An FRET-based and ER-targeting fluorescent probe for tracking superoxide anion (O2•−) in the hippocampus of the depressive mouse

Exploration of the pathway for the excessive generation of O2•− in hippocampus during depression is critical for the study on molecular mechanism of depression, and is currently still inconclusive. Herein, we put forward a hypothesis that depression increases the generation of O2•− in hippocampus by triggering ER stress, and verified this hypothesis by constructing an FRET-based ER-targeting fluorescent probe (ER-CRh) which can provide ratiometric detection of O2•− with high sensitivity and selectivity. The probe ER-CRh showed desirable ER-targeting capability, and could detect the endogenous O2•− in the ER of the hippocampal neuronal cells experiencing ER stress. Fluorescence imaging indicates that ER-CRh possesses the capability to penetrate the blood-brain barrier in mouse, and depression could promote the production of endogenous O2•− in hippocampus. Western blotting analysis reveals that the proteins GRP78 and CHOP from the hippocampus of depressive mouse show an up-regulated expression, and it suggests depression causes ER stress in hippocampal neurons. These findings prove our hypothesis, and could conduce to develop safe and effective antidepressants by the protection and repair of hippocampal neurons.