Gipson Ilene K, Argüeso Pablo
Schepens Eye Research Institute and the Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts 02114, USA.
Int Rev Cytol. 2003;231:1-49. doi: 10.1016/s0074-7696(03)31001-0.
The surface of the eye is covered by a tear film, which is held in place by a wet-surfaced, stratified, corneal and conjunctival epithelia. Both are vital for light refraction and protection of vision. Maintenance of tear film on the ocular surface, lubrication, and provision of a pathogen barrier on this wet surface is facilitated by a class of large, highly glycosylated, hydrophilic glycoproteins--the mucins. In the past 15 years, a number of mucin genes have been cloned, and based on protein sequence, categorized as either secreted or membrane associated. Both types of mucins are expressed by ocular surface epithelia. Goblet cells intercalated within the stratified epithelium of the conjunctiva secrete the large gel-forming mucin MUC5AC, and lacrimal gland epithelia secrete the small soluble mucin MUC7. Apical cells of the stratified epithelium of both corneal and conjunctival epithelium express at least three membrane-associated mucins (MUCs 1, 4, and 16), which extend from their apical surface to form the thick glycocalyx at the epithelium-tear film interface. The current hypothesis regarding mucin function and tear film structure is that the secreted mucins form a hydrophilic blanket that moves over the glycocalyx of the ocular surface to clear debris and pathogens. Mucins of the glycocalyx prevent cell-cell and cell-pathogen adherence. The expression and glycosylation of mucins are altered in drying, keratinizing ocular surface diseases.
眼表覆盖着一层泪膜，泪膜由湿润表面的分层角膜和结膜上皮固定在位。二者对于光折射和视力保护都至关重要。一类大型、高度糖基化的亲水性糖蛋白——黏蛋白，有助于维持眼表的泪膜、润滑以及在这个湿润表面提供病原体屏障。在过去15年里，多个黏蛋白基因已被克隆，并根据蛋白质序列分为分泌型或膜相关型。这两种类型的黏蛋白均由眼表上皮表达。夹在结膜分层上皮内的杯状细胞分泌大型凝胶形成性黏蛋白MUC5AC，泪腺上皮分泌小型可溶性黏蛋白MUC7。角膜和结膜上皮分层上皮的顶端细胞表达至少三种膜相关黏蛋白（MUC1、MUC4和MUC16），它们从顶端表面延伸，在上皮-泪膜界面形成厚厚的糖萼。目前关于黏蛋白功能和泪膜结构的假说是，分泌型黏蛋白形成一层亲水覆盖层，在眼表糖萼上移动以清除碎屑和病原体。糖萼中的黏蛋白可防止细胞间和细胞与病原体的黏附。在干燥、角化性眼表疾病中，黏蛋白的表达和糖基化会发生改变。
