2-Phenyl-APB-144-Induced Retinal Pigment Epithelium Degeneration and Its Underlying Mechanisms

To investigate the efficacy of 2-phenyl-APB-144 (APB)-induced retinopathy in a rat model and its underlying mechanisms, with a particular focus on retinal pigment epithelium (RPE) degeneration.

Electroretinograms (ERGs) were evaluated in APB-administered rats. In ARPE-19 cells, cathepsin, and autophagy marker LC3 were analyzed by western blotting or immunohistochemistry. Organelle pH alterations were detected by Acridine Orange Staining. Endoplasmic reticulum stress-dependent or -independent cell death signaling was analyzed by reporter gene assays of activating transcription factor 4 (ATF4), immunoglobulin heavy-chain binding protein (BiP), inositol-requiring enzyme 1α (IRE1α), quantitative reverse transcription-polymerase chain reaction of CHOP mRNA, and the effects of pharmacological eukaryotic initiation factor 2α (eIF2α) dephosphorylation inhibitor, Salubrinal. The pharmacological effects of Salubrinal were examined by fluorophotometry, electrophysiology, and histopathology.

APB-induced ERG amplitude reduction and fluorescein permeability enhancement into the vitreous body of rats were determined. In ARPE-19 cells, APB-induced organelle pH alterations, imbalances of procathepsin and cathepsin expression, the time-dependent accumulation of LC3-II, and the translational activation of ATF4 were determined. Salubrinal protected against APB-induced cell death and inhibited ATF4 downstream factor CHOP mRNA induction. In APB-induced rat retinopathy, systemic Salubrinal alleviated the enhanced fluorescein permeability into the vitreous body from the RPE, the reductions in ERG amplitudes, and RPE degeneration.

Organelle pH alterations and autophagy impairments are involved in APB-induced RPE cell death. Inhibition of eIF2α dephosphorylation protected the RPE in vivo and in vitro. These findings suggested that APB-induced retinopathy is a valuable animal model for exploring the mechanism of RPE-driven retinopathy.