Cathepsin G, acid phosphatase, and α1-proteinase inhibitor messenger RNA levels in keratoconus corneas

Purpose. Keratoconus is characterized by thinning and scarring of the central region of the cornea. The authors have shown, in corneas obtained from patients with keratoconus, that lysosomal enzyme activities are elevated, whereas levels of protease inhibitors such as α1-proteinase inhibitor (α1-PI) are reduced. This study was undertaken to examine further the gene expression of cathepsin G, acid phosphatase, and α1-PI in keratoconus corneas. Methods. Corneal buttons were collected from patients with keratoconus, normal subjects, and patients with other corneal diseases. In situ hybridization was performed on paraffin sections using a tritium- labeled probe for cathepsin G or α1-PI. Competitive polymerase chain reaction (PCR) was used to determine the messenger RNA (mRNA) levels for lysosomal acid phosphatase and α1-PI in epithelial and stromal cells of keratoconus corneas. Results. Silver grains, indicative of positive in situ hybridization products, were observed in all three cell types of normal corneas for both DNA probes. Compared with normal and other diseased controls, the labeling was enhanced for cathepsin G but was diminished for α1-PI in the epithelium of keratoconus corneas. Competitive PCR showed that the mRNA level for acid phosphatase was higher and that the mRNA level for α1-PI was lower in keratoconus corneas. Conclusions. These results indicate that the mRNA level for degradative enzymes is increased and that for α1-PI it is reduced in keratoconus corneas. This study provides the first evidence that the altered expression of multiple enzymes and inhibition in keratoconus occurs at the gene level. Furthermore, it implicates a possible role of coordinated transcriptional regulation of gene expressions in keratoconus.