Biological function of keratan sulfate glycosaminoglycan for corneal extracellula

硫酸角聚糖（KS）蛋白多糖（PG）是角膜的主要成分之一，对角膜的发育和组织透明度的维持具有重要作用。KS-PG由两种不同的成分组成，核心蛋白质和附加的碳水化合物，称为糖胺聚糖（GAGs）。据推测，KS-PG核心蛋白与胶原原纤维结合并调节原纤维的直径，ks - gag调节纤维间间距。通过包括基因敲除小鼠在内的几种方法，已经很好地研究了KS-PG核心蛋白（如lumican和keratocan）在角膜发育中的重要性，然而，由于碳水化合物的生物合成途径尚未建立，KS-GAG链的生物学功能尚未得到广泛研究。

Keratan sulfate (KS) proteoglycan (PG) is one of the major components of the cornea, and suggested to have important roles for corneal development and maintenance of transparency of the tissue. KS-PG is consists of two different components, core proteins and attached carbohydrates called glycosaminoglycans (GAGs). It has been postulated that KS-PG core proteins bind to collagen fibrils and regulate diameter of the fibrils, and KS-GAGs regulate interfibrillar spacing. By using several approaches including gene-knockout mice, importance of KS-PG core proteins, such as lumican and keratocan, over corneal development has been well investigated, however, biological function of KS-GAG chains has not been extensively studied, since biosynthetic pathway of the carbohydrate has not been established. KS-GAG is a linearly elongated carbohydrate chain that consists of repeating disaccharide units of 3Gal~1-4GlcNAc~1- (Gal, galactose; GlcNAc, Nacetylglucosamine), with sulfate on 6-0 position of Gal and GlcNAc. We have studied biosynthesis of corneal KS carbohydrate, and identified that 4 Golgi-Ioca/ized enzymes, ~1 ,3-N-acetylglucosaminyltransferase 7, ~1 ,4-galactosyltransferase 4, KS galactose 6-0 sulfotransferase and corneal N-acetylglucosamine 6-0 sulfotransferase, are required for KS-GAG production in vitro as well as in vivo. We also found that lack of sulfation of KS carbohydrate alters corneal extracellular matrix (ECM) structure in mouse cornea, and demonstrated functional importance of KS-GAG chain in the cornea. Based on these findings, we hypothesized that molecular structure, such as length and sulfation degree, of KS carbohydrate affects to the formation of organized corneal ECM structure. In other words, we may be able to remodel the corneal ECM structure by manipulating KS carbohydrate structure, which can be controlled by suppression and/or induction of enzymatic activity required for KS synthesis in corneal cells. To test this hypothesis, we will work on the two aims.