UVB activates autophagy in corneal epithelial stem cells

Abstract

Purpose : Ultraviolet B (UVB) irradiation may induce DNA lesions in all directly exposed tissues. In the human body, only two tissues are chronically exposed to UV: the skin and the cornea. The cornea lacks some of the phsycical barrier properties that the skin has, this makes the cornea particularly vulnearable damage. The induction of autophagy, a process that removes damaged cytoplasmic components, is of great importance in the cornea and extremely so in the stem cells that maintain the cornea. Here, we aim to characterise autophagy in isolated corneal epithelial stem cells (CESC) exposed to UV.

Methods : Epithelial cells were extracted from the limbus of discarded donor cornea (n=3). The cells were sorted to remove any fibroblasts. Cells were irradiated with 0.05J/cm² UVB. Autophagy and stem cells markers were observed using qPCR and immunofluorescent imaging. UVB damage was confirmed using DNA-lesion immunofluorescence assay.

Results : The putative stem cell character was assessed with ABCB5 and p63a. In culture, p63a+ epithelial cells have a high expression of mTOR that decreases by -0.96±0.6 log2 fold with UVB irradiation. Additionally, phosphrylated-mTOR (p-mTOR) position changes in CESC after irradiation, concentrating at the nucleus. Other assayed autophagy controllers had increased expression following UVB irradiation. ATG5 expression increased by 6.9±0.08 log2 fold, ATG7 expression increased by 7.7±2.9 log2 fold, ATG12 expression increased by 2.9±0.4 log2 fold, and LC3B expression increased by 1.05±0.3 log2 fold.

Conclusions : The decrease in expression of mTOR expression as well as the relocalisation of p-mTOR to the nucleus suggests that autophagy in CESC cytolasm is no longer inhibited. Additionally, both higher expression and visible presence of key autophagy controllers ATG5, ATG7, ATG12, and LC3B strongly suggests that short UVB exposure triggers autophagy in CESC.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.