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.