. Chloroquine (CQ) induced pH rise in lysosomes was successfully visualized with the probe. The down-regulation and subsequence up-regulation of lysosomal pH during starvation were also revealed in ratiometric manner. We firmly believe that the probe is a desirable tool to investigate lysosomal pH and promote the studies in autophagy and relative biological areas.