Interaction between injured corneal epithelial cells and stromal cells

Purpose: To review the effects of injured corneal epithelial cells on myofibroblastic cell formation in corneal stroma after excimer laser surgery. Methods: Denudation of epithelium alone, photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), and LASIK with denudation of epithelium were performed in rabbit eyes. Postoperative anterior stromal haze was assessed using a standard scale. Immunohistochemical methods were used to detect alpha-smooth muscle actin (alpha-SMA), a marker of myofibroblastic cells, and type III collagen in subepithelial corneal tissue. Rabbit corneal fibroblasts were cultured on collagen gels with or without cocultured corneal epithelial cells, or with partially scraped epithelial cells, on a companion plate separated by a permeable membrane. Gel thickness was measured daily to evaluate fibroblast-induced gel contraction. The total number of fibroblasts per gel was determined. Myofibroblasts were counted using immunocytochemical identification with alpha-SMA. Transforming growth factor (TGF)-beta was assayed in media on days 3 and 6; these procedures were also carried out in the presence of anti-TGF-beta antibody. Results: Three weeks after surgery, the presence of alpha-SMA-positive long-extended and spindle-shaped stromal cells as well as synthesis of type III collagen were observed in the subepithelial stromal layer, corresponding to corneal haze, in eyes that underwent PRK and LASIK with denudation of epithelium, but not in those that underwent denudation of epithelium alone or LASIK. Gel contraction, number of alpha-SMA-positive cells, and total cell number were significantly greater on gels with injured epithelial cells than on those without epithelial cells or with uninjured epithelial cells, as was TGF-beta concentration in media. Anti-TGF-beta antibody eliminated these differences. Conclusions: The intact corneal epithelium might play an important role in curbing differentiation of myofibroblasts in corneal wound healing. Injured epithelial cells stimulate fibroblast myodifferentiation through one or more soluble factors, including TGF-beta.