Abstract: PURPOSE. To investigate the presence and role of fibroblast senescence in the dynamic process of corneal wound healing involving stromal cell apoptosis, proliferation, and differentiation. METHODS. An in vivo corneal wound healing model was performed using epithelial debridement in C57BL/6 mice. The corneas were stained using TUNEL, Ki67, and alpha-smooth muscle actin (alpha-SMA) as markers of apoptosis, proliferation, and myofibroblastic differentiation, respectively. Cellular senescence was confirmed by senescence-associated beta-galactosidase (SA-beta-gal) staining and P16(Ink4a) expression. Mitogenic response and gene expression were compared among normal fibroblasts, H2O2-induced senescent fibroblasts, and TGF-beta-induced myofibroblasts in vitro. The senescence was further detected in mouse models of corneal scarring, alkali burn, and penetrating keratoplasty (PKP). RESULTS. The apoptosis and proliferation of corneal stromal cells were found to peak at 4 and 24 hours after epithelial debridement. Positive staining of SA-beta-gal was observed clearly in the anterior stromal cells at 3 to 5 days. The senescent cells displayed P16(Ink4a) thorn vimentin+ alpha-SMA+, representing the major origin of activated corneal resident fibroblasts. Compared with normal fibroblasts and TGF-beta-induced myofibroblasts, H2O2-induced senescent fibroblasts showed a nonfibrogenic phenotype, including a reduced response to growth factor basic fibroblast growth factor (bFGF) or platelet-derived growth factor-BB (PDGF-BB), increased matrix metalloproteinase (MMP) 1/3/13 expression, and decreased fibronectin and collagen I expression. Moreover, cellular senescence was commonly found in the mouse corneal scarring, alkali burn, and PKP models. CONCLUSIONS. Corneal epithelial debridement induced the senescence of corneal fibroblasts after apoptosis and proliferation. The senescent cells displayed a nonfibrogenic phenotype and may be involved in the self-limitation of corneal fibrosis.
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