Cathepsin S Inhibitor Reduces Lacrimal Gland Inflammation and Increases Tear Flow In a Mouse Model of Sjögren’s Syndrome

Abstract

Purpose : The activity of Cathepsin S (CTSS), a protease implicated in autoimmunity, is increased in tears and lacrimal gland (LG) of the male NOD mouse, a model of autoimmune-mediated dry eye associated with Sjögren’s Syndrome (SS), and also increased in SS patient tears. We hypothesized that inhibition of CTSS can treat the symptoms of autoimmune dacryoadenitis specifically by reducing LG inflammation and increasing aqueous tear production. In this study, we test this hypothesis using the CTSS inhibitor, Z-FL-COCHO (Z-FL), in male NOD mice.

Methods : Z-FL was dissolved in 10%DMSO+40%PEG300+50% PBS (vehicle) and its concentration was validated by HPLC. 14 wk male NOD mice received IP injections of 4 mg/kg, 1 mg/kg of Z-FL or vehicle every other day for 2 wk. At the end of the study, tear secretion was stimulated by application of topical carbachol to LGs, and LGs were evaluated by RT-qPCR and histology. CTSS activity was measured in tears, LG, and spleen. Liver, spleen, and kidneys were assessed for toxicity.

Results : In the 4 mg/kg Z-FL group, CTSS activity was decreased by 2.1-fold in tears (p=0.0337), 1.9-fold in LG (p=0.0062), and 3.2-fold in spleen (p=0.0026) vs vehicle. When compared to the 1 mg/kg Z-FL group, CTSS activity in the 4 mg/kg group was decreased by 2.7-fold in tears (p=0.0043) and 1.9-fold in spleen (p=0.023). In the 1 mg/kg Z-FL group, only spleen CTSS activity was significantly decreased (1.7-fold, p=0.0339) vs vehicle. The total area of the LG occupied by lymphocytic infiltration from the 4 mg/kg Z-FL group was reduced by 1.8-fold vs the vehicle group (p=0.042) and by 1.8 fold vs the 1 mg/kg Z-FL group (p = 0.0216). The stimulated tear volume in the 4 mg/kg Z-FL group was increased by 1.3-fold (p=0.0094) and by 1.4-fold (p=0.0078) relative to vehicle and 1 mg/kg Z-FL groups, respectively. 4 mg/kg Z-FL reduced MHC-II gene expression relative to vehicle (1.4-fold, p=0.0463) and 1 mg/kg Z-FL treated mice (1.6-fold, p=0.0248). There was no significant difference in liver, spleen, and kidney weights between treatment groups, and no histological signs of toxicity were detected in any groups.

Conclusions : IP injection of Z-FL can reduce autoimmune-mediated LG inflammation while improving stimulated tear secretion. Therefore, CTSS could be a potential drug target for treatment of SS-associated dry eye.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.