Resolvin D2 elevates cAMP to increase intracellular [Ca²⁺] and stimulate secretion from conjunctival goblet cells

Under physiologic conditions, conjunctival goblet cells (CGCs) secrete mucins into the tear film to preserve ocular surface homeostasis. Specialized proresolving mediators (SPMs), like resolvins (Rvs), regulate secretion from CGCs and actively terminate inflammation. The purpose of this study was to determine if RvD2 stimulated mucin secretion and to investigate the cellular signaling components. Goblet cells were cultured from rat conjunctiva. Secretion was measured by an enzyme-linked lectin assay, change in intracellular [Ca²⁺] ([Ca²⁺]_i) using Fura-2, and cellular cAMP levels by ELISA. RvD2 (10^-11-10^-8 M) stimulated secretion, increased cellular cAMP levels and the [Ca²⁺]_i. RvD2-stimulated increase in [Ca²⁺]_i and secretion was blocked by Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis and the PKA inhibitor N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride but not by the cAMP exchange protein inhibitor α-[2-(3-chlorophenyl)hydrazinylidene]-5-(1,1-dimethylethyl)-b-oxo-3-isoxazolepropanenitrile. Forskolin, 3-isobutyl-1-methylxanthine, and 8-bromo-cAMP (8-Br-cAMP) increased [Ca²⁺]_i. Increasing cAMP with 8-Br-cAMP inhibited the increase in [Ca²⁺]_i stimulated by the cAMP-independent agonist cholinergic agonist carbachol. In conclusion, RvD2 uses both cellular cAMP and [Ca²⁺]_i to stimulate glycoconjugate secretion from CGCs, but the interaction of cAMP and [Ca²⁺]_i is context dependent. Thus RvD2 likely assists in the maintenance of the mucous layer of the tear film to sustain ocular surface homeostasis and has potential as a novel treatment for dry eye disease.-Botten, N., Hodges, R. R., Li, D., Bair, J. A., Shatos, M. A., Utheim, T. P., Serhan, C. N., Dartt, D. A. Resolvin D2 elevates cAMP to increase intracellular [Ca²⁺] and stimulate secretion from conjunctival goblet cells.