A Selective Melatonin 2 Receptor Agonist, IIK7, Relieves Blue Light-Induced Corneal Damage by Modulating the Process of Autophagy and Apoptosis

Abstract

This study aims to investigate the effect of the selective MT2 receptor agonist, IIK7, on corneal autophagy and apoptosis, aiming to reduce corneal epithelial damage and inflammation from blue light exposure in mice. Eight-week-old C57BL/6 mice were divided into BL-exposed (BL) and BL-exposed with IIK7 treatment (BL + IIK7 group). Mice underwent blue light exposure (410 nm, 100 J) twice daily with assessments at baseline and on days 3, 7, and 14. Corneal samples were analyzed for MT2 receptor expression, autophagy markers (LC3-II and p62), and apoptosis indicators (BAX expression and TUNEL assay). Then, mice were assigned to normal control, BL, and BL + IIK7. Ocular surface parameters, including corneal fluorescein staining scores, tear volume, and tear film break-up time, were evaluated on days 7 and 14. On day 14, reactive oxygen species (ROS) levels and CD4⁺ IFN-γ⁺ T cells percentages were measured. The BL group exhibited higher LC3-II and p62 expression, while the BL + IIK7 group showed reduced expression (p < 0.05). The TUNEL assay showed reduced apoptosis in the BL + IIK7 group compared to the BL group. ROS levels were lower in the BL + IIK7 group. The BL + IIK7 group showed improved ocular surface parameters, including decreased corneal fluorescein staining and increased tear volume. The percentages of CD4⁺ IFN-γ⁺ T cells indicated reduced inflammatory responses in the BL + IIK7 group. The MT2 receptor agonist IIK7 regulates corneal autophagy and apoptosis, reducing corneal epithelial damage and inflammation from blue light exposure.

Keywords: IIK7; apoptosis; autophagy; blue light; corneal damage; melatonin type 2 receptor.

Figure 1

Corneal MT2 receptor expression in BL-exposed (BL) and BL-exposed with IIK7 treatment (BL + IIK7) groups at days 3, 7, and 14. Representative immunofluorescence images (A) and quantitative analysis of MT2 receptor expression levels (B). Data are presented as mean ± SD. * p < 0.05 vs. baseline, ^† p < 0.05 vs. day 3, # p < 0.05, BL + IIK7 vs. BL.

Figure 2

Levels of immunofluorescence of autophagy markers, LC3-II (A) and p62 (B) in the corneal epithelium on days 3, 7, and 14 in BL-exposed (BL) and BL-exposed with IIK7 treatment (BL + IIK7) groups. * p < 0.05 vs. baseline, # p < 0.05, BL + IIK7 vs. BL. Representative immunofluorescence of LC3-II (C) and p62 (D).

Figure 3

Representative immunofluorescence images of apoptotic marker, BAX (A), and intensity of immunofluorescence (B) on days 3, 7, and 14 in BL-exposed (BL) and BL-exposed with IIK7 treatment (BL + IIK7) groups. The mean number of the TUNEL-positive cells and its representative images (C). * p < 0.05 vs. baseline, # p < 0.05, BL + IIK7 vs. BL.

Figure 4

Levels of extracellular ROS measured using 2′,7′-DCF-DA in representative images (A), and frequency of DCF-DA in the cornea (B), conjunctiva (C) of the normal control, BL-exposed (BL), and BL-exposed with IIK7 treatment (BL + IIK7) group at day 14. * p < 0.05, BL + IIK7 vs. BL.

Figure 5

Mean corneal fluorescein-staining scores (A) and representative photographs (B) of BL-exposed (BL) and BL-exposed with IIK7 treatment (BL + IIK7) groups at days 3, 7, and 14. * p < 0.05 vs. normal control, # p < 0.05, BL + IIK7 vs. BL.

Figure 6

Mean tear volumes (A), tear-film break-up time (B) of BL-exposed (BL) and BL-exposed with IIK7 treatment (BL + IIK7) groups at days 7 and 14. Flow cytometry showing CD4⁺ IFN-γ⁺ T cells in representative images (C) and the mean percentages of CD4⁺ IFN-γ⁺ T cells in the cornea (D) and conjunctiva (E). * p < 0.05 vs. BL group, ** p < 0.01 vs. BL group.