Interferon-Gamma Exacerbates Dry Eye-Induced Apoptosis In Conjunctiva Through Dual Apoptotic Pathways

PURPOSE. To investigate the role of interferon (IFN)-gamma in dry eye-associated conjunctival apoptosis.METHODS. Desiccating stress (DS) was created in C57BL/6 (B6) and C57BL/6 IFN-gamma-knockout (B6 gamma KO) mice. A separate group of mice of both strains also received subconjunctival injections of exogenous IFN-gamma or vehicle control (BSA) at days 0, +2, and +4 after DS. Immunoreactivity to active (Ac)-caspase-3, -8, and -9 and terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL) were evaluated in cryosections. Goblet cell apoptosis was assessed by MUC5AC and TUNEL double staining. Levels of caspase-3, -8, -9, Fas, and Fas-associated protein with Death Domain (FADD) mRNA in conjunctiva were measured by real-time PCR. The activity of caspase-3, -8, or -9 was measured using fluorometric assay.RESULTS. Increased Ac-caspase-3 and -8 and TUNEL immunoreactivity were noted in conjunctival epithelia in B6 mice compared with B6 gamma KO mice after DS, and exogenous IFN-gamma administration further increased these parameters. DS-induced conjunctival apoptosis was greatest in the goblet cell area and was accompanied by a decrease in MUC5AC expression in the B6 and B6-IFN-gamma-injected groups compared with the B6 gamma KO and B6-BSA-injected groups. B6 gamma KO mice were resistant to DS-induced apoptosis; however, B6 gamma KO receiving IFN-gamma yielded results similar to those for B6 wild-type. Caspase-9 production and activity were not increased with DS in B6 or B6 gamma KO mice; however, the administration of IFN-gamma significantly increased caspase-9 production and activity in both strains compared with vehicle-injected mice.CONCLUSIONS. IFN-gamma plays a pivotal role in exacerbating conjunctival apoptosis through dual apoptotic pathways with DS. (Invest Ophthalmol Vis Sci. 2011;52:6279-6285) DOI:10.1167/iovs.10-7081