Increased apoptosis and abnormal wound-healing responses in the heterozygous Pax6+/- mouse cornea

Corneal wound healing involves a cascade of interactions between the epithelium and stroma. Pax6 is upregulated, and early events include epithelial cell migration and apoptosis of superficial keratocytes. The mouse heterozygous Pax6 (Pax6+/-) corneal phenotype mimics human aniridia-related keratopathy (ARK), and some aspects of wound healing have been shown to be abnormal, including matrix metalloproteinase (MMP)-9 expression. The purpose of this study was to test whether the Pax6+/- genotype affects corneal wound-healing responses, including stromal cell apoptosis, epithelial cell migration rate, and MMP secretion in culture.

Pax6+/- and wild-type (Pax6+/+) mice were killed and their corneas wounded by epithelial debridement. Whole eyes were cultured in organ culture and corneal epithelial healing rates and keratocyte apoptosis were quantified by topical fluorescein staining and TUNEL, respectively. Dissociated corneal epithelial cells from Pax6+/- and wild-type mice were cultured, and the activities of secreted MMP-9 were determined by zymography.

Wound-healing rates during the first 6 hours were significantly faster for larger wounds and for Pax6+/- corneas. Compared with wild-type, wounded Pax6+/- eyes showed significantly more stromal cell apoptosis, and cultured Pax6+/- corneal epithelial cells produced lower MMP-9 activity.

The cumulative effect of abnormal wound-healing responses, characterized by increased stromal cell apoptosis and reduced levels of MMP-9 secretion may contribute to the corneal changes in the Pax6+/- mice. Possible contributions of elevated stromal cell apoptosis and other abnormal wound-healing responses to ARK are discussed.