Ratiometric fluorescence imaging of lysosomal Zn²⁺ release under oxidative stress in neural stem cells

Zinc dyshomeostasis is a major mechanism of neuronal death, which is involved in many different neuropathological conditions. Lysosomal membrane permeabilisation has an important function in zinc-induced neuronal death under oxidative stress. To investigate lysosomal zinc functions in neurons with high spatial and temporal reliability, we report a ratiometric probe, LysoZn-1. It is derived from the styryl-BODIPY-DPA scaffold with a lysosome-targeted 2-morpholinoethylamine moiety to allow localisation in lysosomes. The electron donor at the meso-position of the BODIPY fluorophore makes the present probe prefer complexing with Zn²⁺ rather than Cd²⁺, which can be explained by HSAB (Hard-Soft Acid-Base) theory and was confirmed by Gaussian calculation. Upon Zn²⁺ binding, LysoZn-1 exhibits obvious fluorescence enhancement (F_578 nm) and ratio (F_578 nm/F_680 nm) changes. The emission intensities of LysoZn-1 and LysoZn-1 + Zn²⁺ do not change significantly under lysosomal pH ranging from 4.5 to 6.0. Confocal imaging experiments indicate that LysoZn-1 is able to localise to lysosomes in neural stem cells (NSCs), MCF-7 and Hela cells and detect exogenous Zn²⁺ levels in NSCs and MCF-7 cells. LysoZn-1 function is not disturbed by chloroquine in living cells. Furthermore, increases in lysosomal Zn²⁺ concentration upon H₂O₂ stimulation in NSCs are observed using LysoZn-1.