M. Ishizaki et al., EXPRESSION OF COLLAGEN-I, SMOOTH-MUSCLE ALPHA-ACTIN, AND VIMENTIN DURING THE HEALING OF ALKALI-BURNED AND LACERATED CORNEAS, Investigative ophthalmology & visual science, 34(12), 1993, pp. 3320-3328
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.