Destructive and protective effects and therapeutic targets of IL-36 family cytokines in dry eye disease

Purpose: To explore the destructive and protective effects and therapeutic targets of IL-36 cytokines in dry eye disease using a murine dry eye model. Methods: A dry eye model was established in C57BL/6 mice exposed to desiccating stress (DS) with untreated mice as controls. A topical challenge model was performed in normal mice with exogenous rmIL-36 alpha, rhIL-38 and 2 % ectoine, or PBS vehicle. IL-36 cytokine expression was assessed by RT-qPCR and immunofluorescent (IF) staining. Corneal epithelial damage was evaluated by corneal smoothness score, Oregon Green Dextran (OGD) fluorescent staining, and tight junction barrier. Results: All members of the IL-36 family were expressed by murine ocular surface epithelium. The expression of IL-36 alpha and IL-361 was upregulated while IL-38 and IL-36RN were down regulated in ocular surface of dry eye mice. A topical challenge of rmIL-36 alpha directly destructed corneal surface with distorted smoothness, increased OGD uptake and IF intensity, and disrupted tight junction proteins ZO-1 and occludin. Co-application with rhIL38 prevented all these corneal damages by rmIL-36 alpha. Ectoine treatment reversed the pathological expression pattern of IL-36 cytokines, protected corneal epithelium from defects, and restored the tight junction barrier in DS mice, and even prevented corneal damage by rmIL-36 alpha. Conclusions: Our findings demonstrate the upregulated pro-inflammatory agonists IL-36 alpha and IL-361 with downregulated antagonists IL-38 and IL-36RA in dry eye model, which provides a previously unknown mechanism and therapeutic targets in dry eye disease. The therapeutic efficacy of ectoine may be through reversing the pathological alteration of IL-36 cytokines in dry eye mice.