Long-term tracking of endoplasmic reticulum autophagy by a fluorescent probe with a long alkyl chain

Autophagy is a process through which cytoplasmic materials are degraded in lysosome. It is critical in the maintenance of cellular homeostasis. Thus, visualization and tracking of the autophagy is very important for understanding complex intracellular events. To monitor autophagy, various specific fluorescent probes to organelles are often used, such as mitochondria probes for mitophagy, lipid droplets probes for lipophagy. However, an endoplasmic reticulum (ER) probe for ER-phagy is still lack and challenging. Herein, we presented an ER fluorescent probe (HTMP-16) with a long alkyl chain. By strong hydrophobic interaction between the long alkyl chain and the lipid bilayers in ER, HTMP-16 can exclusively locate in the ER for a long time. At the same time, HTMP-16 exhibits excellent self-delivery to living cell, which is a prerequisite of a tracking probe. Furthermore, utilizing HTMP-16, in-situ and real-time long-term tracking of ER-phagy has been realized in living cells. Besides, considering its high sensitivity to viscosity, HTMP-16 can visualize the viscous changes of ER induced by temperature changes or tunicamycin.