Change in the molecular structure of extracellular matrix accompanied by diabetic keratopathy : Immunohistochemical study

临床上，糖尿病性角膜常表现为浅表点状角膜病变和持续性上皮缺损及复发性上皮糜烂，被认为是糖尿病性角膜上皮病变的一种形式。我们用免疫组化方法检测了糖尿病角膜细胞外基质的变化。作为非胰岛素依赖型（2型）糖尿病的动物模型，使用Goto-Kakizaki大鼠。电镜观察发现糖尿病大鼠基底膜与基底细胞常发生分离。半桥粒和锚定纤维数量减少。在基底细胞中，糖尿病角膜的半桥粒形成受到干扰。免疫组化法检测基底膜主要成分层粘连蛋白、IV型胶原的定位。在糖尿病角膜层粘连蛋白的免疫反应性的强度下降。IV型胶原免疫反应性无明显变化。基底膜的其他成分纤维连接蛋白、HSPG、VI型胶原不仅分布于基底膜，而且也分布于间质中。未观察到这些免疫反应性的变化。在糖尿病角膜中，随着年龄的增长，后弹力层中长间距胶原蛋白的数量比正常角膜增加得更快。在人类中，有报道称VIII型胶原定位于长间距胶原中。因此，我们研究了大鼠角膜中VIII型胶原的定位。VIII型胶原蛋白定位于后弹力层，在糖尿病角膜中增加。提示角膜上皮基底膜层粘连蛋白减少和后弹力层VIII型胶原增加可能是糖尿病性角膜病变的原因之一。

Clinically, the diabetic cornea often shows superficial punctate keratopathy and persistent epithelial defect and recurrent epithelial erosion that is considered to be a form of diabetic keratoepithliopathy. We examined immunohistochemically the change of the extracellular matrix in the diabetic cornea. As animal model of a non-insulin-dependent type (type 2) diabetes, Goto-Kakizaki rat were used. Electron microscopic study showed that basement membrane in the diabetic rat often detaches from the basal cell. The number of hemidesmosomes and anchoring fibrils decreased. In the basal cell, the hemidesomosome formation was disturbed in the diabetic cornea. Localization of the main components of basement membrane, laminin, type IV collagen was examined immunohistochemically. In the diabetic cornea the intensity of the immunoreactivity of laminin decreased. But immunoreactivity of type IV collagen did not changed. Other components of basement membrane, fibronectin, HSPG, type VI collagen localized not only in the basement membrane but also in the stroma. No change of these immunoreactivities was observed. In the diabetic cornea the number of long-spacing collagen increased more rapidly than normal cornea in the Descemet's membrane with age. In human, there is a report that type VIII collagen localizes in the long spacing collagen. So we examined the localization of type VIII collagen in the rat cornea. Type VIII collagen localized in Descemet's membrane and increased in the diabetic cornea. These results suggest that decrease of laminin in the basement membrane of corneal epithelium and increase of type VIII collagen in the Descemet's membrane may be one of the causes of the diabetic keratopathy.