Objective  Melatonin has been demonstrated an ability to protect retinal cells from oxidative injury ,so it is considered as a potential drug for the treatment of several retinal diseases including age-related macular degeneration(AMD) and diabetic retinopathy(DR).Therefore, a better understanding of the signaling pathway mediates the effect of melatonin is of great importance. The PI3k pathway has been reported to regulate Nrf2-dependent antioxidant response in retinal epithelium. This research was conducted to investigate whether the PI3k/Akt-Nrf2 signaling pathway also plays a major role in the protection of melatonin.

Methods  Cultured retinal müller cells were treated with high glucose culture medium and different concentrations of melatonin for various time points. PI3k inhibitor LY294002 and melatonin receptor antagonist Luzindole were used under the administration of melatonin. Distribution of melatonin membrane receptors MT1 and MT2, and nuclear translocation of Nrf2 were detected by immunocytochemistry. Expression of MT1, MT2, Nrf2, HO-1 and Akt phosphorylation were measured by quantitative RT-PCR and Western Blot analyses.

Results  Both of the melatonin membrane receptors could be found in retinal müller cells. Expressions of MT1, MT2 and HO-1 were elevated under high glucose treatment. Akt phosphorylation, HO-1 expression and Nrf2 nuclear translocation were induced by melatonin in a dose-dependent manner, while the effects were decreased significantly by LY294002 or Luzindole.

Conclusion  Melatonin augments cellular antioxidant defense capacity through receptor-dependent HO-1 induction via the PI3K/Akt-Nrf2 signaling pathway, thereby protecting retinal müller cells from oxidative stress.