O-Glycans on Mucins at the Ocular Surface

项目总结/摘要 粘膜表面，包括眼表面的粘膜表面，被上皮细胞覆盖，上皮细胞对 防止损伤和感染。细胞表面相关粘蛋白是细胞膜上的主要成分， 这种上皮的顶端糖萼，延伸到质膜以上500 nm，远高于 所有其他膜相关蛋白质和脂质。它们表现出大量的O-聚糖链 与蛋白质骨架中的氨基酸串联重复序列相连， 碳水化合物配体的浓度。细胞表面糖基化的改变与 随着眼表面上皮疾病中粘膜屏障的破坏（例如，干眼症），但 导致这种破坏的机制大多仍不明确。在最后一次融资中 我们鉴定了galectin-3是人眼上皮细胞表达的主要碳水化合物结合蛋白， 表面上皮半乳糖凝集素-3是一种多聚体凝集素，可以交联和寡聚蛋白质 显示多个寡糖链。这一发现使我们假设多价O- 聚糖结合半乳糖凝集素-3低聚物，形成牢固且高度组织化的凝集素-碳水化合物晶格 位于角膜和结膜细胞糖萼的波状膜脊之上。在这 应用，我们建议确定是否粘蛋白型O-聚糖在糖萼相关 半乳糖凝集素-3在眼表面上形成顶端细胞表面屏障，以及这种屏障是否 防止外来物质通过质膜流入， 微生物和炎性介质对顶端细胞表面受体的作用。最后，我们建议 确定在患有眼表上皮疾病的患者中， O-聚糖：半乳糖凝集素屏障。了解上皮防御机制，包括 细胞表面糖萼的成分可以帮助开发新的治疗药物， 旨在恢复眼表疾病患者上皮屏障成分的方法 疾病

Project Summary/Abstract 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.