Distribution of cathepsin D in human ocular tissue: An immunohistochemical study

It is well established that cathepsin D as a major lysosomal acid protease plays an important role in the catabolism of protein in various ocular tissues. In the retinal pigment epithelium (RPE), cathepsin D is involved in the degradation of shed discs during the renewal process. To date, the immunohistochemical localization and distribution of cathepsin D in human ocular tissue has not been precisely analyzed. In this study, the cellular localization of cathepsin D immunoreactivity was examined at the light microscopic level in healthy donor eyes using the alkaline phosphatase-antialkaline phosphatase (APAAP) technique. Cathepsin D immunoreactivity was found in the cellular cytoplasm of the following human ocular tissues: retinal pigment epithelium; Muller cells; ganglion cells; pigmented and unpigmented epithelium of the ciliary body; iris tissue; epithelium and endothelium of the cornea and lens epithelium. In addition, cathepsin D reaction product was detected in the glial cells of the optic nerve and in the cytoplasm of the capillary endothelium. The localization and distribution of cathepsin D and its possible role among the various ocular tissues are discussed in connection with the underlying physiological and pathophysiological conditions.