Short-Term UVB Irradiation Leads to Persistent DNA Damage in Limbal Epithelial Stem Cells, Partially Reversed by DNA Repairing Enzymes

SIMPLE SUMMARY: Ultraviolet light from the sun causes DNA damage and is a major exogenous genotoxin, particularly affecting the skin and eyes of humans. UV-induced lesions are repaired by complex DNA repair mechanisms that sometimes fail, leading to burns or cancers. Here, we probe the potential of two ultraviolet damage-specific repair enzymes not found in humans: one from the kangaroo rat and one from an anti-bacterial virus. Both can be produced with relatively low costs. While these two repair enzymes have been studied in the skin and some products are already commercially available, comparatively little research has been conducted for the eyes, and there are no commercially available products. Therefore, we aim to offer new options for the protection of eyes that are particularly sensitive to ultraviolet rays and require more rapid repair than normal. ABSTRACT: The cornea is frequently exposed to ultraviolet (UV) radiation and absorbs a portion of this radiation. UVB in particular is absorbed by the cornea and will principally damage the topmost layer of the cornea, the epithelium. Epidemiological research shows that the UV damage of DNA is a contributing factor to corneal diseases such as pterygium. There are two main DNA photolesions of UV: cyclobutane pyrimidine dimers (CPDs) and pyrimidine-pyrimidone (6–4) photoproducts (6-4PPs). Both involve the abnormal linking of adjacent pyrimide bases. In particular, CPD lesions, which account for the vast majority of UV-induced lesions, are inefficiently repaired by nucleotide excision repair (NER) and are thus mutagenic and linked to cancer development in humans. Here, we apply two exogenous enzymes: CPD photolyase (CPDPL) and T4 endonuclease V (T4N5). The efficacy of these enzymes was assayed by the proteomic and immunofluorescence measurements of UVB-induced CPDs before and after treatment. The results showed that CPDs can be rapidly repaired by T4N5 in cell cultures. The usage of CPDPL and T4N5 in ex vivo eyes revealed that CPD lesions persist in the corneal limbus. The proteomic analysis of the T4N5-treated cells shows increases in the components of the angiogenic and inflammatory systems. We conclude that T4N5 and CPDPL show great promise in the treatment of CPD lesions, but the complete clearance of CPDs from the limbus remains a challenge.