Gipson Ilene K
Department of Ophthalmology, Schepens Eye Research Institute, Harvard Medical School, 20 Staniford Street, Boston, MA 02114-2500, USA.
Exp Eye Res. 2004 Mar;78(3):379-88. doi: 10.1016/s0014-4835(03)00204-5.
Mucins are vital for maintenance of a healthy, wet ocular surface. Once only thought to be secreted by goblet cells, mucins are now also known to be of the membrane-associated type. Stratified ocular surface epithelia express at their apical-tear fluid surface a repertoire of membrane-associated mucins including MUC1, MUC4, MUC16. These mucins are concentrated on the tips of the microplicae, forming a dense glycocalyx at the epithelial tear film interface. A major mucin of the secretory class is the goblet-cell-derived gel-forming mucin MUC5AC. A small soluble mucin, MUC7, is expressed by the lacrimal gland acini. Our hypothesis of the role/distribution of the secreted and membrane-associated mucins at the ocular surface is that the secreted mucins are soluble in the tear fluid, and are moved about and shunted to the nasolacrimal duct and by the eyelids during blinking. Thus, in the tears, the secreted mucins act as clean-up/debris removing multimeric networks that at the same time, through their hydrophilic nature, hold fluids in place and harbor defense molecules secreted by the lacrimal gland. Membrane-associated mucins, on the other hand, form a dense barrier in the glycocalyx at the epithelial tear film interface. This barrier prevents pathogen penetrance and is a lubricating surface that allows lid epithelia to glide over the corneal epithelia without adherence. The secreted mucins move easily over the glycocalyx mucins because both have anionic character that creates repulsive forces between them. Little is known regarding regulation of expression and glycosylation of mucins by ocular surface epithelia. Since ocular surface drying diseases alter both goblet cell and mucin production, and production and glycosylation of membrane-associated mucins, studies of mucin gene regulation and glycosylation may yield treatment modalities for these diseases.
粘蛋白对于维持健康、湿润的眼表至关重要。粘蛋白曾一度被认为仅由杯状细胞分泌，现在也已知其存在膜相关类型。分层的眼表上皮在其顶端泪液表面表达一系列膜相关粘蛋白，包括MUC1、MUC4、MUC16。这些粘蛋白集中在微褶的尖端，在上皮泪膜界面形成致密的糖萼。分泌型的主要粘蛋白是杯状细胞衍生的凝胶形成粘蛋白MUC5AC。泪腺腺泡表达一种小的可溶性粘蛋白MUC7。我们关于分泌型和膜相关粘蛋白在眼表的作用/分布的假设是，分泌型粘蛋白可溶于泪液，在眨眼过程中被移动并分流至鼻泪管和眼睑。因此，在泪液中，分泌型粘蛋白充当清除/去除碎片的多聚体网络，同时通过其亲水性将液体固定在位，并容纳泪腺分泌的防御分子。另一方面，膜相关粘蛋白在上皮泪膜界面的糖萼中形成致密屏障。该屏障可防止病原体穿透，是一个润滑表面，可使睑上皮在角膜上皮上滑动而不粘连。分泌型粘蛋白易于在糖萼粘蛋白上移动，因为两者都具有阴离子特性，在它们之间产生排斥力。关于眼表上皮对粘蛋白表达和糖基化的调节知之甚少。由于眼表干燥疾病会改变杯状细胞和粘蛋白的产生，以及膜相关粘蛋白的产生和糖基化，对粘蛋白基因调节和糖基化的研究可能会产生针对这些疾病的治疗方法。
