Astragaloside IV improves the survival rates of retinal ganglion cells in traumatic optic neuropathy by regulating autophagy mediated by the AMPK-MTOR-ULK signaling pathway.

Abstract

Purpose: Autophagy is involved in the pathological changes of traumatic optic neuropathy (TON), and the regulation of autophagy mediated by the AMPK-mTOR-ULK pathway is a potential therapeutic approach. Astragaloside IV (AS-IV) can regulate autophagy and play a therapeutic role in various diseases. This study aimed to observe the therapeutic effect of astragaloside on TON and the role of AMPK-MTOR-ULK pathway-mediated autophagy in this process.

Methods: After the TON model was established, varying doses of AS-IV were administered as an intervention. Additionally, compound C (an AMPK inhibitor) or 3-methyladenine (an autophagy inhibitor) was administered intraperitoneally in conjunction with AS-IV. Samples were collected following a 7-day intervention period. Western blot analysis was conducted to measure the protein and phosphorylation levels of AMPK, mTOR, and ULK proteins. Moreover, western blot and quantitative reverse transcription PCR assays were used to quantify LC3 levels in retinal tissue. LC3 immunofluorescence was performed to examine autophagy levels in the ganglion cell layer (GCL), while transmission electron microscopy was employed to observe autophagosomes. Additionally, BRN3A immunofluorescence was used to label retinal ganglion cells (RGCs) in the GCL, and terminal deoxynucleotidyl transferase dUTP nick-end labeling staining was used to assess apoptosis within the GCL. Finally, optic nerve conduction function was evaluated using flash visual evoked potentials.

Results: After 7 days, the phosphorylation levels of AMPK, mTOR, and ULK proteins in retinal tissue exhibited significant changes following TON. AS-IV treatment enhanced LC3 messenger RNA and protein levels in TON model rats, and the autophagy-promoting effect of AS-IV was reversed by 3-methyladenine. Moreover, AS-IV elevated P-AMPK and P-ULK levels while decreasing P-mTOR levels. AS-IV also improved the survival rate of RGCs and reduced the P2 peak latency of flash visual evoked potentials. These effects were attenuated by the AMPK inhibitor compound C. Additionally, AS-IV increased the levels of AKT1 and P-AKT1 while decreasing P-S6RP levels in the retinal tissue of TON model rats.

Conclusions: AS-IV can increase the survival rate of RGCs and improve visual function after TON, which may be related to the improvement of autophagy by regulating the AMPK-MTORC1-ULK pathway.