Significance of Ectodomain Shedding of TNF Receptor 1 in Ocular Surface

Abstract

We evaluated an anti-inflammatory effect of TNF receptor 1 (TNFR1) ectodomain shedding in ocular surface. Human corneal epithelial cell (HCEC) was first pretreated by TNF-α. Ectodomain shedding was stimulated by uridine triphosphate (UTP) or peptidoglycan (PGN), with or without shedding inhibition using TNF-α processing inhibitor (TAPI). The phosphorylation of the NF-κB inhibitory protein, IκB, was assessed by Western blotting and concentrations of soluble TNFR1 (sTNFR1) in culture medium were analyzed by ELISA. Tear fluid from patients with Sjögren syndrome and graft-versus-host disease (GVHD) was collected and analyzed by ELISA for sTNFR1 concentration. Five dry eye patients underwent topical treatment using diquafosol sodium eye drops, a purinergic P2Y2 receptor agonist, and the tear fluid of the patients was sampled before and 4 weeks after the treatment for sTNFR1 ELISA. Phosphorylation of IκB was diminished by adding UTP or PGN, and this down-regulation of IκB phosphorylation was reversed by adding TAPI. In HCEC medium, sTNFR1 release was increased significantly by adding UTP or PGN, and inhibited significantly by adding TAPI. In the tears of the patients with Sjögren syndrome and GVHD, sTNFR1 expression was upregulated. In the tears of the patients with short breakup time (BUT) dry eye, sTNFR1 concentrations (ng/mL) in the tears were 1.30 ± 0.58 ng/mL for the pretreatment baseline, and 1.64 ± 0.70 after treatment, statistically significantly higher than those for the pretreatment (P < 0.01). Ectodomain shedding of sTNFR1 blocked TNF-α-induced intracellular signaling in corneal epithelium. The upregulation of sTNFR1 in inflamed ocular surfaces suggests an anti-inflammatory role of sTNFR1 ectodomain shedding at the ocular surface.