REPAIR PHENOTYPE IN CORNEAL FIBROBLASTS IS CONTROLLED BY AN INTERLEUKIN-1-ALPHA AUTOCRINE FEEDBACK LOOP

Purpose. To explore the role of autocrine interleukin-1 alpha (IL-1 al pha) as a central regulator of the repair phenotype in corneal fibrobl asts. Methods. Disruption of the actin cytoskeleton with cytochalasin B (CB), which mimics changes in shape that occur in repair tissues, wa s used to stimulate repair gene expression in early-passage fibroblast s. Changes in expression of IL-1 alpha, IL-8, collagenase, and ENA-78 were determined by Northern blot analysis, radioimmunoassay, and an en zyme-amplified sensitivity immunoassay (EASIA). Expression of repair g enes was also examined in repair fibroblasts, isolated from healing, p enetrating keratectomy wounds in rabbits. Results. Blocking IL-1 alpha activity prevented both constitutive and stimulated increases in synt hesis of IL-8 and collagenase in early-passage cultures of corneal fib roblasts, demonstrating the role of IL-1 alpha as a necessary intermed iate for expression of these genes. Evidence is also presented that th e IL-1 alpha autocrine controls expression of an IL-8 related factor, ENA-78. Unlike early-passage fibroblasts, fibroblasts freshly isolated from the uninjured cornea did not express IL-1 alpha. However, fibrob lasts freshly isolated from remodelling corneal repair tissue 3 weeks after injury were found to express substantial levels of IL-1 alpha, r egulated through an autocrine feedback loop. Neutralization experiment s demonstrated that the IL-1 alpha autocrine is largely responsible fo r controlling both collagenase and IL-8 synthesis in repair fibroblast s, as it is in early-passage fibroblasts. Conclusions. These findings provide evidence that activation of an autocrine IL-1 alpha feedback l oop is an important mechanism by which fibroblasts adopt a repair phen otype during remodelling of the cornea.