Abstract
Purpose :
Lacritin is a basal tear and homeostasis promoting factor in tears whose activity is concentrated in its C-terminus - the latter represented in tears as a naturally processed fragment similar to the synthetic peptide currently in a Phase 2 trial for Sjögren's syndrome dry eye. Lacritin targets cells via a novel 'off/on switch' by which heparanase exposes a latent binding site in syndecan-1 that thereafter is unstable and is likely shed into tears. Here we analyze basal normal and dry eye tears for relative levels of lacritin, C-terminal fragment, lacritin-C splice variant, heparanase and syndecan-1. We also develop the first lacritin tear interactome.
Methods :
Relative levels of lacritin, lacritin-C splice variant, heparanase and syndecan-1 in SDS-PAGE separated basal tears from normal and aqueous dry eye individuals were analyzed by LI-COR. Lacritin interactors were detected by Biogrid, Bioplex, IntAct, String, Mentha and PCViz for analysis by Cytoscape.
Results :
Active lacritin monomer and C-terminal fragment were equally well-represented in normal tears, but deficient in dry eye, as was the lacritin-C splice variant of unknown function, and syndecan-1. A similar pattern was observed for pro- and active forms of heparanase. The predicted lacritin interactome consists of 47 proteins that differed in multiple forms of dry eye.
Conclusions :
Deficiency of active lacritin monomer and C-terminal fragment may underlie lack of shed syndecan-1 in dry eye. Why the pro form of heparanase is apparently downregulated is unknown. Overall, lacritin may have a substantial influence on the tear proteome, beyond its role as an inflammation-insensitive secretory agonist for lipocalin-1 and lactoferrin.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.