Purpose: To explore further the significance of three patterns of cytokine dialogues that have been characterized between human corneal and limbal epithelial cells and fibroblasts.
Methods: Northern hybridization of the transcript expression of type I cytokine receptors (EGFR, IL-1R, and PDGFR-beta), type II cytokines (bFGF, LIF, and TGF-beta 1), and type III cytokines (HGF and KGF) by human corneal and limbal fibroblasts was conducted under the modulation of TGF-alpha, PDGF-BB, IL-1 beta, and EGF (type I cytokines). The mechanism of upregulation by IL-1 beta was studied further with respect to proto-oncogene expression and under the treatment of cycloheximide and actinomycin D.
Results: Results showed that EGF upregulated LIF and HGF but downregulated KGF and M-CSF. Unlike EGF, TGF-alpha upregulated additional EGFR, PDGFR-beta, bFGF, and TGF-beta 1, suggesting that although they share the same EGFR, TGF-alpha, which is produced by epithelium, is more effective in activating fibroblasts than EGF, which is present in tears. The upregulation of PDGF-BB was similar to that of TGF-alpha, except that it further stimulated IL-8, supporting their synergistic roles in promoting wound healing. Uniquely, IL-1 beta upregulated KGF expression by limbal fibroblasts more than corneal fibroblasts and IL-8 and M-CSF expression, but it downregulated PDGFR-beta. In IL-1 beta, the upregulation of cytokines and receptors was preceded by the upregulation of c-fos, c-jun, and c-myc, and it was inhibited by actinomycin D. Its upregulation of LIF was superinduced, but the upregulation of bFGF and KGF was inhibited, and that of the rest was not affected by cycloheximide.
Conclusions: These findings suggest that epithelial cells under stress or injury (producing IL-1) might preferentially activate limbal epithelial stem cells indirectly by fibroblasts and simultaneously might promote inflammation during wound healing.