Astragalus polysaccharide protects photoreceptors from hypoxic injury via a multi-mechanism network involving mitochondrial stabilization and enhanced autophagy.

BACKGROUND: Retinal hypoxia contributes to photoreceptor death in multiple blinding diseases. Astragalus polysaccharide (APS) exhibits broad bioactivity, but its protection against hypoxic photoreceptor injury remains unclear. OBJECTIVE: This study evaluated the cytoprotective effect and mechanism of APS in hypoxic 661W photoreceptor cells, focusing on oxidative stress, mitochondrial function, apoptosis, and autophagy. METHODS: 661W cells were cultured under normoxia (21% O2) or hypoxia (2% O2) with or without APS (100-2000 μg/mL). Cell viability, cytotoxicity, reactive oxygen species (ROS) levels, and mitochondrial membrane potential (ΔΨm) were assessed by Cell Counting Kit-8 (CCK-8), lactate dehydrogenase (LDH), DCFH-DA, and JC-1 assays. Apoptosis was detected by TUNEL staining. HIF-1α, Bcl-2, Bax, cleaved caspase-3, AIF, and LC3 were analyzed by Western blotting. RESULTS: Under normoxia, APS ≤1000 μg/mL was non-cytotoxic, whereas 2000 μg/mL induced toxicity. Under hypoxia, APS significantly attenuated hypoxia-induced cell death in a concentration-dependent manner, with optimal protection observed at 1000 μg/mL, and the protective effect was more pronounced at 24-48 h than at 72 h. Mechanistically, APS reduced intracellular ROS levels, preserved ΔΨm, attenuated hypoxia-induced HIF-1α accumulation, inhibited both caspase-dependent and AIF-mediated apoptotic pathways, and enhanced autophagy. CONCLUSION: APS protects photoreceptors against acute hypoxic injury through a multi-target mechanism modulating oxidative stress, mitochondrial stabilization, dual apoptosis inhibition, and autophagy activation, with a concentration-dependent safety profile. However, its benefit is limited under prolonged hypoxia, suggesting its potential applicability in acute retinal hypoxic conditions.