Discovery of aloe-emodin as an antidepressant agent by targeting RANBP9

Excitotoxicity is a core pathological mechanism underlying various neurological disorders, including depression. It is primarily driven by the overactivation of NMDA receptors and disruption of calcium homeostasis. However, effective therapeutic interventions targeting this process remain limited. In this study, aloe-emodin was shown to reverse NMDA-induced reduction in cell viability, apoptosis, and calcium overload in a dose-dependent manner, while also attenuating NMDA-induced autophosphorylation of CaMKII. In a chronic unpredictable mild stress (CUMS) model, aloe-emodin significantly ameliorated depression-like behaviors, suppressed inflammatory responses and oxidative stress, and downregulated the expression of cleaved-PARP. By conducting biotin pull-down coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis, cellular thermal shift assay (CETSA), drug affinity responsive target stability (DARTS) analysis, and surface plasmon resonance (SPR) analysis, RANBP9 was identified as a direct molecular target of aloe-emodin, with a binding affinity (KD) of 716 nM. Molecular docking and molecular dynamics simulations revealed that aloe-emodin selectively binds to the His332 residue of RANBP9. Aloe-emodin promoted the degradation of RANBP9 via the ubiquitin-proteasome pathway by facilitating the interaction between RANBP9 and the E3 ligase CHIP. After RANBP9 was knocked down, the protective effects of aloe-emodin on cell viability and apoptosis were significantly weakened, confirming that the anti-excitotoxic activity of aloe-emodin is RANBP9-dependent. These findings collectively demonstrate that aloe-emodin is a novel and potent RANBP9-targeting compound with antidepressant activity and suggest that RANBP9 may serve as a promising target for developing antidepressant drugs.