EXPRESSION OF COLLAGEN-I, SMOOTH-MUSCLE ALPHA-ACTIN, AND VIMENTIN DURING THE HEALING OF ALKALI-BURNED AND LACERATED CORNEAS

Purposes. Alkali-burned corneas can seldom heal properly to restore co rneal transparency. To provide a better understanding of this devastat ing corneal injury, we compared the expression of collagen I, smooth m uscle alpha-actin (alpha-SMA), and vimentin in lacerated and alkali-bu rned rabbit corneas. Methods. A radiolabeled cDNA probe of alpha1(I) c hain was used in slot-blot hybridization to determine the levels of al pha1(I) mRNA in alkali-burned corneas. In situ hybridization was used to identify the cell types that express the alpha1(I) chain. Antibodie s against collagen I, alpha-SMA, and vimentin were used in immunohisto chemical studies to determine the tissue distribution of collagen I an d to identify cells expressing alpha-SMA and vimentin. Results. The le vels of alpha1(I) mRNA in alkali-burned corneas increased steadily aft er the alkali burn and reached a plateau within 2 weeks. One day after alkali burn, specific in situ hybridization signals were detected in stromal cells immediately surrounding the edge of the corneal injury. As the healing proceeded, the fibroblastic cells migrated into the inj ured stroma, and they showed positive reactions by in situ hybridizati on and by immunostaining with anti-collagen I probes. In alkali-burned corneas, retrocorneal membranes were formed 1 week after injury. This fibrillar membrane was stained by anti-collagen I antibody, and the f ibroblastic cells in the membrane were hybridized by the H-3-labeled a lpha1(I) cDNA probe. No retrocorneal membrane was formed in the lacera ted corneas, even after the injured corneas were allowed to heal for 3 weeks. The epithelial cells in the epithelial plug of lacerated corne as were positive by in situ hybridization, whereas the epithelial cell s in the regenerated epithelium of alkali-burned cornea was not. Antib odies against alpha-SMA reacted with the migrating fibroblastic cells but did not react with epithelial cells or endothelial cells in the in jured corneas. Anti-vimentin antibody reacted with fibroblastic cells, endothelial cells, and keratocytes in normal and injured corneas, and with the basal epithelial cells of injured corneas. Conclusions. Duri ng wound healing, the keratocytes that migrate to injured stroma trans form into myofibroblasts. These myofibroblasts express high levels of alpha(I) mRNA, alpha-SMA, and vimentin. The healing of alkali-burned c orneas differ from that of lacerated corneas in that the retrocorneal membranes are formed in the former but not in the latter. In addition, the epithelial cells of alkali-burned corneas lack alpha1(I) mRNA, wh ereas it is found in the epithelium of lacerated corneas. These differ ences may result from the persistence of inflammatory cells in the alk ali-burned corneas.