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 α-smooth muscle actin (α-SMA) as markers of apoptosis, proliferation, and myofibroblastic differentiation, respectively. Cellular senescence was confirmed by senescence-associated β-galactosidase (SA-β-gal) staining and P16Ink4a expression. Mitogenic response and gene expression were compared among normal fibroblasts, H2O2-induced senescent fibroblasts, and TGF-β-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-β-gal was observed clearly in the anterior stromal cells at 3 to 5 days. The senescent cells displayed P16Ink4a+ vimentin+ α-SMA+, representing the major origin of activated corneal resident fibroblasts. Compared with normal fibroblasts and TGF-β-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.