Purpose: The eicosanoid 15-(S)-hydroxy-5,8,11,13-eicosatetraenoic acid [15(S)-HETE] is reported to stimulate mucin production in both airway and ocular surface epithelia. The current study was undertaken to evaluate the effects of 15(S)-HETE on secretion of specific ocular mucins by human conjunctiva.
Methods: Segments of human bulbar conjunctival tissue were incubated with 15(S)-HETE (1-1000 nM) for 30 minutes at 37 degrees C. Secretion of human ocular mucins MUC1, MUC2, MUC4, and MUC5AC into the incubation media was measured by dot-blot immunoassay using antibodies directed to unique mucin polypeptide epitopes. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting were used to verify the specificity of anti-mucin antibody binding and to investigate the presence of MUC1 mucin in human tears.
Results: 15(S)-HETE (10(-8)-10(-6) M) stimulated secretion of conjunctival mucins in a concentration-dependent manner. Significant increases in total mucin secretion were observed at 10(-7) M 15(S)-HETE with a maximum response (>50% increase above controls) at 10(-6) M. Results of immunoassays showed that 15(S)-HETE differentially stimulates secretion of MUC1 mucin with no detectable effects on MUC2, MUC4, or MUC5AC release. Western analysis of tear samples from human volunteers indicated that MUC1 is a component of the preocular tear film.
Conclusions: The results demonstrate that 15(S)-HETE is a selective secretogogue for MUC1 in isolated human conjunctival tissue. Although the biochemical mechanism(s) and cellular origins of MUC1 secretion remain to be established, the ubiquitous expression of MUC1 in corneal and conjunctival epithelia and its presence in human tears suggest that secreted MUC1 may contribute to the mucin layer that coats and protects the ocular surface.