Our competitive renewal application addresses dry eye from the perspective of the new ocular-specific tear factor 'lacritin'discovered by us. Lacritin flows onto the ocular surface from lacrimal and meibomian glands to help promote ocular surface wetting. It is also a presumed contributor to corneal renewal via its basal corneal epithelial expression. Selective downregulation of lacritin in tears is associated with blepharitis and contact lens-related dry eye, the only two dry eye syndromes proteomically examined to date. Adding lacritin to eyes of normal rabbits or dry eye female monkeys ovariectomized one to two years earlier triggers elevated and sustained tear flow. These observations are reinforced by human corneal epithelial cell culture in which lacritin stimulates MUC16 protein production more efficiently than serum and by our original observation that lacritin augments tear peroxidase release from cultured rat lacrimal acinar cells independent of the parasympathetic- (carbachol-) stimulation pathway. Also subconfluent cultures of human corneal epithelial cells proliferate in a lacritin domain- and dose-specific manner. How lacritin promotes tearing and renewal is not understood. Our lacritin structure/function and lacritin signaling studies have sketched out a heparanase-dependent mechanism for targeting cell surface proteoglycan syndecan-1. This leads to putative ligation of a G-protein coupled receptor for signaling through G1i or G1o to PLC-PKC1/PLD/mTOR and PLC- PKC1/STIM1/calcineurin/Ca2+/ NFATC1. Differential upregulation of newly identified splice variants lacritin-b or -c (suspected to be incapable of respectively binding the GPCR or syndecan-1) coincident with downregulation of native lacritin, or loss of heparanase (observed preliminarily in dry eye tears) are two potential dry eye-provoking scenarios. Our working hypothesis is that lacritin is a regulator of ocular surface wetting and renewal. Our immediate goal is to characterize the signaling receptor and understand its mechanism of action.
Our first aim i s to understand specific protein-protein interactions constituting the lacritin/syndecan-1/G-protein coupled receptor heterocomplex.
Our second aim i s to characterize how upstream lacritin signaling is generated.
Our third aim asks how downstream lacritin signaling can promote wetting and renewal towards a global appreciation for lacritin's role on the ocular surface.

Public Health Relevance

. Dry eye is very common. This project will work out how a new potential therapeutic for dry eye promotes ocular surface wetting. The therapeutic is based on a natural human tear protein.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Anterior Eye Disease Study Section (AED)
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Mckie, George Ann
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University of Virginia
Anatomy/Cell Biology
Schools of Medicine
United States
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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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