Our multi-disciplinary and multi-institutional application addresses dry eye syndromes from the perspective of the new human prosecretory mitogen 'lacritin'discovered by us. Lacritin is restrictively expressed in lacrimal and meibomian glands and in the cornea and conjunctiva, where it appears to be capable of protecting epithelia of the lacrimal-corneal axis against inflammation-associated cell death. Increased levels of proinflammatory cytokine TNFa in tears of dry eye patients is associated with damage to ocular surface epithelia. Indeed, adding TNFa to cultured human corneal epithelial cells promotes death via caspases-8 and -3. Recently we observed that caspase activation and death is completely prevented by inclusion of 10 nM lacritin. This observation has been reinforced by lacritin deletion analysis that reveals a cytoprotective site within lacritin's C-terminus. Lacritin's utilizes a unique cell targeting mechanism: heparanase unblocks a lacritin binding site within the N-terminal ectodomain of cell surface syndecan-1. Bound lacritin is then likely presented to a GPCR. Since heparanase has a lower pH optimum, it is possible that lacritin is protective against the hypothetical sudden low pH 'danger signal'thought to underlie the initiation of primary Sjogren's syndrome dry eye in some individuals. In rabbit preclinical studies, topical application of lacritin promotes increased tear flow for at least 4 hr without toxicity - even over 30 days of continuous treatment. In cell culture, lacritin stimulates tear secretion by lacrimal acinar cells - the same cells from which it is secreted. It also promotes corneal epithelial MUC16 and lacritin expression. Since lacritin is a natural tear protein, this suggests mechanisms of upstream and downstream autocrine stimulation that prolong lacritin's cytoprotective and prosecretory effects. Tear proteins likely function as bioactive complexes. These activities can be harnessed by recombinant protein engineering. Our working hypothesis is that lacritin is naturally protective against dry eye inflammation. Our immediate goal is to optimize lacritin's cytoprotective activity and understand its mechanism of action.
Our first aim i s to engineer the smallest and most cytoprotective form of lacritin.
Our second aim i s to work out biological pathways that underlie its cytoprotective activity in a search for treatment synergies or counterindications.
Our third aim i s to preclinically test topically applied or genetically induced lacritin in animal models of dry eye.
|Karnati, Roy; Talla, Venu; Peterson, Katherine et al. (2016) Lacritin and other autophagy associated proteins in ocular surface health. Exp Eye Res 144:4-13|
|McKown, Robert L; Coleman Frazier, Erin V; Zadrozny, Kaneil K et al. (2014) A cleavage-potentiated fragment of tear lacritin is bactericidal. J Biol Chem 289:22172-82|
|Vijmasi, Trinka; Chen, Feeling Y T; Balasubbu, Suganthalakshmi et al. (2014) Topical administration of lacritin is a novel therapy for aqueous-deficient dry eye disease. Invest Ophthalmol Vis Sci 55:5401-9|
|Feng, Mary M; Baryla, Julia; Liu, Hong et al. (2014) Cytoprotective effect of lacritin on human corneal epithelial cells exposed to benzalkonium chloride in vitro. Curr Eye Res 39:604-10|
|Zhang, Yinghui; Wang, Ningning; Raab, Ronald W et al. (2013) Targeting of heparanase-modified syndecan-1 by prosecretory mitogen lacritin requires conserved core GAGAL plus heparan and chondroitin sulfate as a novel hybrid binding site that enhances selectivity. J Biol Chem 288:12090-101|
|McKown, Robert L; Raab, Ronald W; Kachelries, Patricia et al. (2013) Conserved regional 3' grouping of rare codons in the coding sequence of ocular prosecretory mitogen lacritin. Invest Ophthalmol Vis Sci 54:1979-87|
|Karnati, Roy; Laurie, Diane E; Laurie, Gordon W (2013) Lacritin and the tear proteome as natural replacement therapy for dry eye. Exp Eye Res 117:39-52|
|Velez V, Francisco; Romano, Jeffrey A; McKown, Robert L et al. (2013) Tissue transglutaminase is a negative regulator of monomeric lacritin bioactivity. Invest Ophthalmol Vis Sci 54:2123-32|
|Wang, Ningning; Zimmerman, Keith; Raab, Ronald W et al. (2013) Lacritin rescues stressed epithelia via rapid forkhead box O3 (FOXO3)-associated autophagy that restores metabolism. J Biol Chem 288:18146-61|
|Laurie, Diane E; Splan, Rebecca K; Green, Kari et al. (2012) Detection of prosecretory mitogen lacritin in nonprimate tears primarily as a C-terminal-like fragment. Invest Ophthalmol Vis Sci 53:6130-6|
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