Endoplasmic reticulum stress and autophagy contribute to cadmium-induced cytotoxicity in retinal pigment epithelial cells

Excessive accumulation of cadmium (Cd) in retina plays an important role in tobacco smoking-associated age-related macular degeneration (AMD). Plenty of evidence has revealed that the retinal pigment epithelium (RPE) is the primary site of pathology in AMD. Our current study demonstrated that Cd induced apoptosis in a human RPE cell line ARPE-19 cells, as it dose-dependently caused cell viability loss and activated caspase-3. The reactive oxygen species (ROS) were confirmed to be important mediators for Cd-triggered cell death in ARPE-19 cells. We found that endoplasmic reticulum (ER) stress was activated as its marker BiP was remarkably upregulated by Cd-exposure. Whereas the antioxidants N-acetylcysteine (NAC) and Tempol significantly suppressed the expression of BiP and CHOP, suggesting that ROS generation is an early trigger of Cd-activated ER stress. Furthermore, we found that Cd-induced oxidative stress significantly increased autophagic flux and p62 expression. A temporal impact of Cd exposure is possibly existed in p62 expression in ARPE-19 cells. Moreover, an ER stress inhibitor salubrinal diminished Cd-induced LC3BII expression and attenuated cytotoxicity, indicating that ER stress mediates autophagy and was implicated in apoptosis of Cd-exposed ARPE-19 cells. However, CHOP expression may not exert impact on the regulation of Cd-caused autophagy. Additionally, inhibition of autophagy with si-Beclin 1 and 3-Methyladenine significantly ameliorated Cd-induced CHOP expression and cytotoxicity, indicating that autophagy was detrimental in Cd-accumulated ARPE-19 cells, and a positive feedback regulation mechanism may exist between Cd-triggered ER stress and autophagy. Taken together, these results suggest that Cd-caused ER stress and autophagy are implicated in RPE cell death associated retinopathies especially related to smoking.