Protective Mechanism of Berberine on Human Retinal Pigment Epithelial Cells against Apoptosis Induced by Hydrogen Peroxide via the Stimulation of Autophagy

Age-related macular degeneration (AMD) is a major cause of severe and irreversible vision loss with limited effective therapies. Diminished autophagy and increased oxidative damage caused by ROS in the retinal pigment epithelium (RPE) have been implicated in the pathogenesis of AMD, and strategies aimed at enhancing autophagy are likely to protect these cells from oxidative damage. We have previously shown that berberine (BBR), an isoquinoline alkaloid isolated from Chinese herbs, was able to protect human RPE cells from H(2)O(2)-induced oxidative damage through AMPK activation. However, the precise mechanisms behind this protective effect remain unclear. Given the essential role of AMPK in autophagy activation, we postulated that BBR may confer protection against H(2)O(2)-induced oxidative damage by stimulating AMPK-dependent autophagy. Our results showed that BBR was able to induce autophagy in D407 cells, whereas autophagy inhibitor PIKIII or silencing of LC3B blocked the protective effect of BBR. Further analysis showed that BBR activated the AMPK/mTOR/ULK1 signaling pathways and that both pharmacological and genetic inhibitions of the AMPK pathway abolished the autophagy-stimulating effect of BBR. Similar results were obtained in primary cultured human RPE cells. Taken together, these results demonstrate that BBR is able to stimulate autophagy in D407 cells via the activation of AMPK pathway and that its protective effect against H(2)O(2)-induced oxidative damage relies on its autophagy-modulatory effect. Our findings also provide evidence to support the potential application of BBR in preventing and treating AMD.