Confocal Imaging of the a 6 and /? 4 Integrin Subunits in the Human Cornea With Aging

Abstract

Purpose. The purpose of this study was to examine changes in the distribution of integrin subunits, a 6 and a 4 , in the normal human cornea with age. Methods. Thirty normal corneas were examined and divided into three groups; corneas from children younger than 2 years, corneas from adults 29 to 70 years, and corneas from adults older than 70 years. The corneas were frozen and the sections were cut, double-stained with monoclonal antibodies to the integrin subunits, and visualized with Texas Red or fluorescein using confocal laser scanning microscopy. Computer imaging was conducted to determine differences. Results. The a 6 subunit was generally localized along the basal and lateral surfaces of basal epithelial cells and projected into Bowman's membrane. The j8 4 subunit was only present along the basal surface. Overall, the major age-related difference was the loss of continuous a 6 and /3 4 subunits along the basal surface of basal epithelial cells. When reconstructed images from corneas of individuals older than 70 years were optically sectioned en face, the a 6 subunit appeared discontinuous. If the same optical images were viewed from corneas of younger individuals, the staining was continuous. The number and distribution of hemidesmosomes along the basal lamina did not change with age in the corneas examined. Conclusions. Using computer imaging associated with confocal laser scanning microscopy, we have demonstrated that there is an age-related change in the localization of the a 6 and /3 4 subunits. Invest Ophthalmol Vis Sci 1993; 34:3103-3109. L he cornea is comprised of five to seven layers of stratified epithelium in which proliferation is limited to the basal layer. Basal cells form hemidesmosomes with the basal lamina that lies over an acellular collagenous region called Bowman's membrane. Increasing evidence demonstrates that extracellular matrix receptors such as integrins play an important role in the formation of cell substrate and cell-cell junctions. Integrins are transmembrane glycoproteins consisting of an alpha and a beta subunit. The ligand specificity of this receptor depends on its heterodimer composition; however, the same integrin can have different ligands in different cell types