Mucosal surfaces, including those of the ocular surface, are covered by epithelium that is critical to preventing damage and infection. Cell surface-associated mucins are major components on the apical glycocalyx of this epithelium, extending up to 500 nm above the plasma membrane, far above all other membrane-associated proteins and lipids. They exhibit large numbers of O-glycan chains tethered to tandem repeats of amino acids in their protein backbone that create a locally high concentration of carbohydrate ligands. Alteration of cell surface glycosylation has been associated with the disruption of the mucosal barrier in ocular surface epithelial disease (e.g., dry eye), but the mechanisms that lead to this disruption remain mostly uncharacterized. During the last funding period, we identified galectin-3 as the major carbohydrate-binding protein expressed by human ocular surface epithelia. Galectin-3 is a multimeric lectin that can cross-link and oligomerize proteins displaying multiple oligosaccharide chains. This finding led us to hypothesize that multivalent O- glycans bind galectin-3 oligomers to form strong and highly organized lectin-carbohydrate lattices above the undulating membrane ridges in corneal and conjunctival cells'glycocalyx. In this application, we propose to determine whether mucin-type O-glycans in the glycocalyx associate with galectin-3 to form an apical cell surface barrier on the ocular surface, and whether this barrier prevents the influx of foreign substances through the plasma membrane and the access of microorganisms and inflammatory mediators to apical cell surface receptors. Finally, we propose to determine whether in patients with ocular surface epithelial disease there is a molecular breach of the O-glycan:galectin barrier. Understanding the mechanism of epithelial defense that includes components of the cell surface glycocalyx could help with the development of new therapeutic approaches aimed to restore components of the epithelial barrier in patients with ocular surface disease.

Public Health Relevance

Mucosal surfaces such as the corneal and conjunctival epithelia of the eye are faced with the critical function of forming a protective barrier that prevents cellular damage and systemic infection, while allowing the exchange of molecules with the extracellular milieu. In this application, we propose to determine the role of mucin carbohydrates (O-glycans) and carbohydrate-binding proteins (galectins) in the formation of this barrier on apical cells of the ocular surface epithelia. The understanding of the O-glycan:galectin barrier, which has not been previously described, may help in the clinical treatment of diseases in which the ocular surface is compromised.

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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Schepens Eye Research Institute
United States
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Rodriguez Benavente, Maria C; Argüeso, Pablo (2018) Glycosylation pathways at the ocular surface. Biochem Soc Trans 46:343-350
Uchino, Yuichi; Woodward, Ashley M; Mauris, Jérôme et al. (2018) Galectin-3 is an amplifier of the interleukin-1?-mediated inflammatory response in corneal keratinocytes. Immunology 154:490-499
Taniguchi, Takazumi; Woodward, Ashley M; Magnelli, Paula et al. (2017) N-Glycosylation affects the stability and barrier function of the MUC16 mucin. J Biol Chem 292:11079-11090
Zahr, Alisar; Alcaide, Pilar; Yang, Jinling et al. (2016) Endomucin prevents leukocyte-endothelial cell adhesion and has a critical role under resting and inflammatory conditions. Nat Commun 7:10363
Mauris, J; Dieckow, J; Schob, S et al. (2015) Loss of CD147 results in impaired epithelial cell differentiation and malformation of the meibomian gland. Cell Death Dis 6:e1726
Uchino, Yuichi; Mauris, Jerome; Woodward, Ashley M et al. (2015) Alteration of galectin-3 in tears of patients with dry eye disease. Am J Ophthalmol 159:1027-1035.e3
Woodward, Ashley M; Argüeso, Pablo (2014) Expression analysis of the transmembrane mucin MUC20 in human corneal and conjunctival epithelia. Invest Ophthalmol Vis Sci 55:6132-8
Mauris, Jerome; Woodward, Ashley M; Cao, Zhiyi et al. (2014) Molecular basis for MMP9 induction and disruption of epithelial cell-cell contacts by galectin-3. J Cell Sci 127:3141-8
Mauris, Jerome; Mantelli, Flavio; Woodward, Ashley M et al. (2013) Modulation of ocular surface glycocalyx barrier function by a galectin-3 N-terminal deletion mutant and membrane-anchored synthetic glycopolymers. PLoS One 8:e72304
Argueso, Pablo (2013) Glycobiology of the ocular surface: mucins and lectins. Jpn J Ophthalmol 57:150-5

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