Corneal disorders in KKAy mouse: a type 2 diabetes model.

PURPOSE To observe the clinical and histopathological changes occurring in corneas of KKAy mice, a model of type 2 diabetes, and to elucidate the possible mechanisms involved in these changes. METHODS Corneal epithelial cell proliferation was analyzed in KKAy and age-matched non-diabetic C57BL/6J control mice using (3)H-thymidine autoradiography. Clinical examination and histopathological analysis were also conducted on both types of mice. RESULTS KKAy mice showed a significant elevation in blood glucose concentration and body weight compared to age-matched control mice. Fragile corneal epithelial cell attachment and subepithelial opacities were observed in the central area of the cornea of 10-week-old KKAy mice. Corneal epithelial cell proliferation decreased significantly in the 16-week-old KKAy mice. Histological study in the older KKAy mice groups revealed the presence of subepithelial deposits, widening of the intracellular spaces between corneal epithelial cells with poor adherence to the basement membrane (BM) and thickening of the BM itself. At the central area of the cornea, remnants of cell components with deposits and lacuna formation were observed, perhaps secondary to the continuous presence of poor adhesion and detachment of epithelial cells in the area. In the 50-week and older KKAy mice, thinning and atrophy of the corneal epithelial cell layer became more prominent at the central cornea with increases in deposition of materials, blood vessel invasion and activation of keratocytes. The deposits were stained black by von Kossa's method, indicating the presence of tissue calcium. Type IV collagen immunoreactivity was observed not only in the corneal and conjunctival BM but also between the stroma, particularly around the central cornea and in the walls of invading vessels. Laminin staining was intense at the BM around the central cornea, and in the walls of invading vessels along the stroma. Pyrraline, which is one of the major components of advanced glycation end products, was also present in the stroma, and around blood vessels. All these corneal changes were not observed with aging in the age-matched C57BL/6J mice. CONCLUSIONS Our findings provide evidence of the existence of corneal disorders in KKAy mice. These observations may provide useful information for the explanation of the mechanisms involved in corneal disorders in non-insulin-dependent diabetes mellitus patients.