Biphasic Cellular Response Triggered by Tetrandrine-Mediated Dysfunction and Lysophagic Clearance of Lysosomes.

Lysosomes play an important role in the degradation of cellular components and are correlated with various other physiological phenomena. Lysophagy is a cellular quality control system that maintains homeostasis by removing damaged lysosomes through autophagy. The involvement of lysosomal dysfunction in the pathogenesis of certain illnesses (e.g., neurodegeneration) highlights the potential of small molecules that regulate lysophagy as drug candidates. Here, we found that tetrandrine, a bis-benzylisoquinoline alkaloid, induces lysophagy, leading to the clearance of damaged lysosomes in mammalian cells. To visualize the target organelles of tetrandrine, we synthesized a chimeric compound in which tetrandrine was connected to boron-dipyrromethene via a polyethylene glycol linker. Flow cytometry analysis confirmed the cellular uptake of the synthesized probe. An organelle-staining assay showed that the fluorescent signal of the probe was specifically colocalized with lysosomes. Tetrandrine transiently increased the lysosomal pH level, which returned to normal at 24 h post treatment. Consistently, the level of mCherry-tagged galectin-3, a marker protein for lysophagy, transiently increased and then diminished under treatment with tetrandrine. Tetrandrine also induced dephosphorylation of transcription factor EB, a regulator of lysosomal biogenesis, promoting its translocation from the cytosol to the nucleus. These results suggest that tetrandrine induces a biphasic cellular response, first disrupting lysosomal function before facilitating cellular lysosomal homeostasis through lysophagy and lysosomal biogenesis. This dual effect distinguishes tetrandrine from existing lysosomal modulators.