The Secreted Ly6/uPAR-Related Protein-1 (SLURP1) Protects the Cornea From Oxidative Stress

Previously, we reported that the secreted Ly6/uPAR-related protein-1 (SLURP1), abundantly expressed by the corneal epithelium (CE) and secreted into the tear fluid, suppresses NF-κB signaling in healthy corneas and is downregulated in response to a variety of stressors, allowing helpful inflammation to progress. Here we investigate whether SLURP1 manifests its broad protective effects by promoting corneal redox homeostasis.

Oxidative stress was induced in the wild-type (WT) and Slurp1-null (Slurp1X-/-) mouse corneas using 1350 J/m2 UV-B, and in human corneal limbal epithelial (HCLE) and SLURP1-overexpressing HCLE-SLURP1 cells with 100 J/m2 UV-B, 0.4 µg/mL mitomycin-C, or 0-100 µM H2O2. We evaluated their (i) redox status (GSH:GSSG ratio) using O-phthalaldehyde; (ii) reactive oxygen species (ROS) accumulation using 2',7'-dichlorodihydrofluorescein diacetate; (iii) antioxidants GPX4, CAT, and SOD2 expression by qRTPCR; (iv) lipid peroxidation by staining for 4-hydroxynonenol, malondialdehyde, and BODIPY-C11; and (v) DNA damage and NF-κB activation by immunostaining for γH2AX, 8-OHdG, NF-κB, and IκB.

Slurp1 was significantly downregulated in the UV-B-irradiated WT corneas. Oxidatively stressed HCLE-SLURP1 cells displayed relatively less ROS accumulation, lipid peroxidation, DNA damage and NF-κB activation, and a higher GSH/GSSG ratio and antioxidant gene expression than the similarly treated control HCLE cells. UV-B-irradiated Slurp1X-/- corneas displayed relatively more ROS accumulation, DNA damage and less GPX4 expression than the similarly treated WT corneas.

Collectively, these results elucidate that SLURP1 serves as an insult-agnostic immunomodulator that upregulates antioxidants and suppresses ROS accumulation to promote redox homeostasis in corneal epithelial cells and protect them from diverse genotoxic stressors.