Quercetin Alleviates All- Trans-Retinal-Induced Photoreceptor Apoptosis and Retinal Degeneration by Inhibiting the ER Stress-Related PERK Signaling

Abstract

All-trans-retinal (atRAL)-induced photoreceptor atrophy and retinal degeneration are hallmark features of dry age-related macular degeneration (AMD) and Stargardt disease type 1 (STGD1). The toxicity of atRAL is closely related to the generation of reactive oxygen species (ROS). Quercetin, a natural product, is known for its potent antioxidant properties; however, its effects in mitigating atRAL-mediated retinal damage remains unclear. This study investigated the protective effects of quercetin against atRAL-induced photoreceptor damage. Using atRAL-loaded 661W photoreceptor cells, we evaluated cell viability, ROS generation, and endoplasmic reticulum (ER) stress under quercetin treatment. Quercetin significantly restored the cell viability (to 70%) and reduced ROS generation in atRAL-treated 661W cells. Additionally, Western blot analysis demonstrated that quercetin mitigated protein kinase RNA-like ER kinase (PERK) signaling, preventing ER stress-induced apoptosis. Importantly, in Abca4^-/-Rdh8^-/- mice, an animal model of light-induced atRAL accumulation in the retina, quercetin treatment effectively alleviated light-exposed photoreceptor atrophy and retinal degeneration by attenuating PERK signaling. Thus, quercetin protected photoreceptor cells from atRAL-induced damage by inhibiting ROS generation and PERK signaling, which suggests its potential as a therapeutic agent for atRAL-related retinal degeneration.

Keywords: ER stress; all-trans-retinal; apoptosis; photoreceptor; quercetin.

Figure 1

Quercetin restores cell viability and suppresses ROS generation in atRAL-treated 661W cells. (A) Structure of quercetin. (B) Cell viability (n = 6). (C) Fluorescence imaging of ROS and ER (n = 3). Scale bars, 10 μm. *** p < 0.001.

Figure 2

Effect of quercetin on the PERK/eIF2α/ATF4/CHOP signaling in atRAL-loaded cells. (A) Immunoblotting analysis and quantification of BiP (n = 3). (B) Immunofluorescence analysis and quantification of p-PERK (n = 3). Scale bars, 10 μm. (C) Immunoblotting analysis of eIF2α, p-eIF2α, ATF4, and CHOP, and quantification of p-eIF2α, ATF4, and CHOP (n = 3). *** p < 0.001.

Figure 3

Effect of quercetin on atRAL-induced apoptosis in 661W cells. (A) Immunoblotting analysis of JNK, p-JNK, and cleaved caspase-3, and quantification of p-JNK and cleaved caspase-3 (n = 3). (B) Immunoblotting analysis of PARP, cleaved PARP, and γH2AX, and quantification of cleaved PARP and γH2AX (n = 3). (C) TUNEL staining (n = 3). Scale bars, 10 μm. ** p < 0.01 and *** p < 0.001.

Figure 4

Effect of quercetin on the structure and function of the retina in light-exposed Abca4^−/−Rdh8^−/− mice. (A) Full-flash ERG. Stimulus luminance, 1 cd s/m². a: the lowest point; b: the highest point (B) Quantification of full-flash ERG (n = 6). Stimulus luminance, 1 cd s/m². (C) OCT imaging and quantification of retina thickness (n = 6). Scale bars, 100 μm. (D) H&E staining and quantification of ONL thickness (n = 6). Scale bars, 20 μm. (E) Fundus imaging. Scale bars, 100 μm. *** p < 0.001.

Figure 5

Effect of quercetin on the PERK/eIF2α/ATF4/CHOP signaling-induced photoreceptor apoptosis in light-exposed Abca4^−/−Rdh8^−/− mice. (A) Immunofluorescence analysis and quantification of p-PERK (n = 3). (B) Immunoblotting analysis of eIF2α and p-eIF2α, and quantification of p-eIF2α (n = 3). (C) Immunofluorescence analysis and quantification of CHOP (n = 3). (D) Immunoblotting analysis of JNK, p-JNK, cleaved caspase-3, and γH2AX, and quantification of p-JNK, cleaved caspase-3, and γH2AX (n = 3). (E) TUNEL staining (n = 3). Scale bars in (A,C,E), 10 μm. *** p < 0.001.

Figure 6

Schematic diagram illustrating the protective effects of quercetin against atRAL-induced apoptosis in photoreceptor cells.