Response of the lysosomal system of the corneal epithelium to tyrosine-induced cell injury.

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Abstract
Rats fed excess tyrosine develop corneal epithelial disease which parallels that found in humans with tyrosine aminotransferase deficiency (tyrosinosis). In the rat, focal lesions develop within the central epithelium and contain crystals (presumably tyrosine) that disrupt cells. We have studied these lesions and localized acid phosphatase and aryl sulfatase at the electron microscope level. Within 60 hr after initiation of diet, cells within the lesions showed an increase in lysosomal enzyme activity. This activity was localized inside some of the crystal ghosts and in numerous lysosomes, including autophagic vacuoles and multivesicular bodies. After 84 hr on diet the entire central corneal epithelium was disrupted and polymorphonuclear leukocytes had infiltrated the area. Crystals were phagocytosed by or developed within polymorphonuclear leukocytes. We hypothesize that crystals form within epithelial cells, disrupt first their lysosomes, and then cells, leading to externalization of lysosomal enzymes. This extracellular lysosomal enzyme release may be responsible for the acute inflammatory response that ensues.