Kj. Strissel et al., A CORNEAL EPITHELIAL INHIBITOR OF STROMAL CELL COLLAGENASE SYNTHESIS IDENTIFIED AS TGF-BETA-2, Investigative ophthalmology & visual science, 36(1), 1995, pp. 151-162
Purpose. To determine the molecular mechanisms whereby substances rele
ased by corneal epithelial cells act to inhibit the elaboration of col
lagenolytic activity by corneal stromal cells and to determine whether
inhibitory activity might be mediated by interleukin-1 receptor antag
onist (IL-1ra) or transforming growth factor (TGF)-beta. Methods. Cond
itioned media were generated from primary cultures of rabbit corneal e
pithelial cells, from passaged cultures of rabbit corneal stromal fibr
oblasts, and from cells of the rabbit corneal epithelial cell, line, S
IRC. Pure populations of stromal cells were isolated from rabbit corne
a and used directly for bioassay of the conditioned media to detect su
bstances that inhibit collagenase synthesis. The mink lung epithelial
cell line, Mv1Lu, was used for bioassay of TGF-beta-like activity. The
addition of specific neutralizing antisera to bioassays allowed an as
sessment of the contribution of each isoform to the net regulatory act
ivity. Reverse transcription-polymerase chain reaction and Northern bl
ot analysis were employed to detect the presence of IL-1ra or TGF-beta
mRNA species in cells from cultures used to generate conditioned medi
a. Results. Both stimulatory and inhibitory substances that regulate t
he synthesis of stromal cell collagenase are released by corneal epith
elial cells in primary culture. In contrast, only stimulatory activity
is produced by corneal fibroblasts or SIRCs. MRNAs for a TGF-beta iso
form, TGF-beta 2, and IL-1ra were identified in epithelial cells. Stro
mal fibroblasts also expressed TGF-beta 2 mRNA, but no evidence was fo
und for expression of TGF-beta 3 mRNA in any of the three cell types.
TGF-beta 2 is released by epithelial cells in both active and latent f
orms. This cytokine mediates the major portion of the net inhibitory a
ctivity against stromal cell collagenase synthesis produced by corneal
epithelial cells. Conclusions. This study demonstrates the expression
of TGF-beta 2 and IL-1ra by corneal epithelial cells in culture. It i
s the TGF-beta 2 that acts as the major inhibitor of collagenase synth
esis by corneal stromal cells in culture. However, IL-1ra and TGF-beta
2 are likely to play important roles in epithelial-mesenchymal intera
ctions regulating corneal development, homeostatic maintenance, and re
pair.