Involvement of Endoplasmic Reticulum Stress in All-Trans-Retinal-Induced Retinal Pigment Epithelium Degeneration

Abstract

Excess accumulation of endogenous all-trans-retinal (atRAL) contributes to degeneration of the retinal pigment epithelium (RPE) and photoreceptor cells, and plays a role in the etiologies of age-related macular degeneration (AMD) and Stargardt's disease. In this study, we reveal that human RPE cells tolerate exposure of up to 5 µM atRAL without deleterious effects, but higher concentrations are detrimental and induce cell apoptosis. atRAL treatment significantly increased production of intracellular reactive oxygen species (ROS) and up-regulated mRNA expression of Nrf2, HO-1, and γ-GCSh within RPE cells, thereby causing oxidative stress. ROS localized to mitochondria and endoplasmic reticulum (ER). ER-resident molecular chaperone BiP, a marker of ER stress, was up-regulated at the translational level, and meanwhile, the PERK-eIF2α-ATF4 signaling pathway was activated. Expression levels of ATF4, CHOP, and GADD34 in RPE cells increased in a concentration-dependent manner after incubation with atRAL. Salubrinal, a selective inhibitor of ER stress, alleviated atRAL-induced cell death. The antioxidant N-acetylcysteine (NAC) effectively blocked RPE cell loss and ER stress activation, suggesting that atRAL-induced ROS generation is responsible for RPE degeneration and is an early trigger of ER stress. Furthermore, the mitochondrial transmembrane potential was lost after atRAL exposure, and was followed by caspase-3 activation and poly (ADP-ribose) polymerase cleavage. The results demonstrate that atRAL-driven ROS overproduction-induced ER stress is involved in cellular mitochondrial dysfunction and apoptosis of RPE cells.

Tunicamycin-induced Endoplasmic Reticulum Stress Upregulates the Expression of Pentraxin 3 in Human Retinal Pigment Epithelial Cells

“…However, in pathologically chronic ER stress, prolonged CHOP expression promotes cell death, and it has been implicated in a number of diseases, including ARMD, neurodegenerative diseases, atherosclerosis, diabetes, and renal disease [27282930]. To investigate the effects of PTX3 knockdown on CHOP expression, we treated control and PTX3 shRNA transfected ARPE-19 cells with tunicamycin (1 µg/mL) and harvested RNA and protein at 6, 12, 24, and 48 hours after treatment.…”

Systemic Retinaldehyde Treatment Corrects Retinal Oxidative Stress, Rod Dysfunction, and Impaired Visual Performance in Diabetic Mice

“…35 In other studies, vitamin A and retinoids were found to exhibit concentration-dependent anti or pro-oxidant effects. [32][33][34][35][70][71][72][73] Thus, it is not universally accepted that all retinaldehydes induce oxidative stress in all conditions. One possible explanation for these disparate findings is that retinaldehydes act in a hermetic fashion as antioxidants in low concentrations and pro-oxidants at higher levels.…”

A2E Suppresses Regulatory Function of RPE Cells in Th1 Cell Differentiation Via Production of IL-1β and Inhibition of PGE2

“…Previous research also indicated that A2E and its precursor alltrans retinal could generate ROS inside the RPE cells. [45][46][47] The possible mechanisms were related to the C/EBP homologous protein (CHOP) and GRP18 pathways 32 and cell damage. 48 Moreover, oxidative stress and inflammation are interrelated.…”